text: Mixing simple metal salts with solutions of amino acids near neutral or elevated pH often affords bis- or tris complexes.  For metal ions that prefer octahedral coordination, these complexes often adopt the stoichiometry M(aa) (aa = amino carboxylate, such as glycinate, HNCHCO).
  Complexes of the 3:1 stoichiometry have the formula is [M(OCC(R)HNH)].  Such complexes adopt octahedral coordination geometry. These complexes can exist in facial and meridional isomers, both of which are chiral.  The stereochemical possibilities increase when the amino acid ligands are not homochiral. Both the violet meridional and red-pink facial isomers of tris(glycinato)cobalt(III) have been characterized  With L-alanine, L-leucine, and other amino acids, one obtains four stereoisomers.  With cysteine, the amino acid binds through N and thiolate.
  Complexes with the 2:1 stoichiometry are illustrated by copper(II) glycinate [Cu(OCC(R)HNH)], which exists both in anhydrous and pentacoordinate geometries.  When the metal is square planar, these complexes can exist as cis and trans isomers.  The stereochemical possibilities increase when the amino acid ligands are not homochiral. Homoleptic complexes are also known where the amino carboxylate is tridentate amino acids.  One such complex is Ni(κ-histidinate).