(3,3′-{(1E,1′E)-1,1′-[Ethane-1,2-diylbis(azan-1-yl-1-yl­idene-κN)]bis­(ethan-1-yl-1-yl­idene)}di­pyrazine 1-oxide-κN⁴)bis­(nitrato-κO)nickel(II) monohydrate

In the title complex, [Ni(NO₃)₂(C₁₄H₁₆N₆O₂)]·H₂O, the Ni^II atom, lying on a twofold rotation axis, is coordinated by a tetra­dentate 3,3′-{(1E,1′E)-1,1′-[ethane-1,2-diylbis(azan-1-yl-1-yl­idene)]bis­(ethan-1-yl-1-yl­idene)}di­pyrazine 1-oxide ligand and two mutually trans monodentate nitrate anions in a distorted o­cta­hedral geometry. The lattice water mol­ecule is located on a twofold rotation axis. The complex mol­ecules are linked by the water mol­ecules through O—H...O hydrogen bonds into a chain along [001]. Further C—H...O hydrogen bonds lead to the formation of a three-dimensional network.

Key indicators

• Single-crystal X-ray study
• T = 293 K
• Mean [sigma](C-C) = 0.004 Å
• R factor = 0.032
• wR factor = 0.070
• Data-to-parameter ratio = 12.1

checkCIF/PLATON results

No syntax errors found



Alert level C
PLAT230_ALERT_2_C Hirshfeld Test Diff for    O2     --  N4      ..        6.7 su
PLAT242_ALERT_2_C Check Low       Ueq as Compared to Neighbors for         N4
PLAT910_ALERT_3_C Missing # of FCF Reflections Below Th(Min) .....          1
PLAT911_ALERT_3_C Missing # FCF Refl Between THmin & STh/L=  0.600          5

Alert level G
PLAT002_ALERT_2_G Number of Distance or Angle Restraints on AtSite          2
PLAT005_ALERT_5_G No _iucr_refine_instructions_details  in the CIF          ?
PLAT199_ALERT_1_G Check the Reported _cell_measurement_temperature        293 K
PLAT200_ALERT_1_G Check the Reported   _diffrn_ambient_temperature        293 K
PLAT860_ALERT_3_G Note: Number of Least-Squares Restraints .......          1

   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
   5 ALERT level G = General information/check it is not something unexpected

   2 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   3 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
   1 ALERT type 5 Informative message, check

---

S1. Comment

Interest in heterocyclic aromatic N-oxides has flourished because of their practical impact on biological activity (Sarma et al., 2010). Several aromatic N-oxide derivatives capable of forming biologically active metal complexes have been reported (Nizhnik et al., 2008). Indeed, most coordinative studies of N-oxide donors have been carried out using pyridine-N-oxide (Karayannis et al., 1973) or bipyridine-N,N'-bisoxide. However, complexes containing ligands with pyrazine single N-oxide site are few (Chupakhin et al., 2011). Herein, we synthesize a new bipyrazine N-oxide Schiff base 3,3'-(1E,1'E)-1,1'-[ethane-1,2-diylbis(azan-1-yl-1-ylidene)] bis(ethan-1-yl-1-ylidene)dipyrazine-1-oxide (L) and its Ni(II) complex.

In the title complex, the Ni^II atom, lying on a twofold rotation axis, exhibits a distorted octahedral geometry, defined by four N atoms from the L ligand, occupying the equatorial plane, and two axial O atoms from two monodentate nitrate anions (Fig. 1). The equatorial Ni—N distances [Ni1—N1 = 2.0855 (19) and Ni1—N3 = 2.0183 (19) Å] are in a normal range for this class of compounds and also very similar to those of Ni—N(pyridine) and Ni—N(imine) found in analogue complexes (Banerjee et al., 2004; Padhi & Manivannan, 2007). Hydrogen bonding plays an important role in the formation of the crystal structure (Table 1). The lattice water molecule is located on a twofold rotation axis and connect two symmetry-related complex molecules through O—H···O hydrogen bonds, so forming a chain structure along [001] (Fig. 2). C—H···O hydrogen bonds lead to a three-dimensional network (Fig. 3).

