Versatile Tailoring of NH₂ -Containing Metal-Organic Frameworks with Paddle-Wheel Units

An amine-containing non-interpenetrating pillar-layer framework, [Zn₂ (dbtcb)(L1)]⋅x solvent (1), has been synthesized from Zn(NO₃ )₂ and the ligands 1,4-dibromo-2,3,5,6-tetrakis(4-carboxyphenyl)benzene (H₄ DBTCB) and 2,5-bis(4-pyridyl)aniline (L1). The [Zn₂ (COO)₄ ] secondary building units (SBUs) are bridged by DBTCB to form two-dimensional layers that are linked by L1 ligands acting as pillars to form a three-dimensional network. This NH₂ -containing framework can undergo versatile tailoring through post-synthetic covalent modification, solvent-assisted linker exchange (SALE), and single-crystal-to-single-crystal (SC-SC) transmetalation reactions. Acetamide-functionalized [Zn₂ (L2)(dbtcb)]⋅xsolvent (2) could be obtained by direct synthesis from Zn(NO₃ )₂ , N-acetyl-2,5-bis(4-pyridyl)aniline (L2) and H₄ DBTCB. Importantly, compound 1 with pure NH₂ ligands as pillars could be obtained by SALE of 2 with L1 in DMSO solution. The transmetalation reactions of 1 with Cu^II , Ni^II , and Co^II were studied; inductively coupled plasma-atomic emission (ICP) analysis revealed that 1 underwent almost complete SC-SC transmetalation with Cu^II within 30 h, whereas with Ni^II and Co^II only 70 and 80 % substitutions were achieved. Photoluminescence studies revealed that 1 and 2 display yellow-green and UV emission, respectively, under a UV lamp. Furthermore, the photoluminescent properties could be tuned by introducing mixed pillar amino ligands L1 and L2 into the MOF to produce multivariate (MTV) MOF 3 displaying overall orange emission.