The viability of a main-group triple bond depends critically on the strength of its π-manifold. Among the 15 possible diatomic homo- and interpnictogens, EE', (E, E' = group 15 element), the NN linkage of dinitrogen stands out as one of the strongest triple bonds that exists, whereas the heavier pnictogens form thermodynamically unstable triple bond motifs that either decompose to single-bonded oligomers or extrude N2, under standard conditions. Considering the fundamentally simple chemistry of a diatomic molecule, coupled with the enticing synthetic challenge of accessing any other EE' dipnictogen than N2, we here survey the chemistry of the mononitride family, EN (E = P, As, Sb, Bi). We describe how these unusual bonding motifs were first observed as transient species in the gas phase, later isolated in cryogenic noble-gas matrix experiments, and recently have become the subject of synthetic studies in solution. We delineate strategies to tame the highly reactive EN motifs by incorporating them into adducts with organic fragments or transition metal nodes, enabling studies of their reaction chemistry under controlled conditions. These efforts have opened fascinating perspectives in pnictogen multiple-bond reactivity, spanning radical and closed-shell transformations, electrophilic as well as nucleophilic reactivity of the EN fragments, oxidative addition, oligomerization, cyclization, inorganic aromaticity, and even EN group transfer. Finally, we identify topics in the triple-bond chemistry of pnictogen mononitrides that remain ambiguous or poorly explored, pointing toward future directions in the field.

Targeted synthesis of Ni/C-containing composite materials was carried out using the matrix isolation method. The Ni content was varied (5-20 wt.% from chitosan). The morphology and physicochemical properties of the obtained materials were characterized using a number of methods: elemental analysis, SEM, TEM, XRD, FTIR, Raman spectroscopy, TPR-H2, and SSA. FTIR showed that nickel ions are immobilized on the chitosan molecule, and heat treatment of the polymer molecule results in the formation of polyconjugation centers. It was also revealed that heat treatment of the salt-polymer films results in the formation of a graphite-like structure (Raman spectroscopy) with the inclusion of nickel in metallic form (XRD, TPR-H2), with a particle size from 2 to 10 nm (TEM). The composites were shown to have a SSA of up to 269 m2/g. The resulting composite materials were used as catalysts for the decomposition of methane to produce hydrogen. High activity was observed in the catalytic methane decomposition at 700 °C (methane conversion up to 25.8%; hydrogen yield up to 1.98 gH2/gNi/h).

The conformational space of N,N-diethyl-2-hydroxyacetamide (DEHyA) was elucidated through an integrated experimental-computational approach combining matrix isolation infrared spectroscopy and density functional theory (DFT) calculations. Quantum chemical analysis revealed 15 distinct conformers, with the CC(g±g±) form constituting the global minimum and the closely related CC(g±g∓) geometry lying slightly higher in energy. Infrared spectral evidence for these conformers was obtained from the O-H, C=O, and C-O stretching regions in N2 and Ar matrices at cryogenic temperatures. Both low-energy structures are primarily stabilized by intramolecular hydrogen bonding, further modulated by hyperconjugative and weak tetrel interactions. The relative energetic and electronic contributions of these effects were quantified through Non-Covalent Interaction (NCI), Electrostatic Potential (ESP) mapping, Intrinsic Bond Strength Index (IBSI), and Natural Bond Orbital (NBO) analyses. These results establish hydrogen bonding as the principal stabilizing force, complemented by secondary hyperconjugative and tetrel effects. Targeted orbital deletion studies further demonstrated that charge-transfer electron delocalization governs the conformational preference, underscoring the cooperative nature of noncovalent interactions in defining the structural stability of DEHyA. A comprehensive comparison with the higher homologue, N,N-dioctyl-2-hydroxyacetamide (DOHyA), was undertaken to elucidate whether conformational modulation arises solely from intrinsic electronic factors or is additionally influenced by steric encumbrance imposed by bulky alkyl substituents.

