Copper complexes five-coordinate

The electronic spectra and magnetic susceptibility of [Ni(21)Cl2] were found to be consistent with a five-coordinate high spin complex. This complex has greater antitumor activity against P388 lymphocytic leukemia test system in mice than cobalt(II), copper(II), zinc(II) and platinum(II) complexes of 21 [187],... 

Krebs and co-workers synthesized a series of dinuclear copper(II) complexes as models for catechol oxidase 91 (365) (distorted SP Cu-Cu 2.902 A), (366) (distorted five-coordinate geometry Cu-Cu 3.002A), (367) (distorted SP Cu-Cu 2.995 A), (368) (distorted five-coordinate geometry Cu-Cu 2.938 A), and (369) (distorted SP Cu-Cu 2.874 A). These complexes were characterized by spectroscopic and electrochemical methods. From kinetic analysis, a catalytic order for catecholase activity (aerial oxidation of 3,5 -di - ter t-buty lcatec h o 1) was obtained.326... 

Copper(l) analogues [(L)Cu(MeCN)][CF3S03] (747) [yellow, four-coordinate (two amine donors, one of the two pyridinyl groups and an MeCN] and [(L)Cu(MeCN)][BF4] (748) [red, five-coordinate (two tertiary amine, two pyridinyl and an MeCN] [L as that in copper(II) complex (241)] were structurally characterized and redox properties of these complexes were also investigated.224... 

A typical spectral feature of coordinated phenoxyls is their intense absorption in the visible at -410 nm (e > 2.0 x 103 M-1 cm-1) and at 600-900 nm. All five-coordinate (phenoxyl)copper(II) complexes have been reported to be EPR silent at cryogenic temperatures. This finding has frequently been taken as an indication for... 

Recently, a somewhat different synthetic approach has been reported. Halcrow et al. (215) synthesized a series of five-coordinate copper(II) complexes comprising a tridentate tris(pyrazolyl)borate ligand and a bidentate phenol derivative. Neutral complexes [Cun(TpPh)(bidentate phenolate)] were synthesized and structurally characterized [Tpph] = hydrido-tris(3-phenylpyrazol-l-yl)borate. The species [Cun(TpPh)(2-hydroxy-5-methyl-3-methylsulfanylbenzaldehydato)] can electro-chemically be converted to the (phenoxyl)copper(II) monocation, which has been characterized in solution by UV-vis spectroscopy. It displays two intense absorption maxima at 907 nm (e = 1.2 x 103 M 1 cm-1), and 1037 (1.1 x 103 M l cm-1), resembling in this respect the radical cofactor in GO (Fig. 7). 

The mechanism of exchange coupling between a Cu(II) ion and a coordinated phenoxyl has been discussed in some detail (204). Complexes [Cun(L BuMet)Cl] (five coordinate) and [Cun(L BuMet)(Ph2acac)] (six coordinate) can both be electrochemically oxidized to the corresponding (phenoxyl)copper(II)... 

In relation with the ongoing discussion, if Cu in aqueous solution has five or six water molecules in its first coordination shell (9,116,117), it is interesting to compare water exchange rates measured on five-coordinate copper complexes. Rates of water exchange on five-coordinate complexes of copper(II) are drastically reduced from the rate of exchange on aqua ions of copper(II) (Table VII) (113). The mechanism of water exchange is of associative character in all examples studied to date with the exception of [Cu(tpy)(H20)2]. For that complex the water exchange is very rapid compared to the other complexes and the mechanism is a Id. 

Large numbers of five-coordinate copper(II) complexes in several stereochemistries are known. The spectra which have been most studied with a view to interpretation are those of the trigonal bipyramidal complexes, for which assignments have been proposed on the basis of molecular orbital, angular overlap, and crystal-field models. 

The p3-bridged carbonato complex posseses a pseudo-3-fold molecular symmetry. Each of the Cu atoms is five coordinate with the four nitrogen atoms of tren and one oxygen atom of the carbonate ligand (C). The coordination polyhedron of the Cu atom can be described as almost (TBP), the copper ions being slightly out of the plane (0.15 A) of the three primary amine groups (Fig. 5). 

The carbonate group retains planarity and the three copper ions deviate from this plane by 0.05 A. The Cu-0 bond lengths in the complex are typical of five coordinate metal complexes... 

Figure 14.4 The three forms of the copper-complexed catenane, each species being either a monovalent or a divalent complex, (a) Four-coordinate complex, (b) five-coordinate complex, and (c) six-coordinate complex.

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... 

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