Ni$^{II}$$_{36}$-Containing 54-Tungsto-6-Silicate: Synthesis, Structure, Magnetic and Electrochemical Studies

Abstract

The 36-Ni$^{II}$-containing 54-tungsto-6-silicate, [Ni$_{36}$(OH)$_{18}$(H$_{2}$O)$_{36}$(SiW$_{9}$O$_{34}$)$_{6}$]$^{6-}$ (Ni$_{36}$) was synthesized by a simple one-pot reaction of the Ni$_{2}$-pivalate complex [Ni$_{2}$(μ-OH$_{2}$)(O$_{2}$CCMe$_{3}$)$_{4}$(HO$_{2}$CCMe$_{3}$)$_{4}$] with the trilacunary [SiW$_{9}$O$_{34}$]$^{10-}$ 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 {Ni$^{II}$$_{36}$SiW$_{9}$} units which are linked by Ni−O−W bridges forming a macrocyclic assembly. Magnetic studies demonstrate that the {Ni$_{6}$} building blocks in Ni$_{36}$ remain magnetically intact while forming a hexagonal ring with antiferromagnetic exchange interactions between adjacent {Ni6} units. Electrochemical studies indicate that the first reduction is reversible and associated with the WVI/V couple, whereas the second reduction is irreversible attributed to the Ni$^{II/0}$ couple