Synthesis and characterization of tributyltin(IV) complexes of 2-[(E)-2-(3-formyl-4-hydroxyphenyl)-1-diazenyl]benzoic acid and 4-[((E)-1-{2-hydroxy-5-[(E)-2-(2-carboxyphenyl)-1-diazenyl]phenyl}methylidene) amino]aryls - Crystal structures of polymeric (Bu(3)Sn[O (2)CC(6)H(4){NN(C6)(3)-4-OH-5- CHO)}-o])n) and (Bu(3)Sn[O(2)CC(6)H) (4){NN(C(6)H(3)-4-OH(C(H)NC(6)H (4)Cl-4))}-o])(n)

Article abstract of DOI:10.1016/j.jorganchem.2004.08.038

The tri-n-butyltin(IV) complexes of 2-[(E)-2-(3-formyl-4-hydroxyphenyl)-1- diazenyl]benzoic acid and 4-[((E)-1-{2-hydroxy-5-[(E)-2-(2-carboxyphenyl)-1- diazenyl]phenyl}methylidene)amino]aryls (aryls = 4-CH₃, 4-Br, 4-Cl, 4-OCH₃) have been synthesized and characterized by ¹H, ¹³C, ¹¹⁹Sn NMR, IR and ^119mSn M?ssbauer spectroscopic techniques in combination with elemental analysis. The crystal structures of two compounds, (Bu₃Sn[O₂CC₆H ₄{NN(C₆H₃-4-OH-5-CHO)}-o])_n and (Bu₃Sn[O₂CC₆H₄{NN(C ₆H₃-4-OH(C(H)NC₆H₄Cl-4))}-o]) _n, are reported.The crystallographic and ¹¹⁹Sn M?ssbauer data both indicate that the tributyltin complexes form single-stranded polymeric structures in which the carboxylate O atoms of each aryl ligand bridge two Sn atoms. The Sn atoms have a slighly distorted trigonal bipyramidal coordination geometry with equatorial butyl groups and carboxylate O atoms occupying axial positions. The ¹¹⁹Sn NMR spectroscopic data and the ¹J(¹³C-^119/117Sn) coupling constant indicate a tetrahedral coordination geometry in non-coordinating solvents. The results of a toxicity study of a tributyltin compound on the second larval instar of Aedes aegypti mosquito larvae are reported.

Full text of DOI:10.1016/j.jorganchem.2004.08.038

Journal of Organometallic Chemistry 689 (2004) 4702–4711
www.elsevier.com/locate/jorganchem
Synthesis and characterization of tributyltin(IV) complexes of
2-[(E)-2-(3-formyl-4-hydroxyphenyl)-1-diazenyl]benzoic acid
and 4-[((E)-1-{2-hydroxy-5-[(E)-2-(2-carboxyphenyl)-1-diazenyl]
phenyl}methylidene)amino]aryls – crystal structures of polymeric
(Bu3Sn[O2CC6H4{N@N(C6H3-4-OH-5-CHO)}-o])n
and (Bu3Sn[O2CC6H4{N@N(C6H3-4-OH(C(H)@NC6H4Cl-4))}-o])n –
toxicity studies on the second instar of Aedes aegypti mosquito larvae
a,
a
b
b
Tushar S. Basu Baul *, Keisham Surjit Singh , Xueqing Song , Alejandra Zapata ,
b
George Eng , Antonin Lycka , Anthony Linden
c
d,
**
a
Department of Chemistry, North-Eastern Hill University, NEHU Permanent Campus, Umshing, Shillong 793 022, India
b
Department of Chemistry and Physics, University of the District of Columbia, 4200 Connecticut Avenue, NW Washington, DC 20008, USA
c
Research Institute for Organic Syntheses, Rybitvi 296, CZ-532 18 Pardubice 20, Czech Republic
d
Institute of Organic Chemistry, University of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland
Received 22 July 2004; revised 26 August 2004; accepted 26 August 2004
Available online 25 September 2004
Abstract
The tri-n-butyltin(IV) complexes of 2-[(E)-2-(3-formyl-4-hydroxyphenyl)-1-diazenyl]benzoic acid and 4-[((E)-1-{2-hydroxy-5-
[(E)-2-(2-carboxyphenyl)-1-diazenyl]phenyl}methylidene)amino]aryls (aryls = 4-CH3, 4-Br, 4-Cl, 4-OCH3) have been synthesized
and characterized by 1H, 13C, 119Sn NMR, IR and 119mSn Mo¨ssbauer spectroscopic techniques in combination with elemental anal-
ysis. The crystal structures of two compounds, (Bu3Sn[O2CC6H4{N@N(C6H3-4-OH-5-CHO)}-o])n and (Bu3Sn[O2CC6H4-
{N@N(C6H3-4-OH(C(H)@NC6H4Cl-4))}-o])n, are reported.The crystallographic and 119Sn Mo¨ssbauer data both indicate that
the tributyltin complexes form single-stranded polymeric structures in which the carboxylate O atoms of each aryl ligand bridge
two Sn atoms. The Sn atoms have a slighly distorted trigonal bipyramidal coordination geometry with equatorial butyl groups
and carboxylate O atoms occupying axial positions. The 119Sn NMR spectroscopic data and the 1J(13C–119/117Sn) coupling constant
indicate a tetrahedral coordination geometry in non-coordinating solvents. The results of a toxicity study of a tributyltin compound
on the second larval instar of Aedes aegypti mosquito larvae are reported.
ꢀ 2004 Elsevier B.V. All rights reserved.
Keywords: Tributyltin; Carboxylates; 2-[(E)-2-(3-formyl-4-hydroxyphenyl)-1-diazenyl]benzoic acid; 4-[((E)-1-{2-hydroxy-5-[(E)-2-(2-carboxyphe-
nyl)-1-diazenyl]phenyl}methylidene)amino]aryls; NMR; Mo¨ssbauer; Crystal structure; Toxicity study
1. Introduction
*
Corresponding authors. Tel.: +91 364 272 2626; fax: +91 364
2550486/2721000.
**
Tel.: +41 44 635 4228; fax: +41 44 635 6812.
Salicylaldehyde and their metal derivatives are well
established [1–3]. More useful organic reagents having
the properties of salicylaldehyde together with other
E-mail addresses: basubaul@nehu.ac.in, basubaul@hotmail.com
(T.S. Basu Baul), alinden@oci.unizh.ch (A. Linden).
