Skip to main content
NCBI home page
Acta Crystallographica Section E: Crystallographic Communications logoLink to Acta Crystallographica Section E: Crystallographic Communications
. 2019 Mar 15;75(Pt 4):447–450. doi: 10.1107/S2056989019003335

Crystal structure of strontium perchlorate anhydrate, Sr(ClO4)2, from laboratory powder X-ray diffraction data

Jooeun Hyoung a, Hyeon Woo Lee a, So Jin Kim a, Hong Rim Shin a, Seung-Tae Hong a,*
PMCID: PMC6509688  PMID: 31161054

The crystal structure of Sr(ClO4)2 is isotypic with its Ca homologue.

Keywords: crystal structure, powder X-ray diffraction, strontium perchlorate anhydrate, isotypism

Abstract

The crystal structure of strontium perchlorate anhydrate, Sr(ClO4)2, was determined and refined from laboratory powder X-ray diffraction data. The material was obtained by dehydration of Sr(ClO4)2·3H2O at 523 K for two weeks. It crystallizes in the ortho­rhom­bic space group Pbca and is isotypic with Ca(AlD4)2 and Ca(ClO4)2. The asymmetric unit contains one Sr, two Cl and eight O sites, all on general positions (Wyckoff position 8c). The crystal structure consists of Sr2+ cations and isolated ClO4 − tetra­hedra. The Sr2+ cation is coordinated by eight O atoms from eight ClO4 − tetra­hedra. The validity of the crystal structure model for Sr(ClO4)2 anhydrate was confirmed by the bond valence method.

Chemical context  

The alkaline earth metal ions (Mg2+, Ca2+, Sr2+ and Ba2+) have received attention as ion carriers for next-generation batteries (Wang et al., 2013 ▸), and their perchlorates are used as inorganic salts of conventional nona­queous electrolytes for electrochemical cells in Mg- and Ca-ion batteries (Whittingham et al., 2018 ▸; Tchitchekova et al., 2017 ▸; Padigi et al., 2015 ▸). It is crucial to obtain anhydrous salts to achieve high electrochemical cell performance since hydrated salts can cause unwanted side reactions as a result of increased water content in the nona­queous electrolyte. Strontium perchlorate is highly hygroscopic and exists in several hydrated forms. So far, Sr(ClO4)2·3H2O, Sr(ClO4)2·4H2O and Sr(ClO4)2·9H2O have been identified by single-crystal X-ray diffraction (Hennings et al., 2014 ▸). However, the crystal structure of the anhydrous phase has not been reported to date because of the difficulty in growing single crystals. Previously, we have determined the structures of anhydrous magnesium, barium and calcium perchlorate from laboratory powder X-ray diffraction data (Lim et al., 2011 ▸; Lee et al., 2015 ▸, 2018 ▸). Using the same techniques for the Sr salt, we were able to determine and refine the crystal structure of strontium perchlorate anhydrate.

Structural commentary  

The crystal structure of anhydrous strontium perchlorate, Sr(ClO4)2, is isotypic with Ca(AlD4)2 (Sato et al., 2009 ▸) and Ca(ClO4)2 (Lee et al., 2018 ▸). Compared with Ca(ClO4)2, the unit-cell parameters a, b and c of Sr(ClO4)2 are increased by 3.0, 2.9 and 3.4%, respectively, because Sr2+ (1.26 Å for eight-coordination) has a larger ionic radius than Ca2+ (1.12 Å for eight-coordination; Shannon, 1976 ▸).

There are one Sr, two Cl and eight O sites in the asymmetric unit, all on general positions 8c. The crystal structure (Fig. 1 ▸) is composed of Sr2+ cations and isolated ClO4 − tetra­hedra. The isolated ClO4 − tetra­hedra are slightly distorted and exhibit a range of 105.4 (7)–113.5 (7)° for the O—Cl—O angles. The local environment around the Sr2+ cation is presented in Fig. 2 ▸. It is coordinated by eight O atoms from eight ClO4 − tetra­hedra, with an average Sr—O distance of 2.582 Å (Table 1 ▸). The latter is inter­mediate between those of Ca—O (2.476 Å; Lee et al., 2018 ▸) and Ba—O (2.989 Å; Lee et al., 2015 ▸) polyhedra, and in good agreement with the sum of the ionic radii of the respective alkaline earth metal and oxygen ions (Shannon, 1976 ▸).

