Diorganotin(IV) dithiocarbamate complexes as chromogenic sensors of anion binding

Article abstract of DOI:10.1016/j.poly.2009.09.010

One dinuclear chlorodiphenyltin (IV) dithiocarbamate complex (1) and four mononuclear complexes of general formula Ph₂Sn(S₂CNR)Cl (2, 3, 5, and 6) have been synthesized and characterized both in solid-state and solution. X-ray struct

Full text of DOI:10.1016/j.poly.2009.09.010

Polyhedron 28 (2009) 3953–3966
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Diorganotin(IV) dithiocarbamate complexes as chromogenic sensors
of anion binding
Juan Pablo Fuentes-Martínez, Isaim Toledo-Martínez, Perla Román-Bravo, Patricia García y García,
*
Carolina Godoy-Alcántar *, Marcela López-Cardoso, Hugo Morales-Rojas
Centro de Investigaciones Químicas, Universidad Autónoma del Estado de Morelos, Av. Universidad 1001, C.P. 62209 Cuernavaca, Mexico
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 18 June 2009
Accepted 14 September 2009
Available online 17 September 2009
One dinuclear chlorodiphenyltin (IV) dithiocarbamate complex (1) and four mononuclear complexes of
general formula Ph2Sn(S2CNR)Cl (2, 3, 5, and 6) have been synthesized and characterized both in solid-
state and solution. X-ray structures for complexes 1, 3 and 6 demonstrated a five-coordination geometry
around of tin atoms, in which dithiocarbamate ligand chelates asymmetrically the metal center. As
shown by 119Sn NMR spectroscopy, five-coordination geometry observed in the solid-state remains in
solution. The stability of these chlorodiphenyltin(IV) dithiocarbamate complexes in the presence of bio-
logically relevant anions such as acetate, dicarboxylates of general formula ꢀOOC-(CH2)n-COOꢀ (n = 2–8),
dihydrogenphosphate, hydrogensulfate, and halides has been examined in acetonitrile solutions. For all
of these organotin(IV) complexes the displacement of the coordinated ligands (i.e., chloride and dithiocar-
bamate) from the organotin(IV) moiety occurred in the presence of monoanions like acetate, dihydrogen-
phosphate, hydrogensulfate and fluoride. A stepwise mechanism for ligand exchange is proposed based
on UV–Vis, 1H, 13C and 119Sn spectroscopic data, as well as mass spectrometry. From UV–Vis titration
experiments it was found that dicarboxylates with small spacers like malonate and succinate, acted dif-
ferently in the exchange of the dithiocarbamate group in comparison to other monoanionic O donor
ligands or dicarboxylates with longer chains, perhaps by following an intramolecular displacement of
the coordinated ligand.
Keywords:
Anion binding
Dithiocarbamate
Organotin complexes
Ligand-exchange
The lability of these organotin(IV) dithiocarbamate compounds in solution hampers their use as stably
host for anions, however, by taking advantage of the intrinsic chromogenic properties of free dithiocar-
bamate anions, or by attaching dithiocarbamate groups to well-known fluorescent moieties such as
antracene, these complexes can sense the presence of O-donor anions at very low concentrations by dis-
placement of the metal-coordinated dithiocarbamate.
Ó 2009 Elsevier Ltd. All rights reserved.
1. Introduction
tin(IV) centers [6]. These receptors were incorporated into poly-
meric membrane ion-selective electrodes and were highly selec-
Anion recognition by Lewis acid moieties has received attention
as an important strategy in developing supramolecular receptors
[1]. Several organometallic compounds containing tin(IV) as elec-
trodeficient center have been previously examined for ion recogni-
tion including macrocycles [2], cryptand-like [3] and calixarene
shaped receptors [4], as well as ferrocene based complexes [5]. In
general anion binding affinity was tested for monoanionic species
such as halides (Fꢀ, Clꢀ, Brꢀ) in solvents like chloroform or dichlo-
romethane using 119Sn NMR spectroscopy as the main detection
tool. Further attempts made by Dakternieks, Jurkshat and cowork-
ers were based on bis(haloorganostannyl)alkanes that linked two
tive for fluoride and phosphate ions, but somewhat unstable. A
recent example of fluoride sensing with bis(di-n-alkyl(fluoro)stan-
nyl)alkanes improved the performance of these ion carriers in
polymeric matrixes [7]. Organotin(IV) sensors of anions based on
optical signaling are scarce, interestingly, a recent report on tin(IV)
complexes of N-confused porphyrins showed remarkable affinity
and selectivity as fluorescent probes for halides, particularly fluo-
ride, with binding constants in the order of 106 Mꢀ1 in CH2Cl2 [8].
General interest in organotin complexes have been geared by
their potential therapeutic use as antifungal, antibacterial, and
antitumoral agents [9]. Mostly, these compounds are organotin(IV)
derivatives with carboxylates [10], aminoacids [11], heterocycles
[12], and various N, O, or S donor ligands [13], particularly dithio-
carbamates [14], given that sulfur ligands coordinated to diorgano-
tin moieties were regarded as very stable in comparison to other
ligands coordinated by N or O [15]. Further interest in the
* Corresponding authors. Tel./fax: +52 777 3297997 (H. Morales-Rojas).
E-mail addresses: cga@uaem.mx (C. Godoy-Alcántar), hugom@uaem.mx (H.
Morales-Rojas).
0277-5387/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2009.09.010

3954
J.P. Fuentes-Martínez et al. / Polyhedron 28 (2009) 3953–3966
structural features of organotin(IV) dithiocarbamate complexes is
based on the wide range of industrial applications such as chemical
vapor deposition processes, flame retardants, polymer stabilizers,
and non-linear optical materials [16].
2. Experimental
2.1. General procedures and methods
Dithiocarbamates as ligands are well known to bind strongly
and selectively to many metal ions [17], so in the past few years
self-assembly directed by metal–dithiocarbamate coordination
have emerged as a useful supramolecular methodology for the
preparation of macrocycles [18], cages [19], catenanes [20], and
nanoparticles [21,22]. In several of these reports transition metal
dithiocarbamate macrocycles displayed anion recognition with
the aid of amides or positively-charged motifs in the macrocycle
structure. For instance, Beer et al. recently reported an amide
functionalized dithiocarbamate ruthenium(II) bis-bipyridyl com-
pound that showed electrochemical sensing of anions such as
H2PO4ꢀ, AcOꢀ, and BzOꢀ [23]. The potential of organotin(IV) com-
plexes in metal-directed self-assembly of macrocyclic and
supramolecular structures have been exploited mainly by Höpfl
et al. employing dicarboxylates and dithiocarbamates as ligands
[24]. Solution chemistry of organotin carboxylates and dicarbox-
ylates have been studied extensively [24,25]. In contrast the solu-
tion chemisty of organotin dithiocarbamates is much less
explored, and to our knowledge, only one report on the use
organotin(IV) dithiocarbamate complexes as host for anions is
available [26].
A comprehensive exploration of organotin(IV) dithiocarbamate
complexes for ion recognition is worthwhile given that Lewis acid-
ity can be modulated by substitution at the organometallic center
and also by substitution at the ancillary ligand (i.e., chloride, or
dithiocarbamate) [27]. Herein, we report on the ligand-exchange
properties of a series of organotin(IV) dithiocarbamates complexes
1–6 (Fig. 1) towards a wide number of biologically relevant anions
such as carboxylates, dicarboxylates, dihydrogenphosphate,
hydrogensulfate, and halides. By taking advantage of the intrinsic
chromogenic properties of dithiocarbamate anions and by attach-
ing dithiocarbamate groups to well-known fluorescent moieties
such as antracene, these complexes can sense the presence of O-
donor anions at very low concentrations by displacement of the
metal-coordinated dithiocarbamate.
All reagents were of commercial grade and were used as re-
ceived. Ph2SnCl2, piperazine, pyrrolidine, and 9-(methylaminom-
ethyl)-antracene were commercially available and were used
without further purification. N-BOC-piperazine was prepared as re-
ported by Lowe and coworkers [28]. The sodium salts of dithiocar-
bamates were prepared by published literature methods [29].
Similarly, tetrabutylammonium salts of dithiocarbamates were
prepared starting from commercial tetrabutylammonium hydrox-
ide solutions in methanol.
IR spectra were recorded in the region 4000–500 cmꢀ1 as KBr
pellets using Bruker Vector 22 FTIR spectrometer. The 1H, 13C and
119Sn NMR spectra were obtained at room temperature on a Varian
Inova 400 spectrometer, using CDCl3, pyridine-d5 or CD2Cl2 as sol-
vent. The chemical shifts are relative to internal Me4Si (1H, 13C) and
external tetramethyltin (119Sn). The FAB mass spectra were mea-
sured on a 3-nitrobenzyl alcohol matrix in the positive ion mode
on a JEOL MStation JMS-700 instrument. The ESI mass spectra were
measured in the positive or negative ion mode using a JEOL MSta-
tion JMS-700 instrument. Elemental analyses were obtained in an
Elemental Vario ELIII TCD instruments using samples previously
dried for 2 h under high vacuum. The electronic absorption spectra
were recorded at 25 °C on a Hewlett-Packard 8452A diode-array
spectrophotometer, and emission spectra were recorded on a Per-
kin–Elmer LS55 spectrofluorimeter.
2.2. Synthesis of complex bis[chlorodiphenyltin(IV)]
piperazinyldithiocarbamate (1)
A solution of the disodium salt of the N0,N00-piperazinyldithioc-
arbamate (0.5 g, 1.772 mmol) in ethanol (20 mL) was treated with
diphenyltin dichloride (1.217 g, 3.544 mmol). The reaction mixture
was stirred for 24 h at room temperature. Then was filtered, the
resulting powder was recrystallized from a CH2Cl2–hexane mixture
afforded white solid of 1 (1.39 g, 84%), m.p. 230–32 °C. Anal. Calc.
for C30H28Cl2N2S4Sn2: C, 42.23; H, 3.31; N, 3.28. Found: C, 41.77;
Ph
Ph
S
S
Ph
Sn Cl
Ph
S
S
N
Sn Cl
N
Cl Sn
Ph
N
S
S
Ph
1
3
4
Ph
Ph
S
S
Sn Cl
Ph
Sn Ph
N
N
BOC
N
S
S
Ph
2
Ph
S
S
5
6
R = Me
Sn Cl
Ph
N
R
R = n-Bu
Fig. 1. Chemical structures of dithiocarbamate organotin (IV) complexes.

