Adamantane bisurea derivatives: anion binding in the solution and in the solid state

1,3-Bis-(3-arylureido)adamantane receptors, bearing phenyl (5,6), 1-naphthyl (7,8) and 9-anthryl (9) fluorophore, were synthesized. Their ability for complexation with F-, Cl-, Br-, OAc-, NO3-, HSO4-, and H2PO4- in solution was investigated by UV-vis and fluorescence spectrophotometry. The binding was compared to that of 2-naphthyl bisurea derivatives with flexible spacers (bearing propylene or pentalene, 2 and 4) and rigid adamantane analogues (1 and 3). In solution, the receptors form stable complexes with all anions except with NO3-. The complexation ability in CH3CN correlates with the basicity of anion and the acidity of the urea N-H, whereas in DMSO the complexes stability variations are less pronounced. The X-ray structure of receptor 1 indicates that incorporation of the adamantane moiety preorganizes the receptor in a tweezer-like conformation for the optimal formation of hydrogen bonding network and high selectivity for H2PO4- anion. Incorporation of the methylene spacers between the adamantane and the urea additionally increases stability of the complexes with anions. X-ray structural analysis was performed on the following complexes: 1 center dot Bu4NH2PO4, 3 center dot Bu4NH2PO4, 5 center dot Bu4NH2PO4 center dot 4H(2)O, and 5 center dot Bu4NOAc center dot 3H(2)O. All H2PO4- complexes include extensive receptor ... H2PO4- hydrogen bonds, essential for the anion recognition, as well as H2PO4- ... H2PO4- hydrogen bonds. (c) 2012 Elsevier Ltd. All rights reserved.