Electron Pair Donor Research Articles

Dative Bonding in Quasimetallatranes Containing Group 15 Donors (Y = N, P, and As) and Group 14 Acceptors (M = Si, Ge, Sn, and Pb).

Metallatranes and their analogous fused ring [3.3.0] bicyclic compounds, quasimetallatranes, have emerged as fascinating molecular systems with intriguing structural, bonding, and conformational properties. We present a comprehensive investigation aimed at unraveling the nature of dative bonding and exploring the conformational flexibility of these compounds. We extensively characterize the dative bond between the metal center and the electron pair donor, using a range of modeling techniques. Our analyses involve structural optimizations, molecular orbital examinations, and covalency ratio calculations, which provide a thorough understanding of the bonding interactions responsible for the stability of these systems. The results confirmed the presence of dative bonds, supported by the close proximity between the metal and the electron-donating group, and the observation of overlapping electron density. Our studies reveal a correlation between the size of the electron-donor and the coordinating metal atom, and the strength of the dative interaction, as indicated by the bond length and the Wiberg bond indices. This bond strength, in turn, influences the conformational preferences adopted by these compounds. This investigation sheds light on the fundamental aspects of the fused ring [3.3.0] bicyclic quasimetallatrane compounds and offers valuable insights into their unique properties.

Fluoride-Ion Donor Properties of AsF5

Fluoride-Ion Donor Properties of AsF₅

N-Benzoyl-morpholine-4-carbothioamides: Crystal structures, Hirshfeld surface analysis, and Density functional theory calculations

The current research work describes facile synthesis, single crystal X-ray structures, Hirshfeld surface (HS) analysis, and density functional theory (DFT) calculations of two N-benzoyl-morpholine-4-carbothioamides (NDMC and NMMC). Consequently, the synthesized compounds, C12H12Cl2N2O2S (NDMC) and C13H16N2O2S (NMMC) crystallized in triclinic and monoclinic crystal systems each having respective space groups of P -1 and P 21, with corresponding a = 7.8045 (3) Å, b = 12.8458 (6) Å, c = 13.4946 (7) Å, α = 97.313 (4)°, β = 94.358 (4)°, γ = 93.348 (3)°, Z = 4 and V = 1334.84 (11) Å3 for compound (NDMC). Similarly, for compound (NMMC),a = 7.3322 (2) Å, b = 5.3045 (1) Å, c = 16.3367 (5) Å, α = 90°, β = 94.285 (3)°, γ = 90°, Z = 2 and V = 633.62 (3) Å3. Subsequently, the asymmetric unit of compound (NDMC) contains two molecules, while compound (NMMC) has single molecule. Strong intermolecular NH⋯O, and weaker CH⋯Cl and CH⋯S hydrogen bonds link the molecules of (NDMC) into dimers, enclosing R22(7) and R22(9) ring motifs. Intermolecular CH⋯S, bifurcated NH⋯O and CH⋯O hydrogen bonds, as well as CH⋯π interactions in (NMMC), attach molecules, enclosing R22(7) and R22(14) ring motifs. Furthermore, HS analysis explored, visualized, and quantified the significance of hydrogen bond contacts, and revealed active contributions for the packed crystals encompasses H…H 33.6 % for (NDMC), and 46.6 % for (NMMC), H…S/S…H 17.9 % for (NDMC), and 17.0 % for (NMMC), H…C/C…H 9.0 % for (NDMC), and 19.7 % for (NMMC), H…O/O…H 14.8 % for (NDMC), and 14.3 % for (NMMC), and H…Cl/Cl…H 17.8 % for (NMMC). Hydrogen bonding and van der Waals contacts strongly influence crystal packings of the crystallized compounds. Similarly, evaluation of energy frameworks (electrostatic, dispersion and total energies) indicated stabilization is strongly dominated by dispersion energy contribution in compound (NMMC). Finally, optimum molecular structures of both the compounds (NDMC and NMMC), were related with the experimental ones employing DFT at B3LYP/6–311G**(d,p) level. The most stable optimized conformation was geometrically complementary with the crystal structure. DFT computed frontier molecular energies and isodensities predicted these compounds to exhibit better electron pair acceptance nature than electron pair donor.

Surface Chemistry of LLZO Garnet Electrolytes with Sulfur in Electron Pair Donor Solvents.

