Synthesis, crystal structures and spectroscopic studies of diorganotin derivatives with mefenamic acid.

Article abstract of DOI:10.1016/S0022-328X(01)01026-9

The complexes [Me₂LSnOSnLMe₂]₂ (1) and [Bu₂LSnOSnLBu₂]₂ (2) where HL is 2-[(2,3-dimethylphenyl)amino]benzoic acid (mefenamic acid), have been prepared and structurally characterized by means of ¹¹⁹Sn M?ssbauer, vibrational and NMR (¹H and ¹³C) spectroscopies. The crystal structures of complexes 1 and 2 have been determined by X-ray crystallography. Each structure is centro-symmetric and features a central rhombus Sn₂O₂ unit with two additional tin atoms linked at the O atoms. Pairs of tin atoms are bridged by bidentate carboxylate ligands and the `external' tin atoms have their coordination geometry completed by a bridging bidentate carboxylate ligand for 1 and by a monodentate carboxylate ligand for 2. Five rings, each containing two tin atoms, are present in the dimeric tetraorganodistannoxane 1 and the geometry around the four tin centers is distorted octahedral for Sn(2) and Sn(2a) and trigonal bipyramidal for Sn(1) and Sn(1a). Three such rings are present in 2 and the geometry around the four five-coordinated tin centers, Sn(1), Sn(1a), Sn(2) and Sn(2a), is distorted square-bipyramidal. Significant π→π, C-H→π stacking interactions and intramolecular hydrogen bonds stabilize structures 1 and 2. The polar imino hydrogen atom participates in intramolecular hydrogen bonds. Complexes 1 and 2 are self-assembled via π→π, C-H→π and stacking interactions.

Full text of DOI:10.1016/S0022-328X(01)01026-9

Journal of Organometallic Chemistry 630 (2001) 205–214
www.elsevier.com/locate/jorganchem
Synthesis, crystal structures and spectroscopic studies of
diorganotin derivatives with mefenamic acid. Crystal and
molecular structures of 1,2:3,4-di-m2-2-[(2,3-dimethylphenyl)amino]-
benzoato-O,O-1,3-bis-2-[(-[(2,3-dimethylphenyl)amino]benzoato-
O-1,2,4:2,3,4-di-m3-oxo-tetrakis[di-methyltin(IV)] and
1,2:3,4-di-m2-2-[(-[(-[(2,3-dimethylphenyl)amino]-benzoato-O,O-1,3-
bis-2-[(-[(-[(2,3-dimethylphenyl)amino]benzoato-O-1,2,4:2,3,4-di-
m3-oxo-tetrakis[di-n-butyltin(IV)]
Vaso Dokorou a, Zbigniew Ciunik b, Umberto Russo c, Dimitra Kovala-Demertzi a,*
a Inorganic Chemistry, Department of Chemistry, Uni6ersity of Ioannina, 45110 Ioannina, Greece
b Faculty of Chemistry, Uni6ersity of Wrocław, 14 F. Joliot-Curie St., 50-383 Wroclaw, Poland
c Dipartimento di Chimica Inorganica, Metallorganica e Analitica, Uni6ersita` di Pado6a, Via Loredan 4, I-35131 Padua, Italy
Received 9 March 2001; received in revised form 31 May 2001; accepted 31 May 2001
Abstract
The complexes [Me2LSnOSnLMe2]2 (1) and [Bu2LSnOSnLBu2]2 (2) where HL is 2-[(2,3-dimethylphenyl)amino]benzoic acid
(mefenamic acid), have been prepared and structurally characterized by means of 119Sn Mo¨ssbauer, vibrational and NMR (1H and
13C) spectroscopies. The crystal structures of complexes 1 and 2 have been determined by X-ray crystallography. Each structure
is centro-symmetric and features a central rhombus Sn2O2 unit with two additional tin atoms linked at the O atoms. Pairs of tin
atoms are bridged by bidentate carboxylate ligands and the ‘external’ tin atoms have their coordination geometry completed by
a bridging bidentate carboxylate ligand for 1 and by a monodentate carboxylate ligand for 2. Five rings, each containing two tin
atoms, are present in the dimeric tetraorganodistannoxane 1 and the geometry around the four tin centers is distorted octahedral
for Sn(2) and Sn(2a) and trigonal bipyramidal for Sn(1) and Sn(1a). Three such rings are present in 2 and the geometry around
the four five-coordinated tin centers, Sn(1), Sn(1a), Sn(2) and Sn(2a), is distorted square-bipyramidal. Significant p“p, CꢀH“p
stacking interactions and intramolecular hydrogen bonds stabilize structures 1 and 2. The polar imino hydrogen atom participates
in intramolecular hydrogen bonds. Complexes 1 and 2 are self-assembled via p“p, CꢀH“p and stacking interactions. © 2001
Elsevier Science B.V. All rights reserved.
