Crystal structure and mol-ecular Hirshfeld surface analysis of acenaphthene derivatives obeying the chlorine-methyl exchange rule.

Instances of crystal structures that remain isomorphous in spite of some minor changes in their respective mol-ecules, such as change in a substituent atom/group, can provide insights into the factors that govern crystal packing. In this context, an accurate description of the crystal structures of an isomorphous pair that differ from each other only by a chlorine-methyl substituent, 5''-(2-chloro-benzyl-idene)-4'-(2-chloro-phen-yl)-1'-methyl-dispiro-[acenaphthene-1,2'-pyrrolidine-3',3''-piperidine]-2,4''-dione, CHClNO, (I), and its analogue 1'-methyl-5''-(2-methyl-benzyl-idene)-4'-(2-methyl-phen-yl)di-spiro-[acenaphthene-1,2'-pyrrolidine-3',3''-piperidine]-2,4''-dione, CHNO, (II), is presented. While there are two C-H⋯O weak inter-molecular inter-actions present in both (I) and (II), the change of substituent from chlorine to methyl has given rise to an additional weak C-H⋯O inter-molecular inter-action that is relatively stronger than the other two. However, the presence of the stronger C-H⋯O inter-action in (II) has not disrupted the validity of the chloro-methyl exchange rule. Details of the crystal structures and Hirshfeld analyses of the two compounds are presented.