Interactions of silicate ions with zinc(II) and aluminum(III) in alkaline aqueous solution

We present (29)Si, (27)Al, and (67)Zn NMR evidence to show that silicate ions in alkaline solution form complexes with zinc(II) (present as zincate, Zn(OH)(3)(-) or Zn(OH)(4)(2-)) and, concomitantly, with aluminate (Al(OH)(4)(-)). Zincate reacts with monomeric silicate at pH 14-15 to form [(HO)O(2)Si-O-Zn(OH)(3)](4-) and with dimeric silicate to produce [HO-SiO(2)-O-SiO(2)-O-Zn(OH)(3)](6-). The exchange of Si between these free and Zn-bound sites is immeasurably fast on the (29)Si NMR time scale. The cyclic silicate trimer reacts relatively slowly and incompletely with zincate to form [(HO)(3)Zn{(SiO(3))(3)}](7-). The concentration of the cyclic trimer becomes further depleted because zincate scavenges the silicate monomer and dimer, with which the cyclic trimer is in equilibrium on the time scale of sample preparation. Identification of these zincate-silicate complexes is supported by quantum chemical theoretical calculations. Aluminate and zincate, when present together, compete roughly equally for a deficiency of silicate to form [(HO)(3)ZnOSiO(2)OH](4-) and [(HO)(3)AlOSiO(2)OH](3-) which exchange (29)Si at a fast but measurable rate.     

Cationic assembly of metal complex aggregates: structural diversity,solution stability,and magnetic properties

The tetradentate imino-carboxylate ligand [L](2)(-) chelates the equatorial sites of Ni(II) to give the complex [Ni(L)(MeOH)(2)] in which a Ni(II) center is bound in an octahedral coordination environment with MeOH ligands occupying the axial sites. Lanthanide (Ln) and Group II metal ions (M) template the aggregation of six [Ni(L)] fragments into the octahedral cage aggregates (M[Ni(L)](6))(x)(+) (1: M = Sr(II); x = 2,2: M = Ba(II); x = 2, 3: M = La(III); x = 3, 4: M = Ce(III); x = 3, 5: M = Pr(III); x = 3, and 6: M = Nd(III); x = 3). In the presence of Group I cations, however, aggregates composed of the alkali metal-oxide cations template various cage compounds. Thus, Na(+) forms the trigonal bipyramidal [Na(5)O](3+) core within a tricapped trigonal prismatic [Ni(L)](9) aggregate to give ((Na(5)O) subset [Ni(L)](9)(MeOH)(3))(BF(4))(2).OH.CH(3)OH, 7. Li(+) and Na(+) together form a mixed Li(+)/Na(+) core comprising distorted trigonal bipyramidal [Na(3)Li(2)O](3+) within an approximately anti-square prismatic [Ni(L)](8) cage in ((Na(3)Li(2)O) subset [Ni(L)](8)(CH(3)OH)(1.3)(BF(4))(0.7))(BF(4))(2.3).(CH(3)OH)(2.75).(C(4)H(10)O)(0.5), 8, while in the presence of Li(+), a tetrahedral [Li(4)O](2+) core within a hexanuclear open cage [Ni(L)](6) in ((Li(4)O) subset [Ni(L)](6)(CH(3)OH)(3))2ClO(4).1.85CH(3)OH, 9, is produced. In the presence of H(2)O, the Cs(+) cation induces the aggregation of the [Ni(L)(H(2)O)(2)] monomer to give the cluster Cs(2)[Ni(L)(H(2)O)(2)](6).2I.4CH(3)OH.5.25H(2)O, 10. Analysis by electronic spectroscopy and mass spectrometry indicates that in solution the trend in stability follows the order 1-6 > 7 > 8 approximately 9. Magnetic susceptibility data indicate that there is net antiferromagnetic exchange between magnetic centers within the cages.     

