Miroslav Boča

Novel complexes of 2,6-bis(benzthiazol-2-yl)pyridine

Abstract New complexes of 2,6-bis(benzthiazol-2-yl)pyridine (L) with Mn(II), Fe(II), Co(II), Ni(II), and Fe(III) were prepared and characterised by spectroscopic methods. The X-ray structure analysis confirmed that the ligand crystallises either in the free form L, or as a protonated product HL·ClO4. In both crystalline forms, the ligand adopts SNS conformation. Two complexes [FeLCl3]·S with the crystal solvent S=CHCl3 and CH3NO2 show an altered way of the crystal packing. The conformation of the ligand is NNN in both cases. The {FeN3Cl3} chromophore adopts geometry of a distorted elongated octahedron and yields a high-spin complex with μeff=6.2μB at room temperature. Depending upon the counteranion and the crystal solvent, the hexacoordinate complexes of Fe(III) show a great variability of the magnetic behaviour: in addition to 6A states also 4T and 2T were identified. The complexes of M(II) show 6A states for Mn(II), 5T for Fe(II), 4T for Co(II), and 3T for tetrahedral Ni(II). The [FeL(phen)](ClO4)2·CHCl3 system shows features of the spin crossover from the low-spin to the intermediate-spin state.

NMR Study of New Ligands as Products of Condensation of 2-Pyridinecarboxaldehyde-N-Oxide with Polyamines

Abstract—New ligands formed as products of the condensation of 2-pyridinecarboxaldehyde-N-oxide with polyamines were prepared andcharacterised by elemental analysis, 13 C NMR spectroscopy and infrared spectroscopy. Schiff base

K(3)TaF(8) from laboratory X-ray powder data.

saturated heterocyclic ringisomerization was found to be quite common in this system; the five- and/or six-membered saturated heterocyclic rings containing twonitrogen atoms are more stable. q2000 Elsevier Science Ltd. All rights reserved. IntroductionCarbon atoms of Schiff base moieties are partially positivecharged and nucleophilic agents can attack them. Anintramolecular nucleophilic attack is possible if the Schiffbases are prepared by the condensation of some aromaticcarboxaldehydes with certain polyamines, or aminescontaining another nucleophilic group, e.g. –SH. Theintramolecular nucleophilic attacks in such cases lead tothe formation of isomers containing saturated hetero-cyclic rings. This isomerization is quite common forSchiff bases prepared from 2-pyridinecarboxaldehyde,

CuII complexes with the new Schiff base ligands as a mono- and bis-condensation products of 2-pyridinecarboxaldehyde-N-oxide with diethylenetriamine

The crystal structure of tripotassium octafluoridotantalate, K(3)TaF(8), determined from laboratory powder diffraction data by the simulated annealing method and refined by total energy minimization in the solid state, is built from discrete potassium cations, fluoride anions and monocapped trigonal-prismatic [TaF(7)](2-) ions. All six atoms in the asymmetric unit are in special positions of the P6(3)mc space group: the Ta and one F atom in the 2b (3m) sites, the K and two F atoms in the 6c (m) sites, and one F atom in the 2a (3m) site. The structure consists of face-sharing K(6) octahedra with a fluoride anion at the center of each octahedron, forming chains of composition [FK(3)](2+) running along [001] with isolated [TaF(7)](2-) trigonal prisms in between. The structure of the title compound is different from the reported structure of Na(3)TaF(8) and represents a new structure type.

Phase transitions of K2TaF7 within 680–800°C

Abstract Cu II complexes with Schiff base ligands as a mono- ( L 2 ) and bis- ( L 1 ) -condensation products of 2-pyridinecarboxaldehyde- N -oxide with diethylenetriamine with perchlorate and chloride counter anions were prepared. Two methods of preparation of Cu II complex containing ligand L 2 are reported. Crystal structure of [Cu L 2 (ClO 4 )(H 2 O)](ClO 4 ) was solved. Chloride Cu II complexes with ligand L 1 are formed in the ratio metal:ligand 1:1 and 2:1. The presence of the ligand L 1 in these complexes does not depend on the excess of Cu II ions contrary to perchlorate complexes where the presence of the ligand L 1 or L 2 is dependent on the amount of Cu II ions. By EPR measurements an exchange interactions were detected in Cu L 1 (ClO 4 ) 2 ·MeOH, Cu L 2 (ClO 4 ) 2 ·0.25EtOH and Cu 2 L 1 Cl 4 ·2H 2 O. Amorphous character of all three complexes was detected by X-ray powder diffraction.

Density and Surface Tension of the System KF–K2TaF7–Ta2O5

Three thermal effects on heating/cooling of K2TaF7 in the temperature interval of 680–800°C were investigated by the DSC method. The values determined for the enthalpy change of the individual processes are: ΔtransIIHm(K2TaF7; 703°C) = 1.7(2) kJ mol−1, ΔtransIHm(K2TaF7; 746°C) = 19(1) kJ mol−1 and ΔtransIIIHm(K2TaF7; 771°C) = 13(1) kJ mol−1. The first thermal effect was attributed to a solid-solid phase transition; the second to the incongruent melting of K2TaF7 and the third to mixing of two liquids. These findings are supported by in situ neutron powder diffraction experiments performed in the temperature interval of 654–794°C.

