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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



Abstract: Donor-acceptor properties of ligands L in Cu4OX6L4 complexes were deduced from experimental Mulliken electronegativity parameters aL and bL 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 bL as follows: a) bL(pyr) > bL(pi) > bL(m or) > bL(cnpi) > bL(qu) > bL(cnpyr), bL(3-quin)-, b) bL(iquinol)≫ bL(quinol) >bL(3-mepy) > bL(4-hmpy), bL(3-hmpy) > bL(pyz) > bL(py) >bL(4-mepy); c) bL(1-meim) > bL(bzim) > bL(1-etim) ≫ bL(im); d) bbL(NH3) > bL(dmf) > bL(dmso) > bL(OPPh3) > bL(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)

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