Conventional Li-S batteries rely on liquid electrolytes based on LiNO3/DOL/DME mixtures that produce a quasistable interface with the lithium anode. Electron pair donor (EPD) solvents, also known as high donor number solvents, provide much higher polysulfide solubility and close-to-ideal sulfur utilization, making them solvents of choice for lean electrolyte Li-S cells. However, their instability to reduction requires incorporation of an ion-conductive membrane that is stable with Li-such as garnet LLZO and also stable with sulfur/polysulfides. We report that even trace amounts of LiOH on a LLTZO surface trigger a complex reaction with sulfur dissolved in typical EPD solvents (i.e., N,N-dimethylacetamide, DMA) to produce a highly resistive impedance layer that quickly grows with time from 1000 to 10,000 Ω cm2 over a few hours, thus impeding Li+ transport across the interface. Decorating the LLZO with protective phosphate groups to produce a modified surface provides a very low charge-transfer resistance of 40 Ω cm2 that is maintained over time and inhibits the reaction of LiOH and dissolved sulfur. Hybrid liquid-solid electrolyte cells constructed on this concept result in a high sulfur utilization of 1400 mAh g-1 which is 85% of theoretical and remains constant over cycling even with conventional, unoptimized carbon/sulfur cathodes.

Synthesis and characterization of a formal 21-electron cobaltocene derivative

Metallocenes are highly versatile organometallic compounds. The versatility of the metallocenes stems from their ability to stabilize a wide range of formal electron counts. To date, d-block metallocenes with an electron count of up to 20 have been synthesized and utilized in catalysis, sensing, and other fields. However, d-block metallocenes with more than formal 20-electron counts have remained elusive. The synthesis and isolation of such complexes are challenging because the metal–carbon bonds in d-block metallocenes become weaker with increasing deviation from the stable 18-electron configuration. Here, we report the synthesis, isolation, and characterization of a 21-electron cobaltocene derivative. This discovery is based on the ligand design that allows the coordination of an electron pair donor to a 19-electron cobaltocene derivative while maintaining the cobalt–carbon bonds, a previously unexplored synthetic approach. Furthermore, we elucidate the origin of the stability, redox chemistry, and spin state of the 21-electron complex. This study reveals a synthetic method, structure, chemical bonding, and properties of the 21-electron metallocene derivative that expands our conceptual understanding of d-block metallocene chemistry. We expect that this report will open up previously unexplored synthetic possibilities in d-block transition metal chemistry, including the fields of catalysis and materials chemistry.

Investigation of Concerted Proton–Electron Donors for Promoting the Selective Production of HCOOH in CO2 Photoreduction

Achieving carbon neutralization by CO2 photoreduction (CO2PR) has attracted extensive attention. However, limited selectivity and harsh reaction conditions impede its practical application. Herein, we introduced a hydrogen storage material, ammonia borane (NH3BH3, AB), as mild proton–electron pair (adsorbed H atom, *H) donors, to realize synergistic hydrogen evolution and selective photocatalytic CO2 reduction to HCOOH. A preeminent HCOOH generation rate of 5237.8 μmol g–1 h–1 (with a HCOOH selectivity of 99.67% in carbonaceous products) was obtained. Intriguingly, *H provided by AB could accelerate selective HCOOH generation over Cu2O/TiO2 by promoting intermediate *HCOO generation in kinetics, and AB adsorption on Cu/TiO2 surface could also reduce the activation energy of HCOOH production in thermodynamics. Furthermore, some other similar *H donors have performed equally well in selective HCOOH, thus providing guidance for the design of a high-performance CO2PR system over the consideration of *H protons to meet the demand of sustainable development in the future.

Precise separation and efficient enrichment of palladium from wastewater by amino-functionalized silica adsorbent

An amine-based functionalized mesoporous silica (SBA-15-TEPA) adsorbent constructed from mesoporous silica was produced to realize efficient and highly selective recovery of palladium from wastewater. SEM-EDS, TEM, TG-DSC, and N2 adsorption-desorption isotherm were used to evaluate the as-prepared SBA-15-TEPA, and the results demonstrate that the material has a good open pore structure, a high loading rate, and a sizable specific surface area. The performance analysis demonstrates that SBA-15-TEPA exhibits excellent selectivity (Separation factor of palladium for impurity ions >5565) in a broad range of acidity and good repeatability (≥5) toward palladium, good repeatability is important for clean adsorption, with a maximal capacity of 94.92 mg Pd/g at pH = 1.5 at 315 K. 0.1 M thiourea - 0.1 M HNO3 was capable of desorbing the adsorbed Pd(II) almost entirely. The mechanism of adsorption and desorption was investigated by FT-IR, XPS and DFT calculation, which proves that the coordination structure occurs mainly between N in the adsorbent and Pd(II) with NO3− participation for change balance, i.e., the strong chemical complexation between the electron pair acceptor Pd(II) and the electron pair donor N. The dynamic separation of Pd(II) by SBA-15-TEPA from simulated electroplating wastes was evaluated by column experiment, and nearly 100% recovery of Pd(II) was obtained with demonstrating outstanding enrichment coefficients (>104). SBA-15-TEPA met the requirements of dynamic adsorption experiments and successfully achieved the complete separation and high enrichment of palladium from waste liquids in high throughput. This result fills the gap where functionalized silicon-based materials could not be separated and enriched for palladium in column experiments and will also provide new ways to address palladium scarcity, environmental protection and ensure cleaner production.

