Preparation, characterization, and structural systematics of diphosphane and diarsane complexes of gallium(III) halides

Article abstract of DOI:10.1021/ic700895r

The diphosphane o-C₆H₄(PMe₂)₂ reacts with GaX₃ (X = Cl, Br, or I) in a 1:1 molar ratio in dry toluene to give trans-[GaX₂{o-C₆H₄(PMe ₂)₂}₂][GaX₄], the cations of which contain the first examples of six-coordinate gallium in a phosphane complex. The use of a 1:2 ligand/GaCl₃ ratio produced [GaCl₂{o-C ₆H₄(PMe₂)₂}][GaCl₄], containing a pseudotetrahedral cation, and similar pseudotetrahedral [GaX ₂{o-C₆H₄(PPh₂)₂}] [GaX₄] complexes are the only products isolated with the bulkier o-C₆H₄(PPh₂)₂. On the other hand, Et₂P(CH₂)₂PEt₂, which has a flexible aliphatic backbone, formed [(X₃Ga)₂{μ-Et ₂P(CH₂)₂PEt₂}], in which the ligand bridges two pseudotetrahedral gallium centers. The diarsane, o-C ₆H₄(AsMe₂)₂, formed [GaX ₂{o-C₆H₄(AsMe₂)₂}] [GaX₄], also containing pseudotetrahedral cations, and in marked contrast to the diphosphane analogue, no six-coordinate complexes form; a very rare example where these two much studied ligands behave differently towards a common metal acceptor. The complexes [(I₃Ga)₂{μ-Ph ₂As-(CH₂)₂AsPh₂}] and [GaX ₃(AsMe₃)] are also described. The X-ray structures of trans-[GaX₂{o-C₆H₄(PMe₂) ₂}₂][GaX₄] (X = Cl, Br or I), [GaCl ₂{o-C₆H₄(PPh₂)₂}] [GaCl₄], [GaX₂{o-C₆H₄(AsMe ₂)₂}][GaX₄] (X = Cl or I), [(I ₃Ga)₂{μ-Ph₂-As(CH₂) ₂AsPh₂}], and [GaX₃(AsMe₃)] (X = Cl, Br or I) are reported, and the structural trends are discussed. The solution behavior of the complexes has been explored using a combination of ³¹P{¹H} and ⁷¹Ga NMR spectroscopy.

Full text of DOI:10.1021/ic700895r

Inorg. Chem. 2007, 46, 7215−7223
Preparation, Characterization, and Structural Systematics of
Diphosphane and Diarsane Complexes of Gallium(III) Halides
Fei Cheng, Andrew L. Hector, William Levason,* Gillian Reid, Michael Webster, and Wenjian Zhang
School of Chemistry, UniVersity of Southampton, Southampton UK SO17 1BJ
Received May 9, 2007
The diphosphane o-C6H4(PMe2)2 reacts with GaX3 (X
trans-[GaX2 o-C6H4(PMe2)2 2][GaX4], the cations of which contain the first examples of six-coordinate gallium in a
phosphane complex. The use of a 1:2 ligand/GaCl3 ratio produced [GaCl2 o-C6H4(PMe2)2 ][GaCl4], containing a
pseudotetrahedral cation, and similar pseudotetrahedral [GaX2 o-C6H4(PPh2)2 ][GaX4] complexes are the only products
isolated with the bulkier o-C6H4(PPh2)2. On the other hand, Et2P(CH2)2PEt2, which has a flexible aliphatic backbone,
formed [(X3Ga)2{µ-Et2P(CH2)2PEt2 ], in which the ligand bridges two pseudotetrahedral gallium centers. The diarsane,
o-C6H4(AsMe2)2, formed [GaX2 o-C6H4(AsMe2)2 ][GaX4], also containing pseudotetrahedral cations, and in marked
) Cl, Br, or I) in a 1:1 molar ratio in dry toluene to give
{
}
{
}
{
}
}
{
}
contrast to the diphosphane analogue, no six-coordinate complexes form; a very rare example where these two
much studied ligands behave differently towards a common metal acceptor. The complexes [(I3Ga)2{µ-Ph2As-
(CH2)2AsPh2
(X Cl, Br or I), [GaCl2
As(CH2)2AsPh2 ], and [GaX3(AsMe3)] (X
solution behavior of the complexes has been explored using a combination of 31
}
] and [GaX3(AsMe3)] are also described. The X-ray structures of trans-[GaX2
o-C6H4(PPh2)2 ][GaCl4], [GaX2 o-C6H4(AsMe2)2 ][GaX4] (X
Cl, Br or I) are reported, and the structural trends are discussed. The
1H and 71Ga NMR spectroscopy.
{
o-C6H4(PMe2)2
}2][GaX4]
)
{
}
)
{
}
) Cl or I), [(I3Ga)2{µ-Ph2-
}
P{ }
Introduction
in the electronics industries in compound semiconductors
based on III-V materials: for example, GaN, GaP, and
GaAs are used extensively in LED applications; GaSb is used
in thermal imaging devices, while GaAs is also widely used
in integrated circuits, displays, and solar cells.5,6 Other
applications of gallium compounds are as gallium gadolinium
garnet in bubble memory devices,6 and the lower Lewis
acidity, compared to that of aluminum halides, has produced
some applications for GaX3 in organic transformations.7 The
radioisotopes 67Ga and 68Ga have found uses in diagnosis
and therapy;8 mostly, these are used as gallium complexes
with O- or N-donor chelates, which resist hydrolysis in vivo
and provide appropriate lipophilicity.
The coordination chemistry of the p-block metals has been
much less thoroughly investigated than that of the transition
elements,1,2 and while detailed studies have been carried out
on individual complexes or systems, the factors which control
stoichiometries and structures often remain unclear.3,4 In
general, p-block chemistry seems less amenable to “fine-
tuning” of the metal center properties by ligand design than
that of familiar d-block elements. However, the p-block
metals have many technologically important applications and
devising improved reagents for existing processes or devel-
oping new synthons depends upon an understanding of how
the ligands control the metal-center chemistry, structure, and
reactivity. In the case of gallium, the major applications lie
(5) O’Brien, P.; Pickett, N. L. In ComprehensiVe Coordination Chemistry
II; McCleverty, J. A., Meyer, T. J., Eds.; Elsevier: Oxford, U.K., 2004;
Vol. 9, pp 1005-1063.
* To whom correspondence should be addressed. E-mail: wxl@soton.ac.uk.
(1) Greenwood, N. N.; Earnshaw, A. Chemistry of the Elements, 2nd ed.;
Butterworth-Heineman: Oxford, U.K., 1997.
(2) Taylor, M. J. In ComprehensiVe Coordination Chemistry; Wilkinson,
G., Gillard, R. D., McCleverty, J. A., Eds.; Pergamon: Oxford, U.K.,
1987; Vol. 3, pp 105-152.
(3) Downs, A. J., Ed. Chemistry of Aluminium, Gallium, Indium and
Thallium; Blackie: London, 1993.
(6) Grant, I. R. In Chemistry of Aluminium, Gallium, Indium and Thallium;
Downs, A. J., Ed.; Blackie: London, 1993; Chapter 5.
(7) (a) Starowieyski, K. B. In Chemistry of Aluminium, Gallium, Indium
and Thallium; Downs, A. J., Ed.; Blackie: London, 1993; Chapter 6.
(b) Kellogg, R. M. Chemtracts 2003, 16, 79-92. (c) Nair, V.; Ros,
S.; Jayan, C. N.; Pillai, B. S. Tetrahedron 2004, 60, 1959-1982.
(8) (a) Reichert, D. E.; Lewis, J. S.; Anderson, C. J. Coord. Chem. ReV.
1999, 184, 3-66. (b) Anderson, C. J.; Welch, M. J. Chem. ReV. 1999,
99, 2219-2234.
(4) Robinson, G. H. In ComprehensiVe Coordination Chemistry II;
McCleverty, J. A., Meyer, T. J., Eds.; Elsevier: Oxford, U.K., 2004;
Vol. 3, pp 347-382.
10.1021/ic700895r CCC: $37.00
Published on Web 07/21/2007
© 2007 American Chemical Society
Inorganic Chemistry, Vol. 46, No. 17, 2007 7215

Cheng et al.
