Tuning trityl radical content in multivariate metal-organic radical frameworks

Persistent organic radicals are attractive building blocks for constructing functional metal-organic frameworks owing to their unique electronic, magnetic, and optical properties. However, tuning the ratio of open- and closed-shell organic linkers within a single metal-organic radical framework (MORF) has remained unexplored. Herein, we report the synthesis of multivariate MORFs incorporating perchlorotriphenylmethyl tricarboxylate (PTMTC) linkers in both their radical (PTMTC^R) and non-radical (PTMTC^NR) forms within the same crystalline structure. By simply varying the ratio of the starting PTMTC^R and PTMTC^NR ligands, we obtained three different multivariate MORFs (MORF-40, MORF-60, and MORF-80) with radical contents of ca. 40, 60, and 80%, respectively, while preserving the same framework architecture. Single-crystal X-ray diffraction directly reveals the statistical co-occupancy of PTMTC^R and PTMTC^NR linkers at the same crystallographic site in MORF-40, providing a rare example of a crystalline framework containing both open- and closed-shell organic building blocks. Complementary Raman spectroscopy, electron paramagnetic resonance, fluorescence microscopy, and Kelvin probe force microscopy confirm the systematic variation in radical content across the series. This ability to tune the radical content without altering the underlying framework architecture provides a versatile strategy for modulating the electronic, optical, and magnetic properties of multivariate metal-organic radical frameworks.