19F NMR method for evaluation of the donor site basicity and coordination modes of chelating ligands in the reaction of α-picolinic acid and its derivatives with titanium tetrafluoride

Article abstract of DOI:10.1134/S0036023613110107

It has been shown by the example of TiF₄ complexes with α-picolinic acid (C₅H₅NCOOH, picH) and its esters (picEt and picSiMe₃) in CH₃CN that the ¹⁹F NMR chemical shifts can be used for estimating the basic properties of nonequivalent donor sites of chelating ligands. TiF₄ reacts with picEt to form adducts: the TiF₄(η²-picEt) chelate and trans-TiF ₄(picEt)₂. The reaction of TiF₄ with an equimolar amount of picH yields the cis-TiF₄ (η²-picH) complex with three nonequivalent fluorine positions. The introduction of a ligand excess leads to a change in the chemical shifts of the fluoro complex, which is interpreted to be due to the formation of H-bonded complexes TiF ₄(η²-picH.picH). The introduction of Et₃N, which binds protons, shifts the equilibrium toward the [TiF₄(η ²-pic)]^- anion. The reaction of TiF₄ with picSiMe₃ occurs in an essentially different way. The major species in solution is the [(μ-F)(μ-OOpic)₂(TiF₃) ₂]^- dimer. Its possible isomeric structures are discussed. On the basis of comparison of the chemical shifts of the fluorine atoms trans to the oxygen and nitrogen atoms of the chelate ligand, the conclusion has been drawn that the basicity of the chelate donor sites increases in the series (η²-picEt)TiF₄ < (η²-picH)TiF ₄ < [(η²-pic)TiF₄]^- and that for all the complexes, the basicity of the nitrogen atom of the chelate is higher than that of the oxygen atom.

Full text of DOI:10.1134/S0036023613110107

ISSN 0036ꢀ0236, Russian Journal of Inorganic Chemistry, 2013, Vol. 58, No. 11, pp. 1330–1334. © Pleiades Publishing, Ltd., 2013.
Original Russian Text © E.G. Il’in, A.V. Tyuremnov, 2013, published in Zhurnal Neorganicheskoi Khimii, 2013, Vol. 58, No. 11, pp. 1484–1489.
PHYSICAL METHODS
OF INVESTIGATION
19F NMR Method for Evaluation of the Donor Site Basicity
and Coordination Modes of Chelating Ligands in the Reaction
of
α
ꢀPicolinic Acid and Its Derivatives with Titanium Tetrafluoride
E. G. Il’in and A. V. Tyuremnov
Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences,
Leninskii pr. 31, Moscow, 119991 Russia
Received December 14, 2012
Abstract—It has been shown by the example of TiF complexes with αꢀpicolinic acid (C H NCOOH, picH)
4
5 5
19
and its esters (picEt and picSiMe3) in CH CN that the F NMR chemical shifts can be used for estimating
3
the basic properties of nonequivalent donor sites of chelating ligands. TiF4 reacts with picEt to form adducts:
2
the TiF4(
η
ꢀpicEt) chelate and trans
ꢀ
TiF (picEt)2. The reaction of TiF with an equimolar amount of picH
4
4
2
yields the cis
ꢀ
TiF (
η
ꢀpicH) complex with three nonequivalent fluorine positions. The introduction of a
4
ligand excess leads to a change in the chemical shifts of the fluoro complex, which is interpreted to be due to
2
the formation of Hꢀbonded complexes TiF4(
tons, shifts the equilibrium toward the [TiF4(
η
ꢀpicH⋅⋅⋅picH). The introduction of Et N,which binds proꢀ
3
2
ꢀpic)]– anion. The reaction of TiF4 with picSiMe3 occurs in
η
–
an essentially different way. The major species in solution is the [(
μꢀF)(
μ
ꢀOOpic) (TiF ) ] dimer. Its possiꢀ
2
3 2
ble isomeric structures are discussed. On the basis of comparison of the chemical shifts of the fluorine atoms
trans to the oxygen and nitrogen atoms of the chelate ligand, the conclusion has been drawn that the basicity
2
2
2
ꢀpic)TiF4]– and that
η
of the chelate donor sites increases in the series
(
η
ꢀpicEt)TiF < (η ꢀpicH)TiF < [(
4
4
for all the complexes, the basicity of the nitrogen atom of the chelate is higher than that of the oxygen atom.
