Supporting information
Crystallographic Information File (CIF) https://doi.org/10.1107/S1600536803001259/mg6020sup1.cif | |
Structure factor file (CIF format) https://doi.org/10.1107/S1600536803001259/mg6020Isup2.hkl |
Key indicators
- Single-crystal X-ray study
- T = 293 K
- Mean (Al-F) = 0.002 Å
- R factor = 0.019
- wR factor = 0.043
- Data-to-parameter ratio = 17.2
checkCIF results
No syntax errors found ADDSYM reports no extra symmetry
A mixture of 457 mg BaF2 (Riedel-de Haën, 97%), 41 mg CaF2 (Merck, Suprapur) and 44 mg AlF3 (CERAC, 99.9%), corresponding to a molar ratio of 5:1:1, was added to 1 g ZnCl2 (Aldrich, 98%) and placed in a platinum crucible. The reaction mixture was then heated under atmospheric conditions to 873 K over a period of 2 h. The flux was kept at that temperature for 2 h and then cooled to 473 K over a period of 12 h. After cooling to room temperature, the solidified melt was leached with demineralized water. Colourless plates of the title compound were isolated from the residue. Additionally, tetragonal plates of matlockite-type BaFCl (Sauvage, 1974) were found in the crystal mixture.
Data collection: SMART (Siemens, 1996); cell refinement: SAINT (Siemens, 1996); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ATOMS for Windows (Dowty, 2000); software used to prepare material for publication: SHELXL97.
BaCaAlF7 | F(000) = 608 |
Mr = 337.40 | Dx = 4.123 Mg m−3 |
Monoclinic, P2/n | Mo Kα radiation, λ = 0.71073 Å |
Hall symbol: -p 2yac | Cell parameters from 3828 reflections |
a = 5.3664 (5) Å | θ = 3.3–30.5° |
b = 5.3846 (6) Å | µ = 8.49 mm−1 |
c = 18.8262 (19) Å | T = 293 K |
β = 92.319 (2)° | Plate, colourless |
V = 543.55 (10) Å3 | 0.12 × 0.08 × 0.06 mm |
Z = 4 |
Area detector diffractometer | 1603 independent reflections |
Radiation source: fine-focus sealed tube | 1477 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.020 |
ω scans | θmax = 30.5°, θmin = 2.2° |
Absorption correction: multi-scan (SADABS; Sheldrick, 1996) | h = −7→7 |
Tmin = 0.429, Tmax = 0.630 | k = −7→7 |
5719 measured reflections | l = −26→26 |
Refinement on F2 | Primary atom site location: structure-invariant direct methods |
Least-squares matrix: full | Secondary atom site location: difference Fourier map |
R[F2 > 2σ(F2)] = 0.019 | w = 1/[σ2(Fo2) + (0.0157P)2 + 1.3785P] where P = (Fo2 + 2Fc2)/3 |
wR(F2) = 0.044 | (Δ/σ)max < 0.001 |
S = 1.11 | Δρmax = 0.76 e Å−3 |
1603 reflections | Δρmin = −0.72 e Å−3 |
