Spectroscopic and structural investigation of two (2,2′-bipyridyl)bis(N-protected-aminoacidato)copper(II) complexes, two compounds containing truly CuN 2O 2 chromophore

Abstract

The compounds of formula [Cu(bipy)(acleuO) 2] (1) and [Cu(bipy)(ts-β-alaO) 2] (2) (bipy = 2,2′-bipyridil, acleuO = N-acetyl-DL-leucinate anion, ts-β-alaO = N-tosyl-β-alaninate anion) were synthesized and characterized by means of spectroscopic and structural measurements. Complex (1) crystallizes in the monoclinic space group C2/c with cell parameters a = 17.465(4), b = 19.740(5), c = 9.080(2) Å, β = 115.0(1)° with Z = 4; complex (2) crystallizes in the triclinic space group P 1 , with cell parameters a = 14.489(3), b = 14.308(3), c = 8.659(1) Å, α = 75.0(1), β = 74.6(1), γ = 66.6(1)°, Z = 2. Both structures were solved by conventional Patterson and Fourier methods and refined to R factors of 4.10 and 3.8% respectively. In both crystals the Cu atom is four-coordinated by the nitrogen atoms of a bipy molecule and two carboxylate oxygens of two N-protected aminoacid anions acting as unidentate ligands. The only significant difference between the coordination geometry of (1) and (2) is in the tetrahedral distortion of the coordination plane. Complex (2) is strictly planar, while in complex (1) the distortion expressed by the dihedral angle between the (N)(1)CuN(1′) and O(1)CuO(1′) planes is 20.8°. The electronic and EPR results agree with these different coordination geometries. The infra-red data are consistent with a truly monodentate carboxylate group. The spectroscopic results on a series of previously investigated [Cu(bipy)(N-protected aminoacidato) 2] complexes of unknown structures are discussed again in the light of the present structural reports.