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In the title salt, C14H18N22+·2C9H5N4O, the 1,1′-diethyl-4,4′-bi­pyridine-1,1′-diium dication lies across a centre of inversion in the space group P21/c. In the 1,1,3,3-tetra­cyano-2-eth­oxy­propenide anion, the two independent –C(CN)2 units are rotated, in conrotatory fashion, out of the plane of the central propenide unit, making dihedral angles with the central unit of 16.0 (2) and 23.0 (2)°. The ionic components are linked by C—H...N hydrogen bonds to form a complex sheet structure, within which each cation acts as a sixfold donor of hydrogen bonds and each anion acts as a threefold acceptor of hydrogen bonds.

Supporting information


Crystallographic Information File (CIF)
Contains datablocks global, I


Structure factor file (CIF format)
Contains datablock I

CCDC reference: 988719

Introduction top

Polynitrile anions have recently received considerable attention in the fields both of coordination chemistry and of molecular materials (Benmansour et al., 2010). These organic anions are of inter­est for their ability to act towards metal centres with various coordination modes and for their high degree of electronic delocalization (Thétiot et al., 2003; Benmansour et al., 2007, 2009; Atmani et al., 2008; Setifi et al., 2007, 2009, 2010). We are inter­ested in using these anionic ligands in combination with other neutral bridging co-ligands to explore their structural features and properties relevant to the field of molecular materials exhibiting the spin crossover (SCO) phenomenon (Dupouy et al., 2008, 2009). In an attempt to prepare such an iron(II) complex of this type using hydro­thermal synthesis, the unexpected title salt 1,1'-Di­ethyl-4,4'-bi­pyridine-1,1'-diium bis­(1,1,3,3-tetra­cyano-2-eth­oxy­propenide), (I) (Fig. 1), has been obtained and its structure is reported here.

Experimental top

Synthesis and crystallization top

The salt K(tcnoet) was prepared following the published method of Middleton et al. (1958). The title compound, (I), was synthesized hydro­thermally from a mixture of iron(II) sulfate heptahydrate (56 mg, 0.2 mmol), 4,4'-bi­pyridyl (16 mg, 0.1 mmol) and K(tcnoet) (90 mg, 0.4 mmol) in water–ethanol (4:1 v/v, 15 ml). The mixture was transferred to a Teflon-lined autoclave and heated at 393 K for 2 d. The autoclave was then allowed to cool to ambient temperature. Pale-yellow crystals of (I) were collected by filtration, washed with water, and dried in air (yield 65%).

Refinement top

Crystal data, data collection and structure refinement details are summarized in Table 1. All H atoms were located in difference maps and then treated as riding atoms in geometrically idealized positions, with C—H = 0.95 (aromatic), 0.98 (CH3) or 0.99 Å (CH2), and with Uiso(H) = kUeq(C), where k = 1.5 for the methyl groups, which were permitted to rotate but not to tilt, and 1.2 for all other H atoms.

Results and discussion top

The title salt consists of 1,1'-Di­ethyl-4,4-bi­pyridine-1,1'-diium dications lying across centres of inversion in the space group P21/c and 1,1,3,3-tetra­cyano-2-eth­oxy­propenide (tcnoet) anions occupying general positions; the reference cation was selected as that lying across (1/2, 1/2, 0). The formation of the cation presumably arises as a result of nucleophilic attack by the 4,4'-bi­pyridyl starting material on the 1,1,3,3-tetra­cyano-2-eth­oxy­propenide anion, with transfer of ethyl groups from oxygen to nitro­gen.

The two pyridine rings in the cation are constrained to be parallel but, in the anion, the two independent –C(CN)2 units are rotated, in conrotatory fashion, out of the plane of the central propenide unit. The dihedral angles between the central C3 unit and the –C(CN)2 units containing atoms C11 and C13 are 16.0 (2) and 23.0 (2)°, respectively; these values, and the sense of the rotations, are typical of those observed in other systems containing this anions (Setifi et al., 2013, 2014). Within the anion, the two central C—C distances (Table 2) are very similar, while the four independent C—N distances are all the same within experimental uncertainty, and they are long for their type [mean value (Allen et al., 1987) = 1.136 Å, upper quartile value = 1.142 Å]. The peripheral C—CN distances span a very narrow range, ca 0.01 Å, and all are short for their type [mean value (Allen et al., 1987) = 1.427 Å, lower quartile value = 1.420 Å], consistent with extensive delocalization of the negative charge, as discussed recently (Setifi et al., 2014).

