Hexa­aqua­zinc(II) di­hydrogen-1,2,4,5-benzene­tetra­carboxyl­ate

The crystal structure of the title compound, [Zn(H₂O)₆][C₁₀H₄O₈], features a three-dimensional hydrogen-bonded network linking octahedral hexa­aqua­zinc(II) dications, occupying special positions on twofold axes, and di­hydrogen-1,2,4,5-benzene­tetra­carboxyl­ate dianions located on crystallographic inversion centres. There are also intramolecular hydrogen bonds between adjacent carboxyl groups in the dianions.

Key indicators

• Single-crystal X-ray study
• T = 293 K
• Mean [sigma](C-C) = 0.003 Å
• R factor = 0.028
• wR factor = 0.075
• Data-to-parameter ratio = 9.1

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry

General Notes



FORMU_01  There is a discrepancy between the atom counts in the
          _chemical_formula_sum and _chemical_formula_moiety. This is
          usually due to the moiety formula being in the wrong format.
          Atom count from _chemical_formula_sum:   C10 H16 O14 Zn1
          Atom count from _chemical_formula_moiety:

---

S1. Comment

Pyromellitic acid (also known as 1,2,4,5-benzenetetracarboxylic acid) is a versatile multi-dentate ligand capable of forming one-, two- and three-dimensional polymeric complexes (Poleti & Karanovic, 1989; Jaber et al., 1997) and generating various molecular architectures. These compounds are materials with zeolite-like structures and magnetic interactions. A considerable number of reports based on pyromellitic acid complexes have appeared in recent years (Rochon et al., 2001; Wang et al., 2000). At the same time, salts of pyromellitic acid have attracted interest as reagents for gravimetric analysis (Ota & Imamura., 1971), heat stabilizers (Grinblat et al., 1973), and additives in dye applications (Ichikawa et al., 1970). The first crystal structure determination of a salt of this acid, viz. [Co(H₂O)₆][C₁₀H₄O₈], was reported by Ward & Luehrs (1983).

As part of our study of benzenepolycarboxylate complexes, we tried to prepare a mixed-ligand Zn²⁺ complex containing 4-(2,5-dihydroxy-1,4-benzoquinonyl)-semicarbazide (Sun et al., 2002) as well as a pyromellitate ligand. Instead, single crystals of the title compound were obtained (Fig.1). Isostructural ionic compounds of the type [M(H₂O)₆][C₆H₂(COO)₂(COOH)₂], with M=Mn²⁺, Co²⁺, and Ni²⁺, have been synthesized and characterized by X-ray diffraction (Rochon et al., 2000). However, the zinc salt of this type has not been obtained and characterized prior to the present study.

The crystalline title compound, (I), has an ionic structure built of [Zn(H₂O)₆]²⁺ dications and dianions of doubly-deprotonated pyromellitic acid, which are linked to each other only through hydrogen bonds and ionic interactions. In the [Zn(H₂O)₆]²⁺ dication, the Zn²⁺ ion is surrounded by six water ligands, exhibiting a slightly distorted octahedral stereochemistry. Zn²⁺ occupies a special position on a twofold axis, one pair of O atoms being on the twofold axis and the other four O atoms being related to each other in pairs by this axis. The Zn—O distances are in the range 2.042 (2)–2.125 (2) Å, and O—Zn—O angles are between 86.08 (5) and 93.92 (5)°.

The endocyclic angles in the benzene ring of the tetracarboxylate dianion are 118.5 (2)° and 117.9 (2)° for the substituted C atoms and 123.6 (2)° for the unsubstituted C atoms. The exocyclic angles C3—C2—C4 and C2—C3—C5 are significantly wider than 120° [127.4 (2)° and 127.4 (2)°, respectively], while the complementary angles C1—C2—C4 and C1ⁱ—C3—C5 [symmetry code: (i) 1/2 − x, 1/2 − y, 1 − z) are obviously narrower [114.1 (2)° and 114.6 (2)°, respectively]. This is similar to the anion in the published stuctures of the Co, Mn and Ni complexes (Rochon et al., 2000), but different from the parent acid, in which all the exocyclic angles are close to 120°.

All O atoms of the pyromellitic acid and all H₂O molecules are involved in the three-dimensional network of hydrogen bonds (Fig. 2). The O···O distances in the H-bonds lie between 2.413 (2) and 2.819 (2) Å.

S2. Experimental

A mixture of pyromellitic dianhydride (0.044 g, 0.2 mmol), Zn(CH₃COO)₂·2H₂O (0.043 g, 0.2 mmol), 4-(2,5-dihydroxy-1,4-benzoquinonyl)-semicarbazide (0.0297 g, 0.1 mmol), and H₂O (6 ml, 333.3 mmol), in a mole ratio of ca 2:2:1:3333, was sealed in a 35 ml stainless-steel reactor with a telflon liner, and was heated at 433 K for 72 h. After cooling, the mixture was filtered. Gold-yellow single crystals suitable for X-ray analysis were obtained by slow evaporation of the yellow filtrate at room temperature.

