The reaction of copper(II) and 2-hydrazino-2-imidazoline leading to the in situ formation of bisimidazoline (biz). Crystal structure and vibrational spectroscopy of mixed-valence [Cu(biz) 2][Cu 2Br 4] complex

• Published in: Polyhedron Vol. 28; no. 8; pp. 1518 - 1524
• Main Authors: Drożdżewski, Piotr, Kubiak, Maria
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 10.06.2009
• Subjects: 2,2′-Bi-2-imidazoline; Biimidazoline; Bisimidazoline; Copper complex; Crystal structure; DFT calculations; Vibrational spectra; Bisimidazoline; Copper complex; Biimidazoline; 2,2′-Bi-2-imidazoline; Vibrational spectra; DFT calculations; Crystal structure
• ISSN: 0277-5387
• DOI: 10.1016/j.poly.2009.03.003

The “ in situ” oxidation of 2-hydrazino-2-imidazoline leading to the formation of the Cu(II) complex cation with 2,2′-bi-2-imidazoline is reported. The X-ray analysis monitored the [Cu 2Br 4] 2− as the counter ion. The structures and vibrational spectra of both ions have been reproduced in the DFT calculations. The latter theoretical results have been used for the interpretation of the observed IR and Raman spectra. The reaction of Cu(OH) 2 and 2-hydrazino-2-imidazoline hydrobromide surprisingly resulted in complex compound where Cu(II) ions are chelated by a new ligand, namely bisimidazoline (biz). As has been found in the X-ray analysis, the [Cu(biz) 2] 2+ cations are accompanied by [Cu 2Br 4] 2− anions, which makes the whole compound of metal-mixed-valency type. Both ions are centrosymmetric and quasi-planar. The Cu(II) coordination environment is a rectangle with almost equal Cu–N bond lengths (1.984(3), 1.987(3) Å). The electrostatic interaction of both complex ions is strengthened by two strong N–H···Br and four weaker (C–H···Br, C–H···N) hydrogen bonds. The relatively simple IR and Raman spectra were interpreted with help of quantum calculations carried out at the B3LYP/LanL2DZ level. The characterization of computed normal vibrations and correlating observed bands is given in terms of approximate D 2h symmetry. The most intense band resulting from the Cu–N stretching vibration ( B 3u) was located at 342 cm −1, by 63Cu and 65Cu isotope substitution. The chemical reactions leading to the formation of presented compound are also proposed.