Cent. Eur. J. Chem. • 8(1) • 2010 • 65–69
DOI: 10.2478/s11532-009-0094-z
Central European Journal of Chemistry
Synthesis of MSn(OH)6 (where M = Mg, Ca, Zn,
Mn, or Cu) materials at room temperature
Research Article
Jonathan W. Kramer, Brandon Kelly, Venkatesan Manivannan*
Department of Mechanical Engineering
Colorado State University
Fort Collins, CO 80523, USA
Received 23 April 2009; Accepted 13 July 2009
Abstract: Applying a metathesis approach (MCl2•xH2O+Na2SnO3•xH2O→MSn(OH)6+NaCl+xH2O), Schoenfliesite-type materials with
general formula MSn(OH)6 (where M=Ca, Cu, Mg, Mn or Zn) were synthesized at room-temperature. The high lattice-energy of the
by-product alkali halide NaCl drives the reaction in the forward direction leading to the formation of the desired materials. The materials
synthesized were characterized by powder X-ray diffraction (XRD) and scanning electron microscopy (SEM) to elucidate structural
and micro structural features.
Keywords: Metathesis Reactions • Perovskites • Powder technology • X-ray diffraction • Ceramics
© Versita Warsaw and Springer-Verlag Berlin Heidelberg.
1. Introduction
Compounds with general formula AB(OH)6 (A = divalent
metal atom, and B = tetravalent metal atom) belong
to the perovskite-based hydroxide class of materials
[1-3]. When B = Sn4+, the compounds are further subgrouped as Schoenfliesite minerals [4,5]. Exposure
to atmosphere has been shown to degrade materials
incorporating hydroxyl (OH) groups. In most of the
MSn(OH)6 materials, however, the hydroxyl groups
are internal to the structure therefore the degradation
is minimized resulting in interesting properties which
position these materials for several technological
applications [6-8].
Perovskite-based hydroxide materials have shown
promise in several applications of current research.
Thin-film coatings based on MgSn(OH)6 materials
form a passivation layer on metal surfaces protecting
the surfaces from corrosion thus improving the
lifetime of the metals [9]. MgSnO3 synthesized by the
decomposition of MgSn(OH)6 was found to have an
electrochemical performance suggesting that it could
be a good electrode material for lithium ion batteries
[10]. CaSn(OH)6 materials were found to exhibit good
luminescence properties, with the phosphor material
emitting in the reddish-orange region of the spectrum
[11]. ZnSn(OH)6 materials impart beneficial properties
to brominated polyesters for use as flame-retardant
materials [12]. Jena et al. have shown that MSn(OH)6
(M = Ba, Ca, Mg, Co, Zn, Fe, or Mn) compounds in
general exhibit good protonic conducting properties [6].
Following are some of the several methods reported
in the literature for synthesis of MSn(OH)6 materials.
Strunz et al. reported the synthesis of MSn(OH)6
(M = Mg, Mn, Ca, or Fe) materials in a teflon pressure
apparatus with reaction time extending up to several
days [2]. A solution based synthesis with careful
control of reacting precursors has been reported for
the synthesis of Cd1-xMgxSn(OH)6, MgSn(OH)6, and
CaSn(OH)6 materials [13-15]. Wet sonochemical, coprecipitation, and hydrothermal methodswith proper care
to avoid formation of competing phases like Ba(OH)2,
was reported by Inagaki et al. [16]. Lu et al. reported the
surfactant-assisted process for the first synthetic route
* E-mail: [email protected]
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Synthesis of MSn(OH)6 (where M = Mg, Ca,
Zn, Mn, or Cu) materials at room temperature
to CaSn(OH)6 [17]. A modified co-precipitation technique
was employed for the synthesis of ZnSn(OH)6 materials
[18]. MSn(OH)6 with M = Sr, Ca, were synthesized by
a hydrothermal process under reaction conditions of
180oC for 16 hours [19]. A closed batch reactor with
a flow of purified N2 was used for synthesis of several
MSn(OH)6 materials by Leoni et al. [20]. BaSn(OH)6
was synthesized by a hydrothermal synthesis using
Ba(OH)2•8H2O as the precursor. SnO2•xH2O and the
Ba precursor were heated in an autoclave at 413 K for
four hours [6]. In addition to the problem of formation
of competing phase, the procedures reported in general
involved complex, tedious and time consuming processes
with the need for proper care and control of the reaction
conditions. A simplified procedure that overcomes these
disadvantages and further improves the potential usage
of MSn(OH)6 materials is highly desirable.
