Bis(3-amino­pyrazine-2-carboxyl­ato-κ²N¹,O)di­aqua­nickel(II) dihydrate

In the title compound, [Ni(C₅H₄N₃O₂)₂(H₂O)₂]·2H₂O, the Ni^II ion lies on an inversion center and is coordinated in an slightly distorted octa­hedral environment by two N,O-chelating 3-amino­pyrazine-2-carboxyl­ate (APZC) ligands in the equatorial plane and two trans-axial aqua ligands. In the crystal, O—H...O, N—H...O and O—H...N hydrogen bonds involving the solvent water mol­ecules, aqua and APZC ligands form layers parallel to (010). These layers are linked further via O—H...O, N—H...O and C—H...O hydrogen bonds involving the axial aqua ligands, amino groups and the carboxyl­ate groups of the APZC ligands, forming a three-dimensional network.

Key indicators

• Single-crystal X-ray study
• T = 150 K
• Mean [sigma](C-C) = 0.004 Å
• R factor = 0.028
• wR factor = 0.073
• Data-to-parameter ratio = 10.4

checkCIF/PLATON results

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Alert level C
PLAT250_ALERT_2_C Large U3/U1 Ratio for Average U(i,j) Tensor ....        2.1
PLAT417_ALERT_2_C Short Inter D-H..H-D       H1A    ..  H2B     ..       2.11 Ang.
PLAT910_ALERT_3_C Missing # of FCF Reflections Below Th(Min) .....          1
PLAT911_ALERT_3_C Missing # FCF Refl Between THmin & STh/L=  0.596          6

Alert level G
PLAT005_ALERT_5_G No _iucr_refine_instructions_details  in the CIF          ?
PLAT007_ALERT_5_G Note: Number of Unrefined Donor-H Atoms ........          2
PLAT909_ALERT_3_G Percentage of Observed Data at Theta(Max) still          75 %

   0 ALERT level A = Most likely a serious problem - resolve or explain
   0 ALERT level B = A potentially serious problem, consider carefully
   4 ALERT level C = Check. Ensure it is not caused by an omission or oversight
   3 ALERT level G = General information/check it is not something unexpected

   0 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   2 ALERT type 2 Indicator that the structure model may be wrong or deficient
   3 ALERT type 3 Indicator that the structure quality may be low
   0 ALERT type 4 Improvement, methodology, query or suggestion
   2 ALERT type 5 Informative message, check

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S1. Comment

The pyrazine-2-carboxylic acid bridging ligand, owing to its ability to act in acidic environments (Zhang & Mitchison, 2003), has been extensively studied for biological applications, such as anti-tubercular (Manju et al., 2010), antipyretic, antitumor, and anticancer (Chanda et al., 2004). An additional amino substitution on 3-amino-2-pyrazine carboxylic acid could be expected to enhance crystal packing through extensive hydrogen bonding. APZC has a large variety of coordination geometries in metal complexes (Leciejewicz et al., 1997, 1998; Ptasiewicz-Bak & Leciejewicz, 1997; Tayebee et al., 2008).

In continuation of our search to enrich the variety of such kinds of hybrid compounds and to investigate the influence of hydrogen bonds on the structural features (Bouacida et al., 2007, 2009), we report here the synthesis and crystal structure of the title compound, (I), as a extention of our earlier work on N,O chelated ligands (Bouchene et al.2013) which can be involved in covalent interactions in metal coordination chemistry.

The asymmetric unit of (I) consists of one-half of the molecule, with the other half generated by a crystallographic inversion center. The molecular structure is shown in Fig. 1. The Ni^II ion is coordinated by two 3-amino-2-pyrazine carboxylate ligands via N,O-chelating groups in the equatorial plane and two aqua O atoms in the axial sites forming a slightly distorted octahedral coordination environment. The Ni—N, Ni—O and Ni—O_aqua distances are consistent with the reported data for the anhydrous Ni(II)(APZC)₂(H₂O)₂ complex (Ptasiewicz-Bak & Leciejewicz, 1999). In the crystal, the solvent water molecules and complex molecules are involved in intermolecular O—H···O, O—H···N and N—H···O hydrogen bonds forming two-dimensional layers parallel to (010) (Fig.2). Further O—H···O hydrogen bonds (Fig.3) involving the aqua ligands, N—H···.O hydrogen bonds the carboxylate groups of the APZC ligands form a three-dimensional network.

