A three-dimensional NbO-type metal–organic framework (MOF) is composed of paddle-wheel-type dinuclear Cu2 secondary units and 1,1′-ethynebenzene-3,3′,5,5′-tetracarboxylate (EBTC4−) linkers. Two types of nanometer-sized cavities are formed in this framework with ca. 8.5 Å in diameter for the small one and dimensions of ca. 8.5 × 8.5 × 21.5 Å for the larger and irregular elongated cavity. The guest molecules, H2O, DMF and DMSO, occupy the cavities of the as-prepared MOF crystal (labeled as MOF 1). MOF 2 was obtained by the guest-exchange approach using CH3OH, and the H2O and CH3OH molecules reside in the cavities of 2. Two MOFs show greenish-turquoise color at ambient temperature due to the d–d transition of Cu2+ ions in the framework, and the reversible thermochromic behavior owing to the change of the coordination environment of Cu2+ ions with varying temperatures. The films of 1 and 2 were fabricated on the α-Al2O3 and SiO2 supports by the seeded growth method, displaying similar reversible thermochromic behavior to the corresponding MOFs. This study suggested the possibility of novel thermochromic materials in the rational design of MOFs.

The second polymorph, the β-crystal, of the nickel-bis-dithiolene compound [4′-CF3bzPy][Ni(mnt)2], where 4′-CF3bzPy = 1-(4′-trifluoromethylbenzyl)pyridinium and mnt2− = maleonitriledithiolate, was obtained. The variable-temperature single crystal structures, magnetic behavior in 1.8–300 K and dielectric nature in 123–373 K have been investigated for the β-crystal. This polymorph experiences two hysteretic magnetic phase transitions in a narrow temperature region (190–217 K) with the thermal hysteresis loops ca. 6 K and ca. 11 K. The two hysteretic magnetic phase transitions are coupled with two isostructural phase transitions (IPTs), respectively, which are driven by the novel step-wise dynamic orientation motion of the anion and cation in the β-crystal. There is an absence of a dielectric anomaly in the structural transformation temperature interval. However, a dielectric relaxation, related to the dipole motion of polar CF3 groups in the cations under an ac electrical field, emerges in the high-temperature phase.

Kaolinite (K), a polar and layered aluminosilicate mineral, was used as the host; ethanolamine (EOA) and ethylene glycol (EG) were inserted into the kaolinite interlayer to give the intercalated supramolecular compounds kaolinite–ethanolamine (K-EOA) and kaolinite–ethylene glycol (K-EG), respectively. The intercalation of EOA and EG resulted in an increase in the d(001)-value by 3.4 and 3.68 Å, which corresponds to expansion of the interlayer space by 156.7 Å3 in K-EOA and 169.6 Å3 in K-EG, respectively. The characteristic infrared-active ν(O–H) modes ν1, ν2 and ν3 besides ν5, which were quite sensitive to the host–guest interaction, were not significantly affected by intercalation in K-EOA and K-EG, and two intercalated compounds showed lower deintercalation temperature (115 and 109 °C for K-EOA and K-EG, respectively). These are due to weakly intermolecular interactions between the intercalant molecules and the kaolinite framework, which is in agreement with the theoretical analysis of crystal structures of the intercalated compounds. K-EOA and K-EG showed novel dielectric relaxation behavior, which originates from the dynamic orientation motion of intercalant molecules.

Two new one-dimensional (1-D) compounds, [CH3-BzPy][Pt(mnt)2] (1) and [CH3-BzPy-d5][Pt(mnt)2] (2) (CH3-BzPy+ = 1-N-(4-CH3-benzyl)pyridinium and the pyridine in CH3-BzPy+ was replaced by pyridine-d5 to give the CH3-BzPy-d5+; mnt2− = maleonitriledithiolate), were synthesized and characterized. 1 and 2 show similar magnetic behavior in 1.8–400 K; they experience a spin-Peierls-type transition around 320 K and show a uniform antiferromagnetic S = 1/2 chain behavior in high temperature (HT) phase, a spin gap feature in low temperature (LT) phase. A symmetry breaking structural phase transition is associated with the spin-Peierls-type transition. Two isostructural compounds crystallize in space group P2(1)/c in HT phase, with a = 12.3066(8) Å, b = 27.0522(18) Å, c = 7.4248(4) Å, β = 104.204(6)° and V = 2396.3(3) Å3 for 1versus a = 12.3331(9) Å, b = 27.087(4) Å, c = 7.4501(9) Å, β = 104.149(13)° and V = 2413.3(6) Å3 for 2 at 353 K, while space group P in LT phase, with a = 7.3203(10) Å, b = 12.2816(16) Å, c = 26.904(4) Å, α = 88.500(4)°, β = 86.731(4)°, γ = 75.421(4)° and V = 2337.0(5) Å3 for 1versus a = 7.3308(8) Å, b = 12.2848(13) Å, c = 26.930(3) Å, α = 88.479(3)°, β = 86.652(4)°, γ = 75.563(3)° and V = 2344.5(4) Å3 for 2 at 296 K. DSC measurements revealed 1 and 2 showing almost the same TC. This observation is distinction from the [Ni(mnt)2]−-based spin-Peierls-type analogues [CH3-BzPy][Ni(mnt)2] and [CH3-BzPy-d5][Ni(mnt)2] where the deuteration leads to TC up shifting 2.3 K.

A three-dimensional metal–organic framework compound with a formula [Cu2(EBTC)(H2O)2·8H2O·DMF·DMSO]∞ (EBTC = 1,1′-ethynebenzene-3,3′,5,5′-tetracarboxylate) shows novel three-step dielectric relaxations arising from the orientational motion of dipolar guest molecules and its guest-free framework displays low-κ dielectric permittivity.

A charge-transfer salt consisting of 1,1′-dioctyl-4,4′-bipyridinium and bis(maleonitriledithiolato)nickelate is described. Its crystal is built from mixed stacks of the anion and cation, with the anions (A) and cations (C) adopting an …ACAC… fashion within a stack. This salt shows a novel non-ferroelectric-type dielectric phase transition at around 324 K and bistability.

A one-dimensional (1-D) magnetic chain compound, [(CD3)2CN-Py][Ni(mnt)2], where (CD3)2CN-Py+ = 1-(propan-d6-2-ylideneamino)pyridinium and mnt2− = maleonitriledithiolate, was synthesized and characterized. This compound undergoes two structural phase transitions, at around 267 K and 325 K. The three phases are sequentially labeled as α (below 267 K), β (between 267 and 325 K) and γ (above 325 K). The [Ni(mnt)2]− anions form irregular stacks, with two values of neighboring Ni⋯Ni distances. The cations align in a straight and regular arrangement along the crystallographic a-axis direction in the β phase. The asymmetric unit switches from one anion–cation pair to two anion–cation pairs in the transition from the β to the α phase. This leads to a doubling of the crystallographic axis length, parallel to the anion stack. It also results in the irregular anion stack showing three non-equivalent neighboring Ni⋯Ni distances, as well as making the straight cation arrangement irregular. The β and γ phases are isostructural and exhibit quite similar packing structures. The anion stack shrinks a little with increasing temperature, with all crystallographic axes showing small reduction from the β to γ phase. The two observed magnetic phase transitions are driven by these various structural phase transitions. A thermal hysteresis loop, with a separation of ∼8 K, appears in the transition between the β and α phases. However, this is absent in the transition between the β and γ phases. A dielectric anomaly appears across the phase transition between the β and γ phases but not between the β and α phases.

