Oxidation of Iron Complex with NHC Ligand with Molecular Iodine

Article abstract of DOI:10.1134/S0036023619110184

Abstract: Complex (η⁵-C₅H₅)₂Fe₂(CO)₄ (I) reacts with 1,3-dimethylimidazolium-2-carboxylate Me₂ImCO₂ to give asymmetric binuclear carbene iron complex (η⁵-C₅H₅)₂Fe₂(CO)₃(Me₂Im) (II) (Me₂Im = 1,3-dimethylimidazol-2-ylidene). The oxidation of compound II with elemental iodine proceeds via two mechanisms, symmetrical and asymmetrical, to form four products: (η⁵-C₅H₅Fe(CO)₂(Me₂Im)I (III), (η⁵-C₅H₅)Fe(CO)₂I (IV), (η⁵-C₅H₅Fe(CO)₂(Me₂Im)I₃ (V), and ferrocene (VI). In each case, two pairs of reaction products have formed, two of which include NHC ligand: neutral iron(III) complex and ionic complex V. Optimal synthesis conditions to obtain preferably one of these complexes have been found. Geometry and transition state energy of supposed reaction mechanism have been calculated by quantum chemistry methods.

Full text of DOI:10.1134/S0036023619110184

ISSN 0036-0236, Russian Journal of Inorganic Chemistry, 2019, Vol. 64, No. 11, pp. 1418–1423. © Pleiades Publishing, Ltd., 2019.
Russian Text © The Author(s), 2019, published in Zhurnal Neorganicheskoi Khimii, 2019, Vol. 64, No. 11, pp. 1191–1197.
COORDINATION
COMPOUNDS
Oxidation of Iron Complex with NHC Ligand with Molecular Iodine
S. S. Shapovalova, *, O. G. Tikhonovaa, I. V. Skabitskiia,
A. V. Kolosa, S. G. Sakharova, and Yu. V. Torubaev a
aKurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences, Moscow, 119991 Russia
*e-mail: schss@yandex.ru
Received April 17, 2019; revised April 24, 2019; accepted May 13, 2019
Abstract—Complex (η5-C5H5)2Fe2(CO)4 (I) reacts with 1,3-dimethylimidazolium-2-carboxylate Me2Im-
CO2 to give asymmetric binuclear carbene iron complex (η5-C5H5)2Fe2(CO)3(Me2Im) (II) (Me2Im = 1,3-
dimethylimidazol-2-ylidene). The oxidation of compound II with elemental iodine proceeds via two mech-
anisms, symmetrical and asymmetrical, to form four products: (η5-C5H5Fe(CO)2(Me2Im)I (III), (η5-
C5H5)Fe(CO)2I (IV), (η5-C5H5Fe(CO)2(Me2Im)I3 (V), and ferrocene (VI). In each case, two pairs of reac-
tion products have formed, two of which include NHC ligand: neutral iron(III) complex and ionic complex V.
Optimal synthesis conditions to obtain preferably one of these complexes have been found. Geometry and tran-
sition state energy of supposed reaction mechanism have been calculated by quantum chemistry methods.
Keywords: cyclopentadienyl, 1,3-dimethylimidazolium-2-carboxylate, carbene, carbonyl
DOI: 10.1134/S0036023619110184
The electrophilic attack of halogens on the metal–
metal bond in coordination compounds often leads to
the cleavage of this bond and formation of one reac-
tion product in the case of symmetric dimers, for
example [(η5-C5Me5)Fe(CO)2]2 [1]. The number of
reaction products increases upon oxidation of asym-
metric binuclear complexes, for example on the pre-
liminary substitution of CO groups by different
ligands. So, the bromination of phosphine complex
Mn2(CO)9(PPh3) leads to Mn(CO)5Br, cis- and trans-
Mn(CO)4Br(PPh3) [2]. At the same time, binuclear
complexes persistent to halogens are known. The reac-
tion of elemental iodine (chlorine) with phosphine com-
plex MoRu(CO)6(dppm)2 (dppm is bis-diphenylmeth-
ane) containing bridging CO group leads to retention of
the metal–metal bond. This reaction leads to formation
When the corresponding dimer is unavailable, the
order of ligand introduction into complex can be
changed. For preparing phosphine iodide (η5-
C5Me5)Fe(dppe)I (dppe = 1,2-bis(diphenylphos-
phino)ethane), iodine atom and next phosphine are
introduced in complex molecule. The substitution of
CO groups by dppe in complex (η5-C5Me5)Fe(CO)2I
proceeds photochemically [1]. The oxidation of resul-
tant (η5-C5Me5)Fe(dppe)I with ferricinium cation
leads to formation of 17-electron paramagnetic com-
−
plex (η5-C5Me5)Fe(dppe)+PF6 [4]. However, the
thermal reaction of the corresponding chlorine-con-
taining complex (η5-C5H5)Fe(CO)2Cl with dppe leads
only to ionic complex (η5-C5H5)Fe(CO)(dppe)+Cl–
of ionic compound [(CO)2Mo(dppm)2(μ-X)(μ- [5]. A neutral iron iodide complex containing N-het-
CO)Ru(CO)2]+[Mo(CO)4X3]−, where cation includes
a bridging halogen atom [3].
