Materials Highlights - Issue 4

An aim of chemists in recent years has been to develop synthetic routes for the preparation of thermotropic, calamitic metallomesogens with high coordination numbers. Bruce and his colleagues (Adv. Mater. 1995, 7, 665) have now reported a methodology for the synthesis of mesogenic complexes formed by the coordination of the [ReBr(CO),] fragment to 1, 4-diaza-1, 3-butadienes, 1. The parent ligands exhibit smectic C and nematic phases while the octahedral complexes are exclusively nematogenic. The destruction of smectic behaviour on complexation is attributed to the bulky [ReBr(CO),] fragment disrupting molecular packing. The nematic-isotropic transition temperatures of the complexes are higher than those of the parent ligands. The authors speculate that this surprising observation may be related to a decrease in the flexibility of the-N=CH-CH=N-segment of the ligand on complexation. It is anticipated that diazabutadienes will become an important synthetic building block for the preparation of new metallomesogens incorporating high coordination number centres.