Figure 1.

Figure 1

Open in a new tab

The local environment of the Sr2+ cation (yellow sphere) surrounded by ClO4 − tetra­hedra (purple). Symmetry codes refer to Table 1 ▸.

Figure 2.

Figure 2

Open in a new tab

The crystal structure of Sr(ClO4)2 in two different viewing directions, i.e. approximately along (a) [001] and (b) [010]. Sr2+ cations are yellow and ClO4 tetra­hedra are purple.

Table 1. Selected bond lengths (Å).

Sr1—O1i 2.512 (5) Cl1—O5 1.436 (5)
Sr1—O2ii 2.591 (5) Cl1—O6 1.436 (5)
Sr1—O3iii 2.546 (5) Cl1—O7 1.426 (5)
Sr1—O4iv 2.622 (5) Cl1—O8 1.423 (5)
Sr1—O5v 2.650 (5) Cl2—O1 1.469 (5)
Sr1—O6ii 2.540 (5) Cl2—O2 1.414 (5)
Sr1—O7vi 2.590 (5) Cl2—O3 1.425 (5)
Sr1—O8 2.604 (8) Cl2—O4 1.422 (5)
Open in a new tab

Symmetry codes: (i) Inline graphic; (ii) Inline graphic; (iii) Inline graphic; (iv) Inline graphic; (v) Inline graphic; (vi) Inline graphic.

Empirical bond valence sums (BVSs) can be used to check structure models (Brown, 2002 ▸). In this regard, the BVSs for the ions in the crystal structure of Sr(ClO4)2 were calculated with the program Valence (Brown & Altermatt, 1985 ▸; Brese & O’Keeffe, 1991 ▸; Hormillosa et al., 1993 ▸). The expected charges of the ions match well with the obtained BVS values (given in valence units), thus confirming the validity of the crystal structure: Sr 2.18, Cl1 6.99, Cl2 6.96, O1 1.91, O2 2.08, O3 2.06, O4 2.03, O5 1.96, O6 2.02, O7 2.03 and O8 2.04.

Synthesis and crystallization  

Anhydrous strontium perchlorate was obtained by dehydration of Sr(ClO4)2·3H2O (98%, Alfa Aesar). The hydrated Sr(ClO4)2 powder was ground thoroughly in an agate mortar and added to a glass bottle. The bottle was placed in an oven at 523 K for two weeks under atmospheric conditions and then transferred to a glove-box under an argon atmosphere. For the powder X-ray diffraction measurements, anhydrous Sr(ClO4)2 was again ground in an agate mortar and placed in a tightly sealed dome-type X-ray sample holder commercially available from Bruker. The dome was double-sealed with vacuum grease to prevent hydration during measurement.

Refinement details  

Details of the crystal data collection and structure refinement are summarized in Table 2 ▸. Powder X-ray diffraction (PXRD) data for anhydrous Sr(ClO4)2 were collected from a Bragg–Brentano diffractometer (PANalytical Empyrean) using Cu Kα1 radiation, a focusing primary Ge(111) monochromator (λ = 1.5406 Å) and a position-sensitive PIXcel 3D 2×2 detector. The angular range was 10 ≤ 2θ ≤ 130°, with a step of 0.0131° and a total measurement time of 8 h at room temperature. The PXRD pattern was indexed using the TREOR90 algorithm (Werner, 1990 ▸) run in CRYSFIRE (Shirley, 2002 ▸) through the positions of 23 reflections, resulting in an ortho­rhom­bic unit cell. Systematic reflection conditions suggested the space group Pbca. The crystal structure was determined by a combination of the powder profile refinement program GSAS (Larson & Von Dreele, 2000 ▸) and the single-crystal structure refinement program CRYSTALS (Betteridge et al., 2003 ▸). For a three-dimensional view of the Fourier electron-density maps, MCE was applied (Rohlícek & Husák, 2007 ▸). Initially, a structural model with only one dummy atom at an arbitrary position in the unit cell was used. Structure factors were extracted from the powder data and then direct methods were applied to calculate the initial solution of the crystal structure using SHELXS97 (Sheldrick, 2008 ▸) run in CRYSTALS, which yielded the Sr site as a starting atomic position. The initial dummy atom model was then replaced with the partial model, and this data was adopted for a Le Bail fit in GSAS. Improved structure factors were then extracted, which were used for the refinement in CRYSTALS. Such processes were iterated until a complete and satisfactory structural model was obtained. Finally, Rietveld refinement in GSAS was employed to complete the structure model, resulting in reasonable isotropic displacement parameters and agreement indices. For the final Rietveld refinement with GSAS, the Sr—O and Cl—O bond lengths were restrained with a tolerance value of 2% with respect to the distances determined from CRYSTALS, which matched reasonably well with the radii sums of Shannon (1976 ▸). The final Rietveld plot is displayed in Fig. 3 ▸.