Imidazolidine ring-formation/cleavage due to intracomplex coordinative activation

The density of the system KF–K2TaF7–Ta2O5 was measured by the Archimedean method and the surface tension by the maximum bubble pressure method in the composition range up to 20 mol% Ta2O5. The density in the system KF–K2TaF7–Ta2O5 increases from KF through K2TaF7 to Ta2O5 and the surface tension increases from K2TaF7 through KF to Ta2O5. Based on the measured density values, the molar volumes of the binary and ternary melts at 860 °C, 900 °C and 950 °C were calculated as well as the partial molar volumes of particular components in different binaries. The small negative deviation from ideal behaviour in the binary system KF–K2TaF7 was identified by the calculation of the molar excess volume. The formation of complex anions [TaF8]3− is expected in this binary system. The surface tension decreases monotonically from KF to K2TaF7 in the binary system KF–K2TaF7. In the next two binaries KF–Ta2O5 and K2TaF7–Ta2O5 decrease of the surface tension was observed with the initial addition of Ta2O5 followed by the increase of the surface tension by further addition of Ta2O5. Based on measured data it was concluded that in binaries KF–Ta2O5 and K2TaF7–Ta2O5 the surface active component is Ta2O5 and in the binary KF–K2TaF7 the surface active component is K2TaF7. Mathematical description of the concentration dependence of the molar volume and surface tension of the measured ternary system was done by the polynomial function at 860°C, 900°C, and at 950°C.

High-Temperature Corrosion Behavior of Superalloys in Molten Salts - A Review

Abstract The condensation product of 2-pyridinecarboxaldehyde N-oxide with triethylenetetramine exists in solution in the contracted form with two outer imidazolidine rings. In the copper and zinc complexes, three ligand isomers, containing none (L1), one (L2) or two (L3) imidazolidine rings, occur as proved by the X-ray structure analysis of [ZnL1](ClO4)2, [CuL2](ClO4)2 and [ZnL3(DMSO)2](ClO4)2.

The dissolution of FeO and FeF3 in cryolite

ABSTRACT The use of molten salts based on fluorides/chlorides/nitrates/sulfates or carbonates is now an accepted practice in energy conversion technologies and many other industrial processes. However, compatibility of molten salts with the structural alloys and materials corrosion has been of real concern at such temperatures (600–900°C). Hence, the material development and corrosion studies turn out to be an essential part of research. The results of recent studies are reviewed to understand the developments that have occurred in the latter part of the last decade. The corrosion kinetics of modern materials in variety of molten salts with focus on reaction mechanisms and corrosion products is investigated by scientists around the globe. Emphasis has also been given on the composition of the oxide films/corrosion products on alloys of interest in wide a range of melts. By and large, molten salt corrosion has been predominantly studied by gravimetric, electrochemical techniques and, morphology and chemical analysis of corrosion products by means of XRD, SEM/EDX, ICP/AAS, etc. This article gives in-depth insight into the composition of materials, the molten salt mixtures, and various aggressive environments mainly high temperatures and long exposures.

Combined Approach for the Structural Characterization of Alkali Fluoroscandates: Solid-State NMR, Powder X-ray Diffraction, and Density Functional Theory Calculations

Abstract Theoretical derivation of relations valid for cryoscopic measurements in solvents with dystectic mode of melting (solvents, which undergo at melting a more or less extended thermal dissociation), when also chemical reaction between solvent and solute takes place, is presented. When one of the products of this chemical reaction is identical with the product of thermal dissociation of the solvent, arise the problem of defining the number of “foreign” substances, originating in the reaction. The presented approach shows that the partially dissociated solvent cannot distinguish as foreign substance between the own dissociation product and the originating one and made it easier to determine the nature of the probable chemical reaction. The presented approach is applied in the systems Na3AlF6–FeO and Na3AlF6–FeF3, which are of great importance in the fundamentals of aluminium electrolysis. In the system Na3AlF6–FeO for the dependence of the temperature of primary crystallization of cryolite on x(Na3AlF6) the equation T pc/K = 1014.4 + 267.86x(Na3AlF6) was obtained, which yields for the Stortenberker’s correction factor the value kSt = 2.09. This means that dissolving FeO in cryolite two new particles are formed. This can be interpreted by the chemical reaction 2Na3AlF6 + FeO ⇔ Na2FeF4 + Na2Al2OF6 + 2NaF. In the system Na3AlF6–FeF3 for the dependence of the temperature of primary crystallization of cryolite on x(Na3AlF6) the equation T pc/K = 1547.2 − 659.88x(Na3AlF6) + 394.99x2 (Na3AlF6) was obtained. For the Stortenbeker’s correction factor the value kSt = 1.02 was then calculated, which means that one new particle is created when FeF3 is dissolved in cryolite. The most probable reaction is 1.5Na3AlF6 + FeF3 ⇔ Na3FeF6 + 1.5NaAlF4.