Application of Halides Complexes of Ruthenium (II) in Metallopharmaceuticals and in Material Science: Part-I

Ruthenium readily forms coordinate-complexes and these complexes have their applications in diverse fields. A survey of literature shows that designing of new ligands that can be complexed with Ruthenium (Ru) in various oxidation states can lead to development of new materials with diverse applications. In 21st century the gravity of approach of material science together with computer science has shifted from, how to make a molecule to what molecule to make, in other words molecular design. And now these are also quantized. As we know that physics, chemistry, and biology were explored at atomic levels and finally mathematical data were fed to grow required software for aimed simulations. The aim of present study is to study halides and mixed halides of Ru(II), which more precisely can help in the development of new Ru(II) complexes of desired application and or can help in fine tuning the property of pre-existing Ru(II) complexes. Thus, this study of atomistic details of halides of Ru(II) compounds along with construction of molecular orbital diagram at a glance will provide an insight of physicochemical, biochemical, electrochemical, thermochemical, magnetic, spectrochemical, catalytic, photoactive, and materialistic details. And this will help to solve the difficulties of synthesis of various complexes yet not synthesized. We know that all chemical reaction of complex compounds will be affected firstly by availability of vacant orbital(s) on metal ion (Ru2+) and secondly by the easiness of donation of electron pair(s) by ligands as we have also studied cloud-expanding effect, nephelauxetic effect, and electrochemical series of these Ruthenium(II) halides. The substitution reaction of complex compounds will also be mechanized and new substitution products (compounds) can also be prepared as topological analysis have also been made, those yet cannot synthesize by ordinary methods in required time and required cost too. Hence the halides of Ru(II) studied firstly. With the help of results of these studies, we will able to study complexation of these halides with selective ligands to form selective complex compounds of Ru(II) yet not prepared or have difficulties in preparation.

Arsenic-Involving Intermolecular Interactions in Crystal Structures: The Dualistic Behavior of As(III) as Electron-Pair Donor and Acceptor

The element arsenic and its compounds pollute fresh water due to their toxicity and are a significant cause of human health problems in some countries. An important way to remove arsenic from freshwater uses intermolecular-interaction-based filters, e.g. based on metal–organic frameworks. Therefore, we need deeper insight and understanding of arsenic-involving intermolecular interactions. In this study, we have selected 77 crystal structures from the Cambridge Structural Database. In each structure, there are one or more As···X interactions (X = I, Br, Cl, S, O, As, N, Te). As(III) species can act ambivalently as Lewis acids or bases since they possess a lone pair, unlike As(V) species, which can only act as Lewis acids. However, As filters have so far only been constructed around the assumption that As acts as a Lewis acid. This means that an optimized design of such filters for the dangerous but less considered As(III) species would be important. To facilitate such efforts, here we compare the dualistic intermolecular interaction modes of As(III) compounds to those in As(V) species by using a complementary bonding analysis involving geometrical parameters, the electron localizability indicator, Hirshfeld surfaces, model energies, molecular electrostatic potentials, quantum theory of atoms in molecules, noncovalent interaction index analyses, and natural bond orbitals.