S3. Refinement

All H atoms were located from a difference Fourier map and their positions and isotropic displacement parameters were refined·The C—H bond lengths were 0.90 (3) Å and the O—H bond lengths were in the range 0.75 (4)–1.06 (4) Å. Even though the distributions of C—O bond lengths in the C4/O1/O2 and C5/O3/O4 groups are faily similar, the difference map yields only one position for atom H2,thus distinguishing unambiguously the protonated carboxylic acid group from the ionized carboxylated group.

Computing details

Data collection: SMART (Bruker, 1999); cell refinement: SMART; data reduction: SAINT (Bruker, 1999) and SHELXTL (Bruker, 1997); program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL.

Figures

	Fig. 1. Structure of the cation and the anion, showing 30% probability displacement ellipsoids [symmetry codes: (i) 0.5 − x, 0.5 − y, 1 − z; (ii) −x, y, 1.5 − z].
	Fig. 2. Packing diagram, viewed down the c axis.

Hexaaqua zinc dihydrogen 1,2,4,5-benzenetetracarboxylate

Crystal data

[Zn(C10H4O8)(H2O)6]	F(000) = 872
Mr = 425.60	Dx = 1.872 Mg m^−3
Monoclinic, C2/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -C 2yc	Cell parameters from 48 reflections
a = 21.972 (3) Å	θ = 1.9–25.1°
b = 9.7717 (12) Å	µ = 1.70 mm^−1
c = 7.3036 (9) Å	T = 293 K
β = 105.562 (2)°	Column, gold–yellow
V = 1510.6 (3) Å^3	0.80 × 0.46 × 0.38 mm
Z = 4

Data collection

Siemems SMART CCD diffractometer	1341 independent reflections
Radiation source: fine-focus sealed tube	1311 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.017
ϕ and ω scans	θmax = 25.1°, θmin = 1.9°
Absorption correction: multi-scan (SADABS; Sheldrick, 1996)	h = −17→26
Tmin = 0.407, Tmax = 0.524	k = −9→11
2454 measured reflections	l = −7→8

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.028	All H-atom parameters refined
wR(F^2) = 0.075	w = 1/[σ^2(Fo^2) + (0.0488P)^2 + 2.3426P] where P = (Fo^2 + 2Fc^2)/3
S = 1.08	(Δ/σ)max < 0.001
1341 reflections	Δρmax = 0.38 e Å^−3
148 parameters	Δρmin = −0.56 e Å^−3
0 restraints	Extinction correction: SHELXL
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.0067 (7)

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	0.29817 (3)	0.7500	0.01967 (18)
O1W	0.0000	0.5147 (2)	0.7500	0.0303 (5)
O2W	−0.08065 (9)	0.28903 (19)	0.5244 (3)	0.0287 (4)
O3W	0.0000	0.0892 (2)	0.7500	0.0355 (6)
O4W	0.05715 (8)	0.31303 (17)	0.5578 (3)	0.0231 (4)
O1	0.27777 (8)	−0.12514 (15)	0.6190 (3)	0.0299 (4)
O2	0.35301 (7)	0.00023 (15)	0.7981 (2)	0.0279 (4)
O3	0.16788 (8)	−0.09047 (16)	0.4558 (3)	0.0386 (5)
O4	0.09910 (7)	0.07611 (16)	0.4343 (3)	0.0306 (4)
C1	0.31208 (10)	0.2317 (2)	0.5922 (3)	0.0179 (4)
C2	0.27083 (10)	0.1219 (2)	0.5827 (3)	0.0173 (4)
C3	0.20668 (9)	0.1406 (2)	0.4881 (3)	0.0172 (4)
C4	0.30251 (10)	−0.0082 (2)	0.6751 (3)	0.0200 (4)
C5	0.15382 (10)	0.0358 (2)	0.4600 (3)	0.0215 (5)
H1	0.3533 (13)	0.219 (2)	0.652 (3)	0.015 (6)*
H2	0.2306 (18)	−0.111 (4)	0.536 (5)	0.063 (11)*
H3	0.0276 (16)	0.045 (4)	0.801 (5)	0.055 (10)*
H4	0.0699 (17)	0.240 (4)	0.529 (5)	0.048 (9)*
H5	0.0884 (15)	0.359 (3)	0.611 (4)	0.032 (7)*
H6	0.0149 (16)	0.565 (4)	0.840 (4)	0.045 (9)*
H7	−0.1002 (16)	0.354 (4)	0.468 (5)	0.044 (9)*
H8	−0.1035 (19)	0.234 (4)	0.532 (5)	0.051 (11)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Zn1	0.0147 (2)	0.0156 (2)	0.0276 (2)	0.000	0.00363 (15)	0.000
O1W	0.0347 (14)	0.0162 (11)	0.0356 (14)	0.000	0.0019 (11)	0.000
O2W	0.0197 (9)	0.0221 (9)	0.0375 (10)	−0.0050 (7)	−0.0042 (8)	0.0061 (7)
O3W	0.0183 (12)	0.0144 (12)	0.0625 (18)	0.000	−0.0086 (12)	0.000
O4W	0.0173 (8)	0.0179 (8)	0.0343 (9)	−0.0033 (6)	0.0071 (7)	−0.0050 (6)
O1	0.0221 (8)	0.0131 (7)	0.0500 (10)	0.0000 (6)	0.0016 (7)	0.0013 (7)
O2	0.0207 (8)	0.0184 (8)	0.0393 (9)	0.0038 (6)	−0.0013 (7)	0.0036 (7)
O3	0.0195 (8)	0.0134 (8)	0.0778 (14)	−0.0034 (6)	0.0041 (8)	−0.0014 (8)
O4	0.0143 (8)	0.0199 (8)	0.0566 (11)	−0.0037 (6)	0.0076 (7)	−0.0061 (7)
C1	0.0122 (10)	0.0168 (10)	0.0247 (10)	0.0017 (8)	0.0052 (8)	−0.0007 (8)
C2	0.0161 (10)	0.0136 (9)	0.0236 (10)	0.0009 (8)	0.0079 (8)	−0.0004 (8)
C3	0.0143 (10)	0.0133 (10)	0.0249 (10)	−0.0016 (7)	0.0067 (8)	−0.0009 (8)
C4	0.0182 (10)	0.0158 (10)	0.0275 (11)	0.0019 (8)	0.0089 (9)	0.0019 (8)
C5	0.0173 (11)	0.0155 (10)	0.0307 (11)	−0.0033 (8)	0.0047 (9)	−0.0008 (8)

