Luminescent organotin complexes with the ligand benzil bis(benzoylhydrazone)

Article abstract of DOI:10.1016/j.jorganchem.2010.07.002

Three organotin complexes have been synthesised by reaction of the ligand benzil bis(benzoylhydrazone) LH₂ with SnR₂Cl₂ or SnR₃Cl (R = Me, Bu, Ph). In all the compounds the ligand is doubly deprotonated and beha

Full text of DOI:10.1016/j.jorganchem.2010.07.002

Journal of Organometallic Chemistry 695 (2010) 2305e2310
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Luminescent organotin complexes with the ligand benzil bis(benzoylhydrazone)
,
b
b
a
Elena López-Torres a , Antonio L. Medina-Castillo , Jorge F. Fernández-Sánchez , M. Antonia Mendiola
*
a Departamento de Química Inorgánica, Avenida Francisco Tomás y Valiente 7, Universidad Autónoma de Madrid, Cantoblanco, 28049-Madrid, Spain
b Departamento de Química Analítica, C/ Fuentenueva s/n, Universidad de Granada, 18071 Granada, Spain
a r t i c l e i n f o
a b s t r a c t
Article history:
Three organotin complexes have been synthesised by reaction of the ligand benzil bis(benzoylhy-
drazone) LH2 with SnR2Cl2 or SnR3Cl (R ¼ Me, Bu, Ph). In all the compounds the ligand is doubly
deprotonated and behaves as N2O2 tetradentate chelate, leading to distorted octahedral arrangements
with the ligand in the equatorial plane and the organic groups in the axial positions. The complexes have
been fully characterised by spectroscopic techniques including 13C and 119Sn NMR in solution and in the
solid state, which confirm that the structure found in the solid state is retained in chloroform solution,
and two of them by single crystal X-ray diffraction. The luminescent properties of the ligand and its
complexes have also been tested as well as the effect of pH, the addition of acetone and the ionic strength
over the luminescence intensity.
Received 5 May 2010
Received in revised form
29 June 2010
Accepted 1 July 2010
Available online 3 August 2010
Keywords:
Benzoylhydrazone ligands
Organotin
Crystal structure elucidation
Luminescence
Ó 2010 Elsevier B.V. All rights reserved.
1. Introduction
Therefore, the preparation of compounds that could be used as
sensors for organotin compounds is an interesting topic to pursue.
Organotin compounds are amongst the most widely used
organometallic compounds, and over the last decades they have
been used in a wide range of industrial and agricultural applica-
tions such as pesticides, fungicides and anti-fouling agents [1,2].
The high amount of organotin derivatives used in agriculture
explains the large accumulation of these compounds in the envi-
ronment. While bans in developed nations have helped to decrease
the overall incorporation of certain organotin species into the
environment, other countries still produce and utilize huge
amounts of these compounds [3,4].
Organotin toxicity is directly linked to the number and nature of
the organic moiety. Highly substituted organotin compounds are
known to be the most toxic (tri- and disubstituted organotins), with
their toxicity decreasing when the length of the alkyl chain
decreases, being independent of the counterions [5]. Organotin
compounds can suffer environmental degradation (speciation) by
physico-chemical factors (UV, pH) and can be metabolized by
prokaryotic and eukaryotic organisms, and in spite of its relatively
high dissociation energy (190e220 kJ/mol), the covalent SneC
bond can be cleaved by a number of environmental sources,
including chemical attacks (nucleophilic or electrophilic), UV
radiation and dealkylation by bacteria [1,2].
Within these sensors, the design and synthesis of fluorescent
molecular sensors that selectively and specifically respond to the
presence of a given analyte (in particular metal ions) in a complex
matrix, is a research area that has received much interest [6e15].
Applications can span from process control to environmental
monitoring, food analysis and medical diagnosis. Chemosensors
based on fluorescence offer many advantages over other types of
sensors in terms of sensitivity, response time and cost, and they are
of crucial importance for the development of methods for the
detection and quantification of metal ions such as zinc [16,17],
cadmium [18,19], lead [20,21], mercury [22,23] and tin [24].
