The structure of R3PBr2 compounds in the solid state and in solution; geometrical dependence on R, the crystal structures of tetrahedral ionic Et3PBr2 and molecular trigonal bipyramidal (C6F5</su

Article abstract of DOI:10.1039/a807241h

Twenty-one triorganophosphorus dibromide compounds, R₃PBr₂ (R₃ = substituted aryl, mixed aryl-alkyl, triaryl or trialkyl) have been synthesized from diethyl ether solution and characterised by analytical and ³¹P

Full text of DOI:10.1039/a807241h

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The structure of R PBr compounds in the solid state and in
3
2
solution; geometrical dependence on R, the crystal structures of
tetrahedral ionic Et PBr and molecular trigonal bipyramidal
3
2
(
C F ) PBr
6
5 3
2
Stephen M. Godfrey, Charles A. McAuliffe, Imran Mushtaq, Robin G. Pritchard and
Joanne M. Sheffield
Department of Chemistry, University of Manchester Institute of Science & Technology,
Manchester, UK M60 1QD
Received 16th September 1998, Accepted 28th September 1998
Twenty-one triorganophosphorus dibromide compounds, R PBr (R = substituted aryl, mixed aryl–alkyl, triaryl or
3
2
3
31
trialkyl) have been synthesized from diethyl ether solution and characterised by analytical and P-{H} NMR data
in CDCl solution, the vast majority being reported for the first time. All but one of the compounds are ionic,
3
[
R PBr]Br in CDCl solution, in keeping with analogous species containing iodine or chlorine, [R PX]X (X = I or Cl)
3 3 3
31
according to P-{H} NMR studies. In contrast, (C F ) PBr has a molecular five-co-ordinate trigonal bipyramidal
6
5
3
2
structure both in CDCl solution and in the solid state. The single crystal structure of this compound has been deter-
3
mined and it represents the only reported R PBr species which contains a five-co-ordinate phosphorus atom. It
3
2
has D symmetry and perfect trigonal bipyramidal geometry. Why (C F ) PBr is the only R PBr compound which
3
6
5
3
2
3
2
adopts trigonal bipyramidal geometry is reasoned to be due to the very low basicity of the parent tertiary phosphine,
which favours this geometry for the dihalogen adducts, a phenomenon previously observed for dichlorine adducts of
tertiary phosphines and dihalogen adducts of tertiary arsines. The crystal structure of the first non-solvated trialkyl-
phosphine dibromide compound, Et PBr , has also been determined and contains a tertrahedral phosphorus atom,
3
2
exhibiting a long Br ؒ ؒ ؒ Br contact, 3.303(2) Å, and is probably better described as ionic, [Et PBr]Br, with significant
3
cation–anion interaction.
Introduction
agreement with solution studies. More recently, a sample of
Ph PBr prepared from diethyl ether solution was examined
crystallographically and shown to adopt the four-co-ordinate
3
2
3
Although compounds of formula R PX (X = Cl, Br or I) have
3
2
1
been recognised for over a century, it is only recently that their
precise structural nature has been elucidated. The interesting
variety, and in some cases unexpected structures of such com-
pounds in the solid state, has sparked considerable renewed
interest in this area. Perhaps surprisingly, no comprehensive
study of compounds of formula R PBr has ever been reported
charge-transfer structure Ph PBr–Br, previously established
3
for the diiodo compound, Ph PI . However, this has been
3
2
15
challenged by Gates and co-workers who spectroscopically
investigated Ph PBr , prepared from both dichloromethane and
3
2
2–7
toluene solution; these workers compared the Raman spectrum
of this material with those of the salts [Ph PBr][BBr ] and
3
2
3
4
despite the fact that Ph PBr is available commercially and has
[Ph PBr][AlBr ]. The similarity between the Raman spectra
3
2
3 4
found significant use in synthetic organic chemistry, being
led the authors to conclude that Ph PBr is better described
3 2
8
widely used in many bromination reactions.
