Isomerism and Biradical Character of Tetrapnictide Dianions: A Computational Study.

We present a computational study on tetrapnictide dianions Pn 4 2- (Pn = P, As, Sb, Bi), using density functional theory (DFT), coupled-cluster [DLPNO-CCSD(T)] and complete active space self-consistent field (CASSCF) methods. Environmental effects such as solvation and coordination of counterions are included. The calculations reveal that out of three isomers (square-planar, butterfly and capped-triangle), the square planar isomers are generally the most stable. The counterion (Li+ and Mg2+) used in the calculations have a substantial effect on the relative stabilities. The square planar isomers show considerable biradical character. Calculated reactions toward alkenes indicate that this unusual electronic structure has significant implications on the reactivity of the Pn 4 2- dianions.

On the Importance of Nonbonding Donor-Acceptor Interactions Involving PO2. Radicals: An ab Initio Study.

In this study, several σ-type and π-hole bonding complexes between PO2. radicals and electron-rich entities have been optimized at the RI-MP2/aug-cc-pVQZ level of theory. We have used Cl- , Br- , I- anions, and ethene, ethyne, HCN, HF, and H2 O as Lewis bases. In addition, we have performed natural bond orbital (NBO) and Mulliken spin density analyses, highlighting the donor-acceptor nature of the interaction. Moreover, an interesting retro-donation from the single electron lone pair of the PO2. radical to the Lewis base also contributes to the stabilization of the complexes studied herein. Finally, the Bader's atoms-in-molecules (AIM) analysis of several complexes has been performed to further characterize the interactions discussed herein.

σ-Hole Opposite to a Lone Pair: Unconventional Pnicogen Bonding Interactions between ZF3 (Z=N, P, As, and Sb) Compounds and Several Donors.

The ability of several pnicogen sp(3) derivatives ZF3 (Z=N, P, As, Sb) to interact with electron-rich entities by means of the opposite face to the lone pair (lp) is investigated at the RI-MP2/aug-cc-pVQZ level of theory. The strength of the interaction ranges from -1 to -87 kJ mol(-1) , proving its favorable nature, especially when the lp is coordinated to a metal center, whereby the strength of the interaction is significantly enhanced. NBO analysis showed that orbital effects are modest contributors to the global stabilization of the pnicogen σ-hole bonded complexes studied. Finally, a selection of Cambridge Structural Database examples are shown that demonstrate the impact of this counterintuitive binding mode in the solid state.

Experimental charge density evidence for pnicogen bonding in a crystal of ammonium chloride.

Chemical binding in crystalline ammonium chloride, a simple inorganic salt with an unexpectedly complex bonding pattern, was studied by using a topological analysis of electron density function derived from high-resolution X-ray diffraction. Supported by periodic quantum chemical calculations, it provided experimental evidence for weak σ-hole bonds (1.5 kcal mol(-1) ) that involve ammonium cations in a crystal. Our results show this type of supramolecular interaction to be more numerous than has been found to date by using gas-phase calculations or statistical analysis of CSD.

A computational study on 3-azonia-, 3-phosphonia-, and 3-arsoniaspiro[2.2]pentanes and related three-membered heterocycles.

A theoretical study at the ab initio MP2/6-311++G(d,p) level of theory is carried out to characterize several heterocyclic spiro[2.2]pentane cations with N, P, and As as spiro atoms. The strain and relative stability of the spiropentanes are obtained through isodesmic reactions. Nucleus-independent chemical shifts (NICS) and 3D NICS isosurfaces show σ-aromatic characteristics, similar to those found in cyclopropane. The interaction with the Cl(-) anion, which results in four different stationary structures, is studied and characterized by means of the atoms in molecules methodology, and Cl⋅⋅⋅pnicogen, Cl⋅⋅⋅H, and Cl⋅⋅⋅C interactions are found. The most stable structure in all cases corresponds to opening of one of the three-membered rings, due to the attack of the Cl atom, and C-Cl bond formation. Furthermore, the reaction with the 3-boranuidaspiro[2.2]pentane anion results in the formation of a new compound through cleavage of one ring of both reactants.

Chiral discrimination in dimers of diphosphines PH2-PH2 and PH2-PHF.

A theoretical study of the conformational profile of two diphosphines, PH2-PH2 and PH2-PHF, is carried using second-order Møller-Plesset perturbation theory (MP2) computational methods. The chiral minima found are used to build homo- and heterochiral dimers. Six minima are found for the (PH2-PH2 )2 dimers and 27 for the (PH2-PHF)2 dimers. Pnicogen and hydrogen bonds, the non-covalent forces that stabilize the complexes, are characterized by Atoms in Molecules (AIM) and Natural Bond Orbital (NBO) methodologies. Those with several pnicogen bonds are more stable than those with hydrogen bonds. The chirodiastaltic energies amount to a total of 1.77 kJ mol(-1) for the Ra:Ra versus Ra:Sa (PH2-PH2 )2 dimers, 0.81 kJ mol(-1) for the RSa:RSa versus RSa:SRa (PH2-PHF)2 dimers, and 2.93 kJ mol(-1) for the RRa:RRa versus RRa:SSa (PH2-PHF)2 dimers. In the first and second cases, the heterochiral complex is favored whereas in the third case, the homochiral complex is favored.

Investigating Variation of the Pnicogen Nucleophilic Heteroatom on Ionic Liquid Solvent Effects in Bimolecular Nucleophilic Substitution Processes.

A series of nucleophiles containing Group 15 nucleophilic heteroatoms has been used to expand and develop the current understanding of ionic liquid solvent effects on bimolecular nucleophilic substitution processes. It was found that when using arsenic-, antimony- and bismuth-based nucleophiles, rate constant enhancement was observed for all solvent compositions containing ionic liquids. This rate constant enhancement was driven by ionic liquid/transition state interactions, which contrasts with previous studies on earlier Group 15 nucleophiles. This study provides a holistic understanding and augments the predictive framework for the effects of ionic liquids on bimolecular nucleophilic substitution processes, with the potential for these periodic trends to be broadly applied.