Syntheses, Raman spectroscopy and crystal structures of alkali hexa-fluorido-rhenates(IV) revisited.

The A2[ReF6] (A = K, Rb and Cs) salts are isotypic and crystallize in the trigonal space group type P [Formula: see text] m1, adopting the K2[GeF6] structure type. Common to all A2[ReF6] structures are slightly distorted octa-hedral [ReF6]2- anions with an average Re-F bond length of 1.951 (8) Å. In those salts, symmetry lowering on the local [ReF6]2- anions from Oh (free anion) to D3d (solid-state structure) occur. The distortions of the [ReF6]2- anions, as observed in their Raman spectra, are correlated to the size of the counter-cations.

Chemical context

The hexa­fluorido­rhenate(IV) anion has been known for 80 years but its chemistry is understudied with respect to the heavier halogen analogs (Ruff & Kwasnik, 1934 ▸). The scarcity of [ReF6]2− salts is attributed to the difficulties in their preparation and purification. K2[ReF6] was the first hexa­fluorido­rhenate(IV) salt to be reported; it was prepared from the solid-state melting reaction (SSMR) of K2[ReBr6] with KHF2 (Ruff & Kwasnik, 1934 ▸). Almost two decades later, ten salts comprising the [ReF6]2– anion and with different counter-cations (Rb+, Cs+, PPh4 + (Ph = C6H5), [Ni(NH3)6]2+, [Co(NH3)6]3+, {[Co(NH3)6](NO3)}2+, {[Cr(NH3)6](NO3)}2+, [Co(NH3)5Cl]2+, [Cr(NH3)5Cl]2+, [Co(NH3)4(CO3)]2+) had been reported (Peacock, 1956 ▸; Weise, 1956 ▸; Pedersen et al., 2014 ▸; Brauer & Allardt, 1962 ▸). Those salts were prepared by cation metathesis starting from (NH4)2[ReF6] or K2[ReF6]. However, the synthetic procedure to prepare (NH4)2[ReF6] or K2[ReF6] was not explained in detail. To date, only the structures of two [ReF6]2− salts have been characterized by single crystal X-ray diffraction (SCXRD): K2[ReF6] (measured at 292 K) and (PPh4)2[ReF6]·H2O (measured at 122 K) (Clark & Russell, 1978 ▸; Pedersen et al., 2014 ▸). Similarly, the synthesis of the K2[TcF6] congener, which was reported in 1963, involves the SSMR of K2[TcBr6] with KHF2 followed by an aqueous work-up (Schwochau & Herr, 1963 ▸). However, [TcF6]2− salts have been reinvestigated recently (Balasekaran et al., 2013 ▸), and various routes for the different salts of A 2[TcF6] [A = Na, K, Rb, Cs and N(CH3)4] were reported. These salts were characterized by Raman and IR spectroscopy and by SCXRD. The A 2[ReF6] salts could serve as suitable precursors to explore the chemistry of rhenium in the oxidation state IV.

Here, we revisited the synthesis of A 2[ReF6] (A = K, Rb, Cs) salts and report their crystal structures determined from single crystal data, and their Raman spectra.

Structural commentary

The title alkaline metal salts A 2[ReF6] (A = K, Rb, Cs) are isotypic. They adopt the K2[GeF6] structure type (Hoard & Vincent, 1939 ▸) and crystallize in the trigonal space group type P m1 (Table 1 ▸), just like the related A 2[TcF6] (A = K, Rb, Cs) compounds (Balasekaran et al., 2013 ▸). Selected bond lengths and angles of the series of [ReF6]2− anions of the present work and the reported [TcF6]2− salts (Balasekaran et al., 2013 ▸) are presented in Table 1 ▸. Representative for all other title compounds, the [ReF6]2− anion of the Cs2[ReF6] salt is given in Fig. 1 ▸. The ReIV atom is located on a position with site symmetry m. (Wyckoff position 1a) at the origin of the trigonal unit cell. The six symmetry-related fluorine ligands form a slightly distorted octa­hedral coordination sphere around the rhenium(IV) atom. The Re—F bond lengths for the K, Rb, and Cs salts of [ReF6]2−, 1.948 (3), 1.945 (7) and 1.9594 (18) Å, respectively, are longer than the Tc—F bond lengths for the congener K, Rb, and Cs salts of [TcF6]2−, 1.928 (1), 1.933 (3), and 1.935 (5) Å, respectively (Balasekaran et al., 2013 ▸).

Table 1

Structural details (Å, °) of the [ReF6]2− anion in this study and of the related anion in [TcF6]2− salts

	M—F, M = Re	F—M—F, M = Re	M—F, M = Tc	F—M—F, M = Tc
K2[MF6]	1.948 (3)	86.08 (12), 93.92 (12), 180	1.928 (6)	86.93 (5), 93.07 (5), 180
Rb2[MF6]	1.945 (7)	86.5 (3), 93.5 (3), 180	1.933 (3)	87.2 (2), 92.8 (2), 180
Cs2[MF6]	1.9594 (18)	86.86 (7), 93.14 (7), 180	1.935 (5)	87.8 (2), 92.2 (2), 180

Note: (a) Balasekaran et al. (2013 ▸).

Figure 1

Representation of the [ReF6]2− anion in Cs2[ReF6]. Displacement ellipsoids are drawn at the 50% probability level. [Symmetry codes: (i) −x, −y, −z; (ii) x − y, x, −z; (iii) −x + y, −x, z; (iv) −y, x − y, z; (v) y, −x + y, −z.]

In A 2[ReF6] (A = K+, Rb+, Cs+), each cation is located on a position with site symmetry 3m. (Wyckoff position 2d) and is surrounded by twelve neighboring F atoms resulting in a [3 + 6 + 3] arrangement with three groups of fluoride ligands with distances of 3.0955 (19) Å (three of such), 3.1655 (6) Å (six of such), and 3.224 (2) Å (three of such) for the Cs+ salt as a representative of the three [ReF6]2− salts. These bond-length distributions are also found in the K+ and Rb+ salts of the [ReF6]2− complexes. This correlates well and confirms that A 2[ReF6] salts are isotypic with K2[GeF6] and the congener A 2[TcF6] (A = K+, Rb+, Cs+) (Balasekaran et al., 2013 ▸; Hoard & Vincent, 1939 ▸). In comparison with the previous structure determination of K2[ReF6] (Clark & Russell, 1978 ▸), the current redetermination resulted in better reliability factors, together with a more precise determination of lattice parameters and atomic coordinates.