J.P. Fuentes-Martínez et al. / Polyhedron 28 (2009) 3953–3966
3955
H, 3.23; N, 3.595%. MS (FAB+, CHCl3) m/z: 817 (8) [M+ꢀCl], C30H28
-
128.9, 130.3, 135.9 and 142.2 (C–Ar); 192.1 (CS2). 119Sn NMR
(CDCl3): d ꢀ311.1.
ClN2S4Sn2+; 663 (2) C18H18ClN2S4Sn2+; 512 (4) C18H18ClN2S3Sn+;
435 (62) C12H13ClN2S3Sn+; 391 (30) C11H13ClN2S2Sn+; 305 (100)
C12H10SSn+; 273 (23) C12H10Sn+. IR (KBr) 3047w,
m
(C–H); 1493
s(C–S); 911w, (C–N); 693m
.
1H NMR (CDCl3): d 4.09 (8H, s)
2.6. Synthesis of the complex triphenyltin(IV)
pyrrolidinyldithiocarbamate (4)
m
m
(C@N); 1229s
as,(C–S); 446 m
m
m
s(CH2–N); 1000s
m
(Sn–S) cmꢀ1
NCH2; 7.46 (12H, m) H–Ar; 8.01 (8H, m) H–Ar. 13C NMR (CDCl3):
d 50.51 (N–CH2); 129.13, 130.66, 135.81 and 141.45 (C–Ar);
199.35 (CS2). 119Sn NMR (CDCl3): d ꢀ309.19.
This compound was prepared in similar fashion to 3, using the
sodium salt of pyrrolidinyldithiocarbamate (0.2 g, 1.18 mmol)
and triphenyltin chloride (0.456 g, 1.18 mmol) to give a white solid
(0.535 g, 91%). M.p. 147 °C. Anal. Calc. for C23H23NS2Sn: C, 55.66; H,
4.67; N, 2.82. Found: C, 55.31; H, 4.54; N, 3.24%. MS (FAB+) m/z:
497 (5) [M+], C23H23NS2Sn+; 420 (30) [M+ꢀPh] C17H18NS2Sn+; IR
2.3. Synthesis of the tetrabutylammonium salt of N0-BOC-piperazinyl-
N00-dithiocarbamate (L2-TBA)
(KBr) 3055w, 2947w
s(CH2–N); 1163m, 1066m, 999m, 950m
695w as,(C–S); 449m
(Sn–S) cmꢀ1 1H NMR (CDCl3): d 2.01 (4H,
m
(C–H); 1476s
m(C@N); 1439m, 1330m
An ethanolic solution of N-BOC-piperazine (0.56 g, 3 mmol in
10 mL) was treated with an equimolar amount of tetrabutylammo-
nium hydroxide (3 mL of 1 M solution in methanol) in presence of
CS2 (0.18 mL, 1 equiv.). The solution was stirred at room tempera-
ture by 6 h, during which turned out yellowish. Solvent was re-
moved by evaporation and the mixture lixiviated with Et2O
(3 ꢁ 15 mL) affording a pale green solid (1.19 g, 79%). M.p. 152–
153 °C. Anal. Calc. for C26H53N3O2S2: C, 61.98; H, 10.60; N, 8.34.
m
m
s(C–S); 911w, (C–N);
m
m
.
m) NCH2; 3.72 (4H, m); 7.37 (9H, m) H–Ar; 7.71 (8H, m) H–Ar.
13C NMR (CDCl3): d 27.0 (N–CH2CH2); 55.3 (N–CH2CH2); 128.6,
129.2, 136.9 and 142.2 (C–Ar); 196.4 (CS2). 119Sn NMR (CDCl3): d
ꢀ175.1.
2.7. Synthesis of complex chlorodiphenyltin(IV) 9-
Found: C, 59.76; H, 10.39; N, 7.99%. IR (KBr) 2964s, 2870s
m
(C–
(methylaminomethyl)-antracenyl dithiocarbamate (5)
H); 1671s
O); 1003s
m
(C@O); 1419m
m(N–CS2); 1373s m(C@N); 1249s
m
(C–
m
s(C–S2); 928m,
m
(C–N) cmꢀ1
.
1H NMR (CDCl3): d 0.95
A
solution of 9-(methylaminomethyl)-antracene (0.5 g,
(12H, t) CdH3, 1.40 (17H, m) C H2 and [C(CH3)3], 1.60 (8H, m)
2.26 mmol) in ethanol (20 mL) was treated with tetrabutylammo-
nium hydroxide (2.27 mL, 1.0 M solution in methanol, 1 equiv.)
and CS2 (0.14 mL, 2.26 mmol). The reaction mixture was stirred
for 18 h at room temperature. Diphenyltin dichloride (0.76 g,
2.26 mmol) was added after this time. A solid was formed after
2 h, the mixture was filtered, affording a yellow powder of 5
(1.07 g, 78.7%). M.p. 251–53 °C. Anal. Calc. for C29H24ClNS2Sn: C,
57.59; H, 4.00; N, 2.32. Found: C, 55.89; H, 3.79; N, 2.48%. MS
(FAB+) m/z: 570 (10) [M+ꢀCl], C29H24NS2Sn+; IR (KBr) 3055w,
c
CbH2, 3.35 (16H, m) C H2 and NCH2, 4.45 (8H, dd) NCH2. 13C
NMR (CDCl3):
[C(CH3)3], 43.69 (N–CH2), 49.98 (N–CH2), 59.32 C H2, 79.8
[C(CH3)3]; 155.1 (C@O), 214.6 (CS2).
a
c
d
14.0 CdH3, 20.08 C H2, 24.51 CbH2, 28.67
a
2.4. Synthesis of the complex chlorodiphenyltin(IV) N0-BOC-
piperazinyl-N00-dithiocarbamate (2)
The salt of tetrabutylammonium N-BOC-piperazinyldithiocar-
bamate (1.0 g, 1.98 mmol) in ethanol (10 mL) was treated with
diphenyltin dichloride (0.68 g, 1.98 mmol) in one portion as a solid.
The reaction mixture was stirred for 6 h at room temperature. Then
was filtered, and the resulting powder was recrystallized from a
CH2Cl2–hexane mixture afforded white-off solid of 2 (0.9 g, 79%),
m.p. 167–168 °C. Anal . Calc. for C22H27ClN2S4Sn: C, 46.38; H,
4.78; N, 4.92. Found: C, 45.62; H, 4.56; N, 4.94%. MS (FAB+) m/z:
m
(C–H); 1489
(C–N); 889w 731s, 562w
m
(C@N); 1392s
m
s(CH2–N); 1072s
m
s(C–S); 980w,
mas,(C–S); 449m
m
(Sn–S) cmꢀ1
.
1H NMR
(pyridine-d5): d 2.78 (3H, s) NCH3, 6.09 (2H, s) NCH2; 7.46 (12H,
m) H–Ar; 8.01 (8H, m) H-Ar. 13C NMR (pyridine-d5): d 40.6 (N–
CH3); 54.0 (N–CH2); signals for aromatics appeared from 125 to
136 ppm overlapping with solvent; 196.04 (CS2). 119Sn NMR (pyr-
idine-d5): d ꢀ328.02.
570 (10) [M+] C22H27ClN2O2S2Sn+, 535 (100) [M+ꢀCl], C22H27
-
2.8. Synthesis of chlorodiphenyltin(IV) 9-(butylaminomethyl)-
antracenyl dithiocarbamate (6)
N2S2Sn+; IR (KBr) 3008w,
m
(C–H); 1734s
(C–O); 1012w
1H NMR (CDCl3): d 1.48 (9H, s) [C(CH3)3], 3.57 (4H, dd)
m
(C@O); 1425m
m
(N–
CS2); 1364s
m
(C@N); 1221s
m
m
s(C–S2); 911w,
m(C–
N) cmꢀ1
.
To a solution of 9-formylanthracene in ethanol (0.5 g, 2.42 mol
in 20 mL) butylamine (0.177 g, 2.42 mmol) was added, and the
mixture was stirred under reflux by 4 h. After this time formation
of the imine was complete. The ethanolic solution was treated with
excess NaBH4 (0.183 g, 4.84 mmol) under stirring at 0 °C, then the
mixture was stirred to room temperature by 8 h. To the reaction
mixture 1 mL of water was added to eliminate excess of NaBH4.
The resultant solution mixture was concentrated to a yellow oil,
partitioned in water and dichloromethane, and from the organic
phase 9-(butylaminomethyl)-anthracene was obtained as a yellow
oil.
NCH2, 3.95 (4H, dd) NCH2; 7.47 (6H, m) H–Ar; 8.04 (4H, m) H–
Ar. 13C NMR (CDCl3): d 28.6 [C(CH3)3], 42.9 (N–CH2), 52.2 (N–
CH2), 81.3 [C(CH3)3]; 129.9, 135.9, 141.9 (C–Ar); 154.3 (C@O),
196.9 (CS2). 119Sn NMR (CDCl3): d ꢀ313.0
2.5. Synthesis of the complex chlorodiphenyltin(IV)
pyrrolidinyldithiocarbamate (3)
A solution of the sodium salt of pyrrolidinyldithiocarbamate
(0.2 g, 1.18 mmol) in ethanol (20 mL) was treated with diphenyltin
dichloride (0.407 g, 1.18 mmol). The reaction mixture was stirred
for 24 h at room temperature. Then was filtered, the resulting pow-
der was recrystallized from a CH2Cl2–hexane mixture afforded
white solid of 3 (0.374 g, 69%). M.p. 143–44 °C. Anal . Calc. for
C17H18ClNS2Sn: C, 44.91; H, 3.99; N, 3.08. Found: C, 42.44; H,
3.08; N, 3.79%. MS (FAB+) m/z: 420 (100) [M+ꢀCl], C17H18NS2Sn+;
The latter product (0.5 g, 2.26 mmol) was dissolved in 20 mL of
ethanol and treated with sodium hydroxide solution (2.5 mL,
2.42 mmol, 1 equiv.) and CS2 (0.15 mL, 2.26 mmol). The reaction
mixture was stirred for 18 h at room temperature. Diphenyltin
dichloride (0.832 g, 2.24 mmol) was added after this time. The so-
lid formed after 2 h was filtered affording a yellow powder of 6
(0.77 g, 49.4%). M.p. 150–152 °C. Anal. Calc. for C32H30ClNS2Sn: C,
59.41; H, 4.67; N, 2.17. Found: C, 59.68; H, 4.65; N, 2.46%. MS
(FAB+) m/z: 612 (10) [M+ꢀCl], C32H30NS2Sn+; IR (KBr) 3050w,
378 (50) [M+ꢀPh] C11H13ClNS2Sn+; IR (KBr) 3050w, 2943w
m(C-
H); 1503
N); 694w
m(C@N); 1153m
ms(CH2–N), 1066w ms(C–S); 945w, (C–
mas,(C–S); 448m m .
(Sn–S) cmꢀ1 1H NMR (CDCl3): d 2.01
(4H, m) NCH2; 3.69 (4H, m); 7.44 (6H, m) H–Ar; 8.08 (4H, m) H–
2958w, 2866w
1172m, 1101m
m
m
(C–H); 1484s
s(C–S); 988w, (C–N); 886w 732s,
m
(C@N); 1428s
m
s(CH2–N); 1225m,
as,(C–S); 446w
Ar. 13C NMR (CDCl3): d 27.0 (N–CH2CH2), 55.4 (N–CH2CH2);
m

