An Mg Solid Solution Affords a Less Toxic and More Stable ZIF-8

Porous coordination polymers (PCPs) and metal–organic frameworks (MOFs) are promising vehicles for drug delivery, provided that their metallic and organic constituents are biologically safe and their structure is stable under physiological conditions. ZIF-8 is the archetypical PCP for such applications; however, high Zn content causes concerns about its long-term use, while poor stability at acidic pH might limit the controlled delivery of active ingredients to target tissues. The combination of Zn²⁺ and Mg²⁺ affords a mixed-metal ZIF-8 analogue with up to 20% of the alkali heart. Besides reducing the dose of zinc, the solid solution shows increased water stability under mildly acidic conditions. DFT calculations point to a reduction of the MOF’s polarizability as a cause for the observed behavior. Ideally, the changes in the Zn/Mg ratio would correspond to a modulation of such stability; however, equal stability improvement was measured over a range of compositions.