Synthesis and Characterization of La3NbSe2O4F2

✍ Scribed by Theodore D. Brennan; Michael F. Mansuetto; James A. Ibers

• Publisher: Elsevier Science
• Year: 1993
• Tongue: English
• Weight: 241 KB
• Volume: 107
• Category: Article
• ISSN: 0022-4596
• DOI: 10.1006/jssc.1993.1380

✦ Synopsis

Crystals of the unusual oxyfluoroselenide (\mathrm{La}{3} \mathrm{NbSe}{2} \mathrm{O}{4} \mathrm{~F}{2}) were obtained during the exploration of the quaternary (\mathrm{La} / \mathrm{Nb} / \mathrm{Cu} / \mathrm{Se}) system. Oxygen was extracted from the silica tube, while fluorine was present as a minor impurity in the La powder. The compound crystallizes in space group (D_{2 h}^{16}-P n m a) of the orthorhombic system with four formula units in a cell with dimensions: (a=11.290(4), b=4.001(1)), and (c=18.062(4) \AA(T=113 \mathrm{~K})). The structure has been determined by single-crystal X-ray methods. The presence of (\mathrm{F}) in the crystals was confirmed by windowless EDAX measurements. The two (\mathrm{F}) sites were distinguished from the four (\mathrm{O}) sites from a combination of the (\mathrm{X})-ray refinement and a bondvalence parameter calculation made with the program EUTAX. In the structure the (\mathrm{Nb}) atom is octahedrally coordinated while each of the three independent La atoms is in a tricapped trigonal prism. The (\mathrm{Nb}) atom is bound to one (\mathrm{Se}) atom and five (\mathrm{O}) atoms while the three La sites are coordinated by various combinations of (\mathrm{Se}, \mathrm{O}), and (\mathrm{F}) atoms. The (\mathrm{NbO}{5} \mathrm{Se}) octahedra corner share and the (\mathrm{LaSe}{x} \mathrm{O}{y} \mathrm{~F}{z}) tricapped trigonal prisms face share in the (b) direction. 1993 Academic Press. Inc.