Crystal structure of the Fe-member of usovite

Weil, M.

doi:10.1107/S2056989015009251

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ISSN: 2056-9890

Volume 71| Part 6| June 2015| Pages 640-643

doi:10.1107/S2056989015009251

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Crystal structure of the Fe-member of usovite

Matthias Weil ^a ^*

^aInstitute for Chemical Technologies and Analytics, Division of Structural Chemistry, Vienna University of Technology, Getreidemarkt 9/164-SC, A-1060 Vienna, Austria
^*Correspondence e-mail: mweil@mail.zserv.tuwien.ac.at

Edited by I. D. Brown, McMaster University, Canada (Received 28 April 2015; accepted 15 May 2015; online 20 May 2015)

Crystals of the title compound, with the idealized composition Ba₂CaFeAl₂F₁₄, dibarium calcium iron(II) dialuminium tetradecafluoride, were obtained serendipitously by reacting a mixture of the binary fluorides BaF₂, CaF₂ and AlF₃ in a leaky steel reactor. The compound crystallizes in the usovite structure type (Ba₂CaMgAl₂F₁₄), with Fe²⁺ cations replacing the Mg²⁺ cations. The principal building units are distorted [CaF₈] square-antiprisms (point group symmetry 2), [FeF₆] octahedra (point group symmetry -1) and [AlF₆] octahedra that are condensed into undulating ²_∞[CaFeAl₂F₁₄]⁴⁻ layers parallel (100). The Ba²⁺ cations separate the layers and exhibit a coordination number of 12. Two crystal structure models with a different treatment of the disordered Fe site [mixed Fe/Ca occupation, model (I), versus underoccupation of Fe, model (II)], are discussed, leading to different refined formulae Ba₂Ca_1.310 (15)Fe_0.690 (15)Al₂F₁₄ [model (I)] and Ba₂CaFe_0.90 (1)Al₂F₁₄ [model (II)].

Keywords: crystal structure; usovite; Fe-containing usovite; disorder; fluorides.

CCDC references: 1401194; 1401194; 1401195

1. Chemical context

Fluoridoaluminates with alkaline earth cations exhibit a rich crystal chemistry (Babel & Tressaud, 1985 ; Weil et al., 2001 ). They are suitable host materials for optical applications as has been shown by luminescence exitation studies of SrAlF₅ or CaAlF₅ doped with Pr³⁺ and Mn²⁺ (van der Kolk et al., 2004 ). In order to prepare large single crystals of a related fluoridoaluminate with composition BaCaAlF₇, a different preparation route was chosen in comparison with the reported crystal-growth procedure. Instead of using a ZnCl₂ melt (Werner & Weil, 2003 ), a carbon tool steel container shielded with a molybdenum foil was used for solid state reactions between a mixture of the binary fluorides (Weil & Kubel, 2002 ). However, during one of these experiments it turned out that the container was not completely lined by the molybdenum foil which consequently led to a reaction with the container wall and an incorporation of iron into parts of the reaction products. Crystal structure analysis of selected crystals from this reaction batch revealed an Fe-containing phase that crystallizes isotypically with the mineral usovite, Ba₂CaMgAl₂F₁₄ (Litvin et al., 1980 ).

Compounds with the usovite-type structure are represented by the general formula Ba₂(M^II1)(M^II2)(M^III3)₂F₁₄ (M^II1 = Ca, Cd, Mn; M^II2 = Mg, Co, Mn, Cu, Cd, Fe; M^III3 = Al, V, Fe, Cr, Ga, Mn) and crystallize with four formula units in the space group C2/c. Most of the usovite-type representatives known so far were prepared and structurally determined by Babel, Tressaud and co-workers over the last three decades (Holler et al., 1984 , 1985 ; Kaiser et al., 2002 ; Le Lirzin et al., 1990 , 1991 , 2008 ; Qiang et al., 1988 ).

2. Structural commentary

The principal building units of the usovite crystal structure are distorted [BaF₁₂] polyhedra, [(M^II1)F₈] sqare-antiprisms (point group symmetry 2) and [(M^II2)F₆] octahedra (point group symmetry $[\overline{1}]$ ), as well as rather regular [(M^III3)F₆] octahedra. The [(M^II2)F₆] and [(M^III3)F₆] octahedra are connected by corner-sharing into infinite crosslinked double chains ¹_∞[(M^II2)F₂F_4/2(M^III3)₂F₈F_4/2] extending parallel to [010] (Fig. 1). Neighbouring chains are linked by the [(M^II1)F₈] square-antiprisms into undulating (100) layers with composition ²_∞[(M^II1)(M^II2)(M^III3)₂F₁₄)]⁴⁻, with the Ba²⁺ cations separating the individual layers (Fig. 2).

Figure 1
[AlF₆] octahedra (yellow, with F atoms green) and [FeF₆] octahedra (orange) are linked into crosslinked double chains parallel to [010]. Displacement ellipsoids are drawn at the 74% probability level.

Figure 2
The crystal structure of the usovite-type title compound, emphasizing the formation of the layered ²_∞[CaFeAl₂F₁₄]⁴⁻ framework parallel to (100), separated by Ba²⁺ cations. Displacement ellipsoids are drawn at the 74% probability level. The colour code is as in Fig. 1

, with [CaF₈] polyhedra in blue and Ba atoms in red.

The unit-cell volume of the title compound [1067.9 (2) Å³] is slightly larger than that of usovite Ba₂CaMgAl₂F₁₄ (1027.9 Å; Litvin et al., 1980) due to the replacement of the Mg²⁺ cations (ionic radius = 0.72 Å; Shannon, 1976 ) by the larger Fe²⁺ cations (ionic radius = 0.78 Å; Shannon, 1976) at the M^II2 site. This is also reflected by the bond lengths within the individual coordination polyhedra (Table 1). Wheras the Ba—F, Ca—F and Al—F distances remain nearly unaltered between the two structures, the Mg—F and Fe—F distances show remarkable differences. The Mg—F distances in the usovite structure range from 1.939 to 2.041 Å, the corresponding Fe—F distances in the title structure from 2.015 (2) to 2.216 (2) Å, with a mean distance of 2.123 Å. The latter is in reasonable agreement with the mean Fe^II—F distance of 2.106 Å in the isotypic crystal structure of Ba₂CaFeV₂F₁₄ (Kaiser et al., 2002). However, the mean bond lengths in both the title structure and Ba₂CaFeV₂F₁₄ are considerably longer than that of 2.074 Å in the structure of the binary compound FeF₂ (Jauch et al., 1993 ).

Table 1
Selected bond lengths (Å) for model (I)

For model (II), bond lengths are the same within their standard uncertainties.

Ba—F7	2.696 (2)	Ca2—F4	2.376 (2)
Ba—F4ⁱ	2.730 (2)	Ca2—F4^ix	2.376 (2)
Ba—F1ⁱ	2.755 (2)	Ca2—F5^x	2.544 (2)
Ba—F2ⁱⁱ	2.765 (2)	Ca2—F5^iv	2.544 (2)
Ba—F5ⁱⁱⁱ	2.766 (2)	Fe1—F7^x	2.015 (2)
Ba—F5^iv	2.827 (2)	Fe1—F7ⁱ	2.015 (2)
Ba—F3^iv	2.889 (2)	Fe1—F2^xi	2.131 (2)
Ba—F1^v	2.889 (2)	Fe1—F2^viii	2.131 (2)
Ba—F3	2.974 (2)	Fe1—F3^x	2.216 (2)
Ba—F6ⁱⁱⁱ	3.101 (2)	Fe1—F3ⁱ	2.216 (2)
Ba—F6^iv	3.158 (2)	Al—F4^xii	1.780 (2)
Ba—F1^vi	3.233 (3)	Al—F1	1.780 (3)
Ca2—F7^vii	2.235 (2)	Al—F6^iv	1.790 (2)
Ca2—F7ⁱ	2.235 (2)	Al—F2^iv	1.799 (2)
Ca2—F6ⁱⁱⁱ	2.369 (2)	Al—F5ⁱⁱⁱ	1.843 (2)
Ca2—F6^viii	2.369 (2)	Al—F3ⁱⁱⁱ	1.846 (2)
Symmetry codes: (i) $[-x+{\script{1\over 2}}, y+{\script{1\over 2}}, -z+{\script{1\over 2}}]$ ; (ii) $[-x+{\script{1\over 2}}, y+{\script{1\over 2}}, -z+{\script{3\over 2}}]$ ; (iii) $[x, -y+1, z-{\script{1\over 2}}]$ ; (iv) $[-x+{\script{1\over 2}}, -y+{\script{1\over 2}}, -z+1]$ ; (v) $[-x+{\script{1\over 2}}, y-{\script{1\over 2}}, -z+{\script{1\over 2}}]$ ; (vi) $[x, -y+1, z+{\script{1\over 2}}]$ ; (vii) $[x-{\script{1\over 2}}, y+{\script{1\over 2}}, z]$ ; (viii) -x, -y+1, -z+1; (ix) $[-x, y, -z+{\script{1\over 2}}]$ ; (x) $[x-{\script{1\over 2}}, -y+{\script{1\over 2}}, z-{\script{1\over 2}}]$ ; (xi) x, y, z-1; (xii) $[x+{\script{1\over 2}}, y+{\script{1\over 2}}, z]$ .

