131 research outputs found
The Chlorido-Bismuth Dication: A Potent Lewis Acid Captured in a Hepta-Coordinate Species with a Stereochemically Active Lone Pair
The stabilization of simple, highly reactive cationic species in molecular complexes represents an important strategy to isolate and characterize compounds with uncommon or even unprecedented structural motifs and properties. Here we report the synthesis, isolation, and full characterization of chlorido-bismuth dications, stabilized only by monodentate dimethylsulfoxide (dmso) ligands: [BiClÂ(dmso)6]Â[BF4]2 (1) and [BiClÂ(ÎŒ2-dmso)Â(dmso)4]2[BF4]4 (2). These compounds show unusual distorted pentagonal bipyramidal coordination geometries along with high Lewis acidities and have been analyzed by multinuclear NMR spectroscopy, elemental analysis, IR spectroscopy, single-crystal X-ray diffraction, and density functional theory calculations. Attempts to generate the bromido- and iodido-analogs gave dmso-stabilized tricationic bismuth species
Chemical Aristocracy: He3 Dication and Analogous Noble-Gas-Exclusive Covalent Compounds
Herein, we predict the first set of covalently bonded triatomic molecular compounds composed exclusively of noble gases. Using a combination of double-hybrid DFT, CCSD(T), and MRCI+Q calculations and a range of bonding analyses, we explored a set of 270 doubly charged triatomics, which included various combinations of noble gases and main group elements. This extensive exploration uncovered nine noble-gas-exclusive covalent compounds incorporating helium, neon, argon, or combinations thereof, exemplified by cases such as He32+ and related systems. This work brings to light a previously uncharted domain of noble gas chemistry, demonstrating the potential of noble gases in forming covalent molecular clusters
Nickel boryl complexes and the nickel-catalyzed alkyne borylation
The first nickel bis-boryl complexes cis [Ni(iPr2ImMe)2(Bcat)2], cis [Ni(iPr2ImMe)2(Bpin)2] and cis [Ni(iPr2ImMe)2(Beg)2] are reported, which were prepared via the reaction of a source of [Ni(iPr2ImMe)2] with the diboron(4) compounds B2cat2, B2pin2 and B2eg2 (iPr2ImMe = 1,3-di-iso-propyl-4,5-dimethylimidazolin-2-ylidene; B2cat2 = bis(catecholato)diboron; B2pin2 = bis(pinacolato)diboron; B2eg2 = bis(ethylene glycolato)diboron). X-ray diffraction and DFT calculations strongly suggest that a delocalized, multicenter bonding scheme dictates the bonding situation of the NiB2 moiety in these square planar complexes, reminiscent to the bonding situation of ânon-classicalâ H2 complexes. [Ni(iPr2ImMe)2] also efficiently catalyzes the diboration of alkynes using B2cat2 as the boron source under mild conditions. In contrast to the known platinum-catalyzed diboration, the nickel system follows a different mechanistic pathway, which not only provides the 1,2 borylation product in excellent yields, but also provides, additionally, an efficient approach to other products such as CâC coupled borylation products or rare tetra-borylated compounds. The mechanism of the nickel-catalyzed alkyne borylation was examined by means of stoichiometric reactions and DFT calculations. Oxidative addition of the diboron reagent to nickel is not dominant; the first steps of the catalytic cycle are coordination of the alkyne to [Ni(iPr2ImMe)2] and subsequent borylation at the coordinated and, thus, activated alkyne to yield complexes of the type [Ni(NHC)2(η2-cis-(Bcat)(R)C=C(R)(Bcat))], exemplified by the isolation and structural characterization of [Ni(iPr2ImMe)2(η2-cis-(Bcat)(Me)C=C(Me)(Bcat))] and [Ni(iPr2ImMe)2(η2-cis-(Bcat)(H7C3)C=C(C3H7)(Bcat))]
A simple copper(II) dppy-based receptor for sensing of L-Cysteine and L-Histidine in aqueous acetonitrile medium
The development of simple yet efficient receptors that rapidly detect and monitor amino acids with high sensitivity and reliability is crucial for the early-stage identification of various diseases. In this work, we report the synthesis and characterisation of a copper(II) complex, CuCl2L, by employing a 2,6-dipyrazinylpyridine (dppy)-based ligand (L = 2,2'-(4-(3,4,5-trimethoxyphenyl)pyridine-2,6-diyl)dipyrazine). The in-situ prepared CuCl2L receptor exhibits an instantaneous response to the presence of L-Cysteine (Cys) and L-Histidine (His) in aqueous acetonitrile (4:1 v/v, 10 mM HEPES buffer, pH 7.4). Furthermore, competitive experiments demonstrate the selectivity of CuCl2L towards Cys (1 equiv.) in the vicinity of other L-amino acids in the aforementioned solvent conditions. The lowest detection limits for Cys and His are calculated as 0.33 ”M and 1.40 ”M, respectively. DFT calculations offer a plausible explanation for the observed selectivity of the CuCl2L receptor towards Cys and His. They reveal that the most stable conformer of Cu:Cys complex (1:1) is a five-membered ring formed through N,S-coordination mode (ÎG = â26.7 kcal molâ1) over various other possible coordination modes, while comparable ÎG values are only obtained for Cu:His complexes featuring two His moieties
