Hexaaqua­zinc(II) dipicrate

In the title compound, [Zn(H₂O)₆](C₆H₂N₃O₇)₂, the Zn^II ion is located on an inversion center and is coordinated by six water mol­ecules in an octa­hedral geometry. The picrate anions have no coordination inter­actions with the Zn^II atom. The three nitro groups are twisted away from the attached benzene ring by19.8 (3), 6.5 (4) and 28.6 (3)°. There are numerous O—H...O hydrogen bonds in the crystal structure.

Key indicators

• Single-crystal X-ray study
• T = 293 K
• Mean [sigma](C-C) = 0.003 Å
• R factor = 0.031
• wR factor = 0.087
• Data-to-parameter ratio = 10.1

checkCIF/PLATON results

No syntax errors found



Alert level C
PLAT042_ALERT_1_C Calc. and Rep. MoietyFormula Strings Differ ....          ?
PLAT066_ALERT_1_C Predicted and Reported Transmissions Identical .          ?
PLAT180_ALERT_3_C Check Cell Rounding: # of Values Ending with 0 =          3
PLAT250_ALERT_2_C Large U3/U1 Ratio for Average U(i,j) Tensor ....       2.55
PLAT720_ALERT_4_C Number of Unusual/Non-Standard Label(s) ........          6
PLAT731_ALERT_1_C Bond    Calc     0.82(4), Rep   0.825(18) ......       2.22 su-Ra
              O2W  -H2WA    1.555   1.555

Alert level G
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 .......          4

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

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

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S1. Comment

Picric acid forms salts with many organic and metallic cations (Gartland et al., 1974). Picrates with various degrees of hydration are formed by metals (e.g. Li, Na), the alkaline earths (e.g. Cd, Hg) and various transition metals (e.g. Al, Y). Crystal structures have been reported for isomorphous NH₄ and K picrates (Maartmann-Moe, 1969), thallium picrate (Herbstein et al., 1977) and recently for manganese picrate (Liu et al., 2008). The present work reports the crystal structure of the title compound, a zinc picrate. This work is part of a systematic investigation on the structures of the metal complexes of picric acid.

In the crystal structure of the title compound, each Zn^II ion is coordinated by the O atoms of six water molecules and not by the O atoms from the picrate anions. The Zn—O distances range from 2.0297 (16) to 2.1126 (17) Å. The coordination polyhedra around the Zn^II ion can be described as a distorted octahedron. The picrate anion adopts a keto form with a C1—O1 bond distance of 1.242 (3) Å; the C6—C1 [1.457 (3) Å] and C2—C1 [1.456 (3) Å] bond distances are longer than the other C—C bond lengths of the benzene ring. The three nitro groups are twisted out of the attached benzene ring by 19.8 (3)° [N1/O2/O3], 6.5 (4)° [N2/O4/O5] and 28.6 (3)° [N3/O6/O7]. The twisting of the nitro groups may be attributed to the O—H···O hydrogen bonding interactions taking place between water and picrate O atoms. The C2—C1—C6 bond angle of 111.20 (18)° is narrower than the corresponding angle in picric acid (116.4 (5)°; Yang et al., 2001).

The packing of molecules is governed by large number of O—H···O hydrogen bonds (Table 1). π···π interactions are observed between the benzene rings of inversion related picrate ions, with a centroid to centroid distance of 3.6268 (11) Å (Fig. 2).

Related literature

For related literature, see: Gartland et al. (1974); Herbstein et al. (1977); Liu et al. (2008); Maartmann-Moe (1969); Yang et al. (2001).

S2. Experimental

Colourless needle shaped single crystals of the title compound were grown from a saturated aqueous solution containing picric acid and zinc chloride in a 1:1 stoichiometric ratio.

S3. Refinement

O-bound H atoms were located in a difference Fourier map and their positional parameters were refined, with U_iso(H) = 1.5U_eq(O). Some of the O—H distances were restrained to 0.85 (2) Å. C-bound H atoms were placed at calculated positions and allowed to ride on their carrier atoms, with C—H = 0.93 Å, and U_iso = 1.2U_eq(C).

Computing details

Data collection: CAD-4 EXPRESS (Enraf–Nonius, 1994); cell refinement: CAD-4 EXPRESS (Enraf–Nonius, 1994); data reduction: XCAD4 (Harms & Wocadlo, 1996); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: PLATON (Spek, 2003); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008).

