Crystal structure of bis­(1-ethyl­pyridinium) dioxonium hexa­cyanidoferrate(II)

Tanaka, R.; Matsushita, N.

doi:10.1107/S2056989017000810

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Volume 73| Part 2| February 2017| Pages 219-222

https://doi.org/10.1107/S2056989017000810

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Crystal structure of bis(1-ethylpyridinium) dioxonium hexacyanidoferrate(II)

Rikako Tanaka ^a and Nobuyuki Matsushita ^a ^*

^aDepartment of Chemistry and Research Center for Smart Molecules, Rikkyo University, Nishi-Ikebukuro 3-34-1, Toshima-ku, 171-8501 Tokyo, Japan
^*Correspondence e-mail: cnmatsu@rikkyo.ac.jp

Edited by M. Weil, Vienna University of Technology, Austria (Received 27 December 2016; accepted 17 January 2017; online 20 January 2017)

The title compound, (C₇H₁₀N)₂(H₃O)₂[Fe(CN)₆] or (Etpy)₂(H₃O)₂[Fe(CN)₆] (Etpy⁺ is 1-ethylpyridinium), crystallizes in the space group Pnnm. The Fe^II atom of the [Fe(CN)₆]⁴⁻ anion lies on a site with site symmetry ..2/m, and has an octahedral coordination sphere defined by six cyanido ligands. Both the Etpy⁺ and the oxonium cations are located on a mirror plane. In the crystal, electron-donor anions of [Fe(CN)₆]⁴⁻ and electron-acceptor cations of Etpy⁺ are each stacked parallel to the b axis, resulting in a columnar structure with segregated moieties. The crystal packing is stabilized by a three-dimensional O—H⋯N hydrogen-bonding network between the oxonium ions and the cyanide ligands of [Fe(CN)₆]⁴⁻.

Keywords: crystal structure; molecular salt; oxonium ion; hexacyanidoferrate(II); ethylpyridinium ion; hydrogen bonds.

CCDC reference: 1527928

1. Chemical context

Prussian blue is a well-known compound which displays a deep-blue colour based on an intervalence charge-transfer interaction between [Fe^II(CN)₆]⁴⁻ electron-donor species and Fe^III electron-acceptor species. Several charge-transfer salts composed of [Fe(CN)₆]⁴⁻ and organic acceptor cations, e.g. 1,1′-dimethyl-4,4′-bipyridinium (methyl viologen) have been reported (Nakahara & Wang, 1963 ; Kostina et al., 2001 ; Kotov et al., 2005 ; Abouelwafa et al., 2010 ). In the majority of cases, the reported charge-transfer salts of [Fe(CN)₆]⁴⁻ are accompanied by dicationic organic acceptor species. On the other hand, charge-transfer salts of [Fe(CN)₆]⁴⁻ accompanied by monocationic species are rather rare (Gorelsky et al., 2007 ).

The present X-ray crystallographic analysis of the title salt, (Etpy)₂(H₃O)₂[Fe(CN)₆] (Etpy⁺ is 1-ethylpyridinium), (I), was performed in order to elucidate the crystal packing of a charge-transfer hexacyanidoferrate(II) anion with a monocationic organic acceptor and an oxonium ion.

2. Structural commentary

The structures of the molecular components of (I) are displayed in Fig. 1. The asymmetric unit of (I) contains half of an Etpy⁺ cation and an oxonium ion (both located on a mirror plane), and one quarter of an [Fe(CN)₆]⁴⁻ anion, the Fe^II atom of which is located on a site with symmetry ..2/m. The Fe^II atom is coordinated by six cyanido ligands in a slightly distorted octahedral configuration [Fe—C = 1.9045 (18), 1.9068 (13) Å; C≡N = 1.157 (2), 1.1598 (17) Å; C—Fe—C_trans = 180.0°; C—Fe—C_cis = 89.60 (7)–90.40 (7)°; Fe—C—N = 178.67 (18), 179.77 (13)°]. The bond angle of the ethyl group of the Etpy⁺ ion [N3—C6—C7 = 110.77 (19) °] is similar to those of Etpy[AlCl₄] [109.2 (11)°; Zaworotko et al., 1989 ] and poly[4-dimethylamino-1-ethylpyridin-1-ium [tri-μ-dicyanamido-κ⁶N¹:N⁵-cadmium]] [111.5 (5)°; Wang et al., 2015 ].

