Synthesis and spectroscopic studies of diorganotin derivatives with 2-[(2,6-dimethylphenyl)amino]benzoic acid (see abstract)

Article abstract of DOI:10.1016/j.jorganchem.2003.10.018

The complexes [Bu₂(DMPA)SnOSn(DMPA)Bu₂]₂ (2) and [Bu₂Sn(DMPA)₂] (3), where HDMPA is 2-[bis(2,6-dimethylphenyl)amino]benzoic acid, have been prepared and structurally characterized by means of, vibrational, ultra-violet, ¹H and ¹³C NMR spectroscopies. The crystal structure of complexes 2 and 3 have been determined by X-ray crystallography. Three distannoxane rings are present to the dimeric tetraorganodistannoxane of planar ladder arrangement of 2. The structure is centro-symmetric and features a central rhombus Sn₂O₂ unit with two additional tin atoms linked at the O atoms. Five- and six-coordinated tin centers are present in the dimmer distannoxane. The crystal structure of 3 consists of discrete molecular units and the two modeprononated ligands are co-ordinated to the SnBu₂ fragment. The ligands act as anisobidentate chelating agents, thus rendering the tin atom six-co-ordinated. Significant π→π, C-H-π stacking interactions and intramolecular hydrogen bonds stabilize the structures 2 and 3. The polar imino hydrogen atom participates in intramolecular hydrogen bonds. Complexes 2 and 3 are self-assembled via π→π C-H-π and stacking interactions.

Full text of DOI:10.1016/j.jorganchem.2003.10.018

Journal of Organometallic Chemistry 689 (2004) 317–325
www.elsevier.com/locate/jorganchem
Synthesis and spectroscopic studies of diorganotin derivatives with
2-[(2,6-dimethylphenyl)amino]benzoic acid. Crystal and
molecular structure of the first complexes of
2-[(2,6-dimethylphenyl)amino]benzoic acid. Crystal and
molecular structures of 1,2:3,4-di-l2-2-[(2,6-dimethylphenyl)amino]-
benzoato-O,O-1,3-bis-2-[(2,6-dimethylphenyl)amino]benzoato-O-
1,2,4:2,3,4-di-l3-oxo-tetrakis[di-butyltin(IV)] and
bis-2-[(2,6-dimethylphenyl)amino]benzoato-di-n-butyltin(IV)
a
Vaso Dokorou , Mavroudis A. Demertzis , Jerry P. Jasinski ,
a
b
a,
*
Dimitra Kovala-Demertzi
a
Inorganic Chemistry, Department of Chemistry, University of Ioannina, 45110 Ioannina, Greece
b
Department of Chemistry, Keene State College, 229 Main Street, Keene, NH 03435-2110, USA
Received 16 September 2003; accepted 16 October 2003
Abstract
The complexes [Bu2(DMPA)SnOSn(DMPA)Bu2]2 (2) and [Bu2Sn(DMPA)2] (3), where HDMPA is 2-[bis(2,6-dimethylphe-
nyl)amino]benzoic acid, have been prepared and structurally characterized by means of, vibrational, ultra-violet, 1H and 13C NMR
spectroscopies. The crystal structure of complexes 2 and 3 have been determined by X-ray crystallography. Three distannoxane rings
are present to the dimeric tetraorganodistannoxane of planar ladder arrangement of 2. The structure is centro-symmetric and
features a central rhombus Sn2O2 unit with two additional tin atoms linked at the O atoms. Five- and six-coordinated tin centers are
present in the dimmer distannoxane. The crystal structure of 3 consists of discrete molecular units and the two modeprononated
ligands are co-ordinated to the SnBu2 fragment. The ligands act as anisobidentate chelating agents, thus rendering the tin atom six-
co-ordinated. Significant p ! p, C–H-p stacking interactions and intramolecular hydrogen bonds stabilize the structures 2 and 3.
The polar imino hydrogen atom participates in intramolecular hydrogen bonds. Complexes 2 and 3 are self-assembled via p ! p
C–H-p and stacking interactions.
Ó 2003 Elsevier B.V. All rights reserved.
