The Structural Dimorphism of Lanthanum Oxide Fluoride Selenide La<sub>2</sub>OF<sub>2</sub>Se
The new colorless lanthanum oxide fluoride selenide La<sub>2</sub>OF<sub>2</sub>Se could be synthesized via solid-state reactions in two different structure types. Lamellar crystals of A-La<sub>2</sub>OF<sub>2</sub>Se were obtained from mixtures of La,...
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MDPI AG
2019-08-01
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| Series: | Crystals |
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| Online Access: | https://www.mdpi.com/2073-4352/9/9/435 |
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| author | Constantin Buyer Hagen Grossholz Thomas Schleid |
| author_facet | Constantin Buyer Hagen Grossholz Thomas Schleid |
| author_sort | Constantin Buyer |
| collection | DOAJ |
| description | The new colorless lanthanum oxide fluoride selenide La<sub>2</sub>OF<sub>2</sub>Se could be synthesized via solid-state reactions in two different structure types. Lamellar crystals of A-La<sub>2</sub>OF<sub>2</sub>Se were obtained from mixtures of La, LaF<sub>3</sub>, La<sub>2</sub>O<sub>3</sub> and Se in molar ratios of 2:2:1:3 with NaCl as flux for seven days in silica-protected sealed tantalum capsules at 850 °C. Needle-shaped crystals of BLa<sub>2</sub>OF<sub>2</sub>Se emerged from reactions of the same educt mixtures in molar ratios of 6:4:4:9 scheduled to produce La<sub>6</sub>O<sub>4</sub>F<sub>4</sub>Se<sub>3</sub> with CsI as flux for four days in niobium ampoules at 700 °C. The Atype form of La<sub>2</sub>OF<sub>2</sub>Se crystallizes in the trigonal space group <i>R</i>3m with <i>a</i> = 418.13(3) and <i>c</i> = 4478.2(4) pm for <i>Z</i> = 6, whereas the Btype form is hexagonal (space group: <i>P</i>6<sub>3</sub>/<i>m</i>) with <i>a</i> = 1396.82(9) and <i>c</i> = 401.08(3) pm for <i>Z</i> = 6. The crystal structure of A-La<sub>2</sub>OF<sub>2</sub>Se shows a close relationship to the fluoride-free La<sub>2</sub>O<sub>2</sub>Se and the oxygen-free La<sub>2</sub>F<sub>4</sub>Se. It can even be discussed as 1:1 intergrowth variety, since it contains the [LaO<sub>4</sub>Se<sub>3</sub>]<sup>11−</sup> and [LaF<sub>7</sub>Se<sub>3</sub>]<sup>10−</sup> polyhedra typical for the ternaries. B-La<sub>2</sub>OF<sub>2</sub>Se appears to be structurally very similar to La<sub>6</sub>O<sub>2</sub>F<sub>8</sub>Se<sub>3</sub> in displaying [LaO<sub>3</sub>FSe<sub>4</sub>]<sup>12−</sup> and [LaOF<sub>6</sub>Se<sub>2</sub>]<sup>9−</sup> polyhedra. With 6.039 versus 6.036 g/cm³ the B-type form of La<sub>2</sub>OF<sub>2</sub>Se is slightly denser than the A-type variant. |
| first_indexed | 2024-04-14T06:48:31Z |
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| last_indexed | 2024-04-14T06:48:31Z |
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| series | Crystals |
