Mixed Transition Metal (Oxy)fluoride Paramagnet Chains: Synthesis, Structure, and Characterization

Abstract

Three mixed transition metal (oxy)fluorides, [Ni(pz)4][VO2F3] (1), [Cu(pz)4][TiF6] (2), and [Cu(mpz)4][ZrF6] (3) (pz = pyrazole; mpz = 3-methylpyrazole) were synthesized by combining asymmetric polyhedra of early transition metal cations, [VO2F3]2–/[TiF6]2–/[ZrF6]2– and basic building units (BBUs) of late transition metal cations, [Ni(pz)4]2+/[Cu(pz/mpz)4]2+ via hydrothermal reactions. Compound 1 consists of chains with disordered F– and O2–, whereas compounds 2 and 3 are composed of chains containing fully ordered F– and O2–. The ordered structures for compounds 2 and 3 are achieved by providing the cationic contacts for [MF6]2– (M = Ti, Zr) anions to [Cu(pz/mpz)4]2+ cations and to pyrazole/3-methylpyrazole ligands through covalent bonding and hydrogen bonding interactions, respectively. Detailed structural analysis suggests that the distinctive structure-directing anionic groups ([VO2F3]2–, [TiF6]2–, or [ZrF6]2–) and hydrogen bonding networks are responsible for the linear chain structures. The lower-energy and higher-energy absorption optical band gaps are generated from the d–d electronic transitions, and the octahedral distortions of M′2+ (M′ = Ni, Cu) cations for all the reported compounds. Both magnetic susceptibility and magnetization measurements of compounds 1, 2, and 3 show no Bonner–Fisher behavior expected for the linear spin chain. Rather, compounds 1, 2, and 3 behave like paramagnets without developing any magnetic order. © 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim