Discovery of two predictable (3,18)-connected topologies based on Wells-Dawson type cages for the design of porous metal phosphonocarboxylate frameworks

Highly connected molecular building blocks (MBBs) have been demonstrated to play a crucial role in reticular chemistry, particularly in predicting the topologies of metal-organic frameworks. Metal phosphonate clusters exhibit considerable advantages in constructing high-connectivity MBBs, owing to the multiple coordination modes offered by phosphonic ligands. Herein, four metal (M = CoII, MnII) phosphonocarboxylate frameworks (CoPCF-1,2 and MnPCF-1,2) were successfully prepared under solvothermal conditions by utilizing the phosphonocarboxylic ligand, 4'-phosphonobiphenyl-3,5-dicarboxylic acid (H4pbpdc), and their structural characterization was performed using single-crystal X-ray diffraction (SCXRD). The structures feature a duodenary nuclear M12(µ3-OH)2(CO2)12(PO3)6(DMF)6/(CH3COO)4.5 cluster, bearing resemblance to the well-known Wells-Dawson ion from polyoxometallate chemistry. It is the first time a Wells-Dawson type cage has served as an 18-connected molecular building block, forming two kinds of porous metal phosphonocarboxylate frameworks with novel (3,18)-connected gez and gea topologies. Their permanent porosities were confirmed through N2 adsorption studies. Notably, the MBB Co12 cluster-based CoPCF-1 shows a loss and recovery process of µ3-OH through single-crystal-to-single-crystal (SCSC) transformation. The magnetic properties of the four compounds exhibit antiferromagnetic behavior.

Chemical and Redox Speciation of Uranyl with Three Environmentally Relevant Bifunctional Chelates: Multi-Technique Approach Combined with Theoretical Estimations

Carbon and phosphorous are two primary elements common to the bio-geosphere and are omnipresent in both biotic and abiotic arenas. Phosphonate and carboxylate are considered as building blocks of glyphosate and humic substances and constituents of the cellular wall of bacteria and are the driving functionalities for most of the chemical interactions involving these two elements. Phosphonocarboxylates, a combination of both the functionalities in one moiety, are ideal models to dig deep into for understanding the chemical interactions of the two functional groups with metal ions. Phosphorous and carbon majorly exist as inorganic/organic phosphate and carboxylate, respectively, in the bio-geosphere. Aquatic contamination is a major concern for uranium, and the presence of complexing agents would alter the uranium concentrations in aquifers. Determination of solution thermodynamic parameters, speciation plots, redox patterns, E_h-pH diagrams, coordination structures, and molecular-level understanding by density functional theory calculations was carried out to interpret the uranyl (UO₂²⁺) interaction with three environmentally relevant phosphonocarboxylates, namely, phosphono-formic acid (PFA), phosphono-acetic acid (PAA), and phosphono-propanoic acid (PPA). UO₂²⁺ forms 1:1 complexes with the three phosphonocarboxylates in the monoprotonated form, having nearly the same stability, and the complexes [UO₂(PFAH)], [UO₂(PAAH)], and [UO₂(PPAH)] involve chelate formation of five, six, and seven membered rings, respectively, through the participation of an oxygen each from the carboxylate and phosphonate, strengthened by an intra-molecular hydrogen bonding through the proton of the phosphonate moiety with uranyl oxygen. The complex formations are favored both enthalpically and entropically, with the latter being more contributive to the overall free energy of formation. The redox speciation showed an aqueous soluble complex formation over a wide pH range of 1-8. Electrospray ionization mass spectrometry and extended X-ray absorption fine structure established the coordination modes, which are further corroborated by density functional calculations. The knowledge gained from the present studies provide potential inputs in framing the cleanup, sequestering, microbial, and bio-remediation strategies for uranyl from aquatic environments.

Flexible bifunctional monoethylphosphonate/carboxylates of Zn(ii) and Co(ii) reinforced with DABCO co-ligand: paradigmatic structural organization with topology

The prototypal [M₂(EtBCP)₂(DABCO)_0.5] MOFs, compliant with isoreticular expansion in two-dimensions, show flexibility manifested by a two-step CO₂ adsorption isotherm, which might be associated to the “lever-action” of the metal-phosphonate moieties.

A highly stable polyoxometalate-based metal–organic framework with an ABW zeolite-like structure

A novel polyoxometalate-based metal–organic framework (POMOF) with an ABW network, NENU-601, was synthesized in situ.

Three Zinc(II) Phosphonates: Syntheses, Structures and Sensing of Copper(II) Ions

Three zinc(II) phosphonocarboxylates, [Zn₃ (m-bpc)₂ (OH)]⋅(CH₃ )₂ NH₂ ⋅H₂ O (1), [Zn₂ (m-bpc)(m-Hbpc)(4,4'-bpy)]⋅(CH₃ )₂ NH₂ ⋅H₂ O (2) and [Zn₃ (m-bpc)₂ (4,4'-bpy)(CH₃ )₂ NH]⋅H₂ O (3) (m-H₃ bpc=3-phosphonobenzoic acid, 4,4'-bpy=4,4'-bipyridine), have been solvothermally synthesised to generate unique topologies, as characterised by single-crystal XRD. Compound 1 possesses a diamond topology, which has rarely been found among phosphonate-based metal-organic frameworks. Compound 2 shows a 2D layered structure with pendant m-Hbpc and 4, 4'-bpy ligands, in which the layers feature as a zeolite-like network. Compound 3 has a 3D sandwich pillared-layer framework with an interesting double-helix structure. Only 1 shows an adsorption capacity for CO₂ of 28.5 cm³  g^-1 at 273 K. Luminescence studies revealed that both 1 and 2 could be potential sensors to copper(II) ions.

Concise template syntheses of gallium phosphates driven by in situ direct alkylation of aliphatic and aromatic precursors by methanol

In situ template design and generation strategy is applied to synthesize microporous materials. We report five new organically templated gallium phosphates with different structures varying from 1D chain to 2D layer and 3D framework.

A highly stable indium phosphonocarboxylate framework as a multifunctional sensor for Cu2+ and methylviologen ions

An indium phosphonocarboxylate framework (InPCF-1) with a novel 3,4,5-connected topology was synthesized, which serves as a selective and sensitive sensor for Cu²⁺ and MV²⁺ ions.

A distorted honeycomb motif in divalent transition metal compounds based on 4-phosphonbenzoic acid and exchange coupled Co(II) and Cu(II): synthesis, structural description and magnetic properties

The first example of a two-dimensional inorganic hybrid material with cobalt as an open-shell transition metal ion and 4-phosphonbenzoic acid as a linker is presented together with its copper analogue. For both metal ions the inorganic part consists of edge-sharing metal-oxygen octahedra leading to a metal honeycomb motif. The magnetic properties of the cobalt compound are reported together with those of the corresponding copper compound based on the remarkably six-coordinated copper(II) ions.