Structure of a Hydrated Sulfonatotitanyl(IV) Complex in Aqueous Solution and the Dimethylsulfoxide Solvated Titanyl(IV) Ion in Solution and Solid State

Article abstract of DOI:10.1007/s10953-017-0581-3

The coordination chemistry of oxotitanium(IV) or titanyl(IV), TiO²⁺, has been studied in solution by X-ray methods. The titanyl(IV) ion hydrolyzes easily in aqueous systems to solid titanium dioxide as long as it is not stabilized through complexation. In this study the structures of the hydrated bissulfatotitanyl(IV) complex and the dimethylsulfoxide (DMSO) solvated titanyl(IV) ions have been determined. In isolated monomeric titanyl complexes titanium(IV) binds strongly to a doubly bound oxo group at ca. 1.64??, to four ligands in the equatorial plane almost perpendicular to the Ti=O bond at ca. 2.02??, and there is one weakly bound ligand, trans to the Ti=O bond, at ca. 2.22??, for oxygen donor ligands; the O=Ti–O_eq bond angles are 95°–100°. The structure of the DMSO solvated titanyl(IV) ion in the solid state is maintained in DMSO solution.

Full text of DOI:10.1007/s10953-017-0581-3

J Solution Chem (2017) 46:476–487
DOI 10.1007/s10953-017-0581-3
Structure of a Hydrated Sulfonatotitanyl(IV) Complex
in Aqueous Solution and the Dimethylsulfoxide Solvated
Titanyl(IV) Ion in Solution and Solid State
Daniel Lundberg1
Ingmar Persson1
•
Received: 29 September 2016 / Accepted: 28 November 2016 / Published online: 27 January 2017
Ó The Author(s) 2017. This article is published with open access at Springerlink.com
Abstract The coordination chemistry of oxotitanium(IV) or titanyl(IV), TiO2?, has been
studied in solution by X-ray methods. The titanyl(IV) ion hydrolyzes easily in aqueous
systems to solid titanium dioxide as long as it is not stabilized through complexation. In
this study the structures of the hydrated bissulfatotitanyl(IV) complex and the dimethyl-
sulfoxide (DMSO) solvated titanyl(IV) ions have been determined. In isolated monomeric
˚
titanyl complexes titanium(IV) binds strongly to a doubly bound oxo group at ca. 1.64 A,
˚
to four ligands in the equatorial plane almost perpendicular to the Ti=O bond at ca. 2.02 A,
˚
and there is one weakly bound ligand, trans to the Ti=O bond, at ca. 2.22 A, for oxygen
donor ligands; the O=Ti–Oeq bond angles are 95°–100°. The structure of the DMSO
solvated titanyl(IV) ion in the solid state is maintained in DMSO solution.
Keywords Titanyl(IV) Á Aqueous solution Á Sulfate Á Structure Á Dimethylsulfoxide
(DMSO)
1 Introduction
The chemistry of titanium(IV) is strongly dominated by different forms of titanium
dioxide, natural rutile, anatase and brookite, two high-pressure forms, akaogiite and TiO2
II, and solid titanate compounds. In these compounds titanium(IV) binds octahedrally six
˚
oxygens at a mean Ti–O bond distance of ca. 1.96 A [1]. Titanium dioxide, in its different
forms, is produced in millions of tons annually to be used in wide ranges of technical
applications as, e.g., pigments and nano-sized materials [2]. Titanium dioxide-based
Electronic supplementary material The online version of this article (doi:10.1007/s10953-017-0581-3)
contains supplementary material, which is available to authorized users.
&
Ingmar Persson
ingmar.persson@slu.se
1
Department of Molecular Sciences, Swedish University of Agricultural Sciences, P.O. Box 7015,
SE-750 07 Uppsala, Sweden
123

