Carboxylate Linkers Research Articles

Six-Membered Ring Directed Assembly of a Zirconium Zeolitic Metal-Organic Framework for Efficient Separation of Hexane Isomers.

The synthesis of zirconium MOFs with zeolite net is quite challenging due to the high connectivity of Zr6 clusters, which is far from tetrahedral connection, a requisite for zeolite net. In this work, we demonstrate a six-membered ring (6MR) strategy through mimicking of mineral zeolites with mixed ditopic and tritopic carboxylate linkers. With this strategy, the ditopic linker cross-links Zr6 clusters to form 4-connected zeolite-like nets, while the tritopic one is used to direct the formation of 6MR and simultaneously consumes extra coordination sites on the cluster. The feasibility of this strategy is shown by one zeolitic metal-organic framework (NNM-5) and this strategy has also led to the synthesis of the other dia-type zirconium MOF (NNM-6). Interestingly, as the tritopic linker not only directs the formation of 6MR but also partitions 6MR into small segments, NNM-5 with SOD topology shows a structural feature of small aperture and big cage, which has led to efficient separation of hexane isomers. With both exceptionally high n-hexane uptake (65.9 cm3 g-1) and size-exclusion selectivity, an exceptional separation capability is verified by breakthrough experiments. Calculation results demonstrate that the large difference of diffusion energy barrier due to the small aperture accounts for the underlying separation mechanism.

Green synthesis of carbon dots nanoparticles from edible swiftlet nest and evaluation of their antioxidant activity

Edible swiftlet nest (ESN) confers various health benefits to humans, including immune system enhancement, anti-inflammatory properties, bone strengthening, and antioxidative effect. ESN is notably rich in protein and minerals, with its proteins serving as non-enzymatic antioxidants capable of binding free radicals. However, the antioxidant capacity of ESN is comparatively lower than that of other free radical scavengers, such as carbon dots nanoparticles (CNPs). CNPs features charged ligands on their surface that act as electron donors for free radical binding. The presence of the carbon chain forming proteins in ESN suggests their potential as the primary source for CNPs formation. The enhancement of hydroxyl groups and delocalized electrons is imperative for enhancing the antioxidant activity of ESN. This study aims to enhance the antioxidant activity of ESN by converting it into CNPs nanoparticles. The results demonstrated the effective synthesis of CNPs from the ESN solution using microwave methods. This was evidenced by XRD patterns indicating CNPs formation, and an average particle size of 4.86 nm as indicated by TEM analysis. The optimal microwave heating duration of 30 min yielded CNPs with a prominent emission spectrum peak at 425 nm and significantly high intensity. Absorbance data revealed the presence of C=C bonds, consistent with aromatic CNPs bonds observed in FTIR studies. CNPs possessed hydroxyl and carboxyl linkages, suggesting their potential as antioxidants. The percent inhibition results indicated that CNPs exhibited a substantial percentage (62.5%) at a concentration of 50 mg ml−1. The free radical scavenging activity of the CNPs significantly elevated compared to ESN.

Six‐Membered Ring Directed Assembly of a Zirconium Zeolitic Metal‐Organic Framework for Efficient Separation of Hexane Isomers

The synthesis of zirconium MOFs with zeolite net is quite challenging due to the high connectivity of Zr6 clusters, which is far from tetrahedral connection, a requisite for zeolite net. In this work, we demonstrate a six‐membered ring (6MR) strategy through mimicking of mineral zeolites with mixed ditopic and tritopic carboxylate linkers. With this strategy, the ditopic linker cross‐links Zr6 clusters to form 4‐connected zeolite‐like nets, while the tritopic one is used to direct the formation of 6MR and simultaneously consumes extra coordination sites on the cluster. The feasibility of this strategy is shown by one zeolitic metal‐organic framework (NNM‐5) and this strategy has also led to the synthesis of the other dia‐type zirconium MOF (NNM‐6). Interestingly, as the tritopic linker not only directs the formation of 6‐MR but also partitions 6‐MR into small segments, NNM‐5 with SOD topology shows a structural feature of small aperture and big cage, which has led to efficient separation of hexane isomers. With both exceptionally high n‐hexane uptake (65.9 cm3·g‐1) and size‐exclusion selectivity, an exceptional separation capability is verified by breakthrough experiments. Calculation results demonstrate that the large difference of diffusion energy barrier due to the small aperture accounts for the underlying separation mechanism.

