Synthesis and crystal structure of anhydrous Na[MnO4]

Article abstract of DOI:10.1515/znb-2016-0099

There are numerous reports in the literature about the amount of hydrate water in sodium permanganate, which is said to be between one half and three water molecules per Na[MnO₄]. Because no structural descriptions of the hydrate and the anhydrous compound can be found yet, this work reports the synthesis of anhydrous Na[MnO₄] via the Muthmann method and its crystal structure. Na[MnO₄] crystallizes as dark purple needles in the monoclinic space group P2₁/n with a = 572.98(5), b = 842.59(7), c = 715.47(6) pm, β = 92.374(3)° and Z = 4. As such and with its isotype to Ag[MnO₄], Na[MnO₄] completes the series of anhydrous alkali-metal permanganates, comprising Li[MnO₄] (orthorhombic, Cmcm, Cr[VO₄] type) and the isostructural heavier congeners A[MnO₄] (A = K, Rb, Cs; orthorhombic, Pnma, Ba[SO₄] type).

Full text of DOI:10.1515/znb-2016-0099

Z. Naturforsch. 2016; 71(9)b: 993–995
Jörg M. Bauchert, Harald Henning and Thomas Schleid*
Synthesis and crystal structure of anhydrous
Na[MnO4]
DOI 10.1515/znb-2016-0099
Received April 28, 2016; accepted May 11, 2016
cation carrying seven independent, vertex-grafted, iso-
lated [MnO4]− anions.
Abstract: There are numerous reports in the literature
about the amount of hydrate water in sodium permanga-
nate, which is said to be between one half and three water
molecules per Na[MnO4]. Because no structural descrip-
tions of the hydrate and the anhydrous compound can be
found yet, this work reports the synthesis of anhydrous
Na[MnO4] via the Muthmann method and its crystal struc-
ture. Na[MnO4] crystallizes as dark purple needles in the
monoclinic space group P21/n with a ꢀ=ꢀ 572.98(5), b ꢀ=ꢀ
842.59(7), c ꢀ=ꢀ 715.47(6) pm, β ꢀ=ꢀ 92.374(3)° and Z ꢀ=ꢀ 4. As
such and with its isotype to Ag[MnO4], Na[MnO4] completes
the series of anhydrous alkali-metal permanganates, com-
prising Li[MnO4] (orthorhombic, Cmcm, Cr[VO4] type) and
the isostructural heavier congeners A[MnO4] (A ꢀ=ꢀ K, Rb,
Cs; orthorhombic, Pnma, Ba[SO4] type).
2 Results and discussion
We were successful in synthesizing anhydrous Na[MnO4],
as opposed to the various hydrated products mentioned
in the literature [1–3]. The thin, dark purple needles of
Na[MnO4] adopt the monoclinic space group P21/n (no. 14)
with a ꢀ=ꢀ 572.98(5), b ꢀ=ꢀ 842.59(7), c ꢀ=ꢀ 715.47(6) pm and β ꢀ=ꢀ
92.374(3)° for four formula units per unit cell (Table 1). In
+
the crystal structure of Na[MnO4] (Table 2), the unique Na
cations reside in a sevenfold oxygen coordination, result-
ing in a distorted pentagonal bipyramid (Fig. 1) as coordi-
nation sphere with d(Na–O) ꢀ=ꢀ 235–277 pm (Table 3). These
[NaO7]13− polyhedra are connected to strands via two O2
atoms, which become further linked to adjacent strands
through shared O3···O3 and O4···O4 edges. Because of
the helical nature of a singular chain, these strands join
together with other strands of this kind to form the achiral
∞3 {[Na(O1)1/1(O2)2/2 (O3)2/2 (O4)2/2 ]7− } framework (Fig. 2),
thereby generating the missing space group symmetry
elements of a glide plane (n) perpendicular to the screw
axis (21) and thus the inversion center. The O1 atom,
which contributes only once to a [NaO7]13− polyhedron,
points into channels running along [010], filled by the
Mn7+ cations thereby forming isolated [MnO4]− tetrahedra
(Fig. 3) with d(Mn–O) ꢀ=ꢀ 159–162 pm. In isotypic Ag[MnO4],
the Mn–O distances within the permanganate units are
slightly longer and range between 160 and 164 pm, while
its lattice parameters (a ꢀ=ꢀ 562.3(4), b ꢀ=ꢀ 834.9(5), c ꢀ=ꢀ
714.0(5) pm, β ꢀ=ꢀ 92.44(5)° [6]) are smaller as compared to
Na[MnO4]. This causes markedly shorter Ag–O distances
(230–267 pm) in a more narrow interval than for the Na–O
distances in Na[MnO4], where only six of them range
from 235 to 259 pm, while the seventh one (Na–O2′) is 277
pm long. In this particular case, the stronger covalently
Keywords: crystal structures; permanganates; sodium.
