Search

Infrared and Raman spectra in the gas phase are reported for trimethoxyborane, B(OCH 3 ) 3 , and its 13 C 3 and d 9 isotopomers. Some liquid phase Raman data were also obtained. Quantum-chemical (QC) studies of structure and force field have been made with B3LYP and MP2 models. These studies highlight the change in configuration of the methyl groups with change in basis set, within the C 3 h point group. Scaled QC force fields together with the new spectra enable assignments of fundamental bands to be improved. A Fermi resonance involving ν 12 is examined. The difference in strength between the two types of C–H bond in each methyl group is reckoned to be rather less than that deduced earlier from IR spectra of B(OCHD 2 ) 3 . This conclusion is supported by QC data for dimethylether. MP2 estimates of certain interaction force constants are superior to those from B3LYP calculations. Abnormal scale factors for the torsional motion involving the O–B–O–C system identify deficiencies in the QC models employed.

The intensity of the ν(NO) stretching band of NO+2 at Δ ν = 1400 cm−1 in the Raman spectra of nitric acid—water—sulphuric acid mixtures has been studied to determine nitronium ion concentrations over the temperature range 293–313 K. The nitronium ion concentration in these mixtures was found to decrease with increase in temperature. The nitrating species for acid mixtures used in mono- and di-nitrations is consistent with nitronium ion, NO+2, but at a typical acid concentration of less than H2SO4:HNO3:H2O = 30:15:55 mole % used in industrial mononitrations, there is no spectroscopic evidence for the presence of NO+2. It is suggested that the nitrating species in these weaker acid solutions is he acid hydrate, H2NO+3, which is a weaker nitrating species than NO+2.

Infrared and Raman spectra have been obtained in the gas phase for the species M( 12 CH 3 ) 2 , M( 13 CH 3 ) 2 , M( 12 CD 3 ) 2 and M( 13 CD 3 ) 2 , where M  Zn, Cd and Hg. All but one of the skeletal bending modes are observed directly in the infrared. 13 C frequency shifts confirm the assignment of a number of combination and overtone bands, including the 1300 cm −1 bands of Zn(CH 3 ) 2 and Cd(CH 3 ) 2 which arise from ν 10 + ν 14 . Infrared spectra in the 1400–1500 cm −1 region are difficult to interpret but the evidence points to both the δ as CH 3 modes lying near 1445 cm −1 . A number of Fermi resonances affecting δ s CD 3 levels are identified in the d 6 species. Some features of the ν as CH 3 bands can be explained in terms of existing free internal rotor theory. Observed values of 13 C frequency shifts are generally in good agreement with those from previous scaled ab initio calculations. There is an urgent need for high resolution studies of jet-cooled samples.

Force constant calculations have been carried out for Ni(PBr3)4 using a simple valence force field with interaction constants. The force constant values are compared for the coordinated and free ligand and also with k(NiP) stretching in the series of molecules Ni(PX3)4 where X=F, Cl, Me. The k(NiP) stretching force constant in Ni(PBr3)4 is much lower than its corresponding values for other members of the series. This is discussed in relation to the observed experimental instability of the compound and the electronegativities of the substituents X in PX3.

Raman spectroscopic studies of silicon (IV) fluoride and tetraethylammonium chloride in chloroform and nitromethane solutions confirm the existence of the hitherto unreported chlorotetrafluorosilicate (IV) ion, SiF 4 Cl − . The observed vibrational wavenumbers for this new species are compared with those calculated using an SVFF approximation based on the SiF 2− 6 and SiCl 4 species, and with the isoelectronic molecule PF 4 Cl.

The potassium (K), sodium (NA), calcium (CA), and magnesium (MG) salts of p-aminosalicylic acid were obtained, and their thermal behavior was characterized by means of differential scanning calorimetry (DSC) and thermogravimetric analysis (TG). Their crystal and molecular structures were determined by single-crystal X-ray diffraction after powder patterns had shown them to be nonisomorphous. Different degrees of hydration were observed for the solid salts, and an assessment of hydrate stability to dehydration was made from thermogravimetric studies. The onset temperature of dehydration (Tt) of each salt varied within the series and exhibited correlation with X-ray determined structure. The observed onset of dehydration of MG and CA was higher than that of NA and is consistent with stronger ion-dipole interactions for the divalent salts. Crystallographic determination of the bond lengths between the metal ion and the water oxygens were 2.4 and 2.9 A for NA, between 2.0 and 2.1 A for MG, and 2.4 A for CA. The open nature and presence of a channel feature in the structure of the sodium salt may have facilitated escape of water molecules from the crystal. Particle presentation (e.g., size, crystallinity) was also shown to affect dehydration behavior.

The intensities of the bands in the Δν = 450 to 500 cm−1 region of liquid boron(III) chloride, characteristic of v(BCl) stretching as a function of temperature in the range 234–287 K are used to determine the average enthalpy of boron—chloride bond formation for the dimer species, (BCl3)2. Intensity measurements show that liquid boron(III) chloride contains 2% and 11% of dimer species at 287 K and 234 K, respectively, and the average ΔH° = −0.52 ± 0.08 kJ mol−. Extrapolation indicates that liquid boron(III) chloride will contain about 20% dimer molecules near its freezing point at 166 K. The ΔH° value for dimer formation is discussed in terms of the molecular interaction.