Keywords: Mefenamic acid; Diorganotin; Crystal structures; Spectroscopic studies
1. Introduction
N-phenylanthranilic acid. NSAIDs are among the most
frequently used medicinal drugs. They are utilized pri-
marily as analgesics, anti-inflammatories and antipyret-
ics and their side effects have been well studied. The
therapeutic activity of these analgesics is believed to be
due to their ability to inhibit the biosynthesis of
prostaglandins by competitive interaction with the cy-
clooxygenase–arachidonic acid complex or by radical-
quenching agents that interfere with the initiation of the
Mefenamic
acid
(i.e.
2-[(2,3-dimethylphenyl)-
amino]benzoic acid or N-(2,3-xylyl)anthranilic acid),
structure 1, belongs to a family of non-steroidal anti-
inflammatory drugs (NSAIDs) that are derivatives of
* Corresponding author. Fax: +30-651-44825.
E-mail address: dkovala@cc.uoi.gr (D. Kovala-Demertzi).
0022-328X/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(01)01026-9

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V. Dokorou et al. / Journal of Organometallic Chemistry 630 (2001) 205–214
cyclooxygenase reaction [1]. Several NSAIDs have been
used in combination with cytotoxic drugs, and the
interactions of mefenamic acid, sulindac and in-
domethacin with cyclophosphamide, melphalanor car-
mustine have been studied [2]. A specific group of
NSAIDs, indomethacin, sulindac, tolmetin, acemetacin,
zomepirac and mefenamic, all at non-toxic levels, sig-
nificantly increased the cytotoxicity of the anthracy-
clines, doxorubicin, daunorubicin and epirubicin, as
well as teniposide, VP-16 and vincristine [3]. Mefenamic
acid chemically resembles tolfenamic [4] and flufenamic
acids and other fenamates in clinical use. Complexes of
mefenamic acid with iron(III) [5a], sodium(I) and calci-
um(II) [5] have been reported. Characterization of the
complexes based on spectroscopic results was per-
formed and possible structures were proposed [5]. The
crystal structures of mefenamic acid and of a copper(II)
complex have been solved [6].
2. Experimental
2.1. General and instrumental
The reagents (Aldrich, Merck) were used as supplied
while the solvents were purified according to standard
procedures. Mefenamic acid was a gift from ‘VIAN-
NEX A.E.’. C, H, and N analyses were carried out by
the microanalytical service of the University of Ioan-
nina. Melting points were determined in open capil-
laries and are uncorrected. Infrared and far-infrared
spectra were recorded on a Nicolet 55XC Fourier trans-
form spectrophotometer using KBr pellets (4000–400
cm−1) and Nujol mulls dispersed between polyethylene
disks (400–40 cm−1). The H (250.13 MHz), and 13C
1
(62.90 MHz) NMR specta were recorded on a Bruker
AC-250 spectrometer. Samples were dissolved in CDCl3
or DMSO-d6 and spectra were obtained at room tem-
perature (r.t.) with the signal of the free DMSO or
CHCl3 (at 2.49 and 7.24 ppm, respectively) as a refer-
ence. Cross-peaking of heteronuclear multiple quantum
correlation (HMQC) and heteronuclear multiple bond
correlation (HMBC) gradient-assisted spectra of mefe-
namic acid were performed. Mo¨ssbauer spectra were
recorded on finely ground materials at 80.0 K using an
Air Liquid cryostat. The Ca119SnO3 source (15 mCi
New England Nuclear) at room temperature (r.t.) was
moved in a constant acceleration mode with a triangu-
lar wave form. Suitable computer programs were em-
ployed in the fitting procedure of the experimental
spectra to Lorentzian line shapes. The estimated errors
(1)
Organotin(IV) carboxylates form an important class
of compound and have received increasing attention in
recent years, not only because of their intrinsic interest
but also owing to their varied applications. These com-
pounds find wide use as catalysts and stabilizers, and
certain derivatives are used as biocides, as antifouling
agents and as wood preservatives [7]. Investigations
have been carried out to test their anti-tumor activity
and it has been observed that indeed several di- and
triorganotin species show potentiality as antineoplastic
agents [8].
Given the pharmacological importance of mefenamic
acid and the potential biological activity of organotin
carboxylates, it was thought of some interest to explore
the chemistry of organotin/mefenamic acid compounds.
As a continuation of our studies of biological organotin
chemistry [9] and on the coordination chemistry and
anti-inflammatory properties of NSAIDs such as di-
clofenac and tolfenamic acids [4,10], we report here the
on the Mo¨ssbauer parameters are 90.01 mm s−1
.
