In situ spectroelectrochemical investigation of Pt(II/IV) oxidation in aqueous solution using X-ray absorption spectroscopy

The oxidation from to in HCl aq. was studied in situ by combining electrochemistry with XAFS spectroscopy. During the oxidation of , isosbestic points were observed in Pt L_III and L_II XANES spectra as a function of time, indicating that the Pt(II/IV) redox equilibrium is the only reaction in the system. The Pt L_III and L_II X-ray absorption edge energies of the initial Pt^IICl₄²⁻ are 11562.9 and 13271.8 eV, respectively, while those of the electrolyzed species are 11564.6 and 13273.7 eV which are identical with those of a reference sample. The coordination of the electrolyzed species was characterized by structural parameters derived from the EXAFS curve fit, and identified to .     

A novel copper(II)-radical complex with ferromagnetic interaction: Synthesis, crystal structure and magnetic properties

A novel copper(II)-radical complex [Cu(NITmPy)(PDA)(H₂O)] · (H₂O) (1) (NITmPy = 2-(3′-pyridyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide, H₂PDA = 2,6-pyridinedicarboxylic acid) has been synthesized and structurally characterized by X-ray diffraction methods. It crystallizes in the triclinic space group . The Cu(II) ion exists in a distorted square pyramid environment. The molecules of [Cu(NITmPy)(PDA)(H₂O)] · (H₂O) are connected as a two-dimensional structure by the intermolecular hydrogen bonds. Magnetic measurements show intramolecular ferromagnetic interactions between NITmPy and Cu(II) ion and intermolecular antiferromagnetic interactions in 1.     

Interaction of gold(I) with thiosulfate-sulfite mixed ligand systems

The system was studied at 25 °C and at I = 0.1 M NaClO₄ using hydrodynamic voltammetry, gold potentiometry, UV-Vis spectrophotometry and Raman spectroscopy. The presence of two mixed-ligand species, Au(S₂O₃)(SO₃)³⁻ and , was detected from the Raman experiments and supported by the gold potentiometric experiments. The stepwise formation constant, log K_11r, for the reaction was found to be 1.1 (r = 1) and 4.8 (r = 2) from the hydrodynamic voltammetric experiments.     

Solid state coordination chemistry of molybdenum oxides with 1,2,3-triazole (Htrz): The crystal structures of [Cu(I)Cu(II)2(trz)2Mo4O13(OH)], [MoO3(Htrz)0.5] and [Cu(I)trz]

Hydrothermal chemistry was used to prepare the bimetallic organic-inorganic hybrid oxide [Cu(I)Cu(II)₂(trz)₂Mo₄O₁₃(OH)] · 6H₂O (1 · 6H₂O). The structure consists of chains linked through into a three-dimensional framework. The structures of the simple metal-triazole phases [MoO₃(Htrz)_0.5] (2) and [Cu(trz)] (3) are also reported. Compound 2 is two-dimensional, constructed from corner-sharing {MoO₅N} octahedra. Compound 3 consists of {Cu(trz)}_n chains linked through weak Cu?Cu contacts into a virtual layer.     

Square-planar and trigonal prismatic silver(I) in bipyrimidine and oxalate bridged tetranuclear complexes and one-dimensional compounds: Synthesis and crystal structures

The reaction of [Ag₄(hfac)₄(THF)₂] (hfac⁻ = 1,1,1,5,5,5-hexafluoroacetylacetonate, THF = tetrahydrofurrane) with 2,2′-bipyrimidine (bpm) leads to single crystals. They crystallise in the triclinic system, space group . Their structure consists of [Ag₄(hfac)₄(μ₂-bpm)₃] tetranuclear complexes. In this complex, Ag(I) ions adopt distorted square planar and trigonal prismatic geometries. When [Ag₄(hfac)₄(THF)₂] is replaced by monohydrated silver(I) perchlorate, a one-dimensional (1D) compound with a formula of [[Ag(μ₂-bpm)]⁺]_n, is obtained as single crystals. They crystallise in the monoclinic system, space group P2₁/c. Their structure consists of [[Ag(μ₂-bpm)]⁺]_n chains separated by non-coordinated perchlorate ions. In the chains, the Ag(I) centres adopt a square planar geometry. Finally, starting from [[Ag(μ₂-bpm)]⁺]_n, and sodium oxalate , another 1D compound with a formula of [Ag(μ₂-bpm)(μ₂-ox)]_n, 4nH₂O is obtained as single crystals. They crystallise in the triclinic system, space group . In these chains, bipyrimidine and oxalate are alternate. They generate a square planar geometry around the Ag(I) cations.     

