Crystal structure of iron(III) perchlorate nona-hydrate.

Since the discovery of perchlorate salts on Mars and the known occurrence of ferric salts in the regolith, there is a distinct possibility that the title compound could form on the surface of Mars. [Fe(H2O)6](ClO4)3·3H2O was crystallized from aqueous solutions at low temperatures according to the solid-liquid phase diagram. It consists of Fe(H2O)6 octa-hedra (point group symmetry -3.) and perchlorate anions (point group symmetry .2) as well as non-coordinating water mol-ecules, as part of a second hydrogen-bonded coordination sphere around the cation. The perchlorate appears to be slightly disordered, with major-minor component occupancies of 0.773 (9):0.227 (9).

Chemical context

Since the discovery of perchlorate salts on the surface of Mars during the Phoenix expedition (Hecht et al., 2009 ▶; Davila et al., 2013 ▶; Kerr, 2013 ▶; Marion et al., 2010 ▶; Navarro-González et al., 2010 ▶), inter­est in the solubility and crystal structures of the perchlorate hydrate phases became more important (Chevrier, Hanley & Altheide, 2009 ▶; Catling et al., 2010 ▶). Based on the red color of the planet, one can expect different iron phases, such as perchlorate and sulfate, to be important constituents of the regolith (Chevrier, Ulrich & Altheide, 2009 ▶; Chevrier & Altheide, 2008 ▶; Hennings et al., 2013 ▶). While investigating the solubility of ferric perchlorate, we obtained the nona­hydrate as a stable phase in the binary salt–water system.

Structural commentary

The central Fe atom is situated on a threefold inversion axis and is octa­hedrally coordinated by six water mol­ecules in the first, and by six water mol­ecules as well as six perchlorate tetra­hedra in the second coordination spheres (Fig. 1 ▶). The water mol­ecules of the second coordination sphere (O4 and symmetry equivalents) are connected to perchlorate tetra­hedra (Fig. 2 ▶ a) via hydrogen bonds (Table 1 ▶). Six O4-water mol­ecules form a second, larger octa­hedron outside the octa­hedron of the first coordination shell (Fig. 2 ▶ b). The perchlorate anion, situated on a twofold rotation axis, appears to be slightly disordered, with major:minor component occupancies of 0.773 (9):0.227 (9).

Figure 1

The mol­ecular units (a) and second coordination sphere (b) of ferric perchlorate nona­hydrate. Dashed lines indicate hydrogen bonds. Displacement ellipsoids are drawn at the 50% probability limit. The minor disorder component of the ClO4 tetrahedron has been omitted. [Symmetry codes: (i) x − y, x, 1 − z; (ii) −x + y, −x, z; (iii) −x, −y, 1 − z; (iv) −y, x − y, z; (v) y, −x + y, 1 − z; (vi)  − x,  − x + y,  − z.]

Figure 2

The connection scheme of water mol­ecules of the second coordination sphere by hydrogen bonds (a) and the formation of a secondary hydration shell (yellow) around the cations (b). The minor disorder component of the ClO4 tetrahedron has been omitted for clarity. Dashed lines indicate hydrogen bonds. [Symmetry code: (i)  − x,  − x + y,  − z.]

Table 1

Hydrogen-bond geometry (, )

DHA	DH	HA	D A	DHA
O1H1AO2i	0.83(5)	1.92(5)	2.745(5)	174(4)
O1H1AO2i	0.83(5)	2.33(5)	3.153(14)	170(4)
O1H1AO3	0.83(5)	2.27(5)	2.864(17)	129(4)
O1H1BO4ii	0.82(5)	1.83(5)	2.642(3)	173(4)
O4H4O2	0.84(4)	2.39(4)	3.073(5)	139(4)
O4H4O3iii	0.84(4)	2.13(4)	2.796(4)	136(4)
O4H4O2	0.84(4)	2.13(5)	2.812(17)	138(4)
O4H4O3iii	0.84(4)	2.12(4)	2.708(12)	127(4)

Symmetry codes: (i) ; (ii) ; (iii) .

Supra­molecular features

From the unit cell of ferric perchlorate nona­hydrate (Fig. 3 ▶ a), it is obvious that the O4 atoms form a secondary hydration shell around the Fe(H2O)6 units. This becomes clearer when drawing the second octa­hedra as water coordination polyhedra (yellow, Fig. 3 ▶ b). The water mol­ecules of the second coordination sphere are closer [4.143 (4) Å] to the Fe atom than the perchlorate tetra­hedra [4.271 (4) Å].

Figure 3

The unit cell of iron(III) perchlorate nona­hydrate with coordination polyhedra of the first (a) and second (b) coordination sphere. The minor disorder component of the ClO4 tetrahedron has been omitted for clarity. Dashed lines indicate hydrogen bonds.

