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A CuO/Mn2O3 heterojunction catalyst is successfully prepared by a simple hydrothermal and calcination method, which exhibits a unique spindle-like morphology with a rough surface that can expose more active sites. Moreover, the formation of a heterogeneous interface accelerates the interfacial electron transfer, and optimizes the desorption and hydrogenation process of CuO/Mn2O3 to intermediates, significantly enhancing the NO3RR activity. Thus, CuO/Mn2O3 exhibits a high NH3 Faradaic efficiency of 98.44%, and a high NH3 yield of 12 990.49 μg h−1 cm−2 at −0.7 V vs. RHE in alkaline medium. [ABSTRACT FROM AUTHOR]

The electrochemical nitrate reduction reaction (ENO3RR) is a green ammonia synthesis method under ambient conditions relative to the traditional Haber–Bosch technology, which does not require high-temperature or high-pressure conditions and can convert nitrate pollutants in the environment into value-added NH3, thus achieving a dual purpose. However, more electrocatalysts with a remarkable performance towards high-efficiency ENO3RR need to be developed. In this work, a Cu/NiO-NF composite electrocatalyst with a nanorod structure on nickel foam was successfully fabricated, which contains heterogeneous interfaces between Cu and NiO toward selective electrocatalytic nitrate reduction for ammonia synthesis. The steric nanorod morphology of the catalyst can significantly increase the surface area, expose more active sites, and improve the reaction activity. Moreover, the construction of the composite and the interface effectively boosts the synergistic effect of the active species Cu and NiO, which can regulate the electronic structure of the catalyst, expose more active sites, enhance the conductivity of the material, and accelerate the interfacial electron transfer, thereby further promoting the ENO3RR performance. This Cu/NiO-NF composite exhibits a high NH3 yield of 0.6 mmol h−1 cm−2 and up to 97.81% faradaic efficiency at the optimal applied potential of −1.0 V (vs. RHE) in a concentration of 0.1 M NO3−-containing 0.1 M PBS. Furthermore, it demonstrates excellent electrochemical cycle stability. This work provides insights into the rational design and fabrication of ENO3RR electrocatalysts for potential electrocatalytic applications. [ABSTRACT FROM AUTHOR]

A novel 3D Eu(III) metal–organic framework (Eu-MOF-1) formulated as [Eu(L)(H2O)(DMA)] (L = 2-(2-nitro-4-carboxylphenyl)terephthalic acid) has been successfully synthesized under solvothermal conditions and characterized by structural analyses. Eu-MOF-1 displays a new 3D framework containing EuIII ions, ligand L, and coordinated DMA molecules and water molecules. The fluorescence investigations indicate that Eu-MOF-1 emits bright red luminescence, and shows relatively high water stability and outstanding chemical stability under a relatively wide range of pH conditions. It is noteworthy that Eu-MOF-1 can quantitatively detect p-aminophenol (PAP) which is a metabolite of phenylamine in human urine. More significantly, Eu-MOF-1 is the first reported multi-responsive luminescent sensor for detecting the biomarker PAP, and MnVII and CrVI anions with high selectivity, sensitivity, recyclability and relatively low detection limits in aqueous solutions. Furthermore, the possible sensing mechanisms of Eu-MOF-1 for selective sensing have also been explored in detail. Eu-MOF-1 could be an ideal candidate as a multi-responsive luminescent sensor in biological and environmental areas. [ABSTRACT FROM AUTHOR]

Three novel Cd(II)/Zn(II) coordination polymers (CPs), namely [Cd(L)(BPDC)0.5H2O]·0.5H2O (1), [Zn2(L)2(BPDC)]·2H2O (2) and [Cd2(L)(BTC)H2O]·3H2O (3) (L = 4-(tetrazol-5-yl)phenyl-4,2′:6′,4′′-terpyridine, H2BPDC = 4,4′-biphenyldicarboxylic acid, and H3BTC = 1,3,5-benzenetricarboxylic acid), have been successfully synthesized and characterized. CP 1 and CP 2 display new two-dimensional double-layered honeycomb frameworks containing uncoordinated nitrogen atoms from pyridine and tetrazole rings, which can easily form hydrogen bonds with various analytes. CP 3 exhibits a 3D framework also with uncoordinated nitrogen atoms from pyridine and tetrazole rings. The fluorescence explorations indicate that CPs 1–3 exhibit strong blue luminescence and excellent chemical stability under a relatively wide range of pH conditions. It is worth noting that CPs 1–3 can quantitatively detect hippuric acid (HA), which is a metabolite of toluene in human urine, with high selectivity, sensitivity, fast response and relatively low detection limits. Moreover, the sensing mechanism of CPs 1–3 for HA can mainly be ascribed to fluorescence resonance energy transfer (FRET). CPs 1–3 could be ideal candidates as HA sensors in human urine samples for practical applications. Notably, to the best of our knowledge, we report for the first time Cd(II)/Zn(II)-based luminescent sensors for detecting HA in simulated urine. [ABSTRACT FROM AUTHOR]

