Ligand reactivity, substituent effects and solvent interactions in the spectra and structure of some oxovanadium(V) chelates with Schiff bases. Proof for dimeric species

Article abstract of DOI:10.1016/S0277-5387(00)00483-6

The reaction of bis(β-dionato)oxovanadium(IV) chelates, VOβ₂, with substituted benzoylhydrazines, XbhH₂, was explored in alcoholic solutions and oxovanadium(V) compounds with Schiff bases as ligands were obtained in high yield. These

Full text of DOI:10.1016/S0277-5387(00)00483-6

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Polyhedron 19 (2000) 2003–2010
Ligand reactivity, substituent effects and solvent interactions in the
spectra and structure of some oxovanadium(V) chelates with Schiff
bases. Proof for dimeric species
Chris Tsiamis *, Byron Voulgaropoulos, Dimitrios Charistos, George P. Voutsas,
Constantin A. Kavounis
Department of Chemistry and Department of Physics, Uni6ersity of Thessaloniki, 54006 Thessaloniki, Greece
Received 29 September 1999; accepted 9 June 2000
Abstract
The reaction of bis(b-dionato)oxovanadium(IV) chelates, VOb2, with substituted benzoylhydrazines, XbhH2, was explored in
alcoholic solutions and oxovanadium(V) compounds with Schiff bases as ligands were obtained in high yield. These VOL(OR)
compounds have alkoxide as coligand and the asymmetic tridentate Schiff base ligands, L2−, bind to the oxovanadium core
through the carbonyl oxygens and the imine nitrogen. Substituents attached to benzoylhydrazines affect the electron density about
the oxovanadium core. While electron attracting substituents appear to favour monomeric square pyramidal chelates, the
derivatives having electron repelling groups seem to encourage formation of dimeric structures and alkoxo bridged dimers are
obtained. The crystal structures of the products of the reaction of bis(1-phenyl-1,3-butanedionato)oxovanadium(IV), VO(bzac)2,
with o-nitrobenzoylhydrazine (o-O2NbhH2) and m-methoxybenzoylhydrazine (m-CH3ObhH2) that are reported demonstrate the
influence of the substituents as well as the role of the solvent. © 2000 Elsevier Science Ltd. All rights reserved.
Keywords: Alkoxo compounds of oxovanadium(V); Crystal structure of compounds of oxovanadium(V); Hydrazonato compounds of oxovanadi-
um(V); Oxovanadium(V) dimers; Reactivity of bis(b-dionato)oxovanadium(IV) chelates; Hydrazonato tridentate Schiff base ligands
bases that are capable of confining metal atoms and
controlling their properties and functionality [11]. Re-
garding b-diones and the oxovanadium(IV) core, the
1-phenyl-1,3-propanedione [6–9] has been gainfully em-
ployed in studies involving the Schiff bases resulting
from the condensation reaction with aroylhydrazines
[4–9]. Recent studies have indicated that solvent inter-
actions with the moieties resulting from the ligation of
such tridentate Schiff bases to the oxovanadium(IV)
core have significant repercussions on the structure of
the resulting chelates since solvent molecules or solvent
fragments participate as coligands [6–9]. Other b-
diones have not been utilised in similar studies, even
though seemingly minor changes in ligand structure
incurred by groups within the b-dionato moiety have a
profound effect on the stereochemistry, the spacing of
the energy levels, the redox potentials and other distinc-
tive physicochemical properties of the b-dionato
chelates [12]. The effects of substituents attached to the
phenyl ring of benzoylhydrazines on the electron distri-
1. Introduction
Vanadium exists in a plethora of oxidation states and
its coordination compounds play an important role in
nitrogen activation and fixation and other biologically
important reactions [1–3]. This revelation has stimu-
lated interest in the stereochemistry and reactivity of its
coordination compounds that contain the diazo and
hydrazido group because they may provide some un-
derstanding of the mechanism of metalloenzymatic re-
duction of dinitrogen. Substituted aroylhydrazones
possessing a suitably disposed amino group, whilst
often bind directly to the metal [4], they may also
interact with compounds containing carbonyl groups,
for example salicylaldehydes and b-diones [5–10]. Such
reactions have been exploited adroitly to form Schiff
* Corresponding author. Tel.: +30-31-997-863; fax: +30-31-427-
218.
E-mail address: tsiamis@chem.auth.gr (C. Tsiamis).
0277-5387/00/$ - see front matter © 2000 Elsevier Science Ltd. All rights reserved.
PII: S0277-5387(00)00483-6

2004
C. Tsiamis et al. / Polyhedron 19 (2000) 2003–2010
bution of the Schiff bases have not been explored
sufficiently. Further, the reactivity of the bis(b-dion-
ato)oxovanadium(IV) chelates, VOb2, has not been
probed adequately in the preparation of tridentate
Schiff base ligands, even though the VOb2 chelates have
been engaged successfully in ligand addition and ligand
exchange reactions and are often used as starting mate-
rial in syntheses [13,14].
