Synthesis,crystal structures,and luminescent properties of Zn(ii), Cd(ii), Eu(iii) complexes and detection of Fe(iii) ions based on a diacylhydrazone Schiff base

Acylhydrazone Schiff bases are rich in N and O atoms to coordinate with metal ions to form multidentate complexes. In this study, a novel diacylhydrazone Schiff base (N′¹E,N′⁴E)-N′¹,N′⁴-bis(2-hydroxy-5-nitrobenzylidene)succinohydrazide (H₄L) was synthesized from the condensation of nitrosalicylaldehyde and succinic dihydrazide. The interactions of H₄L with common monovalent, divalent and trivalent metal ions were investigated by ultraviolet spectroscopy and fluorescence spectroscopy. The results showed that H₄L had no obvious effect on the monovalent metal ions (Li⁺, Na⁺, K⁺), but reacted with most divalent and trivalent metal ions, and showed single selectivity in the fluorescence recognition of Fe³⁺ ions. More importantly, three kinds of binuclear molecular structures, [Zn₂(H₂L)₂]·5DMF (Zn-L), [Cd₂(H₂L)₂]·DMF·H₂O (Cd-L) and [Eu₂(H₂L)₃]·6DMSO (Eu-L), have been studied to further illustrate the interaction mode of diacylhydrazone Schiff base and metal ions. In addition, the optical properties of these crystallized complexes have been studied in DMF solution.

Acylhydrazone Schiff bases are rich in N and O atoms to coordinate with metal ions to form multidentate complexes.     

Dimensionality of luminescent coordination polymers of magnesium ions and 1,1′-ethynebenzene-3,3′,5,5′-tetracarboxylic acid modulated by structural inducing agents

Solvothermal reactions of aromatic 1,1′-ethynebenzene-3,3′,5,5′-tetracarboxylic acid (H₄EBTC) and Mg²⁺ salts in the presence of different supporting ligands afforded the coordination polymers [Mg(H₂EBTC)(DMF)₂(H₂O)₂] (1), [Mg₃(HEBTC)₂(H₂O)₄]·solvent (2) and [Mg₂(EBTC)(H₂O)₅]·solvent (3). The crystal structures of 1–3 were determined by the single crystal X-ray diffraction technique, where CP 1 showed a one-dimensional zigzag MgO₆ coordination octahedral chain structure; 2 exhibited a two-dimensional MgO₆ coordination octahedral framework with trinuclear [Mg₃(COO)₆] SBUs, and 3 featured a three-dimensional MgO₆ coordination octahedral framework with binuclear [Mg₂O(COO)₂] SBUs. The various structures in CPs 1–3 of Mg²⁺ ions with the H₄EBTC ligand were ascribed to the conformational flexibility and the coordination mode diversity of the H₄EBTC ligand. Interestingly, the zwitterionic supporting ligand 2-aminoterephthalic acid or 4-aminobenzenesulphonic acid played a vital role in the initial formation process of nuclear crystals but only as a structural induction agent, which modulated the dimensionality of these Mg²⁺-based CPs. Additionally, the three CPs emitted bright blue luminescence at ambient conditions, and the emission lifetimes and absolute quantum yields were also investigated.

Crystal structure diversity and dimensionality of three Mg²⁺-based CPs, which emit bright ligand-based luminescence at ambient conditions, are modulated by reaction temperature and structural induction agents.     

Reducing-agent-free facile preparation of Rh-nanoparticles uniformly anchored on onion-like fullerene for catalytic applications

Herein we report a very simple ‘mix and heat’ synthesis of a very fine Rh-nanoparticle loaded carbon fullerene-C60 nanocatalyst (Rh(0)NPs/Fullerene-C60) for the very first time. The preparation method used no reducing agent and capping agent to control the morphology of the nanocatalyst. Transmission electron microscopy (TEM) results confirmed the uniform decoration of small Rh-nanoparticles on the surface of fullerene-C60. The Rh-content in Rh(0)NPs/Fullerene-C60 was found to be 2.89 wt%. The crystalline properties of Rh(0)NPs/Fullerene-C60 were studied by X-ray diffraction (XRD). The metallic state of Rh-nanoparticles in Rh(0)NPs/Fullerene-C60 was confirmed by X-ray photoemission spectroscopy (XPS). Raman results depicted good interaction between Rh-nanoparticles and fullerene-C60. To our delight, the present Rh(0)NPs/Fullerene-C60 showed excellent catalytic activity in the reduction of 4-nitrophenol with NaBH₄ in water. Very high k_app, k′ and TOF values of 82.14 × 10⁻³ min⁻¹, 4107 × 10⁻³ min⁻¹ and 138 min⁻¹, respectively, were calculated for the Rh(0)NPs/Fullerene-C60 catalyzed reduction of 4-nitrophenol. To the best of our knowledge, this is the most efficient fullerene-based nanocatalyst for the rapid reduction of 4-nitrophenol reported to date. Moreover, the catalytic activity of Rh(0)NPs/Fullerene-C60 was also tested towards Suzuki cross-coupling reactions. Reusability of the Rh(0)NPs/Fullerene-C60 was also tested.