Database survey

For crystal structure determination of other perchlorate nona­hydrates, see: Davidian et al. (2012 ▶) for the Al, Ga and Sc salts and Hennings et al. (2014 ▶) for the strontium salt. For crystal structure determinations of other FeIII salts with a high water content, see: Schmidt et al. (2013 ▶); Lindstrand (1936 ▶).

Synthesis and crystallization

Iron(III) perchlorate nona­hydrate crystallized from an aqueous solution of 54.41 wt% Fe(ClO4)3 thermostated at 263 K after 2 d. To prepare this solution, ferric perchlorate nona­hydrate (Fluka, pure) was used. The content of FeIII ions was analysed using gravimetric analysis by precipitation with ammonia. All crystals are stable in their saturated solution over a period of at least four weeks.

The samples were stored in a freezer or a cryostat at low temperatures. The crystals were separated and embedded in perfluorinated ether for X-ray diffraction analysis

Refinement

Crystal data, data collection and structure refinement details are summarized in Table 2 ▶. The H atoms were placed in the positions indicated by difference Fourier maps. No further constraints were applied.

Table 2

Experimental details

Crystal data
Chemical formula	[Fe(H2O)6](ClO4)33H2O
M r	516.34
Crystal system, space group	Trigonal, R c:H
Temperature (K)	100
a, c ()	16.1930(15), 11.2421(11)
V (3)	2552.9(5)
Z	6
Radiation type	Mo K
(mm1)	1.46
Crystal size (mm)	0.54 0.37 0.19
Data collection
Diffractometer	STOE IPDS 2T
Absorption correction	Integration (Coppens, 1970 ▶)
T min, T max	0.531, 0.755
No. of measured, independent and observed [I > 2(I)] reflections	8865, 659, 641
R int	0.075
(sin /)max (1)	0.650
Refinement
R[F 2 > 2(F 2)], wR(F 2), S	0.041, 0.092, 1.11
No. of reflections	658
No. of parameters	60
H-atom treatment	All H-atom parameters refined
max, min (e 3)	0.64, 0.80

Computer programs: X-AREA and X-RED (Stoe Cie, 2009 ▶), SHELXS97 and SHELXL2012 (Sheldrick, 2008 ▶), DIAMOND (Brandenburg, 2006 ▶) and publCIF (Westrip, 2010 ▶).

Crystal structure: contains datablock(s) I. DOI: 10.1107/S1600536814024295/pk2533sup1.cif

Structure factors: contains datablock(s) I. DOI: 10.1107/S1600536814024295/pk2533Isup2.hkl

CCDC reference: 1032663

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

[Fe(H2O)6](ClO4)3·3H2O	Dx = 2.015 Mg m−3
Mr = 516.34	Mo Kα radiation, λ = 0.71073 Å
Trigonal, R3c:H	Cell parameters from 47287 reflections
a = 16.1930 (15) Å	θ = 7.0–29.7°
c = 11.2421 (11) Å	µ = 1.46 mm−1
V = 2552.9 (5) Å3	T = 100 K
Z = 6	Needle, colorless
F(000) = 1578	0.54 × 0.37 × 0.19 mm

STOE IPDS 2T diffractometer	659 independent reflections
Radiation source: fine-focus sealed tube	641 reflections with I > 2σ(I)
Detector resolution: 6.67 pixels mm-1	Rint = 0.075
rotation method scans	θmax = 27.5°, θmin = 2.5°
Absorption correction: integration (Coppens, 1970)	h = −20→20
Tmin = 0.531, Tmax = 0.755	k = −20→20
8865 measured reflections	l = −14→14

Refinement on F2	0 restraints
Least-squares matrix: full	Hydrogen site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.041	All H-atom parameters refined
wR(F2) = 0.092	w = 1/[σ2(Fo2) + (0.0269P)2 + 23.9134P] where P = (Fo2 + 2Fc2)/3
S = 1.11	(Δ/σ)max < 0.001
658 reflections	Δρmax = 0.64 e Å−3
60 parameters	Δρmin = −0.80 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	Occ. (<1)
Fe1	0.0000	0.0000	0.5000	0.0188 (3)
O1	0.07420 (15)	0.11666 (15)	0.3991 (2)	0.0252 (5)
O4	0.3333	0.47858 (17)	0.4167	0.0247 (6)
Cl1	0.3333	0.2540 (19)	0.4167	0.0329 (3)	0.773 (9)
O2	0.4134 (3)	0.3438 (3)	0.3808 (4)	0.0342 (8)	0.773 (9)
O3	0.3070 (3)	0.1914 (3)	0.3110 (4)	0.0481 (12)	0.773 (9)
Cl1'	0.3333	0.254 (7)	0.4167	0.0329 (3)	0.227 (9)
O2'	0.3946 (11)	0.3499 (13)	0.3527 (16)	0.0342 (8)	0.227 (9)
O3'	0.2699 (12)	0.1716 (10)	0.3602 (15)	0.0481 (12)	0.227 (9)
H1A	0.129 (3)	0.158 (3)	0.417 (4)	0.047 (12)*
H1B	0.048 (3)	0.138 (3)	0.357 (4)	0.051 (13)*
H4	0.375 (3)	0.468 (3)	0.388 (4)	0.054 (13)*

