Synthesis, spectroscopic, and structural properties of organogermanyl(IV) complexes of pyridine oximes

Article abstract of DOI:10.1080/10426507.2012.717146

Reactions of triorganogermanyl(IV) chlorides and diorganogermanyl(IV) dichlorides with sodium salts of pyridine-2-carbaldehyde oxime and 2-acetylpyridine oxime, respectively, in 1:1 and 1:2 molar ratio produced organogermanyl(IV) oximates. All the derivat

Full text of DOI:10.1080/10426507.2012.717146

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Phosphorus, Sulfur, and Silicon and the
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Synthesis, Spectroscopic, and Structural
Properties of Organogermanyl(IV)
Complexes of Pyridine Oximes
a
a
a
Nelson Joseph P. , Raji Thomas , Pushpa Pardasani & Tulsi
b
Mukherjee
a
Department of Chemistry , University of Rajasthan , Jaipur , India
b
Chemistry Division , BARC , Mumbai , India
Accepted author version posted online: 09 Aug 2012.Published
online: 05 Jul 2013.
To cite this article: Nelson Joseph P. , Raji Thomas , Pushpa Pardasani & Tulsi Mukherjee
(
2013) Synthesis, Spectroscopic, and Structural Properties of Organogermanyl(IV) Complexes of
Pyridine Oximes, Phosphorus, Sulfur, and Silicon and the Related Elements, 188:7, 904-912, DOI:
0.1080/10426507.2012.717146
1
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Phosphorus, Sulfur, and Silicon, 188:904–912, 2013
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Taylor & Francis Group, LLC
C
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426507.2012.717146
SYNTHESIS, SPECTROSCOPIC, AND STRUCTURAL
PROPERTIES OF ORGANOGERMANYL(IV) COMPLEXES
OF PYRIDINE OXIMES
1
1
1
Nelson Joseph P., Raji Thomas, Pushpa Pardasani,
2
and Tulsi Mukherjee
Department of Chemistry, University of Rajasthan, Jaipur, India
Chemistry Division, BARC, Mumbai, India
1
2
GRAPHICAL ABSTRACT
Abstract Reactions of triorganogermanyl(IV) chlorides and diorganogermanyl(IV) dichlo-
rides with sodium salts of pyridine-2-carbaldehyde oxime and 2-acetylpyridine oxime, respec-
tively, in 1:1 and 1:2 molar ratio produced organogermanyl(IV) oximates. All the derivatives
have been characterized by spectroscopic techniques and tetrahedral structures have been
proposed on the basis of spectroscopic data and molecular orbital calculations.
Keywords Pyridine-2-carbaldehyde oxime; 2-acetylpyridine oxime; organogermanium com-
plexes; DFT study
INTRODUCTION
Organometallic compounds of group 14 elements (Ge, Sn, and Pb) are of great interest
1
2–4
owing to a wide variety of structural features ranging from monomers to clusters as well
Received 18 June 2012; accepted 16 July 2012.
Financial support from DAE/BRNS, Mumbai, is gratefully acknowledged.
Address correspondence to Pushpa Pardasani, Department of Chemistry, University of Rajasthan, Jaipur
302055, India. E-mail: pushpa.pardasani@gmail.com
9
04

ORGANOGERMANYL(IV) PYRIDINE OXIMATES
905
5
as pharmacological importance and industrial applications. Oximes are also well known
synthons due to their biological activities and ability to form complexes through oximate
6
oxygen and amido nitrogen. Pyridine-2-carbaldehyde oxime, one of the ligands used in the
present study, is commonly used in human and veterinary practices as acetyl cholinesterase
reactivators. Their metal complexes can act as drugs since complexation protects the ac-
tive site against enzymatic degradations and its activity can be reinforced at a specific
7
organ.
Complexes of germanium have received less attention as compared to the other
elements of this group. Germanium complexes usually prefer tetracoordinated structures
8
though pentacoordinated and hexacoordinated derivatives have also been reported. Germa-
9
,10
nium derivatives are important constituents in optical devices like optical wave guides
1
1,12
and in the field of medicine.
Hence in continuation to our interest in complexes of group
we are reporting herein syntheses of various diorganogermanyl(IV) and
triorganogermanyl(IV) pyridine oximates. Newly synthesized complexes are characterized
by different methods like IR, H, and C NMR spectroscopy and elemental analysis.
Theoretical calculations have been performed at the DFT-B3LYP level on GAUSSIAN 03
program to understand the mode of chelation in the complexes.
1
3–15
14 elements,
1
13
RESULTS AND DISCUSSION
The ligands pyridine-2-carbaldehyde oxime and 2-acetylpyridine oxime have been
synthesized and converted into respective sodium salts by refluxing with sodium methoxide
in methanol. The triorganogermanyl(IV) oximates and diorganogermanyl(IV) oximates
were prepared with above 75% yield by reaction of R3GeCl and R2GeCl2 with sodium
salts of ligands in 1:1 and 1:2 molar ratios, respectively, as depicted in Scheme 1. All
the complexes are moisture sensitive and have been handled in dry conditions or inert
atmosphere with utmost care. They are readily soluble in organic solvents like methanol,
ethanol, benzene, chloroform, etc. and have been characterized by physical analysis as well
as various spectroscopic techniques (Tables 1 and 2).
Scheme 1

