1D Coordination Polymer Research Articles

Redox and guest tunable spin-crossover properties in a polymeric polyoxometalate.

A bifunctionalized polyoxometalate (POM), [V6O19(C16H15N6O)2]2-, which contains a redox active hexavanadate moiety covalently linked to two tridentate 2,6-bis(pyrazol-1-yl)pyridine (1-bpp) ligands, has been prepared and characterized. Reaction of this hybrid molecule with Fe(ii) or Zn(ii) ions produces crystalline neutral 1D networks of formula Fe[V6O19(C16H15N6O)2]·solv (2) and Zn[V6O19(C16H15N6O)2]·solv (3) (solv = solvent molecules). Magnetic properties of 2 show an abrupt spin-crossover (SCO) with the temperature, which can be induced by light irradiation at 10 K (Light-Induced Excited Spin-State Trapping, LIESST effect). Interestingly, this porous and flexible structure enables reversible exchange of solvents in 2, which allows tuning the temperature of the thermal SCO. In 2 and 3, the hexavanadate unit can be reduced by electrochemical or chemical means in a reversible way. Chemical reduction and reoxidation by a postsynthetic method is accompanied by the insertion in the structure of the reductant and oxidant molecules (cobaltocene and tribromide, respectively), which provokes drastic changes in the spin state of Fe(ii). This leads to an elegant switching multifunctional material in which SCO properties of the Fe(ii) complexes coexist with the redox properties of the POM and can be tuned by a variety of stimuli such as temperature, light, solvent exchange or electron transfer. During the reduction process, 3 undergoes a single-crystal-to-single-crystal one-electron reduction, which confirms the presence of cobaltocenium cations by single crystal X-ray diffraction.

Accessing copper selenide nanostructures through a 1D coordination polymer of copper(ii) with 4,4′-dipyridyldiselenide as a molecular precursor

Utility of a newly synthesized and structurally characterized Cu(ii) 1D coordination polymer as a molecular precursor for the selective synthesis of nanometric copper selenides has been demonstrated.

Solvatochromic behaviour of cyclic dithioether-functionalized triphenylamine ligands and their mechano-responsive Cu(I) coordination polymers.

Cu(I)-based coordination polymers (CPs) are known as efficient emissive materials providing an eco-friendly and cost-effective platform for the development of various functional materials and sensors. In addition to the nature of the metal center, organic ligands also play a crucial role in controlling the emissive properties of coordination polymers. Herein, we report on the synthesis of dithiane- and dithiolane-substituted triphenylamine ligands L1 and L2. These ligands were found to be emissive both in the solid state and in solution. In addition, these ligands exhibit solvatochromic behaviour due to the twisted intramolecular charge transfer (TICT) phenomenon. Next, coordination behaviour of these ligands was explored with Cu(I)X salts (X = Br and Cl) and four new 1D coordination polymers [{Cu(μ2-X)2Cu}(μ2-L)]n, CP1 (X = Br, L = L1), CP2 (X = Cl, L = L1), CP3 (X = Br, L = L2), and CP4 (X = Cl, L = L2) were synthesized and crystallographically characterized. The emission behaviour of all the CPs suggests ligand-centered transitions. On mechanical grinding, emission maxima (λem) for CP1 and CP2 were blue-shifted, whereas for CP3 and CP4 red-shifts were observed. All CPs were found to emit at 448 nm with increased intensity after grinding. It is supposed that grinding is responsible for a change in the spatial arrangement (dihedral angles) of the phenyl groups of triphenylamine, causing the observed emission shifts. Furthermore, the higher emission intensity after grinding suggests the occurrence of a similar phenomenon as an aggregation-induced quenching in these CPs.

