Lipophilic chloro-oxo-bis(hydroxamato)vanadium(V) complexes: synthesis methods and structure

Article abstract of DOI:10.1016/j.poly.2020.114421

New methods for the synthesis of vanadium(V) complexes with hydrophobic alkyl- and aryl-substituted hydroxamic acids as well as hydrophilic ones have been developed. A number of novel coordination compounds of the general formula VOL₂Cl (where HL is N-phenylaceto-, N-methylbenzo-, N-methyldecano- or N-methylacetohydroxamic acid) have been synthesized. Complexes of the above formula with alkyl substituents on the ligands have been obtained for the first time. All the compounds obtained have been characterized by UV–Vis, IR, ¹H and ⁵¹V NMR spectroscopy. Studies using the ⁵¹V NMR method showed the presence of two forms of the complexes in solution, which coalesce with increasing temperature. Chloro-oxo-bis(N-methylacetohydroxamato)vanadium(V) has been characterized by X-ray crystallography. The effect of the electron donating properties of the ligand substituents on the structure of the complexes is discussed.

Full text of DOI:10.1016/j.poly.2020.114421

Polyhedron 180 (2020) 114421
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Lipophilic chloro-oxo-bis(hydroxamato)vanadium(V) complexes:
synthesis methods and structure
a
b
Valeriy I. Dzyuba a, Lyudmila I. Koval a, , Olherd O. Shtokvysh , Volodymyr V. Trachevskii ,
⇑
Vasyl I. Pekhnyo a
a V.I. Vernadskii Institute of General and Inorganic Chemistry, Ukrainian National Academy of Sciences, prospect Palladina 32-34, 03680 Kyiv, Ukraine
b Technical Centre of NAS of Ukraine, Ukrainian National Academy of Sciences, vul. Pokrovs’ka 13, 04070 Kyiv, Ukraine
a r t i c l e i n f o
a b s t r a c t
Article history:
New methods for the synthesis of vanadium(V) complexes with hydrophobic alkyl- and aryl-substituted
hydroxamic acids as well as hydrophilic ones have been developed. A number of novel coordination com-
pounds of the general formula VOL2Cl (where HL is N-phenylaceto-, N-methylbenzo-, N-methyldecano-
or N-methylacetohydroxamic acid) have been synthesized. Complexes of the above formula with alkyl
substituents on the ligands have been obtained for the first time. All the compounds obtained have been
characterized by UV–Vis, IR, 1H and 51V NMR spectroscopy. Studies using the 51V NMR method showed
the presence of two forms of the complexes in solution, which coalesce with increasing temperature.
Chloro-oxo-bis(N-methylacetohydroxamato)vanadium(V) has been characterized by X-ray crystallogra-
phy. The effect of the electron donating properties of the ligand substituents on the structure of the com-
plexes is discussed.
Received 21 December 2019
Accepted 25 January 2020
Available online 1 February 2020
Keywords:
Vanadium
Alkyl-
Aryl-substituted hydroxamic acids
Structure elucidation
Synthetic methods
Ó 2020 Published by Elsevier Ltd.
1. Introduction
substituents on the coordination fragment are not known as yet,
possibly due to the lack of suitable methods for the preparation
A series of vanadium(V) complexes with monodentate and
polydentate ligands have the ability to catalyze the oxidation of
organic substrates, using aqueous H2O2 as an oxidant [1–3]. N-sub-
stituted hydroxamato complexes of vanadium(V) are used as effec-
tive homogeneous catalysts for the selective oxidation of aromatic,
heterocyclic, carbocyclic and aliphatic hydrocarbons with hydro-
gen peroxide. The oxidation process proceeds at moderate temper-
atures with a high yield of the desired product [4]. The action of the
vanadium hydroxamato complexes in biochemical systems has
been noted [5]. Vanadium(V) and (IV) complexes containing vari-
ous organic ligands have been tested for their insulin-mimetic
activity, with positive results [6–12]. It is widely accepted that
lipophilic compounds have better cellular permeability than
hydrophilic ones. A number of vanadyl and vanadate (chloro-
oxo) complexes with hydroxamic acids as suitable hydrophobic
ligands showed considerable glucose-lowering activity in tests on
experimental diabetic mice [13]. The presence of aliphatic sub-
stituents on the hydroxamic acids results in their high lipophilicity,
both as proligands and for their coordination compounds [14].
Chloro-oxo-bis(hydroxamato)vanadium(V) complexes with alkyl
of these compounds.
The present article describes methods, developed by us, for the
synthesis of vanadium(V) complexes with hydroxamic acids con-
taining aliphatic substituents, both at the nitrogen atom and at
the carbonyl carbon atoms, taking into account that the develop-
ments could be further used in applied chemistry. The following
novel coordination compounds have been synthesized and investi-
gated: chloro-oxo-bis(N-phenylacetohydroxamato)vanadium(V),
ClOV(N-PhAH)2 (2); chloro-oxo-bis(N-methylbenzohydroxamato)-
vanadium(V),
methyldecanohydroxamato)vanadium(V), ClOV(N-MDH)2 (4);
chloro-oxo-bis(N-methylacetohydroxamato)vanadium(V), ClOV
ClOV(N-MBH)2
(3);
chloro-oxo-bis(N-
(N-MAH)2 (5). In addition, the previously described [4]
chloro-oxo-bis(N-phenylbenzohydroxamato)vanadium(V), ClOV
(N-PhBH)2 (1) was also synthesized by our methods (Scheme 1).