0022-328X/$ - see front matter ꢀ 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2004.08.038

T.S. Basu Baul et al. / Journal of Organometallic Chemistry 689 (2004) 4702–4711
4703
3
B
6
desired features, e.g., having an intense light absorption
in the visible region for colorimetric applications, have
also been reported. These organic reagents are com-
monly known as 5-(arylazo)salicylaldehyde (AAS) and
were used by several workers in order to characterize
U(VI) [4], Pd(II) [4], Co(II) [5], Cu(II) [6,7], Ni(II) [8],
Mn(II) [9], Sn(II) [10] and Sn(IV) [11] complexes in both
solid and solution states. A few transition metal com-
plexes also show semi conducting properties in the tem-
perature range 310–340 K [9]. Later, AAS were
condensed with mono aromatic amine which resulted
in 5-phenylazosalicylidene aniline (PASA) Schiff base
and its metal complexes, viz., Fe(III), Co(II), Ni(II)
and Cu(II) were prepared and characterized [12]. Re-
cently, a few Cu(II) complexes of some Schiff bases ob-
tained by condensation of AAS with di- and tri-amine
have also been reported and in one case the structure
of the complex was determined using single crystal X-
ray crystallography [13]. Although PASA type ligands
have been known for a long time, the extant literature
contains no report of the isolation and characterization
of metal or organometallic complexes of 4-[((E)-1-{2-
hydroxy-5-[(E)-2-(2-carboxyphenyl)-1-diazenyl]phenyl}-
HO
O
OH
2
4
2
A
5
1
5
2
N
N
1
1
3
4
N
3
4
C
6
6
R
5
Fig. 2. Generic structure of the ligand L2–5HH0. Abbreviations.
L2HH0: R = 4-CH3; L3HH0: 4-Br, L4HH0: 4-Cl, L5HH0: 4-OCH3,
where H and H0 represent hydroxyl and carboxyl protons, respectively.
the reasons for the structural variation found in
these systems, we now describe some tri-n-butyl-
tin(IV) complexes derived from (i) 2-[(E)-2-(3-formyl-4-
hydroxyphenyl)-1-diazenyl]benzoic acid (L1HH0) and,
(ii) 4-[((E)-1-{2-hydroxy-5-[(E)-2-(2-carboxyphenyl)-1-
diazenyl]phenyl}methylidene)amino]aryls
The generic structures of the ligand framework are shown
in Figs. 1 and 2.
(L2–5HH0).
2. Experimental
methylidene)amino]aryls. These ligands contain
a
carboxylate group in the ortho-position of the diazo-
forming aryl moiety of the ASA unit, which provides
an opportunity for synthesising a wide variety of com-
plexes of the hetero-functional ligand.
2.1. Materials
(Bu3Sn)2O (Merck), salicylaldehyde (Lancaster) and
the substituted anilines (reagent grade) were used with-
out further purification. The solvents used in the reac-
tions were of AR grade and dried using standard
procedures. Toluene was distilled from sodium benzo-
phenone ketyl.
In addition, tributyltin in the form of halides, oxides
and acetates, displays a large array of biocidal proper-
ties and is used extensively in wood preservatives and
in marine anti-fouling paints [14], although there has
been considerable environmental concern about their
latter use [15]. However, the tributyltin compounds have
not been shown to be neurotoxins, mutagens, terato-
gens, or carcinogens in humans [16]. Recently, some
tributyltin 5-[(E)-2-(aryl)-1-diazenyl]-2-hydroxybenzo-
ates have shown moderate activity towards the second
larval instar stage of the Aedes aegypti mosquito [17].
In addition to their commercial applications, trior-
ganotin carboxylates present an interesting variety of
structural possibilities [18,19]. In line with these develop-
ments and as part of a wider study designed to ascertain
2.2. Physical measurements
Carbon, hydrogen and nitrogen analyses were per-
formed with a Perkin–Elmer 2400 series II instrument.
IR spectra in the range 4000–400 cmꢀ1 were obtained
on a BOMEM DA-8 FT-IR spectrophotometer with
samples investigated as KBr discs. The 1H and 13C
NMR spectra of the ligands were acquired on a Bruker
Avance 500 spectrometer operating at 500.13 and 125.76
MHz, respectively. For the organotin compounds, the
1H, 13C and 119Sn NMR spectra were recorded on a
Bruker AMX 400 spectrometer and measured at
O
1
400.13, 100.62 and 149.18 MHz, respectively. The H,
13C and 119Sn chemical shifts were referred to Me4Si
set at 0.00 ppm, CDCl3 set at 77.0 ppm and Me4Sn set
at 0.00 ppm, respectively. The Mo¨ssbauer spectra of
the complexes in the solid state were recorded using a
Model MS-900 (Ranger Scientific Co., Burleson, TX)
spectrometer in the acceleration mode with a moving
source geometry. A 5 mCi Ca119mSnO3 source was used,
and counts of 30000 or more were accumulated for each
spectrum. The spectra were measured at 80 K using a
OH
2
3
5
O
1
2
3
4
N
B
1
4
N
OH
A
6
6
5
Fig. 1. Generic structure of the ligand, L1HH0.

4704
T.S. Basu Baul et al. / Journal of Organometallic Chemistry 689 (2004) 4702–4711
liquid-nitrogen cryostat (CRYO Industries of America,
Inc., Salem, NH). The velocity was calibrated at ambi-
ent temperature using a composition of BaSnO3 and
tin foil (splitting 2.52 mm sꢀ1). The resultant spectra
were analyzed using the Web Research software pack-
age (Web Research Co., Minneapolis, MN).
[(A) C1], 150.9 [(C) C1], 163.1 [C(H)@N], 163.8 [(B)
C2], 168.5 [CO2H)] ppm.
The other 4-[((E)-1-{2-hydroxy-5-[(E)-2-(2-carboxy-
phenyl)-1-diazenyl]phenyl}methylidene)amino]aryls,
viz., L2HH0, L3HH0 and L5HH0 were prepared analo-
gously by reacting L1HH0 with the appropriate anilines.
The characterization and spectroscopic data are pre-
sented below.
2.3. Synthesis of ligands
2.3.1. Preparation of 2-[(E)-2-(3-formyl-4-hydroxyphe-
nyl)-1-diazenyl]benzoic acid (L1HH0)
2.3.2.2. Preparation of 4-[((E)-1-{2-hydroxy-5-[(E)-2-
(2-carboxyphenyl)-1-diazenyl]phenyl}methylidene)ami-
no]methylbenzene (L2HH0). Recrystallized from abso-
lute ethanol to give reddish brown precipitate in 70%
yield; m.p.: 199–201 ꢁC. Anal. Found. 69.95; H, 4.65;
N, 11.58. Calc. for C21H17N3O3: C, 70.20; H, 4.76; N,
The ligand, L1HH0 was prepared by reacting 2-carb-
oxybenzenediazonium chloride with salicylaldehyde in
alkaline solution under cold conditions by the method
described in our earlier report [20]. The product was
purified by recrystallization from toluene; m.p.: 177–
179 ꢁC. Anal. Found. 62.20; H, 3.65; N, 10.35. Calc.
for C14H10N2O4: C, 62.22; H, 3.70; N, 10.37%.
