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PubMed2001

Reactions of 2-mercaptobenzoic acid with divalent alkaline earth metal ions: synthesis, spectral studies, and single-crystal X-ray structures of calcium, strontium, and barium complexes of 2,2'-dithiobis(benzoic acid).

The treatment of MCl(2).nH(2)O (M = Ca, Sr, or Ba) with 2-mercaptobenzoic acid (H-2-MBA) in a 1:2 ratio in an EtOH/H(2)O/NH(3) mixture leads to the formation of extended polymeric solids [[Ca(OOCC(6)H(4)SSC(6)H(4)COO)(H(2)O)(2)].0.5(C(2)H(5)OH)](n)(1), [[Sr(OOCC(6)H(4)SSC(6)H(4)COO)(H(2)O)(2)].0.5(C(2)H(5)OH)](n)(2), and [[Ba(2)(OOCC(6)H(4)SSC(6)H(4)COO)(2)(H(2)O)(2)].0.5H(2)O](n)(3), respectively. In all of the cases, under the reaction conditions employed, the H-2-MBA ligand undergoes thiol oxidation to form 2,2'-dithiobis(benzoic acid) (H(2)-DTBB). While the DTBB forms a 1:1 complex with heavier alkaline earth metals (1-3), only an ammonium salt, [(HOOCC(6)H(4)SSC(6)H(4)COOH)(HOOCC(6)H(4)SSC(6)H(4)COONH(4))] (4), was obtained as the final product in the reaction of H-2-MBA with MgCl(2).6H(2)O. Compounds 1-4 have been characterized with the aid of elemental analysis, thermal analysis, and infrared spectroscopic studies. All of the products are found to be thermally stable and do not melt on heating to 250 degrees C. Thermogravimetry on complexes 1-3 indicates the loss of coordinated and lattice water/solvent molecules below 200 degrees C (for complex 2) or 350 degrees C (for complexes 1 and 3). The solid-state structures of all of the derivatives 1-4 have been established by single-crystal X-ray diffraction studies. The calcium and strontium coordination polymers 1 and 2 are isomorphous. The DTBB ligands in 1 and 2 are hexadentate, and the compounds have a channel structure in which solvent ethanol molecules are included. In compound 3, barium ion forms a complex 3-dimensional coordination polymer where both the carboxylate and the sulfur centers of the DTBB ligands (which are hepta- and octadentate) coordinate to the metal.

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PubMed2003

Synthesis and structure of Sr3GaN3 and Sr6GaN5: strontium gallium nitrides with isolated planar [GaN3]6- anions.

Two new strontium gallium nitrides were obtained as single crystals by reaction in molten Na. Black Sr(3)GaN(3) is isostructural with its transition metal analogues, Sr(3)MnN(3), Ba(3)MnN(3), Sr(3)CrN(3), Ba(3)CrN(3), and Ba(3)FeN(3), and is the first example of a 313-ternary nitride containing only main group metals. It crystallizes in space group P6(3)/m (No. 176) with a = 7.584(2) A, c = 5.410(3) A, and Z = 2. Black Sr(6)GaN(5) is isostructural with Ca(6)GaN(5) and also with its transition metal analogues, Ca(6)MnN(5) and Ca(6)FeN(5). It crystallizes in space group P6(3)/mcm (No. 193) with a = 6.6667(6) A, c = 12.9999(17) A, and Z = 2. Both Ga compounds contain isolated planar [GaN(3)](6)(-) nitridometallate anions of D(3)(h)() symmetry.

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PubMed2003

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.

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PubMed2006

Two new structurally related strontium gallium nitrides: Sr4GaN3O and Sr4GaN3(CN2).

The strontium gallium oxynitride Sr(4)GaN(3)O and nitride-carbodiimide Sr(4)GaN(3)(CN(2)) are reported, synthesized as single crystals from molten sodium at 900 degrees C. Red Sr(4)GaN(3)O crystallizes in space group Pbca (No. 61) with a = 7.4002(1) Angstroms, b = 24.3378(5) Angstroms, c = 7.4038(1) Angstroms, and Z = 8, as determined from single-crystal X-ray diffraction measurements at 150 K. The structure may be viewed as consisting of slabs [Sr(4)GaN(3)](2+) containing double layers of isolated [GaN(3)](6-) triangular anions arranged in a "herringbone" fashion, and these slabs are separated by O(2-) anions. Brown Sr(4)GaN(3)(CN(2)) has a closely related structure in which the oxide anions in the Sr(4)GaN(3)O structure are replaced by almost linear carbodiimide [CN(2)](2-) anions [Sr(4)GaN(3)(CN(2)): space group P2(1)/c (No. 14), a = 13.4778(2) Angstroms, b = 7.4140(1) Angstroms, c = 7.4440(1) Angstroms, beta = 98.233(1) degrees, and Z = 4].

