Co-ordination behaviour of N-protected aspartic acid in binary and ternary copper(II) complexes. Crystal and molecular structure of [N-acetyl-L-aspartato(2–)-o]bis(2,2′-bipyridine)copper(II)-ethanol tetrahydrate

Abstract

The complexes [Cu(bipy)₂(acaspOO′)]·EtOH·4H₂O(1), [Cu(bipy)₂(bzaspOO′)]·2H₂O (2) and [Cu(bipy)₂(bzloaspOO′)]·EtOH·H₂O (3)[bipy = 2,2′-bipyridine, acaspOO′=N-acetyl-L-aspartate (2–), bzaspOO′=N-benzoyl-L-aspartate (2–), and bzloaspOO′=N-benzyloxycarbonyl-L-aspartate (2–)] were synthesized. The crystal and molecular structure of (1) has been determined by X-ray diffraction. The compound crystallises in the space group P, with a= 12.947(4), b= 12.462(4), c= 11.152(3)Å, α= 115.44(6), β= 106.53(5), γ= 74.32(5)°, and Z= 2. The structure involves monomeric [Cu(bipy)₂(acaspOO′)] units with the copper atom in a basically trigonal bipyramidal stereochemistry. The in-plane co-ordination is form a nitrogen atom of each bipy ligand and a β-carboxylate oxygen of the aspartate anion. Two nitrogen atoms, one from each bipy molecule, are the axial donors. The distortion is toward square-pyramidal stereochemistry with the oxygen atom at the apex. The second oxygen of the β-carboxylate group is at a distance of 2.875(8)Å from copper to give a 4 + 1 + 1* type co-ordination. The crystal packing is determined by hydrogen bonds between water molecules, α-carboxylate and acetyl groups, and ethanol molecules. The stack between symmetry related (and hence parallel) bipy moieties involves interatomic distances of 3.47 and 3.45 Å, respectively. Spectroscopic results suggest that the metal co-ordination geometry is the same in all the complexes.