2. Experimental
2.1. Materials
Acetonitrile, about 2–10 mm granular calcium chloride (drying
agent), chloroform, hexane, molecular sieves (0.3 and 0.4 nm),
toluene and triethylamine were obtained from MERCK. N-phenyl-
⇑
Corresponding author.
E-mail address: l_koval@ionc.kiev.ua (L.I. Koval).
https://doi.org/10.1016/j.poly.2020.114421
0277-5387/Ó 2020 Published by Elsevier Ltd.

2
V.I. Dzyuba et al. / Polyhedron 180 (2020) 114421
benzohydroxamic acid was obtained from ALDRICH. Fluorinated
grease Krytox 240AC was obtained from DUPONT. All the chemi-
cals used were of reagent grade. The solvents were purified by dis-
tillation. Acetonitrile and chloroform were dried over 0.3 and
0.4 nm molecular sieves, respectively.
Vanadium(V) oxytrichloride, VOCl3, was prepared by substan-
tially modifying a published method [15]. 20.0 g (0.11 mol) of
vanadium pentoxide was boiled under reflux (cold finger con-
denser in a Claisen head) in 22.0 ml (0.30 mol) of thionyl chloride,
protected from moisture in the air by granulated calcium chloride,
for two hours at 80 °C until the formation of the condensate
stopped; then the temperature of the reaction mass was adjusted
to 128 °C, and it was boiled for another hour. Water was removed
from the finger condenser and the required amount of the product
was distilled off at 126–127 °C through a descending Liebig con-
denser. The ground glass joints were lubricated with fluorinated
grease.
stirring, and a homogeneous solution was obtained. This solution
was divided into three equal parts. In a 100 ml separatory funnel
was put 20 ml of a 2.5 mmol solution of a copper complex in chlo-
roform. To this, the three above portions were added successively
to extract the copper completely into the aqueous solution. A violet
complex was extracted into the organic phase and this was treated
three times with 10 ml portions of water and dried over sodium
sulfate. The solvent was then evaporated under reduced pressure.
The solid deep violet precipitate was dried under 12 Pa vacuum
at 40 °C to remove any traces of the solvent and the pure com-
plexes were isolated by crystallization and then vacuum drying.
Method 3 (in aqueous media). To a suspension of 0.66 g
(5.6 mmol) of ammonium metavanadate in 8 ml of water was
added 3 ml of concentrated hydrochloric acid with vigorous stir-
ring, and a homogeneous solution was obtained. A solution of
1.0 g (11.2 mmol) of N-MAHA in 5 ml of water was added dropwise
the above solution. After the addition, the deep violet colored reac-
tion mixture was stirred for another 3 h and frozen by rotating the
flask around its axis over liquid nitrogen; water was removed by
freeze drying under 12 Pa vacuum. The pure complexes were iso-
lated by crystallization and then vacuum drying.
The proligands were prepared by published methods:
N-methyldecanohydroxamic acid (N-MDHA) [16]; N-methylaceto-
hydroxamic acid (N-MAHA), N-methylbenzohydroxamic acid
(N-MBHA) and N-phenylacetohydroxamic acid (N-PhAHA) [17].
2.2. Synthesis of the copper complexes
2.3.1. Chloro-oxo-bis(N-phenylbenzohydroxamato)vanadium(V) (1)
Complex 1 was prepared by method 1, taking N-phenylbenzo-
hydroxamic acid (10 mmol, 2.13 g) in dry chloroform as a basis,
and purified by crystallization from a chloroform/hexane mixture
(1/5) at 5 °C. Yield: 1.95 g, 74%. Anal. Found: C, 59.03; H, 3.91; N,
5.25. Calc. for C26H20N2O5ClV (MW 526.85): C, 59.28; H, 3.83; N,
The initial copper complexes were obtained by known proce-
dures: bis(N-phenylbenzohydroxamato)copper(II), Cu(N-PhBH)2
[18]; bis(N-phenylacetohydroxamato)copper(II), Cu(N-PhAH)2, bis
(N-methylbenzohydroxamato)copper(II), Cu(N-MBH)2 [19].
Bis(N-methyldecanohydroxamato)copper(II), Cu(N-MDH)2, was
prepared by the following procedure. To a solution of 6.0 g
(0.03 M) of N-methyldecanohydroxamic acid in 100 ml of ethanol,
was added dropwise a solution of 3.0 g (0.015 M) of copper acetate
monohydrate in 50 ml of water under vigorous stirring. The blue-
green reaction mixture was further stirred for 3 h. The precipitated
mass was filtered and then washed in the filter with three 10 ml
portions of a cooled ethanol–water mixture, taken in a 1/1 ratio,
and dried under 12 Pa vacuum at 50 °C to remove the traces of
the solvent. The solid precipitate was purified by recrystallization
from hexane to obtain blue-grey crystals, which were dried in air
to a constant mass. Yield of Cu(N-MDH)2: 6.7 g, 95%. M.p. 84–
86 °C. Anal. Found: C, 56.42; H, 9.29; N, 6.01. Calcd for C22H44N2O4-
5.32%. UV/Vis kmax(CHCl3)/nm (
e
/dm3 molꢀ1 cmꢀ1): 530 (4327).
