Diaqua­bis(2-oxidopyridinium-3-car­box­yl­ate-κ²O²,O³)zinc(II)

In the title mononuclear complex, [Zn(C₆H₄NO₃)₂(H₂O)₂], the six-coordinate Zn^II atom adopts an octa­hedral coordination geometry and is located on an inversion centre. There is a weak π–π stacking inter­action between adjacent pyridyl rings [the separation between the centroids of the pyridyl rings is 3.840 (2) Å and the perpendicular distance is 3.582 Å]. The crystal packing is stabilized by O—H...O and N—H...O hydrogen bonds.

Key indicators

• Single-crystal X-ray study
• T = 298 K
• Mean [sigma](C-C) = 0.005 Å
• R factor = 0.041
• wR factor = 0.093
• Data-to-parameter ratio = 12.8

checkCIF/PLATON results

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Alert level G
PLAT794_ALERT_5_G Check Predicted Bond Valency for Zn1         (2)       2.18
PLAT860_ALERT_3_G Note: Number of Least-Squares Restraints .......          3

   0 ALERT level A = In general: serious problem
   0 ALERT level B = Potentially serious problem
   0 ALERT level C = Check and explain
   2 ALERT level G = General alerts; check

   0 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   0 ALERT type 2 Indicator that the structure model may be wrong or deficient
   1 ALERT type 3 Indicator that the structure quality may be low
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S1. Comment

Metal complexes containing N-heterocyclic ligands play a pivotal role in the area of modern coordination chemistry, and it has been reported that complexes containing 3-hydroxypicolinamide ligand display strong fluorescent emission (Sakai et al. 2006). The interest in this area prompted us to synthesize the title complex, (I), which crystal structure we report herein.

Fig. 1 shows the asymmetric unit and symmetry-related fragment of (I). The Zn^II atom lies at an inversion centre and adopts a slightly distored octahedral geometry (Table 1). Between neighboring complexes there is a weak π-π stacking interaction, which links adjacent pyridyl rings; the relevant distances are Cg1···Cg1ⁱ = 3.840 (2) Å and Cg1···Cg1ⁱ_perp = 3.582 Å [symmetry codes: (i) X, 1/2-Y, -1/2+Z; Cg1 is the centroid of pyridyl ring; Cg1···Cg1_perp is the perpendicular distance from ring Cg1 to ring Cg1ⁱ]. Table 2 and Fig. 2 show the information of O—H···O and N—H···O hydrogen bonds, which consolidate the crystal structure.

Related literature

For a related crystal structure, see: Sakai et al. (2006).

S2. Experimental

A diluted sodium hydroxide H₂O solution was added dropwise into 30 ml of a, aqueous solution containing Zn(ClO₄)₂.6H₂O (0.1862 g, 0.500 mmol) and 2-hydroxyl-3-carboxylpyridine (0.1232 g, 1.00 mmol) until the pH value reached 4, and the solution was stirred for another a few minutes. Colorless single crystals were obtained after the mixed solutions were allowed to stand at room temperature for one week.

S3. Refinement

H atoms of water molecule and N—H bond were located in a difference Fourier map and refined as riding in their as-found positions, with O—H = 0.842–0.844 Å, U_iso(H) = 1.5 U_eq(O), N—H = 0.86 Å, U_iso(H) = 1.2 U_eq(N). other H atoms were placed in calculated positions, and refined as riding, with C—H = 0.93 Å, U_iso(H) = 1.2_eq(C).

Computing details

Data collection: SMART (Bruker, 1997); cell refinement: SAINT (Bruker, 1997); data reduction: SAINT; program(s) used to solve structure: SHELXTL (Bruker, 2001); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL.

Figures

	Fig. 1. The coordination structure of (I) showing the atom numbering scheme with thermal ellipsoids drawn at the 30% probability level. [Symmetry codes: (i) -x + 1, -y + 1, -z].
	Fig. 2. Unit cell and hydrogen bonds (in broken lines).

