Kinetic studies of tris(2,2′-bipyridine)iron(III) perchlorate with cobaloxime, [Co(dmgBF2)2(H2O)2]

The kinetics of the reduction of by Co(dmgBF₂)₂(H₂O)₂ in 0.041 M HNO₃/NaNO₃ was found to be first-order in both the oxidizing and reducing agents and the second-order rate constant is given by k_obs = k₁ + k₂K[Cl⁻], with k₁=1.59 × 10⁶ M⁻¹ s⁻¹and k₂K = 1.83 × 10⁸ M⁻² s⁻¹, at 25 °C. The term that is first-order in [Cl⁻] is attributed to the formation of an ion-pair between and Cl⁻. For k₁, the activation parameters ΔH* and ΔS* are 2.22 ± 0.02 kcal mol⁻¹ and −22.7 ± 0.8 cal mol⁻¹ K⁻¹, respectively. The self-exchange rate constant of k₂₂ ≈ 8.7 × 10⁻³ M⁻¹ s⁻¹ for was estimated using Marcus theory and the known self-exchange rate constant for .     

New applications of ruthenium solar cell sensitizers N3 and N719 as luminescence turn-on anion sensors

Optical sensing of F⁻, Cl⁻, Br⁻, I⁻, OAc⁻, , , and by cis-dithiocyanatobis(2,2′-bipyridyl-4,4′-dicarboxylic acid)ruthenium(II) (N3) and bis(tetrabutylammonium) cis-dithiocyanatobis(2,2′-bipyridine-4-COOH,4′-COO⁻)ruthenium(II) (N719) have been investigated in dimethyl sulfoxide (DMSO), by means of UV-Vis absorption and emission spectrophotometric titrations. Additions of F⁻, OAc⁻, and in DMSO solution caused obvious UV-Vis spectral changes with appearance of several isosbestic points, and remarkable emission enhancements along with large blue shifts in emission bands. The values of F⁻-induced emission intensity enhancement factor (emission quantum yield enhancement factor), I/I₀ (φ/φ₀), were found to be 40 (86) and 38 (58) for N3 and N719, respectively. No obvious spectral changes were observed upon addition of Cl⁻, Br⁻, I⁻, and in DMSO solutions. Luminescent F⁻ sensing in DMSO/H₂O (4:1, v/v) has also been demonstrated to be operative with a luminescence enhancement factor of 12, indicating that N3 is very potential for practical application as fluorescent anion sensor in aqueous solution. An interaction mechanism of anion-induced deprotonation of N3 and N719 was confirmed, and the deprotonation reaction equilibrium constants of N3 and N719 were derived as well.     

An unprecedented tetranuclear Cu(II) cluster, exclusively bridged by two μ3,η-hydrogenphosphate anions: synthesis, structure, and magnetic properties

A novel tetranuclear μ₃,η³- Cu(II) complex with a new coordination mode of a hydrogenphosphato bridge, [Cu₄(di-2-pyridylamine)₄(μ₃,η³-HPO₄)₂(H₂O)₂(NO₃)₂](NO₃)₂(H₂O)₂ has been synthesised and characterised structurally, spectroscopically and magnetically. The geometry around the Cu(II) ions is distorted square pyramidal for Cu(1) and an intermediate between square pyramidal and trigonal pyramidal. The magnetic susceptibility measurements have been fit for a weak antiferromagnetic interaction of J = −10.3(1) cm⁻¹ between outer Cu ions and J = −5.3(2) cm⁻¹ between inner Cu atoms.     