DOI: 10.1134/S0036023613110107
One of the first works where correlations between stant of fluorine nuclei due to electron density transfer
the 19
NMR chemical shifts of mixedꢀligand fluoro from the fluorine atom to the
orbitals of the metal
F
d
complexes and the basicity of monodentate ligands have atom and the increase in the covalent character of the
been revealed was the study of alkoxy tungsten pentafluꢀ metal–fluorine bond. For titanium tetrafluoride comꢀ
orides WF OR [1]. In studying the TаF5 adducts with plexes with monodentate ligands cis
ꢀ
TiF4L2 (L =
5
phosphorylꢀcontaining bases TаF OP(PhX) with difꢀ CH CN, Et O, H O, (MeO) PO, Ph PO, DMSO), a
5
3
3
2
2
3
3
19
ferent X substituents in the aromatic rings [2], there correlation has been observed [6] between the
F
have been established linear dependences of 19
F
NMR NMR chemical shifts and the Gutmann donor numꢀ
chemical shifts on the parameters characterizing the
donor ability of ligands: the Hammett–Taft and
Kabachnik constants. The remoteness of X from the
donor atom made it possible to ignore steric factors
and attribute the changes in ligand basicity to elecꢀ
tronic effects. Correlations have been observed
bers of the ligands (DN), the enthalpy of formation of
molecular complexes of these ligands with SbCl5 [7].
The present work has focused on studying the appliꢀ
cability of 19
F NMR chemical shifts to the evaluation of
the basic properties of nonequivalent donor sites of
chelating ligands that differ in the nature of the donor
atom or in steric factor, using titanium tetrafluoride
31
between the P NMR chemical shifts and the extracꢀ
tion ability of phosphorylꢀcontaining extractants [3].
19
complexes with
α
ꢀpicolinic acid (С H NCOOH,
It has been demonstrated that the
F
NMR chemical
5 5
picH) and its derivatives, С H NCOOEt (picEt) and
shifts of [EFnL6 – n] complexes relative to the signals of
5
5
С H NCOOSiMe
(picSiMe3), in CH CN as an
3
the corresponding [EF ] hexafluorides can be used for
5
5
3
6
example. These ligands have three donor atoms capaꢀ
assessing the ligand L–central ion bond character
(
donor–acceptor, covalent, multiple), as well as the ble of forming complexes. The best studied among
relative bond strength of nonequivalent fluorine atoms them is
α
ꢀpicolinic acid. It is usually coordinated in
[
4, 5]. The strengthening (shortening) of the bond the anionic form through two donor sites (the nitrogen
0
between the fluorine atom and the central ion in
d
ꢀ
and oxygen atoms) to produce a fiveꢀmembered cheꢀ
transition metal complexes correlates with the downꢀ late ring [8, 9]. Taking into account that the basic type
field shift of 19
F
0
NMR signals caused by the decrease of mutual ligand influence in d ꢀtransition metal
in the diamagnetic contribution and the increase in complexes is trans influence, we may assume that the
the paramagnetic contribution to the shielding conꢀ difference in basicity between the chelate donor atoms
1330

19F NMR METHOD FOR EVALUATION OF THE DONOR SITE BASICITY
1331
19
F NMR parameters of the product of the reaction of TiF with picolinic acid and its derivatives
4
Chemical shift, ppm
F2 F3
SSCC, Hz
Complex
δ
F1
δ
δ
δ
Fbr
J
(F F )
1
2
J
(F F )
1
3
J
(F F )
2
3
(
η
2ꢀpicH)TiF4
120.0
122.0
207.4
274.5
115.0
152.7
130.9
108.6
265.6
172.7
159.2
176.6
266.9
164.1
213.5
183.2
171.5
190.3
32
44
49
50
32
39
39
34
[(
η
2ꢀpic)TiF4]–
36
2
(η
ꢀpic)TiF NEt
36
38
3
3
–
[
[
(
(
μ
ꢀF)(
μꢀp
ic) (TiF ) ]
–21.2
–19.0
161*
50**
2
3 2
–
TiF picEt]
5
η
2ꢀpicEt)TiF4
227.9
38
53
transꢀTiF (picEt)
4
2
–
[
[
TiF NEt ]
167.4
34
5
3
–
Ti F ]
2
9
1
2
*
J(F F ). ** J(F F ).