3956
J.P. Fuentes-Martínez et al. / Polyhedron 28 (2009) 3953–3966
m
(Sn–S) cmꢀ1. 1H NMR (CDCl3): d 0.44 (3H, q) NCH3, 0.8 (2H, m), 1.3
organotin(IV) derivatives 1–6 were prepared by direct reaction of
the diphenyltin dichloride or triphenyltin chloride and the corre-
sponding salt of the dithiocarbamate. All compounds were charac-
terized by elemental analysis, mass spectrometry, FTIR, and
multinuclear NMR (1H, 13C and 119Sn) spectroscopy, as well as sin-
gle-crystal X-ray diffraction for compounds 1, 3 and 6. X-ray struc-
ture for 4 was previously reported [31].
(2H, m), 3.2 (2H, m), 5.99 (2H, s) NCH2; 7.46–7.61 (10H, m) H–Ar;
8.1–8.3 (8H, m) H–Ar, 8.6 (1H, s) H–Ar. 13C NMR (CDCl3): d 13.3
CH3, 19.9 C H2, 29.7 CbH2, 51.9 C H3; 52.89 (N–CH2-Arom);
123.3, 124.1, 125.4, 125.6, 127.8, 129.0, 129.5, 129.7, 130.1,
130.4, 131.4, 131.5, 135.9, 142.3 (C–Ar); 195.9 (CS2). 119Sn NMR
(CDCl3): d ꢀ313.8.
c
a
From the IR spectra of compounds 1–6 (Table 1) valuable struc-
tural information could be obtained since metal-coordinated
dithiocarbamates generally show strong to moderate characteristic
vibrations. It is accepted that metal–dithiocarbamate compounds
exhibit three main regions of interest; the ‘‘thioureide” band ap-
pears in the range 1450–1580 cmꢀ1 due to N–CSS stretching vibra-
tions. Other set of bands are observed in the range of 950–
2.9. X-ray crystallography
Suitable crystals of 1, 3 and 6 were obtained from DCM–hexane
(for 1) and acetonitrile solutions. X-ray diffraction studies were
performed on a Bruker-APEX diffractometer with a CCD area detec-
tor (kMo
= 0.71073 Å, monochromator: graphite). Frames were
Ka
1050 cmꢀ1 for the asymmetric
m
as(SCS) vibration and at approxi-
s(SCS) vibration [32]. In
collected at T = 293 and 100 K via
x
//-rotation at 10 s per frame
mately 450–700 cmꢀ1 for the symmetric
m
(
SMART) [30a]. The measured intensities were reduced to F2 and cor-
complexes 1–6 the N–CSS bonds in the dithiocarbamate functions
rected for absorption with SADABS (SAINT-NT) [30b]. Corrections were
vibrate within 1425–1503 cmꢀ1 indicating an increase in the car-
made for Lorentz and polarization effects. Structure solution,
refinement and data output were carried out with the SHELXTL-NT
program package [30c,d]. Non-hydrogen atoms were refined aniso-
tropically, while hydrogen atoms were placed in geometrically cal-
culated positions using a riding model. For compound 1 the
piperazine ring is disordered over two positions. SAME, SIMU and
DELU instructions have been used to model the disorder. Molecular
structure was illustrated by the SHELXTL-NT software package [30d].
bon-nitrogen double bond character. The mas(SCS) vibrations could
be identified in the region of 999–1101 cmꢀ1, always as a single
band which indicates mostly a symmetrical bonding according to
Bonati and Ugo criterion [33]; vibrations belonging to the N-alkyl
and SCS have similar frequencies, and often coupling is observed,
thus bands within 693–988 cmꢀ1 were assigned to these groups.
Finally, bands associated with m(Sn–S) vibrations appeared in the
region of 446–449 cmꢀ1 in similar fashion to other organotin(IV)
compounds [14,24f–h].
2.10. Solution phase experiments
The 1H NMR spectra for diphenyltin compounds 1–3, 5, and 6
exhibit the expected pattern in the aromatic region for the phenyl
groups on the tin atoms in which coupling Sn–C is observed; these
compounds also showed an upfield shift for the methylene groups
located alpha to the nitrogen atom on the dithiocarbamate com-
plex in comparison to the free amine precursor. Selected values
for 1H, 13C and 119Sn NMR spectroscopic data are included in Table
2. In particular complex 1 displayed a single signal in 4.09 ppm for
2.10.1. Preparation of tetrabutylammonium dicarboxylate salts
Tetrabutylammonium dicarboxylate salts were preparared
in situ by mixing 987
nitrile with 13
l
L of dicarboxylic acid (1 ꢁ 10ꢀ2 M) in aceto-
l
L of tetrabutylammonium hydroxide solution (40%
in methanol) affording a final concentration of the salt c.a.
1 ꢁ 10ꢀ2 M. Stock solutions were prepared freshly to carry out
titration experiments.
2.10.2. UV–Vis titrations
Table 1
UV–Vis titrations were measured at 25 °C in acetonitrile. Ali-
quots of the corresponding tetrabutylammonium anion stock solu-
tion (1 ꢁ 10ꢀ2 M) were added to the organotin(IV) dithiocarbamate
complex solution (i.e., 3.3 ꢁ 10ꢀ5 M for 1, 6.6 ꢁ 10ꢀ5 M for 2, and
7.0 ꢁ 10ꢀ5 M for 3–6), and the spectrum was recorded after each
addition. The spectral changes in absorbance were monitored
within the range k = 200–400 nm. Final concentrations of added
salt in the cuvette were within 8 ꢁ 10ꢀ6 to 4 ꢁ 10ꢀ4 M.
Selected data for vibrational frequencies for complexes 1–6.
Vibration (cmꢀ1
)
1
2a
3b
4b
5b
3055w 3050w
1489s 1484s
6c
m
m
m
m
m
m
m
(Caryl–H)
(N–CSS)
s(N–Calkyl
as(SCS)
as(N–Calkyl
s(SCS)
3047w 3008w
3050w
1503s
3055w
1476s
1493s
1229s
1000s
911w
693m
446m
1425s
)
1364m 1153m 1163m 1392m 1225m
1012s
910w
730w
449m
1066w
945w
735m
448m
999m
950m
728m
449m
1072m 1101m
)
980w
731m
449w
988w
732m
446w
(Sn–S)
a
Also showed the typical vibrations for
m
(C@O) and m(C–O) at 1734 s and
2.10.3. Fluorimetric titrations
1221 s cmꢀ1, respectively.
Fluorimetric titrations were measured at 25 °C in acetonitrile.
Aliquots of the corresponding tetrabutylammonium anion stock
solution (1 ꢁ 10ꢀ4 M) were added to the diorganotin(IV) dithiocar-
bamate complex solution (i.e., 1 ꢁ 10ꢀ7 M for 5). The emission
spectra was recorded after each addition, and the changes in fluo-
rescence intensity were monitored at kem = 380–600 nm using
kex = 368 nm. Final concentrations of added salt in the cell were
within 4 ꢁ 10ꢀ8 to 4.4 ꢁ 10ꢀ7 M. The experimental data were fitted
using non-linear least-squares regression for 1:1 binding isotherm
with Microcal Origin 5.
b
These compounds also showed vibrations for the alkyl chain at 2943 and
2947 cmꢀ1
.
c
Also showed vibrations for butyl chain at 2958 and 2866 cmꢀ1
.
Table 2
Selected 1H, 13C and 119Sn NMR spectroscopic data for compounds 1–6.a
Compound
1H NMR
13C NMR
13C NMR
119Sn NMR
d(CH2NCSS)
d(CH2NCSS)
d(CSS)
1
4.09
4.40
3.95
3.72
3.69
6.09
5.99
50.5
49.9
52.2
55.4
55.3
54.0
51.9
199.3
217.3
196.9
192.1
196.4
196.0
195.9
ꢀ309
–
L2-TBA
2
3
3. Results and discussion
ꢀ313
ꢀ311
ꢀ175
ꢀ328
ꢀ313
4
3.1. Preparation and spectroscopic characterization of complexes 1–6
5b
6
The coordination chemistry of dithiocarbamates is well known,
and often secondary amines are used as starting materials for the
ligand preparation, as these give more stable complexes [17]. The
a
In CDCl3.
In Pyridine-d6.
b

