Unexpected reactivity and coordination in gallium(III) and indium(III) chloride complexes with geometrically constrained thioand selenoether ligands

Article abstract of DOI:10.1021/ic202670v

Reaction of GaCl₃with 1 mol equiv of [14]aneS₄in anhydrous CH₂Cl₂gives the exocyclic chain polymer [GaCl₃([14]-aneS₄)] (1) whose structure confirms trigonal bipyramidal coordination at Ga with a planar GaCl₃unit. In contrast, using [16]aneS₄and GaCl₃or [16]aneSe₄and MCl₃(M = Ga or In) in either a 1:1 or a 1:2 molar ratio produces the anion-cation complexes [GaCl₂([16]aneS₄)][GaCl ₄] (2) and [MCl₂([16]-aneSe₄)][MCl₄] (M = Ga, 3 and M = In, 4) containing transoctahedral cations with endocyclic macrocycle coordination. The ligand-bridged dimer [(GaCl₃) ₂{o-C₆H₄(SMe)₂}] (5) is formed from a 2:1 mol ratio of the constituents and contains distorted tetrahedral Ga(III). This complex is unusually reactive toward CH₂Cl₂, which is activated toward nucleophilic attack by polarization with GaCl₃, producing the bis-sulfonium species [o-C₆H₄(SMeCH ₂Cl)₂][GaCl₄]₂(6), confirmed from a crystal structure. In contrast, the xylyl-based dithioether gives the stable [(GaCl₃)₂{o-C₆H₄(CH ₂SEt)₂}] (8). However, replacing GaCl₃with InCl₃with o-C₆H₄(CH₂SEt) ₂preferentially forms the 4:3 In:L complex [(InCl₃) ₄{o-C₆H₄(CH₂SEt)₂} ₃] (9) containing discrete tetranuclear moieties in which the central In atom is octahedrally coordinated to six bridging Cl's, while the three In atoms on the edges have two bridging Cl's, two terminal Cl's, and two mutually trans S-donor atoms from different dithioether ligands. GaCl₃also reacts with the cyclic bidentate [8]aneSe₂to form a colorless, extremely air-sensitive adduct formulated as [(GaCl₃) ₂([8]aneSe₂)] (10), while InCl₃gives [InCl ₃([8]aneSe₂)] (14). Very surprisingly, 10 reacts rapidly with O₂gas to give initially the red [{[8]aneSe₂} ₂][GaCl₄]₂(11) and subsequently the yellow [{[8]aneSe₂}Cl][GaCl₄] (12). The crystal structure of the former confirms a dimeric [{[8]aneSe₂}₂] ²⁺dication, derived from coupling of two mono-oxidized {[8]aneE ₂}_+·cation radicals to form an Se-Se bond linking the rings and weaker transannular 1,5-Se···Se interactions across both rings. The latter (yellow) product corresponds to discrete doubly oxidized {[8]aneSe₂}²⁺cations (with a primary Se-Se bond across the 1,5-positions of the ring) with a Cl^-bonded to one Se. Tetrahedral [GaCl₄]^-anions provide charge balance in each case. These oxidation reactions are clearly promoted by the Ga(III) since [8]aneSe₂itself does not oxidize in air. The new complexes have been characterized in the solid state by IR and Raman spectroscopy, microanalysis, and X-ray crystallography where possible. Where solubility permits, the solution characteristics have been probed by ¹H, ¹Se{ ¹H}, and ¹Ga NMR spectroscopic studies.

Full text of DOI:10.1021/ic202670v

Article
pubs.acs.org/IC
Unexpected Reactivity and Coordination in Gallium(III) and
Indium(III) Chloride Complexes With Geometrically Constrained Thio-
and Selenoether Ligands
Kathryn George,† Marek Jura,‡ William Levason,† Mark E. Light,† Luke P. Ollivere,† and Gillian Reid*,†
†School of Chemistry, University of Southampton, Southampton, United Kingdom SO17 1BJ
‡ISIS, STFC, Harwell Innovation Campus, Didcot, Oxfordshire, United Kingdom OX11 0QX
S
* Supporting Information
ABSTRACT: Reaction of GaCl3 with 1 mol equiv of [14]aneS4 in
anhydrous CH2Cl2 gives the exocyclic chain polymer [GaCl3([14]-
aneS4)] (1) whose structure confirms trigonal bipyramidal
coordination at Ga with a planar GaCl3 unit. In contrast, using
[16]aneS4 and GaCl3 or [16]aneSe4 and MCl3 (M = Ga or In) in
either a 1:1 or a 1:2 molar ratio produces the anion−cation
complexes [GaCl2([16]aneS4)][GaCl4] (2) and [MCl2([16]-
aneSe4)][MCl4] (M = Ga, 3 and M = In, 4) containing trans-
octahedral cations with endocyclic macrocycle coordination. The
ligand-bridged dimer [(GaCl3)2{o-C6H4(SMe)2}] (5) is formed
from a 2:1 mol ratio of the constituents and contains distorted
tetrahedral Ga(III). This complex is unusually reactive toward
CH2Cl2, which is activated toward nucleophilic attack by polarization with GaCl3, producing the bis-sulfonium species [o-
C6H4(SMeCH2Cl)2][GaCl4]2 (6), confirmed from a crystal structure. In contrast, the xylyl-based dithioether gives the stable
[(GaCl3)2{o-C6H4(CH2SEt)2}] (8). However, replacing GaCl3 with InCl3 with o-C6H4(CH2SEt)2 preferentially forms the 4:3
In:L complex [(InCl3)4{o-C6H4(CH2SEt)2}3] (9) containing discrete tetranuclear moieties in which the central In atom is
octahedrally coordinated to six bridging Cl’s, while the three In atoms on the edges have two bridging Cl’s, two terminal Cl’s, and
two mutually trans S-donor atoms from different dithioether ligands. GaCl3 also reacts with the cyclic bidentate [8]aneSe2 to
form a colorless, extremely air-sensitive adduct formulated as [(GaCl3)2([8]aneSe2)] (10), while InCl3 gives [InCl3([8]aneSe2)]
(14). Very surprisingly, 10 reacts rapidly with O2 gas to give initially the red [{[8]aneSe2}2][GaCl4]2 (11) and subsequently the
yellow [{[8]aneSe2}Cl][GaCl4] (12). The crystal structure of the former confirms a dimeric [{[8]aneSe2}2]2+ dication, derived
from coupling of two mono-oxidized {[8]aneE2}+• cation radicals to form an Se−Se bond linking the rings and weaker
transannular 1,5-Se···Se interactions across both rings. The latter (yellow) product corresponds to discrete doubly oxidized
{[8]aneSe2}2+ cations (with a primary Se−Se bond across the 1,5-positions of the ring) with a Cl− bonded to one Se. Tetrahedral
[GaCl4]− anions provide charge balance in each case. These oxidation reactions are clearly promoted by the Ga(III) since
[8]aneSe2 itself does not oxidize in air. The new complexes have been characterized in the solid state by IR and Raman
spectroscopy, microanalysis, and X-ray crystallography where possible. Where solubility permits, the solution characteristics have
1
been probed by H, 77Se{1H}, and 71Ga NMR spectroscopic studies.
