Synthesis of aromatic polynitroso compounds: Towards functional azodioxy-linked porous polymers.

The polymerization property of aromatic polynitroso compounds could be used to create azodioxy porous networks with possible application for the adsorption of CO2, the main greenhouse gas. Herein, we report the synthesis and characterization of new aromatic polynitroso compounds, with para-nitroso groups attached to the triphenylbenzene, triphenylpyridine, triphenyltriazine and triphenylamine moiety. The synthesis of the pyridine-based trinitroso compound was performed by reduction of the corresponding trinitro derivative to N-arylhydroxylamine followed by oxidation to the trinitroso product. For the synthesis of the benzene- and triazine-based trinitroso compounds, a novel synthetic strategy was implemented, which included cyclotrimerization of the 4-nitrosoacetophenone and 4-nitrosobenzonitrile, respectively. Reduction of the trinitro compound with triphenylamine unit produced the dinitroso product. In a solid state, all synthesized compounds form E-azodioxy oligomers or polymers. While azodioxy polymer with triphenylbenzene moiety is an amorphous solid, other azodioxy oligomers and polymers displayed sharp diffraction peaks pointing to their crystalline nature. A computational study indicated that eclipsed AA configurations are preferred over staggered AB and inclined AA' configurations. The serrated layers may be the most likely outcome when/if 2D layers form an organized polymer network of azodioxy linked triphenyltriazine-based building blocks.

Tailoring Enhanced Elasticity of Crystalline Coordination Polymers.

The approach for enhancing the elasticity of crystals with suboptimal elastic performances through a rational design was presented. A hydrogen-bonding link was identified as a critical feature in the structure of the parent material, the Cd(II) coordination polymer [CdI2(I-pz)2] n (I-pz = iodopyrazine), to determine the mechanical output and was modified via cocrystallization. Small organic coformers resembling the initial organic ligand but with readily available hydrogens were selected to improve the identified link, and the extent of strengthening the critical link was in an excellent correlation with the delivered enhancement of elastic flexibility materials.

Synthesis and Characterization of Benzene- and Triazine-Based Azo-Bridged Porous Organic Polymers.

Porous organic polymers incorporating nitrogen-rich functionalities have recently emerged as promising materials for efficient and highly selective CO2 capture and separation. Herein, we report synthesis and characterization of new two-dimensional (2D) benzene- and triazine-based azo-bridged porous organic polymers. Different synthetic approaches towards the porous azo-bridged polymers were tested, including reductive homocoupling of aromatic nitro monomers, oxidative homocoupling of aromatic amino monomers and heterocoupling of aromatic nitro monomers and a series of aromatic diamines of different lengths and rigidity. IR spectroscopy, 13C CP/MAS NMR spectroscopy, powder X-ray diffraction, elemental analysis, thermogravimetric analysis, nitrogen adsorption-desorption experiments and computational study were used to characterize structures and properties of the resulting polymers. The synthesized azo-bridged polymers are all amorphous solids of good thermal stability, exhibiting various surface areas (up to 351 m2 g-1). The obtained results indicated that the synthetic methods and building units have a pronounced effect on the porosity of the final materials. Reductive and oxidative homocoupling of aromatic nitro and amino building units, respectively, lead to 2D azo-bridged polymers of substantially higher porosity when compared to those produced by heterocoupling reactions. Periodic DFT calculations and Grand-canonical Monte Carlo (GCMC) simulations suggested that, within the used approximations, linear linkers of different lengths do not significantly affect CO2 adsorption properties of model azo-bridged polymers.

Exploring the Co-Crystallization Landscape of One-Dimensional Coordination Polymers Using a Molecular Electrostatic Potential-Driven Approach.

The ability of coordination polymers (CPs) to form multicomponent heteromeric materials, where the key structural features of the parent CP are retained, has been explored via molecular electrostatic potential-driven co-crystallization technologies. Thirteen co-formers presenting hydrogen-bond donors activated through a variety of electron-withdrawing functionalities were employed, and the extent of activation was evaluated using molecular electrostatic potential values. Attempted co-crystallizations of the seven most promising co-formers with a family of nine CPs ([CdX'2(X-pz)2]n; X' = I, Br, and Cl; X = I, Br, and Cl) resulted in six successful outcomes; all four of the structurally characterized compounds displayed the intended hydrogen bond. The rationalization of the main structural features revealed that strict structural and electrostatic requirements were imposed on effective co-formers; only co-formers with highly activated hydrogen-bond donors, and with a 1,4-orientation of electron-withdrawing moieties bearing effective acceptor sites, were successfully implemented into the three-dimensional architectures composed of one-dimensional building units of CPs.

Exploring and predicting intermolecular binding preferences in crystalline Cu(ii) coordination complexes.

A simple model focusing on electrostatic contributions to interaction energies was found to be very effective for rationalizing the appearance of specific supramolecular interactions in a series of Cu(ii) coordination compounds. The experimental space was provided by a combination of Cu(ii) cations with acac-based anions (hexafluoracetylacetonato and trifluoracetylacetonato) and a series of pyridine-oxime ligands (3-pyridinealdoxime, methyl 3-pyridyl ketoxime, 4-pyridinealdoxime, methyl 4-pyridyl ketoxime, phenyl 4-pyridyl ketoxime). The calculated molecular electrostatic potential (MEP) values at competing hydrogen-bond acceptor sites, for ten structurally characterized complexes, provided guidelines for predicting supramolecular connectivity in cases when the MEP difference exceeded certain cut-off values, while two different and well-defined outcomes are possible within the so called 'grey zone', delineated by a range of MEP differences. It was also shown that the structural outcome within this region is determined by the influence of relatively weak, but distinct, auxillary interactions.

Mechanically Responsive Crystalline Coordination Polymers with Controllable Elasticity.

Crystalline coordination polymers tend to be brittle and inelastic, however, we now describe a family of such compounds that are capable of displaying mechanical elasticity in response to external pressure. The design approach successfully targets structural features that are critical for producing the desired mechanical output. The elastic crystals all comprise 1D cadmium(II) halide polymeric chains with adjacent metal centres bridged by two halide ions resulting in the required stacking interactions and short "4 Å" crystallographic axes. These polymeric chains (structural "spines") are further organized via hydrogen bonds and halogen bonds perpendicular to the direction of the chains. By carefully altering the strength and the geometry of these non-covalent interactions, we have demonstrated that it is possible to control the extent of elastic bending in crystalline coordination compounds.

Mechanochemical reactions studied by in situ Raman spectroscopy: base catalysis in liquid-assisted grinding.

In situ Raman spectroscopy was employed to study the course of a mechanochemical nucleophilic substitution on a carbonyl group. We describe evidence of base catalysis, akin to catalysis in solution, achieved by liquid-assisted grinding.