Stabilization of Classical [B2H5]−: Structure and Bonding of [(Cp*Ta)2(B2H5)(μ‐H)L2] (Cp*=η5‐C5Me5; L=SCH2S)

The room‐temperature reaction of [Cp*TaCl₄] with LiBH₄?THF followed by addition of S₂CPPh₃ results in pentahydridodiborate species [(Cp*Ta)₂(μ,η²:η²‐B₂H₅)(μ‐H)(κ²,μ‐S₂CH₂)₂] ( 1 ), a classical [B₂H₅]^? ion stabilized by the binuclear tantalum template. Theoretical studies and bonding analysis established that the unusual stability of [B₂H₅]^? in 1 is mainly due to the stabilization of sp²‐B center by electron donation from tantalum. Reactions to replace the hydrogens attached to the diborane moiety in 1 with a 2 e {M(CO)₄} fragment (M=Mo or W) resulted in simple adducts, [{(Cp*Ta)(CH₂S₂)}₂(B₂H₅)(H){M(CO)₃}] ( 6 : M=Mo and 7 : M=W), that retained the diborane(5) unit.     

Anion-solvent dependence of bistability in a family of meridional N-donor-ligand-containing iron(II) spin crossover complexes

Five mononuclear spin crossover iron(II) bis-meridional ligand complexes of the general formula [Fe(L)(2)](X)(2).solvent, have been synthesized, where X = BF(4)- or ClO(4)-; L = 2-(1-pyridin-2-ylmethyl-1H-pyrazol-3-yl)-pyrazine (picpzpz) or 2-(3-(2-pyridyl)pyrazol-1-ylmethyl)pyridine) (picpypz); solvent = MeOH or EtOH. The magnetic and structural consequences of systematic variation of meridional ligand, solvent, and anion, including a desolvated species, have been investigated. The complex [Fe(picpzpz)(2)](BF(4))(2).MeOH, 1.MeOH, displays several unique properties including a two-step spin transition with a gradual higher-temperature step ((1)T(1/2) = 197 K) and an abrupt low-temperature step with hysteresis ((2)T(1/2) = 91/98 K) and a metastable intermediate spin state below 70 K with quench-cooling. Removal of the solvent methanol results in the loss of the abrupt step and associated hysteresis (T(1/2) = 150 K). The complexes [Fe(picpzpz)(2)](BF(4))(2).EtOH (1.EtOH), [Fe(picpzpz)(2)](ClO(4))(2).MeOH (2.MeOH), [Fe(picpzpz)(2)](ClO(4))(2).EtOH (2.EtOH), and [Fe(picpypz)(2)](BF(4))(2).MeOH (3.MeOH) all show gradual one-step spin transitions with T(1/2) values in the range 210-250 K. Photomagnetic LIESST measurements on 1.MeOH reveal a near-quantitative excitation of high-spin sites and a unique two-step relaxation process related to the two-step thermal spin transition ((1)T(LIESST) = 49 K and (2)T(LIESST) = 70 K). The structural consequences of the unusual spin transition displayed by 1.MeOH have been investigated by single-crystal X-ray diffraction structural analyses between 25 and 293 K. Detailed characterization of the unit cell parameter evolution vs temperature reflects both the gradual high-temperature step and abrupt low-temperature step, including the thermal hysteresis, observed magnetically.     

Enhanced stability of platinized silicon substrates using an unconventional adhesion layer deposited by CSD for high temperature dielectric thin film deposition

Almost all platinized substrates manufactured presently use an TiO₂ adhesion layer to improve the adhesion between the SiO₂ and the Pt. These substrates however are stable till only 800 °C. We show that simply by replacing the TiO₂ with Al₂O₃, the stability of the electrodes can be increased to 1000 °C and more. These substrates can be used for high temperature depositions which standard platinized substrates cannot withstand. Further we show that dielectric thin films of BaTiO₃ and (Ba,Sr)TiO₃ crystallized at higher temperatures show almost a threefold increase in permittivity on these high temperature stable platinized silicon substrates.The large increase in permittivity is attributed to an increase in grain size at high temperatures. PACS 61.82.Fk; 68.35.Np; 68.60.Dv; 77.55.+f; 81.20.Fw     

Dimethylmetall-tropolonate des galliums,indiums und zinns

The reaction of GaMe₃ and InMe₃ (Me = CH₃) with equimolar amounts of α-tropolone forms dimethylgallium tropolonate and dimethylindium tropolonate, respectively, in high yields. Both compounds are monomeric in solution, almost planar 7-/5-ring bicyclic structures of C_2v symmetry can be discussed. According to the X-ray structure determination of Me₂GaTrop (Trop = C₇H₅O₂) this compound is dimeric in the solid state and crystallizes in the monoclinic space group P2₁/c with 4 formula units (2 dimers) per unit cell. Me₂SnTrop₂ is formed by the interaction of Me₂SnCl₂ with LiTrop in a $\text{1}\text{2}$ molar ratio. This ditropolonate is monomeric not only in solution but also in the solid state. The compound crystallizes in the triclinic space group P$\text{1}$ (Z = 4), and the molecules have a cis-structure of approximate C₂-symmetry. The vibrational and NMR spectra of all compounds were measured and are partly assigned.     