Anal. Calcd for C20H32Ga2I6P4: C, 18.5; H, 2.5. Found: C, 18.7;
H, 2.4. 1H NMR (300 MHz, CD2Cl2): δ 7.6-7.8 (m, [4H], C6H4),
1.74 (s, [12H], CH3). 71Ga NMR (CH2Cl2/5% CD2Cl2): δ -457
A number of gallium(III) halide complexes with phosphane
or arsane ligands have been reported, the vast majority being
of the type [GaX3(ER3)] (E ) P or As) with pseudotetra-
hedral gallium.9-12 Two other types identified are the [(I3-
Ga)2{µ-Ph2P(CH2)2PPh2}]13 and the rare cationic [GaX2{o-
C6H4(PPh2)2}][GaX4] (X ) Br or I).14 We have recently
reported complexes with the triarsane, MeC(CH2AsMe2)3,
which adopts a number of coordination modes, but all are
to four-coordinate gallium centers.15 Here, we report detailed
structural and spectroscopic investigations on gallium(III)
halide complexes with diphosphane and diarsane ligands,
with the aim of understanding how the ligand architecture,
electronic requirements, and steric requirements influence
the stoichiometry and properties. The solution properties and
interconversions have been probed by variable-temperature
31P{1H} and 71Ga NMR spectroscopy.
(br). 31P{1H} NMR (CH2Cl2/5% CD2Cl2): δ -43.0 (s). IR (cm-1
Nujol): ν 216 (s), 205 (m). Raman (cm-1): 217 (s).
,
[GaCl2{o-C6H4(PMe2)2}2][GaCl4]. This was prepared in a
manner similar to that described above as a white solid. Yield: 82%.
Anal. Calcd for C20H32Cl6Ga2P4: C, 32.1; H, 4.3. Found: C, 32.2;
H, 4.2. 1H NMR (300 MHz, CD2Cl2): δ 7.6-7.8 (m, [4H], C6H4)
1.75 (s, [12H], CH3). 71Ga NMR (CH2Cl2/5% CD2Cl2): δ 251 (s).
31P{1H} NMR (CH2Cl2/5% CD2Cl2): δ -40.8 (s). IR (cm-1
,
Nujol): ν 372 (vs), 339 (m), 252 (m), 203 (m). Raman (cm-1):
372 (w), 344 (s), 332 (m), 238 (s), 197 (m).
[GaBr2{o-C6H4(PMe2)2}2][GaBr4]. This was prepared in a
manner similar to that described above as a white solid. Yield: 90%.
Anal. Calcd for C20H32Br6Ga2P4: C, 23.7; H, 3.2. Found: C, 23.3;
H, 3.1. 1H NMR (300 MHz, CD2Cl2): δ 7.6-7.8 (m, [4H], C6H4),
1.73 (s, [12H], CH3). 71Ga NMR (CH2Cl2/5% CD2Cl2): δ 63.5 (s).
31P{1H} NMR (CH2Cl2/5% CD2Cl2): δ -41.2 (s). IR (cm-1
,
Experimental Section
Nujol): ν 315 (w), 272 (vs), 250 (w). Raman (cm-1): 333 (m),
273 (m), 239 (m), 210 (vs).
General Procedures. All the reactions and manipulations were
performed in an inert atmosphere (N2) glovebox or with Schlenk
techniques. The solvents toluene, diethyl ether, and hexane were
dried by distillation over sodium/benzophenone, and dichlo-
romethane was dried by distillation from CaH2. Infrared spectra
were measured as Nujol mulls between CsI plates on a Perkin-
Elmer PE983 spectrometer. Raman spectra were recorded from
powdered solid samples using a Perkin-Elmer FT-Raman 2000R
[GaCl2{o-C6H4(PMe2)2}][GaCl4]. This was prepared in a man-
ner similar to that described above as a white solid by reaction of
the ligand and GaCl3 in a 1:2 molar ratio in hot toluene. Yield:
85%. Anal. Calcd for C10H16Cl6Ga2P2: C, 21.8; H, 2.9. Found: C,
22.0; H, 2.9. 1H NMR (300 MHz, CD2Cl2): insoluble. 71Ga NMR
(see text) (MeCN/5% CD3CN): δ 251 (s). 31P{1H} NMR (MeCN/
5% CD3CN): δ -52.2 (br, [P]), -4.0 (br, [P]). 31P-1H coupled
1
with a Nd:YAG laser. H NMR spectra were recorded in CDCl3
NMR (MeCN/5% CD3CN): δ -52.2 (br, [P]), -4.0 (d, [P] 1JPH
)
solution on a Bruker AV300; 31P{1H} (161.9 MHz) and 71Ga (122.0
MHz) NMR spectra were recorded on a Bruker DPX400 and
referenced to 85% H3PO4 and [Ga(H2O)6]3+, respectively. GaCl3
and GaI3 were obtained from Aldrich and used as received. GaBr3
(Aldrich) was sublimed in vacuo at 70 °C. The ligands o-C6H4-
(PMe2)2, o-C6H4(PPh2)2, o-C6H4(AsMe2)2, Ph2P(CH2)2PPh2 and Ph2-
As(CH2)2AsPh2 were prepared by literature methods,16-19 while the
other ligands were obtained from Aldrich or Strem and used as
received. The complexes were made by similar routes and therefore
only representative examples are described. [GaX3(PPh3)] com-
plexes were made as described.11
545 Hz). IR (cm-1, Nujol): ν 410 (s), 380 (vs), 362 (s).
[GaI3{µ-Et2P(CH2)2PEt2}GaI3]. A solution of Et2P(CH2)2PEt2
(0.075 g, 0.364 mmol) in toluene (5 cm3) was added dropwise to
a stirred solution of GaI3 (0.327 g, 0.726 mmol) in toluene (20
cm3) at room temperature. After it was heated at 80 °C for 2 h, the
mixture was returned to room temperature, and the solvent was
reduced to about 6 cm3 in vacuo. The white precipitate was filtered
off and dried in vacuo. Yield: 0.31 g, 77%. Anal. Calcd for C10H24-
1
Ga2I6P2: C, 10.9; H, 2.2. Found: C, 11.6; H, 2.2. H NMR (300
MHz, CDCl3): δ 2.47 (d, [4H], CH2), 2.22-2.00 (m, [8H], CH2),
1.45-1.29 (m, [12H], CH3). 71Ga NMR (CH2Cl2/5% CD2Cl2): δ
-132 (br). 31P{1H} NMR (CH2Cl2/5% CD2Cl2): δ -27.6 (s). IR
(cm-1, Nujol): ν 240 (s), 229 (s). Raman (cm-1): 230 (s).
[GaCl3{µ-Et2P(CH2)2PEt2}GaCl3]. This was prepared in a
manner similar to that described above. Yield: 79%. Anal. Calcd
[GaI2{o-C6H4(PMe2)2}2][GaI4]. GaI3 (0.266 g, 0.590 mmol) was
added to a solution of o-C6H4(PMe2)2 (0.117 g, 0.590 mmol) in
toluene (15 cm3) at room temperature. After it was heated at 80 °C
for 2 h, the mixture was returned to room temperature, and the
solvent was reduced in vacuo to ∼5 cm3. The resulting white
precipitate was filtered off and dried in vacuo. Yield: 0.32 g, 85%.
1
for C10H24Cl6Ga2P2: C, 21.5; H, 4.3. Found: C, 20.7; H, 4.6. H
NMR (300 MHz, CDCl3): δ 2.26 (d, [4H], CH2), 2.13-1.96 (m,
[8H], CH2), 1.44-1.23 (m, [12H], CH3). 71Ga NMR (CH2Cl2/5%
CD2Cl2): δ 274 (br). 31P{1H} NMR (CH2Cl2/5% CD2Cl2): δ -2.0
(s). IR (cm-1, Nujol): ν 376 (s), 350 (m). Raman (cm-1): 381
(m), 353 (s).
(9) Nogai, S.; Schmidbaur, H. Inorg. Chem. 2002, 41, 4770-4774.
(10) (a) Carter, J. C.; Jugie, G.; Enjalbert, R.; Galy, J. Inorg. Chem. 1978,
17, 1248-1254. (b) Carty, A. J. Can. J. Chem. 1967, 45, 345-351;
ibid, 1967, 45, 3187-3192.