93 parameters | Extinction correction: SHELXL97, Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4 |
0 restraints | Extinction coefficient: 0.0038 (3) |
BaCaAlF7 | V = 543.55 (10) Å3 |
Mr = 337.40 | Z = 4 |
Monoclinic, P2/n | Mo Kα radiation |
a = 5.3664 (5) Å | µ = 8.49 mm−1 |
b = 5.3846 (6) Å | T = 293 K |
c = 18.8262 (19) Å | 0.12 × 0.08 × 0.06 mm |
β = 92.319 (2)° |
Area detector diffractometer | 1603 independent reflections |
Absorption correction: multi-scan (SADABS; Sheldrick, 1996) | 1477 reflections with I > 2σ(I) |
Tmin = 0.429, Tmax = 0.630 | Rint = 0.020 |
5719 measured reflections |
R[F2 > 2σ(F2)] = 0.019 | 93 parameters |
wR(F2) = 0.044 | 0 restraints |
S = 1.11 | Δρmax = 0.76 e Å−3 |
1603 reflections | Δρmin = −0.72 e Å−3 |
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. |
x | y | z | Uiso*/Ueq | ||
Ba | 0.24906 (3) | 0.24041 (3) | −0.067757 (8) | 0.01162 (7) | |
Al | 0.20069 (15) | 0.22470 (14) | 0.38092 (4) | 0.00837 (15) | |
Ca1 | 0.7500 | 0.20769 (13) | 0.7500 | 0.00786 (13) | |
Ca2 | 0.2500 | 0.68150 (13) | 0.7500 | 0.00703 (13) | |
F1 | 0.5997 (3) | 0.5949 (3) | 0.56404 (9) | 0.0165 (3) | |
F2 | 0.5649 (3) | 0.8622 (3) | 0.68045 (9) | 0.0141 (3) | |
F3 | 0.0901 (3) | 0.4812 (3) | 0.32626 (9) | 0.0133 (3) | |
F4 | 0.4141 (3) | 0.3614 (3) | 0.69206 (8) | 0.0133 (3) | |
F5 | 0.0530 (3) | 0.7185 (3) | 0.56042 (9) | 0.0159 (3) | |
F6 | 0.0154 (3) | −0.0288 (3) | 0.67494 (8) | 0.0122 (3) | |
F7 | 0.2750 (3) | −0.0454 (3) | 0.43446 (9) | 0.0167 (3) |
U11 | U22 | U33 | U12 | U13 | U23 | |
Ba | 0.01257 (9) | 0.01309 (10) | 0.00916 (9) | 0.00207 (6) | −0.00020 (5) | 0.00030 (5) |
Al | 0.0091 (3) | 0.0089 (4) | 0.0071 (3) | 0.0002 (3) | 0.0000 (3) | 0.0002 (3) |
Ca1 | 0.0084 (3) | 0.0073 (3) | 0.0078 (3) | 0.000 | −0.0005 (2) | 0.000 |
Ca2 | 0.0064 (3) | 0.0077 (3) | 0.0070 (3) | 0.000 | 0.0004 (2) | 0.000 |
F1 | 0.0170 (8) | 0.0201 (8) | 0.0122 (8) | −0.0069 (7) | −0.0017 (6) | −0.0016 (6) |
F2 | 0.0139 (8) | 0.0135 (8) | 0.0153 (8) | −0.0004 (6) | 0.0054 (6) | −0.0031 (6) |
F3 | 0.0129 (7) | 0.0121 (8) | 0.0146 (8) | −0.0013 (6) | −0.0023 (6) | 0.0047 (6) |
F4 | 0.0136 (8) | 0.0140 (8) | 0.0121 (7) | 0.0027 (6) | −0.0017 (6) | −0.0031 (6) |
F5 | 0.0132 (8) | 0.0200 (9) | 0.0151 (8) | 0.0027 (6) | 0.0053 (6) | −0.0009 (6) |
F6 | 0.0107 (7) | 0.0138 (8) | 0.0120 (7) | −0.0022 (6) | −0.0002 (6) | −0.0012 (6) |
F7 | 0.0190 (8) | 0.0144 (8) | 0.0167 (8) | 0.0033 (6) | 0.0005 (7) | 0.0049 (6) |
Ba—F4i | 2.5498 (16) | Ca1—F4xiii | 2.2282 (17) |
Ba—F1i | 2.6763 (17) | Ca1—F4 | 2.2282 (17) |
