OH deformation modes

The dihydroxide (XX) behaves very much as the corresponding aluminum derivative, but is not sufficiently acidic to form a sodium salt (170). A band at 3535 cm-1 in its infrared spectrum is assigned as the OH stretching vibration, while a possible OH deformation mode is observed at 831 cm-1. The complex polymerizes in the following manner at 400°C, with loss of water ... 

Concerning the position of the OH and OD vibration bands in the FTIR spectrum, a shift for the free silanols from 3740 cm 1 to 2760 cm 1 is observed. Generally, the M-O-H deformation mode of a triatomic molecule shift with a factor of about 1.36 towards lower wavenumber.55 For more complex molecules, the H/D shift differs considerably, ranging from 1.40 to 1.28 in silanols.56,57 A thorough study of all FTIR spectral changes was reported by Morrow and McFarlan.30... 

Various types of neutron scattering can be utilized to extract data on structure and dynamics for novel catalytic materials. By selectively deuterating an SSZ-13 zeolite, Cheetham and others" used ND performed on the Dual Beam Neutron Spectrometer (DUALSPEC) diffractometer at the Chalk River Laboratories and found that two acid sites are present in the unit cell of the zeohte. INS can be used to probe the mechanism of the catalytic reaction by looking at the change in the vibrational modes of the adsorbed molecules on the surface. Lennon et alP found that the interaction of HCl with a ]-alumina catalyst results in the dissociative adsorption of HCl, in which the hydroxyl groups terminally bound to A1 are replaced by chlorine. INS spectra reveal an in-plane deformation mode, 5 (OH), that can be resolved into two bands located at 990 and 1050 cm. ... 

Protic solvents always have more complex infrared spectra because of the presence of hydrogen bonding in the liquid state. In methanol, this involves interaction of the acidic proton on the OH group in one molecule with the oxygen atom in an adjacent molecule (fig. 5.15). The infrared spectrum shows a wide band centered at 3346 cm which is due to the -OH stretch. When methanol is dissolved as a dilute solute in carbon tetrachloride, this band is sharp and appears at 3644 cm . An -OH bending mode appears at 1449 cm. Another broad band due to -OH out-of-plane deformation is centered at 663 cm. The other features of the methanol spectrum are due to the vibrational modes of the CH3- group or to skeletal vibrations [27]. 

When the hydroxyl anion OH is bound to a positively charged center, M, two more vibrations appear in the IR spectra a stretching mode v(M—O) and a deformation mode 6(MOH). According to Nakamoto (9), the v(M—O) modes are observed in the region of 900—300 cm, whereas the 6(MOH) vibrations are observed between 1200 and 700 cm. ... 

Very often, the oxygen of a hydroxyl group is connected to more than one cation (in addition to being bound to hydrogen). This situation is realized in bridging hydroxyls Mi—(OH)—M2. In this case, two different v(M—O) modes will be observed and, because the M—O bond order in Ml—(OH)—M2 hydroxyls is about half of the M—O bond order in M—OH hydroxyls, the v(M—O) stretching vibration is expected at lower wavenumbers. The deformation modes also split into two components. 

The v(OH) modes of surface hydroxyl groups are well distinguished in IR spectra, whereas in most cases, the M-O stretching vibrations and the deformation modes are masked by the strong absorbance of the bulk of the solid in the low-frequency region. However, in a few cases (predominantly concerning H-bonded hydroxyls), the direct detection of deformation modes is possible. This situation is encountered for metal oxides (10) and zeolites (11). 

Combination modes are widely used to derive the wavenumbers of vibrations that are not directly observable because they are masked by the strong absorbance of the bulk of the solid. As may be expected, these modes are shifted as a result of H-bond formation with adsorbed molecules, but the shift is smaller than the shift of the fundamental OH stretching vibrations (183). The smaller shift results because H-bonding shifts the stretching and deformation modes in different directions and the two effects are partly canceled in the combination mode. 

Analysis of the deformation modes, overtones, and combination modes may also be very helpfial in resolving particular questions, for example, discrimination between OH groups and adsorbed water. 

---