(11) Baker, L.-J.; Kloo, L. A.; Rickard, C. E. F.; Taylor, M. J. J. Organomet.
Chem. 1997, 545-546, 249-255.
[GaBr3{µ-Et2P(CH2)2PEt2}GaBr3]. This was prepared in a
manner similar to that described above. Yield: 81%. Anal. Calcd
(12) Janik, J. F.; Baldwin, R. A.; Wells, R. L.; Pennington, W. T.; Schimek,
G. L.; Rheingold, A. L.; Liable-Sands, L. M. Organometallics 1996,
15, 5385-5390.
1
for C10H24Br6Ga2P2: C, 14.6; H, 3.0. Found: C, 14.3; H, 3.2. H
NMR (300 MHz, CDCl3): δ 2.35 (d, [4H], CH2), 2.17-1.95 (m,
[8H], CH2), 1.39-1.20 (m, [12H], CH3). 71Ga NMR (CH2Cl2/5%
CD2Cl2): δ 163 (br). 31P{1H} NMR (CH2Cl2/5% CD2Cl2): δ -7.7
(s). IR (cm-1, Nujol): ν 292 (s), 251 (w). Raman (cm-1): 295
(m), 249 (s).
[GaCl2{o-C6H4(PPh2)2}][GaCl4]. A solution of o-C6H4(PPh2)2
(0.29 g, 0.65 mmol) in toluene (25 cm3) was added dropwise to a
stirred solution of GaCl3 (0.23 g, 1.31 mmol) in toluene (4 cm3) at
room temperature. The solution was heated to 80 °C for 2 h, and
then it was cooled to room temperature. The resultant white
(13) Brown, M. A.; Castro, J. A.; Tuck, D. G. Can. J. Chem. 1997, 75,
333-343.
(14) Sigl, M.; Schier, A.; Schmidbaur, H. Eur. J. Inorg. Chem. 1998, 203-
210.
(15) Cheng, F.; Hector, A. L.; Levason, W.; Reid, G.; Webster, M.; Zhang,
W. Dalton Trans. 2007, 2207-2210.
(16) Kyba, E. P.; Liu, S. T.; Harris, R. L. Organometallics 1983, 2, 1877-
1879.
(17) McFarlane, H. C. E.; McFarlane, W. Polyhedron 1983, 2, 303-304.
(18) Aguiar, A. M.; Beisler, J. J. Org. Chem. 1964, 29, 1660-1662.
(19) Feltham, R. D.; Kasenally, A. S.; Nyholm, R. S. J. Organomet. Chem.
1967, 7, 285-288.
7216 Inorganic Chemistry, Vol. 46, No. 17, 2007

Complexes of Gallium(III) Halides
Table 1. Summary of Crystallographic Dataa
[GaCl2{o-C6H4(PMe2)2}2][GaCl4]
C20H32Cl6Ga2P4
[GaBr2{o-C6H4(PMe2)2}2][GaBr4]‚CH2Cl2
[GaI2{o-C6H4(PMe2)2}2][GaI4]‚nCH2Cl2
C20.4H32.8Cl0.8Ga2I6P4
formula
fw
cryst syst
space group
a (Å)
C21H34Br6Cl2Ga2P4
1100.16
orthorhombic
Pnma (No. 62)
14.688(3)
22.978(4)
10.4931(18)
90
748.48
monoclinic
C2/c (No. 15)
13.2556(16)
14.536(2)
16.594(2)
90
104.131(8)
90
3100.6(7)
4
1331.15
orthorhombic
Pnma (No. 62)
15.223(2)
23.406(4)
11.0027(10)
90
90
90
3920.4(9)
4
2.255
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
Z
90
90
3541.5(11)
4
2.063
8.636
2104
D
calcd (g cm-3
)
1.603
2.472
1504
0.026
µ(Mo KR) (mm-1
F(000)
)
)
)
6.328
2435.2
0.050
R1b [I > 2σ(I)]
wR2 [all data]
0.041
0.098
0.064
0.124
[GaCl2{o-C6H4(PPh2)2}][GaCl4]
[(GaBr3)2{Et2P(CH2)2PEt2}]
[(GaI3)2{Et2P(CH2)2PEt2}]
formula
fw
cryst syst
space group
a (Å)
C30H24Cl6Ga2P2
798.57
C10H24Br6Ga2P2
825.13
C10H24Ga2I6P2
1107.07
triclinic
P1h (No. 2)
7.7763(18)
7.818(2)
10.993(3)
86.676(15)
82.577(15)
80.447(18)
653.1(3)
1
triclinic
P1h (No. 2)
10.139(2)
10.593(3)
16.028(4)
72.765(12)
87.616(12)
89.878(12)
1642.6(7)
2
triclinic
P1h (No. 2)
7.4000(16)
7.4685(16)
10.805(2)
85.619(12)
88.087(12)
77.456(12)
581.1(2)
1
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
Z
D
calcd (g cm-3
)
1.615
2.246
796
0.048
2.358
12.760
386
0.037
2.815
9.268
494
0.038
µ(Mo KR) (mm-1
F(000)
R1b [I > 2σ(I)]
wR2 [all data]
0.102
0.071
0.089
[GaCl2{o-C6H4(AsMe2)2}][GaCl4]
[GaI2{o-C6H4(AsMe2)2}][GaI4]
[(GaI3)2{Ph2As(CH2)2AsPh2}]
formula
fw
cryst syst
space group
a (Å)
C10H16As2Cl6Ga2
638.21
C10H16As2Ga2I6
1186.91
orthorhombic
Pnma (No. 62)
15.935(4)
11.374(2)
14.319(3)
90
90
90
2595.4(9)
4
3.038
C26H24As2Ga2I6
1387.13
monoclinic
P21/n (No. 14)
10.1666(10)
15.4125(15)
23.181(2)
90
99.036(5)
90
3587.1(6)
4
monoclinic
P21/m (No. 11)
9.941(2)
10.111(3)
10.206(2)
90
91.303(16)
90
1025.7(4)
2
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
Z
D
calcd (g cm-3
)
2.066
6.597
612
0.067
2.568
8.512
2504
0.045
µ(Mo KR) (mm-1
F(000)
11.736
2088
0.073
0.150
R1b [I > 2σ(I)]
wR2 [all data]
0.146
0.091
2
2
4
a Temp ) 120 K; wavelength(Mo KR) ) 0.71073 Å; θ(max) ) 27.5°. b R1 ) ∑||Fo| - |Fc||/∑|Fo|; wR2 ) [∑w(Fo - Fc )2/∑wFo ]1/2
.
precipitate was filtered off and dried in vacuo. Yield: 0.27 g, 53%.
Anal. Calcd for C30H24Cl6Ga2P2: C, 45.1; H, 3.0. Found: C, 44.8;
filtered off and dried in vacuo. Yield: 0.28 g, 79%. Anal. Calcd
for C10H16As2Cl6Ga2: C, 18.8; H, 2.5. Found: C, 18.8; H, 2.8. 1H
NMR (300 MHz, CDCl3): δ 7.89-7.40 (m, [4H], C6H4), 2.12 (s,
[6H], CH3). 71Ga NMR (CH2Cl2/5% CD2Cl2): δ 256 (br) 250 (s).
IR (cm-1, Nujol): ν 421 (s), 378 (s) 356 (s), 265 (m). Raman
(cm-1): 422 (w), 381 (m), 361 (m), 344 (s), 265 (m).
1
H, 3.2. H NMR (300 MHz, CDCl3): δ 8.01-7.31 (m, Ph). 71Ga
NMR (CH2Cl2/5% CD2Cl2): δ 251 (br). 31P{1H} NMR (CH2Cl2/
5%CD2Cl2): δ -18.9 (br). IR (cm-1, Nujol): ν 404 (m), 385 (s),
370 (s). Raman (cm-1): 402 (w), 388 (m), 374 (m), 346 (s).
[GaX2{o-C6H4(PPh2)2}][GaX4] (X ) Br or I). These com-
[GaBr2{o-C6H4(AsMe2)2}][GaBr4]. This was prepared in a
manner similar to that described above as a white solid. Yield: 72%.