Characterization of silica dissolved in sodium chloride solution using fast atom bombardment mass spectrometry

The chemical species of silica dissolved in sodium chloride (NaCl) solution were identified by means of fast atom bombardment mass spectrometry (negative ion mode). The concentration of silica in 0.1 M NaCl solution is < 0.6 mmol dm(-3) (mM) and application to the identification of the silicate species at low concentrations such as in natural waters level is also possible. An apparent peak at m/z 95, which corresponds to SiO(OH)(3)(-) in 0.1 M NaCl solution, was not confirmed owing to the interference of the peaks corresponding to NaCl(2)(-); however, peaks for complexes such as Si(OH)(2)O(2)Na(-), Si(2)(OH)(5)O(2)(-), Si(2)(OH)(4)O(3)Na(-), Si(2)(OH)(3)O(4)Na(2)(-), Si(2)(OH)(2)O(5)Na(3)(-), Si(4)(OH)(7)O(5)(-), Si(4)(OH)(6)O(6)Na(-) and Si(4)(OH)(5)O(7)Na(2)(-) were detected. The existence of the trimer and its Na(+) complexes such as Si(3)(OH)(7)O(3)(-), Si(3)(OH)(6)O(4)Na(-) and Si(3)(OH)(5)O(5)Na(2)(-) was not clearly shown. These complexes can be confirmed not only in the form of the anion itself (e.g. Si(2)(OH)(5)O(2)(-)), but also in the form of some complexes with sodium ions, such as Si(2)(OH)(4)O(2)Na(-). Copyright 2000 John Wiley & Sons, Ltd.     

Metal complexes of tetrapodal ligands: synthesis, spectroscopic and thermal studies, and X-ray crystal structure studies of Na(I), Ca(II), Sr(II), and Ba(II) complexes of tetrapodal ligands N,N,N',N'-tetrakis(2-hydroxypropyl)ethylenediamine and N,N,N',N'-tetrakis(2-hydroxyethyl)ethylenediamine

Twelve complexes 1-12 of general category [M(ligand)(anion)(x)(water)(y)], where ligand = N,N,N',N'-tetrakis(2-hydroxypropyl/ethyl)ethylenediamine (HPEN/HEEN), anion = anions of picric acid (PIC), 3,5-dinitrobenzoic acid (DNB), 2,4-dinitrophenol (DNP), and o-nitrobenzoic acid (ONB), M = Ca(2+), Sr(2+), Ba(2+), or Na(+), x = 1 and 2, and y = 0-4, were synthesized. All of these complexes were characterized by elemental analysis, IR, (1)H and (13)C NMR, and thermal studies. X-ray crystal studies of these complexes 1-12, [Ca(HPEN)(H(2)O)(2)](PIC)(2).H(2)O (1), [Ca(HEEN)(PIC)](PIC) (2), Ba(HPEN)(PIC)(2) (3), [Na(HPEN)(PIC)](2) (4), Ca(HPEN)(H(2)O)(2)](DNB)(2).H(2)O (5),Ca(HEEN)(H(2)O)](DNB)(2).H(2)O (6), [Sr(HPEN)(H(2)O)(3)](DNB)(2) (7), [Ba(HPEN)(H(2)O)(2)](DNB)(2).H(2)O](2) (8), [[Ba(HEEN)(H(2)O)(2)](ONB)(2)](2) (9), [[Sr(HPEN)(H(2)O)(2)](DNP)(2)](2) (10), [[Ba(HPEN)(H(2)O)(2)](DNP)(2)](2) (11), and [Ca(HEEN)(DNP)](DNP) (H(2)O) (12), have been carried out at room temperature. Factors which influence the stability and the type of complex formed have been recognized as H-bonding interactions, presence/absence of solvent, nature of the anion, and nature of the cation. Both the ligands coordinate the metal ion through all the six available donor atoms. The complexes 1 and 5-11 have water molecules in the coordination sphere, and their crystal structures show that water is playing a dual character. It coordinates to the metal ion on one hand and strongly hydrogen bonds to the anion on the other. These strong hydrogen bonds stabilize the anion and decrease the cation-anion interactions by many times to an extent that the anions are completely excluded out of the coordination sphere and produce totally charge-separated complexes. In the absence of water molecules as in 2 and 3 the number of hydrogen bonds is reduced considerably. In both the complexes the anions case interact more strongly with the metal ion to give rise to a partially charge-separated 2 or tightly ion-paired 3 complex. High charge density Ca(2+) forms only monomeric complexes. It has more affinity toward stronger nucleophiles such as DNP and PIC with which it gives partially charge-separated eight-coordinated complexes. But with relatively weaker nucleophile like DNB, water replaces the anion and produces a seven coordinated totally charge-separated complex. Sr(2+) with lesser charge/radius ratio forms only charge-separated monomeric as well as dimeric complexes. Higher coordination number of Sr(2+) is achieved with coordinated water molecules which may be bridging or nonbridging in nature. All charge-separated complexes of the largest Ba(2+) are dimeric with bridging water molecules. Only one monomeric ion-paired complex was obtained with Ba(PIC)(2). Na(+) forms a unique dinuclear cryptand-like complex with HPEN behaving as a heptadentate chelating-cum-bridging ligand.     

