Cobalt(II) complexes of calix[6]arenes: crystallographic studies into heteroatom bridge influence over discrete versus polymeric structure formation

Methylene-bridged calix[4]arenes have emerged as excellent ligands for polynuclear cluster formation. In this contribution methylene- and oxa-bridged calix[6]arenes have been examined as candidates for cluster formation with cobalt(II) nitrate, affording two markedly different structures. The nature of the structures is highly dependent on the bridging atoms. Reaction of p-tert-butylcalix[6]arene with cobalt(II) nitrate in DMF results in the formation of a coordination polymer in which the calixarene adopts a 'double-partial' cone conformation. A similar reaction with p-tert-butyltetrahomodioxacalix[6]arene affords a discrete complex in which a central heteroatom also coordinates to the metal centre, with the calixarene in a 'double-cone' conformation. The synthesis and structure of both compounds is presented. Crown Copyright (C) 2013 Published by Elsevier Ltd. All rights reserved.