Related literature

For background to hybrid compounds, see: Bouchene et al. (2013); Bouacida et al. (2007, 2009). For the structure of the non-hydrated analogue, see: Ptasiewicz-Bak & Leciejewicz (1999). For 3-aminopyrazine-2-carboxylate–metal (M) complexes, see: Bouchene et al. (2013) [M = Co(II)]; Leciejewicz et al. (1997) [M = Ca(II)]; Leciejewicz et al. (1998) [M = Sr(II)]; Ptasiewicz-Bak & Leciejewicz (1997) [M = Mg(II)]; Tayebee et al. (2008) [M = Na(I)]; Ptasiewicz-Bak & Leciejewicz (1999). For proprieties and applications of pyrazine-2-carboxylic acid, see: Zhang & Mitchison (2003); Manju & Chaudhary, (2010); Chanda & Sangeetika (2004).

S2. Experimental

Nickel dichloride hexahydrate (0.2 mmol) and 3-aminopyrazine-2-carboxylic acid (0.02 mmol) were dissolved in acidified water with concentrated hydrogen chloride acid (37%). Light green crystals, suitable for X-ray diffraction study, were obtained from evaporation of obtained solution for three days.

S3. Refinement

The H atoms bonded to C and N were located in differnce Fourier maps but subsequently introduced in calculated positions and treated as riding on their parent atoms (C or N) with C—H = 0.93 Å and N—H = 0.86 Å with U_iso(H) = 1.2U_eq(C or N). Atoms H1W and H2W were located in a difference Fourier map and refined isotropically wirh U_iso(H) = 1.5U_eq(O).

Computing details

Data collection: APEX2 (Bruker, 2011); cell refinement: SAINT (Bruker, 2011); data reduction: SAINT (Bruker, 2011); program(s) used to solve structure: SIR2002 (Burla et al., 2005); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012) and DIAMOND (Brandenburg & Berndt, 2001); software used to prepare material for publication: WinGX (Farrugia, 2012).

Figures

	Fig. 1. The molecular structure of the title compound. Displacement ellipsoids are drawn at the 50% probability level. H atoms are represented as small spheres of arbitrary radii. Symmetry code: (i)-x+1, -y+1, -z+2.
	Fig. 2. Partial packing plot viewed along the b axis showing the hydrogen bonds (dashed lines) forming layers.
	Fig. 3. Partial packing of (I) showing only the O—H···O hydrogen bonds which connect the layers in Fig. 2 into a three-dimensional network.

Bis(3-aminopyrazine-2-carboxylato-κ²N¹,O)diaquanickel(II) dihydrate

Crystal data

[Ni(C5H4N3O2)2(H2O)2]·2H2O	F(000) = 420
Mr = 406.98	Dx = 1.788 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
a = 9.7939 (15) Å	Cell parameters from 2285 reflections
b = 5.1123 (9) Å	θ = 2.7–25°
c = 16.776 (3) Å	µ = 1.34 mm^−1
β = 115.838 (11)°	T = 150 K
V = 756.0 (2) Å^3	Cube, white
Z = 2	0.18 × 0.16 × 0.15 mm

Data collection

Bruker APEXII CCD diffractometer	1121 reflections with I > 2σ(I)
Radiation source: sealed tube	Rint = 0.051
Graphite monochromator	θmax = 25.1°, θmin = 2.7°
ϕ and ω scans	h = −11→11
6200 measured reflections	k = −6→6
1326 independent reflections	l = −19→19

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.028	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.073	H atoms treated by a mixture of independent and constrained refinement
S = 1.04	w = 1/[σ^2(Fo^2) + (0.0363P)^2 + 0.4886P] where P = (Fo^2 + 2Fc^2)/3
1326 reflections	(Δ/σ)max < 0.001
127 parameters	Δρmax = 0.36 e Å^−3
0 restraints	Δρmin = −0.59 e Å^−3

