In the title compound, poly[hexaaquabis[μ4-3,5-bis(carboxylatomethoxy)benzoato]trizinc(II)], [Zn3(C11H7O8)2(H2O)6]n, there are two crystallographically distinct ZnII cations which are bridged by polycarboxylate ligands in a μ4-bridging mode. A pair of ligands bridges adjacent Zn atoms to give centrosymmetric dimetal building blocks which act as four-connected nodes to be further interlinked into a two-dimensional double-layered framework with (4,4) topology. Other Zn atoms, lying on inversion centres, occupy the cavities of this topological structure. This submission shows a versatile polycarboxylate ligand with rigid and flexible functional groups, the co-operation and complementarity of which would meet the coordination requirements of a variety of topological structures.
Supporting information
CCDC reference: 718105
A mixture of ZnAc2.2H2O (0.0438 g, 0.2 mmol) and H3L (0.1224 g, 0.4 mmol) in H2O (4 ml) and tetrahydrofuran (4 ml) was sealed in a Teflon-lined
steel bomb (15 ml) and then heated at 353 K for 3 d. Colourless block
crystals of (I) were collected (yield: 20%). Elemental analysis, calculated
for C22H26O22Zn3: C 31.50, H 3.10%; found: C 31.32, H 2.92%.
Spectroscopic analysis, IR (Medium?, ν, cm-1): 3494 (m), 1638
(s), 1604 (s), 1546 (s), 1425 (s), 1404
(s), 1359 (m), 1324 (m), 1171 (s), 1097
(m), 1079 (m), 751 (m), 792 (m).
C-bound H atoms were fixed geometrically and treated as riding, with C—H =
0.97 (methylene) or 0.93 Å (aromatic) and with Uiso(H) =
1.2Ueq(C). The H atoms of the water molecules were located in a
difference Fourier map and included in the subsequent refinement using
restraints O—H = 0.85 (1) Å and H···H = 1.39 (2) Å. In the last cycles of
refinement, they were treated as riding on the O atoms to which they are
attached, with Uiso(H) = 1.5Ueq(O).
Data collection: SMART (Bruker, 1998); cell refinement: SAINT (Bruker, 1998); data reduction: SAINT (Bruker, 1998); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: PLATON (Spek, 2003), DIAMOND (Brandenburg, 1999) and
CAMERON (Watkin et al., 1993); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).
poly[hexaaquabis[µ
4-3,5-bis(carboxylatomethoxy)benzoato]trizinc(II)]
top
Crystal data top
[Zn3(C11H7O8)2(H2O)6] | F(000) = 848 |
Mr = 838.54 | Dx = 2.002 Mg m−3 |
Monoclinic, P21/n | Mo Kα radiation, λ = 0.71073 Å |
Hall symbol: -P 2yn | Cell parameters from 4284 reflections |
a = 8.0458 (9) Å | θ = 2.9–27.0° |
b = 14.2074 (16) Å | µ = 2.67 mm−1 |
c = 12.1692 (13) Å | T = 173 K |
β = 90.261 (2)° | Block, colourless |
V = 1391.0 (3) Å3 | 0.42 × 0.37 × 0.19 mm |
Z = 2 | |
Data collection top
Bruker SMART CCD area-detector diffractometer | 3006 independent reflections |
Radiation source: fine-focus sealed tube | 2581 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.021 |
