Synthesis and crystal structure characterization of iron(II), cobalt(II) and nickel(II) complexes with 1,3-bis(2-pyridylmethylthio)propane

Three new mononuclear complexes of nitrogen–sulfur donor sets, formulated as [Fe^II(L)Cl₂] (1), [Co^II(L)Cl₂] (2) and [Ni^II(L)Cl₂] (3) where L = 1,3-bis(2-pyridylmethylthio)propane, were synthesized and isolated in their pure form. All the complexes were characterized by physicochemical and spectroscopic methods. The solid state structures of complexes 1 and 3 have been established by single crystal X-ray crystallography. The structural analysis evidences isomorphous crystals with the metal ion in a distorted octahedral geometry that comprises NSSN ligand donors with trans located pyridine rings and chlorides in cis positions. In dimethylformamide solution, the complexes were found to exhibit Fe^II/Fe^III, Co^II/Co^III and Ni^II/Ni^III quasi-reversible redox couples in cyclic voltammograms with E_1/2 values (versus Ag/AgCl at 298 K) of +0.295, +0.795 and +0.745 V for 1, 2 and 3, respectively.     

Crystal structure,thermal behavior,and microbiological activity of a thiosemicarbazide-type ligand and its cobalt complexes

The synthesis of a potentially bioactive mixed-valence Co^III/Co^II complex with 2-acetylpyridine S-methylisothiosemicarbazone (HL) ligand is described. The crystal and molecular structure of the formed [Co^IIIL₂][Co^IICl₃ py]·Me₂CO (I) compound (py stands for pyridine) is determined by single-crystal X-ray crystallography. It’s thermal decomposition along with the decomposition of the ligand and six structurally related complexes with formulas [CoL₂]NO₃·MeOH (1), [CoL₂]Br·MeOH (2), [CoL₂]HSO₄·MeOH (3), [CoL₂]₂[Co^II(NCS)₄] (4), [Co(HL)(L)]I₂·2MeOH (5), and [Co(HL)(L)][Co^IICl₄]·MeOH (6) was determined by simultaneous TG/DSC measurements. The decomposition pattern is evaluated using TG/DTA-MS data. The results were related to the solvent/moisture content and the decomposition mechanism of the compounds. The antimicrobial activity of the ligand and of all the complexes was tested in vitro for selected gram-negative and gram-positive bacteria and fungi. The activity of the ligand against all tested bacteria is comparable with those obtained for standard antibiotics, while it is less active against fungi. Surprisingly, the activity of the complexes is very low. The low antimicrobial activity of the complexes may be in connection with their high thermodynamic and kinetic inertness in solution. The results are also supported by the relatively high thermal stability of the complexes.     

Synthesis, crystal structures and electrochemical properties of CoIII complexes with hexadentate ligand containing thioether-amidopyridyl donor set

Two new cobalt(III) complexes of the hexadentate ligand [1,4-bis[o-(pyridine-2-carboxamidophenyl)]-1,4-dithiobutane] (H₂bpctb) with N₄S₂ donor set atoms have been synthesized. A reaction of Co(CH₃COO)₂·4H₂O with (H₂bpctb) leads to the formation of [Co^III(bpctb)]PF₆ (1) having a CoN₂(pyridine)N′₂(amide)S₂(thioether) coordination by symmetric bpctb^2? ligand. A similar reaction under slightly different conditions, however, gives [Co^III(L ^a )(L ^b )] (2), resulting from a C–S bond cleavage reaction triggered by an acetate ion as a base, having CoN₂(pyridine)N′₂(amide)S(thioether)S′(thiolate) coordination. These two Co(III) complexes have been characterized by elemental analyses and spectroscopic methods, and the crystal and molecular structures of [Co^III(bpctb)]PF₆ (1) in the form of the solvate (1·MeOH·H₂O) and of [Co^III(L ^a )(L ^b )] (2) have been determined by X-ray crystallography. The Co atoms of both complexes exhibit distorted octahedral geometry. The electrochemical investigation of [Co(bpctb)]PF₆·MeOH·H₂O (1·MeOH·H₂O) and [Co^III(L ^a )(L ^b )] (2) by cyclic voltammetry reveals a reversible Co^III–Co^II redox process at E _1/2 = ?0.32 V (ΔE _p = 80 mV); for 1, and E _1/2 = ?0. 87 V (ΔE _p = 70 mV) for 2.     

