Crystal structure of glycinium arsenate, C2NH8O2+AsO4-

Abstract

C2H8ASN06, monoclinic, Pl2i/cl (No. 14), a= 7.919(2) A, b= 4.744(1) A, c =17.59(1) A, s = 91.71(4)°, V= 660.5 A, Ζ = 4, Rst(F) = 0.021, wR(F) = 0.050, T= 293 K. Source of material The compound was synthesized by controlled evaporation of a water solution of arsenic acid and glycine in molar ratio 1:1. Large single crystals were obtained from which good quality specimens were selected for X-ray measurements. Discussion Glycine arsenate is a new glycine compound. Inspection of the carboxylic C 0 distances clearly shows that the glycine moiety is protonated. Whereas glycine phosphite is ferroelectric below 224 Κ [1], no pyroelectric current was detected either decreasing or increasing the temperature in the range 20 Κ 300 Κ [2]. Small anomalies in the dielectric constant as well as dielectric loss were found around 250 Κ in cooling runs from room temperature. Examination of the crystal structure shows layers of thAsCU tetrahedra alternating with glycine groups, parallel to the ab plane. This feature can be contrasted with that occurring in glycine phosphate where similar groups are found to be parallel to the be plane [3]. Each H2ASO4 group is connected by two hydrogen bonds (2.543(3) A, 2.687(3) A) to its neighbours forming helical chains along the i»-axis. The hydrogen atom of the carboxylic group is involved in an hydrogen bond with one of the bare Ο atoms of the H2ASC>4 ion, the distance O O being rather short (2.566(3) A). Two hydrogen atoms of the NH3 group establish hydrogen bonds with the two bare 0 3 and 0 4 atoms of neighbour H2 AsO^f tetrahedra; the third amino hydrogen atom is donated to atom 0 6 of the closest carboxylic group [4]. Table 1. Data collection and handling. Crystal: colourless, transparent, truncated pyramid, size 0.15 χ 0.20 x 0.25 mm Wavelength: Mo Ka radiation (0.71073 A) μ: 51.25 cm Diffractometer, scan mode: Enraf-Nonius CAD-4, ω/2θ 26max: 49.98° N 2a(/„bs), 974 N(param)KfiTxA' 94 Programs: PLATON [4], SDP [5], SHELXS-97 [6], SHELXL-97 [7], ORTEPII [8] Table 2. Atomic coordinates and displacement parameters (in A). Atom Site X y ζ Uiso H(l) 4e 0.9823 -0.1681 0.6833 0.057 H(2) 4e 0.6377 -0.3499 0.6940 0.050 H(0A) 4e 0.7043 -0.5223 0.8517 0.043 H(0B) 4e 0.5675 -0.3568 0.8822 0.043 H(0C) 4e 0.6388 -0.5910 0.9257 0.043 H(1A) 4e 0.8120 -0.1084 0.8955 0.046 H(1B) 4e 0.8891 -0.3616 0.9425 0.046 H(5) 4e 0.7521 0.1459 1.0642 0.054 * Correspondence author (e-mail: lourdes@pollux.fis.uc.pt) Unauthenticated Download Date | 12/28/16 9:07 PM 536 Glycin ium arsenate Table 3. Atomic coordinates and displacement parameters (in A). Atom Site X y ζ C/i 1 U22 U33 {/12 i/13 U23 As 4e 0.75626(3) 0.04960(6) 0.70741(2) 0.0235(2) 0.0217(2) 0.0193(2) 0.0002(1) 0.0022(1) 0.0023(1) O( l ) 4e 0.9150(3) -0.0838(5) 0.6552(1) 0.032(1) 0.055(2) 0.029(1) 0.016(1) 0.0103(9) 0.007(1) 0(2) 4e 0.6206(3) -0.2213(4) 0.7240(1) 0.042(1) 0.019(1) 0.039(2) -0.0060(9) 0.018(1) -0.0020(9) 0(3) 4e 0.6597(2) 0.2857(4) 0.6515(1) 0.033(1) 0.022(1) 0.025(1) 0.0049(8) 0.0025(9) 0.0045(9) 0(4) 4e 0.8207(3) 0.1752(5) 0.7910(1) 0.032(1) 0.044(1) 0.021(1) -0.006(1) -0.0025(8) -0.006(1) Ν 4e 0.6619(3) -0.4514(5) 0.8939(2) 0.033(1) 0.030(1) 0.024(2) -0.000(1) 0.003(1) -0.003(1) C( l ) 4e 0.7856(4) -0.2599(7) 0.9303(2) 0.032(2) 0.034(2) 0.026(2) -0.005(1) 0.008(1) -0.006(1) C(2) 4e 0.7149(3) -0.1389(6) 1.0019(2) 0.029(1) 0.026(1) 0.020(2) 0.001(1) 0.003(1) -0.001(1) 0(6) 4e 0.6021(3) -0.2517(5) 1.0346(1) 0.043(1) 0.041(1) 0.028(1) -0.014(1) 0.013(1) -0.006(1) 0(5) 4e 0.7879(3) 0.0966(5) 1.0230(1) 0.044(1) 0.035(1) 0.030(1) -0.012(1) 0.012(1) -0.010(1) Acknowledgments. We thank gratefully Dr. J. Albers for his collaboration in the study of betaine compounds. We are indebted to the Cultural Service of the German Federal Republic Embassy, the Deutscher Akademischer Austauschdienst (DAAD) and the German Agency for Technical Cooperation (GTZ) for the offer of a CAD-4 automatic diffractometer which enabled the experimental work to be carried out. This work was supported by the project PRAXIS/2/2. l/FIS/26/94. J. Agostinho Moreira thanks Project PRAXIS XXI for his grant (DB/3192/94).