A novel pentacoordinated dioxovanadium(v) salicylaldiminate: Solvent specific crystallization of dimorphs with contrasting coordination geometries, ligand conformations and supramolecular architectures

Article abstract of DOI:10.1002/ejic.200300612

The reaction of the tridentate salicylaldimine of 2-picolylamine, C ₆H₄(OH)CHNCH₂C₅H₄N (HL), with bis(acetylacetonato)oxovanadium(IV) at room temperature under oxygen (or with VOSO₄·5H₂O plus H₂O₂) furnished crystalline greenish-yellow α-VO₂(L) and green β-VO₂(L) from methanol (or ethanol) and acetonitrile (or dichloromethane), respectively. The dimorphs give rise to the same solution species as revealed by spectroscopic data (UV/Vis, ¹H and ⁵¹V NMR). Both forms react with 3,5-bis(tert-butyl)catechol (H ₂dbcat) furnishing the known pseudooctahedral complex VO(L)(dbcat). In the α form the V(L) fragment is planar and the VO₃N ₂ coordination sphere is distorted trigonal bipyramidal (τ = 0.55) with the two oxo oxygen atoms and the azomethine nitrogen atom defining the trigonal plane. In β-VO₂(L) the V(L) moiety, like that in VO(L)(dbcat), is not planar but consists of two planar parts rotated away from each other along the C-N single bond. In this case the coordination sphere is distorted square pyramidal (T = 0.20) with the three donor sites of the L ligand and an oxo oxygen atom defining the tetragonal plane. Both the α and β crystal lattices consist of dimers which associate further to form supramolecules. The noncovalent intradimer and interdimer bonding interactions are predominantly of aromatic π-π stacking (aryl...pyridyl and pyridyl...pyridyl) and C-H...O hydrogen bonding (azomethine...oxo and aryl...phenolato) types in the α and β dimorphs, respectively. It is proposed that the low polarizability of methanol promotes π-π stacking of planar V(L) fragments, resulting in crystallization of the a form. When the polarizability is relatively high, as in acetonitrile, the β form crystallizes. The geometrically isomeric coordination spheres of the α and β forms are sustained by the respective supramolecular architectures. The Schiff base HL′ of 2-hydroxynapthaldehyde and 2-picolylamine has also afforded two forms of VO₂(L′) in the same manner as for VO₂(L). Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.

Full text of DOI:10.1002/ejic.200300612

FULL PAPER
A Novel Pentacoordinated Dioxovanadium( ) Salicylaldiminate: Solvent
V
Specific Crystallization of Dimorphs with Contrasting Coordination
Geometries, Ligand Conformations and Supramolecular Architectures
[a]
[a]
[a,b]
Bharat Baruah, Sankar Prasad Rath, and Animesh Chakravorty*
Keywords: Vanadium / O ligands / Dimorphism / Supramolecular architecture
The reaction of the tridentate salicylaldimine of 2-picolylam-
ine, C (OH)CHNCH N (HL), with bis(acetylacetona- the α and β crystal lattices consist of dimers which associate
to)oxovanadium(IV) at room temperature under oxygen (or
with VOSO ·5H O plus H ) furnished crystalline greenish-
yellow α-VO (L) and green β-VO (L) from methanol (or eth-
and an oxo oxygen atom defining the tetragonal plane. Both
6
H
4
2 5 4
C H
further to form supramolecules. The noncovalent intradimer
and interdimer bonding interactions are predominantly of
aromatic π-π stacking (aryl···pyridyl and pyridyl···pyridyl)
and C−H···O hydrogen bonding (azomethine···oxo and
aryl···phenolato) types in the α and β dimorphs, respectively.
It is proposed that the low polarizability of methanol pro-
motes π-π stacking of planar V(L) fragments, resulting in
crystallization of the α form. When the polarizability is rela-
tively high, as in acetonitrile, the β form crystallizes. The geo-
4
2
2 2
O
2
2
anol) and acetonitrile (or dichloromethane), respectively. The
dimorphs give rise to the same solution species as revealed
by spectroscopic data (UV/Vis, H and V NMR). Both forms
react with 3,5-bis(tert-butyl)catechol (H dbcat) furnishing
the known pseudooctahedral complex VO(L)(dbcat). In the α
form the V(L) fragment is planar and the VO coordination
1
51
2
3
N
2
sphere is distorted trigonal bipyramidal (τ = 0.55) with the metrically isomeric coordination spheres of the α and β forms
two oxo oxygen atoms and the azomethine nitrogen atom de-
fining the trigonal plane. In β-VO (L) the V(L) moiety, like
are sustained by the respective supramolecular architectures.
