Structure of the solvated thallium(I) ion in aqueous, dimethyl sulfoxide, N,N'-dimethylpropyleneurea, and N,N-dimethylthioformamide solution.

Article abstract of DOI:10.1021/ic010587y

The structure of the solvated thallium(I) ion in aqueous, dimethyl sulfoxide, N,N'-dimethylpropyleneurea, and N,N-dimethylthioformamide solution has been studied by means of large-angle X-ray scattering (LAXS) and complemented by EXAFS studies on two systems. The first solvation shell around the thallium(I) ion comprises significantly different bond distances to the solvent molecules in solution, indicating a stereochemically active lone electron pair. The first hydration shell around the thallium(I) ion in aqueous solution can be modeled by two Tl-O bond distances at 2.73(2) A and about two more at 3.18(6) A. Thallium(I) ions solvated by dimethyl sulfoxide, N,N'-dimethylpropyleneurea, and N,N-dimethylthioformamide seem to have two short and four long Tl-solvent bond distances. The mean Tl-O bond distances of the two groups were 2.66(4) and 3.18(6) A for dimethyl sulfoxide and 2.73(4) and 3.27(8) A for N,N'-dimethylpropyleneurea. For the sulfur donor solvent N,N-dimethylthioformamide the corresponding groups of Tl-S bond distances were refined to 2.96(2) and 3.33(3) A.

Full text of DOI:10.1021/ic010587y

Inorg. Chem. 2002, 41, 192−197
Structure of the Solvated Thallium(I) Ion in Aqueous, Dimethyl
Sulfoxide, N,N′-Dimethylpropyleneurea, and N,N-Dimethylthioformamide
Solution
,†
‡
§
Ingmar Persson,* Farideh Jalilehvand, and Magnus Sandstr o1 m
Department of Chemistry, Swedish UniVersity of Agricultural Sciences, P.O. Box 7015,
SE-750 07 Uppsala, Sweden, Department of Chemistry, Stanford UniVersity,
Stanford, California 94305-5080, and Department of Structural Chemistry, Arrhenius Laboratory,
Stockholm UniVersity, SE-106 91 Stockholm, Sweden
Received June 4, 2001
The structure of the solvated thallium(I) ion in aqueous, dimethyl sulfoxide, N,N′-dimethylpropyleneurea, and N,N-
dimethylthioformamide solution has been studied by means of large-angle X-ray scattering (LAXS) and complemented
by EXAFS studies on two systems. The first solvation shell around the thallium(I) ion comprises significantly different
bond distances to the solvent molecules in solution, indicating a stereochemically active lone electron pair. The
first hydration shell around the thallium(I) ion in aqueous solution can be modeled by two Tl−O bond distances at
2.73(2) Å and about two more at 3.18(6) Å. Thallium(I) ions solvated by dimethyl sulfoxide, N,N′-dimethylpropy-
leneurea, and N,N-dimethylthioformamide seem to have two short and four long Tl−solvent bond distances. The
mean Tl−O bond distances of the two groups were 2.66(4) and 3.18(6) Å for dimethyl sulfoxide and 2.73(4) and
3.27(8) Å for N,N′-dimethylpropyleneurea. For the sulfur donor solvent N,N-dimethylthioformamide the corresponding
groups of Tl−S bond distances were refined to 2.96(2) and 3.33(3) Å.
Introduction
the range 2.7-3.2 Å,4,5 but occasionally single Tl-O bond
6
,7
distances can be as short as 2.45 Å. In some structures the
lone electron pair seems to be stereochemically active, while
in others the coordination figure is highly symmetric.
The aim of the present study is to investigate the structure
of the solvated thallium(I) ion in aqueous, dimethyl sulfoxide
The large monovalent thallium(I) ion, with the ionic radius
1
1.50 and 1.59 Å in 6- and 8-coordination, respectively, has
weak electrostatic interactions with its ligands. Also the
covalent contribution to the bonding is expected to be weak
because of its d s valence shell electron configuration with
a lone electron pair. Accordingly, the thallium(I) ion is
weakly solvated in most solvents2,3 and crystallizes normally
without coordinated solvent molecules. For constructing
models to evaluate the weak and irregular coordination
around the solvated thallium(I) ion in the current structural
study, a literature search was performed. A large number of
crystal structures are reported where thallium(I) is surrounded
by oxygen atoms. Due to the weak interactions no frequent
well-defined coordination figure is found. The most common
coordination number in these compounds is 8, but 6- and
1
0 2
2
(Me SO), N,N′-dimethylpropyleneurea (dmpu), and N,N-
dimethylthioformamide (dmtf) solution, where no packing
forces influence the bonding. However, the weak and
irregular coordination between the thallium(I) ion and its
surrounding solvent shell make structure studies difficult with
available techniques. Consequently, no structural information
seems to be available for the thallium(I) ion in any solvent.
