Barium Complexes Research Articles

ChemInform Abstract: Volatile Barium β-Diketonates for Use as MOCVD Precursors

Metal-organic chemical vapor deposition (MOCVD) techniques have been used to deposit thin superconducting films of YBa2Cu3O7-x. A limitation of the technique lies in the volatility of the barium(II) precursors. A review of attempts to enhance volatility through substitution of fluorinated chelating agents and studies to limit oligomerization of the barium chelates are reviewed. Within the past five years, substantial progress has been made in synthesizing more volatile barium complexes, and the most volatile barium compound yet reported is a monomeric chelate in which five hexafluoroacetylacetonato ligands are bonded to barium(II).

Three novel supramolecular barium complexes with heterocyclic sulfonate ligands: Effect of ligand structure and auxiliary anions

Treatments of heterocyclic sulfonate ligands, viz. 4-(pyridin-2-yl) pyrimidin-2-sulfonate (L 1) and 4-(pyridin-3-yl) pyrimidin-2-sulfonate (L 2), with barium salts have resulted in three compounds ([BaL 1(NO 3)(H 2O)] n ( 1), {[BaL 1 2(H 2O)]·2H 2O} n ( 2) and [BaL 2(ClO 4)(H 2O)] n ( 3)). All the compounds have been structurally determined with interesting architectures, showing that the polarizability and the charge density of the Ba(II) ion, the positional modification of the pyridyl group about ligands as well as auxiliary anion effects play important roles in the formation of three supramolecular architectures.

Heterofunctionalization catalysis with organometallic complexes of calcium, strontium and barium

Despite the routine employment of Grignard reagents and Hauser bases as stoichiometric carbanion reagents in organic and inorganic synthesis, a defined reaction chemistry encompassing the heavier elements of Group II (M = Ca, Sr and Ba) has, until recently, remained unreported. This article provides details of the recent progress in heavier Group II catalysed small molecule transformations mediated by well-defined heteroleptic and homoleptic complexes of the form LMX or MX 2 ; where L is a mono-anionic ligand and X is a reactive σ-bonded substituent. The intra- and intermolecular heterofunctionalization (hydroamination, hydrophosphination, hydrosilylation and hydrogenation) of alkenes, alkynes, dienes, carbodiimides, isocyanates and ketones is discussed.

Allyl complexes of the heavy alkaline-earth metals: molecular structure and catalytic behavior

Reaction of two equivalents of K[1,3-(SiMe3)2C3H3] (= KA′) with SrI2 in thf produces the allyl complex SrA′2(thf)2. In the solid state, the monomeric complex is isostructural with its calcium counterpart; the allyl ligands are bound in a symmetrical trihapto manner to the metals, with an average Sr–C distance of 2.801(5) A. The reaction of KA′ and BaI2 does not result in the expected bis(allyl)barium complex, but rather in a heterometallic barium/potassium species, K(thf)Ba2A′5. The allyls are in fast exchange in solution, and in the solid state, the complex forms a polymeric chiral chain. Each barium center is coordinated by one terminal and two bridging allyl ligands; the potassium center is coordinated by two bridging allyl ligands and one thf molecule. On reaction with iodine, C–C coupling occurs with CaA′2(thf)2, SrA′2(thf)2 and K(thf)Ba2A′5 to give the 1,5-hexadiene, [(SiMe3)2C3H3]2. CaA′2(thf)2, SrA′2(thf)2 and K(thf)Ba2A′5 are initiators for methyl methacrylate polymerization; the analogous magnesium complex is not active.

Synthesis of mixed-ligand alkali earth element dipivaloylmethanates with o-phenanthroline

A one-step method for the synthesis of volatile barium and strontium complexes [M(Thd)2(Phen)2] (M = Ba, Sr; Thd is the dipivaloylmethane anion) was developed. The method is based on the reaction of metal hydroxide octahydrates with dipivaloylmethane (HThd) and o-phenanthroline (Phen) accompanied by removal of water from the reaction mixture as a solvent-water azeotrope. In the case of calcium hydroxide monohydrate, a similar interaction causes destruction of the dipivaloylmethanate ligand to give a mixed-ligand calcium complex with the pivalate anion and o-phenanthroline.