Herein we report a very simple ‘mix and heat’ synthesis of a very fine Rh-nanoparticle loaded carbon fullerene-C60 nanocatalyst (Rh(0)NPs/Fullerene-C60) for the very first time.     

The modulation effect of pi–pi interactions on the electronic and photochromic properties of viologen complexes containing N,N′-bis(carboxyethyl)-4,4′-bipyridinium

Two viologen complexes containing N,N′-bis(carboxyethyl)-4,4′-bipyridinium (BCEbpy) were prepared, namely [Zn(H₂O)₆]·(BCEbpy)·(p-BDC)·3H₂O (1) and [Co(H₂O)₆]·(BCEbpy)·(p-BDC)·3H₂O (2) (p-H₂BDC = 1,4-benzenedicarboxylic acid), and their crystal structures, photochromism, frontier molecular orbitals, Hirshfeld surfaces and 2D fingerprint plots were investigated. The modulation effects of pi–pi interactions were explored on the electronic and photochromic properties of compounds 1 and 2. Due to the existence of photo-response viologen radicals, both complexes 1 and 2 display excellent photo-response properties in the sequence 1 < 2. The results indicate that compound 1 exhibits intramolecular electron transfer; compound 2 exhibits both intramolecular and intermolecular electron transfer, which is mainly due to the change of electronic and steric structures caused by pi–pi interactions with a faster photo-response rate than that of compound 1. The donor–acceptor modes, matching principles and inter/intramolecular atom–atom close contacts were illustrated by the density functional theory (DFT)-B3LYP/6-311(d,p) method.

Two viologen complexes containing BCEbpy were prepared and displayed excellent photo-response properties by the modulation effect of pi–pi interactions.     

A series of four novel alkaline earth metal–organic frameworks constructed of Ca(ii), Sr(ii), Ba(ii) ions and tetrahedral MTB linker: structural diversity,stability study and low/high-pressure gas adsorption properties

A series of four novel microporous alkaline earth metal–organic frameworks (AE-MOFs) containing methanetetrabenzoate linker (MTB) with composition {[Ca₄(μ₈-MTB)₂]·2DMF·4H₂O}_n (UPJS-6), {[Ca₄(μ₄-O)(μ₈-MTB)_3/2(H₂O)₄]·4DMF·4H₂O}_n (UPJS-7), {[Sr₃(μ₇-MTB)_3/2]·4DMF·7H₂O}_n (UPJS-8) and {[Ba₃(μ₇-MTB)_3/2(H₂O)₆]·2DMF·4H₂O}_n (UPJS-9) (UPJS = University of Pavol Jozef Safarik) have been successfully prepared and characterized. The framework stability and thermal robustness of prepared materials were investigated using thermogravimetric analysis (TGA) and high-energy powder X-ray diffraction (HE-PXRD). MOFs were tested as adsorbents for different gases at various pressures and temperatures. Nitrogen and argon adsorption showed that the activated samples have moderate BET surface areas: 103 m² g⁻¹ (N₂)/126 m² g⁻¹ (Ar) for UPJS-7′′, 320 m² g⁻¹ (N₂)/358 m² g⁻¹ (Ar) for UPJS-9′′ and UPJS-8′′ adsorbs only a limited amount of N₂ and Ar. It should be noted that all prepared compounds adsorb carbon dioxide with storage capacities ranging from 3.9 to 2.4 wt% at 20 °C and 1 atm, and 16.4–13.5 wt% at 30 °C and 20 bar. Methane adsorption isotherms show no adsorption at low pressures and with increasing pressure the storage capacity increases to 4.0–2.9 wt% of CH₄ at 30 °C and 20 bar. Compounds displayed the highest hydrogen uptake of 3.7–1.8 wt% at −196 °C and 800 Torr among MTB containing MOFs.