A similar increase of the M—F bond lengths of the [(M^II2)F₆] octahedra was also observed for a series of other usovite-type structures and was associated with an occupational disorder of the M^II2 site. For these models, either a mutual substitution of Ca²⁺ (on the M^II1 site) with corresponding divalent transition metal ions on the M^II2 site, or partial replacement of the divalent transition metal ions by Ca²⁺ at the M^II2 site was considered, resulting in stoichiometric compounds and Ca-richer compounds, respectively (Kaiser et al., 2002). In the case of the title compound, a model with mutual substitution of Ca²⁺ and Fe²⁺ on the M^II1 and M^II2 sites could be ruled out during refinement. However, a model with an incorporation of Ca²⁺ on the Fe²⁺ site resulted in a ratio of Ca:Fe = 0.155 (7):0.345 (7) for this site [model (I); overall refined formula for the compound: Ba₂Ca_1.310 (15)Fe_0.690 (15)Al₂F₁₄] and converged with the same reliability factors and remaining electron densities as the model without an incorporation of Ca²⁺ and underoccupation of the Fe²⁺ site only [model (II); Table 3]. The refined formula for this model is Ba₂Ca₂Fe_0.90 (1)Al₂F₁₄. Bond lengths and angles of the two models are the same within the corresponding standard uncertainties (Table 1).

Kaiser et al. (2002) have discussed in detail the pros and cons of the incorporation of Ca²⁺ (ionic radius = 1.0 Å; Shannon, 1976) at the M^II2 site for various usovite-type structures. Strong arguments supporting an M^II2 site with mixed Fe/Ca occupation are the resulting bond-valence sums (Brown, 2002 ) that deviate significantly from the expected values of 2 if only Fe²⁺ ions are considered to be present at the M^II2 site (Table 2). Contrariwise, the bond-valence sums are in excellent agreement with the expected value if a mixed Fe/Ca occupancy is taken into account. The corresponding numbers are listed in Table 2 and were calculated with the weighted average occupancy ratio of Fe:Ca = 0.77:0.23 that was estimated by the program VaList (Wills, 2010 ). This ratio is in good agreement with the occupancy ratio from the refinement [model (I): Fe:Ca = 0.69:0.31]. The resulting global instability index (Brown, 2002) of 0.04 valence units for model (I) suggests a very tightly bonded structure with little strain. Any strain inherent in the usovite structure is obviously relieved by the substitution of Ca²⁺ on the M^II2 site.

Table 2
Bond-valence sum calculations for model (I) in valence units

Atom	Assumed valence state	Bond-valence sum	Deviation from assumed valence state in valence units	Bond-valence sum under consideration of mixed Fe1:Ca1 occupancy*
Ba	2	1.94	0.06	1.94
Fe1	2	1.73	0.27	2.00
Ca2	2	1.95	0.05	1.95
Al	3	2.97	0.03	2.97
F1	1	0.96	0.04	0.96
F2	1	0.99	0.01	1.03
F3	1	0.93	0.07	0.96
F4	1	1.00	0	1.00
F5	1	0.99	0.01	0.99
F6	1	0.92	0.08	0.92
F7	1	0.97	0.03	1.03
Note: (*) calculated with the weighted average Fe:Ca ratio of 0.77:0.23 at the M2 site.

On the other hand, an M^II2 site without an incorporation of Ca²⁺ would result in an underoccupation of Fe²⁺ [model (II)] and consequently requires the presence of an element in a higher oxidation state (here most probably Fe³⁺) to compensate the negative charge of −2 of the [Ba₂CaAl₂F₁₄] framework. Although in this case rather a decrease of M^II2—F bond lengths should be expected (contrary to the findings of the current study), it cannot competely ruled out that Fe³⁺ ions are present at this site. As a matter of fact, based on diffraction data alone, there is a clear tendency towards model (I) but no definite answer whether Fe is partly replaced by Ca on the M^II2 site [model (I)] or is statistically occupied by Fe²⁺ and small amounts of Fe³⁺ [model (II)]. Complementary analytical techniques like Mössbauer spectroscopy will be needed in future to shed some light on this problem.

3. Synthesis and crystallization

The binary fluorides AlF₃ (Merck, Patinal), CaF₂ (Merck, Suprapur) and BaF₂ (Riedel de Haen, pure) were mixed in the stoichiometric ratio 1:1:1 and thoroughly ground in a ball mill, pressed into tablets and placed in a carbon tool steel container shielded with a molybdenum foil. NH₄F·HF (100 mg, Fluka, p·A.) were added to the mixture to increase the HF pressure, to expel the remaining oxygen and to adjust a slightly reducing atmosphere during the reaction. The reactor was then closed and heated to 1173 K in the course of 20 h, kept at that temperature for 24 h, and then cooled slowly to 973 K at a rate of 10 K h⁻¹, kept at this temperature for 24 h and finally cooled to room temperature overnight. After opening the reactor it became evident that parts of the molybdenum foil were torn apart accompanied by a severe attack of the inner container wall. Single crystals of the title compound were separated from the obtained colourless to light-green bulk material. X-ray powder diffraction of the bulk revealed the formation of α-BaCaAlF₇ as the main phase and the title compound as a minority phase. Some additional reflections were also present that could not be assigned to any known phases.

4. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 3. Coordinates of usovite (Litvin et al., 1980) were used as starting parameters for refinement. The model converged rather smoothly with R1 = 0.034 and wR2 = 0.089. However, negative residual electron density at the Fe atom pointed to an underoccupation and/or a statistical disorder of the M^II2 site with a lighter element present. In fact, free refinement of the site occupation factor for this site resulted in only 90% occupancy and significant better reliability factors (see Table 3). The same procedure applied for all other atoms resulted in full occupancy within the twofold standard uncertainty. For the final models, full occupancy was therefore considered for all atoms except Fe. Model (I) accounts for an incorporation of Ca²⁺ at the Fe site under consideration of full occupancy; in model (II), the site occupation factor of the Fe site was refined freely without contribution of Ca²⁺ at this site. The remaining electron densities (Table 3) are virtually the same for both models. They are associated with truncation effects close to the heavy Ba sites, with the maximum electron density 0.68 Å and the minimum electron density 0.96 Å away from the Ba atom.

Table 3
Experimental details

	Model (I)	Model (II)
Crystal data
Chemical formula	Ba₂Ca_1.31Fe_0.69Al₂F₁₄	Ba₂CaFe_0.90Al₂F₁₄
M_r	685.68	684.98
Crystal system, space group	Monoclinic, C2/c	Monoclinic, C2/c
Temperature (K)	293	293
a, b, c (Å)	13.7387 (12), 5.2701 (5), 14.759 (3)	13.7387 (12), 5.2701 (5), 14.759 (3)
β (°)	92.074 (14)	92.074 (14)
V (Å³)	1067.9 (2)	1067.9 (2)
Z	4	4
Radiation type	Mo Kα	Mo Kα
μ (mm⁻¹)	9.21	9.33
Crystal size (mm)	0.43 × 0.11 × 0.07	0.43 × 0.11 × 0.07

Data collection
Diffractometer	Nonius CAD-4 four-circle diffractometer	Nonius CAD-4 four-circle diffractometer
Absorption correction	ψ scan (North et al., 1968 )	ψ scan (North et al., 1968)
T_min, T_max	0.329, 0.901	0.329, 0.901
No. of measured, independent and observed [I > 2σ(I)] reflections	5922, 1564, 1490	5922, 1564, 1490
R_int	0.055	0.055
(sin θ/λ)_max (Å⁻¹)	0.703	0.703

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.032, 0.078, 1.09	0.032, 0.078, 1.10
No. of reflections	1564	1564
No. of parameters	95	96
Δρ_max, Δρ_min (e Å⁻³)	2.31, −2.03	2.32, −2.03
Computer programs: CAD-4 Software (Enraf–Nonius, 1989 ), HELENA implemented in PLATON (Spek, 2009 ), SHELXS97 and SHELXL97 (Sheldrick, 2008 ), ATOMS for Windows (Dowty, 2006 ) and publCIF (Westrip, 2010 ).