Diaquabis(2-oxidopyridinium-3-carboxylate-κ²O²,O³)zinc(II)

Crystal data

[Zn(C6H4NO3)2(H2O)2]	F(000) = 384
Mr = 377.61	Dx = 1.814 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 899 reflections
a = 7.491 (3) Å	θ = 2.8–23.7°
b = 12.316 (4) Å	µ = 1.82 mm^−1
c = 7.621 (3) Å	T = 298 K
β = 100.437 (5)°	Block, colourless
V = 691.5 (4) Å^3	0.24 × 0.18 × 0.10 mm
Z = 2

Data collection

Bruker SMART APEX CCD diffractometer	1352 independent reflections
Radiation source: fine-focus sealed tube	1069 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.048
φ and ω scans	θmax = 26.0°, θmin = 2.8°
Absorption correction: multi-scan (SADABS; Sheldrick, 1996)	h = −9→7
Tmin = 0.669, Tmax = 0.839	k = −15→15
3479 measured reflections	l = −9→6

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)] = 0.042	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.093	H-atom parameters constrained
S = 1.04	w = 1/[σ^2(Fo^2) + (0.0397P)^2 + 0.1015P] where P = (Fo^2 + 2Fc^2)/3
1352 reflections	(Δ/σ)max < 0.001
106 parameters	Δρmax = 0.57 e Å^−3
3 restraints	Δρmin = −0.40 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
Zn1	0.5000	0.5000	0.0000	0.02360 (19)
O3	0.7719 (3)	0.45670 (17)	−0.0125 (3)	0.0286 (6)
O2	0.4399 (3)	0.34197 (17)	−0.0143 (3)	0.0292 (6)
N1	1.0205 (4)	0.3608 (2)	0.1060 (4)	0.0311 (7)
H4	1.0815	0.4196	0.1018	0.037*
O1	0.4702 (3)	0.16478 (17)	−0.0133 (3)	0.0311 (6)
O4	0.5772 (4)	0.49450 (16)	0.2831 (3)	0.0380 (7)
H6	0.5680	0.5530	0.3379	0.057*
H5	0.5382	0.4413	0.3350	0.057*
C5	0.5381 (4)	0.2586 (3)	0.0077 (4)	0.0228 (8)
C4	0.7405 (5)	0.2668 (2)	0.0606 (4)	0.0223 (7)
C3	0.8381 (5)	0.1755 (3)	0.1208 (5)	0.0314 (8)
H1	0.7760	0.1103	0.1241	0.038*
C6	0.8375 (4)	0.3666 (2)	0.0498 (4)	0.0227 (7)
C1	1.1143 (5)	0.2713 (3)	0.1673 (5)	0.0364 (9)
H3	1.2396	0.2746	0.2030	0.044*
C2	1.0253 (5)	0.1758 (3)	0.1770 (5)	0.0394 (10)
H2	1.0874	0.1130	0.2197	0.047*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Zn1	0.0219 (3)	0.0139 (3)	0.0354 (4)	−0.0001 (2)	0.0063 (2)	0.0005 (2)
O3	0.0201 (12)	0.0185 (12)	0.0485 (16)	0.0002 (10)	0.0099 (11)	0.0047 (11)
O2	0.0235 (13)	0.0132 (12)	0.0500 (17)	−0.0005 (9)	0.0040 (11)	−0.0004 (10)
N1	0.0239 (17)	0.0284 (16)	0.041 (2)	−0.0038 (12)	0.0047 (13)	0.0047 (13)
O1	0.0294 (15)	0.0143 (12)	0.0481 (17)	−0.0043 (9)	0.0030 (12)	−0.0012 (10)
O4	0.0605 (19)	0.0224 (13)	0.0321 (15)	−0.0024 (12)	0.0107 (13)	−0.0018 (11)
C5	0.025 (2)	0.0215 (18)	0.0217 (18)	0.0005 (13)	0.0047 (15)	0.0018 (13)
C4	0.0251 (18)	0.0194 (16)	0.0229 (18)	0.0008 (14)	0.0057 (14)	0.0011 (13)
C3	0.034 (2)	0.0257 (19)	0.035 (2)	0.0005 (15)	0.0062 (16)	0.0052 (15)
C6	0.0184 (17)	0.0271 (18)	0.0235 (18)	0.0024 (13)	0.0059 (14)	−0.0004 (14)
C1	0.0199 (19)	0.047 (2)	0.042 (2)	0.0052 (16)	0.0042 (16)	0.0102 (18)
C2	0.032 (2)	0.036 (2)	0.049 (3)	0.0134 (17)	0.0055 (18)	0.0166 (17)

Geometric parameters (Å, º)