Syntheses,crystal structures,and properties of Ni(II) and Co(III) complexes derived from tripod polypyridine ligands containing N7 or N6 donor set atoms

New complexes [Ni^II(pbpaen)](ClO₄)₂ (1) and [Co^III(pbpaen)](ClO₄)₃ (2) (pbpaen = N′-(pyridin-2-ylmethyl)-N,N-bis {2-[(pyridin-2-ylmethyl)amino]ethyl}ethane-1,2-diamine) have been synthesized and characterized by IR and UV–Vis spectroscopies. An X-ray structure of the nickel(II) complex shows that [Ni(pbpaen)](ClO₄)₂ (1) crystallizes in the monoclinic space group P2_1/c. The cation [Ni(pbpaen)]²⁺ is pseudo-octahedral with one of the three pyridyl nitrogen atom uncoordinated. The crystal lattice of this complex is stabilized by intra and intermolecular hydrogen bonding systems, giving one-dimensional sheets like arrays. All attempts to obtain nickel or cobalt complexes with protonated forms of the ligand resulted in isolation of only [Co^III(bpaen)](ClO₄)₃ (3) compound in which the tripod pbpaen ligand has lost one of the three pyridylmethyl groups, procuring then bpaen ligand {bpaen = N,N-bis{2-[(pyridin-2-ylmethyl)amino]ethyl}ethane-1,2-diamine}. The X-ray crystal structure reveals that the compound 3 crystallizes in the orthorhombic space group Pna2 with the Co³⁺ ion having a distorted-octahedral environment. These two ligands with strong-field N donor stabilise the +3 oxidation state of the Co center.     

Synthesis, characterization, solvatochromic behavior and crystal structures of complexes [CoIII(salophen)(thioacetamide)2]ClO4 and [CoIII(salophen)(thiobenzamide)2]ClO4

Two new cobalt(III) complexes of the Schiff base N,N′-disalicylidene-1,2-phenylendiimine dianion (salophen), trans- [Co^III(salophen)(ta)₂]ClO₄, (ta = thioacetamide) (1) and trans-[Co^III(salophen)(tb)₂]ClO₄, (tb = thiobenzamide) (2) were synthesized and characterized using single-crystal X-ray diffraction and spectroscopic techniques. Both complexes show solvatochromism in a variety of solvents. Complex (1) crystallized from CHCl₃ as a solvate of orthorhombic symmetry, space group Pca2₁ with a = 17.3480(10) Å, b = 18.7522(10) Å, c = 18.8128(11) Å, α = β = γ = 90°, and Z = 8. The cobalt(III) center lies in a distorted octahedral environment. The crystal structure of (1) consists of two independent [Co^III(salophen)(ta)₂]⁺ cations and ClO₄ ^- anions held together essentially via hydrogen bonds and π-π stacking interactions. Complex (2), forming also a CHCl₃ solvate, crystallized in the monoclinic space group P2₁/n with a = 14.710(3) Å, b = 13.506(3) Å, c = 18.595(4) Å, β = 100.295(4)°, and Z = 4. The geometry around cobalt(III) center is a distorted octahedron. The crystal structure of (2) contains a [Co^III(salophen)(tb)₂]⁺ complex with a remarkably twisted salophen ligand. Both complexes, (1) and (2), contain approximately one disordered CHCl₃ molecule per Co in the solid state.     