J Solution Chem (2017) 46:476–487
477
titanates are formed at high temperatures. Orthotitanates and metatitanates have the for-
mulas M2TiO4 and MTiO3, respectively, where M is a divalent metal ion. Their names are
somewhat misleading as they almost never contain TiO44À or TiO32À units, respectively.
One exception is Ba2TiO4 with an identifiable TiO44À unit with a mean Ti–O bond distance
˚
of 1.81 A [3–5]. Also, the metatitanate Rb2TiO3 is four-coordinate in a chain-structure
˚
with a mean Ti–O bond distance of 1.81 A [6, 7]. The orthotitanates, M2TiO4, have the
spinel structure, while the metatitanates have either ilmenite (FeTiO3) or perovskite
(CaTiO3) structures [1, 8]. The ortho- and metatitanates have network structures with
˚
titanium being octahedrally surrounded by six oxygen atoms at ca. 1.96 A [1].
Titanium dioxide can only be dissolved in concentrated acids where the anion is able to
form reasonably stable complexes with the oxotitanium(IV) ion, or, more commonly, the
titanyl(IV) ion, TiO2?, such as in sulfuric acid solution. The titanyl(IV) ion is only
stable and soluble in aqueous solution as complexes with, e.g., sulfate, phosphate, oxalate,
citrate, lactate, malate or tartrate ions [9]. The number of reported crystal structures with an
isolated titanyl(IV) complex is very limited, including Ba2[TiO(Si2O7)2] [10], Sr2
[TiO(PO4)2] [11] (C(NH2)3)4[TiO(CO3)3]Á2H2O [12] and [TiO(OS(CH3)2)5]Cl2 [13, 14].
In Ba2[TiO(Si2O7)2] and [TiO(OS(CH3)2)5]Cl2 titanium(IV) binds strongly to an oxogroup
˚
at ca. 1.64 A, to four oxygens atoms in the equatorial plane perpendicular to the Ti=O bond
˚
at ca. 2.03 A, and in the trans position to the Ti=O bond an oxygen donor ligand is weakly
˚
coordinated at ca. 2.22 A, or the position may be empty as in Ba2[TiO(Si2O7)2]. In Sr2
˚
[TiO(PO4)2] the Ti=O bond distance is longer, 1.747 A, and the ligand in the trans position
to the Ti=O bond is equal in length to the equatorials bonds [11]. Titanium(IV) is seven-
coordinate in (C(NH2)3)4[TiO(CO3)3]Á2H2O with one of the oxygens in each bidentately
bound carbonate ion at significantly shorter Ti–O bond distance than the other, mean
˚
values at 2.08 and 2.18 A, respectively. A structure with a hydrolyzed isolated hexameric
dimethylsulfoxide (DMSO) solvated titanyl(IV) structure has been reported as well,
[Ti6O4(OS(CH3)2)12]Cl4Á5((CH3)2SO)Á0.5H2O [13].
The aim of this study was to determine the structure of the hydrated and DMSO solvated
titanyl(IV) in aqueous and DMSO solutions, respectively, as no structural studies of sol-
vated titanyl(IV) ions or complexes in solution have been reported. The titanyl(IV) ion
displays a range of different bond distances to neutral ligands besides the short Ti=O
double bond, vide supra. In spite of several attempts it has not been possible to stabilize the
hydrated titanyl(IV) ion at concentrations allowing structure determination by X-ray
methods to be applied. The titanyl(IV) ion hydrolyzes easily in aqueous systems to solid
titanium dioxide unless it is not stabilized through complexation. However, complexation
with, e.g., sulfate ions stabilizes titanyl(IV) substantially allowing the structure of a
hydrated [TiO(SO4)n](2n-2)- complex to be studied in dilute sulfuric acid solution. Fur-
thermore, in this work the structure of the DMSO solvated titanyl(IV) ion has been
determined crystallographically as the trifluoromethanesulfonate salt and in DMSO solu-
tion to allow comparisons between a solvate and a complex in aqueous solution.
2 Experimental Section
2.1 Chemicals Used
Dimethylsulfoxide, (CH3)2SO (Merck, puriss), DMSO, was freshly distilled under vacuum
and over calcium hydride, CaH2 (Fluka, puriss), before use. Titanyl(IV) sulfate,
123

478
J Solution Chem (2017) 46:476–487
TiOSO4ÁH2O (Aldrich), barium carbonate, BaCO3 (Fluka, p.a.), and trifluoromethanesul-
fonic acid, CF3SO3H (Fluka, p.a.), were used as purchased.
2.2 Preparation of Salts and Solutions
Barium trifluoromethanesulfonate, Ba(CF3SO3)2, was prepared by dropwise addition of
trifluoromethanesulfonic acid to a slurry of barium carbonate under stirring until a clear
solution was obtained. The obtained solution was cooled to room temperature and filtered,
and thereafter put into an oven at 450 K to boil off water and excess acid. The obtained
white powder was ground into a fine powder and stored in the oven at 450 K.
Pentakis(dmso)titanyl(IV) trifluoromethanesulfonate, [TiO(OS(CH3)2)5](CF3SO3)2, 1,
was prepared by mixing equimolar DMSO solutions of barium trifluoromethanesulfonate
and titanyl(IV) sulfate, the mixture was stirred for 10 min, and the barium sulfate formed
was filtered off. The volume was reduced until compound 1 started to precipitate, and the
mixture was then refrigerated for further crystallization.
The aqueous solution for the LAXS experiment was a commercial titanyl(IV) sulfate
solution (Sigma–Aldrich) and used as purchased after dilution with deionized water. The
DMSO solution of titanyl(IV) trifluoromethanesulfonate was prepared by dissolving 1 in
freshly distilled DMSO. The compositions of the studied solutions are summarized in
Table 1.
2.3 Single Crystal X-ray Diffraction
Data were collected on a Bruker SMART CCD 1 K diffractometer at ambient temperature,
Table 2. The crystal was mounted in a glass capillary, which was sealed by flame
immediately after mounting. The structure was solved by standard direct methods in the
SHELXL 2014/7 program package [15] and refined isotropically by full matrix least-
squares on F2, and finally in the anisotropic approximation on all non-hydrogen atoms.
Hydrogen atoms were refined using a riding model. All structure solutions were performed
with the SHELXL 2014/7 programs in PC version [15]. One of the coordinating DMSO
ligands was refined with its sulfur atom in two positions, denoted as S6 and S6b, with
partial occupancies of 88.6 and 11.4%, respectively. Also, one of the two trifluo-
romethanesulfonate counter ions was refined with two sets of fluorine and oxygens atoms
with partial occupancies of 54 and 46%, respectively. Selected crystal and experimental
data are summarized in Table 2. The atomic coordinates, bond distances and angles are
available in a Crystallographic Information File (CIF) in the Supplementary Material
section, Table S1. The structure has been deposited to the Cambridge Structure database
with CCDC code 1505833.
Table 1 Compositions (in molÁdm-3), densities (q), and linear absorption coefficients (l) of the aqueous
solution of titanyl(IV) (hydrogen)sulfate acidified with sulfuric acid, and the dimethylsulfoxide (DMSO)
solution of titanyl(IV) trifluoromethanesulfonate studied by LAXS and EXAFS, respectively
Sample
[TiO2?
]
[X-]
[solvent]
q/gÁcm-3
l/cm-1
2À
TiO(SO4Þ2 in watera,b
1.454
1.300
8.594
2.600
27.388
11.272
1.400
1.423
5.64
9.93
TiO(CF3SO3)2 in DMSOb
a
LAXS
b
EXAFS
123

