John R. Wasson

Stereoelectronic properties of metalloenzymes—III: A soluble tetrahedral coordination complex of copper(II)—dichloro(sparteine)copper(II)

Abstract Electron spin resonance and optical solution studies of copper(II) complexes of l -sparteine confirm the rare pseudotetrahedral coordination geometry of copper in solution . Crystal field calculations suggest that only the optical transition near 12·0 kK is due to a “ d − d ” transition. Comparisons to the known optical spectra of Type I copper(II) in metalloenzymes suggest the band near 16·0 kK of Type I copper(II) may be due to a forbidden CuS change transfer band.

Complexes with sulfur and selenium donors—X chromium(III) piperidyldithiocarbamates☆

Abstract I.r. (4000-200 cm −1 ), electronic and ESR spectroscopy have been used to characterize tris-(piperidyldithiocarbamoto)chromium(III) chelates. The properties of the complexes were compared to those of the corresponding diethyl derivative. The compounds have g-values of about 1·98 and the zero-field splitting parameters are small. The effective spin-orbit coupling constants for Cr(III), oscillator strengths of electronic transitions, and nephelauxetic parameters for the complexes are all indicative of appreciable metal-ligand covalency. The slightly different properties of the 2-methylpiperidyldithiocarbamate complex have been attributed to the steric requirements of the 2-methyl substituent.

ESR studies of alkylamine complexes of copper(II) imides: the CuN42− chromophore

Abstract The ESR spectra of a number of [Cu(Im) 2 (RNH 2 ) 2 ] (Im = succinimidate, phthalimidate; RNH 2 = alkylamine) complexes have been examined. The ESR data support the essentially square planar geometries proposed for the compounds on the basis of other spectroscopic data. Covalency parameters evaluated from ESR data indicate that the unpaired electron spends only roughly 80 per cent of its time on the central copper ion. Covalency parameters for various CuN 4 complexes are shown to be more indicative of geometry than the degree of metal-ligand covalency. Limitations of ESR studies of Cu(II)-doped biological systems are discussed and an explanation based on the second-order perturbation approach to chemical bonding proposed.

Copper(II) complexes with antipyrine, diantipyrylmethane and diantipyrylpropylmethane

Abstract The pentakis complex of copper(II) perchlorate with antipyrine(apy) and the bis complexes with diantipyrylmethane(dapy) and diantipyrylpropylmethane(dapyp) have been prepared and characterized. Electronic spectral and ESR data for the distortion isomers of Cu(dapy)2(ClO4)2 show that the red form is more tetrahedral than the orange isomer and that green Cu(dapyp)22+ complexes are more planar than the dapy compounds. Crystal field calculations and electronic spectral data permit a gross estimate of the geometries of dapy and dapyp complexes. The g‖ values for the complexes, which indicate very little metal-ligand covalency, are among the highest ever reported for Cu(II) complexes.

Single-crystal ESR spectra of tris(octamethylpyrophosphoramide) manganese (II) perchlorate

Abstract The ESR spectra of manganese(II)-doped single crystals of tris(octamethylpyrophosphoramide) zinc(II) perchlorate have been examined. The magnitude of the manganese nuclear hyperfine splitting parameter (≈99.7×10−4 cm−1 shows that this is one of the most ionic compounds ever investigated.

Solvent effects on the electronic and electron spin resonance spectra of vanadyl(IV) β-diketonates

Abstract Solvent effects on the isotropic electron spin resonance (ESR) and electronic spectra of oxobis(2,4-pentanedionato)vanadium(IV), oxobisbenzoylacetonato)vanadium(IV) and oxobis(dibenzoylmethanato)-vanadium(IV) have been described. Linewidths and intensities of solution ESR spectra, intensities of electronic absorption bands and solid state ESR spectra of a variety of oxovanadium(IV) complexes doped into 4-phenylpyridine are also reported. An explicit crystal field treatment of oxovanadium(IV) chelates possessing effective C2ν symmetry is also given. Various spectra-solvent parameter and spectra-structure correlations are discussed. The ESR spectra of oxovanadium(IV) chelates doped into 4-phenylpyridine give no indication of cis-addition of 4-phenylpyridine as found for the pure 1:1 adduct of 4-phenylpyridine with oxobis(2,4-pentanedionato)vanadium(IV).

Complexes with sulfur and selenium donors-III: Proton nuclear magnetic resonance study of the morpholine adducts of bis(0,0′-dialkyldithiophosphato)nickel(II) complexes

Abstract Electronic and proton nuclear magnetic resonance spectra have been employed to elucidate the nature of the adducts formed by morpholine with a number of bis(0,0′-dialkyldithiophosphato)nickel(II) complexes, Ni(S 2 P( OR ) 2 ) 2 ( R = ethyl, n -propyl, iso propyl, iso butyl, sec -butyl, cyclo hexyl, and 2-phenylethyl). Upfield NMR contact shifts of the -NH- proton were used to assign metal-nitrogen coordination by morpholine. The morpholine adducts exhibit properties consistent with a 5-coordinate (∼C 4 v ) geometry. NMR contact shifts and electron spin-nuclear spin coupling constants are tabulated and electron delocalization mechanisms are discussed.

Pseudotetrahedral transition metal complexes—C2ν d1 compounds

Abstract Phenomenological crystal field and semi-empirical molecular orbital calculations have been performed for the hypothetical pseudotetrahedral (C2ν) VF2Cl2 molecule in order to provide a discussion of the energy levels and properties of low-symmetry complexes of this type. Explicit expressions for the crystal field energy levels have been given and the one-electron levels have been found to appear in the order dz2

Allowed and forbidden transitions in the ESR spectra of manganese(II)-doped tris(octamethylpyrophosphoramide)magnesium(II) perchlorate

The ESR spectra of Mn(OMPA)3(ClO4)2 (OMPA = octamethylpyrophosphoramide) doped into the corresponding magnesium host lattice is reported. The electron spin-nuclear spin hyperfine coupling constant (106 gauss) is indicative of the highly ionic character of the manganese-oxygen bonding. The spectra were interpreted using an axially symmetric spin- Hamiltonian for an S= 52 spin state. The zero-field splitting is predominantly due to interaction of Mn(II) with the trigonal crystalline field. The magnitude and signs of the zero-field splitting parameters D and (a − F) were determined: D = 157 gauss, (a − F) = +9 gauss (g = 2.011). A nuclear quadrupole coupling constant of 0.154 gauss results from an analysis of the forbidden ESR lines.

Dipolar broadening of electron spin resonance lines of free radicals: Spin-trapping studies of free radicals in cigarette smoke

Abstract Electron spin resonance spectra of spin-trapped free radicals from tobacco smoke have been examined. The cigarettes studied were standard IRI research cigarettes supplied by the University of Kentucky Tobacco and Health Research Institute. Substantial changes in the spectra were observed upon aging of the samples. Aging for several days resulted in at least two remaining long-lived spin-adducts. For the experimental configuration employed the efficiency of the spin-trapping apparatus was determined to be about 47%. Utilizing measurement of the broadening of the magnetic resonance lines as function of the amount of smoke passed through the phenyl-t-butyl nitrone spin-trapping solution, a concentration of about 1 × 1018 free radicals per cigarette puff was deduced. The method employed in this determination was tested with a number of stable free radicals in several solvents.