The reaction of phenoxatellurine with single-electron oxidizers revisited

Article abstract of DOI:10.1039/c9nj02401h

The reaction of phenoxatellurine (PT) with the known single-electron oxidizers AlCl₃/CH₂Cl₂, [NO][SbF₆] and [NO][BF₄] provided the diamagnetic products [(PT)CH₂Cl][AlCl₄] (1), [PT₂][SbF₆]₂ (2) and [PT₃][BF₄]₂ (3), respectively, which were fully characterized by X-ray crystallography. The dications [PT₂]²⁺ and [PT₃]²⁺ present in 2 and 3 can be regarded as dimers of the elusive radical cation [PT]⁺ or as adduct between this dimer and neutral PT, respectively. The stacking between the aromatic layers of [PT₂]²⁺ and [PT₃]²⁺ can be best described using the pancake bonding (PB) model. The computational analysis uncovers the essential role of London dispersion effects for the stacking process and reveals the Te-Te interactions to be dominated by non-covalent bonding. The results are compared with those of the related thianthrene (TA) system.

Full text of DOI:10.1039/c9nj02401h

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New Journal of Chemistry - Full Paper
The Reaction of Phenoxatellurine with Single-Electron Oxidizers Revisited
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a
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b*
Farzin Mostaghimi, Enno Lork, Intek Hong, Tracey L. Roemmele, René T. Boeré,
c*
a*
Stefan Mebs, Jens Beckmann
a
Institut für Anorganische Chemie und Kristallographie, Universität Bremen, Leobener Straße 7, 28359
Bremen, Germany
b
Department of Chemistry and Biochemistry, University of Lethbridge, Lethbridge, AB, Canada T1K 3M4
c
Institut für Chemie und Biochemie, Freie Universität Berlin, Fabeckstraße 36a, 14195 Berlin, Germany
Received
Abstract
The reaction of phenoxatellurin€ (PT) with the known single-electron oxidizers AlCl3 /
CH Cl , [NO][SbF ] and [NO][BF ] provided the diamagnetic products [(PT)CH Cl][AlCl ]
2
2
6
4
2
4
(
1), [PT ][SbF ] (2) and [PT ][BF ] (3), respectively, which were fully characterized by X-
2 6 2 3 4 2
2
+
2+
ray crystallography. The dications [PT ] and [PT ] present in 2 and 3 can be regarded as
2
3
+
dimers of the elusive radical cation [PT]˙ or as adduct between this dimer and neutral PT,
2+
2+
respectively. The stacking between the aromatic layers of [PT ] and [PT ] can be best
2
3
described using the pancake bonding (PB) model. The computational analysis uncovers the
essential role of London dispersion effects for the stacking process and reveals the Te-Te
interactions to be dominated by non-covalent bonding. The results are compared with those of
the related thianthrene (TA) system.
*
Correspondence to Jens Beckmann (E-mail: j.beckmann@uni-bremen.de), Stefan Mebs (E-mail:
stebs@chemie.fu-berlin.de) and René T. Boeré (boere@uleth.ca)
1

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DOI: 10.1039/C9NJ02401H
Introduction
As early as 1868, it was noticed that diphenyl disulfide dissolves in conc. sulfuric acid
to give intensely colored solutions. Though unknown at the time, the colour stems from the
+
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thianthrene (TA) radical cation [TA]˙ , which forms after a series of single-electron oxidation
steps (Scheme 1).[1]
Scheme 1.
Serial single-electron oxidation of diphenyl disulfide eventually provides
+
[
TA]˙ (Intermediate species in square brackets have not been isolated).
2
PhS SPh
PhS SPh
PhS SPh
-
e
- e
EPR detection
S
S
2
PhS
-
e
-
2 H
S
S
TA
TA
EPR detection
+
The recognition of the TA radical cation [TA]˙ as member of a unique compound class with
[2]
unpaired electrons arose only a few years after Gomberg’s seminal discovery of the
[3]
triphenylmethyl radical in 1900. Unambiguous proof for the open-shell electronic structure
was provided by the first EPR measurements in 1962.[4-9] Since that time, a great number of
studies dealing with the synthesis, reactivity and its extensive use in organic synthesis have
been reported.[10] The thianthrene radical cation, [TA]˙ , is conveniently prepared by single
electron oxidation from parent thianthrene, TA, using various methods and reagents including
+
HClO / acetic anhydride, SbCl / CHCl , ICl / CCl4,[12] [NO][BF4],[13] AlCl / CH Cl ,
[5]
[11]
[14]
4
5
3
3
2
2
the dodecamethylcarboranyl radical / hexane,[15] by electrolysis in [ Bu N][PF ] / SO ,
n
[16]
4
6
2
[17]
[18]
AlCl / SO
and XeF , Me SiO SCF / CH Cl .
2 3 3 3 2 2
3
2
2