Geometric parameters (Å, º)

Zn1—O3W	2.042 (2)	O1—H2	1.06 (4)
Zn1—O2W	2.073 (2)	O2—C4	1.229 (3)
Zn1—O2W^i	2.073 (2)	O3—C5	1.274 (3)
Zn1—O1W	2.116 (2)	O3—H2	1.36 (4)
Zn1—O4W^i	2.125 (2)	O4—C5	1.231 (3)
Zn1—O4W	2.125 (2)	C1—C3^ii	1.393 (3)
O1W—H6	0.82 (3)	C1—C2	1.394 (3)
O2W—H7	0.81 (4)	C1—H1	0.90 (3)
O2W—H8	0.75 (4)	C2—C3	1.405 (3)
O3W—H3	0.76 (3)	C2—C4	1.518 (3)
O4W—H4	0.81 (4)	C3—C1^ii	1.393 (3)
O4W—H5	0.82 (3)	C3—C5	1.521 (3)
O1—C4	1.284 (3)
O3W—Zn1—O2W	87.53 (5)	Zn1—O4W—H4	114 (2)
O3W—Zn1—O2W^i	87.53 (5)	Zn1—O4W—H5	107 (2)
O2W—Zn1—O2W^i	175.06 (11)	H4—O4W—H5	107 (3)
O3W—Zn1—O1W	180.0	C4—O1—H2	109.4 (19)
O2W—Zn1—O1W	92.47 (5)	C5—O3—H2	110.9 (15)
O2W^i—Zn1—O1W	92.47 (5)	C3^ii—C1—C2	123.6 (2)
O3W—Zn1—O4W^i	93.92 (5)	C3^ii—C1—H1	118.0 (15)
O2W—Zn1—O4W^i	89.85 (7)	C2—C1—H1	118.4 (15)
O2W^i—Zn1—O4W^i	90.48 (7)	C1—C2—C3	118.50 (19)
O1W—Zn1—O4W^i	86.08 (5)	C1—C2—C4	114.09 (18)
O3W—Zn1—O4W	93.92 (5)	C3—C2—C4	127.39 (19)
O2W—Zn1—O4W	90.48 (7)	C1^ii—C3—C2	117.90 (19)
O2W^i—Zn1—O4W	89.85 (7)	C1^ii—C3—C5	114.67 (19)
O1W—Zn1—O4W	86.08 (5)	C2—C3—C5	127.43 (19)
O4W^i—Zn1—O4W	172.16 (9)	O2—C4—O1	120.99 (19)
Zn1—O1W—H6	127 (2)	O2—C4—C2	119.02 (18)
Zn1—O2W—H7	126 (2)	O1—C4—C2	119.92 (19)
Zn1—O2W—H8	115 (3)	O4—C5—O3	122.66 (19)
H7—O2W—H8	109 (4)	O4—C5—C3	118.96 (19)
Zn1—O3W—H3	125 (3)	O3—C5—C3	118.30 (18)

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

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O1—H2···O3	1.06 (4)	1.36 (4)	2.413 (2)	171 (4)
O3W—H3···O4^iii	0.76 (3)	2.00 (3)	2.755 (2)	178 (4)
O4W—H4···O4	0.81 (4)	1.92 (4)	2.733 (2)	173 (3)
O4W—H5···O2^iv	0.82 (3)	1.88 (3)	2.690 (2)	166 (3)
O1W—H6···O4W^v	0.82 (3)	2.00 (3)	2.819 (2)	176 (3)
O2W—H7···O2^vi	0.81 (4)	1.99 (4)	2.794 (2)	172 (3)
O2W—H8···O3^vii	0.75 (4)	2.01 (4)	2.758 (3)	177 (4)

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