Ba—F7ii | 2.7542 (17) | Ca1—F3vii | 2.3880 (16) |
Ba—F1iii | 2.7831 (17) | Ca1—F3xiv | 2.3880 (16) |
Ba—F5i | 2.7860 (17) | Ca1—F6xv | 2.4102 (16) |
Ba—F6i | 2.8244 (16) | Ca1—F6xvi | 2.4102 (16) |
Ba—F5iv | 2.8660 (18) | Ca1—F2xvii | 2.4609 (18) |
Ba—F7i | 2.9510 (17) | Ca1—F2xviii | 2.4609 (18) |
Ba—F5v | 3.0058 (18) | Ca1—Alx | 3.4086 (9) |
Ba—F7vi | 3.0102 (17) | Ca1—Alxix | 3.4086 (9) |
Ba—F3iv | 3.1421 (17) | Ca1—Ca2xvi | 3.7025 (7) |
Ba—Ali | 3.5178 (9) | Ca1—Ca2 | 3.7025 (7) |
Al—F1vii | 1.7535 (19) | Ca2—F4xv | 2.2392 (17) |
Al—F2vii | 1.8038 (17) | Ca2—F4 | 2.2392 (17) |
Al—F7 | 1.8047 (18) | Ca2—F2 | 2.3868 (16) |
Al—F3 | 1.8083 (18) | Ca2—F2xv | 2.3868 (16) |
Al—F5viii | 1.8133 (18) | Ca2—F6xx | 2.4231 (17) |
Al—F6ix | 1.8614 (18) | Ca2—F6xxi | 2.4231 (17) |
Al—Ca1x | 3.4086 (9) | Ca2—F3viii | 2.4389 (17) |
Al—Ca2viii | 3.4201 (9) | Ca2—F3xiv | 2.4389 (17) |
Al—Bai | 3.5178 (9) | Ca2—Alviii | 3.4201 (9) |
Al—Baxi | 3.6427 (8) | Ca2—Alxiv | 3.4201 (9) |
Al—Baxii | 3.9106 (8) | Ca2—Ca1xxii | 3.7025 (7) |
F4i—Ba—F1i | 68.11 (5) | F7—Al—F5viii | 87.15 (8) |
F4i—Ba—F7ii | 80.11 (5) | F3—Al—F5viii | 88.88 (8) |
F1i—Ba—F7ii | 67.93 (5) | F1vii—Al—F6ix | 178.18 (9) |
F4i—Ba—F1iii | 129.51 (5) | F2vii—Al—F6ix | 85.73 (8) |
F1i—Ba—F1iii | 61.48 (6) | F7—Al—F6ix | 88.70 (8) |
F7ii—Ba—F1iii | 78.96 (5) | F3—Al—F6ix | 85.92 (8) |
F4i—Ba—F5i | 85.73 (5) | F5viii—Al—F6ix | 88.51 (8) |
F1i—Ba—F5i | 66.76 (5) | F4xiii—Ca1—F4 | 136.39 (9) |
F7ii—Ba—F5i | 134.60 (5) | F4xiii—Ca1—F3vii | 74.37 (6) |
F1iii—Ba—F5i | 77.55 (5) | F4—Ca1—F3vii | 75.42 (6) |
F4i—Ba—F6i | 67.82 (5) | F4xiii—Ca1—F3xiv | 75.42 (6) |
F1i—Ba—F6i | 135.93 (5) | F4—Ca1—F3xiv | 74.37 (6) |
F7ii—Ba—F6i | 104.80 (5) | F3vii—Ca1—F3xiv | 90.92 (8) |
F1iii—Ba—F6i | 162.52 (5) | F4xiii—Ca1—F6xv | 113.25 (6) |
F5i—Ba—F6i | 109.20 (5) | F4—Ca1—F6xv | 89.87 (6) |
F4i—Ba—F5iv | 156.29 (5) | F3vii—Ca1—F6xv | 163.38 (6) |
F1i—Ba—F5iv | 107.31 (5) | F3xiv—Ca1—F6xv | 77.46 (6) |
F7ii—Ba—F5iv | 120.75 (5) | F4xiii—Ca1—F6xvi | 89.87 (6) |
F1iii—Ba—F5iv | 53.08 (5) | F4—Ca1—F6xvi | 113.25 (6) |
F5i—Ba—F5iv | 71.58 (6) | F3vii—Ca1—F6xvi | 77.46 (6) |
F6i—Ba—F5iv | 112.66 (5) | F3xiv—Ca1—F6xvi | 163.38 (6) |
F4i—Ba—F7i | 152.69 (5) | F6xv—Ca1—F6xvi | 116.22 (8) |
F1i—Ba—F7i | 107.15 (5) | F4xiii—Ca1—F2xvii | 147.39 (6) |
F7ii—Ba—F7i | 73.51 (6) | F4—Ca1—F2xvii | 73.69 (6) |
F1iii—Ba—F7i | 51.97 (5) | F3vii—Ca1—F2xvii | 110.94 (6) |
F5i—Ba—F7i | 117.99 (5) | F3xiv—Ca1—F2xvii | 134.67 (5) |
