trans-Bis(azido-κN)bis­(pyridine-2-carboxamide-κ²N¹,O²)nickel(II)

In the title compound, [Ni(N₃)₂(C₆H₆N₂O)₂], the Ni^II atom lies on an inversion centre. The distorted octa­hedral nickel(II) coordination environment contains two planar trans-related N,O-chelating picolinamide ligands in one plane and two monodentate azide ligands perpendicular to this plane. Mol­ecules are linked into a three-dimensional framework by N—H...N hydrogen bonds.

S1. Comment

Considerable attention has been paid to heteroleptic metal complexes of biologically important ligands owing to their pharmacological effects as drugs in various biological and medicinal processes. Sometimes the metal complexes are more effective than the free ligands. The azide ion, N₃⁻, binds metal ions in a variable manner, giving rise to terminal, end-on bridging and end-to-end bridging modes (Cortes et al., 1994; Ribas et al., 1999; Hong & Do, 1999; Liu et al., 2004). The established various intriguing structures of azido–metal complexes, spanning from discrete molecules to three-dimensional arrays, not only enrich the stereochemistry of the transition metal ions, but also give deeper insight into the role of metal ions in the aforementioned processes on a more fundamental level regarding azide inhibition of the metabolism of mitochondria (Yuwen et al., 2000). As a part of our ongoing research (Đaković et al., 2007a,b) on the preparation and characterization of metal pseudohalide complexes with small organic molecules of biological interest, we synthesized the title complex, (I).

To the best of our knowledge, the title compound is the first azide complex with a pyridine monocarboxamide. Until now, only three Ni complexes with picolinamide (pia) have been reported, viz. two octahedral complexes, [Ni(H₂O)₂(pia-N,O)₂]Cl₂ (Masuko et al., 1967) and [Ni(H₂O)₂(pia-N,O)₂](sac)₂·4H₂O (sac is saccharinate; Paşaoğlu et al., 2004), and one tetrahedral complex, Ni(pia-N,N)₂·2H₂O (Chang et al., 1968; Nawata et al., 1967). In the octahedral complexes, two pia ligands coordinate to the nickel(II) ion as bidentate ligands through the pyridine N and the carboxamide O atoms, thus forming five-membered chelate rings in one plane, while two aqua ligands lie perpendicular to this plane. In the tetrahedral complex, the coordination environment is established by four N atoms, two endocyclic and two from the carboxamide units. The deprotonation of the amide N atom is perfomed by raising the pH to 11.5 by addition of sodium carbonate.

In (I), the octrahedrally coordinated Ni^II atom is located on a crystallographic inversion centre. The coordination environment is occupied by two chelating picolinamide-N,O ligands in one plane and by two terminal azide ligands perpendicular to this plane (Fig. 1). The Ni1—O1 bond distance (Table 1) is slightly longer than in other octahedral nickel(II) complexes with picolinamide {2.030 (1) Å in [Ni(H₂O)₂(pia)₂](sac)₂·4H₂O (Paşaoğlu et al., 2004) and 2.045 Å in [Ni(H₂O)₂(pia)₂]Cl₂ (Masuko et al., 1967)}, while the Ni1—N1 bond distance is consistent with those in the already mentioned compounds. The angles indicating the largest distortion from ideal octahedral geometry are the small bite angles, O1—Ni1—N1, in the picolinamide ligand (Table 1).

The pia ligands are nearly planar. Atoms N1, C1, C6 and O1 of the chelate ring have an r.m.s. deviation from their mean plane of 0.008 Å. Atom Ni1 deviates from this plane by 0.212 (2) Å, so that the chelate ring puckering can best be described as an envelope on Ni1. According to the Cambridge Structural Database (CSD, Version 5.28 of 2007; Allen, 2002), ten crystal structures of octahedral bis-pia complexes have been published so far, nine with trans- and just one with cis-related pia ligands. In the trans complexes, the dihedral angles between the planes of the pyridine ring and the amide group and between those of the pyridine and chelate rings are in the ranges 1.0–4.7 and 1.6–3.7°, respectively, while in the cis complex, the dihedral angles are much larger, viz. 14.1 and 22.7°, respectively. In the title compound, the aforementioned dihedral angles are 5.4 (1) and 3.3 (1)°, respectively; it could therefore be concluded that the pia ligand in (I) is among the less planar ones in trans-pia complexes, probably because of the short H···H intramolecular contact of 2.13 Å between atoms H2 (at C2) and H7 (at N2), which is also one of the shortest found in this class of compounds.