The boron monoxide radical has emerged as a fascinating molecule and a short-lived intermediate, previously observed only under matrix isolation conditions. In this study, we report the successful synthesis and characterization of a stable organic boron monoxide radical, achieved through the reaction of a diboron (6) dianion with nitric oxide (NO). This oxygen-centered radical is uniquely functionalized and stabilized by a triaryl-substituted boryl group. Comprehensive characterization was performed using various spectroscopic and structural techniques, including electron paramagnetic resonance (EPR) spectroscopy and single-crystal X-ray diffraction analysis. Remarkably, this oxygen-centered radical is stabilized by the K cation and exhibits significant stability under argon at room temperature, showing no self-dimerization even when heated or exposed to UV light. However, it can dimerize to form peroxide species when the K cation is fully encapsulated. Furthermore, it can mimic transition-metal complexes by mediating NO coupling to form a boryl hyponitrite (N2O22-) derivative. Finally, this boron monoxide radical also shows promising catalytic potential in Sn-Sn coupling reactions.

The boron methylene (BCH2) free radical has never been identified spectroscopically. We have undertaken a series of abinitio calculations to predict the molecular structures, vibrational frequencies, and energies of the ground and first three electronically excited states of BCH2 and its various isomers and isotopologues. In the ground state, we find that the global minimum is linear HBCH, with C2v BCH2 roughly 3935cm-1 higher and the unstable CBH2 species is a C2v weakly bound structure at 16 384cm-1, which readily isomerizes to the linear radical. HBCH and BCH2 are separated by a large isomerization barrier (12 825cm-1), so it may be possible to prepare boron methylene in the gas phase and detect it with spectroscopic methods. The vibrational frequencies and rotational constants of four ground-state isotopologues of BCH2 have been calculated as an aid to future IR matrix isolation and gas-phase microwave studies. Similar calculations are reported for the ground-state linear HBCH species and its cis- and trans-bent excited states. The C̃2B2-X̃2A1 electronic transition in the 320-290nm region is the only viable option for detecting BCH2 by gas-phase absorption or laser-induced fluorescence techniques. Franck-Condon simulations of the C̃-X̃ absorption and the allowed C̃-X̃ and C̃-B̃ emission transitions have been done for 11BCH2 and 11BCD2. In addition, the rotational structure expected for the 0-0 bands of both isotopologues under supersonic expansion conditions has been simulated. The abinitio data and predicted spectra should be invaluable for attempts to identify the boron methylene free radical in the gas phase.

Electron paramagnetic resonance (EPR) spectroscopy has long been widely utilized to investigate, characterize, and monitor highly reactive paramagnetic chemical species generated in materials upon exposure to ionizing radiation. This personal account presents EPR observations and spectral analyses of several fundamental paramagnetic species, including cations, anions, and neutral radicals, isolated using a low-temperature solid matrix isolation (MI) technique combined with radiation exposure, a method in which the author has extensive experience. These findings are not only of significant interest in the field of molecular science but also demonstrate the utility of the MI technique as a laboratory-based approach to exploring chemical evolution in space. Recent density functional theory analyses, which reveal a second-order Jahn-Teller distortion, suggest that the stability of the distorted structure of the silacyclohexane radical cation is considerably less pronounced than previously indicated by Hartree-Fock-based theoretical calculations. Furthermore, EPR results for the perfluorocubane radical anion, a species that has recently attracted significant attention, are also presented.

Phosphine (PH3) is the simplest phosphorus compound detected in the extrasolar and planetary environments, where it can be subjected to ionizing radiation. In this study, we first report the vibrational spectra of the ionized molecules resulting from phosphine monomer and dimer in solid noble gas matrices upon X-ray irradiation. The assignment was based on the comparative studies using electron paramagnetic resonance and Fourier transform infrared spectroscopy, complemented by the quantum-chemical calculations at the valence-correlated spin unrestricted coupled cluster single-double and perturbative triple [UCCSD(T)] level of theory. We were able to observe three fundamentals of PH3+• and four fundamentals of P2H6+•. The spectroscopic data were also obtained for PD3+•, P2D6+•, and [PH3-PD3]+• radical cations. PH3+• demonstrates a large blue shift of the most intense infrared (IR) absorption related to the P-H stretching vibration (ν1) with respect to the corresponding vibration in the parent neutral. For the P2H6+• radical cation, the most intense IR absorption corresponds to a low-frequency deformational vibration. It was found that the P2H6+• radical cation reveals a photochromic behavior: it decays under the action of light with λ ≤ 400nm and can be partially recovered after subsequent photolysis at λ = 445-525nm. The observed transformations were attributed to the interconversion between P2H6+• and the PH4+…PH2• complex. The dynamics of these transformations was discussed using the data obtained for mixed P2H3D3+• species. The obtained results may be useful for future searches for the manifestations of such species in extraterrestrial environments and studies of the radiation-induced transformations of phosphine in icy media.

