The radical bridged compound [(Ni(TPMA))2-μ-bmtz•–](BF4)3·3CH3CN (bmtz = 3,6-bis(2′-pyrimidyl)-1,2,4,5-tetrazine, TPMA = tris(2-pyridylmethyl)amine) exhibits strong ferromagnetic exchange between the S = 1 NiII centers and the bridging S = 1/2 bmtz radical with J = 96 ± 5 cm–1 (−2JNi-radSNiSrad). DFT calculations support the existence of strong ferromagnetic exchange.

The synthesis of two new radical-bridged compounds [Co3(bptz)3(dbm)3]·2toluene (1) and [Co4(bptz)4(dbm)4]·4MeCN (2) (bptz = 3,6-bis(pyridyl)-1,2,4,5-tetrazine; dbm = 1,3-diphenyl-1,3-propanedionate) is reported. The presence of the ligand-centered radical has been confirmed by X-ray crystallography and SQUID magnetometry. These complexes are the first metallacycles bearing nitrogen heterocyclic radicals as bridges. Magnetic studies reveal strong antiferromagnetic metal···radical coupling with coupling constants of J = −67.5 and −66.8 cm–1 for 1 and 2, respectively. DFT calculations further support the strong antiferromagnetic coupling between CoII ions and bptz radicals and confirm S = 3 and S = 4 spin ground states for 1 and 2, respectively.

A building block approach has been used to prepare a new family of hexanuclear magnetic molecules Mn4Nb2, Fe4Nb2, and Co4Nb2 of general formula {[MII(tmphen)2]4[NbIV(CN)8]2}·solv (M = Mn, Fe, Co; tmphen = 3,4,7,8-tetramethyl-1,10-phenanthroline; solv = MeOH and/or H2O). Mn4Nb2 exhibits a magnetocaloric effect at temperatures close to 1.8 K, and Fe4Nb2 undergoes an incomplete gradual spin crossover and a photomagnetic response related to light-induced excited spin state trapping.

A pair of related dinuclear lanthanide compounds, viz., [Dy(tmhd)3]2(bptz) (1) and {Cp2Co}{[Dy(tmhd)3]2(bptz)} (2) (tmhd = 2,2,6,6-tetramethyl-3,5-heptane dionate; bptz = 3,6-bis(2-pyridyl)-1,2,4,5-tetrazine) are reported. These molecules represent the first study of rare earth ions in which an organic ligand bridged species is isolated in both the neutral and radical anion forms. Both compounds exhibit out-of-phase signals below 4 K. The radical compound is highly air stable, with minimal changes in magnetic behavior after exposure to the atmosphere for two weeks.

The titanium(III) cyanide compound [Et4N][Tp*Ti(CN)3] ([Et4N] = tetraethylamonium; Tp* = 3,5-dimethyltrispyrazolylhydroborate) is reported, which exhibits a trigonally distorted geometry. Magnetic data and ab initio calculations verified that the molecule is an S = 1/2 paramagnet and that it exhibits significant temperature-independent paramagnetism.

A family of isostructural, mononuclear CoII complexes with distorted trigonal bipyramidal coordination environments is reported. The degree of distortion as well as the overall symmetry of the molecules varies among the members of the series. Different experimental procedures resulted in the isolation of solvomorphs (pseudopolymorphs with different solvent content) for some of the family members. Importantly, their disparate packing arrangements lead to very different dynamic magnetic behavior. The results of magnetostructural correlations and ab initio calculations reveal that the deciding factor for SMM behavior is not the degree of distortion which, a priori, would be expected to be the case, but rather the interactions between neighboring molecules in the solid state.

The bifunctional salt [Co(terpy)2](TCNQ)3·CH3CN (terpy = 2,2′;6′,2′′-terpyridine, TCNQ = 7,7,8,8-tetracyanoquino-dimethane) exhibits a high room temperature conductivity of 0.13 S cm−1 and an anomaly in conductivity at ∼190 K as evidenced by variable temperature structural, magnetic and conductivity studies. The anomaly in the conductivity at 190 K has been correlated with the temperature dependent structural breathing and Jahn–Teller distortion of the low spin state of the SCO units, as well as the charge fluctuations and supramolecular π-stacking interactions of partially charged TCNQ radicals. The modular synthetic approach leads to an accessible source of partially charged TCNQ radicals for the facile preparation of bifunctional molecular materials with high electrical conductivity.

