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Article

The Structural Dimorphism of Lanthanum Oxide Fluoride Selenide La2OF2Se

by
Constantin Buyer
,
Hagen Grossholz
and
Thomas Schleid
*
Institute for Inorganic Chemistry, University of Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart, Germany
*
Author to whom correspondence should be addressed.
Crystals 2019, 9(9), 435; https://doi.org/10.3390/cryst9090435
Submission received: 17 July 2019 / Revised: 1 August 2019 / Accepted: 16 August 2019 / Published: 21 August 2019
(This article belongs to the Special Issue Rare-Earth Metal Compounds)
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Abstract

:
The new colorless lanthanum oxide fluoride selenide La2OF2Se could be synthesized via solid-state reactions in two different structure types. Lamellar crystals of A-La2OF2Se were obtained from mixtures of La, LaF3, La2O3 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 B‑La2OF2Se emerged from reactions of the same educt mixtures in molar ratios of 6:4:4:9 scheduled to produce La6O4F4Se3 with CsI as flux for four days in niobium ampoules at 700 °C. The A‑type form of La2OF2Se crystallizes in the trigonal space group R 3 ¯ m with a = 418.13(3) and c = 4478.2(4) pm for Z = 6, whereas the B‑type form is hexagonal (space group: P63/m) with a = 1396.82(9) and c = 401.08(3) pm for Z = 6. The crystal structure of A-La2OF2Se shows a close relationship to the fluoride-free La2O2Se and the oxygen-free La2F4Se. It can even be discussed as 1:1 intergrowth variety, since it contains the [LaO4Se3]11− and [LaF7Se3]10− polyhedra typical for the ternaries. B-La2OF2Se appears to be structurally very similar to La6O2F8Se3 in displaying [LaO3FSe4]12− and [LaOF6Se2]9− polyhedra. With 6.039 versus 6.036 g/cm3 the B-type form of La2OF2Se is slightly denser than the A-type variant.

1. Introduction

Rare-earth metal sesquiselenides (RE2Se3, RE = Sc, Y, La, Ce–Lu) come in three modifications, which offer coordination numbers of eight (C- or Ce2S3-type structure, RE = La–Nd, Sm, Tb, Gd, Ho, Tm; cubic, I 4 ¯ 3d) [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20], seven (U- or U2S3-type structure, RE = Sm–Er; orthorhombic, Pnma) [5,16,21,22,23,24,25] and six (Z- or Sc2S3-type structure RE = Sc, Y, Eu, Tb, Ho–Lu; orthorhombic, Fddd) [3,17,24,26,27,28,29,30,31] for the RE3+ cations, reflecting the consequences of the lanthanoid contraction. They are dark red or black substances and thus not suitable to serve as host materials for luminescent Ln3+ cations, such as Eu3+ or Tb3+, in order to harvest red or green light. This changes a lot, when one considers their derivatives with hard anions like F− or O2−. For the rare-earth metal(III) fluoride selenides (REFSe) tetragonal NdFSe with PbFCl-type structure (P4/nmm) [32] and hexagonal LaFSe in P63/mmc are known [33], both exhibiting C.N.(RE3+) = 9. With cerium there is a trigonal compound (R 3 ¯ m) of the composition Ce2F4Se in the literature providing a tenfold coordination sphere for Ce3+ [34], while HoFSe and ErFSe adopt orthorhombic structures in Pnma with coordination numbers between six and eight for the respective RE3+ cations [35,36,37]. For YFSe, different orthorhombic polymorphs have also been reported, but even monoclinic ones (P21/m) can be found [37,38,39,40]. If oxygen is added to the rare-earth metal(III) selenides, compounds with the compositions RE10OSe14 (RE = La, Ce–Nd; tetragonal, I41/acd) [41,42], RE2OSe2 (RE = Pr; monoclinic, P21/c [42]; RE = Gd: orthorhombic; Pnma [43]) and RE2O2Se (RE = La, Pr, Nd, Sm, Gd, Ho, Er, Yb; trigonal, P21/m1) [42,44] are known. The richer in oxygen these oxide selenides get, the brighter their color becomes, so that Y2O2Se:Ln3+ (Ln = Ce–Nd, Sm–Yb) even shows luminescence [45]. By adding both oxygen and fluorine as O2− or F− to the RE/Se systems tetragonal Ho3OFSe3 (I4/mmm) [46], orthorhombic Ho3OF3Se2 (Ccce) [46], orthorhombic Ce6O4F4Se3 (Pnma) [47] and tetragonal Nd5OF5Se4 (I4/mmm) [36] are found as singularities so far, but several members from the series RE6O2F8Se3 with RE = La–Nd and RE2OF2Se with RE = Nd, Sm, Gd–Ho [48] occur. In the analogous sulfide systems the hexagonal RE6O2F8S3 series with RE = La–Nd, Sm, Gd [49] also exists, but there is an additional one for the formula type RE3OF5S with RE = Y, Nd, Sm, Gd–Ho [50,51,52] showing similar structural features. Despite this difference further analogies refer to compounds with the composition RE3OF3S2 with RE = La, Ce, Er [53,54] and RE3OFS3 with RE = Er [54]. In our ongoing efforts to elucidate the REF3/RE2O3/RE2Se3 systems, we were now able to synthesize two modifications of a lanthanum oxide fluoride selenide with the formula La2OF2Se.

