Synthesis and characterization of organotin(IV) 2,4-dinitrophenoxides

Article abstract of DOI:10.1081/SIM-120020001

Complexes of the composition [R₃Sn(DNP)] and [n-Bu₂SnCl_{2 - x}(DNP)_x] (R=Ph and Me; x=1 and 2; DNP=anion of 2,4-dinitrophenol) have been synthesized by the silver metathesis method, involving the reaction of Ph₃SnCl, Me₃SnCl and n-Bu₂SnCl₂ with the silver salt of 2,4-dinitrophenol in tetrahydrofuran at room temperature and were characterized by elemental analyses, conductivity measurements, IR, and ¹H NMR studies. The IR spectral studies suggest a bidentate mode of coordination of phenol in these complexes. Double phenoxides of the type M₂[R₃Sn(DNP)₃] (M=Na and K) have also been obtained by reacting the parent triorganotin(IV) phenoxides with alkali metal derivatives of the phenol in 1:2 molar ratio. Thermal investigations of these complexes depicted quite interesting behaviour, as the decomposition did not yield any residue, contrary to previous reports. The thermal behaviour of these complexes has shown their ability as high-energy materials.

Full text of DOI:10.1081/SIM-120020001

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Synthesis and Characterization of Organotin(IV)
2,4‐Dinitrophenoxides
N. Sharma a , A. Kaistha a , S. S. Bhatt a & S. C. Chaudhry a
a Department of Chemistry , Himachal Pradesh University , Shimla, 171005, India
Published online: 15 Feb 2007.
To cite this article: N. Sharma , A. Kaistha , S. S. Bhatt & S. C. Chaudhry (2003) Synthesis and Characterization of
Organotin(IV) 2,4‐Dinitrophenoxides, Synthesis and Reactivity in Inorganic and Metal-Organic Chemistry, 33:3, 497-507, DOI:
10.1081/SIM-120020001
To link to this article: http://dx.doi.org/10.1081/SIM-120020001
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SYNTHESIS AND REACTIVITY IN INORGANIC AND METAL-ORGANIC CHEMISTRY
Vol. 33, No. 3, pp. 497–507, 2003
Synthesis and Characterization of Organotin(IV)
2,4-Dinitrophenoxides
*
N. Sharma, A. Kaistha, S. S. Bhatt, and S. C. Chaudhry
Department of Chemistry, Himachal Pradesh University, Shimla, India
ABSTRACT
Complexesofthecomposition[R3Sn(DNP)]and[n-Bu2SnCl2 ꢀ x(DNP)x]
(R = Ph and Me; x = 1 and 2; DNP = anion of 2,4-dinitrophenol) have
been synthesized by the silver metathesis method, involving the reaction
of Ph3SnCl, Me3SnCl and n-Bu2SnCl2 with the silver salt of 2,4-
dinitrophenol in tetrahydrofuran at room temperature and were cha-
racterized by elemental analyses, conductivity measurements, IR, and
1H NMR studies. The IR spectral studies suggest a bidentate mode of
coordination of phenol in these complexes. Double phenoxides of the
type M2[R3Sn(DNP)3] (M = Na and K) have also been obtained by
reacting the parent triorganotin(IV) phenoxides with alkali metal
derivatives of the phenol in 1:2 molar ratio. Thermal investigations of
these complexes depicted quite interesting behaviour, as the decom-
position did not yield any residue, contrary to previous reports. The
thermal behaviour of these complexes has shown their ability as high-
energy materials.
*
Correspondence: N. Sharma, Department of Chemistry, Himachal Pradesh Univer-
sity, Shimla 171005, India; E-mail: ssbhatt2k@yahoo.com.
497
DOI: 10.1081/SIM-120020001
0094-5714 (Print); 1532-2440 (Online)
www.dekker.com
Copyright D 2003 by Marcel Dekker, Inc.

