Isostructural Cobalt Research Articles

Br‐Induced d‐Band Regulation on Superhydrophilic Isostructural Cobalt Phosphide for Efficient Overall Water Splitting

AbstractHighly efficient novel electrocatalysts for hydrogen/oxygen production are urgently required, for noble metal‐based catalysts substitution. Cobalt phosphides have shown great potential for serving as bifunctional catalysts, owing to the cost effectiveness and high conductivity. However, the water splitting ability of them is still not comparative with commercial noble counterparts. In this work, we reported a Br‐induced strategy, to obtain an ultra‐hydrophilic isostructural Br0.036─Co1.085P@NF catalyst by a gas‐solid reaction method. As a typical halogen element, the introduction of Br can greatly enhance the surficial hydrophilicity and thus further impart ideal adsorption ability for water molecules. Meanwhile, the electronic structure could be regulated to further induce the generation of isostructural cobalt phosphides (CoP/Co2P). As a result, the contact angle of Br0.036─Co1.085P@NF catalysts nearly cannot be caught owing to the ultra‐hydrophilicity. It is also confirmed that, the d‐band center of Co shows apparent negative shift after Br introduction, which reduces the adsorption energy of oxygen‐containing intermediates thereby facilitating the desorption process. Besides, the introduction of Br can also reduce the barrier of O2 formation, show more favorable dynamic behaviors. This work proved the accessibility for an effective design strategy on halogen‐induced isostructural transition metal phosphides catalysts for high‐performance overall water splitting.

Putting the squeeze on valence tautomerism in cobalt-dioxolene complexes

Molecules that can reversibly switch between electronic states under an external stimulus are of interest to numerous applications. Complexes of open shell metal ions with redox active ligands undergo valence tautomerism, resulting in magnetic, colour and structural switching, relevant to data storage and actuators. However, the precise structural changes occurring during valence tautomerism in the solid state are unclear due to the lack of atomic-resolution characterization. Here, variable temperature and high-pressure single crystal X-ray diffraction is used to characterize valence tautomerism in two isostructural cobalt complexes, [Co(bis(6-methyl-2-pyridylmethyl) amine)(3,5-di-tert-butyl-1,2-dioxolene)]+ and [Co(tris(6-methyl-2-pyridylmethyl)amine)(3,5-di-tert-butyl-1,2-dioxolene)]+ to atomic resolution. The less sterically hindered dimethylated complex exhibits two-step thermally-induced interconversion between the high-spin CoII-seminquinonate and low-spin CoIII-catecholate forms (valence tautomerism) at 155 and 95 K due to the presence of two symmetry-independent complexes. In contrast, the more sterically hindered trimethylated complex does not display thermal valence tautomerism. Both complexes exhibit unique behaviour under high pressure. The dimethylated species undergoes gradual, one-step valence tautomerism in both symmetry-independent complexes concurrently between 0.43 GPa and 1.30 GPa. In the trimethylated species, pressure is sufficient to overcome steric hindrance, leading to one-step valence tautomerism between 2.60 GPa and 3.10 GPa, demonstrating pressure-triggered valence tautomerism in a thermally inactive complex. This study is among the few investigations using in situ high-pressure single crystal X-ray diffraction to achieve atomic-level structural characterization of valence tautomerism, aiding the development of robust structure-property relationships in these types of complexes.

Microcube formation and characterization of cobalt and nickel selenite dihydrate: Thermal, spectral, and dielectric insights

This paper outlines the template-free preparation of cobalt and nickel selenite dihydrate microcubes using a simple precipitation method from aqueous solutions at room temperature. Structural analysis revealed the formation of pure, well-crystallized isostructural cobalt and nickel selenite dihydrate, exhibiting monoclinic crystal systems of space group P21/n. Thermal analysis showed distinct decomposition patterns for both compounds, highlighting their thermal stabilities. The intermediate formed after water loss were stable up to ∼550 °C, and crystallized before decomposing into their respective oxides via SeO2 sublimation. Scanning electron microscopy (SEM) images illustrated the presence of irregular-sized well-defined microcubes with smooth surfaces and sharp edges, distributed across the material. The formation of these microstructures is likely driven by self-aggregation and the Ostwald ripening process. Dielectric studies on pelletized materials revealed higher dielectric constants at low frequencies with minimal dielectric loss. CoSeO3⋅2H2O exhibited higher dielectric constants than NiSeO3⋅2H2O due to the larger ionic radius of Co2+ ions, which leads to a greater degree of polarization compared to Ni2+ ions. The considerably higher dielectric constant with an insignificant amount of dielectric loss indicates the materials’ potential for applications in dielectric and microwave technologies.

