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Trapping ionic dimers of dinuclear peroxido mandelato complexes of vanadium(V) into cavities constructed from Δ- and Λ-[Ni(phenanthroline)3]2+ cations: a precursor to Ni(VO3)2

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A nickel‒vanadium metal–organic hybrid compound [Ni(phen)3]2[(V2O2(O2)2((S)-mand)2)][(V2O2(O2)2((R)-mand)2)]·18H2O (phen = 1,10-phenanthroline, mand²⁻ = mandelato(2−) ligand, C6H5–CO–COO²⁻) (1) was prepared and characterized by spectral methods, X-ray structure analysis and simultaneous DTA and TG measurements. The crystal structure of 1 contains both Δ and Λ enantiomers of the [Ni(phen)3]²⁺ cations that construct sandwich layers along the crystallographic axis c, in between which sit the vanadium(V) complex anions. These are present as ionic dimers in the form of a robust {[(V2O2(O2)2((S)-mand)2)][(V2O2(O2)2((R)-mand)2)]}⁴⁻ species. The two individual anions are coupled by a pair of weak, yet significant attractions between two vanadium atoms and two peroxido ligands of the adjacent anion at V‒O distances 2.660 Å. The ⁵¹V NMR spectrum of the compound in DMSO solution revealed a complicated course of decomposition reactions of the anion, which led to formation of the [(V2O4(S,R-mand)2]²⁻ anion as a single product. The metal–organic hybrid compound 1 is converted by thermal decomposition into a potential anode material for lithium-ion batteries Ni(VO3)2.
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Transition Metal Chemistry (2019) 44:747–754
https://doi.org/10.1007/s11243-019-00344-0
Trapping ionic dimers ofdinuclear peroxido mandelato
complexes ofvanadium(V) intocavities constructed fromΔ‑
andΛ‑[Ni(phenanthroline)3]2+ cations: aprecursor toNi(VO3)2
MáriaŠimuneková1· PeterSchwendt1· RóbertGyepes2 · LukášKrivosudský1,3
Received: 9 May 2019 / Accepted: 9 July 2019 / Published online: 18 July 2019
© The Author(s) 2019
Abstract
A nickelvanadium metal–organic hybrid compound [Ni(phen)3]2[(V2O2(O2)2((S)-mand)2)][(V2O2(O2)2((R)-mand)2)]·18H2O
(phen = 1,10-phenanthroline, mand2− = mandelato(2−) ligand, C6H5–CO–COO2−) (1) was prepared and characterized by
spectral methods, X-ray structure analysis and simultaneous DTA and TG measurements. The crystal structure of 1 con-
tains both Δ and Λ enantiomers of the [Ni(phen)3]2+ cations that construct sandwich layers along the crystallographic
axis c, in between which sit the vanadium(V) complex anions. These are present as ionic dimers in the form of a robust
{[(V2O2(O2)2((S)-mand)2)][(V2O2(O2)2((R)-mand)2)]}4− species. The two individual anions are coupled by a pair of weak,
yet significant attractions between two vanadium atoms and two peroxido ligands of the adjacent anion at VO distances
2.660Å. The51V NMR spectrum of the compound in DMSO solutionrevealed a complicated course of decomposition
reactions of the anion, which led to formation of the [(V2O4(S,R-mand)2]2− anion as a single product. The metal–organic
hybrid compound 1 is converted by thermal decomposition into a potential anode material for lithium-ion batteries Ni(VO3)2.
Introduction
Nickel vanadates and nickel–vanadium metalorganic
hybrid compounds have attracted considerable attention
because of their physical and chemical properties, which
facilitate technological applications in various fields of
materials science. Thus, nickel vanadates have been studied
as a component for electrochemical capacitors [1], as gas
sensors [2] and semiconductors [3]. Nickel–vanadium hybrid
compounds have alsobeen investigated, e.g. as heterogenous
catalysts [4], photocatalysts [5] or magnetic materials [6].
