Volatile and Thermally Stable Polymeric Tin Trifluoroacetates

Article abstract of DOI:10.1021/acs.inorgchem.9b01308

Tin trifluoroacetates are effective vapor phase single-source precursors for F-doped SnO₂, but their structures have been poorly understood for decades. Here we undertook a comprehensive structural analysis of these compounds in both the solid and gas phases through a combined single-crystal X-ray crystallography, gas phase electron diffraction, and density functional theory investigation. Tin(II) bis(trifluoroacetate) (1) thermally decomposes into a 1:1 mixture of 1 and ditin(II) μ-oxybis(μ-Trifluoroacetate) (2) during sublimation, which then polymerize into hexatin(II)-di-μ₃-oxyoctakis(μ-Trifluoroacetate) (3) upon solidification. Reversible depolymerization occurred readily upon heating, making 3 a useful vapor phase precursor itself. Tin(IV) tetrakis(trifluoroacetate) (5) was also found to be polymeric in the solid state, but it evaporated as a monomer over 130 °C lower than 3. This counterintuitive improvement in volatility by polymerization was possibly due to the large entropy change during sublimation, which offers a strategic new design feature for vapor phase deposition precursors.

Full text of DOI:10.1021/acs.inorgchem.9b01308

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Volatile and Thermally Stable Polymeric Tin Trifluoroacetates
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Goran Bacic,* Conor D. Rankine, Jason D. Masuda, Derek A. Wann, and Sean T. Barry
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ABSTRACT: Tin trifluoroacetates are effective vapor phase single-source
precursors for F-doped SnO2, but their structures have been poorly understood
for decades. Here we undertook a comprehensive structural analysis of these
compounds in both the solid and gas phases through a combined single-crystal X-
ray crystallography, gas phase electron diffraction, and density functional theory
investigation. Tin(II) bis(trifluoroacetate) (1) thermally decomposes into a 1:1
mixture of 1 and ditin(II) μ-oxybis(μ-trifluoroacetate) (2) during sublimation,
which then polymerize into hexatin(II)-di-μ3-oxyoctakis(μ-trifluoroacetate) (3)
upon solidification. Reversible depolymerization occurred readily upon heating,
making 3 a useful vapor phase precursor itself. Tin(IV) tetrakis(trifluoroacetate)
(5) was also found to be polymeric in the solid state, but it evaporated as a monomer over 130 °C lower than 3. This
counterintuitive improvement in volatility by polymerization was possibly due to the large entropy change during sublimation, which
offers a strategic new design feature for vapor phase deposition precursors.
Traditionally, oligomers and polymers were presumed to be
nonvolatile due to their extreme molecular weight,19 and great
lengths were usually taken to ensure that precursors are
monomeric by design.20 While some volatile CVD precursors
were coincidentally polymeric,21 the features that made some
polymers volatile has not been described. Here we prepare and
evaluate tin trifluoroacetates as potential vapor phase
precursors under realistic conditions. Our results show that
polymerization can be exploited to dramatically and counter-
intuitively improve volatility, possibly by a large change in
entropy during evaporation from a polymer to monomers. The
high volatility and thermal stability of these simple fluorinated
compounds, especially compared to their hydrogenated
analogues, make them promising precursors for vapor
deposition of F-doped SnO2.
INTRODUCTION
■
Demand for transparent conductors made entirely of earth-
abundant elements like F-doped SnO2 is rising due to
economic and environmental concerns.1−4 Atomic layer
deposition (ALD) and chemical vapor deposition (CVD) are
attractive high performance methods for their fabrication, and
have become prevalent in industry.5,6 However, there are
currently no ALD processes to deposit F-doped SnO2, likely
because fluorine doping agents are hazardous (e.g., HF)7,8 or
are difficult to use (e.g., metal fluorides, decomposition of
fluorinated ligands).6,9,10 We set out to evaluate fluorinated
single-source precursors with the hopes of developing a simple
ALD process that can be integrated into real-world device
architectures.
Trifluoroacetic acid (HO2CCF3) is an inexpensive, nontoxic,
and environmentally benign ligand.11 Tin(II) bis-
(trifluoroacetate) (1) is known to be one of the best
precursors for F-doped SnO2 by CVD:12−14 highly transparent
films with low resistivities were deposited at atmospheric
pressure above 200 °C with high growth rates using air as the
coreactant. Compound 1 was only been reported once, and
was prepared by condensing blue-black tin(II) oxide with an
excess of trifluoroacetic acid and trifluoroacetic anhydride.15
Additionally, it was only characterized by microanalysis, FTIR
and 119Sn Mossbauer spectroscopy; while structural inves-
tigations were hindered by polymerization, thermal decom-
position, and oxidation.15,16 Despite their simple composition,
tin trifluoroacetates have seen only a handful of structural
analyses over the last 3 decades.15−18 We wished to gain a
fundamental insight into the structure−property relationships
of tin trifluoroacetates to better understand their suitability as
vapor phase precursors.
RESULTS AND DISCUSSION
■
While trying to make tin(II) bis(trifluoroacetate) (1) by
oxidation of Sn0 with copper(II) bis(trifluoroacetate) in
deoxygenated water (eq 1),22 we obtained a colorless powder
after prolonged drying under high vacuum. From this crude
product we were able to sublime a colorless powder (150 °C,
10 mTorr) without any nonvolatile residue, which itself could
be sublimed and recovered quantitatively. The crude yield of
this synthesis was moderate (ca. 65%) assuming conversion to
1. However, both mass spectrometry and NMR spectroscopy
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were not consistent with the formulation of 1, but rather
another unknown species. A combined density functional
theory (DFT) and gas phase electron diffraction (GED)
approach was used to unambiguously determine the species
that evolved during sublimation and by extension infer the
composition of the unknown solid. Our initial structural
guesses were guided by electron impact mass spectrometry
(EIMS, Figure S1, Supporting Information), and we
determined that there was an equal mixture of 1 and ditin(II)
μ-oxybis(μ-trifluoroacetate) (2) in the gas phase by the
exceptional agreement between our theoretical and GED data
(Figure 1, and Figures S3−5, Supporting Information).
3Sn(O2CCF) (s) (1)
3 2
→ 1 + Sn2O(O2CCF) (g) (2) + (CFCO)2O(g)
(2)
(3)
3 2
3
1
2
1 + 2 V Sn6O2(O2CCF) (s) (3)
3 8
In the solid state, asymmetric units of 3 were linked by
covalent bonds between Sn5 on one and O18* on another
(2.360(3) Å), making each a monomer within an extended
polymeric chain (Figure 3). These chains packed in a crystal
Sn0 + Cu(O2CCF) → Cu0 ↓ +Sn(O2CCF) (1)
(1)
3 2
3 2
Figure 1. Gas phase products of the thermal depolymerization of 3
determined by GED: tin(II) bis(trifluoroacetate) (1, left) and
ditin(II) μ-oxybis(μ-trifluoroacetate) (2, right).
The unknown solid was also isolated during the sublimation
of 1 prepared by the previously reported method,15 which was
also confirmed by NMR, EIMS, and GED. A single crystal
suitable for X-ray crystallography was grown by slowly cooling
a doubly sublimed sample of the unknown solid in toluene.
Upon structural determination, we confirmed it was in fact the
polymeric hexatin(II) di-μ3-oxyoctakis(μ-trifluoroacetate) (3,
Figure 2), which had a stoichiometry that equaled a mixture of
Figure 3. Polymeric chain of (3)4. The first monomer (leftmost, gray
highlight) is shown in Figure 1 (colored by element), while the other
monomers are uniformly colored and highlighted (blue, yellow, and
green from left to right) for clarity. Monomers are covalently bound
through Sn5−O18* bonds.
structure with longer Sn−O2CCF3 intra- and intermolecular
coordination where the SnII atoms formed distinct and
extremely distorted pseudosquare pyramidal geometries
(Figure 4). We could glean no obvious trend from the
Figure 2. Asymmetric monomer of hexatin(II) di-μ3-oxyoctakis(μ-
trifluoroacetate) (3). Ellipsoids are set to 50% probability, disordered
CF3 groups are included, and intermolecular contacts are drawn
translucent.
Figure 4. Extremely distorted pseudosquare pyramidal geometry
around each Sn atom in 3. Only the five shortest Sn−O interactions
are shown.