IR (KBr)
m
max/cmꢀ1: 3073 (w), 1600 (m), 1585 (m), 1549 (s), 1530
(vs), 1490 (vs), 1457 (s), 1442 (s), 1430 (vs), 1380 (vs), 1310 (w),
1285 (w), 1270 (m), 1180 (m), 1160 (m), 1142 (m), 1101 (w),
1070 (m), 1040 (m), 1015 (m), 1000 (w), 970 (vs), 937 (s), 840
(w), 770 (vs), 720 (m), 690 (vs), 665 (s), 642 (s), 612 (m), 580 (s),
558 (s), 495 (m), 455 (m), 422 (m), 400 (w). 1H NMR (400 MHz,
CDCl3, 25 °C, TMS), d, ppm: 7.52 (m, 5H, N-C6H5), 7.42 (m, 5H,
C6H5). 51V NMR (105.2 MHz, CDCl3, 25 °C, VOCl3), d, ppm:
ꢀ285.0, ꢀ295.5; (ꢀ283.4, ꢀ292.0, CH3CN).
Complex 1 was also prepared by method 2 using Cu(N-PhBH)2
(2.5 mmol, 1.22 g) and was purified by crystallization. Yield:
1.00 g, 76%. The compound was identified by comparing the IR
spectra of samples prepared by methods 1 and 2, and also to liter-
ature data [4].
Cu (MW 464.15): C, 56.93; H, 9.56; N, 6.03%. IR (KBr) m :
max/cmꢀ1
2930 (m), 2849 (m), 1592 (vs, br), 1468 (vs), 1441 (vs), 1222 (m),
1148 (s), 1103 (m), 1062 (w), 1001 (m), 972 (s), 891 (w, br), 817
(m), 804 (s), 729 (w), 712 (m), 680 (s), 594 (s), 532 (m), 503 (w),
485 (m), 471 (m), 453 (w), 402 (m).
2.3. Synthesis of the vanadium complexes
2.3.2. Chloro-oxo-bis(N-phenylacetohydroxamato)vanadium(V) (2)
Complex 2 was prepared by method 1, taking N-phenylacetohy-
droxamic acid (10 mmol, 1.51 g) in dry chloroform as a basis, and
purified by crystallization from a chloroform/hexane mixture (1/5)
at 5 °C. Yield: 1.39 g, 69%. Anal. Found: C, 47.23; H, 4.32; N, 6.67.
Calc. for C16H16N2O5ClV (MW 402.71): C, 47.72; H, 4.01; N,
Method 1 (in organic aprotic solvents). To a solution of the proli-
gand (10 mmol) and triethylamine (10 mmol, 1.01 g, 1.4 ml) in dry
solvent (100 ml), was added dropwise vanadium(V) oxytrichloride
(5 mmol, 0.867 g, 0.47 ml) with vigorous stirring. After the addi-
tion, the deep violet colored reaction mixture was stirred for
another 3 h. The starting substances were fed and the reaction
was carried out with the complete isolation from atmospheric
moisture by granular CaCl2. After the termination of the stirring,
the (C2H5)3NꢁHCl precipitate that formed was filtered off and
washed on a filter with three 10 ml portions of the solvent; the sol-
vent was then evaporated under reduced pressure. The solid deep
violet precipitate thus obtained was dried under 12 Pa vacuum at
40 °C to remove any traces of the solvent; the pure complexes were
isolated by crystallization and then vacuum drying.
6.96%. UV/Vis kmax(CHCl3)/nm (
e
/dm3 molꢀ1 cmꢀ1): 514 (3175).
IR (KBr)
m
max/cmꢀ1: 3056 (w, br), 2935 (w), 1560 (vs, br), 1458
(vs, br), 1420 (s), 1373 (s), 1312 (w), 1291 (w), 1251 (s), 1166
(w, br), 1086 (m), 1067 (m), 1034 (w), 1005 (vs), 970 (vs), 920
(w), 835 (w, br), 770 (vs), 730 (s), 691 (vs), 644 (s), 596 (m), 551
(s), 526 (vs), 481 (w, br), 449 (m), 416 (w). 1H NMR (400 MHz,
CDCl3, 25 °C, TMS), d, ppm: 7.47 (m, 5H, N-C6H5), 2.33 (s, 3H,
CH3). 51V NMR (105.2 MHz, CDCl3, 25 °C, VOCl3), d, ppm: ꢀ285.7,
ꢀ303.7; (ꢀ280.3, ꢀ295.6, CH3CN).
Complex 2 was also prepared by method 2 using Cu(N-PhAH)2
(2.5 mmol, 0.91 g) and was purified by crystallization. Yield:
0.64 g, 64%. The compound was identified by comparing IR spectra
of samples prepared by methods 1 and 2.