Following our interest in the study of the reactivity of potentially
tetradentate ligands, we have established that the coordinating
behaviour depends both in the reaction conditions and the metal
preferences [25e28]. Thus, in a previous paper we have reported
the synthesis of the title bis(hydrazone) ligand as well as its
complexes with several divalent metals, which depending on the
metal, range from monomers to trinuclear helicates [29]. In this
paper, the ligand benzil bis(benzoylhydrazone) is reacted with di
and triorganotin(IV) chlorides to yield fluorescent organotin
complexes that have been fully characterised. The luminescent
properties have been evaluated to establish if the ligand could be
used as a probe for detecting organotin species.
Among other, the main aim of this paper is the synthesis and
optical characterization of the bis(hydrazone) ligand LH2 and its
organotin(IV) complexes, in order to obtain all the luminescent
* Corresponding author.
E-mail address: elena.lopez@uam.es (E. López-Torres).
0022-328X/$ e see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2010.07.002

2306
E. López-Torres et al. / Journal of Organometallic Chemistry 695 (2010) 2305e2310
information as a previous step for the immobilisation of LH2 into
a solid phase and to test its optical sensing response. For this
reason, the synthesis of the complexes have been evaluated under
different solvents, in order to establish the polarity of the solid
support we can use, and the luminescent properties have been
analysed changing several chemical conditions, such as pH, solvent
or ionic strength.
(Ph), 4.9 (Me) ppm. 13C CP/MAS NMR (300 MHz, 25 ꢁC):
d
¼ 172.5
(CO), 150.1 (CN), 134.5, 130.8, 129.4, 127.4 (Ph), 4.3 (Me) ppm. 119Sn
NMR (300 MHz, CDCl3, 25 ꢁC):
(300 MHz, 25 ꢁC):
(w), 2938 (w) (CHMe), 1600 (w) n(CN), 1585 (m) n(CO), 712 (s), 688
d
¼ ꢀ261 ppm. 119Sn CP/MAS NMR
d
¼ ꢀ275 ppm. IR (KBr): 3050 (w)
n(CHPh), 2973
n
(m)
d
(Ph) cmꢀ1. MS (FABþ): m/z (%) ¼ 595.1 (100) [M þ H]þ, 578.2
(15) [M ꢀ Me]þ. The same complex was obtained when SnMe3Cl
was used.
2. Experimental section
2.1.3. [SnBu2L] 2
2.1. General
The complex was obtained following the same procedure
described above but adding 70 mg (0.22 mmol) of SnBu2Cl2. Single
crystals were also obtained from slow evaporation of the mother
liquor. Yield: 132 mg, 87%. C36H38N4O2Sn (677.01): calcd. C 63.81, H
5.66, N 8.27; found C 63.97, H 5.54, N 8.57. 1H NMR (300 MHz,
Microanalyses were carried out using
a LECO CHNS-932
Elemental Analyzer. IR spectra in the 4000e400 cmꢀ1 range were
recorded as KBr pellets on a Jasco FT/IR-410 spectrophotometer.
Fast atom bombardment mass spectra were recorded on a VG Auto
Spec instrument using Cs as the fast atom and m-nitro-
benzylalcohol (m-NBA) as the matrix. 1H and 13C NMR spectra were
recorded on a Bruker AMX-300 spectrometer using CDCl3 as
solvent and TMS as internal reference. 119Sn NMR spectra were
recorded in the same spectrometer and the chemical shifts are
reported relative to Sn(Me)4 as internal reference. 13C CP/MAS NMR
spectra were recorded at 298 K in a Bruker AV400WB spectrometer
equipped with a 4 mm MAS NMR probe (magic-angle spinning)
and obtained using cross-polarization pulse sequence. The external
magnetic field was 9.4 T, the sample was spun at 10e14 kHz and
spectrometer frequencies were set to 100.61 MHz. For the recorded
spectra a contact time of 4 ms and recycle delays of 4 s were used.
Chemical shifts are reported relative to TMS, using the CH group of
adamantane as a secondary reference (29.5 ppm.). 119Sn CP/MAS
NMR spectra were obtained in the same spectrometer using spin-
ning rates of 10e14 KHz, pulse delays of 30 s, contact times of 8 ms
and TPPM high power proton decoupling. Chemical shifts are
reported relative to Sn(Me)4, using tin(IV) oxide as a secondary
reference. Luminescence spectra and relative fluorescence intensity
(R.F.I.) were carried out with a luminescence spectrometer Varian
Cary-Eclipse fitted with a Xenon discharge lamp (peak pow-
er ¼ 75 kW), Czerny-Turner monochromators, an R-928 photo-
multiplier tube, which is red sensitive even at 900 nm, with manual
or automatic voltage control, using the Cary-Eclipse software for
Windows 95/98/NT system.