Synthesis, characterization, electrochemical studies, and antibacterial activities of cobalt(III) complexes with Salpn-Tipe Schiff base ligands. Crystal structure of trans-[CoIII(L1)(Py)2]ClO4

The synthesis, characterization, spectroscopic and electrochemical properties of trans-[Co^III(L¹)(Py)₂]ClO₄ (I) and trans-[Co^III(L²)(Py)₂]ClO₄ (II) complexes, where H₂L¹ = N,N′-bis(5-chloro-2-hydroxybenzylidene)-1,3-propylenediamine and H₂L² = N,N′-bis(5-bromo-2-hydroxybenzylidene)-1,3-propylenediamine, have been investigated. Both complexes have been characterized by elemental analysis, FT-IR, UV-Vis, and ¹H NMR spectroscopy. The crystal structure of I has been determined by X-ray diffraction. The coordination geometry around cobalt(III) ion is best described as a distorted octahedron. The electrochemical studies of these complexes revealed that the first reduction process corresponding to Co(III/II) is electrochemically irreversible accompanied by dissociation of the axial Co-N(Py) bonds. The in vitro antimicrobial activity of the Schiff bse ligands and their corrsponding complexes have been tested against human pathogenic bacterias such as Staphylococcus aureus, Bacillus subtilis, Pseudomonas aeruginosa, and Escherichia coli. The cobalt(III) complexes showed lower antimicrobial activity than the free Schiff base ligands.     

Synthesis,structure and magnetic properties of a novel Tb4 spin cluster and synthesis of a Tb chain

The syntheses of two new polynuclear Tb^III compounds are reported. A tetranuclear complex [Tb₄(H₂L)₂(H₄L)₂(OAc)₈] (1), with H₄L = 2-((2-hydroxy-benzylidene)-amino)-2-hydroxy-methyl-propane-1,3-diol, has a butterfly-type structure, while [Tb(OAc)₃MeOH]_∞ (2) is a linear chain. A novel binding mode for H₂L²⁻ is observed in 1, with two alkoxides each bridging three Tb^III ions. The magnetic properties of 1 are determined by the superposition of the ligand field split ⁷F₆ states of Tb^III single-ions located on two crystallographically distinct sites. Weak antiferromagnetic exchange interactions possibly contribute to the lowering of the magnetic moment at the lowest temperatures.     

Coexistence of metamagnetism and single chain magnet behavior in a FeIII2CoII layer compound

A cyanide-bridged Fe^III₂Co^II double zigzag chain, {[Fe^III(bipy)(CN)₄]₂Co^II(btab)₂}_n [bipy=2,2′-bipyridine, btab=4,4′-(1,3-phenylene)-bis-4H-1,2,4-triazole] (1), was obtained with tetracyanometalate precursors and Co^II ions. The chains were further linked by the ditopic btab ligands to a layer. Magnetic property studies demonstrate that 1 shows both metamagnetism with a critical field H_c=400 Oe and single-chain magnet behavior.     

Rational synthesis of hexanuclear metallacycles by alkylation reactions of an S-bridged CoIIIPdIICoIII trinuclear complex containing non-binding thiolato groups

The reaction of an S-bridged Co^IIIPd^IICo^III trinuclear complex containing two non-bridging thiolato groups, [Pd{Co(aet)₃}₂]²⁺ (aet = 2-aminoethanethiolate), with o-dibromoxylene (o-xylBr₂) in water produced a cyclic Co^III₄Pd^II₂ hexanuclear complex, [{Co₂Pd(aet)₄}₂(o-L)₂]⁸⁺ ([1]⁸⁺; o-L = o-bis(2-aminoethylthiomethyl)benzene), in which two Co^IIIPd^IICo^III trinuclear units are linked by two o-xyl²⁺ moieties through C–S bonds. A similar cyclic Co^III₄Pd^II₂ complex, [{Co₂Pd(aet)₄}₂(m-L)₂]⁸⁺ ([2]⁸⁺; m-L = m-bis(2-aminoethylthiomethyl)benzene), bearing a relatively large cavity that accommodates water molecule(s), was synthesized by the reaction of [Pd{Co(aet)₃}₂]²⁺ with m-dibromoxylene (m-xylBr₂) in water. While [1]⁸⁺ afforded only the racemic (Δ₄/Λ₄) isomer, both the racemic ([2a]⁸⁺; Δ₄/Λ₄) and the meso ([2b]⁸⁺; Δ₂Λ₂) isomers were formed for [2]⁸⁺. In addition, the meso [2b]⁸⁺ was found to exist as a mixture of two diastereomers, (Δ_S)₂(Λ_R)₂ and (Δ_SΔ_R)(Λ_RΛ_S), which arise from the difference in chiral configurations (R and S) of asymmetric sulfide S atoms, while the racemic [1]⁸⁺ and [2a]⁸⁺ existed as a pair of enantiomers, (Δ_S)₄ and(Λ_R)₄, which were optically resolved. The complexes obtained were characterized on the basis of electronic absorption, CD, and NMR spectroscopies, along with single crystal X-ray analyses.     

