THE CHARGE-DENSITY DISTRIBUTION IN HEXAMETHYLENETETRAMINE AT 120 K

The charge-density distribution has been determined from 333 independe nt X-ray reflections with sin theta/lambda < 1.47 Angstrom(-1), which were collected with Ag K alpha radiation, As found in a recent refinem ent using room-temperature data, full-matrix least squares refinement with a multipole model gives rise to an almost complete correlation be tween certain octapole deformation terms, This is the worst case examp le of a problem which will always arise to some degree when applying t he multipole model in a noncentrosymmetric space group, In this exampl e, the correlation arises between terms which are predominant for desc ribing the bonding density between atoms of the molecule, thereby caus ing the deformation charge density to have little meaning. However, th e total molecular electrostatic potential and the molecular octapole m oment are reliably obtained.