Niobium complexes octahedral

The tetranuclear [La (OC2H4)3N 2 Nb(OPr )4 3] contains eight-coordinated (bicapped trigonal antiprism) La and distorted octahedral niobium (Fig. 4.62). ° A homoleptic trinuclear lanthanum niobium complex [(Pr 0)3Nb(/t-OPr )3La(OPr )(/t-OPr )2Nb(OPr )4] has also been established. The distorted octahedral La is triple-bridged to one Nb and double-bridged to the other, generating a bent (136.2°) NbLaNb axis." ... 

Since niobates and tantalates belong to the octahedral ferroelectric family, fluorine-oxygen substitution has a particular importance in managing ferroelectric properties. Thus, the variation in the Curie temperature of such compounds with the fluorine-oxygen substitution rate depends strongly on the crystalline network, the ferroelectric type and the mutual orientation of the spontaneous polarization vector, metal displacement direction and covalent bond orientation [47]. Hence, complex tantalum and niobium fluoride compounds seem to have potential also as new materials for modem electronic and optical applications. 

S Tantalum and niobium are present in the crystal structure in the form of complex ions. The lowest coordination number, 6, corresponds to the formation of slightly distorted octahedrons. The linking and packaging of the octahedrons depends on the X Me ratio, where X is the total number of oxygen and fluorine atoms, and Me is the total number of tantalum or niobium ions as well as other metals that can replace tantalum or niobium in the octahedral polyhedron. The crystal structure type can be defined based on the X Me ratio, as follows ... 

Rupprecht, G.A., Messerle, L.W., Fellmann, J.D. and Schrock, R.R. (1980) Multiple metal-carbon bonds. 15. Octahedral alkylidene complexes of niobium and tantalum by ligand-promoted a abstraction. J. Am. Chem. Soc., 102, 6236. 

A manganese bis(acetylacetonato)-ethylenediamine complex was employed in the preparation of supramolecular assemblies with an octahedral niobium cyanochloride cluster, [Nb6Cli2(CN)6] . These assemblies range in size from 1.5 to 2.4 nm and their charge varies between —3 and +2, depending on the number of Mn units per cluster. 

Class 4 structures with octahedral anionic groups - complex oxides containing octahedrally coordinated titanium, niobium, tantalum. 

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