Entrapment of a Pseudo‐Tetrahedral CoII Center by Thioether Sulfur Bound {Co2(μ‐L)} Fragments: Synthesis,Field‐Induced Single‐Ion Magnetism and Catechol Oxidase Mimicking Activity

Simultaneous incorporation of both Co^II and Co^III ions within a new thioether S‐bearing phenol‐based ligand system, H₃L (2,6‐bis‐[{2‐(2‐hydroxyethylthio)ethylimino}methyl]‐4‐methylphenol) formed [Co₅] aggregates [Co^IICo^III₄L₂(μ‐OH)₂(μ_1,3‐O₂CCH₃)₂](ClO₄)₄?H₂O ( 1 ) and [Co^IICo^III₄L₂(μ‐OH)₂(μ_1,3‐O₂CC₂H₅)₂](ClO₄)₄?H₂O ( 2 ). The magnetic studies revealed axial zero‐field splitting (ZFS) parameter, D/hc=?23.6 and ?24.3 cm^?1, and E/D=0.03 and 0.00, respectively for 1 and 2 . Dynamic magnetic data confirmed the complexes as SIMs with U_eff/k_B=30 K ( 1 ) and 33 K ( 2 ), and τ₀=9.1×10^?8 s ( 1 ), and 4.3×10^?8 s ( 2 ). The larger atomic radius of S compared to N gave rise to less variation in the distortion of tetrahedral geometry around central Co^II centers, thus affecting the D and U_eff/k_B values. Theoretical studies also support the experimental findings and reveal the origin of the anisotropy parameters. In solutions, both 1 and 2 which produce {Co^III₂(μ‐L)} units, display solvent‐dependent catechol oxidation behavior toward 3,5‐di‐tert‐butylcatechol in air. The presence of an adjacent Co^III ion tends to assist the electron transfer from the substrate to the metal ion center, enhancing the catalytic oxidation rate.     

Kinetics of oxidation of glutathione by an octahedral cobalt(III) complex with phenolate–amide–amine coordination

The reduction of the octahedral cobalt(III) complex Co^III(HL)·9H₂O, H₄L = 1,8-bis(2-hydroxybenzamido)-3,6-diazaoctane by glutathione (GSH) has been studied by conventional spectrophotometry at 25.0 ≤ t/°C ≤ 45.0, 0.02 ≤ [H⁺]/mol dm^?3 ≤ 0.20 and I = 0.3 mol dm^?3 (NaClO₄). The reaction is biphasic. The fast initial phase is attributed to the H⁺-induced formation of the mixed ligand complex, [Co^III(H₂L)GSH]⁺, for which the rate-limiting step is the chelate ring opening via Co^III–NH (amide–N) bond cleavage of the protonated species, [Co^III(H₂L)]⁺. Outer-sphere association equilibria between GSH/GSH₂ ⁺ and [Co^III(H₂L)]⁺ substantially retard the ring opening process and consequently the mixed ligand complex formation. This is then followed by a slow phase involving reduction of [Co^III(H₂L)GSH]⁺ by both GSH and GSH₂ ⁺. The final products are the corresponding Co(II) complex and the oxidized form of GSH, GS–SG. The kinetic data and activation parameters for the redox process are interpreted in terms of an outer-sphere electron transfer mechanism.     

