Hydrothermal synthesis and structure characterization of a Keggin tungstocobaltate [Co(2,2 ′-bipy) 3] 2H 2[CoW 12O 40] · 9.5H 2O

Abstract

A Keggin-type tungstocobaltate [Co(2,2 ′-bipy) 3] 2H 2[CoW 12O 40] · 9.5H 2O was prepared by the hydrothermal method for the first time and characterized by elemental analyses, IR, UV, EPR spectra, TG-DTA analyses and X-ray single crystal diffraction, showing that the complex consists of a Keggin anion [CoW 12O 40] 6− and two isolated chiral ions [Co(2,2 ′-bipy) 2] 2+. The characteristic band of Keggin anion [CoW 12O 40] 6− appears at 298 nm in the UV spectrum. EPR spectra reveal two Co 2+ coordination environments in the title compound, high spin state ( g=5.1, 4.2) and low spin state ( g=2.0). Furthermore, when the temperature increases from 110 K to room temperature, the signal g=5.1 of high spin Co 2+ disappears, caused by the negative zero-field splitting. Thermal analysis indicates that the Keggin anion skeleton begins to decompose at 560.4 °C.