Abstract
Radical (R(•)) and R(•)-hole site-based interactions are comparatively studied, for the first time, using ab initio methods. In this regard, R(•)-bearing molecules (•)XO(3) (where X = Cl, Br, and I) were subjected to direct interaction with NH(3) within dimeric and trimeric forms in the form of NH(3)···(•)XO(3)/(•)XO(3)···NH(3) and NH(3)···(•)XO(3)···NH(3) complexes, respectively. As confirmed by electrostatic potential analysis, the studied R(•)-bearing molecules (•)XO(3) had the outstanding potentiality to interact as Lewis acid centers via two positive sites dubbed as R(•) and R(•)-hole sites. Such an observation proposed the potentiality of the considered (•)XO(3) molecules to engage in unconventional R(•) and well-established R(•)-hole site-based interactions with Lewis bases. This was confirmed by negative interaction (E (int)) energies, ranging from -4.93 to -19.89 kcal/mol, with higher favorability for R(•) site-based interactions over the R(•)-hole site-based ones. MP2 energetic features furnished higher preferability for the R(•) site-based interactions than the R(•)-hole site-based ones in the case of chlorine- and bromine-bearing complexes, and the reverse was true for the iodine-bearing complexes. Moreover, elevated E (int) values were recorded for the NH(3)···(•)XO(3)···NH(3) trimers over the NH(3)···(•)XO(3) and (•)XO(3)···NH(3) dimers, outlining the higher preference of the (•)XO(3) molecules to engage in R(•) and R(•)-hole site-based interactions in the trimeric form over the dimeric one. These results might be considered a requisite linchpin for numerous forthcoming supramolecular chemistry and crystal engineering studies.