On the structure of the N,N′-dimethylpropyleneurea and dimethylsulfoxide solvated gallium(III) and indium(III) ions and bromide complexes in solution and solid state, and the complex formation of the gallium(III) and indium(III) bromide systems in N,N′-dimethylpropyleneurea

Article abstract of DOI:10.1016/j.ica.2009.12.024

The structures of the N,N′-dimethylpropyleneurea (DMPU) solvated gallium(III) and indium(III) ions have been determined in DMPU solution by means of EXAFS. The gallium(III) ion is five-coordinate with a mean Ga-O bond distance of 1.924(5) ?, while the larger indium(III) ion is octahedrally coordinated with a mean In-O bond distance of 2.146(3) ?. The complex formation equilibria in DMPU for the gallium(III) and indium(III) bromide systems have been studied calorimetrically at 298 K. Three relatively strong complexes are formed in the indium(III) bromide system in DMPU, whereas no stability constants could be established in the gallium(III) bromide system as the heats of complex formation were very close to zero. Gallium(III) bromide is present as DMPU solvated GaBr₃ complexes in solution with three equatorial Ga-Br bonds at 2.328(3) ?, and two Ga-O bonds at 1.92(3) ? in the apical positions of a distorted trigonal bipyramid. The DMPU solvated indium(III) bromide has the same configuration with a mean In-Br bond distance of 2.510(3) ?, and two In-O bonds at 2.201(6) ?. Indium(III) binds three bromides and three Me₂SO molecules through the oxygen atoms in octahedral fac-configuration with mean In-Br and In-O bond distances of 2.630(3) and 2.211(15) ?, respectively.

Full text of DOI:10.1016/j.ica.2009.12.024

Inorganica Chimica Acta 363 (2010) 988–994
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
0
On the structure of the N,N -dimethylpropyleneurea and dimethylsulfoxide
solvated gallium(III) and indium(III) ions and bromide complexes in solution
and solid state, and the complex formation of the gallium(III) and indium(III)
0
bromide systems in N,N -dimethylpropyleneurea
1
*
Önder Topel , Ingmar Persson , Daniel Lundberg, Ann-Sofi Ullström
Department of Chemistry, Swedish University of Agricultural Sciences, P.O. Box 7015, SE-750 07 Uppsala, Sweden
a r t i c l e i n f o
a b s t r a c t
0
Article history:
The structures of the N,N -dimethylpropyleneurea (DMPU) solvated gallium(III) and indium(III) ions have
been determined in DMPU solution by means of EXAFS. The gallium(III) ion is five-coordinate with a
mean Ga–O bond distance of 1.924(5) Å, while the larger indium(III) ion is octahedrally coordinated with
a mean In–O bond distance of 2.146(3) Å. The complex formation equilibria in DMPU for the gallium(III)
and indium(III) bromide systems have been studied calorimetrically at 298 K. Three relatively strong
complexes are formed in the indium(III) bromide system in DMPU, whereas no stability constants could
be established in the gallium(III) bromide system as the heats of complex formation were very close to
Received 10 July 2009
Received in revised form 2 December 2009
Accepted 10 December 2009
Available online 16 December 2009
Keywords:
Gallium(III)
Indium(III)
3
zero. Gallium(III) bromide is present as DMPU solvated GaBr complexes in solution with three equatorial
0
Ga–Br bonds at 2.328(3) Å, and two Ga–O bonds at 1.92(3) Å in the apical positions of a distorted trigonal
bipyramid. The DMPU solvated indium(III) bromide has the same configuration with a mean In–Br bond
distance of 2.510(3) Å, and two In–O bonds at 2.201(6) Å. Indium(III) binds three bromides and three
N,N -dimethylpropyleneurea
Dimethylsulfoxide
Bromide
Structure
Me SO molecules through the oxygen atoms in octahedral fac-configuration with mean In–Br and In–O
2
bond distances of 2.630(3) and 2.211(15) Å, respectively.
Ó 2009 Elsevier B.V. All rights reserved.
