A chiral diamine: practical implications of a three-stereoisomer cocrystallization.

A brief comparison of seven straightforward methods for molecular crystal-volume estimation revealed that their precisions are comparable. A chiral diamine, N2,N3-bis[2,6-bis(propan-2-yl)phenyl]butane-2,3-diamine, C28H44N2, has been used to illustrate the application of the methods. Three stereoisomers of the diamine cocrystallize in the centrosymmetric space group P21/c with Z' = 1.5. The molecules occupying general positions are RR and SS, whereas that residing on an inversion center is meso. This is one of only ten examples of three stereoisomers with two asymmetric atoms cocrystallizing together reported to the Cambridge Structural Database (CSD). The conformations of the SS/RR and meso molecules differ considerably and lead to statistically significantly different C(asymmetric)-C(asymmetric) bond lengths in the diastereomers. An advanced Python script-based CSD searching technique for chiral compounds is presented.