ω scans | θmax = 27.0°, θmin = 2.2° |
Absorption correction: multi-scan (SADABS; Bruker, 1998) | h = −5→10 |
Tmin = 0.342, Tmax = 0.602 | k = −18→17 |
7056 measured reflections | l = −15→15 |
Refinement top
Refinement on F2 | Primary atom site location: structure-invariant direct methods |
Least-squares matrix: full | Secondary atom site location: difference Fourier map |
R[F2 > 2σ(F2)] = 0.031 | Hydrogen site location: inferred from neighbouring sites |
wR(F2) = 0.086 | H-atom parameters constrained |
S = 1.05 | w = 1/[σ2(Fo2) + (0.047P)2 + 1.5975P] where P = (Fo2 + 2Fc2)/3 |
3006 reflections | (Δ/σ)max < 0.001 |
214 parameters | Δρmax = 0.96 e Å−3 |
0 restraints | Δρmin = −0.54 e Å−3 |
Crystal data top
[Zn3(C11H7O8)2(H2O)6] | V = 1391.0 (3) Å3 |
Mr = 838.54 | Z = 2 |
Monoclinic, P21/n | Mo Kα radiation |
a = 8.0458 (9) Å | µ = 2.67 mm−1 |
b = 14.2074 (16) Å | T = 173 K |
c = 12.1692 (13) Å | 0.42 × 0.37 × 0.19 mm |
β = 90.261 (2)° | |
Data collection top
Bruker SMART CCD area-detector diffractometer | 3006 independent reflections |
Absorption correction: multi-scan (SADABS; Bruker, 1998) | 2581 reflections with I > 2σ(I) |
Tmin = 0.342, Tmax = 0.602 | Rint = 0.021 |
7056 measured reflections | |
Refinement top
R[F2 > 2σ(F2)] = 0.031 | 0 restraints |
wR(F2) = 0.086 | H-atom parameters constrained |
S = 1.05 | Δρmax = 0.96 e Å−3 |
3006 reflections | Δρmin = −0.54 e Å−3 |
214 parameters | |
Special details top
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes)
are estimated using the full covariance matrix. The cell esds are taken
into account individually in the estimation of esds in distances, angles
and torsion angles; correlations between esds in cell parameters are only
used when they are defined by crystal symmetry. An approximate (isotropic)
treatment of cell esds is used for estimating esds 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 (Å2) top | x | y | z | Uiso*/Ueq | |
Zn1 | 0.64316 (4) | 0.72251 (2) | 0.17782 (2) | 0.01618 (11) | |
Zn2 | 0.5000 | 0.5000 | 0.5000 | 0.01854 (12) | |
O1 | 1.0033 (3) | 0.57204 (14) | −0.35796 (16) | 0.0229 (4) | |
O2 | 1.0332 (2) | 0.68060 (13) | −0.22726 (15) | 0.0184 (4) | |
O3 | 0.7867 (2) | 0.28827 (13) | −0.14645 (16) | 0.0199 (4) | |
O4 | 1.0984 (3) | 0.24290 (15) | −0.34770 (16) | 0.0222 (4) | |
O5 | 1.1177 (2) | 0.25985 (14) | −0.16619 (15) | 0.0181 (4) | |
O6 | 0.6960 (2) | 0.55177 (13) | 0.08566 (15) | 0.0186 (4) | |
O7 | 0.5646 (3) | 0.62160 (13) | 0.27068 (15) | 0.0220 (4) | |
O8 | 0.5101 (3) | 0.47830 (14) | 0.33331 (16) | 0.0217 (4) | |
O9 | 0.5752 (3) | 0.76831 (14) | 0.03126 (16) | 0.0247 (4) | |
H9A | 0.5485 | 0.8239 | 0.0493 | 0.037* | |
H9B | 0.5289 | 0.7549 | −0.0298 | 0.037* | |