Leveraging Isoreticular Principle to Elucidate the Key Role of Inherent Hydrogen-Bonding Anchoring Sites in Enhancing Water Sorption Cyclability of Zr(IV) Metal-Organic Frameworks.

Water adsorption/desorption cyclability of porous materials is a prerequisite for diverse applications, including atmospheric water harvesting (AWH), humidity autocontrol (HAC), heat pumps and chillers, and hydrolytic catalysis. However, unambiguous molecular insights into the correlation between underlying building blocks and the cyclability are still highly elusive. In this work, by taking advantage of the well-established isoreticular synthetic principle in Zr(IV) metal-organic frameworks (Zr-MOFs), we show that the inherent density of hydrogen atoms in the organic skeleton can play a key role in regulating the water sorption cyclability of MOFs. The ease of isoreticular practice of Zr-MOFs enables the successful syntheses of two pairs of isostructural Zr-MOFs (NU-901 and NU-903, NU-950 and SJTU-9) from pyrene- or benzene-cored carboxylate linkers, which feature scu and sqc topological nets, respectively. NU-901 and NU-950 comprised of pyrene skeletons carrying more hydrogen-bonding anchoring sites show distinctly inferior cyclability as compared with NU-903 and SJTU-9 built of benzene units. Single-crystal X-ray crystallography analysis of the hydrated structure clearly unveils the water molecule-involved interactions with the hydrogen-bonding donors of benzene moieties. Remarkably, NU-903 and SJTU-9 isomers exhibit outstanding water vapor sorption capacities as well as working capacities at the desired humidity range with potential implementations covering indoor humidity control and water harvesting. Our findings uncover the importance of hydrogen-bonding anchoring site engineering of organic scaffold in manipulating the framework durability toward water sorption cycle and will also likely facilitate the rational design and development of highly robust porous materials.

Carbohydrate-Based Reprocessable and Healable Covalent Adaptable Biofoams.

Polymeric foams derived from bio-based resources and capable of self-healing and recycling ability are of great demand to fulfill various applications and address environmental concerns related to accumulation of plastic wastes. In this article, a set of polyester-based covalent adaptable biofoams (CABs) synthesized from carbohydrates and other bio-derived precursors under catalyst free conditions to offer a sustainable alternative to conventional toxic isocyanate-based polyurethane foams is reported. The dynamic β-keto carboxylate linkages present in these biofoams impart self-healing ability and recyclability to these samples. These CABs display adequate tensile properties especially compressive strength (≤123MPa) and hysteresis behavior. The CABs swiftly stress relax at 150°C and are reprocessable under similar temperature conditions. These biofoams have displayed potential for use as attachment on solar photovoltaics to augment the output efficiency. These CABs with limited swellability in polar protic solvents and adequate mechanical resilience are suitable for other commodity applications.

Analyzing Stabilities of Metal-Organic Frameworks: Correlation of Stability with Node Coordination to Linkers and Degree of Node Metal Hydrolysis.

Among the important properties of metal-organic frameworks (MOFs) is stability, which may limit applications, for example, in separations and catalysis. Many MOFs consist of metal oxo cluster nodes connected by carboxylate linkers. Addressing MOF stability, we highlight connections between metal oxo cluster chemistry and MOF node chemistry, including results characterizing Keggin ions and biological clusters. MOF syntheses yield diverse metal oxo cluster node structures, with varying numbers of metal atoms (3-13) and the tendency to form chains. MOF stabilities reflect a balance between the number of node-linker connections and the degree of node hydrolysis. We summarize literature results showing how MOF stability (the temperature of decomposition in air) depends on the degree of hydrolysis/condensation of the node metals, which is correlated to their degree of substitution with linkers. We suggest that this correlation may help guide the discovery of stable new MOFs, and we foresee opportunities for progress in MOF chemistry emerging from progress in metal oxo cluster chemistry.

Ligand regulation and capacitive properties of nickel based pyrazole trinuclear copper cluster organic framework

Traditional metal organic framework (MOF) hinders its application as high-performance electrode materials for supercapacitors due to the limited electron transfer efficiency and conjugation of its ligand molecules. Therefore, in this article, highly electrochemical active pyrazole trincore-copper cluster derivatives as the core unit were covalently assembled by Schiff base reaction with organic linkers of different structures to obtain a series of structurally different electroactive ligands. It was found that ligands with multiactive metal chelation site structure with polydentate carboxylate linker and aromatic extension showed high coordination ability and high degree of conjugation. The nickel-based MOF synthesized with this novel electroactive ligand exhibited a high specific capacitance of 1804 Fg−1 at a current density of 1 Ag−1. At a power density of 747.25 W kg−1, the maximum energy density of the assembled asymmetric supercapacitor assembled with Cu-PyAc-Am2Ac-Ni is 58.95 Wh kg−1 with cycling stability of 88.95 % after 5000 charges and discharges. This means that Cu-PyAc-Am2Ac-Ni is a promising electrode material for supercapacitors.

