Search results for "Bond length"
showing 10 items of 209 documents
As(III)/Sb(III)/Bi(III)–halide distances and stretching vibrations. An application of the Varshni relationship upon hypervalent group 15 compounds
1998
Abstract A Varshni treatment between stretching frequencies and bond lengths is given for 16 heterocycles of the types Hal–M(SCH 2 CH 2 ) 2 X and Hal–M(CH 2 CH 2 CH 2 ) 2 X (M=As/Sb/Bi, Hal=Cl/Br/I, X=O, S, NR). The intensities of the Raman emissions for the M–Hal bonds increase in the following order: Cl≪Br −1/2 , decrease in the following order: Cl>Br≫I. Practically, the Varshni constants are used to estimate the complementary quantity, stretching frequency or bond length, in 35 cases.
MCSCF determination of the KO molecule ground state.
1992
Abstract Ab initio calculations at the MC/CASSCF level are used to determine in an accurate way the nature and position of the ground state of the KO molecule. The characteristic 2 Π and 2 Σ + alkali monoxide ionic states show a theoretical energy separation of about 0.04 eV, which produces opposite results by authors in favour of one or the other symmetry. We test the basis set dependence and active space dependence of the calculated energetical ordering of both states, with an extensive study of the active orbitais selection; the results show a ground state of 2 Σ + symmetry.
Hypervalent tin-organic compounds: Vibrational spectroscopy in the solid as a tool for structure determination
1997
Abstract A full set of IR- and Raman spectra down from 600 cm1 has been determined and assigned for 60 penta- or hexacoordinated tin-compounds in the groups RSn(CH2CH2CH2)3N (R = Cl, Br, I, Me), RR'Sn(MCH2CH2)2X (R,R′ = Cl, Br, I, Me, Ph, M = CH2 S; X = NMe, O, S), RPh2SnCH2CH2CH2NMe2 (R = Cl, Br, I) and RMe2Sn—CHD—COOMe (R = F, Cl, Br, I, Me). In these hypervalent compounds an approach of the donor atom X to the central atom tin outlines a ‘path’ of nucleophilic attack from a tetrahedron to a trigonal bipyramid. Along this ‘reaction path’ the bond lengths of the axial ligand increase continuously while the bond lengths of the equatorial ligands slightly decrease. The number of similar hype…
Magnetostructural correlations in parallel square-planar halo-bridged copper(II) dimers. Part II: Structure and magnetic properties of [Cu2(terpy)2Br…
1987
Abstract The crystal and molecular structure of bis-μ- bromo-bis [(2,2′:6′,2″ - terpyridyl) copper (II) ] bis (hexafluorophosphate) has been determined from three dimensional single-crystal X-ray diffraction data, collected by counter techniques. The blue crystals belong to the monoclinic system, space group P21/a, with four formula units in a unit cell of dimensions a=20.40(2), b=13.35(2), c=6.453(8) A and β=97.74(9)°. The structure was solved using a refinement procedure and starting with the atomic positions of the isostructural complex [Cu(terpy)- Cl]2(PF6)2, to final agreement factors R=0.071 (Rw=0.077). The structure consists of dimeric molecules bridged by two bromine atoms. The coor…
DFT Calculations of the Electric Field Gradient at the Tin Nucleus as a Support of Structural Interpretation by119Sn Mössbauer Spectroscopy
2005
DFT calculations, using an all-electron basis set and with full geometry optimization, were performed on 34 Sn(II) and Sn(IV) compounds of known structure and (119)Sn Mössbauer parameters, to obtain the theoretical values of the electric field gradient components, V(xx), V(yy), and V(zz), at the tin nucleus. These were used to determine the quantity V = V(zz)[1+ 1/3((V(xx) - V(yy))/((V(zz))(2)](1/2), for each investigated compound, which is related to the quadrupole splitting (DeltaE) parameter according to DeltaE = 1/2eQV, where e is the electronic charge and Q is the quadrupole moment of the tin nucleus. The linear fitting of the correlation plot of the experimental DeltaE, versus the cor…