Method 2 (extractive (metal exchange) route). To a suspension of
1.76 g (15 mmol) of ammonium metavanadate in 25 ml of water
was added 5 ml of concentrated hydrochloric acid with vigorous

V.I. Dzyuba et al. / Polyhedron 180 (2020) 114421
3
2.3.3. Chloro-oxo-bis(N-methylbenzohydroxamato)vanadium(V) (3)
Complex 3 was prepared by method 1, taking N-methylbenzo-
hydroxamic acid (10 mmol, 1.51 g) in dry chloroform as a basis,
and purified by crystallization from a chloroform/hexane mixture
(1/8) at 5 °C. Yield: 1.57 g, 78%. Anal. Found: C, 47.31; H, 3.92; N,
6.76. Calc. for C16H16N2O5ClV (MW 402.71): C, 47.72; H, 4.01; N,
The elemental analysis was carried out on a Carlo Erba 1106 ana-
lyzer. The 1H and 51V NMR spectra were recorded on a BRUKER
AVANCE 400 spectrometer in CDCl3 and CH3CN solutions with
internal TMS and external VOCl3 standards.
2.5. X-ray crystallography
6.96%. UV/Vis: kmax(CHCl3)/nm (
e
/dm3 molꢀ1 cmꢀ1): 514 (4072).
IR (KBr)
m
max/cmꢀ1: 3064 (w), 3030 (w), 2930 (w, br), 1590 (s),
The structure of compound 5 was determined by X-ray crystal-
1570 (m), 1540 (m), 1496 (s), 1455 (vs), 1425 (vs), 1380 (s),
1313 (w), 1281 (w), 1229 (s), 1185 (s), 1066 (s), 1023 (m), 1000
(w), 965 (vs), 830 (w, br), 777 (s), 735 (s), 692 (s), 655 (s), 620
(m), 577 (s), 550 (m), 512 (w), 494 (w), 446 (s), 417 (w), 404 (w).
1H NMR (400 MHz, CDCl3, 25 °C, TMS), d, ppm: 7.59 (m, 5H,
C6H5), 3.77 (s, 3H, N-CH3). 51V NMR (105.2 MHz, CDCl3, 25 °C,
VOCl3), d, ppm: ꢀ283.7, ꢀ297.3; (ꢀ274.7, ꢀ288.0, CH3CN).
Complex 3 was also prepared by method 2 using Cu(N-MBH)2
(2.5 mmol, 0.91 g) and was purified by crystallization. Yield:
0.71 g, 71%. The compound was identified by comparing IR spectra
of samples prepared by methods 1 and 2.
lography. Suitable deep violet single crystals were formed by crys-
tallization from
a chloroform/ hexane mixture, obtained by
interdiffusion of solvents through the gaseous state in a closed
space. The single crystal X-ray diffraction data collection for the
complex was performed on a BRUKER SMART APEX-II CCD diffrac-
tometer, using Mo K
a radiation with a graphite monochromator
(k = 0.71073 Å) at 205 K. Reflection intensities were integrated
using SAINT software [20] and corrected for absorption by multi-
scan absorption corrections using SADABS [21]. The structure
was solved by the direct method and refined against F2 by the
full-matrix least-squares method using the SHELXTL package
[22]. Positions of the hydrogen atoms were located from electron
density difference maps and refined by the ‘‘riding” model with
Uiso = nUeq of the carrier atom (n = 1.5 for methyl groups and
n = 1.2 for other hydrogen atoms). Crystal data for C8H14Cl7N2O5V
(M = 517.30 g/mol): monoclinic, space group P21 (no. 4), a = 8.2670
2.3.4. Chloro-oxo-bis(N-methyldecanohydroxamato)vanadium(V) (4)
Complex 4 was prepared by method 1, taking N-methylde-
canohydroxamic acid (10 mmol, 2.01 g) in dry toluene as a basis,
and purified by crystallization from a toluene/hexane mixture
(1/5) at ꢀ12 °C. Yield: 1.81 g, 72%. Anal. Found: C, 52.31; H, 9.02;
N, 5.76. Calc. for C22H44N2O5ClV (MW 502.99): C, 52.53; H, 8.82;
(2) Å, b = 13.8107(4) Å, c = 8.6884(2) Å,
a
= 90.00°, b = 98.3290
= 90.00°. V = 981.52(4) Å3, Z = 2, T = 205 K,
) = 1.477 mmꢀ1, Dcalc = 1.750 g/cm3, 23,128 reflections mea-
62.76°), 6393 unique (Rint 0.0302,
(10)°,
c
l
N, 5.57%. UV/Vis kmax(CHCl3)/nm
(e
/dm3 molꢀ1 cmꢀ1): 514
(MoKa
(3955). IR (KBr)
m
max/cmꢀ1: 2935 (m), 2860 (m), 1594 (s), 1560
sured (4.74°
ꢂ
2
H
ꢂ
=
(m), 1457 (s, br), 1392 (m), 1373 (w), 1330 (w, br), 1212 (m, br),
1144 (m), 1103 (m, br), 1060 (w), 1044 (w), 970 (vs), 810 (m),
772 (w, br), 730 (m br), 685 (w, br), 655 (m), 625 (m), 588 (m),
540 (w), 530 (w), 497 (m), 484 (w), 475 (w), 464 (w), 455 (w),
420 (m). 1H NMR (400 MHz, CDCl3, 25 °C, TMS), d, ppm: 3.64 (s,
Rsigma = 0.0274) which were used in all calculations. The final R1
value was 0.0332 (>2sigma(I)) and wR2 was 0.0859 (all data).
