The report includes further development of applications of high-speed computers in crystallographic structure work. A description is given of a precise study of the structure of tetracyanoquinodimethane, heteroaromatic dibenzo-1, 3a, 4, 6a-tetraazapentalene, an aminotroponeimine derivative with aromatic properties, and a ferrocene derivative in which the two cyclopentadienyl rings are joined by a two-carbon bridge. Preliminary reports are given of reinvestigations of the structures of tetracyanoethylene and di-p-xylylene. A description of the structure of the hydrated calcium salt of the unusual acid hexacyanoisobutylene. The anion of this acid is highly stabilized by resonance, and preliminary considerations might suggest that it should be planar in fact, however, we find it to be propeller-shaped, with the arms tilted about 24 degrees. This tilt does not reduce the pi-overlap very much and does relieve intramolecular steric strain considerably.