LiZr4(PO4)3的Na/Li及Ag/Li离子交换

研究了LiZr2(PO4)3在水溶液中的Na/Li和Ag/Li离子交换行为.结果表明,LiZr2(PO4)3对Na+和Ag+离子均具有很高的选择性,且对Ag+的选择性高于Na+.LiZr2(PO4)3与Ag+的离子交换反应是通过形成固溶体的形式进行的,而与Na+的离子交换反应则是通过置换进行的.温度升高有利于提高LiZr2(PO4)3上Na/Li和Ag/Li的离子交换反应速度.     

Isotopic Exchange in Porous and Dense Magnesium Borohydride

Magnesium borohydride (Mg(BH₄)₂) is one of the most promising complex hydrides presently studied for energy‐related applications. Many of its properties depend on the stability of the BH₄^? anion. The BH₄^? stability was investigated with respect to H→D exchange. In situ Raman measurements on high‐surface‐area porous Mg(BH₄)₂ in 0.3 MPa D₂ have shown that the isotopic exchange at appreciable rates occurs already at 373 K. This is the lowest exchange temperature observed in stable borohydrides. Gas–solid isotopic exchange follows the BH₄^?+D^.→BH₃D^?+H^. mechanism at least at the initial reaction steps. Ex situ deuteration of porous Mg(BH₄)₂ and its dense‐phase polymorph indicates that the intrinsic porosity of the hydride is the key behind the high isotopic exchange rates. It implies that the solid‐state H(D) diffusion is considerably slower than the gas–solid H→D exchange reaction at the surface and it is a rate‐limiting steps for hydrogen desorption and absorption in Mg(BH₄)_2.     

Kinetic Study of the Isotope Exchange Reactions of Malonic Acid and Malonate Ion Using 1H NMR Spectroscopy. Inhibition of Acid and Base

The isotope exchange reactions of malonic acid and a malonate ion were investigated in acidic and basic D₂O solutions, respectively, using ¹H NMR spectroscopy. The isotope exchange reaction of malonic acid is inhibited by the presence of DNO₃ (0–3 M) and DSO₄^? ion (0–0.1 M), whereas it is catalyzed by the presence of DSO₄^? ion (> 0.2 M), D₃PO₄, D₂PO₄^? ion or DPO₄^2– ion. The order of relative reactivity for catalyzing the isotope reaction of malonic acid in D₂O is DPO₄^2– > D₂PO₄^? > D₃PO₄ > DSO₄^? > DNO₃. The rate of the isotope exchange reaction of malonate ion in D₂O decreases to a minimum and then increases with increased [NaOD]₀. The mechanism of the isotope exchange reaction of malonic acid in acidic D₂O is different from the general acid-catalyzed mechanism generally observed for organic acids like acetic and dichloroacetic acids. The bimalonate ion plays an important role in the isotope exchange reactions of this system.     

An NMR study of hydrogen exchange in p-hydroxybenzoic acid

The compound has been used over a temperature range in dimethylsulfoxide, with trichloroacetic acid and triethylamine as catalysts. The rate constant for uncatalyzed bimolecular exchange at 25 C is k_N=131 M^–1 sec^–1; the constant for acid-catalyzed exchange is k_A=0.9 · 10⁴ M^–1 sec^–1; and that for base-catalyzed exchange is k_B=0.5 · 10⁴ M^–1 sec^–1. The activation energy for uncatalyzed exchange is 5.75 kcal/mole. The exchange rates in dimethylformamide and acetone are higher, on account of differences in the hydrogen bond. The exchange rates of the isomers fall in the sequence ortho > para > meta, which is due to conjugation and intramolecular hydrogen bonding. The exchange mechanism is discussed. Simple relationships in dimensionless parameters are given for calculating the exchange rate from the shape of the NMR signal.     

