Supporting information
Crystallographic Information File (CIF) https://doi.org/10.1107/S1600536807033818/lh2433sup1.cif | |
Structure factor file (CIF format) https://doi.org/10.1107/S1600536807033818/lh2433Isup2.hkl |
CCDC reference: 657586
Key indicators
- Single-crystal X-ray study
- T = 298 K
- Mean (C-C) = 0.012 Å
- R factor = 0.071
- wR factor = 0.147
- Data-to-parameter ratio = 7.2
checkCIF/PLATON results
No syntax errors found
Alert level A DIFF019_ALERT_1_A _diffrn_standards_number is missing Number of standards used in measurement.
Author Response: Data taken on CCD detector. |
DIFF020_ALERT_1_A _diffrn_standards_interval_count and _diffrn_standards_interval_time are missing. Number of measurements between standards or time (min) between standards.
Author Response: Data taken on CCD detector. |
Alert level B PLAT340_ALERT_3_B Low Bond Precision on C-C Bonds (x 1000) Ang ... 12
Alert level C RINTA01_ALERT_3_C The value of Rint is greater than 0.10 Rint given 0.112 PLAT020_ALERT_3_C The value of Rint is greater than 0.10 ......... 0.11 PLAT089_ALERT_3_C Poor Data / Parameter Ratio (Zmax .LT. 18) ..... 7.19 PLAT241_ALERT_2_C Check High Ueq as Compared to Neighbors for O2A PLAT242_ALERT_2_C Check Low Ueq as Compared to Neighbors for C2B PLAT720_ALERT_4_C Number of Unusual/Non-Standard Label(s) ........ 9 PLAT764_ALERT_4_C Overcomplete CIF Bond List Detected (Rep/Expd) . 1.14 Ratio
Alert level G REFLT03_ALERT_4_G Please check that the estimate of the number of Friedel pairs is correct. If it is not, please give the correct count in the _publ_section_exptl_refinement section of the submitted CIF. From the CIF: _diffrn_reflns_theta_max 25.03 From the CIF: _reflns_number_total 1287 Count of symmetry unique reflns 1288 Completeness (_total/calc) 99.92% TEST3: Check Friedels for noncentro structure Estimate of Friedel pairs measured 0 Fraction of Friedel pairs measured 0.000 Are heavy atom types Z>Si present no PLAT860_ALERT_3_G Note: Number of Least-Squares Restraints ....... 1
2 ALERT level A = In general: serious problem 1 ALERT level B = Potentially serious problem 7 ALERT level C = Check and explain 2 ALERT level G = General alerts; check 2 ALERT type 1 CIF construction/syntax error, inconsistent or missing data 2 ALERT type 2 Indicator that the structure model may be wrong or deficient 5 ALERT type 3 Indicator that the structure quality may be low 3 ALERT type 4 Improvement, methodology, query or suggestion 0 ALERT type 5 Informative message, check
For related literature, see: Brese & O'Keeffe (1991); Chen et al. (2005); Dincã & Long (2005); Huang et al. (2004, 2005); Irish et al. (1991); Park et al. (2006); Rood et al. (2006); Rowsell et al. (2005); Schlapbach & Züttel (2001); Sturm et al. (1975); Tian et al. (2002, 2003); Tian, Chen et al. (2004); Tian, Xu et al. (2004).[Author: double bonds are shown incorrectly in imidazole rings]
For related literature, see: Rowsell & Yaghi (2006).
A solid mixture of magnesium acetate tetrahydrate Mg(CH3COO)2 4H2O (0.670 g, 3.12 × 10 -3mol) and imidazole (1.546 g, 2.27 × 10 -2mol) was dissolved in 20 mL of dimethylformamide in a 50 mL centrifuge tube. The tube was stirred for 30 minutes until all reagents were well dissolved, capped, and heated at a rate of 5 K per minute to 358 K in a progammable oven; this temperature was held constant for 48 h. The oven was then cooled at 0.4 K per minute to room temperature. The mother liquor was decanted off following centrifuge and the sample washed with DMF (10 mL × 3). The colorless plate-like crystals harvested from solution were analyzed by single-crystal x-ray diffraction.
