Dinuclear complexes, cyanide-bridged

The largest family of compounds based on a dinuclear cyanide-bridged core is represented by complexes composed of Ln(III) ions and anions... 

The majority of cyanide-bridged dinuclear complexes described for the combination of metal ions belong to the biologically relevant class of Cu —Fe dimers. These compounds serve as models for the binuclear cyanide-inhibited site of cytochrome c oxidase, an enzyme that contains the heme-copper active site responsible for the O2 reduction chemistry (59). The lethal toxicity of cyanide was traced to its irreversible binding and inhibition of this active site in the enzyme (60). The biologically relevant aspects of these complexes were the subject of many reports (61,62). Our interest is in describing their crystal structure, which will be correlated to the magnetic properties in a later section. 

The second class of dinuclear Cu —Cu complexes is represented by several cascade complexes, in which a pair of cations is encapsulated within a cryptand host (XVII-XIX), with a bridging CN ligand spanning the space between the cations. In these cases, the dinuclear complex is stabilized due to the encapsulated cations rather than by the cyanide bridge. Lu et al., (78) reported a product of this type, [Cu°2(XVII)(CN)](C104)3 (Fig. 9), as a result of the unexpected C C bond cleavage of acetonitrile in the presence of [Cu 2(XVII)]( 104)4. These authors established that the reaction rate exhibits a first-order dependence... 

On incorporating [Cr(CN)6] or [Co(CN)6] with Ln(III) salts (Ln = Nd, Gd, Yb) in aqueous DMF, a series of cyanide-bridged discrete Cr(Co)—Ln dinuclear species or coordination polymers were isolated by Ward and coworkers [161]. In these Cr(Co)—Ln complexes, the d-block luminescence was completely quenched due to fast (> 10 s ) energy transfer to... 

Reaction of Fe(CO)s with dialkyl sulfides in the presence of trimethylamine-A -oxide leads to simple, mono-substituted Fe(CO)4(SR2) complexes (Scheme 71), whereas this reaction performed with cyclic thioethers gave dinuclear complexes. Dinuclear complexes related to 51 with a variety of groups bridging between the two sulfur atoms have been derivatized with cyanide and organic isocyanides. 

If [Rh(diphos)2]Cl is allowed to react with an anion exchange resin in the cyanide form, the corresponding cyanide complex (rc N 2089 cm-1) is formed. Upon dissolution of the product in benzene a diphos ligand is lost and [Rh2(CN)2(diphos)3] is formed.119 The dinuclear product probably contains a bridging diphos ligand (c/. [Cu2(N3)2(diphos)3]251). These reactions and the anion exchange reactions of [Rh(diphos)2]Cl are shown in Scheme 10a. 

This is a remarkable reaction because the transition metal chemistry of N2O is sparse, especially with copper. Most N2O reductases are soluble, periplasmic homodimers however, there are examples of membrane-associated enzymes. " The best characterized N2O reductases are from Paracoccus denitrificans, Pseudomonas nautica, and Pseudomonas stutzeri, and most of the information presented here is derived from experiments on these enzymes. Where comparable data are available, N2O reductases from various organisms appear to be fairly similar, with the exception of the enzyme from Wolinella succinogenes, as noted above. The crystal stractmes of N2O reductase from P. nautica and more recently from P. denitrificans show two distinct copper clusters per subunit a bis-thiolate bridged dinuclear electron-transfer site (Cua), which is analogous to the Cua site in cytochrome c oxidase see Cyanide Complexes of the Transition Metals), and a novel four-copper cluster ligated by seven histidines, the catalytic copper site (Cuz), where N2O is thought to bind and be reduced. Cuz was proposed to be a copper-histidine cluster on the basis of the presence of nine strictly conserved histidine residues, and this was supported by a H NMR study that identified two non-CuA associated resonances that were assigned as copper-histidine N-H protons. ... 

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