Supporting information

CCDC references: 1401194; 1401194; 1401195

Crystal structure: contains datablocks modelI, modelII, global. DOI: 10.1107/S2056989015009251/br2250sup1.cif

Structure factors: contains datablock modelI. DOI: 10.1107/S2056989015009251/br2250modelIsup2.hkl

Structure factors: contains datablock modelII. DOI: 10.1107/S2056989015009251/br2250modelIIsup3.hkl

checkCIF report

Chemical context top

Fluoridoaluminates with alkaline earth cations exhibit a rich crystal chemistry (Babel & Tressaud, 1985; Weil et al., 2001). They are suitable host materials for optical applications as has been shown by luminescence exitation studies of SrAlF₅ or CaAlF₅ doped with Pr³⁺ and Mn²⁺ (van der Kolk et al., 2004). In order to prepare large single crystals of a related fluoridoaluminate with composition BaCaAlF₇, a different preparation route was chosen in comparison with the reported crystal-growth procedure. Instead of using a ZnCl₂ melt (Werner & Weil, 2003), a carbon tool steel container shielded with a molybdenum foil was used for solid state reactions between a mixture of the binary fluorides (Weil & Kubel, 2002). However, during one of these experiments it turned out that the container was not completely lined by the molybdenum foil which consequently led to a reaction with the container wall and an incorporation of iron into parts of the reaction products. Crystal structure analysis of selected crystals from this reaction batch revealed an Fe-containing phase that crystallizes isotypically with the mineral usovite, Ba₂CaMgAl₂F₁₄ (Litvin et al., 1980).

Compounds with the usovite-type structure are represented by the general formula Ba₂(M^II1)(M^II2)(M^III3)₂F₁₄ (M^II1 = Ca, Cd, Mn; M^II2 = Mg, Co, Mn, Cu, Cd, Fe; M^III3 = Al, V, Fe, Cr, Ga, Mn) and crystallize with four formula units in the space group C2/c. Most of the usovite-type representatives known so far were prepared and structurally determined by Babel, Tressaud and co-workers over the last three decades (Holler et al., 1984, 1985; Kaiser et al., 2002; Le Lirzin et al., 1990, 1991, 2008; Qiang et al., 1988).

Structural commentary top

The principal building units of the usovite crystal structure are distorted [BaF₁₂] polyhedra, [(M^II1)F₈] sqare-antiprisms (point group symmetry 2) and [(M^II2)F₆] octahedra (point group symmetry 1), as well as rather regular [(M^III3)F₆] octahedra. The [(M^II2)F₆] and [(M^III3)F₆] octahedra are connected by corner-sharing into infinite crosslinked double chains ¹_∞[(M^II2)F₂F_4/2(M^III3)₂F₈F_4/2] extending parallel to [010] (Fig. 1). Neighbouring chains are linked by the [(M^II1)F₈] square-antiprisms into undulating (100) layers with composition ²_∞[(M^II1)(M^II2)(M^III3)₂F₁₄)]^4-, with the Ba²⁺ cations separating the individual layers (Fig. 2).

The unit-cell volume of the title compound [1067.9 (2) Å³] is slightly larger than that of usovite Ba₂CaMgAl₂F₁₄ (1027.9 Å; Litvin et al., 1980) due to the replacement of the Mg²⁺ cations (ionic radius = 0.72 Å; Shannon, 1976) by the larger Fe²⁺ cations (ionic radius = 0.78 Å; Shannon, 1976) at the M^II2 site. This is also reflected by the bond lengths within the individual coordination polyhedra (Table 1). Wheras the Ba—F, Ca—F and Al—F distances remain nearly unaltered between the two structures, the Mg—F and Fe—F distances show remarkable differences. The Mg—F distances in the usovite structure range from 1.939 to 2.041 Å, the corresponding Fe—F distances in the title structure from 2.015 (2) to 2.216 (2) Å, with a mean distance of 2.123 Å. The latter is in reasonable agreement with the mean Fe^II—F distance of 2.106 Å in the isotypic crystal structure of Ba₂CaFeV₂F₁₄ (Kaiser et al., 2002). However, the mean bond lengths in both the title structure and Ba₂CaFeV₂F₁₄ are considerably longer than that of 2.074 Å in the structure of the binary compound FeF₂ (Jauch et al., 1993).

A similar increase of the M—F bond lengths of the [(M^II2)F₆] octahedra was also observed for a series of other usovite-type structures and was associated with an occupational disorder of the M^II2 site. For these models, either a mutual substitution of Ca²⁺ (on the M^II1 site) with corresponding divalent transition metal ions on the M^II2 site, or partial replacement of the divalent transition metal ions by Ca²⁺ at the M^II2 site was considered, resulting in stoichiometric compounds and Ca-richer compounds, respectively (Kaiser et al., 2002). In the case of the title compound, a model with mutual substitution of Ca²⁺ and Fe²⁺ on the M^II1 and M^II2 sites could be ruled out during refinement. However, a model with an incorporation of Ca²⁺ on the Fe²⁺ site resulted in a ratio of Ca:Fe = 0.155 (7):0.345 (7) for this site [model (I); overall refined formula for the compound: Ba₂Ca_1.310 (15)Fe_0.690 (15)Al₂F₁₄] and converged with the same reliability factors and remaining electron densities as the model without an incorporation of Ca²⁺ and underoccupation of the Fe²⁺ site only [model (II); Table 1]. The refined formula for this model is Ba₂Ca₂Fe_0.90 (1)Al₂F₁₄. Bond lengths and angles of the two models are the same within the corresponding standard uncertainty (Table 1).

Kaiser et al. (2002) have discussed in detail the pros and cons of the incorporation of Ca²⁺ (ionic radius = 1.0 Å; Shannon, 1976) at the M^II2 site for various usovite-type structures. Strong arguments supporting an M^II2 site with mixed Fe/Ca occupation are the resulting bond-valence sums (Brown, 2002) that deviate significantly from the expected values of 2 if only Fe²⁺ ions are considered to be present at the M^II2 site (Table 2). Contrariwise, the bond-valence sums are in excellent agreement with the expected value if a mixed Fe/Ca occupancy is taken into account. The corresponding numbers are listed in Table 2 and were calculated with the weighted average occupancy ratio of Fe:Ca = 0.77:0.23 that was estimated by the program VaList (Wills, 2010). This ratio is in good agreement with the occupancy ratio from the refinement [model (I): Fe:Ca = 0.69:0.31]. The resulting global instability index (Brown, 2002) of 0.04 valence units for model (I) suggests a very tightly bonded structure with little strain. Any strain inherent in the usovite structure is obviously relieved by the substitution of Ca²⁺ on the M^II2 site.

On the other hand, an M^II2 site without an incorporation of Ca²⁺ would result in an underoccupation of Fe²⁺ [model (II)] and consequently requires the presence of an element in a higher oxidation state (here most probably Fe³⁺) to compensate the negative charge of -2 of the [Ba₂CaAl₂F₁₄] framework. Although in this case rather a decrease of M^II2—F bond lengths should be expected (contrary to the findings of the current study), it cannot competely ruled out that Fe³⁺ ions are present at this site. As a matter of fact, based on diffraction data alone, there is a clear tendency towards model (I) but no definite answer whether Fe is partly replaced by Ca on the M^II2 site [model (I)] or is statistically occupied by Fe²⁺ and small amounts of Fe³⁺ [model (II)]. Complementary analytical techniques like Mössbauer spectroscopy will be needed in future to shed some light on this problem.

Synthesis and crystallization top

The binary fluorides AlF₃ (Merck, Patinal), CaF₂ (Merck, Suprapur) and BaF₂ (Riedel de Haen, pure) were mixed in the stoichiometric ratio 1:1:1 and thoroughly ground in a ball mill, pressed into tablets and placed in a carbon tool steel container shielded with a molybdenum foil. NH₄F·HF (100 mg, Fluka, p.A.) were added to the mixture to increase the HF pressure, to expel the remaining oxygen and to adjust a slightly reducing atmosphere during the reaction. The reactor was then closed and heated to 1173 K in the course of 20 h, kept at that temperature for 24 h, and then cooled slowly to 973 K at a rate of 10 K h^-1, kept at this temperature for 24 h and finally cooled to room temperature overnight. After opening the reactor it became evident that parts of the molybdenum foil were torn apart accompanied by a severe attack of the inner container wall. Single crystals of the title compound were separated from the obtained colourless to light-green bulk material. X-ray powder diffraction of the bulk revealed the formation of α-BaCaAlF₇ as the main phase and the title compound as a minority phase. Some additional reflections were also present that could not be assigned to any known phases.

Refinement top

Crystal data, data collection and structure refinement details are summarized in Table 3. Coordinates of usovite (Litvin et al., 1980) were used as starting parameters for refinement. The model converged rather smoothly with R1 = 0.034 and wR2 = 0.089. However, negative residual electron density at the Fe atom pointed to an underoccupation and/or a statistical disorder of the M^II2 site with a lighter element present. In fact, free refinement of the site occupation factor for this site resulted in only 90% occupancy and significant better reliability factors (see Table 1). The same procedure applied for all other atoms resulted in full occupancy within the twofold standard uncertainty. For the final models, full occupancy was therefore considered for all atoms except Fe. Model (I) accounts for an incorporation of Ca²⁺ at the Fe site under consideration of full occupancy; in model (II), the site occupation factor of the Fe site was refined freely without contribution of Ca²⁺ at this site. The remaining electron densities (Table 1) are virtually the same for both models. They are associated with truncation effects close to the heavy Ba sites, with the maximum electron density 0.68 Å and the minimum electron density 0.96 Å away from the Ba atom.

