Synthesis and crystal structures of heterobimetallic Fe-Cd,Fe-Zn,and Fe-In complexes containing hemilabile phosphorus/oxygen and silicon/oxygen bridging ligands

The reactions of K[Fe{Si(OMe)₃}(CO)₃(PY)][PY=Ph₂PCH₂C(O)Ph, Ph₂PCH₂C(O)[(-C₅H₄)FeCp] (Cp=⁵-C₅H₅), Ph₂P(CH₂)₂CN] with CdCl₂·2.5H₂O, ZnX ₂ (X=Cl, I) or InCl₃ afforded Fe-Cd-Fe or Fe-M(-X)₂ M-Fe (M=Cd, Zn, In;X=Cl, I) and Fe-InCl₂ complexes. Some of them contain an unusual and labile -²-SiO alkoxysilyl bridge which may be associated with a bridging mode for the ketophosphine ligand (first such example structurally established), thus providing original results in bimetallic chemistry on the intramolecular coordination of oxygendonor functions ofchemically different hemilabile ligands firmly attached to a neighboring metal center. The structures of the trinuclear complex (3), of the chlorobenzene solvate of the tetranuclear complex (4a·C₆H₅Cl) and of [mer-(OC)₃{(EtO)₃Si} (4e) have been determined by X-ray diffraction. Crystals of 3 are orthorhombic, space groupPbcn, witha=19.010(4),b=11.766(5),c=26.998(7)Å, andZ=4. Crystals of4a·C₆H₅Cl are monoclinic, space groupC2/c witha=22.455(3),b=17.680(2),c=16.627(4)Å, =90.80(4)°, andZ=4. Crystals of4e are monoclinic, space groupC2/c witha=25.392(5),b=18.554(6),c=16.28(1)Å, =120.73(3)°, andZ=4. The structures were solved using direct methods and Fourier difference techniques and refined by blocked full-matrix least squares toR=0.035 (R _w =0.049) for 2719 observed reflections, toR=0.042 (R _w =0.056) for 3082 observed reflections, and toR=0.057 (R _w =0.075) for 1850 observed reflections for3, 4a·C₆H₅Cl and4e, respectively. The Fe-Zn complexes (9a), (9b) and (9c) were prepared and characterized by spectroscopic methods.Part 21 in the Series: Complexes with Functional Phosphines. Part 20: P. Braunstein, S. Coco Cea, A. DeCian, and J. Fischer (1992).Inorg. Chem. 31, 4203.     

A new approach to A,B-difunctionalisation of cyclodextrins using bulky 1,3-bis[bis(aryl)chloromethyl]benzenes as capping reagents

1,3-Bis[bis(4-tert-butylphenyl)chloromethyl]benzene and 1,3-bis[bis(4-anisyl)chloromethyl]benzene were employed as regioselective capping reagents for the preparation of C-6A,C-6B-bridged, permethylated alpha- and beta-CD derivatives; isolated yields up to 55% of proximally capped, methylated CDs were obtained, thus opening the way to the straightforward preparation of a wide range of A,B-functionalised CDs. As revealed by a single crystal X-ray diffraction study, the benzene-1,3-bis[bis(4-tert-butylphenyl)methyl] spacer is perfectly suited for A,B-capping of beta-cyclodextrin.     

catena‐Poly[[aqua­barium(II)]‐μ‐aqua‐bis­(μ‐2′‐carboxy­biphenyl‐2‐carboxyl­ato)]

In the title compound, [Ba{HOOC(C₆H₄)₂CO₂}₂(H₂O)₂] or [Ba(C₁₄H₉O₄)₂(H₂O)₂], the Ba atoms are coordinated by nine O atoms, six from two 2′‐carboxy­biphenyl‐2‐carboxyl­ate (Hbpdc⁻) ligands and three from three coordinated water mol­ecules, resulting in the formation of face‐sharing distorted monocapped square anti­prisms. The Hbpdc⁻ ligands bridge the Ba atoms to form a one‐dimensional helical polymer, with a Ba⋯Ba distance across the chain of 4.1386 (17) Å. Adjacent chains are parallel to each other. The two independent ligands are tetra­dentate and have the same coordination mode, exhibiting μ‐oxo bridges and η⁸‐chelation. The crystal structure is further stabilized by hydrogen bonds within each chain.     

