Synthesis and spectral characterization of homobimetallic molybdenum(VI) complexes derived from bis(2-hydroxy-1-naphthaldehyde)succinoyldihydrazone

Article abstract of DOI:10.1080/00958970903259451

The reaction of bis(2-hydroxy-1-naphthaldehyde)succinoyldihydrazone with bis(acetylaceto-nato)dioxomolybdenum(VI) (MoO₂(acac)₂) in 1: 3 molar ratio in EtOH: water mixture (95: 5) affords a complex of composition [(MoO₂)₂(nsh)(H₂O)₂]·C₂H₅OH. The reaction of [(MoO₂)₂ (nsh)(H₂O)₂]·C₂H₅OH with Lewis bases, namely pyridine,2-picoline,3-picoline, and 4-picoline, yields[(MoO₂)₂(nsh)(B)₂]·C₂H₅OH (where B=pyridine,2-picoline,3-picoline, and 4-picoline). Further, when this complex was reacted with 1,10-phenanthroline and 2,2′-bipyridine in 1:3 molar ratio in anhydrous ethanol the binuclear complexes [(μ₂-O)₂(MoO₂)₂ (H₄nsh)(phen)]·C₂H₅OH and [(μ₂-O)₂(MoO₂)₂ (H₄nsh)(bpy)]·C₂H₅OH were obtained. All of the complexes have been characterized by analytical, magnetic moment, and molar conductivity data. The structures of the complexes have been discussed in the light of electronic, IR, ¹H NMR, and ¹³C NMR spectroscopy.

Full text of DOI:10.1080/00958970903259451

This article was downloaded by: [University of Arizona]
On: 10 July 2013, At: 00:19
Publisher: Taylor & Francis
Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered
office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK
Journal of Coordination Chemistry
Publication details, including instructions for authors and
subscription information:
http://www.tandfonline.com/loi/gcoo20
Synthesis and spectral
characterization of homobimetallic
molybdenum(VI) complexes
derived from bis(2-hydroxy-1-
naphthaldehyde)succinoyldihydrazone
a
a
a
Ram A. Lal , Mithun Chakrabarty , Sanjesh Choudhury , Aziz
a
a
b
Ahmed , Roshmita Borthakur & Arvind Kumar
a
Department of Chemistry, North-Eastern Hill University,
Shillong-793022, Meghalaya, India
b
Academia Sinica, Institute of Chemistry, 128 Academia Road,
Sec.2, Nangkang, Taipei, 115, Taiwan, Republic of China
Published online: 05 Oct 2009.
To cite this article: Ram A. Lal , Mithun Chakrabarty , Sanjesh Choudhury , Aziz Ahmed , Roshmita
Borthakur & Arvind Kumar (2010) Synthesis and spectral characterization of homobimetallic
molybdenum(VI) complexes derived from bis(2-hydroxy-1-naphthaldehyde)succinoyldihydrazone,
Journal of Coordination Chemistry, 63:1, 163-175, DOI: 10.1080/00958970903259451
To link to this article: http://dx.doi.org/10.1080/00958970903259451
PLEASE SCROLL DOWN FOR ARTICLE
Taylor & Francis makes every effort to ensure the accuracy of all the information (the
“
Content”) contained in the publications on our platform. However, Taylor & Francis,
our agents, and our licensors make no representations or warranties whatsoever as to
the accuracy, completeness, or suitability for any purpose of the Content. Any opinions
and views expressed in this publication are the opinions and views of the authors,
and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content
should not be relied upon and should be independently verified with primary sources
of information. Taylor and Francis shall not be liable for any losses, actions, claims,
proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or
howsoever caused arising directly or indirectly in connection with, in relation to or arising
out of the use of the Content.
This article may be used for research, teaching, and private study purposes. Any
substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing,

systematic supply, or distribution in any form to anyone is expressly forbidden. Terms &
Conditions of access and use can be found at http://www.tandfonline.com/page/terms-
and-conditions