Multiply charged naphthalene and its C10H8 isomers: bonding, spectroscopy and implications in AGN environments
Naphthalene (C10H8) is the simplest polycyclic aromatic hydrocarbon (PAH) and
an important component in a series of astrochemical reactions involving
hydrocarbons. Its molecular charge state affects the stability of its isomeric
structures, which is specially relevant in ionised astrophysical environments.
We thus perform an extensive computational search for low-energy molecular
structures of neutral, singly, and multiply charged naphthalene and its isomers
with charge states +q = 0-4 and investigate their geometric properties and
bonding situations. We find that isomerisation reactions should be frequent for
higher charged states and that open chains dominate their low-energy
structures. We compute both the scaled-harmonic and anharmonic infrared spectra
of selected low-energy species and provide the calculated scaling factors for
the naphthalene neutral, cation, and dication global minima. All simulated
spectra reproduce satisfactorily the experimental data and, thus, are adequate
for aiding observations. Moreover, the potential presence of these species in
the emission spectra of the circumnuclear regions of active galactic nuclei
(AGNs), with high energetic X-ray photon fluxes, is explored using the
experimental value of the naphthalene photodissociation cross-section,
\sigma_{ph-d}, to determine its half-life, t_{1/2}, at a photon energy of 2.5
keV in a set of relevant sources. Finally, we show that the computed IR bands
of the triply and quadruply charged species are able to reproduce some features
of the selected AGN sources.Comment: Accepted for publication in the Monthly Notices of the Royal
Astronomical Society. 15 pages, 7 pages, supplementary information available
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Splitting of multiple hydrogen molecules by bioinspired diniobium metal complexes: a DFT study
Splitting of molecular hydrogen (H2) into bridging and terminal hydrides is a common step in transition metal chemistry. Herein, we propose a novel organometallic platform for cleavage of multiple H2 molecules, which combines metal centers capable of stabilizing multiple oxidation states, and ligands bearing positioned pendant basic groups. Using quantum chemical modeling, we show that low-valent, early transition metal diniobium(II) complexes with diphosphine ligands featuring pendant amines can favorably uptake up to 8 hydrogen atoms, and that the energetics are favored by the formation of intramolecular dihydrogen bonds. This result suggests new possible strategies for the development of hydrogen scavenger molecules that are able to perform reversible splitting of multiple H2 molecules
Structure and bonding of proximity-enforced main-group dimers stabilized by a rigid naphthyridine diimine ligand
The development of ligands capable of effectively stabilizing highly reactive main-group species has led to the experimental realization of a variety of systems with fascinating properties. In this work, we computationally investigate the electronic, structural, energetic, and bonding features of proximity-enforced group 13â15 homodimers stabilized by a rigid expanded pincer ligand based on the 1,8-naphthyridine (napy) core. We show that the redox-active naphthyridine diimine (NDI) ligand enables a wide variety of structural motifs and element-element interaction modes, the latter ranging from isolated, element-centered lone pairs (e.g., E = Si, Ge) to cases where through-space Ï bonds (E = Pb), element-element multiple bonds (E = P, As) and biradical ground states (E = N) are observed. Our results hint at the feasibility of NDI-E2 species as viable synthetic targets, highlighting the versatility and potential applications of napy-based ligands in main-group chemistry
A HydrideâSubstituted Homoleptic Silylborate: How Similar is it to its Diborane(6)âDianion Isostere?
