Although a lot of work has been done on the vibrational analysis of urea, there still remain some contradictions and uncertainties, mainly due to interpretation of the vibrational spectrum of crystalline urea based on force field calculations on isolated urea instead of on urea in its crystal phase. We have shown that this approach is not allowed in the case of urea. The vibrational spectrum of urea was interpreted by measuring the solid state infrared spectra of eight isotopomers of urea at room temperature and at −196 °C, and Raman spectra at room temperature and at −120 °C, and of a urea−water solution. Force field calculations from our recently published article on isolated urea and on urea in its crystal structure, at the Hartree−Fock level with a 6-31++G** basis set, were also used. We have also shown that high-pressure measurements using a “diamond anvil cell” are not useful by performing a vibrational analysis.

Vibrational Analysis of Urea

Organic−inorganic hybrids prepared by the sol−gel process are investigated by infrared spectroscopy at room temperature. The matrix of the so-called ureasils is a silica network to which oligopolyo...

Sol−Gel Derived Urea Cross-Linked Organically Modified Silicates. 1. Room Temperature Mid-Infrared Spectra

In this study the geometrical structure and vibrational spectrum are studied for the urea molecule (CO(NH2)2) in the gas phase as well as in its P421m crystal phase. Experimental frequencies for u...

Solids Modeled by Ab-Initio Crystal Field Methods. Part 17. Study of the Structure and Vibrational Spectrum of Urea in the Gas Phase and in Its P4̄21m Crystal Phase

A new type of polyoxometalate (POM), one with a hydrogen dinitrate group associated with a d-electron-substituted polyoxometalate, FeIII[H(ONO2)2]PW11O395− (1), has been developed that catalyzes highly effective aerobic sulfoxidation (RR′S + 0.5 O2 → RR′SO) under ambient conditions (1 atm of air at room temperature). Comparison of the rates for aerobic sulfoxidation of the mustard simulant 2-chloroethyl ethyl sulfide (CEES) catalyzed by 1 and several other species reported to be catalysts for this class of reactions, including NO+, NO2, (NH4)2CeIV(NO3)6 and AuIIICl2NO3(CH3CN) indicate that 1 is clearly the most effective catalyst. Conversions and selectivities for the desired sulfoxide decontamination product (CEESO in these studies) are both effectively quantitative. The low or nonexistent catalytic activity of FeII(NO)PW11O396−, Fe(NO3)3 and HNO3 argues strongly that nitrosyl and nitrate derivatives of the Fe polyoxometalate and nitric acid are not species important in catalytic turnover. The techniques of single crystal X-ray diffraction, solution NMR, FTIR, TGA, DSC, cyclic voltammetry, elemental and wet chemical analyses were applied to the characterization of 1 and these are collectively consistent with the α-Keggin structure with a strongly associated hydrogen dinitrate group and a more weakly associated nitrate of crystallization.

B. Barlič

Papers

The normal coordinate analysis of urea, thiourea, and thier isotopic analogues in the solid phase and in solution

Normal coordinate analysis of the two forms of the hydrogen dinitrate ion

Thermodynamics of protonation of 2-ethyl-, 3-ethyl-, 4-benzyl-, 3-ethyl-4-methyl- and 5-ethyl-2-methyl-substituted pyridine-N-oxides in aqueous media