Host-guest interactions between calixarenes and Cp2NbCl2

► Ab-initio calculations showed inclusion complex between p-SO3-calix[6]arene and Cp2NbCl2. ► Calix[6]arene does not form inclusion complex with Cp2NbCl2 in CDCl3 solution. ► Cp2NbCl2 is not included in the calix[6]arene cavity, possibly due to the lack of sulfonates. ► p-Sulfonic calix[n]arenes provide a good alternative to prepare water soluble metallocene anticancer agents.