Synthesis and solid-state spectroscopic investigation of some novel diorganotin(IV) complexes of tetraazamacrocyclic ligands

Article abstract of DOI:10.1016/j.jorganchem.2008.03.027

The tetradendate macrocyclic ligands, [H₂L-1 = 5,12-dioxa-7,14-dimethyl-1,4,8,11-tetraazacyclotetradeca-1,8-diene] and [H₂L-2 = 6,14-dioxa-8,16-dimethyl-1,5,9,13-tetraazacyclohexadeca-1,9-diene] have been prepared by the condensation reaction of 1,2-diaminoethane and 1,3-diaminopropane, respectively, with ethyl acetoacetate in methanol at room temperature. The diorganotin(IV) complexes of general formula [R₂Sn(L-1)/R₂Sn(L-2)] (R = Me, n-Bu and Ph) have been synthesized by template condensation reaction of 1,2-diaminoethane or 1,3-diaminopropane and ethyl acetoacetate with R₂SnCl₂ (R = Me or Ph) or n-Bu₂SnO in 2:2:1 molar ratio at ambient temperature (35 ± 2 °C) in methanol. The solid-state characterization of resulting complexes have been carried out by elemental analysis, IR, recently developed DART-mass, solid-state ¹³C NMR, ^119mSn Mo?ssbauer spectroscopic studies. These studies suggest that in all of the studied complexes, the macrocyclic ligands act as tetradentate coordinating through four nitrogen atoms giving a skew-trapezoidal bipyramidal environment around tin center. Since, the studied diorganotin(IV) macrocyclic complexes are insoluble in common organic solvents, hence good crystals could not be grown for single crystal X-ray crystallographic studies. Thermal studies of all of the studied complexes have also been carried out in the temperature range 0-1000 °C using TG, DTG and DTA techniques. The end product of pyrolysis is SnO₂ confirmed by XRD analysis.

Full text of DOI:10.1016/j.jorganchem.2008.03.027

Journal of Organometallic Chemistry 693 (2008) 2271–2278
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Synthesis and solid-state spectroscopic investigation of some novel
diorganotin(IV) complexes of tetraazamacrocyclic ligands
a
b
b
Mala Nath a, , Pramendra K. Saini , George Eng , Xueqing Song
*
a Department of Chemistry, Indian Institute of Technology Roorkee, Roorkee 247 667, Uttarakhand, India
b Department of Chemistry and Physics, University of the District of Columbia, Washington, DC 20008, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
The tetradendate macrocyclic ligands, [H2L-1 = 5,12-dioxa-7,14-dimethyl-1,4,8,11-tetraazacyclotetra-
deca-1,8-diene] and [H2L-2 = 6,14-dioxa-8,16-dimethyl-1,5,9,13-tetraazacyclohexadeca-1,9-diene] have
been prepared by the condensation reaction of 1,2-diaminoethane and 1,3-diaminopropane, respectively,
with ethyl acetoacetate in methanol at room temperature. The diorganotin(IV) complexes of general for-
mula [R2Sn(L-1)/R2Sn(L-2)] (R = Me, n-Bu and Ph) have been synthesized by template condensation reac-
tion of 1,2-diaminoethane or 1,3-diaminopropane and ethyl acetoacetate with R2SnCl2 (R = Me or Ph) or
n-Bu2SnO in 2:2:1 molar ratio at ambient temperature (35 2 °C) in methanol. The solid-state character-
ization of resulting complexes have been carried out by elemental analysis, IR, recently developed DART-
mass, solid-state 13C NMR, 119mSn Mössbauer spectroscopic studies. These studies suggest that in all of
the studied complexes, the macrocyclic ligands act as tetradentate coordinating through four nitrogen
atoms giving a skew-trapezoidal bipyramidal environment around tin center. Since, the studied diorga-
notin(IV) macrocyclic complexes are insoluble in common organic solvents, hence good crystals could not
be grown for single crystal X-ray crystallographic studies. Thermal studies of all of the studied complexes
have also been carried out in the temperature range 0–1000 °C using TG, DTG and DTA techniques. The
end product of pyrolysis is SnO2 confirmed by XRD analysis.
Received 6 February 2008
Received in revised form 18 March 2008
Accepted 23 March 2008
Available online 1 April 2008
Keywords:
Diorganotin(IV)
Macrocycles
DART-mass
Solid-state NMR
119mSn Mössbauer
Ó 2008 Elsevier B.V. All rights reserved.
1. Introduction
compounds with specific peptide and DNA sequences offer inter-
esting therapeutic possibilities. The ability of azamacrocycles to
The coordination chemistry of macrocycles is an expeditiously
expanding domain of research having a promising and diverse fu-
ture [1]. Synthetic macrocyclic ligands resemble with natural mac-
rocycles such as porphyrins [2] and cobalamines [3] in electronic
properties and reactivity. Metal complexes of macrocyclic ligands
are very active part of biologically occurring metalloenzymes [4]
and of industrial catalysts [5]. The chemistry of tetraazamacrocy-
clic ligands has been of growing interest to coordination chemists
followed by the earlier work on the metal controlled template syn-
thesis of macrocycles [6]. Studies on azamacrocycles started with
serendipitous discoveries of idiosyncratic imine condensations of
transition element compounds of suitable configured amines with
carbonyl compounds [6]. Much interesting research has focused on
the physiological compatibility of azamacrocyclic compounds and
the elaboration of substituents that confer biomimetic or biomedi-
cally useful properties [7]. Interest in linked azamacrocycles has
been spurred by indications that their compounds show antiviral
activity and inhibit human immuno-deficiency virus (HIV) replica-
tion, at least in vitro [8,9]. Reported interactions of azamacrocycle
bind cations (effectively irreversibly), leaving some coordination
site labile, has implications for catalytic activity in a variety of
fields [10,11]. The tetraazamacrocycles are used as magnetic reso-
nance imaging agents [12], and are able to safely convey radio-
pharmaceutical nuclei to targeted sites [13,14]. In general, there
has been increasing interest in azamacrocycle compounds as bio-
mimetic models and as catalysts, particularly for peroxidation
reactions and for electrochemical CO2 fixation [6].
Azamacrocycles with amide functions (oxo-azamacrocycles) are
usually prepared by conventional non-template methods without
requiring high dilution techniques. The amide functions of oxo-
azamacrocycles are generally reduced by B2H6/THF, providing ver-
satile synthesis of cyclic amines. The cyclic amine–amide and cyc-
lic peptides have many properties analogous to linear peptides and
their metal complexes show functionalities resembling those of
metalloproteins, thereby, making them of biological interest [15].