In lithium-ion battery electrolyte production, LiPF6 is the dominant salt due to its high ionic conductivity and operational stability. One synthesis method involves PF5 and CH3CN reagents, which exhibit contrasting reactivity - PF5 hydrolyzes easily, while CH3CN is chemically inert. Their interaction was studied via cryogenic matrix isolation and computational analysis. New FTIR bands, distinct from isolated monomers, indicated aggregated species with varied geometries. No photoevolution was observed under UV irradiation, and only slight changes became apparent after annealing the sample up to 30 K. Possible structures were explored using the automated docking algorithm and GFN2-xTB, positioning CH3CN (guest) around PF5 (host) to locate energy minima on the potential energy surface (PES). The 100 identified structures were grouped into two sets (CH3CN-PF5 and PF5-H3CCN) based on energy differences. Further optimization with B97M-V/def2-QZVPPD confirmed minima, enabling IR spectrum simulations. The computational model suggests an adduct formation via nitrogen (N) of CH3CN interacting with phosphorus (P) of PF5, aligning well with experimental data. This study provides insights into CH3CN-PF5 interactions relevant to LiPF6 synthesis.

The cycloaddition of nitrenes with olefins is an important method for the synthesis of aziridines. We report here that the reaction of catecholato borylnitrene CatBN with ethene upon long wavelength photoirradiation (λ > 550 nm) gives not only the expected aziridine, but also the imine CatBNCreated by potrace 1.16, written by Peter Selinger 2001-2019]]>CHCH3 under cryogenic matrix isolation conditions in solid neon at 4 K. Computational analysis reveals that the photochemically generated singlet CatBN (1A1 electronic state) can react with ethene to form the aziridine and a singlet 1,3-diradical intermediate. The latter arises from multi-state reactivity involving the nearly degenerate 1A1 and 1A2 nitrene singlet states. The singlet 1,3-diradical has a very low barrier for 1,2-H migration to give the imine. The observation of an imine in the reaction with an alkene reveals chemodivergence by highlighting a previously unobserved reactivity pathway in nitrene chemistry.

Nitrenes (N-R) and heavier pnictinidenes (Pn-R; Pn = P-Bi, R = anionic substituents), which are monovalent group 15 elements, have long been regarded as fleeting reactive intermediates in organic chemistry, with their existence typically confirmed only under matrix isolation conditions. The past few years have witnessed a striking evolution of these species from ephemeral curiosities into isolable, well-defined compounds under ambient laboratory conditions, irrespective of their singlet or triplet ground states. This perspective provides a chronological review of recent advances in the counterintuitive chemistry of nitrenes and pnictinidenes in the condensed phase, including their diverse synthetic methodologies and unusual bonding and structural features.

We developed a matrix isolation experiment utilizing a closed‐cycle helium cryostat, which operates at 2.5 K and enables electron paramagnetic resonance (EPR) measurements in solid para‐hydrogen (p‐H2) matrices. The EPR spectra of the persistent 2,2,6,6‐tetramethylpiperidinyloxyl (TEMPO) radical and an in situ generated P‐centered mono‐radical were recorded at 2.5 K in p‐H2. The spectrum of TEMPO in p‐H2 shows a narrower linewidth compared to argon, and its matrix‐isolated spectrum and simulation are reported. The P‐centered mono‐radical was generated in p‐H2 via in situ photolysis of the corresponding phosphorus iodide, which affords roughly a three‐fold increase in spectral resolution compared to argon, as well as higher sensitivity due to the non‐existing cage effect in soft p‐H2.

Simple imino acids have received sparse consideration as reactive intermediates in the formation of amino acids under prebiotic or astrochemical conditions. Under cryogenic matrix isolation conditions, 2-azidopropionic acid decomposes after ultraviolet (UV) irradiation to dinitrogen and 2-iminopropionic acid, namely, alanine imine, which is the proposed key intermediate in biologically relevant alanine transaminase reactions. Three conformers of alanine imine were spectroscopically characterized by Fourier transform infrared (FT-IR) and ultraviolet-visible (UV/vis) spectroscopy in solid argon at 3.5 K. One high-energy conformer can be selectively prepared by the near-IR induced excitation of an OH-overtone vibration. In the dark, this conformer undergoes H-tunneling CO-bond rotamerization. In aqueous solution, 2-azidopropionic acid decomposes to glyoxylic and pyruvic acid after hydrolysis of the formed imine intermediates as identified by 1H NMR spectroscopy. Under more acidic conditions and prolonged irradiation, the intermediary formed imino acids are reduced to their glycine and alanine amino acid equivalents, respectively.