N,N′-Dimethylpropyleneurea is an oxygen donor solvent with
a rather bulky molecular structure that occupies large space
at coordination. Many metal ions attain, due to steric reasons,
4,5
7
-coordination also occur. The Tl-O bond distances in the
(
4) Allen, F. H.; Bellard, S.; Brice, M. D.; Cartwright, B. A.; Doubleday,
A.; Higgs, H.; Hummelink, T.; Hummelink-Peters, G. G.; Kennard,
O.; Motherwell, W. D. S.; Rodgers, J. R.; Watson, D. G. The
Cambridge Crystallographic Data Centre: computer-based search,
retrieval, analysis and display of information. Acta Crystallogr., Sect.
B 1979, 35, 2331 and references therein.
thallium(I) compounds and complexes are in most cases in
*
Author to whom correspondence should be addressed. E-mail:
ingmar.persson@kemi.slu.se.
†
Swedish University of Agricultural Sciences.
Stanford University.
Stockholm University.
‡
(5) Inorganic Crystal Structure Database, release 98/1; Gmelin Institut,
Fachinformationzentrum: Karlsruhe, Germany, 1998.
(6) Oddon, Y.; Vignalou, J. R.; Pepe, G.; Tranquard, A. J. Chem. Res.,
Synop. 1979, 66.
(7) Domasevich, K. V.; Skopenko, V. V.; Rusanov, E. B. Zh. Neorg. Khim.
1997, 42, 979.
§
(
(
(
1) Shannon, R. D. Acta Crystallogr., Sect. A 1976, 32, 751.
2) Marcus, Y. Pure Appl. Chem. 1983, 55, 977; 1985, 57, 1103.
3) Inerowicz, H. D.; Li, W.; Persson, I. J. Chem. Soc., Faraday Trans.
1994, 90, 2223.
192 Inorganic Chemistry, Vol. 41, No. 2, 2002
10.1021/ic010587y CCC: $22.00 © 2002 American Chemical Society
Published on Web 01/03/2002

Structure of the SolWated Thallium(I) Ion
Table 1. Concentrations (mol‚dm-3), Density (F), and Linear Absorption Coefficient (µ) of the Aqueous, Dimethyl Sulfoxide (Me2SO),
a
N,N′-Dimethylpropyleneurea (DMPU), and N,N-Dimethylthioformamide (DMTF) Solutions Used in the Large-Angle X-ray Scattering (L) and EXAFS
(E) Measurements
-
F/g‚cm-3
µ/g‚cm-1 a
sample
[T1+]
[X ]
[solvent]
54.43
method
TlF in water
TlF in water
TlNO3 in Me2SO
Tl NO3 in DMPU
TlCF3SO3 in DMTF
TlCF3SO3 in DMTF
2.000
0.20
1.034
0.900
1.000
0.50
2.000
1.427
49.89
L
E
L
L
L
E
0.40, pH ) 3 (HClO4)
1.034
0.900
3.00
12.31
8.06
10.75
1.318
1.273
1.609
29.82
22.73
29.46
1.50
a
Linear absorption coefficient for Mo KR radiation.
a lower coordination number when solvated by N,N′-dimethyl-
EXAFS. Tl LIII edge X-ray absorption data were collected in
transmission mode at beam line 4-1, Stanford Synchrotron Radiation
Laboratory (SSRL), Stanford, CA, under dedicated conditions;
SSRL operates at 3.0 GeV and a maximum current of 100 mA. A
Si[220] double monochromator was detuned to 50% of the
maximum intensity at the end of the scans to discard higher order
harmonics. The solutions were kept in cells with 6.3 µm X-ray
polypropylene foil windows and 1-5 mm Teflon spacers. Energy
calibration of the X-ray absorption spectra was performed by
simultaneously recording the spectrum of a thallium foil and
propyleneurea than in their hydrates or dimethyl sulfoxide
8
solvates. N,N-Dimethylthioformamide is a solvent with high
permittivity and some hydrogen bonding ability,9,10 allowing
even highly charged species to be dissolved without ion-
pair formation, an unusual property for a sulfur donor solvent.