J.P. Fuentes-Martínez et al. / Polyhedron 28 (2009) 3953–3966
3957
Table 3
Crystallographic data for compounds 1, 3 and 6.
Crystal data
1a
3b
6a
Formula
C30H28C12N2S4Sn2
0.23 ꢁ 0.19 ꢁ 0.09
853.06
monoclinic
P2(1)/c
C17H18ClNS2Sn
0.57 ꢁ 0.45 ꢁ 0.34
454.58
monoclinic
P2(1)/c
C32H30ClNS2Sn
0.54 ꢁ 0.32 ꢁ 0.17
646.83
monoclinic
P2(1)/n
Crystal size (mm3)
Molecular weight (g molꢀ1
Crystal system
Space group
)
Cell parameters
a (Å)
b (Å)
10.0927(12)
13.0211(16)
25.681(3)
90
12.6949(14)
10.3570(12)
14.0426(16)
90
13.553(2)
14.847(3)
14.715(3)
90
c (Å)
a
(°)
b (°)
95.962(2)
90
3356.7(7)
4
1.919
1.688
105.297(2)
90
1780.9(3)
4
1.814
1.695
106.234(2)
90
2843.0(8)
4
1.511
1.731
c
(°)
V (Å3)
Z
l
(mmꢀ1
)
qcalc (g cmꢀ3
)
Data collection
h Limits (°)
hkl Limits
Number of collected reflections
Number of independent reflections (Rint
Number of observed reflectionsc
1.59 < h < 25.00
11, 12; ꢀ12, 15; ꢀ30, 27
16 672
5914 (0.0496)
4361
2.48 < h < 25.00
ꢀ15, 14; ꢀ12, 12; ꢀ16, 13
9607
3127 (0.0352)
2984
1.81 < h < 25.00
ꢀ14, 16; ꢀ17, 17; ꢀ17, 17
20 823
)
5004 (0.0260)
4798
Refinement
Rc,d
Rw
0.0912
0.2002
470
1.259
ꢀ0.743
1.419
0.0306
0.0785
199
0.953
ꢀ0.417
0.934
0.0352
0.0856
335
1.228
ꢀ0.334
0.618
e,f
Number of variables
Goodness-of-fit (GOF)
D
D
qmin (e Åꢀ3
)
qmax (e Åꢀ3
)
a
b
c
d
e
f
Data collection at T = 293 K.
Data collection at T = 100 K.
I > 2
r(I).
2
2
R =
R
(Fo ꢀ Fc2)/
R
Fo
.
All data.
Rw = [
½
R
w(Fo2 – Fc2)2/
R
w(Fo2)2]
.
the methylene groups CH2–N, that reveal the equivalence of these
protons, due a the interconversión between equal populations of
the two chair conformations of the piperazine ring. This is also sup-
ported by the signal observed in the 13C NMR at d 50.51 ppm as-
signed to the carbon atoms of the piperazine ring. The 13C NMR
signals for dithiocarbamate functions in these complexes fall in
the region at d 192.1–199.3 ppm, located upfield to the corre-
sponding free dithiocarbamate ligands [34].
dination mode. The short Sn–S bond lengths fall in the range of
2.444(6) Å (for 1) to 2.4808 Å (for 6), which are comparable with
the values reported for other diphenyltin(IV) dithiocarbamates like
Ph2Sn(S2CNEt2)Cl (2.4449(13) Å) and Ph2Sn(S2CNpiperidyl)Cl
(2.4737(7) Å) [35,37]. The Sn–S bond distance approximately trans
to the chloride substituent is longer, for instance in compound 1
the bond lengths were 2.944(2) Å and 2.826(11) Å for Sn(1)–S(2)
and Sn(2)–S(4), respectively, which are similar to other reported
dinuclear diorganotin(IV) structures such as [PhSn(S2CNEt2)-
(S)(CH2CH2CH2)SnPh(S2CNEt2)] with values ranging from 2.894(2)
to 2.9573(18) Å [38].
The Sn–Scoord bond distance in compounds 3 and 6 were
2.6766(9) and 2.6748(10) Å, which are similar to other reported
values for mononuclear diorganotin(IV) complexes like Ph2SnCl-
(S2CNEt2) (2.716 Å) [35,39]. The carbon-sulfur bond lengths of
approximately 1.74 and 1.71 Å in these complexes are also indica-
tive of the asymmetric coordination of the sulfur atoms with single
and double bonds, respectively.
The 119Sn NMR chemical shift values for diphenylchloride ti-
n(IV) compounds were found in the range ꢀ309 to ꢀ328 ppm (Ta-
ble 2), indicating that in solution the tin atoms maintained a penta-
coordinated geometry observed in X-ray structures (vide infra), and
in very good agreement with the shift displacements measured for
chlorodiphenyltin N,N-diethyldithiocarbamate, [Ph2Sn(Et2dtc)Cl]
(d = ꢀ327 ppm in CD2Cl2 [35], d = ꢀ325/ꢀ340 ppm in CDCl3 and
d = ꢀ311 ppm in the solid-state [36]).
3.2. X-ray crystallographic study
The coordination geometry around of tin atoms in these com-
pounds can be described as a distorted trigonal bipyramid. The
two carbon atoms of phenyl groups and one of the sulfur atoms
of the dithiocarbamate group occupying the equatorial positions
for each tin atom. The second sulfur atom of each dithiocarbamate
group and the chlorine atom occupying the axial positions with an-
gles Cl–Sn–Scoord of 153.5(5)° and 154.7(2)° for 1, 156.18(3) and
154.72(3) for 3 and 6, respectively, which are comparable with
the typical trigonal bipyramid in related dithiocarbamate com-
pounds [35,39,40].
Compounds 1, 3, and 6 gave single-crystals that were suitable
for X-ray diffraction analysis. The most relevant crystallographic
data and selected geometric parameters are summarized in Tables
3 and 4 (see also Supplementary Tables S1–S3 in support informa-
tion). In compound 1 the unit cell contains two independent mol-
ecules with different chair conformation of the piperazine ring. The
molecular structure of one of the conformers is shown in Fig. 2. The
molecular structure of mononuclear diphenyltin(IV) compounds 3
and 6 is shown in Fig. 3.
In compound 1, two different sets of nitrogen–carbon bonds are
observed, the single N–C in the range 1.448–1.478 Å in the hetero-
The tin centers in these complexes are five-coordinated having
the dithiocarbamate groups with an anisobidentate chelating coor-

