| dc.description.abstract | Amine-templated open-framework gallium arsenates with one- (I), two- (II and IV) and three-dimensionally (III–V) extended structures have been isolated and characterized. The exclusive presence of only one type of SBU in the three-dimensional structures of III and V is noteworthy. The gallium arsenate phases have not been investigated in great detail, and the present study suggests that these compounds also could exhibit the wide structural and compositional diversity that one generally observes in phosphate structures. In addition, the coordination preferences of gallium (4-, 5- and 6-coordination) could be beneficially exploited in the synthesis of such phases.
The synthesis, structure and characterization of three iron arsenates (I–III) and one iron arsenate-oxalate (IV) compound have been accomplished. While I has a simple one-dimensional chain, II–IV possess three-dimensional structures. All the compounds have iron octahedra and arsenate tetrahedra connected through their oxygen vertices. The structure of II, though built up from the expected building units consisting of FeO? and AsO? polyhedra, possesses a new secondary building unit (SBU-5). Iron arsenate layers in III are pillared by a one-dimensional iron arsenate chain, while the oxalate units pillar the iron arsenate layers in IV. The formation of a face-shared Fe-dimer in III within the one-dimensional iron arsenate chain that pillars the layers is noteworthy, as such sharing of octahedral faces is rarely observed. The magnetic studies on III indicate predominant antiferromagnetic interactions within the layers and weakly ferromagnetic polarizations between the layers at low temperatures. Variable temperature powder XRD studies on III and IV indicate they lose crystallinity at ~300 °C forming an amorphous phase that gives way to crystalline FeAsO? at ~650 °C.
Open-framework uranium arsenates with two- and three-dimensional structures have been synthesized and characterized. The uranium exhibits both variable coordination and oxidation states in the compounds, which appears to have some correlation with the synthesis composition. The structures have close resemblance to some of the naturally occurring minerals, suggesting that the hydrothermal condition could replicate the geothermal conditions. The single-crystal-to-single-crystal transformation studies during the dehydration–hydration of the uranium arsenate, [C?N?H??][(UO?)F(HAsO?)]?·4H?O, II, give the first such observation in the family of uranium arsenates. The observation of a two-photon process during the photoluminescence study of [C?N?H??][U?F?(AsO?)(HAsO?)], VI is noteworthy. Magnetic studies suggest antiferromagnetic interactions. The diversity of the structures observed in the present study suggests that the family of uranium arsenates can also exhibit considerable variations in the coordination around uranium as well as the structures. It is likely that many related phases can be prepared by careful choice of the reaction conditions.
? Corrected spelling and grammar:
“fam ily” ? family
“ch oice” ? choice
“som e” ? some
“o f” ? of
Added proper hyphenation: single-crystal-to-single-crystal, two-photon process, open-framework | |
