Models, for coordination compounds

SYNTHESIS HYBRID MOLECULAR MODELS FOR COORDINATION COMPOUNDS... 

HYBRID MODEL FOR COORDINATION COMPOUNDS 4.4.1. Reducing the number of ESVs for CLS... 

The process has been treated theoretically in terms of simplified models.14 58 The quantum mechanics is one of formulating the probability of crossing from an excited to a ground state, summed over all vibrational levels. For coordination compounds, the weak coupling limit is presumably the important approximation. Here, the transition is from low lying vibrational levels of the excited state to very high vibrational levels of the ground state. 

Methods for molecular mechanics modeling of coordination compounds . 

Hay BP. Methods for molecular mechanics modeling of coordination compounds. Coord Chem Rev 1993 126 177-236. 

The synthesis and characterization of coordination polymers was supported by the U.S. Air Force in a search for materials that exhibited high thermal stabilities. However, attempts to prepare stable, tractable coordination polymers that simulate the exceptional thermal and/or chemical stability of model monomeric coordination compounds such as copper(II) ethylenediaminobisacetylacetonate or phthalocyanine have been disappointing ". Typically, only short chains are formed, and the thermally stable monomers lose most of their stability when linked by the metals into polymeric units. The principles in designing coordination polymers are ... 

Figure 24 The Dewar-Chatt-Duncanson model" for coordination of an olefin in which donation of electron density from the filled olefin rr-orbital (an L function) is supplemented by backbonding into the empty 7r -orbital (aZfunction). Depending upon the extent of backbonding, the compound may be described as either a metal-olefin adduct (little backbonding) or a...

VB concept of hybridization proposes the mixing of particular combinations of s, p, and d orbitals to give sets of hybrid orbitals, which have specific geometries. Similarly, for coordination compounds, the model proposes that the number and type of metal-ion hybrid orbitals occupied by ligand lone pairs determine the geometry of the complex ion. Let s discuss the orbital combinations that lead to octahedral, square planar, and tetrahedral geometries. 

Molecular mechanics is covered in Molecular Mechanics Calculations as a Tool in Coordination Chemistry R. D. Hancock, Prog. Inorg. Chem. (1989) 37, 187 Methods for molecular mechanics modelling of coordination compounds B. P. Hay, Coord. Chem. Rev. (1993) 126,177 and a review with a wide variety of examples The relation between ligand structures, coordination stereochemistry, and electronic and thermodynamic properties by P. Comba, Coord. Chem. Rev. (1993) 123, 1. 

The correct crystal structure of materials in a screening study is generally unknown, but often the energy of a given material, compound, or complex can be estimated with sufficient accuracy using simple template or model crystal structures, if the local coordination aroimd the metal atoms is captured by the model structure [17-19]. Such an approach is typically sufficient to discover trends in thermodynamic stabilities or similar and, in particular, to down-select the number of possible candidates which can be subjected for a more thorough analysis. For coordination compounds such simple template structures (see Figure 18.2) can... 

If a monoarylacetylene (ArC = CH) is taken as a model for a transition state of an arenediazonium ion with a nucleophile Nu, two types of transition state can be visualized the first, 7.13, leads to the (Z)-azo compound 7.14, whereas the second, 7.15, results in the (E )-isomer 7.16 (Scheme 7-3). If the transition state is reactantlike (i.e., early on the reaction coordinate), repulsive interaction between the nucleophile and the aryl nucleus is small because the distance Nu-Np is still large. Therefore, the repulsion between the lone pair on Np and the aryl nucleus becomes the decisive factor. It favors an (E )-configuration of the Np lone pair with respect to the aryl nucleus (obviously it is energetically dominant compared with the repulsion between the lone pairs on Na and Np) therefore, transition state 7.13 is at a lower energy level, and Nu attacks NB in the (Z)-configuration. 

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