Ni-36(II)-Containing 54-Tungsto-6-Silicate: Synthesis, Structure, Magnetic and Electrochemical Studies

The 36-Ni-II-containing 54-tungsto-6-silicate, [Ni-36(OH)(18)(H2O)(36)(SiW9O34)(6)](6-) (Ni-36) was synthesized by a simple one-pot reaction of the Ni-2-pivalate complex [Ni-2(mu-OH2)(O2CCMe3)(4)(HO2CCMe3)(4)] with the trilacunary [SiW9O34](10-) polyanion precursor in water and structurally characterized by a multitude of physicochemical techniques including single-crystal XRD, FTIR, TGA, elemental analysis, magnetic and electrochemical studies. Polyanion Ni-36 comprises six equivalent {(Ni6SiW9)-Si-II} units which are linked by Ni-O-W bridges forming a macrocyclic assembly. Magnetic studies demonstrate that the {Ni-6} building blocks in Ni-36 remain magnetically intact while forming a hexagonal ring with antiferromagnetic exchange interactions between adjacent {Ni-6} units. Electrochemical studies indicate that the first reduction is reversible and associated with the W-VI/V couple, whereas the second reduction is irreversible attributed to the Ni-II/0 couple.