Figure 1
The structures of the molecular components of compound (I)

, showing the atomic numbering scheme. Displacement ellipsoids are drawn at the 50% probability level for non-H atoms. [Symmetry codes: (i) −x, −y, −z; (ii) x, y, −z; (iii) −x, −y, z; (iv) x, y, −z + 1.]

3. Supramolecular features

The projection of the crystal structure of (I) along the b axis is shown in Fig. 2.

Figure 2
The crystal packing of compound (I)

in a view along the b axis. H atoms have been omitted for clarify; the probability function is as in Fig. 1

The [Fe(CN)₆]⁴⁻ electron-donor anions and the Etpy⁺ electron-acceptor cations stack separately in columns parallel to the b axis whereby both types of columns are alternately arranged in the a- and c-axis directions.

In the crystal of (I), the oxonium ions and [Fe(CN)₆]⁴⁻ ions form a three-dimensional O—H⋯N hydrogen-bonding network (Table 1). A pair of Etpy⁺ cations is enclosed in the hydrogen-bonding cage formed by six [Fe(CN)₆]⁴⁻ ions and six oxonium ions (Fig. 3). Two pyridinium rings of the Etpy⁺ cations are arranged in parallel and the ethyl groups are alternating with each other. The centroid-to-centroid distance (4.147 Å) and the face-to-face distance of the least-square planes (3.731 Å) between two pyridinium rings indicate that π–π interactions are not developed.

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O1—H1A⋯N1ⁱ	0.90 (3)	1.67 (3)	2.569 (2)	176 (3)
O1—H1B⋯N2	0.931 (18)	1.632 (19)	2.5589 (15)	173.6 (18)
Symmetry code: (i) $[x+{\script{1\over 2}}, -y+{\script{1\over 2}}, -z+{\script{1\over 2}}]$ .

Figure 3
Hydrogen-bonding network composed of [Fe(CN)₆]⁴⁻ anions and oxonium cations. Magenta dashed lines represent hydrogen bonds.

4. Database survey

Several crystal structures of compounds containing the Etpy⁺ cation have been deposited in the Cambridge Structural Database (Groom et al. 2016 ), e.g. Etpy[AlCl₄] (Zaworotko et al., 1989), Etpy[Ni(mnt)₂] (mnt = maleonitrile-1,2-dithiolate; Robertson et al., 1999 ), or (Etpy)₂[CoCl₄] (Felloni et al., 2004 ). A hexacyanidoferrate(II) salt, (Hpy)₂(H₃O)₂[Fe(CN)₆] (Hpy⁺ = N-hydropyridinium; Gorelsky et al., 2007), quite similar to (I), has been also reported.

5. Synthesis and crystallization

H₄[Fe(CN)₆] (106 mg) and L-ascorbic acid (60 mg) were dissolved in water (17 ml). The mixture was added to an aqueous solution of 1-ethylpyridinium bromide (177 mg/17 ml). After standing at 277 K for a day, yellow platelet-shaped crystals suitable for X-ray analysis were obtained. Elemental analysis: found: C, 51.52; H, 5.878; N, 24.06%; calculated for C₂₀H₂₆FeN₈O₂: C, 51.51; H, 5.63; N, 24.03%. Thermogravimetry was measured from 296 to 476 K at a rate of 5 K min⁻¹ under N₂ gas flow (100 ml min⁻¹) on a Rigaku TG-DTA Thermo Plus EVO2 TG8121. Found: 7.85% mass loss; calculated: 7.73%. The mass loss of (I) took place at around 373 to 393 K and corresponds to two water molecules per chemical formula. The result suggests that the water molecules are released from the oxonium ions. Most probably, protons, H⁺, remain in the crystal as counter-cations. The IR spectrum of compound (I) is shown in Fig. 4. Selected IR bands (KBr pellet, cm⁻¹): 3135–2941 (s, C—H, str), 2640 (br, O—H, str), 2075 (s, C≡N, str).

Figure 4
The IR spectrum of compound (I)

6. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 2. In the final refinement of the title compound, three reflections, viz. (0 17 1), (2 16 0) and (5 15 2), were omitted owing to poor agreements between observed and calculated intensities. H atoms of the Etpy⁺ cation were, at first, located in a difference Fourier map, but finally placed in geometrically calculated positions and refined as riding, with C(methylene)—H = 0.92 Å, C(methyl)—H = 0.98 Å and C(aromatic)—H = 0.95 Å, all with U_iso(H) = 1.5U_eq(C). H atoms of the oxonium ion were located in a difference Fourier map and their positions refined with U_iso(H) = 1.5U_eq(O). The maximum and minimum electron density peaks are located 1.00 Å from atom C1 and 0.71 Å from atom Fe1, respectively.

