Matrix Isolation and Spectroscopic Characterization of the Phenylperoxy Radical and Its Rearranged Products

The phenylperoxy radical 1 has been synthesized by the reaction of the phenyl radical 2 with ³O₂. Radical 1 could be either generated in the gas phase and subsequently trapped in solid argon at 10 K, or directly synthesized in argon matrices. By reacting 2 as well as its perdeuterated isotopomer [D₅]‐ 2 with ¹⁶O₂ and with ¹⁸O₂, respectively, the four isotopomers [H₅]‐¹⁶O₂‐ 1 , [D₅]‐¹⁶O₂‐ 1 , [H₅]‐¹⁸O₂‐ 1 , and [D₅]‐¹⁸O₂‐ 1 were matrix‐isolated and characterized by IR spectroscopy. The experimental IR spectra are in excellent agreement with results from DFT calculations. Irradiation of 1 with visible light produces the 2‐oxepinoxy radical 5 in a clean reaction. Subsequent irradiation results in ring‐opening and formation of several conformers of ketoketene 6 . The radicals 1 , 5 , and 6 play an important role in the combustion of aromatic hydrocarbons and could now be isolated and spectroscopically characterized for the first time.     

Generation and Spectroscopic Identification of ClCNS,ClNCS and NCCNS

The photolysis of four chloro‐substituted thiadiazoles (3,4‐dichloro‐, 3‐chloro‐ and 3‐chloro‐4‐fluoro‐1,2,5‐thiadiazole; 3,5‐dichloro‐1,2,4‐thiadiazole) and 3,4‐dicyano‐1,2,5‐thiadiazole was investigated in inert solid‐argon matrices at cryogenic temperatures by means of UV irradiation at selected wavelengths of 254 and 280 nm. The photolysis products were identified by mid‐IR and UV spectroscopy. Evidence for the existence of three novel pseudohalides, namely, chloronitrile sulfide (ClCNS), chlorine isothiocyanate (ClNCS) and cyanogen N‐sulfide (NCCNS), was provided by direct spectroscopic methods supported by quantum chemical calculations. Ground‐state geometries, vibrational frequencies, IR intensities, and UV excitation energies of ClCNS, ClNCS and NCCNS were obtained from calculations using the B3LYP, CCSD(T) and SAC‐CI methods and the aug‐cc‐pV(T+d)Z basis set.     

Infrared and Raman Spectroscopy of Methylcyanodiacetylene (CH3C5N)

A spectroscopic study combining IR absorption and Raman scattering is presented for methylcyanodiacetylene (CH₃C₅N). Gas‐phase, cryogenic matrix‐isolated, and pure solid‐phase substance was analyzed. Out of 16 normal vibrational modes, 14 were directly observed. The analysis of the spectra was assisted by quantum chemical calculations of vibrational frequencies, IR absorption intensities, and Raman scattering activities at density functional theory and ab initio levels. Previous assignments of gas‐phase IR absorption bands were revisited and extended.     

Water Adsorption on Platinum Dioxide and Dioxygen Complex: Matrix Isolation Infrared Spectroscopic and Theoretical Study of Three PtO2–H2O Complexes

The interactions of water molecule with platinum dioxygen complex and dioxide molecule are investigated by means of matrix isolation infrared spectroscopy and density functional calculations. The platinum atoms reacted with dioxygen to form the previously reported Pt(O₂) complex. The Pt(O₂) complex reacted with water molecule to give the Pt(O₂)–H₂O complex, which was characterized to involve hydrogen bonding between one O atom of Pt(O₂) and one H atom of H₂O (structure A ). Upon visible light irradiation, the hydrogen bonded Pt(O₂)???HOH complex rearranged to another Pt(O₂)–H₂O isomer (structure B ), which involves (O₂)Pt???OH₂ interaction. The Pt(O₂)–H₂O complex in structure B can be isomerized to the weakly bound platinum dioxide‐water complex (structure C ) under UV irradiation.     

Electronic Spectroscopy of Methylcyanodiacetylene (CH3C5N)

The results of a study devoted to the electronic spectroscopy of gaseous, solid, and cryogenic matrix‐isolated methylcyanodiacetylene (CH₃C₅N) are reported. UV absorption and optical phosphorescence spectra of the compound are described here for the first time, and the corresponding vibronic assignments are proposed. UV absorption, studied directly or through the excitation of phosphorescence, revealed the ¹E‐‐ ¹A₁ system, very weak ¹A₂– ¹A₁ bands, and a strong, broad absorption feature, tentatively identified as ¹E– ¹A₁. Spectral measurements were assisted by quantum chemical calculations at the DFT and ab initio (coupled cluster) levels of theory.     