Co(III) complexes of Me-salpn and Me-salbn and the ring size effect on the coordination modes and electrochemical properties: The crystal structures of trans-[Co(Me-salpn)(py)2]PF6 and cis-α-[Co(Me-salbn)(4-Mepy)2]BPh4 · 4-Mepy

The synthesis and characterization of a series of cobalt(III) complexes of the general type [Co(N₂O₂)(L₂)]⁺ are described. The N₂O₂ Schiff base ligands used are Me-salpn (H₂Me-salpn = N,N′-bis(methylsalicylidene)-1,3-propylenediamine) (1–3) and Me-salbn (H₂Me-salbn = N,N′-bis(methylsalicylidene)-1,4-butylenediamine) (4–5). The two ancillary ligands L include: pyridine (py) 1, 3-metheylpyridine (3-Mepy) 2, 1-methylimidazole (1-MeIm) 3, 4-methylpyridine (4-Mepy) 4 and pyridine (py) 5. These complexes have been characterized by elemental analyses, IR, UV–Vis, and ¹H NMR spectroscopy. The crystal structures of trans-[Co^III(Me-salpn)(py)₂]PF₆, 1, and cis-α-[Co^III(Me-salbn)(4-Mepy)₂]BPh₄ · 4-Mepy, 4, have been determined by X-ray diffraction. Examination of the solution and crystalline structures revealed that the outer coordination sphere of the complexes exerts a noticeable influence on the inner coordination sphere of the Co(III) ion. The electrochemical reduction of these complexes at a glassy carbon electrode in acetonitrile solution indicates that the first reduction process corresponding to Co^III–Co^II is electrochemically irreversible, which is accompanied by the dissociation of the axial (R-py)–cobalt bonds. It has also been observed that the Co(III) state is stabilized with increasing the flexibility of the ligand environment.     

Synthesis,crystal structures,spectroscopic studies and antibacterial properties of a series of mononuclear cobalt(III) Schiff base complexes

New complexes of cobalt(III) with the tridentate and tetradentate Schiff base ligands: 3-methoxy-2-{(Z)[(2-hydroxyphenyl)imino]methyl}phenol (H₂L¹), 4-[(2-hydroxyphenyl)imino]-2-pentanone (H₂L²); and 2-((E)-1-(2-((E)-1-(2-hydroxy-4,5-dimethylphenyl)ethylideneamino)ethylimino)ethyl)-4,5 dimethylphenol (H₂L³), namely [Co^III(L¹)(N-MeIm)₃]PF₆ (1), [Co^III(L¹)(py)₃]ClO₄ (2), [Co(L¹)(py)₃][Co(L¹)₂] (3) and [Co^III(L²)(N-MeIm)₃]PF₆ (4) and [Co(L³)(N-MeIm)₂]PF₆ (5), were synthesized and characterized by physico-chemical and spectroscopic methods. The crystal structures of the complexes were determined by X-ray crystallography. In each of these complexes, the cobalt(III) centre has a slightly distorted octahedral environment, utilizing all available coordination centres of the ligands. The complexes were also screened for in vitro antibacterial activities against four human pathogenic bacteria, and their minimum inhibitory concentrations indicated good antibacterial activities.     

