Oxygen Atom Stabilization by a Main-Group Lewis Acid: Observation and Characterization of an OBeF Complex with a Triplet Ground State.

Terminal oxygen radicals involving p- and d-block atoms are quite common, but s-block compounds with an oxygen radical character remain rare. Here, we report that alkaline-earth metal beryllium atoms react with OF to form the oxygen beryllium fluorides OBeF and OBeF. These species are characterized by matrix-isolation infrared spectroscopy with isotopic substitution and quantum-chemical calculations.

What Determines the Lewis Acidity of a Bismuthane? Towards Bi-Based FLPs.

Aiming at intramolecular frustrated Lewis pairs (FLPs) based on soft Lewis acidic bismuth centers, a phosphine function was combined with a dichloridobismuthane unit on a phenylene backbone utilizing a scrambling approach. The reaction between two equivalents of BiCl and (o-(PhP)CH)Bi yielded (o-(PhP)CH)BiCl(THF), the structure of which indicated BiP interactions and thus a pronounced Lewis acidity at the bismuth center that was confirmed by the Gutmann-Beckett method. However, the system turned out to be insufficient to be utilized for FLP reactivity.

Investigation of Isolated IrF , IrF Anions and M[IrF] (M=Na, K, Rb, Cs) Ion Pairs by Matrix-Isolation Spectroscopy and Relativistic Quantum-Chemical Calculations.

The molecular IrF , IrF anions and M[IrF] (M=Na, K, Rb, Cs) ion pairs were prepared by co-deposition of laser-ablated alkali metal fluorides MF with IrF and isolated in solid neon or argon matrices under cryogenic conditions. The free anions were obtained as well by co-deposition of IrF with laser-ablated metals (Ir or Pt) as electron sources. The products were characterized in a combined analysis of matrix IR spectroscopy and electronic structure calculations using two-component quasi-relativistic DFT methods accounting for spin-orbit coupling (SOC) effects as well as multi-reference configuration-interaction (MRCI) approaches with SOC.

Spectroscopic Identification of Trifluorosilylphosphinidene and Isomeric Phosphasilene and Silicon Trifluorophosphine Complex.

The perfluorinated silylphosphinidene, FSiP, in the triplet ground state is generated by the reaction of laser-ablated silicon atoms with PF in solid neon and argon matrices. The reactions proceed with the initial formation of a silicon trifluorophosphine complex, FPSi, in the triplet ground state, and a more stable inserted phosphasilene, FPSiF, in the singlet ground state upon deposition. The trifluorosilylphosphinidene was formed through F-migration reactions of FPSiF and FPSi following a two-state mechanism under irradiation with visible light (λ = 470 nm) and full arc light (λ > 220 nm), respectively.

Spin-Symmetry Breaking and Hyperfine Couplings in Transition-Metal Complexes Revisited Using Density Functionals Based on the Exact-Exchange Energy Density.

A small set of mononuclear manganese complexes evaluated previously for their Mn hyperfine couplings (HFCs) has been analyzed using density functionals based on the exact-exchange energy density─in particular, the spin symmetry breaking (SSB) found previously when using hybrid functionals. Employing various strong-correlation corrected local hybrids (scLHs) and strong-correlation corrected range-separated local hybrids (scRSLHs) with or without additional corrections to their local mixing functions (LMFs) to mitigate delocalization errors (DE), the SSB and the associated dipolar HFCs of [Mn(CN)], MnO, [Mn(CN)N], and [Mn(CN)NO] (the latter with cluster embedding) have been examined. Both strong-correlation (sc)-correction and DE-correction terms help to diminish SSB and correct the dipolar HFCs.

Synthesis and structural characterization of stable coinage metal (Cu, Ag, Au) cyclopentadienyl complexes.

The electron withdrawing and oxidatively stable perfluorinated Cp* ligand [C(CF)] allowed for the isolation of rare and unusually stable coinage metal complexes [M(C(CF))(PBu)] (M = Cu, Ag, Au), representing the first complete and structurally comparable series of group 11 Cp coordination compounds. Full characterization and structure analysis revealed distinct and partly unknown coordination motifs with hapticities ranging from η, η/η and η/η for gold, silver and copper, respectively. Quantum-chemical studies using DFT methods confirm these findings and connect them to the unique electronic structure of the given ligand system.

