Biomedical subjects
Publications and source records attributed to Ivana Radosavljevic Evans.
We report the crystal structure and phase transitions of Mo2P4O15 which, despite a simple chemical formula, has 441 crystallographically unique atoms in its asymmetric unit and thus has the most complex structure of any extended oxide reported to date.
This article provides a short tutorial review of how laboratory powder diffraction methods can be used to establish a variety of "non-traditional" pieces of information about solid state materials-information beyond simple phase identification or structure determination at a specific temperature. The examples show how unique insights into synthetic pathways, reaction mechanisms, reaction kinetics, polymorphism, phase transitions and physical properties can be obtained for a variety of different types of materials.
The crystal structure of the iron(II) spin-crossover compound [Fe(C(10)H(8)N(6))(2)](ClO(4))(2) in the high-spin state has been solved from powder X-ray diffraction data using the DASH program and refined using Rietveld refinement. The thermal spin transition has been monitored by following the change in unit-cell parameters with temperature. The title compound has been found to undergo a crystallographic phase change, involving a doubling of the crystallographic a axis, on undergoing the spin transition.
The two polymorphs (Forms I and II) of [R,S]-ethambutol dihydrochloride transform enantiotropically and reversibly in a single-crystal-to-single-crystal phase transformation mode. These structurally very similar forms have been characterized and their thermodynamic relationship has been investigated by variable-temperature solid-state carbon-13 nuclear magnetic resonance, variable-temperature powder X-ray diffraction, differential scanning calorimetry, and optical microscopy. The nuclear magnetic resonance results are compared with those for the two polymorphs of the [S,S] diastereomer with known structures.
The spin crossover compounds [FeL2](BF4)2, L=2,6-di(3-methylpyrazol-1-yl)pyrazine and [FeL2](ClO4)2 have very unusual two stage spin transitions which are initially steep and then become more gradual. A detailed variable temperature single crystal X-ray diffraction study has shown that the course of the spin transition is controlled by an order-disorder transition in the counter anions. The high and low spin states both crystallise in the tetragonal space group I4, the structures of the high and low spin states are presented at 290 and 30 K, respectively. The title compounds are shown to undergo LIESST (Light Induced Excited Spin State Trapping) under irradiation with either red or green laser light with wavelengths of 632.8 and 532.06 nm, respectively, at 30 K. The cell parameters for the tetragonal photo-induced metastable high spin state at this temperature are a= 9.169(6), c= 17.77(1) A for [FeL2](ClO4)2 with an increase in unit cell volume of 21 A3, and a= 9.11(1), c= 17.75(2) A and an increase in volume of 42.8 A3 for [FeL2](BF4)2.
The spin-crossover complex [FeL2](BF4)2 undergoes a LIESST transition at 30 K on irradiation; the structures of the low-spin ground and high-spin metastable states at this temperature are presented.