High-temperature monoclinic α-SrHfF₆, and isostructural α-SrZrF₆: associating Hf₂F₁₂ bipolyhedra and SrF₈ snub disphenoids

The structure of the high-temperature monoclinic variety α-SrHfF₆ (strontium hafnium hexa­fluoride) [and of isostructural α-SrZrF₆ (strontium zirconium hexa­fluoride)] associates Hf₂F₁₂ bipolyhedra and SrF₈ snub disphenoids, forming zigzag twisted [SrF₆]_n layers. The distribution of the Hf and Sr polyhedra forms a three-dimensional framework which can be related to the family of anion-excess ReO₃-related superstructures. α-SrHfF₆ corresponds to a new ABX₆ type and is compared to the other main families already described. A partial amorphization of this structure is observed in samples quenched from the melt.

Computing details

Data collection: COLLECT (Nonius, 2004); cell refinement: DIRAX/LSQ (Duisenberg, 1992); data reduction: EVALCCD (Duisenberg et al., 2003); program(s) used to solve structure: SHELXS96 (Sheldrick, 2008); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015) and WinGX (Farrugia, 2012); molecular graphics: DIAMOND (Brandenburg, 1999); software used to prepare material for publication: WinGX (Farrugia, 2012) and publCIF (Westrip, 2010).

Strontium hafnium hexafluoride

Crystal data

SrHfF6	F(000) = 656
Mr = 760.22	Dx = 4.951 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71070 Å
Hall symbol: -P 2ybc	Cell parameters from 12266 reflections
a = 5.9762 (10) Å	θ = 4.8–25.2°
b = 5.9949 (10) Å	µ = 30.83 mm^−1
c = 14.426 (3) Å	T = 293 K
β = 99.36 (5)°	Spheroidal, colourless
V = 509.96 (18) Å^3	0.04 × 0.03 × 0.02 mm
Z = 2

Data collection

Nonius KappaCCD diffractometer	1160 independent reflections
Radiation source: fine-focus sealed tube	1052 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.042
Detector resolution: 9 pixels mm^-1	θmax = 27.4°, θmin = 4.8°
CCD scans	h = −7→7
Absorption correction: multi-scan (SADABS; Bruker, 2004)	k = −7→7
Tmin = 0.48, Tmax = 0.60	l = −18→18
12266 measured reflections

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.015	w = 1/[σ^2(Fo^2) + (0.0145P)^2 + 1.1913P] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 0.036	(Δ/σ)max = 0.001
S = 1.13	Δρmax = 1.07 e Å^−3
1160 reflections	Δρmin = −0.81 e Å^−3
74 parameters	Extinction correction: SHELXL2014 (Sheldrick, 2015)
0 restraints	Extinction coefficient: 0.00155 (16)

Special details

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds 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 > 2sigma(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 (Ų)

	x	y	z	Uiso*/Ueq
Hf1	0.82383 (3)	0.13602 (3)	0.90159 (2)	0.01007 (8)
Sr1	0.65438 (7)	0.09965 (6)	0.63819 (3)	0.01187 (10)
F1	0.6331 (5)	0.3593 (4)	0.96093 (18)	0.0186 (6)
F2	1.0873 (4)	−0.1061 (4)	0.94722 (17)	0.0147 (5)
F3	0.9048 (5)	−0.0017 (5)	0.78444 (17)	0.0250 (6)
F4	0.6095 (5)	0.2897 (4)	0.79331 (17)	0.0194 (6)
F5	1.0689 (5)	0.3554 (4)	0.9072 (2)	0.0245 (6)
F6	0.6027 (5)	−0.1036 (4)	0.9089 (2)	0.0255 (6)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Hf1	0.01083 (11)	0.01112 (11)	0.00809 (10)	−0.00137 (6)	0.00102 (6)	−0.00015 (6)
Sr1	0.0135 (2)	0.0138 (2)	0.00786 (19)	0.00530 (15)	0.00055 (15)	−0.00065 (14)
F1	0.0235 (14)	0.0215 (13)	0.0110 (12)	0.0091 (11)	0.0032 (11)	−0.0002 (10)
F2	0.0160 (13)	0.0198 (13)	0.0080 (12)	0.0052 (10)	0.0008 (10)	−0.0008 (10)
F3	0.0292 (16)	0.0372 (16)	0.0071 (12)	0.0162 (13)	−0.0009 (11)	−0.0032 (11)
F4	0.0242 (14)	0.0230 (13)	0.0099 (12)	0.0099 (11)	−0.0007 (11)	0.0007 (10)
F5	0.0236 (15)	0.0265 (15)	0.0239 (15)	−0.0166 (12)	0.0053 (12)	0.0028 (12)
F6	0.0260 (16)	0.0231 (15)	0.0264 (16)	−0.0169 (12)	0.0013 (12)	−0.0002 (12)