3. Results and discussion
3H, N-CH3) 2.42 (m, 2H, b-CH2), 1.67 (m, 2H, c-CH2), 1.26 (m,
3
12H, (CH2)6), 0.88 (t, JH–H
=
6.9 Hz, 3H, CH3). 51V NMR
3.1. Synthesis
(105.2 MHz, CDCl3, 25 °C, VOCl3), d, ppm: ꢀ282.5, ꢀ297.0;
(ꢀ270.5, ꢀ285.5, CH3CN).
The overwhelming majority of publications dealing with metal
and metalloid hydroxamato complexes relate to chemical biology
and medicinal chemistry [23]. The pharmaceutical industry
remains completely dependent on the development of synthetic
chemistry methods for the preparation of compounds for new
medicaments [24,25]. One of the key indicators of the possible
implementation of synthesis methods in industry is the availability
of affordable and high-quality raw materials. Multi-megawatt all-
vanadium redox flow battery (VRFB) systems for large-scale energy
storage have been demonstrated worldwide. The electrolyte of
these huge batteries is an aqueous sulfate solution of high-purity
vanadium pentoxide, the intermediate product of which is vana-
dium oxytrichloride, of appropriate purity [26]. This low-cost,
large-tonnage, high-purity product as a precursor opens up broad
prospects for the applied chemistry of chloro-oxo-bis(hydroxam-
ato)vanadium(V) complexes. On the other hand, the preparative
method for the synthesis of vanadium oxytrichloride from vana-
dium pentoxide and thionyl chloride [15] turned out to be accept-
able after minor modifications. A small stoichiometric excess of
V2O5 allows the separation of VOCl3 from the reaction mass by
simple distillation, without first distilling off the excess SOCl2.
The application of fluorinated grease on the ground glass joints
allows the reuse of the same reactor. It should be noted that VOCl3
is extremely easily hydrolyzed and, for example, all syntheses with
bidentate dicarbonyl proligands were carried out in rigorously
dried glassware using freshly dried proligands and solvents [27].
An attempt to adapt the method used to obtain bis(hydroxam-
ato)-dioxo-molybdenum(VI) complexes from MoO2Cl2 [16] for
the synthesis of chloro-oxo-bis(hydroxamato)vanadium(V) com-
plexes involved considerable difficulties. Vanadium oxytrichloride
Complex 4 was also prepared by method 2 using Cu(N–MDH)2
(2.5 mmol, 1.16 g) and was purified by crystallization. Yield:
1.02 g, 81%. The compound was identified by comparing IR spectra
of samples prepared by methods 1 and 2.
2.3.5. Chloro-oxo-bis(N-methylacetohydroxamato)vanadium(V) (5)
Complex 5 was prepared by method 1, taking N-methylacetohy-
droxamic acid (10 mmol, 0.89 g) in dry chloroform as a basis, and
purified by crystallization from a chloroform/hexane mixture (1/1)
at 5 °C. Yield: 0.89 g, 64%. Anal. Found: C, 25.16; H, 4.84; N, 10.65.
Calc. for C6H12N2O5ClV (MW 278.55): C, 25.87; H, 4.34; N, 10.05%.
UV/Vis kmax(CHCl3)/nm (
m
e
/dm3 molꢀ1 cmꢀ1): 514 (2075). IR (KBr)
max/cmꢀ1: 3029 (m), 3010 (m), 2947 (w), 1619 (s), 1556 (s),
1458 (vs), 1444 (vs), 1397 (vs), 1366 (m), 1225 (s), 1208 (s),
1168 (s), 1030 (m), 1009 (m), 994 (m), 965 (vs), 755 (vs), 669
(m), 633 (s), 592 (s), 545 (w), 524 (m), 501 (m), 465 (w), 420 (s).
1H NMR (400 MHz, CDCl3, 25 °C, TMS), d, ppm: 3.77 (s, 3H, N-
CH3), 2.43 (s, 3H, CH3). 51V NMR (105.2 MHz, CDCl3, 25 °C, VOCl3),
d, ppm: ꢀ 280.8, ꢀ 297.6; (ꢀ270.6, ꢀ286.8, CH3CN).
Complex 5 was also prepared by method 3. Yield: 1.01 g, 65%.
The compound was identified by comparing IR spectra of samples
prepared by methods 1 and 3.
2.4. Physical measurements
The IR spectra were recorded in KBr pellets in the range 4000–
400 cmꢀ1 on a Specord M80 spectrophotometer and electronic
spectra on a Specord M40 spectrophotometer, both of which were
equipped with an IBM-compatible operating computing system.

4
V.I. Dzyuba et al. / Polyhedron 180 (2020) 114421
exhibits, despite the relatively high boiling point (127 °C), extre-
mely high volatility and it fills the space of the reaction vessels
with a gaseous product, even in a weak argon flow; on the con-
trary, air moisture protection with granulated CaCl2 allows one
to carry out all the necessary procedures. The liquid aggregate state
of VOCl3 provides its quantitative dropwise addition, without the
use of solvents, to the reaction mass by means of a conventional
graduated glass pipette connected to a syringe with a heat-shrink
tube. All the vanadium complexes presented in this article (1–5)
were synthesized in this way (Eq. (1)).
tion of identical compounds by two alternative synthesis methods
is one of the proofs of their chemical structure.