Large Quadratic Hyperpolarizabilities with Donor–Acceptor Polyenes Exhibiting Optimum Bond Length Alternation: Correlation Between Structure and Hype…
1997
Donor-acceptor polyenes of various lengths, and that combine aro- matic electron-donating moieties with powerful heterocyclic electron-withdraw- ing terminal groups, have been synthe- sized and characterized as efficient non- linear optical (NLO) chromophores. Their linear and nonlinear optical proper- ties have been investigated, and variations in these properties have been related to ground-state polarization (dipole p) and structure. In particular, unprecedented quadratic hyperpolarizabilities (p) have been achieved (up to p(0) =I500 x 10-30esu) by reduction of the bond- length alternation (BLA) in the polyenic chain. In each series of homologous com-
Synthesis and Characterisation of a New Series of Bistable Iron(II) Spin-Crossover 2D Metal-Organic Frameworks
2009
Twelve coordination polymers with formula {Fe(3-Xpy)(2)[M(II)(CN)(4)]} (M(II): Ni, Pd, Pt; X: F, Cl, Br, I; py: pyridine) have been synthesised, and their crystal structures have been determined by single-crystal or powder X-ray analysis. All of the fluoro and iodo compounds, as well as the chloro derivative in which M(II) is Pt, crystallise in the monoclinic C2/m space group, whereas the rest of the chloro and all of the bromo derivatives crystallise in the orthorhombic Pnc2 space group. In all cases, the iron(II) atom resides in a pseudo-octahedral [FeN(6)] coordination core, with similar bond lengths and angles in the various derivatives. The major difference between the two kinds of str…
Novel chiral three-dimensional iron(III) compound exhibiting magnetic ordering at T(c) = 40 K.
2002
The preparation and crystal structure determination of the iron(III) compound of formula [(NH(4))(2)[Fe(2)O(ox)(2)Cl(2)].2H(2)O](n) (1) (ox = oxalate dianion) are reported here. Complex 1 crystallizes in the orthorhombic system, space group Fdd2, with a = 14.956(7) A, b = 23.671(9) A, c = 9.026(4) A, and Z = 8. The structure of complex 1 consists of the chiral anionic three-dimensional network [Fe(2)O(ox)(2)Cl(2)](2-) where the iron(III) ions are connected by single oxo and bisbidentate oxalato groups. The metal-metal separations through these bridging ligands are 3.384(2) and 5.496(2) A, respectively. Ammonium cations and crystallization water molecules are located in the helical pseudohex…
Mono(cyclopentadienyl)titanium complexes containing a sulfide-bridged bis(phenolato) ligand. Molecular structure of Ti{2,2′-S(OC6H2-4-Me-6-tBu)2}(η5-…
2001
A series of titanium complexes containing a sulfur-bridged chelating bis(phenolato) ligand, Ti{2,2′-S(OC 6 H 2 -4-Me-6- t Bu) 2 }(η 5 -C 5 R 5 )Cl (R=H, Me; R 5 =1,3-(SiMe 3 ) 2 H 3 ), were prepared by the reaction of the dilithium derivative Li 2 [2,2′-S(OC 6 H 2 -4-Me-6- t Bu) 2 ] with Ti(η 5 -C 5 R 5 )Cl 3 . Alkylation of the chloro complexes gave complexes of the type Ti{2,2′-S(OC 6 H 2 -4-Me-6- t Bu) 2 }(η 5 -C 5 R 5 )R′ (R′=Me, CH 2 Ph). The crystal structure of the chloro complex Ti{2,2′-S(OC 6 H 2 -4-Me-6- t Bu) 2 }(η 5 -C 5 H 5 )Cl has been determined by X-ray diffraction and shows a monomeric four-legged piano-stool structure with the sulfur and chlorine atoms in trans positions. …
3,4-Bis(4-fluorophenyl)-1,2,5-oxadiazole 2-oxide
2006
The title compound, C14H8F2N2O2, also known as di(4-F-phenyl)furazan N-oxide, was found as a side product in the synthesis of isoxazole derivatives. The are two molecules in the asymmetric unit. The bond length of the dipolar N—O unit is 1.107 (7) A. X-ray analysis confirmed the compound to have the desired structure