Geometric parameters (Å, º)

Hf1—F5	1.960 (3)	Sr1—F1^vi	2.551 (3)
Hf1—F6	1.966 (3)	Sr1—F4	2.564 (3)
Hf1—F3	2.010 (3)	Sr1—F4^v	2.724 (3)
Hf1—F1	2.035 (3)	Sr1—F2^vii	2.763 (2)
Hf1—F4	2.069 (3)	Sr1—Hf1^v	3.9609 (7)
Hf1—F2	2.164 (2)	Sr1—Hf1^vi	4.0386 (11)
Hf1—F2^i	2.167 (2)	Sr1—Sr1^viii	4.2821 (18)
Hf1—Hf1^i	3.6346 (15)	F1—Sr1^ii	2.505 (3)
Hf1—Sr1	3.7763 (12)	F1—Sr1^iii	2.552 (3)
Hf1—Sr1^ii	3.9609 (7)	F2—Hf1^i	2.167 (2)
Hf1—Sr1^iii	4.0386 (11)	F2—Sr1^iv	2.763 (2)
Sr1—F6^ii	2.376 (3)	F4—Sr1^ii	2.724 (3)
Sr1—F5^iv	2.379 (3)	F5—Sr1^vii	2.379 (3)
Sr1—F3	2.456 (3)	F6—Sr1^v	2.376 (3)
Sr1—F1^v	2.505 (3)
F5—Hf1—F6	172.78 (12)	F3—Sr1—F4^v	80.07 (9)
F5—Hf1—F3	91.72 (13)	F1^v—Sr1—F4^v	55.32 (8)
F6—Hf1—F3	90.04 (13)	F1^vi—Sr1—F4^v	119.46 (8)
F5—Hf1—F1	90.41 (12)	F4—Sr1—F4^v	80.65 (5)
F6—Hf1—F1	91.76 (12)	F6^ii—Sr1—F2^vii	77.11 (9)
F3—Hf1—F1	148.43 (11)	F5^iv—Sr1—F2^vii	78.82 (10)
F5—Hf1—F4	95.69 (12)	F3—Sr1—F2^vii	103.55 (9)
F6—Hf1—F4	91.53 (12)	F1^v—Sr1—F2^vii	119.60 (8)
F3—Hf1—F4	75.66 (10)	F1^vi—Sr1—F2^vii	55.38 (8)
F1—Hf1—F4	72.79 (10)	F4—Sr1—F2^vii	104.54 (8)
F5—Hf1—F2	86.32 (11)	F4^v—Sr1—F2^vii	174.66 (7)
F6—Hf1—F2	87.46 (11)	F6^ii—Sr1—Hf1	107.42 (8)
F3—Hf1—F2	73.58 (10)	F5^iv—Sr1—Hf1	103.17 (8)
F1—Hf1—F2	137.98 (9)	F3—Sr1—Hf1	28.81 (6)
F4—Hf1—F2	149.22 (9)	F1^v—Sr1—Hf1	130.88 (6)
F5—Hf1—F2^i	87.40 (11)	F1^vi—Sr1—Hf1	164.67 (6)
F6—Hf1—F2^i	86.72 (12)	F4—Sr1—Hf1	31.25 (6)
F3—Hf1—F2^i	139.41 (10)	F4^v—Sr1—Hf1	75.56 (6)
F1—Hf1—F2^i	72.15 (10)	F2^vii—Sr1—Hf1	109.52 (6)
F4—Hf1—F2^i	144.82 (10)	F6^ii—Sr1—Hf1^v	93.79 (8)
F2—Hf1—F2^i	65.87 (11)	F5^iv—Sr1—Hf1^v	92.62 (7)
F5—Hf1—Sr1	99.01 (9)	F3—Sr1—Hf1^v	105.98 (8)
F6—Hf1—Sr1	86.50 (9)	F1^v—Sr1—Hf1^v	26.08 (6)
F3—Hf1—Sr1	36.09 (8)	F1^vi—Sr1—Hf1^v	90.30 (7)
F1—Hf1—Sr1	112.60 (8)	F4—Sr1—Hf1^v	105.24 (7)
F4—Hf1—Sr1	40.01 (7)	F4^v—Sr1—Hf1^v	29.24 (5)
F2—Hf1—Sr1	109.28 (7)	F2^vii—Sr1—Hf1^v	145.67 (5)
F2^i—Hf1—Sr1	171.84 (6)	Hf1—Sr1—Hf1^v	104.80 (4)
F5—Hf1—Sr1^ii	92.97 (9)	F6^ii—Sr1—Hf1^vi	72.79 (8)