Synthesis and Structural Characterization of 1,2‐Benzenedisulfonate Complexes of the Heavy Group 2 Elements

AbstractReaction of the commercially available potassium 1,2‐benzenedisulfonate (K2L) with calcium chloride, strontium nitrate, and barium chloride in aqueous solution yielded [Ca2L2(H2O)4], [Sr4L4(H2O)8]·1.5H2O and [Ba2L2(H2O)5]·H2O in a form suitable for single‐crystal X‐ray determination. From one preparation of the calcium complex a few crystals of [K2CaL2(H2O)3]·0.5H2O were obtained but were not representative of the bulk product. From reaction of CaCO3 with H2L and recrystallization from aqueous ethanol, crystals of [Ca2L2(H2O)6]·EtOH deposited. All complexes are coordination polymers with metal atoms being bridged and chelated by 1,2‐benzenedisulfonate groups, which show an enormous variety of coordination modes, and coordinated by water molecules, some of which are bridging. Calcium has an eight‐coordinate ion in all compounds, potassium six‐coordinate in the bimetallic complex; the strontium complex has eight‐ and nine‐coordinate strontium atoms and the barium complex nine‐ and eleven‐coordinate barium atoms.

1,2,4-Diazaphospholide Complexes of Barium: Mechanism of Formation and Crystallographic Characterization

A number of barium 1,2,4-diazaphospholide (dp(-)) complexes have been prepared by protonolysis of barium bis[bis(trimethylsilyl)]amide (Ba[N(SiMe(3))(2)](2)(THF)(2)) and the corresponding 1,2,4-diazaphospholes. The bis(3,5-diphenyl-1,2,4-diazaphospholide)-tetrakis(tetrahydrofuran)barium [eta(2)(N,N)-3,5-Ph(2)dp)(2)Ba(THF)(4)] (1) and bis(3,5-diphenyl-1,2,4-diazaphospholide)-tetrakis(dimethylsulfoxide)barium [eta(2)(N,N)-3,5-Ph(2)dp)(2)Ba(DMSO)(4)] (2) were prepared by the reactions of Ba[N(SiMe(3))(2)](2)(THF)(2) and 3,5-diphenyl-1,2,4-diazaphosphole (H[3,5-Ph(2)dp]) in tetrahydrofuran (THF) or dimethylsulfoxide (DMSO), respectively, while the bis(3,5-disubstituted-1,2,4-diazaphospholide)-(18-crown-6) barium complexes [trans-eta(2)(N,N)-dp)(2)Ba(18-crown-6)] (3), [cis-eta(2)(N,N)-tBu(2)dp)(2)Ba(18-crown-6)] (4), [trans-eta(2)(N,N)-tBu(2)dp)(2)Ba(18-crown-6)] (5), [cis-eta(2)(N,N)-Ph(2)dp)(2)Ba(18-crown-6)] (6), and [trans-eta(2)(N,N)-Ph(2)dp)(2)Ba(18-crown-6)] (7) were synthesized by the reaction of Ba[N(SiMe(3))(2)](2)(THF)(2) and the corresponding 1,2,4-diazaphospholes in the presence of 18-crown-6 in THF or DMSO. Complexes 1, 2, 3, 4, and 7 have been structurally characterized. Complex 4 is the first structurally characterized barium complex in which the two organic ligands are located on the same side of 18-crown-6 (cis conformation). The (31)P{(1)H} NMR spectra suggested a partial dissociation of the barium 1,2,4-diazaphospholides 2, 4, and 7 into the corresponding ion associated complexes in solutions.

