Square-pyramidal coordination, vanadium

Khalif et al.141 conclude from measurements of the heat of adsorption of 02 and e.s.r. measurements that there is unactivated adsorption on vanadium ions with a low co-ordination number of 3 or 4, whereas activated adsorption is observed at higher temperatures on ions with square pyramidal coordination. 02 adsorption occurs only as O2- in (V=0) or (V—O—V) groups and not as radicals which, according to these authors, is different from the behaviour of catalysts obtained by impregnation. 

Spectra of octahedral vanadium(V) oxide compounds are presented in Figure 2. Undistorted vanadium(V) oxide compounds do not exist, and all vanadia octahedra are highly distorted, which give rise to short V-0 bonds. This is reflected in the Raman band position for the distorted octahedral vanadium oxide compounds which always occur in the 900-1000 cm region. The vanadia structure in 2 5 approaches a square-pyramidal coordination and the individual vanadia are linked... 

All of the above compounds are oxides. The application of the fluorine route already described for AlPOs and GaPOs has shown that it is also possible to obtain open framework structures with fluoride in the VPOs. This led to the discovery by Riou and Ferey [72] of the first open-framework fluorovanado(V)phosphate, ULM-7 or (H3N(CH2-CH2)NH3)[(V 02)2(P04)F], in which the building units are V2P trimers. Vanadium exhibits both octahedral and square pyramidal coordination, and fluoride ion is shared between them. The three-dimensional network generated by comer-sharing of these trimers, exhibits 10-membered rings occupied by diprotonated amines. 

A pentadentate 03N2-donor ligand was found to bind two vanadyl ions. One amino and one alkoxy donor from each ligand bind to each vanadium while a third alkoxy donor bridges the two vanadium atoms the square-pyramidal coordination spheres are completed by a bridging pyr-azolate molecule.668... 

The complexes typically have square pyramidal (11) or bipyramidal structure (12) with vanadyl oxygen apical, the vanadium atom lying 0.035-0.055 A above the plane defined by the equatorial ligands.354 There have been reports of five-coordinate trigonal bipyramidal complexes (13) with structures determined by X-ray diffraction techniques. 

VO(Et2NCS2)2] has discrete molecules with five-coordinate square pyramids, with thf oxygen at the apex with d(V=0) = 1.59 A.667 The vanadium atom lies approximately 0.75 above the plane of the four sulfur atoms and the average V—S distance is 2.402 A, shorte than for most vanadium dithiolate complexes 667 IR, electronic and ESR spectra are consisten... 

The V02+ phthalocyanine [VO(pc)] has been the subject of patents as it is useful in photoelectrophoretic and xerographic imaging.887 It can exist in at least three solid phases888 and the structure of so-called phase II was determined.889 It is composed of sheets of parallel and overlapping [VO(pc)] molecules and no discrete dimer pair exists. The vanadium is five-coordinate and square pyramidal, and is 0.575 A above the plane of the four nitrogens. The V—N distances do not differ significantly with a mean of 2.026 A the V=0 distance is 1 1.580 A. 

Figure 39 The molecular structure of (a) [VO(H2daaen)], (b) [VO(H2daanpn)], (c) [CuVO(daaen)]-H20 (179) and (d) [(VO)2(daaen)]. In all four molecules, the vanadium atom is coordinated in a square pyramidal geometry and is displaced above the 0202 plane by ca. 0.56 A (for (d), no data are given)897...

Kriihnkite-type chain. In [HN(CH2)6NH][(VO)2(OH)2-(S04)2],H20, III, there are five-coordinated vanadium sites [V(l) and V(2)] with the square-pyramidal geometry with the... 

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