Keywords: 2-[bis(2,6-dimethylphenyl)amino]benzoic acid; Diorganotin adducts; Crystal structures; Spectroscopic studies
1. Introduction
inhibit by 48.0% on triiodothyronine (T3) uptake by H4
hepatocytes and octanol–water partition coefficient was
found to be 5.337 [1a]. The anti-inflammatory activity of
HDMPAÕs was measured by the anti-UV-erythema test
and the minimum effective dose (MED) was found to be
50 mg/kg [1b].
2-[(2,6-dimethylphenyl)amino]benzoic acid or N-(2,6-
dimethylphenyl)anthranilic acid), HDMPA, 1, Scheme 1,
resembles mefenamic, tolfenamic, flufenamic acids and
other fenamates in clinical use. HDMPA was found to
Organotin(IV) carboxylates form an important class
of compounds and have been receiving increasing at-
tention in recent years, not only because of their intrinsic
interest but owing to their varied applications. Some
* Corresponding author. Tel.: +30-265098425; fax: +30-265044825.
E-mail address: dkovala@cc.uoi.gr (D. Kovala-Demertzi).
0022-328X/$ - see front matter Ó 2003 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2003.10.018

318
V. Dokorou et al. / Journal of Organometallic Chemistry 689 (2004) 317–325
2.2. Synthesis
HDMPA (1). HDMPA was synthesized according
to published procedure, the Ullmann–Goldberg
condensation [1]. 2,6-dimethylbenzenamine (5.60 g, 46
mmol), potassium 2-bromobenzoate (11.36 g, 47 mmol),
4-ethylmorpholine (5.46 g, 47 mmol) and 0.5 g of anhy-
drous copper acetate in 20 ml of distilled N,N-dimethyl-
formamide under nitrogen atmosphere were refluxed at
145° for 3 h. In the resulting solution was added 13 ml of
distilled N,N-dimethylformamide, and 19 ml of 12% hy-
drochloric acid. The aqueous layer was decanted and
methanol was added. The solid was collected and re-
crystallized three times from acetone., m.p.: 209–210°;
Yield 24,35% (2,70 gr). Anal. Found: C, 73.94; H, 6.59;
N, 5.79. Calc.: C, 74.18; H, 6.46; N, 5.81%.
[Bu2(DMPA)SnOSn(DMPA)Bu2]2 (2). Di-n-butyl ox-
ide (0.286 g, 1.15 mmol), HDMPA (0.2410 g, 1.0 mmol)
and 40 ml of benzene were refluxed overnight with azeo-
tropic removal of water via a Dean–Stark trap. The re-
sultingclearsolutionwasrotaryevaporatedundervacuum
toasmallvolume(3ml),chilledandtrituratedwithacetone
to give a white solid. The white powder was dried in vacuo
over silica gel. m.p. 160–162 °C; yield 35%. Anal. Found:
C, 57.30; H, 6.83; N, 2.76. Calc.: C, 57.41; H, 6.70; N,
2.91%.
Crystals of 2 suitable for X-ray analysis were obtained
by slow evaporation of a fresh CHCl3/EtOH solution.
[Bu2Sn(DMPA)2] (3). Di-n-butyltin(IV) oxide (0.2489
g, 1 mmol), HDMPA (0.5187 g, 2.15 mmol), and 40 ml of
benzene were refluxed 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 acetone were added and, after slow evaporation,
white powder was isolated, m.p. 115–117 °C; yield
78.30%. Anal. Found: C, 64.10; H, 6.70; N, 3.97. Calc.: C,
63.98; H, 6.49; N, 3.93%.
Scheme 1.
examples find wide use as catalysts and stabilizers, and
certain derivatives are used as biocides, as anti-fouling
agents and as wood preservatives [2]. Information on the
structures of organotin carboxylates continues to accu-
mulate, and at the same time new applications of such
compounds are being discovered in industry, ecology
and medicine. In recent years, investigations have been
carried out to test their anti-tumour activity and it has
been observed that indeed several diorganotin species, as
well as triorganotin species, show potential as anti-
neoplastic agents [3].