Ligand-Mediated Regulation of the Chemical/Thermal Stability and Catalytic Performance of Isostructural Cobalt(II) Coordination Polymers.

Regulating the chemical/thermal stability and catalytic activity of coordination polymers (CPs) to achieve high catalytic performance is topical and challenging. The CPs are competent in promoting oxidative cross-coupling, yet they have not received substantial attention. Here, the ligand effect of the secondary ligand of CPs for oxidative cross-coupling reactions was investigated. Specifically, four new isostructural CPs [Co(Fbtx)1.5(4-R-1,2-BDC)]n (denoted as Co-CP-R, Fbtx = 1,4-bis(1,2,4-triazole-1-ylmethyl)-2,3,5,6-tetrafluorobenzene, 4-R-1,2-BDC = 4-R-1,2-benzenedicarboxylate, R = F, Cl, Br, CF3) were prepared. It was found that in the reactions of oxidative amination of benzoxazoles with secondary amines and the oxidative coupling of styrenes with benzaldehydes, both the chemical and thermal stabilities of the four Co-CPs with the R group followed the trend of -CF3 > -Br > -Cl > -F. Density functional theory (DFT) calculations suggested that the difference in reactivity may be ascribed to the effect of substituent groups on the electron transition energy of the cobalt(II) center of these Co-CPs. These findings highlight the secondary ligand effect in regulating the stability and catalytic performance of coordination networks.

Nonlinear optical properties of novel crystalline complexes of cobalt (II) and nickel (II) with 4-bromo-3-methyl-1H-pyrazole: combined experimental and computational study

Two new isostructural cobalt [Co(II)(C4H5BrN2)4(Cl)2], I and nickel [Ni(II)(C4H5BrN2)4(Cl)2], II complexes were synthesized for linear and nonlinear optical (NLO) responses using the finite field method. The synthesized complexes were characterized using elemental analysis, infrared and H-NMR spectroscopy, TG/DSC analysis, and X-ray crystallography. The crystal analysis indicates that both complexes I and II are mononuclear, and crystallize in the monoclinic space group P21/c. The metal ion in each complex is six coordinated with four nitrogen atoms (from 4-bromo-3-methyl-1H-pyrazole ligand) and two chloride ligands adopting octahedral coordination geometry. Furthermore, the computational predictions for molecular geometries and average third-order nonlinear polarizabilities of I and II are made in current study. The average theoretically predicted third-order nonlinear polarizabilities 〈γ〉 of I and II are 95.50 × 10−36 and 91.25 × 10−36 esu, respectively. The 〈γ〉 amplitudes values of complexes I and II are ∼5.26 and ∼5.0 times greater than the prototype NLO molecule of para-nitroaniline (p-NA) at same level of theory, which indicates their decent potential as efficient NLO materials.

Compositionally Controlled Electron Transfer in Metallo-Organics.

We demonstrate here the assembly of a nanolayer of electrochromic iron complexes on the top of composite layers of cobalt and ruthenium complexes. Depending on the ratio of the latter two complexes, we can tailor materials that show different electron transport pathways, redox activities, and color transitions. No redox activity of the top layer, consisting of iron complexes, is observable when the relative amount of the ruthenium complexes is low in the underlying composite layer because of the insulating properties of the isostructural cobalt complexes. Increasing the amount of ruthenium complexes opens an electron transport channel, resulting in charge storage in both the cobalt and iron complexes. The trapped charges can be chemically released by redox-active ferrocyanide complexes at the film-water interface.

