Syntheses, optical properties and electronic structures of copper(I) tantalates: Cu5Ta11O30 and Cu3Ta7O19

Two copper tantalates, Cu₅Ta₁₁O₃₀ (1) and Cu₃Ta₇O₁₉ (2), were synthesized by solid-state and flux synthetic methods, respectively. A synthetic route yielding 2 in high purity was found using a CuCl flux at 800^oC and its structure was characterized using powder X-ray diffraction (XRD) data (P6₃/m (no. 176), Z=2, a=6.2278(1) Å, and c=20.1467(3) Å). The solid-state synthesis of 1 was performed using excess Cu₂O that helped to facilitate the growth of single crystals and their characterization by XRD (P6¯2c (no. 190), Z=2, a=6.2252(1) Å, and c=32.516(1) Å). The atomic structures of both copper tantalates consist of alternating single and double layers of TaO₇ pentagonal bipyramids that are bridged by a single layer of isolated TaO₆ octahedra and linearly-coordinated Cu⁺. Measured optical bandgap sizes of ∼2.59 and ∼2.47 eV for 1 and 2 were located well within visible-light energies and were consistent with their orange-yellow colours. Each also exhibits optical absorption coefficients at the band edge of ∼700 and ∼275 cm⁻¹, respectively, and which were significantly smaller than that for NaTaO₃ of ∼1450 cm⁻¹. Results of LMTO calculations indicate that their visible-light absorption is attributable mainly to indirect bandgap transitions between Cu 3d¹⁰ and Ta 5d⁰ orbitals within the TaO₇ pentagonal bipyramids.     

A three‐dimensional heterometallic CuI/VIV 1,2‐bis(1,2,4‐triazol‐4‐yl)ethane framework: a new insight into the structure of vanadium oxyfluoride coordination hybrids

The bitopic ligand 1,2‐bis(1,2,4‐triazol‐4‐yl)ethane (tr₂eth) provides an unprecedented short‐distance N¹:N²‐triazole bridging of Cu^I and V^IV ions in poly[bis[μ₄‐1,2‐bis(1,2,4‐triazol‐4‐yl)ethane]di‐μ₂‐fluorido‐tetrafluoridodi‐μ₂‐oxido‐dicopper(I)divanadium(IV)], [Cu₂V₂F₆O₂(C₆H₈N₆)₂]_n. The Cu^I ions and tr₂eth linkers afford a two‐dimensional square‐grid topology involving centrosymmetric (tr)Cu(μ‐tr)₂Cu(tr) [tr is triazole; Cu—N = 1.9525 (16)–2.0768 (18) Å] binuclear net nodes, which are expanded in a third dimension by centrosymmetric [V₂O₂F₆]²⁻ pillars. The concerted μ‐tr and μ‐O bridging between the Cu^I and V^IV ions allows a multi‐centre accommodation of the vanadium oxyfluoride moiety on a cationic Cu/tr₂eth matrix [Cu—O = 2.1979 (15) Å and V—N = 2.1929 (17) Å]. The distorted octahedral coordination of [VONF₄] is completed by two terminal and two bridging F⁻ ions [V—F = 1.8874 (14)–1.8928 (13) and 2.0017 (13)–2.1192 (12) Å, respectively]. The resulting three‐dimensional framework has a primitive cubic net topology and adopts a threefold interpenetration.     

Enzymatic Resolution of O‐(Methoxymethyl)‐Protected Tropane‐diols

A convenient synthetic route to enantiomerically pure tropane‐diol building blocks is described. The reaction sequence started from tropenone derivatives 1 , which were dihydroxylated to give 6,7‐dihydroxytropanone derivatives 2 . After introduction of the methoxymethyl (MOM) protecting group in diol 2a , a lipase‐mediated resolution of the resulting racemic mono‐MOM ether (±)‐ 5d with vinyl acetate and vinyl trifluoroacetate gave the acetates (?)‐ 6d and (?)‐ 6f , respectively, with 96–99% ee, and MOM ether (+)‐ 5d with up to 89% ee. Deacetylation of (?)‐ 6d afforded quantitatively MOM ether (?)‐ 5d with 99% ee, the absolute configuration of which was assigned via the modified Mosher method to be (R) at C(6). Enzymatic treatment of unprotected diol 2a with vinyl trifluoroacetate or alkoxycarbonylation resulted in the formation of C_s‐symmetrical products 9 and 12 rather than the desired desymmetrized derivatives.     