A novel single-phase white-light-emitting microscale lanthanide metal–organic framework [Eu0.06Tb0.04Gd0.9(HDPNC)1.5(H2O)(DMF)]·2H2O (H3DPNC = 5-(3′,5′-dicarboxylphenyl) nicotinic acid) abbreviated as Eu0.06Tb0.04Gd0.9-DPNC was obtained successfully under 365 nm excitation, by adjusting the molar ratio of Ln3+ and different excitation wavelengths, with the Commission Internationale de l'Eclairage (CIE) coordinates of (0.3328, 0.3296). The tri-emission lanthanide metal–organic framework (Eu0.06Tb0.04Gd0.9-DPNC), acting as an effective fluorescent platform, not only exhibits notable fluorescence quenching (turn-off) toward MnO4− in water through the fluorescence resonance energy transfer (FRET) mechanism, with a linear recognition range of 0–0.2 mM and a low detection limit (LOD) of 0.0197 μM, but also shows fluorescence enhancement (turn-on) for the detection of folic acid (FA) in water through host–guest interactions, and a linear relationship in the concentration range of 0–18 μM with a LOD of 0.0883 μM. This is the first time folic acid detection is carried out based on a Ln–MOF, and is also one of the very rare examples of application of white-light-emitting MOFs for fluorescence detection. Furthermore, interestingly, another fluorescence further enhanced (named turn-on plus) system was designed and successfully obtained by adding FA to the fluorescence quenched Eu0.06Tb0.04Gd0.9-DPNC@MnO4− system, in which the mechanism of further fluorescence enhancement can be ascribed to the redox reaction between MnO4− and FA under alkaline conditions and the production of another fluorescent compound. Additionally, the Boolean logic system was also constructed based on the dual-component analysis (MnO4− and FA) of Eu0.06Tb0.04Gd0.9-DPNC in water. [ABSTRACT FROM AUTHOR]

A coordination framework formulated as [ CO 3 (L) 4 (OH) 2 (H 2 O) 2 ] n (1) (L = 4-(tetrazol-5-yl)phenyl-4,2′:6′,4′′-terpyridine) was synthesized and was structurally and magnetically characterized. Compound 1 features 1D chains in which unprecedented triangular non-uniform chains with mixed μ3-OH and (μ3-OH)(μ-N-N-tetrazolate)2 bridges are interlinked by the ligands into a 2D coordination framework. Magnetic investigations indicate that 1D ferrimagnetic chains, single-chain magnet like behaviors and large hysteresis coexist in the magnetic system of 1. The activation energies for magnetic reversal in the infinite- and finite-chain regimes are Δτ1/k = 180 K and Δτ2/k = 75 K, respectively. [ABSTRACT FROM AUTHOR]

A 2D zinc(ii) metal–organic framework (Zn-MOF-1) formulated as [Zn2(L)2(TPA)]·2H2O, (L = 4-(tetrazol-5-yl)phenyl-4,2′:6′,4′′-terpyridine, TPA = terephthalic acid) was successfully obtained under solvothermal conditions. Zn-MOF-1 shows a new 2D double-layered honeycomb structure containing Zn2+ ions, ligand L and TPA, with uncoordinated nitrogen atoms (from pyridine rings and tetrazol rings) of L and uncoordinated carboxylate oxygen atoms of TPA, which easily form hydrogen bonds with analytes. Fluorescence analysis reveals that Zn-MOF-1 generates strong blue luminescence, which can be assigned to ligand-centered emission. More importantly, it is the first reported recyclable multi-responsive Zn-MOF fluorescence sensor for pesticide 2,6-dichloro-4-nitroaniline, Fe(iii) and Cr(vi) (CrO42−/Cr2O72− ions) detection with high sensitivity, selectivity and low detection limit in methanol or water via fluorescence quenching. Furthermore, selective sensing by Zn-MOF-1 of 2,6-dichloro-4-nitroaniline, Fe3+ ions, and CrO42− or Cr2O72− ions can mainly be attributed to the absorption by the analytes of the excitation and/or emission light of Zn-MOF-1 and the electronic interactions between Zn-MOF-1 and the analytes. [ABSTRACT FROM AUTHOR]

