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

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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 FeII 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−.

1. Chemical context

Prussian blue is a well-known compound which displays a deep-blue colour based on an inter­valence charge-transfer inter­action between [FeII(CN)6]4− electron-donor species and FeIII 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[Nakahara, A. & Wang, J. H. (1963). J. Phys. Chem. 67, 496-498.]; Kostina et al., 2001[Kostina, S. A., Ilyukhin, A. B., Lokshin, B. V. & Kotov, V. Y. (2001). Mendeleev Commun. 11, 12-13.]; Kotov et al., 2005[Kotov, V. Y., Ilyukhin, A. B., Lunina, V. K. & Shpigun, L. K. (2005). Mendeleev Commun. 15, 95-96.]; Abouelwafa et al., 2010[Abouelwafa, A. S., Mereacre, V., Balaban, T. S., Anson, C. E. & Powell, A. K. (2010). CrystEngComm, 12, 94-99.]). 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[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.]).

[Scheme 1]

The present X-ray crystallographic analysis of the title salt, (Etpy)2(H3O)2[Fe(CN)6] (Etpy+ is 1-ethyl­pyridinium), (I)[link], 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)[link] are displayed in Fig. 1[link]. The asymmetric unit of (I)[link] 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 FeII atom of which is located on a site with symmetry ..2/m. The FeII 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—Ctrans = 180.0°; C—Fe—Ccis = 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[Zaworotko, M. J., Cameron, T. S., Linden, A. & Sturge, K. C. (1989). Acta Cryst. C45, 996-1002.]] and poly[4-di­methyl­amino-1-ethyl­pyridin-1-ium [tri-μ-dicyanamido-κ6N1:N5-cadmium]] [111.5 (5)°; Wang et al., 2015[Wang, H.-T., Zhou, L. & Wang, X.-L. (2015). Acta Cryst. C71, 717-720.]].

[Figure 1]
Figure 1
The structures of the mol­ecular components of compound (I)[link], 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)[link] along the b axis is shown in Fig. 2[link].

[Figure 2]
Figure 2
The crystal packing of compound (I)[link] in a view along the b axis. H atoms have been omitted for clarify; the probability function is as in Fig. 1[link].

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)[link], the oxonium ions and [Fe(CN)6]4− ions form a three-dimensional O—H⋯N hydrogen-bonding network (Table 1[link]). 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[link]). 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 ππ inter­actions are not developed.

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A D—H H⋯A DA 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]
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[Groom, C. R., Bruno, I. J., Lightfoot, M. P. & Ward, S. C. (2016). Acta Cryst. B72, 171-179.]), e.g. Etpy[AlCl4] (Zaworotko et al., 1989[Zaworotko, M. J., Cameron, T. S., Linden, A. & Sturge, K. C. (1989). Acta Cryst. C45, 996-1002.]), Etpy[Ni(mnt)2] (mnt = maleo­nitrile-1,2-di­thiol­ate; Robertson et al., 1999[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.]), or (Etpy)2[CoCl4] (Felloni et al., 2004[Felloni, M., Hubberstey, P., Wilson, C. & Schröder, M. (2004). CrystEngComm, 6, 87-95.]). A hexa­cyanidoferrate(II) salt, (Hpy)2(H3O)2[Fe(CN)6] (Hpy+ = N-hydro­pyridinium; Gorelsky et al., 2007[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.]), quite similar to (I)[link], 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)[link] 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)[link] is shown in Fig. 4[link]. 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]
Figure 4
The IR spectrum of compound (I)[link].

6. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 2[link]. 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 Uiso(H) = 1.5Ueq(C). H atoms of the oxonium ion were located in a difference Fourier map and their positions refined with Uiso(H) = 1.5Ueq(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]
Mr 466.34
Crystal system, space group Orthorhombic, Pnnm
Temperature (K) 173
a, b, c (Å) 11.8807 (4), 12.1279 (7), 8.3962 (2)
V3) 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[Higashi, T. (1995). ABSCOR. Rigaku Corporation, Tokyo, Japan.])
Tmin, Tmax 0.907, 0.952
No. of measured, independent and observed [I > 2σ(I)] reflections 25575, 2216, 1840
Rint 0.034
(sin θ/λ)max−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
Δρmax, Δρmin (e Å−3) 0.50, −0.70
Computer programs: RAPID-AUTO (Rigaku, 2006[Rigaku (2006). RAPID-AUTO. Rigaku Corporation, Tokyo, Japan.]), SHELXT2014 (Sheldrick, 2015a[Sheldrick, G. M. (2015a). Acta Cryst. A71, 3-8.]), SHELXL2014 (Sheldrick, 2015b[Sheldrick, G. M. (2015b). Acta Cryst. C71, 3-8.]), DIAMOND (Brandenburg, 2016[Brandenburg, K. (2016). DIAMOND. Crystal Impact GbR, Bonn, Germany.]) and publCIF (Westrip, 2010[Westrip, S. P. (2010). J. Appl. Cryst. 43, 920-925.]).