Facile Layer Diffusion Technique for Synthesis of Terbium-Based Metal Organic Framework for Fluorometric Sensing of Hydroquinone.

A photoluminescent terbium (III)-based Metal Organic Framework (MOF) was synthesized at room temperature by layer diffusion method utilizing mixed carboxylate linkers (4,4'-oxybis(benzoic acid) and benzene-1,3,5 tricarboxylic acid). Synthesized MOF has crystalline nature and rod-shaped morphology and is thermally stable up to 455°C. The fluorescence emission spectra and theoretical results revealed that carboxylate linkers functioned as sensitizers for Tb(III) photoluminescence which resulted in four distinct emission peaks at 495, 547, 584, and 621nm corresponding to the transitions 5D4 → 7F6, 5D4 → 7F5, 5D4 → 7F4, and 5D4 → 7F3. Using synthesized MOF as fluorescent probe, hydroquinone was detected in aqueous medium with a detection limit of 0.048μM, remarkable recovery (95.6-101.1%), and relative standard deviation less than 2.25%. The quenching phenomenon may be ascribed to electron transfer from synthesized probe to oxidized hydroquinone via carboxylic groups on thesurface of MOF, which is further supported by photo-induced electron transfer mechanism. This study introduces a cheaper, faster, and more accurate method for hydroquinone detection.

A carboxylate linker strategy mediated densely accessible Fe-N4 sites for enhancing oxygen electroreduction in Zn-air batteries

Iron-nitrogen-carbon single-atom catalysts derived from zeolitic-imidazolate-framework-8 (ZIF-8) have presented its great potential for the oxygen reduction reaction (ORR) in Zn-air batteries (ZABs). However, due to insufficient active Fe-N sites, its ORR activity is inferior to Pt-based catalysts. Herein, a carboxylate (OAc) linker strategy is proposed to design a ZIF-8-derived FeNCOAc catalyst with abundant accessible Fe-N4 single-atom sites. Except that imidazole groups can coordinate with Fe ions, the OAc linker on the unsaturated coordination Zn nodes can anchor and coordinate with more Fe ions, resulting in a significant increase in Fe-N4 site density. Meanwhile, the corrosion of carbon skeleton by OAc oxidation during heat-treatment leads to improved porosity of catalyst. Benefitting from the highly dense Fe-N4 sites and hierarchical pores, the FeNCOAc endows superior performance in alkaline medium (E1/2 = 0.906 V), which is confirmed by density functional theory calculation results. Meanwhile, the assembled liquid ZAB delivers a favorable peak power density of 173.9 mW cm−2, and a high specific capacity of 770.9 mAh g−1 as well as outstanding durability. Besides, the solid-state ZAB also shows outstanding discharge performance.

Isoreticular Contraction of Cage-like Metal-Organic Frameworks with Optimized Pore Space for Enhanced C2H2/CO2 and C2H2/C2H4 Separations.

The C2H2 separation from CO2 and C2H4 is of great importance yet highly challenging in the petrochemical industry, owing to their similar physical and chemical properties. Herein, the pore nanospace engineering of cage-like mixed-ligand MFOF-1 has been accomplished via contracting the size of the pyridine- and carboxylic acid-functionalized linkers and introducing a fluoride- and sulfate-bridging cobalt cluster, based on a reticular chemistry strategy. Compared with the prototypical MFOF-1, the constructed FJUT-1 with the same topology presents significantly improved C2H2 adsorption capacity, and selective C2H2 separation performance due to the reduced cage cavity size, functionalized pore surface, and appropriate pore volume. The introduction of fluoride- and sulfate-bridging cubane-type tetranuclear cobalt clusters bestows FJUT-1 with exceptional chemical stability under harsh conditions while providing multiple potential C2H2 binding sites, thus rendering the adequate ability for practical C2H2 separation application as confirmed by the dynamic breakthrough experiments under dry and humid conditions. Additionally, the distinct binding mechanism is suggested by theoretical calculations in which the multiple supramolecular interactions involving C-H···O, C-H···F, and other van der Waals forces play a critical role in the selective C2H2 separation.

