Reaction of Ba 0.50[Ag 2Cr(C 2O 4) 3]·5H 2O with Ag 2SO 4 in an aqueous solution of sulfuric acid (pH ≈ 3) yielded the silver(I)/chromium(III) oxalate salt H 0.50[Ag 2.50Cr(C 2O 4) 3]·5H 2O (1). Compound 1 can be best described as an anionic silver-deficient oxalatochromate(III) complex [Ag 2.50Cr(C 2O 4) 3] 0.5- with nanochannels containing hydrogen-bonded water molecules and protons. Thermal analyses show significant weight losses corresponding to the elimination of water molecules of crystallization followed by the decomposition of the network.
Recent advances in the field of chemistry have triggered the emergence of new open framework materials with a wide range of exotic properties which are expected to promote modern technologies. These so-called “multifunctional materials” may, indeed, be exploited in many domains such as catalysis [
In the course of the past few years, the tris-chelated chromium complex anion, [Cr(C2O4)3]3-, has been used to develop a series of silver-deficient nonmolecular coordination polymers with a variable Ag-Cr-oxalate channel lattice, formulated as [(MxAg0.50-x)(H2O)3]@[Ag2.50Cr(C2O4)3] (0 ≤ x ≤ 0.50; M = K, Cs, Ag) [
Recently, our research group reported a closely related channel lattice network with chemical composition [Ag2.90Cr(C2O4)3]0.10−, where the silver charge deficit (0.10) per formula unit is solely compensated by an equivalent charge from 0.10 proton embedded amongst hydrogen-bonded water molecules within the channels [
In the present work, we aimed to widen the scope of this family of nanochanneled coordination polymers, a special emphasis being set on increasing the amount of protons within the channels defined by the negative host lattice grid substantially. Herein, we report a novel open framework silver-deficient oxalatochromate(III) compound, Ag2.50H0.50[Cr(C2O4)3]・5H2O (1). Its host lattice grid has the chemical composition [Ag2.50Cr(C2O4)3]0.50-, accusing a deficiency of 0.50 in Ag+ ion per formula unit which is compensated by an equivalent charge from 0.50 H+, the highest amount of protons known so far for this family of materials.
Elemental analysis for carbon and hydrogen was performed on a Vario EL (Heraeus) CHNS analyzer. The infrared spectrum (4000 - 400 cm−1) of the solid sample was recorded on a Perkin-Elmer 2000 FT-IR spectrometer as KBr disks. UV/Vis spectrum of the solution was measured on an AQUALYTIC spectrophotometer in the range 300 - 800 nm. Thermal analyses (TGA and DSC) were performed with a Mettler Toledo TGA/SDTA 851 thermal analyzer. The powdered sample (ca. 15 mg) was heated in air atmosphere from 25˚C to 500˚C with a rate of 10˚C min−1.
Ag2SO4 and H2SO4 (Riedel de Haën) were used as purchased. The precursor salt Ba0.50[Ag2Cr(C2O4)3]・5H2O was prepared as described in the literature [
Powder of Ag2SO4 (0.16 g, 0.5 mmol) was added in successive small portions to a stirred aqueous solution (50 mL) of Ba0.50[Ag2Cr(C2O4)3]・5H2O (1.38 g, 2 mmol) acidified with 2 drops of concentrated H2SO4. After 2 hours of stirring at 70˚C, the mixture was cooled to room temperature and a white precipitate of BaSO4 was filtered off. The resulting indigo-blue solution was allowed to evaporate in a hood at room temperature. Elongated violet needle-shaped crystals suitable for X-ray diffraction were formed within ten days. Anal. Calcd. for C6H10.50Ag2.50CrO17 (676.30 g mol−1): C, 10.66; H, 1.56%. Found: C, 10.51; H, 1.48%. IR (KBr, cm−1): ν = 3587 (w), 3246 (w), 1623 (s), 1378 (s), 1258 (w), 899 (w), 801 (s), 543 (s), 474 (s). UV-Vis (H2O solution, nm): 430; 570.
A violet crystal with dimensions 0.38 × 0.32 × 0.20 mm3 was taken directly out of the mother liquor, immersed in perfluorinated polyether, and fixed on top of a glass capillary. Graphite monochromated Mo Kα radiation (λ = 0.71073 Å) was used throughout. Intensity data were collected on a Siemens SMART CCD-de- tector. The temperature was set to 293 K. Data collection was performed by a hemisphere run taking 20 frames at intervals of 0.3˚ about ω. The data were corrected for Lorentz and polarization effects. A multi-scan absorption correction using the program SADABS [
Reaction of Ag2SO4 with Ba0.50[Ag2Cr(C2O4)3]・5H2O in an aqueous solution of H2SO4 acid (pH ≈ 3) afforded the compound Ag2.50H0.50[Cr(C2O4)3]・5H2O (1) as violet needles. This acidic medium may be responsible for the easy formation of the title compound. Compound 1 is an air-stable material which does not melt up to 250˚C.