Volatility Enhancement in Calcium, Strontium, and Barium Complexes Containing β-Diketiminate Ligands with Dimethylamino Groups on the Ligand Core Nitrogen Atoms

Treatment of M(N(SiMe3)2)2(THF)2 with 2 equiv of 4-(2,2-dimethylhydrazino)dimethylhydrazone-3-penten-2-one (LNMe2H) in toluene at ambient temperature afforded Ca(η2-LNMe2)2 (88%), [Sr(η5-LNMe2)(μ-η1:η5-LNMe2)]2 (85%), and [Ba(η5-LNMe2)(μ-η2:η3-LNMe2)]2 (83%) as colorless or pale yellow crystalline solids. The formulations of the new complexes were assigned from spectral and analytical data and by X-ray crystal structure determinations. In the solid state, Ca(η2-LNMe2)2 exists as a tetrahedral monomer. [Sr(η5-LNMe2)(μ-η1:η5-LNMe2)]2 is a dimer that contains a terminal η5-LNMe2 ligand on each strontium ion. The dimer is held together by two μ-η1:η5-LNMe2 ligands, in which one dimethylamino moiety per LNMe2 ligand acts as a donor ligand to the adjacent strontium ion. [Ba(η5-LNMe2)(μ-η2:η3-LNMe2)]2 crystallizes as a dimer that contains a terminal η5-LNMe2 ligand on each barium ion. The two bridging LNMe2 ligands adopt a μ-η2:η3-coordination mode, where each LNMe2 ligand is bonded to one barium ion through the...

Heterobimetallic copper–barium complexes for deposition of composite oxide thin films

Heterobimetallic molecular precursors [Ba(dmap)4Cu4(OAc)6·THF] (1) and [Ba(dmap)4Cu4(TFA)6·THF] (2) [dmap = N,N-dimethylaminopropanolate, OAc = acetate and TFA = trifluoroacetate] for the deposition of barium–copper composite oxide thin films, were prepared by the interaction of Ba(dmap)2 with Cu(OAc)2 for 1 and Cu(TFA)2 for 2, in THF. Both heterobimetallic complexes were characterized by melting point, elemental analysis, FT-IR spectroscopy, mass spectrometry and single crystal X-ray diffraction. X-Ray crystallography shows that complex 1 crystallizes in the orthorhombic space groupP212121 with the cell dimensions a = 11.2621(11) A, b = 18.2768(17) A and c = 24.541(2) A, while complex 2 crystallizes in the monoclinic space groupC2/c with a = 23.9288(14) A, b = 19.8564(12) A, c = 25.5925(15) A and β = 112.4390(10)°. Thermal gravimetric analysis shows that both complexes 1 and 2 undergo controlled thermal decomposition at 450 °C and 400 °C, respectively, to give mixed metal oxide composite thin films. Scanning electron microscopy (SEM), energy dispersive X-ray (EDX) and X-ray powder diffraction (XRD) analyses of the thin films suggest the formation of good quality crystalline thin films of BaCuO2–CuO composites from both 1 and 2, with average grain sizes of 105 to 175 nm and 110 to 205 nm, respectively.

Stability of cyclopentadienyl aryloxide complexes of calcium and barium

The synthesis of mono(cyclopentadienyl)aryloxide complexes of calcium and barium has been investigated. The reaction of ICa(ODipp)(thf) 4 (Odipp = [2,6- iPr-OC 6H 3O] −) with K[C 5Me 5], (Cp 3Si) 2Ca (Cp 3Si = C 5(SiMe 3) 3H 2) with K[ODipp], and IBa(BHT)(thf) 3 (BHT = [2,6- tBu-4-Me-C 6H 2O] −) with K[C 5Me 5] in THF produces Cp*Ca(Odipp)(thf) 3, (Cp 3Si)Ca(Odipp)(thf) 2, and Cp*Ba(BHT)(thf), respectively. The crystal structures of the two monomeric calcium complexes are reported. All three compounds are stable against Schlenk rearrangement in THF and aromatic solvents. DFT calculations suggest that the presence of THF has less of an effect on the thermodynamics of Schlenk rearrangements of the aryloxide systems than it does on comparable Cp′CaI compounds.

