Binuclear Cobalt Research Articles

Ultrasound-Promoted Synthesis and Characterization of Nanoparticles of Coordination Polymer [Co2(pydc)2(H2O)6]n.2nH2O

Nanoparticles of coordination polymer [Co2(pydc)2(H2O)6]n.2n H2O [H2pydc = pyridine-2,5-dicarboxylic acid] have been synthesized by sonochemical method and characterized by elemental analysis, infrared spectroscopy, powder X-ray diffraction, scanning electron microscopy, DLS particle size analysis and TGA/DTA. The structure of single crystalline coordination polymer developed from nanosized coordination polymer was determined by X-ray crystallography. The XRPD studies reveal that nanoparticles of coordination polymer [Co2(pydc)2(H2O)6]n.2nH2O have same structure as that of bulk single crystalline polymer. The coordination polymer posses a 1-D chain like extended structure with binuclear cobalt(II) nodal unit. The coordination geometry around two cobalt atom Co(1) and Co(2) can be described as slightly distorted octahedron. The average particle size of nanoparticles calculated by using least square method of Modified Scherrer formula was found ~27 nm. The nanoparticles are composed of polyhedral blocks with definite edges. Dynamic Light Scattering (DLS) measurements show a narrow size distribution. The nanoparticles are thermally stable up to 352 K and thereafter decompose in well defined steps.

Synthesis, electrochemical property and photocatalytic H2 evolution of a novel binuclear complex under irradiation of visible light

A new binuclear cobalt complex, namely [Co2(dmgH)4(μ-4,4′-bpy)Cl2](1), had been synthesized by the reaction of [Co(dmgH)(dmgH2)Cl2] with 4,4′-bipyridine(μ-4,4′-bpy) and characterized by IR, 1H NMR, CV. An efficient homogeneous photocatalytic system was constructed by combination of noble-metal-free cobalt complex as catalyst, Eosin Y dye (EY2−) as photosensitizer and TEOA as sacrificial reagent under visible-light irradiation (λ>420nm). The maximum H2 yield of 1488.3±34.5μmol (160.0±3.7TON vs. 1) and H2 evolution rate of 744.2±17.3μmolh−1 were recorded under the optimal conditions with 1 of 3.7×10−4molL−1, EY2− of 4×10−4molL−1, TEOA of 20% (v/v) and pH 10 in 2h irradiation. Furthermore, the mechanism of H2 evolution in the homogeneous photolysis system was also briefly discussed. The electron transfer from the excited 1*EY2− to Co catalytic center of complex 1 in the designed system was also confirmed to be thermodynamically feasible.

Synthesis, crystal structures, electrochemically studies and antibacterial properties of three new mono-nuclear and one very rare bi-nuclear cobalt(III) Schiff base complexes

Three new mononuclear and one new binuclear cobalt(III) complexes of tetradentate N2O2 donor Schiff base ligands [CoIII(L1)(3-Mepy)2]PF6 (1), [CoIII(L2)(3-Mepy)2]PF6 (2), [CoIII(L2)(4-Mepy)2]PF6 (3) and [CoIII2(L1)2(4-Mepy)4(PF6)4(K)2] (4) were synthesized by reaction of the resp. tetradentate ligands (L1=bis(acetylacetone)ethylenediimine dianion, L2=bis(benzoylacetone)ethylenediimine dianion) with the corresponding cobalt(II) salts in the presence of 3-Mepy and 4-Mepy. These complexes were characterized by FT-IR, 1H NMR and UV–Vis spectroscopy. The crystal structures of the complexes were determined by X-ray crystallography on solvated crystals. In dimeric cobalt(III) complex, two Co-Schiff base units were connected to two K(+) and four PF6 molecules to form the centrosymmetric, dimeric bi-nuclear complex, in which the Co(3+) cations showed distorted octahedral coordinations, while K(+) cations had different coordination numbers in two symmetry-independent moieties: in one of them it is 9-coordinated (irregular tricapped trigonal prism) and in the other 8-coordinated (distorted square prism). Biological activities of the complexes were studied on Staphylococcus aureus, Salmonella typhi, Escherichia coli, and Bacillus subtilis by the well diffusion method. The electrochemical behavior of these complexes with the goal of evaluating the structural effects on the redox properties was also studied.