Table 2
Experimental details

Crystal data
Chemical formula	(C₇H₁₀N)₂(H₃O)₂[Fe(CN)₆]
M_r	466.34
Crystal system, space group	Orthorhombic, Pnnm
Temperature (K)	173
a, b, c (Å)	11.8807 (4), 12.1279 (7), 8.3962 (2)
V (Å³)	1209.79 (9)
Z	2
Radiation type	Mo Kα
μ (mm⁻¹)	0.65
Crystal size (mm)	0.28 × 0.13 × 0.08

Data collection
Diffractometer	Rigaku R-AXIS RAPID imaging-plate
Absorption correction	Multi-scan (ABSCOR; Higashi, 1995 )
T_min, T_max	0.907, 0.952
No. of measured, independent and observed [I > 2σ(I)] reflections	25575, 2216, 1840
R_int	0.034
(sin θ/λ)_max (Å⁻¹)	0.746

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.036, 0.093, 1.11
No. of reflections	2213
No. of parameters	88
H-atom treatment	H atoms treated by a mixture of independent and constrained refinement
Δρ_max, Δρ_min (e Å⁻³)	0.50, −0.70
Computer programs: RAPID-AUTO (Rigaku, 2006 ), SHELXT2014 (Sheldrick, 2015a ), SHELXL2014 (Sheldrick, 2015b ), DIAMOND (Brandenburg, 2016 ) and publCIF (Westrip, 2010 ).

Supporting information

CCDC reference: 1527928

Crystal structure: contains datablock I. DOI: https://doi.org/10.1107/S2056989017000810/wm5355sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2056989017000810/wm5355Isup2.hkl

checkCIF report

Computing details top

Data collection: RAPID-AUTO (Rigaku, 2006); cell refinement: RAPID-AUTO (Rigaku, 2006); data reduction: RAPID-AUTO (Rigaku, 2006); program(s) used to solve structure: SHELXT2014 (Sheldrick, 2015a); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015b); molecular graphics: DIAMOND (Brandenburg, 2016); software used to prepare material for publication: publCIF (Westrip, 2010).

Bis(1-ethylpyridinium) dioxonium hexacyanidoferrate(II) top

Crystal data top

(C₇H₁₀N)₂(H₃O)₂[Fe(CN)₆]	D_x = 1.280 Mg m⁻³
M_r = 466.34	Mo Kα radiation, λ = 0.7107 Å
Orthorhombic, Pnnm	Cell parameters from 8639 reflections
a = 11.8807 (4) Å	θ = 3.4–32.0°
b = 12.1279 (7) Å	µ = 0.65 mm⁻¹
c = 8.3962 (2) Å	T = 173 K
V = 1209.79 (9) Å³	Block, pale-yellow
Z = 2	0.28 × 0.13 × 0.08 mm
F(000) = 488

Data collection top

Rigaku R-AXIS RAPID imaging-plate diffractometer	2216 independent reflections
Radiation source: X-ray sealed tube	1840 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.034
Detector resolution: 10.00 pixels mm^-1	θ_max = 32.0°, θ_min = 3.4°
ω scans	h = −17→17
Absorption correction: multi-scan (ABSCOR; Higashi, 1995)	k = −18→18
T_min = 0.907, T_max = 0.952	l = −12→10
25575 measured reflections

Refinement top

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)] = 0.036	Hydrogen site location: difference Fourier map
wR(F²) = 0.093	H atoms treated by a mixture of independent and constrained refinement
S = 1.11	w = 1/[σ²(F_o²) + (0.0356P)² + 0.6061P] where P = (F_o² + 2F_c²)/3
2213 reflections	(Δ/σ)_max < 0.001
88 parameters	Δρ_max = 0.50 e Å⁻³
0 restraints	Δρ_min = −0.70 e Å⁻³

