Halogen bonded supramolecular assemblies of [Ru(bipy)(CN)4]2- anions and N-methyl-halopyridinium cations in the solid state and in solution.

The interactions between the [Ru(bipy)(CN)4]2− anion and N-methyl-halopyridinium cations have been examined in both the solid state and in solution. In the solid state, crystal structures of [Ru(bipy)(CN)4]2− salts containing iodinated cations (N-methyl-3-iodopyridinium and N-methyl-3,5-diiodopyridinium) show clear C−I···NC(Ru) halogen bonds between the externally directed cyanide lone pairs of the anion and the iodine atoms of the cation which dominates the structures. In contrast the analogous brominated cations (N-methyl-3-bromopyridinium and N-methyl-3,5-dibromopyridinium) do not exhibit C−Br···NC(Ru) interactions in the solid state, with the cyanide groups instead involved in hydrogen bonding, principally to lattice water molecules. The charge-assisted C−I···NC(Ru) interactions are therefore clearly of value as synthons in crystal engineering applications. In CH2Cl2 solution, spectroscopic titrations between [Ru(4,4′-tBu2-bipy)(CN)4]2− and both N-methyl-3-iodopyridinium and N-methyl-3-bromopyridinium...