Biphenyl-Bridged 6-(1-Aryliminoethyl)-2-iminopyridylcobalt Complexes: Synthesis, Characterization, and Ethylene Polymerization Behavior

A series of biphenyl-bridged 6-(1-aryliminoethyl)-2-iminopyridine derivatives reacted with cobalt dichloride in dichloromethane/ethanol to afford the corresponding binuclear cobalt complexes. The cobalt complexes were characterized by FT-IR spectroscopy and elemental analysis, and the structure of a representative complex was confirmed by single-crystal X-ray diffraction. Upon activation with either MAO or MMAO, these cobalt complexes performed with high activities of up to 1.2 × 107 g (mol of Co)−1 h–1 in ethylene polymerization, which represents one of the most active cobalt-based catalytic systems in ethylene reactivity. These biphenyl-bridged bis(imino)pyridylcobalt precatalysts exhibited higher activities than did their mononuclear bis(imino)pyridylcobalt precatalyst counterparts, and more importantly, the binuclear precatalysts revealed a better thermal stability and longer lifetimes. The polyethylenes obtained were characterized by GPC, DSC, and high-temperature NMR spectroscopy and mostly possessed unimodal and highly linear features.

The novel hydrogen-rich binuclear cobalt complex anion, [(CoH3)2H3]5−

Hydrogen reacts with a mixture of cobalt bromide and phenylmagnesium bromide to yield a novel cobalt hydride species. EXAFS analysis reveals a binuclear cobalt hydride complex comprising three absorbers, principally a Co-Co centre, and also two types of supporting hydride ligands. Further, DFT, XANES, (1)H NMR spectra and elemental analyses also support the title formulation.

CO2 Complexation and Activation by a Trost‐Bis(ProPhenol)Cobalt Complex

AbstractA binuclear cobalt complex, [Co2BPP], derived from the (R,R)‐Trost‐bis‐ProPhenol (BPP) ligand, has been investigated as a catalyst for CO2 uptake and its electrochemical reduction. The complex exhibits labile acetate ligands that can be readily exchanged with CO2, leading to pronounced changes in its vibrational spectra, with νC=O peaks observed at 1700 and 1596 cm–1. The electrochemical reduction of the CoIII centers at –0.5 V was significantly enhanced in the presence of CO2, evidencing a chemical reaction coupled to an electrode process. Instead of yielding CO or HCOOH as observed in most artificial systems, formaldehyde was identified as the major product below –1.0 V, showing that CO2 can undergo four‐electron reduction by the [Co2BPP] electrocatalyst.

Photocatalytic H2 generation based on noble-metal-free binuclear cobalt complexes using visible-light

Two new binuclear cobalt complexes, namely {[Co(dmgH)(dmgH2)]2L1} (I) and {[Co(dmgH)(dmgH2)]2L2} (II) (dmgH = dimethylglyoximate monoanion; dmgH2 = dimethylglyoxime, L1 = 1,3-bis(4-pyridyl)propane), L2 = 1,3-bis(imidazol-1-ylmethyl)benzene), have been synthesized by the self-assembly of [Co(dmgH)(dmgH2)] and L1 or L2, respectively. An efficient photocatalytic system was constructed by combining a noble-metal-free cobalt complex as the catalyst with Eosin Y dye (EY(2-)) as the photosensitizer to give an efficient H2 generating system under visible-light irradiation (λ > 420 nm) using triethanolamine (TEOA) as a sacrificial electron donor. The maximum amount of H2 generated was 1013 TON for I and 1134 TON for II over a 2 h irradiation period (λ > 420 nm) under the conditions of pH 8.0, 5% TEOA (v/v), an EY(2-) concentration of 4.0 × 10(-4) M and a catalyst concentration of 4.0 × 10(-4) M in the mixed solvent system of CH3CN-H2O (3 : 1, v/v). In addition, the mechanism of H2 generation in the photolysis system was briefly discussed.

