This report describes the syntheses, characterization, crystal structures and magnetic properties of five dinuclear Fe^IIINi^II compounds derived from two Robson-type tetraiminodiphenol macrocyclic ligands H₂L¹ and H₂L², which are the [2+2] condensation products of 4-ethyl-2,6-diformylphenol and 1,3-diaminopropane (for H₂L¹) or 2,2-dimethyl-1,3-diaminopropane (for H₂L²). The compositions of the compounds are [Fe^III(N₃)₂L¹Ni^II(H₂O)₂](ClO₄) (1), [Fe^III(benzoato)L¹Ni^II(H₂O)(μ_1,3-benzoato)](ClO₄) (2), [Fe^III(benzoato)L²Ni^II(H₂O)(μ_1,3-benzoato)](ClO₄) (3), [Fe^IIIL²Ni^II(μ_1,3-acetato)₂](ClO₄)·H₂O (4) and [Fe^IIIL²Ni^II(μ_1,3-propionato)₂](ClO₄)·H₂O (5). The bridging moieties between the two metal ions and the azido and carboxylato moieties in these compounds are of the following types: (1) In 1, the bridging moiety is a bis(μ-phenoxido) ligand, and two azido ligands are monodentate to the Fe^III centre; (2) In 2 and 3, the bridging moiety is a bis(μ-phenoxido)-μ_1,3-benzoato ligand, and the second benzoato ligand is monodentate to the Fe^III centre; (3) In 4 and 5, the bridging moiety is a bis(μ-phenoxido)bis(μ_1,3-acetato/propionato) ligand. Variable-temperature and variable-field magnetic data reveal ferromagnetic interactions in 2–5 and an antiferromagnetic interaction in 1 with J values of –9.22 cm^–1 for 1, 0.50 cm^–1 for 2, 5.65 cm^–1 for 3, 13.00 cm^–1 for 4 and 14.57 cm^–1 for 5. An excellent magnetostructural correlation and interesting structural aspects regarding the bond lengths to the Fe^III or Ni^II centres in some structures have been obtained.

Syntheses, characterization and crystal structures of fourdesigned host–guest compounds of the compositions [{Cu^IIL¹}₂⊂(H₃N(ethylene)NH₃)](NO₃)₂ (1), [{Cu^IIL¹}₂⊂(H₃N(propylene)NH₃)](NO₃)₂ (2), [{Cu^IIL¹}₂⊂(H₃N(butylene)NH₃)](NO₃)₂ (3) and [{Cu^IIL²}₂⊂(H₃N(ethylene)NH₃)](NO₃)₂ (4) are described in this investigation [H₂L¹ = N,N′-ethylenebis(3-methoxysalicylaldimine); H₂L² = N,N′-ethylenebis(3-ethoxysalicylaldimine); ethylene = (CH₂)₂; propylene = (CH₂)₃; butylene = (CH₂)₄]. Compounds 2 and 3 crystallize in the orthorhombic Pcab and monoclinic C2/c systems, respectively, while the space group of compounds 1 and 4 is triclinic P. In all of these four compounds 1–4, the two ⁺NH₃ sites of the [H₃N(CH₂)_nNH₃]²⁺ dication (n = 2–4) behave as guests in the O₄ compartment of two [Cu^IIL¹/L²] moieties through bifurcated N–H···O(phenoxo) and N–H···O(methoxy/ethoxy) hydrogen-bonding interactions. Evidently, two mononuclear copper(II) moieties are interlinked by bridging supramolecular synthons, resulting in the formation of a supramolecular dimer in the title compounds. From the extent of displacement of the N atoms of [H₃N(CH₂)_nNH₃]²⁺ from the least-squares O(phenoxo)₂O(methoxy/ethoxy)₂ plane, it is clear that [Cu^IIL¹] is a better host than [Cu^IIL²] for the diprotonated diamine guests. Comparison of the inclusion of water and diprotonated diamines in [Cu^IIL¹/L²] is also described in the present investigation. Interestingly, of the two guest species, water and diprotonated diamines, [Cu^IIL²] prefers the former and [Cu^IIL¹] prefers the latter.

