Metal carbonyl complexes binary

Jahn, H. A. Teller, E. Proc. Roy. Soc. bond. A 1937, 161, 220-235. Mckinlay, R. G. Paterson, M. J. The Jahn-Teller Effect in Binary Transition Metal Carbonyl Complexes. In The Jahn-Teller Effect Fundametals and Implications for Physics and Chemistry , Eds. Koppel, H. Yarkony,... 

Binary metal carbonyl complexes, with technetium, 5, 835 Binary technetium isocyanides, preparation and properties,... 

Metal carbonyl complexes are an interesting series of coordination compounds in which the ligands are CO molecules, and in many cases the metals are present in a zero oxidation state. In these complexes, both the metal and ligand are soft according to the Lewis acid-base definitions. Although the discussion at first will be limited to the binary compounds containing only metal and CO, many mixed complexes are known that contain both CO and other ligands. 

The highest oxidation states for Ir are VI and V, stabilized by ligands such as F. IrFg (a yellow crystalline sohd, /Xeff = 2.9 /xb at 300 K) is formed by the direct fluorination of Ir metal. Molecules of IrFe are octahedral, and the stmcture has been studied in the gas phase by electron diffraction and in the sohd phase by EXAFS. IrFe is hydrolyzed by water, and reactions (1-4) illustrate its general reactivity. Reaction four represents the formation of the first binary, tripositive metal carbonyl complex. ... 

The Jahn-Teller Effect in Binary Transition Metal Carbonyl Complexes... 

Binary metal-carbonyl complexes are known for most transition metals and they are, in general, the more appropriate starting material in pyrolitic and photolytic synthetical methods. 

This observation parallels that of anionic binary transition metal cyanide complexes where the photodissociation of an electron i.s observed (Chapter 3). Photoinduced electron transfer reactions are also observed with binary metal carbonyl complexes... 

In contrast to the vast number of mono- and multinuclear binary carbonyl complexes of the transition metals, no isolable binary carbonyls of titanium, zirconium, or hafnium have been reported. 

Because Ni(CO)4 is volatile (b.p. 43 °C) and cobalt will not react under these conditions, this process afforded a method for separating Ni from Co by the process now known as the Mond process. Although there are many complexes known that contain both carbonyl and other ligands (mixed carbonyl complexes), the number containing only a metal and carbonyl ligands is small. They are known as binary metal carbonyls, and they are listed in Table 21.1. The structures of most of these compounds are shown later in Figures 21.1 through 21.3. 

The effective atomic number rule (the 18-electron rule) was described briefly in Chapter 16, but we will consider it again here because it is so useful when discussing carbonyl and olefin complexes. The composition of stable binary metal carbonyls is largely predictable by the effective atomic number (EAN) rule, or the "18-electron rule" as it is also known. Stated in the simplest terms, the EAN rule predicts that a metal in the zero or other low oxidation state will gain electrons from a sufficient number of ligands so that the metal will achieve the electron configuration of the next noble gas. For the first-row transition metals, this means the krypton configuration with a total of 36 electrons. 

The reactivity of these metal hydride-metal carbonyl reactions can be correlated with the nature of the reactants in a manner consistent with the proposed mechanism nucleophilic attack by hydride on coordinated CO. Thus reactions involving the highly nucleophilic group IV hydride, Cp gZrHg, are much faster than those of group V metal hydrides. On the other hand, the relatively electrophilic neutral binary metal carbonyls all react with Cp2NbH under mild conditions (20-50° C), whereas more electron-rich complexes such as cyclopentadienylmetal carbonyls (Cp2NbH(C0), CpV(CO) ) or anionic carbonyls (V(CO)g ) show no reaction under these conditions. 

The prototypically zero oxidation state complexes of the group are the binary hexacarbonyls M(CO)6. Early studies of the electrochemistry of these 18-electron closed-shell systems in nonaqueous electrolytes has perhaps been seminal in understanding the electron-transfer reactions of more substituted systems and of metal carbonyls in general. 

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