Niobium distorted octahedral

The niobium atom has a slightly distorted octahedral coordination. Interatomic distances between the niobium atom and the two oxygen atoms in trans positions, O-Nb-O are 1.81 and 2.14 A. The niobium atom is shifted from the base plane of the octahedron by 0.23 A, and this shift, in adjacent chains, is in opposite directions. Pakhomov and Kaidalova [204] concluded that the shorter Nb-O bond (1.81 A) is an intermediate between a single and double bond. 

Examples of derivatives of zerovalent niobium and tantalum are very rare. Cocondensation of vapors of the metals, generated by an electron gun furnace at 3000 °C, operating at a positive potential with dmpe, gave excellent yields (>60%) of stable crystalline [M(dmpe)3], which displays a distorted octahedral geometry. Attempts to obtain the corresponding niobium compound by reduction of NbCls with sodium naphthalenide at room temperature in the presence of an excess of dmpe failed and led to metal deposition. By contrast, reduction of MX5 by sodium amalgam in the presence of bipy or o-phen (LL) afforded the paramagnetic M(LL)3 adducts in ca. 80% yield. ... 

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." ... 

TiOj is known to exist in mainly three crystalhne forms, each with distinctive properties anatase, rutile, and brookite. Anatase, the metastable state, and rutile, the stable form, are the only forms of interest for Ti02 applications (Diebold, 2003 Antolini and Gonzalez, 2009). Pure stoichiometric TiOj exists in a distorted octahedral configuration and has a low electrical conductivity of only 10" S cm at 298 K however, substochiometric compositions or added n-type dopants such as vanadium, niobium, and tantalum can create oxygen deficiencies within the lattice structure thereby drastically increasing the conductivity of these materials. 

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 ... 

A), and bear two chlorine atoms in apical and two acetonitrile ligands in equatorial positions. The octahedral environment of the metal is distorted as a result of niobium-niobium interactions (2.862(2)-2.872(3) A). 

The crystal structures of both (PPN)[M(CO)6] derivatives have been determined.717 The coordination polyhedron is octahedral (Nb—C 2.098(5) A CNbC 89.2(2)°). The PPN moiety is constrained to be centrosymmetric, and thus linear. These compounds correspond to the lowest oxidation state of niobium and tantalum for which structural data are available. A single v(CO) is found in the IR (1854 and 1852 cm-1 for Nb and Ta respectively). Comparable spectra are observed for Na[M(CO)6] in pyridine, but in solvents of lower dielectric constants such as tetrahydrofuran, additional bands attributed to distortion of the anion by the countercation are observed. [Nb(CO)6] appears to be the most labile carbonyl of the group VA analogs. 

The geometry around the hepta-coordinated niobium atom in the Nb(02)F52 anion has been viewed as a distorted monocapped octahedron with one oxygen capping an octahedral face. The EPR spectroscopic results indicate that the unpaired electron in the Nb(02)F5 radical anion resides in the non-bonding orbital of the peroxide group this was further supported by EHMO calculations done on the precursor. 

Tetranuclear monoadducts with asymmetrical M- O 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 Ugands cis to each other, one being trans to the 0x0 bond, which is short (typical Nb=0 Bond Length 1.70 A). The coordination polyhedron is distorted as a result of the niobium-oxygen multiple bond (see Valence Shell Electron Pair Repulsion Model). ... 

The nbo or niobium oxide net is built from perpendicular oriented square planar units, sec Figure 5.11. This is the second most common four-connected net, and as the square planar geometry is mostly restricted to the metal ions Co(I), Rh(I), Ir(I), Ni(II), Pd(Il) and Pt(II) this may seem a bit surprising. However, the connectivity at the node is not necessarily the same as the coordination number of the metal atom (if this is a metal ion centred net), and thus this net is frequently encountered for five-coordinated Cu(II) in distorted square-planar pyramidal geometries, [27-301 or in octahedral complexes with two non-bridging axial ligands as in our example shown in Figure 5.12. 

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