共查询到20条相似文献,搜索用时 265 毫秒
1.
Gh. H. Rounaghi A. Soleamani K. R. Sanavi 《Journal of inclusion phenomena and macrocyclic chemistry》2007,58(1-2):43-48
The complexation reactions between Ag+, Hg2+ and Pb2+ metal cations with aza-18-crown-6 (A18C6) were studied in dimethylsulfoxide (DMSO)–water (H2O) binary mixtures at different temperatures using the conductometric method. The conductance data show that the stoichiometry
of the complexes in most cases is 1:1(ML), but in some cases 1:2 (ML2) complexes are formed in solutions. A non-linear behaviour was observed for the variation of log K
f of the complexes vs. the composition of the binary mixed solvents. Selectivity of A18C6 for Ag+, Hg2+ and Pb2+ cations is sensitive to the solvent composition and in some cases and in certain compositions of the mixed solvent systems,
the selectivity order is changed. The values of thermodynamic parameters (ΔH
co, ΔS
co) for formation of A18C6–Ag+, A18C6–Hg2+ and A18C6–Pb2+ complexes in DMSO–H2O binary systems 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
2.
Fatemeh Hesami Gholam Hossein Rounaghi Massoumeh Mohajeri Somayeh Tarahomi 《Journal of solution chemistry》2011,40(8):1408-1417
The complexation reactions of 4′-nitrobenzo-15-crown-5 (4′NB15C5) with Zn2+, Mn2+, Cr3+ and Sn4+ cations were studied in acetonitrile–ethanol (AN–EtOH) binary solvent mixtures at different temperatures by the electrical
conductometry method. The stability constants of the resulting 1:1 complexes were determined from computer fitting of the
conductance versus mole ratio data. The results show that the selectivity order of 4′NB15C5 for the metal cations in the AN–EtOH
(mol-%AN=76) binary solvent at 298.15 K is: Cr3+>Mn2+≈Zn2+>Sn4+, but the selectivity order changes with the composition of the mixed solvents. A nonlinear relationship was observed between
the stability constants (log 10
K
f) of these complexes and the composition of the AN–EtOH binary solvents. The corresponding thermodynamic parameters (DHco, DSco)(\Delta H_{\mathrm{c}}^{\mathrm{o}}, \Delta S_{\mathrm{c}}^{\mathrm{o}}) were obtained from the temperature dependence of the stability constants using van’t Hoff plots. The results show that the
values and also the sign of these parameters are influenced by the nature and composition of the mixed solvents. 相似文献
3.
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
4.
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
5.
Xiaoying Xie Wenwen Liu Luyang Zhao Chengde Huang 《Journal of Solid State Electrochemistry》2010,14(9):1585-1594
Manganese–vanadium oxide had been synthesized by a novel simple precipitation technique. Scanning electron microscopy, X-ray
diffraction, Brunauer–Emmett–Teller, thermogravimetric analysis/differential scanning calorimetry, and X-ray photoelectron
spectroscopy were used to characterize Mn–V binary oxide and δ-MnO2. Electrochemical capacitive behavior of the synthesized Mn–V binary oxide and δ-MnO2 was investigated by cyclic voltammetry, galvanostic charge–discharge curve, and electrochemical impedance spectroscope methods.
The results showed that, by introducing V into δ-MnO2, the specific surface area of the mixed oxide increased due to a formation of small grain size. The specific capacitance
increased from 166 F g−1 estimated for MnO2 to 251 F g−1 for Mn–V binary oxide, and the applied potential window extended to −0.2–1.0 V (vs. saturated calomel electrode). Through
analysis, it is suggested that the capacitance performance of Mn–V binary oxide materials may be improved by changing the
following three factors: (1) small grain and particle size and large activity surface area, (2) appropriate amount of lattice
water, and (3) chemical state on the surface of MnO2 material. 相似文献
6.
Yutaka Mizuta Yusuke Daiko Atsushi Mineshige Tetsuo Yazawa 《Journal of Sol-Gel Science and Technology》2012,62(1):92-97
Phenyltriethoxysilane (PhTES) and tetraethoxysilane (TEOS) coatings [xPhTES·(100 − x)TEOS (mol%)] (x = 0–80) were prepared using methanol (Film A) or 1-propanol (Film B) as a solvent on polycarbonate (PC) substrate, and the effect of alcohol solvents on both the adhesion and distribution of
phenyl groups were studied. The alcohol evaporation rates for Films A and B were monitored by using quartz crystal microbalance (QCM). QCM measurements revealed that the migration of phenyl group to
the PC substrate side was strongly related with the alcohol solvent. Transmission fourier transform infrared measurements
for these films suggest that a phase-separation between SiO2 and PhSiO3/2 networks occur during the alcohol evaporation. 相似文献
7.