Supporting information


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]Dx = 1.280 Mg m3
Mr = 466.34Mo Kα radiation, λ = 0.7107 Å
Orthorhombic, PnnmCell parameters from 8639 reflections
a = 11.8807 (4) Åθ = 3.4–32.0°
b = 12.1279 (7) ŵ = 0.65 mm1
c = 8.3962 (2) ÅT = 173 K
V = 1209.79 (9) Å3Block, pale-yellow
Z = 20.28 × 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 tube1840 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.034
Detector resolution: 10.00 pixels mm-1θmax = 32.0°, θmin = 3.4°
ω scansh = 1717
Absorption correction: multi-scan
(ABSCOR; Higashi, 1995)
k = 1818
Tmin = 0.907, Tmax = 0.952l = 1210
25575 measured reflections
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.036Hydrogen site location: difference Fourier map
wR(F2) = 0.093H atoms treated by a mixture of independent and constrained refinement
S = 1.11 w = 1/[σ2(Fo2) + (0.0356P)2 + 0.6061P]
where P = (Fo2 + 2Fc2)/3
2213 reflections(Δ/σ)max < 0.001
88 parametersΔρmax = 0.50 e Å3
0 restraintsΔρmin = 0.70 e Å3
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
xyzUiso*/Ueq
Fe10.00000.00000.00000.02095 (10)
C10.05743 (16)0.14661 (15)0.00000.0257 (3)
C20.10536 (11)0.04026 (10)0.16115 (15)0.0255 (2)
N10.09019 (17)0.23642 (15)0.00000.0371 (4)
N20.16963 (11)0.06441 (11)0.25910 (15)0.0352 (3)
N30.00181 (15)0.25836 (14)0.50000.0333 (3)
C30.1469 (2)0.4327 (2)0.50000.0485 (6)
H30.19780.49300.50000.073*
C40.10987 (15)0.38888 (16)0.3591 (2)0.0498 (4)
H40.13440.41920.26070.075*
C50.03717 (15)0.30083 (14)0.3608 (2)0.0431 (4)
H50.01180.26980.26330.065*
C60.0794 (2)0.16567 (19)0.50000.0485 (6)
H6A0.06700.11930.59540.073*
C70.1981 (2)0.2077 (2)0.50000.0570 (7)
H7A0.25030.14520.50000.086*
H7B0.21080.25270.59530.086*
O10.30049 (12)0.08078 (12)0.50000.0279 (3)
H1A0.342 (2)0.143 (2)0.50000.042*
H1B0.2513 (15)0.0800 (15)0.414 (2)0.042*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Fe10.02418 (17)0.02126 (16)0.01740 (15)0.00227 (12)0.0000.000
C10.0302 (8)0.0250 (8)0.0218 (7)0.0048 (6)0.0000.000
C20.0299 (6)0.0246 (5)0.0220 (5)0.0015 (4)0.0015 (5)0.0001 (4)
N10.0454 (10)0.0307 (8)0.0353 (9)0.0104 (7)0.0000.000
N20.0383 (6)0.0393 (6)0.0280 (5)0.0029 (5)0.0044 (5)0.0030 (5)
N30.0364 (8)0.0254 (7)0.0380 (9)0.0019 (6)0.0000.000
C30.0341 (11)0.0473 (13)0.0641 (16)0.0065 (10)0.0000.000
C40.0518 (9)0.0524 (9)0.0451 (9)0.0064 (8)0.0172 (8)0.0013 (8)
C50.0522 (9)0.0434 (8)0.0336 (7)0.0007 (7)0.0058 (7)0.0083 (7)
C60.0506 (13)0.0276 (10)0.0674 (17)0.0047 (9)0.0000.000
C70.0469 (14)0.0416 (13)0.083 (2)0.0110 (11)0.0000.000
O10.0292 (6)0.0287 (6)0.0257 (6)0.0063 (5)0.0000.000
Geometric parameters (Å, º) top
Fe1—C1i1.9045 (18)C3—C4iv1.369 (2)
Fe1—C11.9045 (18)C3—H30.9500
Fe1—C2i1.9068 (13)C4—C51.373 (2)
Fe1—C2ii1.9068 (13)C4—H40.9500
Fe1—C2iii1.9068 (13)C5—H50.9500
Fe1—C21.9069 (13)C6—C71.499 (4)
C1—N11.157 (2)C6—H6A0.9900
C2—N21.1598 (17)C7—H7A0.9800
N3—C5iv1.3447 (19)C7—H7B0.9800
N3—C51.3447 (19)O1—H1A0.90 (3)
N3—C61.482 (3)O1—H1B0.931 (18)
C3—C41.369 (2)O1—H1Biv0.931 (18)
C1i—Fe1—C1180.0C5—N3—C6119.61 (10)
C1i—Fe1—C2i89.78 (5)C4—C3—C4iv119.5 (2)
C1—Fe1—C2i90.22 (5)C4—C3—H3120.2
C1i—Fe1—C2ii90.22 (5)C4iv—C3—H3120.2
C1—Fe1—C2ii89.78 (5)C3—C4—C5119.65 (17)
C2i—Fe1—C2ii89.60 (7)C3—C4—H4120.2
C1i—Fe1—C2iii89.78 (5)C5—C4—H4120.2
C1—Fe1—C2iii90.22 (5)N3—C5—C4120.20 (16)
C2i—Fe1—C2iii90.40 (7)N3—C5—H5119.9
C2ii—Fe1—C2iii180.00 (11)C4—C5—H5119.9
C1i—Fe1—C290.22 (5)N3—C6—C7110.77 (19)
C1—Fe1—C289.78 (5)N3—C6—H6A109.5
C2i—Fe1—C2180.0C7—C6—H6A109.5
C2ii—Fe1—C290.40 (7)C6—C7—H7A109.4
C2iii—Fe1—C289.60 (7)C6—C7—H7B109.5
N1—C1—Fe1178.67 (18)H7A—C7—H7B109.5
N2—C2—Fe1179.77 (13)H1A—O1—H1B110.5 (14)
C5iv—N3—C5120.8 (2)H1A—O1—H1Biv110.5 (14)
C5iv—N3—C6119.61 (10)H1B—O1—H1Biv102 (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···AD—HH···AD···AD—H···A
O1—H1A···N1v0.90 (3)1.67 (3)2.569 (2)176 (3)
O1—H1B···N20.931 (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

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