Anal. Calcd for C10H16As2Br6Ga2: C, 13.3; H, 1.8. Found: C, 13.5;
H, 1.7. 1H NMR (300 MHz, CDCl3): δ 7.90-7.40 (m, [4H], C6H4),
2.11 (s, [6H], CH3). 71Ga NMR (CH2Cl2/5% CD2Cl2): δ 141 (br),
64 (s). IR (cm-1, Nujol): ν 280 (s), 254 (m). Raman (cm-1): 280
(w), 264 (w), 232 (m), 209 (s).
pounds were made as described.14
[GaCl2{o-C6H4(AsMe2)2}][GaCl4]. A solution of o-C6H4-
(AsMe2)2 (0.163 g, 0.57 mmol) in toluene (5 cm3) was added
dropwise to a stirred solution of GaCl3 (0.200 g, 1.14 mmol) in
toluene (3 cm3) at room temperature. The mixture was heated to
80 °C for 2 h and cooled, and the resulting white precipitate was
Inorganic Chemistry, Vol. 46, No. 17, 2007 7217

Cheng et al.
Table 2. Selected Bond Lengths (Å) and Angles (deg) for
[GaX2{o-C6H4(PMe2)2}2][GaX4] (X ) Cl, Br or I)
Table 3. Selected Bond Lengths (Å) and Angles (deg) for
[GaCl2{o-C6H4(PPh2)2}][GaCl4]
[GaCl2{o-C6H4(PMe2)2}2][GaCl4]a
Ga1-Cl1
Ga1-Cl2
Ga1-P1
Ga1-P2
2.1457(11)
2.1575(12)
2.3787(12)
2.3865(11)
Ga2-Cl3
Ga2-Cl4
Ga2-Cl5
Ga2-Cl6
2.1757(13)
2.1806(13)
2.1748(12)
2.1647(12)
Ga1-Cl1
Ga1-P1
Ga1-P2
2.3585(5)
2.4806(5)
2.4794(6)
Ga2-Cl2
Ga2-Cl3
2.1774(5)
2.1695(5)
P2-Ga1-P1
81.751(15)
87.570(15)
111.11(3)
108.64(2)
Cl1-Ga1-P1
87.321(19)
Cl1-Ga1-P1
Cl2-Ga1-P1
Cl1-Ga1-P2
Cl2-Ga1-P2
Cl1-Ga1-Cl2
P1-Ga1-P2
112.11(4)
109.34(4)
108.15(4)
124.34(4)
113.97(5)
85.42(4)
Cl3-Ga2-Cl4
Cl5-Ga2-Cl3
Cl5-Ga2-Cl4
Cl6-Ga2-Cl3
Cl6-Ga2-Cl4
Cl6-Ga2-Cl5
108.75(5)
108.60(5)
111.12(5)
109.80(5)
108.16(5)
110.40(5)
Cl1-Ga1-P2
Cl2-Ga2-Cl2a
Cl3-Ga2-Cl2a
Cl3-Ga2-Cl2
Cl3-Ga2-Cl3a
109.17(2)
110.10(3)
b
[GaBr2{o-C6H4(PMe2)2}2][GaBr4]‚CH2Cl2
Ga1-Br1
Ga1-P1
Ga1-P2
2.5276(6)
2.4751(12)
2.4875(12)
Ga2-Br2
Ga2-Br3
Ga2-Br4
2.3440(10)
2.3311(7)
2.3370(10)
Table 4. Selected Bond Lengths (Å) and Angles (deg) for
[(GaX3)2{µ-Et2P(CH2)2PEt2}] (X ) Br or I)
P1-Ga1-P2
82.47(4)
94.39(3)
109.33(4)
109.05(3)
P2-Ga1-Br1
92.88(3)
[(GaBr3)2{Et2P(CH2)2PEt2}]
[(GaI3)2{Et2P(CH2)2PEt2}]
P1-Ga1-Br1
Br3-Ga2-Br3a
Br2-Ga2-Br3
Ga1-Br1
Ga1-Br2
Ga1-Br3
Ga1-P1
2.3033(8)
2.3226(8)
2.3246(8)
2.3614(13)
Ga1-I1
2.5200(10)
2.5405(10)
2.5418(9)
2.3769(15)
Br3-Ga2-Br4
Br2-Ga2-Br4
110.82(3)
107.72(4)
Ga1-I2
Ga1-I3
Ga1-P1
c
[GaI2{o-C6H4(PMe2)2}2][GaI4]‚nCH2Cl2
Ga1-I1
Ga1-P1
Ga1-P2
2.7481(6)
2.487(2)
2.499(2)
Ga2-I2
Ga2-I3
Ga2-I4
2.5509(14)
2.5559(14)
2.5401(10)
Br1-Ga1-Br2
Br1-Ga1-Br3
Br2-Ga1-Br3
Br1-Ga1-P1
Br2-Ga1-P1
Br3-Ga1-P1
111.69(3)
113.81(3)
110.15(3)
110.36(4)
106.95(4)
103.37(4)
I1-Ga1-I2
I1-Ga1-I3
I2-Ga1-I3
I1-Ga1-P1
I2-Ga1-P1
I3-Ga1-P1
111.47(3)
114.90(3)
111.28(3)
108.99(5)
107.14(5)
102.38(4)
P1-Ga1-P2
P1-Ga1-I1
I2-Ga2-I3
I4-Ga2-I4a
81.67(7)
86.49(5)
107.46(5)
108.39(5)
P2-Ga1-I1
85.89(5)
I4-Ga2-I2
I4-Ga2-I3
110.84(3)
109.65(3)
Table 5. Selected Bond Lengths (Å) and Angles (deg) for
[GaX2{o-C6H4(AsMe2)2}][GaX4] (X ) Cl or I)
a Symmetry operation: a 2 - x, y, 1/2 - z. b Symmetry operation: a x,
1/2 - y, z. c Symmetry operation: a x, 3/2 - y, z.
[GaCl2{o-C6H4(AsMe2)2}][GaCl4]a
Ga1-Cl1
Ga1-As1
Ga2-Cl4
2.123(3)
2.442(1)
2.174(4)
Ga1-Cl2
Ga2-Cl3
Ga2-Cl5
2.164(3)
2.159(2)
2.198(4)
[GaI2{o-C6H4(AsMe2)2}][GaI4]. This was prepared in a manner
similar to that described above as a white solid. Yield: 69%. Anal.
Calcd for C10H16As2Ga2I6: C, 10.1; H, 1.4. Found: C, 10.5; H,
1.1. 1H NMR (CDCl3): δ 7.90-7.40 (m, [4H], C6H4), 2.01 (s, [6H],
CH3). 71Ga NMR (CH2Cl2/5% CD2Cl2): δ -166.0 (s), -450.7 (s).
IR (cm-1, Nujol): ν 266 (m), 223 (s), 216 (sh). Raman (cm-1):
263 (m), 223 (s), 218 (m).
Cl1-Ga1-Cl2
Cl2-Ga1-As1
Cl3-Ga2-Cl3b
Cl3-Ga2-Cl5
118.65(12)
107.84(7)
108.87(13)
111.46(9)
Cl1-Ga1-As1
As1-Ga1-As1a
Cl3-Ga2-Cl4
Cl4-Ga2-Cl5
113.96(7)
91.05(6)
111.00(9)
102.99(15)
[GaI2{o-C6H4(AsMe2)2}][GaI4]b
[GaI3{µ-Ph2As(CH2)2AsPh2}GaI3]. A solution of Ph2As(CH2)2-
AsPh2 (0.113 g, 0.23 mmol) in dichloromethane (3 cm3) was added
to stirred solution of GaI3 (0.209 g, 0.465 mmol) in the same solvent
(20 cm3) at room temperature. After the mixture was stirred at room
temperature overnight, the solvent was reduced to ∼3 cm3 to give
a white precipitate. The precipitate was filtered off, washed using
CH2Cl2, and dried in vacuo. Yield: 0.19 g, 61%. Anal. Calcd for
C26H24As2Ga2I6: C, 22.5; H, 1.7. Found: C, 23.1; H, 1.6. 1H NMR
(300 MHz, CDCl3): δ 7.60-7.43 (m, [20H], Ph), 3.09 (s, [4H],
Ga1-I1
Ga1-As1
Ga2-I4
2.491(3)
2.450(2)
2.547(3)
Ga1-I2
Ga2-I3
Ga2-I5
2.496(3)
2.563(3)
2.537(2)
I1-Ga1-I2
As1-Ga1-I2
I5-Ga2-I5a
I3-Ga2-I5
127.78(10)
110.57(8)
110.83(10)
109.54(6)
As1-Ga1-I1
As1-Ga1-As1a
I3-Ga2-I4
105.90(8)
89.26(10)
106.71(9)
110.07(6)
I4-Ga2-I5
a Symmetry operation: a x, 1/2 - y, z; b x, 3/2 - y, z. b Symmetry
operation: a x, 1/2 - y, z.
