The speciation of aluminum in aqueous solutions of aluminum carboxylates. Part I. X-ray molecular structure of Al[OC(O)CH(OH)CH3]3

Abstract The crystal structure of tris(2-hydroxypropanoate-(L))aluminum(III) was determined by X-ray crystallography and refined to R =0.044. The molecular structure is uncomplicated and contains monomeric [Al(lact) 3 ]entities, in which the metal atom is surrounded by a distorted octahedral {O 6 } coordination sphere where the oxygen atoms of the carboxylate and of the hydroxyl group are the donating sites. The major source of the geometrical distortion is in the OAlO angles of the metallo-organic ring ( c 83°. The AlO distances range from 1.86 to 1.91 A. All hydroxyl hydrogen atoms are involved in very tight intermolecular hydrogen bonds ( c . 2.50 A) which involve the carbonyl groups of adjacent Al(lact) 3 unities. The solid state IR spectrum of Al(lact) 3 is interpreted in terms of monohapto ‘end on’ coordination of the carboxylate donating site to Al III .