The Schiff base HLЈ of 2-hydroxynapthaldehyde and 2-pico-
2
that in VO(L)(dbcat), is not planar but consists of two planar
parts rotated away from each other along the C−N single
lylamine has also afforded two forms of VO
manner as for VO (L).
2
(LЈ) in the same
2
bond. In this case the coordination sphere is distorted square ( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
pyramidal (τ = 0.20) with the three donor sites of the L ligand
Germany, 2004)
Introduction
2).[8Ϫ10] The latter geometry is particularly relevant in the
[
2]
context of the RNase transition state and haloperoxid-
[
3]
ase activity.
The long-standing interest in the structure and properties
؉
[1]
of mononuclear VO2 complexes has multiplied with the
emergence of bioinorganic linkages to the RNase transition
[
2]
[3,4]
state, vanadium dependent haloperoxidase
and insulin
[
5]
؉
mimicry. The coordination number of the metal in VO2
complexes can be six,[ but the focus of the present work
1,6]
is on pentacoordinate species of type VO (tridentate),
2
which have attracted special attention in recent years. The
geometry of structurally characterized compounds of the
latter type is (relatively rarely) distorted trigonal bipyrami-
dal (dtbp, α form, as shown in 1),[ the common geometry
being distorted square pyramidal (dsp, β form, as in
7]
In the present work we report the synthesis and charac-
terization of a remarkable pentacoordinate VO2 system
؉
which has been isolated in two distinct crystalline forms by
merely varying the solvent employed in the synthesis. The
solid-state structural features of the dimorphs (which other-
Department of Inorganic Chemistry, Indian Association for the wise display identical chemical composition and solution
[
[
a]
b]
Cultivation of Science,
properties) differ dramatically in coordination geometry, li-
Kolkata 700 032, India
Jawaharlal Nehru Centre for Advanced Scientific Research,
Bangalore 560064, India
Fax: (internat.) ϩ91-33-2473-2805
E-mail: icac@mahendra.iacs.res.in
gand conformation and supramolecular architecture. To the
best of our knowledge, structural dimorphism of the pre-
؉
sent type is unprecedented in VO2 solid-state chemistry.
Eur. J. Inorg. Chem. 2004, 1873Ϫ1878
DOI: 10.1002/ejic.200300612
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1873

B. Baruah, S. P. Rath, A. Chakravorty
FULL PAPER
Results and Discussion
Synthesis of Dimorphs
similarities to that in β-VO (L); the significance of this is
2
considered later.
VO
2
(L) ϩ H
2
dbcat Ǟ VO(L)(dbcat) ϩ H
2
O
(1)
The tridentate ligand concerning us in this work is the
salicylaldimine of 2-picolylamine (HL, 3). It reacted
smoothly with VO(acac) in methanol solution at room
2
temperature in the presence of oxygen, furnishing in excel-
lent yield a greenish-yellow crystalline complex of compo-
sition VO (L), designated as the α dimorph.
2
Structure
The α and β dimorphs have distinctive crystal, molecular
and supramolecular structures. They belong respectively to
the monoclinic and triclinic crystal systems. Molecular
views are given in Figure 1 and 2; selected bond parameters
are listed in Table 1. In both forms, the VO fragment has
2
A similar reaction occurred in acetonitrile solution to a cis geometry and the tridentate ligand is meridionally dis-
give the β dimorph; this complex had the same compo- posed. The coordination sphere is of type VO N . The
3
2
sition, but was green. The same dimorphs were also synthe- metalϪligand bond lengths in the two forms are equal to
˚
sized by reacting VOSO ·5H O with HL using hydrogen within 0.02 A. However, there are major differences in the
4
2
peroxide as the oxidant (Scheme 1). The possible role of coordination geometry, V(L) conformation and noncoval-
the solvent in crystallization of specific dimorphs will be ent intermolecular interactions.
considered later.
