Chemically Resistant,Shapeable, and Conducting Metal‐Organic Gels and Aerogels Built from Dithiooxamidato Ligand

Metal‐organic gels (MOGs) appear as a blooming alternative to well‐known metal‐organic frameworks (MOFs). Porosity of MOGs has a microstructural origin and not strictly crystalline like in MOFs; therefore, gelation may provide porosity to any metal‐organic system, including those with interesting properties but without a porous crystalline structure. The easy and straightforward shaping of MOGs contrasts with the need of binders for MOFs. In this contribution, a series of MOGs based on the assembly of 1D‐coordination polymer nanofibers of formula [M(DTA)]_n (M^II: Ni, Cu, Pd; DTA: dithiooxamidato) are reported, in which properties such as porosity, chemical inertness, mechanical robustness, and stimuli‐responsive electrical conductivity are brought together. The strength of the M? S bond confers an unusual chemical resistance, withstanding exposure to acids, alkalis, and mild oxidizing/reducing chemicals. Supercritical drying of MOGs provides ultralight metal‐organic aerogels (MOAs) with densities as low as 0.03 g cm^?3 and plastic/brittle behavior depending on the nanofiber aspect ratio. Conductivity measurements reveal a semiconducting behavior (10^?12 to 10^?7 S cm^?1 at 298 K) that can be improved by doping (10^?5 S cm^?1). Moreover, it must be stressed that conductivity of MOAs reversibly increases (up to 10^?5 S cm^?1) under the presence of acetic acid.     

Massive Anisotropic Thermal Expansion and Thermo‐Responsive Breathing in Metal–Organic Frameworks Modulated by Linker Functionalization

Functionalized metal–organic frameworks (fu‐MOFs) of general formula [Zn₂(fu‐L)₂dabco]_n show unprecedentedly large uniaxial positive and negative thermal expansion (fu‐L = alkoxy functionalized 1,4‐benzenedicarboxylate, dabco = 1,4‐diazabicyclo[2.2.2]octane). The magnitude of the volumetric thermal expansion is more comparable to property of liquid water rather than any crystalline solid‐state material. The alkoxy side chains of fu‐L are connected to the framework skeleton but nevertheless exhibit large conformational flexibility. Thermally induced motion of these side chains induces extremely large anisotropic framework expansion and eventually triggers reversible solid state phase transitions to drastically expanded structures. The thermo‐responsive properties of these hybrid solid–liquid materials are precisely controlled by the choice and combination of fu‐Ls and depend on functional moieties and chain lengths. In principle, this combinatorial approach allows for a targeted design of extreme thermo‐mechanical properties of MOFs addressing the regime between crystalline solid matter and the liquid state.