Four novel microporous alkaline earth metal–organic frameworks (AE-MOFs) containing methanetetrabenzoate linker (MTB): UPJS-6, UPJS-7, UPJS-8 and UPJS-9 have been successfully prepared, characterized and tested as adsorbents for different gases.     

Two d10 luminescent metal–organic frameworks as dual functional luminescent sensors for (Fe3+,Cu2+) and 2,4,6-trinitrophenol (TNP) with high selectivity and sensitivity

Two luminescent 3D supramolecular structures [Cd₃(L)₂(2,2-bipy)₂](DMF)₃(CH₃CH₂OH)₂(H₂O) (1) and [Zn₃(L)₂(2,2-bipy)₂(DMF)₂](DMF)₂(CH₃CH₂OH)₂(H₂O) (2) (H₃L = 4,4′,4′′-nitrilotribenzoic acid) have been successfully synthesized under solvothermal conditions using Cd(NO₃)₂·4H₂O or Zn(NO₃)₂·6H₂O as the metal sources, and 4,4′,4′′-nitrilotribenzoic acid (H₃L), 2,2-bipy as the ligands in DMF solvent. Compound 1 displays a bi-nodal (2,3,6)-coordinated net with {8³}₂{8⁶·12⁶·16³}{8}₆ topology, compound 2 can be described as a (3,6)-connected 2-nodal net with kgd topology. The phase purity of compound 1 and 2 is characterized by X-ray powder diffraction (XRPD), thermogravimetric analysis (TGA) and Fourier transform infrared (FT-IR) spectroscopy. Compound 1 and 2 can serve as effective luminescent sensors for Fe³⁺, Cu²⁺ and TNP via luminescent quenching.

Two luminescent 3D supramolecular structures which serve as effective luminescent sensors for Fe³⁺, Cu²⁺ and TNP via luminescent quenching have been synthesized under solvothermal conditions.     

Solvent-tuned magnetic exchange interactions in Dy2 systems ligated by a μ-phenolato heptadentate Schiff base

A series of binuclear dysprosium compounds, namely, [Dy(api)]₂ (1), [Dy(api)]₂·2CH₂Cl₂ (2), [Dy(Clapi)]₂·2C₄H₈O (3), and [Dy(Clapi)]₂·2C₃H₆O (4) (H₃api = 2-(2-hydroxyphenyl)-1,3-bis[4-(2-hydroxyphenyl)-3-azabut-3-enyl]-1,3-imidazoline; H₃Clapi = 2-(2′-hydroxy-5′-chlorophenyl)-1,3-bis[3′-aza-4′-(2′′-hydroxy-5′′-chlorophenyl)prop-4′-en-1′-yl]-1,3-imidazolidine), have been isolated by the reactions of salen-type ligands H₃api/H₃Clapi with DyCl₃·6H₂O in different solvent systems. Structural analysis reveals that each salen-type ligand provides a heptadentate coordination pocket (N₄O₃) to encapsulate a Dy^III ion and all of the Dy^III centers in 1–4 adopt a distorted square antiprism geometry with D_4d symmetry. Magnetic studies showed that compound 1 did not exhibit single-molecule magnetic (SMMs) behavior. With the introduction of different lattice solvents, compounds 2–4 showed filed-induced slow magnetic relaxation with barriers U_eff of 18.2 K (2), 28.0 K (3) and 16.4 K (4), respectively. Ab initio calculations were employed to interpret the magnetization behavior of 1–4. The combination of experimental and theoretical data reveal the importance of the weak exchange interaction between the Dy^III ions in the observation of slow magnetic relaxation, and a relaxation mechanism has been developed to rationalize the observed difference in the U_eff values. The different lattice solvents influence Dy–O–Dy bond angles and thus alter the torsion of the square antiprism geometry, consequently resulting in distinct magnetic interactions and the magnetic behavior.

Solvent-tuning changes the magnetic exchange interaction and results in different magnetic relaxation dynamics in Dy₂ systems ligated by a μ-phenolato heptadentate Schiff base.     