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[TA2]2+
[TA3]2+
[TA3]2+
(crossed triple-decker)
(
double-decker)
(parallel triple-decker)
2
+
2+
Figure 1.
Known structures of [TA ] and [TA ] dications
2 3
Structural characterization of the obtained salts was only achieved much later and revealed
reversible) oligomerisation and electron pairing in the solid state (Figure 1). In 1994, Bock et
al. isolated a diamagnetic dimer in [TA ][AlCl ] comprised of stacks of parallel and eclipsed
(
2
4 2
TA units (double-decker structure).[14] A very similar structural arrangement was found in
[16]
2
009 by Beck et al. in [TA ][PF ] . In 2012, the same group described a diamagnetic trimer
2 6 2
in [TA ][Al Cl ] comprised of stacks of parallel and eclipsed TA units (parallel triple-decker
3
2
7 2
structure),[17] whereas Kochi et al. in 2007 reported a diamagnetic trimer in [TA ][C H B ]
3
13 36 11 2
comprised of stacks of parallel TA rings, in which the central unit is rectangular to two
eclipsed outer units (crossed triple-decker structure).[15] It has been shown by UV-Vis
+
spectroelectrochemistry that, in solution, [TA]˙ is in a concentration-dependent equilibrium
2+ [9]
with its dimer [TA ] .
2
While the TA radical cation has been studied exhaustively, rather little information is
available about radical cations based on dibenzo-1,4-dioxin type heterocycles containing the
heavier chalcogens. A notable exception involves the one-electron oxidation of 9,10-
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DOI: 10.1039/C9NJ02401H
selenanthrene [SeA ], carried out by Beck et. al. in 2012, which provided a dimer [SeA]
2
•+ [17]
[
AlCl ] of the corresponding yet undetected (by EPR) radical cation [SeA] .
4 2
Although these dimeric and trimeric solid-state structures have been established
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unambiguously, the electronic reason for the aggregation remains unclear: in 2005, Nishinaga
and Komatsu proposed in their review that multicentre -bonding between the aromatic rings
is responsible for the aggregation rather than multicenter -bonding between the chalcogen
atoms.[19] This idea is supported by the fact that substituted anthracene radial cations lacking
heteroatoms also undergo oligomerisation, e.g. [OMA ][SbCl ] (OMA = 1,2,3,4,5,6,7,8-
2
6 2
octamethylanthracence)[20] and [TMDMA ][SbCl ] (TMDMA = 2,3,6,7-tetramethoxy-9,10-
3
6 2
dimethylantharacene).[21] Nowadays, it is understood that the multicentre -bonding in radical
dimers is mostly due to the SOMO-SOMO stabilization, which is commonly referred to as
pancake bonding (PB).[22] However, unpaired electrons are not even required for the
oligomerisation. For example, partly protonated phenazine (PA) gives rise to a double-decker
[23]
structure [H-PA ][O SCF ] and a triple-decker structure [(H-PA )(PA)][O SCF ] . In the
2
3
3 2
2
3
3 2
presence of anthracene (AC) a triple-decker structure [(H-PA )(AC)][O SCF ] with different
2
3
3 2
polycylic aromatic hydrocarbons was even formed.[24] For these examples a SOMO-SOMO
stabilization can be clearly ruled out and London dispersion[25] might be exclusively
2
+
responsible for the -bonding. Sophisticated ab initio calculations of the dimers [TA ] and
2
2+
2+
[
SeA ] as well as the parallel and crossed trimers [TA ] suggest that both (multicentre) -
2
3
and -bonding are operative. In all calculated structures, the ground states are singlets and, in
the parallel stacks, intermolecular two-electron/three- or four-center (2e3c or 2e4c) bonds are
formed between the S and Se atoms.[26]
In 1926, Drew discovered a facile route for the synthesis to phenoxatellurin(e) (PT).[27]
He noticed that upon contact with conc. sulfuric acid or nitric acid, intensely colored species
evolve some of which he was able to isolate. While these compounds were characterized only
4

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by combustion analyses at the time, no reference was made to either the parallel behavior of
TA nor to radicals in general. However, in 1929 Witzinger recognized the link between these
dibenzodioxin type heterocycles and suggested that the intensely colored species are radical
cations [PT]˙+,[28] a view that was later reinforced by Gioabă and Gioabă.[29] However, all
attempts to structurally characterize these intensely colored species were deemed unsuccessful
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[30]
and provided only the tellurium(IV) species [PT](NO ) and [PT] O(NO )
3 2
Rotated-disk
3 2
2
voltammetry (RDE) studies on PT by Cauquis and Maurey-Mey in 1973[31] and cyclic-
voltammetry (CV) on related alkoxylated derivatives by Engman et al. in 1988[32] confirmed
single-electron oxidation processes, but EPR characterization of the radical cations was not
achieved. Cauquis and Maurey-Mey concluded not only that dimerisation occurred very
+
rapidly but also that the equilibrium constant, unlike for [TA]˙ , must be very large. The same
authors also succeeded in the isolation of the salt [PT ][ClO ] , which was, however, never
3
4 2
structurally characterized.
We have now reinvestigated the oxidation of PT using the reagents AlCl / CH Cl ,
3
2
2
+
[
NO][BF ] and [NO][SbF ] which were previously employed to prepare salts of [TA]˙ and
4
6
similar species. These reactions provided the salts [(PT)CH Cl]AlCl (1), [PT ][SbF ] ·3.5
2
4
2
6 2
MeCN (2·3.5 MeCN) and [PT ][BF ] ·3 MeCN (3·3 MeCN), which have been fully
3
4 2
2+
2+
characterized by X-ray crystallography and feature [PT ] and [PT ] dications deriving
2
3
+
from dimerisation of the elusive radical cation [PT]˙ (along with an additional molecule of
PT in the latter case). The bonding situation of phenoxatellurin(e) based species PT, [PT]˙+,
2+
2+
[
PT ] and [PT ] has been computationally analyzed by a set of real-space bonding
2 3
indicators (RSBIs), which complement orbital-based studies in comparison with the
∙
+
2+
2+ [17,26]
thianthrene based species TA, [TA] , [TA ] and [TA ] .
2
3
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Results and discussion
Electrochemical studies
The electrochemical oxidation of PT and, for comparison, TA was studied by CV at a
n
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platinum (Pt) electrode using [ Bu N][PF ] as electrolyte in CH Cl , at concentrations
4
6
2
2
relevant to the chemical oxidation reactions. Under these conditions, both PT and TA show
푎
+/0
irreversible oxidations with anodic peak potentials 퐸 = 0.52 V and 0.81 V vs. Fc (Fc =
푝1
ferrocene), respectively (Figure S2). The magnitude of the oxidation peak potentials suggests
that all oxidizing reagents suitable for TA can be also used for PT.[33] A thorough
investigation of the voltammetric behaviour of PT at analytical concentrations was then
n
n
undertaken in both CH Cl /[ Bu N][PF ] and CH CN/[ Bu N][PF ] using square-wave
2
2
4
6
3
4
6
voltammetry (SWV) and CV at both glassy carbon (GC) and Pt electrodes (Table 1). The
experiments in CH Cl are referenced to internal cobaltocenium hexafluorophosphate (Cc),
2
2
+
/0 [34]
which is known to appear at −1.35 ± 0.01 V vs. Fc . The experiments in CH CN are
3
referenced to internal Fc. A typical SWV is presented in Figure 2.
n
Figure 2.
SWV of PT (1.0 mM) at a GC electrode in CH Cl /[ Bu N][PF ] (0.4 M) at RT
2
2
4
6
+
/0
vs. Fc . (a) Background scans showing the accessible solvent/electrolyte window. (b) Anodic
scan on the PT solution.
6

