Synthesis and structures of complexes ofN-2-nitroxyethylpicolinamide and 2-(2-pyridyl)-2-oxazoline with PdCl2

The reaction ofN,N′-bis(2-nitroxyethyl)pyridine-2,6-dicarboxamide with PdCl₂ afforded previously unknowncis-(N-2-nitroxyethylpicolinamide-N,N′)dichloropalladium(II) andcis-[2-(2-pyridyl)-2-oxazoline-N,N′]dichloropalladium(II), which were isolated as a cocrystallizate of the molecular compounds. Its structure was established by X-ray diffraction analysis. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1604–1606, August, 1999.     

Synthesis,structure and vibrational spectroscopy of palladium(II) complexes with 2-thiophenecarboxylic hydrazide (tch): Crystal structure of [PdCl2(tch)2]·2dmf

The X-ray single crystal investigation revealed that Pd²⁺ ion is bonded to tch ligands only via amine nitrogen atoms, forming with two chloride ions a quasi-square metal environment. The crystal slowly looses dmf molecules transforming into complex which can also be obtained by mixing the PdCl₂ and tch water solutions. Both compounds, together with their bromo derivatives, have been intensively investigated by vibrational spectroscopy methods employing the palladium isotope substitution, deuteration and theoretical calculations on the DFT level. All those attempts resulted in complete assignment of the observed bands, in terms of potential energy distribution.     

Thermal and kinetic analyses of 2,5-bis(2-hydroxyphenyl)thiazolo[5,4-d]thiazole

Thermal behavior and UV–Vis absorption properties of 2,5-bis(2-hydroxyphenyl)thiazolo[5,4-d]thiazole were investigated in the present study. It was found that decomposition occurs in two stages which correspond to removal of both phenolic rings and degradation of remaining core structure, respectively. After the characterization of decomposition stages, apparent activation energy values of each stage were calculated using model-free isoconversional methods (FWO and KAS). Apparent activation energies of decomposition stages are determined by both methods. Their averages are calculated as 98.232 and 123.253 kJ mol^?1 in consecutive order. UV–Vis absorption properties of this compound have been determined with using different solvents.     

Synthesis and structure of the complex of 2-(2-pyridyl)-2-oxazoline with PdCl2

The reaction ofN-2-nitroxyethylpicolinamide with PdCl₂ afforded the new complexcis-[2-(2-pyridyl)-2-oxazoline-N,N′]dichloropalladium(u). The structure of this complex was established by X-ray diffraction analysis. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 561–563, March, 2000.     

Fast hydrogen elimination from the [Ru(PH3)3(CO)(H)2] and [Ru(PH3)4(H)2] complexes in the first singlet excited states: a diabatic quantum dynamics study

The photodissociation dynamics of [Ru(PH3)3(CO)(H)2] and cis-[Ru(PH3)4(H)2] is theoretically analyzed in the lowest two excited singlet states. Energies obtained through electronic density functional theory calculations that use the time-dependent formalism are fitted to analytical reduced two-dimensional potential energy surfaces (2D-PES). The metal-H2 (R) and H-H (r) distances are the variables of these 2D-PES, the rest of the parameters being kept frozen at the values of the minimum energy structure in the ground electronic state. The time evolution in these 2D-PES is exactly followed by means of a fast Fourier transform algorithm applied to solve the time-dependent Schr?dinger equation. A simple diabatization scheme is devised to take into account the probability of transitions between both excited states. The quantum dynamics results point out that photoelimination is almost inexistent if the H2 fragment is to be expelled without further rearrangement of the rest of the complex. Conversely, when the geometries of the complex are optimized by keeping r and R frozen at the hydrogen elimination barrier coordinates, the new 2D-PES so obtained are highly dissociative, the H2 fragment being expelled in less than 100 fs. Finally the picture of the whole reaction that emerges from our theoretical results is described and the main differences between both complexes are examined.     