498
Sharma et al.
INTRODUCTION
While nitrophenates of transition metals, because of their immense
importance in explosive composition,[1–3] have been the subject of in-
tensive research interest, the literature on analogous organotin(IV) com-
plexes is rather scant.[4–7] Interestingly, the phenolic ligands containing a
second donor atom incorporated at the ortho position are known to exhibit a
unique bonding behaviour wherein an ortho donor atom may coordinate to
a metal atom in addition to the phenolic oxygen[8,9] (Figure 1).
Hence, in the present investigation, 2,4-dinitrophenol has been chosen
as an ancillary ligand towards the synthesis of new organotin(IV) com-
plexes with the aim to study its coordination chemistry and to gain an
insight into the structure and behaviour of these complexes. The reactivity
of these complexes towards alkali metal derivatives has also been exa-
mined. A study of the thermal behaviour of these complexes has provided
convincing evidence for their potential utility as high-energy materials.
EXPERIMENTAL
Materials and Methods
2,4-Dinitrophenol (85%, moist solid containing 15% water) (Merck)
was recrystallized from THF and was then warmed to ꢁ 100 °C. The purity
was checked by the melting point. The purity of Ph3SnCl, Me3SnCl and
Bu2SnCl2 (Fluka and Merck) was checked both by chlorine analysis and
melting point. The silver salt of 2,4-dinitrophenol was prepared by the
reaction of an ethanolic solution of the phenol with an aqueous solution of
silver nitrate in equimolor ratios by stirring at room temperature. Tin was
determined gravimetrically as SnO2. Chlorine was analyzed by Volhard’s
method. Microanalyses for carbon and hydrogen were performed on a
Coleman CHN analyzer. The conductance measurements in nitrobenzene
were made on an NDC-732 Elico digital conductivity bridge. Infrared
spectra (KBr) were recorded from 4000-100 cm–1 with a Nicolet-Avtar 1000
Figure 1. Bidentate mode of bonding of 2,4-dinitrophenol.

Organotin(IV) 2,4-Dinitrophenoxides
499
1
FTIR spectrophotometer and H NMR spectra on a Jeol JNM PMX 60 SI
spectrometer using CDCl3 as solvent. Thermograms were recorded on a
simultaneous DT-40 DT-TG Shimadzu thermal analyzer in air; heating rate:
10 °C min–1/ 20 °C min–1; sample size: 1–4 mg; reference: Al2O3; ther-
mocouple: Pt/ Pt-Rh 10%.
Preparation of Complexes [R3Sn(DNP)] (R = Ph and Me)
To a solution of Ph3SnCl (1.5 g, 3.8 mmol) and Me3SnCl (1.5 g,
7.5 mmol) in THF (20 mL) was added an equimolar amount of AgDNP
(1.106 g, 3.8 mmol and 2.18 g, 7.5 mmol), respectively, in THF (20 mL).
Mixing of these solutions resulted in a colour change and an instan-
taneous separation of a white solid (AgCl) was observed. After stirring
for 5–6 hours, it was filtered off and the filtrate was concentrated by
evaporating the solvent under vacuum, when a yellow solid appeared, It
was repeatedly washed with petroleum ether and dried under vacuum; the
yields were 1.742 g for Ph3Sn(DNP) and 2.134 g for Me3Sn(DNP).
Preparation of Complexes [n-Bu2SnCl2 ꢀ x(DNP)x] (x = 1 or 2)
To a solution of n-Bu2SnCl2 (1.2 g, 3.8 mmol) in THF (25 mL) were
added stoichiometric amounts of AgDNP (1.106 g, 3.8 mmol or 2.212 g,
7.6 mmol) dissolved in THF (25 mL) in separate experiments. An
immediate formation of a white solid (AgCl) resulted. After stirring for
5–6 hours, AgCl was removed from the reaction mixture by filtration. The
filtrate was reduced to half of its volume under vacuum and was then
treated with petroleum ether (40–60 °C) to give pale yellow crystals
which were subsequently dried under vacuum; the yields were 1.391 g for
Bu2SnCl(DNP) and 2.069 g for Bu2Sn(DNP)2.
Preparation of M2[R3Sn(DNP)3] (M = Na, K; R = Ph and Me)
To a solution of Ph3Sn(DNP) (2.06 g, 3.8 mmol) in THF (25 mL)was
added a suspension of NaDNP (1.59 g, 7.7 mmol) in THF (20 mL) in the
tin:alkali metal molar ratio 1:2. It was stirred for ꢁ 2 hours until the
reactants completely went into the solution. The solvent was then removed
under vacuum and the remaining concentrated solution was treated with
petroleum ether when a bright yellow solid resulted. It was dried under
vacuum. The yield of Na2[Ph3Sn(DNP)3] was 3.19 g. The following
complexes were prepared by similar method:
Na2[Me3(DNP)3] from the reaction of Me3Sn(DNP) (1.31 g, 3.7 mmol)
with NaDNP (1.55 g, 7.4 mmol); yield 2.24 g. K2[Ph3Sn(DNP)3] from
Ph3SnDNP (2.02 g, 3.7 mmol) with KDNP (1.68 g, 7.5 mmol); yield 3.0 g.