A large number of workers [16–18] are currently engaged in the
synthesis of polyamide macrocycles and their coordination chem-
istry which is of particular interest in view of two potential donor
atoms, i.e., amide nitrogen and amide oxygen [17,19–26].
However, in the most of the polyamide macrocyclic complexes,
amide nitrogen is involved in coordination and not oxygen. The
* Corresponding author. Tel.: +91 01332 285797; fax: +91 1332 273560.
E-mail address: malanfcy@iitr.ernet.in (M. Nath).
0022-328X/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2008.03.027

2272
M. Nath et al. / Journal of Organometallic Chemistry 693 (2008) 2271–2278
Scheme 1.
tetraazamacrocycle (H2tmtaa) (H2tmtaa = dibenzotetramethyltet-
raaza[14]annulene) and its dianion (tmtaa) have a saddle structure
in which the four nitrogen atoms lie in a plane, thereby, creating a
natural location (cavity size ca. 1.9 Å) for metal encapsulation [27].
In comparison to a large number of transition metal complexes of
oxo-tetraazamacrocycles (as cited above), only two references on
tin(II) [26] and Si(IV)/Sn(IV) [28] have been reported so far. In view
of this, we report herein the synthesis and solid-state characteriza-
tion of several new complexes of diorganotin(IV) moiety with mac-
rocyclic ligands H2L-1 and H2L-2 (Scheme 1), derived from the
condensation of ethyl acetoacetate with 1,2-diaminoethane and
1,3-diaminopropane, respectively.
used was cross-polarization from proton (cp-ramp). 13C and 1H
NMR of H2L-1 and H2L-2 in CDCl3 were recorded on a Bruker
Avance (400 MHz) FT NMR spectrometer using TMS as the inter-
nal standard at the Punjab University, Chandigarh, India. The
DART-mass spectra of the compounds were recorded on a Jeol
AccuTOF DART JMS-T100LC mass spectrometer having TOF mass
analyzer and DART (Direct Analysis in Real Time) source at the
Central Drug Research Institute, Lucknow, India. The solid sam-
ples were subjected directly in front of DART source. Dry helium
was used with 4 LPM (liter per minute) flow rate for ionization at
350 °C. The orifice 1 set at 28 V and spectra were collected and
print outs are averaged spectra of 6–8 scans. 119mSn Mössbauer
spectra were recorded on a Mössbauer spectrometer model MS-
900 according to the procedure reported previously [30], at the
Department of Chemistry and Physics, University of The District
of Columbia, Washington, DC. Thermal measurements were car-
ried out on a Perkin–Elmer (Pyris Diamond) thermal analyzer in
air, in the temperature range 0–1000 °C with heating rate 10 °C/
min in a platinum crucible using alumina powder as a reference
material at I.I.C., Indian Institute of Technology Roorkee. The X-
ray powder diffraction (XRD) of residues obtained by pyrolysis
of the studied diorganotin(IV) derivatives of macrocyclic ligands
were recorded on a Bruker AXS diffractometer at I.I.C., Indian
Institute of Technology Roorkee, using nickel mono chromated
Cu Ka radiation (k = 1.541 Å).
2. Experimental
2.1. Materials
All of the syntheses were carried out under an anhydrous nitro-
gen atmosphere and precautions to avoid the presence of oxygen
were taken at every stage. n-Dibutyltin(IV) oxide, dimethyltin(IV)
dichloride were purchased from Merk-Schuchardt and used as re-
ceived. Diphenyltin(IV) dichloride was synthesized according to
the reported method [29]. Ethyl acetoacetate (Thomas Baker),
1,2-diaminoethane (BDH) and 1,3-diaminopropane (Merk-Schuc-
hardt) were used as received. Solvents such as methanol and cyclo-
hexane (Qualigens) were dried and distilled, and stored under
nitrogen before use.
2.3. Synthesis
2.3.1. Synthesis of 5,12-dioxa-7,14-dimethyl-1,4,8,11-
2.2. Measurements
tetraazacyclotetradeca-1,8-diene H2L-1 (1) and 6,14-dioxa-8,16-
dimethyl-1,5,9,13-tetraazacyclohexadeca-1,9-diene H2L-2 (2)
The ligand, H2L-1 was prepared according to the previously re-
ported method [24] and H2L-2 was synthesized using the similar
procedure. To a methanol solution of ethyl acetoacetate (1.301 g,
10.0 mmol) was added 1,2-diaminoethane for H2L-1 (0.601 g,
10.0 mmol) or 1,3-diaminopropane for H2L-2 (0.741 g, 10.0 mmol)
in 10 ml of methanol with constant stirring. The reaction mixture
was stirred for 8–12 h at room temperature (35 2 °C). The con-
tents were then left at room temperature for 12 h which resulted
in the formation of fine shining colorless crystalline solid in case
of H2L-1, but H2L-2 was crystallized after keeping the contents
for a few days. The solid product was washed with chilled metha-
The melting points of the synthesized complexes were deter-
mined on a Toshniwal capillary melting point apparatus and were
uncorrected. Carbon, hydrogen and nitrogen were analyzed on
elemental analyzer system VarioEL CHNS analyzer. IR and Far-IR
spectra of the solid compounds were recorded on a Nicolet NEXUS
Aligent 1100 FT-IR spectrometer in the range 4000–400 cmꢀ1 in
KBr discs and 500–200 cmꢀ1 in CsI discs. 13C NMR spectra (at fre-
quency 125 MHz) of the compounds in the solid-state were re-
corded on a Bruker Avance WB (Wide Bore) 500 MHz FT NMR
spectrometer using Adamantane as the external reference at the
Tata Institute of Fundamental Research, Mumbai, India. The sam-
ple was packed in 4 mm rotor weight ꢁ 72 mg and pulse program

M. Nath et al. / Journal of Organometallic Chemistry 693 (2008) 2271–2278
2273
nol and dried in vacuo. The purity of these macrocycles was
checked by TLC.
Found (calc.): 512.12 (512.30). Selected IR data (KBr, mmax/cmꢀ1):
1562s (C@N), 1636vs (C@O), 2954w, 2929w (C–H), 596s (mas Sn–C),
567s (ms Sn–C), 420sh (Sn–N), 419m (Sn N).