confined spaces such as narrow pores or trenches has prompted
development of their coordination chemistry and organo-
metallic chemistry to provide molecular reagents for these
purposes.4 Third, the trivalent ions in Group 13 (Al, Ga, and
In) are important Lewis acids in organic/organometallic
transformations and catalysis.5 Finally, the need for a more
thorough understanding of their fundamental chemistry so that
the key differences between the coordination behavior of p-
block ions and d-block ions may be better understood. Within
this context, factors such as ligand denticity, donor type(s), and
architecture combined with the lability inherent to closed-shell
INTRODUCTION
■
Renewed interest in the coordination chemistry of p-block
elements1 can be attributed to several influences. First, the
increased use and availability of certain isotopes of these
elements for radiopharmaceutical applications in imaging and
therapy (e.g., 68Ga, 111In, 113mIn, 117mSn, 123I)1,2 and as
molecular carriers for 18F in PET applications, e.g., in Al−F
complexes based upon carboxylate derivatives of 1,4,7-
triazacyclononane which are attracting interest at present,3
demands a much more thorough understanding of their
coordination chemistry. Second, the importance of many of
the p-block elements in III−V and III−VI semiconductors and
other electronic materials together with the increased focus on
controlling deposition of the materials as thin films or into
Received: October 17, 2011
Published: January 27, 2012
© 2012 American Chemical Society
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Inorganic Chemistry
Article
Preparations. [GaCl3([14]aneS4)] (1). [14]aneS4 (0.053 g, 0.20
mmol) was dissolved in CH2Cl2 (5 mL) and added to a solution of
GaCl3 (0.035 g, 0.20 mmol) dissolved in CH2Cl2 (5 mL) with
constant stirring. After 45 min the volume of the solvent was reduced
in vacuo to 5 mL. Colorless crystals suitable for X-ray diffraction
studies were obtained from the solution which was kept in a freezer for
several days. Yield: 0.073 g, 83%. Anal. Calcd for C10H20Cl3GaS4·1/
systems and variations in ionic radii are key considerations
within the p-block, although how they combine to produce the
observed chemistry is often unclear.
The increasing ionic radii of the elements and trivalent ions
down Group 13 results in four coordination being prevalent for
Al(III) and Ga(III) with most common ligands, except for
those based upon hard anionic mixed N/O-donor systems,
where five- and six-coordinate species can occur.2a In contrast,
five and more commonly six coordination dominates with the
larger In(III) ion. In an earlier paper we reported the first
systematic series of Ga(III) halide complexes involving neutral
(soft) thio- and selenoether ligands, specifically mono-, bi-, and
tripodal tridentate ligands incorporating various linking back-
1
2CH2Cl2: C, 25.9; H, 4.3. Found: C, 26.0; H, 4.0. H NMR (CD2Cl2,
295 K): 2.07 (quin, [4H], CH2CH2CH2), 2.90 (t, [8H], SCH2CH2),
3.01 (s, [8H], SCH2CH2S), 5.3 (s, CH2Cl2). IR (cm−1, Nujol): 381
(s,br). Raman (cm−1): 386 (w), 331 (s).
[GaCl2([16]aneS4)][GaCl4] (2). [16]aneS4 (0.025 g, 0.08 mmol) was
dissolved in anhydrous CH2Cl2 (10 mL) and added to a solution of
GaCl3 (0.030 g, 0.17 mmol) in anhydrous MeCN (5 mL) with
constant stirring. After 30 min the volume of the solvent was reduced
in vacuo to 7 mL. A white precipitate was obtained from the solution,
which was kept in the freezer overnight. Colorless crystals suitable for
X-ray diffraction studies were also obtained from the solution. Yield:
0.037 g, 68% (combined). The bulk solid and crystals are
spectroscopically identical. Microanalytical measurements showed
variable %C and %H values but always lower than predicted, and
data on the crystals gave values which decreased steadily during
n
bone architectures and terminal substituents (Me, Ph, Bu). A
combination of solution NMR spectroscopic data and single-
crystal X-ray structural studies on these and related species
reported subsequently showed that neutral complexes based
upon distorted tetrahedral Ga(III) (X3E donor set; E = S or Se)
were the only species observed, irrespective of ligand denticity,
and that displacement of coordinated halide did not occur.6 We
noted then that these observations contrasted with those for
Ga(III) complexes with diphosphines and diarsines where
neutral pseudo-tetrahedral X3P/As coordination, cationic
pseudo-tetrahedral X2P2/As2 coordination, and pseudo-octahe-
dral X2P4 coordination have been observed depending upon the
steric and electronic properties of the phosphine/arsine
employed.7 On the other hand, InX3 show much wider
coordination chemistry with similar chalcogenoether ligands,
forming both distorted tetrahedral and octahedral species as
well as incorporating higher chalcogen:M ratios cf. Ga.8 In an
effort to gain further insights into the factors that influence the
coordination chemistry of Ga(III) and In(III) and to explore
this chemistry in more detail, we have undertaken a study of
MCl3 (M = Ga and In) with a series of macrocyclic thio- and
selenoethers and with the (semi)rigid dithioethers o-
C6H4(SMe)2 and o-C6H4(CH2SEt)2. This work has established
that a much wider range of complexes with differing
coordination numbers and geometries exists as well as
unprecedented reaction chemistry. These results are described
herein.
1
analysis, suggesting decomposition. H NMR (CD2Cl2, 295 K): 2.14
(quin, [8H], SCH2CH2), 2.95 (t, [16H], SCH2CH2). IR (cm−1,
Nujol): 368 (br), 301 (br). Raman (cm−1): 370 (w), 346 (s). 71Ga
NMR: CD2Cl2, no resonance observed; MeCN, 251 ppm ([GaCl4]−).
[GaCl2([16]aneSe4)][GaCl4] (3). [16]aneSe4 (0.07 g, 0.14 mmol)
was dissolved in CH2Cl2 (10 mL) and added to a solution of GaCl3
(0.05 g, 0.28 mmol) in CH2Cl2 (5 mL) with constant stirring. After 45
min the volume of the solvent was reduced in vacuo to 7 mL.
Colorless crystals suitable for X-ray diffraction studies were obtained
from the solution which was kept in a freezer for several days. Yield:
0.059 g, 50%. Anal. Calcd for C12H24Cl6Ga2Se4: C, 17.2; H, 2.9.
1
Found: C, 16.9; H, 2.6. H NMR (CDCl3, 295 K): 2.15 (quin, [8H],
CH2CH2CH2), 2.85 (t, [16H], SeCH2). 77Se{1H} NMR (CD2Cl2, 295
K) 138. IR (cm−1, Nujol): 371 (s). Raman (cm−1): 373 (w), 346 (s).
[InCl2([16]aneSe4)][InCl4] (4). [16]aneSe4 (0.22 g, 0.45 mmol) was
dissolved in CH2Cl2 (5 mL) and added to a suspension of InCl3 (0.10
g, 0.45 mmol) in CH2Cl2 (5 mL) with constant stirring. After 30 min
the white solid was collected by filtration. The volume of the filtrate
was reduced in vacuo to 5 mL. Colorless crystals suitable for X-ray
diffraction studies were obtained from the filtrate which was kept in a
freezer for several days. Yield: 0.127 g, 40% (combined). The bulk
solid and crystals are spectroscopically identical. Anal. Calcd for
1
C12H24Cl6In2Se4: C, 15.5; H, 2.6. Found: C, 15.3; H, 2.4. H NMR
(CDCl3, 295 K): 2.07 (quin, [8H], CH2CH2CH2), 2.71 (t, [16H],
SeCH2). 77Se{1H} NMR (CD2Cl2, 295 K): 158. 115In NMR (CD2Cl2,
298 K): 446 ([InCl4]−). IR (cm−1, Nujol): 338 (s), 323 (m), 275 (m).
Raman (cm−1) 346 (w), 336 (w), 320 (s), 281 (s), 242 (s).
