Oxo-transfer catalysis from t-BuOOH with C-H bond insertion using tridentate Schiff-base-chelate complexes of ruthenium(III)

Mixed-chelate complexes of ruthenium have been synthesized using tridentate Schiff-base ligands (TDLs) derived by condensation of aldehydes (salicyldehyde, 2-pyridinecarboxaldehyde) with 2-aminobenzoic acid, and bidentate ligands (2,2^′-bipyridine or picolinic acid). [Ru^III(cpsd)(bipy)(H₂O)]⁺ (1), [Ru^III(cpsd)(pic)(H₂O)] (2), [Ru^III(cppc)(bipy)(H₂O)]²⁺ (3) and [Ru^III(cppc)(pic)(H₂O)]⁺ (4) complexes (where, cpsd²⁻=(N-(2-carboxyphenyl)salicylaldiminato); cppc⁻=N-2-carboxyphenylpyridine-2-carboxaldiminato; bipy=2,2^′-bipyridine and pic⁻=picolinate) were characterized by analytical, spectral (IR and UV-Vis), conductance, magnetic moment and electrochemical studies. Catalysis of hydrocarbon oxidations for cyclohexene, cyclohexane, cyclohexanol, toluene, benzyl alcohol, and tetrahydrofuran have been studied using various O-atom transfer agents (t-BuOOH, H₂O₂, NaOCl, KHSO₅ and pyridinium-N-oxide). The influence of product yield as a function of solvent was evaluated for CH₂Cl₂, CH₃CN, and 1,4-dioxane. Coordinating solvents suppress the reactivity by inhibiting coordination of t-BuOOH, and compete for the Ru^VO group through their own intrinsic C-H reactivity. The main pathway transfers the oxo group from the [RuO(TDL)(XY)] intermediate, TDL=cpsd²⁻ and cppc²⁻; XY=bipy or pic⁻, with insertion of the oxo group into a C-H bond of all substrates tested (rather than olefin epoxidation for cyclohexene). A mechanism involving intermediacy of a high valent Ru(V)-oxo species is proposed for the catalytic oxidation processes.     

Electronic spectrum and magnetic properties of a dinuclear nickel(II) complex with two nickel(II) ions of C2-twisted octahedral geometry

A dinickel(II) complex [Ni₂(sym-hmp)₂](BPh₄)₂·3.5DMF·0.5(2-PrOH) (1) was synthesized with a dinucleating ligand, 2,6-bis[(2-hydroxyethyl)methylaminomethyl]-4-methyl-phenol [H(sym-hmp)]. The complex 1 (C₉₀H_118.50B₂N_7.50Ni₂O₁₀) crystallized in the triclinic space group with dimensions a = 14.7446(4) Å, b = 15.4244(4) Å, c = 18.7385(6) Å, α = 86.9495(9)°, β = 76.7263(10)°, γ = 86.5370(8)°, and V = 4136.8(2) Å³ and with Z = 2; this is isomorphous to a previous cobalt(II) complex [Co₂(sym-hmp)₂](BPh₄)₂. Single-crystal X-ray analysis revealed a bis(μ-phenoxo)dinickel(II) core structure containing two distorted octahedral nickel(II) ions of C₂ symmetry. The order of the coordination bond lengths is Ni-O(phenoxo) < Ni-O(hydroxy) < Ni-N. The electronic spectrum of 1 was typical for the octahedral nickel(II) complexes, but the axial elongation and the C₂-twist of the equatorial plane were found after a detailed analysis. The bond angles obtained by the electronic spectrum agreed with the crystallographically obtained bond angles within 2.3°. The order of the AOM parameters was e_{σ,O(phenoxo)} > e_{σ,O(hydroxy)} > e_σ,N, which was consistent with the order of the coordination bond lengths. Magnetic susceptibility data for 1 were fitted well with the parameters 2J = −69.7 cm⁻¹, D = 0.00 cm⁻¹, g = 2.17, and TIP = 265 × 10⁻⁶ cm³ mol⁻¹. The result indicates significant antiferromagnetic exchange interaction and negligible zero-field splitting, while the isostructural cobalt(II) complex showed an anisotropic behavior.     