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PubMed2006

Syntheses and structures of strontium, barium, and europium bis(diphosphanylamido) complexes.

Bis(diphosphanylamido) complexes of strontium and europium, [{(Ph(2)P)(2)N}(2)M(THF)(3)] (M = Sr (1), Eu (2)), have been prepared by reaction of [K(THF)(n)()][N(PPh(2))(2)] (n = 1.25, 1.5) and MI(2). The single-crystal X-ray structures of compounds 1 and 2 always show a eta(2) coordination of the ligand via the nitrogen and one phosphorus atom. In solution, a dynamic behavior of the ligand is observed, which is caused by the rapid exchange of the two different phosphorus atoms. As a result of the radius of the larger ion, treatment of [K(THF)(n)()][N(PPh(2))(2)] with BaI(2) gives the coordination polymer [{(Ph(2)P)(2)N}(2)Ba(THF){(Ph(2)P)(2)N}K](n)() (3). Two of the three {(Ph(2)P)(2)N}(-) ligands of compound 3 bind to the metal in eta(2) (N, P) while the third shows a heteroallylic (P, P) coordination mode. In the solid state, the infinite chain is formally held together by pi coordination of the phenyl rings to the potassium atoms.

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PubMed2006

Diverse structures and dimensionalities in hybrid frameworks of strontium and lanthanum with isomeric dihydroxybenzoates.

Investigations of Sr and La derivatives of 2,3-, 2,4-, 3,5-, and 2,6-dihydroxybenzoic acids have revealed that it is possible to obtain chain and layered structures of these materials. [Sr2(2,3-DHB)4(H2O)4].3H2O, I, and [Sr(2,4-DHB)2(H2O)4].H2O, II, are both one-dimensional coordination polymers based on dimers; both the carboxylate and phenolic oxygens bond to the metal in I and only the carboxylate oxygens bond to the metal in II. [Sr(3,5-DHB)2(H2O)2].4H2O, III, has a one-dimensional chain structure with large channels and involves extended Sr-O-Sr connectivity. [Sr(CH3CO2)(2,4-DHB)(H2O)3].H2O, IV, also has a chain structure with extended Sr-O-Sr connectivity, but the chain structure is formed by bridging acetate units, unlike in III where the Dihydroxybenzoate (DHB) is the bridging unit. [Sr(2,6-DHB)2(H2O)2].0.5H2O, V, is a two-dimensional coordination polymer where both carboxylate and phenolic oxygens coordinate to the metal. A lanthanum compound with the composition [La(CH3CO2)2(2,4-DHB)H2O].0.18H2O, VI, with a one-dimensional chain structure with extended La-O-La connectivity, has been prepared. Besides these chain and layered structures, zero-dimensional dimers of rare-earth DHBs with the general formula [La(CH3CO2)2(DHB)(H2O)2], with 3,5- (VII), 2,6- (VIII), and 2,3-dihydroxybenzoic acids (IX) have been synthesized. The diverse structures of the strontium and lanthanum DHBs are described. The study demonstrates that it is possible to obtain interesting structures of metal DHBs with different dimensionalities. The structures appear to be controlled largely by geometrical rather than electronic factors.

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PubMed1996

Synthesis and Structure of Two New Strontium Germanium Nitrides: Sr(3)Ge(2)N(2) and Sr(2)GeN(2).

We report the structures of two new strontium germanium nitrides synthesized as crystals from the elements in sealed Nb tubes at 750 degrees C using liquid Na as a growth medium. Sr(3)Ge(2)N(2) is isostructural with the previously reported Ba analogue. It crystallizes in P2(1)/m (No. 11), with a = 9.032(2) Å, b = 3.883(1) Å, c = 9.648(2) Å and beta = 112.42(3) degrees, and has two formula units per unit cell. It contains GeN(2)(4)(-) units and additionally |Ge(2)(-) zigzag chains. Sr(2)GeN(2) crystallizes in P4(2)/mbc (No. 135) with a= b = 11.773(2) Å and c= 5.409(1) Å and has Z = 8. It also contains GeN(2)(4)(-) units which have 18 valence electrons and, consequently are bent, like the isoelectronic molecule SO(2).

