Introducing a Longer versus Shorter Acylhydrazone Linker to a Metal-Organic Framework: Parallel Mechanochemical Approach, Nonisoreticular Structures, and Diverse Properties

A 20-angstrom-long diacylhydrazone linker was used for the first time as a building block for the construction of a metal-organic framework (MOF). The terephthalaldehyde di-isonicotinoylhydrazone (tdih ) is considerably longer than its 11-angstrom-long monoacylhydrazone counterpart, 4-pyridinecarboxaldehyde isonicotinoylhydrazone (pcih), used so far as a MOF linker. By utilizing the two ditopic hydrazone linkers providing linear connectivity, two nonisoreticular cadmium-organic frameworks, {[Cd-2(oba)(2)(hydrazone)(2)]}(n) (with oba = 4,4'-oxybis(benzenedicarboxylate) colinker) were obtained by solution and mechanochemical methods. In spite of the same secondary building units, the frameworks differ in dimensionality as well as exhibit various stability and adsorption behavior, which are compared and discussed. The insights into structure- property relationships are provided by single-crystal X-ray diffraction (SC-XRD), temperature-dependent powder XRD, thermogravimetric analysis, CO2 (at 195 K), N-2 (at 77 K) and H2O (at 298 K) gas adsorption measurements, as well as quasiequilibrated temperature-programmed desorption and adsorption (QE-TPDA). The work opens possibilities to synthesize new functional materials based on the longer linker.