Vanadium(IV and v) complexes of pyrazolone based ligands: Synthesis, structural characterization and catalytic applications

Article abstract of DOI:10.1039/c6dt03425j

The ONO donor ligands obtained from the condensation of 4-benzoyl-3-methyl-1-phenyl-2-pyrazoline-5-one (Hbp) with benzoylhydrazide (H₂bp-bhz I), furoylhydrazide (H₂bp-fah II), nicotinoylhydrazide (H₂bp-nah III) and isonicotinoylhydrazide (H₂bp-inh IV), upon treatment with [V^IVO(acac)₂], lead to the formation of [V^IVO(bp-bhz)(H₂O)] 1, [V^IVO(bp-fah)(H₂O)] 2, [V^IVO(bp-nah)(H₂O)] 3 and [V^IVO(bp-inh)(H₂O)] 4, respectively. At neutral pH the in situ generated aqueous K[H₂V^VO₄] reacts with ligands I and II, forming potassium salts, K(H₂O)₂[V^VO₂(bp-bhz)] 5 and K(H₂O)₂[V^VO₂(bp-fah)] 6, while ligands III and IV give neutral complexes, [V^VO₂(Hbp-nah)] 9 and [V^VO₂(Hbp-inh)] 10, respectively. Acidification of aqueous solutions of 5 and 6 with HCl also gives neutral complexes [V^VO₂(Hbp-bhz)] 7 and [V^VO₂(Hbp-fah)] 8, respectively. Complexes 1-4, upon slow aerial oxidation in methanol, convert into monooxidovanadium(v) complexes, [V^VO(bp-bhz)(OMe)] 11, [V^VO(bp-fah)(OMe)] 12, [V^VO(bp-nah)(OMe)] 13 and [V^VO(bp-inh)(OMe)] 14, respectively. All complexes were characterized by various spectroscopic techniques like FT-IR, UV-visible, EPR (for complexes 1-4) and NMR (¹H, ¹³C and ⁵¹V), elemental analysis, thermogravimetry and single crystal X-ray diffraction (for complexes 5-10 and 12). In the solid state, all complexes characterized by X-ray diffraction show the metal ion 5-coordinated in a distorted square pyramidal geometry. Complexes 11-14 were tested as catalysts for the one-pot three-component (ethylacetoacetate, benzaldehyde and ammonium acetate) dynamic covalent assembly, via Hantzsch reaction, using hydrogen peroxide as oxidant in solution and under solvent-free conditions. The complexes are also active catalysts for the oxidation of tetralin to tetralone with H₂O₂ as oxidant. The influence of the amounts of catalyst and oxidant, and solvent, temperature and time on the catalyzed reactions was investigated.

Full text of DOI:10.1039/c6dt03425j

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Vanadium(IV and V) complexes of pyrazolone based ligands: Structural characterization
and catalytic application for the three components dynamic covalent assembly via
Hantzsch reaction and for the selective oxidation of tetralin †
Mannar R. Maurya a,*, Bithika Sarkar a, Fernando Avecilla b and Isabel Correia c,*
a
Department of Chemistry, Indian Institute of Technology Roorkee, Roorkee–247667, India. E–
mail: rkmanfcy@iitr.ernet.in; Fax: +91 1332 273560; Tel: +91 1332 285327
b Departamento de Química Fundamental, Universidade da Coruña, Campus de A Zapateira, 15071
A Coruña, Spain
c Centro de Química Estrutural, Instituto Superior Técnico, Universidade Lisboa, 1049–001 Lisboa,
Portugal. E–mail: icorreia@ist.utl.pt; Fax: +351 21 8464455; Tel: +351 21 8419177
Keywords: Vanadium complexes / benzoyl pyrazolone / NMR spectroscopy / three components
dynamic covalent assembly via Hantzsch reaction /oxidation of tetraline.
_________________________________
†Electronic supplementary information (ESI) available: Details of EPR, 51V NMR and other
spectral studies. CCDC 1502023–1502029. For ESI and crystallographic data in CIF or other
electronic format see DOI: xxxxxxxx.
1

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Abstract
The ONO donor ligands, obtained from the condensation of 4ꢀbenzoylꢀ3ꢀmethylꢀ1ꢀphenylꢀ2ꢀ
pyrazolineꢀ5ꢀone (Hbp) with benzoylhydrazide (H2bpꢀbhz I), furoylhydrazide (H2bpꢀfah II),
nicotinoylhydrazide (H2bpꢀnah III) and isonicotinoylhydrazide (H2bpꢀinh IV), upon treatment
with [VIVO(acac)2] lead to the formation of [VIVO(bpꢀbhz)(H2O)] 1, [VIVO(bpꢀfah)(H2O)] 2,
[VIVO(bpꢀnah)(H2O)] 3 and [VIVO(bpꢀinh)(H2O)] 4, respectively. At neutral pH the in situ
generated aqueous K[H2VVO4] reacts with ligands I and II forming the potassium salts,
K(H2O)2[VVO2(bpꢀbhz)] 5 and K(H2O)2[VVO2(bpꢀfah)] 6, while ligands III and IV give neutral
complexes, [VVO2(bpꢀnah)] 9 and [VVO2(bpꢀinh)] 10, respectively. Acidification of aqueous
solutions of 5 and 6 with HCl also gives neutral complexes [VVO2(Hbpꢀbhz)] 7 and [VVO2(Hbpꢀ
fah)] 8, respectively. Complexes 1ꢀ4, upon slow aerial oxidation in methanol, convert into
monooxidovanadium(V) complexes, [VVO(bpꢀbhz)(OMe)] 11, [VVO(bpꢀfah)(OMe)] 12,
[VVO(bpꢀnah)(OMe)] 13 and [VVO(bpꢀinh)(OMe)] 14, respectively. All complexes were
characterized by various spectroscopic techniques like, FTꢀIR, UVꢀVisible, EPR (for complexes
1ꢀ4) and NMR (1H, 13C and 51V), elemental analysis, thermogravimetry and single crystal Xꢀray
diffraction (for complexes 5ꢀ10 and 12). In the solid state all complexes characterized by Xꢀray
diffraction show the metal ion 5ꢀcoordinated in a distorted square pyramidal geometry.
Complexes 11ꢀ14 were tested as catalysts for the oneꢀpot three components (ethylacetoacetate,
benzaldehyde and ammonium acetate) dynamic covalent assembly, via Hantzsch reaction, using
hydrogen peroxide as oxidant in solution and solventꢀfree condition. Various parameters were
optimized and the temperature and oxidant amount are the ones controlling the conversion and
selectivity of the desired product. The complexes are also active catalysts for the oxidation of
tetralin to tetralone with H2O2 as oxidant. The influence of amount of catalyst, oxidant, solvent,
temperature and time on the catalyzed reactions was investigated.
Introduction
Hantzsch 1,4ꢀdihydropyridines (1,4ꢀDHPs) are one of the most significant groups of heterocyclic
compounds because of their pharmacological activity as calcium antagonists or agonists.1
Substituted 1,4ꢀDHPs are extensively used in other pharmacological applications such as:
antitumor,2 bronchodilating3 antidiabetic,4 neurotropic5 and antianginal.6 First reported in 1882,
2