Special interest is focused on nickel vanadates that may be
used as anode materials for lithium-ion batteries. The most
studied compounds in this respect are Ni3V2O8 [711] and a
mixed-ion vanadate LiNiVO4 [1216]. In fact, the simplest
nickel vanadate Ni(VO3)2 itself does not suit in such appli-
cations; however, synthesis of Ni(VO3)2 doped by lithium
ions represents a viable option for the development of a dif-
ferent class of lithium-ion batteries [17, 18]. Therefore, the
research on innovative methods for the synthesis of nickel
vanadates including Ni(VO3)2 capable of accommodat-
ing lithium ions is ongoing. Peroxido complexes of vana-
dium may serve as useful precursors in this manner, as has
alreadybeen shown in the case of the synthesis of Ni2V2O7
by thermal decomposition of [Ni(NH3)6][VO(O2)2(NH3)]2
[19]. A notable obstacle is the fact that the final products
of a thermal decomposition can scarcely be predicted with
certainty. Despite the fact that initial stoichiometry of the
coordination compound with n(Ni): n(V) = 1: 2 could favour
formation of Ni(VO3)2, the calcination product was actu-
ally obtained as a mixture of Ni2V2O7 and V2O5. Because
peroxido complexes of vanadium are a well-investigated
* Lukáš Krivosudský
lukas.krivosudsky@univie.ac.at
Mária Šimuneková
maria.simunekova@uniba.sk
Peter Schwendt
peter.schwendt@uniba.sk
Róbert Gyepes
gyepes@natur.cuni.cz
1 Department ofInorganic Chemistry, Faculty ofNatural
Sciences, Comenius University inBratislava, Mlynská
dolina, Ilkovičova 6, 84215Bratislava, Slovakia
2 Department ofInorganic Chemistry, Faculty ofScience,
Charles University, Hlavova 2030, 12800Prague,
CzechRepublic
3 Universität Wien, Fakultät für Chemie, Institut für
Biophysikalische Chemie, Althanstraße 14, 1090Vienna,
Austria
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748 Transition Metal Chemistry (2019) 44:747–754
1 3
group of vanadium compounds providing an advantage of
relatively low temperatures required for the release of the
oxygen atoms of the peroxide group and combustion of the
organic components (usually 100–300°C), new precursors
for possible preparation of nickel vanadates are of current
interest. Thermal decomposition of vanadium peroxido com-
plexes with transition metal cations has been utilized also
for the synthesis of other vanadates, such as Zn(VO3)2 and
Cu(VO3)2 [24].
In recent years, we have reported on transition
metal–vanadium compounds, comprised ofthecombina-
tions Mn–V [20], Fe–V, Ni–V [21, 22] and Cu–V [2329]
that were investigated mostly for their chiral proper-
ties. In continuation of our studies on stereochemistry of
vanadium(V) complexes, we present here the synthesis and
characterization of [Ni(phen)3]2[(V2O2(O2)2((S)-mand)2)]
[(V2O2(O2)2((R)-mand)2)]·18H2O (phen = 1,10-phenanth-
roline, mand2− = mandelato(2−), C6H5–CO–COO2−).
Experimental
Synthesis andcharacterization
Materials andmethods
The starting materials were obtained from commercial
sources: H2O2 (35%, p. a., Centralchem), NiCl2·6H2O (p.
a., Lachema), KBr (for IR spectra, Lachema), 1,10-phen-
anthroline (p. a., AFT Bratislava), rac-mandelic acid (for
synth., Merck), (S)-mandelic acid (99% +, Acros Organ-
ics), dimethyl sulfoxide (DMSO, p. a., Penta), acetonitrile
(99.5%, Centralchem). NH4VO3 (purum, Lachema) was
purified according tothe literature [22].
