Solvent dependent reactivities of di-, tetra- and hexanuclear manganese complexes: syntheses, structures and magnetic properties

Abstract

An unusual solvent effect on the synthesis of five manganese complexes [Mn₂(L₁)₂(Py)₄](1), [Mn₂(L₁)₂(DMSO)₄](2), [Mn₄(L₂)₄(OH)₄](3), [Mn₄(L₃)₂(DMSO)₇(H₂O)](4), and [Mn₆O₂(L₄)₄(OAc)₂(OMe)₂(DMSO)₄]·MeOH] (5), (H₃L₁ = 5-(2-oxyphenyl)-pyrazole-3-carboxylic acid; H₂L₂ = 5-(2-oxyphenyl)-pyrazole-3-carboxylic acid amide; H₄L₃ = di-[5-(2-oxyphenyl)-pyrazole]-3-hydroxamic ether; and H₂L₄ = 5-(2-oxyphenyl)-pyrazole-3-carboxylic acid methyl ester) has been reported. Five complexes have been characterized by X-ray single crystal diffraction, IR, element analysis, thermogravimetric analysis and UV-vis spectra. The analysis reveals that complexes 1 and 2 are isostructural with a bimetallic six-membered ring and L₁ from the decomposition of the original H₄ppha (H₄ppha = 5-(2-hydroxyphenyl)-pyrazole-3-hydroxamic acid) ligand. Complexes 3 and 4 are two tetranuclear clusters, and 3 possesses an aza12-metallacrown-4 core with L₂ from the amide functionalization of the decomposition L₁; while 4 represents a novel linear [Mn₄N₈O₂] core with L₃ from the condensation of L₁ and H₄ppha. Complex 5 is the first Mn₆ cluster linked by two stacked, off-set 8-azametallacrown-3 subunits with [M–N–N–M–N–N–M–O] connectivity, and L₄ derived from the esterification of L₁. The magnetic behaviour of complexes 1–5 show the dominant antiferromagnetic interactions between metal centers, whereas complex 5 further reveals the coexistence of antiferromagnetic and ferromagnetic interactions, and slow magnetic relaxation at T < 6 K with S = 4 ground state, as well as field induced magnetization saturation.