Stereospecific π–π stacking interactions between pseudo-enantiomeric sulfur-bridged dinuclear Co(III)–Pd(II) and Co(III)–Pt(II) complexes with optically active propanediamines

Assemblies between pseudo-enantiomers with different d⁸ metal centers, Δ-[M(bpy){Co(aet)₂(R-pn)}]³⁺ (M?=?Pd or Pt, bpy?=?2,2′-bipyridine, aet?=?2-aminoethanethiolate, pn?=?1,2-propanediamine), and Λ-[M′(bpy){Co(aet)₂(S-pn)}]³⁺ (M′ ≠ M, M′?=?Pd or Pt), have been examined from stereo- and spectrochemical aspects. A mixture of equimolar amounts of the optically active sulfur-bridged dinuclear complex, Δ-[M(bpy){Co(aet)₂(R-pn)}](NO₃)₃·7H₂O, and its pseudo-enantiomer, Λ-[M′(bpy){Co(aet)₂(S-pn)}](NO₃)₃·7H₂O, in H₂O crystallizes as [M(bpy){Co(aet)₂(R-pn)}][M′(bpy){Co(aet)₂(S-pn)}](NO₃)₆·4H₂O, in which two complex cations with imperfect enantiomorphisms form a 1?:?1 π–π stacked unit.     

Synthesis and crystal structure of d–f heteronuclear Gd(III)–Co(II) system

A carboxylate-bridged Co(II)–Gd(III) complex, [(bipy)CoL₃Gd(NO₃)L₃Co(bipy)] (HL =?α-methylacrylic acid, bipy =?2,2′-bipyridine), was prepared and characterized. Single crystal X-ray analysis reveals that the complex assumes a carboxylate-bridged CoGdCo unit. Magnetic measurements showed χ_m T decreases when the temperature is lowered.     

Synthesis and magnetic characterization of Ln(III)–Co(II) complexes with 1,10-phenanthroline ligands

Four heteronuclear complexes, [Ln₂Co₂L₁₀(H₂O)(phen)₂] · n(H₂O) (Ln = La 1, n = 2; Ln = Nd 2, Sm 3, Gd 4, n = 0; HL = α-methylacrylic acid, phen = 1,10-phenanthroline), have been synthesized and characterized by elemental analysis, IR and X-ray diffraction. The complexes with a discrete Co–Ln–Ln–Co tetranuclear molecule are isomorphous in the triclinic space group P 1 and Z = 1, in which all metal ions are bridged by bidentate α-methylacrylato groups. Magnetic measurements of 1, 2 and 3 show antiferromagnetic exchange interaction between paramagnetic centers.     

Novel heterometallic Schiff base complexes featuring unusual tetranuclear {Co(III)2Fe(III)2(μ-O)6} and octanuclear {Co(III)4Fe(III)4(μ-O)14} cores: direct synthesis, crystal structures, and magnetic properties

A one-pot reactions of cobalt powder with iron(II) chloride in dimethylformamide (DMF; 1) or dimethyl sulfoxide (DMSO; 2) solutions of polydentate salicylaldimine Schiff base ligands (H(2)L(1), 1; H(4)L(2), 2) based on 2-aminobenzyl alcohol (1) or tris(hydroxymethyl)aminomethane (2), formed in situ, yielded two novel heterometallic complexes, [Co(III)(2)Fe(III)(2)(L(1))(6)]·4DMF (1) and [Co(III)(4)Fe(III)(4)(HL(2))(8)(DMSO)(2)]·18DMSO (2). Crystallographic investigations revealed that the molecular structure of 1 is based on a tetranuclear core, {Co(III)(2)Fe(III)(2)(μ-O)(6)}, with a chainlike metal arrangement, while the structure of 2 represents the first example of a heterometallic octanuclear core, {Co(III)(4)Fe(III)(4)(μ-O)(14)}, with a quite rare manner of metal organization, formed by two pairs of {CoFe(HL(2))(2)} and {CoFe(HL(2))(2)(DMSO)} moieties, which are joined by O bridges of the Schiff base ligands. Variable-temperature (1.8-300 K) magnetic susceptibility measurements showed a decrease of the μ(B) value at low temperature, indicative of antiferromagnetic coupling (J/hc = -32 cm(-1) in 1; J/hc = -20 cm(-1) in 2) between the Fe(III) magnetic centers in both compounds. For 2, three J constants between Fe(III) centers were assumed to be identical. High-frequency electron paramagnetic resonance spectra allowed one to find spin Hamiltonian parameters in the coupled-spin triplet and quintet states of 1 and estimate them in 2. The "outer" and "inner" Fe atoms in 2 appeared separately in the M?ssbauer spectra.     

