Synthesis and Crystal Structures of New Palladium(II)-Gallium(III) Complexes with Bridging Halogenide Ligands

Article abstract of DOI:10.1002/zaac.200300339

The reaction of palladium(II) bromide or palladium(II) iodide with the respective gallium(III) halogenide in the presence of aromatic solvents leads to the formation of palladium(II) tetrabromo- and tetraiodogallate. The compounds are isostructural {monoclinic, C2/m, Pd[GaBr₄] ₂: a=1267(2), b=808(1), c= 722(1) pm, β=94.5(1)°; Pd[GaI₄]₂: a=1363(1), b=849.9(4), c= 756.6(7) pm, β=95.38(3)°}. The structures contain mononuclear complexes Pd[GaX ₄]₂, where X - Br^- (1), I^- (2). The crystal structures of 1 and 2 were determined by single-crystal X-ray diffraction. Crystals of both compounds turned out to be similarly twinned.

Full text of DOI:10.1002/zaac.200300339

Synthesis and Crystal Structures of New Palladium(II)؊Gallium(III)
Complexes with Bridging Halogenide Ligands
Mikhail Gorlov, Andreas Fischer, and Lars Kloo*
Stockholm / Sweden, Department of Chemistry, Inorganic Chemistry, The Royal Institute of Technology (KTH)
Received October 2nd, 2003.
Abstract. The reaction of palladium(II) bromide or palladium(II)
iodide with the respective gallium(III) halogenide in the presence
of aromatic solvents leads to the formation of palladium(II)
tetrabromoϪ and tetraiodogallate. The compounds are isostructu-
ral {monoclinic, C2/m, Pd[GaBr4]2: aϭ1267(2), bϭ808(1), cϭ
722(1) pm, βϭ94.5(1)°; Pd[GaI4]2: aϭ1363(1), bϭ849.9(4), cϭ
756.6(7) pm, βϭ95.38(3)°}. The structures contain mononuclear
complexes Pd[GaX4]2, where XϪ ϭ BrϪ (1), IϪ (2). The crystal
structures of 1 and 2 were determined by single-crystal X-ray dif-
fraction. Crystals of both compounds turned out to be similarly
twinned.
Keywords: Palladium; Gallium; Crystal structures; Arenes
Synthese und Kristallstrukturen neuer Palladium(II)-Gallium(III)-Komplexe mit
überbrückenden Halogenidliganden
Inhaltsübersicht. Die Reaktion von Palladium(II)bromid und Palla-
dium(II)iodid mit dem jeweiligen Gallium(III)halogenid in Gegen-
wart aromatischer Lösungsmittel führt zur Bildung von
Palladium(II)tetrabromoϪ und tetraiodogallat. Die Verbindungen
sind isostrukturell {monoklin, C2/m, Pd[GaBr4]2: aϭ1267(2), bϭ
808(1), cϭ722(1) pm, βϭ94.5(1)°; Pd[GaI4]2: aϭ1363(1), bϭ
849.9(4), cϭ756.6(7) pm, βϭ95.38(3)°}. Die Strukturen enthalten
einkernige Komplexe Pd[GaX4]2 [XϪ ϭ BrϪ (1), IϪ (2)]. Die Kri-
stallstrukturen beider Verbindungen wurden durch Einkristallrönt-
genbeugung bestimmt. Kristalle beider Verbindungen erwiesen sich
als auf gleiche Weise verzwillingt.
Introduction
bromide and iodide reactants, we have found that not only
organometallic compounds are obtained but also inorganic
complexes. Here, we report the synthesis and crystal struc-
tures of two new palladium(II)Ϫgallium(III) compounds
Pd[GaX4]2, where XϪ ϭ BrϪ and IϪ.
