Rolf Berger

Supercritical fluids crystallization of budesonide and flunisolide

AbstractPurpose: Budesonide and flunisolide anhydrate were crystallized using the solution enhanced dispersion by supercritical fluids (SEDS) technique. The aim was to investigate the possibility of preparing different pure polymorphs. Methods: 0.25% w/v solutions of each drug were prepared from acetone and methanol. Operating conditions were 40-80°C and 80-200 bars. The flow rate of drug solution was 0.3 mL/min and that of CO2 was 9-25 mL/min. Sample characterizations included differential scanning calorimetry, X-ray powder diffraction, variable temperature X-ray diffraction, scanning electron microscopy, and solubility studies. Results: The particle morphology of budesonide was dependent on the nature of the solvent. SEDS processing of flunisolide with acetone at 100 bars resulted in the formation of polymorphic mixtures at 80°C and a new polymorph III at 60 C and 40°C. With methanol at 100 bars another new polymorph IV was formed with different particle morphology at 80°C and a polymorphic mixture at 60°C. Conclusion: Using the SEDS, microparticles of crystalline budesonide were prepared and new polymorphs of flunisolide were produced. Particle characteristics were controlled by the temperature, pressure and relative flow rates of drug solution and CO2.

A phase-analytical study of the TlCuSe system

Abstract High-temperature silica-tube syntheses and room-temperature copper extraction experiments of the single phases found with the former technique have established five new ternary phases in the Tl Cu Se system. The compositions were determined by microprobe analysis. The new phases have been crystallographically characterized by means of single-crystal and powder diffraction: TlCu 3 Se 2 (CsAg 3 S 2 type), a = 15.2128(7)A, b = 4.0115(2)A, c = 8.3944(4)A, β = 111.700°(4); Tl 5 Cu 14 Se 10 (new type), C2/m ?) a = 18.097(2)A, b = 3.9582(2)A, c = 18.118(2)A, β = 116.089°(7); TlCu 5 Se 3 (new type, P 4¯n2?), a = 12.9023(2)A, c = 3.9905(1)A; TlCu 5− x Se 3 (new type, Pnn 2?), a = 12.43(1)A, b = 12.80(1)A, c = 3.93(1)A; TlCu 7 Se 4 (NH 4 Cu 7 S 4 type), a = 10.4524(2)A, c = 3.9736(1)A. The latter phase may be considered as stoichiometric crookesite.

Room temperature synthesis and structural characterization of monoclinic LiCuO2 by X-ray and neutron diffraction

LiCuO2 was synthesized at room temperature by delithiation of Li2CuO2 using bromine in acetonitrile. The product shows broad diffraction lines which were analysed by the Rietveld refinement technique on X-ray and neutron powder data. The phase conforms to the NaCuO2 structure type

Structure refinements of LiCu2O2 and LiCu3O3 from neutron powder diffraction data

Abstract In its inherent ability to discern light elements in a heavy-atom matrix, neutron powder diffraction has been used at room temperature to confirm structure hypotheses of LiCu 2 O 2 ( R I = 2.18%; R P = 4.21%) and LiCu 3 O 3 ( R I = 2.19%; R rmP = 5.45%), inferred from previous X-ray diffraction studies. LiCu 2 O 2 is orthorhombic, described by the space group Pnma ( Z =4), as suggested from a structure determination from twin-crystal data. The cell parameters found were a=5.7260(4) A , b=2.8587(2) A and c=12.4137(7) A . The apparent tetragonal symmetry independently advocated must be definitively discarded as an artifact from twinning. LiCu 3 O 3 was successfully refined on a tetragonal cell-with a=2.8142(1) A and c=8.8956(5) A -in P4/mmm (Z=1) using a single-crystal model. The data were insufficient to test any superstructure model.

Potentiometric measurements of copper diffusion in polycrystalline chalcocite, chalcopyrite and bornite

Abstract Diffusion measurements have been performed by an electrochemical potentiometric method on polycrystalline synthetic chalcocite (Cu 2 S), chalcopyrite (CuFeS 2 ) and bornite (Cu 5 FeS 4 ) in the temperature range 5–50 °C. The chemical ( D ) diffusion coefficients (in cm 2 /s) are as follows: chalcocite, D = 38.7 exp ( −5600 T ) ; chalcopyrite, D = 15.4 exp ( −6000 T ) and bornite, D = 14.5 exp ( −4900 T ) . The component diffusion coefficients ( D ) are obtained by using the thermodynamic factor, this being 4250, 6500 and 1500, respectively. The diffusion coefficients obtained are in reasonable agreement with literature data, even for chalcopyrite and bornite, with values previously acquired with a tracer technique at much higher temperatures.