J Solution Chem (2017) 46:476–487
479
Table 2 Crystallographic data and structure refinement details for pentakis(dimethylsulfoxide)-titanyl(IV)
trifluoromethanesulfonate, 1
1
Formula
MW/gÁmol-1
Diffractometer system
[TiO(CH3)2SO)5](CF3SO3)2
752.68
Bruker Smart CCD
0.71073
˚
Radiation (k/A)
Crystal system
Space group
Triclinic
P-1 (No. 2)
10.198(5)
˚
a/A
˚
b/A
13.495(6)
˚
c/A
13.797(6)
a/°
b/°
c/°
99.002(9)
110.814(8)
110.231(8)
1578.5(13)
295(2)
3
˚
V/A
T/K
Z
2
Dc/gÁcm-1
1.584
F2
772
l/mm-1
Crystal size/mm
h range/°
Index ranges
0.816
0.60 9 0.20 9 0.15
2.93–24.93
–11 B h B 11
–14 B k B 14
–7 B l B 15
5575
Measured reflections
Unique reflections
3327
Data/restraints/params
Goodness of fit
4170/24/410
1.092
Refinement method
Final R1, wR2 [I [ 2r(I)]a
Final R1, wR2 [all data]
Full-matrix least-sq. F2
0.0721, 0.2031
0.0856, 0.2216
0.612/–0.795
-3
˚
Max. peak/hole eA
h
h
i.
h
ii
0:5
À
Á
À
Á
P
P
P
P
2
2
a
R values are defined as: R1 ¼ jjFojÀjFcjj= jFoj; wR2 ¼
w Fo2ÀFc2
w Fo2
2.4 XAFS: Data Collection
Titanium K-edge X-ray absorption spectra were recorded at the wiggler beam line 4-1 at
the Stanford Synchrotron Radiation Lightsource (SSRL). The EXAFS station was equip-
ped with a Si[111] double crystal monochromator. SSRL operated at 3.0 GeV and a current
of 97–100 mA in the top up mode. The data collection was performed simultaneously in
the transmission mode, using ion chambers with a gentle flow of nitrogen gas, and in the
fluorescence mode using a 13-element Ge array solid state detector at ambient temperature.
Higher order harmonics were reduced by detuning the second monochromator crystal to
123

