Cs Symmetry Research Articles

Gas-phase molecular structure of 1,1,1,2-tetrabromo-2,2-dimethyldisilane: theoretical and experimental investigation of a super-halogenated disilane and computational investigation of the F, Cl and I analogues

The molecular structure of 1,1,1,2-tetrabromo-2,2-dimethyldisilane (Br3SiSiBrMe2) has been determined in the gas phase by electron diffraction and ab initio molecular-orbital calculations. The computational investigation was used to augment the experimental investigation using the Structure Analysis Restrained by Ab initio Calculations for Electron diffractioN (SARACEN) method. The structure was found to adopt a staggered structure with Cs symmetry by both theory and experiment. Important structural parameters (rh1) include: rSi–Si 235.6(5) pm, rSi–C 185.4(3) pm, rSi–Brav 220.3(1) pm, ∠Si–Si–Br(14) 106.1(4)°, ∠Si–Si–C 109.2(8)° and ϕBr–Si–Si–Br 180.0°(fixed). These experimental observations are supported by theoretical predictions obtained at the MP2/6-311+G* level. An analogous theoretical investigation was also performed for the series X3SiSiXMe2 (X = F, Cl and I) and structural trends identified. The Si–X bond was observed to lengthen as a function of the halogen substituent, with corresponding changes to the Si–Si–X bond angles in the SiX3 groups. The Si–Si–X bond angle in the SiXMe2 groups displayed rather different behaviour, and was relatively stable to substitution until X = I. The flexible nature of bond angles about silicon atoms was observed, even in this relatively sterically unhindered system.

Characterization of the t-Butyl Radical and Its Elusive Anion.

The t-butyl radical and its anion are studied theoretically using state-of-the-art quantum mechanical methods including coupled cluster theory with full single, double, and triple excitations (CCSDT) and CCSDT with perturbative quadruple excitations [CCSDT(Q)], in concert with large correlation-consistent cc-pVXZ and aug-cc-pVXZ (X = D, T, Q, 5) basis sets. The relative energies are extrapolated to the complete basis set limit (CBS). The lowest energy structure of the t-butyl radical has a nonplanar carbon backbone with overall C3v symmetry. Low-lying C3h and Cs symmetry transition states, for pyramidal inversion and methyl group rotation, respectively, between equivalent C3v minima are investigated. The barriers for these interconversions are both less than 1 kcal mol(-1), but the corresponding barriers on the anion potential energy surface are more pronounced. Using the focal point analysis technique, we obtain a value of -0.48 kcal mol(-1) for the t-butyl radical adiabatic electron affinity at the CCSDT(Q)/CBS level of theory, where the negative sign indicates that the formation of the t-butyl anion is adiabatically unfavorable. We show that the electron affinity, whose sign has been the subject of debate, is very sensitive to both the basis set and the correlation treatment, and previous experimental and theoretical estimates of its value bracket the value computed herein. Our results indicate that the t-butyl anion is classically metastable with a vertical detachment energy of over 10 kcal mol(-1) to reach the neutral potential energy surface. However, the inclusion of the zero-point vibrational effects seems to favor its nonexistence.

CASPT2 and CCSD(T) calculations of dipole moments and polarizabilities of acetone in excited states

The acetone molecule is investigated in its ground state and valence 1,3n-π*, 1,3π-π*, and 1,3σ-π* excited states and Rydberg 1,3n-3s, 1,3π-3 , 1,3n-3py and 1,3π-3py states using the CASSCF, CASPT2, and CCSD(T) methods. Equilibrium geometries of excited states are obtained and their changes with respect to the ground state are discussed. For most excited states the C2v symmetry of the ground state is lowered to the Cs symmetry. A series of valence vertical and adiabatic excitation energies is presented along with excitation energies for Rydberg states. The main body of the paper contains Finite-Field Perturbation Theory (FFPT) calculations of electric properties of the vertically as well as geometry relaxed excited states. Dipole moments of valence excited states decrease significantly upon excitation, being about one half of the ground state dipole moment. Polarizabilities usually change upon excitation much less (increase by about 30%) but hyperpolarizabilities are enhanced up to one or two orders of magnitude. The orientation of the dipole moment is reversed in some vertically excited Rydberg states. Properties of the ground and excited states are discussed considering alterations of the electronic structure and shifts in the geometry.