The Bânucleophilic 9Hâ9âborafluorene dianion reacts with 9âchloroâ9âsilafluorene to afford airâ and moistureâstable silylborate salts M[Ar2(H)BâSi(H)Ar2] (M[HBSiH], M=Li, Na). Li[HBSiH] and Me3SiCl give the Bâpyridine adduct Ar2(py)BâSi(H)Ar2 ((py)BSiH) or the chlorosilane Li[Ar2(H)BâSi(Cl)Ar2] (Li[HBSiCl]) in C6H6âpyridine or THF. In both cases, the first step is Hâ abstraction at the B center. The resulting free borane subsequently binds a py or thf ligand. While the py adduct is stable at room temperature, the thf adduct undergoes a 1,2âH shift via the cyclic B(ÎŒâH)Si intermediate BHSi, which is afterwards attacked at the Si atom by a Clâ ion to give Li[HBSiCl]. DFT calculations were employed to support the proposed reaction mechanism and to characterize the electronic structure of BHSi. Treatment of Li[HBSiCl] with the Nâheterocyclic carbene IMe introduces the neutral donor at the Si atom and leads to Ar2(H)BâSi(IMe)Ar2 (HBSi(IMe)), a donorâacceptorâstabilized silylene
Decoding the molecular complexity of the solar-type protostar NGC 1333 IRAS 4A
The characterisation of the molecular inventory of solar-type protostars is of crucial importance for a deep understanding of the chemical complexity underlying our cosmic origins. In this context, we present here the full millimetre line survey of the Class 0 protostellar object NGC 1333 IRAS 4A in the spectral bands at 3, 2 and 1.3 mm. In recognition of the powerful tool that unbiased spectral studies provide for investigating the chemistry and physics of star-forming regions, we provide a detailed description of the survey and the results of the analysis. We describe the identification of 1474 spectral lines belonging to 97 different molecular species, including complex organic molecules (COMs), which together cover the most ubiquitous chemical elements of life on Earth, namely carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulphur (CHNOPS). The abundances obtained herein are compared with the Class 0 protostellar objects L483 and L1527, and selected molecular ratios are used as tracers of physicochemical properties of the sources. Particularly, the dominance of oxygen-bearing species and the presence of distinct excitation temperature regimes support the attribution of NGC 1333 IRAS 4A as a hot corino featuring three physical components with distinguished and diverse chemical composition
Destruction and multiple ionization of PAHs by X-rays in circumnuclear regions of AGNs
The infrared signatures of polycyclic aromatic hydrocarbons (PAHs) are
observed in a variety of astrophysical objects, including the circumnuclear
medium of active galactic nuclei (AGNs). These are sources of highly energetic
photons (0.2 to 10 keV), exposing the PAHs to a harsh environment. In this
work, we examined experimentally the photoionization and photostability of
naphthalene (CH), anthracene (CH),
2-methyl-anthracene (CHCH) and pyrene (CH)
upon interaction with photons of 275, 310 and 2500 eV. The measurements were
performed at the Brazilian Synchrotron Light Laboratory using time-of-flight
mass-spectrometry (TOF-MS). We determined the absolute photoionization and
photodissociation cross sections as a function of the incident photon energy;
the production rates of singly, doubly and triply charged ions; and the
molecular half-lives in regions surrounding AGNs. Even considering moderate
X-ray optical depth values () due to attenuation by the dusty
torus, the half-lives are not long enough to account for PAH detection. Our
results suggest that a more sophisticated interplay between PAHs and dust
grains should be present in order to circumvent molecular destruction. We could
not see any significant difference in the half-life values by increasing the
size of the PAH carbon backbone, N, from 10 to 16. However, we show that
the multiple photoionization rates are significantly greater than the single
ones, irrespective of the AGN source. We suggest that an enrichment of multiply
charged ions caused by X-rays can occur in AGNs.Comment: 20 pages (appendix: 3 pages), 10 figures, 4 tables. Accepted for
publication in the Montly Notices of the Royal Astronomical Society (MNRAS).
Accepted 2019 April
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