Complexes hexacoordinated

Chromium(III) forms stable salts with all the common anions and it complexes with virtually any species capable of donating an electron-pair. These complexes may be anionic, cationic, or neutral and, with hardly any exceptions, are hexacoordinate and octahedral, e.g. ... 

The disappearance of the first band at 600 cm 1 in IR spectra of melts K2TaF7 - KBr takes place at a lower KBr concentration compared to both KF and KC1 containing systems (see Fig. 78, b). If KBr concentration equals or exceeds 0.5 mol fraction, a single band, which is attributed to hexacoordinated complex ions is observed. In the case of the K2TaF7 - KI molten system (Fig. 78, c) this phenomenon is observed at KI concentration as low as 0.4 mol fraction. 

The third factor that strongly affects the equilibrium between hexa- and heptacoordinated complexes (85) is the nature of the second, outer-sphere cations. Increasing the ionic radii of the cations causes the equilibrium in Equation (85) to shift to the left, forming mostly hexacoordinated complexes MeF6 The mechanism of interionic equilibrium in fluoride melts can be presented schematically as follows ... 

Higher temperatures, increased K2TaF7 concentrations and other factors mentioned above shift the equilibrium in Equation (174) to the left and lead to the formation of coarser tantalum particles. Form this point of view, it can be concluded that smaller hexacoordinated complexes, TaF6 lead to the formation of coarser tantalum powder, whereas the predominant presence of larger heptacoordinated complexes ions initiates the formation of finer particles. 

Photochemistry of hexacoordinate complexes of the heavier transition metals. P. C. Ford, J. D. Petersen andR. E. Hintze, Coord. Chem. Rev., 1974,14, 67-105 (109). 

While ytterbium(II) benzamidinate complexes have been known for many years/ the synthesis of the first divalent samarium bis(amidinate) required the use of a sterically hindered amidinate ligand, [HC(NDipp)2l (Dipp = C6H3Pr2-2,6)/ As illustrated in Scheme 54, the dark green compound Sm(DippForm)2(THF)2 (DippForm = [HC(NDipp)2] ) can be prepared by three different synthetic routes. Structural data indicated that hexacoordinated... 

Let us examine the properties of molecules where a central atom M is surrounded by five ligands A, B, C, D, E. We assume that the ligands are at the vertices of a trigonal bipyramid. This assumption is adequate for most pentacoordinate complexes but we ougth to mention that the description of stereoisomerization we propose could be applied if another polytopal form—the tetragonal pyramid, for example—was the stable one. The same type of description has already been undertaken for hexacoordinate octaedral complexes . ... 

Fig. 7.63 Mossbauer spectra of some hexacoordinated ammine and pyridine complexes of trivalent iridium taken at 4.2 K with a source of Os in Os metal. The stick spectra indicate the positions and relative intensities of the individual resonance lines (from [285])...

With P-donors a variety of different structures are formed. Two complexes (359a,b) with a five-coordinate square pyramidal geometry and one S-donor in the apical position are reported.934,933 In a related complex (360) the nickel center reveals a distorted square planar geometry, because one xanthate ligand switched to a monodentate coordination mode. 6 By reaction of [NiL2] complexes with Ph2P(CH2)2P(Ph)(CH2)2PPh2, compound (362) is formed, which consists of a five-coordinate cation and a hexacoordinate anion. 7... 

Triply bridging carbonates between three zinc centers have been identified in nine different X-ray structures deposited in the CSD 458,461,465-467 For example, a binuclear ft-OH zinc complex with a tetradentate /V-donor ligand absorbs atmospheric carbon dioxide to a triply bridged carbonate.468 Examples are also known where the metal atoms are in varying coordination environments. The complex cation [Zn3(bipyridine)6(/U3-C03)(H20)2]4+ contains one penta- and two hexacoordinate zinc centers.469 A tetrapodal compartmental ligand forms a tetrameric complex with zinc that contains the carbonate bridging between three of the four zinc centers.470... 

A hexadentate N202S2 ligand (116) has been synthesized as a dithiaalkyl-substituted triazene-1-oxide and forms an unusual hexacoordinated zinc complex with thioether donors. Both the phenyl and the methyl derivatives form structurally characterized octahedral complexes.896... 

Stable hypervalent silicon complexes with chelating diphosphinomethanide ligands similar to II, but with hexacoordinated silicon centers are obtained from 2 and SiCl4 (Eq.(4)). 

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