480
J Solution Chem (2017) 46:476–487
30% of maximum intensity at the end of the scans. The solutions were placed in cells with
1.0 mm Teflon spacers and 6 lm polypropylene foil windows. The energy scale of the
X-ray absorption spectra was calibrated by assigning the first inflection point of the K edge
of a titanium foil to 4966 eV [16]. For each sample 5 scans were averaged, giving satis-
factory data (k -weighted) in the k-range 2–13 A-1. The EXAFSPAK program package
was used for the data treatment [17].
3
˚
2.5 EXAFS: Data Analysis
The EXAFS oscillations were extracted from raw averaged data using standard procedures
for pre-edge subtraction, spline removal and data normalization. In order to obtain quan-
titative information of the coordination structure of the metal ions, the experimental k3-
weighted EXAFS oscillations were analyzed by non-linear least-squares fits of the data to
the EXAFS equation, refining the model parameters, number of backscattering atoms, Ni,
mean interatomic distances R, Debye–Waller factor coefficients, r2, and threshold energy,
Eo. Data analysis was performed using the EXAFSPAK program package [17]. Model
fitting was performed with theoretical phase and amplitude functions calculated by the
ab initio code FEFF (version 7.02) [18]. The standard deviations reported for the obtained
refined parameters listed in Tables 3 and 4 are those related to the least-squares refine-
ments and do not include any systematic errors. Variations in the refined parameters
obtained using different models and data ranges indicate that the accuracy of the distances
˚
given for the separate complexes is within 0.005–0.02 A, which is typical for well-
defined interactions.
2.6 Large-Angle X-ray Scattering
A large-angle h–h diffractometer was used to measure the scattering of Mo Ka radiation
˚
(k = 0.7107 A) on the free surface of an aqueous solution of titanyl(IV) sulfate acidified
with dilute sulfuric acid. The solution was contained in a Teflon cuvette inside a radiation
shield with beryllium windows. After monochromatization of scattered radiation, by means
of a focusing LiF crystal, the intensity was measured at 450 discrete points in the range
2
Table 3 Mean bond distances, d/A, number of distances, N, temperature coefficients, b/A , and the half-
˚
˚
˚
height full width, l/A, in the LAXS studies of the hydrated (hydrogen)sulfatotitanyl complex in aqueous
solution at ambient room temperature
Speciesa
Interaction
N
d
b
l
(Hydrogen)sulfatotitanyl(IV) complex in solution acidified with dilute sulfuric acid
[Ti(OSO3)2]2- a
Ti=O
1
4
1
4
4
4
2
1.642(5)
2.025(3)
2.21(2)
0.0019(5)
0.0030(2)
0.021(3)
0.06(1)
Ti–Oeq
Ti–Oax
Ti–(O)–S
S–O
0.077(3)
0.20(2)
3.513(6)
1.505(4)
2.458(7)
2.834(8)
0.0068(8)
0.0044(2)
0.0072(5)
0.0214(14)
0.117(6)
0.094(2)
0.120(4)
0.207(7)
SO24À(aq)
OSO4ÁÁÁOSO4
OÁÁÁO
OÁÁÁOb
[Ti(OSO3)2]2- may also be [Ti(OSO3)(OSO3H)]- and/or [Ti(OSO3H)2]
a
b
Intermolecular OÁÁÁO distances including water–water in the aqueous bulk and sulfate oxygen–water
123

J Solution Chem (2017) 46:476–487
481
˚
˚
Table 4 Number of distances, N, mean bond distances, R/A, maximum of bond distance distribution, Rm/A,
2
2
2
˚
Debye–Waller factor coefficients, r /A , refined threshold energy, Eo, amplitude reduction factor, So, and
the error square sum as defined in the EXAFSPAK program package the EXAFS studies of the
dimethylsulfoxide (DMSO) solvated titanyl(IV) ion in solution at room temperature
Scattering
path
N
d
r2
Eo
So2
F
(Hydrogen)sulfatotitanyl(IV) complex in sulfuric acid–water
Ti=O
1
1.646(5)
2.036(4)
2.22(2)
3.96(4)
3.493(7)
3.51(2)
0.0038(7)
0.0064(4)
0.008(2)
0.023(5)
0.0076(6)
0.009(2)
–7.9(1.3)
0.95(9)
11.8
Ti–Oeq
Ti–Oax
MS(TiO4,sq)
TiÁÁÁS
4
1
394
2
4
Ti–O–S
DMSO solvated titanyl(IV)ion in DMSO solution
Ti=O
1
1.646(5)
2.035(4)
2.22(2)
0.0044(7)
0.0064(4)
0.016(2)
0.023(5)
0.0137(6)
0.0046(9)
–7.7(1.2)
0.92(9)
17.8
Ti–Oeq
Ti–Oax
MS(TiO4,eq)
TiÁÁÁS
4
1
394
4.06(4)
2
4
3.193(7)
3.386(9)
Ti–O–S
Solid [TiO(dmso)5](CF3SO3)2, 1
Ti=O
1
1.648(2)
2.040(4)
2.23(1)
0.0034(7)
0.0064(4)
0.0112(8)
0.023(5)
–7.6(8)
0.85(9)
10.2
Ti–O
4
Ti–Oax
MS(TiO4,eq)
TiÁÁÁS
1
394
4.08(4)
2
3
3.200(7)
3.393(9)
0.0055(6)
0.0146(9)
Ti–O–S
1 \ h \ 65° (the scattering angle is 2h). A total of 100,000 counts was accumulated at
each angle and the whole angular range was scanned twice, corresponding to a statistical
uncertainty of about 0.3%. The divergence of the primary X-ray beam was limited by 1° or
1/4° slits for different h regions with overlapping of some parts of the data for scaling
purposes.
All data treatment was carried out by using of the KURVLR program [19] that has been
described in detail previously [20]. The experimental intensities were normalized to a
stoichiometric unit of volume containing one titanium atom, using the scattering factors f
for neutral atoms, including corrections for anomalous dispersion, Df0 and Df00 [21], and
values for Compton scattering [22]. For a better alignment of the intensity function, a
Fourier back-transformation was applied to eliminate spurious (not related to any inter-
˚
atomic distances) peaks below 1.2 A in the radial distribution function [23]. Least-squares
refinements of the model parameters were performed by means of the STEPLR program
Â
Ã
2
[24] to minimize the error square sum U ¼ RwðsÞ Â iexpðsÞ ÀicalðsÞ .
123