Rydberg electron stabilizes the charge localized state of the diamine cation.

A previous controversial discussion regarding the interpretation of Rydberg spectra of gaseous dimethylpiperazine (DMP) as showing the co-existence of a localized and delocalized mixed-valent DMP radical cation is revisited. Here we show by high-level quantum-chemical calculations that an apparent barrier separating localized and delocalized DMP minima in previous multi-reference configuration-interaction (MRCI) calculations and in some other previous computations were due to unphysical curve crossings of the reference wave functions. These discontinuities on the surface are removed in state-averaged MRCI calculations and with some other, orthogonal high-level approaches, which do not provide a barrier and thus no localized minimum.

Persilylation of ferrocene: the ultimate discipline in sterically overcrowded metal complexes.

We report the preparation and structural characterization of the first persilylated metallocene the metalation of decabromoferrocene. Although Grignard conditions turned out to be insufficient due to the steric and electronic effects of silyl groups causing a decreased nucleophilicity of the metalated intermediates, stepwise lithium-halogen exchange yields complex mixtures of polysilylated compounds FeCDMSH ( = 10, 9, 8) including the targeted decasilylated ferrocene. These mixtures were successfully separated allowing a systematic study of silylation effects on ferrocene by XRD, CV, NMR and UV/vis spectroscopy supported by DFT calculations.

Spin-State Splittings in 3d Transition-Metal Complexes Revisited: Toward a Reliable Theory Benchmark.

A new composite method for the calculation of spin-crossover energies in 3d transition-metal complexes based on multireference methods is presented. The method reduces to MRCISD+Q at the complete-basis-set (CBS) level for atomic ions, for which it gives excitation energies with a mean absolute error of only ca. 0.

Spin-State Splittings in 3d Transition-Metal Complexes Revisited: Benchmarking Approximate Methods for Adiabatic Spin-State Energy Differences in Fe(II) Complexes.

The CASPT2+δMRCI composite approach reported in a companion paper has been extended and used to provide high-quality reference data for a series of adiabatic spin gaps (defined as Δ = - ) of [FeL] complexes (L = CNH, CO, NCH, NH, HO), either at nonrelativistic level or including scalar relativistic effects. These highly accurate data have been used to evaluate the performance of various more approximate methods. Coupled-cluster theory with singles, doubles, and perturbative triples, CCSD(T), is found to agree well with the new reference data for Werner-type complexes but exhibits larger underestimates by up to 70 kJ/mol for the π-acceptor ligands, due to appreciable static correlation in the low-spin states of these systems.

Solving the Azobenzene Entropy Puzzle: Direct Evidence for Multi-State Reactivity.

A solution to the azobenzene "entropy puzzle" [ , 2017, 29, 314002] is provided. Previous computational studies of the thermal  →  (back-)isomerization of azobenzene could not describe the experimentally observed large negative activation entropies. Here it is shown that the experimental results are only compatible with a more complicated multistate rotation mechanism that involves a triplet excited state.

Unusually Large Effects of Charge-assisted C-H⋅⋅⋅F Hydrogen Bonds to Anionic Fluorine in Organic Solvents: Computational Study of F NMR Shifts versus Thermochemistry.

A comparison of computed F NMR chemical shifts and experiment provides evidence for large specific solvent effects for fluoride-type anions interacting with the σ*(C-H) orbitals in organic solvents like MeCN or CH Cl . We show this for systems ranging from the fluoride ion and the bifluoride ion [FHF] to polyhalogen anions [ClF ] . Discrepancies between computed and experimental shifts when using continuum solvent models like COSMO or force-field-based descriptions like the 3D-RISM-SCF model show specific orbital interactions that require a quantum-mechanical treatment of the solvent molecules.

Fluorinated click-derived tripodal ligands drive spin crossover in both iron(II) and cobalt(II) complexes.

Control of the spin state of metal complexes is important because it leads to a precise control over the physical properties and the chemical reactivity of the metal complexes. Currently, controlling the spin state in metal complexes is challenging because a precise control of the properties of the secondary coordination sphere is often difficult. It has been shown that non-covalent interactions in the secondary coordination sphere of transition metal complexes can enable spin state control.