•A new one-dimensional molecular solid was achieved.•This molecular solid shows a hysteretic magnetic transition occurs at ca. 80 K upon cooling with 5.6 K thermal hysteresis.•Intramolecular vibrational modes cooperate with the magnetic phase transition.•There exists pre-transition phenomenon up until 100 K in this molecular solid.A new one-dimensional molecular solid, [I-BzPy-d5][Pt(mnt)2] (mnt2− = maleonitriledithiolate, I-BzPy-d5+ = 1-N-(4-iodobenzyl)pyridinium-d5) was synthesized. [I-BzPy-d5][Pt(mnt)2] and its analog [I-BzPy][Pt(mnt)2] are isostructural, crystallized in space group P−1 at ambient temperature. A hysteretic magnetic transition occurs at ca. 80 K with 5.6 K thermal hysteresis upon cooling. [I-BzPy-d5][Pt(mnt)2] features an alternating S = 1/2 Heisenberg antiferromagnetic linear chain magnetic behavior with spin gap of 131 K in high-temperature phase, while 306 K in low-temperature phase. There is no significant isotope effect of both magnetism and phase transition by comparison of [I-BzPy-d5][Pt(mnt)2] and [I-BzPy][Pt(mnt)2]. The variable-temperature IR spectra in 10–293 K revealed the existence of pre-transition phenomenon up until 100 K and five intramolecular vibrational modes cooperating with the magnetic phase transition.

Eight metal–dithiolene compounds, [Cn-Apy][Ni(mnt)2] (Cn-Apy+ = 1-alkyl-4-aminopyridinium with n = 2–5 and 7–10; mnt2− = maleonitriledithiolate), were synthesized and characterized, amongst which the crystal structures were determined for six compounds (n = 3, 5, 7–10). The anions and cations form alternatively layered arrangement. The anion layer is built from the irregular stacks, the neighboring stacks are aligned along the long molecular axis direction of anions, and the alignment pattern is related to hydrocarbon chain length in 1-alkyl-4-aminopyridinium. Seven compounds exhibit the thermotropic liquid crystalline behaviors with the smetic A phase fingerprints. The mesophase observed in a propyl chain compound is uncommon compared with the suggested rule that a dodecyl hydrocarbon chain is necessary at least in the pyridinium-based ionic liquid crystals. The [Cn-Apy][Ni(mnt)2] compounds showed distinct magnetic behaviors. This is due to the magnetic couplings between anions being achievable through pathways of weakly intermolecular interactions.A series of layered compounds of [1-alkyl-4-aminopyridinium][Ni(mnt)2] where mnt2− = maleonitriledithiolate show the thermotropic liquid–crystalline behaviors with the typical fingerprints of smetic A phase.

The compound [4′-CF3bzPy][Ni(mnt)2] (1) (where 4′-CF3bzPy = 1-(4′-(trifluoromethyl)benzyl)pyridinium and mnt2– = maleonitriledithiolate) was synthesized and displays a magnetic bistability with a surprisingly large thermal hysteresis loop (∼49 K). X-ray crystallographic studies reveal that in the high-temperature (HT) phase the anions and cations form mixed stacks, with alternating anion dimers (AA) and cation dimers (CC) in an ...AACCAACC... fashion along the crystallographic a + b direction, and disordered CF3 groups in the cations are aligned into a molecular layer parallel to the crystallographic (001) plane. However, in the low-temperature (LT) phase, the c-axis length of the unit cell is roughly doubled, and the asymmetric unit switches from one [4′-CF3bzPy][Ni(mnt)2] pair in the HT phase to two [4′-CF3bzPy][Ni(mnt)2] pairs. Most interestingly, the CF3 group in the cations becomes ordered, and the conformation of one of two crystallographically different cations changes significantly. A dislocation motion between the neighboring molecular layers emerges as well. The analyses of the magnetic susceptibilities and the density functional theory calculations suggest that the antiferromagnetic exchange interaction within one of two types of [Ni(mnt)2]22– dimers in the LT phase is much stronger than that within the [Ni(mnt)2]22– dimer in the HT phase. The lattice reorganization during this phase transition is proposed to be responsible for the wide thermal hysteresis loop.

A new one-dimensional (1-D) ion-pair compound, [1,7-bis(1-methylimidazolium)heptane][Ni(mnt)2]2 (mnt2− = maleonitriledithiolate), was synthesized and characterized structurally and magnetically. This compound shows a spin-Peierls-type transition at around 235 K. Its crystal structure belongs to the monoclinic system with space group C2/c and the magnetic [Ni(mnt)2]− anions form uniform stacks in the high-temperature (HT) phase. The crystal undergoes a transformation into the triclinic space group P accompanied by the magnetic transition and the anion stacks become dimerized in the low-temperature (LT) phase. The entropy changes (ΔS) are estimated to be 0.772 J K−1 mol−1 for the spin-Peierls-type transition, from DSC data, which is much less than the spin entropy change (ΔS = Rln 2 ≈ 5.76 J K−1 mol−1), indicating that a substantial short-range order persists above the transition temperature. The variable temperature IR spectra showed that the peak positions and intensities for the bands near 1160 and 725 cm−1, which correspond respectively to the ν(C–C) + ν(C–S) mode of the mnt2− ligands and the rocking vibration mode of the methylene group γr(CH2) in the cation moiety, undergo an abrupt change at around 240 K, close to the transition temperature. This observation demonstrates that the intramolecular vibrations of both the anion and the counter-cation probably couple with the spins to cooperate with the spin-Peierls-type phase transition in this 1-D spin system.

A metal–organic framework (MOF) compound, comprised of Sr2+ and thiophene-2,5-dicarboxylic acid (H2TDA) with a formula of Sr(TDA)(DMF), was prepared via the solvothermal method, this MOF compound crystallizes in the monoclinic space group P21/c with unit cell parameters a = 6.0078(4) Å, b = 16.9401(12) Å, c = 13.0061(8) Å, β = 116.158(3)° and V = 1188.10(14) Å3. The spaces of rhombus channels in the MOF crystal are occupied by the disordered DMF molecules. The striking structural feature is that the connectivity between inorganic hendecahedron units of SrO7 and TDA2− ligands gives rise to the uncommon I1O2 type 3-D framework of 1. The dielectric relaxation and novel dielectric bistability behaviors were observed for this MOF compound in the lower frequency regime (f < 103 Hz) and the higher temperature (T > 160 °C), which originated from the orientation motion of the disordered polar DMF molecules under an ac electric field. This study suggested the possibility of dielectric bistability in the designed MOFs with pores or channels.

A ferroelectric MOF with a formula [Sr(μ-BDC)(DMF)]∞ (1) was transformed into [Sr(μ-BDC)(CH2Cl2)x]∞ (2) using a solvent exchange approach, where DMF = N,N-dimethylformamide and BDC2− = benzene-1,4-dicarboxylate. The lattice solvents, CH2Cl2 molecules, in 2 were removed by heating to give the solvent-free metal–organic framework [Sr(μ-BDC)]∞ (3) and the crystal-to-crystal transformation is reversible between 1 and 3. The release of DMF molecules from 1 results in the metal–organic framework of [Sr(μ-BDC)]∞ expanding a little along the a- and b-axes. The crystal structure optimizations for 1 and 3 disclosed that the lattice expansion is associated with the alternations of the bond distances and angles in the Sr2+ ion coordination sphere along the a- and b-axes directions. The metal–organic framework 3 collapses at temperatures of more than 600 °C; such an extremely high thermal stability is related to the closed-shell electronic structure of the Sr2+ ion, namely, the coordinate bond between the closed-shell Sr2+ ion and the bridged BDC2− ligands does not have a preferred direction, which is favored for reducing lattice strains and is responsible for the higher thermal stability. The comparative investigations for the dielectric and ferroelectric behaviors of 1 and 3 confirmed that the motion of the polar DMF molecules, but not the [Sr(μ-BDC)]∞ framework, is responsible for the ferroelectric properties of 1.

