[Cu₂(HF₂)(H₂O)₈][FeF₆]·2H₂O

The title compound, octaaqua­(hydrogenfluorido)dicopper(II) hexa­fluoridoferrate(III) dihydrate, was synthesized under hydro­thermal conditions. The Cu atom is coordinated by one F and five O atoms within a highly distorted octa­hedron, forming dimeric [Cu₂(H₂O)₈HF₂]³⁺ units by edge sharing. These units are hydrogen bonded to [FeF₆]³⁻ anions and to an inter­stitial water mol­ecule. The former feature Fe³⁺ on a special position (). The dimeric copper units are linked to adjacent dimers by F—H...F hydrogen bonds. Additional O—H...O and O—H...F hydrogen bonds help to consolidate the crystal packing.

Key indicators

• Single-crystal X-ray study
• T = 293 K
• Mean [sigma](Cu-O) = 0.003 Å
• R factor = 0.040
• wR factor = 0.080
• Data-to-parameter ratio = 24.8

checkCIF/PLATON results

No syntax errors found



Alert level B
PLAT417_ALERT_2_B Short Inter D-H..H-D       H42    ..  H52     ..       1.98 Ang.

Alert level C
            Value of measurement temperature given =   293.000
            Value of melting point given =     0.000
PLAT222_ALERT_3_C Large Non-Solvent    H     Ueq(max)/Ueq(min) ...       3.75 Ratio
PLAT232_ALERT_2_C Hirshfeld Test Diff (M-X)  Cu     --  F4      ..       6.96 su
PLAT355_ALERT_3_C Long    O-H Bond (0.82A)   O1     -   H11    ...       1.01 Ang.
PLAT355_ALERT_3_C Long    O-H Bond (0.82A)   O2     -   H21    ...       1.02 Ang.
PLAT355_ALERT_3_C Long    O-H Bond (0.82A)   O3     -   H31    ...       1.07 Ang.
PLAT355_ALERT_3_C Long    O-H Bond (0.82A)   O3     -   H32    ...       1.04 Ang.
PLAT355_ALERT_3_C Long    O-H Bond (0.82A)   O4     -   H41    ...       1.02 Ang.
PLAT355_ALERT_3_C Long    O-H Bond (0.82A)   O4     -   H42    ...       1.01 Ang.
PLAT355_ALERT_3_C Long    O-H Bond (0.82A)   O5     -   H51    ...       1.01 Ang.
PLAT355_ALERT_3_C Long    O-H Bond (0.82A)   O5     -   H52    ...       1.05 Ang.

Alert level G
PLAT860_ALERT_3_G Note: Number of Least-Squares Restraints .......         15
PLAT199_ALERT_1_G Check the Reported _cell_measurement_temperature        293 K
PLAT200_ALERT_1_G Check the Reported _diffrn_ambient_temperature .        293 K

   0 ALERT level A = In general: serious problem
   1 ALERT level B = Potentially serious problem
  10 ALERT level C = Check and explain
   3 ALERT level G = General alerts; check

   2 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   2 ALERT type 2 Indicator that the structure model may be wrong or deficient
  10 ALERT type 3 Indicator that the structure quality may be low
   0 ALERT type 4 Improvement, methodology, query or suggestion
   0 ALERT type 5 Informative message, check

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S1. Comment

[Cu(H₂O)₄H_0.5F]₂(FeF₆)(H₂O)₂ is the third hydrated copper–iron fluoride, the two previous ones being Cu₃Fe₂F₁₂(H₂O)₁₂ (Kummer & Babel, 1987) and CuFe₂F₈(H₂O)₂ (Leblanc & Ferey, 1990). In this new compound, an almost perfect (FeF₆)^3- octahedron, placed on an inversion center, is connected exclusively by hydrogen bonding to edge-sharing bi-octahedral [Cu₂(H₂O)₈HF₂]³⁺ units and to an interstitial water molecule. The copper atom can be considered to be five-coordinated by four water molecules and one F atom in the fashion of a square pyramid (Figure 1). The square is constituted by the F atom and three water molecules at distances in the 1.906–1.977 Å range (Table 1), whereas Ow(4), at the top of the pyramid is at 2.349 Å (Jahn-Teller distortion). However, if one considers the next neighbour Ow(3) at 2.715 Å as sixth ligand, thecoordination can be described as very distorted octahedral, yielding centrosymmetric, dimeric units with a Cu—Cu distance of 3.575 Å. The dimers are bonded to adjacent dimers through F(4) by a HF₂^- ion (figure 2), however the F—F distance (2.597 Å) is much larger (Table 2) than usually observed (2.27 Å in LiHF₂ (Frevel & Rinn, 1962), 2.28 in BaHF₃ (Massa & Herdtweck, 1983). Moreover, the hydrogen atom H(6) which would have been expected at the 1/2, 1/2, 1/2 special position, exactly at the middle of the F(4)—F(4) atoms, in order to form a linear (F—H—F)^- ion, was seen on the Fourier difference map as occupying more probably half a general position. It is then more a F—H···F bridge than a F—H—F one. Such asymmetrical F—H···F hydrogen bonding was observed in many cases for F—F distances going up to 2.686 Å in [(η⁵-C₅Me₅)NbF₄(HF)AsF₃]₂ (Roesky et al., 1990), 2.429 to 2.512 Å in [OsO₃F](HF)₂[AsF₆] (Gerken et al., 2002), 2.326 to 2.402 Å in Rb_2-xK_xZrF₆(HF)₂ (Gerasimenko et al., 2007).

