Transition-Metal Monofluorophosphate Ba2M2(PO3F)F6 (M = Mn, Co, and Ni): Varied One-Dimensional Transition-Metal Chains and Antiferromagnetism.

ABSTRACT

Four transition-metal monofluorophosphates, with a chemical formula of Ba2M2(PO3F)F6 (M = Mn, Co, Ni, and Cu), have been synthesized hydrothermally using phosphoric and fluorophosphoric acids. The structures of Ba2M2(PO3F)F6 were intensively investigated by single-crystal and powder X-ray diffraction. Their networks exhibited three-dimensional frameworks formed by cis-MO2F4 octahedra and PO3F tetrahedra. Ba2M2(PO3F)F6 (M = Mn, Co, and Cu) are isostructural, crystallizing in the monoclinic space group P21/c, while Ba2Ni2(PO3F)F6 adopted an unpredetermined structure, crystallizing in the monoclinic space group P21/n. The different arrangements of the same cis-MO2F4 moieties and PO3F groups within one-dimensional chains lead to different frameworks in this late-first-row transition-metal series. By a comparison of normalized bond lengths with their normal counterparts, the more elongated octahedral cis-MO2F4 units in Ba2Cu2(PO3F)F6 reveal the presence of static Jahn-Teller distortion, uncovering the puzzling reason for the exceptional structure of Ba2Ni2(PO3F)F6 in the series. Ba2M2(PO3F)F6 (M = Mn, Co, and Ni) forms spin chains of M2+ made of coupled dimers or tetramers, showing dominant antiferromagnetic behavior.