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1.
T. M. El‐Gogary A. El‐Dissouky A. S. Hilali 《International journal of quantum chemistry》2003,91(6):685-694
The geometry of metal ions (La3+, Ce3+, UO, and Th4+) complexes with 5‐azorhodanine derivatives was optimized at the level of molecular mechanics. Two stoichiometric ratios of metal to ligand (i.e., 1:1 and 1:2) were investigated. Tetracoordinate and hexacoordinate of each stoichiometric ratio have been studied. Effect of substitution in the ligand on the geometry of the complexes was discussed in the light of electron donating–accepting properties of these substituents. The influence of the nuclear effective charge of the central metal ions on the metal–ligand (M–L) bonding was discussed and the effect of the number of ligands on the M–L bond length was also discussed and correlated to the experimental results. The total energies of the different metal complexes were computed using the extended Huckel method. The effect of substituents in ligand, metal type, and stoichiometry of the complexes on the complex total energies were discussed. Stability constant of (La3+, Ce3+, UO, and Th4+) metal ions with 5‐azorhodanine derivaties have been determined potentiometrically in 0.1 M KCl and 50% (v/v) ethanol–water mixture. The order of the stability constants of the formed complexes was found to be La3+ < Ce3+ < UO < Th4+. The influence of substituents on the stability of the complexes was examined on the basis of electron‐repelling property of the substituent. The effect of temperature on the stability of the complexes formed was studied and the corresponding thermodynamic parameters (ΔG, ΔH, and ΔS) were derived and discussed. The stoichiometries of these complexes were determined conductometrically and indicated the formation of 1:1 and 1:2 (metal:ligand) complexes. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003 相似文献
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3.
Zur Stabilität der Metallkomplexe von Methantriessigsäure und cis,cis-1,3,5-Cyclohexantricarbonsäure
The stabilities of the Mn2+-, Co2+-, Ni2+-, Cu2+- and Zn2+-complexes with 2-(carboxymethyl)glutaric acid ( 2 ) and cis,cis-1,3,5-cyclohexanetricarboxylic acid ( 3 ) were measured potentiometrically at 25° and I = 0.5 (KNO3). Beside the complexes ML? protonated species MLH and MLH are also formed. Their stability constants are given in Table 1. A comparison between the stabilities of 2 or 3 and those of acetate, as a model for a monocarboxylate, or succinate and glutarate, as examples for dicarboxylates, indicates that in all species only one carboxylate is strongly bound whereas the second and third ones are probably not. The observation that Δlog K1 = log K ? log K as well as Δlog K2 = log K ? log K are practically constants with values of 0.34 ± 0.05 and 0.49 ± 0.07, respectively, for both ligands and the five metal ions studied is also in line with the proposed monodentate structures of the complexes ML?, MLH and MLH. 相似文献
4.
The stability constants of the ternary complexes containing UTP, 2,2′-bipyridyl (bipy), and Co2+, Ni2+, Cu2+, or Zn2+ (M2+) have been determined by potentiometric titrations (Table 1). Changes in stability are quantified by Δlog KM = log K–log K. For the Co2+, Ni2+, Cu2+, and Zn2+ systems Δlog KM is 0.10, ?0.13, 0.36, and 0.15, respectively. All these ternary complexes are considerably more stable than would be expected on statistical grounds; indeed, for Co2+, Cu2+, and Zn2+, UTP4? binds more tightly to M (bipy)2+ than to M2+. An UV. difference spectroscopic study suggests that stacked adducts between bipyridyl and the pyrimidine moiety of uridine are formed. 1H-NMR. studies of the bipy/uridine, bipy/UTP, and bipy/UTP/Zn2+ systems (Figs. 1 and 2) confirm the presence of stacking in the binary adducts and in the ternary complex. There is also evidence for the existence of the stacked protonated complex, Zn(bipy) (HUTP)?, with the proton at the γ-phosphate group. The acidity constant of this ternary complex has been measured (Fig. 3). The observed stability enhancement of stacked adducts by the formation of a metal ion bridge is discussed (Fig. 4) and biological implications are indicated. 相似文献
5.
