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C2 Symmetry (c2 + symmetry)
Kinds of C2 Symmetry Selected AbstractsDinuclear Complexes of MII Thiocyanate (M = Ni and Cu) Containing a Tridentate Schiff-Base Ligand: Synthesis, Structural Diversity and Magnetic PropertiesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 12 2005Suparna Banerjee Abstract A dinuclear NiII complex, [Ni2(L)2(H2O)(NCS)2]·3H2O (1) in which the metal atoms are bridged by one water molecule and two ,2 -phenolate ions, and a thiocyanato-bridged dimeric CuII complex, [Cu(L)NCS]2 (2) [L = tridentate Schiff-base ligand, N -(3-aminopropyl)salicylaldimine, derived from 1:1 condensation of salicylaldehyde and 1,3-diaminopropane], have been synthesized and characterized by IR and UV/Vis spectroscopy, cyclic voltammetry and single-crystal X-ray diffraction studies. The structure of 1 consists of dinuclear units with crystallographic C2 symmetry in which each NiII atom is in a distorted octahedral environment. The Ni,O distance and the Ni,O,Ni angle, through the bridged water molecule, are 2.240(11) Å and 82.5(5)°, respectively. The structure of 2 consists of dinuclear units bridged asymmetrically by di-,1,3 -NCS ions; each CuII ion is in a square-pyramidal environment with , = 0.25. Variable-temperature magnetic susceptibility studies indicate the presence of dominant ferromagnetic exchange coupling in complex 1 with J = 3.1 cm,1, whereas complex 2 exhibits weak antiferromagnetic coupling between the CuII centers with J = ,1.7 cm,1. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] First Total Synthesis of the Potent Anticancer Natural Product Dideoxypetrosynol A: Preparation of the "Skipped" (Z)-Enediyne Moiety by Oxidative Coupling of Homopropargylphosphonium YlideEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 28 2008Benjamin W. Gung Abstract Dideoxypetrosynol A is a C30 polyacetylenic alcohol with C2 symmetry. The first total synthesis of both enantiomers of the potent anti-cancer natural product (+)- and (,)-dideoxypetrosynol A is reported. The key step is an oxidative coupling of a homopropargylphosphonium ylide to prepare the "skipped" (Z)-enediyne moiety. The natural dideoxypetrosynol A was isolated as a racemic mixture as shown in structure 1. The absolute configurations of the chiral centers are established for the (+)- and (,)-enantiomers using Burgess' enzymatic resolution procedure with Pseudomonas AK lipase. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Synthesis and Structure of Macrolactams of 3,-Aminodeoxycholanic AcidEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 2 2006Martin Feigel Abstract The macrolactams cyclo(3,-aminodeoxycholic amide)2 (1) and cyclo(3,-aminodeoxycholic amide)3 (2) were prepared in high yields (1: 32,%; 2: 41,%) from the pentafluorophenyl esters of the linear precursors. The solid-state structures of both macrocycles were determined by X-ray diffraction. Compound 1 forms a cleft of C2 symmetry which holds two methanol and two water molecules fixed by hydrogen bonds. The crystals of compound 2 contain two slightly different macrolactam rings of 7,8 Å diameter. The polar ,-surface of the deoxycholanic parts and the amide NH groups are oriented into the center of the rings. The cavity formed by the ring system and the void volume between the macrocycles is filled by disordered solvent molecules. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Chiral discrimination in hydrogen-bonded complexes of 2-methylol oxirane with hydrogen peroxideINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 5 2009Guiqiu Zhang Abstract A systematic quantum chemical study reveals the effects of chirality on the intermolecular interactions between two chiral molecules bound by hydrogen bonds. The methods used are second-order Møller,Plesset perturbation theory (MP2) with the 6-311++g(d,p) basis set. Complexes via the OH···O hydrogen bond formed between the chiral 2-methylol oxirane (S) and chiral HOOH (P and M) molecules have been investigated, which lead to four diastereomeric complexes. The nomenclature of the complexes used in this article is enantiomeric configuration sign corresponding to English letters. Such as: sm, sp. The relative positions of the methylol group and the hydrogen peroxide are designated as syn (same side) and anti (opposite side). The largest chirodiastaltic energy was ,Echir = ,1.329 kcal mol,1 [9% of