Three independent hydrogen bonds, all of the C—H···N type, are present in the structure (Table 3); the components of the asymmetric unit were selected so that the most nearly linear of the hydrogen bonds falls within the selected asymmetric unit. The hydrogen bond involving atom C2 has a C—H···N angle of only 136° (cf. Wood et al., 2009), but this inter­action is nonetheless regarded as structurally significant since it is a charge-assisted hydrogen bond (Gilli et al., 1994) between a donor which is a component of a dication and an acceptor which is a component of an anion. Moreover, the donor atom concerned, C2, is immediately adjacent to the quaternary N atom, while there is delocalization of the negative charge of the anion onto the terminal N atoms, as noted above.

Because of the inversion symmetry of the cation, this ion acts as a sixfold donor of hydrogen bonds. Such that the reference cation centred across (1/2, 1/2, 0) is directly linked to the six anions at (x, y, z), (-x+1, -y+1, -z), (x, y+1, z), (-x+1, -y, -z), (x, -y+1/2, z+1/2) and (-x+1, y+1/2, -z-1/2). Consistent with the overall stoichiometry, the reference anion at (x, y, z) is directly linked to the three cations centred at (1/2, 1/2, 0), (1/2, -1/2, 0) and (1/2, 0, -1/2), so generating a form of 6:3 coordination, albeit only in two dimensions, as discussed below. Atom N111 is the only N atom in the anion not to participate in the hydrogen bonding; the shortest inter­molecular N···H distance involving atom N111 is 2.90 Å, to atom H8A at (x, -y+1/2, z+1/2), far too long to be structurally significant. Despite the large number of hydrogen bonds formed by the cation, the supra­molecular assembly is only two-dimensional, in the form of a sheet lying parallel to (100). However, the sheet is of considerable complexity, and the supra­molecular assembly can most readily be analysed in terms of the three sub-structures (Ferguson et al., 1998a,b; Gregson et al., 2000) which are formed by the three different combinations of just two of the three hydrogen bonds.

The simplest of the three substructures involves atoms C2 and C6 as the hydrogen-bond donors. Here, the cations centred at (1/2, 1/2, 0) and (1/2, 0, 1/2) provide hydrogen-bond donors, using atoms C2 and C6, respectively, to the anion at (x, -y+1/2, z+1/2), and propagation by inversion of these two inter­actions leads to the formation of a C22(15) (Bernstein et al., 1995) chain running parallel to the [011] direction (Fig. 2). A more complex but still one-dimensional substructure is generated by the two hydrogen bonds having atoms C5 and C6 as the donors, producing a chain of centrosymmetric R22(22) rings running parallel to the [010] direction, in which the cations centred at (1/2, n+1/2, 0) alternate with R22(22) rings centred at (1/2, n, 0), where n represents an integer in each case (Fig. 3). The final possible combination of two hydrogen bonds involves atoms C2 and C5 as the donors, thus excluding the hydrogen bond within the selected asymmetric unit. This combination generates a two-dimensional substructure in the form of a sheet lying parallel to (100) (Fig. 4), but this, of course, does not represent the full complexity of the overall supra­molecular assembly, as it does not include all of the possible hydrogen bonds. The full complexity of the sheet results from the combination of all three substructural motifs.