Synthesis, structure and magnetic properties of an oxo-bridged dinuclear iron(III) complex [(TPyA)FFeOFeF(TPyA)](BF4)2 · 0.5MeOH (TPyA = tris(2-pyridylmethyl)amine) containing the FFeOFeF linkage

The reaction of [Fe^II(H₂O)₆](BF₄)₂ with tris(2-pyridylmethyl)amine (TPyA) and triethylamine in methanol under aerobic conditions forms [(TPyA)FFe^IIIOFe^IIIF(TPyA)](BF₄)₂ · 0.5MeOH (1), in which each Fe(III) ion is coordinated to a TPyA and an F⁻ ion as well as an oxo ion (O²⁻) linking two Fe(III) ions. 1 has offset face-to-face π-π interactions between the dimers, and possesses a supramolecular network structure. The magnetic susceptibility of 1 can be fit with g = 2.0, J/k_B = − 153 K (106 cm⁻¹), and θ = − 0.3 K [H = − 2JS_a · S_b]. These indicate that very strong antiferromagnetic interactions occur via the oxo bridge within the Fe(III) dimer and weak antiferromagnetic interactions between the dimers.     

Structural and equilibrium studies on mixed ligand complexes of Co(II), Ni(II), Cu(II) and Zn(II) with N-(2-benzimidazolyl)methyliminodiacetic acid and typical N, N donor ligands

Mixed ligand complexes: [Co(L)(bipy)] · 3H₂O (1), [Ni(L)(phen)] · H₂O (2), [Cu(L)(phen)] · 3H₂O (3) and [Zn(L)(bipy)] · 3H₂O (4), where L²⁻ = two -COOH deprotonated dianion of N-(2-benzimidazolyl)methyliminodiacetic acid (H₂bzimida, hereafter, H₂L), bipy = 2,2′ bipyridine and phen = 1,10-phenanthroline have been isolated and characterized by elemental analysis, spectral and magnetic measurements and thermal studies. Single crystal X-ray diffraction studies show octahedral geometry for 1, 2 and 4 and square pyramidal geometry for 3. Equilibrium studies in aqueous solution (ionic strength I = 10⁻¹ mol dm⁻³ (NaNO₃), at 25 ± 1 °C) using different molar proportions of M(II):H₂L:B, where M = Co, Ni, Cu and Zn and B = phen, bipy and en (ethylene diamine), however, provides evidence of formation of mononuclear and binuclear binary and mixed ligand complexes: M(L), M(H₋₁L)⁻, M(B)²⁺, M(L)(B), M(H₋₁L)(B)⁻, M₂(H₋₁L)(OH), (B)M(H₋₁L)M(B)⁺, where H₋₁L³⁻ represents two -COOH and the benzimidazole N₁-H deprotonated quadridentate (O⁻, N, O⁻, N), or, quinquedentate (O⁻, N, O⁻, N, N⁻) function of the coordinated ligand H₂L. Binuclear mixed ligand complex formation equilibria: M(L)(B) + M(B)²⁺ ? (B)M(H₋₁L)M(B)⁺ + H⁺ is favoured with higher π-acidity of the B ligands. For Co(II), Ni(II) and Cu(II), these equilibria are accompanied by blue shift of the electronic absorption maxima of M(II) ions, as a negatively charged bridging benzimidazolate moiety provides stronger ligand field than a neutral one. Solution stability of the mixed ligand complexes are in the expected order: Co(II) < Ni(II) < Cu(II) > Zn(II). The Δ log K_M values are less negetive than their statistical values, indicating favoured formation of the mixed ligand complexes over the binary ones.     