9
06

9
07

9
08
N. JOSEPH P. ET AL.
Spectroscopic Studies
The IR spectra of the complexes were interpreted by comparison with the spectra
1
of free oximes. The νC=N absorption band for oximes HL and HL appeared at 1515
−
1
and 1480 cm , respectively. The hydroxyl absorption peak of the oxime ligands in the
−1
region 3258–3014 cm was absent in the IR spectra of all the derivatives indicating metal-
ligand bond formation through the oxygen atom. The νC=N and νN–O absorption bands for
oximes are shifted to lower wave number on complexation. The formation of complexes
−1
is further confirmed by the appearance of two new bands in the region 860–820 cm and
−1
16
17
6
80–620 cm , which can be assigned to νGe–O and νGe–C , respectively.
1
13
The H and C NMR spectra of all compounds exhibited characteristic signals and
multiplicities for R–Ge and ligand protons. The hydroxyl proton of free ligands at δ 11.74
and δ 11.37 was absent in all these complexes suggesting the deprotonation of the NOH
18
group and complexation with metal through the Ge–O bond. There is no appreciable shift
for ligand ring protons indicating the absence of coordination through heteroatom present
1
in the aromatic ring in these complexes. In the H NMR, trimethyl derivatives showed a
singlet at δ 1.66 and δ 1.64 of methyl protons in compounds 1 and 3, respectively, while
dimethyl derivatives 5 and 8 showed singlets at δ 0.70 and δ 0.69, respectively. For diethyl
derivatives 6 and 9, multiplets were observed in the range δ 1.01–δ 1.51.
13
1
In the C NMR spectra of ligands HL and HL , carbon resonance due to >C=NOH
carbon appeared at δ 149.10 and δ 148.20, whereas in complexes, only a slight deviation
in ligand ring carbon signals was observed, thus confirming that the nitrogen atom in the
pyridine ring is not involved in coordinate bond formation with the central metal atom. For
trimethylgermanyl(IV) oximates 1 and 3, methyl carbon signal was observed at δ 23.92
and δ 23.45, the dimethyl derivatives 5 and 8 showed corresponding methyl resonance at δ
4.52 and δ 4.33.
Theoretical Studies
In order to confirm the structure of the synthesized complexes, molecular orbital
calculations have been carried out using GAUSSIAN 03 suit of program at DFT/B3LYP
level with 3-21G as basis set.1 These types of calculations are very useful in detecting
9
1
the mode of chelation in the molecules. In ligands HL and HL , syn isomer is more stable
than the anti isomer with a difference of 17.41 and 14.58 kcal/mol, respectively. It may
be attributed to the formation of a hydrogen bond with the pyridine nitrogen ligand. The
optimized geometries of ligands are shown in Figure 1.
(
-260169.83kcal/mol)
(-260155.25kcal/mol)
(-284709.88kcal/mol)
(-284692.47kcal/mol)
Figure 1 Optimized geometries of ligands (Color figure available online).