11.69%. IR (cmꢀ1): 1725 m(OCO)asym
.
1H NMR
(DMSO-d6/500.13 MHz); dH: 2.38 [s, 3H, CH3], 7.18
[d, 1H, (B) H3], 7.32 [part of AA0BB0 system, 2H, (A)
H3 and H5], 7.43 [part of AA0BB0 system, 2H, (A) H2
and H6], 7.60 [m, 1H, (C) H4], 7.61 [m, 1H, (C) H6],
7.69 [m, 1H, (C) H5], 7.84 [m, 1H, (C) H3], 7.98 [dd,
1H, (B) H4], 8.29 [d, 1H, (B) H6], 9.16 [s, 1H,
C(H)@N], 12.91 [br s, 1H, CO2H], 14.16 [br s, 1H,
OH] ppm. 13C NMR (DMSO-d6/125.76 MHz); dC:
20.7 [CH3], 118.3 [(B) C3], 118.33 [(C) C6], 119.2 [(B)
C1], 121.4 [(A) C2 and C6], 126.5 [(B) C4], 129.2[(B)
C6], 129.3 [(C) C3], 129.9 [(C) C4], 130.1 [(A) C3 and
C5], 130.2 [(C) C2], 131.7 [(C) C5], 137.1 [(A) C4],
144.5 [(A) C1], 144.9 [(B) C5], 150.9 [(C) C1], 161.7
[C(H)@N], 164.5 [(B) C2], 168.5 [CO2H] ppm.
2.3.2. Preparation of 4-[((E)-1-{2-hydroxy-5-[(E)-2-
(2-carboxyphenyl)-1-diazenyl]phenyl}methylidene)ami-
no]aryls (L2–5HH0)
A typical procedure is described below.
2.3.2.1. Preparation of 4-[((E)-1-{2-hydroxy-5-[(E)-2-
(2-carboxyphenyl)-1-diazenyl]phenyl}methylidene)ami-
no]chlorobenzene (L4HH0). An equimolar amount of
p-chloroaniline (0.42 g, 3.36 mmol) in hot absolute eth-
anol solution (15 ml) was added to hot toluene (30 ml)
containing L1HH0 (0.91 g, 3.36 mmol) and the reaction
mixture was refluxed for 5 h. The water formed during
the reaction was removed using a Dean-Stark appara-
tus. The reaction mixture was concentrated to half of
the initial solvent volume on a hot plate, cooled to
room temperature and was kept overnight in a refriger-
ator whereupon a dark brown solid precipitated. The
precipitate was filtered, washed with absolute ethanol
(3 · 5 ml) followed by diethyl ether (2 · 5 ml), and then
dried in air. The crude product was washed with hexane
to remove any tarry materials and recrystallized from
ethanol to yield pure orange crystalline L4HH0 (0.78
g, 56%); m.p.: 225–226 ꢁC. Anal. Found. 63.20; H,
3.65; N, 11.13. Calc. for C20H14N3O3Cl: C, 63.24; H,
2.3.2.3. Preparation of 4-[((E)-1-{2-hydroxy-5-[(E)-2-
(2-carboxyphenyl)-1-diazenyl]phenyl}methylidene)ami-
no]bromobenzene (L3HH0). Recrystallized from abso-
lute ethanol to give an orange precipitate in 49% yield;
m.p.: 213–214 ꢁC. Anal. Found. 56.50; H, 3.30; N,
10.01. Calc. for C20H14N3O3 Br: C, 56.60; H, 3.32; N,
9.90%. IR (cmꢀ1): 1723 m(OCO)asym
.
1H NMR
(DMSO-d6/500.13 MHz); dH: 7.21 [d, 1H, (B) H3], 7.48
[part of AA0MM0 system, 2H, (A) H2 and H6], 7.60 [m,
1H, (C) H6], 7.61 [m, 1H, (C) H4], 7.70 [m, 1H, (C)
H5], 7.71 [part of AA0MM0 system, 2H, (A) H3 and
H5], 7.84 [m, 1H, (C) H3], 7.99 [dd, 1H, (B) H4], 8.31
[d, 1H, (B) H6], 9.16 [s, 1H, C(H)@N], 12.99 [br s, 1H,
CO2H], 13.57 [br s, 1H, OH] ppm. 13C NMR (DMSO-
d6/125.76 MHz); dC: 118.2 [(B) C3], 118.4 [(C) C6],
119.4 [(B) C1], 120.4 [(A) C4], 123.7 [(A) C2 and C6],
126.9 [(B) C4], 128.8 [(B) C6], 129.3 [(C) C3], 129.9 [(C)
C4], 130.2 [(C) C2], 131.7 [(C) C5], 132.5 [(A) C3 and
C5], 145.1 [(B) C5], 147.0 [(A) C1], 150.9 [(C) C1], 163.1
[C(H)@N], 163.8 [(B) C2], 168.5 [CO2H] ppm.
3.71; N, 11.06%. IR (cmꢀ1): 1725 m(OCO)asym 1H
.
NMR (DMSO-d6/500.13 MHz); dH: 7.21 [d, 1H, (B)
H3], 7.53 [part of AA0BB0 system, 2H, (A) H3 and
H5], 7.57 [part of AA0BB0 system, 2H, (A) H2 and
H6], 7.60 [m, 1H, (C) H6], 7.61 [m, 1H, (C) H4], 7.69
[m, 1H, (C) H5], 7.83 [m, 1H, (C) H3], 7.99 [dd, 1H,
(B) H4], 8.31 [d, 1H, (B) H6], 9.16 [s, 1H, C(H)@N],
12.97 [br s, 1H, CO2H], 13.59 [br s, 1H, OH] ppm.
