Spectroscopic, and thermal studies of some new binuclear transition metal(II) complexes with hydrazone ligands containing acetoacetanilide and isoxazole

A new chelating ligand, 2-(2-(5-tert-butylisoxazol-3-yl)hydrazono)-N-(2,4-dimethylphenyl)-3-oxobutanamide (HL), and its four binuclear transition metal complexes, M(2)(L)(2) (micro-OCH(3))(2) [M=Ni(II), Co(II), Cu(II), Zn(II)], were synthesized using the procedure of diazotization, coupling and metallization. Their structures were postulated based on elemental analysis, (1)H NMR, MALDI-MS, FT-IR spectra and UV-vis electronic absorption spectra. Smooth films of these complexes on K9 glass substrates were prepared using the spin-coating method and their absorption properties were evaluated. The thermal properties of the metal(II) complexes were investigated by thermogravimetry (TG) and differential scanning calorimetry (DSC). Different thermodynamic and kinetic parameters namely activation energy (E*), enthalpy of activation (DeltaH*), entropy of activation (DeltaS*) and free energy change of activation (DeltaG*) are calculated using Coats-Redfern (CR) equation.     

Large ground-state entropy changes for hydrogen atom transfer reactions of iron complexes

Reported herein are the hydrogen atom transfer (HAT) reactions of two closely related dicationic iron tris(alpha-diimine) complexes. FeII(H2bip) (iron(II) tris[2,2'-bi-1,4,5,6-tetrahydropyrimidine]diperchlorate) and FeII(H2bim) (iron(II) tris[2,2'-bi-2-imidazoline]diperchlorate) both transfer H* to TEMPO (2,2,6,6-tetramethyl-1-piperidinoxyl) to yield the hydroxylamine, TEMPO-H, and the respective deprotonated iron(III) species, FeIII(Hbip) or FeIII(Hbim). The ground-state thermodynamic parameters in MeCN were determined for both systems using both static and kinetic measurements. For FeII(H2bip) + TEMPO, DeltaG degrees = -0.3 +/- 0.2 kcal mol-1, DeltaH degrees = -9.4 +/- 0.6 kcal mol-1, and DeltaS degrees = -30 +/- 2 cal mol-1 K-1. For FeII(H2bim) + TEMPO, DeltaG degrees = 5.0 +/- 0.2 kcal mol-1, DeltaH degrees = -4.1 +/- 0.9 kcal mol-1, and DeltaS degrees = -30 +/- 3 cal mol-1 K-1. The large entropy changes for these reactions, |TDeltaS degrees | = 9 kcal mol-1 at 298 K, are exceptions to the traditional assumption that DeltaS degrees approximately 0 for simple HAT reactions. Various studies indicate that hydrogen bonding, solvent effects, ion pairing, and iron spin equilibria do not make major contributions to the observed DeltaS degrees HAT. Instead, this effect arises primarily from changes in vibrational entropy upon oxidation of the iron center. Measurement of the electron-transfer half-reaction entropy, |DeltaS degrees Fe(H2bim)/ET| = 29 +/- 3 cal mol-1 K-1, is consistent with a vibrational origin. This conclusion is supported by UHF/6-31G* calculations on the simplified reaction [FeII(H2N=CHCH=NH2)2(H2bim)]2+...ONH2 left arrow over right arrow [FeII(H2N=CHCH=NH2)2(Hbim)]2+...HONH2. The discovery that DeltaS degrees HAT can deviate significantly from zero has important implications on the study of HAT and proton-coupled electron-transfer (PCET) reactions. For instance, these results indicate that free energies, rather than enthalpies, should be used to estimate the driving force for HAT when transition-metal centers are involved.     

Chlorine dioxide reduction by aqueous iron(II) through outer-sphere and inner-sphere electron-transfer pathways

