A thermal decomposition study on cobalt(II) complexes of 1,2-bis(IMINO-4'-antipyrinyl)ethane

The phenomenological, kinetic and mechanistic aspects of thermal decomposition of perchlorate, nitrate, chloride, bromide and iodide complexes of cobalt(II) with the Schiff base 1,2-bis(imino-4'-antipyrinyl)ethane (GA) have been studied by TG and DTG analyses. The kinetic parameters like the activation energy, pre-exponential factor and entropy of activation were calculated. The decomposition reactions follow 'random nucleation with one nucleus on each particle - Mampel model'. This revised version was published online in July 2006 with corrections to the Cover Date.     

Spin-crossover complexes in solution,II solvent effects on the high spin-low spin-equilibrium of [Fe(bzimpy)2](ClO4)2

Summary The influence of the solvent on the spin-equilibrium of [Fe(bzimpy)₂](ClO₄)₂ (bzimpy=2,6-bis(benzimidazol-2-yl)pyridine) has been investigated in several nonaqueous solvents by means of UV-Vis spectroscopy and magnetic susceptibility measurements. In methanol, a bis-tris ligation equilibrium is found. Both, the FeL ₂ ²⁺ and FeL ₃ ²⁺ species show spin-crossover behaviour in solution. Photometric and magnetic properties of the complex in various solvents are related. The spin-equilibrium of [Fe(bzimpy)₂](ClO₄)₂ shows the strongest sensitivity towards changes of the solvent that has ever been observed for spin-crossover compounds. Increase in solvent donor number (DN) from DN=14.1 (Acetonitril) to DN=19.1 (Methanol) causes a shift from _exp=4.21 (78% High-Spin (HS)) to _exp=3.0 (56% HS). In solvents with DN 30 deprotonation of the complex occurs yielding a low-spin species. The solvent effects are discussed in terms of the donor-acceptor concept.Dedicated to Professor Harry J. Emeléus with heartiest congratulations to his 90^th birthday on 22^th June 1993.     

Determination of empirical polarity parameters of the cellulose solvent N,N-dimethylacetamide/LiCl by means of the solvatochromic technique

Empirical solvatochromic polarity parameters (α-, β-, and $ \pi ^* $, AN and DN, as well as E_T(30)-values) for cellulose, N,N-dimethylacetamide (DMA)/LiCl and cellulose dissolved in DMA/LiCl are presented. The following solvent polarity indicators were applied: 2,6-diphenyl-4-(2,4,6-triphenyl-1- pyridinio)-1-phenolate ( 1 ), bis(4-N,N-dimethylamino)-benzophenone (MK, 2 ), iron(II)-di-cyano-bis(1,10)-phenanthroline, Fe(phen)₂(CN)₂, ( 3 ), and copper(II)-N,N,N′,N′-tetramethyl-ethylendiamine-acetylacetonate tetraphenylborate/chloride/bromide (Cu(tmen)(acac)⁺ X⁻ ( 4 )). The solvatochromic shifts (ν_max) of the indicators 1 , 2 , 3 , and 4 adsorbed to cellulose or dissolved in DMA/LiCl reflect the corresponding properties of the surrounding, the dipolarity/polarizability ($ \pi ^* $), the hydrogen bond donating ability or Lewis acidity (α), and the hydrogen bond accepting ability or Lewis basicity (β), respectively. Any indicator employed is well characterized (r > 0.97) by a linear solvation energy relationship (LSER) taking the Kamlet and Taft parameter into account: ν_max(indicator) = ν_max,0 + s$ \pi ^* $ + aα + bβ. Cellulose, DMA/LiCl, and the cellulose/DMA/LiCl solution approach a similar polarity with an E_T(30) parameter about 52 to 53 kcal mol⁻¹. The hypothetical interaction strength parameter (acid-base interactions, dipolar–dipolar interactions) between cellulose and DMA/LiCl are calculated by means of the individual Kamlet–Taft parameters α, β, and $ \pi ^* $ of cellulose and DMA/LiCl via a multiparameter equation. The specific chloride/cellulose interaction plays a dominant role in the cellulose solvent DMA/LiCl. Comparison of the polarity parameters of DMA/LiCl with the polarity parameters of other mixtures—such as N,N-dimethyl- formamide/LiCl, DMA/NaCl, or DMA/LiBr—are presented as well. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1945–1955, 1998     

Tuning of spin crossover behaviour in iron(III) complexes involving pentadentate Schiff bases and pseudohalides