Ferrocene-Based Terpolyamides and Their PDMS-Containing Block Copolymers: Synthesis and Physical Properties

Aromatic polyamides are well-known as high-performance materials due to their outstanding properties making them useful in a wide range of applications. However, their limited solubility in common organic solvents restricts their processability and becomes a hurdle in their applicability. This study is focused on the synthesis of processable ferrocene-based terpolyamides and their polydimethylsiloxane (PDMS)-containing block copolymers, using low-temperature solution polycondensation methodology. All the synthesized materials were structurally characterized using FTIR and 1H NMR spectroscopic techniques. The ferrocene-based terpolymers and block copolymers were soluble in common organic solvents, while the organic analogs were found only soluble in sulfuric acid. WXRD analysis showed the amorphous nature of the materials, while the SEM analysis exposed the modified surface of the ferrocene-based block copolymers. The structure-property relationship of the materials was further elucidated by their water absorption and thermal behavior. These materials showed low to no water absorption along with their high limiting oxygen index (LOI) values depicting their good flame-retardant behavior. DFT studies also supported the role of various monomers in the polycondensation reaction where the electron pair donation from HOMO of diamine monomer to the LUMO of acyl chloride was predicted, along with the calculation of various other parameters of the representative terpolymers and block copolymers.

Metal-Metal Bond Umpolung in Heterometallic Extended Metal Atom Chains.

Understanding the fundamental properties governing metal-metal interactions is crucial to understanding the electronic structure and thereby applications of multimetallic systems in catalysis, material science, and magnetism. One such property that is relatively underexplored within multimetallic systems is metal-metal bond polarity, parameterized by the electronegativities (χ) of the metal atoms involved in the bond. In heterobimetallic systems, metal-metal bond polarity is a function of the donor-acceptor (Δχ) interactions of the two bonded metal atoms, with electropositive early transition metals acting as electron acceptors and electronegative late transition metals acting as electron donors. We show in this work, through the preparation and systematic study of a series of Mo2M(dpa)4(OTf)2 (M = Cr, Mn, Fe, Co, and Ni; dpa = 2,2'-dipyridylamide; OTf = trifluoromethanesulfonate) heterometallic extended metal atom chain (HEMAC) complexes that this expected trend in χ can be reversed. Physical characterization via single-crystal X-ray diffraction, magnetometry, and spectroscopic methods as well as electronic structure calculations supports the presence of a σ symmetry 3c/3e- bond that is delocalized across the entire metal-atom chain and forms the basis of the heterometallic Mo2-M interaction. The delocalized 3c/3e- interaction is discussed within the context of the analogous 3c/3e- π bonding in the vinoxy radical, CH2CHO. The vinoxy comparison establishes three predictions for the σ symmetry 3c/3e- bond in HEMACS: (1) an umpolung effect that causes the Mo-M interactions to become more covalent as Δχ increases, (2) distortion of the σ bonding and non-bonding orbitals to emphasize Mo-M bonding and de-emphasize Mo-Mo bonding, and (3) an increase in Mo spin population with increasing Mo-M covalency. In agreement with these predictions, we find that the Mo2···M covalency increases with increasing Δχ of the Mo and M atoms (ΔχMo-M increases as M = Cr < Mn < Fe < Co < Ni), an umpolung of the trend predicted in the absence of σ delocalization. We attribute the observed trend in covalency to the decreased energic differential (ΔE) between the heterometal orbital and the σ bonding molecular orbital of the Mo2 quadruple bond, which serves as an energetically stable, "ligand"-like electron-pair donor to the heterometal ion acceptor. As M is changed from Cr to Ni, the σ bonding and nonbonding orbitals do indeed distort as anticipated, and the spin population of the outer Mo group is increased by at least a factor of 2. These findings provide a predictive framework for multimetallic compounds and advance the current understanding of the electronic structures of molecular heteromultimetallic systems, which can be extrapolated to applications in the context of mixed-metal surface catalysis and multimetallic proteins.

A Three-Component Approach to (Hetero)arenes with Two N-Containing Heterocycle Motifs

AbstractA one-pot, three-component reaction involving SNAr-decarboxylative redox isomerization starting from an electron-withdrawing group bearing fluorobenzaldehyde or fluorothiophenecarbaldehyde (electron-pair diacceptor), secondary amine, and trans-4-hydroxy-l-proline or indoline-2-carboxylic acid (electron-pair donor) has been developed to give N-[(pyrrolylmethyl)-substituted (het)aryl]- and N-[(indolyl­methyl)-substituted (het)aryl]pyrrolidines, -piperidines, -morpholines, and -azocanes. The highlights of this protocol are its great convenience in the simultaneous construction of a C(sp2)–N bond and a C(sp3)–N bond with simple operation; the reaction can be performed on a gram scale. This efficient one-pot multicomponent reaction has potential as a novel method for drug synthesis, especially involving polycyclic compounds.

Lewis acid-base adducts of Al(N(C6F5)2)3 and Ga(N(C6F5)2)3 - structural features and dissociation enthalpies.