Raman spectroscopy

As reported previously for K2[ReF6] and A 2[TcF6] (A = K, Rb, Cs) (Bettinelli et al., 1987 ▸; Balasekaran et al., 2013 ▸), the [ReF6]2− anions are compressed along the crystallographic c axis, thus lowering the ideal mol­ecular symmetry of the [ReF6]2− anions from O to D 3 in the solid state. The representive unit-cell plot of Cs2[ReF6] is given in Fig. 2 ▸. The effect of symmetry lowering among the alkali metal salts of [TcF6]2− and its correlation with the vibrational spectra are well described (Balasekaran et al., 2013 ▸). Here, a similar trend occurs for the A 2[ReF6] series (A = K, Rb, Cs; Fig. 3 ▸). In the case of K2[ReF6], the Raman spectrum exhibits four bands at 624, 539, 244 and 224 cm−1. The latter two vibrations correspond to the F 2 band split due to the symmetry lowering. In the Raman spectra of A 2[MF6] complexes (A = K, Rb, Cs; M = Tc, Re), the F 2 splitting decreases from K2[ReF6] to Cs2[ReF6] due to differences in M—F bond length. Furthermore, the slight increase of M—F bond lengths from K2[MF6] to Cs2[MF6] are well represented in the Raman spectra which causes the Raman bands to shift to lower wavenumbers.

Figure 2

A packing diagram of Cs2[ReF6]. Displacement ellipsoids are drawn at the 50% probability level.

Figure 3

Raman spectra of A 2[ReF6] (A = K, Rb, Cs).

Synthesis and crystallization

Ammonium perrhenate, ammonium bifluoride, potassium fluoride, rubidium fluoride, cesium fluoride, and hydro­bromic acid (48%) were purchased from Sigma Aldrich and used without any further purification. This work was performed in a well-ventilated fume hood due to the corrosive nature of bifluoride. K2[ReBr6] was prepared as described in the literature (Watt et al., 1963 ▸), and the detailed synthesis of A 2[ReF6] (A = K, Rb, Cs) is described below. Single crystals of A 2[ReF6] (A = K, Rb, Cs) were obtained by slow evaporation at room temperature of an aqueous solution of the respective salt.

Synthesis of K

K2[ReF6] was prepared by melting K2[ReBr6] (2 g, 2.69 mmol) with excess KHF2 (14 g, 0.18 mol) in a nickel crucible at 673 K for 30 min in a box furnace. The resulting greyish solid product formed was allowed to cool to room temperature and was washed first with MeOH (4 × 10 ml). Subsequently, the product was washed with several aliquots of an H2O/MeOH mixture (3 × 5 ml, 1:4 volume ratios) and centrifuged. The pink solid obtained was dissolved in warm water (5–10 ml, 353 K) and evaporated slowly at room temperature. The resultant pink crystals of K2[ReF6] were recrystallized from warm water (5 ml, 353 K) and colorless crystals of K2[ReF6] were obtained. Yield: 661 mg, 1.7 mmol (65%). IR (KBr, cm−1): 518, 484 sh (Re—F).

Syntheses of = Rb, Cs) salts

K2[ReF6] (151 mg, 0.4 mmol) was dissolved in 4 ml of hot water (353 K). MF (M = Rb, Cs) (0.8 mmol) dissolved in 1 ml of hot water (353 K) was added dropwise. The solution was allowed to evaporate slowly at room temperature. Crystals of Rb2[ReF6] and Cs2[ReF6] were formed in 24 h and washed first with cold water (3 × 2 ml) to remove other fluoride impurities followed by iso­propanol (3 × 1 ml), and diethyl ether (3 × 1 ml). Rb2[ReF6] yield: 156 mg, 0.33 mmol (83%). IR (KBr, cm−1): 521 (Re—F). Cs2[ReF6] yield: 175 mg, 0.276 mmol (77%). IR (KBr, cm−1): 507, 480 sh (Re—F).

IR spectra were measured on a Shimadzu IR Affinity-1 spectrometer between 400 and 4000 cm−1. Raman spectra were recorded on a HORIBA T64000 triple spectrometer operating at 30 mW in subtractive mode. The spectra were taken from pure single crystals at room temperature using the 514.5 nm (Kr/Ar) laser line.

Refinement

Crystal data, data collection and structure refinement details are summarized in Table 2 ▸.

Table 2

Experimental details

	K2[ReF6]	Rb2[ReF6]	Cs2[ReF6]
Crystal data
M r	378.40	471.14	566.02
Crystal system, space group	Trigonal, P m1	Trigonal, P m1	Trigonal, P m1
Temperature (K)	100	100	100
a, c (Å)	5.834 (2), 4.546 (2)	5.9926 (13), 4.7177 (10)	6.268 (1), 4.931 (1)
V (Å3)	134.00 (11)	146.72 (7)	167.77 (6)
Z	1	1	1
Radiation type	Mo Kα	Mo Kα	Mo Kα
μ (mm−1)	24.26	37.22	28.83
Crystal size (mm)	0.10 × 0.07 × 0.04	0.08 × 0.07 × 0.04	0.25 × 0.12 × 0.11
Data collection
Diffractometer	Bruker D8 QUEST	Bruker D8 QUEST	Bruker D8 QUEST
Absorption correction	Multi-scan (SADABS; Bruker, 2015 ▸)	Numerical (SADABS; Bruker, 2015 ▸)	Multi-scan (SADABS; Bruker, 2015 ▸)
T min, T max	0.14, 0.44	0.11, 0.30	0.05, 0.15
No. of measured, independent and observed [I > 2σ(I)] reflections	2148, 180, 180	1526, 115, 111	2683, 218, 218
R int	0.054	0.073	0.040
(sin θ/λ)max (Å−1)	0.714	0.593	0.713
Refinement
R[F 2 > 2σ(F 2)], wR(F 2), S	0.016, 0.041, 1.13	0.027, 0.074, 1.30	0.013, 0.036, 1.25
No. of reflections	180	115	218
No. of parameters	12	12	13
Δρmax, Δρmin (e Å−3)	1.80, −1.37	1.91, −1.36	0.68, −2.92

Computer programs: APEX3 and SAINT (Bruker, 2015 ▸), SHELXS (Sheldrick, 2008 ▸), SHELXL2014 (Sheldrick, 2015 ▸), DIAMOND (Brandenburg, 2007 ▸) and publCIF (Westrip, 2010 ▸).