	U11	U22	U33	U12	U13	U23
Fe1	0.0157 (3)	0.0157 (3)	0.0251 (5)	0.00784 (15)	0.000	0.000
O1	0.0165 (10)	0.0195 (10)	0.0341 (11)	0.0050 (8)	−0.0004 (8)	0.0045 (8)
O4	0.0269 (15)	0.0164 (9)	0.0344 (16)	0.0135 (8)	0.0102 (12)	0.0051 (6)
Cl1	0.0221 (5)	0.0137 (4)	0.0659 (8)	0.0110 (2)	−0.0180 (5)	−0.0090 (2)
O2	0.0180 (19)	0.0381 (15)	0.051 (2)	0.0174 (13)	−0.0027 (15)	0.0098 (16)
O3	0.045 (3)	0.0345 (19)	0.067 (3)	0.0210 (19)	−0.0055 (19)	−0.0276 (19)
Cl1'	0.0221 (5)	0.0137 (4)	0.0659 (8)	0.0110 (2)	−0.0180 (5)	−0.0090 (2)
O2'	0.0180 (19)	0.0381 (15)	0.051 (2)	0.0174 (13)	−0.0027 (15)	0.0098 (16)
O3'	0.045 (3)	0.0345 (19)	0.067 (3)	0.0210 (19)	−0.0055 (19)	−0.0276 (19)

Fe1—O1i	2.007 (2)	Cl1—O2	1.439 (18)
Fe1—O1ii	2.007 (2)	Cl1—O3vi	1.479 (17)
Fe1—O1iii	2.007 (2)	Cl1—O3	1.479 (17)
Fe1—O1iv	2.007 (2)	Cl1'—O3'vi	1.37 (6)
Fe1—O1v	2.007 (2)	Cl1'—O3'	1.37 (6)
Fe1—O1	2.007 (2)	Cl1'—O2'vi	1.54 (7)
Cl1—O2vi	1.439 (18)	Cl1'—O2'	1.54 (7)
O1i—Fe1—O1ii	180.00 (9)	O1v—Fe1—O1	180.00 (10)
O1i—Fe1—O1iii	91.19 (9)	O2vi—Cl1—O2	112 (2)
O1ii—Fe1—O1iii	88.81 (9)	O2vi—Cl1—O3vi	105.8 (3)
O1i—Fe1—O1iv	88.81 (9)	O2—Cl1—O3vi	109.42 (19)
O1ii—Fe1—O1iv	91.19 (9)	O2vi—Cl1—O3	109.42 (19)
O1iii—Fe1—O1iv	180.00 (10)	O2—Cl1—O3	105.8 (3)
O1i—Fe1—O1v	91.19 (9)	O3vi—Cl1—O3	114 (2)
O1ii—Fe1—O1v	88.81 (9)	O3'vi—Cl1'—O3'	106 (7)
O1iii—Fe1—O1v	91.19 (9)	O3'vi—Cl1'—O2'vi	124.0 (13)
O1iv—Fe1—O1v	88.81 (9)	O3'—Cl1'—O2'vi	105.4 (10)
O1i—Fe1—O1	88.81 (9)	O3'vi—Cl1'—O2'	105.4 (10)
O1ii—Fe1—O1	91.19 (9)	O3'—Cl1'—O2'	124.0 (13)
O1iii—Fe1—O1	88.81 (9)	O2'vi—Cl1'—O2'	94 (6)
O1iv—Fe1—O1	91.19 (9)

D—H···A	D—H	H···A	D···A	D—H···A
O1—H1A···Cl1	0.83 (5)	2.86 (5)	3.642 (2)	157 (4)
O1—H1A···O2vi	0.83 (5)	1.92 (5)	2.745 (5)	174 (4)
O1—H1A···O2′vi	0.83 (5)	2.33 (5)	3.153 (14)	170 (4)
O1—H1A···O3′	0.83 (5)	2.27 (5)	2.864 (17)	129 (4)
O1—H1B···O4vii	0.82 (5)	1.83 (5)	2.642 (3)	173 (4)
O4—H4···O2	0.84 (4)	2.39 (4)	3.073 (5)	139 (4)
O4—H4···O3viii	0.84 (4)	2.13 (4)	2.796 (4)	136 (4)
O4—H4···O2′	0.84 (4)	2.13 (5)	2.812 (17)	138 (4)
O4—H4···O3′viii	0.84 (4)	2.12 (4)	2.708 (12)	127 (4)