Synthesis of LiAlTiO4 and its selectivity to Li+ exchange

The ion-exchanger LiAlTiO₄ of spinel type was prepared by the common precipitation/hydrothermal crystallization method, and was acid-modified. Its ion-exchange properties for alkali ions such as saturation capacity of exchange, distribution coefficient and pH titration curve were determined. LiAlTiO₄ was characterized by the X-ray diffraction method. The acid treatment of LiAlTiO₄ caused Li⁺ extraction ratio to change from 28% to 72%, while the dissolution of Al is less than 6.8%. This inorganic ion-exchanger (LiAlTiO₄-700) has a higher saturation capacity of exchange for Li than for other alkali ions, the saturation capacity of exchange for Li⁺ reaches 4.29 mmol/g (30.03 mg/g); LiAlTiO₄-700(H) has a higher selectivity of ion exchange for Li⁺ than for other alkali ions. These results show LiAlTiO₄-700(H) has better memory and selectivity of ion exchange, and higher capacity of ion exchange for Li⁺. It is a kind of prospective ionic sieve for Li⁺. __________ Translated from Chinese Journal of Applied Chemistry, 2005, 22 (7) (in Chinese)     

New Mechanistic Insight into Stepwise Metal‐Center Exchange in a Metal–Organic Framework Based on Asymmetric Zn4 Clusters

Herein, a mechanism of stepwise metal‐center exchange for a specific metal–organic framework, namely, [Zn₄(dcpp)₂(DMF)₃(H₂O)₂]_n (H₄dcpp=4,5‐bis(4′‐carboxylphenyl)phthalic acid), is disclosed for the first time. The coordination stabilities between the central metal atoms and the ligands as well as the coordination geometry are considered to be dominant factors in this stepwise exchange mechanism. A new magnetic analytical method and a theoretical model confirmed that the exchange mechanism is reasonable. When the metathesis reaction occurs between Cu^II ions and framework Zn^II ions, the magnetic exchange interaction of each pair of Cu^II centers gradually strengthens with increasing amount of framework Cu^II ions. By analyzing the changes of coupling constants in the Cu‐exchanged products, it was deduced that Zn4 and Zn3 are initially replaced, and then Zn1 and Zn2 are replaced later. The theoretical calculation further verified that Zn4 is replaced first, Zn3 next, then Zn1 and Zn2 last, and the coordination stability dominates the Cu/Zn exchange process. For the Ni/Zn and Co/Zn exchange processes, besides the coordination stability, the preferred coordination geometry was also considered in the stepwise‐exchange behavior. As Ni^II and Co^II ions especially favor octahedral coordination geometry in oxygen‐ligand fields, Ni^II ions and Co^II ions could only selectively exchange with the octahedral Zn^II ions, as was also confirmed by the experimental results. The stepwise metal‐exchange process occurs in a single crystal‐to‐single crystal fashion.     

Speciative determination of phosphorus in environmental water by the isotope exchange method

An isotope exchange method for the speciative determination of phosphorus (PO ₄ ^3– , PO ₃ ^3– and total P) in natural water samples is proposed by using the exchange system of moly bdophosphate in the aqueous phase and tetraphenylarsonium molybdophosophate in the organic phase. In this exchange system, only PO ₄ ^3– exchanges and is determined. When the sample water is treated with Br₂ water in advance, the amount of PO ₄ ^3– +PO ₃ ^3– can be obtained. When the sample is treated with H₂SO₄ and HNO₃, then the amount of total P can be determined.     

Isotope exchange of strontium and molybdate ions in strontium polymolybdates

The heterogeneous isotopic exchange reactions in strontium polymolybdates of Sr²⁺ and MoO₄ ^2- ions in the strontium nitrate and sodium molybdate solutions have been studied using ⁹⁰Sr and ⁹⁹Mo as tracers. Electrometric methods have been used to study the compositions of strontium molybdates obtained by adding strontium chloride to a progressively acidified solution of sodium molybdate. It has been found that the exchange fraction increases with increasing chain length of strontium polymolybdate. The exchange equilibrium constant (K _ex) has been calculated between 298 and 348 K as well as DG°, DH° and DS°. The results indicate that Sr²⁺ cations have a much higher affinity for exchangers than MoO₄ ^2- anions. By fitting the data to the Dubinin-Radushkevich (D-R) isotherm it has been shown that the exchange capacity (X _m ) for both ions is affected by the ion adsorption process at low temperatures and by the ion exchange process at high temperatures. At high concentrations, the recrystallization process contributes to on the cation exchange but is ineffective on the anion exchange mechanism.     