Syntheses, Structural Insight and HirshFeld Surface Analysis of Two Heteroleptic Coordination Polymer of Cu(II)

Using a solvothermal method, we have synthesized two coordination polymers of Cu(II). One is a 1D polymer {[Cu(bpy)(NDC)(H 2 O)].2H 2 O} n (1, 1D) formed with 1,8-naphthalene dicarboxylic acid (H 2 NDC) and 2,2′ -bipyridine (bpy) as an auxiliary ligand, while the other is a 2D polymer {[Cu 3 (TMA)(Imd) 3 ].5H 2 O.2DMF} n (2, 2D) formed with trimellitic acid (H 3TMA) and imidazole (Imd) as an auxiliary ligand. Both coordination polymers 1 and 2 were formed through an in situ hydrolytic ring opening reaction of 1,8-naphthalic anhydride and trimelitic anhydride with bipyridine and imidazole ligands, respectively. The asymmetric unit of polymer 1 contains asymmetric η 1 binding mode (one of the carboxylate) linking distorted square-pyramidal [Cu(NDC)(bpy)(H 2 O)] 2+ coordination units. The syn-syn-η 1 :η 1 linear polymer conformation exist in the 1D coordination polymer with adjacent Cu…Cu distance is 6.849Å. A chain of cyclic tetrameric water clusters is present between the stacked layers of the 3D supramolecular structure. The formation of the 3D supramolecular structure is guided by various weak interactions such as OH…O, CH…O, CH…π and π…π interactions. The coordination polymers 2 forms 3D supramolecular architecture guided by various weak interactions such as OH…O, CH…O and NH…O interactions. The crystal structures of both coordination polymers have been determined using single crystal X-ray diffraction and their structural features are described.

A p-type semi-conducting copper(i)-1,3-benzenedithiolate 2D coordination polymer with high Seebeck coefficient

A p-type semi-conducting and 2D coordination polymer, made of 1D copper(i)–sulfur inorganic networks, exhibits very high Seebeck coefficient for thermoelectricity.

EXPLORATION OF COPPER-BASED COORDINATION POLYMER AS CATALYST: HIGH YIELD OXIDATIVE COUPLING OF BENZYLAMINE TO IMINE

Benzylamine to imine conversion through oxidative coupling reaction has been achieved with almost 91% yield under very mild conditions by applying a one-dimensional coordination polymer as a catalyst and tert-butyl hydroperoxide (TBHP) as an oxidizing agent. The 1D-coordination polymer, [{Cu2(2,3-pydc)2(2,2ʹ-bpy) (H2O)2}.4H2O]n(A) has been re-synthesized by different synthetic process using the ligands 2,3- pyridinedicarboxylic acid (2,3-pydc) and 2,2Ꞌ-bipyridine (2,2Ꞌ-bpy) and it has been characterized by utilizing different physicochemical techniques such as IR-spectroscopy, UV-Vis spectroscopy, elemental analysis and TGDTA analysis including reestablishment of X-ray single crystal structure. The proposed mechanism of the reaction indicates that the catalytic reaction is facilitated by a flexible and coordinatively unsaturated Cu(II) center and through the formation of tert-butyl peroxy radical.

Robust and highly emissive copper(I) halide 1D-coordination polymers with triphenylarsine and a series of bridging N-heteroaromatic co-ligands.

Various 1D-coordination polymers with dinuclear rhombic {Cu2X2} cores (X = Br, I) were synthesized using a spontaneous evaporation method employing triphenylarsine (AsPh3) and six types of bidentate N-heteroaromatic co-ligands. The coordination polymers exhibited intense emission even at 298 K (quantum yield: up to 0.60), and their emission color was dependent on the N-heteroaromatic co-ligand. The emission efficiencies of these coordination polymers were higher than those of the discrete complexes with AsPh3 and monodentate N-heteroaromatic co-ligands reported in our previous work. In addition, the luminescence of these coordination polymers was more resistant to mechanical stimuli than that of the discrete ones.

Preparation of one-dimensional coordination polymers of a flexible tripyridyl disulfide with diverse topologies

The combination of a novel flexible tripyridyl disulfide (L) and coinage metal (CuII and AgI) salts yields diverse types of one-dimensional coordination polymers exhibiting loop chain, ribbon, and ladder topologies.

