Octahedral Coordination Spheres

MOMEC is a force field for describing transition metal coordination compounds. It was originally parameterized to use four valence terms, but not an electrostatic term. The metal-ligand interactions consist of a bond-stretch term only. The coordination sphere is maintained by nonbond interactions between ligands. MOMEC generally works reasonably well for octahedrally coordinated compounds. 

Crystal structure of solids. The a-crystal form of TiCla is an excellent catalyst and has been investigated extensively. In this particular crystal form of TiCla, the titanium ions are located in an octahedral environment of chloride ions. It is believed that the stereoactive titanium ions in this crystal are located at the edges of the crystal, where chloride ion vacancies in the coordination sphere allow coordination with the monomer molecules. 

This compound has an octahedral coordination sphere slightly distorted towards a trigonal prism. Oxidation by air leads to Ru2(S2CNEt2)5 which exists in two isomeric forms (Figure 1.52) [138]. 

The ligand field of a quasi-octahedral coordination sphere acting on the (i-orbitals lifts the degeneracy of the excited spin quartet (and others) as sketched in tier (3). The nature of the resulting states and their energy depends on the strength... 

By definition, the coordination number includes the adjacent atoms, and lone electron pairs are not counted. On the other hand, now we are considering lone pairs as occupying polyhedron vertices. To take account of this, we regard the coordination sphere as including the lone pairs, but we designate them with a //, for example -octahedral = octahedron with two lone electron pairs and four ligands. 

Due to the steric constraints of the ligand, the partially protonated H2cdta binds as a pentadentate ligand in psri(H2cdta)(H20)] where a water molecules completes the octahedral coordination sphere.1191, 192... 

V,/V-bis(2-hydroxy-di-3,5-/-butylphenyl)amine forms complexes of zinc which have ligand-based redox processes with four oxidation levels of the coordinated anion.864 2 1 and 1 1 complexes are formed in the presence of zinc with the 2 1 complex coordinated in an octahedral geometry and the 1 1 complex square planar with a triethylamine ligand completing the coordination sphere. The complexes, at the different redox levels, have been investigated by EPR, spectro-electrochemistry, l I NMR, and magnetochemistry, as appropriate. 

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