The present investigation describes syntheses, characterization and studies of the mononuclear compound [Cu^IIL⊂(H₂O)] (1), the triangular, trinuclear monophenoxido-bridged compounds [{Cu^IIL}₂M^II(H₂O)₂](ClO₄)₂·nH₂O [2 (M = Cu, n = 0), 3 (M = Ni, n = 3), 4 (M = Co, n = 0), 5 (M = Fe, n = 0)] and the tetrametallic self-assembled complex [{Cu^IILMn^II(H₂O)₃}{Cu^IIL}₂](ClO₄)₂·H₂O (6) derived from compartmental Schiff base ligand, H₂L, which is the [2+1] condensation product of 3-methoxysalicylaldehyde and trans-1,2-diaminocyclohexane. Single-crystal X-ray structures of 2, 5 and 6 were determined. Two pairs of terminal···central metal ions in the trinuclear cores in 2 and 5 are monophenoxido-bridged. Interestingly, the CuO₆ and FeO₆ environments have tetragonally compressed octahedral geometries. On the other hand, the structure of 6 reveals that it is a [2×1+1×2] cocrystal of one diphenoxido-bridged dinuclear [Cu^IILMn^II(H₂O)₃]²⁺ dication and two mononuclear [Cu^IIL] moieties. Cocrystallization in 6 takes place as a result of water encapsulation. The variable-temperature (2–300 K) magnetic susceptibilities of compounds 2–6 have been measured. The exchange integrals obtained are: the Cu^II₃ compound 2, J = –78.9 cm^–1; the Cu^IINi^IICu^II compound 3, J = –22.8 cm^–1; the Cu^IICo^IICu^II compound 4, J = –7.8 cm^–1; the Cu^IIFe^IICu^II compound 5, J = –3.0 cm^–1; the Cu^II₃Mn^II compound 6, J = –15.1 cm^–1. The monophenoxido-bridging core in 3 and 4 has been proposed after comparison of the structures and magnetic properties of these two compounds with those of 2, 5 and related other compounds. This paper presents rare examples of monophenoxido-bridged Cu^IIM^IICu^II (M = Cu, Ni, Co and Fe) compounds, provides an understanding of the structures from magnetic exchange integrals, and, most importantly, reports on the first example of a cocrystal derived from a 3-methoxysalicylaldehyde diamine compartmental ligand.

The syntheses, characterization and structures of a mononuclear nickel(II) compound [Ni^IIL¹⊂(H₂O)] (1) and [2 × 1+1 × 2] cocrystals [{Ni^IIL¹M^II(H₂O)₃}{Ni^IIL¹}₂](ClO₄)₂ [M = Cu (2), Ni (3), Co (4), Fe (5) and Mn (6)] derived from the hexadentate Schiff base compartmental ligand N,N′-ethylenebis(3-ethoxysalicylaldimine) (H₂L¹) have been described in this investigation. Compound 1 is an inclusion product in which the water molecule is encapsulated in the O₄ compartment by forming bifurcated hydrogen bonds. Reactions of 1 with perchlorate salts of copper(II), nickel(II), cobalt(II), iron(II) and manganese(II) in open atmosphere produce compounds 2–6, which have similar structures. These compounds are [2 × 1+1 × 2] tetrametallic systems containing self-assembled and cocrystallized one dinuclear [Ni^IIL¹M^II(H₂O)₃]²⁺ cation and two mononuclear [Ni^IIL¹] moieties. Among three coordinated water molecules of the dinuclear cores in 2–6, two are encapsulated in the O₄ cavity of two mononuclear [Ni^IIL¹] moieties by forming bifurcated hydrogen bonds. Evidently, the formation of inclusion product 1 and dinuclear–mononuclear cocrystals 2–6 are related to the affinity of the O₄ compartment to encapsulate a water molecule. Electrospray ionization mass spectrometry (ESI+) spectra of compounds 1–6 have been recorded. The mass spectra of 2–6 reveal that not only the tetrametallic self-assemblies are ruptured but also the second metal ion in the dinuclear core leaves the O₄ cavity. For the Ni^II₃Cu^II (2) and Ni^II₃Fe^II (5) compounds, metal substitution takes place in solution, resulting in the formation of [Cu^IIL¹Na]⁺ and [{Cu^IIL¹}₂Na]⁺ for 2 and [1 × 1+1 × 1] species [{Ni^IIL¹}·{Fe^IIIL¹}]⁺ for 5.

