[C5Li5]Mgn[C5Li5] (n?=?2–8): novel sandwich complexes containing –Mg–Mg– chain

A density functional theory (DFT) investigation on novel sandwich-type D ₅ [C₅Li₅]Mg _n [C₅Li₅] (n = 2–8) complexes containing –Mg–Mg– chain has been performed in this work. The equilibrium geometries, electronic structures, vibrational frequencies, and stabilities of these complexes are researched by B3LYP and BP86 methods at 6-311+G(d) levels of theory. The Mg _n ²⁺ sandwich complexes with D ₅ symmetry are all true minima on the potential energy surface. NBO analyses for the series of complexes reveal that the Mg–Mg bond is a weak σ covalent bond. There are mainly electrostatic interactions between C₅Li₅ ⁻ ligands and Mg _n ²⁺(n = 2–8) nuclear in these complexes. The NICS and NICS_zz computed with GIAO-B3LYP/6-311+G(d) indicates that the C₅Li₅ ⁻ rings in the series of complexes are aromatic. These novel complexes turn out to be strongly thermodynamically favored in the gas phases and may be targeted in future experiments to expand the structural domain of sandwich-type complexes.     

Processes of dissociative electron capture by 20-hydroxyecdysone molecules

The peculiarities of dissociative electron capture by 20-hydroxyecdysone molecules with the formation of fragment negative ions were studied. In the region of high electron energies (5–10 eV), processes of skeleton bond rupture are accompanied by the elimination of H₂O and H₂ molecules. In the region of thermal energies of electrons (≈0 eV), the mass spectrum is formed mainly by the [M−nH₂O]^.− (n=1–3) and [M−H₂−nH₂O]^.− (n=0−3) ions that are generated exclusively by the rearrangement. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 709–712, April, 2000.     

Coordination behavior of the core and valence levels of low-coordinated oxygen ions on the surface of magnesium oxide

For low-coordinated (N=2,3,4,5) oxygen ions on the surface and in the bulk of magnesium oxide, the behavior of the core O1s- and valence O2s-, O2p-levels is considered. The MgO ₆ ¹⁰⁻ , OMg ₆ ¹⁰⁺ , Mg₁₃O ₁₄ ²⁻ , O₁₃Mg ₁₄ ²⁺ , Mg₄O ₇ ⁶⁻ , and OMg ₂ ²⁺ clusters are calculated by the SCF-Xα-SW method. The binding energies of oxygen 1s-, 2s-, and 2p-states decrease with coordination. This coordination dependence is explained by the greater change of the Madelung potential as compared to variations of the purely electronic terms of the binding energies of oxygen ions. The dependence of oxygen atomic charges and relaxation energies on coordination is also discussed. Institute of Catalysis, Siberian Branch, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 36, No. 1, pp. 16–26, January–February, 1995. Translated by the authors     

Study of Complex Formation between N-Phenylaza-15-Crown-5 with Mg2+, Ca2+, Ag+ and Cd2+ Metal Cations in Some Binary Mixed Aqueous and Non-aqueous Solvents using the Conductometric Method

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.     

Competition between reactivity and relaxation in free electron attachment to molecules

The reactivity of the C₆F₅X (X=F, Cl, Br, I) molecules following low energy (0–15 eV) electron attachment is studied in the gas phase under single collision conditions, free molecular clusters and condensed molecules by means of crossed beams and surface experiments. All four molecules exhibit a very prominent resonance for low energy electron attachment (<1 eV, attachment cross section >10⁻¹⁴ cm²). Under collision free conditions thermal electron capture generates long lived molecular parent anions C₆F₅X^−*. Along the line Cl, Br, I dissociation into X⁻+C₆F₅ and X+C₆F₅-increasingly competes until for X=1 only chemical fragmentation is observed on the mass spectrometric time scale. In free molecular clusters chemical fragmentation is quantitatively quenched at low energies in favour of associative attachment yielding undissociated, relaxed ions (C₆F₅X)⁻ _n,n≥1. A further dissociative resonance at 6.5 eV in C₆F₅Cl is considerably enhanched in clusters. If these molecules are finally condensed on a solid surface, one observes a prominent Cl⁻ desorption resonance at 6.5 eV. While the quantitative quenching of the chemical reactivity at low energies is due to the additional possibilities of energy dissipation under aggregation, the enhanched reactivity at 6.5 eV is interpreted by the conversion of a core excited open channel resonance in single molecules into a closed channel (Feshbach) resonance when it is coupled to environmental molecules.     