Special details top

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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
Fe1	0.0000	0.0000	0.0000	0.02095 (10)
C1	−0.05743 (16)	0.14661 (15)	0.0000	0.0257 (3)
C2	0.10536 (11)	0.04026 (10)	0.16115 (15)	0.0255 (2)
N1	−0.09019 (17)	0.23642 (15)	0.0000	0.0371 (4)
N2	0.16963 (11)	0.06441 (11)	0.25910 (15)	0.0352 (3)
N3	0.00181 (15)	0.25836 (14)	0.5000	0.0333 (3)
C3	0.1469 (2)	0.4327 (2)	0.5000	0.0485 (6)
H3	0.1978	0.4930	0.5000	0.073*
C4	0.10987 (15)	0.38888 (16)	0.3591 (2)	0.0498 (4)
H4	0.1344	0.4192	0.2607	0.075*
C5	0.03717 (15)	0.30083 (14)	0.3608 (2)	0.0431 (4)
H5	0.0118	0.2698	0.2633	0.065*
C6	−0.0794 (2)	0.16567 (19)	0.5000	0.0485 (6)
H6A	−0.0670	0.1193	0.5954	0.073*
C7	−0.1981 (2)	0.2077 (2)	0.5000	0.0570 (7)
H7A	−0.2503	0.1452	0.5000	0.086*
H7B	−0.2108	0.2527	0.5953	0.086*
O1	0.30049 (12)	0.08078 (12)	0.5000	0.0279 (3)
H1A	0.342 (2)	0.143 (2)	0.5000	0.042*
H1B	0.2513 (15)	0.0800 (15)	0.414 (2)	0.042*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Fe1	0.02418 (17)	0.02126 (16)	0.01740 (15)	0.00227 (12)	0.000	0.000
C1	0.0302 (8)	0.0250 (8)	0.0218 (7)	0.0048 (6)	0.000	0.000
C2	0.0299 (6)	0.0246 (5)	0.0220 (5)	0.0015 (4)	0.0015 (5)	−0.0001 (4)
N1	0.0454 (10)	0.0307 (8)	0.0353 (9)	0.0104 (7)	0.000	0.000
N2	0.0383 (6)	0.0393 (6)	0.0280 (5)	−0.0029 (5)	−0.0044 (5)	−0.0030 (5)
N3	0.0364 (8)	0.0254 (7)	0.0380 (9)	0.0019 (6)	0.000	0.000
C3	0.0341 (11)	0.0473 (13)	0.0641 (16)	−0.0065 (10)	0.000	0.000
C4	0.0518 (9)	0.0524 (9)	0.0451 (9)	−0.0064 (8)	0.0172 (8)	0.0013 (8)
C5	0.0522 (9)	0.0434 (8)	0.0336 (7)	−0.0007 (7)	0.0058 (7)	−0.0083 (7)
C6	0.0506 (13)	0.0276 (10)	0.0674 (17)	−0.0047 (9)	0.000	0.000
C7	0.0469 (14)	0.0416 (13)	0.083 (2)	−0.0110 (11)	0.000	0.000
O1	0.0292 (6)	0.0287 (6)	0.0257 (6)	−0.0063 (5)	0.000	0.000

Geometric parameters (Å, º) top

Fe1—C1ⁱ	1.9045 (18)	C3—C4^iv	1.369 (2)
Fe1—C1	1.9045 (18)	C3—H3	0.9500
Fe1—C2ⁱ	1.9068 (13)	C4—C5	1.373 (2)
Fe1—C2ⁱⁱ	1.9068 (13)	C4—H4	0.9500
Fe1—C2ⁱⁱⁱ	1.9068 (13)	C5—H5	0.9500
Fe1—C2	1.9069 (13)	C6—C7	1.499 (4)
C1—N1	1.157 (2)	C6—H6A	0.9900
C2—N2	1.1598 (17)	C7—H7A	0.9800
N3—C5^iv	1.3447 (19)	C7—H7B	0.9800
N3—C5	1.3447 (19)	O1—H1A	0.90 (3)
N3—C6	1.482 (3)	O1—H1B	0.931 (18)
C3—C4	1.369 (2)	O1—H1B^iv	0.931 (18)