The reduction of ClO(2) to ClO(2)(-) by aqueous iron(II) in 0.5 M HClO(4) proceeds by both outer-sphere (86%) and inner-sphere (14%) electron-transfer pathways. The second-order rate constant for the outer-sphere reaction is 1.3 x 10(6) M(-1) s(-1). The inner-sphere electron-transfer reaction takes place via the formation of FeClO(2)(2+) that is observed as an intermediate. The rate constant for the inner-sphere path (2.0 x 10(5) M(-1) s(-1)) is controlled by ClO(2) substitution of a coordinated water to give an inner-sphere complex between ClO(2) and Fe(II) that very rapidly transfers an electron to give (Fe(III)(ClO(2)(-))(H(2)O)(5)(2+))(IS). The composite activation parameters for the ClO(2)/Fe(aq)(2+) reaction (inner-sphere + outer-sphere) are the following: DeltaH(r)++ = 40 kJ mol(-1); DeltaS(r)++ = 1.7 J mol(-1) K(-1). The Fe(III)ClO(2)(2+) inner-sphere complex dissociates to give Fe(aq)(3+) and ClO(2)(-) (39.3 s(-1)). The activation parameters for the dissociation of this complex are the following: DeltaH(d)++= 76 kJ mol(-1); DeltaS(d)++= 32 J K(-1) mol(-1). The reaction of Fe(aq)(2+) with ClO(2)(-) is first order in each species with a second-order rate constant of k(ClO2)- = 2.0 x 10(3) M(-1) s(-1) that is five times larger than the rate constant for the Fe(aq)(2+) reaction with HClO(2) in H(2)SO(4) medium ([H(+)] = 0.01-0.13 M). The composite activation parameters for the Fe(aq)(2+)/Cl(III) reaction in H(2)SO(4) are DeltaH(Cl(III))++ = 41 kJ mol(-1) and DeltaS(Cl(III))++ = 48 J mol(-1) K(-1).     

Role of entropy in increased rates of intramolecular reactions

The rates of intramolecular condensation of a series of monoesters of dicarboxylic acids have been shown to be highly dependent on the nature of the intervening groups. To understand the origin of this effect, we estimated DeltaS(NAC,S), the entropy difference between the ensemble of accessible ground state conformers and a single ground state conformer having transition-state-like geometry. DeltaS(NAC,S) differs from the activation entropy for the reaction by DeltaS(TS,NAC), the difference in vibrational entropy between the selected ground state conformer and the transition state. The estimated values of DeltaS(NAC,S) correlate well (R(2) = 0.96 and 0.73 using dielectric constant values of 80 and 1, respectively) with experimentally determined reaction rate constants. Normal-mode analysis performed on minimized ground state conformations of each molecule suggests that the change in vibrational entropy makes only a small contribution to the total activation entropy. These results indicate that the conformational entropy difference between the transition and the ground states contributes significantly to the free energy of activation.     

Using meta conjugation to enhance charge separation versus charge recombination in phenylacetylene donor-bridge-acceptor complexes

A pair of donor-bridge-acceptor electron-transfer complexes, with a carbazole donor and a naphthalimide acceptor connected by either a para- or meta-conjugated phenylacetylene bridge, are synthesized and studied using time-resolved and steady-state spectroscopy. These experiments show that the charge separation times, which depend on the coupling of the donor and acceptor through the excited bridge moiety, are similar for the two molecules (Meta and Para). The charge recombination time, however, is a factor of 10 slower for Meta than for Para. These results are related to changes in the electronic coupling of the bridge depending on its electronic state, and show that meta-conjugated bridges provide a possible motif for the design of asymmetric molecular wires.     

Vibrational spectrum of the spin crossover complex [Fe(phen)(2)(NCS)(2)] studied by IR and Raman spectroscopy, nuclear inelastic scattering and DFT calculations

The vibrational modes of the low-spin and high-spin isomers of the spin crossover complex [Fe(phen)(2)(NCS)(2)] (phen = 1,10-phenanthroline) have been measured by IR and Raman spectroscopy and by nuclear inelastic scattering. The vibrational frequencies and normal modes and the IR and Raman intensities have been calculated by density functional methods. The vibrational entropy difference between the two isomers, DeltaS(vib), which is--together with the electronic entropy difference DeltaS(el)--the driving force for the spin-transition, has been determined from the measured and from the calculated frequencies. The calculated difference (DeltaS(vib) = 57-70 J mol(-1) K(-1), depending on the method) is in qualitative agreement with experimental values (20-36 J mol(-1) K(-1)). Only the low energy vibrational modes (20% of the 147 modes of the free molecule) contribute to the entropy difference and about three quarters of the vibrational entropy difference are due to the 15 modes of the central FeN(6) octahedron.     

