Seven and eight-coordinate Fe(III) complexes containing pre-organized ligand 1,10-phenanthroline-2,9-dicarboxylic acid: Solvent effects, supramolecular interactions and DFT calculations

Observation of Iron with Eight Coordination in Iron Trifluoride under High Pressure

The chemistry of hypercoordination has been a subject of fundamental interest, especially for understanding structures that challenge conventional wisdom. The small ionic radii of Fe ions typically result in coordination numbers of 4 or 6 in stable Fe-bearing ionic compounds. While 8-coordinated Fe has been observed in highly compressed oxides, the pursuit of hypercoordinated Fe still faces significant challenges due to the complexity of synthesizing the anticipated compound with another suitable anion. Through first-principles simulation and advanced crystal structure prediction methods, we predict that an orthorhombic phase of FeF3 with exclusively 8-coordinated Fe is energetically stable above 18 GPa-a pressure more feasibly achieved compared to oxides. Inspired by this theoretical result, we conducted extensive experiments using a laser-heated diamond anvil cell technique to investigate the crystal structures of FeF3 at high-pressure conditions. We successfully synthesized the predicted orthorhombic phase of FeF3 at 46 GPa, as confirmed by in situ experimental X-ray diffraction data. This work establishes a new ionic compound featuring rare 8-coordinated Fe in a simple binary Fe-bearing system and paves the way for discovering Fe hypercoordination in similar systems.

Six metal-organic architectures from a 5-methoxyisophthalate linker: assembly, structural variety and catalytic features

A methoxy-functionalized isophthalic acid, 5-methoxy isophthalic acid (H2mia), was used a versatile linker for assembling six new metal(ii) compounds under hydrothermal conditions. The obtained products were [Cu2(μ2-mia)2(phen)2(H2O)2]·2H2O (1), [Mn(μ3-mia)(phen)]n (2), [Co(μ2-mia)(2,2'-bipy)(H2O)]n·nH2O (3), [Co(μ3-mia)(μ2-4,4'-bipy)]n·nH2O (4), [Co(μ3-mia)(py)2]n (5), and [Cd(μ2-mia)(py)(H2O)2]n·nH2O (6), where phen(1,10-phenanthroline), 2,2'-bipy(2,2'-bipyridine), 4,4'-bipy(4,4'-bipyridine) or py(pyridine) were incorporated as auxiliary ligands. The crystal structures of 1-6 range from 0D (1) and 1D (2, 3, 5, 6) CPs to a 2D network (4) with a variety of topological types. The catalytic behavior of 1-6 was studied in the cyanosilylation reaction between trimethylsilyl cyanide and aldehydes, resulting in up to 99% yields of products under optimized conditions. Various reaction parameters as well as catalyst recycling and substrate scope were investigated. This study widens the use of H2mia as a versatile dicarboxylate linker for assembling a diversity of functional metal-organic architectures with remarkable structural features and catalytic properties.

Theoretical insights into selective extraction of uranium from seawater with tetradentate N,O-mixed donor ligands

The competition of uranium and vanadium ions is a major challenge in extracting uranium from seawater. In-depth exploration of the complexation of uranium and vanadium ions with promising ligands is essential to design highly efficient ligands for selective recovery of uranium. In this work, we systematically explored the uranyl and vanadium extraction complexes with three tetradentate N,O-mixed donor analogues including the rigid backbone ligands 1,10-phenanthroline-2,9-dicarboxylic acid (PDA, L¹) and 5H-cyclopenta[2,1-b:3,4-b']dipyridine-2,8-dicarboxylate acid (L³), as well as the flexible ligand [2,2'-bipyridine]-6,6'-dicarboxylate acid (L²) using density functional theory (DFT). These ligands coordinate to the uranyl cation in a tetradentate fashion, while L¹ and L³ act as tridentate ligands toward VO₂⁺ due to the smaller ionic radius of VO₂⁺ and larger cleft sizes of L¹ and L³. Bonding analyses show that the metal-ligand bonding orbitals of the uranyl complexes [UO₂L(CO₃)]^2-, [UO₂L(OH)]^-, and [UO₂L(H₂O)] mainly arise from the interactions of the U 5f, 6d orbitals and N, O 2p orbitals. Because of the rigid structure and more suitable chelate ring size, the L¹ ligand possesses a stronger complexing ability for uranyl ions than other ligands, while the L³ ligand has weaker binding affinity than L¹ and L². All these ligands prefer to coordinate with the uranyl cation rather than vanadium ion, indicating the selectivity of these ligands to [UO₂(CO₃)₃]^4- over H₂VO₄^- and HVO₄^2- in seawater. This is mainly attributed to the metal ion size-based selectivity and structural preorganization of the ligands. These results demonstrate that the backbone of these ligands affect their extraction behaviors. It is expected that this work might prove useful in designing efficient ligands for uranium extraction from seawater.

Fe-MOGs-based enzyme mimetic and its mediated electrochemiluminescence for in situ detection of H2O2 released from Hela cells

Enzyme mimetics have attracted wide interest due to their inherent enzyme-like activity and unique physicochemical properties, as well as promising applications in disease diagnosis, treatment and monitoring. Inspired by the attributes of nonheme iron enzymes, synthetic models were designed to mimic their capability and investigate the catalytic mechanisms. Herein, metal-organic gels (Fe-MOGs) with horseradish peroxidase (HRP) like Fe-N_X structure were successfully synthesized though the coordination between iron and 1,10-phenanthroline-2,9-dicarboxylic acid (PDA) and exhibited excellent peroxidase-like activity. Its structure-activity relationship and the in-situ electrochemiluminescence (ECL) detection of H₂O₂ secreted by Hela cells were further investigated. The highly dispersed Fe-N_X active sites inside Fe-MOGs were able to catalyze the decomposition of H₂O₂ into large amounts of reactive oxygen species (ROS) via a Fenton-like reaction under a low overpotential. Due to the accumulation of ROS free radicals, the luminol ECL emission was significantly amplified. A proof-of-concept biosensor was constructed with a detection limit as low as 2.2 nM and a wide linear range from 0.01 to 40 μM. As a novel metal organic gels based enzyme mimetic, Fe-MOGs show great promises in early cancer detection and pathological process monitoring.