CH2). 71Ga NMR (CH2Cl2/5% CD2Cl2): δ -206 (br). IR (cm-1
Nujol): ν 244 (s), 233 (s). Raman (cm-1): 247 (m), 233 (m).
,
1
6.3; H, 1.5. Found: C, 6.4; H, 1.5. H NMR (300 MHz, CDCl3):
δ 1.49 (s). 71Ga NMR (CH2Cl2/5% CD2Cl2): δ -169.5. IR (cm-1
Nujol): ν 227 (m).
[GaCl3(AsMe3)]. A solution of AsMe3 (0.15 g, 1.24 mmol) in
Et2O (5 cm3) was added dropwise to stirred solution of GaCl3 (0.22
g, 1.24 mmol) in Et2O (5 cm3) at -78 °C. After it was stirred at
-78 °C for 30 min, the mixture was allowed to warm to room
temperature and was stirred for another 5 h. The solvent was
reduced to ∼2 cm3, and the resultant white precipitate was filtered
off and dried in vacuo. Yield: 0.22 g, 76%. Anal. Calcd for C3H9-
AsCl3Ga: C, 12.2; H, 3.1. Found: C, 11.7; H, 3.1. 1H NMR (300
MHz, CDCl3): δ 1.59 (s). 71Ga NMR (CH2Cl2/5% CD2Cl2): δ
264.5 (br). IR (cm-1, Nujol): ν 390 (s), 344 (s).
,
X-ray Crystallography. Brief details of the crystallographic data
and refinement parameters are given in Table 1. Crystals were
grown from CH2Cl2 solutions by vapor diffusion of hexane. Data
collections used a Bruker-Nonius Kappa CCD diffractometer fitted
with Mo KR radiation (λ ) 0.71073 Å) and either a graphite
monochromator or confocal mirrors, with the crystals held at 120
K in a nitrogen gas stream. Structure solution and refinement were
straightforward,20,21 with H atoms introduced into the models in
calculated positions. Selected bond lengths and angles are given in
Tables 2-6.
[GaBr3(AsMe3)]. This was prepared in a manner similar to that
for the chloride. Yield: 77%. Anal. Calcd for C3H9AsBr3Ga: C,
1
8.4; H, 2.1. Found: C, 7.9; H, 2.3. H NMR (300 MHz, CDCl3):
δ 1.53 (s). 71Ga NMR (CH2Cl2/5% CD2Cl2): δ 147. IR (cm-1
Nujol): ν 265 (s), 252 (sh).
,
(20) Sheldrick, G. M. SHELXS-97, Program for crystal structure solution;
University of Go¨ttingen: Go¨ttingen, Germany, 1997.
(21) Sheldrick, G. M. SHELXL-97, Program for crystal structure refine-
ment; University of Go¨ttingen: Go¨ttingen, Germany, 1997.
[GaI3(AsMe3)]. This was prepared in a manner similar to that
described above. Yield: 70%. Anal. Calcd for C3H9AsGaI3: C,
7218 Inorganic Chemistry, Vol. 46, No. 17, 2007

Complexes of Gallium(III) Halides
Table 6. Selected Bond Lengths (Å) and Angles (deg) for
[(GaI3)2{µ-Ph2As(CH2)2AsPh2}]
Ga1-I1
Ga1-I2
Ga1-I3
Ga1-As1
2.5181(9)
2.5118(9)
2.5198(9)
2.4875(10)
Ga2-I4
Ga2-I5
Ga2-I6
Ga2-As2
2.5270(9)
2.4944(9)
2.5329(9)
2.4885(10)
As1-Ga1-I1
As1-Ga1-I2
As1-Ga1-I3
I1-Ga1-I2
I1-Ga1-I3
I2-Ga1-I3
100.21(3)
106.02(3)
105.19(3)
116.36(3)
113.69(3)
113.42(3)
As2-Ga2-I4
As2-Ga2-I5
As2-Ga2-I6
I4-Ga2-I5
I4-Ga2-I6
I5-Ga2-I6
99.21(3)
105.90(3)
105.06(3)
119.01(3)
111.92(3)
113.46(3)
Figure 1. Crystal structure of the cation in [GaCl2{o-C6H4(PMe2)2}2]-
[GaCl4] showing the atom numbering scheme adopted. Ellipsoids are
drawn at the 50% probability level, and H atoms are omitted for clarity.
The molecule has a center of symmetry. Symmetry operation: a 1 - x,
-y, 1 - z.
Results
Diphosphanes. The diphosphane o-C6H4(PMe2)2, which
is an exceptionally strong σ-donor with small steric demands
and is preorganized for chelation,22 reacted with GaX3 (X
) Cl, Br or I) in a 1:1 molar ratio in hot toluene to form
white powders with microanalyses consistent with 1:1
complexes. Crystals of all three complexes were obtained
from CH2Cl2 solution and were revealed to be trans-[GaX2-
{o-C6H4(PMe2)2}2][GaX4], which are the first examples of
gallium(III) phosphanes with six-coordinate gallium centers.
All show tetrahedral anions and trans pseudo-octahedral
cations (Table 2, Figures 1 and 2). The cations are cen-
trosymmetric and show the “stepped” arrangement found in
many o-phenylene diphosphane or diarsane transition metal
complexes.23 The Ga-X and Ga-P distances in the cations
are longer than in the pseudotetrahedral [GaX3(PR3)]
complexes,9-13 attributable to the increased coordination
number of the metal, but the Ga-P distances increase only
slightly as the halogen coligands change Cl f Br f I in the
three complexes. The small chelate bite of the diphosphane
results in quite acute P-Ga-P of ∼82°. Six-coordination
is also present in the 2,2′-bipyridyl complexes [GaX2(2,2′-
bipy)2][GaX4], but the cations are cis isomers.24,25 The
diphosphane complexes are poorly soluble in chlorocarbons
but give single sharp 31P{1H} NMR resonances with small
high-frequency coordination shifts, showing them to be
exclusively the trans isomers in solution. Only the [GaX4]-
anions were observed in the 71Ga NMR spectra;26 fast
relaxation in the lower-symmetry cations accounts for the
absence of the resonances (see below). The far-IR and Raman
spectra are dominated by strong features assigned to [GaX4]-,27
and definite assignment of the a1g (Raman) and a2u (IR) GaX2
vibrations of the cations was not possible. The Experimental
Figure 2. Crystal structure of the cation in [GaBr2{o-C6H4(PMe2)2}2]-
[GaBr4]‚CH2Cl2 showing the atom numbering scheme adopted. Ellipsoids
are drawn at the 50% probability level, and H atoms are omitted for clarity.
The molecule has a center of symmetry. Symmetry operation: a -x, 1 -
y, 1 - z. The iodo analogue is isomorphous.
Section lists the major vibrations below 400 cm-1. The
reaction of o-C6H4(PMe2)2 with two molar equivalents of
GaCl3 in hot toluene gave a white powder with the composi-
tion 2GaCl3/o-C6H4(PMe2)2, which was insoluble in chlo-
rocarbons and decomposed by MeCN, MeNO2, or DMSO
with liberation of the diphosphane (and formation of [o-C6H4-
(PMe2)(PMe2H)]+, identified by 31P{1H} NMR spectros-
copy). The far-IR spectrum shows a strong band at 380 cm-1
assigned as ν3 of [GaCl4]-, and two strong bands at 410 and
362 cm-1 are also assigned as Ga-Cl stretches. This complex
is tentatively formulated as [GaCl2{o-C6H4(PMe2)2}][GaCl4],
containing a pseudotetrahedral cation (cf., the diarsane
complexes described below), but its insolubility has pre-
vented us from obtaining crystals to confirm this by an X-ray
structural study.