the counterpoise correct average binding energy De(corr)] between the sm-syn and sp-anti in favor of sm-syn. The largest diastereofacial energy was ,1.428 kcal mol,1 between sm-syn and sm-anti in favor of sm-syn. To take into account solvents effect, the polarizable continuum model (PCM) method has been used to evaluate the chirodiastaltic energies, and diastereofacial energies of the 2-methylol oxirane···HOOH complexes. The chiral 2,3-dimethylol oxirane (S, S) is C2 symmetry which offers two identical faces. Hence, the chirodiastaltic energy is identical to the diastereomeric energy, and is ,Echir = 0.563 kcal mol,1 or 5.3% of the De(corr) in favor of s,s-p. The optimized structures, interaction energies, and chirodiastaltic energies for various isomers were estimated. The harmonic frequencies, IR intensities, rotational constants, and dipole moments were also reported. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 [source] Using 1,3-butadiene and 1,3,5-hexatriene to model the cis-trans isomerization of retinal, the chromophore in the visual pigment rhodopsinINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 4-5 2002Fredrik Blomgren Abstract The short polyenes 1,3-butadiene and 1,3,5-hexatriene are used to model the cis-trans isomerization of the protonated Schiff base of retinal (PSBR) in rhodopsin (Rh). We employed the complete active space self-consistent field (CASSCF) method for calculation of the potential energy surfaces (PESs) in C2 symmetry. In the calculations, the central bond was twisted from 0 to 180° in the first singly excited singlet state (Sse), i.e., the state dominated by a configuration with one electron excited from HOMO to LUMO. It was found that the PES of 1,3-butadiene has a maximum whereas the PES of 1,3,5-hexatriene has a minimum for a twist angle of 90°. This is explained by a shift in border of single and double bonds in the Sse state. The first step in the cis-trans isomerization of PSBR, which is the formation of the C6C7 (see Scheme 1 for numbering) twisted PSBR in the first excited singlet state (S1), inside the protein binding pocket of the visual pigment Rh is modeled using crystal coordinates and the calculations performed on 1,3-butadiene and 1,3,5-hexatriene. More specifically, a plausible approximate structure is calculated in a geometric way for the C6C7 90° twisted PSBR, which fits into the protein binding pocket in the best possible way. It has been shown earlier that PSBR has an energy minimum for this angle in S1. The CASSCF method was used to investigate the wave function of the calculated structure of PSBR. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002 [source] IR/Raman spectroscopy and DFT calculations of cyclic di-amino acid peptides.JOURNAL OF RAMAN SPECTROSCOPY, Issue 11 2009Part III: comparison of solid state, solution structures of cyclo(L -Ser- L -Ser) Abstract B3-LYP/cc-pVDZ calculations of the gas-phase structure and vibrational spectra of the isolated molecule cyclo(L -Ser- L -Ser), a cyclic di-amino acid peptide (CDAP), were carried out by assuming C2 symmetry. It is predicted that the minimum-energy structure is a boat conformation for the diketopiperazine (DKP) ring with both L -seryl side chains being folded slightly above the ring. An additional structure of higher energy (15.16 kJ mol,1) has been calculated for a DKP ring with a planar geometry, although in this case two fundamental vibrations have been calculated with imaginary wavenumbers. The reported X-ray crystallographic structure of cyclo(L -Ser- L -Ser), shows that the DKP ring displays a near-planar conformation, with both the two L -seryl side chains being folded above the ring. It is hypothesized that the crystal packing forces constrain the DKP ring in a planar conformation and it is probable that the lower energy boat conformation may prevail in the aqueous environment. Raman scattering and Fourier-transform infrared (FT-IR) spectra of solid state and aqueous solution samples of cyclo(L -Ser- L -Ser) are reported and discussed. Vibrational band assignments have been made on the basis of comparisons with the calculated vibrational spectra and band wavenumber shifts upon deuteration of labile protons. The experimental Raman and IR results for solid-state samples show characteristic amide I vibrations which are split (Raman: 1661 and 1687 cm,1, IR: 1666 and 1680 cm,1), possibly due to interactions