1 and 2 (eq 3). Thermal depolymerization of 3 into 1 and 2
was reversible, and 3 was recovered quantitatively after
repeated sublimations. If the material isolated following both
synthetic methods before heating under vacuum was in fact 1,
it is likely that 1 decomposes by eliminating trifluoroacetic
anhydride during sublimation to form gaseous 1 and 2 (eq 2),
which polymerize into 3 upon solidification (eq 3). The
oxidation of metallic tin was easily scalable, and multigram
batches (>25 g) were routinely prepared in good yields. Benign
metal waste, mild reaction conditions, and simple workup
make it a convenient green synthetic protocol23 and the most
promising route to prepare 3.
coordination geometries. The plastic behavior of 3 in the solid
state, its facile thermal depolymerization into 1 and 2, and its
seemingly random Sn−O2CCF3 bond lengths suggested the
ligands in 3 were labile in the condensed phase. Nevertheless,
by comparing the five shortest Sn−O distances in 3, we were
able to group the Sn−O bonds into three types: “weak” above
average length bonds, “strong” below average length bonds,
and short μ3-oxy bonds (Figure S9, Supporting Information).
These bond definitions ultimately revealed the fate of the
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structural elements of 3 when evaporating into 1 and 2 (Figure
5).
Figure 5. Asymmetric unit of 3 showing the fate upon evaporation of
Sn1 and Sn6 as 1 (gold, white; left and right) and Sn[2−3] and
Sn[4−5] as 2 (blue, green; middle).
Each Sn atom in 3 was bound to trigonal planar μ3-bridging
oxygen atoms with similar bond lengths (ca. 2.0 Å with a 0.2 Å
deviation of μ3-O from Sn−Sn−Sn plane). This was
reminiscent of the recently prepared “trapped” SnO complex.24
Natural bond order (NBO) analysis previously showed the
trapped oxygen to have a strongly ionic character with three σ-
bonds from lone pairs on the oxygen to empty orbitals on the
three Sn atoms. Despite similarities, it is misleading to describe
the μ3-oxygen in 3 as representing a “trapped” SnO species:
one of the three Sn−μ3-O bonds was shorter than the other
two (i.e., Sn3 and Sn6), opposite to what was expected for
trapped SnO donating to two other Sn atoms. This suggested
that two Sn atoms in the Sn3−μ3-O group formed Lewis basic
covalently bound Sn−O−Sn bridges, and the other accepted σ-
electron density as a Lewis acid. Frontier orbital analysis of 1
and 2 supported this description, implying 3 was the polymeric
Lewis pair (1 ← 2)∞ (Figure 5). This was an important
distinction since it also predicted that the polymer should
break into these Lewis acid/base units upon evaporation, as
observed by GED. The orbital energies and distributions in the
1 and 2 fragments supported their roles as acid and base,
respectively. Only the basic Sn−O−Sn bridge in 2 and
complementary acidic orbitals in 1 had the appropriate
symmetry to allow overlap to form Lewis pairs (Figure 6).
Our difficulty growing crystals of 3 was not surprising.
Previous reports of attempts to grow single crystals of 1
produced species like those we isolated. Compound 3 ligated
with free trifluoroacetic acid was previously grown by heating 1
in a sealed evacuated tube, where protons from hydroxyl
groups on the tube’s walls were presumably abstracted by
trifluoroacetic anhydride to form the acid ligand.16 The
hydrated cluster compound tetratin(II) monotin(IV) di-μ3-
oxyoctakis(μ-trifluoroacetate) (4) was previously grown by
oxidation in O(OCCF3)2/HO2CCF3;15 while we found
crystals of anhydrous 4 near the seal of a pressure vessel
after sublimation of pure 3 (Figure 11), presumably formed by
oxidation with air that diffused through a degraded O-ring seal.
Both of these previously reported compounds share structural
motifs with 3, highlighting the rich coordination chemistry in
this tin−oxytrifluoroacetate system.
Figure 6. Frontier orbitals of 1 (left) and 2 (right), calculated with
the SOGGA11-X functional and DKH-TZP basis set, viewed from the
top (inside) and sides (outside). Lewis acidic and basic orbitals with
the correct orbital symmetry overlap are highlighted in gold and blue,
respectively.
structure of 5 consisted of symmetrical, linear, noninteracting
polymeric chains of octahedral SnIV with four equatorial μ-
bridging and two monodentate axial ligands (Figure 7). Unlike
Figure 7. Solid state structure of polymeric 5. Disordered CF3 groups
are shown, and ellipsoids are displayed at 50% probability.
3, compound 5 was very sensitive to air and moisture, and its
preparation and handling were more difficult. But its
combination of high volatility and reactivity, along with a
lack of Sn−C bonds gives 5 the potential to be a near-room
temperature precursor for SnO2 that may bypass current issues
of low growth rate and high carbon contamination from other
precursors.25,26 GED analysis showed that 5 evolves the
expected monomer 6 with pseudododecahedral coordination
of four η2-trifluoroacetates upon evaporation (Figure 8). As
with compound 3, the bulk composition of 5 was supported by
the high quality of our refined GED data.
The solid state structures of 3 and 5 showed differences to
their hydrogenated cousins tin(II) diacetate (7) and tin(IV)
tetraacetate (8). Both 3 and 7 are linear polymers via “strong”
Sn−O bonds (vide supra), where each Sn atom is
tetracoordinate with Sn−OAc bonds in the range 2.17−2.37
Å.27 However, 3 displays interchain coordination via bridging
Tin(IV) tetrakis(trifluoroacetate) (5) was also polymeric in
the solid state yet was surprisingly volatile. A single crystal
suitable for X-ray crystallography was grown by sublimation
under nitrogen in a gently heated sealed tube (ca. 50 °C). The
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Figure 8. Gas phase structure of 6.
trifluoroacetate ligands while 7 forms tetrameric columns of
(7)n chains with their stereochemically active lone pairs
oriented inward and acetate ligands outward. This organization
was explained as a steric effect, but the possibility of CH3−O
interactions could not be ruled out.27 Compounds 1 and 7 are
isostructural in the gas phase with C2 symmetry, showing very
similar Sn−O bond lengths [2.186(22) and 2.395(25) Å vs
2.192(8) and 2.337(12) Å, respectively].28 This is different
from the gas-phase structure of 2, and there is no precedent in
the literature of compounds with an unligated SnII−O−SnII
bridge, making 2 the first structurally characterized example.
Comparison of 6, the gas phase monomer of 5, with the solid
state structure of 8 shows that both are pseudododecahedral
with four bidentate ligands and have similar Sn−O bond
lengths in the range 2.13−2.29 Å.29
Figure 10. Vapor pressure of 3 (green circles), 7 (gold squares), 2
(blue triangles), and 8 (gray diamonds) as estimated by
thermogravimetric analysis. Enthalpies (in kJ mol−1) of evaporation
(for 3) and sublimation (2, 7, and 8) were estimated by the
Clausius−Clapeyron equation.
its thermal properties. We were able to reproduce the
previously reported promising thermal behavior of 1:12 no
films were deposited at 400 °C in a commercial ALD reactor
after 2000 × 8 s pulses without an oxidizing coreactant. This
strongly suggests 1 and 2 can form a stable monolayer that is
critical to ALD growth. The ease of synthesis and handling,
high thermal stability, and good volatility make 3 a promising
ALD precursor for F-doped SnO2.
Thermogravimetric analysis (TGA) of 3 and 5 showed their
excellent thermal stability and volatility compared to 7 and 8
(Figures 9 and 10). Both 3 and 5 had single step volatilization
The dramatic difference in volatility among this family of
compounds could not be explained by their enthalpies of
vaporization: the temperature at which they reached 1 Torr of
vapor pressure decreased from 8 (218 °C), 3 (191 °C), 7 (154
°C), to 5 (84 °C), while their ΔHvap increased in the order 3
(72 kJ mol−1), 7 (81 kJ mol−1), 5 (83 kJ mol−1), 8 (98 kJ
mol−1). One would expect 8, a coordinately saturated complex
of moderate molecular weight, to be more volatile than the
polymeric compounds. But it was the least volatile by a large
margin, reaching a pressure of 1 Torr at 134 °C higher than 5.
It is also surprising that 3 has the smallest ΔHvap even though
many O → Sn coordinative bonds must be broken to
evaporate as 1 and 2.