Kinetic studies of the reduction of hexaaquacobalt(III) perchlorate by a cobaloxime, [Co(dmgBF2)2(H2O)2]

The reaction of with Co(dmgBF₂)₂(H₂O)₂ in 1.0 M HClO₄/LiClO₄ was found to be first-order in both reactants and the [H⁺] dependence of the second-order rate constant is given by k_2obs = b/[H⁺], b at 25 °C is 9.23 ± 0.14 × 10² s⁻¹. The [H⁺] dependence at lower temperatures shows some saturation effect that allowed an estimate of the hydrolysis constant for as K_a = 9.5 × 10⁻³ M at 10 and 15 °C. Marcus theory and the known self-exchange rate constant for Co(OH₂)₅OH^2+/+ were used to estimate an electron self-exchange rate constant of k₂₂ = 1.7 × 10⁻⁴ M⁻¹ s⁻¹ for .     

New butane-1,2,3,4-tetracarboxylato bridged cobalt(II) complexes

Four butane-1,2,3,4-tetracarboxylato bridged supramolecular complexes [Co₂(H₂O)₅(BTC)]·2H₂O 1, [Co₂(H₂O)₅(BTC)]·2H₂O 2, [Co₂(H₂O)₆(bpy)₂(BTC)]·4H₂O 3 and [Co₂(H₂O)₂(bpy)₂(BTC)] 4, (H₄BTC = butane-1,2,3,4-tetracarboxylic acid, 2,2-bpy = 2,2-bipydine) are synthesized and characterized by single-crystal X-ray diffraction. IR spectroscopy, TG-DTA analyses, elemental analyses, powder X-ray diffraction and magnetic measurements for 3 and 4 are carried out. The dinuclear Co unit in 2 is bridged by BTC⁴⁻ anions into 2D layers, which are assembled via interlayer hydrogen bonds into a 3D (4⁴·6²)(4⁵·6⁵)₂(4⁶·6⁸·8) topological supramolecular architecture. In 3, the [Co₂(H₂O)₆(bpy)₂(BTC)] molecules are aggregated to 2D layers via π-π stacking interactions, the resulting layers are engaged in hydrogen bonding leading to a novel 3D supramolecular architecture with the schläfli symbol of (10².12)₂(4.10²)₂(4².10².12²). The Co atoms in 4 are linked by BTC⁴⁻ anions into a 1D chain, then the hydrogen bonding and π-π stacking interactions result in formation of a 3D novel (4³.6².8)₂(4⁶.6⁶.8³)(6³)₂ topological networks. The variable temperature magnetic characterizations on 3 and 4 suggest weak antiferromagnetic or ferromagnetic coupling exchange via π···π stacking interactions (J = -0.03 cm⁻¹ for 3, J = 0.11 cm⁻¹ for 4).     

Synthesis and catalytic performance for olefin epoxidation of a novel dioxomolybdenum (VI) (ferrocenylmethyleneamino)alcoholate complex

A novel dioxomolybdenum (VI) complex of (ferrocenylmethyleneamino)alcoholate was easily synthesized via the reaction of MoO₂Cl₂(THF)₂ with N-hydroxyethyl ferrocenylimine ligand [(η⁵-C₅H₅)Fe{(η⁵-C₅H₄)-CHN-CH₂-CH₂-OH}], and characterized by FR-IR, ¹H NMR, UV-Vis spectroscopy and elemental analysis. In the presence of the catalytic amount of the dioxomolybdenum (VI) complex, good to excellent selectivities of epoxides (77-95%) were obtained for epoxidation of styrene and cyclohexene with tert-butyl hydroperoxide (TBHP) as oxidant in 1,2-dichloroethane at 12 h. Higher initial activity of the complex was observed for the catalyzed styrene epoxidation (451 mol mol_Mo⁻¹ h⁻¹) than that of cyclohexene epoxidation (164 mol mol_Mo⁻¹ h⁻¹) at 1 h. Meanwhile, influences of reaction temperature, solvents, reaction time as well as catalyst amount for olefin epoxidation were also investigated.     

