M. Maltese

Infrared levels of monomeric uracil in cryogenic matrices

Abstract The infrared spectrum of monomeric uracil, trapped in Ar and N 2 cryogenic matrices, is presented and compared with the infrared and Raman spectra recorded for this same compound in associated forms, as observed in its pure solid state and in solution. The monomeric molecules are all in the 2,4-diketotautomeric form and are planar, as can be deduced indirectly from the absence of band multiplicity due to conformeric equilibrium. The assignment is based on comparison with previous works on uracil and with matrix isolation studies on other cis - and trans -imides and is supported by spectral comparison with N,N -dideuterouracil trapped in the same cryogenic matrices. With few exceptions, the assignment is consistent with that obtained by theoretical approaches. On passing from an Ar to an N 2 matrix, the bands due to νNH and γNH shift to lower and higher wavenumbers, respectively, as a result of a specific interaction between the NH groups and the N 2 molecules.

Infrared study on niobium pentahalides and oxytrihalides trapped in cryogenic matrices

Abstract The i.r. spectra of Ar and N 2 matrices trapping vapours coming from solid NbX 5 , NbOX 3 and mixtures NbX 5 /Nb 2 O 5 (X = Cl, Br, I) have been investigated. Differences in the spectra of NbCl 5 taken at different vaporization temperatures point to the presence of polymeric species in the vapour. The bands due to monomeric NbCl 5 , at 443 cm −1 (the E′ NbCl stretch) and at 395 cm −1 (the A ″ 2 NbCl stretch), can be recognized since they are more intense for matrices trapping vapours taken at higher furnace temperature. Annealing experiments also help in assigning monomer absorptions since they decrease in intensity under diffusion. It is remarkable, however, that the polymeric species formed in the matrix on annealing are different from that present in the vapour. The furnace temperature does not affect significantly the spectrum of NbBr 5 and the only two observed absorptions, at 315 cm −1 (the E′ NbBr stretch) and at 288 cm −1 (the A ″ 2 NbBr stretch) are referred to the monomer. Here, also, the assignment is supported by the decrease in intensity undertaken by these two absorptions on annealing the matrix. Changes in furnace temperature do not give rise to detectable changes in the spectrum of matrices trapping Nb oxytrihalides, NbOX 3 . In this case, the absorptions of monomers have been recognized on the grounds of the tendency to decrease under annealing. The A 1 NbO stretch is observed at 993 (X = Cl), 989 (X = Br) and 977 (X = I) cm −1 . The E NbX stretch is at 443 (X = Cl) and 339 (X = Br) cm −1 . The other A 1 NbX stretch has never been observed. The spectrum is complicated by band multiplicity probably due to multiple site trapping.

Infrared spectra and structure of bridging carbonyls in Fe2Ru(CO)12 and Fe3(CO)12

IR spectra of crystal, solution and pseudo-gas phases (argon and nitrogen matrices) of Fe2Ru(CO)12 and of crystal and solution phases of Fe3(CO)12 were recorded. By quantitative data-handling procedures, structures and bond angles for bridging carbonyls were estimated. Fe2Ru(CO)12 in crystal has a bridging structure analogous to that of Fe3(CO)12, with two bridged carbonyls and C2v or pseudo-C2v symmetry. In solution, both samples contain the same carbonyl bridged structure of C2v symmetry,just as in pseudo- gas phase; the latter, however, contains other bridged molecules of unknown structures, too.

Infrared spectra of matrix-isolated gaseous ternary oxides: Part VI. The infrared spectra of lithium, cesium and thallium sulfates and indium and thallium molybdates

Abstract Infrared spectra of Li 2 SO 4 , Cs 2 SO 4 , Tl 2 SO 4 , In 2 MoO 4 and Tl 2 MoO 4 molecules isolated in nitrogen matrices at 12 K have been obtained. D 2d symmetry of these species is proposed. The splitting of the v 3 ( F 2 ) mode on passing from T d to D 2d symmetry is briefly discussed.

Infrared matrix spectra of tetrahedral ternary oxides of alkali and thallium metals

Abstract In this paper are reported the infrared spectra of the gaseous ternary oxides Li, Na, K, Rb, Cs, Tl perrhenates, Li, Na and Cs molybdates and tungstates and Li, Na, K and Tl chromates in nitrogen, matrices at 10K over the frequency range 200–4000 cm −1 . The results are compared with those of the corresponding solids and free anions. The observed spectra suggest that the vibrational properties of these species may well be described as ion pairs in which the coordinated anion is not detectably polarized by the alkali metal cation.

Infrared polarized spectra of hexamethylbenzene above and below the λ point at 116 K

Abstract The i.r. spectrum of hexamethylbenzene (HMB) has been investigated above and below the λ point between phase II (stability range 383-116 K) and phase III (below 116 K) in order (i) to get information on the molecular and/or crystal modifications involved in the phase transition and (ii) to assign i.r. absorptions. Spectra of randomly oriented samples and of single crystals having ab and bc as predominant faces were taken at different temperatures. In phase II the number of bands and their polarizations clearly indicate that the benzene like modes feel a potential of symmetry higher than that of the site, whilst the band broadness of the absorptions due to methyl stretchings and bendings does not allow any indication on “peripheral” potential. Changes occurring in the spectrum of the low temperature phase should indicate a more ordered situation in which the molecular symmetry is D 3 d or S 6 .

Polarized i.r. spectra of hexamethylbenzene-d18 above and below its λ point

Abstract The i.r. polarized spectrum of a single crystal of hexamethylbenzene- d 18 having bc as predominant face, is investigated above and below the low temperature λ-transition. The proposed vibrational assignment is compared with that of the parent molecule hexamethylbenzene. The molecular symmetry in phase II and III is deduced.

Infrared matrix and polarised spectrum of bis(diethyldithio-carbamato)-nickel(II)

Abstract The IR spectra (300–4000 cm −1 ) of bis-(N,N-diethyldithiocarbamato)-nickel(II) as N 2 matrix and oriented polycrystalline layer are reported. All the observed bands are assigned and classified on the grounds of their polarisation in the symmetry classes of D 2h , the highest possible molecular symmetry. Remarkably, polarisation of the absorptions around 1000 cm −1 rules out the assignment to any C-S stretching, in contrast with previous assignments. The room temperature crystal spectra do not show evidence for crystal splitting. The matrix spectrum shows features related to the existence of rotamers around the H 2 C-N bond, which give useful assistance in the assignment.

A matrix isolation i.r. study on molecular complexes of hexamethylbenzene and tetracyanoethylene

Abstract The i.r. spectra of Ar and N 2 matrices containing trapped hexamethylbenzene (HMB), tetracyanoethylene (TCNE) and their complex species are presented. The formation of complex species (essentially the 1:1 complex) is indicated by the arising of new bands at 1295 cm −1 (the A 1g CCH 3 stretching of HMB) and at 1546 cm −1 (the CC stretching of TCNE). However, the comparison with the spectra of the crystalline 1:1 and 2:1 complexes (HMB:TCNE), indicates that the contribution of vibronic mechanisms to band intensities is greatly reduced by the isolation of complex units in the matrix.

The infrared spectrum of C2F5Cl in cryogenic matrices

Abstract We have measured the infrared spectrum of pentafluoroethyl chloride in cryogenic matrices of argon, nitrogen, krypton, and xenon from 880 to 1360 cm−1. Numerous combination bands were observed; assignments and symmetries are reported for most. Appreciably more structure was observed in argon than in other matrices. The observed splitting of the fundamental bands in an argon matrix into two or more components may be due to multiple trapping sites.