Computing details top

Data collection: CAD-4 Software (Enraf–Nonius, 1989) for modelI; CAD-4 Software (Enraf-Nonius, 1989) for modelII. Cell refinement: CAD-4 Software (Enraf–Nonius, 1989) for modelI; CAD-4 Software (Enraf-Nonius, 1989) for modelII. For both compounds, data reduction: HELENA implemented in PLATON (Spek, 2009); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008). Molecular graphics: ATOMS for Windows (Dowty, 2006) for modelI; Atoms for Windows (Dowty, 2006) for modelII. For both compounds, software used to prepare material for publication: publCIF (Westrip, 2010).

Figures top

	Fig. 1. [AlF₆] octahedra (yellow, with F atoms green) and [FeF₆] octahedra (orange) are linked into crosslinked double chains parallel to [010]. Displacement ellipsoids are drawn at the 74% probability level.
	Fig. 2. The crystal structure of the usovite-type title compound, emphasizing the formation of the layered ²_∞[CaFeAl₂F₁₄]^4- framework parallel to (100), separated by Ba²⁺ cations. Displacement ellipsoids are drawn at the 74% probability level. The colour code is as in Fig. 1, with [CaF₈] polyhedra in blue and Ba atoms in red.

(modelI) Dibarium calcium iron(II) dialuminium tetradecafluoride top

Crystal data top

Ba₂CaFeAl₂F₁₄	F(000) = 1233
M_r = 685.68	D_x = 4.265 Mg m⁻³
Monoclinic, C2/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -C 2yc	Cell parameters from 25 reflections
a = 13.7387 (12) Å	θ = 16.0–28.7°
b = 5.2701 (5) Å	µ = 9.21 mm⁻¹
c = 14.759 (3) Å	T = 293 K
β = 92.074 (14)°	Lath, colourless
V = 1067.9 (2) Å³	0.43 × 0.11 × 0.07 mm
Z = 4

Data collection top

Nonius CAD-4 four-circle diffractometer	1490 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	R_int = 0.055
Graphite monochromator	θ_max = 30.0°, θ_min = 2.8°
ω/2θ scans	h = −19→19
Absorption correction: ψ scan (North et al., 1968)	k = −7→7
T_min = 0.329, T_max = 0.901	l = −20→20
5922 measured reflections	3 standard reflections every 240 min
1564 independent reflections	intensity decay: none

Refinement top

Refinement on F²	Primary atom site location: isomorphous structure methods
Least-squares matrix: full	w = 1/[σ²(F_o²) + (0.0527P)² + 2.0371P] where P = (F_o² + 2F_c²)/3
R[F² > 2σ(F²)] = 0.032	(Δ/σ)_max < 0.001
wR(F²) = 0.078	Δρ_max = 2.31 e Å⁻³
S = 1.09	Δρ_min = −2.03 e Å⁻³
1564 reflections	Extinction correction: SHELXL97 (Sheldrick, 2008), Fc^*=kFc[1+0.001xFc²λ³/sin(2θ)]^-1/4
95 parameters	Extinction coefficient: 0.0022 (2)
0 restraints

Crystal data top

Ba₂CaFeAl₂F₁₄	V = 1067.9 (2) Å³
M_r = 685.68	Z = 4
Monoclinic, C2/c	Mo Kα radiation
a = 13.7387 (12) Å	µ = 9.21 mm⁻¹
b = 5.2701 (5) Å	T = 293 K
c = 14.759 (3) Å	0.43 × 0.11 × 0.07 mm
β = 92.074 (14)°

Data collection top

Nonius CAD-4 four-circle diffractometer	1490 reflections with I > 2σ(I)
Absorption correction: ψ scan (North et al., 1968)	R_int = 0.055
T_min = 0.329, T_max = 0.901	3 standard reflections every 240 min
5922 measured reflections	intensity decay: none
1564 independent reflections

Refinement top

R[F² > 2σ(F²)] = 0.032	95 parameters
wR(F²) = 0.078	0 restraints
S = 1.09	Δρ_max = 2.31 e Å⁻³
1564 reflections	Δρ_min = −2.03 e Å⁻³

Special details top

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq	Occ. (<1)
Ba	0.308721 (14)	0.46574 (4)	0.379963 (13)	0.01408 (12)
Fe1	0.0000	0.5000	0.0000	0.0122 (2)	0.690 (15)
Ca1	0.0000	0.5000	0.0000	0.0122 (2)	0.310 (15)
Ca2	0.0000	0.44616 (15)	0.2500	0.01239 (19)
Al	0.38007 (8)	0.50390 (18)	0.12342 (7)	0.0111 (2)
F1	0.25596 (18)	0.4521 (4)	0.0896 (2)	0.0240 (5)
F2	0.08574 (15)	0.1721 (4)	0.97491 (13)	0.0184 (4)
F3	0.37359 (16)	0.2100 (4)	0.55132 (14)	0.0197 (4)
F4	0.00268 (16)	0.0837 (4)	0.15434 (15)	0.0190 (4)
F5	0.34180 (14)	0.2933 (4)	0.71743 (13)	0.0157 (4)
F6	0.12186 (16)	0.2677 (4)	0.80391 (15)	0.0207 (4)
F7	0.43370 (17)	0.0715 (4)	0.37866 (16)	0.0208 (4)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Ba	0.01226 (15)	0.01401 (16)	0.01593 (15)	−0.00069 (5)	−0.00023 (9)	0.00074 (5)
Fe1	0.0106 (4)	0.0124 (3)	0.0136 (4)	0.0004 (2)	−0.0005 (3)	−0.0029 (2)
Ca1	0.0106 (4)	0.0124 (3)	0.0136 (4)	0.0004 (2)	−0.0005 (3)	−0.0029 (2)
Ca2	0.0131 (4)	0.0124 (4)	0.0118 (4)	0.000	0.0019 (3)	0.000
Al	0.0114 (5)	0.0096 (3)	0.0123 (5)	−0.0007 (3)	−0.0004 (4)	0.0005 (3)
F1	0.0130 (11)	0.0219 (11)	0.0366 (14)	−0.0017 (8)	−0.0069 (10)	−0.0007 (9)
F2	0.0218 (10)	0.0183 (9)	0.0148 (8)	0.0033 (8)	−0.0016 (7)	−0.0026 (7)
F3	0.0269 (11)	0.0140 (8)	0.0184 (9)	−0.0003 (8)	0.0027 (8)	−0.0032 (7)
F4	0.0100 (9)	0.0247 (9)	0.0224 (10)	−0.0014 (8)	0.0000 (7)	−0.0087 (8)
F5	0.0155 (9)	0.0173 (8)	0.0145 (8)	−0.0037 (7)	0.0027 (6)	0.0004 (7)
F6	0.0220 (10)	0.0161 (8)	0.0243 (10)	0.0037 (8)	0.0035 (8)	0.0076 (8)
F7	0.0183 (11)	0.0239 (10)	0.0206 (10)	0.0009 (9)	0.0052 (8)	−0.0067 (8)

Geometric parameters (Å, º) top

Ba—F7	2.696 (2)	Ca2—F4	2.376 (2)
Ba—F4ⁱ	2.730 (2)	Ca2—F4^ix	2.376 (2)
Ba—F1ⁱ	2.755 (2)	Ca2—F5^x	2.544 (2)
Ba—F2ⁱⁱ	2.765 (2)	Ca2—F5^iv	2.544 (2)
Ba—F5ⁱⁱⁱ	2.766 (2)	Fe1—F7^x	2.015 (2)
Ba—F5^iv	2.827 (2)	Fe1—F7ⁱ	2.015 (2)
Ba—F3^iv	2.889 (2)	Fe1—F2^xi	2.131 (2)
Ba—F1^v	2.889 (2)	Fe1—F2^viii	2.131 (2)
Ba—F3	2.974 (2)	Fe1—F3^x	2.216 (2)
Ba—F6ⁱⁱⁱ	3.101 (2)	Fe1—F3ⁱ	2.216 (2)
Ba—F6^iv	3.158 (2)	Al—F4^xii	1.780 (2)
Ba—F1^vi	3.233 (3)	Al—F1	1.780 (3)
Ca2—F7^vii	2.235 (2)	Al—F6^iv	1.790 (2)
Ca2—F7ⁱ	2.235 (2)	Al—F2^iv	1.799 (2)
Ca2—F6ⁱⁱⁱ	2.369 (2)	Al—F5ⁱⁱⁱ	1.843 (2)
Ca2—F6^viii	2.369 (2)	Al—F3ⁱⁱⁱ	1.846 (2)