2.3.1.1. H2L-1 (1). Colorless crystalline; m.p., 133–135 °C [24];
Yield, 71%; Anal. Calc. for C12H20N4O2 (252.32): C, 57.12; H, 7.99;
N, 22.21%. Found: C, 57.01; H, 7.73; N, 21.91%. (MH+/z) Found
(calc.): 253.18 (253.33). Selected IR data (KBr, mmax/cmꢀ1): 1605vs
(C@N), 1649s (C@O), 2987vs, 2951vs (C–H), 3296vs (N–H). 1H
NMR (CDCl3, d/ppm): d 8.64 (s, 2H, H-4, H-11); 4.09, 4.06 (dd
(9.2, 9.2 Hz), 4H, H-2, H-9); 3.36, 3.34 (dd (4.0, 7.3 Hz), 4H, H-3,
H-10); 4.46 (s, 4H, H-6, H-13); 1.91s, 1.23t (6.5 Hz, 6H, H-15, H-16).
2.3.5. Synthesis of dimethyl/diphenyltin(IV) complexes of H2L-1/H2L-2
using template method
The dimethyltin(IV) and diphenyltin(IV) complexes of H2L-1
and H2L-2 were prepared by a drop wise addition of methanol
solution (ꢂ10 ml for each) of ethyl acetoacetate (1.301 g,
10.0 mmol) and 1,2-diaminoethane (0.601 g, 10.0 mmol)/1,3-
diaminopropane (0.741 g, 10.0 mmol) to the solution of dimethyl-
tin(IV) dichloride (1.098 g, 5.0 mmol) (4/7) or diphenyltin(IV)
dichloride (1.720 g, 5.0 mmol) (5/8) in dry methanol (ꢂ20 ml) with
constant stirring at room temperature under inert atmosphere of
dry nitrogen. The mixture thus obtained was stirred for 15 h at
room temperature (35 2 °C). The excess of solvent was reduced
under vacuum and solid product was washed thoroughly by dry
cyclohexane, and then dried in vacuo.
2.3.1.2. H2L-2 (2). Colorless crystalline; m.p., 45–47 °C; Yield, 69%;
Anal. Calc. for C14H24N4O2 (280.37): C, 59.98; H, 8.63; N, 19.98%.
Found: C, 59.96; H, 8.74; N, 19.87%. (MH+/z) Found (calc.):
281.18 (281.38). Selected IR data (KBr, mmax/cmꢀ1): 1606vs (C@N),
1646s (C@O), 2985vs, 2947vs (C–H), 3296m (N–H). 1H NMR
(CDCl3, d/ppm): d 8.56 (s, 2H, H-50, H-130); 4.04, 4.08 (dd (9.6,
9.4 Hz), 4H, H-20, H-100); 2.80 (m, 4H, H-30, H-110); 3.27, 3.32 (dd
(8.6, 8.6 Hz), 4H, H-40, H-120); 3.80 (s, 4H, H-70, H-150); 1.91s,
1.24t (9.7 Hz, 6H, H-170, H-180).
2.3.5.1. Me2Sn(L-1) (4). White solid; m.p., 180–182 °C; Yield, 76%;
Anal. Calc. for C14H24N4O2Sn (399.08): C, 42.14; H, 6.06; N, 14.04;
Sn, 29.75%. Found: C, 42.26; H, 6.00; N, 14.39; Sn, 29.64%. (MH+/
2.3.2. Synthesis of diorganotin(IV) complexes of H2L-1 and H2L-2
The diorganotin(IV) complexes of 5,12-dioxa-7,14-dimethyl-
1,4,8,11-tetraazacyclotetradeca-1,8-diene (H2L-1) and 6,14-dioxa-
8,16-dimethyl-1,5,9,13-tetraazacyclohexadeca-1,9-diene (H2L-2)
have been synthesized by following methods.
z) Found (calc.): 400.11 (400.09). Selected IR data (KBr, mmax/
cmꢀ1): 1566s (C@N), 1634vs (C@O), 2982m (C–H), 653w (mas Sn–
C), 620w (ms Sn–C), 465m (Sn–N), 410m (Sn N).
2.3.5.2. Ph2Sn(L-1) (5). White solid; m.p., 210 (dec.) °C; Yield, 82%;
Anal. Calc. for C24H28N4O2Sn (523.22): C, 55.09; H, 5.39; N, 10.71;
Sn, 22.69%. Found: C, 54.64; H, 5.31; N, 10.38; Sn, 22.45%. (MH+/
2.3.3. Attempted synthesis of dibutyltin(IV) complexes of H2L-1/H2L-2
by azeotropic removal of water method
z) Found (calc.): 523.31 (524.23). Selected IR data (KBr, mmax
/
The ligand, H2L-1 or H2L-2 (5.0 mmol) dissolved in methanol
(30 ml) was added drop wise to a methanol solution (30 ml) of
n-dibutyltin(IV) oxide (1.245 g, 5.0 mmol) with constant stirring
under dry nitrogen atmosphere. The resulting mixture was then
stirred for additional 40 h at room temperature (35 2 °C), fol-
lowed by refluxing for 2–3 h. The excess of solvent was removed
under vacuum, but no complexation took place, instead macrocy-
clic ligand and n-dibutyltin oxide separated out. Therefore, this
method was not used for synthesis of dimethyltin(IV) and diphe-
nyltin(IV) complexes.
cmꢀ1): 1562vs (C@N), 1639m (C@O), 2978m (C–H), 279m
(mas Sn–C), 230s (ms Sn–C), 456m (Sn–N), 422w (Sn N).
2.3.5.3. Me2Sn(L-2) (7). White solid; m.p., >300 °C; Yield, 75%; Anal.
Calc. for C16H28N4O2Sn (427.13): C, 44.99; H, 6.61; N, 13.12; Sn,
27.79%. Found: C, 44.85; H, 6.29; N, 13.07; Sn, 27.43%. (MH+/z) Found
(calc.): 428.27 (428.14). Selected IR data (KBr, mmax/cmꢀ1): 1530w,
1565sh (C@N), 1626vs,br (C@O), 2996m, 2920w (C–H), 561vs (mas
Sn–C), 521w (ms Sn–C), 446m (Sn–N), 406w (Sn N).
2.3.5.4. Ph2Sn(L-2) (8). White solid; m.p., >300 °C; Yield, 80%; Anal.
Calc. for C26H32N4O2Sn (551.28): C, 56.65; H, 5.85; N, 10.16; Sn,
21.53%. Found: C, 56.72; H, 5.68; N, 9.79; Sn, 21.34%. (MH+/z)
Found (calc.): 552.35 (552.29). Selected IR data (KBr, mmax/cmꢀ1):
1565sh (C@N), 1630vs,br (C@O), 3059m, 2956m (C–H), 279m (mas
Sn–C), 225m (ms Sn–C), 470s (Sn–N), 420vs (Sn N).