Dedicated to: Professor Hanskarl Müller-Buschbaum on the
occasion of his 85th birthday.
1 Introduction
Several permanganates of sodium have been reported in
the literature [1–3], but all of them seem to contain water
of hydration in varying amounts, ranging from Na[MnO4] ·
1/2 H2O to Na[MnO4] · 3 H2O. Neither of these publications
offers a detailed crystal structure of the reported pro-
ducts, however. The work reported shows a successful
way to synthesize anhydrous Na[MnO4] and its crystal
structure determination, which clearly reveals the isotype
+
to Ag[MnO4] [4–6], exhibiting a sevenfold coordinated Na
+
bonded Ag cation (ΔEN(Ag/O) ꢀ=ꢀ 1.5 vs. ΔEN(Na/O) ꢀ=ꢀ 2.5)
*Corresponding author: Thomas Schleid, Institut für Anorganische
Chemie, Universität Stuttgart, Pfaffenwaldring 55, D-70569
Stuttgart, Germany, Fax: +49-(0)-711/685-64241,
E-mail: schleid@iac.uni-stuttgart.de
Jörg M. Bauchert and Harald Henning: Institut für Anorganische
Chemie, Universität Stuttgart, Stuttgart, Germany
[11], which is considered larger (ri ꢀ=ꢀ 115 pm for CN ꢀ=ꢀ 6) [12]
+
than Na (ri ꢀ=ꢀ 102 pm for CN ꢀ=ꢀ 6) [12], does not only lead
to a shrinking of the unit cell in comparison to Na[MnO4],
but seems to compensate this marginally by expanding
the [MnO4]− tetrahedron.
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ꢀꢀꢀꢁ
994ꢀ ꢀJ.M. Bauchert et al.: Anhydrous Na[MnO4]
Table 1:ꢀCrystallographic data for Na[MnO4] and numbers pertinent
Table 2:ꢀFractional atomic coordinates and equivalent isotropic
displacement parameters (Ueq, pm2) for Na[MnO4].
to data collection and structure refinement.a
Formula
Na[MnO4]
Atom
x/a
y/b
z/c
Ueq, pm2
Molecular mass Mr
Crystal system
141.93
Na
Mn
O1
O2
O3
O4
0.2518(3)
0.25709(9)
0.2511(6)
0.9932(6)
0.8802(6)
0.4049(6)
0.0364(2)
0.18805(6)
0.0616(4)
0.2235(4)
0.1504(3)
0.1171(4)
0.1593(2)
0.65959(7)
0.4932(4)
0.7159(4)
0.0917(4)
0.8381(4)
385(4)
267(2)
440(7)
414(6)
393(6)
400(6)
monoclinic
Space group
P21/n (no.14)
Formula units, Z
Lattice constants a, pm
b, pm
4
572.98(5)
842.59(7)
c, pm
β, deg
715.47(6)
92.374(3)
All atoms occupy the general Wykoff sites 4e.
