A B3LYP and MP2 theoretical investigation into host-guest interaction between calix[4]arene and Li(+) or Na (+).

The DFT-B3LYP and MP2 methods with 6-311G** and 6-311++G** basis sets have been applied to study the complexation energies of the host-guest complexes between the cone calix[4]arene and Li(+) or Na(+) on the B3LYP optimized geometries. A comparison of the complexation energies obtained from the MP2(full) with those from MP2(fc) method is also carried out. The result shows that it is essential to introduce the diffuse basis set into the geometry optimizations and complexation energy calculations of the alkali-metal cation-pi interaction complexes of calix[4]arene, and the D (e) values show a maximum of 21.13 kJ mol(-1) (14.45% of relative error) between the MP2(full)/6-311++G** and MP2(fc)/6-311++G** method. For Li(+) cation, the complexation is mainly energetically stabilized by the lower rim/cation (namely O-Li(+)) interaction. However, binding energies and NBO analyses confirm that Na(+) cation prefers to enter the calix[4]arene cavity and the cation-pi interaction is predominant, which contradicts the previous low-level theoretical studies. Furthermore, the complexation with Li(+) is preferred over that with Na(+) by at least 12.70 kJ mol(-1) at MP2(full)/6-311++G**//B3LYP/6-311++G** level.