Of course, the Gibbs free energy of evaporation depends on
the change in entropy ΔS as well as change in enthalpy ΔH,
and the change in entropy of a system from condensed phase
to the vapor phase is related to the number of possible
microstates W available in that phase by the Boltzmann
equation. Since vaporization is an endothermic process where
ΔG ≤ 0, ΔH and ΔS must then both be positive. For highly
symmetrical polymers like 5, ΔS is large due to the
depolymerization from one (5)n polymer into n gas phase
monomers (naively, Wg ∼ nWc, where Wc represents the
condensed phase, and Wg the gas phase), lowering the
temperature required to satisfy ΔH ≤ TΔS. A similar argument
can be made for the symmetrical polymer 7,27,28 but its lower
vapor pressure is likely due to the secondary factor of increased
intermolecular interactions between more polarizable CH3
groups (when compared to CF3).27 The complexity and
lability of 3 in the condensed phase lessens the difference
between Wg and Wc, increasing the temperature required to
satisfy the Gibbs inequality, decreasing its volatility. Similarly,
the change in entropy upon vaporization of 8 is small due to its
monomeric nature in the solid state29 and gas phase. Overall,
Figure 9. Ramped thermogravimetric analysis (TGA) curves of 3
(left, green), 7 (left, gold), 5 (right, blue) and 8 (right, gray). Stress
tests (inset) reveal the stability of 3 (green circles) and 5 (blue
triangles) with no increase in residual mass with increasing initial mass
loading; and highlight the instability of 7 (gold squares) with a
positive correlation. 8 was omitted as it decomposed considerably
even at low mass loading (ca. 10 mg), so its comparison became
trivial.
with no decomposition, which was ideal behavior for potential
ALD precursors. Decomposition during TGA can be evaluated
simply by increasing the initial mass loading, in what is called a
“thermal stress” test.20 Simply, a higher loading of analyte
requires more time to evaporate, so a higher mass of analyte is
exposed to higher temperatures for longer time. Thus, higher
temperature decomposition events may occur and be observed
during an experiment as an increase in nonvolatile residual
mass. This stress test can be used to qualitatively evaluate the
onset of decomposition and overall stability of a potential
precursor.20,30 While 7 decomposed to SnO at 238 °C,31
3
shows negligible decomposition up to at least 275 °C by TGA,
at which temperature the analyte had completely evaporated.
Despite its relatively lower volatility, 3 performed excep-
tionally well under realistic ALD process conditions, surviving
over a week of continuous heating at 170 °C with no change in
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this suggests a new strategy in precursor design: volatility can
be increased by forming highly symmetrical coordination
polymers to exploit their inherently large change in entropy
upon evaporation into monomers.
has not yet been successful, but the combination of these
building blocks and other Lewis acids and bases opens a
potentially versatile toolbox of thermally robust and ampho-
teric tin-containing supramolecular complexes.
The variability in polymerization we found in 3 suggested
that addition of additional Lewis bases could easily disrupt its
structure. Exploiting this, we structurally characterized several
other compounds and uncovered some patterns of tin
trifluoroacetate supramolecular organization: the cage-like
cluster hexakis[tin(II) bis(trifluoroacetate) trimethylphos-
phine] [(1 ← PMe3)6]; the anhydrous partial oxidation
product of 3, compound 4;15 and the diethyl ether σ-adduct 6
← (OEt2)2 (Figure 11). These are also similar to the
CONCLUSION
■
Contrary to conventional wisdom, our results demonstrate that
polymerization does not need to be avoided in precursor
design if reversible thermal depolymerization can be achieved.
In fact, it may increase the volatility over monomeric
analogues. Despite its relatively lower volatility; the low cost,
safe handling, and easy preparation of 3 make it the more
attractive F-doped SnO2 precursor for many applications.
Compound 5 has potential as a complementary precursor for
specialized application in very low temperature deposition. We
are currently exploring processes using 3 or 5 as precursors to
F-doped SnO2 by ALD.
EXPERIMENTAL DETAILS
■
General Synthetic Considerations. Most of the preparations
reported below are oxygen- and moisture-sensitive, so they were
performed under an inert atmosphere in a nitrogen-filled (“4.8”
99.998% purity) MBraun Labmaster 130 drybox or under ultrapure
nitrogen gas (“5.0” 99.999% purity) using standard Schlenk
techniques. Those that can be performed under ambient conditions
are noted as such. Low vacuum was achieved by a digitally regulated
diaphragm pump (Buchi VacoboxTM, min. ∼10 Torr), and high
vacuum by single-stage rotary vane pumps (Edwards RV5) whose
absolute base pressures were measured to be 1−10 mTorr by a Hg-
filled McLeod gauge. All solvents (e.g., toluene, hexanes, diethyl
ether) were ACS Reagent grade or higher, degassed by an MBraun
Solvent Purifier System using nitrogen gas (″4.8″ 99.998% purity),
and stored in a drybox over freshly regenerated 4 Å molecular sieves
(Millipore-Sigma) for at least 24 h before use. Deuterated solvents
were either used from a freshly opened ampule, or degassed by three
freeze−pump−thaw cycles then dried and stored over molecular
sieves. Reverse osmosis water was deionized using a Milli-Q system
until its resistance reached 18 MΩ. All purchased chemicals were used
as received. Tin(II) oxide (≥95%), copper(II) oxide (powder, < 10
μm, 98%), silver(I) oxide (ReagentPlus, 99%), trifluoroacetic acid
(ReagentPlus, 99%), trifluoroacetic anhydride (ReagentPlus, ≥ 99%),
and tin(IV) bromide (99%) were purchased from Millipore-Sigma.
Tin metal (powder, 100 mesh, 99.5%) was purchased from Strem
Chemicals. Tin(II) diacetate,31 tin(IV) tetraacetate,34 silver(I)
trifluoroacetate,35 and copper(II) bis(2,2,6,6-tetramethylheptane-3,5-
dionate)36 [Cu(tmhd)2] were prepared according to literature
methods. Proton and heteronuclear NMR spectra were collected
with a Bruker Avance II 300 MHz spectrometer at room temperature.
Synthetic Procedures. Caution! During experiments using
trifluoroacetic acid, all ground glass fittings were sealed with PTFE
thread. Silicone vacuum grease is very soluble in trifluoroacetic acid:
prolonged reflux will lead to frozen joints and leaks, and filtration by
inversion through a filter stick will allow trifluoroacetic acid to pass
unimpeded through the glass joint, posing a serious safety risk due to acid
burns from exposure to the vapor or liquid.
Figure 11. Molecular structures 6 ← (OEt2)2 (left), (1 ← PMe3)6
(center), and 4 (right). Basic groups (i.e., Et2O, 2, and PMe3) are
highlighted in blue, and acidic groups (i.e., 1 and 6) are highlighted in
gold to show how 4 can be described as 6 ← 22. Ellipsoids displayed
at 50% probability; CF3 groups and hydrogens are omitted from (1 ←
PMe3)6 for clarity.
previously reported mixed valence cluster ditin(II) ditin(IV)
di-μ3-oxyoctakis(μ-trifluoroacetate) (9).18 With these pieces
we can complete the picture of supramolecular organization in
the tin−oxytrifluoroacetate system: SnII atoms adopt distorted
square pyramidal five-coordinate geometries. SnIV atoms adopt
octahedral geometries which distort upon coordination to SnII
atoms. Homoleptic trifluoroacetates naturally act as Lewis
acids, while trifluoroacetate groups bridge rather than chelate
Sn centers to fill their coordination spheres, and bond more
strongly to SnIV (bond lengths ca. 2.1 Å) than the more
electron-rich SnII centers (bond lengths >2.3 Å). Trifluoro-
acetic anhydride is apparently readily eliminated,17,32,33 leaving
oxy moieties that donate σ-electron density to form basic Sn−
O−Sn bridges and thus μ3-oxy-bridged Lewis pairs.