Elemental analyses C, H, N were determined on a Vario
MIKRO cube (Elementar). Vanadium was determined using
ICP-MS (Perkin-Elmer Sciex Elan 6000), and nickel was
determined using F-AAS (Perkin-Elmer 1100). DTA and
TG curves were recorded on an SDT 2960 (TA Instruments)
device in static air atmosphere in the temperature range
20–600°C and with the heating rate 10°Cmin−1. UV–Vis
spectra in DMSO solutions were measured on a Jasco V-530
(Shimadzu) apparatus in 2-mm quartz cuvettes at ambient
temperature in the range 200–1000nm. Infrared spectra in
KBr discs, Nujol mulls or spectra using the ATR technique
were recorded on a Nicolet FTIR 6700 spectrometer. 51V
NMR spectra in DMSO solutions were recorded at 298K
on Varian Unity Inova 600MHz spectrometer operating at
157.68MHz (51V); chemical shifts are related to VOCl3 used
as the external standard (δ = 0ppm).
Synthesis of[Ni(phen)3]2[(V2O2(O2)2((S)‑mand)2)][(V2O2(O2)2
((R)‑mand)2)]·18H2O (1) NH4VO3 (0.233 g, 2 mmol) was
dissolved in water (15 cm3); subsequently H2O2 (30%,
0.5cm3) and rac-H2mand (0.305g, 2mmol) were added.
To the red solution soobtained, a solution of NiCl2·6H2O
(0.237g, 1mmol) and phen (0.541g, 3mmol) in acetoni-
trile (25cm3) and water (5cm3) was added under continu-
ous stirring. The final orange solution was allowed to crys-
tallize at 5°C, and orange-red block crystals were isolated
after 24h. The compound is insoluble in water and ethanol
and partially soluble in DMSO.
Anal. Calc. for NiV2O21C52H54N6 (1259.58g/mol) (fresh
sample): C 49.58; H 4.32; N 6.67; V 8.09; Ni 4.66%; found:
C 49.56; H 4.03; N 6.65; V 7.88; Ni 4.34%.
The compound slowly releases molecules of water of
crystallization even in a refrigerator. The analysis after stor-
ing for 5months at 5°C: C 51.43; H 3.31; N 7.25%.
Structure determination details
Single-crystal X-ray diffraction data were collected using
aNonius Kappa CCD diffractometer equipped with Bruker
Apex II detector with Mo Kα radiation (λ = 0.71073nm) at
120K. Absorption corrections were applied using the pro-
gram SADABS [30]. The structure was solved with direct
methods by using the SHELXT program [31] and refined
with SHELXL 2015 [32]. All non-hydrogen atoms were
refined anisotropically. Hydrogen atoms were placed at
idealized positions and refined with a riding model. The
oxygen atoms of water molecules were heavily disordered,
and we were obliged to use SQUEEZE programme [33] to
expel them to obtain a stable model. The structure has been
deposited with the Cambridge Crystallographic Data Centre
(CCCDC) with the deposition number 1915001. This data
can be obtained free of charge under https ://www.ccdc.cam.
ac.uk/struc tures /.
Results anddiscussion
Crystal structure ofcompound 1
Table1 summarizes crystal structure data and refinement
details for compound 1. The asymmetric unit consists of
one cation [Ni(phen)3]2+ and one anion [(V2O2(O2)2(m
and)2)]2− as well as water molecules of crystallization that
were not modelled. Because the compound crystallizes in
the space group P−1, the asymmetric unit contains only one
set of the individual stereoisomers; in the case of our model
[(V2O2(O2)2((S)-mand)2)]2− and Λ-[Ni(phen)3]2+ (Fig.1) with
their related enantiomers being generated by a centre of sym-
metry. The key geometrical parameters of the two ionic com-
ponents are summarized in Table2. The Ni–N distances and
N–Ni–N angles in the [Ni(phen)3]2+ cations point to slightly
irregular octahedral geometry. The molecular structure of
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749Transition Metal Chemistry (2019) 44:747–754