erocyclic carbene (NHC) as a ligand was obtained in
two stages from C5H5Fe(CO)2I (Scheme 1) [6]:
I
N stirring
20 h
hν, 16 h
Fe
+
Fe
Fe
I
N
CO
CO
I
N
N
CO
OC
CO
N
N
58%
86%
Scheme 1.
1418

OXIDATION OF IRON COMPLEX WITH NHC LIGAND WITH MOLECULAR IODINE
1419
At the first stage, (η5-C5H5)Fe(CO)2I reacts with
in toluene (10 mL) for 1 h on cooling with an isopro-
panol–liquid nitrogen mixture. The color of the mix-
ture became brown. The reaction mixture was stirred
for 1 h and the solvents were removed under reduced
pressure. The brown–green residue was extracted with
CH2Cl2 (10 mL), the product was precipitated with
hexane (7 mL) and reprecipitated from CH2Cl2–hex-
free carbene Me2Im (Me2Im = 1,3-dimethylimidazol-
2-ylidene) to give cationic complex (η5-
C5H5)Fe(CO)2(Me2Im)+I–. Further prolonged pho-
tochemical reaction of ionic complex leads to forma-
tion of neutral complex (η5-C5H5)Fe(CO)(Me2Im)I.
Similar iron complexes containing both carbonyl
ligands [7] and coordinated NHC ligand [8] are widely
used in homogeneous catalysis. In this work, we stud-
ied an alternative approach to the preparation of (η5-
C5H5)Fe(CO)(Me2Im)I: the oxidation of binuclear
iron carbene complex with molecular iodine.
ane mixture. Compounds III, (η5-C5H5)Fe(CO)2I
(IV), and ferrocene (VI) were isolated from the resid-
ual green solution by column chromatography (eluents
are hexane, benzene, and CH2Cl2, respectively). A
single crystal suitable for X-ray diffraction study was
obtained by pentane vapor diffusion into a saturated
solution of II in CH2Cl2. Yield: green powder, 0.100 g,
39%. The results of elemental analysis are given below.
EXPERIMENTAL
All manipulations for the synthesis and isolation of
compounds were performed under an argon atmo-
sphere in anhydrous solvents. Compound Me2ImCO2
was obtained by procedure [9]. Commercial chemicals
[(η5-C5H5)Fe(CO)2]2 (I) and I2 were used without
additional purification. Elemental analysis was per-
formed with the use of an EuroVector ЕА3000 CHNS
analyzer. IR spectra were obtained on a Bruker Alpha
FTIR spectrometer with a Platinum ATR add-on unit.
For C11H13FeIN2O, anal. calcd. (%): C, 32.52; H,
3.52; N, 7.53.
Found (%): C, 32.10; H, 3.35; N, 7.28.
1H NMR (CDCl3, δ, ppm): 4.09 (s, 6H, 2Me),
4.48 (s, 5H, C5H5), 7.01 (s, 2H, CH); 13C NMR
(CDCl3, δ, ppm): 40.9, 80.1, 124.3, 185.7, 223.8.
ATR-FTIR (ν, cm–1): 3167 (vw), 3105 (vw, br),
2946 (vw, br), 2041 (vw), 1993 (vw), 1918 (vs, br), 1576
(vw), 1453 (vw), 1425 (vw), 1397 (vw), 1371 (vw), 1356
(vw, br), 1305 (vw), 1224 (vw), 1116 (vw), 1081 (vw),
1001 (vw), 840 (vw), 818 (vw, br), 750 (vw), 727 (vw,
br), 680 (vw), 558 (vw), 533 (vw), 469 (vw), 433 (vw),
422 (vw).
