Kazunori Sakata

Transition-metal complexes of pyrrole pigments. I. Electronic and vibrational spectra of cobalt(II), nickel(II) and copper(II) complexes of some dipyrromethenes

The cobalt, nickel(II), and copper(II) complexes of 3,4,5-trimethyl-, 3,3′,5,5′-tetramethyl- and 3,3′,4,4′,5,5′-hexamethyldipyrromethene have been synthesized in this work and investigated by visible, near-infrared, infrared and far-infrared spectroscopy. The ligand-field bands for these metal complexes have provided valuable information on their geometry around the central metal atoms. Namely, the copper complexes assume the tetragonally distorted tetrahedral configuration while the nickel and cobalt complexes are approximately regular tetrahedral. Moreover, the removal of the 5′-methyl group of a dipyrromethene moiety in the copper complexes results in a significant structural alteration to the further flattened tetrahedron. In the far-infrared spectra, the prominent absorption peaks which can be associated with the metal-ligand stretching modes have been observed in the 400–350 cm−1 range. In addition, strong bands appearing at ∼1600 cm−1 have been assigned to the pyrroles-skeletal stretching mode. After examination of these infrared spectral data, the strength of the coordinate bonds has been noticed to increase in the order: Cu<Ni≳Co. The lowered strength of coordinate bonds for the copper complexes and the nature of coordinate bonds involved in the metal complexes of this work were discussed in connection with their stereochemistry.

Transition-metal complexes of pyrrole pigments. Part VI. Some bivalent metal complexes of 3,3′,4,4′-tetrachloro-5,5′-diethoxycarbonyldipyrromethene

The cobalt(II), nickel(II), copper(II), and zinc(II) complexes of 3,3′,4,4′-tetrachloro-5,5′-diethoxycarbonyldipyrro-methene were investigated by means of electronic, vibrational, and e.s.r. spectroscopy as well as X-ray diffraction measurements of powdered samples. I.r. and visible spectral data proved the distorted tetrahedral co-ordination of M–N4 type for the cobalt(II) and zinc(II) complexes. The nickel(II) and copper(II) complexes showed two kinds of carbonyl bands in their i.r. spectra, and the d→d transition bands were consistent with the distorted octahedral (C2) co-ordination. E.s.r. spectra of the copper complex were characteristic of rhombic co-ordination, showing g1≃g2 > g3 and A3 > A2≃A1. Both nickel and copper complexes consequently possess a distorted octahedral configuration of M–N4O2 type around the central metal atoms. The characteristic features of X-ray diffraction patterns for the four metal complexes were consistent with these structural assignments.

SYNTHESIS AND STRUCTURE OF NOVEL 1,8-BRIDGED FLUORENOPHANES

A novel 1,8-bridged fluorenophane (4a) is found to assume an

Transition metal complexes of pyrrole pigments. IV. Electronic and vibrational spectra of cobalt(II), nickel(II), and copper(II) complexes of some substituted dipyrromethenes

lsquoinward-folded’ conformation with the bulky tert-butyl group located in the cavity, a situation which is different from the conformation of the corresponding dithiafluorenophane (3a).