Despite an outstanding importance of palladium(II) com-
plexes of Lewis acids, such as group 13 metal halides, in
various catalytic processes [1, 2], crystallographic data for
inorganic compounds, containing both palladium and
group 13 metals are very scarce. The existence of vapour
phase complexes PdAl2X8, where XϪ ϭ ClϪ, BrϪ, was de-
scribed by Papatheodorou [3, 4]. On the basis of Raman
spectra, electronic absorption spectra and magnetic proper-
ties of these compounds a square-planar coordination of
palladium has been proposed [5, 6]. Subsequently, only one
complex, Pd[AlCl4]2, has been structurally characterized [7]
among complexes of the general formulae Pd[MX4]2 (where
M ϭ Al, Ga, In; XϪ ϭ ClϪ, BrϪ, IϪ).
The main interest of our group was the synthesis and
reactivity of low-valent palladiumϪgallium clusters stabil-
ized by arene ligands [8]. The reaction between pal-
ladium(II) and gallium(III) chlorides in aromatic solvents
is the simplest and most efficient pathway to compounds of
this type. But in the course of our work, using palladium(II)
Results and Discussion
Heating PdBr2 and GaBr3 in benzene for a relatively short
time (1 hour) leads to a dark red solution. Red crystals
suitable for X-ray analysis can be isolated after 24 hours.
The product of this reaction is a mononuclear palladium(II)
complex, Pd[GaBr4]2 (1). The complex in the crystal struc-
ture of Pd[GaBr4]2 is displayed in Figure 1; Figure 2 shows
the arrangement in the unit cell. The corresponding
Pd[GaI4]2 compound (2) was obtained in a similar way, al-
beit even shorter heating times were required. Both struc-
tures contain monomeric complexes Pd[GaX4]2. These con-
sist of a Pd2ϩ cation, which is coordinated by four XϪ ions
of the gallates yielding a square planar coordination. The
Pd atom lies on a special position (2/m), which makes all
four halogen atoms and both Ga atoms crystallographically
equivalent. The arrangement shows remarkably little distor-
tion: the bond angles deviate less than 1° from ideality
(Table 3). The bond lengths (PdϪBr: 246.0 and PdϪI:
261.2 pm) agree well with those in palladium(II) bromide
(245.3 pm [9]) and β-palladium iodide (261.9 pm [10]).
* Prof. L. Kloo
Department of Chemistry, Royal Institute of Technology
S-10044 Stockholm/Sweden
Tel.: ϩ46-8-790-9343
Fax: ϩ46-8-790-9349
E-mail address: Larsa@inorg.kth.se
324
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DOI: 10.1002/zaac.200300339
Z. Anorg. Allg. Chem. 2004, 630, 324Ϫ326

New Palladium(II)ϪGallium(III) Complexes with Bridging Halogenide Ligands
Notably, long-term heating of PdBr2 and GaBr3 in ben-
zene (4 hours) gives rise to reduction of palladium and the
formation of binuclear palladium(I) complex
a
[Pd2(GaBr4)2(benzene)2], whose synthesis and crystal struc-
ture are reported separately [13]. The reaction between
PdBr2 and GaBr3 in other aromatic solvents, such as tolu-
ene and p-xylene, also leads to binuclear palladium(I) com-
plexes [Pd2(GaBr4)2(arene)2] instead of Pd[GaBr4]2.
In contrast to palladium(II) bromide, palladium(II) iod-
ide reacts with gallium(III) iodide in benzene or p-xylene to
give only the palladium(II) complex 2. Dark brown crystals
suitable for X-ray analysis formed from the p-xylene system
(crystals obtained from the benzene system have the same
shape and color). All attempts to isolate palladium(I) com-
plexes from the palladium(II)Ϫgallium(III) iodide system
were unsuccessful.
Fig. 1 The complex Pd[GaBr4]2 in the crystal structure. Thermal
ellipsoids are drawn at a 70% probability level. Symmetry opera-
tions: i: Ϫx, Ϫy, Ϫz; ii: x, Ϫy, z; iii: Ϫx, y, Ϫz.