The charge of the cations is balanced by the centrosymmetric anion [FeF₆]^3–. There are 14 water molecules around the (FeF₆)^3- octahedron, the H(51) atom corresponds to a bifurcated hydrogen bond towards F(2) and F(3) (figure 3). This helps the bond valence calculations to provide relatively satisfying results (Table 3), the largest disagreements being on O(4) and F(4). The contribution from the long Cu—Ow(3) distance is negligible.

Comparing with the Cu₃Fe₂F₁₂(H₂O)₁₂ crystal structure (Kummer & Babel, 1987), also triclinic, there are strong differences. The three copper atoms and two Fe atoms are all placed on inversion centers. One (FeF₆)^3- octahedron is isolated, and the other forms chiolite-like square meshes by sharing F corners with tetra-hydrated Cu(H₂O)₄F₂ elongated octahedra (the long distances are the two Cu—F ones, close to 2.32 Å for the three independent copper sites). In CuFe₂F₈(H₂O)₂ (Leblanc & Ferey, 1990), the CuF₄(H₂O)₂ octahedra show two long Cu—F distances (2.451 Å). So, in both cases, the long distances are Cu—F ones, which is not the case of the title compound.

A study of the magnetic properties is currently in progress.

Related literature

For other hydrated copper-iron fluorides, see: Kummer & Babel (1987); Leblanc & Ferey (1990). For F···F distances, see: Frevel & Rinn (1962); Massa & Herdtweck (1983). For asymmetrical F—H···F hydrogen bonding, see: Roesky et al. (1990); Gerasimenko et al. (2007); Gerken et al. (2002). For Pb₈MnFe₂F₂₄, see: Le Bail & Mercier (1992). Valence-bond analysis was performed according to the empirical expression from Brown & Altermatt (1985), using parameters for solids from Brese & O'Keeffe (1991).

S2. Experimental

Hydrothermal growth at 493 K from (2PbF₂/2CuF₂/FeF₃) in HF 5M or 1M solutions, produced large crystals which could be identified as corresponding to Cu₃Fe₂F₁₂(H₂O)₁₂ (Kummer & Babel, 1987) (5M solution) or to the title compound (1M). Both compounds are occurring with the same intense blue color and could have been confused if no powder pattern had been recorded. At other starting compositions, mixtures of both compounds could be observed, and also together especially with Pb₈CuFe₂F₂₄ (starting from 2PbF₂/CuF₂/2FeF₃ for instance), isostructural with Pb₈MnFe₂F₂₄ (Le Bail & Mercier, 1992).

S3. Refinement

The hydrogen atoms were all located on the difference Fourier map. Those of the water molecules were restrained to have Ow—H and H—H distances respectively close to 1.0 and 1.59 Å, their U_iso values were refined by groups of two. The hydrogen atom of the HF group was let at its difference Fourier map position with a fixed U_iso.

Computing details

Data collection: STADI4 (Stoe & Cie, 1998); cell refinement: STADI4 (Stoe & Cie, 1998); data reduction: X-RED (Stoe & Cie, 1998); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: DIAMOND (Brandenburg, 1999) and ORTEP-3 (Farrugia, 1997); software used to prepare material for publication: publCIF (Westrip, 2009).

Figures

	Fig. 1. ORTEP-3 view (Farrugia, 1997) of the FeF6^3- octahedron, the isolated water molecule and the Cu(H2O)4F^+ square-based pyramid which is forming octahedra dimeric units when considering the very long Cu-O3 distance (2.715Å). Displacement ellipsoids are shown at the 50% probability level. Symmetry-equivalent F atoms in the FeF6 group are generated by (i) -x, -y, -z. Symmetry-equivalent atoms in the [Cu2(H2O)8HF2]^3+ unit are generated by (iii) 1-x, 1-y, -z.
	Fig. 2. Crystal packing with view along [010]. Hydrogen bonding is shown as dashed lines. Copper coordination shown as distorted octahedra (adding O(3) at 2.715 Å from Cu) sharing an edge.
	Fig. 3. The 14 water molecules, from the Cu coordination sphere or isolated, involved in hydrogen bonding with the FeF6^3- octahedron.

