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1.
New divalent transition metal 3,5-pyrazoledicarboxylate
hydrates of empirical formula Mpz(COO)2(H2O)2,
where M=Mn, Co, Ni, Cu, Zn and Cd (pz(COO)2=3,5-pyrazoledicarboxylate),
metal hydrazine complexes of the type Mpz(COO)2N2H4
where M=Co, Zn or Cd and Mpz(COO)2nN2H4·H2O,
where n=1 for M=Ni
and n=0.5 for M=Cu
have been prepared and characterized by physico-chemical methods. Electronic
spectroscopic data suggest that Co and Ni complexes adopt an octahedral geometry.
The IR spectra confirm the presence of unidentate carboxylate anion (Δν=νasy(COO–)–νsym(COO–)>215
cm–1) in all the complexes and bidentate
bridging hydrazine (νN–N=985–950 cm–1)
in the metal hydrazine complexes. Both metal carboxylate and metal hydrazine
carboxylate complexes undergo endothermic dehydration and/or dehydrazination
followed by exothermic decomposition of organic moiety to give the respective
metal oxides as the end products except manganese pyrazoledicarboxylate hydrate,
which leaves manganese carbonate. X-ray powder diffraction patterns reveal
that the metal carboxylate hydrates are isomorphous as are those of metal
hydrazine complexes of cobalt, zinc and cadmium. 相似文献
2.
S. F. Ledenkov V. N. Vandyshev A. S. Molchanov 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2012,86(6):959-964
Enthalpies of the interaction of protonated dopamine with a hydroxide ion in water-ethanol mixtures in the concentration range
of 0–0.8 EtOH mole fractions are measured calorimetrically. The neutralization process of dopamine hydrochloride is shown
to occur endothermally in solvents with an ethanol concentration of ≥0.5 mole fractions. Standard thermodynamic characteristics
(Δr
H
○, Δr
G
○, and Δr
S
○) of the first-step acid dissociation of dopamine hydrochloride in solutions are calculated with regard to the autoprotolysis
enthalpy of binary solvents. It is found that dissociation enthalpies vary within 9.1–64.8 kJ/mol, depending on the water-ethanol
solvent composition. 相似文献
3.
The change of picture for the r
–1 operator which occurs on passing from the four component relativistic schemes to two component theories is investigated for the spin-averaged Douglas–Kroll approximation and the recently proposed infinite-order approach. For nuclei already with moderately large values of the nuclear charge the change of picture contribution is found to be relatively important. Its neglect significantly affects the calculated values of the total relativistic contribution to the expectation value of r
–1. A numerical method for the calculation of the total relativistic contribution to the expectation values of r
–1, which avoids the explicit use of the appropriately transformed r
–1 operator, is devised and tested. Also the differences between the Douglas–Kroll approximation and the infinite-order scheme are investigated. 相似文献
4.
Paul Rademacher 《Structural chemistry》2006,17(1):19-25
The electronic and geometrical structures of fluorocyclopropanes (1–12) have been analysed using DFT B3LYP calculations. A linear relationship, Δɛω=−0.172 Δr−0.171 (n=12, R=0.931), between Δɛω (in eV), the difference of the energies of the Walsh orbitals ωS and ωA, and Δr (in pm), the difference of vicinal and distal C–C bond lengths, is established. Correcting the orbital splitting by the basic value at Δr=0.00 pm, an even better linear correlation Δɛω
eff=0.0720 Δr (n=12, R=0.984) is obtained. The results confirm the general applicability of the two-orbitals model for the relationship between geometrical and electronic structures for substituted cyclopropanes.
1For Part 4 see Ref. [17]. 相似文献
5.
