Kinetic study of the interaction of adenosine 5′‐monophosphate with diaqua (2‐hydrazinopyridine) palladium(II) in aqueous medium

The interaction of the palladium(II) complex [Pd(hzpy)(H₂O)₂]²⁺, where hzpy is 2‐hydrazinopyridine, with purine nucleoside adenosine 5′‐monophosphate (5′‐AMP) was studied kinetically under pseudo‐first‐order conditions, using stopped‐flow techniques. The reaction was found to take place in two consecutive reaction steps, which are both dependent on the actual 5′‐AMP concentration. The activation parameters for the two reaction steps, i.e. ΔH = 32 ±2 kJ mol^?1, ΔS = ?168 ±7 J K^?1 mol^?1, and ΔH = 28 ± 1 kJ mol^?1, ΔS = ?126 ± 5 J K^?1 mol^?1, respectively, were evaluated and suggested an associative mode of activation for both substitution processes. The stability constants and the associated speciation diagram of the complexes were also determined potentiometrically. The isolated solid complex was characterized by C, H, and N elemental analyses, IR, magnetic, and molar conductance measurements. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 42: 132–142, 2010     

Both spacer length and parity influence the thermal and light-induced properties of iron(II) alpha,omega-bis(tetrazole-1-yl)alkane coordination polymers

A new series of [mu-tris-{1,n-bis(tetrazol-1-yl)alkane-N4,N4'}iron(II)] bis(perchlorate) spin-crossover coordination polymers ([Fe(nditz)3](ClO4)2]; n = 4-9) has been synthesised and characterised. The ditetrazole bridging ligands provide octahedral symmetry at the iron(II) centres while allowing the distance between iron(II) centres to be varied. These polymers have therefore been investigated to determine the effects of spacer length on their thermal and light-induced spin-transition behaviour. An increase in the number of carbon atoms in the spacer (n) raises the thermal spin-crossover temperature, while decreasing the stability of the light-induced metastable state generated through the light-induced excited spin state trapping (LIESST) effect by irradiating the sample at 530 nm. Remarkably, however, the parity of the spacer also has an effect, enabling the series of complexes to be divided into two sub-series depending on whether the bridging ligand possesses an even or an odd number of carbon atoms. An explanation at the molecular level using the single configurational coordinate (SCC) model is presented.     

Thermolytic investigations on nickel(II) complexes of 4‐N‐(4′‐antipyrylmethylidene)aminoantipyrine with various counterions

Phenomenological characteristics and kinetic and mechanistic aspects of the thermal decomposition of nitrate, chloride, bromide, and iodide complexes of nickel(II) with 4‐N‐(4′‐antipyrylmethylidene)aminoantipyrine have been studied using thermogravimetric (TG) and differential thermogravimetric (DTG) techniques. Kinetic parameters such as activation energy, preexponential factor, and entropy of activation were quantified. The rate‐controlling process in all stages of decomposition was found to be based on random nucleation with one nucleus on each particle according to the Mampel model. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 39: 53–58, 2007     

Selective imidazolidine ring opening during complex formation of iron(III), copper(II), and zinc(II) with a multidentate ligand obtained from 2-pyridinecarboxaldehyde N-oxide and triethylenetetramine

The condensation of 2-pyridinecarboxaldehyde N-oxide and triethylenetetramine yields a product with two imidazolidine rings, as proven by a solid-state X-ray structure analysis as well as by NMR solution spectra. This ligand, L1, undergoes a ring-opening reaction on complex formation with Cu(II), yielding [CuL2]2+ where L2 functions as a pentadentate ligand, containing only one imidazolidine ring. On complexation with Zn(II) and Fe(III), both rings are opened and the complexes [ZnL3]2+ and [FeL3]3+ with a hexadentate L3 ligand are formed. The recrystallization of [ZnL3]2+ from DMSO solution results in the complex [ZnL1(DMSO)2]2+ in which L1 behaves as a tetradentate ligand. Thus L1, L2, and L3 are structural isomers with two, one, or no imidazolidine rings, as confirmed by X-ray structure analyses. The intramolecular ring formation is the result of the nucleophilic addition of the N(amino) group to the electrophilic sp2-hybridized -HC delta+=N site. Owing to the absence of the chelate effect on the sp3-hybridized carbon atom belonging to the imidazolidine ring, the ring opening is facilitated and readily observed upon complex formation with Cu(II), Zn(II), and Fe(III).     

Metal chelates of Triazine-Schiff-bases: Complex formation of 3-(α-phenyl)ethylidenehydrazino-5,6-diphenyl-1,2,4-triazine with copper(II)

Summary Complex formation of copper(II)-ions with 3-(-Phenyl)ethylidenehydrazino-5,6-diphenyl-1,2,4-triazine (BHT) has been investigated using UV-VIS-, IR-, and electrochemical methods. Optimal pH for the 1:1 complex formation (and therefore for analytical applications) was found at 5.4. This complex could be isolated. The acid dissociation constant of the free ligand ispK _a=13.60; formation constants for 1:1 and 1:2 complexes were found to be logK ₁=12.0 and logK ₂=10.4, respectively. Polarographic reduction of both the free ligand and the Cu(II)-complexes is irreversible, diffusion controlled and like the stability of the complexpH-dependent.In course of absence of the Faculty of Education, Ain Schams University, Roxy, Cairo, Egypt.     

Reversed-phase liquid chromatography of alkaloids: Masking effects of inorganic salts

The addition of salts (investigated cations Na(+), NH(+)(4), K(+), KBu(+)(4) combined with the anions acetate, Br(-), SCN(-) and I(-)) can be used to eliminate peak tailing and to decrease retention of cationic species in the course of the separation of alkaloids from Chelidonium majus L. by reversed-phase chromatography on a ODS Hypersil column, using water-acetonitrile-methanol mixture as eluent. These findings are interpreted in terms of a silanol masking effect. The extended donor-acceptor concept is used to interpret the effectiveness of different salts in masking the active sites of the stationary phase.     

Spin-crossover complexes in solution,I. Substitutional lability of [Fe(bzimpy)2](ClO4)2

Summary The iron(II) complexes of the nitrogen donor ligand 2,6-bis(benzimidazol-2-yl)pyridine (bzimpy) have been investigated in nonaqueous solvents using various spectrophotometric methods. Measurements in methanol at 20°C revealed thatbzimpy can act as a bi-or tridendate ligand towards iron(II) in this solvent, forming [Fe(bzimpy)]²⁺ (tridendate, logK=5.54), [Fe(bzimpy)₂]²⁺ (bistridentate, logK=4.12) and [Fe(bzimpy)₃]²⁺ (tris-bidentate, logK=3.85). The pronounced thermochromism of the compound is shown to be the result of both spin-crossover and dissociation equilibria. Furthermore, in solvents of higher donor numbers (30), partial or complete deprotonation of the complex [Fe(bzimpy)₃]²⁺ is observed. Triethylamine added stepwise to methanolic solutions causes successive deprotonation.This paper is dedicated to Professor Dr. Wolfgang Beck on the occasion of his 60th birthday with warmest personal wishes