13
1H and C NMR spectra were recorded on a Bruker
Avance 300 spectrometer.
5
Synthesis of (η -C5H5)2Fe2(CO)3(Me2Im) (II). A
brown solution of 0.305 g (0.862 mmol) of [(η5-
C5H5)Fe(CO)2]2 and 0.238 g (1.700 mmol) of Me2Im-
CO2 in a mixture of toluene (10 mL) and acetonitrile
(10 mL) was refluxed for 3 h. The solvents were
removed under reduced pressure and the oily residue
was extracted with toluene (25 mL). The green solu-
tion was filtered, concentrated to 1/4 volume, and kept
at –26°C for 24 h. The green crystals were washed with
pentane (2 × 5 mL) and dried. Crystals suitable for
5
Reaction of (η -C5H5)2Fe2(CO)3(Me2Im) with I2 in
5
СH2Cl2, synthesis of (η -C5H5)Fe(CO)2(Me2Im)I3 (V).
A crimson solution of 0.120 g (0.472 mmol) of I2 in
CH2Cl2 (5 mL) was added dropwise to a green solution
of 0.191 g (0.453 mmol) of (C5H5)2Fe2(CO)3(Me2Im)
in CH2Cl2 (10 mL). The color of the mixture became
X-ray diffraction study were grown by pentane vapor brown. Reaction course was monitored by IR spec-
diffusion into benzene solution of the complex. Yield troscopy. Hexane (10 mL) was added to the brown
of green crystals was 0.205 g, 57%. The results of ele- solution and the mixture was concentrated to 1/2V.
mental analysis are given below.
For C13H13Fe2N2O3, anal. calcd. (%): C, 51.23; H,
4.30; N, 6.64.
The dark green solution was filtered, the brown oily
residue was washed with hexane (2 × 3 mL), dried,
and dissolved in MeCN. Product V was crystallized as
triiodide by Et2O vapor diffusion into a saturated solu-
Found (%): C, 50.60; H, 4.31; N, 6.67.
tion in MeCN. Compounds III, (η5-C5H5)Fe(CO)2I
(IV), and ferrocene (VI) were isolated from dark green
solution by column chromatography (eluents are hex-
ane, benzene, and CH2Cl2 , respectively). Yield:
brown oil, 0.098 g, 54%.
ATR-FTIR (ν, cm–1): 3170 (w), 3117 (w, br), 2947
(w, br), 1920 (vs), 1880 (w), 1698 (vs, br), 1575 (w),
1543 (w), 1448 (m), 1416 (w), 1394 (w), 1352 (m),
1297 (w), 1219 (m), 1175 (w), 1110 (w), 1062 (w, br),
1019 (w), 999 (w), 926 (w), 857 (w), 839 (m), 831 (m),
818 (s), 749 (w), 724 (m), 684 (s), 659 (vs, br), 599 (m),
588 (s), 559 (vs), 511 (m), 468 (m), 452 (m), 443 (m),
427 (w), 419 (m), 408 (m).
1H NMR (CD3CN, δ, ppm): 3.76 (s, 6H, 2Me),
5.29 (s, 5H, C5H5), 7.29 (s, 2H, CH).
ATR-FTIR (ν, cm–1): 3167 (vw), 3093 (vw, br),
2952 (vw), 2037 (vs), 1990 (vs), 1577 (vw), 1460 (w),
1424 (vw), 1399 (vw), 1375 (vw, br), 1359 (vw), 1227
(w), 1127 (vw), 1082 (vw), 1059 (vw), 1004 (vw), 863
(vw), 732 (vw, br), 678 (w), 611 (w), 580 (w), 558 (w),
505 (vw), 472 (vw), 438 (vw), 411 (vw).
5
Reaction of (η -C5H5)2Fe2(CO)3(Me2Im) with I2 in
5
toluene, synthesis of (η -C5H5)Fe(CO)(Me2Im)I (III).
A crimson solution of 0.180 g (0.709 mmol) of I2 in
10 mL of toluene was added dropwise to a green solution
of 0.292 g (0.692 mmol) of (C5H5)2Fe2(CO)3(Me2Im)
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 64 No. 11 2019

1420
SHAPOVALOV et al.
