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The nature of halogen bonding under different dielectric conditions remains underexplored, especially for inorganic systems. The structural and energetic properties of model halogen bonded complexes (R₃M−I—NH₃for R=H and F, and M=C, Si, and Ge) are examined computationally for relative permittivities between 1 and 109 using an implicit solvent model. We confirm and assess the exceptionally high maximum potentials at the sigma hole on I (V_s,max) in F₃Ge−I relative to cases where M=C or Si. In particular, Ge far outperforms Si in mediating inductive effects. Linear relationships, typically with R²>0.97, are identified betweenV_s,max, the full point charge on I in R₃M−I, and the interaction energy, and optimized I—N distance in the complexes. An anomalous trend is identified in which, for each M, F₃M−I—NH₃becomeslessstable as the optimized I—N distance getsshorterin different dielectric environments; it is explained using the F−I—NH₃complex as a reference.

 

The aromaticity and dynamics of a set of recently proposed neutral 5- and 6-membered heterocycles that are closed by dative (donor–acceptor) or multi-center σ bonds, and have resonance forms with a Hückel number of π-electrons, are examined. The donors and acceptors in the rings include N, O, and F, and B, Be, and Mg, respectively. The planar geometry of the rings, coupled with evidence from different measures of aromaticity, namely the NICS zz , and NICS πzz components of the conventional nucleus independent chemical shifts (NICS), and ring current strengths (RCS), indicate non-trivial degrees of aromaticity in certain cases, including the cyclic C 3 B 2 OH 6 and C 3 BOH 5 isomers, both with three bonds to the O site in the ring. The former is lower in energy by at least 17.6 kcal mol −1 relative to linear alternatives obtained from molecular dynamics simulations in this work. Some of the other systems examined are best described as non-aromatic. Ring opening, closing, and isomerization are observed in molecular dynamics simulations for some of the systems studied. In a few cases, the ring indeed persists. 

We have explored the structural and energetic properties of a series of RMX₃‐NH₃(M=Si, Ge; X=F, Cl; R=CH₃, C₆H₅) complexes using density functional theory and low‐temperature infrared spectroscopy. In the minimum‐energy structures, the NH₃binds axially to the metal, opposite a halogen, while the organic group resides in an equatorial site. Remarkably, the primary mode of interaction in several of these systems seems to be hydrogen bonding (C‐H‐‐N) rather than a tetrel (N→M) interaction. This is particularly clear for the RMCl₃‐NH₃complexes, and analyses of the charge distributions of the acid fragment corroborate this assessment. We also identified a set of metastable geometries in which the ammonia binds opposite the organic substituent in an axial orientation. Acid fragment charge analyses also provide a clear rationale as to why these configurations are less stable than the minimum‐energy structures. Matrix‐isolation infrared spectra provide clear evidence for the occurrence of the minimum‐energy form of CH₃SiCl₃–NH₃, but analogous results for CH₃GeCl₃–NH₃are less conclusive. Computational scans of the M‐N distance potentials for CH₃SiCl₃–NH₃and CH₃GeCl₃–NH₃, both in the gas phase and bulk dielectric media, reveal a great deal of anharmonicity and a propensity for condensed‐phase structural change.