F7—Ba—F4ⁱ	64.22 (7)	F6ⁱⁱⁱ—Ca2—F6^viii	100.95 (11)
F7—Ba—F1ⁱ	158.04 (7)	F7^vii—Ca2—F4	139.26 (9)
F4ⁱ—Ba—F1ⁱ	97.60 (7)	F7ⁱ—Ca2—F4	73.58 (8)
F7—Ba—F2ⁱⁱ	89.56 (7)	F6ⁱⁱⁱ—Ca2—F4	133.25 (7)
F4ⁱ—Ba—F2ⁱⁱ	65.13 (7)	F6^viii—Ca2—F4	109.76 (8)
F1ⁱ—Ba—F2ⁱⁱ	70.80 (7)	F7^vii—Ca2—F4^ix	73.58 (8)
F7—Ba—F5ⁱⁱⁱ	102.89 (6)	F7ⁱ—Ca2—F4^ix	139.26 (9)
F4ⁱ—Ba—F5ⁱⁱⁱ	63.11 (6)	F6ⁱⁱⁱ—Ca2—F4^ix	109.76 (8)
F1ⁱ—Ba—F5ⁱⁱⁱ	77.18 (7)	F6^viii—Ca2—F4^ix	133.25 (7)
F2ⁱⁱ—Ba—F5ⁱⁱⁱ	113.14 (6)	F4—Ca2—F4^ix	73.00 (12)
F7—Ba—F5^iv	94.51 (6)	F7^vii—Ca2—F5^x	86.30 (7)
F4ⁱ—Ba—F5^iv	134.23 (6)	F7ⁱ—Ca2—F5^x	110.96 (8)
F1ⁱ—Ba—F5^iv	107.32 (7)	F6ⁱⁱⁱ—Ca2—F5^x	165.39 (7)
F2ⁱⁱ—Ba—F5^iv	159.58 (6)	F6^viii—Ca2—F5^x	70.35 (7)
F5ⁱⁱⁱ—Ba—F5^iv	85.46 (4)	F4—Ca2—F5^x	61.35 (7)
F7—Ba—F3^iv	108.42 (7)	F4^ix—Ca2—F5^x	71.46 (7)
F4ⁱ—Ba—F3^iv	168.26 (6)	F7^vii—Ca2—F5^iv	110.96 (8)
F1ⁱ—Ba—F3^iv	87.26 (7)	F7ⁱ—Ca2—F5^iv	86.30 (7)
F2ⁱⁱ—Ba—F3^iv	106.93 (6)	F6ⁱⁱⁱ—Ca2—F5^iv	70.35 (7)
F5ⁱⁱⁱ—Ba—F3^iv	128.56 (6)	F6^viii—Ca2—F5^iv	165.39 (7)
F5^iv—Ba—F3^iv	52.84 (6)	F4—Ca2—F5^iv	71.46 (7)
F7—Ba—F1^v	58.57 (7)	F4^ix—Ca2—F5^iv	61.35 (7)
F4ⁱ—Ba—F1^v	122.79 (7)	F5^x—Ca2—F5^iv	120.53 (9)
F1ⁱ—Ba—F1^v	138.03 (11)	Fe1^ix—Ca2—Ca1^ix	0.0
F2ⁱⁱ—Ba—F1^v	113.81 (7)	F4^xii—Al—F1	175.02 (12)
F5ⁱⁱⁱ—Ba—F1^v	128.75 (7)	F4^xii—Al—F6^iv	93.99 (12)
F5^iv—Ba—F1^v	53.35 (7)	F1—Al—F6^iv	90.60 (11)
F3^iv—Ba—F1^v	50.92 (7)	F4^xii—Al—F2^iv	93.23 (11)
F7—Ba—F3	59.03 (6)	F1—Al—F2^iv	88.30 (12)
F4ⁱ—Ba—F3	90.21 (6)	F6^iv—Al—F2^iv	94.65 (11)
F1ⁱ—Ba—F3	111.82 (7)	F4^xii—Al—F5ⁱⁱⁱ	87.88 (10)
F2ⁱⁱ—Ba—F3	52.19 (6)	F1—Al—F5ⁱⁱⁱ	90.20 (12)
F5ⁱⁱⁱ—Ba—F3	153.12 (6)	F6^iv—Al—F5ⁱⁱⁱ	90.11 (11)
F5^iv—Ba—F3	113.88 (6)	F2^iv—Al—F5ⁱⁱⁱ	175.02 (11)
F3^iv—Ba—F3	78.06 (7)	F4^xii—Al—F3ⁱⁱⁱ	88.87 (11)
F1^v—Ba—F3	61.81 (7)	F1—Al—F3ⁱⁱⁱ	86.45 (11)
F7—Ba—F6ⁱⁱⁱ	149.96 (6)	F6^iv—Al—F3ⁱⁱⁱ	176.00 (12)
F4ⁱ—Ba—F6ⁱⁱⁱ	127.50 (6)	F2^iv—Al—F3ⁱⁱⁱ	87.98 (11)
F1ⁱ—Ba—F6ⁱⁱⁱ	50.94 (6)	F5ⁱⁱⁱ—Al—F3ⁱⁱⁱ	87.19 (10)
F2ⁱⁱ—Ba—F6ⁱⁱⁱ	120.41 (6)	Al—F1—Ba^v	114.10 (11)
F5ⁱⁱⁱ—Ba—F6ⁱⁱⁱ	68.78 (5)	Al—F1—Baⁱ	96.30 (9)
F5^iv—Ba—F6ⁱⁱⁱ	56.89 (6)	Ba^v—F1—Baⁱ	138.03 (11)
F3^iv—Ba—F6ⁱⁱⁱ	63.59 (6)	Al—F1—Baⁱⁱⁱ	90.11 (11)
F1^v—Ba—F6ⁱⁱⁱ	103.02 (6)	Ba^v—F1—Baⁱⁱⁱ	111.43 (8)
F3—Ba—F6ⁱⁱⁱ	137.04 (6)	Baⁱ—F1—Baⁱⁱⁱ	95.98 (7)
F7—Ba—F6^iv	58.76 (6)	Al^iv—F2—Ca1^xiii	136.08 (11)
F4ⁱ—Ba—F6^iv	67.12 (6)	Al^iv—F2—Fe1^xiii	136.08 (11)
F1ⁱ—Ba—F6^iv	127.71 (7)	Ca1^xiii—F2—Fe1^xiii	0.0
F2ⁱⁱ—Ba—F6^iv	130.73 (6)	Al^iv—F2—Ba^xiv	106.09 (9)
F5ⁱⁱⁱ—Ba—F6^iv	50.92 (6)	Ca1^xiii—F2—Ba^xiv	117.51 (8)
F5^iv—Ba—F6^iv	67.24 (5)	Fe1^xiii—F2—Ba^xiv	117.51 (8)
F3^iv—Ba—F6^iv	118.00 (6)	Al^vi—F3—Ca1^v	125.67 (12)
F1^v—Ba—F6^iv	82.68 (7)	Al^vi—F3—Fe1^v	125.67 (12)
F3—Ba—F6^iv	117.62 (5)	Ca1^v—F3—Fe1^v	0.0
F6ⁱⁱⁱ—Ba—F6^iv	97.89 (5)	Al^vi—F3—Ba^iv	94.81 (9)
F7—Ba—F1^vi	105.96 (6)	Ca1^v—F3—Ba^iv	131.32 (9)
F4ⁱ—Ba—F1^vi	113.22 (7)	Fe1^v—F3—Ba^iv	131.32 (9)
F1ⁱ—Ba—F1^vi	68.57 (8)	Al^vi—F3—Ba	97.28 (9)
F2ⁱⁱ—Ba—F1^vi	48.35 (6)	Ca1^v—F3—Ba	98.63 (7)
F5ⁱⁱⁱ—Ba—F1^vi	144.90 (6)	Fe1^v—F3—Ba	98.63 (7)
F5^iv—Ba—F1^vi	111.48 (6)	Ba^iv—F3—Ba	101.94 (7)
F3^iv—Ba—F1^vi	58.64 (6)	Al^xv—F4—Ca2	107.90 (10)
F1^v—Ba—F1^vi	84.02 (7)	Al^xv—F4—Ba^v	142.62 (11)
F3—Ba—F1^vi	46.95 (6)	Ca2—F4—Ba^v	109.17 (8)
F6ⁱⁱⁱ—Ba—F1^vi	94.27 (6)	Al^vi—F5—Ca2^iv	99.49 (9)
F6^iv—Ba—F1^vi	163.69 (5)	Al^vi—F5—Ba^vi	116.54 (9)
F7^x—Fe1—F2^xi	85.92 (8)	Ca2^iv—F5—Ba^vi	103.29 (7)
F7ⁱ—Fe1—F2^xi	94.08 (8)	Al^vi—F5—Ba^iv	96.93 (8)
F7^x—Fe1—F2^viii	94.08 (8)	Ca2^iv—F5—Ba^iv	117.45 (8)
F7ⁱ—Fe1—F2^viii	85.92 (8)	Ba^vi—F5—Ba^iv	121.50 (7)
F7^x—Fe1—F3^x	82.86 (8)	Al^iv—F6—Ca2^viii	133.22 (12)
F7ⁱ—Fe1—F3^x	97.14 (8)	Al^iv—F6—Ba^vi	100.10 (9)
F2^xi—Fe1—F3^x	95.71 (8)	Ca2^viii—F6—Ba^vi	113.52 (8)
F2^viii—Fe1—F3^x	84.29 (8)	Al^iv—F6—Ba^iv	102.40 (9)
F7^x—Fe1—F3ⁱ	97.14 (8)	Ca2^viii—F6—Ba^iv	101.02 (7)
F7ⁱ—Fe1—F3ⁱ	82.86 (8)	Ba^vi—F6—Ba^iv	102.46 (6)
F2^xi—Fe1—F3ⁱ	84.29 (8)	Ca1^v—F7—Fe1^v	0.0
F2^viii—Fe1—F3ⁱ	95.71 (8)	Ca1^v—F7—Ca2^xvi	120.98 (11)
F7^vii—Ca2—F7ⁱ	145.63 (12)	Fe1^v—F7—Ca2^xvi	120.98 (11)
F7^vii—Ca2—F6ⁱⁱⁱ	80.29 (8)	Ca1^v—F7—Ba	113.91 (9)
F7ⁱ—Ca2—F6ⁱⁱⁱ	78.02 (8)	Fe1^v—F7—Ba	113.91 (9)
F7^vii—Ca2—F6^viii	78.02 (8)	Ca2^xvi—F7—Ba	120.86 (10)
F7ⁱ—Ca2—F6^viii	80.29 (8)