Table 1. Crystallographic data and structure refining parameters for complexes III and IV
Parameter
Molecular formula
FW
III
V
C11H13N2OFeI
371.98
C12H13FeI3N2O2
653.79
Radiation, λ, Å
Temperature, K
Syngony
Space group
а, Å
b, Å
c, Å
α, deg
MoKα, 0.71073
MoKα, 0.71073
150
Monoclinic
P21/n
7.3700(5)
12.2094(8)
13.8458(9)
90
120
Orthorhombic
Pbca
10.9064(7)
15.5051(10)
20.9548(15)
90
β, deg
γ, deg
V, Å3
93.2750(9)
90
1243.86(14)
90
90
3543.6(4)
Z
4
8
ρ(calcd.), g/cm–3
1.986
3.674
2.451
6.080
μ, mm–1
F(000)
720.0
2400.0
Scanning range θ, deg
Scanning mode
4.452–61.062
3.888–59.998
ω
Independent reflections (N1)
Reflections with I > 2σ(I) (N2)
Number of refined parameters
3804 (Rint = 0.0208)
5165 (Rint = 0.0421)
3433
193
4456
183
GOОF (F2)
R1 for N2
wR2 for N1
1.052
0.0186
0.0432
1.036
0.0234
0.0525
Δρmax/Δρmin, e Å–3
0.35/–0.52
1.66/–1.52
X-ray diffraction study was performed on a Bruker
APEX II CCD diffractometer. Crystallographic data
and structure refining parameters for compounds III
and V are given in Table 1. Data were corrected for
absorption with the SADABS program [10]. The
structures of III and V were solved by direct methods
and refined by least squares relative to F2 in anisotro-
pic approximation for non-hydrogen atoms using
SHELX-2014 [11] and OLEX2 [12] software packages.
The coordinates of disordered atoms of the cyclopen-
tadienyl ligand in complex III were refined in aniso-
tropic approximation with confinement of distance
equality and rigid bond confinement for thermal
parameters (SAME and DELU instructions). Posi-
tions of hydrogen atoms were calculated geometrically.
Atom coordinates and other parameters of structures III
and V were deposited in the Cambridge Crystallo-
graphic Data Center (nos. 1910061 and 1910062,
RESULTS AND DISCUSSION
To introduce carbene ligand into monomeric iron
complex, we reacted 1,3-dimethylimidazolium-2-car-
boxylate (Me2ImCO2) with complexes of type (η5-
C5H5)Fe(CO)2L (L
=
I, Cl) and (η5-
C5H5)Fe(CO)2(MeCN)+PF6− on heating in a tolu-
ene–acetonitrile mixture (1 : 1). Dimeric complex
[(η5-C5H5)Fe(CO)2]2 (I) was isolated as a product of
each these reactions. This fact indicates that the het-
erocyclic zwitterion behaves as a reducing agent.
Since the strategy of sequential introduction of
NHC ligand into iodide failed, we used an approach to
obtain carbene iodine-containing iron complex from
the initial dimeric complex. Therefore, we reacted com-
pound I with two equivalents of dimethylimidazolium-
2-carboxylate on heating in a toluene–acetonitrile (1 : 1)
mixture. The reaction resulted in monosubstituted
binuclear iron complex (η5-C5H5)2Fe2(CO)3(Me2Im)
(II) as a sole product, no substitution of next carbonyl
group occurred (Scheme 2).
respectively,
http://www.ccdc.cam.ac.uk/data_re-
quest/cif). The main bond distances and valence
angles are presented in the captions to Figs. 1 and 2.
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OXIDATION OF IRON COMPLEX WITH NHC LIGAND WITH MOLECULAR IODINE
1421
C(9)
C(8)
C(12)
C(6)
C(9)
C(10)
C(8)
C(10)
C(7)
N(1)
C(11)
C(11)
Fe(4)
C(5)
I(1)
C(4)
N(2)
C(1)
C(3)
O(1)
N(1)
C(5)
C(3)
C(7)
C(2)
Fe(1)
C(1)
I(1)
O(2)
I(2)
N(2)
C(4)
C(6)
C(2)
O(1)
I(3)
Fig. 1. Molecular structure of complex III. Hydrogen
atoms are omitted for clarity. The main bond distances
(Å): Fe(1)–I(1), 2.6554(3); Fe(1)–C(1), 1.963(2); Fe(1)–
C(6), 1.747(2).