Journal of Coordination Chemistry
Vol. 63, No. 1, 10 January 2010, 163–175
Synthesis and spectral characterization of
homobimetallic molybdenum(VI) complexes derived
from bis(2-hydroxy-1-naphthaldehyde)succinoyldihydrazone
RAM A. LAL*y, MITHUN CHAKRABARTYy, SANJESH CHOUDHURYy,
AZIZ AHMEDy, ROSHMITA BORTHAKURy and ARVIND KUMARz
yDepartment of Chemistry, North-Eastern Hill University,
Shillong-793022, Meghalaya, India
zAcademia Sinica, Institute of Chemistry, 128 Academia Road,
Sec.2, Nangkang, Taipei, 115, Taiwan, Republic of China
(
Received 13 February 2009; in final form 14 July 2009)
The reaction of bis(2-hydroxy-1-naphthaldehyde)succinoyldihydrazone with bis(acetylaceto-
nato)dioxomolybdenum(VI) (MoO (acac) ) in 1 : 3 molar ratio in EtOH : water mixture (95 : 5)
affords a complex of composition [(MoO (nsh)(H O) OH. The reaction of [(MoO
] ꢀ C
nsh)(H O) OH with Lewis bases, namely pyridine, 2-picoline, 3-picoline, and
] ꢀ C
-picoline, yields [(MoO
2
2
2
)
2
2
2
2
H
5
2 2
)
(
2
2
2 5
H
4
2
)
2
(nsh)(B)
2
] ꢀ C
2
H
5
OH (where B ¼ pyridine, 2-picoline, 3-picoline,
0
and 4-picoline). Further, when this complex was reacted with 1,10-phenanthroline and 2,2 -
bipyridine in 1 : 3 molar ratio in anhydrous ethanol the binuclear complexes [(ꢀ
)
2 2 2 2
-O) (MoO )
(H
4
nsh)(phen)] ꢀ C
2
H
5
OH and [(ꢀ -O) (MoO (H nsh)(bpy)] ꢀ C OH were obtained. All of
2
2
2
2
4
2 5
H
the complexes have been characterized by analytical, magnetic moment, and molar conductivity
data. The structures of the complexes have been discussed in the light of electronic, IR,
H NMR, and C NMR spectroscopy.
1
13
Keywords: Molybdenum(VI); Bis(2-hydroxy-1-naphthaldehyde)succinoyldihydrazone; Homo-
bimetallic; Spectroscopic studies
1. Introduction
Molybdenum functions as a heterogeneous catalyst for the oxidation of organic
compounds in high oxidation states. Homogeneous oxo-transfer chemistry of MoO is
known to be biomimetic [1].
2
2
þ
Research in molybdenum complexes is mainly due to its biochemical role in
metalloenzymes [2] and rather complex chemistry. Molybdenum is the only element of
the second transition series essential for life; as a constituent of enzymes it participates
in redox reactions, e.g., oxidation of aldehydes, xanthine, and other purines [3], and
reduction of nitrate to molecular nitrogen [4, 5]. Molybdenum’s biochemical role is
based on its ability to facilitate electron exchange and to form stable complexes with
oxygen, nitrogen, and sulfur containing ligands. The useful role of molybdenum is not
*
Corresponding author. Email: ralal@rediffmail.com
Journal of Coordination Chemistry
ISSN 0095-8972 print/ISSN 1029-0389 online ß 2010 Taylor & Francis
DOI: 10.1080/00958970903259451

1
64
R.A. Lal et al.
only restricted to biological systems, but also plays important roles in a variety of
chemical reactions such as hydrodesulfurization, oxygen transfer reactions (e.g., olefin
epoxidation), and olefin metathesis. The cis-dioxo compounds displaying catalytic
activities [6] are models for enzymes [7, 8] and are useful material precursors [9].
Catalytic activity is frequently linked to coordinative unsaturation and the active sites
in various molybdenum oxidation catalysts are believed to contain coordinatively
unsaturated molybdenum centers [10–12]. In all of these biological and industrial
reactions, molybdenum plays the role of a catalytic redox site. Molybdoenzymes
consist of two Mo atoms per molecule, suggesting binuclear Mo-sites joined by one or
two oxo- or sulfido-bridges [13].
Close proximity of metal ions in multimetallic complexes considerably varies the
properties of the system which may be significantly different from properties of
monometallic complexes. Homomultimetallic complexes have the potential to mediate
chemical reactions of industrial relevance either more efficiently than, or in a different
manner to, monometallic complexes. They exhibit distinct reactivity patterns compared
to corresponding monometallic complexes [14]. As a result, synthesis and character-
ization of homobimetallic complexes continue to attract attention [15]. Especially, the
2þ
role of cis-MoO2 in metalloenzymes has led to studies of complexes with ligands
containing nitrogen, sulfur, or oxygen donors and the analysis of their chemical,
spectroscopic, and structural properties [16].
A survey of literature reveals that although metal complexes of Schiff bases derived
from the condensation of a variety of aldehydes and ketones with several aliphatic and
aromatic amines have been studied in detail [17, 18], metal complexes of Schiff bases
derived from monoacyl-, aroyl-, and pyridoyl-hydrazines have been studied to much
less extent [19–24]. Further, there are reported dicopper complexes of multihydrazones
[
25] and molybdenum complexes of thiosemicarbazones [26]. Moreover, although
a few homobimetallic complexes of salicylaldehyde, o-hydroxy aromatic aldehyde, and
ketone dihydrazones with first series transition metal ions have been synthesized
and characterized [27–31], those derived from dihydrazones having bulky fragments
in their molecular skeleton have received scant attention [32, 33].
In view of the importance of multimetallic complexes and much less work on the
multimetallic complexes of the dihydrazones containing bulky fragments in their
molecular skeleton, it was of interest to synthesize homobimetallic complexes of the
title dihydrazone and characterize the resulting products by various physico-chemical
and spectral techniques. Accordingly, the present article describes the synthesis and
characterization of homobimetallic complexes of Mo(VI) derived from bis(2-hydroxy-
1-naphthaldehyde)succinoyldihydrazone (H nsh) (figure 1) in ethanolic media and their
4
characterization by various physico-chemical techniques and spectroscopic methods.
The numbering scheme of the carbons in the ligand and the complexes are shown
in figure 1 and figure S1 in ‘‘Supplementary material’’. The carbons in axial and
equatorial positions have been designated by the letters ‘‘a’’ and ‘‘b’’, respectively [33].
2. Experimental
Ammonium molybdate ((NH ) Mo O ꢀ 4H O), diethyl succinate ((CH ) (CO Et) ),
4
6
7
24
2
2 2
2
2
hydrazine hydrate (N H ꢀ H O), and 2-hydroxy-1-naphthaldehyde (C H (OH)(CHO)
2
4
2
10
6