Crystal structure: contains datablock(s) global, global_1, global_2, SMB_K2ReF6_1, SMB_Rb2ReF6_j, SMB_Cs2ReF6_1a. DOI: 10.1107/S2056989018005297/wm5432sup1.cif

Structure factors: contains datablock(s) SMB_K2ReF6_1. DOI: 10.1107/S2056989018005297/wm5432SMB_K2ReF6_1sup2.hkl

Structure factors: contains datablock(s) SMB_Cs2ReF6_1a. DOI: 10.1107/S2056989018005297/wm5432SMB_Cs2ReF6_1asup3.hkl

Structure factors: contains datablock(s) SMB_Rb2ReF6_j. DOI: 10.1107/S2056989018005297/wm5432SMB_Rb2ReF6_jsup4.hkl

Structure factors: contains datablock(s) SMB_ReF6_f. DOI: 10.1107/S2056989018005297/wm5432SMB_ReF6_fsup5.hkl

Hexafluororhenate(IV) - revisited. DOI: 10.1107/S2056989018005297/wm5432sup6.pdf

Syntheses, Raman spectroscopy and crystal structures of alkali hexafluoridorhenates(IV) - revisited. DOI: 10.1107/S2056989018005297/wm5432sup7.pdf

CCDC references: 1834616, 1834615, 1834614

Additional supporting information: crystallographic information; 3D view; checkCIF report

K2[ReF6]	Dx = 4.689 Mg m−3
Mr = 378.40	Mo Kα radiation, λ = 0.71073 Å
Trigonal, P3m1	Cell parameters from 2236 reflections
a = 5.834 (2) Å	θ = 4.0–30.5°
c = 4.546 (2) Å	µ = 24.26 mm−1
V = 134.00 (11) Å3	T = 100 K
Z = 1	Hexagonal, translucent colourless
F(000) = 167	0.10 × 0.07 × 0.04 mm

Bruker D8 QUEST diffractometer	180 independent reflections
Radiation source: sealed tube, Siemens KFFMo2K-90	180 reflections with I > 2σ(I)
Curved graphite monochromator	Rint = 0.054
Detector resolution: 8.3333 pixels mm-1	θmax = 30.5°, θmin = 4.0°
φ and ω scans	h = −8→8
Absorption correction: multi-scan (SADABS; Bruker, 2015)	k = −8→8
Tmin = 0.14, Tmax = 0.44	l = −6→6
2148 measured reflections

Refinement on F2	0 restraints
Least-squares matrix: full	Primary atom site location: structure-invariant direct methods
R[F2 > 2σ(F2)] = 0.016	Secondary atom site location: difference Fourier map
wR(F2) = 0.041	w = 1/[σ2(Fo2) + (0.0194P)2 + 0.517P] where P = (Fo2 + 2Fc2)/3
S = 1.13	(Δ/σ)max < 0.001
180 reflections	Δρmax = 1.80 e Å−3
12 parameters	Δρmin = −1.37 e Å−3

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.

	x	y	z	Uiso*/Ueq
Re1	0	0	0	0.00863 (14)
F1	0.3254 (6)	0.1627 (3)	0.2299 (6)	0.0137 (5)
K1	0.3333	0.6667	0.2955 (4)	0.0111 (3)

	U11	U22	U33	U12	U13	U23
Re1	0.00883 (16)	0.00883 (16)	0.0082 (2)	0.00441 (8)	0	0
F1	0.0119 (13)	0.0162 (10)	0.0117 (12)	0.0060 (6)	−0.0012 (10)	−0.0006 (5)
K1	0.0118 (5)	0.0118 (5)	0.0096 (6)	0.0059 (2)	0	0