Ligand-directed structure evolution from a titanium-oxo cluster to coordination capsule and one-dimensional coordination polymer based on {Ti3O} units

With connection of phosphite, {Ti3(μ3-O)} can transform into a discrete {Ti6P2}-based cluster, {Ti9P3}-based coordination capsule and {Ti6P2}-based 1D coordination polymer by tuning the geometry and size of the ligand.

1D hybrid metal coordination polymer-derived hierarchical Co1-xS/MnS/NC nanowires for advanced sodium-ion batteries.

Hierarchical Co1-xS/MnS/NC nanowires have been successfully prepared by a simple hydrothermal reaction and the subsequent annealing process of its one-dimensional (1D) coordination polymer precursors. The Co1-x/MnS/NC heterostructure nanowires can not only buffer the volume expansion during the discharging and charging process but also conspicuously enhance electronic conductivity, which is favourable for improving the rate performance and cycling stability, which can maintain 612.9 mA h g-1 after 100 cycles at 0.5 A g-1 and 544.6 mA h g-1 after 200 cycles at 1.0 A g-1 for SIBs.

The impact of solution vs. slurry vs. mechanochemical syntheses upon the sorption performance of a 2D switching coordination network

Comparison of solution, slurry and mechanochemical syntheses of a 1D coordination polymer intermediate and effect upon the sorption performance of its 2D switching coordination network product.

Differential supercapacitor and Schottky diode behaviours in two new isostructural coordination polymers based on redox active metal ions

Two isostructural 2D coordination polymers utilizing redox-active metal ions, Fe(ii) and Mn(ii), were synthesized. The Mn-based compound showed higher capacitance values and ten times higher conductivity compared to the Fe-based compound.

Bifunctional Cu(II)-based 2D coordination polymer and its composite for high-performance photocatalysis and electrochemical energy storage.

Coordination polymers (CPs) have been widely proven as sacrificial electrode materials for energy storage applications because of their high porosity, specific surface area and tunable structural topology. In this work, a new 2D Cu(II)-based CP, formulated as [Cu2(btc)(μ-Cl)2(H2O)4]n (CP-1) (H3btc = benzene-1,3,5-tricarboxylic acid), fabrication of copper oxide nanoparticles (CuO NPs) and its composite (CuO@CP-1) were successfully synthesized using solvothermal, precipitation and mechanochemical grinding approaches. Single-crystal X-ray analysis authenticated a two-dimensional (2D) layered network of CP-1. Further, CP-1, CuO NPs and composite were characterized by diffraction (Powder-XRD), spectroscopic (FTIR), microscopic (SEM), and thermal (TGA) techniques. The porosity and surface behavior of CP-1 and the composite were demonstrated using BET analyzer. Topological simplification of CP-1 shows a 3-c connected hcb periodic net. The photocatalytic behavior of CP-1 was examined over methyl red (MR) dye in the presence of sunlight and showed a promising degradation efficiency of 96.80%. The electrochemical energy storage properties of CP-1, CuO NPs and composite were investigated using cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) analysis under aqueous 1 M H2SO4 electrolyte. The electrochemical results show better charge storage performance of CP-1 with a specific capacitance of 602.25 F g-1 at 1 A g-1 current density by maintaining a retention of up to 84.51% after 5000 cycles at 10 A g-1 current density. Comparative electrochemical studies reveal that CP-1 is a promising electrode material for energy storage.

A dual-functional 2D coordination polymer exhibiting photomechanical and electrically conductive behaviours.

A photoactive two-dimensional coordination polymer (2D CP) [Zn2(4-spy)2(bdc)2]n (1) [4-spy = 4-styrylpyridine and H2bdc = 1,4-benzendicarboxylic acid] undergoes a photochemical [2 + 2] cycloaddition reaction upon UV irradiation. Interestingly, the crystals of 1 show different photomechanical effects, such as jumping, swelling, and splitting, during UV irradiation. In addition, the CP was employed for conductivity measurements before and after UV irradiation via current density-voltage characteristics and impedance spectroscopy, which suggest that they are semiconducting in nature and can be used as Schottky diodes. Thus, this work demonstrates the potential dual applications of a 2D CP based on photosalient and conductivity properties.