Ca2+- and Mg2+-induced molecular interactions in a dehydrocholic acid/didodecyldimethylammonium bromide mixed monolayer

The aim of this article is the evaluation of Ca²⁺ and Mg²⁺ subphases presence effect on mixed monolayers composed by dehydrocholic acid (HDHC) and didodecyldimethylammonium bromide (DDAB). The monolayer stability was analyzed by the evaluation of thermodynamic parameters, ΔG _mix^E and α. At all calcium ion-tested concentration, the mixed systems X _HDHC = 0.6 and 0.8 at π = 30 mJ m⁻² were always the most favored proportions. The X _HDHC = 0.6 system was also stable in magnesium presence, and the X _HDHC = 0.2-mixed monolayer went through a stable to an unstable state as the content of Ca²⁺ or Mg²⁺ augment. Finally, the X _HDHC = 0.4 monolayer showed a particular behavior, i.e., remained stable at low cation concentration, unstable at intermediate concentration and stable again at high concentration. The effect was similar at Mg²⁺ presence.     

DFT study of the structure and stability of Pu(III) and Pu(IV) chloro complexes

The structural characteristics and energies of PuCl _n ^{(3 − n)+} and PuCl _n ^{(4 − n)+} complexes (n = 2–8) have been studied by the density functional theory (DFT) method in the SVWN5 local functional approximation.     

Preparation of solutions of amidomagnesium chlorides in poly(ethylene oxide) and their characterization by conductivity measurements

Polymer electrolyte systems were prepared for the first time by dissolution of amidomagnesium chlorides in poly(ethylene oxide), (PEO). For the preparation, solutions of (hexamethyldisilylamido)magnesium chloride, (dimethylpyrrolyl)magnesium chloride, (diisopropylamido)magnesium chloride, piperidinomagnesium chloride and morpholinomagnesium chloride were chosen. The composition of these polymer electrolyte systems corresponds to the general formula R₂NMgCl·P(EO)_n·THF. Most work has been done with the system (hexamethyldisilylamido)magnesium chloride in PEO, (Me₃Si)₂NMgCl·P(EO)_n·THF, with n= 3, 4, 5, or 7. The electrolytes have a soft rubber-like consistency. At 30 °C, electrical conductivities of 10⁻⁶–10⁻⁵ S/cm were found. The conductivities were measured in the temperature range 20–60 °C. Within this temperature range a linear dependence of the logarithms of the conductivity on the inverse temperature was found and activation energies for the conducting process of 30–60 kJ/mol were calculated. Using those polymer electrolytes with a high content of the amidomagnesium compound, a reversible magnesium deposition takes place by cathodic reduction at potentials below −1.9 V vs. a Ag/AgCl reference electrode. These polymer electrolytes were found to be stable against oxidation up to about −0.3 V vs. Ag/AgCl. Electronic Publication     

Synthesis,spectroscopic, thermal and biological aspect of mixed ligand copper(II) complexes

