A comparison of the solid state structures of the selenium(IV) compounds PhSeX3 (X = Cl, Br)

Article abstract of DOI:10.1039/b504241k

Solid state structures of selenium(IV) compounds PhSeX₃ (X=Cl, Br) were compared. Crystals of PhSeX₃ (X=Cl, Br) were produced by recrystallization from refluxing diethyl ether. The structure of PhSeCl ₃ showed polymeric ch

Full text of DOI:10.1039/b504241k

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C O M M U N I C A T I O N
A comparison of the solid state structures of the selenium(IV)
compounds PhSeX3 (X = Cl, Br)
Nicholas A. Barnes, Stephen M. Godfrey, Ruth T. A. Halton and Robin G. Pritchard
Department of Chemistry, University of Manchester (North Campus), Manchester, UK M60
1QD. E-mail: stephen.godfrey@manchester.ac.uk; Fax: 0161 200 4559; Tel: 0161 200 4525
Received 24th March 2005, Accepted 12th April 2005
First published as an Advance Article on the web 22nd April 2005
The crystal structures of PhSeX3 (X = Cl, Br,) and their
spectroscopic data are reported, with the structure of
PhSeBr3 exhibiting interesting molecular, charge transfer,
and ionic bonding aspects.
orange (PhSeBr3)14 crystals, respectively. Independently, samples
of both materials were submerged in inert oil and suitable
crystals for analysis by single crystal X-ray diffraction were
chosen after examination under the microscope. The structure
of PhSeCl3 is shown in Fig. 1(a), and exhibits the polymeric
chain structure commonly observed for RSeCl3 compounds,15–17
whereby individual PhSeCl2 units are linked by two bridging
chlorine atoms, Fig. 1(b). The geometry at selenium is square
pyramidal with the phenyl group occupying the apical position.
The reaction of organoselenides with dihalogens is an area
of significant current interest, with halogenated adducts of
diorganoselenides,1,2 selenoamides3–5 and diorganodiselenides6
having been recently reported. Organo Se(IV) halides are
commonly either of stoichiometry R2SeX2 or RSeX3. R2SeX2
compounds are prepared by direct reaction of diselenides
with dihalogens, and the structure of the resultant adduct is
dependent on the identity of the halogen. For example, reaction
of dimethylselenide with diiodine produces the charge transfer
(CT) complex Me2SeI–I whereas the corresponding reaction
with the lighter halogens produces the disphenoidal see-saw
compounds Me2SeX2 (X = Cl, Br).1 However, in the case of the
chloro compound, Me2SeCl2, it was also noted that long range
Se–Cl contacts distorted the see-saw geometry of the selenium
atom towards distorted octahedral geometry. No such distortion
was observed for the analogous Ph2SeCl2.7
The reaction of diorganodiselenides with the lighter halo-
gens produces complexes of formula RSeX3 (X = Br, Cl,
F). These organoselenium trihalides have found use in the
introduction of selenium into organic molecules. For example,
PhSeCl3 reacts with enolisable aldehydes and ketones to give
the corresponding a-phenylselenenyl aldehydes/ketones8 which
are hydrolysable to give enones.9 PhSeX3 (X = Br, Cl) and
(2,4-dinitrophenyl)selenium trichloride are also known to add
across double bonds of cyclic and non-cyclic olefins to pro-
duce unsaturated compounds.10 Although a large number of
organic selenium trihalides have been prepared (since the first,
ethylselenium tribromide, which was synthesized serendipitously
in 1926),11 very little is known about their structure. In this study
we describe the structures of the compounds synthesised from
the reaction of Ph2Se2 with three molar equivalents of sulfuryl
chloride and dibromine at ambient temperature to produce
PhSeX3 (X = Cl and Br, respectively),12 see eqns. (1) and (2).
Fig. 1 (a) X-Ray structure of the repeated unit in the polymer of
PhSeCl3 with 50% probability thermal ellipsoids. Selected interatomic
◦
˚
distances (A) and angles ( ) Se(1)–Cl(1): 2.227(5), Se(1)–Cl(2): 2.198(4),
Se(1)–Cl(3): 2.628(5), Se(2)–Cl(4): 2.251(5), Se(2)–Cl(5): 2.220(5),
Se(2)–Cl(3): 2.677(5), Se(1)–Cl(6): 2.726(5), Se(2)–Cl(6): 2.616(5),
Se(1)–C(1): 1.962(15), Se(2)–C(7): 1.966(17); Se(1)–Cl(3)–Se(2):
108.21(15), Se(2)–Cl(6)–Se(1): 107.73(15), C(1)–Se(1)–Cl(3): 88.4(4),
Cl(1)–Se(1)–Cl(3): 175.53(18), Cl(1)–Se(1)–Cl(2): 95.07(17), C(7)–
Se(2)–Cl(3): 88.2(5), Cl(4)–Se(2)–Cl(6): 173.73.(16), Cl(4)–Se(2)–Cl(5):
94.21(17). (b) Extended polymeric chain of PhSeCl3 showing Se · · · Cl
contacts.
