Characterisation of the tetrahalophosphonium cations PBrnI4 - n+ (0 ≤ n ≤ 4) by 31P MAS NMR, IR and Raman spectroscopy and the crystal structures of PI4+AlCl4-, PI4+AlBr4- and PI4+GaI4-

Article abstract of DOI:10.1039/b101197i

The novel tetrahalophosphonium salts PBr₄⁺AsF₆^-, PI₄⁺AlCl₄^- and PI₄⁺EBr₄^- (E = Al, Ga) have been synthesised. A variety of solid complexes containing PBr₄⁺ (e.g. PBr₄⁺AsF₆^-, PBr₄⁺AlBr₄^- PBr₄⁺GaBr₄^-), PI₄⁺ (e.g. PI₄⁺AlCl₄^-, PI₄⁺AlBr₄^-, PI₄⁺GaBr₄^-) or the mixed species PBr_nI_{4 - n}⁺ (0 ≤ n ≤ 4, containing AlBr₄^-, GaBr₄^-, AsF₆^- or SbF₆^-) have been studied by solid-state ³¹P MAS NMR and vibrational spectroscopy. The influence of the counter-ion on the chemical shift and the vibrational frequencies are discussed. The crystal structures of PI₄⁺AlCl₄^-, PI₄⁺AlBr₄^- and PI₄⁺GaI₄^- are reported. Evidence for the existence of the hitherto unknown mixed bromoiodophosphonium cations PBr₃I⁺, PBr₂I₂⁺ and PBrI₃⁺ has been confirmed by spin-orbit corrected density functional calculations of isotropic ³¹P chemical shifts for PBr_nI_{4 - n}⁺.

Full text of DOI:10.1039/b101197i

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؉
Characterisation of the tetrahalophosphonium cations PBr I
(
n 4 Ϫ n
31
0 ≤ n ≤ 4) by P MAS NMR, IR and Raman spectroscopy and
؉ Ϫ ؉ Ϫ ؉ Ϫ
the crystal structures of PI AlCl , PI AlBr and PI GaI
4
4
4
4
4
4
a
b
a
a
Christoph Aubauer, Martin Kaupp, Thomas M. Klapötke,* Heinrich Nöth,†
a
a
a
a
Holger Piotrowski,† Wolfgang Schnick, Jürgen Senker* and Max Suter†
a
Department of Chemistry, Ludwig-Maximilians-University, Butenandtstr. 5-13 (D),
D-81377 Munich, Germany. E-mail: tmk@cup.uni-muenchen.de
Institute of Inorganic Chemistry, University of Würzburg, Am Hubland, D-97074 Würzburg,
Germany
b
Received 6th February 2001, Accepted 12th April 2001
First published as an Advance Article on the web 18th May 2001
ϩ
Ϫ
ϩ
Ϫ
ϩ
Ϫ
The novel tetrahalophosphonium salts PBr AsF , PI AlCl and PI EBr (E = Al, Ga) have been synthesised.
4
6
4
4
4
4
ϩ
4
ϩ
Ϫ
ϩ
4
Ϫ
4
ϩ
4
Ϫ
4
ϩ
4
ϩ
4
Ϫ
4
A variety of solid complexes containing PBr (e.g. PBr AsF , PBr AlBr PBr GaBr ), PI (e.g. PI AlCl ,
PI AlBr , PI GaBr ) or the mixed species PBr I
have been studied by solid-state P MAS NMR and vibrational spectroscopy. The influence of the counter-ion on
the chemical shift and the vibrational frequencies are discussed. The crystal structures of PI AlCl , PI AlBr and
PI GaI are reported. Evidence for the existence of the hitherto unknown mixed bromoiodophosphonium cations
PBr I , PBr I and PBrI3 has been confirmed by spin–orbit corrected density functional calculations of isotropic
4
ϩ
4 Ϫ n
6
ϩ
4
Ϫ
4
ϩ
4
Ϫ
4
Ϫ
Ϫ
Ϫ
Ϫ
(0 ≤ n ≤ 4, containing AlBr , GaBr , AsF or SbF )
n
4 4 6 6
3
1
ϩ
Ϫ
4
ϩ
4
Ϫ
4
4
ϩ
4
Ϫ
4
ϩ
ϩ
ϩ
3
2 2
31
ϩ
.
P chemical shifts for PBrnI4 Ϫ n
Introduction
evidence for the existence of the mixed tetrahalophosphonium
ϩ ϩ
cations PBrnI
4 Ϫ n
(1 ≤ n ≤ 3). Only the existence of the PBr3I
ϩ 1
ϩ 2,3
The binary tetrahalophosphonium cations PF , PCl ,
4
4
cation has been assumed in the reaction of PBr and I in acetic
ϩ 2a,3,4
ϩ 5–7
3
2
PBr4
and PI4
have been known for some time and
14
anhydride in a conductivity study.
3
1
were characterised by vibrational and P NMR spectroscopic
studies. Additionally, several crystal structure determinations
have been reported for PCl compounds with a large variation
of the counter-ion. PBr4 and PI4 have been characterised
In this paper we report the preparation and characterisation
of a complete series of the mixed bromoiodophosphonium
ϩ
4
ϩ
31
cations by means of solid-state P MAS NMR spectroscopy.
2a,8
ϩ
31
To allow unequivocal assignment, we have computed the
NMR chemical shifts of the free cations PBrnI
4 Ϫ n
P
ϩ
4
Ϫ 9
onlyϩ by X-ray crystallography in the salts PBr Br ,
ϩ
(0 ≤ n ≤ 4)
Ϫ 10
ϩ
Ϫ 11
PBr Br
and PI AlI .
4
3
4 4
by density functional theory (DFT) methods corrected for SO
6
Recently, we showed in a combined theoretical and experi-
31
coupling. The results of the P MAS NMR and the vibrational
ϩ
4
mental study, that the PI cation has an extremely large nega-
spectra clearly indicate that the counter-ion has a dramatic
31
ϩ
4
Ϫ
tive P chemical shift in the compounds PI AsF (δ = Ϫ519)
6
influence on the chemical shift and the vibrational frequencies
ϩ
Ϫ
and PI SbF (δ = Ϫ517), which is due to spin–orbit (SO) con-
ϩ
4
6
of the tetrahalophosphonium species. Additionally, PI -
4
tributions from the four heavy iodine substituents, transmitted
to the phosphorus nucleus by a very effective Fermi-contact
mechanism. The less negative solid-state P NMR chemical
Ϫ
4
ϩ
4
Ϫ
4
ϩ
4
Ϫ
4
AlCl , PI AlBr
and PI GaI
have been structurally
characterised by single-crystal X-ray diffraction.
3
1
ϩ
Ϫ
shifts found in the polymeric PI AlI
(δ = Ϫ305) and
4
4
ϩ
Ϫ
Results and discussion
PI GaI (δ = Ϫ295), suggest that the P–I bond orders are
4
4
ϩ
4
reduced due to intermolecular I ؒ ؒ ؒ I interaction between PI
Synthesis
Ϫ
6
cations and EI4 (E = Al, Ga) anions.
ϩ
Ϫ
ϩ
ϩ
2
ϩ
Tetrabromophosphonium hexafluoroarsenate, PBr AsF ,
4 6
PCl Br , PCl Br and PClBr3 have been characterised by
3
2
31
was prepared by the reaction of one equivalent of PBr with
3
ϩ Ϫ
P NMR and Raman spectroscopy in solids and solutions
containing mixtures of the chlorobromophosphonium cations
one equivalent of Br AsF , reaction 1, eqn. 1, in CFCl .
3
6
3
ϩ
3,12
PCl Br
(0 ≤ n ≤ 4).
Replacement of a chlorine by a
n
4 Ϫ n
bromine causes an upfield shift of about 40 ppm. Solution-state
(1)
3
1
P NMR studies showed that there is a characteristic chemical
shift range dependent upon the nature of the counter-ion
ϩ
The colourless product formed was characterised by solid-
31
present. The variation of the P chemical shift for PCl Br
31
n
4 Ϫ n
state P MAS NMR and vibrational spectroscopy. Addition-
(
0 ≤ n ≤ 4) as a function of the anion in the solid-state is even
31
ally, we recorded the solid-state P MAS NMR spectra of
3
ϩ
larger. The mixed chloroiodophosphonium cations PCl I and
PCl2I2 formed from the reaction of PI with the strongly acidic
ϩ
4
Ϫ
4
ϩ
4
ϩ
Ϫ
4
Ϫ
3
PBr AlBr and PBr GaBr , which were prepared according
ϩ
3
2e
ϩ
Ϫ
to the literature. PI AlBr and PI GaBr were prepared
4
4
4
4
solvent HSClO were characterised by means of solution-state
3
from the reaction of PI with IBr and EBr (reactions 2 and 3,
31
13
3
3
P NMR spectroscopy.