Comment on: “FT-IR, FT-Raman and UV spectral investigation; computed frequency estimation analysis and electronic structure calculations on 1-nitronaphthalene” by M. Govindarajan and M. Karabacak [Spectrochim. Acta A 85 (2012) 251–260

The title paper [1] incorrectly establishes that, in gas phase the global minimum energy structure of 1-nitronaphthalene is planar (Cs symmetry). By contrast, present calculations indicate that the planar Cs form is an unstable structure on the potential energy surface, exhibiting an imaginary vibrational wavenumber value corresponding to the torsional mode of the nitro group around the C–N bond. At the B3LYP/6-311++G(d,p) level of calculation the global minimum energy structure of 1-nitronaphthalene in gas phase has a non-planar geometry, characterized by O–N–C–C dihedral angles of ca. 30° and lying 0.35kcal/mol below the Cs form.

Testing a new analytical approach for determination of vibrational transition moment directions in low symmetry planar molecules: 1-D- and 2-D-naphthalene

A new analytical approach for improving the precision in determination of vibrational transition moment directions of low symmetry molecules (lacking orthogonal axes) is discussed in this paper. The target molecules are partially uniaxially oriented in nematic liquid crystalline solvent and are studied by IR absorption spectroscopy using polarized light. The fundamental problem addressed is that IR linear dichroism measurements of low symmetry molecules alone cannot provide sufficient information on molecular orientation and transition moment directions. It is shown that computational prediction of these quantities can supply relevant complementary data, helping to reveal the hidden information content and achieve a more meaningful and more precise interpretation of the measured dichroic ratios.The combined experimental and theoretical/computational method proposed by us recently for determination of the average orientation of molecules with Cs symmetry has now been replaced by a more precise analytical approach. The new method introduced and discussed in full detail here uses a mathematically evaluated angle between two vibrational transition moment vectors as a reference. The discussion also deals with error analysis and estimation of uncertainties of the orientational parameters. The proposed procedure has been tested in an analysis of the infrared linear dichroism (IR–LD) spectra of 1-D- and 2-D-naphthalene complemented with DFT calculations using the scaled quantum mechanical force field (SQM FF) method.

Orthorhombic polymorph of (2E)-2-(2,3-dihydro-1H-inden-1-ylidene)-2,3-dihydro-1H-inden-1-one

The title compound, C18H14O, is polymorphic at 123 K. The ortho­rhom­bic form reported herein has two independent mol­ecules in the asymmetric unit, with mol­ecular volume 313.5 Å3. The previously reported triclinic (P-1) form [Raston & Scott (2000 ▶). Green Chem., 2, 49–52] has mol­ecular volume 309.6 Å3 at the same temperature. All three mol­ecules deviate significantly and systematically from the putative Cs symmetry (δr.m.s. = 0.0265, 0.0256, 0.0497 Å). Comparison of the two molecules in the orthorhombic polymorph shows that 16 of the 19 equivalent pairs of framework atoms have a mirror-image pattern of deviations (above/below plane), suggesting that the two are quasi-enanti­omorphs. The pattern of deviations in the triclinic form is nearly the same (13 of 19 atom pairs) as the ortho­rhom­bic form.

Photoabsorption spectroscopy of dimethyl sulfoxide at the O1s, C1s, S2s, and S2p Regions: A comparison with acetone

AbstractThe S2p, S2s, C1s, and O1s Total Ion Yield (TIY) spectra of gaseous dimethyl sulfoxide (DMSO) and the C1s and O1s TIY spectra of acetone were measured using tunable synchrotron radiation. To establish a complete and accurate spectral analysis, the assignments for the main experimental bands were carried out using density functional theory (DFT) calculations based on half core hole (HCH) method, as implemented in the StoBe‐deMon program, and ab initio calculations, based on the improved virtual orbital (IVO) method, as implemented in the GSCF3 program, using Hartree‐Fock. The hole state was calculated in Huzinaga basis sets for the IVO method and IGLO‐III basis sets for the HCH method. A nonlocal BE88‐PD86 DFT method was used. The geometric parameters were calculated using the DFT‐B3LYP method with the 6‐311+G** basis sets. The experimental and theoretical results for the ionization potentials and the threshold energies are quite similar. The results reflect some differences for both molecules, likely caused by the presence of the S=O (Cs symmetry) as well as the C=O (C2v symmetry) groups. © 2012 Wiley Periodicals, Inc.