Lithium calix[4]arenes: structural studies and use in the ring opening polymerization of cyclic esters

We have structurally characterized a number of lithiated calix[4]arenes, where the bridge in the calix[4]arene is thia (–S–, L^SH₄), sulfinyl (–SO–, L^SOH₄), sulfonyl (–SO₂–, L^SO2H₄), dimethyleneoxa (–CH₂OCH₂–, L^COCH₄) or methylene (–CH₂–, LH₄). In the case of L^4SH₄, interaction with LiOtBu led to the isolation of the complex [Li₈(L^4S)₂(THF)₄]·5THF (1·5THF), whilst similar interaction of L^4SOH₄ led to the isolation of [Li₆(L^4SOH)₂(THF)₂]·5(THF) (2·5THF). Interestingly, the mixed sulfinyl/sulfonyl complexes [Li₈(calix[4]arene(SO)(SO₂)(SO_1.68)₂)₂(THF)₆]·8(THF) (3·8THF) and [Li₅Na(L^SO/3SO2H)₂(THF)₅]·7.5(THF) (4·7.5(THF) have also been characterized. Interaction of LiOtBu with L^SO2H₄ and L^COCH₄ afforded [Li₅L^4SO2(OH)(THF)₄]·2THF (5·2THF) and [Li₆(L^COC)₂(HOtBu)₂]·0.78THF·1.22hexane (6·0.78THF·1.22hexane), respectively. In the case of LH₄, reaction with LiOtBu in THF afforded a monoclinic polymorph [LH₂Li₂(thf)(OH₂)₂]·3THF (7·3THF) of a known triclinic form of the complex, whilst reaction of the de-butylated analogue of LH₄, namely de-BuLH₄, afforded a polymeric chain structure {[Li₅(de-BuL)(OH)(NCMe)₃]·2MeCN}_n (8·2MeCN). For comparative catalytic studies, the complex [Li₆(L^Pr)₂(H₂O)₂]·hexane (9 hexane), where L^Pr2H₂ = 1,3-di-n-propyloxycalix[4]areneH₂, was also prepared. The molecular crystal structures of 1–9 are reported, and their ability to act as catalysts for the ring opening (co-)/polymerization (ROP) of the cyclic esters ε-caprolactone, δ-valerolactone, and rac-lactide has been investigated. In most of the cases, complex 6 outperformed the other systems, allowing for higher conversions and/or greated polymer M_n.

Novel Li-calix[n]arene complexes (n = 3, 4) having (–S–), (–SO–), (–SO₂–), (–CH₂OCH₂–) or (–CH₂–) bridges have been synthesized and fully characterized. Their catalytic activity in the ring opening polymerization of lactones has been studied.     

Hybrid compound based on diethylenetriaminecopper(ii) cations and scarce V-monosubstituted β-octamolybdate as water oxidation catalyst

Herein, we report on a new hybrid compound (NH₄){[Cu(dien)(H₂O)₂]₂[β-VMo₇O₂₆]}·1.5H₂O (1), where dien = diethylenetriamine, containing an extremely rare mixed-metal pseudo-octamolybdate cluster. An ex situ EPR spectroscopy provided insights into the formation of paramagnetic species in reaction mixture and in solution of 1. The magneto-structural correlations revealed weak antiferromagnetic exchange interactions between the [Cu(dien)]²⁺ cations transmitted by intermolecular pathways. The cyclic voltammetry showed the one-electron process associated with the Cu³⁺/Cu²⁺ oxidation followed by the multi-electron catalytic wave due to water oxidation with a faradaic yield of 86%. The title compound was thus employed in homogeneous water oxidation catalysis using tris(bipyridine)ruthenium photosensitizer. At pH 8.0, efficiency of the catalytic system attained 0.19 turnovers per second supported by the relatively mild water oxidation overpotential of 0.54 V.

A new hybrid compound (NH₄){[Cu(dien)(H₂O)₂]₂[β-VMo₇O₂₆]}·1.5H₂O was employed in homogeneous water oxidation catalysis. At pH 8.0, its efficiency attains 0.19 turnovers per second, supported by the relatively mild water oxidation overpotential of 0.54 V.     