Related literature

For background to complexes with heterocyclic aromatic N-oxide ligands, see: Chupakhin et al. (2011); Karayannis et al. (1973); Nizhnik et al. (2008); Sarma et al. (2010). For related structures, see: Banerjee et al. (2004); Padhi & Manivannan (2007).

S2. Experimental

Synthesis of 2-acetylpyrazine-N-oxide: 2-Acetylpyrazine (12.2 g, 0.1 mol), glacial acetic acid (75 ml) and 30% hydrogen peroxide (14 ml) were heated with reflux at 70–80°C for 3 h. Additional 30% H₂O₂ (10 ml) was added and the temperature was maintained at 70–80°C for a further 10 h. The solvent was removed by rotary evaporation and upon standing brown yellow solid was formed, filtered and dried.

Synthesis of the L ligand : 1,2-Diaminoethane (0.100 g, 1.66 mmol) in 5 cm³ methanol was added dropwise to a hot stirred solution of 2-acetylpyrazine-N-oxide (0.455 g, 3.3 mmol) in 25 ml of methanol. The mixture was refluxed for 5 h. Brown precipitate was filtered, washed with methanol and air dried (yield: 0.68 g, 68.7%).

Synthesis of the title complex: Ni(NO₃)₂.6H₂O (0.290 g, 0.1 mmol) in 5 cm³ of CH₃CN was added dropwise to a hot stirred solution of the ligand L (0.030 g, 0.1 mmol) in a mixture of CH₃OH/CH₃CN (v/v = 2:1) and the mixture was stirred for 30 min. Diethyl ether was slowly diffused into the solution and block brown crystals suitable for X-ray diffraction analysis were collected by filtration within two weeks.

S3. Refinement

C-bound H atoms were positioned geometrically and refined as riding atoms, with C—H = 0.93 (aromatic), 0.97 (CH₂) and 0.96 (CH₃) Å and with U_iso(H)= 1.2(1.5 for methyl)U_eq(C). The water H atom was located on a difference Fourier map and refined isotropically.

Computing details

Data collection: APEX2 (Bruker, 2007); cell refinement: SAINT (Bruker, 2007); data reduction: SAINT (Bruker, 2007); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: DIAMOND (Brandenburg, 1999); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).

Figures

	Fig. 1. The molecular structure of the title complex. Displacement ellipsoids are drawn at the 30% probability level. H atoms and water molecule have been omitted for clarity. [Symmetry code: (i) -x, y, -z+1/2.]
	Fig. 2. : O—H···O hydrogen bonds (dashed lines) between water molecule and two adjacent complex molecules, which lead to a chain along [001]. H atoms not involved in hydrogen bonds are omitted for clarity.
	Fig. 3. The crystal packing of the title complex, viewed along the c axis. Hydrogen bonds are shown as dashed lines.

(3,3'-{(1E,1'E)-1,1'-[Ethane-1,2-diylbis(azan-1-yl-1-ylidene-κN)]bis(ethan-1-yl-1-ylidene)}dipyrazine 1-oxide-κN⁴)bis(nitrato-κO)nickel(II) monohydrate

Crystal data

[Ni(NO3)2(C14H16N6O2)]·H2O	F(000) = 1032
Mr = 501.05	Dx = 1.697 Mg m^−3
Monoclinic, C2/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -C 2yc	Cell parameters from 2097 reflections
a = 16.993 (5) Å	θ = 2.5–23.4°
b = 16.218 (5) Å	µ = 1.06 mm^−1
c = 7.754 (2) Å	T = 293 K
β = 113.427 (3)°	Block, brown
V = 1960.8 (10) Å^3	0.23 × 0.21 × 0.19 mm
Z = 4

