Coordination number eight-coordinated complex

It was assumed that tantalum, when added to the melt in the form of potassium heptafluorotantalate, K2TaF7, interacts with KF or KC1 to form a compound with an increased tantalum coordination number of up to eight. The compound is present in the melt in its dissociated form, yielding potassium ions and octa-coordinated complexes of tantalum, namely TaFg3 or TaF7Cl3. ... 

In the solid state the stereochemistry of copper(I) in its mononuclear complexes, as determined by X-ray crystallography (Figure 4.1), is dominated by four coordination. A significant number of three- and two-coordinate complexes are known, very few five-coordinate complexes exist and six coordination (or above) is unknown. This contrasts with the predominance of six coordination in the chemistry of copper(II) (see Section 53.4.2) and the absence of two or three coordination in the solid state, and with the formation of a significant number of seven- and eight-coordinate geometries.47,48... 

A number of chloride complexes include Pr(terpy)Cl3.8H2O X-ray diffraction established the presence of a [Pr(terpy)C1(H20)5] + ion. Lanthanide nitrates react with 1 mole of terpy in MeCN to give [La(terpy)(N03)3(H20) ] (Ln = La, = 2 Ln = Ce-Ho, n = 1 Ln = Er-Lu, n = 0) with coordination numbers decreasing from 11 (La) to 9 (Er-Lu) if these are crystallized from water [Ln(terpy)(N03)2(H20)4] NO3 (Ln = La-Gd) and [Ln(terpy)(N03)2(H20)3]N03.2H20 (Ln = Tb-Lu) are formed these have both biden-tate and ionic nitrate and nine- and eight-coordinate lanthanides, respectively. Thiocyanate complexes Ln(terpy)2(NCS)3(Ln = Pr, Nd) are also nine coordinate. 

A number of fluoride complexes have been made, both by crystallization for the ammonium salts like (NH4)4CeFg, which has square-antiprismatic coordination of cerium, also found in the (CeF6 )oo chains in (NH4)2CeF6, its thermal decomposition product. (NH4)3CeF7-H20 acquires dodecahedral eight-coordination by dimerization. (NH4)4[CeFg] can... 

Large coordination numbers. For example, the coordination number of 3d transition metals is generally four or six. However, the most common coordination number of lanthanide complexes is eight or nine. This number is close to the sum of the 6s, 6p, and 5d orbitals. Another fact responsible for the large coordination number of lanthanide complexes... 

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