Highly Connected Three-Dimensional Metal-Organic Frameworks Based on Polynuclear Secondary Building Units

A series of new highly connected MOFs [Cd(L)(PBEA)(0.5)]center dot H2O (1), [Cd-2(mu(3)-OH)(L)(PBEA)] (2), [Cd-3(mu(3)-OH)(L)(2)(PBEA)(1.5)]center dot H2O (3), and [Mn(mu(2)-H2O)(L)(PBEA)0.5] (4) have been synthesized by hydrothermal reactions of 3,5-di(imidazol-1-yl)benzoic acid (HL) and 1,4-benzenediacetic acid (H(2)PBEA) with different metal salts, and these compounds were fully characterized by X-ray diffraction, IR, elemental analysis, TGA. The photoluminescence of 1-4 and magnetic property of 4 were investigated. Complex 1 is a binodal (3,8)-connected tfz-d net based on the binuclear [Cd-2(COO)(2)] secondary building units (SBU1); while 2 is a binodal (3,10)-connected 3D net based on the tetranuclear motif [Cd-4(mu(3)-OH)2(COO)(6)](SBU2). Complex 3 is the first example of trinodal (3,8,10)-connected net based on SBU1 and SBU2, which can be considered as combination of the structural features presented in 1 and 2. Complex 4 is an unprecedented (3,8)-connected net based on the binuclear species [Mn-2(mu(2)-H2O)(COO)(2)] (SBU3), which showed weak antiferromagnetic interactions between the metal ions. Complexes 1-3 were synthesized under the same experimental conditions except that different Cd(II) salts were used in the syntheses. Notably, although the counteranions of Cd(II) salts are absent from the resulting structures, yet they show subtle influence on the self-assembly process to provide different complexes. The approach of incorporating polynuclear metal cluster into highly connected frameworks and linking the SBUs by organic ligands provides opportunities for the design of new MOFs.