Metal-organic frameworks (MOFs) are a chemically and topologically diverse family of materials composed of inorganic nodes and organic linkers bound together by coordination bonds. Presented here are two significant innovations in this field. The first is the use of a new coordination group, phenylene-1,4-bis(methylphosphinic acid) (PBPA), a phosphinic acid analogue of the commonly used terephtalic acid. Use of this new linker group leads to the formation of a hydrothermally stable and permanently porous MOF structure. The second innovation is the application of electron-diffraction tomography, coupled with dynamic refinement of the EDT data, to the elucidation of the structure of the new material, including the localization of hydrogen atoms.

In September 2018, the First European Workshop on Metal Phosphonates Chemistry brought together some prominent researchers in the field of metal phosphonates and phosphinates with the aim of discussing past and current research efforts and identifying future directions. The scope of this perspective article is to provide a critical overview of the topics discussed during the workshop, which are divided into two main areas: synthesis and characterisation, and applications. In terms of synthetic methods, there has been a push towards cleaner and more efficient approaches. This has led to the introduction of high-throughput synthesis and mechanochemical synthesis. The recent success of metal–organic frameworks has also promoted renewed interest in the synthesis of porous metal phosphonates and phosphinates. Regarding characterisation, the main advances are the development of electron diffraction as a tool for crystal structure determination and the deployment of in situ characterisation techniques, which have allowed for a better understanding of reaction pathways. In terms of applications, metal phosphonates have been found to be suitable materials for several purposes: they have been employed as heterogeneous catalysts for the synthesis of fine chemicals, as solid sorbents for gas separation, notably CO2 capture, as materials for electrochemical devices, such as fuel cells and rechargeable batteries, and as matrices for drug delivery.

Microbial colonization of biomedical devices is a recognized complication contributing to healthcare-associated infections. One of the possible approaches to prevent surfaces from the biofilm formation is antimicrobial photodynamic inactivation based on the cytotoxic effect of singlet oxygen, O(Δ), a short-lived, highly oxidative species, produced by energy transfer between excited photosensitizers and molecular oxygen. We synthesized porphyrin-based covalent organic frameworks (COFs) by Schiff-base chemistry. These novel COFs have a three-dimensional, diamond-like structure. The detailed analysis of their photophysical and photochemical properties shows that the COFs effectively produce O(Δ) under visible light irradiation, and especially three-dimensional structures have strong antibacterial effects toward Pseudomonas aeruginosa and Enterococcus faecalis biofilms. The COFs exhibit high photostability and broad spectral efficiency. Hence, the porphyrinic COFs are suitable candidates for the design of antibacterial coating for indoor applications.

Zirconium-based metal–organic frameworks were recently investigated as catalysts for degradation of organophosphate toxic compounds, such as pesticides or chemical warfare agents. The most utilized UiO-66 is considered as a stable material for these applications in an aqueous environment. However, the presented results indicate that the properties of UiO-66 are changing considerably in aqueous media under common conditions used for organophosphate degradations, and therefore its catalytic activity is not related to the number of structural defects created during the material synthesis. We delineate the stability of UiO-66 in water of various pHs, the in situ formation of new catalytic sites, and the correlation of these two parameters with the degradation rate of a model organophosphate pollutant, dimethyl-4-nitrophenyl phosphate (methyl-paraoxon). The stability was quantified using high-performance liquid chromatography (HPLC) by measuring the amounts of leached terephthalic acid, the linker of UiO-66, and monocarboxylic acids, the modulators bound at UiO-66 defects. We demonstrate that the HPLC analysis is a more suitable method for metal–organic frameworks stability assessment than commonly used methods, e.g., powder X-ray diffraction, adsorption isotherms, or electron microscopy.

Recent studies have unraveled the potential of octahedral molybdenum cluster complexes (Mo 6 ) as relevant red phosphors and photosensitizers of singlet oxygen, O 2 ( 1 Δ g ), for photobiological applications. However, these complexes tend to hydrolyze in an aqueous environment, which deteriorates their properties and limits their applications. To address this issue, we show that phenylphosphinates are extraordinary apical ligands for the construction of Mo 6 complexes. These new complexes display unmatched luminescence quantum yields and singlet oxygen production in aqueous solutions. More importantly, the complex with diphenylphosphinate ligands is the only stable complex of these types in aqueous media. These complexes internalize in lysosomes of HeLa cells, have no dark toxicity, and yet are phototoxic in the submicromolar concentration range. The superior hydrolytic stability of the diphenylphosphinate complex allows for conservation of its photophysical properties and biological activity over a long period, making it a promising compound for photobiological applications.

No abstract

Layered materials provide a two-dimensional interlayer space suitable for accommodating molecules with a designed functionality. In this study, inorganic−organic hybrids were prepared by intercalation of anionic porphyrin sensitizers into the host structure of layered zinc hydroxide salts. The inorganic host offers stabilization and protection, whereas the guest species provide the photofunction. The properties and arrangement of porphyrin molecules in the interlayer space were studied by a combination of experimental techniques and molecular simulations. Intercalation of porphyrins led to a gallery height that is comparable with the size of porphyrin molecules. Molecular simulations showed that the interlayer space is filled with disordered porphyrin units. The porphyrin sulfonate groups interact with the brucite-like layers via dominant electrostatic interactions similarly to layered double hydroxides. The photophysical experiments proved that intercalated anionic Pd porphyrins produce singlet oxygen, O2(1Δg), with long effective lifetimes, suggesting that layered zinc hydroxide salts are good carriers of porphyrin sensitizers.

Rare-earth layered hydroxides with intercalated tetrasulfonated porphyrins and corresponding to the chemical formula Ln2(OH)4.7(Por)0.33·2H2O (Ln = Eu(3+), Tb(3+); Por = 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin (TPPS) and PdTPPS) have been prepared to investigate their photophysical properties. A slight variation of the synthetic procedure led to the metal-organic framework (MOF) assembled from a distorted octahedral oxometalate clusters [Eu6(μ6-O)(μ3-OH)8(H2O)14](8+). These secondary building units (SBUs) are linked together by six distorted porphyrin units. During activation, the original SBU loses not only water molecules from the coordination sphere but also the central μ6-O atom. The loss of the central atom results in the distortion of the octahedral [Eu6(μ6-O)(μ3-OH)8(H2O)14](8+) SBU into a trigonal antiprismatic [Eu6(μ3-OH)8(H2O)2](10+) SBU with two μ3-OH groups nearly in plane with the europium atoms and the reduction of pores to approximately 2 × 3 Å. As a result, the MOF has no accessible porosity. This transformation was thoroughly characterized by means of single-crystal X-ray crystallographic analysis of both phases. Solid-state photophysical investigations suggest that the MOF material is fluorescent; however, in contrast to the prepared layered hydroxides, the as-prepared MOF is an effective sensitizer of singlet oxygen, O2((1)Δg), with a relatively long lifetime of 23 ± 1 μs. The transition is also accompanied by variation in photophysical properties of the coordinated TPPS. The alteration of the fluorescence properties and of the O2((1)Δg) lifetime presents an opportunity for preparation of MOFs with oxygen-sensing ability or with oxidation potential toward organic molecules by O2((1)Δg).