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the Hantzsch reaction is a convenient way to prepare the 1,4ꢀDHPs, involving the condensation
of an aldehyde with 2 equivalents of a βꢀketo ester and a nitrogen donor.7 Aromatization of
DHPs has received considerable attention because the conversion of 1,4ꢀDHPs into the
corresponding pyridine derivatives is one of the main metabolic pathways of the above drugs.
1,4ꢀDHP based calciumꢀchannel blockers are oxidatively converted to pyridine derivatives by
cytochrome Pꢀ450 in the liver8 and these show antiꢀhypoxic and antiꢀischemic activities.9 In
recent years, Bocker and coꢀworkers10 have studied the metabolism of Hantzsch 1,4ꢀDHPs and
showed that the first metabolic step includes aromatization to the corresponding pyridine
derivative. Moreover, the products of aromatization (substituted pyridines) have found use in the
treatment of atherosclerosis and various coronary diseases.11 Therefore, the oxidative
aromatization of DHPs has attracted substantial attention from organic and medicinal chemists.
Numerous reagents and procedures have been suggested for the oxidation of DHPs. Strong
oxidizing reagents such as pyridinium chlorochromate (PCC),12 metallic salts e.g. Zr(NO3)4,13
(NH4)4Ce(NO3)6,14 urea nitrate, photochemical oxidation15 silver salts, iodine monochloride,
inorganic acidic salts,16 sodium nitrite/ nitrate and O2ꢀactivated carbon have been used.17
However, most of the reported oxidation procedures involve long reaction times, strong
oxidizing agents in large excess, low selectivity and yield, harsh reaction condition, use of toxic
and expensive reagents, corrosive solvents, tedious workꢀups, etc. Furthermore, the
aromatization leads to dealkylation of the 4ꢀposition or formation of side products.18 Therefore,
the development of more efficient and mild methods for aromatization of DHPs is still required.
Recently, it has been reported that manganese Schiff base complexes,19 cobalt silica grafted
complexes,20 MoOCl4,21 SbCl522 and vanadium salts23 can be used as catalysts in the presence of
the mild oxidant H2O2 for aromatization and all these processes produce higher yields in lower
reaction times.
Among various transition metals, vanadium has been extensively used in catalytic
oxidation reactions of various organic substrates including sulphoxidation,24 bromination,25
oxidation of alcohols,26 epoxidation of olefins,27 hydroxylation of aromatic hydrocarbons,28 etc.
However, to the best of our knowledge, the aromatization by vanadium azine complexes has not
been reported. Therefore, we have synthesized oxidovanadium(IV), oxidovanadium(V) and
dioxidovanadium(V) complexes of pyrazolone based ligands (Scheme 1) and used the
3

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oxidovanadium(V) complexes for a milder and more selective catalyzed aromatization of 1,4ꢀ
DHPs.
R
Ligands
R
Ligands
4.I
4.II
4.III
4.IV
Scheme 1. Structure of pyrazoline based ligands used in this study.
We have also extended the catalyst scope towards the selective oxidation of tetralin to
tetralone. Tetralone is a ketoꢀhydronaphthalene which is used as a reactive intermediate in dyes,
pharmaceuticals, and agrochemicals.29,30 Tetralone can be prepared by FriedelꢀCrafts acylation of
aromatics with acid halide/anhydride or oxidation reactions. The corrosive AlCl3 catalyst or
KMnO4/ K2Cr2O7 oxidizing agent have been used in both processes.31 Many efforts have been
put forward recently in the development of environmentally friendly and economically
sustainable processes for the selective oxidation of alkylaromatics and cycloalkanes to higherꢀ
value added ketones. In this scope, catalytic systems (homogeneous and heterogeneous)
involving ‘‘green’’ oxidants like O2 and H2O2 have been developed for the oxidation of
tetralin.32,33 In the present work, we have used the oxidovanadium(V) complexes as a catalyst for
the oxidation of tetralin by H2O2 at 80 ⁰C.
Experimental Section
Materials and methods
Acetylacetone, furoylhydrazide, (Aldrich Chemicals Co., U.S.A.), ethylbenzoate,
hydrazine hydrate, isonicotinoylhydrazide (Loba Chemie, Mumbai, India), nicotinoylhydrazide
4

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(Acros organics, New Jersey, USA), ethylacetoacetate, ammonium acetate, diethylether,
benzaldehyde, tetraline and 30% aqueous H2O2, (Renkem, India) were used as received. Other
chemicals and solvents were of analytical reagent grade. [VIVO(acac)2]34 and ligands H2bpꢀbhz I,
H2bpꢀfah II, H2bpꢀnah III and H2bpꢀinh IV35 were prepared according to methods reported in the
literature.
Instrumentation
Elemental analysis (C, H and N) were carried out on an elementer model VarioꢀE1ꢀIII. IR
spectra were recorded as KBr pellets on a Nicolet 1100 FTꢀIR spectrometer after grinding the
samples. Electronic absorption spectra were measured in methanol with a Shimadzu UVꢀ1601
1
PC UVꢀvisible spectrophotometer. H and 13C NMR spectra were recorded in DMSOꢀd6 on a
51
Bruker Advance 500 MHz spectrometer. V NMR spectra were recorded on a Bruker Avance
III 400 MHz instrument. 51V chemical shifts were referenced relative to neat VVOCl3 as external
standard. EPR spectra were recorded at 77 K with a Bruker ESP 300E Xꢀband spectrometer
coupled to a Bruker ER041 Xꢀband frequency meter (9.45 GHz). The complexes were dissolved
at room temperature in DMSO p.a. grade, previously degassed by passing N2 for 10 min, to
obtain ca. 3 mM solutions. Spectra were measured at 77K and simulated with a program
developed by Rockenbauer and Korecz. [36]. Thermogravimetric analyses of the complexes were
carried out under oxygen atmosphere using a TG Stanton Redcroft STA 780 instrument. A
Shimadzu 2010 plus gasꢀchromatograph fitted with a Rtxꢀ1 capillary column (30 m × 0.25 mm ×
0.25 ꢁm) and a FID detector was used to analyze the reaction products and their quantification
was made based of the relative peak area of each product. The identity of the products was
confirmed using a GCꢀMS model PerkinꢀElmer, Clarus 500 and by comparing the fragments of
each product with the library available.
Preparation of the complexes
[VIVO(bp-bhz)(H2O)] 1. The ligand H2bpꢀbhz (0.34 g, 0.0010 mol) was dissolved in absolute
methanol (15 mL) and filtered. A solution of [VIVO(acac)2] (0.26 g, 0.0010 mol) in methanol
(15 mL) was added to the above solution with stirring. The reaction mixture was refluxed for 4
h. The final solution was reduced to 10 ml and kept in the fridge. Gradually a black solid
precipitated, which was filtered, washed with methanol, followed by petroleum ether (b.p. 60 oC)
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and dried in a desiccator over silica gel. Yield: 0.36 g (75 %). Found: C, 60.2; H, 4.4; N, 11.6;
C24H20N4O4V (479.38 g mol−1) requires C, 60.13; H, 4.21; N, 11.69.
[VIVO(bp-fah)(H2O)] 2, [VIVO(bp-nah)(H2O)] 3 and [VIVO(bp-inh)(H2O)] 4. Complexes 2ꢀ4
were prepared from H2bpꢀfah II, H2bpꢀnah III and H2bpꢀinh IV, respectively, following the
method outlined for 1.
2: Yield: 0.39 g (83 %). Found: C, 56.5; H, 4.0; N, 11.8; C22H18N4O5V (469.34 g mol−1) requires
C, 56.30; H, 3.87; N, 11.9.
3: Yield: 0.34 g (71 %). Found: C, 57.5; H, 3.8; N, 14.6; C23H19N5O4V (480.37 g mol−1) requires
C, 57.51; H, 3.99; N, 14.58.
4: Yield: 0.36 g (75 %). Found: C, 57.1; H, 3.7; N, 14.4; C23H19N5O4V (480.37 g mol−1)
requires C, 57.51; H, 3.99; N, 14.58.
K(H2O)2[VVO2(bp-bhz)] 5. Vanadium(V) oxide, V2O5 (0.18 g, 0.0010 mol), was suspended in
an aqueous solution of KOH (0.11 g, 0.0020 mol in 5 mL H2O) and stirred for 2 h with
occasional heating at 50 oC. The resulting solution was then filtered. A filtered solution of I (0.67
g, 0.0020 mol), dissolved in 50 mL of aqueous KOH (0.22 g, 0.0040 mol), was added to the
above solution. After 4 h of stirring the pH of the reaction mixture was slowly adjusted to ca. 7.5
with 4 M HCl. The yellowishꢀorange solid of 5 started to separate. The solution was filtered, the
solid washed with cold methanol (2×5 mL) and dried in a desiccator over silica gel. Yield: 0.33 g
(60 %). Color: yellow. Found: C, 52.2; H, 3.9; N, 10.4; C24H22KN4O6V (552.49 g mol−1) requires
C, 52.17; H, 4.01; N, 10.14.
K(H2O)2[VVO2(bp-fah)] 6. Complex 6 was prepared following the method outlined for 5 using
ligand II. Yield: 0.37 g (68 %). Colour: yellow. Found: C, 48.8; H, 3.7; N, 10.3; C22H20KN4O7V
(542.46 g mol−1) requires C, 48.71; H, 3.72; N, 10.33.
[VVO2(Hbp-bhz)] 7 and [VVO2(Hbp-fah)] 8. Complex 5 (0.53 g, 0.0010 mol) or 6 (0.52 g,
0.0010 mol) were dissolved in water (40 ml) and treated with aqueous HCl (1 mL of HCl diluted
in 5 ml of water) with stirring until most of the complex had precipitated as a yellow solid. The
solution was filtered, the residue washed with water and dried in a desiccator over silica gel.
7: Yield: 0.28 g (60 %). Colour: yellow. Found: C, 60.5; H, 3.8; N, 11.9; C24H19N4O4V (478.37
g mol−1) requires C, 60.26; H, 4.00; N, 11.71.
6