Five new 3D isostructural lanthanide metal organic frameworks (Ln-MOFs), [Ln(HL)1.5(H2O)(DMF)]·2H2O (Ln = GdIII (1), SmIII (2), DyIII (3), EuIII (4) and TbIII (5), H3L = 5-(3′,5′-dicarboxylphenyl) nicotinic acid) were synthesized by solvothermal methods and studied by structural analyses, magnetic analyses and luminescence sensing. Crystallographic studies revealed that these compounds are 3D frameworks in which the LnIII-COO chains with alternating four and two carboxylate bridges are interlinked by the organic ligands L, and contain microporous channels with accessible Lewis-base sites, coordinated water molecules and uncoordinated carboxyl groups, which are easy to combine and recognise various analytes. Magnetic studies demonstrated that the carboxylate bridges transmit interchain dominant ferromagnetic interactions in Gd-MOF (1) and Dy-MOF (3), while the decrease of the χT value in Sm-MOF (2) is due to the thermal depopulation effect of the excited levels. Furthermore, Dy-MOF (3) also shows slow magnetic relaxation behaviour under a zero dc field. The luminescence selective sensing experiments showed that Eu-MOF (4) and Tb-MOF (5) can act as recyclable sensors towards Fe3+ ions in water and the simulated biological fluids, and towards ketones in a water system with high sensitivity, selectivity and relatively low detection limits. [ABSTRACT FROM AUTHOR]

A 2D zinc(ii) metal–organic framework (Zn-MOF-1) formulated as [Zn(L)(H2O)]·H2O (1) (H2L = 5-(2-methylpyridin-4-yl)isophthalic acid) with blue fluorescence has been successfully obtained under hydrothermal conditions. Zn-MOF-1 contains microporous parallelogram channels with accessible Lewis-base sites, coordinated water molecules and uncoordinated carboxylates, which are easy to anchor and recognise various analytes. The fluorescence investigations demonstrated that the blue-light-emitting behaviour of Zn-MOF-1 possesses excellent water and pH stability. More importantly, this is the first reported recyclable multi-responsive Zn-MOF fluorescence sensor for Cr(iii), Cr(vi) (CrO42−/Cr2O72− ions) and 4-NP (4-nitrophenol) simultaneously with high selectivity and sensitivity and low detection limits in aqueous solution through fluorescence quenching. Furthermore, the mechanism for the selective sensing of Cr3+, CrO42−, Cr2O72− or 4-NP can mainly be explained by the competition between the absorption of the analytes and the excitation/emission of Zn-MOF-1, and the electronic interactions between Zn-MOF-1 and the analytes. [ABSTRACT FROM AUTHOR]

Five Mn(ii) coordination polymers containing azide and carboxylate as simultaneous bridges have been derived from different imidazolium-carboxylate zwitterionic ligands: 1-methyl-3-(carboxylatomethyl)imidazolium (L1), 1,3-bis(carboxylatomethyl)imidazolium (L2), (S,S)-, (R,R)-, and (R,S)-1,3-bis(1-carboxylatoethyl)imidazolium (S,S-L3, R,R-L3 and R,S-L3). The compounds are formulated as [Mn(L1)(N3)2] (1), [Mn(L2)(N3)] (2), [Mn(R,R-L3)(N3)]·0.5CH3OH (3-R), [Mn(S,S-L3)(N3)]·0.5CH3OH (3-S), [Mn(R,S-L3)(N3)] (4). In compound 1, the neutral monocarboxylate zwitterion ligand (L1) leads to uniform chains with bis(azide)(carboxylate) bridges. For compounds 2–4, the anionic dicarboxylate zwitterions L2 and L3 lead to (azide)bis(carboxylate) bridges, but the overall coordination networks are different. In 2 and 3-S (or 3-R), chains with the (azide)bis(carboxylate) bridges are connected by L2 and S,S-L3 (or R,R-L3), respectively, to give achiral and chiral 2D coordination networks with different connecting topologies. In compounds 4, which is derived from the mesomeric ligand R,S-L3, linear trinuclear units with the (azide)bis(carboxylate) bridges are linked by μ-1,3 azides to give 2D layers, and the layers are pillared into a 3D framework by the 1,3-dimethyleneimidazolium tethers. Magnetic analyses suggested that compounds 1–3 behave as 1D antiferromagnetic systems, while 4 shows canted antiferromagnetism with weak ferromagnetic ordering below TC = 12.4 K. [ABSTRACT FROM AUTHOR]