as ionic, [Ph PBr]Br, in the solid state despite the fact that the
3
2
9
Recent studies by us and other workers have established the
Br–Br distance, 3.12(1) Å, lies well within bonding distance
if the van der Waals radius for two bromine atoms, 3.9 Å, is
considered. Clearly triorgano-phosphorus and -arsenic dihalide
compounds could conceivably be regarded as either molecular
diiodide compounds, R PI , as charge-transfer species, (R =
3
2
3
2
2
2
t 9
Ph , PhMe or Bu 3 ). However, a sample of Ph PI prepared
from nitrobenzene, a more polar solvent, was claimed to be
ionic, [Ph PI]I, from solid state P-{H} NMR spectroscopy,
3
3
2
10
31
charge-transfer ‘spoke’ structures R EX–X (E = P or As;
3
3
thus illustrating the structural dependence of R PI compounds
X = Br or I) which exhibit a weak donor–acceptor X–X bond or
3
2
on the nature of the solvent in which they are prepared.
The analogous dibromine compounds, R PBr , have received
as ionic species, [R EX]X (E = P or As; X = Br or I), which
exhibit significant cation–anion interactions; which of these
3
3
2
very little attention, especially in the solid state. Solution
structures is correct is probably dependent on the R, E and
31
P-{H} NMR studies regarding such compounds are limited
X variables for any given R EX2 compound. It has been
3
10
n
3
i
3
11
to Ph PBr , Bu PBr , Pr PBr , as well as the nitrogen
established by Raman spectroscopy that Ph AsI does exist as a
3
2
2
2
3
2
containing compounds (Et N) PBr , (Me N) PBr and
donor–acceptor charge-transfer compound, Ph AsI–I, similarly
2
3
2
2
3
2
3
12
Me(Me N) PBr . All the compounds were assigned an ionic
Ph PI has been shown to be a donor-acceptor compound of
2
2
2
3
2
ϩ
Ϫ
structure [R PBr]Br, in acetonitrile solution. Such reports are
[Ph PI] and I . The perceived ambiguity regarding the solid-
3
3
in agreement with conductimetric studies by Harris and co-
state structure of R EX compounds indicates that a theoretical
3
2
13
workers who also assigned R PBr2 compounds an ionic
study of these compounds would certainly be worthwhile. No
trigonal bipyramidal compound of formula R PBr has been
3
structure, [R PBr]Br, again in acetonitrile solution. Solid state
3
3
2
investigations of R PBr compounds are limited to an infrared
crystallographically characterised and the ionic structure of
3
2
1
4
31
study of Me PBr2 and a solid state1 P-{H} NMR study of
R PBr compounds, [R PBr]Br, which has been suggested from
3
3
2
3
0
Ph PBr prepared from nitrobenzene. Both compounds were
several NMR, infrared and conductimetric studies, had never
3
2
assigned an ionic structure, [R PBr]Br (R = Me or Ph) in
been confirmed crystallographically. However, very recently
3
J. Chem. Soc., Dalton Trans., 1998, 3815–3818
3815

View Article Online
7
du Mont and co-workers reported the crystal structure of the
Table 1 Analytical and spectroscopic data for the compounds R PBr
3 2
i
solvated compound Pr PBr ؒ0.5CH Cl . This molecule exhibits
a long Br ؒ ؒ ؒ Br contact [3.369(2) Å] and is essentially ionic; the
bromide ions of two such ion pairs are ‘bridged’ by a CH Cl2
3
2
2
2
a
Analysis (%)
3
1
Pb -{H},
2
Compound
C F ) PBr
2
C
H
Br
δ
molecule.
We are currently engaged on a comprehensive study of
R EX compounds (E = P or As; X = Cl , Br , I or IBr ).