Although the space group is noncentrosymmetric, an absolute configuration could not be obtained, as shown by an indeterminate Flack parameter value of 0.0 (8). This is attributable to the structure containing only light atoms. Therefore, the Friedel opposites were merged before the final refinement. The Rint value of 0.1184 shows the poor agreement between equivalent reflections, and the overall weakness of scattering by the preferentially chosen crystal is indicated by the average σ(I)/Inet value of 0.0564. These lead to low bond precision in the C—C bonds (0.012 Å). The methyl H atoms were refined as idealized rotating groups with isotropic thermal parameters set to 1.5 times the isotropic thermal parameter of the corresponding methyl carbon. The H atoms on the imidazoles were refined as idealized aromatic H atoms riding on their bonding partners with isotropic thermal parameters set to 1.2 times that of their corresponding bonding partner. The hydrogen on the carboxylate oxygen was refined as an idealized hydroxyl hydrogen with an isotropic thermal parameter set to 1.5 times the isotropic thermal parameter of the hydroxyl oxygen. It should be noted that the chosen crystal was the best of many that were examined.
Crystal frameworks incorporating imidazole are of special interest in materials chemistry, especially in the design of metal-organic frameworks (MOFs) that imitate important zeolite topologies. It was found that imidazole may be placed as an organic linker between two coordination centers to bridge metals at the identical angle to the essential bond in most zeolites: the Si—O—Si bond exhibiting a bond angle of 145° (Park et al., 2006). Therefore, this five membered ring makes an ideal organic linker for zeolite analogue frameworks.
Many examples of imidazole zeolite analog structures have been reported, spanning nearly every zeolite topology, a number of different transition metal centers, and various organic linkers incorporating the imidazole ring. The earliest such example is in crystal frameworks of cobalt and imidazole that date back to the 1970 s (Sturm et al., 1975). Numerous other examples of cobalt imidazoles have bee reported to show such zeolite topologies as CAG, among others (Tian et al., 2002, 2003; Tian, Xu et al., 2004; Tian, Chen et al., 2004). Similar copper imidazoles revealing analagous structures to zeolites have also been reported (Huang et al., 2004, 2005). It is important to note that to date, all zeolite analog structures incorporating imidazole have been made with transition metals, mostly from the first row of the d-block.
Our interests in these MOFs have been directed toward synthesizing imidazole structures that incorporate smaller alkali and alkaline earth metals, specifically magnesium. This is appealing because such materials have the potential to be lightweight in comparison to transition metal equivalents and may serve as better candidates for hydrogen or methane gas storage (Rowsell et al., 2005; Rowsell & Yaghi, 2006; Schlapbach & Züttel, 2001; Dincã & Long, 2005; Chen et al., 2005). Other research has begun to be conducted with magnesium and formate as a linking agent; a structural and gas sorption study was recently reported of a porous magnesium formate framework with similar intentions (Rood et al., 2006).
Although this is not a three-dimensional zeolite analog framework, it proves that such a framework may be possible with magnesium. Imidazole does not here serve in its intended role as a zeolitic linker. However, a new and interesting cluster species has been discovered.
The local coordination environment around each magnesium atom may be described as distorted octahedral. The magnesium atoms are related by symmetry and both are coordinated by two terminal imidazole ligands, two bridging acetate ligands, a terminal acetate ligand, and a bridging oxygen. The bond angles reported here match very closely to those reported for magnesium diacetate tetrahydrate (Irish et al., 1991). Bond valences for each coordinative bond may be derived from the bond lengths by specific parameters for a given bond (Brese & O'Keeffe, 1991).
The stucture of the title compound is shown in Figure 1.