Succinoyldihydrazone
165
7a
O
6
a
8a
9a
H
H
N
5a
C
C
2a
4a
3a
N
3
a
1
a
1
0a
H C
2
1
1a
H
O
1
1
2a
O
12b
1
3b
1
1b
H
N
H C
2
10b
2
C
b
3
C
H
b
1
b
N
H
4b
9b
8b
5
b
b
6
O
7
b
4
Figure 1. Structure along with numbering scheme of H nsh.
were of E-Merck, Qualigens, Hi-Media or equivalent grade reagents and were used
without purification. Acetyl acetone, pyridine, 1-picoline, 2-picoline, 3-picoline, and
4-picoline were Lanchaster or equivalent grade reagents. The solvents ethanol,
methanol, diethyl ether, dimethyl sulfoxide (DMSO), and dimethyl formamide (DMF)
were used after purification by standard literature methods. Bis(acetylacetonato)
dioxomolybdenum(VI) (MoO (acac) ) was prepared by the literature method [34].
2
2
2
.1. Analysis of the complexes
Elemental analyses (C, H, and N) were performed on a Perkin–Elmer 2400 CHNS/O
Analyzer 11. Water, ethanol, pyridine, 3-picoline, and 4-picoline were determined from
the percentage weight losses obtained by heating the samples in the temperature
ꢁ
range 60–250 C. The detailed thermal analyses of 1, 2, 4, and 5 in the temperature
range 60–250 C were carried out. The samples were heated manually at each of the
ꢁ
ꢁ
temperatures (60, 65, 70, . . . , 250 C) for half an hour. The weight loss was determined
by subtracting the weight of the complex obtained after heating from the weight of the
complex before heating, and thus the weight losses and percentage weight losses were
calculated. Molybdenum content of the complexes was determined by the standard
literature procedure [35].
2
.2. Physical measurements
ꢂ3
Molar conductance of the complexes at 10 M in DMSO was determined using a
Wayne Kerr B 905 Automatic Precision Bridge with a dip-type conductivity cell.
ꢂ1
Infrared spectra from 4000 to 400/500 cm were obtained on either a BX-III/FT-IR
Perkin–Elmer spectrophotometer or a Nicolet-Impact 410 FT-IR spectrophotometer as
KBr discs. Electronic spectra of the ligand and complexes in DMF were recorded on a
ꢂ3
1
Perkin–Elmer Lambda 25 spectrophotometer at 10 M. H and C NMR spectra were
13

1
66
R.A. Lal et al.
recorded on a Bruker AC-F 300 MHz and AMX 400 High-Resolution Multinuclear
FT-NMR Spectrometer in DMSO-d . Tetramethylsilane (TMS) was used as an internal
standard.
6
2
.3. Preparation of the ligand
Bis(2-hydroxy-1-naphthaldehyde)succinoyldihydrazone was prepared in two steps.
In the first step, succinoyldihydrazine (SDH) was prepared by reacting diethyl
succinate with hydrazine hydrate in 1 : 2.5 molar ratio. In the second step, SDH (1.00 g,
6.84 mmol) was allowed to react with 2-hydroxy-1-naphthaldehyde (2.59 g, 15.04 mmol)
in 1 : 2.2 molar ratio in ethanol under reflux for 30 min. The yellow precipitate thus
obtained was purified by washing with hot ethanol and dried over anhydrous CaCl .
2
ꢁ
The m.p. was 254 C (Anal.: Found(%): C, 68.81; H, 4.80; and N, 12.65). Required for
C H O N (%): C, 68.72; H, 4.84; and N, 12.33.
2
6
22
4
4
2
.4. Preparation of [(MoO ) (nsh)(H O) ] C H OH (1)
.
2
2
2
2
2 5
The dihydrazone ligand (H nsh) (1.00 g, 2.20 mmol) was suspended in ethanol : water
4
ꢁ
mixture (100 mL (95 : 5)) and stirred for 30 min at 70 C. A solution of bis(acetylace-
tonato)dioxomolybdenum(VI) (MoO (acac) ) (2.15 g, 6.59 mmol) in ethanol (50 mL)
2
2
for molar ratio 1 : 3 was added to this. The reaction mixture was refluxed for 3 h which
yielded an orange precipitate. The product was filtered hot, washed several times with hot
ethanol and then with ether, and dried over anhydrous CaCl . Yield: 0.66 g.
2
.
2
.5. Preparation of [(MoO ) (nsh)(B) ] C H OH (where B ^ pyridine (py, 2);
2
2
2
2
5
2
-picoline (2-pic, 3); 3-picoline (3-pic, 4); 4-picoline (4-pic, 5))
Complex 1 (1.00 g, 1.27 mmol) was suspended in ethanol (100 mL) accompanied by
ꢁ
gentle stirring for 15 min at 60–70 C. Pyridine (1.02 mL, 12.64 mmol) was added (molar
ratio 1 : 10) to this suspension. The reaction mixture was refluxed for 3 h which
precipitated a yellowish-orange compound. The compound thus obtained was filtered
and collected. Yield: 0.7 g.
Complexes 3–5 were prepared similarly using 2-picoline, 3-picoline, and 4-picoline
instead of pyridine. Yield: 0.75 g (3); 0.73 g (4); and 0.72 g (5).
.
2
.6. Preparation of [(l -O) (MoO ) (H nsh)(BB)] C H OH (where BB ^ 1,10-
2
2
2 2
4
2
5
0
phenanthroline (phen, 6); (2,2 -bipyridine) (bpy, 7))
Complex 1 (1.00 g, 1.27 mmol) was suspended in ethanol (100 mL) accompanied by
ꢁ
gentle stirring for 15 min at 60–70 C. A solution of 1,10-phenanthroline (0.76 g,
3
.83 mmol) in ethanol (50 mL) for 1 : 3 molar ratio was added to this. The reaction
mixture was refluxed for 3 h precipitating a light yellow compound. The compound was
filtered hot, washed with hot ethanol and then with ether, and dried over anhydrous
CaCl . Yield: 0.72 g.
2
0
Complex 7 was prepared in a similar manner using 2,2 -bipyridine instead of 1,10-
phenanthroline. Yield: 0.71 g.