1
. Introduction
It has been shown that space-demanding solvent molecules
such as N,N -dimethylpropyleneurea (DMPU, IUPAC name:
0
The hydrated gallium(III) and indium(III) ions have regular
octahedral (O ) configuration in both aqueous solution [1] and in
solid compounds [2,3]. The mean Ga–O and In–O bond distances
in the hydrates in aqueous solution, as determined by large angle
X-ray scattering (LAXS) and EXAFS, are 1.959 and 2.131 Å, respec-
tively [1], and in solid hydrates they are 1.946 and 2.125 Å,
3,4,5,6-tetrahydro-1,3-dimethyl-2(1H)-pyrimidinone),
1,1,3,3-
h
tetramethylurea (TMU) and hexamethylphosphoric triamide
(HMPA) force the coordination number of solvated metal ions to
be lower than found in hydrates and solvates of small solvent mol-
2
ecules such as Me SO and DMF. Of the space-demanding solvents,
we have chosen to work with DMPU, as both TMU and HMPA have
been reported to be carcinogenic [7,8]. DMPU was developed as a
less harmful substitute for TMU and HMPA, though one study
has shown that also DMPU may act as a possible chemical mutagen
in fruit flies [9]. DMPU is a polar, aprotic solvent with a wide range
of uses including solvent for organic reactions and additive in
paints and plastics [10]. The two methyl groups bordering the
coordinating oxygen atom and the semi-rigid ring structure have
been shown to obstruct the normal coordination, thereby forming
solvates with lower coordination number [11–14], as previously
also shown for TMU [15,16] and HMPA [17]. The nickel(II) and ir-
on(III) ions have been shown to be five-coordinate in DMPU solu-
tion with square-pyramidal [11] and trigonal bipyramidal [12]
configuration, respectively. The DMPU solvated zinc(II) and cad-
mium(II) ions are five- and six-coordinate in solution with mean
Zn–O and Cd–O bond distances of 2.00 and 2.24 Å, respectively,
Table S1 [2,3]. The dimethylsulfoxide (Me
4] and indium(III) ions [4b,5], are also octahedral in solution as
well as in solid compounds with mean Ga–O bond distances of
2
SO) solvated gallium(III)
[
1
2
.955 and 1.967 Å, and mean In–O bond distances of 2.135 and
.142 Å, respectively. The N,N-dimethylformamide (DMF) solvated
gallium(III) ion is octahedral with a mean Ga–O bond distance of
.960 Å in the solid hexabromodigallate(III) salt [6]. No solvate
1
structures of gallium(III) and indium(III) ions with neutral, mono-
dentate N- and S-donor solvents have been reported so far [2,3].
*
Corresponding author. Tel.: +46 18 671547; fax: +46 18 673476.
E-mail address: Ingmar.Persson@kemi.slu.se (I. Persson).
Present address: Department of Chemistry, Faculty of Arts and Sciences, Akdeniz
1
University, 07058 Antalya, Turkey.
0
020-1693/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2009.12.024

Ö. Topel et al. / Inorganica Chimica Acta 363 (2010) 988–994
989
while they are four-and six-coordinate in the solid state with mean
bond distances of 1.925 and 2.26 Å, respectively [13]. The DMPU
solvated lanthanoid(III) ions, except the lutetium(III) ion, are se-
ven-coordinate in DMPU solution, while the solid solvates, as well
as the lutetium(III) ion in solution, are octahedral [14].
complex formation in the gallium(III) and indium(III) bromide sys-
tems in DMPU calorimetrically, and to determine the structures of
the DMPU and Me SO solvated gallium(III) and indium(III) bro-
2
mide systems in solution and solid state as a continuation on the
studies of structure and reactivity of metal ions with forced low
coordination numbers due to steric reasons [11,19].
Complex formation studies of the nickel(II) and iron(III) bro-
mide systems in water, Me
very weak complexes are formed in water and Me
2
SO and DMPU have shown that only
SO [18], where
2
2
. Materials
the metal solvates are octahedral, while much more stable com-
plexes are formed in DMPU [11,19], where the metal solvates have
lower symmetry. The stability of complexes increases in general
with decreasing solvating ability of the solvent. However, DMPU
2.1. Chemicals
2 3 3 2 2
N,N’-dimethylpropyleneurea, (CH ) (CH ) N CO (Aldrich), and
is a significantly better electron-pair donor, D
water and dimethylsulfoxide, D = 18.0 and 27.5, respectively
20]. In protic solvents, the stability of metal complexes is affected
S
= 34 [11], than
dimethylsulfoxide, (CH
hydride, CaH
(Fluka), under reduced pressure (ꢁ6 kPa), and stored
in dark glass bottles over 3 Å molecular sieves. Tetrabutylammo-
nium bromide, (n-C NBr (Merck), and tetrabutylammonium
perchlorate, (n-C NClO (Fluka), were used after being dried
in a desiccator over phosphorous pentaoxide, P 10, under vacuum
at room temperature. Anhydrous gallium(III) and indium(III) bro-
mide, GaBr and InBr (Aldrich, 99.9%), were used as purchased.