Quantitative Raman spectroscopic measurements of the intensity of the ν(NO) symmetric stretching band of NO2+ in aqueous solutions of nitric and sulfuric acid mixtures have been carried out over the temperature range 293–313 K. From the spectroscopic data it was found that the NO2+ species concentration decreased with an increase in temperature. Equilibrium constants for the reaction HNO3+ 2H2SO4⇌ NO2++ H3O++ 2HSO4– were determined at 293 and 313 K and the average enthalpy of NO2+ formation was found to be ΔH=–25 ± 5 kJ mol–1.

The Raman spectra of the cyclohexyl halide-thiourea clathrates have been investigated. It is found that whereas cyclohexyl chloride and bromide exist only in the axial conformation in the clathrate, cyclohexyl iodide exists in both the axial and equatorial conformations in the clathrate.

The force constants of phosphorus (III) cyanide and arsenic (III) cyanide have been calculated using a simple valence force-field approximation with interaction constants. Several revisions are proposed to the existing vibrational assignments for the As(CN) 3 species and the vibrational assignments for P(CN) 3 are confirmed.

The force constants of methyl phosphorus(III) dicyanide and methyl arsenic(III) dicyanide have been calculated using a simple valence force-field approximation with interaction constants. The assignments of the observed infrared and Raman spectra are discussed in the light of these calculations. Several revisions of the previous tentative assignments are proposed.

Force constants for an SVFF approximation have been calculated for the molecules Ni[P(CH3)3]4, Pt[P(CH3)3]4 and P(CH3)3 using an FG matrix method and vibrational assignments with the assumption of methyl point masses. The observed wavenumbers of the M[P(CH3)3]4 species were fitted using six primary and eight interaction force constants. The vibrational assignments for the Ni[P(CH3)4]4 and Pt[P(CH3)3]4 species are confirmed by the force constant calculations. Comparisons are made with the force constants for the related molecules Ni(PF3)4, Pt(PF3)4 and Ni(PCl3)4. The metal—phosphorus stretching force constant in Pt(PF3)4 is 3.5 times larger than the corresponding value in Ni(PMe3)4. Changes in the force constants are discussed in terms of the metal—phosphorus—methyl bonding in the M[P(CH3)3]4 species.

Urea/n-paraffin clathrates enable Raman spectroscopic studies of oriented single n-paraffin molecules in the extended planar zig-zag configuration to be made. Raman spectra in the region 0–3500 cm−1 are reported for various orientations of single crystals of the following urea and urea-d4/n-paraffin clathrates: urea/n-tetradecane, urea/n-hexadecane and urea/n-undecane. Assignments have been made for the vibration of the urea host lattice and the guest n-paraffin molecules in the extended planar zig-zag configuration, utilising the orientation measurements.

Force constants calculation have been carried out for the Ni(CO) 3 SbCl 3 molecule by the Fg-matrix method and a simplified valency force filed (SVFF) with interaction constants. Some reassignments of the observed vibrational frequencies are proposed on the basis of these calculations. The ν(NiSb) stretching frequency at 232 cm −1 was confirmed and the force constant of 1.51 mdyne A −1 evaluated. The k (NiSb) force constant is compared with k (NiP) in the related species Ni(Pcl 3 ) 4 . Bond stretching and bending force constants are compared for Ni(CO) 3 SbCl 3 and the parent molecules SbCl 3 and Ni(CO) 4 .

Normal coordinate analyses have been carried out for the ClCH 2 HGCl and BrCH 2 HgBr molecules by use of the FG-matrix method and a simple valence force field incorporating ten primary five interaction force constants. Some re-assignments and modifications of the published experimental vibrational assignments are proposed, and other tentative assignments are confirmed by these calculations. A decrease in value of the HgC stretching force constant on going from (CH 3 ) 2 Hg to ClCH 2 HgCl is observed. A comparison is made of the stretching force constants for the series of molecules (CH 3 ) 2 Hg, ClCH 2 HgCl and Cl 3 CHgCl, and the effect of substitution of the Cl atom in a methyl group of (CH 3 ) 2 Hg is discussed.

Some reactions of tin oxide chloride with pyridine and with tetrahydrothiophen are reported, and it is suggested that products are normally of the form SnO2 and SnCl4,L2. Reaction of tin oxide chloride or titanium oxide chloride with acetylacetone appears to lead to the known compounds MCl2(acac)2(where Hacac = acetylacetone, M = Sn or Ti). Several preparations of “TiO(acac)2” did not (with the present authors) lead to a monomeric species. The nature of the cation TiOCl42– is discussed as is the characterisation of “metal–oxygen double bonds” using vibrational spectroscopy.

Complete vibrational spectra and assignments are reported for the following species: PCl5, PCl6–, AsCl4+, AsCl6– SbCl5, SbCl6–, and GeCl62–. Partial data are reported for the species GeCl5–, SnCl5–, and SnCl62–. It is suggested that the compound AsCl5,SbCl5 is correctly formulated as AsCl4+SbCl6– while the related compound PCl5,AsCl5(although not obtained pure) is probably the salt PCl4+AsCl6–. Calculated and observed data are compared for all the MCl5 species mentioned above.