Phenazineoxonium chloranilatomanganate and chloranilatoferrate: synthesis, structure, magnetic properties, and Mössbauer spectra

Crystalline compounds (H3O)2(phz)3M2(C6O4Cl2)3·(CH3COCH3) n ·(H2O) n (n = 0−2, M = Mn (1), Fe (3)) were obtained in an acetone-water-tetrahydrofuran medium by the reaction of metal sulfates with chloranilic acid and phenazine (phz). The molecular and crystal structure of 1 was studied by X-ray diffraction at 300, 200, and 150 K. The crystal structure is composed of polymeric cationic [(H3O)2(phz)3] n 2n+ and anionic [Mn2(C6O4Cl2)3] n 2n− layers having honeycomb structure and stacked in such a way that open-ended through-going channels accommodating H2O and CH3COCH3 solvent molecules are formed; the H3O+ cations in the crystal structure are disordered. Magnetic studies indicate antiferromagnetic coupling of Mn2+ ions through chloranilate ligands; transition to a magnetically ordered state occurs at T = 5 K. According to powder X-ray diffraction data, complex 3 is isostructural with compound 1 but differs crucially from 1 in the electronic structure. According to Fe57 Mossbauer spectroscopy, complex 3 exists in delocalized mixed-valence Fe2+/Fe3+ state and, as a consequence, shows ferromagnetic character of magnetic correlations and semiconductor type of electrical conductivity. These features were ascribed to the valence tautomerism Fe2+ + (C6O4Cl2)2− → Fe3+ + (C6O4Cl2)·3−, which was observed for the first time for iron in a honeycomb structure.