Our studies regarding the related chloro-compounds, R PCl ,
have shown that the structure of such compounds is dependent
on the nature of R and, in some cases, the nature of the solvent
used for their preparation. In most cases the compounds are
ionic both in the solid state and in solution, this being
illustrated crystallographically for Pr PCl . In contrast, the
(
31.0 (31.2) 0.0 (0.0) 23.2 (23.1) Ϫ59.1
6
5
3
16
5
3
2
4
3
2
2
2
2
2
(p-FC H ) PBr
45.4 (45.4) 2.8 (2.5) 33.2 (33.6)
47.3 (47.2) 3.1 (2.8) 34.9 (34.9)
40.8 (41.1) 2.4 (2.3) 30.3 (30.4)
55.4 (54.3) 4.9 (4.5) 33.3 (34.5)
51.6 (52.3) 3.9 (4.2) 33.4 (33.9)
47.0
44.3
48.1
45.9
54.4
52.3
49.2
64.4
72.2
55.0
63.0
67.7
83.7
81.2
102.5
101.6
100.0
89.8
105.5
48.2
6
4
3
2
5
3
2
(p-FC H )Ph PBr
6
4
2
2
(p-ClC
H
4
)
PBr
6
3
2
(
(
(
m-MeC H ) PBr
6
4
3
2
o-MeC H )Ph PBr
6
4
2
2
p-MeC H )Ph PBr 48.7 (48.4) 3.9 (4.2) 33.4 (33.9)
6
4
2
2
Ph PBr
3
51.5 (51.2) 3.8 (3.6) 37.7 (37.9)
49.4 (49.1) 7.7 (7.5) 36.1 (36.4)
51.5 (50.5) 5.1 (4.9) 36.0 (37.4)
46.1 (46.4) 4.2 (4.4) 39.9 (41.2)
43.3 (43.3) 3.5 (3.6) 44.5 (44.4)
31.9 (32.2) 3.8 (3.7) 53.7 (53.7)
43.8 (43.8) 6.3 (6.5) 41.8 (41.7)
40.3 (40.7) 5.4 (5.4) 45.2 (45.1)
39.5 (39.8) 7.2 (7.5) 43.8 (44.2)
33.6 (33.7) 6.9 (6.6) 49.6 (50.0)
26.1 (25.9) 5.6 (5.4) 57.1 (57.5)
54.3 (54.3) 4.6 (4.5) 34.1 (34.5)
48.5 (49.1) 8.3 (7.5) 35.8 (36.4)
22.0 (22.3) 5.9 (5.6) 49.0 (49.5)
2
n
3
2
Ph (C H N)PBr
2 5 4 2
compounds R PCl2 [R = (C F ) or Ph (C F )] are five-
Ph (C H )PBr
3
3
6
5
3
2
6
5
2
6
11
2
n
co-ordinate molecular trigonal bipyramidal species. Interest-
ingly, Ph PCl2 appears to represent a borderline case and
is solvent dependent, Ph PCl2 prepared from diethyl ether
again being molecular trigonal bipyramidal whereas the
same material prepared in the same way but using CH Cl2
as a solvent produces the ionic solvated dinuclear species
Ph PCl ؒ ؒ ؒ Cl ؒ ؒ ؒ ClPPh ]Clؒ2CH Cl .
The aims of the present study are therefore as follows: first to
report a comprehensive study of R PBr compounds which
Ph
2
Pr PBr
2
Ph MePBr
2
2
2
3
PhMe PBr
2
3
n
PhBu PBr
2
2
n
PhPr PBr
2
2
n
2
Bu PBr
Pr PBr
3
2
n
3
2
[
Et
3
PBr
2
3
3
2
2
(
(
(
PhCH ) PBr
2 3 2
C H ) PBr
2
6
11
3
3
2
Me N) PBr
2
3
2
contain a wide variety of different R groups on the phosphorus
atoms, secondly to characterise crystallographically the first
five-co-ordinate trigonal bipyramidal R PBr compound and
a
b
Calculated values in parentheses. Shifts recorded in CDCl relative to
3
concentrated phosphoric acid standard.
3
2
thirdly to characterise crystallographically the first ionic
solvent-free [R PBr]Br compound to compare with du Mont’s
3
i
3
7
Pr PBr ؒ0.5CH Cl . Considering the familiarity of R PBr2
The chemical shifts recorded in Table 1 are also similar to
2
2
2
3
1
5
compounds to both inorganic and organic chemists alike,
establishing their structures is of fundamental importance and
is of considerable current interest.
those previously observed for analogous R PI2 and R PCl2
3 3
compounds which have also been shown to adopt the ionic
[R PX]X (X = Cl or I) structure in CDCl solution.
that the CDCl3 solution
P-{H} NMR shifts for [R PCl]Cl are more positive than those
3
3
2,5
We have previously observed
31
3
Results and discussion
of [R PI]I. In keeping with this phenomenon, the values
3
All of the triorganophosphorus dibromides synthesized for this
study were prepared by the reaction of equimolar quantities of
tertiary phosphine and dibromine in diethyl ether, eqn. (1)
recorded here for [R
recorded for [R PCl]Cl and [R
phosphine. The P-{H} NMR resonance for (C
3
PBr]Br are intermediate between those
PI]I, for a given parent tertiary
PBr
3
3
31
F )
5
,
2
6
3
δ Ϫ59.1, is clearly anomalous and is particularly interesting
Et
2
O, N
r.t.
