Ethyl 2-methoxy-6-[(triphenylphosphoranylidene) amino] nicotinate and ethyl 2-methylsulfanyl-6-[(triphenylphosphoranylidene) amino] nicotinate

The molecules of ethyl 2-methoxy-6-[(triphenylphosphoranyl-idene) amino] nicotinate, C27H25N2O3P, (I), and ethyl 2-methylsulfanyl6-[(triphenylphosphoranylidene)amino] nicotinate, C27H25N2O2PS, (II), have almost identical bond lengths and molecular conformations, and both show evidence for polarized electronic structures. However, the crystal structures, as illustrated by the weak hydrogen bonds linking the molecules, are significantly different. The significance of this study lies in the observation that two compounds which are almost identical in constitution, configuration and conformation nonetheless adopt different crystal structures.