The FTIR spectrum of 1 (
The UV-V is spectrum of 1 (
Empirical formula | C6H10.5Ag2.5CrO17 |
---|---|
Formula weight | 676.30 |
T (K) | 293(2) |
Wavelength (Å) | 0.71073 |
Crystal system | monoclinic |
Space group | C2/c |
Unit cell parameters | |
a (Å) | 18.230(3) |
b (Å) | 14.652(3) |
c (Å) | 12.276(3) |
α (°) | 90 |
β (°) | 113.700(2) |
γ (°) | 90 |
V (Å3) | 3002.4(11) |
Z | 8 |
Dcalc (g/cm3) | 2.981 |
μ (mm−1) | 4.03 |
F(000) | 2572 |
Crystal size (mm) | 0.38 × 0.32 × 0.20 |
θ range for data collection (°) | 2.2 - 25.0 |
Index ranges | −19 ≤ h ≤ 21, −17 ≤ k ≤ 16, −14 ≤ l ≤ 14 |
Total reflections | 7233 |
Unique reflections (Rint) | 2630 (0.0236) |
Absorption correction | Multi-scan |
Refinement method | Full-matrix least squares on F2 |
Data/restraints/parameters | 2630/0/240 |
Goodness-of-fit (GOF) on F2 | 1.07 |
R factor[I > 2 σ(I)] | R1 = 0.0784, wR2 = 0.2312 |
R factor (all data) | R1 = 0.0814, wR2 = 0.2282 |
Largest diff. peak and hole (eÅ−3) | 2.42 and −3.60 |
present electronic absorption spectrum is virtually super imposable with that reported since the spectral informations thus obtained solely relate to the [Cr(C2O4)3]3− species.
The TG curve of 1 depicted in
The solid state structure of 1, Ag2.50H0.50[Cr(C2O4)3]・5H2O, has been established by single-crystal X-ray diffraction. Compound 1 crystallizes, like many other members of open-framework silver-deficient oxalate chromate(III) salts [
[
A large cross-section of the three-dimensional structure packing of 1 projected down [
Cr1?O2 | 1.969(8) | O7vi?Cr1?O2 | 93.1(3) |
---|---|---|---|
Cr1?O3 | 1.962(7) | O6vi?Cr1?O3 | 94.5(3) |
Cr1?O6vi | 1.958(8) | O6vi?Cr1?O9vii | 91.7(3) |
Cr1?O7vi | 1.956(7) | O7vi?Cr1? O9vii | 93.9(3) |
Cr1?O9vii | 1.973(7) | O2?Cr1?O9vii | 92.0(3) |
Cr1?O12vii | 1.976(7) | O6vi?Cr1? O12vii | 93.2(3) |
Ag1?O9 | 2.333 (7) | O9?Ag1?O5 | 130.1(3) |
Ag1?O5 | 2.408 (9) | O5?Ag1?O4 | 91.2(3) |
Ag1?O4 | 2.412 (8) | O9?Ag1?O4 | 130.0(3) |
Ag1?O8 | 2.572 (9) | O9?Ag1?O8 | 83.4(3) |
Ag1?O1i | 2.686 (9) | O9?Ag1?O1i | 108.5(3) |
Ag2?O11 | 2.370 (7) | O11?Ag2?O10 | 70.2(2) |
Ag2?O11iv | 2.370 (7) | O11iv?Ag2?O10iv | 70.2(2) |
Ag2?O10 | 2.505 (8) | O11iv?Ag2?O10 | 138.0(2) |
Ag2?O10iv | 2.505 (8) | O11?Ag2?O10iv | 138.0(2) |
Ag2?O6v | 2.618 (7) | O11? Ag2?O6v | 84.6(2) |
Ag2?O6vi | 2.618 (7) | O11iv?Ag2?O6vi | 84.6(2) |
Ag3?O12ii | 2.322(7) | O12ii?Ag3?O1 | 135.7(3) |
Ag3?O1 | 2.446(9) | O1?Ag3?O24 | 96.1(7) |
Ag3?O24 | 2.640 (3) | O12ii?Ag3?O24 | 113.2(6) |
Ag3?O10i | 2.651 (8) | O1?Ag3?O10i | 88.1(3) |
Ag3?O4 | 2.664(9) | O12ii?Ag3?O4 | 85.7(2) |
Ag3?Ag3iii | 3.173 (3) | O12ii?Ag3?Ag3iii | 125.60(18) |
Symmetry transformations used to generate equivalent atoms for (1): (i) ?x + 1/2, −y + 1/2, −z + 1; (ii) ?x + 1/2, y + 1/2, −z + 1/2; (iii) ?x + 1, y, −z + 3/2; (iv) −x, y, −z + 1/2; (v) x−1/2, y−1/2, z; (vi) ?x + 1/2, y−1/2, −z + 1/2; (vii) x, −y, z + 1/2.
