Metal-organic compounds, definition

In introductory chemistry courses, much emphasis is necessarily placed on the concept of stoichiometry, that is, the fact that elements combine in certain definite proportions by weight, proportions that reflect their valences and atomic masses. For much of the chemistry of the main group elements and organic compounds, this concept works extremely well, but in transition metal chemistry in particular it is common for ions of more than one oxidation state to form with comparable ease, and sometimes to occur together in the same ionic solid. The presence of more highly oxidized cations... 

Is tetramethyldiarsine an organometallic compound By definition, arsenic is a so-called metalloid or semi-metal , not a metal, and thus organoarsenic compounds like the organic compounds of boron or silicon are not per se organometallics. There is no doubt that the preparation of tetramethyldiarsine and the elucidation of its structure may in retrospect be linked to the development of organometallic chemistry, but it would be far beyond the scope of this book, if the chemistry of the organic compounds of the metalloids in its entirety was discussed. 

A large number of covalently linked systems are currently being synthesized and investigated, differing in the nature of A, B, and L, as well as in the number of functional units in the supramolecular system (nuclearity). It is common to call simple two-component donor-acceptor systems such as that of Eq. 2 dyads , and progressively more complex systems triads , tetrads , pentads , etc.. Systems where all the A and B units are organic molecules are dealt with in Chapter 1 of this section. The present chapter deals with systems where at least one of the A/B functional units is a transition metal coordination compound. From this definition, however, are excluded (a) systems where A and/or B are porphyrins or related species (dealt with in Chapter 2) and (b) systems of high nuclearity with dendritic structures (dealt with in Chapter 9). 

Still one more class of alkyl derivatives should be mentioned in this part of our study. These are compounds of the alkyl radicals with metals, and are known in general as organo-metallic compounds. A large number of metals form compounds of this kind, and the ease of formation seems to have a definite relation to the position of the metal in the periodic system. Compounds of the alkali metals with organic radicals have not been isolated, but they probably exist as intermediate products and also as double compounds with other metallic alkyl compounds. The two groups of these compounds which we shall briefly consider are those of zinc and magnesium. 

The broadest definition of corrosion is the degradation of a material s properties or mass over time because of the effect of the environment. We can think of this in simpler terms by recognizing this process as the tendency for a material to return to its most thermodynamically stable state. For most metallic materials, this means the formation of oxides or sulfides, or other basic metallic compounds generally considered to be ores. For polymeric materials, the end result could be a variety of simple organic compounds. Only in vacuums or under inert atmospheres can corrosion processes be expected to halt entirely. In most cases, these processes are slow enough to afford useful and practical equipment life. 

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