| Well-orchestrated noncovalent interactions provide us directional "linkers" for fashioning desirable structures.In particular,the anion-? interaction,which stands for the attraction between an anion and the electron-deficient aromatic derivatives,emerges recently.The change of the ? electron density distribution subsequently impacts the interaction of substituted benzenes or other cyclic conjugated rings with anions.Fluorine,as one of the most wildly adopted electron-withdrawing substituents on the anion receptors,is a ?-electron acceptor but ?-electron donor.The critical justification of the resonance effect requires a theoretical approach which can define electron-localized(resonance or Lewis)state as reference.This can be achieved by the VB theory,where a molecular wavefunction can be defines with a linear combination of resonance states and each resonance state can be defined with the Heilter-London-Slater-Pauling function.The BLW method is the simplest ab initio VB method which combines the computational efficiency of MO theory and the chemical intuition of VB theory,and can derive the optimal electron-localized state self-consistently.In this work,the resonance-impaired/assisted(RI/A)phenomenon in anion-? interactions has been directly evidenced theoreticaly,by the means of block-localized wavefunction(BLW)method,which can construct and optimize the resonance-free state selfconsistently.The frozen interactions,in which the electrostatic attraction is involved,has been proved to be the governing factor for the overall attraction and also the RI/A charicteristic,using the energy decomposition approach based on BLW(BLW-ED).The ESP distribution along the binding direction has also been analyzed and the importance of ESP at the centroid of acceptors to the ?-hole has been emphasized.Intriguingly,the anion-? interactions were further simplified as attraction between a negative point charge(anion)and a group of local dipoles,using an empirical point charges(PC)model.Novel anion receptors via anion-? interactions can facilitate the applications of this versatile interaction and are expected.In this work,perfluorinated cycloparaphenylenes(F-[n]CPP,n=5-8),boron nitride nanohoop(F-[5]BNNH),and buckybowls(F-BBs)were proposed as anion receptors with halide anions(Cl-,Br-and I-),and remarkable bond strengths up to-312.2 kJ/mol were observed.The energy decomposition approach based on block-localized wave function method(BLW-ED)were employed,in order to reveal the nature of anion-? interaction and its selectivities.Key role of frozen energy,in which the electrostatic interactions are included,was observed,and the remarkable bond strengths with F-[n]CPPs can be attributed to the accumulated attraction between the anion and each conjugated ring on the hoop,while for F-BBs,additional stability originating from the curved frameworks,which distribute electrons unequally on ?-faces,is significant.Furthermore,the strongest host was proved to be the F-[5]BNNH,which exhibit the most significant anisotropy of ESP distribution due to the difference in electronegativities of nitrogen and boron.Alternatively,the attractive N-B local dipoles,which is absent in the skeletons of carbon based receptors,may also rationalize the enhanced anion-? interactions with F-[5]BNNH.The selectivities of hosts for anions were explored and Cl-turns out to be most favorable anion for all receptors,due to the smallest ionic radius and the accompanied weakest destabilizing Pauli exchange repulsion. |
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