The supra­molecular assembly of compound (I) may be compared with that of the somewhat similar salt (II) (Androš et al., 2011), as compounds (I) and (II) show some inter­esting resemblances as well as differences (see Scheme). In compound (II), as in compound (I), the cation lies across a centre of inversion, although here in the space group P1 rather than P21/c, and the mono-negative anion occupies a general position; the cation in (II) acts as a sixfold donor of hydrogen bonds, while the anion contains four potential hydrogen-bond acceptors. However, whereas the cation in compound (I) only forms C—H···N hydrogen bonds, that in (II) forms both N—H···O and C—H···O hydrogen bonds; in addition, the anion, as well as containing an intra-anion O—H···O hydrogen bonds, can also acts as a donor in inter-ion hydrogen bonds. Accordingly, the supra­molecular assembly in (II) is different from that in (I), and indeed it is rather simpler; an important building block in the supra­molecular assembly of compound (II) is a centrosymmetric hydrogen-bonded dimer containing two anions, in which an overall R22(10) motif is subdivided into a central R22(4) ring flanked by two inversion-related S(5) rings. These dimeric units are linked by to the cations by three-centre N—H···(O)2 hydrogen bonds, forming a chain containing S(5), R22(4) and R12(5) rings running parallel to the [321] direction [not the [121] direction as stated in the original report (Androš et al., 2011)]. Chains related by translation along [111] are linked by two independent C—H···O hydrogen bonds to form an almost planar sheet lying parallel to (121) which contains, in addition to the ring types within the [321] chains, rings of R42(10), R33(12) and R44(16) types between these chains. Finally, the sheets in compound (II) are linked by ππ stacking inter­actions, whereas such inter­actions are absent from the structure of compound (I), possibly precluded on steric grounds by the presence of the N-ethyl substituent.

Related literature top

For related literature, see: Allen et al. (1987); Androš et al. (2011); Atmani et al. (2008); Benmansour et al. (2007, 2009, 2010); Bernstein et al. (1995); Dupouy et al. (2008, 2009); Ferguson et al. (1998a, 1998b); Gilli et al. (1994); Gregson et al. (2000); Middleton et al. (1958); Setifi et al. (2007, 2009, 2010, 2013, 2014); Thétiot et al. (2003); Wood et al. (2009).

Computing details top

Data collection: APEX2 (Bruker, 2009); cell refinement: APEX2 and SAINT (Bruker, 2009); data reduction: SAINT (Bruker, 2009); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: PLATON (Spek, 2009); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008) and PLATON (Spek, 2009).