Succinoyldihydrazone
167
3. Results and discussion
The complexes isolated in the present study together with their molecular formula,
color, decomposition point, percentage yield, analytical data, magnetic moment, molar
conductance, and electronic spectral data are reported in table 1.
ꢁ
All of the complexes are colored, air stable and decompose above 300 C without
ꢁ
melting, except 6 which melts at 217 C. Such thermal behavior of 6 indicates covalent
character, whereas the remaining complexes are more ionic. All of the complexes are
insoluble in water, partly soluble in ethanol, methanol, acetone, benzene, chloroform,
hexane, and ether, and soluble in DMSO or DMF.
Efforts were taken to crystallize the complexes under different experimental
conditions in DMSO and DMF. Thus, both saturated and dilute solutions of the
complexes in various solvent systems such as DMSO, DMF, DMSO–CH CN, DMSO–
3
CH Cl , DMF–CH CN, and DMF–CH Cl were kept for 0.5, 1, and 2 months either at
2
2
3
2
2
room temperature or under a freezer to grow crystals. Furthermore, the solutions were
ꢁ
ꢁ
ꢁ
gently evaporated at 40 C, 50 C, and 60 C in a hot electronic oven to promote crystal
growth. Efforts were also made to crystallize these complexes either by layering the
above solutions with ether or by solvent diffusion methods. Unfortunately, in all
our efforts only amorphous compounds precipitated, which prevented analyses of the
complexes by X-ray crystallography.
All the complexes were diamagnetic indicating that molybdenum is þ6 in these
0
complexes with d electronic configuration, indicating no reduction of the
molybdenum(VI) under the influence of the ligand.
3
.1. Thermal studies
The detailed decomposition studies [36] of 1, 2, 4, and 5 were carried out in the
ꢁ
temperature range of 60–250 C. The weight loss occurs in two prominent steps,
ꢁ
ꢁ
i.e., 75–80 C and 200–240 C, for 2, 4, and 5 while 1 showed weight loss in the range
ꢁ
ꢁ
ꢁ
of 70–80 C and 160–180 C. The vapors evolved in the range of 75–80 C in all of the
complexes gave a yellow precipitate with a solution of sodium hydroxide and
iodine, confirming that they are ethanol. The loss of ethanol molecules in the
ꢁ
temperature range of 75–80 C indicates that they are present in the lattice of the
complexes. Weight loss corresponds to one ethanol supporting the number of ethanol
molecules present. When vapors in the range of 160–180 C in 1 were passed over
ꢁ
anhydrous copper sulfate in a test tube, it turned blue, confirming the presence of
water. The loss of weight corresponds to two water molecules in the coordination
sphere of the metal [36]. Complexes 2, 4, and 5 showed further weight loss in the
ꢁ
range of 200–240 C. The vapors evolved from 2 in this temperature range turned
the color of CHCl containing a drop of 5 M NaOH solution to red, confirming the
3
presence of pyridine. Similarly, vapors evolved from 4 and 5 in this temperature
range turned the color of cyanogen bromide solution to green-violet and blue,
respectively, on treatment with phloroglucinol solution, suggesting the presence of
3
-picoline and 4-picoline in 4 and 5, respectively. The weight loss in this temperature
range corresponds to one molecule each of pyridine, 3-picoline, and 4-picoline per
metal center.

1
68
R.A. Lal et al.