Complexes 2–5 have an intense dark purple color. The UV–Vis
spectra of their solutions in chloroform have k max, as well as val-
ues of the molar extinction e, similar to those of complex 1 [4].
The chemical shifts and integral intensities of the signals in the
1H NMR spectra of complexes 1–5 corroborate the above chemical
structure (Scheme 1). The absence of broadening of the NMR sig-
nals indicates the valence of the central atom –V(V), as well as
the absence of any paramagnetic impurity from copper(II) com-
plexes in the desired reaction products from the ‘‘extraction”
method. The presence of an additional signal (in the form of a
þ 2 NEt3
VOCl3 þ 2 HL
!
VOL2Cl þ 2 NEt3 ꢁ HCl
ð1Þ
shoulder or a neighboring peak (
D
d < 18 ppm)) in the 51V NMR
½dry solventꢃ
spectra of complexes 1–5 can be explained by the presence of
two different forms: with near and distant arrangements of identi-
cal fragments of chelate rings in the molecules. The presence of the
aforementioned shoulder was shown earlier for complex 1 [30].
The rise (not above 325 K) of the temperature of solutions leads
to a rapid, on the timescale of NMR, exchange process and with
the merging of the signals of these species (Fig. 1).
The presence of aryl substituents on the hydroxamate fragment
of a molecule of the complex noticeably shifts the 51V NMR signal
to the strong field region, especially for the complexes with aryl
substituents at the nitrogen atom, which indicates a noticeable
flow of electron density from the ligand to the central atom with
the participation of the free electron pair of the nitrogen atom.
The shape of the 51V NMR spectra of complexes 1–5 in acetonitrile
(a much more polar solvent than chloroform) remains similar to
that for solutions in chloroform. At a tenfold dilution of the ace-
tonitrile solutions, the shape of the 51V NMR spectra do not change.
This excludes the interpretation of several closely spaced 51V NMR
signals as a manifestation of different degrees of association of the
complexes in solution.
Another, preparatively convenient method turned out to be an
‘‘extraction” method – the synthesis of complexes at a liquid phase
boundary [28]. Hydroxamic acids are relatively unstable com-
pounds, so their copper complexes are used for purification and
storage [29]. Since complexes 1–4 are stable in a strongly acidic
medium, they were synthesized from their corresponding copper
complexes due to a shift in the reaction equilibrium towards the
formation of the VOL2Cl complexes (Eq. (2)), which are stable in
an acidic medium unlike the original CuL2. By adding concentrated
HCl to an NH4VO3 suspension in water, a homogeneous, relatively
temporally stable, sufficiently concentrated precursor for the
above synthesis was obtained. Complexes 2–4, obtained by us
using both methods, were identical; additionally, complex 1 is
identical to that previously reported [4].
þ4HCl
NH4VO3 þ CuL2
!
ꢃ VOL2Cl þ NH4Cl þ CuCl2 þ 2 H2O ð2Þ
½H2O=CHCl3
However, the above technique does not pertain to the chloro-
oxo-bis(N-methyl-acetohydroxamato)vanadium(V) complex (5),
since like the original proligand, it is soluble in water, so the syn-
thesis as per Eq. (3) was carried out. Complex 5, in a two-phase
water-chloroform system, is distributed in the aqueous phase
and therefore was separated from the frozen aqueous solution by
freeze drying.
3.3. Structure of chloro-oxo-bis(N-
methylacetohydroxamato)vanadium(V) (5)
According to the data of the X-ray structural analysis, each
metal complex molecule in the crystal co-crystallizes with two
chloroform molecules. The coordination polyhedron of the central
vanadium atom has the geometry of a distorted octahedron. The
vanadium atom is surrounded by four oxygen atoms of chelating
hydroxamate ligands, an oxygen atom of the oxo group and a chlo-
rine atom (Fig. 2). A disordering of the ClVO fragment at two posi-
tions, A and B with occupancies of 34 and 66%, respectively, is
observed. At both positions, solely the carbonyl oxygen atoms of
ligands, O2 and O4, are trans disposed to the oxo group and chlo-
rine atom (Fig. 3).
The lengths of the V@O bonds in the coordination polyhedron
vary over the ranges 1.885(2)–2.239(2) Å (for the chelate oxygen
atom) and 1.575(4)–1.581(5) Å (for the oxo group) and those of
V-Cl bonds over the range 2.287(3)–2.293(2) Å. The values of the
valence angles O-V-Cl and O-V-O in the coordination polyhedron
vary over the range 71.76(10)–100.48(9)° (Table 1).
þ2 HCl
½H2Oꢃ
NH4VO3 þ 2 HL ! VOL2Cl þ NH4Cl þ 2H2O
ð3Þ
It turned out to be identical to complex 5 obtained from VOCl3
by the earlier method.
3.2. Spectral analysis
The IR spectral data of the compounds under investigation cor-
roborate the complex formation. The vibrations of the CAO groups
bonded to the metal manifest themselves in the lower-frequency
spectral region in comparison to the stretching vibration frequen-
cies of the C@O groups of free hydroxamic acid (1660–1600 cmꢀ1).
Additionally, intense characteristic vibrational bands of the
m
(V@O) group in the range of 980–950 cmꢀ1 are observed in the
spectra of the complexes, like those of complex 1 [4]. The prepara-
Scheme 1. Chemical structure of the studied complexes.