Synthesis, Structure, and Properties of the New Mixed-Valent Dodecahalogenotrimetallate In4Ti3Br12 and its Relation to Compounds A3Ti2X9 (A = K, In; X = Cl, Br)

Black single crystals of the new dodecahalogenotrimetallate In(4)Ti(3)Br(12) were obtained by reacting InBr(3) with Ti-wire at 450 °C in a silica tube sealed under vacuum. In(4)Ti(3)Br(12) (Pearson symbol hR57, space group R3m, Z = 3, a = 7.3992(8) Å, c = 36.673(6) Å, 643 refl., 25 param., R(1)(F) = 0.025; wR(2)(F(2)) = 0.046) is a defect variant of a 12 L-perovskite. In(+) cations are 12-fold coordinated in two different ways: In1 as an anticuboctahedron and In2 as a cuboctahedron. In both cases the 5s(2) configuration results in 3 short, 6 medium, and 3 long In-Br distances which might be explained as lone pair effect or second order Jahn-Teller instability. Furthermore there are isolated linear trimers [Ti(3)Br(12)](4-) consisting of facesharing octahedra similar to [Ru(3)Cl(12)](4-). The [Ti(3)Br(12)](4-)-unit has to be described as a mixed-valent d(1)-d(2)-d(1) system. According to magnetic measurements, the Ti-atoms in In(4)Ti(3)Br(12) show strong antiferromagnetic interactions (Θ = -1216(6) K) which might be addressed as weak Ti(3+)-Ti(2+)-Ti(3+) bonds. For comparison, single crystals of K(3)Ti(2)X(9) (X = Cl, Br) were synthesized and their structures refined. The rotation of the Ti(2)X(9)(3-) dimers reduced the symmetry of the well-known Cs(3)Cr(2)Cl(9) type from P6(3)/mmc to P6(3)/m and resulted in the formation of merohedral twins. According to the unit cell volumes In(+) is smaller than K(+) in all cases.

Molecular Structure of Methyldifluoroisocyanato Silane: A Combined Microwave Spectral and Theoretical Study

The structure of methyldifluoroisocyanato silane, MeF2SiNCO (2), has been studied by molecular rotational spectroscopy. The rotational spectrum has a complicated structure from (14)N nuclear quadrupole coupling and internal rotation of the methyl group. Cavity Fourier-transform microwave spectroscopy measurements were important for providing high spectral resolution to analyze the quadrupole and internal rotation fine structure. Broadband chirped-pulse Fourier-transform microwave spectroscopy was used to achieve high measurement sensitivity making it possible to observe the lower abundance C, N, O, and Si isotopologues in natural abundance for structure determination. Analysis of the microwave spectrum of the most abundant isotopomer of MeF2SiNCO (2) yields the rotational constants: A = 3827.347(7), B = 1264.5067(14), and C = 1240.6182(11) MHz. The spectrum has been analyzed in the I(r) representation for Cs symmetry, with inclusion of the 3-fold rotor (V3 = 446(50) cm(-1)). A partial substitution structure was obtained for the C, Si, N, and O atoms. The analysis was assisted by calculations of the equilibrium structure, using a 6-311++G (3df, 3pd) basis set, with calculations at each of the B3LYP, MP2, and CCSD(T) levels. The calculated and experimental rotational constants are only consistent with a trans-orientation at each of the HCSiN, CSiNC, and SiNCO centers; there is relatively close agreement between the experimental and the theoretical structures, especially at the CCSD(T) level. In addition, the observed low value for the (14)N quadrupole coupling term (χbb - χcc) implies a wide SiNC angle, which is consistent with the calculated values: 165.3° (B3LYP), 157.6° (MP2), and 157.4° (CCSD(T)). The skeletal bending potential is discussed.

