Microporous mixed-metal layer-pillared [Zn_1-xCu _x(bdc)(dabco)_0.5] MOFs: Preparation and characterization

A series of mixed-metal layer-pillared MOFs of general formula [Zn _1-xCu_x(bdc)(dabco)_0.5] (bdc = 1,4-benzenedicarboxylate, dabco = 1,4-diazabicyclo[2.2.2]octane, 0 < x < 1) have been synthesized by a solvothermal approach. Different amounts x of Cu²⁺ were introduced to substitute for Zn²⁺ centers. The prepared mixed-metal MOFs were shown to be structurally very similar to their parent monometallic [Zn(bdc)(dabco)_0.5] and [Cu(bdc)(dabco) _0.5] frameworks by single-crystal and powder X-ray diffraction studies. Interestingly, upon inclusion of copper, a distortion of the paddle-wheel units is observed. In addition, the incorporation of Cu ²⁺ ions into the [Zn₂(bdc)(dabco)_0.5] framework and the formation of heterometallic Zn-Cu paddle-wheel units along with monometallic Cu-Cu and Zn-Zn units in the prepared mixed-metal MOFs were confirmed by continuous-wave EPR spectroscopy. The synthesized materials [Zn_1-xCu_x(bdc)(dabco)_0.5] are thermally stable up to 260 °C and exhibit permanent porosity with BET surface areas in the range of 800-2430 m²g^-1.