A facile building block approach was employed for the self-assembly of metal–organic macrocyclic complexes and organocyanide dianions into one-dimensional coordination polymers. The conformation of the organocyanide dianions as well as π–π stacking and hydrogen bonding interactions were found to be critical factors that determine the formation of a particular structure. In the case of 1,3-dicyanamidobenzene dianion (DCNB2–) bridging ligands, the absence of water resulted in an unprecedented aperiodic quadruple helical structure in which the π–π stacking interaction dominates, whereas, in the presence of water, a zigzag chain compound in which hydrogen bonding interactions prevail is formed.

The incorporation of TCNQ˙− (7,7,8,8-tetracyanoquinodimethane) radicals as counterions for the spin-crossover material [Co(pyterpy)2](TCNQ)2·solvent (pyterpy = 4′-(4′′′-pyridyl)-2,2′:6′,2′′-terpyridine) leads to structural distortions of the [Co(pyterpy)2]2+ spin-crossover cation as compared to [Co(pyterpy)2](PF6)2. Variable temperature structural and magnetic studies indicate that the supramolecular π-stacking interactions between the terminal pyridyl groups and TCNQ radicals play a crucial role in the spin-crossover properties.

The pentanuclear compound [VII(tmphen)2]3[MoIII(CN)6]2 (tmphen = 3,4,7,8-tetramethyl-1,10-phenanthroline) exhibits a record antiferromagnetic exchange coupling constant of JV–Mo = −114 cm–1. This is the first example of a heterobimetallic cyanide compound with such strong magnetic coupling.

The π–π stacking interactions between tptz units from adjacent Sm(tptz)(HCOO)3 coordination nanotubes leads to additional 1D channels (tptz = 2,4,6-tris(2-pyridyl)-s-triazine). The present compound is a rare case of a tubular porous material with both hydrophobic and hydrophilic channels. Permanent porosity was confirmed by N2 adsorption isotherms.

•Syntheses and characterization of a novel polyoxometalate cluster.•Structure of an oxofluorovanadium(IV) cluster with phosphonate ligating groups.•Encapsulation of cationic species in oxofluorometalate cluster void space.•Magnetic properties of a V(IV) cluster.Hydrothermal reactions of sodium vanadate, methylenediphosphonic acid, hydrogen fluoride and the appropriate organoamine yielded the vanadium(IV)-oxyfluoride compounds [NH3(CH2)2(NH2)(CH2)2NH3]3[{Na(H2O)} ⊂ {V4O4F2(O3PCH2PO3)4}]·8H2O (1·8H2O) and [NH3(CH2)2(NH2)(CH2)2(NH2)(CH2)NH3]2[{Na(H2O)} ⊂ {V4HO4F2(O3PCH2PO3)4}]·7H2O (2·7H2O). The vanadium-oxyfluoride cationic unit {V4O4F2(O3PCH2PO3)4}10 − of the compounds consists of pairs of fluoride bridged {VFO5} octahedra linked through η4-diphosphonate ligands into a three polyhedra thick band. The {Na(H2O)n}+ groups occupy the interior of the band but are displaced from the centroid toward one face so as to project the aqua ligands into the extra-annular domain. The fluoride ligands bridge two vanadium sites as well as coordinating to the sodium cation.Hydrothermal syntheses provided oxofluorovanadium(IV) clusters encapsulating sodium cations: [{Na(H2O)n} ⊂ {V4O4F4(O3PCH2PO3)4}]10 − (n = 1 (1) and n = 2 (2)). A polyhedral/ball and stick representation of the cluster with n = 1 are shown.

