Cerium(Iii) Chelate Complex with Monoprotonated Nitrilo-Tris(Methylenephosphonic) Acid: Structure and Chemical Bonding

Abstract

Hepta-potassium bis-[mono-hydrogene-nitrilo-tris(methylenephosphonato)]-cerium hydrate K7[CeIII{N(CH2PO3)3H}2]⋅8¼H2O (sp. gr. С2/c, Z=4, a = 17.4211(2) Å, b = 12.53630(10) Å, c = 16.4230(2) Å, β = 93.8030(10)°) was synthesized, detached and thoroughly characterized. In a cerium complex anion, the Ce atom is coordinated by two ligand molecules in an elongated rhombohedral crystal structure. The six nearest vertices of the rhombohedron are occupied by oxygen atoms of different PO3 groups, with nitrogen atoms of the ligand molecules occupying two distant vertices. Each ligand molecule is monoprotonated on the oxygen atom of one of the PO3 groups, and the nitrogen atom being double-protonated and forming a dative covalent (co-ordinate) bond with the cerium atom. Complex anions are surrounded by potassium atoms and molecules of hydrated water, forming endless helically twisted ribbons. A crystal packing exhibits layered stacking, with hydrated K+ ions arranging between the layers of the ribbons.

Keywords: Cerium, Nitrilo-tris(methylenephosphonic) acid, chelate complex structure, coordination polyhedron, dipolar bond