The complexes of 4-chloro-2-methoxybenzoic acid anion with Mn2+,
Co2+, Ni2+, Cu2+
and Zn2+ were obtained as polycrystalline solids
with general formula M(C8H6ClO3)2·nH2O and colours typical for M(II) ions (Mn – slightly pink, Co –
pink, Ni – slightly green, Cu – turquoise and Zn – white).
The results of elemental, thermal and spectral analyses suggest that compounds
of Mn(II), Cu(II) and Zn(II) are tetrahydrates whereas those of Co(II) and
Ni(II) are pentahydrates. The carboxylate groups in these complexes are monodentate.
The hydrates of 4-chloro-2-methoxybenzoates of Mn(II), Co(II), Ni(II), Cu(II)
and Zn(II) heated in air to 1273 K are dehydrated in one step in the range
of 323–411 K and form anhydrous salts which next in the range of 433–1212
K are decomposed to the following oxides: Mn3O4,
CoO, NiO and ZnO. The final products of decomposition of Cu(II) complex are
CuO and Cu. The solubility value in water at 293 K for all complexes is in
the order of 10–3 mol dm–3.
The plots of χM
vs.
temperature of 4-chloro-2-methoxybenzoates of Mn(II), Co(II), Ni(II) and Cu(II)
follow the Curie–Weiss law. The magnetic moment values of Mn2+,
Co2+, Ni2+ and Cu2+
ions in these complexes were determined in the range of 76−303 K and
they change from: 5.88–6.04 μB for Mn(C8H6ClO3)2·4H2O, 3.96–4.75
μB for Co(C8H6ClO3)2·5H2O, 2.32–3.02 μB for Ni(C8H6ClO3)2·5H2O and 1.77–1.94
μB for Cu(C8H6ClO3)2·4H2O. 相似文献
8.
Summary. Conformational analysis and frequency calculation were achieved for 1-phenyl-1,2-propandione 1-oxime and its four tautomers:
1-nitroso-1-phenyl-1-propen-2-ol, 1-nitroso-1-phenyl-2-propanone, 2-hydroxy-1-phenyl-propenone oxime, and 3-nitroso-3-phenyl-propen-2-ol.
Calculations were carried out at the Hartree–Fock (HF), Density Functional Theory (B3LYP), and the second-order M?ller–Plesset perturbation (MP2) levels of theory using 6-31G* and 6-311G** basis sets. Five conformers with no imaginary vibrational frequency were obtained by free rotations around three single bonds
of 1-phenyl-1,2-propandione-1-oxime: Ph–C(NOH)C(O)CH3, PhC(NOH)–C(O)CH3, and PhC(N–OH)C(O)CH3. Similarly, eight structures with no imaginary vibrational frequency were encountered upon rotations around three single
bonds of 1-nitroso-1-phenyl-1-propen-2-ol: Ph–C(NO)C(OH)CH3, PhC(N–O)C(OH)CH3, and PhC(NO)C(–OH)CH3. In the same manner, six minima were found through rotations around three single bonds of 1-nitroso-1-phenyl-2-propanone:
Ph–CH(NO)C(O)CH3, PhCH(–NO)C(O)CH3, and PhCH(NO)–C(O)CH3. Also, two minima were found through rotations around four single bonds of 2-hydroxy-1-phenyl-propenone oxime: Ph–C(NOH)C(OH)CH2, PhC(N–OH)C(OH)CH2, PhC(NOH)–C(OH)CH2, and Ph-C(NOH)C(–OH)CH2. Finally, two minima were found through rotations around four single bonds of 3-nitroso-3-phenyl-propen-2-ol: Ph–CH(NO)C(OH)CH2, PhCH(–NO)C(OH)CH2, PhCH(NO)–C(OH)CH2, and PhCH(NO)C(–OH)CH2. Interconversions within the above sets of conformers were probed through scanning (one and/or two dimensional), and/or QST3
techniques. The order of the stability of global minima encountered was: 1,2-propandione-1-oxime > 1-nitroso-1-phenyl-2-propanone
> 1-nitroso-1-phenyl-1-propen-2-ol > 2-hydroxy-1-phenyl-propenone oxime > 3-nitroso-3-phenyl-propen-2-ol. Hydrogen bonding
appears significant in tautomers of 1-nitroso-1-phenyl-1-propen-2-ol and 2-hydroxy-1-phenyl-propenone oxime. The CIS simulated
λmax for the first excited singlet state (S1) of 1-phenyl-1,2-propandione 1-oxime is 300.4 nm, which was comparable to its experimental λmax of 312.0 nm. The calculated IR spectra of 1-phenyl-1,2-propandione 1-oxime and its tautomers were compared to the experimental
spectra. 相似文献
9.