br br
will be mainly reflected in the chemical shifts of the triplets of the same intensity at 227.8 and 213.1 ppm
fluoride ions trans to the respective donor atoms. and the line with an unresolved fine structure
ТiF4 was synthesized by fluorination of the metal (expected to a doublet of doublets) with twice as large
with elemental fluorine followed by sublimation and intensity at 152.7 ppm (Fig. 1, table).
condensation in a fluorine flow. The derivatives of
picolinic acid were synthesized in the laboratory of signals to the molecular adduct (
The intensity ratio 1 : 1 : 2 allowed us to assign these
2
η
ꢀpicEt)TiF (1),
4
Academician V.P. Kukhar’ (Institute of Organic with three nonequivalent fluorine positions (table), in
Chemistry, National Academy of Sciences of which the ester is bidentately coordinated to the cenꢀ
Ukraine). For study, a 20% TiF4 solution in dry tral ion through the nitrogen atom and the terminal
CH CN was prepared. Into this solution, an equimoꢀ oxygen atom of the C(O)OEt group. The singlet at
3
lar amount of a ligand was initially introduced, and 130.9 ppm indicated the presence of the transꢀ
then its excess was gradually added. 19
F NMR spectra TiF (picEt)2 tetrafluoro complex (
2
4
), containing two
were recorded on a Bruker WPꢀ80 spectrometer. The ester molecules monodentately coordinated, in our
19
F chemical shifts were measured from CCl3F
.
opinion, through the nitrogen atom (table). The forꢀ
The major species in a TiF4 solution in CH CN mation of only the trans isomer with monodentately
3
were the molecular adduct TiF (CH CN)2, the cis
[
ꢀ
coordinated ester molecules can be attributed to steric
TiF (CH CN) ] cation, the [Ti F ] anion, and hindrances.
4
3
+
3 3 3 2 9
–
dimeric and polymeric titanium complexes containing
The introduction of a ligand excess had no effect on
fluoride ions and acetonitrile molecules in the inner the 1 F chemical shifts of the fluorine atoms in the
9
4n – x
sphere with fluorine bridges, [Ti F (CH CN) ]
complexes. At the same time, the signal of the dimeric
n
x
3
y
–
[
10].
anion [Ti F ] with three fluorine bridges disappeared,
2
9
After the introduction of an equimolar amount of and doublet and quintet appeared (table) due to the
–
the picEt ester into the initial solution of TiF4 in formation of the pentafluoro complex [TiF picEt]
5
19
CH CN, the F NMR spectrum showed, in addition
(3)
, in which the ester was monodentately coordinated
3
to the strong signals of polymeric titanium complexes through the nitrogen atom. The relative concentraꢀ
4n – x
with fluorine bridges [Ti F (CH CN) ]
, three sigꢀ tions of tetrafluoro complexes
1 and 2 somewhat
n
x
3
y
nals with the intensity ratio 1 : 1 : 2: two doublets of increased.
