The Phosphorus Bond, or the Phosphorus-Centered Pnictogen Bond: The Covalently Bound Phosphorus Atom in Molecular Entities and Crystals as a Pnictogen Bond Donor

Abstract

The phosphorus bond in chemical systems, which is an inter- or intramolecular noncovalent interaction, occurs when there is evidence of a net attractive interaction between an electrophilic region associated with a covalently or coordinately bonded phosphorus atom in a molecular entity and a nucleophile in another, or the same, molecular entity. It is the second member of the family of pnictogen bonds, formed by the second member of the pnictogen family of the periodic table. In this overview, we provide the reader with a snapshot of the nature, and possible occurrences, of phosphorus-centered pnictogen bonding in illustrative chemical crystal systems drawn from the ICSD (Inorganic Crystal Structure Database) and CSD (Cambridge Structural Database) databases, some of which date back to the latter part of the last century. The illustrative systems discussed are expected to assist as a guide to researchers in rationalizing phosphorus-centered pnictogen bonding in the rational design of molecular complexes, crystals, and materials and their subsequent characterization.

The Pnictogen Bond: The Covalently Bound Arsenic Atom in Molecular Entities in Crystals as a Pnictogen Bond Donor

“…On the empirical scale of Choudhary, Ranjan & Chakraborty (CR & C) [ 129 ], the polarizability α (CR & C) in the halogen series follows the order: F = 0.46, Cl = 1.02, Br = 1.67, and I = 1.97. Clearly, the bonding of F with As in AsF 3 does not allow it to conceive a σ -hole on its surface along the As–F bond extension, as observed in NF 3 and PF 3 along the N–F [ 68 ] and P–F [ 67 ] bond extensions, respectively. The (marginally) less electronegativity ( χ (Pauling) of As = 2.18, P = 2.19, N = 3.44; χ (Allen) As = 2.211, P = 2.253, N = 3.610) and more polarizability of As ( α (CR & C) = 1.97, P = 1.34, N = 0.52) has little ability to pull the electron density from F towards the bonding region; this may explain why the σ -hole on F along the As–F bond extensions in AsF 3 is neutral.…”

“…Some studies [ 5 , 30 , 67 , 68 ] have already provided illustrative overviews of pnictogen bonding formed by the first three elements of Group 15, N, P, and As. However, accounts elucidating the basis of such noncovalent interactions involving the heavier pnictogen derivatives, As, Sb, Bi, and (theoretically) Mc, are rare [ 5 , 30 , 67 , 68 ].…”

“…Some studies [ 5 , 30 , 67 , 68 ] have already provided illustrative overviews of pnictogen bonding formed by the first three elements of Group 15, N, P, and As. However, accounts elucidating the basis of such noncovalent interactions involving the heavier pnictogen derivatives, As, Sb, Bi, and (theoretically) Mc, are rare [ 5 , 30 , 67 , 68 ]. This is clearly a gap in our knowledge since the typical inter- and intramolecular geometry, orientation, energy, and charge density profiles of arsenic-, antimony-, or bismuth-centered noncovalent interactions have rarely been examined computationally, although a few studies have discussed the characteristics of arsenic-centered noncovalent interactions and their technical implications in materials design and discovery [ 69 , 70 ]; we also have recently provided our viewpoint on the diversity of stibium bonding in chemical systems.…”

The Nitrogen Bond, or the Nitrogen-Centered Pnictogen Bond: The Covalently Bound Nitrogen Atom in Molecular Entities and Crystals as a Pnictogen Bond Donor

“…The 0.001 a.u. (electrons bohr −3 ) isoelectron density envelope that arbitrarily defines the van der Waals surface of a molecular entity was used on which to compute the electrostatic potential [87][88][89]. We used the sign and magnitude of these potentials to infer whether specific regions on the surfaces of these molecular entities are electrophilic or nucleophilic [51, [89][90][91].…”

“…or 0.0020 a.u., on which to compute the potential. We have discussed the usefulness of these envelopes elsewhere [22,25,87,89].…”