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Two new molecule-based materials of formulas 3D-{[K(H(2)O)(6)](0.5)[K(18-crown-6)](0.5)[MnCu(3)(Hmesox)(3)].5.25H(2)O} (1) and 3D-{(Ph(4)P)(2)[MnCu(3)(Hmesox)(3)Cl].3.5H(2)O} (2) have been prepared from a tricopper(II) secondary building unit (SBU), [Cu(3)(Hmesox)(3)](3-) (H(4)mesox = mesoxalic acid, 2-dihydroxymalonic acid). Compound 1 is obtained by means of the reaction of the SBU with manganese(II) acetate in the presence of potassium cations and the 18-crown-6 ether, whereas compound 2 is obtained by means of the reaction of the SBU with manganese(II) acetate in the presence of Ph(4)PCl. The [MnCu(3)(Hmesox)(3)](-) and [MnCu(3)(Hmesox)(3)Cl](2-) moieties in compounds 1 and 2, respectively, yield chiral 3-connected three-dimensional (3D) anionic (10,3)-a (srs, SrSi(2)) nets. In the cubic and centrosymmetric structures (Pa3) of 1, two inversion-symmetry-related anion nets interpenetrate to a racemic structure. The Ph(4)P(+) cations in 2 are organized in a supramolecular (10,3)-a net through the 6-fold phenyl embrace. In 2, both the cationic and anionic nets are homochiral and enantiopure with opposite handedness and form interpenetrating supramolecular and covalent (10,3)-a nets in the noncentrosymmetric Sohncke space group P 2(1)2(1)2(1). Both compounds display ferrimagnetic interaction with long-range magnetic ordering below 2.5 and 15.2 K for 1 and 2, respectively. A dehydrated phase of 2 exhibits a T(c) of 21.8 K. The saturation of magnetization, M(S), indicates two different ground states, S = (1)/(2) and (3)/(2), for the tricopper(II) units in 1 and 2, respectively. The different spin states of the tricopper(II) unit in 1 and 2 has been explained by means of a density functional theory (DFT) study performed in the [Cu(3)(Hmesox)(3)](3-) and [Cu(3)(Hmesox)(3)Cl](4-) fragments, for 1 and 2, respectively. A further DFT study has allowed one to analyze the structural parameters that lead to the different spin ground states for the trinuclear units in both compounds.

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The synthesis, structure, and magnetic characterization of [Fe(L1)(HIm)2] Y (Y = ClO4 - (1a), PF6 - (1b), and BPh4 - (1c)), [Fe(L2)(HIm)2]ClO4 (2a), [Fe(L2)(HIm)2]ClO4·H2O (2b), [NaFe(L2)(HIm)2(ClO4)2] (2c), [Fe(L3)(HIm)2]ClO4 (3), [Fe(L4)(HIm)2]ClO4 (4a), and [Fe(L4)(HIm)2] BPh4·H2O (4b) are reported (L1 = N,N‘-3,4-toluenebis(3-ethoxysalicylideneimine), L2 = N,N‘-4-chloro-o-phenylenebis(3-methoxysalicylideneimine), L3 = N,N‘-4-chloro-o-phenylenebis(3-ethoxysalicylideneimine), L4 = N,N‘-1,2-propylenebis(3-methoxysalicylideneimine), and HIm = imidazole). Compound 1a crystallizes in the triclinic system, space group P1̄, Z = 2, with a = 10.609(3) Å, b = 10.762(3) Å, c = 15.043(3) Å, α = 105.13(2)°, β = 90.67(2)°, and γ = 102.09(2)°. Compound 2c crystallizes in the monoclinic system, space group C2/c, Z = 4, with a = 14.969(6) Å, b = 17.324(6) Å, c = 13.050(10) Å, and β = 100.85(6)°. Compound 4a crystallizes in the orthorhombic system, space group P212121, Z = 4, with a = 12.402(2) Å, b = 14.354(2) Å, c = 15.773(2) Å. The structures of 1a and 4a are made up of discrete [Fe(L1)(HIm)2]+ and [Fe(L4)(HIm)2]+ cationic units, while 2c consists of dinuclear neutral entities [NaFe(L2)(HIm)2(ClO4)2]. The iron(III) ion is six-coordinated, the equatorial plane being occupied by the cis tetradentate Schiff base and the axial positions by the imidazole ligands. The metal−ligand bond distances as well as the relative orientation of the imidazole ligands are discussed in relation with the spin state of the title compounds. The magnetic properties reveal that 1a − c, 2a, 3, and 4b are high-spin species while 2c is a low-spin complex, and 2b and 4a display spin-crossover behavior. The thermodynamic model of Slichter and Drickamer was applied to account for the temperature variable high-spin molar fraction deduced from the magnetic behavior. The intermolecular interaction parameter, Γ, the enthalpy, ΔH, and the entropy, ΔS, changes associated with the spin transition of 2b were estimated as Γ = 1.6 kJ mol-1, ΔH = 12 kJ mol-1, and ΔS = 60 J mol-1 K-1.