Derivative of 8-hydroxyquinoline i.e. Clioquinol is well known for its antibiotic properties, drug design and coordinating ability towards metal ion such as Copper(II). The structure of mixed ligand complexes has been investigated using spectral, elemental and thermal analysis. In vitro anti microbial activity against four bacterial species were performed i.e. Escherichia coli, Pseudomonas aeruginosa, Serratia marcescens, Bacillus substilis and found that synthesized complexes (15–37 mm) were found to be significant potent compared to standard drugs (clioquinol i.e. 10–26 mm), parental ligands and metal salts employed for complexation. The kinetic parameters such as order of reaction (n = 0.96–1.49), and the energy of activation (E _a = 3.065–142.9 kJ mol⁻¹), have been calculated using Freeman–Carroll method. The range found for the pre-exponential factor (A), the activation entropy (S* = −91.03 to−102.6 JK⁻¹ mol⁻¹), the activation enthalpy (H* = 0.380–135.15 kJ mol⁻¹), and the free energy (G* = 33.52–222.4 kJ mol⁻¹) of activation reveals that the complexes are more stable. Order of stability of complexes were found to be [Cu(A⁴)(CQ)OH] · 4H₂O > [Cu(A³)(CQ)OH] · 5H₂O > [Cu(A¹)(CQ)OH] · H₂O > [Cu(A²)(CQ)OH] · 3H₂O     

Solid-solute phase equilibria in aqueous solution. VI. Solubilities,complex formation,and ion-interaction parameters for the system Na+−Mg2+−ClO 4 − −CO2−H2O at 25°C

The stoichiometric solubility constant of eitelite (NaMg _0.5 CO ₃ +2H⁺ ⇄ Na⁺+0.5Mg ²⁺ +CO ₂ (g)+H ₂ O, log^*K _pso ^I =14.67±0.03 was determined at I=3 m (mol kg⁻¹) (NaClO ₄ ) and 25°C. The stability of magnesium (hydrogen-)carbonato complexes in this ionic medium was explicitely taken into account. Consequently, trace activity coefficients of free ionic species, calculated from the Pitzer model with ion-interaction parameters from the literature, were sufficient for an evaluation of the thermodynamic solubility constants and Gibbs energies of formation for eitelite (−1039.88±0.60), magnesite (−1033.60±0.40), hydromagnesite (−1174.30±0.50), nesquehonite (−1724.67±0.40), and brucite (−835.90±0.80 kJ-mol ⁻¹ ). The increasing solubilities of nesquehonite and eitelite at higher sodium carbonate molalities were explained by invoking a magnesium dicarbonato complex (Mg²⁺+2CO ₃ ²⁻ ⇄ Mg(CO₃) ₂ ²⁻ , log β_z = 3.90 ± 0.08). A set of ion-interaction parameters was obtained from solubility and dissociation constants for carbonic acid in 1 to 3.5 m NaClO ₄ media which reproduce these constants to 0.02 units in log K. The following Pitzer parameters are consistent with the previously studied formation of magnesium (hydrogen-)carbonato complexes in 3m NaClO ₄ . The model and Gibbs functions of solid phases derived here reproduce original solubility data (−log [H⁺], [Mg ²⁺ ] _tot ) measured in perchlorate medium within experimental uncertainty. Presented at the XXII International Conference on Solution Chemistry, July 14–19, 1991, Linz, Austria.     

Theoretical studies on anionic clusters of sulfate anions and carbon dioxide, SO 4?1/?2 (CO2)n, n?=?1?4

Geometry optimizations were performed on monoanionic and dianionic clusters of sulfate anions with carbon dioxide, SO₄^−1/−2(CO₂) _n , for n = 1–4, using the B3PW91 density functional method with the 6-311 + G(3df) basis set. Limited calculations were carried out with the CCSD(T) and MP2 methods. Binding energies, as well as adiabatic and vertical electron detachment energies, were calculated. No covalent bonding is seen for monoanionic clusters, with O₃SO–CO₂ bond distances between 2.8 and 3.0 ?. Dianionic clusters show covalent bonding of type [O₃S–O–CO₂]⁻², [O₃S–O–C(O)O–CO₂]⁻², and [O₂C–O–S(O₂)–O–CO₂]⁻², where one or two oxygens of SO₄⁻² are shared with CO₂. Starting with n = 2, the dianionic clusters become adiabatically more stable than the corresponding monoanionic ones. Comparison with SO₄^−1/−2(SO₂) _n and CO₃^−1/−2(SO₂) _n clusters, the binding energies are smaller for the present SO₄^−1/−2(CO₂) _n systems, while stabilization of the dianion occurs at n = 2 for both SO₄⁻²(CO₂) _n and SO₄⁻²(SO₂) _n , but only at n = 3 for CO₃⁻²(SO₂) _n .     