The phenyl-substituted diphosphane, o-C6H4(PPh2)2, is also
preorganized for chelation but is considerably bulkier, and
although it forms six-coordinate complexes with some
transition metals,22 we find in agreement with Sigl et al.14
that with GaX3 only [GaX2{o-C6H4(PPh2)2}][GaX4] com-
plexes are isolated even with excess diphosphane. The
structure of the chloro complex (Table 3, Figure 3) shows a
very distorted tetrahedral cation with P-Ga-P ) 85.4°
and with Ga-Cl ) 2.157(1), 2.146(1) Å and Ga-P ) 2.379-
(1), 2.386(1) Å, ∼0.2 and 0.1 Å shorter, respectively, than
in the six-coordinate complex above. In [GaI2{o-C6H4-
(PPh2)2}]+, Ga-P ) 2.398(1) and 2.409(1) Å,14 indicating
weaker Lewis acidity in the di-iodogallium cation and
(22) Levason, W. In The Chemistry of Organophosphorus Compounds;
Hartley, F. R., Ed.; Wiley: New York, 1990; Vol. 1, pp 568-641.
(23) (a) Higgins, S. J.; Jewiss, H. C.; Levason, W.; Webster, M. Acta.
Crystallogr., Sect. C 1985, 41, 695-697. (b) Champness, N. R.;
Levason, W.; Pletcher, D.; Webster, M. J. Chem. Soc., Dalton Trans.
1992, 3243-3247.
(24) Carty, A. J. Can. J. Chem. 1968, 46, 3779-3784.
(25) Restivo, R.; Palenik, G. J. J. Chem. Soc., Dalton Trans. 1972, 341-
344.
(26) Mason, J. Multinuclear NMR; Plenum: New York, 1987. The 71Ga
NMR chemical shifts for [GaX4]- are X ) Cl , δ 251; X ) Br, δ 64;
X ) I , δ -455 (all in CH2Cl2 solution).
(27) Tetrahedral [GaX4]- show one IR active stretch (ν3, t2) and two Raman
active stretches (ν1, a1 and ν3, t2). Literature values (cm-1) are X )
Cl ν1 ) 346, ν3 ) 386; X ) Br ν1 ) 210, ν3 ) 278; X ) I ν1 ) 145,
ν3 ) 222. Data from Nakamoto, K. IR Spectra of Inorganic and
Coordination Compounds, 2nd ed.; Wiley: New York, 1970.
Inorganic Chemistry, Vol. 46, No. 17, 2007 7219

Cheng et al.
Figure 4. Crystal structure of [(GaBr3)2{Et2P(CH2)2PEt2}] showing the
atom numbering scheme adopted. Ellipsoids are drawn at the 50%
probability level, and H atoms are omitted for clarity. The molecule has a
center of symmetry. Symmetry operation: a 1 - x, -y, -z.
Figure 3. Crystal structure of the cation in [GaCl2{o-C6H4(PPh2)2}][GaCl4]
showing the atom numbering scheme adopted. Ellipsoids are drawn at the
50% probability level, and H atoms are omitted for clarity.
perhaps steric crowding, although the P-Ga-P angle (84.5°)
is little different. The complexes are characterized by singlet
31P{1H} NMR resonances to low frequency of the ligand
chemical shift, which are invariant over the temperature range
of 295-183 K. The 71Ga NMR spectra show only the sharp
resonances of the [GaX4]- anions, the resonances of the
cations were not observed. Solutions of [GaX2{o-C6H4-
(PPh2)2}][GaX4] containing excess (∼3-fold) o-C6H4(PPh2)2
show evidence for the formation of other species, although
only the [GaX2{o-C6H4(PPh2)2}][GaX4] have been isolated
as solids. Thus, a dichloromethane solution of [GaI2{o-C6H4-
(PPh2)2}][GaI4] containing excess o-C6H4(PPh2)2 shows a
new 71Ga resonance at δ ) -162, and the 31P{1H} NMR
spectrum shows ligand (δ ) -13) and resonances at δ )
-24 and -19, which we tentatively attribute to [GaI3{κ1-
o-C6H4(PPh2)2}]. It is notable that even with a large excess
(∼10-fold) of added o-C6H4(PPh2)2, significant amounts of
[GaI2{o-C6H4(PPh2)2}][GaI4] are still present. Similar but
more complex behavior was evident in mixtures of [GaCl2-
{o-C6H4(PPh2)2}][GaCl4]/o-C6H4(PPh2)2 in CH2Cl2 solution,
which seems to contain several species including the hy-
drolysis product [o-C6H4(PPh2)(PPh2H)]+.28
Figure 5. Crystal structure of [(GaI3)2{Et2P(CH2)2PEt2}] showing the atom
numbering scheme adopted. Ellipsoids are drawn at the 50% probability
level, and H atoms are omitted for clarity. The molecule has a center of
symmetry. Symmetry operation: a 2 - x, 2 - y, -z.
of the two GaX3 residues is determined by the inversion
center in the molecule.
Diarsanes. The reaction of GaCl3 with o-C6H4(AsMe2)2
in hot toluene produced a white complex with the composi-
tion 2:1 GaCl3/diarsane, regardless of the ratio of reagents
used. This was identified as [GaCl2{o-C6H4(AsMe2)2}]-
[GaCl4] by a crystal structure determination (see below) and
is the correct formulation for the substance formulated as
[GaCl2{o-C6H4(AsMe2)2}2][Ga3Cl10] (based on microana-
lytical and conductivity data only) in an early report.29 The
reaction of GaX3 (X ) Br or I) with o-C6H4(AsMe2)2 in a
2:1 mole ratio similarly affords [GaX2{o-C6H4(AsMe2)2}]-
[GaX4], but with a 1:1 metal/ligand ratio, substances with
higher and variable C and H content were obtained. However,
the IR and Raman spectra of these materials are very similar
to those of (crystallographically authenticated) [GaX2{o-
C6H4(AsMe2)2}][GaX4], differing only in the relative intensi-
ties of the bands assigned to the [GaX4]- anions, which are
very weak in some samples, while the bands associated with
the cations appear unchanged. We conclude that these
substances with a higher C, H content are almost certainly
mixtures of [GaX2{o-C6H4(AsMe2)2}]X and [GaX2{o-C6H4-
(AsMe2)2}][GaX4], although we have been unable to obtain
samples free of the tetrahalogallate(III) anions. In contrast
to the pseudooctahedral cations with the diphosphane of the
The diphosphane Et2P(CH2)2PEt2,which usually behaves
as a strongly bound chelate to transition metals,22 gives [(X3-
Ga)2{µ-Et2P(CH2)2PEt2}] with bridging diphosphane ligands
coordinated to pseudotetrahedral GaX3 units as the only
complex type in the gallium(III) systems. The 31P{1H} and
71Ga NMR spectra show these are the only significant species
present in CH2Cl2 solution over the temperature range of
295-183 K, and apart from small temperature drifts, the
spectra are little affected by varying the temperature; no
spin-spin couplings were resolved. Structures of [(X3Ga)2-
{µ-Et2P(CH2)2PEt2}] (X ) Br or I) were determined, and
the results are presented in Figures 4 and 5 and Table 4.
The Ga-P bond length is slightly shorter in [(I3Ga)2{µ-
Et2P(CH2)2PEt2}] (2.377(1) Å) than in [(I3Ga)2{µ-Ph2P(CH2)2-
PPh2}] (2.40(1), 2.41(1) Å)13 which suggests that the
alkyldiphosphane is more strongly bound. The conformation
(28) Sigl, M.; Schier, A.; Schmidbaur, H. Z. Naturforsch., Teil B 1998,
53, 1313-1315.
(29) Nyholm, R. S.; Ulm, K. J. Chem. Soc. 1965, 4199-4203.
7220 Inorganic Chemistry, Vol. 46, No. 17, 2007

Complexes of Gallium(III) Halides
Figure 6. Crystal structure of the cation in [GaCl2{o-C6H4(AsMe2)2}]-
[GaCl4] showing the atom numbering scheme adopted. Ellipsoids are drawn
at the 50% probability level, and H atoms are omitted for clarity. The cation
has mirror plane symmetry. Symmetry operation: a x, 1/2 - y, z.