Octaaqua(hydrogenfluorido)dicopper(II) hexafluoridoferrate(III) dihydrate

Crystal data

[Cu2(H2F)(H2O)8][FeF6]·2H2O	Z = 1
Mr = 516.12	F(000) = 257
Triclinic, P1	Dx = 2.294 Mg m^−3
Hall symbol: -P 1	Mo Kα radiation, λ = 0.71069 Å
a = 6.659 (2) Å	Cell parameters from 28 reflections
b = 7.450 (3) Å	θ = 2.7–35°
c = 8.377 (5) Å	µ = 3.91 mm^−1
α = 107.37 (4)°	T = 293 K
β = 106.89 (5)°	Platelet, blue
γ = 94.26 (3)°	0.11 × 0.10 × 0.05 mm
V = 373.6 (3) Å^3

Data collection

Siemens AED2 diffractometer	2044 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.000
Graphite monochromator	θmax = 35.0°, θmin = 2.7°
2θ/ω scans	h = −10→10
Absorption correction: gaussian (SHELX76; Sheldrick, 2008)	k = −12→11
Tmin = 0.698, Tmax = 0.845	l = 0→13
3303 measured reflections	3 standard reflections every 120 min
3303 independent reflections	intensity decay: 15%

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.040	H atoms treated by a mixture of independent and constrained refinement
wR(F^2) = 0.080	w = 1/[σ^2(Fo^2) + (0.03P)^2] where P = (Fo^2 + 2Fc^2)/3
S = 1.00	(Δ/σ)max = 0.004
3303 reflections	Δρmax = 0.62 e Å^−3
133 parameters	Δρmin = −0.63 e Å^−3
15 restraints	Extinction correction: SHELXL97 (Sheldrick, 2008), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.0072 (17)

Special details

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 (Ų)

	x	y	z	Uiso*/Ueq	Occ. (<1)
Cu	0.60473 (5)	0.55727 (4)	0.23479 (4)	0.01662 (8)
Fe	0.0000	0.0000	0.0000	0.01433 (10)
F1	0.2310 (3)	−0.0246 (2)	−0.0944 (2)	0.0270 (3)
F2	0.2029 (3)	0.1318 (2)	0.2331 (2)	0.0275 (3)
F3	−0.0278 (3)	0.2400 (2)	−0.0437 (2)	0.0272 (4)
F4	0.4365 (3)	0.5885 (3)	0.3872 (2)	0.0338 (4)
O1	0.5648 (3)	0.2890 (3)	0.2113 (3)	0.0283 (4)
O2	0.5992 (3)	0.8217 (3)	0.2411 (3)	0.0244 (4)
O3	0.7470 (3)	0.5094 (3)	0.0530 (3)	0.0219 (4)
O4	0.9139 (3)	0.6601 (3)	0.4849 (3)	0.0262 (4)
O5	0.2376 (4)	0.8884 (3)	0.4476 (3)	0.0291 (4)
H11	0.641 (6)	0.188 (5)	0.158 (6)	0.064 (10)*
H12	0.424 (5)	0.226 (6)	0.201 (6)	0.064 (10)*
H21	0.667 (7)	0.876 (7)	0.167 (5)	0.084 (12)*
H22	0.604 (8)	0.935 (5)	0.341 (5)	0.084 (12)*
H31	0.866 (7)	0.623 (6)	0.067 (8)	0.117 (16)*
H32	0.829 (8)	0.398 (6)	0.022 (8)	0.117 (16)*
H41	0.937 (15)	0.679 (15)	0.615 (5)	0.24 (3)*
H42	1.049 (10)	0.734 (13)	0.487 (12)	0.24 (3)*
H51	0.211 (11)	0.909 (10)	0.330 (6)	0.16 (2)*
H52	0.315 (12)	0.770 (8)	0.430 (10)	0.16 (2)*
H6	0.4219	0.4979	0.4375	0.080*	0.50