Synthesis, crystal structure, spectral properties and catalytic activity of hexakis(imidazole)manganese(II) bisindole-2-carboxylato bisneocuproine bisdimethyl sulfoxide solvates {[Mn(Im)6] · 2(2-IC) · 2(NC) · 2(DMSO)}

Synthesis, X-ray crystal structure and IR spectrum of {[Mn^II(Im)₆] · 2(2-IC) · 2(NC) · 2(DMSO)} (Im = imidazole, 2-HIC = indole-2-carboxylic acid, NC = 2,9-dimethyl-1,10-phenanthroline, DMSO = dimethyl sulfoxide) are reported. The manganese(II) ion has octahedral geometry with a MnN₆ core. The crystal structure is completed by two NC, two 2-IC⁻ and two DMSO solvate molecules. The individual cations are linked into chains running parallel to the a axis by four intermolecular hydrogen bonding involving two 2-IC⁻solvate. Moreover, these chains are connected by π-π stacking interactions which occur between neocuproine molecules related through inversion center. In IR spectroscopy, the compound spectrum is roughly similar to the imidazole one: (i) above 1800 cm⁻¹, the bands are broad, but when focussing on some of them a doublet structure can be found; (ii) below 1800 cm⁻¹, the bands are sharp and it is then possible to point out the modification of S-O band when this later is involved in bifurcated hydrogen bonding to a second solvate 2-IC⁻. The compound catalyses the disproportionation of H₂O₂; moreover an additional quantity of imidazole increases the reaction rate.     

Structure and spectroscopic studies of cis-bis(bipyridine) ruthenium(II) complexes of phenylcyanamide ligands

New ruthenium(II) complexes with cyanamide ligands, cis-[Ru(bpy)₂(Ipcyd)₂] (1) and [Ru(bpy)₂(OHpcyd)₂] (2) (bpy = 2,2′-bipyridine, Ipcyd = 4-iodophenylcyanamide anion, OHpcyd = 4-(3-hydroxy-3-methylbut-1-ynil)phenylcyanamide), have been prepared and characterized by UV-Vis, IR and ¹H NMR spectroscopies as well as electrochemical technique (CV). The complex cis-[Ru(bpy)₂(Ipcyd)₂] (1) crystallized with empirical formula of C₃₄H₂₄I₂N₈Ru in a monoclinic crystal system and space group of P2₁/c with a = 11.769(7) Å, b = 24.188(12) Å, c = 11.623(2) Å, β = 91.63(3)°, V = 3308(3) ų and Z = 4.     

Structures and magnetic properties of dicopper(II) and dinickel(II) complexes with end-on azido bridges

An asymmetric single EO azido bridged dinuclear copper(II) complex, [Cu₂(dmterpy)₂(μ-1,1-N₃)(N₃)₂] · NO₃ · (H₂O)₂1 [dmterpy = 5,5″-dimethyl-2,2′:6′,2″-terpyridine], and a double EO azido bridged dinuclear nickel(II) complex, [Ni₂(pbdiim)₄(μ-1,1-N₃)₂] · 2(N₃) · 6(H₂O) 2 [pbdiim = 2-(2′-pyridyl)benzo[1,2-d:4,5-d′]diimidazole], have been synthesized and characterized structurally and magnetically. Compound 1 consists of a single EO azido bridged Cu^II dimer in which each Cu^II ion is five-coordinated in the form of a distorted square-based pyramid. The N_(μ−1,1) atom holds on the apical position of one Cu^II pyramid with an elongated bond length of 2.305 Å and on the basal plane of another distorted Cu^II pyramid with a bond length of 1.991 Å. The Cu-N_(μ−1,1)-Cu angle is 117.4 (2)°. The copper(II) dimer forms a 1 D zig-zag chain via hydrogen bondings between azide ions, water molecules and the nitrate anion. Compound 2 consists of a double EO azido bridged Ni^II dimer with the Ni-N_(μ−1,1)-Ni bond angle of 102.96 (13)°. The coordination geometry of Ni^II is octahedral. Their magnetic properties have been measured in the range from 300 to 2 K and correlated with the molecular structures. Compound 1 shows weak ferromagnetic interactions within the copper(II) dimer (J = 2.88 cm⁻¹), despite the large EO azide bridge angle (117.4 (2)°). The intramolecular coupling between the Ni^II (S = 1) ions in compound 2 was found to be ferromagnetic (J = 27.87 cm⁻¹).     