Aroylhydrazone derivative as fluorescent sensor for highly selective recognition of Zn2+ ions: syntheses, characterization, crystal structures and spectroscopic properties

A new Zn(2+) fluorescent chemosensor N'-(3,5-di-tert-butylsalicylidene)-2-hydroxybenzoylhydrazine (H(3)L(1)) and its complexes [Zn(HL(1))C(2)H(5)OH](∞) (1) and [Cu(HL(1))(H(2)O)]CH(3)OH (2) have been synthesized and characterized in terms of their crystal structures, absorption and emission spectra. H(3)L(1) displays high selectivity for Zn(2+) over Na(+), K(+), Mg(2+), Ca(2+) and other transition metal ions in Tris-HCl buffer solution (pH = 7.13, EtOH-H(2)O = 8?:?2 v/v). To obtain insight into the relation between the structure and selectivity, a similar ligand 3,5-di-tert-butylsalicylidene benzoylhydrazine (H(2)L(2)), which lacks the hydroxyl group substituent in salicyloyl hydrazide compared with H(3)L(1), and its complex [Zn(2)(HL(2))(2)(CH(3)COO)(2)(C(2)H(5)OH)] (3), [Co(L(2))(2)][Co(DMF)(4)(C(2)H(5)OH)(H(2)O)] (4), [Fe(HL(2))(2)]Cl·2CH(3)OH (5), have also been investigated as a reference. H(3)L(1) exhibits improved selectivity for Zn(2+) compared to H(2)L(2). The findings indicate that the hydroxyl group substituent exerts an effect on the spectroscopic properties, complex structures and selectivity of the fluorescent sensor.     

Uptake of cesium, strontium and europium by a poly(sodium acrylate-acrylic acid) hydrogel

The uptake of cesium, strontium and europium from dilute nitric acid solutions by a poly(sodium acrylate-acrylic acid) PAA hydrogel has been investigated. pH variations are consistent with cation exchange processes: COO(-), Na (+)H (+), COO(-), Na (+)M (m+) ( M (m+) = Cs (+)and Sr (2+)) and COOH Eu (3+). Saturation of the gel is achieved for metal/carboxylate ratios R = 0.5. The swelling ratios of gels loaded with metal cations are those of uncharged, shrunk gels (Sr, Eu) or of charged, swollen gels (Cs) in agreement with the formation of uncharged (COO)(2)Sr, (COO)(2)EuX (X = NO(3) or OH) type complexes and (COO(-), Cs(+)) ion pairs. The metal cations are extracted in the gels following the order of their affinities with carboxylic groups Eu(3+) > Sr(2+) > Cs(+). An increase of the ionic strength of the metal aqueous solution up to 0.5M NaNO(3) leads to slightly decrease the europium uptake by the PAA hydrogel, but 0.1M NaNO(3) is sufficient to prevent the Sr and Cs extractions.     

Dramatic effect of the metal cation in dealkylation reactions of phosphinic esters promoted by complexes of polyether ligands with metal iodides

Metal ion electrophilic catalysis has been revealed in dealkylation reactions of phosphinic esters 1-4 promoted by complexes of polyether ligands 5-7 with metal iodides MI(n) (M[n+] = Li(+), Na(+), K(+), Rb(+), Ca(2+), Sr(2+), Ba(2+)) in low polarity solvents (chlorobenzene, 1,2-dichlorobenzene, and toluene) at 60 degrees C. The catalytic effect increases with increasing the Lewis acid character of the cation, in the order Rb(+)< K(+)< Na(+)< Li(+) and Ba(2+)< Sr(2+)< Ca(2+). The results are interpreted in terms of a transition state where the complexed cation (M[n+] subset Lig) assists the departure of the leaving group Ph(2)P(O)O(-) and, at the same time, favors the attack at carbon of the nucleophile I(-) ("push-pull" mechanism). The rate sequence found for 1-4 (Me > Et > i-Pr and t-Bu) shows that this reaction can be utilized for the selective dealkylation of these substrates.     