Table 2. Experimental details.

Crystal data
Chemical formula Sr(ClO4)2
M r 286.52
Crystal system, space group Orthorhombic, P b c a
Temperature (K) 298
a, b, c (Å) 14.18206 (10), 9.78934 (11), 9.37624 (10)
V (Å3) 1301.73 (2)
Z 8
Radiation type Cu Kα1, λ = 1.5405 Å
Specimen shape, size (mm) Flat sheet, 24.9 × 24.9
 
Data collection
Diffractometer PANalytical Empyrean
Specimen mounting Packed powder
Data collection mode Reflection
Scan method Step
2θ values (°) 2θmin = 10.009, 2θmax = 129.991, 2θstep = 0.013
 
Refinement
R factors and goodness of fit R p = 0.086, R wp = 0.125, R exp = 0.096, R(F 2) = 0.14871, χ2 = 1.716
No. of parameters 40
No. of restraints 23
Open in a new tab

Computer programs: X’Pert Data Collector (PANalytical, 2011 ▸), GSAS (Larson & Von Dreele, 2000 ▸), X’Pert HighScore Plus (PANalytical, 2011 ▸), SHELXS97 (Sheldrick, 2008 ▸), CRYSTALS (Betteridge et al., 2003 ▸) and VESTA (Momma & Izumi, 2011 ▸).

Figure 3.

Figure 3

Open in a new tab

PXRD Rietveld refinement profiles for anhydrous Sr(ClO4)2 measured at ambient temperature. Black dots mark experimental data, the solid red line represents the calculated profile and the solid green line is the background. The bottom trace presents the difference curve (blue) and the ticks denote the expected Bragg reflection positions (magenta).

Supplementary Material

Crystal structure: contains datablock(s) I. DOI: 10.1107/S2056989019003335/wm5484sup1.cif

e-75-00447-sup1.cif (378.6KB, cif)

CCDC reference: 1901870

Additional supporting information: crystallographic information; 3D view; checkCIF report

supplementary crystallographic information

Crystal data

Sr(ClO4)2 Z = 8
Mr = 286.52 F(000) = 1088.0
Orthorhombic, Pbca Dx = 2.925 Mg m−3
Hall symbol: -P_2ac_2ab Cu Kα1 radiation, λ = 1.5405 Å
a = 14.18206 (10) Å T = 298 K
b = 9.78934 (11) Å white
c = 9.37624 (10) Å flat_sheet, 24.9 × 24.9 mm
V = 1301.73 (2) Å3 Specimen preparation: Prepared at 298 K
Open in a new tab

Data collection

PANalytical Empyrean diffractometer Data collection mode: reflection
Radiation source: sealed X-ray tube, PANalytical Cu Ceramic X-ray tube Scan method: step
Specimen mounting: packed powder 2θmin = 10.009°, 2θmax = 129.991°, 2θstep = 0.013°
Open in a new tab