Fragmentation of sputtered vanadium and niobium cluster ions,kinetic release and dissociation energy

The generation and unimolecular fragmentation of V _n ⁺ and Nb _n ⁺ clusters formed in sputtering vanadium and niobium surfaces by Xe⁺ ions has been studied. The method of measuring the kinetic energy of fragment ions (kinetic energy release distribution) has been used to determine the dissociation energy. Kinetic energy spectra have been measured in the field-free zone (corresponding to a time window of 10⁻⁵–10⁻⁴ sec after emission) of an ion microanalyzer with double focusing in reverse geometry. The results of spectra measurement were treated using the Rice-Ramsperge-Kassel theory of unimolecular reactions and the “evaporative ensemble”, which allowed us to calculate the dissociation energies of homonuclear V _n ¹ (n= 5–11) and Nb _n ¹ (n = 3–8) clusters.     

DNA—metal(ii) ion—phosphatidylcholine complexes: structure calculations and stability estimates by molecular mechanics

The structures and formation energies of nucleic acid—phospholipid complexes both in the absence and in the presence of Mg²⁺ ions were calculated taking double-stranded trinucleoside diphosphates NpNpN or heptanucleotides ApAp(NpNpN)pApA, composed of 64 possible combinations of genetic code, and phosphatidylcholine as model compounds. The dependence of intramolecular interactions on the primary structure of nucleic acid molecules and on the presence of a cationic bridge was revealed. The formation energies and structure of oligonucleotides were found by molecular mechanics calculations with the AMBER force field. The structures of phospholipid and MgCl₂ molecules were calculated by the semiempirical PM3 method, while the energies of phospholipid—oligonucleotide complexes were calculated by the molecular mechanics method. Calculations of complexes were carried our with consideration of solvation effects. Considerable gain in the formation energy of triple complexes (13–14 kcal mol⁻¹) is achieved due to the presence of the electroneural metal bridge. A tendency toward increasing the stability of triple complexes containing guanosine-and cytidine-enriched triplets was revealed. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2068–2071, November, 1999.     

Mixed-ligand complexation of calcium and magnesium ions with heparin and glycine

Chemical equilibria in dilute aqueous solutions containing high-molecular-weight heparin (Na₄hep) and Glycine (HGly), as well as in solutions of the MCl₂-Na₄hep-HGly-H₂O-NaCl system (M = Ca²⁺, Mg²⁺) against the background of 0.15 M NaCl at 37°C, have been studied by mathematical modeling of chemical equilibria on the basis of pH-metric titration data. The model of equilibria of the Na₄hep-HGly-H₂O-NaCl system for the range 2.30 ≤ pH ≤ 10.50 at different ratios of initial heparin and glycine concentrations showed that, in the pH range of blood plasma stability (pH 6.80–7.40), the protonated H H₃hepGly₃⁴⁻ species prevailed. This was supported by UV absorption spectra of heparin and glycine solutions in the presence of 0.15 M NaCl and absorbance dynamics for solutions containing heparin and glycine. The results of modeling equilibria in the five-component MCl₂-Na₄hep-HGly-H₂O-NaCl systems (M = Ca²⁺, Mg²⁺) showed that the Ca²⁺ and Mg²⁺ ions form with heparin and glycine stable protonated mixed-ligand complexes M H₃hepGly₃²⁻. The formation constants of these species are one order of magnitude higher than the formation constants of the homoligand calcium and magnesium with heparin. In the pH range 6.80–7.40, the calcium content decreases depending on the ratio of the initial concentrations of Na₄hep, HGly, and CaCl₂: at the 1 : 3 : 1 ratio, it decreases by a factor of 5.7 owing to the formation of the predominant species CaH₃hepGly₃²⁻, and at equimolar amounts of the reagents (1 : 1 : 1), the calcium content decreases by a factor of 3.5 (the CaH₃hepGly₃²⁻ concentration is three time as low as the NaCahep⁻ concentration).     

