1,721,093 research outputs found
Co-crystallization of racemic amino acids with ZnCl2: An investigation of chiral selectivity upon coordination to the metal centre
Full text linkThe amino acids alanine, valine, proline, isoleucine, serine, asparagine, tyrosine, and threonine in their racemic forms have been reacted with ZnCl2 under different preparative conditions (grinding and LAG, both manual and ball milling, and co-crystallization from solvent). In most cases, relatively stable (from days to months) oils were obtained; only in those cases for which single crystals could grow from oils, structural characterisation was possible via X-ray diffraction. Aim of the work has been the investigation of the occurrence of chiral selectivity upon the formation of tetrahedral metal coordination complexes or polymers. It has been shown that co-crystallization reactions lead, in the majority of cases, to crystals of racemic-AA2ZnCl2, formed by 0D homochiral complexes of formula l-AA2ZnCl2 and d-AA2ZnCl2. With the dl-amino acid threonine, however, crystals of meso-AA2ZnCl2 have also been obtained, made of 0D heterochiral complexes of formula dl-AA2ZnCl2. With dl-proline, both the known racemic and the new meso-AA2ZnCl2 solids were obtained. Formation of 1D coordination polymers has been observed in the cases of dl-asparagine and dl-tyrosine with alternating d and l amino acids along the polymeric chain. This journal i
Tuning the Solubility of the Herbicide Bentazon: From Salt to Neutral and to Inclusion Complexes
Full text linkWe report on the mechanochemical synthesis of inclusion complexes obtained by reacting the neutral crystalline herbicide bentazon (HBtz) with native cyclodextrins (CDs). The reaction of HBtz with γ-CD resulted in the formation of the inclusion complexes [β-CD·HBtz]·6H2O and [γ-CD·HBtz]·8H2O, which were characterized via a combination of X-ray diffraction, Fourier transform infrared (FTIR) spectroscopy, and calorimetric measurements. No complexation, on the contrary, was achieved upon the reaction of HBtz with α-CD. The salt NaBtz·1.75H2O, widely used as a water-soluble salt of bentazon for the manufacturing of agrochemicals, was also synthesized and structurally characterized, and its solubility and dissolution properties were compared to those of neutral HBtz and of the β-CD and γ-CD inclusion complexes. It was found that the behavior of [β-CD·HBtz]·6H2O and [γ-CD·HBtz]·8H2O in water is similar, with dissolution rates of 28.4 ng·L-1·min-1and 39.8 ng·L-1·min-1, respectively, and is intermediate between those of NaBtz·1.75H2O (228 ng·L-1·min-1) and neutral bentazon (3.5 ng·L-1·min-1). These results were also compared with those of the dehydrated inclusion complexes, which displayed intermediate dissolution rates between hydrous complexes and NaBtz·1.75H2O. All findings indicate that the inclusion of HBtz in β-CD and γ-CD might represent a viable alternative for the preparation of environmentally friendly agrochemicals with controlled bentazon release to be used in the formulation of herbicides
DYNAMIC PROCESSES IN THE SOLID-STATE - DIENE FLIP AND RING REORIENTATION IN CRYSTALLINE ZIRCONOCENE COMPLEXES
No full textThe dynamic processes that the zirconocene species (C5H5)2ZrCl2 (1), (C5H4(t)Bu)2ZrCl2 (2), (C5H5)2ZrC4H4Me2 (3), and (C5H4(t)Bu)2ZrC4H6 (4) undergo in the solid state have been examined. The results of potential energy barrier calculations and packing analyses are discussed in light of the dynamic information obtained by C-13 magic angle spinning NMR spectroscopy. The potential energy barriers to reorientation of the C5H5 ligands in 1 and 3 are estimated, while the C5H4(t)Bu groups in 2 and 4 are found to be blocked in their motion. An alternative interpretation of the diene flip, detected in 3 and 4 by the NMR experiments, is put forward
Ionic Cocrystals of Levodopa and Its Biological Precursors l-Tyrosine and l-Phenylalanine with LiCl
No full textIonic cocrystals (ICCs) of LiCl with levodopa and its biological precursors l-tyrosine and l-phenylalanine, namely, l-phe·LiCl·nH2O, l-tyr·LiCl, and l-dopa·LiCl·H2O, were synthesized by mechanochemical mixing of the reactants in the presence of a small quantity of ethanol. In the case of l-dopa, a polymorph of l-dopa·LiCl·H2O was also obtained from solution crystallization. All compounds were investigated by solid state methods, and the structures were determined either from single crystal or from powder diffraction data
