Supramolecular Assembly, Solvent-Induced, and Mechanochromic Luminescence of Au(I) Quinoline-8-thiolates.

AuCl(PMe) and AuCl(PEt) were used to react with quinoline-8-thiolate (8-QNS) to give three Au(I) complexes, i.e., [8-QNS(AuPMe)]ClO (), [(8-QNS)Ag(AuPMe)]ClO (), and [8-QNS(AuPEt)]ClO (), which have been structurally determined by X-ray diffraction to show various intra- and intermolecular metal···metal contacts (i.

Mechanochromic and Solvent-Induced Luminescence of a Supramolecular Pt(II)-Bipyridine Complex with Di(4-pyridylmethyl)aminedithiocarbamate.

[Pt(bpy)(DPMACS)]Cl•3HO (•3HO) (bpy = 2,2'-bipyridine, DPMACS = di(4-pyridylmethyl)aminedithiocarbamate) was synthesized and characterized by X-ray diffraction studies, and its crystal structure displayed intermolecular Pt(II)···Pt(II) contacts of 3.471 and 5.065 Å.

Unconventional gas-phase synthesis of biphenyl and its atropisomeric methyl-substituted derivatives.

The biphenyl molecule (CH) acts as a fundamental molecular backbone in the stereoselective synthesis of organic materials due to its inherent twist angle causing atropisomerism in substituted derivatives and in molecular mass growth processes in circumstellar environments and combustion systems. Here, we reveal an unconventional low-temperature phenylethynyl addition-cyclization-aromatization mechanism for the gas-phase preparation of biphenyl (CH) along with -, -, and -substituted methylbiphenyl (CH) derivatives through crossed molecular beams and computational studies providing compelling evidence on their formation bimolecular gas-phase reactions of phenylethynyl radicals (CHCC, XA) with 1,3-butadiene- (CD), isoprene (CHC(CH)CHCH), and 1,3-pentadiene (CHCHCHCHCH). The dynamics involve de-facto barrierless phenylethynyl radical additions submerged barriers followed by facile cyclization and hydrogen shift prior to hydrogen atom emission and aromatization to racemic mixtures (, ) of biphenyls in overall exoergic reactions.

Gas-phase preparation of the dibenzo[]pyrene (CH) butterfly molecule a phenyl radical-mediated ring annulation.

A high temperature phenyl-mediated addition-cyclization-dehydrogenation mechanism to form peri-fused polycyclic aromatic hydrocarbon (PAH) derivatives-illustrated through the formation of dibenzo[]pyrene (CH)-is explored through a gas-phase reaction of the phenyl radical (CH˙) with triphenylene (CH) utilizing photoelectron photoion coincidence spectroscopy (PEPICO) combined with electronic structure calculations. Low-lying vibrational modes of dibenzo[]pyrene exhibit out-of-plane bending and are easily populated in high temperature environments such as combustion flames and circumstellar envelopes of carbon stars, thus stressing dibenzo[]pyrene as a strong target for far-IR astronomical surveys.

Thermal Synthesis of Carbamic Acid and Its Dimer in Interstellar Ices: A Reservoir of Interstellar Amino Acids.

Reactions in interstellar ices are shown to be capable of producing key prebiotic molecules without energetic radiation that are necessary for the origins of life. When present in interstellar ices, carbamic acid (HNCOOH) can serve as a condensed-phase source of the molecular building blocks for more complex proteinogenic amino acids. Here, Fourier transform infrared spectroscopy during heating of analogue interstellar ices composed of carbon dioxide and ammonia identifies the lower limit for thermal synthesis to be 62 ± 3 K for carbamic acid and 39 ± 4 K for its salt ammonium carbamate ([HNCOO][NH]).

Competing SiCH-H and SiCH-SiH Channels in the Bimolecular Reaction of Ground-State Atomic Carbon (C(P)) with Disilane (SiH, XA) under Single Collision Conditions.

The bimolecular gas-phase reaction of ground-state atomic carbon (C(P)) with disilane (SiH, XA) was explored under single-collision conditions in a crossed molecular beam machine at a collision energy of 36.6 ± 4.5 kJ mol.