E = Al, Ga) in a 1 : 1 : 1 molar ratio, eqn. 2, in CS under
2
To our knowledge, prior to this study there had been no
nitrogen.
(
2)
†
Crystal structure analyses.
1
880
J. Chem. Soc., Dalton Trans., 2001, 1880–1889
This journal is © The Royal Society of Chemistry 2001
DOI: 10.1039/b101197i

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ϩ
Table 1 MP2-optimised bond distances [Å] and bond angles [Њ] for the tetrahalophosphonium cations PBrnI4 Ϫ n (0 ≤ n ≤ 4) compared to experi-
mental values
ϩa
ϩ
Ϫb
ϩ
ϩ
ϩ
ϩa
ϩ
Ϫc
ϩ
Ϫd
ϩ
Ϫe
PBr4
In PBr4 Br
PBr3I
PBr2I2
PBrI3
PI4
In PI4 AlCl4
In PI4 AlBr4
In PI4 GaI4
Point group Td
C3v
C2v
C3v
Td
P–Br
P–I
2.153
109.5
2.13(3)–2.17(3)
2.162
2.399
2.171
2.407
2.177
2.415
2.423 2.361(4)–2.372(4) 2.376(3)–2.387(4) 2.378(4)–2.423(4)
109.5 108.8(2)–110.5(2) 107.4(1)–112.0(1) 106.9(1)–112.6(2)
Br–P–Br
Br–P–I
I–P–I
107.9(16)–110.0(10)
108.6
110.4
107.7
109.4
111.4
108.6
110.4
a
b
c
d
e
See ref. 6. See ref. 9. See Table 4. See Table 2. See Table 3.
3
1
71
ϩ
Ϫ
Solid-state P and Ga MAS NMR studies (see below)
Table 2 Selected bond lengths [Å] and angles [Њ] for PI AlBr
4 4
ϩ
Ϫ
showed that for PI GaBr the tetrabromogallate() anion is
partly substituted by mixed bromoiodogallate anions, arising
from a halogen exchange during the preparation.
Tetraiodophosphonium tetrachloroaluminate, PI AlCl
was obtained from the reaction of PI with ICl and AlCl in a
4
4
P–I(1)
P–I(2)
P–I(3)
P–I(4)
2.380(4)
2.387(4)
2.381(4)
2.376(3)
Al–Br(1)
Al–Br(2B)
Al–Br(3)
Al–Br(4)
2.290(5)
2.30(1)
2.314(4)
2.312(5)
ϩ
Ϫ
4
4
3
3
1
: 1 : 1 molar ratio, reaction 4, eqn. 3, in CS2.
I(1)–P–I(2)
I(1)–P–I(3)
I(1)–P–I(4)
I(2)–P–I(3)
I(2)–P–I(4)
I(3)–P–I(4)
109.4(2)
112.0(1)
109.5(1)
107.4(1)
110.6(1)
107.9(2)
Br(1)–Al–Br(2B)
Br(1)–Al–Br(3)
Br(1)–Al–Br(4)
Br(2B)–Al–Br(3)
Br(2B)–Al–Br(4)
Br(3)–Al–Br(4)
116.8(5)
108.0(2)
108.0(2)
108.1(7)
108.3(3)
107.3(2)
(
3)
The synthesis of pure compounds containing the mixed
bromoiodophosphonium ions is extremely difficult. Attempts
ϩ
to prepare pure PBr3I species were unsuccessful. Initial pre-
ϩ
Ϫ
parations involving reactions of PBr with I MF (reactions
3
3
6
5
and 6, M = As, Sb) in CFCl or PBr with IBr and EBr
3
3
3
(
reactions 7 and 8, E = Al, Ga) in CS , led to products which
2
ϩ
were obviously mixtures of PBrnI4 Ϫ n
.
All products reported here exist only in the solid-state.
ϩ
Ϫ
Dissolving e.g. PI AlBr in CS gives a solution that con-
4
4
2
ϩ
4
Ϫ
6
tains essentially the starting materials, while PBr AsF is not
soluble in common solvents.
Structures
The P–X distances and X–P–X angles for the isolated tetra-
ϩ
halophosphonium cations PBrnI4 Ϫ n (0 ≤ n ≤ 4), computed at
the MP2 level of theory, are summarised in Table 1. The results
ϩ
ϩ
for PBr4 and PI4 agree very well with the available X-ray
data.
ϩ
Ϫ
The unit cell of PI AlBr is shown in Fig. 1, selected bond
4
4
ϩ
4
Ϫ
4
lengths and angles are listed in Table 2. PI AlBr crystallises
in the monoclinic space group P2 /c with four molecules in
1
ϩ
the unit cell. The PI4 unit has a considerably distorted tetra-
hedral geometry. The P–I bonds are almost equal: 2.376(3)–
ϩ
Ϫ
.
Fig. 1 Unit cell of PI4 AlBr4
2
.387(4) Å, the I–P–I bond angles range between 107.4(1)
Ϫ
and 112.0(1)Њ. The AlBr4 anion is also significantly dis-
torted exhibiting bond angles between 107.3(2) and 116.8(5)Њ
and Al–Br distances between 2.290(5) and 2.314(4) Å,
which are comparable with the bond lengths found in
ϩ
4
Ϫ
4
structure of PI GaI shows rather short interatomic I ؒ ؒ ؒ I
distances in the range of 3.357(2)–3.430(2) Å (Fig. 2) between
the PI4 and the GaI4 units, which are significantly shorter
than the sum of the van der Waals radii (ca. 4.30 Å), indi-
ϩ
Ϫ
ϩ
Ϫ 15
16
SeBr AlBr .
3
ϩ
4
Ϫ
PI GaI (Fig. 2, Table 3) crystallises in the orthorhombic
cating strong cation ؒ ؒ ؒ anion interactions, while the crystal
4
4
ϩ
Ϫ
space group Pna2 with four molecules in the unit cell. The
structure of PI AlBr shows considerably weaker interatomic
1
4 4
ϩ
4
Ϫ 11
4
structure is isotypic with PI AlI . The tetrahedra of the
I ؒ ؒ ؒ Br contacts of 3.380(2)–3.449(2) Å (sum of van der Waals
16
cations and anions are significantly distorted, exhibiting I–E–I
radii: ca. 4.10 Å, Fig. 1).
The crystal structure of PI AlCl (Fig. 3, Table 4), which is
ϩ
ϩ
Ϫ
angles between 106.9(1) and 112.6(1)Њ (PI ) and between
4
4
4
Ϫ
ϩ
Ϫ
1
07.12(6) and 112.90(5)Њ (GaI ). P–I distances vary from
isotypic with PI AlBr , displays a more isolated character for
4 4
ϩ
4
2
.378(4) to 2.423(4) Å, Ga–I distances from 2.510(1) to 2.573(2)
PI4 in this species, exhibiting rather short P–I bond distances
(2.361(4)–2.371(4) Å), significantly diminished interatomic
I ؒ ؒ ؒ Cl distances (3.315(8)–3.511(3) Å, sum of van der Waals
Å. P–I bond lengths and I–P–I bond angles are comparable to
ϩ
4
Ϫ 11
those found in PI AlI .
4
ϩ
Ϫ
16
The average P–I bond length of PI AlBr (2.381(4) Å) is
radii: ca. 3.95 Å) and a less distorted tetrahedral geometry
(108.8(2)–110.5(2)Њ) compared to the structures of PI GaI
and PI AlBr .