Structural and thermal properties of three novel alkaline earth metal coordination polymers based on 5-hydroxyisophthalate ligand

Three novel coordination polymers [Ca(5-OH-BDC)(H₂O)₃] · H₂O (1), [Sr(5-OH-BDC)(H₂O)₄] · H₂O (2) and [Ba(5-OH-BDC)(H₂O)₃] (3) were obtained by self-assembly of the corresponding alkaline earth metal chlorate with a ligand, 5-hydroxyisophthalic acid (5-OH-H₂BDC), and their structures were determined by X-ray crystallography. The results revealed that complexes 1, 2 and 3 have two-dimensional network with (6, 3) topology observed in the bc plane. Moreover, the two-dimensional layers can be assembled into three-dimensional supramolecular architectures via intermolecular hydrogen bonds. The two carboxylate groups of 5-OH-BDC²⁻ ligand adopt the same coordination mode in complex 1 as that in 2: a μ3-η2:η1 mode and a chelated mode while in complex 3 they coordinate to Ba(II) ions in a μ3-η2:η1 mode and a monodentate mode, which is not observed in previous reports. The constant-volume combustion energies, Δ_cU, of these complexes were determined by a precise rotating-bomb calorimeter at 298.15 K, then their standard enthalpies of combustion, , and the standard enthalpies of formation, , have been calculated.     

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.     

Ruthenium(II) complexes possessing the η-p-cymene ligand

Complexes possessing a soft donor η⁶-arene and hard donor acetylacetonate ligand, [(η⁶-p-cymene)Ru(κ²-O,O-acac-μ-CH)]₂[OTf]₂ (1) (OTf = trifluoromethanesulfonate; acac = acetylacetonate) and {Ar′ = 3,5-(CF₃)-C₆H₃}, were prepared and fully characterized. The lability of the μ-CH linkage for complex 1 and the THF ligand of 2 allow access to the unsaturated cation [(η⁶-p-cymene)Ru(κ²-O,O-acac)]⁺. The reaction of with KTp {Tp = hydridotris(pyrazolyl)borate} produces . The azide complex forms upon reaction of with N₃Ar (Ar = p-tolyl), and reaction of with CHCl₃ at 100 °C yields the chloride-bridged binuclear complex . The details of solid-state structures of [(η⁶-p-cymene)Ru(κ²-O,O-acac-μ-CH)]₂[OTf]₂ (1), and are disclosed.     

A rare all-Mn decametallic cage from distorted face-sharing cubes

The preparation and crystal structure of a decametallic Mn^II carboxylate cluster containing neutral 2-pyridinealdoxime, (py)C(H)NOH, and its anion, (py)C(H)NO⁻, is reported. The reaction between Mn(O₂CPh)₂ · 2H₂O and (py)C(H)NOH in CH₂Cl₂, in the presence of NH₄PF₆, produces the complex [Mn₁₀(O₂CPh)₁₂{(py)C(H)CNO}₆{(py)C(H)NOH}₂](PF₆)₂ · 2.6CH₂Cl₂ · 1.3H₂O (1 · 2.6CH₂Cl₂ · 1.3H₂O) in good yield. The cationic complex consists of ten Mn^II ions assembled together by four η¹:η¹:η³:μ₄ and two η¹:η¹:η²:μ₃ oximato(−1) ligands, and four η¹:η²:μ₃ ligands to form an unprecedented core, where R = PhCO and R′ = (py)C(H)N. Peripheral ligation is provided by a combination of bridging benzoates and chelating (py)C(H)NOH ligands. Dc magnetic susceptibility studies reveal the presence of dominant antiferromagnetic interactions leading to a spin ground-state of S_T = 0. A survey of the ternary reaction system is attempted with comparisons to previously reported complexes.     

Syntheses and structural analyses of chiral rhenium containing amines of the formula (η-C5H5)Re(NO)(PPh3)((CH2)nNRR′) (n = 0, 1)

