Eight-coordinate compounds stereochemistry

Edge-coalesced icosahedra eleven-coordinate compounds, 99 repulsion energy coefficients, 33, 34 Effective atomic number concept, 16 Effective bond length ratios non-bonding electron pairs, 37 Effective aqueous solution, 479-490 multimetallic systems, 485 non-aqueous solutions, 493 Electrodes... 

The most common coordination number of titanium is six, although four-, five-, seven-, and eight-coordinate compounds are known (Table 2). Table 3 summarizes the common oxidation states of titanium with the associated coordination numbers and stereochemistries. Zirconium shows a similar range of oxidation states (see Zirconium Hafnium Inorganic Coordination Chemistry), however, Zr and Flfr are much less stable, relative to Zr and Hf, than is the case for titanium. 

The most common coordination number of titanium is six (recognized for all oxidation states of the metal), although compounds are known in which the coordination number is four, five, seven or eight. The common oxidation states of titanium with the associated coordination numbers and stereochemistries are summarized in Table 3. The properties of these molecules will be discussed in the appropriate sections. In brief, however, titanium compounds in the +III or lower oxidation states are readily oxidized to the +IV state. Furthermore, titanium compounds can usually be hydrolyzed to compounds containing Ti—O linkages. 

Most of the nickel compounds in the solid state and almost all in aqueous solution contain the metal in the oxidation state +2, which, by consequence, can be considered the ordinary oxidation state for nickel in its compounds. The electronic structure and stereochemistry of nickel(II) were reviewed in 1968.6 The most stable electronic configuration of the free Ni ion is [Ar]3d8 which is also the ground state configuration in its complexes. The overwhelming majority of nickel(II) complexes have coordination numbers of four, five and six. Complexes with coordination numbers of three, seven and eight are still quite rare. 

Another aspect of Nyholm s extensive study of metal comi exes of the diarsine (1) was the occurrence of unusually high coordination numbers, e,g., six for Pd(Il) and R(II) and eight for Ti(IV) and V(1V). Nyholm s interest in these high coordination numbers extended to the stereochemistry involved, and his research group established the stereochemistry of some of these complexes by X-ray crystallography. The compounds [Ml2(As-As)2 ] (M = Pd, Pt) were shown to be distorted octahedral with the four arsenic atoms in the plane of the square and the two iodine atoms in the apical positions with unusually long bonds(45), while the complex [TiCl4(As-As)2l was shown to be dodecahedral 46). 

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