Re1—F1	1.948 (3)	F1—K1viii	2.9325 (10)
Re1—F1i	1.948 (3)	F1—K1vi	2.946 (3)
Re1—F1ii	1.948 (3)	K1—F1xi	2.762 (3)
Re1—F1iii	1.948 (3)	K1—F1x	2.762 (3)
Re1—F1iv	1.948 (3)	K1—F1xii	2.762 (3)
Re1—F1v	1.948 (3)	K1—F1xiii	2.9325 (11)
Re1—K1i	3.6263 (13)	K1—F1xiv	2.9325 (10)
Re1—K1vi	3.6263 (13)	K1—F1iv	2.9325 (11)
Re1—K1vii	3.6263 (13)	K1—F1xv	2.9325 (11)
Re1—K1	3.6263 (13)	K1—F1xvi	2.9325 (11)
Re1—K1viii	3.6263 (13)	K1—F1xvii	2.946 (3)
Re1—K1ix	3.6263 (13)	K1—F1ii	2.946 (3)
F1—K1x	2.762 (3)	K1—F1vi	2.946 (3)
F1—K1	2.9325 (11)
F1—Re1—F1i	180.0	K1—F1—K1viii	168.22 (13)
F1—Re1—F1ii	86.08 (12)	Re1—F1—K1vi	93.38 (11)
F1i—Re1—F1ii	93.92 (12)	K1x—F1—K1vi	105.55 (10)
F1—Re1—F1iii	93.92 (12)	K1—F1—K1vi	94.27 (6)
F1i—Re1—F1iii	86.08 (12)	K1viii—F1—K1vi	94.27 (6)
F1ii—Re1—F1iii	180.00 (19)	F1xi—K1—F1x	65.46 (11)
F1—Re1—F1iv	93.92 (12)	F1xi—K1—F1xii	65.46 (11)
F1i—Re1—F1iv	86.08 (12)	F1x—K1—F1xii	65.46 (11)
F1ii—Re1—F1iv	86.08 (12)	F1xi—K1—F1xiii	62.44 (10)
F1iii—Re1—F1iv	93.92 (12)	F1x—K1—F1xiii	127.81 (6)
F1—Re1—F1v	86.08 (12)	F1xii—K1—F1xiii	95.05 (6)
F1i—Re1—F1v	93.92 (12)	F1xi—K1—F1xiv	62.44 (10)
F1ii—Re1—F1v	93.92 (12)	F1x—K1—F1xiv	95.05 (6)
F1iii—Re1—F1v	86.08 (12)	F1xii—K1—F1xiv	127.81 (6)
F1iv—Re1—F1v	180.00 (7)	F1xiii—K1—F1xiv	58.10 (11)
F1—Re1—K1i	126.206 (14)	F1xi—K1—F1iv	95.05 (6)
F1i—Re1—K1i	53.794 (14)	F1x—K1—F1iv	127.81 (6)
F1ii—Re1—K1i	125.81 (9)	F1xii—K1—F1iv	62.44 (10)
F1iii—Re1—K1i	54.19 (9)	F1xiii—K1—F1iv	61.22 (12)
F1iv—Re1—K1i	126.205 (14)	F1xiv—K1—F1iv	118.98 (2)
F1v—Re1—K1i	53.795 (14)	F1xi—K1—F1xv	95.05 (6)
F1—Re1—K1vi	54.19 (9)	F1x—K1—F1xv	62.44 (10)
F1i—Re1—K1vi	125.81 (9)	F1xii—K1—F1xv	127.81 (6)
F1ii—Re1—K1vi	53.794 (14)	F1xiii—K1—F1xv	118.98 (2)
F1iii—Re1—K1vi	126.206 (14)	F1xiv—K1—F1xv	61.22 (12)
F1iv—Re1—K1vi	126.205 (14)	F1iv—K1—F1xv	168.22 (13)
F1v—Re1—K1vi	53.795 (14)	F1xi—K1—F1xvi	127.81 (6)
K1i—Re1—K1vi	107.11 (3)	F1x—K1—F1xvi	62.44 (10)
F1—Re1—K1vii	125.81 (9)	F1xii—K1—F1xvi	95.05 (6)
F1i—Re1—K1vii	54.19 (9)	F1xiii—K1—F1xvi	168.22 (13)
F1ii—Re1—K1vii	126.206 (14)	F1xiv—K1—F1xvi	118.98 (2)
F1iii—Re1—K1vii	53.794 (14)	F1iv—K1—F1xvi	118.98 (2)
F1iv—Re1—K1vii	53.795 (14)	F1xv—K1—F1xvi	58.10 (11)
F1v—Re1—K1vii	126.205 (14)	F1xi—K1—F1	127.81 (6)
K1i—Re1—K1vii	72.89 (3)	F1x—K1—F1	95.05 (6)
K1vi—Re1—K1vii	180.0	F1xii—K1—F1	62.44 (10)
F1—Re1—K1	53.794 (14)	F1xiii—K1—F1	118.98 (2)
F1i—Re1—K1	126.206 (14)	F1xiv—K1—F1	168.22 (13)
F1ii—Re1—K1	54.19 (9)	F1iv—K1—F1	58.09 (11)
F1iii—Re1—K1	125.81 (9)	F1xv—K1—F1	118.98 (2)
F1iv—Re1—K1	53.794 (14)	F1xvi—K1—F1	61.22 (11)
F1v—Re1—K1	126.206 (14)	F1xi—K1—F1xvii	105.55 (10)
K1i—Re1—K1	180.0	F1x—K1—F1xvii	144.70 (4)
K1vi—Re1—K1	72.89 (3)	F1xii—K1—F1xvii	144.70 (4)
K1vii—Re1—K1	107.11 (3)	F1xiii—K1—F1xvii	53.80 (10)
F1—Re1—K1viii	53.795 (14)	F1xiv—K1—F1xvii	53.80 (10)
F1i—Re1—K1viii	126.205 (14)	F1iv—K1—F1xvii	85.73 (6)
F1ii—Re1—K1viii	126.206 (14)	F1xv—K1—F1xvii	85.73 (6)
F1iii—Re1—K1viii	53.794 (14)	F1xvi—K1—F1xvii	114.69 (6)
F1iv—Re1—K1viii	125.81 (9)	F1—K1—F1xvii	114.69 (6)
F1v—Re1—K1viii	54.19 (9)	F1xi—K1—F1ii	144.70 (4)
K1i—Re1—K1viii	72.90 (3)	F1x—K1—F1ii	144.70 (4)
K1vi—Re1—K1viii	72.90 (3)	F1xii—K1—F1ii	105.55 (10)
K1vii—Re1—K1viii	107.10 (3)	F1xiii—K1—F1ii	85.73 (6)
K1—Re1—K1viii	107.10 (3)	F1xiv—K1—F1ii	114.69 (6)
F1—Re1—K1ix	126.205 (14)	F1iv—K1—F1ii	53.80 (10)
F1i—Re1—K1ix	53.795 (14)	F1xv—K1—F1ii	114.69 (6)
F1ii—Re1—K1ix	53.794 (14)	F1xvi—K1—F1ii	85.73 (6)
F1iii—Re1—K1ix	126.206 (14)	F1—K1—F1ii	53.80 (10)
F1iv—Re1—K1ix	54.19 (9)	F1xvii—K1—F1ii	60.91 (10)
F1v—Re1—K1ix	125.81 (9)	F1xi—K1—F1vi	144.70 (4)
K1i—Re1—K1ix	107.10 (3)	F1x—K1—F1vi	105.55 (10)
K1vi—Re1—K1ix	107.10 (3)	F1xii—K1—F1vi	144.70 (4)
K1vii—Re1—K1ix	72.90 (3)	F1xiii—K1—F1vi	114.69 (6)
K1—Re1—K1ix	72.90 (3)	F1xiv—K1—F1vi	85.73 (6)
K1viii—Re1—K1ix	180.0	F1iv—K1—F1vi	114.69 (6)
Re1—F1—K1x	161.08 (14)	F1xv—K1—F1vi	53.80 (10)
Re1—F1—K1	93.79 (6)	F1xvi—K1—F1vi	53.80 (10)
K1x—F1—K1	84.95 (6)	F1—K1—F1vi	85.73 (6)
Re1—F1—K1viii	93.79 (6)	F1xvii—K1—F1vi	60.91 (10)
K1x—F1—K1viii	84.95 (6)	F1ii—K1—F1vi	60.91 (10)