Kinetics of thermal unfolding of phenylalanine hydroxylase variants containing different metal cofactors (FeII, CoII, and ZnII) and their isokinetic relationship

The kinetics of thermal unfolding of apo- and holo-Chromobacterium violaceum phenylalanine hydroxylase (cPAH) was investigated using circular dichroism (CD) over the temperature range 44-76 degrees C. In addition to the native cofactor (FeII), the unfolding kinetics of holo-cPAH was characterized using ZnII and CoII as cofactors. Kinetic profiles for apo- and holo-cPAH showed a single-phase exponential rise in the CD signal at lambda=222 nm and a first-order dependence on protein concentration. The extrapolated unfolding rate constants (ku) at ambient temperature followed the order apo>Fe>Zn>Co. Transition-state analysis of the activation parameters revealed an isokinetic correlation, which suggests a common mechanism for the enzyme variants. The values of the entropy of activation (DeltaS++) for apo- and Fe-cPAH were negative but small: -34+/-24 and -32+/-18 J mol(-1) K(-1), respectively. On the other hand, DeltaS++ values for Zn- and Co-cPAH were large and positive: 54+/-9 and 175+/-27 J mol(-1) K(-1), respectively. Therefore, at higher temperatures the unfolding rates of Zn- and Co-cPAH are affected significantly by entropy, while the unfolding rates of apo- and Fe-cPAH are dominated by enthalpy even at higher temperatures. The rate of unfolding of holo-cPAH did not depend on excess metal concentrations and maintained single-phase kinetic profiles, refuting the occurrence of adventitious metal binding and the notion that unfolding occurs via apo-cPAH exclusively. Isothermal titration calorimetry (ITC) was employed to measure cPAH binding affinities for Fe, Zn, and Co as well as the enthalpy of metal coordination. Dissociation constants (Kd) decreased in the order Fe>Zn>Co. The non-native metals, Zn and Co, were bound more tightly than Fe. The activation enthalpy for unfolding (DeltaH++) displayed a linear correlation with the enthalpy of metal binding obtained from ITC measurements (DeltaHITC). On this basis, a common mechanism (transition state) is suggested for this family of metal cofactors, and the varying enthalpy of activation arises from the differing stabilities of enzyme variants having different metal cofactors.     

Dynamic NMR study of the hindered Pt-N(bipyridine) rotation in metal-directed self-assembled macrocycles

[reaction: see text] The activation parameters for the hindered Pt-N(bipyridyl) rotation observed for a self-assembled rectangle and triangle have been investigated by temperature-dependent and selective inversion recovery (SIR) NMR spectroscopy. The enthalpy of activation (DeltaH) and change in entropy (DeltaS) were determined to be +52.2 kJ/mol and -58.2 J/mol.K for the rectangle and +59.1 kJ/mol and -71.8 J/mol.K for the triangle, respectively, by SIR.     

Spectral and thermal studies of 4-(1H-pyrazolo (3,4-d) pyrimidin-4-ylazo) benzene-1,3-diol complexes of cobalt(II), nickel(II) and copper(II)

4-(1H-Pyrazolo (3,4-d) pyrimidin-4-ylazo) benzene-1,3-diol was synthesized and characterized by various spectral and analytical techniques. Semiempirical quantum calculations using the AM1 method have been performed in order to evaluate the geometry and electronic structure of the title azodye in the ground state. The complex formation between Co(II), Ni(II) and Cu(II) ions and the title azodye was studied conductometrically and spectrophotometrically. The spectrophotometric determination of the title metal ions and titration using EDTA are reported. Co(II), Ni(II) and Cu(II) complexes of the title azodye have been synthesized and characterized by elemental analysis, conductivity, magnetic susceptibility, IR, UV-Vis and thermal analysis (TGA and DTA).The spectral and magnetic data suggested the octahedral geometry for Co(II) and Ni(II) complexes while Cu(II) complexes have square planar geometry. The thermal studies confirmed the chemical formulations of the title complexes. The thermal degradation takes place in two or three steps depending on the type of the metal and the geometry of the complexes. The kinetics of the decomposition was examined by using Coats-Redfern relation. The activation energies and other activation parameters (DeltaH, DeltaS and DeltaG) were computed and related to the bonding and stereochemistry of the complexes.     

Thermodynamic and electron-transfer properties of copper(II/I) polyaminothiaether complexes