Reaction Entropies in Solution from Analytical Three-Dimensional Reference Interaction Site Model Derivatives with Application to Redox and Spin-Crossover Processes.

An analytical approach to compute the excess entropy of solvation at constant pressure in three-dimensional reference interaction site model (3D-RISM) calculations is presented. It includes the changes in the macroscopic dielectric constant of the solvent upon variation of temperature and density. The approach is exact within the framework of force-field descriptions of the solute and gives reasonable results for self-consistently determined electrostatics as used in the 3D-RISM-self-consistent field approach, particularly for entropy differences.

Spin-state control of cobalt(II) and iron(II) complexes with click-derived tripodal ligands through non-covalent and fluorine-specific interactions.

The fine-tuning of intermolecular or intramolecular non-covalent interactions (NCIs) and thus the precise synthesis of metal complexes in which the spin states can be controlled by NCIs remains challenging, even though several such complexes have been intensively studied. In this regard, we present mononuclear cobalt(II) and iron(II) complexes with "click"-derived tripodal ligands that contain fluorinated benzyl substituents in the secondary coordination sphere. The complexes were co-crystallized with different solvent molecules to decipher the effect of the crystallized solvents on NCIs, and on the spin state of the metal ion.

Novel synthetic pathway for the production of phosgene.

Chloride ions are efficient catalysts for the synthesis of phosgene from carbon monoxide and elemental chlorine at room temperature and atmospheric pressure. Control experiments rule out a radical mechanism and highlight the role of triethylmethylammonium trichloride, [NEtMe][Cl], as active species. In the catalytic reaction, commercially available [NEtMe]Cl reacts with Cl to form [NEtMe][Cl], enabling the insertion of CO into an activated Cl─Cl bond with a calculated energy barrier of 56.

Orthogonal coiled coils enable rapid covalent labelling of two distinct membrane proteins with peptide nucleic acid barcodes.

Templated chemistry offers the prospect of addressing specificity challenges occurring in bioconjugation reactions. Here, we show two peptide-templated amide-bond forming reactions that enable the concurrent labelling of two different membrane proteins with two different peptide nucleic acid () barcodes. The reaction system is based on the mutually selective coiled coil interaction between two thioester-linked -peptide conjugates and two cysteine peptides serving as genetically encoded peptide tags.

Enabling Cysteine-Free Native Chemical Ligation at Challenging Junctions with a Ligation Auxiliary Capable of Base Catalysis.

Ligation auxiliaries are used in chemical protein synthesis to extend the scope of native chemical ligation (NCL) beyond cysteine. However, auxiliary-mediated ligations at sterically demanding junctions have been difficult. Often the thioester intermediate formed in the thiol exchange step of NCL accumulates because the subsequent S→N acyl transfer is extremely slow.

The Supramolecular Structural Chemistry of Pentafluorosulfanyl and Tetrafluorosulfanylene Compounds.

The analysis of crystal structures of SF - or SF -containing molecules revealed that these groups are often surrounded by hydrogen or other fluorine atoms. Even though fluorine prefers F⋅⋅⋅H over F⋅⋅⋅F contacts, the latter appeared to be important in many compounds. In a significant number of datasets, the closest F⋅⋅⋅F contacts are below 95 % of the van der Waals distance of two F atoms.

Evaluation of an Efficient 3D-RISM-SCF Implementation as a Tool for Computational Spectroscopy in Solution.

The 3D-RISM-SCF solvent-model implementation of Gusarov et al. [ 2006, 110, 6083-6090] in the Amsterdam density functional program has been improved and extended. In particular, an accurate yet efficient representation of the solute electrostatic potential is provided.

Thermochemistry of FeOH Species: Assessment of Some DFT Functionals.

Thermochemical data for 20 anionic, cationic, and neutral gas-phase species, including Fe, FeO, FeOH, FeO, OFeOH, Fe(OH), Fe(HO), and Fe(HO) with oxidation states between +I and +IV for Fe and -I and -II for O, compiled by Schröder [ 2008, 112, 13215], are used to assess the performance of the "Jacob's ladder" functionals PBE, TPSS, PBE0, and TPSSh for the SVP, TZVP, and QZVP basis sets. In addition, the BP86 and B3LYP functionals are considered. The TPSSh functional performs best.