Bonding in transition metal compounds

1) Donor-acceptor bonding in main-group compounds has been recognized in recent years as an important bonding motifnot only for classical group-13/15 Lewis acid-base pairs. This is discussed in chapter 4 in Volume 2. 

The Chemical Bond Chemical Bonding Across the Periodic Table, First Edition. 

We do not strive in this article to present as many classes of compounds as possible rather, a discussion of the chemical bonding in representative classes of TM compounds, which exempHfies characteristic types of metal-Ugand interactions, is given. Unlike a textbook, we do not present a systematic discussion of the differences between the first, second and third TM compounds nor do we compare molecules of the early TM atoms with the late TMs. But we think that the chosen examples cover most aspects of chemical bonding of the TMs. Prior to this, a discussion of the essential features of the TM valence orbitals is presented. 

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The general understanding of the electronic structure and the bonding properties of transition-metal silicides is in terms of low-lying Si(3.s) and metal-d silicon-p hybridization. There are two dominant contributions to the bonding in transition-metal compounds, the decrease of the d band width and the covalent hybridization of atomic states. The former is caused by the increase in the distance between the transition-metal atoms due to the insertion of the silicon atoms, which decreases the d band broadening contribution to the stability of the lattice. 

Metal-metal bonds in transition metal compounds. M. C. Baird, Prog. Inorg. Chem., 1968,9,1-159 (899). 

Baird, Michael C., Metal-Metal Bonds in Transition Metal Compounds. 9 1... 

Bonding in transition metal compounds can be analyzed analogously to that in transition metal complexes, by considering each oxygen or sulphur atom to contribute two electrons to the complex and an s-type orbital. The resulting orbital schemes are given in Fig. 4.13. 

Nuclear quadrupole coupling constants can thus provide much valuable information about chemical bonding in transition metal compounds since they can be obtained both for the metal and, or for the attached atom in many cases. There are, however, a number of disadvantages inherent in the technique. The resonances are often of very low intensity thus necessitating a large sample size (up to 10 grams). Furthermore, the complete region of interest, 2—1,000 MHz, cannot be covered by one... 

The understanding of the bonding in transition metal compounds presents a special challenge for theoretical chemistry. Just as in the case of the main group elements,8 it could be shown that a classification of the bonds between a transition metal and a ligand into... 

A18. J. J. Eisch, The Chemistry of Organometallic Compounds—the Main Group Elements. Macmillan, New York, 1967. In spite of the title, contains some material on bonding in transition metal compounds. 

Metal-metal bonds in transition metal compounds... 

Bonding in Transition Metal Compounds and Coordination Complexes... 

Most transition metals have a number of stable oxidation states that lead to different kinds of chemical bonds and facilitate electron transfer reactions. Molecular orbital theory satisfactorily describes bonding in transition metal compounds and coordination complexes. 

G. Frenking and N. Frohlich, Bonding in Transition-Metal Compounds, Chem. Rev., 2000,100, 717. 

The CASSCF model and its implementation into efficient computer programs will be discussed in more detail in the following sections. The main emphasis will, however, not be put on the technical problems concerning the search for efficient MCSCF optimization schemes. A comprehensive discussion of these problems has recently been published in this series . The present contribution will instead concentrate around problems concerning the application of the CASSCF method to different chemieal problems, ranging from accurate calculations of properties of small molecules to studies of the chemical bond in transition-metal compounds. Nevertheless a discussion on the computational strategies developed to obtain a CASSCF wavefunction is necessary and will be given below. However, the main emphasis will be on the... 

G. Frenking, N. Frohlich, The nature of the bonding in transition-metal compounds, Chem. Rev. 100 (2000) 717. 

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