The reactions of manganese(ii) acetate or perchlorate, sodium azide or sodium cyanate, and the zwitterionic dicarboxylate ligand 1,4-bis(4-carboxylatopyridinium-1-methylene)benzene (L) under different conditions yielded three different Mn(ii) coordination polymers with mixed carboxylate and azide (or cyanate) bridges: {[Mn (L1)0.5(N3)(OAc)]·3H2O}n(1), {[Mn4(L1)(N3)8(H2O)4(CH3OH)2]·[L1]}n(2), and {[Mn3(L1)(NCO)6(H2O)4]·[L1]·[H2O]2}n(3). The compounds exhibit diverse structures and magnetic properties. In 1, the 1D uniform anionic [Mn(N3)(COO)2]nchains with the (μ-EO-N3)(μ-COO)2triple bridges (EO = end-on) are interlinked by the dipyridinium L ligands into highly undulated 2D layers. Magnetic studies on 1reveal that the mixed triple bridges induce antiferromagnetic coupling between Mn(ii) ions. Compounds 2and 3consist of 1D neutral polymeric chains and co-crystallized zwitterions, and the chains are formed by the L ligands interlinking linear polynuclear units. The polynuclear unit in 2is tetranuclear with (μ-EO-N3)2as central bridges and (μ-EO-N3)2(μ-COO) as peripheral bridges, while that in 3is trinuclear with (μ-NCO)2(μ-COO) bridges. Magnetic studies demonstrate that the magnetic coupling through the mixed azide/isocyanate and carboxylate bridges in 2and 3is antiferromagnetic. An expression of magnetic susceptibility based on a 2-Jmodel for linear tetranuclear systems of classical spins has been deduced and applied to 2. [ABSTRACT FROM AUTHOR]

Two isomorphous 3D Mn(II) and Co(II) coordination polymers with a dicarboxylate inner salt and cyanate as coligands were synthesized and structurally characterized, and their magnetic properties have been studied. In the compounds, [M(L)(NCO)]n·nH2O (M = Mn, Co, L = 1-carboxymethylpyridinium-4-carboxylate), neighboring metal ions are linked by the 3-fold bridges of an end-on cyanate and two syn–syncarboxylate bridges to give an anionic chain of [M(µ-NCO)(µ–COO)2]n, and each chain is interlinked to four other chains by the cationic 1-methylpyridinium spacers to generate a 3D structure with the 42· 63· 8 net topology. They are the first compounds with mixed cyanate and carboxylate bridges. Magnetic studies reveal that the 3-fold mixed bridge propagates antiferromagnetic coupling in the Mn(II) compound but ferromagnetic coupling in the Co(II) compound. The rather complex magnetic behaviors of the Co(II) compound are analyzed taking into account the first-order spin-orbital coupling and the intrachain ferromagnetic interactions. [ABSTRACT FROM AUTHOR]

A series of isomorphous 3D CoSTACKABOVEII/ABOVEBELOW1−x/BELOW/STACKNiSTACKABOVEII/ABOVEBELOWx/BELOW/STACK MOFs based on ferromagnetic chains show SCM-type slow relaxation and the Co-rich system can exhibit a higher blocking temperature than both CoII and NiII parent materials. [ABSTRACT FROM AUTHOR]

A single-chain magnet consisting of CoIIchains with (EO-N3)2and (μ-COO)2(μ-EO-N3) bridges reversibly transforms into an antiferromagnetic phase with metamagnetic character and modified slow magnetic relaxation upon dehydration. [ABSTRACT FROM AUTHOR]

A novel 2D coordination polymer consisting of ferromagnetic Ni(ii) chains with alternating double EO-azide bridges and (EO-azide)bis(carboxylate) triple bridges exhibits solvent-modulated metamagnetism, and the reversible dehydration/hydration processes are accompanied by significant changes in critical temperature, critical field and hysteresis. [ABSTRACT FROM AUTHOR]

