Transition metal carboxylate complex
Transition metal carboxylate complexes are coordination complexes with carboxylate (RCO) ligands. Reflecting the diversity of carboxylic acids, the inventory of metal carboxylates is large. Many are useful commercially, and many have attracted intense scholarly scrutiny. Carboxylates exhibit a variety of coordination modes, most common are κ- (O-monodentate), κ (O,O-bidentate), and bridging. Acetate and related monocarboxylates. Structure and bonding. Carboxylates bind to single metals by one or both oxygen atoms, κ- and κ-. In terms of electron counting, κ- and κ- are "X", a pseudohalide, and "L-X ligands", i.e. a combination of a  Lewis base (L) and a pseudohalide (X). Carboxylates are classified as hard ligands, in HSAB theory. For simple carboxylates, the acetate complexes are illustrative. Most transition metal acetates are mixed ligand complexes. One common example is hydrated nickel acetate, Ni(OCCH)(HO), which features intramolecular hydrogen-bonding between the uncoordinated oxygens and the protons of aquo ligands. Stoichiometrically simple complexes are often multimetallic. One family are the basic metal acetates, of the stoichiometry [MO(OAc)(HO)]. Anhydrous or nearly anhydrous acetates often are coordination polymers. Some however adopt the Chinese lantern structure . Well studied examples include the dimetal tetraacetates (M(OAc)) where M = Cu(II ), Rh(II), Cr(II), and Mo(II). Platinum(II) acetate|Platinum diacetate and Palladium(II) acetate|palladium diacetate feature Pt and Pd cores, further illustrating the tendency of acetate ligands to stabilize multimetallic structures. File:Co(OAc)2(H2O).svg|thumb|right|Segment of the Co(OAc)(HO) chain, illustrating two modes for bridging carboxylate ligands. Reactions and applications. Metal acetates are common catalyst s or precatalysts. Particularly useful are the lipophlic complexes of ethylhexanoate s. Di- and polycarboxylates. Benzenedi- and tricarboxylates. Metal organic framework s, porous, three-dimensional coordination polymers, are often derived from metal carboxylate clusters. These clusters, called secondary bonding units (SBU's), are often linked by the conjugate bases of benzenedi- and  tricarboxylic acids. Aminopolycarboxylates. A commercially important family of metal carboxylates are derived from aminopolycarboxylate s, e.g., EDTA . Related to these synthetic chelating agents are the amino acid s, which form large families of amino acid complex es. Two amino acids, glutamate and aspartate, have carboxylate side chains, which function as ligands for iron in nonheme iron proteins, such as hemerythrin . References. Category:Ligands Category:Coordination chemistry Category:Salts of carboxylic acids