The role of 4,7-phenanthroline in coordination polymer construction

The reactions of 4,7-phenanthroline (4,7-phen) with a variety of metal salts have been investigated and the products structurally characterised by single crystal X-ray diffraction. Reaction of CoX2 (X = Cl, Br) or M(NO3)(2) (M = Cd, Zn, Ni) salts with 4,7-phen all afford one-dimensional coordination polymers, [CoX2(4,7-phen)](infinity) (1, 2) or [M(NO3)(2)(4,7-phen)(H2O)](infinity) (M = Cd 3, Zn 4, Ni 5), in which the metal centres are linked via 4,7-phen ligands which act in a bridging bidentate manner. The remaining metal coordination sites are occupied by either halide (1, 2) or NO3- and H2O ligands (3-5). In{[Ni(NO3)(2)(4,7-phen)(H2O)].(4,7-phen)}8, 5 an additional, uncoordinated, molecule of 4,7-phen is included in the structure, hydrogen bonded to a coordinated H2O molecule. In contrast, reaction of CuX2 (X = Cl, Br) or Cu(NO3)(2) with 4,7-phen leads to the formation of discrete complexes, [CuX2(4,7-phen)(2)] (X = Cl 6, Br 7, NO(3)8) in which the N-donor ligand coordinates in a monodentate fashion and pi-pi interactions between coordinated 4,7-phen molecules generate an extended structure in the solid state. Investigation of the phase purity of 4 and 5 revealed that in the case of 4 the coordination polymer formed only in the presence of a previously reported hydrogen bonded structure, while 5 was shown to be contaminated with an unidentified phase. The role and diversity of the interactions adopted by 4,7-phen in forming coordination polymers and related species are discussed.