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PubMed1996

Synthesis and Characterization of Polyether Adducts of Barium and Strontium Carboxylates and Their Use in the Formation of MTiO(3) Films.

The synthesis, characterization, and reactivity of new polyether adducts of strontium and barium carboxylates of general composition M(O(2)CCF(3))(n)()(L) (M = Ba, L = 15-crown-5, (1); M = Ba (2), Sr (3), respectively, with L = tetraglyme are reported. The compounds were synthesized by reaction of BaCO(3) or MH(2) (M = Sr or Ba) with organic acids in the presence of the polyether ligands. These compounds have been characterized by IR and (13)C and (1)H NMR spectroscopies, elemental analyses, and thermogravimetric analysis. The species Ba(2)(O(2)CCF(3))(4)(15-crown-5)(2) (1) and [Ba(2)(O(2)CCF(3))(4)(tetraglyme)](infinity) (2), were also characterized by single-crystal X-ray diffraction. Ba(2)(O(2)CCF(3))(4)(15-crown-5)(2) (1) crystallizes in the orthorhombic space group Cccm with cell dimensions of a = 13.949(1) Å, b = 19.376(2) Å, c = 16.029(1) Å, and Z = 8. [Ba(2)(O(2)CCF(3))(4)(tetraglyme)](infinity) (2) crystallizes in the monoclinic space group C2/c with cell dimensions of a = 12.8673(12) Å, b = 16.6981(13) Å, c = 15.1191(12) Å, beta = 99.049(8) degrees, and Z = 4. Compounds 1-3 thermally decompose at high temperatures in the solid state to give MF(2). However, solutions of compounds 1-3 dissolved in ethanol with Ti(O-i-Pr)(4) give crystalline perovskite phase MTiO(3) films, or in the case of mixtures of 2 and 3, Ba(1)(-)(x)()Sr(x)()TiO(3) films below 600 degrees C when spin coated onto silicon substrates and thermally treated. The crystallinity, purity, and elemental composition of the films was determined by glancing angle X-ray diffraction and Auger electron spectroscopy.

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PubMed2002

Synthesis of single-crystalline perovskite nanorods composed of barium titanate and strontium titanate.

We report the solution-based synthesis of single-crystalline nanorods composed of barium titanate (BaTiO3) and strontium titanate (SrTiO3), which yields well-isolated nanorods with diameters ranging from 5 to 60 nm and lengths reaching up to >10 mum. Electron microscopy and diffraction measurements show that these nanorods are composed of single-crystalline cubic perovskite BaTiO3 and SrTiO3 with a principal axis of the unit cell preferentially aligned along the wire length. These BaTiO3 and SrTiO3 nanorods should provide promising materials for fundamental investigations on nanoscale ferroelectricity, piezoelectricity, and paraelectricity.

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PubMed2006

Dynamics of lithium ions in bismuthate glasses: influence of strontium ions.

The influence of strontium ions on the relaxation dynamics of lithium ions in bismuthate glasses has been investigated in the frequency range of 10 Hz to 2 MHz. We have observed that the conductivity increases and the activation energy decreases with the increase of SrO content in the glass compositions with fixed Li2O content. We have also observed that the conductivity increases and the activation energy decreases when Sr2+ ions are replaced by Li+ ions, keeping the glass former content fixed. We have shown that the estimated mobile ion concentration is almost independent of temperature and SrO content in the compositions. We have further shown that a fraction of total lithium ions are mobile for all glass compositions. The results have been interpreted on the basis of the modification of the bismuthate network by the addition of SrO, which enhances the mobility of Li ions, without altering the mobile Li+ ion concentration. We have also shown that the conductivity relaxation in these glasses is independent of temperature and composition, and the nonexponential parameter is less than that for the lithium bismuthate glasses without SrO.

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PubMed2001

Strontium isotopes reveal distant sources of architectural timber in Chaco Canyon, New Mexico.