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8: Yield: 0.27 g (66 %). Colour: yellow. Found: C, 56.6; H, 3.5; N, 11.8; C22H17N4O5V (468.34
g mol−1) requires C, 56.42; H, 3.66; N, 11.96.
[VVO2(Hbp-nah)] 9 and [VVO2(Hbp-inh)] 10. Vanadium(V) oxide, V2O5 (0.18 g, 0.0010 mol),
was suspended in an aqueous solution of KOH (0.11 g, 0.0020 mol in 5 mL H2O) and stirred for
1 h with occasional heating at 50 oC. The resulting solution was then filtered. A filtered solution
of ligand H2bpꢀnah III (0.79 g, 0.0020 mol) or H2bpꢀinh IV (0.79 g, 0.0020 mol), dissolved in 50
mL of aqueous KOH (0.22 g, 0.0040 mol), was added to the above solution with stirring. The
resulting reaction mixture was allowed to stir for 4 h. After that, the pH of the reaction mixture
was slowly adjusted to ca. 7.5 with 4 M HCl where orange solids of 9 or 10 slowly started to
separate. After 1 h, the separated solids were filtered, washed with cold water (2×5 mL) and
dried in a desiccator over silica gel.
9: Yield: 0.25 g (60 %). Colour: yellow. Found: C, 57.7; H, 3.7; N, 14.8; C23H18N5O4V (479.36
g mol−1) requires C, 57.63; H, 3.78; N, 14.61.
10: Yield: 0.25 g (61 %). Colour: yellow. Found: C, 51.2; H, 3.9; N, 16.6; C23H18N5O4V (479.36
g mol−1) requires C, 57.63; H, 3.78; N, 14.61.
[VVO(bp-bhz)(OMe)] 11. Complex 1 (0.48 g, 0.0010 mol) was dissolved in MeOH (25 mL) and
allowed to stand in the open flask for slow evaporation/oxidation. The black crystals separated
within a week. Yield: 0.38 g (77 %). Found: C, 60.7; H, 4.4; N, 11.6; C25H21N4O4V (492.40 g
mol−1) requires C, 60.98; H, 4.30; N, 11.38.
[VVO(bp-fah)(OMe)] 12, [VVO(bp-nah)(OMe)] 13 and [VVO(bp-inh)(OMe)] 14. These
complexes were prepared similarly to 11 from the respective oxidovanadium(IV) 2ꢀ4 complexes.
12: Yield: 0.39 g (80 %). Found: C, 57.5; H, 4.0; N, 11.6; C23H19N4O5V (482.36 g mol−1),
requires C, 57.27; H, 3.97; N, 11.62.
13: Yield: 0.34 g (70 %). (Found: C, 58.5; H, 3.8; N, 14.6; C24H20N5O4V (493.39 g mol−1),
requires, C, 58.42; H, 4.09; N, 14.19).
14: Yield: 0.37 g (75 %). (Found: C, 58.6; H, 3.9; N, 14.2; C24H20N5O4V (493.39 g mol−1),
requires, C, 58.42; H, 4.09; N, 14.19).
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Catalytic activity
Aromatization of Hantzsch 1,4-dihydropyridines
Benzaldehyde (0.53 g, 0.0050 mol), ethylacetoacetate (1.1 g, 0.010 mol) and ammonium
acetate (0.38 g, 0.0050 mol) were mixed in a flask and after adding the selected catalyst
precursor (0.0010 g) the reaction mixture was allowed to stir for 1 h at room temperature.
Progress of the reaction was monitored by GC withdrawing small aliquots of the reaction
mixture, extracting with nꢀhexane and injection to the GC column. The structures of the products
were confirmed by GCꢀMS and comparison with authentic samples reported in the literature.
Oxidation of tetralin
In a typical reaction, tetralin (1.3 g, 0.010 mol) and 30% H2O2 (2.3 g, 0.020 mol) were
taken in 5 mL of CH3CN and 0.0020 g of the complex was added. Then the reaction mixture was
stirred at 80 ⁰C for the desired time. The obtained reaction product was identified by GC analysis
and confirmed by GCꢀMS.
X-Ray crystal structure determination
Threeꢀdimensional Xꢀray data were collected on a Bruker Kappa Apex CCD
diffractometer at low temperature for 5 and 7, and at room temperature for 6, 8, 9, 10 and 12, by
the
φ
ꢀ
ω
scan method. Reflections were measured from a hemisphere of data collected from
.A total of 38439 reflections measured for 5, 35394 for 6,
frames, each of them covering 0.3º in
ω
24559 for 7, 44518 for 8, 29571 for 9, 47446 for 10 and 28005 for 12 were corrected for Lorentz
and polarization effects and for absorption by multiꢀscan methods based on symmetryꢀequivalent
and repeated reflections. Of the total independent reflections, 4288 for 5, 3365 for 6, 2533 for 7,
3381 for 8, 3140 for 9, 4556 for 10 and 3431 for 12 exceeded the significance level (F/σF)
> 4.0. After data collection, in each case a multiꢀscan absorption correction (SADABS)37 was
applied, and the structure was solved by direct methods and refined by full matrix leastꢀsquares
on F2 data using SHELX suite of programs.38 Hydrogen atoms were located in a difference
Fourier map and left to refine freely in 5, except for O(1W), which were located in a difference
Fourier map and fixed to the oxygen atom. In 6 and 7the hydrogen atoms were included in
calculated positions and refined in the riding mode, except for the water molecules, which were
8

