Inhibition, Binding of Organometallics, and Thermally Induced CO Release in an MFU-4-Type Metal-Organic Framework Scaffold with Open Bidentate Bibenzimidazole Coordination Sites.

Triazolate-based MFU-4-type metal-organic frameworks are promising candidates for various applications, of which heterogeneous catalysis has emerged as a hot topic owing to the facile post-synthetic metal and ligand exchange in Kuratowski secondary building units (SBUs). Herein, we present the largest non-interpenetrated isoreticular MFU-4-type framework CFA-19 ([Co5IICl4(H2-bibt)3]; H4-bibt = 1,1',5,5'-tetrahydro-6,6'-biimidazo[4,5-f]benzotriazole; CFA-19 = Coordination Framework Augsburg University-19) and the CFA-19-Tp derivative featuring trispyrazolylborate inhibited SBUs as a scaffold with open bibenzimidazole coordination sites at the backbone of the H4-bibt linker. The proof-of-principle incorporation of accessible MIBr(CO)3 (M = Re, Mn) sites in CFA-19-Tp was revealed by single-crystal X-ray diffraction, and a thermally induced CO release was observed for MnBr(CO)3. Deprotonation of bibenzimidazole was also achieved by the reaction with ZnEt2.

Cooperative Large-Hysteresis Spin-Crossover Transition in the Iron(II) Triazolate [Fe(ta)2] Metal-Organic Framework.

The metal-organic framework [Fe(ta)2] (Hta = 1H-1,2,3-triazole) containing Fe(II) ions and 1,2,3-triazolate ligands shows a reversible phase transition while retaining the cubic crystal symmetry and space group Fd3m (no. 227). The phase transition between room temperature (RT-[Fe(ta)2]; a = 16.6315(2) Å, V = 4600.39(8) Å3) and high temperature (HT-[Fe(ta)2]; a = 17.7566(4) Å, V = 5598.6(1) Å3) phases occurs at a temperature above 290 °C, whereas the phase transition between HT- and RT-[Fe(ta)2] starts at a temperature below 210 °C. Both [Fe(ta)2] polymorphs have identical bond topologies, but they differ by a large increase of the unit cell's volume of 22% for HT-[Fe(ta)2]. The compounds are characterized by powder X-ray diffraction, differential scanning calorimetry, and thermogravimetric analyses. Additionally, Mössbauer spectroscopy, magnetic studies, and the electronic structure of both phases are discussed in detail with respect to the spin-crossover transition from the low-spin (RT-[Fe(ta)2]) to the high-spin phase (HT-[Fe(ta)2]).

Combining Theory and Experiments To Study the Influence of Gas Sorption on the Conductivity Properties of Metal-Organic Frameworks.

With a view on adding to their use in trace gas sensing, we perform a combined experimental and theoretical study of the change of the conductivity of a metal organic framework (iron (1,2,3)-triazolate, Fe(ta)2) with the uptake of chemically inert gases. To align our first-principles calculations with experimental measurements, we perform an ensemble average over different microscopic arrangements of the gas molecules in the pores of the metal-organic framework (MOF). Up to the experimentally reachable limit of gas uptake, we find a good agreement between both approaches. Thus, we can employ theory to further interpret our experimental results in terms of changes to the parameters of the Bardeen-Shockley band theory, electron-phonon coupling (in the form of the deformation potential), bulk modulus, and carrier effective mass. We find the first of these to be most strongly influenced through the gas uptake. Furthermore, we find the changes to the deformation potential to strongly depend on the individual microscopic arrangements of molecules in the pores of the MOF. This hints at a possible synthetic engineering of the material, e.g., by closing off certain pores, for a stronger, more interpretable electric response upon gas sorption.