Electrochemical nitrate reduction to ammonia (ENO 3 RR) has attracted great attention owing to its characteristics of treating wastewater while producing high value-added ammonia. In this study, we successfully prepared a heterojunction electrocatalyst Fe 2 O 3 /ZnO consisting of Fe 2 O 3 nanosheets and ZnO nanoparticles, where the construction of the Fe 2 O 3 /ZnO heterojunction not only increased the exposure of the active sites of the catalyst, accelerated the interfacial electron transfer, and improved the conductivity of the catalyst but also optimized its overall electronic structure. Thus, Fe 2 O 3 /ZnO demonstrated a high Faraday efficiency of 97.4% and an ammonia yield of 6327.2 μg h -1 cm -2 at -1.0 V ( vs. RHE) in 0.1 M KNO 3 and 0.1 M PBS. DFT calculations also confirmed that the constructed Fe 2 O 3 /ZnO heterojunction effectively decreased the reaction energy barrier of *NO → *NHO and accelerated the reaction kinetics, which is favourable for ENO 3 RR. This study provides a new and facile design strategy of catalysts for electrochemical nitrate reduction to ammonia.

Utilizing renewable energy such as offshore wind power to electrolyze seawater for hydrogen production offers a sustainable development pathway to address energy and climate change issues. In this study, by incorporating nitrogen-doped carbon quantum dots (N-CDs) into precursors, we successfully synthesized a nitrogen-doped carbon (NC)-layer-coated Co(OH)F/CoP 2 catalyst NC@Co(OH)F/CoP 2 /NF loaded on nickel foam (NF). The introduction of N-CDs induced significant morphology change of the catalyst, facilitating the exposure of numerous active sites, ensuring the presence of catalytically active species CoP 2 in nanoparticle form and avoiding agglomeration, which was advantageous to enhancing the overall hydrogen evolution reaction (HER) activity of the catalyst. The formation of Co-N bonds accelerated electron transfer, regulated the electronic structure, and optimized the catalyst's adsorption capacity for H* intermediates, which resulted in remarkably improved HER performance. In addition, Co(OH)F can also serve as a structural support, preventing the catalyst from collapsing during the HER catalytic process. NC@Co(OH)F/CoP 2 /NF exhibited excellent HER activity in alkaline freshwater and alkaline seawater, respectively requiring overpotentials of only 107 and 128 mV to achieve a current density of 100 mA cm -2 . More importantly, it also demonstrated excellent HER activity at high current densities, with overpotentials of 189 and 237 mV at a current density of 1000 mA cm -2 in alkaline freshwater and alkaline seawater, respectively. This work provides new insights into the design and construction of highly efficient HER catalysts for applications in alkaline freshwater and seawater.

The electrochemical nitrate reduction reaction (ENO 3 RR) is a green ammonia synthesis method under ambient conditions relative to the traditional Haber-Bosch technology, which does not require high-temperature or high-pressure conditions and can convert nitrate pollutants in the environment into value-added NH 3 , thus achieving a dual purpose. However, more electrocatalysts with a remarkable performance towards high-efficiency ENO 3 RR need to be developed. In this work, a Cu/NiO-NF composite electrocatalyst with a nanorod structure on nickel foam was successfully fabricated, which contains heterogeneous interfaces between Cu and NiO toward selective electrocatalytic nitrate reduction for ammonia synthesis. The steric nanorod morphology of the catalyst can significantly increase the surface area, expose more active sites, and improve the reaction activity. Moreover, the construction of the composite and the interface effectively boosts the synergistic effect of the active species Cu and NiO, which can regulate the electronic structure of the catalyst, expose more active sites, enhance the conductivity of the material, and accelerate the interfacial electron transfer, thereby further promoting the ENO 3 RR performance. This Cu/NiO-NF composite exhibits a high NH 3 yield of 0.6 mmol h -1 cm -2 and up to 97.81% faradaic efficiency at the optimal applied potential of -1.0 V ( vs. RHE) in a concentration of 0.1 M NO 3 - -containing 0.1 M PBS. Furthermore, it demonstrates excellent electrochemical cycle stability. This work provides insights into the rational design and fabrication of ENO 3 RR electrocatalysts for potential electrocatalytic applications.