Oxide layers with titanium and zirconium phosphates

Oxide-phosphate layers 20 to 150 μm thick were obtained on titanium by plasma electrolytic deposition in individual and mixed aqueous electrolytes with polyphosphate complexes of zirconium(IV), barium(II), and copper(II). Formation features, thickness, elemental and phase compositions, and surface morphology of the films are presented. Depending on the electrolyte composition, synthesis conditions, and temperature of annealing in air, some simple and double phosphates of titanium and zirconium are formed, including ZrP2O7, NaTi2(PO4)3, BaTi2(P2O7)2, Zr0.2Ti0.8P2O7, and CuTi2(PO4)3.

Structure of a Barium(II) Complex Sandwiched by a Schiff Base Macrocycle

Abstract A barium complex sandwiched by an octaaza Schiff base macrocycle prepared by [2+2] condensation of diimine and phenanthroline dicarbaldehyde has been studied; the ten-coordinate structure of the complex and increase of absorption intensity on coordination has been revealed.

Synthesis, Structures and DFT Calculations on Alkaline‐Earth Metal Azide‐Crown Ether Complexes

The first examples of azide complexes of calcium, strontium or barium with crown ethers have been prepared and fully characterised, notably [Ba([18]crown-6)(N3)2(MeOH)], [Sr([15]crown-5)(N3)2(H2O)], [Ca([15]crown-5)(N3)2(H2O)] and [Sr([15]crown-5)(N3(NO3)]. Crystal structures reveal the presence of a variety of coordination modes for the azide groups including kappa 1-, mu-1,3- and linkages via H-bonded water molecules, in addition to azide ions. The [Ba([18]crown-6)(N3)2(MeOH)].1/3 MeOH contains dinuclear cations with three mu-1,3-NNN bridges, the first example of this type in main group chemistry. The structures obtained have been compared with molecular structures computed by density functional theory (DFT). This has allowed the effects of the crystal lattice to be investigated. A study of the M--N terminal metal-azide bond length and charge densities on the metal (M) and terminal nitrogen centre (N terminal) in these complexes has allowed the nature of the metal-azide bond to be investigated in each case. As in our earlier work on alkali metal azide-crown ether complexes, the bonding in the alkaline-earth complexes is believed to be predominantly ionic or ion-dipole in character, with the differences in geometries reflecting the balance between maximising the coordination number of the metal centre, and minimising ligand-ligand repulsions.

Photoluminescence investigations of Eu3+ doped BaTiO3 nanopowders fabricated using heterometallic tetranuclear alkoxide complexes

The synthesis of Ba–Ti precursors was achieved by a self-assembly synthesis starting from barium metal, titanium n-propoxide and 2,2,6,6-tetramethyl-heptanedione (Hthd) in nPrOH. The structure of the obtained Ba2Ti2(thd)4(OnPr)8(nPrOH)2 compound is of the M2M′2X16 type—one of the most widespread for both the homo- and heterometallic tetranuclear alkoxide complexes. It remains unchanged in solution according to the NMR data, which are easily interpreted in terms of the same molecular structure as that revealed by crystallography for the solid state. In order to form BaTiO3 phase doped with 1% of the Eu3+ the heterometallic alkoxide complex of barium and titanium with the necessary amount of Eu dissolved in the reaction mixture were hydrolyzed by moist ethanol on reflux in 1 M solution in n-propanol. The obtained gels were dried in vacuum and have been heat treated at different temperatures (700–1100 °C). XRD measurements were performed in order to study the phase formation and grain size. TEM images have been taken for the morphology and grain size characterization. Emission spectra and decay times were measured for the description of the luminescence properties of the obtained system.