Photocatalytic properties of two new isostructural cobalt(II) and nickel(II) complexes having terphenyl-3,3″,4,4″-teteacarboxylic acid

The effective and rapid removal of organic pollutants from wastewater is very important for the safety of aquatic environment. Photocatalytic degradation is a feasible strategy that can safely eliminate the organic pollutants from the wastewater discharge. Amongst varied class of photocatalysts, the coordination polymers (CPs) are important class of material that can be used to remove and degrade the organic dyes from wastewater. Herein, two isostructural coordination polymers, having compositions [Ni2(H2L)2(phen)4·H4L·6H2O)] (1) and [Co2(H2L)2(bipy)4·H4L·6H2O)] (2) (H4L = terphenyl-3,3″,4,4″-teteacarboxylic acid, phen = 1,10-phenanthroline and bipy = 2,2′-bipyridine) have been synthesized and characterized. Both of the isostructural compounds display dinculear architecture, where metal centers are coordinated to two carboxylic groups, which further forms a 2D supramolecular layer via hydrogen bonds formed between the water molecules and uncoordinated carboxylate groups. Both the compounds have been used as photocatalysts to catalyze the photodegradation of methylene blue (MB) and methylene violet (MV) under UV irradiation. The Ni(II)-based photocatalyst 1 exhibited the good photocatalytic performance in comparison to that of 2. The observed differences in the photocatalytic properties of both the CPs have been addressed using Hirshfeld surface analyses.

Synthesis, crystal structure and electrochemical properties of poly(cadmium 1,1′-ferrocenediyl-bis(H-phosphinate))

The new redox active coordination polymer [Cd(H2O)2(fc(PHOO)2)·2H2O]n (fc = 1,1′-ferrocenediyl) was synthesized and structurally characterized by single-crystal X-ray diffraction. In this compound cadmium atoms are bound by phosphinate fragments to give infinite chains, the latter are interconnected by ferrocene groups to form 2D coordination polymer. Electrochemical properties of CP were investigated. It’s found that Cd-polymer is harder to oxidize than its isostructural cobalt analogue. This means that increase in the length of the M − O bond in coordination polymer, oxidation becomes harder.

Bi‐Microporous Metal–Organic Frameworks with Cubane [M4(OH)4] (M=Ni, Co) Clusters and Pore‐Space Partition for Electrocatalytic Methanol Oxidation Reaction

Embedding cubane [M4 (OH)4 ] (M=Ni, Co) clusters within the matrix of metal-organic frameworks (MOFs) is a strategy to develop materials with unprecedented synergistic properties. Herein, a new material type based on the pore-space partition of the cubic primitive minimal-surface net (MOF-14-type) has been realized. CTGU-15 made from the [Ni4 (OH)4 ] cluster not only has very high BET surface area (3537 m2 g-1 ), but also exhibits bi-microporous features with well-defined micropores at 0.86 nm and 1.51 nm. Furthermore, CTGU-15 is stable even under high pH (0.1 m KOH), making it well suited for methanol oxidation in basic medium. The optimal hybrid catalyst KB&CTGU-15 (1:2) made from ketjen black (KB) and CTGU-15 exhibits an outstanding performance with a high mass specific peak current of 527 mA mg-1 and excellent peak current density (29.8 mA cm-2 ) at low potential (0.6 V). The isostructural cobalt structure (CTGU-16) has also been synthesized, further expanding the application potential of this material type.

Bi‐Microporous Metal–Organic Frameworks with Cubane [M4(OH)4] (M=Ni, Co) Clusters and Pore‐Space Partition for Electrocatalytic Methanol Oxidation Reaction

AbstractEmbedding cubane [M4(OH)4] (M=Ni, Co) clusters within the matrix of metal–organic frameworks (MOFs) is a strategy to develop materials with unprecedented synergistic properties. Herein, a new material type based on the pore‐space partition of the cubic primitive minimal‐surface net (MOF‐14‐type) has been realized. CTGU‐15 made from the [Ni4(OH)4] cluster not only has very high BET surface area (3537 m2 g−1), but also exhibits bi‐microporous features with well‐defined micropores at 0.86 nm and 1.51 nm. Furthermore, CTGU‐15 is stable even under high pH (0.1 m KOH), making it well suited for methanol oxidation in basic medium. The optimal hybrid catalyst KB&CTGU‐15 (1:2) made from ketjen black (KB) and CTGU‐15 exhibits an outstanding performance with a high mass specific peak current of 527 mA mg−1 and excellent peak current density (29.8 mA cm−2) at low potential (0.6 V). The isostructural cobalt structure (CTGU‐16) has also been synthesized, further expanding the application potential of this material type.