It was thought of interest to explore the chemistry of
organotin/phenylanthranilic acid compounds, as a con-
tinuation of our studies of organotin chemistry [4] and
on the coordination chemistry of non-steroidal anti-
inflammatory drugs, phenylanthranilic acids such as
diclofenac, mefenamic and tolfenamic acids [5]. The
novel complexes [Bu2(DMPA)SnOSn(DMPA)Bu2]2(2)
and [Bu2Sn(DMPA)2] (3) (DMPA is the deprotonated
N-(2,6-dimethylphenyl)anthranilic acid), have been
structurally characterized by means of vibrational, ultra-
violet and 1H- and 13C-NMR spectroscopic studies, and
the crystal and molecular structures of 2 and 3 are
described.
Crystals of 3 suitable for X-ray analysis were ob-
tained by slow evaporation of a fresh C6H6/CH3CN
solution.
2. Experimental details
2.1. General and instrumental
2.3. X-ray crystallography
The reagents (Aldrich, Merck) were used as supplied
while the solvents were purified according to standard
procedures. Melting points were determined in open
capillaries and are uncorrected. Infrared and far-infrared
spectra were recorded on a Nicolet 55XC Fourier
transform spectrophotometer using KBr pellets (4000–
400 cmꢀ1) and nujol mulls dispersed between polyethyl-
ene disks (400–40 cmꢀ1). UV spectra were acquired with a
JASCO V-570 spectrophotometer UV/VIS/NIR. The 1H
(250.13 MHz), 13C (62.90 MHz) NMR spectra were re-
corded on a Bruker AMX-400 and on a Bruker AC-250
spectrometer. Samples were dissolved in CDCl3 and
spectra were obtained at room temperature with the
signal of free CDCl3 (at 7.24 ppm) as a reference.
Crystal data are given in Table 1, together with
refinement details. All measurements of crystals were
performed on a Rigaku AFC6S diffractometer with
graphite monochromated Mo Ka radiation. The data
were collected using the x–2h scan technique to a
maximum 2h value of 55.0°. Omega scans of several
intense reflections, made prior to data collection, had an
average width at half-height of 0.31° and 0.23° for 2 and
3 respectively with a take-off angle of 6.0°. Scans of
(1.52 + 0.34 tanh)° were made at a speed of 8.0°/min (in
x). The weak reflections (I < 10:0rðIÞ) were rescanned
(maximum of four scans) and the counts were accumu-
lated to ensure good counting statistics. Stationary

V. Dokorou et al. / Journal of Organometallic Chemistry 689 (2004) 317–325
319
Table 1
Crystal data and refinement for 2 and 3
background counts were recorded on each side of the
reflection. The ratio of peak counting time to back-
ground counting time was 2:1. The diameter of the in-
cident beam collimator was 1.0 mm, the crystal to
detector distance was 400 mm, and the detector aperture
was 9:0 ꢁ 13:0 mm (horizontal ꢁ vertical). The structure
2 was solved by heavy-atom Patterson methods [6a] and
3 by direct methods [6b] and expanded using Fourier
techniques [6c]. The structures were refined by the full-
matrix least-squares method on all F 2 data using the
SHELXL97 programs [6d]. The non-hydrogen atoms
were refined anisotropically. Hydrogen atoms were lo-
cated by difference maps and refined isotropically.
Neutral atom scattering factors were taken from Cromer
and Waber [7a]. Anomalous dispersion effects were in-
cluded in Fcalc [7b]; the values for Df 0 and Df 00 were
those of Creagh and McAuley [7c]. All calculations were
performed using the teXsan [7d] crystallographic soft-
ware package of Molecular Structure Corporation ex-
cept for refinement, which was performed using
SHELXL-97 [6d].
