Variable-temperature IR spectra

Figure 4.16 Variable-temperature IR spectra in the v(CO) region of dihydride [(triphos)Ru(CO)H2] in CH2CI2 at 190 K (1) and in the presence of a 10-fold excess of (CF3)2CH0H recorded between 190 and 230 K (curves 2 to 6). (Reproduced with permission from ref. 28.)...

Figure 4.16 shows variable-temperature IR spectra recorded in the v (CO) region for a CH2CI2 solution of this dihydride upon addition of a 10-fold excess of (CF3)2CH0H. The temperature evolution of the v (CO) intensities in such spectra is analyzed easily to give the equilibrium constants. The pattern in Figure 4.17 shows the temperature dependence of these constants leading to —AH° and —AS° values of 6.7 kcahmol and 19.6 eu, respectively. 

Dihydrogen bonding energies can be determined in solution by variable-temperature IR spectra in the framework of van t Hoffs method or from the frequency shifts, Av (HX) [or integral intensity, AA(XH)], determined in the IR spectra of proton-donor components, which correlate with the bonding energy. 

Figure 7.4 Variable-temperature IR spectra recorded in a CH2CI2 solution of ReH2(CO)(NO)(PEt3)2 in the presence of PFTB [(CFslsCOH] in the range of v(NO) and v(ReH). (Reproduced with permission from ref. 9.)...

Figure S. Variable temperature ir spectra of (Et4NXHW< CO) o). The sample temperatures are probably higher than the measured temperatures...

Matrix-IR spectra of CO/N2H4 mixtures show the formation of 3 weak complexes, identified by comparison with ab initio and DFT calculations.521 The variable-temperature IR spectra (—105 — 150°C) of Me2NNH2 in liquid krypton show that only the gauche conformer is present.522 DFT calculations gave vibrational wavenumbers for (XMYH)n rings and clusters, where M = Al, Ga or In Y = N, P or As n = 1-6.523... 

Fig. 8. Variable-temperature IR spectra of supramolecular hydrogen-bonded complex 5 (n = 4) consisting of 4-butoxybenzoic acid 2 and bipyridine 4 in the range 1500-1800 cm from 100-180 °C...

To examine the stability of mesogenic carboxylic acid dimers, variable temperature IR spectra have been obtained for 4-alkylbenzoic acids [71], The monomeric molecule of a benzoic acid appears once the compound melts to a nematic state. For 4-pentylbenzoic acid 55 (X = CH2, n = 4) (nematic 88-127 °C), the fraction of the carbonyl peak due to the monomer becomes 6,2 mol% at T, In the isotropic state, a steady increase in the free monomeric component is observed as the temperature increases. No monomeric species is observed for carboxylic acid/pyridine complexes, which are formed by more stable H-bonding [31, 341,... 

The vAl-O-Al IR band was used to study the effects of the caustic ratio on the structure of sodium aluminate solutions.118 Variable-temperature Raman spectra of the spinel MgAl204 showed a band at 727 cm" 1 for samples annealed above 800°C. This was ascribed to cation disorder in these samples.119 The angular force constant method was used to analyse vibrational modes for MA1204, where M = Mg or Zn.120 Ab initio calculations have been made of vibrational wavenumbers involving the OH group in topaz, Al2Si04(0H)2.121... 

Both the H and 13C variable temperature NMR spectra of (ir)4-CsHs) Fe(CO)3 have been reported. What information could be determined using 13C NMR that could not be determined using H NMR 33 5-13 Whereas the compound [Cr 5-C5H5)Fe(CO)]2 has bands in the infrared at 1904 and 1958 cm-1, [(ri5-C5Me5)Fe(CO)]2 (Me = methyl) has bands at 1876 and 1929 cnr1.34... 

The FT-IR spectra of amorphous forms are often less well defined and can be used to characterize various pol5rmorphic forms. Heating experiments are also possible using IRS, where the variable temperature IRS is conducted to confirm that a solid-solid transition takes place on heating various forms of the compotmds. 