Together, 1, 2, 6, and “OSnIV(O2CCF3)2” (10, the inferred
trifluoroacetic anhydride elimination product of 6) make up
the elementary building blocks of tin−oxytrifluoroacetate
clusters and polymers. Consequently, 3 is more appropriately
described as (1 ← 2)∞, compound 4 as 6 ← 22, and
compound 9 as (1 ← 10)2. It is notable that 6 and 10 do not
form a stable cosubliming complex like 1 and 2 do in 3. If 9 is a
typical example and 10 dimerizes like the central four-
membered Sn2O2 heterocycle, then it is likely that intimate
coordination between 6 and 10 is prevented by steric
hindrance. The preparation and isolation of free 2 and 10
Hexatin(II) Di-μ3-oxyoctakis(μ-trifluoroacetate) (3). By Oxi-
dation of Sn0 with CuII(O2CCF3)2. Copper(II) bis(trifluoroacetate)
was prepared in situ according to a modified literature method under
ambient conditions.37 One equivalent of copper(II) oxide (9.325 g,
116.0 mmol) was suspended in 200 mL water in a 500 mL round-
bottom flask with vigorous magnetic stirring. Two equivalents of
trifluoroacetic acid (26.459 g, 232.1 mmol) was added in a continuous
stream through an addition funnel. An exotherm occurred and the
mixture was stirred with gentle (40 °C, overnight) or no heating (3
days) until it became azure blue and mostly transparent. The mixture
was then filtered with suction through a Celite pad and a medium
porosity fritted glass filter to remove unreacted CuO and other
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insoluble impurities to yield a clear azure blue solution. This was then
deoxygenated by sparging for 30 min with a vigorous nitrogen flow
through a fritted glass gas-diffusion tube.
PTFE-capped O-ring sealed glass pressure vessel in a drybox and
heating in an oven at 200 °C for 2 h until the sample had completely
evaporated. Heating was stopped, and the oven was allowed to cool
slowly. Large sticky crystals (presumably 3) were deposited
throughout the vessel but could not be successfully harvested. Smaller
cubic crystals of 4 suitable for crystallography were found near the cap
of the vessel.
Then, an excess of tin metal powder (27.548, 232.1 mmol) was
added all at once to the aqueous Cu(O2CCF3)2 solution under a
stream of nitrogen gas at ambient temperature. Copper metal was
clearly visible after an hour as shiny flakes, which were obscured after
a day by redeposition of excess tin. Completion of the reaction was
indicated by a fast settling, dark gray precipitate (Cu plated with Sn)
and a colorless supernatant liquid, which was separated from the
precipitate by filtration through a fritted glass filter stick under
nitrogen to yield a colorless solution. Volatiles were removed from the
filtrate first by heating under low vacuum (∼10 Torr, 60 °C, 4 h) to
yield a pale-yellow syrup that eventually becomes a colorless solid.
This was dried with heating under high vacuum (1−10 mTorr, 100
°C, 8h) to yield 27.753 g of a colorless crystalline solid (87% crude
yield based on CuO and HO2CCF3 used, assuming conversion to 1/6
eq. of 3). Sublimation by vacuum-transfer (1−10 mTorr, 170 °C) into
a cooled (−78 °C) receiving flask yielded 3 (26.120 g, 82% yield) as a
colorless, sticky, amorphous solid that becomes a colorless crystalline
solid that can be powdered upon cooling to −45 °C overnight. The
title compound was deliquescent, and must be stored dry, although
dry O2 does not appear to degrade samples. Oxidation occurs slowly
and 1 can be briefly handled under ambient conditions. It was very
soluble in coordinating solvents (e.g., THF, ACN, DMSO), and
slightly soluble in aromatic hydrocarbons. It forms a stable solution in
water in the absence of O2, showing no hydrolysis. Mp 127 °C,
sublimed. Crystals suitable for X-ray crystallography were grown by
slow cooling of a toluene solution of 3 that was previously sublimed
twice. HRMS (EI+): found m/z = 578.7624, calcd Sn2(O2CCF3)3
578.7595, dev. 2.69 mmu; m/z = 481.7718, calcd Sn2O(O2CCF3)2
481.7694, dev. 2.40 mmu; m/z = 364.7866, calcd Sn2O(O2CCF3)
364.7867, dev. 0.1 mmu; m/z = 276.8633, calcd Sn(O2CCF3)CO2
276.8771, dev. 13.8 mmu. NMR chemical shifts of 3 in D3CCN, (δ0 =
1.94 ppm): silent; 13C{1H} (δ0 = 1.32 ppm): 117.03 ppm (q,
O2CCF3, 1JC−F = 288 Hz), 162.19 ppm (q, O2CCF3, 2JC−F = 38.7 Hz);
19F (external reference, HO2CCF3 in D2O δ0 = −75.15 ppm): −
75.61 ppm (s). 119Sn (external reference, Sn[N(SiMe3)2]2 in C6D6 δ0
= 770 ppm): silent. (Note: the combined effects of dynamic solvent
Tin(IV) Tetrakis(trifluoroacetate) (5). Acidolysis of tetraphe-
nyltin was performed according to a known literature procedure with
modified workup.38 Tetraphenyltin (4.271 g, 10.00 mmol) was placed
in a 250 mL Schlenk flask, then degassed and dried under high
vacuum at room temperature for 1 h. One equivalent of trifluoroacetic
anhydride (2.100 g, 10.00 mmol) in a large excess of trifluoroacetic
acid (100 mL) was cannulated into the flask. The suspension was
stirred until it became a clear green/tan solution (about 1 day), then
the volatiles were removed at ambient temperature under high
vacuum. The resulting pale yellow/green solid was purified by vacuum
transfer (10 mTorr, 60 °C) to yield a colorless crystalline solid
contaminated with a less volatile byproduct (observed by TGA)
believed to be the product upon elimination of trifluoroacetic
anhydride (i.e., “SnO(O2CCF3)2”, 10). The solid was sublimed again
(10 mTorr, 60 °C) to yield 5 (3.140 g, 55% based on Ph4Sn, mp 115
°C, lit. 114−115 °C38) as a colorless crystalline and very moisture-
sensitive solid. Compound 5 is very soluble in trifluoroacetic acid,
coordinating aprotic solvents, and moderately soluble in aromatic
hydrocarbons. Solutions of 5 fume when exposed to ambient
conditions, but the solid can be briefly handled in air without
significant hydrolysis. Crystals suitable for X-ray crystallography were
grown by sublimation: 5 (250 mg) was placed in a PTFE-capped O-
ring-sealed glass pressure vessel in a glovebox and placed on top of an
oven in a warm zone at approximately 50 °C. After about 3 weeks,
crystals of 5 deposited on the cooler end of the vessel. Crystals of the
bis(etherate) were grown by slow cooling to −45 °C of a solution of 5
in 1:1 diethyl ether/pentane, after 2 days crystals of 6 ← (OEt2)2
were deposited.
Thermogravimetric Analysis (TGA). TGA was performed on Pt
pans with a TA Instruments Q50 housed in an MBraun Labmaster
130 drybox filled with nitrogen gas (″4.8″ 99.998% purity). Pt pans
were cleaned by sequential ultrasonication in dilute nitric acid (∼3
N), water, then 2-propanol. They were then heated until red hot by a
propane torch flame in air to remove remaining impurities. Ramp
experiments were performed under a flow of ultrapure nitrogen (“5.0”
99.999% purity, 60 sccm) at 10 °C min−1 to a maximum temperature
of 500 °C. Stress-tests were performed under the same conditions
sequentially on freshly cleaned pans with incrementally increasing
initial mass loadings.
Vapor pressures were estimated using a modified literature
method.39 Vaporization constants α (from the Langmuir equation)
were obtained for our instrument by calibrating compounds with
known Antoine equation parameters and volatilities similar to the
analyte. Benzoic acid (αloT = 2.016 × 10−4) was used for high
volatility compounds (i.e., 5), and Cu(tmhd)240 (αhiT = 4.512 × 10−5)
was used for low volatility compounds (i.e., 3, 7, and 8). The
temperature program was set to jump by increments of 10 °C, then
hold that temperature for 7 min to allow the evaporating system to
reach equilibrium, and then the derivative of mass with respect to
temperature dm/dT was taken from the linear regions of the isotherm
steps for each temperature. These data were used to find the pressure
p as a function of T, thus ln p as a function of T−1, which can be
modeled with the Clausius−Clapeyron equation. The slope of this
line is equal to the enthalpy of sublimation (before melting) and
evaporation (after melting) divided by the gas constant ΔH/R.
Evaluation of Atomic Layer Deposition (ALD) Potential of 3.
The potential for 3 to form a thermally stable self-limiting monolayer
under operando ALD conditions was evaluated in a commercial
Picosun R-150 hot-wall viscous flow ALD reactor. Powdered samples
of 3 (up to 10 g) were loaded into an open-cup glass-lined stainless
steel bubbler in a drybox, capped with a rubber septum, then loaded
into the bubbler heating jacket under a strong flow of ultrapure
nirogen (“5.0” 99.999%, 250 sccm). The bubbler and lines were
2
2
2
3
exchange and compounded JSn−C, J119Sn‑119Sn, J119Sn‑117Sn, JSn−C, and
4JSn−F coupling likely led to extreme broadening of the signal to the point
where it could not be detected.)