The solid-state metathesis (SSM) approach has
been established as a viable alternative for synthesizing
inorganic materials of technological importance [21-23].
In a typical SSM reaction such as in Reaction 1:
with little or no need for external energy. Applying such
a method, Gillan et al., Parkin et al. and Gopakrishnan
et al., have synthesized several inorganic materials
[26-33]. Ramanan et al. synthesized biologically
important hydroxy apatite materials via a metathesis
approach assisted by microwave energy [34-38]. We
have also shown the versatility of this approach by
synthesizing several novel nanostructural materials of
commercial importance [39].
The objective of the present work was to synthesize
MSn(OH)6 (M = Ca, Cu, Mg, Mn, or Zn) materials by
applying a metathesis approach. The SSM reaction
was performed at room temperature by reacting
stoichiometric quantities of the appropriate precursors.
Such an approach of study, i.e., synthesis of MSn(OH)6
(M = Ca, Cu, Mg, Mn, or Zn) materials by an SSM
reaction at room temperature has not been reported so
far.
Na2CrO4 + ZnCl2 → ZnCr2O4 + 2NaCl
MgCl2•6H2O, CaCl2•6H2O, ZnCl2•6H2O, MnCl2•4H2O,
CuCl2•2H2O, and Na2SnO3•3H2O purchased from Alfa
Aesar, USA were employed for the preparation of the
title compounds. Synthesis of MnSn(OH)6 material was
carried out at room temperature by reacting MnCl2•6H2O
(0.5 g) and Na2SnO3•3H2O (0.674 g) in a 1:1 molar ratio
using a pestle and mortar. The resultant product was
washed thoroughly with deionized water and ethanol
to remove the NaCl byproduct then allowed to dry
overnight on a hot plate at 90oC. XRD was performed
on the samples before and after washing. The same
(1)
the formation of a high lattice energy byproduct like NaCl
drives the reaction in the forward direction [24]. SSM
reactions are characterized by large enthalpy (∆H) and
free energy (∆G) changes. SSM reactions can be self
initiated by mixing of the precursors or can be initiated
by subjecting the reactants to external energy sources
such as contact of the precursors with a heated filament
[25]. This approach has advantages over the other
traditional synthetic methods in terms of reaction rate
2. Experimental procedure
Figure 1. XRD of MnSn(OH)6 before washing (bottom) and after washing (top). * indicates phases corresponding to NaCl.
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J.W. Kramer, B. Kelly, V. Manivannan
Figure 2. XRD of MSn(OH)6 materials
M = (a) Cu, (b) Zn, (c) Mg, and (d) Ca.
procedure was followed for synthesizing other MSn(OH)6
(M = Ca, Cu, Mg, Mn, and Zn) materials.
Structural properties of the materials were determined
by performing X-ray and SEM characterizations. XRD
patterns were collected with a Scintag X2 diffractometer
using Cu Kα radiation. A scan rate of 1° min-1 with a step
size of 0.02o was employed to obtain the XRD patterns.
Search match analysis was performed using Bruker
EVA software. SEM characterization was performed
on JSM-6500F with the in-lens thermal field emission
electron gun.
3. Results and Discussion
The balanced metathesis reaction between the
precursors at room temperature is represented as:
MnCl2•4H2O + Na2SnO3•3H2O →
→ MnSn(OH)6 + 2 NaCl + 4 H2O
(1)
XRD of the as-prepared material was taken (Fig. 1),
which showed Bragg reflections corresponding to both
NaCl and MnSn(OH)6 phases. The presence of NaCl
strongly suggested the reaction had proceeded in a
metathesis way and the formation of the high lattice
energy byproduct halide salt, was indeed the driving
force for the metathesis reaction as also is established
in the literature (Fig. 1a) [22]. The NaCl byproduct was
removed by washing with deionized water thoroughly.
