Trinuclear Cu(II) capsules self-assembled by nitrilotripropionate

Five trinuclear copper(II) complexes supported by nitrilotripropionate (ntp) have been prepared at acidic pH values and characterized by elemental, infrared and X-ray diffraction methods, [Cu3(H2O)6(Hntp)2](ClO4)2·2.5H2O (1), [Cu3(H2O)6(Hntp)2](CF3SO3)2·3.5H2O (2), [Cu3(H2O)9(Hntp)2](SO4)·4H2O (3), (H5O2)[Cu3Cl3(H2O)3(Hntp)2] (4), and (H5O2)[Cu3(NO3)3(H2O)3(Hntp)2] (5). The structure of the polynuclear complexes show the presence of well-defined capsules formed by three Cu(II) cations and two protonated Hntp2− ligands in a tritopic arrangement. The counter ion of the copper salt used in the preparation influences the final structure, by changing the connection between the capsules. In 1 and 2 the capsules are joint together by means of carboxylate–copper interactions with no intervention of the anions. In the case of 3, sulfate anions provide intercapsule interactions through hydrogen bonds. Chloride and nitrate have a different role in the structure of the capsules. 4 is an anionic capsule due to the participation of Cl− in the copper coordination sphere. It also provides further capsule–capsule interaction through long-distance Cu–Cl bonds. 5 is a special case because nitrate is a bridging ligand, being bidentate towards one copper atom and monodentate towards another copper ion of an adjacent capsule.