between molecules in a crystallographic unit cell. The cis amide I band is differentiated by its deuterium shift of ,30 cm,1, which is larger than that previously reported for trans amide I deuterium shifts. A cis amide II mode has been assigned to a Raman band located at 1520 cm,1. The occurrence of this cis amide II mode at a wavenumber above 1500 cm,1 concurs with results of previously examined CDAP molecules with low molecular weight substituents on the C, atoms, and is also indicative of a relatively unstrained DKP ring. Copyright © 2009 John Wiley & Sons, Ltd. [source] Predictable close-packing similarities between cis - and trans -2-hydroxy-1-cyclooctanecarboxylic acids and trans -2-hydroxy-1-cyclooctanecarboxamideACTA CRYSTALLOGRAPHICA SECTION B, Issue 5 2002Alajos Kálmán In order to extend the experimental data already available on the close packing of cyclopentanes substituted with vicinal COX (X,=,OH, NH2) and OH groups to the analogous cyclohexanes, cycloheptanes and cyclooctanes, (1R*,2S*) -cis- 2-hydroxy-1-cyclooctanecarboxylic acid (8C), (1R*,2R*)- trans -2-hydroxy-1-cyclooctanecarboxylic acid (8T) and (1R*,2R*)- trans -2-hydroxy-1-cyclooctanecarboxamide (8T*) were subjected to X-ray crystal structure analysis. In 8T and 8T*, the hydrogen bonds form infinite ribbons of dimers joined by (12) rings with Ci symmetry. Two types of dimer alternate along each ribbon. The dimers differ in the donor and acceptor roles of the functional groups. This pattern was previously deduced topologically among the possible forms of association for heterochiral dimers [Kálmán et al. (2002). Acta Cryst. B58, 494,501]. As they have the same pattern of hydrogen bonds, 8T and 8T* are isostructural. The additional donor (i.e. the second hydrogen of the NH2 group) present in 8T* links the adjacent ribbons so as to form smaller (8) rings between them. The crystals of the cis stereoisomer 8C are built up from antiparallel hydrogen-bonded helices. The topology and symmetry of this structure are the same as for the close packing of (1R*,2R*,4S*)-4- tert -butyl-2-hydroxy-1-cyclopentanecarboxamide [Kálmán et al. (2001). Acta Cryst. B57, 539,550]; only the hydrogen-bond donors and acceptors are interchanged, in the same way as in the two dimer types of 8T and 8T* ribbons. This analogy suggests that helices may originate as homochiral dimers with C2 symmetry and polymerize into helices during crystal formation. The conformational characteristics of the heterochiral dimers observed in the title compounds and in closely related structures are discussed. [source] Titanium complexes with sulfur-linked bis(phenolate) ligandsACTA CRYSTALLOGRAPHICA SECTION C, Issue 11 2009Thomas S. Dols High-quality crystals of two bis(phenolate)titanium complexes, namely dichlorido{4,4,-dimethyl-2,2,-[cyclohexane-1,2-diylbis(sulfanediyl)]diphenolato}titanium(IV), [Ti(C20H22O2S2)Cl2], (I), and dichlorido{2,2,-[cyclohexane-1,2-diylbis(sulfanediyl)]diphenolato}titanium(IV), [Ti(C18H18O2S2)Cl2], (II), were obtained by reactive crystallization. Depending on the solvent, compound (II) was obtained as unsolvated (IIa) or as the toluene hemisolvate, [Ti(C18H18O2S2)Cl2]·0.5C7H8, (IIb). These systems without bulky substituents on the aromatic phenolate rings serve as ideal model compounds for precatalysts. The excellent X-ray diffraction data will help clarify the nature of the mismatched interactions between the soft S atoms within the ligand and the hard titanium center. Molecule (I) has crystallographic C2 symmetry. [source] Three isomorphous 2,6-dibromopyridinium tetrabromidometallates: (C5H4Br2N)2[MBr4]·2H2O (M = Cu, Cd and Hg)ACTA CRYSTALLOGRAPHICA SECTION C, Issue 11 2009Rawhi H. Al-Far The structures of three isomorphous compounds, namely bis(2,6-dibromopyridinium) tetrabromidocuprate(II) dihydrate, (C5H4Br2N)2[CuBr4]·2H2O, bis(2,6-dibromopyridinium) tetrabromidocadmate(II) dihydrate, (C5H4Br2N)2[CdBr4]·2H2O, and bis(2,6-dibromopyridinium) tetrabromidomercurate(II) dihydrate, (C5H4Br2N)2[HgBr4]·2H2O, show a crystal supramolecularity represented by M,Br...H,O,H...Br,M intermolecular interactions along with (,)N,H...OH2 hydrogen-bonding interactions forming layers connected via aryl,aryl face-to-face stacking of cations, leading to a three-dimensional network. The anions have significantly distorted tetrahedral geometry and crystallographic C2 symmetry. The stability of this crystal lattice