New luminescent heteronuclear Ln(III)–Bi(III) complexes (Ln = Nd,Eu, Tb,Yb) based on aminopolycarboxylic acids

New heteronuclear Ln(III)–Bi(III) complexes (Ln?=?Nd, Eu, Tb, Yb, Lu) with ethylenediamine-N,N,N′,N′-tetraacetic (H₄edta), trans-1,2-cyclohexane-diamine-N,N,N′,N′-tetraacetic (H₄cdta), diethylenetriamine-N,N,N′,N″,N″-pentaacetic (H₅dtpa), and triethylenetetraamine-N,N,N′,N″,N″′,N″′-hexaacetic (H₆ttha) acids have been synthesized with a different synthetic approach. Bi(III) is a sensitizer of the 4f-luminescence in visible and near IR region. Emission spectra of Eu(III)–Bi(III) complexes were studied and the asymmetry of Eu(III) coordination environment was estimated, in good agreement with molecular models. The complexes synthesized by self-assembly are characterized by higher values of the 4f-luminescence quantum yield than other Ln(III)–Bi(III) complexes.     

Novel mixed-valent Co(II)₂Co(III)₄Ln(III)₄ aggregates with ligands derived from tris-(hydroxymethyl)aminomethane (Tris)

Isostructural Co(II)?Co(III)?Ln(III)? (Ln = Y (1), Gd (2) and Dy (3)) coordination clusters formed using the ligand Tris are the first examples of 3d-4f complexes involving this ligand and show weak ferromagnetic coupling between the Co(II) ions and slow relaxation (SMM) behaviour for 3.     

Ferrocene-containing ligands in the self-assembly of trinuclear μ3-oxocentered carboxylate complexes of chromium(III, III, III)carboxylate complexes of chromium(III, III, III)

New trinuclear μ₃-oxocentered chromium(III, III, III) complexes were obtained by the self-assembly of ferrocenecarboxylate ligands and the Cr₃O fragment. The complexes were investigated by fast-atom bombardment (FAB) mass spectrometry, cyclic voltammetry, and electronic and IR spectroscopy. V. I. Vernadskii Institute of General and Inorganic Chemistry, National Academy of Sciences of Ukraine, 32/34 Prospekt Akademika Vernadskogo, Kiev 03142, Ukraine. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 36, No. 4, pp. 233–237, July–August, 2000.     

Polynuclear Heteroligand Yb(III)–Er(III) Complexes as Potential Upconversion Materials

Russian Journal of Coordination Chemistry - The synthesis of complexes LnI(C6F5O)2 and LnCp(L)2 (Ln = Er, Yb; L = C6F5O, SONF), which are convenient precursors for the preparation of heteroligand...     

Ion-Exchange Processes M(II) → Fe(III) and Fe(III) → M(II) in Metal Hexacyanoferrate(II) Gelatin-Immobilized Matrices (M = Mn,Co, Ni,Cu, Zn,Cd)

Ion-exchange reactions M²⁺ Fe³⁺ and Fe³⁺ M²⁺ (M = Mn, Co, Ni, Cu, Zn, Cd) were studied in metal(II) hexacyanoferrate(II) gelatin-immobilized matrices M₂[Fe(CN)₆] in contact with aqueous FeCl₃ solutions and Fe₄[Fe(CN)₆]₃ in contact with aqueous MCl₂ solutions. It was shown that in both cases, M²⁺ was replaced by Fe³⁺ and Fe³⁺ was replaced by M²⁺ to some extent, but no complete replacement was observed in the M₂[Fe(CN)₆]–FeCl₃ or Fe₄[Fe(CN)₆]₃–MCl₂ systems under study. No electrophilic substitution Fe³⁺ Mn²⁺ was found to occur in any noticeable degree during the contact of Fe₄[Fe(CN)₆]₃ with aqueous MnCl₂ solutions even when this contact occurred for 1 h and longer.     

Stereospecific interactions through π -conjugated systems of sulfur-bridged dinuclear Co(III)-Pd(II) and Co(III)-Pt(II) complexes of optically active penicillaminates