Figures top
[Figure 1] Fig. 1. The ionic components of compound (I), showing the atom-labelling scheme and the C—H···N hydrogen bond within the selected asymmetric unit. Displacement ellipsoids are drawn at the 30% probability level, and the atoms marked 'a' are at the symmetry position (-x+1, -y+1, -z).
[Figure 2] Fig. 2. A stereoview of part of the crystal structure of compound (I), showing the formation of one-dimensional substructure in the form of a C22(15) chain parallel to the [011] direction formed using only atoms C2 and C6 as the hydrogen-bond donors. For the sake of clarity, H atoms not involved in the motif shown have been omitted.
[Figure 3] Fig. 3. A stereoview of part of the crystal structure of compound (I), showing the formation of one-dimensional substructure in the form of a chain of R22(22) rings parallel to the [010] direction formed using only atoms C5 and C6 as the hydrogen-bond donors. For the sake of clarity, H atoms not involved in the motif shown have been omitted.
[Figure 4] Fig. 4. A stereoview of part of the crystal structure of compound (I), showing the formation of two-dimensional substructure in the form of a sheet parallel to (100) formed using only atoms C2 and C5 as the hydrogen-bond donors. For the sake of clarity, H atoms not involved in the motif shown have been omitted.
1,1'-Diethyl-4,4'-bipyridine-1,1'-diium bis(1,1,3,3-tetracyano-2-ethoxypropenide top
Crystal data top
C14H18N22+·2C9H5N4OF(000) = 612
Mr = 584.64Dx = 1.243 Mg m3
Monoclinic, P21/cMo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybcCell parameters from 6245 reflections
a = 10.6881 (7) Åθ = 2.0–34.8°
b = 15.2125 (8) ŵ = 0.08 mm1
c = 10.2455 (6) ÅT = 150 K
β = 110.391 (7)°Block, pale yellow
V = 1561.46 (16) Å30.32 × 0.20 × 0.10 mm
Z = 2
Data collection top
3578 independent reflections
Radiation source: fine-focus sealed tube2876 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.035
ω–2θ scansθmax = 27.5°, θmin = 2.4°
Absorption correction: multi-scan
(SADABS; Sheldrick, 2003)
h = 1313
Tmin = 0.967, Tmax = 0.992k = 1917
10001 measured reflectionsl = 1313
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)] = 0.054Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.121H-atom parameters constrained
S = 1.12 w = 1/[σ2(Fo2) + (0.0432P)2 + 0.5424P]
where P = (Fo2 + 2Fc2)/3
3578 reflections(Δ/σ)max = 0.001
201 parametersΔρmax = 0.21 e Å3
0 restraintsΔρmin = 0.21 e Å3
Crystal data top
C14H18N22+·2C9H5N4OV = 1561.46 (16) Å3
Mr = 584.64Z = 2
Monoclinic, P21/cMo Kα radiation
a = 10.6881 (7) ŵ = 0.08 mm1
b = 15.2125 (8) ÅT = 150 K
c = 10.2455 (6) Å0.32 × 0.20 × 0.10 mm
β = 110.391 (7)°
Data collection top
3578 independent reflections
Absorption correction: multi-scan
(SADABS; Sheldrick, 2003)
2876 reflections with I > 2σ(I)
Tmin = 0.967, Tmax = 0.992Rint = 0.035
10001 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0540 restraints
wR(F2) = 0.121H-atom parameters constrained
S = 1.12Δρmax = 0.21 e Å3
3578 reflectionsΔρmin = 0.21 e Å3
201 parameters
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
N10.71639 (14)0.36359 (9)0.25561 (14)0.0279 (3)
C20.68195 (18)0.44238 (11)0.29166 (17)0.0326 (4)
C30.59660 (17)0.49695 (11)0.19394 (16)0.0295 (4)
C40.54419 (15)0.47065 (10)0.05454 (15)0.0216 (3)
C50.57855 (17)0.38725 (10)0.02190 (17)0.0268 (3)
C60.66381 (17)0.33512 (11)0.12366 (17)0.0289 (4)
C70.8126 (2)0.30753 (13)0.36364 (19)0.0419 (5)
C80.9434 (2)0.35362 (18)0.4293 (2)0.0611 (7)
C110.78557 (17)0.02696 (10)0.34610 (17)0.0272 (3)
C120.74379 (15)0.05961 (10)0.35496 (16)0.0244 (3)
C130.68960 (17)0.11623 (10)0.24024 (17)0.0278 (4)
C1110.86714 (17)0.07327 (11)0.46718 (18)0.0296 (4)
N1110.93116 (16)0.11456 (10)0.56078 (17)0.0404 (4)
C1120.74700 (19)0.07493 (11)0.21941 (18)0.0329 (4)
N1120.7174 (2)0.11723 (10)0.12027 (18)0.0493 (5)