Coordination polymers from an unexplored biphenyl-tricarboxylate linker: hydrothermal synthesis, structural traits and catalytic cyanosilylation

3,2′,4′-Biphenyl-tricarboxylic acid (H₃bta) was used as a versatile linker for preparing a new series of metal(ii) (Zn, Ni, and Cd) coordination polymers and complexes with notable structural, luminescence and catalytic features.

D151 resin preloaded with Fe3+ as a salt resistant adsorbent for glyphosate from water in the presence 16% NaCl

D151 resin preloaded with Fe3+ [denoted as R-Fe3+] was to investigate R-Fe3+ as an adsorbent for glyphosate from water in the presence high concentration of salt. The adsorption mechanism revealed the coordination of Fe3+ inside R-Fe3+ with O atoms of P-O and N atoms in glyphosate molecule. The adsorption capacity of glyphosate by R-Fe3+ was much larger than that of D151 resin preloaded with Ni2+, Cu2+, Na+ and H+. Even in glyphosate solutions containing 16% NaCl, R-Fe3+ showed the constant adsorption capacity of glyphosate. The result provided the first evidence of R-Fe3+ as a salt resistant adsorbent for glyphosate. The adsorption capacity of glyphosate was the maximum at pH 3.35. The adsorption thermodynamics showed that the adsorption of glyphosate by R-Fe3+ was the ligand exchange of glyphosate and water. The maximum coordination ratio of glyphosate to Fe3+ inside R-Fe3+ was 1:1. The maximum adsorption capacity of glyphosate by R-Fe3+ was up to 481.85 mg/g, which is much higher than that of other reported adsorbents in the presence 16% NaCl. 2  mol/L NaOH, 2  mol/L H2SO4 and 2  mol/L Fe2(SO4)3 could all be used to achieve over 97% regeneration of R-Fe3+.

Design and programmable self-assembly of an eight-coordinate Cu(ii) heterometallic structure via a dipalladium corner as a building block

An eight-coordinate (8C) [Cu(ii)O₈] heteromultimetallic complex displaying a distorted dodecahedral structure has been synthesized via the coordination-driven programmable self-assembly of dipalladium metalloligands containing heteroditopic ligands.

H-Bonded and metal(ii)-organic architectures assembled from an unexplored aromatic tricarboxylic acid: structural variety and functional properties

This study reports the application of an aromatic tricarboxylic acid, 2,5-di(4-carboxylphenyl)nicotinic acid (H3dcna) as a versatile and unexplored organic building block for assembling a new series of metal(ii) (M = Co, Ni, Zn, Fe, and Mn) complexes and coordination polymers, namely [M(Hdcna)(phen)2(H2O)]·H2O (M = Co (1), Ni (2)), [Zn(μ-Hdcna)(phen)]n (3), [Co(μ-Hdcna)(bipy)(H2O)2]n·nH2O (4), [Zn2(μ-Hdcna)2(bipy)2(H2O)4]·6H2O (5), [Zn(μ3-Hdcna)(H2biim)]n (6), [Ni2(Hdcna)2(μ-bpb)(bpb)2(H2O)4] (7), [Fe(μ4-Hdcna)(μ-H2O)]n·nH2O (8), and [Mn3(μ5-dcna)2(bipy)2(H2O)2]n·2nH2O (9). Such a diversity of products was hydrothermally prepared from the corresponding metal(ii) salts, H3dcna as a principal multifunctional ligand, and N-donor mediators of crystallization (1,10-phenanthroline, phen; 2,2'-bipyridine, bipy; 2,2'-biimidazole, H2biim; or 1,4-bis(pyrid-4-yl)benzene, bpb). The obtained products 1-9 were fully characterized by standard methods (elemental analysis, FTIR, TGA, PXRD) and the structures were established by single-crystal X-ray diffraction. These vary from the discrete monomers (1, 2) and dimers (5, 7) to the 1D (3, 4, 6) and 2D (8, 9) coordination polymers (CPs). Structural and topological characteristics of hydrogen-bonded or metal-organic architectures in 1-9 were highlighted, revealing that their structural multiplicity depends on the type of metal(ii) source and crystallization mediator. Thermal stability as well as luminescent, magnetic, or catalytic properties were explored for selected compounds. In particular, the zinc(ii) derivatives 3, 5, and 6 were applied as efficient heterogeneous catalysts for the cyanosilylation of aldehydes with trimethylsilyl cyanide at room temperature. The catalytic reactions were optimized by tuning the different reaction parameters (solvent composition, time, catalyst loading) and the substrate scope was also explored. Compound 5 revealed superior catalytic activity leading to up to 75% product yields, while maintaining its original performance upon recycling for at least four reaction cycles. Finally, the obtained herein products represent the unique examples of coordination compounds derived from H3dcna, thus opening up the use of this multifunctional tricarboxylic acid for generating complexes and coordination polymers with interesting structures and functional properties.

Diverse structural assemblies of U-shaped hydrazinyl-sulfonamides: experimental and theoretical analysis of non-covalent interactions stabilizing solid state conformations

The preparation and structures of five new U-shaped hydrazinyl-sulfonamides are reported.