1 3
the [(V2O2(O2)2(mand)2)]2− anion was previously reported
for few vanadium(V) peroxido complexes [29, 34, 35]. Both
vanadium atoms adopt pentagonal pyramidal coordination
geometry and are coordinated by one oxido ligand in the
apical position as well as two oxygen atoms of the peroxido
ligands and one oxygen atom of the carboxylate group of the
mandelato ligand in the pentagonal pseudoplane. The oxygen
atoms coming from the hydroxyl groups of mandelic acid
act as bridging ligands between two vanadium atoms of the
anion. The vanadium atoms are displaced from the calcu-
lated pentagonal pseudoplanes towards the oxido ligands by
0.4569(4)Å (V1) and 0.3579(3)Å (V2). As noted earlier, the
mandelato ligands of the anion have the same configuration
(S). The partnered anion involving mandelato ligand of the
opposite configuration (R) is related by a centre of symmetry
in the crystal packing and may be actually found in a rela-
tively close distance to the [(V2O2(O2)2((S)-mand)2)]2− anion
(Fig.2). The closest contact between the enantiomers is the
V2···O6 interaction at 2.660 Å. This distance is too large
to consider it as a regular coordination bond, but still too
short to be neglected; especially when in general the atom
in the trans position towards to oxido ligand of the V=O
bond (if present) usually comes from a solvent molecule or
other components present in the crystal structure [36]. There-
fore, the related enantiomers may be considered as a bulky
ionic dimer {[(V2O2(O2)2((S)-mand)2)][(V2O2(O2)2((R)-
mand)2)]}4− trapped in a cavity that is formed by surround-
ing [Ni(phen)3]2+ cations. In the crystal packing along the
crystallographic c axis the cations are located in layers above
and below the positions of the dimers (Fig.2). The enantiom-
ers in the two layers have alternate configurations. Interest-
ingly, there is no obvious ππ stacking between the phenyl
groups of the mandelato and phenanthroline ligands. In one of
the similar previously studied systems, we employed Δ- and
Λ-[Ni(bpy)3]2+ cations (bpy = 2,2-bipyridine) and tetranuclear
chiral vanadium(V) tartrato complexes [V4O8((2R,3R)-tart)2]
Table 1 Crystal structure data and refinement details for compound 1
CCDC code 1915001
Empirical formula C52 H36 N6 Ni O12 V2 [+ solvent]
Formula weight 1097.46
Temperature 120(2)K
Wavelength 0.71073A
Crystal system, space group Triclinic, P − 1
Unit cell dimensions a = 13.0006(9) α = 116.555(2)°
b = 15.7426(12) β = 93.875(3)°
c = 16.0027(12) γ = 103.254(2)°
Volume 2796.7(4) Å3
Z, Calculated density 2, 1.303
Absorption coefficient 0.722mm−1
F(000) 1120
Crystal size 0.286 × 0.194 × 0.168mm
Theta range for data collection 2.347°–27.565°
Limiting indices − 16 ≤ h ≤ 16, − 20 ≤ k ≤ 18,
− 19 ≤ l ≤ 20
Reflections collected/unique 56,503/12,874 [Rint = 0.0363]
Completeness to θ = 25.242 99.8%
Absorption correction Semi-empirical from equivalents
Max. and min. transmission 0.90 and 0.86
Refinement method Full-matrix least-squares on F2
Data/restraints/parameters 12,874/12/658
Goodness of fit on F21.023
Final R indices [I > 2σ(I)] R1 = 0.0382, wR2 = 0.0841
R indices (all data) R1 = 0.0550, wR2 = 0.0902
Largest diff. peak and hole 0.613 and − 0.703eÅ−3
Fig. 1 Molecular structures of [(V2O2(O2)2((S)-mand)2)]2− (left) and
Λ-[Ni(phen)3]2+ (right) present incompound 1 as revealed by X-ray
structure analysis with atom labelling scheme. The displacement
ellipsoids of non-hydrogen atoms are shown at 50% probability level.
Colour code: V orange, Ni green, O red, N blue, C black, H white.
