Neutral metal monoxides

The electron configurations for the transition metals discussed here and in Appendix B are for individual metal atoms in the gas phase. Most chemists work with the transition metals either in the metallic state or as coordination compounds (see Chapter 25). A solid transition metal has a band structure of overlapping d and s orbital levels (see Section 13-7). When transition metal atoms have other types of atoms or molecules bonded to them, however, the electronic configuration usually becomes simpler in that the d orbitals fill first, followed by the next higher s orbital. This is illustrated by Cr, which has a 4s 3d electronic configuration as a free atom in the gas phase. But in the compound Cr(CO)5, chromium hexacarbonyl, which contains a central Cr atom surrounded by six neutral carbon monoxide (or carbonyl) groups, the chromium atom has a 3d electronic configuration. 

Studies of oxides containing only one main-group element atom were reviewed in 2002 [21]. The electronic structure of the diatomic MO molecules was reviewed in 2000 [98]. Finally, in a review article in 2001, the bonding in neutral and cationic transition-metal monoxides was compared [99]. Most matrix-isolation studies concentrate on small molecules containing one or two metal atoms. 

Figure 2.6 Comparison between the 0 K bond dissociation energies Dq(M-O) for neutral and cationic metal monoxides. (Data from Tables 5 and 6 in Ref. [99].)...

Fig. 2.1 Schematic representation of the formation metal nanoparticles (M ) Left from metal carbonyl compounds (M(CO)n within the collapsing bubbles in an organic solvent Right by the reduction of metal ions in aqueous solutions by reducing radicals (RR) generated within the bubbles. M—neutral metal atom CO—carbon monoxide ligand M+—metal ion RH—organic solute...

Kietzschmar, L, Schroder, D., Schwarz, H., Armentrout, P.B., 2001. The binding in neutral and cationic 3d and 4d transition-metal monoxides and sulfides. In Duncan, M.A. (Ed.), Advances in Metal and Semiconductor Clusters. Metal Ion Solvation and Metal-Ligand Interactions, vol. 5. Elsevier Science, Amsterdam. 

The most common types of intrinsic point defects are Schottky and Frenkel defects (Figure 3.1). A Schottky defect consists of a vacant cation lattice site and a vacant anion lattice site. To form a Schottky defect, ions leave their normal lattice positions and relocate at the crystal surface, preserving overall charge neutrality. Hence, for a metal monoxide, MO, vacant sites must occur equally in the cation and anion sublattice and form a Schottky pair, whereas in binary metal oxides, MO2, a Schottky defect consists of three defects a vacant cation site and two vacant anion sites. A Frenkel defect forms when a cation or anion is displaced from its regular site onto an interstitial site, where, the resulting vacancy and interstitial atom form a Frenkel defect pair. 

In nature most metals have a greater tendency to exist in ores than as neutral metals. Therefore, when metals are mined they are already in oxidized states. To be useful in industry, they must be reduced to the neutral metals. Iron, for example, is most commonly foimd in the minerals hmonite (FeO), hematite (Fe Oj), magnetite (FejO ), or in iron ores mixed with other metals. With hmonite, metallic iron is produced in a blast furnace by reacting FeO with carbon monoxide (CO) at elevated temperatures, as shown ... 

Examples of complexes in this class are given in Table 25. The taUe shows that these complexes are closely related to the corresponding complex cyanides, in their occurrence, colour and magnetic properties. This close analogy arises since the cyanide and acetylide anions are iso-electronic and presumably bond to the metal in a similar manner. Both ligands would be expected to have acceptor properties as does the neutral carbon monoxide molecule, which is also isoelectronic. The bonding in the systems M—C X, where X = O, N or CR, may be represented as shown in Figure 67. 

The other more electronegative elements are non-metals and form oxides which are entirely covalent and usually acidic. For example, sulphur yields the oxides SO2 and SO3, dissolving in bases to form the ions SO3 and SO4" respectively. A few non-metallic oxides are often described as neutral (for example carbon monoxide and dinitrogen oxide) because no directly related acid anion is known to exist. 

Carbon monoxide [630-08-0] (qv), CO, the most important 7T-acceptor ligand, forms a host of neutral, anionic, and cationic transition-metal complexes. There is at least one known type of carbonyl derivative for every transition metal, as well as evidence supporting the existence of the carbonyls of some lanthanides (qv) and actinides (1) (see AcTINIDES AND THANSACTINIDES COORDINATION COMPOUNDS). 

The vertical IPs of CO deserve special attention because carbon monoxide is a reference compound for the application of photoelectron spectroscopy (PES) to the study of adsorption of gases on metallic surfaces. Hence, the IP of free CO is well-known and has been very accurately measured [62]. A number of very efficient theoretical methods specially devoted to the calculation of ionization energies can be found in the literature. Most of these are related to the so-called random phase approximation (RPA) [63]. The most common formulations result in the equation-of-motion coupled-cluster (EOM-CC) equations [59] and the one-particle Green s function equations [64,65] or similar formalisms [65,66]. These are powerful ways of dealing with IP calculations because the ionization energies are directly obtained as roots of the equations, and the repolarization or relaxation of the MOs upon ionization is implicitly taken into account [59]. In the present work we remain close to the Cl procedures so that a separate calculation is required for each state of the cation and of the ground state of the neutral to obtain the IP values. 

---