2
since it arises from the R PBr compound which contains the
3
2
R P ϩ Br2
R PBr2
(1)
3
3
more acidic (or least basic) parent tertiary phosphine. In
addition, this value is similar to the chemical shift in the
3
1
(
r.t. = room temperature). Reaction times were dependent on
P-{H} NMR of (CF ) PBr , δ Ϫ64.5, recorded by Cavell
3 3 2
17
the tertiary phosphine; triaryl tertiary phosphines took ca. 3 d
to reach complete reaction with dibromine whereas the corre-
sponding trialkyl tertiary phosphines reacted with dibromine
in a matter of hours. In all cases a white flocculent solid was
produced which was isolated by standard Schlenk techniques.
All the products described are very moisture sensitive,
especially those containing parent trialkyl tertiary phosphines,
which smoke profusely when exposed to the atmosphere,
therefore strictly anhydrous conditions must be adhered to dur-
ing their synthesis and subsequent manipulation. Elemental
et al., who assigned a trigonal bipyramidal structure to this
R PBr2 compound. However, no five-co-ordinate R PBr2
3
3
species has been crystallographically characterised. Conse-
quently we decided to investigate the structure of (C F ) PBr
6
5
3
2
by single crystal X-ray diffraction.
Recrystallisation of (C F ) PBr from dichloromethane
6
5
3
2
solution at room temperature produced a large quantity of
huge colourless crystals on standing for ca. 7 d. Of these, one
was selected for analysis by X-ray diffraction. In contrast to
all previous reports regarding compounds of formula R PBr ,
3
2
31
analyses of the compounds, together with their P-{H} NMR
which relate to phosphorus in tetrahedral geometry, (C F ) -
6 5 3
chemical shifts recorded in CDCl solution, are presented in
Table 1.
PBr2 is trigonal bipyramidal, with a five-co-ordinate phos-
phorus atom, Fig. 1. In addition to being the first reported
trigonal bipyramidal R PBr compound, (C F ) PBr is also
3
With one notable exception, (C F ) PBr , all of the R PBr
6
3
5
3
2
3
2
3
2
6
5
3
2
1
compounds exhibit high positive P-{H} NMR resonances.
Such resonances are indicative of an ionic structure in CDCl3
solution, irrespective of their solid state structure. Further-
more, the values recorded herein are in good agreement with
the limited studies regarding such compounds performed by
only the second non-solvated R PBr compound to be studied
3 2
crystallographically. The reason why (C F ) PBr adopts this
6
5
3
2
geometry in contrast to all the other reported R PBr com-
3
2
pounds reported herein must be due to the very low basicity of
the parent tertiary phosphine. It exhibits crystallographically
1
0–12
¯
previous workers.
Of the compounds described here only
imposed (space group R3c) trigonal bipyramidal geometry (D3
10
n
11
12
Ph PBr , Bu PBr , and (Me N) PBr have previously been
symmetry) with d(P–Br) of 2.4105(9) Å, significantly longer
3
2
3
2
2
3
2
31
3
the subject of a solution P-{H} NMR spectroscopic study;
the present values for these compounds δ 49.2, 102.5 and 48.2,
are in good agreement with the previously reported values of
than that exhibited by Ph PBr , 2.181(2) Å , as expected with
3
2
the higher co-ordination number at the phosphorus atom.