Hydrothermal reactions of cobalt or nickel sulfate with the appropriate substituted tetrazole yielded a series of compounds of the M(II)/tetrazolate/sulfate family. While the parent compound [Co(prztet)2(H2O)2]·0.5H2O (1·0.5H2O; prztet = pyrazinetetrazolate) is molecular, the remaining materials exhibit extended structures. Thus, [Co2(4-pyrtet)(SO4)(OH)(H2O)]·1.5H2O (2·1.5H2O), [Co3F2(SO4)(3-pyrtet)2(H2O)4] (4) and [Ni3F2(SO4)(3-pyrtet)2(H2O)4] (5) are two-dimensional, in contrast to [Co4(prztet)6(SO4)(H2O)2] (3) and [Ni5(3-pyrtet)4(SO4)2(OH)2(H2O)2]·0.5H2O (6·0.5H2O) which are three-dimensional (3-pyrtet = 3-pyridinetetrazolate; 4-pyrtet = 4-pyridinetetrazolate). The sulfate-containing phases exhibit a variety of cluster-based secondary building units: variants of the common trinuclear motifs in 2, 4 and 5, a tetranuclear cluster core in 3, and a pentanuclear building block in 6. The sulfate ligands adopt monodentate and μ2-, μ3- and μ4-bridging modes in the structures.Hydrothermal reactions of cobalt or nickel sulfate with the appropriate substituted tetrazole yielded a series of compounds of the M(II)/tetrazolate/sulfate family. The two-dimensional structure of [Co2(4-pyrtet)(SO4)(OH)(H2O)] is illustrated.

The syntheses, structures, and magnetic properties of four new complex salts, (PPN){[MnIII(salphen)(MeOH)]2[MIII(CN)6]}·7MeOH (Mn2M·7MeOH) (M = Fe, Ru, Os and Co; PPN+ = bis(triphenylphosphoranylidene)ammonium cation; H2salphen = N,N′-bis(salicylidene)-1,2-diaminobenzene), and a mixed metal Co/Os analogue (PPN){[MnIII(salphen)(MeOH)]2[CoIII0.92OsIII0.08(CN)6]}·7MeOH were undertaken. It was found that all compounds exhibit switchable single-molecule magnet (SMM) and exchange-bias behavior depending on the interstitial methanol content. The pristine (PPN){[Mn(salphen)(MeOH)]2[Os(CN)6]}·7MeOH (Mn2Os·7MeOH) behaves as an SMM with an effective barrier for the magnetization reversal, (Ueff/kB), of 17.1 K. Upon desolvation, Mn2Os exhibits an increase of Ueff/kB to 42.0 K and an opening of the hysteresis loop observable at 1.8 K. Mn2Os·7MeOH shows also exchange-bias behavior with magnetic hysteresis loops exhibiting a shift in the quantum tunneling to 0.25 T from zero-field. The FeIII and RuIII analogues were prepared as reference compounds for assessing the effect of the 5d versus 4d and 3d metal ions on the SMM properties. These compounds are also SMMs and exhibit similar effects but with lower energy barriers. These findings underscore the importance of introducing heavy transition elements into SMMs to improve their slow relaxation of the magnetization properties. The (PPN){[MnIII(salphen)(MeOH)]2[CoIII(CN)6]}·7MeOH (Mn2Co·7MeOH) analogue with a diamagnetic CoIII central atom and the mixed Co/Os (PPN){[MnIII(salphen)(MeOH)]2[CoIII0.92OsIII0.08(CN)6]}·7MeOH (Mn2Co/Os·7MeOH) “magnetically diluted” system with a 9:1 Co/Os metal ratio were prepared in order to further probe the nature of the energy barrier increase upon desolvation of Mn2Os. In addition, inelastic neutron scattering and frequency-domain Fourier-transform THz electron paramagnetic resonance spectra obtained on Mn2Os·7MeOH and Mn2Os in combination with the magnetic data revealed the presence of anisotropic exchange interactions between MnIII and OsIII ions.

A pair of related dinuclear lanthanide compounds, viz., [Dy(tmhd)3]2(bptz) (1) and {Cp2Co}{[Dy(tmhd)3]2(bptz)} (2) (tmhd = 2,2,6,6-tetramethyl-3,5-heptane dionate; bptz = 3,6-bis(2-pyridyl)-1,2,4,5-tetrazine) are reported. These molecules represent the first study of rare earth ions in which an organic ligand bridged species is isolated in both the neutral and radical anion forms. Both compounds exhibit out-of-phase signals below 4 K. The radical compound is highly air stable, with minimal changes in magnetic behavior after exposure to the atmosphere for two weeks.