Between A.D. 900 and 1150, more than 200,000 conifer trees were used to build the prehistoric great houses of Chaco Canyon, New Mexico, in what is now a treeless landscape. More than one-fifth of these timbers were spruce (Picea) or fir (Abies) that were hand-carried from isolated mountaintops 75-100 km away. Because strontium from local dust, water, and underlying bedrock is incorporated by trees, specific logging sites can be identified by comparing (87)Sr/(86)Sr ratios in construction beams from different ruins and building periods to ratios in living trees from the surrounding mountains. (87)Sr/(86)Sr ratios show that the beams came from both the Chuska and San Mateo (Mount Taylor) mountains, but not from the San Pedro Mountains, which are equally close. Incorporation of logs from two sources in the same room, great house, and year suggest stockpiling and intercommunity collaboration at Chaco Canyon. The use of trees from both the Chuska and San Mateo mountains, but not from the San Pedro Mountains, as early as A.D. 974 suggests that selection of timber sources was driven more by regional socioeconomic ties than by a simple model of resource depletion with distance and time.

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PubMed2001

Plasticity and an inverse brittle-to-ductile transition in strontium titanate.

The use of ceramic materials is often restricted by a transition from ductile behavior to brittle fracture with decreasing temperature. For example, strontium titanate ( SrTiO3) is known to be extremely fragile and brittle below 1300 K. It is therefore surprising to find that SrTiO3 single crystals can be deformed in compression below 1050 K again. Extensive plastic deformation up to 7% strain at low yield stresses of the order of only 120 MPa is possible at room temperature. Low temperature plasticity is carried by the same [110] [110] dislocations as the high temperature deformation along the [001] axis. From this we conclude that these dislocations must exist in two different core configurations.

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PubMed2003

Noncollinear optical frequency doubling in strontium barium niobate.

The observation of a novel noncollinear optical second-harmonic generation mechanism is reported. In strontium barium niobate crystals, a circular cone of second-harmonic light is generated when a fundamental beam of intensive laser light is directed along the crystallographic c axis. It can be shown that the effect is caused by the nonlinear polarization of antiparallel ordered ferroelectric microdomains.

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PubMed2003

Precision frequency measurement of visible intercombination lines of strontium.

We report the direct frequency measurement of the visible 5s(2) 1S0-5s5p 3P1 intercombination line of strontium that is considered a possible candidate for a future optical-frequency standard. The frequency of a cavity-stabilized laser is locked to the saturated fluorescence in a thermal Sr atomic beam and is measured with an optical-frequency comb generator referenced to the SI second through a global positioning system signal. The 88Sr transition is measured to be at 434 829 121 311 (10) kHz. We measure also the 88Sr-86Sr isotope shift to be 163 817.4 (0.2) kHz.

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PubMed2004

Lifetime measurement of the 3P2 metastable state of strontium atoms.

We have measured the lifetime of the 5s5p 3P2 metastable state of strontium atoms by magneto-optically trapping the decayed atoms to the ground state, which allowed sensitive detection of the rare decay events. We found that the blackbody radiation-induced decay was the dominant decay channel for the state at T=300 K. The lifetime was determined to be 520(+310)(-140) s in the limit of zero temperature, arguably the longest lifetime ever determined in a laboratory environment.

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PubMed2004

Kink in the dispersion of layered strontium ruthenates.

We present detailed energy dispersions near the Fermi level along the high symmetry line GammaX on the monolayer and bilayer strontium ruthenates Sr2RuO4 and Sr3Ru2O7, determined by high-resolution angle-resolved photoemission spectroscopy. A kink in the dispersion is clearly shown for the both ruthenates. The energy position of the kink and the slope in the low-energy part near the Fermi level are almost identical between them, whereas the dispersion in the high-energy part varies, like the behavior of the kink for the cuprate superconductors.

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PubMed2006

Perfect softening of the ferroelectric mode in the isotope-exchanged strontium titanate of SrTi18O3 studied by light scattering.

The mode of the isotope-induced ferroelectric strontium titanate shows a perfect softening at the ferroelectric phase transition temperature , where the frequency of the underdamped mode approaches completely to zero within the instrumental resolution. The spectra of the Raman inactive soft mode have been successfully observed owing to local symmetry breaking and by long-term accumulation of the spectral intensity with a high resolution technique. The mechanism of the phase transition is concluded to be an ideal displacive-type accompanied with perfect softening of the Slater-type polar mode. The difference between the soft mode behavior of and indicates that the origin of the quantum paraelectric state of lies in the quantum fluctuation of the oxide octahedron in the perovskite structure.

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