Cobalt 2,2′-biimidazole complexes co-crystallised with di-acids — synthesis, structure and quantum chemical calculations

Abstract

The synthesis and crystal structure of [Co(Hbiim)₂(H₂biim)]₂(p-OOCC₆H₄COOH)₂·H₂O (2) is presented. The cobalt(III) complexes are bridged by terephthalates and water molecules, giving a rare, five-fold interpenetrated, net built from 3-connected nodes. The vertex symbol (topology) of this net is determined to 4 12₂ 12₂, 4 12₆, 12₄ 12₆ 12₆, or 4 12², 4 12², 12³, using the Wellsian point symbol system. However, depending on the interpretation of the hydrogen bond pattern, this structure may also be interpreted as a single self-interpenetrating net via a water bridge. Quantum chemical calculations (DFT and semi-empirical methods) were used to investigate which is the more appropriate description by estimation of the directional forces in the structure. This approach favours five interpenetrating nets.