In electron-transfer reactions, the change in the oxidation states of the reactants is generally accompanied by structural changes, which influence the electron-transfer kinetics. Previous studies on the systems of Cu(II)/(I) complexes involving cyclic tetrathiaether ligands indicated that inversion of coordinated donor atoms is a major geometric change during the overall electron-transfer process. Complex formation and isomerization studies on complexes with the 1,4,8,11-tetraazacyclotetradecane ligand have demonstrated that a necessary condition for conformational change is deprotonation followed by inversion of coordinated N atoms. When one or more nitrogen donor atoms in a ligand are replaced with sulfur, there is a choice of N or S inversion. It has been hypothesized that donor atom inversion (N or S donors) is a major factor that can lead to conformationally limited electron-transfer kinetics of copper systems. In the current study, the thermodynamic properties, electron-transfer kinetics and conformational changes in copper(II)[1,4,8-trithia-11-azacyclotetradecane], copper(II)[1,8-dithia-4,11-diazacyclotetradecane] and copper(II)[1,11,-dithia-4,8-diazacyclotetradecane] were determined in order to determine the effect of inversion of coordinated N atoms on electron-transfer rates as a function of low concentrations of water in an aprotic solvent (acetonitrile). By using controlled amounts of water as a hydrogen ion acceptor, deprotonation of amine nitrogen and nitrogen donor inversion was followed by comparing self-exchange rate constants for reduction and oxidation of the copper complexes. Data on thermodynamic properties and electron-transfer kinetics are presented. Possible conformational changes and kinetic pathways for complexes with ligands having mixed N and S donor sets are presented.     

Synthesis, spectral and thermal studies of Co(II), Ni(II) and Cu(II) complexes 1-(4,6-dimethyl-pyrimidin-2-ylazo)-naphthalen-2-ol

The electronic absorption spectra of 1-(4,6-dimethyl-pyrimidin-2-ylazo)-naphthalen-2-ol is studied in organic solvents of different polarity as well as in buffer solutions of varying pH values at different temperatures and different ratios of methanol. The probable structure of the azodye has been assigned on the basis of spectral studies (IR and (1)H NMR). The effect of Co(II), Ni(II) and Cu(II) ions on the emission spectrum of the free azodye is also assigned. The stoichiometry of the metal complexes is determined spectrophotometrically and conductometrically. Novel complexes of Co(II), Ni(II) and Cu(II) with the pyrimidine azodye have been synthesized and characterized on the basis of elemental analyses, molar conductance, magnetic susceptibility measurements, IR, electronic as well as ESR spectral studies The thermal decomposition of the metal complexes is studied by TGA and DTA techniques. The kinetic parameters like activation energy, pre-exponential factor and entropy of activation are estimated.     

A correlation between spin state and electrochemical electron-transfer rate for tris(N,N-disubtituted dithiocarbamato) iron(III) complexes

The electrochemical electron-transfer rate constants for the redox systems Fe(IV)L₃⁺/Fe(III)L₃ (L=N,N-disubstituted dithicarbamate ion) and Fe(III)L₃/Fe(II)L₃^? with a variety of substituents were measured at a platinum electrode in acetonitrile with the galvanostatic double-pulse method. It is known that each of the Fe(III) complexes exists both in a highspin state ⁶A₁ and a low-spin state ²T₂ in equilibirium of which position is widely changed by a subtle change in substituent. The standard rate constants for Fe(IV)L₃⁺/Fe(III)L₃ were larger or smaller than those for Fe(III)L₃/Fe(II)L₃^? according as the Fe(III)L₃ complexes are predominantly low- or high-spin complexes. Since the Fe(IV) and Fe(II) complexes are low-and high-spin complexes respectively, these findings suggest that electrochemical electron-transfer reactions accompanied by a spin-state change are slower than those without it. Such spin-state effect on electrode reactions has rarely been discussed so far.     

Kinetics and mechanism of the oxidation of guanosine derivatives by Pt(IV) complexes

The kinetics of redox reactions of the PtIV complexes trans-Pt(d,l)(1,2-(NH2)2C6H10)Cl4 ([PtIVCl4(dach)]) and Pt(NH2CH2CH2NH2)Cl4 ([PtIVCl4(en)]) with 5'- and 3'-dGMP (G) have been studied. These redox reactions involve substitution followed by an inner-sphere electron transfer. The substitution is catalyzed by PtII and follows the classic Basolo-Pearson PtII-catalyzed PtIV-substitution mechanism. We found that the substitutution rates depend on the steric hindrance of PtII, G, and PtIV with the least sterically hindered PtII complex catalyzing at the highest rate. 3'-dGMP undergoes substitution faster than 5'-dGMP, and [PtIVCl4(en)] substitutes faster than [PtIVCl4(dach)]. The enthalpies of activation of the substitution, DeltaH double dagger s, of 3'-dGMP is only 70% greater than that of 5'-dGMP (50.4 vs 30.7 kJ mol(-1)), but the entropy of activation of the substitution, DeltaS double dagger s, of 3'-dGMP is much greater than that of 5'-dGMP (-59.4 vs -129.5 J K(-1) mol(-1)), indicating that steric hindrance plays a major role in the substitution. The enthalpy of activation of electron transfer, DeltaH double dagger e, of 3'-dGMP is smaller than that of 5'-dGMP (88.8 vs 137.8 kJ mol(-1)). The entropy of activation of electron transfer, DeltaS double dagger e, of 3'-dGMP is negative, but that of 5'-dGMP is positive (-27.8 vs +128.8 J K-1 mol-1). The results indicate that 5'-hydroxo has less rotational barrier than 5'-phosphate, but it is geometrically unfavorable for internal electron transfer. The electron-transfer rate also depends on the reduction potential of PtIV. Because of its higher reduction potential, [PtIVCl4(dach)] has a faster electron transfer than [PtIVCl4(en)].     

