Density Studies of Transition Metal Compounds

Charge Density Studies of Transition Metal Compounds 

The electron density in transition metal complexes is of unusual interest. The chemistry of transition metal compounds is of relevance for catalysis, for solid-state properties, and for a large number of key biological processes. The importance of transition-metal-based materials needs no further mention after the discovery of the high-Tc superconducting cuprates, the properties of which depend critically on the electronic structure in the CuOz planes. 

In inorganic and organometallic solids, the average electron concentration tends to be high. This means that absorption and extinction effects can be severe, and that the use of hard radiation and very small crystals is frequently essential. Needless to say that the advent of synchrotron radiation has been most helpful in this respect. The weaker contribution of valence electrons compared with the scattering of first-row-atom-only solids implies that great care must be taken during data collection in order to obtain reliable information on the valence electron distribution. 

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Charge Density Studies of Transition Metal Compounds 217... 

Charge Density Studies of Transition Metal Compounds 221 where Qr is the expectation value of r-3 defined as... 

With the advent of appropriate DFT-based methods, NMR properties of transition-metal compounds have now become amenable to theoretical computations (8). Suitable density functionals have been identified (9) which permit calculations of transition-metal chemical shifts with reasonable accuracy, typically within a few percent of the respective shift ranges. Thus, it is now possible to investigate possible NMR/reactivity correlations for transition-metal complexes from first principles several such studies have already been undertaken (10,11,12). 

Crystallographic studies of transition metal hydride complexes Stereochemistry of six-coordination Five-coordinate structures Stereochemistry of five-coordinate Co complexes Absolute stereochemistry of chelate complexes Stereochemistry of optically-active transition metal complexes Electron density distributions in inorganic compounds... 

The two main methods currently used in computational and combined computational/experimental studies in the general area of transition metal coordination compounds, and specifically also with macrocyclic ligands, are DFT and MM. While DFT yields structural data, energies and molecular vibrations, as well as electronic information (the ground state wave function, spin density, charge distribution etc ), the latter is missing in MM. 

The general conclusion from studies of calculated HOMO-LUMO gaps in a wide variety of compounds including organic pi systems and small molecules of first row atoms, and now also transition metal compounds, is that using the local density approximation and different GGAs calculated band gaps that are... 

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