Figures

	Fig. 1. The molecular structure of the title compound, showing 30% probability displacement ellipsoids and the atom-numbering scheme. Atoms labeled with the suffix a and double prime (") are generated by the symmetry operations (-x, 1 - y, 1 - z) and (1 - x,1 - y, 1 - z), respectively.
	Fig. 2. A packing diagram of the title compound. Dashed lines indicate π-π interactions.

Hexaaquazinc(II) dipicrate

Crystal data

[Zn(H2O)6](C6H2N3O7)2	Z = 1
Mr = 629.68	F(000) = 320
Triclinic, P1	Dx = 1.874 Mg m^−3
Hall symbol: -P 1	Mo Kα radiation, λ = 0.71073 Å
a = 7.8571 (4) Å	Cell parameters from 25 reflections
b = 8.3311 (6) Å	θ = 2–25°
c = 8.9897 (7) Å	µ = 1.22 mm^−1
α = 89.8350 (11)°	T = 293 K
β = 83.097 (1)°	Needle, colourless
γ = 72.8370 (9)°	0.13 × 0.11 × 0.10 mm
V = 557.84 (7) Å^3

Data collection

Nonius MACH-3 diffractometer	1908 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.006
Graphite monochromator	θmax = 25.0°, θmin = 2.3°
ω–2θ scans	h = −1→9
Absorption correction: ψ scan (North et al., 1968)	k = −9→9
Tmin = 0.854, Tmax = 0.886	l = −10→10
2441 measured reflections	2 standard reflections every 60 min
1971 independent reflections	intensity decay: none

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)] = 0.031	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.087	H atoms treated by a mixture of independent and constrained refinement
S = 1.14	w = 1/[σ^2(Fo^2) + (0.0559P)^2 + 0.2704P] where P = (Fo^2 + 2Fc^2)/3
1971 reflections	(Δ/σ)max = 0.001
196 parameters	Δρmax = 0.43 e Å^−3
4 restraints	Δρmin = −0.71 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	0.0000	0.5000	0.5000	0.02629 (14)
O1W	0.2724 (2)	0.4246 (2)	0.4648 (2)	0.0388 (4)
H1WA	0.325 (5)	0.498 (5)	0.458 (4)	0.058*
H1WB	0.328 (5)	0.351 (5)	0.513 (4)	0.058*
O2W	−0.0055 (3)	0.5054 (2)	0.73549 (19)	0.0421 (4)
H2WB	0.085 (3)	0.504 (5)	0.774 (4)	0.063*
H2WA	−0.055 (5)	0.439 (4)	0.775 (4)	0.063*
O3W	−0.0111 (2)	0.7546 (2)	0.4830 (2)	0.0404 (4)
H3WA	0.014 (5)	0.812 (4)	0.549 (3)	0.061*
H3WB	−0.104 (3)	0.817 (4)	0.455 (4)	0.061*
O1	0.6551 (2)	−0.1387 (2)	0.37983 (19)	0.0378 (4)
O2	0.8538 (3)	0.0707 (2)	0.3227 (3)	0.0595 (6)
O3	0.7109 (3)	0.3187 (3)	0.2651 (3)	0.0595 (6)
