Preparation and Spectral Properties of Oxovanadium(IV), Nickel(II), Copper(II), and Palladium(II) Complexes of Tetraaza[14]annulenes

Abstract

Abstract The oxovanadium(IV), nickel(II), copper(II), and palladium(II) complexes of 5,14-dihydrodibenzo[b,i][1,4,8,1l]tetraazacyclotetradecine and 7,8,15,16,17,18-hexahydrodibenzo[b,j][1,4,8,1l]tetraazacyclotetradecine have been synthesized, and studied by electronic, vibrational, NMR, ESR, and ESCA spectroscopy. The absorption bands appearing in the energy region greater than 16800 cm−1 were attributed to π→π* transitions within a ligand molecule and metal to ligand charge-transfer transitions. The ligand-field bands were not assigned for the present complexes, because all the ligand-field bands were obscured by the π→π* and charge-transfer bands of high intensity. The metal complexes assume the square-planar configurations since no significant absorption band was detected in the region below 17000 cm−1. A strong band appearing at ca. 1620 cm−1 was assigned to the C=N stretching mode, and this band was shifted to lower frequency upon metal coordination. A V=O streching band was observed at ca. 950 cm−1 for the oxovanadium complexes. The oxovanadium, nickel, copper, and palladium complexes showed a single nitrogen Is peak by ESCA spectroscopy, whereas the metal-free ligand, 5,14-dihydrodibenzo[b,i][1,4,8,1l]tetraazacyclotetradecine, revealed double nitrogen Is peaks. ESR spectra were measured in xylene–benzene (2: 1 v/v) as well as in the corresponding ligand matrices at room temperature. Judging from g tensors, the copper complexes were confirmed to have D2h coordination symmetry with an unpaired electron in the dxy orbital. On the other hand, vanadium(IV) is in C4v coordination symmetry with an unpaired electron in the dx2−y2.