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Table 1.
Voltammetric data for PT in solution
푎
푐
푎
퐼 /μA 퐼푐 퐼푎
푐
푆푊푉
푆푊푉
푆푊푉
Experiment
퐸 /V 퐸 /V
∆
퐸
퐼
퐸
/V
퐸
퐸
23
푝1
푝1
푝1
푝1
1
2
푎 ― 푐
/μA
/V
/V
/mV
+0.60 a
+1.65 a
GC, CH Cl , 0.50 mM +0.561 +0.409 152
13
–13 1.00
–99 0.86
–60 0.41
–13 0.39
–18 0.26
–3 0.6
2
2
GC, CH Cl , 4.0 mM +0.567 +0.192 375
+115
+148
+33
+68
+5
2
2
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
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0
1
2
3
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1
2
3
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9
0
GC, CH Cl , 5.0 mM +0.623 +0.101 522
2
2
b
b
GC, CH CN, 1.0 mM +0.409 +0.327 82
+0.38
+0.36
+0.46
+0.41
+0.41
+1.93 −2.68
+1.97 −2.68
+1.61
3
GC, CH CN, 2.0 mM +0.415 +0.307 108
3
Pt, CH Cl , 0.50 mM +0.590 +0.299 291
2
2
Pt, CH CN, 1.0 mM +0.441 +0.267 175
+9
–3 0.33
–7 0.25
+1.87
+1.87
3
Pt, CH CN, 3.0 mM +0.543 +0.069 474
+28
3
a
b
1
.00 mM, in a separate experiment. Process only observed at this electrode in this solvent.
At the GC electrode, first and second oxidations are observed within the accessible window
n
푆푊푉
= +0.60 and 퐸 푆2 푊푉 = +1.65 V. In CH CN, two oxidations are
for CH Cl /[ Bu N][PF ] at 퐸
2
2
4
6
1
3
also observed at +0.38 and +1.93 V, but this medium also allows observation of a single
reduction peak, 퐸 푆3 푊푉, at −2.68 V. Surprisingly on the Pt electrode, 퐸푆푊푉 = +0.46 in
1
n
푆푊푉
CH Cl /[ Bu N][PF ], i.e. almost the same value as in CH CN (+0.41 V) whereas at GC 퐸
2
2
4
6
3
1
= +0.22 V. To further probe this difference in behaviour, a detailed concentration- and scan
rate-dependent CV study was undertaken. Insight into the voltammetric behaviour is provided
by the concentration dependence, illustrated for example at a GC electrode in CH Cl (Figure
2
2
3
).
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Figure 3.
Anodic scan CVs (0.2 V/s, starting and ending at -0.18 V vs. Fc ) of PT in
DOI: 10.1039/C9NJ02401H
n
CH Cl /[ Bu N][PF ] (0.4 M) at RT on a GC electrode showing the changes with increasing
2
2
4
6
concentration. Referenced using added internal Cc+/0 (not shown).
At sub-analytical concentrations, as in trace (a) at 0.50 mM, the CV response appears quasi-
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8
9
0
1
2
3
4
5
6
7
8
9
0
푐
푎
푎 ― 푐
reversible (QR) with 퐼 퐼 = 1.0 but ∆퐸
= 152 mV. The QR nature of the response is
confirmed by the increase of ∆퐸푎 ― 푐 with increasing scan rate (Figure S4). In the case of PT,
a straightforward explanation for QR behaviour is a slowed heterogeneous electron transfer
rate associated with the large structural changes attending the one-electron oxidation (bent PT
+
vs. planar PT , see below); this corresponds to a large activation energy for the forward and
reverse electron transfer due to flattening or bending, respectively. However, increasing the
concentrations to as little as 1.0 and up to 5.0 mM induces a significant change to an
irreversible CV response (Figure 3b,c), resulting in a strong offset of especially the cathodic
푐
푐
푎
peak potentials 퐸 and an 퐼 퐼 ratio significantly less than 1.0. Chemical and
푝1
•+
spectroelectrochemical evidence (see below) confirms that the cation radical [PT] is not
2
+
2+
destroyed by oxidation, but rather that it associates to dimers [PT ] and trimers [PT ] .
2
3
Hence, the CV behaviour at higher (and synthetically relevant) concentrations is fully
consistent with an electrochemically irreversible but chemically reversible (EirrCrev)
mechanism. The cathodic peak therefore increasingly reflects reduction of the oligomeric
species as their equilibrium concentrations increase. However, in view of the complexity of
the isolated oligomers (dimer and trimer dications isolated; implying that the existence of the
•+
dimeric radical cation [PT ] as an undetected intermediate cannot be excluded), no attempt
2
has been made in this work to analyze the mechanism in detail. We note that a similar
mechanistic proposal was put forward by Cauquis and Maurey-Mey to explain their rotated-
disk voltammetry and bulk electrolysis experiments.[31] There is a strong electrode material
influence on the CV behaviour so that at a Pt electrode the electrochemical irreversibility is
already observed at 0.50 mM and the scan-rate dependent experiments display almost double
8

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the values for ∆퐸푎 ― 푐 for the same scan-rate range (Figure S5). In view of the somewhat View Article Online
DOI: 10.1039/C9NJ02401H
complex E C behaviour, direct comparison of the peak potentials between electrodes is of
irr rev
limited value. However, the data in Table 1 generally indicate that oxidation in CH CN
3
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
should be about 200 mV more facile than in CH Cl .
2
2
Spectroelectrochemistry
UV-Vis spectroelectrochemical measurements of PT and TA reveal new absorptions in the
visible spectrum upon oxidation at max = 380 and 570 nm for PT and at max = 545 nm for
TA, which disappear again upon reduction (Figure S6). This confirms the voltammetric
evidence for an E C mechanism for the 1e oxidation process. All attempts to generate the
irr rev
+
[
PT]˙ radical cation via in-situ spectroelectrochemistry and detect it by EPR spectroscopy
2
+
failed. A high association constant for the [PT ] diamagnetic dimer has been used to
2
rationalize these results.[31]
Synthetic aspects
The reaction of PT with AlCl / CH Cl , a known single-electron oxidizer with an estimated
3
2
2
0
’
+/0 [14,35]
E = +1.1 V vs. Fc ,
proceeded via a two-electron oxidative addition providing the
telluronium(IV) ion in [(PT)CH Cl][AlCl ] (1), a compound isolated as a brown crystalline
2
4
+
solid in yields of 56% (Scheme 2). Nitrosyl ions, [NO ], are also common single-electron
0’
+/0
[ 33]
oxidizers with an E = +1.00 V vs. Fc in CH Cl .
The reaction of PT with NO(SbF ) and
6
2
2
NO(BF ) gave intensely violet-blue solutions, from which [PT ][SbF ] ·3.5 MeCN (2·3.5
4
2
6 2
MeCN) and [PT ][BF ] ·3 MeCN (3·3 MeCN) were isolated as crystalline materials in yields
3
4 2
of 35% and 31%, respectively (Scheme 2). Compounds 2·3.5 MeCN and 3·3 MeCN are
pleochromic. They are violet with an orange luster and dark-blue in reflective light, whereas
smaller fragments are red in transmitted light. All compounds are essentially ionic. The
9