Scheme 1. Synthesis of dimorphic VO
2
(L) at room temperature; (i)
; (iv) MeCN, H
MeOH, O ; (ii) MeCN, O ; (iii) MeOH, H
2
2
2
O
2
2 2
O
Spectra and Solution Behaviour
Spectral data are given in the Exp. Sect. Both forms dis-
Ϫ1
play two VϭO stretches near 920 and 940 cm (KBr disk),
consistent with cis geometry of the VO moiety. Both di-
2
morphs are insoluble except in solvents like N,N-dimeth-
ylformamide and dimethyl sulfoxide. The pale yellow solu-
tions display identical UV/Vis spectra (within experimental
error), and display a band at 395 nm. In dimethyl sulfoxide
2
Figure 1. Perspective view and atom labeling scheme of α-VO (L).
All non-hydrogen atoms are represented by 30% thermal prob-
ability ellipsoids
5
1
solutions the two forms give rise to identical V NMR
spectra, with a signal at δ ϭ Ϫ535 ppm. The well-resolved
1
H NMR spectra of both the α and β forms in [D ]dimethyl
6
sulfoxide are also superimposable. Thus, α-VO (L) and β-
2
VO (L) must give rise to the same species in mobile solu-
2
tion.
Reaction with a Catechol
In dichloromethane suspension, both α and β-VO (L) re-
2
act [as shown in Equation (1)] with aromatic diols such as
3
,5-di-tert-butylcatechol (H dbcat) furnishing the violet
2
complex VO(L)(dbcat) (4), which is already known from the
Figure 2. Perspective view and atom labeling scheme of β-VO
All non-hydrogen atoms are represented by 30% thermal prob-
conformation of the L ligand in VO(L)(dbcat) has close ability ellipsoids
2
(L).
[
11]
reaction of VO(acac) with HL and H dbcat in air.
The
2
2
1874
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Eur. J. Inorg. Chem. 2004, 1873Ϫ1878

A Novel Pentacoordinated Dioxovanadium(V) Salicylaldiminate
FULL PAPER
˚
by a similar amount to 139.7(1)°. The O3ϪVϪN1 angle is
also contracted by about 7° to 151.7(1)°. The net result of
these angular changes is that the O2, O3, N1 and N2 atoms
in the β form constitute an approximate tetragonal plane,
from which the metal atom is displaced by 0.51 A towards
the O1 atom. Therefore, the coordination geometry in the
Table 1. Selected bond lengths [A] and angles [°] for α-VO
2
(L) and
β-VO (L)
2
α-VO
2
(L)
2
β-VO (L)
˚
VϪO(1)
VϪO(2)
VϪO(3)
VϪN(1)
1.617(2)
1.615(2)
1.901(2)
2.113(2)
2.129(2)
1.613(2)
1.627(2)
1.903(2) β form can be aptly described as dsp, which is also consist-
2.134(2) ent with its low τ value of 0.20.
2.145(2)
VϪN(2)
The structure of β-VO (L) bears certain qualitative simi-
2
O(1)ϪVϪO(2)
O(1)ϪVϪO(3)
O(2)ϪVϪO(3)
O(1)ϪVϪN(1)
O(1)ϪVϪN(2)
O(2)ϪVϪN(1)
O(2)ϪVϪN(2)
O(3)ϪVϪN(1)
O(3)ϪVϪN(2)
N(1)ϪVϪN(2)
109.4(1)
109.2(1)
105.5(1)
97.1(1)
98.2(1)
109.4(1)
89.4(1)
139.7(1)
151.7(1)
83.4(1)
74.2(1)
[
11]
larities to that of pseudooctahedral V(L)(dbcat) 4. A sig-
nificant feature is that the nonplanar V(L) fragment in 4
also consists of two planar fragments of types A and B
100.2(1)
100.7(1)
90.9(1)
123.0(1)
92.3(1)
125.8(1)
159.0(1)
83.8(1)
75.2(1)
(
dihedral angle 19.7°). The approximate tetragonal plane is
again of N O type from which the metal atom is displaced
towards the oxo atom (by 0.28 A). The nonplanarity of the
V(L) fragment appears to be crucial for achieving a tetrag-
2
2
˚
onal equator, be it in β-VO (L) or in VO(L)(dbcat).