Solid state Raman spectra of 2 contains two very broad
bands at 225 and 1520 cmϪ1, due to fluorescence. In com-
parison with a saturated solution of GaI3 in p-xylene Ra-
man spectra of 2 in p-xylene solution only show one ad-
ditional weak band at 139 cmϪ1. Raman spectra of 1 in
benzene contain a weak band at 203 cmϪ1 (a band at
202 cmϪ1 is also observable in the Raman spectra of a p-
xylene solution of GaBr3). Unfortunately, the very low solu-
bility of 1 and 2 in arenes prevents any detailed spectral
analysis.
Conclusion
Two new mononuclear palladium(II) compounds,
Pd[GaBr4]2 and Pd[GaI4]2, were obtained by reaction be-
tween PdBr2 or PdI2 and the respective gallium(III) halog-
enide in aromatic solvents. Crystal structures of both com-
plexes were determined. Palladium atoms exhibit a square-
planar arrangement, whereas gallium atoms are surrounded
by four halogen atoms in a distorted tetrahedral coordi-
nation.
Fig. 2 The unit cell of Pd[GaBr4]2 in a view along the crystallogra-
phic c axis.
Experimental
Synthesis
All experiments were performed in a glove box under an inert at-
mosphere of deoxygenated and dried nitrogen (< 1 ppm H2O).
GaBr3, GaI3 (Alfa Aesar Company, 99.999 %), PdBr2 (Aldrich
Chemical Company, 99 %) and PdI2 (Alfa Aesar Company, 99.9 %)
were used as received.
The surrounding of Ga is very distorted. This may be a
consequence of the ’fixed’ position of two of the bridging
halogen atoms (the square-planar arrangement of four hal-
ogen atoms around palladium atom appears much more ri-
gid than the tetrahedral arrangement around the gallium
atoms). Therefore, the XϪGaϪX angles in the GaX4 tetra-
hedron deviate significantly from the ideal value and are
close to 90° in the bridging GaX2 unit and between 111.2°
and 115.3° in the terminal GaX2 part. The average GaϪX
bond lengths (GaϪBr: 235.5 pm) are slightly longer than in
other structures of bromogallates, such as K[GaBr4]
(232.0 pm [11]). The GaϪI bonds, on the other hand, are
highly similar to those in the potassium compound
(253.9 pm as compared to 254.8 pm [12]).
Pd[GaBr4]2. Benzene (3 ml) was added to the solid mixture of
PdBr2 (37.0 mg, 0.139 mmol) and GaBr3 (122 mg, 0.394 mmol).
The mixture was heated for 1 hour (80-90 °C) without stirring and
then slowly cooled to room temperature. After 24 hours red crys-
tals formed.
Pd[GaI4]2. p-Xylene (3 ml) was added to the solid mixture of PdI2
(30.0 mg, 0.083 mmol) and GaI3 (150 mg, 0.333 mmol). The mix-
ture was heated for 10 minutes (80-90 °C) without stirring and then
slowly cooled to room temperature. After 24 hours dark brown
needles formed together with yellow crystals of GaI3.
Z. Anorg. Allg. Chem. 2004, 630, 324Ϫ326
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 2004 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim
325

M. Gorlov, A. Fischer, L. Kloo
Table 1 Crystallographic data and results of the structure determi-
nations of Pd[GaBr4]2 and Pd[GaI4]2.
