Ligand field calculations

So, ligand-field theory is the name given to crystal-field theory that is freely parameterized. The centrally important point is that ligand-field calculations, whether numerical or merely qualitative, explicitly or implicitly employ a ligand-field Hamiltonian, very much like the crystal-field Hamiltonian, operating upon a basis set of pure d orbitals. Instead of the crystal-field Hamiltonian (Eq. 6.15),... 

For a given dx configuration the ligand field calculation reduces to the construction of the perturbation matrices of elements H m = ( jj H 11pm) where... 

Many ligand field calculations have been performed on five-coordinate nickel(II) complexes to assign the electronic transitions,518,573"577 but no systematic application of these calculations has been reported. The suggested assignment of the electronic transitions is shown in Tables 31-33. 

The basis of molecular modeling is that all important molecular properties, i. e., stabilities, reactivities and electronic properties, are related to the molecular structure (Fig. 1.1). Therefore, if it is possible to develop algorithms that are able to calculate a structure with a given stoichiometry and connectivity, it must be possible to compute the molecular properties based on the calculated structure, and vice versa. There are many different approaches and related computer programs, including ab-initio calculations, various semi-empirical molecular orbital (MO) methods, ligand field calculations, molecular mechanics, purely geometrical approaches, and neural networks, that can calculate structures and one or more additional molecular properties. 

The result in Eq. 41 is reminiscent of the expression for anisotropic interelec-tronic repulsion presented in Sect. 3.2. However unlike in the latter case, no attempt was made to analyze the orbital mechanisms underlying the spin-orbit anisotropy. Instead it was shown later on that the zfs in ruby could be accounted for by a full ligand field calculation combining isotropic s.o.c. with a trigonal perturbation of the ligand field [46,47],... 

Figure 13. Left ligand field energy-level diagram calculated for plastocyanin. Center contains energies and wavefunctions of the copper site. Energy levels determined after removing the rhombic distortions to give and C symmetries are shown in the left and right columns, respectively (from Ref. 11). Right electronic structural representation of the plastocyanin active site derived from ligand field calculations (from Ref. 11).

The electronic spectrum of RhF6 has not been reported, but ligand field calculations have been used to predict its spectrum.1279 The IR spectrum of RhF6 has been reported,1280 and it is consistent with the expected Oh symmetry. Like IrF6, the rhodium hexafluoride does not show the Jahn-Teller splittings of the Eg mode observed for the analogous Tc, Re and Os hexafluorides. 

Extended X-ray absorption fine structure (EXAFS) studies in aqueous solutions have shown that a water molecule in wild-type bovine S(i)D is 2.5 A (Cu-0 distance) from the metal 203). From H NMR studies the same distance is proposed (see later). Ligand field calculations have shown that the water molecule essentially does not affect the energy levels 89, 204). 

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