O10 | 0.5310 (4) | 0.35424 (17) | 0.51517 (19) | 0.0478 (7) | |
H10A | 0.5326 | 0.3166 | 0.4608 | 0.072* | |
H10B | 0.4596 | 0.3334 | 0.5603 | 0.072* | |
O11 | 0.7595 (3) | 0.5174 (2) | 0.4939 (2) | 0.0514 (8) | |
H11A | 0.8146 | 0.5433 | 0.5459 | 0.077* | |
H11B | 0.7732 | 0.4576 | 0.5017 | 0.077* | |
C1 | 0.8994 (3) | 0.53836 (19) | −0.1798 (2) | 0.0150 (5) | |
C2 | 0.8819 (3) | 0.44336 (19) | −0.2071 (2) | 0.0174 (5) | |
H2 | 0.9189 | 0.4208 | −0.2744 | 0.021* | |
C3 | 0.8079 (3) | 0.38322 (18) | −0.1316 (2) | 0.0160 (5) | |
C4 | 0.7476 (3) | 0.41724 (18) | −0.0324 (2) | 0.0160 (5) | |
H4 | 0.6983 | 0.3766 | 0.0176 | 0.019* | |
C5 | 0.7616 (3) | 0.51305 (18) | −0.0087 (2) | 0.0154 (5) | |
C6 | 0.8408 (3) | 0.57380 (18) | −0.0809 (2) | 0.0161 (5) | |
H6 | 0.8543 | 0.6371 | −0.0634 | 0.019* | |
C7 | 0.9851 (3) | 0.60155 (18) | −0.2611 (2) | 0.0161 (5) | |
C8 | 0.8479 (3) | 0.2495 (2) | −0.2458 (2) | 0.0196 (6) | |
H8A | 0.7999 | 0.2840 | −0.3070 | 0.023* | |
H8B | 0.8107 | 0.1848 | −0.2515 | 0.023* | |
C9 | 1.0352 (3) | 0.25173 (18) | −0.2559 (2) | 0.0167 (5) | |
C10 | 0.6224 (3) | 0.48551 (18) | 0.1594 (2) | 0.0159 (5) | |
H10C | 0.7036 | 0.4378 | 0.1789 | 0.019* | |
H10D | 0.5298 | 0.4545 | 0.1231 | 0.019* | |
C11 | 0.5621 (3) | 0.53333 (18) | 0.2618 (2) | 0.0166 (5) | |
Atomic displacement parameters (Å2) top | U11 | U22 | U33 | U12 | U13 | U23 |
Zn1 | 0.01836 (17) | 0.01714 (17) | 0.01307 (17) | −0.00019 (11) | 0.00296 (11) | 0.00069 (11) |
Zn2 | 0.0232 (2) | 0.0190 (2) | 0.0135 (2) | −0.00064 (17) | 0.00466 (17) | −0.00293 (16) |
O1 | 0.0308 (11) | 0.0223 (10) | 0.0155 (10) | −0.0027 (8) | 0.0078 (8) | −0.0010 (8) |
O2 | 0.0224 (10) | 0.0170 (9) | 0.0157 (9) | −0.0043 (8) | 0.0027 (7) | 0.0008 (7) |
O3 | 0.0245 (10) | 0.0148 (9) | 0.0204 (10) | −0.0035 (8) | 0.0085 (8) | −0.0039 (7) |
O4 | 0.0247 (10) | 0.0273 (10) | 0.0147 (10) | 0.0045 (8) | 0.0011 (8) | −0.0024 (8) |
O5 | 0.0180 (9) | 0.0219 (10) | 0.0144 (9) | −0.0022 (7) | −0.0009 (7) | 0.0010 (7) |
O6 | 0.0282 (10) | 0.0136 (9) | 0.0141 (9) | −0.0015 (8) | 0.0084 (7) | −0.0016 (7) |
O7 | 0.0344 (11) | 0.0159 (9) | 0.0157 (9) | −0.0014 (8) | 0.0089 (8) | −0.0016 (7) |
O8 | 0.0332 (11) | 0.0187 (9) | 0.0132 (9) | −0.0028 (8) | 0.0055 (8) | −0.0008 (7) |
O9 | 0.0346 (12) | 0.0239 (11) | 0.0157 (10) | 0.0006 (9) | −0.0050 (8) | −0.0015 (8) |
O10 | 0.095 (2) | 0.0257 (12) | 0.0226 (12) | 0.0065 (13) | 0.0228 (13) | −0.0015 (9) |
O11 | 0.0246 (12) | 0.092 (2) | 0.0381 (15) | −0.0032 (13) | 0.0022 (10) | −0.0332 (14) |
C1 | 0.0129 (11) | 0.0182 (13) | 0.0141 (12) | 0.0017 (10) | 0.0011 (9) | 0.0009 (10) |
C2 | 0.0186 (12) | 0.0193 (13) | 0.0142 (12) | 0.0010 (10) | 0.0030 (10) | −0.0011 (10) |
C3 | 0.0144 (12) | 0.0136 (12) | 0.0198 (13) | 0.0008 (9) | 0.0013 (10) | −0.0008 (10) |
