Mild Hydrothermal Synthesis of the Complex Hafnium-Containing Fluorides Cs2[M(H2O)6][Hf2F12] (M = Ni, Co, Zn), CuHfF6(H2O)4, and Cs2Hf3Mn3F20 Based on HfF7 and HfF6 Coordination Polyhedra.

A series of new Hf(IV)-containing fluorides with three different compositions, Cs2[M(H2O)6][Hf2F12] (M = Ni, Co, Zn), CuHfF6(H2O)4, and Cs2Hf3Mn3F20, were synthesized as high-quality single crystals via a mild hydrothermal route. The compounds with compositions of Cs2[M(H2O)6][Hf2F12] (M = Ni, Co, Zn) and CuHfF6(H2O)4 crystallize in the monoclinic space groups P21/n and P21/c, respectively, while the Cs2Hf3Mn3F20 phase crystallizes in the orthorhombic space group Pmmn. Cs2[M(H2O)6][Hf2F12] (M = Ni, Co, Zn) exhibits a complex three-dimensional (3D) crystal structure consisting of edge-sharing dimers of HfF7 polyhedra, which are linked to the divalent metal octahedra via hydrogen bonding. Cs2Hf3Mn3F20 features corner-sharing HfF7 and MnF7 dimers as well as isolated MnF6 octahedra, while the CuHfF6(H2O)4 phase exhibits a 3D structure that consists of HfF6 octahedra linked with neighboring copper octahedral units by hydrogen-bonding interactions. UV-vis spectra of the title compounds were collected and exhibit absorption bands due to electronic transitions in the divalent metal cations (Ni2+, Co2+, Cu2+, and Mn2+). Magnetic susceptibility measurements revealed paramagnetic behavior in the compounds containing the magnetic cations Ni, Co, Cu, and Mn.