XRD of MnSn(OH)6 after removing the NaCl byproduct
is shown in Fig. 1b which confirmed the single-phase
nature of the material when compared with JCPDF
standard 20-0727 and the pattern was indexed
accordingly. MnSn(OH)6 crystallizes in a Pn3m space
group with a cubic lattice parameter a of 7.873 Å. The
above mentioned synthesis was followed for preparation
of other MSn(OH)6 (M = Ca, Cu, Mg, or Zn) materials and
the corresponding XRD patterns are shown in Fig. 2. The
single-phase nature of these materials was confirmed
with JCPDF standard [40]. Crystal structure details
of the corresponding materials are given in Table 1.
A plot of ionic radius in Å vs ?? (not shown) showed a
systematic trend as expected [6].
SEM was performed to gain microstructural details
of the MSn(OH)6 compounds synthesized (Fig. 3). All
compounds have well-defined or controlled morphologies
with almost all of them having cubic morphologies. In
general, the particles are sub-micron in size and are
agglomerated, revealing the inter-connected feature of
the particles. The differences in particle size could be
due to variation in the particle sizes of starting precursor
materials.
Table 1. Crystal structure details of MSn(OH)6 materials (M = Ca,
Materials
Cu, Mg, Mn, and Zn).
Lattice
Volume (Å3)
parameter(s)
Space group
a(Å) 7.873(1)
488.00
Pn3m
MgSn(OH)6
a(Å) 7.771(2)
469.11
Pn3m
CuSn(OH)6
a(Å) 7.586(1),
c(Å) 8.103(1)
466.31
P42/ nnm
CaSn(OH)6
a(Å) 8.128(2)
536.97
Pn3m
ZnSn(OH)6
a(Å) 7.765(1)
474.55
Pn3m
MnSn(OH)6
3.1. Thermodynamic considerations
The metathesis reaction between the precursors is highly
exothermic, accompanied by a large enthalpy change.
The energy produced during the room temperature
reaction positions the metathesis reaction to enter in to
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Synthesis of MSn(OH)6 (where M = Mg, Ca,
Zn, Mn, or Cu) materials at room temperature
Figure 3. SEM images of MSn(OH)6 materials M = (a) Mn, (b) Cu, (c) Zn, (d) Mg, and (e) Ca. Markers in the images represent 1 μm for all except
(b) and (e) (100 nm).
a self-propagating mode to yield the desired products
[23]. Considering the real driving force for the completion
of reaction is the formation of 2 mol of NaCl (∆Hf
~ –60 Kcal mol-1) for each mole of the product, it could
lead to change in free-energy (∆G = ∆H – T ∆S) being
negative [22]. Applying the Kapustinskii equation:
Uo = [120,200γυ Z+ Z-/ro] * (1-34.5/ro) (kJ mol-1)
(2)
where:
υ is the number of ions per molecules of the compound
and
ro is estimated as the sum of the ionic radii,
the overall lattice energy change calculated for the
reaction:
MgCl2 •6H2O+ 2Na2SnO3•3H2O →
→ MgSn(OH)6 + 2NaCl + 6H2O
(3)
was found to be -1774 kJ mol-1. The calculated value for
MgCl2 is -2512 kJ mol-1, and for NaCl it is -750 kJ mol-1;
both are in agreement with the literature values [41-44].
The rather large, negative heat of formation suggested that
the MgSn(OH)6 compound would be easy to synthesize.
The free energy associated with the reaction favors the
metathesis reaction and indeed acts as the driving force.
The metathesis reactions occur rapidly such that all of the
enthalpy released is essentially used to heat up the solid
products, usually raising the alkali halide near or above
its normal boiling point and accordingly recognized as
adiabatic in nature. The real driving force for metathesis
reactions is from the formation of thermodynamically
stable salts such as NaCl [21-23].
4. Conclusion
Schoenfliesite-type MSn(OH)6 (M = Ca, Cu, Mg, Mn or
Zn) materials were synthesized by applying a solid-state
metathesis approach at room temperature. The proposed
method is simple, less labor-intensive and has the
potential for easy scale up. The materials synthesized
are single-phase with a controlled morphology and
the synthesis procedure is well positioned to realize
technological usage for these materials.
Acknowledgement
The authors thank Professor Allan Kirkpatrick, Head of
the Department, Department of Mechanical Engineering,
Colorado State University for his continued support, help
and encouragement.
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J.W. Kramer, B. Kelly, V. Manivannan
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