The reaction of the racemic chiral methyl complex (η⁵-C₅H₅)Re(NO)(PPh₃)(CH₃) (1) with CF₃SO₃H and then NH₂CH₂C₆H₅ gives [(η⁵-C₅H₅)Re(NO)(PPh₃)(NH₂CH₂C₆H₅)]⁺ ([4a-H]⁺; 73%), and deprotonation with t-BuOK affords the amido complex (η⁵-C₅H₅)Re(NO)(PPh₃)(NHCH₂C₆H₅) (76%). Reactions of 1 with Ph₃C⁺ X⁻ and then primary or secondary amines give [(η⁵-C₅H₅)Re(NO)(PPh₃)(CH₂NHRR′)]⁺ X⁻ ([6-H]⁺ X⁻; R/R′/X = a, H/NH₂CH₂C₆H₅/BF₄; a′, H/NH₂CH₂C₆H₅/PF₆; b, H/NH₂CH₂(CH₂)₂CH₃/PF₆; c, H/(S)-NH₂CH(CH₃)C₆H₅/BF₄); d, CH₂CH₃/CH₂CH₃/PF₆; e, CH₂(CH₂)₂CH₃/CH₂(CH₂)₂CH₃/PF₆; f, CH₂C₆H₅/CH₂C₆H₅/PF₆; g, -CH₂(CH₂)₂CH₂-/PF₆; h, -CH₂(CH₂)₃CH₂-/PF₆; i, CH₃/CH₂CH₂OH/PF₆ (62-99%). Deprotonations with t-BuOK afford the amines (η⁵-C₅H₅)Re(NO)(PPh₃)(CH₂NRR′) (6a-i; 99-40%), which are more stable and isolated in analytically pure form when R ≠ H. Enantiopure 1 is used to prepare (R_ReS_C)-[6c-H]⁺, (R_ReS_C)-6c, (S)-[6g-H]⁺, and (S)-6g. The crystal structures of [4a-H]⁺, a previously prepared NH₂CH₂Si(CH₃)₃ analog, [6a′,d,f,h-H]⁺, (R_ReS_C)-6c, and 6f are determined and analyzed in detail, particularly with respect to cation/anion hydrogen bonding and conformation. In contrast to analogous rhenium containing phosphines, 6a-i show poor activities in reactions that are catalyzed by organic amines.     

Synthesis and structural investigation of vanadocene(IV) complexes of non-linear pseudohalides

Two series of vanadocene complexes of the type (Cp′ = η⁵-C₅H₅, η⁵-C₅H₄Me; X = dicyanamide, tricyanomethanide, dicyanonitrosomethanide) were prepared by the reaction of appropriate vanadocene dichloride complex with alkali salt of non-linear pseudohalide. The bonding mode of pseudohalide ligands was determined by spectroscopic measurements and X-ray diffraction analyses.     

Luminescent metalloreceptors with pendant macrocyclic ionophore: Synthesis, characterization, electrochemistry and ion-binding study

Metalloreceptors containing ruthenium(II) bipyridine unit as fluorophore and pendant macrocyclic units as ionophore have been synthesized and their luminescence and electrochemical properties have been investigated. Ion-binding study of these fluoroionophore with the anions F⁻, Cl⁻, Br⁻, I⁻, , , , , CH₃COO⁻, and and cations Na⁺, K⁺, Mg²⁺, Ca²⁺, Zn²⁺, Ba²⁺, Sr²⁺ Cd²⁺, Hg²⁺, Pb²⁺ and Cu²⁺, monitored by luminescence and ¹H NMR spectral changes, reveal strong interactions of and F⁻ for 2 and 3 and of Cu²⁺ only for 3. Luminescence titrations for 2 and 3 have been carried out to determine binding constants (K_s), and the calculated values are in the range 2.85 × 10² to 4.48 × 10⁴ M⁻¹. The ¹H NMR spectral changes for 2 and 3 with the addition of increasing concentration of F⁻ and exhibit substantial low-field shift of the CONH proton indicating its involvement in complex formation with the anions. The adduct of 2 and 3 have been isolated and characterized by ¹H and ³¹P NMR, mass and IR spectroscopy. The results are discussed in light of selectivity, structures of the anion bound complexes and their luminescence property.     

