Rotational spectra, dipole moment, and structure of the SiF4–NH3 dimer

A model based on the molecular electrostatic potential (MESP) is employed for the investigation of structures and energies of complexes of ammonia with propane and cyclopropane. The electrostatic model geometries are employed as starting points for an ab initio investigation at the self-consistent ®eld and second-order Mùller-Plesset (MP2) levels. The most stable structures of C 3 H 6 ..NH 3 and C 3 H 8 ..NH 3 complexes have the interaction energies of 10.07 kJ/mol and 8.15 kJ/mol, respectively, at the MP2/6-31G(d,p) level. The energy rank order of the structures is not altered with the use of the 6-31++G(d,p) basis set, and the basis set superposition error has little eect. The interaction energy decomposition analysis shows that the electrostatic component is dominant over the other ones. MESP topography thus seems to oer valuable hints for predicting the structures of weakly bonded complexes.

show abstract

“…The location and MESP value at the CP implies that NH 3 is a proton acceptor. This result is supported by experimental studies [19].…”

Section: Methodssupporting

confidence: 85%

Complexes of ammonia with propane and cyclopropane: electrostatic guidelines for ab initio treatment

Gadre

Bhadane

1998

Theoretical Chemistry Accounts: Theory, Computation, and Modeli

View full text Add to dashboard Cite

show abstract

“…The spectra were observed using a Stark cage assembly, 20 calibrated as described previously. 21 The assignment of the K=O isotopic sequences (Tables III-V) presented no major problems. The fit of the transitions by Eqs.…”

Section: Stark Effect Measurementsmentioning

confidence: 97%

Rotational spectrum and structure of the Ne–HCN dimer

Gutowsky

Keen

Germann

et al. 1993

The Journal of Chemical Physics

Self Cite

View full text Add to dashboard Cite

Microwave rotational transitions have been observed at low J (0-3) for several isotopic species of the Ne-HCN dimer using the Balle/Flygare Mark II Fourier transform spectrometer with a pulsed nozzle as the source. For 2oNe-HC 14N, the main K =0 transitions give rotational constants B, D J, and H J of 2772.816 and 1.280 MHz and 1.173 kHz. The 14N nuclear quadrupole constant increases linearly with J(J+ 1) at a slope Dx of -12.7 kHz fro~ a value for Xa( 14 N) of -0.957 MHz at J=O. The pseudodiatomic approximation for Band Xact 4 N) leads to a value of 3.89 A for the Ne to HC 14N center-of-mass (c.m.) distance R, and to 46.8° for the "average" bend angle () of HC 14N. Some of the K=O, J= 1 ..... 2, and J=2 ..... 3 transitions exhibit one or two weak satellites -30 MHz away, usually below, but also both above and below. The J= 1 ..... 2 low frequency satellites for 2oNe-HC 14N and 2oNe_ HC 15N, nominally 1 11 ..... 2 12 , are symmetrical doublets with splittings of 305 and 439 kHz, respectively. The 14N hyperfine structure (hfs) is identical for the two 2oNe-HC 14N components as is the Stark effect for 2oNe-HC 15N. The molecular mechanics for clusters (MMC) model was used to calculate potential energy surfaces for Rg-HCN dimers, giving stabilities of 21, 37, 85, and 108 cm -I with He, Ne, Ar, and Kr as the rare gas. A qualitative comparison of the experimental properties for the dimers with Ne, Ar, and Kr as the rare gas is based on the surfaces. The extremely mobile internal dynamics of Ne-HCN are attributed to its potential surface, which is both very shallow and isotropic.

show abstract

“…Complex formation is estimated to be more exothermic with the MP2 method of electron correla- [47] Ϫ [e] Structure from ref. [7] tion than with B3LYP, while diffuse functions have a minor influence.…”

Section: Alternative Complex Configurations: Cis Vs Transmentioning

confidence: 99%

“…[1f] Most complexes between silanes and typical Lewis bases are hitherto found only in the solid state or in polar solvents, some exist at very low temperatures only with matrix isolation, [6] and SiF 4 (NH 3 ) is the only example of a silane adduct known to the author, that has been detected in the gas phase, but at very low temperatures. [7] tween the trans and cis configurations of SiF 4 (py) 2 . The standard free enthalpy of complex formation is negative only for complexes between halosilanes and F − , i.e.…”

Section: Introductionmentioning

confidence: 99%

Molecular “Floppyness” and the Lewis Acidity of Silanes: A Density Functional Theory Study

Fleischer

2001

Eur. J. Inorg. Chem.

View full text Add to dashboard Cite

A comprehensive set of Lewis acid‐base adducts of silanes was investigated by means of the density functional theory geometry optimization [B3LYP/6−31G(d)], and thermochemical calculations, [B3LYP/6−311+G(2d,p)//B3LYP/6−31G(d)]. Complex formation was found to weaken Si−Cl and Si−Br bonds more than Si−F or Si−H bonds. Comparable distances between Si and a Lewis base L (L = NH3, OH2, F−) are shorter in hexa‐ than in pentacoordinated complexes. The molecular structures of the pentacoordinated Si complexes allowed for a mapping of an SN2 reaction pathway by correlating the lengths of the Si−X and Si−L bonds. Complex formation was found to be exothermic for most of the coordination compounds, and the analysis of the natural atomic charges revealed a high ionic character of the dative bonds. Formation of the anionic complexes and of SiH2X2(py)2 is most exothermic with X = Cl or Br and otherwise most exothermic with X = F. Only small enthalpy differences were found between the trans and cis configurations of SiF4(py)2. The standard free enthalpy of complex formation is negative only for complexes between halosilanes and F−, i.e. all other silane Lewis base adducts are thermodynamically unstable under standard conditions with respect to dissociation. It is inferred that the existence of some of the silicon complexes in the solid state or in solution is caused by stabilizing intermolecular forces, and silanes are classified as very weak Lewis acids. The thermochemistry of complex formation was analyzed in terms of molecular “floppyness” of the silanes and the energy of interaction between the deformed silane and the Lewis base. The enhanced complex stability of SiCl4(py)2 compared to SiH4(py)2 and of GeF4(NH3), [GeF5]− and [GeF6]2− compared to the analogues silane adducts does not result from a stronger Lewis acid base interaction but from an increased “floppyness” of SiCl4 and GeF4 compared to SiH4 and SiF4, respectively.

show abstract

Rotational spectra, dipole moment, and structure of the SiF4–NH3 dimer

Cited by 58 publications

References 26 publications

Complexes of ammonia with propane and cyclopropane: electrostatic guidelines for ab initio treatment

Complexes of ammonia with propane and cyclopropane: electrostatic guidelines for ab initio treatment

Rotational spectrum and structure of the Ne–HCN dimer

Molecular “Floppyness” and the Lewis Acidity of Silanes: A Density Functional Theory Study

Contact Info

Product

Resources

About