PVC ion-selective electrodes based on calcium bis-[dialkyl- and di-(4-alkylphenyl) phosphates] and mixed solvent mediators

PVC calcium ion-selective electrodes based on either calcium bis-di(n-decyl)phosphate or calcium bis-di[4-(1,1,3,3-tetramethylbutyl)phenyl]phosphate with various solvent mediators (alone or in pairs) have been evaluated with particular respect to interference from Na(+), K(+), Mg(2+), Sr(2+), Ba(2+), Mn(2+), Cu(2+), Ni(2+) and Zn(2+) ions. PVC calcium ion-selective electrodes based on calcium bis-di[4-(n-octyl)phenyl]phosphate with varied amounts of decan-l-ol plus di-n-octyl phenylphosphonate showed a continuous gradation in selectivity coefficients on going from a high fraction of decan-l-ol to a high fraction of the second mediator. Thus, k(pot)(Ca,Mg) changed from 1.6 for an electrode based exclusively on decan-l-ol to 4.9 x 10(-4) for one based completely on di-n-octyl phenylphosphonate. The corresponding k(pot)(Ca,Na) values were 7.0 x 10(-2) and 1.1 x 10(-3).     

Determination of borate ion-pair stability constants by potentiometry and non-approximative linearization of titration data

Borate anions, B(OH)(-)(4), are known to associate with alkali and alkaline-earth metal cations in sea-water. The borate cation ion-pairs are of the general form MB(OH)((n-1)+)(4), where M(n+) is the cation. In this work, the cation borate stability constants (K*(MB)) have been evaluated for Na(+), Li(+), Mg(2+), Ca(2+) and Sr(2+) where K*(MB) = [MB(OH(4))((n-1)+)]/[M(n+)][B(OH)(-)(4)]. The K*(MB) values were obtained from values found for the stability constant of boric acid (K*(B)) in various electrolyte media at 25 degrees and an ionic strength of 0.7. Acid-base potentiometric titrations were performed in the electrolyte media with a standard Pt/H(2) electrode and a junctionless Ag/AgCl reference electrode to monitor the emf. A non-approximative equation was used to linearize the titration data. The values obtained were: K*(Lib) = 0.89 +/- 0.02, K*(NaB) = 0.44 +/- 0.01, K*(MgB) = 13.6 +/- 0.7, K*(CaB) = 11.4 +/- 0.15, K*(SrB) = 3.47 +/- 0.06. The values for K*(MB) correlate with the charge-density parameter z(2)/(r + 0.85), where r is the radius of the cation. The speciation of boron in sea-water was predicted from the K*(MB), data for the major cations present.     

Self-assembly of a 1D heterotrimetallic Cu(II)-Sr(II)-Na(I) propeller-like chiral coordination polymer with ferromagnetic interactions

Self-assembly of metalloligand [CuL](-)(H(3)L =N-5-bromosalicylaldehydeglycyl-l-tyrosine) with Sr(2+) and Na(+) results in a 1D micro(2)-carboxylate- and H(2)O-bridged heterotrimetallic chiral coordination polymer [[Na(CuL)(3)Sr(H(2)O)(3)].9H(2)O]](n), which exhibits weak ferromagnetic exchange interactions and optical activity.     

Evolution of nickel speciation during preparation of Ni-SiO(2) catalysts: effect of the number of chelating ligands in [Ni(en)x(H2O)6-2x]2+ precursor complexes