(Color figure online)
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750 Transition Metal Chemistry (2019) 44:747–754
1 3
and [V4O8((2S,3S)-tart)2] (H4tart4− = tartar ic acid) [22]. In
the case where all four chiral components were present in the
crystal structure, it was possible to observe a homochiral lay-
ers of the cations, while the enantiomers of the anions were
not related in a certain interaction and they were alternat-
ing along the homochiral layers of the cations. In the crys-
tal structure of 1, however, the homochiral layers of Δ- and
Λ-[Ni(phen)3]2+ are indeed present, while the anions favour
intermolecular interactions and formation of a centrosymmet-
ric entity. We assume that this is a consequence of the bulki-
ness of the [Ni(phen)3]2+ cations that enforce squeezing of
the anions into cavities; a process that is also supported by an
available free coordination site in the trans position towards
the V=O group. Consequently, the protruding phenyl groups
of the chiral mandelato ligands determine the configuration
of the cations of the layer with which they interact (or vice
versa).
Spectroscopic data
UV–Vis spectra
The UV–Vis spectrum of compound1 in DMSO exhibits
bands due to the ππ* transitions of the phen ligand in the
UV region. We assign the band at 417nm to the O22− V
charge transfer transition [36] and that at 790nm to the dd
transition of Ni(II) (Table3, Fig.3) [22]. The dominant band
in the visible region of the spectrum corresponding to the
CT transition in the compound is responsible for the red
colour typical for monoperoxido complexes of vanadium(V),
while the pink colour expected for the [Ni(phen)3]2+ cation
is entirely suppressed [37].
Infrared spectra
The IR spectrum ofcompound 1 contains characteris-
tic bands of coordinated phen ligands, the bands of the
VO(O2) group, as well as the bands of water molecules
(Fig.4). Stretching vibrations of water molecules occur at
3374 and 3280cm−1. The very strong band correspond-
ing to ν(C=O) is observed at 1622cm−1, and the strong
bands assigned to coordinated phen molecules at 1516,
1426, 849 and 726cm−1. The characteristic bands of the
VO(O2) group occur at 968–990cm−1 for (ν(V=O)) and
at 929cm−1 for (ν(Op–Op) (Op—oxygen atom of peroxido
ligand).
51V NMR spectra
The decomposition of the complex in solution proceeds with
the consecutive release of oxygen from the peroxide group.
We investigated the decomposition process in DMSO by
Table 2 Structural parameters of ions [Ni(phen)3]2+ and [(V2O2(O2)
2(mand)2]2− in 1
OP—Oxygen atom of the peroxido ligand, OH—oxygen atom of the
original hydroxy group, OC—coordinated oxygen atom of the carbox-
ylic group
Parameter Bond length in
Å, bond angle
in °
[Ni(phen)3]2+
Ni(1)–N(1) 2.0850 (17)
Ni(1)–N(2) 2.0860 (16)
Ni(1)–N(3) 2.0672 (16)
Ni(1)–N(4) 2.0851 (16)
Ni(1)–N(5) 2.0722 (17)
Ni(1)–N(6) 2.0951 (17)
N(3)–Ni(1)–N(5) 94.27 (6)
N(3)–Ni(1)–N(1) 91.76 (6)
N(5)–Ni(1)–N(1) 170.89 (7)
N(3)–Ni(1)–N(4) 80.09 (7)
N(5)–Ni(1)–N(4) 94.54 (7)
N(1)–Ni(1)–N(4) 93.22 (6)
N(3)–Ni(1)–N(2) 169.34 (7)
N(5)–Ni(1)–N(2) 94.77 (7)
N(1)–Ni(1)–N(2) 79.98 (7)
N(4)–Ni(1)–N(2) 93.56 (7)
N(3)–Ni(1)–N(6) 96.75 (7)
N(5)–Ni(1)–N(6) 80.09 (7)
N(1)–Ni(1)–N(6) 92.43 (7)
N(4)–Ni(1)–N(6) 173.60 (7)
N(2)–Ni(1)–N(6) 90.37 (7)
[(V2O2(O2)2(mand)2]2−