do-tubes are well isolated from one another by thick walls. The nanochannel structure of 1 is reminiscent of aluminosilicate zeolites [
Compounda | Host lattice network | Charge balance | Total silver deficit | Refs. |
---|---|---|---|---|
Ag0.50[Ag2.50Cr(ox)3](H2O)3 | [Ag2.5Cr(ox)3]0.50− | [Ag0.50]0.50+ | 0.00 | [ |
K0.28Ag0.22[Ag2.50Cr(ox)3](H2O)3 | [Ag2.50Cr(ox)3]0.50− | [K0.28Ag0.22]0.50+ | 0.28 | |
Cs0.19Ag0.31[Ag2.50Cr(ox)3](H2O)3 | [Ag2.50Cr(ox)3]0.50− | [Cs0.19Ag0.31]0.50+ | 0.19 | |
Cs0.41Ag0.09[Ag2.50Cr(ox)3](H2O)3 | [Ag2.50Cr(ox)3]0.50− | [Cs0.41Ag0.09]0.50+ | 0.41 | |
Cs0.43Ag0.07[Ag2.50Cr(ox)3](H2O)3 | [Ag2.50Cr(ox)3]0.50− | [Cs0.43Ag0.07]0.50+ | 0.43 | |
H0.10[Ag2.90Cr(ox)3]・3.75H2O | [Ag2.90Cr(ox)3]0.10− | [H0.10]0.10+ | 0.10 | [ |
[(Ag0.25/Cr0.25)(H2O)@ [Ag2Cr(ox)3]・4H2O | [Ag2Cr(ox)3]− | [(Ag0.25Cr0.25)]+ | 0.75 | [ |
[(Ag0.25/Co0.25)(H2O)@ [Ag2Co(ox)3]・4H2O | [Ag2Co(ox)3]− | [(Ag0.25Co0.25)]+ | 0.75 | |
K0.70[Ag2.30Co(ox)3]・3H2O | [Ag2.30Co(ox)3]0.70− | [K0.70]0.70+ | 0.70 | [ |
Ag0.26K0.24[Ag2.50Cr(ox)3]・3H2O | [Ag2.50Cr(ox)3]0.50− | [K0.24Ag0.26]0.50+ | 0.24 | [ |
Ag2.50H0.50[Cr(ox)3]・5H2O | [Ag2.50Cr(ox)3]0.50− | 0.50 H+ | 0.50 | This work |
aox = dianion oxalate (
our knowledge, the highest value observed so far for this family of materials. Structural data and compositions of a series of host lattice networks for some selected nanochannel Ag(I)/Cr(III)-oxalate complexes are summarized in
A new open framework silver-deficient complex salt, Ag2.50H0.50[Cr(C2O4)3]・5H2O (1), has been obtained from an acidic aqueous medium (pH ≈ 3) as violet elongated crystals. Compound 1 self-assembles into a 3D network with nanochannels accommodating hydrogen-bonded water molecules and protons. A feature of paramount interest in the present structure is the compensation of the negative charge (0.50−) of the lattice grid [Ag2.50Cr(C2O4)3]0.50− by exclusively an equivalent charge from 0.50 H+ embedded in the channels, the highest amount of protons, indeed, known so far for this family of compounds. In continuation of the present work, the results of which demonstrate the great synthetic flexibility for the construction of supramolecular assemblies, our forthcoming researches will definitely be focused on the preparation of other members of this family of silver-deficient coordination polymers. Our main concern, thereby, shall be targeted at the attempts to obtain both the ultimate deficiency of 1 Ag+ ion per formula unit and an equivalent charge balance of 1H+, thus leading to the ideal stoichiometric chemical composition Ag2H[Cr(C2O4)3]・nH2O [
Crystallographic data of compound 1 have been deposited at the Cambridge Crystallographic Data Centre, CCDC 875775. These data can be obtained free of charge from the Cambridge Crystallographic Data Centre via http://www.ccdc.cam.ac.uk/data_request/cif.
We thank Prof. You Song (Nanjing University, China) for his help with the X-ray structural analysis and valuable suggestions.
Eboga, C.T., Bebga, G., Mbiangué, Y.A., Nfor, E.N., Djonwouo, P.L., Bélombé, M.M. and Nenwa, J. (2017) Anionic Nanochanneled Silver- Deficient Oxalatochromate(III) Complex with Hydroxonium as Counter Ion: Synthesis, Characterization and Crystal Structure. Open Journal of Inorganic Chemistry, 7, 75-87. https://doi.org/10.4236/ojic.2017.73005