Anhydrous gallium(III) and indium(III) trifluoromethanesulfonate,
M(CF SO , were prepared by adding an excess trifluoromethane-
sulfonic acid, CF SO H (Fluka), drop-wise to aqueous slurries of
gallium(III) oxide, Ga (Fluka), and indium(III) hydroxide,
In(OH) (Fluka), respectively. The slurries were refluxed for 2 h un-
2 3
) SO (Merck), were distilled over calcium
S
2
[
by hydrogen bonding to the ligands. From this point of view, it is
expected that complex formation is slightly stronger in aprotic sol-
vents than protic ones [21]. The reason for the increased stability of
the nickel(II) and iron(III) bromide complexes in DMPU is therefore
most probably due to the significantly lower stability of the five-
coordinate solvate complexes in comparison to the octahedral ones
4
9 4
H )
4
H
9
)
4
4
4
O
3
3
[
11,19].
The complex formation in the gallium(III) and indium(III) bro-
3
3 3
)
3
3
mide systems in aqueous media has been reported in several stud-
ies, Table 1 and Table S2 [18]. These systems form quite weak
2 3
O
ꢀ1
3
3
complexes with mean b
respectively [22,23]. For the indium(III) bromide system, some
studies in aprotic solvents, i.e. Me SO [24], DMF [25] and formam-
1
values of ca. 0.6 and 125 mol dm ,
til clear solutions were obtained. The solutions were filtered, and
water and excess acid were boiled off at ca. 450 K. Anhydrous gal-
lium(III) and indium(III) trifluoromethanesulfonate were stored in
an oven at ca. 450 K to avoid uptake of water.
2
ide [26] have been reported as well, Table 1, while there are no
such investigations reported for the gallium(III) bromide system.
2
The complex formation in Me SO and DMF is significantly stronger
than in water. Furthermore, formamide forms strong hydrogen
bonds, and consequently, the indium(III) bromide complexes are
2.2. Solutions and crystals
weaker in formamide than in Me
The aim of this study is to determine the structure of the DMPU
solvated gallium(III) and indium(III) ions in solution, to study the
2
SO, DMF and water, cf. Table 1.
The DMPU solutions of gallium(III) and indium(III) trifluoro-
methanesulfonate and gallium(III) bromide for EXAFS studies were
prepared by dissolving respective salt in freshly distilled solvent.
Table 1
Overall stability constants, b
j
, and thermodynamic functions for the individual steps in the complex formation of the indium(III)- and gallium(III) bromide systems in water,
0
dimethylsulfoxide (Me
2
SO), formamide (FA), N,N-dimethylformamide (DMF) and N,N -dimethylpropyleneurea (DMPU) at 25 °C.
(mol dmꢀj)
D
G
0
(kJ mol
ꢀ1
)
D
H
0
(kJ mol
ꢀ1
)
0
ꢀ1
ꢀ1
Solvent
j
b
j
j
j
j
DS (J K mol )
3
+
ꢀ
In –Br
Watera
1
2
3
9.5(5) ꢂ 10
3.6(3) ꢂ 10
1
ꢀ11.3(2)
ꢀ3.4(2)
1.96(4)
5.64(4)
44.4(8)
30.5(3)
2
3
Me
2
SOb
1
2
3
4
1
2
3
6.92 ꢂ 10
ꢀ29.9
ꢀ8.8
ꢀ1.3
ꢀ10.7
ꢀ8.3
ꢀ2.1
ꢀ3.9
6
6.03 ꢂ 10
7
1 ꢂ 10
8
7.41 ꢂ 10
FAc
2.8 ꢂ 10
1
1
6.5 ꢂ 10
2
3.1 ꢂ 10
DMFd
1
2
3
4
1
2
3
3.24 ꢂ 10
3
ꢀ20.0
5
6.3 ꢂ 10
ꢀ13.1
8
2.0 ꢂ 10
ꢀ14.2
1
0
3.2 ꢂ 10
ꢀ16.2
DMPUe
7.18(7) ꢂ 10
2.08(3) ꢂ 10
2
5
ꢀ16.3(1)
ꢀ14.1(4)
ꢀ13.9(4)
8.1(1)
19.1(3)
3.3(4)
81.8(4)
111(2)
58(1)
7
5.64(18) ꢂ 10
3
+
ꢀ
Ga –Br
Waterf
1
2
0.58
0.32
ꢀ1.37
ꢀ2.85
a
b
c
d
e
f
Ref. [23].