A novel 3D Eu(iii) metal-organic framework (Eu-MOF-1) formulated as [Eu(L)(H2O)(DMA)] (L = 2-(2-nitro-4-carboxylphenyl)terephthalic acid) has been successfully synthesized under solvothermal conditions and characterized by structural analyses. Eu-MOF-1 displays a new 3D framework containing EuIII ions, ligand L, and coordinated DMA molecules and water molecules. The fluorescence investigations indicate that Eu-MOF-1 emits bright red luminescence, and shows relatively high water stability and outstanding chemical stability under a relatively wide range of pH conditions. It is noteworthy that Eu-MOF-1 can quantitatively detect p-aminophenol (PAP) which is a metabolite of phenylamine in human urine. More significantly, Eu-MOF-1 is the first reported multi-responsive luminescent sensor for detecting the biomarker PAP, and MnVII and CrVI anions with high selectivity, sensitivity, recyclability and relatively low detection limits in aqueous solutions. Furthermore, the possible sensing mechanisms of Eu-MOF-1 for selective sensing have also been explored in detail. Eu-MOF-1 could be an ideal candidate as a multi-responsive luminescent sensor in biological and environmental areas.

Three novel Cd(ii)/Zn(ii) coordination polymers (CPs), namely [Cd(L)(BPDC) 0.5 H 2 O]·0.5H 2 O (1), [Zn 2 (L) 2 (BPDC)]·2H 2 O (2) and [Cd 2 (L)(BTC)H 2 O]·3H 2 O (3) (L = 4-(tetrazol-5-yl)phenyl-4,2':6',4''-terpyridine, H 2 BPDC = 4,4'-biphenyldicarboxylic acid, and H 3 BTC = 1,3,5-benzenetricarboxylic acid), have been successfully synthesized and characterized. CP 1 and CP 2 display new two-dimensional double-layered honeycomb frameworks containing uncoordinated nitrogen atoms from pyridine and tetrazole rings, which can easily form hydrogen bonds with various analytes. CP 3 exhibits a 3D framework also with uncoordinated nitrogen atoms from pyridine and tetrazole rings. The fluorescence explorations indicate that CPs 1-3 exhibit strong blue luminescence and excellent chemical stability under a relatively wide range of pH conditions. It is worth noting that CPs 1-3 can quantitatively detect hippuric acid (HA), which is a metabolite of toluene in human urine, with high selectivity, sensitivity, fast response and relatively low detection limits. Moreover, the sensing mechanism of CPs 1-3 for HA can mainly be ascribed to fluorescence resonance energy transfer (FRET). CPs 1-3 could be ideal candidates as HA sensors in human urine samples for practical applications. Notably, to the best of our knowledge, we report for the first time Cd(ii)/Zn(ii)-based luminescent sensors for detecting HA in simulated urine.

Five new 3D isostructural lanthanide metal organic frameworks (Ln-MOFs), [Ln(HL)1.5(H2O)(DMF)]·2H2O (Ln = GdIII (1), SmIII (2), DyIII (3), EuIII (4) and TbIII (5), H3L = 5-(3',5'-dicarboxylphenyl) nicotinic acid) were synthesized by solvothermal methods and studied by structural analyses, magnetic analyses and luminescence sensing. Crystallographic studies revealed that these compounds are 3D frameworks in which the LnIII-COO chains with alternating four and two carboxylate bridges are interlinked by the organic ligands L, and contain microporous channels with accessible Lewis-base sites, coordinated water molecules and uncoordinated carboxyl groups, which are easy to combine and recognise various analytes. Magnetic studies demonstrated that the carboxylate bridges transmit interchain dominant ferromagnetic interactions in Gd-MOF (1) and Dy-MOF (3), while the decrease of the χT value in Sm-MOF (2) is due to the thermal depopulation effect of the excited levels. Furthermore, Dy-MOF (3) also shows slow magnetic relaxation behaviour under a zero dc field. The luminescence selective sensing experiments showed that Eu-MOF (4) and Tb-MOF (5) can act as recyclable sensors towards Fe3+ ions in water and the simulated biological fluids, and towards ketones in a water system with high sensitivity, selectivity and relatively low detection limits.