3958
J.P. Fuentes-Martínez et al. / Polyhedron 28 (2009) 3953–3966
Table 4
3.3. Solution phase behavior of compounds 1 and 2 in the presence of
anions
Selected bond lengths (Å), and bond angles (°) of compounds 1, 3, and 6.
1a
3
6
Initially anion binding experiments were carried out with
bis(chlorodiphenyltin(IV)) complex 1 using as potential guest the
following anions: chloride, acetate (AcOꢀ), and dicarboxylates of
general formula ꢀOOC-(CH2)n-COOꢀ (n = 2–8) as tetrabutylammo-
nium salts in acetonitrile solutions. Complex 1 holds two organotin
centers separated by 11.446 Å, suitable to possibly bind some of
the dicarboxylates anions in cooperative fashion. The use of a polar
organic solvent like acetonitrile instead of chloroform or dichloro-
methane is preferred due to the higher stability of the solutions
and better reproducibility.
Bond lengths (Å)
Sn–C
2.087(12)
2.125(11)
2.110(12)
2.102(11)
2.441(3)
2.441(3)
2.944(2)
2.826(11)
2.457(6)
2.444(6)
1.740(16)
1.706(16)
1.728(16)
1.697(13)
1.340(2)
1.321(17)
2.136(3)
2.142(3)
2.132(3)
2.136(3)
Sn–Cl
Snꢂ ꢂ ꢂS
Sn–S
C–S
2.4678(9)
2.6766(9)
2.4549(9)
2.4557(10)
2.6748(10)
2.4808(9)
1.722(3)
1.742(3)
1.744(3)
1.716(3)
Complex 1 showed an electronic absorption spectra in acetoni-
trile at 25 °C with characteristic bands for
p
ꢀ
–
p
* transitions in the
UV region and absorption coefficients of
252 = 38600 Mꢀ1 cmꢀ1
,
C–Ndtc
1.303(4)
1.316(4)
and ꢀ
286 = 13200 Mꢀ1 cmꢀ1. The spectrum was stable for several
days at room temperature. Fig. 4 shows the changes in the absorp-
tion spectra during the titration of complex 1 (3.5 ꢁ 10ꢀ5 M) with
different amounts of chloride, acetate, and glutarate in CH3CN.
Qualitatively the spectral changes occurring in response to an
increasing concentration of the anion are different in each case.
For instance, a decrease in the absorption bands located at kmax
252 and 286 nm was observed upon the addition of chloride
(Fig. 4a), conversely the addition of acetate caused a decrease in
the absorption bands of complex 1 along with the appearance of
two new absorption bands in the region of kmax 274 and 308 nm
(see Fig. 4b). In the latter case an isosbestic point is clearly seen.
Titrations of complex 1 with glutarate dianion and other dicarbox-
ylates (Supplementary Fig. S1) also caused the appearance of new
absorptions bands at longer wavelengths similar to the titration
with acetate, however, the spectral changes were not as smooth
and the isobestic was not observed (see Fig. 4c for glutarate).
A comparison of the changes in the molar absorption coefficient
at k = 300 nm during titration of compound 1 with chloride, ace-
tate, malonate, glutarate, and succinate is shown in Fig. 5. Only
in the presence of the carboxylate anions the bands at longer
wavelengths raised concomitant to the addition of the anion. Note
that there are differences in the curves displayed by acetate and
dicarboxylates anions, for instance, dicarboxylates such as malon-
ate, succinate or glutarate started a steep increase of the absorp-
tion coefficient at about 1 molar equivalent of the added anion
Bond angles (°)
C–Sn–C
119.9(5)
119.1(5)
97.4(3)
98.7(3)
98.4(3)
96.7(3)
67.7(8)
66.2(2)
153.5(5)
154.7(2)
87.0(3)
87.0(3)
119.8(5)
119.3(3)
118.61(12)
120.32(12)
C–Sn–Cl
94.49(9)
98.31(10)
95.85(10)
97.32(9)
S–Sn–S
70.37(3)
69.08(3)
Cl-Snꢂ ꢂ ꢂScoord
Cl–Sn–Scov
S–C–S
156.18(3)
86.85(3)
154.72(3)
86.84(3)
117.54(19)
115.58(18)
a
There are two independent molecules with different chair conformation of the
piperazine ring.
cycle of the bis-dithiocarbamate ligand are significantly longer
than the exocyclic in 1.34 and 1.321 Å for N(1)–C(1) and N(2)–
C(6) suggesting a partial double bond character. In the mononu-
clear compounds 3 and 6, this double character is more evident
having even shorter nitrogen-carbon bonds with values of
1.303(4) and 1.316(4), respectively. These data are consistent with
the IR data shown in Table 1 (vide supra). The sp2 hybridization of
the nitrogen atoms is also supported by the angles nitrogen (C–
N–C) 360°.
P
Fig. 2. Molecular structure of dinuclear compound 1. Ellipsoids are shown at the 50% probability level.