Ref. [24].
Ref. [25].
Ref. [26].
This work.
Ref. [22].

9
90
Ö. Topel et al. / Inorganica Chimica Acta 363 (2010) 988–994
Solid tris(dimethylsulfoxide)trisbromoindium(III) and bis(N,N’-
dimethylpropyleneurea)trisbromoindium(III) were prepared by
dissolving anhydrous indium(III) bromide in freshly distilled sol-
vent to saturation in vials under nitrogen atmosphere while care-
fully heating them in an oil bath to maximum 323 K. The vials
were left in the oil bath, which were allowed to slowly cool to
room temperature, and single crystals suitable for crystallographic
studies were obtained.
bration of the X-ray absorption spectra was performed by simulta-
neously recording the edge spectrum of a metallic gallium or
indium foil during the data collection, and assigning the first K-
edge inflection point to 10368.2 and 27940.0 eV, respectively
[30]. The EXAFSPAK program package was used for the data treatment
[31]. The EXAFS oscillations were extracted using standard proce-
dures for pre-edge subtraction, spline removal and data normaliza-
tion. Model fitting, including both single and multiple back-
scattering pathways, was performed with theoretical phase and
amplitude functions calculated ab initio by means of the computer
3
. Methods
3
code FEFF7 [32]. The k weighted EXAFS oscillation was analyzed
by a non-linear least-squares fitting procedure of the model
parameters.
3.1. Calorimetric measurements
The standard deviations given for the refined parameters in Ta-
ble 2 are obtained from k weighted least-squares refinements of
Calorimetric titrations were performed on a ThermoMetric
277 TAM microcalorimeter to determine the heat of complex for-
3
2
the EXAFS function (k), and do not include systematic errors of
the measurements. These statistical error values provide a measure
of the precision of the results and allow reasonable comparisons
e.g. of the significance of relative shifts in the distances. However,
the variations in the refined parameters, including the shift in the
mation of gallium(III) and indium(III) with bromide in DMPU solu-
tion at 298.15 ± 0.01 K. The titrations were carried out in a titration
3
vessel rhodium-plated for chemical inertness, V = 4.0 cm . The stir-
rer was a gold propeller. The start volume in the titrations was
ꢀ3
3
.00 cm3 of 2.0 mmol dm metal(III) trifluoromethanesulfonate
o
E value (for which k = 0), using different models and data ranges,
ꢀ3
in DMPU containing 0.100 mol dm tetrabutylammonium per-
chlorate as a supporting electrolyte. These solutions were titrated
indicate that the absolute accuracy of the distances given for the
separate complexes is within ±0.005 to 0.02 Å for well-defined
interactions. The ‘‘standard deviations” given in the text have been
increased accordingly to include estimated additional effects of
systematic errors.
ꢀ3
portionwise with 0.100 mol dm tetrabutylammonium bromide
3
in DMPU. In every titration point 5 mm ligand solution was added
by a computer-controlled pump driving a microliter syringe
through a very thin gold capillary. In total, 111 portions were
added in the indium(III) bromide system in each titration series,
while totally 74 portions per series were added in the gallium(III)
bromide system. At least three titration series were carried out
for each system. Two titration series to determine the heats of dilu-
tion of metal(III) and bromide ions in DMPU were performed. All
heats of dilution were very small, and used to correct the experi-
mental heats of complex formation. The stability constants and
the corresponding enthalpy changes were calculated by means of
the least-squares program KALORI [27]. The calorimeter system
was calibrated with the barium-18-crown-6 system in water. The
3
.3. Single crystal X-ray diffraction
Data collection were performed on a Bruker SMART platform
equipped with a CCD area detector [33] and a graphite monochro-
mator using Mo K (k = 0.7107 Å) radiation at room temperature. A
a
hemisphere data with 1271 frames was collected for each structure
using the omega scan method. The crystal to detector distance was
.0 cm. The first 50 frames were re-measured at the end of the data
5
collection to check crystal and instrument stability. No correction
was necessary for the crystals studied. Both structures were solved
by direct methods in SHELXTL [34], and refined using full-matrix
3
3
ꢀ1
ꢀ1
values of K
1
= 6.0 ꢂ 10 dm mol and
D
H = ꢀ30.6 kJ mol were
obtained for the system. The corresponding literature data is:
2
3
3
ꢀ1
ꢀ1
least-squares on F . Non-hydrogen atoms were treated anisotropi-
K
1
= 7.41 ꢂ 10 dm mol and
D
H = ꢀ31.7 kJ mol [28].