This investigation was undertaken in order to explore
the reactivity of certain bis(b-dionato)oxovanadium(IV)
chelates with aroylhydrazines, to assess the influence of
the reaction medium in the formation of products, to
appraise the effect of substituents in the structure and
the spectroscopic properties of the chelates formed, to
assay the possibility of oxygen bridge creation and
formation dimeric structures and to determine the stere-
ochemistry of the resulting compounds. In this work
the preparation of some b-dionate(benzoyl)hydrazo-
nato(2-)oxovanadium(V) chelates is reported, the struc-
tures of [ethoxo(4-phenyl-2,4-butanedione(2%-nitroben-
zoyl)hydrazonato(2-))oxo-vanadium(V)] and the anti-
coplanar bis[m2-methoxo(4-phenyl-2,4-butanedione(3%-
methoxybenzoyl)hydrazonato(2-))oxovanadium(V)] are
described and the results of the investigation are pre-
sented and discussed.
tone, thtfH), were purchased from Sigma–Aldrich. The
bis(b-dionato)oxovanadium(IV) chelates (VOb2), that
were used as starting materials, were prepared and
purified as described in the literature [15,16]. The com-
pound (n-C4H9)4NVO3 was prepared by established
procedures [17]. The substituted aroylhydrazines,
XbhH2, were procured from Fluka. Certain Schiff bases
resulting from the reaction of benzoylacetone or trifl-
uorobenzoylacetone with substituted benzoylhydrazines
were prepared by literature methods [18] and character-
ised. The synthesis of the new vanadium chelates was
accomplished as follows:
In a 200 cm3 conical flask containing a magnetic
follower are placed 10 mmol of VOb2 and ꢀ80 cm3
alcohol and the mixture is stirred at ambient tempera-
ture until complete dissolution. Then 20 mmol of aroyl-
hydrazine (also dissolved in the same alcohol) are
added while stirring and the colour of the reaction
mixture changes from brown to red–brown. The stir-
ring continued for an additional 20 h. The VO(Xbh)OR
compounds precipitated as red–brown solids. Recrys-
tallisation was achieved by redissolving the solid in
alcohol and allowing crystals to grow under
refrigeration.
The chelates prepared, their stoichiometry and melt-
ing points are given in Table 1.
2. Experimental
2.2. X-ray crystallographic analysis of
[VO(o-O2Nbhbzac)OC2H5] and of
[VO(m-CH3Obhbzac)(v2-OCH3)]2
2.1. Preparation and characterisation of the
VO(ibh)OR compounds
Intensities of X-ray reflections within two octants of
the reciprocal sphere were collected by means of a
four-circle Philips-STOE computer-controlled X-ray
diffractometer employing graphite-filtered Mo Ka radi-
ation. The orientation matrix and refined unit cell
dimensions of the crystal of [ethoxo(4-phenyl-2,4-
The b-diones, bH, namely 2,4-pentanedione (acetyl-
acetone, acacH), 1-phenyl-1,3-butanedione (benzoyl-
acetone, bzacH), 1-phenyl-4,4,4-trifluoro-1,3-butane-
dione (trifluorobenzoylacetone, bztfH) and 1-thenyl-
4,4,4-trifluoro-1,3-butanedione
(trifluorothenoylace-
Table 1
Elemental analyses and physicochemical data of some aroylhydrazonato(2-)oxovanadium(V) chelates containing alkoxo ligands, VOL(OR)
Compound
Yield (%)
M.p. (°C) a
C (%)
H (%)
N (%)
1
2
3
4
5
6
7
8
VO(p-NO2bhacac)OMe
VO(p-NO2bhacac)OEt
VO(p-NO2bhacac)OCHMe2
VO(p-NO2bhbzac)OMe
VO(p-NO2bhbzac)OEt
VO(p-NO2bhbzac)OCHMe2
VO(o-NO2bhbzac)OMe
VO(o-NO2bhbzac)OEt
VO(o-NO2bhbzac)OCHMe2
VO(p-NO2bhbztf)OCHMe2
VO(p-NO2bhthtf)OEt
73
77
91
95
83
87
93
90
82
81
71
74
91
81
131d
153d
251d
180d
210d
180d
207d
180d
202d
177d
230d
184d
219d
185d
43.7 (43.47)
44.7 (45.05)
46.7 (46.49)
51.3 (51.32)
52.3 (52.42)
53.8 (53.46)
51.1 (51.32)
51.9 (52.42)
53.2 (53.46)
47.7 (47.73)
41.3 (41.22)
42.4 (42.45)
55.8 (56.17)
44.1 (43.79)
3.93 (3.93)
4.27 (4.32)
4.72 (4.68)
3.79 (3.83)
4.20 (4.17)
4.52 (4.49)
3.86 (3.83)
4.21 (4.17)
4.37 (4.49)
3.37 (3.40)
2.68 (2.65)
3.01 (2.97)
4.71 (4.71)
3.01 (3.03)
11.4 (11.70)
11.8 (12.26)
11.1 (10.84)
9.87 (9.97)
9.75 (9.65)
9.47 (9.35)
10.2 (9.97)
9.57 (9.65)
9.29 (9.35)
8.39 (8.35)
8.44 (8.48)
8.28 (8.25)
6.84 (6.89)
5.94 (6.01)
9
10
11
12
13
14
VO(p-NO2bhthtf)OCHMe2
[VO(m-CH3Obhbzac)OMe]2
[VO(m-CH3Obhthtf)OMe]2
a d, decomposition.

C. Tsiamis et al. / Polyhedron 19 (2000) 2003–2010
2005
Table 2
for the unit cells. All intensities were corrected as usual
for Lorentz and polarization effects. In view of the low
v value no correction for absorption deemed necessary.