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1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
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5
5
5
5
5
5
5
5
5
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+
2+
2+ View Article Online
molecular structures of the [(PT)CH Cl] cation present in 1 and the [PT ] and [PT ]
2
2
3
DOI: 10.1039/C9NJ02401H
dications present in 2 and 3, respectively, are shown in Figures 4 - 6.
Scheme 2.
Reaction of PT with one-electron oxidizing agents
Cl
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Te
Te
AlCl / CH Cl
2
3
2
[AlCl4]
-
HCl
O
O
1
Te
Te
2
[NO][SbF6]
- 2 NO
2
3
[SbF6]2
2
O
2
O
Te
Te
2 [NO][BF4]
- 2 NO
[BF4]2
3
O
3
O
+
In the first coordination sphere, the Te atom of the [(PT)CH Cl] cation present in 1 is
2
coordinated by 3 C atoms. The exocyclic Te-C bond length of 1 (2.171(2) Å) is longer than
the endocyclic Te-C bond lengths (2.077(2), 2.083(2) Å), which are slightly shorter than those
of the parent PT (2.095(2), 2.099(2) Å). The endocyclic C-Te-C angle of 1 (91.90(8)°) is
slightly increased compared to the parent PT (88.98(6)°). In the crystal lattice, the
+
–
[(PT)CH Cl] cations and [AlCl ] anions of 1 are associated by secondary Te···Cl
2
4
interactions (3.385(2), 3.401(2), 3.449(1) Å). Considering the first and second coordination
spheres, the spatial arrangement at the Te atom is distorted octahedral. The structures of 2 and
2
+
2+
3 feature the [PT ] and [PT ] dications, respectively, possessing stacks of parallel PT
2
3
moieties, similar to those reported for [TA2]2+[14,16] and [TA3]2+[17] (Figure 1).
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1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
+
Figure 4.
Molecular structure of the [(PT)CH Cl] cation present in 1 drawn with 50%
2
–
probability ellipsoids ([AlCl ] omitted).
4
Figure 5.
Molecular structure of the [PT2]2+ dication present in 2 drawn with 50%
–
probability ellipsoids ([SbF ] omitted).
6
Figure 6.
Molecular structure of the [PT3]2+ dication present in 3 drawn with 50%
–
probability ellipsoids ([BF ] omitted).
4
1
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2
2
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2
2
2
2
2
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3
3
3
3
3
3
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2+
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The interlayer Te-Te bond lengths of [PT ] , containing two crystallographically
2
2
+
independent, albeit similar, conformers (2.897(1), 2.903(1) Å) and [PT ] (3.1034(7),
3
3.1381(7) Å), are substantially longer than the Te-Te single bond length in PhTeTePh
2.712(2) Å) and point to bond orders smaller than 1.[36] This situation is typical for PB in
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
(
radical dimers.[23] The Te-C bond lengths and the C-Te-C angles of the [PT ] and [PT ]
2+
2+
2
3
+
dications fall within the range observed for the structures of parent PT and the [(PT)CH Cl]
2
2
+
2+
cation (see above). In the crystal lattice, the Te atoms of the [PT ] and [PT ] dications are
2
3
–
–
associated with F atoms of the [SbF ] and [BF ] counterions, as well as N atoms of CH CN
6
4
3
solvate molecules. The secondary Te···N and Te···F contacts range from 2.882(8) to 3.278(7)
Å and from 2.996(9) to 3.257(7) Å, respectively, in 2 and from 2.951(8) to 3.593(9) Å and
from 2.983(8) to 3.483(6) Å, respectively, in 3. In all structures the PT moieties are
significantly flatter than the parent PT, which adopts a butterfly conformation. The extent of
folding within the butterfly structure can be quantitatively expressed by the fold angle  of
the two planes defined by phenyl rings plus the Te and O atoms (for coplanar rings,  is zero).
For the parent PT[37] and 1 the fold angles  are 37.5° and 17.8°, respectively. The fold angles
2+

of the two independent [PT ] conformers of 2 (Te1: 10.8°, Te2: 15.1° and Te3: 3.4°, Te4:
2
2
+
2
0.8°) and [PT ] of 3 (Te1: 1.1°, Te2: 22.2°, Te3: 33.6°) spread over a larger range, which
3
points to a flat bending potential.
Compounds 1 - 3 are only sparingly soluble in non-polar solvents. The highest
solubility was observed in acetonitrile, from which the NMR data were acquired. The 125Te
NMR spectra (MeCN-D ) of 1 - 3 display only one signal each at  = 562.8, 1896.4 and
3
1
697.1 ppm, respectively, which are shifted to lower frequency compared to the parent PT (
420.0 ppm). The observation that 3 gives rise to only one 125Te resonance points to a
=
dynamic exchange process in solution that occurs fast on the NMR time scale. This is also
13
supported by the C NMR spectrum (CH CN-D ) of 3 that shows only one set of signals
3
3
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suggesting that the PT moieties are equivalent in solution. We hypothesize that this dynamic
2
+
2+
exchange process involves the reversible dissociation of [PT ] into [PT ] and neutral PT.
3
3
This hypothesis is supported by the fact that no EPR signals could be detected from solutions
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
of 2 and 3 in CH CN. In order to predict what such spectra could look like, simulations of
3
•+
•+
EPR spectra were made for [TA] and [PT] based on DFT calculated hyperfine splitting
(
HFS) values (Tables S2,3). The predicted 125Te HFS is extremely small despite a high spin-
density at this nucleus, possibly due to an inadequacy of the basis set. Nevertheless, the low
natural abundance (7%) of 125Te could produce only weak ‘satellites’ of the main signal. For
both radicals, the splitting of the high-abundance signals are to aromatic H atoms and thus are
very small. The expected strong spin-orbit coupling to Te with its large spin density (SD) is
likely to cause extensive line-broadening and potentially to weaken the signal intensity much
more than the simple prediction shown in Table S3. In contrast to the materials isolated by
Drew,[25] 2 and 3 are extremely sensitive to air exposure, both in solution and in the solid-
state. Upon contact with air, the violet and blue colors fade within seconds. Even when the
crystals were covered by perfluorinated oil, fading of the colour was observed after a few
minutes.
Computational Analysis
+
∙+
PT, TA and their radical cations [PT]˙ and [TA] were fully optimized in the gas phase. As
anticipated, the neutral parent molecules PT and TA display butterfly structures, whereas the
+
∙+
radical cations [PT]˙ and [TA] possess planar structures. Results of the atoms-in-molecules
(
AIM) analysis,[38] Electron-Localizability-Indicator (ELI-D)[39] iso-surfaces as well as
electrostatic potentials (ESPs) are shown in Figures 7 and 8. Topological bond descriptors
derived from AIM theory are listed in Table 2. Basin integration provided atomic and
fragmental AIM charges, which are collected in Table 3. The SD of the radical cations [PT]˙+
+
and [TA]˙ is shown in Figure 9.
1
3