V = O V(1)–O(12) 1.5846 (14)
V(2)–O(7) 1.5959 (12)
V–OPV(2)–O(5) 1.8792 (14)
V(2)–O(6) 1.8709 (14)
V(1)–O(10) 1.8543 (15)
V(1)–O(11) 1.8886 (16)
VOCV(2)–O(3) 2.0189 (14)
V(1)–O(8) 2.0276 (16)
VOHV(1)–O(1) 1.9611 (13)
V(2)–O(1) 2.0024 (14)
V(1)–O(2) 1.9952 (14)
V(2)–O(2) 1.9878 (13)
OPVOPO(6)–V(2)–O(5) 44.80 (6)
O(10)–V(1)–O(11) 45.00 (7)
VOHV V(1)–O(1)–V(2) 110.41 (6)
V(2)–O(2)–V(1) 109.61 (6)
OHVOCO(1)–V(1)–O(8) 76.60 (6)
O(2)–V(2)–O(3) 77.83 (6)
OHVOHO(1)–V(1)–O(2) 70.21 (5)
O(2)–V(2)–O(1) 69.53 (5)
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751Transition Metal Chemistry (2019) 44:747–754
1 3
means of 51V NMR spectroscopy, although due to the com-
plexity of the spectra we were able to make only a tentative
assignment of chemical shifts [29, Table4, Fig.5]. Based on
our previous speciation study of vanadates in DMSO solu-
tions [29], we can rule out the presence of common vana-
dates as decomposition products in this system as their sig-
nals should appear in the region −545 to −570ppm (i.e.,
H2VO4, H2V2O72−, V4O124−, V5O155−).
The 51V NMR spectrum of the complex in DMSO solu-
tioncontains nine signals besides several very weak peaks.
These nine signals exhibit different behaviour, when the time
dependence of the spectra is taken into account:
Fig. 2 Schematic represen-
tation of the ionic dimer
{[(V2O2(O2)2((S)-mand)2)]
[(V2O2(O2)2((R)-mand)2)]}4−
(upper, H atoms are omitted for
clarity) and its position in the
crystal packing (lower frame)
viewed along the c axis. The
enantiomers Λ-[Ni(phen)3]2+
and Δ-[Ni(phen)3]2+ are illus-
trated as blue and green propel-
lers, respectively
Table 3 Electronic spectral data
of 1 in DMSO
Electronic spectra were meas-
ured at different concentrations:
7.4 × 10−6 mol/L (bands: (271,
297 nm) and 4.7 × 10−4 mol/L
(417, 790nm)
* stands for “antibonding
orbital”
λ (nm) Assignment
271 π π*
297 π π*
417 CT O22− V
790 3A2g 3T2g
Fig. 3 Electronic spectra of 1 in DMSO measured at various concen-
trations: 7.4 × 10−6mol/L (a) and 4.7 × 10−4mol/L (b, c)
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752 Transition Metal Chemistry (2019) 44:747–754
1 3
(i) Monotonous decrease of the intensity with time. This
is valid for the most intense signal in the spectrum
measured immediately after dissolution at −553ppm
(Fig.5a). We attribute this signal to the original
anion in the compound, which undergoes successive
decomposition. Similar behaviour is observed for the
weak signal at −597ppm, which can be assigned to
diperoxido species [29, Table4] and signals at −522
and −463ppm attributable to monoperoxido mande-
lato complexes of vanadium.
(ii) The intensity of signals increases at the beginning,
then decreases. This behaviour concerns the signals
at −540, −534 and −511ppm, which can be assigned
to peroxidovanadium species (without mandelic acid)
[29] and asignal at −495ppm attributable to monop-
eroxido mandelato complexes of vanadium [29].
(iii) The intensity of only one signal increases continually
with time. This signal at −504ppm can be reliably
attributed to the [V2O4(mand)2]2− anion (designated
as V2L2).
Thus, in spite of the complicated course of the decom-
position process the whole decomposition reaction cor-
responds to the release of oxygen from the anion in
1: [V2O2(O2)2(mand)2]2− [V2O4(mand)2]2− + O2.
