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Acta Cryst. (2014). E70, m6    [ doi:10.1107/S1600536813032558 ]

Bis(4-amino­pyridinium) hexa­aqua­nickel(II) bis­(sulfate)

T. Sahbani, W. Smirani Sta and M. Rzaigui

Abstract top

In the title compound, (C5H7N2)2[Ni(H2O)6](SO4)2, the NiII cation is located on an inversion centre and is coordinated by six aqua ligands in a slightly distorted octa­hedral coordination environment. The [Ni(H2O)6]2+ ions are connected through an extensive network of O-H...O hydrogen bonds to sulfate anions, leading to the formation of layers parallel to (001). The 4-amino­pyridinium cations are located between these layers and are connected to the anionic framework by N-H...O hydrogen bonds. Weak [pi]-[pi] inter­actions between the pyridine rings, with a centroid-centroid distance of 3.754 (9) Å, provide additional stability to the crystal packing.

Comment top

4-Aminopyridine (fampridine) is clinically used in the treatment of the Lambert-Eaton myasthenic syndrome and of multiple sclerosis. It prolongs action potentials by blocking potassium channels, thereby increases transmitter release at the neuromuscular junction (Judge & Bever, 2006; Schwid et al., 1997; Strupp et al., 2004). The combination of this amine with sulfuric acid leads to the formation of bis(4-aminopyridinium) sulfate monohydrate (Quah et al., 2010). In general, sulfates combined with transition metal and organic groups can lead to interesting materials as model compounds of ferroelectric and ferroelastic domains, but also to potentially applicable compounds with interesting magnetic properties (Rekik et al., 2008). For this reasons, we focused to study the crystal structure of the title compound, (C5H7N2)2[Ni(H2O)6](SO4)2, (I).

The crystal structure of compound (I) has an asymmetric unit consisting of one half of the cationic complex [Ni(H2O)6]2+, an uncoordinating sulfate anion, and one 4-aminopyridinium cation, C5H7N22+ (Fig. 1). The Ni(II) ion, located on an inversion centre, exhibits a distorted octahedral coordination environment with Ni–O distances ranging from 2.0388 (11) to 2.0701 (12) Å. The values of O—Ni—O angles are between 86.04 (5) and 180.00 (7). These values agree with those for other [Ni(H2O)6]2+ groups (Hajlaoui et al., 2011).

A proton transfer from sulfuric acid to atom N2 of 4-aminopyridine resulted in the formation of a 4-aminopyridinium cation. This protonation leads to the widening of the C3–N2–C4 angle of the pyridine ring to 121.02 (15)°, compared to 115.25 (13)° in the unprotonated 4-aminopyridine (Anderson et al., 2005). Such a protonation is observed in various 4-aminopyridine acid complexes (Rotondo et al., 2009). The 4-aminopyridine ring is essentially planar with a maximum deviation from planarity of 0.002 (9) Å.

In the crystal structure, intermolecular O—H···O hydrogen bonds, established between the complex cations and sulfate anions, generate layers parallel to (001) (Fig. 2). The crystal packing of the title complex is stabilized by N—H···O hydrogen bonds between C5H7N22+ cations and sulfate anions and by π···π interactions between parallel pyridine rings [ring centroid-to-centroid distance: 3.754 (9) Å], which link the different species into a three dimensional network (Fig. 3).

Related literature top

For applications of metal sulfate complexes, see: Rekik et al. (2008). For clinical background to 4-aminopyridine, see: Judge & Bever (2006); Schwid et al. (1997); Strupp et al. (2004). For related compounds, see: Anderson et al. (2005); Hajlaoui et al. (2011); Quah et al. (2010); Rotondo et al. (2009).

Experimental top

4-Aminopyridine (0.19g, 2 mmol) and nickel sulfate hexahydrate (0.26g, 1 mmol) were dissolved in 15 ml of water. The resulting solution was added to an aqueous solution of sulfuric acid (0.1 M). The mixture was stirred for 20 min at room temperature. After slow evaporation during few days at ambient temperature, blue single crystals of the title compound appeared in the solution.

Refinement top

The H atoms bonded to C and N2 atoms were positioned geometrically and treated as riding on their parent atoms, [N—H = 0.86, C—H =0.93 Å with Uiso(H) = 1.2 Ueq(C,N), but those attached to N1 were located in a difference Fourier map and refined freely. O—H bond lengths and distances between two H atoms of each water molecule were restrained to be 0.85 (2) and 1.37 (2) Å, with Uiso(H) = 1.5 Ueq(O).