The evolution of nickel speciation during the successive preparation steps of Ni-SiO(2) catalysts is studied by UV-Vis-NIR, FT-IR, DTG, TPR and TEM. The study focuses on the effect of the number of chelating ligands in the precursor complexes [Ni(en)(x)(H(2)O)((6-2x))](2+) (en = ethylenediamine, x = 1, 2, 3) on the adsorption on silica, and on nickel speciation after thermal treatment. When the en:Ni ratio in solution increases from 1 to 3, the most abundant complex is [Ni(en)(H(2)O)(4)](2+) (64% of all Ni complexes), [Ni(en)(2)(H(2)O)(2)](2+) (81%) and [Ni(en)(3)](2+) (61%), respectively. Equilibrium adsorption of [Ni(en)(x)(H(2)O)((6-2x))](2+) on SiO(2) results in the selective grafting of [Ni(en)(H(2)O)(4)](2+) and [Ni(en)(2)(H(2)O)(2)](2+), through the substitution of two labile H(2)O ligands by two surface SiO(-) groups. The surface [Ni(en)(H(2)O)(2)(SiO)(2)] complex formed by the grafting of [Ni(en)(H(2)O)(4)](2+) onto silica tends to transform into NiO and nickel phyllosilicate after calcination, which consequently leads to large and heterogeneously distributed metallic Ni particles upon reduction. In contrast, [Ni(en)(2)(SiO)(2)], resulting from the grafting of [Ni(en)(2)(H(2)O)(2)](2+) onto silica, no longer has aqua ligands able to react with other nickel complexes or silicium-containing species. Calcination transforms these complexes into isolated Ni(2+) ions, which are reduced into small metallic Ni particles with a more homogeneous size distribution, even at higher Ni loading.     

Effect of ions on the polymorphism, effective charge, and stability of human telomeric DNA. Photon correlation spectroscopy and circular dichroism studies

The effect of different ions on the formation and behavior of quadruplex structures of the human telomere sequence d(TTAGGG)(4) has been studied by photon correlation spectroscopy (PCS) and circular dichroism (CD). The saturation and melting curves obtained in the presence of K(+), Na(+), Rb(+), Li(+), Cs(+), and Sr(2+) ions were recorded by CD spectroscopy and indicated the formation of monomeric quadruplexes. Analysis of the saturation curves obtained at 2 degrees C has shown that the presence of a single Sr(2+) ion per oligomer is sufficient for the formation of a monomeric quadruplex of the DNA sequence studied. In the presence of SrCl(2) at a concentration of 50 mM, the formation of tetrameric quadruplexes has been detected. The effect of Sr(2+) ions on the formation of quadruplex structures by the human telomere sequence d(TTAGGG)(4) is stronger and different from that of the other ions tested. The paper also presents results of a study of electrostatic interactions in solution. The translation diffusion coefficients D(T) of the structures present in solution have been determined by photon correlation spectroscopy and the effective charges on the structures have been calculated by combining the experimental data with the results based on the coupled mode theory. Analysis of the melting points monitored by the CD method has permitted a determination of Deltan, the number of ions released in the process of thermal denaturation. All the results are in good agreement with the predictions based on the theory of polyelectrolytes. The effect of ions on the formation and behavior of quadruplex structures of the human telomere sequence d(TTAGGG)(4) has been studied by photon correlation spectroscopy and circular dichroism.     

Electrospray ionization tandem mass spectrometric study of salt cluster ions: part 2--salts of polyatomic acid groups and of multivalent metals

Salt cluster ions formed from 0.05 M solutions of CaCl(2), CuCl(2) and Na(A)B (where A = 1 or 2 and B = CO(3)(2-), HCO(3)(-), H(2)PO(4)(-) and HPO(4)(2-)) were studied by electrospray ionization tandem mass spectrometry. The effects on salt cluster ions of droplet pH and of redox reactions induced by electrospray provide information on the electrospray process. CaCl(2) solution yielded salt cluster ions of the form (CaCl(2))(n)(CaCl)(x)(x+) and (CaCl(2))(n)(Cl)(y)(y-), where x, y = 1-3, in positive- and negative-ion modes, respectively. Upon collision induced dissociation (CID), singly charged CaCl(2) cluster ions fragmented, doubly charged cluster ions generated either singly or both singly and doubly charged fragment ions, depending on the cluster mass, and triply charged clusters fragmented predominantly by the loss of charged species. CuCl(2) solution yielded nine series of cluster ions of the form (CuCl(2))(n)(CuCl)(m) plus Cu(+), CuCl(+), or Cl(-). CuCl, the reductive product of CuCl(2), was observed as a neutral component of positively and negatively charged cluster ions. Free electrons were formed in a visible discharge that bridged the gap between the electrospray capillary and the sampling cone brought about the reduction of Cu(2+) to Cu(+). Upon CID, these cluster ions fragmented to lose CuCl(2), CuCl, Cl, and Cl(2). Na(2)CO(3) and NaHCO(3) solutions yielded cluster ions of the form (Na(2)CO(3))(n) plus Na(+) or NaCO(3)(-). Small numbers of NaHCO(3) molecules were found in some cluster ions obtained with the NaHCO(3) solution. For both Na(2)HPO(4) and NaH(2)PO(4) solutions, ions of the form (Na(2)HPO(4))(h), (NaH(2)PO(4))(i), (Na(3)PO(4))(j), (NaPO(3))(k) plus Na(+), PO(3)(-) or H(2)PO(4)(-) were observed. In addition, ions having one or two phosphoric acid (H(3)PO(4)) molecules were observed from the NaH(2)PO(4) solution while ions containing one sodium hydroxide (NaOH) molecule were observed from the Na(2)HPO(4) solution. The cluster ions observed from these four salts of polyatomic acid groups indicate that changes in pH occur in both directions during the electrospray process principally by solvent evaporation; the pH value of the acidic solution became lower and that of the basic solution higher.     

