Density functional theory study of the potassium complexation of an unsymmetrical 1,3-alternate calix[4]-crown-5-N-azacrown-5 bearing two different crown rings
Theoretical studies of an unsymmetrical calix[4]-crown-5-N-azacrown-5 (1) in a fixed 1,3-alternate conformation and the complexes 1 center dot K(+)(a), 1 center dot K(+)(b), 1 center dot K(+)(c) and 1 center dot K(+)K(+) were performed using density functional theory (DFT) at the B3LYP/6-31G* level. The fully optimized geometric structures of the free macroligand and its 1:1 and 1:2 complexes, as obtained from DFT calculations, were used to perform natural bond orbital (NBO) analysis. The two main types of driving force metal-ligand and cation-pi interactions were investigated. NBO analysis indicated that the stabilization interaction energies (E (2)) for OaEuro broken vertical bar K(+) and NaEuro broken vertical bar K(+) are larger than the other intermolecular interactions in each complex. The significant increase in electron density in the RY* or LP* orbitals of K(+) results in strong host-guest interactions. In addition, the intermolecular interaction thermal energies (Delta E, Delta H, Delta G) were calculated by frequency analysis at the B3LYP/6-31G* level. For all structures, the most pronounced changes in the geometric parameters upon interaction are observed in the calix[4]arene molecule. The results indicate that both the intermolecular electrostatic interactions and the cation-pi interactions between the metal ion and pi orbitals of the two pairs that face the inverted benzene rings play a significant role.
calix[4]-crown-5-n-azacrown-5 density functional theory (dft) natural bond orbital (nbo) cation-pi interactions supramolecular chemistry