ORGANOGERMANYL(IV) PYRIDINE OXIMATES
909
Table 3 Minimum energy of complexes for different structures
Energy in kcal/mol
Compound
Tetrahedral
Trigonal bipyramidal
Octahedral
1
2
3
4
5
6
7
8
9
−1631656.1517
−1990639.9829
−1656195.9793
−2015181.0703
−1849628.8641
−1915728.0262
−2105888.2558
−1915656.2806
−1964728.2006
−2154973.3563
−1631649.2933
–
–
–
–
−1990629.8135
−1656194.5825
−2015174.3223
–
–
–
–
–
–
−1848903.3371
−1915643.2759
−2105882.3309
−1915635.8928
−1964707.5516
−2154959.4618
1
0
The nitrogen atom of pyridine in ligands can coordinate with the central germanium
atom to give trigonal bipyramidal and octahedral structures for triorganogermanyl(IV)
oximates and diorganogermanyl(IV) oximates, respectively. The minimum energy values
of optimized geometries are tabulated in Table 3. From the data mentioned in Table 3, it is
evident that tetrahedral geometries are more stable than trigonal bipyramidal and octahedral
geometries. During complex formation the more stable syn form of ligands tends to change
into anti form. The central germanium metal prefers to stay in tetracoordinated nature rather
than pentacoordinated and hexacoordinated, like tin and lead.
From the data mentioned in Table 3, it is evident that the minimum energy is high
for ethyl complexes (6 and 9) as compared to methyl derivatives (5 and 8). This accounts
for the high moisture sensitiveness of methyl derivatives as compared to ethyl and phenyl
germanium complexes. The Ge–C and Ge–O bond lengths and C–Ge–O bond angle,
obtained from the optimized geometries of tetrahedral structures, are tabulated in Table 4
2
0,21
and are in good agreement with the literature value.
Table 4 Selected bond lengths and bond angles of organogermanium oximates
Bond length in Å
◦
Bond angle in
O–Ge–C
Compound
Ge–O
Ge–C
1
2
3
4
5
6
7
8
9
1.8136
1.8196
1.8128
1.8174
1.8051
1.7953
1.8050
1.7924
1.7947
1.8042
1.9553
1.9322
1.9558
1.9329
1.9421
1.9457
1.9219
1.9428
1.9473
1.9229
109.1817
110.2251
109.2689
110.3522
110.1912
111.4307
111.9112
111.2554
111.6499
111.7471
1
0

9
10
N. JOSEPH P. ET AL.
CONCLUSION
On the basis of spectroscopic observations and molecular orbital calculations, tetra-
hedral structures have been proposed for diorganogermanyl(IV) and triorganogermanyl(IV)
pyridine oximates. The optimized geometries of complexes (1–10) are shown in Figure 2.
EXPERIMENTAL
All chemicals have been purchased from Merck and Aldrich and used without further
purification. All reactions were carried out under nitrogen atmosphere and moisture was
rigorously excluded throughout the experimental manipulations. Solvents were dried by
standard methods.22 The IR spectra were recorded in KBr pellets on a Nicolet DX FTIR
−1
1
13
spectrometer in the range 4000–400 cm . H and C NMR spectra were recorded in
CDCl3 or DMSO-d6 solvent with TMS as internal standard on a JEOL 300AL FTNMR
spectrometer operating at 300 and 75.47 MHz, respectively. The mps were recorded on a
23
Perfit mp apparatus and are uncorrected. Germanium was estimated as germanium oxide.
Theoretical calculations have been performed at DFT-B3LYP level on GAUSSIAN 03
program with 3-21G as the basis set.
Figure 2 Optimized geometries of tri/diorganogermanyl(IV) oximates (Color figure available online).

ORGANOGERMANYL(IV) PYRIDINE OXIMATES
911
Synthesis of Ligands
Pyridine-2-carbaldehyde oxime (HL): The ligand HL was prepared according to
the literature method.24
1
1
2
-Acetylpyridine oxime (HL ): HL was prepared by refluxing 2-acetylpyridine
25
with hydroxylamine hydrochloride in the presence of a base.
Synthesis of Complexes
Trimethylgermanyl(lV) pyridine-2-carbaldehyde oximate: To a methanolic solu-
tion (10 mL) of the sodium salt of the ligand (prepared by the reaction of Na [0.092 g,
4.0 mmol] with pyridine-2-carbaldehyde oxime [0.488 g, 4 mmol] in refluxing methanol),
a benzene solution (10 mL) of trimethylgermanyl chloride (0.6433 g, 4.2 mmol) was added
dropwise and refluxed for 4 h. NaCl formed during the reaction was filtered off and the
filtrate was dried in vacuo and was recrystallized from dichloromethane:hexane (1:1) to
obtain a violet colored crystalline solid (0.72 g, yield 75%).
All other triorganogermanyl(IV) oximates of pyridine-2-carbaldehyde oxime and
2-acetylpyridine oxime were prepared analogously.
Dimethylgermanyl(lV) 2-pyridinecarboxaldehyde oximate: To a methanolic so-
lution (10 mL) of the sodium salt of ligand (prepared by the reaction of Na [0.092 g,
.0 mmol] with pyridine-2-carbaldehyde oxime [0.488 g, 4 mmol] in refluxing methanol),
4
a benzene solution (10 mL) of dimethylgermanyl dichloride (0.3645 g, 2.1 mmol) was
added dropwise and refluxed for 6 h. NaCl formed during the reaction was filtered off
and the filtrate was dried in vacuo to obtain a yellow solid, which was recrystallized from
dichloromethane:hexane (1;1) to afford a light yellow powder (0.60 g, yield 83%).
All other diorganogermanyl(IV) oximates of pyridine-2-carbaldehyde oxime and 2-
acetyl pyridine oxime have similarly been synthesized.
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