CDCl3, 25 ꢁC):
Bu), 1.55 (q, 4H, Bu), 1.32 (sx, 4H, Bu), 0.83 (t, 6H, Bu) ppm. 13C NMR
(300 MHz, CDCl3, 25 ꢁC):
¼ 173.7 (C]O),149.0 (C]N),135.1,132.5,
131.2, 130.7, 129.2, 128.7, 128.0, 127.5 (Ph), 27.6, 26.2, 25.4, 13.6
(Bu) ppm. 13C CP/MAS NMR (300 MHz, 25 ꢁC):
¼ 174.7 (CO), 151.5
d
¼ 8.10 (d, 4H, Ph), 7.47e7.26 (m,16H, Ph),1.74 (t, 4H,
d
d
(CN), 136.7, 134.3, 131.7, 129.1 (Ph), 28.1, 27.5, 25.2, 14.5 (Bu) ppm.
119Sn NMR (300 MHz, CDCl3, 25 ꢁC):
NMR (300 MHz, 25 ꢁC):
2955 (m), 2924 (m), 2872 (m), 2857 (m)
d
¼ ꢀ284 ppm. 119Sn CP/MAS
d
¼ ꢀ273 ppm. IR (KBr): 3057 (w) (CHPh),
(CN),
n(CO), 712 (s), 687 (s) d
(Ph) cmꢀ1. MS (FABþ): m/z
n
n
(CHBu), 1598 (w) n
1588 (m)
(%) ¼ 679.2 (100) [M þ H]þ, 620.9 (75) [M ꢀ Bu]þ, 568.1 (20)
[M ꢀ 2Bu þ H]þ. The same complex was synthesised starting from
SnBu3Cl.
2.1.4. [SnPh2L] 3
The complex was obtained following the same procedure
described for complex 1 but adding 91 mg (0.22 mmol) of SnPh2Cl2.
Yield: 151 mg, 74%. C40H30N4O2Sn (716.95): calcd. C 66.95, H 4.22, N
7.81; found C 67.13, H 4.30, N 7.68. 1H NMR (300 MHz, CDCl3, 25 ꢁC):
d
¼ 8.18 (d, 8H, Ph), 7.78e7.71 (m, 8H, Ph), 7.50e7.23 (m, 24H,
Ph) ppm. 13C NMR (300 MHz, CDCl3, 25 ꢁC):
¼ 172.1 (CO), 148.7
(CN), 136.2, 131.9, 130.9, 129.5, 128.9, 128.7, 128.1, 127.4 (Ph) ppm.
13C CP/MAS (300 MHz, 25 ꢁC):
¼ 173.0 (CO), 151.3 (CN), 132.5,
128.4 (Ph) ppm. 119Sn NMR (300 MHz, CDCl3, 25 ꢁC):
¼ ꢀ235 ppm.
119Sn CP/MAS NMR (300 MHz, 25 ꢁC):
¼ ꢀ240 ppm. IR (KBr): 3056
d
d
d
d
(w)
(s), 688 (m)
n(CHPh), 1599 (w) n(CN), 1586 (m) n(CO), 732 (m), 712 (s), 693
d
(Ph) cmꢀ1. MS (FABþ): m/z (%) ¼ 719.2 (100) [M þ H]þ,
2.1.1. Benzil bis(benzoylhydrazone), LH2
641.2 (40) [M ꢀ Ph]þ. The same complex was isolated when
The ligand was prepared following a previously reported
SnPh3Cl was used as the starting material.
procedure [29]. Selected spectroscopic data: 1H NMR (300 MHz,
The three complexes can also be synthesised in good yield in
other solvents such as water, methanol or ethanol.