2.3.4. Synthesis of dibutyltin(IV) complexes of H2L-1/H2L-2 using
template method
The dibutyltin(IV) complexes of H2L-1/H2L-2 were prepared by
a drop wise addition of methanol (ꢂ10 ml for each) solution of
ethyl acetoacetate (1.301 g, 10.0 mmol) and 1,2-diaminoethane
(0.601 g, 10 mmol)/1,3-diaminopropane (0.741 g, 10.0 mmol) to
the suspension of dibutyltin(IV) oxide (1.245 g, 5.0 mmol) (3/6)
in methanol (ꢂ30 ml) with constant stirring at room temperature
under inert atmosphere of dry nitrogen. The mixture thus obtained
was stirred for 40 h at 35 2 °C. The water formed during the reac-
tion was removed azeotropically. The solution was filtered, and the
excess of solvent was gradually removed by evaporation under
vacuum. The solid product was washed thoroughly with dry cyclo-
hexane, and then dried in vacuo.
Note: vs: very strong; s: strong; m: medium; w: weak; br:
broad; sh: shoulder.
3. Results and discussion
3.1. Synthesis, reactivity and solid-state characteristics
The reaction of R2SnCl2 (R = Me and Ph) or n-Bu2SnO with the
1,2-diaminoethane or 1,3-diaminopropane and ethyl acetoacetate
in 1:2:2 molar ratio at room temperature in a single step (using
template method) led to the formation of the complexes according
to Eq. (Ia and Ib). The reactions involved in the synthesis of diorga-
notin(IV) complexes of macrocyclic ligands, H2L-1 and H2L-2, were
found to be quite feasible and required 15 h of stirring at ambient
temperature (35 2 °C), except n-Bu2Sn(L-1)/(L-2), which required
40 h stirring at (35 2 °C). However; even prolonged stirring for
40 h followed by refluxing for 2–3 h of a mixture of macrocyclic
ligand, H2L-1 or H2L-2, synthesized according to the previously
reported method, and n-Bu2SnO in a 1:1 molar ratio in methanol
did not result in complexation.
2.3.4.1. n-Bu2Sn(L-1) (3). Yellow solid; m.p., 230–232 °C; Yield,
80%; Anal. Calc. for C20H36N4O2Sn (483.24): C, 49.71; H, 7.51; N,
11.59; Sn, 24.56%. Found: C, 49.76; H, 8.01; N, 11.12; Sn, 24.72%.
Selected IR data (KBr, mmax/cmꢀ1): 1566m (C@N), 1634vs (C@O),
2565w (C–H), 648w (mas Sn–C), 607vw (ms Sn–C), 465m (Sn–N),
417m (Sn N).
2.3.4.2. n-Bu2Sn(L-2) (6). White solid; m.p., >320 °C; Yield, 81%;
Anal. Calc. for C22H40N4O2Sn (511.29): C, 51.68; H, 7.89; N, 10.96;
Sn, 23.22%. Found: C, 51.29; H, 7.16; N, 10.76; Sn, 23.69%. (MH+/z)

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M. Nath et al. / Journal of Organometallic Chemistry 693 (2008) 2271–2278
R2Sn(L-1)/(L-2)
l
C
n
S
O
O
R
-(Ia)
(CH2)n
+
H2N
C2H5O
CH3
NH2
n-Bu2Sn(L-1)/(L-2)
-(Ib)
(where n = 2 or 3, R = Me or Ph)
All of the synthesized complexes are white solid, except n-
Bu2Sn(L-1), which is yellow in color, and are stable towards air
and moisture. The macrocyclic ligands, H2L-1 and H2L-2 are soluble
in chloroform, toluene, xylene, methanol, dichloromethane, ace-
tone, acetonitrile and nitrobenzene but insoluble in benzene,
diethyl ether, carbon tetrachloride, water, kerosene and cyclohex-
ane, while the diorganotin(IV) complexes are insoluble in all of the
above mentioned solvents except methanol in which they have
very poor solubility. The analytical data of these complexes are
in agreement with the proposed 1:1 metal to ligand stoichiometry.
In order to confirm the template cyclization of amine and diketone
in the resulting diorganotin(IV) macrocyclic complexes, the free
macrocyclic ligands, H2L-1 and H2L-2, have also been prepared
and characterized. The elemental analyses and molecular ion peaks
in the mass spectra of H2L-1 and H2L-2, supports their proposed
macrocyclic ligand frame work (Scheme 1) derived from the con-
densation of 1,2-diaminoethane or 1,3-diaminopropane with ethyl
acetoacetate. Further, the molecular ion peaks observed in the
DART-mass spectra of diorganotin(IV) complexes of H2L-1 or
H2L-2, also support the formation of macrocyclic ligand frame
work (Scheme 1) in the synthesized diorganotin(IV) complexes.
The observed spectroscopic data (discussed in subsequent sec-
tions) are consistent with a structure (in the solid-state) in which
R2Sn(IV) moiety is bonded to the four nitrogen atoms resulting in
a six-coordinated geometry around the tin center. Such an arrange-
ment is depicted in Figs. 2 and 3 with the ligand in its usual saddle
conformation and the two substituent group (R) may be cis or
trans. Since, diorganotin(IV) macrocyclic complexes studied herein
are insoluble in above mentioned solvents, hence all the solid-state
spectral studies, viz. infrared, far-infrared solid-state 13C NMR,
119mSn mössbauer and recently developed DART-mass have been
utilized in order to establish the structural characterization of
the synthesized diorganotin(IV) macrocyclic complexes.
respectively. The major changes observed in the IR spectra of the
corresponding diorganotin(IV) macrocyclic complexes are the red
shift in the m(C@N) mode which appear in the region 1566–
1530 cmꢀ1, and are in agreement with the values reported for
other analogues complexes [32]. Whereas the band corresponding
to m(N–H) mode of vibrations are not observed in IR spectra of dior-
ganotin(IV) complexes of macrocyclic ligands indicating the depro-
tonation of amide group. Since the deprotonated nitrogen is
involved in coordination, the amide I band undergoes a small shift
in comparison to the free macrocyclic ligands. This may be due to
the dispersion of the electronic charge in the coordinated amide
group (O@C–N–Sn). However, the positions of amide II, III and IV
bands remain unchanged in the spectra of diorganotin(IV) macro-
cyclic complexes indicating the non-involvement of C@O group in
coordination, which was further confirmed by the absence of m(Sn–
O) band. Further, new bands observed in the region (470–
406 cmꢀ1) assignable to m(Sn–N)/(Sn N) vibrational modes in
the spectra of diorganotin(IV) complexes, which are absent in the
spectra of free macrocycles, confirm the coordination of azome-
thine nitrogen (C@N) and deprototonated amide nitrogen to tin
center [33]. The mas (Sn–C) and m(Sn–C) bands in all dialkyltin(IV)
complexes have been observed at 639 36 and 572 35 cmꢀ1
,
respectively, whereas corresponding vibrational bands in diphe-
nyltin(IV) analogues are observed in far-IR region at 279 and
228 3 cmꢀ1, respectively [34].
