Volume 1, Issue 3

The title complex has been synthesised for the first time and characterised by elemental analysis and spectroscopic analyses. The kinetics of the acid hydrolysis and formation of the title complex have been studied using the stopped-flow technique. The acid hydrolysis experiments were carried out over the ranges, 0.01 < [H'] < 0.14 mol dm 3 , 22.4° C < θ < 30.1 C and at ionic strength 1.0 mol dm 3 (NaNO 3 ), whereas the formation kinetics were studied over the ranges 7.22 < pH < 8.18 and 25.0 C < θ < 33.9 C, with ionic strength 1.0 mol dm 3 (NaClO 4 ). The rate of acid hydrolysis is inversely dependent on [Η ' ] which has been ascribed to the expansion of the coordination number of the molybdenum(VI) from four to six on protonation, along with resonance stabilisation. The rate constant, k f o r the hydrolysis is 22.6 ± 0.3 s 1 at 25.1 C for which ΔΗ' = 89±5 kJ mol 1 and ΔS'= 81 ± 2 1 J mol 1 Κ 1 The rate constants for the reactions of (NH 3 ) 5 CrOH 3 and (NH 3 ) 5 CrOH 2 to form the title complex are (1.18 ±0.07) x 10 7 mol 1 dm 3 s 1 and (1.13 ± 0.05) x 105 mol 1 dm 3 s 1 respectively at 25.0 C. The results indicate that both processes are occurring via a mechanism involving Mo VI -O bond breakage.

The kinetics of the interaction of adenosine with [Pt( en )(H 2 O) 2 ] 2+ has been studied spectrophotometrically as a function of [Pt( en )(H 2 O) 2+ ], [Adenosine] and temperature at a particular pH (4.0) where the substrate complex exists predominantly as the diaqua species and the ligand adenosine as a neutral molecule. The interaction reaction shows distinct two step consecutive process; the first step is the ligand assisted anation and the second step is the chelation step. The activation parameters for both the steps are calculated (Δ H ≠ 1 = 63.7 ± 1.6 kJ mol -1 ΔS 1 ≠ = - 58± 5 JK -1 mol -1 and Δ H 2 ≠ = 41.0 ± 0.5 kj mol -1 ΔS 2 ≠ = 197 ± 1.5 JK 1 mol- 1 ).

The title trivalent nickel complex, Ni(III)L, oxidizes formate in slightly acidic solutions via an inner sphere, single electron, rate determining step. The rate of oxidation of the formate in Ni(III)L(H 2 O) (HCO 2 ) +2 is considerably faster than in Ni(III)L(H 2 PO 4 )(HCO 2 - ) + and in Ni(III)L(HCO 2 - ) + 2 . The results point out that formate has an ambivalent role in this process; on the one hand it is the reducing agent but on the other hand it stabilizes the trivalent nickel complex.

The substitution reactions on cis-[Pd( L -Histidine)- (H 2 O) 2 ] 2 + by chloride, adenine, guanosine, adenosine, 5 -GMP, 5'-AMP, 3-AMP, d(ApG) and d(GpA) has been studied at pH = 1.0-3.0 at different temperatures. The study at physiological pH had to be avoided due to undesired polymerization reactions. The results indicate a certain degree of unsensitivity of the substitution reactions by purine based ligands at this low pH when compared with other published studies. In particular, no cooperative effect is observed in the 5'-monophosphates and N(7)adenine and N(7)guanine are found to react at the same rate within experimental error. Results agree with the published values for similar systems and differences for the 5'- and 3'-monophosphates are detected both in the monophosphates and in the dinucleotides.

New complexes of Ln(III) nitrate with 2-hydroxy-lbenzylidene- 2-furoyl hydrazine having the general formula [Ln(L) 2 NO 3 ]H 2 O (where Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Er, Yb, Y; L = 2-hydroxy-l-benzylidene- 2-furoyl hydrazine) have been prepared and characterized by elemental analysis, molar conductance, magnetic measurements, electronic, infrared, 1 H NMR and thermal studies. Kinetic and thermodynamic parameters were computed from the thermal decomposition data. Based on the spectral and TG studies, a coordination number of eight around the metal ions is proposed.

The kinetics of oxidation of L-cystine by alkaline permanganate follows the rate law, where Κ is the formation constant for the complex between L-cystine and permanganate and k is the decomposition rate constant. The data suggest that the oxidation of L-cystine proceeds via the formation of a complex between L-cystine and permanganate which decomposes slowly, followed by a fast reaction between the free radical of L-cystine and another molecule of permanganate to give the products. The reaction constants involved in the mechanism are derived. There is good agreement between the observed and calculated rate constants under varying experimental conditions. The activation parameters are computed with respect to the slow step of the mechanism.

The reaction between [Ru(H 2 O) 6 ] 2+ and dimethylformamide (DMF) was studied as a function of the temperature and the pressure at pH 1. When a slight excess of Ru aquaion is used, [Ru(H 2 O) 5 DMF] 2+ is the only product of the reaction observed in the NMR spectra and the DMF is bound through the oxygen atom. From variable temperature experiments, the rate constants, activation enthalpies and entropies for the formation and the dissociation of the monocomplex were determined. These are as follows: 10 4 x k f 298 =(8.2 ± 0.4) kg mol -1 s -1 ΔΗ ☨ f = 83.6 ± 3 k J mol -1 Δ S ☨ f = -23.7 ± 10 J K -1 mol -1 for the formation reaction, 10 3 x kd 298 = (1.10 ± 0.04) s -1 ΔΗ ☨ f = 90.2 ± 2 kJ mol -1 ΔS ☨ f , = +1.0 ± 7 J Κ -1 mol -1 for the dissociation reaction. The thermodynamic parameters (equilibrium constant at 298.15 K, reaction enthalpy and entropy) were also determined:K 298 eq = 0.74 ± 0.02 kg mol -1 , ΔH 0 = -6.6 ± 2 k j mol -1 , ΔS 0 =-24.7 ± 6 JK -1 . The k f value is similar to the previously reported rate constants for monocomplex formation reactions with other ligands and confirms that the entering ligand has no effect on the rate. From variable pressure experiments, the activation volumes for the formation and the dissociation reactions and the reaction volume were determined: ΔV f ☨ = +2.7 ± 0.6 cm3 mol -1 , ΔV d ☨ = 0.9 ± 0.7 cm 3 mol -1 , ΔV° = +3.6 ± 0 . 9 cm3 mol -1 respectively. These results show that the volume of the transition state is intermediate between the volume of the reactants and the volume of the products. It demonstrates that the mechanism is the same as for the water exchange on [Ru(H 2 O) 6 ] 2+ , i.e. an Id mechanism. Contraction of the bonds between Ru and the spectator ligands at the transition state may explain the abnormally small activation volumes. The need of theoretical calculations on these systems is emphasized.