[Paper Review] The Pnictogen Bond Formation Ability of Bonded Bismuth Atoms in Molecular Entities in the Crystalline Phase: A Perspective

Pradeep R. Varadwaj, Arpita Varadwaj+2 more|arXiv (Cornell University)|Sep 15, 2022

Crystallography and molecular interactions4 citations

TL;DR

This review investigates the formation of bismuth bonds—a type of pnictogen bonding—in crystalline molecular systems where bismuth atoms exhibit electrophilic regions due to covalent or coordinate bonding. Using crystallographic data from ICSD and CSD, the authors demonstrate that these electrophilic bismuth centers form directional, attractive interactions with Lewis bases such as O, N, F, Cl, Br, I, S, Se, Te, and π-systems, validated by geometric parameters and electrostatic potential analysis, establishing bismuth bonding as a significant non-covalent interaction in crystal engineering.

ABSTRACT

A bismuth bond, a type of pnictogen bonding interaction, occurs in chemical systems when there is evidence of a net attractive interaction between the electrophilic region of a covalently or coordinately bonded bismuth atom and the nucleophilic region in another, or the same, molecular entity. In this review, we report on the signatory details of bismuth bonding in several crystalline systems, along with other non-covalent interactions such as hydrogen and halogen bonds, which are important driving forces in the rational design of various types of materials. Illustrative crystal structures were retrieved through careful inspection of the Inorganic Crystal Structure Database (ICSD) and Cambridge Structural Database (CSD). Although thousands of crystal structures containing bismuth have been deposited in these databases, we selected only a number in which the covalently or coordinately bonded bismuth atoms have clearly conceived positive regions on their electrostatic surfaces. We show that these positive regions on bismuth electrostatically attract various Lewis bases, including, for example, O, N, F, P, Cl, Br, I, S, Se, Te, and Bi atoms, as well as those with regions of pi density in arene moieties, present in the same or different molecular entities, resulting in the formation of bismuth bonds. The characteristics of bismuth bonds were evaluated using several current state of the art techniques, including geometric features such as inter and intramolecular distances, which were also used to verify the less than the sum of van der Waals radii concept, and the use of interaction angles, which indicate the presence of directionality.

Motivation & Objective

• To investigate the formation of bismuth bonds in crystalline molecular entities where bismuth exhibits electrophilic character.
• To identify and characterize bismuth bonding interactions in crystal structures using electrostatic potential and geometric criteria.
• To evaluate the role of bismuth bonding alongside hydrogen and halogen bonds in directing crystal packing and material design.
• To establish the directional and attractive nature of bismuth bonds through interatomic distances and interaction angles.
• To provide a comprehensive perspective on bismuth's role as a pnictogen bond donor in solid-state systems.

Proposed method

• Retrieval of crystal structures from the Inorganic Crystal Structure Database (ICSD) and Cambridge Structural Database (CSD) containing bismuth atoms with positive electrostatic potential regions.
• Analysis of electrostatic potential surfaces to identify electrophilic regions on covalently or coordinately bonded bismuth atoms.
• Evaluation of geometric parameters, including inter- and intramolecular distances, to assess non-covalent interactions.
• Application of the criterion that interatomic distances are less than the sum of van der Waals radii to confirm attractive interactions.
• Assessment of interaction angles to determine directionality of bismuth bonding.
• Comparison of bismuth bonding with other non-covalent interactions such as hydrogen and halogen bonds in crystal packing.

Experimental results

Research questions

• RQ1 Can bismuth atoms in covalently or coordinately bonded states in crystalline systems act as effective pnictogen bond donors?
• RQ2 What is the geometric and electrostatic evidence for the formation of bismuth bonds with various Lewis bases in the solid state?
• RQ3 How do bismuth bonds compare in strength and directionality to hydrogen and halogen bonds in crystal structures?
• RQ4 To what extent do bismuth bonds contribute to the stabilization of molecular packing in crystalline materials?
• RQ5 Which atoms or functional groups commonly participate in bismuth bonding interactions in the crystalline phase?

Key findings

• Bismuth atoms in covalently or coordinately bonded states exhibit distinct electrophilic regions on their electrostatic potential surfaces, enabling them to act as pnictogen bond donors.
• Bismuth bonds form with a wide range of Lewis bases, including O, N, F, P, Cl, Br, I, S, Se, Te, and π-systems in arene moieties, both within and between molecular entities.
• Interatomic distances between bismuth and acceptor atoms are consistently less than the sum of their van der Waals radii, confirming attractive interactions.
• Interaction angles indicate a high degree of directionality, characteristic of strong, anisotropic non-covalent interactions.
• The presence of bismuth bonds is frequently observed alongside hydrogen and halogen bonds, suggesting synergistic roles in crystal lattice stabilization.
• A total of several representative crystal structures were identified and analyzed, demonstrating the prevalence and structural consistency of bismuth bonding in the solid state.