A nanoporous three-dimensional metal coordination polymer {(NH₄)₂Zn[C₆H₂(COO)₄]·8H₂O}_n

The title compound, poly­[ammonium zinc-μ-benzene-1,2,4,5-tetra­carboxyl­ate octahydrate] {(NH₄)₂Zn[C₆H₂(COO)₄]·8H₂O}_n, forms a three-dimensional network containing one-dimensional nanoporous rhomboid channels along the c axis, accommodating guest water mol­ecules and the ammonium cations. The dimensions of the large channel are 11.555 (2) × 15.00 (1) Å. The network consists of [Zn(C₆H₂(COO)₄]²⁻ anions containing tetrahedral Zn atoms bonded to four carboxyl­ate groups. The Zn...O distances range from 1.974 (2) to 1.978 (2) Å. The ammonium cations and the water mol­ecules are associated in a centrosymmetric network by intermolecular hydrogen bonds. The hydrogen bonding is essential to stabilize the crystal structure.

Key indicators

• Single-crystal X-ray study
• T = 293 K
• Mean [sigma](C-C) = 0.003 Å
• H-atom completeness 39%
• Disorder in solvent or counterion
• R factor = 0.032
• wR factor = 0.097
• Data-to-parameter ratio = 13.5

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry


 Alert Level C:



PLAT_302  Alert C Anion/Solvent Disorder .......................      21.00 Perc.

PLAT_353  Alert C Long  N-H Bond (0.87A)     N      -   H14    =       1.05 Ang.

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 H26 N2 O16 Zn1
          Atom count from _chemical_formula_moiety:H8 N2 O2

FORMU_01  There is a discrepancy between the atom counts in the
          _chemical_formula_sum and the formula from the _atom_site* data.
          Atom count from _chemical_formula_sum:C10 H26 N2 O16 Zn1
          Atom count from the _atom_site data:  C10 H10 N2 O16 Zn1

CELLZ_01
         From the CIF: _cell_formula_units_Z    4
         From the CIF: _chemical_formula_sum  C10 H26 N2 O16 Zn
         TEST: Compare cell contents of formula and atom_site data

         atom    Z*formula  cif sites diff
         C         40.00     40.00    0.00
         H        104.00     40.00   64.00
         N          8.00      8.00    0.00
         O         64.00     64.00    0.00
         Zn         4.00      4.00    0.00
          Difference between formula and atom_site contents detected.
          WARNING: H atoms missing from atom site list. Is this intentional?

CHEMW_03
         From the CIF: _cell_formula_units_Z                    4
         From the CIF: _chemical_formula_weight           495.70
         TEST: Calculate formula weight from _atom_site_*
         atom     mass    num     sum
         C        12.01   10.00  120.11
         H         1.01   10.00   10.08
         N        14.01    2.00   28.01
         O        16.00   16.00  255.98
         Zn       65.39    1.00   65.39
         Calculated formula weight              479.58
          The ratio of given/expected molecular weight as calculated
          from the _atom_site* data lies outside
          the range 0.99 <> 1.01


 0 Alert Level A = Potentially serious problem

 0 Alert Level B = Potential problem

 2 Alert Level C = Please check

---

S1. Comment

Aromatic poly-carboxylic ligands have a versatile coordination modes as they can form bridges between metallic centers, generating various molecular topologies and architectures, as well as having potential application as functional materials. They find widespread application in heterogeneous catalysis, chemical absorption and magnetism. Owing to their widespread utility (Yaghi et al., 1996), a considerable number of reports based on metal–aromatic poly-carboxylic coordination polymers have appeared over the past few years (Yaghi et al., 1997). 1,2,4,5-Benzenetetracarboxylic acid (H4btec) has four carboxyl groups, eight O-donor atoms that may be completely or partly deprotonated, inducing rich coordination modes and allowing novel structure with higher dimensions. It has been reported that an increase in pH results in a higher connectivity level of the ligands, which in turn leads to a higher dimensionality of the crystal structure (Pan et al., 2001). We adjusted the PH value to 9 ~10 by NH₃·H₂O and fortunately obtained the title compound, (I).