Five one-dimensional (1D) ion-pair compounds [4′-R-Bz-NH2Py][M(mnt)2] (mnt2− = maleonitriledithiolate, 4′-R-Bz-NH2Py+ = 1-(4′-R-benzyl)-4-aminopyridinium and M = Pt, R = F (1), Br (2), I (3), CF3 (4); M = Ni, R = CF3 (5)) were investigated structurally and magnetically. Compounds 2 and 3 are isostructural; 4 and 5 are isomorphic. The magnetic [M(mnt)2]− anions form a 1D tetrameric stack in crystal 1, while dimeric stack in crystals 2–5. Compounds 1, 2 and 4 are diamagnetism over the temperature range 1.8–300 K, 3 shows a spin-Peierls-type transition around 124 K and 5 displays the typically magnetic character of a low-dimensional antiferromagnetic spin system with a broad maximum centered around 70 K. The attempts are failed to fit variable temperature magnetic susceptibility of both 3 in high-temperature phase and 5 over 1.8–350 K by an S = ½ Heisenberg dimer and 1D alternating chain models, probably due to anisotropic exchange interactions. Five compounds show a broad and intense near-IR absorption band in 750–1600 nm region.Graphical abstractA series of metal-bis-1,2-dithiolene ion-pair compounds exhibit diverse ion-pair arrangements, versatile magnetic properties and intense near-infrared absorption.Highlights► S = 1/2 Magnetic chain compounds show versatile ion-pair arrangements and magnetic behaviors. ► Substituent and metal ion affect ion-pair arrangement and magnetic property. ► Ion-pair compounds exhibit broad and intense near-infrared absorbance.

•New one-dimensional iodoplumbate-based hybrid compound.•Inorganic iodoplumbate chain consists of PbI6 octahedra via sharing I–I–I triangular faces.•Dynamically dipole motion via polar group rotation.•Dielectric relaxation in low-frequency and high-temperature regime.An inorganic–organic hybrid compound, [4′-methyl-1-aminopyridinium][PbI3] (1), has been synthesized and characterized structurally. The hybrid crystal crystallizes in space group P21/c, in which the Pb2 + ion, surrounded by six iodides, adopts the distorted octahedral coordination geometry; the neighboring PbI6 octahedra form the face-sharing PbI6 octahedral chain and the organic cations are aligned into stack along c-axis direction. Hybrid compound shows normal dielectric constant (ε′ < 20) below 130 °C in the frequency range of 1–107 Hz, but higher dielectric constant above 160 °C, especially, in the low-frequency regime. In addition, a novel dielectric relaxation process was observed in the frequency regime f < 106 Hz, which exhibits the characteristic activated or Arrhenius behavior, such a dielectric relaxation process ARISES from the dynamically dipole motion of the 4′-methyl-1-aminopyridinium cations under ac electrical field.An inorganic–organic hybrid compound, [4′-methyl-1-aminopyridinium][PbI3], in which crystal is built from PbI6 octahedral chains and cation stacks, shows novel thermally assisted dielectric relaxation behavior.

Taking into account that an intercalation reaction, an entropy and volume reducing process, can be promoted by increased pressure in a reactor, we developed a facile and efficient strategy for rapid preparation of DMSO and urea intercalated Kaolinites under mild reaction conditions by means of an autoclave, reducing the reaction time from several days to 6 h. The Kaolinite is a noncentrosymmetric layered inorganic host, the polar DMSO or urea molecules were inserted into the inter-layers of Kaolinite to create the hybrid ferroelectric or giant dielectric materials. Our results will shed light on the design and preparation of new hybrid functional materials with technologically important ferroelectricity and giant dielectric properties.

The ion-pair complexes of [4-NH2-PyH][M(mnt)2] (M = Pt for 1 and Ni for 3) and their deuterated analogues [4-NH2-PyD][M(mnt)2] (M = Pt for 2 and Ni for 4) are isostructural with each other. Four complexes crystalline in monoclinic space group C2/c, whose asymmetric unit consists of two halves of [M(mnt)2]− anions and one cation, show quite similar cell parameters and almost identical packing structures as well. In the crystals of 1–4, two types of crystallographically inequivalent [M(mnt)2]− anions construct individual layers, which are separated by the cation layer; the supramolecular networks are formed via the H-bonding interactions between the [M(mnt)2]− and 4-NH2-PyH+ (or 4-NH2-PyD+) ions as well as the weakly π⋯π stacking interactions between the [M(mnt)2]− anions. The four isostructural complexes exhibit canted antiferromagnetism, arising from the non-collinearity of the magnetic moments between the crystallographically inequivalent anion layers, with TC ≈ 14.8 K for 1, 13.6 K for 2, 7.7 K for 3 and 8.8 K for 4, respectively. Ac magnetic susceptibility measurements revealed that 1 and 2 show spin canting, while 3 and 4 show hidden-spin canting characteristics. The isostructural 1 and 3 were deuterated to give the divergent isotope effects on the cell volume and TC.

Three crystalline phases of [4′-CH3-Bz-NH2Py][Pt(mnt)2] (1) (4′-CH3-Bz-NH2Py+ = 1-N-(4′-methylbenzyl)-4-aminopyridinium and mnt2– = maleonitriledithiolate) were isolated, identified, and characterized. The pure 1α·solvent and 1β phases can be obtained by the evaporation of 1 in CH3CN/CH2Cl2 (V:V = 1:5) and CH3CN/CH3OH (V:V = 1:1) mixed solvents at ambient temperature, respectively; the pure 1γ phase is easily formed via the evaporation of 1 in CH3OH or mixed solvent of CH3OH/CH2Cl2 at room temperature. 1α·solvent and 1β phases crystallize in the triclinic space group P1̅ and possess quite similar cell parameters and packing structures. The anions and cations form the segregated and regular stacks in both 1α·solvent and 1β phases; moreover, the cations show the same orientation in a stack. The phase 1γ with monoclinic space group P21/c exhibits the separated and non-equidistant stacks of anion and cation, and the neighboring cations are aligned in a chair-type conformation in a stack. Charge-assisted intermolecular hydrogen-bonds exist between the anions and cations in three different crystalline phases. Dramatically different magnetic properties were observed for three crystalline phases, a spin-Peierls-type transition occurred around 260 K for 1α·solvent, while it did not appear over the temperature range 1.8–300 K for 1β, although two crystalline phases show rather analogous crystal structures. The phase 1γ shows the magnetic behavior of an S = 1/2 Heisenberg alternating-exchange antiferromagnetic linear chain.

