Hydrogen-bonded networks through second-sphere coordination

The reaction of 4, 7-phenanthroline (1) with aqueous transitionmetal complexes Mn(H2O)6]NO3]2, Co(H2O)6]NO3]2, Ni(H2O)6NO3]2, Mn(H2O)6]ClO4]2, and Co(H2O)6]ClO4]2 does not produce coordination complexes between these metal cations and the N-donor ligand as expected. Instead, supramolecular hydrogenbonded networks are formed between the nitrogen donor atoms of 4, 7-phenanthroline and the OH groups of coordinated water molecules: M-O-H...N interactions. This motif of second-sphere coordination for 1 can be exploited as a tool for crystal engineering. As a demonstration of the generality of this new interaction as a supramolecular building block, five X-ray crystal structures are reported that utilise this hydrogen bonding scheme; Co(H2O)4(NO3)2].(1)2 (2a), Co(MeCN)2(H2O)4]ClO4]2.(1)2 (2b), Ni(H2O)4(NO3)2].(1)2 (3a), Mn(H2O)4(NO3)2].(1)2 (4a), and Mn(H2O)6]ClO4]2.(1)(4).4H2O (4b). Each network involves complete saturation of the hydrogen-bond donor sets between the aqua complex and 1 using primarily M-O-H...N(1) and M-O-H...O(anion), interactions. Thermogravimteric analysis shows these materials to have stabililities similar to coordination polymers involving metal-ligand bonds; this demonstrates that second-sphere hydrogen bonding has potential for the construction of polymeric metal-containing materials.