Central Cobalt Ion Research Articles

The Catalytic Mechanism of a Highly Active Cobalt Chlorin Complex for Photocatalytic Water Oxidation.

Highly active catalysts for electrocatalytic and photocatalytic water oxidation are strongly demanded to realize artificial photosynthesis. A cobalt complex with a chlorin derivative ligand (CoII(Ch)) exhibited high activity for electrocatalytic water oxidation with an overpotential of 0.45 V at pH 9.0. Spectroelectrochemistry (UV-vis) unveiled the formation of two intermediates by successive one-electron oxidations. Also, the Pourbaix diagram depicted by the pH dependence of redox potentials indicated that the water oxidation proceeded after the oxidation of both the central cobalt ion and chlorin ligand with proton-coupled electron transfer (PCET). Then, the photocatalytic activity of CoII(Ch) was examined for water oxidation using [RuII(bpy)3]2+ (bpy: 2,2'-bipyridine) and S2O82- as a photosensitizer and a sacrificial electron acceptor, respectively. The turnover number, turnover frequency, and oxygen yield reached as high as 980, 5.2 s-1, and 98%, respectively, under optimized conditions. The O2-evolution rates increased in proportion to the square of the catalyst concentration in the reaction solution, suggesting that the formation of the O-O bond regarded as the rate-determining step of water oxidation proceeded by the interaction of two metal centers (I2M) mechanism in which two molecules of high-valent metal oxo or oxyl radical species react with each other.

A prediction of high temperature magnetic coupling in transition metal phthalocyanines.

In spintronics, a perennial goal has been the generation of organic spin-bearing semiconductor materials with magnetic ordering stable at room temperature. To this end, the class of transition metal phthalocyanines has shown much promise in fulfilling this ambition. In particular, alpha-phase cobalt (II) phthalocyanine (α-CoPc) exhibits strong antiferromagnetic exchange interactions producing a long range order up to ∼100K. However, the underlying mechanism by which this magnetic interaction proceeds is not well understood. In this report, a simple mechanism has been proposed based on the Hubbard Hamiltonian, which elucidates the exchange coupling in α-CoPc. The mechanism provides stipulations for increasing the magnetic coupling, and this directs to a proposal that substitution of the central cobalt ion for rhodium will lead to a significant increase in coupling strength. The strength of this exchange interaction has been evaluated using broken symmetry hybrid exchange density functional theory and indicates that the novel rhodium (II) phthalocyanine system is indeed predicted to exhibit significantly stronger magnetic ordering. This study, therefore, identifies the coupling mechanism in α-CoPc as primarily attributable to kinetic exchange, explains its previously reported strong coupling relative to its first-row transition metal counterparts, and suggests that rhodium (II) phthalocyanine is likely to exhibit stable magnetic ordering at room temperature.

Chemiresistive NH3 and H2S sensors based on thin films of vitamin B12 derivatives

Despite the large number of materials, e.g. semiconducting oxides, carbon nanomaterials, conducting polymers and others, that are used as active layers of chemiresistive sensors to ammonia and hydrogen sulfide, the search for new materials remains an urgent task. Special attention is paid to the search for environmentally friendly materials. Corrinoids are naturally occurring coordination complexes consisting of a central cobalt ion and a tetrapyrrole ligand called a corrin ring. Cobalamins and their derivatives are widely used as active layers of optical and electrochemical sensors. At the same time, vitamin B12 derivatives have not been studied as active layers of chemiresistive gas sensors. In this work, films of two vitamin B12 derivatives, viz. dicyanocobyrinic acid heptabutyl ester (DC) and its aquacyano form, aquacyanocobyrinic acid heptabutyl ester (AC), deposited by spin coating and drop casting techniques onto interdigitated electrodes, were tested for the first time as active layers of chemiresistive sensors for the detection of low concentrations of ammonia and hydrogen sulfide (1–50 ppm) in air. It was shown that films of both vitamin B12 derivatives demonstrated reversible sensor response to NH3 and H2S at room temperature. The limit of detection (LOD) of H2S was 0.1 ppm for both vitamin B12 derivatives, while LOD of ammonia was noticeably lower (0.06 ppm) in the case of AC films than in the case of DC films (0.4 ppm). Both sensors demonstrated a fairly low regeneration time, which did not exceed 180 s for 5 ppm of NH3 and 185 s for 5 ppm of H2S.