4
4
ϩ
Ϫ
significantly shorter than the average P–I bond length found in
4
4
ϩ
4
Ϫ
4
ϩ
4
Ϫ
4
ϩ
Ϫ
PI GaI (2.408(4) Å). Similar to PI AlI the molecular
4 4
J. Chem. Soc., Dalton Trans., 2001, 1880–1889
1881

View Article Online
ϩ
Ϫ
Table 3 Selected bond lengths [Å] and angles [Њ] for PI4 GaI4
P–I(1)
P–I(2)
P–I(3)
P–I(4)
2.416(4)
2.423(4)
2.414(3)
2.378(4)
Ga–I(5)
Ga–I(6)
Ga–I(7)
Ga–I(8)
2.573(2)
2.510(2)
2.359(2)
2.548(2)
I(1)–P–I(2)
I(1)–P–I(3)
I(1)–P–I(4)
I(2)–P–I(3)
I(2)–P–I(4)
I(3)–P–I(4)
106.9(1)
112.6(1)
110.0(1)
110.5(1)
108.8(1)
108.0(1)
I(5)–Ga–I(6)
I(5)–Ga–I(7)
I(5)–Ga–I(8)
I(6)–Ga–I(7)
I(6)–Ga–I(8)
I(7)–Ga–I(8)
112.90(5)
107.60(6)
107.12(6)
111.83(6)
108.69(6)
108.50(6)
ϩ
Ϫ
Table 4 Selected bond lengths [Å] and angles [Њ] for PI4 AlCl4
P–I(1)
P–I(2)
P–I(3)
P–I(4)
2.367(4)
2.372(4)
2.371(4)
2.361(4)
Al–Cl(1)
Al–Cl(2)
Al–Cl(3B)
Al–Cl(4B)
2.129(6)
2.144(6)
2.18(4)
2.05(4)
31
ϩ
Ϫ
Fig.
4
MϪ AS solid-state
P NMR spectra of PI4 AlBr4 and
ϩ
PI4 AlCl4 at a spinning frequency of 20 kHz. Asterisks denote
spinning side bands.
I(1)–P–I(2)
I(1)–P–I(3)
I(1)–P–I(4)
I(2)–P–I(3)
I(2)–P–I(4)
I(3)–P–I(4)
110.1(2)
110.0(2)
108.8(2)
109.1(2)
110.5(2)
108.4(2)
Cl(1)–Al–Cl(2)
106.8(2)
105(1)
127(2)
112(1)
107.8(6)
104(2)
Cl(1)–Al–Cl(3B)
Cl(1)–Al–Cl(4B)
Cl(2)–Al–Cl(3B)
Cl(2)–Al–Cl(4B)
Cl(3B)–Al–Cl(4B)
3
1
71
Fig. 5 MAS solid-state P and Ga NMR spectra for reaction 3
PI ϩ IBr ϩ GaBr ) at a spinning frequency of 25 and 27 kHz,
respectively. The isotropic chemical shifts are indicated by arrows.
Asterisks denote spinning side bands.
(
3
3
ϩ
Ϫ
.
Fig. 2 Unit cell of PI4 GaI4
spectrum consisting of a single resonance of chemical shift
31
Ϫ83 ppm. The P chemical shift agrees with literature values
ϩ
3
reported for PBr 4ϩ compounds (δ = Ϫ72 to Ϫ80) and can be
Ϫ
6
assigned as PBr AsF . As expected, the comparison with
4
6
31
ϩ
4
Ϫ
the P MAS NMR chemical shifts of PBr AlBr (δ = Ϫ79)
4
ϩ
Ϫ
and PBr GaBr (δ = Ϫ80) shows that the chemical shift of
4
4
ϩ
Ϫ
PBr AsF is slightly shifted to low frequency, due to the non-
4
6
coordinating character of the counter-ion.
31
ϩ
Ϫ
4
The P MAS NMR spectrum of PI AlBr (reaction 2,
4
Table 5, Fig. 4) shows one single resonance at δ = Ϫ416, and
is in the range between the isotropic shifts of the polymeric
ϩ
4
Ϫ
4
ϩ
4
Ϫ
6
6
PI GaI (δ = Ϫ295) and the isolated PI AsF (δ = Ϫ519).
This appears consistent with the molecular structure of
ϩ
Ϫ
PI AlBr , which might also be described as intermediate
4
4
between these two extremes.
The P MAS NMR spectrum of the product of reaction 3
ϩ
Ϫ
.
31
Fig. 3 Molecular structure of PI4 AlCl4
(
PI /IBr/GaBr , Table 5, Fig. 5) shows one main signal at
3 3
δ = Ϫ387 (rel. int. 65%), which can be attributed to the iso-
3
1
Solid-state P NMR spectroscopy
ϩ
Ϫ
tropic shift of PI GaBr , as well as four other less intense
4
4
؉
PX4 salts. The solid obtained by the reaction of PBr
and Br AsF (reaction 1, Table 5) gives a P MAS NMR
resonances at δ = Ϫ376 (rel. int. 18%), Ϫ358 (rel. int. 10%),
Ϫ344 (rel. int. 2%) and Ϫ312 (rel. int. 5%).
3
ϩ
Ϫ
31
3
6
1
882
J. Chem. Soc., Dalton Trans., 2001, 1880–1889

View Article Online
31
Table 5
P NMR isotropic chemical shifts [ppm vs. 85% H PO ] for reactions 1–8
3 4
Reaction
δ
Rel. intensity [%]
ωrot/kHz
Assignment
ϩ
Ϫ
31
ϩ
Ϫ
1
2
3
PBr ϩ Br AsF6
3
P
P
P
Ϫ83
100
100
5
25
20
25
PBr AsFϪ6
3
3
4
3
1
1
ϩ
PI ϩ IBr ϩ AlBr
PI ϩ IBr ϩ GaBr
Ϫ416
Ϫ312
Ϫ344
Ϫ358
Ϫ376
Ϫ387
37
Ϫ64
Ϫ456
Ϫ83
Ϫ195
Ϫ315
Ϫ33
Ϫ81
Ϫ196
Ϫ79
PI4 AϩlBr
3
4
3
Ϫ
PBrI GaBr
3
3
3
4
ϩ
Ϫ
2
PI4 GaBrI3
PI4 GaBr2I2
PI4 GaBr3I
PI4 GaBr
GaBr4
GaBrI
ϩ
Ϫ
10
18
65
78
22
100
81
17
2
11
85
4
46
35
16
3
2
6
5
34
6
35
12
ϩ
Ϫ
ϩ
Ϫ
4
7
1
1
Ϫ
Ga
27
Ϫ
3
3
ϩ
Ϫ
4
5
PI ϩ ICl ϩ AlCl
PBr ϩ I AsF6
P
P
20
25
PI4 Aϩ lCl
3
3
4
ϩ
Ϫ
31
Ϫ
PBr4 AsF6
3
3
ϩ Ϫ
PBr I AsF
3 6
ϩ Ϫ
PBr I AsF
6
2
2
ϩ
Ϫ
31
ϩ
Ϫ
6
7
PBr ϩ I SbF6
P
P
25
30
PF4 SbF6
3
3
ϩ Ϫ
PBr4 SbF6
ϩ
Ϫ
PBr I SbF
3
6
3
1
ϩ
Ϫ
PBr ϩ IBr ϩ AlBr
PBr4 AlBr4
3
3
ϩ
Ϫ
Ϫ167/Ϫ171
Ϫ250
Ϫ331
Ϫ68
Ϫ74
Ϫ78
PBr I AlBr
3
4
ϩ
Ϫ
PBr2I2 AlBr4
ϩ
Ϫ
PBrI3 AlBr4
3
1
ϩ
Ϫ
8
PBr ϩ IBr ϩ GaBr
P
30
PBr4 GaBrI3
3
3
ϩ
Ϫ
Ϫ
PBr4 GaBr2I2
ϩ
Ϫ
PBr4 GaBr3I
ϩ
Ϫ
Ϫ80
PBr4 GaBr4
ϩ
Ϫ155
Ϫ170
Ϫ254
PBr I GaBr I
3
3
ϩ
Ϫ
PBr I GaBr
3
4
ϩ
Ϫ
PBr2I2 GaBr4
Ϫ
substitution of the GaBr4 by mixed tetrahalogenogallate()
anions has occurred during the reaction. The resonances at
δ = Ϫ376, Ϫ358 and Ϫ344 with a decreasing relative intensity
ϩ
Ϫ
can be attributed to the chemical shifts of PI GaBr I ,
4
3
ϩ
4
Ϫ
2
ϩ
4
Ϫ
3
PI GaBr I and PI GaBrI . Moreover, the presence of
2
different tetrahalogenogallate() anions in the solid obtained
71
by reaction 3 was confirmed by solid-state Ga MAS NMR
71
spectroscopy. The Ga MAS NMR spectrum (Fig. 5, Table 5)
at a spinning frequency of 27 kHz reveals two broad resonances
centred at δ = 37 (rel. int. 78%) and Ϫ64 (rel. int. 22%). The
7
1
Ga isotropic chemical shifts for the two resonances are
71
comparable with the previous results of the solution-state Ga
NMR studies for GaBr I
Ϫ
and can be assigned to the
n
71
4 Ϫ n
31
ϩ
ϩ
Ϫ
71
Fig. 6
P NMR chemical shifts for some PBr4 and PI4 species.
