Crystal Structures of Mixed Ligand Copper(II) Complexes Containing l-Amino Acids. I. l-Asparaginato-l-histidinato-copper(II) and Its Hydrate

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Abstract
Two copper complexes containing l-histidine and l-asparagine crystallize from aqueous solution at pH 7.0. Both crystals are monoclinic, space group P21. l-Asparaginato-l-histidinatocopper(II): a=10.913(3), b=12.911(4), c=10.206(3) Å, β=113.83(2)°, Z=4. l-Asparaginato-l-histidinatoaquacopper(II) trihydrate: a=12.654(4), b=11.623(4), c=5.931(2) Å, β=100.47(3)°, Z=2. In both structures, four coordinating atoms in an approximately planar arrangement around copper are the α-amino and imidazole δ-nitrogen atoms of l-histidine and α-amino nitrogen and α-carboxyl oxygen of l-asparagine. The fifth coordination site is occupied by the α-carboxyl oxygen of l-histidine. Difference between the two complex crystals is found at the sixth coordination site; a water molecule is coordinated in the hydrated crystal to complete a distorted octahedral environment, while in the anhydrous crystal this site is unoccupied so that the geometry of the complex is square-pyramidal.

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