A new three-dimensional cobalt(II) coordination polymer based on V-shaped 3,4'-oxydibenzoate: synthesis, crystal structure and magnetic properties

Self-assembly of a cobalt(II)-based metal-organic framework as an effective water-splitting heterogeneous catalyst for light-driven hydrogen production

The solar photocatalysis of water splitting represents a significant branch of enzymatic simulation by efficient chemical conversion and the generation of hydrogen as green energy provides a feasible way for the replacement of fossil fuels to solve energy and environmental issues. We report herein the self-assembly of a Co^II-based metal-organic framework (MOF) constructed from 4,4',4'',4'''-(ethene-1,1,2,2-tetrayl)tetrabenzoic acid [or tetrakis(4-carboxyphenyl)ethylene, H₄TCPE] and 4,4'-bipyridyl (bpy) as four-point- and two-point-connected nodes, respectively. This material, namely, poly[(μ-4,4'-bipyridyl)[μ₈-4,4',4'',4'''-(ethene-1,1,2,2-tetrayl)tetrabenzoato]cobalt(II)], [Co(C₃₀H₁₆O₈)(C₁₀H₈N₂)]_n, crystallized as dark-red block-shaped crystals with high crystallinity and was fully characterized by single-crystal X-ray diffraction, PXRD, IR, solid-state UV-Vis and cyclic voltammetry (CV) measurements. The redox-active Co^II atoms in the structure could be used as the catalytic sites for hydrogen production via water splitting. The application of this new MOF as a heterogeneous catalyst for light-driven H₂ production has been explored in a three-component system with fluorescein as photosensitizer and trimethylamine as the sacrificial electron donor, and the initial volume of H₂ production is about 360 µmol after 12 h irradiation.

Tuning of crystallization method and ligand conformation to give a mononuclear compound or two-dimensional SCO coordination polymer based on a new semi-rigid V-shaped bis-pyridyl bis-amide ligand

With the new semi-rigid V-shaped bidentate pyridyl amide compound 5-methyl-N,N'-bis(pyridin-4-yl)benzene-1,3-dicarboxamide (L) as an auxiliary ligand and the Fe^II ion as the metal centre, one mononuclear complex, bis(methanol-κO)bis[5-methyl-N,N'-bis(pyridin-4-yl)benzene-1,3-dicarboxamide-κN]bis(thiocyanato-κN)iron(II), [Fe(SCN)₂(C₁₉H₁₆N₄O₂)₂(CH₃OH)₂] (1), and one two-dimensional coordination polymer, catena-poly[[[bis(thiocyanato-κN)iron(II)]-bis[μ-5-methyl-N,N'-bis(pyridin-4-yl)benzene-1,3-dicarboxamide-κ²N:N']] methanol disolvate dihydrate], {[Fe(SCN)₂(C₁₉H₁₆N₄O₂)₂]·2CH₃OH·2H₂O}_n (2), were prepared by slow evaporation and H-tube diffusion methods, respectively, indicating the effect of the method of crystallization on the structure type of the target product. Both complexes have been structurally characterized by elemental analysis, IR spectroscopy and single-crystal X-ray crystallography. The single-crystal X-ray diffraction analysis shows that L functions as a monodentate ligand in mononuclear 1, while it coordinates in a bidentate manner to two independent Fe(SCN)₂ units in complex 2, with a different conformation from that in 1 and the ligands point in two almost orthogonal directions, therefore leading to a two-dimensional grid-like network. Investigation of the magnetic properties reveals the always high-spin state of the Fe^II centre over the whole temperature range in 1 and a gradual thermally-induced incomplete spin crossover (SCO) behaviour below 150 K in 2, demonstrating the influence of the different coordination fields on the spin properties of the metal ions. The current results provide useful information for the rational design of functional complexes with different structure dimensionalities by employing different conformations of the ligand and different crystallization methods.

A cyanide-bridged FeIII-MnII heterobimetallic one-dimensional coordination polymer: synthesis, crystal structure, experimental and theoretical magnetism investigation

A new cyanide-bridged Fe^III-Mn^II heterobimetallic coordination polymer (CP), namely catena-poly[[[N,N'-(1,2-phenylene)bis(pyridine-2-carboxamidato)-κ⁴N,N',N'',N''']iron(III)]-μ-cyanido-κ²C:N-[bis(4,4'-bipyridine-κN)bis(methanol-κO)manganese(II)]-μ-cyanido-κ²N:C], {[FeMn(C₁₈H₁₂N₄O₂)(CN)₂(C₁₀H₈N₂)₂(CH₃OH)₂]ClO₄}_n, (1), was prepared by the self-assembly of the trans-dicyanidoiron(III)-containing building block [Fe(bpb)(CN)₂]^- [bpb^2- = N,N'-(1,2-phenylene)bis(pyridine-2-carboxamidate)], [Mn(ClO₄)₂]·6H₂O and 4,4'-bipyridine, and was structurally characterized by elemental analysis, IR spectroscopy, single-crystal X-ray crystallography and powder X-ray diffraction (PXRD). Single-crystal X-ray diffraction analysis shows that CP 1 possesses a cationic linear chain structure consisting of alternating cyanide-bridged Fe-Mn units, with free perchlorate as the charge-balancing anion, which can be further extended into a two-dimensional supramolecular sheet structure via inter-chain π-π interactions between the 4,4'-bipyridine ligands. Within the chain, each Mn^II ion is six-coordinated by an N₆ unit and is involved in a slightly distorted octahedral coordination geometry. Investigation of the magnetic properties of 1 reveals an antiferromagnetic coupling between the cyanide-bridged Fe^III and Mn^II ions. A best fit of the magnetic susceptibility based on the one-dimensional alternating chain model leads to the magnetic coupling constants J₁ = -1.35 and J₂ = -1.05 cm^-1, and the antiferromagnetic coupling was further confirmed by spin Hamiltonian-based density functional theoretical (DFT) calculations.