Synthesis, characterisation and catalytic activities of manganese(III) complexes of pyridoxal-based ONNO donor tetradenatate ligands

Reaction of Mn^II(CH₃COO)₂ with dibasic tetradentate ligands, N,N′-ethylenebis(pyridoxylideneiminato) (H₂pydx-en, I), N,N′-propylenebis(pyridoxylideneiminato) (H₂pydx-1,3-pn, II) and 1-methyl-N,N′-ethylenebis(pyridoxylideneiminato) (H₂pydx-1,2-pn, III) followed by aerial oxidation in the presence of LiCl gives complexes [Mn^III(pydx-en)Cl(H₂O)] (1) [Mn^III(pydx-1,3-pn)Cl(CH₃OH)] (2) and [Mn^III(pydx-1,2-pn)Cl(H₂O)] (3), respectively. Crystal and molecular structures of [Mn(pydx-en)Cl(H₂O)] (1) and [Mn(pydx-1,3-pn)Cl(CH₃OH)] (2) confirm their octahedral geometry and the coordination of ligands through ONNO(2-) form. Reaction of manganese(II)-exchanged zeolite-Y with these ligands in refluxing methanol followed by aerial oxidation in the presence of NaCl leads to the formation of the corresponding zeolite-Y encapsulated complexes, abbreviated herein as [Mn^III(pydx-en)]-Y (4), [Mn^III(pydx-1,3-pn)]-Y (5) and [Mn^III(pydx-1,2-pn)]-Y (6). These encapsulated complexes are used as catalysts for the oxidation, by H₂O₂, of methyl phenyl sulfide, styrene and benzoin efficiently. Oxidation of methyl phenyl sulfide under the optimized reaction conditions gave ca. 86% conversion with two major products methyl phenyl sulfoxide and methyl phenyl sulfone in the ca. 70% and 30% selectivity, respectively. Oxidation of styrene catalyzed by these complexes gave at least five products namely styrene oxide, benzaldehyde, benzoic acid, 1-phenylethane-1,2-diol and phenylacetaldehyde with a maximum of 76.9% conversion of styrene by 4, 76.3% by 5 and 76.0% by 6 under optimized conditions. The selectivity of the obtained products followed the order: benzaldehyde > benzoic acid > styrene oxide > phenylacetaldehyde > 1-phenylethane-1,2-diol. Similarly, ca. 93% conversion of benzoin was obtained by these catalysts, where the selectivity of the products followed the order benzil > benzoic acid > benzaldehyde-dimethylacetal. Tests for the recyclability and heterogeneity of the reactions have also been carried. Neat complexes are equally active. However, the recycle ability of encapsulated complexes makes them better over neat ones.     

Synthesis,structure, and biological properties of mixed cobalt(III) dioximates with guanidine derivatives

Two Co(III) dioximates, cyanoguanidine complex {[Na₂(µ-H₂O)₂(L¹)₂(H₂O)₂]-[Co^III(DmgH)₂(N₃)₂]} _n [Co^III(DmgH)₂(N₃)₂] _n (L¹ = (H₂N)₂C=N–C=N) (I) and aminoguanidine complex [H₃L²][Co(DmgH)₂(N₃)₂] (H₂L² = H₂N–C(=NH)–NH–NH₂) (II), were synthesized from the [CoCl(DmgH)₂(H₂O)] structural unit (DmgH^– is the dimethylglyoxime monoanion). The implementation of the synthesis was confirmed by chemical analysis, IR spectroscopy, and X-ray diffraction (CIF files CCDC 1531845 (I), 1531846 (II)). Both compounds are ionic. Compound I consists of cations representing centrosymmetrical 2D coordination polymers, {[Na₂(µ-H₂O)₂(L¹)₂(H₂O)₂][Co^III(DmgH)₂(N₃)₂]} ⁿ⁺ _n , and monomeric [Co(DmgH)₂(N₃)₂]^– anions, while in II, the charge of the [Co(DmgH)₂(N₃)₂]^– complex anion is counterbalanced by the organic [H₃L²]⁺ cation. In I, L¹ is coordinated to the metal as a monodentate neutral ligand, while in II, H₂L² occurs in the complex as a protonated uncoordinated component. Since L¹ in I and H₂L² in II contain functional amine groups able to form intermolecular hydrogen bonds acting as proton donors, the component packing mode in the crystals was analyzed assuming various types of interactions, apart from electrostatic ones. The biological properties of the complexes were tested considering their effect on the biosynthesis of proteases by the micromycete Fusarium gibbosum CNMN FD 12 strain. Culturing the producer on a culture medium containing complex I in the selected optimal concentrations of 5–10 mg/L was found to increase the acid protease activity by 140–150%.     