O4	0.2551 (3)	0.3894 (2)	−0.0507 (2)	0.0517 (5)
O5	0.0834 (3)	0.2284 (3)	−0.0310 (2)	0.0547 (5)
O6	0.4083 (3)	−0.3049 (3)	0.3983 (2)	0.0514 (5)
O7	0.2971 (3)	−0.3042 (3)	0.1909 (2)	0.0571 (5)
N1	0.7226 (3)	0.1697 (2)	0.2785 (2)	0.0353 (4)
N2	0.2129 (3)	0.2680 (3)	0.0013 (2)	0.0380 (5)
N3	0.3679 (3)	−0.2413 (3)	0.2789 (2)	0.0350 (4)
C1	0.5553 (3)	−0.0462 (3)	0.2971 (2)	0.0265 (4)
C2	0.5767 (3)	0.1112 (3)	0.2393 (2)	0.0275 (4)
C3	0.4649 (3)	0.2134 (3)	0.1486 (2)	0.0303 (5)
H3	0.4833	0.3143	0.1178	0.036*
C4	0.3249 (3)	0.1648 (3)	0.1037 (2)	0.0302 (5)
C5	0.2933 (3)	0.0163 (3)	0.1492 (2)	0.0304 (5)
H5	0.1993	−0.0154	0.1173	0.037*
C6	0.4035 (3)	−0.0836 (3)	0.2424 (2)	0.0278 (4)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Zn1	0.0234 (2)	0.0250 (2)	0.0316 (2)	−0.00531 (14)	−0.01323 (14)	0.00959 (13)
O1W	0.0258 (8)	0.0363 (9)	0.0567 (11)	−0.0088 (7)	−0.0161 (7)	0.0218 (8)
O2W	0.0460 (11)	0.0465 (10)	0.0327 (9)	−0.0074 (8)	−0.0172 (8)	0.0094 (7)
O3W	0.0395 (10)	0.0272 (9)	0.0598 (11)	−0.0089 (7)	−0.0290 (8)	0.0117 (8)
O1	0.0341 (9)	0.0369 (9)	0.0472 (10)	−0.0110 (7)	−0.0233 (7)	0.0217 (7)
O2	0.0513 (12)	0.0418 (11)	0.0980 (16)	−0.0184 (9)	−0.0471 (11)	0.0189 (10)
O3	0.0736 (14)	0.0418 (11)	0.0806 (15)	−0.0325 (10)	−0.0394 (12)	0.0258 (10)
O4	0.0565 (12)	0.0461 (11)	0.0510 (11)	−0.0064 (9)	−0.0245 (9)	0.0264 (9)
O5	0.0469 (11)	0.0612 (12)	0.0593 (12)	−0.0097 (10)	−0.0363 (10)	0.0197 (10)
O6	0.0471 (11)	0.0599 (12)	0.0616 (12)	−0.0293 (9)	−0.0297 (9)	0.0399 (10)
O7	0.0721 (14)	0.0606 (13)	0.0585 (12)	−0.0428 (11)	−0.0275 (11)	0.0166 (10)
N1	0.0406 (11)	0.0325 (10)	0.0379 (10)	−0.0134 (9)	−0.0182 (9)	0.0084 (8)
N2	0.0372 (11)	0.0385 (11)	0.0298 (10)	0.0053 (9)	−0.0136 (8)	0.0075 (8)
N3	0.0278 (10)	0.0398 (11)	0.0412 (11)	−0.0128 (8)	−0.0119 (8)	0.0136 (9)
C1	0.0245 (10)	0.0266 (10)	0.0260 (10)	−0.0023 (8)	−0.0079 (8)	0.0063 (8)
C2	0.0292 (11)	0.0272 (10)	0.0267 (10)	−0.0065 (9)	−0.0105 (8)	0.0047 (8)
C3	0.0359 (12)	0.0257 (10)	0.0262 (10)	−0.0028 (9)	−0.0083 (9)	0.0058 (8)
C4	0.0292 (11)	0.0316 (11)	0.0244 (10)	0.0022 (9)	−0.0107 (8)	0.0065 (8)
C5	0.0232 (10)	0.0387 (12)	0.0270 (10)	−0.0034 (9)	−0.0087 (8)	0.0046 (9)
C6	0.0257 (10)	0.0300 (11)	0.0272 (10)	−0.0062 (8)	−0.0069 (8)	0.0083 (8)