The combined use of 1,2,4,5‐benzenetetracarboxylic acid (H4bta) and 4,4′‐bipyridine (bpy) as ligands with MnII and CoII ions afforded two polymeric compounds with the formulae [Mn(Hbta)(Hbpy)(H2O)2] (1) and [H2bpy][Co(bta)(bpy)(H2O)2] (2). 1 and 2 were prepared under hydrothermal conditions (145 °C, 3 h) and characterized by elemental analysis, IR spectroscopy, TG‐DTA analysis and single‐crystal X‐ray diffraction methods. 1 exhibits a novel double chain structure growing along the b axis where the manganese atoms are linked by tris‐monodentate Hbta3− ligands. The values of the manganese···manganese intrachain separations are 7.627(2) Å [Mn(1)···Mn(1c); c = −x + 1/2, y − 1/2, −z] and 9.274(4) Å [Mn(1)···Mn(1d); d = x, y + 1, −z]. Adjacent double chains in 1 are further linked through hydrogen bonds between the NH fragment of the Hbpy+ cation and one of the carboxylate groups of the Hbta3− anion along the a axis, resulting in a sheetlike structure. 2 exhibits a rectangular grid arrangement of cobalt atoms bridged by bis‐monodentate bta4− and bpy ligands in the bc plane, the cobalt···cobalt separations across them being 6.228(2) and 10.074 (2) Å, respectively. The metal atoms in 1 and 2 are six‐coordinate with two water molecules in trans positions (1 and 2), three (1)/two (2) carboxylate oxygen atoms and one (1)/two (2) pyridyl nitrogen atoms forming a distorted octahedral environment. The varying nature of the divalent metal ions [Mn 1 and Co 2] along with the differing degrees of protonation of the tetracaboxylate [Hbta3− 1 and bta4− 2] and bipyridyl [Hbpy+ 1 and bpy and H2bpy2+ 2] species account for the structural differences between 1 and 2. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

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The compounds [ H,im] ,[ M o8OZ6( H im),] 1, [ N H,Me,] ,[ Mo,O,( H im)J-3H2O 2, [l -Hmim],[ Mo,O,,( 1mim),]~2H,O 3 and [2-Hmim],[Mo80,,(2-mim),]=3H,0 4 (where Him = imidazole, 1 -mim = 1 -methylimidazole and 2-mim = 2-methylimidazole) have been synthesized. Compounds 1 and 3 were prepared by the reaction between molybdenum trioxide and imidazole or 1 -methylimidazole in aqueous medium, whilst 2 and 4 were synthesized by reaction of molybdenum trioxide with imidazole or 2methylimidazole in dmf-H,O (dmf = dimethylformamide). The compounds have been characterized by elemental analysis, infrared and 'H and 13C N M R spectroscopies and thermal measurements. The structures of compounds 2 and 3 were determined by X-ray crystallography and showed that both anions are composed of two MONO, and six MOO, edge-sharing octahedra. The Mo-N and Mo-0 bond strengths of

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