The crystal structure of hexam ethylenetetramine I. X -ray studies at 298, 100 and 34 °K

Abstract

On account of its cubic molecular and crystal symmetry, hexamethylenetetramine is a key substance in the study of the lattice vibrations of molecular crystals; its anisotropic atomic-vibration amplitudes have been determined at 298, 100 and 34 °K from three-dimensional single crystal X-ray data. Two independent sets of experiments were done with Cu and Mo radiation; these led to results in very close agreement with one another (and with results derived from previous X-ray and neutron data at room temperature). Typical final discrepancy factors obtained from full-matrix least-squares refinements are 3.4 % for 95 Mo reflexions and 6.3 % for 44 Cu reflexions at 34 °K. The studies at the three temperatures provide direct support for the rotational-oscillation correction for atomic co-ordinates. The corrected weighted-mean dimensions from eight determinations are C—N = 1.476 ± 0.002 Å, ∠N—C—N = 113.6 ± 0.2°, ∠C—N—C = 107.2 ± 0.1°, and from the neutron study C—H = 1.088 ± 0.011 Å. The compact arrangement of molecules in the crystal is described.