In both cases the vanadium position was deduced by
direct methods employing the SHELXS-86 and the SIR-97
programs [19,20] and used to compute a first-approxi-
mation electron-density synthesis, which revealed the
position of all remaining atoms except the hydrogens.
After least-squares refinements with the non-hydrogen
atoms, the hydrogen atoms were also located in the
difference Fourier map using the SHELX-97 program
[21]. The figures of the clinographic projection were
produced with the DIAMOND and ATOMS programs [22].
Refinement was carried out by full-matrix least-squares,
with unit weight to all reflections.
Crystal data and experimental details for the structural study of (a)
[VO(o-O2Nbhbzac)OC2H5] and (b) [VO(m-CH3Obhbzac)(m2-OCH3)]2
Formula
Formula mass, Mr
(a) C19H18N3O6V (b) C19H19N2O5V
435.31 406.31
Crystal parameters
Crystal shape
dark brown plates deep brown
rectangular prisms
Crystal size (mm)
Crystal system
Space group
0.75×0.45×0.25
monoclinic
P21/n
0.70×0.55×0.32
triclinic
(
P1
Unit-cell dimensions
,
a (A)
11.033(5)
7.537(5)
23.369(9)
90.00
93.920(5)
90.00
7.550(3)
10.010(3)
13.637(5)
106.99(2)
92.76(2)
105.70(3)
939.8(6)
2
,
b (A)
,
c (A)
h (°)
i (°)
k (°)
3
,
Vc (A )
1938.7(16)
4
3. Results and discussion
Units per cell, Z
Dcalc (Mg m−3
)
1.4914(12)
1.43548(9)
Many oxometallates undergo condensation reactions
in which polyatomic groups replace the oxygen ligand.
For example, the diazenido and the hydrazido groups
are attached to molybdenum by employing oxomolyb-
denum compounds as precursors [23]. In the case of
bis(b-dionato)oxovanadium(IV) chelates, the mixing of
alcoholic solutions of VOb2 and a substituted benzoyl-
hydrazine, XbhH2, is accompanied by a change in
colour (suggesting commencement of a reaction) and
formation of a precipitate as the main product. The
elemental analysis of the recrystallised precipitate re-
vealed the presence of nitrogen while the stoichiometry
disclosed dependence on the alcohol employed as sol-
vent. Interestingly, the yield is maximised when the
metal-to-benzoylhydrazine molecule is 1:2 and the reac-
tion mixture is accessible to atmospheric oxygen. Fur-
ther, in a series of reactions using the same alcohol as
solvent and the same XbhH2 but different chelate
VOb2, the composition of the main product suggested
abstraction of a b-ketoenol and entrapment of a aroyl-
hydrazine molecule by the vanadium atom. The dia-
magnetic behaviour of the new compounds indicated
absence of unpaired electrons while the lack of absorp-
tion in the electronic excitation spectra at wavenumber
below ꢀ2.50 mm−1 reaffirmed the absence of electrons
localised in the d orbital manifold [12,13]. These obser-
vations suggested an oxidative displacement reaction in
the oxovanadium core converting the metal to vanadi-
um(V) with sacrificial species one of the ligated b-dion-
ato anions and formation of chelates corresponding to
the general formula VOL(OR), where OR− is an alkox-
ide and L2− denotes the Schiff base resulting from the
partial addition-elimination reaction of the b-dionato
anion with an aroylhydrazine. To verify this hypothesis,
aroylhydrazones and either 1-phenyl-1,3-butanedione
(bzacH) or trifluorobenzoylacetone (bztfH) were em-
ployed to obtain Schiff bases which were subsequently
Measurement of intensity data
Instrument PW100-STOE
Mo Ka,
u=0.71069
,
Radiation (A)
Temperature (K)
Monochromometer
Scan mode
298(2)
Graphite
ꢀ–2q
q Range (°)
1.76–27.57
1.097
1.58–30.00
1.14
Linear absorption
coefficient, v (mm−1
)
Reflections measured
Independent reflections
Reflections observed
(I\2|(I))
4233
3825
2647
4728
4671
3454
Indices limits
h
k
l
−14–9
0–9
0–30
−10–5
−14–13
0–19
Refinement and final discrepancy factors
Refinement
full-matrix
full-matrix
least-squares on
least-squares on F2
F2
Parameters refined
323
301
Largest difference peak 0.399, −0.397
0.351, −0.416
−3
,
and hole (e A
)
R=S(ꢀFoꢀ−ꢀFcꢀ)/SꢀFoꢀ
Rw=[Sw(ꢀFoꢀ−ꢀFcꢀ)2/
Sw(ꢀFoꢀ)2]1/2
0.0512
0.0777
0.0387
0.1026
butanedione(2%-nitrobenzoyl)hydrazonato(2-))oxovana-
dium(V)], [VO(o-O2Nbhbzac)OC2H5] and of bis[m2-
methoxo(4-phenyl-2,4-butanedione(3%-methoxybenzoyl)-
hydrazonato(2-))oxovanadium(V)],
[VO(m-CH3Obh-
bzac)(m2-OCH3)], were obtained from independent
reflections of high intensity (125q515°). Details of
crystal analysis, data collection and structure refine-
ment are given in Table 2, together with the final values

2006
C. Tsiamis et al. / Polyhedron 19 (2000) 2003–2010
reacted with (n-C4H9)4NVO3 to produce chelates. The
later reaction afforded products identical to those ob-
tained by the reaction of the appropriate VOb2 chelates
with aroylhydrazines. Interestingly the yield of the one-
pot synthesis was appreciably higher. Further informa-
tion regarding the structure of the new compounds was
acquired from their electronic absorption spectra.
tion suggests that the dp–pp overlap between the vana-
dium and the oxygen atoms is influenced by the
substituents and the coligands. The implication of these
observations is that the condensation reaction of hydra-
zine does not involve the oxo ligand. Further, it tran-
spires that while one of the b-dionato anions, b−,
participates in the condensation reaction, the other
becomes the sacrificial species of the oxidative displace-
ment reaction.