C1ⁱ—Fe1—C1	180.0	C5—N3—C6	119.61 (10)
C1ⁱ—Fe1—C2ⁱ	89.78 (5)	C4—C3—C4^iv	119.5 (2)
C1—Fe1—C2ⁱ	90.22 (5)	C4—C3—H3	120.2
C1ⁱ—Fe1—C2ⁱⁱ	90.22 (5)	C4^iv—C3—H3	120.2
C1—Fe1—C2ⁱⁱ	89.78 (5)	C3—C4—C5	119.65 (17)
C2ⁱ—Fe1—C2ⁱⁱ	89.60 (7)	C3—C4—H4	120.2
C1ⁱ—Fe1—C2ⁱⁱⁱ	89.78 (5)	C5—C4—H4	120.2
C1—Fe1—C2ⁱⁱⁱ	90.22 (5)	N3—C5—C4	120.20 (16)
C2ⁱ—Fe1—C2ⁱⁱⁱ	90.40 (7)	N3—C5—H5	119.9
C2ⁱⁱ—Fe1—C2ⁱⁱⁱ	180.00 (11)	C4—C5—H5	119.9
C1ⁱ—Fe1—C2	90.22 (5)	N3—C6—C7	110.77 (19)
C1—Fe1—C2	89.78 (5)	N3—C6—H6A	109.5
C2ⁱ—Fe1—C2	180.0	C7—C6—H6A	109.5
C2ⁱⁱ—Fe1—C2	90.40 (7)	C6—C7—H7A	109.4
C2ⁱⁱⁱ—Fe1—C2	89.60 (7)	C6—C7—H7B	109.5
N1—C1—Fe1	178.67 (18)	H7A—C7—H7B	109.5
N2—C2—Fe1	179.77 (13)	H1A—O1—H1B	110.5 (14)
C5^iv—N3—C5	120.8 (2)	H1A—O1—H1B^iv	110.5 (14)
C5^iv—N3—C6	119.61 (10)	H1B—O1—H1B^iv	102 (2)

Symmetry codes: (i) −x, −y, −z; (ii) x, y, −z; (iii) −x, −y, z; (iv) x, y, −z+1.

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
O1—H1A···N1^v	0.90 (3)	1.67 (3)	2.569 (2)	176 (3)
O1—H1B···N2	0.931 (18)	1.632 (19)	2.5589 (15)	173.6 (18)

Symmetry code: (v) x+1/2, −y+1/2, −z+1/2.

Acknowledgements

The authors would acknowledge a Special Fund for Research (SFR) from Rikkyo University.

References

Abouelwafa, A. S., Mereacre, V., Balaban, T. S., Anson, C. E. & Powell, A. K. (2010). CrystEngComm, 12, 94–99. CSD CrossRef CAS Google Scholar
Brandenburg, K. (2016). DIAMOND. Crystal Impact GbR, Bonn, Germany. Google Scholar
Felloni, M., Hubberstey, P., Wilson, C. & Schröder, M. (2004). CrystEngComm, 6, 87–95. Web of Science CSD CrossRef CAS Google Scholar
Gorelsky, S. I., Ilyukhin, A. B., Kholin, P. V., Kotov, V. Y., Lokshin, B. V. & Sapoletova, N. V. (2007). Inorg. Chim. Acta, 360, 2573–2582. CSD CrossRef CAS Google Scholar
Groom, C. R., Bruno, I. J., Lightfoot, M. P. & Ward, S. C. (2016). Acta Cryst. B72, 171–179. Web of Science CSD CrossRef IUCr Journals Google Scholar
Higashi, T. (1995). ABSCOR. Rigaku Corporation, Tokyo, Japan. Google Scholar
Kostina, S. A., Ilyukhin, A. B., Lokshin, B. V. & Kotov, V. Y. (2001). Mendeleev Commun. 11, 12–13. CSD CrossRef Google Scholar
Kotov, V. Y., Ilyukhin, A. B., Lunina, V. K. & Shpigun, L. K. (2005). Mendeleev Commun. 15, 95–96. CSD CrossRef Google Scholar
Nakahara, A. & Wang, J. H. (1963). J. Phys. Chem. 67, 496–498. CrossRef CAS Google Scholar
Rigaku (2006). RAPID-AUTO. Rigaku Corporation, Tokyo, Japan. Google Scholar
Robertson, N., Bergemann, C., Becker, H., Agarwal, P., Julian, S. R., Friend, R. H., Hatton, N. J., Underhill, A. E. & Kobayashi, A. (1999). J. Mater. Chem. 9, 1713–1717. CSD CrossRef CAS Google Scholar
Sheldrick, G. M. (2015a). Acta Cryst. A71, 3–8. Web of Science CrossRef IUCr Journals Google Scholar
Sheldrick, G. M. (2015b). Acta Cryst. C71, 3–8. Web of Science CrossRef IUCr Journals Google Scholar
Wang, H.-T., Zhou, L. & Wang, X.-L. (2015). Acta Cryst. C71, 717–720. CSD CrossRef IUCr Journals Google Scholar
Westrip, S. P. (2010). J. Appl. Cryst. 43, 920–925. Web of Science CrossRef CAS IUCr Journals Google Scholar
Zaworotko, M. J., Cameron, T. S., Linden, A. & Sturge, K. C. (1989). Acta Cryst. C45, 996–1002. CSD CrossRef CAS IUCr Journals Google Scholar

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