2. Materials and Methods

Both forms of La2OF2Se were synthesized by mixing lanthanum powder (La: ChemPur, 99.9%, company, city, country), lanthanum trifluoride powder (LaF3: ChemPur, 99.9%, company, Karlsruhe, Germany), lanthanum sesquioxide powder (La2O3: ChemPur, 99.9% company, city, country) and selenium powder (Se: Alfa–Aesar, 99.999% company, city, country) (in sum: about 300 mg) in a glove box under argon atmosphere. For A-type La2OF2Se the stoichiometric molar ratio 2:2:1:3 was used as well as an excess of about 500 mg sodium chloride powder (NaCl: ChemPur, 99.9% company, city, country) to work as the fluxing agent. After heating this mixture at 850 °C for seven days in a sealed tantalum capsule, protected by an evacuated secondary silica ampoule, colorless platelets with triangular cross-section were obtained. B-type La2OF2Se emerged as colorless needles from the same educt mixture in molar ratio of 6:4:4:9, because the target compound was La6O4F4Se3 in analogy to Ce6O4F4Se3 [47]. This mixture was charged with 300 mg cesium iodide powder (CsI: ChemPur, 99.9%) as fluxing agent and heated at 700 °C for four days in a sealed niobium tube encapsulated into an evacuated silica ampoule. After cooling down to room temperature directly with 5 K/h in the NaCl-flux case and to 540 °C with 3 K/h and CsI as flux before shutting down the furnace, washing with water, ethanol and ether removed the alkali-metal halides and left the air- and water-stable (but not phase-pure) samples of La2OF2Se behind. For B-type La2OF2Se the applied stoichiometry leads to La2O2Se [44] besides B-La2OF2Se according to 6 La + 4 LaF3 + 4 La2O3 + 9 Se → 2 La2OF2Se + La2O2Se.
For the data collections enabling X-ray structure analyses a IPDS diffractometer (Stoe and Cie) for A-type La2OF2Se and a κ-CCD diffractometer (Bruker–Nonius) for B-type La2OF2Se with graphite-monochromatized Mo-Kα radiation (λ = 71.07 pm) was used. The collected data were processed with the program SHELX-97 [55,56] for the structure solutions and refinements. Crystallographic data, atomic positions, equivalent isotropic displacement coefficients, selected interatomic distances and angles can be found in Table 1, Table 2, Table 3, Table 4 and Table 5, while Table 6 displays the motifs of mutual adjunction for both forms of La2OF2Se. The CIF data sheets of the crystal-structure investigations are available under CSD-1919109 for A-La2OF2Se and CSD-1919110 for B-La2OF2Se from the Fachinformationszentrum (FIZ) Karlsruhe, D-76344 Eggenstein–Leopoldshafen, Germany (e-mail: [email protected]) (or see Supplementary Materials).
For the determination of the element ratios in B-type La2OF2Se an electron-beam microprobe technique has been applied. After performing X-ray diffraction, the single crystal was placed on a conductive carbon pad and vaporized with carbon. This setup entered the electron-beam microprobe (Cameca SX-100), which is equipped with an energy-dispersive X-ray spectrometer (EDXS). The measured energy-dispersive X-ray spectrum with its assigned peaks is shown in later in the running text and the calculated mass content compared to theoretical mass content of each element under consideration can be taken from Table 7.