Symmetry codes: (i) −x+1/2, y+1/2, −z+1/2; (ii) −x+1/2, y+1/2, −z+3/2; (iii) x, −y+1, z−1/2; (iv) −x+1/2, −y+1/2, −z+1; (v) −x+1/2, y−1/2, −z+1/2; (vi) x, −y+1, z+1/2; (vii) x−1/2, y+1/2, z; (viii) −x, −y+1, −z+1; (ix) −x, y, −z+1/2; (x) x−1/2, −y+1/2, z−1/2; (xi) x, y, z−1; (xii) x+1/2, y+1/2, z; (xiii) x, y, z+1; (xiv) −x+1/2, y−1/2, −z+3/2; (xv) x−1/2, y−1/2, z; (xvi) x+1/2, y−1/2, z.

(modelII) top

Crystal data top

Al₂Ba₂CaF₁₄Fe_0.90	F(000) = 1240
M_r = 684.98	D_x = 4.260 Mg m⁻³
Monoclinic, C2/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -C 2yc	Cell parameters from 25 reflections
a = 13.7387 (12) Å	θ = 16.0–28.7°
b = 5.2701 (5) Å	µ = 9.33 mm⁻¹
c = 14.759 (3) Å	T = 293 K
β = 92.074 (14)°	Lath, colourless
V = 1067.9 (2) Å³	0.43 × 0.11 × 0.07 mm
Z = 4

Data collection top

Nonius CAD-4 four-circle diffractometer	1490 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	R_int = 0.055
Graphite monochromator	θ_max = 30.0°, θ_min = 2.8°
ω/2θ scans	h = −19→19
Absorption correction: ψ scan (North et al., 1968)	k = −7→7
T_min = 0.329, T_max = 0.901	l = −20→20
5922 measured reflections	3 standard reflections every 240 min
1564 independent reflections	intensity decay: none

Refinement top

Refinement on F²	Primary atom site location: isomorphous structure methods
Least-squares matrix: full	w = 1/[σ²(F_o²) + (0.0532P)² + 1.6437P] where P = (F_o² + 2F_c²)/3
R[F² > 2σ(F²)] = 0.032	(Δ/σ)_max = 0.001
wR(F²) = 0.078	Δρ_max = 2.32 e Å⁻³
S = 1.10	Δρ_min = −2.03 e Å⁻³
1564 reflections	Extinction correction: SHELXL, Fc^*=kFc[1+0.001xFc²λ³/sin(2θ)]^-1/4
96 parameters	Extinction coefficient: 0.0022 (2)
0 restraints

Crystal data top

Al₂Ba₂CaF₁₄Fe_0.90	V = 1067.9 (2) Å³
M_r = 684.98	Z = 4
Monoclinic, C2/c	Mo Kα radiation
a = 13.7387 (12) Å	µ = 9.33 mm⁻¹
b = 5.2701 (5) Å	T = 293 K
c = 14.759 (3) Å	0.43 × 0.11 × 0.07 mm
β = 92.074 (14)°

Data collection top

Nonius CAD-4 four-circle diffractometer	1490 reflections with I > 2σ(I)
Absorption correction: ψ scan (North et al., 1968)	R_int = 0.055
T_min = 0.329, T_max = 0.901	3 standard reflections every 240 min
5922 measured reflections	intensity decay: none
1564 independent reflections

Refinement top

R[F² > 2σ(F²)] = 0.032	96 parameters
wR(F²) = 0.078	0 restraints
S = 1.10	Δρ_max = 2.32 e Å⁻³
1564 reflections	Δρ_min = −2.03 e Å⁻³

Special details top

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq	Occ. (<1)
Ba	0.308719 (14)	0.46574 (4)	0.379962 (12)	0.01408 (12)
Ca	0.0000	0.44617 (15)	0.2500	0.01239 (19)
Al	0.38008 (8)	0.50390 (18)	0.12340 (7)	0.0111 (2)
Fe	0.0000	0.5000	0.0000	0.0114 (3)	0.901 (5)
F1	0.25596 (18)	0.4521 (4)	0.0896 (2)	0.0240 (5)
F2	0.08572 (15)	0.1721 (4)	0.97492 (13)	0.0184 (4)
F3	0.37360 (16)	0.2100 (4)	0.55132 (14)	0.0197 (4)
F4	0.00267 (15)	0.0837 (4)	0.15434 (15)	0.0190 (4)
F5	0.34178 (14)	0.2932 (4)	0.71742 (13)	0.0157 (4)
F6	0.12185 (16)	0.2677 (4)	0.80392 (14)	0.0207 (4)
F7	0.43372 (16)	0.0715 (4)	0.37867 (16)	0.0208 (4)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Ba	0.01226 (16)	0.01399 (16)	0.01592 (15)	−0.00069 (5)	−0.00023 (9)	0.00074 (5)
Ca	0.0131 (4)	0.0124 (4)	0.0118 (4)	0.000	0.0019 (3)	0.000
Al	0.0114 (5)	0.0096 (3)	0.0123 (5)	−0.0007 (3)	−0.0003 (4)	0.0005 (3)
Fe	0.0098 (4)	0.0115 (3)	0.0128 (4)	0.0004 (2)	−0.0005 (3)	−0.0030 (2)
F1	0.0129 (11)	0.0219 (11)	0.0366 (14)	−0.0017 (8)	−0.0068 (10)	−0.0007 (9)
F2	0.0219 (10)	0.0184 (9)	0.0148 (8)	0.0032 (8)	−0.0016 (7)	−0.0026 (7)
F3	0.0270 (11)	0.0140 (8)	0.0184 (9)	−0.0004 (8)	0.0027 (8)	−0.0031 (7)
F4	0.0100 (9)	0.0247 (9)	0.0224 (10)	−0.0013 (8)	0.0000 (7)	−0.0086 (8)
F5	0.0156 (9)	0.0172 (8)	0.0145 (8)	−0.0038 (7)	0.0027 (6)	0.0004 (7)
F6	0.0221 (10)	0.0160 (8)	0.0243 (10)	0.0037 (8)	0.0036 (8)	0.0076 (8)
F7	0.0182 (11)	0.0238 (9)	0.0207 (10)	0.0008 (8)	0.0053 (8)	−0.0067 (8)

Geometric parameters (Å, º) top

Ba—F7	2.696 (2)	Ca—F4	2.376 (2)
Ba—F4ⁱ	2.730 (2)	Ca—F4^ix	2.376 (2)
Ba—F1ⁱ	2.755 (2)	Ca—F5^x	2.544 (2)
Ba—F2ⁱⁱ	2.766 (2)	Ca—F5^iv	2.544 (2)
Ba—F5ⁱⁱⁱ	2.767 (2)	Fe—F7ⁱ	2.015 (2)
Ba—F5^iv	2.826 (2)	Fe—F7^x	2.015 (2)
Ba—F3^iv	2.889 (2)	Fe—F2^viii	2.131 (2)
Ba—F1^v	2.889 (2)	Fe—F2^xi	2.131 (2)
Ba—F3	2.974 (2)	Fe—F3^x	2.216 (2)
Ba—F6ⁱⁱⁱ	3.101 (2)	Fe—F3ⁱ	2.216 (2)
Ba—F6^iv	3.159 (2)	Al—F4^xii	1.779 (2)
Ba—F1^vi	3.232 (3)	Al—F1	1.780 (3)
Ca—F7^vii	2.235 (2)	Al—F6^iv	1.790 (2)
Ca—F7ⁱ	2.235 (2)	Al—F2^iv	1.799 (2)
Ca—F6ⁱⁱⁱ	2.369 (2)	Al—F5ⁱⁱⁱ	1.843 (2)
Ca—F6^viii	2.369 (2)	Al—F3ⁱⁱⁱ	1.846 (2)

