Syntheses,Crystal Structures,and Spectroscopic and Magnetic Properties of [Mn_2~(III)(H_2L~1)(Cl_4Cat)_4 centre dot 2H_2O]_(infinity) and [Mn_2~(III)(H_2L~2)(Cl_4Cat)_4 centre dot 2CH_3CN centre dot 2H_2O]_infinity:Temperature-Dependent Valence Tauto

摘要

The synthesis,X-ray data,and electronic structures of two manganese(III) 1D polymers ligated by tetrachlorocatechol,[Mn_2~(III)(H_2L~1)(Cl_4Cat)_4 centre dot H_2O]_(infinity) (1) and [Mn_2~(III)(H_2L~2)(Cl_4Cat)_4 centre dot 2CH_3CN centre dot 2H_2O]_(infinity)(2),are reported.The electronic structures of the complexes have been determined by UV-vis-near-IR,IR,electron paramagnetic resonance (EPR),and magnetic susceptibility measurements.Both 1 and 2 are air stable in the solid state and in solution,unlike most of the previously reported o-quinone-chelated transition-metal complexes.Electronic spectroscopy exhibits a strong near-IR band near 1900 nm for both,suggesting the presence of a mixed-valence semiquinone-catecholate oxidation state of the catechol ligands,Mn_2~(III)(Cl_4Cat)_2(Cl_4SQ)_2,together with the pure catecholate forms.The presence of this isomer was further supported by EPR and magnetic susceptibility measurements.The complexes undergo intramolecular electron transfer (valence tautomerism) upon an increase of the temperature involving the equilibrium Mn_2~(III)(Cl_4Cat)_2(Cl_4SQ)_2 <=> Mn_2~(II)(Cl_4SQ)_4.This phenomenon is reversible and is studied in solution using UV-vis-near-IR spectroscopy.