3. Results

3.1. Structure Description of A-Type La2OF2Se

The A-type and the B-type form of La2OF2Se show markedly different crystal structures. A-type La2OF2Se crystallized in the trigonal space group R 3 ¯ m with a = 418.13(3) and c = 4478.2(4) pm (c/a = 10.710) for Z = 6. Its crystal structure (Figure 1) revealed a close relationship to the oxygen-free La2F4Se (trigonal, R 3 ¯ m; a = 417.86(2) pm, c = 2326.78(9) pm, Z = 3) [33,57] on the one hand and the fluoride-free La2O2Se (trigonal, P 3 ¯ m1; a = 408.27(3) pm, c = 717.19(5) pm, Z = 1) [44,58] on the other. As a consequence two crystallographically different positions for La3+ cations exist. The first one (La1) is surrounded by four O2− and three Se2− and anions to build an oxide-capped trigonal antiprism with Se2− on the bottom and O2− on the top (Figure 2a), without participation of any F− anion. The distance to the capping oxide anion is with 249 pm a little larger than those to the oxygen atoms within the triangular face of the [(La1)O4Se3]11− polyhedron (d(La3+–O2−) = 247 pm, 3×). The second La3+ cation (La2) is coordinated by seven F− and three Se2− anions, which erect a quadruple-capped trigonal prism [(La2)(F1)3(F2)4Se3]10− with Se2− at the bottom, (F2)− as the top cap, (F2)− in the triangular top face and (F1)− capping the three side faces (Figure 2b). The distances from (La2)3+ to the capping F− anions range between 242 pm (3× to F1) and 245 pm (1× to F2), while the (La2)3+–(F2)− distance to the top triangular face is 266 pm (3×). The O2− anion is surrounded by a tetrahedron of four (La1)3+ cations (Figure 2c) at distances of 247 pm (3×) and 249 pm (1×), whereas the Se2− anions has contact to six La3+ cations arranged as triangular antiprism with 3× La1 at 317 pm and 3× La2 at 321 pm distance (Figure 2f). The coordination sphere of (F1)− appeared triangularly planar by three La3+ cations (d(F1)−–(La2)3+ = 242 pm), while as (F2)− centers a tetrahedron (Figure 2d,e) of four La3+ cations (d(F2)−–(La2)3+ = 245 pm (1×), 266 pm (3×)). Selected interatomic distances can be seen in detail in Table 4, while the fractional atomic coordinates and the Ueq values are summarized in Table 2.