Extraction properties for alkali metal picrates of macrocyclic trinuclear (p-cymene)ruthenium(II) and (pentamethylcyclopentadienyl)rhodium(III) complexes

The solvent extraction properties of macrocyclic trinuclear organometallic complexes, [(p-cymene)Ru(pyO₂)]₃ and [Cp^∗Rh(pyO₂)]₃, for Li⁺, Na⁺, and K⁺ picrates have been investigated in a dichloromethane-water system at 25 °C. The extraction rates of the alkali metal picrates with these macrocyclic complex ligands are unusually slow; the shaking times required to attain equilibrium are at least 1 h for [(p-cymene)Ru(pyO₂)]₃ and 20-40 h for [Cp^∗Rh(pyO₂)]₃. From analysis of the equilibrium data, the extraction constants (K_ex = [ML⁺A⁻]_o/[M⁺][L]_o[A⁻]; M⁺ = alkali metal ion, L = macrocyclic ligand, A⁻ = picrate ion, o = organic phase) have been determined. The log K_ex value varies in the sequences, Li⁺ (5.72) > Na⁺ (4.50) > K⁺ (2.88) for [(p-cymene)Ru(pyO₂)]₃ and Li⁺ (4.79) > Na⁺ (2.70) ≈ K⁺ (2.69) for [Cp^∗Rh(pyO₂)]₃. The K_ex values of 6,6-dibenzyl-14-crown-4 (DBz14C4), which is one of the best Li⁺-selective crown ethers, have also been determined for comparison. It is revealed that [Cp^∗Rh(pyO₂)]₃ is much superior to DBz14C4 both in the extractability for Li⁺ and the selectivity for Li⁺ over Na⁺.     

Hydrothermal synthesis and structure of a Cu(I) bromide coordination polymer, [(tpyprz)3Cu10Br10] (tpyprz = tetra-2-pyridylpyrazine)

The hydrothermal reaction of CuBr₂ and tpyprz in the presence of NH₄VO₃ and HF for 72 h at 170 °C provided [(tpyprz)₃Cu₁₀Br₁₀] (1) in 20% yield. The two-dimensional structure of 1 may be described as Cu(I)-tpyprz chains, linked through {Cu₄Br₅}⁻ clusters in the ac-plane and decorated with {Cu₃Br₅}²⁻ clusters projecting from one face of the layer in the b-direction. The Cu(I) sites exhibit distorted trigonal coordination {CuBr₃} and distorted tetrahedral geometries, {CuBr₂N₂} and {CuN₄}. Crystal data for 1: monoclinic space group C2, a = 12.7561(8) Å, b = 19.359(1) Å, c = 15.860(1) Å, β = 97.178(1)°, V = 3885.8(4) Å³, Z = 2, D_calc = 2.222 g cm⁻³, μ(Mo Kα) = 78.75 cm⁻¹.     

Laboratory experiments on the effects of variable suspended sediment concentrations on the ecophysiology of the porcelain crab Petrolisthes elongatus (Milne Edwards, 1837)

The porcelain crab Petrolisthes elongatus is a particulate suspension feeding species common to coastal areas of New Zealand (NZ). Consistent with the responses of other suspension feeding species, it is likely to be negatively influenced by elevated suspended sediment concentrations. Laboratory experiments were conducted to quantify the effect of temperature (12 °C, 15 °C and 18 °C) and suspended sediment concentration (total particulate matter (TPM): low < 100 mg L^− 1; medium 100-1000 mg L^− 1; high > 1000 mg L^− 1) on the clearance rate (CR in L h^− 1), oxygen uptake rate (VO₂ in mL h⁻¹), net absorption efficiency (AE), and net energy budget (NEB in J h^− 1) of P. elongatus across a range of sizes. Variation in CR and AE was independent of temperature and of body size, but were significantly different (P < 0.05) at low and medium suspended sediment concentrations compared with high suspended sediment concentrations. CR responded in a non-linear manner to changes in TPM, increasing with TPM up to a maximum value at medium-low concentrations (approximately 250 mg L^− 1) and then decreasing thereafter. CR had almost completely shut down at TPM concentrations of > 1000 mg L^− 1 and at particulate organic matter (POM) concentrations of > 250 mg L^− 1. AE was zero at approximate TPM and POM values of 1200 mg L^− 1 and 300 mg L^− 1, respectively. VO₂ was positively correlated with body size and with temperature, but was independent of TPM. NEB values for P. elongatus were low (approx 110 J g^− 1 h^− 1) at low sediment concentrations, were high (approx 320 J g^− 1 h^− 1) at medium sediment concentrations, and were negative (approx − 114 J g^− 1 h^− 1) at high sediment concentrations. These findings indicate that P. elongatus is likely to be food-limited at sediment concentrations of < 100 mg L^− 1, and severely negatively affected at sediment concentrations of > 1000 mg L^− 1, at least for the duration of such events which may persist for 2-3 days in coastal environments where this crab occurs.     

