Pnicogen Bonds Pairing Anionic Lewis Acid with Neutral and Anionic Bases

Area of Science:

• * Computational chemistry
• * Inorganic chemistry
• * Quantum chemistry

Background:

• * Anionic ZCl4- species (Z = P, As, Sb) can engage in non-covalent interactions.
• * Pnicogen bonds (ZB) are a type of non-covalent interaction crucial in molecular recognition and crystal engineering.
• * Understanding complexation behavior in different phases is vital for predicting chemical reactivity and stability.

Purpose of the Study:

• * To investigate the complexation of anionic ZCl4- with neutral (HCN, pyridine) and anionic (CN-) species.
• * To elucidate the role of pnicogen bonds in stabilizing these complexes.
• * To compare complexation energetics in the gas phase versus aqueous solution.

Main Methods:

• * High-level ab initio calculations were employed to model the interactions.
• * Potential energy surfaces were analyzed to determine reaction pathways and energetics.
• * Structural rearrangements of ZCl4- upon complexation were examined.

Main Results:

• * Pnicogen bonds stabilize complexes between ZCl4- and all studied Lewis bases, despite the absence of a positive sigma-hole.
• * Gas-phase complexation with HCN and CN- is endothermic due to Coulomb repulsion and weak basicity, respectively.
• * Pyridine complexation is exothermic in the gas phase, while dianionic complex formation becomes exothermic in aqueous solution.
• * Solvation significantly influences the energetics, enhancing exothermicity for pyridine and reducing endothermicity for HCN.

Conclusions:

• * Pnicogen bonds are effective in forming stable complexes with ZCl4- anions.
• * The phase (gas vs. aqueous) and nature of the interacting species critically affect complexation thermodynamics.
• * Computational methods provide valuable insights into the intricate details of non-covalent interactions and solvation effects.