2.2. Synthesis
2.2.1. [Me2LSnOSnLMe2]2 (1)
A solution of mefenamic acid (0.262 g, 1 mmol) was
added to a solution of dimethyl tin oxide (0.198 g, 1.15
mmol) in benzene (40 ml). The reaction mixture was
refluxed for 24 h with azeotropic removal of water via
a Dean–Stark trap. The resulting clear yellow solution
was rotary evaporated under vacuum to a small vol-
ume, chilled and triturated with n-pentane to give a
yellow solid. The solid was filtered off, washed with
Et2O and dried in vacuo over silica gel; m.p. 183–
184 °C; yield 65%. Anal. Found: C, 51.59; H, 5.11; N,
3.26. Calc.: C, 51.42; H, 5.04; N, 3.52%.
synthesis
and
spectral
characterization
of
[R2LSnOSnLR2]2 (where R=CH3 (1), Bu (2) and L is
deprotonated mefenamic acid). The complexes have
been structurally characterized in the solid state by
means of 119Sn Mo¨ssbauer and vibrational spectroscopy
and in solution by 1H- and 13C-NMR spectroscopic
studies. The crystal and molecular structures of 1 and 2
are also described, these being the first structures of
organometallic mefenamic acid derivatives to be
reported.
2.2.2. [Bu2LSnOSnLBu2]2 (2)
Di-n-butyl tin oxide (0.286 g, 1.15 mmol) and mefe-
namic acid (0.241 g, 1.00 mmol) were refluxed in 40 ml
benzene for 24 h with azeotropic removal of water via
a Dean–Stark trap. The resulting clear solution was
rotary evaporated under vacuum to a small volume.
Drops of n-pentane were added and after slow evapora-
tion, a yellow powder was isolated; m.p. 115–117 °C;

V. Dokorou et al. / Journal of Organometallic Chemistry 630 (2001) 205–214
207
yield 53%. Anal. Found: C, 57.95; H, 6.80; N, 2.76.
Calc.: C, 57.45; H, 6.65; N, 2.91%.
anisotropic thermal parameters; hydrogen atoms were
included from the molecular geometry and Dz maps
but were not refined. For 2 one symmetry-independent
butyl group is partly disordered (the C(7), C(8), C(7%),
and C(8%) atoms). The occupancy parameters for the
respective groups of atoms are 0.6 and 0.4.
2.3. X-ray crystallography
Crystal data are given in Table 1, together with
refinement details. All measurements of crystals were
performed on a Kuma KM4CCD kappa-axis diffrac-
tometer with graphite-monochromated Mo–Ka radia-
tion. The crystals were positioned at 65 mm from the
KM4CCD camera. Six hundred and twelve frames were
measured at 0.75° intervals with a counting time of 30
s. The data were corrected for Lorentz and polarization
effects. No absorption correction was applied. Data
reduction and analysis were carried out with the Kuma
Diffraction (Wroclaw) programs. The structures were
solved by direct methods and refined by the full-matrix
least-squares method on all F2 data using the SHELXL97
program [11]. Non-hydrogen atoms were refined with
3. Results and discussion
3.1. Crystal structures of 1 and 2
Compounds 1 and 2 are obtained by azeotropic
removal of water produced by the reaction between the
diorganotin oxide and mefenamic acid in the molar
ratio 1:1. The molecular structures of 1 and 2 are
shown in Figs. 1 and 2, respectively, and selected
interatomic parameters are collected in Table 2. Com-
pounds 1 and 2 are centro-symmetric dimers built up
around the planar cyclic Sn2O2 unit. The two oxygen
atoms O(1) and O(1a) are triply bridging, each linking
one exo-cyclic (Sn(1) or Sn(1a)) and two endo-cyclic
(Sn(2) and Sn(2a)) atoms. Additional links between the
exo- and endo-cyclic tin centers Sn(1) and Sn(2), respec-
tively, are provided by four bidentate bridging carboxy-
late ligands for 1, while for 2 the coordination geometry
about each exo-cyclic tin atom, Sn(1), is completed by
one bridging and one monodentate carboxylate ligand.