Herein we present the molecular structures of six neutral Lewis acid-base adducts of the Lewis superacid Al(N(C6F5)2)3 and its higher homolog Ga(N(C6F5)2)3 with the electron pair donors MeCN, CNtBu, THF and PMe3. The crystal structures reveal crucial structural changes compared to the free Lewis acids as a consequence of the adduct formation. Furthermore, we calculated the corresponding dissociation enthalpies of the adducts which lie between 69 and 141 kJ mol-1 and are therefore considerably lower compared to the values for the formation of the anionic fluoride or chloride metallates.

One-pot synthesis of carbon fiber/carbon nanotube hybrid using lanthanum (III) chloride for tensile property enhancement of epoxy composites

This study presents a one-pot method for facile synthesis of carbon fiber (CF) / carbon nanotube (CNT) hybrid, which is achieved by the surface reaction of CF and carboxylated carbon nanotubes (CNT-COOH) in the eco-friendly lanthanum (III) chloride (LaCl3)-urea-ethanol solution. The control variate method is utilized to investigate the formation mechanism of the CF/CNT hybrid. Based on the scanning electron microscopy, X-ray powder diffraction, Fourier transform infrared and X-ray photoelectron spectroscopy results, it is found that La (III) coordinates with two or more atoms from different material surface so as to link different material, and urea serves as lone electron pair donor to provide extra binding sites for La (III), then both La (III) and urea play the role of bridge to connect CF and CNT-COOH. The prepared CF/CNT hybrid improves the tensile strength (modulus) of epoxy composites by 59.0% (78.5%), and corresponding improving mechanism has been revealed. The one-pot synthesis of CF/CNT hybrid is convenient, eco-friendly and thus suitable for green industrial application.

1,2-Dihydro-1,3,2-diazaborinine tautomer as an electron-pair donor in hydrogen-bonded complexes

Ab initio MP2/aug’-cc-pVTZ calculations have been carried out to investigate 1,2-dihydro-1,3,2-diazaborinine:HX complexes for HX = H+, HF, HCl, H2O, HCN, NH3, HCP, and HCCH. Most complexes are stabilized by linear, traditional hydrogen bonds except for those with H2O and NH3, which have bridging structures and nonlinear hydrogen bonds. H-atom transfer from N to B can occur in complexes with HF and HCl, with formation of a traditional F–H···N bond and a proton-shared Cl···H···N bond. The binding energies of the uncharged complexes range from 25 to 88 kJ mol−1. Spin-spin coupling constants have been used to characterize these hydrogen-bonded complexes.

Hybrid organic/inorganic hybrid surface technology for increasing the performance of LC/MS(MS)-based drug metabolite identification studies: Application to gefitinib and metabolites in mouse plasma and urine

The detection, identification and quantification of drug metabolites plays a key role in drug discovery and development. Liquid chromatography (LC) coupled to mass spectrometry (MS) has become the primary technology for these studies due to its sensitivity and specificity. However, the presence of transition metals in the chromatography system and columns can result in non-specific and unwanted interactions with the drug and/or its metabolites, via electron-pair donation, leading to poor chromatography and analyte loss. The use of a hybrid organic/inorganic surface applied to the metal surfaces of the chromatography system and column has been demonstrated to reduce or eliminate these effects. When employed for the analysis of mouse urine, derived from the oral dosing of mice with the EGFR inhibitor gefitinib, we observed more symmetrical LC peaks. This resulted in a 33 % improvement in peak capacity for a 10 min reversed – phase gradient separation, a two-fold increase in MS response, cleaner MS spectra and improved peak response reproducibility. This hybrid surface barrier appears to offer significant advantages in the analysis of low-concentration metabolites, potentially facilitating the accurate determination of the elimination phase of the pharmacokinetic (PK) curve and detection of drug metabolites in microdosing or microsampling studies.

Modulating MAPbI3 perovskite solar cells by amide molecules: Crystallographic regulation and surface passivation

A controllable crystallization is of practical importance to produce high-quality perovskite thin films with reduced structural defects. Lewis bases as electron-pair donor chemicals can strongly coordinate to lead ions and have been extensively employed to manipulate the growth of perovskite crystals. In this work, we demonstrate a series of Lewis-base amides, for morphological regulation of methylammonium lead triiodide (MAPbI3) thin films. The screened acetamide was demonstrated to decently improve the grain size, along with a spatial distribution at grain boundaries (GBs). The mesostructured solar cells of acetamide-modified absorbers yielded an optimized power conversion efficiency (PCE) of 20.04% with a mitigated open-circuit voltage (VOC) deficit of 0.39 V. This work provides a facile and cost-effective strategy toward controllable fabrication of high-performance MAPbI3 solar cells.