CDCl3, 25 ꢁC):
d
¼ 9.01 (s, 2H, NH), 7.83 (m, 4H, Ph), 7.40e7.22 (m,
16H, Ph) ppm. 13C CP/MAS NMR (300 MHz, 25 ꢁC):
¼ 164.4
(CO), 147.5 (CN), 133.8, 132.3, 128.3, 123.8 (Ph) ppm. IR (KBr): 3232
(m), 3178 (m) (NH); 3063 (w) (CH); 1674 (s), 1643 (s) (CO), 1604
(w) (CN), 712, 687 (s)
(Ph) cmꢀ1
d
2.2. X-ray structure determination
n
n
n
n
d
.
Data for complexes 1 and 2 were acquired using a Bruker AXS
Kappa Apex-II diffractometer equipped with an Apex-II CCD area
detector using a graphite monochromator (Mo Ka radiation,
2.1.2. [SnMe2L] 1
To a solution containing 100 mg (0.22 mmol) of LH2 in 5 mL of
dichloromethane with four drops of Et3N were added 52 mg
(0.22 mmol) of SnMe2Cl2 dissolved in 5 mL of the same solvent and
the deep orange solution was stirred overnight. The solution was
evaporated to dryness and 20 mL of diethyl ether were added. The
white precipitate corresponding to Et3N$HCl was discarded and the
orange solution was allowed to evaporate slowly until orange
crystals suitable for X-ray analysis were obtained in good yield
(122 mg, 92%). C30H26N4O2Sn (592.91): calcd. C 60.72, H 4.42, N
9.45; found C 60.53, H 4.30, N 9.58. 1H NMR (300 MHz, CDCl3,
l
¼ 0.71073 Å). The substantial redundancy in data allows empirical
absorption corrections (SADABS) [30] to be applied using multiple
measurements of symmetry-equivalent reflections. The raw inten-
sity dataframes wereintegrated with theSAINTprogram, whichalso
applied corrections for Lorentz and polarization effects [31].
The software package SHELXTL version 6.10 was used for space
group determination, structure solution and refinement. The
structures were solved by direct methods (SHELXS-97) [32],
completed with difference Fourier syntheses, and refined with full-
matrix least-squares using SHELXL-97 minimizing
u
(F20ꢀF2c).
25 ꢁC):
d
¼ 8.08 (d, 4H, Ph), 7.54e7.22 (m, 16H, Ph), 0.98 (s, 6H, Me,
Weighted R factors (Rw) and all goodness of fit S are based on F2 and
conventional R factors (R) are based on F [33]. All non-hydrogen
atoms were refined with anisotropic displacement parameters and
2JSn,H ¼ 94.0 Hz) ppm. 13C NMR (300 MHz, CDCl3, 25 ꢁC):
d
¼ 173.5
(CO), 148.7 (CN), 134.9, 132.2, 131.3, 130.8, 129.4, 128.6, 128.0, 127.4

E. López-Torres et al. / Journal of Organometallic Chemistry 695 (2010) 2305e2310
2307
Table 1
the hydrogen atoms were positioned in idealised positions after
Crystal and structure refinement data for complexes 1 and 2.
each cycle of refinement. All scattering factors and anomalous
dispersions factors are contained in the SHELXTL 6.10 program
library.
1
2
Formula
M
Crystal system
Space group
a/Å
C30H26N4O2Sn
593.24
Orthorhombic
Pbca
10.1467(6)
15.5452(9)
33.127(2)
90
90
90
5225.3(5)
8
1.508
1.013
2400
0.988
42262
6478 [R(int)
¼ 0.0567]
C36H38N4O2Sn
677.39
Monoclinic
Pc
10.4155(6)
16.6850(9)
18.7548(10)
90
102.280(3)
90
3184.7(3)
4
1.413
0.840
1392
3. Results and discussion
The reactions were carried out in dichloromethane at room
temperature in the presence of Et3N (Scheme 1), which is essential
to induce the ligand deprotonation. As a result, a white crystalline
material, Et3N$HCl, is formed but it can be eliminated due to its
insolubility in diethyl ether. Elemental analysis of the complexes
indicates a 1:1 ligand:tin ratio, as well as the absence of Clꢀ. The
same complexes were obtained starting from the triorganotin
derivatives, as well as working in other solvents such as water or
alcohols.