In addition to crystallographically characterising the first tri-
gonal bipyramidal R PBr compound, we were also interested
10–12
δ 48.3, 105.0 and 47.0 respectively. Previous workers
also
3
2
assigned an ionic structure, [R PBr]Br, in solution to these
in crystallographically characterising an R PBr2 compound
3
3
compounds.
which adopts an ionic structure but doesn’t contain a dichloro-
3
816
J. Chem. Soc., Dalton Trans., 1998, 3815–3818

View Article Online
the structure is probably best described as ionic, [Et PBr]Br
3
with cation–anion interaction. This interaction is similar to
i
that exhibited by Pr PBr ؒ0.5CH Cl , 3.369(2) Å, reported by
3
2
7
2
2
du Mont and co-workers.
Conclusion
The results reported here clearly show that all of the R PBr2
3
compounds except one ionise in CDCl solution to produce
3
31
[
R PBr]Br, from P-{H} NMR studies. However when a very
3
weakly basic parent tertiary phosphine is employed, (C F ) P, a
6
5 3
trigonal bipyramidal R PBr compound is revealed in the solid
3
2
state which also persists in CDCl solution. The geometrical
3
dependence of R PBr compounds on R is therefore clearly
3
2
illustrated. This phenomenon has previously been observed for
15
5
R AsBr2 and R PCl2 compounds.
3
3
The solid state structure of Et PBr , prepared and recrystal-
3
2
lised from Et O, is interesting to compare to the solvated
2
i
7
Pr PBr ؒ0.5CH Cl . Both structures exhibit long Br–Br con-
3
2
2
2
tacts [3.303(2) and 3.369(2) Å, respectively] and are essentially
ionic.
Fig. 1 Molecular structure of (C F ) PBr (the molecule has crystal-
6
5
3
2
lographically imposed D symmetry). Selected bond lengths (Å) and
angles (Њ): Br(1)–P(1) 2.4105(9), P(1)–C(1) 1.819(7); C(1)–P(1)–C(1)
3
Experimental
1
1
20, C(1)–P(1)–Br(1) 90, Br(1)–P(1)–Br(1) 180, C(2)–C(1)–P(1)
21.6(3).
All of the compounds reported here are moisture sensitive,
some intensely so, decomposing in a few seconds if exposed
to the atmosphere. Consequently, strictly anaerobic and
anhydrous conditions were employed for their synthesis. Any
subsequent manipulations were carried out inside a Vacuum
Atmospheres HE-493 glove-box. Diethyl ether (BDH) was
dried by standing over sodium wire for ca. 1 d and subsequently
refluxed over CaH in an inert atmosphere and distilled directly
2
into the reaction vessel. Anhydrous CH Cl was obtained com-
2
2
mercially (Aldrich) and used as received. Tertiary phosphines
were either synthesized by standard Grignard techniques, R P
3
[
(
(
R = (p-FC H ) , (p-FC H )Ph , (p-ClC H ) , (m-MeC H ) ,
3
6
4
3
6
4
2
6
n
4
3
6
4 3
n
o-MeC H )Ph , (p-MeC H )Ph , PhBu , PhPr or Ph2-
6
4
2
6
4
2
2
2
C H )] or obtained commercially, R P [R = (C F ) , Ph ,
6
11
3
3
6
5
3
3
n
n
n
Ph (C H N), Ph Pr , Ph Me, PhMe , Bu or Pr 3 (Aldrich);
2
5
4
2
2
2
3
R = Et , (CNCH CH ) , (PhCH ) or (C H ) , (Strem); R =
3
2
2
3
2
3
6
11 3
Me N (Lancaster)]. The purity of all the tertiary phosphines
2
31
used was confirmed by elemental analysis and P-{H} NMR
spectroscopy prior to use. Dibromine was obtained com-
mercially (Aldrich) and used as received.
All the R PBr compounds were synthesized in a similar
3
2
way, that of Ph PBr being typical. Triphenylphosphine (2.00 g,
3
2
3
7
.63 mmol) was suspended in Et O (ca. 75 cm ) and sub-
2
3
sequently dibromine (1.22 g, 0.39 cm , 7.63 mmol) was added.
After reaction completion, the resultant white solid was
isolated using standard Schlenk techniques. The solids were
then transferred to pre-dried argon-filled ampoules which were
flame sealed.