3.2. Structure Description of B-Type La2OF2Se

B-type La2OF2Se crystallizes isotypically to the structure of the RE2OF2Se series with RE = Nd, Sm, Gd–Ho and similar with the compounds of the RE6O2F8Se3 series with RE = La–Nd [48], both adapting the hexagonal space group P63/m with a = 1396.82(9) and c = 401.08(3) pm (c/a = 0.287) for Z = 6 in the case of B-type La2OF2Se. Thus the a- and c-axes of B-La2OF2Se are larger than for La6O2F8Se3 with a = 1394.41(9) and c = 403.97(2) pm (c/a = 0.289) for Z = 2, but show a smaller c/a-ratio. Four unit cells of B-type La2OF2Se in comparison to La6O2F8Se3 are shown in Figure 3. There are two crystallographically different La3+ cations present in both structures. The first one (La1 in B-La2OF2Se) is surrounded by a square antiprism consisting of four Se2− anions in the bottom square, but one (F2)− and three O2− anions creating the top (Figure 4a). The distances from La1 to the oxide and fluoride anions range between 243 and 251 pm, whereas to the selenide anions four times 318 pm are found. The second one (La2) has a coordination number of nine residing in a tricapped trigonal prism erected by two Se2−, one O2− and six F− anions (Figure 4b) with distances of 244.5 pm to the oxide anion, between 246 and 261 pm to the fluoride anions and again two times 318 pm to the selenide anions. While the (F1)− anion in A-type La2OF2Se centers the triangular plane of three La3+ cations, in B-type La2OF2Se the analogous (F1)− particle is located outside of this triangle with a deflection of about 94 pm (Figure 4d) in a distance of 246.6 pm (2×) and 260.9 pm to the (La2)3+ anions. The (F2)− and the O2− anions are in both structures of La2OF2Se surrounded by (La3+)4 tetrahedra (Figure 4c,e) with distances of about 244 pm in the oxygen and 250 pm in the fluorine case. While the Se2− anions in A-type La2OF2Se are surrounded octahedrally, they center trigonal prisms of six La3+ cations in B-type La2OF2Se (Figure 4f) with six distances of about 318 pm. These [SeLa6]16+ prisms share vertical edges to form a triple and trans-oriented triangular faces to build a chain along the c-axis (Figure 5). The inner channels of these chains remain empty, in B-type La2OF2Se, but host F−-anions in La6O2F8Se3 [48] to increase the coordination number of (La1)3+ from eight to nine. Along with this the position of O2− has to be substituted partly with F− anions to secure the charge balance of La6O2F8Se3 [48]. There is also a not filled tube along the c-axis in B-type La2OF2Se and La6O2F8Se3, which can be partly filled with Na+ cations like in NaCe18O9F19Se9 [59].

3.3. Single-Crystal Data of A- and B-Type La2OF2Se

In Table 1 the crystallographic data of A- and B-type La2OF2Se as well as their determination can be seen. Table 2 and Table 3 show fractional atomic coordinates and Ueq values of both structures and Table 4 and Table 5 some selected interatomic distances and angles in the crystal structures. The motifs of mutual adjunction in are summarized in Table 6.

3.4. Energy-Dispersive X-Ray Spectrum of B-Type La2OF2Se

Table 7 summarizes the results of an EDXS measurement on a single crystal of B-type La2OF2Se, which is shown in Figure 6. The content of oxygen was calculated in such a way that there was no change left in the stoichiometric composition La2OF2Se. For this reason no error margins can be given.
It can be seen from Table 7, that the measured and the theoretical element content almost coincide. The measured carbon as shown in Figure 6 also was not considered in the calculation, since it originated from the sample preparation.

