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 (H 2 O) 13 ( 1 ) and [Cu 4 (azadendtriz)Br 4 ](Br) 4 (H 2 O) 28 ( 2 ), determined from single‐crystal X‐ray data, reveal that the π‐acidic receptor binds a chloride anion through anion–π interactions in 1 , whereas it hosts a water molecule through lone‐pair–π interactions in 2 . This differentiation between Br – and Cl – may be explained by the different size of the (hydrated) anions.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)