Abstract
The nitrogen bond in chemical systems occurs when there is evidence of a net attractive interaction between the electrophilic region associated with a covalently or coordinately bound nitrogen atom in a molecular entity and a nucleophile in another, or the same molecular entity. It is the first member of the family of pnictogen bonds formed by the first atom of the pnictogen family, Group 15, of the periodic table, and is an inter- or intra-molecular non-covalent interaction. In this featured review, we present several illustrative crystal structures deposited in the Cambridge Structure Database (CSD) and the Inorganic Crystal Structure Databases (ICSD) to demonstrate that imide nitrogen is not the only instance where nitrogen can act as an electrophilic agent. Analysis of a set of carefully chosen illustrative crystal systems shows that a covalently bound nitrogen atom in a variety of molecular entities features a σ-hole or even a π-hole, and these have the ability to sustain attractive engagements with negative sites to form inter- and/or intramolecular interactions that drive, or assist, the formation of a crystalline phase.
Highlights
IUPAC definitions, features and characteristic properties that can be used to identify non-covalent interactions, such as hydrogen bonding, chalcogen bonding and halogen bonding in chemical systems have been promulgated in 2011 [1], 2013 [2] and 2019 [3], respectively
We highlighted the importance and nature of the modes of nitrogen-centered pnictogen bonding observed in many crystals deposited in the Cambridge Structure Database (CSD) and Inorganic Crystal Structure Databases (ICSD)
We have shown that the singular occurrence of pnictogen bonding in crystals is very rare, and is accompanied or reinforced by other primary/secondary interactions in a great majority of crystals, such as halogen bonds, hydrogen bonds, and/or π···π stacking interactions
Summary
IUPAC definitions, features and characteristic properties that can be used to identify non-covalent interactions, such as hydrogen bonding, chalcogen bonding and halogen bonding in chemical systems have been promulgated in 2011 [1], 2013 [2] and 2019 [3], respectively. The characterization of non-covalent interactions in many crystal structures has been undertaken based on the “less than the sum of the van der Waals (vdW) radii” concept [64], a widespread concept that has been invoked, for example, in structural and supramolecular chemistry [64–66], biological and medicinal chemistry [67,68], and crystallography [69–74] According to this concept, when the inter- or intramolecular distance of separation is associated with a structural motif, for example, Pn···D (Pn = the pnictogen atom; D = an electron donor, such as O, N, a halogen anion, etc.), is less than the sum of the vdW radii of Pn and D, it possible that Pn and D atomic basins are bonded to each other by an attractive engagement. Emphasize that the examples given below are not exhaustive, but illustrative, since our ultimate aim is to inform the reader of the potential significance of nitrogen-centered pnictogen bonding in crystals so that this can be borne in mind when new materials are designed in silico
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