b/Å
c/Å
ꢁ
ꢁ
a
/
b
/
ꢁ
g
/
U/Å3
Z
Dc/Mgmꢀ3
Absorption coefficient mmꢀ1
F(000)
Goodness of fit on F2
Reflections collected
Independent reflections
1.083
45827
13750 [R(int)
¼ 0.0768]
0.49(3)
0.0475, 0.1054
ꢀ1.488, 1.127
3.1. X-ray analysis
Absolute structure parameter
The crystal structure of complexes 1 and 2 have been deter-
mined and their crystallographic and refinement data are
summarized in Table 1. In both complexes the ligand is doubly
deprotonated and behaves as a tetradentate N2O2 chelate, coordi-
nation mode that leads to the formation of three five-membered
chelate rings that confer high stability to the compounds. This
coordination behaviour was previously reported for a nickel
complex. By contrast, with lead and cadmium the ligand behaves
also as a bridge through one of the oxygen atoms to form dinuclear
complexes and with zinc and copper is pentadentate, but tridentate
N2O chelate to one metal and bidentate NO chelate to another to
yield trinuclear helicates [29]. Table 2 shows the ligand bond
lengths in the complexes as well as in the uncoordinated LH2 [29]. It
can be concluded that deprotonation of the ligand induces more
electronic delocalisation.
The molecular structure of complex 1 consists of discrete
molecules of [SnMe2L], in which the tin atom is in a strongly dis-
torted octahedral arrangement with the deprotonated ligand in the
equatorial plane and the methyl groups in the axial positions (Fig. 1,
Table 3). There are not relevant differences between SneN bond
distances, as well as happens with SneO and SneC bonds, and all of
them are in the normal range found for this kind of complexes. The
ligand skeleton can be considered planar with a maximum devia-
tion from the least-squares plane of 0.059 Å for N(3). The phenyl
rings of the hydrazone form dihedral angles with this plane of
24.96ꢁ for C(11)eC(16) and 8.08ꢁ for C(41)eC(46), while with the
rings coming from benzil are 53.44ꢁ and 48.81ꢁ for C(21)eC(26)
and C(31)eC(36) respectively.
Final R1and wR2[I > 2
Residual electron density
(min, max) (e Åꢀ3
s
(I)]
0.0312, 0.0766
ꢀ0.674, 0.688
)
the two butyl ligands have different conformation, while one of
them is anti the other is gauche, probably due to the steric
requirements of the phenyl rings. The ligands are less planar than in
the methyl derivative, with one of the oxygens quite deviated from
the least-squares plane formed by the rest of the skeleton. For the
molecule containing Sn(1) the maximum deviation is 0.0913 Å for N
(1) and O(1) is 0.44 Å above this plane and for the unit containing
Sn(2) the maximum deviation is 0.062 Å for C(13) with O(3) 0.26 Å
under the plane. The dihedral angles of the phenyl groups are
similar to those found in complex 1, 16.06ꢁ for C(11A)eC(16A),
49.35ꢁ for C(21A)eC(26A), 56.72ꢁ for C(31A)eC(36A), 8.70ꢁ for C
(41A)eC(46A), 6.94 for C(51A)eC(56A), 46.19ꢁ for C(61A)eC(66A),
58.53ꢁ for C(71A)eC(76A) and 14.43ꢁ for C(81A)eC(86A).
3.2. IR spectroscopy
In all the complexes, coordination of the carbonyl group to the
metal is confirmed by the shift of the
frequencies compared with that of the free ligand. By contrast, the
(CN) bands are not very shifted, but the crystal structure deter-
n(CO) band to lower
n
mination of complexes 1 and 2 confirm that the ligand is
Table 2
Selected bond distances (Å) of the ligand skeleton in LH2 [29] and complexes 1 and 2.