Rb2[ReF6]	Dx = 5.332 Mg m−3
Mr = 471.14	Mo Kα radiation, λ = 0.71073 Å
Trigonal, P3m1	Cell parameters from 1612 reflections
a = 5.9926 (13) Å	θ = 3.9–28.3°
c = 4.7177 (10) Å	µ = 37.22 mm−1
V = 146.72 (7) Å3	T = 100 K
Z = 1	Hexagonal plate, translucent colourless
F(000) = 203	0.08 × 0.07 × 0.04 mm

Bruker D8 QUEST diffractometer	115 independent reflections
Radiation source: sealed tube, Siemens KFFMo2K-90	111 reflections with I > 2σ(I)
Curved graphite monochromator	Rint = 0.073
Detector resolution: 8.3333 pixels mm-1	θmax = 24.9°, θmin = 3.9°
φ and ω scans	h = −7→7
Absorption correction: numerical (SADABS; Bruker, 2015)	k = −7→7
Tmin = 0.11, Tmax = 0.30	l = −5→5
1526 measured reflections

Refinement on F2	0 restraints
Least-squares matrix: full	Primary atom site location: heavy-atom method
R[F2 > 2σ(F2)] = 0.027	Secondary atom site location: difference Fourier map
wR(F2) = 0.074	w = 1/[σ2(Fo2) + (0.0175P)2 + 3.5548P] where P = (Fo2 + 2Fc2)/3
S = 1.30	(Δ/σ)max < 0.001
115 reflections	Δρmax = 1.91 e Å−3
12 parameters	Δρmin = −1.36 e Å−3

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.

	x	y	z	Uiso*/Ueq
Re1	0	0	0	0.0157 (5)
F1	0.3151 (14)	0.1576 (7)	0.2231 (15)	0.0151 (17)
Rb1	0.3333	0.6667	0.2971 (4)	0.0138 (6)

	U11	U22	U33	U12	U13	U23
Re1	0.0133 (6)	0.0133 (6)	0.0205 (8)	0.0066 (3)	0	0
F1	0.015 (4)	0.017 (3)	0.012 (3)	0.0077 (19)	0.001 (3)	0.0007 (14)
Rb1	0.0131 (8)	0.0131 (8)	0.0152 (12)	0.0065 (4)	0	0