Succinoyldihydrazone
169
3.2. Molar conductance
All of the complexes have molar conductance values from 1.2 to
4
2
.7 cm Ohm mol in DMSO at 10 M, suggesting that they are nonelectrolytes [37].
ꢂ1
ꢂ1
ꢂ3
3
.3. Electronic spectra
ꢂ3
Electronic spectra of the complexes have been recorded in DMF at 10 M. The ligand
shows bands at 310–325 nm and 350–370 nm assigned to intraligand ꢂ ! ꢂ* and n ! ꢂ*
transitions. These blue bands shift on complexation. This indicates that dihydrazone is
coordinated to the metal. In addition to the intraligand bands, all of the complexes
show a new band at 429–436 nm, assigned to ligand-to-metal charge transfer (LMCT).
1
.4. H NMR spectra
3
The two proton doublets (Supplementary material) are observed at ꢃ 11.61 and
1
2.73 ppm and two proton singlets at ꢃ 9.99 and 11.14 ppm in the H NMR spectra
1
of the free dihydrazone. These signals are assigned to naphtholic –OH and secondary
1
NH, respectively. These signals do not appear in the H NMR spectra of 1–5. The
absence of signals in the region ꢃ 20–11 ppm in the complexes indicates the coordination
of dihydrazone in the enol form through naphtholic oxygen via deprotonation and
carbonyl oxygen via enolization/deprotonation. The ligand shows doublets at ꢃ 9.05
and ꢃ 8.60 ppm assigned to azomethine protons which shift downfield about 0.32–
0.52 ppm in 1–5. The downfield shift is attributed to the loss of electron density from
the nitrogen of azomethine group to the metal [33]. The most crucial feature of the
1
H NMR spectra of 1–5 is the collapse of the doublets corresponding to ꢃ-CH¼N in
the free ligand into a single resonance, suggesting that the dihydrazone which exists
in the anti–cis configuration in the free state attains staggered configuration in 1–5.
Similar coordination of the related malonoyl dihydrazone to the metal has been
reported by Gopinath et al. [31] and Lal et al. [38]. The naphthyl proton multiplet
appears at ꢃ 7.15–8.23 ppm in 1–5; 2–5 show additional resonances in the region ꢃ 7.16–
8
.57 ppm from ortho proton(s) of pyridine, 2-picoline, 3-picoline, and 4-picoline. These
signals are upfield shifted compared to their position in free pyridine, 2-picoline,
-picoline, and 4-picoline [36], attributed to the coordination of pyridyl nitrogen. The
3
methyl proton signals also show upfield shift in the complexes compared to their
position in free picoline, indicating the coordination of ring nitrogen.
1
The H NMR spectra of 6 and 7 are significantly different compared to 1–5. The two
proton doublets at ꢃ 11.61 and ꢃ 12.73 ppm due to naphtholic –OH protons in the
free dihydrazone are upfield shifted in 6 and 7 to ꢃ 11.60–12.59 ppm. Similarly, ꢃ NH
protons at ꢃ 9.99 and 11.14 ppm are downfield shifted to ꢃ 11.14 in both the complexes.
The presence of ꢃ NH in these complexes suggests that the dihydrazone is coordinated
in the keto form. The azomethine proton signals, on average, show a downfield shift
by about ꢃ 0.32–0.21 ppm as a doublet in these complexes as against a singlet in 1–5.
Such a feature associated with ꢃ (–CH¼N) may be attributed to coordination of the
dihydrazone to the metal center in the anti–cis configuration [39] in which only
the azomethine nitrogens of the dihydrazone are coordinated to the metal. As a result of
anti–cis configuration of the ligand, one hydrazone attains axial position while the

1
70
R.A. Lal et al.
other remains equatorial. Hence, equatorial protons appear upfield as compared to
axial protons and coupling between axial protons and equatorial protons leads to a
doublet for each. Stereospecific long-range coupling has been reported in hydrazones
[
these complexes, merged with signals due to aromatic protons of 1,10-phenanthroline
39, 40]. The naphthyl proton multiplet appears in the region of ꢃ 7.15–8.23 ppm in
0
and 2,2 -bipyridine. All the complexes show a triplet, a quartet, and a triplet at ꢃ 1.04,
ꢃ 3.44–3.01, and ꢃ 4.36–4.34 ppm, respectively, which correspond to methyl, methylene,
and –OH of ethanol present in the lattice.
1
3
.5. C nuclear magnetic resonance spectroscopy
3
1
Complexes 1, 3, and 5 were characterized by C NMR spectroscopy (Supplementary
3
1
3
material). Comparison of the C NMR spectra of the ligand and the complexes
indicates that the ligand and complexes have different configuration. Hence, the
spectral features of the complexes (with respect to the number of signals) are entirely
1
3
different from that of the ligand. The C NMR spectra of the free ligand and 3 are
provided in Supplementary material.
Signals associated with carbons near the coordinated sites in the complexes are
remarkably deshielded in comparison to the free ligand. The effect of molybdenum on
carbon resonances of naphthyl ring thus shifts upfield the signals due to C(6), C(7),
C(8), and C(9) by 1.46–2.44 ppm, while those due to C(3a), C(11), and C(13) are shifted
upfield even more since they are closer to the coordinated oxygen and nitrogen.
As a consequence, signals due to C(2a) and C(2b), which are in the free ligand were
at ꢃ 195.32 and 187.24 ppm, respectively, appear at ꢃ 172.26 ppm. The signal at ꢃ
160.00 ppm assigned to C(13) in the free ligand was observed at ꢃ 167.48 and
167.22 ppm giving a chemical shift change of 7.35 ppm. Similarly, the signal at
ꢃ 151.61 ppm is assigned to azomethine carbon which in the free ligand was at 160.81
and 159.86 ppm giving a chemical shift change of 8.73 ppm. The signals at ꢃ 132.41 and
1
24.65 ppm are assigned to C(10) and C(5) which in the free dihydrazone were at
ꢃ 134.47 and 132.20 ppm and ꢃ 127.63 and 127.43 ppm giving chemical shift changes
of 0.93 and 2.88 ppm, respectively. The signal at ꢃ 108.35 ppm assigned to C(4) in the
free ligand remained almost unaltered.
1
3
C NMR spectrum of the ligand shows 13 resonances and all of the signals appear as
pairs except signals due to C(12), C(4), and C(7). Each resonance forms a pair which
1
3
corresponds to the axial and equatorial carbon atoms. C NMR spectra of the
complexes shows 13 signals only, all as a singlet, supporting staggered configuration
1
of the ligand coordinated, which are consistent with H NMR spectra.
3
.6. Infrared spectra
A comparison of the IR spectra of the complexes with that of the free ligand H nsh
4
(Supplementary material) suggests that the dihydrazone coordinates to the metal center
in enol form in all complexes except 4 and 7 in which the ligand coordinates in
keto form.
The IR spectra of 1–5 are drastically changed compared to the free dihydrazone.
ꢂ1
The strong band at 1672 cm assigned to ꢄ(C¼O) of the uncoordinated dihydrazone