Fig. 2 Molecular structure of [Et PBr]Br (only one of each of the
3
disordered methylene groups is illustrated for clarity). Selected bond
lengths (Å) and angles (Њ): Br(2)–Br(1) 3.303(2), Br(2)–P(1) 2.173(3);
Br(1)–Br(2)–P(1) 177.5(1).
Elemental analyses were performed by the analytical
laboratory of this department. The P-{H} NMR spectra
31
methane solvent molecule since, as observed in [Ph PCl ؒ ؒ ؒ
3
were recorded as CDCl solutions on a Bruker AC200 high-
3
i
3
Cl ؒ ؒ ؒ ClPPh ]Clؒ2CH Cl and Pr PBr ؒ0.5CH Cl , the long-
3
2
2
2
2
2
resolution multiprobe spectrometer relative to concentrated
phosphoric acid as standard.
range electrostatic interactions between the solvent and the
ionic molecule influence the product formed. Consequently, we
recrystallised a sample of Et PBr previously prepared in Et O
3
2
2
Crystallography
from Et O (and not CH Cl to avoid its possible inclusion in
2
2
2
the structure) at room temperature. On standing for ca. 6 d a
number of colourless crystals formed which were removed from
the reaction vessel in an inert atmosphere and plunged into
an inert oil. From these, a suitable crystal was chosen for
examination by single crystal X-ray diffraction. The crystal
structure of Et PBr is illustrated in Fig. 2. The structure repre-
sents the first crystallographically characterised non-solvated
trialkylphosphine dibromide compound and contains the
phosphorus atom in tetrahedral geometry, as expected. A long
contact [3.303(2) Å] exists between the two bromine atoms and
Crystals of (C F ) PBr were mounted in Lindemann tubes
6
5
3
2
under an atmosphere of dry argon. Crystals of Et PBr were
3
2
submerged in an inert oil under anaerobic conditions and a
suitable crystal was chosen by examination under the micro-
scope. The crystal, with its protective coating of oil, was then
mounted on a glass fibre and transferred to the diffractometer
and cooled to ca. 183(2) K in the cold gas stream derived from
liquid nitrogen. Measurements were performed on a MAC 3
CAD 4 diffractometer employing graphite-monochromated
Mo-Kα radiation (λ = 0.71069 Å) and ω–2θ scans. Both
3
2
J. Chem. Soc., Dalton Trans., 1998, 3815–3818
3817

View Article Online
Table 2 Crystal data and details of refinement for R PBr
McAuliffe, R. G. Pritchard and P. J. Kobryn, J. Chem. Soc., Dalton
Trans., 1993, 101; N. Bricklebank, S. M. Godfrey, H. P. Lane,
C. A. McAuliffe, R. G. Pritchard and J. M. Moreno, J. Chem. Soc.,
Dalton Trans., 1995, 2421.
3
2
(
C F ) PBr
[Et PBr]Br
6
5
3
2
3
3
4
5
N. Bricklebank, S. M. Godfrey, A. G. Mackie, C. A. McAuliffe and
R. G. Pritchard, J. Chem. Soc., Chem. Commun., 1992, 355.
N. Bricklebank, S. M. Godfrey, C. A. McAuliffe and R. G.
Pritchard, J. Chem. Soc., Dalton Trans., 1993, 2261.
S. M. Godfrey, C. A. McAuliffe, R. G. Pritchard and J. M. Sheffield,
Chem. Commun., 1996, 2521; S. M. Godfrey, C. A. McAuliffe,
R. G. Pritchard, J. M. Sheffield and G. M. Thompson, J. Chem.
Soc., Dalton Trans., 1997, 4823.
M. A. H. A. Al-Juboori, P. N. Gates and A. S. Muir, J. Chem.
Soc., Chem. Commun., 1991, 1270.
F. Ruthe, W. W. du Mont and P. G. Jones, Chem. Commun., 1997,
1947.
G. A. Wiley, B. M. Rein and R. L. Hershkowitz, Tetrahedron
Lett., 1964, 2509; A. G. Anderson and F. J. Freenor, J. Am. Chem.
Soc., 1964, 86, 5037; J. Org. Chem., 1972, 27, 626.
W. W. du Mont, M. Bätcher, S. Pohl and W. Saak, Angew. Chem.,
Int. Ed. Engl., 1987, 26, 912.