V.I. Dzyuba et al. / Polyhedron 180 (2020) 114421
5
Fig. 1. 51V NMR spectra of complex 4 at 298 and 318 K.
Table 1
Selected bond lengths (Å) and angles (deg) for 5.
Position A
Position B
V1-O1
V1-Cl1
V1-O2
V1-O3
V1-O4
V1-O5
1.581(5)
2.287(3)
2.239(2)
1.917(3)
1.949(2)
1.923(3)
94.4(6)
1.575(4)
2.2928(19)
1.9346(17)
1.925(2)
2.2022(17)
1.885(2)
97.1(2)
O1-V1-Cl1
O1-V1-O2
O1-V1-O3
O1-V1-O4
O1-V1-O5
O2-V1-Cl1
O3-V1-Cl1
O3-V1-O2
O3-V1-O4
O3-V1-O5
O4-V1-Cl1
O4-V1-O2
O5-V1-Cl1
O5-V1-O2
O5-V1-O4
164.7(5)
93.1(5)
98.7(2)
109.3(2)
165.2(2)
91.5(2)
100.8(5)
112.6(5)
85.84(13)
97.66(14)
71.76(10)
93.23(13)
154.04(13)
160.74(18)
82.55(10)
84.25(14)
82.62(10)
79.07(12)
159.32(10)
83.41(8)
78.79(8)
85.53(8)
158.31(9)
84.35(7)
83.87(8)
100.48(9)
92.44(9)
73.74(7)
Table 2
Halogen bonds for 5.
R-Hal. . .A
d(R-Hal), Å
d(Hal-A), Å
<(R-Hal-A), deg
C7-Cl2. . .O2#1
C8-Cl7. . .O4#2
1.746(2)
1.743(2)
2.973
3.062
172.43
163.83
Fig. 2. Molecular structure of complex 5.
#1 2 ꢀ x, 1/2 + y, 2 ꢀ z #2 ꢀ1 + x, y, ꢀ1 + z.
Fig. 3. Model of the disorder in the crystal structure of 5 (chloroform molecules are omited for clarity).

6
V.I. Dzyuba et al. / Polyhedron 180 (2020) 114421
Table 3
Selected short contacts for 5.
Atom1
Atom2
Symm. op. Atom2
Length, Å
Sum. of VdW, Å [31]
Length-VdW, Å
O1A
O4
Cl1A
Cl1A
C2
H1A
H4C
C2
Cl1A
O5
H7
H7
Cl3
Cl4
Cl4
Cl2
Cl5
Cl7
H8
H8
x, ꢀ1 + y, z
2.643
2.580
3.291
3.194
3.344
2.896
2.904
3.411
2.675
2.336
2.72
2.72
3.50
3.50
3.45
2.95
2.95
3.45
2.95
2.72
ꢀ0.077
ꢀ0.140
ꢀ0.209
ꢀ0.306
ꢀ0.106
ꢀ0.054
ꢀ0.046
ꢀ0.039
ꢀ0.275
ꢀ0.384
x, ꢀ1 + y, z
1 ꢀ x, ꢀ1/2 + y, 1 ꢀ z
1 ꢀ x, ꢀ1/2 + y, 2 ꢀ z
1 ꢀ x, ꢀ1/2 + y, 2 ꢀ z
2 ꢀ x, ꢀ1/2 + y, 2 ꢀ z
1 + x, y, z
1 + x, y, 1 + z
1 ꢀ x, 1/2 + y, 1 ꢀ z
1 ꢀ x, 1/2 + y, 1 ꢀ z
Fig. 4. Crystal structure of complex 5.
In the crystal, the metal complex molecules are bonded to the
chloroform molecules through intermolecular halogen bonds
(Table 2), and the formation of a large number of short contacts
is observed (Table 3). In this case, a three-dimensional molecular
network is formed in the crystal (Fig. 4).
CRediT authorship contribution statement
Valeriy I. Dzyuba: Conceptualization, Methodology, Investiga-
tion, Writing - original draft. Lyudmila I. Koval: Conceptualization,
Methodology, Investigation, Data curation, Writing - review & edit-
ing, Visualization. Olherd O. Shtokvysh: Methodology, Investiga-
tion, Visualization, Software. Volodymyr V. Trachevskii:
Methodology, Investigation. Vasyl I. Pekhnyo: Supervision,
Validation.
4. Conclusion
In this work, new methods for the synthesis of complexes of
vanadium(V) with hydrophobic alkyl- and aryl-substituted
hydroxamic acids as well as hydrophilic ones have been developed.
Four novel coordination compounds of the general formula VOL2Cl
(where HL is N-phenylaceto-, N-methylbenzo-, N-methyldecano-
and N-methylacetohydroxamic acids) have been successfully syn-
thesized. The counter synthesis of the above compounds confirmed
the declared chemical structure. Chloro-oxo-bis(N-methylacetohy-
droxamato)vanadium(V) has been characterized by X-ray crystal-
lography, which also confirmed the chemical structure presented
in this article. Complexes of this type with alkyl substituents on
the ligands have been obtained for the first time. Using the 51V
NMR method, the presence of two forms of the complexes in solu-
tion, which coalesce with increasing temperature, has been shown.
