The crystal structures of two zinc(II) 5,15-dioxo-porphyrins (porphodimethenes) have been determined to investigate the coordination chemistry of porphyrins with interrupted conjuga­ tion system. Both compounds have a five-coordinated zinc center with pyridine as axial ligand and show overall structural parameters very similar to porphyrins. The oxidized meso-posi­ tions are, however, easily id...

We propose and analyze a new tool to help solve sparse linear least-squares problems minx ‖Ax − b‖2. Our method is based on a sparse QR factorization of a low-rank perturbation Ä of A. More precisely, we show that the R factor of Ä is an effective preconditioner for the least-squares problem minx ‖Ax−b‖2, when solved using LSQR. We propose applications for the new technique. When A is rank defi...

A graphemic representation of vowel mutated a is first documented in Middle High German texts. As a consequence of a strict letter-to-letter pronunciation, graphemic <ä> was pronounced as [ɛ(ː)] in Early New High German and was subsequently prescribed in pronunciation dictionaries. Especially the pronunciation of long [ɛː] has become an issue of debate. Many scholars point out that [ɛː] had mer...

The structure of zinc chloride complexes with different ratios of chloride to zinc, formed in concentrated ZnCl2 aqueous solutions, were determined f rom large-angle X-ray scattering using concentrations of the chloride complexes estimated by complementary Raman spectroscopic measurements. The highest chloro complex, [ZnCl4]~, is tetrahedral with a Zn-Cl bond length of 2.294(4) Ä. The trichloro...

The crystal structure of (Ph 3 P) 2 AgOC 6 H 2 Cl 3 (I) is reported along with the syntheses and C1 and 6 Cu NQR spectra of I and several related silver (I) and copper (I) 2,6-diand 2,4,6-trichlorophenolates containing phosphines, phosphites, and pyridine as co-ligands. I crystallizes in space group P2 Jc with a= 16.692(4) Ä, b= 17.942 (4) A, c = 12.857 (3) Ä, /? = 97.60 (1)°, F = 3816.68 Ä, an...

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Alexander V. Sienkiewicz*, Anatoliy A. Kapshuk Department of Chemistry, University of Kiev, 252017 Kiev, Ukraine Z. Naturforsch. 49b, 441-444 (1994); received September 13,1993 X-Ray, Antimony Trichloride-Phosphoryl Isothiocyanate The crystal and molecular structure of the tetrameric complex of the composition [SbCl3-OP(NCS)3]4 synthesized from SbCl3 and OP(NCS)3 in CC14 waso determined by X-ra...