EXPERIMENTAL SECTION
■
Infrared spectra were recorded as Nujol mulls between CsI plates
using a Perkin-Elmer Spectrum100 spectrometer over the range
4000−200 cm−1. Raman spectra were obtained using a Perkin-Elmer
FT2000R with a Nd:YAG laser. Significant bands in the range 400−
[(GaCl3)2{o-C6H4(SMe)2}] (5). GaCl3 (0.22 g, 1.24 mmol) was
dissolved in CH2Cl2 (5 mL), and o-C6H4(SMe)2 (0.11 g, 0.62 mmol)
was added dropwise with constant stirring. The solution was stirred for
a further 10 min and then concentrated in vacuo, yielding a pale
orange precipitate. The product was filtered off, washed with hexane
(3 mL), and dried in vacuo. Yield: 0.22 g, 68%. Anal. Calcd for
C8H10Cl6Ga2S2: C, 18.4; H, 1.9. Found: C, 19.0; H, 2.4. IR (cm−1,
1
200 cm−1 are listed below. H NMR spectra were recorded in CDCl3
or CD2Cl2 unless otherwise stated using a Bruker AV300
spectrometer. 71Ga, 77Se{1H}, and 115In NMR spectra were recorded
using a Bruker DPX400 spectrometer and are referenced to aqueous
[Ga(H2O)6]3+ (71Ga), neat Me2Se (77Se), and aqueous [In(H2O)6]3+
at pH = 1 (115In). Electrospray (ES) MS data were obtained from
solutions in MeCN using a VG Biotech Platform. Microanalyses were
undertaken by Medac Ltd. Solvents were dried by distillation prior to
use: CH2Cl2 from CaH2, hexane from sodium benzophenone ketyl.
GaCl3, InCl3, [14]aneS4 (1,4,8,11-tetrathiacyclotetradecane), and
[16]aneS4 (1,5,9,13-tetrathiacyclohexadecane) (Aldrich) were used
as received. Ligands [8]aneSe2 (1,5-diselenocyclooctane), [16]aneSe4
(1,5,9,13-tetraselenacyclohexadecane),9 o-C6H4(SMe)2,10 o-
C6H4(CH2SEt)2,11 C(CH2SMe)4, C(CH2SeMe)4, and 1,2,4,5-
1
Nujol): 395(br), 366(sh). H NMR (CDCl3, 295 K): 2.92 (s, [6H],
Me), 7.6−7.7 (m, [4H], aromatic CH). 71Ga NMR: (CH2Cl2, 295 K):
250 (w1/2 = 1100 Hz).
[o-C6H4(SMeCH2Cl)2][GaCl4]2 (6). A solution of [(GaCl3)2{o-
C6H4(SMe)2}] in anhydrous CH2Cl2 was left to stand at −20 °C
under an inert atmosphere for ca. 1 week, furnishing a small number of
pale yellow crystals shown by X-ray crystallographic analysis to be [o-
C6H4(SMeCH2Cl)2}][GaCl4]2. Positive-ion ESMS (MeCN) on the
crystals: found m/z = 219 [o-C6H4(SMe)(SMeCH2Cl)]+. Negative-
ion ESMS (MeCN): found m/z = 211 [GaCl4]−. IR (cm−1, Nujol):
381 (s).
12
C6H2(CH2SMe)4 were prepared via literature methods or minor
modifications thereof. All preparations were performed under an
atmosphere of dry N2 using Schlenk techniques, and spectroscopic
samples were prepared in a dry N2-purged glovebox.
[InCl3{o-C6H4(SMe)2}] (7). InCl3 (0.22 g, 1.0 mmol) was suspended
in CH2Cl2 (7 mL), and o-C6H4(SMe)2 (0.17 g, 1.0 mmol) was added
dropwise with constant stirring. The solution was stirred for a further 1
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Inorganic Chemistry
Article
a
Table 1. Crystal Data and Structure Refinement Details
1
2
3
4
formula
M
C10H20Cl3GaS4
444.57
C12H24Cl6Ga2S4
648.69
C12H24Cl6Ga2Se4
836.29
orthorhombic
Pbca (no. 61)
9.9535(10)
21.461(4)
23.331(4)
90
C12H24Cl6In2Se4
926.49
cryst syst
space group
a [Å]
monoclinic
C2/c (no. 15)
21.781(4)
6.5370(10)
12.307(2)
90
monoclinic
P21/n (no. 14)
14.503(4)
21.168(5)
15.591(3)
90
monoclinic
P21/m (no. 11)
6.9436(15)
22.508(5)
8.4877(15)
90
b [Å]
c [Å]
α [deg]
β [deg]
γ [deg]
U [Å3]
Z
108.560(10)
90
100.711(10)
90
90
100.735(10)
90
90
1661.2(5)
4
4703.1(18)
8
4983.7(14)
8
1303.3(4)
2
−1
μ(Mo Kα) [mm ]
total reflns
2.622
3.325
8.646
7.967
10 950
31 853
31 334
5697
14 834
unique reflns
Rint
1897
8246
3064
0.0264
0.123
0.055
0.082
no. of params, restraints
83, 0
439, 0
217, 0
115, 0
b
R1 [Io > 2σ(Io)]
0.019
0.098
0.037
0.065
R1 [all data]
0.021
0.189
0.056
0.118
b
wR2 [Io > 2σ(Io)]
0.041
0.210
0.075
0.101
wR2 [all data]
0.042
0.267
0.085
0.120
6
8
9·2CH2Cl2
11
12·CH2Cl2
formula
C10H14Cl10Ga2S2
692.27
C12H18Cl6Ga2S2
578.52
monoclinic
C2/c (no. 15)
18.561(4)
10.809(3)
13.495(3)
90
C38H58Cl16In4S6
1733.68
monoclinic
C2/c (no. 15)
24.016(5)
18.726(5)
14.995(4)
90
C12H24Cl8Ga2Se4
907.19
C7H14Cl7GaSe2
573.97
M
cryst syst
space group
a [Å]
monoclinic
P21/c (no. 14)
9.4813(15)
14.009(3)
18.403(3)
90
monoclinic
P21/n (no. 14)
9.0156(15)
14.148(3)
10.4855(15)
90
monoclinic
P21/n (no. 14)
7.3566(10)
12.521(2)
18.670(3)
90
b [Å]
c [Å]
α [deg]
β [deg]
104.377(10)
90
126.201(5)
90
114.76(2)
90
99.204(10)
90
93.107(10)
90
γ [deg]
U [Å3]
2367.9(6)
4
3.384
6123(3)
4
1320.2(4)
2
1717.2(4)
4
Z
4
μ(Mo Kα) [mm−1]
total no. reflns
unique reflns
Rint
3.576
3.384
2.419
8.365
6.908
27 701
11 619
2500
69 930
16 831
17 301
5415
7092
3030
3907
0.066
0.0425
100, 0
0.1492
0.042
0.0349
no. of params, restraints
217, 0
290, 0
118, 0
154, 0
b
R1 [Io > 2σ(Io)]
0.073
0.074
0.083
0.027
0.020
R1 [all data]
0.099
0.103
0.123
0.0355
0.024
b
wR2 [Io > 2σ(Io)]
0.181
0.126
0.146
0.0527
0.0486
wR2 [all data]
0.199
0.140
0.160
0.056
0.051
a
b
2
Common items: temperature = 120 K; wavelength (Mo Kα) = 0.71073 Å; θ(max) = 27.5°. R1 = Σ||Fo| − |Fc||/Σ|Fo|. wR2 = [Σw(Fo − Fc2)2/
4
ΣwFo ]1/2
.
h and filtered, and the solid was washed with CH2Cl2 (5 mL). The
product was then dried in vacuo to yield a white solid. Yield: 0.20 g,
51%. Anal. Calcd for C8H10Cl3InS2: C, 24.5; H, 2.6. Found: C, 24.3; H,
2.6. IR (cm−1, Nujol): 302 (s), 257 (s). Raman (cm−1): 307 (s), 280
(s). 1H NMR (CDCl3, 295 K): 2.50 (s, [6H], Me), 7.1−7.4 (m, [4H],
aromatic CH).