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cu	0.02080 (15)	0.01342 (14)	0.01901 (15)	0.00339 (11)	0.01121 (12)	0.00561 (11)
Fe	0.0157 (2)	0.0129 (2)	0.0174 (2)	0.00267 (17)	0.00901 (19)	0.00591 (18)
F1	0.0276 (8)	0.0268 (8)	0.0391 (9)	0.0100 (6)	0.0248 (7)	0.0139 (7)
F2	0.0255 (8)	0.0296 (8)	0.0217 (8)	−0.0025 (6)	0.0064 (6)	0.0038 (6)
F3	0.0295 (8)	0.0181 (7)	0.0442 (10)	0.0077 (6)	0.0185 (8)	0.0176 (7)
F4	0.0475 (11)	0.0338 (9)	0.0375 (10)	0.0184 (8)	0.0290 (9)	0.0192 (8)
O1	0.0285 (10)	0.0151 (8)	0.0470 (13)	0.0038 (7)	0.0227 (9)	0.0086 (8)
O2	0.0386 (11)	0.0138 (8)	0.0261 (10)	0.0040 (7)	0.0177 (8)	0.0074 (7)
O3	0.0270 (9)	0.0179 (8)	0.0281 (10)	0.0056 (7)	0.0191 (8)	0.0079 (7)
O4	0.0243 (9)	0.0267 (10)	0.0261 (10)	0.0042 (8)	0.0076 (8)	0.0074 (8)
O5	0.0359 (11)	0.0279 (10)	0.0264 (10)	0.0109 (9)	0.0128 (9)	0.0093 (8)

Geometric parameters (Å, º)

Cu—F4	1.9058 (19)	F2—O5^v	2.888 (3)
Cu—O1	1.939 (2)	F3—O3^iii	2.577 (2)
Cu—O2	1.958 (2)	F3—O3^vi	2.668 (3)
Cu—O3	1.977 (2)	F3—O5^vii	3.072 (4)
Cu—O4	2.349 (3)	F4—F4^iv	2.597 (4)
Fe—F1	1.9204 (16)	F4—O1	2.632 (3)
Fe—F2^i	1.930 (2)	F4—O5	2.676 (3)
Fe—F3	1.9402 (17)	F4—O2	2.730 (3)
F1—O1^ii	2.590 (3)	F4—O4	3.006 (3)
F1—O2^iii	2.595 (3)	O1—O3	2.804 (3)
F1—F2	2.709 (3)	O2—O5^viii	2.699 (3)
F1—F3^i	2.728 (2)	O2—O3	2.814 (3)
F1—F3	2.732 (2)	O2—O4	3.061 (3)
F1—F2^i	2.736 (3)	O2—O3^iii	3.113 (4)
F1—O1	3.051 (4)	O3—O3^iii	3.128 (4)
F2—O1	2.679 (3)	O4—O4^ix	2.768 (4)
F2—F3^i	2.714 (3)	O4—O5^x	2.793 (3)
F2—F3	2.759 (3)	Cu—O3^iii	2.715 (3)
F2—O4^iv	2.766 (3)	Cu—Cu^iii	3.575 (3)
F4—Cu—O1	86.42 (9)	F1^i—Fe—F2^i	89.43 (9)
F4—Cu—O2	89.89 (8)	F1—Fe—F3	90.08 (7)
O1—Cu—O2	171.49 (9)	F1^i—Fe—F3	89.92 (7)
F4—Cu—O3	173.09 (9)	F2^i—Fe—F3	89.06 (9)
O1—Cu—O3	91.47 (9)	F2—Fe—F3	90.94 (9)
O2—Cu—O3	91.30 (8)	H11—O1—H12	109 (3)
F4—Cu—O4	89.27 (9)	H21—O2—H22	104 (3)
O1—Cu—O4	97.50 (10)	H31—O3—H32	98 (3)
O2—Cu—O4	90.11 (9)	H41—O4—H42	103 (4)
O3—Cu—O4	97.53 (9)	H51—O5—H52	102 (3)
F1—Fe—F2^i	90.57 (9)

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

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O1—H11···F1^ii	1.00 (4)	1.59 (4)	2.590 (3)	173 (4)
O1—H12···F2	0.99 (4)	1.71 (4)	2.679 (3)	167 (4)
O2—H21···F1^iii	1.02 (5)	1.61 (5)	2.595 (3)	161 (4)
O2—H22···O5^viii	0.98 (4)	1.82 (4)	2.699 (3)	147 (5)
O3—H31···F3^iii	1.07 (5)	1.52 (5)	2.577 (2)	167 (5)
O3—H32···F3^x	1.04 (5)	1.64 (5)	2.668 (3)	171 (5)
O4—H41···F2^iv	1.02 (4)	2.07 (9)	2.766 (3)	123 (8)
O4—H42···O5^x	1.01 (9)	1.81 (9)	2.793 (3)	164 (8)
O5—H51···F2^xi	1.01 (6)	2.05 (7)	2.888 (3)	139 (5)
O5—H51···F3^vii	1.01 (6)	2.23 (5)	3.072 (4)	140 (6)
O5—H52···F4	1.05 (7)	1.63 (7)	2.676 (3)	175 (6)
F4—H6···F4^iv	0.91	1.82	2.597 (4)	142

Symmetry codes: (ii) −x+1, −y, −z; (iii) −x+1, −y+1, −z; (iv) −x+1, −y+1, −z+1; (vii) −x, −y+1, −z; (viii) −x+1, −y+2, −z+1; (x) x+1, y, z; (xi) x, y+1, z.