SYNTHESIS, CRYSTAL-STRUCTURES AND VIBRATIONAL-SPECTRA OF ZINC HYPOPHOSPHITES

The preparation, crystal structure, infrared and Raman spectra are rep orted for zinc hypophosphites, Zn(hyp)(2) and zinc hypophosphite monoh ydrate, Zn(hyp)(2) . H2O (hyp = H2PO2). Both structures are polymeric, and the coordination geometry of zinc is octahedral. In Zn(hyp)(2) th e coordination is to six oxygen atoms of the hypophosphite groups, and in Zn(hyp)(2) . H2O, via one oxygen atom of a water molecule, and fiv e hypophosphite oxygen atoms. The hypophosphite vibrational modes give rise to multiple structures in the infrared and Raman spectra, and th ese bands are interpreted under unit cell group selection rules in a c onsistent manner with the crystallographic data. The infrared spectral region between 1940-2350 cm(-1) comprises numerous combination bands, whose intensities are enhanced through Fermi resonance with the P-H s tretching modes. The breadth and wavenumbers of water modes observed i n the vibrational spectra of Zn(hyp)(2) . H2O indicate the presence of medium-strong hydrogen bonding to hypophosphito-oxygen atoms. The X-r ay data show a slight lengthening of the mean P-O bond distance, and s hortening of the mean P-H distance for the hydrated compound. Whereas the changes in PH2 stretching, and PH2 and PO2 bending wavenumbers bet ween the two compounds are as expected from this, the PO2 stretching m odes show that change of the unit cell group symmetry must also be con sidered. The mean Zn-O bond distance is similar (near 2.1 Angstrom) in both Zn(hyp)(2) and Zn(hyp)(2) . H2O, and the infrared active Zn-O an tisymmetric stretching modes are observed near 328 and 300 cm(-1), res pectively. Structural factors, in addition to the cation ionic radii, determine the trends in M(II)-(O-hypophosphito) antisymmetric stretchi ng modes for other divalent cations. Copyright (C) 1996 Elsevier Scien ce Ltd