482
J Solution Chem (2017) 46:476–487
3 Results and Discussion
3.1 Hydrated Sulfonatotitanyl(IV) Complex
The complexation with sulfate ions stabilizes titanyl(IV) substantially, and in this work the
structure of the hydrated [TiO(SO4)n](2n-2)- or [TiO(HSO4)n](n-2)- complex has been
determined in dilute sulfuric acid; the applied methods cannot distinguish between sulfate
and hydrogensulfate ion bound to titanyl(IV). Due to this fact, below we will refer to the
ion as (hydrogen)sulfate. Two studies on the complex formation of titanyl(IV) sulfate
systems are reported. In one study the formation of two complexes was reported [25, entry
1969BMg], while in the other a very unusual pattern of stability constants with
K1 \ K2 \ K3 is proposed [25, entry 1969VVa]. The experimental radial distribution
function (RDF) from the LAXS measurement of the dilute sulfuric acid aqueous solution of
˚
titanyl(IV) (hydrogen)sulfate shows peaks at 1.5, 2.75 and 4.3 A, and shoulders at 2.0 and
˚
3.6 A, Fig. 1. The strong peak at 1.5 A corresponds to the S–O bond distance within the
˚
28
24
20
16
12
8
Fig. 1 (Top plot) LAXS radial
distribution curves for a
1.454 molÁdm-3 acidic aqueous
solution of titanyl(IV)
(hydrogen)sulfate acidified with
dilute sulfuric acid. Upper part
separate model contributions
(offset: 14) of the hydrated
bis(hydrogen)sulfatotitanyl(IV)
complex (black line), the
hydrated sulfate ion (grey line)
and aqueous bulk (dark grey
line). (Middle plot) experimental
RDF: D(r) - 4pr2 qo (grey line),
sum of model contributions
(black line), and difference (dark
grey line). (Bottom plot) reduced
LAXS intensity functions: s.i(s),
black line; model s.icalc(s), grey
line
4
0
-4
-8
-12
-16
0
2
4
6
8
10
r/Å
1.5
1.0
0.5
0.0
-0.5
-1.0
-1.5
0
2
4
6
8
10
12
14
16
s/Å-1
123