Complex 2 crystallises in the chiral monoclinic group Pc as
a racemic mixture. The asymmetric unit is made up by two crys-
tallographically distinct units of [SnBu2L]. There are no relevant
differences in the bond lengths and angles (Tables 2 and 4), so in
Fig. 2 is only depicted one of the molecules. The tin atom has the
same coordination environment found in complex 1. In each unit
LH2
1
2
C(1)eO(1)
C(13)eO(3)
C(1)eN(1)
C(13)eN(5)
N(1)eN(2)
N(5)eN(6)
C(2)eN(2)
C(14)eN(6)
C(2)eC(3)
C(14)eC(15)
C(3)eN(3)
C(15)eN(7)
N(3)eN(4)
N(7)eN(8)
1.2225(15)
1.269(3)
1.295(9)
1.274(9)
1.334(10)
1.335(9)
1.363(8)
1.372(9)
1.292(10)
1.307(10)
1.471(11)
1.508(11)
1.307(10)
1.304(10)
1.374(8)
1.396(8)
1.344(10)
1.331(9)
1.277(9)
1.276(9)
1.3764(16)
1.3753(15)
1.2891(16)
1.507(2)
1.340(3)
1.365(3)
1.308(3)
1.482(3)
1.305(3)
1.375(3)
1.331(3)
1.276(3)
Ph
N
Ph
N
R
Sn
R
SnR2Cl2 or SnR3Cl
Et3N, DCM
N
N
1.2891(16)
1.3753(15)
1.3753(15)
1.2225(15)
HN
N
N NH
O
O
O
O
Ph
Ph
R = Me, 1
R = Bu, 2
R = Ph, 3
N(4)eC(4)/
N(8)eC(16)
C(4)eO(2)
C(16)eO(4)
LH2
Scheme 1.

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E. López-Torres et al. / Journal of Organometallic Chemistry 695 (2010) 2305e2310
Fig. 1. Molecular structure of complex [SnMe2L] 1. Thermal ellipsoids at 50% probability. Hydrogen atoms of the methyl groups have been omitted for clarity.
tetradentate N2O2. Having a look at the bond distances found in
the crystal structures it can be seen that while C]O bonds change
considerably with respect to those of the free ligand, C]N bond
distances are very similar, explaining the small shifts observed in
the IR spectra.
LockharteManders equation could not be used to get the value of
the CeSneC angle.
The 119Sn chemical shift of tin complexes appear to depend not
only on coordination number, but it is also very sensitive to the type
of donor atoms bonded to the metal ion, so it is a useful tool to
determine the chemical environment of the tin atom. In addition,
solid-state NMR is an important technique to bridge the informa-
tion gap between X-ray diffraction and solution NMR spectroscopic
data. Holecek established for n-butyl derivatives that four-coordi-
3.3. NMR spectroscopy
The 1H NMR spectra of the complexes confirm the ligand
deprotonation, due to the loss of the signal corresponding to the NH
groups, as well as the presence of the organic groups bonded to the
tin. Satellites corresponding to the coupling with tin can only be
observed in the spectrum of complex 1. Substitution of 2JSn,H value
into the corresponding LockharteManders equation [34] (empirical
relationship between the coupling constants and the CeSneC
angle) gives an angle of 154ꢁ, which is close to the value found in
the crystal structure, 147ꢁ. This similarity indicates that the struc-
ture found in the solid state is retained in solution.
nate compounds have
þ200 to ꢀ60 ppm, five-coordinate compounds from
ꢀ190 ppm and six-coordinate compounds from
d
(
119Sn) values in solution ranging from
ꢀ90 to
ꢀ210 to
d
d
d
ꢀ400 ppm [35]. The values found in solution (ꢀ261, ꢀ284
and ꢀ235 ppm, for complexes 1, 2 and 3 respectively) and in the
solid state (ꢀ275, ꢀ273 and ꢀ240 ppm) (see ESI) are within the
range expected for six-coordinate complexes, which agree with the
environments found in the crystal structures of 1 and 2. The simi-
larity in the 119Sn chemical shifts found in solution and in the solid
state indicates that the coordination environments of the three
complexes do not change in chloroform solution.
13C NMR CP/MAS spectra of all the complexes show that the
signals corresponding to the CO and CN are shifted with respect to
the free ligand, indicating coordination of these groups to the tin.
The CO bond signals are much more shifted than the CN ones, as
happens with the IR spectra and what can also be explained with
the X-ray diffraction data. The signals belonging to the organic
groups are also observed. Comparison with the 13C NMR spectra in
solution indicates that the structure found in the solid state is
Table 4
Selected bond distances (Å) and angles (ꢁ) for complex [SnBu2L] 2.
Sn(1)eN(3).
Sn(1)eN(2)
Sn(1)eO(1).