Oxidative Addition Reactions Of I2 With [hir4(co)10-n(pph3)n(μ-pph 2)] (n = 1 And 2) And Crystal And Molecular Structure Of [hir4(μ-i)2(co)7(pph3)(μ- Pph2)]
No full textThe reactions of the cluster compounds [HIr4(CO)10-n(PPh3)n(μ-PPh 2)] [n = 0, (1); 1, (2) and 2, (3)] with I2 have been investigated. Compound 1 does not react, however, the presence of PPh3 in place of CO ligand(s) activates the cluster. Both compounds 2 and 3 react with I2 under mild conditions to give [HIr4(μ-I)2(CO)7(PPh3)(μ- PPh2)] (4), as the result of oxidative addition of I2 and dissociation of two CO ligands, or one CO and one PPh3 ligands, respectively. The molecular structure of 4, determined by an X-ray diffraction study, exhibits a butterfly arrangement of iridium atoms with the wings spanned by a μ-PPh2 ligand, the hinge bridged by a μ-H ligand, two hinge to wing tip edges bridged by iodine atoms and all metal atoms bearing two CO ligands, with the exception of one of the hinge atoms that contains a CO and a PPh3 ligands. This cluster exhibits the shortest average Ir-Ir bond length [2.698(2) Å] observed so far for a derivative of 1 and this is in accord with the relatively high average oxidation state of its metal atoms (+1) for a carbonyl cluster compound.135682686Livotto, F.S., Raithby, P.R., Vargas, M.D., (1993) J. Chem. Soc., Dalton Trans., p. 1797Araujo, M.H., (1995), Ph.D. Thesis, Universidade Estadual de Campinas, BrazilVargas, M.D., Pereira, R.M.S., Braga, D., Grepioni, F., (1993) J. Chem. Soc., Chem. Commun., p. 1008Vargas, M.D., Pereira, R.M.S., Braga, D., Grepioni, F., (1999) J. Braz. Chem. Soc., 10, p. 35Benvenutti, M.H.A., Vargas, M.D., Braga, D., Grepioni, F., Parisini, E., Mann, B.E., (1993) Organometallics, 12, p. 2955Benvenutti, M.H.A., Vargas, M.D., Braga, D., Grepioni, F., Mann, B.E., Naylor, S., (1993) Organometallics, 12, p. 2947Benvenutti, M.H.A., Hitchcock, P.B., Nixon, J.F., Vargas, M.D., (1994) J. Chem. Soc., Chem. Commun., p. 1869Araujo, M.H., Hitchcock, P.B., Nixon, J.F., Vargas, M.D., (1998) J. Braz. Chem. Soc., 9, p. 563Hitchcock, P.B., Nixon, J.F., Vargas, M.D., Ziglio, C.M., (2000) J. Chem. Soc., Dalton Trans., p. 2527Collman, J.P., Hegedus, L.S., Norton, J.R., Finke, R.G., (1987) Principles and Applications of Organometallic Chemistry, 2nd Ed., , University Science Books: Mill Valley, CALivotto, F.S., Raithby, P.R., Vargas, M.D., (1993) J. Chem. Soc., Dalton Trans., p. 1797Sheldrick, G.M., (1997) SHELXL97 - Single Crystal Structure Determination Software, , University of Göttingen, GermanyKeller, E., (1999) SCHAKAL99 - Graphical Representation of Molecular Models, , University of Freiburg, GermanyCarty, A.J., MacLaughlin, S.A., Nucciaroni, D., (1987) Phosphorus 31-NMR Spectroscopy in Stereochemical Analysis, , Verkade, J. G.Quin, L. D., eds, VCH: Deerfield Beach, FL, ch 16Riera, V., Ruiz, M.A., Villafañe, F., Bois, C., Jeannin, Y., (1993) Organometallics, 12, p. 124Johnson, B.F.G., Lewis, J., Nicholls, J.N., Puga, J., Whitmire, K.H., (1983) J. Chem. Soc., Dalton Trans., p. 787Johnson, B.F.G., Lewis, J., Nelson, W.J.H., Nicholls, J.N., Vargas, M.D., (1984) J. Chem. Soc., Dalton Trans., p. 1809Mingos, D.M.P., Wales, D.J., (1990) Introduction to Cluster Chemistry, , Prentice Hall: New JerseyVargas, M.D., Nicholls, J.N., (1986) Adv. Inorg. Radiochem., 30, p. 123Sanati, H., Becalska, A., Ma, A.K., Pomeroy, R.K., (1990) J. Chem. Soc., Chem. Commun., p. 197Hui, J.W.S., Wong, W.T., (1990) Organometallics, 9, p. 132
Carbon-carbon Coupling On Tetrahedral Iridium Clusters: X-ray Molecular Structures And Multinuclear Nmr Studies Of The Two Isomeric Forms Of [ir4(co)6(μ3-η2 -hccph)(μ2-η4-c4h2 Ph2)(μ-pph2)2]
No full textThe reactions of [HIr4(CO)9 (Ph2PC ≡CPh)(μ-PPh2)] (1) or [Ir4(CO) 8 (μ3-η2-HCCPh) (μ-PPh2)2] (2) with HC ≡ CPh gave two isomeric forms of [Ir4(CO)6 (μ3-η2HCCPh)(μ2 -η4-C4H2Ph2) (μ-PPh2)2] (3 and 4) in good yields as the only products. These compounds were characterized with analytical and spectroscopic data including 1H, 13C and 31P NMR (1 and 2D) spectroscopy and their molecular structures were established by X-ray diffraction studies. Compounds 3 and 4 exhibit the same distorted butterfly metal polyhedral arrangement of metal atoms with two μ-PPh2 that occupy different positions in the structures of the two isomers. Both molecules contain a HCCPh ligand bonded in a μ3 -η2-// mode to one of