Direct Observation of Carbamoylnitrenes

As the prototype Curtius rearrangement reaction, carbamoyl azide decomposes into aminoisocyanate and molecular nitrogen. However, the key intermediate carbamoylnitrene was previously undetected, even though the decomposition of carbamoyl azides has been studied frequently since its discovery in the 1890s. Upon ArF laser (λ=193 nm) photolysis, the stepwise decomposition of the two simplest carbamoyl azides H₂NC(O)N₃ and Me₂NC(O)N_3, isolated in solid noble gas matrices, occurs with the formation of the corresponding carbamoylnitrenes H₂NC(O)N and Me₂NC(O)N. Both triplet species are characterized for the first time by combining matrix‐isolation IR spectroscopy and quantum‐chemical calculations. Subsequent visible‐light irradiations cause efficient rearrangement of these nitrenes into the respective aminoisocyanates.     

Difluoro‐λ5‐Phosphinonitrile F2PN: Matrix Isolation and Photoisomerization into FPNF

Splendid isolation : Monomeric phosphazene F₂PN (¹A₁) was prepared for the first time through irradiation of F₂PN₃ in an argon matrix with an ArF excimer laser (λ=193 nm). Upon subsequent irradiation with a high‐pressure mercury arc lamp (λ=255 nm), F₂PN undergoes a 1,2‐fluorine shift to give iminophosphane cis‐FP?NF.

     

Infrared-spectroscopic and density-functional-theory investigations of the LaCO, La2[eta2(mu2-C,O)], and c-La2(mu-C)(mu-O) molecules in solid argon

Reactions of laser-ablated lanthanum atoms with CO molecules in solid argon have been studied. The neutral lanthanum monocarbonyl (LaCO), produced upon sample deposition at 7 K, exhibits a C-O stretching frequency of 1772.7 cm(-1); to the best of our knowledge this is the lowest yet observed for a terminal CO in a neutral metal-carbonyl molecule (MCO, M = metal atom), implying anomalously enhanced metal-to-CO back-bonding. The infrared (IR) absorption band at 1145.9 cm(-1) is assigned to the C-O stretching mode of the side-on-bonding CO in the La2[eta2(mu2-C,O)] molecule. This CO-activated molecule undergoes an UV/Vis-photoinduced rearrangement to the CO-dissociated molecule, c-La2(mu-C)(mu-O). Density functional theory (DFT) calculations have been performed on these molecules, the results of which lend strong support to the experimental assignments of the IR spectra. LaCO is predicted to have a quartet ground state, corresponding to a linear geometry. Its formation involves La 6s-->4f promotion, which increases the strength of La-CO bonding by decreasing the sigma repulsion and, remarkably, by increasing the La 5d and 4f-->CO 2pi back-bonding. The observations schematically depict the whole process, starting with the interaction of CO with metal and ending with CO dissociation by the lanthanum dimer.     

Infrared spectrum and structure of thorimine (HN=ThH2)

Laser-ablated thorium atoms react with ammonia to form thorimine (NH=ThH(2)), the first actinide imine to be reported. This work underscores the high reactivity of thorium atoms, particularly for N-H bond activation, reveals a new type of multiple bond to actinide atoms, and shows that this bond is strong for thorium as a result of an important contribution from the f orbitals.     

Photoisomerization of a Chiral Imine Molecular Switch Followed by Matrix‐Isolation VCD Spectroscopy

Characterizing the stereochemistry of transient photoisomerization products remains a big challenge for the design of molecular machines, such as unidirectional molecular motors. Often these states are not stable long enough to be characterized in detail using conventional spectroscopic tools. The structurally simple camphorquinone imine 1 serves to illustrate the advantage of combining the matrix‐isolation technique with vibrational circular dichroism (VCD) spectroscopy for the investigation of photoisomerizations of chiral molecules. In particular, it is shown that both (E )‐ and (Z )‐ 1 can be generated photochemically at cryogenic temperatures in an argon matrix, and more importantly, that the stereochemistry of both switching states can be characterized reliably.     

Polyfluorides and Neat Fluorine as Host Material in Matrix‐Isolation Experiments

The use of neat fluorine in matrix isolation is reported, as well as the formation of polyfluoride monoanions under cryogenic conditions. Purification procedures and spectroscopic data of fluorine are described, and matrix shifts of selected molecules and impurities in solid fluorine are compared to those of common matrix gases (Ar, Kr, N₂, Ne). The reaction of neat fluorine and IR‐laser ablated metal atoms to yield fluorides of chromium (CrF₅), palladium (PdF₂), gold (AuF₅), and praseodymium (PrF₄) has been investigated. The fluorides have been characterized in solid fluorine by IR spectroscopy at 5 K. Also the fluorination of Kr and the photo‐dismutation of XeO₄ have been studied by using IR spectroscopy in neat fluorine. Formation of the [F₅]^? ion was obtained by IR‐laser ablation of platinum in the presence of fluorine and proven in a Ne matrix at 5 K by two characteristic vibrational bands of [F₅]^? at $\tilde \nu $ =850.7 and 1805.0 cm^?1 and its photo‐behavior.