Color tuning and white light emission by codoping in isostructural homochiral lanthanide metal–organic frameworks

Four lanthanide-based homochiral metal–organic frameworks (Ln-HMOFs), {[Ln₂(HL)₂(H₂O)₄]·2Cl·5H₂O}_n [Ln = Gd (1), Eu (2), Tb (3) and Dy (4)], have been synthesized through solvothermal reactions of chiral ligand (S)-5-(((1-carboxyethyl)amino)methyl)isophthalic acid (H₃L) with corresponding LnCl₃·6H₂O. They are binodal (3,6)-connected frameworks with kgd nets based on binuclear cluster units and zwitterionic (HL)²⁻ linkers. Considering the isostructuralism of these Ln-HMOFs as well as the blue emission of compound 1 and the strong typical Eu³⁺ and Tb³⁺ emissions of compounds 2 and 3, single-phase mixed-lanthanide HMOFs have been prepared by doping of Ln³⁺ into the Ln-HMOFs to modulate light-emitting color. Interestingly, the bimetallic doped Eu/Tb-HMOFs [(Eu_xTb_1−x)₂(HL)₂(H₂O)₄]·2Cl·5H₂O display a fluent change of light-emitting color among green, yellow, orange, orange-red, and red by adjusting the doping concentration of Eu³⁺ ions into the Tb-HMOF. Very importantly, the trimetallic doped Eu/Gd/Tb-HMOF [(Eu_0.1388Gd_0.6108Tb_0.2504)₂(HL)₂(H₂O)₄]·2Cl·5H₂O emits white light upon excitation at 355 nm, whose emission can also be switched between different colors when excited with different ultraviolet light. Furthermore, the fluorescence response of Tb-HMOF to various usual metal ions, and especially fluorescent sensing behaviours to Fe³⁺, Cr³⁺ and Al³⁺ have been preliminarily investigated.

Pure white-light emission and fluent light-emitting color change can be facilely obtained by codoping isostructural homochiral lanthanide metal–organic frameworks.     

Molybdenum imidazole citrate and bipyridine homocitrate in different oxidation states – balance between coordinated α-hydroxy and α-alkoxy groups

Oxo and thiomolybdenum(iv/vi) imidazole hydrocitrates K₂{Mo^IV₃O₄(im)₃[Mo^VIO₃(Hcit)]₂}·3im·4H₂O (1), (Him)₂{Mo^IV₃SO₃(im)₃[Mo^VIO₃(Hcit)]₂}·im·6H₂O (2), molybdenum(v) bipyridine homocitrate trans-[(Mo^VO)₂O(H₂homocit)₂(bpy)₂]·4H₂O (3) and molybdenum(vi) citrate (Et₄N)[Mo^VIO₂Cl(H₂cit)]·H₂O (4) (H₄cit = citric acid, H₄homocit = homocitric acid, im = imidazole and bpy = 2,2′-bipyridine) with different oxidation states were prepared. 1 and 2 are the coupling products of [Mo^VIO₃(Hcit)]³⁻ anions and incomplete cubane units [Mo^IV₃O₄]⁴⁺ ([Mo^IV₃SO₃]⁴⁺) with monodentate imidazoles, respectively, where tridentate citrates coordinate with α-hydroxy, α-carboxy and β-carboxy groups, forming pentanuclear skeleton structures. The molybdenum atoms in 1 and 2 show unusual +4 and +6 valences based on charge balances, theoretical bond valence calculations and Mo XPS spectrum. The coordinated citrates in 1 and 2 are protonated with α-hydroxy groups, while 3 and 4 with higher oxidation states of +5 and +6 are deprotonated with α-alkoxy group even under strong acidic condition, respectively. This shows the relationship between the oxidation state and protonation of the α-alkoxy group in citrate or homocitrate, which is related to the protonation state of homocitrate in FeMo-cofactor of nitrogenase. The homocitrate in 3 chelates to molybdenum(v) with bidentate α-alkoxy and monodentate α-carboxy groups. Molybdenum(vi) citrate 4 is only protonated with coordinated and uncoordinated β-carboxy groups. The solution behaviours of 1 and 2 are discussed based on ¹H and ¹³C NMR spectroscopies and cyclic voltammograms, showing no decomposition of the species.

Oxo and thiomolybdenum(iv/vi) citrates, molybdenum(v) homocitrate and molybdenum(vi) citrate were obtained, showing the influence of coordinated α-hydroxy and α-alkoxy groups with different oxidation states.     