Barbara Pilawa Andrzej B. Więckowski Robert Pietrzak Helena Wachowska 《Central European Journal of Chemistry》2007,5(1):330-340
Microwave saturation of multi-component EPR spectra of oxidized lignite Mequinenza (Spain) with a carbon content of 65.1 wt
% and with a high sulphur content of 10.3 wt % was studied. The coal was oxidized with nitric acid (NHO3), peroxyacetic acid (PAA), and in O2/Na2CO3 system. Three different groups of paramagnetic centres exist in the coal samples analyzed. The EPR spectrum of the demineralised
coal was a superposition of broad Gauss (ΔB
pp
= 0.75 mT), broad Lorentz 1 (ΔB
pp
= 0.42 mT) and narrow Lorentz 3 lines (ΔB
pp
= 0.08 mT). The three EPR components with linewidths: 0.58–0.77 mT (Gauss line), 0.30–0.39 mT (Lorentz 1 line) and 0.05–0.06
mT (Lorentz 3 line) were recorded for the oxidized coal. The g-values were obtained for the samples studied in the ranges 2.0043–2.0046 (Gauss lines), 2.0035–2.0038 (Lorentz 1 lines) and
2.0032–2.0034 (Lorentz 3 lines). The broad Gauss and Lorentz 1 lines saturate at low microwave powers. The narrow Lorentz
3 lines of demineralised coal were not saturated at microwave power from the range considered. After the coal oxidation with
HNO3, PAA and in O2/Na2CO3 system, the microwave saturation of the narrow Lorentz 3 lines was also observed, which indicated a degradation of the multi-ring
aromatic structures upon oxidation.
相似文献
10.
Conformational analysis and frequency calculation were achieved for 1-phenyl-1,2-propandione 1-oxime and its four tautomers:
1-nitroso-1-phenyl-1-propen-2-ol, 1-nitroso-1-phenyl-2-propanone, 2-hydroxy-1-phenyl-propenone oxime, and 3-nitroso-3-phenyl-propen-2-ol.
Calculations were carried out at the Hartree–Fock (HF), Density Functional Theory (B3LYP), and the second-order M?ller–Plesset perturbation (MP2) levels of theory using 6-31G* and 6-311G** basis sets. Five conformers with no imaginary vibrational frequency were obtained by free rotations around three single bonds
of 1-phenyl-1,2-propandione-1-oxime: Ph–C(NOH)C(O)CH3, PhC(NOH)–C(O)CH3, and PhC(N–OH)C(O)CH3. Similarly, eight structures with no imaginary vibrational frequency were encountered upon rotations around three single
bonds of 1-nitroso-1-phenyl-1-propen-2-ol: Ph–C(NO)C(OH)CH3, PhC(N–O)C(OH)CH3, and PhC(NO)C(–OH)CH3. In the same manner, six minima were found through rotations around three single bonds of 1-nitroso-1-phenyl-2-propanone:
Ph–CH(NO)C(O)CH3, PhCH(–NO)C(O)CH3, and PhCH(NO)–C(O)CH3. Also, two minima were found through rotations around four single bonds of 2-hydroxy-1-phenyl-propenone oxime: Ph–C(NOH)C(OH)CH2, PhC(N–OH)C(OH)CH2, PhC(NOH)–C(OH)CH2, and Ph-C(NOH)C(–OH)CH2. Finally, two minima were found through rotations around four single bonds of 3-nitroso-3-phenyl-propen-2-ol: Ph–CH(NO)C(OH)CH2, PhCH(–NO)C(OH)CH2, PhCH(NO)–C(OH)CH2, and PhCH(NO)C(–OH)CH2. Interconversions within the above sets of conformers were probed through scanning (one and/or two dimensional), and/or QST3
techniques. The order of the stability of global minima encountered was: 1,2-propandione-1-oxime > 1-nitroso-1-phenyl-2-propanone
> 1-nitroso-1-phenyl-1-propen-2-ol > 2-hydroxy-1-phenyl-propenone oxime > 3-nitroso-3-phenyl-propen-2-ol. Hydrogen bonding
appears significant in tautomers of 1-nitroso-1-phenyl-1-propen-2-ol and 2-hydroxy-1-phenyl-propenone oxime. The CIS simulated
λmax for the first excited singlet state (S1) of 1-phenyl-1,2-propandione 1-oxime is 300.4 nm, which was comparable to its experimental λmax of 312.0 nm. The calculated IR spectra of 1-phenyl-1,2-propandione 1-oxime and its tautomers were compared to the experimental
spectra. 相似文献
11.