Thiophenol-spaced 2D coordination polymers with extraordinary alkali resistance and efficient photothermal conversion.

Coordination polymers (CPs) based on metal-sulfur bonds are rare; we herein realize a series of thiol-functionalized linker-based CPs (thiol-CPs), MTBT (M = Fe, Co and Zn; TBT = dehydrated 4,4'-thiobisbenzenethiol), which feature an anionic two-dimensional (2D) network, [M(TBT)2]n2n-, with the tetrahedral coordination unit {MS4} serving as a node. These compounds exhibit excellent hydrolytic stability, especially in alkaline solution (20M NaOH for five days), which is the highest value reported for CPs so far. In addition, among them, CoTBT displays favorable photo-thermal conversion effectiveness under an energy power of 0.5 W cm-2 808 nm laser irradiation for 15 s, with the temperature rising rapidly from room temperature to 135.2 °C.

Designing of a Zn(ii)-isonicotinohydrazido thiophenyl based 2D coordination polymer: structure, augmented photoconductivity and superior biological activity

A novel Zn(ii)-isonicotinohydrazido-thiophenyl based 2D coordination polymer reveals a drastic increase in electrical conductivity upon light irradiation and its application in anti-cancer activity.

Structural influence of the length and functionality of N,N-donor spacers in Cd(II) ladder-type coordination polymers

The understanding of the effect generated by small differences of the organic ligands on the molecular and supramolecular arrangement of coordination polymers (CPs) is a key factor to control their properties. Therefore, the study of structurally related ligands differing in some factors inter alia functional group orientation, length, or functionality is a crucial task for crystal engineers. In this contribution, the reactions between Cd(OAc)2·2H2O, α-acetamidocinnamic acid (HACA) and different N,N-donor spacers with increasing length (pyrazine, pyz; 4,4’-bipyridine, 4,4’-bipy; 1,2-bis(4-pyridyl)ethylene, 1,2-bpe), as well as additional functionalities (4,4’-azopyridine, 4,4’-azpy) have been successfully performed. Their crystal structures have been elucidated revealing a family of ladder-type 1D CPs showing molecular arrays with single pillars for {[Cd2(μ-ACA)2(ACA)2(pyz)(H2O)2]·2EtOH}n (1), and double pillars for [Cd2(μ-ACA)2(ACA)2(4,4’-bipy)2]n (2), [Cd2(μ-ACA)2(ACA)2(1,2-bpe)2]n (3) and {[Cd2(μ-ACA)2(ACA)2(4,4’-azpy)2]·4,4’-azpy·9H2O}n (4). Remarkably, the effect of the addition of the azo group in 4 compared with 2 and 3 has led to a CP with the same molecular arrangement but different crystal packing, allowing the introduction of one non-coordinated 4,4’-azpy and nine water molecules. Finally, their solid-state UV-Vis and photoluminescence have been measured observing their blue-emitting properties.

Zinc(II) and copper(II) complexes with N-substituted imines derived from 4-amino-1,2,4-triazole: Synthesis, crystal structure, and biological activity

Reactions of copper(II) and zinc(II) acetates with polynitrogen Schiff bases, namely 4-(pyridin-2-yl)methyleneamino-1,2,4-triazole (L1), 4-(pyridin-3-yl)methyleneamino-1,2,4-triazole (L2) and 4-(pyridin-4-yl)methyleneamino-1,2,4-triazole (L3), were studied. The reaction of Zn(OAc)2·2H2O and L1 gave crystals of trinuclear complex [Zn3(OAc)6(L1)2] (1). A similar reaction of Zn(OAc)2·2H2O and L2 resulted in 1D coordination polymer [Zn(OAc)2(L2)]n (2). The reactions of Cu(OAc)2·H2O with L2 or L3 gave crystals of 1D coordination polymer {[Cu2(OAc)4(L2)]·2MeCN}n (3) and binuclear complex [Cu2(OAc)2(L3)2]·2MeCN (4), respectively. The structures of the coordination compounds thus obtained were determined by single-crystal X-ray diffraction analysis. Complexes 1–4 demonstrated better antibacterial and antifungal activities in comparison with free L1, L2, and L3 ligands: the strongest antimicrobial activity was observed against E. coli for 2 and 3, and the highest antifungal activity was found for 1 and 2.

