The factors stabilizing square-planar geometries in -bonding amine adducts: crystal and molecular structure of bis(N-tosyl--alaninato)bis(piperidine)copper(II).

A violet, air-stable, crystalline compound of empirical formula [Cu(Ts-β-ala)2(pipd)2] (Ts=4- toluene sulfonyl group, hereafter abbreviated as tosyl group, Ts-β-ala=N-tosyl-β-alaninate ion, pipd = piperidine) was synthesized and characterized by means of structural and spectroscopic measurements. The crystal structure of the compound was determined from three-dimensional diffractometric data. The crystals are triclinic, space group PView the MathML source, a = 9.305(1), b = 9.637(2), c = 12.727(2) Å, α = 61.50(2), β = 63.26(1), γ = 71.68(1)°, Z = 1. The structure was solved by the heavy atom method and refined through least-squares calculations to R = 0.032 for 2911 observed reflections. The copper atom lies on the symmetry center coordinating two piperidine and two carboxylic oxygens of N-tosyl-β-alanine in a square-planar arrangement. The second carboxylic oxygen is not involved in metal coordination. Electronic data are also discussed in comparison with those of other ternary Cu(II) carboxylate amine complexes.