2
Aromatic Stacking and Hydrogen Bonding: Dimers and
Supramolecules
Coordination Geometry
In the α form, the V(L) fragment constitutes a plane
mean deviation, 0.03 A), which makes a dihedral angle of
All the hydrogen atoms in both α-VO (L) and β-VO (L)
2
2
˚
(
9
were directly located by difference Fourier maps. Both the
lattices consist of dimers, which associate further to form
supramolecules. The noncovalent intradimer and interdimer
bonding interactions are primarily of the π-π stacking and
CϪH···O hydrogen-bonding type. These interactions can be
seen in the partial packing diagrams shown in Figure 3 and
0.5 with the VO plane. The double bonds in the latter
2
fragment constrain the O1ϪVϪO2 angle to about 109°, as
is generally observed among pentacoordinated VO2
[
7Ϫ10]
complexes.
An important feature of the α structure is that the metal
˚
atom is shifted only by about 0.1 A from the O1ϪO2ϪN2
4
; the relevant distances are listed in Table 2.
plane towards the O3 atom, and the N2 atom is approxi-
mately symmetrically positioned with respect to the Ol and
O2 atoms, the O1ϪVϪN2 and O2ϪVϪN2 angles being
˚
1
23.0(1) and 125.8(1)°, respectively [N2···O1, 3.301(7) A
˚
and N2···O2, 3.341(7) A]. The rigidity of the L ligand con-
strains the O3ϪVϪN1 angle to 159.0(1)°.
The coordination geometry of α-VO (L) is thus best de-
2
scribed as dtbp (trigonal plane O1ϪO2ϪN2). The τ param-
[
12]
eter
(equal to ∆/60°, where ∆ is the difference between
the largest and the next-to-largest ligandϪmetalϪligand
angles) is a useful geometrical discriminator; ∆ ϭ 60, τ ϭ 1
[
12]
for idealized tbp and ∆ ϭ 0, τ ϭ 0 for idealized sp). The
τ value of α-VO (L) is 0.55. In representative structures of
2
VO (tridentate) species the τ values generally lie well below
2
7Ϫ10]
0
.50 and in most cases below 0.40.[
Thus α-VO (L) ap-
2
proaches the tbp geometry more closely than any other
known member of the VO (tridentate) family.
2
The V(L) moiety in the β form is not planar and it actu-
ally consists of two highly planar fragments: C1ϪC6, N1,
˚
V (plane A, mean deviation, 0.01 A) and C7ϪC13, N2, O3
(
2
Figure 3. Supramolecular structure of the α-VO (L) lattice; hydro-
gen atoms other than H3, H7 and H12 have been omitted for clar-
ity and noncovalent interactions are indicated by dotted lines
˚
plane B, mean deviation, 0.02 A). Plane A is rotated away
from plane B by 11.2° along the C6ϪN2 bond. The metal
atom is shifted from plane B by 0.53 A, and thus the six-
˚
membered chelate ring is folded by 20.4° along the
N2···O3 line.
In the α dimers the (virtually parallel) V(L) planes are
held together by a pair of aryl···pyridyl π-π interactions and
Whereas the rigid O1ϪVϪO2 angle remains virtually un- a pair of azomethine···oxo (C7ϪH7···O1) hydrogen bond-
changed near 109°, V(L) nonplanarity results in major ing interactions(Figure 3). The distance between the centro-
changes in the other angles at the metal compared to those ids of the overlapping aryl and pyridyl rings (ar···py in
˚
[13,14]
in the α form. Thus, the O1ϪVϪN2 angle decreases by Table 2), 3.716(7) A, is consistent
with the presence of
about 14° to 109.4(1)° and the O2ϪVϪN2 angle increases an attractive π-π interaction. The ar···py line subtends an
Eur. J. Inorg. Chem. 2004, 1873Ϫ1878
www.eurjic.org
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1875

B. Baruah, S. P. Rath, A. Chakravorty
FULL PAPER
nearly
linear
C12ϪH12···O3
moiety.
Interdimer
aryl···pyridyl stacking (offset 19.9°) also contributes to sup-
ramolecule formation in the β form.
Solvent Specific Crystallization
In summary, π-π stacking and CϪH···O hydrogen bond-
ing are the respective dominant features in the supramol-
ecular architectures of the α and β forms of VO (L). This
2
provides some insight into the possible nature of the role of
solvent in dimorph crystallization. It is known that solvents
like water and small alcohols with low polarizability and
high cohesive interaction lead to aggregation of lipophilic
2
Figure 4. Supramolecular structure of the β-VO (L) lattice. Hydro-
gen atoms other than H7 and H12 have been omitted for clarity
and noncovalent interactions are indicated by dotted lines
[
13,20]
molecular π surfaces in solutes.
