Unusual cadmium(II)–adenine paddle-wheel units for the construction of a metal-organic framework with mog topology

Crystal Engineering and Self-Assembled Nanoring Formation with Purine-CdII /HgII Supramolecular Frameworks

We report three complexes of CdII and HgII with two purine rare tautomers, N9-(pyridin-2-ylmethyl)-N6 -methoxyadenine, L1 and N7-(pyridin-2-ylmethyl)-N6 -methoxyadenine, L2, highlighting diverse crystallographic signatures exhibited by them. Influence of substituents, binding sites, steric effects and metal salts on the different modes of binding enabled an insight into metal-nucleobase interactions. L1 interacted with two and three equivalents of Cd(NO3 )2 .4H2 O and HgCl2 , respectively, while L2 interacted with two equivalents of HgCl2 , altogether leading to three different complexes (1 [C48 H48 Cd6 N34 O50 ], 2 [C12 H12 Cl4 Hg2 N6 O] and 3 [C12 H12 Cl2 HgN6 O]) possessing varied dimensionality and stabilising interactions. The photoluminescent properties of these coordination frameworks have also been probed. Notably, nanoring-like structures were obtained, as a result of self-assembly of 3 when investigated by transmission electron microscopy, additionally supported by molecular dynamics simulations.

Tetrahedral Imidazolate Frameworks with Auxiliary Ligands (TIF-Ax): Synthetic Strategies and Applications

Zeolitic imidazolate frameworks (ZIFs) are an important subclass of metal-organic frameworks (MOFs). Recently, we reported a new kind of MOF, namely tetrahedral imidazolate frameworks with auxiliary ligands (TIF-Ax), by adding linear ligands (Hint) into the zinc-imidazolate system. Introducing linear ligands into the M2+-imidazolate system overcomes the limitation of imidazole derivatives. Thanks to the synergistic effect of two different types of ligands, a series of new TIF-Ax with interesting topologies and a special pore environment has been reported, and they have attracted extensive attention in gas adsorption, separation, catalysis, heavy metal ion capture, and so on. In this review, we give a comprehensive overview of TIF-Ax, including their synthesis methods, structural diversity, and multi-field applications. Finally, we also discuss the challenges and perspectives of the rational design and syntheses of new TIF-Ax from the aspects of their composition, solvent, and template. This review provides deep insight into TIF-Ax and a reference for scholars with backgrounds of porous materials, gas separation, and catalysis.

Two Cd-Based Luminescent Coordination Polymers Constructed from a Truncated Linker

Two cadmium coordination polymers, WSU-30 and WSU-31, were synthesized through solvothermal methods by using the low-symmetry TPE-based linker m-H₄ETTC. The m-H₄ETTC linker and both coordination polymers were fully characterized by using single-crystal X-ray diffraction, infrared spectroscopy, and photoluminescent emission spectroscopy. Structural analysis of WSU-30 and WSU-31 showed that each compound contains previously unknown tetranuclear cadmium(II) secondary building units. The topological analysis revealed that the 4,8-connected net of WSU-30 contains the underlying topology, alb-4,8-P21/c-1, while the mixed linker WSU-31 possesses a 3,10-connected net known as 3,10T31 topology. If the m-ETTC linker is considered as two 3-connected nodes, WSU-30 possesses a very rare 3,3,8-connected 3,3,8T25 topology, and WSU-31 possesses a previously unknown 3,12-connected net, named 3,12T61.

Shedding Light on the Protonation States and Location of Protonated N Atoms of Adenine in Metal-Organic Frameworks

We report the syntheses and structures of five metal–organic frameworks (MOFs) based on transition metals (Ni^II, Cu^II, and Zn^II), adenine, and di-, tri-, and tetra-carboxylate ligands. Adenine, with multiple N donor sites, was found to coordinate to the metal centers in different binding modes including bidentate (through N7 and N9, or N3 and N9) and tridentate (through N3, N7, and N9). Systematic investigations of the protonation states of adenine in each MOF structure via X-ray photoelectron spectroscopy revealed that adenine can be selectively protonated through N1, N3, or N7. The positions of H atoms connected to the N atoms were found from the electron density maps, and further supported by the study of C–N–C bond angles compared to the literature reports. DFT calculations were performed to geometrically optimize and energetically assess the structures simulated with different protonation modes. The present study highlights the rich coordination chemistry of adenine and provides a method for the determination of its protonation states and the location of protonated N atoms of adenine within MOFs, a task that would be challenging in complicated adenine-based MOF structures.

The protonation states and positions of hydrogen atoms in five adenine-based metal−organic frameworks were revealed using geometrical studies based on single-crystal XRD data supported by XPS spectra and DFT calculations.

Silver-induced reconstruction of an adeninate-based metal-organic framework for encapsulation of luminescent adenine-stabilized silver clusters

Bright luminescent silver-adenine species were successfully stabilized in the pores of the MOF-69A (zinc biphenyldicarboxylate) metal-organic framework, starting from the intrinsically blue luminescent bio-MOF-1 (zinc adeninate 4,4'-biphenyldicarboxylate). Bio-MOF-1 is transformed to the MOF-69A framework by selectively leaching structural adenine linkers from the original framework using silver nitrate solutions in aqueous ethanol. Simultaneously, bright blue-green luminescent silver-adenine clusters are formed inside the pores of the recrystallized MOF-69A matrix in high local concentrations. The structural transition and concurrent changes in optical properties were characterized using a range of structural, physicochemical and spectroscopic techniques (steady-state and time-resolved luminescence, quantum yield determination, fluorescence microscopy). The presented results open new avenues for exploring the use of MOFs containing luminescent silver clusters for solid-state lighting and sensor applications.

Crystal engineering with a purine rare tautomer: structures and luminescence properties

Cadmium interacts with purine nucleobases through N7 imino nitrogen and alters their amino–imino tautomeric equilibrium. Herein, we report unique crystallographic signatures and luminescence properties of cadmium complexes of N9-benzyl-N⁶-methoxyadenine exhibiting a variety of coordination numbers and spatial geometries.