Zn1—O2	1.996 (2)	O1—C5	1.261 (4)
Zn1—O2^i	1.996 (2)	O4—H6	0.8415
Zn1—O3^i	2.124 (2)	O4—H5	0.8440
Zn1—O3	2.124 (2)	C5—C4	1.500 (4)
Zn1—O4	2.131 (3)	C4—C3	1.374 (4)
Zn1—O4^i	2.131 (3)	C4—C6	1.438 (4)
O3—C6	1.270 (4)	C3—C2	1.390 (5)
O2—C5	1.256 (4)	C3—H1	0.9300
N1—C1	1.345 (4)	C1—C2	1.361 (5)
N1—C6	1.362 (4)	C1—H3	0.9300
N1—H4	0.8600	C2—H2	0.9300
O2—Zn1—O2^i	180.0	Zn1—O4—H5	116.4
O2—Zn1—O3^i	92.22 (9)	H6—O4—H5	111.5
O2^i—Zn1—O3^i	87.78 (9)	O2—C5—O1	121.3 (3)
O2—Zn1—O3	87.78 (9)	O2—C5—C4	121.3 (3)
O2^i—Zn1—O3	92.22 (9)	O1—C5—C4	117.4 (3)
O3^i—Zn1—O3	180.00 (13)	C3—C4—C6	118.4 (3)
O2—Zn1—O4	92.38 (8)	C3—C4—C5	119.1 (3)
O2^i—Zn1—O4	87.62 (8)	C6—C4—C5	122.6 (3)
O3^i—Zn1—O4	92.82 (9)	C4—C3—C2	123.1 (3)
O3—Zn1—O4	87.18 (9)	C4—C3—H1	118.4
O2—Zn1—O4^i	87.62 (8)	C2—C3—H1	118.4
O2^i—Zn1—O4^i	92.38 (8)	O3—C6—N1	117.6 (3)
O3^i—Zn1—O4^i	87.18 (9)	O3—C6—C4	127.1 (3)
O3—Zn1—O4^i	92.82 (9)	N1—C6—C4	115.3 (3)
O4—Zn1—O4^i	180.0	N1—C1—C2	119.8 (3)
C6—O3—Zn1	120.79 (19)	N1—C1—H3	120.1
C5—O2—Zn1	132.0 (2)	C2—C1—H3	120.1
C1—N1—C6	125.8 (3)	C1—C2—C3	117.6 (3)
C1—N1—H4	117.1	C1—C2—H2	121.2
C6—N1—H4	117.1	C3—C2—H2	121.2
Zn1—O4—H6	116.3
O2—Zn1—O3—C6	−30.0 (2)	C6—C4—C3—C2	2.1 (5)
O2^i—Zn1—O3—C6	150.0 (2)	C5—C4—C3—C2	−178.3 (3)
O4—Zn1—O3—C6	62.5 (2)	Zn1—O3—C6—N1	−153.4 (2)
O4^i—Zn1—O3—C6	−117.5 (2)	Zn1—O3—C6—C4	29.8 (4)
O3^i—Zn1—O2—C5	−164.5 (3)	C1—N1—C6—O3	−176.6 (3)
O3—Zn1—O2—C5	15.5 (3)	C1—N1—C6—C4	0.6 (5)
O4—Zn1—O2—C5	−71.6 (3)	C3—C4—C6—O3	175.3 (3)
O4^i—Zn1—O2—C5	108.4 (3)	C5—C4—C6—O3	−4.3 (5)
Zn1—O2—C5—O1	−177.9 (2)	C3—C4—C6—N1	−1.6 (4)
Zn1—O2—C5—C4	2.3 (4)	C5—C4—C6—N1	178.8 (3)
O2—C5—C4—C3	165.9 (3)	C6—N1—C1—C2	0.0 (6)
O1—C5—C4—C3	−13.9 (4)	N1—C1—C2—C3	0.4 (6)
O2—C5—C4—C6	−14.5 (5)	C4—C3—C2—C1	−1.5 (6)
O1—C5—C4—C6	165.6 (3)

Symmetry code: (i) −x+1, −y+1, −z.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H4···O3^ii	0.86	2.06	2.895 (4)	162
O4—H5···O1^iii	0.84	1.88	2.711 (3)	170
O4—H6···O1^iv	0.84	1.98	2.798 (3)	165

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