Condensation of SnO with trifluoroacetic acid was performed
according to a modified literature procedure.15 Blue-black tin(II)
oxide (6.310 g, 46.84 mmol) was placed in a 250 mL Schlenk flask
and dried under high vacuum (10 mTorr) at room temperature for 3
h. The flask was refilled with nitrogen and fitted with a water-cooled
reflux condenser, previously flamed-dried under vacuum, closed with a
rubber septum. One equivalent of trifluoroacetic anhydride (9.838 g,
46.84 mmol) in a large excess of trifluoroacetic acid (100 mL, 760
mmol) was deoxygenated by three freeze−pump−thaw cycles and
then cannulated onto the SnO through the condenser. The mixture
was heated to reflux with vigorous stirring under nitrogen for 8 days
and then cooled to room temperature to yield a colorless supernatant
liquid and a sticky beige precipitate. This mixture was filtered through
a fritted glass filter stick under nitrogen to yield a colorless solution.
The filtrate was worked up and purified in a manner identical to the
one detailed above to yield a colorless solid (11.676 g, 85% yield
assuming conversion to 3) that had identical thermal and
spectroscopic characteristics to the material prepared by redox.
Hexakis[tin(II) Bis(μ-trifluoroacetate) Trimethylphosphine] [(1 ←
PMe3)6]. Compound 3 (1.000 g, 0.6066 mmol) was suspended in
toluene (10 mL) and trimethylphosphine (0.221 g, 2.90 mmol, in 10
mL of toluene) was added dropwise resulting in a clear colorless
solution. (The PMe3 was added in excess due to our presumption that
the starting material was 1, M = 344.74 g/mol, before we discovered it
was 3.) Crystals of (1 ← PMe3)6 were grown by slow cooling this
solution to −45 °C for a week.
Tetratin(II) Monotin(IV) Di-μ3-oxyoctakis(μ-trifluoroacetate) (4).
Crystals of 4 were grown by placing a sample of 3 (∼100 mg) in a
F
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evacuated to the base operating pressure of the reactor (ca. 10 hPa) to
remove any water or oxygen that may have become trapped in the
bubbler during loading. Then the bubbler and delivery lines were
heated to 170 °C for 1 h before deposition to allow the precursor to
melt and heat evenly. Precursor vapor was delivered into the
deposition chamber with a “pulse”: two pneumatic ALD valves were
opened between the carrier gas inlet, the precursor, and the reactor,
and nitrogen carrier gas was flowed over the heated precursor at 200
sccm for 8 s under active vacuum, after which the valves were closed
in reverse order. The lines and reactor chamber were purged with
nitrogen carrier gas at 150 sccm for 8 s to remove any unreacted 3
vapor and byproducts of its self-assembly into a molecular layer on the
surface.
During evaluation, several substrates were loaded into the
deposition chamber: single-side polished “mechanical grade” high-
purity hydrogen terminated single-crystalline (100) Si (RCA cleaned,
sonicated in 2% HF(aq) for 30 min immediately prior to use), 100
nm Al2O3 films (deposited by 900 cycles of ALD using
trimethylaluminum and water at 250 °C on bare Si), 100 nm SiO2
(thermally grown on Si at 1200 °C in O2) and soda-lime glass
microscope slides (cleaned by sonication for 30 min each in acetone,
2-propanol, and deionized water). No films could be observed after
2000 pulses of 1 at a reactor temperature of 400 °C by eye (evident as
interference patterns on reflective and color changes on transparent
substrates), ellipsometry, or scanning electron microscopy (SEM).
Preliminary ALD experiments using an oxidizing coreagent (e.g., air)
deposited uniform and transparent films. Above 420 °C, an
uncharacterized patchy mottled blue-gray material was observed on
all substrates without coreagent, indicating CVD growth behavior and
the absence of ALD-like growth.
X-ray Crystallography. Crystals were attached to the tip of an
appropriately sized μm MicroLoop with Paratone-N oil. Measure-
ments were made on a Bruker APEXII CCD equipped diffractometer
(30 mA, 50 mV) using monochromated Mo Kα radiation (λ =
0.71073 Å) at 125 K. APEX2 software41 was used for the initial
orientation and unit cells were indexed using a least-squares analysis
of a random set of reflections collected from three series of 0.5° wide
scans, 10 s per frame, and 12 frames per series that were well
distributed in reciprocal space. For data collection, four ω-scan frame
series were collected with 0.5° wide scans, 5 s frames, and 366 frames
per series at varying φ angles (φ = 0°, 90°, 180°, and 270°). The
crystal-to-detector distance was set to 6 cm and a complete sphere of
data was collected. Cell refinement and data reduction were
performed with the Bruker APEX3 software, which corrects for
beam inhomogeneity, possible crystal decay, Lorentz and polarization
effects. Data processing and a multiscan absorption correction was
applied using the APEX3 software package.42 The structure was
solved using intrinsic phasing,43 and all non-hydrogen atoms were
refined anisotropically using SHELXL44 using a combination of the
shelXle graphical user interface45 and OLEX2.46 Figures were made
using UCSF Chimera47 and Adobe Photoshop CC 2018. CCDC
1885252−1885256 contains the supplementary crystallographic data
for complexes 3, 5, (1 ← PMe3)6, 6 ← (OEt2)2, and 4, respectively.
These data can be obtained free of charge from the Cambridge
Crystallographic Database Centre via https://summary.ccdc.cam.a-
c.uk/structure-summary-form.
successfully modeled. Another toluene model was found but attempts
at modeling failed; the SQUEEZE routine was used and 48 electrons
were removed, closely matching the expected 50 electrons for a
toluene molecule. Details of crystal data, data collection, and structure
refinement are listed in Table S6.
Tin(IV) Tetrakis(trifluoroacetate)−trans-Bis(diethyl ether) [6 ←
(OEt2)2]. Details of crystal data, data collection, and structure
refinement are listed in Table S9.
Tetratin(II) Monotin(IV) Di-μ3-oxyoctakis(μ-trifluoroacetate) (4).
This compound was found to be a two-component inversion twin and
was treated appropriately. Details of crystal data, data collection, and
structure refinement are listed in Table S12.
Theoretical Calculations. All theoretical calculations were
carried out using the Gaussian09 Rev.D0148 software suite. All
geometry optimizations of Sn(O2CCF3)2 (1) and Sn2O(O2CCF3)2
(2) were performed in the C2 symmetry point group, and
Sn(O2CCF3)4 (6) was performed in the D2d symmetry point group.
The highest-level geometry optimizations accounted for scalar
relativistic effects using the second-order Douglas−Kroll−Hess
(DKH) Hamiltonian49−52 and employed the SOGGA11-X53 density
functional of Truhlar and Peverati, coupled with the all electron
double-ζ and triple-ζ-quality DZP-DKH and TZP-DKH basis sets of
Jorge et al.54−56 The point-nuclei model was used in the DKH
treatment.
To establish flexible restraints for use in a SARACEN57−59 GED
refinement, additional optimizations were carried out using the
M06,60 M11,61 and SOGGA11-X53 density functionals coupled with
the def2-SVP, def2-TZVP, and def2-QZVP basis sets.62,63 The
characters of all optimized geometries were verified via vibrational
frequency analysis and were confirmed to correspond to minima on
the ground-state potential energy surface. Cartesian coordinates of all
optimized geometries are found in Tables S18−S39 (for 1 and 2) and
Tables S48−S58 (for C). Theoretical rh1-type amplitudes of vibration
(uh1) and curvilinear distance corrections (kh1) were generated for 1,
2, and 6 from force fields computed at the SOGGA11-X/def2-SVP
level using the SHRINK software package.64,65
Gas-Phase Electron Diffraction (GED). GED data for 1, 2, and 6
were acquired using the University of York gas electron
diffractometer.66 An accelerating potential of 42.22 kV was applied
to produce an electron emission current of 0.66 μA and an electron
wavelength of ca. 5.85 pm. The scattered electrons were recorded via
exposures of image plates (Fuji BAS-IP MS 2025) at nozzle-to-image-
plate distances of 234.5 and 477.0 mm for 1 and 2 and at nozzle-to-
image-plate distances of 233.5 and 486.0 mm for 6. Five exposures
were recorded at each nozzle-to-image-plate distance. To acquire data
for 1 and 2, the sample and the nozzle were heated to 463 and 473 K,
respectively, during exposures at both nozzle-to-image-plate distances.