Sn(1)eO(2)
Sn(1)eC(9)
Sn(1)-C(5)
2.237(6)
2.240(7)
2.283(5)
2.290(5)
2.128(8)
2.144(7)
149.4(3)
105.8(3)
99.4(3)
99.6(3)
105.2(3)
70.2(2)
84.9(3)
87.2(3)
Sn(2)eN(7).
Sn(2)eN(6)
Sn(2)eO(3)
Sn(2)eO(4)
Sn(2)eC(21)
Sn(2)eC(17)
2.225(6)
2.240(7)
2.285(5)
2.340(5)
2.127(7)
2.134(7)
151.8(3)
104.3(2)
98.4(3)
100.1(3)
103.0(3)
71.4(2)
85.6(2)
87.9(3)
1
retained in chloroform. The satellites corresponding to the JSn,C
cannot be observed in any spectrum, so the corresponding
C(9)eSn(1)eC(5)
C(9)eSn(1)eN(3)
C(5)eSn(1)eN(3)
C(9)eSn(1)eN(2)
C(5)eSn(1)eN(2)
N(3)eSn(1)eN(2)
C(9)eSn(1)eO(1)
C(5)eSn(1)eO(1)
N(3)eSn(1)eO(1)
N(2)eSn(1)eO(1)
C(9)eSn(1)eO(2)
C(5)eSn(1)eO(2)
N(3)eSn(1)eO(2)
N(2)eSn(1)eO(2)
O(1)eSn(1)eO(2)
C(21)-Sn(2)eC(17)
C(21)eSn(2)eN(7)
C(17)eSn(2)eN(7)
C(21)eSn(2)eN(6)
C(17)eSn(2)eN(6)
N(7)eSn(2)eN(6)
C(21)eSn(2)eO(3)
C(17)eSn(2)eO(3)
N(7)eSn(2)eO(3)
N(6)eSn(2)eO(3)
C(21)eSn(2)eO(4)
C(17)eSn(2)eO(4)
N(7)eSn(2)eO(4)
N(6)eSn(2)eO(4)
O(3)eSn(2)eO(4)
Table 3
Selected bond distances (Å) and angles (ꢁ) for complex [SnMe2L] 1.
Sn(1)eN(2)
Sn(1)eN(3)
2.238(2)
2.246(2)
Sn(1)eO(2)
Sn(1)eC(5)
2.2960(19)
2.106(3)
Sn(1)eO(1)
2.2675(19)
147.63(11)
106.07(10)
100.32(10)
104.86(10)
101.26(9)
70.77(7)
Sn(1)eC(6)
2.117(3)
69.40(7)
C(5)eSn(1)eC(6)
C(5)eSn(1)eN(2)
C(6)eSn(1)eN(2)
C(5)eeSn(1)eN(3)
C(6)eSn(1)eN(3)
N(2)eSn(1)eN(3)
C(5)eSn(1)eO(1)
C(6)eSn(1)eO(1)
N(2)eSn(1)eO(1)
N(3)eSn(1)eO(1)
C(5)eSn(1)eO(2)
C(6)eSn(1)eO(2)
N(2)eSn(1)eO(2)
N(3)eSn(1)eO(2)
O(1)eSn(1)eO(2)
140.17(7)
85.61(10)
86.13(10)
139.94(7)
69.19(7)
139.5(2)
69.5(2)
87.2(3)
85.6(2)
69.3(2)
139.9(2)
68.6(2)
88.1(3)
84.7(2)
68.4(2)
86.21(10)
85.84(10)
150.61(7)
139.2(2)
151.22(18)
139.8(2)
151.61(18)

E. López-Torres et al. / Journal of Organometallic Chemistry 695 (2010) 2305e2310
2309
300
200
100
a
0
600
400
200
b
c
d
0
800
600
400
200
Fig. 2. Molecular structure of complex [SnBu2L] 2. Thermal ellipsoids at 50% proba-
bility. Hydrogen atoms have been omitted for clarity.
0
300
3.4. Mass spectrometry
200
100
0
All the complexes show the peak corresponding to the molec-
ular mass [SnR2L þ H]þ, as well as the fragment corresponding to
the loss of one of the organic groups [SnRL]þ. In the butyl derivative
the peak corresponding to the loss of the two organic groups
[SnL þ H]þ is also observed. In all the peaks the found and calcu-
lated isotopic patterns are identical.
