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Suitably functionalized porous matrices represent versatile platforms to support well-dispersed catalytic centers. In the present study, porous organic polymers (POPs) containing phosphine oxide groups were fabricated to bind transition metals and to be investigated for potential electrocatalytic applications. Cross-linking of mono- and di-phosphine monomers with multiple phenyl substituents was subject to the Friedel-Crafts (F-C) reaction and the oxidation process, which generated phosphine oxide porous polymers with pore capacity up to 0.92 cm3/g and a surface area of about 990 m2/g. The formation of the R3P·BH3 borohydride adduct during synthesis allows to extend the library of phosphine-based monomeric entities when using FeCl3. The porous polymers were loaded with 0.8-4.2 w/w % of cobalt(II) and behaved as hydrogen evolution reaction (HER) catalysts with a Faradaic efficiency of up to 95% (5.81 × 10-5 mol H2 per 11.76 C) and a stable current density during repeated controlled potential experiments (CPE), even though with high overpotentials (0.53-0.68 V to reach a current density of 1 mA·cm-2). These studies open the way to the effectiveness of tailored phosphine oxide POPs produced through an inexpensive and ecofriendly iron-based catalyst and for the insertion of transition metals in a porous architecture, enabling electrochemically driven activation of small molecules.

Achieving sophisticated juxtaposition of geared molecular rotors with negligible energy-requirements in solids enables fast yet controllable and correlated rotary motion to construct switches and motors. Our endeavor was to realize multiple rotors operating in a MOF architecture capable of supporting fast motional regimes, even at extremely cold temperatures. Two distinct ligands, 4,4′-bipyridine (bipy) and bicyclo[1.1.1]pentanedicarboxylate (BCP), coordinated to Zn clusters fabricated a pillar-and-layer 3D array of orthogonal rotors. Variable temperature XRD, 2H solid-echo, and 1H T1 relaxation NMR, collected down to a temperature of 2 K revealed the hyperfast mobility of BCP and an unprecedented cascade mechanism modulated by distinct energy barriers starting from values as low as 100 J mol-1 (24 cal mol-1), a real benchmark for complex arrays of rotors. These rotors explored multiple configurations of conrotary and disrotary relationships, switched on and off by thermal energy, a scenario supported by DFT modeling. Furthermore, the collective bipy-ring rotation was concerted with the framework, which underwent controllable swinging between two arrangements in a dynamical structure. A second way to manipulate rotors by external stimuli was the use of CO2, which diffused through the open pores, dramatically changing the global rotation mechanism. Collectively, the intriguing gymnastics of multiple rotors, devised cooperatively and integrated into the same framework, gave the opportunity to engineer hypermobile rotors (107 Hz at 4 K) in machine-like double ligand MOF crystals.

Coordination-driven self-assembly of metals and properly designed molecular linkers can lead to the formation of discrete supramolecules of specific geometrical shapes, which can in turn self-assemble into complex crystalline architectures enabling the fabrication of porous materials. We reported the formation of cyclic hexameric structures of Ag(I) or Cu(I) coordinated with multipodal bis(pyrazolyl)methane moiety. The anions play a crucial role in the arrangement of the cyclic hexamers forming two families of permanently porous 3D crystalline structures, that are able to reversibly entrap vapors and gases. The crystalline structures contain cavities with Platonic solid geometries, which can absorb reversibly CO2 and CH4. The localization of the gas molecules within the cavities was investigated by 2D 1H−13C solid state NMR on samples loaded with enriched 13CO2, showing that the cavities are accessible to guest molecules from the gas phase. Moreover, we prepared new 1D metal–organic frameworks formed by the packing of discrete metal-organic nanotubes through weak hydrophobic interactions. The self-assembly process leads to the formation of microcrystals and nanorods depending on the synthesis conditions. The CO2 absorption kinetics drastically increased from the micrometric crystals to the nanorods, highlighting the effects of the particle sizes. We have recently discovered an innovative property of porous materials: the intrinsic dynamics for the presence of fast molecular rotors in their structure with correlation times on the nanosecond scale. Solid state NMR played an important role for the determination of motional trajectories of chemical groups in the frameworks. We achieved the systematic regulation of the rotor speed by the absorption of chemical species such as I2, opening perspectives in responsive materials. Ref. J. Am. Chem. Soc. 2014,136,14883; J. Am. Chem. Soc. 2012,134, 9142; J. Am. Chem. Soc. 2014,136,618.