A Mössbauer study of antiferromagnetic ordering in iron deficient TlFe2−xSe2

Abstract TlFe 2- x Se 2 compounds with x values around 0.4 have been characterized by X-ray diffraction and examined by Mossbauer spectroscopy. The iron vacancies are ordered to some extent, but a ThCr 2 Si 2 type subcell structure can be recognized. Antiferromagnetic ordering occurs below a Neel temperature which is strongly dependent on x . The transition seems to be of first order. In contrast to a previous study on a single crystal, these specimens show less pronounced vacancy ordering and a higher extrapolated Neel temperature, which may be explained by a larger number of iron nearest neighbours. The magnetic transition regions are broad, indicating weak interactions between the layers containing iron. A difference in the isomer shifts for the coexisting para- and antiferromagnetic phases was observed, tentatively explained by a difference in the conduction electron density owing to iron vacancies. The electric quadrupole interaction has a T 3 2 dependence in the paramagnetic phase.

Characterization of TlCu7S4, a crookesite analogue

Previous claims of a compound TlCu9S5 are rejected. The true composition is TlCu7S4, the compound being isostructural with NH4Cu7S4 and TlCu7Se4 (crookesite). The body-centred tetragonal cell (a=10.1797 Å andc=3.8585 Å) contains two formula units.ZusammenfassungFrühere Feststellungen, daß im pseudobinären System Tl2S-Cu2S eine Verbindung TlCu9S5 existiert, erwiesen sich als unzutreffend. Die korrekte Formel muß TlCu7S4 lauten. TlCu7S4 besitzt eine raumzentrierte tetragonale Elementarzelle (a=10.1797 Å,c=3.8585 Å;Z=2) und ist isostrukturell mit NH4Cu7S4 und TlCu7Se4 (Crookesit).

A study of the structural and magnetic properties of TlCo2−xCuxSe2

Abstract The structural and magnetic properties of TlCo 2− x Cu x Se 2 have been investigated experimentally. The antiferromagnetic coupling already found in TlCo 2 Se 2 prevails on copper substitution but is weakened. For high copper contents, x >1.3, Pauli paramagnetism occurs. The susceptibility measurements point towards a picture of ferromagnetic Co moments aligned perpendicular to the c -axis. The cobalt atoms are confined to sheets, between which there is antiferromagnetic coupling. Structurally we observe a change in symmetry from I-centred tetragonal ( Z =2) to face-centred orthorhombic ( Z =4) in the range 0 x 2 Se 2 has been re-investigated by neutron powder diffraction. Below T N ∼80 K, it is characterised by a helimagnetic arrangement of spins confined to the Co sheets, the helix running along the c -axis. The moments lie in the (002) planes with a helical turn angle of about 121° between two adjacent Co layers. At 10 K, the moment refined to 0.46 μ B /Co atom.

The Crystal Structure of TlCu5Se3

Abstract The crystal structure of copper-deficient TlCu5Se3 has been refined from single-crystal X-ray diffraction data. The previously suggested new structure type was confirmed with agreement factors RF = 0.033 and RwF = 0.035. The symmetry is tetragonal, space group P4 2 mnm (136). For the investigated composition, TlCu4.8Se3, the cell dimensions are a = 12.900 and c = 3.968 A (Z = 4). The structure has features common to other thallium copper chalcogenides such as TlCu3Se2 and TlCu7Se4. Similarities to some multinary alkali metal oxide structures are emphasized.

NMR and susceptibility characterization of two oxocuprates with antiferromagnetic Cu-chains: LiCuO2 and LiCu2O2

Abstract The CuO2 compounds LiCuO2 and LiCu2O2 both contain CuO4 squares knit together in linear chains. These chains are all equivalent in LiCuO2 and grouped in pairs in LiCu2O2. From susceptibility measurements the spin interaction in both compounds is seen to be dominated by Heisenberg antiferromagnetic exchange. In LiCuO2 the strongly reduced magnetic moment and χ(T)-behavior are typical for random exchange interactions. The Cu-spins in LiCu2O2 form an antiferromagnetically coupled Heisenberg chain with likely some spread in J-values. The differences in the 7Li NMR relaxation rates support these models.