Figure 7. Crystal structure of the cation in [GaI2{o-C6H4(AsMe2)2}][GaI4]
showing the atom numbering scheme adopted. Ellipsoids are drawn at the
50% probability level, and H atoms are omitted for clarity. The cation has
mirror symmetry. Symmetry operation: a x, 1/2 - y, z.
type trans-[GaX2{o-C6H4(PMe2)2}2]+ described above, the
diarsane affords only pseudotetrahedral [GaX2{o-C6H4-
(AsMe2)2}]+. We note that [GaX2{o-C6H4(AsMe2)2}2][GaX4]
compounds proposed to contain six-coordinate cations were
reported in the early study (based only on microanalytical
and molecular weight data),29 but it seems clear that these
were [GaX2{o-C6H4(AsMe2)2}]X. The different stoichiom-
etries obtained with gallium halides for these two o-
phenylene ligands contrasts starkly with their very extensive
transition metal chemistry, where they form analogous
complexes in almost all cases, which differ only slightly in
stability or spectroscopic properties.22,30 The crystal structures
of [GaX2{o-C6H4(AsMe2)2}][GaX4] show distorted pseudot-
etrahedral cations and close to tetrahedral anions (Table 5,
Figures 6 and 7).31 The cations (X ) Cl or I) have As-
Ga-As angles close to 90° as a result of the rigid ligand’s
bite, and correspondingly, the X-Ga-X angles are 118.6-
(1)° (Cl) and 127.8(1)° (I). The Ga-As distances are very
similar, 2.442(1) (Cl) and 2.450(2) Å (I); the Ga-X distances
in the anions are somewhat longer than in the cations.
The far-IR spectrum of [GaCl2{o-C6H4(AsMe2)2}][GaCl4]
contains strong bands at 421 and 356 cm-1, which we assign
as the a1 + b1 GaCl2 vibrations of the cation; the bands
appear at similar frequencies but with reversed relative
intensities in the Raman spectrum. The 71Ga NMR spectrum
shows only a sharp feature at δ 250 assigned to [GaCl4]-
superimposed on a broader feature δ ∼256. The far-IR
spectrum of [GaBr2{o-C6H4(AsMe2)2}][GaBr4] contains fea-
tures at 264 and 233 cm-1 assigned as the a1 + b1 GaBr2
vibrations, and corresponding features in the spectrum of
[GaI2{o-C6H4(AsMe2)2}][GaI4] are found at 226 and 216
cm-1. The 71Ga NMR spectrum of [GaBr2{o-C6H4(AsMe2)2}]-
[GaBr4] shows resonances at δ 64 ([GaBr4]-)26 and 141,
while the iodo complex has 71Ga resonances at δ -451
([GaI4]-)26 and -166. The second resonance in each complex
could be from [GaX2{o-C6H4(AsMe2)2}]+, which would
indicate that the electric field gradients around the gallium
center in these two cations are small, despite the distortions
from cubic symmetry produced by the chelate ligand and
the As2X2 donor set, and hence quadrupolar relaxation is
slowed sufficiently for the resonance to be observed.
However, the two gallium resonances in each complex
deviate markedly from 1:1 relative intensities, and it seems
more likely that the second resonance in each complex is
the result of a GaX3As environment produced by rearrange-
ment in solution. The δ values in each case are close to those
observed in C3V GaX3As species (see Table 7), but since we
have no values for GaX2As2 from other systems, it is not
possible to rule out the alternative assignment. It should be
noted that all our attempts to prepare [GaCl2(PR3)2]+ cations
from [GaCl3(PR3)], PR3, and SbCl5 in dry CH2Cl2 failed;
the products identified by a combination of 71Ga, 31P and
1H NMR spectroscopy were unchanged [GaCl3(PR3)] and
[PR3Cl]+, the latter resulting from chlorination of the PR3
32
by SbCl5.
Since no other gallium diarsane complexes have been
reported, we prepared [(I3Ga)2{µ-Ph2As(CH2)2AsPh2}] which
is an exact analogue of [(I3Ga)2{µ- Ph2P(CH2)2PPh2}].13 The
crystals (Table 6, Figure 8) are isomorphous, and the
structure reveals the expected ligand bridged dimer geometry;
the Ga-I distances in the two complexes are very similar.
The 71Ga NMR exhibits a single resonance at δ -206, which
may be compared with the δ -220 value in [GaI3(AsPh3)]11
and δ -169.5 in [GaI3(AsMe3)]. The three [GaX3(AsMe3)]
(X ) Cl, Br or I) were also prepared for comparison
purposes; details of their structures are given in the Sup-
porting Information.
(30) Warren, L. F.; Bennett, M. A. Inorg. Chem. 1976, 15, 3126-3140.
(31) The X-ray data for [GaBr2{o-C6H4(AsMe2)2}][GaBr4] gave a largish
Rint (0.11) with the systematic absences suggesting space groups Pmmn
(No. 59) or Pmn21 (No. 31) (both in the standard setting). A solution
in the centrosymmetric Pmmn readily emerged with the cation having
mirror symmetry, but two of the aromatic carbon atoms showed very
elongated displacement ellipsoids perpendicular to the plane of the
ring (R1 ≈ 0.10). This suggested the lower symmetry solution, but
attempts here gave unsatisfactory refinement and no improvement to
the model. Although the chemical identity is not in doubt, the structure
is not presented here.
71Ga NMR Studies and Some Comparisons. Gallium
has two naturally occurring isotopes, 69Ga (60.1%) and
(32) Corcoran, S. M.; Levason, W.; Patel, R.; Reid, G. Inorg. Chim. Acta
2005, 358, 1263-1268.
Inorganic Chemistry, Vol. 46, No. 17, 2007 7221

Cheng et al.
Table 7. Selected 71Ga and 31P{1H} NMR Data
b
δ(31P)a
∆
δ(71Ga)c
[GaCl3(PPh3)]
[GaBr3(PPh3)]
[GaI3(PPh3)]
-5.4 (m) (273 K)
-10.7 (m)
-29.7 (m)
-2.0 (s)
+0.6
-4.7
-23.7
+16.0
+10.3
-9.6
-5.9
-8.8
-17.7
+14.2
+13.8
+12.0
264 (br d, J ) 721)
152 (d, J ) 693)
-151 (d, J ) 466)
274 (s)
[(GaCl3)2{Et2P(CH2)2PEt2}]
[(GaBr3)2{Et2P(CH2)2PEt2}]
[(GaI3)2{Et2P(CH2)2PEt2}]
[GaCl2{o-C6H4(PPh2)2}][GaCl4]
[GaBr2{o-C6H4(PPh2)2}][GaBr4]
[GaI2{o-C6H4(PPh2)2}][GaI4]
[GaCl2{o-C6H4(PMe2)2}2][GaCl4]
[GaBr2{o-C6H4(PMe2)2}2][GaBr4]
[GaI2{o-C6H4(PMe2)2}2][GaI4]
[(GaI3)2{Ph2As(CH2)2AsPh2}]
[GaCl3(AsMe3)]
-7.7 (s)
160 (s)
-27.6 (s)
-18.9 (s)
-21.8 (s)
-30.7 (s)
-40.8 (s)
-41.2 (s)
-43.0 (s)
-132 (s)
251d
64d
-456d
251d
66d
-457d
-206 (s)
264.5 (s)
147 (s)
[GaBr3(AsMe3)]
[GaI3(AsMe3)]
-169.5 (s)
a At 295 K in CH2Cl2 solution unless indicated otherwise, relative to 85% H3PO4. b Coordination shift δ(complex) - δ(ligand). Ligand chemical shifts
are PPh3 (-6), Et2P(CH2)2PEt2 (-18), o-C6H4(PPh2)2 (-13), o-C6H4(PMe2)2 (-55). c At 295 K relative to [Ga(H2O)6]3+ in water at pH 1. d Resonance of
[GaX4]- anion only, see text.
donor sets lying in the range from ∼260 to 280, Br3P from
∼150 to 160, and I3P from ∼-130 to -150 ppm. The
incorporation of arsenic in place of phosphorus has little
effect on the 71Ga resonance frequency as shown by the data
on [GaX3(AsMe3)] (Table 7). The δ(71Ga) in the chloro
complexes are only slightly to high frequency of that in
[GaCl4]- (δ ) 251),26 but replacement of the single phos-
phane by bromide or iodide results in marked low-frequency
shifts (cf. [GaBr4]- δ ) 64 and [GaI4]- δ ) -455). In
contrast to the C3V complexes, we were unable to observe
71Ga resonances from either the pseudotetrahedral cations
[GaX2{o-C6H4(PPh2)2}]+ or the pseudooctahedral [GaX2{o-
C6H4(PMe2)2}2]+, in both cases the lower symmetry produc-
ing unfavorable electric field gradients and fast relaxation.