2
3
Empirical formula
Formula weight
Temperature/K
C92H128N4O10Sn4
1924.82
296
C38H46N2O4Sn
713.48
296
ꢀ
Wavelength/A
Mo Ka 0.71069
Triclinic
P-1
Mo Ka 0.71069
Triclinic
P-1
Crystal system
Space group
ꢀ
a/A
12.275(4)
19.340(6)
11.438(4)
90.89(3)
116.11(3)
71.97(3)
2295.3(16)
1
12.234(4)
16.148(5)
10.449(4)
98.50(3)
114.90(3)
71.01(3)
1770.3(12)
2
ꢀ
b/A
ꢀ
c/A
a/°C
b/°C
c/°C
3
ꢀ
Volume/A
Z
Dc/mg mꢀ3
Absorption coefficient,
l/mmꢀ1
F(0 0 0)
1.335
1.132
1.339
0.762
988
740
Crystal size/mm
Diffractometer
h range for data
collection/°C
Ranges of h; k; l
0.30 ꢁ 0.40 ꢁ 0.50
Rigaku AFC6S
1.9, 27.5
0.20 ꢁ 0.40 ꢁ 0.50
Rigaku AFC6S
1.9, 27.5
0: 15; )23: 25;
)14: 13
11027
0: 15; )19: 20;
)13: 12
8499
Reflections collected
Independent reflections
3. Results and discussion
10532 (0.095)
8115 (0.136)
(Rint
)
3.1. Crystal structures of 2 and 3
Data/parameters
Goodness-of-fit (F 2)
Final R1/wR2 indices
(I > 2rI )
10532/496
1.08
0.0524, 0.2099
8115/406
0.98
0.0563, 0.2027
Compounds 2 and 3 are obtained by azeotropic re-
moval of water from the reaction between the di-n-butyl
oxide and HDMPA acid in the molar ratio 1:1 and 1:2
respectively conducted in benzene. The molecular
Largest difference
ꢀ3
1.65/)1.86
)0.86, 0.69
ꢀ
peak/hole/e A
Fig. 1. Perspective view of [Bu2(DMPA)SnOSn(DMPA)Bu2]2 (2) showing the atomic numbering scheme.

320
V. Dokorou et al. / Journal of Organometallic Chemistry 689 (2004) 317–325
Table 2
ꢀ
Bond lengths (A) and angles (°) for 2 and 3
2
3
Sn(1)–O(1)
Sn(1)–O(3)
Sn(1)–O(4)
Sn(1)–C(31)
Sn(1)–C(35)
Sn(2)–O(2)
Sn(2)–O(3)
Sn(2)–C(39)
Sn(2)–C(43)
Sn(2)–O(3)a
O(1)–C(16)
O(2)–C(16)
O(4)–C(1)
2.325(9)
2.021(6)
2.172(8)
2.118(11)
2.115(14)
2.241(9)
2.041(6)
2.118(9)
2.123(11)
2.193(7)
1.271(14)
1.250(12)
1.296(12)
1.238(13)
1.396(15)
1.418(14)
1.382(14)
1.419(14)
89.0(3)
Sn(1)–O(2A)
Sn(1)–O(2B)
Sn(1)–O(1A)
Sn(1)–O(1B)
Sn(1)–C(16A)
Sn(1)–C(16B)
O(1A)–C(1A)
O(1B)–C(1B)
O(2A)–C(1A)
O(2B)–C(1B)
N(1A)–C(3A)
N(1A)–C(8A)
N(1B)–C(3B)
N(1B)–C(8B)
2.085(6)
2.064(6)
2.562(7)
2.563(7)
2.106(10)
2.112(11)
1.246(11)
1.234(10)
1.298(12)
1.285(11)
1.367(11)
1.412(12)
1.358(10)
1.441(11)
O(5)–C(1)
N(1)–C(22)
N(1)–C(23)
N(2)–C(7)
N(2)–C(8)
O(1)–Sn(1)–O(3)
O(1)–Sn(1)–O(4)
O(1)–Sn(1)–C(31)
O(1)–Sn(1)–C(35)
O(3)–Sn(1)–O(4)
O(3)–Sn(1)–C(31)
O(3)–Sn(1)–C(35)
O(4)–Sn(1)–C(31)
O(4)–Sn(1)–C(35)
C(31)–Sn(1)–C(35)
O(2)–Sn(2)–O(3)
O(2)–Sn(2)–C(39)
O(2)–Sn(2)–C(43)
O(2)–Sn(2)–O(3)]a
O(3)–Sn(2)–C(39)
O(3)–Sn(2)–C(43)
O(3)–Sn(2)–O(3)a
C(39)–Sn(2)–C(43)
O(3)a–Sn(2)–C(39)
O(3)a–Sn(2)–C(43)
Sn(1)–O(1)–C(16)
Sn(2)–O(2)–C(16)
Sn(1)–O(3)–Sn(2)
Sn(1)–O(3)–Sn(2)a
Sn(2)–O(3)–Sn(2)a
Sn(1)–O(4)–C(1)
170.0(2)
83.6(4)
82.8(4)
O(2A)–Sn(1)–O(2B)
O(2A)–Sn(1)–C(16A)
O(2A)–Sn(1)–C(16B)
O(2B)–Sn(1)–C(16A)
O(2B)–Sn(1)–C(16B)
C(16A)–Sn(1)–C(16B)
O(1A)–Sn–O(1B)
83.1(2)
103.7(4)
109.3(3)
111.2(3)
102.5(4)
134.9(4)
168.0(2)
83.1(2)
82.1(2)
111.6(4)
109.4(4)
95.4(4)
104.4(4)
136.4(5)
91.7(3)
O(2B)–Sn–O(2A)
O(2B)–Sn–O(1B)
54.5(2)
55.1(2)
136.8(2)
O(2A)–Sn–O(1A)
O(2A)–Sn–O(1B)
91.5(4)
84.5(4)
167.2(3)
108.9(4)
109.6(4)
76.6(2)
141.5(5)
97.1(4)
94.6(4)
131.0(6)
134.7(8)
134.6(3)
121.6(3)
103.4(2)
106.0(6)
a Symmetry operation (i) ꢀx, 1 ꢀ y, 1 ꢀ z.