cally. Hydrogen atoms were calculated in ideal positions riding on
their respective carbon atom.
3
.2. Extended X-ray absorption fine structure measurements
Gallium and indium K edge X-ray absorption data were re-
4. Results and discussion
corded at the wiggler beam-lines I811 at MAX-lab, Lund Univer-
sity, Sweden, and 4–1 at Stanford Synchrotron Radiation
Lightsource (SSRL), Stanford, USA, respectively. The beam-lines
were equipped with Si[1 1 1] and Si[2 2 0] double crystal mono-
chromators, respectively. The storage ring at MAX-lab operated
at 1.5 GeV and a maximum current of 220 mA, and at SSRL it oper-
ated at 3.0 GeV and a maximum current of 100 mA. Data collection
at the gallium K edge was carried out in transmission and fluores-
cence mode simultaneously, using ion chambers with a stationary
gas mixture of helium and nitrogen, and a Lytle detector [29] filled
with argon gas. Higher order harmonics were rejected by detuning
the second monochromator crystal to 50% of maximum intensity at
the end of the scan. Data collection at the indium K edge was only
carried out in transmission mode, using ion chambers with a flow
of a gas mixture of nitrogen and argon. The second monochromator
crystal was detuned to 80% of maximum intensity to reject higher
order harmonics. The gallium solutions were kept in cells with My-
lar tape windows and an 1–2 mm thick Teflon spacer, while for the
indium solution a 5 mm Teflon spacer was used. The solids were
ground to homogeneous mixture with an appropriate amount of
boron nitride (BN) to achieve an edge step of unity and placed in
a 1.5 mm aluminum frame with Mylar tape windows. Energy cali-
4.1. The N,N’-dimethylpropyleneurea solvated gallium(III) and
indium(III) ions
The EXAFS data of the DMPU solvated gallium(III) ion in solu-
tion give a mean Ga–O bond distance of 1.924(2) Å, with no multi-
ple scattering (MS) within the first coordination shell, but strong
MS within the Ga–O–C entity. According to the ionic radii given
by Shannon for the gallium(III) ion in four-, five- and six-coordina-
tion [35], the expected Ga–O bond distances should be 1.81, 1.89,
and 1.96 Å, respectively, assuming that the oxygen radius is
1.34 Å, as in coordinated water [2e]. However, Shannon’s value
for five-coordination is listed as the most uncertain one albeit
without any comment. A literature search of five-coordinated gal-
lium(III) complexes, mainly polymeric phosphate–gallium com-
plexes, show that the mean Ga–O bond distance is 1.905 Å (range
1.876–1.928 Å), Table S3. This shows that the Ga–O bond distance
in the DMPU solvated gallium(III) ion is within the expected range
for five-coordination. This is in full agreement with the results
from previous studies on the DMPU solvated nickel(II), zinc(II)
and iron(III) ions which all have a slightly larger ionic radius than
gallium(III). The Ga–O–C angle, 146(2)°, is significantly larger than

Ö. Topel et al. / Inorganica Chimica Acta 363 (2010) 988–994
991
Table 2
2
2
Bond distances, d/Å, Debye–Waller factors,
r
/Å , and number of distances, n, for the DMPU solvated gallium(III) and indium(III) ions in solution, and DMPU and
2
dimethylsulfoxide solvated gallium(III) bromide in solution determined by EXAFS at room temperature; E
o
is the refined threshold energy and So is refined amplitude reduction
factor.
