Niobium halides

Niobium Halides and Oxyhalides. AH possible haUdes of pentavalent niobium are known and preparations of lower valent haUdes generally start with the pentahaUde. Ease of reduction decreases from iodide to fluoride. 

We have studied homopolycyclotrimerizations of aliphatic terminal diynes with various alkylene spacer lengths catalyzed by tantalum and niobium halides or by binary mixtures of the metal halides and tetraphenyltin (Scheme 18) [64-66]. Under optimized conditions, completely soluble diyne homopolymers with high molecular weights (Mw up to 1.4 x 106) and pre-... 

The alkali metal rhenium- and technetium chalcogenide clusters described in Section 5.6 are also octahedral.These clusters have M6Es units with eight face-capping anions on the octahedral faces in contrast to the niobium halide or oxide clusters. The A4M6S14 (A = alkali metal, M — Re, Tc), Cs6Rc6Si2, and... 

In addition to their applications in organic synthesis, all of the niobium halide complexes described here serve as convenient precursors to a variety of known coordination complexes of niobium(III) and (IV) as well as organo-metallic compounds. ... 

Tantalum and niobium halides also initiate the polymerization of acetylenes see Ch. 10. 

Bibliography survey was conducted on the thermodynamics of the pure niobium halides and their mixtures with alkali chlorides. 

Few data exist on niobium halides due to the great reactivity of these compounds which makes it extremely difficult to obtain oxychloride-free halides. Also experimental investigations are not easy since they have high vapor pressure and low melting points compared to the alkali halides melts.The data relative to the pure niobium halides reported on thermodynamic tables 77,8/ were mostly obtained by estimation. ... 

Phase diagrams were reported for the mixtures formed by niobium halides and alkali halides They are often questionable for the same reasons and disagreement exists between the results of different authors on the same system. 

The replacement of neutral ligands by halides in [Mo6Cl8L8] or [Nb6Cli2L8] results indeed in the generation of extended structures as illustrated in Fig. 2.21 for two niobium halide derivatives. 

Ligand Exchange in Metal Halide Clusters. Rhenium, molybdenum, tantalum and niobium halides are high-valence metal clusters that formally behave as Lewis acids towards halide ions forming anionic complexes that retain the structure of the original cluster. 

B. Peric, R. Gautier, C.J. Pickard, M. Bosiocic, M.S. Grbic, M. Pozek, Solid-state NMR/NQR and first-principles study of two niobium halide cluster compounds. Solid State Nucl. Magn. Reson. 59—60 (2014) 20—30. 

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