Ph2Se2 + 3 SO2Cl2 →2 PhSeCl3 + 3 SO2
(1)
Ph2Se2 + 3 Br2→ 2 PhSeBr3
(2)
Crystals of PhSeX3 (X = Cl, Br) were easily produced by re-
crystallisation from refluxing diethyl ether. Slow cooling to room
temperature produced large crops of yellow (PhSeCl3)13 and dark
Table 1 A comparison of Se–Cl bond lengths in RSeCl3 compounds
˚
Compound
Se–Cl Bond lengths/A
Ref.
Terminal
Bridging
CF3SeCl3
2.13(2)–2.25(2)
2.51(2)–2.75(2)
15
16
17
1,2-(SeCl3)2C6H4
4-(Me3Si)2N-3,5-(iPr)2C6H2SeCl3
C6H5SeCl3
2.193(4)–2.259(4)
2.206(2)–2.257(2)
2.198(4)–2.251(5)
2.497(3)–2.697(4)
2.587(2)–2.749(2)
2.616(5)–2.726(5)
This work
T h i s j o u r n a l i s
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The selenium atom lies just above the basal plane, with the
angles around the selenium atom being slightly distorted from
the expected 90◦. The terminal Se–Cl bonds range from 2.198(4)
˚
to 2.251(5) A, in contrast to the bridging Se–Cl bonds of 2.616(5)
˚
to 2.726(5) A. These compare well with values for previously
reported structures of RSeCl3 compounds, see Table 1.15–17 Each
of the characterised examples exhibits a Se(l-Cl)2Se motif with
unequal bridging and terminal Se–Cl distances. PhSeCl3 is
isostructural with the analogous tellurium compounds PhTeX3
(X = Cl, Br) previously described by Alcock and Harrison,18,19
although the secondary Te · · · X interactions present in the solid
state structures of the tellurium analogues are not observed for
PhSeCl3. The Raman spectrum of PhSeCl3 displays three Se–
Cl stretching vibrations, as expected, according to the observed
Cs symmetry of the molecule. Peaks at 150 and 123 cm−1 are
assumed to be the Se–Cl bending modes. The peaks at 372,
333 and 302 cm−1 are assigned to the m(Se–Cl) symmetric and
asymmetric stretching bands of the molecule based on reported
data for Ph2SeCl2.20
Since there are no reported crystallographic studies of any
compound of stoichiometry RSeBr3 we have also undertaken a
study of the solid state structure of PhSeBr3. This compound
has previously been studied by Raman spectroscopy by Clarke
and Al-Turaihi,21 who postulated a distorted octahedral envi-
ronment for the selenium atom on the basis of their findings.
The Raman spectrum of PhSeBr3 displays three m(Se–Br) bands
at 197, 216 and 286 cm−1, and one m(Se–Ph) band at 248 cm−1,
and these values are consistent with the previous observations,21
however the single crystal X-ray structure of PhSeBr3 shows a
square pyramidal geometry for the selenium centre, Fig. 2(a), as
observed for PhSeCl3. The structure however is not isostructural
with PhSeCl3, or the analogous PhTeBr3.19 Instead of displaying
two terminal and two bridging Se–Br bonds, the structure
displays an unusual combination of molecular, ionic and CT
aspects. The square pyramidal geometry around selenium is
more distorted than in PhSeCl3, with the phenyl ring again
occupying the apical position. There are two short Se–Br bonds
˚
[Se(1)–Br(1): 2.3538(14), Se(1)–Br(2): 2.3590(13) A], and two
longer Se · · · Br contacts [Se(1)–Br(4): 3.0976(13), Se(1)–Br(4ꢀ):
˚
3.0891(13) A], completing the square pyramidal environment.
The atoms Br(1) and Br(2) have added across the selenium atom,
and the Se–Br distances are unusually short, compared to Se–Br
22
˚
˚
distances of 2.52(1) A in Ph2SeBr2, and 2.546(4)/2.551(4) A
in Me2SeBr2.1 These Se–Br bonds are not terminal but instead
participate in a polymeric network of bromine atoms, Fig. 2(b),
which may be considered as a weak CT array, with almost linear
Se–Br–Br angles, Se(1)–Br(1)–Br(3): 179.45(5)◦, and a Br(1)–
˚
Br(3) bond of 3.0099(12) A, which is considerably longer than
˚
that of molecular dibromine (2.28 A), and rather shorter than the
Br–Br distance of 3.123(2) A in Ph3PBr–Br.23 The Br(3) atom lies
˚
above the Br(1)–Br(1ꢀ)–Br(2ꢀ)–Br(2) plane, with a Br(2)–Br(3)–
Br(2ꢀ) angle of 154.47(6)◦.
