Polymorphism and phase transition behavior of 6,6′-bis(chloromethyl)-1,1′,4,4′-tetramethyl-3,3′-(p-phenylenedimethylene)bis(piperazine-2,5-dione)

A crystallographic investigation of the title compound, C22H28Cl2N4O4, using crystals obtained under different crystallization conditions, revealed the presence of two distinct polymorphic forms. The mol­ecular conformation in the two polymorphs is very different: one adopts a ‘C’ shape, whereas the other adopts an ‘S’ shape. In the latter, the molecule lies across a crystallographic twofold axis. The ‘S’-shaped polymorph undergoes a reversible ortho­rhom­bic-to-monoclinic phase transition on cooling, whereas the structure of the ‘C’-shaped polymorph is temperature insensitive.