Gabriel Germain

On the application of phase relationships to complex structures. V. Finding the solution

Multisolution direct methods for solving crystal structures lead to many plausible sets of phases and some means of determining the correct set is necessary. For centrosymmetric structures, figures of merit are usually quite discriminating and the examination of only one or two E maps is necessary. For noncentrosymmetric structures, figures of merit are unreliable and the necessity of examining a large number of E maps can sometime prove to be an almost insuperable obstacle to finding the correct structure. A procedure is described for overcoming this difficulty. The Cooley-Tukey fast-Fourier-transform technique is used to compute E maps and all peaks greater than a certain height are located. A selection of the highest of these peaks, whose number is chosen by the program user, is then analysed with respect to bond lengths and angles. Favourable projections of coherent groups of peaks are output on the line printer in the form of integers representing the ranking order of the peaks and in positions which represent an undistorted projection of the group. Computing time is of the order of one minute per set of phases and the examination of a set of 32 maps and finding the correct solution takes about 30 minutes.

Chemical Studies of Marine-invertebrates .43. Novel Sesquiterpenes From Clavularia-inflata and Clavularia-koellikeri (coelenterata, Octocorallia, Stolonifera)

Abstract Two novel sesquiterpenes, 12-acetoxycyclosinularane ( 1 ) and 12-acetoxysinularene( 2 ),have been isolated from Clavularia inftata . Their structures have been determined by X-ray diffraction analysis and chemical correlation respectively. Moreover, the new aromadendrane sesquiterpene(1R * , 1aS * , 4R * , 7R * , 7aS * , 7bS * , 5Z)-4,4a,7-trihydroxyaromadendr-5-en-8-oic acid methyl ester ( 19 ) has been isolated from the related species C. koellikeri . Its structure has been established by X-ray diffraction analysis. These compounds are the first sesquiterpenes isolated from Octocorallia of the order Stolonifera.

A Novel Type of Bis-quinolizidine Alkaloid From the Sponge Petrosia-seriata

Abstract The structure of petrosin, the major alkaloid isolated from the sponge Petrosia seriata , has been determined by X-ray diffraction analysis. Petrosin is the first member of a new class of bis-quinolizidine alkaloids containing a C-16 macrocycle.

Crystal structures of two new heptamolybdates and of a pyrazole incorporating a gamma-octamolybdate anion

Two new heptamolybdates, one containing calcium and imidazole and the other with urea and ammonium cations, have been prepared. X-ray crystallographic studies of single crystals of both compounds have been carried out. In the mixture of calcium and imidazole [(Himi)(4)][Ca(H2O)(6)(mu-O)(2)][Mo7O24]. 2(imi). 3H(2)O (1), the calcium(II) cation is surrounded by six water molecules and two oxygen atoms from the polyanion, and bridges in trans position two [Mo7O24](6-) polyanions forming a linear composite with alternating Mo7O24 and Ca(H2O)(6) units. The urea compound [CO(NH2)H](3)(NH4)(9)[Mo7O24](2). 5[CO(NH2)(2)]. 4H(2)O (2) presents [Mo7O24](6-) heptamolybdate anions bound by hydrogen bonds from NH4+, [CO(NH2)H] cations and H2O molecules. A new crystalline phase of a gamma-octamolybdate containing pyrazole coordinatively bound to molybdenum has also been prepared [(Hpyr)(4)][(pyr)(2)(Mo8O26)]CH3COCH3. 2H(2)O (3). The structure has been solved by X-ray diffraction from a single crystal. The Mo-N bond length is 2.262(3) Angstrom. All compounds have been characterised by IR,H-1 NMR and thermal analysis

A Non-obvious Reaction Pathway in the Formation of 2-aminobenzene-1,3-dicarbonitriles From Alpha,Beta-unsaturated Ketones Or Aldehydes

Key intermediates demonstrating a non-obvious reaction pathway leading to 2-aminobenzene-1,3-dicarbonitriles from enones have been isolated and characterised in tire reaction between (E)-4-phenyl-3-butene-2-one and propanedinitrile in a basic hydro-alcoholic medium. (E)-4-Phenyl-3-butene-2-one reacts with three molecules of propanedinitrile to give a 6-amino-2-iminobicyclo[2.2.2]-5-octene-1,3,3,5-tetracarbonitrile system which evolves to a substituted cyclohexadiene by elimination of the sodium salt of 1,1,1-tricyanomethane. Further oxidation leads to the final 2-aminobenzene-1,3-dicarbonitrile. The proposed pathway involves more steps and more difficult transformations than previously presented for similar systems. We can not exclude a simpler reaction pathway derived from the double Michael and Knoevenagel adduct of (E)-4-phenyl-3-butene-2-one and propanedinitrile, however we have not found any evidence for this simpler process.

