A crystalline and permanently porous copper phosphonate monoester framework has been synthesized from a tetraaryl trigonal phosphonate monoester linker. This material has a surface area over 1000 m g , as measured by N sorption, the highest reported for a phosphonate-based metal-organic framework (MOF). The monoesters result in hydrophobic pore surfaces that give a low heat of adsorption for CO and low calculated selectivity for CO over N and CH in binary mixtures. By careful manipulation of synthetic conditions, it is possible to selectively remove some of the monoesters lining the pore to form a hydrogen phosphonate while giving an isomorphous structure. This increases the affinity of the framework for CO giving higher ambient uptake, higher heat of adsorption, and much higher calculated selectivity for CO over both N and CH . Formation of the acid groups is noteworthy as complexation with the parent acid gives a different structure.

Four new phosphonate MOFs were prepared with cationic dimethylbipiperdinium units: [La2(H2 L)1.5(AcO)2Br·3.25H2O], α-PCMOF-21-Br; [La2(H2 L)1.5(AcO)­Cl2·5.25H2O], α-PCMOF-21-Cl; [La­(H2 L) (AcO)­Br0.5·4.93H2O­(HBr)1.11], β-PCMOF-21-Br; and [La­(H2 L) (AcO)0.5Cl·5.42H2O­(HCl)1.79], β-PCMOF-21-Cl. All frameworks have the same La phosphonate network structure but differ in the secondary anions (acetate, bromide, chloride), both coordinated and free. All frameworks showed the ability to dehydrate reversibly. Different phases result from very subtle differences in preparation; specifically, the degree of hydration of the ligand impacts the product phase even though syntheses are carried out in water. The alpha phases show a flexible structure by powder X-ray diffraction. The beta phases contain a reproducible stoichiometry of free ligands in the pores that both locks and partially fills the open structure. Alternating current impedance analysis was performed to study proton conductivity. All compounds, except for β-PCMOF-21-Cl, conduct better than 10–3 S cm–1 at 85 °C and 95% RH. The trends show that the alpha phases conduct better than the partially pore-blocked beta phases and also that the bromide structures conduct better than the chlorides. To further study the role of the anion, 35Cl and 81Br solid-state NMR was performed to elucidate dynamics. These studies also showed the ability of anions to be volatilized from the pores, and TGA–MS confirmed the loss of HX species. Impedance analysis showed a clear decrease in proton conductivity after the loss of the halides, more pronounced in the bromide-containing structures.

Working with silica nanoparticle encapsulated BODIPY and xanthene photosensitizers, we have determined that singlet oxygen spends up to 78% of its lifetime inside the nanocarriers. Our systematic investigation indicates that hydrophobicity rules the photosensitizer distribution in nanoparticles, which in turn dictates the ability of these structures to release singlet oxygen.

Phosphonate monoesters (PMEs) as ligands for metal–organic frameworks can potentially direct topology, enhance water stability, and modify pore chemistry. Here, we show, experimentally and computationally, not only that is the ratio of phosphonate to phosphonate monoester significant, but also that gas sorption depends on the distribution of the monoesters in the structure. A phosphonate monoester ligand, 1,3,5-tri­(4-phosphonato)­benzene-tris­(monoethylester), was coordinated to copper­(II) to form two different frameworks based on the same copper–phosphonate chain building units, one dense (1) and the other with an experimental surface area over 1000 m2 g–1 (CALF-33-Et 3 ). One of the three phosphonate monoesters in CALF-33-Et 3 can be hydrolyzed to make an isostructural material, CALF-33-Et 2 H, with approximately the same surface areas but vastly superior CO2 sorption. Controlling the hydrolysis at this site allowed the partially hydrolyzed variants, CALF-33-Et 3–x H x (where 0 < x < 1), to be prepared and their gas sorption studied by experiment and simulation to determine CO2 binding sites and binding energies. These results show that each PME group can impact multiple gas sorption sites meaning that clustering versus random distributions of ester groups gives very different gas uptake. Finally, an algorithm is put forward that allows the CO2 uptake of the hydrolyzed MOF to be simulated by algebraically combining the isotherms of the nonhydrolyzed and fully hydrolyzed forms. This method can be used to assess both the degrees of ester hydrolysis and the distribution of ester groups in the solid.