A NOVEL OPTICAL COMPLEX BETWEEN AN ORGANIC SUBSTRATE AND A POLYOXOMETALATE - CRYSTAL AND MOLECULAR-STRUCTURE OF LPHA-H4SIW12O40-CENTER-DOT-4HMPA-CENTER-DOT-2H(2)O (HMPA EQUALS HEXAMETHYLPHOSPHORAMIDE)

A solvated complex of alpha-H4SiW12O40. 4HMPA . 2H(2)O composed the he teropolytungstate alpha-H4SiW12O40 and the organic substrate hexamethy lphosphoramide (HMPA) has been synthesised, purified, and characterize d. The electronic spectra (lambda = 220-500 nm) as well as the H-1 NMR spectra for the title compound dissolved in CD3CN establish that this complex dissociates into free SiW12O404- and HMPA moieties in solutio n unless the organic substrate HMPA is present in very high concentrat ions. The solid reflectance electronic spectra and LR spectra indicate that there is interaction between the alpha-H4SiW12O40 and the organi c substrate. The complex has no photosensitivity under irradiation of sunlight, but under the near-UV light result in a charge transfer by o xidation of the HMPA and the reduction of the polyoxometalate. Light y ellow polyhedrons of the title compound crystallize from the aqueous s olvent of acetonitrile and aqueous solution as the formula of alpha-H4 SiW12O40. 4HMPA . 2H(2)O in the monoclinic, space group P2(1). The uni t cell has a = 12.791(3) Angstrom, b = 22.103(6) Angstrom, c = 15.532( 4) Angstrom, beta = 102.860(10)degrees, and Z = 2. From the bond-valen ce parameters, it was found that the four hydrogen atoms of the polyox ometalate were combined with the N atoms of the four HMPA respectively . The title compound shows a certain second-order and third-order nonl inear optical response of I-2 omega = 0.71(KDP)(2 omega) and ((3)(chi) ) = 2.63 x 10(-11) esu, respectively.