Molecular orbital calculations clusters

The reaction between a trinuclear metal carbonyl cluster and trimetbyl amine borane has been investigated (41) and here the cluster anion functions as a Lewis base toward the boron atom, forming a B—O covalent bond (see Carbonyls). Molecular orbital calculations, supported by stmctural characterization, show that coordination of the amine borane causes small changes in the trinuclear framework. 

The recent interest in the exploration of electrocatalytic phenomena from first principles can be traced to the early cluster calculations of Anderson [1990] and Anderson and Debnath [1983]. These studies considered the interaction of adsorbates with model metal clusters and related the potential to the electronegativity determined as the average of the ionization potential and electron affinity—quantities that are easily obtained from molecular orbital calculations. In some iterations of this model, changes in reaction chemistry induced by the electrochemical environment... 

M. Saeki, S. i. Ishiuchi, M. Sakai, and M. Fujii, Structure of 1 naphthol/alcohol clusters studied by IR dip spectroscopy and ab initio molecular orbital calculations. J. Phys. Chem. A 105, 10045 10053 (2001). 

In bridged metal-metal bonded dimeric complexes, the relative importance of metal-metal and bridging ligand effects are more difficult to unravel. Dahl and his co-workers have elegantly exploited systematic crystallographic analyses to detail the stereochemical consequences of valence-electron addition or removal in dimeric metal complexes (46, 47, 65, 230) and clusters (66, 88, 204, 205, 213, 216, 222). Their experimental work has been neatly underpinned by nonparameterized approximate Hartree-Fock molecular orbital calculations (217) on the phosphido-bridged dimers [Cr2(CO)80ti-PR2)2]n"2 and [Mn2(CO)g(/i.-PR2)2]n (rt = 0, + 1, or +2) ... 

The bonding capabilities of transition metal clusters (no nonmetals in the framework), based on molecular orbital calculations, has been nicely summarized by Lauher14 (Table 16.3). Within this table we see three structures (tetrahedron, butterfly, and square plane) for tetranuclear metal clusters. The tetrahedron is a 60-electron cluster, while the butterfly and square plane clusters have 62 and 64 electrons. respectively. When we go from a tetrahedron to a butterfly, one of the edges of the tetrahedron is lengthened corresponding to bond breaking. 

Spectroscopic measurements and molecular orbital calculations have also been carried out315 on Cu clusters, n = 2-6, and mass spectral measurements on the vapour of CuCl316 suggest that the [Cui4Cli3]+ cation has an enhanced stability calculations317 are consistent with an extended cluster model. 

The electronic structures of Fe3 and Fe3 -Fe2 bearing clays and oxides are described with reference to SCF-Xa-SW molecular orbital calculations on Fe06> Fe04 and Fe2O10 clusters. The results are used to interpret the optical spectra of iron bearing clays and iron oxides and provide some insight onto the possible mechanisms of photochemical redox reactions associated with those minerals. 

A basic understanding of the electronic structures of iron bearing clays and oxides is needed before one can understand the mechanisms of electron transfer and photochemical reactions associated with these minerals. This chapter will discuss the electronic structures of iron bearing clays and oxides (primarily from cluster molecular orbital calculations) and compare theoretical results with experiment. The discussion will be... 

The theoretical results described here give only a zeroth-order description of the electronic structures of iron bearing clay minerals. These results correlate well, however, with the experimentally determined optical spectra and photochemical reactivities of these minerals. Still, we would like to go beyond the simple approach presented here and perform molecular orbital calculations (using the Xo-Scattered wave or Discrete Variational method) which address the electronic structures of much larger clusters. Clusters which accomodate several unit cells of the crystal would be of great interest since the results would be a very close approximation to the full band structure of the crystal. The results of such calculations may allow us to address several major problems ... 

The nature of the bonding in heteronuclear gold cluster compounds has been investigated primarily by means of semiempirical molecular orbital calculations and the results of these studies have allowed a number of structural generalizations to be made. These theoretical developments have been discussed in detail in a series of papers by Mingos et al. (210, 256, 279-282) and only a brief description of the results of this work will be given in this section. 

MO diagram for the tetrahedral [FeOJ cluster The molecular orbitals calculated for Fe3+ in the tetrahedral cluster [FeOJ-5 indicate that the antibonding e and t2 molecular orbitals, corresponding to the iron 3 d orbitals in a tetrahedral crystal field, are mostly localized on the iron atom (Sherman, 1985a). Furthermore, although allowed by symmetry, there appears to be little Fe 4p character in these orbitals, casting some doubt on the intensification mechanism of absorption bands in crystal field spectra of tetra-hedrally coordinated cations ( 3.7.1). 

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