3.3. DART-mass spectral studies
The mass spectra of the complexes (5–8) have been recorded in
the solid-state by a recently developed technique DART (Direct
Analysis in Real Time) mass spectrometer using Time of Flight
(TOF) mass analyzer, which give accurate mass capability. The
analysis was performed in the DART beam of excited helium atoms
which involves predominantly the formation of ionized water clus-
ter followed by proton transfer reaction. The helium 2 3S state has
energy of 19.8 eV and reacts with water efficiently with an esti-
mated reaction cross section of 100 Å [35] (Scheme 2).
3.2. Infrared and far-infrared spectral studies
The characteristic infrared absorption bands (in cmꢀ1) of H2L-1,
H2L-2 and their diorganotin(IV) complexes along with their assign-
ments are given in experimental section. The preliminary identifi-
cation of the synthesized macrocyclic ligands have been obtained
from their IR spectra which show the absence of uncondensed
functional groups (NH2, O–R), stretching modes of starting materi-
als and the appearance of bands characteristic of imine and amide
groups. In the IR spectra of the ligands, H2L-1/H2L-2, the appear-
ance of a strong absorption band at 1605 1 cmꢀ1 corresponds to
C@N stretching frequency. In addition to it, four amide bands have
also been identified in the IR spectra of H2L-1/H2L-2 at 1649(vs)/
1646(vs), 1510(vs)/1510(vs), 1260(m)/1259(m) and 724(vs)/
725(s) cmꢀ1 assignable to amide-I, II, III and IV vibrational modes,
respectively, similar to that reported for different tetraazamacro-
cyclic ligands [31].
The molecular ion peaks (due to 119Sn isotope) in all the synthe-
sized complexes have been observed at m/z 400.11, 523.31, 512.12,
428.27 and 552.35, suggesting the proposed molecular formula of
(4), (5), (6), (7) and (8) for these complexes, respectively. It also
provides the evidence for the monomeric nature of all the synthe-
sized complexes. The peaks at M+1, Mꢀ1 and Mꢀ2, have also been
observed due to the presence of 120Sn, 118Sn and 117Sn isotopes
[36,37]. For illustration, one of depicted in Fig. 1, shows the magni-
He(2 3S) + H2O
H2O + He(1 1S) + e-
H3O+ + OH
H2O + H2O
H3O+ + nH2O
A single strong to medium intensity band observed for the mac-
rocyclic ligands at 3296 cmꢀ1 corresponds to m(N–H) assigned for
secondary amine [16]. The absorption bands at 2986 1 and
1410–1465 cmꢀ1 in free macrocyclic ligands may reasonably cor-
respond to (C–H) stretching and (C–H) bending vibrational modes,
[(H2O)nH]+
[(H2O)nH]+ + M
MH+ + nH2O
Scheme 2.

M. Nath et al. / Journal of Organometallic Chemistry 693 (2008) 2271–2278
2275
have been formed by the condensation reaction. The spectra of
both macrocyclic ligands, H2L-1 and H2L-2, exhibit a sharp singlet
at d 1.91 ppm and triplet at 1.23–1.24 ppm, which may be assigned
to CH3 protons (6H). The CH2 (4H) protons of alkyl acetoacetate
moiety (i.e., H-6, H-13 in H2L-1 and H-70, H-150 in H2L-2) are also
observed as singlet at d 4.46 and d 3.80 ppm, respectively [38]. A
broad sharp resonance observed at d 8.64 ppm and d 8.56 ppm in
H2L-1 and H2L-2, respectively, has been assigned to the amide pro-
tons (–NHC@O, 2H) [39]. The expected signals of the diaminoe-
thane/diaminopropane moiety have also been observed and
assigned.
13C NMR spectral data of H2L-1 and H2L-2 recorded in CDCl3 are
presented in Table 1. All the magnetically non-equivalent carbons
of alkyl groups of macrocyclic frame work have been assigned. The
carbonyl (C@O) carbon (C-5, C-12 in H2L-1 and C-60, C-140 in H2L-2)
and imine carbon (C-7, C-14 in H2L-1 and C-80, C-160 in H2L-2) res-
Fig. 1. Mass spectrum of n-Bu2Sn(L-2) (6) (with full scan).
fied region of the full scan DART mass spectrum with the charac-
teristic isotopic peaks in complex (6).
onances have been observed at
d 170.36 0.15 ppm and d
161.30 0.09 ppm, respectively. Since the diorganotin(IV) com-
plexes of both macrocyclic ligands are insoluble in NMR solvents,
hence solid-state 13C NMR spectra of the studied complexes have
been recorded which are also presented in Table 1 and discussed
in the following section.
In complexes (4) and (5) two peaks other than molecular ion
peak have also been observed at m/z 253 and 239, indicating the
fragmentation of complexes and responsible for [(H2L-1)H+] and
[(H2L-1-CH3)H+], respectively. Whereas in complexes (6), (7) and
(8), few more intense peaks have been observed at m/z 279, 183,
99 and 61 which indicate the fragmentation of complexes in
[(HL-2)H+], [(H2L-2)-(NC(Me)CH2CON)H+], [(C4H6N2O)H+] and
[(C2H6NO)H+], respectively. The mass spectral data provide a little
help to establish the structure, but it is more informative about
purity and molecular weight of the synthesized complexes.
