Syntheses, Crystal Structures, and Magnetic Properties of a Family of Tetra- and Octanuclear Mixed-Valent Manganese Clusters

摘要

Reactions of manganese perchlorate and a quinquedentate Schiff base ligand (H_3L), derived from o-vanillin and 3- amino-1,2-propanediol, together with a solution of coligands NaN_3 or NaO_2CH or NaO_2CPh in methanol produced three new tetranuclear manganese clusters that contain a mixedvalent tetrahedral Mn~(II)Mn_3~(III) core with the corresponding general formula [NaMn~(II)Mn_3~(III) (μ_4-O_(2-))(HL)_3(N_3)_3]ClO_4?1.5H_2O (1), [NaMn~(II)Mn_3~(III) (μ_4-O_(2-))(HL)_3(HCO_2)_3]ClO_4?4H_2O (2), and [NaMn~(II)Mn_3~(III) (μ_4-O_(2-))(HL)_3(PhCO_2)(H_2O)_2](ClO_4)_2(PhCO_2)? PhCO_2H?H_2O?CH_3OH (3). According to the feature of the tetrahedral Mn~(II)Mn_3~(III) core, we used a terephthalic acid disodium salt (Na_2TA) instead of NaO_2CPh and obtained an octanuclear manganese cluster that contained two tetrahedral Mn~(II)Mn_3~(III) cores bridged by a TA~(2-) ligand with the general formula [Na_2Mn_2~(II) Mn_6~(III) (μ_4-O_(2-))_2(HL)_6(HCO_2)_2(CH_3OH)_2- (TA)](TA)(ClO_4)_2?4CH_3OH?9.5H_2O (4). Variable-temperature, solid-state direct-current (dc) magnetization studies were carried out on compounds 1-4 in the 2.0-300 K range. The magnetic susceptibility data of these four compounds were fit to the theoretical χ_mT versus T expression derived by the use of an isotropic Heisenberg spin Hamiltonian and the Van Vleck equation. The fitting results revealed the presence of both antiferromagnetic and ferromagnetic interactions between the metal centers.