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located in a difference Fourier map, calculated and refined by wingx program39 and fixed on the
oxygen atom. In 8 and 9 the hydrogen atoms were located in a difference Fourier map and left to
refine freely, except for C(4), which were included in calculated positions and refined in the
riding mode. In 10 the hydrogen atoms were located in a difference Fourier map and left to refine
freely, except for C(1S), C(2S) and C(4), which were included in calculated positions and refined
in the riding mode. In 12 the hydrogen atoms were located in a difference Fourier map and left to
refine freely, except for C(1S), C(4) and C(20), which were included in calculated positions and
refined in the riding mode. Refinements were done with allowance for thermal anisotropy of all
nonꢀhydrogen atoms. A final difference Fourier map showed no residual density outside: 0.425
and ꢀ0.654 e.Å–3 for 5, 0.617 and ꢀ0.772 e.Å–3 for 6, 1.182 and ꢀ0.429 e.Å–3 for 7, 0.370 and ꢀ
0.406 e.Å–3 for 8, 0.501 and ꢀ0.507 e.Å–3 for 9, 0.676 and ꢀ0.382 e.Å–3 for 10 and 0.272 and ꢀ
2
0.380 e.Å–3 for 12. A weighting scheme w = 1/[σ2(Fo ) + (0.061000 P)2 + 0.708500 P] for 5, w =
1/[σ2(Fo ) + (0.115500 P)2 + 0.00000 P] for 6, w = 1/[σ2(Fo ) + (0.142000 P)2 + 0.000000 P] for
2
2
2
2
7, w = 1/[σ2(Fo ) + (0.058700 P)2 + 3.998300 P] for 8,w = 1/[σ2(Fo ) + (0.076200 P)2 + 0.00000
2
2
P] for 9, w = 1/[σ2(Fo ) + (0.065700 P)2 + 0.371500 P] for 10 andw = 1/[σ2(Fo ) + (0.068700 P)2
+ 3.405000 P] for 12, where P = (|Fo|2 + 2|Fc|2)/3, were used in the latter stages of refinement.
Further details of the crystal structure determination are given in Table 1.
Table 1. Crystal data and structure refinement for [K(H2O)2{VVO2(bpꢀbhz)}]2 5,
[K(H2O)2{VVO2(bpꢀfah)}]2 6, [VVO2(Hbpꢀbhz)]·1.5H2O 7·1.5H2O, [VVO2(Hbpꢀfah)] 8,
[VVO2(Hbpꢀnah)] 9, [VVO2(Hbpꢀinh)]·DMSO 10·DMSO and [VVO(bpꢀfah)(OCH3)] 12.
7·1.5H2O
C24 H22 N4 O5.50
505.40
5
6
8
Formula
Formula weight
T, K
C48 H44 K2 N8 O12 V2
1104.99
C44 H40 K2 N8 O14 V2
1084.90
V
C22 H17 N4 O5 V
468.34
100(2)
293(2)
100(2)
293(2)
Wavelength, Å
Crystal system
Space group
a/Å
0.71073
0.71073
0.71073
0.71073
Monoclinic
C2/c
Triclinic
P1
Monoclinic
P21/c
Triclinic
P1
8.5326(3)
10.2707(3)
14.0922(5)
87.943(2)
82.422(2)
70.9430(10)
11.6725(8)
22.2312(15)
9.1846(6)
8.5590(16)
10.2574(18)
14.448(2)
83.719(11)
78.317(11)
71.534(11)
25.862(3)
7.1899(7)
21.357(2)
b/Å
c/Å
α/º
β/º
γ/º
96.914(2)
98.156(5)
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V/Å3
1157.07(7)
1
2366.0(3)
2
1176.8(4)
2
3931.0(7)
Z
8
F000
568
1108
522
1920
Dcalc/g cmꢀ3
1.586
1.520
1.426
1.583
/mmꢀ1
0.659
0.646
0.467
0.550
ꢀ
1.46 to 26.39
0.0336
1.76 to 28.62
0.0515
1.44 to 26.43
0.0706
1.59 to 26.38
0.0474
θ
/ (º)
Rint
Crystal size/ mm3
Goodnessꢀofꢀfit on F2
R1[I>2σ(I)] a
0.41 × 0.25 × 0.20
1.132
0.31 × 0.29 × 0.13
1.024
0.16 × 0.11 × 0.08
1.012
0.16 × 0.14 × 0.13
1.107
0.0313
0.0595
0.0705
0.0315
wR2 (all data) b
Largest differences
peak and hole (eÅꢀ3)
0.1074
0.1961
0.2421
0.1040
0.425 and ꢀ0.654
0.617 and ꢀ0.772
1.186 and ꢀ0.437
0.370 and ꢀ0.406
10·DMSO
C25 H24 N5 O5 S V
557.49
9
12
Formula
Formula weight
T, K
C
23 H18 N5 O4 V
C23 H19 N4 O5 V
482.36
479.36
293(2)
293(2)
293(2)
Wavelength, Å
Crystal system
Space group
a/Å
0.71073
Triclinic
P1
0.71073
0.71073
Monoclinic
C2/c
Triclinic
P1
9.0595(8)
9.6948(9)
12.4414(13)
95.526(6)
98.606(6)
94.410(6)
1070.77(18)
2
8.2826(7)
11.0071(9)
14.2227(12)
87.501(5)
81.094(5)
82.501(4)
1269.69(18)
2
14.133(4)
11.772(4)
26.621(8)
b/Å
c/Å
α/º
β/º
103.350(17)
γ/º
V/Å3
4309(2)
8
Z
F000
492
576
1984
Dcalc/g cmꢀ3
1.487
1.458
1.487
/mmꢀ1
0.505
0.519
0.504
ꢀ
1.67 to 26.41
0.0711
1.45 to 26.42
0.0378
1.57 to 28.43
0.0431
θ
/ (º)
Rint
Crystal size/ mm3
Goodnessꢀofꢀfit on F2
R1[I>2σ(I)] a
0.22 × 0.13 × 0.06
1.055
0.49 × 0.17 × 0.12
1.109
0.32 × 0.20 × 0.16
1.060
0.0457
0.0331
0.0495
wR2 (all data) b
Largest differences
peak and hole (eÅꢀ3)
0.1318
0.1128
0.1476
0.501 and ꢀ0.507
0.676 and ꢀ0.382
0.272 and ꢀ0.380
2 2
aR1 = ΣFo ꢀ Fc/ΣFo. bwR2 = {Σ[w(Fo2 ꢀFc2)2]/Σ[w(Fo ) ]}1/2
10

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Results and discussion
Synthesis and characterization of the complexes
Scheme 2 depicts an overview of the complexes reported in this work. The structures of
1
13
the complexes are based on elemental analyses, spectroscopic data (IR, UV/Vis, EPR, H, C
and 51V NMR), thermogravimetric studies and Xꢀray diffraction analyses of complexes 5-10 and
12.
Reaction of [VIVO(acac)2] with an equimolar amount of the ligands in methanol leads to
the formation of oxidovanadium(IV) complexes [VIVO(bpꢀbhz)(H2O)] 1, [VIVO(bpꢀfah)(H2O)] 2,
[VIVO(bpꢀnah)(H2O)] 3 and [VIVO(bpꢀinh)(H2O)] 4 [eqn (1)]. All ligands coordinate to the
metal ion in the dianionic [ONO2−] enolate tautomeric form (see Scheme 2).
2[VIVO(acac)2] + H2L + H2O → [VIVO(L)(H2O)] + 2Hacac (1)
(H2L = ligands I –IV)
Aerial oxidation, along with prolonged crystallisation of these complexes in MeOH, results
in the formation of [VVO(L)(OMe)] 11-14 [eqn (2) considering complex 1 as representative].
2[VIVO(apꢀbhz)(H2O)] + ½ O2 + 4 MeOH → 2[VVO(apꢀbhz)(OMe)] + 3H2O (2)
Complexes [K(H2O)2][VVO2(bpꢀbhz)] 5 and [K(H2O) 2][VVO2(bpꢀbhz)] 6 were isolated
from the reaction of vanadate, prepared in situ by stirring V2O5 in aqueous KOH, with ligands I
and II, respectively, while adjusting the pH to ca. 7 using HCl, eqn (3).
K[H2VO4] + H2L → [K(H2O)2][VVO2L] (H2L = I: 5; H2L = II: 6) (3)
Due to protonation of the pyridinic nitrogen, ligands III and IV gave complexes [VVO2(Hbpꢀ
nah)] 9 and [VVO2(Hbpꢀinh)] 10, respectively, under similar reaction conditions, eqn (4).
K[H2VO4] + H2L + HCl → [VVO2HL] + KCl + 2H2O (H2L = III: 9; H2L = IV: 10) (4)
Similar complexes [VVO2(Hbpꢀbhz)] 7 and [VVO2(Hbpꢀfah)] 8, where the ligands coordinate
the metal ion in the ketonic (hydrazide) form, were isolated upon acidification of aqueous
solution of complexes 5 and 6, respectively, with dilute HCl, eqn (4).
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[K(H2O)2][VVO2L] + HCl → [VVO2HL] + KCl + 2H2O (H2L = I: 7; H2L = II: 8)
(4)
Scheme 2. Proposed structures for the complexes reported in this work.
Structure descriptions
Several crystals suitable for Xꢀray diffraction studies were obtained and their structural
features are analyzed below. Table 2 provides selected bond lengths and angles for all
compounds. In all crystal structures, which were found for compounds 5ꢀ10 and 12, the metal
center is five coordinated and the geometry is best described as square pyramidal (see discussion
below).
12