The azide ligands in (I) are coordinated in the nonlinear mode to the central metal ion (Table 1). In other reported nickel(II) complexes with monodentate azide ligands, the analogous angles are in the range 103–151°, according to 98 structures obtained from the CSD. The azide ligands are usually slightly bent and the already mentioned search of the CSD shows that the azide bond angle in terminal azides is between 175 and 180°. In complex (I), the azide N—N—N bond angle also deviates slightly from linearity (Table 1).

The crystal structure is predominantly determined by hydrogen bonding. Typical amide N—H···O hydrogen bonds of the R₂²(8) type are not found. Instead, an extensive network of N—H···N hydrogen bonding is established. The geometric parameters are given in (Table 2). There are two hydrogen bonds of the type N—H···N in the crystal structure of (I) (Fig. 2). The N2—H8···N5ⁱⁱⁱ bond [symmetry code: (iii) −x + 2, −y + 1, −z + 1], involving the amide N atom and the outer atom, N5ⁱⁱⁱ, of an adjacent azide ligand, forms R₂²(16) rings between two neighbouring molecules. The other interaction, N2—H7···N3ⁱⁱ [symmetry code: (ii) x, 3/2 − y, z − 1/2], between the same amide N atom and the coordinated azide atom, N3ⁱⁱ, of a different adjacent molecule, links the molecules into zigzag C₂²(12) chains. The combination of these hydrogen-bonding interactions links the molecules into an infinite threedimensional network.

Related literature

For related literature, see: Chang et al. (1968); Cortes et al. (1994); Hong & Do (1999); Liu et al. (2004); Masuko et al. (1967); Nawata et al. (1967); Paşaoğlu et al. (2004); Ribas et al. (1999); Yuwen et al. (2000);Đaković et al. (2007a,b).

S2. Experimental

Aqueous solutions of picolinamide (0.24 g, 2 mmol in 20 ml of H₂O) and of nickel(II) nitrate hexahydrate (0.29 g, 1 mmol in 20 ml of H₂O) were mixed together. Into the resulting solution was then added an aqueous solution of sodium azide (0.13 g, 2 mmol in 10 ml of H₂O). The reaction mixture was left to stand for 4 d until green crystals of (I) suitable for X-ray analysis were obtained (0.25 g, 65%). IR (KBr pellet, ν, cm⁻¹): 3281 (m–s), 3124 (s), 3079 (m–s), 2058 (vs), 2035 (vs), 1675 (s), 1620 (m), 1585 (s), 1568 (s), 1534 (w), 1425 (s), 1345 (w), 1310 (m), 1292 (w), 1276 (w–m), 1182 (w), 1158 (w–m), 1124 (m), 1094 (w), 1056 (w), 1027 (m), 927 (vw), 825 (w–m), 790 (w–m), 771 (s), 705 (w–m), 668 (m–s), 663 (m–s), 654 (m), 619 (w–m), 514 (w), 452 (w). The crystals detonate without melting when warmed to 538 K.

S3. Refinement

Aromatic H atoms were fixed in geometrically calculated positions and refined using a riding model [C—H = 0.95 Å and U_iso(H) = 1.2U_eq(C)]. H atoms on the carboxamide N atom were found in a difference Fourier map at the final stage of refinement and refined freely.

Computing details

Data collection: CrysAlis PRO (Oxford Diffraction, 2007); cell refinement: CrysAlis PRO (Oxford Diffraction, 2007); data reduction: CrysAlis PRO (Oxford Diffraction, 2007); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997) and Mercury (Bruno et al., 2002); software used to prepare material for publication: PLATON (Spek, 2003).

Figures

	Fig. 1. The title compound, with the atom-numbering scheme. Displacement ellipsoids for non-H atoms are drawn at the 50% probability level.
	Fig. 2. The perspective view of the packing of the title compound, showing the hydrogen bonds as dashed lines. H atoms have been omitted for clarity [symmetry code: (ii) x, −y + 3/2, z − 1/2, (iii) −x + 2, −y + 1, −z + 1].

trans-Bis(azido-κN)bis(pyridine-2-carboxamide-κ²N¹,O²)nickel(II)

Crystal data

[Ni(N3)2(C6H6N2O)2]	F(000) = 396
Mr = 387.01	Dx = 1.660 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 20257 reflections
a = 7.6237 (1) Å	θ = 2.4–34.7°
b = 11.9574 (2) Å	µ = 1.29 mm^−1
c = 9.5112 (3) Å	T = 183 K
β = 116.767 (2)°	Plate, green
V = 774.13 (3) Å^3	0.59 × 0.30 × 0.06 mm
Z = 2

