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This work focuses on solid-state syntheses of tin compounds and some of their
properties. Most of these compounds were obtained by solid-state metathesis (SSM)
reactions between lithium carbodiimide and tin halides. Furthermore, some halides and
oxide halides have been synthesized. The majority of the described compounds have
been characterized by single-crystal X-ray diffraction (XRD).
In the reaction of Li2(CN2) and SnCl2, Sn(CN2) was produced, along with Sn2O(CN2),
as a byproduct. Further research has led to the discovery of Sn4Cl2(CN2)3 and
Sn9O5Cl4(CN2)2. Moreover, Sn4Cl2(CN2)3 was shown to act as a precursor compound
in the syntheses of Sn(CN2), Sn2O(CN2), and Sn9O5Cl4(CN2)2. Sn4Cl2(CN2)3 is formed
in these syntheses at temperatures below 200 °C and transforms into either Sn(CN2),
Sn2O(CN2), or Sn9O5Cl4(CN2)2 at temperatures above 300 °C. CuWO4-based
photoanodes mixed with Sn2O(CN2) showed improved efficiencies compared to pure
CuWO4 electrodes. Some tin carbodiimides were investigated by density functional
theory (DFT) calculations, revealing their electronic structures, and indicating them to
be semiconductors with band gaps on the order of 1 to 3 eV. The divalent tin
carbodiimide compounds Sn4Cl2(CN2)3, Sn9O5Cl4(CN2)2, and Sn2O(CN2) were studied
by Mössbauer spectroscopy to identify possible traces of Sn4+. No tin IV could be
detected in samples of Sn4Cl2(CN2)3; however, samples of Sn9O5Cl4(CN2)2 and
Sn2O(CN2) showed the presence of tetravalent tin. This Sn4+ presumably originates
from the starting material SnO, which has also been shown to contain tin in the
oxidation state IV.
Analogous reactions with Li2(CN2) and SnBr2 (instead of SnCl2) led to the discovery of
two compounds, Sn4Br2(CN2)3 and LiSn2Br3(CN2). Sn4Br2(CN2)3 is isotypic to
Sn4Cl2(CN2)3, whereas LiSn2Br3(CN2) is isotypic to the mineral bideauxite
(AgPb2Cl3(F,OH)2). LiSn2Br3(CN2) is thought to show negative thermal expansion at
temperatures below 25 K, as indicated by density functional perturbation theory
(DFPT) calculations.
Reactions between tetravalent tin halides and lithium or sodium carbodiimide led to the
formation of already known ternary compounds containing either Li or Na, e.g.,
A2Sn(CN2)3, A = Li, Na. To avoid the formation of ternary Li/Na containing
dinitridocarbonates, reactions of Pb(CN2) and SnBr4 were carried out, leading to the
formation of yellow single crystals, that were identified as Pb14.66Sn7.34Br26(CN2)7O2.
VIII
The compound containing only divalent tin has a complex crystal structure, where one
metal site is occupied by both tin and lead. The tin to lead ratio could be determined
by energy-dispersive X-ray spectroscopy (EDX) and is consistent with the crystal
structure refinement.
In course of explorative syntheses in the system of Li2(CN2), SnO, and SnX2, (X = Cl,
Br, I), three tin oxide halides, Sn7O4Cl6, Sn7O4Br6, and Sn4OI6, were obtained. Since
some tin oxide halides (in particular tin oxide chloride) were mentioned in the literature
several decades ago, but without any crystal structure data, the discovery of these
three compounds closed a long-standing gap between tin(II) oxide and tin halides.
From similar reactions with Li2(CN2) and SnI2, a ternary lithium tin iodide, LiSn3I7, was
obtained and later synthesized from SnI2 and LiI. Its crystal structure is closely related
to SnI2, but with one shared position of lithium and tin. Recorded 7Li, 119Sn, and 127I
solid-state nuclear magnetic resonance (ssNMR) spectra of LiSn3I7 and some related
compounds demonstrated the incorporation of Li into the structure and showed the
presence of two distinct tin sites.
Besides syntheses with tin halides, reactions between lithium carbodiimide and
tungsten oxide halides were carried out to synthesize a tungsten oxide carbodiimide.
Since reactions with tungsten oxide chlorides and tungsten oxide bromide failed, a
tungsten oxide iodide known from textbooks and articles, WO2I2, was synthesized to
perform further reactions with it. Single crystals of WO2I2 were synthesized and its
previously unknown crystal structure was determined. In addition, a second compound
with the composition W2O3I4 was obtained and structurally characterized.
WO2I2 was synthesized from a mixture of WO3, W, and I2 at a temperature gradient of
800 to 300 °C. WO2I2 has been reported in the literature to play an important role in
chemical transport reactions in tungsten halogen lamps, although its crystal structure
was previously unknown. When heated above 400 °C, WO2I2 transforms into W2O3I4,
a compound completely unknown in the literature so far. |
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