74 Search Results

Tellurocyanate, [TeCN]⁻, is the heaviest group 16 congener of the cyanate anion, [OCN]⁻. Due to the relative instability of the C─Te bond, tellurocyanate chemistry has seen only scarce attention. Here, we present the facile synthesis and thorough characterization of [K@crypt-222][TeCN]. The anion is essentially linear with interatomic distances C─N = 1.150(6)Å and C─Te = 2.051(4)Å, thus approximating a C≡N triple bond and for C─Te a bond order between 1 and 2. Fully ¹³C and ¹⁵N labeled [Te¹³C¹⁵N]⁻ allowed for the extraction of chemical shifts and all possible coupling constants (¹³C = 77.8 ppm, ¹⁵N = 285.7 ppm, ¹²⁵Te = −566more » ppm, ¹J_13C-15N = 8 Hz, ¹J_13C-125Te = 748 Hz, ²J1_5N-125Te = 55 Hz), which were also determined independently by quantum chemical calculations. In the series [ChCN]⁻ (Ch = O─Te), [TeCN]⁻ shows the strongest spin-orbit coupling (SOC) induced heavy-atom effect on the light-atom shielding (SO-HALA-effect). In contrast, ¹⁵N shifts are also well described without considering relativistic effects and/or SOC. Negative-ion photoelectron spectroscopy was used to extract the electron affinity (EA = 3.034 eV) and spin-orbit splitting (3807 cm⁻¹) of [TeCN]^•. These values continue the trends of falling EA and rising SOC in the series [ChCN]^•.« less

Electrolyte anions are pivotal for lithium battery performance, yet their fundamental electronic structural properties are not well understood. In this work, we employ a combination of negative-ion photoelectron spectroscopy (NIPES), ab initio calculations, and molecular dynamics (MD) simulations to investigate the electronic structures of three representative electrolyte anions. This multiscale approach enables us to elucidate how their intrinsic electronic properties govern anion–solvent interactions in gas-phase clusters, as well as lithium-ion (Li⁺) solvation structures and ion transport behavior in the condensed phase. NIPES reveals that difluoro(oxalato)borate (DFOB^–), bis(fluorosulfonyl)imide (FSI^–), and bis(oxalato)borate (BOB^–) all exhibit high electron binding energies, with vertical/adiabatic detachmentmore » energies increasing from DFOB^– (6.09/5.70 eV) to FSI^– (6.80/6.10 eV) to BOB^– (6.82/6.40 eV), correlating with enhanced oxidation stability. Ab initio calculations reveal that DFOB^–/FSI^––solvent complexes bind Li⁺ ∼ 10 kcal/mol stronger than BOB^– series, aligning with the strength of a Li⁺–anion model. DFOB^– exhibits pronounced charge localization on both oxygen and fluorine atoms, enabling their involvement in Li⁺ coordination. In contrast, fluorine atoms in FSI^– are largely electron-depleted and remain excluded from direct Li⁺ binding. MD simulations further demonstrate that LiDFOB and LiFSI systems exhibit Li⁺ diffusion coefficients three and five times higher than those of LiBOB across four common solvents. Notably, LiFSI salt in acetonitrile (AN) exhibits the fastest Li⁺ diffusion among 12 electrolyte systems, highlighting the synergistic effect of FSI^– and AN in promoting ion mobility. In conclusion, these findings provide a molecular-level understanding of the critical roles of anion and its microsolvation in optimizing Li⁺ diffusion dynamics, once again emphasizing the positioning of FSI^– and DFOB^– as prime candidates for next-generation electrolytes.« less

Three undercoordinated iridium chloride anions, IrCl_n⁻ (n = 3–5), and their neutral counterparts were investigated by cryogenic anion photoelectron spectroscopy and theoretical calculations. Photodetachment of IrCl_n⁻ leads to the formation of the corresponding neutral complex, i.e., a triplet ground state for n = 3, a quartet for n = 4, and close-lying singlet and triplet for n = 5. The vertical detachment energies are determined to be 3.89, 4.98, and 5.14 eV for n = 3, 4, and 5, respectively, revealing superhalogen anion properties with increasing electron detachment energies as chloride ligands added. The IrCl₃⁻ spectrum features an extremely broad,more » lowest electron binding energy band, attributed to resonant autodetachment with prominent non-Franck–Condon profiles. In IrCl₅⁻, detachment prompts a d-orbital rearrangement that drives a structural transformation from a twisted square-based pyramidal to a trigonal–bipyramidal geometry in the singlet state. In conclusion, these findings provide insights into the electronic and structural adaptability of iridium halides, advancing our understanding of ligand exchange reactions and dissociative stability in transition metal complexes.« less

