5,5′-Dicyano-2,2′-bipyridine silver complexes: discrete units or co-ordination polymers through a chelating and/or bridging metal–ligand interaction

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Abstract
The ambidentate ligand 5,5′-dicyano-2,2′-bipyridine (L) was found to function as a bi-, tri- or tetra-dentate chelate or chelate/bridging ligand in the co-ordination of silver ions. The mode of co-ordination depends on the anion and the crystallization conditions and was elucidated by single crystal X-ray diffractometry. With metal-co-ordinating anions such as NO3 – and CF3SO3 – a tridentate co-ordination mode of L is observed which involves the two bipyridine nitrogen donor atoms and one cyano group. The latter bridges to a neighboring silver center so that a one-dimensional co-ordination polymer results. For NO3 – this co-ordination polymer forms a 21 helix. With less co-ordinating anions such as BF4 – and PF6 – monomeric bis-chelate complexes are obtained, where L assumes a bidentate co-ordination mode involving only the bipyridine nitrogen donor atoms. In the case of the PF6 – anion a variation in the solvent of crystallization also produced a two-dimensional hexagonal co-ordination polymer where L functions as a tetradentate ligand using all four nitrogen donor atoms in chelation and bridging to the silver centers.

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