Tuning the transition temperature and cooperativity of bapbpy-based mononuclear spin-crossover compounds: interplay between molecular and crystal engineering

In this study, we show that 1) different isomers of the same mononuclear iron(II) complex give materials with different spin‐crossover (hereafter SCO) properties, and 2) minor modifications of the bapbpy (bapbpy=N6,N6′‐di(pyridin‐2‐yl)‐2,2′‐bipyridine‐6,6′‐diamine) ligand allows SCO to be obtained near room temperature. We also provide a qualitative model to understand the link between the structure of bapbpy‐based ligands and the SCO properties of their iron(II) compounds. Thus, seven new trans‐[Fe{R₂(bapbpy)}(NCS)₂] compounds were prepared, in which the R₂bapbpy ligand bears picoline ( 9 – 12 ), quin‐2‐oline ( 13 ), isoquin‐3‐oline ( 14 ), or isoquin‐1‐oline ( 15 ) substituents. From this series, three compounds ( 12 , 14 , and 15 ) have SCO properties, one of which ( 15 ) occurs at 288 K. The crystal structures of compounds 11 , 12 , and 15 show that the intermolecular interactions in these materials are similar to those found in the parent compound [Fe(bapbpy)(NCS)₂] ( 1 ), in which each iron complex interacts with its neighbors through weak N? H ??? S hydrogen bonding and π–π stacking. For compounds 12 and 15 , hindering groups located near the N? H bridges weaken the N? S intermolecular interactions, which is correlated to non‐cooperative SCO. For compound 14 , the substitution is further away from the N? H bridges, and the SCO remains cooperative as in 1 with a hysteresis cycle. Optical microscopy photographs show the strikingly different spatio‐temporal evolution of the phase transition in the noncooperative SCO compound 12 relative to that found in 1 . Heat‐capacity measurements were made for compounds 1 , 12 , 14 , and 15 and fitted to the Sorai domain model. The number n of like‐spin SCO centers per interacting domain, which is related to the cooperativity of the spin transition, was found high for compounds 1 and 14 and low for compounds 12 and 15 . Finally, we found that although both pairs of compounds 11 / 12 and 14 / 15 are pairs of isomers their SCO properties are surprisingly different.     

A sequential injection method for the determination of Tween-80 in natural water samples using a fluorescence enhancement of the dye Eosin-B.

A simple sequential injection (SI) method is reported for the determination of the non-ionic surfactant polyoxyethylene sorbitan monoleate (Tween-80). The proposed method is based on a fluorescence enhancement of the probe 4',5'-dibromo-2',7'-dinitro fluorescein, disodium salt (Eosin B) in the presence of a surfactant. The procedure is optimized using the univariate method of optimization. The optimum operating conditions are as follows: reagent concentration, 40 ppm; pH, 4.5; aspirated volumes of sample and reagent, 120 microL and 100 microL, respectively. With the optimum conditions described, linear calibration curves were obtained from 10-200 ppm. The detection limit was 1.7 ppm and the maximum relative standard deviation of the method was 2.7% (n = 5). The fluorescence excitation and emission were fixed at lambda(ex) = 545 mn and lambda(em) = 585 nm. The method was successfully applied to the determination of (TW-80) in natural water samples.     

Determination of platinum in urine and airborne particulate matter from Budapest and Vienna

Urine samples taken from 100 adults living in the city centres of the two capitals were analysed by the same inductively coupled plasma quadrupole mass spectrometer following their 10-fold dilution with bidistilled water. The mean concentration values of platinum related to creatinine were about three times higher in the Hungarian samples than in the Austrian ones. Six particulate matter samples were collected by a Gent-type two-stage sampler in the districts of the two capitals, which have high traffic density. The polycarbonate filters containing the fine (d<2 μm) and the coarse (d=2–10 μm) fractions were digested in a microwave assisted digestion system and analysed by the same high-resolution inductively coupled plasma mass spectrometer. The respirable, fine fractions of aerosols collected in Budapest contained approximately twice as much platinum than the aerosols from Vienna. However, the coarse fraction showed a contrary picture, with five times higher Pt concentration in the samples collected in Vienna.     