Helmut Sigel Dong Chen Nicolas A. Corf Fridrich Greg Antonin Holý Milan Strak 《Helvetica chimica acta》1992,75(8):2634-2656
The stability constants of the 1:1 complexes formed between Mg2+, Ca2+, Sr2+, Ba2+, Mn2+, Co2+, Ni2+, Cu2+, (in part) Zn2+, or Cd2+ and (phosphonylmethoxy)ethane (PME2?) or 9?[2?(phosphonylmethoxy)ethyl]adenine (PMEA2?) were determined by potentiometric pH titration in aqueous solution (I = 0.1M , NaNO3; 25°). The experimental conditions were carefully selected such that self-association of the adenine derivative PMEA and of its complexes was negligibly small; i.e., it was made certain that the properties of the monomeric [M(PMEA)] complexes were studied. Recent measurements with simple phosphate monoesters, R–MP2– (where R is a non-coordinating residue; S. S. Massoud, H. Sigel, Inorg. Chem. 1988 , 27, 1447), were used to show that analogously simple phosphonates (R? PO) – we studied now the complexes of methyl phosphonate and ethyl phosphonate – fit on the same log K/logK vs. pK/ pK straight-line plots. With these reference lines, it could be demonstrated that for all the [M(PME)] complexes with the mentioned metal ions an increased complex stability is measured; i.e., a stability higher than that expected for a sole phosphonate coordination of the metal ion. This increased stability is attributed to the formation of five-membered chelates involving the ether oxygen present in the ? O? CH2? PO residue of PME2? (and PMEA2?); the formation degree of the five-membered [M(PME)] chelates varies between ca. 15 and 40% for the alkaline earth ions and ca. 35 to 65% for 3d ions and Zn2+ or Cd2+. Interestingly, for the [M(PMEA)] complexes within the error limits exactly the same observations are made indicating that the same five-membered chelates are formed, and that the adenine residue has no influence on the stability of these complexes, with the exception of those with Ni2+ and Cu2+. For these two metal ions, an additional stability increase is observed which has to be attributed to a metal ion-adenine interaction giving thus rise to equilibria between three different [M(PMEA)] isomers. These equilibria are analyzed, and for [Cu(PMEA)] it is calculated that 17(±3)% exist as an isomer with a sole Cu2+-phosphonate coordination, 34(±10)% form the mentioned five-membered chelate involving the ether oxygen, and the remaining 49(±10)% are due to an isomer containing also a Cu2+-adenine interaction. Based on various arguments, it is suggested that this latter isomer contains two chelate rings which result from a metal-ion coordination to the phosphonate group, the ether oxygen, and to N(3) of the adenine residue. For [Ni(PMEA)], the isomer with a Ni2+-adenine interaction is formed to only 22(±13)%; for [Cd(PMEA)] and the other [M(PMEA)] complexes if at all, only traces of such an isomer are occurring. In addition, the [M(PMEA)] complexes may be protonated leading to [M(H·PMEA)]+ species in which the proton is mainly at the phosphonate group, while the metal ion is bound in an adenosine-type fashion to the nucleic base residue. Finally, the properties of [M(PMEA)] and [M(AMP)] complexes are compared, and in this connection it should be emphasized that the ether oxygen which influences so much the stability and structure of the [M(PMEA)] complexes in solution is also crucial for the antiviral properties of PMEA. 相似文献
6.