A seven-coordinate Fe compound: [Fe{O(CH2CO2)2}(H2O)2(NO3)]. Preparation, structure and magnetic properties

A seven-coordinate Fe^III complex, [Fe(oda)(H₂O)₂(NO₃)], was obtained after dissolving Fe(NO₃)₃ · 9H₂O in an aqueous solution of oxydiacetic acid (H₂oda) at room temperature. In the solid state, the Fe^III center adopts a pentagonal bipyramid geometry with an {FeO₇} core formed by a tridentate oda²⁻ and a bidentate in the equatorial plane, and two axial water molecules. Magnetic measurements and EPR spectra revealed the presence of S = 5/2 Fe^III centers with rhombic zero field splitting parameters (D = 0.81 cm⁻¹, E/D = 0.33 ). Weak antiferromagnetic interactions with J ≈ −0.06 cm⁻¹ operating between neighboring Fe ions connected through Fe-O-C-O?H-O-Fe paths are estimated using the molecular field approximation.     

The R* rule and energy flux in a plant-nutrient ecosystem

The R* rule predicts that the species that can survive in steady state at the lowest level of limiting resource, R*, excludes all other species. Simple models indicate that this concept is not necessarily consistent with Lotka's conjecture that an ecological system should evolve towards a state of maximum power, Max(G), where G is the power, or rate of biomass production of the system. To explore the relationship in detail, we used a published model of a plant-nutrient system in which a plant can use various strategies, S, of allocation of energy between foliage, roots, and wood. We found that the allocation strategy, S_MinR*, that leads to , where is a limiting nutrient in soil pore water in our model (and equivalent to R* in Tilman's notation), is the same as the strategy, S_{MaxG_root}, for which energy flux to roots is maximized. However, that allocation strategy is different from the strategy, S_MaxG, that produces maximum power, or maximum photosynthetic rate, for the plant system, Max(G). Hence, we conclude that and Max(G) should not necessarily co-occur in an ecological system. We also examined which strategy, S_fit, was fittest; that is, eliminated any other strategies, when allowed to compete. The strategy S_fit differed from S_MinR*, S_MaxG, and S_{MaxG_root}, which we demonstrated mathematically. We also considered the feasible situation in which a plant is able to positively influence external nutrient input to the system. Under such conditions, the strategy, S_{MaxG_root}, that maximizes energy flux to roots was the same as the strategy, S_MaxR*, that leads to maximum concentration of available nutrient in soil pore water, , and not same as S_MinR*, for .     

Synthesis of bimetallic fulvalene and bis(cyclopentadienyl)methane derivatives of niobium and tantalum tetracarbonyl

Ring coupled bimetallic derivatives (μ-η^5:5-C₅H₄C₅H₄)[Nb(CO)₄]₂ and [μ-CH₂(η⁵-C₅H₄)₂][M(CO)₄]₂, where M = Nb and Ta have been prepared. The molecular structures of the latter two compounds have been determined: , triclinic, , a = 8.028(2) Å, b = 11.414(1) Å, c = 12.711(2) Å, α = 75.020(8)°, β = 80.34(2)°, γ = 79.46(2)°, V = 1097.3(4) ų, Z = 2, R(F) = 2.79%; [μ-CH₂(η⁵-C₅H₄)₂][Ta(CO)₄]₂, triclinic, , a = 7.815(3) Å, b = 10.275(4) Å, c = 13.135(4) Å, α = 104.25(3)°, β = 100.26(4)°, γ = 96.86(3)°, V = 991.2(6) ų, Z = 2, R(F) = 3.00%.     

Synthesis, spectroscopy, computational evaluation and first X-ray structural characterization of a primary amine containing boronium ion

Stable (CF₃SO₂)₂N⁻, I⁻ and salts of the boronium ion [(tert-butylamine)(1-methylimidazole)BH₂]⁺ have been isolated and characterized. A single-crystal X-ray structure of the salt provides the first unambiguous proof for a boronium ion supported by a primary amine ligand.     

Nucleophilic addition to the η-iridathiabenzene ligand in [η-Cp*Ir(C,S-2,5-Me2T)]FeCp

The η⁶-iridathiabenzene ring coordinated to CpFe⁺ in [η⁶-Cp*Ir(C,S-2,5-Me₂T)]FeCp⁺ (2) undergoes attack by nucleophiles. Phosphorus-donors, CN-Buⁿ, and CN⁻ add to the Ir to give products with an η⁵-coordinated iridathiabenzene ligand. Hydride (Et₃BH⁻, ) and Ph⁻ nucleophiles attack at the sulfur to give products with Ir-SH and Ir-SPh groups and an iridacyclopentadiene unit. Other reactions of 2 are described together with structure determinations of key compounds.     