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2
2
2
2
2
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3
3
3
3
3
3
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DOI: 10.1039/C9NJ02401H
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9
0
1
2
3
4
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8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Figure 7. (a,d) AIM-topology, (b,e) ELI-D iso-surface (Y = 1.3), and (c,f) ESP (in a.u.)
+
mapped on the 0.001 a.u. ED surface for compounds PT (left) and [PT]˙ (right). For the ESP,
solid and transparent modes are shown.
–
l
The vertical and adiabatic ionization energies of PT (703.13 and 674.02 KJ mol ) and TA
–1
(
731.69 and 684.67 KJ mol ) are surprisingly similar, but overall confirm the trend
established by voltammetry that PT can be oxidized more easily than TA. During the change
from a butterfly to a planar structure upon oxidation, the C-E (E = O, S, Te) bonds become
shorter by 0.02 to 0.04 Å. The ELI-D iso-surfaces display regions of increased electron
localizability, e.g. bonding electrons or lone-pairs. The parent PT and TA monomers show
two spatially separated lone pairs at each chalcogen atom, which shrink and almost fuse
+
+
together upon one-electron oxidation to form [TA]˙ and [PT]˙ . The electron population
within these basins decreases by 0.2 e (S), 0.5 e (O) and 0.7 e (Te), which is counter balanced
by increased electron population of ca. 0.2 e in each E-C bonding basin (E = O, S, Te).
1
4