Fig. 2. Molecular structure of complex V. Hydrogen atoms
are omitted for clarity. The main bond distances (Å):
Fe(4)–C(1), 1.774(3); Fe(4)–C(2), 1.777(3); Fe(4)–
C(3), 1.969(3), I(1)–I(2) 2.9460(3); I(2)–I(3), 2.8849(3).
N
O
O
N
N
2
O
O
N
CO
C
C
Fe
Fe
Fe
Fe
toluene/MeCN
reflux
C
O
C
O
OC
OC
I
II
Scheme 2.
The IR spectrum of complex II shows absorption donor ability of NHC ligand as compared with iso-
bands at 1920 and 1698 cm–1 corresponding to the
stretching vibrations of terminal and bridging carbonyl
groups. The introduction of carbene ligand into com-
plex structure causes a shift of vibration frequency of
bridging CO group to the short-wavelength spectral
region by ∼60 cm–1 (vibration frequencies of CO
groups for [(η5-C5H5)Fe(CO)2]2 in ATR spectrum are
structural phosphine complex [(η5-C5H5)(μ-η5:κ1-
C5H4CH2PPh2)Fe2(μ-CO)2(CO)] obtained by the
photochemical reaction of Ph2PCH2PPh2 with [(η5-
C5H5)Fe(CO)2]2 (vibration frequency of bridging CO
group is 1727 cm–1) [14].
Binuclear monosubstituted carbene complex II
undergoes oxidation with molecular iodine to give
1976, 1953, 1933, and 1758 cm–1, which corresponds
to the trans isomer [13]). This shift indicates a larger σ- four products (Scheme 3):
N
I3
O
N
I2
C
Fe
Fe
Fe
+
+
+
Fe
Fe
Fe
CO
CO
I
CO
N
I
N
C
O
OC
OC
CO
N
N
II
III
IV
VI
V
Scheme 3.
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 64 No. 11 2019

1422
SHAPOVALOV et al.
−
The
isolated
neutral
(III)
complexes
and
[(η5-
nation compounds also often leads to formation of
I3
C5H5)Fe(CO)(Me2Im)I
[(η5-
anion. For example, the long-term reaction of dimer
[(η5-C5Me5)Mo(CO)3]2 with iodine leads to ionic
C5H5)Fe(CO)2I (IV) contain coordinated iodide
ligand and have a three-legged stool structure. Com-
plex III was obtained previously [6] by the photo-
chemical decarbonylation of ionic complex [(η5-
C5H5)Fe(CO)2(Me2Im)+I–, its structure was estab-
lished in this work by X-ray diffraction analysis. Cat-
−
complex [(η5-C5Me5)2Mo2(μ-I)4]+
as the main
product [20]. The oxidation of bivalent platinum com-
plex [Me2Pt(μ-dmpm)2PtMe2] (dmpm is
Me2PCH2PMe2) under the action of halogens leads to
the transfer of methyl group from one metal atom on
neighboring metal atom to give mixed-valence com-
−
I3
ionic
dicarbonyl
complex
[(η5-
C5H5)Fe(CO)2(Me2Im)]I3 (V) containing coordi-
nated 1,3-dimethylimidazol-2-ylidene was isolated
with triiodide anion. Furthermore, ferrocene (VI) was
isolated as the fourth reaction product (Fig. 1).
plex [Me3Pt(μ-dmpm)2(μ-I)PtI]+ [21].
I3
By the analogy with the above mechanism of com-
plex [(η5-C5H5)Fe(CO)2]2 iodination [22], we sup-
posed a reaction mechanism for the iodination of car-
bene binuclear complex II (Scheme 4). Electrophilic
attack at the iron–iron bond leads to formation of
ionic dimer containing a bridging iodine atom. Next,
two possibilities can be realized: nucleophilic attack to
form two neutral complexes with iodide ligands (III
and IV) or asymmetric cleavage to give products V and
VI. The formation of complex IV containing carbene
ligand is caused by the preferable attack of I– nucleop-
hile at more electrophilic iron atom. The remained
[(η5-C5H5)Fe(CO)I] fragment undergoes decarbon-
ylation and decomposes into ferrocene and iron
iodide. Similar disproportionation of [(η5-
C5R5)FeX]2 complexes into bivalent iron halides and
According to X-ray diffraction data, Fe–Csp2 and
Fe–I bond distances in complex III are 1.963(2) and
2.6554(3)
Å,
respectively.
