Search results for "Bond length"
showing 10 items of 209 documents
Molecular equilibrium structures from experimental rotational constants and calculated vibration–rotation interaction constants
2002
A detailed study is carried out of the accuracy of molecular equilibrium geometries obtained from least-squares fits involving experimental rotational constants B(0) and sums of ab initio vibration-rotation interaction constants alpha(r)(B). The vibration-rotation interaction constants have been calculated for 18 single-configuration dominated molecules containing hydrogen and first-row atoms at various standard levels of ab initio theory. Comparisons with the experimental data and tests for the internal consistency of the calculations show that the equilibrium structures generated using Hartree-Fock vibration-rotation interaction constants have an accuracy similar to that obtained by a dir…
Electrochemical properties of crystallized dilithium squarate: insight from dispersion-corrected density functional theory.
2012
International audience; The stacking parameters, lattice constants, and bond lengths of solvent-free dilithium squarate (Li(2)C(4)O(4)) crystals were investigated using density functional theory with and without dispersion corrections. The shortcoming of the GGA (PBE) calculation with respect to the dispersive forces appears in the form of an overestimation of the unit cell volume up to 5.8%. The original Grimme method for dispersion corrections has been tested together with modified versions of this scheme by changing the damping function. One of the modified dispersion-corrected DFT schemes, related to a rescaling of van der Waals radii, provides significant improvements for the descripti…
A very short uranium-uranium bond: The predicted metastable U22+
2005
Quantum chemical calculations, based on multiconfigurational wave functions and including relativistic effects, show that the U(2)2+ system has a large number of low-lying electronic states with S of 0 to 2 and Lambda ranging from zero to ten. These states share a very small bond length of about 2.30 A, compared to 2.43 A in neutral U2. The Coulomb explosion to 2 U+ lowers the energy by only 1.6 eV and is separated by a broad barrier.
Synthesis and spectroscopic characterization of diethyltin (IV) derivatives of dipeptides: Crystal and molecular structure of diethyltin glycyltrosin…
1992
Dipeptide complexes of the diethyltin(IV) moiety, Et2SnL, have been synthesized, H2L being glycylglycine (H2GlyGly), glycylalanine (H2GlyAla), alanylalanine (H2AlaAla), glycylvaline (H2GlyVal), valylvaline (H2ValVal), glycylmethionine (H2GlyMet), glycyltyrosine (H2GlyTyr). The crystal and molecular structure of the complex Et2SnGlyTyr has been determined by singlecrystal X-ray diffraction. It consists of monomeric units, with the tin atom having a considerably distorted trigonal bipyramidal environment. The dipeptide acts as a tridentate ligand bonding the tin of the C2Sn fragment (equatorial carbon atoms) with the peptide nitrogen atom (equatorial) and axial (monodentate) carboxyl oxygen a…
Adsorption of the herbicide 4-chloro-2-methylphenoxyacetic acid (MCPA) by goethite.
2014
Interaction between the goethite surface and 4-chloro-2-methylphenoxyacetic acid (MCPA) herbicide was studied using density functional theory (DFT) calculations combined with molecular dynamics (MD). The important step made here lies in the use of a periodic DFT method enabling the study of a mineral surface of different protonation states, in strong contrast with previous molecular modeling studies limited to single protonation state corresponding to the point of zero charge. Different surface OH groups and MCPA proton states were used to mimic the strong effects of pH on the outer- and inner-sphere surface complexes that are theoretically possible, together with their binding energies, an…
A new calcium sulfate hemi-hydrate
2010
Calcium sulfate hydrates receive significant attention due to numerous large scale industrial applications. There has been a long debate on the possible existence of two gypsum hemi-hydrate polymorphs, denoted alpha- and beta-CaSO(4).0.5H(2)O. In this work, a new crystal structure of calcium sulfate hemi-hydrates is presented, denoted beta-CaSO(4).0.5H(2)O. The structure was solved using powder neutron diffraction data, the space group is P3(1) and the unit cell in a hexagonal setting a = 6.9268(1), c = 12.7565(3) A. The structure has two calcium-oxygen coordination polyhedra: Ca1 is eight coordinated and has Ca-O bond lengths in the range 2.31(3) to 2.89(2) A and Ca2 is nine coordinated an…
Structure and physical properties of [mu-tris(1,4-bis(tetrazol-1-yl)butane-N4,N4 ')iron(II)] bis(hexafluorophosphate), a new Fe(II) spin-crossover co…
2004
[mu-Tris(1,4-bis(tetrazol-1-yl)butane-N4,N4')iron(II)] bis(hexafluorophosphate), [Fe(btzb)(3)](PF6)(2), crystallizes in a three-dimensional 3-fold interlocked structure featuring a sharp two-step spin-crossover behavior. The spin conversion takes place between 164 and 182 K showing a discontinuity at about T-1/2 = 174 K and a hysteresis of about 4 K between T-1/2 and the low-spin state. The spin transition has been independently followed by magnetic susceptibility measurements, Fe-57-Mossbauer spectroscopy, and variable temperature far and midrange FIR spectroscopy. The title compound crystallizes in the trigonal space group P (3) over bar (No. 147) with a unit cell content of one formula u…
N-(3-Methoxypropyl)-1,8-naphthalimide
2003
In the title compound, C16H15NO3, the 1,8-naphthalenodicarboximide group is nearly planar and, in the naphthalimide ring system, the characteristic alternating pattern of bond lengths is observed. In the crystal, the molecules are connected by a weak C—H⋯O hydrogen bond and extend in the direction parallel to the b axis.
[Bis(dimethylsulphoxide) protium][trans-bisdimethylsulphoxidetetrachloroiridate(III)]
1988
Abstract [(DMSO)2H]trans-[IrCl4(DMSO)2] (DMSO = dimethylsulphoxide) has been structurally characterized. The hydrogen bonded cation [DMSOHDMSO]+ has a very short OHO bond distance (2.405 A) which compares well with that in the known rhodium analogue. The two DMSO ligands are trans on iridium and coordinate via the sulphur atoms. Earlier work had assigned the cis structure to the anion in this compound.
Synthesis and crystal structure of the low-spin iron(II) complex [Fe(bpym)3](ClO4)2·1/4H2O (bpym=2,2′-bipyrimidine)
1997
Abstract Single crystals of the mononuclear iron(II) complex of formula [Fe(bpym)3](ClO4)2·1/4H2O (bpym=2,2′-bipyrimidine) have been prepared and characterized crystallographically. The complex is monoclinic, P21/c, a=13.688(5), b=19.391(6), c=11.554(5) A, β=102.22(3)°, V=2997(2) A3, Z=4, R=0.063 and Rw=0.068. The structure analysis reveals a distorted octahedral geometry around the iron atom. The average Fe–N bond length and N–Fe–N bidentate angle are 1.970(5) A and 81.0(1)°, respectively. The value of the Fe–N distance and that of the room temperature magnetic moment are in agreement with its singlet 1A1 ground state.