Computing details top

Data collection: CAD-4 EXPRESS (Enraf–Nonius, 1994); cell refinement: CAD-4 EXPRESS (Enraf–Nonius, 1994); data reduction: XCAD4 (Harms & Wocadlo, 1995); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012); software used to prepare material for publication: WinGX (Farrugia, 2012).

Figures top
[Figure 1] Fig. 1. View of the molecular entities of the title compound with atom numbering scheme. Displacement ellipsoids for non-H atoms are drawn at the 30% probability level. [Symmetry code: i) -x, -y, -z].
[Figure 2] Fig. 2. View of a corrugated layer of the title compound parallel to (001). Sulfate polyhedra are shown in yellow and cobalt polyhadra in cyan. Hydrogen bonds are denoted by dashed lines.
[Figure 3] Fig. 3. View of the molecular arrangement in the title structure viewed along [100]. Hydrogen bonds are denoted by dashed lines.
Bis(4-aminopyridinium) hexaaquanickel(II) bis(sulfate) top
Crystal data top
(C5H7N2)2[Ni(H2O)6](SO4)2Z = 1
Mr = 549.18F(000) = 286
Triclinic, P1Dx = 1.773 Mg m3
Hall symbol: -P 1Ag Kα radiation, λ = 0.56085 Å
a = 6.212 (2) ÅCell parameters from 25 reflections
b = 7.015 (3) Åθ = 9–11°
c = 12.422 (2) ŵ = 0.64 mm1
α = 100.61 (3)°T = 293 K
β = 99.26 (2)°Block, blue
γ = 99.57 (2)°0.30 × 0.20 × 0.20 mm
V = 514.3 (3) Å3
Data collection top
Enraf–Nonius TurboCAD-4
diffractometer
Rint = 0.014
Radiation source: fine-focus sealed tubeθmax = 28.0°, θmin = 2.4°
Graphite monochromatorh = 1010
ω scansk = 1111
5919 measured reflectionsl = 220
5022 independent reflections2 standard reflections every 120 min
3986 reflections with I > 2σ(I) intensity decay: 5%
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)] = 0.038Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.097H atoms treated by a mixture of independent and constrained refinement
S = 1.11 w = 1/[σ2(Fo2) + (0.0459P)2 + 0.2397P]
where P = (Fo2 + 2Fc2)/3
5022 reflections(Δ/σ)max = 0.001
174 parametersΔρmax = 0.75 e Å3
6 restraintsΔρmin = 1.06 e Å3
Crystal data top
(C5H7N2)2[Ni(H2O)6](SO4)2γ = 99.57 (2)°
Mr = 549.18V = 514.3 (3) Å3
Triclinic, P1Z = 1
a = 6.212 (2) ÅAg Kα radiation, λ = 0.56085 Å
b = 7.015 (3) ŵ = 0.64 mm1
c = 12.422 (2) ÅT = 293 K
α = 100.61 (3)°0.30 × 0.20 × 0.20 mm
β = 99.26 (2)°
Data collection top
Enraf–Nonius TurboCAD-4
diffractometer
Rint = 0.014
5919 measured reflectionsθmax = 28.0°
5022 independent reflections2 standard reflections every 120 min
3986 reflections with I > 2σ(I) intensity decay: 5%
Refinement top
R[F2 > 2σ(F2)] = 0.038H atoms treated by a mixture of independent and constrained refinement
wR(F2) = 0.097Δρmax = 0.75 e Å3
S = 1.11Δρmin = 1.06 e Å3
5022 reflectionsAbsolute structure: ?
174 parametersAbsolute structure parameter: ?
6 restraintsRogers parameter: ?
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.