Metallocycle and ring-opening polymerization of silver(I) complexes with 1,3-bis(4,5-dihydro-1H-imidazol-2-yl)benzene ligand

The reaction of 1,3-bis(4,5-dihydro-1H-imidazol-2-yl)benzene (bib) ligand with silver(I) nitrate in a 1:1 molar ratio generated a [2 + 2] metallocyclic complex [Ag₂(bib)₂](NO₃)₂ · 2H₂O, in which bib ligand displayed in cis configuration. When the additional competing ligands/counterions, such as oxlate salt, 1,2-diaminoethene (en), 1,3-diaminopropane (pn), and were introduced, respectively, to the above-mentioned reaction solution, ring-open polymerization of sliver(I) complexes {[Ag(bib)]NO₃ · H₂O}_n (1), {[Ag(bib)₂]X}_n ( (2), (3)), {[Ag₂(bib)₂(NO₂)](NO₂) · 19/8H₂O}_n (4) and {[Ag₂(bib)₂](V₄O₁₂)_0.5 · 3H₂O · 2MeCN}_n (5) were generated. In compounds 1, 4 and 5, bib ligand adopts trans configuration and twists around the Ag-Ag axis, giving rise to single-stranded helical structure with short adjacent Ag?Ag distances of 3.56, 3.56, 3.50 and 3.63 Å, respectively. Compounds 2 and 3 are 1D coordination polymers fusing the [2 + 2] metallocycle [Ag₂(bib)₂]²⁺, in which bib ligand exhibits in cis configuration and the metallocycles have longer Ag?Ag distances of 8.52 Å in 2 and 8.61 Å in 3 along with the strong intracyclicπ-π interactions between phenyl groups. Cis and trans configurations of bib coexist in solution and crystallize in complexes 1 and 2 in the solid state in the presence of en or pn. The solution of 1 and 2 can be converted into 3 via the addition of the bulky counter anion or into 4 through introduction of the competing ligand/conuterion .     

Construction of two novel tungsten(VI)-silver(I) mixed metal clusters controlled by bis(diphenylphosphino) methane and coordinated inorganic anions

By the reaction of [Ag₃(dppm)₃I₂]I with (NH₄)₂WS₄ in MeCN/DMF (1:1), a trigonal bipyramid-shaped cluster [Ag₃ I (dppm)₂ WS₄] (1) was isolated [dppm = bis (diphenylphosphino) methane]. By the reaction of (NH₄)₂WS₄ with AgSCN and dppm in MeCN/DMF (1:1) in the presence of 1,10-phenathroline, an insect-shaped cluster [Ag₄ (SCN)₂ (dppm)₄WS₄]·H₂O (2) was synthesized. Compounds 1 and 2 were characterized by single-crystal X-ray diffraction, luminescence, IR, UV-Vis, ¹H and ³¹P NMR spectroscopy. In 1, and μ₃-I are coordinated to three Ag atoms, which are further bridged by two dppm ligands. In 2, Ag1 and Ag4 are coordinated by two P atoms from two dppm ligands, one μ₃-S from and one S atom from SCN⁻ while Ag2 and Ag3 are coordinated by one μ₂-S atom and one μ₃-S atom from , two P atoms from two dppm ligands.     

