Molecular orbitals complex ions

In addition to a set of nd valence orbitals, the transition metal ions have available (n + l)s and (n + l)p valence orbitals. Since the transition metal ion is centrally located in most complexes, the molecular orbitals are conveniently written in the form... 

These arguments raise the question of whether n-effects need be considered at all. Clearly, however, charge neutralization fails to account for the stabilization of low spin Fe(II) and Co (II) ions in their crown thioether complexes. Similarly, it does not account for the small Ag values of thioether complexes, or the high nephelauxetic influence of the ligands. Thus, in summary, m-acceptance and the accumulation of cationic charge combine to generate the characteristic electronic properties of thioether complexes. Last, molecular orbital calculations support the ability of thioethers to serve as 71-acceptors [38, 39]. 

Adsorption of benzene on transition metal chlorides dispersed on silica gel was studied by Takahashi et al. (2000). A weak r-complexation bond was formed between benzene and these metal ions. Molecular orbital calculations for the bonding of benzene and chlorides of these metals were performed at the Hartree-Fock (HF) and density functional theory (DFT) levels using effective core potentials. The experimental values of heat of adsorption and the calculated bond... 

Each of these tools has advantages and limitations. Ab initio methods involve intensive computation and therefore tend to be limited, for practical reasons of computer time, to smaller atoms, molecules, radicals, and ions. Their CPU time needs usually vary with basis set size (M) as at least M correlated methods require time proportional to at least M because they involve transformation of the atomic-orbital-based two-electron integrals to the molecular orbital basis. As computers continue to advance in power and memory size, and as theoretical methods and algorithms continue to improve, ab initio techniques will be applied to larger and more complex species. When dealing with systems in which qualitatively new electronic environments and/or new bonding types arise, or excited electronic states that are unusual, ab initio methods are essential. Semi-empirical or empirical methods would be of little use on systems whose electronic properties have not been included in the data base used to construct the parameters of such models. 

Organic Polymers, Natural and Synthetic 610 Appendix 1 Units, Constants, and Reference Data 635 Appendix 2 Properties of the Elements 641 Appendix 3 Exponents and Logarithms 643 Appendix 4 Nomenclature of Complex Ions 648 Appendix 5 Molecular Orbitals 650... 

Figure 4.17 A qualitative molecular orbital scheme for a cr-bonded complex ion [AuL2]+. (Reprinted with permission from Inorg. Chem., 1982, 21, 2946. Copyright (1982) American...

There are two major theories of bonding in d-metal complexes. Crystal field theory was first devised to explain the colors of solids, particularly ruby, which owes its color to Cr3+ ions, and then adapted to individual complexes. Crystal field theory is simple to apply and enables us to make useful predictions with very little labor. However, it does not account for all the properties of complexes. A more sophisticated approach, ligand field theory (Section 16.12), is based on molecular orbital theory. 

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