4. Discussion

Both crystal structures of La2OF2Se show striking resemblance to either La2O2Se and La2F4Se in the trigonal A-type or La6O2F8Se3 in the hexagonal B-type case. A-La2OF2Se displays the coordination polyhedra with the lowest ([LaO4Se3]11−, C.N. = 7) and the highest coordination numbers ([LaF7Se3]10−, C.N. = 10) for both, while for B-La2OF2Se they range in the middle ([LaO3FSe4]12−, C.N. = 8; [LaOF6Se2]9−, C.N. = 9), but carry the more diverse charges. With A-La2OF2Se (a = 418.13(3), c = 4478.2(4) pm) being a perfect intergrowth adduct of La2O2Se (a = 408.27(3), c = 717.19(5) pm) [58] and La2F4Se (a = 417.86(2), c = 2326.78(9) pm) [57] the occurrence of the same polyhedra does not surprise, but the La2O2Se compartment of A-La2OF2Se appears a little more dilated (d(La3+–O2−) = 3 × 246.9 and 1 × 248.9 pm, d(La3+–Se2−) = 3 × 317.1 pm) as compared to the original ternary (d(La3+–O2−) = 1 × 241.9 and 3 × 243.9 pm, d(La3+–Se2−) = 3 × 313.3 pm) [58], whereas the La2F4Se part (d(La3+–F−) = 3 × 242.1, 1 × 245.2 plus 3 × 266.5 pm, d(La3+–Se2−) = 3 × 320.9 pm) outstandingly agrees with La2F4Se (d(La3+–F−) = 3 × 241.9, 1 × 242.9 plus 3 × 266.5 pm, d(La3+–Se2−) = 3 × 319.7 pm) [57] itself. Hence the Madelung part of the lattice energy (MAPLE) [61,62,63] shows a slightly better agreement between the value for A-La2OF2Se (12141 kJ/mol) and the sum of the ternaries (La2O2Se: 13477 kJ/mol, La2F4Se: 11045 kJ/mol) according to 1 2 × MAPLE(La2O2Se) + 1 2 × MAPLE(La2F4Se) = 6739 + 5523 = 12262 kJ/mol in comparison with B-La2OF2Se (12111 kJ/mol). The latter, B-La2OF2Se (a = 1396.82(9), c = 401.08(3) pm), has a lot more in common with La6O2F8Se3 (a = 1394.41(9), c = 402.96(3) pm) [48], as the similar interatomic distances (d(La3+–O2−) = 243–245 pm, d(La3+–F−) = 247–253 plus 261 pm, d(La3+–Se2−) = 318–319 pm versus d(La3+–O2−) = 244–252 pm, d(La3+–F−) = 245–256 pm, d(La3+–Se2−) = 316–318 pm) prove, in spite of some mixed occupation of O2− and F− anions in tetrahedral surrounding of La3+ cations in hexagonal La6O2F8Se3. The slightly higher density of 6.039 g/cm3 for B-La2OF2Se versus 6.036 g/cm3 A-La2OF2Se should predestine the B-type structure of La2OF2Se to be the high-pressure form or the A-type structure to represent the high-temperature modification of La2OF2Se, which needs to become verified as soon as we shall have phase-pure samples in hands.

Supplementary Materials

The CIF of the title compounds are available online at https://www.mdpi.com/2073-4352/9/9/435/s1, or in the ICSD with the number 1919109 for A-type or 1919110 for B-type.

Author Contributions

H.G. synthesized the A-type form of La2OF2Se and C.B. the B-type. H.G. and T.S. solved the crystal structure of A-La2OF2Se and C.B. and T.S. of the B-type. T.S. contributed the reagents, the materials, the scientific equipment and the infrastructure. C.B. wrote the paper and T.S. reviewed it.

Funding

This research was funded by the State of Baden–Württemberg (Stuttgart) and the Deutsche Forschungsgemeinschaft (DFG, Bonn).

Acknowledgments

We thank Falk Lissner for the single-crystal X-ray diffraction measurements and Felix C. Goerigk for the electron-beam microprobe experiment.

Conflicts of Interest

The authors declare no conflict of interest.