F7—Ba—F4ⁱ	64.22 (7)	F7ⁱ—Ca—F4^ix	139.26 (9)
F7—Ba—F1ⁱ	158.04 (7)	F6ⁱⁱⁱ—Ca—F4^ix	109.75 (8)
F4ⁱ—Ba—F1ⁱ	97.60 (7)	F6^viii—Ca—F4^ix	133.25 (7)
F7—Ba—F2ⁱⁱ	89.56 (7)	F4—Ca—F4^ix	73.01 (12)
F4ⁱ—Ba—F2ⁱⁱ	65.12 (7)	F7^vii—Ca—F5^x	86.30 (7)
F1ⁱ—Ba—F2ⁱⁱ	70.80 (7)	F7ⁱ—Ca—F5^x	110.95 (8)
F7—Ba—F5ⁱⁱⁱ	102.89 (6)	F6ⁱⁱⁱ—Ca—F5^x	165.38 (7)
F4ⁱ—Ba—F5ⁱⁱⁱ	63.12 (6)	F6^viii—Ca—F5^x	70.34 (7)
F1ⁱ—Ba—F5ⁱⁱⁱ	77.18 (7)	F4—Ca—F5^x	61.35 (7)
F2ⁱⁱ—Ba—F5ⁱⁱⁱ	113.14 (6)	F4^ix—Ca—F5^x	71.47 (7)
F7—Ba—F5^iv	94.51 (6)	F7^vii—Ca—F5^iv	110.95 (7)
F4ⁱ—Ba—F5^iv	134.23 (6)	F7ⁱ—Ca—F5^iv	86.30 (7)
F1ⁱ—Ba—F5^iv	107.33 (6)	F6ⁱⁱⁱ—Ca—F5^iv	70.34 (7)
F2ⁱⁱ—Ba—F5^iv	159.58 (6)	F6^viii—Ca—F5^iv	165.38 (7)
F5ⁱⁱⁱ—Ba—F5^iv	85.46 (4)	F4—Ca—F5^iv	71.47 (7)
F7—Ba—F3^iv	108.42 (6)	F4^ix—Ca—F5^iv	61.35 (7)
F4ⁱ—Ba—F3^iv	168.26 (6)	F5^x—Ca—F5^iv	120.54 (9)
F1ⁱ—Ba—F3^iv	87.26 (7)	F4^xii—Al—F1	175.02 (12)
F2ⁱⁱ—Ba—F3^iv	106.93 (6)	F4^xii—Al—F6^iv	94.00 (11)
F5ⁱⁱⁱ—Ba—F3^iv	128.56 (6)	F1—Al—F6^iv	90.60 (11)
F5^iv—Ba—F3^iv	52.85 (6)	F4^xii—Al—F2^iv	93.23 (11)
F7—Ba—F1^v	58.57 (7)	F1—Al—F2^iv	88.31 (12)
F4ⁱ—Ba—F1^v	122.79 (7)	F6^iv—Al—F2^iv	94.65 (11)
F1ⁱ—Ba—F1^v	138.03 (11)	F4^xii—Al—F5ⁱⁱⁱ	87.88 (10)
F2ⁱⁱ—Ba—F1^v	113.81 (7)	F1—Al—F5ⁱⁱⁱ	90.18 (12)
F5ⁱⁱⁱ—Ba—F1^v	128.76 (7)	F6^iv—Al—F5ⁱⁱⁱ	90.11 (11)
F5^iv—Ba—F1^v	53.36 (6)	F2^iv—Al—F5ⁱⁱⁱ	175.02 (10)
F3^iv—Ba—F1^v	50.92 (7)	F4^xii—Al—F3ⁱⁱⁱ	88.87 (11)
F7—Ba—F3	59.02 (6)	F1—Al—F3ⁱⁱⁱ	86.45 (11)
F4ⁱ—Ba—F3	90.21 (6)	F6^iv—Al—F3ⁱⁱⁱ	175.99 (12)
F1ⁱ—Ba—F3	111.81 (7)	F2^iv—Al—F3ⁱⁱⁱ	87.98 (10)
F2ⁱⁱ—Ba—F3	52.19 (6)	F5ⁱⁱⁱ—Al—F3ⁱⁱⁱ	87.19 (10)
F5ⁱⁱⁱ—Ba—F3	153.12 (6)	F7ⁱ—Fe—F2^viii	85.92 (8)
F5^iv—Ba—F3	113.88 (6)	F7^x—Fe—F2^viii	94.08 (8)
F3^iv—Ba—F3	78.06 (7)	F7ⁱ—Fe—F2^xi	94.08 (8)
F1^v—Ba—F3	61.81 (6)	F7^x—Fe—F2^xi	85.92 (8)
F7—Ba—F6ⁱⁱⁱ	149.97 (6)	F7ⁱ—Fe—F3^x	97.13 (8)
F4ⁱ—Ba—F6ⁱⁱⁱ	127.50 (6)	F7^x—Fe—F3^x	82.87 (8)
F1ⁱ—Ba—F6ⁱⁱⁱ	50.94 (6)	F2^viii—Fe—F3^x	84.30 (8)
F2ⁱⁱ—Ba—F6ⁱⁱⁱ	120.42 (6)	F2^xi—Fe—F3^x	95.70 (8)
F5ⁱⁱⁱ—Ba—F6ⁱⁱⁱ	68.77 (5)	F7ⁱ—Fe—F3ⁱ	82.87 (8)
F5^iv—Ba—F6ⁱⁱⁱ	56.89 (6)	F7^x—Fe—F3ⁱ	97.13 (8)
F3^iv—Ba—F6ⁱⁱⁱ	63.59 (6)	F2^viii—Fe—F3ⁱ	95.70 (8)
F1^v—Ba—F6ⁱⁱⁱ	103.02 (6)	F2^xi—Fe—F3ⁱ	84.30 (8)
F3—Ba—F6ⁱⁱⁱ	137.04 (6)	Al—F1—Ba^v	114.10 (11)
F7—Ba—F6^iv	58.77 (6)	Al—F1—Baⁱ	96.30 (9)
F4ⁱ—Ba—F6^iv	67.12 (6)	Ba^v—F1—Baⁱ	138.03 (10)
F1ⁱ—Ba—F6^iv	127.71 (7)	Al—F1—Baⁱⁱⁱ	90.11 (11)
F2ⁱⁱ—Ba—F6^iv	130.72 (6)	Ba^v—F1—Baⁱⁱⁱ	111.43 (8)
F5ⁱⁱⁱ—Ba—F6^iv	50.93 (5)	Baⁱ—F1—Baⁱⁱⁱ	95.98 (7)
F5^iv—Ba—F6^iv	67.24 (5)	Al^iv—F2—Fe^xiii	136.08 (11)
F3^iv—Ba—F6^iv	118.00 (6)	Al^iv—F2—Ba^xiv	106.08 (9)
F1^v—Ba—F6^iv	82.69 (7)	Fe^xiii—F2—Ba^xiv	117.52 (8)
F3—Ba—F6^iv	117.62 (5)	Al^vi—F3—Fe^v	125.66 (11)
F6ⁱⁱⁱ—Ba—F6^iv	97.89 (5)	Al^vi—F3—Ba^iv	94.81 (9)
F7—Ba—F1^vi	105.96 (6)	Fe^v—F3—Ba^iv	131.32 (9)
F4ⁱ—Ba—F1^vi	113.22 (7)	Al^vi—F3—Ba	97.27 (9)
F1ⁱ—Ba—F1^vi	68.57 (8)	Fe^v—F3—Ba	98.64 (7)
F2ⁱⁱ—Ba—F1^vi	48.36 (6)	Ba^iv—F3—Ba	101.94 (7)
F5ⁱⁱⁱ—Ba—F1^vi	144.89 (5)	Al^xv—F4—Ca	107.92 (10)
F5^iv—Ba—F1^vi	111.48 (6)	Al^xv—F4—Ba^v	142.62 (11)
F3^iv—Ba—F1^vi	58.64 (6)	Ca—F4—Ba^v	109.17 (8)
F1^v—Ba—F1^vi	84.02 (7)	Al^vi—F5—Ca^iv	99.48 (9)
F3—Ba—F1^vi	46.95 (6)	Al^vi—F5—Ba^vi	116.53 (9)
F6ⁱⁱⁱ—Ba—F1^vi	94.27 (6)	Ca^iv—F5—Ba^vi	103.28 (7)
F6^iv—Ba—F1^vi	163.69 (5)	Al^vi—F5—Ba^iv	96.94 (8)
F7^vii—Ca—F7ⁱ	145.64 (12)	Ca^iv—F5—Ba^iv	117.45 (7)
F7^vii—Ca—F6ⁱⁱⁱ	80.29 (8)	Ba^vi—F5—Ba^iv	121.51 (7)
F7ⁱ—Ca—F6ⁱⁱⁱ	78.04 (8)	Al^iv—F6—Ca^viii	133.22 (12)
F7^vii—Ca—F6^viii	78.04 (8)	Al^iv—F6—Ba^vi	100.10 (9)
F7ⁱ—Ca—F6^viii	80.29 (8)	Ca^viii—F6—Ba^vi	113.52 (8)
F6ⁱⁱⁱ—Ca—F6^viii	100.95 (11)	Al^iv—F6—Ba^iv	102.40 (9)
F7^vii—Ca—F4	139.26 (9)	Ca^viii—F6—Ba^iv	101.01 (7)
F7ⁱ—Ca—F4	73.57 (8)	Ba^vi—F6—Ba^iv	102.45 (6)
F6ⁱⁱⁱ—Ca—F4	133.25 (7)	Fe^v—F7—Ca^xvi	120.99 (11)
F6^viii—Ca—F4	109.75 (8)	Fe^v—F7—Ba	113.91 (9)
F7^vii—Ca—F4^ix	73.57 (8)	Ca^xvi—F7—Ba	120.85 (10)