F6i—Ba—F7i | 112.10 (5) | F6xv—Ca1—F2xvii | 71.17 (6) |
F5iv—Ba—F7i | 50.75 (5) | F6xvi—Ca1—F2xvii | 61.58 (5) |
F4i—Ba—F5v | 112.88 (5) | F4xiii—Ca1—F2xviii | 73.69 (6) |
F1i—Ba—F5v | 155.78 (5) | F4—Ca1—F2xviii | 147.39 (7) |
F7ii—Ba—F5v | 88.15 (5) | F3vii—Ca1—F2xviii | 134.67 (5) |
F1iii—Ba—F5v | 111.77 (5) | F3xiv—Ca1—F2xviii | 110.94 (6) |
F5i—Ba—F5v | 136.74 (6) | F6xv—Ca1—F2xviii | 61.58 (5) |
F6i—Ba—F5v | 52.08 (5) | F6xvi—Ca1—F2xviii | 71.17 (6) |
F5iv—Ba—F5v | 81.12 (5) | F2xvii—Ca1—F2xviii | 81.79 (8) |
F7i—Ba—F5v | 60.06 (5) | F4xv—Ca2—F4 | 79.34 (9) |
F4i—Ba—F7vi | 112.88 (5) | F4xv—Ca2—F2 | 151.92 (7) |
F1i—Ba—F7vi | 154.80 (5) | F4—Ca2—F2 | 75.25 (6) |
F7ii—Ba—F7vi | 137.13 (7) | F4xv—Ca2—F2xv | 75.25 (6) |
F1iii—Ba—F7vi | 113.73 (5) | F4—Ca2—F2xv | 151.92 (7) |
F5i—Ba—F7vi | 88.07 (5) | F2—Ca2—F2xv | 131.87 (9) |
F6i—Ba—F7vi | 52.00 (4) | F4xv—Ca2—F6xx | 114.63 (6) |
F5iv—Ba—F7vi | 60.92 (5) | F4—Ca2—F6xx | 125.05 (6) |
F7i—Ba—F7vi | 83.08 (5) | F2—Ca2—F6xx | 72.22 (6) |
F5v—Ba—F7vi | 48.98 (5) | F2xv—Ca2—F6xx | 77.31 (6) |
F4i—Ba—F3iv | 58.84 (5) | F4xv—Ca2—F6xxi | 125.05 (6) |
F1i—Ba—F3iv | 95.87 (5) | F4—Ca2—F6xxi | 114.63 (6) |
F7ii—Ba—F3iv | 138.91 (5) | F2—Ca2—F6xxi | 77.31 (6) |
F1iii—Ba—F3iv | 127.61 (5) | F2xv—Ca2—F6xxi | 72.22 (6) |
F5i—Ba—F3iv | 50.21 (4) | F6xx—Ca2—F6xxi | 99.85 (8) |
F6i—Ba—F3iv | 60.14 (4) | F4xv—Ca2—F3viii | 73.17 (6) |
F5iv—Ba—F3iv | 99.88 (4) | F4—Ca2—F3viii | 74.72 (6) |
F7i—Ba—F3iv | 146.66 (4) | F2—Ca2—F3viii | 110.68 (6) |
F5v—Ba—F3iv | 105.15 (4) | F2xv—Ca2—F3viii | 86.55 (6) |
F7vi—Ba—F3iv | 66.75 (4) | F6xx—Ca2—F3viii | 158.97 (6) |
F1vii—Al—F2vii | 95.58 (9) | F6xxi—Ca2—F3viii | 61.92 (6) |
F1vii—Al—F7 | 90.02 (9) | F4xv—Ca2—F3xiv | 74.72 (6) |
F2vii—Al—F7 | 90.26 (8) | F4—Ca2—F3xiv | 73.17 (6) |
F1vii—Al—F3 | 95.26 (9) | F2—Ca2—F3xiv | 86.55 (6) |
F2vii—Al—F3 | 93.15 (8) | F2xv—Ca2—F3xiv | 110.68 (6) |
F7—Al—F3 | 173.40 (9) | F6xx—Ca2—F3xiv | 61.92 (6) |
F1vii—Al—F5viii | 90.13 (9) | F6xxi—Ca2—F3xiv | 158.97 (6) |
F2vii—Al—F5viii | 173.74 (9) | F3viii—Ca2—F3xiv | 137.88 (8) |
Symmetry codes: (i) −x+1/2, y, −z+1/2; (ii) x−1/2, −y, z−1/2; (iii) x−1/2, −y+1, z−1/2; (iv) x+1/2, −y+1, z−1/2; (v) −x+1/2, y−1, −z+1/2; (vi) x+1/2, −y, z−1/2; (vii) −x+1, −y+1, −z+1; (viii) −x, −y+1, −z+1; (ix) −x, −y, −z+1; (x) −x+1, −y, −z+1; (xi) x−1/2, −y, z+1/2; (xii) x−1/2, −y+1, z+1/2; (xiii) −x+3/2, y, −z+3/2; (xiv) x+1/2, −y+1, z+1/2; (xv) −x+1/2, y, −z+3/2; (xvi) x+1, y, z; (xvii) x, y−1, z; (xviii) −x+3/2, y−1, −z+3/2; (xix) x+1/2, −y, z+1/2; (xx) −x+1/2, y+1, −z+3/2; (xxi) x, y+1, z; (xxii) x−1, y, z. |