Synthesis and characterization of Mn(II), Au(III) and Zr(IV) hippurates complexes

Mn(II), Au(III) and Zr(III) complexes with N-benzoylglycine (hippuric acid) (abbreviation hipH) were synthesized and characterized by elemental analysis, molar conductivity, magnetic measurements, spectral methods (mid-infrared, (1)H NMR, mass, X-ray powder diffraction and UV/vis spectra) and simultaneous thermal analysis (TG and DTG) techniques. The molar conductance measurements proved that all hippuric acid complexes are non-electrolytes. The electronic spectra and magnetic susceptibility measurements were used to infer the structures. The IR spectra of the ligand and its complexes are used to identify the type of bonding. The kinetic thermodynamic parameters such as: E*, DeltaH*, DeltaS* and DeltaG* are estimated from the DTG curves. The free ligand and its complexes have been studied for their possible biological antifungal activity.     

Donor-acceptor (electronic) coupling in the precursor complex to organic electron transfer: intermolecular and intramolecular self-exchange between phenothiazine redox centers

Intermolecular electron transfer (ET) between the free phenothiazine donor (PH) and its cation radical (PH*+) proceeds via the [1:1] precursor complex (PH)(2)*+ which is transiently observed for the first time by its diagnostic (charge-resonance) absorption band in the near-IR region. Similar intervalence (optical) transitions are also observed in mixed-valence cation radicals with the generic representation: P(br)P*+, in which two phenothiazine redox centers are interlinked by p-phenylene, o-xylylene, and o-phenylene (br) bridges. Mulliken-Hush analysis of the intervalence (charge-resonance) bands afford reliable values of the electronic coupling element H(IV) based on the separation parameters for (P/P*+) centers estimated from some X-ray structures of the intermolecular (PH)(2)*+ and the intramolecular P(br)P*+ systems. The values of H(IV), together with the reorganization energies lambda derived from the intervalence transitions, yield activation barriers DeltaG(ET)() and first-order rate constants k(ET) for electron-transfer based on the Marcus-Hush (two-state) formalism. Such theoretically based values of the intrinsic barrier and ET rate constants agree with the experimental activation barrier (E(a)) and the self-exchange rate constant (k(SE)) independently determined by ESR line broadening measurements. This convergence validates the use of the two-state model to adequately evaluate the critical electronic coupling elements between (P/P*+) redox centers in both (a) intermolecular ET via the precursor complex and (b) intramolecular ET within bridged mixed-valence cation radicals. Important to intermolecular ET mechanism is the intervention of the strongly coupled precursor complex since it leads to electron-transfer rates of self-exchange that are 2 orders of magnitude faster (and activation barrier that is substantially lower) than otherwise predicted solely on the basis of Marcus reorganization energy.     

Thermal, pressure and light induced spin transition in the two-dimensional coordination polymer [Fe(pmd)2[Cu(CN)2]2

A complete structural, calorimetric, and magnetic characterisation of the 2D coordination spin crossover polymer [Fe(pmd)(2)[Cu(CN)(2)](2)] is reported. The crystal structure has been investigated below room temperature at 180 K and 90 K, and at 30 K after irradiating the sample at low temperature with green light (lambda = 532 nm). The volume cell contraction through the thermal spin transition is only 18 A(3) which is lower than the usually observed value of around 25-30 A(3) while the average Fe-N bond distances decrease by the typical value of about 0.19 A. The structural data of the irradiated state indicate that the high spin state is well induced since the cell parameters are consistent with the data at 180 K. Calorimetric and photo-calorimetric experiments have also been performed. The entropy content for the thermal spin transition, DeltaS = 35-37 J mol(-1) K(-1) lies in the lowest range of the typical values and correlates with the low volume cell contraction. The combination of the crystallographic and calorimetric data predicts, in accordance with a mean-field approach, a linear pressure dependence of the critical temperature with a slope of 302 K GPa(-1). Magnetic measurements under pressure reveal an anomalous behaviour since the critical temperature and hysteresis do not change up to 0.22 GPa but an apparent linear dependence is obtained for higher pressures (up to 0.8 GPa) with a slope two times higher than the mean-field estimation.     