A series of isomorphous three-dimensional metal-organic frameworks [Co II 1- x Zn II x (L)(N 3 )]·H 2 O ( x = 0.26, 0.56 and 0.85) based on bimetallic Co II 1- x Zn II x ( x = 0.26, 0.56 and 0.85) chains with random metal sites have been synthesized and magnetically characterized. The Co II 1- x Zn II x series, which intrinsically feature random anisotropic/diamagnetic sites, shows complex magnetic interactions. By gradually introducing the diamagnetic Zn II ions into the pure anisotropic Co II single-chain magnets system, the ferromagnetic interactions between Co II ions are gradually diluted. Moreover, the slow magnetic relaxation behaviour of the mixed metal Co II 1- x Zn II x systems also changes. In this bimetallic series Co II 1- x Zn II x , the Co-rich materials exhibit slow relaxation processes that may arise from SCM mechanism, while the Zn II -rich materials show significantly low slow magnetic relaxation. A general trend is that the activation energy and the blocking temperature decrease with the increase in diamagnetic Zn II content, emphasizing the importance of anisotropy for slow relaxation of magnetization., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Two Mn(ii) complexes with azide and a new zwitterionic tetracarboxylate ligand 1,2,4,5-tetrakis(4-carboxylatopyridinium-1-methylene)benzene (L(1)), {[Mn5(L(1))2(N3)8(OH)2]·12H2O}n () and {[Mn5(L(1))2(N3)8(H2O)2](ClO4)2·6H2O}n (), have been synthesized and characterized crystallographically and magnetically. and contain similar alternating chains constructed by azide and carboxylate bridges. The independent sets of bridges alternate in an ABCCB sequence between adjacent Mn(ii) ions: (EO-N3)2 double bridges (EO = end-on) (denoted as A), [(EO-N3)(OCO)2] triple bridges (denoted as B) and [(EO-N3)(OCO)] double bridges (denoted as C). The alternating chains are interlinked into 2D coordination networks by the tetrapyridinium spacers. Magnetic studies demonstrate that the magnetic coupling through the double EO azide bridges is ferromagnetic and that through mixed azide/carboxylate bridges is antiferromagnetic. The unprecedented F/AF/AF'/AF'/AF coupling sequence along the chain dictates an uncompensated ground spin state (S = 5/2 per Mn5 unit) and leads to one-dimensional topological ferrimagnetism, which features a minimum in the χT versus T plot.

Five Mn(II) coordination polymers containing azide and carboxylate as simultaneous bridges have been derived from different imidazolium-carboxylate zwitterionic ligands: 1-methyl-3-(carboxylatomethyl)imidazolium (L(1)), 1,3-bis(carboxylatomethyl)imidazolium (L(2)), (S,S)-, (R,R)-, and (R,S)-1,3-bis(1-carboxylatoethyl)imidazolium (S,S-L(3), R,R-L(3) and R,S-L(3)). The compounds are formulated as [Mn(L(1))(N3)2] (1), [Mn(L(2))(N3)] (2), [Mn(R,R-L(3))(N3)]·0.5CH3OH (3-R), [Mn(S,S-L(3))(N3)]·0.5CH3OH (3-S), [Mn(R,S-L(3))(N3)] (4). In compound 1, the neutral monocarboxylate zwitterion ligand (L(1)) leads to uniform chains with bis(azide)(carboxylate) bridges. For compounds 2-4, the anionic dicarboxylate zwitterions L(2) and L(3) lead to (azide)bis(carboxylate) bridges, but the overall coordination networks are different. In 2 and 3-S (or 3-R), chains with the (azide)bis(carboxylate) bridges are connected by L(2) and S,S-L(3) (or R,R-L(3)), respectively, to give achiral and chiral 2D coordination networks with different connecting topologies. In compounds 4, which is derived from the mesomeric ligand R,S-L(3), linear trinuclear units with the (azide)bis(carboxylate) bridges are linked by μ-1,3 azides to give 2D layers, and the layers are pillared into a 3D framework by the 1,3-dimethyleneimidazolium tethers. Magnetic analyses suggested that compounds 1-3 behave as 1D antiferromagnetic systems, while 4 shows canted antiferromagnetism with weak ferromagnetic ordering below T(C) = 12.4 K.

Three isostructural Mn(II) compounds with a zwitterionic dicarboxylate ligand and different pseudohalides were synthesized, and then structurally and magnetically characterized. They are formulated as [Mn(L)(X)(2)(H(2)O)(2)](n) [X = N(3)(-) (1), NCO(-) (2), NCS(-) (3), L = 1,4-bis(4-carboxylato-1-pyridinium)butane]. In these compounds, adjacent Mn(II) ions are connected into coordination chains by long zwitterionic linkers and into hydrogen-bonded chains by short double O-H···N bridges involving coordinated water and pseudohalide ligands. Magnetic studies revealed for the first time that the double hydrogen bridges induce ferromagnetic coupling between the Mn(II) ions.

