Coordinate bond theory

This reactivity pattern can be rationalized in terms of a diabatic model which is based upon the principle of spin re-coupling in valence (VB) bond theory [86]. In this analysis the total wavefunction is represented as a combination of two electronic configurations arising from the reactant (reaction coordinate. At the outset of the reaction, is lower in energy than [Pg.141]

In this review, CPOs constructed by covalent bonds are mainly focused on however, stable coordination bonds comparable to the stability of the covalent bonds have potential for future enhanced molecular design of novel CPOs. One representative is the bond between pyridine-type nitrogen and metal, which is widely used in supramolecular chemistry, that is, the cyclic supramolecular formation reaction between pyridine-substituted porphyrin and metal salts (Fig. 6d) [27,28]. Palladium salts are frequently used as the metal salts. From the viewpoint of the hard and soft acid and base theory (HSAB), this N-Pd coordination bond is a well-balanced combination, because the bonds between nitrogen and other group X metals, N-Ni and Ni-Pt coordination bonds, are too weak and too strong to obtain the desired CPOs, respectively. For the former, the supramolecular architectures tend to dissociate into pieces in the solution state, and for the latter. 

It was G. N. Lewis who extended the definitions of acids and bases still further, the underlying concept being derived from the electronic theory of valence. It provided a much broader definition of acids and bases than that provided by the Lowry-Bronsted concept, as it furnished explanations not in terms of ionic reactions but in terms of bond formation. According to this theory, an acid is any species that is capable of accepting a pair of electrons to establish a coordinate bond, whilst a base is any species capable of donating a pair of electrons to form such a coordinate bond. A Lewis acid is an electron pair acceptor, while a Lewis base is an electron pair donor. These definitions of acids and bases fit the Lowry-Bronsted and Arrhenius theories, and cover many other substances which could not be classified as acids or bases in terms of proton transfer. 

While our primary focus has been on stable closed-shell (or low-spin) coordination species in which covalency effects are pronounced, it is also useful to examine the opposite extreme of weak coordinate bonding and free-atom -like spin multiplicities, corresponding to the original assumptions of crystal-field theory. 

Note to the student The AP chemistry exam does not emphasize complex ions or coordination compounds. There is nothing on the AP exam that involves the concepts of crystal-field theory, low versus high spin, valence bond theory, or other related areas. If you understand the questions presented here, then you are basically "safe" in this area of the exam. Most high school AP chemistry programs do not focus much on this area of chemistry because of time constraints. 

Continuity equation electrochemical reactor, 30 311 mass transport, 30 312 Continuous-flow stirred-tanlt reactor, 31 189 Continuous reactor, 33 4-5 Continuous stirred-tank reactor, 27 74-77 ControUed-atmosphere studies, choice of materials for construction, 31 188 Conversion theory, 27 50, 51 Coordinatimi number, platinum, 30 265 Coordinative bonding, energy of, 34 158 Coordinative chemisorption on silicon, 34 155-158... 

The combination of modem valence bond theory, in its spin-coupled (SC) form, and intrinsic reaction coordinate calculations utilizing a complete-active-space self-consistent field (CASSCF) wavefunction, is demonstrated to provide quantitative and yet very easy-to-visualize models for the electronic mechanisms of three gas-phase six-electron pericyclic reactions, namely the Diels-Alder reaction between butadiene and ethene, the 1,3-dipolar cycloaddition of fulminic acid to ethyne, and the disrotatory electrocyclic ringopening of cyclohexadiene. 

None of the theories proposed before 1951 to explain the nature of the bonding in metal-olefin complexes was entirely satisfactory (35). Chatt (S3) suggested that, in addition to the ordinary coordinate bond, some sort of bond involving the filled d-orbitals of the metal atom was essential for coordination of the olefin, but such a bond was difficult to formulate until Dewar (64) described it in terms of molecular orbitals. The structure which he proposed for the silver-olefin complexes, and that subsequently proposed for the platinum-olefin complexes by Chatt and Duncanson (35) are shown schematically in structures (I) and (II). The type bond, which has also been called a ji-bond (64, 4), is formed by the overlap of the filled bonding... 

After a short introduction the experimental methods are reported (Chapters 1 and 2). Because of the importance of the coordination of the monomer in the processes under consideration the coordinative bonding of an olefin to a transition metal has been treated in some detail in Chapter 3. It has been written to help the reader not familiar with the language of MO theory. 

The model that largely replaced valence bond theory for interpreting the chemistry of coordination compounds was Ihe crystal field theory, first proposed in 1929 by Hans Bethe.11 As originally conceived, it was a model based on a purely electrostatic... 

Chapter 11 Coordination Chemistry Bonding, Spectra, and Magnetism 387 Bonding in Coordination Compounds 391 Valence Bond Theory 391 Crystal Field Theory 394 Molecular Orbital Theory 413 Electronic Spectra of Complexes 433 Magnetic Properties of Complexes 459... 

LEWIS ELECTRON THEORY. A theory involving acid and base formation, neutralization, and related phenomena on the basis of exchange of electrons between substances and the formation of coordinate bonds. It represented an important advance in chemical theory. largely replacing earlier concepts. Advanced in 1923 by Gilbert N Lewis, it contributed much to the development of coordination chemistry- in which the base is represented by the ligand and the acid by the metal ion. 

According to the valence bond theory (Section 7.10), the bonding in metal complexes arises when a filled ligand orbital containing a pair of electrons overlaps a vacant hybrid orbital on the metal ion to give a coordinate covalent bond ... 

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