Sequential Transformation of Zirconium(IV)-MOFs into Heterobimetallic MOFs Bearing Magnetic Anisotropic Cobalt(II) Centers

Heterometallic metal-organic frameworks (MOFs) allow the precise placement of various metals at atomic precision within a porous framework. This new level of control by MOFs promises fascinating advances in basic science and application. However, the rational design and synthesis of heterometallic MOFs remains a challenge due to the complexity of the heterometallic systems. Herein, we show that bimetallic MOFs with MX₂ (INA)₄ moieties (INA=isonicotinate; M=Co²⁺ or Fe²⁺ ; X=OH^- , Cl^- , Br^- , I^- , NCS^- , or NCSe^- ) can be generated by the sequential modification of a Zr-based MOF. This multi-step modification not only replaced the linear organic linker with a square planar MX₂ (INA)₄ unit, but also altered the symmetry, unit cell, and topology of the parent structure. Single-crystal to single-crystal transformation is realized so that snapshots for transition process were captured by successive single-crystal X-ray diffraction. Furthermore, the installation of Co(NCS)₂ (INA)₄ endows field-induced slow magnetic relaxation property to the diamagnetic Zr-MOF.