Abstract
Abstract The copper(II) and zinc(II) complexes of 1,19-dideoxy-8,12-dicarbethoxy-1,3,7,13,17,19-hexamethylbiladiene-ac were synthesized and investigated by near-ultraviolet, visible, near-infrared, infrared, NMR, and ESR measurements as well as X-ray diffraction measurements of powdered samples. The ligand-field bands appeared at 701 and 752 mμ for the copper complex provided information on its geometry around the central metal atom. Namely, the copper atom is subjected to the square-planar ligand-field in the complex. Infrared bands characteristic of asymmetric stretching vibration of the carbethoxy groups at 8 and 12, and X-ray powder diffraction pattern gave another support to this structure by referring to the corresponding data for the nickel complex. ESR measurements also provided the spin Hamiltonian parameters consistent with the square-planar coordination. The most plausible structure for the zinc complex was concluded to be the binuclear form with tetrahedral coordination in conformity with that for the cobalt complex, which was revised in this work. Infrared bands in the 1100–1300 cm−1 range due to asymmetric vibration of the ester groups at 8 and 12, and X-ray powder pattern provided the evidence for this structure in reference to the corresponding data for the cobalt complex. The up-field shift of proton signals due to the methyl groups at 1, 7, 13, and 19, the 10-methylene group, and to the ethyl moiety of carbethoxy groups at 8 and 12 upon coordination are consistent with the tetrahedral coordination with dimeric structure. The molecular weight determination also confirmed the dimeric nature of the zinc complex.
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