Research ArticleGEOCHEMISTRY

Minerals with metal-organic framework structures

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Science Advances  05 Aug 2016:
Vol. 2, no. 8, e1600621
DOI: 10.1126/sciadv.1600621
  • Fig. 1 Stepanovite is a mineral with an MOF structure.

    (A) Stepanovite sample, Chai-Tumus coal deposit (Sakha-Yakutia, Siberia, Russia; sample from E. I. Nefedov’s collection). (B) schematic of an open anionic hcb framework composed of MI and MIII nodes bridged by oxalates. (C) A single layer of an analogous zinc-based proton-conducting MOF material, including guests (11). (D) Crystals of synthetic stepanovite. (E) A single metal-organic layer in stepanovite, viewed along the crystallographic c axis, displaying the anionic hcb [NaFe(ox)3]2− framework, with apertures occupied by Mg(H2O)62+. Hydrogen bonds between Mg(H2O)62+ guests and [NaFe(ox)3]2− framework are highlighted as yellow dotted lines.

  • Fig. 2 Structure of stepanovite and PXRD patterns of MOF minerals.

    (A) Hydrogen bonding environment of water guests between hcb layers of stepanovite. (B) Stepanovite structure viewed parallel to crystallographic a axis (water molecules were omitted for clarity), with offset ABCABC arrangement evident from stacking of Na+, Mg2+, and Fe3+ ions (blue, green, and orange, respectively) in neighboring layers. (C) Comparison of PXRD patterns (top to bottom): natural stepanovite, synthetic stepanovite, simulated NaMgFe(ox)3⋅9H2O, natural zhemchuzhnikovite, synthetic zhemchuzhnikovite, and simulated NaMgFe0.41Al0.59(ox)3⋅9H2O. The PXRD pattern of natural stepanovite is affected by the presence of a number of other minerals, of which the most abundant one is glushinskite, as well as amorphous organic material. For clarity, principal reflections of stepanovite are designated with “*.” List of indexed x-ray reflections for natural stepanovite and zhemchuzhnikovite is given in tables S1 and S2.

  • Fig. 3 Crystal structure of zhemchuzhnikovite and role of aluminum in its formation.

    (A) Zhemchuzhnikovite structure viewed down the crystallographic c axis, demonstrating the alignment of MOF layers into channels occupied by Mg(H2O)62+. For clarity, the hcb layers are shown in space-filling mode, Mg(H2O)62+, and interstitial water molecules using capped sticks. (B) PXRD patterns (top to bottom): simulated NaMgFe0.41Al0.59(ox)3⋅9H2O, simulated NaMgFe(ox)3⋅9H2O, NaMgAl(ox)3⋅9H2O, products of LAG of NaMgFe(ox)3⋅9H2O and NaMgAl(ox)3⋅9H2O in different stoichiometric ratios (50:50, 70:30, 80:20, and 90:10), and product of dry milling of NaMgFe(ox)3⋅9H2O and NaMgAl(ox)3⋅9H2O in 50:50 ratio. The PXRD patterns reveal formation of zhemchuzhnikovite structure for Fe/Al ratios up to ~80:20, whereas a higher Fe/Al ratio favors stepanovite structure. Two characteristic reflections that distinguish zhemchuzhnikovite and stepanovite structures are highlighted by “z” and “s,” respectively.

  • Fig. 4 Hydrogen-bonded motifs in stepanovite and zhemchuzhnikovite and reversibility of thermal dehydration of zhemchuzhnikovite.

    (A) The 3D hydrogen-bonded network of Mg(H2O)62+ ions and interlayer water molecules in stepanovite. (B) Three parallel hydrogen-bonded columns of Mg(H2O)62+ ions and interlayer water molecules in zhemchuzhnikovite, each propagating through a channel formed by the overlap of hcb layers. For clarity, the metal-organic hcb layers are omitted. (C) The reversibility of structural changes upon dehydration and rehydration of synthetic zhemchuzhnikovite is demonstrated by comparison of PXRD patterns (top to bottom): simulated zhemchuzhnikovite NaMgFe0.41Al0.59(ox)3⋅9H2O; simulated for stepanovite NaMgFe(ox)3⋅9H2O; and zhemchuzhnikovite after one, two, and three cycles of thermal dehydration at 90°C and rehydration by exposure to 100% relative humidity (RH) at room temperature.

  • Table 1 Crystallographic data for stepanovite and zhemchuzhnikovite.

    Comparison of crystallographic and general parameters reported by Knipovich et al. (8) to the investigated natural and synthetic samples in this study.

    Stepanovite
    Reported by Knipovich et al. (8)NaturalSynthetic
    Crystal systemTrigonalTrigonalTrigonal
    FormulaNaMgFe(C2O4)3·8-9H2ONaMgFe(C2O4)3·9H2ONaMgFe(C2O4)3·9H2O
    Space groupNot reportedR3cR3c
    a (Å)9.78*9.8367(13)*9.887(13)*
    c (Å)36.6736.902(5)37.03(5)
    a/c ratio1:3.73–1:3.76*1:3.75*1:3.75*
    V3)30703092.2(7)3135(9)
    Z666
    ColorGreenGreenish yellowGreen
    Density (g cm)1.691.71 (calculated)1.68 (calculated)
    Zhemchuzhnikovite
    Reported by Knipovich et al. (8)NaturalSynthetic
    Crystal systemTrigonalTrigonalTrigonal
    FormulaNaMg(Fe0.4Al0.6)(C2O4)3·8-9H2ONaMg(Fe0.31Al0.69)(C2O4)3·9H2ONaMg(Fe1−xAlx)(C2O4)3·9H2O
    Space groupNot reportedP3c1P3c1
    a (Å)16.6716.809(7)16.919(2)§
    c (Å)12.5112.658(6)12.561(2)§
    a/c ratio1:0.75–1:0.7391:0.7531:0.742§
    V3)30013097(2)3113.8(9)§
    Z666
    ColorGreenGreenish yellowYellow-green
    Density1.62–1.661.64 (calculated)1.63 (calculated)