Calculated density Dx, g cm−3
Molar volume Vm, cm3 mol−1
Electron sum, F(000)/e
Diffractometer; radiation
Wavelength λ, pm
2.732
51.97(2)
272
IPDS-I (STOE); MoKα
λ ꢂ=ꢂ 71.07c
Index range, h, k,
θ range, deg
l
10, 12, 8
2.8–28.3
Absorption coefficient μ, mm−1
Number of refined parameters
Refined extinction coefficient, g
Data corrections
3.79
56
0.130(12)
Background, polarization and
Lorentz factors; numerical
absorption correction; program
Habitus [7]
Collected vs. unique reflections
Rint, Rσ
4941, 1280
0.049, 0.043
Program package Shelxs/l-97
[8, 9]
Structure solution and
refinement
Scattering factors
International tables, Vol. C [10]
0.066; 879
0.045; 0.122
1.032
–0.60; 0.93
R1, reflections with |Fo| ꢂ>ꢂ 4 σ(Fo)
R1; wR2 for all reflections
Goodness of fit (GooF)
Residual electron densities
(ρ/e · 10−6 pm3), min; max
aFurther details of the crystal structure investigation may be
obtained from Fachinformationszentrum Karlsruhe, 76344
Eggenstein-Leopoldshafen, Germany (fax: +49-7247-808-666;
e-mail: crysdata@fiz-karlsruhe.de, https://www.fiz-karlsruhe.de/
en/leistungen/kristallographie/kristallstrukturdepot/order-form-
request-for-deposited-data.html) on quoting the deposition number
CSD-431105.
Fig. 1:ꢀCoordination sphere of the [NaO7]13− polyhedron in Na[MnO4]
(top) and its connectivity to seven vertex-grafted [MnO4]− tetrahedra
(bottom).
3 Conclusions
Anhydrous Na[MnO4] with its sevenfold coordinated
sodium cations crystallizes in the monoclinic space group
P21/n and thus isotypically with Ag[MnO4] [6]. It fits well structure of Ba[SO4] allowing for an 8- to 12-fold coordi-
+
into the series of the anhydrous alkali-metal permanga- nation of the A cations (A ꢀ=ꢀ K, Rb, Cs) by oxygen atoms.
nates, which starts with Li[MnO4] [13] crystallizing in the As opposed to what can be found in the literature, where
orthorhombic space group Cmcm with the Cr[VO4]-type sodium permanganate occurs with from one half up to
structure and displaying a sixfold coordination of oxygen three water molecules per formula unit, the sodium per-
+
around the Li cations. The permanganates A[MnO4] of manganate now prepared via the Muthmann method crys-
the heavier homologues potassium, rubidium and cesium tallizes anhydrously just like the structurally prototypic
[14–16] all crystallize in the orthorhombic space group Ag[MnO4], even though the samples are synthesized from
Pnma with the very flexible and adaptive baryte-type aqueous solution.
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ꢁꢀꢀꢀ
J.M. Bauchert et al.: Anhydrous Na[MnO4]ꢃ
ꢃ995
Table 3:ꢀMotifs of mutual adjunction, selected interatomic
distances (d, pm) and bond angles (, deg) in Na[MnO4].
of 100 mmol Ba[MnO4]2 in 50 mL demineralized water,
obtained through the Muthmann method described else-
where in detail [17, 18]. After the complete metathesis and
the removal of the precipitated Ba[SO4] from the deep
purple solution, needle-shaped single crystals, a few mil-
limeters in length, of anhydrous Na[MnO4] with the same
color grew by fast isothermal evaporation in a P2O5-filled,
evacuated desiccator. We were successful in synthesiz-
ing a single-phase product, from which we selected thin,
needle-shaped, dark purple crystals for single-crystal
X-ray diffraction.
O1
O2
O3
O4
Na
1/1
2/2
247.5(3)
276.9(4)
1/1
2/2
236.7(3)
248.2(3)
1/1
2/2
235.5(3)
258.4(3)
1/1
161.8(3)
–O1:
109.7(2)
239.8(4)
Mn
1/1
159.7(3)
–O2:
108.6(2)
–O3:
109.5(2)
160.9(3)
–O3:
161.7(3)
–O4:
110.2(2)
–O4:
109.7(2)
109.1(2)
Acknowledgments: The financial support by the Deutsche
Forschungsgemeinschaft (SFB 706: “Selective Catalytic
Oxidation of C–H Bonds with Molecular Oxygen”), Bonn,
and the Ministerium für Wissenschaft, Forschung und
Kunst des Landes Baden-Württemberg, Stuttgart, is grate-
fully acknowledged.
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+
shown as a tetrahedron with its immediate Na surrounding.
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4 Experimental section
Na[MnO4] was synthesized by adding 100 mmol Na2[SO4]
dissolved in 50 mL demineralized water to a solution
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