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Crystals 09 00435 g001 550
Figure 1. Comparison of the crystal structures of A-type La2OF2Se (mid) with La2O2Se (left) and La2F4Se (right).
Figure 1. Comparison of the crystal structures of A-type La2OF2Se (mid) with La2O2Se (left) and La2F4Se (right).
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Crystals 09 00435 g002 550
Figure 2. Coordination polyhedra in A-type La2OF2Se.
Figure 2. Coordination polyhedra in A-type La2OF2Se.
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Crystals 09 00435 g003 550
Figure 3. Comparison of the crystal structures of B-type La2OF2Se (top) and La6O2F8Se3 (bottom) as viewed along their c-axes.
Figure 3. Comparison of the crystal structures of B-type La2OF2Se (top) and La6O2F8Se3 (bottom) as viewed along their c-axes.
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Crystals 09 00435 g004 550
Figure 4. Coordination polyhedra in B-type La2OF2Se.
Figure 4. Coordination polyhedra in B-type La2OF2Se.
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Crystals 09 00435 g005 550
Figure 5. Connected trigonal prisms of La3+ cations surrounding the Se2− anions in B-La2OF2Se, which build a triple chain along the c-axis.
Figure 5. Connected trigonal prisms of La3+ cations surrounding the Se2− anions in B-La2OF2Se, which build a triple chain along the c-axis.
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Crystals 09 00435 g006 550
Figure 6. The energy-dispersive X-Ray spectrum (EDXS) of a single crystal of B-type La2OF2Se.
Figure 6. The energy-dispersive X-Ray spectrum (EDXS) of a single crystal of B-type La2OF2Se.
Crystals 09 00435 g006
Table
Table 1. Crystallographic data of A- and B-type La2OF2Se and their determination.
Table 1. Crystallographic data of A- and B-type La2OF2Se and their determination.
CompoundA-La2OF2SeB-La2OF2Se
crystal systemtrigonalhexagonal
space groupR 3 ¯ m (no. 166) P63/m (no. 172)
lattice parameters,
a/pm418.13(3)1396.82(9)
c/pm4478.2(4)401.08(3)
c/a10.7100.287
number of formula units (Z)66
unit-cell volume (Vuc in nm3)0.67804(9)0.67771(8)
molar volume (Vm in cm3/mol)68.05368.020
calculated density (Dx in g/cm3)6.0366.039
diffractometerIPDS (Stoe and Cie)κ-CCD (Bruker-Nonius)
wavelength (λ in pm)Mo-Kα (λ = 71.07 pm)Mo-Kα (λ = 71.07 pm)
index range (±hmax, ±kmax, ±lmax)6/6/6719/19/5
number of e− per unit cell (F(000))10441044
absorption coefficient (μ in mm−1)26.5926.60
number of collected vs. unique reflections3237/38313042/749
data-set residuals (Rint/Rσ)0.070/0.0270.097/0.052
structure residuals (R1/wR2)0.026/0.0880.052/0.120
goodness of fit (GooF)1.0721.028
residual electron density (max./min. in e− 10−6 pm−3)3.12/−2.673.57/−1.98
CSD number19191091919110
Table
Table 2. Fractional atomic coordinates and Ueq valuesa for A-La2OF2Se.
Table 2. Fractional atomic coordinates and Ueq valuesa for A-La2OF2Se.
AtomSitex/ay/bz/cUeq/pm2
La16c000.133109(14)206(3)
La26c000.293363(14)111(2)
O6c000.18868(19)248(18)
F16c000.03591(17)178(14)
F26c000.34832(17)171(13)
Se6c000.42052(2)138(3)
aUeq = 1 3 [U33 + 4 3 (U11 + U22 − U12)] [60].
Table
Table 3. Fractional atomic coordinates and Ueq valuesa for B-La2OF2Se.
Table 3. Fractional atomic coordinates and Ueq valuesa for B-La2OF2Se.