Balancing the Components of Biomass and the Reactivity of Pyrolysis Gas: Biomass-Assisted Recycling of Spent LiCoO2 Batteries.

Waste biomass is one of the promising feedstocks to supply syngas that can be used as fuels, chemicals, reductants, etc. However, the relationship between the component of biomass and the constituent of pyrolysis gas remains unclear. Here, we study the pyrolysis behaviors of various biomasses and reveal the relationship between the biomass components and gas compositions. Further, different pyrolysis gases are applied for the reduction of spent lithium cobalt oxide (LiCoO2) below 500 °C. The pyrolysis gas with a higher concentration of CO has a higher reductivity to convert LiCoO2 to CoO and Li2CO3 with a conversion rate close to 100% in 1 h at 500 °C. The biomass rich in cellulose and with a lower content of lignin tends to produce pyrolysis gas with a high concentration of CO, which comes from the deliberate breakdown of carboxyl, carbonyl, ether, and ester linkages. Moreover, LiCoO2 exerts catalytic functions over the deoxygenation and enhancement of oxygenates and single-ring aromatics. Overall, this paper offers a tailored approach to regulating biomass pyrolysis gases, enabling highly efficient battery recycling and syngas production.

Reticular chemistry guided precise construction of zirconium-pentacarboxylate frameworks with 5-connected Zr6 clusters.

Zirconium-based metal-organic frameworks (Zr-MOFs) have been extensively studied due to their very rich structural chemistry. The combination of nearly unlimited carboxylic acid-based linkers and Zr6 clusters with multiple connectivities has led to diverse structures and specific properties of resultant Zr-MOFs. Herein, we demonstrate the successful use of reticular chemistry to construct two novel Zr-MOFs, HIAM-4040 and HIAM-4040-OH, with zfu topology. Based on a thorough structural analysis of (4,4)-connected lvt-type Zr-tetracarboxylate frameworks and a judicious linker design, we have obtained the first example of a Zr-pentacarboxylate framework featuring unprecedented 5-connected organic linkers and 5-connected Zr6 clusters. Compared with HIAM-4040, a larger Stokes shift is achieved in HIAM-4040-OH via hydroxyl group induced excited-state intramolecular proton transfer (ESIPT). HIAM-4040-OH exhibits high chemical and thermal stability and is used for HClO detection in aqueous solution with excellent sensitivity and selectivity.

Photoinduced Dynamic Ligation in Metal-Organic Frameworks.

Metal organic frameworks (MOFs), a class of porous crystalline materials consisting of metal-based nodes and organic linkers, have emerged as a promising platform for photocatalysis due to their ultrahigh functional surface area, customizable topologies, and tunable energetics. While interesting photochemistry has been reported, the related photoinduced structural dynamics of MOFs remains unclear. The consensus is that the coordination bonds between MOF nodes and linkers are considered static during photoexcitation, while the open-metal sites on the nodes are taken as the key active sites for catalysis. In this work, through a complementary time-resolved visible and infrared (IR) spectroscopic investigation, along with computational studies, we report for the first time light-induced structural bond dissociation (COO-M) and reformation in an iron-oxo framework, MIL-101(Fe). The probed excited state displayed ligand-to-metal charge transfer (LMCT) characteristics and exhibited a ca. 30 μs lifetime. The incredibly long excited-state lifetime led us to probe potential structural rearrangements that facilitated charge separation in MIL-101(Fe). By probing the vibrational fingerprints of the carboxylate linker upon LMCT photoexcitation, we observed the reversible transition of the carboxylate-Fe bond from a bidentate bridging mode to a monodentate mode, indicating the partial dissociation of the carboxylate ligand. Importantly, the bidentate configuration is recovered on the same time scale of the excited state lifetimes as probed via visible transient absorption spectroscopy. The elucidated photoinduced configurational dynamics provides a foundation for an in-depth understanding of MOF-based photocatalytic mechanisms.

Benzene-1,4-Di(dithiocarboxylate) Linker-Based Coordination Polymers of Mn2+, Zn2+, and Mixed-Valence Fe2+/3.