2
2
o
n
d
r
E
o
S
0
N,N -dimethyl propyleneurea
Gallium(III) Ion
Ga–O
5
5
10
5
1.924(2)
3.058(4)
3.136(11)
3.19(2)
0.0069(2)
0.0025(3)
0.017(4)
0.004(2)
ꢀ11.7
1.00(2)
Gaꢃ ꢃ ꢃC
Ga–O–C
Ga–O–C–O
Gallium(III) Bromide
Ga–Br
Ga–O
Indium(III) Ion
In–O
3
2
2.328(1)
1.915(14)
0.0054(1)
0.029(3)
–15.6(5)
–17.4
0.99(4)
1.00(2)
6
6
12
2.146(1)
3.16(2)
3.29(1)
0.0048(2)
0.019(3)
0.019(2)
InꢃꢃꢃC
In–O–C
Dimethyl sulfoxide
Gallium(III) Bromide
Ga–O
6
6
1.958(1)
3.114(2)
3.303(9)
3.98(1)
0.0047(2)
0.0067(2)
0.013(2)
0.011(2)
–14.9
0.93(3)
Gaꢃ ꢃ ꢃS
Ga–O–S
12
3 ꢂ 6
MS
observed in DMPU solvated metal ions and complexes without ste-
ric restrictions, 125–130° [11]. The large Ga–O–C bond angle, and
the relatively long Ga–O bond distance being five-coordinate, sup-
ports the view that the bound DMPU molecules are affected by ste-
ric restrictions. The structure parameters are summarized in
Table 2, and the fit of the EXAFS data and the Fourier transform
are shown in Figs. 1 and 2.
8
7
6
5
4
3
2
1
0
FT Magnitude
(a)
The EXAFS data of the DMPU solvated indium(III) ion in solution
gives a mean In–O bond distance of 2.146(1) Å, which is in the ex-
pected range for six-coordination of oxygen donor solvents, see
Introduction. The larger indium(III) ion is able to accommodate
0
six N,N -dimethylpropyleneurea ligands, and the packing around
indium(III) ion is less crowded than around gallium(III), seen by
a significantly smaller In–O–C angle, 134(2)°. The contribution
(b)
from the multiple scattering within the InO
6
core is strongly
4
4
3
3
2
1
1
8
2
6
0
4
8
2
6
0
6
.
3
(c)
χ
(k) k
(
d)
(
a)
R -
Δ
R /Å
0
1
2
3
4
5
Fig. 2. Fourier transforms of (a) gallium(III) trifluoromethanesulfonate in DMPU, (b)
gallium(III) bromide in DMPU, (c) gallium(III) bromide in dimethylsulfoxide, and (d)
indium(III) trifluoromethanesulfonate in DMPU.
(b)
damped due to the short core hole life time at the indium K edge
36].
[
(
c)
0
4
.2. Indium(III) bromide in N,N -dimethylpropyleneurea
(d)
Calorimetric measurements on the indium(III) bromide system
2
-1
in DMPU showed that three complexes with b
dm ) ,
dm ) , respectively, are formed. The obtained values in this
study, and literature data in oxygen donor solvents, are summa-
rized in Table 1 for comparison. The total molar enthalpy changes
and the complex distribution functions are shown in Figs. 3 and 4.
= 7.2(2)ꢃ10 (mol
1
k /Å
ꢀ
3 -1
5
ꢀ3 -2
7
-
b
2
= 2.1(1)ꢃ10 (mol dm
)
and
b
3
= 5.6(2)ꢃ10 (mol
2
3
4
5
6
7
8
9
10 11 12 13 14
ꢀ3 -3
Fig. 1. Fit of the EXAFS data of (a) gallium(III) trifluoromethanesulfonate in DMPU,
(
(
b) gallium(III) bromide in DMPU, (c) gallium(III) bromide in dimethylsulfoxide, and
d) indium(III) trifluoromethanesulfonate in DMPU.