X-ray structure of 3′,5′-diacetyl-2′-deoxy-2′-fluorouridine: A pyrimidine nucleoside in the syn conformation

The X-ray structure analysis of 3′,5′-diacetyl-2′-deoxy-2′-fluorouridine is reported. The title compound crystallized from water in the monoclinic space group P21 with cell constants a = 10.874 A, b = 7.379 A, c = 9.971 A, β = 111.41°. The structure was solved by direct methods and refined to a discrepancy index R = 0.039. Contrary to most of the pyrimidine nucleosides the orientation of the nucleobase with respect to the sugar is syn and the conformation about the C(4′)—C(5′) bond is trans—gauche. The ribose exhibits a C(3′)-endo—C(4′)-exo twist conformation and despite the fluoro substitution, bond angles and distances compare well with averaged data for unmodified C(3′)-endo puckered riboses. There are close contacts between the 3′- and 5′-acetate groups which are orientated roughly parallel to each other. The NMR results by Blandin, M., Tran—Dinh, S., Catlin, J.C. and Guschlbauer, W. (1974) Biochim. Biophys. Acta 361, 249–256 (preceding paper), suggest that the conformations in the crystal and in solution are similar.

Secotrinervitane, a Novel Bicyclic Diterpene Skeleton From a Termite Soldier

Abstract The structure of 3α-acetoxy-15β-hydroxy-7,16-secotrinervita-7,11-diene, a diterpene possessing a novel bicyclic cembrane-derived carbon skeleton, has been determined by X-ray diffraction analysis.

Synthesis and characterization of cyclometallated complexes of benzalazines. Crystal and molecular structure of [{Pd(p-ClC6H3CHN–)Cl(PEt3)2}2]

The reaction of benzalazines, (p-RC6H4CHN–)2(R = H, Cl, NO2, or NMe2), with PdCl2 leads in the the first two cases to the formation of cyclometallated polymeric species that react with phosphines to yield dimetallated compounds [{Pd(p-RC6H3CHN–)Cl(PR′3)2}2](R′= Et or Ph) and/or [{[graphic omitted]–)Cl(PPh3)}2]. Phosphine exchange reactions give the complex [{Pd(p-RC6H3CHN–)Cl(PEt3)(PPh3)}2]. The molecular structure of [{Pd(p-ClC6H3CHN–)Cl(PEt3)2}2] has been determined by a single-crystal X-ray analysis. The crystals are monoclinic, space group P21/n, a= 11.124(3), b= 10.062(2), c= 22.566(5)A, β= 102.95(3)°, and Z= 2; R= 0.052 for 3 306 reflections. Palladium atoms are five-co-ordinated, the Pd–N distance being 2.743 A. However, n.m.r. spectra show that, in solution, free rotation around the C(aromatic)–C(azomethine) bonds does occur even at –100 °C.

Crystal structure and spectroscopic study of 2-[(2,6-dichlorophenyl)amino]phenylacetoxyacetic acid (Aceclofenac)

The crystal structure of the title compound has been determined. The crystals are monoclinic:P21n(NO. 14),a=12.279(7),b=8.223(1),c=15.504(7)Å,β=96.16(2)°,Vc=1556(2)Å3,Z=4,Dx=1.511 g cm−3,λ=(MoKα)=0.71069 Å. The structure was solved by direct methods and refined with 1970 reflections to a finalR value of 0.057. Analytical, mass, spectral, and physicochemical data are also reported.

REACTIONS OF CATIONIC IRON P-COORDINATED (DIPHENYLPHOSPHINO) ALKYNES WITH DICOBALT OCTACARBONYL

Reaction of the P-coordinated transition metal complexes [(Fp)Ph(2)PC=CR][BF4] (R = H, CH3, Ph, p-tolyl; Fp = CpFe(CO)(2)) with cobalt octacarbonyl at room temperature affords the cationic heterometallic complexes [(Fp)Ph(2)PC=CR{Co-2(CO)(6)}][BF4] (1-4) in high yields. A single-crystal X-ray structural analysis of 3 showed that the hexacarbonyldicobalt fragment is rr-bonded to the alkynyl group of the P-coordinated (diphenylphosphino)alkyne without significant interaction between the iron and cobalt fragments. Spectroscopic data for 1-4 and structural data for 3 suggest that the positive charge is mainly located on the iron fragment.