STUDY OF THE FAMILY OF GLYCINE SELENIOUS ACID ADDITION-COMPOUNDS - CRYSTAL-STRUCTURE OF DIGLYCINE HYDROGEN SELENITE AND VIBRATIONAL-SPECTRAAND DSC MEASUREMENT OF DIGLYCINE HYDROGEN SELENITE AND MONOGLYCINE SELENIOUS ACID CRYSTALS

The X-ray structural analysis of diglycine hydrogen selenite has been carried out. The substance crystallizes in the monoclinic space group P2(1)/c, a = 12.2651(7), b = 4.8079(6), c = 19.9550(10) Angstrom, beta = 122.745(4)degrees, V = 989.73(14) Angstrom(3), Z = 4, R = 0.0338 fo r 1647 observed reflections. The crystal structure is formed by zwitte rions of glycine (CH2NH3+COO-), glycinium cations (CH2NH3+COOH), and h ydrogen selenite anions (HSeO3-) connected by an extensive system of h ydrogen bonds. The FTIR and FT Raman spectra of natural and deuterated diglycine hydrogen selenite and monoglycine-selenious acid crystals w ere recorded and interpreted. The FTIR spectra were studied down to a temperature of 90 K. DSC measurements for both compounds were carried out in the temperature range 95-380 K. No phase transition was found i n this temperature range by DSC and FTIR. The existence of ferroelectr ic properties of diglycine hydrogen selenite and monoglycine-selenious acid crystals can be excluded because of the centrosymmetry of their space groups. (C) 1998 Academic Press.