Virtual screening identifies broad-spectrum \u03b2-lactamase inhibitors with activity on clinically relevant serine- and metallo-carbapenemases

Bacteria are known to evade β-lactam antibiotic action by producing β-lactamases (BLs), including carbapenemases, which are able to hydrolyze nearly all available β-lactams. The production of BLs represents one of the best known and most targeted mechanisms of resistance in bacteria. We have performed the parallel screening of commercially available compounds against a panel of clinically relevant BLs: class A CTX-M-15 and KPC-2, subclass B1 NDM-1 and VIM-2 MBLs, and the class C P. aeruginosa AmpC. The results show that all BLs prefer scaffolds having electron pair donors: KPC-2 is preferentially inhibited by sulfonamide and tetrazole-based derivatives, NDM-1 by compounds bearing a thiol, a thiosemicarbazide or thiosemicarbazone moiety, while VIM-2 by triazole-containing molecules. Few broad-spectrum BLs inhibitors were identified; among these, compound 40 potentiates imipenem activity against an NDM-1-producing E. coli clinical strain. The binary complexes of the two most promising compounds binding NDM-1 and VIM-2 were obtained at high resolution, providing strong insights to improve molecular docking simulations, especially regarding the interaction of MBLs with inhibitors.

EXAFS Study on the Coordination Chemistry of the Solvated Copper(II) Ion in a Series of Oxygen Donor Solvents.

The structures of the solvated copper(II) ion in water and nine organic oxygen donor solvents with similar electron-pair donor ability, but with different space-demanding properties at coordination, have been studied by EXAFS. N,N′-Dimethylpropyleneurea and N,N,N′,N′-tetramethylurea are sufficiently space demanding at coordination to make the axial positions not accessible, resulting in square-planar copper(II) solvate complexes with an intense green color. The mean Cu–O bond distances in these two solvate complexes are 1.939(3) and 1.935(3) Å, respectively. The best fits of the remaining solvates, which are light blue in different hues, are obtained with a Jahn–Teller distorted-octahedral model consisting of four strongly bound solvent molecules in the equatorial positions at 1.96(2) Å and two in the axial positions but with different Cu–Oax bond distances: ca. 2.15 and 2.32 Å. This is in agreement with observations in solid-state structures of compounds containing hexaaquacopper(II) complexes crystallizing in noncentrosymmetric space groups and all reported crystal structures containing a [Cu(H2O)5(O-ligand)] complex with Jahn–Teller distortion. Such a structure is in agreement with previous EPR and EXAFS studies proving the hydrated copper(II) ion to be a noncentrosymmetric complex in aqueous solution. The refinements of the EXAFS data of the solids [Cu(H2O)6](ClO4)2, [Cu(H2O)6](BrO3)2, [Cu(H2O)6]SiF6, Cu(NO3)2·2.5H2O, and CuSO4·5H2O gave Cu–O bond distances significantly different from those reported in the crystallographic studies but similar to the configuration and bond distances in the hydrated copper(II) ion in aqueous solution. This may depend on whether the orientation of the axial positions is random in one or three dimensions, giving a mean structure of the solid with symmetry higher than that of the individual complexes. This study presents the very first experimental data from the new X-ray absorption spectroscopy beamline Balder at the MAX IV synchrotron radiation facility in Lund, Sweden, as well as the utilized properties of the beamline.

Microwave spectrum and structure of the SO3−SO2 weakly bound complex

The microwave spectrum and structure of the weakly bound complex SO3–SO2 are reported. The parent species, as well as the isotopologues with 34S and 33S single substitution on each sulfur atom have been observed. Together with the measured 33S nuclear quadrupole coupling constants, the structure of the complex has been determined. MP2/6-311++G(3df) calculations identify two nearly isoenergetic conformations, one of which corresponds to the observed structure. In the observed complex, an oxygen atom of the SO2 approaches the sulfur of the SO3 with an intermolecular S⋯O distance of 2.635(28) Å. The experimental S⋯S distance is 3.7517(83) Å, and the SO2 is positioned so as to direct an oxygen lone electron pair roughly along the C3 axis of the SO3. This structure reflects the strong acidity of SO3 insofar as it is suggestive of incipient electron pair donation from the SO2 oxygen to the acidic site of the SO3.