[(GaCl3)2{o-C6H4(CH2SEt)2}] (8). GaCl3 (0.22 g, 1.24 mmol) was
dissolved in CH2Cl2 (5 mL), and o-C6H4(CH2SEt)2 (0.14 g, 0.62
mmol) was added dropwise. The solution was stirred for a further 10
min and then concentrated in vacuo, yielding a pale yellow precipitate.
The product was filtered off, washed with cold CH2Cl2 (3 mL), and
dried in vacuo. Yield: 0.23 g, 64%. Crystals were grown from the
filtrate stored at −20 °C for 2 days. Anal. Calcd for C12H18Cl6Ga2S2:
C, 24.9; H, 3.1. Found: C, 24.5; H, 2.5. IR (cm−1, Nujol): 394 (s), 357
(m). 1H NMR (d6-acetone, 295 K): 1.23 (t, [6H], 3J = 6 Hz,
CH2CH3), 2.50 (q, [4H], CH2CH3), 3.94 (s, [4H], SCH2Ar), 7.2−7.4
(m, [4H], aromatic CH). 71Ga NMR: (CH2Cl2, 295 K): 233 (w1/2
=
10 000 Hz).
[(InCl3)4{o-C6H4(CH2SEt)2}3] (9). InCl3 (0.22 g, 1.0 mmol) was
suspended in CH2Cl2 (7 mL), and o-C6H4(CH2SEt)2 (0.23 g, 1.0
mmol) was added dropwise with constant stirring. After 1 h the solid
was filtered to remove undissolved InCl3, and the filtrate was placed in
the freezer at −18 °C for 2 weeks to give colorless crystals. Yield:
0.043 g, 10%. Anal. Calcd for C36H54Cl12In4S6·2CH2Cl2: C, 26.3; H,
3.4. Found: C, 26.1; H, 3.8. IR (cm−1, Nujol): 341(s), 330(s), 307(s).
3
1H NMR (CD2Cl2, 295 K): 1.28 (t, [6H], J = 6 Hz, CH2CH3), 2.54
(q, [4H], CH2CH3), 3.94 (s, [4H], SCH2Ar), 7.2−7.4 (m, [4H],
aromatic CH).
[(GaCl3)2([8]aneSe2)] (10). [8]aneSe2 (0.069 g, 0.28 mmol) was
dissolved in anhydrous CH2Cl2 (5 mL) and added to a solution of
GaCl3 (0.100 g, 0.57 mmol) in anhydrous CH2Cl2 (5 mL) with
constant stirring to give a pale yellow solution. After 30 min a white
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Inorganic Chemistry
Article
Scheme 1
Scheme 2
precipitate had formed, which was collected by filtration and dried in
vacuo. Yield: 0.082 g, 46%. H NMR (CDCl3, 295 K): 2.47 (quin,
[8H], SeCH2). IR (cm−1, Nujol): 298 (m), 283 (s). Raman (cm−1):
278 (s), 252 (m).
1
[4H], SeCH2CH2), 3.23 (t, [8H], SeCH2CH2). 71Ga NMR (CDCl3,
295 K): 237 (w1/2 = 4500 Hz). 77Se{1H} NMR (CDCl3, 203 K):
112.1. IR spectrum (cm−1, Nujol): 386 (s), 360 (m). Satisfactory
microanalyses were not obtained due to the extreme sensitivity of this
complex, leading to severe difficulties in handling the solid.
[8]aneSe2Cl4 (13). [8]aneSe2 (0.040 g) was added to a saturated
solution of Cl2 in CCl4 (6 mL) with stirring. A pale yellow precipitate
formed immediately. After 1 h the reaction mixture was filtered to
yield a pale yellow solid, which was washed with CH2Cl2 (2 × 2 mL)
and dried in vacuo. Yield: essentially quantitative. Anal. Calcd for
C6H12Cl4Se2: C, 18.8; H, 3.2. Found: C, 19.5; H, 3.2. 13C{1H} NMR
((CD3)2SO, 295 K): 49.1 (SeCH2), 44.2 (CH2CH2CH2). 77Se{1H}
NMR ((CD3)2SO, 295 K): 656.5 (s).
[InCl3([8]aneSe2)2] (14). [8]aneSe2 (0.121 g, 0.50 mmol) was
dissolved in CH2Cl2 (5 mL) and added to a suspension of InCl3
(0.111 g, 0.50 mmol) in CH2Cl2 (5 mL) with constant stirring. After
30 min the white solid was collected by filtration, washed with CH2Cl2,
and dried in vacuo. Yield: 0.062 g, 35% (based on [8]aneSe2). Anal.
Calcd for C12H24Cl3InSe4: C, 20.4; H, 3.4. Found: C, 20.9; H, 3.8. 1H
NMR (CD3CN, 295 K): 2.23 (quin, [4H], CH2CH2CH2), 2.89 (t,
X-ray Crystallography. Details of the crystallographic data
collection and refinement parameters are given in Table 1. Crystals
were obtained as described above. Data collection used a Nonius
Kappa CCD diffractometer fitted with monochromated (confocal
mirrors) Mo Kα X-radiation (λ = 0.71073 Å). Crystals were held at
120 K in a nitrogen gas stream. Structure solution and refinement were
generally routine,13,14 except as described below, with hydrogen atoms
on C added to the model in calculated positions and using the default
C−H distance. The data obtained for the crystal of 2 were weak;
however, given the similarity of this structure to those of 3 and 4 it was
not considered necessary to recollect the data. The data for 8
(Supporting Information) display characteristics indicative of a
modulated structure. Indexing was possible using most reflections
and a large cell (a = 13.4632 Å, b = 53.8898 Å, c = 15.1497 Å, β =
99.554° (P)) but this did not lead to a solution. Indexing was also
possible using a smaller C-centered monoclinic cell and a modulation
vector 0.0069, −0.6039, −0.0036 up to order 1. Using this cell and
conventional data reduction, ignoring the modulation, leads to the
solution presented here. The data for 9 were originally collected as
triclinic (P) and later transformed to the monoclinic (C) cell
presented here. The crystal quality for 9 was modest, and structure
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refinement revealed some disorder of the C atoms of the Et
substituents associated with S3 (and S3a) (elongated thermal
ellipsoids), possibly suggesting that the molecule is disordered across
the crystallographic mirror plane.
CCDC reference numbers 847024−847032 contain the supple-
mentary crystallographic data for the crystal structures reported in this
paper. These data can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/
cif.
RESULTS AND DISCUSSION
■
Figure 1. View of the structure of a section of the chain polymer of 1
with atom-numbering scheme. Ellipsoids are shown at the 50%
probability level, and H atoms are omitted for clarity. Symmetry
operators: a = 1/2 − x, 1/2 − y, − z; b = 1 − x, y, 1/2 − z.
The complex syntheses (Schemes 1 and 2) were typically
undertaken in anhydrous CH2Cl2 solution to prevent
competition from coordination of the solvent, although in
some specific cases (see Experimental Section) a small amount
of MeCN was added to aid solubility (especially of the InCl3),
promoting cleaner reactions and typically higher yields. IR and
Raman spectroscopy readily identified the presence or absence
of [MCl4]− in the products15,16 (or S/Se coordinated MCl3 by
comparison with literature data)6,8 and, together with micro-
analyses, allowed initial identification of the products and their
stoichiometries. Due to the known lability of Ga(III) and
In(III) complexes in solution, NMR spectroscopic studies
provide limited structural information, although where possible
77Se, 71Ga, and 115In NMR spectroscopic studies17 were
performed to provide supporting evidence for the solution
speciation. X-ray crystallographic studies have enabled un-
ambiguous identification of the structures of key complexes.