C4 | 0.0179 (12) | 0.0139 (12) | 0.0164 (13) | −0.0020 (10) | 0.0030 (10) | 0.0024 (10) |
C5 | 0.0182 (12) | 0.0162 (12) | 0.0117 (12) | 0.0023 (10) | 0.0015 (10) | −0.0009 (9) |
C6 | 0.0161 (12) | 0.0148 (12) | 0.0173 (13) | −0.0001 (10) | 0.0006 (10) | −0.0005 (10) |
C7 | 0.0131 (12) | 0.0185 (12) | 0.0165 (13) | 0.0018 (10) | 0.0017 (9) | 0.0027 (10) |
C8 | 0.0202 (13) | 0.0180 (12) | 0.0205 (14) | −0.0014 (10) | 0.0018 (10) | −0.0055 (10) |
C9 | 0.0217 (13) | 0.0110 (11) | 0.0174 (13) | 0.0005 (10) | −0.0015 (10) | 0.0000 (10) |
C10 | 0.0192 (13) | 0.0149 (12) | 0.0136 (12) | −0.0008 (10) | 0.0025 (10) | 0.0001 (10) |
C11 | 0.0182 (13) | 0.0175 (13) | 0.0140 (12) | 0.0003 (10) | −0.0014 (10) | −0.0004 (10) |
Geometric parameters (Å, º) top
Zn1—O7 | 1.9335 (19) | O10—H10A | 0.8510 |
Zn1—O5i | 1.9457 (19) | O10—H10B | 0.8501 |
Zn1—O9 | 1.973 (2) | O11—H11A | 0.8539 |
Zn1—O2ii | 2.0051 (18) | O11—H11B | 0.8615 |
Zn2—O8 | 2.0537 (19) | C1—C6 | 1.389 (4) |
Zn2—O10 | 2.094 (2) | C1—C2 | 1.397 (4) |
Zn2—O11 | 2.104 (2) | C1—C7 | 1.505 (4) |
O1—C7 | 1.260 (3) | C2—C3 | 1.390 (4) |
O2—C7 | 1.257 (3) | C2—H2 | 0.9300 |
O2—Zn1iii | 2.0051 (18) | C3—C4 | 1.390 (4) |
O3—C3 | 1.372 (3) | C4—C5 | 1.396 (3) |
O3—C8 | 1.419 (3) | C4—H4 | 0.9300 |
O4—C9 | 1.235 (3) | C5—C6 | 1.389 (4) |
O5—C9 | 1.281 (3) | C6—H6 | 0.9300 |
O5—Zn1i | 1.9457 (19) | C8—C9 | 1.513 (4) |
O6—C5 | 1.380 (3) | C8—H8A | 0.9700 |
O6—C10 | 1.431 (3) | C8—H8B | 0.9700 |
O7—C11 | 1.259 (3) | C10—C11 | 1.501 (4) |
O8—C11 | 1.244 (3) | C10—H10C | 0.9700 |
O9—H9A | 0.8485 | C10—H10D | 0.9700 |
O9—H9B | 0.8511 | | |
| | | |
O7—Zn1—O5i | 117.63 (9) | O3—C3—C4 | 114.4 (2) |
O7—Zn1—O9 | 133.07 (9) | O3—C3—C2 | 124.8 (2) |
O5i—Zn1—O9 | 99.31 (8) | C4—C3—C2 | 120.8 (2) |
O7—Zn1—O2ii | 91.50 (8) | C3—C4—C5 | 119.4 (2) |
O5i—Zn1—O2ii | 113.10 (8) | C3—C4—H4 | 120.3 |
O9—Zn1—O2ii | 99.97 (8) | C5—C4—H4 | 120.3 |
O8iv—Zn2—O10 | 93.82 (8) | O6—C5—C6 | 117.2 (2) |
O8—Zn2—O10 | 86.18 (8) | O6—C5—C4 | 122.0 (2) |
O8—Zn2—O11iv | 93.48 (9) | C6—C5—C4 | 120.8 (2) |
O8—Zn2—O11 | 86.52 (9) | C5—C6—C1 | 118.8 (2) |
O10—Zn2—O11 | 90.07 (12) | C5—C6—H6 | 120.6 |
O10iv—Zn2—O11 | 89.93 (12) | C1—C6—H6 | 120.6 |
C7—O2—Zn1iii | 124.09 (17) | O2—C7—O1 | 124.5 (2) |
C3—O3—C8 | 116.7 (2) | O2—C7—C1 | 117.3 (2) |
C9—O5—Zn1i | 117.29 (17) | O1—C7—C1 | 118.2 (2) |
C5—O6—C10 | 114.86 (19) | O3—C8—C9 | 114.3 (2) |
C11—O7—Zn1 | 133.91 (17) | O3—C8—H8A | 108.7 |
C11—O8—Zn2 | 127.72 (18) | C9—C8—H8A | 108.7 |
Zn1—O9—H9A | 98.2 | O3—C8—H8B | 108.7 |
Zn1—O9—H9B | 146.5 | C9—C8—H8B | 108.7 |
H9A—O9—H9B | 108.9 | H8A—C8—H8B | 107.6 |
Zn2—O10—H10A | 123.7 | O4—C9—O5 | 124.5 (3) |
Zn2—O10—H10B | 108.7 | O4—C9—C8 | 119.0 (2) |
H10A—O10—H10B | 107.3 | O5—C9—C8 | 116.4 (2) |
