Practical applications involving the magnetic bistability of single-molecule magnets (SMMs) for next-generation computer technologies require nanostructuring, organization, and protection of nanoscale materials in two- or three-dimensional networks, to enable read-and-write processes. Owing to their porous nature and structural long-range order, metal–organic frameworks (MOFs) have been proposed as hosts to facilitate these efforts. Although probing the channels of MOF composites using indirect methods is well established, the use of direct methods to elucidate fundamental structural information is still lacking. Herein we report the direct imaging of SMMs encapsulated in a mesoporous MOF matrix using high-resolution transmission electron microscopy. These images deliver, for the first time, direct and unambiguous evidence to support the adsorption of molecular guests within the porous host. Bulk magnetic measurements further support the successful nanostructuring of SMMs. The preparation of the first magnetic composite thin films of this kind furthers the development of molecular spintronics.

Two isostructural microporous zwitterionic metal-organic frameworks (ZW MOFs), {[M(bdcbpy)(OH2)4]·4H2O}n with M = Mn (1) and Ni (2), were synthesized by the rational design of the flexible anionic viologen derivate, 1,1'-bis(3,5-dicarboxybenzyl)-4,4'-bipyridinium dibromide dihydrate solvate (H4bdcbpyBr2·2H2O), and its self-assembly with metal(II) acetates in an aqueous medium. Single-crystal structure analyses revealed that both compounds exhibit three-dimensional hydrogen-bonded supramolecular frameworks with one-dimensional channel pores. Significantly, the pore surfaces are lined with charge gradients employed by the ZW ligand bdcbpy(2-) leading to the adsorption of hydrogen attributed to polarization effects. The thermostabilty and activation conditions were systematically investigated by thermogravimetric analysis, differential scanning calorimetry, and powder X-ray diffraction experiments. Furthermore, repeating cycles of reversible color changes are observed in air upon irradiation with UV light attributed to the formation of viologen radicals via an intermolecular electron transfer. This work also contains an in-depth literature analysis on ZW MOFs, which shows the need for the development of alternative routes for the rational design of new porous ZW MOFs.

A viologen based ligand has been explored as a functional building block to synthesize a series of nine new zwitterionic metal–organic frameworks with this contribution reporting on their structural, thermal and photochromic properties.

Polymorphic phase transitions remain frequently undetected in routine metal-organic framework (MOF) studies; however, their discovery is of major importance in interpreting structure-property relationships. We herein report a reversible enantiotropic single-crystal to single-crystal polymorphic phase transition of a new microporous MOF [Eu(BDC)(NO3)(DMF)2]n (H2BDC = 1,4-benzenedicarboxylic acid; DMF = dimethylformamide). While modification 1LT at 170 K crystallizes in the monoclinic space group P21/c with unit cell dimensions of a = 17.673(2) Å, b = 20.023(2) Å, c = 10.555(9) Å, β = 90.129(4)°, modification 1HT at 290 K crystallizes in higher symmetry space group C2/c with unit cell dimensions of a = 17.200(7) Å, b = 10.737(4) Å, c = 10.684(4) Å, β = 90.136(2)°. This temperature-induced phase transition is accompanied by a small change in the solvent-accessible voids from 46.8 in 1LT to 49.8% in 1HT, which triggers a significant change in the adsorption properties as compared to a reported isostructural compound. Detailed investigations on the phase transition were studied with variable-temperature single-crystal X-ray diffraction (SCXRD), powder X-ray diffraction, and differential scanning calorimetry measurements. The herein-presented investigations emphasize the importance of polymorphic phase transitions in routine MOF studies originating from low-temperature SCXRD data and high-temperature physical property characterizations in avoiding the use of a wrong structure in interpreting structure-property relationships.

The isoreticular expansion and functionalization of charged-polarized porosity has been systematically explored by the rational design of eleven isostructural zwitterionic metal-organic frameworks (ZW-MOFs). This extended series of general structural composition {[M3F(L1)3(L2)1.5]•guests}n was prepared by employing the solvothermal reaction of Co and Ni tetrafluoroborates with a binary ligand system composed of zwitterionic pyridinium derivatives and traditional functionalized ditopic carboxylate auxiliary ligands (HL1•Cl = 1-(4