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

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Abstract

Reactions of manganese perchlorate and a quinquedentate Schiff base ligand (H3L), derived from o-vanillin and 3-amino-1,2-propanediol, together with a solution of coligands NaN3 or NaO2CH or NaO2CPh in methanol produced three new tetranuclear manganese clusters that contain a mixed-valent tetrahedral MnIIMnIII3 core with the corresponding general formula [NaMnIIMn3III4-O2–)(HL)3(N3)3]ClO4·1.5H2O (1), [NaMnIIMn3III4-O2–)(HL)3(HCO2)3]ClO4·4H2O (2), and [NaMnIIMn3III4-O2–)(HL)3(PhCO2)(H2O)2](ClO4)2(PhCO2)·PhCO2H·H2O·CH3OH (3). According to the feature of the tetrahedral MnIIMnIII3 core, we used a terephthalic acid disodium salt (Na2TA) instead of NaO2CPh and obtained an octanuclear manganese cluster that contained two tetrahedral MnIIMnIII3 cores bridged by a TA2– ligand with the general formula [Na2Mn2IIMn6III4-O2–)2(HL)6(HCO2)2(CH3OH)2(TA)](TA)(ClO4)2·4CH3OH·9.5H2O (4). Variable-temperature, solid-state direct-current (dc) magnetization studies were carried out on compounds 14 in the 2.0–300 K range. The magnetic susceptibility data of these four compounds were fit to the theoretical χmT 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.

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