Ab initio calculations of the lowest electronic states in the CuNO system

The lowest singlet and triplet electronic levels of the A' and A" symmetry species of the neutral copper-nitrosyl (CuNO) system are calculated by ab initio methods at the multi-reference configuration interaction (MRCI) level of theory with single and double excitations, and at the coupled cluster level of theory with both perturbational (CCSD(T)) and full inclusion of triple excitations (CCSDT). Experimental data are difficult to obtain, hence the importance of carrying out calculations as accurate as possible to address the structure and dynamics of this system. This paper aims at validating a theoretical protocol to develop global potential energy surfaces for transition metal nitrosyl complexes. For the MRCI calculations, the comparison of level energies at linear structures and their values from C(2v) and C(s) symmetry restricted calculations has allowed to obtain clear settings regarding atomic basis sizes, active orbital spaces and roots obtained at the multi-configurational self-consistent field (MCSCF) level of theory. It is shown that a complete active space involving 18 valence electrons, 11 molecular orbitals and the prior determination of 12 roots in the MCSCF calculation is needed for overall qualitatively correct results from the MRCI calculations. Atomic basis sets of the valence triple-zeta type are sufficient. The present calculations yield a bound singlet A' ground state for CuNO. The CCSD(T) calculations give a quantitatively more reliable account of electronic correlation close to equilibrium, while the MRCI energies allow to ensure the qualitative assessment needed for global potential energy surfaces. Relativistic coupled cluster calculations using the Douglas-Kroll-Hess Hamiltonian yield a dissociation energy of CuNO into Cu and NO to be (59 ± 5) kJ mol(-1) ((4940 ± 400) hc cm(-1)). Favorable comparison is made with some of previous theoretical results and a few known experimental data.

Reduced bandwidth chirped-pulse microwave spectroscopy for analysis of weakly bound dimers: Rotational spectrum and structural analysis of CH2ClF⋯FHC[dbnd]CH2

A reduced bandwidth (480MHz) chirped-pulse Fourier-transform microwave spectrometer has been used to record the rotational spectrum of the weakly bound complex between chlorofluoromethane and fluoroethylene (CH2ClF⋯FHCCH2). Spectra of both the 35Cl and 37Cl isotopologues were assigned from a 7 to 18GHz broadband scan. Derived rotational constants (35Cl: A=5602.82(28)MHz, B=918.5894(4)MHz, C=795.1888(4)MHz; 37Cl: A=5453.14(9)MHz, B=913.6372(5)MHz, C=788.4024(4)MHz) are consistent with a Cs symmetry structure in which the CH2ClF is angled toward the fluorine and hydrogen atoms at the end of the fluoroethylene subunit. The CH2ClF hydrogen atoms straddle the fluorine atom on fluoroethylene, while the chlorine atom from CH2ClF points towards the geminal hydrogen atom on fluoroethylene. Dipole moment components of μa=2.342(6)D, μb=0.022(7)D and μtot=2.342(7)D were also determined.

Molecular structure and relative stability of trans and cis isomers of formanilide: gas-phase electron diffraction and quantum chemical studies

Molecular structure of formanilide is determined by gas-phase electron diffraction (GED) augmented by quantum chemical calculations (B3LYP/cc-pVTZ and MP2/cc-pVTZ) and literature microwave (MW) data. The combined GED and MW data are well reproduced for the mixture of trans and cis isomers with the relative abundance of 59 ± 5 and 41 ± 5 %, respectively, at T = 410 K. The trans isomer (C s symmetry) is planar, while the cis isomer (C 1 symmetry) has the twisted structure with the amide group rotated by 36.7 ± 2.7° with respect to the phenyl ring. In accord with theoretical calculations, the amide bond –NH–C(O)– is planar in trans formanilide and a somewhat nonplanar in cis isomer. Accurate structural parameters were obtained by a simultaneous fit of the rotational constants reported in the literature and GED intensities obtained in this study. The N–C(O) and N–CPh bond dissociation energies in formanilide are calculated using Gaussian-4 method. It is revealed that the strength of N–C(O) bond in formanilide is 50 kJ/mol less than that in benzamide. On the contrary, the strength of adjacent bond (N–CPh) increases by 35 kJ/mol compared to aniline. It is rather unexpectedly that the bond strength weakening does not result in the bond elongating, and vice versa.