Refinement

Least-squares matrix: full Profile function: CW Profile function number 4 with 18 terms Pseudovoigt profile coefficients as parameterized in P. Thompson, D.E. Cox & J.B. Hastings (1987). J. Appl. Cryst.,20,79-83. Asymmetry correction of L.W. Finger, D.E. Cox & A. P. Jephcoat (1994). J. Appl. Cryst.,27,892-900. Microstrain broadening by P.W. Stephens, (1999). J. Appl. Cryst.,32,281-289. #1(GU) = 0.000 #2(GV) = 0.000 #3(GW) = 0.000 #4(GP) = 9.252 #5(LX) = 0.900 #6(ptec) = 0.00 #7(trns) = 0.00 #8(shft) = -3.8100 #9(sfec) = 0.00 #10(S/L) = 0.0208 #11(H/L) = 0.0005 #12(eta) = 0.7500 #13(S400 ) = 0.0E+00 #14(S040 ) = 7.8E-04 #15(S004 ) = 1.5E-04 #16(S220 ) = 3.7E-04 #17(S202 ) = 6.1E-04 #18(S022 ) = -1.1E-03 Peak tails are ignored where the intensity is below 0.0010 times the peak Aniso. broadening axis 0.0 0.0 1.0
Rp = 0.086 40 parameters
Rwp = 0.125 23 restraints
Rexp = 0.096 (Δ/σ)max = 0.05
R(F2) = 0.14871 Background function: GSAS Background function number 1 with 34 terms. Shifted Chebyshev function of 1st kind 1: 118.082 2: -166.900 3: 123.865 4: -59.7925 5: 10.6865 6: 21.3336 7: -31.0975 8: 23.2200 9: -6.96687 10: -9.51726 11: 20.8794 12: -23.8022 13: 18.4347 14: -9.14997 15: -1.10995 16: 9.35323 17: -13.3633 18: 13.2873 19: -9.61569 20: 4.08246 21: 1.61524 22: -5.79316 23: 6.77390 24: -5.01271 25: 2.27833 26: 0.646733 27: -2.78842 28: 3.78393 29: -3.23100 30: 2.18997 31: -0.908158 32: -0.401332 33: 0.778547 34: -0.792308
9139 data points Preferred orientation correction: March-Dollase AXIS 1 Ratio= 0.79858 h= 1.000 k= 0.000 l= 0.000 Prefered orientation correction range: Min= 0.71363, Max= 1.96360
Open in a new tab

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2)

x y z Uiso*/Ueq
Sr1 0.60125 (9) 0.46444 (17) 0.2136 (2) 0.0206 (3)*
Cl1 0.4370 (3) 0.2794 (4) 0.4905 (4) 0.0254 (3)*
Cl2 0.1592 (2) 0.3965 (4) 0.6866 (4) 0.0275 (3)*
O1 0.1833 (5) 0.2549 (6) 0.7237 (14) 0.0271 (14)*
O2 0.2200 (4) 0.4878 (11) 0.7587 (12) 0.0335 (14)*
O3 0.1636 (7) 0.4175 (13) 0.5363 (6) 0.0364 (14)*
O4 0.0665 (4) 0.4250 (10) 0.7362 (11) 0.0225 (14)*
O5 0.3759 (6) 0.2145 (7) 0.3888 (11) 0.0356 (14)*
O6 0.3829 (6) 0.3692 (11) 0.5799 (10) 0.0361 (14)*
O7 0.4728 (6) 0.1764 (11) 0.5835 (12) 0.0315 (14)*
O8 0.5132 (6) 0.3514 (12) 0.4267 (12) 0.0305 (14)*
Open in a new tab

Geometric parameters (Å, º)