Comparative properties of fluorous phosphine ligand complexes: W(CO)5L. Crystal structure of W(CO)5P(C6H4-4-CH2CH2(CF2)7CF3)3

The compounds W(CO)₅P(C₆H₄-4-CH₂CH₂(CF₂)₇CF₃)₃ (1) and W(CO)₅P(CH₂CH₂(CF₂)₅CF₃)₃ (2) were synthesized in order to probe the electronic and physical effects of ligation by perfluorocarbon substituted tertiary phosphine ligands in a W(CO)₅L complex. The π-accepting ability of the fluorous phosphines was found to rank with non-fluorous comparators as P(CH₂CH₂(CF₂)₅CF₃)₃ > P(C₆H₄-4-CH₂CH₂(CF₂)₇CF₃)₃ > PPh₃ > P(p-tolyl)₃ > P(n-octyl)₃. The X-ray crystal structure of W(CO)₅P(C₆H₄-4-CH₂CH₂(CF₂)₇CF₃)₃ shows strong intermolecular association of fluorous components but confirms that the para fluorocarbon subtituents have an insignificant effect on the tungsten coordination environment. Partition coefficients (toluene/perfluoromethylcyclohexane) were measured for compounds 1 and 2.     

Equilibrium and structural studies on Co(II), Ni(II), Cu(II) and Zn(II) complexes with N-(2-benzimidazolyl)methyliminodiacetic acid: crystal structures of Ni(II) and Cu(II) complexes

Combined pH-metric, UV-Vis, ¹H NMR and EPR spectral investigations on the complex formation of M(II) ions (M=Co, Ni, Cu and Zn) with N-(2-benzimidazolyl)methyliminodiacetic acid (H₂bzimida, hereafter H₂L) in aqueous solution at a fixed ionic strength, I=10⁻¹ mol dm⁻³, at 25 ± 1 °C indicate the formation of M(L), M(H₋₁L)⁻ and M₂(H₋₁L)⁺ complexes. Proton-ligand and metal-ligand constants and the complex formation equilibria have been elucidated. Solid complexes, [M(L)(H₂O)₂] · nH₂O (n=1 for M = Co and Zn, n=2 for M = Ni) and {Cu (μ-L) · 4H₂O}_n, have been isolated and characterized by elemental analysis, spectral, conductance and magnetic measurements and thermal studies. Structures of [Ni(L)(H₂O)₂] · 2H₂O and {Cu(μ-L) · 4H₂O}_n have been determined by single crystal X-ray diffraction. The nickel(II) complex exists in a distorted octahedral environment in which the metal ion is coordinated by the two carboxylate O atoms, the amino-N atom of the iminodiacetate moiety and the pyridine type N-atom of the benzimidazole moiety. Two aqua O atoms function as fifth and sixth donor atoms. The copper(II) complex is made up of interpenetrating polymeric chains of antiferromagnetically coupled Cu(II) ions linked by carboxylato bridges in syn-anti (apical-equatorial) bonding mode and stabilized via interchain hydrogen bonds and π-π stacking interactions.     