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 > 2sigma(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 (Å2) top
xyzUiso*/Ueq
Ni10.00000.00000.00000.01654 (6)
O10.15341 (17)0.21342 (15)0.07350 (9)0.02370 (18)
O20.28416 (17)0.11424 (15)0.12233 (10)0.0257 (2)
O30.10291 (17)0.16756 (15)0.10704 (9)0.02297 (18)
C10.9486 (2)0.2906 (2)0.45752 (12)0.0243 (2)
N20.9660 (3)0.1384 (2)0.68016 (12)0.0418 (4)
H10.97140.09030.74960.050*
C30.7706 (3)0.2354 (3)0.61472 (15)0.0395 (4)
H30.64340.25070.64540.047*
C51.1512 (3)0.1901 (2)0.53005 (15)0.0316 (3)
H51.28300.17520.50320.038*
C41.1524 (3)0.1156 (3)0.63905 (16)0.0389 (4)
H41.28560.04730.68610.047*
N10.9396 (3)0.3609 (3)0.35006 (12)0.0338 (3)
C20.7559 (3)0.3115 (3)0.50454 (13)0.0305 (3)
H20.61910.37730.46010.037*
H1030.056 (4)0.261 (3)0.1106 (18)0.030 (5)*
H2030.236 (3)0.205 (3)0.1029 (16)0.023 (4)*
H71.061 (5)0.333 (4)0.327 (2)0.062 (8)*
H60.827 (5)0.410 (4)0.307 (2)0.048 (7)*
S10.62063 (5)0.35433 (4)0.81367 (3)0.02033 (7)
O50.85539 (16)0.44487 (16)0.86606 (11)0.0306 (2)
O70.53371 (17)0.21768 (17)0.88249 (10)0.0295 (2)
O40.48753 (19)0.50858 (17)0.81131 (13)0.0354 (3)
O60.6085 (2)0.2407 (2)0.70136 (11)0.0420 (3)
H1O10.257 (3)0.228 (3)0.0278 (18)0.047 (7)*
H2O10.065 (4)0.327 (3)0.098 (2)0.059 (8)*
H1O20.363 (4)0.225 (2)0.129 (2)0.047 (7)*
H2O20.367 (3)0.034 (3)0.1328 (19)0.032 (5)*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Ni10.01578 (10)0.01730 (10)0.01684 (10)0.00301 (7)0.00362 (7)0.00442 (7)
O10.0239 (4)0.0213 (4)0.0263 (5)0.0059 (3)0.0053 (4)0.0045 (4)
O20.0219 (4)0.0216 (4)0.0301 (5)0.0031 (3)0.0012 (4)0.0038 (4)
O30.0195 (4)0.0242 (4)0.0287 (5)0.0051 (3)0.0078 (4)0.0113 (4)
C10.0253 (6)0.0268 (6)0.0222 (6)0.0068 (5)0.0044 (5)0.0081 (5)
N20.0545 (10)0.0452 (8)0.0222 (6)0.0137 (7)0.0035 (6)0.0014 (6)
C30.0401 (9)0.0538 (10)0.0278 (7)0.0136 (8)0.0131 (7)0.0080 (7)
C50.0255 (6)0.0327 (7)0.0340 (7)0.0020 (5)0.0014 (6)0.0079 (6)
C40.0395 (8)0.0317 (8)0.0358 (8)0.0025 (6)0.0064 (7)0.0006 (6)
N10.0303 (6)0.0498 (8)0.0217 (6)0.0093 (6)0.0061 (5)0.0071 (6)
C20.0256 (6)0.0398 (8)0.0253 (6)0.0043 (6)0.0061 (5)0.0064 (6)
S10.01526 (12)0.02018 (13)0.02486 (15)0.00201 (10)0.00201 (10)0.00623 (11)
O50.0164 (4)0.0257 (5)0.0454 (7)0.0001 (3)0.0019 (4)0.0076 (5)
O70.0222 (4)0.0331 (5)0.0390 (6)0.0067 (4)0.0098 (4)0.0184 (5)
O40.0231 (5)0.0246 (5)0.0571 (8)0.0068 (4)0.0024 (5)0.0124 (5)
O60.0400 (7)0.0518 (8)0.0275 (6)0.0023 (6)0.0070 (5)0.0019 (5)
Geometric parameters (Å, º) top
Ni1—O3i2.0388 (11)N2—C41.336 (3)
Ni1—O32.0388 (11)N2—C31.342 (3)
Ni1—O12.0578 (12)N2—H10.8600
Ni1—O1i2.0578 (12)C3—C21.357 (2)
Ni1—O2i2.0701 (12)C3—H30.9300
Ni1—O22.0701 (12)C5—C41.357 (3)
O1—H1O10.818 (15)C5—H50.9300