Novel monomeric barium complexes as volatile precursors for chemical vapour deposition

A new range of barium complexes with single encapsulating ligands have been prepared for use in chemical vapour deposition (CVD). A novel pathway providing an unprecedented sequence of barium carbamates is reported. New dianionic bis β-ketoesterates and their barium, strontium and calcium derivatives were synthesised. High resolution mass spectrometry showed some barium derivatives to be monomeric, and preliminary testing indicated some volatility in these species. Calcium and strontium complexes were found to have nuclearities that varied according to their ionic radii relative to the chain length of the encapsulating ligand.

Strukturen von polaren Bariumorganylen: Synthese und Struktur von Ether‐, Pyridin‐ und Kronenether‐Addukten des Bis(fluorenyl)bariums

AbstractThe synthesis and structure of six bis(fluorenyl)barium complexes is reported. Bis(fluorenyl)barium (1) was synthesized from barium bis(hexamethyldisilazide) and fluorene. Tetrahydrofuran, dimethoxyethane, and pyridine containing complexes (1a, 1b, 2, and 3a) could be synthesized by crystallizing 1 from THF, DME, or pyridine. The X‐ray structures of all crystalline compounds reveal a bent‐sandwich structure with Ba–C distances between 303.3 and 322.2 pm to the five‐membered rings of the fluorenyl ligands and a ring centroid–Ba distance of 288.2 to 289.0 pm. The ring centroid–Ba–ring centroid angles are 134.8 to 137.0°. Three THF (1a, 1b), two DME (2), or three pyridine molecules (3a) complete the coordination sphere of the barium atom. Two crown ether complexes (4a and 5a) of bis(fluorenyl)barium were synthesized by reacting 1 with the crown ethers 18‐crown‐6 and dibenzo‐18‐crown‐6. From pyridine as solvent the following two compounds could be obtained in single crystals: [Ba(C13H9)(18‐crown‐6)(pyridine)]+[C13H9]−·pyridine (4a) and [Ba(C13H9)(dibenzo‐18‐crown‐6)(pyridine)]+[C13H9]−·2 pyridine (5a). The structures of 4a and 5a could be determined by X‐ray diffraction, too. The complexes 4a and 5a have a salt‐like structure with a complex [Ba(C13H9)(18‐crown‐6)(pyridine)]+‐cation and a free fluorenide anion.

Stability and structure in solution of potassium and barium complexes with N,N’-diaryldiaza-18-crown-6: Crystal structure of N,N’-Bis(4-dimethylaminophenyl)diaza-18-crown-6 and its complex with barium perchlorate

It has been shown that N,N’-diaryldiaza-18-crown-6 ethers with p-dimethylamino-and p-methoxy groups in the benzene ring (aryl is 4-Mc2NC6H4) (I) and 4-MeOC6H4 (II) form complexes with potassium and barium salts. The influence of these salts on the UV and 1H NMR spectra of crown ethers I and II has been studied. The stability constants (logβ) of the complexes increase in the series II · Ba(ClO4)2 (2.0), I · Ba(ClO4)2 (2.3), II · KBr (2.8), I · KBr (3.0). N,N’-bis(4-dimethylphenylamine)diaza-18-crown-6 (L, I) and its complex with barium perchlorate Ba(ClO4)2 · L (III) are characterized by X-ray crystallography. The crystals of I are monoclinic: a = 13.778(2) A, b = 5.9731(9) A, c = 17.542(3) A, β = 106.65(1)°, V = 1383.1(4) A3, Z = 2, space group P21/n, R = 0.0374 for 990 reflections with I > 2σ(I). The crystals of III are monoclinic: a = 17.275(4) A, b = 8.017(2) A, c = 26.935(4) A, β = 100.47(2)°, V = 3669(1) A3, Z = 4, space group C2/c, R = 0.0320 for 1897 reflections with I > 2σ(I). The molecules of I and III are centrosymmetric. In III, the Ba atom is in the center of substituted diaza-18-crown-6 (DA18C6). The Ba atom is coordinated by all six donor atoms of diaza-18-crown-6 (av. Ba-O, 2.779(3) A; Ba-N, 3.004(4) A) and four oxygen atoms of two asymmetrically bound perchlorate groups (Ba-O, 2.832(4) and 3.031(4) A) arranged below and above the plane of substituted diaza-18-crown-6. The conformations of the macrocycle in free and coordinated L are different.