The structure also shows some ionic behaviour, which is
consistent with previous reports that PhSeBr3 is weakly ionic
on the basis of conductivity measurements.21 The weaker Se–
Br interactions to two Br(4) anions complete the polymeric
structure, Fig. 2(c), with the bromine anions sitting in a distorted
tetrahedral environment linking to four selenium atoms in
neighbouring PhSeBr2 units, with Se–Br(4)–Se angles of 98.42(3)
and 103.81(3)◦.
The structures of PhSeX3 are therefore not isostructural,
with PhSeBr3 displaying an unique compromise between the
structural types (molecular, ionic, CT) commonly seen for
organoselenium halogen species.
Fig. 2 (a) X-Ray crystal structure of the asymmetric unit in the polymer
of PhSeBr3 with 50% probabil◦ity thermal ellipsoids. Selected interatomic
˚
distances (A) and angles ( ) Se(1)–Br(1): 2.3538(14), Se(1)–Br(2):
2.3590(13), Se(1)–Br(4): 3.0976(13), Se(1)–Br(4ꢀ): 3.0891(13), Br(1)–
Br(3): 3.0099(12), Br(2)–Br(3): 3.0047(12), Se(1)–C(1): 1.928(9);
Br(1)–Se(1)–Br(2): 97.66(5), Br(1)–Se(1)–C(1): 98.0(3), Br(2)–Se(1)–
C(1): 97.5(2), Br(1)–Br(3)–Br(1): 179.45(5), Br(2)–Br(3)–Br(2ꢀ):
154.47(6), Br(4)–Se(1)–Br(4ꢀ): 81.58(3), Se(1)–Br(4)–Se(1ꢀ): 98.42(3). (b)
Molecular packing showing extended bromine–bromine contacts. (c)
Alternative view of packing, showing bromine anions linking to four
selenium atoms.
Acknowledgements
We are grateful to EPSRC for a research studentship to RTAH,
and also for the UMIST FT IR-Raman facility (Grant No:
GR/M30135).
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13 Crystal data for C6H5SeCl3, M = 262.41, triclinic, a = 7.186(4), b =
Notes and references
◦
˚
8.489(3), c = 13.772(8) A, a = 98.96(3), b = 92.70(3), c = 90.73(3) ,
3
¯
˚
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5.414 mm−1, 2870 reflections measured, 2870 unique (R1 = 0.0792)
which were used in all calculations. The final wR (F2) was 0.1816 (all
data). The Se and Cl atoms were refined anisotropically. Data for the
structures were collected on a Nonius j-CCD 4-circle diffractometer
˚
using graphite-monochromated Mo-Ka radiation (k = 0.71073 A).
CCDC reference number: 267208.
14 Crystal data for C6H5SeBr3,
M
=
395.76, monoclinic,
a
=
◦
˚
11.206(2), b = 22.240(4), c = 8.0823(2) A, b = 111.13(2) , T =
3
˚
203(2) K, space group C2/c, Z = 8, V = 1879.0(7) A , l(Mo-
Ka) = 16.682 mm−1, 3357 reflections measured, 1620 unique
(R1 = 0.0461) which were used in all calculations. The final
wR (F2) was 0.1104 (all data). CCDC reference number: 267209.
See http://www.rsc.org/suppdata/dt/b5/b504241k/ for crystallo-
graphic data in CIF or other electronic format..
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12 Both reactions were performed in diethyl ether solution using
standard schlenk techniques. Ph2Se2 (1 g, 3.20 mmol, Aldrich) was
dissolved in 40 ml diethyl ether. Br2 (0.49 ml, 9.60 mmol) or SO2Cl2
(0.77 ml, 9.60 mmol) was added and the mixture stirred for 1 h. The
soild was isolated by filtration, and dried in vacuo. PhSeCl3: Yellow
solid, yield = 70%, mp: 125–30 ◦C. Calculated for C6H5Cl3Se: C,
27.5; H, 1.9; Cl, 40.5; Found: C, 27.7; H, 1.8; Cl, 39.9%. Raman:
m(cm−1): 3079, 1568, 1013, 372, 333, 302, 275. PhSeBr3: Orange solid,
yield = 73%, mp: 104–106 ◦C. Calculated for C6H5Br3Se: C, 18.2;
H, 1.3; Br, 60.6; Found: C, 18.6; H, 1.3; Br, 60.3%. Raman: m(cm−1):
3068, 1550, 1040, 990, 286, 248, 217, 197.
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