The synthesis, structure, magnetic and electrochemical properties of the heterobridged μ-phenoxido–μ_1,1-azide dinickel(II) compound [Ni^II₂(HL¹)₃(μ_1,1-N₃)]·3H₂O (1) derived from the tetradentate Schiff base ligand N-(2-hydroxyethyl)-3-methoxysalicylaldimine (H₂L¹) are described. The title compound crystallizes in the triclinic system (space group P). Electrochemical analyses reveal that compound 1 exhibits two-step quasireversible couples in the reduction window with E_1/2 values of –1412 and –1762 mV. The variable-temperature (2–300 K) magnetic susceptibilities at 1 T of the title compound were measured. The interaction between the metal centres is weak ferromagnetic (J = 5.0 cm^–1, g = 2.23, D₁ = 29.2 cm^–1 and D₂ = 10.7 cm^–1). Comparison of the exchange integral of 1 with that of the only reported μ-phenoxido–μ_1,1-azide dinickel(II) compound results in the emergence of a unique example of the dependence of strength of magnetic exchange interaction on the metal–ligand bridge distance. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

The syntheses, structures, and magnetic properties of the trinuclear triangular compounds [{Cu^IIL¹}₂Cu^II(H₂O)₂](ClO₄)₂·H₂O (1) and [{Cu^IIL¹}₂M^II(H₂O)₂](ClO₄)₂ {M = Ni (2), Co (3), Fe (4)} derived from N,N′-ethylenebis(3-methoxysalicylaldimine) (H₂L¹) are described. Compound 1 crystallizes in the monoclinic P2₁/n space group, while the crystal system for the isomorphous compounds 2–4 is monoclinic P2₁/c. In the cations of these compounds, two copper(II) ions occupy the salen type N₂O₂ cavity of two [L¹]^2– ligands, while one phenoxido and one methoxy oxygen atom of each of these two [Cu^IIL¹] moieties coordinate to a central metal ion, which results in the formation of the trinuclear Cu^II₂M^II systems in which the two pairs of central···terminal metal ions are monophenoxido-bridged. In addition, to the two phenoxido bridges, the central metal ion is coordinated to two methoxy and two water oxygen atoms. The coordinated water molecules are strongly hydrogen bonded to the phenoxido and methoxy oxygen atoms. The presence of the coordinated water molecules and the interaction of these water molecules with the phenoxido and methoxy oxygen atoms are proposed to be the governing factors for the stabilization of the rare example of the monophenoxido-bridged Cu^II₃ compound 1 and of the first examples of the monophenoxido-bridged Cu^II₂M^II compounds 2–4. The three metal ions define an isosceles triangle. The phenoxido bridge angles in these compounds are significantly obtuse and vary between 121.10(12)° and 129.84(13)°. On the other hand, the trinuclear cores are highly twisted as evidenced from the range of the dihedral angles (58.5–143.7°) between the basal planes of the terminal and the central metal ions. The variable-temperature (2–300 K) magnetic susceptibilities of compounds 1–4 have been measured. The magnetic data for 1 have been analyzed by using a model of two exchange integrals for the two pairs of adjacent metal ions, while one J value is considered for the other three complexes. The exchange integrals obtained are: Cu^II₃ compound 1: J₁ = –97.6 cm^–1, J₂ = –89.5 cm^–1; Cu^II₂Ni^II compound 2: J = –25.4 cm^–1; Cu^II₂Co^II compound 3: J = –9.0 cm^–1; Cu^II₂Fe^II compound 4: J = –6.5 cm^–1. These moderate to weak antiferromagnetic interactions in 1–4 are related to the twisting of the trinuclear cores. The relative order of the exchange integrals can been understood from the nature of the magnetic orbitals. The structural and magnetic results have been compared with previously reported related compounds.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Refluxing of the red compound [Cu^IIL¹blabla(H₂O)] (1) in acetone forms two new species: green [Cu^IIL¹(H₂O)] (2) and brown [Cu^IIL¹] (3) [H₂L¹ = N,N′-ethylenebis(3-ethoxysalicylaldimine)]. Whereas both 1 and 2 are converted into 3 upon heating, 3 is converted back into 1 when exposed to air. The structures of all three compounds were determined crystallographically, from which the interesting hydrate isomerism of 1 and 2 are identified; in 1 a water molecule is encapsulated into the O₄ section of the ligand through bifurcated hydrogen bonding, whereas in 2 a water molecule coordinates directly to the metal centre. Despite the metal ion binding to the ligand in the same manner in all three cases, the formation of different mononuclear complexes resulting from the presence or absence of water and its coordination or encapsulation is an interesting observation. Thermogravimetric analyses of compounds 1 and 2 showed that the encapsulated water in the former compound is removed at slightly lower temperature than that of the coordinated water molecule, as expected. Although three crystals 1, 2 and 3 were isolated, the composition of species in solution is probably the same as evidenced by ¹H NMR spectroscopy. Therefore, the formation of three crystals and the hydrate isomerism described in this investigation are solid-state phenomena.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)