Three new coordination polymers (CPs) constructed from the linker 1,4-di(dithiocarboxylate) (BDDTC2-)─the sulfur-analog of 1,4-benzenedicarboxylate (BDC2-)─together with Mn-, Zn-, and Fe-based inorganic SBUs are reported with description of their structural and electronic properties. Single-crystal X-ray diffraction revealed structural diversity ranging from one-dimensional chains in [Mn(BDDTC)(DMF)2] (1) to two-dimensional (2D) honeycomb sheets observed for [Zn2(BDDTC)3][Zn(DMF)5(H2O)] (2). Gas adsorption experiments confirmed a 3D porous structure for the mixed-valent material [Fe2(BDDTC)2(OH)] (3). 3 contains a 1:1 ratio of Fe2+/3+ ions, as evidenced by 57Fe Mössbauer, X-band EPR, and X-ray absorption spectroscopy. Its empirical formula was established by elemental analysis, thermal gravimetric analysis, infrared vibrational spectroscopy, and X-ray absorption spectroscopy in lieu of elusive single-crystal X-ray diffraction data. In contrast to the Mn- and Zn-based compounds 1 and 2, the Fe2+/3+ CP 3 showed remarkably high electrical conductivity of 5 × 10-3 S cm-1 (according to van der Pauw measurements), which is within the range of semiconducting materials. Overall, our study confirms that sulfur derivatives of typical carboxylate linkers (e.g., BDC) are suitable for the construction of electrically conducting CPs, due to acceptedly higher covalency in metal-ligand bonding compared to the electrically insulating carboxylate CPs or metal-organic frameworks. At the same time, the direct comparison between insulating CPs 1 and 2 with CP 3 emphasizes that the electronic structure of the metal is likewise a crucial aspect to construct electrically conductive materials.

Linker-length dependency of unsaturated Ni-oxo clusters in metal hydroxide-organic framework for photocatalytic CO2 reduction

A series of two-dimensional (2D) Ni-based metal hydroxide-organic frameworks (Ni-MHOFs), where hydroxide sheets crosslinked using aromatic carboxylate linkers, were studied for photo-driven CO2 reduction to CO. The molar ratio of metal to ligand in Ni-MHOFs was analysed to estimate coordinatively unsaturated Ni-oxo sites based on inductively coupled plasma (ICP) of metal Ni and 1H NMR of ligands. Photoluminescence quenching of Ru-based photosensitizer (PS) was measured to understand photoelectron transfer mechanism. Ni-MHOF with the longest ligand afforded more accessible unsaturated Ni-oxo catalytic sites, which promoted the photoelectron transfer from PS to catalyst and then engendered better CO evolution performance. This work demonstrates the linker-length dependencies of metal-oxo clusters in 2D MOFs, which suggests a way to modulate the coordinative environment of catalytic sites to fulfill efficient photocatalysis.

Conductive Lanthanide Metal-Organic Frameworks with Exceptionally High Stability.

Electrically conductive metal-organic frameworks (MOFs) have been extensively studied for their potential uses in energy-related technologies and sensors. However, achieving that goal requires MOFs to be highly stable and maintain their conductivity under practical operating conditions with varying solution environments and temperatures. Herein, we have designed and synthesized a new series of {[Ln4(μ4-O)(μ3-OH)3(INA)3(GA)3](CF3SO3)(H2O)6}n (denoted as Ln4-MOFs, Ln = Gd, Tm, and Lu, INA = isonicotinic acid, GA = glycolic acid) single crystals, where electrons are found to transport along the π-π stacked aromatic carbon rings in the crystals. The Ln4-MOFs show remarkable stability, with minimal changes in conductivity under varying solution pH (1-12), temperature (373 K), and electric field as high as 800 000 V/m. This stability is achieved through the formation of strong coordination bonds between high-valent Ln(III) ions and rigid carboxylic linkers as well as hydrogen bonds that enhance the robustness of the electron transport path. The demonstrated lanthanide MOFs pave the way for the design of stable and conductive MOFs.

Room-temperature self-healing polysiloxane networks for highly sensitive piezoresistive pressure sensor with microdome structures

Soft piezoresistive pressure sensor is an important component for next generation flexible electronics. Micropatterning of such sensors significantly improves the pressure sensitivity, however, the short device lifetime due to scratches and motions limits the translation to industrial applications. Herein, we report a novel poly(ODMS-co-MAA) for self-healing piezoresistive sensor to effectively overcoming such shortcoming. Self-healing capability was achieved by incorporating dynamic Fe(III)-carboxylate linkages in the polymer networks. These linkages work as sacrificial bonds and dissipate energy caused by mechanical damage. The bonds subsequently reform and functionality of the sensor can be restored. The poly(ODMS-co-MAA)-based self-healing polymer networks (SPN) were effectively healed from damages showing the recovery of electrical resistance (>95%) within 10 hrs. SPN was fabricated with microdome structures and exhibited a superior pressure sensitivity (2 kPa−1) as well as stability compared to planar features (9.13 × 10−3 kPa−1), demonstrating its excellent potential as pressure sensor. Combined results demonstrate the potential of the self-healing networks for next generation piezoresistive pressure sensors.