Succinoyldihydrazone
171
disappears in the complexes, again suggesting the collapse of the amide structure
of the ligand in coordination to the metal through carbonyl oxygen in the enol
form [31]. In the free dihydrazone, ꢄ(C¼N) appears as a couple of bands at 1633 and
–
1
ꢂ1
1
593 cm , shifting to 1623–1602 cm in 1–5, indicating the coordination of azomethine
nitrogen.
The free dihydrazone shows a medium intensity band at 1540 cm due to mixed
contribution of amide II and ꢄ(C–O) (naphtholic) [36]. This band shows a considerable
ꢂ1
ꢂ1
shift to higher frequency in 1–5, 1554–1558 cm . Such a shift indicates bonding
through naphtholic oxygen via deprotonation [36]. The intensity of the band in this
region is considerably increased compared to that in free dihydrazone, probably due
ꢂ
to overlap with the band due to newly created NCO as a result of enolization [29].
ꢂ1
Complexes 2–5 show a new, but very weak, band in the region 1036–1065 cm
characteristic of coordinated pyridine, 2-picoline, 3-picoline, and 4-picoline.
IR spectra of 6 and 7 are very similar to the uncoordinated dihydrazone, indicating
secondary NH and naphtholic –OH in the complexes. The strong amide I band at
ꢂ1
ꢂ1
1
672 cm in the free ligand shifts to 1675 cm , suggesting nonbonding of 4C¼O [27].
ꢂ1
A couple of strong bands at 1633 and 1503 cm assigned to ꢄ(C¼N) shift to lower
ꢂ1
frequency by 2–3 cm , indicating the coordination of azomethine nitrogen to the
–
1
metal. The medium intensity band at 1540 cm due to the mixed contribution of amide
II and ꢄ(CꢂO) (naphtholic) remains almost unshifted in 6 and 7, indicating
noninvolvement of 4C¼O and naphtholic –OH in coordination.
ꢂ1
Intense bands at 636 and 725 cm due to out-of-plane motion of the hydrogen
on the heterocyclic ring and the central ring [41] were observed in the IR spectrum
ꢂ1
of 6. Comparison with the bands at 787 and 734 cm in the IR spectrum of free 1,10-
phenanthroline indicates that these bands shift to lower frequency upon complexation.
Characteristic bands of free bipyridine [42] due to C–H out-of-plane deformation as
ꢂ1
ꢂ1
a strong band at 758 cm and a weak satellite at 739 cm are shown in 7. The band at
ꢂ1
ꢂ1
ꢂ1
758 cm was almost unshifted, while the weak satellite at 739 cm shifts to 622 cm .
The presence of these bands in 6 and 7 indicate the bidentate N–N coordination of
,10-phenanthroline and 2,2 -bipyridine [41, 42]. All complexes show two very strong
0
1
ꢂ1
2þ
to medium intensity bands in the region 884–956 cm , indicating cis-MoO2 . The
ꢄ(Mo¼O) of 6 and 7 shift considerably to lower frequency compared to those
in corresponding pyridine and substituted pyridine analogues. The band of medium
ꢂ1
intensity at 780–796 cm in 6 and 7 is assigned to the stretching of doubly bridged
Mo O .
2
2
From the stoichiometry of 6 and 7 and spectral evidence presented above, an
additional oxo-group was generated during the reaction of 1 with 1,10-phenanthroline
0
and 2,2 -bipyridine, but not for 2–5. Hence, bidentate ligands induce the migration of
protons from water coordinated to molybdenum, generating an oxo-group which binds
to molybdenum center in 6 and 7; monodentate nitrogen donors are unable to induce
migration of protons from water. The probable mechanism for the generation of the
oxo groups in 6 and 7 is shown in scheme 1. Phenanthroline and bipyridine are able to
simultaneously bind the two hydrogens of water, breaking the O–H bond and
generating an oxo. Once the bidentate ligands are hydrogen bonded to water, the
2
2
þ
complex undergoes isomerization to anti–cis configuration where MoO groups are
brought closer to each other.