One-dimensional azido bridge [1-ethyl-2-(phenylazo)imidazole]manganese(II): Structure of low bridge angle system and magnetism

The reaction of 1-ethyl-2-(phenylazo)imidazole (PaiEt), NaN₃ and Mn(OAc)₂ · 4H₂O at 1:2:1 molar ratio has isolated azido bridge 1-D coordination polymer. In monomeric unit of the complex, MnN₆ distorted octahedral coordination is achieved by two EO-N₃, two EE-N₃ and N,N′-chelation of PaiEt. Bridge angle Mn-(EO)N₃-Mn is 98.55(10)°. Variable temperature (300-2 K) magnetic measurements determine J values −13.63 ± 0.10 and 2.31 ± 0.15 cm⁻¹ and support antiferromagnetic (EE-N₃) and ferromagnetic (EO-N₃) interaction, respectively. Maximum susceptibility (χ_M = 0.0251 cm³ mol⁻¹) is observed at 43 K.     

Thiodiacetato-copper(II) chelates with or without N-heterocyclic donor ligands: molecular and/or crystal structures of [Cu(tda)]n, [Cu(tda)(Him)2(H2O)] and [Cu(tda)(5Mphen)] · 2H2O (Him = imidazole, 5Mphen = 5-methyl-1,10-phenanthroline)

Three new thiodiacetato-Cu(II) chelates have been synthesized and studied by X-ray crystallography and by thermal, spectral and magnetic methods. [Cu(tda)]_n (1) is a 3D-polymer with a pentadentate tda, which acts with a fac-O₂ + S(apical)-tridentate chelating conformation and as a twofold anti, syn-μ-η¹:η¹ carboxylate bridge. In its square pyramidal Cu(II) coordination (type 4 + 1) four O(carboxylate) donors define a close regular square base, but the Cu-S(apical) bond deviates 27.4° from the perpendicular to the mean basal plane. Each anti,syn-bridging carboxylate group exhibits two C-O (average 1.26(1) Å) and two Cu-O bonds (average 1.958(7) Å), which are very similar in length to each other. In contrast, the mixed-ligand complexes of [Cu(tda)(Him)₂(H₂O)] (compound 2, distorted octahedral, type 4 + 1 + 1) and [Cu(tda)(5Mphen)] · 2H₂O (compound 3, distorted square pyramidal, type 4 + 1) have molecular structures and the tda ligand displays only a fac-O₂ + S(apical)-tridentate conformation. The Cu-S(apical) bond lengths (2.570(1), 2.623(1) or 2.573(1) Å for 1, 2 or 3, respectively) are shorter than those previously reported for closely related Cu(II)-tda derivatives. The different tda ligand roles in their Cu(II) derivatives are rationalized on the basis of crystal packing forces driving in the absence or presence of auxiliary ligands (with two or three N-donor atoms).     

Mixed-valency with cyanides as terminal ligands: Diruthenium(III,II) complexes with the 3,6-bis(2-pyridyl)-1,2,4,5-tetrazine bridge and variable co-ligands (CN vs. bpy or NH3)