resonances of GaBr (δ Ga = 37 in the solid-state; δ Ga = 65
4
18 Ϫ 71
in solution) and GaBr3I (δ Ga = Ϫ64 in the solid-state;
31
71
18
Fig. 6 summarises the P NMR chemical shifts of some
δ
Ga = Ϫ48 in solution). The expected less intense signals
ϩ
ϩ
Ϫ
71
18
Ϫ
PBr4 and PI4 species in the presence of different counter-
for GaBr I
(δ Ga = Ϫ173 in solution) and GaBrI3
18
2
2
ϩ
71
anions. The chemical shift of PX4 is dependent on the nature
(δ Ga = Ϫ309 in solution) at higher field could not be
71
of the counter-anion. Significant bridging cation ؒ ؒ ؒ anion
resolved due to the large linewidths of the Ga resonances and
overlapping spinning side bands. Similar halogen exchange
interactions in the lattice result in a weakening of the P–X
ϩ
71
bonds in PX . The comparison of the crystal structures of
mechanisms were reported in recent Ga NMR studies on
ligand-exchange reactions between GaX4 and GaY4 (X,
Y = Cl, Br, I). The Ga chemical shifts for all possible
four-coordinate gallates GaX4 (X = Cl, Br, I) and mixed-halide
4
ϩ
4
Ϫ
4
ϩ
4
Ϫ
4
ϩ
ϩ
4
Ϫ
4
ϩ
Ϫ
Ϫ
PI AlCl , PI AlBr and PI GaI show a more isolated
character for the PI4 cations in PI AlCl and PI AlBr
Ϫ
4
ϩ
4
Ϫ
4
71
4
Ϫ
with weaker interatomic cation ؒ ؒ ؒ anion interactions and con-
ϩ
Ϫ
Ϫ
18
siderably shorter P–I bond lengths than found in PI GaI .
species GaX Y
(X, Y = Cl, Br, I) were found. Note that
4
4
n
4 Ϫ n
The more isolated the cation, the more efficient is the Fermi-
the low frequency shift with increasing number of iodine sub-
19
contact mechanism that transfers the SO-induced spin density
stituents is also due to SO effects. The impurity at δ = Ϫ312 in
3
1
17
31
31
to the P nucleus. The P resonance is shifted to low fre-
the P NMR spectra of reaction 3 may be attributed to the
6
ϩ
ϩ
Ϫ
quency. In case of the PBr4 cation the chemical shift range is
resonance of PBrI GaBr .
3 4
31
ϩ
very small and varies from δ = Ϫ72 to Ϫ83. In contrast, for PI4
The P NMR chemical shift of δ = Ϫ456 found for
ϩ Ϫ
species the anion has a significant influence. Due to much larger
PI AlCl (Fig. 4, Table 5, reaction 4) is at lower frequency,
4 4
ϩ Ϫ
6
31
ϩ
spin–orbit effects, the P chemical shift for PI4 salts varies
as compared to PI EX (E = Al, Ga; X = Br, I). This suggests
4 4
ϩ ϩ Ϫ
ϩ
Ϫ
over a considerably larger range, between δ = Ϫ295 (PI GaI )
and Ϫ519 (PI AsF ). Thus, it is possible to take the low fre-
quency P chemical shift as a measure of the intermolecular
interactions. For mixed PI EBr I
that the PI4 cation in PI AlCl has a more isolated character
4 4
4
4
ϩ
Ϫ
and smaller I ؒ ؒ ؒ Cl interactions in the solid-state, which is in
agreement with the crystal structure.
4
6
31
ϩ
Ϫ
(0 ≤ n ≤ 4) species it is
4
n 4 Ϫ n
؉
expected that a gradual replacement of bromine by iodine in
the counter-anion causes a trend towards high frequency for the
Reaction products containing mixtures of PBr I
. Density
n
4 Ϫ n
31
functional calculations of the P chemical shifts in isolated
PBrnI4 Ϫ n (Table 6, Fig. 7) show the significant influence of
3
1
ϩ
4
ϩ
P chemical shift of PI .
31
The P MAS NMR spectrum of the product of reaction 3
clearly indicates that halogen exchange resulting in a partial
SO effects. While the non-relativistic calculations would pre-
31
ϩ
ϩ
4
dict a slight increase in δ P from PBr4 through PI , SO
J. Chem. Soc., Dalton Trans., 2001, 1880–1889
1883

View Article Online
3
1
Table 6 Comparison of computed and experimental P shifts [ppm vs. 85% H PO ]
3
4
Ee xp.
f
g
h
i
j
k
δNRb
δSOc
δNRϩSOd
ϩa
PBr4
179
197
207
212
211
Ϫ205
Ϫ317
Ϫ415
Ϫ588
Ϫ734
Ϫ26
Ϫ120
Ϫ208
Ϫ376
Ϫ523
Ϫ83
Ϫ196
Ϫ315
Ϫ81
Ϫ195
Ϫ79
Ϫ80
ϩ
PBr3I
Ϫ167
Ϫ250
Ϫ331
Ϫ416
Ϫ170
Ϫ254
Ϫ312
Ϫ387
ϩ
PBr2I2ϩ
PBrI3
ϩa
a
a
a
a
PI4
Ϫ519
Ϫ517
Ϫ456
Ϫ305
Ϫ295
a
b
c
d
e
Ϫ
f
Ϫ
See ref. 6. Non-relativistic DFT calculation. One- and two-electron spin–orbit corrections. Spin–orbit corrected result. AsF6 salts. SbF6
g
Ϫ
h
Ϫ
i
Ϫ
j
Ϫ
k
Ϫ
salts. AlCl4 salt. AlBr4 salts. GaBr salts. AlI salt. GaI4 salt.
4
4
3
1
Fig. 7 Comparison of the computed and experimental isotropic
P
shifts (data from Table 6). Dotted line: non-relativistic calculations;
dashed line: results with one- and two-electron SO corrections; solid
line: experimental data.
3
1
Fig. 8 MAS solid-state P NMR spectrum for reaction 7 (PBr /IBr/
3
contributions increase from δ Ϫ205 to Ϫ734 and thus are
AlBr ) and reaction 8 (PBr /IBr/GaBr ) at a spinning frequency of
3
3
3
responsible for the observed large low frequency shifts upon
increasing substitution by iodine. Based on these computa-
30 kHz. The isotropic chemical shifts are indicated by arrows.
6
tional results for the isolated cations, we assigned the experi-
ϩ
Ϫ
allocated to PBr I GaBr . The weaker resonance at δ =
3
4
31
mentally observed resonances found in the P NMR spectra of
ϩ
Ϫ
Ϫ153 ppm may be attributed to PBr I GaBr I . The resonance
at δ = Ϫ254 is close to that observed for PBr I AlBr and can
be assigned to PBr I GaBr .
2 2 4
Ϫ
In most cases, the AsF6 and SbF6 salts are thought to
3
3
the solids formed by reactions 5 to 8.
ϩ
2
Ϫ
4
2
ϩ
4
Products from reactions 5 and 6 are clearly mixtures of PBr
ϩ
Ϫ
ϩ
ϩ
4
Ϫ
6
ϩ
4
Ϫ
6
and PBr3I species (PBr AsF : δ = Ϫ83; PBr SbF : δ =
Ϫ
ϩ
Ϫ
ϩ
Ϫ
6
Ϫ81; PBr I AsF : δ = Ϫ195; PBr I SbF : δ = Ϫ196). A small
Ϫ
3
6
3
be representative of "ideal" ionic species, whereas for EX4
(E = Al, Ga; X = Br, I) salts non-negligible interactions between
ϩ
Ϫ
amount of formed PBr I AsF could be detected as a broad
resonance at δ = Ϫ315 in the P MAS NMR spectrum of
2
2
6
3
1
complex cations and anions have to be considered. On average
31
reaction 5 (Table 5). An additional peak at δ = Ϫ33 in the
P
ϩ
ϩ
the low frequency shift from PBr4 to PI4 increases in intervals
MAS NMR spectrum of reaction 6 corresponds with literature
Ϫ
of roughly 85 ppm for AlBr . In contrast, the increasing
4
31
ϩ
values of the P chemical shift for the PF4 cation and indicates
31
Ϫ
tendency to lower frequency of the P resonances of the AsF6
that a partial fluorination at phosphorus has obviously
ϩ
ϩ
ϩ
species from PBr4 to PBr3I (112 ppm) and from PBr3I to
1
c
occurred during the reaction.