Gallium(III) complexes of DOTA and DOTA-monoamide: kinetic and thermodynamic studies

Given the practical advantages of the (68)Ga isotope in positron emission tomography applications, gallium complexes are gaining increasing importance in biomedical imaging. However, the strong tendency of Ga(3+) to hydrolyze and the slow formation and very high stability of macrocyclic complexes altogether render Ga(3+) coordination chemistry difficult and explain why stability and kinetic data on Ga(3+) complexes are rather scarce. Here we report solution and solid-state studies of Ga(3+) complexes formed with the macrocyclic ligand 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid, (DOTA)(4-), and its mono(n-butylamide) derivative, (DO3AM(Bu))(3-). Thermodynamic stability constants, log K(GaDOTA) = 26.05 and log K(GaDO3AM(Bu)) = 24.64, were determined by out-of-cell pH-potentiometric titrations. Due to the very slow formation and dissociation of the complexes, equilibration times of up to ～4 weeks were necessary. The kinetics of complex dissociation were followed by (71)Ga NMR under both acidic and alkaline conditions. The GaDOTA complex is significantly more inert (τ(1/2) ～12.2 d at pH = 0 and τ(1/2) ～6.2 h at pH = 10) than the GaDO3AM(Bu) analogue (τ(1/2) ～2.7 d at pH = 0 and τ(1/2) ～0.7 h at pH = 10). Nevertheless, the kinetic inertness of both chelates is extremely high and approves the application of Ga(3+) complexes of such DOTA-like ligands in molecular imaging. The solid-state structure of the GaDOTA complex, crystallized from a strongly acidic solution (pH < 1), evidenced a diprotonated form with protons localized on the free carboxylate pendants.     

Copper(II) [(4-methylphenyl)sulfonyl]-1H-imino-(2-phenyl-2-oxazoline) complexes

Neutral copper complexes of the deprotonated [(4-methylphenyl)sulfonyl]-1H-imino-(2-phenyl-2-oxazoline) proligands, [HTs-ROz], R = H, 5-Me, 4-Me, 4-Et, 4-ⁱPr, have been prepared by electrochemical oxidation of anodic copper in an MeCN solution of the corresponding proligand. The [Cu(Ts-ROz)₂] complexes were characterised by microanalysis, i.r. and electronic spectroscopies, and by e.p.r. and magnetic measurements. The crystal structures of HTs-5MeOz, [Cu(Ts-Oz)₂], [Cu(Ts-5MeOz)₂] and [Cu(Ts-4MeOz)₂] were determined by X-ray diffraction.     

Two new [Ni(tren)2]2+ complexes: [Ni(tren)2]Cl2 and [Ni(tren)2]WS4

Both title compounds, bis­[tris(2‐amino­ethyl)­amine]­nickel(II) dichloride, [Ni(tren)₂]Cl₂, (I), and bis­[tris(2‐amino­ethyl)­amine]­nickel(II) tetra­thio­tungstate, [Ni(tren)₂]WS₄, (II), contain the [Ni(tren)₂]²⁺ cation [tren is tris(2‐amino­ethyl)­amine, C₆H₁₈N₄]. The tren mol­ecule acts as a tridentate ligand around the central Ni atom, with the remaining primary amine group not bound to the central atom. In (I), Ni²⁺ is located on a centre of inversion surrounded by one crystallographically independent tren mol­ecule. In the [Ni(tren)₂]²⁺ cation of (II), the Ni atom is bound to two crystallographically independent tren mol­ecules. The Ni atoms in the [Ni(tren)₂]²⁺ complexes are in a distorted octahedral environment consisting of six N atoms from the chelating tren mol­ecules. The counter‐ions are chloride anions in (I) and the tetrahedral [WS₄]^2? anion in (II). Hydro­gen bonding is observed in both compounds.     

Characterization of antibodies against benzo[a]pyrene with thermodynamic and kinetic constants

Antibodies of a polyclonal antiserum against benzo[a]pyrene were characterized by determining thermodynamic and kinetic constants of the antigen–antibody reaction. Label-free binding assays with optical detection based on reflectometric interference spectroscopy were performed to determine these constants. Different evaluation methods for kinetic measurements were compared. Also, cross-reactivity against two other polycyclic aromatic hydrocarbons, chrysene and pyrene, was checked. The affinity constant between the antibodies and benzo[a]pyrene in homogeneous phase was determined to be K=(5.3±0.3)×10⁷ M⁻¹ which was in the middle of the usual range of antibody affinities. The association rate constant for the reaction at the surface was determined to be (3.8±0.9)×10⁵ M⁻¹ s⁻¹, the dissociation rate constant as (9.7±0.5)×10⁻³ s⁻¹. Different evaluation methods applied to the kinetic measurements led to the same results. This antiserum would be suitable for the selective determination of benzo[a]pyrene in concentrated samples.     