Synthesis, crystal structure and thermochemical behaviour of a barium complex [Ba(5-OH–BDC)(H 2O) 3] [5-OH–H 2BDC = 5-hydroxyisophtalic acid

A novel complex [Ba(5-OH–BDC)(H 2O) 3] [5-OH–H 2BDC = 5-hydroxyisophtalic acid] was synthesized and characterized by X-ray crystallography. The complex is Monoclinic P2 1/ c, a = 11.1069(4), b = 14.8192(6), c = 6.5005(2) Å, β = 103.465(3)° and Z = 4, which exhibits a three-dimensional framework formed by linkage of adjacent two-dimensional (6, 3) layers via intermolecular hydrogen bonds. The title complex has been studied by IR spectrum and TG–DTG. The constant-volume combustion energy of the complex, Δ c U, was determined as being (−3210.45 ± 1.41) kJ mol −1 by a precise rotating-bomb calorimeter at 298.15 K. The standard enthalpy of combustion, Δ c H m θ , and the standard enthalpy of formation, Δ H m θ f , were calculated as being (−3207.97 ± 1.41) and (−1922.80 ± 1.76) kJ mol −1, respectively. A calculation model for determining the specific heat capacity of the complex with an improved RD496-III microcalorimeter is also derived. The specific heat capacity of the complex was (6158.387 ± 0.187) J mol −1 K −1.

The crystal and molecular structures of sodium and barium complexes of dibenzo-24-crown-8 ether

Abstract The sodium and barium isothiocyanate complexes of 6,7,9,10,12,13,20,21,23,24,26,27-dodecahydro-dibenzo[b,n]-1,4,7,10,13,16,19,22-octaoxacyclotetracosin (dibenzo-24-crown-8 ether=DB24C8) were synthesized and analyzed by X-ray diffraction. The sodium complex, [Na(DB24C8)(NCS)(H2O)] 1, crystallizes in the orthorhombic space group Fdd2 with 16 molecules in the unit cell. The coordination number of Na is 6 and the central ion is located in a distorted octahedric environment. Only four of the crown ether oxygen atoms are involved. The coordination polyhedron is completed by the isothiocanate anion and by a water molecule, which is stabilized by hydrogen bonds. The barium complex, [Ba(DB24C8)(NCS)2] 2, crystallizes in the trigonale space group P3121 with 3 molecules in the unit cell. Crystallographic C2 symmetry is observed for the complex. The coordination number of Ba is 10. Barium is coordinated with the eight oxygen atoms of the macrocyclic ligand and with two isothiocyanate anions. The absolute structure was estimated using the FLACK parameter.

Solvent extraction of barium picrate by p-tert-butylcalix[4]arene-tetrakis (N,N-diethylacetamide)

From extraction experiments andg-activity measurements, the extraction constant of the Ba2+(aq)+2A-(aq)+L(nb)UBaL2+(nb)+2A-(nb) equilibrium in the two-phase water-nitrobenzene system (L = p-tert-butylcalix[4]arene-tetrakis (N,N-diethylacetamide); aq = aqueous phase, nb = nitrobenzene phase) was evaluated as logK ex(BaL2+,2A-)=6.5±0.1. Furthermore, the stability constant of the p-tert -butylcalix[4]arene-tetrakis (N,N-diethylacetamide)barium complex in nitrobenzene saturated with water was calculated for at 25 °C as logb nb(BaL2+)=15.4±0.1.