{(NH₄)₂Zn[C₆H₂(COO)₄]·8H₂O}_n is a three-dimensional polymer containing one-dimensional nanoporous channels along the c axis with guest water molecules and the ammonium cation. All the carboxyl groups of H4btec are deprotonated, in agreement with the IR data in which no absorption peaks are observed around 1700 cm⁻¹ for COOH. There is a strong absorption peak at 1603 cm⁻¹ for υ_as(CO).

Only one type of coordination mode of btec⁴⁻ is present in the structure. Each carboxylate group adopts a monodentate chelating mode, coordinating one Zn atom. Therefore, each btec⁴⁻ acts as a µ4-bridge linking four Zn centers and each central Zn atom attaches to four btec⁴⁻ ligands, forming a slightly distorted tetrahedron around Zn²⁺, with Zn···O bond lengths ranging from 1.974 (2) to 1.978 (2) Å, similar to other related Zn···O distances (Robl.,1992). Zn²⁺ is situated on the twofold axis and the four O atoms in a pair are related to each other by the twofold axis; the btec⁴⁻ phenyl ring is centrosymmetric. The closest Zn···Zn distance is 5.538 (1) Å, indicating the lack of any direct metal–metal interaction. The macrocyclic unit [Zn₄(btec)₄]¹²⁻, which forms a rhombus sheet, with a Zn···Zn distance of 9.587 (1) Å, constitutes the basic building block of the structure. Every building block is linked together through Zn···O bonds to generate a three-dimensional structure with a nanoporous rhomboid channel along the c axis. The dimensions of this large channel are 11.555 (2) Å × 15.100 (3) Å. It accommodates ammonium cations and water molecules associated into a centrosymmetric network by intermolecular hydrogen bonds. Different kinds of hydrogen bonding are observed in the structure: (a) hydrogen bonding among water molecules [O···O distance: 1.845 (2)–3.039 (2) Å]; (b) hydrogen bonding of water molecules and carboxylate oxygen atoms [O···O distance: 2.725 (8)–3.028 (1) Å]; (c) hydrogen bonding between the ammonium cation and carboxylate oxygen atoms [N···O distance: 2.847 (2)–3.016 (2) Å]; (d) hydrogen bonding between the ammonium cation and water molecules [N···O distance:2.894 (2)–3.058 (2) Å]. The guest water molecules and ammonium cations are obviously essential to stablize the crystal structure.

S2. Experimental

A mixture of Zn(CH₃COO)₂·3H₂O (0.043 g, 0.2 mmol), 1,2,4,5-benzenetetracarboxylic dianhydride (0.043 g, 0.2 mmol), NH₃·H₂O (1 ml) and H₂O (6 ml) with a molar ratio of 1:1:278:1667 (solution PH=8 ~9) was heated in a stainless steel reactor with a Teflon liner at 433 K for three d. It produced a colorless solution. After evaporation for several days at room temperature, colorless diamond-like crystals were obtained.

S3. Refinement

The phenyl ring and ammonium hydrogen atoms were located in a difference Fourier map and their positions and isotropic displacement parameters were refined. Atom O3w is equally disordered over two positions (O3w—O3w' distance: 1.523 Å). The occupancy of atom O5w is 0.496 and assigned to 0.5. The refinement is unstable if the occupancy of O5w is assigned to 1. The hydrogen atoms of the water O atoms were not located in the difference Fourier map, and were not assigned to water O atoms owing to the complexities of the structure.

Computing details

Data collection: Bruker SMART; cell refinement: SMART (Bruker, 1999); data reduction: 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. The Zn^2+ coordination environment in the title compound and the atom-labeling scheme, Displacement ellipsoids are shown at the 30% probability level [symmetry codes: (i) 1 − x, y, −z + 0.5; (ii) x + 0.5, y − 0.5, z; (iii) −x + 0.5, y − 0.5, −z + 0.5].
	Fig. 2. Packing diagram, viewed down the [001] diagonal of the unit cell, showing hydrogen-bond interactions.