Uranyl and strontium salt solvation in room-temperature ionic liquids. A molecular dynamics investigation

Using molecular dynamics simulations, we compare the solvation of uranyl and strontium nitrates and uranyl chlorides in two room-temperature ionic liquids (ILs): [BMI][PF(6)] based on 1-butyl-3-methylimidazolium(+),PF(6)(-) and [EMI][TCA] based on 1-ethyl-3-methylimidazolium(+),AlCl(4)(-). Both dissociated M(2+),2NO(3)(-) and associated M(NO(3))(2) states of the salts are considered for the two cations, as well as the UO(2)Cl(2) and UO(2)Cl(4)(2)(-) uranyl complexes. In a [BMI][PF(6)] solution, the "naked" UO(2)(2+) and Sr(2+) ions are surrounded by 5.8 and 10.1 F atoms, respectively. The first-shell PF(6)(-) anions rotate markedly during the dynamics and are coordinated, on the average, monodentate to UO(2)(2+) and bidentate to Sr(2+). In an [EMI][TCA] solution, UO(2)(2+) and Sr(2+) coordinate 5.0 and 7.4 Cl atoms of AlCl(4)(-), respectively, which display more restricted motions. Four Cl atoms sit on a least motion pathway of transfer to uranyl, to form the UO(2)Cl(4)(2)(-) complex. The free NO(3)(-) anions and the UO(2)Cl(4)(2)(-) complex are surrounded by imidazolium(+) cations ( approximately 4 and 6-9, respectively). The first shell of the M(NO(3))(2) and UO(2)Cl(2) neutral complexes is mostly completed by the anionic components of the IL, with different contributions depending on the solvent, the M(2+) cation, and its counterions. Insights into energy components of solvation are given for the different systems.     

不同金属盐改性对硅胶的水蒸气吸附性能影响

用不同的金属盐溶液对中孔硅胶进行了改性,并进行了吸附水蒸气动力学实验.讨论了改性硅胶的吸湿性与离子半径之间的关系及吸附速率与平均孔径的关系.实验结果表明:(1) CaCl2,LiCl,MgCl2,ZnCl2改性硅胶,可以使硅胶的吸湿性能明显增加.其中用CaCl2改性的硅胶的吸湿量最大,其平衡吸湿量是未改性硅胶的3倍;(2) 用CaCl2溶液改性的中孔硅胶其吸湿量已接近微孔硅胶的吸湿量,但其吸附速率明显大于微孔硅胶的吸附速率;(3) 用CaCl2和ZnCl2的混合溶液改性硅胶对其吸湿量的提高没有明显效果.     

Effective interaction potentials for alkali and alkaline earth metal ions in SPC/E water and prediction of mean ion activity coefficients