Re1—F1i	1.945 (7)	F1—Rb1viii	3.0181 (11)
Re1—F1ii	1.945 (7)	F1—Rb1vi	3.058 (7)
Re1—F1iii	1.945 (7)	Rb1—F1xi	2.907 (7)
Re1—F1iv	1.945 (7)	Rb1—F1x	2.907 (7)
Re1—F1v	1.945 (7)	Rb1—F1xii	2.907 (7)
Re1—F1	1.945 (7)	Rb1—F1xiii	3.0181 (11)
Re1—Rb1i	3.7330 (10)	Rb1—F1xiv	3.0181 (11)
Re1—Rb1vi	3.7330 (11)	Rb1—F1v	3.0181 (11)
Re1—Rb1vii	3.7330 (11)	Rb1—F1xv	3.0181 (11)
Re1—Rb1	3.7330 (10)	Rb1—F1xvi	3.0181 (11)
Re1—Rb1viii	3.7330 (11)	Rb1—F1xvii	3.058 (7)
Re1—Rb1ix	3.7330 (11)	Rb1—F1ii	3.058 (7)
F1—Rb1x	2.907 (7)	Rb1—F1vi	3.058 (7)
F1—Rb1	3.0181 (11)
F1i—Re1—F1ii	93.5 (3)	Rb1—F1—Rb1viii	166.2 (3)
F1i—Re1—F1iii	86.5 (3)	Re1—F1—Rb1vi	93.9 (2)
F1ii—Re1—F1iii	180.0 (3)	Rb1x—F1—Rb1vi	104.5 (2)
F1i—Re1—F1iv	93.5 (3)	Rb1—F1—Rb1vi	94.26 (14)
F1ii—Re1—F1iv	93.5 (3)	Rb1viii—F1—Rb1vi	94.26 (14)
F1iii—Re1—F1iv	86.5 (3)	F1xi—Rb1—F1x	65.8 (2)
F1i—Re1—F1v	86.5 (3)	F1xi—Rb1—F1xii	65.8 (2)
F1ii—Re1—F1v	86.5 (3)	F1x—Rb1—F1xii	65.8 (2)
F1iii—Re1—F1v	93.5 (3)	F1xi—Rb1—F1xiii	62.7 (2)
F1iv—Re1—F1v	180.0	F1x—Rb1—F1xiii	128.31 (8)
F1i—Re1—F1	180.0	F1xii—Rb1—F1xiii	96.30 (14)
F1ii—Re1—F1	86.5 (3)	F1xi—Rb1—F1xiv	62.7 (2)
F1iii—Re1—F1	93.5 (3)	F1x—Rb1—F1xiv	96.30 (14)
F1iv—Re1—F1	86.5 (3)	F1xii—Rb1—F1xiv	128.31 (8)
F1v—Re1—F1	93.5 (3)	F1xiii—Rb1—F1xiv	56.0 (3)
F1i—Re1—Rb1i	53.64 (2)	F1xi—Rb1—F1v	96.30 (14)
F1ii—Re1—Rb1i	125.2 (2)	F1x—Rb1—F1v	128.31 (8)
F1iii—Re1—Rb1i	54.8 (2)	F1xii—Rb1—F1v	62.7 (2)
F1iv—Re1—Rb1i	53.64 (2)	F1xiii—Rb1—F1v	63.1 (3)
F1v—Re1—Rb1i	126.36 (2)	F1xiv—Rb1—F1v	118.68 (6)
F1—Re1—Rb1i	126.36 (2)	F1xi—Rb1—F1xv	96.30 (14)
F1i—Re1—Rb1vi	125.2 (2)	F1x—Rb1—F1xv	62.7 (2)
F1ii—Re1—Rb1vi	53.64 (2)	F1xii—Rb1—F1xv	128.31 (8)
F1iii—Re1—Rb1vi	126.36 (2)	F1xiii—Rb1—F1xv	118.68 (5)
F1iv—Re1—Rb1vi	53.64 (2)	F1xiv—Rb1—F1xv	63.1 (3)
F1v—Re1—Rb1vi	126.36 (2)	F1v—Rb1—F1xv	166.2 (3)
F1—Re1—Rb1vi	54.8 (2)	F1xi—Rb1—F1xvi	128.31 (8)
Rb1i—Re1—Rb1vi	106.77 (3)	F1x—Rb1—F1xvi	62.7 (2)
F1i—Re1—Rb1vii	54.8 (2)	F1xii—Rb1—F1xvi	96.30 (14)
F1ii—Re1—Rb1vii	126.36 (2)	F1xiii—Rb1—F1xvi	166.2 (3)
F1iii—Re1—Rb1vii	53.64 (2)	F1xiv—Rb1—F1xvi	118.68 (6)
F1iv—Re1—Rb1vii	126.36 (2)	F1v—Rb1—F1xvi	118.68 (5)
F1v—Re1—Rb1vii	53.64 (2)	F1xv—Rb1—F1xvi	56.0 (3)
F1—Re1—Rb1vii	125.2 (2)	F1xi—Rb1—F1	128.31 (8)
Rb1i—Re1—Rb1vii	73.23 (3)	F1x—Rb1—F1	96.30 (14)
Rb1vi—Re1—Rb1vii	180.0	F1xii—Rb1—F1	62.7 (2)
F1i—Re1—Rb1	126.36 (2)	F1xiii—Rb1—F1	118.68 (6)
F1ii—Re1—Rb1	54.8 (2)	F1xiv—Rb1—F1	166.2 (3)
F1iii—Re1—Rb1	125.2 (2)	F1v—Rb1—F1	56.0 (3)
F1iv—Re1—Rb1	126.36 (2)	F1xv—Rb1—F1	118.68 (5)
F1v—Re1—Rb1	53.64 (2)	F1xvi—Rb1—F1	63.1 (3)
F1—Re1—Rb1	53.64 (2)	F1xi—Rb1—F1xvii	104.5 (2)
Rb1i—Re1—Rb1	180.0	F1x—Rb1—F1xvii	144.30 (9)
Rb1vi—Re1—Rb1	73.23 (3)	F1xii—Rb1—F1xvii	144.30 (9)
Rb1vii—Re1—Rb1	106.77 (3)	F1xiii—Rb1—F1xvii	52.0 (2)
F1i—Re1—Rb1viii	126.36 (2)	F1xiv—Rb1—F1xvii	52.0 (2)
F1ii—Re1—Rb1viii	126.36 (2)	F1v—Rb1—F1xvii	85.74 (14)
F1iii—Re1—Rb1viii	53.64 (2)	F1xv—Rb1—F1xvii	85.74 (14)
F1iv—Re1—Rb1viii	54.8 (2)	F1xvi—Rb1—F1xvii	114.25 (9)
F1v—Re1—Rb1viii	125.2 (2)	F1—Rb1—F1xvii	114.25 (9)
F1—Re1—Rb1viii	53.64 (2)	F1xi—Rb1—F1ii	144.30 (9)
Rb1i—Re1—Rb1viii	73.23 (3)	F1x—Rb1—F1ii	144.30 (9)
Rb1vi—Re1—Rb1viii	73.23 (3)	F1xii—Rb1—F1ii	104.5 (2)
Rb1vii—Re1—Rb1viii	106.77 (3)	F1xiii—Rb1—F1ii	85.74 (14)
Rb1—Re1—Rb1viii	106.77 (3)	F1xiv—Rb1—F1ii	114.25 (9)
F1i—Re1—Rb1ix	53.64 (2)	F1v—Rb1—F1ii	52.0 (2)
F1ii—Re1—Rb1ix	53.64 (2)	F1xv—Rb1—F1ii	114.25 (9)
F1iii—Re1—Rb1ix	126.36 (2)	F1xvi—Rb1—F1ii	85.74 (14)
F1iv—Re1—Rb1ix	125.2 (2)	F1—Rb1—F1ii	52.0 (2)
F1v—Re1—Rb1ix	54.8 (2)	F1xvii—Rb1—F1ii	62.2 (2)
F1—Re1—Rb1ix	126.36 (2)	F1xi—Rb1—F1vi	144.30 (9)
Rb1i—Re1—Rb1ix	106.77 (3)	F1x—Rb1—F1vi	104.5 (2)
Rb1vi—Re1—Rb1ix	106.77 (3)	F1xii—Rb1—F1vi	144.30 (9)
Rb1vii—Re1—Rb1ix	73.23 (3)	F1xiii—Rb1—F1vi	114.25 (9)
Rb1—Re1—Rb1ix	73.23 (3)	F1xiv—Rb1—F1vi	85.74 (14)
Rb1viii—Re1—Rb1ix	180.0	F1v—Rb1—F1vi	114.25 (9)
Re1—F1—Rb1x	161.6 (3)	F1xv—Rb1—F1vi	52.0 (2)
Re1—F1—Rb1	95.10 (14)	F1xvi—Rb1—F1vi	52.0 (2)
Rb1x—F1—Rb1	83.70 (14)	F1—Rb1—F1vi	85.74 (14)
Re1—F1—Rb1viii	95.10 (14)	F1xvii—Rb1—F1vi	62.2 (2)
Rb1x—F1—Rb1viii	83.70 (14)	F1ii—Rb1—F1vi	62.2 (2)