For related literature, see: Brese & O'Keeffe (1991); Chen et al. (2005); Dincã & Long (2005); Huang et al. (2004, 2005); Irish et al. (1991); Park et al. (2006); Rood et al. (2006); Rowsell et al. (2005); Schlapbach & Züttel (2001); Sturm et al. (1975); Tian et al. (2002, 2003); Tian, Chen et al. (2004); Tian, Xu et al. (2004).[Author: double bonds are shown incorrectly in imidazole rings]
For related literature, see: Rowsell & Yaghi (2006).
Data collection: SMART (Bruker, 2003); cell refinement: SAINT (Bruker, 2003); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL (Bruker, 2001); software used to prepare material for publication: SHELXTL.
[Mg2(C2H3O2)2O(C3H4N2)4(C2H4O2)2] | F(000) = 1208 |
Mr = 575.14 | Dx = 1.366 Mg m−3 |
Orthorhombic, Aba2 | Mo Kα radiation, λ = 0.71073 Å |
Hall symbol: A 2 -2ac | Cell parameters from 1685 reflections |
a = 8.6927 (14) Å | θ = 2.4–22.2° |
b = 19.106 (3) Å | µ = 0.15 mm−1 |
c = 16.834 (3) Å | T = 298 K |
V = 2795.8 (8) Å3 | Block, colourless |
Z = 4 | 0.12 × 0.10 × 0.05 mm |
Bruker SMART APEX diffractometer | 1287 independent reflections |
Radiation source: fine-focus sealed tube | 1034 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.112 |
ω scans | θmax = 25.0°, θmin = 2.1° |
Absorption correction: multi-scan (SADABS; Bruker, 2004) | h = −10→10 |
Tmin = 0.986, Tmax = 0.994 | k = −22→22 |
10414 measured reflections | l = −20→19 |
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)] = 0.071 | Hydrogen site location: inferred from neighbouring sites |
wR(F2) = 0.147 | H-atom parameters constrained |
S = 1.17 | w = 1/[σ2(Fo2) + (0.0579P)2 + 3.9683P] where P = (Fo2 + 2Fc2)/3 |
1287 reflections | (Δ/σ)max < 0.001 |
179 parameters | Δρmax = 0.24 e Å−3 |
1 restraint | Δρmin = −0.25 e Å−3 |
[Mg2(C2H3O2)2O(C3H4N2)4(C2H4O2)2] | V = 2795.8 (8) Å3 |
Mr = 575.14 | Z = 4 |
Orthorhombic, Aba2 | Mo Kα radiation |
a = 8.6927 (14) Å | µ = 0.15 mm−1 |
b = 19.106 (3) Å | T = 298 K |
c = 16.834 (3) Å | 0.12 × 0.10 × 0.05 mm |
Bruker SMART APEX diffractometer | 1287 independent reflections |
Absorption correction: multi-scan (SADABS; Bruker, 2004) | 1034 reflections with I > 2σ(I) |
Tmin = 0.986, Tmax = 0.994 | Rint = 0.112 |
10414 measured reflections |
R[F2 > 2σ(F2)] = 0.071 | 1 restraint |
wR(F2) = 0.147 | H-atom parameters constrained |
S = 1.17 | Δρmax = 0.24 e Å−3 |
1287 reflections | Δρmin = −0.25 e Å−3 |
179 parameters |
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. |
x | y | z | Uiso*/Ueq | ||
Mg1 | 0.3999 (3) | 0.08395 (10) | 0.18240 (17) | 0.0326 (6) | |