Change in the Electronic Structure of the Cobalt(II) Ion in a One-Dimensional Polymer with Flexible Linkers Induced by a Structural Phase Transition

A new 1D-coordination polymer [Co(Piv)2(NH2(CH2)6NH2)]n (1, Piv is Me3CCO2- anion) was obtained, the mononuclear fragments {Co(O2CR)2} within which are linked by μ-bridged molecules of hexamethylenediamine (NH2(CH2)6NH2). For this compound, two different monoclinic C2/c (α-1) and P2/n (β-1) phases were found at room temperature by single-crystal X-ray diffraction analysis, with a similar structure of chains and their packages in unit cells. The low-temperature phase (γ-1) of crystal 1 at 150 K corresponds to the triclinic space group P-1. As the temperature decreases, the structural phase transition (SPT) in the α-1 and β-1 crystals is accompanied by an increase in the crystal packing density caused by the rearrangements of both H-bonds and the nearest ligand environment of the cobalt atom ("octahedral CoN2O4 around the metal center at room temperature" → "pseudo-tetrahedral CoN2O2 at 150 K"). The SPT was confirmed by DSC in the temperature range 210-150 K; when heated above 220 K, anomalies in the behavior of the heat flow are observed, which may be associated with the reversibility of SPT; endo effects are observed up to 300 K. The SPT starts below 200 K. At 100 K, a mixture of phases was found in sample 1: 27% α-1 phase, 61% γ-1 phase. In addition, at 100 K, 12% of the new δ-1 phase was detected, which was identified from the diffraction pattern at 260 K upon subsequent heating: the a,b,c-parameters and unit cell volume are close to the structure parameters of γ-1, and the values of the α,β,γ-angles are significantly different. Further heating leads to a phase transition from δ-1 to α-1, which both coexist at room temperature. According to the DC magnetometry data, during cooling and heating, the χMT(T) curves for 1 form a hysteresis loop with ~110 K, in which the difference in the χMT values reaches 9%. Ab initio calculations of the electronic structure of cobalt(II) in α-1 and γ-1 have been performed. Based on the EPR data at 10 K and the ab initio calculations, the behavior of the χMT(T) curve for 1 was simulated in the temperature range of 2-150 K. It was found that 1 exhibits slow magnetic relaxation in a field of 1000 Oe.

Cu(I)/Cu(II) Creutz–Taube Mixed‐Valence 2D Coordination Polymers

Graphene-like 2D coordination polymers (GCPs) have been of central research interest in recent decades with significant impact in many fields. According to classical coordination chemistry, Cu(II) can adopt the dsp2 hybridization to form square planar coordination geometry, but not Cu(I); this is why so far, there has been few 2D layered structures synthesized from Cu(I) precursors. Herein a pair of isostructural GCPs synthesized by the coordination of benzenehexathiol (BHT) ligands with Cu(I) and Cu(II) ions, respectively, is reported. Spectroscopic characterizations indicate that Cu(I) and Cu(II) coexist with a near 1:1 ratio in both GCPs but remain indistinguishable with a fractional oxidation state of +1.5 on average, making these two GCPs a unique pair of Creutz-Taube mixed-valence 2D structures. Based on density functional theory calculations, an intramolecular pseudo-redox mechanism is further uncovered whereby the radicals on BHT ligands can oxidize Cu(I) or reduce Cu(II) ions upon coordination, thus producing isostructures with distinct electron configurations. For the first time, it is demonstrated that using Cu(I) or Cu(II), one can achieve 2D isostructures, indicating an unusual fact that a neutral periodic structure can host a different number of total electrons as ground states, which may open a new chapter for 2D materials.