ꢀ
2.172(8) A and Sn(1)–O(5) 2.736(9) A). The Sn(1)–O(5)
ꢀ
distance 2.736(9) A is considered long to indicate signifi-
cant bonding interactions, however, the range of dis-
ꢀ
tances Sn–O of 2.61–3.02 A, has been confidently
reported for intramolecular bonds [8].
Analysis of the shape determining angles for 2, using
the approach of Reedijk and coworkers [9], yields
sðða ꢀ bÞ=60Þ a value of 0.43 for Sn(2) (s ¼ 0:0 and 1.0
for SP and TBP geometries respectively). The metal
coordination geometry is therefore described as dis-
torted square pyramidal with the O(3) atom occupying
the apical positions for Sn(2). The donor O(3) is chosen
as apex by the simple criterion that it should not be one
of the oxygens which define either of the two largest
ꢀ
structure of 2 is shown in Fig. 1 and selected interatomic
parameters are collected in Table 2.
Compound 2 is a centrosymmetric dimmer distan-
noxane built up around the planar cyclic Sn2O2 unit.
The two oxygen atoms of this unit are tridentate as they
link three Sn centres, two endo-cyclic and one exo-
cyclic. The distance between the endocyclic and exocyclic
tin atoms is 3.7483(16) and the distance between the two
endocyclic tin centers is 3.3240(16). The additional links
between the endo- and exo-cyclic Sn atoms are provided
by bidentate carboxylate ligands that form asymmetrical
ꢀ
bridges (Sn(1)–O(1) 2.325(9) A and Sn(2)–O(2) 2.241(4)
ꢀ
A). Each exocyclic Sn atom is also coordinated by an
anisobidentate chelating carboxylate ligand (Sn(1)–O(4)

V. Dokorou et al. / Journal of Organometallic Chemistry 689 (2004) 317–325
321
L–Sn–L angles, a and b [9]. Distortions from the ideal
geometries may be related to the close approach 2.918(6)
ꢀ
A of the O(4A) atom to Sn(2), (symmetry operation i:
ꢀx, 1 ꢀ y, 1 ꢀ z). This distance is long for primary Sn–O
bonding, but represent a type of secondary interaction
[5]. The structures of dimeric distannoxane of
anthranilic acid, [Me2(NH2-o-H4C6CO2)SnOSn(NH2-o-
H4C6CO2)Me2]2 and its p-isomer[Me2(NH2-po-H4C6CO2)
SnOSn(NH2-p-H4C6CO2)Me2]2 were reported by
Holmes et al. [10]. The o-isomer has solid state structure
closely resembling the 2, both in the geometry of the
central core (Sn2O2)2, the coordination mode of an-
thranilic acid and the presence of weaker interactions
(2.746(7)–2.909(6)), while the p-isomer exhibits all an-
isobidentate chelating carboxylate ligands [10]. For 2,
the Sn(1)–O(1), Sn(2)–O(2) bond distances involving the
ꢀ
bridging carboxylate ligand, 2.325(9) and 2.241(9) A
ꢀ
respectively, differ by only 0.084 A indicating a nearly
symmetrical bridge. The anisobidentate bidentate car-
ꢀ
boxylate has a difference of 0.058 A between its C–O
bonds while for the bidentate carboxylato this difference
ꢀ
is only 0.021 A; the variations in the C–O bond distances
Fig. 2. Packing diagram of [Bu2(DMPA)SnOSn(DMPA)Bu2]2 (2)
viewed along the b axis.