Two novel Mn(II) coordination polymers with azide and 4-(4-pyridyl)benzoic acid N-oxide (4,4-Hopybz) were synthesized and structurally and magnetically characterized. They are formulated as {[Mn(2)(4,4-opybz)(2)(N(3))(2)(H(2)O)(2)]·H(2)O}(n) (1) and {[Mn(4)(4,4-opybz)(5)(N(3))(H(2)O)(8)](N(3))(2)·2H(2)O}(n) (2). Compound 1 contains 2D coordination layers in which the infinite Mn(II) chains with alternating (μ-EO-N(3))(2)(μ-COO) (EO = end-on) and (μ-COO)(μ-O) bridges are interlinked by the backbones of the organic ligands. Compound 2 is a 3D metal-organic framework in which the unique linear tetranuclear clusters with (μ-EO-N(3))(μ-COO) and (μ-COO)(μ-O) bridges are cross-linked by organic backbones, and it represents a new example of the rare 8-connected self-catenated 3D net with the point symbol 4(16)·6(12). Magnetic analyses on the compounds have been performed in the classical-spin approximation, revealing that all the above-mentioned mixed bridging motifs induce weak antiferromagnetic interactions between Mn(II) ions.

Two isomorphous Co(II) and Ni(II) coordination polymers with azide and the 4-(4-pyridyl)benzoic acid N-oxide ligand (4,4-Hopybz) were synthesized, and structurally and magnetically characterized. They are formulated as [M(4,4-opybz)(N(3))(H(2)O)](n) (M = Co, 1 and Ni, 2). The compounds consist of 2D coordination networks, in which 1D coordination chains with (μ-N(3))(μ-COO) bridges are interlinked by the 4,4-opybz spacers, and the structure also features intra- and interchain O-HO hydrogen-bonding bridges between metal ions. Both compounds exhibit ferromagnetic interactions through the intrachain (μ-N(3))(μ-COO)(O-HO) bridges and antiferromagnetic interactions through the interchain O-HO bridges. The ferromagnetic chains are antiferromagnetically ordered, and the antiferromagnetic phases exhibit field-induced metamagnetic transition. It is found that 1 displays slow relaxation of magnetization, typical of single-chain magnets, while 2 does not. The difference emphasizes the great importance of large magnetic anisotropy for single-chain-magnet dynamics., (This journal is © The Royal Society of Chemistry 2011)

A novel 2D metamagnetic compound composed of ferromagnetic Co(II) chains exhibits the intrinsic slow dynamics of single-chain magnets in the antiferromagnetic ordered phase and in the field-induced ferromagnetic phase.

Two isomorphous Co(II) and Mn(II) three-dimensional coordination polymers with tetrazolate-5-carboxylate as magnetic mediator exhibit an unprecedented 3,4-connected self-penetrating net topology; a combination of canted antiferromagnetism and metamagnetism was observed in the Co(II) compound, whereas the Mn(II) compound shows typical antiferromagnetic behaviors.

Six coordination compounds of bis(5-tetrazolyl)amine (H2bta) with different metal ions, M{M3(mu3-X)(bta)3(H2O)6}2] (X = OH for M = Mn(II) 1, and Cd(II) 2; X = F for M = Mn(II) 3), [Mn(bta)(H2O)3].0.5H2O (4), [Zn(bta)(NH3)2]0.5H2O (5) and [Zn(Hbta)2(H2O)2]H2O (6) have been described. The compounds were synthesized using one-pot hydrothermal methods involving the in situ generation of the ligand from dicyanamide and azide (1-4, 6), or by the methods using the pre-synthesized H2bta ligand (4, 5). The bta ligand in 1-3 assumes the mu3 tetradentate mode with both 1,2- and 1,4-tetrazole bridges, generating an unusual 2D layer, in which [M3(mu3-X)] triangular motifs act as three-connecting nodes and the mononuclear motifs acting as six-connecting nodes that are inter-linked by the ligands. The 2D layer in 1 and 3 represents a novel type of a geometrically spin-frustrated lattice. Both 4 and 5 consist of co-crystallized binuclear motifs and 1D polymeric chain motifs, which arise from two different mu2 tridentate bridging modes of bta with 1,2- and 1,4-tetrazole bridges, respectively. In 6, the mono-anionic Hbta ligands chelate Zn in the non-bridging bidentate mode to generate mononuclear molecules, which are assembled through extended hydrogen bonds to generate a 3D architecture with a ten-connected net topology. Magnetic investigations revealed that interactions through the different bridges in 3 and 4 are all antiferromagnetic, and also confirmed that 3 is a geometrically-frustrated antiferromagnet (T(N) = 2.5 K).