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1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
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4
4
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5
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5
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5
6
0
1
2
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4
5
6
7
8
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0
1
2
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6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Figure 8. (a,d) AIM-topology, (b,e) ELI-D iso-surface (Y = 1.3), and (c,f) ESP (in a.u.)
+
mapped on the 0.001 a.u. ED surface for compounds TA (left column) and [TA]˙ (right
column). For the ESP, solid and transparent modes are shown.
AIM provides a complementary picture. The basin integration shows that each C H -fragment
6
4
+
+
has lost ca. 0.4 e in [TA]˙ and 0.3 e in [PT]˙ , whereas quite different values of 0.2 e (S), 0.0
e (O), and 0.4 e (Te) are obtained for the chalcogen atoms (Table 3). The electrostatic
potential (ESP) shows negative areas (in red) at the central ring of neutral PT and TA close to
the chalcogen atoms, which after one-electron oxidation turns into the most positive area (in
+
+
purple) for [PT]˙ and [TA]˙ (Figures 7c,f and 8c,f). This is reflected by the SD distribution,
which is also mostly localized at the central ring (Figure 9). The double decker structures of
2
+
2+
2+
2+
[
PT ] and [TA ] as well as the triple decker structures [PT ] and [TA ] were fully
2 2 3 3
characterized in the gas phase, with and without an empirical dispersion correction, which
revealed the importance of London dispersion for the stabilization of the -stacked structures.
1
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2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
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6
Topological bond descriptors derived from AIM theory.†
View Article Online
DOI: 10.1039/C9NJ02401H
Table 2.
2
d
ρ(r)
 ρ(r)
ɛ
G/ρ(r)bcp H/ρ(r)bcp
[a.u.] [a.u.]
0.52
bcp
–3
bcp
–5
model
contact
Te-C
O-C
[Å] [eÅ ]
[eÅ ]
§
(
(
PT)
PT)
2.070
1.361
1.735
0.90
1.94
1.41
0.30
0.25
0.23
0.04
0.04
0.19
0.15
0.05
0.05
0.04
0.05
0.05
–0.6 0.16
–9.2 0.04
–9.0 0.18
0.2 0.04
0.4 0.04
0.5 0.05
0.6 0.79
0.6 4.34
1.0 0.05
1.0 0.06
0.6 1.50
0.6 2.64
0.4 4.25
0.5 2.52
0.5 4.31
–0.56
–1.54
–0.76
–0.19
–0.15
–0.14
0.14
§
1.21
0.31
0.25
0.27
0.28
0.87
0.91
0.45
0.47
0.75
0.57
0.55
0.59
0.58
§
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
(TA)
PT2]
PT2]
PT3]
S-C
2+
[
[
[
Te···Te 3.090
Te···Te 3.203
Te···Te 3.239
2
+
+
+
2
2
[PT2]
[
O···O
O···O
S···S
S···S
3.101
3.173
2.982
3.103
2+
PT3]
TA2]
TA3]
0.17
2
2
+
+
[
[
[
[
[
–0.07
–0.04
0.15
0.14
0.14
PT3]2 O4···C20 3.095
+
2+
PT2]
PT3]
C5···C17 3.321
C9···C22 3.464
C3···C25 3.255
2
+
2
+
[TA2]
[
0.16
0.15
TA3]2+ C9···C31 3.316
†d is the bond distance, ρ(r)bcp is the ED at the bcp,  ρ(r) is the Laplacian of the ED,
2
bcp
ɛ is the bond ellipticity, G/ρ(r)bcp and H/ρ(r)bcp are the respective kinetic and total
§
energy density over ρ(r)bcp ratios. Averaged values for all compounds of this group
2
+
2+
2+
2+
including PT, [PT ] , and [PT ] , or TA, [TA ] , and [TA ] . For atom labels, see
2
3
2
3
supporting information.
Results of the AIM analysis, ELI-D iso-surfaces as well as the non-covalent interaction
NCI)[40] iso-surface analysis are shown in Figures 10 and 11. Stacking of [PT]˙ and [TA]˙
+
+
(
radical cations and related compounds is governed by chalcogen-chalcogen interactions as
well as by C -C -contacts. The importance of the latter becomes especially apparent in simple
π
π
gas-phase calculations of dimers and trimers, which are not restricted by crystal field of
solvation effects. The inclusion of an empirical dispersion correction in the computations
afforded the desired stacked clusters, whereas the organic C H -fragments try to avoid each
6
4
2+
2+
other if such a dispersion correction is lacking. For [TA ] and [TA ] , this leads to
2
3
increased intermolecular S-S distances and increased fold angles  within each molecule
(Figure 11a,b).
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1
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1
1
1
1
1
1
2
2
2
2
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2
2
2
2
2
3
3
3
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3
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3
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3
4
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0
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0
1
2
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0
1
2
3
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0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
•
+
•+
Figure 9. SD of the radical cations [PT] (left) and [TA] (right).
Table 3.
AIM atomic and fragmental charges (in e).
PT [PT]∙+ [PT2]2+ [PT3]2+
TA [TA]∙+ [TA2]2+ [TA3]2+
ph(1)
Te
O
ph(2)
Te
0.30
0.56
–1.17 –1.16
0.59
0.97
0.60
1.00
–1.17
0.57
0.47 ph(1) –0.13
0.78
0.22
0.27
0.13
0.37
0.07
0.22
S
0.11
–1.18
0.51 ph(2)
0.94
0.13
0.37
0.09
0.32
0.98
S
O
–1.17
–1.18
ph(3)
Te
0.50 ph(3)
0.84
0.07
0.24
S
O
–1.17
Frag1 0.00
Frag2
Frag3
0.99
0.99
1.04
0.95
0.54 Frag1 –0.03
0.78 Frag2
0.67 Frag3
0.97
0.97
1.00
1.00
0.59
0.82
0.62
2.04
tot
0.00
2.00
2.00
tot
–0.03
2.01
The two S-S contacts connecting each pair of molecules prevent rotation along the stacking
axis so that the molecules nevertheless remain on top of each other. The individual molecules
in [PT2]2+ and [PT ] , however, are rotated along the Te-Te axis by ca. 90° and 180°,
2+
3
respectively, since the O-O contacts are too weak to prevent rotation (Figure 10a,b). Taking
2
+
2+
2+
into account the dispersion correction, the optimized structures of [PT ] , [PT ] , [TA ]
2
3
2
2+
and [TA ] resemble the parallel stacking also found by X-ray diffraction (Figures 10c,d and
3
2
+
2+
1
1c,d). [TA ] and [TA ] are observed to be centrosymmetric, whereas asymmetric
2 3
2
+
2+
stacking is observed for [PT ] and [PT ] .
2
3
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0
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0
1
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0
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0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Figure 10. AIM-topology of [PT ]2+ and [PT3]2+ without (a,e) and with (b,f) empirical
2
dispersion correction, (c,g) ELI-D iso-surface (Y = 1.3), and (d,h) NCI iso-surface (s(r) = 0.5)
2
+
2+
for compounds [PT ] (left column) and [PT ] (right column).
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1
1
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1
1
1
2
2
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2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
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5
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5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Figure 11. AIM-topology of [TA2]2+ and [TA3]2+ without (a,e) and with (b,f) empirical
dispersion correction, (c,g) ELI-D iso-surface (Y = 1.3), and (d,h) NCI iso-surface (s(r) = 0.5)
2+
2+
for compounds [TA ] (left column) and [TA ] (right column).
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3
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For [TA ] , this leads to the formation of two identical fragments, each of which exhibit a
2
fold angle  of 10.8°, which is between values observed for TA in the gas-phase ( = 46.1°)
+
2+
and the corresponding radical cation [TA]˙ ( = 0°). For [TA ] the outer molecules are
3
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
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9
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0
1
2
3
4
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7
8
9
0
similarly tilted ( = 14.5°), whereas the central molecule is flat. By contrast, the existence of
two different chalcogen atoms, Te and O, in TA reduces the symmetry of its monomers (e.g.
+
from C in TA to C in PT), dimers and trimers. For [PT]˙ the fold angle  is 39.7°. In
2
v
s
2
+
2+
[
PT ] , fold angles  of 21.5° and 4.2° are observed. Corresponding angles  for [PT ] are
2
3
3
6.8°, 23.4°, and 7.9°. These trends are reflected in the electronic bond descriptors (see
below). Interestingly, the basis-set superposition error (BSSE) corrected complexation
2
+
–1
2+
energies (Ecompl) are found to be larger for the dimers [PT ] (–201 kJ mol ) and [TA ] (–
2
2
–
1
2+
–1
2+
–1
232 kJ mol ) than for the trimers [PT ] (–94 kJ mol ) and [TA ] (–161 kJ mol ). Bond
3
3
path analyses according to the topological AIM approach reveal S-S, O-O, or Te-Te
2
+
2+
2+
2+
interactions in compounds [TA ] , [TA ] , [PT ] and [PT ] (Figures 10c,d and
2
3
2
3
11c,d).Additional intermolecular C-C bond paths reflect π-π-contacts. Electronic bonding
parameters at the bond critical points (bcp) for relevant bonds are collected in Table 2. They
include polar-covalent E-C contacts (E = Te, S, O), which are characterized by significant
3
concentration of electron density at the bcp (ED or ρ(r)bcp = 0.9 – 1.9 eÅ ), a negative
2
5
Laplacian ( ρ(r) = –9.2 – –0.6 eÅ ), and a largely negative total energy density over ED
bcp
ratio (H/ρ(r)bcp = –0.6 – –1.5 a.u.). With increasing difference of the electronegativity, bond
polarization increases, which is reflected in the kinetic energy density over ED ratio (G/ρ(r)bcp
=
0.3 (S-C) – 1.2 (O-C) a.u.). Since all E-C bonds are involved in the π-system, bond
ellipticities (ɛ) are larger than 0.1 for Te-C and S-C bonds. As the E-C bonds are almost
unaffected by the stacking, values have been averaged. Long-ranging E-E contacts (d > 3 Å)
3
are characterized by significantly lower ED values (ρ(r)bcp = 0.1 – 0.3 eÅ ), a positive
2
5
Laplacian ( ρ(r) = 0.2 – 1.0 eÅ ), and a small negative or even positive H/ρ(r) = –0.1 –
bcp
bcp
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0
.2 a.u.. Whereas some degree of covalency remains in the S-S and Te-Te contacts, the bond
DOI: 10.1039/C9NJ02401H
characteristics of the O-O contacts already resemble those of the weak C -C contacts, which
π
π
are dominated by non-covalent bonding aspects. The C -C contacts are visible in NCI iso-
π
π
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
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5
6
0
1
2
3
4
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6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
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0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
surfaces as flat and long-ranging light-green and blue regions between the molecules (Figure
0g,h and 11g,h). Small NCI basins are also obtained for S-S and O-O contacts, whereas
1
large, convex and red-colored basins are visible along the Te-Te axis, suggesting attractive
non-covalent Te-Te-bond contributions.
Conclusion
The oxidation of PT using AlCl / CH Cl , [NO][SbF ] and [NO][BF ] afforded the
3
2
2
6
4
diamagnetic salts [(PT)CH Cl][AlCl ] (1), [PT ][SbF ] (2) and [PT ][BF ] (3), which have
2
4
2
6 2
3
4 2
2
+
2+
been fully characterized. The dications [PT ] and [PT ] of 2 and 3 can be regarded as the
2
3
+
dimer of the elusive radical cation [PT]˙ or as an adduct between this dimer and neutral PT,
respectively. The dications crystallize with parallel stacks of PT moieties that are significantly
more planar than their neutral parent PT. These stacks are held together by SOMO-SOMO
interactions and non-covalent Te-Te interactions (PB) as well as London dispersion
interactions.
Experimental Section
General aspects. Reagents were obtained commercially (Sigma-Aldrich, Germany) and were
used as received. Dry solvents were collected from a SPS800 mBraun solvent system. PT was
prepared in two steps according to slightly modified literature procedures (see ESI for
details).[27] 1H-, C- and 125Te-NMR spectra were recorded at RT (unless otherwise stated)
13
1
13
using a Bruker Avance-360 spectrometer and are referenced to tetramethylsilane ( H, C) and
1
25
telluric acid ( Te). Chemical shifts are reported in parts per million (ppm) and coupling
constants (J) are given in Hertz (Hz). Electron impact mass spectrometry (EI-MS) was carried
2
1