Cobalamin decyanation by the membrane transporter BtuM

BtuM is a bacterial cobalamin transporter that binds the transported substrate in the base-off state, with a cysteine residue providing the α-axial coordination of the central cobalt ion via a sulfur-cobalt bond. Binding leads to decyanation of cobalamin variants with a cyano group as the β-axial ligand. Here, we report the crystal structures of untagged BtuM bound to two variants of cobalamin, hydroxycobalamin and cyanocobalamin, and unveil the native residue responsible for the β-axial coordination, His28. This coordination had previously been obscured by non-native histidines of His-tagged BtuM. A model in which BtuM initially binds cobinamide reversibly with low affinity (KD= 4.0μM), followed by the formation of a covalent bond (rate constant of 0.163 s-1), fits the kinetics data of substrate binding and decyanation of the cobalamin precursor cobinamide by BtuM. The covalent binding mode suggests a mechanism not used by any other transport protein.

Structural, physicochemical characterization and antimicrobial activities of a new tris(8-quinolinolato-κ2N,O)cobalt(III) ethanol solvate [Co(C9H6NO)3].(C2H6O)

We report herein the synthesis and physicochemical characterization of a new 8-hydroxyquinoline cobalt(III) complex ethanol solvate with formula [Co(C9H6NO)3].(C2H6O). This compound was been prepared by slow evaporation at room temperature and characterized by single crystal X-ray diffraction. It crystallizes in the monoclinic system, spaces group P21/n. The central cobalt ion has a slightly distorted square bipyramidal environment, coordinated by three chelating 8-hydroxyquinoline molecules. Structural cohesion is primarily established by π-π interactions between the neighboring rings of quinoline groups and intermolecular hydrogen bonds O-H…O connecting the cobalt complex entities and uncoordinated ethanol molecules.The title compound has been characterized by the infrared (IR) and the UV–Visible (UV–Vis) spectra. Intermolecular interactions in the crystal structure were quantified by Hirshfeld surface analysis. The band gap of the complex was calculated using solid-state reflectance spectra, and the results show that the complex acts as a semiconductor. Moreover, the new compound exhibits high antibacterial and antifungal activities, as detected by the well agar diffusion against various bacterial and fungal clinical strains. The superior inhibitory effect was observed against Klebsiella pneumoniae, Candida albicans and Candida glabrata with zones inhibition of about 17.5, 17.5 and 17 mm, respectively.

Cobalt(II) and nickel(II) complexes based on 2,5-di(pyridine-4-yl)thiazolo[5,4-d]thiazole and dicarboxylate ligands: synthesis, structures and properties

Abstract Two metal coordination polymers [Ni(oba)(Py2TTz)1.5(H2O)]·2H2O·DMF (1) and [Co(oba)(Py2TTz)(H2O)4]·2H2O (2) have been synthesized under solvothermal conditions [H2oba = 4,4′-oxybis(benzoic acid) and Py2TTz = 2,5-di(pyridine-4-yl)thiazolo[5,4-d]thiazole]. Crystals of compound 1 belong to the orthorhombic system, space group Ibam, with a = 38.928(8), b = 7.7113(14), c = 28.508(6) Å, V = 8558(3) Å3, Z = 8. Compound 2 crystallizes in the monoclinic crystal system, space group C2/c, with a = 33.816(3), b = 6.2697(6), c = 13.5821(13) Å, β = 96.393(3)°, V = 2861.7(5) Å3, Z = 4. The oba2− dianions link two Ni atoms through unidentate carboxylate moieties in a μ 1 − η 1:η 0 coordination mode. Compound 1 features a three-dimensional (3D) framework structure with Py2TTz and oba2− ligands. In compound 2, the central cobalt ion is in an octahedral geometry, which is defined by four oxygen atoms from four different coordinated water molecules and two nitrogen atoms from two different Py2TTz ligands. It is noteworthy that the dicarboxylate ligands oba2− with four oxygen atoms do not directly coordinate with the cobalt ion, and only act as a counter-anion. The luminescence properties of 1 and 2 were also investigated.