Synthesis of substituted thienopyrimidine-4-ones

The parallel solution-phase synthesis of more than 3000 substituted thienopyrimidin-4-ones has been accomplished. Key reactions include assembly of the 2-thioxopyrimidin-4-one ring by condensation of isomeric aminothiophenecarboxylates or their appropriate reactive derivatives (isothiocyanates or dithiocarbamates) with the corresponding isothiocyanates or amines. The libraries from libraries were then obtained in good yields and purities using solution-phase alkylation and acylation methodologies. Simple manual techniques for parallel reactions using special CombiSyn synthesizers were coupled with easy purification procedures (crystallization from the reaction mixtures) to give high-purity final products. The scope and limitations of the developed approach are discussed.     

Non-isothermal film casting: Determination of draw resonance

The important industrial process of casting polymeric films suffers from the “draw resonance” instability that appears as sudden oscillations in the product dimensions. This instability influences the quality of the end-product and negatively limits productivity and efficiency of the process. The draw resonance originates when a material is being processed beyond the limits of its intrinsic properties. Research is conducted with the intention to find those process and material properties that allow to optimize the production process while keeping it stable.This paper concentrates on a non-isothermal analysis of the stability of the film casting. The mathematical model of the process is given by a quasi-linear system of first order PDEs with two point boundary conditions. The constitutive polymer behavior is approximated by the modified Giesekus model. Linear stability analysis combined with the Laplace transformation of the resulting linear system is applied to find parameters that determine mathematical and thus process instability. It all comes down to determining the spectrum of a compact operator; corresponding eigenfunctions can be regarded as the characteristic modes of the system. For implementation, the modification of Galerkin approach is used. The major advantage of the mathematical and numerical method is that the full spectrum is calculated in a matter of seconds. Our results agree perfectly with the ones from literature for isothermal case, and with the experimental data for the non-isothermal case. The results also indicate that non-isothermality is highly important and cannot be excluded from modeling.     

Platinum stilbazoles: ring-walking coupled with aryl-halide bond activation

The reaction between tetrakis(triethylphosphine)platinum(0) and 4-[trans-2-(4-bromophenyl)vinyl]pyridine (1) is examined. Initially, the metal center coordinates to the bridging double bond of 1. Complexes 2 and 3 were fully characterized, and their X-ray crystallography structures are presented. Upon heating, either in solution or in the solid state, complex 2 undergoes C-Br oxidative addition to give complex 3. Kinetic studies revealed that this conversion is unimolecular and does not involve dissociation of the metal center from the double bond. Density functional studies show that a plausible mechanism involves the metal center "walking" around the pi-system from the bridging C=C double bond to the C-Br bond.     

Electrogenerated chemiluminescence in systems with tetraphenylborate anion as a co-reactant

The study of electrogenerated chemiluminescence (ECL) in aqueous and non-aqueous media with tetraphenylborate anion as a co-reactant is reported. The obtained results indicate that tetraphenylborate acts according to an oxidative reduction scheme and forms a strong reducer after being homogeneously oxidized by a radical cation or dication of luminophore. Spectral measurements prove that light emission originates from the luminophore present in solution and practically no emission occurs when only tetraphenylborate ion is oxidized at the electrode. Since the tetraphenylborate ion is a well known analytical reactant and precipitates a number of metal and organic cations its electrochemiluminescent detection can be used for their assay. It can also be applied as an efficient co-reactant for electrogenerated chemiluminescence excitation both in aqueous and non-aqueous media.