J.P. Fuentes-Martínez et al. / Polyhedron 28 (2009) 3953–3966
3959
Fig. 3. Molecular structures of mononuclear compounds 3 (left) and 6 (right). Ellipsoids are shown at the 50% probability level.
whereas addition of acetate increases absorption afꢀter two molar
equivalents. Other O donor monoanions like H2PO4 also showed
curves similar to acetate (Supplementary Fig. S1).
the 1H NMR signals corresponding to the piperazinyl moiety
CH2–CS2 or CH2–N-BOC, however, the aromatic protons bound to
the tin(IV) center were shifted to higher fields. Upon the addition
of a second equivalent of the acetate, the CH2–CS2 signals shifted
towards lower fields nearly to the region corresponding to the free
dithiocarbamate anion. The signals corresponding to CH2–N-BOC
also suffered a displacement to higher fields.
Above observations were in full agreement with the changes in
the 13C and 119Sn NMR spectrum for these mixtures summarized in
Table 5 and the reaction sequence proposed in the Scheme 1.
13C NMR signal for CSS originally located at d 195.45 ppm for
complex 2 is displaced to lower fields (199.38 ppm) in the
presence of one molar equivalent of acetate, thus indicating
the formation of an intermediate complex 2a (see Scheme 1),
in which dithiocarbamate group is still coordinated to the tin
center and only chloride is displaced; addition of a second molar
equivalent of acetate anion caused a greater shift to 218 ppm, a
region usually assigned to the free dithiocarbamate anion (for
instance, ligand L2 shows d 217.3 in CD3CN see Table 2). The
intermediate species 2a is more likely to be a neutral complex
where one acetate has substituted chloride in a stepwise fashion
changing tin(IV) coordination geometry from pentacoordinated
to an hexacoordinated complex. This coordination geometry has
In these experiments the absorption band at 300 nm reached
saturation when excess of the anion salt was added, however,
while for acetate about 12 molar equivalents of the anion were re-
quired, dicarboxylates such as malonate, succinate or glutarate dis-
played a maximum at about 4 molar equivalents, leveling off at the
same absorption coefficient as in the titration with acetate (see
Fig. 5). Attempts to fit the experimental titration plots to the for-
mation of a 1:1 or 1:2 host–guest complexes failed, indicating that
a more complicated process was taking place. Note also that the
behavior of dicarboxylates is particularly odd because their curves
go through a maximum.
In order to assign the absorption bands appearing at longer
wavelengths during the experiments described above, UV–Vis
and 1H NMR titration experiments were performed using chlorodi-
phenyltin(IV) complex 2, in which only one organotin(IV) center is
present.1 Changes of the absorption coefficient at 301 nm during
titration of complex 2 with acetate, succinate and glutarate as TBA
salts in acetonitrile solutions are depicted in Fig. 6. In general these
curves showed a similar behavior for carboxylate anions with com-
plex 2 as in titrations of complex 1. A pure sample of the tetrabutyl-
ammonium N-BOC-piperazinyl-1-carbodithioate salt (i.e., L2-TBA)
was also prepared, dissolved in acetonitrile and examined by UV–
Vis spectroscopy. The maximum of the absorption bands fully agree
with those observed during the titration experiments with complex
2 (ꢀ268 = 12100 Mꢀ1 cmꢀ1, ꢀ300 = 12500 Mꢀ1 cmꢀ1 in acetonitrile),
indicating that the dithiocarbamate groups are indeed being dissoci-
ated by the carboxylate ions from the tin coordination sphere [41].
Further support was obtained from 1H NMR titration experi-
ments between AcOTBA and complex 2 in a deuterated acetonitrile
solution. Fig. 7 shows the 1H NMR signals for complex 2 in the ab-
sence of acetate and in the presence of about one and two molar
equivalents of the salt. For comparison the spectrum of the corre-
sponding dithiocarbamate salt L2-TBA and AcOTBA were also
included.
been previously seen with macrocycles derived from
c-amino-
acid dithiocarbamates and diorganotin(IV) centers as depicted
below for 7 and 8 [26].
O
N
R
R
O
7 R= Ph
S
S
Sn
R
Sn
S
S
8 R= n-Bu
O
R
N
O
Furthermore, the 119Sn NMR signal for the equimolar mixture of
2 and AcOTBA appeared at d ꢀ374.8 (see Table 5 below), in very
good agreement with the chemical shift displacement found for
diphenyltin(IV) macrocycle 7 (d ꢀ371.6 ppm in CDCl3) that con-
tains both carboxylate and dithiocarbamate groups coordinated
to the tin center.
After 1 molar equivalent of acetate anion had been added to
complex 2, only slight chemical shift displacements occurred for
1
Low solubility of complex
1 in acetonitrile hampered its use at higher
concentrations required for NMR experiments.

3960
J.P. Fuentes-Martínez et al. / Polyhedron 28 (2009) 3953–3966
organotin(IV) dithiocarbamate complexes involved in anion recog-
3.5
3.0
2.5
2.0
1.5
1.0
0.5
nition was not fulfilled because dithiocarbamate ligands did not re-
main within the coordination sphere in the presence of carboxylate
anions; nevertheless, the process of binding a new ligand is directly
indicated by the appearance of the absorption bands at longer
wavelengths (i.e., 300 nm), corresponding to the free dithiocarba-
mate ligand. Certainly, free dithiocarbamate can be detected by
other means like 1H NMR, however, the intrinsic chromogenic
properties of dithiocarbamate anion can be viewed as advanta-
geous because it becomes a reporter of the binding event and also
allows for a direct comparison of the binding ability of different an-
ions for the organotin(IV) moiety in solution.
a
To this aim, we studied in further detail more simple di- and tri-
organotin(IV) complexes 3 and 4 derived from pyrrolidine (for
their synthesis see Section 2). Titrations of these compounds were
monitored by following spectral changes in the UV region, in par-
ticular, the increase of the band located at 294–295 nm. A compar-
ison of the changes in the molar absorption coefficient at 294 nm
during titration of compound 3 with several anions including ha-
lides (chloride, fluoride, and bromide), carboxylates (acetate, maꢀl-
0.0
3.5
225
250
275
300
325
350
375
400
λ (nm)
3.0
2.5
2.0
1.5
1.0
0.5
onate, glutarate, and succinate) and other O donor ligands (H2PO4
,
b
c
HSO4ꢀ) is shown in Fig. 8. Three types of behaviors can be distin-
guished: (i) dicarboxylates (malonate, succinate, and glutarate)
rapidly increased the intensity of the absorption at anion/complex
concentration ratios lower than two and displayeꢀd a transient max-
imum in the observed
Dꢀ
294; (ii) AcOꢀ, H2PO4 and Fꢀ also in-
creased the absorption at 294 nm but in a more steady fashion,
ꢀ
and (iii) Clꢀ, Brꢀ, and HSO4 did not show any enhancement of
0.0
3.5
the absorption within the concentration range explored (i.e., about
ten times excess anion over 3).
225
250
275
300
325
350
375
400
λ (nm)
The general trends of the results with chlorodiphenyltin(IV)
complex 3 are similar to those obtained previously with complexes
1 and 2, however titration plots of monoanions with 3 allowed to
further note that anions like acetate, dihydrogenphosphate, and
fluoride – all able to fully displace the dithiocarbamate group-
showed differences in their titrations curves (Supplementary
Fig. S2), pointing out that the interplay of affinities between the
incoming anion and the coordinated ligand for the diphenyltin(IV)
moiety is of great importance. In this regard, hydrogen sulfate,
chloride and bromide anions displayed lesser affinity than dithio-
carbamates for diphenyltin(IV).
The mechanism that operates in the cleavage of 3 by carboxyl-
ates must be to some extent similar to the proposed in Scheme 1
for complex 2 in the presence of acetate anion. In a mixture of
complex 3 (1.3 ꢁ 10ꢀ2 M) and malonate (0.33 M as TBA salt) in
acetonitrile, it was possible to observe the intermediate species
3a (m/z 521, FABꢀ) indicating that displacement of chloride oc-
curred before the exchange of the dithiocarbamate group. In the
same mixture it was also observed a diphenyltin(IV) product with
m/z 256 (FAB+). The only feasible structure matching this result is
3b (below), which pointed out to an intramolecular displacement
of the dithiocarbamate group by the remaining free carboxylate
in the coordinated malonate. It is reasonable to expect that this
kind of mechanism also holds for other small dicarboxylates like
succinate and glutarate but not for the larger members of this
group.
3.0
2.5
2.0
1.5
1.0
0.5
0.0
225
250
275
300
325
350
375
400
λ (nm)
Fig. 4. Changes in the absorption spectra during the titration of 1 (3.5 ꢁ 10ꢀ5 M)
with different quantities of (a) chloride (0–5.0 ꢁ 10ꢀ4 M), (b) acetate (0–
4.7 ꢁ 10ꢀ4 M) and (c) glutarate (0–2.1 ꢁ 10ꢀ4 M) as TBA salts in CH3CN. The arrows
indicate the spectral changes occurring in response to an increasing concentration
of anion.
Evidence that the mechanisms proposed in Scheme 1 may also
be valid for compound 1 was obtained from mass spectrometry. In
a mixture of 1 (0.01 M) and excess of AcOTBA, peaks corresponding
to the species Ph2Sn(AcO)2 (m/z 392, FAB+) were observed. Simi-
larly, in a mixture of 2 (0.01 M) and excess of AcOTBA peaks of
L2 anion were observed (m/z 262, FABꢀ).
O
Ph
Sn
3.4. Compounds 3 and 4 in the presence of anions
S
S
O
O
Ph
Ph
O
O
O
O
CH2
N
The ligand-exchange process of the organotin(IV) complexes 1
and 2 in the presence of carboxylate anions is explained by the
stepwise reactions occurring at the tin center as indicated in
Scheme 1, and apparently there is no influence of other structural
features in these complexes. Thus, the expectation of stable
Sn
Ph
O
3a
3b