Generation of Site-Selective Structural Vacancies in a Multinary Metal-Organic Framework for Enhanced Catalysis.

Generating structural vacancies in metal-organic frameworks (MOFs) by partially removing the inorganic and organic units from the scaffolds is an effective strategy to modulate the pore parameters of the extended structures. However, pore enlargement is accomplished at the cost of loss in the number of active sites in typical MOFs, since dissociations of coordination linkages to create vacancies are not site-selective. Here, we performed site-specific vacancy generation in a multinary MOF (FDM-6) by selectively hydrolyzing the weak Zn─carboxylate linkages and keeping the strong Cu─pyrazolate linkages untouched. Surface area and pore size range of the materials could be systematically tuned by adjusting the water content and hydrolysis time. More than 56% of the Zn(II) sites in FDM-6 could be vacant, as evidenced by the atom occupancy analysis using powder X-ray diffraction, while most of the redox-active Cu sites are held in the backbone. The vacancies create highly connected mesopores, thus guaranteeing facile transportation of the guest molecules toward the active sites. Compared with the pristine MOF, FDM-6 with site-selective vacancies shows enhanced catalytic activity in bulky aromatic alcohol oxidation. Overall, the multinary MOF provides a platform in which both pore size enhancement and full retainment of active sites could be delivered in one framework by simple vacancy engineering.

Enhancement in Two-Photon Absorption and Photoluminescence in Single Crystals of Cd(II) Metal Organic Frameworks.

The emergence of metal organic frameworks (MOFs) as advanced photonic materials has placed them at the forefront of exploration. Nonlinear optical (NLO) phenomena such as simultaneous two-photon absorption and consequent upconversion emission have been in demand for promising applications. A rational design approach based on the fundamental structure-property relationship is key for the fabrication of nonlinear optically active MOF materials. Here, we investigate two-photon-absorption (2PA)-induced photoluminescence of four new Cd(II) MOFs based on an acceptor-π-donor-π-acceptor trans, trans-9, 10-bis(4-pyridylethenyl)anthracene chromophore linker. The use of auxiliary carboxylate linkers resulted in the variation of crystal structures, leading to the modulation of NLO properties. On comparison with a standard Zn(II)-MOF, two MOFs showed enhancement in 2PA, while the other two showed a mild decrease. We tried to establish a structural correlation to explain the trend in NLO activity. The interplay of various factors such as chromophore density, degree of interpenetration, chromophore orientation, and π···π interactions between the individual networks affects the NLO activities. These results show the modulation of the optical properties of MOFs based on a combined strategy for the development of tunable single crystal NLO devices.

Structure–Activity Relationships in Ni- Carboxylate-Type Metal–Organic Frameworks’ Metamorphosis for the Oxygen Evolution Reaction

Metal–organic frameworks (MOFs) have been reported to catalyze the oxygen evolution reaction (OER). Despite the established links between the pristine MOFs and their derived metal hydroxide electrocatalysts, several limitations still preclude understanding of the critical factors determining the OER performance. Of prime importance appears the choice of MOF and how its compositions relate to the catalyst stability and in turn to the reconstruction or metamorphosis mechanisms into the active species under OER conditions. An isoreticular series of Ni-carboxylate-type MOFs [Ni2(OH)2L] was chosen to elucidate the effects of the carboxylate linker length expansion and modulation of the linker–linker π–π interactions (L = 1,4-benzodicarboxylate, 2,6-napthalenedicarboxylate, biphenyl-4,4′-dicarboxylate, and p-terphenyl-4,4″-dicarboxylate). Degradation and reconstruction of MOFs were systematically investigated. The linker controls the transformation of Ni-MOF into distinct nickel hydroxide phases, and the conversion from α-Ni(OH)2 to β-Ni(OH)2, thus correlating the Ni-MOF composition with the OER activity of the Ni-MOF-derived metastable nickel hydroxide phase mixture.