Experimental details
Crystal data | |
Chemical formula | BaCaAlF7 |
Mr | 337.40 |
Crystal system, space group | Monoclinic, P2/n |
Temperature (K) | 293 |
a, b, c (Å) | 5.3664 (5), 5.3846 (6), 18.8262 (19) |
β (°) | 92.319 (2) |
V (Å3) | 543.55 (10) |
Z | 4 |
Radiation type | Mo Kα |
µ (mm−1) | 8.49 |
Crystal size (mm) | 0.12 × 0.08 × 0.06 |
Data collection | |
Diffractometer | Area detector diffractometer |
Absorption correction | Multi-scan (SADABS; Sheldrick, 1996) |
Tmin, Tmax | 0.429, 0.630 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 5719, 1603, 1477 |
Rint | 0.020 |
(sin θ/λ)max (Å−1) | 0.713 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.019, 0.044, 1.11 |
No. of reflections | 1603 |
No. of parameters | 93 |
Δρmax, Δρmin (e Å−3) | 0.76, −0.72 |
Computer programs: SMART (Siemens, 1996), SAINT (Siemens, 1996), SAINT, SHELXS97 (Sheldrick, 1997), SHELXL97 (Sheldrick, 1997), ATOMS for Windows (Dowty, 2000), SHELXL97.
Ba—F4i | 2.5498 (16) | Ca1—F4x | 2.2282 (17) |
Ba—F1i | 2.6763 (17) | Ca1—F4 | 2.2282 (17) |
Ba—F7ii | 2.7542 (17) | Ca1—F3vii | 2.3880 (16) |
Ba—F1iii | 2.7831 (17) | Ca1—F3xi | 2.3880 (16) |
Ba—F5i | 2.7860 (17) | Ca1—F6xii | 2.4102 (16) |
Ba—F6i | 2.8244 (16) | Ca1—F6xiii | 2.4102 (16) |
Ba—F5iv | 2.8660 (18) | Ca1—F2xiv | 2.4609 (18) |
Ba—F7i | 2.9510 (17) | Ca1—F2xv | 2.4609 (18) |
Ba—F5v | 3.0058 (18) | Ca2—F4xii | 2.2392 (17) |
Ba—F7vi | 3.0102 (17) | Ca2—F4 | 2.2392 (17) |
Ba—F3iv | 3.1421 (17) | Ca2—F2 | 2.3868 (16) |
Al—F1vii | 1.7535 (19) | Ca2—F2xii | 2.3868 (16) |
Al—F2vii | 1.8038 (17) | Ca2—F6xvi | 2.4231 (17) |
Al—F7 | 1.8047 (18) | Ca2—F6xvii | 2.4231 (17) |
Al—F3 | 1.8083 (18) | Ca2—F3viii | 2.4389 (17) |
Al—F5viii | 1.8133 (18) | Ca2—F3xi | 2.4389 (17) |
Al—F6ix | 1.8614 (18) |
Symmetry codes: (i) −x+1/2, y, −z+1/2; (ii) x−1/2, −y, z−1/2; (iii) x−1/2, −y+1, z−1/2; (iv) x+1/2, −y+1, z−1/2; (v) −x+1/2, y−1, −z+1/2; (vi) x+1/2, −y, z−1/2; (vii) −x+1, −y+1, −z+1; (viii) −x, −y+1, −z+1; (ix) −x, −y, −z+1; (x) −x+3/2, y, −z+3/2; (xi) x+1/2, −y+1, z+1/2; (xii) −x+1/2, y, −z+3/2; (xiii) x+1, y, z; (xiv) x, y−1, z; (xv) −x+3/2, y−1, −z+3/2; (xvi) −x+1/2, y+1, −z+3/2; (xvii) x, y+1, z. |
Complex fluorides are interesting host lattices for doping with rare-earth or transition metal ions to obtain luminescent materials with slightly different characteristics as compared to the widespread used oxides (Rubio, 1991; Kubel et al., 1997; Joubert et al., 2001).