ϩ
PBr2I2 (120 ppm) is significantly higher.
31
The P MAS NMR spectrum of the solid yielded by the
PBr /IBr/AlBr reaction system (reaction 7) at 30 kHz (Fig. 8,
3
3
Vibrational spectroscopy
Table 5) indicates the existence of all considered mixed bromo-
؉
Ϫ
ϩ
Ϫ
iodophosphonium complexes. The main signal at δ = Ϫ79 can
PBr AsF . The Raman spectrum of PBr AsF is shown
4 6 4 6
ϩ
Ϫ
be assigned as PBr AlBr . The two resonances found at
in Fig. 9. The vibrational frequencies and their assignment in
4
4
31
ϩ
ϩ Ϫ
δ = Ϫ167 and Ϫ171 represent the P chemical shifts for PBr3I
comparison with PBr EBr (E = Al, Ga) and the computed
4 4
ϩ 4c
species. The weak and broad lines at δ = Ϫ250 and Ϫ331 can be
normal modes for PBr4 are summarised in Table 7. The fre-
3
1
ϩ
ϩ
allocated to the P MAS NMR chemical shifts for the PBr2I2
quencies of the PBr4 cation are fairly consistent with literature
ϩ
and PBrI tetrabromoaluminate() salts, respectively.
values. The Raman-active symmetric ν (A ) stretching mode
3
1
1
31
ϩ
The P MAS NMR spectrum of the solid obtained from
reaction 8 (PBr /IBr/GaBr ) at 30 kHz (Fig. 8, Table 5) indi-
of the PX4 species is a characteristic frequency to indicate
the extent of intermolecular cation ؒ ؒ ؒ anion interactions.
3
3
Ϫ1
ϩ
Ϫ
cates that in this mixture there are four, two and one resonances
The ν (A ) stretching mode at 266 cm in PBr AsF is at
1 1 4 6
ϩ Ϫ
ϩ
4
ϩ
ϩ
2
associated with the PBr , PBr I and PBr I regions, respec-
considerably higher frequency than in PBr EBr (E = Al:
4 4
Ϫ1 Ϫ1 4c
3
2
tively. This suggests that a similar halogen exchange as found
for reaction 3 has occurred during the preparation. Besides the
256 cm , Ga: 258 cm ). This is consistent with the well-
Ϫ
known non-coordinating character of AsF6 anions, and
ϩ
Ϫ
signal for PBr GaBr at δ = Ϫ80 three narrow lines appear
with the expectation that no significant interactions between
4
4
at higher frequency which can be attributed to the signals of
cations and anions occur for this system. A similar phenom-
ϩ
Ϫ
ϩ
Ϫ
ϩ
PBr GaBr I (δ = Ϫ78), PBr GaBr I (δ = Ϫ74 ppm), and
enon is reported for the (i-Pr) PI cation. The P–I stretching
4
3
4
2
2
3
ϩ
Ϫ
3
31
ϩ
Ϫ
Ϫ1
PBr GaBrI
(δ = Ϫ68). The P resonance at δ = Ϫ170 dis-
vibration of (i-Pr) PI SbF at 157 cm is raised to higher
3 6
ϩ Ϫ Ϫ1
4
ϩ
Ϫ
4
plays the same value as assigned for PBr I AlBr and can be
wavenumbers than found in (i-Pr) PI I (ν (P–I): 150 cm ) and
3
3
1
884
J. Chem. Soc., Dalton Trans., 2001, 1880–1889

View Article Online
Ϫ1
ϩ
Table 7 Calculated and observed fundamental frequencies [cm ] for PBr4
ϩ
Ϫ
ϩ
Ϫ
ϩ
Ϫ
PBr4 AsF6
PBr4 AlBr
PBr4 GaBr
4
4
ϩ
a
b
b
PBr4 calculation
Raman
IR
Raman
IR
Raman
IR
Assignment
ϩ
5
2
1
11 (126)
63 (0)
50 (1)
512 (8)
513 s
512 sh/510 (4)/500 (5)
256 (100)
150 (43)
515/490
264 m
145 vs
98 w
505 (4, br)
258 (100)
153 sh/150 (50)
104 (23)
510 s
ν (T , PBr
)
3
2
4
ϩ
266 (100)
153 (66)
106 (34)
250 w
155 m
108 m
ν (A , PBr )
1 1 4
ϩ
ν (T , PBr )
4 2 4
ϩ
9
0 (0)
104 (11)
ν2 (E, PBr4
2 × ν (T , PBr )
4
)
ϩ
3
7
6
5
07 (13)
01 (4)
75 (28)
77 (5)
4
2
Ϫ
697 vs
676 m
580 w
ν (T , AsF )
3 1u 6
Ϫ
ν (A , AsF )
1 1g 6
Ϫ
ν (E , AsF )
6
2
g
Ϫ
3
91 s
ν (T , AsF
ν (T , AsF
5 2g 6
)
)
4
1u
6
Ϫ
3
68 (61)
a
Ϫ1
b
IR intensity [km mol ] in parentheses. See ref. 4c.
ϩ
Ϫ
ϩ
Ϫ
ϩ
Ϫ
Fig. 10 Raman spectra of PI4 AlBr4 , PI4 GaBr4 and PI4 AlCl4
.
ϩ
Ϫ
.
Fig. 9 Raman spectrum of PBr4 AsF6
Ϫ1
ϩ
Ϫ
Ϫ1
ϩ
Ϫ
3
93 cm (PI AlBr ) and 263 cm (PI GaBr ) can be
4 4 4 4
ϩ
Ϫ
3
Ϫ1
in (i-Pr) PI I (ν (P–I): 148 cm ), due to shorter P–I distances
3
assigned to the antisymmetric stretching mode, ν (T ), of
3
2
20
Ϫ
4
31
71
and less pronounced intermolecular interactions.
The IR spectrum of PBr AsF shows two expected IR
active modes, ν (T ) and ν (T ), at 697 and 391 cm for a free
AsF6 anion, which are consistent with literature values.Ϫ The
Raman active ν (A ), ν (E ) and ν (T ) modes for AsF were
observed at 675, 577 and 368 cm . The appearance of two
EBr . Confirmed by the results of the P and Ga MAS
ϩ
Ϫ
4
6
NMR data, the sample of reaction 3 was a mixture of mostly
Ϫ1
ϩ
4
Ϫ
4
ϩ
4
Ϫ
3
1u
4
1u
PI GaBr and small amounts of PI EBr I
. Two intense
4 Ϫ n
ϩ Ϫ
n
Ϫ
21
Ϫ1
bands at 278 and 240 cm in the IR spectrum of PI GaBr
4
4
1
1g
2
g
5
Ϫ1
2g
6
can be assigned to stretching vibrations of the partially
Ϫ ϩ Ϫ
4
replaced GaBr3I anion. Both Raman spectra of PI EBr
4
Ϫ1
Ϫ1
absorptions at 676 and 580 cm in the IR spectrum of
(
E = Al, Ga) exhibit weak peaks at ca. 182 cm due to small I2
ϩ
Ϫ
PBr AsF , which can be assigned to the ν (A ) and ν (E )
4
6
1
1g
2
g
impurities.
Ϫ
31
modes of AsF , leads to the conclusion that the octahedral
symmetry of the anion in PBr AsF may be slightly distorted.
6
Consistent with the P MAS NMR results the experi-
ϩ
Ϫ
4
6
mentally observed symmetric P–I [ν (A )] stretching mode
1
1
ϩ
4
Ϫ
4
Ϫ1
of the more isolated salt PI AlCl at 169 cm appears at
؉
4
Ϫ
4
PI EBr (E ؍ Al, Ga). The solid-state Raman spectra of
considerably higher wavenumbers than found in the com-
ϩ Ϫ
ϩ
Ϫ
ϩ
Ϫ
PI EBr (E = Al, Ga) and PI AlCl are shown in Fig. 10.