Tetradentate Ligands. In order to probe the effect ligand
architecture has on the complexes with MCl3 (M = Ga and In)
within the series of tetradentate ligands, the following
chalcogenoethers were examined: the macrocycles [14]aneS4,
[16]aneS4, and [16]aneSe4, C(CH2EMe)4 (E = S or Se) and
1,2,4,5-C6H2(CH2SMe)4.18 The only structurally characterized
example of a tetrathia macrocyclic complex with Group 13
halides is [InCl2([14]aneS4)][InCl4],8 although Atwood,
Robinson, and co-workers reported several examples of
AlMe3 complexes with thia-macrocycles and Al(III) chloride
complexes with crown ethers.19
Table 2. Selected Bond Lengths (Angstroms) and Angles
a
(degrees) for 1
Ga1−Cl1
Ga1−S1
Cl2−Ga1−Cl2b
Cl2−Ga1−S1
Cl2−Ga1−S1b
2.1828(7)
2.5744(6)
120.64(3)
88.54(2)
91.81(2)
Ga1−Cl2
2.1835(4)
119.681(13)
89.653(10)
89.653(10)
179.31(2)
Cl1−Ga1−Cl2
Cl1−Ga1−S1
Cl1−Ga1−S1b
S1−Ga1−S1b
a
Symmetry operators: a = 1/2 − x, 1/2 − y, − z; b = 1 − x, y, 1/2 − z.
Cl). This species presents the first example where the three Cl
ligands adopt a trigonal planar geometry, the pyramidal GaCl3
fragment being much more common. It was surprising to us
that there appeared to be no tendency toward chelation
(endocyclic coordination) in this system despite the presence
of the four S donor atoms in the macrocyclic ring. The
polymeric structure also contrasts with the product from the
InCl3/[14]aneS4 reaction system reported previously, which
forms the ionic complex cis-[InCl2([14]aneS4)][InCl4], in
which the cation adopts a distorted octahedral geometry with
S4 coordination of the macrocycle.8 The smaller ionic radius of
Ga(III) vs In(III) would suggest there is no intrinsic reason
why a similar coordination mode would not be possible;
however, we have not been able to isolate a pure, single product
when using higher Ga:macrocycle ratios.
Reaction of GaCl3 with 1 mol equiv of the macrocycle
[14]aneS4 (1,4,8,11-tetrathiacyclotetradecane) led initially to a
white precipitate which redissolved as the 1:1 Ga:macrocycle
ratio was reached. Concentration of the solution in vacuo
allowed isolation of a white solid formulated as the neutral
[GaCl3([14]aneS4)] (1) from IR/Raman and microanalyses.
Upon the basis of our earlier work on Ga(III) halide thioether
complexes, distorted tetrahedral Cl3S coordination was
considered most likely. However, the IR and Raman spectra
support local D3h symmetry (tbp Cl3S2 coordination at Ga),
showing the e′ mode at 381 and the a1′ mode at 331 cm−1 for
the GaCl3 unit. The crystal structure of this 1:1 complex
provides confirmation of this, showing (Figure 1, Table 2) an
infinite chain structure formed via Ga atoms coordinated to
three Cl ligands occupying a trigonal plane and two further axial
S atoms from bridging [14]aneS4 molecules, giving a distorted
trigonal bipyramidal (exocyclic) coordination geometry at Ga.
Within the chains the macrocyclic rings are centrosymmetric,
and there is a crystallographic 2-fold axis passing through the
Ga atoms.
Given the unexpected five-coordinate Cl3S2 environment in
1, the reaction was repeated using the larger ring [16]aneS4,
leading to a white product, this time with a 2:1 Ga:macrocycle
stoichiometry. The same species was obtained using either a 1:1
or a 2:1 ratio of reactants, and IR and Raman spectroscopy
clearly show the presence of the [GaCl4]− anion (in addition, a
further band in the far-IR region is attributed to the b1 Ga−Cl
stretching mode from trans-[GaCl2([16]aneS4)]+). Although
data were obtained from a rather small, weakly diffracting
crystal, structure determination (Figure 2, Table 3) confirmed
the product as [GaCl2([16]aneS4)][GaCl4] (2). The asym-
metric unit contains four independent cations (each with a
center of symmetry), and two [GaCl4]− anions in general
positions. Within each cation the Ga(III) ion is octahedrally
coordinated, occupying the ring and coordinated via the four S-
donor atoms as well as two trans Cl ligands.
Investigation of the reaction of the tetraselenoether crown
[16]aneSe4 with GaCl3 furnished the ionic product trans-
[GaCl2([16]aneSe4)][GaCl4] (3) as a colorless solid with
similar IR and Raman spectroscopic features. The crystal
structure of this product confirms it is isostructural with the
analogous thioether complex, comprising a distorted octahedral
cation (Figure 3, Table 4) and a tetrahedral anion. In the
The Ga−S distances (2.5744(6) Å) are considerably longer
than those in [(GaCl3)2(L−L)] (L−L = PhS(CH2)2SPh and o-
C6H4(CH2SMe)2) (2.389(1) and 2.357(2) Å, respectively).6
Although less pronounced, a similar trend is evident for d(Ga−
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Table 4. Selected Bond Lengths (Angstroms) and Angles
(degrees) for 3
Ga1−Cl1
Ga1−Se1
Ga1−Se3
2.3220(12)
2.6106(8)
2.6098(8)
178.96(5)
92.20(3)
Ga1−Cl2
Ga1−Se2
Ga1−Se4
2.3058(11)
2.6031(7)
2.5906(7)
91.85(4)
Cl1−Ga1−Cl2
Cl1−Ga1−Se2
Cl1−Ga1−Se4
Cl2−Ga1−Se2
Cl2−Ga1−Se4
Se1−Ga1−Se3
Se2−Ga1−Se3
Se3−Ga1−Se4
Cl3−Ga2−Cl5
Cl4−Ga2−Cl5
Cl5−Ga2−Cl6
Cl1−Ga1−Se1
Cl1−Ga1−Se3
Cl2−Ga1−Se1
Cl2−Ga1−Se3
Se1−Ga1−Se2
Se1−Ga1−Se4
Se2−Ga1−Se4
Cl3−Ga2−Cl4
Cl3−Ga2−Cl6
Cl4−Ga2−Cl6
85.86(4)
87.13(3)
89.11(4)
87.41(3)
93.19(4)
93.26(3)
88.56(2)
177.60(3)
92.23(2)
91.71(2)
179.28(3)
108.69(6)
110.22(7)
108.93(8)
87.47(2)
109.18(7)
109.99(7)
109.83(8)
Figure 2. View of the cation in 2 with atom-numbering scheme.
Ellipsoids are shown at the 50% probability level, and H atoms are
omitted for clarity. Symmetry operation: a = 2 − x, − y, 1 − z.
reported tetrahedral complexes [GaCl3(SeMe2)] (2.4637(7) Å)
and [(GaCl3)2{nBuSe(CH2)2SenBu}] (2.4683(11) Å).6 The
same trend occurs for the Ga−Cl distances within the cation
(2.306(1), 2.322(1) Å) compared to those in the tetrahedral
[GaCl4]− anion (2.163(2)−2.175(2) Å).
