Coordination compounds interaction

MOMEC is a force field for describing transition metal coordination compounds. It was originally parameterized to use four valence terms, but not an electrostatic term. The metal-ligand interactions consist of a bond-stretch term only. The coordination sphere is maintained by nonbond interactions between ligands. MOMEC generally works reasonably well for octahedrally coordinated compounds. 

Electron correlation is often very important as well. The presence of multiple bonding interactions, such as pi back bonding, makes coordination compounds more sensitive to correlation than organic compounds. In some cases, the HF wave function does not provide even a qualitatively correct description of the compound. If the weight of the reference determinant in a single-reference CISD calculation is less than about 0.9, then the HF wave function is not qualitatively correct. In such cases, multiple-determinant, MSCSF, CASPT2, or MRCI calculations tend to be the most efficient methods. The alternative is... 

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. 

Many complexes and coordination compounds exist as isomers, compounds that contain the same numbers of the same atoms but in different arrangements. For example, the ions shown in (13a) and (13b) differ only in the positions of the Cl ligands, but they are distinct species, because they have different physical and chemical properties. Isomerism is of more than academic interest for example, anticancer drugs based on complexes of platinum are active only if they are the correct isomer. The complex needs to have a particular shape to interact with DNA molecules. 

The interactions in such compounds are now better understood, and the term complex now has a more specific meaning. Not all transition-metal compounds are complexes, but many are. The terms complex and coordination compound are now used almost interchangably. 

Nickel-selenium coordination compounds have received attention in recent years, because a unique Ni-selenocysteine interaction was revealed in the active site of [FeNiSe]-hydrogenases.1083,1084 Of particular interest in this regard are mixed CO/selenolate complexes. Distorted square planar (393) was prepared from [CpNi(CO)]2, PhSeSePh, and [Fe(CO)3(SePh)3] and provides the first example of CO bound to a square planar Ni11 center in thiolate/selenolate environment.1085,1086 Upon addition of RSSR, species of the series [Ni(CO)(SR) (SePh)3 ] are formed. //(CO) ranges from 2,023 cm-1 to 2,043 cm-1 and is regarded as a spectroscopic reference for the CO binding site in [NiFeSe] hydrogenases. 

Planar coordination compounds with aromatic ligands, especially those having extended 7r-systems, show 7r-7r interactions in the solid state. The ligands shown in Figure 8 form complexes with silver(I) which have a supramolecular structure through 7r-7r interactions.586-596... 

This procedure has been used successfully to determine the composition of many complexes in solution. It is possible to extend this method to cases where more than one complex is formed but the application is quite difficult. Like the logarithmic method, Job s method can be applied to other cases of molecular interaction and is not limited to the formation of coordination compounds. Both methods are based on the assumption that one complex is dominant in the equilibrium mixture. Numerous other methods for determining the number of metal ions and ligands in complexes have been devised, but they are beyond the introduction to the topic presented here. 

Whereas 3c/4e hypervalent interactions (4.77) tend to be relatively uncommon and fragile in main-group compounds (often leading to transition states for nucleophilic displacement reactions, rather than stable equilibrium species), the corresponding interactions in transition-metal coordination compounds are ubiquitous and robust. The far higher prevalence of hypervalent co-bonding in transition-metal chemistry may be attributed to three major factors. 

Hitoshi dedicated his life to Science and to the organization of Science. As a scientist, I remember the studies by X-ray of the coordination compounds in solution of metal ions with monodentate ligands which constituted milestones in the field. Eventually, he started simulating through informatic tools the interaction of solvents and ligands with metal ions. 

Armaroli N, Accorsi G, Cardinali F9, Listorti A (2007) Photochemistry and Photophysics of Coordination Compounds Copper. 280 69-115 Armitage BA (2005) Cyanine Dye-DNA Interactions Intercalation, Groove Binding and Aggregation. 253 55-76... 

It is especially important to investigate the molecular structure of coordination compounds in the vapor phase because the relatively weak coordination interactions may be considerably influenced by intermolecular interactions in solutions and especially in crystals. It has been shown that the geometrical variations can be correlated with other properties of the molecular complexes ). In particular the structural changes in the F3B N(CH3)3 and CI3B N(CH3)3 molecules ) relative to the respective monomeric species unambiguously indicated boron trichloride to be a stronger acceptor than boron trifluoride. Data on the geometry and force field have also been correlated ). 

Basic Mechanisms of Adhesion Acid-Base Interactions. The understanding of polymer adhesion has been greatly advanced in recent years by the recognition of the central role of acid-base interactions. The concept of an acid was broadened by G. N. Lewis to include those atoms, molecules, or ions in which at least one atom has a vacant orbital into which a pair of electrons can be accepted. Similarly, a base is regarded as an entity which possesses a pair of electrons which are not already Involved in a covalent bond. The products of acid-base interactions have been called coordination compounds, adducts, acid-base complexes, and other such names. The concept that... 

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