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Compounds 5 and 6 show a dimeric structure due to the presence of cationꢀπ interactions
between the neutral aromatic systems and K+ ions, which control the assembly in dimeric
aggregates. Figs. 1 and 2 depict ORTEP representations of the asymmetric units, while Figs. 3
and 4 show the dimeric aggregates. In both crystal structures the metal centers are coordinated by
one terminal oxygen atom [V(1)ꢀO(1), 1.6264(15) Å in 5 and 1.605(2) Å in 6], one bridging
oxygen atom with the K+ ion [V(1)ꢀO(2), 1.6386(15) Å in 5 and 1.639(2) Å in 6], two oxygen
atoms of the ligands (bpꢀbhz in 5 and bpꢀfah in 6) [V(1)ꢀO(3), 1.9185(14) Å in 5 and 1.936(2) Å
in 6 and V(1)ꢀO(4), 1.9634(15) Å in 5 and 1.968(2) Å in 6] and one nitrogen atom of the
azomethine group [V(1)ꢀN(1), 2.1672(16) Å in 5 and 2.190(3) Å in 6]. The geometric parameter
τ = (β − α)/60, where β and α are the two largest L–M–L angles, can be used to describe the
polyhedron defined by five coordinated atoms. It has a value of 1 if the structure is pentagonal
bipyramidal and 0 if it is square pyramidal. For 5 (αO2ꢀV1ꢀN1= 146.55º, βO3ꢀV1ꢀO4= 147.53º) and 6
(αO2ꢀV1ꢀN1= 146.04º, βO3ꢀV1ꢀO4= 145.74º) the τ values of 0.02 and 0.01, respectively, indicate a
square pyramidal geometry.40 Nevertheless, they are not isostructural compounds around the K+
ions. In 5 the alkali metal coordinates to the πꢀface of the phenyl group of the ligand (bpꢀbhz)
[mean of the distances to carbon atoms 3.325(2) Å], two water molecules [K(1)ꢀO(1W), 2.827(2)
Å and K(1)ꢀO(2W) 2.7739(18) Å], two oxygen bridging atoms, which present an important
asymmetry, one of them being one the oxido groups [V(1)ꢀO(2), 1.6386(15) Å and K(1)ꢀO(2),
2.7576(16) Å] and the other the oxygen atom of the hydrazide group [V(1)ꢀO(4), 1.9634(15) Å
and K(1)ꢀO(4), 3.2355(16) Å], one MꢀNazomethine dative bond [K(1)ꢀN(2), 2.8736(17) Å] and one
lateral η1ꢀcationꢀπ interaction with a carbon atom [distance K(1)ꢀC(14), 3.188(2) Å] of the other
phenyl group. In 6, the K+ ion coordinates to the πꢀface of the phenyl group of the ligand (bpꢀ
fah) [mean of the distances to carbon atoms 3.341(2) Å], two water molecules (one of them
presenting a disorder) [K(1)ꢀO(1W), 2.844(4) Å and K(1)ꢀO(2WA), 2.693(8) Å and K(1)ꢀ
O(2WB), 2.83(2) Å], one oxido group [V(1)ꢀO(2), 1.639(2) Å and K(1)ꢀO(2), 2.781(3) Å] and
one enolic oxygen atom of the pyrazolone group [V(1)ꢀO(3), 1.936(2) Å and K(1)ꢀO(3), 3.256(2)
Å], one MꢀNazomethine dative bond [K(1)ꢀN(2), 2.914(3) Å] and one oxygen atom of the furan ring
[K(1)ꢀO(5), 2.706(2) Å]. The distances KꢀPhcentroid are 3.022(2) Å in 5 and 3.042(2) Å in 6,
similar to those found in other compounds with the same type of cationꢀπ interactions.41
The pyrazol group (C1, C2, C3, N3, N4) and the phenyl of hydrazide group (C13, C14,
C15, C16, C17, C18) are not coplanar in 5 [mean deviation from planarity, 0.1386(17) Å]. In 6,
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the furan ring of the hydrazide group (C19, C20, C21, C22, O5) and pyrazolone group (C1, C2,
C3, N3, N4) are coplanar [mean deviation from planarity, 0.0679(25) Å], and the other phenyl
group (C12, C13, C14, C15, C16, C17) forms a torsion angle of 25.78(14)º, over the previous. In
5, the vanadium atom is displaced toward the apical oxido ligand (O1) from the equatorial plane
defined by O2, O3, O4 and N1 atoms, 0.4979(7) Å, [mean deviation from planarity, O2, O3, O4,
N1, 0.0034(8)Å]. In 6, the displacement is 0.5228(11) Å, [mean deviation from planarity, O2,
O3, O4, N1, 0.0174(12)Å]. The two apical oxygen atoms present V=O bonds characteristic of
oxidoꢀtype O atoms with strong
π
bonding.42,43 The VꢀK separations, depend on the position of
the K+ ion in the dimeric aggregates and are 3.8532(6) Å in 5 and 3.7644(11) Å in 6.
In addition πꢀπ interactions, hydrogen bonding and electrostatic interactions are present
in the crystal structures of compounds 5 and 6. This results in different crystal packings in the
two compounds. In 5 there are πꢀπ interactions between dimeric aggregates (see Fig. S1) through
faceꢀtoꢀface motifs [distance between centroids of phenyl rings bonded to pyrazolone group, dc1ꢀ
c2, 3.569(8) Å, [c1(C19H, C20H, C21H, C22H, C23H, C24H) and c2(C19T, C20T, C21T, C22T,
C23T, C24T)] and edgeꢀtoꢀface motifs between phenyl groups dC11sꢀc3, 3.502(9) Å, [c3(C13J,
C14J, C15J, C16J, C17J, C18J)]. In 6 the dimeric aggregates are placed differently in the crystal
packing, due to the absence of πꢀπ interactions, the hydrogen bonds (see Table 2) being the
predominant interaction (see Fig. S2).
Compounds 7, 8, 9 and 10 contain vanadium mononuclear complexes with ligands bpꢀ
bhz, bpꢀfah, bpꢀnah and bpꢀinh respectively, which are all protonated. The ligands bpꢀbhz and
bpꢀfah are protonated at the azomethine nitrogen atom, N(2), and the ligands bpꢀnah and bpꢀinh
at the nitrogen atom of the pyridine ring. Figs. 5ꢀ8 show ORTEP representations of the
complexes in the asymmetric units. For 7 (αO3ꢀV1ꢀO4= 149.69º, βO2ꢀV1ꢀN1= 142.36º), 8 (αO3ꢀV1ꢀO4
=
=
153.35º, βO2ꢀV1ꢀN1= 141.83º), 9 (αO3ꢀV1ꢀO4= 148.60º, βO2ꢀV1ꢀN1= 145.05º) and 10 (αO3ꢀV1ꢀO4
146.53(6)º, βO2ꢀV1ꢀN1= 147.59(7)º) the calculated τ values of 0.122, 0.192, 0.059 and 0.018
respectively, indicate a distorted square pyramidal geometry.40
The pyrazol group (C1, C2, C3, N3, N4) and the phenyl, furan and pyridine rings of the
hydrazide groups (C13, C14, C15, C16, C17, C18 in 7; C19, C20, C21, C22, O5 in 8; C13, C14,
C15, C16, C17, N5 in 9 and C13, C14, C15, C16, C17, N5 in 10) are coplanar in 7, 8 and 9
[mean deviation from planarity, 0.0923(39) Å, 0.0386(16) Å and 0.0372(22) Å, respectively] and
14

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not coplanar in 10 [mean deviation from planarity, 0.2078(17) Å]. Again, the vanadium atoms in
complexes 7, 8, 9 and 10 are displaced towards the apical oxido ligand (O1) from the equatorial
plane defined by O2, O3, O4 and N1 atoms, 0.5011(7) Å, 0.4591(8) Å, 0.5011(10) Å and
0.4975(7) Å [mean deviation from planarity, O2, O3, O4, N1, 0.0819(18) Å, 0.1425(7) Å,
0.0529(10) Å and 0.0120(8) Å], respectively. The two apical oxygen atoms present V=O bonds
characteristic of oxidoꢀtype O atoms with strong
π bonding.
In Figs. S3ꢀS6 the crystal packing of compounds 7ꢀ 10 is depicted. For complex 7 it can
be described as layers of vanadium complexes interacting by van der Waals forces. Water
molecules are placed between layers in a network of hydrogen bonds (see Table 2). The crystal
packing of compound 8 presents dimeric aggregates, which interact by hydrogen bonds. In 9 the
crystal packing also presents layers, however the interaction between layers is through πꢀπ
stacking between delocalized πꢀclouds around the NꢀN azomethine bond and pyridine rings, dc4ꢀ
c5, 3.385(10) Å, [c4(N3DꢀN4D) and c5(C13C, C14C, C15C, C16C, C17C, N5C)], and also by
hydrogen bonds (see Fig. S5). The crystal packing of complex 10 is also in layers of vanadium
complexes and DMSO molecules interacting through van der Waals forces (see Fig. S6).
The crystal structure of compound 12 contains an oxidomethoxidovanadium(V)
mononuclear complex with the ligand bpꢀfah. Fig. 9 shows the ORTEP drawing of the complex
present in the asymmetric unit. For this complex the τ value of 0.192 [αO3ꢀV1ꢀO4= 144.17(9)º and
β
O2ꢀV1ꢀN1= 152.49(10)º], suggests a distorted square pyramidal geometry.40
The pyrazol group (C1, C2, C3, N3, N4) and the furan ring of the hydrazide group (C19,
C20, C21, C22, O5) are coplanar [mean deviation from planarity 0.0700(23) Å]. The vanadium
atom is displaced towards the apical oxido ligand (O1) from the equatorial plane defined by O2,
O3, O4 and N1 atoms by 0.4947(10) Å [mean deviation from planarity, O2, O3, O4, N1,
0.0464(11) Å]. The apical oxygen atom presents a V=O bond characteristic of oxidoꢀtype O
atoms with strong
π bonding. In Fig. S7 the crystal packing of compound 12 is shown. The
complexes are placed in layers, which interact by van der Waals forces.
15