13C NMR (DMSO-d6/125.76 MHz); dC: 118.1 [(B)
C3], 118.4 [(C) C6], 119.4 [(B) C1], 123.4 [(A) C2 and
C6], 126.9 [(B) C4], 128.7 [(B) C6], 129.3 [(C) C3],
129.5 [(A) C3 and C5], 129.9 [(C) C4], 130.2 [(C) C2],
131.6 [(A) C4], 131.7 [(C) C5], 145.1 [(B) C5], 146.6
2.3.2.4. Preparation of 4-[((E)-1-{2-hydroxy-5-[(E)-2-
(2-carboxyphenyl)-1-diazenyl]phenyl}methylidene)ami-
no]methoxybenzene (L5HH0). Recrystallized from
absolute ethanol to give a dark red precipitate in 54%

T.S. Basu Baul et al. / Journal of Organometallic Chemistry 689 (2004) 4702–4711
4705
yield; m.p.: 174–176 ꢁC. Anal. Found. 67.25; H, 4.60; N,
11.18. Calc. for C21H17N3O4: C, 67.21; H, 4.56; N,
The solvent was then distilled off to dryness and the res-
idue was dried in vacuo. The solid mass was washed
with hexane (2 · 5 ml) under cold conditions and was
recrystallized from hexane to yield orange crystals of
the desired product. Yield (0.74 g, 79%); m.p.: 63–64
ꢁC. Anal. Found: C, 55.76; H, 6.39; N, 5.20. Calc. for
C26H36N2O4Sn: C, 55.84; H, 6.48; N, 5.00%. IR
11.19%. IR (cmꢀ1): 1723 m(OCO)asym
.
1H NMR
(DMSO-d6/500.13 MHz); dH: 3.84 [s, 3H, OCH3], 7.08
[part of AA0MM0 system, 2H, (A) H3 and H5], 7.17
[d, 1H, (B) H3], 7.53 [part of AA0MM0 system, 2H,
(A) H2 and H6], 7.60 [m, 1H, (C) H4], 7.61 [m, 1H,
(C) H6], 7.70 [m, 1H, (C) H5], 7.83 [m, 1H, (C) H3],
7.96 [dd, 1H, (B) H4], 8.26 [d, 1H, (B) H6], 9.16 [s,
1H, C(H)@N], 12.90 [br s, 1H, CO2H], 14.24 [br s,
1H, OH] ppm. 13C NMR (DMSO-d6/125.76 MHz);
dC: 55.5 [OCH3], 114.8 [(A) C3 and C5], 118.2 [(B)
C3], 118.3 [(C) C6], 119.3 [(B) C1], 122.9 [(A) C2 and
C6], 126.3 [(B) C4], 128.9 [(B) C6], 129.3 [(C) C3],
129.8 [(C) C4], 130.2 [(C) C2], 131.7 [(C) C5], 139.8
[(A) C1], 144.9 [(B) C5], 150.9 [(C) C1], 158.9 [(A) C4],
160.4 [C(H)@N], 164.3 [(B) C2], 168.5 [CO2H] ppm.
(cmꢀ1): 1660 m(OCO)asym
.
2.4.2. Synthesis of Bu3SnL4H (4)
Bu3SnL1H (0.79 g, 1.41 mmol) in absolute ethanol
(30 ml) was added dropwise to a hot stirred ethanolic
solution (20 ml) containing p-chloroaniline (0.18 g,
1.41 mmol). The reaction mixture was then refluxed
using a Dean-Stark moisture trap and a water cooled
condenser for 3 h and filtered while hot. The filtrate
was collected and the volatiles were removed using a ro-
tary evaporator. The residue was dried in vacuo, washed
with hexane (2 · 1 ml), extracted into chloroform and
filtered. The crude product was obtained after evapora-
tion and this was then recrystallized from a chloroform-
hexane mixture (1:1, v/v) to yield orange crystals of the
desired product. Yield (0.83 g, 82.4%); m.p.: 88–90 ꢁC.
Anal. Found: C, 57.40; H, 6.19; N, 6.20. Calc. for
C32H40ClN3O3Sn: C, 57.43; H, 6.02; N, 6.27%. IR
2.4. Synthesis of the tributyltin complexes
Two typical methods are described below.
2.4.1. Synthesis of Bu3SnL1H (1)
The compound was synthesized by mixing L1HH0
(0.90 g, 3.33 mmol) and (Bu3Sn)2O (1.0 g, 1.67 mmol)
in 50 ml of anhydrous toluene in a 100 ml flask equipped
with a Dean-Stark moisture trap and a water cooled
condensor. The reaction mixture was refluxed for 7 h.
(cmꢀ1): 1616 m(OCO)asym
.
The other tributyltin complexes of the ligands, viz.,
L2HH0, L3HH0 and L5HH0 were prepared by reacting
Table 1
1H NMR data (d, ppm) for the tributyltin complexes in CDCl3
Ringa /Other/Sn–Bub protons
Proton number
Compound
1
2
3
4
5
A
2
3
5
6
8.20
–
7.24
7.24
7.24
7.24
7.19
7.56
7.56
7.19
7.25
7.25
7.25
7.25
7.32
6.97
6.97
7.32
7.10
8.14
B
C
3
4
5
6
7.84
7.49
7.49
7.49
7.15
7.99
–
7.12
8.01
–
7.12
8.01
–
7.11
7.98
–
8.04
8.05
8.04
8.02
3
4
5
6
–
–
–
–
7.82
7.53
7.44
7.53
7.82
7.52
7.44
7.52
7.82
7.42
7.42
7.51
7.82
7.51
7.43
7.51
Other
C(H)@O/C(H)@N
OH
CH3/OCH3
10.02
11.35
–
8.73
14.0
2.40
8.69
13.6
–
8.71
13.6
–
8.71
14.0
3.85
Sn–Bu
1*
2*
3*
4*
1.68
1.34
1.34
0.88
1.62
1.30
1.30
0.87
1.61
1.31
1.31
0.87
1.61
1.31
1.31
0.86
1.61
1.32
1.32
0.86
a
Refer to Fig. 1 (for compound 1) and Fig. 2 (for compounds 2–5) for the numbering scheme of the ligand skeleton (Ring A, B and/or C).
Numbering scheme for Sn–Bu skeleton as shown below:
b
4*
CH
1*
CH
3*
CH
2*
CH
.