New diruthenium complexes (PPN)₄[(NC)₄Ru(μ-bptz)Ru(CN)₄], (PPN)₄1, and [(bpy)₂Ru(μ-bptz)Ru(CN)₄], 2, (PPN⁺ = bis(triphenylphospine)iminium; bptz = 3,6-bis(2-pyridyl)-1,2,4,5-tetrazine; bpy = 2,2′-bipyridine), were synthesised and characterised by spectroscopic and electrochemical techniques. The comproportionation constant K_c = 10^7.0 of the mixed-valent species [(NC)₄Ru(μ-bptz)Ru(CN)₄]³⁻ as obtained by oxidation of 1⁴⁻ in CH₃CN is much lower than the K_c = 10^15.0 previously detected for [(H₃N)₄Ru(bptz)Ru(NH₃)₄]⁵⁺, reflecting the competition between CN⁻ and bptz for the π-electron density of the metals. Comparison with several other bptz-bridged diruthenium(II,III) complexes reveals an approximate correlation between K_c and the diminishing effective π acceptor capacity of the ancillary terminal ligands. In addition to the intense MLCT absorption at λ_max = 624 nm, the main IVCT (intervalence charge transfer) band of 1³⁻ was detected by spectroelectrochemistry at λ_max = 1695 nm (in CH₃CN; ε = 3200 M⁻¹ cm⁻¹). The experimental band width at half-height, Δν_1/2 = 2700 cm⁻¹, is slightly smaller than the theoretical value Δν_1/2 = 3660 cm⁻¹, calculated from the Hush approximation for Class II mixed-valent species. In agreement with comparatively moderate metal-metal coupling, the mixed-valent intermediate 1³⁻ was found to be EPR silent even at 4 K. The unsymmetrical mixed-valent complex [(bpy)₂Ru^II(μ-bptz)Ru^III(CN)₄]⁺, obtained in situ by bromine oxidation of 2 in CH₃CN/H₂O, displays a broad NIR absorption originating from an IVCT transition at λ_max = 1075 nm (ε ≈ 1000 M⁻¹ cm⁻¹, Δν_1/2 ≈ 4000 cm⁻¹). In addition, the lifetime of the excited-state of the mononuclear precursor complex [Ru(bptz)(CN)₄]²⁻ was measured in H₂O by laser flash photolysis; the obtained value of τ = 19.6 ns reveals that bptz induces a metal-to-ligand electronic delocalisation effect intermediate between that induced by bpy and bpz (bpz = 2,2′-bipyrazine) in analogous tetracyanoruthenium complexes.     

Synthesis, characterization, and magnetic study of pyrazine bridged polymeric complexes of copper(II)

The synthesis, structural characterization and magnetic property of two new coordination polymers [Cu(pyz)(μ-CH₃CO₂)₄]_n (1) and [Cu(pyz)(μ-CCl₃CO₂)₄]_n (2) (pyz = pyrazine) are reported. Here, the carboxylato bridged two dinuclear copper(II) complexes are linked through pyrazine giving a 1-D alternating chain. The magnetic property of the complexes indicates a significant difference originated from the introduction of electron withdrawing substituent on the bridging dicarboxylate. Complex 1 exhibits strong antiferromagnetic interactions with J = −344.61 cm⁻¹, whereas 2 exhibits comparatively less strong antiferromagnetic coupling with J = −238.53 cm⁻¹.     

Multinuclear magnetic resonance study of Pt(II) compounds with sulfoxide ligands and crystal structures of complexes of the types [Pt(R2SO)X3] and Pt(R2SO)2Cl2

Pt(II) complexes of the types K[Pt(R₂SO)X₃], NR₄[Pt(R₂SO)X₃] and Pt(R₂SO)₂Cl₂ (where X = Cl or Br) were characterized by multinuclear magnetic resonance spectroscopy (¹⁹⁵Pt, ¹H and ¹³C). In ¹⁹⁵Pt NMR, the chloro ionic compounds have shown signals between −2979 and −3106 ppm, while the cis disubstituted complexes were observed at higher fields, between −3450 and −3546 ppm. The signal of the compound trans-Pt(DPrSO)₂Cl₂ was found at higher field (−3666 ppm) than its cis analogue (−3517 ppm), since π-back-donation is considerably less effective in the trans geometry. In ¹H NMR, a single signal was observed for the sulfoxide in [Pt(DMSO)Cl₃]⁻, but for the other more sterically hindered ligands, two series of resonances were observed for the protons in α and β positions. The coupling constant ³J(¹⁹⁵Pt-¹H) are between 15 and 33 Hz. The ¹³C NMR results were interpreted in relation to the concept of inversed polarization of the π sulfoxide bond. The ²J(¹⁹⁵Pt-¹³C) values vary between 35 and 66 Hz, while a few ³J(¹⁹⁵Pt-¹³C) couplings were observed (13-26 Hz). The crystal structures of five monosubstituted ionic compounds N(n-Bu)₄[Pt(TMSO)Cl₃], N(Me)₄[Pt(DPrSO)Cl₃], K[Pt(EMSO)Cl₃], K[Pt(TMSO)Br₃] · H₂O and N(Et)₄[Pt(DPrSO)Br₃] and one disubstituted complex cis-Pt(DBuSO)₂Cl₂ were determined. The trans influence of the different ligands is discussed.