M. Niyaz Khan 《国际化学动力学杂志》2001,33(1):29-40
Pseudo‐first‐order rate constants (kobs) for the cleavage of phthalimide in the presence of piperidine (Pip) vary linearly with the total concentration of Pip ([Pip]T) at a constant content of methanol in mixed aqueous solvents containing 2% v/v acetonitrile. Such linear variation of kobs against [Pip]T exists within the methanol content range 10%–∼80% v/v. The change in kobs with the change in [Pip]T at 98% v/v CH3OH in mixed methanol‐acetonitrile solvent shows the relationship: kobs = k[Pip]T + k[Pip], where respective k and k represent apparent second‐order and third‐order rate constants for nucleophilic and general base‐catalyzed piperidinolysis of phthalimide. The values of kobs, obtained within [Pip]T range 0.02–0.40 M at 0.03 M NaOH and 20 as well as 50% v/v CH3OH reveal the relationship: kobs = k0/(1 + {kn[Pip]/kOX[−OX]T}), where k0 is the pseudo‐first‐order rate constant for hydrolysis of phthalimide, kn and kOX represent nucleophilic second‐order rate constants for the reaction of Pip with phthalimide and for the XO−‐catalyzed cyclization of N‐piperidinylphthalamide to phthalimide, respectively, and [−OX]T = [NaOH] + [−OXre], where [−OXre] = [−OHre] + [CH3Ore−]. The reversible reactions of Pip with H2O and CH3OH produce −OHre and CH3Ore− ions. The effects of mixed methanol‐water solvents on the rates of piperidinolysis of PTH reveal a nonlinear decrease in k with the increase in the content of methanol. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 33: 29–40, 2001 相似文献
7.
Bernard Dietrich Jean Guilhem Jean-Marie Lehn Claudine Pascard Etienne Sonveaux 《Helvetica chimica acta》1984,67(1):91-104
The crystal structures of four anion cryptates [X? ? BT -6H+] formed by the protonated macrobicyclic receptor BT -6H+ with F?, Cl?, Br? and N have been determined. They provide a homogeneous series of anion coordination patterns with the same ligand. The small F?-ion is tetracoordinated, while Cl? and Br? are bound in an octahedron of H-bonds. The non-complementarity between these spherical anions and the ellipsoïdal cavity of BT -6H+ is reflected in ligand distortions. Structural complementarity is achieved for the linear triatomic substrate N, which is bound by two pyramidal arrays of three H-bonds, each interacting with a terminal N-atom of N. The formation constants of the complexes formed by BT -6H+ with a variety of anions (halides, N, NO, carboxylates, SO, HPO, AMP2?, ADP3?, ATP4?, P2O) have been determined. Very strong complexations are found, as well as marked electrostatic and structural effects on stability and selectivity; in particular the binding of F?, Cl?, Br?, and N may be analyzed in terms of the crystal structure data. The cryptand BT -6H+ is a molecular receptor containing an ellipsoïdal recognition site for linear triatomic substrates of size compatible with the size of the molecular cacity. Further developments of various aspects of anion coordination chemistry are considered. 相似文献
8.
N. C. Bera I. Bhattacharyya A. K. Das 《International journal of quantum chemistry》2007,107(5):1067-1072
Ab initio and density functional methods are applied to study the spectroscopic constants and molecular properties of the diatomic cations He, Ne, Ar, HeNe+, and HeAr+. Among these cations, HeAr+ is found to be weakly bound and its spectroscopic constants are calculated using the Lennard‐Jones potential. The other molecules that are strongly bound obey Morse potential, and their spectroscopic constants are calculated accordingly. The calculated spectroscopic constants agree very well with the theoretical and experimental values wherever available. Most of the spectroscopic constants and molecular properties are reported for the first time. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 相似文献
9.
Mauro Micheloni Piero Paoletti Stephan Bürki Thomas A. Kaden 《Helvetica chimica acta》1982,65(2):587-594
The interaction of solvents and of unidentate ligands such as N, SCN?, OCN? and OH? with the Co2+-, Ni2+ and Cu2+-complexes of 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane (TMC) have been studied by Spectrophotometric and calorimetric techniques. The spectra in different solvents (Table 2) show that the Ni2+- and probably also the Cu2+-complex with TMC exist as square planar or pentacoordinate species or as a mixture of both, depending on the donor properties of the solvent. The [Co(TMC)]2+-complex is pentacoordinate in all the solvents studied. Ternary complexes [M(TMC)X]n+ are also formed by the unidentate ligands X = N, OCN?, OH?, F? and NH3 and their stability constants have been determined. Interesting is the high selectivity of [Ni(TMC)]2+ towards the addition of a further donor (Table 3). Only small ligands such as those listed above form stable adducts, whereas the larger ones such as imidazole or pyridine do not. This is a consequence of the special structure of the complex and of the trans-I-(RSRS)- conformation of the ligand in these complexes. Since the four methyl groups are all on the side of the macrocycle to which the additional unidentate ligand binds, steric interaction between the four methyl groups and the larger ligands prevents the formation of the adducts. The calorimetric measurements show that the stability of the complexes [M(TMC)X]n+ is due to both an enthalpic and entropic contribution which differ in their magnitude (Table 4). This indicates that several antagonistic factors are important in determining the overall stability. 相似文献
10.