O1—H2O10.860 (15)C4—H40.9300
O2—H1O20.828 (15)N1—H70.85 (3)
O2—H2O20.839 (14)N1—H60.79 (3)
O3—H1030.77 (2)C2—H20.9300
O3—H2030.82 (2)S1—O61.4574 (14)
C1—N11.324 (2)S1—O41.4686 (12)
C1—C21.412 (2)S1—O51.4793 (12)
C1—C51.413 (2)S1—O71.4897 (12)
O3i—Ni1—O3180.00 (5)C2—C1—C5117.08 (14)
O3i—Ni1—O192.26 (5)C4—N2—C3121.02 (15)
O3—Ni1—O187.74 (5)C4—N2—H1119.5
O3i—Ni1—O1i87.74 (5)C3—N2—H1119.5
O3—Ni1—O1i92.26 (5)N2—C3—C2121.01 (17)
O1—Ni1—O1i180.00 (7)N2—C3—H3119.5
O3i—Ni1—O2i93.96 (5)C2—C3—H3119.5
O3—Ni1—O2i86.04 (5)C4—C5—C1119.69 (16)
O1—Ni1—O2i89.83 (5)C4—C5—H5120.2
O1i—Ni1—O2i90.17 (5)C1—C5—H5120.2
O3i—Ni1—O286.04 (5)N2—C4—C5121.31 (16)
O3—Ni1—O293.96 (5)N2—C4—H4119.3
O1—Ni1—O290.17 (5)C5—C4—H4119.3
O1i—Ni1—O289.83 (5)C1—N1—H7115.4 (19)
O2i—Ni1—O2180.00 (7)C1—N1—H6123 (2)
Ni1—O1—H1O1109.7 (18)H7—N1—H6121 (3)
Ni1—O1—H2O1112.7 (19)C3—C2—C1119.88 (16)
H1O1—O1—H2O1107.0 (19)C3—C2—H2120.1
Ni1—O2—H1O2123.5 (17)C1—C2—H2120.1
Ni1—O2—H2O2114.9 (14)O6—S1—O4111.02 (9)
H1O2—O2—H2O2108.4 (18)O6—S1—O5109.76 (8)
Ni1—O3—H103118.3 (16)O4—S1—O5110.07 (7)
Ni1—O3—H203118.9 (13)O6—S1—O7108.89 (8)
H103—O3—H203103.5 (18)O4—S1—O7109.07 (8)
N1—C1—C2121.41 (14)O5—S1—O7107.96 (7)
N1—C1—C5121.51 (14)
Symmetry code: (i) x, y, z.
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N2—H1···O2ii0.862.433.102 (2)136
N2—H1···O3iii0.862.232.983 (2)147
O1—H1O1···O7ii0.82 (2)2.03 (2)2.8231 (16)163 (2)
O1—H2O1···O5iv0.86 (2)1.82 (2)2.6741 (16)172 (2)
O2—H1O2···O4v0.83 (2)1.90 (2)2.6952 (17)161 (2)
O2—H2O2···O7ii0.84 (2)1.95 (2)2.7480 (16)159 (2)
N1—H6···O4ii0.80 (3)2.17 (3)2.957 (2)173 (3)
N1—H7···O5vi0.86 (3)2.55 (3)3.153 (2)129 (2)
N1—H7···O6vi0.86 (3)2.15 (3)2.998 (2)170 (2)
O3—H103···O5vii0.77 (2)1.96 (2)2.7072 (15)164 (2)
O3—H203···O7viii0.815 (19)1.876 (19)2.6682 (15)164 (2)
Symmetry codes: (ii) x+1, y, z+1; (iii) x+1, y, z+1; (iv) x1, y1, z1; (v) x+1, y+1, z+1; (vi) x+2, y, z+1; (vii) x1, y, z1; (viii) x, y, z1.
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N2—H1···O2i0.862.433.102 (2)136
N2—H1···O3ii0.862.232.983 (2)147
O1—H1O1···O7i0.82 (2)2.03 (2)2.8231 (16)163 (2)
O1—H2O1···O5iii0.86 (2)1.82 (2)2.6741 (16)172 (2)
O2—H1O2···O4iv0.832 (18)1.895 (17)2.6952 (17)161 (2)
O2—H2O2···O7i0.84 (2)1.95 (2)2.7480 (16)159 (2)
N1—H6···O4i0.80 (3)2.17 (3)2.957 (2)173 (3)
N1—H7···O5v0.86 (3)2.55 (3)3.153 (2)129 (2)
N1—H7···O6v0.86 (3)2.15 (3)2.998 (2)170 (2)
O3—H103···O5vi0.77 (2)1.96 (2)2.7072 (15)164 (2)
O3—H203···O7vii0.815 (19)1.876 (19)2.6682 (15)164 (2)
Symmetry codes: (i) x+1, y, z+1; (ii) x+1, y, z+1; (iii) x1, y1, z1; (iv) x+1, y+1, z+1; (v) x+2, y, z+1; (vi) x1, y, z1; (vii) x, y, z1.
references
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