Mixed ligand complexes of AEE hexafluoroacetylacetonates with diglyme: Synthesis,crystal structure and thermal behavior

The novel mixed ligand complexes [Ca(hfa)₂(diglyme)(H₂O)] (I), [Sr(hfa)₂(diglyme)(H₂O)] (II) and [Ba(hfa)₂(diglyme)₂] (III) (Hhfa = 1,1,1,5,5,5-hexafluoropentane-2,4-dione, diglyme = 2,5,8-trioxanonane) were synthesized by the reactions of the alkaline earth element (AEE) carbonates in n-hexane with a mixture of Hhfa and diglyme, and they were characterized by elemental analysis, ¹H and ¹³C NMR, and FTIR spectroscopy. The crystal structures of I–III, consisting of mononuclear isolated molecules, have been determined. The thermal behavior and composition of the vapor phase have been studied for I–III by thermal analysis at low pressure and mass spectrometry using a Knudsen cell. The stability of the mixed ligand complexes [M(hfa)₂(diglyme)_n] to the removal of diglyme molecules under heating decreases in the row I > II ≈ III, and only I evaporates as the mixed ligand complex after water removal.     

Hexanuclear Co4Dy2, Zn4Dy2, and Co4Y2 Complexes with Defect Tetracubane Cores: Syntheses,Structures, and Magnetic Properties

A hexanuclear heterometallic cluster of composition [Dy₂Co₄(L)₄(NO₃)₂(OH)₄(C₂H₅OH)₂] ⋅ 2 C₂H₅OH ( 1 ) was synthesized by employing a Schiff base 2-(((2-hydroxy-3-methoxybenzyl) imino)methyl)-4-methoxyphenol (H₂L) as ligand and utilizing Dy(NO₃)₃ ⋅ 6H₂O and Co(NO₃)₂ ⋅ 6H₂O as metal ion sources. X-ray single-crystal diffraction analysis indicated that complex 1 contains a defect tetracubane core and possesses central symmetric structure, with two Dy^III ions being in the central body position of the molecule and four Co^II ions being arranged at the outer sites. Magnetic studies reveal that complex 1 behaves as single-molecule magnet (SMM) with energy barrier of 27.50 K. To investigate the individual contribution of Dy^III and Co^II ions to the SMM behavior, another two complexes of formulae [Dy₂Zn₄(L)₄(NO₃)₂(OH)₄] ⋅ 4CH₃OH ( 2 ) and [Y₂Co₄(L)₄(NO₃)₂(OH)₄(C₂H₅OH)₂] ⋅ 2 C₂H₅OH ( 3 ) were prepared. Complexes 1 and 3 are isomorphous. The coordination geometries of Dy^III ions in 1 and 2 are different. The Dy^III ions are eight-coordinated in 2 and nine-coordinated in 1 . Complex 2 exhibits SMM behavior with energy barrier of 69.67 K, but complex 3 does not display SMM property. These results reveal that the SMM behaviors of 1 and 2 are mainly originated from Dy^III ions. It might be the higher symmetry of Dy^III ions in 2 that results in the higher energy barrier.     

A new octahedral cobalt(III) complex of (1,8)- bis (2-hydroxybenzamido)-3,6-diazaoctane incorporating phenolate-amide-amine coordination: synthesis, X-ray crystal structure, ligand substitution and redox activity with sulfur(IV) and l -ascorbic acid

