Three Sequential Hydrolysis Products of the Ubiquitous Cu24 Isophthalate Metal–Organic Polyhedra

Comprehensive Qualitative and Quantitative Colorimetric Sensing of Volatile Organic Compounds Using Monolayered Metal-Organic Framework Films

Cross-responsive chemical sensors are in high demand owing to their ability to distinguish a broad range of analytes. In this study, a vapochromic sensor array based on metal-organic frameworks (MOFs), which exhibits distinct patterns when exposed to volatile organic compounds (VOCs) and humidity, is developed. Conventional sensor arrays consist of various receptors that produce different responses. The vapochromic MOF-based sensor comprises dicopper paddlewheel clusters and dimethylamine azobenzene as binary colorimetric sensing moieties. Upon exposure to VOCs, the constructed sensor encompasses a broad spectrum of colors, ranging from green to red. Furthermore, the color of the MOF is influenced by the solvent used during the pretreatment. Consequently, monolayered MOF thin films can be adapted to multicomponent array systems by immersing the MOF in different solvents. This system provides both qualitative and quantitative sensing, generating unique color patterns corresponding to specific VOC types. Notably, the sensor successfully discriminates each of 14 common VOCs and water and accurately categorizes unknown samples. Moreover, the system undergoes reversible color changes in response to humidity, obviating the need for high-temperature regeneration steps. This novel approach offers insights into the versatile applications of MOFs by creating a colorimetric sensor array capable of detecting various analytes.

Metallic–Organic Cages (MOCs) with Heterometallic Character: Flexibility-Enhancing MOFs

The dichotomy between metal–organic frameworks (MOFs) and metal–organic cages (MOCs) opens up the research spectrum of two fields which, despite having similarities, both have their advantages and disadvantages. Due to the fact that they have cavities inside, they also have applicability in the porosity sector. Bloch and coworkers within this evolution from MOFs to MOCs manage to describe a MOC with a structure of Cu2 paddlewheel Cu4L4 (L = bis(pyrazolyl)methane) with high precision thanks to crystallographic analyses of X-ray diffraction and also SEM-EDX. Then, also at the same level of concreteness, they were able to find the self-assembly of Pd(II)Cl2 moieties on the available nitrogen donor atoms leading to a [Cu4(L(PdCl2))4] structure. Here, calculations of the DFT density functional allow us to reach an unusual precision given the magnitude and structural complexity, explaining how a pyrazole ring of each bis(pyprazolyl)methane ligand must rotate from an anti to a syn conformation, and a truncation of the MOC structure allows us to elucidate, in the absence of the MOC constraint and its packing in the crystal, that the rotation is almost barrierless, as well as also explain the relative stability of the different conformations, with the anti being the most stable conformation. Characterization calculations with Mayer bond orders (MBO) and noncovalent interaction (NCI) plots discern what is important in the interaction of this type of cage with PdCl2 moieties, also CuCl2 by analogy, as well as simple molecules of water, since the complex is stable in this solvent. However, the L ligand is proved to not have the ability to stabilize an H2O molecule.

Assembly of a Heterometallic Cu(II)-Pd(II) Cage by Post-assembly Metal Insertion

Porous structures based on multi-metallic motifs are receiving growing interest, but their general preparation still remains a challenge. Here, we report the self-assembly and structure of a Cu^II metal-organic cage (MOC) that is functionalized with free bis(pyrazolyl)methane sites. The homometallic Cu₄L₄ cage is isolated as a water-stable crystalline solid, and its formation is dependent on metal-ligand stoichiometry and the pre-organization of the Cu₂ paddlewheel. We show by X-ray diffraction and SEM-EDX that Pd^II chloride can be quantitatively inserted into the free chelating sites of the MOC to yield a [Cu₄(L(PdCl₂))₄] structure. Moreover, the solvent employed in the metalation dictates the solid-state isomerism of the heterometallic cage─a further handle to control the MOC's structural diversity and permanent porosity.

Mining Knowledge from Crystal Structures: Oxidation States of Oxygen-Coordinated Metal Atoms in Ionic and Coordination Compounds

We propose a universal scheme for predicting the oxidation states of metal atoms in ionic and coordination compounds with a small set of structural descriptors, which include the parameters of atomic Voronoi polyhedra. The scheme has been trained and checked with more than 35,000 crystal structures containing more than 90,000 metal atoms in the oxygen environment. The accuracy of the prediction exceeded 95%; we have detected a number of wrong oxidation states and incorrect chemical compositions in the crystallographic databases using this scheme. The scheme is easily extendable to any kind of atomic environment and can be used to search for correlations between geometrical and physical properties of crystal structures.