Experimental Section
Preparation of Samples. Anhydrous thallium(I) fluoride (ICN)
and thallium(I) nitrate (Merck) were used as purchased. Dimethyl
sulfoxide (Merck) and N,N′-dimethylpropyleneurea (BASF) were
distilled over calcium hydride (Fluka) and stored over 3 Å molecular
sieves in dark bottles. N,N-Dimethylthioformamide was prepared
by reacting phosphorus pentasulfide (Merck) and N,N-dimethyl-
1
4
assigning the first LIII-edge inflection point to 12660 keV. Four
scans of each sample were recorded, energy calibrated, and
averaged. The EXAFS functions were extracted using standard
procedures for preedge subtraction, spline removal, and data
normalization,15 using the EXAFSPAK program package. To
16
formamide (Merck) in benzene, according to a procedure devised
by Gutmann et al.11 After repeated distillations the 1H NMR
3
obtain quantitative information the k -weighted EXAFS oscillations
were analyzed by nonlinear fitting of the model parameters by
means of the WinXAS program package.17 Model fitting including
both single and multiple scattering pathways was performed with
theoretical phase and amplitude functions calculated by means of
the ab initio code FEFF7.18
spectrum no longer showed traces of unreacted N,N-dimethylfor-
mamide. Anhydrous thallium(III) trifluoromethanesulfonate was
prepared as described elsewhere.12
The aqueous thallium(I) solution was prepared by dissolving a
weighed amount of thallium(I) fluoride in deionized water, slightly
acidified with some drops of perchloric acid to prevent hydrolysis.
The fluoride salt was chosen as the fluoride ion forms weaker
complexes than the anions in other available thallium(I) salts.13
Large-Angle X-ray Scattering. The scattering of Mo KR X-ray
radiation (λ ) 0.7107 Å) from the free surface of an aqueous
thallium(I) fluoride solution, of dimethyl sulfoxide, and N,N′-
dimethylpropyleneurea solutions of thallium(I) nitrate, and of
thallium(I) in N,N-dimethylthioformamide solution was measured
by means of a large-angle θ-θ diffractometer. The solutions were
contained in a Teflon cup inside an airtight radiation shield with
beryllium windows. The scattered radiation was monochromatized
in a focusing LiF crystal monochromator, and the intensity was
measured at discrete points in the range 1 < θ < 65°; the scattering
angle is 2θ. A total of 100 000 counts was accumulated at each
preset angle, and the entire angular range was scanned twice, which
corresponds to a statistical error of about 0.3 %. The divergence
of the primary X-ray beam was limited by 1°, 1/4°, or 1/12° slits
for different θ regions, with overlapping data for scaling purposes.
The experimental setup and the theory of the data treatment and
Weighed amounts of thallium(I) nitrate were dissolved in freshly
distilled dimethyl sulfoxide and N,N′-dimethylpropyleneurea. An-
hydrous thallium(III) trifluoromethanesulfonate was dissolved in
N,N-dimethylthioformamide shortly before the structural studies.
However, the experimental result showed that thallium(III) was
completely reduced to thallium(I) by the solvent, because only one
signal in 2 Tl NMR at 1414 ppm was observed. The oxidation
product of N,N-dimethylthioformamide, probably a sulfone, could
not be detected in the LAXS study. A similar reaction also takes
place in N,N′-dimethylpropyleneurea independent of the anion
05
(trifluoromethanesulfonate and perchlorate) giving a single signal
at 781 ppm. The composition of the studied solutions is summarized
in Table 1.
19
modeling have been presented elsewhere. All data treatment was
carried out by means of the KURVLR program.20 The experimental
intensities were normalized to a stoichiometric unit of volume
containing one thallium atom, using the scattering factors f for
(
8) N a¨ slund, J.; Lindqvist-Reis, P.; Pattanaik, S.; Sandstr o¨ m, M.; Persson,
I. Inorg. Chem. 2000, 39, 4006. N a¨ slund, J.; Persson, I.; Sandstr o¨ m,
M. Inorg. Chem. 2000, 39, 4012.
(
9) Diggle, J.; Bogs a´ nyi, D. J. Phys. Chem. 1974, 78, 1018.
(
(
(
10) Borrmann, H.; Persson, I.; Sandstr o¨ m, M.; Stålhandske, C. M. V. J.
Chem. Soc., Perkin Trans.2 2000, 393.
11) Gutmann, V.; Danksagm u¨ ller, K.; Duschek, O. Z. Phys. Chem. Neue
Folge (Frankfurt) 1974, 92, 199.