Data collection

Oxford Diffraction Xcalibur diffractometer with a Ruby detector	2257 independent reflections
Radiation source: Enhance (Mo) X-ray Source	2023 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.030
Detector resolution: 10.4498 pixels mm^-1	θmax = 30.0°, θmin = 2.9°
CCD scans	h = −10→10
Absorption correction: multi-scan (CrysAlis PRO; Oxford Diffraction, 2007)	k = −16→16
Tmin = 0.490, Tmax = 0.930	l = −13→13
27299 measured reflections

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)] = 0.027	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.073	H atoms treated by a mixture of independent and constrained refinement
S = 1.08	w = 1/[σ^2(Fo^2) + (0.0347P)^2 + 0.5288P] where P = (Fo^2 + 2Fc^2)/3
2257 reflections	(Δ/σ)max < 0.001
123 parameters	Δρmax = 0.37 e Å^−3
0 restraints	Δρmin = −0.33 e Å^−3

Special details

Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All su's are estimated from the variances of the (full) variance-covariance matrix. The cell e.s.d.'s are taken into account in the estimation of distances, angles and torsion angles

Refinement. Refinement on F² for ALL reflections except those flagged by the user for potential systematic errors. Weighted R-factors wR and all goodnesses of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The observed criterion of F² > σ(F²) is used only for calculating -R-factor-obs 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	0.50000	0.50000	0.50000	0.0161 (1)
O1	0.65750 (15)	0.55448 (8)	0.38338 (12)	0.0217 (3)
N1	0.41885 (17)	0.66349 (9)	0.46732 (13)	0.0168 (3)
N2	0.75809 (18)	0.71011 (10)	0.30663 (15)	0.0222 (3)
N3	0.74702 (19)	0.54476 (10)	0.71584 (15)	0.0238 (3)
N4	0.88038 (18)	0.48045 (10)	0.77193 (14)	0.0199 (3)
N5	1.00937 (19)	0.41667 (11)	0.82807 (16)	0.0278 (4)
C1	0.51692 (19)	0.72592 (10)	0.40785 (15)	0.0163 (3)
C2	0.4841 (2)	0.83979 (11)	0.38169 (17)	0.0213 (3)
C3	0.3420 (2)	0.88961 (11)	0.41457 (18)	0.0242 (4)
C4	0.2385 (2)	0.82500 (11)	0.47290 (17)	0.0222 (3)
C5	0.2824 (2)	0.71179 (11)	0.49869 (16)	0.0202 (3)
C6	0.65232 (19)	0.65825 (11)	0.36540 (15)	0.0176 (3)
H2	0.55700	0.88280	0.34220	0.0260*
H3	0.31600	0.96740	0.39720	0.0290*
H4	0.13970	0.85740	0.49480	0.0270*
H5	0.21310	0.66730	0.53990	0.0240*
H7	0.754 (3)	0.7819 (18)	0.294 (2)	0.033 (5)*
H8	0.832 (3)	0.6701 (17)	0.277 (2)	0.029 (5)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Ni1	0.0194 (1)	0.0108 (1)	0.0218 (1)	0.0008 (1)	0.0124 (1)	0.0010 (1)
O1	0.0278 (5)	0.0143 (4)	0.0313 (5)	0.0023 (4)	0.0207 (4)	0.0021 (4)
N1	0.0188 (5)	0.0135 (5)	0.0200 (5)	0.0001 (4)	0.0105 (4)	−0.0002 (4)
N2	0.0246 (6)	0.0162 (5)	0.0334 (6)	0.0010 (4)	0.0199 (5)	0.0020 (4)
N3	0.0245 (6)	0.0185 (5)	0.0270 (6)	0.0023 (4)	0.0104 (5)	−0.0036 (4)
N4	0.0195 (5)	0.0213 (5)	0.0220 (5)	−0.0041 (4)	0.0121 (4)	−0.0040 (4)
N5	0.0235 (6)	0.0261 (6)	0.0360 (7)	0.0028 (5)	0.0153 (5)	−0.0004 (5)
C1	0.0190 (6)	0.0131 (5)	0.0191 (5)	0.0001 (4)	0.0105 (5)	−0.0004 (4)
C2	0.0255 (6)	0.0140 (5)	0.0281 (6)	0.0010 (5)	0.0154 (5)	0.0022 (5)
C3	0.0285 (7)	0.0141 (6)	0.0324 (7)	0.0048 (5)	0.0159 (6)	0.0016 (5)
C4	0.0225 (6)	0.0193 (6)	0.0273 (6)	0.0046 (5)	0.0135 (5)	−0.0014 (5)
C5	0.0210 (6)	0.0192 (6)	0.0236 (6)	0.0007 (5)	0.0129 (5)	−0.0006 (5)
C6	0.0187 (6)	0.0157 (5)	0.0208 (5)	0.0010 (4)	0.0109 (5)	0.0006 (4)

