Spectral and voltammetric studies on titanium suhstituted Keggin-type heteropolyanions

摘要

Bonding and redox properties of mono- and dititanium substituted 12-heteropolytungsto- phosphates and their complexes with bivalent Mn, Co, Ni and Cu are studied by UV-Vis, ESR and cyclicvoltammetric techniques. The heteropoly blue analogue [Ti~(III)Ti~(IV)W_(10)PO_(40)]~(8-) is unstable and its presence in solution is proved by optical and ESR spectroscopy. ESR results reveal that the odd electron is trapped on the titanium atom at 77 K. The optical electronegativity of Ti(III) in this heteropoly blue is estimated to be 2.4 from the intervalence charge transfer (IVCT) bands. X-ray powder diffraction results show that the complexes K_5M~(II)[Ti_2W_(10)PO_(40)].xH_2O(M~(II) = Cu or Mn) are isomorphous with K_7[Ti_2W_(10)PO_(40)].6H_2O. Electronic spectroscopy indicates very high symmetry around the bivalent metal ion M in the K_5M~(II)[Ti_2W_(10)PO_(40)].xH_2O complexes. This high symmetry is confirmed in K_5Cu[Ti_2W_(10)PO_(40)] by the observation of dynamic Jahn-Teller (JT) distortion at 300 K andstatic JT distortion at 77 K.