G. Xie S. P. Chen S. L. Gao X. X. Meng Q. Z. Shi 《Journal of Thermal Analysis and Calorimetry》2006,83(3):693-700
A novel solid complex, formulated as Ho(PDC)3
(o-phen), has been obtained from the reaction
of hydrate holmium chloride, ammonium pyrrolidinedithiocarbamate (APDC) and
1,10-phenanthroline (o-phen·H2O)
in absolute ethanol, which was characterized by elemental analysis, TG-DTG
and IR spectrum. The enthalpy change of the reaction of complex formation
from a solution of the reagents, ΔrHmθ (sol), and the molar heat capacity of the complex, cm,
were determined as being –19.161±0.051 kJ mol–1
and 79.264±1.218 J mol–1 K–1
at 298.15 K by using an RD-496 III heat conduction microcalorimeter. The enthalpy
change of complex formation from the reaction of the reagents in the solid
phase, ΔrHmθ(s), was calculated as
being (23.981±0.339) kJ mol–1 on the
basis of an appropriate thermochemical cycle and other auxiliary thermodynamic
data. The thermodynamics of reaction of formation of the complex was investigated
by the reaction in solution at the temperature range of 292.15–301.15
K. The constant-volume combustion energy of the complex, ΔcU, was determined as being –16788.46±7.74
kJ mol–1 by an RBC-II type rotating-bomb
calorimeter at 298.15 K. Its standard enthalpy of combustion, ΔcHmθ, and standard enthalpy of formation,
ΔfHmθ, were calculated to be –16803.95±7.74 and –1115.42±8.94
kJ mol–1, respectively. 相似文献
6.
Numerous published data on the structure and thermodynamics of formation of molecular complexes are analyzed. The enthalpies
of complexation (−ΔH) are related to the characteristic parameter Δr = [r
DA−a
1(r
D+r
A)], where r
DA is the donor-acceptor bond length determined by microwave spectroscopy and X-ray analysis, r
D and r
A are the tabulated values of the homopolar covalent radii of the heteroatoms that form the donor-acceptor bond, and a
1 is an empirical coefficient equal to 0.901±0.007. The relation between −ΔH and Δr values has the form −ΔH = a
2/Δr (a
2 = 21.6±1.6 kJ Å mol−1), with a mean relative error of approximation of about 15% and a correlation coefficient of 0.97. As the strength of the
complex increases, the donor-acceptor bond length approaches the sum of the heteropolar covalent radii of the atoms involved
in the bond (Δr tends to zero). At Δr ≫ 1, the strength of complexes is determined by weak van der Waals interactions between the complex components and the −ΔH values tend to zero.
Dedicated to the memory of E. N. Guryanova (1911–2004), a prominent scientist who formulated the basic principles elaborated
by her disciples in this review.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1869–1878, October, 2007. 相似文献
7.
Z. Fengqi G. Hongxu L. Yang H. Rongzu C. Pei G. Sheng-li Y. Xu-wu S. Qizhen 《Journal of Thermal Analysis and Calorimetry》2006,85(3):791-794
The constant-volume combustion energies of
the lead salts of 2-hydroxy-3,5-dinitropyridine (2HDNPPb) and 4-hydroxy-3,5-dinitropyridine
(4HDNPPb), ΔU
c
(2HDNPPb(s) and 4HDNPP(s)),
were determined as –4441.92±2.43 and –4515.74±1.92
kJ mol–1 , respectively, at 298.15 K. Their
standard enthalpies of combustion, Δc
m
H θ(2HDNPPb(s) and 4HDNPPb(s), 298.15 K), and standard enthalpies of formation,
Δr
m H θ(2HDNPPb(s) and 4HDNPPb(s),
298.15 K) were as –4425.81±2.43, –4499.63±1.92 kJ
mol–1 and –870.43±2.76, –796.65±2.32
kJ mol–1 , respectively. As two combustion
catalysts, 2HDNPPb and 4HDNPPb can enhance the burning rate and reduce the
pressure exponent of RDX–CMDB propellant. 相似文献
8.
Abstract
The electronic structure of Hg(II) ions, [Hg(L) n (H2O) m ] q (L = HO−, Cl−, HS−, S2−) has been studied. Geometries were fully optimized. The B3LYP and PBE functionals give structures in good agreement with available experimental data. Calculated stretching frequencies generally correlate well with bond lengths. The role of the water molecule(s) in the solvated Hg(II) complexes has been investigated. The solvent can act as nucleophile, as hydrogen bond acceptor or as a spectator. The trans-effect results in lengthening of the Hg–L bond length. It can be understood as a competition between ligands in trans positions for the ability to donate their electron density to the 6s AO of Hg(II). The effect of the presence of water molecules on the Hg–L bond length depends on whether or not the water molecules form a direct coordination bond with Hg(II); it will not guarantee an increase in the stability of the complexes. The interaction energy, which represents the interaction between Hg(II) and ligand L and excludes all other interactions, is nucleophilicity-dependent. The interaction energy and the strength of the ligand nucleophilicity follow the order: S2− > HS− > HO− > Cl− > H2O. The charge transfer, ΔN, is an indication for the type and strength of the interaction between ligand and Hg(II). Increasing the positive and negative value of ΔN will decrease and increase the Hg(II) total NBO charge, respectively, while decreasing the electrophilicity of Hg(II) will decrease its charge and the charge transfer, ΔN. 相似文献9.