3.1. Electronic excitation spectra
In addition to IR absorptions originating from VꢁO
core and the b-dione fragment of the Schiff base, the
bands may be distinguished in those arising from the
entrapped hydrazine species and in those emerging
from the alkoxy group. The presence of substituents
attached to the b-dionato moiety and the existence of
groups appended to the phenyl ring of the aroylhy-
drazine engender absorption bands and spectral shifts.
Whenever the b-diones employed are non-symmetric
the site of the attack becomes important. In the case of
bzac− the phenyl ring renders the adjacent carbonyl
group immune to the attack while in (bztf−) the strong
electron attracting ability of the trifluoro group ensures
that the attack is targeted in the carbonyl neighbouring
the phenyl ring. In the ensuing Schiff bases, the ꢁNH
proton is prone to form intermolecular and intramolec-
ular hydrogen bonds as the bands observed at ꢀ3400
(broad) and 1630 cm−1 indicated. These bands are not
present whenever the bis(b-dionato)oxovanadium(IV) is
employed, as the b-dione source and the chelates are
obtained in the one-pot synthesis. In the chelates pre-
pared the intense absorption observed at ꢀ1600910
cm−1 probably emanates from the azomethine (CꢁN)
stretching mode [26] while the high intensity band
occurring at ꢀ1520915 cm−1 and is tentatively
assigned to the ꢂCꢁNꢀNꢁCPhO(−) entity indi-
cates extensive delocalisation. The prototropic
ꢂCꢁNNHCOPh entity in the Schiff base apparently
undergoes hydrogen abstraction from the tautomeric
form, ꢂCꢁNꢀNꢁC(OH)Ph, to produce the electron-
rich hydrazido(2-) species because no band could be
associated with vibrations of either the NꢀH or the
OꢀH bonds. The process of hydrogen abstraction is
accomplished presumably with the aid of atmospheric
oxygen that facilitates the oxidation of the metal to
vanadium(V). Taking into consideration the strongly
electron-attracting nature of the metal and the
availability of electron density at the nitrogen atoms the
wholly reasonable assumption may be made that they
may be involved in bonding interactions. On the basis
of previous structural data and the geometry of the
resulting Schiff base, the nitrogen atom engaged in the
condensation reaction is presumed to be bonded to the
metal atom. This assumption is further supported by
the relatively weak bands at around 475910 cm−1
that are assigned to the stretching vibrations of the
VꢀN bonds [27]. The stretching vibrations of the VꢀO
In the electronic excitation spectra of the VOL(OR)
chelates no absorptions attributable to the ligand field
excitations happen. The lack of paramagnetic interac-
tions and the absence of ligand field transitions indicate
oxidation of the metal to vanadium(V) and disallow
any inference about the ordering of the d orbitals. A
strong broad band (or envelope) is observed at ꢀ2.50
mm−1 and is solvent depended. The absorption in this
region, for energy and intensity reasons, should be
attributed to a charge transfer excitation most likely
from a p ligand orbital to the manifold of the d metal
orbitals. The influence of the solvent in this band is
clearly evident in the spectra of the monomers in which
shifts and alterations of band shape are notable upon
change of solvent. Actually in the spectra of the
monomers obtained from 1,2-dichloroethane solutions
this LMCT excitation affords an envelope with no
definite maximum. From the shape of the envelope and
the preliminary analysis the occurrence of a band with
maximum at ꢀ2.0 mm−1 is deduced. In the spectra of
the monomers obtained employing acetonitrile or
DMSO as solvent, a well-formed band is evident at
ꢀ2.3 mm−1. This shift suggests change of the ordering
of the d orbitals effected by the occupation of the
vacant coordination site. Further information regarding
bonding in the chelates under consideration were
sought from the infrared spectra.