Gas-Phase Preparation of 1-Germavinylidene (HCGe; XA), the Isovalent Counterpart of Vinylidene (HCC; XA), via Non-adiabatic Dynamics through the Elementary Reaction of Ground State Atomic Carbon (C; P) with Germane (GeH; XA).

1-Germavinylidene (HCGe; XA), the germanium analogue of vinylidene (HCC; XA), was prepared via a directed gas-phase synthesis through the bimolecular reaction of ground state atomic carbon (C; P) with germane (GeH; XA) under single-collision conditions. The reaction commences with the barrierless insertion of carbon into the Ge-H bond followed by intersystem crossing from the triplet to singlet surface and migration of atomic hydrogen to germylene (HGeCH), which predominantly decomposes via molecular hydrogen loss to 1-germavinylidene (HCGe; XA). Therefore, the replacement of a single carbon atom in the acetylene-vinylidene system by germanium critically impacts the chemical bonding, molecular structure, and thermodynamic stability of the carbene-type structures favoring 1-germavinylidene (HCGe) over germyne (HGeCH) by 160 kJ mol.

Luminescent Pt(II) Complexes Containing (1-Aza-15-crown-5)dithiocarbamate and (1-Aza-18-crown-6)dithiocarbamate: Mechanochromic and Solvent-Induced Luminescence.

The strong tendency to stack in the solid state and rich luminescence for the Pt(II) complexes makes them potential candidates as new mechanochromic materials and sensing applications. Six mononuclear complexes [Pt(ppy)(ONCS)] (), [Pt(bpy)(ONCS)]ClO (), [Pt(ppy)(ONCS)] (), [Pt(phen)(ONCS)]ClO·CHOH (), [Pt(phen)(ONCS)]ClO (), and [Pt(phen)(ONCS)]ClO (), one dinuclear complex [Pt(phen)(NaONCS)(ClO)]ClO (), and one one-dimensional (1-D) coordination polymer {[Pt(bpy)(NaONCS)(ClO)](ClO)} () were synthesized by reacting [Pt(ppy)Cl], Pt(bpy)Cl, and Pt(phen)Cl (ppy = 2-phenylpyridine, bpy = 2,2'-bipyridine, and phen = 1,10-phenanthroline) with (1-aza-15-crown-5)dithiocarbamate (ONCS) or (1-aza-18-crown-6)dithiocarbamate (ONCS), respectively, which have been isolated and structurally characterized by X-ray diffraction. Neutral complexes and contain no intermolecular Pt(II)···Pt(II) contact, whereas cationic complexes , , , and with ClO as counteranions show alternative intermolecular Pt(II)···Pt(II) contacts of 3.

Formation of the Elusive Silylenemethyl Radical (HCSiH; XB) via the Unimolecular Decomposition of Triplet Silaethylene (HCSiH; aA″).

We investigated the formation of small organosilicon molecules─potential precursors to silicon-carbide dust grains ejected by dying carbon-rich asymptotic giant branch stars─in the gas phase via the reaction of atomic carbon (C) in its P electronic ground state with silane (SiH; XA) using the crossed molecular beams technique. The reactants collided under single collision conditions at a collision energy of 13.0 ± 0.

Combined Spectroscopic and Computational Investigation on the Oxidation of -Tetrahydrodicyclopentadiene (JP-10; CH) Doped with Titanium-Aluminum-Boron Reactive Metal Nanopowder.

We report the results on the combustion of single, levitated droplets of -tetrahydrodicyclopentadiene (JP-10) doped with titanium-aluminum-boron (Ti-Al-B) reactive metal nanopowders (RMNPs) in an oxygen (60%)-argon (40%) atmosphere by exploiting an ultrasonic levitator with droplets ignited by a carbon dioxide laser. Ultraviolet-visible (UV-vis) emission spectroscopy revealed the presence of gas-phase aluminum (Al) and titanium (Ti) atoms. These atoms can be oxidized in the gas phase by molecular oxygen to form spectroscopically detected aluminum monoxide (AlO) and titanium monoxide (TiO) transients.

