Metal acetylide
Acetylide refers to chemical compounds with the chemical formulas MC≡CH and MC≡CM, where M is a metal. The term is used loosely and can refer to substituted acetylides have the general structure RC≡CM (where R is an organic side chain). Acetylides are reagents in organic synthesis. The calcium acetylide commonly called calcium carbide is a major compound of commerce.
Alkali metal and alkaline earth metal acetylides of the general formula MC≡CM are salt-like Zintl phase compounds, containing C22− ions. Evidence for this ionic character can be seen in the ready hydrolysis of these compounds to form acetylene and metal oxides, there is also some evidence for the solubility of C22− ions in liquid ammonia. The C22− ion has a closed shell ground state of 1Σg+, making it isoelectronic to a neutral molecule N2, which may afford it some stability.
Analogous acetylides prepared from other metals, particularly transition metals, show covalent character and are invariably associated with their metal centers. This can be seen in their general stability to water (i.e. silver acetylide, copper acetylide) and radically different chemical applications.
Acetylides of the general formula RC≡CM (where R = H or alkyl) generally show similar properties to their doubly substituted analogues. In the absence of additional ligands, metal acetylides adopt polymeric structures wherein the acetylide groups are bridging ligands.
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