A pentacyclic and a tricyclic ring system with the
central unit of Sn2O2 are exhibited by 1 and 2, respec-
tively. The coordination number around each tin is five
for 2 and five and six around Sn(1) and Sn(2), respec-
tively, for 1. Analysis of the shape determining angles
for 2, using the approach of Reedijk and coworkers
[12], yields ~ ((h−i)/60) values of 0.40 and 0.38 for
Sn(1) and Sn(2), respectively (~=0.0 and 1.0 for SPY
and TBPY geometries, respectively). The metal coordi-
nation geometry is therefore described as distorted
square pyramidal with the O(1) atom occupying the
apical positions for both Sn(1) and Sn(2). The donor
O(1) is chosen as apex by the simple criterion that it
should not be one of the oxygens which defines either
of the two largest LꢀSnꢀL angles, h and i [12]. Distor-
tions from the ideal geometries may be related to the
Table 1
Crystal data and structure refinement parameters for 1 and 2
1
2
Empirical formula
Formula weight
Temperature (K)
C68H80N4O10Sn4
1588.12
100(2)
C
92H128N4O10Sn4
1924.74
100(2)
,
Wavelength (A)
0.71073
Triclinic
0.71073
Triclinic
Crystal system
Space group
(
(
P1
P1
Unit cell dimensions
,
a (A)
9.898(1)
12.009(1)
15.498(1)
68.14(1)
76.52(1)
87.03(1)
1661.4(2)
1
11.319(1)
12.115(1)
19.101(2)
92.29(1)
105.34(1)
116.66(1)
2218.9(4)
1
,
b (A)
,
c (A)
h (°)
i (°)
k (°)
3
,
Volume (A )
Z
Dcalc (Mg m−3
Absorption
)
1.587
1.545
1.440
1.171
coefficient (mm−1
)
F(000)
796
988
Crystal size (mm)
Diffractometer
q range for data
collection (°)
0.12×0.07×0.07
Kuma KM4CCD
3.40–28.76
0.20×0.20×0.12
Kuma KM4CCD
3.29–28.77
,
close approach (2.800(3) A) of the O(4a) atom to Sn(2),
Index ranges
−135h510,
−155k515,
−205l520
−145h511,
−165k516,
−245l524
16 067
,
and of the O(5) atom to Sn(1) (2.727(3) A) (symmetry
operation (i): 1−x, −y, −z). These distances are long
for primary SnꢀO bonding, but are similar to an inter-
molecular approach in the Bu2Sn(IV) complex of pirox-
icam [9e] and other complexes [13] and therefore
represent a type of secondary interaction. Analysis of
the shape determining angles for Sn(1) in 1 gives a ~
value of 0.80. The metal coordination geometry is
therefore described as distorted trigonal bipyramidal
with the O(2) and O(5a) atoms occupying the axial
positions and O(1), C(1) and C(2), the equatorial
positions.
Reflections collected 12 028
Independent
reflections
7568 [Rint=0.0267]
10 103 [Rint=0.0230]
Data/parameters
Final R indices
[I\2|(I)]
7568/548
10 103/514
R1=0.0445
wR2=0.0971
1.067
R1=0.0278
wR2=0.0592
0.987
Goodness-of-fit on
F2
Largest difference
1.682 and −0.778
2.486 and −1.384
peak and hole
−3
,
(e A
)

208
V. Dokorou et al. / Journal of Organometallic Chemistry 630 (2001) 205–214
Fig. 1. Perspective view of [Me2SnLOLSnMe2]2 (1) showing the atomic numbering scheme.
Fig. 2. Perspective view of [Bu2SnLOLSnBu2]2 (2) showing the atomic numbering scheme.
For 1, the SnꢀO bond distances involving the bridg-
bidentate carboxylato this difference is only 0.034. The
,
ing carboxylate ligands differ by 0.3254 and 0.2312 A
indicating asymmetrical bridges; the variations in the
CꢀO bond distances are much less and suggest charge
delocalization over the carboxylato group COO. For 2,
the Sn(1)ꢀO(2), Sn(2)ꢀO(3) bond distances involving
the bridging carboxylate ligand, 2.290(3) and 2.227(3)
different modes of bonding of the acetates, i.e. bridging
or hanging, are thus easily differentiated by the relevant
bond lengths.
The phenyl rings are planar. The dihedral angles
between the planes of the phenyl rings in 1 are
88.48(16) and 48.13(16)° for the bidentate ligands
bridging the two centers Sn(1)ꢀSn(2) and Sn(1)ꢀSn(2a),
respectively. The dihedral angles between the planes of
the phenyl rings for 2 are 73.8(4) and 47.0(3)°, respec-
tively, for the bidentate bridging and the monodentate
ligands. The aminobenzoate portion of each carboxy-
lato ligand is effectively planar which presumably facil-
,
,
A, respectively, differ by only 0.063 A indicating a
nearly symmetrical bridge; this is supported by both
distances being longer than the Sn(1)ꢀO(4) bond dis-
,
tance, 2.171(3) A, formed by the monodentate carboxy-
lato ligand. The monodentate carboxylato has a
difference of 0.112 between its CꢀO bonds while for the

V. Dokorou et al. / Journal of Organometallic Chemistry 630 (2001) 205–214
209
itates the formation of intramolecular N(28)ꢀH···O(2)
and N(48)ꢀH···O(5) interactions of 2.643(9) and
tetramer ‘faces’ the corresponding phenyl ring of an
,
adjacent tetramer at a distance of 3.587 A showing
,
2.632(5) A, respectively. By contrast, significant twists
significant p“p stacking interactions. For 2, the
between the aromatic fragments of bidentate and
monodentate ligands are noted.