Selected bond lengths (Å) for (modelI) top

Ba—F7	2.696 (2)	Ca2—F4	2.376 (2)
Ba—F4ⁱ	2.730 (2)	Ca2—F4^ix	2.376 (2)
Ba—F1ⁱ	2.755 (2)	Ca2—F5^x	2.544 (2)
Ba—F2ⁱⁱ	2.765 (2)	Ca2—F5^iv	2.544 (2)
Ba—F5ⁱⁱⁱ	2.766 (2)	Fe1—F7^x	2.015 (2)
Ba—F5^iv	2.827 (2)	Fe1—F7ⁱ	2.015 (2)
Ba—F3^iv	2.889 (2)	Fe1—F2^xi	2.131 (2)
Ba—F1^v	2.889 (2)	Fe1—F2^viii	2.131 (2)
Ba—F3	2.974 (2)	Fe1—F3^x	2.216 (2)
Ba—F6ⁱⁱⁱ	3.101 (2)	Fe1—F3ⁱ	2.216 (2)
Ba—F6^iv	3.158 (2)	Al—F4^xii	1.780 (2)
Ba—F1^vi	3.233 (3)	Al—F1	1.780 (3)
Ca2—F7^vii	2.235 (2)	Al—F6^iv	1.790 (2)
Ca2—F7ⁱ	2.235 (2)	Al—F2^iv	1.799 (2)
Ca2—F6ⁱⁱⁱ	2.369 (2)	Al—F5ⁱⁱⁱ	1.843 (2)
Ca2—F6^viii	2.369 (2)	Al—F3ⁱⁱⁱ	1.846 (2)

Bond-valence sum calculations for model (I) in valence units top

Atom	Assumed valence state	Bond-valence sum	Deviation from assumed valence state in valence units	Bond-valence sum under consideration of mixed Fe1:Ca1 occupancy*
Ba	2	1.94	0.06	1.94
Fe1	2	1.73	0.27	2.00
Ca2	2	1.95	0.05	1.95
Al	3	2.97	0.03	2.97
F1	1	0.96	0.04	0.96
F2	1	0.99	0.01	1.03
F3	1	0.93	0.07	0.96
F4	1	1.00	0	1.00
F5	1	0.99	0.01	0.99
F6	1	0.92	0.08	0.92
F7	1	0.97	0.03	1.03

Note: (*) calculated with the weighted average Fe:Ca ratio of 0.77:0.23 at the M2 site

Experimental details

	(modelI)	(modelII)
Crystal data
Chemical formula	Ba₂CaFeAl₂F₁₄	Al₂Ba₂CaF₁₄Fe_0.90
M_r	685.68	684.98
Crystal system, space group	Monoclinic, C2/c	Monoclinic, C2/c
Temperature (K)	293	293
a, b, c (Å)	13.7387 (12), 5.2701 (5), 14.759 (3)	13.7387 (12), 5.2701 (5), 14.759 (3)
β (°)	92.074 (14)	92.074 (14)
V (Å³)	1067.9 (2)	1067.9 (2)
Z	4	4
Radiation type	Mo Kα	Mo Kα
µ (mm⁻¹)	9.21	9.33
Crystal size (mm)	0.43 × 0.11 × 0.07	0.43 × 0.11 × 0.07

Data collection
Diffractometer	Nonius CAD-4 four-circle diffractometer	Nonius CAD-4 four-circle diffractometer
Absorption correction	ψ scan (North et al., 1968)	ψ scan (North et al., 1968)
T_min, T_max	0.329, 0.901	0.329, 0.901
No. of measured, independent and observed [I > 2σ(I)] reflections	5922, 1564, 1490	5922, 1564, 1490
R_int	0.055	0.055
(sin θ/λ)_max (Å⁻¹)	0.703	0.703

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.032, 0.078, 1.09	0.032, 0.078, 1.10
No. of reflections	1564	1564
No. of parameters	95	96
Δρ_max, Δρ_min (e Å⁻³)	2.31, −2.03	2.32, −2.03

Computer programs: CAD-4 Software (Enraf–Nonius, 1989), CAD-4 Software (Enraf-Nonius, 1989), HELENA implemented in PLATON (Spek, 2009), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), ATOMS for Windows (Dowty, 2006), Atoms for Windows (Dowty, 2006), publCIF (Westrip, 2010).

Acknowledgements

The X-ray centre of the Vienna University of Technology is acknowledged for providing access to the single-crystal diffractometer. I thank I. D. Brown for very helpful comments and suggestions regarding the bond-valence method.

References

Babel, D. & Tressaud, A. (1985). Inorganic Solid Fluorides, edited by P. Hagenmuller, pp. 79–203. Orlando: Academic Press. Google Scholar
Brown, I. D. (2002). In The Chemical Bond in Inorganic Chemistry: The Bond Valence Model. Oxford University Press. Google Scholar
Dowty, E. (2006). ATOMS for Windows. Shape Software, Kingsport, Tennessee, USA. Google Scholar
Enraf–Nonius (1989). CAD-4 Software. Enraf–Nonius, Delft, The Netherlands. Google Scholar
Holler, H., Babel, D., Samouel, M. & de Kozak, A. (1984). Rev. Chim. Miner. 21, 358–369. CAS Google Scholar
Holler, H., Pebler, J. & Babel, D. (1985). Z. Anorg. Allg. Chem. 522, 189–201. CrossRef CAS Google Scholar
Jauch, W., Palmer, A. & Schultz, A. J. (1993). Acta Cryst. B49, 984–987. CrossRef CAS Web of Science IUCr Journals Google Scholar
Kaiser, V., Le Lirzin, A., Darriet, J., Tressaud, A., Holler, H. & Babel, D. (2002). Z. Anorg. Allg. Chem. 628 2617–2626. CrossRef CAS Google Scholar
Kolk, E. van der, Dorenbos, P., Van Eijk, C. W. E., Vink, A. P., Weil, M. & Chaminade, J.-P. (2004). J. Appl. Phys. 95, 7867–7872. Google Scholar
Le Lirzin, A., Darriet, J., Tressaud, A. & Babel, D. (2008). Z. Anorg. Allg. Chem. 634 2737–2739. CrossRef CAS Google Scholar
Le Lirzin, A., Quiang, X., Darriet, J., Soubeyroux, J. L., Kaiser, V., Pebler, J. & Babel, D. (1990). Eur. J. Solid State Inorg. Chem. 27, 791–803. CAS Google Scholar
Le Lirzin, A., Soubeyroux, J. L., Tressaud, A., Georges, R. & Darriet, J. (1991). J. Chim. Phys. Phys.-Chim. Biol. 88, 2173–2189. CAS Google Scholar
Litvin, A. L., Petrunina, A. A., Ostapenko, S. S. & Povarennykh, A. S. (1980). Dopov. Akad. Nauk Ukr. RSR Ser. pp. 47–50. Google Scholar
North, A. C. T., Phillips, D. C. & Mathews, F. S. (1968). Acta Cryst. A24, 351–359. CrossRef IUCr Journals Web of Science Google Scholar
Qiang, X., Darriet, J., Tressaud, A., Soubeyroux, J. L. & Hagenmuller, P. (1988). Mater. Res. Bull. 23, 637–645. Google Scholar
Shannon, R. D. (1976). Acta Cryst. A32, 751–767. CrossRef CAS IUCr Journals Web of Science Google Scholar
Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122. Web of Science CrossRef CAS IUCr Journals Google Scholar
Spek, A. L. (2009). Acta Cryst. D65, 148–155. Web of Science CrossRef CAS IUCr Journals Google Scholar
Weil, M. & Kubel, F. (2002). J. Solid State Chem. 164, 150–156. CrossRef CAS Google Scholar
Weil, M., Zobetz, E., Werner, F. & Kubel, F. (2001). Solid State Sci. 3, 441–453. Web of Science CrossRef CAS Google Scholar
Werner, F. & Weil, M. (2003). Acta Cryst. E59, i17–i19. CrossRef IUCr Journals Google Scholar
Westrip, S. P. (2010). J. Appl. Cryst. 43, 920–925. Web of Science CrossRef CAS IUCr Journals Google Scholar
Wills, A. S. (2010). VaList. Program available from www.CCP14.ac. uk. Google Scholar

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Volume 71| Part 6| June 2015| Pages 640-643

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research communications\(\def\hfill{\hskip 5em}\def\hfil{\hskip 3em}\def\eqno#1{\hfil {#1}}\)

Crystal structure of the Fe-member of usovite

1. Chemical context

2. Structural commentary

3. Synthesis and crystallization

4. Refinement

Supporting information

Acknowledgements

References

research communications