Preparation and Spectral Properties of Oxovanadium(IV), Nickel(II), Copper(II), and Palladium(II) Complexes of Tetraazaannulenes

Article abstract of DOI:10.1246/bcsj.53.2262

The oxovanadium(IV), nickel(II), copper(II), and palladium(II) complexes of 5,14-dihydrodibenzo-<1,4,8,11>tetraazacyclotetradecine and 7,8,15,16,17,18-hexahydrodibenzo<1,4,8,11>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 ?-?^* transitions within a ligand molecule and metal to ligand charge-transfer transitions.The ligand-field bands were not assigned for the present complex, because all the ligand-field bands were obscured by the ?->?^* 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 stretching band was observed at ca. 950 cm^-1 for the oxovanadium complexes.The oxovanadium, nickel, copper, and palladium complexes showed a single nitrogen 1s peak by ESCA spectroscopy, whereas the metal-free ligand, 5,14-dihydrodibenzo<1,4,8,11>tetraazacyclotetradecine, revealed double nitrogen 1s 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 D_2b coordination symmetry with an unpaired electron in the d_xy orbital.On the other hand, vanadium(IV) is in C_4v coordination symmetry with an unpaired electron in the d_<*> orbital.