3.4.2. Solid-state 13C NMR spectral studies
X-ray crystallography is the most accurate method of determin-
ing molecular structure in the crystalline state, and it has pro-
foundly influenced our understanding of molecular structure and
bonding. Few other methods are sufficiently sensitive to structural
features to be capable even of questioning X-ray determined struc-
tures. In contrast to the solution NMR spectra, the solid-state NMR
spectra are very broad, as the full effects of anisotropic or orienta-
tion-dependent interactions are observed in the spectrum. High-
resolution solid-state NMR spectra can provide the same type of
information that is available from corresponding solution NMR
spectra, but a number of special techniques/equipment are needed,
including magic-angle spinning, cross-polarization, etc. The
3.4. NMR spectral studies
3.4.1. 1H and 13C NMR spectral studies of H2L-1 and H2L-2 in solution
The 1H and 13C NMR spectra of the synthesized macrocyclic li-
gands, H2L-1 and H2L-2, were recorded in CDCl3. The 1H NMR spec-
tra of the ligands do not show any signal assignable to primary
amino protons suggesting that the proposed macrocyclic skeleton
Table 1
13C NMR spectral data d (ppm) of ligands (in solution) and their diorganotin(IV) complexes (in the solid-state)
Carbon no./sl. no.a
(1)b
(2)b
(3)c
(4)c
(5)c
(6)c
(7)c
(8)c
C-2,9
56.36
61.94
61.39
61.40
C-3,10
C-5,12
C-6,13
C-7,14
C-15,16
43.77
170.51
40.86
161.21
14.53
48.13
172.65
39.58
164.74
17.51
47.57
172.09
38.08
164.16
16.94
47.63
172.12
38.042
164.20
16.97
19.13
C-20,100
C-30,110
C-40,120
C-60,140
C-70,150
C-80,160
C-170,180
C-a
57.88
64.17
62.55
61.93
19.32
40.23
170.21
33.59
161.39
14.24
20.22
43.73
174.40
38.52
164.53
16.93
29.94
32.72
21.64
42.56
174.19
36.66
164.24
16.94
8.03
20.93
40.38
174.22
35.55
164.19
17.02
141.97
136.82
27.27
31.72
29.95
25.54
16.83
NO
9.530
144.93,139.67
137.60
C-b
C-c
C-d
130.38
133.00
NO
25.53
22.32
NO
127.93
130.94
719.30
139.9
1J[13C–119Sn]d
\C–Sn–C (°)e
807.63
147.6
710.42
139.1
a
Sl. no. as indicated in Section 2.
In CDCl3.
In solid-state; NO: not observed.
b
c
γ
β
β
d
e
In Hz.
β
γ
α
δ
α
1
α
Calculated by the Eq.: j Jj = 11.4(h) ꢀ 875; δ
.
Sn
;
-
;
Sn-CH2-CH2-CH2-CH3
Sn CH3
γ

2276
M. Nath et al. / Journal of Organometallic Chemistry 693 (2008) 2271–2278
Table 2
presence of broad NMR line shapes, once thought to be a hin-
drance, actually provides much information on chemistry, struc-
ture and dynamics in the solid-state. The anisotropies in the local
fields of the protons broadened the 1H NMR spectra such that no
spectral lines could be resolved. A number of methods have been
developed in order to minimize large anisotropic NMR interaction
between nuclei and increase S/N in rare spin (e.g. 13C, 15N) high-
resolution solid-state NMR spectra. Cross-polarization is one of
the most important techniques in high-resolution solid-state
NMR. In this technique, polarization from abundant spins such as
1H or 19F is transferred to dilute spins such as 13C or 15N in order
to enhance S/N and reduce waiting time between successive exper-
iments. The solid-sate 13C NMR spectral data of the studied diorga-
notin(IV) complexes of macrocyclic ligands are presented in Table
1.
119mSn Mössbauer data of diorganotin(IV) complexes of H2L-1 and H2L-2
Complex
no.
Q.S.
I.S.
q(Q.S./
I.S.)
s1 (L) s2 (R) \C–Sn–C
(°)
(mm Sꢀ1
)
(mm Sꢀ1
)
(3)
(4)
(5)
(6)
(7)
(8)
2.312
3.338
2.112
2.147
2.632
1.946
1.008
1.243
0.892
1.015
1.044
0.895
2.3
2.7
2.4
2.1
2.5
2.2
1.116 1.294 107
2.085 2.245 137
1.162 1.363 106
1.814 1.891 100
1.897 1.927 117
2.065 2.159
97
Q.S: quadrupole splitting; I.S: isomer shift; s1 (L): half line width left doublet
component; s2 (R): half line width right doublet component.
tin(IV) complexes exhibit a doublet centered in the isomer shift
(I.S.) value range 0.89–1.24 mm sꢀ1 and the quadrupole splitting
(Q.S) values in the range 2.11–3.34 mm sꢀ1 show that the electric
field gradient around tin nucleus is generated by inequalities in
tin–nitrogen (ligand) r bond and is also due to the geometric dis-
tortions. The q (Q.S./I.S.) value of 2.3–2.7 in the studied diorgano-
tin(IV) complexes indicate a coordination number of tin either 5
or 6 [44]. The low value of Q. S. for Ph2SnL is due to greater polar-
izability of the phenyl groups.
The comparison of 13C NMR spectral data of the ligands, H2L-1
and H2L-2, in CDCl3 and solid-state 13C NMR spectral data of the
studied diorganotin(IV) complexes of these macrocyclic ligands
indicated that imine carbon and carbonyl carbon resonances under
go a small shift towards lower field [28,40]. This suggests the coor-
dination of macrocyclic ligands through the imine nitrogen and
deprotonation of amide proton (-NHCO) and its subsequent bond-
ing with tin. Further, all the alkyl carbons of ethyl acetoacetate and
diaminoethane/diaminopropane moieties of the macrocyclic frame
work are shifted towards lower field which also support the coor-
dination of macrocyclic ligands through all the four nitrogens to tin
[28]. All magnetically non-equivalent carbons of the alkyl or phe-
nyl groups attached to tin have been identified and their chemical
shift values are in close agreement with reported values [34].
The 1J(13C–119Sn) values have been calculated for complexes (4),
(7) and (8) from their solid-state NMR spectra which show the sat-
ellites. But the 117Sn and 119Sn satellites are not well resolved in the
solid-state spectra, so 1J(13C–119Sn) was calculated from the dis-
tance separating the center of fused 117Sn and 119Sn satellites X
1.023 (because the natural abundances of 117Sn and 119Sn are sim-
ilar (7.6% and 8.6%, respectively) the differences between the sep-
aration of the centers of unresolved satellites and 1J(13C–119Sn) is
closely approximated by multiplying the separation, in hertz by
one half the ratio of the gyromagnetic ratio of 119Sn and 117Sn) [41].