12) Ma, G.; Molla-Abbassi, A.; Ilyukhin, A.; Kessler, V.; Skripkin, M.;
Sandstr o¨ m, M.; Glaser, J.; N a¨ slund, J.; Persson, I. Inorg. Chem., in
press (IC010453).
(14) Center for X-Ray Optics, X-Ray Data Booklet; PUB-490 rev; Lawrence
Livermore Laboratory: Berkley, CA, 1993.
(15) Sayers, D. E.; Bunker, B. A. In X-ray absorption: Principles,
Applications, Techniques of EXAFS, SEXAFS and XANES; Konings-
berger, D. C., Prins, R., Eds.; Wiley-Interscience: New York, 1988;
Chapter 6.
(16) George, G. N.; Pickering, I. J. EXAFSPAK; Stanford University:
Stanford CA, 1993.
(17) Ressler, T. J. Synchrotron Radiat. 1998, 5, 118.
(18) Zabinsky, S. I.; Rehr, J. J.; Ankudinov, A.; Albers, R. C.; Eller, M. J.
J. Phys. ReV. B 1995, 52, 2995. Ankudinov, A. L.; Rehr, J. J. Phys.
ReV. B 1997, 56, R1712. The FEFF program is available from the
following: http://Feff.phys.washington.edu/feff.
(
13) Sill e´ n, L. G.; Martell, A. E. Stability Constants of Metal-Ion
Complexes; Special Publ. Nos. 17 and 25; The Chemical Society:
London, 1964 and 1971. H o¨ gfeldt, E. Stability Constants of Metal-
Ion Complexes, Part A, Inorganic Ligands; IUPAC Chemical Data
Series No. 21; Pergamon Press: Oxford, U.K., 1982. Perrin, D. D.
Stability Constants of Metal-Ion Complexes, Part B, Organic Ligands;
IUPAC Chemical Data Series No. 22; Pergamon Press: Oxford, U.K.,
1979.
Inorganic Chemistry, Vol. 41, No. 2, 2002 193

Persson et al.
neutral atoms, including corrections for anomalous dispersion,21 ∆f ′
and ∆f ′′, and values for Compton scattering.22 Least-squares
refinements of the model parameters were carried out by means of
23
the STEPLR program, where the expression U ) ∑[siexp(s) -
2
si
c
(s)] is minimized. The refinements of the model parameters were
made for data in the high-s region where the intensity contribution
from the long-range distances can be neglected.2 To obtain a better
alignment of the intensity function before the refinements, a Fourier
back-transformation procedure was used to correct the iexp(s)
functions by removing spurious nonphysical peaks below 1.2 Å in
the experimental radial distribution function (RDF).25
4
Results and Discussion
Hydrated Thallium(I) Ion. The radial distribution func-
tion of an aqueous solution of 2.0 mol‚dm- thallium(I)
fluoride shows two peaks, at 2.9 and 4.3 Å, with shoulders
at about 3.3 and 4.8 Å (Figure 1). The first peak corresponds
to several interactions, a Tl-O bond distance in the hydrated
thallium(I) ion, the F‚‚‚(H)-O distance of the hydrated
fluoride ion, reported to be 2.60-2.69 Å in aqueous
3
26
solution, and O-(H)‚‚‚O distances within the aqueous bulk,
27
about 2.89 Å in pure water. The shoulder at 3.2 Å appears
to be a second Tl-O bond distance in the hydrated thallium-
(I) ion. The peak and the shoulder at 4.3 and 4.8 Å,
respectively, are assumed to be caused by a second hydration
sphere of thallium(I). The most plausible model was found
to include two Tl-O bonds at about 2.7 Å and two at about
3.2 Å. Higher coordination numbers result in unrealistically
large temperature factors.
The O‚‚‚O distances within the first solvation shell of the
thallium(I) ions were not included in the models, because
the large temperature factors of the Tl-O bond distances
indicate a large spread also of the O‚‚‚O distances within
the first coordination sphere. This is consistent with the lack
of such features in the experimental RDF, and it is not
possible from the present LAXS data to draw conclusions
about the configuration of water ligands around the thallium-
Figure 1. LAXS: (top) separate model peak shapes for all contributing
interactions, Tl-O in the first and second hydration shell (solid line),
F‚‚‚O for the hydrated fluoride ion (dashed line), and hydrogen-bonded
O‚‚‚O distances in the aqueous bulk (dotted line); (middle) experimental
2
D(r) - 4πr Fo (solid line), model (dashed line), difference (dash-dotted
line); (bottom) reduced LAXS intensity functions, si(s) (solid line), model
sicalc(s) (dashes).
