Organometallic molecules

Organometallic Molecules.—Carbonyl Complexes. Three molecules of the type [Cr(CO) Lo ], where L is a phosphine or a phosphite ligand, have been investigated. In all of these the chromium atom exhibits octahedral co-ordination. The approximate symmetry of the cw-[Cr(CO)2(PH3)4] molecule is C3, the Cr-C distance is 1.817(7) A, and the Cv-V trans to CO) distance of 2.338(4) A is longer than the Cv-P trans to P) distance of 2.282(4) A. In frara-[Cr(CO)4 P(OPh)3 2] the Cr-C and Cr-P distances 

As such, they are much more resistant to acid- or base-induced dissociation or hydrolysis than are coordination complexes [e.g., Fen(TPP) is stable in the presence of 1 M H30+ or 1 M HO , whereas Feu(NH3)4+ is not]. An especially useful review of the electrochemistry of metalloporphyrins in nonaqueous media is available,3 which is complemented by a review of the electrochemistry of metalloproteins.4 

---

Cotton, F. A., Frenz, B. A., Deganello, G. Shaver, A. (1973) Fluxional organometallic molecules. XXXIV. The structure and temperature-dependent NMR spectrum of cis-(l,2,6-trihap/o- 3,4,5-fri/iapto-bicyclo[6.2.0]deca-l,3,5-lriene)hexacarbonyldi iron(Fe—Fe)," J. Organomet. Chem. 50,227-240. 

Cotton, F. A., DeBoer, B. G. Marks, T. J. (1971) Stereo-chemically nonrigid organometallic molecules. XXIX. Cyclo-heptatrienediiron hexacarbonyl, J. Am. Chem. Soc. 93, 5069-5075. 

Braga D (1999) Static and Dynamic Structures of Organometallic Molecules and Crystals. 4 47-68... 

We thank Prof. Janet Blumel, Texas A M University, and the Gesellschaft Deutscher Chemiker for allowing us to reproduce solid state NMR spectra. In addition we thank Klaus Jurkschat and Bernhard Lippert and their groups for making available samples of organometallic molecules. Thanks also go to Andrea Bokelmann and Bernhard Griewel for their valuable technical help. 

Not included in the present review is the fascinating new chemistry which results from reaction between diazo compounds and low-valent transition-metal complexes bearing easily displaceable two-electron ligands as well as with metal-metal multiple bonds and metal hydrides whereby a variety of novel organometallic molecules could be obtained. This field has been covered, in accord with its rapid development, by successive reviews of Hermann 19 22) and Atbini23). 

Molecular Motions and Dynamic Structures. Molecular motions are of quite general occurrence in the solid state for molecules of high symmetry (22,23). If the motion does not introduce disorder into the crystal lattice (as, for example, the in-plane reorientation of benzene which occurs by 60° jumps between equivalent sites) it is not detected by diffraction measurements which will find a seemingly static lattice. Such molecular motions may be detected by wide-line proton NMR spectroscopy and quantified by relaxation-time measurements which yield activation barriers for the reorientation process. In addition, in some cases, the molecular reorientation may be coupled with a chemical exchange process as, for example, in the case of many fluxional organometallic molecules. ... 

Marks TJ, Yang W, Stern CL (1991) Models for organometallic molecule-support complexes. Very large counterion modulation of cationic actinide alkyl reactivity. Organometallics 10 840-842... 

The site of reaction on an unsaturated organometallic molecule is not restricted to the most probable position of the metallic atom or cation or to a position corresponding to any one resonance structure of the anion. This has been discussed in a previous section with reference to the special case of reaction with a proton. Although the multiple reactivity is particularly noticeable in the case of derivatives of carbonyl compounds, it is not entirely lacking even in the case of the derivatives of unsaturated hydrocarbons. Triphenylmethyl sodium reacts with triphenylsilyl chloride to give not only the substance related to hexaphenylethane but also a substance related to Chichi-babin s hydrocarbon.401 It will be recalled that both the triphenyl-carbonium ion and triphenylmethyl radical did the same sort of thing. 

It is a useful notion to consider that the reaction of a molecular solid, whether formed of organic, organometallic molecules or coordination compounds, with a vapour is conceptually related to the supramolecular reaction of a crystalline material with a volatile solvent to form a new crystalline solid (Fig. 18). Indeed, the two processes, solid-gas reaction and solid-gas solvation, differ only in the... 

We have attempted to collect in appendix B a list of the most used thermochemical databases. Each one has been built with a particular class of substances and a specific set of properties in mind. We can find compilations of thermochemical values for gas-phase ions, for condensed and gas-phase pure organic compounds, for organometallic molecules, for gas-phase organic free radicals, for inorganic substances, and so on. Most are available in printed form, some are distributed in a software package, and a few can be used online, through the World Wide Web. 

As shown in Figure 5.3, chemicals, such as iron, can be present in a rariety of species and phases that span a large size spectrum. The dissolved fraction can include inorganic complexes, organometallic molecules, and the uncomplexed ions. In the case of iron, two oxidation states are possible, so the free ion can be in the form of Fe (aq) or Fe " (aq). In the colloidal and particulate phases, iron can be present as part of a mineral (inorganic) or an organic molecule. Within the particulate phase, a distinction is often made between the fraction that is adsorbed, usually electrostatically as an ion, onto the surface and the fraction that is covalently bound into the crystal lattice. 

In the studies on detecting intermediates many of the structural conclusions drawn were based on our (often empirical) understanding of chemical shifts and spin-spin interactions. In the following two sections we show a selection of these in connection with (mostly) catalytically relevant organometallic molecules. 

Keywords Solid-state reaction Crystal engineering Organometallic molecule ... 

This chapter will deal with both types of processes, namely reactions between solids and reactions between solids and gases. In the first section we will discuss examples of gas-solid reactions between molecular solids (operatively taken as crystals formed by neutral molecules or molecular ions) and vapours of small molecules, while the second section will deal with solid-solid reactions between molecular crystals to yield co-crystals. Even though examples will come mainly from our own work with organometallic molecules, coverage of the work of many scientists in the field will be attempted. The reader should be warned, however, that this chapter has no review-type ambitions. 

---