It is therefore logical
to propose that such effects lead to π-π stacking in the case
of VO (L), with consequent crystallization of the α form
Table 2. Distances [A] and angles [°] characterizing aromatic π-π from methanol (we have found ethanol to be just as effec-
2
˚
stacking and CϪH···O hydrogen bonding in the two dimorphs
tive). The planar V(L) configuration and the associated
dtbp geometry may very well be the consequence of maxim-
ization of the π-π stacking interactions in the lattice. The
tendency towards lipophilic aggregation is considerably di-
minished in solvents of significantly higher polarizability
α-VO (L) β-VO (L)
2
2
ar···py[
py···py
a]
3.716(7)
3.520(6)
3.752(7)
Ϫ
[
a]
C(7)···O(1)
H(7)···O(1)
C(12)···O(3)
H(12)···O(3)
C(7)ϪH(7)···O(1)
C(12)ϪH(12)···O(3)
3.185(7)
2.62(9)
3.550(7)
2.95(8)
120(1)
123(1)
3.063(6) such as acetonitrile (dichloromethane is found to behave
[
20c]
2.51(8)
3.431(6)
2.56(9)
123(1)
176(1)
similarly);
in these cases the β form crystallizes, with a
structure dominated by polar interactions (viz. strong
CϪH···O hydrogen bonding) rather than π-π stacking. This
is best achieved when the V(L) configuration is nonplanar
and consequently the coordination geometry is dsp. The
[
a]
ar ϭ aryl ring centroid; py ϭ pyridyl ring centroid.
synthesis of α and β forms of VO (L) is an instance of sol-
2
vent-directed crystal engineering. The two geometrical iso-
angle of 10.4° with the aryl ring normal, and 10.8° with the meric coordination spheres are sustained by their character-
pyridyl ring normal. The offset of the parallel rings is thus istic supramolecular architectures.
small, signifying strong stacking. In metal complexes of py-
On the basis of the above logic we expected that 2-
ridyl ligands π-π stacking is usually associated with a larger hydroxynapthaldimine(HLЈ, 5) of 2-picolylamine should
offset (about 20°).[
13]
The bond parameters of the also yield dimorphs. Indeed, two forms of VO (LЈ) have
2
C7ϪH7···O1 fragment (Table 2) are consistent with the been isolated by the same procedures employed for the
presence of significant hydrogen bonding. The accepted VO (L) dimorphs.
2
˚
˚
ranges are 3.0Ϫ3.5 A (C···O), 2.3Ϫ3.0 A (H···O) and
1
00Ϫ180° (CϪH···O).[
15Ϫ18]
Interdimer bonding in the α form consists of a relatively
strong pyridyl···pyridyl πϪπ overlap [py···py, 3.520(6) A]
˚
with
C12ϪH12···O3) hydrogen bonding which is significantly
weaker than the intradimer C7ϪH7···O1 bonding. There is
a very small offset (5.6°), and aryl···phenol
(
also a weak interdimer edge-to-face interaction[
13,17,19]
be-
tween the pyridyl C3ϪH3 and aryl fragments, the centroid
˚
˚
of the latter being 3.31(9) A and 3.889(8) A away from the
Selected characterization data is given in the Exp. Sect.
H3 and C3 atoms, respectively. The C3ϪH3···ar angle is
Unfortunately, neither α-VO (LЈ) nor β-VO (LЈ) afforded
2
2
1
24°. The C10 carbon atom of the aryl ring lies closest to
˚
single crystals suitable for structure determination. A search
H3 [distance 2.91(8) A].
for other examples of the VO (tridentate) family showing
2
The nonplanarity of the V(L) fragment in the β form
similar dimorphism is continuing.
results in increased intradimer aryl···pyridyl separation,
˚
marginalizing the π-π interaction [ar···py, 4.086(8) A]. On
the other hand, the azomethine function now lies closer to
the O1 atom, thus resulting in stronger intradimer
C7ϪH7···O1 hydrogen bonds than in the α dimer (Table 2).
