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) A s , ؍ 122.745(4)°, V ؍ 989.73(14) A s 3 , Z ؍ 4, R ؍ 0.0338 for 1647 observed reflections. The crystal structure is formed by zwitterions of glycine (CH 2 NH ؉ 3 COO ؊ ), glycinium cations (CH 2 NH ؉ 3 COOH), and hydrogen selenite anions (HSeO ؊
3 ) connected by an extensive system of hydrogen bonds. The FTIR and FT Raman spectra of natural and deuterated diglycine hydrogen selenite and monoglycine-selenious acid crystals were 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 in this temperature range by DSC and FTIR. The existence of ferroelectric properties of diglycine hydrogen selenite and monoglycine-selenious acid crystals can be excluded because of the centrosymmetry of their space groups.
1998 Academic Press EXPERIMENTAL Crystalline DGSe(IV) was prepared by dissolving a mixture (in a molar ratio of 2 : 1) of glycine (99%, Aldrich) and selenious oxide (Sigma) in water. The 35% solution formed was left to crystallize spontaneously at laboratory temperature. The obtained colorless crystals were collected under vacuum on an S4 frit, washed with ethanol, and dried in the air.
Crystals of MGSe(IV) were prepared and isolated in a similar manner, with the difference that, on the basis of the results of a previous study (4), an input molar ratio of glycine and selenious oxide of 1 : 2 was used. A modified method of crystallization in tetramethoxysilane (TMS) gel (5) was employed as an alternative method of preparation. An amount of TMS (98%, Fluka) sufficient to ensure that the final mixture contained 10% TMS was added to a 30% aqueous solution of glycine and selenious acid (molar ratio of 4 : 3). Following mixing on a magnetic stirrer, this clear solution was poured into a test tube, which was closed with 71