The computed and experimentally observed vibrational fre-
quencies and their assignments are summarised in Table 8 in
comparison with the vibrational frequencies found for PI EI
E = Al, Ga) and PI MF (M = As, Sb).
plexes PI EX (E = Al, Ga; X = Br, I). The Raman and
4 4
Ϫ1
4
4
4
4
IR frequencies at 496 (ν ), 350 (ν ), 219 (ν ) and 134 cm (ν2)
3 1 4
2c
agree with literature values reported for the fundamental
ϩ
Ϫ
Ϫ
frequencies of AlCl4 and confirm the presence of this counter-
4
4
ϩ
Ϫ
(
anion.
4
6
The symmetric ν (A ) stretching mode for the anions in
1
1
ϩ
Ϫ
؉
PI EBr (E = Al, Ga) can be observed as the most intense
Reaction products containing mixtures of PBrnI4 Ϫ n . The
4
4
Ϫ1
peaks in the Raman spectra at 165 (E = Al) and 163 cm
E = Ga), respectively. When compared with the vibrational
spectra of PI EI (E = Al, Ga), the ν (A ) stretching mode
is significantly shifted to higher frequencies (12–14 cm ).
In contrast to these results, the ν (A ) stretching mode was
found close to 194 cm in PI MF (M = As, Sb). This
solids formed from reactions 5 to 8 gave very complex IR and
Raman spectra. Assignment of the fundamental frequencies
of the mixed bromoiodophosphonium complexes is con-
(
ϩ
4
Ϫ
4
1
1
Ϫ1
ϩ
sequently very difficult. Besides the frequencies for PBr , the
4
Ϫ
Ϫ
fundamental modes for the anions AsF6 (reaction 5), SbF6
(reaction 6), AlBr4 (reaction 7) and GaBr4 (reaction 8) were
found in the vibrational spectra. With respect to the computed
vibrational frequencies and the results of the P MAS NMR
data, we attempted to assign the fundamental frequencies of
the PBr I cation in a reasonable way, as summarised in Table 9.
The Raman active stretching mode, ν (A ), can be observed
as intense peaks at 240 (AsF , reaction 5), 237 (SbF , reaction
6) and 222 (GaBr , reaction 8) cm in the Raman spectra.
1
1
Ϫ
Ϫ1
ϩ
4
5
Ϫ
Ϫ
6
appears consistent with the suggestion that the vibration
frequencies should be at lower wavenumbers, because the
31
ϩ
Ϫ
P–I bond order in the compounds PI EBr (E = Al, Ga)
4
4
ϩ
is reduced by weak I ؒ ؒ ؒ Br cation ؒ ؒ ؒ anion interactions,
3
ϩ
ϩ
4
Ϫ
6
whereas the PI4 cation in PI MF (M = As, Sb) is almost
1
1
Ϫ
Ϫ
isolated.
6
6
Ϫ
Ϫ
Ϫ1
The presence of the anions EBr4 (E = Al, Ga) is confirmed
4
Ϫ1
by the symmetric stretching mode, ν (A ), at 210 cm
As expected, significant increases in frequency occur for all
modes of the PBr3I cation on passing from complexes where
tetrahaloaluminate and tetrahalogallate anions are present to
1
1
ϩ
Ϫ
4
Ϫ1
ϩ
4
Ϫ
4
ϩ
(
PI AlBr ) and 207 cm (PI GaBr ). They are consistent
4
Ϫ
Ϫ1 22
Ϫ
with literature values (ν1 (AlBr ): 212 cm ; ν1 (GaBr ):
4
4
Ϫ1 23
Ϫ
Ϫ
6
2
10 cm
). The strong absorptions in the IR spectra at
those with the anions AsF6 and SbF .
J. Chem. Soc., Dalton Trans., 2001, 1880–1889
1885

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Conclusion
31
ϩ
4
The solid-state P MAS NMR studies for PI species show
extremely large negative P isotropic shifts ranging from
31
δ = Ϫ295 to Ϫ519. They depend considerably on the nature of
ϩ
the counter-ion. The more isolated the character of the PI4
cation (shorter P–I bond lengths, weaker cation ؒ ؒ ؒ anion
interactions), the larger the P–I bond order becomes. Con-
sequently, the Fermi-contact mechanism that transfers the
spin–orbit induced spin density to the phosphorus nucleus is
17
31
6
more efficient, and the P resonance is shifted to higher field.
Significant donor–acceptor contacts between cation and anion
in the solid-state lead to less pronounced low frequency
31
isotropic P shifts. Additionally, a trend towards higher
ϩ
wavenumbers for the fundamental frequencies of PI could be
4
ϩ
Ϫ
observed from the polymeric [PI EI (E = Al, Ga)] to the
4
4
ϩ
Ϫ
ϩ
"
ideal" ionic cases [PI MF (M = As, Sb)]. For PBr4 species
4 6
these effects are less pronounced.
31
Based on the results of the computed isotropic P chemical
ϩ
shifts for isolated PBrnI4 Ϫ n cations, we found evidence for the
existence of the hitherto unknown mixed bromoiodophos-
ϩ
ϩ
ϩ
phonium cations PBr I , PBr I and PBrI3 by means of solid-
3
2 2
31
state P MAS NMR spectroscopy.
Due to increasing spin–orbit effects, the δ P shifts of the
31
Ϫ
EBr4 salts (E = Al, Ga) move increasingly to low frequency
ϩ
ϩ
ϩ
ϩ
ϩ
along the series PBr4 < PBr I < PBr I < PBrI3 < PI , in
3
2
2
4
Ϫ
intervals of about 85 ppm. In the case of MF6 counter-anions
M = As, Sb), the corresponding increments to low frequency
(
are significantly larger, due to the essentially isolated nature of
the cations.
Experimental
General methods
All compounds reported here are moisture sensitive. Con-
sequently, strictly anaerobic and anhydrous conditions were
employed for their synthesis. Any subsequent manipulations
were carried out inside a glove-box under dry nitrogen.
AlBr , AlCl , Br , GaBr , IBr, ICl, I , PBr and PI (all Aldrich)
3
3
2
3
2
3
3
ϩ
4
Ϫ 4c
ϩ
4
Ϫ 4c
were used as received. PBr AlBr , PBr GaBr
PI GaI
preparation of Br AsF , I AsF
and
4
4
ϩ
4
Ϫ 6
4
were prepared according to the literature. The
ϩ
3
Ϫ 24
6
ϩ
3
Ϫ 25
6
ϩ
Ϫ 26
6
and I SbF
also
3
followed literature procedures. CFCl and CS were refluxed
3
2
with P O and distilled before used.
4
10
31
71
P and Ga NMR spectra were measured at 202.49 and
52.48 MHz, respectively, with a BRUKER DSX AVANCE 500
1
FT NMR spectrometer under fast spinning conditions about
the magic-angle (MAS). A standard double-bearing MAS
probe designed for zirconia dioxide rotors (diameter: 2.5 mm)
was used with spinning frequencies up to 30 kHz. For the
31
P NMR measurements a single pulse acquisition was used
and the 90Њ pulse length was adjusted to 2.0 µs. The recycle
delay was set to values between 5 and 60 s, depending on the
spin lattice relaxation time, to ensure correct relative signal
intensities. 7
1
For the Ga NMR measurements a 16-fold phase cycled
Hahn echo sequence (90Њ–t –180Њ–t –acquisition) was used.
1
1
The interpulse distance t was set to the inverse spinning fre-
1
quency (t = 1/ν = 1/27 kHz). The 90Њ (1.6 µs) and 180Њ (3.1 ns)
1
rot
pulses were adjusted to maximal signal intensity.
Due to fast spinning conditions (νrot > 20 kHz), the recorded
spectra contain only few spinning side bands which are clearly
separated from the isotropic chemical shift resonances.
Therefore, the values for the isotropic chemical shifts of
the cations under study could be extracted directly from the
spectra without simulations taking into account the chemical
shift anisotropy. Overlapping signals were deconvoluted using a
pseudo-Voigt profile. The samples were filled under a nitrogen
31
atmosphere in a glove-box. The P spectra were referenced to
1
886
J. Chem. Soc., Dalton Trans., 2001, 1880–1889

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71
8
5% H PO in CDCl , isotropic Ga chemical shifts to an
Reaction 8 (PBr ؉ IBr ؉ GaBr ). PBr (0.27 g, 1.00 mmol)
3 3 3
3
4
3
external 1.0 M solution of Ga(NO ) .
was reacted with IBr (0.20 g, 1.00 mmol) and AlBr (0.31 g,
3
3
3
Raman spectra were obtained of powdered solid samples
contained in glass capillary tubes with a Perkin-Elmer 2000
NIR spectrometer in the range 800–50 cm . IR spectra were
1.00 mmol) in CS (20 mL) with stirring at room temperature.