J Solution Chem (2017) 46:476–487
483
˚
(hydrogen)sulfate ion, the broad peak at 2.75 A corresponds to OÁÁÁO and OaqÁÁÁOaq dis-
tances within the (hydrogen)sulfate ion and the aqueous bulk solution, respectively, and the
˚
˚
peak at 4.3 A to the second hydration sphere, TiÁÁÁOII. The shoulder at 2.0 A corresponds to
˚
the equatorial Ti–O bond distances, and the shoulder at 3.6 A to the Ti–(O)–S distance.
The structure parameters for the bis(hydrogen)sulfatotitanyl(IV) ion or complex have been
˚
˚
refined to 1.642(5) A for the Ti=O bond, and 2.025(8) A for the four oxygens in the equatorial
˚
plane and to 2.21(5) A for the oxygen trans to the Ti=Obond, Table 3. The Ti–(O)–S distance
˚
was refined to 3.51(1) A showing that the (hydrogen)sulfate ions bind monodentately to
titanium with a Ti–O–S bond angle close to linearity. The mean S–O bond distance of the
˚
(hydrogen)sulfate ions has been refined to 1.505(2) A, which is slightly longer than for the
˚
hydrated sulfate ion in aqueous solution, 1.495 A [26]. The reason for this difference could be
incomplete hydration as there is not sufficient water in the solution for complete hydration of
the (hydrogen)sulfate ions, and those binding to the titanyl(IV) ion have a distorted S–O bond
distance distribution. A second hydration sphere to the two water molecules binding to
˚
titanium was refined to 4.21(1) A. This indicates that the composition of the predominant
complex in aqueous solution at high (hydrogen)sulfate concentration, according to the LAXS
study, is hydrated [TiO(SO4)2]2-, [TiO(SO4)(HSO4)]-, or [TiO(HSO4)2]. The refined
structural parameters from the LAXS measurement are summarized in Table 3, and the
experimental and the calculated RDFs are shown in Fig. 1, together with the individual
contributions from the respective complexes and ions and intermolecular OÁÁÁO distances.
The EXAFS study on the same aqueous solution as studied by LAXS fully supports the
structural information obtained by LAXS. The structure parameters have been refined to
˚
˚
1.65(1) A for the Ti=O bond, 2.036(8) A for the four oxygens in the equatorial plane and
˚
2.22(4) A for the oxygen in the axial position, Table 1. The Ti–(O)–S single scattering
˚
distance was refined to 3.49(2) A and the corresponding Ti–O–S 3-leg scattering path to
˚
3.51(4) A, showing that the (hydrogen)sulfate ions bind to titanium with an almost linear
Ti–O–S bond angle. The fit of the EXAFS spectrum is shown in Fig. 2, and the refined
structure parameters are given in Table 4.
3.2 Dimethylsulfoxide Solvated Titanyl(IV) Ion
The O-donor solvent DMSO solvates titanyl(IV) well, e.g., as seen in the fact that the only
reported structures of solvated titanyl(IV) ions are two determinations of the chloride salt
[10, 11]. In this study, the structures of the pentakis(DMSO)titanyl(IV) complex in both
solution and in the solid state, as the trifluoromethanesulfonate salt, 1, are reported. The
crystal structure of 1 shows that the pentakis(DMSO)titanyl(IV) unit has an almost iden-
tical structure as the one reported for the chloride salt [10, 11] with a Ti=O bond distance
˚
of 1.644 A, a mean Ti–O bond distance to the equatorially bound DMSO molecules of
˚
˚
2.035 A, and a Ti–O bond distance to the axially bound DMSO molecule of 2.217 A. The
equatorial plane of four DMSO molecules is slightly tilted away from the titanyl double
bond with a mean O=Ti–Oeq bond angle of 97.3°, Table 5. Selected bond distances and
angles are given in Table 5, a comparison of bond distances of structures containing titanyl
ions in Table 6, and the .cif file of 1 in supplementary Table S1. The structure of the
[TiO(OS(CH3)2)5]2? unit is shown in Fig. 3, and its position in the unit cell in supple-
mentary Fig. S1. The structure parameters obtained crystallographically are fully supported
by the EXAFS study with Ti=O, Ti–Oeq and Ti–Oax bond distances of 1.648(8), 2.040(5)
˚
and 2.23(2) A, respectively, Table 4 and Fig. 2.
An EXAFS study of the DMSO solvated titanyl(IV) ion in DMSO solution shows that
the structure in the solid state is maintained in DMSO solution with refined Ti=O, Ti–Oeq
123

484
J Solution Chem (2017) 46:476–487
12
10
8
Fig. 2 The experimental (upper)
and the fitted Fourier-transform
(lower) of the k3-weighted
EXAFS data of the hydrated
bis(hydrogen)sulfatotitanyl(IV)
complex, and the
TiO(SO4)2/aq
TiO2+/dmso
6
4
dimethylsulfoxide solvated
titanyl ion in dimethylsulfoxide
solution and in solid state as
trifluoromethanesulfonate salt;
experimental data, black line;
model, grey line
2
0
-2
-4
TiO(dmso)5(ClO4)2 (s)
2
3
4
5
6
7
8
9
10 11 12 13
k/Å-1
1.6
1.2
0.8
0.4
0.0
TiO(SO4)2/a
TiO2+/dmso
TiO(dmso)5(ClO4)
0
1
2
3
4
5
R- R/Å
˚
Table 5 Selected bond lengths (A) and angles (°) in 1
Bond distances
Bond angles
Ti=O1
Ti–O2
Ti–O5
Ti–O3
Ti–O4
Ti–O6
1.644(4)
O1=Ti–O2
O1=Ti–O3
O1=Ti–O4
O1=Ti–O5
O1=Ti–O6
100.1(2)
95.1(2)
95.6(2)
98.3(2)
176.9(2)
O2–Ti–O3
O2–Ti–O4
O2–Ti–O5
O2–Ti–O6
O3–Ti–O4
O3–Ti–O5
O3–Ti–O6
O4–Ti–O5
O4–Ti–O6
O5–Ti–O6
88.8(2)
2.025(4)
2.032(4)
2.037(4)
2.047(4)
2.217(4)
164.3(2)
88.3(2)
82.2(2)
91.1(2)
166.6(2)
82.8(2)
88.1(2)
82.2(2)
83.8(2)
82.8
Mean O1=Ti–Oeq
97.3
Mean O6–Ti–Oeq
˚
and Ti–Oax bond distances of 1.65(2), 2.035(10) and 2.22(4) A, respectively, Table 4 and
Fig. 2. However, the Debye–Waller coefficients are significantly larger for the complex in
solution than in the solid state, indicating a larger bond distance distribution of the complex
in solution. This is clearly seen in a comparison of the EXAFS spectra collected in solution
and solid state with the same features in the EXAFS spectra but smoothed out in the
solution spectrum, Fig. 2. The structure parameters are summarized in Table 4, and the fit
of the EXAFS data are shown in Fig. 2.
123