Geometric parameters (Å, º)

Ni1—O1	2.073 (1)	N2—H7	0.87 (2)
Ni1—N1	2.032 (1)	C1—C6	1.503 (2)
Ni1—N3	2.137 (1)	C1—C2	1.3865 (18)
O1—C6	1.2507 (16)	C2—C3	1.390 (2)
N1—C1	1.3480 (19)	C3—C4	1.386 (2)
N1—C5	1.336 (2)	C4—C5	1.3895 (19)
N2—C6	1.324 (2)	C2—H2	0.9500
N3—N4	1.1921 (19)	C3—H3	0.9500
N4—N5	1.167 (2)	C4—H4	0.9500
N2—H8	0.88 (2)	C5—H5	0.9500
O1—Ni1—N1	79.96 (5)	N1—C1—C2	121.99 (14)
O1—Ni1—N3	87.89 (5)	N1—C1—C6	113.11 (11)
O1—Ni1—O1^i	180.00	C2—C1—C6	124.81 (13)
O1—Ni1—N1^i	100.04 (5)	C1—C2—C3	118.46 (14)
O1—Ni1—N3^i	92.12 (5)	C2—C3—C4	119.54 (13)
N1—Ni1—N3	88.96 (5)	C3—C4—C5	118.58 (15)
N1—Ni1—N1^i	180.00	N1—C5—C4	122.12 (14)
N1—Ni1—N3^i	91.04 (5)	O1—C6—N2	122.32 (14)
N3—Ni1—N3^i	180.00	O1—C6—C1	118.73 (13)
Ni1—O1—C6	113.25 (10)	N2—C6—C1	118.94 (12)
Ni1—N1—C1	114.13 (10)	C1—C2—H2	121.00
Ni1—N1—C5	126.58 (10)	C3—C2—H2	121.00
C1—N1—C5	119.29 (11)	C2—C3—H3	120.00
Ni1—N3—N4	118.3 (1)	C4—C3—H3	120.00
N3—N4—N5	178.9 (2)	C3—C4—H4	121.00
C6—N2—H7	122.2 (16)	C5—C4—H4	121.00
C6—N2—H8	118.8 (14)	N1—C5—H5	119.00
H7—N2—H8	119 (2)	C4—C5—H5	119.00
N1—Ni1—O1—C6	8.26 (10)	Ni1—O1—C6—C1	−8.05 (15)
N3—Ni1—O1—C6	−81.06 (10)	Ni1—N1—C1—C2	−178.33 (11)
N1^i—Ni1—O1—C6	−171.74 (10)	Ni1—N1—C1—C6	5.13 (14)
N3^i—Ni1—O1—C6	98.94 (10)	C5—N1—C1—C2	1.6 (2)
O1—Ni1—N1—C1	−7.09 (9)	C5—N1—C1—C6	−174.90 (12)
O1—Ni1—N1—C5	172.94 (12)	Ni1—N1—C5—C4	179.58 (10)
N3—Ni1—N1—C1	80.95 (10)	C1—N1—C5—C4	−0.4 (2)
N3—Ni1—N1—C5	−99.03 (12)	N1—C1—C2—C3	−1.6 (2)
O1^i—Ni1—N1—C1	172.91 (9)	C6—C1—C2—C3	174.50 (13)
O1^i—Ni1—N1—C5	−7.06 (12)	N1—C1—C6—O1	2.12 (18)
N3^i—Ni1—N1—C1	−99.05 (10)	N1—C1—C6—N2	−179.57 (12)
N3^i—Ni1—N1—C5	80.97 (12)	C2—C1—C6—O1	−174.30 (13)
O1—Ni1—N3—N4	−81.96 (13)	C2—C1—C6—N2	4.0 (2)
N1—Ni1—N3—N4	−161.94 (13)	C1—C2—C3—C4	0.4 (2)
O1^i—Ni1—N3—N4	98.04 (13)	C2—C3—C4—C5	0.8 (2)
N1^i—Ni1—N3—N4	18.06 (13)	C3—C4—C5—N1	−0.8 (2)
Ni1—O1—C6—N2	173.71 (11)

Symmetry code: (i) −x+1, −y+1, −z+1.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N2—H7···N3^ii	0.87 (2)	2.20 (2)	3.046 (2)	168 (2)
N2—H8···N5^iii	0.88 (2)	2.15 (2)	3.021 (2)	172 (2)
C2—H2···N3^ii	0.95	2.42	3.356 (2)	168
C3—H3···N5^iv	0.95	2.54	3.255 (2)	133
C4—H4···N5^v	0.95	2.52	3.403 (2)	154

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