An Electron-Poor Host Receptor for Electron-Rich Guests Involving Anion-π and Lone-Pair-π Interactions

The binding of the ligand N,N',N '',N '''-tetrakis{2,4-bis[(dipyridin-2-yl) amino]-1,3,5-triazin-2-yl}-1,4,8,11-tetraazacyclotetradecane (azadendtriz) to four copper(II) ions generates two electron-deficient cavities formed by four coordinated pyridine rings that are capable of hosting electron-rich guests. The molecular structures of [Cu-4(azadendtriz)Cl-4](Cl)(4)- (H2O)(13) (1) and [Cu-4(azadendtriz)Br-4](Br)(4)(H2O)(28) (2), determined from single-crystal X-ray data, reveal that the pi-acidic receptor binds a chloride anion through anion-pi interactions in 1, whereas it hosts a water molecule through lone-pair-pi interactions in 2. This differentiation between Br- and Cl- may be explained by the different size of the (hydrated) anions. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)