Surface chemistry of metal-organic polyhedra

Metal-organic polyhedra (MOPs) are discrete, intrinsically-porous architectures that operate at the molecular regime and, owing to peripheral reactive sites, exhibit rich surface chemistry. Researchers have recently exploited this reactivity through post-synthetic modification (PSM) to generate specialised molecular platforms that may overcome certain limitations of extended porous materials. Indeed, the combination of modular solubility, orthogonal reactive sites, and accessible cavities yields a highly versatile molecular platform for solution to solid-state applications. In this feature article, we discuss representative examples of the PSM chemistry of MOPs, from proof-of-concept studies to practical applications, and highlight future directions for the MOP field.

Topological transformations in metal–organic frameworks: a prospective design route?

We apply a topological approach based on the underlying net and transformation pattern concepts as well as on the ‘supernet–subnet’ formalism to uncover mechanisms of solid-state transformations in coordination polymers and metal–organic frameworks.

Morphology-Dependent Peroxidase Mimicking Enzyme Activity of Copper Metal-Organic Polyhedra Assemblies

The morphology of nanomaterials (geometric shape and dimension) play a significant role in its various physical and chemical properties. Thus, it is essential to link morphology with performance in specific applications. For this purpose, the morphology of copper metal-organic polyhedra (Cu-MOP) can be modulated through distinct assembly process, which facilitates the exploration of the relationship between morphology and catalytic performance. In this work, the assemblies of Cu-MOP with three different morphologies (nanorods, nanofibers and nanosheets) were facilely prepared by the variation of solvent mixture of N, N-dimethylformamide (DMF) and methanol, revealed the important role of the interaction between the surface group and the solvent on the morphology of these assemblies. Cu-MOP nanofibers exhibited the highest mimetic peroxidase enzyme activity over the Cu-MOP nanosheets and nanorods, which have been utilized in the detection of glucose. Cu-MOPs assemblies with tunable morphology accompanied with adjustable mimic peroxidase activity, had great potential applications in the field of bioanalytical chemistry and biomedicals.

Assembly and Covalent Cross-Linking of an Amine-Functionalised Metal-Organic Cage

The incorporation of reactive functional groups onto the exterior of metal-organic cages (MOCs) opens up new opportunities to link their well-defined scaffolds into functional porous solids. Amine moieties offer access to a rich catalogue of covalent chemistry; however, they also tend to coordinate undesirably and interfere with MOC formation, particular in the case of Cu₂ paddlewheel-based MOCs. We demonstrate that tuning the basicity of an aniline-functionalized ligand enables the self-assembly of a soluble, amine-functionalized Cu₄L₄ lantern cage (1). Importantly, we show control over the coordinative propensity of the exterior amine of the ligand, which enables us to isolate a crystalline, two-dimensional metal-organic framework composed entirely of MOC units (2). Furthermore, we show that the nucleophilicity of the exterior amine of 1 can be accessed in solution to generate a cross-linked cage polymer (3) via imine condensation.

Coordination Properties of Hydroxyisophthalic Acids: Topological Correlations, Synthesis, Structural Analysis, and Properties of New Complexes

Hydroxyisophthalic acids are valuable polytopic ligands for the design of functional materials based on coordination polymers due to the variety of charges and coordination modes they possess. Herein, we describe the synthesis, thermal stability, nonlinear optical (NLO) and spectroscopic properties of five novel coordination compounds, [K₂ L(H₂ O)₂ ], [MgL(H₂ O)₂ ] ⋅ 3H₂ O, [CaL(H₂ O)₃ ], [SrL(H₂ O)₃ ] ⋅ H₂ O, [BaL(H₂ O)(H₂ O)₅ ], and one salt, (NH₄ )₂ L ⋅ 2H₂ O, with 4,5,6-trihydroxyisophthalic acid (H₂ L), which has not been tested in assembling crystalline coordination networks before. The peculiarities of the structural organization of the compounds were analyzed and compared with those for other hydroxyisophthalates. The coordination properties of hydroxyisophthalic acids were studied from the topological point of view, and a comparative topological analysis of coordination and H-bonded networks was performed. Structural correlations revealed in this study could be useful for the design of hydroxyisophthalate-based coordination networks, including porous metal-organic frameworks, proton conductors, and NLO materials.

Constructing an Interpenetrated NiII-Based Coordination Polymer Based on a Flexible Dicarboxylate Ligand and an N-Donor Ligand: Preparation, Topological Diversity, and Catalytic Properties

A novel coordination polymer (CP) was constructed using 1,3-bis(4-carboxyphenoxy) propane (H2bcp), 1,4-bis(1-imidazol-yl)-2,5-dimethyl benzene (bimb), and NiII ions. [Ni(bcp)(bimb)]·H2O]n (1) shows an interesting 2D+2D → 3D inclined polyrotaxane topology. The structure was characterised by many methods. This work indicates that the flexible and neutral pyridine ligand plays a significant role in constructing CPs. Furthermore, 1 is a highly efficient catalyst for the reaction of CO2 and epoxides.