Contrasting preferences of N and P substituted heteroaromatics towards metal binding: probing the regioselectivity of Li+ and Mg2+ binding to (CH)6-m-nNmPn

High level ab initio and hybrid DFT methods have been employed to investigate the interactions of metal ions (Li+ and Mg2+) with N and P substituted six membered heteroaromatics (CH)(6-m-n)NmPn. The binding energy (BE) of metal ions with the N and P substituted heteroaromatics has been computed at the CCSD(T)/cc-pVTZ//MP2/cc-pVTZ level with counterpoise correction. In the present study we systematically examined the preferential modes of binding of metal ions to the heteroaromatics. N-Substituted heteroaromatics show a strong preference for cation-sigma mode of binding whereas the P-substituted heteroaromatics prefer cation-pi mode of binding with the metal ions. Energy decomposition analysis (EDA) using the DFT-SAPT scheme has been carried out to analyse the contribution of various energy components to the BE. The results illustrate that for the cation-pi complexes, the contribution of the induction term is more whereas in the case of cation-sigma there is a competition between induction and electrostatic terms in the interaction energy.