O1A | 0.5000 | 0.0000 | 0.2501 (4) | 0.0333 (17) | |
O2A | 0.2900 (6) | 0.0160 (2) | 0.1101 (4) | 0.0469 (15) | |
C2B | 0.3038 (8) | −0.0453 (3) | 0.0872 (4) | 0.0298 (16) | |
O2C | 0.4045 (6) | −0.0881 (2) | 0.1118 (4) | 0.0438 (14) | |
C2D | 0.1915 (12) | −0.0706 (4) | 0.0281 (7) | 0.073 (3) | |
H2D1 | 0.1459 | −0.1134 | 0.0466 | 0.109* | |
H2D2 | 0.2429 | −0.0789 | −0.0215 | 0.109* | |
H2D3 | 0.1128 | −0.0360 | 0.0207 | 0.109* | |
O3A | 0.5018 (6) | 0.1576 (2) | 0.2544 (3) | 0.0436 (14) | |
C3B | 0.6049 (8) | 0.1524 (4) | 0.3047 (5) | 0.0383 (18) | |
O3C | 0.6644 (6) | 0.0947 (3) | 0.3253 (4) | 0.0529 (16) | |
H3CA | 0.6183 | 0.0625 | 0.3038 | 0.079* | |
C3D | 0.6620 (11) | 0.2178 (4) | 0.3447 (6) | 0.059 (2) | |
H3D1 | 0.7089 | 0.2479 | 0.3060 | 0.089* | |
H3D2 | 0.7364 | 0.2056 | 0.3845 | 0.089* | |
H3D3 | 0.5771 | 0.2417 | 0.3691 | 0.089* | |
N4A | 0.2875 (7) | 0.1689 (3) | 0.1191 (4) | 0.0374 (16) | |
C4E | 0.1930 (9) | 0.1640 (4) | 0.0553 (5) | 0.044 (2) | |
H4E | 0.1779 | 0.1237 | 0.0254 | 0.053* | |
C4D | 0.1237 (10) | 0.2263 (4) | 0.0416 (6) | 0.056 (2) | |
H4D | 0.0547 | 0.2370 | 0.0012 | 0.067* | |
N4C | 0.1753 (7) | 0.2691 (3) | 0.0985 (4) | 0.0426 (17) | |
H4CA | 0.1477 | 0.3119 | 0.1055 | 0.051* | |
C4B | 0.2761 (9) | 0.2343 (4) | 0.1422 (5) | 0.045 (2) | |
H4B | 0.3318 | 0.2537 | 0.1839 | 0.054* | |
N5A | 0.2107 (6) | 0.0828 (3) | 0.2699 (4) | 0.0400 (16) | |
C5B | 0.0607 (9) | 0.0839 (4) | 0.2574 (7) | 0.054 (2) | |
H5B | 0.0150 | 0.0823 | 0.2075 | 0.065* | |
N5C | −0.0174 (7) | 0.0874 (4) | 0.3264 (5) | 0.0530 (19) | |
H5CA | −0.1158 | 0.0897 | 0.3314 | 0.064* | |
C5E | 0.2252 (9) | 0.0836 (4) | 0.3508 (5) | 0.050 (2) | |
H5E | 0.3181 | 0.0821 | 0.3782 | 0.060* | |
C5D | 0.0842 (10) | 0.0868 (5) | 0.3855 (6) | 0.059 (2) | |
H5D | 0.0630 | 0.0884 | 0.4396 | 0.070* |
U11 | U22 | U33 | U12 | U13 | U23 | |
Mg1 | 0.0281 (12) | 0.0214 (11) | 0.0482 (14) | 0.0010 (10) | −0.0043 (11) | −0.0019 (13) |
O1A | 0.027 (4) | 0.024 (3) | 0.049 (5) | 0.003 (3) | 0.000 | 0.000 |
O2A | 0.049 (3) | 0.025 (2) | 0.067 (4) | 0.006 (2) | −0.015 (3) | −0.008 (3) |
C2B | 0.030 (4) | 0.022 (3) | 0.037 (4) | −0.001 (3) | 0.002 (3) | −0.002 (3) |
O2C | 0.040 (3) | 0.027 (3) | 0.064 (4) | 0.002 (2) | −0.010 (3) | −0.001 (3) |
C2D | 0.074 (7) | 0.037 (4) | 0.106 (8) | 0.012 (5) | −0.040 (7) | −0.013 (5) |
O3A | 0.043 (3) | 0.034 (3) | 0.054 (4) | −0.001 (2) | −0.014 (3) | −0.003 (3) |
C3B | 0.030 (4) | 0.046 (5) | 0.039 (5) | −0.013 (4) | 0.004 (4) | −0.004 (4) |
O3C | 0.040 (3) | 0.041 (3) | 0.078 (4) | −0.002 (3) | −0.021 (3) | −0.005 (3) |