2
After stirring for 2 h the solvent was removed under dynamic
vacuum, leaving an orange solid. Yield: 0.59 g, mp 67–69 ЊC
(decomp.).
Ϫ1
recorded on Nujol mulls between CsI plates in the range 800–
Ϫ1
2
00 cm on a Nicolet 520 FT IR spectrometer. For the
determination of decomposition points, samples were heated in
sealed glass capillaries in a Büchi B450 instrument.
Crystallography
ϩ
4
Ϫ
4
ϩ
4
Ϫ
ϩ
4
Ϫ
4
Single crystals of PI AlCl , PI AlBr
and PI GaI
4
suitable for X-ray structure determination were grown from
Syntheses
CS and covered with perfluoropolyether oil. The selected crys-
2
؉
Ϫ
6
Reaction 1: preparation of PBr AsF . PBr (0.61 g, 2.25
mmol) was reacted with Br AsF (0.97 g, 2.25 mmol) in
tals were mounted on the tip of a glass fibre and placed on a
goniometer head.
4
3
ϩ
3
Ϫ
6
CFCl (15 mL) with stirring at room temperature in a two-
3
bulbed glass vessel incorporating a coarse sintered-glass frit and
؉
Ϫ
Crystal data for PI AlCl . AlCl I P, M = 707.35, mono-
4
4
4 4
a Young valve. An intense brown solution of Br over a colour-
2
clinic, a = 6.523(6), b = 15.81(1), c = 14.34(1) Å, β = 92.09(1)Њ,
U = 1478(2) Å , T = 193(2) K, space group P2 /c, Z = 4.
Siemens CCD area detector, scan type: hemisphere, µ(Mo-
Kα, λ = 0.71073 Å) = 9.277 mm , reflections collected: 5309,
independent reflections: 1627 (Rint = 0.0308), observed reflec-
tions: 1292 [F > 4σ(F)]. Absorption correction: SADABS.
Structure solution and refinement program: SHELXL-97,
direct methods, final R indices for all atoms in anisotropic
description [F > 4σ(F)]: R1 = 0.0440, wR2 = 0.1023, R1 =
.0613, wR2 = 0.1099 (all data).
less solid was obtained. After stirring for 2 h the solution was
3
1
filtered. Solvent and traces of remaining Br were removed
2
under dynamic vacuum, leaving a colourless solid. Yield: 0.35 g
Ϫ1
(
29%), mp 144–148 ЊC (decomp.).
27
؉
4
Ϫ
4
Reaction 2: preparation of PI AlBr . PI (0.41 g, 1.00
28
3
mmol) was reacted with IBr (0.20 g, 1.00 mmol) and AlBr (0.27
3
g, 1.00 mmol) in CS (20 mL) with stirring at room temperature.
2
After stirring for 2 h the solvent was removed under dynamic
vacuum, leaving a red solid. Yield: 0.82 g (93%), mp 109 ЊC
0
(
decomp.).
؉
Ϫ
Crystal data for PI AlBr . AlBr I P, M = 885.19,
4
4
4 4
monoclinic, a = 6.6475(8), b = 16.471(2), c = 14.534(4) Å,
β = 91.832(2)Њ, U = 1590.5(3) Å , T = 188(2) K, space group
Reaction 3 (PI ؉ IBr ؉ GaBr ). PI (0.41 g, 1.00 mmol)
3
3
3
3
was reacted with IBr (0.20 g, 1.00 mmol) and GaBr (0.31 g,
3
P2 /c, Z = 4. Siemens CCD area detector, scan type: hemi-
1
1
.00 mmol) in CS (20 mL) with stirring at room temperature.
Ϫ1
2
sphere, µ(Mo-Kα, λ = 0.71073 Å) = 17.996 mm , reflections
After stirring for 2 h the solvent were removed under dynamic
vacuum, leaving a red solid. Yield: 0.79 g, mp 86 ЊC (decomp.).
collected: 6541, independent reflections: 2056 (Rint = 0.0374),
observed reflections: 1673 [F > 4σ(F)]. Absorption correction:
27
SADABS. Structure solution and refinement program:
؉
4
Ϫ
4
Reaction 4: preparation of PI AlCl . PI (0.82 g, 2.00 mmol)
28
3
SHELXL-97, direct methods, final R indices for all atoms in
was reacted with ICl (0.32 g, 2.00 mmol) and AlCl (0.27 g, 2.00
3
anisotropic description [F > 4σ(F)]: R1 = 0.0447, wR2 = 0.1080,
R1 = 0.0580, wR2 = 0.1145 (all data).
mmol) in CS (30 mL) with stirring at room temperature. After
2
stirring for 2 h the solvent and traces of ICl were removed at
5
0
0 ЊC under dynamic vacuum, leaving an orange solid. Yield:
.97 g (69%), mp 70 ЊC (decomp.).
؉
Ϫ
Crystal data for PI GaI . GaI P, M = 1115.89, ortho-
4
4
8
rhombic, a = 11.0101(7), b = 10.4007(7), c = 15.1835(9) Å,
U = 1738.7(2) Å , T = 200(2) K, space group Pna2 Z = 4. Stoe
IPDS diffractometer, µ(Mo-Kα, λ = 0.71073 Å) = 15.839 mm ,
reflections collected: 9490, independent reflections: 3879
3
؉
3
Ϫ
6
1,
Reaction 5 (PBr ؉ I AsF ). PBr (0.27 g, 1.00 mmol) was
Ϫ1
3
3
ϩ
Ϫ
reacted with I AsF (0.57 g, 1.00 mmol) in CFCl (15 mL)
3
6
3
with stirring at room temperature in a two-bulbed glass vessel
incorporating a coarse sintered-glass frit and a Young valve. An
intense dark purple solution over a pale brownish solid was
obtained. After stirring for 24 h the solution was filtered, and
refiltered several times, by condensing about half the solvent
back and refiltering. Solvent and traces of remaining I were
removed under dynamic vacuum, leaving a pale brownish solid.
Yield: 0.31 g, mp 146 ЊC (decomp.).
(
Rint = 0.0257), observed reflections: 3142 [F > 2σ(I)]. Absorp-
tion correction: numerical. Structure solution and refinement
28
program: SHELXL-97, direct methods, final R indices for all
atoms in anisotropic description [F > 2σ(I)]: R1 = 0.0377,
wR2 = 0.0758, R1 = 0.0516, wR2 = 0.0785 (all data).
CCDC reference numbers 158050–158052.
See http://www.rsc.org/suppdata/dt/b1/b101197i/ for crystal-
lographic data in CIF or other electronic format.
2
؉
3
Ϫ
6
Reaction 6 (PBr ؉ I SbF ). PBr (1.04 g, 3.84 mmol) was
3
3
ϩ
Ϫ
Computational methods
reacted with I SbF (2.37 g, 3.84 mmol) in CFCl (20 mL)
3
6
3
ϩ
with stirring at room temperature in a two-bulbed glass vessel
incorporating a coarse sintered-glass frit and a Young valve. An
intense dark purple solution over a pale brownish solid was
obtained. After stirring for 24 h the solution was filtered, and
refiltered several times, by condensing about half the solvent
The structures of the isolated PBrnI4 Ϫ n (0 ≤ n ≤ 4) were opti-
mised at the second-order Møller–Plesset (MP2) level with
the program package Gaussian 98. Quasirelativistic pseudo-
potentials and DZP valence basis sets were employed for P, I,
29
30
and Br. All species were characterised as minima by harmonic
31
back and refiltering. Solvent and traces of remaining I were
vibrational frequency analysis. It should be noted that the
calculations were performed on isolated (gas-phase) cations.
There may well be significant differences between gas-phase
and solid-state data.
The DFT calculations of P chemical shifts were carried
out at the same theoretical level as in ref. 6. The initial,
non-relativistic nuclear shielding calculations (uncorrected
for spin–orbit coupling) used the sum-over-states density
2
removed under dynamic vacuum, leaving a pale brownish solid.
Yield: 1.25 g, mp 90 ЊC (decomp.).
31
Reaction 7 (PBr ؉ IBr ؉ AlBr ). PBr (0.27 g, 1.00 mmol)
3
3
3
was reacted with IBr (0.20 g, 1.00 mmol) and AlBr (0.27 g,
3
1
.00 mmol) in CS (20 mL) with stirring at room temperature.