Intracluster O–O Coupling Pathway Evidenced for an Anderson-Type Single-Cobalt Polymolybdate Water Oxidation Catalyst

Toward the establishment of a carbon-neutral society, artificial photosynthesis, replacing fossil fuels with renewable energies (H2, HCOOH, CH3OH, etc.), has attracted great attention in recent years. One of the most important issues in this area has been to advance our knowledge and technical skills in handling water oxidation (WO) catalysis often considered as the bottleneck in the overall photosynthetic processes. The polyoxometalate water oxidation catalysts (WOCs) studied herein belong to one of the most highly active as well as the most highly robust family of WOCs. Nevertheless, due to their structural complexity and the high molecular weight associated with the high content of heavy elements, their mechanism of action remains largely unexplored from both theoretical and experimental viewpoints. To solve these problems, here we focus on one of the smallest and lightest polyoxometalate WOCs, single-cobalt polyoxometalate (NH4)3[CoMo6O24H6]·5H2O (Co-POM-Mo), which was previously demonstrated to be highly active for WO [Tanaka, S. , Chem. Commun. 2012, 48, 1653−1655]. The temperature dependence of the WO rate observed by mixing Co-POM-Mo and [RuIII(bpy)3]3+ using a stopped-flow technique revealed a positive entropy of activation (ΔS‡ = ca. 20–40 cal mol–1 K–1), revealing the promotion of intramolecular O–O coupling via the dissociative activation of the oxygens preinstalled in the cluster. The 17O NMR and 18O-labeling experiments, conducted to understand the source of oxygens in the O2 evolved, clarified the major contribution of the preinstalled 16O oxygens in the O–O coupling by Co-POM-Mo. The O2 evolved from the three catalysis cycles by Co-POM-Mo (100% in 16O) from an 18O-enriched aqueous solution (49% in 18O) resulted in the 16O2, 16O18O, and 18O2 abundances of 46, 40, and 14%, respectively. The Monte Carlo simulation reproduced the observed abundances under the assumption that the three consecutive O–O coupling proceed by only adopting a single μ3-OH site among the six available sites. Our simulation also supposed the O–O coupling process competes with the exchange of the catalytically active μ3-OH oxygen with the bulk water oxygen with the former twice higher in rate than the latter. Our DFT results also agree well with the promotion of O–O coupling between the inner μ3-OH oxygen bound to the central cobalt ion and the adjacent μ2-O oxygen constructing the Mo6(μ2-O)6 ring. This study strongly suggests that the O–O coupling among the preinstalled oxygens is the only available pathway to promote the WO by one of the highly active polyoxometalate WOCs, providing a new perspective on the catalysis by oxo clusters.

Cobalt complexes with multi-dentate N-donor ligands: Redox, X-ray photoelectron spectroscopic and theoretical study

Five CoII complexes were prepared with different multi-dentate N-donor ligands (5-Nitro-1,10-phenanthroline, 1,10-phenanthroline, 2,2′:6′,2″-terpyridine, 2,2′-dipyridyl or 4,4′-dimethoxy-2,2′-bipyridine). Complexation was confirmed with the blue-shift of stretching frequency of the CN moiety of the ligands as measured by ATR FTIR and by XPS spectra. The average XPS binding energies (BE) of the main and satellite structures of Co 2p3/2 photoelectron lines for CoII were ca. 780.3 eV and 785.0 eV respectively. The diffusion controlled formal reduction potential E0′ of the CoII/III redox couple measured in aqueous medium ranged between 0.08 and 0.58 V versus NHE. Ihe CoII/I redox couple measured in DMF ranged between between −1.1 and −1.7 V vs HFc/HFc+. Directly proportional relationships were established between the E0′ of both the CoII/III and CoII/I redox couples and the BE of the main CoII 2p3/2 photoelectron lines and DFT calculated energies and charges. These relationships all illustrate the electronic influence of the different N-donor ligands on the effective charge of the central cobalt(II) ion the ligands are coordinated to, can be quantised by the different experimental redox and XPS BE values and DFT calculated electronic descriptors.

