Spectroscopic studies upon some transition-metal complexes

• Main Author: Guzy, Christopher M.
• Published: University of Leicester 1968
• Subjects: 540
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.673936

Isotopically pure 63copper phthalocyanine diluted in the metal-free phthalocyanine host lattice yields a high resolution e.s.r. spectrum of far greater complexity than obtained by previous workers. Since the local symmetry of the copper-nitrogen bond is perpendicular to the molecular symmetry axis, the s.h.f.s. around g, exhibits a linewidth occurrence of the pyrrole nitrogen atoms; this was analysed to yield an accurate anisotropic ligand tensor from which the ligand hybridisation was found to be sp2. A detailed analysis of the e.s.r. data yielded B12 = 0.74, B22 = 1, E2 0.6. A theoretical line shape analysis of spectra containing common copper points to considerable errors in most of the published work on copper complexes. Other phthalocyanines investigated were the species formed when chromium, iron, nickel, copper and metal-free phthalocyanines are reduced by sodium in tetrahydrofuran and hexamethylphosphoramide. Hyperfine structure attributable to the interaction of a single unpaired electron with four equivalent nitrogen nuclei was observed in reduced iron phthalocyanine; in reduced chromium phthalocyanine both chromium and nitrogen h.f.s. were observed. The results of the investigation are compared with those for related systems and are systematised in terms of a general energy level scheme. A general study of vanadyl complexes showed that good correlations can be drawn between e.s.r. and optical parameters and the total covalency of the complex, rather than merely upon the covalency of the orbital containing the unpaired electron. The methods are extrapolated to study the nature of the major interactions occurring between certain transition-metal complexes and a wide variety of pure solvents, rationalised mainly in terms of solvent-induced perturbations upon the spectral properties of the complex. In vanadyl bisacetylacetonate the principle solvent interactions are found to be axial sigma (rather than pi) bonding between the negative charge centre of the solvent dipole and the vanadium atom, and hydrogen-bonding between the solvent positive charge centre and the pi clouds localised around the vanadyl oxygen atom. For iron (I) bisdiethyldithiocarbamate nitrosyl the nitrosyl group and the antibonding |A,g* electron cause axial solvation to the iron atom to be energetically unfavourable; the negative solvent charge centre interacts with the nitrosyl pi level in the vicinity of the nitrosyl nitrogen atom, and hydrogen-bonding to the nitrosyl oxygen atom may also occur. The results of the investigation are discussed in terms of solvent ranking and demonstrate that the concept of Polarity as an independent solvent property fails when applied to these systems.