250
350
450
550
650
Wavelength (nm)
Bearing these data in mind, we propose for complex 3 a struc-
ture analogous to that found for methyl and butyl derivatives, in
which the metal is in a distorted N2O2C2 octahedral arrangement
(Scheme 1).
Fig. 3. Fluorescence excitation (grey line) and emission (black line) spectra of a) LH2 b)
complex 1, c) complex 2 and d) complex 3 in solution. See Table 5 for experimental
conditions.
386 a.u., respectively. Thus, it can be concluded that the formation
of the complexes provide an increase of the fluorescence emission
with enhancement factors of 57, 75 and 35, respectively; therefore
the ligand could be used as an optical probe for developing Sn-
sensitive optical sensing.
The luminescent properties of the complexes are affected by the
pH (see Fig. 4 and ESI). Complex 1 shows a maximum fluorescence
emission at pH ¼ 5; the maximum emission intensities of
3.5. Luminescence spectroscopy
Table 5 shows the fluorescence properties of LH2 and its
complexes 1, 2 and 3 in powder and in solution, and Fig. 3 shows
the fluorescence excitation and emission spectra in solution of
these compounds (Electronic supporting information, ESI, shows
the excitation and emission spectra in powder). It can be observed
that the complexes show an emission around 570 nm, while LH2
emits at 415 nm. In addition, when the emission of LH2 is recorded
at the same conditions than the three complexes (see Table 5), it
does not emit any luminescence (R.F.I. of LH2 around 11 a.u.) while
the complexes 1, 2 and 3 provide R.F.I. signals of 635, 830 and
1000
800
600
400
200
0
Table 5
Luminescent
properties
of
LH2
and
complexes
1,
2
and
3.
[LH2] ¼ [2] ¼ [3] ¼ 10ꢀ6 mol Lꢀ1, [1] ¼ 10ꢀ5 mol Lꢀ1, scan rate ¼ 2 nm/s.
Luminescence
properties
Powder
LH2
Solution
LH2
1
2
3
1
2
3
lexc (nm)
lem (nm)
Slitsexc/em
352 552 481,518 548 350
414 590 551,573 600 412
5/5 5/5 10/10
458
566
486
566
482
572
3
4
5
6
7
8
9
10
11
5/5 10/10 10/10 10/10 10/10
pH
Detector voltage (V) 600 530 580
600 800
700
5
0
800
5e9
0
800
5e9
25
pHoptimum
e
e
7
0
Fig. 4. Effect of the pH on the relative fluorescence intensity of complexes 1 (-), 2 (C)
and 3 (:). See Table 5 for experimental conditions.
Acetoneoptimun (%v.v.)
e
e

2310
E. López-Torres et al. / Journal of Organometallic Chemistry 695 (2010) 2305e2310
complexes 2 and 3 are obtained between pH 5 and 9. Thus, strong
acid or basic media provide a decrease of the fluorescence intensity
for the three complexes. We have checked by 119Sn NMR that
addition of HCl leads to ligand protonation followed by complex
decomposition, yielding SnR2Cl2 and LH2. By contrast, addition of
NaOH seems to have no effect on complex structures, but induces
their precipitation.
With respect to the addition of acetone to the media (see ESI),
complex 1 is not affected by the percentage of the organic solvent,
complex 2 decreases its luminescence intensity when acetone is
added to the media and complex 3 increases their fluorescent
emission with the percentage of acetone.
Appendix A. Supplementary material
CCDC numbers 755426 and 755427 contain the supplementary
crystallographic data for complexes 1 and 2, respectively. These
data can be obtained free of charge from the Cambridge Crystal-
lographic Data Centre via www.cdcc.cam.ac.uk/data_request/cif.
Supplementary data associated with this article can be found, in the
online version, at doi:10.1016/j.jorganchem.2010.07.002.
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Reactions of the ligand benzil bis(benzoylhydrazone) LH2 with
SnR2Cl2 or SnR3Cl (R ¼ Me, Bu, Ph) in the presence of Et3N yield
three coordination compounds with general formula [SnR2L]. In the
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ELT and MAM thank to César J. Pastor for the crystal measure-
ments and to MICINN, Instituto de Salud Carlos III, for funding
(Project PS09/00963) ALMC and JFFS thank to the Junta de Anda-
lucía for funding (Project P07-FQM-02738).