Mesogenic Ni(II) complexes of Cs symmetry forming Colh phase by dipole-dipole interaction

New Ni(II) metallomesogens are described, having their chelating centre constructed from two non-identical fragments: enaminoketone and barbiturylidenomethyleno-amine rings, thus low Cs symmetry. Various side chains were attached to the mesogenic core. Despite a triangular molecular shape, almost all synthesised compounds exhibit a liquid crystalline hexagonal disordered columnar phase (Colh) with high clearing temperature. The ability to create the columnar phase is probably connected with the permanent dipole moment appearing in the non-symmetric molecules and dipole–dipole interactions between molecules in columns. This work is dedicated to Prof. Michael Hanack, with best wishes, on the occasion of his 80th birthday.

Electronic spectra of the jet-cooled 1-methylvinylthio radical

Electronic spectra of the B̃-X̃ transition of the 1-methylvinylthio radical were observed in a discharged jet of propylene sulfide by laser-induced fluorescence spectroscopy. Identification of the spectral carrier was made by comparing the observed spectra with results of molecular orbital calculations, in particular, for vibrational frequencies, rotational contour simulations, and the Franck-Condon simulations. Vibrational structures observed in the electronic spectra indicate that the 1-methylvinylthio radical can be regarded as a molecule with C(s) symmetry at the zero-point levels of both the excited and ground states.

Control of Cross-Sections and Optical Nonlinearity of Pt Nanowires and the Roughness Effect

In this paper we review our fabrication of Pt nanowire arrays on MgO(110) faceted templates by a shadow deposition method and our control of their cross-sectional shapes by adjusting the deposition directions of platinum. We obtained nanowire arrays with Cs and C2v macroscopic symmetries. These macroscopic symmetries influence optical second harmonic generation (SHG) susceptibility elements of the nanowire arrays sensitively. On the other hand, the roughness of the nanowires had an effect on the rotational SHG patterns as a function of the sample rotation angle around the surface normal. We tried to explain the pattern change by a second-order perturbation scheme with respect to the roughness amplitude.

Tautomeric properties and gas-phase structure of 3-methyl-2,4-pentanedione

The tautomeric and structural properties of 3-methyl-2,4-pentanedione, CH3C(O)CH(CH3)C(O)CH3, have been studied by gas-phase electron diffraction (GED) and quantum chemical calculations (B3LYP and MP2 approximation with different basis sets up to aug-cc-pVTZ). Analysis of GED intensities resulted in the presence of 100(3)% enol tautomer at 274(7)K. Quantum chemical calculations predict enol concentrations from 8% at MP2/6-31G(d,p) level to 100% at B3LYP/aug-cc-pVTZ. This would show the failure of the MP2/6-31G(d,p) method. The enol ring possesses CS symmetry with a strongly asymmetric hydrogen bond. The experimental geometric parameters are reproduced very closely by the B3LYP/aug-cc-pVTZ method.

Calculation of vibrational energy levels of triatomic molecules with the C 2v and C s symmetries by summing divergent series of the Rayleigh-Schrödinger perturbation theory

The Rayleigh-Schrodinger perturbation theory is applied to calculation of vibrational energy levels of triatomic molecules with the C2v and Cs symmetries: SO2, H2S, F2O, HOF, HOCl, and DOCl. Particular attention is given to the states coupled by anharmonic resonances; for such states, the perturbation theory series diverge. To sum these series, the known methods of Pade, Pade-Borel, and Pade-Hermite and the method of power moments are used. For low-lying levels, all the summation methods give satisfactory results, while the method of quadratic Pade-Hermite approximants appears to be more efficient for high-excited states. Using these approximants, the structure of singularities of the vibrational energy, as a function in the complex plane, is studied.