Ion triplets of the chloride salts of two commonly used weakly coordinating cations are reported (i.e., Cl^–·NMe₄⁺Cl^– (1^–) and Cl^–·PPh₄⁺Cl^– (2^–)). Negative ion photoelectron spectra at 20 K afford vertical and adiabatic detachment energies of 5.18 and 5.00 eV (1^–) and 5.03 and 4.70 eV (2^–), respectively. These results are well reproduced by coupled cluster calculations with single, double, and perturbative triple excitations (CCSD(T)) whereas M06-2X is systematically too small by ~0.3 eV (i.e., 7 kcal mol^–1). The structures of both 1^– and 2^– have five or six C–H···Cl^– interactions that stabilize these cluster anions by 32 (1^–) and 27more » (2^–) kcal mol^–1 as given by their chloride dissociation enthalpies. In conclusion, these values drop to 7.4 and 3.8 kcal mol^–1 in dichloromethane based up conductor-like polarizable continuum model calculations and suggest that X^–·M⁺X^– ion triplets with a weakly coordinating cation maybe the reactive form of salts under some conditions.« less

Due to their unique physiochemical properties that may be tailored for specific purposes, ionic liquids (ILs) have been investigated for various applications, including chemical separations, catalysis, energy storage, and space propulsion. The different cations and anions comprising ILs may be selected to optimize a range of desired properties, such as thermal stability, ionic conductivity, and volatility, leading to the designation of certain ILs as designer “green” solvents. The effect of counterions on the properties of ILs is of both fundamental scientific interest and technological importance. Herein, we report a systematic experimental and theoretical investigation of the size, charge, stability towardmore » dissociation, and geometric/electronic structure of 1-ethyl-3-methyl imidazolium (EMIM)-based IL clusters containing two different atomic counterions (i.e., bromide [Br⁻] and iodide [I⁻]). This work extends our studies of EMIM⁺ cations with atomic chloride (Cl⁻) and molecular tetrafluoroborate (BF₄⁻) anions reported previously by Baxter et al. [Chem. Mater. 34, 2612 (2022)] and Zhang et al. [J. Phys. Chem. Lett. 11, 6844 (2020)], respectively. Distributions of anionic IL clusters were generated in the gas phase using electrospray ionization and characterized by high mass resolution mass spectrometry, energy-resolved collision-induced dissociation, and negative ion photoelectron spectroscopy experiments. The experimental results reveal anion-dependent trends in the size distribution, relative abundance, ionic charge state, stability toward dissociation, and electron binding energies of the IL clusters. Complementary global optimization theory provides molecular-level insights into the bonding and electronic structure of a selected subset of clusters, including their low energy structures and electrostatic potential maps, and how these fundamental characteristics are influenced by anion substitution. Collectively, our findings demonstrate how the fundamental properties of ILs, which determine their suitability for many applications, may be tuned by substituting counterions. These observations are critical in the sub-nanometer cluster size regime where phenomena do not scale predictably to the bulk phase, and each atom counts toward determining behavior.« less

Noncovalent interactions (NCIs) are crucial for the formation and stability of host-guest complexes, which have wide-ranging implications across various fields, including biology, chemistry, materials science, pharmaceuticals, and environmental science. However, since NCIs are relatively weak and sensitive to bulk perturbation, direct and accurate measurement of their absolute strength has always been a significant challenge. This concept article aims to demonstrate the gas-phase electrospray ionization (ESI)-negative ion photoelectron spectroscopy (NIPES) as a direct and precise technique to measure the absolute interaction strength, probe nature of NCIs, and reveal the electronic structural information for host-guest complexes. Here, our recent studies in investigatingmore » various host-guest complexes that involve various types of NCIs such as anion–π, (di)hydrogen bonding, charge-separated ionic interactions, are overviewed. Finally, a summary and outlook are provided for this field.« less