Lanthanide complexes based on a conjugated pyridine carboxylate ligand: structures,luminescence and magnetic properties

Three lanthanide compounds have been synthesized, namely, {[Dy₂(bpda)₃(H₂O)₃]₄·2H₂O}(Dy-1), {[Sm(bpda)₂·(H₂O)]·H₂O}_n (Sm-2) and {[Tb₂(bpda)₃(H₂O)₃]₄·2H₂O} (Tb-3) (H₂bpda = 2,2′-bipyridine-6,6′-dicarboxylic acid). Their structures were determined by single crystal X-ray diffraction and characterized by elemental analysis, infrared spectroscopy and thermogravimetric analysis. Dy-1 and Tb-3 are isostructural with a conjugate bimolecular four-nuclear cluster structure constructed with intramolecular hydrogen bonds and they form a 3D supramolecular structure with intermolecular hydrogen bonding. Sm-2 is a one-dimensional chain structure and is further connected by intricate hydrogen bonds into a three-dimensional supramolecular structure. These three compounds exhibit significant characteristic luminescence from the ligand to the central Ln(iii) ion, which is found by solid-state photoluminescence measurement. Sm-2 exhibits a long luminescence lifetime and high fluorescence quantum yield. A slow relaxation phenomenon is observed for the dysprosium compound by measuring the alternating-current susceptibility at low temperature and the underlying mechanism was further confirmed by theoretical calculations.

The structures, fluorescence and magnetic properties of series three lanthanide complexes have been investigated. Dysprosium complex exhibit the single-molecule behavior.     

PHB/PCL fibrous membranes modified with SiO2@TiO2-based core@shell composite nanoparticles for hydrophobic and antibacterial applications

In order to prepare multifunctional fibrous membranes with hydrophobicity, antibacterial properties and UV resistance, we used silica and titanium dioxide for preparing SiO₂@TiO₂ nanoparticles (SiO₂@TiO₂ NPs) to create roughness on the fibrous membranes surfaces. The introduction of TiO₂ was used for improving UV resistance. N-Halamine precursor and silane precursor were introduced to modify SiO₂@TiO₂ NPs to synthesize SiO₂@TiO₂-based core@shell composite nanoparticles. The hydrophobic antibacterial fibrous membranes were prepared by a dip-pad process of electrospun biodegradable polyhydroxybutyrate/poly-ε-caprolactone (PHB/PCL) with the synthesized SiO₂@TiO₂-based core@shell composite nanoparticles. TEM, SEM and FT-IR were used to characterize the synthesized SiO₂@TiO₂-based core@shell composite nanoparticles and the hydrophobic antibacterial fibrous membranes. The fibrous membranes not only showed excellent hydrophobicity with an average water contact angle of 144° ± 1°, but also appreciable air permeability. The chlorinated fibrous membranes could inactivate all S. aureus and E. coli O157:H7 after 5 min and 60 min of contact, respectively. In addition, the chlorinated fibrous membranes exhibited outstanding cell compatibility with 102.1% of cell viability. Therefore, the prepared hydrophobic antibacterial degradable fibrous membranes may have great potential application for packaging materials.

Schematic illustration of the synthesis of SiO₂@TiO₂-based core@shell composite nanoparticles (top) and antibacterial hydrophobic behavior of fibrous membranes (bottom).     

Two-dimensional square-grid iron(ii) coordination polymers showing anion-dependent spin crossover behavior

Two Fe(ii)-based coordination polymers [Fe(tpmd)₂(NCS)₂]·5.5H₂O (1) and [Fe(tpmd)₂(NCSe)₂]·7H₂O (2) with the framework of square-grid type have been assembled from FeSO₄·7H₂O, N,N,N′,N′-tetrakis(pyridin-4-yl)methanediamine (tpmd), and KNCS/KNCSe in methanol and characterized. By utilizing two pyridine groups of a tpmd ligand, 1 and 2 are formed in two-dimensional layered structures through coordination of octahedral iron(ii) ions with the tpmd to NCS⁻/NCSe⁻ ligands in which they have a supramolecular isomorphous conformation. 1 shows a paramagnetic behavior between 2 and 300 K, while 2 exhibits two-step spin crossover (ca. 145 and 50 K) in the temperature range due to the coordination of NCSe⁻ ligands. At 300 K 2 is fully high-spin state. However, at 100 K 2 becomes ca. 50% high spin and 50% low spin iron(ii) ions, which is verified by magnetic moments. In the structural analysis of 2 at 100 K, two different layers are observed with different bond distances around iron(ii) ions in which the layers are stacked alternately.

Two-dimensional Fe-based coordination polymers with square-grid shapes were prepared by self-assembly and exhibited an interesting spin crossover behavior depending on the coordinated counter ions.     