    *The originally reported lattice parameter a for stepanovite was 9.28 Å. This is inconsistent with the a/c ratio reported in the same study, and in accepting the naming of this mineral, L. G. Berry (9) suggested it was a typographical error, with the real value being a = 9.78 Å. Herein reported a/c values for natural and synthetic stepanovite are consistent with that of Knipovich et al. (8, 9).

    †For different crystals, x varied from 0.59 to 0.27.

    ‡Isotructural to NaMgAl(ox)3·9H2O (CCDC code YODWUK).

    §Crystallographic parameters for the crystal with composition NaMg(Fe0.41Al0.59)(C2O4)3·9H2O.

    Supplementary Materials

    • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/2/8/e1600621/DC1

      fig. S1. Scanning electron microscopy image of aggregates of isometric zhemchuzhnikovite crystals from Chai-Tumus coal deposit, Sakha-Yakutia, Russia (sample from E. I. Nefedov’s collections).

      fig. S2. Morphologies for stepanovite, reported by Knipovich et al. (8).

      fig. S3. Morphologies for zhemchuzhnikovite.

      fig. S4. TGA of bulk synthetic stepanovite.

      fig. S5. TGA of bulk synthetic zhemchuzhnikovite.

      fig. S6. Comparison of PXRD patterns for synthetic stepanovite after one, two, and three cycles of dehydration at 90°C and rehydration at 100% RH.

      fig. S7. Thermal analysis of zhemchuzhnikovite after thermal dehydration at 90°C for 16 hours: TGA (top) and DSC (bottom).

      fig. S8. Thermal analysis of zhemchuzhnikovite after thermal dehydration at 90°C, followed by exposure to 100% RH: TGA (top) and DSC (bottom).

      fig. S9. Thermal analysis of stepanovite after thermal dehydration at 90°C: TGA (top) and DSC (bottom).

      fig. S10. Thermal analysis of stepanovite after thermal dehydration at 90°C, followed by exposure to 100% RH: TGA (top) and DSC (bottom).

      fig. S11. Overlay of FTIR-ATR spectra for mechanochemically prepared zhemchuzhnikovite analogs with different Al:Fe ratios.

      table S1. PXRD data of bulk stepanovite from Chai-Tumus coal deposit, Siberia, Russia, were indexed on the basis of herein determined crystal structure.

      table S2. PXRD data of bulk zhemchuzhnikovite from Chai-Tumus coal deposit, Siberia, Russia, were indexed on the basis of herein determined crystal structure.

      data file S1. Crystallographic data for crystal structures of natural and synthetic samples of stepanovite and zhemchuzhnikovite.

      data file S2. checkCIF for crystal structures of natural and synthetic samples of stepanovite and zhemchuzhnikovite.

    • Supplementary Materials

      This PDF file includes:

      • fig. S1. Scanning electron microscopy image of aggregates of isometric zhemchuzhnikovite crystals from Chai-Tumus coal deposit, Sakha-Yakutia, Russia (sample from E. I. Nefedov’s collections).
      • fig. S2. Morphologies for stepanovite, reported by Knipovich et al. (8).
      • fig. S3. Morphologies for zhemchuzhnikovite.
      • fig. S4. TGA of bulk synthetic stepanovite.
      • fig. S5. TGA of bulk synthetic zhemchuzhnikovite.
      • fig. S6. Comparison of PXRD patterns for synthetic stepanovite after one, two, and three cycles of dehydration at 90°C and rehydration at 100% RH.
      • fig. S7. Thermal analysis of zhemchuzhnikovite after thermal dehydration at 90°C for 16 hours: TGA (top) and DSC (bottom).
      • fig. S8. Thermal analysis of zhemchuzhnikovite after thermal dehydration at 90°C, followed by exposure to 100% RH: TGA (top) and DSC (bottom).
      • fig. S9. Thermal analysis of stepanovite after thermal dehydration at 90°C: TGA (top) and DSC (bottom).
      • fig. S10. Thermal analysis of stepanovite after thermal dehydration at 90°C, followed by exposure to 100% RH: TGA (top) and DSC (bottom).
      • fig. S11. Overlay of FTIR-ATR spectra for mechanochemically prepared zhemchuzhnikovite analogs with different Al:Fe ratios.
      • table S1. PXRD data of bulk stepanovite from Chai-Tumus coal deposit, Siberia, Russia, were indexed on the basis of herein determined crystal structure.
      • table S2. PXRD data of bulk zhemchuzhnikovite from Chai-Tumus coal deposit, Siberia, Russia, were indexed on the basis of herein determined crystal structure.
      • Legends for data file S1 and S2

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      Other Supplementary Material for this manuscript includes the following:

      • data file S1 (.cif format). Crystallographic data for crystal structures of natural and synthetic samples of stepanovite and zhemchuzhnikovite.
      • data file S2 (.pdf format). checkCIF for crystal structures of natural and synthetic samples of stepanovite and zhemchuzhnikovite.

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