Study of dynamic structure and heat and mass transfer of a vertical ceramic tiles dryer using CFD simulations

In this study, we developed a two-dimensional Computational Fluid Dynamics (CFD) model to simulate dynamic structure and heat and mass transfer of a vertical ceramic tiles dryer (EVA 702). The carrier’s motion imposed the choice of a dynamic mesh based on two methods: “spring based smoothing” and “local remeshing”. The dryer airflow is considered as turbulent (Re = 1.09 × 10⁵ at the dryer inlet), therefore the Re-Normalization Group $k - \in$ model with Enhanced Wall Treatment was used as a turbulence model. The resolution of the governing equation was performed with Fluent 6.3 whose capacities do not allow the direct resolution of drying problems. Thus, a user defined scalar equation was inserted in the CFD code to model moisture content diffusion into tiles. User-defined functions were implemented to define carriers’ motion, thermo-physical properties… etc. We adopted also a “two-step” simulation method: in the first step, we follow the heat transfer coefficient evolution (H_c). In the second step, we determine the mass transfer coefficient (H_m) and the features fields of drying air and ceramic tiles. The found results in mixed convection mode (Fr = 5.39 at the dryer inlet) were used to describe dynamic and thermal fields of airflow and heat and mass transfer close to the ceramic tiles. The response of ceramic tiles to heat and mass transfer was studied based on Biot numbers. The evolutions of averages temperature and moisture content of ceramic tiles were analyzed. Lastly, comparison between experimental and numerical results showed a good agreement.     

Size effects in reactive circular site interactions

The complete series solution for the reactant diffusion and reaction at two diffusion-controlled chemically reactive surface sites of radii a(1) and a(2), located in an inert plane an arbitrary center-to-center distance d apart, is presented. Rigorous, analytical forms are developed to calculate the site reaction rates in terms of the dimensionless intersite distance σ[=d/(a(1) + a(2))] and the site radius ratio γ(=a(1)∕/a(2)). Numerical simulation and approximate theoretical results from the recent literature are compared to the exact site reaction rates. While general agreement was noted over the ranges of γ and σ, significant errors in the Wilemski-Fixman-Weiss site rates were found at small γ and σ < 3.     

Induced Nematic Phase of New Synthesized Laterally Fluorinated Azo/Ester Derivatives

A new series of laterally fluorinated mesomorphic compounds, namely 2-fluoro-4-((4-(alkyloxy)phenyl)diazenyl)phenyl 4-substitutedbenzoate (In_x) were prepared and evaluated for their mesophase behavior. The synthesized series constitutes five members that possess different terminally attached polar groups (X). Their molecular structures were confirmed by elemental analyses and both FT-IR and NMR spectroscopy. Examination of the prepared derivatives was conducted via experimental and theoretical tools. Mesomorphic investigations were carried by polarized optical microscopy (POM) and differential scanning calorimetry (DSC). DSC and POM measurements indicated that except for the un-substituted analogue, all other derivatives were purely nematogenic, possessing their nematic (N) mesophase enantiotropically. This is to say that insertions of terminal polar substituents on their mesogenic structures induced the N phase. In addition, the location of lateral and terminal polar moieties played a considerable role in achieving good thermal N stability. Computational calculations were investigated to determine the deduced optimized molecular structures. Theoretical data indicated that both size and polarity of the terminal substituent (X) have essential impact on the thermal parameters and optical properties of possible geometries.     