J.P. Fuentes-Martínez et al. / Polyhedron 28 (2009) 3953–3966
3961
35000
30000
25000
20000
15000
10000
5000
0
malonate
succinate
glutarate
acetate
chloride
0
2
4
6
8
10
12
14
16
[anion]/[1]
Fig. 5. Changes of absorption coefficient at 300 nm during the titration of 1 (3.5 ꢁ 10ꢀ5 M) with different quantities of (a) chloride (0–5.0 ꢁ 10ꢀ4 M), (b) acetate (0–
4.7 ꢁ 10ꢀ4 M), (c) dicarboxylates like malonate, succinate and glutarate (0–2.1 ꢁ 10ꢀ4 M) as TBA salts in CH3CN.
change. Titration data for complex 4 with AcOꢀ and Fꢀ were ade-
16000
14000
12000
10000
8000
6000
4000
2000
0
quately fitted to a 1:1 binding model obtaining the following
constants of 460 34 Mꢀ1 and 8572 716 Mꢀ1, for Fꢀ and AcOꢀ,
respectively. However, titration with dihydrogenphosphate
showed a different curvature and do not fit well to a 1:1 binding
model.
The ligand-exchange behavior of these acyclic organotin(IV)
complexes studied here (1–6) is markedly different to the observed
in the cases of macrocyclic compounds 7 and 8 [26]. In these
macrocycles acetate bound weakly (about 15 Mꢀ1 in chloroform
solution), and they were stable at equimolar host–guest concentra-
tions. Ligand-exchange of the dithiocarbamate functionality hap-
pened under a high excess of the acetate anion over 8 (ꢃ200-fold),
indicating that 8 is less prone to decomposition than any of the
acyclic complexes.
malonate
glutarate
acetate
0
1
2
3
4
5
6
3.5. Compounds 5 and 6 in the presence of anions
[anion] / [2]
Among optical probes and sensors, those displaying fluores-
cence signaling are usually preferred given the enhanced detection
limit and sensibility in comparison to measuring the absorbance in
solution [42]. Neither diorganotin(IV) complexes nor dithiocarba-
mate anions displayed intrinsic fluorescence or phosphorescence,
therefore we seek to add this feature by employing a well-known
fluorescence moiety such as antracene linked to the dithiocarba-
mate ligand. There are several examples in which 9-(amino-
methyl)anthracenyl unit is used in conjunction to chelating
ligands to detect both anions and cations [43,44]. Typically fluores-
cence of the anthracenyl moiety is quenched by the benzylic nitro-
gens due to PET. Fluorescence enhancement is then detected as an
indication of a binding event or protonation on the amine site. In
this regard, a related ligand containing anthracenyl and dithiocar-
bamate groups linked by a piperazine moiety reported a threefold
quenching of fluorescence of the free ligand upon complexation to
a Cu(II) center [44].
Fig. 6. Changes of absorption spectra during the titration of 2 (6.6 ꢁ 10ꢀ5 M) with
different quantities of (a) acetate (0–4.7 ꢁ 10ꢀ4 M), (b) malonate (0–3.6 ꢁ 10ꢀ4 M),
and (c) glutarate (0–3.6 ꢁ 10ꢀ4 M) as TBA salts in CH3CN.
For the sake of comparison, UV–Vis titrations with complex 4
and the same set of anions used with 3 were studied and the re-
sults are depicted in Fig. 9. Note that complex 4 bears only one
exchangeable ligand in its structure (i.e., N-pyrrolidinyldithiocar-
bamate), and therefore it was expected that titration curves show
different features than those observed for 3 (see Fig. 8). Dicarbox-
ylates increased quite steeply the absorption at this wavelength in
comparison to AcOꢀ, Fꢀ and H2PO4ꢀ, however, the transient maxi-
mum observed with complex 3 was not longer present, indicating
that in this case there is a direct displacement of the dithiocarba-
mate by the incoming anion. Absorption coefficient at 295 nm sat-
urate at the same value at the end of the titrations plots for all
anions that were able to displace the dithiocarbamate group. Anio-
nic species such as Brꢀ, and HSO4ꢀ did not significantly change the
absorption even at a large excess of the anion over 4, and there was
only a slight increase with Clꢀ. These data show that even simple
triorganotin dithiocarbamates may display selective ligand-ex-
Chlorodiphenyltin(IV) complex 5 was prepared starting from
commercial 9-(methylaminomethyl)-anthracene. In similar fash-
ion, complex 6 was synthesized starting from 9-(methylaminobu-
tyl)-anthracene (for synthetic details see Section 2). The absorption
spectra in acetonitrile for complex 5 and 6 displayed three well-de-
fined bands in the region 340–390 nm in addition to the UV bands