The UV-induced photolysis of 2-aminothiazole-4-carboxylic acid (ACA), a biologically active molecule, was studied using the infrared matrix isolation method. As the first step of photolysis, a decarboxylation reaction occurred. Subsequently, two main photolysis pathways of 2-aminothiazole were observed, during which a number of new molecules, including potential prebiotic carbodiimides or molecular complexes, were identified. The CS–CN bond cleavage path produced N-(1-sulfanylethen-2-yl)carbodiimide (fp1), N-(thiiran-2-yl)carbodiimide (fp3), N-(1-thioethan-2-yl)carbodiimide (fp2), N-(1-thioethan-1-yl)carbodiimide (fp4) and N-(1-thioethan-2-yl)cyanamide (fp33), which were identified for the first time. In this channel, additional disruption of the N–C bond produced cyanamide (fp27) and thiirene (fp28) and subsequent photoreactions generated carbodiimide (fp29) or ethynethiol (fp30). The CS–CC bond cleavage path occurred simultaneously and produced several new molecules: N’-ethynylcarbamimidothioic acid (fp14), N-ethynylcarbamimidothioic acid (fp17), N-ethenylidenecarbamimidothioic acid (fp18) and N-ethenylidenethiourea (fp15). In this channel, additional disruption of the N–C bond produced acetylene (fp23) and N-thiolcarbodiimide (fp26). Among the small molecules, N-thiolcarbodiimide and thiirene, as well as all molecular complexes, were observed for the first time.

Quantum chemical calculations have been performed to investigate the structure, stability, and bonding in noble gas (Ng) bound Be2B5 + complexes. The present results show that Be2B5 +, a charge-separated [Be]2+[B5]3-[Be]2+ cluster, can employ both its cationic Be center and anionic B center to bind Ng atoms. It can bind a total of seven Ng atoms, resulting in the formation of a highly symmetric (NgBe)2Be2(NgB)5B5 + complex, having D5h point group. The thermochemical analyses reveal that the Ng-Be bonds are stronger than the Ng-B bonds. (NgBe)2Be2B5 + (Ng = Ar-Rn) complexes are stable against the dissociation of Ng atoms even at room temperature. But, (NgBe)2Be2B5 + (Ng = He and Ne) and (NgBe)2Be2(NgB)5B5 + (Ng = Ar-Rn) complexes are stable only at very low temperatures. Therefore, they can be suitable candidates for low-temperature matrix isolation. A thorough bonding analysis, through charge and energy decomposition methods, discloses that despite the Ng-B interaction being weaker than the Ng-Be interaction, the former bond is more covalent than the latter one. In fact, in the Ng-B bonds, both the orbital and electrostatic interactions are larger in magnitude than the Ng-Be bonds; however, significantly larger Pauli repulsion in the former bonds makes them weaker than the latter bonds. In both Ng-Be and Ng-B bonds, the covalent interaction originates from a strong Ng(pσ) → Be2B5 + σ donation, complemented by two weak Ng(pπ) → Be2B5 + π donations.

Influence of methyl substituents on the conformational stability of Si3N3(CH3)6: molecules first principles and FT-IR matrix isolation study

The perfluorobenzyl peroxyl radical (C6F5CF2O2) was prepared by the reaction of the perfluorobenzyl radical, generated in the gas phase by vacuum pyrolysis of the perfluorobenzyl iodide, with molecular oxygen. The IR spectra of the radicals C6F5CF2O2 and C6F5CF218O2 trapped in argon matrices at 10 K were measured for the first time and assigned to two conformers with the O-O moiety in anti- and gauche orientation with respect to the C-C bond by comparing the results of the matrix isolation IR spectroscopy study with the data of quantum chemical calculations at the B3LYP/aug-cc-pVTZ and CBS-QB3 levels of theory. UV photolysis of this peroxyl radical resulted in the elimination of F2C═O with the formation of the perfluorophenoxyl radical C6F5O, which formed complexes in the matrix. This reaction pathway considerably differs from that observed for the unsubstituted benzyl peroxyl radical, which decomposes to hydroxyl radical and benzaldehyde.