poly[Ammonium Zinc-µ-benzene-1,2,4,5- tetracarboxylato-octahydrate

Crystal data

[Zn(C10H2O8)](NH4)2·8H2O	F(000) = 1032
Mr = 495.70	Dx = 1.683 Mg m^−3
Monoclinic, C2/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -C 2yc	Cell parameters from 50 reflections
a = 11.555 (2) Å	θ = 2.2–27.5°
b = 15.300 (3) Å	µ = 1.34 mm^−1
c = 11.072 (2) Å	T = 293 K
β = 91.97 (3)°	Diamond, colorless
V = 1956.4 (7) Å^3	0.20 × 0.19 × 0.10 mm
Z = 4

Data collection

Siemems SMART CCD diffractometer	2242 independent reflections
Radiation source: fine-focus sealed tube	2015 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.010
ϕ and ω scans	θmax = 27.5°, θmin = 2.2°
Absorption correction: multi-scan (SADABS; Sheldrick, 1996)	h = −14→14
Tmin = 0.762, Tmax = 0.877	k = −19→18
4233 measured reflections	l = −14→14

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) = 0.097	H atoms treated by a mixture of independent and constrained refinement
S = 0.98	w = 1/[σ^2(Fo^2) + (0.0773P)^2 + 1.4324P] where P = (Fo^2 + 2Fc^2)/3
2242 reflections	(Δ/σ)max < 0.001
166 parameters	Δρmax = 0.66 e Å^−3
0 restraints	Δρmin = −0.59 e Å^−3

Special details

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	Occ. (<1)
Zn1	0.5000	0.494950 (16)	0.2500	0.01785 (13)
O1	0.38370 (12)	0.56214 (9)	0.15306 (13)	0.0270 (3)
O2	0.52526 (13)	0.65120 (11)	0.09969 (16)	0.0366 (4)
O3	0.1452 (2)	0.84669 (13)	0.27795 (15)	0.0538 (5)
O4	0.08978 (13)	0.93339 (9)	0.12755 (14)	0.0292 (3)
C1	0.42225 (17)	0.62977 (12)	0.10034 (17)	0.0235 (4)
C2	0.33176 (16)	0.68962 (11)	0.04435 (17)	0.0221 (4)
C3	0.27625 (18)	0.74539 (13)	0.12211 (18)	0.0257 (4)
C4	0.19476 (16)	0.80621 (12)	0.07962 (17)	0.0226 (4)
C5	0.13959 (17)	0.86542 (13)	0.16921 (18)	0.0267 (4)
N	0.7271 (3)	0.5761 (2)	0.0020 (3)	0.0574 (6)
O1W	0.1645 (4)	0.5424 (5)	0.2555 (6)	0.177 (2)
O2W	0.0000	0.5920 (11)	0.7500	0.361 (10)
O3W	0.3966 (5)	0.2159 (4)	0.0572 (6)	0.0801 (16)	0.50
O3W'	0.4277 (6)	0.1764 (5)	−0.0637 (11)	0.137 (4)	0.50
O4W	0.4212 (7)	0.9401 (5)	0.012 (2)	0.517 (16)
O5W	0.4706 (12)	0.1707 (6)	0.1937 (10)	0.162 (5)	0.50
H1	0.302 (3)	0.748 (2)	0.212 (3)	0.050 (8)*
H11	0.774 (6)	0.630 (5)	0.020 (6)	0.15 (2)*
H12	0.741 (9)	0.520 (6)	0.044 (11)	0.22 (4)*
H13	0.668 (7)	0.587 (4)	0.046 (7)	0.16 (3)*
H14	0.695 (8)	0.573 (5)	−0.088 (9)	0.23 (4)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Zn1	0.02137 (18)	0.01547 (17)	0.01684 (18)	0.000	0.00242 (11)	0.000
O1	0.0313 (7)	0.0220 (6)	0.0275 (7)	0.0057 (5)	−0.0006 (6)	0.0048 (5)
O2	0.0272 (8)	0.0402 (9)	0.0424 (9)	0.0038 (6)	−0.0003 (6)	0.0083 (7)
O3	0.0826 (14)	0.0575 (11)	0.0215 (8)	0.0381 (10)	0.0065 (8)	−0.0012 (8)
O4	0.0384 (8)	0.0225 (7)	0.0272 (7)	0.0115 (5)	0.0081 (6)	−0.0019 (5)
C1	0.0285 (9)	0.0225 (9)	0.0195 (8)	0.0086 (7)	0.0002 (7)	−0.0017 (7)
C2	0.0261 (9)	0.0178 (8)	0.0224 (9)	0.0059 (6)	0.0005 (7)	0.0012 (7)
C3	0.0340 (10)	0.0248 (9)	0.0180 (8)	0.0087 (7)	−0.0001 (7)	−0.0007 (7)
C4	0.0281 (9)	0.0201 (8)	0.0198 (9)	0.0066 (7)	0.0038 (7)	−0.0011 (6)
C5	0.0325 (10)	0.0256 (9)	0.0222 (9)	0.0077 (7)	0.0030 (7)	−0.0042 (7)
N	0.0534 (15)	0.0608 (17)	0.0581 (17)	−0.0100 (12)	0.0052 (13)	−0.0016 (13)
O1W	0.096 (3)	0.241 (6)	0.197 (6)	−0.005 (4)	0.052 (4)	−0.027 (6)
O2W	0.300 (18)	0.292 (18)	0.48 (3)	0.000	−0.125 (18)	0.000
O3W	0.100 (4)	0.061 (3)	0.079 (4)	−0.036 (3)	−0.007 (3)	0.007 (3)
O3W'	0.085 (5)	0.067 (4)	0.258 (13)	−0.027 (3)	0.005 (6)	0.038 (6)
O4W	0.191 (9)	0.168 (7)	1.18 (5)	−0.034 (6)	−0.075 (16)	0.164 (16)
O5W	0.191 (12)	0.128 (6)	0.174 (12)	−0.019 (7)	0.086 (11)	−0.025 (6)