Geometric parameters (Å, º)

Zn1—O1W^i	2.0297 (16)	O4—N2	1.228 (3)
Zn1—O1W	2.0297 (16)	O5—N2	1.224 (3)
Zn1—O3W^i	2.1025 (16)	O6—N3	1.230 (3)
Zn1—O3W	2.1025 (16)	O7—N3	1.221 (3)
Zn1—O2W^i	2.1126 (17)	N1—C2	1.451 (3)
Zn1—O2W	2.1126 (17)	N2—C4	1.451 (3)
O1W—H1WA	0.83 (4)	N3—C6	1.451 (3)
O1W—H1WB	0.80 (4)	C1—C2	1.456 (3)
O2W—H2WB	0.822 (18)	C1—C6	1.457 (3)
O2W—H2WA	0.825 (18)	C2—C3	1.374 (3)
O3W—H3WA	0.837 (18)	C3—C4	1.381 (3)
O3W—H3WB	0.824 (19)	C3—H3	0.93
O1—C1	1.242 (3)	C4—C5	1.383 (3)
O2—N1	1.223 (3)	C5—C6	1.374 (3)
O3—N1	1.224 (3)	C5—H5	0.93
O1W^i—Zn1—O1W	180.0	O3—N1—C2	118.43 (19)
O1W^i—Zn1—O3W^i	92.05 (7)	O5—N2—O4	123.3 (2)
O1W—Zn1—O3W^i	87.95 (7)	O5—N2—C4	118.6 (2)
O1W^i—Zn1—O3W	87.95 (7)	O4—N2—C4	118.1 (2)
O1W—Zn1—O3W	92.05 (7)	O7—N3—O6	122.8 (2)
O3W^i—Zn1—O3W	180.0	O7—N3—C6	118.70 (19)
O1W^i—Zn1—O2W^i	92.82 (8)	O6—N3—C6	118.5 (2)
O1W—Zn1—O2W^i	87.18 (8)	O1—C1—C2	124.7 (2)
O3W^i—Zn1—O2W^i	93.38 (8)	O1—C1—C6	124.1 (2)
O3W—Zn1—O2W^i	86.62 (8)	C2—C1—C6	111.20 (18)
O1W^i—Zn1—O2W	87.18 (8)	C3—C2—N1	115.76 (19)
O1W—Zn1—O2W	92.82 (8)	C3—C2—C1	124.3 (2)
O3W^i—Zn1—O2W	86.62 (8)	N1—C2—C1	119.89 (18)
O3W—Zn1—O2W	93.38 (8)	C2—C3—C4	119.3 (2)
O2W^i—Zn1—O2W	180.0	C2—C3—H3	120.3
Zn1—O1W—H1WA	118 (2)	C4—C3—H3	120.3
Zn1—O1W—H1WB	120 (3)	C3—C4—C5	121.54 (19)
H1WA—O1W—H1WB	107 (3)	C3—C4—N2	119.3 (2)
Zn1—O2W—H2WB	121 (3)	C5—C4—N2	119.1 (2)
Zn1—O2W—H2WA	111 (3)	C6—C5—C4	118.8 (2)
H2WB—O2W—H2WA	112 (4)	C6—C5—H5	120.6
Zn1—O3W—H3WA	125 (3)	C4—C5—H5	120.6
Zn1—O3W—H3WB	116 (2)	C5—C6—N3	115.6 (2)
H3WA—O3W—H3WB	104 (3)	C5—C6—C1	124.8 (2)
O2—N1—O3	121.6 (2)	N3—C6—C1	119.51 (18)
O2—N1—C2	119.98 (19)
O2—N1—C2—C3	−160.3 (2)	O5—N2—C4—C5	6.7 (3)
O3—N1—C2—C3	19.3 (3)	O4—N2—C4—C5	−172.1 (2)
O2—N1—C2—C1	20.3 (3)	C3—C4—C5—C6	0.6 (3)
O3—N1—C2—C1	−160.1 (2)	N2—C4—C5—C6	177.90 (19)
O1—C1—C2—C3	−179.5 (2)	C4—C5—C6—N3	−176.93 (19)
C6—C1—C2—C3	1.8 (3)	C4—C5—C6—C1	−0.7 (3)
O1—C1—C2—N1	−0.2 (3)	O7—N3—C6—C5	26.2 (3)
C6—C1—C2—N1	−178.87 (19)	O6—N3—C6—C5	−152.9 (2)
N1—C2—C3—C4	178.65 (19)	O7—N3—C6—C1	−150.2 (2)
C1—C2—C3—C4	−2.0 (3)	O6—N3—C6—C1	30.7 (3)
C2—C3—C4—C5	0.7 (3)	O1—C1—C6—C5	−179.1 (2)
C2—C3—C4—N2	−176.59 (19)	C2—C1—C6—C5	−0.4 (3)
O5—N2—C4—C3	−176.0 (2)	O1—C1—C6—N3	−3.0 (3)
O4—N2—C4—C3	5.2 (3)	C2—C1—C6—N3	175.65 (19)

Symmetry code: (i) −x, −y+1, −z+1.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O3W—H3WB···O1^ii	0.82 (2)	2.02 (2)	2.781 (2)	153 (3)
O3W—H3WB···O2^ii	0.82 (2)	2.38 (3)	2.972 (3)	130 (3)
O3W—H3WA···O2^iii	0.84 (2)	2.07 (2)	2.880 (3)	164 (3)
O2W—H2WB···O3^iii	0.82 (2)	2.48 (3)	3.083 (3)	131 (3)
O1W—H1WA···O6^iv	0.83 (4)	1.99 (4)	2.799 (3)	164 (3)
O1W—H1WB···O1^v	0.80 (4)	1.99 (4)	2.705 (2)	149 (3)
O1W—H1WB···O6^v	0.80 (4)	2.24 (4)	2.839 (2)	132 (3)
O2W—H2WB···O4^vi	0.82 (2)	2.22 (3)	2.931 (3)	144 (3)
O2W—H2WA···O5^vi	0.82 (2)	2.57 (3)	3.097 (3)	123 (3)
O2W—H2WA···O7^vii	0.82 (2)	2.46 (2)	3.223 (3)	154 (3)

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