Search results for "stereochemistry"
showing 10 items of 4831 documents
Synthesis and characterisation of polymeric metal-ion carboxylates from benzene-1,3,5-tricarboxylic acid with Mn(II), Co(II) or Zn(II) and 2,2-bipyri…
2001
A total of 13 new co-ordination solids have been prepared of composition [Co(HBTC)(PHEN)(H2O)] (12), [Mn-3(BTC)(2)(PHEN)(3)] (13), [Mn(HBTC)(6)(H2O)] (14), [Mn(HBTC)(7)(H2O)] (15), [Zn-3(BTC)(2)(6)(3)(H2O)(3)]. 4H(2)O (16), [Zn-(HBTC)(6)(H2O)] (17), [Zn(H2BTC)(2)(6)] (18), [Zn(HBTC)(7)(H2O)] (19), [Zn(HBTC)(8)(H2O)] (20), [Zn-2(HBTC)(2)(9)(2)]. 2H(2)O (21), [Zn(HBTC)(10)(H2O)].H2O (22), [Co(HBTC)(10)(H2O)].H2O (23) and [Co(HBTC)(11)(H2O)] (24) 6 = pyridine-2-(1-methyl-1H-pyrazol-3-yl); 7 = pyridine-2-(1-methyl-4-bromo-1H-pyrazol-3-yl); 8 = pyridine-2-(1-methyl-4-nitro-1H-pyrazol-3-yl); 9 = pyridine-2-(1-methyl-5-trifluoromethyl-1H-pyrazol-3-yl); 10 = pyridine-2-(1-methyl-5-tert-butyl-1H-pyr…
Crystal and molecular structure of the tris(1,10-phenanthroline)potassium salt of μ-hydridobis[pentacarbonylchromium(0)]
1984
Abstract The crystal and molecular structure of [K(phen)3][Cr2(CO)10(μ-H)] has been determined by X-ray diffraction. The compound crystallizes in the space group P 1 with a 11.884(4), b 13.968(4), c 15.612(6) A, α 112.6(1), β 99.7(1) and γ 106.2(1)° and Z = 2. The structure was refined to R = 0.066 and RW = 0.067 for 3692 counter data with I ⩾ 3σ(I). The complex anion [Cr2(CO)10(μ-H)] adopts a bent Cr-H-Cr configuration with the equatorial carbonyl groups of the two independent Cr(CO)5 moieties in an eclipsed configuration. The Cr⋯Cr distance is 3.394(3) A and the two CrH bonds are 1.74(7) and 1.71(7) A. The CrHCr bond angle is 159(3)°. In the dimeric complex cation [K(phen)3]2, located …
Tritopic phenanthroline and pyridine tail-tied aza-scorpiands
2010
The synthesis of two new tritopic double-scorpiand receptors in which two equivalent 5-(2-aminoethyl)-2,5,8-triaza[9]-(2,6)-pyridinophane moieties have been linked with 2,6-dimethylpyridine (L1) or 2,9-dimethylphenanthroline (L2) units is reported for the first time. Their acid-base behaviour and Zn(2+) coordination chemistry have been studied by pH-metric titrations, molecular dynamic calculations, NMR, UV-Vis and steady-state fluorescence techniques. L1 and L2 behave, respectively, as hexaprotic and heptaprotic bases in the experimental conditions used (298.1 +/- 0.1 K, 0.15 mol dm(-3) NaCl, pH range under study 2.0-11.0). These ligands are able to form mono-, bi- and trinuclear Zn(2+) co…
Oxidative DNA damage of mixed copper(II) complexes with sulfonamides and 1,10-phenanthroline
2003
Abstract Mixed coordination compounds of Cu(II) with sulfonamides and 1,10-phenanthroline as ligands have been prepared and characterised. Single crystal structural determination of the complex [Cu( N -quinolin-8-yl- p -toluenesulfonamidate) 2 (phen)] shows Cu(II) ions are located in a highly distorted octahedral environment, probably as a consequence of the Jahn–Teller effect. The FT-IR and electronic paramagnetic resonance (EPR) spectra are also discussed. The mixed complexes prepared undergo an extensive DNA cleavage in the presence of ascorbate and hydrogen peroxide. Two of the complexes have higher nucleolytic efficiency than the bis( o -phenanthroline)copper(II) complex.