2
After stirring for 2 h the solvent was removed under dynamic
vacuum, leaving a brown solid. Yield: 0.51 g, mp 97 ЊC
32,33
functional perturbation theory approach (SOS-DFPT),
34
(
decomp.).
with individual gauges for localised orbitals (IGLO ). The
J. Chem. Soc., Dalton Trans., 2001, 1880–1889 1887

View Article Online
Ϫ1
ϩ
Table 9 Calculated and observed fundamental frequencies [cm ] for PBr3I
PBr /I AsF PBr /I SbF
PBr /IBr/AlBr
Reaction 7
IR
PBr /IBr/GaBr
Reaction 8
Raman
3
3
6
3
3
6
3
3
3
3
b
Reaction 5
Raman
Reaction 6
Raman
ϩ
a
PBr3I calculation
IR
IR
IR
Assignment
ϩ
4
4
2
1
1
97 (108)
62 (119)
37 (1)
39 (1)
32 (1)
498 m
466 m
242 w
497 m
464 m
239 w
486 m
456 m
226 m
486 (5)
452 (6)
223 (100)
138 (39)
124 (47)
482 m
447 m
222 m
ν (A , PBr I )
4
1
3
ϩ
ν (E, PBr I )
2 3
ϩ
240 (25)
141 (16)
136 (17)
237 (100)
ν (A , PBr I )
1 1 3
ϩ
ν (E, PBr I )
3 3
ϩ
ν (A , PBr I )
6 1 3
ϩ
8
8 (0)
ν (E, PBr I )
5 3
a
Ϫ1
b
IR intensity [km mol ] in parentheses. The Raman spectrum of the product showed fluorescence and therefore no Raman data was available.
underlying Kohn–Sham calculations employed the gradient-
4 (a) W. Gabes and H. Gerding, Recueil, 1971, 90, 157; (b) W. Gabes,
K. Olie and H. Gerding, Recueil, 1972, 91, 1367; (c) J. Shamir,
S. Schneider and B. J. van der Kehlen, J. Raman Spectrosc., 1986, 17,
35
corrected PW91 exchange-correlation functional. All calcula-
36
tions were carried out with the deMon-KS and deMon-
4
63.
32
NMR codes.
5
I. Tornieporth-Oetting and T. M. Klapötke, J. Chem. Soc., Chem.
Commun., 1990, 132.
34
IGLO-II all-electron basis sets were used on all atoms
omitting f-functions on iodine due to program limitations),
(
6 M. Kaupp, Ch. Aubauer, G. Engelhardt, T. M. Klapötke and
O. L. Malkina, J. Chem. Phys., 1999, 110, 3687.
with density and exchange-correlation potential fitting aux-
iliary basis sets of the sizes 5,4 (P) and 5,5 (Br, I) (n,m denotes n
7
Ch. Aubauer, T. M. Klapötke and A. Schulz, Int. J. Vibr. Spectrosc.,
1999, 3, 4 (http://www.ijvs.com/volume3/edition2/section4.htm).
(a) H. Preiss, Z. Anorg. Allg. Chem., 1971, 380, 51; (b) H. Preiss,
Z. Anorg. Allg. Chem., 1971, 380, 56; (c) W. F. Zelezny and
N. C. Baenzinger, J. Am. Chem. Soc., 1952, 74, 6151; (d) D. Clark,
H. M. Powell and A. F. Wells, J. Chem. Soc., 1942, 642;
(e) J. C. Taylor and A. B. Waugh, Polyhedron, 1983, 2, 211;
( f ) J. Shamir, S. Schneider, A. Bino and S. Cohen, Inorg. Chim. Acta,
36
s-functions and m spd-shells with shared exponents ). All six
8
Cartesian components of d-basis functions were kept. The
34
37
IGLO procedure employed the Boys localisation scheme.
For comparison to experiment, the computed absolute shield-
ings σ were converted to relative shifts δ via the absolute shield-
38
ing value of 328.4 ppm for 85% H PO given by Jameson et al.
3
4
1
986, 114, 35; (g) J. Shamir, S. Schneider, A. Bino and S. Cohen,
Spin–orbit corrections to the nuclear shieldings were
computed separately by the combined finite-perturbation/
SOS-DFPT ansatz of ref. 32. A recently implemented and
Inorg. Chim. Acta, 1986, 114, 141; (h) C. F. Erdbrügger, P. G. Jones,
R. Schelbach, E. Schwarzmann and G. M. Sheldrick, Acta
Crystallogr., Sect. C, 1987, 43, 1857; (i) H. Preut, D. Lennhoff
and R. Minkwitz, Acta Crystallogr., Sect. C, 1992, 48, 1648;
(j) M. L. Ziegler, B. Nuber, K. Weidenhammer and G. Hoch, Z.
Naturforsch., Teil B, 1977, 32, 18; (k) P. H. Collins and M. Webster,
Acta Crystallogr., Sect. B, 1972, 28, 1260; (l) B. Krebs, B. Buss
and W. Berger, Z. Anorg. Allg. Chem., 1973, 397, 1; (m) T. J.
Kistenmacher and G. D. Stucky, Inorg. Chem., 1968, 7, 2150;
39
validated mean field approximation was used to compute the
one- and two-electron SO integrals. An IGLO choice of gauge
origin has been used in the calculation of the SO corrections.
The calculations of the spin–orbit corrections used the same
basis sets described above, but the spherical d-basis functions
were projected out for compatibility with the SO integral code.
(
n) T. J. Kistenmacher and G. D. Stucky, Inorg. Chem., 1971, 10, 122;
40
6
4 points of radial quadrature and the PP86 functional were
(o) A. Finch, A. N. Fitch and P. N. Gates, J. Chem. Soc., Chem.
Commun., 1993, 957; (p) P. N. Gates, H. C. Knachel, A. Finch, A. V.
Fratini, A. N. Fitch, O. Nardone, J. C. Otto and D. A. Snider,
J. Chem. Soc., Dalton Trans., 1995, 2719; (q) B. Neumüller, C: Lau
and K. Dehnicke, Z. Anorg. Allg. Chem., 1996, 622, 1847;
employed. The initial finite perturbation (with a perturbation
Ϫ5
parameter λ = 10 arbitrary units) was chosen to be the nuclear
magnetic moment of the phosphorus nucleus.
(
r) G. V. Khvorykh, S. I. Troyanov, A. I. Baranov and A. A. Sereov,
Z. Anorg. Allg. Chem., 1998, 624, 1026; (s) A. I. Baranov,
G. V. Khvorykh and S. I. Troyanov, Z. Anorg. Allg. Chem., 1999,
625, 1240; (t) J. Beck, K. Müller-Buschbaum and F. Wolf, Z. Anorg.
Allg. Chem., 1999, 625, 975.
Acknowledgements
We gratefully acknowledge the support of the Fonds der
Chemischen Industrie and the University of Munich. In
addition we would like to thank Prof. Peter N. Gates and Prof.
Günther Engelhardt, Dr Axel Schulz and Dipl.-Chem. Gernot
Kramer for valuable discussions and Andrea Barra for NMR
spectroscopic measurements. M.K. is grateful to Deutsche
Forschungsgemeinschaft for support (Schwerpunktprogramm
9
W. Gabes and K. Olie, Acta Crystallogr., Sect. B, 1970, 26, 443.
1
1
0 G. L. Breneman and R. D. Willett, Acta Crystallogr., 1967, 23,
4
67.
1 S. Pohl, Z. Anorg. Allg. Chem., 1983, 498, 15.
12 (a) A.-R. Grimmer, Z. Anorg. Allg. Chem., 1973, 400, 105;
(b) K. B. Dillon and P. N. Gates, J. Chem. Soc., Chem. Commun.,
1
972, 348; (c) A. Finch, P. N. Gates, F. J. Ryan and F. F. Bentley,
"Relativistische Effekte") and thanks Dr Vladimir G. Malkin
J. Chem. Soc., Dalton Trans., 1973, 1863; (d) K. B. Dillon,
M. P. Nisbet and T. C. Waddington, Inorg. Nucl. Chem. Lett, 1973,
and Dr Olga L. Malkina for helpful discussions.
9
(
, 63; (e) K. B. Dillon and A. W. G. Platt, Polyhedron, 1982, 1, 123;
f ) K. B. Dillon and A. W. G. Platt, Polyhedron, 1983, 2, 641.
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