ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

Structural and electronic effects involving pyridine rings in 4-methylpyridine Cu₄OX₆L₄ complexes. I. Vibrational spectra of Cu₄OBr _n Cl_{(6− n )}(4-Mepy)₄ complex

Gregor Ondrejovič, Marian Koman, and Adela Kotočová

Department of Inorganic Chemistry, Institute of Inorganic Chemistry, Technology and Materials, Faculty of Chemical and Food Technology, Slovak University of Technology, Radlinského 9, 812 37 Bratislava, Slovakia

E-mail: gregor.ondrejovic@stuba.sk

Received: 5 December 2007  Revised: 13 February 2008  Accepted: 22 February 2008

Abstract: Gaussian analysis of bands between 500 cm⁻¹ and 600 cm⁻¹ attributed to the ~u as (Cu₄O) stretching vibration of the tetrahedral Cu₄O core in Cu₄OBr _n Cl_(6−n)(4-Mepy)₄ (n = 0–6) complexes showed two bands, symmetry reduction of the T ₂ mode of vibration towards the A ₁ and E modes and vibrational coupling with an R-sensitive in-plane pyridine ring bending. The Cu-O bond is considered as vibrationally coupled with the Cu-N bond and the pyridine ring through the donor-acceptor vibrational coupling and the corresponding equilibrium charge distribution. The linear correlation between ~u as (Cu₄O) and the number of bromides in Cu₄OBr _n Cl_(6−n)(4-Mepy)₄ complexes was used for the estimation of partial charges on the 4-Mepy ligands which were positive for the prevailing donors and negative for the prevailing acceptors thus evoking a π-back bonding between the Cu(II) atoms and the 4-Mepy ligands. Correlations involving selected bond lengths and bond angles in the molecular structure of the Cu₄OCl₆(4-Mepy)₄ complex with four symmetrically independent molecules present in the unit cell indicate a symmetry reduction of the T ₂ mode of vibration and the π-back bonding between the Cu(II) atoms and the 4-Mepy ligands.

Keywords: tetranuclear copper(II) complexes - donor-acceptor vibrational coupling - symmetry reduction -  π-back bonding

Full paper is available at www.springerlink.com.

DOI: 10.2478/s11696-008-0055-6

Chemical Papers 62 (5) 480–486 (2008)