Zn2—O11—H11A | 122.4 | O6—C10—C11 | 111.0 (2) |
Zn2—O11—H11B | 90.4 | O6—C10—H10C | 109.4 |
H11A—O11—H11B | 106.1 | C11—C10—H10C | 109.4 |
C6—C1—C2 | 121.4 (2) | O6—C10—H10D | 109.4 |
C6—C1—C7 | 120.8 (2) | C11—C10—H10D | 109.4 |
C2—C1—C7 | 117.8 (2) | H10C—C10—H10D | 108.0 |
C3—C2—C1 | 118.7 (2) | O8—C11—O7 | 124.8 (2) |
C3—C2—H2 | 120.7 | O8—C11—C10 | 114.0 (2) |
C1—C2—H2 | 120.7 | O7—C11—C10 | 121.1 (2) |
Symmetry codes: (i) −x+2, −y+1, −z; (ii) x−1/2, −y+3/2, z+1/2; (iii) x+1/2, −y+3/2, z−1/2; (iv) −x+1, −y+1, −z+1. |
Hydrogen-bond geometry (Å, º) top
D—H···A | D—H | H···A | D···A | D—H···A |
O9—H9A···O1ii | 0.85 | 1.90 | 2.703 (3) | 159 |
O9—H9B···O4v | 0.85 | 1.81 | 2.654 (3) | 169 |
O10—H10A···O5vi | 0.85 | 2.01 | 2.828 (3) | 161 |
O10—H10B···O7iv | 0.85 | 2.16 | 2.742 (3) | 125 |
O11—H11A···O1vii | 0.85 | 1.96 | 2.769 (3) | 159 |
O11—H11B···O10 | 0.86 | 2.45 | 2.970 (4) | 120 |
Symmetry codes: (ii) x−1/2, −y+3/2, z+1/2; (iv) −x+1, −y+1, −z+1; (v) −x+3/2, y+1/2, −z−1/2; (vi) x−1/2, −y+1/2, z+1/2; (vii) x, y, z+1. |
Experimental details
Crystal data |
Chemical formula | [Zn3(C11H7O8)2(H2O)6] |
Mr | 838.54 |
Crystal system, space group | Monoclinic, P21/n |
Temperature (K) | 173 |
a, b, c (Å) | 8.0458 (9), 14.2074 (16), 12.1692 (13) |
β (°) | 90.261 (2) |
V (Å3) | 1391.0 (3) |
Z | 2 |
Radiation type | Mo Kα |
µ (mm−1) | 2.67 |
Crystal size (mm) | 0.42 × 0.37 × 0.19 |
|
Data collection |
Diffractometer | Bruker SMART CCD area-detector diffractometer |
Absorption correction | Multi-scan (SADABS; Bruker, 1998) |
Tmin, Tmax | 0.342, 0.602 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 7056, 3006, 2581 |
Rint | 0.021 |
(sin θ/λ)max (Å−1) | 0.639 |
|
Refinement |
R[F2 > 2σ(F2)], wR(F2), S | 0.031, 0.086, 1.05 |
No. of reflections | 3006 |
No. of parameters | 214 |
H-atom treatment | H-atom parameters constrained |
Δρmax, Δρmin (e Å−3) | 0.96, −0.54 |
Selected geometric parameters (Å, º) topZn1—O7 | 1.9335 (19) | Zn2—O8 | 2.0537 (19) |
Zn1—O5i | 1.9457 (19) | Zn2—O10 | 2.094 (2) |
Zn1—O9 | 1.973 (2) | Zn2—O11 | 2.104 (2) |
Zn1—O2ii | 2.0051 (18) | | |
| | | |
O7—Zn1—O5i | 117.63 (9) | O8iii—Zn2—O10 | 93.82 (8) |
O7—Zn1—O9 | 133.07 (9) | O8—Zn2—O10 | 86.18 (8) |
O5i—Zn1—O9 | 99.31 (8) | O8—Zn2—O11iii | 93.48 (9) |
O7—Zn1—O2ii | 91.50 (8) | O8—Zn2—O11 | 86.52 (9) |
O5i—Zn1—O2ii | 113.10 (8) | O10—Zn2—O11 | 90.07 (12) |
O9—Zn1—O2ii | 99.97 (8) | O10iii—Zn2—O11 | 89.93 (12) |
Symmetry codes: (i) −x+2, −y+1, −z; (ii) x−1/2, −y+3/2, z+1/2; (iii) −x+1, −y+1, −z+1. |
Hydrogen-bond geometry (Å, º) top
D—H···A | D—H | H···A | D···A | D—H···A |
O9—H9A···O1ii | 0.85 | 1.90 | 2.703 (3) | 158.5 |
O9—H9B···O4iv | 0.85 | 1.81 | 2.654 (3) | 169.2 |
O10—H10A···O5v | 0.85 | 2.01 | 2.828 (3) | 160.6 |