A study of the structure and conformation of 1,1-dicyclopropylethene by gas electron diffraction and ab initio calculations

Abstract The molecular structure of 1,1-dicyclopropylethene, c-(C3H5)2C CH2, has been determined by gas electron diffraction (GED) and ab initio calculations. The potential energy surface as a function of the two torsional angles was calculated to examine the conformation of the molecule. The structural model for the GED data analysis was constructed using ab initio calculations at the MP2(full)/aug-cc-pVTZ level of theory. The conformational mixture at about 293 K was determined to be 36(14)% for the trans-gauche form with C1 symmetry and 64(14)% for the gauche-gauche form (mixture of the gauche-gauche form with C2 symmetry (38(27)%) and the gauche-gauche’ form with Cs symmetry (26%)). The uncertainty of the gauche-gauche form with C2 symmetry was estimated by the Hamilton R-factor ratio test. The present result is in agreement with that reported in a previous GED study (Traetteberg et al. J. Mol. Struct. 485–486 (1999) 73). The conformational abundances determined by GED are different from those in liquid xenon determined by a vibrational spectroscopic study (Durig et al., J. Phys. Chem. A. 109 (2005) 1650).

Do enantiomers of benzenesulfonic acid exist? Electron diffraction and quantum chemical study of molecular structure of benzenesulfonic acid

Molecular structure of benzenesulfonic acid was studied by gas-phase electron diffraction and quantum chemical (B3LYP/cc-pVTZ, МР2/cc-pVDZ, МР2/cc-pVTZ) methods. On the base of mass spectrometric analysis it was found that saturated vapor at Т=396(9)K is represented by only molecular species, monomeric benzenesulfonic acid. Theoretical calculations showed that the molecule has two mirror conformers of C1 symmetry which can invert to each other via transition state of Cs symmetry by rotation of OH-group around SO(H) bond. Both computational methods, B3LYP and MP2, resulted in the same structure of enantiomers; the MP2/cc-pVDZ calculations denoted a over-barrier transition between enantiomers at the temperature of electron diffraction experiment, while B3LYP and MP2 calculations with cc-pVTZ basis set estimated the barrier height to be comparable with the thermal energy value. Two geometric models of C1 and Cs symmetry were examined in gas electron diffraction structural analysis. It was established that the structure of C1 symmetry (Rf=3.3%) demonstrated the best fit with GED data in comparison with Cs structure (Rf=3.8%).In conformer of C1 symmetry an ordinary bond SO(Н) is located almost orthogonal to benzene ring plane, and an OH bond practically eclipses one of SO bonds of SO3H fragment. The following internuclear distances (Å) in benzenesulfonic acid were determined: rh1(CH)av=1.116(6), rh1(CC)ср=1.402(4), rh1(CS)=1.770(5), rh1(SO)av=1.438(4), rh1(SO)=1.623(4), rh1(OH)=0.870(17).Calculations of internal rotation potential functions and NBO-analysis of electron density distribution in a conformer and transition states between enantiomers were performed to establish the reasons of stability of the found asymmetric structure of the studied molecule. The structure of free molecule of benzenesulfonic acid was compared with that of molecular form in crystal.

Novel Capsular Aggregates from Flexible Tripodal Triureas with Cs Symmetry

Tris(2- and 3-ureidobenzyl)amines with C(s) symmetry self-assemble in solution forming mixtures of regioisomeric capsular aggregates, one of which is chiral and the other centrosymmetric. Under certain conditions, a predominance of the centrosymmetric regioisomer is found before equilibrium, that is, a mixture close to the statistical ratio of the two species is reached. In the solid state, there is a preference for the centrosymmetric capsules. Molecular models of both regioisomeric aggregates have been built and analyzed for comparison. Guests inside capsules formed by self-assembly of desymmetrized tris(3-ureidobenzyl)amines feel different magnetic environments, depending on whether they are inside a chiral or an achiral regioisomeric container. Of special significance are the experiments with a more flexible triurea endowed with an ureidopropylic arm, which self-assembles with the same efficiency as the more rigid tris(ureidobenzyl)amines.