Heavy-Atom Tunneling in the Covalent/Dative Bond Complexation of Cyclo[18]carbon–piperidine

Recent quantum chemical computations demonstrated the electron-acceptance behavior of this highly reactive cyclo[18]carbon (C18) ring with piperidine (pip). The C18–pip complexation exhibited a double-well potential along the N–C reaction coordinate, forming a van der Waals (vdW) adduct and a more stable, strong covalent/dative bond (DB) complex by overcoming a low activation barrier. By means of direct dynamical computations using canonical variational transition state theory (CVT), including the small-curvature tunneling (SCT), we show the conspicuous role of heavy atom quantum mechanical tunneling (QMT) in the transformation of vdW to DB complex in the solvent phase near absolute zero. Below 50 K, the reaction is entirely driven by QMT, while at 30 K, the QMT rate is too rapid (kT ~ 0.02 s-1), corresponding to a half-life time of 38 s, indicating that the vdW adduct will have a fleeting existence. We also explored the QMT rates of other cyclo[n]carbon–pip systems. This study sheds light on the decisive role of QMT in the covalent/DB formation of the C18–pip complex at cryogenic temperatures.

Exploring Structural Nuances in Germanium Halide Perovskites using Solid-state 73Ge and 133Cs NMR Spectroscopy

Metal-halide perovskites remain top candidates for better-performing photovoltaic devices but concerns with leading lead-based materials continue. Ge perovskites remain understudied for use in solar cells compared to their Sn-based counterparts. In this work, we undertake a combined 133Cs and 73Ge solid-state NMR and DFT study of the bulk CsGeX3 (X = Cl, Br, I) series. We show how seemingly small structural variations within germanium halide perovskites have major consequences on their 73Ge and 133Cs NMR signatures and reveal a near cubic-like phase at room temperature for CsGeCl3 with severe local Ge polyhedral distortion. Quantum chemical computations are effective at predicting the structural impact on NMR parameters for 73Ge and 133Cs. This study demonstrates the value of a combined experimental and theoretical approach for investigating attractive materials for energy applications – providing information that is out of reach with conventional characterization methods – and adds the challenging 73Ge nucleus to the toolkit.

A Computational Journey across Nitroxide Radicals: From Structure to Spectroscopic Properties and Beyond

Nitroxide radicals are characterized by a long-lived open-shell electronic ground state and are strongly sensitive to the chemical environment, thus representing ideal spin probes and spin labels for paramagnetic biomolecules and materials. However, the interpretation of spectroscopic parameters in structural and dynamic terms requires the aid of accurate quantum chemical computations. In this paper we validate a computational model rooted into double-hybrid functionals and second order vibrational perturbation theory. Then, we provide reference quantum chemical results for the structures, vibrational frequencies and other spectroscopic features of a large panel of nitroxides of current biological and/or technological interest.

Crystal Structure, Thermodynamic Properties and DFT Studies of 5,6-dimethyl-1H-benzo[d]imidazol-3-ium 3-((2,4-dioxo-1,5-dioxaspiro[5.5]undecan-3-ylidene)methyl) -2,4-dioxo-1,5-dioxaspiro[5.5]undecane Hydrate

A new 1,5-dioxaspiro[5.5] derivative coupled with a benzimidazole moiety: 5,6-dimethyl-1H-benzo[d]imidazol-3-ium 3-((2,4-dioxo-1,5-dioxaspiro[5.5]undecan-3-ylidene) methyl) -2,4-dioxo-1,5-dioxaspiro[5.5]undecane hydrate (DBH) was prepared. The crystal structure confirmed that it belongs to triclinic, P-1 space group. The title compound includes one (C19H21O8)− anion, one (C9H11N2)+ cation and one water molecule, which assembled into a 2D-net framework by O–H···O and N–H···O hydrogen bonds. The quantum chemical computations using the B3LYP/6-311G (d, p) basis level of theory reveal that the optimized geometric structure is suitable to study the molecule. The theoretically simulated FT-IR spectra and electronic spectra of DBH are compared with experimental data. The results show that the B3LYP/6-311g (d, p) method fits well with the molecular structure. In addition, the thermodynamic properties have also been studied to determine the nature of the DBH.

Is Aromatic Nitration Spin Density Driven?

The mechanism of aromatic nitration is critically reviewed with particular emphasis on the paradox of the high positional selectivity of substitution in spite of low substrate selectivity. Early quantum chemical computations in the gas phase have suggested that the retention of positional selectivity at encounter-limited rates could be ascribed to the formation of a radical pair via an electron transfer step occurring before the formation of the Wheland intermediate, but calculations which account for the effects of solvent polarization and the presence of counterion do not support that point of view. Here we report a brief survey of the available experimental and theoretical data, adding a few more computations for better clarifying the role of electron transfer for regioselectivity.

Ionic cocrystals of dithiobispyridines: the role of I...I halogen bonds in the building of iodine frameworks and the stabilization of crystal structures

It has been confirmed that mercaptopyridines undergo spontaneous condensation in redox reaction with iodine-forming dithiopyridines. In the solid state, these compounds are protonated at the N atoms and cocrystallize with iodine forming salt structures, namely, 2-[(pyridin-2-yl)disulfanyl]pyridinium triiodide sesquiiodine, C10H9N2S2 +·I3 −·1.5I2, and 4,4′-(disulfanediyl)dipyridinium pentaiodide triiodide, C10H10N2S2 2+·I5 −·I3 −. Dithiopyridine cations are packed among three-dimensional frameworks built from iodide anions and neutral iodine molecules, and are linked by hydrogen, halogen and chalcogen interactions. Quantum chemical computations indicated that dithiopyridines exhibit anomalously high nitrogen basicity which qualify them as potential proton sponges.