Radical Reactions Enabled By Porphyrinoids

“ Look deep into nature , and then you will understand everything better.” Albert Einstein Porphyrinoids, also known as the pigments of life, are a class of naturally occurring organic dyes. They play key roles in crucial processes that support life - oxygen transport (hem), electron transport (cytochrome c), photosynthesis (chlorophyll a), and synthesis of DNA (vitamin B12). Vitamin B12 - a co-factor in many catalytic processes. Following nature, we have been exploiting the potential of this compound in catalysis.Vitamin B12 - catalysis has been successfully translated into the laboratory and used in a small collection of reactions.[1-2] The advantage of using vitamin B12 as a catalyst lays in the complete stability of the central cobalt ion and by the definition it is nontoxic. It has also been well documented that the reaction mechanism usually follows a radical pathway, bringing a new dimension to this already interesting field.[2] Along this line, we have developed new vitamin B12-catalyzed reactions involving reduction of Co(III) to Co(I) or Co(II) and subsequent reactions with electrophiles or radicals. Vitamin B12 derivative unusually catalyzes a new olefinic sp2 C-H alkylation reaction with diazo reagents as a carbene source,[3], acylation of activated olefins, alkylation of strained molecules.[4-6] These key findings emphasize the unique feature of vitamin B12 as a catalyst to achieve something unachievable with other methodologies or to find a greener approach.

Highly-stable cobalt metal organic framework with sheet-like structure for ultra-efficient water oxidation at high current density

The development of efficient and robust non-precious electrocatalysts for water oxidation at a mild condition is extremely desirable for industrial water splitting. Herein we developed a facile solvothermal strategy to synthesize cobalt metal organic frameworks (Co-MOFs) with sheet-like structure, which showed highly promising performance for electrocatalytic oxygen evolution. The best Co-MOF sample afforded an ultra-high oxygen evolution current density of 63.4 mA cm−2 at 1.75 V in 1 M KOH with a catalyst loading of only 0.21 mg cm−2. Notably, its electrochemical performance remained unchanged after 10,000 cyclic voltammograms indicating very promising long-term stability. Detailed study of the mechanism of the oxygen evolution by density functional theory (DFT) indicated that the strong π-conjugation formed between the central cobalt ion and adjacent aromatic rings favored the high electrocatalytic performance. The solvothermally synthesized MOFs proposed in this paper are expected to inspire the rational design of high-performance electrocatalysts for water oxidation with atomic and molecular level structural control and the exploration of structure-performance relationships to understand the electrocatalytic origin.

Mechanisms of Reaction Between Co(II) Complexes and Peroxymonosulfate

AbstractAdvanced oxidation technologies often use peroxymonosulfate in the presence of CoIIaq. It is commonly assumed that the reaction of Co(H2O)62+ with HSO5− yields CoIIIaq and SO4.−. DFT results point out that first CoII(SO5)(H2O)2 is formed. The homolysis of CoII(SO5)(H2O)2 to yield (H2O)CoII(SO5)OH.+SO4.−, is exothermic but has a large activation energy. However the cobalt is not oxidized in this reaction. CoII(SO5)(H2O)2 reacts with a second HSO5− to form CoII(SO5)2(H2O)2− that decomposes via disproportionation of the monoperoxysulfate ions without oxidation of the central cobalt ion. Surprisingly even in the presence of ligands, L, that stabilize CoIII, i. e., pyrophosphate; tri‐polyphosphate and ATP, the experimentally observed reaction mechanism involves the formation of LCoII‐OOSO3aq which then reacts with another HSO5− to form LCoII‐(OOSO32−)2. The latter complex decomposes via disproportionation of the monoperoxysulfate ligands followed by oxidation of the central cobalt cation. Alternatively, in the presence of excess CoIILaq, LCoII‐OOSO3aq reacts with CoIILaq to form 2CoIIILaq. These results point out that the mechanism of advanced oxidation processes initiated by a mixture of Co(H2O)62+ and HSO5− must be re‐considered.