Kinetics and mechanism of the oxidation of oxalic acid by tetrachloroaurate(III) ion

The oxidation of oxalic acid by tetrachloroaurate(III) ion in 0.005 ? [HClO₄] ? 0.5 mol dm⁻³ is first order in and a fractional order in [oxalic acid], the reactive entities being AuCl₃(OH)⁻ and ions. The pseudo first-order rate, k_obs, with respect to [Au(III)], is retarded by increasing [H⁺] and [Cl⁻]. The retardation by H⁺ ion is caused by the dissociation equilibrium . A mechanism in which a substitution complex, is formed from AuCl₃(OH)⁻ and ions prior to its rate limiting disproportionation into products is suggested. The rate limiting constant, k, has been evaluated and its activation parameters are reported. The equilibrium constant K₁ for the formation of the substitution complex and its thermodynamic parameters are also reported.     

Effects of bis(salicylidene)trimethylenediamine and 2,2′-bipyridyl on luminescence and extraction of tris(pivaloyltrifluoroacetonato)Eu(III)

The UV, excitation and luminescence spectra of EuA₃B to be the extracted species as well as the extraction of Eu(III) with pivaloyltrifluoroacetone, HA, and/or Lewis bases, B (2,2′-bipyridyl, bpy, and bis(salicylidene)trimethylenediamine, H₂saltn) into CHCl₃ were measured. The results are summarized: the stability constants of EuA₃bpy and EuA₃H₂saltn complexes are 5.85 ± 0.05 and 2.95 ± 0.06 as , respectively. The present results suggest that because of intramolecular hydrogen bonding, the stability and luminescence of the H₂saltn complex including the quantum yield are smaller than those of the bpy complex. The weaker luminescence is also concerned with the fact that the less stable complexes easily dissociate in solvents to diminish the essential concentration.     

A new tyrosinase model with 1,3-bis[(2-dimethylaminoethyl)iminomethyl]benzene: Binuclear copper(I) and phenoxo/hydroxo-bridged dicopper(II) complexes

The ligand 1,3-bis[(2-dimethylaminoethyl)iminomethyl]benzene (baib) reacts with [Cu(MeCN)₄][ClO₄] to form a binuclear copper(I) complex . Crystal structure analysis reveals that the distorted tetrahedral coordination of each copper(I) center is satisfied by one bidentate arm of each ligand. The complex undergoes ready aromatic ring hydroxylation at position 2 of the phenyl ring when reacted with molecular oxygen in MeCN/MeOH/CH₂Cl₂, producing a four-coordinate μ-phenoxo- and μ-hydroxo-bridged dicopper(II) complex, [Cu₂(baib-O)(OH)(OClO₃)₂] · 1.5H₂O (2) (baib-OH: 1,3-bis[(2-dimethylaminoethyl)iminomethyl]phenol). This reaction mimics the reactivity of the copper monooxygenase tyrosinase. A trend is observed for the extent of aromatic ring hydroxylation (25 °C): MeCN > MeOH > CH₂Cl₂. Cyclic voltammetric experiment of 1 in MeCN reveals an appreciably high redox potential (anodic peak potential, E_pa = 0.69 V versus SCE) for the redox process. Complex 2 has been characterized by single-crystal X-ray crystallography. Variable temperature (60-300 K) magnetic susceptibility measurements on 2 establish that the copper(II) centers in 2 are antiferromagnetically coupled (2J = −280 cm⁻¹).     

Unusual kinetic and thermodynamic control in the formation of Pt(II)-complexes of a new C1-symmetric phosphine-phosphite

Versatile synthetic routes have been applied to prepare the new asymmetric phosphine-phosphite ligands 8 and 12. The chiral ligands have been designed so that the corresponding ligating groups have similar electronic properties and steric bulk, but 8 forms 6-, while 12 forms 7-membered chelate rings in their coordination compounds. The chelate size variation results in a markedly different coordination behavior towards Pt(II). In their reactions with Pt(PhCN)₂Cl₂ at 1:1 stoichiometry 12 forms the expected Pt(12)Cl₂ complex, while 8 gives the cation quantitatively. In the kinetically controlled reaction is the major product even at a 8:Pt(PhCN)₂Cl₂ = 1:2 ratio. Most interestingly, at 1:1 ligand to precursor ratio, cation rearranges to Pt(8)Cl₂ within one day, indicating that the neutral complex is thermodynamically more favorable.     