Investigations on a series of eight novel mononuclear iron(III) Schiff base complexes with the general formula [Fe(L(5))(L(1))]·S (where H(2)L(5) = pentadentate Schiff-base ligand, L(1) = a pseudohalido ligand, and S is a solvent molecule) are reported. Several different aromatic 2-hydroxyaldehyde derivatives were used in combination with a non-symmetrical triamine 1,6-diamino-4-azahexane to synthesize the H(2)L(5) Schiff base ligands. The consecutive reaction with iron(III) chloride resulted in the preparation of the [Fe(L(5))Cl] precursor complexes which were left to react with a wide range of the L(1) pseudohalido ligands. The low-spin compounds were prepared using the cyanido ligand: [Fe(3m-salpet)(CN)]·CH(3)OH (1a), [Fe(3e-salpet)(CN)]·H(2)O (1b), while the high-spin compounds were obtained by the reaction of the pseudohalido (other than cyanido) ligands with the [Fe(L(5))Cl] complex arising from salicylaldehyde derivatives: [Fe(3Bu5Me-salpet)(NCS)] (2a), [Fe(3m-salpet)(NCO)]·CH(3)OH (2b) and [Fe(3m-salpet)(N(3))] (2c). The compounds exhibiting spin-crossover phenomena were prepared only when L(5) arose from 2-hydroxy-1-naphthaldehyde (H(2)L(5) = H(2)napet): [Fe(napet)(NCS)]·CH(3)CN (3a, T(1/2) = 151 K), [Fe(napet)(NCSe)]·CH(3)CN (3b, T(1/2) = 170 K), [Fe(napet)(NCO)] (3c, T(1/2) = 155 K) and [Fe(napet)(N(3))], which, moreover, exhibits thermal hysteresis (3d, T(1/2)↑ = 122 K, T(1/2)↓ = 117 K). These compounds are the first examples of octahedral iron(III) spin-crossover compounds with the coordinated pseudohalides. We report the structure and magnetic properties of these complexes. The magnetic data of all the compounds were analysed using the spin Hamiltonian formalism including the ZFS term and in the case of spin-crossover, the Ising-like model was also applied.     

Synthesis, thermal behavior, and spectral properties of mixed-metal Cu(I)-VO(IV)-thiourea coordination polymers

Abstract  

The heterometallic complexes [Cu(VO)₂(CSN₂H₄)₃Cl(OH)₄]·H₂O, [Cu₂(VO)₂(CSN₂H₄)₂(C₂H₃O₂)₂·(OH)₄], and [Cu₂(VO)₃(CSN₂H₄)₄(C₂H₃O₂)₄(OH)₄] were prepared and characterized in terms of their molecular electrical conductivity, electronic and IR spectra, and thermal behavior. A polymeric structure is proposed in which a thiourea ligand is bonded via a sulfur atom to the tetracoordinated copper(I) and via amino groups to the oxovanadium(IV) ion. The polymeric nature of the complexes is due to bridging via the OH, thiourea, and/or acetate moieties between oxovanadium(IV) coordination centers.     

Kinetics and Mechanism of the Interaction of Di-μ-hydroxobis(1,10-phenanthroline)dipalladium(II) Perchlorate with Thioglycolic Acid and Glutathione in Aqueous Solution

The kinetics of interaction between di-μ-hydroxobis(1,10-phenanthroline)dipalladium(II) perchlorate and thioglycolic acid and with glutathione has been studied spectrophotometrically in aqueous medium as a function of the complex concentration as well as the ligand concentrations, pH, and temperature at constant ionic strength. The observed pseudo-first-order rate constants k _obs (s^?1) obeyed the equation k _obs = k ₁[Nu] (Nu = nucleophile). At pH = 6.5, the interaction with thioglycolic acid shows two distinct consecutive steps and both steps are dependent on the concentration of thioglycolic acid. The rate constants for the process are: k ₁ ≈ 10^?5 s^?1 and k ₂ ≈ 10^?3 dm³ · mol^?1 · s^?1. The association equilibrium constant (K _E) for the outer sphere complex formation has been evaluated together with the rate constants for the two subsequent steps. The other bio-active ligand, glutathione, showed a single step reaction depending on [ligand] with a second-order anation rate constant: the 10² (k ₂) values are (61.72, 79.20, 109.24 and 154.33) dm³ · mol^?1 · s^?1 at 20, 25, 30 and 35 °C, respectively. On the basis of the kinetic observations and evaluated activation parameters, plausible associative mechanisms are proposed for both interaction processes.