(I) ion aqueous solution. However, the presence of two
different groups of Tl-O bond distances implicates that the
lone electron pair on thallium(I) is stereochemically active.
Therefore, the configuration around the hydrated thallium-
at 2.732(10) and 3.18(3) Å. The F‚‚‚(H)-O distance in the
hydrated fluoride ion, assumed to be surrounded by six water
molecules, was refined to 2.63(4) Å, which is in accordance
(
I) ion may be similar to that proposed for the hydrated tin(II)
26
with previous results. The O-(H)‚‚‚O distance within the
28,29
ion,
which comprises two short and two long M-O bond
aqueous bulk and between the hydrogen bonded water
molecules in the first and second hydration sphere was
obtained as 2.94(1) Å. This is longer than in pure water,
distances opposite the lone electron pair. Least-squares
refinements of such a model resulted in Tl-O bond distances
2
.89 Å, indicating that the thallium(I) ion is a structure
(19) Stålhandske, C. M. V.; Persson, I.; Sandstr o¨ m, M.; Kamienska-
breaker in aqueous solution. The structural parameters are
summarized in Table 2. The fits of the model to the
experimental intensity data and to the radial distribution
function (RDF) are displayed in Figure 1.
A Tl LIII edge EXAFS study of an 1.0 mol‚dm- aqueous
solution of thallium(I) nitrate showed the backscattering to
be weak, and the Fourier transform had a very broad feature
around 3 Å (Figure 2). Curve-fitting using backscattering
parameters ab initio calculated by the FEFF program gave
Piotrowicz, E. Inorg. Chem. 1997, 36, 3174.
(
(
20) Johansson, G.; Sandstr o¨ m, M. Chem Scr. 1973, 4, 195.
21) International Tables for X-Ray Crystallography; Wilson, A. J. C., Ed.;
Kluwer Academic Publishers: Dordrecht, The Netherlands, 1995; Vol.
C. International Tables for X-Ray Crystallography; Wilson, A. J. C.,
Ed.; Kynoch Press: Birmingham, U.K., 1974; Vol. 4.
22) Cromer, D. T. J. Chem. Phys. 1969, 50, 4857.
23) Molund, M.; Persson, I. Chem. Scr. 1985, 25, 197.
3
(
(
(
24) Sandstr o¨ m, M.; Persson, I.; Ahrland, S. Acta Chem. Scand., Ser. A
1978, 32, 607.
(
25) Levy, H. A.; Danford, M. D.; Narten, A. H. Data Collection and
EValuation with an X-Ray Diffractometer Designed for the Study of
Liquid Structure; Report ORNL-3960; Oak Ridge National Labora-
tory: Oak Ridge, TN, 1966.
(
26) Ohtaki, H.; Radnai, T. Chem. ReV. 1993, 93, 1157 and references
(28) Johansson, G.; Ohtaki, H. Acta Chem. Scand. 1973, 27, 643.
(29) Yamaguchi, T.; Lindqvist, O.; Claeson, T.; Boyce, J. B. Chem. Phys.
Lett. 1982, 93, 528.
therein.
(27) Johansson, G. AdV. Inorg. Chem. 1992, 39, 159 and references therein.
194 Inorganic Chemistry, Vol. 41, No. 2, 2002

Structure of the SolWated Thallium(I) Ion
2
2
Table 2. Model Fitting of LAXS and EXAFS Data: Mean Bond Distances, d/Å, Debye-Waller Factor, σ /Å , Number of Distances, N, Shift in the
2
Threshold Energy in the EXAFS Studies, ∆E0/eV, and Amplitude Reduction Factor, So , of the Solvated Thallium(I) Ion in Solid and Solution as
Determined by EXAFS (E) and LAXS (L) at Room Temperature
solvent
water
interactn
N
d
σ2
∆E0
So2
method
L
Tl-Osh
Tl-Olo
F‚‚‚O
2
2
6
3
2
2
2
4
2
4
2
4
2
4
2
4
2.732(10)
3.18(3)
2.63(4)
2.935(10)
2.75(4)
3.00(4)
0.0040(6)
0.014(2)
0.0036(5)
0.0049(8)
0.012(4)
0.017(8)
0.0041(6)
0.012(1)
0.0072(6)
0.018(1)
0.0062(11)
0.013(2)
0.0045(5)
0.0125(4)
0.013(2)
0.025(4)
O‚‚‚O
Tl-Osh
Tl-Olo
Tl-Osh
Tl-Olo
Tl‚‚‚Ssh
Tl‚‚‚Slo
Tl-Osh
Tl-Olo
Tl-Ssh
Tl-Slo
Tl-Ssh
Tl-S1o
0.5(4)
0.95(3)
E
L
Me2SO
2.660(16)
3.178(30)
3.672(10)
4.048(14)
2.72(2)
DMPU
DMTF
Tl(I)
L
L
E
3.31(2)
2.964(5)
3.325(12)
2.99(2)
0.5(4)
0.95(3)
3.17(2)
weak interactions is much less in EXAFS than in LAXS
3
0
data. Therefore, it is likely that the long Tl-O mean bond
distance from the LAXS measurement gives a better average
than the result from the EXAFS study, where the most well-
defined (the shortest) Tl-O distances get higher weight. The
fits of the EXAFS data and the Fourier transform are shown
in Figure 2, the structural parameters are given in Table 2,
and the individual contributions to the model are shown in
Figure S1a.