F1
F1
Ti
F2
N
F1
Ti
N
F2
F1
F2
EtOOC
N
N
Ti
F1
2
COOEt
F
F3
C
1 COOEt
O
OEt
F
F1
F1
1
3
The introduction of an equimolar amount of picH signals of the TiF (CH CN) adduct and the trifluoꢀ
4
3
2
into the initial solution led to the disappearance of the ride cation, a decrease in the concentration of polyꢀ
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 58 No. 11 2013

1332
IL’IN, TYUREMNOV
D''
C''
C
C'
B'
C'
D'
D
B
D
B''
B'''
А'
А
А'' + C
А'
А
B
E
B'
200
180
160
140
120
100
80
ppm
250
200
150
100
50
0 ppm
Fig. 2. 19
an excess of
CH Cl2. A, A', and A''—F , F , and
F NMR spectrum of a TiF4 solution in CH CN with
3
Fig. 1. 19
solution in CH CN. А and A'—
F
NMR spectrum of an equimolar TiF –picOEt
4
α
ꢀpicН neutralized with an Et N solution in
3
1
2
4
–
1
3
2
2
F
and
F
in [Ti F ] ; B,
F
in
(
η
ꢀpic)TiF NEt3;
3
2
9
2
3
n
–
x
2
1
2
B', B'', and B'''—F’s in [Ti F (CH CN) ]
; C, C', and
B and B'—
F
and
F
in cis
ꢀ
TiF (NEt ); C and C'—
F
and
n
in
x
(
3
y
4
3
3
2
1
2
1
–
3
2
1
2
η
C''—F , F , and
F
η
ꢀpicEt)TiF4; D—trans
ꢀ
F
in [TiF NEt ] ; D, D', and D''—F , F , and
F
in [(
ꢀ
5
3
ꢀ
2–
TiF (picEt)2.
pic)TiF4] ; E—[TiF6] .
4
meric titanium complexes, and the appearance of appearance of the fine structure of resonance lines but
three signals at 183.2, 172.7, and 120.0 ppm with the also in further change in the chemical shifts of the sigꢀ
1
: 1 : 2 intensity ratio. The fine structure of these sigꢀ nals of the tetrafluoro complex. The upfield signal due
nals was not observed even when the solution was to the trans fluorine atoms shifted only slightly (to
gradually cooled to freezing (240 K). Taking into 121.3 ppm); on the contrary, the signals of the fluorine
account the intensity ratio, we assigned these signals to ions trans to the donor atoms of the bidentately coorꢀ
the cisꢀtetrafluoro titanium complex with three nonꢀ dinated ligand shifted more significantly to 178.9 and
equivalent fluorine positions in which the ligand was 168.4 ppm, respectively. In addition, three weak sigꢀ
bidentately coordinated to the central ion through the nals of equal intensity appeared in the spectrum at
nitrogen and oxygen atoms. However, two complexes 207.4, 190.3, and 176.6 ppm.
could be consistent with this assignment: the molecuꢀ
After the introduction of an Et N excess into the
solution, all signals in the spectrum had a fine strucꢀ
ture (Fig. 2). The strong doublet of doublets (D'') at
2
3
lar adduct (
η
ꢀpicН)TiF (4), in which the ligand
4
forms with the titanium cation two donor–acceptor
2
–
bonds, and the [(
η
ꢀpic)TiF4] anion (5), in which the
1
22.0 ppm and two doublets of triplets (D, D') at 171.5
and 159.2 ppm of twice lower intensity than the
upfield signal were assigned to chelate anion
oxygen ion is covalently bound to the titanium ion.
5.
F1
Ti
F1
Ti
Three lines (doublets of doublets) of the same
F2
F3
F2
F3
N
N
intensity A, A' and A'' (Fig. 2, table) were assigned to
2
the molecular complex (
η
ꢀpic)TiF NEt (
6), conꢀ
3
3
C
C
O
OH
O
O
taining three nonequivalent fluoride ions. In addition,
F1
F1
the signals of pentaꢀ and tetrafluoro complexes with
–
triethylamine [TiF NEt ] (
7)
and cis
ꢀ
TiF (NEt ) (
8)
4
5
5
3
4
3 2
appeared in the spectrum.