Data collection

Bruker APEXII CCD diffractometer	1828 independent reflections
Radiation source: fine-focus sealed tube	1515 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.034
φ and ω scans	θmax = 25.5°, θmin = 2.5°
Absorption correction: multi-scan (SADABS; Sheldrick, 1996)	h = −20→20
Tmin = 0.793, Tmax = 0.824	k = −19→18
6930 measured reflections	l = −9→9

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)] = 0.032	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.070	H atoms treated by a mixture of independent and constrained refinement
S = 1.04	w = 1/[σ^2(Fo^2) + (0.0282P)^2 + 1.9388P] where P = (Fo^2 + 2Fc^2)/3
1828 reflections	(Δ/σ)max < 0.001
151 parameters	Δρmax = 0.26 e Å^−3
1 restraint	Δρmin = −0.23 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
Ni1	0.0000	0.22687 (3)	0.2500	0.02616 (14)
C1	0.11963 (16)	0.08324 (15)	0.4745 (4)	0.0364 (6)
H1	0.0798	0.0464	0.3947	0.044*
C2	0.19290 (17)	0.05229 (17)	0.6107 (4)	0.0461 (7)
H2	0.2022	−0.0043	0.6214	0.055*
C3	0.23627 (16)	0.18666 (15)	0.7095 (3)	0.0352 (6)
H3A	0.2760	0.2238	0.7884	0.042*
C4	0.16163 (14)	0.21473 (14)	0.5717 (3)	0.0282 (5)
C5	0.13925 (15)	0.30501 (15)	0.5473 (3)	0.0308 (5)
C6	0.19245 (18)	0.36564 (17)	0.6900 (4)	0.0528 (8)
H6A	0.1707	0.4202	0.6515	0.079*
H6B	0.2507	0.3625	0.7015	0.079*
H6C	0.1902	0.3533	0.8091	0.079*
C7	0.03112 (17)	0.40247 (15)	0.3526 (4)	0.0397 (6)
H7A	0.0746	0.4444	0.3731	0.048*
H7B	0.0006	0.4150	0.4319	0.048*
H1W	0.961 (7)	0.337 (9)	0.670 (19)	0.65 (10)*
N1	0.10253 (12)	0.16371 (12)	0.4506 (3)	0.0289 (5)
N2	0.25192 (14)	0.10433 (13)	0.7301 (3)	0.0437 (6)
N3	0.07187 (12)	0.32112 (11)	0.4021 (3)	0.0302 (5)
N4	−0.08220 (14)	0.16354 (17)	0.4974 (3)	0.0462 (6)
O1	0.32056 (13)	0.07731 (13)	0.8616 (3)	0.0739 (7)
O2	−0.06595 (11)	0.22970 (11)	0.4291 (2)	0.0413 (4)
O3	−0.11896 (19)	0.16980 (18)	0.6043 (4)	0.0997 (10)
O4	−0.06439 (14)	0.09594 (13)	0.4506 (3)	0.0603 (6)
O5	1.0000	0.3575 (3)	0.7500	0.0993 (13)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Ni1	0.0253 (2)	0.0206 (2)	0.0280 (2)	0.000	0.00583 (18)	0.000
C1	0.0348 (14)	0.0261 (14)	0.0407 (14)	−0.0021 (11)	0.0071 (12)	0.0025 (11)
C2	0.0413 (16)	0.0265 (14)	0.0576 (18)	0.0033 (12)	0.0059 (14)	0.0085 (13)
C3	0.0284 (14)	0.0325 (14)	0.0376 (14)	−0.0053 (11)	0.0055 (11)	0.0030 (11)
C4	0.0262 (12)	0.0287 (13)	0.0288 (12)	−0.0019 (10)	0.0100 (10)	0.0012 (10)
C5	0.0292 (14)	0.0282 (13)	0.0336 (13)	−0.0052 (11)	0.0110 (11)	−0.0025 (10)
C6	0.0490 (18)	0.0387 (17)	0.0501 (17)	−0.0044 (14)	−0.0021 (14)	−0.0097 (14)
C7	0.0454 (17)	0.0208 (13)	0.0458 (15)	0.0011 (11)	0.0106 (13)	−0.0029 (11)
N1	0.0278 (11)	0.0226 (10)	0.0336 (11)	−0.0015 (9)	0.0092 (9)	0.0011 (9)
N2	0.0331 (13)	0.0363 (13)	0.0476 (13)	0.0022 (10)	0.0011 (11)	0.0110 (10)
N3	0.0330 (12)	0.0218 (11)	0.0330 (11)	−0.0011 (9)	0.0102 (10)	−0.0021 (9)
N4	0.0339 (13)	0.0634 (17)	0.0408 (13)	−0.0025 (12)	0.0144 (11)	0.0077 (12)
O1	0.0487 (13)	0.0509 (14)	0.0815 (16)	0.0081 (11)	−0.0169 (12)	0.0172 (12)
O2	0.0453 (11)	0.0378 (10)	0.0453 (10)	0.0033 (9)	0.0226 (9)	0.0051 (9)
O3	0.118 (2)	0.125 (2)	0.100 (2)	0.0031 (19)	0.090 (2)	0.0153 (17)
O4	0.0714 (15)	0.0405 (12)	0.0721 (15)	−0.0098 (11)	0.0319 (12)	0.0052 (11)
O5	0.126 (4)	0.113 (3)	0.068 (2)	0.000	0.047 (2)	0.000

