Unusual Complexes of P(CH)3 with FH, ClH, and ClF.

Janet E Del Bene,Ibon Alkorta,José Elguero

doi:10.3390/molecules25122846

Abstract

Ab initio MP2/aug’-cc-pVTZ calculations have been performed to determine the structures and binding energies of complexes formed by phosphatetrahedrane, P(CH)3, and HF, HCl, and ClF. Four types of complexes exist on the potential energy surfaces. Isomers A form at the P atom near the end of a P-C bond, B at a C-C bond, C at the centroid of the C-C-C ring along the C3 symmetry axis, and D at the P atom along the C3 symmetry axis. Complexes A and B are stabilized by hydrogen bonds when FH and ClH are the acids, and by halogen bonds when ClF is the acid. In isomers C, the dipole moments of the two monomers are favorably aligned but in D the alignment is unfavorable. For each of the monomers, the binding energies of the complexes decrease in the order A > B > C > D. The most stabilizing Symmetry Adapted Perturbation Theory (SAPT) binding energy component for the A and B isomers is the electrostatic interaction, while the dispersion interaction is the most stabilizing term for C and D. The barriers to converting one isomer to another are significantly higher for the A isomers compared to B. Equation of motion coupled cluster singles and doubles (EOM-CCSD) intermolecular coupling constants J(X-C) are small for both B and C isomers. J(X-P) values are larger and positive in the A isomers, negative in the B isomers, and have their largest positive values in the D isomers. Intramolecular coupling constants 1J(P-C) experience little change upon complex formation, except in the halogen-bonded complex FCl:P(CH3) A.

Highlights

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We have investigated the P4 molecule in complexes stabilized by hydrogen, halogen, and pnicogen bonds [25]
The parent molecule P(CH)3 is pyramidal with C3v symmetry

Summary

Results and Discussion

The parent molecule P(CH) is pyramidal with C3v symmetry. the experimental structure of this molecule is not known, a derivative P(C-t-butyl) has been synthesized. The second maximum has a value of 0.005 au, and is found below the centroid of the C-C-C ring on the C3 symmetry axis Bond formation in this region should have P(CH) acting as the acid, that is, as an electron acceptor. BTianbalrey1Cpomrepsleenxtess tAhe binding energies, intermolecular distances, selected angles, charge-transfer energies, and coupling constants across intermolecular bonds for these complexes. Charge-transfer energies Plp—σ*X-H of 17.6 and 16.4 kJ mol−1 are found for the hydrogen-bonded complexes. This energy changes dramatically in the halogen-bonded FCl:P(CH) complex. The third-order trendline has a correlation coefficient of 0.999 The curvature of this trendline at short distances suggests that complexes with these distances would have chlorine-shared halogen bonds [27,28]. This large difference may be attributed primarily to the weakening of the interacting P-C bond of P(CH), as indicated by the significant lengthening of this bond

Binary Complexes B

Structures A-tr and B-tr

Conclusions