The crystal structures and magnetic properties were investigated experimentally and theoretically for two S = ½ spin chain complexes, which consist of [M(mnt)2]− (M = Pt for 1 or Pd for 2) with 1-(4′-bromo-2′-flurobenzyl)-4-aminopyridinium (1-BrFBz-4-NH2Py+). The 1-BrFBz-4-NH2Py+ cations exhibit different molecular conformations and arrangements in 1 and 2; the [M(mnt)2]− anions form regular stacks in 1, whereas they form irregular stacks in 2. In addition, the intermolecular interactions between the [M(mnt)2]− anions and cations are also different from each other in the crystals of 1 and 2. Complex 1 shows the magnetic characteristics of a low-dimensional antiferromagnetic coupling spin system with a spin-Peierls-type transition around 7 K, and complex 2 exhibits diamagnetism over the temperature range of 5–300 K. Theoretical analyses, based on the calculations for the charge density distributions of [Pt(mnt)2]− and [Pd(mnt)2]− anions and the magnetic exchange constants within the anion spin chains, addressed the diverse molecular alignments in the crystals of 1 and 2 and distinct magnetic behaviors between 1 and 2.

A highly thermally stable, polar MOF built from the rigid ligand benzene-1,4-dicarboxylate and the main-group metal ion Sr2+ shows ferroelectricity. With the ultimate goal of making components for use in devices, the fabrication of MOF thin films on Al2O3, SrAl2O4, and Al foil substrates using the in situ solvothermal method was explored. The mechanism of macroscopic polarization reversals in the ferroelectric MOF under an ac electric field and the dependence of the morphology of the MOF thin film on the nature of the substrate surface are discussed.

Two deuteriumed quasi-one-dimensional (quasi-1D) spin-Peierls-type compounds, 4-X-benzylpyridinium-d5 bis(maleo-nitriledithiolato)nickelate (the substituent X = Br or Cl), were structurally characterized. Compared with the corresponding non-deuteration compounds, the transition temperature TC shifts to higher temperature. The isotopic effect of countercations on TC is probably related to the change of phonon frequency ω0 and ‘chemical pressure’ resulted from the substitution of pyridine by pyridine-d5.

Three [1-N-(4′-R-benzyl)-4-aminopyridinium][Pt(mnt)2] compounds were structurally and magnetically characterized, where the substituent was attached to the para-position of the phenyl ring (R = CN (1), Cl (2), and H (3); mnt2− = maleonitriledithiolate). 1 and 2 crystallized in the monoclinic space group P2(1)/c, with the cations and anions forming segregated columnar stacks. Their structural differences involved two aspects: (1) both anion and cation stacks were regular in 1 and irregular in 2; (2) the neighboring cations were arranged in the boat-type pattern in 1, whereas these cations were in the chair-type pattern in 2 within the cation stack. 3 belonged to the triclinic space group P1̅, where the anions were assembled into the stack with a tetrameric [Pt(mnt)2]− subunit, but the cations did not form the columnar stack. Magnetic measurements disclosed that a spin-Peierls-type transition occurred around 240 K for 1, whereas a long-range, antiferromagnetic ordering took place at about 5.8 K, and a metamagnetic phenomenon was observed with HC ≈ 1000 Oe for 2; 3 showed very strong antiferromagnetic interactions with diamagnetism in the temperature range 5−300 K. Combined with our previous studies, the correlation between the stacking pattern of benzylpyridinium derivatives in a cation stack and the spin-Peierls-type transition is discussed for the series of quasi-1-D [M(mnt)2]− (M = Ni, Pd and Pt) compounds.

In this review article, we have illustrated the strategies developed to achieve inorganic–organic hybrid compounds with technologically important physical properties. A series of target inorganic–organic hybrid compounds have been accomplished by incorporating the functional organic components (with a large hyperpolarizability and luminophore Schiff base cation) into the highly polarizable one-dimensional (1-D) iodoplumbate chain network. The effect of substituent features in the phenyl ring of the Schiff base cation on its molecular conformation as well as the crystal packing structure of the hybrid compound will be discussed and the multiple physical properties (ferroelectricity, NLO and multiple band emission) will also be mentioned.

Two novel lanthanide coordination polymers, [Eu2(EBTC)(DMF)5(NO3)2]·DMF (1) and [Eu2(BBTC)1.5(CH3OH)2(H2O)2]·7DMF·HNO3 (2) (EBTC4− = 1,1′-ethynebenzene-3,3′,5,5′-tetracarboxylate; BBTC4− = 1,1′-butadiynebenzene-3,3′,5,5′-tetracarboxylate), were successfully synthesized from conjugated ligands of EBTC4− and BBTC4−. Although the two tetracarboxylate ligands have similar structures, their different rigidity/flexibility results in quite different networks upon complexation. Complex 1 has a two-dimensional (2-D) layered structure with two crystallographically independent Eu3+ ions, one in a distorted monocapped square-antiprism and the other in a distorted square-antiprism coordination geometry. Complex 2 exhibits a three-dimensional (3-D) porous framework, with one type of Eu3+ in a distorted square-antiprism and the other in a trigondodecahedron environment. Both 1 and 2 emit the intensely red characteristic luminescence of Eu3+ ion at room temperature, with a long lifetime of up to 1.3 and 0.7 ms, respectively, during which the ligand emission of EBTC4−/BBTC4− was quenched by the Eu3+ ion, indicating the existence of efficient energy transfer between the conjugated ligand of EBTC4−/BBTC4− and the Eu3+ ion. Thus, both EBTC4− and BBTC4− are ideal ligands with an “antenna” effect for the Eu3+ ion. The two complexes show the single-ion magnetic behaviors of Eu3+ with strong spin–orbit coupling interactions even if there are shorter distances (5.714 Å for 1versus 4.275 and 5.360 Å for 2) between the neighboring Eu3+ ions connected by oxygen atoms of the tetracarboxylates.

A heteroleptic nickel-bis-1,2-dithiolene ion–pair complex, [BzQl][Ni(dmit)(mnt)] (where BzQl+ = 1-(benzyl)quinolinium; dmit2− = 2-thioxo-1,3-dithiole-4,5-dithiolate, mnt2− = maleonitriledithiolate), was synthesized and characterized structurally, which exhibited novel magnetic bistability. The compound crystallized in triclinic system with space group P-1. The anions and cations form alternating layered alignments, and the anionic layer is built by the irregularly heteroleptic [Ni(dmit)(mnt)]− chains, where the neighboring anions are connected via lateral-to-lateral S…S contacts of dmit2− ligands. The temperature dependences of magnetic susceptibility follow the S = ½ Heisenberg alternating linear-chain model in high-temperature phase and Curie–Weiss law in low-temperature phase.A heteroleptic nickel-bis-1,2-dithiolene compound contains a one-dimensional S = ½ magnetic chain and exhibits an unusual hysteretic magnetic transition behavior.Highlights► A heteroleptic nickel-bis-1,2-dithiolene complex as magnetic molecular architecture. ► New one-dimensional irregular S = ½ magnetic chain. ► Double maximums of magnetic susceptibility. ► Hysteretic magnetic transition.