On the electronic structure of nitro-substituted bipyridines and their platinum complexes

We report the preparation and electrochemical studies of a systematic series of mono- and di-nitro-substituted 2,2'-bipyridine (bipy) compounds [x-NO(2)-bipy (x = 3,4) and x,x'-(NO(2))(2)-bipy (x,x' = 3, 4, 5)] and their complexes with platinum(II), [Pt(x-NO(2)-bipy)Cl(2)] and [Pt(x,x'-(NO(2))(2)-bipy)Cl(2)]. The effect of the number and substitution pattern of the nitro groups on the low-lying acceptor molecular orbitals (involved in charge transfer transitions) is probed by in situ UV/Vis/NIR and EPR spectroelectrochemical methods, supported by DFT calculations. The LUMOs of x-NO(2)-bipy (x = 3-5) are largely localised on the NO(2)-pyridyl moiety; this is also true of their {PtCl(2)} complexes but with a small but significant shift of electron density from the nitro groups. The LUMOs of x,x'-(NO(2))(2)-bipy with x = 3 and 5 are delocalised over both NO(2)-pyridyl rings, but for 4,4'-(NO(2))(2)-bipy is localised on a single NO(2)-pyridyl ring. In all cases the LUMO of the [Pt(x,x'-(NO(2))(2)-bipy)Cl(2)] complexes is delocalised over both nitro-pyridyl rings. For all complexes, the 4(4') derivatives allows greatest overlap with metal valence orbitals in the LUMO.     

The composition and antimicrobial activities of Cyperus conglomeratus, Desmos chinensis var. lawii and Cyathocalyx zeylanicus essential oils

The essential oil compositions of the rhizomes of Cyperus conglomeratus (Cyperaceae) collected from Oman and the leaves of two Annonaceae plants, Desmos chinensis var. lawii and Cyathocalyx zeylanicus collected from India were studied by GC, GC-MS and 13C NMR spectroscopy. Twenty-six compounds, representing 84.4% of the oil were identified in C. conglomeratus, where eugenol (31.3%), alpha-cyperone (10.5%) and cyperotundone (8.4%) were the major compounds. Twelve compounds, constituting 100%, were identified in D. lawii oil, of which benzyl benzoate (58.7%), beta-caryophyllene (23.2%), limonene (4.9%) and alpha-humulene (4.0%) were the major constituents. Thirty-two compounds, comprising 98.0%, were identified in C. zeylanicus oil, of which beta-caryophyllene (21.6%), alpha-pinene (20.4%) and E-beta-ocimene (11.8%) were the major components. The antibacterial and antifungal activities of the oils were tested against a panel of five bacterial and two fungal strains. The oils showed moderate activity against all the tested microbial strains. The minimum inhibitory concentrations of the oils were also determined.     

Experimental study of the E(m, λ)/E(m, 1064) ratio as a function of wavelength,fuel type,height above the burner and temperature

The optical properties of soot have been studied for many years with a particular attention focused on refractive index. In the present study, the two-excitation wavelength laser-induced incandescence technique has been applied to determine the ratio of the soot absorption function as a function of the wavelength. The advantage of this technique is to provide the determination of the E(m) ratio using a non-intrusive laser-based method without being disturbed by scattering. Measurements have been carried out in a methane premixed flat flame and in a diesel turbulent spray one. Four pairs of wavelength have been used to evaluate the spectral behavior of E(m) ratios from ultraviolet (UV) to near infrared (NIR). The two-excitation wavelength LII method implies heating soot the same way using two different laser excitations. Particular operating conditions must be selected to insure the equality of the LII signals, such an equality being necessary to derive the E(m) ratio. A laser excitation at 1064 nm has been chosen as a reference, and the obtained results have been compared with those issued from the use of UV and visible wavelengths of 266, 355, 532 and 660 nm. Results show a significant decrease of the E(m) ratio from UV to visible while it tends to become constant from 532 nm to NIR. The use of different experimental conditions allows to analyze the dependence of the E(m) ratios with the height above the burner, the fuel type and the soot temperature. No significant influence of these parameters has been pointed out on the relative E(m) values determined in the flame conditions investigated here.