The octahedral complex, [Co^III(HL)]·9H₂O (H₄L = (1,8)-bis(2-hydroxybenzamido)-3,6-diazaoctane) incorporating bis carboxamido-N-, bis sec-NH, phenolate, and phenol coordination has been synthesized and characterized by analytical, NMR (¹H, ¹³C), e.s.i.-Mass, UV–vis, i.r., and Raman spectroscopy. The formation of the complex has also been confirmed by its single crystal X-ray structure. The cyclic voltammetry of the sample in DMF ([TEAP] = 0.1 mol dm⁻³, TEAP = tetraethylammonium perchlorate) displayed irreversible redox processes, [Co^III(HL)] → [Co^IV(HL)]⁺ and [Co^III(HL)] → [Co^II(HL)]⁻ at 0.41 and −1.09 V (versus SCE), respectively. A slow and H⁺ mediated isomerisation was observed for the protonated complex, [Co^III(H₂L)]⁺ (pK = 3.5, 25 °C, I = 0.5 mol dm⁻³). H₂Asc was an efficient reductant for the complex and the reaction involved outer sphere mechanism; the propensity of different species for intra molecular reduction followed the sequence: [{[Co^III(HL)],(H₂Asc)}–H]⁻ <<< {[Co^III(H₂L)],(H₂Asc)}⁺ < {[Co^III(HL)],(H₂Asc)}. A low value (ca. 3.7 × 10⁻¹⁰ dm³ mol⁻¹ s⁻¹, 25 °C, I = 0.5 mol dm⁻³) for the self exchange rate constant of the couple [Co^III(HL)]/[Co^II(HL)]⁻ indicated that the ligand HL³⁻ with amido (N-) donor offers substantial stability to the Co^III state. HSO₃⁻ and [Co^III(HL)] formed an outer sphere complex {[Co^III(HL)],(HSO₃⁻)}, which was slowly transformed to an inner sphere S-bonded sulfito complex, [Co^III(H₂L)(HSO₃)] and the latter was inert to reduction by external sulfite but underwent intramolecular S^IV → Co^III electron transfer very slowly. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Synthesis,characterization, and reactivity of a novel ruthenium carbonyl cluster containing tri-O-benzyl-d-glucal as a chiral carbohydrate ligand

A chiral carbohydrate ligand 3,4,6-tri-O-benzyl-d-glucal (L) reacts with the cluster triruthenium dodecacarbonyl Ru₃(CO)₁₂ giving a novel chiral cluster Ru₃(μ-H)₂(CO)₉(L-2H) (I) that shows fluxional behavior at room temperature. The reaction of Ru₃(μ-H)₂(CO)₉(L-2H) (I) with triphenylphosphine and diphenylphosphinoethane (dppe) gives two new clusters Ru₃(μ-H)₂(CO)₇(L-2H)(PPh₃)₂ (II) and Ru₃(μ-H)₂(CO)₇(L-2H)(dppe) (III). The new compounds I, II and III have been characterized by a combination of elemental analysis, mass spectrometry, infrared and variable temperature NMR spectroscopy.     

A novel blue luminescent high-spin iron(III) complex with interlayer O–H⋯Cl bridging: Synthesis,structure and spectroscopic studies

A blue luminescent high-spin (s = 5/2) iron(III) complex, [Fe^III(HL¹)₂]Cl (2), was synthesized with the acyclic tridentate salicylaldehyde 2-pyridyl hydrazone ligand, H₂L¹ (1), and it can subsequently be deprotonated and methylated into blue luminescent iron(III) complexes, [Fe^III(L²)₂]Cl (3) and [Fe^III(MeL¹)₂]Cl (4) respectively. On excitation at 390 nm, the ligand and the complexes display fluorescence in the blue region (λ_em = 440–450 nm) of the spectrum. The association constant, (K_ass = 4.6421 × 10⁴ at 298 K) and the thermodynamic parameters for complex 2 have been determined by UV–Vis spectroscopy. The iron(III)–iron(II) reduction potentials lie near – 0.2 V versus SCE. The X-ray crystal structure of the complex, [Fe^III(HL¹)₂]Cl · H₂O (2), was determined, revealing meridional binding of the two ligands affording a cis-FeN₄O₂ geometry with alternate chlorine and water molecules at the interface of the main molecule, resulting in interesting interlayer O–H?Cl bridging.