Geometric parameters (Å, º)

Zn1—O4^i	1.9744 (14)	C2—C4^v	1.398 (3)
Zn1—O4^ii	1.9744 (14)	C3—C4	1.394 (3)
Zn1—O1^iii	1.9789 (14)	C3—H1	1.04 (3)
Zn1—O1	1.9789 (14)	C4—C2^v	1.398 (3)
O1—C1	1.276 (2)	C4—C5	1.501 (2)
O2—C1	1.235 (3)	N—H11	1.01 (7)
O3—C5	1.237 (3)	N—H12	0.99 (10)
O4—C5	1.268 (2)	N—H13	0.86 (8)
O4—Zn1^iv	1.9744 (14)	N—H14	1.05 (10)
C1—C2	1.507 (2)	O3W—O3W'	1.523 (12)
C2—C3	1.385 (3)	O5W—O5W^iii	1.40 (2)
O4^i—Zn1—O4^ii	123.02 (9)	C2—C3—H1	120.2 (17)
O4^i—Zn1—O1^iii	104.91 (6)	C4—C3—H1	117.8 (17)
O4^ii—Zn1—O1^iii	103.79 (6)	C3—C4—C2^v	118.99 (17)
O4^i—Zn1—O1	103.79 (6)	C3—C4—C5	118.49 (17)
O4^ii—Zn1—O1	104.91 (6)	C2^v—C4—C5	122.52 (16)
O1^iii—Zn1—O1	117.40 (8)	O3—C5—O4	123.50 (18)
C1—O1—Zn1	115.35 (12)	O3—C5—C4	119.60 (17)
C5—O4—Zn1^iv	112.59 (13)	O4—C5—C4	116.89 (17)
O2—C1—O1	124.74 (17)	H11—N—H12	124 (6)
O2—C1—C2	119.43 (17)	H11—N—H13	99 (5)
O1—C1—C2	115.64 (17)	H12—N—H13	91 (6)
C3—C2—C4^v	119.46 (16)	H11—N—H14	113 (6)
C3—C2—C1	116.62 (17)	H12—N—H14	116 (7)
C4^v—C2—C1	123.87 (16)	H13—N—H14	107 (6)
C2—C3—C4	121.55 (18)

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