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Table 2. Bond lengths (Å) and angles (º) for the compounds [K(H2O)2{VVO2(bpꢀbhz)}]2 5,
[K(H2O)2{VVO2(bpꢀfah)}]2 6, [VVO2(Hbpꢀbhz)]·1.5H2O 7·1.5H2O, [VVO2(Hbpꢀfah)] 8,
[VVO2(Hbpꢀnah)] 9, [VVO2(Hbpꢀinh)]·DMSO 10·DMSO and [VVO(bpꢀfah)(OMe)] 12.
Bond lengths
7·1.5H2O
5
6
8
V(1)ꢀO(1)
V(1)ꢀO(2)
V(1)ꢀO(3)
V(1)ꢀO(4)
V(1)ꢀN(1)
V(1)ꢀK(1)
K(1)ꢀO(2)
K(1)ꢀO(3)
K(1)ꢀO(4)
K(1)ꢀO(5)
K(1)ꢀO(2W)
K(1)ꢀO(2WA)
K(1)ꢀO(2WB)
K(1)ꢀO(1W)
K(1)ꢀN(2)
K(1)ꢀC(6)
K(1)ꢀC(7)
K(1)ꢀC(8)
K(1)ꢀC(9)
K(1)ꢀC(10)
K(1)ꢀC(11)
K(1)ꢀC(14)
1.6264(15)
1.6386(15)
1.9185(14)
1.9634(15)
2.1672(16)
3.8532(6)
1.605(2)
1.594(3)
1.612(3)
1.914(3)
1.993(3)
2.169(4)
1.6265(14)
1.6143(14)
1.9387(13)
2.0255(14)
2.1958(16)
1.639(2)
1.936(2)
1.968(2)
2.190(3)
3.7644(11) #2
2.781(3) #2
3.255(2) #2
2.7576(16)
3.2355(16)
2.7739(18)
2.706(2)
2.693(8)
2.889(18) #2
2.844(4) #3
2.915(3)
3.313(3)
3.346(3)
3.376(4)
3.351(4)
3.330(4)
3.330(3)
2.827(2)
2.8736(17) #1
3.257(2) #1
3.200(2) #1
3.239(2) #1
3.381(2) #1
3.476(2) #1
3.396(2) #1
3.188(2) #1
10·DMSO
1.6156(15)
1.6238(13)
1.9460(14)
1.9666(14)
2.1789(15)
6
Bond lengths
V(1)ꢀO(1)
V(1)ꢀO(2)
V(1)ꢀO(3)
V(1)ꢀO(4)
V(1)ꢀN(1)
Angles
9
12
1.618(2)
1.6317(19)
1.9404(18)
1.9514(19)
2.172(2)
5
1.573(2)
1.761(2)
1.8727(19)
1.8840(19)
2.104(2)
7·1.5H2O
8
O(1)ꢀV(1)ꢀO(2)
O(1)ꢀV(1)ꢀO(3)
O(2)ꢀV(1)ꢀO(3)
O(1)ꢀV(1)ꢀO(4)
O(2)ꢀV(1)ꢀO(4)
O(3)ꢀV(1)ꢀO(4)
O(1)ꢀV(1)ꢀN(1)
O(2)ꢀV(1)ꢀN(1)
107.95(8)
105.78(7)
95.76(7)
107.95(13)
104.66(11)
92.27(11)
105.70(12)
93.11(10)
145.76(10)
105.70(12)
146.04(11)
108.6(2)
108.92(7)
102.27(6)
96.62(7)
97.05(6)
94.24(6)
153.35(6)
108.56(6)
141.83(7)
104.09(16)
96.17(16)
101.42(17)
90.88(15)
149.71(14)
107.93(16)
142.41(17)
103.69(7)
89.89(7)
146.55(6)
103.09(7)
147.53(7)
16