C3D | 0.070 (6) | 0.056 (5) | 0.053 (6) | −0.003 (5) | −0.031 (5) | −0.011 (5) |
N4A | 0.038 (4) | 0.032 (3) | 0.042 (4) | 0.006 (3) | −0.001 (3) | −0.002 (3) |
C4E | 0.047 (5) | 0.035 (4) | 0.051 (5) | 0.002 (4) | −0.009 (5) | −0.002 (4) |
C4D | 0.051 (5) | 0.060 (5) | 0.057 (6) | 0.008 (4) | −0.016 (5) | −0.001 (5) |
N4C | 0.034 (3) | 0.023 (3) | 0.071 (5) | 0.008 (3) | −0.003 (3) | −0.001 (3) |
C4B | 0.041 (5) | 0.034 (4) | 0.060 (5) | 0.009 (4) | −0.009 (4) | −0.002 (4) |
N5A | 0.021 (3) | 0.042 (3) | 0.057 (5) | 0.005 (3) | −0.002 (3) | 0.006 (3) |
C5B | 0.034 (4) | 0.048 (5) | 0.080 (7) | 0.003 (4) | −0.003 (5) | −0.001 (5) |
N5C | 0.027 (3) | 0.057 (4) | 0.075 (5) | 0.005 (3) | 0.008 (4) | −0.002 (4) |
C5E | 0.027 (4) | 0.064 (5) | 0.058 (6) | −0.001 (4) | −0.006 (4) | −0.003 (5) |
C5D | 0.048 (5) | 0.068 (6) | 0.060 (6) | 0.001 (4) | 0.010 (5) | −0.009 (5) |
Mg1—O2A | 2.021 (6) | C3D—H3D2 | 0.9600 |
Mg1—O3A | 2.058 (6) | C3D—H3D3 | 0.9600 |
Mg1—O2Ci | 2.076 (6) | N4A—C4B | 1.312 (9) |
Mg1—O1A | 2.151 (5) | N4A—C4E | 1.355 (10) |
Mg1—N4A | 2.173 (6) | C4E—C4D | 1.354 (10) |
Mg1—N5A | 2.208 (7) | C4E—H4E | 0.9300 |
Mg1—Mg1i | 3.649 (4) | C4D—N4C | 1.337 (11) |
O1A—Mg1i | 2.151 (5) | C4D—H4D | 0.9300 |
O2A—C2B | 1.239 (8) | N4C—C4B | 1.323 (10) |
C2B—O2C | 1.267 (8) | N4C—H4CA | 0.8600 |
C2B—C2D | 1.475 (11) | C4B—H4B | 0.9300 |
O2C—Mg1i | 2.076 (6) | N5A—C5B | 1.320 (10) |
C2D—H2D1 | 0.9600 | N5A—C5E | 1.368 (11) |
C2D—H2D2 | 0.9600 | C5B—N5C | 1.347 (12) |
C2D—H2D3 | 0.9600 | C5B—H5B | 0.9300 |
O3A—C3B | 1.237 (9) | N5C—C5D | 1.330 (11) |
C3B—O3C | 1.265 (9) | N5C—H5CA | 0.8600 |
C3B—C3D | 1.505 (10) | C5E—C5D | 1.359 (12) |
O3C—H3CA | 0.8200 | C5E—H5E | 0.9300 |
C3D—H3D1 | 0.9600 | C5D—H5D | 0.9300 |
O2A—Mg1—O3A | 176.5 (2) | C3B—O3C—H3CA | 109.5 |
O2A—Mg1—O2Ci | 93.8 (2) | C3B—C3D—H3D1 | 109.5 |
O3A—Mg1—O2Ci | 87.6 (2) | C3B—C3D—H3D2 | 109.5 |
O2A—Mg1—O1A | 91.78 (19) | H3D1—C3D—H3D2 | 109.5 |
O3A—Mg1—O1A | 91.4 (2) | C3B—C3D—H3D3 | 109.5 |
O2Ci—Mg1—O1A | 90.1 (2) | H3D1—C3D—H3D3 | 109.5 |
O2A—Mg1—N4A | 88.4 (2) | H3D2—C3D—H3D3 | 109.5 |
O3A—Mg1—N4A | 88.4 (2) | C4B—N4A—C4E | 104.7 (7) |
O2Ci—Mg1—N4A | 93.4 (2) | C4B—N4A—Mg1 | 126.9 (6) |
O1A—Mg1—N4A | 176.6 (3) | C4E—N4A—Mg1 | 127.5 (5) |
O2A—Mg1—N5A | 92.5 (3) | N4A—C4E—C4D | 110.1 (7) |
O3A—Mg1—N5A | 86.3 (2) | N4A—C4E—H4E | 125.0 |
O2Ci—Mg1—N5A | 173.0 (3) | C4D—C4E—H4E | 125.0 |
O1A—Mg1—N5A | 86.6 (2) | N4C—C4D—C4E | 105.5 (7) |
N4A—Mg1—N5A | 90.0 (2) | N4C—C4D—H4D | 127.3 |
O2A—Mg1—Mg1i | 70.15 (14) | C4E—C4D—H4D | 127.3 |