The stability constants of the Ni2+ and Co2+ complexes with 1,5-diazacyclooctane-N,N′-diacetic acid (H2DACODA) have been determined potentiometrically in 0.5M KNO3 at 25°. Only M(DACODA) and M(DACODA)OH? were observed. In addition the formation and dissociation kinetics of the pentacoordinate complexes M(DACODA) has been studied in aqueous solution using a stopped-flow technique. Formation follows the rate law vf = kf [M2+] [HDACODA?]/[H+], which can be interpreted as a bimolecular process either between M2+ and DACODA2? (k) or between MOH+ and HDACODA? (k). The second order rate constants k are much higher than those expected from water exchange and can only be explained by a strong internal conjugate base effect. In the limiting case, however, this is equivalent to the second possible explanation, which assumes MOH+ and HDACODA? as reactive species. The dissociation rate is given by vd = (kML + k [H+]) · [M(DACODA)]. 相似文献
11.
The ternary Cu2+?2,2′-bipyridyl-adenosine-5′-monophosphate-N(1)-oxide complex was investigated and compared with the binary Cu2+-adenosine-5′-monophosphate-N(1)-oxide complex (I) (cf. [2]). In both complexes Cu2+ is bound to the o-amino-N-oxide group of adenosine-5′-monophosphate-N(1)-oxide (HL). The stabilities of the complexes monoprotonated at the phosphate group are of the same order: log K = 11,20, and log K = 11,19. The acidity constants for the deprolonation of the phosphate group in these complexes are slightly different (pK = 5,55, and pK = 5,88), but as expected both values are lower than the corresponding value pK = 6,12 of the ligand. 相似文献
12.
The 12-16 membered tetraazamacrocycles 1 - 6 were synthesized, their protonation constants and complexation kinetics measured at 25° and I = 0.50. The results of Table 1 Show that pK is strongly influenced by the ring size whereas pK and pK are relatively insensitive to it. This can be understood in terms of electrostatic interactions of the positive charges when located on adjacent amino groups. The kinetics of complex formation between the macrocyclic ligands and several transition metal ions have been studied by pH-stat and stopped-flow techniques and the results have been analyzed as bimolecular reactions between the metal ion and the different protonated species of the ligands. The rate constants, given in Table 2, show that the macrocycles react less rapidly than analogous open chain amines. However, for a given protonated species of the ligand the rate of complexation follows the order Cu2+ > Zn2+ > Co2+ > Ni2+ which parallels the sequence of their water exchange rates. For the diprotonated tetraamines LH reacting with Cu2+ the slower rates seem to be mainly a consequence of electrostatic interactions, since a correlation between logk and pK exists. For LH+, however, the complexation rates of a metal ion with the different macrocycles are all in one order of magnitude and do not depend in a regular way on the ring size or the basicity of the ligand. It is therefore suggested that in this case other factors such as unfavourable preequilibria must be considered as important. 相似文献
13.
The solubility of precipitated Cd(OH)2 was determined at 25°C in 1 M NaClO4, as a function of pH and of the ammonia content of the solutions. Formation constants were obtained for the following hydroxo, ammine and hydroxo-ammine complexes: CdOH+, Cd(OH)2, Cd(OH), CdNH, Cd(NH3), Cd(NH3), Cd(NH3) and Cd(OH)2NH3. The solubility product of the hydroxide was also calculated. The presence of polynuclear species was investigated by titrimetric determinations of the hydrogen ion concentration at constant metal concentration. 相似文献
14.