Numerous phases in the pseudobinary system MF2—AlF3 with M = Ca, Sr, Ba have been reported and the corresponding structures solved and refined either from single-crystal or powder data [M = Ca: CaAlF5 (Hemon & Courbion, 1991) and Ca2AlF7 (Domesle & Hoppe, 1980); M = Sr: two polymorphs of SrAlF5 (von der Muehll et al., 1971; Kubel, 1998; Weil et al., 2001) and Sr5Al2F16 (Weil, 2001); M = Ba: four polymorphic forms of BaAlF5 (Domesle & Hoppe, 1982a; Le Bail et al., 1990; Weil et al., 2001), three polymorphic forms of Ba3AlF9 (Renaudin et al., 1990; Renaudin et al., 1991; Le Bail, 1993) and Ba3Al2F12 (Domesle & Hoppe, 1982b)], whereas the number of structurally well characterized compounds in the pseudo-ternary system MF2–M'F2–AlF3 (M, M' = Ca, Sr, Ba) is restricted to only three representatives, with composition Ba0.43Sr0.57AlF5 (Kubel, 1998), Sr0.92Ca0.08AlF5 and Sr0.67Ca0.33AlF5 (Weil et al., 2001) (all single-crystal data). Additionally, two more phases with composition SrCaAlF7 and BaCaAlF7 are reported, each with three polymorphic forms denoted as α, β and γ (Hoffman, 1972). For four modifications (all SrCaAlF7 polymorphs and α-BaCaAlF7), non-indexed powder data are given and their EuII activation was measured. The latter phase is a very interesting candidate as a luminescent material since it shows a high EuII emission line. Fig. 1 shows that the phase previously described as α-BaCaAlF7 is identical to the title compound. Except for an impurity line at 2θ = 27.4°, the entry in the powder diffraction file (PDF # 27–0090; ICDD, 2001) is in agreement with the powder pattern calculated on the basis of the single-crystal structure refinement.
α-BaCaAlF7 is isotypic with BaCaGaF7 and BaCaCrF7 (Holler & Babel, 1985). According to the slightly smaller ionic radius of AlIII (0.54 Å) with respect to GaIII and CrIII (both 0.62 Å, values from Shannon, 1976), the unit-cell volume of the title compound is slightly smaller (Al: 544 Å3; Ga: 553 Å3; Cr: 556 Å3). The structure is built up from triple layers which extend parallel to (001) and consist of a central unit and two side units (Fig. 2). The central unit is composed of edge-sharing 2∞[CaF8/2] polyhedra with distorted square antiprisms as the corresponding coordination figures. Although the intrapolyhedral geometry differs significantly from that of a cube found in the ideal fluorite structure, this arrangement can be considered as part of a distorted CaF2 structure. This assumption is confirmed by comparable distances d(Ca1—Ca2) of 3.703 (1) and 3.902 (1) Å, as well as the average Ca—F distance of 2.372 Å and the value of the a and b axis with respect to the distances and the lattice parameter in CaF2 itself [d(Ca—Ca) = 3.869 Å, d(Ca—F) = 2.369 Å and a = 5.471 Å; values from Zhurova et al. (1996)]. The side units are made up from isolated [AlF6] octahedra which share common edges with the central fluorite-type 2∞[CaF8/2] layer. The average Al—F distance of 1.808 Å is in the typical range for [AlF6] octahedra found in other complex aluminium fluorides. The largest deviation from the ideal octahedral angle is 6.6°. Two triple layers are stacked along [001] with a stacking unit of c/2 and are held together by 11-fold coordinated Ba atoms. The resulting [BaF11] polyhedron might be described as a distorted tricapped rectangular prism (Fig. 3), with an average Ba—F distance of 2.850 Å. The F atoms exhibit either a coordination number (CN) of 3, resulting in a distorted trigonal planar environment (F1, F2 and F4), or CN = 4, with a distorted tetrahedral coordination geometry (F3, F5, F6 and F7).