J Solution Chem (2017) 46:476–487
485
˚
Table 6 Summary of Ti=O and Ti–O bond distances (A) in isolated titanyl(IV) complexes both in solid
state and solution
Titanyl(IV) Complex
d(Ti=O) d(Ti–Oeq
)
d(Ti–Oax
)
Ref. Method
Solid state
Ba2[TiO(Si2O7)2] (s)
Sr2[TiO(PO4)2]
1.634
1.747
1.650
1.648
1.644
1.648
4*2.001
–
[7]
[8]
XRD
XRD
2.001/2.010/2.022/2.032
2.017/2.021/2.040/2.049
2.025/2.028/2.040/2.047
2.025/2.032/2.037/2.047
4*2.040
2.042
2.223
2.234
2.217
2.23
[TiO(DMSO)5]Cl2(s)
[TiO(DMSO)5]Cl2(s)
[TiO(DMSO)5](CF3SO3)2(s)
[TiO(DMSO)5](CF3SO3)2(s)
[10] XRD
[11] XRD
*
XRD
*
EXAFS
XRD
(C(NH2)3)4[TiO(CO3)3]Á2H2O 1.680
Solution
2.071/2.083/2.088/2.138/2.158 2.230
[9]
[TiO(DMSO)5]2?/DMSO
[TiO(SO4)2]2-/aq
[TiO(SO4)2]2-/aq
1.646
1.642
1.646
4*2.035
4*2.025
4*2.036
2.22
2.21
2.22
*
*
*
EXAFS
LAXS
EXAFS
* Denotes this work
Fig. 3 Structure of [TiO(dmso)5]2? unit in 1. Thermal ellipsoids of 50%. Hydrogen atoms have been
removed for clarity. The lower occupancy sulfur atom on oxygen O6 has been shaded, as is the case with its
dashed bonds
4 Conclusions
The titanyl(IV) ion must be stabilized through complexation or strong solvation, by, e.g.,
(hydrogen)sulfate ion and DMSO, respectively, to be able to exist as individual units as
described in this paper. Without stabilization in aqueous systems, it will immediately be
hydrolyzed to titanium(IV) oxide. The structure of the titanyl(IV) ion consists of a short
123

486
J Solution Chem (2017) 46:476–487
˚
˚
Ti=O bond at ca. 1.64 A, four solvent molecules or ligands at ca. 2.02 A and with a O=Ti–
O bond angle of 95°–100°, and a weakly bound ligand trans to the Ti=O bond with a Ti–O
bond distance of ca. 2.22 A. For a comparison of the titanyl(IV) ion being stabilized by
ligands such as sulfate, phosphate, silicate, and DMSO, see Table 6.
˚
˚
Acknowledgements The study was funded by the Swedish Research Council (Vetenskapsradet). We
gratefully acknowledge the Stanford Synchrotron Radiation Laboratory (SSRL) for the allocation of beam
time and laboratory facilities. Use of the Stanford Synchrotron Radiation Lightsource, SLAC National
Accelerator Laboratory, is supported by the U.S. Department of Energy, Office of Science, Office of Basic
Energy Sciences under Contract No. DE-AC02-76SF00515. The SSRL Structural Molecular Biology Pro-
gram is supported by the DOE Office of Biological and Environmental Research and by the National
Institutes of Health, National Institute of General Medical Sciences (including P41GM103393). The con-
tents of this publication are solely the responsibility of the authors and do not necessarily represent the
official views of NIGMS or NIH.
Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 Inter-
national License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution,
and reproduction in any medium, provided you give appropriate credit to the original author(s) and the
source, provide a link to the Creative Commons license, and indicate if changes were made.
References
1. Inorganic Crystal Structure Database, National Institute of Standards and Technology and FIZ Karl-
sruhe, release 2016/1
2. http://www.nanopartikel.info/en/nanoinfo/materials/titanium-dioxide. Accessed January 2017
3. Bland, J.A.: The crystal structure of barium orthotitanate, Ba2TiO4. Acta Crystallogr. 14, 875–881
(1961)
4. Wu, K.K., Brown, I.D.: The crystal structure of b-bariumtitanate, b-Ba2TiO4, and the bond strength
length curve of Ti-O. Acta Crystallogr. Sect. B 29, 2009–2012 (1973)
5. Guenter, J.R., Jameson, G.B.: Orthorhomic barium orthotitante, a-Ba2TiO4. Acta Crystallogr. Sect. C
40, 207–210 (1984)
6. Schartau, W., Hoppe, R.: Rb2TiO4, ein neues oxotitanat mit det koordinationzahl 4. Z. Anorg. Allg.
Chem. 408, 60–74 (1974)
¨
7. Weiss, C., Hoppe, R.: Was heißt eigentlich Festkorper? Neue molekulare Aspekte am Beispiel Rb2[-
TiO3]. Z. Anorg. Allg. Chem. 622, 1019–1026 (1996)
8. Greenwood, N.N., Earnshaw, A.: Chemistry of the Elements, Chap. 21.3. Elsevier, Amsterdam (2009),
ISBN 978-0-7506-3365-9
9. The IUPAC Stability Constants Database, release 5. Academic Software, Sourby Old Farm, Timble,
Otley, Yorks, LS21 2PW, UK
10. Shpanchenko, R.V., Tsirlin, A.A., Hadermann, J., Antipov, E.V.: Synthesis and crystal structure of a
novel titanyl phosphate, Sr2TiO(PO4)2. Russ. Chem. Bull. Int. Ed. 57, 552–556 (2008)
11. Moore, P.B., Louisnathan, S.J.: The crystal structure of fresnoite, Ba2(TiO)Si2O7. Z. Kristallograph.
Kristallgeom. Kristallphys. Kristallchem. 130, 438–448 (1969)
12. Peng-Ju, L., Sheng-Hua, H., Kun-Yao, H., Ru-Ji, W.: Crystal structure of tetra-guanidinium tri(car-
bonato)oxotitanium(IV) dihydrate, [C(NH2)3]4[TiO(CO3)3]Á2H2O. Inorg. Chim. Acta 175, 105–110
(1990)
13. Rabe, S., Mu¨ller, U.: Oxotitan-addukte mit dimethylsulfoxid: [TiO(OSMe2)5]Cl2 und [Ti4O6(-
OSMe2)12]Cl4Á5Me2SOÁ1/2H2O/Oxotitanium compounds with dimethylsulfoxide: [TiO(OSMe2)5]Cl2
and [Ti4O6(OSMe2)12]Cl4Á5Me2SOÁ1/2H2O. Z. Naturforsch. Teil B 52, 1291–1295 (1997)
14. Enders, M., Rudolph, R., Pritzkow, H.: Synthese und kristallstruktur von pentakis(dimethylsulfoxid)-
oxo-titan(IV)chlorid/Synthesis and crystal structure of pentakis(dimethylsulfoxide)-oxo-titanium(IV)
chloride. Z. Naturforsch. Teil B 52, 496–499 (1997)
¨
15. Sheldrick, G.M.: SHELX 2014/7: Program for Crystal Structure Refinement. University of Gottingen,
¨
Gottingen, Germany (2014)
16. Thompson, A., Attwood, D., Gullikson, E., Howells, M., Kim, K., Kirz, J., Lindau, I., Pianetta, P.,
Robinson, A., Scofield, J., Underwood, J., Vaughan, D., Williams, G., Winick, H.: X-ray Data Booklet,
2nd edn. Lawrence Berkeley National Laboratory, Berkeley (2001)
123