H. Razafindralambo S. Dufour M. Paquot M. Deleu 《Journal of Thermal Analysis and Calorimetry》2009,95(3):817-821
Isothermal titration calorimetry was applied for studying the binding interactions of cyclic and linear surfactins with different
ionic charge (z= −2 and −3) and lipid chain length (n=14 and 18) to 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidyl-choline (POPC) vesicles in 10mMTris buffer at pH8.5with 150mMNaCl at 25°C. Surfactin analogues interacted
spontaneously (ΔG
D
w→b < 0) with POPC vesicles. The binding reactions were endothermic (ΔH
D
w→b > 0) and entropy-driven process (ΔS
D
w→b > 0). Moreover, significant differences in the binding constant values (K) ranging from 6.6·103 to 9.6·104 M−1 show that cyclic structure and the increase of lipid chain length are favourable on the surfactin binding affinity to POPC
vesicles, whereas the rise of the number of negative charges has an opposite effect. 相似文献
10.
Average inner < r
< > and outer < r
> > radii are studied for 28 singly-excited 1 snl singlet and triplet states (0 ≤ l ≤ n ≤ 5) of the He atom. In all the cases, the average inner radius < r
< > is close to 0.75 bohr, which indicates that one of the two electrons behaves like the 1s electron in He+. On the other hand, an analysis of the average outer radius < r
> > shows that the other electron of the 1snl states behaves approximately like an snl electron in the hydrogen atom. The average outer radius < r
> > reflects more diffuse character of the singlet electron distribution.
This paper is dedicated to the late Professor Serafin Fraga for his great contribution to quantum sciences.
Contribution to the Serafin Fraga Memorial Issue. 相似文献
11.
M. A. García del Cid M. G. Prolongo C. Salom C. Arribas M. Sánchez-Cabezudo R. M. Masegosa 《Journal of Thermal Analysis and Calorimetry》2012,108(2):741-749
Epoxy–clay nanocomposites have been prepared with an organically modified montmorillonite. The epoxy network was based on
diglycidyl ether of bisphenol A (DGEBA) cured with diaminodiphenylmethane (DDM). The stoichiometry DGEBA–DDM was varied, the
molar ratio of amine hydrogen/epoxy groups, r, ranged from 0.85 to 1.15. The influence of stoichiometry on curing and properties of the nanocomposites was studied using
differential scanning calorimetry, dynamic mechanical thermal analysis and X-ray diffraction. All nanocomposites had intercalated
clay structures. The clays accelerated the curing reaction whose rate was also increased when increasing r. The heat of reaction, −ΔH (J/g epoxy), increased as r increased, reaching a constant value for r ≥ 1. In the presence of clays −ΔH was lower than in the neat DGEBA–DDM. The glass transition temperature (T
g) of the neat epoxy thermosets reached a maximum at r = 1; however, the nanocomposites showed the T
g maximum at 0.9 < r < 1. The presence of clay lowered the T
g for r > 0.94 and raised T
g for r ≤ 0.85. The elastic modulus of neat epoxy thermosets reached a maximum in the rubber state and a minimum in the glassy state
at r = 1. The nanocomposites showed similar behavior, but the maximum and the minimum values of the elastic modulus were reached
at stoichiometry r < 1. The comparison of the properties of neat epoxy with those of the nanocomposites varying the stoichiometry indicates
that the clay itself induces stoichiometric changes in the system. 相似文献
12.
