Showing papers by "Oscar E. Piro published in 1989"

Molecular structure of bis(L-leucinato)zinc(II) and single-crystal EPR spectra of the substitutionally copper(II)-63-doped complex

Abstract: The title compound, Zn(H{sub 2}NCHCO{sub 2}CH{sub 2}CH(CH{sub 3}){sub 2}){sub 2} (abbreviated as Zn(L-Leu){sub 2}), crystallizes in the monoclinic system, space group P2{sub 1}, with a = 9.584 (4) {angstrom}, b = 5.389 (2) {angstrom}, c = 14.866 (3) {angstrom}, {beta} = 106.84 (3){degree}, and Z = 2. The two L-leucine molecules per formula unit act as bidentate ligands of the Zn(II) ion, forming a N{sub 2}O{sub 2} squashed tetrahedral configuration. The carboxyl oxygen of a third amino acid molecule completes a pentagonal coordination around Zn(II). The crystal structure of Zn(L-Leu){sub 2} was compared to the quasi-isomorphous structure of the Cu(L-Leu){sub 2} complex. Room-temperature EPR data of substitutional {sup 63}Cu(II) impurities in single crystals of Zn(L-Leu){sub 2} were taken at 34 GHz. The EPR results are discussed in terms of the structure of Zn(L-Leu){sub 2} and compared with EPR data in the structurally related Cu(L-Leu){sub 2} complex. Lattice distortions at the impurity sites of Zn(L-Leu){sub 2} are detected and discussed. 29 refs., 6 figs., 5 tabs.

Structures of the potassium nitroprusside 2•5 and 0•8 hydrates

Abstract: Potassium pentacyanonitrosylferrate hydrate (1/2.5), K2[Fe(CN)sNO].2.5H20, M r = 339.18, monoclinic, P21/n (No. 14), a=10 .054 (4 ) , b-24.510(5), c = 1 1 . 0 1 8 ( 6 ) A , f l=109 .60(4) ° , V = 2558 (3) A 3, Z = 8 , D m=1.75, D _ = l . 7 6 2 g c m -3, Mo K0t radiation, 2 = 0.71073/~, g(Mo Ktx) = 18 cm -~, F(000)= 1352. Potassium pentacyanonitrosylferrate hydrate (1/0.8), Kz[Fe(CN)sNO].0.8H20 , Mr=311.98, orthorhombic, Pna21 (No. 33), a 30.000(8), b=11 .272(3) , c = 1 6 . 0 5 3 ( 4 ) A , V = 5428 (2) A 3, Z = 20, D x -1.909 g cm -3, Mo Ktx radiation, 2=0 .71073 A, g(MoKc0 = 21 cm -l, F(000) = 3108. Both structures were solved by the heavy-atom technique and refined anisotropically to R factors 0.040 and 0.059, from 2805 and 3436 I > 30(/) independent reflections, respectively. In both structures the water molecules are not involved in strong hydrogen bonds. The low specificity of these interactions is probably responsible for the occurrence of the three different hydrates reported [Amalvy, Varetti, Aymonino, Castellano, Piro & Punte (1986). J. Crystallogr. Spectrosc. Res. 16, 537-555]. Hydrate Crystal shape Crystal size (mm) 0-15 x 0.35 x 0.55 Scan technique to-20 Scanning speed range 6.7-20 (o rain -~) No. of centered reflections 25 0 range of centered 8-24 reflections (o) Orange for data collection (°) 0-24 hklranges -11 <_h < I0 0_

Attenuated total reflectance infrared spectra of strongly absorbing anisotropic crystals: orthorhombic Na2[Fe(CN)5NO]•2H2O

Abstract: Attenuated total reflectance (ATR) from principal faces of orthorhombic (and higher symmetry) crystals in spectral regions including strongly polar optic modes is considered. A detailed, quantitative comparison between experimental and calculated ATR infrared (IR) spectra of orthorhombic sodium nitroprusside dihydrate (SNP), Na2[Fe(CN)5NO]⋅2H2O, single crystals in the 500–3800 cm−1 region is presented. Calculated ATR spectra are generated employing the dielectric tensor of SNP obtained from Kramers–Kronig analysis of external reflectance data. The dependence of intensities, profiles, and locations of bands in the spectra upon the relative refractive index of the sample against the ATR prism and the polarization state of the reflected IR beam will be discussed. Both theoretical and experimental evidence of the coupling of the TM‐polarized evanescent wave with strong in‐plane‐polarized optic modes at about their LO frequencies will be given with reference to the case of the strong NO stretching mode of SNP....