Sr1—Cl1 3.931 (4) Cl2—Sr1ix 3.945 (3)
Sr1—Cl1i 3.937 (4) Cl2—Sr1ii 3.778 (3)
Sr1—Cl1ii 3.779 (4) Cl2—Sr1x 3.746 (4)
Sr1—Cl1iii 3.669 (4) Cl2—Sr1xi 3.898 (4)
Sr1—Cl2iv 3.945 (3) Cl2—O1 1.469 (5)
Sr1—Cl2ii 3.778 (3) Cl2—O2 1.414 (5)
Sr1—Cl2v 3.746 (4) Cl2—O3 1.425 (5)
Sr1—Cl2vi 3.898 (4) Cl2—O4 1.422 (5)
Sr1—O1v 2.512 (5) O1—Sr1x 2.512 (5)
Sr1—O2ii 2.591 (5) O1—Cl2 1.469 (5)
Sr1—O3vi 2.546 (5) O2—Sr1ii 2.591 (5)
Sr1—O4iv 2.622 (5) O2—Cl2 1.414 (5)
Sr1—O5iii 2.650 (5) O3—Sr1xi 2.546 (5)
Sr1—O6ii 2.540 (5) O3—Cl2 1.425 (5)
Sr1—O7i 2.590 (5) O4—Sr1ix 2.622 (5)
Sr1—O8 2.604 (8) O4—Cl2 1.422 (5)
Cl1—Sr1 3.931 (4) O5—Sr1viii 2.650 (5)
Cl1—Sr1vii 3.937 (4) O5—Cl1 1.436 (5)
Cl1—Sr1ii 3.779 (4) O6—Sr1ii 2.540 (5)
Cl1—Sr1viii 3.669 (4) O6—Cl1 1.436 (5)
Cl1—O5 1.436 (5) O7—Sr1vii 2.590 (5)
Cl1—O6 1.436 (5) O7—Cl1 1.426 (5)
Cl1—O7 1.426 (5) O8—Sr1 2.604 (8)
Cl1—O8 1.423 (5) O8—Cl1 1.423 (5)
O1v—Sr1—O2ii 71.2 (3) O5iii—Sr1—O8 136.8 (4)
O1v—Sr1—O3vi 84.3 (4) O6ii—Sr1—O7i 139.7 (3)
O1v—Sr1—O4iv 138.9 (3) O6ii—Sr1—O8 74.3 (4)
O1v—Sr1—O5iii 144.9 (3) O7i—Sr1—O8 78.3 (4)
O1v—Sr1—O6ii 109.2 (4) O5—Cl1—O6 109.7 (5)
O1v—Sr1—O7i 88.9 (4) O5—Cl1—O7 108.0 (7)
O1v—Sr1—O8 71.3 (4) O5—Cl1—O8 113.5 (7)
O2ii—Sr1—O3vi 77.6 (3) O6—Cl1—O7 105.4 (7)
O2ii—Sr1—O4iv 143.6 (3) O6—Cl1—O8 110.3 (7)
O2ii—Sr1—O5iii 75.5 (3) O7—Cl1—O8 109.7 (7)
O2ii—Sr1—O6ii 73.8 (3) O1—Cl2—O2 110.0 (7)
O2ii—Sr1—O7i 146.3 (3) O1—Cl2—O3 111.1 (7)
O2ii—Sr1—O8 118.0 (4) O1—Cl2—O4 108.8 (6)
O3vi—Sr1—O4iv 117.7 (3) O2—Cl2—O3 110.7 (8)
O3vi—Sr1—O5iii 77.9 (3) O2—Cl2—O4 106.4 (6)
O3vi—Sr1—O6ii 141.9 (4) O3—Cl2—O4 109.6 (6)
O3vi—Sr1—O7i 73.4 (3) Sr1x—O1—Cl2 139.0 (5)
O3vi—Sr1—O8 142.8 (4) Sr1ii—O2—Cl2 139.4 (5)
O4iv—Sr1—O5iii 76.1 (3) Sr1xi—O3—Cl2 157.0 (6)
O4iv—Sr1—O6ii 75.8 (3) Sr1ix—O4—Cl2 153.3 (6)
O4iv—Sr1—O7i 67.6 (3) Sr1viii—O5—Cl1 125.1 (4)
O4iv—Sr1—O8 71.2 (4) Sr1ii—O6—Cl1 142.2 (5)
O5iii—Sr1—O6ii 70.9 (4) Sr1vii—O7—Cl1 156.2 (7)
O5iii—Sr1—O7i 114.04 (3) Sr1—O8—Cl1 153.9 (7)
Open in a new tab

Symmetry codes: (i) x, −y+1/2, z−1/2; (ii) −x+1, −y+1, −z+1; (iii) −x+1, y+1/2, −z+1/2; (iv) −x+1/2, −y+1, z−1/2; (v) x+1/2, −y+1/2, −z+1; (vi) x+1/2, y, −z+1/2; (vii) x, −y+1/2, z+1/2; (viii) −x+1, y−1/2, −z+1/2; (ix) −x+1/2, −y+1, z+1/2; (x) x−1/2, −y+1/2, −z+1; (xi) x−1/2, y, −z+1/2.