Gas Phase Preparation of the Elusive Monobridged Ge(μ-H)GeH Molecule through Nonadiabatic Reaction Dynamics.

The hitherto elusive monobridged Ge(μ-H)GeH (X A') molecule was prepared in the gas phase by bimolecular reaction of atomic germanium with germane (GeH ). Electronic structure calculations revealed that this reaction commenced on the triplet surface with the formation of a van der Waals complex, followed by insertion of germanium into a germanium-hydrogen bond over a submerged barrier to form the triplet digermanylidene intermediate (HGeGeH ); the latter underwent intersystem crossing from the triplet to the singlet surface. On the singlet surface, HGeGeH predominantly isomerized through two successive hydrogen shifts prior to unimolecular decomposition to Ge(μ-H)GeH isomer, which is in equilibrium with the vinylidene-type (H GeGe) and dibridged (Ge(μ-H )Ge) isomers.

Identification of Elusive Keto and Enol Intermediates in the Photolysis of 1,3,5-Trinitro-1,3,5-Triazinane.

Enols have emerged as critical reactive intermediates in combustion processes and in fundamental molecular mass growth processes in the interstellar medium, but the elementary reaction pathways to enols in extreme environments, such as during the decomposition of molecular energetic materials, are still elusive. Here, we report on the original identification of the enol and keto isomers of oxy--triazine, as well as its deoxygenated derivative 1,3,5-triazine, formed in the photodecomposition processes of 1,3,5-trinitro-1,3,5-triazinane (RDX)-a molecular energetic material. The identification was facilitated by exploiting isomer-selective tunable photoionization reflectron time-of-flight mass spectrometry (PI-ReTOF-MS) in conjunction with quantum chemical calculations.

Formation of phosphine imide (HN[double bond, length as m-dash]PH) and its phosphinous amide (HN-PH) isomer.

We present the first formation of the previously elusive phosphine imide (HN[double bond, length as m-dash]PH3) along with its phosphinous amide (H2N-PH2) isomer via exposure of phosphine (PH3) and ammonia (NH3) ices to ionizing radiation. Our approach may be extended to prepare, separate, and detect highly reactive compounds such as intermediates of Wittig reactions.

Combined Experimental and Computational Study on the Reaction Dynamics of the D1-Silylidyne(SiD) - Silane (SiH) System.

Small silicon hydrides have attracted extensive interest because of their role in the chemical evolution of circumstellar envelopes of evolved carbon stars and applications in surface growth processes and as transients in semiconductor manufacturing. Combined with electronic structure calculations, we demonstrate that monobridged silylidynesilylenes [(Si(μ-D)SiH, Si(μ-H)SiHD, Si(μ-H)SiH] and silylsilylidyne [HSiSi, HDSiSi], which are nearly isoenergetic, can be prepared via molecular hydrogen loss channels in the crossed molecular beam study of the reaction of D1-silylidyne (SiD; XΠ) with silane (SiH; XA) in a crossed molecular beams machine. Compared to the dynamics of the isovalent methylidyne (CH) - methane (CH) system, our study delivers a unique view at the intriguing isomerization processes and reaction dynamics of dinuclear silicon hydride transients, thus contributing to our knowledge on the chemical bonding of silicon hydrides at the molecular level.

Gas phase identification of the elusive oxaziridine (cyclo-HCONH) - an optically active molecule.

The hitherto elusive oxaziridine molecule (cyclo-HCONH) - an optically active, high energy isomer of nitrosomethane (CHNO) - is prepared in processed methane-nitrogen monoxide ices and detected upon sublimation in the gas phase. Electronic structure calculations reveal likely routes via addition of carbene (CH) to the nitrogen-oxygen double bond of nitrosyl hydride (HNO). Our findings provide a fundamental framework to explore the preparation and stability of racemic oxaziridines exploited in chiral substrate-controlled diastereoselective preparation such as Sharpless asymmetric epoxidation, thus advancing our fundamental understanding of the preparation and chemical bonding of strained rings in small organic molecules.