Geometric parameters (Å, º)

Ni1—N3	2.0183 (19)	C5—C6	1.488 (3)
Ni1—N1	2.0855 (19)	C6—H6A	0.9600
Ni1—O2	2.1032 (17)	C6—H6B	0.9600
C1—N1	1.334 (3)	C6—H6C	0.9600
C1—C2	1.368 (3)	C7—N3	1.468 (3)
C1—H1	0.9300	C7—C7^i	1.521 (5)
C2—N2	1.355 (3)	C7—H7A	0.9700
C2—H2	0.9300	C7—H7B	0.9700
C3—N2	1.358 (3)	N2—O1	1.283 (3)
C3—C4	1.371 (3)	N4—O3	1.224 (3)
C3—H3A	0.9300	N4—O4	1.230 (3)
C4—N1	1.351 (3)	N4—O2	1.275 (3)
C4—C5	1.506 (3)	O5—H1W	0.780 (5)
C5—N3	1.274 (3)
N3—Ni1—N3^i	81.53 (11)	N3—C5—C4	113.8 (2)
N3—Ni1—N1^i	160.01 (8)	C6—C5—C4	120.1 (2)
N3^i—Ni1—N1^i	78.71 (8)	C5—C6—H6A	109.5
N3—Ni1—N1	78.71 (8)	C5—C6—H6B	109.5
N3^i—Ni1—N1	160.01 (8)	H6A—C6—H6B	109.5
N1^i—Ni1—N1	121.17 (11)	C5—C6—H6C	109.5
N3—Ni1—O2^i	90.67 (7)	H6A—C6—H6C	109.5
N3^i—Ni1—O2^i	87.44 (7)	H6B—C6—H6C	109.5
N1^i—Ni1—O2^i	91.42 (7)	N3—C7—C7^i	109.44 (14)
N1—Ni1—O2^i	89.81 (7)	N3—C7—H7A	109.8
N3—Ni1—O2	87.44 (7)	C7^i—C7—H7A	109.8
N3^i—Ni1—O2	90.67 (7)	N3—C7—H7B	109.8
N1^i—Ni1—O2	89.81 (7)	C7^i—C7—H7B	109.8
N1—Ni1—O2	91.42 (7)	H7A—C7—H7B	108.2
O2^i—Ni1—O2	177.50 (10)	C1—N1—C4	116.2 (2)
N1—C1—C2	123.2 (2)	C1—N1—Ni1	130.95 (16)
N1—C1—H1	118.4	C4—N1—Ni1	112.79 (15)
C2—C1—H1	118.4	O1—N2—C2	121.5 (2)
N2—C2—C1	119.9 (2)	O1—N2—C3	120.2 (2)
N2—C2—H2	120.1	C2—N2—C3	118.3 (2)
C1—C2—H2	120.1	C5—N3—C7	125.5 (2)
N2—C3—C4	119.7 (2)	C5—N3—Ni1	118.92 (16)
N2—C3—H3A	120.2	C7—N3—Ni1	114.52 (15)
C4—C3—H3A	120.2	O3—N4—O4	121.7 (3)
N1—C4—C3	122.7 (2)	O3—N4—O2	117.7 (3)
N1—C4—C5	115.32 (19)	O4—N4—O2	120.6 (2)