The Reactivity of Manganites in 18O Isotope Exchange Reactions

The effect of the structural properties and the oxidation state of Mn on the ¹⁸O isotope exchange behaviour of ternary manganites (La_1–xSr_xMnO₃, La_0.5Sr_1.5MnO₄ and SrMnO₃) has been studied. All types of ¹⁸O isotope exchange homomolecular, partially and completely heteromolecular) take place on the very active manganites with perovskite (LaMnO₃ and La_0.7Sr_0.3MnO₃) and perovskite-like (SrMnO₃) structure, but not on the less active K₂NiF₄-structure (La_0.5Sr_1.5MnO₄). The highest ¹⁸O exchange activity is observed for La_0.7Sr_0.3MnO₃, for which the completely heteromolecular ¹⁸O exchange starts to occur at 520 K, already, a T_on which is typical for excellent redox catalysts. The influence of the structural properties on the ¹⁸O exchange and oxygen diffusion behaviour of the manganites is much more pronounced than that of the Mn³⁺/Mn⁴⁺ ratio. The different reduction behaviour of the manganites with perovskite and K₂NiF₄-structure can be explained by means of the bond-valence model.This revised version was published online in November 2005 with corrections to the Cover Date.     

A study of ion exchange selectivity coefficient by cyclic voltammetric measurement

An equation to express ion exchange selectivity coefficient was derived and used for calculating that of PPY film with the results obtained by cyclic voltammetric measurement. PPY film was synthesized by electrochemical method in aqueous solution using K₄Fe(CN)₆ as supporting electrolyte, and the anions were doped into the film. Ion exchange behaviour of doped Fe (CN)₆^3-/4- in the PPY film with Cl^?, NO₃^? or F^? ions in solution has been studied, and the corresponding ion exchange selectivity coefficients were determined.     

Reactive collisions in quadrupole cells. 3: H/D exchange reactions of protonated aromatic amines with ND3

The H/D exchange reactions of a variety of protonated aromatic amines with ND₃ m the collision cell of a hybrid BEqQ tandem mass spectrometer have been studied. The MH⁺ ions were prepared by CH₄, t-C₄H₁₀, and NH₃ chemical ionization (CI) and, for some amines, by fast-atom bombardment (FAB). Evidence is presented that the kinetic energy of the incident ion as well as its internal energy must be dissipated by nonexchanging collisions before exchange occurs, once deactivated the MH⁺ ions exchange efficiently, which leads, in most cases, to [MHJ⁺ d _x ions m which all active hydrogens have been exchanged. The MH⁺ ion of 1,3-phenylenediamine formed by gas-phase CI exchanges only very slightly with ND₃ whereas a significant fraction of the MH⁺ ions formed by FAB exchange efficiently. This difference is rationalized in terms of dominant formation of the ring-protonated species in gas-phase CI reactions and significant formation of the N-protonated species by FAB with only the N-protonated species exchanging efficiently. Similar, although less pronounced, differences are observed for the MH⁺ ion of m-anisidine. In a number of cases apparent exchange of aromatic hydrogens also is observed. Evidence is presented for the interchange of ring and amine hydrogens in protonated aromatic amines and it is suggested that only the N-protonated species undergoes significant exchange with ND₃.     

Separation of lithium isotopes by N4S2 azacrown ion exchanger

The novel N₄S₂ azacrown ion exchange resin was prepared. The ion exchange capacity of N₄S₂ ion exchanger was 0.34 meq/g dry resin. A study on the separation of lithium isotopes was carried out with N₄S₂ azacrown ion exchange resin. The lighter isotope,⁶Li is concentrated in the resin phase, while the heavier isotope,⁷Li is enriched in the solution phase. With column chromatography [0.1 cm (I.D.)×32 cm (height)] using 2.0M NH₄Cl as an eluent, separation factor, a=1.034 was obtained.     

EPR studies of isotopic exchange involving adsorbed oxygen species on MgO

In the EPR spectra of ¹⁷O₂^? adsorbed on MgO, the hyperfine lines due to ¹⁷O(I = $\text{5}\text{2}$) have been used to monitor the isotopic exchange with gas phase oxygen. The predicted behaviour of the different possible mechanisms (place exchange and/or isotopic exchange) is compared with the experimental results which show that, on MgO at room temperature, isotopic exchange occurs via an intermediate species which is tentatively identified as O₄^?.     