In
complex
Fe(CO)3(Me2Im)I2 [15], Fe–Csp2 bond distance is
1.984(4), while Fe–I bond distance is 2.665(1) and
2.667(1) Å.
IR spectrum of complex V shows frequencies of CO
group vibrations of 2037 and 1990 cm–1. For isostruc-
tural
phosphine
cation
[(η5-
C5H5)Fe(CO)2(PH2Mes*)+ (Mes* = 2,4,6-C6H2t Bu3),
the corresponding values are 2065 and 2021 cm–1 [16],
which also indicates a larger σ-donor ability of NHC
ligand. According to X-ray diffraction data, Fe–CNHC
bond distance in complex V is 1.969(3) Å (Fig. 2).
The formation of polyhalides is common for the corresponding substituted ferrocenes was noted in
p-block elements [17–19], the halogenation of coordi- [23].
N
N
N
O
C
O
C
I
I
O
C
CO
Fe
OC
Fe
N
I2
N
N
Fe
Fe
Fe
Fe
C
O
I
I
OC
OC
OC
II
–OC
I
FeI2
Fe
Fe
Fe
CO
Fe
CO
I
I
N
CO
N
OC
CO
N
N
V
VI
Scheme 4.
III
IV
Taking into account the above mechanism, one
Drawing analogy between the described symmetric
can suppose the possible effect of reaction conditions and asymmetric cleavage and homo- and heterolytic
on reaction route. Thus, a polar solvent will provide bond cleavage, one may extend the factors affecting
asymmetric cleavage of initial complex to stabilize the cleavage type to the iodination reaction as well. The
first transition state, while nonpolar solvent will favor variation of such factors as solvent nature and reaction
reaction via the second route.
temperature, we conducted a series of experiments
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY
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OXIDATION OF IRON COMPLEX WITH NHC LIGAND WITH MOLECULAR IODINE
1423
Table 2. Reaction conditions and yields for the reaction of
complex II with I2
6. L. Mercs, G. Labat, A. Neels, et al., Organometallics
25, 5648 (2006).
7. M. Itazaki, U. Kensuke, and H. Nakazawa, Angew.
Yield, %
Chem. 48, 3313 (2009).
Conditions
II
III
IV
V
8. K. Riener, S. Haslinger, A. Raba, et al., Chem. Rev.
114, 5215 (2014).
CH2Cl2, 25°C
Benzene, 4°C
Toluene, –40°C
16
29
39
18
41
40
54
19
14
12
9. A. M. Voutchkova, L. N. Appelhans, A. R. Chianese, et
11
7
al., J. Am. Chem. Soc. 127, 17624 (2005).
10. G. M. Sheldrick, SADABS. Göttingem (Germany),
Univ. of Göttingem (2005).
11. G. M. Sheldrick, Acta Crystallogr. A 64, 112 (2008).
that confirmed the assumption on the legitimacy to
use the analogy (the results are given in Table 2).
12. O. V. Dolomanov, L. J. Bourhis, R. J. Gildea, et al., J.
Appl. Crystallogr. 42, 339 (2009).
13. R. F. Bryan, P. T. Greene, M. J. Newlands, et al., J.
Chem. Soc. A, 3068 (1970).
CONCLUSIONS
The variation of conditions for the iodination of
carbene-containing dimer I provides the preparation
of both neutral complex II containing coordinated
1,3-dimethylimidazol-2-ylidene and cationic complex
III in one stage avoiding long-term photochemical
reaction.
14. C. M. Alvarez, B. Galan, and M. E. García, Organo-
metallics 22, 5504 (2003).
15. B. Li, T. Liu, C. V. Popescu, et al., Inorg. Chem. 48,
11283 (2009).
16. M. A. Alvarez, M. E. García, D. García-Vivo, et al., In-
org. Chem. 51, 3698 (2012).
17. M. S. Chernov’yants, I. V. Burykin, Z. A. Starikova, et
al., Russ. J. Inorg. Chem. 61, 217 (2016).
FUNDING
https://doi.org/10.1134/S0036023616020054
This work was financially supported by the Russian Sci-
ence Foundation (project no. 17-73-10503).
18. I. D. Gorokh, S. A. Adonin, M. N. Sokolov, et al., In-
org. Chim. Acta 469, 583 (2018).
19. S. A. Adonin, L. I. Udalova, P. A. Abramov, et al.,
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