Copper complexes coordination numbers, examples

The types of compounds formed by gold(I) and gold(III) often differ from those of other metals due to the constraints imposed by coordination number and electron count at the metal. Thus, for example, whereas 7r-bonded cyclopentadienyl complexes of palladium and platinum are numerous (336), and a copper(I) species of this type is known (337), cyclopentadienyl complexes of univalent (94, 96, 97) and trivalent (228) gold have invariably been found to be fluxional behavior, similar to that in dicyclopentadienylmercury, was involved (228). 

In these compounds, an alternative structure to the cubane cluster is found, for example in [Ph3PAgI]4.106 This is the chair or step type of arrangement, illustrated in Figure 2, in which two of the four halogen atoms retain a coordination number of three. This arrangement has also been found in some copper(I) halide complexes with bis(diphenylphosphino)methane.1O7 10S The pyramidal coordination of the halogen atom is similar to that in the cubane structure, although often more distorted. 

The coordination number of divalent copper in its complexes is almost always four. The aquo- and halo- complexes have been mentioned, and the reader should recall the blue-purple Cu(NH3)l+ complex which may have been introduced to him as his first example of a complex ion. The Cu(OH)4 complex is only moderately stable, and divalent copper is thus very slightly amphoteric. The four bonds attached to copper in these complexes generally point to the corners of a square. 

Copper complexes are known in oxidation states ranging from 0 to +4, although the +2 (cupric) and the +1 (cuprous) oxidation states are by far the most common, with the divalent state predominating. Only a relatively small number of Cu complexes have been characterized and the Cu° and oxidation states are extremely rare. A few mixed valence (see Mixed Valence Compounds) polynuclear species have also been isolated examples include a CuVCu species and a Cu /Cu catenane. The coordination numbers and geometries (see Coordination Numbers Geometries) of copper complexes vary with oxidation state. Thus, the majority of the characterized Cu complexes are square planar and diamagnetic, as is common for late transition metals with d electronic configurations. 

There are many examples of borohydride compounds of these metals, e.g., Cu, Ag, Zn and Cd-BH as neutral and anionic complexes in which the mode of bonding of BH is dependent on the coordination number of the metaP. Higher borane anions also combine with Cu and Ag, yielding both neutral and anionic complexes. Although no borohydrides of Au are isolated, treatment of Au-halide complexes with, e.g., NaBH, is a standard method for the preparation of Au-cluster compounds Copper(I) hydride, first reported in 1844, has the ZnS structure [d(Cn-H) = 0.173 nm (1.73 A) d(Cu-Cu) = 0.289 nm (2.89 A)] and decomposes to the elements when heated. At >100°C the decomposition is explosive. 

The other examples of electrochemically driven ring motions in [2]catenanes are from the class of metal complexed catenanes (i.e., catenates) that have been synthesized and studied in our groups. These compounds, the synthesis of which relies on the ability of copper( I) to gather the bidentate phenanthroline ligand around its tetrahedral coordination sphere, are produced in remarkable yield [9, 28, 57f]. The principle of operation is essentially based on the different stereoelectronic requirements of copper(I) and copper(II). Whereas a coordination number of 4, with a tetrahedral or distorted tetrahedral arrangement is preferred by copper(I),... 

The number of covalent bonds that a cation tends to form with electron donors is its coordination number. Typical values for coordination numbers are 2,4, and 6. The species formed as a result of coordination can be electrically positive, neutral, or negative. For example, copper(II), which has a coordination number of 4, forms a cationic ammine complex, Cu(NH3)4 a neutral complex with glycine, Cu(NH2CH2COO)2 and an anionic complex with chloride ion, CuClj. ... 

In a number of cases, the initial bond-length distribution was clearly not uni-modal, e.g. Figure A.2a. Where possible, such distributions were resolved into their unimodal components (as in Figure A.2c) on chemical or structural criteria. The case illustrated in Figure A.2, for Cu-Cl bonds, is one of the most spectacular examples, owing to the dramatic consequences of changes in oxidation state and coordination number and of Jahn-Teller effects on the structures of copper complexes. 

While discrete two- and three-coordinate Cu(I) compounds have been reported, the favored coordination number of the metal is four. Quite frequently, two or more copper atoms will share ligands, resulting in the formation of polynuclear clusters. Complexes of stoichiometry CU4X4L4 (X = Cl, Br, I L = PR3, ASR3) for example, exist as tetrameric units whose structure depends upon the steric demands of X and R. In... 

Notice that a transition metal complex ion is written in square brackets and the overall charge on the ion is written outside the brackets. In this example, the copper ion carries two positive charges and the water molecules are neutral, so the overall charge on the ion is 2-I-. The number of atoms directly attached to the central metal atom (in this example, six) is called the coordination number. 

A coordination number of 1 is rare for stable complexes. The examples that are known involve a very bulky ligand such as the aryl radical, 2,4,6—Ph3C6H2, which forms ML complexes with copper and silver (2-97). The M-L unit can also be considered as a fragment in a complex with a higher coordination number, such as W-CO in the complex [( l -acetylene)3W(CO)] (2-98). 

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