Sn
2
3
2
2

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T.S. Basu Baul et al. / Journal of Organometallic Chemistry 689 (2004) 4702–4711
Bu3SnL1H with the appropriate anilines by following
analogous procedures. The characterization data of the
complexes are given below while the spectroscopic data
are presented in Tables 1–3.
were made at low temperature on a Nonius Kappa
CCD diffractometer [21] with graphite-monochromated
˚
Mo Ka radiation (k = 0.71073 A) and an Oxford Cryo-
systems Cryostream 700 cooler. Data reduction was per-
formed with HKL Denzo and Scalepack [22]. The
intensities were corrected for Lorentz and polarization
effects, and an empirical absorption correction based
on the multi-scan method [23] was applied. Equivalent
reflections were merged. The data collection and refine-
ment parameters are given in Table 4, and views of seg-
ments of the polymeric structures are shown in
Figs. 3–5. The structure of 1 was solved by employing
heavy-atom Patterson methods [24], followed by the
Fourier expansion routine of DIRDIF94 [25], while that
of 4 was solved by direct methods using SIR92 [26]. In
each structure, the non-hydrogen atoms were refined
anisotropically, while employing restraints when neces-
sary as described below.
2.4.3. Bu3SnL2H (2)
Yield: 80%; m.p.: 89–91 ꢁC. Anal. Found: C, 61.20;
H, 6.75; N, 6.53. Calc. for C33H43N3O3Sn: C, 61.10;
H, 6.68; N, 6.47%. IR (cmꢀ1): 1622 m(OCO)asym
.
2.4.4. Bu3SnL3H (3)
Yield: 78%; m.p.: 86–88 ꢁC. Anal. Found: C, 53.80;
H, 5.60; N, 5.98. Calc. for C32H40BrN3O3Sn: C, 53.86;
H, 5.65; N, 5.88%. IR (cmꢀ1): 1618 m(OCO)asym
.
2.4.5. Bu3SnL5H (5)
Yield: 93%; m.p.: 84–86 ꢁC. Anal. Found: C, 59.73;
H, 6.49; N, 6.50. Calc. for C33H43N3O4Sn: C, 59.63;
H, 6.52; N, 6.32%. IR (cmꢀ1): 1619 m(OCO)asym
.
In 1, there are two symmetry-independent fragments
of the polymer in the asymmetric unit, with each frag-
ment being comprised of four repeats of the principle
chemical unit. The root-mean-square fit of the atoms
2.5. X-ray crystallography
˚
Crystals of compounds 1 and 4 suitable for an X-ray
crystal-structure determination were obtained from hex-
ane and CHCl3/hexane, respectively. All measurements
of one fragment to those of the other is 0.17 A. This
close fit, plus the equivalence of the unit cell parameters
b and c, and the similarity of the unit cell parameters b
Table 2
13C NMR data (d, ppm) for the tributyltin complexes in CDCl3
Ringa/Other Sn–Bubcarbon
Carbon number
Compound
1
2
3
4
5
A
1
2
3
4
5
6
164.1
120.5
129.9
146.4
118.7
130.2
145.2
121.0
130.2
137.5
130.2
121.0
147.0
122.8
132.7
120.9
132.7
122.8
146.5
122.5
129.7
131.6
129.7
122.5
140.7
122.4
114.8
159.3
114.8
122.4
B
C
1
2
3
4
5
6
131.9
151.7
130.8
131.2
130.3
117.7
118.9
164.3
117.8
127.3
145.9
128.6
118.7
164.0
117.7
127.6
146.0
128.9
118.7
164.0
117.7
127.6
146.0
127.6
119.0
164.2
117.8
127.0
146.0
128.5
1
2
3
4
5
6
–
–
–
–
–
–
152.0
130.9
129.2
129.9
131.5
118.1
151.9
130.9
129.3
129.9
131.6
118.1
151.9
130.9
129.3
129.9
133.1
118.1
152.0
130.9
129.2
129.9
131.5
117.9
Other
C(H)@O/C(H)@N
CH3/OCH3
COO
196.6
–
172.7
161.0
21.1
172.5
162.5
–
172.4
162.4
–
172.6
159.7
55.6
172.7
Sn–Bu
1*
2*
3*
4*
16.8 (336)
27.8 (20)
27.3 (64)
13.8 (–)
16.8 (342)
27.9 (20 )
27.1 (64)
13.6 (–)
16.8 (362)
27.9 (20)
27.1 (64)
13.6 (–)
16.8 (362)
27.9 (20)
27.1 (64)
13.6 (–)
16.8 (342)
27.9 (20)
27.1 (64)
13.6 (–)
a
Refer to Fig. 1 (for compound 1) and Fig. 2 (for compounds 2-5) for the numbering scheme of the ligand skeleton (Ring A, B and/or C).
Numbering scheme for Sn–Bu skeleton as shown in Table 1. nJ(13C–119/117Sn) mean values are given in parentheses.
b

T.S. Basu Baul et al. / Journal of Organometallic Chemistry 689 (2004) 4702–4711
4707
Table 3
119Sn NMR data (d, ppm) and 119Sn Mo¨ssbauer parameters (mm sꢀ1) for the tributyltin complexes
Compound
119Sn NMR dataa
119Sn Mo¨ssbauer data
d
D
q = D/d
C1
C2
1
2
3
4
5
116.6
116.0
116.2
116.1
116.0
1.44
1.50
1.52
1.53
1.50
3.84
3.79
3.77
3.83
3.80
2.7
2.5
2.5
2.5
2.5
1.53
1.00
0.95
0.96
1.05
1.62
1.01
0.96
0.98
1.05
Parameters: d, isomer shifts; D, quadrupole splitting; C1 and C2, line widths.
In CDCl3 solution.
a
Table 4
Crystallographic data and structure refinement parameters for the
tributyltin complexes 1 and 4
1
4
Empirical formula
Formula weight
Crystal size (mm)
Crystal shape
C26H36N2O4Sn
559.18
C32H40ClN3O3Sn
668.74
0.05 · 0.15 · 0.22 0.17 · 0.25 · 0.27
Plate
160(1)
Triclinic
Prism
160(1)
Temperature (K)
Crystal system
Space group
Monoclinic
P21/n
ꢀ
P1
˚
a (A)
20.4071(4)
23.8710(4)
26.1342(4)
86.3718(9)
66.9966(8)
67.0400(7)
10730.4(3)
16
14.1136(2)
9.9787(1)
23.2971(3)
90
˚
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
105.3959(7)
90
3
˚
V (A )
3163.31(7)
4
1.404
Z
Dx (g cmꢀ3
)
1.384
0.983
0.711, 0.969
l (mmꢀ1
)
0.927
0.780, 0.860
Fig. 3. One of the two symmetry-independent three-unit segments of
the polymeric [Bu3SnL1H]n chain in the asymmetric unit of 1 (50%
probability ellipsoids).
