COORDINATION CHEMISTRY OF NEW SULFUR-CONTAINING LIGANDS .17. PREPARATION, CHARACTERIZATION, AND CRYSTAL AND MOLECULAR-STRUCTURE OF [N,N'-TRIMETHYLENEBIS(METHYL 2-AMINO-1-CYCLOPENTENEDITHIOCARBOXYLATO)]COPPER(II), A HIGHLY DISTORTED CUN2S2 COMPOUND

The copper(II) complex of the N2S2 tetradentate ligand N, N‘-trimethylenebis(methyl 2-amino-1 -cyclopentenedithiocarboxylate) was prepared by reaction of the neutral ligand with an equivalent amount of copper acetate in methanol. A low-energy, broad, and asymmetric absorption band at 10.5 cm-1 in the electronic spectrum, coupled with the observed electron spin resonance parameters A|| = 160 G, g|| = 2.132, A0 = 67.9 G, g0 = 2.060), suggests a copper(II) coordination site intermediate between planar and pseudotetrahedral geometry. Since the recent structural results of the type I copper(II)-containing metalloenzyme plastocyanim indicates a distorted N2S2 coordination,21 the further structural study of this compound is warranted. The crystal and molecular structure of the title compound was solved at 24 ± 1 °C by a single-crystal X-ray diffraction study. The complex crystallizes in the centrosymmetric monoclinic space C2/c with a = 16.7219 (17) Å, b = 8.4009 (7) Å, c = 14.5507 (16) Å, β = 108.337 (8)°, V= 1940.3 Å3, p(obsd) 1.54 g cm-3, and p(calcd) = 1.53 g cm-3 for mol wt 448.2 and Z = 4. Diffraction data were collected with a Syntex P21 automated diffractometer using graphite-monochromatized Mo K α radiation. The copper and two sulfur atoms were located in a Patterson synthesis; all other nonhydrogen atoms were located via difference Fourier techniques, and hydrogen atoms were placed in calculated positions. Final refinement resulted in discrepancy indices of RF = 4.31% and RwF = 4.42% for all 1273 symmetry-independent reflections with 4° ≤ 2θ ° 45° (none rejected). The molecules are monomelic, are well separated, and lie on a C2 axis. The copper-sulfur distance is 2.2225 (11) Å and the copper-nitrogen distance is 1.9498 (30) Å. Bond distances in the five-membered chelate ring indicate that a great deal of π derealization exists. The plane defined by the copper and two ligand sulfur atoms intersects the plane defined by the copper and two nitrogen atoms, forming a dihedral angle of 53° (90° would be ideal for a C2v inner coordination sphere geometry while 0° would be ideal for planar geometry) indicating the extent of distortion in the inner coordination sphere. The spectral properties of the copper(II) atom are discussed in terms of the geometry and the ligand atom type. © 1979, American Chemical Society. All rights reserved.