J Solution Chem (2017) 46:476–487
487
17. George, G.N., Pickering, I.J.: EXAFSPAK—A Suite of Computer Programs for Analysis of X-ray
Absorption Spectra. Stanford Synchrotron Radiation Laboratory, Stanford, CA, USA (2000)
18. Zabinsky, S.I., Rehr, J.J., Ankudinov, A., Albers, R.C., Eller, M.J.: Multiple scattering calculations of
X-ray absorption spectra. Phys. Rev. B 52, 2995–3009 (1995)
¨
19. Johansson, G., Sandstrom, M.: Computer programs for the analysis of data on X-ray diffraction by
liquids. Chem. Scr. 4, 195–198 (1973)
˚
¨
20. Stalhandske, C.M.V., Persson, I., Sandstrom, M., Kamienska-Piotrowicz, E.: A large angle scattering
and vibrational spectroscopic study of the solvated zinc, cadmium and mercury(II) ions in N,N-
dimethylthioformamide solution. Inorg. Chem. 36, 3174–3182 (1997)
21. International Tables for X-ray Crystallography, vol. 4. Kynoch Press, Birmingham, U.K. (1974)
22. Cromer, D.T.: Compton scattering factors for aspherical free atoms. J. Chem. Phys. 50, 4857–4859
(1969)
23. 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. Technical Report ORNL-3960, Oak Ridge National Lab-
oratory, Oak Ridge, TN (1966)
24. Molund, M., Persson, I.: STEPLR—A program for refinements of data on X-ray scattering by liquids.
Chem. Scr. 25, 197 (1985)
25. IUPAC Stability Constants Database, Academic Software and Royal Society of Chemistry, entries
1969BMg {Babko, A., Mazurenko, B., Nabivanets, B.: Zh. Neorg. Khim. 14, 2079 (1969)} and
1969VVa {Vasilev, V., Vorobev, P., Belyakova, A. Isvest. VUZ. Khim. 12, 115, (1969)}
26. Vchirawongkwin, V., Rode, B.M., Persson, I.: Structure and dynamics of sulfate ion in aqueous
solution—An ab initio QMCF MD simulation and large angle X-ray scattering study. J. Phys. Chem. B
111, 4150–4155 (2007)
123