Self-assembly and anion-exchange properties of a discrete cage and 3D coordination networks based on cage structures

By using tridentate ligand 4-(3-pyridinyl)-1,2,4-triazole (pytrz), cage-like complexes of {[Cu(mu2-pytrz)2](ClO4)(SO4)0.5C2H5OH.0.25 H2O}6 (1), {[Cu3(mu3-pytrz)4(mu2-Cl)2(H2O)2](ClO4)2Cl(2).2 H2O}n (2), and {[Cu3(mu3-pytrz)3(mu3-O)(H2O)3](ClO4)2.5(BF4)(1.5)5.25 H2O}n (3) have been synthesized with different copper(II) salts. Complex 1 represents the second example of a M6L12 metal-organic octahedron with an overall Th symmetry. Complex 2 is constructed from a 3(8) cage-building unit (CBU) and each CBU connects six neighboring cages to give the first 3D metal-organic framework (MOF) based on octahedral M6L12. Complex 3 is built from Cu24(pytrz)12 CBUs with the trinuclear copper clusters serving as second building units (SBUs) and decorating each corner of the M24L12 polyhedron. The Cu24(pytrz)12 building unit is linked by extra ligands to give an extended 3D framework that has the formula Cu24(pytrz)24 and possesses a CaB6 topology. The mixed anions ClO4- and BF4- in 3 are both included in the inner cavity of the cage and can be completely exchanged by ClO4- through the open windows of the cage, as evidenced by the crystal structure of the 3D MOF {[Cu3(mu3-pytrz)3(mu3-O)(H2O)3](ClO4)(4)4.5 H2O}n (4). Complex 4 can also be synthesized when employing 1 as a precursor in an extensive study of the anion-exchange reaction. This represents the first successful conversion of a discrete cage into a 3D coordination network based on a cage structure. Complex 2 remains invariable during anion-exchange reactions because uncoordinated Cl- ions are located in the comparatively small inner cavity.