Copper(ii) and Zn(ii) coordination chemistry of tetraaza[n]cyclophanes
2003
The acid–base behaviour and Zn2+ and Cu2+ metal coordination chemistry of the novel orthocyclophane ligands 2,5,8,11-tetraaza[12]orthocyclophane (L2) and 2,5,9,12-tetraaza[13]orthocyclophane (L3) and metacyclophane 2,5,8,11-tetraaza[12]metacylophane (L1) are studied. Important differences in the chemistry of these compounds are found depending on the substitution of the aromatic ring. The ortho derivatives are much more basic in their first two protonation steps while the metacyclophane presents much larger constants in the third and fourth protonation stages. The crystal structure of the picrate salt of [H2L3]2+ shows an alternate disposition of the protons in the molecule with formation o…
Presenegenin Glycosides from Securidaca welwitschii
2010
) Centre de Recherche Phytochimique, Universite´ de Lie`ge, Institut de Chimie-B6, Sart Tilman,B-4000-Lie`ge IThe five new presenegenin glycosides 1–5 were isolated from Securidaca welwitschii, together withone known sucrose diester. Compounds 1–4 were obtained as pairs of inseparable (E)/(Z)-isomers of a3,4-dimethoxycinnamoyl derivative, i.e., 1/2 and 3/4. Their structures were elucidated mainly by 2D-NMR techniques and mass spectrometry as 3-O-(b-d-glucopyranosyl)presenegenin 28-{O-b-d-xylopyr-anosyl-(1!4)-O-a-l-rhamnopyranosyl-(1!2)-O-[b-d-glucopyranosyl-(1!3)]-4-O-[(E)-3,4-dimeth-oxycinnamoyl]-b-d-fucopyranosyl} ester (1) and its (Z)-isomer 2, 3-O-(b-d-glucopyranosyl)presenege-nin 28-{O…
Alcoholysis of Aluminum Alkyls Supported by Bulky Phenoxide Ligands: Synthesis, Characterization, and ε-Caprolactone Polymerization Activity of Two D…
2000
Reaction of trialkylaluminum Al2R6 (R = Me, Et) with 2,2′-methylenebis(6-tert-butyl-4-methylphenol) (mbmpH2) gives the dimeric mono(alkyl) complex [Al(mbmp)R]2 with bridging oxygen atoms. Reaction of [Al(mbmp)R]2 with one equiv. of 2-propanol results in the formation of the dimeric isopropoxide [Al(mbmp)(μ-OiPr)]2. Single-crystal X-ray analysis shows a C2h-symmetric structure with a planar Al2O2 core. Monomeric methylbis(2,6-di-tert-butyl-4-methylphenolato)aluminum, AlMe(OC6H2-2,6-tBu2-4-Me)2 (MAD), was found to react with one equiv. of 2-propanol to give a dimeric isopropoxide [AlMe(OC6H2-2,6-tBu2-4-Me)(μ-OiPr)]2 in which the bulky phenolate, instead of the methyl group, has been displaced…
Co-ordination of copper(II) ions by prolyl-α,β-dehydroamino acids: comparative studies and general considerations
1996
Potentiometric and spectroscopic measurements and theoretical calculations have revealed that α,β-dehydroamino acid residues have a considerable effect on the co-ordination ability of an adjacent amide nitrogen towards Cu2+ ions. Also the side chain of such residues affects the stability constants and, in some cases, the binding mode of short peptides containing α,β-dehydroamino acid residues. The theoretical calculations showed that all dehydroamino acids except α,β-dehydroalanine tend to bend a peptide chain towards a turn conformation. This has a very strong impact on the co-ordination ability of a dehydropeptide ligand.
Highly Luminescent Half-Lantern Cyclometalated Platinum(II) Complex: Synthesis, Structure, Luminescence Studies, and Reactivity.
2012
The half-lantern compound [{Pt(bzq)(μ-C 7H 4NS 2-κN,S)} 2]•Me 2CO (1) was obtained by reaction of equimolar amounts of potassium 2-mercaptobenzothiazolate (KC 7H 4NS 2) and [Pt(bzq)(NCMe) 2]ClO 4. The Pt(II)•••Pt(II) separation in the neutral complex [{Pt(bzq)(μ-C 7H 4NS 2-κN,S)} 2] is 2.910 (2) Å, this being among the shortest observed in half-lantern divalent platinum complexes. Within the complex, the benzo[h]quinoline (bzq) groups lie in close proximity with most C•••C distances being between 3.3 and 3.7 Å, which is indicative of significant π-π interactions. The reaction of 1 with halogens X 2 (X 2 = Cl 2, Br 2, or I 2) proceeds with a two-electron oxidation to give the corresponding d…
Effective complexation of psychotropic phenethylammonium salts from a disodium dipyrazolate salt of macrocyclic structure
2002
The equilibrium stability constants (Ks) of ammonium pyrazolate complexes [L2−]2RN(R′)H2+ (3, R′ = H and 4, R′ = Me) formed from a macrocyclic disodium dipyrazolate salt 2[L2−] 2Na+ and ammonium salts (RNH3+X− or RN(Me)H2+X−) of psychotropic drugs and neurotransmitter catecholamines have been evaluated by electrochemical methods in DMSO solution. The resulting Ks values demonstrate that, except for (±)-amphetamine, the complexes formed by lipophilic primary [mescaline, (+)-amphetamine, (±)-p-methoxyamphetamine (PMA), (±)-3,4-methylenedioxyamphetamine (MDA)] and secondary [(±)-methamphetamine, (+)-methamphetamine and (±)-3,4-methylenedioxymethamphetamine (MDMA ‘ecstasy’)] phenethylamines are…