An ionic metal–dithiolene complex, 1,1'-didecyl-4,4'-bipyridinium bis(maleonitriledithiolato)zincate(II) ([Zn(mnt)2]2−), was synthesized and characterized by elemental analysis, infrared spectroscopy and crystal structure. In the [Zn(mnt)2]2− moiety, the complex shows distorted tetrahedral geometry with Zn2+ coordinated to four S-atoms from two mnt2− ligands, and its long molecular axis adopts a similar orientation with 1,1'-didecyl-4,4'-bipyridinium. Two distinguishable redox processes occur in the voltage region of − 1.0 to 1.0 V, with the irreversible and reversible redox couples corresponding to [Zn(mnt)2]2−/[Zn(mnt)2]− and 1,1'-didecyl-4,4'-bipyridinium+/1,1'-didecyl-4,4'-bipyridinium2+, respectively. An uncommon nematic mesophase behavior in this complex was confirmed by polarized-light optical microscopy (POM) and differential scanning calorimetry (DSC) measurements.An uncommon nematic mesophase behavior was observed in a charge transfer salt consisted of bis(maleonitriledithiolato)zincate dianion with 1,1'-didecyl-4,4'-bipyridiniumResearch Highlights► A viologen derivative, 1,1'-didecyl-4,4'-bipyridinium, as liquid crystal architecture. ► A charge-transfer-salt-type ionic liquid crystal. ► Ionic liquid crystal shows nematic mesophase. ► Formation of mesophase arises from the hydrocarbon chain melting.

1D spin-Peierls-like complexes assembled from [Ni(mnt)2]− with Λ-shaped 1-(4′-R-benzyl)pyridinium derivatives (R represents a substituent) are reviewed, with data on their crystal structures, magnetic properties under ambient conditions as well as under pressure, and the nature of the paramagnetic-to-nonmagnetic transition. In this series of 1D spin systems, the correlation between the magnetic exchange and the anion stacking pattern is addressed by application of density functional theory (DFT) combined with a broken-symmetry approach. The qualitative relationship between the transition enthalpy change and the variation of the magnetic susceptibility in the low-temperature phase is determined. The influence of nonmagnetic doping on the structural and magnetic properties and the magnetic transitions are reported. Furthermore, the effect of the substituent group in the phenyl ring of the cation on the transition temperature and the origin of the transition are discussed.

An ion-pair complex of [Ni(mnt)2]2− with p-N-benzylpyridinium α-nitronyl nitroxide radical cations (p-BzPYNN) in acetonitrile shows a moderate and broad absorbance in near-IR region. In the crystal of this complex, two radical cations form a dimer via strong H-bonding interaction; such kinds of dimers are connected into H-bonding chain by [Ni(mnt)2]2− dianions through weak H-bonding interactions. The neighboring H-bonding chains are arranged into supramolecular sheet via π…π stacking interactions between the five-membered chelate-ring of anion and the superimposed pyridyl rings of cations. The polycrystalline EPR spectrum exhibits two isotropic EPR signals. Based on the analyses of crystal structure, variable temperature magnetic susceptibility and electronic spectrum, the stronger EPR signal is assigned to the radical cation, the weaker one probably arises from a trace amount of [Ni(mnt)2]1− species.The polycrystalline EPR spectrum of an ion-pair complex of [Ni(mnt)2]2− with p-N-benzylpyridinium α-nitronyl nitroxide radicals (p-BzPYNN) exhibits two isotropic EPR signals, which origins were discussed.

Three complexes of [Ni(mnt)2]− (mnt2− = maleonitriledithiolate) with benzylpyridinium derivatives, 1-(2′,6′-dichlorobenzyl)-4-aminopyridinium (abbr. Cl2BzNH2Py+) and 1-(2′,6′-dichlorobenzyl)quinolinium (abbr. Cl2BzQl+), have been characterized structurally and magnetically. The [Cl2BzNH2Py][Ni(mnt)2] solution in MeCN was slowly evaporated to give the crystals of 2, whilst its solution in i-PrOH/MeCN yields 2·0.5i-PrOH. The [Ni(mnt)2]− anions are arranged in the mixed stacks of anions and cations in 2, and the segregated stacks of anions and cations in 2·0.5i-PrOH and 4. Even though three complexes exhibit different stacking pattern of magnetic anions, their temperature dependences of magnetic susceptibilities in 2–300 K range show a common feature, namely, two broad maxima of magnetic susceptibility. Powder X-ray examination for three complexes excluded that the impurity causes such complicated magnetic behaviors. Combined with the single crystal structure analyses, the double broad maxima of magnetic susceptibility is probably attributed to anisotropic magnetic exchange interactions between magnetic anions.

The hydrothermal synthesis and structure for a new iron phosphate based open-framework solid, (NH4)[Fe2(OH)(H2O)(PO4)2]·1.5H2O, is presented. The three-dimensional (3-D) framework is built from butterfly-shaped tetranuclear iron-oxygen clusters, which are coordinated by eight PO4 tetrahedra to create 8-membered windows along the a-, b- and c-axes; the lattice water molecules as well as the counter NH4+ cations reside in the cross channels. The new open-framework solid is a pseudo-polymorph with the known structure of the mineral sphenicidite, and exhibits spontaneous magnetization in the low temperature regime with TN ≈ 25 K, which is a result of canted spin antiferromagnetism.

Three ion-pair complexes, [4-NH2-Py]2[M(mnt)2] (4-NH2-Py1+ = 4-amino-pyridinium; mnt2− = maleonitriledithiolate; M = Pt (1), Pd (2) or Ni (3)), have been synthesized and characterized. In the crystal of 1, the strong H-bonding interaction was found from the protonated N-atom of pyridinium to the CN group of [Pt(mnt)2]2− together with a weak Pt…H interaction between the anion and the cation. The crystals of 2 and 3 are isostructural with very similar lattice parameters and packing structures, which are distinct from the crystal of 1. Two kinds of strong H-bonding interactions are observed in the crystals of 2 and 3 between the CN groups of [M(mnt)2]2− anion and the protonated N-atom of 4-NH2-Py1+ cation as well as the CN groups of [M(mnt)2]2− anion and the amino group of 4-NH2-Py1+ cation. Complex 1 shows an intense near-IR absorbance in acetonitrile and solid state, such an absorption band is probably assigned to IPCT transition as well as a trace amount of [Pt(mnt)2]1− species; complex 3 possesses a weak near-IR absorption band which can be attributed to the mixture of d–d transition in [Ni(mnt)2]2− and IPCT transition as well as a trace amount of [Ni(mnt)2]1− species.

Four isostructural inorganic−organic hybrid ferroelectric compounds, assembled from achiral 3-R-benzylidene-1-aminopyridiniums (R = NO2, Br, Cl, or F for 1−4, respectively) and [PbI3]− anions with the chiral Kagomé-shaped tubular aggregating architecture, show larger spontaneous polarizations.

The crystal structures and magnetic properties of two new ion-pair complexes, [N-NH2Py][Ni(mnt)2] (1) and [N-NH2Ql][Ni(mnt)2] (2) (N-NH2Py+ = 1-aminopyridinium, N-NH2Ql+ = 1-aminoquinolinium; mnt2− = maleonitriledithiolate) have been investigated. The differences of the molecular topology and size of the counter cation result in distinct anionic and cationic stacking patterns in the crystals, namely, in the crystal of 1 the anions (A) and cations (C) alternate to stack into a mixed column in the fashion of …AACCAACC…, and the neighboring columns are connected together via intermolecular H-bonding interactions as well as van der Waals forces; while, in the crystal of 2, the anions and cations alternate to form a mixed columnar stack in the manner of …ACAC…, and the adjacent columns are held together via weak van der Waals forces. Investigations of variable-temperature magnetic susceptibility indicated that 1 is a spin gap system but its magnetic behavior does not follow the Bleaney–Bowers spin dimer model; 2 shows a magnetic feature of linear decrease of χmT value upon cooling, and this kind of magnetic behavior is probably related to the presence of temperature independent paramagnetism.The molecular geometry of counter cation effect on the stacking structures as well as the magnetic properties of [Ni(mnt)2]− complexes.