Conclusions
A remarkable case of solvent-directed crystal engineering
The interdimer association is also dominated by the rela- has been revealed in the synthesis of VO (L) in dimorphic
2
tively strong hydrogen bonding which occurs between the α and β forms, isolated from methanol and acetonitrile,
aryl and phenolato functions, the site of action being the respectively.
1876
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Eur. J. Inorg. Chem. 2004, 1873Ϫ1878

A Novel Pentacoordinated Dioxovanadium(V) Salicylaldiminate
FULL PAPER
The two forms differ strongly in both their coordination 5.60 (s, 2 H, ϪCH
2
Ϫ), 9.06 (s, 1 H, ϪCHϭN), 8.95 (br., 1 H,
ϪC
H, ϪC
H, ϪC
6
H
4
), 8.15 (t, J ϭ 6.0 Hz, 1 H, ϪC
6
H
4
), 7.80 (d, J ϭ 6.0 Hz, 1
), 7.64 (t, J ϭ 6.0 Hz,
geometries (dtbp versus dsp) and supramolecular architec-
ture (aromatic π-π stacking versus CϪH···O hydrogen
bonding), the former being a consequence of the latter.
This solvent-specific dimorph crystallization is qualitat-
6
H
4
), 7.52 (t, J ϭ 7.5 Hz, 1 H, ϪC
6
H
4
5
1
2
5
H
4
N), 6.87 ppm (d, J ϭ 6.0 Hz, 2 H, ϪC
5
H
4
N) ppm.
V
6
NMR ([D ]DMSO): δ ϭ Ϫ535 ppm.
ively consistent with relative polarizability; the VO (LЈ) di- Synthesis from VOSO ·5H O: Prepared as for α-VO (L), but using
2
4
2
2
morphs appear to be similar to those of VO (L).
acetonitrile instead of methanol. Yield: 0.174 g (75%).
2
α-VO (LЈ): Prepared as for α-VO (L), but using HLЈ instead of
2
2
HL. Yield: 0.197 g (76%). C17 V (344.24): calcd. C 59.32,
H 3.81, N 8.14; found C 59.38, H 3.89, N. 8.17. IR (KBr): ν˜ ϭ
13 2 3
H N O
Experimental Section
Ϫ1
9

25, 941 (s, VϭO), 1626 (s, CϭN) cm . UV/Vis (DMF): λmax. (ε,
General: Bis(acetylacetonato)oxovanadium() was prepared by lit-
Ϫ1
Ϫ1
1
·cm ) ϭ 412 nm (2068). H NMR ([D
H, ϪCH Ϫ), 9.89 (s, 1 H, ϪCHϭN), 8.94 (d, J ϭ 6.0 Hz, 1 H,
), 8.42 (d, J ϭ 6.0 Hz, 1 H, ϪC10 ), 8.21 (t, J ϭ 6.0 Hz,
H, ϪC10 ), 8.09 (d, J ϭ 9.0 Hz, 1 H, ϪC10 ), 7.42 (t, J ϭ 7.5
Hz, 1 H, ϪC10 ), 7.14 (d, J ϭ 9.0 Hz, 1 H, ϪC10 ), 7.88 (t, J ϭ
.5 Hz, 2 H, ϪC N), 7.65 (d, J ϭ 9.0 Hz, 2 H, ϪC N) ppm.
6
]DMSO): δ ϭ 5.76 (s,
[
21]
erature methods. 2-Picolylamine, salicylaldehyde, 2-hydroxynap-
thaldehyde and acetylacetone were obtained from Aldrich. Vanadyl
sulfate pentahydrate was purchased from Loba Chemie (India) and
2
2
ϪC10
1
H
6
H
6
H
6
H
6
30% hydrogen peroxide was obtained from S. D. Fine Chem. (In-
H
6
H
6
dia). All other chemicals and solvents were of analytical grade and
were used as received. Spectra were recorded using the following
equipment: IR (KBr disk), Nicolet Magna 750 Series II spec-
7
5
H
4
5 4
H
2 4 2
Synthesis of α-VO (LЈ) from VOSO ·5H O: Prepared as for α-
1
trometer. UV/Vis, Shimadzu UVPC 1601 spectrometer. H NMR,
VO (L), but using HLЈ instead of HL. Yield 0.193 g (71%).
