Molecular tectonics of metal-organic frameworks (MOFs): A rational design strategy for unusual mixed-connected network topologies

To systematically explore the higher-dimensional network structures with mixed connectivity, a series of two-dimensional (2D) and three-dimensional (3D) metal-organic frameworks (MOFs) with unusual (3,6)-connected net topologies are presented. These crystalline materials include [{[Mn(btza)(2)(H2O)(2)]center dot 2H(2)O}(n)] (1), [{[Zn(btza)(2)(H2O)(2)]center dot 2H(2)O}(n)] (2), [{[Cu-(btza)(2)]center dot H2O}(n)] (3), and [{[Cd-(btza)(2)]center dot 3H(2)O}(n)] (4), which have been successfully assembled through a pre-designed three-connected organic component bis(1,2,4-triazol-1-yl) acetate (btza) with a variety of octahedral metal cores based on the modular synthetic methodology. The topological paradigms shown in this work cover the 2D CdCl2, 3D (4(2).6)(2)(4(4).6(2).8(7).10(2)), and pyrite (pyr) types. That is, when properly treated with the familiar first-row divalent metal ions, btza may perfectly furnish the coordination spheres for effective connectivity to result in diverse (3,6)-connected nets. Beyond this, a detailed analysis of network topology for all known 3D (3,6)-connected frameworks in both inorganic and inorganic-organic hybrid materials is described. Specific network connectivity of these MOFs indicates that the metal centers represent the most significant and alterable factor in structural assembly, although they show reliable and similar geometries. In this context, the combination of the distinct d(10) Ag-I ion with btza in different solvents affords two isomorphous MOFs [{[Ag-(btza)]center dot glycol}(n)] (5) and [{[Ag-(btza)]center dot CH3OH}(n)] (6) with a binodal 4-connected 3D SrAl2 (sra) topology. The network structures of MOFs 1-3 and 5 turn out to be more complicated and interesting if one considers the hydrogen bonding between the host coordination frameworks and the intercalated solvent molecules. Furthermore, the role of the included solvents in the generation and stabilization of MOFs 1-6 is also investigated.