A charge-transfer compound, [NO2BzPz][Ni(mnt)2] (NO2BzPz+ = 1-(4′-nitrobenzyl)pyrazinium and mnt2− = maleonitriledithiolate), has been structurally characterized, which shows rare noncovalently intermolecular interactions between lone-pair electron and electron-deficient pyrazine rings (NO2⋯π and CN⋯π), theoretical analysis reveals that such intermolecular interactions can be attributed to Coulomb interaction. The paramagnetic [Ni(mnt)2]− anions in [NO2BzPz][Ni(mnt)2] form a dimerized stack and strong antiferromagnetic coupling interaction is observed in such a spin dimer which lead to weak paramagnetic feature in this compound.NO2⋯π interaction between the O-atoms of NO2 and pyrazine rings as well as CN⋯π interaction between the N-atom of CN and pyrazine ring is observed in the crystal of 1-(4′-nitrobenzyl)pyrazinium bis(maleonitriledithiolato)nickelate(III).

A novel heterostranded double-helical coordination polymer is self-assembly from two flexible ligands, 4-carboxymethylbenzoic acid (H2L) and 1,1′-(1,4-butanediyl)bis(imidazole) (abbr. as bbi), with Zn2+ ion under solvent-thermal condition. The heterostranded double-helix constructs a chiral channel, which is filled by lattice water molecules; the adjacent heterostranded double-helical channels share Zn2+ ions to develop into a homochiral helical two-dimensional sheet, and the right- and left-handed chiral sheets further array in an alternating fashion to generate a racemic crystal via van de Waals forces. This coordination polymer emits blue fluorescence in the solid state.A novel heterostranded double-helix constructs a chiral channel which further develops into a homochiral helical two-dimensional sheet, and such a coordination polymer emits blue fluorescence.

Three new ion-pair complexes, consisting of 1-benzyl-4-aminopyridinium with [M(mnt)2]2− where mnt2− = maleonitriledithiolate and M = Ni2+, Pd2+ or Pt2+ for complexes 1–3, have been synthesized and structurally characterized. X-ray single crystal studies revealed that three complexes are isostructural and crystallize in monoclinic space group C2/c, and there exist weak H-bonding interactions between –NH2 groups of cation and –CN group of anion as well as weak M…H-bonding interactions between anions and cations. The calculations of charge density distribution disclosed that the M…H-bonding interaction in crystals of 1–3 is mainly attributed to static electric interactions. Two types of H-bonding interactions lead to the formation of two-dimensional sheet structure which is parallel to the crystallographic bc-plane in the crystals of 1–3. A near-IR absorbance appears in the UV–vis-NIR spectra of 1 and 3, respectively, while does not come out in the spectra of 2.

Two quasi-one-dimensional (quasi-1D) compounds, [4′-CH3Bz-4-RPy][Ni(mnt)2] (mnt2− = maleonitriledithiolate), where 4′-CH3Bz-4-RPy+ = 1-(4′-methylbenzyl)pyridinium (denoted as compound 1) and 1-(4′-methylbenzyl)-4-aminopyridinium (denoted as compound 2), show a spin-Peierls-like transition with TC ≈ 182 K for 1 and TC ≈ 155 K for 2. The enthalpy changes for the transition are estimated to be ΔH = 316.6 J·mol−1 for 1 and 1082.1 J·mol−1 for 2. From fits to the magnetic susceptibility, the magnetic exchange constants in the gapless state are calculated to be J = 166(2) K with g = 2.020(23) for 1 versus J = 42(0) K with g = 2.056(5) for 2. In the high-temperature (HT) phase, 1 and 2 are isostructural and crystallize in the monoclinic space group P21/c. The nonmagnetic cations and paramagnetic anions form segregated columns with regular anionic and cationic stacks. In the low-temperature (LT) phase, the crystals of the two compounds undergo a transformation to the triclinic space group P-1, and both anionic and cationic stacks dimerize. In the transformation from the HT to LT phases, the two compounds exhibit divergent structural features, with lattice compression for 1 but lattice expansion for 2, due to intermolecular slippage. Combined with our previous studies, it is also noted that the transition temperature, TC, is qualitatively related to the cell volume in the HT phase for the series of compounds [1-(4′-R-benzylpyridinium][Ni(mnt)2] (where R represents the substituent). When there is a single substituent in the para position of benzene, giving a larger cell volume, the transition temperature increases.

Three complexes, Cd(8-aminoql)2×2 (8-aminoql=8-aminoquinoline; X−=ClO4−, SCN−, 1 and 2, respectively) and Cd(8-aminoql)(N3)2 (3), were synthesized and structurally characterized. For each complex, the Cd2+ ion exhibits distorted octahedral coordination geometry. Two 8-aminoquinoline molecules and two counter-anions are coordinated to the Cd2+ center to form a mononuclear species with two trans-ClO4− anions for 1, while two SCN− anions adopt a cis-configuration for 2. The intermolecular H-bonding interactions between the –NH2 groups and the O atom (1) and the S atom (2) result in the formation of a 2-D layered structure. In the crystal of 3, the N3− anions bridging the neighboring Cd(8-aminoql)2+ units form a 1-D coordination polymer. The three complexes emit green luminescence. The emission bands possess a broad asymmetric feature, which can be assigned to L′LCT transitions based on DFT and TDDFT calculations.

Two isostructural bimetallic tetranuclear chiral complexes, [K(18-crown-6)]3[Fe(ox)3] · 9H2O and [K(18-crown-6)]3[Cr(ox)3] · 9H2O, crystallize in rhombohedral R3 space group, the tetranuclear cluster is respectively built from one [Fe(ox)3]3− or [Cr(ox)3]3− species with three K(18-crown-6 ether) supramolecular cations linked by oxalate groups, and lattice water molecules form the double helical chains. Two complexes are second-harmonic-generation (SHG) active with the SHG response about 0.5 times that of urea.Two bimetallic tetranuclear (K3–Fe or K3–Cr) complexes with three-blade propeller shape contain double helical water chains and exhibit second-order NLO properties.

X-band single-crystal electron paramagnetic resonance (EPR) studies of the molecular alloy [NO2BzPy][Au0.57Ni0.43(mnt)2] are presented in this paper. At room temperature, EPR spectra show both intense resonance signals (main signals) and weak satellite quartet lines. The characteristics of both intense and weak EPR signals depend on the magnetic field orientation. The main signals arise from two magnetically nonequivalent [Ni(mnt)2]− anions, and their corresponding principal values of the g tensor are (gx′)1 = 2.04653, (gy′)1 = 2.00096, and (gz′)1 = 2.15319 and (gx′)2 = 2.04520, (gy′)2 = 1.99734, and (gz′)2 = 2.15361, respectively. The weak satellite lines, whose patterns strongly depend on the magnetic field direction, can be attributed to the hyperfine coupling of the electron spin with the 197Au nucleus of the [Au(mnt)2]− species. Density functional theory calculations for the spin and charge distributions of the dimer {[Ni(mnt)2][Au(mnt)2]}2− indicate that the hyperfine interaction of the electron spin with the 197Au nuclear spins is caused, in part, by the charge transfer between the [Ni(mnt)2]− and the [Au(mnt)2]− species.