O10—H10B···O7iii | 0.85 | 2.16 | 2.742 (3) | 125.2 |
O11—H11A···O1vi | 0.85 | 1.96 | 2.769 (3) | 158.7 |
O11—H11B···O10 | 0.86 | 2.45 | 2.970 (4) | 119.8 |
Symmetry codes: (ii) x−1/2, −y+3/2, z+1/2; (iii) −x+1, −y+1, −z+1; (iv) −x+3/2, y+1/2, −z−1/2; (v) x−1/2, −y+1/2, z+1/2; (vi) x, y, z+1. |
Carboxylate-containing ligands have been intensively investigated to construct metal–organic frameworks with an intriguing variety of topologies and potential applications in gas sorption, separation and/or catalysis (Eddaoudi et al., 2001; Kitagawa et al., 2004; Rao et al., 2004). A wide variety of metal–carboxylate architectures are obtained by varying the nature of the reactants or the synthetic conditions. Polycarboxylate ligands with suitable spacers are good choices for such architectures because the topological structures can be adjusted not only by the carboxylate groups but also by organic spacers. Rigid spacer-based ligands such as phenyldicarboxylate have commonly been used to design functional metal–organic frameworks since these ligands allow for a certain level of control of steric effects in the assembly process and result in predictable motifs (Bourne et al., 2001; Kim et al., 2001). Nevertheless, it is also known that flexible ligands have good conformational freedom, which manifests itself in the various connecting modes that offer opportunities to create structurally diverse molecular architectures (Chen et al., 2007). In addition, compounds that are capable of rotational motion in response to outside driving forces such as light, heat or electric fields are intriguing for the development of molecular devices (Horike et al., 2006). Therefore, efforts recently focusing on manipulating flexible ligands for metal–organic frameworks have been increasing. Considering the respective advantages of rigid and flexible ligands, their cooperation has been proved to be successful in creating metal–organic architectures with intriguing topological structures and/or potential applications (Wang et al., 2007; Wei et al., 2008).
As part of our ongoing investigation of metal–organic frameworks involving semi-rigid organic ligands (Wang et al., 2008), we have developed a versatile polycarboxylate ligand, 3,5-di(carboxymethoxy)benzoate acid (H3L), which contains non-equivalent carboxylate groups from a rigid benzoate group and two flexible carboxymethoxy groups. The complementarity of the coordination function and geometric conformation from these different carboxylate groups matches the requirement for structural variety in metal–organic frameworks. Here, we report the title compound, (I), a two-dimensional zinc-containing double-layered framework structure, prepared by reacting H3L with ZnAc2.2H2O under hydrothermal conditions.