Potentiometric Study of the Effect of Sodium Dodecylsulfate and Dioxane on the Hydrolysis of the Aluminum(III) Ion

Hydrolytic equilibria of the aluminum(III) ion were studied in the presence of a surfactant, sodium n-dodecylsulfate (SDS) and, separately, in mixed water + dioxane and water + dioxane + surfactant media at 298.15 K, by using potentiometric measurements with a glass electrode. The concentration of SDS was between 1.25 and 25.0 mmol-dm⁻³, whereas the volume percent of dioxane was varied from 10 to 50. The supporting strong electrolyte was 0.1 mol-dm⁻³ LiCl. A general least-squares treatment of the data indicates the formation of mononuclear hydrolytic complexes of the form Al(OH)_m^{3 − m} (m = 1–3) at all studied compositions. At lower concentrations of SDS (≤ 12.5 mmol-dm⁻³) it was necessary to include polynuclear hydrolytic complexes in the hydrolytic model. On increasing the concentration of SDS, the formation of polynuclear complexes is suppressed, and at the SDS concentration of 25.0 mmol-dm⁻³, only Al(OH)²⁺ and Al(OH)₂⁺ are observed in solution. At lower volume percentages of dioxane, the speciation involved polynuclear complexes in addition to mononuclear complexes. At dioxane concentrations higher than 20 vol% only mononuclear complexes are formed. The simultaneous presence of the SDS and dioxane as ionic medium modifiers produces only the mononuclear complexes Al(OH)²⁺ and Al(OH)₂⁺, which have significantly higher stability constants than in the pure ionic medium.     

A quantum chemical study of lead(II) thiocomplexes with mono- and bidentate ligands

Model Pb(II) thiocomplexes with mono- and bidentate ligands of the composition [Pb(L^1,2) _n ]²⁻ⁿ (L¹ is (SC₆H₅)⁻ (thiophenolate ion), L² is (S₂CN(CH₃)₂)⁻ (dithiocarbamate ion), n is the number of ligands of 2–6), which simulate fragments of the crystal structures of Pb(II) complex compounds with organic ligands, are studied within density functional theory. Geometric and energy parameters of model complexes with different coordination geometries of the Pb atom are determined and the stereochemical activity of the lone electron pair (LEP, E) of the Pb²⁺ ion is estimated in them. In the studied complexes, the highest Pb-S binding energy is found for the Pb atom surrounded by 2–4 ligands. The geometry of the Pb atom coordinated by S donor atoms can be described in terms of the valence shell electron pair repulsion (VSEPR) model with stereochemically active LEP. The coordination number (cn) of the Pb atom in the most energetically favorable complexes [Pb(SC₆H₅) _n ]²⁻ⁿ is (3+E) − (4+E), and in [Pb(S₂CN(CH₃)₂) _n ]²⁻ⁿ complexes, it is (4+E) and (6+E). Configurations with the mentioned cns are most often observed in the crystal structures of Pb(II) thiocomplex compounds.     

Complexation of 4′-nitrobenzo-15-crown-5 with Mg<Superscript>2+</Superscript>, Ca<Superscript>2+</Superscript>, Sr<Superscript>2+</Superscript> and Ba<Superscript>2+</Superscript> metal cations in acetonitrile-methanol binary solutions

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.     

Conductance Studies on Complex Formation Between Aza-18-Crown-6 with Ag+, Hg2+ and Pb2+ Cations in DMSO–H2O Binary Solutions

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 _c^o, ΔS _c^o) 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.     

