Ab initio calculated structures of conformers for 1,3-dimethoxy-p-tert-butylcalix[4]crown-5-ether complexed with potassium cation

Stable molecular conformations were calculated for the 1,3-dimethyl ether of p-tert-butylcalix[4]crown-5-ether (1) in the various conformers and their potassium-ion complexes. The structures of three distinct conformations have been optimized using ab initio RHF/6-31G methods. After geometry optimizations, B3LYP/6-31+G(d,p) single point calculations of the final structures are done to include the effect of electron correlation and the basis set with diffuse function and polarization function. Relative stability of free host 1 is in following order: cone (most stable)>partial-cone>1,3-alternate conformer. For two different kinds of complexation mode, the potassium cation in the crown-5-ether moiety (cr) has much better complexation efficiency than in the benzene-rings (bz) pocket for all three kinds of conformation of host molecule 1. The relative stability of complex (1+K+) in the cr-binding mode is in following order: cone ∼1,3-alternate>partial-cone conformer.