The interaction between apigenin (Ap) and bovine serum albumin (BSA) in physiological buffer (pH = 7.4) is investigated by
fluorescence quenching technique and UV-vis absorption spectra. The results reveal that Ap could strongly quench the intrinsic
fluorescence of BSA. The quenching mechanism of Ap for BSA varies with the change of Ap concentration. when Ap concentration
is lower, it is a static quenching procedure, when Ap concentration is higher, a combined quenching (both static and dynamic)
would operate. The apparent binding constants Ka and number of binding sites n of Ap with BSA are obtained by fluorescence
quenching method. The thermodynamic parameters, enthalpy change (Δr
H
m
and entropy change (Δr
S
m
), are calculated to be −15.382 kJ mol−1 K−1 < 0 and 104.888 J mol−1 K−1 > 0, respectively, which indicate that the interaction of Ap with BSA is driven mainly by hydrogen bonding and hydrophobic
interactions. The distance r between BSA and Ap is calculated to be 1.89 nm based on F?rster’s non-radiative energy transfer theory. The results of synchronous
fluorescence spectra show that binding of Ap with BSA cannot induce conformational changes in BSA. 相似文献
13.
The study is concerned with analysis of the energies of formation (E), frequency shifts (Δν) in IR spectra, ionization potentials (IP) of H-complexes, hydrogen bond lengths (r), and spin densities (sd) in H-complexes involving radical cations, obtained from quantum chemical calculations for 20 series
of H-complexes. It was for the first time established that the E, IP, r, and sd values and the changes in enthalpy (δH) depend not only on the inductive and resonance effects but also on the polarizability effect of the substituents bound to
the donor and acceptor centers in the H-complexes. Interrelations between the polarizability effect and the molecular structure
of H-complexes are considered.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 602–608, April, 2006. 相似文献
14.
S. P. Chen X. X. Meng Q. Shuai B. J. Jiao S. L. Gao Q. Z. Shi 《Journal of Thermal Analysis and Calorimetry》2006,86(3):767-774
A
solid complex Eu(C5H8NS2)3(C12H8N2) has been obtained from reaction of
hydrous europium chloride with ammonium pyrrolidinedithiocarbamate (APDC)
and 1,10-phenanthroline (o-phen⋅H2O)
in absolute ethanol. IR spectrum of the complex indicated that Eu3+
in the complex coordinated with sulfur atoms from the APDC and nitrogen atoms
from the o-phen. TG-DTG investigation provided
the evidence that the title complex was decomposed into EuS.
The
enthalpy change of the reaction of formation of the complex in ethanol, Δr
H
m
θ(l), as –22.214±0.081 kJ mol–1,
and the molar heat capacity of the complex, c
m,
as 61.676±0.651 J mol–1 K–1,
at 298.15 K were determined by an RD-496 III type microcalorimeter. The enthalpy
change of the reaction of formation of the complex in solid, Δr
H
m
θ(s), was calculated as 54.527±0.314 kJ mol–1
through a thermochemistry cycle. Based on the thermodynamics and kinetics
on the reaction of formation of the complex in ethanol at different temperatures,
fundamental parameters, including the activation enthalpy (ΔH
≠
θ),
the activation entropy (ΔS
≠
θ),
the activation free energy (ΔG
≠
θ),
the apparent reaction rate constant (k),
the apparent activation energy (E), the
pre-exponential constant (A) and the reaction
order (n), were obtained. The constant-volume
combustion energy of the complex, Δc
U,
was determined as –16937.88±9.79 kJ mol–1
by an RBC-II type rotating-bomb calorimeter at 298.15 K. Its standard enthalpy
of combustion, Δc
H
m
θ,
and standard enthalpy of formation, Δf
H
m
θ,
were calculated to be –16953.37±9.79 and –1708.23±10.69
kJ mol–1, respectively. 相似文献
15.
