A series of oxyfluoride chains containing asymmetric basic building units of both early- and late-transition metal cations

Abstract

Four new transition metal oxyfluorides revealing chain structures composed of asymmetric basic building units of [MO2F4](2-) = (M = Mo and W) and [M'(pz/mpz)(4)](2+) (M' = Cu and Ni) polyhedra, i.e., [Cu(mpz)(4)][MoO2F4] (1), [Cu(pz)(4)](2)[WO2F4](2) (2), [Ni(Pz)(4)](2)[MoO2F4](2) (3), and [Ni(pz)(4)][WO2F4] (4) (pz = pyrazole; mpz = 3-methyl pyrazole) have been synthesized via hydrothermal reactions. The linear chain structures found from the title compounds are attributable to the trans-directing [MO2F4](2-) octahedral moiety and hydrogen bonding interactions. Strong Jahn-Teller distortions are observed for Cu2+ cations with d(9) configuration in compounds 1 and 2. All the compounds show both lower-energy and higher-energy absorption band gaps, which originate from the d-d transitions and the distortion of octahedral geometry of M2+ cations, respectively. The magnetism of [Cu(mpz)(4)][MoO2F4] turns out to be described by noninteracting Cu2+ spins rather than a spin chain due to long exchange path mediated via the nonmagnetic Mo6+ ions. The title compounds have been also thoroughly characterized using spectroscopic and thermal analyses along with calculations of local dipole moments and the extent of out-of-center distortions.