Olaf Baake Peter S. Hoffmann Andreas Klein Beatrix Pollakowski Burkhard Beckhoff Marina L. Kosinova Nadeshda I. Fainer Veronica S. Sulyaeva Valentina A. Trunova Wolfgang Ensinger 《Analytical and bioanalytical chemistry》2009,395(6):1901-1909
Films of BC
x
N
y
were produced in a plasma-enhanced chemical vapor deposition process using trimethylborazine as precursor and with H2, He, N2, and NH3, respectively, as auxiliary gas. These films deposited on Si(100) wafers or fused quartz glass substrates were characterized
chemically by X-ray photoelectron spectroscopy and by synchrotron radiation-based total-reflection X-ray fluorescence combined
with near-edge X-ray absorption fine structure. Independent of the auxiliary gas, the B–N bonds are dominating. Furthermore,
B–C and N–C bonds were identified. Oxygen, present in the bulk (in contrast to the surface layer of some nanometers, where
molecular oxygen and/or water are absorbed) as an impurity, is bonded to boron or to carbon, respectively. The relation of
boron and nitrogen changes with the character of the auxiliary gas: c
B/c
N ≈ 4:3 (for H2 and He) and c
B/c
N ≈ 1 (for N2 or NH3). Furthermore, physical properties such as the refractive index and the optical band-gap energy were determined. 相似文献
12.
Silylcobalt tetracarbonyls were reacted with various amines (B) in non-polar solvents to form silylammonium tetracarbonylcobaltate contact ion pairs formulated as [BSiR
3
+
, −Co(CO)4]. The compounds were characterized by IR and multinuclear magnetic resonance spectroscopy both in solution and in solid state.
Their properties are analogous to the known ion pairs [BH+, −Co(CO)4] and to amine adducts of halosilanes as well. 相似文献
13.
Veena Dhayal Mukesh Kumar Atal Banwari Lal Choudhary Meena Nagar Rakesh Bohra 《Journal of Sol-Gel Science and Technology》2009,52(1):97-108
Ti(OPri)4 reacts with HOSi(OtBu)3 in anhydrous benzene in 1:1 and 1:2 molar ratios to afford alkoxy titanosiloxane precursors, [Ti(OPri)3{OSi(OtBu)3}] (A) and [Ti(OPri)2{OSi(OtBu)3}2] (B), respectively. Further reactions of (A) or (B) with glycols in 1:1 molar ratio afforded six complexes of the types [Ti(OPri)(O–G–O){OSi(OtBu)3}] (1A–3A) and [Ti(O–G–O){OSi(OtBu)3}2] (1B–3B), respectively [where G = (CH2)2 (1A, 1B); (CH2)3 (2A, 2B) and {CH2CH2CH(CH3)} (3A, 3B)]. Both (A) and (B) are liquids while all the other products are viscous liquids which get solidified on ageing. Cryoscopic molecular weight
measurements of the fresh products indicate their monomeric nature. FAB mass studies of (A) and (B) also indicate monomeric nature. However, FAB mass spectra of the two representative solids (1A) and (2B) suggest dimeric behavior of the glycolato derivatives. (A) distills at 85 °C/5 mm while other products get decomposed even under reduced pressure. TG analyses of (A), (B), (1A), and (1B) suggest formation of titania–silica materials at 200 °C for (A) and (B) and 350 °C for (1A) and (1B). The products have been characterized by elemental analyses, FTIR and 1H, 13C & 29Si-NMR techniques. All these products are soluble in common organic solvents indicating a homogenous distribution of the components
on the molecular scale. The Si/Ti ratio of the oxide may be controlled easily by the composition of the starting precursors.