500
Sharma et al.
K2[Me3Sn(DNP)3] from Me3SnDNP (1.32 g, 3.8 mmol) with KDNP
(1.68 g, 7.6 mmol); yield, 2.67 g.
RESULTS AND DISCUSSION
Interaction between various organotin(IV) chlorides and the silver salt
of 2,4-dinitrophenol in tetrahydrofuran in stoichiometric amounts at room
temperature proceeds smoothly and quantitatively with instantaneous
separation of silver chloride according to Eqs. 1 and 2:
THF
R3SnCl þ AgDNP ! ½R3SnðDNPފ þ AgCl #
ð1Þ
25 °C
ðR ¼ Ph and MeÞ
THF
n - Bu2SnCl2 þ xAgDNP ! n - Bu2SnCl2ꢀxðDNPÞx þ xAgCl #
25 °C
ð2Þ
ðx ¼ 1 and 2Þ
Silver chloride is easily removed by filtration, and the title com-
plexes crystallized out in good yields from the filtrate. The elemental
analyses support the stoichiometric formulations (Table 1). The compounds
are light yellow to dark yellow, crystalline solids with sharp melting points
and are readily soluble in common organic solvents such as CCl4, C6H6,
C2H2Cl2. The molar conductances of the complexes in nitrobenzene
(10–3 M solution) are very low, indicating the non-electrolytic nature of
the complexes.
Infrared Spectra
Formation of the new complexes has been inferred from a comparison
of IR spectra with those of free phenol, the silver salt and the previous
data[7,8] reported for other tin(IV) and organotin(IV) complexes. The cha-
racteristic ligand bands for the complexes are observed in the fingerprint
region. The most important and diagnostic band due to the phenolic n(C–O)
mode observed at 1255 cm–1 in the phenol under study has remained almost
unchanged in the complexes, in contrast to a significant decrease in the
frequency of this band reported to be observed in metal alkoxides and
aryloxides.[10,11] The observed trend of n(C–O) may be ascribed to the
weaker coordination of the dinitrophenolic ligand perhaps due to ring
conjugation. The occurrence of new vibrational modes in the region 520–