3.2. Infrared spectra
In the IR spectra of the compounds resulting from
the reaction of the substituted benzoylhydrazines with
bis(b-dionato)oxovanadium(IV) chelates, the absence of
absorptions above 3100 cm−1 implied that the hydra-
zino group, ꢀNHNH2, has taken part in an addition–
elimination reaction and that proton transfer has taken
place. The marginal shift in the diminished band that
turns out at ꢀ1578910 cm−1 and is associated with
the stretching vibration of a carbonyl group of the
b-dionato anion [13] suggested that carbonyl oxygen
remains bonded to vanadium since the CꢀO bending
mode appears as a rather strong band around 1160
cm−1. Further, the intense band occurring at ꢀ9709
30 cm−1 and assigned to the VꢁO stretching vibration
[23–25] indicated that the VꢁO core stays intact, while
the variation in frequency to the VꢁO stretching vibra-

C. Tsiamis et al. / Polyhedron 19 (2000) 2003–2010
2007
Table 3
Selected interatomic distances (A) and bond angles (°) of [VO(o-NO2bhbzac)OC2H5]
,
VꢀO(1)
VꢀO(4)
VꢀO(2)
VꢀO(3)
1.580(2)
1.758(2)
1.860(2)
1.915(2)
2.061(2)
1.324(3)
1.318(3)
1.216(3)
1.225(3)
1.453(5)
1.286(3)
N(1)ꢀN(2)
N(2)ꢀC(2)
N(3)ꢀC(13)
C(1)ꢀC(2)
C(4)ꢀC(5)
C(2)ꢀC(3)
C(3)ꢀC(4)
C(5)ꢀC(10)
C(5)ꢀC(6)
C(6)ꢀC(7)
C(7)ꢀC(8)
1.394(3)
1.327(3)
1.461(4)
1.493(4)
1.475(4)
1.401(4)
1.367(4)
1.391(4)
1.396(4)
1.366(5)
1.384(5)
C(8)ꢀC(9)
1.374(5)
C(9)ꢀC(10)
C(11)ꢀC(12)
C(12)ꢀC(13)
C(12)ꢀC(17)
C(13)ꢀC(14)
C(14)ꢀC(15)
C(15)ꢀC(16)
C(16)ꢀC(17)
C(18)ꢀC(19)
1.380(5)
1.475(4)
1.391(4)
1.393(4)
1.391(4)
1.368(5)
1.379(5)
1.373(5)
1.442(6)
VꢀN(2)
O(2)ꢀC(4)
O(3)ꢀC(11)
O(5)ꢀN(3)
O(6)ꢀN(3)
O(6)ꢀC(18)
N(1)ꢀC(11)
O(1)ꢀVꢀO(4)
O(1)ꢀVꢀO(2)
O(4)ꢀVꢀO(2)
O(1)ꢀVꢀO(3)
O(4)ꢀVꢀO(3)
O(2)ꢀVꢀO(3)
O(1)ꢀVꢀN(2)
O(4)ꢀVꢀN(2)
O(2)ꢀVꢀN(2)
O(3)ꢀVꢀN(2)
C(4)ꢀO(2)ꢀV
C(11)ꢀO(3)ꢀV
C(18)ꢀO(4)ꢀV
C(11)ꢀN(1)ꢀN(2)
C(2)ꢀN(2)ꢀN(1)
C(2)ꢀN(2)ꢀV
N(1)ꢀN(2)ꢀV
106.05(11)
107.15(10)
95.94(9)
107.96(10)
89.71(9)
141.26(10)
99.99(9)
152.86(10)
83.40(9)
O(5)ꢀN(3)ꢀO(6)
O(5)ꢀN(3)ꢀC(13)
O(6)ꢀN(3)ꢀC(13)
O(2)ꢀC(4)ꢀC(3)
O(2)ꢀC(4)ꢀC(5)
C(3)ꢀC(4)ꢀC(5)
C(4)ꢀC(3)ꢀC(2)
N(2)ꢀC(2)ꢀC(3)
N(2)ꢀC(2)ꢀC(1)
C(3)ꢀC(2)ꢀC(1)
C(10)ꢀC(5)ꢀC(6)
C(10)ꢀC(5)ꢀC(4)
C(6)ꢀC(5)ꢀC(4)
C(7)ꢀC(6)ꢀC(5)
C(6)ꢀC(7)ꢀC(8)
C(9)ꢀC(8)ꢀC(7)
124.2(3)
118.0(2)
117.7(2)
120.8(3)
115.8(2)
123.3(3)
124.6(3)
120.9(2)
120.2(2)
118.9(2)
118.0(3)
120.3(3)
121.7(3)
121.2(3)
120.2(4)
119.5(3)
C(10)ꢀC(9)ꢀC(8)
C(9)ꢀC(10)ꢀC(5)
N(1)ꢀC(11)ꢀO(3)
N(1)ꢀC(11)ꢀC(12)
O(3)ꢀC(11)ꢀC(12)
C(13)ꢀC(12)ꢀC(17)
C(13)ꢀC(12)ꢀC(11)
C(17)ꢀC(12)ꢀC(11)
C(16)ꢀC(17)ꢀC(12)
C(15)ꢀC(14)ꢀC(13)
C(14)ꢀC(15)ꢀC(16)
C(15)ꢀC(16)ꢀC(17)
C(14)ꢀC(13)ꢀC(12)
C(14)ꢀC(13)ꢀN(3)
C(12)ꢀC(17)ꢀN(3)
O(4)ꢀC(18)ꢀC(19)
120.6(3)
120.5(3)
121.7(2)
119.1(2)
119.2(2)
116.5(3)
123.6(2)
119.8(3)
121.5(3)
118.7(3)
120.5(3)
120.4(4)
122.4(3)
117.0(3)
120.4(2)
109.6(4)
74.90(9)
133.94(18)
117.74(16)
124.6(2)
108.1(2)
115.5(2)
128.24(18)
116.25(17)
bonds appear as rather medium intensity bands around
525920 cm−1. Some of the metal–ligand absorptions
are not related to the Schiff base and are solvent
dependent. For instance, in the IR spectra of the
product of the reaction of m-methoxybenzoylhydrazine
with VOb2 in methanol a very broad feature centred
around 340 cm−1 propounded the possibility of addi-
tional metalꢀoxygen bonds and suggested the likely
occurrence of dimeric structures [27]. The broad feature
appears to consist of a number of overlapping peaks
attributable to deformations of bridging VꢀOꢀV bonds
and vibrational coupling of low frequency modes that
complicate the assignments in this region. The notion of
the existence of dimeric structures was enhanced by the
shift of the bands due to the CꢀO vibrations to higher
wave-numbers by 10–30 cm−1 that suggested absence
of additional bonding interactions of the carbonyl oxy-
gens. The oxo ligand was not implicated in the forma-
tion of the dimeric species, because the shift of the band
due to the VꢁO stretching vibration was imperceptible
[23–25]. Since neither the infrared spectra nor the
elemental analyses revealed the presence of water
molecules, the alkoxo groups were implicated in the
formation of dimeric species. Confirmation of their
existence and details of the structures of representative
compounds of the new chelates were acquired from the
X-ray diffraction study.