Synthesis and properties of a POM-based trinuclear copper(ii) triazole framework

A novel POM-based trinuclear copper(ii) triazole framework, namely, [H₂{Cu₆(trz)₆(μ₃-OH)₂}Mo₅O₁₈]·3H₂O (1) was isolated using a hydrothermal method, which displays a 3D network constructed from trinuclear copper(ii) units and triazole ligands with [Mo₅O₁₈]⁶⁻ anions as templates. 1 has been identified by single crystal X-ray diffraction, elemental analysis, thermogravimetric analysis, powder X-ray diffraction and FT-IR. Magnetic studies indicate that antiferromagnetic interactions exist in 1. In addition, 1 exhibits good Lewis acid catalytic activity for the synthesis of cyclohexanone ethylene ketal with 95% conversion. The HOMO–LUMO gap (E_g) of 1 is 2.34 eV calculated using the Kubelka–Munk equation (Fhν)^0.5, indicating that its forbidden bandwidth belongs to the semiconductor category. Visible-light photodegradation of RhB catalyzed by 1 was investigated, which shows high activity with an above 98% degradation rate.

A novel POMs-based trinuclear copper(ii) triazole framework, namely, {[H₂Cu₆(trz)₆(μ₃-OH)₂]} [Mo₅O₁₈]·3H₂O (1) was isolated by hydrothermal method, which displays remarkable Lewis acid catalytic activity and photocatalytic activity.     

Nanochannel-based heterometallic {ZnIIHoIII}–organic framework with high catalytic activity for the chemical fixation of CO2

The exquisite combination of Zn^II and Ho^III generated the highly robust [ZnHo(CO₂)₆(OH₂)]-based heterometallic framework of {[ZnHo(TDP)(H₂O)]·5H₂O·3DMF}_n (NUC-30, H₆TDP = 2,4,6-tri(2′,4′-dicarboxyphenyl)pyridine), which featured outstanding physicochemical properties, including honeycomb nanochannels, high porosity, large specific surface area, the coexistence of highly open Lewis acid–base sites, good thermal and chemical stability, and resistance to most organic solvents. Due to its extremely unsaturated metal tetra-coordinated Zn(ii) ions, hepta-coordinated Ho(iii) and high faveolate void volume (61.3%), the conversion rate of styrene oxide and CO₂ into cyclic carbonates in the presence of 2 mol% activated NUC-30 and 5 mol% n-Bu₄NBr reached 99% under the mild conditions of 1.0 MPa and 60 °C. Furthermore, the luminescence sensing experiments proved that NUC-30 could be used as a fast, sensitive and highly efficiency sensor for the detection of Fe³⁺ in aqueous solution. Therefore, these results prove that nanoporous MOFs assembled from pyridine-containing polycarboxylate ligands have wide applications, such as catalysis and as luminescent materials.

The robust, double-walled, honeycomb material {[ZnHo(TDP)(H₂O)]·2DMF·4H₂O}_n exhibits an excellent catalytic performance in the chemical fixation of CO₂ and the efficient detection of Fe(iii) ions in aqueous solution.     

Structural and thermal properties of Na2Mn(SO4)2·4H2O and Na2Ni(SO4)2·10H2O

The title compounds were prepared via a wet chemistry route and their crystal structures were determined from single crystal X-ray diffraction data. Na₂Mn(SO₄)₂·4H₂O crystallizes with a monoclinic symmetry, space group P2₁/c, with a = 5.5415(2), b = 8.3447(3), c = 11.2281(3) Å, β = 100.172(1)°, V = 511.05(3) ų and Z = 2. Na₂Ni(SO₄)₂·10H₂O also crystallizes with a monoclinic symmetry, space group P2₁/c, with a = 12.5050(8), b = 6.4812(4), c = 10.0210(6) Å, β = 106.138(2)°, V = 780.17(8) ų and Z = 2. Na₂Mn(SO₄)₂·4H₂O is a new member of the blödite family of compounds, whereas Na₂Ni(SO₄)₂·10H₂O is isostructural with Na₂Mg(SO₄)₂·10H₂O. The structure of Na₂Mn(SO₄)₂·4H₂O is built up of [Mn(SO₄)₂(H₂O)₄]²⁻ building blocks connected through moderate O–H⋯O hydrogen bonds with the sodium atoms occupying the large tunnels along the a axis and the manganese atom lying on an inversion center, whereas the structure of Na₂Ni(SO₄)₂·10H₂O is built up of [Ni(H₂O)₆]²⁺ and [Na₂(SO₄)₂(H₂O)₄]²⁻ layers. These layers which are parallel to the (100) plane are interconnected through moderate O–H⋯O hydrogen bonds. The thermal gravimetric- and the powder X-ray diffraction-analyzes showed that only the nickel phase was almost pure. At a temperature above 300 °C, all the water molecules evaporated and a structural phase transition from P2₁/c-Na₂Ni(SO₄)₂·10H₂O to C2/c-Na₂Ni(SO₄)₂ was observed. C2/c-Na₂Ni(SO₄)₂ is thermally more stable than Na₂Fe(SO₄)₂ and therefore it would be suitable as the positive electrode for sodium ion batteries if a stable electrolyte at high voltage is developed.

