Niobium oxygen ligands

When the niobium oxychloride clusters contain four oxygen ligands as inner ligands, different types of 2D cluster frameworks have been obtained. Their structures are briefly described below. 

Tetranuclear monoadducts with asymmetrical M- 0-M bridges related to those of [M2OCI9] have been characterized but most structural data concern monomeric NbOCls bis adducts. In such derivatives, the metal is octahedrally surrounded with the neutral ligands cis to each other, one being trans to the 0x0 bond, which is short (typical Nb=0 Bond Length K). The coordination polyhedron is distorted as a result of the niobium-oxygen multiple bond see Valence Shell Electron Pair Repulsion Model). ... 

Niobium(V) complexes Af-acetamido, 622 alkoxo, 601 oxygen ligands, 604 properties, 602... 

Some complexes are known in which carbon dioxide is bonded to a transition metal. Aresia era/. [19) isolated the nickel complex (1)in which the CO ligand is coordinated througli the carbon atom and one of the oxygen atoms. Fachinetti et al. [20] found the polymeric cobalt complex (2), in which carbon dioxide is C bonded to cobalt and 0-bonded to two different potassium ions. Lappert isolated tlie remarkably stable niobium complex (3). which was the first authentic CO complex of an early d-block metal [21 j. 

Even fewer complexes with nitrogen donor ligands have been reported and all are methyl cyanide adducts (Tables X and XI). Protactinium pentabromide forms a soluble 1 3 complex in contrast to the 1 1 complexes formed by niobium and tantalum pentahalides (46). Other actinide pentahalide-methyl cyanide complexes are still unknown. Protactinium tetrachloride, tetrabromide, and tetraiodide react with anhydrous, oxygen-free methyl cyanide to form slightly soluble 1 4 complexes (44, 48) which are isostructural with their actinide tetrahalide analogs. 

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