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

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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.