C3—C4—C5	122.0 (2)	N4—O2—Ni1	121.09 (16)
N3—C5—C6	126.1 (2)
N1—C1—C2—N2	0.4 (4)	C4—C3—N2—O1	−178.2 (2)
N2—C3—C4—N1	−1.4 (4)	C4—C3—N2—C2	0.8 (4)
N2—C3—C4—C5	177.5 (2)	C6—C5—N3—C7	−3.4 (4)
N1—C4—C5—N3	−7.4 (3)	C4—C5—N3—C7	174.4 (2)
C3—C4—C5—N3	173.6 (2)	C6—C5—N3—Ni1	−170.6 (2)
N1—C4—C5—C6	170.5 (2)	C4—C5—N3—Ni1	7.1 (3)
C3—C4—C5—C6	−8.5 (3)	C7^i—C7—N3—C5	164.2 (3)
C2—C1—N1—C4	−1.0 (4)	C7^i—C7—N3—Ni1	−28.1 (3)
C2—C1—N1—Ni1	176.96 (19)	N3^i—Ni1—N3—C5	179.1 (2)
C3—C4—N1—C1	1.4 (3)	N1^i—Ni1—N3—C5	170.39 (19)
C5—C4—N1—C1	−177.5 (2)	N1—Ni1—N3—C5	−3.94 (17)
C3—C4—N1—Ni1	−176.86 (18)	O2^i—Ni1—N3—C5	−93.61 (18)
C5—C4—N1—Ni1	4.2 (2)	O2—Ni1—N3—C5	88.02 (18)
N3—Ni1—N1—C1	−178.5 (2)	N3^i—Ni1—N3—C7	10.46 (13)
N3^i—Ni1—N1—C1	−169.8 (2)	N1^i—Ni1—N3—C7	1.8 (3)
N1^i—Ni1—N1—C1	3.71 (19)	N1—Ni1—N3—C7	−172.56 (17)
O2^i—Ni1—N1—C1	−87.8 (2)	O2^i—Ni1—N3—C7	97.77 (17)
O2—Ni1—N1—C1	94.4 (2)	O2—Ni1—N3—C7	−80.60 (17)
N3—Ni1—N1—C4	−0.56 (15)	O3—N4—O2—Ni1	178.3 (2)
N3^i—Ni1—N1—C4	8.2 (3)	O4—N4—O2—Ni1	−4.6 (3)
N1^i—Ni1—N1—C4	−178.30 (17)	N3—Ni1—O2—N4	−134.41 (18)
O2^i—Ni1—N1—C4	90.16 (15)	N3^i—Ni1—O2—N4	144.10 (18)
O2—Ni1—N1—C4	−87.66 (15)	N1^i—Ni1—O2—N4	65.39 (18)
C1—C2—N2—O1	178.7 (3)	N1—Ni1—O2—N4	−55.78 (18)
C1—C2—N2—C3	−0.3 (4)

Symmetry code: (i) −x, y, −z+1/2.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O5—H1W···O2^ii	0.78 (12)	2.46 (14)	3.086 (4)	139 (14)
C3—H3A···O2^iii	0.93	2.58	3.389 (3)	146
C6—H6A···O1^iv	0.96	2.56	3.453 (4)	156

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