Computational analyses of cooperativity between pnicogen and halogen bonds in H2FP:pyrimidine: ClF complex

The substituent effects on cooperativity between pnicogen and halogen bonds in ternary complexes involving pyrimidine with substituents X in the 5-position (X = CN, NC, CF3, Br, Cl, F, H, CH3, C(CH3)(3), NH2, N(CH3)(2)), H2FP, and ClF are investigated using theoretical calculations at the MP2/aug-cc-pVDZ level. The reduced density gradient (RDG) analysis indicates that the halogen and pnicogen interactions clearly stand out as attractive interactions. The calculated synergetic energies in ternary complexes are positive, which demonstrates the antagonist effect of pnicogen and halogen interactions upon each other. According to geometrical parameters, binding energies, molecular electrostatic potentials (MEPs), and the results of natural bond orbital (NBO), atoms in molecules (AIM), and nuclear magnetic resonance (NMR) analyses, pnicogen and halogen bonds are weakened in the ternary complexes where two pnicogen and halogen bonds coexist. The results indicate reduced electron density values, second-order perturbation energies, charge transfer values, and two-bonded spin-spin coupling constants for both pnicogen and halogen bonds in the ternary complex as compared to the isolated binary systems. Also, the results show that substituent effects on cooperativity between N horizontal ellipsis P pnicogen and N horizontal ellipsis Cl halogen bonds in considered system can be expressed by Hammett constants.