The crystal structure and variable temperature 119mSn Mössbauer study of trimethyltin glycinate, a one-dimensional, amino-bridged polymer

The crystal structure of trimethyltin glycinate has been determined by Patterson and Fourier techniques to a final “R”-factor of 0.066 for 1103 unique reflections. The crystals are tetragonal with space group P41with a = b = 7.839(9) and c = 14.659(11) A, Z = 4, and are composed of stacks of linearly polymeric trimethyltin glycinate molecules bridled axially at tin through the amino nitrogen atoms of the amino acid. There is hydrogen bonding between carbonyl oxygen and amino group NH moieties along the chains and between the chains to produce a perpendicular weave of one-dimensional polymer threads. The axial NSnO connections make an angle approaching linearity, but the tin atom is distinctly displaced toward the oxygen to give non-planar SnC3 units which are eclipsed in the chain. This bridging rather than chelated amino acid configuration is only found in glycinatosilver(I) hemihydrate. Tin-119m Mossbauer resonance area data have been collected in the temperature range 77 ⩽ T ⩽ 185 K, and a logarithmic plot of the normalized area vs. temperature is linear in this range and the slope of −1.15 x 10−2 K−1 yields values of the logarithmic tempemture coefficient of the recoil-free fraction (which at 296 is less than a tenth of its value at 77 K). These data have been used to evaluate the isotropic mean-square amplitudes of vibration of the tin atom, normalized to the value at 296 K available from the crystallographic study, in the same temperature range. Isotropic-mean-square values of the vibrational amplitude increase from 1.78 x 10−2 at 77 to 2.63 x 10−2 at 185 and 3.5 x 10−2 at 296 K. From the doublet line asymmetry data assuming that the electric field gradient tensor, Vzz, is positive in sign and lies along the polymer axis (oblate field about the cylindrical axis), it is concluded that the tin atom vibrates with greater amplitude normal to the propagating axis ( = 1.93 x 10−2 at 77 and 3.11 x 10−2 A2 at 185 K) than along it ( = 1.48 x 10−2 at 77 and 1.67 x 10−2 A2 at 185 K). The temperature coefficient of the motion normal to the axis is also greater over the range examined. The differrence in the mean-square amplitudes perpendicular and parallel to the axis 2.96 x 10−2 from the Mossbauer treatment and 4.24 x 10−2 A2 from the X-ray anisotropic thermal ellipsoids at 296 K.