To acquire data for 6, the sample and the nozzle were heated to 398
and 403 K, respectively, during exposures at both nozzle-to-image-
plate distances. A flatbed image plate scanner (Fuji BAS-1800II) was
used to digitize the scattering intensities recorded on the image plates.
Summaries of the experimental conditions used to acquire data for 1
and 2 and for 6, can be found in Tables S17 and S47, respectively.
Reduction and Refinement. Digitized diffraction patterns were
reduced to molecular intensity curves (MICs) using the data
extraction package xtract.67 MICs were refined using the ed@ed
v3.0 least-squares refinement package,68 employing the electron
scattering factors of Ross et al.69
Hexatin(II) Di-μ3-oxyoctakis(μ-trifluoroacetate) (3). Two − CF3
groups were found to be best modeled using a two-component
disorder model, one in a 66:34 ratio (on C8) and the other in a 73:27
(on C14). Details of crystal data, data collection, and structure
refinement are listed in Table S1.
Tin(IV) Tetrakis(trifluoroacetate) (5). One of the CF3 groups was
modeled with a two-component disorder model in a 53:47 ratio.
Details of crystal data, data collection, and structure refinement are
listed in Table S4.
Hexakis[tin(II) bis(μ-trifluoroacetate) trimethylphosphine] [(1 ←
PMe3)6]. One CF3 exhibited three-position disorder (53:33:14). Other
CF3 groups had larger thermal parameters, but attempts to model the
disorder did not yield better models so they were left as is. One
toluene molecule was found in the difference map and was
The least-squares refinement procedures employed parametrized
molecular models: one de- scribing both 1 and 2, each within the C2
symmetry point group, in terms of 23 refinable parameters comprising
11 distances (p1−p11), 5 angles (p12−p14, p19, and p23), and 7 dihedral
angles (p15−p18 and p20−p22) with the option to weight the fraction of
each 1 and 2, and one describing 6 within the D2d symmetry point
group in terms of 12 refinable parameters comprising 8 distances (p1−
p8) and 4 angles (p9−p12). Definitions of the refinable parameters
used for 1 and 2, and 6, are given in Tables S40 and S59, respectively.
The FORTRAN90 code for the parametrized molecular models is
available free-of-charge at DOI: 10.15124/5cb0c982-b280-47e9-
9d46-08e675dfe0af.
G
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Inorg. Chem. XXXX, XXX, XXX−XXX

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The least-squares refinement procedures used the SARACEN
approach and yielded internuclear distances of the rh1 type; rh1-type
internuclear distances are related to the vibrationally averaged ra-type
distances determined directly via the GED experiment by the
AUTHOR INFORMATION
Corresponding Author
■
̌
́
Goran Bacic − Carleton University, Ottawa, Canada;
orcid.org/0000-0003-2437-2418; Email: gibacic@
gmail.com
2
relationship ra3 ≈ ra + uh 1/ra − kh1. SARACEN restraints were
centered on values obtained from geometry optimizations at the
SOGGA11-X/TZP-DKH level. For the refinement of 1 and 2, and for
the refinement of 6, restraints were applied to 9 of the 23 and to 7 of
the 12, parameters, respectively, with the remaining parameters being
allowed to refine free from restraint. Seven parameters remained
unrefined after finalizing the refinement of 1 and 2; no parameters
remained unrefined after finalizing the refinement of 6. Estimates of
the uncertainties associated with the SARACEN restraint values were
derived from sequential geometry optimizations using the M06, M11,
and SOGGA11-X density functionals coupled with the def 2-SVP, def
2-TZVP, and def 2-QZVP basis sets.
Other Authors
Conor D. Rankine − University of York, Heslington, York,
U.K.
Jason D. Masuda − Saint Mary’s University, Halifax,
Canada; orcid.org/0000-0002-6195-9691
Derek A. Wann − University of York, Heslington, York,
U.K.; orcid.org/0000-0002-5495-274X
́
Sean T. Barry − Carleton University, Ottawa, Canada;
The weighting points for off-diagonal weight matrices, scaling
factors, and correlation parameters associated with the refinement of 1
and 2 and with the refinement of 6, can be found in Tables S41 and
S60, respectively. Summaries of the refined (rh1-type) and theoretical
(re-type, SOGGA11-X/TZP-DKH) parameters p1 to p23 (describing 1
and 2), and parameters p1 to p12 (describing 6)accompanied, in
each case, by uncertaintiescan be found in Tables S42 and S61,
respectively. Correlation matrices can be found in Tables S43 and
S62, respectively. All amplitudes of vibration were refined as outlined
in ref 36. Summaries of internuclear distances, refined and theoretical
amplitudes of vibration, rh1-type distance corrections, and SARACEN
restraints (where applied) are tabulated for 1 and 2 in Table S44 and
for 6 in Table S63. Cartesian coordinates for the refined geometries of
1, 2, and 6 are found in Tables S45, S46, and S64, respectively.
orcid.org/0000-0001-5515-4734
Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.inorgchem.9b01308
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We wish to thank Dr. Sharon Curtis at the University of
Ottawa for mass spectrometry, and Tomas Lock Feixas and
Justas Benetis for assisting with GED data acquisition. G.B. and
S.T.B. acknowledge the QEII-OGSST program for funding and
Carleton University for support. J.D.M. thanks the NSERC for
funding in the form of a Discovery Grant (RGPIN-2015-
03825) and acknowledges the Canada Foundation for
Innovation (CFI) and Nova Scotia Research and Innovation
Trust Fund for equipment funding (CFI/30368). D.A.W.
thanks the EPSRC for funding his fellowship (EP/I004122)
and C.D.R. thanks the EPSRC for funding his studentship
(EP/1651146). All GED and DFT data created during this
research are available by request from the University of York
Data Catalogue (DOI: 10.15124/5cb0c982-b280-47e9-9d46-
08e675dfe0af).
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.inorgchem.9b01308.
■
sı
Crystallographic details for 3, 4, 5, [1 ← PMe3]6, and 6
← (OEt2)2, Electron-impact (EI) and electrospray
ionization (ESI) mass spectrograms of 3 (Figures S1
and S2), radial distribution curves (RDC) and molecular
intensity curves (MIC) from GED of 1 and 2 and 6
(Figures S3−S5). Crystallographic figures and tables
(Figures S4−S11 and Tables S0−S16), Cartesian
coordinates and energies of DFT-optimized geometries
(Tables S18−S39 and S48−S58), summary of fixed
(nonrefinable) parameter values (Tables S40 and S59),
summary of GED experimental parameters (Tables S41
and S60), a summary of refined and theoretical refinable
parameter values with SARACEN restraints (Tables S42
and S61), least-squares correlation matrix (Tables S43
and S62), ra-type internuclear distances and refined and
theoretic amplitudes of vibration and distance correc-
tions with SARACEN restraints (Tables S44 and S63),
and the refined Cartesian coordinates for the GED-
determined structure (Table S45−S46 and S64) of 1
and 2, and 6, respectively (PDF)
REFERENCES
■
(1) Kumar, A.; Zhou, C. The Race to Replace Tin-Doped Indium
Oxide: Which Material Will Win? ACS Nano 2010, 4 (1), 11−14.
(2) Ellmer, K. Past Achievements and Future Challenges in the
Development of Optically Transparent Electrodes. Nat. Photonics
2012, 6 (12), 809.
(3) Gordon, R. G. Criteria for Choosing Transparent Conductors.
MRS Bull. 2000, 25 (8), 52−57.
(4) Andersson, A.; Johansson, N.; Broms, P.; Yu, N.; Lupo, D.;
̈
Salaneck, W. R. Fluorine Tin Oxide as an Alternative to Indium Tin
Oxide in Polymer LEDs. Adv. Mater. 1998, 10 (11), 859−863.
(5) George, S. M. Atomic Layer Deposition: An Overview. Chem.
Rev. 2010, 110 (1), 111−131.
̈
(6) Miikkulainen, V.; Leskela, M.; Ritala, M.; Puurunen, R. L.
Crystallinity of Inorganic Films Grown by Atomic Layer Deposition:
Overview and General Trends. J. Appl. Phys. 2013, 113, 021301.
(7) Choi, Y.-J.; Park, H.-H. A Simple Approach to the Fabrication of
Fluorine-Doped Zinc Oxide Thin Films by Atomic Layer Deposition
at Low Temperatures and an Investigation into the Growth Mode. J.
