Competitive formation of crystalline phases and its structural properties within the system [CuxNi(1−x){N(CH2PO3)3}]Na4·nH2O (x = 0…1)

Abstract

During the crystallization of mixed coordination complex compounds of copper and nickel with Nitrilo-tris(Methylene-phosphonic acid) [CuxNi(1−x) {N(CH2PO3)3}]Na4·nH2O (x = 0…1), two phases are competitively formed from aqueous solutions. In case the atomic fraction of copper in the solution exceeds ¼, the triclinic phase [(Cu,Ni){N(CH2PO3)3}]Na4·13H2O is mainly formed. Cu and Ni atoms are coordinated in the environment of the trigonal bipyramid based on oxygen atoms of three different PO3-group of the ligand molecule, with the nitrogen atom in one vertex, and the oxygen atom of the neighbouring ligand molecule in the opposite one. If the atomic fraction of copper in the solution is less than ¼, the monoclinic nickel-containing phase [Ni(H2O){N(CH2PO3)3}]Na4·11H2O is formed. The coordination polyhedron of nickel is an octahedron, with oxygen atoms of different PO3-group of the ligand molecule in three meridional vertices, and a nitrogen atom, a water molecule and an oxygen atom of the neighbouring ligand molecule in three other vertices.Copper atoms in the triclinic phase can be easily replaced by nickel atoms to form crystals of heterometallic complexes containing up to 32.8% of Ni. The possibility of substitution of nickel atoms in the monoclinic phase for copper atoms is insignificant. Therefore, the monoclinic phase contains only trace amounts of copper. In the wide range of solution composition values crystalline products are formed in both phases.