The air-stable mononuclear Co(II) compounds [CoII(Tpm)2][ClO4]2 (1, Tpm = tris(pyrazol-1-yl)methane), [CoII(Tpm)2][BPh4]2·2MeCN (2) with trigonal antiprismatic geometry (trigonally elongated octahedral geometry) are reported. Magnetic and theoretical studies reveal that the complexes exhibit single-molecule magnet behavior with uniaxial anisotropy and a huge energy difference between ground and first excited Karmers' doublets (∼200 cm−1). Under applied DC fields, compounds 1 and 2 exhibit frequency and temperature dependence of the imaginary susceptibility. The fit of the data to an Orbach relaxation process yields effective energy barriers of 30.6(1) and 44.7(6) cm−1 for 1 and 2, respectively, but there is no real state at that energy. The inclusion of tunneling, direct and Raman relaxation processes leads to the conclusion that the inclusion of an Orbach process is not required to provide a good fit to the data. More interestingly, a detailed study of the dependence of the relaxation time with field shows that for these Kramers' ions, tunneling is the predominant process at low temperature and that differences in the counteranion allow for a tuning of the Raman process at higher temperatures. These findings underscore the fact that large uniaxial anisotropy can be achieved in hexacoordinate Co(II) trigonal antiprismatic complexes which is an unexplored geometry in mononuclear single molecule magnets.

Host–guest interactions between the aromatic molecules benzene, toluene, aniline and nitrobenzene and the redox-active TCNQ-based metal–organic framework (MOF), Fe(TCNQ)(4,4′-bpy) (1) (TCNQ = 7,7,8,8-tetracyanoquinodimethane), have been found to modulate spontaneous magnetization behaviours at low temperatures. An analogous MOF, Mn(TCNQ)(4,4′-bpy) (2) with isotropic Mn(II) ions as well as the two-dimensional compound Fe(TCNQ)(DMF)2·2DMF (3·2DMF), were also prepared as models for studying the effects of single-ion magnetic anisotropy and structural distortion on spin canting. The results indicate guest-dependent long range magnetic ordering occurs at low temperatures, which correlates with the electrostatic and steric effects of the incorporated aromatic guests.

The incorporation of TCNQ˙− (7,7,8,8-tetracyanoquinodimethane) radicals as counterions for the spin-crossover material [Co(pyterpy)2](TCNQ)2·solvent (pyterpy = 4′-(4′′′-pyridyl)-2,2′:6′,2′′-terpyridine) leads to structural distortions of the [Co(pyterpy)2]2+ spin-crossover cation as compared to [Co(pyterpy)2](PF6)2. Variable temperature structural and magnetic studies indicate that the supramolecular π-stacking interactions between the terminal pyridyl groups and TCNQ radicals play a crucial role in the spin-crossover properties.

The π–π stacking interactions between tptz units from adjacent Sm(tptz)(HCOO)3 coordination nanotubes leads to additional 1D channels (tptz = 2,4,6-tris(2-pyridyl)-s-triazine). The present compound is a rare case of a tubular porous material with both hydrophobic and hydrophilic channels. Permanent porosity was confirmed by N2 adsorption isotherms.

The bifunctional salt [Co(terpy)2](TCNQ)3·CH3CN (terpy = 2,2′;6′,2′′-terpyridine, TCNQ = 7,7,8,8-tetracyanoquino-dimethane) exhibits a high room temperature conductivity of 0.13 S cm−1 and an anomaly in conductivity at ∼190 K as evidenced by variable temperature structural, magnetic and conductivity studies. The anomaly in the conductivity at 190 K has been correlated with the temperature dependent structural breathing and Jahn–Teller distortion of the low spin state of the SCO units, as well as the charge fluctuations and supramolecular π-stacking interactions of partially charged TCNQ radicals. The modular synthetic approach leads to an accessible source of partially charged TCNQ radicals for the facile preparation of bifunctional molecular materials with high electrical conductivity.