9
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Ö. Topel et al. / Inorganica Chimica Acta 363 (2010) 988–994
The complex formation is endothermic in all three steps, and
1.0
0
thereby entropy-driven. The large endothermic value of
D
H
2
,
3+
[
In ]
and the large entropy gain at the formation of the second bromide
0
0
.8
.6
0
[
3
InBr ]
complex,
2
DS , are strong indicators of substantial desolvation and
a coordination switch at this step [37]. In general, as long as the
complex formation is considered only as substitution of a solvent
α
j
molecule in the first solvation shell, a monotonous decrease of
0
0.4
the
D
S
j
values is expected at each step. However, when a coordi-
0
nation change at any step takes place,
j
DH becomes more positive
2
+
+
0
.2
[InBr
]
[InBr2
]
due to increase of required energy for desolvation and the libera-
tion of more solvent molecules results in a large increment of
0
D
S
j
. By increasing the free ligand concentration, the third complex
0.0
-
5
-4
-3
-2
-1
becomes more dominant. It is important to stress that the complex
formation of the indium(III) bromide system in DMPU is slightly
-
Log[Br ]
weaker than the corresponding one in Me
DMPU is a stronger electron-pair donor than Me
2
SO. This is expected as
SO, and indiu-
Fig. 4. Complex distribution function for the indium(III) bromide system in DMPU.
2
m(III) a fairly soft electron-pair acceptor. This shows that the com-
plex formation of indium(III) in DMPU behaves as expected as the
starting solvate has an octahedral configuration. Furthermore, the
complex formation in DMPU is stronger than in water due to sig-
nificantly weaker solvation of the bromide ion [38].
0
The crystal structure of bis(N,N -dimethylpropyleneurea)trisb-
romoindium(III) was solved in the orthorhombic space group
Fdd2 (No. 43). The crystallographic data show that the structure
is five-coordinate with three bromides in a plane and two oxygens
from DMPU in the apical positions of a slightly distorted trigonal
bipyramid, Fig. 5. The indium(III) ion is in the same plane as the
three bromide atoms. The oxygen atoms in the apical positions
are equidistant, 2.201 Å, and with an O–In–O angle of 172.2°.
One In–Br bond distance, 2.495 Å, is slightly shorter than the other
two, 2.518 Å. The angle between the longer In–Br bonds is unex-
pectedly larger, 134.0°, than the other two Br–In–Br angles,
1
13.0°. This unexpected behavior with the largest angle between
the longest M–Br bonds is also seen in the crystal structure of
0
bis(N,N -dimethylpropyleneurea)trisbromoiron(III)
[19].
The
DMPU molecules are oriented according to the bisector at the angle
between the longer In–Br bonds. The mean In–O distance, 2.201 Å,
is somewhat longer than in the DMPU solvated indium(III) ion,
2
.146 Å. This shows that indium(III) binds bromide more strongly
than DMPU as expected. Crystallographic data and selected bond
distances and angles are given in Table 3 and Table S4, respectively.
0
4
.3. Gallium(III) bromide system in N,N -dimethylpropyleneurea
The EXAFS data on the gallium(III) bromide solution in DMPU
shows that the shape of oscillations is obviously different from that
of DMPU solvated gallium(III), Fig. 1. The maximum in the EXAFS
ꢀ1
function envelope is at about 9–10 Å showing that bromide is
3
2
2
1
1
0
5
0
5
0
5
0
-
1
Δh /kJ.mol
ν
0
Fig. 5. Molecular structure of bis(N,N -dimethylpropyleneurea)trisbromoindium
(
III).
n
the main back-scatterer. Data analysis reveals three Ga–Br bonds
at 2.328(1) Å in a triangular configuration. The shoulder at ca.
0
1
2
3
1
.9 Å has been assigned to two Ga–O bonds, refined to 1.92(3) Å,
Fig. 3. The total molar enthalpy change
the indium(III) bromide system in DMPU. The symbols show different titration
series and the solid line is calculated from the corresponding b and DH values in
j j
Dh
m
, as a function of ligand number nꢀ for
completing a trigonal bipyramidal configuration. The Debye–
Waller parameter indicates a large distribution in the Ga–O
distance, but the value is in agreement with Ga–O distance in the
0
Table 1.

Ö. Topel et al. / Inorganica Chimica Acta 363 (2010) 988–994
993
Table 3
five-coordinate DMPU solvated gallium(III) ion, see above. The
structure parameters from the EXAFS studies are summarized in
Table 2. The fit of EXAFS oscillations and the corresponding Fourier
transform are given in Figs. 1 and 2.
Crystallographic data on the solid bis(N,N’-dimethylpropyleneurea)trisbromoindi-
um(III) and bis(dimethylsulfoxide)trisbromoindium(III) complexes at room
temperature.