Compound (I) is a two-dimensional double-layer polymer in which the asymmetric unit contains one ligand, two crystallographically independent ZnII ions and three coordinated water molecules (Fig. 1). The coordination geometry of atom Zn1 can be described as a distorted tetrahedron consisting of three carboxylate O atoms from three different ligands and one aqua O atom [O7, O9, O5i and O2ii; symmetry codes: (i) -x+2, -y+1, -z; (ii) x-1/2, -y+3/2, z+1/2]. Atom Zn2 is located on an inversion centre at (1/2, 1/2, 1/2) and is coordinated by two carboxylate O atoms from two different ligands and four aqua O atoms [O8, O10, O11 and their symmetry-related atoms at 1-x, 1-y, 1-z)], giving a slightly distorted octahedral geometry. The whole ligand is completely deprotonated in this complex and acts in a µ4-bridging mode. One carboxymethoxy group is approximately coplanar with the aromatic ring, with a C5—O6—C10—C11 torsion angle of 177.2 (2)°, while another deviates from this ring, with a C3—O3—C8—C9 torsion angle of 67.0 (3)° and a dihedral angle between the carboxylate group and the aromatic ring plane of 102.8 (2)°. The carboxylate group of the coplanar carboxymethoxy group behaves as a syn–anti bidentate bridging ligand to coordinate atoms Zn1 and Zn2, while each of the other two carboxylate groups adopts a monodentate coordination mode to bridge different Zn1 atoms. The Zn1—O6 distance of 2.706 (2) Å shows some weak interaction between Zn1 and an uncoordinated ether O atom from the coplanar carboxymethoxy group, which may be viewed as a semi-chelating coordination mode. Such a weak interaction could lead to the result of this carboxymethoxy group being coplanar with the phenyl ring. Therefore, the environment of atom Zn1 can also be described as a significantly distorted trigonal bipyramid, with atoms O6 and O2ii located at the apical positions and atoms O7, O9 and O5i in the equatorial positions.
Analysis of this polymeric network suggests a functional centrosymmetric dimetallic building block unit, generated by a pair of symmetry-related ligands bridging adjacent Zn1 atoms (Fig. 2a) with its centre located on an inversion centre. The pair of ligands adopts an antiparallel mode, with a phenyl ring-centroid distance of 3.895 (4) Å, a interplanar distance of 3.513 (2) Å and a ring-centroid slippage of 1.683 Å, indicating that the two phenyl rings do not overlap. Such building blocks can be regarded as double-layered motifs and they adopt a four-connected node (each pair of connections associated with one layer) to be further interlinked through Zn1—Obenzoate bonds into two-dimensional double-layered framework with (4,4) topology. Four adjacent building blocks are interlinked to form a cavity which is occupied by one octahedral Zn2 atom that links two opposite building blocks through O4 atoms at (x, y, z) and (1 - x, 1 - y, 1 - z), stabilizing the cavity (Fig. 2b). Therefore, the double-layered framework is formed by assembling the building blocks, whereas the ZnO6 fragments occupy the cavities. Further analysis of this structure shows that each layer consists of independent one-dimensional zigzag metal–organic chains constructed by consecutive linking between atom Zn1 and the ligands through carboxylate O atoms from the benzoate and coplanar carboxymethoxy groups, respectively (Fig. 3). The combination of cross-linking and linking through Zn2—O bonds between chains belonging to different layers forms the double-layered framework.
All coordinated water molecules in complex (I) act as double-proton donors to participate in typical hydrogen bonding, with carboxylate O atoms acting as the acceptors (Table 2). The ether O atoms are not involved in hydrogen bonding. The four atoms H9A, H10A, H10B and H11A participate in the hydrogen bonding to consolidate the two-dimensional double-layered structure, whereas atoms H9B and H11A form hydrogen bonds with carboxylate O atoms from neighbouring double-layered structures to form a three-dimensional supramolecular structure. Adjacent double-layered structures stack antiparallel in an ABAB··· pattern.