1
72
R.A. Lal et al.

Succinoyldihydrazone
173
4. Conclusion
Some transition metal complexes of monoacyl-, aroyl-, and pyridoyl-hydrazones
have appeared, yet those derived from multihydrazines have received attention in recent
years only. All of the studies reported so far describe the first series transition metal
complexes of monohydrazones and multihydrazones, those on the second transition
series metal complexes are virtually absent. In this article, some homobimetallic
complexes of molybdenum from polyfunctional H nsh have been reported. The
4
reaction of the dihydrazone H nsh with MoO (acac) in 1 : 3 molar ratio yields
4
2
2
homobimetallic molybdenum(VI) complex (1). Reaction with excess pyridine and
substituted pyridines yield 2–5. The dihydrazone coordinates to the metal as a
tetrabasic hexadentate ligand in enol form and assumes staggered configuration in 1–5.
1
The H NMR spectra suggest that the dihydrazone, which exists in anti–cis
configuration uncoordinated, isomerizes to staggered configuration in the metal
complexes. In staggered configuration, the different hydrazone parts of the dihydrazone
are coordinated to different metal centers through naphtholate and enolate oxygens and
azomethine nitrogens. In 6 and 7, the dihydrazone is coordinated to the metal center as
a neutral bidentate ligand in the keto form through azomethine nitrogens only in
anti–cis configuration. The bidentate 1,10-phenanthroline and bipyridine ligands induce
B
1
2b
11b
O
O
1
0b
9
b
Mo
O
1
3b
O
N
8b
4b
5b
3
b
C
7b
H
6b
C
N
1
a
1b
CH2
2
b
7
a
2
a
CH2
6
a
8a
N
C
H
O
5
a
9
a
C
N
O
4
a
3
a
1
0a
1a
Mo
O
1
O
1
3a
1
2a
B
Figure 2. Structure along with numbering scheme of the carbon atoms in [(MoO
O (1), py (2), 2-pic (3), 3-pic (4), 4-pic (5)).
2
)
2
(nsh)(B)
2
] ꢀ C
2 5
H OH
(B ¼ H
2
N
N
O
O
N
O
O
N
O
O
O
O
Mo
N
Mo
O
Mo
Mo
O
N
N
O
O
N
(
6)
(7)
OH (BB ¼ 1,10-phenanthroline (6),
Figure 3. Tentative structure of [(ꢀ
0
2
-O)(MoO
2
)
2
(H
4
nsh)(BB)] ꢀ C
2 5
H
2
,2 -bipyridine (7)).

