A series of compounds containing various (oxalato)tantalate(v) complex anions - synthesis, properties and the mixed-metal oxide formation viathermal decomposition

• Published in: CrystEngComm Vol. 15; no. 3; pp. 533 - 543
• Main Authors: Andros, Lidija, Matkovic-Calogovic, Dubravka, Planinic, Pavica
• Format: Journal Article
• Language: English
• Published: 01.12.2012
• Subjects: Anions; Cations; Distortion; Nickel; Oxalates; Oxides; Oxygen atoms; Tantalum
• ISSN: 1466-8033
• DOI: 10.1039/c2ce26391b

Four new ionic, oxalate containing complexes, [Hphen][Ni(phen) sub(3)][Ta(C sub(2)O sub(4)) sub(4)].6.5H sub(2)O (1), [Ni(phen) sub(3)][Ta(OH)(C sub(2) O sub(4)) sub(3)].8H sub(2)O (2), [Ni(phen) sub(3)][Ta(OC sub(2)H sub(5))(C sub(2)O sub(4)) sub(3)].H sub(2)O (3) and [Ni(phen) sub(3)][Ta(OCH sub(3))( C sub(2)O sub(4)) sub(3)].H sub(2)O (4) (phen = 1,10-phenanthroline) were obtained by using an (oxalato)tantalate(v) solution as a source of complex anions. Crystal structures of all four compounds were solved. The complexes contain the same [Ni(phen) sub(3)] super(2+) cation but different (oxalato)tantalate(v) complex anions. The nickel(ii) atom in the cation is coordinated with six nitrogen atoms in a trigonally distorted octahedral environment. The coordination sphere around the tantalum atom is subject to change due to the solvent change. In the complex anion of 1 the tantalum(v) atom is octacoordinated by eight oxygen atoms from the four oxalate groups, whereas in the anions of 2, 3 and 4 the coordination polyhedron around tantalum is a distorted pentagonal bipyramid comprising six oxygen atoms from the three oxalate groups and another oxygen atom from the additional oxygen ligand. Different complex anions in 1-4 give rise to the variability of the structural architectures. Crystallization water molecules and the (oxalato)tantalate(v) anions direct diverse hydrogen bonding patterns: from one-dimensional hydrogen-bonded chains in 3 and 4, to an extended three-dimensional framework in 2. Compound 1 contains two different cations, [Hphen] super(+) and [Ni(phen) sub(3)] super(2+), that are involved in a two-dimensional stacking arrangement. The compounds were studied also by TG/DTA analysis, and the composition of the oxides, as the final decomposition product, was checked by the powder X-ray diffraction method. The results indicate that the new compounds are prospective and applicable Ni-Ta precursors for the synthesis of nickel tantalate, NiTa sub(2)O sub(6).