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2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
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4
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4
4
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out using a Finnigan MAT 95. The spectra were collected for one minute and averaged. The
spectrum was collected for 30 seconds and averaged. The electrospray ionization mass
spectrometry (ESI-MS) spectrum was also obtained on the Bruker Impact II. Acetonitrile
–
1
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
solutions were injected directly into the spectrometer at a flow rate of 3 μL min . Nitrogen
was used both as a drying gas and for nebulization with flow rates of approximately 4 L/min
and a pressure of 0.4 bar. The spectrum was collected for one minute and averaged.
Electrochemistry and spectroelectrochemistry. CV and UV-Vis spectroelectrochemical
experiments in Bremen were undertaken in a TSC 1600 “Sealable Measuring Cell” provided
by rhd instruments GmbH & Co (Darmstadt, Germany) at glass-sealed Pt wire working and
auxiliary electrodes and a silver wire pseudo reference electrode with added internal Fc for
determining the zero of potential. Experiments were controlled with an Autolab PGSTAT101
supported by Nova 2.1 software (Metrohm AG, Herisau, Switzerland). In a glovebox under
Ar atmosphere, 5.5 mg of PT or 5.7 mg of TA were dissolved in 1.0 mL of 0.1 M
[nBu N][PF ] solutions in CH Cl and transferred to the measuring cell. The cell was sealed
4
6
2
2
and connected to the potentiostat. The measurements were realized with a scan rate of 0.2
−
1
Vs . CV and SWV experiments in Lethbridge used a three-electrode cell with 1.6 mm
diameter Pt or 3.0 mm diameter GC working electrodes (BASi, West Lafayette IN, USA) and
Pt wires for both the auxiliary and pseudo reference electrodes in a nitrogen-filled glove box
n
loaded with the indicated concentrations of PT in either CH Cl /[ Bu N][PF ] (0.4 M) or
2
2
4
6
n
CH CN/[ Bu N][PF ] (0.1 M). CV and SWV experiments were performed using a PARSTAT
3
4
6
2
273 potentiostat via PowerSuite 2.58 software (AMETEK Scientific Instruments, USA).
-1
CVs were performed using scan rates of 0.20-10.0 V s , with all potentials being reported
versus the Fc+/0 redox couple. The electrodes were polished with 0.05 휇m alumina, rinsed
with distilled water and dried with a tissue before use. In-situ EPR spectroelectrochemical
experiments were carried out using a miniature quartz flat cell (Wilmad WG-808) with a Pt
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2

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foil working electrode, and Pt wires as the reference and auxiliary electrodes.[41] The
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measurements were obtained on a Bruker EMXplus spectrometer operating at X-band
frequencies (9.8 GHz). Electrolysis was controlled using a BAS CV50 potentiostat (BASi).
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Synthesis of [(PT)CH Cl][AlCl ] (1). A 100 ml Schlenk flask was charged with AlCl (140
2
4
3
mg, 1.01 mmol) and a solution of PT (300 mg, 1.01 mmol) in dichloromethane (20 ml) was
slowly added. Immediately, the yellow solution turned brown. The solution was stirred for 30
min and was then left standing overnight. The brown crystals that formed were collected by
filtration to give 1 (290 mg, 0.56 mmol, 56%).
1
H-NMR (360 MHz, d -MeCN): δ = 7.40 – 7.93 (m, 12H, C -H), 4.74 (s, 2H, Te-CH -Cl)
3
Ar
2
1
3
ppm. C-NMR (90 MHz, d -MeCN): δ = 154.8 (C -CH-O), 121.1, 126.9, 136.0, 137.2 (C ),
3
Ar
Ar
1
25
1
03.7 (C -CH-Te), 41.1 (Te-CH -Cl) ppm. Te-NMR (110 MHz, d -MeCN): δ = 562.8
Ar 2 3
+
ppm. ESI-MS (CH CN, positive mode): m/z (rel. int.) = 347 (100) [M] , 298 (98)
3
+
–
[
C H OTe] . ESI-MS (CH CN, negative mode): m/z (rel. int.) = 169 (100) [AlCl ] . UV/VIS
1
2
8
3
4
(
CH Cl ): λ = 279 nm, 323 nm.
2
2
max
Sythesis of [PT ][SbF ] (2). A 100 ml Schlenk flask was charged with [NO][SbF ] (900 mg,
2
6 2
6
3
.38 mmol) and a solution of PT (1.00 g, 3.38 mmol) in diethyl ether (20 ml) was slowly
added. Immediately, the yellow solution turned dark violet-blue. The solution was stirred for
0 min and was then left standing overnight. The dark violet single crystals (orange lustre)
3
that formed were collected by filtration to give 2·3.5 NCMe (1.42 g, 0.591 mmol, 35%).
1
H-NMR (360 MHz, d -MeCN): δ = 7.06 – 7.91 (m, 12H, C -H), 1.94 (s, 3H, CH -CN) ppm.
3
Ar
3
1
3
C-NMR (90 MHz, d -MeCN): δ = 120.7, 126.4, 135.6, 136.7 (C ), 102.4 (C -CH-Te),
3
Ar
Ar
1
25
1
52.7 (C -CH-O), 1.3 (CH CN), 117.9 (CH CN) ppm. Te-NMR (110 MHz, d -MeCN): δ
Ar 3 3 3
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3