Two compounds were prepared via a supersaturation method. Their crystal structures were solved and compared to Na₂M(SO₄)₂·nH₂O (M = Mn, Ni and n = 0, 1, 2, 3, 4, 5, 6, 10, 16). Furthermore, phase transitions as a function of temperature were observed.     

Construction of cost-effective bimetallic nanoparticles on titanium carbides as a superb catalyst for promoting hydrolysis of ammonia borane

Bimetallic cost-effective CoNi nanoparticles (NPs) are conveniently supported on titanium carbides (MXene) by a simple one-step wet-chemical method. The synthesized CoNi/MXene catalysts are characterized by XPS, TEM, STEM-HAADF and ICP-AES. The as-prepared CoNi NPs with a size of 2.8 nm are well dispersed on the MXene surface. It is found that among the CoNi bimetallic system, Co_0.7Ni_0.3 shows the best performance toward catalyzing ammonia borane (AB) decomposition with a turnover frequency value of 87.6 mol_H2 mol_cat⁻¹ min⁻¹ at 50 °C. The remarkable catalytic performance is attributed to the mild affiliation of MXene to NPs, which not only stabilizes NPs to maintain a good dispersion but also leaves sufficient surface active sites to facilitate the catalytic reaction.

Bimetallic cost-effective CoNi nanoparticles are supported on MXene by a simple one-step wet-chemical method. The Co_0.7Ni_0.3/MXene shows the best performance toward catalyzing AB decomposition with TOF of 87.6 mol_H2 mol_cat⁻¹ min⁻¹ at 50 °C.     

Synthesis of MOFs/GO composite for corrosion resistance application on carbon steel

Two unreported metal–organic frameworks [Cu(6-Me-2,3-pydc)(1,10-phen)·7H₂O]_n (namely Cu-MOF) and [Mn₂(2,2′-bca)₂(H₂O)₂]_n (namely Mn-MOF) were synthesized by a solvothermal method and their structures were characterized and confirmed by elemental analysis, X-ray single crystal diffraction, Fourier infrared spectroscopy and thermogravimetric analysis. Cu-MOF/graphene (Cu-MOF/GR), Cu-MOF/graphene oxide (Cu-MOF/GO), Mn-MOF/graphene (Mn-MOF/GR) and Mn-MOF/graphene oxide (Mn-MOF/GO) composite materials were successfully synthesized by a solvothermal method and characterized and analyzed by PXRD, SEM and TEM. In order to study the corrosion inhibition properties of the Cu-MOF/GR, Cu-MOF/GO, Mn-MOF/GR and Mn-MOF/GO composite materials on carbon steel, they were mixed with waterborne acrylic varnish to prepare a series of composite coatings to explore in 3.5 wt% NaCl solution by electrochemical measurements and results showed that the total polarization resistance of the 3% Cu-MOF/GO and 3% Mn-MOF/GO composite coatings on the carbon steel surface were relatively large, and were 55 097 and 55 729 Ω cm², respectively, which could effectively protect the carbon steel from corrosion. After immersion for 30 days, the 3% Mn-MOF/GO composite still maintained high corrosion resistance, the |Z| values were still as high as 23 804 Ω cm². Therefore, MOFs compounded with GO can produce a synergistic corrosion inhibition effect and improve the corrosion resistance of the coating; this conclusion is well confirmed by the adhesion capability test.

Two unreported metal–organic frameworks [Cu(6-Me-2,3-pydc)(1,10-phen)·7H₂O]_n (namely Cu-MOF) and [Mn₂(2,2′-bca)₂(H₂O)₂]_n (namely Mn-MOF) were synthesized and characterized. Cu-MOF and Mn-MOF all can form a three-dimensional structure.