Pnicogen bonds in complexes with CO and CS: differentiating properties

ABSTRACT

Ab initio MP2/aug’-cc-pVTZ calculations have been performed on pnicogen-bonded complexes with CO and CS as electron-pair donors to PH₂X, for X = F, NC, OH, CN, CCH, and H. CO:PH₂X and OC:PH₂X complexes are stabilised by traditional pnicogen bonds. CS is an electron-pair donor through its in-plane π system to four PH₂X molecules. It forms C···P phosphorus-shared bonds with some ion-pair character with PH₂F, PH₂(OH-Z), and PH₂(OH-E), and traditional pnicogen bonds with all PH₂X except PH₂F. C-O and C-S stretching frequencies are blue-shifted for C···P pnicogen bonds, and red-shifted for O···P and S···P bonds. EOM-CCSD spin-spin coupling constants ^1pJ(P-C) for OC:PH₂X and ^1pJ(P-O) for CO:PH₂X are characteristic of complexes stabilised by traditional pnicogen bonds. Coupling constants ^1pJ(P-C) as a function of the P-C distance for SC:PH₂X illustrate the evolution of the C···P pnicogen bond. They increase as the P-C distance decreases in complexes with traditional bonds, reach a maximum for SC:PH₂OH transition structures as the P-C distance further decreases and the bonds gain phosphorus-shared character, and then change sign and continue to decrease as the P-C distance further decreases and the phosphorus-shared pnicogen bonds gain ion-pair character. They approach the values of ¹J(P-C) for the cation (H₂PCS)⁺.

GRAPHICAL ABSTRACT

KEYWORDS:

• Pnicogen bonds
• geometry
• energy
• shared bonds
• spin-spin coupling constants

Disclosure statement

No potential conflict of interest was reported by the authors.

ORCID

Janet E. Del Bene http://orcid.org/0000-0002-9037-2822

Ibon Alkorta http://orcid.org/0000-0001-6876-6211

José Elguero http://orcid.org/0000-0002-9213-6858

Additional information

Funding

This work was carried out with financial support from the Ministerio de Economía, Industria y Competitividad [project number. CTQ2015-63997-C2-2-P] and Comunidad de Madrid [grant number S2013/MIT2841, Fotocarbon]. Thanks are also given to the Ohio Supercomputer Center and CTI (CSIC) for their continued computational support.