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2
3
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9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
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5
5
5
5
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=
1896.4 ppm. ESI-MS (CH CN /CH OH 1:10, positive mode): m/z (rel. int.) = 329 (100)
3
3
–
+
+
+
+
[(C H OTe) H (CH OH)] , 315 (18) [C H OTeOH] , 298 (73) [C H OTe] . ESI-MS
12 8 3 12 8 12 8
–
(CH CN /CH OH 1:10, negative mode): m/z (rel. int.) = 495 (95) [Na(SbF ) ] , 235 (100)
3
3
6 2
–
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
[SbF ] . UV/VIS (CH Cl ): λ = 286 nm.
6 2 2 max
Synthesis of [PT ][BF ] (3). A 100 ml Schlenk flask was charged with [NO][BF ] (120 mg,
3
4 2
4
1.01 mmol) and a solution of PT (300 mg, 1.01 mmol) in diethyl ether (20 ml) was slowly
added. Immediately, the yellow solution turned dark violet blue. The solution was stirred for
3
0 min. and was then left standing overnight. The dark blue crystals that formed were
collected by filtration to give 2·3 NCMe (370 mg, 0.104 mmol, 31%).
1
H-NMR (360 MHz, d -MeCN): δ = 7.40 – 8.05 (m, 12H, C -H), 1.94 (s, 3H, CH -CN) ppm.
3
Ar
3
1
3
C-NMR (90 MHz, d -MeCN): δ = 120.2, 124.1, 131.5, 132.1 (C ), 118.4 (C -CH-Te),
3
Ar
Ar
1
25
1
51.2 (C -CH-O), 1.3 (CH CN), 118.2 (CH CN) ppm. Te-NMR (110 MHz, d -MeCN): δ
Ar 3 3 3
=
1697.1 ppm. ESI-MS (CH CN, positive mode): m/z (rel. int.) = 627 (100)
3
+
+
2+
– +
2+
– +
[
M+(C H OTeOH) +CH OH] , 329 (66) [M +CH O ] , 315 (100) [M +OH ] , 298 (23)
12 8 3 3
+
–
[M ]. ESI-MS (CH CN, negative mode): m/z (rel. int.) = 436 (16) [(C H OTeOH)+BF +Cl] ,
3
12
8
4
–
8
7 (100) [BF ] . UV/VIS (CH Cl ): λ = 283 nm.
4 2 2 max
Crystallography. Intensity data of 1, 2·3.5 NCMe, and 2·3 NCMe were collected on a
Bruker Venture D8 diffractometer at 100 K with graphite-monochromated Mo-K (0.7107 Å)
2
radiation. All structures were solved by direct methods and refined based on F using the
SHELX program package as implemented in WinGX.[42] All non-hydrogen atoms were
refined using anisotropic displacement parameters. Hydrogen atoms attached to carbon were
included in geometrically calculated positions using a riding model. Crystal and refinement
data are collected in Table 4. Figures were created using DIAMOND.[43]
2
4

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Table 4.
Crystal data and structure refinement of 1 2·3.5 NCMe and 3·3 NCMe.
,
1
2·3.5 NCMe
3·3 NCMe
Formula
C H AlCl OTe
C H F N O Sb Te C H B F N O Te
62 53 24 7 4 4 4 42 33 2 8 3 3 3
13 10
5
Formula weight, g mol–1
2413.51
1184.13
514.04
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
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4
4
4
4
4
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5
5
5
5
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5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
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Crystal system
Crystal size, mm
Space group
a, Å
monoclinic
triclinic
triclinic
0.15  0.05  0.03
0.07  0.06  0.05
P1
0.09  0.09  0.07
P1
P2 /c
1
10.4998(5)
13.2979(7)
13.2281(7)
7.8579(4)
13.2378(7)
36.414(2)
11.2438(6)
13.7621(8)
14.1152(7)
92.195(3)
b, Å
c, Å
, º
90
87.470(2)
89.732(2)
84.874(2)
, º
107.021(2)
90
104.598(3)
101.316(3)
2063.7(2)
2
, º
V, Å3
1766.1(2)
4
3769.0(3)
2
Z
calcd, Mg m–3
 (Mo Kα), mm–1
F(000)
1.933
2.127
1.906
2.484
3.044
2.187
984
2268
1136

range, deg
2.22 to 28.37
2.33 to 27.61
2.42 to 30.10
–15  h  15
–19  k  19
–19  l  19
76825
Index ranges
–14  h  14
–10  h  10
–16  k  17
–47  l  47
83412
–
–
17  k  17
17  l  17
No. of reflns collected
Completeness to  max
No. indep. Reflns
46773
99.5%
4398
98.2%
99.5%
17186
10990
No. obsd reflns with (I>2(I)) 3918
13959
7531
No. refined params
190
948
553
GooF (F2)
1.044
1.097
1.285
R1 (F) (I > 2(I))
0.0214
0.0550
0.0644
2
wR (F ) (all data)
0.0519
0.1210
0.1102
2
Largest diff peak/hole, e Å–3
CCDC number
1.022 / –0.457
1895454
2.105 / –1.615
1895455
1.545 / –1.013
1895456
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View Article Online
DOI: 10.1039/C9NJ02401H
Crystallographic data for the structural analyses have been deposited with the Cambridge
Crystallographic Data Centre. Copies of this information may be obtained free of charge from
The Director, CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (Fax: +44-1223-336033; e-
mail: deposit@ccdc.cam.ac.uk or http://www.ccdc.cam.ac.uk).
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Computational Methodology. Starting from XRD atomic coordinates, geometry
+
2+
2+
+
2+
2+
optimizations of PT, [PT]˙ , [PT ] and [PT ] as well as TA, [TA]˙ ,[TA ] and [TA ] , in
2
3
2
3
the gas phase were performed at the B3PW91/6-311+G(2df,p)[44] level of theory using
Gaussian09.[45] For the Te atoms, effective core potentials (ECP28MDF) and a corresponding
cc-pVTZ basis set were applied.[44] The resulting wavefunction files were used for topological
analysis of the electron density (ED) according to the Atoms-In-Molecules[38] space-
partitioning scheme using AIM2000,[45] whereas DGRID[46] was used to generate and analyze
the ELI-D related real-space bonding descriptors applying a grid step size of 0.05 a.u.. NCI
grids were computed with NCIplot.[47] Bond paths are displayed with AIM2000,[45] ELI-D,
ESP, and NCI figures are displayed with MolIso.[48] AIM affords atomic basins which can be
integrated to give volumes and charges. In addition, a bond paths motif is provided, which
resembles the molecular structure and uncovers all kind of atom-atom interactions, from very
weak to strong.[49] Other RSBI derived from the ED include spin densities (SDs), the
2
1/3
4/3
electrostatic potential (ESP), and the reduced density gradient, s(r) = [1/2(3π ) ]|ρ|/ρ ,
following to the Non-Covalent Interactions (NCI) index[50] method. The latter is especially
useful to uncover non-covalent bonding regions. Mapping the ED times the sign of the second
eigenvalue of the Hessian (sign(λ )ρ) on iso-surfaces of s(r) facilitates the assignment of
2
different contact types including non-bonding/repulsive (λ > 0), Van-der-Waals like (λ ≈ 0),
2
2
and attractive (λ < 0). A proper tool for the investigation of covalent (including dative) bonds
2
is given by the topological dissection of the pair-density according to ELI-D[39] approach,
which provides core, bonding and lone-pair basins. Notably, ELI-D and NCI iso-surfaces
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often show complementary spatial distribution suggesting spatial separation of covalent and
non-covalent bonding aspects.[51] The combination of all RSBI allows to monitor electronic
rearrangements due to structural changes, which is highly relevant e.g. for strained systems,
ligand variation, or unusual bonds.
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Conflicts of interest
There are no conflicts to declare.
Acknowledgements
The Deutsche Forschungsgemeinschaft (DFG) and the Natural Sciences and Engineering
Research Council (NSERC-Canada) are gratefully acknowledged for financial support.
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