3962
J.P. Fuentes-Martínez et al. / Polyhedron 28 (2009) 3953–3966
e
d
c
b
a
PPM 8.4
8.0
7.6
7.2
6.8
6.4
6.0
5.6
5.2
4.8
4.4
4.0
3.6
3.2
2.8
2.4
2.0
1.6
1.2
0.8
0.4
Fig. 7. 1H NMR spectra for 2 upon addition of AcOTBA in CD3CN. (a) Complex 2; (b) 2 +1 molar equiv. AcOTBA; (c) 2 +2 molar equiv. AcOTBA; (d) L2-TBA salt, (e) AcOTBA salt.
tures were similar between these complexes, however complex 6
possessed a much better solubility in acetonitrile than 5.
As before titrations of compounds 5 and 6 were carried out
employing the same set of anions tested with 3 and 4, monitoring
the spectral changes in the UV region at 299 nm. Fig. 10 (and Sup-
plementary Fig. S3 for complex 5) shows a comparison of the
changes observed in ꢀ299 during the titration of 6 in the presence
of anions.
Table 5
13C and 119Sn NMR chemical shifts observed during titration of 2 with AcOTBA in
CD3CN.
Entry Mixture
13C (CSS, ppm) 119Sn (ppm)
1
2
3
2 (8.8 ꢁ 10ꢀ2 M)
195.45
2 (8.8 ꢁ 10ꢀ2 M) + AcOTBA ꢃ 1 equiv. 199.38
2 (8.8 ꢁ 10ꢀ2 M) + AcOTBA ꢃ 2 equiv. 218.82a
ꢀ321.35
ꢀ374.81b
ꢀ489.66
a
For comparison, chemical shift of L2-TBA salt is observed at 217.3 ppm in
The trends observed here were the same as with 3, however the
behavior of the dicarboxylates malonate and succinate is particu-
CD3CN, see Table 2.
b
Diphenyltin(IV) macrocycle derived from
c-aminoacid dithiocarbamate in
which Sn is coordinated to one carboxylate and one dithiocarbamate units in
hexacoordinate fashion showed signal at ꢀ371.6 ppm (in CDCl3) [26].
larly remarkable because
Dꢀ299 goes through a well-defined max-
imum at about 1 molar equivalent of added ligand. At similar
concentrations the observed changes with monoanions such as
ꢀ
AcOꢀ, Fꢀ or H2PO4 are very small.
corresponding to the diphenyltin(IV) group. Excitation at kexc
368 nm produced an emission spectrum containing well-defined
and structured bands centered at 417 nm. Other spectroscopic fea-
The presence of this maximum in the titration curves has been
observed with every chlorodiphenyltin(IV) complex studied in this
Ph
O
Ph
S
O
Cl
S
Ph
Cl
+
Sn
Ph
Sn
R2N
+
R2N
S
O
O
S
2a
Ph
Sn
Ph
S
Ph
O
O
O
+
S
O
+
Sn
Ph
O
O
R2N
R2N
S
S
O
O
Scheme 1. Stepwise ligand substitution for complex 2 occurring in the presence of acetate anion.

J.P. Fuentes-Martínez et al. / Polyhedron 28 (2009) 3953–3966
3963
malonate
succinate
glutarate
fluoride
18000
16000
14000
12000
10000
8000
6000
4000
2000
0
-
4
H PO
2
acetate
bromide
-
HSO
4
chloride
0
2
4
6
8
10
[anion] / [3]
Fig. 8. Changes of absorption coefficient at 294 nm during the titration of 3 (7 ꢁ 10ꢀ5 M) with different anions including halides (chloride, fluoride, bromide), carboxylates
(acetate, malonate, glutarate, and succinate) and other O donor ligands (H2PO4ꢀ, HSO4ꢀ) as TBA salts in CH3CN.
14000
malonate
succinate
12000
glutarate
fluoride
acetate
H2PO4-
10000
HSO4-
bromide
chloride
8000
6000
4000
0
2
4
6
8
10
12
[anion] / [4]
Fig. 9. Changes of absorption coefficient at 295 nm during the titration of 4 (7 ꢁ 10ꢀ5 M) with different anions including halides (chloride, fluoride, and bromide),
carboxylates (acetate, malonate, glutarate, and succinate) and other O donor ligands (H2PO4ꢀ, HSO4ꢀ) as TBA salts in CH3CN.
work (1, 2, 3, 5 and 6) in their interaction with malonate and suc-
cinate, and to a less extent with glutarate, indicating that the
mechanism of ligand exchange in the presence of small dicarbox-
ylates (i.e., malonate and succinate) is different than the one de-
picted in Scheme 1 for compound 2 with acetate. Only for
complex 4, which lacks of the chloride coordinated ligand, titration
curves did not show any maximum in the presence of small dicar-
boxylates. According to our previous results the bands with
absorption maxima located about 294–300 nm correspond to free
dithiocarbamate ligand and therefore, we would expect approxi-
mately the same value of absorption coefficient at the end of titra-
tion plots when all bound dithiocarbamate ligand had been
released, as it was observed in the case of monoanions AcOꢀ, Fꢀ,
and H2PO4 (see Fig. 10). A closer examination of the absorption
ꢀ
spectra in the titration of complex 6 (or complexes 2 and 3) with
acetate and malonate did not shed light on the molecular basis
for this behavior. Perhaps differences in the mechanism of cleaving
the dithiocarbamate group by acetate that may follow an stepwise
displacement of chloride and dithiocarbamate groups, respectively,
and by small dicarboxylates, which may follow an intramolecular
displacement of the dithiocarbamate group, accounts for the
appearance of the maximum in the titrations of chlorodiphenyl-

3964
J.P. Fuentes-Martínez et al. / Polyhedron 28 (2009) 3953–3966
malonate
deal of attention they have earned in the context of biological
succinate
glutarate
fluoride
activity and therapeutic applications [9,14,15]. Thus, the solution
stability of chlorodiphenyltin(IV) dithiocarbamate complexes
examined here demonstrated that these complexes in the presence
of O donors anions like as acetate, dicarboxylates of general for-
mula ꢀOOC-(CH2)n-COOꢀ (n = 2–8), dihydrogenphosphate, and
fluoride, were prone to readily exchange their coordinated ligands
in stepwise fashion by first displacing chloride, and then follow by
the dithiocarbamate group under excess of the incoming anion.
This ligand-exchange reaction could be nicely monitored by trac-
ing changes in the UV absorption region for the free dithiocarba-
mate (i.e., 294–300 nm), which becomes a chromogenic reporter
of the binding. By attaching an anthracenyl moiety to the dithio-
carbamate ligand it was observed a more selective displacement
of dihydrogenphosphate anion over other O donor ligands.
14000
13000
12000
11000
10000
9000
acetate
H2PO4-
8000
7000
6000
5000
4000
3000
0
2
4
6
8
10
From UV–Vis titration experiments it was found that dicarbox-
ylates with small spacers like malonate and succinate, acted differ-
ently in the exchange of the dithiocarbamate group, perhaps by
following an intramolecular displacement of the coordinated li-
gand. Also, it was noted that the extent of dithiocarbamate ex-
change in these complexes depended directly on the nature of
the anion, and on their relative affinity for the diorganotin(IV) moi-
ety following a stability trend such as: dicarboxyꢀlates > O donor
[anion] / [6]
Fig. 10. Changes of absorption coefficient at 299 nm during the titration of 6
(7 ꢁ 10ꢀ5 M) with different anions including carboxylates (acetate, malonate,
glutarate, and succinate), H2PO4ꢀ, and Fꢀ as TBA salts in CH3CN.
H2PO4-
monoanions ꢄ fluoride > other halides and HSO4
. When only
6
dithiocarbamate is present such as in triphenyltin(IV) complex 4,
a similar trend in displacement of the dithiocarbamate was also
observed indicating that that even simple triorganotin(IV) dithio-
carbamates may display selective ligand-exchange.
5
4
Acknowledgements
3
HSO4-
We thank Dr. Herbert Höpfl for X-ray analysis of 1. The authors
thank CONACyT Project SEP-2004-C01-47347 for financial support.
J.P.F.-M. and I.T.-M. acknowledge PROMEP and CONACyT
fellowships.
2
acetate
malonate
1
glutarate
1.0x10-7 2.0x10-7 3.0x10-7 4.0x10-7
0.0
Appendix A. Supplementary data
[guest], M
CCDC 684317, 734761 and 734760 contain the supplementary
crystallographic data for 1, 3 and 6. These data can be obtained free
of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or
from the Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail: de-
posit@ccdc.cam.ac.uk. Supplementary data associated with this
article can be found, in the online version, at doi:10.1016/
j.poly.2009.09.010.
Fig. 11. Changes in fluorescence intensity at 440 nm (kexc 368 nm) during the
titration of
5
(1 ꢁ 10ꢀ7 M)ꢀwith different anions including acetate, malonate,
glutarate, H2PO4ꢀ, and HSO4 as TBA salts in CH3CN.
tin(IV) complexes. In line with this scheme, dicarboxylate anions
with larger spacer groups like adipate, suberate, or azelate, did
not show any maximum in their titration plots (see Supplementary
Fig. S1) suggesting that intramolecular displacement is not possi-
ble in these cases.
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