Light-Triggered Release of Trapped Charges in Molecular Assemblies.

We demonstrate the mediation of charge transport and release in thin films and devices by shifting the redox properties of layers of metal complexes by light. The nanoscale surface arrangement of both photo- and electrochemically-active components is essential for the function of the thin films. Layers of well-defined ruthenium complexes on indium-tin-oxide electrodes provide electron-transport channels that allow the electrochemical addressing of layers of isostructural cobalt complexes. These cobalt complexes are electrochemically inactive when assembled directly on transparent metal-oxide electrodes. The interlayer of ruthenium complexes on such electrodes allows irreversible oxidation of the cobalt complexes. However, shifting the redox properties of the ruthenium complexes by excitation with light opens up an electron-transport channel to reduce the cobalt complexes; hence releasing the trapped positive charges.

Light‐Triggered Release of Trapped Charges in Molecular Assemblies

AbstractWe demonstrate the mediation of charge transport and release in thin films and devices by shifting the redox properties of layers of metal complexes by light. The nanoscale surface arrangement of both photo‐ and electrochemically‐active components is essential for the function of the thin films. Layers of well‐defined ruthenium complexes on indium‐tin‐oxide electrodes provide electron‐transport channels that allow the electrochemical addressing of layers of isostructural cobalt complexes. These cobalt complexes are electrochemically inactive when assembled directly on transparent metal‐oxide electrodes. The interlayer of ruthenium complexes on such electrodes allows irreversible oxidation of the cobalt complexes. However, shifting the redox properties of the ruthenium complexes by excitation with light opens up an electron‐transport channel to reduce the cobalt complexes; hence releasing the trapped positive charges.

High-temperature reversible phase transitions and exceptional dielectric anomalies in cobalt(ii) based ionic crystals: [Me3NCH2X]2[CoX4] (X = Cl and Br).

Two isostructural ionic cobalt(ii) halides, trimethylchloromethyl ammonium tetrachlorocobalt(ii) (1, [Me3NCH2Cl]2[CoCl4]) and trimethylbromomethyl ammonium tetrabromocobalt(ii) (2, [Me3NCH2Br]2[CoBr4]), have been discovered as new high-temperature phase transition materials. 1 exhibits two successive structural phase transitions from P212121 to P21/c at 252 K and then to Pnma at 335 K, accompanied by step-like dielectric anomalies. The two-step sequential reversible phase transitions of 1 derive from the order-disorder transformation of CoCl4 anions and organic Me3NCH2Cl cations, respectively. Its analogue 2 also crystallizes in P21/c at 293 K by changing the halogen atoms of both cations and anions of 1. Unlike 1, 2 displays only one structural phase transition with a much higher transition temperature at 387 K, which is mainly influenced by intermolecular interactions and more energy is required to provide the freedom of the motion. All the findings in the present work indicate that the phase transition temperature and properties of materials can be tuned by using halogens in this series of compounds, which could open a new way to design and assemble novel high-temperature phase transition materials.

Crystal Structure and Magnetic and Magnetocaloric Properties of Cobalt Hydroxychlorides Co2(OH)4–xClx

A series of isostructural cobalt hydroxychloride salts with the formula Co2(OH)4–xClx were fabricated by using a precipitation method from aqueous solutions of CoCl2 and NaOH with different mixing ratios. The crystal structure was resolved from neutron powder diffraction data, including the location of H atoms of the hydroxide groups. The structure (space group R3m) consists of an open network of edge‐sharing CoO6 and CoO6–2xCl2x octahedra, forming intercrossed 1D channels where the hydrogen atoms reside. Unusually high values of the magnetic entropy change were observed for all samples, probably due to the geometrically frustrated magnetic structure; for example, the magnetic entropy change was 8.3 J/kg K for the sample with Co/Cl > 2.5 at 10 K in a magnetic field change of 20 kOe.

