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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.

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.

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