The crystal structures of 1 and 2 show ring stacking
interactions. For 1, the phenyl ring C(39)ꢀC(46) of the
phenyl ring C(22)ꢀC(27) ‘faces’ the phenyl ring
,
C(42)ꢀC(47) at a distance of 3.785 A. Further, CꢀH“p
interactions and intramolecular hydrogen bonds stabi-
lize the two structures. The polar imino hydrogen
atoms on N(18), N(38) and N(28), N(48) for 1 and 2,
respectively, participate in a bifurcated intramolecular
hydrogen bond system, as shown in Table 3. In this
case complexes 1 and 2 are self-assembled via CꢀH“p
and p“p stacking interactions and a different packing
arrangement from bis(2-[(2,6-dichlorophenyl)amino]-
phenyl]acetate) oxide results [9f]. The overall geometry
found in the structures of 1 and 2, allowing for differ-
ences in chemistry, are remarkably similar to com-
pounds with the general formula [R2(R%CO2)SnOSn-
(O2CR%)R2]2 [14]. Views of the crystal packing along the
h axes for 1 and 2 are shown in Figs. 3 and 4,
respectively.
Table 2
a
,
Bond lengths (A) and bond angles (°) for 1 and 2
1
2
Bond lengths
Sn(1)ꢀO(1)
Sn(1)ꢀC(1)
Sn(1)ꢀC(2)
Sn(1)ꢀO(2)
Sn(1)ꢀO(5i)
Sn(2)ꢀO(1i)
Sn(2)ꢀC(3)
Sn(2)ꢀO(1)
Sn(2)ꢀC(4)
Sn(2)ꢀO(4)
Sn(2)ꢀO(3)
O(1)ꢀSn(2i)
O(2)ꢀC(11)
O(3)ꢀC(11)
O(4)ꢀC(31)
O(5)ꢀC(31)
2.0059(18)
2.107(3)
2.108(3)
2.1656(19)
2.1911(19)
2.0935(19)
2.102(3)
2.1055(18)
2.107(3)
2.4223(18)
2.491(2)
2.0935(19)
1.275(3)
1.265(3)
1.268(3)
Sn(1)ꢀO(1)
Sn(1)ꢀC(5)
Sn(1)ꢀC(1)
Sn(1)ꢀO(4)
Sn(1)ꢀO(2)
Sn(2)ꢀO(1)
Sn(2)ꢀC(13)
Sn(2)ꢀC(9)
Sn(2)ꢀO(1i)
Sn(2)ꢀO(3)
O(1)ꢀSn(2i)
O(2)ꢀC(21)
O(3)ꢀC(21)
O(4)ꢀC(41)
O(5)ꢀC(41)
2.027(3)
2.123(5)
2.125(4)
2.171(3)
2.290(3)
2.034(3)
2.117(4)
2.122(4)
2.173(3)
2.227(3)
2.173(3)
1.233(5)
1.345(5)
1.301(5)
1.267(6)
3.2. Spectroscopy
3.2.1. Infrared spectroscopy
The most prominent absorptions are shown in Table
4. Compounds 1 and 2 gave bands at ꢀ3340 and 3290
cm−1 attributable to intramolecular hydrogen bonds
NH···O. The was(COO) and wsym(COO) bands appear at
ꢀ1610–1500 and ꢀ1450–1260 cm−1, respectively.
The difference, D [was(COO)−wsym(COO)] between
these frequencies for 1 is close to that found for bridg-
1.271(3)
Bond angles
O(1)ꢀSn(1)ꢀC(1)
O(1)ꢀSn(1)ꢀC(2)
C(1)ꢀSn(1)ꢀC(2)
O(1)ꢀSn(1)ꢀO(2)
C(1)ꢀSn(1)ꢀO(2)
C(2)ꢀSn(1)ꢀO(2)
O(1)ꢀSn(1)ꢀO(5i)
C(1)ꢀSn(1)ꢀO(5i)
C(2)ꢀSn(1)ꢀO(5i)
O(2)ꢀSn(1)ꢀO(5i)
O(1i)ꢀSn(2)ꢀC(3)
O(1i)ꢀSn(2)ꢀO(1)
C(3)ꢀSn(2)ꢀO(1)
O(1i)ꢀSn(2)ꢀC(4)
C(3)ꢀSn(2)ꢀC(4)
O(1)ꢀSn(2)ꢀC(4)
O(1i)ꢀSn(2)ꢀO(4)
C(3)ꢀSn(2)ꢀO(4)
O(1)ꢀSn(2)ꢀO(4)
C(4)ꢀSn(2)ꢀO(4)
O(1i)ꢀSn(2)ꢀO(3)
C(3)ꢀSn(2)ꢀO(3)
O(1)ꢀSn(2)ꢀO(3)