Broad peaks often remain at ca. 4 Å in the LAXS differ-
ence function for aqueous solutions of large and weakly hy-
drated ions (cf. Figure 1, Figures 1-6 in ref 31, and Figure
2
in ref 32). This probably reflects a distribution of
O-(H)‚‚‚O distances shorter than normal in the water
structure, caused by a partial breakdown of the hydrogen
bonding due to the presence of the large structure-breaking
ions poorly fitting into the bulk structure. Detailed theoretical
modeling to explain these experimental observations is still
lacking.
The reason the hydrated thallium(I) ion in aqueous solution
has a somewhat different structure than the nonaqueous
solvates (see below) is probably the hydrogen bonding. In
pure water the hydrogen bonding is stronger (O-(H)‚‚‚O,
2
.89 Å) than between the water molecules in the first and
second hydration sphere of thallium(I), ca. 2.94 Å; see Table
. It seems therefore reasonable that the hydrogen bonding
2
system in water strongly affects the structure of the hydrated
thallium(I) ion in aqueus solution, while in the aprotic
solvents the solvation of the thallium(I) ion is much less
affected by the intermolecular interactions in the solvent.
Dimethyl Sulfoxide Solvated Thallium(I) Ion. The RDF
from the LAXS data of a dimethyl sulfoxide solution of
thallium(I) nitrate shows three peaks below 5 Å. The first
peak at 1.5 Å corresponds to intramolecular distances within
the dimethyl sulfoxide molecule and the nitrate ion, and two
Figure 2. EXAFS: (top) Fourier transforms of EXAFS data (solid lines);
bottom) Fourier-filtered EXAFS data (solid lines) with a model formed
by ab initio calculated scattering paths from the program FEFF (dotted lines),
a) acidic aqueous solution of thallium(I) fluoride and (b) N,N-dimethylth-
(
(
ioformamide solution of thallium(I) trifluoromethanesulfonate.
two groups of Tl-O bond distances, 2.70(2) and 3.00(4) Å.
Thus, the LAXS and EXAFS measurements show good
agreement for the short Tl-O bond distance, while there is
a substantial difference in the long Tl-O mean bond
distance; a similar result is obtained for the thallium(I) ion
in N,N-dimethylthioformamide; see below. We propose that
the short Tl-O bond distance is well-defined enough to be
fairly accurately determined by both methods, while the
distribution of the long and poorly defined Tl-O bond
distances is large. The relative contribition from long and
(30) Persson, I.; Sandstr o¨ m, M.; Yokoyama, H.; Chaudhry, M. Z. Natur-
forsch. 1995, 50a, 21. Jalilehvand, F. In Structure of Hydrated Ions
and Cyano Complexes by X-Ray Absorption Spectroscopy; Doctoral
Thesis; Royal Institute of Technology: Stockholm, 2000; http://
media.lib.kth.se: 8080/dissengrefhit.asp?dissnr)2963.
(
(
31) Lyxell, D.-G.; Pettersson, L.; Persson, I. Inorg. Chem. 2001, 40, 584.
32) Jalilehvand, F.; Spångberg, D.; Lindqvist-Reis, P.; Hermansson, K.;
Persson, I.; Sandstr o¨ m, M. J. Am. Chem. Soc. 2001, 123, 431.
Inorganic Chemistry, Vol. 41, No. 2, 2002 195

Persson et al.