Organotin(IV) 2,4-Dinitrophenoxides
501

502
Sharma et al.
480 cm–1 (not present in the ligand) attributable to n(Sn–O) stretching
frequencies[12] has supported the linkage between oxygen and tin metal.
The IR spectra of the complexes reveal that bands observed at ꢁ 1545 and
1342 cm–1 attributed to antisymmetric and symmetric stretching vibrations,
respectively, of the NO2 group in free phenol and in its silver salt have
been found to shift to lower frequencies on complexation and have
appeared in the regions 1542–1520 and at ꢁ 1332 cm–1, suggesting
coordination of the ortho NO2 group through oxygen to the metal. These
observations are thus indicative of a probable bidentate nature of the
phenolic ligand. Nevertheless, a slight ambiguity in these assignments may
be anticipated due to the overlapping of many other ligand vibrations in this
region. The bands observed ꢁ 280 and 240 cm–1 in the far-IR spectra of
these complexes have tentatively been assigned to nasym and nsym (Sn–C)
modes, respectively.
1H NMR Spectra
1
The H NMR spectral data of free 2,4-dinitrophenol have provided a
basis for interpreting the spectra of its organotin complexes. The spectra
showed three distinct resonances due to aromatic protons which are attri-
buted to three types of ring hydrogens, apart from the one due to hydroxyl
(phenolic protons) at d 4.65 ppm. The assignments for the three resonances
observed at 9.1, 8.5 and 7.35 ppm were made by taking into account the
electron withdrawing effect of the NO2 substituents on the phenolic ring.
These resonances have been attributed to two different kinds of meta
protons, (m) having two neighboring NO2 groups at 2 and 4-positions, meta
(m’) protons with one adjacent NO2–4 group and the third ortho to the
1
phenolic group, respectively. In the H NMR spectra of the complexes, the
complete absence of a signal at d 4.65 ppm due to the phenolic OH proton
in free 2,4-dinitrophenol confirmed the deprotonation of this group.
The spectra of the triphenyltin(IV) complex indicated that (m and m’)
protons are displaced slightly upfield compared to that of free phenol,
which may be attributed to the shielding effect exerted on these protons by
the aromatic protons of the phenyl ring attached to the tin metal. A
complex pattern between 7.0 and 8.0 ppm as a result of superposition of
phenyl protons attached to tin and phenolic ortho protons has been
1
observed. In the H NMR spectra of the Me3Sn(IV) complex the signals
due to aromatic protons have been observed to undergo a very small
downfield shift amounting to 0.01 to 0.15 ppm. The signal due to the
methyl protons is seen at 0.7 ppm.
In the spectra of the dibutyltin(IV) complexes, the signal assignments
have been ascertained with respect to those of the starting materials,

Organotin(IV) 2,4-Dinitrophenoxides
503
n-Bu2SnCl2 and phenol. In n-Bu2SnCl2, methyl and methylene resonances
appear at ꢁ 0.9, 1.30 and 1.77 ppm. It is interesting to note that, compared
to a moderate downfield shift observed for the n-Bu protons, the aromatic
protons appear almost at the same position as in the free ligand.
Nevertheless, integration supports the proposed formulations.
Based upon the available analytical and spectral data, a trigonal
bipyramidal structure for triorganotin(IV) and chlorodibutyltin(IV) com-
plexes and a distorted octahedral structure for the dibutylbis(2,4-dini-
trophenoxo)tin(IV) complex may tentatively be suggested in accordance
with earlier reports[13] (Figure 2).
Double Aryloxides
In the course of the present study, we have also investigated the
reactivity of the title complexes towards alkali metal derivatives of 2,4-
dinitrophenol with an objective of ascertaining their ability to form double
aryloxides. Although our attempts to prepare complexes of the composition
M{R3Sn(DNP)2} were not successful, products of the composition
M2{R3Sn(DNP)3} containing six-coordinating anions[14] were prepared by
the following reaction:
R3SnðDNPÞ þ MDNP ꢀ! M2½R3SnðDNPÞ3Š
½R ¼ Ph; Me; M ¼ Na; KŠ
ð3Þ
The complexes are bright yellow solids and are insoluble in common
organic solvents. The molar conductance values of millimolar solutions
of these complexes in nitrobenzene have indicated their appreciable
electrolytic nature (Table 1). The IR spectra of the complexes have shown
the characteristic stretching frequencies of phenolic bonding in the regions
1256–1108, 927–916 and 679–640 cm–1 supporting their formation.
Figure 2. Proposed structures for the complexes.