M
T/K
Crystal system
Space group
a/Å
691.97
293(2)
277.97
183(2)
Rhombohedral
Orthorhombic
Pbca (no. 61)
16.387(6)
14.585(2)
9.369(2)
2239(1)
8
1.649
1088
73.20
1746
¯
R3c (no. 167)
11.539(3)
—
26.389(5)
3043(1)
6
2.266
1968
42.17
596
b/Å
c/Å 3
U/Å
6
7
8
Z
Ϫ3
D /g cm
c
F(000)
µ/cm
Total data measured
Maximum 2θ/Њ
No. unique reflections
No. observed reflections
Ϫ1
49.8
596
50.0
1746
9
[
I > 2.00σ(I)]
596
58
0.0317
0.0529
1746
95
0.063
0.012
1
0 K. B. Dillon and T. C. Waddington, Nature (London) Phys. Sci.,
971, 230, 158.
No. parameters
Final R
Final RЈ
1
1
1
1 G. A. Wiley and W. R. Stine, Tetrahedron Lett., 1967, 24, 2321.
2 R. Bartsch, O. Stelzer and R. Schmutzler, Z. Naturforsch, Teil B,
1
981, 36, 1349; J. Fluorine Chem., 1982, 20, 85.
structures were solved by direct methods. Unit-cell dimensions
were derived from the setting angles of 25 accurately centred
reflections. Lorentz-polarisation corrections were applied.
Details of the X-ray measurements and subsequent structure
determinations are presented in Table 2. Hydrogen atoms were
confined to chemically reasonable positions. In the structure
1
3 A. D. Beveridge and G. S. Harris., J. Chem. Soc., 1964, 6077; A. D.
Beveridge, G. S. Harris and F. Inglis, J. Chem. Soc. A, 1966, 520;
A. D. Beveridge, G. S. Harris and D. S. Payne, J. Chem. Soc. A, 1966,
7
26; G. S. Harris and M. F. Ali, Tetrahedron Lett., 1968, 37; Inorg.
Nucl. Chem. Lett., 1968, 4, 5; M. F. Ali and G. S. Harris, J. Chem.
Soc., Dalton Trans., 1980, 1545; G. S. Harris and J. S. McKechnie,
Polyhedron, 1985, 4, 115.
of [Et PBr]Br each of the methylene groups is disordered over
3
14 J. Goubeau and R. Baumgartner, Z. Electrochem., 1960, 64, 598.
15 M. A. H. A. Al-Juboori, P. N. Gates and A. S. Muir, J. Chem. Soc.,
Dalton Trans., 1994, 1441.
6 N. Bricklebank, S. M. Godfrey, H. P. Lane, C. A. McAuliffe,
R. G. Pritchard and J. M. Moreno, J. Chem. Soc., Dalton Trans.,
two semi-populated sites.
Neutral atom scattering factors were taken from ref. 18.
Anomalous dispersion effects were taken from ref. 19. All
calculations were performed using SHELXS 86 and SHELXL
1
1
995, 3873.
7 R. G. Cavell, J. A. Gibson and K. I. The, J. Am. Chem. Soc., 1977,
9, 784.
20,21
9
3 crystallographic software packages.
CCDC reference number 186/1174.
1
1
1
2
2
9
8 International Tables for X-Ray Crystallography, Kynoch Press,
Birmingham, 1974, vol. 4, Table 2.2A.
Acknowledgements
We are grateful to the EPSRC for a research studentship (to
J. M. S.).
9 International Tables for X-Ray Crystallography, Kynoch Press,
Birmingham, 1974, vol. 4, Table 2.3.1.
0 G. M. Sheldrick, SHELXS 86, in Crystallographic Computing 3,
ed. G. M. Sheldrick, Oxford University Press, 1985, p. 175.
1 G. M. Sheldrick, SHELXL 93, University of Göttingen, 1993.
References
1
2
A. M. Liebigs, Ann. Chem., 1876, 181, 256.
S. M. Godfrey, D. G. Kelly, A. G. Mackie, C. A. McAuliffe, R. G.
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163; N. Bricklebank, S. M. Godfrey, A. G. Mackie, C. A.
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