Table 3. Selected Bond Lengths (Angstroms) and Angles
(degrees) for 2
Ga1−Cl1
2.276(3)
2.492(4)
2.515(4)
2.296(3)
2.499(4)
2.496(4)
88.28(12)
90.60(12)
91.81(13)
91.83(12)
90.40(13)
92.01(14)
Ga1−S1
2.518(4)
2.293(3)
2.464(4)
2.486(4)
2.292(3)
2.482(4)
92.27(12)
88.35(12)
89.57(12)
91.24(12)
91.19(12)
90.02(13)
Ga1−S2
Ga2−Cl2
Ga2−S3
Ga2−S4
The corresponding In(III) complex (4) obtained similarly
(Figure 4) also contains a trans-octahedral cation with the In
Ga3−Cl3
Ga3−S5
Ga3−S6
Ga4−Cl4
Ga4−S7
Ga4−S8
Cl1−Ga1−S1
S1−Ga1−S2
Cl2−Ga2−S4
Cl3−Ga3−S5
S5−Ga3−S6
Cl4−Ga4−S8
Cl1−Ga1−S2
Cl2−Ga2−S3
S3−Ga2−S4
Cl3−Ga3−S6
Cl4−Ga4−S7
S7−Ga4−S8
Figure 4. View of the structure of the centrosymmetric cation in 4
with atom-numbering scheme. Ellipsoids are shown at the 40%
probability level, and H atoms are omitted for clarity. Symmetry
operation: a = −x, 1 − y, 2 − z. Selected bond lengths (Angstroms)
and angles (degrees): In1−Cl1 = 2.475(2), In1−Se1 = 2.7189(10),
In1−Se2 = 2.7394(11); Cl1−In1−Se1 = 88.04(6), Cl1−In1−Se2 =
88.10(6).
atom in the Se4 plane. In this case the cation is
centrosymmetric, with d= (In−Se) = 2.719(1) and 2.739(1)
Å, similar to those in trans-[InBr2{MeSe(CH2)2SeMe}2]+.8
Figure 3. View of the structure of the cation in 3 with atom-
numbering scheme. Ellipsoids are shown at the 50% probability level,
and H atoms are omitted for clarity.
1
Solution H NMR spectroscopic studies in CH2Cl2 on 2, 3,
and 4 show small high-frequency shifts, while 71Ga and 115In
NMR spectra each show a resonance corresponding to the
[MCl4]− anion, but resonances from the six-coordinate cations
are not observed. This is as expected for complexes involving
the quadrupolar 71Ga and 115In nuclei for which small
distortions from regular Oh (or Td) geometry give rise to
nonzero electric field gradients and significant line broadening.
No 71Ga (or 115In) resonances were observed for the distorted
octahedral trans-[MX2{o-C6H4(E′Me2)2}2] (E′ = P or As) or
distorted tetrahedral [MX2{o-C6H4(PMe2)2}].7 Selenium-77
former the Ga occupies the center of the macrocyclic ring and
is coordinated equatorially to the four Se atoms (2.5906(7)−
2.6106(8) Å) with two mutually trans Cl atoms completing the
coordination. The four Se atoms are almost coplanar, and the
Ga atom is only ca. 0.03 Å out of this plane, suggesting a very
good size match between Ga(III) and the macrocyclic binding
cavity; this may be important in promoting formation of this
endocyclic cation. The Ga−Se bond distances in the six-
coordinate cation are significantly longer than in the previously
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NMR spectroscopic data for 3 (in CH2Cl2) shows a singlet at
134 ppm to low frequency of the parent [16]aneSe4 ligand (158
ppm), while in MeCN solution the resonance is a very sharp
singlet at 158 ppm, suggesting the ligand is extensively
dissociated in the more competitive MeCN solvent. As
observed previously for InX3 complexes with mono- and
bidentate selenoethers 4 also appears to be extensively
dissociated (or shows a negligible coordination shift), exhibiting
a singlet at 158 ppm even in noncoordinating CH2Cl2.
The acyclic tetrathioethers C(CH2SMe)4 and 1,2,4,5-
C6H2(CH2SMe)4 (L) react with 4 mol equiv of GaCl3 to
form complexes of stoichiometry [(GaCl3)4(L)] and with InCl3
to form the 2:1 complex [(InCl3)2{C(CH2SMe)4}] (Support-
ing Information). Reaction of GaCl3 with the tetraselenoether
C(CH2SeMe)4 in anhydrous CH2Cl2 leads to fragmentation at
C−Se, forming a yellow oil containing a complex mixture of
species including the selenonium cation [(CH2)2C-
(CH2)2SeMe]+ identified by positive-ion ESMS (m/z = 163)
and [GaCl4]− (IR, Raman and ESMS data) as well as other
unidentified species.
Bidentate Ligands. As described in the Introduction, a
range of GaX3 and InX3 complexes with simple mono- and
flexible bidentate thio- and selenoethers was the basis of our
earlier work. In this study we studied the effects of introducing
geometric or steric constraints in the bidentate ligand
architectures using the rigid o-C6H4(SMe)2, the semirigid o-
C6H4(CH2ER)2 (E = S; R = Me or Et; E = Se, R = Me), as well
as the cyclic [8]aneSe2 (Schemes 1 and 2).
Figure 5. View of the structure of the dication in 6 with atom-
numbering scheme. Ellipsoids are shown at the 50% probability level,
and H atoms are omitted for clarity. Selected bond lengths
(Angstroms) and angles (degrees): S1−C1 = 1.786(8), S1−C2 =
1.820(8), S1−C3 = 1.779(7), S2−C8 = 1.790(7), S2−C9 = 1.821(9),
S2−C10 = 1.812(9); C1−S1−C2 = 101.3(4), C1−S1−C3 = 104.9(4),
C2−S1−C3 = 103.5(4), C8−S2−C9 = 101.1(4), C8−S2−C10 =
104.0(4), C9−S2−C10 = 100.7(4).
The complex is formulated as [(InCl3)4{o-C6H4(CH2SEt)2}3]
(9) also on the basis of crystal structure determination (Figure
Reaction of MCl3 with o-C6H4(SMe)2 gives [(GaCl3)2{o-
C6H4(SMe)2}] (5) and [InCl3{o-C6H4(SMe)2}] (7), respec-
tively. On the basis of the spectroscopic data both in solution
and in the solid state these are assigned as adopting distorted
tetrahedral Cl3S coordination for M = Ga, whereas for M = In a
chloro-bridged dimer with a distorted octahedral Cl4S2 donor
set is likely; there is no evidence for [MCl4]− in either case.
Redissolving 5 in CH2Cl2 and leaving this solution to stand
at −20 °C over several days leads to further reaction with the
CH2Cl2 solvent and produced yellow crystals. Examination of
these revealed the product to be [o-C6H4(SMeCH2Cl)2]-
[GaCl4]2 (6) containing discrete bis-sulfonium dications
(Figure 5) and tetrahedral [GaCl4]− anions. IR spectroscopic
data on this material shows [GaCl4]−, which was also the only
significant anion evident in the negative-ion electrospray MS
(MeCN). Positive-ion MS shows [o-C6H4(SMe)-
(SMeCH2Cl)]+ to be the major species present, although
there is a weaker feature consistent with [o-C6H4(SMe)-
(SMe2)]+ also clearly evident. This reaction is readily
reproducible, and mechanistically the sulfonium dication is
likely to be formed via nucleophilic attack of the thioether
sulfur on the CH2Cl2. Bis-sulfonium formation in this reaction
is very unusual and is clearly promoted by the GaCl3 polarizing
the CH2Cl2. The thioether itself is stable in CH2Cl2 solution.