2
Bruker FT 300 MHz spectrometer (assignments were based on
chemical shifts and spin-spin structures) and 51V NMR, Varian
2
2
β-VO
stead of methanol. Yield: 0.183 g (71%). C17
PerkinϪElmer 240C elemental analyzer was used for microanalysis calcd. C 59.32, H 3.81, N 8.14; found C 59.34, H 3.85, N. 8.15. IR
(LЈ): Prepared as for α-VO
(LЈ), but using acetonitrile in-
78.8 MHz spectrometer (VOCl
3
external reference).
A
13 2 3
H N O
V (344.24):
Ϫ1
(C, H, N).
(KBr): ν˜ ϭ 923, 942 (s, VϭO), 1623 (s, CϭN) cm . UV/Vis
Ϫ1
Ϫ1
412 nm (2026). 1H NMR
2
Ϫ), 9.89 (s, 1 H, ϪCHϭN),
(
(
8
DMF):
[D ]DMSO): δ ϭ 5.76 (s, 2 H, ϪCH
.94 (d, J ϭ 6.0 Hz, 1 H, ϪC10 ), 8.42 (d, J ϭ 6.0 Hz, 1 H,
ϪC10 ), 8.21 (t, J ϭ 6.0 Hz, 1 H, ϪC10 ), 8.09 (d, J ϭ 9.0 Hz,
H, ϪC10 ), 7.42 (t, J ϭ 7.5 Hz, 1 H, ϪC10 ), 7.14(d, J ϭ 9.0
Hz, 1 H, ϪC10 ), 7.88 (t, J ϭ 7.5 Hz, 2 H, ϪC N), 7.65 (d,
J ϭ 9.0 Hz, 2 H, ϪC N) ppm.
λmax. (ε,  ·cm ) ϭ
HL: 2-Picolylamine (0.885 g, 8.2 mmol) was added to a solution of
salicylaldehyde (1 g, 8.2 mmol) in ethanol (15 mL). After refluxing
the mixture for half an hour, the solvent was removed in a rotary
evaporator and the yellow oil thus obtained used without further
purification.
6
H
6
H
6
H
6
1
H
6
H
6
H
6
5 4
H
5
H
4
HLЈ: Prepared similarly, using 2-hydroxynapthaldehyde in place
of salicylaldehyde.
Synthesis of β-VO
VO (LЈ), but using acetonitrile instead of methanol. Yield:
.201 g (74%).
2 4 2
(LЈ) from VOSO ·5H O: Prepared as for α-
α-VO
2
(L): A solution of HL (0.159 g, 0.75 mmol) in methanol
(0.2 g, 0.75 mmol) in
2
0
(5 mL) was added to a solution of VO(acac)
2
methanol (50 mL). Pure oxygen was bubbled through the deep red
solution for 5 h with stirring. The greenish-yellow precipitate that
appeared was filtered off, washed with dichloromethane, and dried
Conversion of VO
dbcat) (0.076 g, 0.34 mmol) was added to a suspension of either
form of VO (L) (0.10 g, 0.34 mmol) in dichloromethane (20 mL).
The mixture was stirred for 8 h and the violet-coloured solution
concentrated and left to evaporate in the air. The crystalline prod-
uct thus obtained was washed with cold methanol and dried in
2
(L) to VO(L)(dbcat): 3,5-Bis(tert-butyl)catechol
(H
2
2
in vacuo over fused CaCl
2
. Yield: 0.171 g (77%). C13
H
11
N
2
O
3
V
(
9
294.18): calcd. C 53.08, H 3.77, N 9.52; found C 53.14, H 3.85, N
Ϫ1
.58. IR (KBr): ν˜ ϭ 921, 939 (s, VϭO), 1621 (s, CϭN) cm . UV/
Vis (DMF): λmax. (ε,  ·cm ) ϭ 395 nm (1810). 1H NMR
Ϫ1
Ϫ1
vacuo over fused CaCl
found to be identical in all respects with that reported earlier.
2
. Yield: 0.134 g (76%). This complex was
(
8
[D
.95 (br., 1 H, ϪC
J ϭ 6.0 Hz, 1 H, ϪC
t, J ϭ 6.0 Hz, 2 H, ϪC
ϪC
N) ppm. 51V NMR ([D
6
6
]DMSO): δ ϭ 5.60 (s, 2 H, ϪCH
), 8.15 (t, J ϭ 6.0 Hz, 1 H, ϪC
), 7.52 (t, J ϭ 7.5 Hz, 1 H, ϪC
N), 6.87 ppm (d, J ϭ 6.0 Hz, 2 H,
]DMSO): δ ϭ Ϫ535 ppm.