O1210.75622 (12)0.08330 (7)0.48549 (11)0.0291 (3)
C1210.78374 (19)0.17461 (11)0.53058 (18)0.0333 (4)
C1220.8659 (2)0.17263 (13)0.68351 (19)0.0389 (4)
N1310.53505 (17)0.24711 (11)0.23439 (17)0.0419 (4)
C1310.60543 (18)0.18855 (11)0.24026 (17)0.0307 (4)
N1320.7310 (2)0.09459 (10)0.00947 (17)0.0474 (4)
C1320.71189 (19)0.10195 (11)0.11281 (18)0.0323 (4)
Atomic displacement parameters (Å2) top
N10.0345 (8)0.0254 (7)0.0236 (7)0.0027 (6)0.0099 (6)0.0024 (5)
C20.0447 (10)0.0299 (9)0.0209 (8)0.0042 (7)0.0082 (7)0.0033 (6)
C30.0411 (10)0.0246 (9)0.0224 (8)0.0048 (7)0.0105 (7)0.0038 (6)
C40.0238 (8)0.0215 (8)0.0209 (7)0.0028 (6)0.0097 (6)0.0008 (6)
C50.0342 (9)0.0233 (8)0.0222 (8)0.0031 (6)0.0090 (7)0.0039 (6)
C60.0384 (10)0.0226 (8)0.0273 (9)0.0022 (7)0.0136 (7)0.0015 (6)
C70.0586 (13)0.0344 (10)0.0267 (9)0.0167 (9)0.0074 (9)0.0067 (7)
C80.0474 (13)0.0751 (17)0.0455 (13)0.0225 (12)0.0029 (10)0.0035 (11)
C110.0321 (9)0.0250 (8)0.0260 (8)0.0012 (7)0.0118 (7)0.0011 (6)
C120.0248 (8)0.0257 (8)0.0254 (8)0.0048 (6)0.0122 (6)0.0011 (6)
C130.0343 (9)0.0230 (8)0.0283 (8)0.0019 (6)0.0136 (7)0.0008 (6)
C1110.0334 (9)0.0241 (8)0.0336 (9)0.0032 (7)0.0146 (8)0.0017 (7)
N1110.0432 (9)0.0366 (9)0.0392 (9)0.0039 (7)0.0115 (8)0.0057 (7)
C1120.0474 (11)0.0209 (8)0.0324 (9)0.0006 (7)0.0166 (8)0.0035 (7)
N1120.0854 (14)0.0266 (9)0.0366 (9)0.0050 (8)0.0222 (9)0.0014 (7)
O1210.0408 (7)0.0244 (6)0.0265 (6)0.0020 (5)0.0170 (5)0.0013 (4)
C1210.0424 (10)0.0268 (9)0.0318 (9)0.0008 (7)0.0145 (8)0.0046 (7)
C1220.0436 (11)0.0410 (11)0.0312 (10)0.0011 (8)0.0120 (8)0.0048 (8)
N1310.0503 (10)0.0410 (10)0.0369 (9)0.0149 (8)0.0184 (8)0.0141 (7)
C1310.0359 (9)0.0315 (9)0.0260 (8)0.0009 (7)0.0124 (7)0.0076 (7)
N1320.0815 (13)0.0317 (9)0.0365 (9)0.0048 (8)0.0301 (9)0.0021 (7)
C1320.0467 (11)0.0213 (8)0.0293 (9)0.0035 (7)0.0138 (8)0.0016 (6)
Geometric parameters (Å, º) top
N1—C61.342 (2)C11—C121.404 (2)
N1—C21.343 (2)C11—C1111.429 (2)
N1—C71.489 (2)C11—C1121.419 (2)
C2—C31.374 (2)C111—N1111.151 (2)
C2—H20.9500C112—N1121.150 (2)
C3—C41.399 (2)C12—O1211.3462 (18)
C3—H30.9500C12—C131.409 (2)
C4—C51.394 (2)C13—C1311.421 (2)
C4—C4i1.484 (3)C13—C1321.423 (2)
C5—C61.373 (2)O121—C1211.461 (2)
C5—H50.9500C121—C1221.506 (2)
C7—C81.498 (3)C121—H12B0.9900
C8—H8B0.9800C131—N1311.154 (2)
C8—H8C0.9800C132—N1321.152 (2)
C6—N1—C2120.42 (14)H8A—C8—H8C109.5
C6—N1—C7120.15 (14)H8B—C8—H8C109.5
C2—N1—C7119.43 (14)C12—C11—C112122.95 (15)
N1—C2—C3121.00 (15)C12—C11—C111121.20 (15)
N1—C2—H2119.5C112—C11—C111115.82 (14)
C3—C2—H2119.5O121—C12—C11113.07 (14)
C2—C3—C4119.95 (14)O121—C12—C13122.33 (14)
C2—C3—H3120.0C11—C12—C13124.56 (14)
C4—C3—H3120.0C12—C13—C131123.33 (15)
C5—C4—C3117.40 (14)C12—C13—C132121.37 (15)
C5—C4—C4i121.25 (17)C131—C13—C132115.26 (15)
C3—C4—C4i121.35 (17)N111—C111—C11176.44 (18)
C6—C5—C4120.29 (15)N112—C112—C11176.89 (19)
C6—C5—H5119.9C12—O121—C121120.53 (12)
C4—C5—H5119.9O121—C121—C122106.87 (14)
N1—C6—C5120.85 (15)O121—C121—H12A110.3
N1—C7—C8111.15 (17)C122—C121—H12B110.3
H8A—C8—H8B109.5N131—C131—C13177.19 (19)
C7—C8—H8C109.5N132—C132—C13176.76 (18)
C6—N1—C2—C32.6 (3)C112—C11—C12—O121160.94 (15)
C7—N1—C2—C3178.00 (17)C111—C11—C12—O12117.0 (2)
N1—C2—C3—C40.0 (3)C13—C12—C11—C111165.22 (16)
C2—C3—C4—C52.1 (2)C13—C12—C11—C11216.9 (3)
C2—C3—C4—C4i177.66 (18)O121—C12—C13—C13121.3 (2)
C3—C4—C5—C61.9 (2)C11—C12—C13—C131156.34 (16)
C4i—C4—C5—C6177.93 (17)O121—C12—C13—C132161.40 (15)
C2—N1—C6—C52.8 (2)C11—C12—C13—C13221.0 (3)
C7—N1—C6—C5177.73 (16)C11—C12—O121—C121149.08 (15)
C4—C5—C6—N10.6 (2)C13—C12—O121—C12133.0 (2)
C6—N1—C7—C8121.38 (19)C12—O121—C121—C122148.22 (15)
C2—N1—C7—C859.2 (2)
Symmetry code: (i) x+1, y+1, z.
Hydrogen-bond geometry (Å, º) top
C2—H2···N132ii0.952.373.131 (2)136
C5—H5···N131iii0.952.413.270 (2)150
C6—H6···N1120.952.473.366 (2)157
Symmetry codes: (ii) x, y+1/2, z+1/2; (iii) x+1, y, z.