Generation of fluorescent adducts of malondialdehyde and amino acids: toward an understanding of lipofuscin

Lipofuscin is a yellow-brown, highly fluorescent pigment that undergoes an age-related progressive accumulation in animal cells, mainly in postmitotic cells. It is a heterogeneous, high-molecular weight material associated with proteins, lipids and nucleic acids. Lipofuscin is implicated in many aspects of human health, including aging, oxidative stress, macular degeneration, lipid peroxidation, atherosclerosis, dementia (Alzheimer's Disease) and diseases associated with prions. Although the fluorescent properties of lipofuscin have long been recognized, neither histologists nor chemists have yet isolated the pigments themselves or characterized their optical properties. We have prepared lipofuscinlike species by reacting malondialdehyde (MDA) with cysteine (Cys). MDA:Cys adducts 3:2 and 2:2 are two of those that have been identified among the many that were present in the reaction. Whereas previous attempts to synthesize lipofuscinlike species resulted in compounds that were either nonfluorescent or emitted principally in the blue, the MDA:Cys adducts reported in this study are not only fluorescent but also emit over a broader range.     

Triazine‐based Organic Polymer‐catalysed Conversion of Epoxide to Cyclic Carbonate under Ambient CO2 Pressure

In this work we have achieved epoxide to cyclic carbonate conversion using a metal‐free polymeric catalyst under ambient CO₂ pressure (1.02 atm) using a balloon setup. The triazine containing polymer (CYA‐ANIS) was prepared from cyanuric chloride (CYA?Cl) and o‐dianisidine (ANIS) in anhydrous DMF as solvent by refluxing under the N₂ gas environment. The presence of triazine and amine functional groups in the polymer results in the adsorption of CO₂ up to 7 cc/g at 273 K. This inspired us to utilize the polymer for the conversion of a series of functionalised epoxides into their corresponding cyclic carbonates in the presence of tetrabutyl ammonium iodide (TBAI) as co‐catalyst. The product has wide range of applications like solvent in lithium ion battery, precursor for polycarbonate, etc. The catalyst was efficient for the conversion of different mono and di‐epoxides into their corresponding cyclic carbonates under atmospheric pressure in the presence of TBAI as co‐catalyst. The study indicates that epoxide attached with electron withdrawing groups (like, CH₂Cl, glycidyl ether, etc.) displayed better conversion compared to simple alkane chain attached epoxides. This is mainly due to the stabilization of electron rich intermediates produced during the reaction (e. g. epoxide ring opening or CO₂ incorporation into the halo‐alkoxide anion). This catalyst mixture was capable to maintain its reactivity up to five cycles without losing its activity. Post catalytic characterization clearly supports the heterogeneous and recyclable nature of the catalyst.     

Mechanochemical Synthesis of Functionalized Quinolines by Iodine Mediated Oxidative Annulation

An iodine‐mediated environmentally benign synthesis of multi‐substituted quinoline derivatives is developed using a solvent‐free mechanochemical process. Appropriately designed and easily accessible protecting group‐free aniline derivatives were used for the oxidative annulation reaction, and a series of quinoline derivatives with variable functionalities were synthesized up to 89 % isolated yield. Importantly, the activator iodine remains in the quinoline molecule and promotes further functionalizations. The present methodology is beneficial with regard to operational simplicity and mild reaction conditions.     

Predicting the Surface Tension of Deep Eutectic Solvents: A Step Forward in the Use of Greener Solvents

Deep eutectic solvents (DES) are an important class of green solvents that have been developed as an alternative to toxic solvents. However, the large-scale industrial application of DESs requires fine-tuning their physicochemical properties. Among others, surface tension is one of such properties that have to be considered while designing novel DESs. In this work, we present the results of a detailed evaluation of Quantitative Structure-Property Relationships (QSPR) modeling efforts designed to predict the surface tension of DESs, following the Organization for Economic Co-operation and Development (OECD) guidelines. The data set used comprises a large number of structurally diverse binary DESs and the models were built systematically through rigorous validation methods, including ‘mixtures-out’- and ‘compounds-out’-based data splitting. The most predictive individual QSPR model found is shown to be statistically robust, besides providing valuable information about the structural and physicochemical features responsible for the surface tension of DESs. Furthermore, the intelligent consensus prediction strategy applied to multiple predictive models led to consensus models with similar statistical robustness to the individual QSPR model. The benefits of the present work stand out also from its reproducibility since it relies on fully specified computational procedures and on publicly available tools. Finally, our results not only guide the future design and screening of novel DESs with a desirable surface tension but also lays out strategies for efficiently setting up silico-based models for binary mixtures.