The semirigid o-xylyl ligands o-C6H4(CH2SEt)2 also exhibit
unexpected chemistry with MCl3 (Scheme 2). Reaction of o-
C6H4(CH2SEt)2 with 2 mol equiv of GaCl3 gives the simple
dinuclear [(GaCl3)2{o-C6H4(CH2SEt)2}] (8) from the spectro-
scopic data and a crystal structure determination (Supporting
Information) with tetrahedral Cl3S coordination at Ga and the
S substituents anti. Maintaining the same conditions but
replacing GaCl3 with InCl3 in the reaction with o-
C6H4(CH2SEt)2 produces a colorless crystalline complex
containing a 4:3 In:dithioether ratio (from microanalytical
data) and without any tetrachloroindate in the IR spectrum.
Figure 6. View of the structure of [(InCl3)4{o-C6H4(CH2SEt)2}3], 9,
with atom-numbering scheme. Ellipsoids are shown at the 50%
probability level, and H atoms are omitted for clarity. Symmetry
operation: a = −x, y, 1/2 − z.
6, Table 5), which shows a discrete tetranuclear moiety with
mirror symmetry. The central In atom (In3) is octahedrally
coordinated through six bridging Cl’s, whereas the three In
atoms on the edges (In1, In2, and In2a) have two bridging Cl’s,
two terminal Cl’s, and two mutually trans S-donor atoms from
different dithioether ligands. The structure is very unexpected;
there is only one precedent, [(BiCl3)4{o-C6H4(CH2SMe)2}3],
in which the thioether also incorporates the large o-xylyl
linkage.20 This suggests that this particular linkage leads to
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Table 5. Selected Bond Lengths (Angstroms) and Angles
(degrees) for 9·2CH2Cl2
Scheme 3
a
In1−Cl1
In1−S1
In2−Cl4
In2−Cl6
In2−S3
In3−Cl5
2.396(3)
2.646(2)
2.407(3)
2.639(2)
2.657(3)
2.496(2)
105.25(14)
96.10(8)
164.03(9)
89.77(9)
75.89(11)
90.76(9)
96.18(9)
86.87(8)
94.47(9)
166.07(9)
90.14(8)
80.97(8)
163.13(13)
102.72(8)
86.17(8)
83.30(8)
167.02(8)
102.58(13)
99.49(8)
In1−Cl2
In2−Cl3
In2−Cl5
In2−S2
In3−Cl2
In3−Cl6
2.693(3)
2.408(2)
2.658(3)
2.655(3)
2.509(3)
2.546(3)
92.87(8)
165.20(12)
88.38(8)
79.93(8)
100.67(9)
168.49(9)
93.17(8)
93.83(9)
83.33(9)
168.99(8)
78.49(8)
87.37(9)
90.01(8)
82.63(12)
167.02(8)
86.17(8)
87.99(9)
100.74(9)
98.71(8)
Cl1a−In1−Cl1
Cl1−In1−S1
Cl1−In1−Cl2a
Cl1−In1−Cl2
Cl2a−In1−Cl2
Cl4−In2−Cl6
Cl4−In2−S2
Cl6−In2−S2
Cl3−In2−S3
S2−In2−S3
Cl3−In2−Cl5
S2−In2−Cl5
Cl5a−In3−Cl5
Cl5−In3−Cl2
Cl5a−In3−Cl6
Cl5−In3−Cl6
Cl2a−In3−Cl6
Cl6a−In3−Cl6
In2−Cl5−In3
Cl1a−In1−S1
S1−In1−S1a
S1−In1−Cl2a
S1−In1−Cl2
Cl4−In2−Cl3
Cl3−In2−Cl6
Cl3−In2−S2
Cl4−In2−S3
Cl6−In2−S3
Cl4−In2−Cl5
Cl6−In2−Cl5
S3−In2−Cl5
Cl5a−In3−Cl2
Cl2a−In3−Cl2
Cl2a−In3−Cl6
Cl5a−In3−Cl6
Cl2−In3−Cl6
In1−Cl2−In3
In2−Cl6−In3
at Ga(III). The same product is formed from reaction of a
suspension of GaCl3 in hexane solution with [8]aneSe2.
Bubbling O2 gas through a solution of 10 in CH2Cl2 led to
rapid appearance of a red/orange-colored solution which
precipitated a red solid within a few minutes, leaving the
supernatant colorless. Selenium-77 and 71Ga NMR experiments
on this supernatant solution showed complete loss of the
original resonances (and no new peak). Addition of Me2CO to
the red precipitate caused dissolution with formation of a bright
yellow solution initially which lightened to pale yellow after a
few minutes, suggesting that further reaction (oxidation) had
occurred. The 71Ga NMR spectrum of this solution showed a
strong sharp singlet at 249.8 ppm indicative of [GaCl4]−;
however, no 77Se NMR signal was evident (out as far as +1000
ppm) either at 298 or 183 K, even after long data acquisitions,
suggesting a dynamic process was occurring. Electrospray mass
spectrometry (MeCN) on this product shows {[8]aneSe2}+ and
[GaCl4]− as the only significant species in the positive-ion and
negative-ion modes, respectively. In order to probe this reaction
further, a solution of GaCl3 and [8]aneSe2 in CH2Cl2 was
exposed to air briefly and then placed in a freezer (−18 °C) for
several days, leading to formation of both red and yellow
crystals. Crystal structure determinations were undertaken on
both crystal types.
a
Symmetry operation: a = −x, y, 1/2 − z.
more stable species with the ligand bridging two metals in this
arrangement rather than chelating to form a seven-membered
ring. It also contrasts with the majority of transition metal
complexes incorporating this ligand architecture where
bidentate chelation occurs, albeit with E−M−E angles
significantly greater than 90°, suggesting a mismatch between
the metal and the ligand.11,21 While this will lead to a relatively
less stable arrangement, the inherently stronger M−S bonds
where M is a d-block ion compared to a p-block ion (likely to
be much more kinetically labile) presumably allows the chelate
structure to be retained in the former but not in the latter.
The In−S and In−Cl bond distances are comparable with
those in the only other indium thioether complexes,8 and we
note that while S and Cl are neighboring elements in the
periodic table, the In−S bond distances (ca. 2.65 Å) are
approximately 0.25 Å longer than the terminal In−Cl bonds.
This suggests weak, secondary In···S coordination.
The red crystals were shown to be [([8]aneSe2)2][GaCl4]2
(11) containing a dimeric [([8]aneSe2)2]2+ dication (Figure 7).
The structure of this cation shows the Se−Se distance linking
the two rings together is 2.6667(7) Å, while the intraring
d(Se···Se) is 2.891(1) Å, consistent with a transannular
hypervalent Se(II)···Se(III) 1,5-interaction. This dication
appears likely to be formed via coupling two {[8]aneSe2}+•
monocation radicals produced via oxidation of [8]aneSe2 by O2
in the presence of GaCl3. Consistent with this description, the
Se−C distances also fall into two groups; those connected to
the Se−Se bond (Se1) are slightly longer (1.980(3) and
1.981(3) Å) than those connected to Se2 (1.957(3) and
1.962(3) Å). Note that [8]aneSe2 itself is not air sensitive even
over periods of several months.