Cs2[ReF6]	Dx = 5.602 Mg m−3
Mr = 566.02	Mo Kα radiation, λ = 0.71073 Å
Trigonal, P3m1	Cell parameters from 135 reflections
a = 6.268 (1) Å	θ = 3.8–32.6°
c = 4.931 (1) Å	µ = 28.83 mm−1
V = 167.77 (6) Å3	T = 100 K
Z = 1	Hexagonal plate, clear colourless
F(000) = 239	0.25 × 0.12 × 0.11 mm

Bruker D8 QUEST diffractometer	218 independent reflections
Radiation source: sealed tube, Siemens KFFMo2K-90	218 reflections with I > 2σ(I)
Curved graphite monochromator	Rint = 0.040
Detector resolution: 8.3333 pixels mm-1	θmax = 30.4°, θmin = 3.8°
φ and ω scans	h = −8→8
Absorption correction: multi-scan (SADABS; Bruker, 2015)	k = −8→8
Tmin = 0.05, Tmax = 0.15	l = −7→7
2683 measured reflections

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)] = 0.013	w = 1/[σ2(Fo2) + (0.0181P)2 + 0.1419P] where P = (Fo2 + 2Fc2)/3
wR(F2) = 0.036	(Δ/σ)max < 0.001
S = 1.25	Δρmax = 0.68 e Å−3
218 reflections	Δρmin = −2.92 e Å−3
13 parameters	Extinction correction: SHELXL2014 (Sheldrick, 2015)
0 restraints	Extinction coefficient: 0.029 (2)

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.

	x	y	z	Uiso*/Ueq
Re1	0	0	0	0.00427 (15)
F1	0.3027 (3)	0.15135 (17)	0.2165 (4)	0.0092 (4)
Cs1	0.3333	0.6667	0.30027 (9)	0.00615 (14)

	U11	U22	U33	U12	U13	U23
Re1	0.00483 (16)	0.00483 (16)	0.0032 (2)	0.00241 (8)	0	0
F1	0.0088 (8)	0.0107 (6)	0.0075 (9)	0.0044 (4)	−0.0023 (6)	−0.0012 (3)
Cs1	0.00661 (16)	0.00661 (16)	0.0052 (2)	0.00331 (8)	0	0

