The Crystal-Chemical Features of Phases and the Nature of the Coordination Bond in the System [Cu_xNi_(1 – x){N(CH₂PO₃)₃}]Na₄ · nH₂O (x = 0–1)

The structural features of the phases formed during crystallization of mixed copper and nickel complexes with nitrilotris(methylenephosphonic acid) [Cu_xNi_(1 – x){N(CH₂PO₃)₃}]Na₄ · nH₂O (x = 0–1) and the character of the M ← O(P) coordination bond have been investigated. The copper-dominant phase [(Cu,Ni){N(CH₂PO₃)₃}]Na₄ · 13H₂O (sp. gr. P$\overline{1}$, Z = 2, a = 10.0096(2)–10.0118(2) Å, b = 11.0311(3)–11.0330(2) Å, c = 12.2893(2)–12.3038(3) Å, α = 84.7180(10)°–84.785(2)°, β = 79.504(2)°–79.544(2)°, γ = 66.971(2)°–67.058(2)°) is characterized by the trigonal bipyramidal coordination of the metal atom (oxygen atoms of three different PO₃ groups of the ligand molecule lie in the pyramid-base plane, and a nitrogen atom and the oxygen atom of the neighboring ligand molecule occupy opposite vertices). The nickel-containing phase [Ni(H₂O){N(CH₂PO₃)₃}]Na₄ · 11H₂O (sp. gr. C2/c, Z = 4, a = 11.9924(2)–12.05510(10) Å, b = 18.6049(3)–18.7152(2) Å, c = 21.0724(4)–21.1266(2) Å, β = 104.096(2)°–104.4960(10)°) is characterized by octahedral coordination of the Ni atom (oxygen atoms of different PO₃ groups of the ligand molecule are located at three meridian octahedron vertices, and a nitrogen atom, a water molecule, and the oxygen atom of the neighboring ligand molecule occupy the rest three vertices). The dependence of the interatomic distances and bond angles in the coordination sphere of the metal atom on the Cu : Ni ratio has been studied. It is shown that the transition from the trigonal bipyramidal coordination to the octahedral coordination is accompanied by a sharp increase in the ionicity of the M ← O(P) coordination bond.