Transmission factors
(min, max)
2hmax (ꢁ)
50
60
Reflections measured
Independent reflections (Rint
Reflection with I > 2r(I)
Number of parameters
Number of restraints
R(F) (I > 2r(I) reflns)
wR(F2) (all data)
176976
37789 (0.121)
21227
71033
9248 (0.062)
7081
)
2619
2805
390
18
0.056
0.148
0.034
0.082
1.01
GOF(F2)
1.02
1.07, ꢀ0.74
3
˚
max., min. Dq (e/A )
1.08, ꢀ0.59
and c, suggests that the independent fragments are al-
most related by a superstructure. If parameters b and c
were identical, the structure could be defined in the
higher symmetry space group C2/c, where only one frag-
ment would need to be defined in the asymmetric unit.
However, the difference between the unit cell parameters
b and c means that the superstructure relationship is only
approximate. This was confirmed in a test of the atomic
coordinates for a relationship from a higher symmetry
space group using the program PLATON [27], which indi-
cated that additional crystallographic symmetry was not
present. Nine of the 24 unique butyl groups in the struc-
ture are disordered over two conformations. Two sets of
Fig. 4. The asymmetric unit of [Bu3SnL4H]n 4 showing the atom-
labelling scheme (50% probability ellipsoids).
overlapping positions were defined for all atoms of one
butyl group, for the terminal propyl segment of five butyl
groups and for the terminal ethyl segment of another

4708
T.S. Basu Baul et al. / Journal of Organometallic Chemistry 689 (2004) 4702–4711
matrix least-squares procedures, which minimized the
function
P
2
wðF 2o ꢀ F 2cÞ . Corrections for secondary
extinction were not applied. One reflection, whose inten-
sity was considered to be an extreme outlier, was omitted
from the final refinement in the case of 1. All calculations
were performed using the SHELXL97 [28] program.
2.6. Biological tests
2.6.1. Preparation of the organotin stock solution
A stock solution (360 ppm) of the tributyltin com-
pound, 1, was prepared by dissolving the compound in
95% ethanol. The dissolution of the organotin com-
pound in the organic media was to facilitate the disper-
sion of the compounds in water.
2.6.2. Hatching of the mosquito eggs
Dried Aedes aegypti (Ae. aegypti) mosquito eggs were
obtained from the laboratory of Dr. Daniel Strickman,
Entomology Department at the Walter Reed Army
Institute of Research, Washington, DC. Approximately
0.01 g of the Ae. aegypti eggs were placed in a stainless
steel tray (30 cm · 20 cm · 5 cm) containing approxi-
mately 1l of deionized water. After 24 h, finely-ground
dog food (0.2–0.5 g) was added as the nutrient. The con-
tainer was kept at 25–29 ꢁC with a humidity of 80%. The
second instar stage was attained after 2–3 days.
Fig. 5. A three-unit segment of the polymeric [Bu3SnL4H]n chain in 4
(50% probability ellipsoids).
three butyl groups. Refinement of the site occupation
factors of the disordered groups indicated that most dis-
ordered conformations are approximately equally occu-
pied. Similarity restraints were applied to the
chemically equivalent bond lengths and angles within
all butyl groups, including the ordered ones. Bond length
restraints were also applied to any Sn–C bonds involving
a disordered butyl C atom. Furthermore, neighbouring
atoms within and between each conformation of the dis-
ordered butyl groups and within the ordered butyl
groups were restrained to have similar atomic displace-
ment parameters.
In 4, the terminal methyl groups in two of the butyl
ligands are disordered over two conformations. The
refinement of constrained site occupation factors for
the two orientations yielded values of 0.63(3) and
0.61(1) for the major conformation of each disordered
group. Similarity restraints were applied to the chemi-
cally equivalent bond lengths involving disordered C
atoms and neighbouring disordered atoms were re-
strained to have similar atomic displacement parameters.
The hydroxy H atom in 4 was placed in the position
indicated by a difference electron density map and its
position was allowed to refine together with an isotropic
displacement parameter. All of the remaining H atoms in
both 1 and 4 were placed in geometrically calculated posi-
tions and refined using a riding model where each H atom
was assigned a fixed isotropic displacement parameter
with a value equal to 1.2Ueq of its parent atom (1.5Ueq
for the methyl and hydroxy groups). The orientation of
each hydroxy O–H vector in 1 was optimised to corre-
spond with the direction that would bring the H atom
closest to the nearest hydrogen bond acceptor. Refine-
ment of each structure was carried out on F2 using full-
2.6.3. Larval toxicity studies
The toxicity studies were performed in 100 · 15 mm2
disposable Petri dishes using ten Ae. aegypti larvae in the
second instar stage. The Ae. aegypti larvae were trans-
ferred into the Petri dishes using a 100 ll micro-pipetter.
An additional 15 ml of water was added. No turbidity
was observed upon the addition of the water. Aliquots
of the organotin solution and deionized water were then
added to the Petri dish containing the larvae to give the
desired concentration. The total assay volume in each
case was 20 ml. Both positive and negative controls were
used in the assay. Each assay was done in triplicate. The
larvae were exposed to the organotin compounds for 24
h and the mortality rates for the mosquito larvae were
determined by visual counting. Mosquito larvae that
showed a slight reflex to disturbance were considered
alive. Probit analyses [29] were used to determine the
LC50 values (concentration at which the test compound
killed 50% of the tested organisms).
3. Results and discussion
3.1. Syntheses
The 2-[(E)-2-(3-formyl-4-hydroxyphenyl)-1-diazenyl]-
benzoic acid ligand (L1HH0) was prepared by the diazo-
coupling reaction between the anthranilic acid and

T.S. Basu Baul et al. / Journal of Organometallic Chemistry 689 (2004) 4702–4711
4709
salicylaldehyde in alkaline medium under cold condi-
tions. The 4-[((E)-1-{2-hydroxy-5-[(E)-2-(2-carboxyphe-
nyl)-1-diazenyl]phenyl}methylidene)amino]aryls ligand
frameworks were usually generated by the reaction of
Bu3SnL1H with the appropriate para-substituted ani-
line. The free ligands (L2–5HH0) were also prepared by
condensation of L1HH0 with the appropriate substituted
aniline in an anhydrous toluene-ethanol mixture. The
basic ligand framework is shown in Figs. 1 and 2 along
with the abbreviations and numbering schemes for
spectroscopic analyses. The details of their synthesis
and characterization are presented in the experimental
section.