In conclusion, the solvolysis of the complex anion
Fig. 4 IR spectra ofcompound
1 a in KBr disc, b ATR
Table 4 51V NMR spectra of 1 in DMSO. Chemical shifts with the relative intensity in parenthesis
M indicates the presence of mandelato ligand in unknown stoichiometry
a Time after dissolution
b Monoperoxido mandelato complex of vanadium
c [V2O4(mand)2]2−
d Monoperoxido complex of vanadium (without mandelato ligand)
e Diperoxido complex of vanadium (without mandelato ligand)
f w—Very weak signal
T/haVO(O2)MbVO(O2)MbV2L2
cVO(O2)dVO(O2)MbVO(O2)dVO(O2)d1VO(O2)2
e
0 463 (2.3) 495 (9.1) 505 (1.9) 511 (2.7) 522 (6.2) 534 (1.9) 540 wf553 (75) 597 wf
3463 wf495 (19) 505 (4.3) 511 (12.5) 522 (3.9) 534 (2.9) 540 (6) 553 (51) 597 wf
6463 wf495 (19) 505 (12.8) 511 (21.9) 522 (2.4) 534 (3.1) 539 (12.9) 533 (27.9) 597 wf
24 504 (90.8) 510 wf534 wf540 wf
48 504 (100)
Fig. 5 51V NMR spectra of 1 (c = 5 × 10−3mol/L) in DMSO: a 0h, b
3h, c 6h, d 24h and e 48h after preparation
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753Transition Metal Chemistry (2019) 44:747–754
1 3
[V2O2(O2)2(mand)2]2− provides a rare example in
vanadium(V) chemistry, when upon dissolution several spe-
cies are formed which give rise to a single product. Based on
51V NMR investigations, the ligandvanadate equilibria are
usually complicated, and the presence of vanadate oligomers
is common. In the case of compound 1, however, we observed
a completely opposite type of reactivity.
Thermal decomposition
The TG curves of [Ni(phen)3]2[(V2O2(O2)2((S)-mand)2)]
[(V2O2(O2)2((R)-mand)2)]·18H2O proceeds in several steps
(Fig.6). We can propose the release of crystal water (endo-
thermic peak at ≈ 100°C, calc. mass loss 12.87%, found
9.56%). The difference between calculated and experimen-
tal mass loss is due to the instability of the compound (as
mentioned in the Experimental section). Moreover, solvent
can be liberated also at higher temperatures and an over-
lap between the processes of the release of the solvent and
decomposition of a peroxide group can occur.
The next steps of decomposition that are accompanied by
exothermic effects on the DTA curves at ≈ 175, 420 and
504°C correspond to the decomposition of the peroxidic
oxygen and organic ligands. The final product of thermal
decomposition is Ni(VO3)2 with a very small admixture of
V2O5 (calc. residue 20.37%, found 20.61%). Figure7 fea-
tures a typical IR spectrum of Ni(VO3)2 [22] with a very
weak band of V2O5 at ~ 1020cm−1.
Conclusion
We havereported herein the synthesis and characterization
of [Ni(phen)3]2[(V2O2(O2)2((S)-mand)2)][(V2O2(O2)2((R)-
mand)2)]·18H2Oasa new hybrid metal–organic compound
comprised of nickel(II) and vanadium(V) coordination enti-
ties coupled stereoselectively in the solid state by packing
into homochiral layers. The compound provides Ni(VO3)2
as the dominating product of its thermal decomposition.
Upon dissolution in DMSO, the compound gives rise to
[V2O4(mand)2]2− as the single final product.
Acknowledgements Open access funding provided by Austrian Sci-
ence Fund (FWF). This work was supported by the Scientific Grant
Agency of the Ministry of Education of Slovak Republic and Slovak
Academy of Sciences VEGA Project No. 1/0507/17, as well as by
the Slovak Research and Development Agency (APVV-17-0324). LK
acknowledges support from the Austrian Science Fund (FWF), Project
No. M2200, and the University of Vienna. RG acknowledges support
from Charles University Centre of Advanced Materials (CUCAM) (OP
VVV Excellent Research Teams) CZ.02.1.01/0.0/0.0/15_003/0000417.
Open Access This article is distributed under the terms of the Crea-
tive Commons Attribution 4.0 International License (http://creat iveco
mmons .org/licen ses/by/4.0/), which permits unrestricted use, distribu-
tion, 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.
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