[InBr
3
(dmpu)
2
]
[InBr
3
2 3
(OSMe ) ]
The EXAFS data have shown that the DMPU solvated gallium(III)
ion and gallium(III) bromide complex are both five-coordinate
most probably in slightly distorted trigonal bipyramidal fashion
in solution. This also strongly indicates that the stabilities of the
gallium(III) bromide complexes in DMPU solution are relatively
strong. Furthermore, the heats of complex formation are endother-
mic, but very small. This shows that the complex formation takes
place in substitution reactions and that the bond strength of the
Ga–Odmpu and Ga–Br bonds is similar, and that the complex forma-
tion is entropy-driven due to release of bound solvent molecules at
the complex formation. Unfortunately, the very small and similar
Formula
C
12
H
24
N
4
O
2
Br
3
In
C
6
H
18
S
3
O
3
Br In
3
Molecular weight
Crystal system
Space group
a (Å)
b (Å)
c (Å)
610.90
588.93
triclinic
P 1ꢀ (No. 2)
orthorhombic
Fdd2 (No. 43)
17.698(14)
27.72(3)
8.1520(16)
90
90
90
3999(5)
298(2)
8
8.138(3)
9.141(3)
13.884(4)
89.780(6)
77.513(6)
66.120(5)
918.0(5)
298(2)
a
(°)
b (°)
(°)
c
3
V (Å )
T (K)
Z
2
heats of complex formation do not allow determination of the b
and bn values from the calorimetric data.
n
Density(calculated) (g cmꢀ3)
(mm
2.030
7.188
2.131
8.149
D
H
ꢀ
1
l
)
Crystal size (mm)
h Range (°)
Index ranges
0.45 ꢂ 0.25 ꢂ 0.15
0.48 ꢂ 0.26 ꢂ 0.10
2.45–28.37
ꢀ9 6 h 6 8
2.735–23.984
4.4. Dimethylsulfoxide solvated gallium(III) and indium(III) bromide in
ꢀ20 6 h 6 19
ꢀ
28 6 k 6 32
9 6 l 6 9
ꢀ10 6 k 6 10
ꢀ16 6 l 6 12
4501
the solid state
ꢀ
Measured reflections
Unique reflections (Rint
Refinement method
4416
The EXAFS oscillations on Me
in the solid state show that gallium is present as Me
2
SO solvated gallium(III) bromide
SO solvated
)
1732 (0.0854)
full-matrix least-
3155 (0.029)
2
2
gallium(III) ions. The bond distances were modeled with the main
contributions from the Ga–O and Gaꢃ ꢃ ꢃS single back-scattering
paths, a three-leg Ga–O–S back-scattering path, and multiple scat-
squares on F
Final R
1
, wR
2
[I > 2s(I)]a
0.0522, 0.1240
0.0636, 0.1933
0.0748, 0.2018
(all data)
0.0684, 0.1302 (all
data)
1.267
tering within the GaO
and the fitted parameters are in agreement with those reported
for the Me SO solvated gallium(III) ion [4b]. No Ga–Br scattering
path was found to improve the fit of the experimental data. The
structure parameters from the refined EXAFS data are given Table 2.
The fit of EXAFS data and the corresponding Fourier transform are
given in Figs. 1 and 2.
6
core. The shape of the EXAFS oscillations
Largest difference
1.373
ꢀ
3
in peak (e Å
)
Largest difference
ꢀ0.927
P jjF
ꢀ1.840
2
ꢀ
3
in hole (e Å
)
R
values are defined as
R
1
¼
o
j ꢀ jF
c
jj=
P jF
o
j, wR
2
¼ ½P
½wðFo ꢀ F Þꢄ=
a
2
2
c
P½
wðF Þ ꢄꢄ
.
2
2 0:5
o
Fig. 6. Molecular structure of tris(dimethylsulfoxide)trisbromoindium(III).

9
94
Ö. Topel et al. / Inorganica Chimica Acta 363 (2010) 988–994
The crystallographic data on tris(dimethylsulfoxide)trisbromo-
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of Turkey (TUBITAK) BIDEB-2214 research fellowship program for
financial support to Ö. Topel, the Department of Chemistry, Insti-
tute of Natural Sciences of Akdeniz University, Antalya, Turkey,
for giving leaving permission to one of us (Ö.T.). The MAX-lab at
Lund University, Sweden is acknowledged for the allocation of
beam time and laboratory facilities. Portions of this research were
carried out at beamline I811, MAX-lab synchrotron radiation
source, Lund University, Sweden. Funding for the beamline I811
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