Reactions with [8]aneSe2. The chemistry of [8]aneSe2
with GaCl3 is illustrated in Scheme 3. Two mole equivalents of
GaCl3 reacted with the cyclic diselenoether, [8]aneSe2, in
anhydrous CH2Cl2 to give a colorless solution, from which an
extremely air-sensitive white solid was isolated. On the basis of
spectroscopic data this product is assigned as [(GaCl3)2([8]-
aneSe2)] (10), most likely based upon tetrahedral coordination
1
at each Ga(III). Its H NMR spectrum shows the expected
resonances with significant high-frequency coordination shifts
relative to the diselenoether itself, while at 298 K the 77Se{1H}
NMR spectrum of a freshly prepared (colorless) solution of the
complex shows a singlet at 118.8 ppm, which shifts slightly to
low frequency (112.1 ppm) at 203 K, ca. 25 ppm to low
frequency of [8]aneSe2 (137 ppm). The 71Ga NMR spectrum
shows no [GaCl4]−, but a broad resonance is observed at 237
ppm (w1/2 = 4500 Hz), consistent with the Cl3Se environment
The yellow crystals obtained from the same reaction mixture
correspond to [{[8]aneSe2}Cl][GaCl4]·CH2Cl2 (12)·CH2Cl2
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Inorganic Chemistry
Article
undergoes further oxidation to form {[8]aneSe2}2+. In the
yellow crystal formed from CH2Cl2 solution a Cl− anion is
associated with one Se atom giving 12 determined by X-ray
diffraction. The crystal structure of {[8]aneSe2}(BF4)2·MeCN
gives d(Se−Se) = 2.382(2) Å,22d somewhat shorter than
observed in the present work for 12·CH2Cl2 (2.5229(4) Å).
The {[16]aneSe4}2+ dication, derived from Cu(II) oxidation of
[16]aneSe4, has also been structurally characterized, and the
Se···Se distances within the ring are 2.592(2), 2.669(1), and
3.394(1) Å.23
In a separate experiment NOBF4 was added to a solution of
10 in degassed CH2Cl2, also leading to a rapid red coloration,
which dissipated over ca. 1 min to a pale yellow solution,
indicating a similar process occurs. However, oxidation of a
CH2Cl2 solution of [8]aneSe2 by addition of a few drops
(excess) of Cl2-saturated CCl4 caused a bright yellow
precipitate to form. NMR spectroscopic studies (1H, 13C{1H},
and 77Se{1H}) on this product were consistent with formation
of the tetrachloride derivative, [8]aneSe2Cl4 (13).
Figure 7. View of the structure of the dimeric cation in 11 with atom-
numbering scheme. Ellipsoids are shown at the 50% probability level,
and H atoms are omitted for clarity. Symmetry operation: a = −x, −y,
−z. Selected bond lengths (Angstroms) and angles (degrees): Se1−C1
= 1.980(3), Se1−C6 = 1.981(3), Se1−Se1a = 2.6662(7), Se1···Se2 =
2.891(1), Se2−C3 = 1.957(3), Se2−C4 = 1.962(3); C1−Se1−C6 =
99.69(13), C3−Se2−C4 = 99.71(15).
in which the cation (Figure 8) may be considered as a doubly
oxidized {[8]aneSe2}2+ unit with a Cl− associated with one of
CONCLUSIONS
■
This work has clearly demonstrated a much wider chemistry of
MCl3 (M = Ga or In) with thio- and selenoethers exists than
previously thought. In particular, the work established that the
highly Lewis-acidic GaCl3 promotes unprecedented chemistry,
on one hand, promoting sulfonium cation formation from o-
C6H4(SMe)2 and CH2Cl2 and, on the other, promoting
oxidation of selenoether groups in the case of [8]aneSe2 with
O2. Neither of these reactions occur in the absence of GaCl3.
Crystallographic evidence unequivocally authenticates the
products.
The work has also produced the first series of five- and six-
coordinate gallium halide complexes with thio- and selenoether
ligation, specifically forming distorted tbp-coordinated Ga in
the polymeric (1) and distorted octahedral Ga(III) in the
cations present in 2, 3, and 4. The latter also provide the first
evidence for halide substitution by a neutral chalcogenoether
ligand; undoubtedly, the macrocyclic framework and ring size
available play important roles in dictating this chemistry. We
note that only the sterically rigid, very strong σ-donor
phosphine and arsine ligands o-C6H4(E′Me2)2 (E′ = P or As)
have been shown to produce six-coordinate trans-[GaX2{o-
C6H4(E′Me2)2}2]+.7 The importance of the ligand architecture
within p-block chemistry in particular is also clearly evident, no
more so than in the tetranuclear 9, a structural motif that has
not been replicated in d-block chalcogenoether chemistry.
Figure 8. View of the structure of the cation in 12·CH2Cl2 with atom-
numbering scheme. Ellipsoids are shown at the 50% probability level,
and H atoms are omitted for clarity. Selected bond lengths
(Angstroms) and angles (degrees): Se2−Cl1 = 2.5346(6), Se1−C1
= 1.970(2), Se1−C6 = 1.967(2), Se1−Se2 = 2.5229(4), Se2−C3 =
1.981(2), Se2−C4 = 1.978(2); C1−Se1−C6 = 99.66(9), C3−Se2−C4
= 101.93(9), C4−Se2−Cl1 = 89.39(6), C3−Se2−Cl1 = 88.09(6),
Se1−Se2−Cl1 = 175.23(2).
the Se atoms (Se−Cl = 2.5346(6) Å). The Se−Se distance of
2.5229(4) Å is consistent with this description, formed through
coupling of the two radical cations across the ring. In both of
these species tetrahedral [GaCl4]− ions provide charge balance.
Oxidation of cyclic selenoethers has been investigated
previously.22,23 Of particular relevance, electrochemical studies
on [8]aneE2 (E = S, Se, or Te) in MeCN solution show that
the mono-oxidized {[8]aneSe2}+• radical cation (Eo1 = 0.102 V
vs ferrocene/ferrocenium in MeCN) is thermodynamically very
unstable; thus, oxidation of the second E atom occurs at a lower
potential (Eo2 = 0.058 V) than that of the first E atom (inverted
potential). This causes spontaneous conversion of {[8]-
aneSe2}+• to {[8]aneSe2}2+. Our experiments show that both
the mono- and the doubly oxidized species are formed and that
oxidation by O2 is promoted by Ga(III). Furthermore, the
{[8]aneSe2}+• cation radical formed initially undergoes rapid
coupling to form the dimeric 11 (red), which is isolated
probably by virtue of the low solubility of its tetrachlorogallate
salt in CH2Cl2 solution, allowing its crystallographic authenti-
cation. Consistent with the electrochemical studies, we found
that immediately upon dissolving this solid in either MeCN or
acetone rapid decoloration occurs, which we attribute to the
intrinsic thermodynamic instability of the red dimer, which
ASSOCIATED CONTENT
■
S
* Supporting Information
Preparative details for GaCl3 and InCl3 complexes with acyclic
tetrathio- and tetraselenoethers and crystallographic details for
[(GaCl3)2{o-C6H4(CH2SEt)2}]; cif files for all crystal structures
described. This material is available free of charge via the
Internet at http://pubs.acs.org.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: gr@soton.ac.uk.
Notes
The authors declare no competing financial interest.
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Inorganic Chemistry
Article
1982, 1, 1081. (c) Self, M. F.; Pennington, W. T.; Laske, J. A.;
Robinson, G. H. Organometallics 1991, 10, 36. (d) Robinson, G. H.;
Zhang, H.; Atwood, J. L. Organometallics 1987, 6, 887.
(20) Levason, W.; Maheshwari, S.; Ratnani, R.; Reid, G.; Webster,
M.; Zhang, W. Inorg. Chem. 2010, 49, 9036.
ACKNOWLEDGMENTS
■
We thank the EPSRC and CMSD at STFC for funding (K.G.).
We also thank Dr. M. Webster for assistance with the
crystallographic studies.
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̈
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̈
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(15) Tetrahedral [MCl4]− show two Raman-active stretches (a1 + t2)
and one IR-active stretch (t2). M = Ga: a1 = 346, t2 = 386 cm−1. M =
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× 10−28 m2, Dc = 1890].
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2240
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