Gas Phase Synthesis of the Elusive Trisilacyclopropyl Radical (SiH) via Unimolecular Decomposition of Chemically Activated Doublet Trisilapropyl Radicals (SiH).

The gas phase reaction of the simplest silicon-bearing radical silylidyne (SiH; XΠ) with disilane (SiH; XA) was investigated in a crossed molecular beams machine. Combined with electronic structure calculations, our data reveal the synthesis of the previously elusive trisilacyclopropyl radical (SiH)-the isovalent counterpart of the cyclopropyl radical (CH)-along with molecular hydrogen via indirect scattering dynamics through long-lived, acyclic trisilapropyl (i-SiH) collision complex(es). Possible hydrogen-atom roaming on the doublet surface proceeds to molecular hydrogen loss accompanied by ring closure.

Gas Phase Identification of the Elusive -Hydroxyoxaziridine (c-HCON(OH)): A Chiral Molecule.

The hitherto elusive -hydroxyoxaziridine molecule (c-HCON(OH)), a chiral, high energy isomer of nitromethane (CHNO) and one of the simplest representatives of an oxaziridine, is detected in the gas phase. Electronic structure calculations propose an impending synthesis eventually via addition of carbene (CH) to the nitrogen-oxygen double bond of nitrous acid (HONO). The oxaziridine ring demonstrates an unusual kinetic stability toward ring opening compared to the isoeletronic cyclopropane (CH) counterpart.

The Elusive Ketene (H CCO) Channel in the Infrared Multiphoton Dissociation of Solid 1,3,5-Trinitro-1,3,5-Triazinane (RDX).

Understanding of the fundamental mechanisms involved in the decomposition of 1,3,5-trinitro-1,3,5-triazinane (RDX) still represents a major challenge for the energetic materials and physical (organic) chemistry communities mainly because multiple competing dissociation channels are likely involved and previous detection methods of the products are not isomer selective. In this study we exploited a microsecond pulsed infrared laser to decompose thin RDX films at 5 K under mild conditions to limit the fragmentation channels. The subliming decomposition products during the temperature programed desorption phase are detected using isomer selective single photoionization time-of-flight mass spectrometry (PI-ReTOF-MS).

Synthesis of Polycyclic Aromatic Hydrocarbons by Phenyl Addition-Dehydrocyclization: The Third Way.

Polycyclic aromatic hydrocarbons (PAHs) represent the link between resonance-stabilized free radicals and carbonaceous nanoparticles generated in incomplete combustion processes and in circumstellar envelopes of carbon rich asymptotic giant branch (AGB) stars. Although these PAHs resemble building blocks of complex carbonaceous nanostructures, their fundamental formation mechanisms have remained elusive. By exploring these reaction mechanisms of the phenyl radical with biphenyl/naphthalene theoretically and experimentally, we provide compelling evidence on a novel phenyl-addition/dehydrocyclization (PAC) pathway leading to prototype PAHs: triphenylene and fluoranthene.

Origin of alkylphosphonic acids in the interstellar medium.

For decades, the source of phosphorus incorporated into Earth's first organisms has remained a fundamental, unsolved puzzle. Although contemporary biomolecules incorporate P(+V) in their phosphate moieties, the limited bioavailability of phosphates led to the proposal that more soluble P(+III) compounds served as the initial source of phosphorus. Here, we report via laboratory simulation experiments that the three simplest alkylphosphonic acids, soluble organic phosphorus P(+III) compounds, can be efficiently generated in interstellar, phosphine-doped ices through interaction with galactic cosmic rays.

Directed Gas-Phase Formation of the Germaniumsilylene Butterfly Molecule (Ge(μ-H)Si).