the wings of the butterfly and a metallacyclic ring, which resulted from head-to-tail coupling, in the case of [Ir4(CO)6 (μ3-η2-HCCPh){μ-η4 -(H)CC(Ph)C(H)C(Ph)}(μ-PPh2)2] (3) and tail-to-tail coupling, in that of [Ir4(CO)6 (μ3-η2-HCCPh){μ2 -η4-(H)CC(Ph)C(Ph)C(H)}(μ-PPh2) 2] (4), and which is linked to two metal atoms of the second wing of the butterfly. © Elsevier B.V. All rights reserved.6892235133519Sappa, E., Tiripicchio, A., Braunstein, P., (1983) Chem. Rev., 83, p. 203Raithby, P.R., Rosales, M.J., (1985) Adv. Inorg. Chem. Radiochem., 29, p. 169Mallors, R.L., Blake, A.J., Dyson, P.J., Johnson, B.F.G., Parsons, S., (1997) Organometallics, 16, p. 1668Sappa, E., (1994) J. Cluster Sci., 5, p. 211. , and references thereinCarty, A.J., (1982) Pure Appl. Chem., 54, p. 113Choualeb, A., Braunstein, P., Rose, J., Welter, R., (2004) Inorg. 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Embroidering Ionic Cocrystals with Polyiodide Threads: The Peculiar Outcome of the Mechanochemical Reaction between Alkali Iodides and Cyanuric Acid
Full text linkWe report here the preparation and structural characterization of a series of new crystalline materials obtained by mechanochemical mixing of cyanuric acid (CA) and alkali halides (LiI, NaI, and KI) in the presence of molecular iodine, namely, the isomorphous catena-poly[tetra(cyanuric acid)·lithium tetraiodide], n[CA4·LiI4], and catena-poly[tetra(cyanuric acid)·sodium tetraiodide], n[CA4·NaI4], featuring three-dimensional (3D) cationic frameworks able to segregate linear, infinite n[I4-] chains in their squared open channels and the layered solid [CA·KI3]2·I2·2H2O characterized by alternating sheets of (i) hydrated potassium cations and CA molecules and (ii) I3- anions and discrete I2 molecules. The combination of X-ray diffraction (XRD), Raman spectroscopy, and thermal analyses allowed us to elucidate the compound's structural features and to discuss the effect of cation size on the stoichiometry and architecture of the three ionic cocrystals (ICCs)
THE SYNTHESIS AND CHARACTERIZATION OF THE OCTARUTHENIUM-BENZENE CLUSTER [RU8H4(CO)(18)(ETA(6)-C6H6)]
No full textThe reaction of cyclohexene, C6H10, with RU(3)(CO)(12) yields the new octaruthenium-benzene cluster [RU(8)H(4)(CO)(18)(eta(6)-C6H6)] which has been fully characterised in solution,by conventional spectroscopic methods and in the solid state by a single crystal X-ray diffraction analysis
Ionic co-crystals of enantiopure and racemic histidine with calcium halides
No full textIonic co-crystals (ICCs) of l- and dl-histidine with CaCl2, CaBr2 and CaI2 were prepared by mechanochemical and solution methods and were structurally characterized by either single crystal or powder X-ray diffraction methods. The l-histidine molecules bridge Ca2+ cations forming enantiopure ribbons in the homochiral crystals (l-His)2·CaX2·nH2O (X = Cl and Br n = 3, X = I n = 4), as well as in the partial dehydration product of (l-His)2·CaI2·4H2O, namely (l-His)2·CaI2·3H2O. In the racemic (dl-His)2·CaX2·4H2O cases (X = Cl, Br, X = I), molecules of both chiralities are accommodated in the coordination sphere of the Ca2+ cation forming ribbons with homochiral rims as in the enantiopure crystals. Intrinsic dissolution rate measurements show that the histidine-CaCl2 co-crystals have a much higher IDR with respect to both enantiopure and racemic histidine solids
CATION CONTROL ON THE CRYSTAL ORGANIZATION OF HEXANUCLEAR CARBONYL CLUSTER ANIONS
No full textThe crystal structures of 28 hexanuclear carbonyl cluster anions have been investigated by means of empirical packing potential energy calculations, van der Waals volume analysis, and computer graphics. Data were retrieved from the Cambridge Structural Database. The relationship between shape, size, and charge of the component ions and the formation of preferential aggregates (piles, ''snakes'', layers) in the crystal lattice has been analyzed. It has been shown that, with large organic cations, the packing pattern is essentially that of molecular mixed crystals, while small cations drive toward monodimensional aggregation of the anions. It has been shown that there is a (fairly precise) ratio between the relative volumes of the component ions above which one-dimensional or two-dimensional networks are preferentially established. Some representative cases are discussed in detail
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