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O(3)ꢀV(1)ꢀN(1)
O(4)ꢀV(1)ꢀN(1)
O(1)ꢀV(1)ꢀK(1)
O(2)ꢀV(1)ꢀK(1)
O(3)ꢀV(1)ꢀK(1)
O(4)ꢀV(1)ꢀK(1)
N(1)ꢀV(1)ꢀK(1)
84.62(6)
73.54(6)
130.01(6)
38.17(5)
111.79(4)
57.03(4)
111.97(4)
83.55(9)
83.12(13)
73.63(13)
82.27(6)
74.23(5)
73.35(9)
138.23(9) #2
42.31(9) #2
59.85(7) #2
104.62(7) #2
110.07(7) #2
10·DMSO
108.07(8)
104.92(8)
94.54(7)
103.88(8)
92.42(6)
146.53(6)
103.69(7)
147.59(7)
83.28(6)
73.63(6)
Angles
9
12
O(1)ꢀV(1)ꢀO(2)
O(1)ꢀV(1)ꢀO(3)
O(2)ꢀV(1)ꢀO(3)
O(1)ꢀV(1)ꢀO(4)
O(2)ꢀV(1)ꢀO(4)
O(3)ꢀV(1)ꢀO(4)
O(1)ꢀV(1)ꢀN(1)
O(2)ꢀV(1)ꢀN(1)
O(3)ꢀV(1)ꢀN(1)
O(4)ꢀV(1)ꢀN(1)
110.05(10)
104.20(9)
93.23(9)
102.38(9)
93.13(9)
148.60(8)
104.50(9)
145.05(10)
83.12(8)
74.24(8)
107.31(12)
106.09(11)
91.39(9)
106.79(11)
92.17(9)
144.17(9)
99.78(10)
152.49(10)
85.58(8)
75.19(8)
Symmetry transformations used to generate equivalent atoms: #1 ꢀx+1,ꢀy+1,ꢀz #2 ꢀx+1,ꢀy,ꢀz+1 #3 ꢀx+1,ꢀy,ꢀz
Table 3. Hydrogen bonds in the compounds [K(H2O)2{VVO2(bpꢀbhz)}]2 5, [K(H2O)2{VVO2(bpꢀ
fah)}]2 6, [VVO2(Hbpꢀbhz)]·1.5H2O 7·1.5H2O, [VVO2(Hbpꢀfah)] 8, [VVO2(Hbpꢀnah)] 9 and
[VVO2(Hbpꢀinh)]·DMSO 10·DMSO
DꢀH...A (compound)
d(DꢀH)
d(H...A)
d(D...A)
<(DHA)
O(1W)ꢀH(1WB)...O(1)#1 (5)
O(1W)ꢀH(1WB)...O(2)#1 (5)
O(1W)ꢀH(1WA)...O(4) (5)
1.01
1.01
1.85
2.57
2.00
2.785(3)
151.7
3.381(3)
2.800(2)
2.914(2)
3.010(2)
2.998(4)
2.983(13)
2.879(10)
3.000(9)
3.156(8)
2.790(11)
2.839(15)
136.8
128.6
176(3)
152(3)
173.6
176.0
126.5
112.6
173.1
122.5
113.3
1.07
O(2W)ꢀH(2WA)...O(1)#2 (5)
O(2W)ꢀH(2WB)...O(2)#3 (5)
O(1W)ꢀH(1WA)...O(4)(6)
0.80(3)
0.84(4)
0.85
2.11(3)
2.24(4)
2.15
O(1W)ꢀH(1WB)...O(2WB)#4(6)
O(2WA)ꢀH(2WA)...O(1W)#5(6)
O(2WA)ꢀH(2WA)...O(2)#5(6)
O(2WA)ꢀH(2WB)...O(2)#6(6)
O(2WB)ꢀH(2WD)...O(2)#7(6)
O(1W)ꢀH(1WB)...O(2W) (7)
0.85
2.13
0.85
2.29
0.85
2.57
0.85
2.31
0.85
2.24
0.85
2.39
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O(1W)ꢀH(1WA)...O(2)#8(7)
N(2)ꢀH(2N)...O(1W) (7)
N(2)ꢀH(2N)...O(1)#8 8
N(5)ꢀH(5N)...O(2)#9 9
N(5)ꢀH(5N)...O(7)#10 10
N(5)ꢀH(5N)...S(1)#10 10
0.85
0.88
1.91
1.98
2.757(5)
2.770(5)
2.770(2)
2.612(3)
2.661(2)
3.6899(18)
175.6
148.8
0.84(3)
1.02(3)
0.82(3)
0.82(3)
1.99(3)
1.65(3)
1.84(3)
2.94(3)
153(2)
155(3)
178(3)
153(2)
Symmetry transformations used to generate equivalent atoms:
#1 ꢀx+1,ꢀy,ꢀz #2 ꢀ x+1,y,z #3 ꢀx+2,ꢀy,ꢀz #4 x,y,zꢀ1 #5 ꢀx+1,yꢀ1/2,ꢀz+1/2 #6 ꢀx+1,ꢀy,ꢀz+1 #7 x,ꢀy+1/2,z+1/2
#8 ꢀx,ꢀy+1,ꢀz+1 #9 2 x,yꢀ1,z #10 ꢀx,ꢀy,ꢀz #11 ꢀx+1,ꢀy+1,ꢀz+1 #12 x+1,y,z
Fig. 1. ORTEP plot of asymmetric unit of compound [K(H2O)2{VVO2(bpꢀbhz)}]2 5. All the nonꢀ
hydrogen atoms are presented by their 50% probability ellipsoids. Hydrogen atoms are omitted
for clarity.
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Fig. 2. ORTEP plot of asymmetric unit of compound [K(H2O)2{VVO2(bpꢀfah)}]2 6. All the nonꢀ
hydrogen atoms are presented by their 50% probability ellipsoids. Hydrogen atoms are omitted
for clarity.
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Fig. 3. Dimeric aggregate in the compound [K(H2O)2{VVO2(bpꢀbhz)}]2 5. Dashed black lines
show πꢀface and lateral η1ꢀcationꢀπ interactions of K+ ions and phenyl groups. All the nonꢀ
hydrogen atoms are presented by their 50% probability ellipsoids. Hydrogen atoms are omitted
for clarity.
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Fig. 4. Dimeric aggregate in the compound [K(H2O)2{VVO2(bpꢀfah)}]2 6. All the nonꢀhydrogen
atoms are presented by their 50% probability ellipsoids. Hydrogen atoms are omitted for clarity.
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Fig. 5. ORTEP plot of vanadium complex in [VVO2(Hbpꢀbhz)]·1.5H2O 7·1.5H2O. All the nonꢀ
hydrogen atoms are presented by their 50% probability ellipsoids. Hydrogen atoms and water
molecules are omitted for clarity.
Fig. 6. ORTEP plot of [VVO2(Hbpꢀfah)] 8. All the nonꢀhydrogen atoms are presented by their
50% probability ellipsoids. Hydrogen atoms are omitted for clarity.
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Fig. 7. ORTEP plot of [VVO2(Hbpꢀnah)] 9. All the nonꢀhydrogen atoms are presented by their
50% probability ellipsoids. Hydrogen atoms are omitted for clarity.
Fig. 8. ORTEP plot of vanadium complex in [VVO2(Hbpꢀinh)]·DMSO 10·DMSO. All the nonꢀ
hydrogen atoms are presented by their 50% probability ellipsoids. Hydrogen atoms and DMSO
molecule are omitted for clarity.
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Fig. 9. ORTEP plot of [VVO(Hbpꢀfah)(OMe)] 12. All the nonꢀhydrogen atoms are presented by
their 50% probability ellipsoids. Hydrogen atoms are omitted for clarity.
Thermal analysis
Thermogravimetric analysis of the complexes was carried out under an oxygen
atmosphere and relevant data are presented in Table S1. All complexes are stable up to ca. 110
oC and thereafter they decompose exothermically in a few steps. Quantitative measurement of
weight loss at different stages was not possible due to their overlap. Complexes 1-4 lose mass
roughly equal to one H2O molecule above 110 oC, indicating the presence of weekly coordinated
H2O to the metal center. Upon further increment of the temperature, the complexes decompose in
three overlapping steps giving V2O5 as final product at ca. 500 ⁰C. Complexes 5 and 6 lose mass
o
at ca. 130 C which is assigned to two water molecules that we attribute to the water molecules
associated with the K ions. The waterꢀfree species decomposes in multiple exothermic but
overlapping steps on further increasing the temperature, which are complete at ca. 600 °C to give
KVO3 as the final product. Complexes 7ꢀ10 are stable up to ca. 580 °C and beyond this
temperature they decompose exothermically to give V2O5 as the final product. Complexes 11ꢀ14
undergo mass loss roughly equivalent to one methoxide (–OMe) group in the temperature range
120–160 °C, indicating the presence of one coordinated –OMe group. These complexes finally
decompose giving the final product V2O5 in the temperature range 480–510 °C.
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IR spectral studies
The IR spectral bands for ligands and complexes are presented in Table S2. Comparison of
the spectra of the complexes and corresponding ligands elucidates the coordination mode of the
ligands. The ketonic nature of the ligands in the solid state is indicated by the presence of ν(NH)
and ν(C=Ohydrazide/pyrazolone
)
stretches at 3027ꢀ3090 and 1632ꢀ1647/1587ꢀ1594 cm−1.
Disappearance of these bands in the spectra of the complexes (except for 7 and 8) indicates the
enolization of the ketonic group and replacement of the H atom by the metal ion. A sharp band
appearing in the region 1248ꢀ1265 cm–1 is assigned to the ν(CꢀOenolic) mode. The sharp band at
1531ꢀ1541 cm−1 due to ν(C=N) (azomethine), in the ligands’ spectra, shifts to lower
wavenumbers in the complexes’ spectra, appearing at 1520–1528 cm−1, indicating the
coordination of the azomethine nitrogen to the metal center. This is further supported by the shift
of the ν(NꢀN), which appears at 976ꢀ979 cm–1 in the ligands and at 1044–1066 cm−1 in the
complexes. The shift of the ν(NꢀN) band to higher frequency is expected because of the reduced