Hydrolysis of the glycol modified derivative, (1A) by the Sol–Gel technique affords the desired homogenous titania–silica material, TiO2·SiO2 in nano-size while, the precursor (A) yields a non-stiochiometric silica doped titania material. However, pyrolysis of (A) yields nano-sized crystallites of TiO2·SiO2. All these materials were characterized by FTIR, powder XRD patterns, SEM images, and EDX analyses. 相似文献
14.
Mohammad Khodadadi-Moghaddam Aziz Habibi-Yangjeh Mohamad Reza Gholami 《Monatshefte für Chemie / Chemical Monthly》2009,140(3):329-334
Abstract Solvatochromic parameters (E
T
N, normalized polarity parameter; π*, dipolarity/polarizability; β, hydrogen-bond acceptor basicity; α, hydrogen-bond donor acidity) have been determined for binary mixtures of propan-2-ol, propan-1-ol, ethanol, methanol and
water with recently synthesized ionic liquid (IL; 2-hydroxyethylammonium formate) at 25 °C. In all solutions except aqueous
solution, E
T
N values of the media increase abruptly with the ILs mole fraction and then increase gradually to the value of pure IL. A synergistic
behavior is observed for the α parameter in all solutions. The behavior of π* and β are nearly ideal for all solutions except for solutions of methanol with the IL. The applicability of nearly ideal combined
binary solvent/Redlich–Kister equation was proved for the correlation of various solvatochromic parameters with solvent composition.
The correlation between the calculated and the experimental values of various parameters was in accordance with this model.
Solute–solvent and solvent–solvent interactions were applied to interpret the results.
Graphical Abstract Predicted values of solvatochromic parameters (SP) (E
T
N, normalized polarity parameter; π*, dipolarity/polarizability; β, hydrogen-bond acceptor basicity; α, hydrogen-bond donor acidity) from the correlation equations versus its experimental values for binary mixtures of 2-hydroxyethylammonium
formate with water, methanol, ethanol, propan-1-ol and propan-2-ol.
相似文献
15.
The Flory–Huggins interaction parameter, χ
23, characterizing the interaction between solvents in a mixed stationary phase has been calculated using inverse gas chromatography
(IGC). The χ
23 parameters for four mixed solvent systems formed by mixing a non-polar branched alkane, 19, 24-dioctadecyldotetracontane
(C78), with four different polar solvents are analysed as a function of temperature. Two of the polar solvents are formed
by replacing one of the –CH3 groups of C78 by –OH (POH) group and –CN (PCN) group and the other two polar solvents are formed by replacing all the four
–CH3 groups of C78 by four –CF3 (TTF) groups and four –OCH3 (TMO) groups. The five solvents have similar structures and nearly the same molar volume and in mixtures, they form regular
solutions. For the mixture, C78 + POH, χ
23 was calculated at two compositions and for the remaining three mixtures χ
23 was calculated at equimolar composition. Eight solute probes representing all possible chemical structures and polarity were
used under conditions approaching infinite dilution. The effects of temperature, concentration of the mixed solvent and probe
solute on χ
23 are presented and discussed. The probe-independent χ
23 values were also calculated by linear regression analysis using the retention data of all the solute probes. In all the mixed
solvents considered here the χ
23 values are probe-dependent and decrease with increase of temperature. 相似文献
16.
Mark A. Fox Carlo Nervi Antonella Crivello Andrei S. Batsanov Judith A. K. Howard Kenneth Wade Paul J. Low 《Journal of Solid State Electrochemistry》2009,13(10):1483-1495
The influence of aryl ring substituents X (F, OMe, NMe2, NH2, OH and O−) on the physical and electronic structure of the ortho-carborane cage in a series of C,C′-diaryl-ortho-carboranes, 1-(4-XC6H4)-2-Ph-1,2-C2B10H10 has been investigated by crystallographic, spectroscopic [nuclear magnetic resonance (NMR), UV–vis], electrochemical and
computational methods. The cage C1–C2 bond lengths in this carborane series show small variations with the electron-donating
strength of the substituent X, but there is no evidence of a fully evolved quinoid form within the aryl substituents in the
ground state. In the 11B and 13C NMR spectra, the ‘antipodal’ shift at B12, and the C1 shift correlates with the Hammett σ
p value of the substituent X. The UV–visible absorption spectra of the cluster compounds show marked differences when compared
with the spectra of the analogous substituted benzenes. These spectroscopic differences are attributed to variation in contributions
from the cage orbitals to the unoccupied/virtual orbitals involved in the transitions responsible for the observed absorption
bands. Electrochemical studies (cyclic and square-wave voltammetry) carried out on the diarylcarborane series reveal that
one-electron reduction takes place at the cage in every case with the voltage required for reduction of the cage influenced
by the electron-donating strength of the substituent X, affording a series of carborane radicals with formal [2n + 3] electron
counts.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
17.