AtomSitex/ay/bz/cUeq/pm2
La16h0.12574(8)0.51625(8) 1 4 231(3)
La26h0.23351(8)0.28450(8) 1 4 239(3)
O6h0.4323(7)0.4156(8) 1 4 114(19)
F16h0.1895(9)0.0901(9) 1 4 335(24)
F26h0.0696(8)0.3151(8) 1 4 263(21)
Se6h0.48066(14)0.19870(14) 1 4 232(4)
aUeq = 1 3 [U33 + 4 3 (U11 + U22 − U12)] [60].
Table
Table 4. Selected interatomic distances (d/pm) and angles (∢/°) in the crystal structure of A-type La2OF2Se.
Table 4. Selected interatomic distances (d/pm) and angles (∢/°) in the crystal structure of A-type La2OF2Se.
Distance (d/pm)Angle (∢/°)
La1–O(3×)246.9La1–O–La1(3×)102.1
La1–O’(1×)248.9La1–O–La1′(3×)115.8
La1–Se(3×)317.1La2–F1–La2(3×)119.4
La2–F1(3×)242.1La2–F2–La2(3×)103.4
La2–F2(1×)245.2La2–F2–La2′(3×)115.1
La2–F2′(3×)266.5La1–Se–La1(3×)82.5
La2–Se(3×)320.9La1–Se–La2(6×)98.1
O–La1 (3×)246.9La1–Se–La2′(3×)179.2
O–La1′(1×)248.9La2–Se–La2(3×)81.3
F1–La2 (3×)242.1
F2–La2(1×)245.2
F2–La2′(3×)266.5
Se–La1(3×)317.1
Se–La2(3×)320.9
Table
Table 5. Selected interatomic distances (d/pm) and angles (∢/°) in the crystal structure of B-type La2OF2Se.
Table 5. Selected interatomic distances (d/pm) and angles (∢/°) in the crystal structure of B-type La2OF2Se.
Distance (d/pm) Angle (∢/°)
La1–O(1×)243.0La1–O–La1(2×)105.4
La1–O’(2×)243.5La1–O–La1′(1×)110.9
La1–F2(1×)251.1La1–O–La2(2×)109.8
La1–Se(2×)318.0La1′–O–La2(1×)115.3
La1–Se’(2×)318.3La2–F1–La2′(2×)100.4
La2–O(1×)244.5La2–F1–La2(1×)110.9
La2–F1(1×)246.6La1–F2–La2(2×)105.9
La2–F1′(2×)260.9La1–F2–La2′(1×)112.7
La2–F2(2×)249.8La2–F2–La2(1×)106.8
La2–F2′(1×)253.5La2–F2–La2′(2×)112.5
La2–Se(2×)318.3La1–Se–La1(2×)78.1
O–La1(1×)243.0La1–Se–La1′(2×)89.8
O–La1′(2×)243.5La1–Se–La2(2×)82.5
O–La2(1×)244.4La1′–Se–La2(2×)80.6
F1–La2(1×)246.6La2–Se–La2(2×)78.1
F1–La2′(2×)260.9
F2–La1(1×)251.1
F2–La2(2×)249.8
F2–La2′(1×)253.5
Se–La1(2×)318.0
Se–La1′(2×)318.3
Table
Table 6. Motifs of mutual adjunction in A- and B-type La2OF2Se.
Table 6. Motifs of mutual adjunction in A- and B-type La2OF2Se.
A-La2OF2Se:
F1F2OSeC.N.
La1 0 0 0 0 4 4 3 3 7
La2 3 3 4 4 0 0 3 3 10
C.N. 3 4 4 6
B-La2OF2Se:
F1F2OSeC.N.
La1 1 1 3 3 4 4 8
La2 3 3 1 1 2 2 9
C.N. 3 4 4 6
Table
Table 7. Results of an energy-dispersive X-ray spectrometer (EDXS) measurement on a single crystal of B-type La2OF2Se.
Table 7. Results of an energy-dispersive X-ray spectrometer (EDXS) measurement on a single crystal of B-type La2OF2Se.
ElementMeasured Content [wt-%]Theoretical Content [wt-%]
La68.4(5)67.63
O4.153.90
F9.66(14)9.25
Se17.79(16)19.22

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Buyer, C.; Grossholz, H.; Schleid, T. The Structural Dimorphism of Lanthanum Oxide Fluoride Selenide La2OF2Se. Crystals 2019, 9, 435. https://doi.org/10.3390/cryst9090435

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Buyer C, Grossholz H, Schleid T. The Structural Dimorphism of Lanthanum Oxide Fluoride Selenide La2OF2Se. Crystals. 2019; 9(9):435. https://doi.org/10.3390/cryst9090435

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Buyer, Constantin, Hagen Grossholz, and Thomas Schleid. 2019. "The Structural Dimorphism of Lanthanum Oxide Fluoride Selenide La2OF2Se" Crystals 9, no. 9: 435. https://doi.org/10.3390/cryst9090435

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