Special details

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s 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 > σ(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 (Ų)

	x	y	z	Uiso*/Ueq
C1	0.2428 (3)	0.2367 (5)	0.99519 (16)	0.0089 (5)
C2	0.2750 (3)	0.4494 (4)	1.06347 (15)	0.0079 (5)
C3	0.1864 (3)	0.4915 (5)	1.11094 (15)	0.0090 (5)
C4	0.3430 (3)	0.8353 (5)	1.18295 (16)	0.0098 (5)
H4	0.3692	0.9711	1.2239	0.012*
C5	0.4304 (3)	0.7942 (5)	1.13805 (15)	0.0097 (5)
H5	0.5141	0.8999	1.1492	0.012*
N1	0.3937 (2)	0.6010 (4)	1.07831 (13)	0.0074 (4)
N2	0.2227 (2)	0.6890 (4)	1.17019 (13)	0.0102 (4)
N3	0.0696 (2)	0.3396 (4)	1.10092 (14)	0.0125 (5)
H1N	0.0202	0.3689	1.1316	0.015*
H2N	0.0436	0.2122	1.0637	0.015*
O1	0.33555 (17)	0.2240 (3)	0.96010 (11)	0.0090 (4)
O2	0.13487 (18)	0.0885 (3)	0.97784 (12)	0.0137 (4)
O1W	0.6426 (2)	0.2542 (4)	1.10017 (12)	0.0102 (4)
H1A	0.726 (3)	0.312 (6)	1.1356 (19)	0.015*
H1B	0.652 (3)	0.124 (6)	1.083 (2)	0.015*
O2W	0.0735 (2)	0.6137 (4)	0.76616 (12)	0.0133 (4)
H2A	0.046 (4)	0.472 (6)	0.754 (2)	0.02*
H2B	0.104 (3)	0.663 (6)	0.733 (2)	0.02*
Ni1	0.5	0.5	1	0.00664 (16)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.0073 (11)	0.0071 (12)	0.0116 (12)	0.0010 (9)	0.0036 (10)	0.0014 (10)
C2	0.0067 (12)	0.0078 (12)	0.0087 (11)	0.0002 (9)	0.0029 (10)	0.0009 (9)
C3	0.0078 (11)	0.0088 (12)	0.0098 (11)	0.0029 (10)	0.0031 (9)	0.0029 (11)
C4	0.0114 (12)	0.0077 (12)	0.0105 (12)	−0.0014 (9)	0.0050 (10)	−0.0024 (10)
C5	0.0068 (12)	0.0089 (12)	0.0137 (13)	−0.0011 (9)	0.0048 (10)	−0.0017 (10)
N1	0.0040 (10)	0.0067 (10)	0.0102 (10)	0.0004 (8)	0.0019 (8)	0.0009 (8)
N2	0.0097 (10)	0.0101 (11)	0.0123 (10)	−0.0008 (8)	0.0061 (9)	0.0001 (8)
N3	0.0094 (10)	0.0139 (11)	0.0195 (11)	−0.0052 (9)	0.0113 (9)	−0.0056 (9)
O1	0.0069 (8)	0.0093 (8)	0.0137 (9)	−0.0018 (7)	0.0073 (7)	−0.0032 (7)
O2	0.0092 (9)	0.0135 (9)	0.0213 (10)	−0.0055 (7)	0.0092 (8)	−0.0059 (8)
O1W	0.0077 (9)	0.0081 (9)	0.0147 (9)	−0.0015 (7)	0.0046 (8)	−0.0030 (8)
O2W	0.0148 (10)	0.0129 (9)	0.0169 (10)	−0.0035 (8)	0.0115 (8)	−0.0018 (8)
Ni1	0.0049 (2)	0.0062 (2)	0.0106 (2)	−0.00089 (17)	0.00506 (18)	−0.00108 (18)

Geometric parameters (Å, º)