Interaction of adenine with dichloro-[1-alkyl-2-(naphthylazo)-imidazole]palladium(II) complexes: kinetic and mechanistic studies

Interaction of adenine (A) with dichloro-[1-alkyl-2-(α-naphthylazo)imidazole] palladium(II) [Pd(α-NaiR)Cl₂], 1 and dichloro-[1-alkyl-2-(β-naphthylazo)imidazole] palladium(II) [Pd(β-NaiR)Cl₂], 2 {where R=Me (a), Et (b) or Bz (c)} in MeCN-water (50% v/v) medium to yield [{1-alkyl-2-(α-naphthylazo)imidazole}(adenine)]palladium(II) perchlorates (3a, 3b, 3c) and [{1-alkyl-2-(β-naphthylazo)imidazole}(adenine)]palladium(II) perchlorates (4a, 4b, 4c) was studied. The products were characterized by physico-chemical and spectroscopic methods. The reaction kinetics were second order overall, being first order in both the Pd(II) complex and adenine. The effect of adding chloride was consistent with rate-limiting dissociation of chloride from the complex. Thermodynamic parameters were determined from temperature variation experiments. The second-order rate constant k ₂ corroborates with the experimental Δ^‡H° values, while the negative values of Δ^‡S° indicate that the reaction proceeds through an associative inner sphere mechanism.     

Transition-metal complexes with bidentate ligands spanning trans-positions. V. Crystal and molecular structures of complexes [RhCl(CO) (1)] and [PdCl2(1)]; 1 = 2,11-bis (diphenylphosphinomethyl)benzo [c]phenanthrene

The structures of [RhCl(CO) ( 1 )] and [PdCl₂ ( 1 )], where 1 is the bidentate ligand (C₆H₅)₂P·CH₂·C₁₈H₁₀· CH₂·P(C₆H₅)₂, have been determined from threedimensional X-ray counter data collected on single crystals of the C₆H₅·CN solvates. The two compounds are isomorphous and crystallize in the triclinic system, space group P 1 , Z = 2: a = 14.580 (8), b = 13.029 (10), c = 11.909 (6) Å, α = 106.33 (5), β = 100.47 (4), γ = 95.73 (5)° for the rhodium complex; a = 14.361 (5), b = 13.044 (7), c = 11.897 (4) Å, α = 105.97 (4), β = 100.27 (3), γ = 94.76 (4)°, for the palladium complex. In both complexes the metal atom is four-coordinate with slightly distorted square-planar configuration. In both cases the ligand 1 spans trans positions with M-P bond lengths in the ranges of the literature data. Also the other bond distances fall in regular ranges. Ligand 1 has almost the same conformation in both complexes and is characterized by a strong out-of-plane deformation of the benzophenanthrene system as a consequence of severe overcrowding.     

Triplet electronic states in d(2) and d(8) complexes probed by absorption spectroscopy: a CASSCF/CASPT2 analysis of [V(H2O)6]3+ and [Ni(H2O)6]2+

Octahedral complexes of transition metal ions with d(2) and d(8) electron configurations have triplet electronic states with identical T(2g), A(2g), T(1g)((3)F), and T(1g)((3)P) symmetry labels. CASSCF and CASPT2 calculations indicate the predominant electronic configurations for each triplet state. The two (3)T(1g) states show strong configuration mixing in the d(8) complex [Ni(H(2)O)(6)](2+), but much weaker mixing occurs between these states in the d(2) compound [V(H(2)O)(6)](3+). Calculated vibrational frequencies and equilibrium geometries for the triplet states are used to obtain theoretical absorption spectra that are in agreement with the experimental data.