Conductometric and voltammetric studies on the bis(triphenyl phosphine) ruthenium(II) complex, cis-[RuCl2(L)(PPh3)2], where L: 2-(2′-pyridyl)quinoxaline

Conductometric investigation on the bis(triphenyl phosphine) ruthenium(II) complex, cis-[RuCl₂(L)(PPh₃)₂] (A) (where PPh₃: triphenyl phosphine and L: 2-(2′-pyridyl)quinoxaline, C₁₃N₃H₉), in dimethylsulfoxide (DMSO) was performed at temperatures ranging from 25 to 50 °C. In addition, cyclic voltammograms of A were recorded on platinum working electrode in dichloromethane (DCM) and dimethylsulfoxide (DMSO) using n-tetrabutylammonium hexafluorophosphate (NBu₄PF₆) as supporting electrolyte at 25 °C. The molar conductivities (Λ) demonstrate that A behaves as uni-univalent electrolyte in DMSO over the whole temperature range. This behavior can be explained in terms of the replacement upon dissolution of chlorine and PPh₃ ligands by DMSO molecules, and consequently, the formation of the ion-pair [RuCl(L)(PPh₃)(DMSO)₂]Cl [B⁺Cl⁻] which is dissociated in some extent. The Λ values were analyzed by means of the Lee-Wheaton conductivity equation in order to estimate the limiting molar conductivities (Λ^o) and the ion-pair association constants (K_A) of [B⁺Cl⁻]. The limiting ion conductivities for the B⁺ ion were evaluated using n-tetrabutylammonium chloride (NBu₄Cl) as “reference electrolyte”. The thermodynamic functions related with the ion association, such as Gibbs free energy , enthalpy , and entropy , were evaluated as well. The mobility of B⁺ was found to increase linearly with rising temperature and the consequent decrease of the viscosity (η) of DMSO. The K_A and values indicate that the association of [B⁺Cl⁻] increases to some extent with the rise of the temperature followed by the decrease of the dielectric constant (ε) of DMSO. The voltammetric experiments indicated that the couple Ru^3+/2+ is reversible and diffusion controlled in DCM and completely irreversible in DMSO.     

Anation kinetics of pentacyanoaquachromate(III) by thiocyanate and azide

The kinetics of the reaction of Cr(CN)₅(H₂O)²⁻ with NCS⁻ and were studied at pH 5.0 and at pH 6.3-7.0, respectively, as a function of the temperature between 25.0 and 55.0 °C, and at various ionic strengths. Anation occurs in competition with aquation of CN⁻, with rate constants that exhibit less-than-first-order dependence on the concentration of the entering anions. The results are interpreted in terms of ligand interchange in a context of association of the two reacting anions mediated by the Na⁺ or Ca²⁺ counterions. The degree of aggregation depends mainly on the total cationic charge rather than on the ionic strength, and is ca. 2-fold larger for than for NCS⁻. Within the associated species, is a better entering ligand than NCS⁻ by a factor of 4.5. The Cr(CN)₅(NCS)³⁻ and Cr(CN)₅(N₃)³⁻ complexes were also synthesized, and the rates of aquation of NCS⁻ and were measured at pH 5.0 and between 55.0 and 80.0 °C, over the same range of ionic strengths. The ionic strength enhances the anation rates but has little effect on the aquation rates. The average activation enthalpies of the interchange step are 80 ± 3 and 76 ± 3 kJ mol⁻¹ for entry of NCS⁻ and , respectively. Those of the corresponding aquation reactions are 94 ± 4 and 107 ± 4 kJ mol⁻¹. Within error limits, all ΔH^‡ values are independent of the ionic strength. The results are consistent with an I_d mechanism for substitution in Cr(CN)₅X^z− complexes.     

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.