Self-consistent reaction field calculation of solvent reorganization energy in electron transfer: a dipole-reaction field interaction model

Based on the continuum dielectric model, this work has established the relationship between the solvent reorganization energy of electron transfer (ET) and the equilibrium solvation free energy. The dipole-reaction field interaction model has been proposed to describe the electrostatic solute-solvent interaction. The self-consistent reaction field (SCRF) approach has been applied to the calculation of the solvent reorganization energy in self-exchange reactions. A series of redox couples, O₂/O⁻ ₂, NO/NO⁺, O₃/O⁻ ₃, N₃/N⁻ ₃, NO₂/NO⁺ ₂, CO₂/CO⁻ ₂, SO₂/SO⁻ ₂, and ClO₂/ClO⁻ ₂, as well as (CH₂)₂C-(-CH₂-) _n -C(CH₂)₂ (n=1 ∼ 3) model systems have been investigated using ab initio calculation. For these ET systems, solvent reorganization energies have been estimated. Comparisons between our single-sphere approximation and the Marcus two-sphere model have also been made. For the inner reorganization energies of inorganic redox couples, errors are found not larger than 15% when comparing our SCRF results with those obtained from the experimental estimation. While for the (CH₂)₂C–(–CH₂–) _n –C(CH₂)₂ (n=1 ∼ 3) systems, the results reveal that the solvent reorganization energy strongly depends on the bridge length due to the variation of the dipole moment of the ionic solute, and that solvent reorganization energies for different systems lead to slightly different two-sphere radii. Received: 19 April 2000 / Accepted: 6 July 2000 / Published online: 27 September 2000     

Phase composition, electroconductivity, oxygen ion transport number, and microhardness of Ln1 ? xSrxGa0.5 ? y/2Al0.5 ? y/2MgyO3 ? δ (Ln = La, Pr, Nd; x, y = 0.10, 0.15)

Phase composition, electroconductivity, oxygen ion transport number, and microhardness of samples of Ln_{1 − x} Sr_xGa_{0.5 − y/2}Al_{0.5 − y/2}Mg_yO_{3 − δ} (Ln = La, Pr, Nd; x, y = 0.10, 0.15) synthesized by a ceramic methods are studied. Methods of x-ray diffraction analysis and scanning electron microscopy reveal the La-containing samples to be homogeneous and have a perovskite structure. Magnesium does not dissolve in Pr-and Nd-containing systems but forms an individual phase based on magnesium oxide. Apart from magnesium oxide, in these systems there form extrinsic phases, specifically, LnSrGa₃O₇ and an unknown phase. The electroconductivity of La_{1 − x} Sr_xGa_{1 − y} Mg_yO_{3 − δ} decreases after substituting Al for Ga. Ceramic La_{1 − x} Sr_xGa_{0.5 − y/2}Al_{0.5 − y/2}Mg_yO_3−δ is a purely ionic conductor in the temperature interval 500 to 1000°C; Nd_xSr_xGa_{0.5 − y/2}Al_{0.5 − y/2}Mg_yO_{3 − δ} has predominantly ionic conduction; and the predominant type of conduction in Pr_{1 − x} Sr_xGa_{0.5 − y/2}Al_{0.5 − y/2}Mg_yO_{3 − δ} is electronic below 700–800°C, with the contribution of ionic conduction increasing at higher temperatures. Substituting Al for Ga raises the hardness of ceramics under study. Among the compositions studied, La_0.85Sr_0.15Ga_0.45Al_0.45Mg_0.10O_{3 − δ} and La_0.85Sr_0.15Ga_0.425Al_0.425Mg_0.15O_{3 − δ} exhibit a combination of electroconductivity and hardness that is optimal for application as electrolyte at reduced temperatures (600–800°C). The Pr_{1 − x} Sr_xGa_{0.5 − y/2}Al_{0.5 − y/2}Mg_yO_{3 − δ} system possesses mixed ionic-electronic conduction and high hardness, which makes it appealing for application as oxygen-penetrable membranes. Original Russian Text ? Yu.V. Danilov, A.D. Neuimin, L.A. Dunyushkina, L.A. Kuz’mina, N.S. Zybko, Z.S. Martem’yanova, A.A. Pankratov, 2007, published in Elektrokhimiya, 2007, Vol. 43, No. 1, pp. 57–65.