O3A—Mg1—Mg1i | 113.34 (17) | C4B—N4C—C4D | 108.2 (6) |
O2Ci—Mg1—Mg1i | 69.12 (15) | C4B—N4C—H4CA | 125.9 |
O1A—Mg1—Mg1i | 31.98 (19) | C4D—N4C—H4CA | 125.9 |
N4A—Mg1—Mg1i | 150.55 (18) | N4A—C4B—N4C | 111.4 (7) |
N5A—Mg1—Mg1i | 110.26 (16) | N4A—C4B—H4B | 124.3 |
Mg1—O1A—Mg1i | 116.0 (4) | N4C—C4B—H4B | 124.3 |
C2B—O2A—Mg1 | 138.5 (5) | C5B—N5A—C5E | 104.4 (8) |
O2A—C2B—O2C | 125.2 (7) | C5B—N5A—Mg1 | 129.0 (7) |
O2A—C2B—C2D | 117.1 (6) | C5E—N5A—Mg1 | 126.5 (5) |
O2C—C2B—C2D | 117.8 (6) | N5A—C5B—N5C | 111.2 (9) |
C2B—O2C—Mg1i | 136.7 (4) | N5A—C5B—H5B | 124.4 |
C2B—C2D—H2D1 | 109.5 | N5C—C5B—H5B | 124.4 |
C2B—C2D—H2D2 | 109.5 | C5D—N5C—C5B | 108.0 (7) |
H2D1—C2D—H2D2 | 109.5 | C5D—N5C—H5CA | 126.0 |
C2B—C2D—H2D3 | 109.5 | C5B—N5C—H5CA | 126.0 |
H2D1—C2D—H2D3 | 109.5 | C5D—C5E—N5A | 110.2 (8) |
H2D2—C2D—H2D3 | 109.5 | C5D—C5E—H5E | 124.9 |
C3B—O3A—Mg1 | 131.2 (5) | N5A—C5E—H5E | 124.9 |
O3A—C3B—O3C | 123.7 (7) | N5C—C5D—C5E | 106.2 (8) |
O3A—C3B—C3D | 118.5 (7) | N5C—C5D—H5D | 126.9 |
O3C—C3B—C3D | 117.8 (7) | C5E—C5D—H5D | 126.9 |
Symmetry code: (i) −x+1, −y, z. |
Experimental details
Crystal data | |
Chemical formula | [Mg2(C2H3O2)2O(C3H4N2)4(C2H4O2)2] |
Mr | 575.14 |
Crystal system, space group | Orthorhombic, Aba2 |
Temperature (K) | 298 |
a, b, c (Å) | 8.6927 (14), 19.106 (3), 16.834 (3) |
V (Å3) | 2795.8 (8) |
Z | 4 |
Radiation type | Mo Kα |
µ (mm−1) | 0.15 |
Crystal size (mm) | 0.12 × 0.10 × 0.05 |
Data collection | |
Diffractometer | Bruker SMART APEX |
Absorption correction | Multi-scan (SADABS; Bruker, 2004) |
Tmin, Tmax | 0.986, 0.994 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 10414, 1287, 1034 |
Rint | 0.112 |
(sin θ/λ)max (Å−1) | 0.595 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.071, 0.147, 1.17 |
No. of reflections | 1287 |
No. of parameters | 179 |
No. of restraints | 1 |
H-atom treatment | H-atom parameters constrained |
Δρmax, Δρmin (e Å−3) | 0.24, −0.25 |
Computer programs: SMART (Bruker, 2003), SAINT (Bruker, 2003), SAINT, SHELXS97 (Sheldrick, 1997), SHELXL97 (Sheldrick, 1997), SHELXTL (Bruker, 2001), SHELXTL.
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Crystal frameworks incorporating imidazole are of special interest in materials chemistry, especially in the design of metal-organic frameworks (MOFs) that imitate important zeolite topologies. It was found that imidazole may be placed as an organic linker between two coordination centers to bridge metals at the identical angle to the essential bond in most zeolites: the Si—O—Si bond exhibiting a bond angle of 145° (Park et al., 2006). Therefore, this five membered ring makes an ideal organic linker for zeolite analogue frameworks.