2
Ϫ), 9.06 (s, 1 H, ϪCHϭN),
), 7.80 (d,
), 7.64
[
11]
6
H
4
6 4
H
6
H
4
6
H
4
Crystal Structure Determination: Single crystals of α-VO
β-VO (L) were obtained directly during synthesis but without stir-
(L) and
2
(
5 4
H
2
5
H
4
ring of the oxygen-saturated reaction mixture (vide supra). The un-
disturbed solution deposited suitable single crystals within a few
days. Data were collected with a Nicolet R3m/V four-circle dif-
Synthesis from VOSO ·5H O: 30% Hydrogen peroxide (1 mL) was
4
2
added to a suspension of VOSO ·5H O (0.2 g, 0.79 mmol) in meth-
anol (50 mL). 15 min of stirring resulted in the formation of an
orange-red solution, to which solution of HL (0.168 g,
.79 mmol) in methanol (5 mL) was added. The dark-brown solu-
4
2
fractometer with graphite-monochromated Mo-K
α
radiation (λ ϭ
˚
0.71073 A) using the ω-scan technique (3 Յ 2θ Յ 48° for both the
a
α and β forms). All data were corrected for Lorentz polarization,
and an empirical absorption correction[ was performed on each
set of data on the basis of the azimuthal scans of six reflections.
All calculations of data reduction, structure solution and refine-
0
22]
tion was kept undisturbed in air at room temperature. After 24
h, the crystalline product deposited was filtered off, washed with
methanol and dried in vacuo under fused CaCl
.168 g (72%) of α-VO (L).
2
. This afforded
[
23]
ment were done with the programs of SHELXTL, version 5.03.
0
2
The two structures were solved by direct methods and refined by
2
β-VO
2
(L): Prepared as for α-VO
2
(L), but using acetonitrile instead
full-matrix least-squares on F . All non-hydrogen atoms were re-
of methanol. Yield: 0.164 (74%). C13
H
11
N
2
O
3
V (294.18): calcd. C fined anisotropically. All the hydrogen atoms in two structures were
located in the difference Fourier maps. Significant crystal data are
ν˜ ϭ 918, 939 (s, Vϭ O), 1626 (s, CϭN) cm . UV/Vis (DMF): listed in Table 3. Supplementary crystallographic data have been
53.08, H 3.77, N 9.52; found C 53.19, H 3.82, N 9.57. IR (KBr):
Ϫ1
Ϫ1
Ϫ1
1
λ
max. (ε,  ·cm ) ϭ 395 nm (1789). H NMR ([D
6
]DMSO): δ ϭ deposited.
Eur. J. Inorg. Chem. 2004, 1873Ϫ1878 www.eurjic.org
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1877

B. Baruah, S. P. Rath, A. Chakravorty
FULL PAPER
[
[
5]
CCDC-168305 [for α-VO
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(L)] and -168304 [for β-VO
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trieving.html [or from the Cambridge Crystallographic Data Cen-
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β-VO (L)
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294.18
13
H
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N
2
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V
13 11 2 3
C H N O V
294.18
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293(2)
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P2
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P1 (no. 2)
˚
a (A)
10.723(2)
10.270(2)
11.944(2)
Ϫ
108.36(3)
Ϫ
7.798(2)
8.363(2)
9.585(2)
80.92(3)
89.47(3)
82.76(3)
612.3(2)
2
1.596
0.814
0.0085
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V. Vergopoul-
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β [°]
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[9d]
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2, 1844Ϫ1849.
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3
V (A )
1248.4(4)
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[9e]
2459Ϫ2466.
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0.799
0.0189
2115
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wR
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[I Ͼ 2σ (I)]
[I Ͼ 2σ (I)]
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0.0759
1.087
0.0279
0.0766
1.101
[10d]
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2
2
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Acknowledgments
We acknowledge financial support received from the Department
of Science and Technology and Council of Scientific and Industrial
Research, New Delhi. We are thankful to Prof. G. K. Lahiri for
help.
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Early View Article
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1878
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Eur. J. Inorg. Chem. 2004, 1873Ϫ1878