Figure 3. LAXS: (top) separate model peak shapes for the Tl-O and
Tl‚‚‚S distances of the dimethyl sulfoxide solvated thallium(I) ion (solid
line), the nitrate ion (dashed line), and the dimethyl sulfoxide solvent
molecules (dotted line); (middle) experimental D(r) - 4πr Fo (solid line),
model (dashed line), difference (dash-dotted line); (bottom) reduced LAXS
intensity functions, si(s) (solid line), model sicalc(s) (dashes).
Figure 4. LAXS: (top) separate model peak shapes for the N,N′-dimethyl-
propyleneurea-solvated thallium(I) ion (solid line), the trifluoromethane-
sulfonate ion (dashed line), and the N,N′-dimethylpropyleneurea solvent
molecules (dotted line); (middle) experimental D(r) - 4πr Fo (solid line),
model (dashed line), difference (dash-dotted line); (bottom) reduced LAXS
intensity functions, si(s) (solid line), model sicalc(s) (dashes).
2
2
functions to the experimental intensity and the radial
distribution functions are shown in Figure 3.
other peaks at 2.7 and 3.9 Å correspond to Tl-O and Tl‚‚‚S
distances within the dimethyl sulfoxide solvated thallium(I)
ion. Besides these peaks there is a weak shoulder at about
N,N′-Dimethylpropyleneurea-Solvated Thallium(I) Ion.
-
3
The RDF from the LAXS study of a 0.90 mol‚dm N,N′-
dimethylpropyleneurea solution of thallium(I) nitrate displays
three peaks below 5 Å at 1.5, 2.5, and 4.3 Å, all of which
correspond to intramolecular distances within the N,N′-
dimethylpropyleneurea molecule and the nitrate ion; see
Figure 4. The Tl-O distances in the N,N′-dimethylpropy-
leneurea solvated thallium(I) ion give rise to a broad feature
around 3 Å. An acceptable fit to the experimental data is
achieved when using a model with two groups of Tl-O bond
distances in a coordination geometry similar to that for the
dimethyl sulfoxide solvated ion. The refinements correspond
to two short Tl-O distances at a mean value of 2.73(2) Å
and four long at 3.27(4) Å. The structure of the nitrate ion
3.2 Å (Figure 3). The contribution from the nitrate ion is
very small, and the structure of the nitrate ion in the solid
state has been applied for the modeling.33 When the same
basic coordination model as in aqueous solution is applied
for the thallium ion, a 2 + 2 configuration, the contributions
from the longer Tl-O and Tl‚‚‚S distances become too small.
The most plausible model with a satisfactory fit to the
experimental data comprises two short and four long Tl-O
bonds to the solvent molecules. Refinement gave Tl-O bond
distances in two groups at 2.66(2) and 3.18(3) Å, respec-
tively, and the corresponding Tl‚‚‚S distances were refined
to 3.67(2) and 4.05(2) Å, respectively. Assuming an S-O
bond length of 1.52(1) Å for the weakly coordinated dimethyl
sulfoxide ligands, this corresponds to mean Tl-O-S angles
33
in the solid state has been applied. The structural parameters
of the model are summarized in Table 2, and the fit to the
experimental intensity data and the radial distribution func-
tion (RDF) is shown in Figure 4.
12
of 120(3) and 114(3)°, respectively. The structural param-
eters are summarized in Table 2, and the fits of the model
N,N-Dimethylthioformamide-Solvated Thallium(I) Ion.
The RDF obtained from a LAXS study of an N,N-dimeth-
(
33) Kalliom a¨ ki, M. S.; Meisalo, V. P. J. Acta Crystallogr., Sect. B 1979,
35, 2829.
196 Inorganic Chemistry, Vol. 41, No. 2, 2002

Structure of the SolWated Thallium(I) Ion
modeling.39 There seems to be two groups of Tl-S bond
distances in the N,N-dimethylthioformamide-solvated thal-
lium(I) ion, two close to 3.0 Å and another four at about 3.3
Å; refinements gave 2.96(1) and 3.33(2) Å (Table 2). The
model fit is displayed in Figure 5.
An EXAFS study of the same solution gave Tl-S bond
distances of 2.99(2) and 3.17(4) Å (Table 2). The mean value
of the longer Tl-S bond distances is again found to be much
shorter by EXAFS than by LAXS, probably for the same
reason as discussed above (cf. Hydrated Thallium(I) Ion
section). The model fit to the EXAFS data and the Fourier
transform is shown in Figure 2, with the individual contribu-
tions from the model displayed in Figure S1b.