Vitamin B12 – Bioinspiration for Catalysis

Nature constructs and decomposes complex molecules with the help of enzymes and light as the ultimate energy source. However, despite enzyme’s fundamental benefits, their industrial application can be limited by their availability, instability towards certain reaction conditions, cost, scale, lack of suitable enzyme etc. A complementary approach to sustainable methodologies relies on the formation or cleavage of chemical bonds using bioinspired methods (methods imitating the efficient and elegant designs of biology) and recruiting light, the most abundant free energy source.Vitamin B12 - a cofactor of many enzymes seems inspirational.[1,2] This type of catalysis has been successfully translated into the laboratory and used in a small collection of reactions.[2, 3] The advantage of using vitamin B12 as a catalyst lays in the complete stability of the central cobalt ion and by the definition it is nontoxic. It has also been well documented that the reaction mechanism usually follows a radical pathway, bringing a new dimension to this already interesting field.Along this line, we have developed new vitamin B12-catalyzed reactions involving reduction of Co(III) to Co(I) or Co(II) and subsequent reactions with electrophiles or radicals. Under light irradiation vitamin B12 derivative unusually catalyzes a new olefinic sp2 C-H alkylation reaction, with diazo reagents as a carbene source, instead of the expected cyclopropanation, acylation of activated olefins. Light-induced vitamin B12-catalyzed methods are also suitable for C-O bond cleavage. These key findings emphasize the unique feature of vitamin B12 as a catalyst to achieve something unachievable with other methodologies or to find a greener approach.[1] Banerjee, R. Chemistry and Biochemistry of B12, John Wiley & Sons, Inc, 1999; [2] K. ó Proinsias, M. Giedyk, D. Gryko, Chem. Soc. Rev. 2013, 42, 6605-6619. [3] Giedyk, M.; Fedosov, S.; Gryko, D. Chem. Commun. 2014, 50, 4674-4676. Figure 1

A Rare Angular Trinuclear Mixed Valence Cobalt(III-II-III) Complex With Azido Bridges And Salpn-Type Schiff-Base Ligand: Synthesis, Crystal Structure And DFT Study

We describe herein a novel angular trinuclear Co(III)–Co(II)–Co(III) mixed-valence Schiff base complex of formula [{(μ-L)(μ-N3)CoIII(N3)}2CoII(H2O)2]⋅MeOH⋅1.5H2O (1), obtained by aerial oxidation of [CoIIL] (2) precursor, where H2L = N,N′-bis(5-bromosalicylidene)-1,3-diaminopropane. The crystal structure of complex 1 reveals that the two terminal cobalt(III) ions are connected to the central cobalt(II) ion through single phenoxo- and single end-on azido bridges giving rise to this unique bent configuration to the (Co3}-core. The oxidation states and geometries around the cobalt atoms in the complexes are confirmed by spectroscopic studies and magnetic moment measurements, which are strongly supported by NBO analysis. It is found that the quartet spin state of the title complex has the lowest energy, both for the X-ray and optimized geometries. The HOMO/LUMO gap values calculated in implicit methanol indicate high stability of complex 1 in solution. The substantial value for the hydrogen bond energy is considered as a major contributing factor to the stabilization of complex 1. We have provided insight in the electronic structural features, including charge and spin distribution, of complex 2 based on the theoretical investigations of the optimized structure. Detailed study on facile synthesis enables us to propose a tentative mechanism of the reaction pathway.

Hydrogen bond-induced abrupt spin crossover behaviour in 1-D cobalt(II) complexes - the key role of solvate water molecules.

The magnetic properties and structural aspects of the 1-D cobalt(ii) complexes, [Co(pyterpy)Cl2]·2H2O (1·2H2O; pyterpy = 4'-(4'''-pyridyl)-2,2':6',2''-terpyridine) and [Co(pyethyterpy)Cl2]·2H2O (2·2H2O; pyethyterpy = 4'-((4'''-pyridyl)ethynyl)-2,2':6',2''-terpyridine) are reported. In each complex the central cobalt(ii) ion displays an octahedral coordination environment composed of three nitrogen donors from the terpyridine moiety, a nitrogen donor from a pyridyl group and two chloride ligands which occupy the axial sites. 1·2H2O exhibits abrupt spin-crossover (SCO) behaviour (T1/2↓ = 218 K; T1/2↑ = 227 K) along with a thermal hysteresis loop, while 2·2H2O and the dehydrated species 1 and 2 exhibit high-spin (HS) states at 2-300 K as well as field-induced single-molecule magnet (SMM) behaviour attributed to the presence of magnetic anisotropic HS cobalt(ii) species (S = 3/2). 1·2H2O exhibited reversible desorption/resorption of its two water molecules, revealing reversible switching between SCO and SMM behaviour triggered by the dehydration/rehydration processes. Single crystal X-ray structural analyses revealed that 1·2H2O crystalizes in the orthorhombic space group Pcca while 2 and 2·2H2O crystallize in the monoclinic space group P2/n. Each of the 1-D chains formed by 1·2H2O in the solid state are bridged by hydrogen bonds between water molecules and chloride groups to form a 2-D layered structure. The water molecules bridging 1-D chains in 1·2H2O interact with the chloride ligands occupying the axial positions, complementing the effect of Jahn-Teller distortion and contributing to the abrupt SCO behaviour and associated stabilization of the LS state.