is evidenced by the crystallization of a whole series of isomorphous compounds. [source] Crystallographic report: The [bis(,5 -cyclopentadienyl)titanium(IV)-bis(L -methionine)] dichlorideAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 6 2004Radim Bína Abstract The structure of ionic complex [Cp2Ti(L -Met)2]2+[Cl,]2 (where Cp = ,5 -C5H5) possessing C2 symmetry is presented. Discrete cationic units with distorted tetrahedral geometry around the central titanium atom are connected through intermolecular H···Cl bonds between ammonium group protons of ,-amino acid ligands and chloride anions. Copyright © 2004 John Wiley & Sons, Ltd. [source] (P,M)-1,2,3,9,10,11-Hexamethoxy-5,7-dihydrodibenz[c,e]oxepine and (P,M)-1,11-dimethyl-5,5,7,7-tetraphenyl-5,7-dihydrodibenz[c,e]oxepineACTA CRYSTALLOGRAPHICA SECTION C, Issue 4 2004Anthony Linden The title compounds, C20H24O7 and C40H32O, respectively, are racemic oxepines, the molecules of which contain a chiral axis. Both molecules possess crystallographic C2 symmetry and the seven-membered ring adopts a twisted-boat conformation. [source] catena -Poly[[bis[,-1,2-bis(1-methyltetrazol-5-yl)ethane-,2N4:N4,]bis[chlorocopper(II)]]-di-,-chloro]ACTA CRYSTALLOGRAPHICA SECTION C, Issue 6 2003Dmitry O. Ivashkevich In the title compound, [Cu2Cl4(C6H10N8)2]n, the ligand has C2 symmetry, and the Cu and Cl atoms lie on a mirror plane. The coordination polyhedron of the Cu atom is a distorted square pyramid, with the basal positions occupied by two N atoms from two different ligands [Cu,N,=,2.0407,(18),Å] and by the two Cl atoms [Cu,Cl,=,2.2705,(8) and 2.2499,(9),Å], and the apical position occupied by a Cl atom [Cu,Cl,=,2.8154,(9),Å] that belongs to the basal plane of a neighbouring Cu atom. The [CuCl2(C6H10N8)]2 units form infinite chains extending along the a axis via the Cl atoms. Intermolecular C,H,Cl contacts [C,Cl,=,3.484,(2),Å] are also present in the chains. The chains are linked together by intermolecular C,H,N interactions [C,N,=,3.314,(3),Å]. [source] Ethyl 6-acetylamino-6,7-dihydro-5H -dibenzo[a,c]cycloheptene-6-carboxylateACTA CRYSTALLOGRAPHICA SECTION C, Issue 5 2002Lakshminarasimhan Damodharan The title compound, C20H21NO3, is a derivative of Aib (,-aminoisobutyric acid) and is cyclized at the C, position by biphenyl rings. The seven-membered ring possesses C2 symmetry. The C, cyclization causes the backbone to assume a helical conformation in the crystal structure. The packing of the molecules is stabilized by intermolecular C,H,O, C,H,, and N,H,O hydrogen bonds. [source] Dispiro[fluorene-9,5,-[1,2,3,4]tetrathiane-6,,9,,-fluorene]ACTA CRYSTALLOGRAPHICA SECTION C, Issue 6 2001Anthony Linden The tetrathiane ring of the title compound, C26H16S4, has a chair conformation and the molecule has approximate C2 symmetry. Each of the two fluorene ring systems is virtually planar, with the ring planes intersecting at an angle of 67.58,(5)°. This novel compound has been formed as a side product from the treatment of 9H -fluorene-9-thione with methyl N -[(benzylidene)phenyl]glycinate in the presence of LiBr and 1,6-diazabicyclo[5.4.0]undecane. [source] A comparison of 2,7-dihydro-2,2,7,7-tetramethyl-3,6-diphenyl-1,4,5-thiadiazepine and the corresponding 1,1-dioxideACTA CRYSTALLOGRAPHICA SECTION C, Issue 4 2001Eric Cuthbertson The structures of the highly substituted title heterocycles, C20H22N2S and C20H22N2O2S, have been determined at 123,(1),K. Both molecules possess exact C2 symmetry and the seven-membered rings have very similar twist-boat conformations. The magnitudes of the C,S,C bond angles, 107.13,(6) and 108.27,(7)°, respectively, are influenced significantly by the four substituent methyl groups on the seven-membered rings. [source] Structure and Stability of B20N20 ClusterCHINESE JOURNAL OF CHEMISTRY, Issue 2 2005Xiao-Ying Cui Abstract B3LYP/6-31G* density functional theory calculations have been carried out on the structure and stability of ten B20N20 clusters. It was found that two new proposed isomers with two octagons, twelve hexagons, eight squares in C4h and C2 symmetry were more stable than the isomer with sixteen hexagons and six squares in C2 symmetry which was previously deemed to the most stable by 79.5 and 13.8 kJ/mol respectively. The isomer with two decagons in S10 symmetry is much higher in energy than the most stable structure in C4h symmetry by 637.2 kJ/mol. [source] | ||||||||||