Experimental details

Crystal data
Chemical formulaC14H18N22+·2C9H5N4O
Crystal system, space groupMonoclinic, P21/c
Temperature (K)150
a, b, c (Å)10.6881 (7), 15.2125 (8), 10.2455 (6)
β (°) 110.391 (7)
V3)1561.46 (16)
Radiation typeMo Kα
µ (mm1)0.08
Crystal size (mm)0.32 × 0.20 × 0.10
Data collection
DiffractometerBruker APEXII CCD
Absorption correctionMulti-scan
(SADABS; Sheldrick, 2003)
Tmin, Tmax0.967, 0.992
No. of measured, independent and
observed [I > 2σ(I)] reflections
10001, 3578, 2876
(sin θ/λ)max1)0.650
R[F2 > 2σ(F2)], wR(F2), S 0.054, 0.121, 1.12
No. of reflections3578
No. of parameters201
H-atom treatmentH-atom parameters constrained
Δρmax, Δρmin (e Å3)0.21, 0.21

Computer programs: APEX2 (Bruker, 2009), APEX2 and SAINT (Bruker, 2009), SAINT (Bruker, 2009), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008) and PLATON (Spek, 2009).

Selected geometric parameters (Å, º) top
C11—C121.404 (2)C12—C131.409 (2)
C11—C1111.429 (2)C13—C1311.421 (2)
C11—C1121.419 (2)C13—C1321.423 (2)
C111—N1111.151 (2)C131—N1311.154 (2)
C112—N1121.150 (2)C132—N1321.152 (2)
C13—C12—C11—C111165.22 (16)C11—C12—C13—C131156.34 (16)
C13—C12—C11—C11216.9 (3)C11—C12—C13—C13221.0 (3)
Hydrogen-bond geometry (Å, º) top
C2—H2···N132i0.952.373.131 (2)136
C5—H5···N131ii0.952.413.270 (2)150
C6—H6···N1120.952.473.366 (2)157
Symmetry codes: (i) x, y+1/2, z+1/2; (ii) x+1, y, z.

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