Terminal versus bridging methylborole ligands and agostic hydrogen atoms in binuclear cobalt carbonyl derivatives

Density functional theory predicts an (η5-C4H4BCH3)2Co2(CO)4 structure having terminal methylborole ligands and two bridging CO groups similar to the experimental structure of the product synthesized from Co2(CO)8 and suitable borole derivatives as well as analogous to experimentally known (η4-C4H4)2Co2(CO)2(μ-CO)2 and (η5-C5H5)2Fe2(CO)2(μ-CO)2. However, the unsaturated tricarbonyl (η5-C4H4BCH3)2Co2(CO)3 has a more complicated potential energy surface with low energy singlet and triplet structures having one, two, or three bridging CO groups. The lowest energy structure for the dicarbonyl (η5-C4H4BCH3)2Co2(CO)2 is a singlet with terminal methylborole ligands and bridging CO groups as well as a short Co≡Co distance of ∼2.2 Å suggesting a formal triple bond. However, another low energy (η5-C4H4BCH3)2Co2(CO)2 structure has a bridging methylborole ligand and two terminal CO groups. In the lowest energy (C4H4BCH3)2Co2(CO) structure the pendent methyl groups of the methylborole ligands participate in the ligand-metal bonding through agostic hydrogen atoms forming C–H–Co three-center bonds. A bridging methylborole ligand with such an agostic hydrogen atom is a six-electron donor to the Co2 system.

Synthesis, Crystal Structure and Magnetic Characterization of Azido-bridged Binuclear Cobalt(Ⅱ) Coordination Polymer

用水热法合成了以邻菲啰啉（phen）为辅助配体叠氮桥联Co2＋配位聚合物：[Co2（μ1,1-N3）2（phen）2（N3）2]。用IR和元素分析进行了表征,用单晶XRD测定晶体结构,属于三斜晶系,P1空间群,a=0.69272（14）nm,b=1.0318（2）nm,c=1.0381（2）nm,α=6.447（3）°,β=71.02（3）°,γ=85.79（3）°,Z=1,V=0.6312（2）nm3,D=1.701 mg/mm3,F（000）=326。确定N3-为μ-1,1桥联配位。测定了配合物固体的变温磁化率,证明配合物为亚铁磁性物质,其临界温度为15 K。

Binuclear cobalt complex with Schiff base ligand: Synthesis, characterization and catalytic properties in partial oxidation of cyclohexane

A new binuclear cobalt complex with Schiff base ligand and amino acid was synthesized and characterized using XRD, elemental analysis, IR spectroscopy, XPS and electrochemical measurements. The presence of cobalt in the oxidation state 3+ in this complex was proved. The catalytic activity of this complex was investigated in the reaction of partial cyclohexane oxidation with air, and high activity and selectivity for cyclohexanol and cyclohexanone formation were demonstrated. The possibility of complex reuse in cyclohexane oxidation was studied and it was shown that the activity slightly decreases in a second oxidation cycle along with changes in main product distribution due to partial transfer of Co3+ to Co2+.

Binuclear fluoroborylene (BF) cobalt carbonyls: Comparison with homoleptic cobalt carbonyls