3.3. Description of the structures
The X-ray diffraction study of [ethoxo(4-phenyl-2,4-
dione(2% - nitrobenzoyl)hydrazonato(2 - )oxovanadium-
(V)], [VO(o-NO2bhbzac)OC2H5], disclosed that in the
unit cell there are four vanadium atoms. The positional
parameters, the interatomic distances and the bond
angles (Table 3) reveal that the coordination environ-
ment in which the vanadium atoms exist is approxi-
mately square pyramidal with the oxo ligand engaging
the apical position. The oxygen of the ethoxy group,
the carbonyl oxygens and the nitrogen of the primary
amino group that reacted with the b-dione, are in the
immediate vicinity of vanadium. While the aforemen-
tioned oxygen and nitrogen atoms are virtually in the
same plane (the basal plane), the central atom is above
,
the basal plane by 0.480(2) A and is directed towards
the oxo ligand. The VꢀOoxo interatomic distance at
,
1.580(2) A is in accord with other pentacoordinate
oxovanadium compounds (Table 4). These data
reaffirm the indications of coordination unsaturation
suggested by the solvent shifts in the electronic excita-
tion spectra. The Schiff base ligand forms a six-mem-
bered and a five-membered chelate ring and the
interatomic distances within the C(2)ꢀN(2)ꢀN(1)ꢀC(11)
group reassert that no hydrogen is bonded to the
nitrogen atoms and that extensive electron delocalisa-

2008
C. Tsiamis et al. / Polyhedron 19 (2000) 2003–2010
tion has taken place. The planar aromatic rings form a
dihedral angle of 34.53(5)°. A clinographic projection
of [VO(o-NO2bhbzac)OC2H5] and its labelling scheme
is shown in Fig. 1.
The X-ray diffraction study of bis[m2-methoxo-
(4-phenyl -2,4-dione(3% -methoxybenzoyl)hydrazonato-
(2-))oxovanadium(V)],
[VO(m-CH3Obhbzac)OCH3]2,
disclosed that in the unit cell there are only two vana-
dium atoms. The positional parameters (Table 4) show
that the coordination environment in which the vana-
dium atoms exist resembles closely that of the metal in
[VO(o-NO2bhbzac)OC2H5] and other [VO(L)OR]
chelates. The vanadium atoms are separated by a dis-
,
tance of only 3.370(2) A, suggesting the possibility of a
dimeric structure. The oxo ligand binds to one vana-
,
dium atom but exists at a distance of 4.750(2) A from
the other vanadium centre, implying absence of bond-
Fig. 1. A clinographic projection and labelling scheme of [ethoxo(4-
phenyl - 2,4 - butanedione(2% - nitrobenzoyl)hydrazonato(2 - ))oxovana-
dium(V)]. The ATOMS drawing shows the thermal ellipsoids at the
50% probability level. Hydrogen atoms are omitted for clarity.
,
ing interactions. However, at a distance of 2.360(2) A
from the vanadium centre the position trans to the oxo
ligand is engaged by the oxygen of another alkoxo lig-
and. The methoxo group is strongly ligated to one
vanadium centre and interacts with the other forming a
bridge. The resulting distorted octahedral structures of
the oxovanadium centres are bridged by one shared
edge leading to the creation of a {VO(m2-OR)2VO}4+
core. As the oxygen atom of the alkoxo group becomes
involved in covalent interactions with the other vana-
dium atom, the VꢀOalkox distance increases and the
change in electron density should affect the interactions
of the nitrogen atom in trans position. A diminution of
the distance of the nitrogen atom in trans position from
the vanadium centre is envisaged and, indeed, such a
trend becomes apparent when the interatomic distances
listed in Table 5 are considered. The compounds de-
scribed in this work do not follow exactly the expected
trend.
In the binuclear compound [VO(m-CH3Obhbzac)-
OCH3]2, the {VO(m2-OR)2VO}4+ core forms a paral-
lelepiped and the mutual steric requirements of the
Table 4
Bond lengths in some oxovanadium chelates with tridentate Schiff bases and other ligands
c
a
Compound
VꢀOoxo
VꢀN
VꢀOb
VꢀOh
VꢀOalk
VꢀO b
NꢀN
V···V
Ref.