Double salts of copper(I) chloride incorporated hydroxylpyrimidine and tetrazole ligands

Hydrothermal reaction of copper(II) chloride with 2-hydroxypyrimidine generated double salt of [Cu₂Cl(μ₄-pymo)] (1) (Hpymo = hydroxylpyrimidine) while hydrothermal treatment of CuCl₂, NaN₃ and acetonitrile resulted in double salt of [Cu₂(mtta)Cl] (2) (Hmtta = 5-methyltetrazole) in which in situ [2 + 3] cycloaddition reactions of acetonitrile with azide formed mtta ligand. X-ray single crystal structural analyses revealed that 1 shows a two-dimensional layer formed by fusion of one-dimensional structural motifs. The two-dimensional layers in 1 are held together by C-H?Cl hydrogen bonds to form three-dimensional supramolecular array. Compound 2 has a three-dimensional framework constructed from ribbons and [Cu₈Cl₄]⁴⁺ units. Uncommon coordination modes of μ₄-1,2κO:3κN:4κN′ pymo and μ₄-Cl (Cl at the apex of a Cu₄Cl square pyramid) in 1 and μ₄-η¹:η¹:η¹:η¹ mtta in 2 were also observed. The short Cu(I)?Cu(I) distances were found in 1 and 2, indicating the existence of Cu(I)?Cu(I) interactions.     

Crystal structure, magnetic and electrochemical properties of five-coordinate copper (II) complexes with 1,10-phenanthroline-5,6-dione

Three new five-coordinate Cu^II complexes, [Cu(tpy)(phen-dione)](PF₆)₂, [Cu(phen)(phen-dione)Cl]PF₆ and [Cu(bpy)(phen-dione)Cl]PF₆ (tpy = 2,2′;6′,2″-terpyridine, phen = 1,10-phenanthroline and phen-dione = 1,10-phenanthroline-5,6-dione) have been prepared and characterized by elemental analysis, IR and UV-Vis spectroscopies and cyclic voltammetry.The complex of [Cu(tpy)(phen-dione)](PF₆)₂ crystallized with one molecule of acetonitrile. The ortep drawing of [Cu(tpy)(phen-dione)](PF₆)₂ · CH₃CN shows that the coordination geometry around Cu^II is a distorted trigonal- bipyramid. Due to the steric hindrance of in the unit cell, the tpy ligands in each complex cation cannot interact in a π-π fashion. The effective magnetic moment (μ_eff) of the complexes was measured by the Evans method. The cyclic voltammograms at Pt disk electrode for these complexes display only one reversible Cu(II)/Cu(I) redox couple.     

Anionic effects on the formation of tridentate 4′-chloro-2,2′:6′,2″-terpyridine copper(II) complexes having 1:1 or 1:2 ratio of metal and ligand and their crystal symmetry

A facile synthetic procedure has been used to prepare one five-coordinate and four six-coordinate copper(II) complexes of 4′-chloro-2,2′:6′,2″-terpyridine (tpyCl) ligand with different counterions (, , , , and ) in high yields. They are formulated as [Cu(tpyCl-κ³N,N′,N′′)(SO₄-κO)(H₂O-κO)] · 2H₂O (1), trans-[Cu(tpyCl-κ³N,N′,N″)(NO₃-κO)₂(H₂O-κO)] (2), [Cu(tpyCl-κ³N,N′,N″)₂](BF₄)₂ (3), [Cu(tpyCl-κ³N,N′,N″)₂](PF₆)₂ (4) and [Cu(tpyCl-κ³N,N′,N″)₂](ClO₄)₂ (5) and versatile interactions in supramolecular level including coordinative bonding, O-H?O, O-H?Cl, C-H?F, and C-H?Cl hydrogen bonding, π-π stacking play essential roles in forming different frameworks of 1-5. It is concluded that the difference of coordination abilities of the counterions used and the experimental conditions codominate the resulting complexes with 1:1 or 1:2 ratio of metal and ligand.     