1
74
R.A. Lal et al.
transfer of oxygen from coordinated water molecules to molybdenum. To the best of
our knowledge, this is the first work in hydrazone coordination chemistry in which
the transfer of oxygen from coordinated water to the ligated metal has been reported.
On the basis of various physico-chemical and spectral studies and their discussion
as given above, the complexes are suggested to have the structures shown in figures 2
and 3.
Acknowledgments
We gratefully acknowledge the NMR Research Centre, Indian Institute of Science,
Bangalore, India, for the provision of NMR facilities. Further, we are thankful to the
Head, SAIF, Shillong, for C, H, and N analyses. R.A. Lal thanks UGC, New Delhi,
India, for the grant of financial assistance through major research project.
References
[
1] S.K. Maiti, S. Banerjee, A.K. Mukherjee, K.M. Abdul Malik, R. Bhattacharyya. New J. Chem., 29,
54 (2005).
5
2] R.J.P. Williams, J.J.R.F. Da Silva. Biochem. Res. Commun., 292, 293 (2002).
[
[
[
[
[
3] E.I. Stiefel. Science, 272, 1599 (1996).
4] D. Sellman. Angew. Chem. Int. Ed., 32, 64 (1993).
5] J. Kim, D. Wood, D.C. Ress. Biochemistry, 32, 7104 (1993).
6] M.H. Chisholm. In Inorganic Chemistry: Towards the 21st Century, ACS Symposium Series 211,
M.H. Chisholm (Ed.), pp. 243–288, American Chemical Society, Washington, DC (1983).
7] J. Berg, R.H. Holm. J. Am. Chem. Soc., 106, 3035 (1984).
[
[
[
8] J. Berg, R.H. Holm. J. Am. Chem. Soc., 107, 917 (1985).
9] J. Jarupatrakoru, M.P. Coles, T.D. Tilley. Chem. Mater., 17, 1818 (2005).
[
[
[
[
10] J.M. Mitchell, N.S. Finney. J. Am. Chem. Soc., 123, 862 (2001).
11] M.K. Trost, R.G. Bergman. Organometallics, 10, 1172 (1991).
12] J. Belgacem, J. Kress, J.A. Osborn. J. Am. Chem. Soc., 114, 1501 (1992).
13] (a) E. Kahrovic, K. Molcanov, L. Tusek-Bozic, B. Kojic-Prodic. Polyhedron, 25, 2459 (2006);
(b) T.A. Hanna, A.K. Ghosh, C. Ibarra, M.A. Mendez-Rojas, A.L. Rheingold, W.H. Watson. Inorg.
Chem., 43, 1511 (2004).
[
[
[
[
14] J.B. Carlson, G. Davies, P. Vorous. Inorg. Chem., 33, 2334 (1994).
15] S.K. Dutta, K.K. Nanda, U. Florke, M. Bhadbhade, K. Nag. J. Chem. Soc. Dalton Trans., 2371 (1996).
16] V.N. Nemykin, P. Basu. Inorg. Chem., 44, 7494 (2005).
17] A.D. Garnovskii, I.S. Vasilchauko, D.A. Garnvoskii, B.I. Kharisov. J. Coord. Chem., 62, 151 (2009) and
references therein.
[
[
[
[
[
[
[
18] N. Raman, S.J. Raja, A. Sakthivel. J. Coord. Chem., 62, 691 (2009).
19] V.P. Singh, A. Katiyar, S. Singh. J. Coord. Chem., 62, 1336 (2009).
20] S. Pal, S. Pal. J. Chem. Soc., Dalton Trans., 2102 (2002).
21] R. Dinda, P. Sengupta, S. Ghosh, H.M. Figge, W.S. Sheldrick. J. Chem. Soc., Dalton Trans., 4437 (2002).
22] G.A. Al-Hazmi, A. El-Asmy. J. Coord. Chem., 62, 337 (2009).
23] R. Dinda, P. Sengupta, S. Ghosh, W.S. Sheldrick. Eur. J. Inorg. Chem., 363 (2003).
24] M.R. Bermejo, R. Pedrido, A.M.G. Noya, M.J. Romearo, M. Vazquez, L. Sorace. New J. Chem., 27,
1753 (2003).
[
[
[
25] C.G. Yan, J. Han, L. Li, D.M. Lui. J. Coord. Chem., 62, 825 (2009).
26] E.I. Ceylan, Y. Kurt, B. Olkuseven. J. Coord. Chem., 62, 757 (2009) and references therein.
27] A. Bacchi, L.P. Bhattaghia, M. Carcelli, C. Pelizzi, G. Pelizzi, C. Solinas, M.A. Zorundu. J. Chem. Soc.,
Dalton Trans., 773 (1993).
[
28] (a) A. EL-Toukhy, A.F.M. Henry, L. El-Sayad, M.F. Iskandar. Mh. Chem., 113, 171 (1982);
(b) M.F. Iskander, A.F.M. Hefny, L. El-Sayad, S.E. Zayan. J. Inorg. Nucl. Chem., 38, 2209 (1976).

Succinoyldihydrazone
175
[
29] D.L. Arora, K. Lal, S.P. Gupta, S.K. Sahni. Polyhedron, 15, 1499 (1986); Indian J. Chem., 24A, 980
1987).
30] R.A. Lal, S. Das, R.K. Thapa. Inorg. Chim. Acta, 132, 129 (1987).
(
[
[
[
[
31] S. Gopinathan, S.S. Tavale, V.G. Puranik, M.P. Degaonkar. Bull. Chem. Soc. Jpn., 41, 1797 (1994).
32] B. Ji, Q. Du, K. Ding, Y. Li, Z. Zhou. Polyhedron, 15, 403 (1996).
33] (a) R.A. Lal, A.N. Siva, S. Adhikari, A. Pal. Indian J. Chem., 34A, 1000 (1995); (b) R.A. Lal, S. Adhikari,
A. Pal, A.N. Siva, A. Kumar. J. Chem. Res. (S), 122 (1997); J. Chem. Res. (M), 0749 (1997).
34] G.J.J. Chen, J.W. McDonald, W.E. Newton. Inorg. Chem., 15, 2612 (1976).
[
[
35] A.I. Vogel. A Text Book of Quantitative Inorganic Analysis Including Elementary Instrumentation
Analysis, 5th Edn, ELBS and Longman, London (1989).
36] (a) R.A. Lal, D. Basumatary, S. Adhikari, A. Kumar. Spectrochim. Acta A, 69, 706 (2008);
[
(b) M.K. Singh, N.K. Kar, R.A. Lal. J. Coord. Chem., 61, 3158 (2008).
[
[
[
37] W.J. Geary. Coord. Chem. Rev., 7, 81 (1971).
38] R.A. Lal, D. Basumatary, J. Chakraborty, S. Bhaumik, A. Kumar. Indian J. Chem., 45A, 619 (2006).
39] L.M. Jackman, S. Sternhell. Application of Nuclear Magnetic Resonance Spectroscopy in Organic
Chemistry, Vol. 10, 2nd Edn, Chap. 3, Pergamon Press, Amsterdam (1978).
[40] R. Gup, B. Kurkan. Spectrochim. Acta A, 62, 1188 (2005).
[41] Mudasir, N. Yoshioka, H. Inoue. Transition Met. Chem., 24, 210 (1999).
[42] A.K. Boudalis, U. Nastopoulos, S.P. Perlepes, C.P. Raptopoulu, A. Terzis. Transition Met. Chem., 26,
276 (2001).