1J(13C–119Sn) values calculated for complexes (4), (7) and (8)
were 807.63 Hz, 710.42 Hz and 719.30 Hz, respectively which lie
in the range (P630), typical for hexacoordinated diorganotin(IV)
complexes [42]. Moreover, the calculated values of \C–Sn–C using
the observed 1J(13C–119Sn) values in the equation given by Lockhart
The Q.S. values for trans- and cis-octahedral [R2SnX4]2ꢀ are
around 4.00 and 2.00 mm sꢀ1, respectively [45]. Further, it has
been reported [45] that I.S. values for cis-[R2SnX4]2ꢀ are less the
1.00 mm sꢀ1 while those for trans-[R2SnX4]2ꢀ are approximately
1.2–1.3 mm sꢀ1. The observed values of Q.S. and I.S. of the studied
diorganotin(IV) complexes of macrocyclic ligands are substantially
lower than the values for trans-octahedral configuration and
slightly higher than the values for cis-octahedral configuration.
Further, the \C–Sn–C for the studied diorganotin(IV) complexes
has been calculated by using Parish’s relationship [46]:
Q.S. = 4[R][1 ꢀ 3/4 sin2 2h]1/2, where \C–Sn–C is (180 ꢀ 2h)° and
[R] is the partial quadruple splitting for alkyl and phenyl groups
bonded to tin. The reported values of [R] for alkyl and phenyl
groups are ꢀ1.03 mm sꢀ1 and ꢀ0.95 mm sꢀ1, respectively [47,48].
The calculated values of \C–Sn–C in the studied diorganotin(IV)
complexes of macrocyclic ligands are in the range of 97–137°,
which is again intermediate between the corresponding cis-octa-
hedral with \C–Sn–C = 90° and trans-octahedral with \C–Sn–
C = 180°. Thus, the structures of R2Sn(L-1) and R2Sn(L-2) are best
described by the highly distorted square bipyramidal/ skew-trape-
zoidal bipyramidal configuration with the two organic groups (Me,
n-Bu or Ph) in bent axial position and trapezoidal plane being de-
fined by the four Sn–N coordination/interactions and macrocyclic
ligand is in usual saddle conformation (Figs. 2b and 3b). The ob-
served mas(Sn–C) and ms(Sn–C) stretching vibrations in the IR spec-
tra of the studied diorganotin(IV) complexes indicate a non-planar
1
and Manders [43] (j Jj = 11.4(h) ꢀ 875) are in the range of 139.1–
147.6° (Table 1) indicating a pseudooctahedral geometry.
The solid-state 13C NMR spectra of a number of structurally
characterized methyltin(IV) compounds have reported that the
13C (methyl-Sn) chemical shifts are very sensitive to slight differ-
ences in magnetic environment (i.e., slight difference in distance
to neighboring atoms) [41]. In the studied Me2Sn(L-1) and
Me2Sn(L-2), a single methyl resonance has been observed. The nar-
row single dimethyltin resonance observed in these complexes re-
flects the presence of mirror plane through tin and the macrocyclic
ligands, which interconvert the two methyl groups.
3.5. 119mSn Mössbauer spectral studies
It is instructive to compare the structural analysis of the studied
diorganotin(IV) complexes of macrocyclic ligands by solid-state
NMR with the routinely employed 119mSn Mössbauer technique.
Mössbauer isomer shift (I.S.) and quadrupole splitting (Q.S.)
parameters are used to obtain information about the coordination
number and bonding geometry of organotin compounds. 119mSn
Mössbauer spectral data of all of the studied diorganotin(IV) com-
plexes are given in Table 2. Mössbauer spectra of all the diorgano-
Fig. 2. Proposed structures of diorganotin(IV) complexes of H2L-1 where R = Me, n-
Bu or Ph.

M. Nath et al. / Journal of Organometallic Chemistry 693 (2008) 2271–2278
2277
weight loss along with the species lost as well as enthalpy of
DTA peaks are presented in Table 3. The main diffraction lines ob-
served in the residues obtained by the pyrolysis of these organo-
tin(IV) macrocyclic complexes are summarized in Table 4. n-
Bu2Sn(L-1) decomposes in three steps in air. The weight loss in
the first step of decomposition, which extends from 100 to
240 °C, corresponds to the loss of two butyl groups and a part of
ligand moiety (2CO) {C10H18O2; wt. loss obsd. 37.01%: calc.
35.23%}. Thereafter, C6H10N2 of the remaining ligand moiety is lost
(wt. loss obsd. 22.36%: calc. 22.80%) in the second step followed by
the loss of rest of ligand moiety (C4H8N2) {wt. loss obsd. 15.38%:
calc. 17.41%} along with oxidation in the third step of decomposi-
tion leaving 2.56 mg (25.25%) residue (relative to 10.13 mg of sam-
ple taken) up to 500 °C (for SnO2: calc. residue 31.24%). The
Fig. 3. Proposed structures of diorganotin(IV) complexes of H2L-2 where R = Me, n-
Bu or Ph.
Table 4
The main diffraction lines (intensity) in residues obtained by pyrolysis of organo-
tin(IV) derivatives of tetraazamacrocyclic ligands
SnC2 fragment and rule out the possibility of trans-octahedral
structure (Figs. 2a and 3a). The proposed skew-trapezoidal bipyra-
midal structure for R2Sn(L-1) and R2Sn(L-2) has been attributed to
an octahedral distortion by steric demands of the ligands [49]. A
similar structure has also been reported [28] for [Me2M(tmtaa)]
and [Cl2M(tmtaa)] (M = Si and Sn, H2tmtaa = dibenzotetramethyl-
tetraaza[14]annulene). Such as arrangement depicted in Figs. 2b
and 3b, with the ligand (tmtaa) in its usual saddle conformation
and the two substituent groups (R) mutually cis, has also been re-
ported for the group 4(d0) counterparts [Cl2M(tmtaa)] (M = Ti [50],
Zr [51,52]) and [(PhCH2)2Zr(tmtaa)] [52] and is, infact, common to
all such transition metal complexes [R2M(tmtaa)], with the sole
exception of [(PMePh2)2Ru(tmtaa)] [53].