The recent synthesis by Vidović and Aldridge of the complex (η5-C5H5)2Ru2(CO)4(μ-BF) containing the fluoroborylene ligand (BF), isoelectronic with CO, suggests the possibility of introducing the BF ligand into binuclear cobalt carbonyl derivatives of the type Co2(BF)2(CO)n (n=7, 6, 5, 4, 3). This has now been explored using density functional theory. Structures in which both BF groups bridge a cobalt–cobalt bond are energetically preferred for the Co2(BF)2(CO)n (n=6, 5, 4, 3) derivatives over other types of structures. Thus the Co2(μ-BF)2(CO)6 structure with two bridging BF groups lies more than 18kcal/mol below the next lowest Co2(BF)2(CO)6 structure and appears to be a reasonable synthetic objective. This differs from the well-known isoelectronic Co2(CO)8 for which the structures with two bridging CO groups and with all terminal CO groups are so close in energy that they are found experimentally to exist in equilibrium. Examples of Co2(B2F2)(CO)n (n=7, 4, 3) derivatives are found in which the two BF groups have coupled to form a bridging difluorodiborene (B2F2) ligand with a B–B distance of ∼1.9Å. However, the Co2(B2F2)(CO)7 structures do not appear to be viable since loss of a CO group to give Co2(BF)2(CO)6 is predicted to be an exothermic process.

Metal Complexes of Bridging Neutral Radical Ligands: pymDTDA and pymDSDA

Metal complexes of the 4-(2'-pyrimidyl)-1,2,3,5-dithiadiazolyl (pymDTDA) neutral radical ligand and its selenium analogue (pymDSDA) are presented. The following series of metal ions has been studied using M(hfac)(2) as the coordination fragment of choice (hfac = 1,1,1,5,5,5-hexafluoroacetylacetonato): Mn(II), Co(II), Ni(II), and Zn(II). The binuclear cobalt and nickel complexes of pymDTDA both exhibit ferromagnetic (FM) coupling between the unpaired electrons on the ligand and the metal ion, while the binuclear zinc complex of pymDTDA is presented as a comparative example incorporating a diamagnetic metal ion. The binuclear manganese complex of pymDTDA, reported in a preliminary communication, is compared to the pymDSDA analogue, and new insight into the magnetic behavior reveals that intermolecular magnetic coupling, mediated by chalcogen-oxygen contacts, gives rise to a significant increase in the χT product at low temperature. Surprisingly, the binuclear nickel complex of pymDSDA forms dimers in the solid state, as do the mononuclear complexes of cobalt and nickel with pymDTDA. In addition, mixed mononuclear/binuclear complexes of Mn- and Zn(pymDTDA) have been identified.

Cobalt analogs of Ru-based water oxidation catalysts: overcoming thermodynamic instability and kinetic lability to achieve electrocatalytic O2 evolution

Several binuclear cobalt(III) complexes that mimic Ru-based water oxidation catalysts have been prepared. The initial complexes exhibited thermodynamic instability and kinetic lability that complicated efforts to use these cobalt complexes as electrocatalysts for water oxidation. Binuclear cobalt(III) complexes supported by a bridging bispyridylpyrazolate (bpp) ligand overcome these limitations. Two bpp-ligated dicobalt(III)-peroxo complexes were prepared and structurally characterized, and electrochemical investigation of these complexes supports their ability to serve as molecular electrocatalysts for water oxidation under acidic conditions (pH 2.1).

Double-pillared cobalt Pacman complexes: synthesis, structures and oxygen reduction catalysis

The syntheses and structures of binuclear cobalt complexes of a double-pillared cofacial Schiff-base pyrrole macrocycle (L) were determined and their activity as catalysts for the oxygen reduction reaction evaluated. The new binuclear cobalt complex, [Co(2)(L)], 1 was formed in good yield using a salt-elimination method and was characterised as adopting a cofacial structure in solution by NMR spectroscopy and as its THF and pyridine solvates in the solid state by X-ray crystallography. Using a variety of spectroscopic techniques, this complex was found to react reversibly with dioxygen to form a new paramagnetic complex. Furthermore, the new aqua-hydroxy double salt [Co(2)(μ-H(3)O(2))(py)(2)(L)][BF(4)] 2 was characterised by X-ray crystallography. In acidified benzonitrile solution, 1 behaves as a catalyst for the selective four-electron reduction of dioxygen to water and showed a large improvement in efficacy compared to its o-phenylene Schiff-base analogues.