The introduction of a ligand excess into the soluꢀ
tion led to a further decrease in the concentration of
polymeric species. The chemical shifts of the tetrafluꢀ
oro chelate complex somewhat changed being 181.5,
F1
F2
Ti
F1
F2
F3
F1
F1
F1
N
F2
NEt3
NEt3
1
71.3, and 120.6 ppm, respectively. The lack of the fine
Ti
Ti
C
F1 F2
structure of the resonance lines is evidence of
exchange processes in the system and can be caused by
the presence of protons. To bind these protons and
eliminate the proton from the OH group of the coorꢀ
dinated ligand, we introduced into the NMR tube a
stronger base (Et N) as a solution in CH Cl2. Indeed, ions trans to the chelating ligand (with an increase in
the addition of the amine resulted not only in the the basicity of a medium) pointed to the weakening of
O
O
F1
NEt3
NEt3
6
7
8
The upfield displacement of the signals of fluoride
3
2
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 58 No. 11 2013

19F NMR METHOD FOR EVALUATION OF THE DONOR SITE BASICITY
1333
their bond to the central ion and, hence, to the equimolar amount of the ligand led to the deposition
strengthening of the bond to the donor atoms of the of a precipitate and to the appearance in the 19
NMR
chelant. Previously [11, 12], we observed the change in spectrum of the signal of Me SiF; i.e., some of fluoride
F
3
the 19
ligand) fluorine atom of the EF LH complexes (E = P, major titanium species in the solution was [(
F
NMR chemical shifts of the axial (trans to the ions were transferred from titanium to silicon. The
ꢀF)(
As; LH = alcohols, amines) caused by the formation рic) (TiF ) ] , which was responsible for three multipꢀ
μ
μ
ꢀ
5
–
2
3 2
of hydrogen bonds involving the hydrogen atom of the lets in the spectrum: a doublet of triplets, a doublet of
coordinated ligand and free ligand molecules. The doublets, and a triplet of triplets with the 2 : 4 : 1 intenꢀ
concomitant polarization of the LH bond of the ligand sity ratio (table).
in the first coordination sphere leads to an increase in
the basicity of the coordinated nitrogen and oxygen
donor atoms. The observed change in the chemical
shifts of the titanium tetrafluoro complexes can be a
The upfield position of the weakest signal (triplet of
triplets) at –21.2 ppm, in the range of signals of bridgꢀ
ing fluorine atoms, enabled the conclusion that the
complex is dimeric. A specific feature of complexes
with fluorine bridges is a significant difference
proof of the formation in solution of hydrogen bonds
2
between the molecular adduct
(
η
ꢀpicН)TiF4 and the
between the spin–spin coupling constants J(FF) of
free base. As a result, the polarization of the OH bond
leads to an increase in electron density on the donor
atoms of the coordinated chelant, which is responsible
for the change in the chemical shifts of the fluorine
atoms trans to the donor atoms.
the bridging fluorine nucleus to the fluorine nuclei
being cis and trans to it. For the latter, the constant is
two–threefold larger than for the cis fluorine nuclei.
On the basis of the observed fine structure parameters
(
table), the doublet of triplets in the lowest field, which
This enables the conclusion that the reaction of
was twice as strong as the signal of the bridging fluoꢀ
rine, was assigned to two fluorine atoms trans to the
fluorine bridge in the dimer. The third multiplet, a
doublet of doublets, which was four times stronger
than the signal of the fluorine bridge, is evidence of the
presence of two equivalent terminal fluorine atoms in
each of the dimer fragments. Inasmuch as the chelatꢀ
equimolar amounts of the reagents in solution leads to
2
the molecular complex [
(
η
ꢀpicН)TiF4] (table), which
forms a hydrogenꢀbonded complex with the free
ligand, and that the introduction of an analogous or
stronger (Et N) base leads to the elimination of the
3
proton from the coordinated ligand to form anion
table).