Table 3 Selected bond lengths/pm and angles/deg in the structures
of 1 and 2
Pd[GaBr4]2
Pd[GaI4]2
Pd[GaBr4]2
Pd[GaI4]2
Lattice constants
aϭ1267(2) pm
bϭ808(1) pm
cϭ722(1) pm
βϭ94.5(1)°
736(2)
4.00
885.1
aϭ1363(1) pm
bϭ849.9(4) pm
cϭ756.6(7) pm
βϭ95.38(3)°
873(1)
4.80
1261.1
Pd Ϫ Br(1)
246.0(3)
242.9(3)
228.7(4)
227.5(4)
242.9(3)
89.1(1)
90.9(1)
90.5(2)
113.0(1)
111.2(1)
Pd Ϫ I(1)
261.2(2)
262.0(3)
249.0(4)
246.5(4)
262.0(3)
90.8(1)
89.2(1)
90.4(1)
113.1(1)
111.3(1)
115.1(1)
Gaiii Ϫ Br(1i)
Gaiii Ϫ I(1i)
Gaiii Ϫ Br(2iii)
Gaiii Ϫ I(2iii)
Gaiii Ϫ Br(3iii)
Gaiii Ϫ I(3iii)
Cell volume/106 pm3
Density(cal.)/g·cmϪ3
Formula weight
Number of formula units
Crystal system, space group
Temperature
Gaiii Ϫ Br(1iii)
Gaiii Ϫ I(1iii)
Br(1) Ϫ Pd Ϫ Br(1iii)
Br(1i) Ϫ Pd Ϫ Br(1iii)
Br(1i) Ϫ Ga Ϫ Br(1iii)
Br(1i) Ϫ Ga Ϫ Br(2iii)
Br(1i) Ϫ Ga Ϫ Br(3iii)
I(1) Ϫ Pd Ϫ I(1iii)
I(1i) Ϫ Pd Ϫ I(1iii)
I(1i) Ϫ Ga Ϫ I(1iii)
I(1i) Ϫ Ga Ϫ I(2iii)
I(1i) Ϫ Ga Ϫ I(3iii)
I(2iii) Ϫ Ga Ϫ I(3iii)
2
monoclinic, C2/m (No. 12)
299 K
299 K
Bruker-Nonius KappaCCD
Ag-Kα, λϭ56.085 pm
Diffractometer
Br(2iii) Ϫ Ga Ϫ Br(3iii) 115.4(2)
Radiation
Absorption coefficient/cmϪ1
θmax
141.4
21.4
96.1
19.0
the bromogallate was used as starting model for refinement. All
atoms were refined on F2 using anisotropic thermal parameters
for all atoms [18]. Table 1 summarizes the results of the structure
determinations, Table 2 the atomic positions and Table 3 selected
bond lengths.
no. of reflections
1888
606, 0.067
433
2043
528, 0.062
411
no. of independent reflections, Rint
no. of reflections with I>2σ(I)
number of parameters
R(obs. reflections)
R(all reflections)
wR2
GooF
32
32
0.0428
0.0712
0.0997a)
1.133
0.0358
0.0551
0.0824b)
1.136
Further details of the crystal structure investigations can be ob-
tained from the Fachinformationszentrum Karlsruhe, 76344 Eg-
genstein-Leopoldshafen, Germany, (Fax: ϩ49(7247)808-666, e-
mail: crysdata@fiz-karlsruhe.de) on quoting the depository num-
bers CSD-413 229 (Pd[GaBr4]2) and CSD-413 230 (Pd[GaI4]2).
largest difference peaks
0.66/Ϫ0.92
0.85/Ϫ0.85
a) wϭ[σ2Fo2ϩ(0.0208P)2 ϩ 10.6 P]Ϫ1 where Pϭ(Fo2ϩ2Fc2)/3
b) wϭ[σ2Fo2ϩ(0.0277P)2 ϩ 16.2 P]Ϫ1 where Pϭ(Fo2ϩ2Fc2)/3
Table 2 Atomic positions and isotropic displacement parameters B/
104 pm2 of the atoms in the structure of Pd[GaBr4]2 and Pd[GaI4]2.
Standard deviations are given in parentheses.
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Pd[GaBr4]2:
Pd
Ga
Br(1)
Br(2)
Br(3)
2a
4i
8j
4i
4i
0
0
0
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0.6329(3)
0.2957(3)
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0
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0.1609(1)
0.3877(1)
0.3397(3)
0.1477(1)
0.6490(2)
0.3135(2)
0.2184(1)
0
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I(3)
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Due to the extreme sensitivity towards humidity, crystals of all
compounds were sealed inside glass capillaries in a dry nitrogen
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to be twinned in the same way. The twinning element is a 180°
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