[VO(bhbzac)OC2H5]
[VO2(bzacGRP)]
1.595(3)
1.601(3)
1.583(4)
1.598(5)
1.580(2)
1.584(2)
2.070(3)
2.133(4)
2.093(4)
2.043(6)
2.061(2)
2.083(2)
1.848(2)
1.929(4)
1.883(3)
1.835(5)
1.860(2)
1.848(1)
1.907(2)
1.980(4)
1.937(3)
1.893(5)
1.915(2)
1.922(2)
1.750(3)
1.616(3)
1.789(3)
1.770(4)
1.758(2)
1.824(2)
1.400(6)
1.405(5)
1.408(5)
1.409(7)
1.394(3)
1.396(2)
[7]
[9]
[10]
[28]
This work
This work
[VO(bhbzac)O(CH2)2OH]
[VO(m-Cl bhbzac)OC2H5]
[VO(o-O2Nbhbzac)OC2H5]
[VO(m-CH3Obhbzac)-
OCH3]2
2.286(3)
2.360(2)
1.977(3)
3.370(2)
3.301(3)
3.068(4)
K4[VO(cit)]2·6H2O
[VO(SalAHE)]2
1.608(3)
1.619(10)
1.548(9)
1.598(4)
1.591(4)
1.619(6)
1.626(4)
1.611(4)
2.022(3)
1.892(10)
1.888(10)
1.880(4)
1.888(4)
1.915(4)
1.894(4)
1.897(4)
2.041(3)
1.985(10)
1.963(10)
1.805(4)
1.828(4)
2.120(5)$
1.966(4)
1.996(3)
2.171(3)
1.980(9)
1.979(9)
1.857(4)
1.759(4)
1.665(4)
1.635(4)
1.627(3)
[29]
[14]
2.009(11)
2.034(11)
2.130(5)
2.115(5)
2.162(5)
2.143(5)
2.128(3)
{[VO(SalAMHP)]2}O
[14]
3.06
3.222(7)
[VO2(1,2-pnSal)]2
[VO2(salGRP)]·CH3OH
[VO2(salGRT)]
2.427(5)
[30]
[31]
[31]
1.409(7)
1.403(5)
a Atoms in the basal position of the alkoxo oxygen.
b Atoms in the basal position of the oxygen of the aroyl group.
c bhbzac=4-phenylbutane-2,4-dionebenzoylhydrazonato(2-); m-Clbhbzac=4-phenylbutane-2,4-dione(m-chloro)benzoyl-hydrazonato(2-); cit=
citrate; Sal=Salicylaldehyde; GRP and GRT=Girard’s reagent P and T, respectively; H2SalAHE=2-(salicylideneamino)-1-hydroxyethane;
H2SalAMHP=2-(salicylideneamino)-1-hydroxypropane; 1,2-pnSal=1(N-salicylideneamino)-2-aminopropane; bzacGRP=4-phenylbutane-2,4-
dione((1-carboxymethyl)pyridinium chloride)hydrazonato(2-); SalGRP=2-(salicyl(1-carboxymethyl)pyridinium chloride)hydrazonato(2-); Sal-
GRT=2-(salicyl(1-carboxymethyl)trimethylammonium chloride)hydrazonato(2-). 2-{2-[(2-hydroxyphenyl)methylidene]hydrazino}-N,N,N-trime-
thyl-2-oxo-1-ethanaminium chloride.

C. Tsiamis et al. / Polyhedron 19 (2000) 2003–2010
2009
Table 5
Selected interatomic distances (A) and bond angles (°) of [VO(m-CH3Obhbzac)(m2-OCH3)]2
,
VꢀO(1)
VꢀO(5)
VꢀO(2)
VꢀO(3)
VꢀN(2)
VꢀO(5)
O(2)ꢀC(4)
O(3)ꢀC(11)
O(4)ꢀC(14)
O(4)ꢀC(18)
O(5)ꢀC(19)
1.584(2)
1.824(2)
1.848(1)
1.922(2)
2.083(2)
2.360(2)
1.322(2)
1.314(2)
1.358(3)
1.400(4)
1.418(3)
N(1)ꢀC(11)
N(1)ꢀN(2)
N(2)ꢀC(2)
C(1)ꢀC(2)
C(2)ꢀC(3)
C(3)ꢀC(4)
C(4)ꢀC(5)
C(5)ꢀC(6)
C(5)ꢀC(10)
C(6)ꢀC(7)
1.295(3)
1.396(2)
1.315(2)
1.496(3)
1.419(3)
1.362(3)
1.472(3)
1.399(3)
1.401(3)
1.377(3)
C(7)ꢀC(8)
C(8)ꢀC(9)
1.382(4)
1.384(4)
1.378(3)
1.475(3)
1.388(3)
1.391(3)
1.383(3)
1.387(3)
1.363(4)
1.385(3)
C(9)ꢀC(10)
C(11)ꢀC(12)
C(12)ꢀC(13)
C(12)ꢀC(17)
C(13)ꢀC(14)
C(14)ꢀC(15)
C(15)ꢀC(16)
C(16)ꢀC(17)
a
O(1)ꢀVꢀO(5)
O(1)ꢀVꢀO(2)
O(5)ꢀVꢀO(2)
O(1)ꢀVꢀO(3)
O(5)ꢀVꢀO(3)
O(2)ꢀVꢀO(3)
O(1)ꢀVꢀN(2)
O(5)ꢀVꢀN(2)
O(2)ꢀVꢀN(2)
O(3)ꢀVꢀN(2)
O(1)ꢀVꢀO(5) a
O(5)ꢀVꢀO(5) a
O(2)ꢀVꢀO(5) a
O(3)ꢀVꢀO(5) a
N(2)ꢀVꢀO(5) a
C(4)ꢀO(2)ꢀV
C(11)ꢀO(3)ꢀV
C(14)ꢀO(4)ꢀC(18)
102.43(8)
99.69(8)
104.12(6)
98.22(8)
89.99(6)
154.14(7)
98.88(8)
155.48(7)
83.91(7)
74.99(7)
175.58(7)
73.39(7)
80.19(6)
83.36(6)
85.51(6)
133.70(12)
118.28(13)
118.8(2)
C(19)ꢀO(5)ꢀV
C(19)ꢀO(5)ꢀV a
VꢀO(5)ꢀV a
C(11)ꢀN(1)ꢀN(2)
C(2)ꢀN(2)ꢀN(1)
C(2)ꢀN(2)ꢀV
124.75(15)
122.32(14)
106.61(7)
C(6)ꢀC(7)ꢀC(8)