Two quasi-1D molecular magnets, [RBzPy][Ni(mnt)2] (RBzPy+ = 1-(4′-nitrobenzyl)pyridinium (1) and 1-(4′-brominobenzyl)pyridinium (2); mnt2− = maleonitriledithiolate), are isostructural and possess a spin-Peierls-like transition at Tc ≈ 184 K for 1 and ≈112 K for 2 at ambient pressure. The magnetic susceptibility measurements under different applied pressures disclosed two compounds exhibiting similar magnetic behaviors. For each compound, the spin transition shifts to higher temperature with pressure and the paramagnetism in high-temperature phase is suppressed. These trends seem to be explicable by the shortened distances induced by the pressure between magnetic [Ni(mnt)2]− anions and thus leading to enhancements of antiferromagnetic interactions.Influence of pressure on spin-Peierls-like transition in quasi-1D Heisenberg spin chain with S = 1/2.

Two novel lanthanide coordination polymers, [Eu2(EBTC)(DMF)5(NO3)2]·DMF (1) and [Eu2(BBTC)1.5(CH3OH)2(H2O)2]·7DMF·HNO3 (2) (EBTC4− = 1,1′-ethynebenzene-3,3′,5,5′-tetracarboxylate; BBTC4− = 1,1′-butadiynebenzene-3,3′,5,5′-tetracarboxylate), were successfully synthesized from conjugated ligands of EBTC4− and BBTC4−. Although the two tetracarboxylate ligands have similar structures, their different rigidity/flexibility results in quite different networks upon complexation. Complex 1 has a two-dimensional (2-D) layered structure with two crystallographically independent Eu3+ ions, one in a distorted monocapped square-antiprism and the other in a distorted square-antiprism coordination geometry. Complex 2 exhibits a three-dimensional (3-D) porous framework, with one type of Eu3+ in a distorted square-antiprism and the other in a trigondodecahedron environment. Both 1 and 2 emit the intensely red characteristic luminescence of Eu3+ ion at room temperature, with a long lifetime of up to 1.3 and 0.7 ms, respectively, during which the ligand emission of EBTC4−/BBTC4− was quenched by the Eu3+ ion, indicating the existence of efficient energy transfer between the conjugated ligand of EBTC4−/BBTC4− and the Eu3+ ion. Thus, both EBTC4− and BBTC4− are ideal ligands with an “antenna” effect for the Eu3+ ion. The two complexes show the single-ion magnetic behaviors of Eu3+ with strong spin–orbit coupling interactions even if there are shorter distances (5.714 Å for 1versus 4.275 and 5.360 Å for 2) between the neighboring Eu3+ ions connected by oxygen atoms of the tetracarboxylates.

The ion-pair complexes of [4-NH2-PyH][M(mnt)2] (M = Pt for 1 and Ni for 3) and their deuterated analogues [4-NH2-PyD][M(mnt)2] (M = Pt for 2 and Ni for 4) are isostructural with each other. Four complexes crystalline in monoclinic space group C2/c, whose asymmetric unit consists of two halves of [M(mnt)2]− anions and one cation, show quite similar cell parameters and almost identical packing structures as well. In the crystals of 1–4, two types of crystallographically inequivalent [M(mnt)2]− anions construct individual layers, which are separated by the cation layer; the supramolecular networks are formed via the H-bonding interactions between the [M(mnt)2]− and 4-NH2-PyH+ (or 4-NH2-PyD+) ions as well as the weakly π⋯π stacking interactions between the [M(mnt)2]− anions. The four isostructural complexes exhibit canted antiferromagnetism, arising from the non-collinearity of the magnetic moments between the crystallographically inequivalent anion layers, with TC ≈ 14.8 K for 1, 13.6 K for 2, 7.7 K for 3 and 8.8 K for 4, respectively. Ac magnetic susceptibility measurements revealed that 1 and 2 show spin canting, while 3 and 4 show hidden-spin canting characteristics. The isostructural 1 and 3 were deuterated to give the divergent isotope effects on the cell volume and TC.

The second polymorph, the β-crystal, of the nickel-bis-dithiolene compound [4′-CF3bzPy][Ni(mnt)2], where 4′-CF3bzPy = 1-(4′-trifluoromethylbenzyl)pyridinium and mnt2− = maleonitriledithiolate, was obtained. The variable-temperature single crystal structures, magnetic behavior in 1.8–300 K and dielectric nature in 123–373 K have been investigated for the β-crystal. This polymorph experiences two hysteretic magnetic phase transitions in a narrow temperature region (190–217 K) with the thermal hysteresis loops ca. 6 K and ca. 11 K. The two hysteretic magnetic phase transitions are coupled with two isostructural phase transitions (IPTs), respectively, which are driven by the novel step-wise dynamic orientation motion of the anion and cation in the β-crystal. There is an absence of a dielectric anomaly in the structural transformation temperature interval. However, a dielectric relaxation, related to the dipole motion of polar CF3 groups in the cations under an ac electrical field, emerges in the high-temperature phase.

Taking into account that an intercalation reaction, an entropy and volume reducing process, can be promoted by increased pressure in a reactor, we developed a facile and efficient strategy for rapid preparation of DMSO and urea intercalated Kaolinites under mild reaction conditions by means of an autoclave, reducing the reaction time from several days to 6 h. The Kaolinite is a noncentrosymmetric layered inorganic host, the polar DMSO or urea molecules were inserted into the inter-layers of Kaolinite to create the hybrid ferroelectric or giant dielectric materials. Our results will shed light on the design and preparation of new hybrid functional materials with technologically important ferroelectricity and giant dielectric properties.

Two new one-dimensional (1-D) compounds, [CH3-BzPy][Pt(mnt)2] (1) and [CH3-BzPy-d5][Pt(mnt)2] (2) (CH3-BzPy+ = 1-N-(4-CH3-benzyl)pyridinium and the pyridine in CH3-BzPy+ was replaced by pyridine-d5 to give the CH3-BzPy-d5+; mnt2− = maleonitriledithiolate), were synthesized and characterized. 1 and 2 show similar magnetic behavior in 1.8–400 K; they experience a spin-Peierls-type transition around 320 K and show a uniform antiferromagnetic S = 1/2 chain behavior in high temperature (HT) phase, a spin gap feature in low temperature (LT) phase. A symmetry breaking structural phase transition is associated with the spin-Peierls-type transition. Two isostructural compounds crystallize in space group P2(1)/c in HT phase, with a = 12.3066(8) Å, b = 27.0522(18) Å, c = 7.4248(4) Å, β = 104.204(6)° and V = 2396.3(3) Å3 for 1versus a = 12.3331(9) Å, b = 27.087(4) Å, c = 7.4501(9) Å, β = 104.149(13)° and V = 2413.3(6) Å3 for 2 at 353 K, while space group P in LT phase, with a = 7.3203(10) Å, b = 12.2816(16) Å, c = 26.904(4) Å, α = 88.500(4)°, β = 86.731(4)°, γ = 75.421(4)° and V = 2337.0(5) Å3 for 1versus a = 7.3308(8) Å, b = 12.2848(13) Å, c = 26.930(3) Å, α = 88.479(3)°, β = 86.652(4)°, γ = 75.563(3)° and V = 2344.5(4) Å3 for 2 at 296 K. DSC measurements revealed 1 and 2 showing almost the same TC. This observation is distinction from the [Ni(mnt)2]−-based spin-Peierls-type analogues [CH3-BzPy][Ni(mnt)2] and [CH3-BzPy-d5][Ni(mnt)2] where the deuteration leads to TC up shifting 2.3 K.