The direct photodetachment and two-photon photodissociation–photodetachment processes of a series of PtI_n^- (n = 2–5) anions were systematically studied using cryogenic anion photoelectron spectroscopy and first-principles electronic structure calculations. The adiabatic/vertical detachment energies (ADEs/VDEs) of these anions were determined from their 193 nm photoelectron (PE) spectra, i.e., 3.54/3.63, 4.04/4.09, 4.33/4.36, and 4.37/4.41 eV for n = 2–5, respectively, and well reproduced by B3LYP-D3(BJ)/aug-cc-pVTZ-pp calculations. As the coordination number increases, the electron affinity (EA) of PtI_n• (n = 2–5) neutrals (equivalent to the corresponding anion’s ADE) gradually increases, exceeding the EA of Cl at n = 3 and exhibiting superhalogen characteristics for nmore » ≥ 3. Meanwhile, the ground state transition contributed from detaching electrons in the highest occupied molecular orbital gradually evolves from the central metal Pt to the iodine ligands. For the PtI₃^- anion, besides one-photon direct detachment, four distinct two-photon photodissociation–photodetachment channels were identified, and the competition between them was discussed.« less

Here, we report a joint spectroscopic and theoretical study probing spin-orbit coupling (SOC) in a variety of molecular complexes between an iodine atom and a ligand (L) with L ranging from Ar, HF to formic/acetic acids, and glycine/N-methylated glycine derivatives. Cryogenic photoelectron spectroscopy of L·I^- (L=HCOOH, CH₃COOH) reveals three distinct peaks, identified as three SOC states, denoted as X(1/2), A(3/2), and B(l/2) for the corresponding neutrals. The X and A separation ΔE_XA is measured to be 0.10 eV for both, whereas the X and B gap ΔE_XB is 0.98 and 0.97 eV for formic and acetic acid, respectively. These newmore » ΔE_XA values are compared with the previously reported values for the molecular complexes L·I· with L=Ar, HF, glycine, and A-methylated glycines. All together these complexes encompass a diversity of intermolecular interactions, from van der Waals to weak and strong hydrogen bonding. While the ΔE_XB remains similar, the ΔE_XA is shown to be extremely sensitive to the type of ligands and interactions, spanning from 5 meV to 150 meV. High-level relativistic quantum calculations including explicit SOC formulism nicely reproduce all experimental SOC splitting. A direct correlation between the magnitude of ΔE_XA with the intermolecular interaction strength or bond distance of the neutral complexes—the stronger interaction (shorter bond length), the greater splitting, is established.« less

Microhydrated closo-Boranes have attracted great interests due to their superchaotropic activity related to well-known Hofmeister effect and important applications in biomedical and battery fields. In this work, we report a combined negative ion photoelectron spectroscopy and quantum chemical investigation on hydrated closo-decaborate clusters [B₁₀H₁₀]^2-·nH₂O (n = 1 – 7) with a direct comparison to their analogues [B₁₂H₁₂]^2-·nH₂O and free water clusters. A single H₂O molecule is found sufficient to stabilize the intrinsically unstable [B₁₀H₁₀]^2- dianion. The first two water molecules strongly interact with the solute forming B-H···H-O dihydrogen bonds while additional water molecules show substantially reduced binding energies. Unlike [B₁₂H₁₂]^2-·nH₂Omore » possessing highly structured water network with the attached H₂O molecules arranged in a unified pattern by maximizing B-H···H-O dihydrogen bonding, distinct structural arrangements of the water clusters within [B₁₀H₁₀]^2–·nH₂O are achieved with the water cluster networks from trimer to heptamer resembling free water clusters. Such a distinct difference arises from the variations in size, symmetry, and charge distributions between these two dianions. Finally, the present finding again confirms the structural diversity of hydrogen-bonding networks in microhydrated closo-boranes and enrich our understanding of aqueous borate chemistry.« less

The oxidation of phenolic compounds is one of the most important reactions prevalent in various biological processes, often explicitly coupled with proton transfers (PTs). Quantitative descriptions and molecular-level understanding of these proton-coupled electron transfer (PCET) reactions have been challenging. This work reports a direct observation of PCET in photodetachment (PD) photoelectron spectroscopy (PES) of hydrogen-bonded phenolic (ArOH) nitrate (NO₃^-) complexes, in which a much slower rising edge provides a spectroscopic signature to evidence PCET. Electronic structure calculations unveil the PCET processes to be isomer-specific, occurred only in those with their HOMOs localized on ArOH, leading to charge-separated transient states ArOH^•+·NO₃^-more » triggered by ionizing phenols while simultaneously promoting PT from ArOH^•+ to NO₃^-. Importantly, this study showcases that gas-phase PD-PES is a generic means enabling to identify PCET reactions with explicit structural and binding information.« less