Zinc Substitution of Cobalt in Vitamin B12: Zincobyric acid and Zincobalamin as Luminescent Structural B12‐Mimics

AbstractReplacing the central cobalt ion of vitamin B12 by other metals has been a long‐held aspiration within the B12‐field. Herein, we describe the synthesis from hydrogenobyric acid of zincobyric acid (Znby) and zincobalamin (Znbl), the Zn‐analogues of the natural cobalt‐corrins cobyric acid and vitamin B12, respectively. The solution structures of Znby and Znbl were studied by NMR‐spectroscopy. Single crystals of Znby were produced, providing the first X‐ray crystallographic structure of a zinc corrin. The structures of Znby and of computationally generated Znbl were found to resemble the corresponding CoII‐corrins, making such Zn‐corrins potentially useful for investigations of B12‐dependent processes. The singlet excited state of Znby had a short life‐time, limited by rapid intersystem crossing to the triplet state. Znby allowed the unprecedented observation of a corrin triplet (ET=190 kJ mol−1) and was found to be an excellent photo‐sensitizer for 1O2 (ΦΔ=0.70).

Zinc Substitution of Cobalt in Vitamin B12 : Zincobyric acid and Zincobalamin as Luminescent Structural B12 -Mimics.

Replacing the central cobalt ion of vitamin B12 by other metals has been a long‐held aspiration within the B12‐field. Herein, we describe the synthesis from hydrogenobyric acid of zincobyric acid (Znby) and zincobalamin (Znbl), the Zn‐analogues of the natural cobalt‐corrins cobyric acid and vitamin B12, respectively. The solution structures of Znby and Znbl were studied by NMR‐spectroscopy. Single crystals of Znby were produced, providing the first X‐ray crystallographic structure of a zinc corrin. The structures of Znby and of computationally generated Znbl were found to resemble the corresponding CoII‐corrins, making such Zn‐corrins potentially useful for investigations of B12‐dependent processes. The singlet excited state of Znby had a short life‐time, limited by rapid intersystem crossing to the triplet state. Znby allowed the unprecedented observation of a corrin triplet (E T=190 kJ mol−1) and was found to be an excellent photo‐sensitizer for 1O2 (ΦΔ=0.70).

Vitamin B12 - a Bioinspired Catalyst for Organic Reactions

Nature constructs and decomposes complex molecules with the help of enzymes and light as the ultimate energy source. However, despite enzyme’s fundamental benefits, their industrial application can be limited by their availability, instability towards certain reaction conditions, cost, scale, lack of suitable enzyme etc. A complementary approach to sustainable methodologies relies on the formation or cleavage of chemical bonds using bioinspired methods (methods imitating the efficient and elegant designs of biology) and recruiting light, the most abundant free energy source. Vitamin B12 - a cofactor of many enzymes seems inspirational.[1,2] This type of catalysis has been successfully translated into the laboratory and used in a small collection of reactions.[2, 3] The advantage of using vitamin B12 as a catalyst lays in the complete stability of the central cobalt ion and by the definition it is nontoxic. It has also been well documented that the reaction mechanism usually follows a radical pathway, bringing a new dimension to this already interesting field. Along this line, we have developed new vitamin B12-catalyzed reactions involving reduction of Co(III) to Co(I) or Co(II) and subsequent reactions with electrophiles or radicals. Under light irradiation vitamin B12 derivative unusually catalyzes a new olefinic sp2 C-H alkylation reaction, with diazo reagents as a carbene source, instead of the expected cyclopropanation, acylation of activated olefins. Light-induced vitamin B12-catalyzed methods are also suitable for C-O bond cleavage. These key findings emphasize the unique feature of vitamin B12 as a catalyst to achieve something unachievable with other methoologies or to find a greener approach. Banerjee, R. Chemistry and Biochemistry of B12, John Wiley & Sons, Inc, 1999K. ó Proinsias, M. Giedyk, D. Gryko, Chem. Soc. Rev. 2013, 42, 6605-6619.Giedyk, M.; Fedosov, S.; Gryko, D. Chem. Commun. 2014, 50, 4674-4676. Figure 1