repulsion between the lone pairs of adjacent nitrogen atoms. All ligands exhibit a broad band at
ca. 3000 cm–1 due to the involvement of ꢀOH groups in intramolecular hydrogen bonding. The
presence of this band at 3380ꢀ3430 cm–1 in the complexes’ spectra is possibly due to the
breaking of hydrogen bonding as well as coordination of water (in complexes 1ꢀ6) and
methoxide molecules (in complexes 11-14). An additional band at 3066ꢀ3166 cm–1 in complexes
7ꢀ10 indicates the presence of the hydrazinic proton (in 7 and 8) or protonated pyridinic nitrogen
(in 9 and 10).
A sharp band at 976–996 cm–1 (in the VIVO complexes 1 – 4) and at 968ꢀ983 cm–1 (in VVO
complexes 11 – 14) is characteristic of ν(V=O) stretch. The VVO2ꢀcomplexes exhibit two sharp
bands in the 899–937 cm–1 region due to νsym(O=V=O) and νasym(O=V=O) modes.
UV-vis spectral studies
A list of UVꢀvis spectral data of ligands and complexes is presented in Table S3. Fig. 10
depicts UVꢀvis spectra of all complexes. Detailed spectral studies of ligands, IꢀIV, and their
dioxidomolybdenum(VI) complexes have recently been reported by us.35 The ligands exhibit
three absorption bands at 204ꢀ205, 250ꢀ253 and 346ꢀ365 nm due to φ → φ*, π → π* and n →π*
transitions, respectively. All these bands are also observed in the complexes’ spectra but slightly
shifted, indicating rearrangement of the ligand upon coordination to the metal ion. In addition, a
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new band of medium intensity appears at ca. 395–405 nm, which is assigned to a ligand to metal
charge transfer (LMCT) band, doubtlessly arising due to transfer of electron density from the
filled pꢀorbital of coordinated oxygen atoms to a vacant dꢀorbital of vanadium. At higher
concentrations, two weak bands centered at 480–510 (shoulder) and 650–680 nm in the
oxidovanadium (IV) complexes’ spectra are observed and assigned to d–d transitions.
b
a
c
d
Fig. 10. (a) UVꢀvis spectra of the oxidovanadium(IV) complexes in methanol. Concentration
2.0±0.2 ×10–4 M. (b) Vis spectra showing the dꢀbands of the oxidovanadium(IV) complexes in
DMSO: 1 (conc. 4.4×10–3 M), 2 (conc. 3.9×10–3 M), 3 (conc. 2.5×10–3 M) and 4 (conc. 2.2×10–3
M ). (c) UVꢀvis spectra of the dioxidovanadium(V) complexes in methanol: 7 (conc. 1.6×10–4
M), 8 (conc. 1.7×10–4 M), 9 (conc. 1.8×10–4 M ) and 10 (conc. 1.9×10–4 M). (d) UVꢀvis spectra
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of the oxidomethoxidovanadium(V) complexes in methanol: 11 (conc. 1.3×10–4 M), 12 (conc.
1.9×10–4 M), 13 (conc. 2.1×10–4 M ) and 14 (conc. 1.8×10–4 M ).
1H NMR spectral study
Further evidence for the coordination mode of the ligands in the vanadium(V) complexes
1
was established from NMR spectroscopy. H NMR spectra of ligands I – IV and their
VVO/VVO2ꢀcomplexes were recorded in [DMSO]ꢀd6 and the relevant spectral data are collected
in Table 4 and representative spectra of H2bpꢀfah II, K(H2O)2[VVO2(bpꢀfah)] 6, [VVO2(Hbpꢀ
fah)] 8 and [VVO(bpꢀfah)(OMe)] 12 are presented in Fig. 11. They give further support to the
assignments made by IR and UVꢀvis absorption spectroscopy. In the ligands’ spectra the signal
appearing at δ = 10.96ꢀ11.00 ppm due to the NH proton and at δ = 1.38ꢀ1.47 ppm due to the ring
proton of the pyrazole residue indicate the ketonic form of both C=O groups in solution. The
absence of these signals in complexes 5, 6, 11ꢀ14 corroborates the enolisation and subsequent
substitution of the proton by the metal ion. The neutral complexes 7 and 8 exhibit the ꢀNH
resonance at nearly the same chemical shift possibly due to protonation of the hydrazido nitrogen
(see description of the crystal structures) to compensate the charge. In complexes 9 and 10 such
resonance could not be located. Protons due to the methyl group appear at 1.38ꢀ1.41 ppm in both
the ligands’ and complexes’ spectra. Aromatic protons appear in the expected regions with slight
shifts in their positions in the complexes’ spectra. Coordinated methoxide (in complexes 11ꢀ14)
is confirmed by the presence of a signal due to methyl protons at δ = 3.18ꢀ3.13 ppm.
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Table 4. 1H NMR spectral data of ligands and vanadium(V) complexes recorded in DMSO–d6.
Compounds
ꢀOH/ꢀ Pyrazolo
CH3
ArꢀH
ne (CH)
NH
H2apꢀbhz I
11.00
1.45
1.42 (s,3H)
1.38 (s.3H)
1.40 (s,3H)
1.43 (s,3H)
1.38 (s,3H)
1.34 (s, 3H)
1.38 (s, 3H)
1.40 (s, 3H)
1.42 (s,3H)
8.00ꢀ7.98 (t, 2H), 7.97ꢀ7.94 (m, 2H), 7.70ꢀ7.68 (m,
1H), 7.63ꢀ7.53 (m, 2H) , 7.52ꢀ 7.38 (m, 8H)
7.95ꢀ7.91 (d,2H), 7.87ꢀ7.84 (m,2H), 7.67ꢀ7.65
(m,1H), 7.60ꢀ7.51 (m,2H) , 7.48ꢀ 7.35 (m,8H)
7.94ꢀ7.89 (d,2H), 7.85ꢀ7.78 (m,2H), 7.67ꢀ7.63
(m,1H), 7.56ꢀ7.50 (m,2H) , 7.45ꢀ 7.40 (m,8H)
8.00ꢀ7.95 (d,2H), 7.91ꢀ7.86 (m,2H), 7.78ꢀ7.75
(m,1H), 7.58ꢀ7.52 (m,2H) , 7.49ꢀ 7.45 (m,8H)
8.01ꢀ7.97 (m, 2H), 7.82 (s, 1H), 7.69ꢀ7.40 (m, 8H),
7.09ꢀ7.08 (d, 1H), 6.59ꢀ6.58 (d, 1H)
(s,1H) (s,1H)
K(H2O)2[VVO2(bpꢀbhz)] 5
[VVO2(Hbpꢀbhz)] 7
[VVO(bpꢀbhz)(OMe)] 11
H2apꢀfah II
10.96
1.48
(s,1H) (s,1H)
K(H2O)2[VVO2(bpꢀfah)] 6
[VVO2(Hbpꢀfah)] 8
[VVO(bpꢀfah)(OMe)] 12
H2apꢀnah III
7.84ꢀ7.82(d, 2H), 7.62(s, 1H), 7.52ꢀ7.41(m, 5H),
7.23ꢀ7.19(t, 1H), 6.71(s, 1H), 6.48 (s, 1H)
7.84ꢀ7.82(d, 2H), 7.62(s, 1H), 7.52ꢀ7.41(m, 5H),
7.23ꢀ7.19(t, 1H), 6.71(s, 1H), 6.48 (s, 1H)
7.84ꢀ7.82(d, 2H), 7.62(d, 2H), 7.37ꢀ7.31(m, 6H),
7.23ꢀ7.19(m, 3H)
11.20
(s,1H)
1.46
(s,1H)
8.69ꢀ8.61 (m,2H), 8.01ꢀ7.87 (m,3H), 7.70ꢀ7.67
(t,1H), 7.62ꢀ7.40 (m,8H)
[VVO2(Hbpꢀnah)] 9
[VVO(bpꢀnah)(OMe)] 13
H2apꢀinh IV
1.41 (s,3H)
1.44 (s,3H)
1.41 (s,3H)
8.65ꢀ8.56 (m,3H), 7.97ꢀ7.86 (m,4H), 7.65ꢀ7.61 (t,
2H), 7.62ꢀ7.47 (m,4H), 7.24 (s,1H)
8.65ꢀ8.56 (m,2H), 7.97ꢀ7.86 (m,5H), 7.65ꢀ7.61
(t,2H), 7.62ꢀ7.47 (m,3H), 7.34(d, 2H)
11.46
(s,1H) (s,1H)
1.47
8.78ꢀ8.66 (d, 2H), 7.99ꢀ7.91 (q, 2H), 7.86ꢀ7.67 (m,
2H), 7.62ꢀ7.40 (m, 8H)
[VVO2(Hbpꢀinh)] 10
1.42 (s,3H)
1.46 (s,3H)
8.56 (s, 1H), 7.84ꢀ7.82 (d, 2H), 7.64ꢀ7.62 (d, 1H),
7.56ꢀ7.48 (m, 5H), 7.46ꢀ7.39 (m, 4H), 7.24ꢀ7.22 (t,
1H)
[VVO(bpꢀinh)(OMe)] 14
8.34ꢀ8.29 (q, 2H), 7.86ꢀ7.82 (m, 2H), 7.60ꢀ7.40 (m,
6H), 7.40ꢀ7.35(m, 3H), 7.20ꢀ7.16 (t, 1H)
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Fig. 11. 1H NMR spectra of H2bpꢀfah II, K(H2O)2[VVO2(bpꢀfah)] 6, [VVO2(Hbpꢀfah)] 8 and
[VVO(bpꢀfah)(OMe)] 12 recorded in DMSO–d6. Star (*) in the figure indicates the signal due to
water in DMSO/ DMSO itself.
13C NMR spectral study
The coordination mode of the ligands in the complexes can be further elucidated by
measurement of 13C NMR spectra (Table 5 and Fig. 12). Ligands I, II, III and IV exhibit 20, 18,
19 and 19 13C NMR signals against a total of 24, 22, 23 and 23 carbon atoms, respectively. Metal
complexes exhibit normally the same or higher number of signals compared to the ligands’
spectra. Significant downfield shifts, ꢂδ = [δ(complex) − δ(ligand)], were observed for the
carbon atoms present in the vicinity of the coordinating atoms O, N and O [i.e. pyrazolone
oxygen (C1), azomethine nitrogen (C4) and enolic oxygen (C18)], confirming the coordination
of these functionalities to the vanadium center. Signals due to methyl and other aromatic carbons
29