A versatile synthesis of retinoids via condensation of the side-chain to cyclic ketones

A simple synthesis of ethyl 3,7-dimethyl-2,4,6-nonatriene-8-ynoates and their corresponding alcohols is presented; codensation with various cyclic ketones can lead to retinoids having modified ring structures.     

Lyapunov-type inequalities for fractional difference operators with discrete Mittag-Leffler kernel of order 2 &lt; <Emphasis Type="Italic">α</Emphasis> &lt; 5/2

Fractional difference operators with discrete-Mittag-Leffler kernels of order α > 1 are defined and their corresponding fractional sum operators are confirmed. We prove existence and uniqueness theorems for the discrete fractional initial value problems in the frame of discrete Caputo (ABC) and Riemann (ABR) operators by using Banach contraction theorem. Then, we prove Lyapunov type inequality for a Riemann type fractional difference boundary value problem of order 2 < α < 5∕2 within discrete Mittag-Leffler kernels, where the limiting case α → 2⁺ results in the ordinary difference Lyapunov inequality. Examples are given to clarify the applicability of our results and an application about the discrete fractional Sturm-Liouville eigenvalue problem is analyzed.     

Polymeric tetra­aqua­tris­(malonato)­dilanthanum(III) monohydrate

The title compound, [La₂(C₃H₂O₄)₃(H₂O)₄]·H₂O, forms a layer‐type polymeric structure. The layers, which contain infinite puckered four‐membered La—O—La—O rings in a pseudo‐ternary symmetry, are formed by the lanthanum and one independent malonate group. They are interconnected by the second independent malonate group, giving a three‐dimensional framework in which wide channels accommodate one disordered water mol­ecule of crystallization. The La atom lies on a twofold axis and is ten‐coordinated by eight O atoms from carboxyl­ate groups and two water mol­ecules. One malonate group is monodentate and triply bridging chelating, whilst the other is doubly monodentate. The extensive network of hydrogen bonds and bridge bonds observed in this structure enhances the structural stability. Despite some identical subfeatures, this structure is quite different from that observed in [La₂(C₃H₂O₄)₃(H₂O)₃]·2H₂O.     

Integration and dimensional modeling approaches for complex data warehousing

With the broad development of the World Wide Web, various kinds of heterogeneous data (including multimedia data) are now available to decision support tasks. A data warehousing approach is often adopted to prepare data for relevant analysis. Data integration and dimensional modeling indeed allow the creation of appropriate analysis contexts. However, the existing data warehousing tools are well-suited to classical, numerical data. They cannot handle complex data. In our approach, we adapt the three main phases of the data warehousing process to complex data. In this paper, we particularly focus on two main steps in complex data warehousing. The first step is data integration. We define a generic UML model that helps representing a wide range of complex data, including their possible semantic properties. Complex data are then stored in XML documents generated by a piece of software we designed. The second important phase we address is the preparation of data for dimensional modeling. We propose an approach that exploits data mining techniques to assist users in building relevant dimensional models.     

Humulene derivatives from Saharian Asteriscus graveolens

Three new sesquiterpene-humulenes, (?)- asteriscunolides I (1), J (2) and (?)-(2Z,6E,9Z)-8-oxo-1α-acetoxy-2,6,9-humulatrien-12-oic acid (3) were isolated from the leaves-flowers of the Saharan medicinal plant Asteriscus graveolens along with six known compounds. The structures of the compounds were determined on the basis of spectroscopic mono and bidimensional NMR, mass spectrometry and by single-crystal X-ray diffraction. Compounds 1–3 were evaluated for cytotoxic assay, no significant activity was detected.     

VISUAL PIGMENTS AND BACTERIORHODOPSINS FORMED FROM AROMATIC RETINAL ANALOGS

Abstract— Rhodopsin (Rh) and bacteriorhodopsin (bR) analogs have been prepared from retinals containing various aromatic and heterocyclic nuclei. In the case of Rh, aromatic methyl substituents facilitate the regeneration and stabilize the pigments formed; in bR, however, methyl substituents seem to have little influence. Rhodopsins derived from unsubstituted aromatic retinals show fine structure in the relatively stable "pre-pigment" intermediate and their maxima are red-shifted compared to pigments derived from methylated aromatic retinals. This implies that in these aromatic rhodopsins the ring moiety adopts a more planar conformation when unsubstituted. In bR derivatives also the aromatic ring adopts a close-to-planar conformation when unsubstituted, but comparison with indene-derived bR suggests that even the unsubstituted phenyl ring may not be coplanar with the side-chain.