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Donor-Acceptor Properties of N- and 0-Donor Ligands in Cu₄OX₆L₄ Complexes as Indicated by Infrared Spectra

G. Ondrejovič and A. Kotočová

Department of Inorganic Chemistry, Faculty of Chemical Technology, Slovak University of Technology, SK-812 37 Bratislava

E-mail: ondrejov@chtf.stuba.sk

Abstract: Donor-acceptor properties of ligands L in Cu₄OX₆L₄ complexes were deduced from experimental Mulliken electronegativity parameters a_L and b_L and partial charges estimated by the electronegativity equalization method. Four groups of ligands L were examined, a) N-donor ligands with saturated ring: pyrrolidine (pyr), N-cyanopyrrolidine (cnpyr), piperidine (pi), N-cyanopiperidine (cnpi), morpholine (mor), quinuclidine (qu), and 3-quinuclidinone (3-quin); b) N-donor ligands with pyridine ring: pyridine (py), 3-methylpyridine (3-mepy), 4-methylpyridine (4-mepy), 3-hydroxymethylpyridine (3-hmpy), 4-hydroxymethylpyridine (4-hmpy), quinoline (quinol), isoquinoline(iquinol), and pyrazine (pyz); c) N-donor ligands with imidazole ring: imidazole (im), 1-methylimidazole (1-meim), 1-ethylimidazole (1-etim), and benzimidazole (bzim); d) acyclic N- or O-donor ligands: NH₃, 1,3-diisopropylcarbodiimide (cd), dimethylformamide (dmf), dimethyl sulfoxide (dmso), and triphenylphosphine oxide (OPPh₃). Calculated partial charges on the ligands L indicate that 3-mepy, quinol, iquinol, 1-meim, 1-etim, and bzim are stronger electron acceptors than electron donors and 4-hmpy, 3-hmpy, pyz, py, 4-mepy, im, cd, dmf, dmso, and OPPh₃ are stronger electron donors than electron acceptors. The partial charges calculated for pyr, pi, mor, cnpi, qu, cnpyr, 3-quin, and NH₃ indicate the donor properties of these ligands. The ligands in the individual groups were ordered according to the electronegativity parameter b_L as follows: a) b_L(pyr) > b_L(pi) > b_L(m or) > b_L(cnpi) > b_L(qu) > b_L(cnpyr), b_L(3-quin)-, b) b_L(iquinol)≫ b_L(quinol) >b_L(3-mepy) > b_L(4-hmpy), b_L(3-hmpy) > b_L(pyz) > b_L(py) >b_L(4-mepy); c) b_L(1-meim) > b_L(bzim) > b_L(1-etim) ≫ b_L(im); d) bb_L(NH₃) > b_L(dmf) > b_L(dmso) > b_L(OPPh₃) > b_L(cd). The ligands with high b(L) values are hard, especially 1-meim and iquinol. NH₃, dmf, dmso, and OPPh₃ are classified as rather hard ligands. However, py, im, cnpyr, 3-quin, and especially 4-mepy are significantly soft ligands.

Full paper in Portable Document Format: 554a221.pdf

Chemical Papers 55 (4) 221–228 (2001)