Re1—F1i	1.9594 (18)	F1—Cs1viii	3.1655 (6)
Re1—F1ii	1.9594 (18)	F1—Cs1vi	3.224 (2)
Re1—F1iii	1.9594 (18)	Cs1—F1xi	3.0955 (19)
Re1—F1iv	1.9594 (18)	Cs1—F1x	3.0955 (19)
Re1—F1v	1.9594 (18)	Cs1—F1xii	3.0955 (19)
Re1—F1	1.9594 (18)	Cs1—F1xiii	3.1655 (6)
Re1—Cs1i	3.9100 (6)	Cs1—F1xiv	3.1655 (6)
Re1—Cs1vi	3.9100 (6)	Cs1—F1iii	3.1655 (6)
Re1—Cs1vii	3.9100 (6)	Cs1—F1xv	3.1655 (6)
Re1—Cs1	3.9100 (6)	Cs1—F1xvi	3.1655 (6)
Re1—Cs1viii	3.9100 (6)	Cs1—F1xvii	3.224 (2)
Re1—Cs1ix	3.9100 (6)	Cs1—F1iv	3.224 (2)
F1—Cs1x	3.0955 (19)	Cs1—F1vi	3.224 (2)
F1—Cs1	3.1655 (6)
F1i—Re1—F1ii	93.14 (7)	Cs1—F1—Cs1viii	163.82 (6)
F1i—Re1—F1iii	86.86 (7)	Re1—F1—Cs1vi	94.78 (7)
F1ii—Re1—F1iii	180.00 (4)	Cs1x—F1—Cs1vi	102.55 (5)
F1i—Re1—F1iv	93.14 (7)	Cs1—F1—Cs1vi	94.07 (3)
F1ii—Re1—F1iv	93.14 (7)	Cs1viii—F1—Cs1vi	94.07 (3)
F1iii—Re1—F1iv	86.86 (7)	F1xi—Cs1—F1x	67.11 (6)
F1i—Re1—F1v	86.86 (7)	F1xi—Cs1—F1xii	67.11 (6)
F1ii—Re1—F1v	86.86 (7)	F1x—Cs1—F1xii	67.11 (6)
F1iii—Re1—F1v	93.14 (7)	F1xi—Cs1—F1xiii	62.38 (6)
F1iv—Re1—F1v	180.00 (8)	F1x—Cs1—F1xiii	129.122 (17)
F1i—Re1—F1	180.0	F1xii—Cs1—F1xiii	97.70 (3)
F1ii—Re1—F1	86.86 (7)	F1xi—Cs1—F1xiv	62.38 (6)
F1iii—Re1—F1	93.14 (7)	F1x—Cs1—F1xiv	97.70 (3)
F1iv—Re1—F1	86.86 (7)	F1xii—Cs1—F1xiv	129.122 (17)
F1v—Re1—F1	93.14 (7)	F1xiii—Cs1—F1xiv	53.43 (7)
F1i—Re1—Cs1i	53.533 (6)	F1xi—Cs1—F1iii	97.70 (3)
F1ii—Re1—Cs1i	53.533 (6)	F1x—Cs1—F1iii	129.122 (17)
F1iii—Re1—Cs1i	126.467 (6)	F1xii—Cs1—F1iii	62.38 (6)
F1iv—Re1—Cs1i	124.74 (6)	F1xiii—Cs1—F1iii	65.44 (7)
F1v—Re1—Cs1i	55.26 (6)	F1xiv—Cs1—F1iii	118.323 (15)
F1—Re1—Cs1i	126.467 (6)	F1xi—Cs1—F1xv	97.70 (3)
F1i—Re1—Cs1vi	124.74 (6)	F1x—Cs1—F1xv	62.38 (6)
F1ii—Re1—Cs1vi	53.533 (6)	F1xii—Cs1—F1xv	129.122 (17)
F1iii—Re1—Cs1vi	126.467 (6)	F1xiii—Cs1—F1xv	118.323 (14)
F1iv—Re1—Cs1vi	53.532 (6)	F1xiv—Cs1—F1xv	65.44 (7)
F1v—Re1—Cs1vi	126.468 (6)	F1iii—Cs1—F1xv	163.82 (6)
F1—Re1—Cs1vi	55.26 (6)	F1xi—Cs1—F1	129.123 (17)
Cs1i—Re1—Cs1vi	106.554 (9)	F1x—Cs1—F1	97.70 (3)
F1i—Re1—Cs1vii	55.26 (6)	F1xii—Cs1—F1	62.38 (6)
F1ii—Re1—Cs1vii	126.467 (6)	F1xiii—Cs1—F1	118.323 (15)
F1iii—Re1—Cs1vii	53.533 (6)	F1xiv—Cs1—F1	163.82 (6)
F1iv—Re1—Cs1vii	126.468 (6)	F1iii—Cs1—F1	53.43 (7)
F1v—Re1—Cs1vii	53.532 (6)	F1xv—Cs1—F1	118.323 (15)
F1—Re1—Cs1vii	124.74 (6)	F1xi—Cs1—F1xvi	129.122 (17)
Cs1i—Re1—Cs1vii	73.446 (9)	F1x—Cs1—F1xvi	62.38 (6)
Cs1vi—Re1—Cs1vii	180.0	F1xii—Cs1—F1xvi	97.70 (3)
F1i—Re1—Cs1	126.467 (6)	F1xiii—Cs1—F1xvi	163.82 (6)
F1ii—Re1—Cs1	126.467 (6)	F1xiv—Cs1—F1xvi	118.323 (15)
F1iii—Re1—Cs1	53.533 (6)	F1iii—Cs1—F1xvi	118.323 (15)
F1iv—Re1—Cs1	55.26 (6)	F1xv—Cs1—F1xvi	53.43 (7)
F1v—Re1—Cs1	124.74 (6)	F1—Cs1—F1xvi	65.44 (7)
F1—Re1—Cs1	53.533 (6)	F1xi—Cs1—F1xvii	102.55 (5)
Cs1i—Re1—Cs1	180.0	F1x—Cs1—F1xvii	143.51 (2)
Cs1vi—Re1—Cs1	73.447 (8)	F1xii—Cs1—F1xvii	143.51 (2)
Cs1vii—Re1—Cs1	106.553 (8)	F1xiii—Cs1—F1xvii	49.86 (5)
F1i—Re1—Cs1viii	126.467 (6)	F1xiv—Cs1—F1xvii	49.86 (5)
F1ii—Re1—Cs1viii	55.26 (6)	F1iii—Cs1—F1xvii	85.93 (3)
F1iii—Re1—Cs1viii	124.74 (6)	F1xv—Cs1—F1xvii	85.93 (3)
F1iv—Re1—Cs1viii	126.467 (6)	F1—Cs1—F1xvii	113.96 (2)
F1v—Re1—Cs1viii	53.533 (6)	F1xvi—Cs1—F1xvii	113.96 (2)
F1—Re1—Cs1viii	53.533 (6)	F1xi—Cs1—F1iv	143.51 (2)
Cs1i—Re1—Cs1viii	73.447 (8)	F1x—Cs1—F1iv	143.51 (2)
Cs1vi—Re1—Cs1viii	73.447 (9)	F1xii—Cs1—F1iv	102.55 (5)
Cs1vii—Re1—Cs1viii	106.553 (9)	F1xiii—Cs1—F1iv	85.93 (3)
Cs1—Re1—Cs1viii	106.553 (9)	F1xiv—Cs1—F1iv	113.96 (2)
F1i—Re1—Cs1ix	53.533 (6)	F1iii—Cs1—F1iv	49.86 (5)
F1ii—Re1—Cs1ix	124.74 (6)	F1xv—Cs1—F1iv	113.96 (2)
F1iii—Re1—Cs1ix	55.26 (6)	F1—Cs1—F1iv	49.86 (5)
F1iv—Re1—Cs1ix	53.533 (6)	F1xvi—Cs1—F1iv	85.93 (3)
F1v—Re1—Cs1ix	126.467 (6)	F1xvii—Cs1—F1iv	64.10 (5)
F1—Re1—Cs1ix	126.467 (6)	F1xi—Cs1—F1vi	143.51 (2)
Cs1i—Re1—Cs1ix	106.553 (8)	F1x—Cs1—F1vi	102.55 (5)
Cs1vi—Re1—Cs1ix	106.553 (9)	F1xii—Cs1—F1vi	143.51 (2)
Cs1vii—Re1—Cs1ix	73.447 (9)	F1xiii—Cs1—F1vi	113.96 (2)
Cs1—Re1—Cs1ix	73.447 (9)	F1xiv—Cs1—F1vi	85.93 (3)
Cs1viii—Re1—Cs1ix	180.0	F1iii—Cs1—F1vi	113.96 (2)
Re1—F1—Cs1x	162.67 (9)	F1xv—Cs1—F1vi	49.86 (5)
Re1—F1—Cs1	96.61 (3)	F1—Cs1—F1vi	85.93 (3)
Cs1x—F1—Cs1	82.30 (3)	F1xvi—Cs1—F1vi	49.86 (5)
Re1—F1—Cs1viii	96.61 (3)	F1xvii—Cs1—F1vi	64.10 (5)
Cs1x—F1—Cs1viii	82.30 (3)	F1iv—Cs1—F1vi	64.10 (5)