Multinuclear clusters

The formation of multinuclear clusters is much more favorable for rhodium than for cobalt. Additional evidence was obtained in comparative hydroformylation rate studies of 1-heptene and of cyclohexene at 75°C and 150 atm 1/1 H2/CO (19). For the acyclic olefin the kinetics followed the kinetic expression (except at low olefin) ... 

Monomeric arrangements are rare for alkoxide complexes of bismuth and require excess anionic ligands or bulky substituents. Otherwise the alkoxide ligands typically impose dimerization or multinuclear clustering, which are expressed in a variety of currently unusual structural arrangements (Table I). 

In the multinuclear clusters of transition metal with high degree of electron delocalization, an addition or subtraction of one or two electrons does not cause a significant rearrangement of the nuclear frame. Thus, this molecule can serve as an effective electron donor and acceptor. 

Molybdenum is found in the active site of nitrogenase as part of a multinuclear cluster with iron (the so-called M-cluster), but in all other enzymes it comprises a mononuclear center (Hille, 1996 Kisker et al., 1997a). The distinguishing characteristic of this latter group of enzymes is that, while other redox-active centers are often present, the molybdenum center itself possesses only a single equivalent of the transition metal. This large and diverse group of enzymes is the subject of the present account. 

Mn Optical/EPR/XAS Multinuclear cluster(s) Water oxidation 4 Interface 33 and D-1 or D-2... 

While the Mn stoichiometry is well-determined, the organization and valence states of these ions remain uncertain. From both spectroscopic and mechanistic considerations, one expects that the metal ions function as multinuclear cluster(s) and evidence in the literature may be used to argue for either two binuclear manganese centers or for a single tetranuclear cluster. At least four different experimental approaches are relevant to this question as well as to the related valence issue. These include X-ray, UV-Vis, and magnetic resonance spectroscopies and extraction/quantitation techniques. 

Definition of the lower size limit for nanoparticles is fairly subjective because it is difficult to distinguish the smallest nanoparticles from multinuclear clusters and dissolved chemical species. However, the changes in physical and chemical properties of a cluster as it converts to a nanoparticle makes the smaller end of the nanoparticle size range very interesting ... 

P-10 Complexes 106, 107 and others in the same family consist of multinuclear clusters, where the W atom occupies the center of an incomplete icosahedron and the Au atoms are at certain vertices of the icosahedron. Distances between proximate Au atoms vary in the approximate range from 0.276 to 0.305 nm and Au—W distances from 0.275 to 0.284 nm202. 

Multinuclear Cluster Compounds Containing o-Borane Ligands. 138... 

Each major class of oxygenase and monooxygenase enzyme has a vast literature. A general pattern, however, is that most such enzymes have either Fe or Cu as active site metals, often in multinuclear cluster centers. For iron, the Fe(lI)/(III) couple is often accessed with Fe(IV) present in certain cases. For copper, the typical states are Cu(I)/(II) with Cu(lII) also present in some cases. Since O2 is a 4e oxidant, while the low-valent metals are 1 or 2e reductants, a cluster site can help attain compatibility of oxidant and reductant by allowing the site to take up more than one electron. 

K. Find organometallic multinuclear cluster compounds with similar organic species attached and discuss their bonding behavior (bond distances, binding sites, and bond angles) [61]. 

The computed orientation of the shift tensors (not available from experiment) was discussed in terms of low-lying (tt -type orbitals." Recent SOS-DFPT results for the P shift tensor in a ruthenium phosphinidene cluster, a rare example for which the orientation has been known experimentally from single-crystal solid-state NMR studies, indicate that the computed orientation of the tensor should be very accurate (the agreement was better than As the orientation of the shift tensor provides a relatively direct link between NMR data and the electronic structure of the system, studies of this type should be useful to obtain a more general theoretical picture of chemical shifts in multinuclear clusters. 

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