Many examples of imidazole zeolite analog structures have been reported, spanning nearly every zeolite topology, a number of different transition metal centers, and various organic linkers incorporating the imidazole ring. The earliest such example is in crystal frameworks of cobalt and imidazole that date back to the 1970 s (Sturm et al., 1975). Numerous other examples of cobalt imidazoles have bee reported to show such zeolite topologies as CAG, among others (Tian et al., 2002, 2003; Tian, Xu et al., 2004; Tian, Chen et al., 2004). Similar copper imidazoles revealing analagous structures to zeolites have also been reported (Huang et al., 2004, 2005). It is important to note that to date, all zeolite analog structures incorporating imidazole have been made with transition metals, mostly from the first row of the d-block.
Our interests in these MOFs have been directed toward synthesizing imidazole structures that incorporate smaller alkali and alkaline earth metals, specifically magnesium. This is appealing because such materials have the potential to be lightweight in comparison to transition metal equivalents and may serve as better candidates for hydrogen or methane gas storage (Rowsell et al., 2005; Rowsell & Yaghi, 2006; Schlapbach & Züttel, 2001; Dincã & Long, 2005; Chen et al., 2005). Other research has begun to be conducted with magnesium and formate as a linking agent; a structural and gas sorption study was recently reported of a porous magnesium formate framework with similar intentions (Rood et al., 2006).
Although this is not a three-dimensional zeolite analog framework, it proves that such a framework may be possible with magnesium. Imidazole does not here serve in its intended role as a zeolitic linker. However, a new and interesting cluster species has been discovered.
The local coordination environment around each magnesium atom may be described as distorted octahedral. The magnesium atoms are related by symmetry and both are coordinated by two terminal imidazole ligands, two bridging acetate ligands, a terminal acetate ligand, and a bridging oxygen. The bond angles reported here match very closely to those reported for magnesium diacetate tetrahydrate (Irish et al., 1991). Bond valences for each coordinative bond may be derived from the bond lengths by specific parameters for a given bond (Brese & O'Keeffe, 1991).
The stucture of the title compound is shown in Figure 1.