Bu3SnL1H was obtained from the reaction of L1HH0
with (Bu3Sn)2O in anhydrous toluene in a 2:1 molar ra-
tio. The compound, Bu3SnL1H was used as the starting
materials for synthesizing the rest of the tributyltin com-
pounds. The other tributyltin derivatives, Bu3SnL2–5H,
were synthesized by condensing Bu3SnL1H with the
appropriate the para-substituted aniline in absolute eth-
anol. However, Bu3SnL2–5H could also be prepared by
reacting the appropriate 4-[((E)-1-{2-hydroxy-5-[(E)-2-
(2-carboxyphenyl)-1-diazenyl]phenyl}methylidene)ami-
no]aryl (Fig. 2) with (Bu3Sn)2O and the yield of the
product was found to be lower. Synthetic convenience
led to the choice of the former procedure. The character-
ization data of the complexes are given in the experi-
mental section. The complexes were obtained in good
yield and purity. They are stable in air and are soluble
in all common organic solvents.
nuclear single-quantum correlation (HMQC) and
heteronuclear multiple-bond connectivities (HMBC)
experiments. The conclusions drawn from the ligand
assignments were then subsequently extrapolated to
the complexes owing to the data similarity. The 1H
and 13C chemical shift assignment (Tables 2 and 3,
respectively) of the tributyltin moiety is straightfor-
ward from the multiplicity patterns, resonance intensi-
ties and also by examining the nJ(13C–119/117Sn)
1
coupling constants [30–32]. The H NMR integration
values were completely consistent with the formulation
of the products.
Four-coordinated tributyltin compounds, however,
exhibit couplings 1J(13C–119/117Sn) in the range 325–
390 Hz, and five-coordinated ones in the range 440-
540 Hz [33–36]. The tributyltin complexes of the
1
present investigation exhibit J(13C–119/117Sn) coupling
satellites in the range 336–362 Hz in CDCl3 solution,
suggesting that the tin atom is four-coordinate in solu-
tion. In contrast, a polymeric structure with five-coor-
dinate tin atoms is found in the solid state (see
Sections 3.4 and 3.5); this is possibly lost in solution
to generate a monomeric four-coordinated tetrahedral
structure [32]. The 119Sn NMR chemical shifts of trib-
utyltin complexes in CDCl3 solution are listed in Table
3. The complexes exhibit a single sharp resonance at
around 116 ppm, consistent with the range specified
for tetrahedral triorganotin compounds [35]. This is
further supported by our recent work on analogous tri-
organotin azocarboxylates [30–32].
3.4. 119Sn Mo¨ssbauer data
3.2. Infrared data
The Mo¨ssbauer spectra of the complexes are listed in
Table 3. The ratio of the quadrupole splitting value to
isomer shift value (q = D/d) can be used to distinguish
between the different coordination states of the central
tin atom [37]. Tin compounds which are four coordinate
have q values less than 1.8 while q values larger than 2.1
would indicate compounds with greater than four coor-
dination. As can be seen in Table 3, all the complexes
have q values greater than 2.1 suggesting that the com-
plexes have a coordination number greater than four.
Furthermore, the tributyltin complexes exhibited quad-
rupole splitting (QS) values of approximately 3.80 mm
Diagnostically important infrared absorption fre-
quencies for the carboxylate antisymmetric [masym(O-
CO)] stretching vibration of the ligands and the
complexes are given in the experimental section. The
assignment of the symmetric [msym(OCO)] stretching
vibration band could not be made owing to the com-
plex pattern of the spectra. The assignment of the
band is based on comparison with the spectra of the
free ligands (LHH0). The antisymmetric [masym(OCO)]
stretching vibrations for the uncomplexed ligands have
been detected at 1733 cmꢀ1 in L1HH0 and around the
1725 cmꢀ1 region for L2–5HH0. In the complexes, the
carbonyl stretching frequencies are found to be shifted
to lower wavenumber which is ascribed to carboxylate
coordination in accordance with earlier reports
[30,31].
s
ꢀ1. These values are within the range 3.0–4.1 mm sꢀ1
,
which are consistent with a trans-trigonal bipyramidal
geometry with a planar Bu3Sn unit and two axial carb-
oxylate oxygen atoms [38]. Further, the QS data for
complexes 1–5 matches closely with the data of com-
plexes having a trans-trigonal bipyramidal geometry in
a polymeric structure [31,32], which was subsequently
also found here from the crystal structures (see Section
3.5). The QS values for the complexes are in the same or-
der of magnitude, suggesting that they adopt the same
structural motif.
1
3.3. H, 13C and 119Sn NMR data
The 1H and C NMR data of L1HH0 were re-
13
ported in our earlier [20] and the signals were assigned
by the use of correlated spectroscopy (COSY), hetero-

4710
T.S. Basu Baul et al. / Journal of Organometallic Chemistry 689 (2004) 4702–4711
3.5. X-ray crystallography
R3SnO2CR0 compounds [32] and the general description
of the structure of [Me3Sn(O2CR0)]n (R0 = 2-[(E)-2-(2-
hydroxy-5-methylphenyl)-1-diazenyl]benzoate) given
The crystal structures of two of the tributyltin com-
plexes (1 and 4) have been determined. The two struc-
tures conform to the same motif in which the
carboxylate O atoms of a single aryl ligand bridge two
Sn atoms and the pattern then repeats itself to give a
continuous single-stranded polymeric structure, as illus-
trated in Figs. 3–5. The Sn atoms in each structure have
a slightly distorted trans-R3SnO2 trigonal bipyramidal
coordination geometry with equatorial butyl groups
and carboxylate O atoms occupying axial positions,
one being from each of two aryl ligands. The carboxy-
late C–O bond lengths are not equivalent, which shows
some distinction between the carbonyl and carboxylic
acid O atoms. Correspondingly, the Sn–O bond lengths
involving these O atoms are also not equivalent, with the
Sn–O bond to the carbonyl O atom being the longer, as
would be expected on electronic grounds. Selected geo-
metric parameters for 4 are given in Table 5 and the cor-
responding parameters for 1 are equivalent. The length
of the intramolecular Snꢁ ꢁ ꢁO(2) separation in 4 is
there applies equally well to 1 and 4. As in the earlier re-
port [32], the polymeric chain in the structures of both 1
and 4 propagates in a 21 screw fashion, with this being a
crystallographic 21 screw axis in the case of 4 and a non-
crystallographic pseudo-21 screw axis in 1. In 4, the re-
˚
peat Snꢁ ꢁ ꢁSn distance is 5.2601(2) A, which agrees very
well with the mean repeat distance found in other type
II carboxylate-bridged triorganotin species of
˚
5.19 0.21 A [39], i.e., the repeat distance is independ-
ent of the nature of the tin-bound substituents and carb-
oxylate residues. In 1, the eight symmetry-independent
˚
Snꢁ ꢁ ꢁSn distances range from 5.1288(9) to 5.548(1) A.
