Hydrogen bonding in diaquatetrakis(urea-κO)MII dinitrates, with M = Ni and Co

The isomorphous title compounds, [ Ni{( NH2)(2)CO}(4)( H2O)(2)]( NO3)(2) and [ Co{( NH2)(2)CO}(4)( H2O)(2)]( NO3)(2), feature discrete centrosymmetric cations in octahedral coordinations, formed by four urea molecules linked via their O atoms to the central ion in equatorial positions and two water molecules in trans positions. The complexes are packed in a pseudo- hexagonal manner separated by the nitrate counter- ions. All H atoms are involved in moderate hydrogen bonds of four types: N - H center dot center dot center dot O = C, N - H center dot center dot center dot O - N, O - H center dot center dot center dot O - N and N - H center dot center dot center dot O - H. Graph- set analysis was applied to distinguish the hydrogen- bond patterns at unitary and higher level graph sets.