F6—Hf1—Sr1^ii	92.58 (9)	F5^iv—Sr1—Hf1^vi	74.20 (8)
F3—Hf1—Sr1^ii	115.67 (8)	F3—Sr1—Hf1^vi	128.42 (7)
F1—Hf1—Sr1^ii	32.76 (7)	F1^v—Sr1—Hf1^vi	89.21 (6)
F4—Hf1—Sr1^ii	40.04 (7)	F1^vi—Sr1—Hf1^vi	24.99 (6)
F2—Hf1—Sr1^ii	170.74 (6)	F4—Sr1—Hf1^vi	129.75 (6)
F2^i—Hf1—Sr1^ii	104.89 (7)	F4^v—Sr1—Hf1^vi	144.45 (6)
Sr1—Hf1—Sr1^ii	79.96 (4)	F2^vii—Sr1—Hf1^vi	30.39 (5)
F5—Hf1—Sr1^iii	89.43 (9)	Hf1—Sr1—Hf1^vi	139.879 (15)
F6—Hf1—Sr1^iii	88.76 (9)	Hf1^v—Sr1—Hf1^vi	115.28 (3)
F3—Hf1—Sr1^iii	178.76 (9)	F6^ii—Sr1—Sr1^viii	77.42 (8)
F1—Hf1—Sr1^iii	31.99 (7)	F5^iv—Sr1—Sr1^viii	77.61 (8)
F4—Hf1—Sr1^iii	104.70 (7)	F3—Sr1—Sr1^viii	147.23 (7)
F2—Hf1—Sr1^iii	106.03 (7)	F1^v—Sr1—Sr1^viii	32.46 (6)
F2^i—Hf1—Sr1^iii	40.17 (6)	F1^vi—Sr1—Sr1^viii	31.79 (6)
Sr2—Hf1—Sr1^iii	144.095 (14)	F4—Sr1—Sr1^viii	147.81 (6)
Sr2^ii—Hf1—Sr1^iii	64.72 (3)	F4^v—Sr1—Sr1^viii	87.72 (6)
F6^ii—Sr1—F5^iv	145.91 (10)	F2^vii—Sr1—Sr1^viii	87.15 (5)
F6^ii—Sr1—F3	134.91 (10)	Hf1—Sr1—Sr1^viii	163.228 (19)
F5^iv—Sr1—F3	74.37 (9)	Hf1^v—Sr1—Sr1^viii	58.52 (3)
F6^ii—Sr1—F1^v	85.18 (10)	Hf1^vi—Sr1—Sr1^viii	56.762 (15)
F5^iv—Sr1—F1^v	86.08 (10)	Hf1—F1—Sr1^ii	121.16 (11)
F3—Sr1—F1^v	127.85 (10)	Hf1—F1—Sr1^iii	123.02 (12)
F6^ii—Sr1—F1^vi	73.55 (10)	Sr2^ii—F1—Sr1^iii	115.75 (10)
F5^iv—Sr1—F1^vi	72.96 (10)	Hf1—F2—Hf1^i	114.14 (11)
F3—Sr1—F1^vi	143.98 (10)	Hf1—F2—Sr1^iv	136.42 (10)
F1^v—Sr1—F1^vi	64.25 (10)	Hf1^i—F2—Sr1^iv	109.44 (9)
F6^ii—Sr1—F4	76.24 (9)	Hf1—F3—Sr1	115.10 (12)
F5^iv—Sr1—F4	133.63 (9)	Hf1—F4—Sr1	108.74 (11)
F3—Sr1—F4	59.73 (8)	Hf1—F4—Sr1^ii	110.72 (10)
F1^v—Sr1—F4	126.48 (9)	Sr2—F4—Sr1^ii	140.23 (10)
F1^vi—Sr1—F4	146.79 (8)	Hf1—F5—Sr1^vii	161.74 (15)
F6^ii—Sr1—F4^v	103.22 (10)	Hf1—F6—Sr1^v	160.15 (15)
F5^iv—Sr1—F4^v	98.59 (9)

Symmetry codes: (i) −x+2, −y, −z+2; (ii) −x+1, y+1/2, −z+3/2; (iii) x, −y+1/2, z+1/2; (iv) −x+2, y−1/2, −z+3/2; (v) −x+1, y−1/2, −z+3/2; (vi) x, −y+1/2, z−1/2; (vii) −x+2, y+1/2, −z+3/2; (viii) −x+1, −y, −z+1.