Coordination versatility of 1,3-bis[3-(2-pyridyl)pyrazol-1-yl]propane: Co(II) and Ni(II) complexes

The ligand 1,3-bis[3-(2-pyridyl)pyrazol-1-yl]propane (L⁸) has afforded six-coordinate monomeric and dimeric complexes [(L⁸)Co^II(H₂O)₂][ClO₄]₂ (1), [(L⁸)Ni^II(MeCN)₂][BPh₄]₂ (2), [(L⁸)Ni^II(O₂CMe)][BPh₄] (3), and . The crystal structures of 1, 2 · MeCN, 3, and 4 revealed that the ligand L⁸ is flexible enough to expand its coordinating ability by fine-tuning the angle between the chelating fragments and hence folds around cobalt(II)/nickel(II) centers to act as a tetradentate chelate, allowing additional coordination by two trans-H₂O, cis-MeCN, and a bidentate acetate affording examples of distorted octahedral , , and coordination. The angles between the two CoN₂/NiN₂ planes span a wide range 23.539(1)° (1), 76.934(8)° (2), and 69.874(14)° (3). In contrast, complex 4 is a bis-μ-1,3-acetato-bridged (syn-anti coordination mode) dicobalt(II) complex [Co?Co separation: 4.797(8) Å] in which L⁸ provides terminal bidentate pyridylpyrazole coordination to each cobalt(II) center. To our knowledge, this report provides first examples of such a coordination versatility of L⁸. Absorption spectral studies (MeCN solution) have been done for all the complexes. Complexes 1-3 are uniformly high-spin. Temperature-dependent (2-300 K) magnetic studies on 4 reveal weak ferromagnetic exchange coupling between two cobalt(II) (S = 3/2) ions. The best-fit parameters obtained are: Δ (axial splitting parameter) = −765(5) cm⁻¹, λ (spin-orbit coupling) = −120(3) cm⁻¹, k (orbital reduction factor) = 0.93, and J (magnetic exchange coupling constant) = +1.60(2) m⁻¹.     

Influence of coanions on construction of copper(II)/4,4′-dipyridyl sulfide(dps) coordination polymers

The influence of coanion on self-assembly of CuSO₄ and 4,4′-dipyridyl sulfide (dps) was studied in this paper. During the formation of Cu(II)/dps coordination polymers, coanions Cl⁻, SCN⁻ and were added in the solution respectively. Three novel coordination polymers were obtained, {[Cu(dps)₂ · (SO₄)₂][Cu(dps) · Cl · (H₂O)₂]₂ · 12H₂O}_n (1 · 12H₂O, a 3D network), {[Cu(SCN)₂(dps)(CH₃OH)₂][Cu(dps)₂ · SO₄][Cu(dps)(CH₃CH₂OH)₂ · SO₄] · 5H₂O}_n (2 · 5H₂O, a 3D network), and {[Cu(dps)₂(H₂O)₂] · (PF₆)₂ · 3H₂O}_n (3 · 3H₂O, a 2D lattice network). Different coanion shows different influence on framework construction. In 1 and 2, Cl⁻ and SCN⁻ act as terminal ligands and similar 3D frameworks were composed of [Cu(dps)] layer with larger cavity (ca. 400 Å) and sulfate bridge; in 3, replaces entirely and the 3D framework was broken due to the removal of bridging anions. However, a 2D [Cu(dps)]₄ undulating grid was preserved in 3.     