A. G. Falaleyev V. A. Andreyev V. I. Vovna 《International journal of quantum chemistry》1992,43(4):573-578
For the CF, PF, SF, and MoF ions appearing after the F1s photoionization, the possibility of dissociation has been shown by the ab initio MO LCAO method within the Z + 1 core equivalent model. According to the calculations, the decay channel AF → AF + F(1s12p6) is energetically open for the ions. So the interpretation of the gas-phase emission FKα spectra, in which the bands are assigned to the discrete transition energies, can be unacceptable for these ions. The conditions and signs of such failure are discussed. 相似文献
15.
Mechanistic studies on the oxidation of indole [IND] by HSO in aqueous CH3CN medium (80:20 v/v) have been carried out, and the reaction is characterized by the rate law ?d[HSO]/dt = k[IND][HSO]HSO and SO are probably the respective electrophiles in acidic and basic mediums. Nucleophilic attack of the ethylenic bond on the persulfate oxygen is envisaged to explain the reactivity. The reaction fails to initiate polymerization, and a radical mechanism is ruled out. Thermodynamic parameters very much suggest a bimolecular process. No significant catalytic activity is observed for the reaction system in the presence of Ag+, Cu2+, and heteroaromatic N‐bases. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 39: 46–51, 2007 相似文献
16.
Preparation of Fluorophosphates, Difluorophosphates, Fluorophosphonates, and Fluorophosphites in Fluoride-containing Urea Melts Phosphoric acid, phosphonic acid, and organylphosphonic acid react on heating in fluoride-containing urea melts in high yields to fluorophosphates, MPHO2F, organylfluorophosphonates, M1RPO2F, organylpolyfluorophosphonates, MR1CX(PO2F)2, MN(CH2PO2F)3, and phosphonoorganylfluorophosphonates, MR1CX(PO3)PO2F (M1 = K, NH4; R = organic substituent; R1 = H, organic substituent; X = OH, NH2, NR2). The reaction mechanism of the formation of fluorophosphate ions in fluoride containing urea melts is discussed. 相似文献
17.
Masao Kaneko Masahisa Ochiai Kazuhiko Kinosita Akira Yamada 《Journal of polymer science. Part A, Polymer chemistry》1982,20(4):1011-1019
The characteristics of the photoinduced electron transfer reaction from polystyrene pendant tris(2,2′-bipyridyl)ruthenium (II) complex [Ru(bpy)] to methylviologen (MV2+) were studied. The rate constant k1 from the excited state of the complex, Ru(bpy), to MV2+ were determined for both the polymeric and monomeric complexes from the lifetime τ of Ru(bpy) and the quenching rate of Ru(bpy) by MV2+. The polymer pendant Ru(bpy) showed three kinds of τ components ranging from 7 to 474 ns, in contrast to the monomeric complex, which showed one component of 350 ns. The k1 values for both complexes were almost the same, on the order of 108 L/mol s. The photoinduced electron transfer from solid-phase Ru(bpy) to liquid-phase MV2+ was realized by utilizing the polymer complex, and the solid–liquid interphase reaction system is discussed. 相似文献
18.
Hyperfine coupling constants (HFCC ) of the 19F and 35Cl atoms and the 19F and 35Cl radical anions have been calculated by the unrestricted Hartree–Fock (UHF ) method using polarization and diffuse functions with contracted double-zeta as well as uncontracted basis sets. The Adip values are fairly insensitive to changes in the basis set and show good accordance with experimental and other theoretical studies. The isotropic HFCCS aN of 19F, 19F, and 35Cl show strong dependence on d functions and the state of contraction of the s, p set. Spin-projected UHF wave functions lead to better agreement with experiment. 相似文献
19.
C. Lifshitz M. Iraqi T. Peres J. E. Fischer 《Rapid communications in mass spectrometry : RCM》1991,5(5):238-239
Measurements of the translational energy loss accompanying the charge-stripping reactions M++N→M2++N+e− and M2++N→M3++N+e− have been performed for C, C and C, C respectively. The energy nesessary to remove the second electron from Buckminsterfullerene was determined, Q=IE(C→C=12.25±0.5 eV. 相似文献
20.
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 相似文献