Complexation of decamethylcucurbit[5]uril with alkali metal ions

Abstract

Four coordination compounds, namely [Na(H 2O)(H 2O) 2⊂C 40H 50N 20O 10](C 6H 6O 2) 2Cl·8H 2O ( 1), [K 2(H 2O) 2(H 2O)⊂C 40H 50N 20O 10](C 6H 6O 2) 2Cl 2·7H 2O ( 2), [Rb 2(H 2O) 2(H 2O)⊂C 40H 50N 20O 10](C 6H 6O 2) 2Cl 2·7H 2O ( 3) and [Cs(H 2O) 2(H 2O⊂C 40H 50N 20O 10)](C 6H 6O 2) 2Cl·6H 2O ( 4), were obtained by the reactions of the corresponding alkali metal salts with decamethylcucurbit[5]uril (Me 10Q[5]) in the presence of hydroquinone, and their structures were determined by single-crystal X-ray diffraction. The results revealed that in compounds 1 and 4 each Me 10Q[5] ligand coordinates one Na + or Cs + ion to form a molecular bowl structure, while in compounds 2 and 3 each Me 10Q[5] ligand coordinates two K + or Rb + ions to form a closed molecular capsule structure, and adjacent molecular capsules bridge each other through water molecules to form 1D coordination polymers. In addition, we found that the coordination distances for the metal ions and the height of the metal ions out-of-portal-plane for the four compounds are in the same order, 1 < 2 < 3 < 4, which is attributed to the fact that the radius of alkali cations is in the order Na + < K + < Rb + < Cs +. Although each portal of Q[6] binds with two alkali cations (not including Cs +), the Q[6]-based alkali cations complexes display similar structural trends.