C(4)ꢀSn(2)ꢀO(3)
O(4)ꢀSn(2)ꢀO(3)
114.16(14)
116.39(11)
129.43(16)
89.31(7)
93.84(13)
85.44(11)
90.52(7)
89.12(13)
91.80(11)
176.82(7)
101.78(11)
75.95(8)
99.69(10)
101.06(11)
152.08(14)
101.24(11)
84.77(7)
O(1)ꢀSn(1)ꢀC(5)
O(1)ꢀSn(1)ꢀC(1)
C(5)ꢀSn(1)ꢀC(1)
O(1)ꢀSn(1)ꢀO(4)
C(5)ꢀSn(1)ꢀO(4)
C(1)ꢀSn(1)ꢀO(4)
O(1)ꢀSn(1)ꢀO(2)
C(5)ꢀSn(1)ꢀO(2)
C(1)ꢀSn(1)ꢀO(2)
O(4)ꢀSn(1)ꢀO(2)
O(1)ꢀSn(2)ꢀC(13)
O(1)ꢀSn(2)ꢀC(9)
C(13)ꢀSn(2)ꢀC(9)
O(1)ꢀSn(2)ꢀO(1i)
C(13)ꢀSn(2)ꢀO(1i)
C(9)ꢀSn(2)ꢀO(1i)
O(1)ꢀSn(2)ꢀO(3)
C(13)ꢀSn(2)ꢀO(3)
C(9)ꢀSn(2)ꢀO(3)
O(1i)ꢀSn(2)ꢀO(3)
Sn(1)ꢀO(1)ꢀSn(2)
110.91(18)
112.51(15)
134.9(2)
80.33(11)
102.2(2)
96.52(14)
89.38(11)
84.3(2)
ing bidentate carboxylato groups (142 and 126 cm−1
)
and for 2 is close to that found for monodentate (313
cm−1) and bridging bidentate carboxylato groups (123
cm−1) [4,15]. This is totally consistent with the X-ray
84.43(15)
169.23(12)
108.38(14)
108.44(14)
142.94(17)
76.18(12)
94.14(13)
98.49(14)
91.12(11)
84.06(14)
91.15(15)
165.95(11)
135.39(14)
structures. Two bands at 490–470 and 430–420 cm−1
,
for each of 1 and 2, are assigned to was,sym(SnO)2,
indicating nonlinear OꢀSnꢀO moieties, while the bands
at 250–200 cm−1 are assigned to the tinꢀoxygen (COO)
stretching modes [4,14].
3.2.2. Mo¨ssbauer spectroscopy
82.06(10)
160.62(7)
84.26(10)
162.81(7)
82.10(11)
86.90(7)
The spectra present slightly asymmetrical quadrupole
split doublets, whose parameters are typical of diorgan-
otin complexes [7b]. The linewidths were narrow
enough (around 0.8 mm s−1) to consider the existence
of a single tin site and the parameters pointed to a
severely distorted penta-coordinated site. This was ac-
Sn(1)ꢀO(1)ꢀSn(2i) 120.31(13)
Sn(2)ꢀO(1)ꢀSn(2i) 103.82(12)
80.81(11)
112.41(6)
C(21)ꢀO(2)ꢀSn(1)
C(21)ꢀO(3)ꢀSn(2)
C(41)ꢀO(4)ꢀSn(1)
C(2)ꢀC(1)ꢀSn(1)
134.1(3)
134.9(2)
107.4(3)
115.1(3)
ceptable for compound 2, l, 1.47; DEQ, 3.27 mm s−1
,
Sn(1)ꢀO(1)ꢀSn(2i) 127.89(9)
Sn(1)ꢀO(1)ꢀSn(2) 127.86(9)
Sn(2i)ꢀO(1)ꢀSn(2) 104.05(8)
C(11)ꢀO(2)ꢀSn(1) 126.46(18)
C(11)ꢀO(3)ꢀSn(2) 118.76(18)
C(31)ꢀO(4)ꢀSn(2) 118.83(17)
C(31)ꢀO(5)ꢀSn(1i) 120.19(17)
because of the agreement with the crystal structure. On
the contrary, this solution is unacceptable for com-
pound 1, so a fitting of the data to two doublets with
the same area was attempted, l, 1.47 and 1.27; DEQ,
3.43 and 3.12 mm s−1. The new solution gives a small
improvement in the quality of fit and parameters rea-
sonable for distorted penta- and hexa-coordinated tin
a Symmetry operation (i) −x, −y, 1−z.