We describe the first spectroscopic identification ofhithertoexperimentally unreported hydroxy isocyanate HONCO, a potential candidatefor interstellar medium and prebiotic chemistry. This planar chainmolecule was prepared in the gas phase through flash vacuum pyrolysisof phenyl N-hydroxycarbamate at 650 °C and wassubsequently trapped in argon matrices at 3.5 K. Its characterizationwas accomplished by means of matrix isolation IR and UV/vis spectroscopytogether with quantum chemical computations. Upon UV light (λ= 313 nm) irradiation, HONCO decomposes into hydrogen-bonded complexesof HON and HNO with CO.

The structure of the newly synthesised compound, 1-chlorosilacyclopentane (1-ClSiCP), was investigated using vibrational spectroscopy and theoretical calculations. ATR FT-IR and Raman spectroscopy were used to analyse the liquid sample. Matrix isolation FT-IR spectroscopy was used for the analysis of closely located infrared spectral bands of 1-ClSiCP. Spectroscopic data analysis was performed using theoretical methods such as density functional theory (DTF) and ab initio calculations. FT-IR spectra of 1-ClSiCP isolated in Ne and N2 matrices were collected before and after annealing. During the theoretical structural analysis, the envelope (1E) and twisted (2T3) ring shapes, with the chlorine atom in axial and equatorial positions, were investigated utilising the aug-cc-pVTZ basis set included in the MP2 and DFT calculations. Potential energy surface scans were performed to trace the energy changes and the structure of transition states during the ring conversion. Depending on the method applied, the theoretical results indicate the presence of different conformers, including twisted and envelope ring shapes. The experimental results confirm the existence of only one conformer in the twisted ring configuration. Good agreement between the experimental matrix isolation spectra and in the anharmonic approximation calculated IR absorption spectrum of the 2T3 conformer is observed. The difference between the calculated and experimental frequencies of the normal modes does not exceed 2%.

This study addresses two persistent challenges in uranium fluoride chemistry: resolving decades-long spectral assignment conflicts across UF2, UF3, and UF4 species, and conclusively settling the symmetry controversy of UF4. By the cryogenic matrix isolation IR spectroscopy technique in combination with relativistic quantum chemical calculations, we experimentally tracked the stepwise formation of UF to UF6 in neon and argon matrices. Theoretical validation has led to a reassignment of the infrared absorption bands for UF2, UF3, and UF4, defining their molecular geometries. While UF2 exhibits a V-shaped C2v structure and UF3 has a pyramidal C3v configuration, UF4 adopts a D2d geometry rather than a Td symmetry, arising from the Jahn-Teller distortion, which was verified by complete active space second-order perturbation theory (CASPT2) calculations incorporating spin-orbit coupling, supporting predictions from relativistic density functional theory and BW-MRCCSD calculations by Johnson et al. Moreover, weak van der Waals interactions between UFn (n = 2-4) and argon atoms induced vibrational redshift. Bonding analyses revealed that U-F bonds in UFn (n = 1-6) possess dual ionic-covalent character, with ionic contributions of 78-88%. The covalent enhancement in fluorides arises from the overlap of U 5f/6d orbitals with F 2p orbitals and their near-degeneracy. These findings reconcile historical discrepancies, establish definitive benchmarks, and advance uranium fluoride chemistry for nuclear fuel applications.

Organophosphorus compounds are fundamental building blocks in organic synthesis, pharmaceuticals, and most notably as optoelectronic materials. In this study, we describe the generation and matrix isolation of a dibenzophosphole-based P-centered radical via photolysis or pyrolysis from an iodo precursor in Ar, and para-hydrogen (p-H2). The radical is experimentally characterized by infrared (IR), UV/Vis and electron spin resonance (ESR) spectroscopy. Based on a detailed analysis of the spectroscopic data, supported by quantum chemical calculations, the P-dibenzophospholyl radical is a π-radical with a 2B1 electronic ground state, where the unpaired electron resides in a p-orbital perpendicular to the molecular plane and with some degree of electron density delocalization over the aromatic rings. We compared the experimental and computational results of the P-dibenzophospholyl radical with its nitrogen analogue, the N-carbazolyl radical, which is a highly delocalized π-radical.