Mater. Chem. C 2014, 2 (1), 98.
GED determined structure of 1 (XYZ)
GED determined structure of 2 (XYZ)
GED determined structure of 6 (XYZ)
Accession Codes
CCDC 1885252−1885256 contain the supplementary crys-
tallographic data for this paper. These data can be obtained
free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by
emailing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
(8) Lee, Y.; Sun, H.; Young, M. J.; George, S. M. Atomic Layer
Deposition of Metal Fluorides Using HF–Pyridine as the Fluorine
Precursor. Chem. Mater. 2016, 28 (7), 2022−2032.
̈
(9) Pilvi, T.; Puukilainen, E.; Kreissig, U.; Leskela, M.; Ritala, M.
Atomic Layer Deposition of MgF2 Thin Films Using TaF5 as a Novel
Fluorine Source. Chem. Mater. 2008, 20 (15), 5023−5028.
H
https://dx.doi.org/10.1021/acs.inorgchem.9b01308
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
pubs.acs.org/IC
Article
(10) Putkonen, M.; Szeghalmi, A.; Pippel, E.; Knez, M. Atomic
Layer Deposition of Metal Fluorides through Oxide Chemistry. J.
Mater. Chem. 2011, 21 (38), 14461−14465.
Crystallogr., Sect. B: Struct. Crystallogr. Cryst. Chem. 1979, 35 (1), 80−
83.
̌
́
(30) Bacic, G.; Zanders, D.; Mallick, B.; Devi, A.; Barry, S. T.
Designing Stability into Thermally Reactive Plumbylenes. Inorg.
Chem. 2018, 57 (14), 8218−8226.
(11) Boutonnet, J. C.; Bingham, P.; Calamari, D.; Rooij, C. de;
Franklin, J.; Kawano, T.; Libre, J.-M.; McCul-loch, A.; Malinverno, G.;
Odom, J. M.; et al. Environmental Risk Assessment of Trifluoroacetic
Acid. Hum. Ecol. Risk Assess. 1999, 5 (1), 59−124.
(31) Donaldson, J. D.; Moser, W.; Simpson, W. B. 1147. Tin (II)
Acetates. J. Chem. Soc. 1964, 5942−5947.
(12) Maruyama, T.; Tabata, K. Fluorine-Doped Tin Dioxide Thin
Films Prepared by Chemical Vapor Deposition. J. Appl. Phys. 1990, 68
(8), 4282−4285.
(32) Sartori, P.; Weidenbruch, M. Trifluoroacetates of Silicon,
Germanium, and Tin. Angew. Chem., Int. Ed. Engl. 1965, 4 (12), 1079.
̈
(33) Sartori, P.; Weidenbruch, M. Uber Die Darstellung Und
(13) Korotkov, R. Y.; Ricou, P.; Farran, A. J. E. Preferred
Orientations in Polycrystalline SnO2 Films Grown by Atmospheric
Pressure Chemical Vapor Deposition. Thin Solid Films 2006, 502 (1−
2), 79−87.
(14) Belanger, D.; Dodelet, J. P.; Lombos, B. A.; Dickson, J. I.
Thickness Dependence of Transport Properties of Doped Polycrystal-
line Tin Oxide Films. J. Electrochem. Soc. 1985, 132 (6), 1398−1405.
(15) Birchall, T.; Faggiani, R.; Lock, C. J. L.; Manivannan, V.
Preparation and Partial Oxidation of Tin (II) Trifluoroacetate:
Spectroscopic Properties and X-Ray Crystal Structure of Di-μ3-Oxo-
Octakis-μ-Trifluoroacetato-Tetratin (II) Tin (IV). J. Chem. Soc.,
Dalton Trans. 1987, No. 7, 1675−1682.
(16) Batchelor, R. J.; Birchall, T.; Johnson, J. P. The Crystal
Structure of Sn6O2(CF3CO2)8·CF3CO2H. Can. J. Chem. 1987, 65 (9),
2187−2193.
(17) Birchall, T.; Johnson, J. P. Crystal Structure of Di-μ3-Oxo-
Octakis-μ-(Trifluoroacetato)-Ditin (II) Ditin (IV)–Benzene (1/1). J.
Chem. Soc., Dalton Trans. 1981, No. 1, 69−73.
(18) Zabula, A. V.; Filatov, A. S.; Petrukhina, M. A. Coordinatively
Unsaturated Polynuclear Mixed-Valent SnII−SnIV and CuII−SnIV Oxo-
Centered Carboxylates. J. Cluster Sci. 2010, 21 (3), 361−370.
(19) Daly, S. R.; Kim, D. Y.; Girolami, G. S. Lanthanide N,N-
Dimethylaminodiboranates as a New Class of Highly Volatile
Chemical Vapor Deposition Precursors. Inorg. Chem. 2012, 51 (13),
7050−7065.
(20) Coyle, J. P.; Sirianni, E. R.; Korobkov, I.; Yap, G. P. A.; Dey, G.;
Barry, S. T. Study of Monomeric Copper Complexes Supported by N-
Heterocyclic and Acyclic Diamino Carbenes. Organometallics 2017,
36 (15), 2800−2810.
(21) Cheng, Y.; Emge, T. J.; Brennan, J. G. Polymeric Cd(Se-2-
NC5H4)2 and Square Planar Hg(Se-2-NC5H4)2: Volatile CVD
Precursors to II-VI Semiconductors. Inorg. Chem. 1994, 33 (17),
3711−3714.
(22) Donaldson, J. D.; Moser, W. 789. Pure Tin (II) Sulphate. J.
Chem. Soc. 1960, 4000−4003.
(23) Anastas, P. T.; Zimmerman, J. B. Peer Reviewed: Design
Through the 12 Principles of Green Engineering. Environ. Sci. Technol.
2003, 37 (5), 94A−101A.
(24) Gao, Y.; Yang, Y.; Zheng, W.; Su, Y.; Zhang, X.; Roesky, H. W.
Germanium and Tin Monoxides Trapped by Oxophilic Germylene
and Stannylene Ligands. Inorg. Chem. 2017, 56 (17), 10220−10225.
(25) Weimer, M. S.; Hu, B.; Kraft, S. J.; Gordon, R. G.; Segre, C. U.;
Hock, A. S. Synthetic and Spectroscopic Study of the Mechanism of
Atomic Layer Deposition of Tin Dioxide. Organometallics 2016, 35
(9), 1202−1208.
(26) Mackus, A. J. M.; MacIsaac, C.; Kim, W.-H.; Bent, S. F.
Incomplete Elimination of Precursor Ligands during Atomic Layer
Deposition of Zinc-Oxide, Tin-Oxide, and Zinc-Tin-Oxide. J. Chem.
Phys. 2017, 146 (5), 052802.
Eigenschaften von Perfluoracyloxy-Verbindungen Der Vierten Gruppe
Des Periodensystems. Chem. Ber. 1967, 100 (6), 2049−2063.
(34) Sawyer, A. K.; Frey, C. A Simple Synthesis of Tin(IV) Acetate
from Tetraphenyltin. Synth. React. Inorg. Met.-Org. Chem. 1983, 13
(2), 259−262.
(35) Janssen, D. E.; Wilson, C. V. 4-Iodoveratrole. Org. Synth. 1963,
36, 46.
(36) Rees, W. S.; Carris, M. W.; Girolami, G. S.; You, Y. Bis(2,2,6,6-
Tetramethyl-3,5-Heptanedionato) Copper. Inorg. Synth. 2007, 286−
288.
(37) Cotton, F. A.; Dikarev, E. V.; Petrukhina, M. A. Syntheses and
Crystal Structures of ″Unligated’’ Copper(I) and Copper(II)
Trifluoroacetates. Inorg. Chem. 2000, 39 (26), 6072−6079.
(38) Birchall, T.; Johnson, J. P. Preparation and Characterization of
Mixed-Oxidation-State Tin Carboxylates and Related Tin (IV)
Carboxylates. Inorg. Chem. 1982, 21 (10), 3724−3731.
(39) Kunte, G. V.; Shivashankar, S. A.; Umarji, A. M.
Thermogravimetric Evaluation of the Suitability of Precursors for
MOCVD. Meas. Sci. Technol. 2008, 19 (2), 025704.
(40) Colominas, C.; Lau, K. H.; Hildenbrand, D. L.; Crouch-Baker,
S.; Sanjurjo, A. Vapor Pressures of the Copper and Yttrium β-
Diketonate MOCVD Precursors. J. Chem. Eng. Data 2001, 46 (2),
446−450.