Table 3
,
Distances (A) and angles (°) of CꢀH–p, p–p interactions and intramolecular hydrogen bonds for 1 and 2
CꢀH–p, p–p interactions and intramolecular hydrogen bonds for
1
2
/
CꢀH(I)“Cg(J)
H···Cg
2.99
C···Cg
3.556
ÚCꢀH···Cg
121
CꢀH(I)“Cg(J)
H···Cg
3.07
3.23
3.25
3.00
3.14
2.81
2.86
C···Cg
3.851
3.597
3.945
3.475
3.825
3.660
3.798
ÚCꢀHꢀCg
138
105
130
112
131
153
167
C(15)ꢀH(15)“Cg(7)I
C(8)ꢀH(8B)“Cg(4)iii
C(10)ꢀH(10B)“Cg(1)iv
C(11)ꢀH(11B)“Cg(3)v
C(14)ꢀH(14A)“Cg(1)iv
C(30)ꢀH(30)“Cg(6)i
C(51)ꢀH(51)“Cg(4)vi
C(55)ꢀH(55C)“Cg(6)vi
a
c
c
Cg(I)“Cg(J)
CgꢀCg b
3.587
i
CgI-Perp d
3.475
CgJ-Perpe
3.475
Cg(I)“Cg(J) a
Cg(3)“Cg(5)i
Cg(5)“Cg(3)vii
CgꢀCg b
3.785
3.785
i
CgI-Perp d
3.562
3.425
CgJ-Perp e
3.425
3.562
Cg(8)“Cg(8)ii
14.40
25.19
19.74
D
H
A f
O(3)
O(4)
O(5)
D···A
H···A
ÚDꢀH···A
141(3)
137(3)
D
H
A f
D···A
H···A
1.97
1.99
2.40
2.45
ÚDꢀH···A
132
141
101
101
N(18)
N(38)
C(33)
H(18)
H(38)
H(33)
2.712(4)
2.687(3)
2.741(4)
2.07(3)
2.05(3)
2.42(3)
N(28)
N(48)
C(23)
C(43)
H(28)
H(48)
H(23)
H(43)
O(2)
O(5)
O(3)
O(4)
2.643(9)
2.632(5)
2.730(6)
2.775(6)
630
1
102(2)
205
a Cg(7) and Cg(8) are referred to the centroids C(32)ꢀC(38) and C(39)ꢀC(44) for 1, Cg(1), Cg(3), Cg(4), Cg(5) and Cg(6) are referred to the centroids Sn(2)ꢀO(1)ꢀSn(2a)ꢀO(1a), C(22)ꢀC(27),
C(29)ꢀC(34), C(42)ꢀC(47) and C(49)ꢀC(54) for 2.
214
b Cg–Cg is the distance between ring centroids; symmetry transformations: (i) x, −1+y, z; (ii) −x, 3−y, −z; (iii) −1+x, y, z; (iv) 1−x, −y, −z; (v) 2−x, −y, −z; (vi) 2−x, 1−y, 1−z;
(vii) x, 1+y, z.
c i is the angle Cg(I)“Cg(J) or Cg(i)“Me vector and normal to plane I (°).
d CgI-Perp is the perpendicular distance of Cg(I) on ring J.
e CgJ-Perp is the perpendicular distance of Cg(J) on ring I.
f D is donor and A is acceptor.

V. Dokorou et al. / Journal of Organometallic Chemistry 630 (2001) 205–214
211
Fig. 3. Packing diagram of the complex of [Me2SnLOLSnMe2]2 (1) viewed along the h axis.
Fig. 4. Packing diagram of the complex of [Bu2SnLOLSnBu2]2 (2) viewed along the h axis.
Table 4
Selected IR absorption bands (cm−1) of organotin(IV) complexes
No.
w(NH)
was(COO)
wsym(COO)
D
w(SnO)2
w(SnC)
w(SnO)
l(SnO)
NaL
1
3291s
3310m
3248s
1580s
1615s
1580s
1390s
1473s
1454ms
180
142
126
473ms
426vs
550mw
522m
246m
219m
174mw
147mw
505vs
555mw
534m
2
3325s
3254s
1615s
1579s
1272s
1456
313
123
479ms
428s
237mw
212mw
185mw
155mw
507m

Table 5
1H- and 13C-NMR data
COOH
NH
H3
H4
H5
H6
H4%
H5%
H6%
2%-CH3; 3%-CH3
b
Mef a
9.11s
9.52s
9.35br 8.00br
8.03d
7.94d
6.69dd
6.71dd
6.99d
7.28t
7.32t
7.10d
6.69dd 7.10m c 7.10m
7.10m
7.08m
7.18m
2.18s/2.34s
2.13s/230s
2.17s/2.32
Mef d 13.12
6.71dd 7.08m
7.08m
7.18m
1 a
1 a
2 a
Me2Sn
6.79d
6.75d
6.75d
7.18m
7.10m
7.11m
/
0.96s/1.05s
1.55s/1.55s
Me2Sn
0.75t/0.85t
0.85t/1.23m
Bu2Sn
9.77br 8.26/8.30br
6.96d/6.11d
7.21t/7.89
7.10m
7.11m
7.10m
7.11m
2.08s/2.50s
2.17s/2.50s
9.45
8.10d
6.84d
7.17t
Hd: 0.90, Hg: 1.25, Ha, 9.19
b: 1.54
COOH
Mef. a,e 173.05
C1
C2
C3
C4
C5
C6
C1%
C2%
C3%
C4%
C5%
C6%
2%-CH3; 3%-CH3
150.3
149.8
149.8
109.2
110.9
113.3
132.4
133.2
133.4
116.1
116.2
115.8
135.2
134.8
135.0
113.7
113.5
113.3
138.4
138.2
137.4
132.9
132.2
132.6
138.8
138.2
139.3
123.7 126.0 127.2 20.7/14.3
122.6 125.7 126.2 20.5/14.0
122.5 125.7 126.2 20.6/13.9
1 a
2 a
COOH 177.0
Me2Sn: 5.0/8.5
Bu2Sn Cd: 12.5, Cg:
26.9, Cb: 27.7, Ca:25.6
630
(
a Spectrum recorded in CDCl3.
