Tuning Carbon Dioxide Adsorption Affinity of Zinc(II) MOFs by Mixing Bis(pyrazolate) Ligands with N-Containing Tags

The four zinc(II) mixed-ligand metal-organic frameworks (MIXMOFs) Zn(BPZ)x(BPZNO2)1-x, Zn(BPZ)x(BPZNH2)1-x, Zn(BPZNO2)x(BPZNH2)1-x, and Zn(BPZ)x(BPZNO2)y(BPZNH2)1-x-y (H2BPZ = 4,4′-bipyrazole; H2BPZNO2 = 3-nitro-4,4′-bipyrazole; H2BPZNH2 = 3-amino-4,4′-bipyrazole) were prepared through solvothermal routes and fully investigated in the solid state. Isoreticular to the end members Zn(BPZ) and Zn(BPZX) (X = NO2, NH2), they are the first examples ever reported of (pyr)azolate MIXMOFs. Their crystal structure is characterized by a three-dimensional open framework with one-dimensional square or rhombic channels decorated by the functional groups. Accurate information about ligand stoichiometric ratio was determined (for the first time on MIXMOFs) through integration of selected ligands skeleton resonances from 13C cross polarized magic angle spinning solid-state NMR spectra collected on the as-synthesized materials. Like other poly(pyrazolate) MOFs, the four MIXMOFs are thermally stable, with decomposition temperatures between 708 and 726 K. As disclosed by N2 adsorption at 77 K, they are micro-mesoporous materials with Brunauer-Emmett-Teller specific surface areas in the range 400-600 m2/g. A comparative study (involving also the single-ligand analogues) of CO2 adsorption capacity, CO2 isosteric heat of adsorption (Qst), and CO2/N2 selectivity in equimolar mixtures at p = 1 bar and T = 298 K cast light on interesting trends, depending on ligand tag nature or ligand stoichiometric ratio. In particular, the amino-decorated compounds show higher Qst values and CO2/N2 selectivity vs the nitro-functionalized analogues; in addition, tag "dilution" [upon passing from Zn(BPZX) to Zn(BPZ)x(BPZX)1-x] increases CO2 adsorption selectivity over N2. The simultaneous presence of amino and nitro groups is not beneficial for CO2 uptake. Among the compounds studied, the best compromise among uptake capacity, Qst, and CO2/N2 selectivity is represented by Zn(BPZ)x(BPZNH2)1-x

Formation of dibutyl carbonate and butylcarbamate via CO2 insertion in titanium(IV) butoxide and reaction with n-butylamine

The species resulting from insertion of 12CO2 and 13CO2 into titanium(IV) butoxide is for the first time fully characterized by means of infrared and nuclear magnetic resonance spectroscopy. Results show formation of Ti-monobutylcarbonate, that easily undergoes nucleophilic attack by an aliphatic amine. The hydrolysis of the resulting species produces butylcarbamate and dibutylcarbonate as the only main products. Characterization results of the carbonate-like adduct, along with its reactivity with amine molecules open the route to new ways of CO2 utilization as building block for valuable organic compounds

Production of dibutyl carbonate by insertion of CO2 in titanium(IV) tetrabutoxide

The species resulting from insertion of 12CO2 and 13CO2 into titanium(IV) butoxide is for the first time fully characterized by means of infrared and nuclear magnetic resonance spectroscopy. Results show formation of Ti-monobutylcarbonate, that easily undergoes nucleophilic attack by an aliphatic amine. The hydrolysis of the resulting species produces butylcarbamate and dibutylcarbonate as the only main products. Characterization results of the carbonate-like adduct, along with its reactivity with amine molecules open the route to new ways of CO2 utilization as building block for valuable organic compounds

Nitrogen doped Titanium dioxide active in photocatalytic reactions with visible light. A multi technique characterisation of differently prepared materials

Nitrogen-doped TiO2 materials were successfully prepared following three different preparation routes (sol-gel, mechanochemistry, and oxidation of TiN) and characterized by X-ray diffraction, electron microscopy, and various spectroscopic techniques. All samples absorb visible light, and the one obtained via sol-gel, showing the anatase structure, is the most active in the decomposition of organic compounds under visible light. Various nitrogen-containing species have been observed in the materials, whose presence and abundances depends on the preparative route. Ammonium NH4 + ions are residual of the synthesis using ammonium salts (sol-gel, mechanochemistry) and are quite easily eliminated, as shown by the parallel behavior of both NMR and XPS spectra. Cyanide CN- ions form at high temperature in parallel with the phase transition of the solid to rutile. Molecular nitric oxide forms in the case of materials exhibiting close porosity. The already reported bulk radical species, Nb \u2022, is the only paramagnetic center observed in all types of samples, and is responsible for the visible light sensitization of TiO2. A mechanism for the formation of such a species in chemically prepared N-doped TiO2 materials is for the first time proposed based on the reduction of Nitric Oxide (NO) at oxygen vacancie

Blue and red shift hydrogen bonds in crystalline cobaltocinium complexes

Typical hydrogen-bonded cobaltocinium salts of formula [Cp2Co+][A(-)] [with Cp = C5H5 and A = PF6 (1), AsF6 (2), SbF6 (3), I (4), I-3 (5), Co(CN)(6) (6), Co(CO)(4) (7), Br-3 (8), FeI4 (9) and HCl2 (10)] were studied by means of a combined structural, spectroscopic (IR, Raman, solid-state NMR) and theoretical approach. The solid-state vibrational spectra show blue or red shift hydrogen bond behavior depending on the anionic species, i.e. high-or low-frequency nu(CH) shift with respect to the solution value. The crystal structure of the new complex [Cp2Co+][SbF6-], a blue-shifted system, is reported while the [Cp2Co+][I-] complex, a red-shifted system disordered at room temperature, reveals a novel ordered polymorph at 150 K. The weak interactions (C center dot center dot center dot H, H center dot center dot center dot H, H center dot center dot center dot X, C center dot center dot center dot X) between cations and anions were analyzed by means of the Hirshfeld surfaces model, which permits their clear graphic visualization. HS fingerprint plots and normalized contact distances visually describe the difference between blue-and red-shifted complexes. Chemical shift tensors and shielding anisotropy values of the Cp carbon atoms, extracted from C-13 CPMAS solid-state NMR spectra, allow the evaluation of Cp rotational motions which are related to the intermolecular contact extent. Finally, a DFT computational model is able to rationalize all the experimental data. It shows that the prevalence of one between two forces, that is, the attractive polarization of C-H bonds and the repulsive effect of electronic clouds, leads to the blue or red shift phenomenon