Cu-S clusters

We have also synthesized several other polyoxometalates, which contain cluster cations. For example, [MS4Cu4(y-MePy)g][M60i9] (M= Mo, W)" contains M-Cu-S cluster cation and polyoxometalate anion. The compound [Ag(PPh3)4]2[M060i9] 3CH2Cl2 is a hexamolybdate with two tetrakis(triphenylphosphine)silver cations acting as counter ions." ... 

The results are given in Figures 3.53 and 3.54, respectively. The corresponding graphs for the Cu-S clusters (see Figures 3.4f) and 3.41) are reproduced once more for comparison. 

The carbon monoxide dehydrogenase of the aerobe Oligotropha carboxidovorans contains both Cu and Mo in the form of a cluster in which the Mo is bound to the thiol groups of molybdopterin cytosine nucleotide, and the Cu to cysteine residue in the form of a Cu-S-Mo(=0)OFl cluster (Dobbek et al. 2002). 

Studies on the cubic NLO properties of Mo/W-S/Se-Cu/Ag clusters have been reviewed,539-541 and some related species which contain pseudo-square planar Pd11 centers instead of CuVAg1 have also been investigated.542-545 However, such complexes, e.g., the hexanuclear windmill cluster... 

SC4N2)2(p-dppm)4],488 or hexanuclear as [M6(p-ER)4( i-dppm)4]2+ (M=Cu (48), Ag E=S, Se) (Scheme 16).489,490 Many of these complexes present luminescence properties. There are also three-coordinated Cu(I) derivatives with chelating amine ligands as [Cu(SMes)(phenMe4)]491 or [Cu(S-Mes )(btmgp)] (btmgp=6z, s(tetramethylguanidine).492 A series of cluster... 

The dependence of rate constants for approach to equilibrium for reaction of the mixed oxide-sulfide complex [Mo3((i3-S)((i-0)3(H20)9] 1+ with thiocyanate has been analyzed into formation and aquation contributions. These reactions involve positions trans to p-oxo groups, mechanisms are dissociative (391). Kinetic and thermodynamic studies on reaction of [Mo3MS4(H20)io]4+ (M = Ni, Pd) with CO have yielded rate constants for reaction with CO. These were put into context with substitution by halide and thiocyanate for the nickel-containing cluster (392). A review of the chemistry of [Mo3S4(H20)9]4+ and related clusters contains some information on substitution in mixed metal derivatives [Mo3MS4(H20)re]4+ (M = Cr, Fe, Ni, Cu, Pd) (393). There are a few asides of mechanistic relevance in a review of synthetic Mo-Fe-S clusters and their relevance to nitrogenase (394). 

The P4 molecule also reacts with the copper sulfide cluster anions generally giving products involving addition of P2 and in some cases the addition of a further P2 unit (257). Only Cu6S4 was unreactive toward P4 and even [Cu3S3p reacted, albeit slowly, to produce the P2 adduct. The CID studies of Cu2S2P2 (XIV) yielded P2S, and [Cu2S3P2p XV yielded P2S and PS2, consistent with calculated structures that showed insertion of P2 into the Cu-S bonds as shown in XIV and XV. 

Lack of reactivity in copper sulfide cluster anions has been associated with structural features such as linear S-Cu-S bonding. Reactivity of metal sulfide cluster anions is associated with exposed under-coordinated metal atoms able to bond to coordinating molecules this is the essence of this chapter. 

Cysteine can bind to either one or two metal ions, and is frequently found as a ligand to iron (in Fe-S clusters—see later) and to Cu+ (for example in the copper chaperones, which transfer copper to specific copper-binding proteins). Histidine can bind metal ions in two... 

Resonance Raman studies of Fe- and Cu-contalnlng proteins have led to the Identification of tyrosine, histidine, cysteine, and hydroxide ligands as well as Fe-0 and Fe-S clusters. For the Fe-0 clusters, the frequency and oxygen Isotope dependence of the Fe-O-Fe symmetric stretch relates to Fe-O-Fe bond angle, while the peak Intensity relates to the disposition of the other ligands In the cluster. 

The properties of the [CujI S - cluster are quite remarkable. This intense blue diamagnetic cluster (Amax 654 nm, e 46,100) can be described formally as a mixed-valence Cu(I), Cu(III) cluster (164). The crystal structure of this molecule (Fig. 59) supports this formalism and reveals a Cu5 rectangular pyramidal core (166). The basal copper atoms are three-coordinate and nearly planar and can be considered as Cu(I) units. The axial copper is four-coordinate and strictly planar, a coordination geometry appropriate for ad8 Cu(III) center. 

The 2D network contains cubane-like Cu4I4 clusters located at the nodes of the square grid and coordinated to four L44 ligands by Cu S bonds forming... 

Fig. 6.23. Energy-level diagrams calculated for the tetrahedral CuS/ and FeSj " clusters using the MS-SCF-Za method. Occupied orbitals are shown as solid lines, and unoccupied orbitals as broken lines. Energies are in eV relative to the average energy of the 11, orbital. The MS distances employed were, respectively, Cu-S = 2.302 A and Fe-S = 2.258 A (after Tossell et ah, 1982).

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