504
Sharma et al.
Thermal Studies
The decomposition behavior of the ligand 2,4-dinitrophenol (DNPH),
the silver salt of 2,4-dinitrophenol, (AgDNP) and the organotin(IV) and
bimetallic 2,4-dinitrophenoxides have also been investigated by thermo-
gravimetric measurements and differential thermal analysis in view of the
importance of substances containing NO2 groups as flame sensitizers and
high-energy materials or explosives. The results obtained from TG and
DTA curves are summarized in Table 2. The TG/DT curves of 2,4-
dinitrophenol indicate its melting temperature to be 111.1 °C, depicted as a
sharp endotherm in the DT curve and its stability up to 121.8 °C, after
which temperature it sublimes quantitatively. On the other hand,
AgOC6H3(NO2)2-2,4 begins to decompose at ꢁ 23.5 °C and undergoes
explosive decomposition without leaving any residue. The possibility of the
substance being blown out during the explosive decomposition can’t be
ruled out. The decomposition is accompanied by a sharp exothermic effect
at 319.5 °C. No exotherm, however, was observed in the case of the
free phenol. An induction period of ꢁ 2 minutes for this exothermic change
is suggestive of its being a high-energy material due to the dinitrophenolic
ligand bonded to silver ion.
Thermograms of Ph3SnDNP, Me3SnDNP, n-Bu2SnClDNP and
n-Bu2Sn(DNP)2 have shown these compounds to be stable up to 113.4,
113.2, 118.9 and 110.2 °C, respectively. The melting endotherms have been
observed at 79.9, 112.0, 106.9 and 106.0 °C for the respective complexes. A
striking feature of the decomposition of these complexes is that there is
neither any explosion during decomposition nor any sharp exothermic
peak in the DTA curves, as was observed in AgDNP. Hence, the 100%
weight loss in organotin(IV) 2,4-dinitrophenoxides may be attributed to
their volatile nature. These complexes, therefore, represent, to our know-
ledge, the first example of its kind, which have not yielded any residue
from their thermal decomposition processes, contrary to previous re-
ports[15,16] wherein SnO2, SnO and Sn have resulted as end products.
A thorough scrutiny of the thermal decomposition behaviour of
NaDNP, KDNP and the bimetallic phenoxides of the compositions
Na2[Ph3Sn(DNP)3] and K2[Me3Sn(DNP)3] has offered some unique results:
1) an initial decomposition process is accompanied by a small weight loss
and a weak endotherm; 2) the main decomposition process proceeds with a
significant weight gain, subsequently followed by an abrupt weight loss
over a very small range of temperature leaving no residue; 3) the major fast
decomposition process in the DTA exhibits a very strong and sharp
exothermic peak due to violent decomposition accompanied by a cracking

Organotin(IV) 2,4-Dinitrophenoxides
505

506
Sharma et al.
sound and 4) a weight gain in the TG and corresponding exothermic peak
in DTA appear in close proximity to each other.
Of all the complexes, the violent decomposition was more pronounced
with NaDNP and KDNP. Moreover, the present observations of the DTA
indicate a close resemblance with the characteristic features of high-energy
materials, such as TNT, HMX (octogen) and RDX (hexogen).
In conclusion, the present study has shown that novel tri and dior-
ganotin(IV) complexes of 2,4-dinitrophenol can be synthesized by the re-
action of the respective chlorides with the silver salt of the phenol by the
silver metathesis method. Based on the thermal decomposition of these
complexes involving 100 % weight loss, they are proposed to be volatile.
Double phenoxides of these complexes, however, have been found to
exhibit a significant explosive nature and are likely to be quite useful as
high-energy materials in the future.
ACKNOWLEDGMENTS
The authors are grateful to Prof. M.S. Hundal, Department of Che-
mistry, Guru Nanak Dev University, Amritsar, for obtaining the FTIR spectra.
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Received: July 12, 2001
Accepted: November 21, 2002
Referee II: J. M. Iriarte-Gross
Referee III: F. P. Gabbai