Synthesis and Structure Evolution in Metal Carbazole Diphosphonates Followed by Electron Diffraction

To access porous metal phosphonates, a new V-shaped, rigid, and sterically demanding diphosphonic acid, namely 3,6-diphosphono-9H-carbazole (H₄L), was designed and employed in a high-throughput investigation. Screening of different metal salts and subsequent optimization studies resulted in the isolation of two porous metal phosphonates [Cu₂(H₂O)₂(L)]·2H₂O (CAU-37) and [Zn_6.75(H₂O)_1.5(HL)_2.5(L)_1.5]·8H₂O (CAU-57). Structure determination was accomplished by electron diffraction and the dehydration behavior of CAU-37 was followed in situ. A rare case of intralayer water de-/adsorption in CAU-37 was found which leads to a cell volume change of 11.9%. Rod-shaped inorganic building units (IBUs) are connected to layers and structural flexibility is due to "accordion-like" structural changes within the layers. In contrast, in CAU-57 a layered IBU is found, which usually results in the formation of dense structures. Due to the shape and rigidity of the linker, the interconnection of the IBUs results in the formation of pores. Water sorption measurements in combination with powder X-ray diffraction data confirmed the reversibility under structural retention.

Synthesis and crystal structure of bis-[trans-di-aqua-(1,4,8,11-tetra-aza-cyclo-tetra-decane-κ4 N 1,N 4,N 8,N 11)nickel(II)] trans-(1,4,8,11-tetra-aza-cyclo-tetra-decane-κ4 N 1,N 4,N 8,N 11)bis-[4,4',4''-(1,3,5-tri-methyl-benzene-2,4,6-tri-yl)tris-(hydrogen phenyl-phospho-nato-κO)]nickel(II) deca-hydrate

The components of the title compound, [Ni(C10H24N4)(H2O)2]2[Ni(C10H24N4)(C27H24O9P3)2]·10H2O are two centrosymmetric [Ni(C10H24N4)(H2O)2]2+ dications, a centrosymmetric [Ni(C10H24N4)(C27H24O9P3)2]4- tetra-anion and five crystallographically unique water mol-ecules of crystallization. All of the nickel ions are coordinated by the four secondary N atoms of the macrocyclic cyclam ligands, which adopt the most energetically stable trans-III conformation, and the mutually trans O atoms of either water mol-ecules in the cations or the phospho-nate groups in the anion in a tetra-gonally distorted NiN4O2 octa-hedral coordination geometry. Strong O-H⋯O hydrogen bonds between the protonated and the non-protonated phospho-nate O atoms of neighboring anions result in the formation of layers oriented parallel to the bc plane, which are linked into a three-dimensional network by virtue of numerous N-H⋯O and O-H⋯O hydrogen bonds arising from the sec-NH groups of the macrocycles, phospho-nate O atoms and coordinated and non-coordinated water mol-ecules.

New isoreticular phosphonate MOFs based on a tetratopic linker

The tetratopic linker 1,1,2,2-tetrakis(4-phosphonophenyl)ethylene (H₈TPPE) was used to synthesize the three new porous metal-organic frameworks of composition [M₂(H₂O)₂(H₂TPPE)]·xH₂O (M = Al³⁺, Ga³⁺, Fe³⁺), denoted as M-CAU-53 under hydrothermal reaction conditions, using the corresponding metal nitrates as starting materials. The crystal structures of the compounds were determined ab initio from powder X-ray diffraction data, revealing small structural differences. Proton conductivity measurements were carried out, indicating different conductivity mechanisms. The differences in proton conductivity could be linked to the individual structures. In addition, a thorough characterization via thermogravimetry, elemental analysis, IR-spectroscopy as well as N₂- and H₂O-sorption is given.

A Tetratopic Phosphonic Acid for the Synthesis of Permanently Porous MOFs: Reactor Size-Dependent Product Formation and Crystal Structure Elucidation via Three-Dimensional Electron Diffraction

Following the strategy of installing porosity in coordination polymers predefined by linker geometry, we employed the new tetratopic linker molecule 1,1,2,2-tetrakis[4-phosphonophenyl]ethylene (H₈TPPE) for the synthesis of new porous metal phosphonates. A high-throughput study was carried out using Ni²⁺ and Co²⁺ as metal ions, and a very strong influence of the reactor size on the product formation is observed while maintaining the same reaction parameters. Using small autoclaves (V = 250 μL), single crystals of isostructural mononuclear complexes of the composition [Ni(H₃DPBP)₂(H₂O)₄] (1) and [Co(H₃DPBP)₂(H₂O)₄] (2) are formed. They contain the linker molecule H₄DPBP (4,4'-diphosphonobenzophenone), which is formed in situ by oxidation of H₈TPPE. Using autoclaves with a volume of V = 2 mL, two new 3D metal-organic frameworks (MOFs) of composition [Ni₂(H₄TPPE)(H₂O)₆]·4H₂O (CAU-46) and [Co₂(H₄TPPE)(H₂O)₄]·3H₂O (CAU-47) were isolated in bulk quantities, and their crystal structures were determined from three-dimensional electron diffraction (3D ED) and powder X-ray diffraction data. Using even larger autoclaves (V = 30 mL), another 3D MOF of the composition [Co₂(H₄TPPE)]·6H₂O (Co-CAU-48) was obtained, and a structure model was established via 3D ED measurements. Remarkably, the isostructural compound [Ni₂(H₄TPPE)]·9H₂O (Ni-CAU-48) is only obtained indirectly, i.e., via thermal activation of CAU-46. As the chosen linker geometry leads to the formation of MOFs, topological analyses were carried out, highlighting the different connectivities observed in the three frameworks. Porosity of the compounds was proven via water sorption experiments, resulting in uptakes of 126 mg/g (CAU-46), 105 mg/g (CAU-47), 210 mg/g (Ni-CAU-48), and 109 mg/g (Co-CAU-48).

Investigating the effect of positional isomerism on the assembly of zirconium phosphonates based on tritopic linkers

Combination of the novel linker 2,4,6-tris[3-(phosphonomethyl)phenyl]-1,3,5-triazine and Zr(iv) afforded a layered compound that lacks extended inorganic connectivity and displays good proton conductivity.

Metal phosphonates incorporating metalloligands: assembly, structures and properties

This feature article summarizes the current status of metal–metalloligand phosphonates including the synthetic strategies, crystal structures and properties. Future challenges in this field are discussed.

New Directions in Metal Phosphonate and Phosphinate Chemistry

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.

A cobalt arylphosphonate MOF – superior stability, sorption and magnetism

We report a novel metal organic framework (MOF) based on a cobalt arylphosphonate, namely, [Co₂(H₄-MTPPA)]·3NMP·H₂O (1·3NMP·H₂O), which was prepared solvothermically from the tetrahedral linker tetraphenylmethane tetrakis-4-phosphonic acid (H₈-MTPPA) and CoSO₄·7H₂O in N-methyl-2-pyrrolidone (NMP).

Zinc-diphosphonates with extended dipyridine units: synthesis, structures, in situ reactions, and photochromism

We report two zinc-diphosphonates bearing extended dipyridine units. In situ reactions and photochromism are observable in the title compounds.