The hitherto elusive dibridged germaniumsilylene molecule (Ge(μ-H)Si) has been formed for the first time via the bimolecular gas-phase reaction of ground-state germanium atoms (Ge) with silane (SiH) under single-collision conditions. Merged with state-of-the-art electronic structure calculations, the reaction was found to proceed through initial formation of a van der Waals complex in the entrance channel, insertion of the germanium into a silicon-hydrogen bond, intersystem crossing from the triplet to the singlet surface, hydrogen migrations, and eventually elimination of molecular hydrogen via a tight exit transition state, leading to the germaniumsilylene "butterfly". This investigation provides an extraordinary peek at the largely unknown silicon-germanium chemistry on the molecular level and sheds light on the essential nonadiabatic reaction dynamics of germanium and silicon, which are quite distinct from those of the isovalent carbon system, thus offering crucial insights that reveal exotic chemistry and intriguing chemical bonding in the germanium-silicon system on the most fundamental, microscopic level.

A vacuum ultraviolet photoionization study on the formation of methanimine (CHNH) and ethylenediamine (NHCHCHNH) in low temperature interstellar model ices exposed to ionizing radiation.

Methylamine (CH3NH2) and methanimine (CH2NH) represent essential building blocks in the formation of amino acids in interstellar and cometary ices. In our study, by exploiting isomer selective detection of the reaction products via photoionization coupled with reflectron time of flight mass spectrometry (Re-TOF-MS), we elucidate the formation of methanimine and ethylenediamine (NH2CH2CH2NH2) in methylamine ices exposed to energetic electrons as a proxy for secondary electrons generated by energetic cosmic rays penetrating interstellar and cometary ices. Interestingly, the two products methanimine and ethylenediamine are isoelectronic to formaldehyde (H2CO) and ethylene glycol (HOCH2CH2OH), respectively.

An interstellar synthesis of phosphorus oxoacids.

Phosphorus signifies an essential element in molecular biology, yet given the limited solubility of phosphates on early Earth, alternative sources like meteoritic phosphides have been proposed to incorporate phosphorus into biomolecules under prebiotic terrestrial conditions. Here, we report on a previously overlooked source of prebiotic phosphorus from interstellar phosphine (PH) that produces key phosphorus oxoacids-phosphoric acid (HPO), phosphonic acid (HPO), and pyrophosphoric acid (HPO)-in interstellar analog ices exposed to ionizing radiation at temperatures as low as 5 K. Since the processed material of molecular clouds eventually enters circumstellar disks and is partially incorporated into planetesimals like proto Earth, an understanding of the facile synthesis of oxoacids is essential to untangle the origin of water-soluble prebiotic phosphorus compounds and how they might have been incorporated into organisms not only on Earth, but potentially in our universe as well.

Synthesis of the hitherto elusive formylphosphine (HCOPH) in the interstellar medium - a molecule with an exotic phosphorus peptide bond.

The formylphosphine (HCOPH2) molecule was detected in the gas phase via isomer selective photoionization reflectron time-of-flight mass spectrometry (PI-ReTOF-MS). Synthesized in carbon monoxide (CO)-phosphine ices (PH3) exposed to ionizing radiation, the formation mechanism involves an initial phosphorus-hydrogen bond rupture in phosphine yielding the phosphino radical (PH2) along with atomic hydrogen, addition of the suprathermal hydrogen atom to carbon monoxide leading to the formyl radical (HCO), and recombination of both radicals to formylphosphine (HCOPH2). This molecule represents the isovalent counterpart of the ubiquitous interstellar formamide (HCONH2).

Are Nonadiabatic Reaction Dynamics the Key to Novel Organosilicon Molecules? The Silicon (Si(P))-Dimethylacetylene (CH(XA)) System as a Case Study.

The bimolecular gas phase reaction of ground-state silicon (Si; P) with dimethylacetylene (CH; XA) was investigated under single collision conditions in a crossed molecular beams machine. Merged with electronic structure calculations, the data propose nonadiabatic reaction dynamics leading to the formation of singlet SiCH isomer(s) and molecular hydrogen (H) via indirect scattering dynamics along with intersystem crossing (ISC) from the triplet to the singlet surface. The reaction may lead to distinct energetically accessible singlet SiCH isomers (p8-p24) in overall exoergic reaction(s) (-107 kJ mol).