The cases of [GaX2{o-C6H4(AsMe2)2}]+ (X ) Br or I) have
been discussed above.
Figure 8. Crystal structure of [(GaI3)2{Ph2As(CH2)2AsPh2}] showing the
atom numbering scheme adopted. Ellipsoids are drawn at the 50%
The 31P{1H} NMR spectra are singlets, sharp for the
cations (showing that fast quadrupolar relaxation effectively
decouples the gallium nuclei) and rather broader for the C3V
X3P coordination environments. For a fixed ligand, the 31P
chemical shifts move to low frequency as the halide changes
Cl f Br f I, but the coordination shifts, ∆, are irregular
(Table 7), giving both positive and negative values. This
phenomenon has been observed before in p-block chemis-
try,14,33 although the reasons remain unclear. In contrast, the
majority of coordination shifts in transition metal phosphane
complexes are to high frequency (positive). Examination of
the data in Table 7 shows that the stronger σ-donor
phosphanes tend to produce higher frequency coordination
shifts than the weaker donor arylphosphanes.
probability level, and H atoms are omitted for clarity.
71Ga (39.9%), both with I ) 3/2, the less abundant 71Ga being
preferred for NMR studies because of its lower quadrupole
moment (Q), which results in narrower lines and a higher
receptivity (Rc) (69Ga, Q ) 0.178 × 10-28 m2, Rc ) 237;
71Ga, Q ) 0.112 × 10-28 m2, Rc ) 319).26 The key factor
governing whether a 71Ga resonance can be observed or
gallium coupling resolved on 31P NMR resonances will be
the electric field gradient surrounding the gallium center.
Given the relatively favorable nuclear parameters, 71Ga
resonances should be easily observed in cubic symmetry,
but decreasing symmetry (and increasing field gradients) will
broaden and then lead to loss of the gallium resonance. The
71Ga resonances are easily observed for the tetrahedral
[GaX4]- anions and for the X3P environments in the C3V
[GaX3(PR3)] and [(X3Ga)2(µ-diphosphane)] complexes (Table
7). Typically, in these complexes, the 71Ga resonances had
line widths of a few hundred Hertz at ambient temperatures,
although lines often broadened upon cooling of the solutions,
but with only small temperature drifts in the chemical shifts.
In none of the complexes in this work was the doublet
coupling to 31P resolved (although it is observed for [GaX3-
Conclusions
This systematic study of the complexes of GaX3 with
diphosphanes and diarsanes with flexible and rigid linking
groups and differing steric requirements has revealed the first
examples of six-coordinate (distorted octahedral) Ga(III)
cations, based on the sterically small and very strong σ-donor
(33) (a) Davis, M. F.; Clarke, M.; Levason, W.; Reid, G.; Webster, M.
Eur. J. Inorg. Chem. 2006, 2773-2782. (b) Genge, A. R. J.; Levason,
W.; Reid, G. Inorg. Chim. Acta 1999, 288, 142-149.
1
(PPh3)] (X ) Cl, Br, or I), with J(71Ga-31P) falling with
X, Cl f Br f I).11 The δ(71Ga) are characteristic, with Cl3P
7222 Inorganic Chemistry, Vol. 46, No. 17, 2007

Complexes of Gallium(III) Halides
o-C6H4(PMe2)2, and a rare, but distinct, difference in the
ligand properties of this diphosphane compared to the
analogous diarsane, o-C6H4(AsMe2)2 (which gives only the
pseudotetrahedral [GaX2{o-C6H4(AsMe2)2}]+ cations).
The study has also confirmed a clear preference for the
Ga(III) center in phosphane complexes to be four-coordinate
with a X3P donor set. Even for the strong σ-donating (but
flexible) Et2P(CH2)2PEt2, bridging bidentate coordination is
observed. The reluctance to form six-coordinate Ga(III)
compounds must reflect electronic preference, since gallium-
(III) (ionic radius in six-coordination34 r+ ) 62 pm) is of
similar size to later 3d metals such as Fe3+ (r ) 64.5 pm) or
Co3+ (r ) 61 pm) which readily form octahedral complexes.
A second striking difference between the present complexes
and phosphane or arsane complexes of the 3d metals is in
the relative affinity for the halide versus the P(As) ligand.
In the neutral four-coordinate gallium complexes, typically
d(Ga-Cl) ) ∼2.17 Å, d(Ga-P) ) ∼2.35 Å, and d(Ga-
As) ) ∼2.48 Å, with d(Ga-Br) in the corresponding
bromides being ∼2.32 Å, that is, Ga-Cl is much shorter
than Ga-P which is similar or slightly longer than Ga-Br,
with d(Ga-As) being longest (see Tables 2, 4, and 5). In
contrast, for low-spin six-coordinate phosphane or arsane
complexes of Fe(III) or Co(III), the d(M-P) values are
usually slightly shorter than the d(M-Cl) distances, with
d(M-Br) being much longer. Correspondingly, d(M-As)
is usually shorter than d(M-Br).22,23,30 Thus, in the gallium
compounds, one may conclude that the primary interaction
is Ga-X, with weaker binding of the neutral ligand complet-
ing the distorted tetrahedron. Similar behavior is observed
in the six-coordinate [SnX4(diphosphane)], where d(Sn-Cl)
< d(Sn-Br) ≈ d(Sn-P),33 and the disparity between M-X
and M-P is even greater in complexes of Group 15 halides
(M′X3, M ) As, Sb, or Bi), although here the varying degree
of stereochemical activity of the M-based lone pair further
complicates structural comparisons.35,36 Although the number
of examples is relatively small, the comparison of neutral
+
GaEX3 with cationic GaE2X2 (for fixed E) shows Ga-X
is shorter in the cationic species, whereas Ga-P(As) is little
changed, again evidence that the Ga-X is the dominant
interaction (see Tables 3-6 and refs 11-15). We discount
any explanation involving π-acceptance as contributing to
the shorter M-P bonds in the transition metal systems; for
oxidation state III of Co or Fe, any π component of the
bonding will be small, rather the explanation must lie in the
different σ bonding effects in the d- and p-block systems.
Acknowledgment. We thank RCUK (EP/C006731/1) and
the Royal Society (University Research Fellowship to ALH)
for support.
Supporting Information Available: X-ray crystallographic data
in CIF format for the compounds in Table 1 and for the isomorphous
[GaX3(AsMe3)], (X ) Cl, Br or I) together with an ORTEP picture
of the Br compound. This material is available free of charge via
the Internet at http://pubs.acs.org. Crystallographic data are also
available from the Cambridge Crystallographic Data Centre with
CCDC deposition numbers 645884-645895 at www.ccdc.cam.ac.
uk/data_request/cif.
IC700895R
(35) Genge, A. R. J.; Hill, N. J.; Levason, W.; Reid, G. J. Chem. Soc.,
Dalton Trans. 2001, 1007-1012.
(36) (a) Clegg, W.; Errington, R. J.; Flynn, R. J.; Green, M. E.; Hockless,
D. C. R.; Norman, N. C.; Gibson, V. C.; Tavakkoli, K. J. Chem. Soc.,
Dalton Trans. 1992, 1753-1754. (b) Clegg, W.; Elsegood, M. R. J.;
Graham, V.; Norman, N. C.; Pickett, N. L.; Tavakkoli, K. J. Chem.
Soc., Dalton Trans. 1994, 1743-1751.
(34) Shannon, R. D.; Prewitt, C. T. Acta Crystallogr., Sect. B 1970, 26,
1046-1048.
Inorganic Chemistry, Vol. 46, No. 17, 2007 7223