Conclusions
The thallium(I) ion is weakly solvated in all the studied
solvents, and the thallium(I) solvates seem to have two
groups of different Tl-solvent bond distances. This indicates
that the lone electron pair has a significant stereochemical
role for the solvated thallium(I) ion in a similar way as the
lone electron pair has for the hydrated tin(II) ion.2
8,29
The
isoelectronic divalent lead(II) ion occasionally shows a
stereochemical effect of the lone electron pair, especially in
complexes with soft donor ligands, e.g. the lead(II) alkylx-
4
0-42
anthate and dithiocarbamate complexes,
while no such
effect has been observed for the likewise isoelectronic but
8
trivalent bismuth(III) ion.
It is not possible from this study to give a detailed account
of the coordination and ligand configuration around the
solvated thallium(I) ion in solution. The large displacement
factors of the mean bond distances in the models show that
the bonds indeed are weak and with a wide distribution of
the bond distances.
Figure 5. LAXS: (top) separate model peak shapes for the N,N-
dimethylthioformamide-solvated thallium(I) ion (solid line), the trifluo-
romethanesulfonate ion (dashed line), and the N,N-dimethylthioformamide
solvent molecules (dotted line); (middle) experimental D(r) - 4πr Fo (solid
line), model (dashed line), difference (dash-dotted line); (bottom) reduced
LAXS intensity functions, si(s) (solid line), model sicalc(s) (dashes).
2
Acknowledgment. We gratefully acknowledge the Swed-
ish Research Council for financial support and the Stanford
Synchrotron Radiation Laboratory (SSRL) for allocation of
beam time and laboratory facilities. SSRL is operated by
the Department of Energy, Office of Basic Energy Sciences.
The SSRL Biotechnology Program is supported by the
National Institutes of Health, National Center for Research
Resources, Biomedical Technology Program, and by the
Department of Energy, Office of Biological and Environ-
mental Research. We thank BASF, Ludwigshafen, Germany,
for a gift of N,N′-dimethylpropyleneurea.
ylthioformamide solution of thallium(III) trifluoromethane-
sulfonate shows four broad peaks below 5 Å, at 1.5, 3.0,
3.8 and 4.7 Å, and a distinct shoulder at 2.5 Å (Figure 5).
The absence of a strong peak at about 2.47 or 2.67 Å, the
III
expected Tl -S bond distances in tetrahedral and octahedral
configuration, respectively,3
4-38
shows that thallium(III) has
been reduced to thallium(I). This was also confirmed by
2
05
Tl NMR measurements; see Experimental Section. The
contributions at 1.5, 2.5, 3.8, and 4.7 Å correspond to
intramolecular distances within the N,N-dimethylthioforma-
1
0,39
mide molecule and the trifluoromethanesulfonate ion.
Supporting Information Available: Figures S1 and S2, show-
ing the EXAFS contributions from separate backscattering pathways
for the aqueous solution of thallium(I) fluoride and the N,N-
dimethylthioformamide solution of thallium(I) trifluoromethane-
sulfonate. This material is available free of charge via the Internet
at http://pubs.acs.org.
The solid-state structure of the trifluoromethanesulfonate ion,
which has been found in previous LAXS studies in organic
8
solvents to give a good description, has been applied in the
(
34) Bosch, B. E.; Eisenhawer, M.; Kersting, B.; Kirschbaum, K.; Krebs,
B.; Giolando, D. M. Inorg. Chem. 1996, 35, 6599.
(
(
35) Day, R. O.; Holmes, R. R. Inorg. Chem. 1982, 21, 2379.
36) Kepert, D. L.; Raston, C. L.; Roberts, N. K.; White, A. H. Aust. J.
Chem. 1978, 31 1927.
IC010587Y
(
37) Abrahamson, H.; Heiman, J. R.; Pignolet, L. H. Inorg. Chem. 1975,
(39) Niewpoort, G.; Verschoor, G.; Reedijk, J. J. Chem. Soc., Dalton Trans.
1983, 531.
14, 2070.
(
38) Casas, J. S.; Castellano, E. E., Castineiras, A.; Sanchez, A.; Sordo, J.;
Vazquez-Lopez, E. M.; Zukerman-Schpector, J. J. Chem. Soc., Dalton
Trans. 1995, 1403.
(40) Hagihara, H.; Yamashita, S. Acta Crystallogr. 1966, 21, 350.
(41) Hagihara, H.; Watanabe, Y. Acta Crystallogr., Sect. B 1968, 24, 960.
(42) Ito, T. Acta Crystallogr., Sect. B 1972, 28, 1034.
Inorganic Chemistry, Vol. 41, No. 2, 2002 197