Reactions that occur in a CH CN solution can be
2
(
–
ing or bridging coordination of the pic anion through
3
the nitrogen and oxygen atoms would lead to nonꢀ
equivalence of the fluorine atoms trans to them, which
is not the case, we can state that the ligand is bidenꢀ
tately coordinated through two oxygen atoms to form
presented by the scheme:
2
TiF +
4
α
ꢀpicH
→
(η ꢀpicН)TiF
4
4n –
+
[Ti F (CH CN) ] x,
n
x
3
y
TiF4(
2
chelate
9 or bridge 10. Since fourꢀmembered chelate
2
2ꢀpicН…picН),
rings are unstable, we believe that dimeric structure 10
(
η
ꢀpicН)TiF +
4
α
ꢀpicH
→
η
is the most probable. In addition to the fluorine bridge,
two pic anions form bridges through the oxygen
2
–
+
(
η
ꢀpicН)TiF + Et N
3
→
[(
η
ꢀpic)TiF ] + Et NH
ꢀ
4
4
3
2
–
+
(
η
ꢀpic)TiF NEt + [TiF NEt ] + cisꢀTiF (NEt ) .
−
3
3
5
3
4
3 2
atoms: {(
μ
ꢀF)[
μ
(О,О)ꢀрic]2(TiF3)2
(10). Such a coorꢀ
The reaction of TiF4 with the trimethylsilyl ester dination mode for carboxylate anions is well known
picSiMe3 appreciably differed from the above reacꢀ [13]; however, for the picolinate anion, this coordinaꢀ
tion. The introduction in the initial solution of an tion mode is observed for the first time.
N
N
C
C
F1
F1
O
F1
O
O
F1
F1
O
O
O
O
F2
F2
F2
F2
Ti
Fbr
Ti
C
Ti
Fbr
C
Ti
F1
F1
F1
O
N
N
9
10
Thus, as distinct from picolinic acid and its ethyl SiMe3F and to the unusual coordination mode of the
ester, the reaction of picSiMe3 with TiF4 leads to fluoꢀ picolinate anion (as a bridging group) through two
rine transfer from tetrafluoride to silicon to form oxygen atoms of the carboxylate group.
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 58 No. 11 2013

1334
IL’IN, TYUREMNOV
δ
Ftr, ppm
F
2
60
40
20
00
80
60
40
CH CN
3
Ftr
Ftr
N
Ti
2
2
2
1
1
1
O
O
picꢀEt
Et O
2
F
H O
2
N
(
MeO) PO
3
Ph PO
3
picH
Me
2
SO
O
pic–
N
O
N
14
16 18 20 22 24 26 28 30 32 34 36 DN
Fig. 3. Correlation of 19F NMR chemical shifts with the Gutmann donor number DN for fluoride ions trans to the ligand L (F )
tr
2
2
in the TiF L complexes (L = CH CN, Et O, H O, (MeO) PO, Ph PO, DMSO) and (
(
η
ꢀpicEt)TiF , ( ꢀpicH)TiF4, and
η
4
2
3
2
2
3
3
4
2
–
[( ꢀpic)TiF4] chelates.
η
Comparison of the relative position of the signals of
ACKNOWLEDGMENTS
fluorine atoms trans to the oxygen and nitrogen atoms
of the chelating ligand enables the conclusion that, in
all complexes, the basicity of the nitrogen atom of the
chelate is higher than that of the oxygen atom and
This study was carried out in the framework of the
program of the Presidium of the RAS “Development
and Improvement of Methods of Chemical Analysis
and Investigation of the Structures of Substances and
Materials.”