The Intramolecular Rearrangement of Phosphinohydrazides [R′2P–NR–NR–M] → [RN═PR′2–NR–M]: General Rules and Exceptions. Transformations of Bulky Phosphinohydrazines (R–NH–N(PPh2)2, R =tBu, Ph2P)

Reactions of diphosphinohydrazines R-NH-N(PPh(2))(2) (R = tBu (1), Ph(2)P (3)) with some metalation reagents (Co[N(SiMe(3))(2)](2), LiN(SiMe(3))(2), La[N(SiMe(3))(2)](3), nBuLi, MeLi) were performed. Compound 1 was synthesized by the reaction of Ph(2)PCl with tert-butylhydrazine hydrochloride in 83% yield. This compound reveals temperature-dependent (31)P NMR spectra due to hindered rotation about the P-N bonds. Complicated redox reaction of 1 with Co[N(SiMe(3))(2)](2) proceeds with cleavage of the P-N and N-N bonds to form a binuclear cobalt complex [Co{HN(PPh(2))(2)-κ(2)P,P'}(2)(μ-PPh(2))](2) (2) demonstrating a short Co···Co distance of 2.3857(5) Å, which implies a formal double bond between the Co atoms. Strong nucleophiles (nBuLi, MeLi) cause fragmentation of the molecules 1 and 3, while reactions of 3 with lithium and lanthanum silylamides give products of the NNP → NPN rearrangement [Li{Ph(2)P(NPPh(2))(2)-κ(2)N,N'}(THF)(2)] (4) and [La{Ph(2)P(NPPh(2))(2)-κ(2)N,N'}{N(SiMe(3))(2)}(2)] (5), respectively. These complexes represent the first examples of a κ(2)N,N' bonding mode for the triphosphazenide ligand [(Ph(2)PN)(2)PPh(2)](-). DFT calculations showed large energy gain (52.1 kcal/mol) of the [NNP](-) to [NPN](-) anion rearrangement.

Five-electron donor versus seven-electron donor bridging phospholyl rings in binuclear cobalt carbonyl derivatives

The lowest energy (C 4H 4P) 2Co 2(CO) n ( n = 3, 2, 1) structures have exclusively terminal phospholyl ligands and correspond closely to those of the analogous cyclopentadienyl derivatives (C 5H 5) 2Co 2(CO) n . Thus the lowest energy (C 4H 4P) 2Co 2(CO) n structures are the singly bridged trans-(η 5-C 4H 4P) 2Co 2(CO) 2(μ-CO) with a formal Co–Co single bond, the doubly bridged (η 5-C 4H 4P) 2Co 2(μ-CO) 2 with a formal Co Co double bond, and either singlet or triplet singly bridged (η 5-C 4H 4P) 2Co 2(μ-CO). Higher energy triplet (C 4H 4P) 2Co 2(CO) n structures are found with a five-electron donor η 5,η 1-C 4H 4P ligand bridging a cobalt–cobalt bond. None of the (C 4H 4P) 2Co 2(CO) n ( n = 3, 2, 1) structures has a seven-electron donor η 5,η 1-C 4H 4P ligand without a metal–metal bond in contrast to the lowest energy (C 4H 4P) 2Mn 2(CO) n ( n = 5, 4) structures.

A new Schiff base as a bridge in binuclear cobalt(III) dioximate

A new Schiff base as a bridge in binuclear cobalt(III) dioximate

The quest for trifluorophosphine as a bridging ligand in homoleptic binuclear and tetranuclear cobalt complexes