LiMg0.5Mn1.5O4的合成及对Li+的离子交换选择性

锂及其化合物在航空航天、化工、医药、空调、高能电池和热核反应等方面都有广泛应用，对锂及其化合物的需求与日俱增。我国液体锂资源非常丰富，开发利用其中的锂资源具有重要意义。从盐湖水、地下卤水、盐田母液、油气田水等咸水资源中提取锂的方法有碳酸盐沉淀法、离子交换法、萃取法等。离子     

WQD-1沸石离子交换性能的研究

测定了W_QD-1沸石在一价碱金属离子混合溶液中的分配系数、饱和交换量和在25℃时，NH⁺₄/K⁺、NH⁺₄/Na⁺交换等温线。得出该沸石一价离子选择性序列为：Cs⁺>Rb⁺>K⁺>Na⁺>Li⁺, Na⁺/K⁺交换自由焓变ΔG(T,P)=-6.745 KJ/mol。     

Counterion Dynamics in an Interpenetrated Coordination Cage Capable of Dissolving AgCl

In solution, the eight BF₄^? counterions of a positively charged D₄‐symmetric interpenetrated [Pd₄ligand₈]⁸⁺ double cage ( 1 ) are localized in distinct positions. At low temperatures, one BF₄^? ion is encapsulated inside the central pocket of the supramolecular structure, two BF₄^? ions are bound inside the equivalent outer pockets, and the remaining five BF₄^? ions are located outside the cage structure (expressed by the formula [3 BF₄@ 1 ][BF₄]₅). On warming, the two BF₄^? ions in the outer pockets are found to exchange with the exterior ions in solution whereas the central BF₄^? ion stays locked inside the central cavity (here written as [BF₄@ 1 ][BF₄]₇). The exchange kinetics were determined by exchange spectroscopy (EXSY) NMR experiments and line‐shape fitting in different solvents. The tremendously high affinity of this double cage for the binding of two chloride ions inside the outer pockets allows for complete exchange of two BF₄^? ions by the addition of solid AgCl to give [2 Cl+BF₄@ 1 ][BF₄]₅. The uptake of the two chloride ions is allosteric and is thus accompanied by a structural rearrangement (compression along the Pd₄ axis) of the double cage structure. An analysis by using 900 MHz NOESY NMR spectroscopy shows that this compression of about 3.3 % is associated with a helical twist of 8°, which together resemble a screw motion. As a consequence of squeezing each of the outer two pockets by 53 %, the volume of the central pocket is increased by 43 %, which results in an increase of 36 % in the ¹⁹F spin‐lattice relaxation time (T₁) of the central BF₄^? ion. The packing coefficients (PC) for the ions in the outer pockets (103 % for BF₄^? and 96 % for Cl^?) were calculated.     

Fluorine exchange in some phosphorus and arsenic compounds

The rate of intermolecular fluorine exchange in the system PhPF₄ + PhPF^?₅ ? PhPF₄FPhPF^?₄ was studied by ¹⁹F and ³¹P dynamic NMR techniques. The anion PhPF^?₅ was generated by adding potassium fluoride in crown ether to PhPF₄.Attempts to initiate exchange in Ph₂AsF₂Me by adding fluoride ion donors were unsuccessful, instead, fluoride acceptors such as HF produced rapid intermolecular fluorine exchange in Ph₂AsF₂Me, presumably via an intermediate cation Ph₂AsFMe⁺. Experimental results and proposed mechanisms of fluorine exchange will be discussed.     