Complexation and thermogravimetric investigation on tin(II) and tin(IV) with norfloxacin as antibacterial agent

The interaction of tin(II) and tin(IV) chlorides with norfloxacin (NOR) has been investigated. Elemental analysis, infrared, mass spectra and thermal analysis have been used to characterize the isolated solid complexes. The results support the formation of complexes with the formula [Sn(NOR)₂]Cl₂·4H₂O and [Sn(NOR)₃]Cl₄. The infrared spectra of the isolated solid complexes suggested that NOR act as bidentate ligand through the carbonyl oxygen atom and one oxygen atom of the carboxylic group forming six-membered rings with the tin ions. The interpretation, mathematical analysis and evaluation of kinetic parameters of thermogravimetric (TGA) and its differential (DTG), such as entropy of activation, pre-exponential factors, activation energy evaluated by using Coats–Redfern and Horowitz–Metzger equations are carried out for two complexes. The data obtained indicate that the two complexes decompose in one stage and general mechanisms describing the decomposition are suggested. Furthermore, the electronic, and ¹H?NMR spectra have been studied.     

Oxidative addition of n-alkyl halides to diimine-dialkylplatinum(II) complexes: a closer look at the kinetic behaviors

The n-alkyl halides, RX, were oxidatively added to the platina(II)cyclopentane complexes [Pt[(CH2)4](NN)], in which NN = bpy (2,2'-bipyridyl) or phen (1,10-phenanthroline), to give the platinum(IV) complexes [PtRX[(CH2)4](NN)], R = Et and X = Br or I; R = nBu and X = I, 1-3. The same reactions with the analogous dimethyl complex [PtMe2(bpy)] gave the expected platinum(IV) complexes [PtRXMe2(bpy)], R = Et or nPr and X = Br or I; R = nBu and X = I, 4-8. Kinetics of the reactions in benzene and acetone was studied using UV-vis spectrophotometery and a common S(N)2 mechanism was suggested for each case. The platina(ii)cyclopentane complexes reacted faster than the corresponding dimethyl analogs by a factor of 2-3. This is described as being due to a lower positive charge, calculated by density functional theory (DFT), on the platinum atom of [Pt[(CH)2)4](bpy)] compared with that on the platinum atom of the dimethyl analog [PtMe2(bpy)]. The values of DeltaDeltaS(double dagger) = DeltaS(double dagger)(acetone) - DeltaS(double dagger)(benzene) were found to be either positive or negative in different reactions and this is related to the solvation of the corresponding alkyl halide. It is suggested that in these reactions of RX reagents, for a given X, the electronic effects of the R group are mainly responsible for the change in the rates of the reactions and the bulkiness of the group is far less important.     

Spectrophotometric, conductometric and thermal studies of Co(II), Ni(II) and Cu(II) complexes with 2-(2-hydroxynaphthylazo)-4-hydroxy-6-methyl-1,3-pyrimidine

The electronic absorption spectra of 2-(2-hydroxynaphthylazo)-4-hydroxy-6-methyl-1,3-pyrimidine in pure organic solvents of different polarities and in buffer solutions of varying pH are studied. The important bands in the IR and the main signals in the (1)H NMR spectra are assigned. The observed UV-vis absorption bands are assigned to the corresponding electronic transitions. The molecular stoichiometry, stability constant, absorption maximum, molar absorptivity and Sandell's sensitivity of the complexes are calculated. Obeyence to Beer's law and Ringbom optimum concentration ranges are also determined. The ability of using the titled azodye as metalochromic indicator in complexometric titrations was also studied. The effect of Co(II), Ni(II) and Cu(II) ions on the fluorescence of the azodye is also considered. The solid Cu(II) complexes of the titled azodye have been prepared and characterized by elemental, IR, UV-vis spectra as well as by conductometric and magnetic measurements. The data suggest square planar geometry for 1:1 and 1:2 (M:L) complexes. The thermal behaviour of the complexes has been studied. The kinetic parameters (n, E, A, deltaH, DeltaS and deltaG) of the thermal decomposition steps are computed using Coats-Redfern equations.