Vanadium oxytrichloride, as a precursor, has a certain univer-
sality: it is suitable for the synthesis of both lipophilic and hydro-
philic VOL2Cl complexes with a high yield of the target products.
Large-tonnage production of high-purity VOCl3 opens prospects
for the reproduction of the developed method on an industrial
scale.
Acknowledgments
We are grateful to Dr. Dyakonenko V. V. for the support with the
X-ray studies.
This research did not receive any specific grant from funding
agencies in the public, commercial, or not-for-profit sectors.
Appendix A. Supplementary data
CCDC 1920450 contains the supplementary crystallographic
data for complex 5. These data can be obtained free of charge via
http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail:
deposit@ccdc.cam.ac.uk. Supplementary data to this article can
be found online at https://doi.org/10.1016/j.poly.2020.114421.
References
[1] G. Romanowski, J. Kira, M. Wera, Polyhedron 67 (2014) 529–539.
[2] Y. Zhang, T. Yang, B.Y. Zheng, M.Y. Liu, N. Xing, Polyhedron 121 (2017) 123–
129.
Conflicts of interest
There are no conflicts of interest to declare.
[3] L. Deng, W.T. Jin, W.Z. Weng, Z.H. Zhou, Polyhedron 159 (2019) 375–381.

V.I. Dzyuba et al. / Polyhedron 180 (2020) 114421
7
[4] T.K. Si, K. Chowdhury, M. Mukherjee, D.C. Bera, R. Bhattacharyya, J. Mol. Catal.
[16] V.I. Dzyuba, L.I. Koval, V.V. Bon, V.I. Pekhnyo, Polyhedron 29 (2010) 2900–
2906.
A: Chem. 219 (2004) 241–247.
[5] D. Rehder, Bioinorganic Vanadium Chemistry, John Wiley
Chichester, 2008.
[6] C.T. Miranda, S. Carvalho, R.T. Yamaki, E.B. Paniago, R.H.U. Borges, V.M. De
Bellis, Polyhedron 29 (2010) 897–903.
&
Sons Ltd,
[17] B. Monzyk, A.L. Crumbliss, J. Org. Chem. 45 (1980) 4670–4675.
[18] D.A. Brown, D. McKeith, W.K. Glass, Inorg. Chim. Acta 35 (1979) 5–10.
[19] V.I. Dzyuba, T.V. Ternovaya, N.A. Kostromina, A.I. Ksaverov, Ukr. Khim. Zh. 52
(1986) 453–457.
[7] N. Wang, Z. Wang, X. Niu, X. Yang, J. Inorg. Biochem. 152 (2015) 104–113.
[8] K.H. Thompson, J. Chiles, V.G. Yuen, J. Tse, J.H. McNeill, C. Orvig, J. Inorg.
Biochem. 98 (2004) 683–690.
[9] K.H. Thompson, C. Orvig, Coord. Chem. Rev. 219–221 (2001) 1033–1053.
[10] S. Ahmad, A.A. Isab, S. Ali, A.R. Al-Arfaj, Polyhedron 25 (2006) 1633–1645.
[11] A. Sheela, S.M. Roopan, R. Vijayaraghavan, Eur. J. Med. Chem. 43 (2008) 2206–
2210.
[12] I. Goldwaser, S. Qian, E. Gershonov, M. Fridkin, Y. Shechter, Mol. Pharm. 58
(2000) 738–746.
[13] M. Haratake, M. Fukunaga, M. Ono, M. Nakayama, J. Biol. Inorg. Chem. 10
(2005) 250–258.
[20] APEX 2 and SAINT, Bruker AXS Inc. Madison, Wisconsin, USA. 2007.
[21] SADABS, Bruker AXS Inc. Madison, Wisconsin, USA. 2001.
[22] G.M. Sheldrick, Acta Crystallogr., A 64 (2008) 112–122.
[23] R. Codd, Coord. Chem. Rev. 252 (2008) 1387–1408.
[24] A. Nadin, C. Hattotuwagama, I. Churcher, Angew. Chem. Int. Ed. 51 (2012)
1114–1122.
[25] N.P.E. Barry, P.J. Sadler, Chem. Commun. 49 (2013) 5106–5131.
[26] C. Fan, H. Yang, Q. Zhu, Sep. Purif. Technol. 185 (2017) 196–201.
[27] B.J. Blackburn, J.H. Crane, C.E. Knapp, M.J. Powell, P. Marchand, D. Pugh, J.C.
Bear, I.P. Parkin, C.J. Carmalt, Mater. Des. 108 (2016) 780–790.
[28] R. Pande, S.G. Tandon, J. Inorg. Nucl. Chem. 42 (1980) 1509.
[29] V.I. Dzyuba, L.I. Koval, A.V. Dudko, V.I. Pekhnyo, J. Coord. Chem. 67 (2014)
1437–1448.
[14] V.M. Nurchi, G. Crisponi, T. Pivetta, E. Tramontano, F.C. Marincola, J.I.
Lachowicz, Polyhedron 28 (2009) 763–768.
[15] H. Hecht, G. Jander, H. Schlapmann, Z. Anorg, Allg. Chem. 254 (1947) 255–
264.
[30] C. Weidemann, W. Priebsch, D. Rehder, Chem. Ber. 122 (1989) 235–243.
[31] A. Bondi, J. Phys. Chem. 68 (3) (1964) 441–451.