| spelling | doaj.art-7051d26b3a1c4203913d5349c36edb532022-12-22T02:07:06ZengMDPI AGCrystals2073-43522019-08-019943510.3390/cryst9090435cryst9090435The Structural Dimorphism of Lanthanum Oxide Fluoride Selenide La<sub>2</sub>OF<sub>2</sub>SeConstantin Buyer0Hagen Grossholz1Thomas Schleid2Institute for Inorganic Chemistry, University of Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart, GermanyInstitute for Inorganic Chemistry, University of Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart, GermanyInstitute for Inorganic Chemistry, University of Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart, GermanyThe new colorless lanthanum oxide fluoride selenide La<sub>2</sub>OF<sub>2</sub>Se could be synthesized via solid-state reactions in two different structure types. Lamellar crystals of A-La<sub>2</sub>OF<sub>2</sub>Se were obtained from mixtures of La, LaF<sub>3</sub>, La<sub>2</sub>O<sub>3</sub> and Se in molar ratios of 2:2:1:3 with NaCl as flux for seven days in silica-protected sealed tantalum capsules at 850 °C. Needle-shaped crystals of BLa<sub>2</sub>OF<sub>2</sub>Se emerged from reactions of the same educt mixtures in molar ratios of 6:4:4:9 scheduled to produce La<sub>6</sub>O<sub>4</sub>F<sub>4</sub>Se<sub>3</sub> with CsI as flux for four days in niobium ampoules at 700 °C. The Atype form of La<sub>2</sub>OF<sub>2</sub>Se crystallizes in the trigonal space group <i>R</i>3m with <i>a</i> = 418.13(3) and <i>c</i> = 4478.2(4) pm for <i>Z</i> = 6, whereas the Btype form is hexagonal (space group: <i>P</i>6<sub>3</sub>/<i>m</i>) with <i>a</i> = 1396.82(9) and <i>c</i> = 401.08(3) pm for <i>Z</i> = 6. The crystal structure of A-La<sub>2</sub>OF<sub>2</sub>Se shows a close relationship to the fluoride-free La<sub>2</sub>O<sub>2</sub>Se and the oxygen-free La<sub>2</sub>F<sub>4</sub>Se. It can even be discussed as 1:1 intergrowth variety, since it contains the [LaO<sub>4</sub>Se<sub>3</sub>]<sup>11−</sup> and [LaF<sub>7</sub>Se<sub>3</sub>]<sup>10−</sup> polyhedra typical for the ternaries. B-La<sub>2</sub>OF<sub>2</sub>Se appears to be structurally very similar to La<sub>6</sub>O<sub>2</sub>F<sub>8</sub>Se<sub>3</sub> in displaying [LaO<sub>3</sub>FSe<sub>4</sub>]<sup>12−</sup> and [LaOF<sub>6</sub>Se<sub>2</sub>]<sup>9−</sup> polyhedra. With 6.039 versus 6.036 g/cm³ the B-type form of La<sub>2</sub>OF<sub>2</sub>Se is slightly denser than the A-type variant.https://www.mdpi.com/2073-4352/9/9/435lanthanum oxide fluoride selenidespolymorphismX-ray diffractioncrystal structurerare-earth metal compounds |
| spellingShingle | Constantin Buyer Hagen Grossholz Thomas Schleid The Structural Dimorphism of Lanthanum Oxide Fluoride Selenide La<sub>2</sub>OF<sub>2</sub>Se Crystals lanthanum oxide fluoride selenides polymorphism X-ray diffraction crystal structure rare-earth metal compounds |
| title | The Structural Dimorphism of Lanthanum Oxide Fluoride Selenide La<sub>2</sub>OF<sub>2</sub>Se |
| title_full | The Structural Dimorphism of Lanthanum Oxide Fluoride Selenide La<sub>2</sub>OF<sub>2</sub>Se |
| title_fullStr | The Structural Dimorphism of Lanthanum Oxide Fluoride Selenide La<sub>2</sub>OF<sub>2</sub>Se |
| title_full_unstemmed | The Structural Dimorphism of Lanthanum Oxide Fluoride Selenide La<sub>2</sub>OF<sub>2</sub>Se |
| title_short | The Structural Dimorphism of Lanthanum Oxide Fluoride Selenide La<sub>2</sub>OF<sub>2</sub>Se |
| title_sort | structural dimorphism of lanthanum oxide fluoride selenide la sub 2 sub of sub 2 sub se |
| topic | lanthanum oxide fluoride selenides polymorphism X-ray diffraction crystal structure rare-earth metal compounds |
| url | https://www.mdpi.com/2073-4352/9/9/435 |
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