Rapid synthesis of bis (2,2′-bipyridine) nitratocopper(II) nitrate using a hydrothermal method and its application to dye-sensitized solar cells

In this study we synthesized bis (2,2′-bipyridine) nitratocopper(II) nitrate in order to examine its the crystal structure, optical property and application to dye-sensitized solar cells (DSSCs). Single X-ray analysis results revealed that the acquired complex exhibited five-coordination with four nitrogen atoms of bipyridine and the oxygen bond of the ion. The reflectance UV-Vis absorptions showed three absorptions that were assigned to ligand-to-ligand at around 230-350 nm, metal-to-ligand charge transfer at around 350-600 nm, and d-d transfer at around ∼650 nm. Cyclic voltammetry in acetonitrile revealed a reversible Cu(I) → Cu(II) oxidation process at a highest occupied molecular orbital (HOMO) and a lowest unoccupied molecular orbital (LUMO) levels of −4.692 and −4.071 eV, respectively. The photoelectric efficiency in DSSCs was approximately 0.032% with the nanometer-sized TiO₂ in the condition of an open-circuit voltage (V_oc) of 0.346 V, a short-circuit current density (J_sc) of 0.166 mA/cm² at an incident light intensity of 100 mW/cm².     

Heterodimetallic Pd-based carboxylate-bridged complexes: Synthesis and structure of single-crystalline Pd-M (M = Mn, Co, Ni, Cu, Zn, Nd, Eu, Ce) acetates

A series of crystalline Pd^II-based heterodimetallic acetate-bridged complexes containing the transition (Mn^II, Co^II, Ni^II, Cu^II), post-transition (Zn^II) and rare-earth (Ce^IV, Nd^III, Eu^III) metals were synthesized starting from Pd₃(OOCMe)₆ and the complementary metal(II, III) acetates. The crystal and molecular structures of the binuclear Pd^IIM^II(μ-OOCMe)₄L (M = Mn, Co, Ni, Zn; L = H₂O, MeCN), trinuclear and tetranuclear (M = Nd, Eu) and complexes were established by X-ray diffraction.     

Oligomerization of the Cu(II) and Ni(II) tetraazaannulene complexes: A pulse radiolysis study of the associated reaction mechanism

The oligomerization of [Cu^II(H_x(tmdnTAA))]^x+ (x = 0, 1, 2 and (tmdnTAA))²⁻ is 2,4,9,11-tetramethyl-dinaphto[14]-2,4,6,9,11,13-hexaeneN₄) was initiated in homogeneous solution via the reaction of this Cu(II) complex with pulse radiolytically generated radicals. The reaction produces Cu(III) intermediates which are rapidly converted to Cu(II) ligand-radical species. In contrast to the mechanism proposed for the electrochemical oligomerization, where the local concentration of radicals is probably high, the reaction kinetics in homogeneous solution is propagated by a process where the Cu(II) ligand-radical precursors react with [Cu^II(H_x(tmdnTAA))]^x+.     

Synthetic, spectroscopic and X-ray crystallographic structural studies on copper(II) complexes of the aminoguanizone of pyruvic acid

Copper(II) complexes of general empirical formula, CuX(Hagpa) · nH₂O and Cu(agpa) · 2H₂O (H₂agpa = aminoguanizone of pyruvic acid, X = Cl⁻, Br⁻, , CH₃COO⁻, , n = 0, 1, 1.5, 2), have been synthesized and characterized by IR, EPR spectroscopy and X-ray crystallography. The IR spectra of the complexes showed the ONN coordination of the ligand to copper(II) ion. The crystal structures of H₂agpa · H₂O and complexes [Cu(Hagpa)Br] and [Cu₂(Hagpa)₂(H₂O)₂(SO₄)] · DMSO showed an invariable conformation and coordination mode for the uninegatively charged tridentate ligand and revealed the formation of linear polymers in which bromide or sulfate anions bridge the copper(II) ions. The EPR spectra for complexes CuX(Hagpa) · nH₂O are described by spin Hamiltonian for S = 1/2, without hyperfine structure. The g-tensor is symmetrical for Cu(agpa) · 2H₂O, has tri-axial anisotropy for sulfate complexes, and exhibits axial symmetry for the other compounds investigated.