Zhi-Wei Zhao Hui-Yan Zhao Jing Wang Qing-Min Ma Ying Liu You-Cheng Li 《Journal of Cluster Science》2012,23(1):133-145
The lowest-energy configurations, electronic structures and magnetic moments of small Lu
n
(n = 2–20) clusters have been investigated within the framework of density functional theory. The results show that Lu
n
(n = 4, 8, 13, and 18) clusters are more stable than their respective neighbors, and structural transformation reveals at n = 16. As the number of atoms increases, the magnetic moments increase in an alternating fashion until they reach a maximum
of 4.00 μB for Lu8 clusters, followed by even–odd oscillation between 0.00 and 1.00 μB over the range n = 9–20. 相似文献
18.
The complex formation reactions between Mg2+, Ca2+, Sr2+ and Ba2+ metal cations with macrocyclic ligand, 4′-nitrobenzo-15C5, were studied in acetonitrile (AN)-methanol (MeOH) binary mixtures
at different temperatures using conductometric method. The results show that 4′-nitrobenzo-15C5 forms 1:1 [ML] complexes with
Mg2+, Ca2+ and Sr2+ metal cations in solutions. But in the case of Ba2+ cation a 1:2 [ML2] complex is formed in these solvent systems. The stability of the complexes is sensitive to the solvent composition and a
non-linear behavior was observed for variation of logK
f of the complexes versus the composition of the binary mixed solvents. The stability constants of complexes decrease suddenly
with increasing the concentration of methanol in this binary system. The values of thermodynamic parameters (ΔH
c° and ΔS
c°) for formation of (4′-nitrobenzo-15C5.Mg)2+, (4′-nitrobenzo-15C5.Ca)2+ and (4′-nitrobenzo-15C5.Sr)2+ complexes were obtained from temperature dependence of the stability constants and the results show that these parameters
are affected by the nature and composition of the mixed solvents. A non-linear behavior is observed between the ΔS
c° and the composition of the mixed solvents. 相似文献
19.
Viscosity B-coefficients for cesium chloride and lithium sulfate in methanol + water mixtures at 25 and 35 °C are reported. A general
treatment of the quasi-thermodynamics of viscous flow of electrolyte solutions is described. ΔG
3
Θ
(1→1′), the contribution made to the Gibbs energy of activation of the solution by the influence of the solute on the solvent,
is a function of solute–solvent interactions only; but, ΔH
3
Θ
(1→1′) and ΔS
3
Θ
(1→1′) also reflect the solvent–solvent interactions. In aqueous solution all alkali-metal ions except Li+ are sterically unsaturated, having solvent co-ordination numbers n<n
max , the maximum allowed sterically. Such complexes exchange molecules with the solvent more readily than saturated ones and
have energy–reaction co-ordinate diagrams in forms that explain the negative B or ΔG
3
Θ
(1→1′) values found in aqueous solution. Saturated complexes are the norm in non-aqueous solvents, and the ΔG
3
Θ
(1→1′) values are determined mainly by the secondary solvation. Behavior in mixed solvents reflects the transition from aqueous
to non-aqueous behavior across the range of solvent composition. 相似文献
20.
Masoud Nazarian-Samani Ali Reza Kamali Mahboobeh Nazarian-Samani Roohallah Mobarra Saber Naserifar 《Journal of Thermal Analysis and Calorimetry》2012,107(1):265-269
A combination of differential thermal analysis and detailed X-ray diffraction (XRD) analyses were used for the thermokinetic
study of phase evolution during heating–cooling of the mechanically alloyed (MA-ed) Ni–15 wt% B. According to the results
obtained, different phase transition sequences led to the formation of nanocrystalline Ni–B alloys comprising of Ni2B + o-Ni4B3 and Ni2B + m-Ni4B3 + B. Using the XRD studies, it was found that the Ni2B is the most stable intermetallic compound in the Ni–B binary phase diagram, and its nanocrystalline nature retained unchanged
even after annealing up to temperatures near the melting point. In addition, average enthalpy as well as activation energy
of occurred reactions was calculated; the latter was estimated using two well-known Kissinger and Augis & Bennett methods. 相似文献