The potential of mean force (PMF) acting between two simple ions surrounded by SPC/E water have been determined by molecular dynamics (MD) simulations using a spherical cavity approach. Such effective ion-ion potentials were obtained for Me-Me, Me-Cl-, and Cl(-)-Cl- pairs, where Me is a Li+, Na+, K+, Mg2+, Ca2+, Sr2+, and Ba2+ cation. The ionic sizes estimated from the effective potentials are not pairwise additive, a feature in the frequently used primitive model for electrolytes. The effective potentials were used in Monte Carlo (MC) simulations with implicit water to calculate mean ion activity coefficients of LiCl, NaCl, KCl, MgCl2, CaCl2, SrCl2, and BaCl2. Predicted activities were compared with experimental ones in the electrolyte concentration range 0.1-1 M. A qualitative agreement for LiCl and a satisfactory agreement for NaCl were found, whereas the predictions for KCl by two K+ models were less coherent. In the case of alkaline earth metal ions, all experimental activities were successfully reproduced at c = 0.1 M. However, at higher concentrations, similar deviations occurred for all divalent cations, suggesting that the dependence of the permittivity on the salt concentration and the polarization deficiency arising from the ordering of water molecules in the ion hydration shells are important in such systems.     

Redox reactivity of photogenerated osmium(II) complexes

Powerful reductants [Os(II)(NH(3))(5)L](2+) (L = OH(2), CH(3)CN) can be generated upon ultraviolet excitation of relatively inert [Os(II)(NH(3))(5)(N(2))](2+) in aqueous and acetonitrile solutions. Reactions of photogenerated Os(II) complexes with methyl viologen to form methyl viologen radical cation and [Os(III)(NH(3))(5)L](3+) were monitored by transient absorption spectroscopy. Rate constants range from 4.9 × 10(4) M(-1) s(-1) in acetonitrile solution to 3.2 × 10(7) (pH 3) and 2.5 × 10(8) M(-1) s(-1) (pH 12) in aqueous media. Photogeneration of five-coordinate Os(II) complexes opens the way for mechanistic investigations of activation/reduction of CO(2) and other relatively inert molecules.     

Interactions of diethylenetriaminepentaacetic acid (dtpa) and triethylenetetraaminehexaacetic acid (ttha) with major components of natural waters

The binding ability of diethylene triamine pentaacetate (dtpa(5-)) and triethylene tetraamine hexaacetate (ttha(6-)) ligands towards major components, H(+), Na(+), Mg(2+) and Ca(2+), of natural waters was studied in both single and mixed ionic media at different ionic strengths and at T=25 degrees C. Some measurements, performed in Mg(2+)-Ca(2+) mixtures, allowed us to find the formation of new mixed species MgCa(dtpa), MgCa(ttha) and MgCaH(ttha), here reported for the first time. All the complexes formed in the various systems were characterized in terms of both stoichiometry and stability, and an attempt was made to find general rules for the stability of mixed metal complexes in comparison with that of simple species. To obtain quantitative information on the complexing ability of dtpa and ttha in seawater, measurements have been carried out in artificial seawater ionic medium (Na(+), K(+), Ca(2+), Mg(2+), Cl(-) and SO(4)(2-)). Calculations, performed by considering the salt mixture as single salt BA, allowed us to find some quite stable B(i)H(j)L species. Under the natural seawater conditions [S(salinity)=35], we found for the most important species logbeta( B(dtpa))=9.64 and. Literature data comparison is also reported.     

Complexes of bivalent metal cations in electrospray mass spectra of common organic compounds

In the standard electrospray ionization mass spectra of many common, low molecular mass organic compounds dissolved in methanol, peaks corresponding to ions with formula [3M + Met](2+) (M = organic molecule, Met = bivalent metal cation) are observed, sometimes with significant abundances. The most common are ions containing Mg(2+), Ca(2+) and Fe(2+). Their presence can be easily rationalized on the basis of typical organic reaction work-up procedures. The formation of [3M + Met](2+) ions has been studied using N-FMOC-proline methyl ester as a model organic ligand and Mg(2+), Ca(2+), Sr(2+), Ba(2+), Fe(2+), Ni(2+), Mn(2+), Co(2+) and Zn(2+) chlorides or acetates as the sources of bivalent cation. It was found that all ions studied form [3M + Met](2+) complexes with N-FMOC-proline methyl ester, some of them at very low concentrations. Transition metal cations generally show higher complexation activity in comparison with alkaline earth metal cations. They are also more specific in the formation of [3M + Met](2+) complexes. In the case of alkaline earth metal cations [2M + Met](2+) and [4M + Met](2+) complex ions are also observed. It has been found that [3M + Met](2+) complex ions undergo specific fragmentation at relatively low energy, yielding fluorenylmethyl cation as a major product. [M + Na](+) ions are much more stable and their fragmentation is not as specific.