Edwin H. Battley 《Journal of Thermal Analysis and Calorimetry》2011,104(1):13-22
Calculations are made using the equations Δr
G = Δr
H − TΔr
S and Δr
X = Δr
H − Δr
Q where Δr
X represents the free energy change when the exchange of absorbed thermal energy with the environment is represented by Δr
Q. The symbol Q has traditionally represented absorbed heat. However, here it is used specifically to represent the enthalpy listed in tabulations
of thermodynamic properties as (H
T
− H
0) at T = 298.15 K, the reason being that for a given substance TS equals 2.0 Q for solid substances, with the difference being greater for liquids, and especially gases. Since Δr
H can be measured, and is tangibly the same no matter what thermodynamics are used to describe a reaction equation, a change
in the absorbed heat of a biochemical growth process system as represented by either Δr
Q or TΔr
S would be expected to result in a different calculated value for the free energy change. Calculations of changes in thermodynamic
properties are made which accompany anabolism; the formation of anabolic, organic by-products; catabolism; metabolism; and
their respective non-conservative reactions; for the growth of Saccharomyces cerevisiae using four growth process systems. The result is that there is only about a 1% difference in the average quantity of free
energy conserved during growth using either Eq. 1 or 2. This is because although values of TΔr
S and Δr
Q can be markedly different when compared to one another, these differences are small when compared to the value for Δr
G or Δr
X. 相似文献
16.
The well-known linear relationship (TΔS# =αΔH# +β, where 1 >α > 0,β > 0) between the entropy (ΔS#) and the enthalpy (ΔH#) of activation for reactions in polar liquids is investigated by using a molecular theory. An explicit
derivation of this linear relation from first principles is presented for an outersphere charge transfer reaction. The derivation
offers microscopic interpretation for the quantitiesα andβ. It has also been possible to make connection with and justify the arguments of Bell put forward many years ago 相似文献
17.
G. G. Gorboletova S. N. Gridchin S. A. Shabunin 《Russian Journal of General Chemistry》2012,82(3):417-421
A direct calorimetric method was used to measure the heat effects in the reactions of formation of Cu(II) complexes with L-asparagine
in aqueous solutions at 298.15 K and ionic strength 0.5, 1.0, 1.5 (KNO3). The standard thermodynamic characteristics (Δr
H
0, Δr
G
0, Δr
S
0) of the processes of complex formation in the system under study were calculated. 相似文献
18.
Gholam Hossein Rounaghi Razyeh Sanavi Khoshnood Mohammad Hossein Arbab Zavvar 《Journal of inclusion phenomena and macrocyclic chemistry》2006,54(3-4):247-252
The complexation reactions between Mg2+, Ca2+, Ag+ and Cd2+ metal cations with N-phenylaza-15-crown-5 (Ph-N15C5) were studied in acetonitrile (AN)–methanol (MeOH), methanol (MeOH)–water (H2O) and propanol (PrOH)–water (H2O) binary mixtures at different temperatures using the conductometric method. The conductance data show that the stochiometry of all of the complexes with Mg2+, Ca2+, Ag+ and Cd2+ cations is 1:1 (L:M). The stability of the complexes is sensitive to the solvent composition and a non-linear behaviour was observed for variation of log K
f of the complexes versus the composition of the binary mixed solvents. The selectivity order of Ph-N15C5 for the metal cations in neat MeOH is Ag+>Cd2+>Ca2+>Mg2+, but in the case of neat AN is Ca2+>Cd2+>Mg2+>Ag+. The values of thermodynamic parameters (ΔH
c
o
, ΔS
c
o
) for formation of Ph-N15C5–Mg2+, Ph-N15C5–Ca2+, Ph-N15C5–Ag+ and Ph-N15C5–Cd2+ complexes were obtained from temperature dependence of stability constants and the results show that the thermodynamics of complexation reactions is affected by the nature and composition of the mixed solvents. 相似文献
19.
20.
I. G. Zenkevich 《Journal of Analytical Chemistry》2010,65(3):267-275
A criterion was proposed to estimate the necessity of the derivatization of organic substances for their determination on
conventional nonpolar phases, based on such characteristic of analytes as molecular weight (M
r), normal boiling point (T
bp), and molar refraction (MR
D). All these constants can be presented as indices relative to nonpolar n-alkanes (similarly to chromatographic retention indices), I(M), I(T), and I(MR
D), which can be compared to each other as differences ΔT − M = I(T) − I(M) and ΔT − M
R
D = I(T) − I(MR
D). Substances do not require derivatization if ΔT − M < 400 and ΔT − M
R
D < 600, while at ΔT − M > 600 and ΔT − MRD > 800, derivatization is necessary. 相似文献