Syntheses and crystal structures of metal (Mn, Co, Ni) chloride complexes with 3-hydroxypyridin-2-one and contribution of O[sbnd]H⋯Cl hydrogen bonds to their structural diversity

Reactions of MCl2·nH2O (M = Mn, Co, Ni) and 3-hydroxypyridin-2-one (dhpyH2 = C5H5NO2) afforded novel molecular complexes [MCl2(dhpyH2)4] (M = Mn (1), Co (3)) and binuclear [Co2Cl2(µ-Cl)2(dhpyH2)2(MeCN)2] (4), as well as ionic complexes [M(dhpyH2)4(ROH)2]Cl2·2ROH (R = Et, M = Co (6), Ni (8); R = Me, M = Ni (9)), and [Ni(dhpyH2)4(MeOH)2]Cl2 (10). In addition, two cocrystals, namely [MCl2(dhpyH2)4][M(dhpyH2)4L2]Cl2·S, (M = Mn, L = H2O, S = 4THF (2), M = Co, L = MeOH, S = 2MeOH (5)) were prepared. Single crystal X-ray analyses reveal two modes of 3-hydroxypyridin-2-one ligation; a chelate coordination to central cobalt ion in binuclear complex 4 and a monodentate coordination in complexes 1–3, 5, 6, 8–10. The monodentate coordination of four 3-hydroxypyridin-2-one molecules to central ion is favored due to the stabilization by strong intramolecular hydrogen bonds and formation of a macrocycle resembling 16-membered crown ethers. Coordination modes of 3-hydroxypyridin-2-one, ancillary ligands and solvate molecules determine connectivity patterns in crystal structures. Various hydrogen-bonding motifs and off-center parallel stacking arrangements of coordinated 3-hydroxypyridin-2-one molecules result in layered (4, 6, 8, 9) and 3D structures (1–3, 5, 10). Coordinated or free chloride ions are in some complexes the only (and in other complexes, prevailing) acceptors of intermolecular hydrogen bonds. A variety of D–H⋯Cl (D = O, N) geometries of hydrogen bonds in complexes is investigated. Chloride ions are in the majority of these complexes concomitantly engaged as acceptors in two hydrogen bonds, if coordinated to metal ions, and in three hydrogen bonds, if not ligated.

Ligand Noninnocence in Cobalt Dipyrrin-Bisphenols: Spectroscopic, Electrochemical, and Theoretical Insights Indicating an Emerging Analogy with Corroles.

Three cobalt dipyrrin-bisphenol (DPPCo) complexes with different meso-aryl groups (pentafluorophenyl, phenyl, and mesityl) were synthesized and characterized based on their electrochemistry and spectroscopic properties in nonaqueous media. Each DPPCo undergoes multiple oxidations and reductions with the potentials, reversibility, and number of processes depending on the specific solution conditions, the specific macrocyclic substituents, and the type and number of axially coordinated ligands on the central cobalt ion. Theoretical calculations of the compounds with different coordination numbers are given in the current study in order to elucidate the cobalt-ion oxidation state and the innocence or noninnocence of the macrocyclic ligand as a function of the changes in the solvent properties and degree of axial coordination. Electron paramagnetic resonance spectra of the compounds are obtained to experimentally assess the electron spin state. An X-ray structure of the six-coordinate complex is also presented. The investigated chemical properties of DPPCo compounds under different solution conditions are compared to those of cobalt corroles, where the macrocycle and metal ion also possess formal 3- and 3+ oxidation states in their air-stable forms.

Synthetic Approaches toward Vitamin B12 Conjugates

AbstractThe ability to conjugate functional molecules to vitamin B12 (cobalamin) is an important strategy for the construction of hybrid molecules with various applications in medicinal chemistry, diagnostics, and biological sciences. Cobalamin, as an exogenous compound, reaches mammalian cells via a system of transport proteins and therefore the position of conjugation must be selected in such a way that the recognition process is not disturbed. The complex structure of vitamin B12 provides many routes for the synthesis of conjugates containing cargos appended at different sites, however, only the e‐propionamide chain, β‐axial position and R5′‐OH are found to meet the aforementioned criteria. Over the years, a number of synthetic approaches leading to cobalamin conjugates have been developed and, herein, we summarize those leading to conjugates with a cargo tethered at the central cobalt ion, macrocyclic core, ribonucleotide moiety, or a combination thereof.