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 [MO 2 F 4 ] 2− (M = Mo and W) and [M’(pz/mpz) 4 ] 2+ (M′ = Cu and Ni) polyhedra, i.e., [Cu(mpz) 4 ][MoO 2 F 4 ] (1), [Cu(pz) 4 ] 2 [WO 2 F 4 ] 2 (2), [Ni(pz) 4 ] 2 [MoO 2 F 4 ] 2 (3), and [Ni(pz) 4 ][WO 2 F 4 ] (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 [MO 2 F 4 ] 2- octahedral moiety and hydrogen bonding interactions. Strong Jahn–Teller distortions are observed for Cu 2+ 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 M 2+ cations, respectively. The magnetism of [Cu(mpz) 4 ][MoO 2 F 4 ] turns out to be described by noninteracting Cu 2+ spins rather than a spin chain due to long exchange path mediated via the nonmagnetic Mo 6+ 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.