Search results for "MOLECULE"
showing 10 items of 5162 documents
A spectroelectrochemical study of poly(dithienothiophenes)
1997
Abstract The use of n- and p-dopable conjugated polymers as both the working and counter electrodes in an electrochemical device has always attracted chemists and has stimulated the design of new molecules with a low energy gap that can be p- and n-doped efficiently. The present paper reports the spectroelectrochemical study of polymers obtained from several dithienothiophene isomers, molecules with three thiophene rings fused in different positions. Of the six isomers, poly(dithieno[3,4-b:3′,2′-d]thiophene) and poly(dithieno[3,4-b:2′,3′-d] thiophene) were tested against poly(dithieno[3,2-b:2′,3′-d]thiophene) and poly(dithieno[3,4-b:3′,4′-d]thiophene). The differences in their performance, …
Weak non-covalent interactions control the relative molecular orientation in the crystals of N-pentafluorobenzyl aniline derivatives
2010
The crystal structures of N-pentafluorobenzyl aniline derivatives are controlled by versatile aromatic–aromatic interactions between the electron deficient and electron rich aromatics; the parent compound (1) possesses an L shape while protonation (2–5) induces a conformational change resulting in a planar arrangement of molecules which pack in layer type structures with different molecular orientations.
Synthesis, Structures and DFT Calculations on Alkaline-Earth Metal Azide-Crown Ether Complexes
2008
The first examples of azide complexes of calcium, strontium or barium with crown ethers have been prepared and fully characterised, notably [Ba([18]crown-6)(N3)2(MeOH)], [Sr([15]crown-5)(N3)2(H2O)], [Ca([15]crown-5)(N3)2(H2O)] and [Sr([15]crown-5)(N3(NO3)]. Crystal structures reveal the presence of a variety of coordination modes for the azide groups including kappa 1-, mu-1,3- and linkages via H-bonded water molecules, in addition to azide ions. The [Ba([18]crown-6)(N3)2(MeOH)].1/3 MeOH contains dinuclear cations with three mu-1,3-NNN bridges, the first example of this type in main group chemistry. The structures obtained have been compared with molecular structures computed by density fun…
Metamagnetic Behavior in [M (tvp) (NCS)2] Coordination Polymers (M = Fe(II) and Co(II); tvp = 1,2-di-(4-pyridyl)-ethylene)
1999
Abstract We report the synthesis and magnetic properties of two new coordination polymers of formula [M(tvp)(NCS)2] (M = Fe(II) and Co(II)). The magnetic data reveal the occurrence of metamagnetic behavior. Switching from bulk antiferromagnetic to ferromagnetic behavior occurs for magnetic fields greater than 1300 G (Fe(II)) and 450 G (Co(II)) at temperatures lower than 4 K. Both compounds are isomorphous. A molecular structure is suggested in the light of the magnetic properties and precedent data on related systems.
Sn<sup>IV</sup> and Zr<sup>IV</sup> Compounds of a <i>C</i>&l…
2017
This contribution describes the synthesis and structural characterization of a triaminoguanidinium (TAG)-based ligand [H6(OMe)3Limin]BF4 (1) containing imine bonds (Limin) and its reduction with a dimethylamino borane complex to the corresponding amine compound (Lamin)[H9(OMe)3Lamin]OTs (2). In solution, both ligands are C3-symmetric but crystal structures show the great influence of the reduction on the molecular structure. We show that the planar imine ligand is converted to a highly flexible compound which has nine potential coordination sites, three phenoxy and six amine donors, for binding metal ions. First solid state structures of 1:1 (metal:ligand) coordination compounds with SnIV a…
Copper(II) complexes of 3-aminopropanols. Synthesis and structure of (3-aminopropanolato)formatocopper(II)
1987
Abstract The crystal and molecular structure of the title compound has been determined from single-crystal X-ray data and refined to a final R value of 0.030 for 971 reflections. The compound crystallizes in the monoclinic space group P21/c with two dimeric molecules in a cell of dimensions a=856.9(1), b= 887.7(1), c=837.0(1) pm and β=99.55(1)°. The blue crystals of Cu(ap)(HCOO) (ap=3-aminopropanolato ion) are made of centrosymmetric dialkoxy bridged dimers (Cu…Cu 296.4(1) pm). The dimers are polymerized along the c axis into chains via two NHO hydrogen bonds (Cu…Cu 547.9(1) pm). These chains are joined together along the b axis by CuOCOCu bridges and NHO hydrogen bonds (Cu…Cu 462.2(1) pm…
Synthesis, Protonation and Cu II Complexes of Two Novel Isomeric Pentaazacyclophane Ligands: Potentiometric, DFT, Kinetic and AMP Recognition Studies
2008
The synthesis and coordination chemistry of two novel ligands, 2,6,9,12,16-pentaaza[17]metacyclophane (L1) and 2,6,9,12,16-pentaaza[17]paracyclophane (L2), is described. Potentiometric studies indicate that L1 and L2 form a variety of mononuclear complexes the stability constants of which reveal a change in the denticity of the ligand when moving from L1 to L2, a behaviour that can be qualitatively explained by the inability of the paracyclophanes to simultaneously use both benzylic nitrogen atoms for coordination to a single metal centre. In contrast, the formation of dinuclear hydroxylated complexes is more favoured for the paraL2 ligand. DFT calculations have been carried out to compare …
The first spiroconjugated TTF- and TCNQ-type molecules: a new class of electroactive systems?
2005
[Structure: see text] Spiroconjugated TTF-type electron donors (13a-c) and TCNQ-type electron acceptors (10, 11) have been prepared from spiroquinone 9. Cyclic voltammetry reveals a relatively weak accepting ability for 10 and 11, and a strong electron-donor character for 13a-c. Whereas the spiroconjugation introduces a destabilization of the LUMO for compounds 9-11, the opposite is observed for compound 13, thus justifying the redox potential values.
Study of the conformations of the molecules in amorphous polymers by computer simulation
2008
It is investigated by computer simulation whether space problems prevent a closing packing of chain molecules if the chain molecules are randomly coiled. Chains consisting of 100 beads were introduced into a primitive cubic lattice in such a way that each lattice point is occupied by not more than one bead. It was possible to occupy up to 88% of the lattice points. The average square end-to-end distance of the chains in the concentrated system is the same as for a single chain. Neither perfect chain bundles nor imperfect chain bundles occur in a considerable amount. This shows that it is possible to pack closely randomly coiled chains.
Theoretical study of the OH addition to the β-pinene
2004
The initial step of the mechanism of the OH + β-pinene gas-phase reaction was investigated by means of ab initio calculations. Four different possibilities for the OH addition to the double bond are discussed, corresponding to the addition on each C atom of the double bond, and for each one, either the syn or anti OH attack to the two methyl groups on the (bi)cyclic molecule. Energy barriers calculated at the QCISD(T)/6-31G(d) level of theory on UMP2/6-31G(d) optimised structures, show that there are preferred orientations for the OH addition under atmospheric conditions of temperature and pressure.