C1—O2	1.228 (3)	N1—Ni1	2.0657 (19)
C1—O1	1.281 (3)	N3—H1N	0.86
C1—C2	1.510 (3)	N3—H2N	0.86
C2—N1	1.327 (3)	O1—Ni1	2.0233 (16)
C2—C3	1.427 (3)	O1W—Ni1	2.0755 (18)
C3—N3	1.331 (3)	O1W—H1A	0.83 (3)
C3—N2	1.351 (3)	O1W—H1B	0.74 (3)
C4—N2	1.332 (3)	O2W—H2A	0.77 (3)
C4—C5	1.381 (3)	O2W—H2B	0.78 (3)
C4—H4	0.93	Ni1—O1^i	2.0233 (16)
C5—N1	1.340 (3)	Ni1—N1^i	2.066 (2)
C5—H5	0.93	Ni1—O1W^i	2.0755 (18)
O2—C1—O1	124.7 (2)	H1N—N3—H2N	120
O2—C1—C2	119.8 (2)	C1—O1—Ni1	115.72 (15)
O1—C1—C2	115.5 (2)	Ni1—O1W—H1A	118 (2)
N1—C2—C3	120.2 (2)	Ni1—O1W—H1B	113 (2)
N1—C2—C1	116.0 (2)	H1A—O1W—H1B	110 (3)
C3—C2—C1	123.7 (2)	H2A—O2W—H2B	108 (3)
N3—C3—N2	117.7 (2)	O1—Ni1—O1^i	180
N3—C3—C2	122.7 (2)	O1—Ni1—N1	80.54 (7)
N2—C3—C2	119.6 (2)	O1^i—Ni1—N1	99.46 (7)
N2—C4—C5	122.8 (2)	O1—Ni1—N1^i	99.46 (7)
N2—C4—H4	118.6	O1^i—Ni1—N1^i	80.54 (7)
C5—C4—H4	118.6	N1—Ni1—N1^i	180.0000 (10)
N1—C5—C4	119.5 (2)	O1—Ni1—O1W^i	89.81 (7)
N1—C5—H5	120.3	O1^i—Ni1—O1W^i	90.19 (7)
C4—C5—H5	120.3	N1—Ni1—O1W^i	90.92 (7)
C2—N1—C5	119.9 (2)	N1^i—Ni1—O1W^i	89.08 (7)
C2—N1—Ni1	112.20 (15)	O1—Ni1—O1W	90.19 (7)
C5—N1—Ni1	127.92 (16)	O1^i—Ni1—O1W	89.81 (7)
C4—N2—C3	117.9 (2)	N1—Ni1—O1W	89.08 (7)
C3—N3—H1N	120	N1^i—Ni1—O1W	90.92 (7)
C3—N3—H2N	120	O1W^i—Ni1—O1W	180.00 (9)
O2—C1—C2—N1	180.0 (2)	N3—C3—N2—C4	177.5 (2)
O1—C1—C2—N1	1.0 (3)	C2—C3—N2—C4	−1.1 (3)
O2—C1—C2—C3	0.2 (4)	O2—C1—O1—Ni1	178.74 (18)
O1—C1—C2—C3	−178.8 (2)	C2—C1—O1—Ni1	−2.3 (3)
N1—C2—C3—N3	−177.5 (2)	C1—O1—Ni1—N1	2.15 (16)
C1—C2—C3—N3	2.3 (4)	C1—O1—Ni1—N1^i	−177.85 (16)
N1—C2—C3—N2	1.0 (3)	C1—O1—Ni1—O1W^i	−88.81 (16)
C1—C2—C3—N2	−179.2 (2)	C1—O1—Ni1—O1W	91.19 (16)
N2—C4—C5—N1	0.5 (4)	C2—N1—Ni1—O1	−1.50 (15)
C3—C2—N1—C5	0.0 (3)	C5—N1—Ni1—O1	179.2 (2)
C1—C2—N1—C5	−179.9 (2)	C2—N1—Ni1—O1^i	178.50 (15)
C3—C2—N1—Ni1	−179.41 (17)	C5—N1—Ni1—O1^i	−0.8 (2)
C1—C2—N1—Ni1	0.8 (2)	C2—N1—Ni1—O1W^i	88.16 (16)
C4—C5—N1—C2	−0.7 (3)	C5—N1—Ni1—O1W^i	−91.1 (2)
C4—C5—N1—Ni1	178.57 (17)	C2—N1—Ni1—O1W	−91.84 (16)
C5—C4—N2—C3	0.4 (3)	C5—N1—Ni1—O1W	88.9 (2)

Symmetry code: (i) −x+1, −y+1, −z+2.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O1W—H1A···O2W^i	0.83 (3)	1.97 (3)	2.789 (3)	169 (3)
O1W—H1B···O1^ii	0.75 (3)	1.94 (3)	2.690 (3)	176 (4)
N3—H1N···O2W^iii	0.86	2.27	3.117 (3)	168
O2W—H2A···O2W^iv	0.77 (3)	2.12 (3)	2.867 (3)	164 (4)
O2W—H2B···N2^v	0.78 (3)	2.03 (3)	2.792 (3)	168 (3)
N3—H2N···O2	0.86	2.10	2.733 (3)	130
N3—H2N···O2^vi	0.86	2.20	2.871 (3)	135
C5—H5···O1W^vii	0.93	2.54	3.377 (4)	150

Symmetry codes: (i) −x+1, −y+1, −z+2; (ii) −x+1, −y, −z+2; (iii) −x, −y+1, −z+2; (iv) −x, y−1/2, −z+3/2; (v) x, −y+3/2, z−1/2; (vi) −x, −y, −z+2; (vii) x, y+1, z.