A three-dimensional NbO-type metal–organic framework (MOF) is composed of paddle-wheel-type dinuclear Cu2 secondary units and 1,1′-ethynebenzene-3,3′,5,5′-tetracarboxylate (EBTC4−) linkers. Two types of nanometer-sized cavities are formed in this framework with ca. 8.5 Å in diameter for the small one and dimensions of ca. 8.5 × 8.5 × 21.5 Å for the larger and irregular elongated cavity. The guest molecules, H2O, DMF and DMSO, occupy the cavities of the as-prepared MOF crystal (labeled as MOF 1). MOF 2 was obtained by the guest-exchange approach using CH3OH, and the H2O and CH3OH molecules reside in the cavities of 2. Two MOFs show greenish-turquoise color at ambient temperature due to the d–d transition of Cu2+ ions in the framework, and the reversible thermochromic behavior owing to the change of the coordination environment of Cu2+ ions with varying temperatures. The films of 1 and 2 were fabricated on the α-Al2O3 and SiO2 supports by the seeded growth method, displaying similar reversible thermochromic behavior to the corresponding MOFs. This study suggested the possibility of novel thermochromic materials in the rational design of MOFs.

Two deuteriumed quasi-one-dimensional (quasi-1D) spin-Peierls-type compounds, 4-X-benzylpyridinium-d5 bis(maleo-nitriledithiolato)nickelate (the substituent X = Br or Cl), were structurally characterized. Compared with the corresponding non-deuteration compounds, the transition temperature TC shifts to higher temperature. The isotopic effect of countercations on TC is probably related to the change of phonon frequency ω0 and ‘chemical pressure’ resulted from the substitution of pyridine by pyridine-d5.

In this review article, we have illustrated the strategies developed to achieve inorganic–organic hybrid compounds with technologically important physical properties. A series of target inorganic–organic hybrid compounds have been accomplished by incorporating the functional organic components (with a large hyperpolarizability and luminophore Schiff base cation) into the highly polarizable one-dimensional (1-D) iodoplumbate chain network. The effect of substituent features in the phenyl ring of the Schiff base cation on its molecular conformation as well as the crystal packing structure of the hybrid compound will be discussed and the multiple physical properties (ferroelectricity, NLO and multiple band emission) will also be mentioned.

Kaolinite (K), a polar and layered aluminosilicate mineral, was used as the host; ethanolamine (EOA) and ethylene glycol (EG) were inserted into the kaolinite interlayer to give the intercalated supramolecular compounds kaolinite–ethanolamine (K-EOA) and kaolinite–ethylene glycol (K-EG), respectively. The intercalation of EOA and EG resulted in an increase in the d(001)-value by 3.4 and 3.68 Å, which corresponds to expansion of the interlayer space by 156.7 Å3 in K-EOA and 169.6 Å3 in K-EG, respectively. The characteristic infrared-active ν(O–H) modes ν1, ν2 and ν3 besides ν5, which were quite sensitive to the host–guest interaction, were not significantly affected by intercalation in K-EOA and K-EG, and two intercalated compounds showed lower deintercalation temperature (115 and 109 °C for K-EOA and K-EG, respectively). These are due to weakly intermolecular interactions between the intercalant molecules and the kaolinite framework, which is in agreement with the theoretical analysis of crystal structures of the intercalated compounds. K-EOA and K-EG showed novel dielectric relaxation behavior, which originates from the dynamic orientation motion of intercalant molecules.

A new one-dimensional (1-D) ion-pair compound, [1,7-bis(1-methylimidazolium)heptane][Ni(mnt)2]2 (mnt2− = maleonitriledithiolate), was synthesized and characterized structurally and magnetically. This compound shows a spin-Peierls-type transition at around 235 K. Its crystal structure belongs to the monoclinic system with space group C2/c and the magnetic [Ni(mnt)2]− anions form uniform stacks in the high-temperature (HT) phase. The crystal undergoes a transformation into the triclinic space group P accompanied by the magnetic transition and the anion stacks become dimerized in the low-temperature (LT) phase. The entropy changes (ΔS) are estimated to be 0.772 J K−1 mol−1 for the spin-Peierls-type transition, from DSC data, which is much less than the spin entropy change (ΔS = Rln 2 ≈ 5.76 J K−1 mol−1), indicating that a substantial short-range order persists above the transition temperature. The variable temperature IR spectra showed that the peak positions and intensities for the bands near 1160 and 725 cm−1, which correspond respectively to the ν(C–C) + ν(C–S) mode of the mnt2− ligands and the rocking vibration mode of the methylene group γr(CH2) in the cation moiety, undergo an abrupt change at around 240 K, close to the transition temperature. This observation demonstrates that the intramolecular vibrations of both the anion and the counter-cation probably couple with the spins to cooperate with the spin-Peierls-type phase transition in this 1-D spin system.

A ferroelectric MOF with a formula [Sr(μ-BDC)(DMF)]∞ (1) was transformed into [Sr(μ-BDC)(CH2Cl2)x]∞ (2) using a solvent exchange approach, where DMF = N,N-dimethylformamide and BDC2− = benzene-1,4-dicarboxylate. The lattice solvents, CH2Cl2 molecules, in 2 were removed by heating to give the solvent-free metal–organic framework [Sr(μ-BDC)]∞ (3) and the crystal-to-crystal transformation is reversible between 1 and 3. The release of DMF molecules from 1 results in the metal–organic framework of [Sr(μ-BDC)]∞ expanding a little along the a- and b-axes. The crystal structure optimizations for 1 and 3 disclosed that the lattice expansion is associated with the alternations of the bond distances and angles in the Sr2+ ion coordination sphere along the a- and b-axes directions. The metal–organic framework 3 collapses at temperatures of more than 600 °C; such an extremely high thermal stability is related to the closed-shell electronic structure of the Sr2+ ion, namely, the coordinate bond between the closed-shell Sr2+ ion and the bridged BDC2− ligands does not have a preferred direction, which is favored for reducing lattice strains and is responsible for the higher thermal stability. The comparative investigations for the dielectric and ferroelectric behaviors of 1 and 3 confirmed that the motion of the polar DMF molecules, but not the [Sr(μ-BDC)]∞ framework, is responsible for the ferroelectric properties of 1.

The crystal structures and magnetic properties were investigated experimentally and theoretically for two S = ½ spin chain complexes, which consist of [M(mnt)2]− (M = Pt for 1 or Pd for 2) with 1-(4′-bromo-2′-flurobenzyl)-4-aminopyridinium (1-BrFBz-4-NH2Py+). The 1-BrFBz-4-NH2Py+ cations exhibit different molecular conformations and arrangements in 1 and 2; the [M(mnt)2]− anions form regular stacks in 1, whereas they form irregular stacks in 2. In addition, the intermolecular interactions between the [M(mnt)2]− anions and cations are also different from each other in the crystals of 1 and 2. Complex 1 shows the magnetic characteristics of a low-dimensional antiferromagnetic coupling spin system with a spin-Peierls-type transition around 7 K, and complex 2 exhibits diamagnetism over the temperature range of 5–300 K. Theoretical analyses, based on the calculations for the charge density distributions of [Pt(mnt)2]− and [Pd(mnt)2]− anions and the magnetic exchange constants within the anion spin chains, addressed the diverse molecular alignments in the crystals of 1 and 2 and distinct magnetic behaviors between 1 and 2.