205
b Carboxyl proton exchanged in CDCl3.
c These resonances formed a multiplet.
d Spectrum recorded in DMSO-d6.
e Ref. [15].
214

V. Dokorou et al. / Journal of Organometallic Chemistry 630 (2001) 205–214
213
sites. However, both solutions are acceptable from a
4. Supplementary material
Mo¨ssbauer point of view, thereby demonstrating that
the molecular structures cannot be derived from Mo¨ss-
bauer data in isolation.
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC nos. 159477 and 159478 for com-
pounds 1 and 2, respectively. Copies of this information
may be obtained free of charge from The Director,
CCDC, 12 Union Road, Cambridge CB2 1EZ, UK
(Fax: +44-1223-336033; e-mail: deposit@ccdc.cam.
ac.uk or www: http://www.ccdc.cam.ac.uk.
3.2.3. NMR spectra
The 1H- and 13C-NMR data for mefenamic acid,
structure 1 and the complexes are summarized in Table
5. These results, together with the published data on
mefenamic acid [16] allowed complete assignment of all
signals in the spectra of both the mefenamic acid and
organotin complexes. The downfield chemical shift for
HN in mefenamic acid indicates that this proton is
involved in hydrogen bonding. The crystal structure of
mefenamic acid suggests the presence of hydrogen-
bonded dimers linked by two intermolecular O···HꢀO
hydrogen bonds and an intramolecular hydrogen bond
between the HN group and the carbonyl group of the
carboxyl acid [6a]. The existence of the HN resonance
in the 1H-NMR spectra indicates that the nitrogen
Acknowledgements
D.K.D. thanks VIANNEX A.E. for the generous gift
of mefenamic acid. This work was supported by the
EPEAEK Program ‘Bioinorganic Chemistry’, Director
Professor N. Hadjiliadis and by the Ministry of Devel-
opment General Secretariat for Research and Technol-
ogy (project no AP 17975 to D.K.D. and U.R.).
1
atoms remain protonated in 1 and 2. In the H-NMR
spectrum of 1, three singlets appear in the region of the
tin-bound methyl groups, in the case of the multiple
signal emerging at 1.55 ppm, two methyl groups are
present. For 1, the appearance of two resonances for
each of H(3), H(4) and H(5), shows the existence of two
inequivalent ligands in DMSO-d6 solution. Deshielding
of protons H(3) and H(4) is observed in complexes 1
and 2, which should be related to the electrophilicity of
the tin. A s-charge donation from the COO− donor to
the tin center removes electron density from the ligand
and produces this deshielding which will attenuate at
positions remote from the metal. All shifts are
downfield except for that due to H(5) which is shifted
upfield. The upfield shift observed for H(5) and its
corresponding carbon atom C5, para to the tin center,
could be due to the flow of charge from the tin into the
aromatic ring [18]. Involvement of the carboxyl group
in bonding to Sn is confirmed by the resonances as-
cribed to C2 and C3, which exhibit the greatest shifts
upon coordination. The remaining resonances due to
the aromatic carbon atoms do not shift significantly on
binding to Sn. No resonance attributable to the car-
boxyl C nucleus was found for 2, behavior that has
been noted previously for related systems [4]. In the
13C-NMR spectra, the greatest downfield shift is exhib-
ited by the carbonyl C (4.0 ppm) for 2, while the C3
atom shifts downfield by 0.8–1.0 ppm. The C5 reso-
nance, by contrast, shifts upfield. Three resonances
attributed to the tin-bound methyl carbons are found, a
result that is consistent with the presence of a dimer in
solution by analogy with related compounds [4,17].
Application of the Lockhart–Manders equation [19] to
1 predicted, in CDCl3 solution, CꢀSnꢀC angles of 133
(two values), 118 and 137°, and in (CD3)SO solution
corresponding values of 132 (two angles), 114 and 159°.
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