Funding Statement

This work was funded by Ministry of Science, ICT and Future Planning grant 2015M3D1A1069707.

References

  1. Betteridge, P. W., Carruthers, J. R., Cooper, R. I., Prout, K. & Watkin, D. J. (2003). J. Appl. Cryst. 36, 1487.
  2. Brese, N. E. & O’Keeffe, M. (1991). Acta Cryst. B47, 192–197.
  3. Brown, I. D. (2002). In The Chemical Bond in Inorganic Chemistry. Oxford University Press.
  4. Brown, I. D. & Altermatt, D. (1985). Acta Cryst. B41, 244–247.
  5. Hennings, E., Schmidt, H. & Voigt, W. (2014). Acta Cryst. E70, 510–514. [DOI] [PMC free article] [PubMed]
  6. Hormillosa, C., Healy, S., Stephen, T. & Brown, I. D. (1993). Bond Valence Calculator. Version 2.0. McMaster University, Canada. http://www.CCP14.ac.uk/solution/bond_valence/.
  7. Larson, A. C. & Von Dreele, R. B. (2000). General Structure Analysis System (GSAS). Report LAUR 86-748. Los Alamos National Laboratory, New Mexico, USA.
  8. Lee, D., Bu, H., Kim, D., Hyoung, J. & Hong, S.-T. (2018). Acta Cryst. E74, 514–517. [DOI] [PMC free article] [PubMed]
  9. Lee, J. H., Kang, J. H., Lim, S.-C. & Hong, S.-T. (2015). Acta Cryst. E71, 588–591. [DOI] [PMC free article] [PubMed]
  10. Lim, H.-K., Choi, Y. S. & Hong, S.-T. (2011). Acta Cryst. C67, i36–i38. [DOI] [PubMed]
  11. Momma, K. & Izumi, F. (2011). J. Appl. Cryst. 44, 1272–1276.
  12. Padigi, P., Goncher, G., Evans, D. & Solanki, R. (2015). J. Power Sources, 273, 460–464.
  13. PANalytical (2011). X’Pert Data Collector and X’Pert HighScore Plus. PANalytical BV, Almelo, The Netherlands.
  14. Rohlíček, J. & Hušák, M. (2007). J. Appl. Cryst. 40, 600–601.
  15. Sato, T., Sørby, M. H., Ikeda, K., Sato, S., Hauback, B. C. & Orimo, S. (2009). J. Alloys Compd. 487, 472–478.
  16. Shannon, R. D. (1976). Acta Cryst. A32, 751–767.
  17. Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122. [DOI] [PubMed]
  18. Shirley, R. (2002). The Crysfire 2002 System for Automatic Powder Indexing: User’s Manual. Guildford, UK: The Lattice Press.
  19. Tchitchekova, D. S., Monti, D., Johansson, P., Bardé, F., Randon-Vitanova, A., Palacín, M. R. & Pnrouch, A. (2017). J. Electrochem. Soc. 164, A1384–A1392.
  20. Wang, R. Y., Wessells, C. D., Huggins, R. A. & Cui, Y. (2013). Nano Lett. 13, 5748–5752. [DOI] [PubMed]
  21. Werner, P. E. (1990). TREOR90 University of? Stockholm, Sweden.
  22. Whittingham, M. S., Siu, C. & Ding, J. (2018). Acc. Chem. Res. 51, 258–264. [DOI] [PubMed]

Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

Crystal structure: contains datablock(s) I. DOI: 10.1107/S2056989019003335/wm5484sup1.cif

e-75-00447-sup1.cif (378.6KB, cif)

CCDC reference: 1901870

Additional supporting information: crystallographic information; 3D view; checkCIF report

Articles from Acta Crystallographica Section E: Crystallographic Communications are provided here courtesy of International Union of Crystallography

RESOURCES