Tin compound/residue of
complex
Main diffraction lines d (Å) (intensity (%)) (hkl)
1
2
3
4
5
Sna
2.92
2.79
(90)
(101)
3.00
(50)
2.64
(80)
(101)
2.64
(92)
2.64
(80)
2.64
(97)
2.65
(92)
2.64
(95)
2.06
(34)
(220)
2.89
(90)
2.37
(25)
(200)
2.37
(21)
2.36
(22)
2.37
(22)
2.37
(24)
2.37
(26)
2.02
(74)
(211)
2.67
(90)
1.77
(65)
(211 )
1.76
(85)
1.76
(66)
1.76
(87)
1.76
(83)
1.76
(97)
1.48
(23)
(112)
1.77
(80)
1.68
(18)
(220)
1.68
(19)
1.67
(15)
1.68
(20)
1.68
(16)
1.68
(20)
(100)
(200)
3.39
(100)
3.35
(100)
(110)
3.35
(100)
3.34
(100)
3.35
(100)
3.35
(100)
3.35
(100)
SnOa
a
SnO2
n-Bu2Sn(L-1)
Ph2Sn(L-1)
n-Bu2Sn(L-2)
Me2Sn(L-2)
Ph2Sn(L-2)
3.6. Thermal studies
The thermal decomposition behavior of complex no. (3)–(8) in
air have been studied using TG, DTG and DTA techniques. The TG
temperature ranges, peak temperatures in DTA and DTG, percent
a
Ref. [54].
Table 3
Thermal analysis data of organotin(IV) derivatives in air
Compound Step no. Temperature range in TG (°C) Peak temperature in DTG (°C) Peak temperature in DTA (°C) Enthalpy (mJ/
Loss of mass %
Observed
(calc.)
Species lost
2CO + 2C4H9
mg)
Bu2Sn(L-1)
I
100–240
218
123 (endothermic)
232 (exothermic)
293 (exothermic)
447 (exothermic)
40.50
37.01 (35.23)
ꢀ39.30
II
III
240–308
308–500
277
447
ꢀ177
22.36 (22.80)
15.38 (17.41)
C6H10N2
N2C4H8
ꢀ1368
Me2Sn(L-
1)
I
99–166
156
120 (endothermic)
159 (endothermic)
215 (endothermic)
161
23.38 (21.57)
56.43 (48.68)
15.83
2CH3 + 2CO
II
III
166–252
252–560
196
219
526
161
C10H18N4
525 (exothermic)
ꢀ465
Sublimation
Ph2Sn(L-1)
Bu2Sn(L-2)
I
II
100–245
245–286
185
259
273
435
116 (endothermic)
276 (exothermic)
33
ꢀ26.3
41.48 (40.18)
23.38 (21.05)
2CO + 2C6H5
C6H10N2
III
I
286–660
433 (exothermic)
551 (exothermic)
643 (exothermic)
ꢀ61.8
ꢀ191
ꢀ36
ꢀ914
ꢀ86.2
14.28 (16.08)
C4H8N2
99–310
288
302 (exothermic)
885 (broad exothermic)
52.95 (54.48)
C14H22N4O2
Sublimation
Me2Sn(L-
2)
I
II
III
100-160
160–265
265–350
152
186
268, 293
153 (endothermic)
46
07.70 (7.04)
31.01 (32.35)
24.95 (32.82)
2CH3
C8H10O2
C6H12N4
317 (exothermic)
164 (endothermic)
ꢀ664
27.6
Ph2SnL-2
I
II
III
100–244
244–287
287–500
164
263
330
26.60 (27.97)
24.75 (25.06)
19.56 (25.43)
2C6H5
C8H10O2
C6H12N4
401 (exothermic)
ꢀ411

2278
M. Nath et al. / Journal of Organometallic Chemistry 693 (2008) 2271–2278
amount of the residue left at 1000 °C (maximum temperature re-
corded) is 24.59% and the residue obtained at ꢂ500–525 °C is
SnO2 which has been identified by XRD (Table 4).
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Me2Sn(L-1) decomposes in two steps. The weight losses in the
first and second steps of decomposition correspond to the loss of
two methyl groups attached to Sn + 2CO groups and the remaining
ligand moiety (C10H18N4), respectively. The unexpected mass loss
is observed in the temperature range 252–560 °C leaving a residue
of 4.36% (relative to 10.25 mg of sample) at 560 °C and 3.64% at
800 °C, which indicates the slow sublimation of metallic particles.
In case of Ph2Sn(L-1), the decomposition take place in three steps
in the temperature range 100–660 °C, corresponding to the loss
of phenyl groups attached to tin and the ligand moiety with simul-
taneous oxidation of the material to SnO2. The mass of residue left
is 20.86% at 660 °C (for SnO2, calc. 28.86%) which sublimed slowly
up to 800 °C leaving 19.6% of the residue (relative to 10.56 mg of
sample). The XRD of the residue obtained at 660 °C indicates the
formation of SnO2 (Table 4).
Me2Sn(L-2) and Ph2Sn(L-2) decompose in three steps whereas a
single step decomposition pattern is observed in n-Bu2Sn(L-2) in
the temperature range 99–310 °C. The mass loss observed in case
of n-Bu2Sn(L-2) is 52.95% (calc. 54.48%), which corresponds to
the loss of macrocyclic ligand moiety along with partial oxidation
of material (residue left 45.64% at 800 °C; for SnO2 calc. residue %:
29.53%). The amount of residue left at 800 °C corresponds to the
formation of n-Bu2SnO2 rather than SnO2, but XRD of the residue
at 350 °C corresponds to that of SnO2 (Table 4). Me2Sn(L-2) and
Ph2Sn(L-2) follow the same three steps decomposition pattern
involving the loss of 2Me/2Ph groups in the first step followed by
the decomposition of the macrocyclic ligand moiety in the second
and third steps (Table 3) along with oxidation of the material. The
mass of the residue obtained in case of Me2Sn(L-2) is 36.34% at
300 °C (for SnO2, calc. 35.35%) which sublimed very slowly leaving
35.97% of the residue at 800 °C. The amount of the residue obtained
in the case of Ph2Sn(L-2) is 29.09% (for SnO2, calc. 27.39) in the
temperature range 500–800 °C. Further, the XRD analysis of the
residues confirms the formation of SnO2 (Table 4).
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Acknowledgements
The authors are thankful to the Tata Institute of Fundamental
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tre, the Central Drug Research Institute, Lucknow, India for
providing DART Mass spectral data. One of the authors (Mr. Pra-
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Industrial Research, New Delhi, India, for awarding Junior Research
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spectra of the samples from the National Institute of Health Minor-
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