Gas-phase reactivity and molecular modeling studies on triply protonated dodecapeptides that contain four basic residues

Gas-phase deprotonation and hydrogen/deuterium (H/D) exchange reactions for ions from three model dodecapeptides were studied by Fourier transform ion cyclotron resonance mass spectrometry. Molecular dynamics calculations were employed to provide information on conformations and Coulomb energies. The peptides, (KGG)₄, (K₂G₄)₂, and K₄G₈, each contain four high basicity lysine residues and eight low basicity glycine residues; however, in the present work only three lysine residues were protonated. Proton transfer reactions with a series of reference amines revealed apparent gas-phase acidities in a narrow range of 207. 3–209. 6 kcal/mol, with deprotonation efficiencies following the order [K₄G₈+3H]³⁺ > [(KGG)₄+3H]³⁺ > [(K₂G₄)₂+3H]³⁺. The three ions also react similarly with d ₄-methanol: each exchanged a maximum of 23–25 of their 25 labile hydrogens, with the first 15–17 exchanges occurring at rate constants of (1. 6–2. 6) × 10^?11 cm³ molecule^?1 s^?1. The experimental results agree with molecular modeling findings of similar conformations and Coulomb energies for the three peptide ions. The [M+3H]³⁺ data are compared to data obtained previously in our laboratory for the “fully” protonated [M+4H]⁴⁺ (Zhang, X.; Ewing, N. P.; Cassady, C. J. Int. J. Mass Spectrom. Ion Phys., in press). For (KGG)₄ and (K₂G₄)₂, there is a marked difference in H/D exchange reactivity between 3+ ions and 4+ ions. The 4+ ions, which have diffuse conformations, slowly exchange only 14 hydrogens, whereas their more compact 3+ counterparts exchange 23–25 hydrogens at a 5-times greater rate. In contrast, the 3+ and 4+ ions of K₄G₈ have similar compact conformations and exchange reactivity. The results indicate that a multiply hydrogen-bonded intermediate between the deuterating reagent and the peptide ion is necessary for facile H/D exchange. The slower, incomplete H/D exchange of [(KGG)₄+4H]⁴⁺ and [(K₂G₄)₂+4H]⁴⁺ is attributed to the inability of their protonated lysine n-butylamino groups (which extend away from the peptide backbone) to form this intermediate.     

Water exchange rates and mechanisms in tetrahedral [Be(H2O)4]2+ and [Li(H2O)4]+ complexes using DFT methods and cluster‐continuum models

The water exchange reactions in aquated Li⁺ and Be²⁺ ions were investigated with density functional theory calculations performed using the [Li(H₂O)₄]⁺·14H₂O and [Be(H₂O)₄]²⁺·8H₂O systems and a cluster‐continuum approach. A range of commonly used functionals predict water exchange rates several orders of magnitude lower than the experimental ones. This effect is attributed to the overstabilization of coordination number four by these functionals with respect to the five‐coordinated transition states responsible for the associative ( A ) or associative interchange ( I_a ) water exchange mechanisms. However, the M06 and M062X functionals provide results in good agreement with the experimental data: M062X/TZVP calculations yield a concerted I_a mechanism for the water exchange in [Be(H₂O)₄]²⁺·8H₂O that gives an average residence time of water molecules in the first coordination sphere of 260 μs. For [Li(H₂O)₄]⁺·14H₂O the water exchange reaction is predicted to follow an A mechanism with a residence time of inner‐sphere water molecules of 25 ps.     

Kinetic study of the isotope exchange reactions of malonic acid and its derivatives in various acidic D2O media using 1H NMR spectroscopy. Implication in the Belousov‐Zhabotinsky reaction

The kinetics of the isotope exchange reactions of RCH(COOH)₂ (RH, D, Me, Et, Bu, and Ph) in D₂O solution were studied by using ¹H NMR spectroscopy. It was observed that the rate of isotope exchange reaction was inhibited by the presence of 1 M of DNO₃, DCl, DBr or D₂SO₄ and catalyzed by the presence of 4 M of D₂SO₄. No inhibition effect was observed in the case of D₃PO₄. The effect of inorganic acids follows the order of D₃PO₄>D₂SO₄ ≫ (DNO₃, DCl, DBr). The conjugated base (RCH(COOD)(COO⁻)) of RCH(COOD)₂ plays an important role in the isotope exchange reaction. The presence of deuterium ion suppresses the generation of RCH(COOD)(COO⁻) ion from RCH(COOD)₂ and inhibits the rate of isotope exchange. In general, the order of reactivity of RCH(COOH)₂ toward isotope exchange with deuterium atom is RPh>(H, Br)>Me>(Et, Bu). © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 455–461, 1999