Magnesium cinnamate complex, [Mg(cinn)2(H2O)2]n; structural, spectroscopic, thermal, biological and pharmacokinetical characteristics

The composition and structure of the magnesium complex with cinnamic acid, [Mg(cinn)2(H2O)2]n(1), were determined using single crystal X-ray diffraction data, IR, NMR spectroscopies, thermal and mass spectrometry analysis. Magnesium cinnamate complex, like the isostructural cobalt(II) species reported in the literature, appears to belong to the group of coordination polymers forming layered solids with pseudooctahedral coordination around the metal centre and OCO bridging units. The vibrational assignments of the experimental spectra of the complex (1) were performed on the basis of the DFT results obtained for the [Mg(cinn)4(H2O)2]2− ion, serving as a model. The complex was found to exhibit a very low cytotoxicity against neoplastic: A549 (lung), MCF-7 (breast), P388 (murine leukemia) and normal BALB3T3 (mouse fibroblasts) cell lines. In silico pharmacokinetical parameter calculations for (1) and seven known magnesium complexes with carboxylic acids: lactic, malic, glutamic, hydroaspartic and aspartic allowed for comparison of their potential bioavailability. Magnesium cinnamate complex appeared to exhibit a superior lipophilic property that suggests an optimal pharmacokinetics profile.

Synthesis and bio-catalytic activity of isostructural cobalt(III)-phenanthroline complexes

We have synthesized two isostructural mononuclear cobalt(III) complexes [1]NO3⋅3H2O and [1]NO3⋅CH3CO2H⋅H2O {[1] + = [Co(1,10-phenanthroline)2Cl2]+} and characterized by single crystal X-ray structural analyses. Mass spectral studies of the complexes indicate both the compounds to produce identical cationic species viz., [Co(phen)2Cl2]+ in methanol solution. [1]+ has been evaluated as model system for the catechol oxidase enzyme by using 3,5-di-tert-butylcatechol (3,5-DTBC) as the substrate in methanol medium, which revealed that the cationic complex efficiently inhibits catalytic activity with kcat value 9.65 ×102 h−1. [1]+ cleaved pBR 322 DNA without addition of an activating agent. Further, the anti-cancer activity of [1]+ on human hepatocarcinoma cell line (HepG2) has been examined. The induction of apoptosis induced in the cell line was assessed base on the changes in cell morphology, which showed the efficacy of [1] + to induce apoptosis in 53% of cells during 24 h treatment. Interestingly, the observed IC50 values reveal that [1]+ brings about conformational change on DNA strongly and exhibits remarkable cytotoxicity. The cationic cobalt(III) complex exhibits good catalytic activity in saturated oxygen environment towards 3,5-ditertbutylcatechol with kcat value 9.65×102 h-1. It also exhibits important cytotoxicity against human hepatocarcinoma cell line (HepG2).

Two isostructural cobalt(II) coordination polymers with both polyrotaxane and polycatenane features assembled with a V-shaped rigid ligand

Two novel cobalt(II) coordination polymers (CPs), [Co(BPFP)2(sca)]n (1), [Co(BPFP)2(sda)]n (2), [BPFP=2,8-di(pyridin-4-yl)dibenzo[b,d]furan, H2sca=succinic acid, H2sda=thiophene-2,5-dicarboxylic acid], have been synthesized hydrothermally based on a V-shaped rigid ligand BPFP. Their structures were fully characterized by elemental analysis, FT-IR spectroscopy and X-ray single-crystal diffraction methods. Compound 1 is a 2-fold parallel interpenetrating network consist of two identical sets of 2D layer motifs and shows both polyrotaxane and polycatenane characters. Compound 2 has the same structural feature as compound 1, except that the sca2− anions are replaced by the sda2− anions. The Powder X-ray diffraction (PXRD) analyses and thermogravimetric analyses were carried out to confirm the phase purity and the thermal stabilities of the compounds 1 and 2. In addition, the solid-state UV–vis absorption spectra were also investigated.

Reactivity of a series of isostructural cobalt pincer complexes with CO2, CO, and H(+).