2
2
increases in the series
(
η
ꢀpicEt)TiF < ( ꢀpicH)TiF , <
η
4
4
[
(
ꢀpic)TiF4]–. The 19F NMR shifts of the cisꢀtetꢀ
η
2
rafluoro titanium complexes are summarized in the
table. It was of interest to quantify the basic properties
of the donor atoms of the chelates. To do this, we used
the previously observed correlation between the
REFERENCES
1. F. E. Brinckman, R. B. Johannesen, R. F. Hammerꢀ
19
F NMR chemical shifts of titanium tetrafluoride
complexes with monodentate ligands cis TiF4L2 (L =
CH CN, Et O, H O, (MeO) PO, Ph PO, DMSO)
schmidt, and L. B. Handly, J. Fluorine Chem.
(1975).
6, 427
ꢀ
3
2
2
3
3
2. E. G. Il’in, M. E. Ignatov, Yu. A. Buslaev, and
and the DN of these ligands [6] (Fig. 3). Plotting the
chemical shift values for the fluorine atoms trans to the
chelate ring on this diagram allows us to estimate, on
the basis of DN, the basic properties of the donor sites
of the chelating ligands under consideration.
A. A. Shvets, Dokl. Akad. Nauk SSSR 240, 865 (1978).
3
4
5
6
7
. V. V. Yakshin, N. M. Meshcheryakov, E. G. Il’in, et al.,
Dokl. Akad. Nauk SSSR 278, 162 (1984).
. Yu. A. Buslaev and E. G. Ilyin, J. Fluorine Chem. 25
,
5
7 (1984).
The DN values for the oxygen and nitrogen atoms of
the chelate of the ethyl ester coordinated in the molecꢀ
ular form are 20.5 and 24 and are close to the basicity
of Et О and (МеО) РО, respectively. For the anion of
. Yu. A. Buslaev and E. G. Ilyin, Sov. Sci. Rev. Sect. B:
Chem. Rev. , 1 (1987).
1
. G. B. Nikiforov, Candidate’s Dissertation in Chemistry
IONKh RAN Moscow, 2000).
2
3
(
–
the chelating ligand pic , the respective DN values are
close to 34 and 37; i.e., when the hydroxyl proton is
removed from the coordinated ligand, the donor propꢀ
erties of the chelate oxygen and nitrogen atoms
become more pronounced than those of the oxygen
atom of such a strong donor as DMSO. The relatively
small differences between the chemical shifts of the
. V. Gutmann, Coordination Chemistry in NonꢀAqueous
Solutions (Springer, BerlinꢀNew York, 1968).
8. Z. Szabo and I. Grenthe, Inorg. Chem. 37, 6214
(1998).
9
. E. G. Il’in, M. N. Shcherbakova, M. E. Ignatov, et al.,
Dokl. Akad. Nauk SSSR 283, 904 (1985).
2
ꢀpic)TiF4]– anion and the
2
[(
η
( ꢀpicН)TiF4 complex
η
1
1
1
1
0. E. G. Il’in, G. B. Nikiforov, M. E. Ignatov, and
can point either to a high degree of proton dissociation
of the latter on to the polarization of the OH bond of
the coordinated ligand due to the formation of a
hydrogen bond with the free chelant [11, 12].
Yu. A. Buslaev, Dokl. Chem. 369 (4–6), 299 (1999).
1. Yu. A. Buslaev, E. G. Il’in, and A. P. Nazarov, Dokl.
Akad. Nauk SSSR 244, 897 (1979).
2. Yu. A. Buslaev, E. G. Il’in, U. Kalov, and L. Kolditts,
Thus, it has been shown that 19
F NMR chemical
Dokl. Akad. Nauk SSSR 270, 1148 (1983).
shifts are applicable to the estimation of coordination
modes and basic properties of the donor sites of
chelating ligands that differ in the nature of donor
atom and steric hindrance.
3. D. P. Bullivant, M. F. A. Dove, and M. J. Haley,
J. Chem. Soc. Dalton, No. 1, 109 (1980).
Translated by G. Kirakosyan
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 58 No. 11 2013