Deformation electron density of α-glycine at 120 K

Abstract

A study of the charge density in a-glycine, C2HsNO2, has been carried out employing X-ray and neutron diffraction data measured at 120 K. The crystal is monoclinic, space group P21/n, with the following cell dimensions: a = 5.084(1), b = 11.820(2), c = 5.458 (1) A and fl = 111.95 (2) °. The X-ray data were collected in the sin 0/4 range 0.00-1.20A-k The deformation densities were computed both by the X-N method, using positional and thermal parameters from the neutron diffraction study, and by a multipole refinement method, where the asphericity in the electron charge distribution was accounted for in the refinement. Well defined peaks of deformation charge density are found in all covalent bonds. The positions of the peaks, however, vary slightly depending on the method used. The X-N maps in the bonding regions are * Hydrogen-Bond Studies. CXL. t Present address:

Some diffractometer test crystals: a summary

“…§ § Converted from kxu units by multiplying by 1.00202 (see Batchelder & Simmons, 1964). References: (a) Marsh (1958), (b) J6nsson & Kvick (1972), (c) Legros & Kvick (1980), (d) Webster (1991a), (e) Carroll (1995), (f) Carroll (1997), (g) Spek (1987), (h) van Bommel & Bijvoet 11958), (i) Le Page et al, (1990), (j) Webster (1990), (k) Abrahams etal. (1970), (I) Okaya etal.…”

“…Denne (1972) grew crystals on a microscope slide and noted no deterioration of the diffracted intensities over time (see also J6nsson & Kvick, 1972). Coating of the crystals after mounting on a glass fibre has been carried out (Legros & Kvick, 1980). An early careful study by Marsh (1958) using film techniques established good cell dimensions as part of a structure (re)determination.…”

“…Crystals have been obtained by slow evaporation of an aqueous solution (Marsh, 1958;J6nsson & Kvick, 1972) and by slow cooling of hot (concentrated) aqueous solution (Legros & Kvick, 1980;Power et al, 1976). Denne (1972) grew crystals on a microscope slide and noted no deterioration of the diffracted intensities over time (see also J6nsson & Kvick, 1972).…”

The Two-Channel Maximum-Entropy Method Applied to the Charge Density of a Molecular Crystal: α-Glycine

“…An upgraded version of the program MOLLY (Hansen & Coppens, 1978), LSMOL90, was used in a multipolar refinement of the experimental data on the ot-glycine data set of Legros & Kvick (1980). The positional and thermal parameters of the C, N, O and H atoms, the x parameters and the multipole populations were varied in the leastsquares refinement.…”

“…As a test case, we have selected a low-temperature experimental single-crystal X-ray data set on the small-unit-cell crystal of a-glycine by Legros & Kvick (1980). The crystal is monoclinic, centrosymmetric, space group P21/n, and the X-ray data span the range sin 0/2 = 0.00-1.20,~-1, with 1205 reflections for which F > 2or(F).…”