The preparation and characterization of a series of isostructural cobalt complexes [Co(t-Bu)2P(E)Py(E)P(t-Bu)2(CH3CN)2][BF4]2 (Py = pyridine, E = CH2, NH, O, and X = BF4 (1a-c)) and the corresponding one-electron reduced analogues [Co(t-Bu)2P(E)Py(E)P(t-Bu)2(CH3CN)2][BF4]2 (2a-c) are reported. The reactivity of the reduced cobalt complexes with CO2, CO, and H(+) to generate intermediates in a CO2 to CO and H2O reduction cycle are described. The reduction of 1a-c and subsequent reactivity with CO2 was investigated by cyclic voltammetry, and for 1a also by infrared spectroelectrochemistry. The corresponding CO complexes of (2a-c) were prepared, and the Co-CO bond strengths were characterized by IR spectroscopy. Quantum mechanical methods (B3LYP-d3 with solvation) were used to characterize the competitive reactivity of the reduced cobalt centers with H(+) versus CO2. By investigating a series of isostructural complexes, correlations in reactivity with ligand electron withdrawing effects are made.

Cobalt(II)–Lanthanide(III) Heterometallic Metal–Organic Frameworks with Unique (6,6)‐Connected Nia Topologies with 1H‐1,2,3‐Triazole‐4,5‐dicarboxylic Acid: Syntheses, Structures and Magnetic Properties

AbstractFour isostructural cobalt(II)–lanthanide(III) heterometallic metal–organic frameworks (MOFs), formulated as {[(CH3)2NH2]3[Co3Ln(tda)3(HCOO)3] 2H2O 0.75dmf}n [Ln = Eu (Co‐Eu), Gd (Co‐Gd), Tb (Co‐Tb), and Dy (Co‐Dy); H3tda = 1H‐1,2,3‐triazole‐4,5‐dicarboxylic acid] have been successfully synthesized and structurally characterized in detail. In these Co‐Ln heterometallic MOFs, three neighboring CoII ions are connected by HCOO– anions to form triangular [Co3(HCO2)3]3+ clusters. The equivalent triangular [Co3(HCO2)3]3+ clusters are connected by six tda3– anions to generate a 1D trigonal prismatic chain, which are further interconnected through LnIII ions to give unique 3D (6,6)‐connected nia nets with the Schläfli symbol of (412 63) (49 66). The magnetic properties of the four isostructural Co‐Ln heterometallic MOFs have also been studied.

Sodium-Centered Dodecanuclear Co(II) and Ni(II) Complexes with 2-(Phosphonomethylamino)succinic Acid: Studies of Spectroscopic, Structural, and Magnetic Properties

Two new isostructural cobalt(II) and nickel(II) polynuclear complexes with 2-(phosphonomethyl)aminosuccinic acid, H4PMAS, namely, Na[Co12(PMAS)6(H2O)17(OH)]·x2H2O, 1·x2H2O, and Na[Ni12(PMAS)6(H2O)17(OH)]·xH2O, 2·xH2O, have been synthesized for the first time from aqueous solutions and studied by single crystal X-ray diffraction, infrared, and UV-visible diffuse reflectance spectroscopy; TG/DTA analysis; and magnetochemistry. Both 1 and 2 crystallize in the rhombohedral crystal system with the R3[overline] space group with 1/6 of the Co12(PMAS)6 or Ni12(PMAS)6 moieties in the asymmetric unit. The X-ray refinements reveal the presence of 18 water sites, but unit cell charge balance requires that one water molecule must be an OH(-) anion, an anion which is disordered over the 18 sites. The PMAS(4-) ligand forms two five-membered and one six-membered chelation ring. Both 1 and 2 contain 24-membered metallacycles as a result of the bridging nature of the PMAS(4-) ligands. The resulting three-dimensional structures have one-dimensional channels with a sodium cation at the center of symmetry. The temperature dependence of the magnetic susceptibility reveals the presence of weak antiferromagnetic exchange coupling interactions in both 1 and 2. Two exchange coupling constants, J1 = -15.3(7) cm(-1) and J2 = -1.06(2) cm(-1) with S1 = S2 = 3/2 for the Co(1)···Co(1) and Co(1)···Co(2) exchange pathways, respectively, are required for 1, and J1 = -1.17(6) cm(-1) and J2 = -4.00(8) cm(-1) with S1 = S2 = 1 for the Ni(1)···Ni(1) and Ni(1)···Ni(2) exchange pathways, respectively, are required for 2, in order to fit the temperature dependence of the observed magnetic susceptibilities.