The reaction of trans(N)-[Co(D-pen)₂]^? (pen = penicillaminate) or trans(N)-[Co(L-pen)₂]^? with [MCl₂(L)] (M = Pd or Pt, L = 2,2′-bipyridine (bpy) or 4,4′-dimethyl-2,2′-bipyridine (dmbpy)) stereoselectively gave an optically active S-bridged dinuclear complex, [M(L){Co(D-pen)₂}]Cl · 3H₂O or [M(L){Co(L-pen)₂}]Cl · 3H₂O. The mixture of equimolar amounts of these two enantiomers in H₂O crystallizes as [M(L){Co(D-pen)₂}]_0.5[M(L){Co(L- pen)₂}]_0.5Cl · nH₂O (1cCl · 7H₂O: M = Pd, L = bpy, n = 7; 2cCl · 7H₂O: M = Pd, L = dmbpy, n = 7; 3cCl · 6H₂O: M = Pt, L = dmbpy, n = 6), in which the enantiomeric complex cations are included in the ratio of 1 : 1. In the crystals of 1cCl · 7H₂O, [Pd(bpy){Co(D-pen)₂}]⁺ (1a) and [Pd(bpy){Co(L-pen)₂}]⁺ (1b) are arranged alternately while overlapping the bpy planes along the a axis, and the π electronic systems of bpy moieties interact with each other. This is quite a contrast to the optically active 1aCl · 3H₂O or 1bCl · 3H₂O, which exist as monomers without intermolecular interactions. In crystals of 2cCl · 7H₂O and 3cCl · 6H₂O, similarly, the two enantiomeric complex cations interact with each other through the dmbpy frameworks. However, the interplane distances between the stacked π systems in these dmbpy complexes are considerably longer than in the bpy complexes. Such structural characteristics significantly reflect their diffuse reflectance spectra.     

Strongly decussated π-stacking in a Ag(I)–Co(III) complex containing a Ag2Co2 44 square tile motif

A mixed Co–Ag complex with 2,6-dicarboxypyridine (H₂PDC), AgCo(PDC)₂, was synthesized under hydrothermal conditions. The complex adopts a 2D layer structure formed by intramolecular π-stacking. Each Co(III) ion is chelated by two 2,6-dicarboxypyridine anions to give the [Co(PDC)₂]^? anion that is further extended by Ag⁺ to form 4⁴ square grids.     

Crystal structure of Co(III) α-dimethylglyoximates with imidazole

Two new dimethylglyoximate complexes [Co(DmgH)₂(Im)Cl] (I) and (ImH)[Co(DmgH₂)₂Cl₂] (II), where DmgH^? is the dimethylglyoxime residue and Im is the imidazole molecule, are synthesized. The composition and structure of the crystals are determined from the elemental analysis, IR spectra, and single crystal X-ray diffraction. Complex I is molecular, containing the Im molecule as a coordinated ligand; complex II is of the ionic type with (ImH)⁺ involved as an outer-sphere organic cation. The mode of component packing in the crystals mainly depends on the imidazole position in the compounds.     

Scandium(III) Triflate–Catalyzed Coumarin Synthesis

Scandium(III) triflate is an excellent catalyst in the von Pechmann condensation. The solvent-free catalytic reactions proceed smoothly with a range of phenols and β-ketoesters in the presence of 10 mol% scandium(III) triflate at 80 °C. This simple method affords various 4-substituted coumarins in good to excellent yield and is superior to the classical method in several aspects: solvent-free conditions, short reaction times, a decreased catalyst loading, a mild reaction temperature, and an easy workup.     

Co(III), Rh(III) & Ir(III)-Catalyzed Direct C−H Alkylation/Alkenylation/Arylation with Carbene Precursors

Metal carbenes play a pivotal role in transition-metal-catalyzed synthetic transfer reactions. The metal carbene is generated either from a diazo compound through facile extrusion of N₂ with a metal catalyst or in situ generated from other sources like triazoles, pyriodotriazoles, sulfoxonium ylides and iodonium-ylide. On the other hand, Co(III), Rh(III) & Ir(III)-catalyzed C−H functionalizations have been well established as a key synthetic step to enable the construction of various synthetic transformations. Interestingly, in recent years, merging of these two concepts C−H activation and carbene migratory insertion gained much attention, in particular group 9 metal-catalyzed arene C−H functionalizations with carbene precursors via carbene migratory insertion. In this review, we summarize recent advances in Co(III), Rh(III) & Ir(III)-catalyzed direct C−H alkylation/alkenylation/arylation with carbene precursors and also discuss key synthetic intermediates within the catalytic cycles.     

Studies on synthesis,determination of CMC values,kinetics and the mechanism of iron(II) reduction of surfactant–Co(III)–ethylenediamine complexes in aqueous acid medium

