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

The ambidentate ligand 5,5'-dicyano-2,2'-bipyridine (L) was found to functi on as a bi-, tri- or tetra-dentate chelate or chelate/bridging ligand in th e co-ordination of silver ions. The mode of co-ordination depends on the an ion and the crystallization conditions and was elucidated by single crystal X-ray diffractometry. With metal-co-ordinating anions such as NO3- and CF3 SO3- a tridentate co-ordination mode of L is observed which involves the tw o bipyridine nitrogen donor atoms and one cyano group. The latter bridges t o a neighboring silver center so that a one-dimensional co-ordination polym er results. For NO3- this co-ordination polymer forms a 2(1) helix. With le ss co-ordinating anions such as BF4- and PF6- monomeric bis-chelate complex es are obtained, where L assumes a bidentate co-ordinating mode involving o nly the bipyridine nitrogen donor atoms. In the case of the PF6- anion a va riation in the solvent of crystallization also produced a two-dimensional h exagonal co-ordination polymer where L functions as a tetradentate ligand u sing all four nitrogen donor atoms in chelation and bridging to the silver centers.