C(7)ꢀC(8)ꢀC(9)
120.4(2)
119.9(2)
120.1(2)
120.6(2)
122.24(18)
119.57(18)
118.10(18)
120.02(19)
118.90(19)
121.0(2)
120.0(2)
124.6(2)
115.6(2)
119.8(2)
119.9(2)
121.4(2)
118.9(2)
C(10)ꢀC(9)ꢀC(8)
C(9)ꢀC(10)ꢀC(5)
N(1)ꢀC(11)ꢀO(3)
N(1)ꢀC(11)ꢀC(12)
O(3)ꢀC(11)ꢀC(12)
C(13)ꢀC(12)ꢀC(17)
C(13)ꢀC(12)ꢀC(11)
C(17)ꢀC(12)ꢀC(11)
C(14)ꢀC(13)ꢀC(12)
O(4)ꢀC(14)ꢀC(13)
O(4)ꢀC(14)ꢀC(15)
C(13)ꢀC(14)ꢀC(15)
C(16)ꢀC(15)ꢀC(14)
C(15)ꢀC(16)ꢀC(17)
C(16)ꢀC(17)ꢀC(12)
108.13(16)
115.71(16)
127.58(14)
116.29(12)
121.13(17)
120.63(19)
118.24(18)
124.84(18)
121.09(18)
114.75(16)
124.13(18)
118.39(19)
121.75(18)
119.83(18)
120.5(2)
N(1)ꢀN(2)ꢀV
N(2)ꢀC(2)ꢀC(3)
N(2)ꢀC(2)ꢀC(1)
C(3)ꢀC(2)ꢀC(1)
C(4)ꢀC(3)ꢀC(2)
O(2)ꢀC(4)ꢀC(3)
O(2)ꢀC(4)ꢀC(5)
C(3)ꢀC(4)ꢀC(5)
C(6)ꢀC(5)ꢀC(10)
C(6)ꢀC(5)ꢀC(4)
C(10)ꢀC(5)ꢀC(4)
C(7)ꢀC(6)ꢀC(5)
a Symmetry transformations used to generate equivalent atoms: −x,−y+1,−z+1.
metal coordination spheres exert strong influence on the
V···V separation, the hybridisation of the bridging oxy-
gen, and hence the bridge angle about oxygen which is
106.61(7)°. Since the C(19)ꢀO(5)ꢀV angles exceed 120°,
it transpires that the hybridisation of the oxygen is
rather near sp2. Dimeric vanadium chelates with a
{VO(m2-OR)2VO}4+ core may exist in five possible
configurations classified according to the orientation of
the vanadyl groups in respect to the plane defined by
the vanadium centres and the bridging oxygen atoms
[32]. The configurations are syn-orthogonal, anti-or-
thogonal, syn-coplanar, anti-coplanar, and twist. It has
been suggested [33] that, when several structures differ-
ing very little in energy are possible, the centrosymmet-
ric structure is preferred by crystal packing require-
ments. In dimeric vanadium chelates with a {VO(m2-
OR)2VO}4+ core, the anti-structures are favorites. In
the [VO(m-CH3Obhbzac)(m2-OCH3)]2 chelate, the
atoms of the ligands are symmetrically disposed relative
to the centre of the{VO(m2-OR)2VO}4+ core and the
disposition of the oxovanadium groups is anti-copla-
Fig. 2.
A clinographic projection and labelling scheme of bis-
nar,
a configuration sporadically encountered in
[methoxo(4-phenyl-2,4-butanedione(3%-methoxybenzoyl)hydrazonato-
(2-))-oxovanadium(V)]. The DIAMOND drawing shows the thermal
ellipsoids at the 50% probability level. Hydrogen atoms are omitted
for clarity.
dimeric oxovanadium compounds [34,35]. A clino-
graphic projection of [VO(m-CH3Obhbzac)OCH3]2 is
shown in Fig. 2.

2010
C. Tsiamis et al. / Polyhedron 19 (2000) 2003–2010
677. (c) G.E. Mannix, A.P. Zipp, J. Inorg. Nucl. Chem. 41
4. Supplementary data
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Crystallographic data have been deposited with the
Cambridge Crystallographic Data Centre, CCDC Nos.
134611 and 134612 for bis[m2-methoxo(4-phenyl-2,4-
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SIR-97, A Package for Crystal Structure Solution by Direct
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Copies of this information may be obtained free of
charge from The Director, CCDC, 12 Union Road,
Cambridge, CB2 1EZ, UK (fax: +44-1223-336033;
e-mail: deposit@ccdc.cam.ac.uk or www: http://
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