3.6. Larval toxicity studies
Compound 1 and the ligand were screened against
the second larval instar stage of the Ae. aegypti mos-
quito. The LC50 for compound 1 is 0.27 mg lꢀ1 while
the ligand had a 100-fold decrease (greater than 20 mg
˚
3.138(2) A, and is similar for the corresponding interac-
l
ꢀ1) in toxicity. These results clearly indicate that the
tions in 1. Although these distances are well inside the
sum of the van der Waals radii of the Sn and O atoms
˚
(ca. 3.6 A), there does not appear to be any significant
distortion of the trigonal bipyramidal coordination
geometry as a result of this contact.
toxicity of the compound is due to the tributyltin moiety
of the molecule. This is not surprising since it is known
that tributyltins have various biocidal activities [40]
including those against various mosquitoes [17,41].
The toxicities for a series of tributyl- and triphenyltin-
azocarboxylates previously screened against the second
larval instar stage of the Ae. aegypti mosquito [17] and
compound 1 were compared since the ligand structures
of the two systems are somewhat similar. The results indi-
cated that compound 1 is more effective in its activity than
either the tributyl- (0.53–1.23 mg lꢀ1) or triphenyltin
(1.82–3.50 mg lꢀ1) azocarboxylates reported earlier [17].
As the results indicated, the toxicity of compound 1 is sig-
nificant when compared with the triphenyl derivative.
This observation is in agreement with the work of Nguyen
et al. [42] in which several series of triorganotins were
screened against this same species of mosquito.
The toxicity of compound 1 is not as effective as
organophosphorus insecticides [43] in their larvicidal
capabilities; however, it should not be excluded as a pos-
sible larvicidal candidate. Its advantages lie in its biode-
gradability and lack of known resistance by this species
of mosquitoes. For example, many strains of Ae. aegypti
have shown some resistance to several organophospho-
rus insecticides [43,44], with that to Malathion being
the highest [43]. It has also been established that highly
toxic triorganotins biodegrade in the environment [45]
to non-toxic inorganic tin species through the progres-
sive removal of the organic groups attached to the tin
atom. These are important aspects for an insecticide.
Furthermore, some countries have banned the use of
organophosphorus compounds for the control of mos-
quitoes due to their toxic side effects [46]. In view of
In 4, the asymmetric unit of the crystal structure con-
tains just one of the principle chemical units, which then
repeats to form the polymeric structure. By contrast, the
asymmetric unit in 1 contains two symmetry-independ-
ent fragments of the polymer, with each fragment being
comprised of four repeats of the principle chemical unit.
Thus there are eight symmetry-independent Sn atoms in
the structure.
The hydroxy group in each ligand forms an intraligand
hydrogen bond with the adjacent aldehyde O atom in 1
and with the adjacent imino N atom in 4. Some of the bu-
tyl groups in each structure are disordered, as is common
for complexes involving the Bu3Sn core (see Section 2).
The structures of 1 and 4 correspond with the type II
polymeric motif described by Willem et al. for related
Table 5
a
˚
Selected bond lengths (A) and angles (ꢁ) for 4
Sn–O(1)
Sn–O(2)i
Sn ꢁ ꢁ ꢁ O(2)
2.213(2)
2.454(2)
3.138(2)
Sn–C(21)
Sn–C(25)
Sn–C(29)
2.143(2)
2.147(2)
2.134(2)
O(1)–Sn–O(2)i
O(1)–Sn–C(21)
O(1)–Sn–C(25)
O(1)–Sn–C(29)
O(2)i–Sn–C(21)
a
173.19(5)
96.25(7)
89.68(8)
93.12(7)
89.80(7)
O(2)i–Sn–C(25)
O(2)i–Sn–C(29)
C(21)–Sn–C(25)
C(21)–Sn–C(29)
C(25)–Sn–C(29)
84.55(7)
86.19(7)
120.58(9)
122.68(9)
115.88(9)
i
Atom labels with superscript refer to atoms from the next sym-
metrically-related ligand in the polymeric chain.

T.S. Basu Baul et al. / Journal of Organometallic Chemistry 689 (2004) 4702–4711
4711
[17] T.S. Basu Baul, S. Dhar, E. Rivarola, F.E. Smith, R. Butcher, X.
Song, M. McCain, G. Eng, Appl. Organomet. Chem. 17 (2003) 261.
[18] E.R.T. Tiekink, Appl. Organomet. Chem. 5 (1991) 1.
[19] E.R.T. Tiekink, Trends Organomet. Chem. 1 (1994) 71.
[20] T.S. Basu Baul, S.P. Pyke, K.K. Sarma, E.R.T. Tiekink, Main
Group Met. Chem. 19 (1996) 807.
these two advantages over organophosphorus insecti-
cides, in addition to the overall effectiveness of com-
pound 1 against the Ae. aegypti larvae, this compound
can be considered a good candidate for the control of
this species of mosquito larvae.
[21] R. Hooft, Kappa CCD Collect Software, Nonius BV, Delft, The
Netherlands, 1999.
[22] Z. Otwinowski, W. Minor, in: C.W. CarterJr., R.M. Sweet (Eds.),
Methods in Enzymology, Macromolecular Crystallography, Part
A, vol. 276, Academic Press, New York, 1997, pp. 307–326.
[23] R.H. Blessing, Acta Crystallogr., Sect. A 51 (1995) 33.
[24] P.T. Beurskens, G. Admiraal, G. Beurskens, W.P. Bosman, S.
Garcia-Granda, R.O. Gould, J.M.M. Smits, C. Smykalla,
PATTY: The DIRDIF program system, Technical Report of the
Crystallography Laboratory, University of Nijmegen, The Neth-
erlands, 1992.
4. Supplementary material
CCDC-244249 and CCDC-244250 contain the sup-
plementary crystallographic data for complexes 1 and
4, respectively. These data can be obtained free of
charge via www.ccdc.cam.ac.uk/conts/retrieving.html
(or from the Cambridge Crystallographic Data Centre,
12 Union Road, Cambridge CB2 1EZ, UK; fax: +44
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Acknowledgements
The financial support of the Department of Science &
Technology, New Delhi, India (Grant No. SP/S1/F26/
99, TSBB), the National Institutes of Health Minority
Biomedical Research Support Program, USA (Grant
No. GM08005, G E) and the Grant Agency of the Czech
Republic (Grant No. 203/03/1118, AL) are gratefully
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