Metal Complexes Electronic Structure and Properties

An F term arising from a d configuration correlates with Tig T2g + A2 terms in an Oh complex. The multiplicity is unchanged by the correlation, so the terms in Oh symmetry are ig, T2g, and A2g. Similarly, a D term arising from a d configuration correlates with T2g + Eg terms in an Oj, complex. The Oh terms retain the singlet character of the D free ion term, and so are T2 and Eg. 

3 The formula for the spin-only moment is p/pB = t(/V)(iV + 2)] where N is the number of unpaired electrons. Therefore, the spin-only contributions are  

5 (a) Cr(OH2)6l or [Mn(OH2)6 - The chromium complex is expected to have a larger crystal field stabilization 

13 (a) 4 s. You can approach this exercise in the way described in Section 20,2 for the d configuration (see Table 20.6). You first write down all possible microstates for the s configuration, then write down the Mi and iWj values for each microstate, then infer the values of Z and S to which the microstates belong. In this case, the procedure is not lengthy because there are only two possible microstates, (0 ) and (0 ). The only possible values of Mi and Ms are 0 and 1/2, respectively. If Mi can only be 0, then Z must be 0, which gives an S term (remember that L can take on all values Mi, (A4-1),. .., 0,. .. -Mi). Similarly, if Ms can only be +1/2 or -1/2, then S must be 1/2, which gives a multiplicity 25+1 -2. I herefore, the one and only term that arises from a 4s configuration is S. 

A term that contains a microstate with Mi = 2 must be a D term (Z = 2). This term can only be a singlet because if both electrons have m/ = 1 they must be spin-paired. Therefore, one of the terms of the 3p configuration is D, which contains five microstates. To account for these, you can cross out (I , T), (-1 , -1 ), and one microstate 

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Chapter 20 d-Metal Complexes Electronic Structure and Properties... 

In the present paper we demonstrated the feasibility of a semiempirical description of electronic structure and properties of the Werner TMCs on a series of examples. The main feature of the proposed approach was the careful following to the structural aspects of the theory in order to preclude the loss of its elements responsible for description of qualitative physical behavior of the objects under study, in our case of TMCs. If it is done the subsequent parameterization becomes sensible and successful solutions of two long lasting problems semi-empirical parameterization of transition metals complexes and of extending the MM description to these objects can be suggested. 

ELECTRON GAS. The term electron gas is used to denote a system of mobile electrons, as. for example, the electrons in a metal that are free to move. In the free electron theory of metals, these electrons move through the metal in the region of nearly uniform positive potential created by the ions of the crystal lattice. This theory when modified by the Pauli exclusion principle, serves to explain many properties of metals, especially the alkali metals. For metals with more complex electronic structure, and semiconductors, the band theory of solids gives a better picture. 

For example, [MoC+,]3 has a total of thirty-nine valence electrons from the molybdenum 4d5 5s and six chlorine 3p5 configurations, and the —3 charge on the ion. Its electron configuration is therefore cr12 n24 (2/2 )3. Thus the MO theory of these ML6 complex ions confirms that the electrons of prime importance are those occupying the t2g and eg levels on the metal, as predicted by crystal-field theory. However, the MO theory points the way to the more accurate calculation of electronic structure and properties. 

However, from calculations on transition metal complexes whose structural and electronic properties are known with higher accuracy it became evident that ah initio treatments have to be carried to the level of configuration interaction (25,26), at least for the late transition elements (iron group and beyond). A useful computational method for such systems must be able to deal with the quite diffuse valence s orbitals and the rather localized valence d orbitals with their characteristic directional properties in a balanced manner in order to achieve a proper description of transition metal ligand bonds (25). 

The chemistry of early transition metal complexes containing a chalcogenido-metal bond is an area of continuing interest because of their unusual electronic structures and properties, and the relevance of such compounds as models for several important industrial catalytic processes. A variety of titanium complexes containing Ti-S bonds are known and this chemistry has been reviewed.1003,1004... 

I. B. Bersuker, Electronic Structure and Properties of Transition Metal Complexes. Introduction to the Theory , John Wiley Sons, New York, 1996. 

Until about 20 years ago, the valence bond model discussed in Chapter 7 was widely used to explain electronic structure and bonding in complex ions. It assumed that lone pairs of electrons were contributed by ligands to form covalent bonds with metal atoms. This model had two major deficiencies. It could not easily explain the magnetic properties of complex ions. 

Bray KL (2001) High Pressure Probes of Electronic Structure and Luminescence Properties of Transition Metal and Lanthanide Systems. 213 1 - 94 Bunz UHF (1999) Carbon-Rich Molecular Objects from Multiply Ethynylated rr-Complexes. 201 131-161... 

We first examine the relationships between electron structure and the emission and absorption spectroscopy of metal complexes. Transition metal complexes are characterized by partially filled d orbitals. To a large measure the ordering and occupancy of these orbitals determines emissive properties. Figure 4.2 shows an orbital and state diagram for a representative octahedral MX6 d6 metal complex where M is the metal and X is a ligand that coordinates or binds at one site. The octahedral crystal field of the ligands splits the initially degenerate five atomic d-orbitals by an amount... 

Neutral square coplanar complexes of divalent transition metal ions and monoanionic chelate or dianionic tetrachelate ligands have been widely studied. Columnar stack structures are common but electrical conductivities in the metal atom chain direction are very low and the temperature dependence is that of a semiconductor or insulator. However, many of these compounds have been shown to undergo partial oxidation when heated with iodine or sometimes bromine. The resulting crystals exhibit high conductivities occasionally with a metallic-type temperature dependence. The electron transport mechanism may be located either on predominantly metal orbitals, predominantly ligand re-orbitals and occasionally on both metal and ligand orbitals. Recent review articles deal with the structures and properties of this class of compound in detail.89 90 12... 

To answer these questions requires some understanding of the properties of small metal particles, both structural and electronic. In this review we shall examine first the evidence relating to metal particles prepared by direct methods, e.g., vapour deposition or condensation in the gas phase. Then we shall consider whether this information can be applied to the case of supported metals where both precursor decomposition and support effects may add to the complexity of the total system. We shall then consider whether further changes in catalytic properties occur after preparation, i.e., during the catalytic reaction. Finally, we shall summarize some of the more recent evidence concerning the nature of structure sensitivity. 

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