Transition metal complexes with bridging PF3 groups are unknown analogous to metal carbonyls with bridging carbonyl groups. The possibility of bridging PF3 groups in binuclear Co2(PF3) n complexes (n = 9, 8, 7, 6, 5) and the tetranuclear Co4(PF3)12 has now been investigated by density functional theory (DFT). The lowest energy Co2(PF3)8, Co2(PF3)7, and Co4(PF3)12 structures are predicted to be unbridged structures with cobalt-cobalt bond distances of ∼2.8 Å, ∼2.5 Å, and ∼2.6 Å, respectively. The lowest energy Co2(PF3)6 structure is an unsymmetrical unbridged structure with a Co–Co distance of ∼2.5 Å. For the more highly unsaturated Co2(PF3)5 both triplet and singlet structures are found, consisting of two Co(PF3)2 units linked by two bridges, namely a PF2 group and a F atom. Such Co2(PF3)5 structures have square planar cobalt coordination and a Co…Co distance too long for direct bonding. In addition, a singlet Co2(PF3)5 structure is found, with two semi-bridging PF3 groups and a very short Co ··· Co distance of ∼2.1 Å indicative of the formal quadruple bond required to give both cobalt atoms the favoured 18-electron configuration. Bridging PF3 groups with no cobalt-cobalt bond are found in a high energy structure of Co2(PF3)7 and in a Co2(PF3)9 structure unstable with respect to PF3 loss to give Co2(PF3)8. The dissociation of Co2(PF3)8 into two Co(PF3)4 radicals is predicted to be only slightly endothermic at −14.3 kcal/mol (B3LYP) or 7.1 kcal/mol (BP86). However, in contrast to its carbonyl analogue Co4(CO)12, the dissociation of Co4(PF3)12 into 2 Co2(PF3)6 is highly exothermic. Optimization of the structure of the experimentally known but not structurally characterized bis(difluorophosphido) derivative Co2(PF3)6(µ-PF2)2 predicts the expected structure with a long Co ··· Co distance of ∼3.5 Å indicating the lack of a direct cobalt-cobalt bond. DFT predicts tetrahedral structures for Co(PF3)4 and HCo(PF3)3 as well as the experimentally known trigonal bipyramidal structure for HCo(PF3)4.

ChemInform Abstract: The Chemistry of the Binuclear 34-Electron System (C5R5M(μ-PMe2))2 How Inert are M-PMe2-M Bridges?

Abstract The binuclear cobalt and rhodium complexes, [C5H5Co(μ-PMe2)]2 (1) and [C5Me5Rh(μ-PMe2)]2 (2), behave as metal bases and react with electrophiles by addition to the metal-metal bond. Whereas with acids such as CF3CO2H cations of general composition [(C5R5M)2(μ-H)(μ-PMe2)2]+ which still show a strong M-M interaction are formed, the reaction with CH2X2 (X = Br, I) leads to M-M bond cleavage and insertion of CH2 into one of the M-PMe2-M bridging bonds. The chalcogens (O, S, Se and Te) and activated alkynes RC≡CCO2Me (R = H, Me, CO2Me) behave similarly. The essence of this Comment is that M-PMe2-M bridges are less rigid than originally expected and in various cases play a specific role in reactivity.

Binuclear cobalt(II), nickel(II), copper(II) and palladium(II) complexes of a new Schiff-base as ligand: Synthesis, structural characterization, and antibacterial activity

A binucleating new Schiff-base ligand with a phenylene spacer, afforded by the condensation of glycyl–glycine and o-phthalaldehyde has been served as an octadentate N 4O 4 ligand in designing some binuclear complexes of cobalt(II), nickel(II), copper(II), and palladium(II). The binding manner of the ligand to the metal and the composition and geometry of the metal complexes were examined by elemental analysis, conductivity measurements, magnetic moments, IR, 1H, 13C NMR, ESR and electronic spectroscopies, and TGA measurements. There are two different coordination/chelation environments present around two metal centers of each binuclear complex. The composition of the complexes in the coordination sphere was found to be [M 2(L)(H 2O) 4] (where M = Co(II) and Ni(II)) and [M 2(L)] (where M = Cu(II) and Pd(II)). In the case of Cu(II) complexes, ESR spectra provided further information to confirm the binuclear structure and the presence of magnetic interactions. All the above metal complexes have shown moderate to good antibacterial activity against Gram-positive and Gram-negative bacteria.