(41) Bruker. APEX2 v2008.5; Bruker AXS: Madison, WI, 2008.
(42) Bruker. APEX3 v2016.1-0; Bruker AXS: Madison, WI, 2016.
(43) Sheldrick, G. M. SHELXT–Integrated Space-Group and
Crystal-Structure Determination. Acta Crystallogr., Sect. A: Found.
Adv. 2015, 71 (1), 3−8.
(44) Sheldrick, G. M. Crystal Structure Refinement with SHELXL.
Acta Crystallogr., Sect. C: Struct. Chem. 2015, 71 (1), 3−8.
(45) Hubschle, C. B.; Sheldrick, G. M.; Dittrich, B. ShelXle: A Qt
̈
Graphical User Interface for SHELXL. J. Appl. Crystallogr. 2011, 44
(6), 1281−1284.
(46) Dolomanov, O. V.; Bourhis, L. J.; Gildea, R. J.; Howard, J. A.
K.; Puschmann, H. OLEX2: A Complete Structure Solution,
Refinement and Analysis Program. J. Appl. Crystallogr. 2009, 42 (2),
339−341.
(47) Pettersen, E. F.; Goddard, T. D.; Huang, C. C.; Couch, G. S.;
Greenblatt, D. M.; Meng, E. C.; Ferrin, T. E. UCSF Chimera–a
Visualization System for Exploratory Research and Analysis. J.
Comput. Chem. 2004, 25 (13), 1605−1612.
(48) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci,
B.; Petersson, G. A.; et al. Gaussian 09, Revision D.01.
(49) Douglas, M.; Kroll, N. M. Quantum Electrodynamical
Corrections to the Fine Structure of Helium. Ann. Phys. 1974, 82
(1), 89−155.
(50) Hess, B. A. Applicability of the No-Pair Equation with Free-
Particle Projection Operators to Atomic and Molecular Structure
Calculations. Phys. Rev. A: At., Mol., Opt. Phys. 1985, 32 (2), 756.
(51) Hess, B. A. Relativistic Electronic-Structure Calculations
Employing a Two-Component No-Pair Formalism with External-
Field Projection Operators. Phys. Rev. A: At., Mol., Opt. Phys. 1986, 33
(6), 3742.
(27) Stafeeva, V. S.; Mitiaev, A. S.; Abakumov, A. M.; Tsirlin, A. A.;
Makarevich, A. M.; Antipov, E. V. Crystal Structure and Chemical
Bonding in Tin (II) Acetate. Polyhedron 2007, 26 (18), 5365−5369.
(28) Smart, B. A.; Griffiths, L. E.; Pulham, C. R.; Robertson, H. E.;
Mitzel, N. W.; Rankin, D. W. H. Molecular Structure of Tin (II)
Acetate as Determined in the Gas Phase by Electron Diffraction and
Ab Initio Calculations. J. Chem. Soc., Dalton Trans. 1997, No. 9,
1565−1570.
(52) Jansen, G.; Hess, B. A. Revision of the Douglas-Kroll
Transformation. Phys. Rev. A: At., Mol., Opt. Phys. 1989, 39 (11),
6016−6017.
(53) Peverati, R.; Truhlar, D. G. Communication: A Global Hybrid
Generalized Gradient Approximation to the Exchange-Correlation
(29) Alcock, N. W.; Tracy, V. L. Acetates and Acetato Complexes.
IV. The Crystal and Molecular Structure of Tin Tetraacetate. Acta
I
https://dx.doi.org/10.1021/acs.inorgchem.9b01308
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
pubs.acs.org/IC
Article
Functional That Satisfies the Second-Order Density-Gradient
Constraint and Has Broad Applicability in Chemistry. J. Chem.
Phys. 2011, 135 (19), 191102.
(54) Jorge, F. E.; Canal Neto, A.; Camiletti, G. G.; Machado, S. F.
Contracted Gaussian Basis Sets for Douglas−Kroll−Hess Calcu-
lations: Estimating Scalar Relativistic Effects of Some Atomic and
Molecular Properties. J. Chem. Phys. 2009, 130 (6), 064108.
(55) Barros, C. L.; de Oliveira, P. J. P.; Jorge, F. E.; Canal Neto, A.;
Campos, M. Gaussian Basis Set of Double Zeta Quality for Atoms Rb
through Xe: Application in Non-Relativistic and Relativistic
Calculations of Atomic and Molecular Properties. Mol. Phys. 2010,
108 (15), 1965−1972.
(56) Campos, C. T.; Jorge, F. E. Triple Zeta Quality Basis Sets for
Atoms Rb through Xe: Application in CCSD(T) Atomic and
Molecular Property Calculations. Mol. Phys. 2013, 111 (2), 167−173.
(57) Mitzel, N. W.; Smart, B. A.; Blake, A. J.; Robertson, H. E.;
Rankin, D. W. H. Conformational Analysis of 1, 4-Disilabutane and
1,5-Disilapentane by Combined Application of Gas-Phase Electron
Diffraction And ab Initio Calculations and the Crystal Structure of
1,5-Disilapentane at Low Temperatures. J. Phys. Chem. 1996, 100
(22), 9339−9347.
(58) Blake, A. J.; Brain, P. T.; McNab, H.; Miller, J.; Morrison, C. A.;
Parsons, S.; Rankin, D. W. H.; Robertson, H. E.; Smart, B. A.
Structure Analysis Restrained By ab Initio Calculations: The
Molecular Structure of 2,5-Dichloropyrimidine in Gaseous and
Crystalline Phases. J. Phys. Chem. 1996, 100 (30), 12280−12287.
(59) Mitzel, N. W.; Rankin, D. W. H. SARACEN – Molecular
Structures from Theory and Experiment: The Best of Both Worlds.
Dalton Trans. 2003, No. 19, 3650.
(60) Zhao, Y.; Truhlar, D. G. The M06 Suite of Density Functionals
for Main Group Thermochemistry, Thermochemical Kinetics,
Noncovalent Interactions, Excited States, and Transition Elements:
Two New Functionals and Systematic Testing of Four M06-Class
Functionals and 12 Other Function. Theor. Chem. Acc. 2008, 120 (1−
3), 215−241.
(61) Peverati, R.; Truhlar, D. G. Improving the Accuracy of Hybrid
Meta-GGA Density Functionals by Range Separation. J. Phys. Chem.
Lett. 2011, 2 (21), 2810−2817.
(62) Weigend, F.; Ahlrichs, R. Balanced Basis Sets of Split Valence,
Triple Zeta Valence and Quadruple Zeta Valence Quality for H to Rn:
Design and Assessment of Accuracy. Phys. Chem. Chem. Phys. 2005, 7
(18), 3297.
(63) Weigend, F. Accurate Coulomb-Fitting Basis Sets for H to Rn.
Phys. Chem. Chem. Phys. 2006, 8 (9), 1057.
(64) Sipachev, V. A. Calculation of Shrinkage Corrections in
Harmonic Approximation. J. Mol. Struct.: THEOCHEM 1985, 121,
143−151.
(65) Sipachev, V. A. Local Centrifugal Distortions Caused by
Internal Motions of Molecules. J. Mol. Struct. 2001, 567−568, 67−72.
(66) Rankine, C. D.; Nunes, J. P. F.; Feixas, T. W. B. L.; Young, S.;
Wann, D. A. Structure of 4-(Dimethylamino)Benzonitrile Using Gas
Electron Diffraction: A New Lease of Life for the Only Gas Electron
Diffractometer in the U.K. J. Phys. Chem. A 2018, 122 (25), 5656−
5665.
(67) Nunes, J. P. F. Personal Communication. University of York,
Heslington, U.K., 2017.
(68) Hinchley, S. L.; Robertson, H. E.; Borisenko, K. B.; Turner, A.
R.; Johnston, B. F.; Rankin, D. W. H.; Ahmadian, M.; Jones, J. N.;
Cowley, A. H. The Molecular Structure of Tetra-tert-Butyldiphos-
phine: An Extremely Distorted, Sterically Crowded Molecule. Dalton
Trans. 2004, No. 16, 2469−2476.
(69) Wilson, A. J. C. International Tables for Crystallography:
Mathematical, Physical, and Chemical Tables; International Union of
Crystallography: 1992; Vol. 3.
J
https://dx.doi.org/10.1021/acs.inorgchem.9b01308
Inorg. Chem. XXXX, XXX, XXX−XXX