The surfactant–Co(III) complexes of the type cis-[Co(en)₂AX]²⁺ (A?=?Tetradecylamine, X?=?Cl^?,?Br^?) were synthesised from corresponding dihalogeno complexes by the ligand substitution method. The critical micelle concentration (CMC) values of these surfactant complexes in aqueous solution were obtained from conductance measurements. The kinetics and mechanism of iron(II) reduction of surfactant–Co(III) complexes, cis-[Co(en)₂(C₁₄H₂₉NH₂)Cl](ClO₄)₂ and cis-[Co(en)₂(C₁₄H₂₉NH₂)Br] (ClO₄)₂ ions were studied spectrophotometrically in an aqueous acid medium by following the disappearance of Co(III) using an excess of the reductant under pseudo-first-order conditions: [Fe(II)]?=?0.25?mol?dm^?3, [H⁺]?=?0.1?mol?dm^?3, [μ]?=?1.0?mol?dm^?3 ionic strength in a nitrogen atmosphere at 303, 308 and 313?K. The reaction was found to be of second order and showed acid independence in the range [H⁺]?=?0.05–0.25?mol?dm^?3. The second-order rate constant increased with surfactant–Co(III) concentration and the presence of aggregation of the complex itself altered the reaction rate. The effects of [Fe(II)], [H⁺] and [μ] on the rate were determined. Activation and thermodynamic parameters were computed. It is suggested that the reaction of [Fe(II)] with Co(III) complex proceeds by an inner-sphere mechanism.     

[Phthalocyaninato(2–)]­antimony(III) chloride

The title antimony(III) complex, [Sb(C₃₂H₁₆N₈)]Cl or [SbPc]Cl (where Pc = C₃₂H₁₆N₈²⁻), has been obtained from the reaction of pure powdered antimony with 1,2-di­cyano­benzene under a stream of ICl vapour. The asymmetric unit of this complex consists of an [SbPc]⁺ cation and a Cl⁻ anion. The phthalocyaninate residue [SbPc]⁺ is not planar. The Sb atom lies 1.057 (3) Å from the plane defined by the four iso­indole N atoms. A combination of ionic and donor–acceptor interactions links the [SbPc]Cl mol­ecules to form centrosymmetric [(SbPc)Cl]₂ pseudo-dimers in the crystal. The Sb—Cl distances in the pseudo-dimer are not equivalent [3.043 (2) and 3.201 (2) Å]. The pseudo-dimers are weakly linked through Cl⃛H—C_benzo interactions to form a three-dimensional network. As a result of these interactions, the four Sn—N_isoindole bond lengths in the [SbPc]⁺ residue are not equivalent and the symmetry of the Sb—N core is only close to C_s.     

Cyanide-bridged bi- and trinuclear heterobimetallic Fe(III)–Mn(III) complexes: Synthesis,crystal structures and magnetic properties

By employing trans-dicyano or pentacyanometalate as building block and using a bicompartimental Schiffbase based manganese(III) compound as assemble segment, two new cyanide-bridged heterometallic Fe(III)–Mn(III) complexes {[Mn(L)(H₂O)][Febpb(CN)₂]}·2CH₃OH (1) and {[Mn(L)(H₂O)]₂··[Fe(CN)₅NO]} (2) (bpb^2– = 1,2-bis(pyridine-2-carboxamido)benzenate, L = N,N'-ethylene-bis(3-ethoxysalicylideneiminate) have been synthesized and characterized by elemental analysis, IR spectroscopy and X-ray structure determination. Single X-ray diffraction analysis reveals binuclear FeMn and trinuclear FeMn₂ structure, respectively, in which the cyanide precursor acts as mono- or bidentate ligand to connect the Mn(III) Schiff-base unit(s). Furthermore, these two complexes are self-complementary through coordinated aqua ligands from one complex and the free O₄ compartments from the neighboring complex, giving dimeric and 1D single chain supramolecular structure. Investigation of the magnetic susceptibility of 1 reveals weak antiferromagnetic coupling between the adjacent Mn(III) ions. Based on the binuclear FeMn model, best fit of the magnetic susceptibilities of 1 leads to the magnetic coupling constants J =–1.37 cm^–1 and zJ′ =–0.72 cm^–1 (1).     

Facile and Reversible Formation of Iron(III)–Oxo–Cerium(IV) Adducts from Nonheme Oxoiron(IV) Complexes and Cerium(III)

Ceric ammonium nitrate (CAN) or Ce^IV(NH₄)₂(NO₃)₆ is often used in artificial water oxidation and generally considered to be an outer-sphere oxidant. Herein we report the spectroscopic and crystallographic characterization of [(N4Py)Fe^III-O-Ce^IV(OH₂)(NO₃)₄]⁺ ( 3 ), a complex obtained from the reaction of [(N4Py)Fe^II(NCMe)]²⁺ with 2 equiv CAN or [(N4Py)Fe^IV=O]²⁺ ( 2 ) with Ce^III(NO₃)₃ in MeCN. Surprisingly, the formation of 3 is reversible, the position of the equilibrium being dependent on the MeCN/water ratio of the solvent. These results suggest that the Fe^IV and Ce^IV centers have comparable reduction potentials. Moreover, the equilibrium entails a change in iron spin state, from S=1 Fe^IV in 2 to S=5/2 in 3 , which is found to be facile despite the formal spin-forbidden nature of this process. This observation suggests that Fe^IV=O complexes may avail of reaction pathways involving multiple spin states having little or no barrier.