Equilibrium competitive binding between H20 and H2 is shown by variable-pressure IR spectra of a solution of W(CO)3(PiPr3)2 in 1% H20/THF.2 H2 pressures in excess of 1000 psi are required to quantitatively form W(CO)3(PiPr3)2(H2) at 25°C, as monitored by relative intensities of vro. The equilibrium constants for displacement of H2 by H20 can be determined at pressures of several atm H2 at 25 to -70°C. As the temperature is lowered, the peaks owing to the H2 complex decrease and new peaks owing to the H20 complex appear. The thermodynamic parameters for Eq. (7.9) are readily obtained from van t Hoff plots ... 

In a study of a reductase inhibitor [59], IR spectra of a hydrate exposed to relative humidities of 3.5-84% all show a sharp v(O-H) band at 3640cm" indicating that the water molecules are bound within the lattice. This is contrary to the results from DSC which show no dehydration endotherm. These results in combination suggest a channel hydrate with channels in the crystal lattice which can take up varying levels of water molecules, but that within the channels the water is bound to other water molecules and/or the drug molecule via hydrogen bonding. The continuous nature of the hydration was confirmed by a variable temperature IR experiment which showed that as a hydrated sample was heated, the intensity of the 3640 cm" band reduced as toe water level decreased. 

This review is devoted to the IR spectra of transition metal and main group element hydrides focusing on the Vmh bands and their response to hydrogen bonding and proton transfer. The aim is to show what advantages can be provide by variable temperature IR spectroscopy in structure and reactivity studies of hydrides. 

Reaction of ds-[PtCl2(C2H4)(py)] with cis-[Ru(bipy)2(CN)2] is first order in each compound, with a 2 value of 10.6 M s at room temperature in dimethylformamide solution. There is spectroscopic evidence for 1 1 and 1 2 binuclear products. " Two coalescence temperatures have been reported from variable-temperature NMR studies of the dithiahexane complex [Ru(dth)2Cl2]. Simple inversion at sulfur, a sufficient explanation for variable-temperature NMR spectra of, for instance, [M(dth)Cl4]" with M = Rh(III), Ir(III), Pt(IV) (q.v.), is clearly not a sufficient explanation here. "" ... 

IR and Raman spectra of (cyc/o-C3H5)SiCl2H show the presence of both cis and gauche conformers in fluids, but only gauche in the solid. " Variable-temperature Raman spectra of Cl2C=CCl-SiCl3 are consistent with the presence of both syn and anti conformers - with the anti form of lower energy. 

Variable-temperature Raman spectra of aqueous solutions containing Cd(OH2)6 show vCdOe bands at 235 cm and 185 cm , assigned to Cg and t2g modes respectively. The IR spectra of cadmium(II) bis(acetylacetonate) and its bis-piperazine adduct show that vCdO decreases on the additional coordination of the V-donor. 2... 

The utilization of IR spectroscopy is very important in the characterization of pseudopolymorphic systems, especially hydrates. It has been used to study the pseudopolymorphic systems SQ-33600 [36], mefloquine hydrochloride [37], ranitidine HC1 [38], carbovir [39], and paroxetine hydrochloride [40]. In the case of SQ-33600 [36], humidity-dependent changes in the crystal properties of the disodium salt of this new HMG-CoA reductase inhibitor were characterized by a combination of physical analytical techniques. Three crystalline solid hydrates were identified, each having a definite stability over a range of humidity. Diffuse reflectance IR spectra were acquired on SQ-33600 material exposed to different relative humidity (RH) conditions. A sharp absorption band at 3640 cm-1 was indicative of the OH stretching mode associated with either strongly bound or crystalline water (Fig. 5A). The sharpness of the band is evidence of a bound species even at the lowest levels of moisture content. The bound nature of this water contained in low-moisture samples was confirmed by variable-temperature (VT) diffuse reflectance studies. As shown in Fig. 5B, the 3640 cm-1 peak progressively decreased in intensity upon thermal... 

Fig. 5 A, diffuse reflectance IR spectra of SQ-33600 displaying the absorption band due to bound water of hydration after exposure to different relative humidity conditions of (a) initial sample containing 3.5% water, (b) 6%, (c) 15%, (d) 31%, (e) 43%, (f) 52%, (g) 70%, and (h) 84%. B, variable-temperature diffuse reflectance IR spectra of SQ-33600 initially containing 3.5% water.

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