Characterizing
Traditional and Chlorine-Shared Halogen
Bonds in Complexes of Phosphine Derivatives with ClF and Cl<sub>2</sub>
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Abstract
Ab initio MP2/aug’-cc-pVTZ
calculations have been carried
out on the halogen-bonded complexes H<sub>2</sub>XP:ClF and H<sub>2</sub>XP:Cl<sub>2</sub>, with X = F, Cl, OH, NC, CN, CCH, CH<sub>3</sub>, and H. H<sub>2</sub>XP:ClF complexes are stabilized by chlorine-shared
halogen bonds with short P–Cl and significantly elongated Cl–F
distances. H<sub>2</sub>XP:Cl<sub>2</sub> complexes with X = OH and
CH<sub>3</sub> form only chlorine-shared halogen bonds, while those
with X = H, NC, and CN form only traditional halogen bonds. On the
H<sub>2</sub>FP:Cl<sub>2</sub>, H<sub>2</sub>(CCH)P:Cl<sub>2</sub>, and H<sub>2</sub>ClP:Cl<sub>2</sub> potential surfaces small barriers
separate two equilibrium structures, one with a traditional halogen
bond and the other with a chlorine-shared bond. The binding energies
of H<sub>2</sub>XP:ClF and H<sub>2</sub>XP:Cl<sub>2</sub> complexes
are influenced by the electron-donating ability of H<sub>2</sub>XP
and the electron accepting ability of ClF and ClCl, the nature of
the halogen bond, other secondary interactions, and charge-transfer
interactions. Changes in electron populations on P, F, and Cl upon
complex formation do not correlate with changes in the chemical shieldings
of these atoms. EOM-CCSD spin–spin coupling constants for complexes
with chlorine-shared halogen bonds do not exhibit the usual dependencies
on distance. <sup>2X</sup><i>J</i>(P–F) and <sup>2X</sup><i>J</i>(P–Cl) for complexes with chlorine-shared
halogen bonds do not correlate with P–F and P–Cl distances,
respectively. <sup>1X</sup><i>J</i>(P–Cl) values
for H<sub>2</sub>XP:ClF correlate best with the Cl–F distance,
and approach the values of <sup>1</sup><i>J</i>(P–Cl)
for the corresponding cations H<sub>2</sub>XPCl<sup>+</sup>. Values
of <sup>1X</sup><i>J</i>(P–Cl) for complexes H<sub>2</sub>XP:ClCl with chlorine-shared halogen bonds correlate with
the binding energies of these complexes. <sup>1</sup><i>J</i>(F–Cl) and <sup>1</sup><i>J</i>(Cl–Cl) for
complexes with chlorine-shared halogen bonds correlate linearly with
the distance between P and the proximal Cl atom. In contrast, <sup>2X</sup><i>J</i>(P–Cl) and <sup>1X</sup><i>J</i>(P–Cl) for complexes with traditional halogen bonds
exhibit more normal distance dependencies
