Synthesis , Structure and Recognition Properties of Macrocyclic Crown Ethers with Oxadiazole

A series of macrocyclic crown ethers containing oxadiazole groups were synthesized and their single crystals were obtained. Their structures were characterized by nuclear magnetic resonance( NMR), high resolution electrospray ionization mass spectroscopy ( HRESI-MS) and X-ray single crystal diffraction. The single crystal X-ray diffraction revealed that 2 , 3 , 11 , 12-dibenzo-4 , 7 , 10 ,16-tetraoxa-14 , 15-diazabicyclo [ 11.2.1] - hexadecane-13 ,15-diene( 2) belonged to orthorhombic crystal system with space group Pna2(1), 2,3 , 14 , 15-dibenzo-4 ,7 ,10 ,13 ,19- pentaoxa-17 ,18-diazabicyclo[14.2.1]-nonadecane-16 ,18-diene( 3 ) belongs to monoclinic crystal system with space group C2/c and 2 , 3, 17 , 18-dibenzo-4, 7 , 10 , 13 , 16 , 22-hexaoxa-20 , 21-diazabicyclo [ 17. 2. 1 ] -docosadecane-19 , 21-diene ( 4 ) belonged to orthorhombic crystal system with space group Pbca. Three crown ethers were all connected to form a three-dimensional supramolecular structure by C-H center dot center dot center dot O or C-H center dot center dot center dot N hydrogen bond intramolecular and pi-pi stacking. The bonding behaviors of 2 , 5-bis [ 2( 2-methoxyethoxy ) phenyl ] -1,3 , 4-oxadiazole ( 1) and crown ethers 2-4 with different sizes to metal ions Li+, Na+, Rb+, Mg2+ and Ca2+ was determined by fluorescence spectroscopy. The results showed that open- chain crown ether 1 and macrocyclic crown ether 4 exhibited fluorescence quenching behavior and good bonding ability and selectivity on alkaline earth metal Ca2+. While crown ether 2 showed good bonding ability to Na+ and K+ and poor Na+/K+ selectivity.