suggest charge delocalization over the carboxylato
group COO. The different modes of bonding of the ac-
etates, i.e. bridging or chelating, are thus easily differ-
entiated by the relevant bond lengths.
The complex 3 comprise discrete molecular units, in
which the carboxylato group functions as an anisobid-
entate chelating ligand [Sn–O(2A) 2.085(6), Sn–O(1A)
2.562(7) and Sn–O(2B) 2.064(6), Sn–O(1A) 2.563(7) re-
spectively for the two ligands], thus rendering the tin
atom six-coordinated. The intramolecular hydrogen
bond formed from the imino group N(1A) and N(1B)
contributes in causing the longer Sn–O(1a) and Sn–
O(1B) bonds. The two C–O bond distances of the car-
bonyl group are unequal [0.049 and 0.052 are the bond
The phenyl rings are planar. The dihedral angles be-
tween the planes of the phenyl rings for 2 are 81.7(9) and
59.6(6)° for the bidentate bridging and the anisobidentae
chelating ligands respectively. The aminobenzoate por-
tion of each carboxylato ligand is effectively planar
which presumably facilitates the formation of intramo-
lecular N(1)–Hꢂ ꢂ ꢂO(1) and N(2)–Hꢂ ꢂ ꢂO(5) interactions
ꢀ
of 2.654(13) and 2.662(14) A, respectively. The crystal
ꢀ
structure of 2 shows ring stacking interactions. The
monomers are stacked to a chain by double strong
p ! p interactions (C(2)–C(7) ! C(17)–C(22), C(17)–
C(22) ! C(2)–C(7); the phenyl rings C(2)–C(7) and
C(17)–C(22) ÔfaceÕ the phenyl rings C(17)–C(22) and
differences for the two ligands A] with the longer C–O
distance being associated with the shorter Sn–O bond
and vice versa. The phenyl rings are planar. The dihe-
dral angle between the planes of the phenyl rings in 3 is
86.7(5) and 75.4(4) for the two ligands C(1A)–C(15A)
and C(1B)–C(15B) respectively. The crystal structure of
3 shows C–H-p interactions and intramolecular hydro-
gen bonds. The polar imino hydrogen atoms on N,
participates in an intramolecular hydrogen bond, Table
3. Complex 3 is self-assembled via C–H-p and p ! p
stacking interactions.
ꢀ
C(2)–C(7) respectively at a distance of 3.941 A). These
p ! p interactions play an important role in the stabil-
ization of the stacked molecular chains. In addition, C–
H ! p play a role in the stabilization of the chains. The
butyl groups are pointed between the layers into the
channels. In this case complex 2 is self-assembled via C–
H-p and p ! p stacking interactions. View of the crystal
packing along the b axis for 2 is shown in Fig. 2. The
polar imino hydrogen atoms on N(1), and N(2) partic-
ipate in a bifurcated intramolecular hydrogen bond
system, as shown in Table 3. The overall geometry
found in 2, allowing for differences in chemistry, is re-
markably similar to compounds with the general for-
mula [R2(R0CO2)SnOSn(O2CR0)R2]2 [11].
3.2. Spectroscopy
3.2.1. Infrared spectroscopy
The most prominent absorptions are shown in Table 4.
As the carboxylic hydrogen is more acidic than the
imino hydrogen the deprotonation occurs in the car-
boxylic group. This is confirmed by the IR spectra of the
complexes, showing the characteristic bands for the
secondary amino groups and for the coordinated car-
The molecular structure of 3 is shown in Fig. 3
and selected interatomic parameters are collected in
Table 2.
boxylate group [12]. The strong band at 3340 cmꢀ1
,

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V. Dokorou et al. / Journal of Organometallic Chemistry 689 (2004) 317–325
Table 3
ꢀ
Distances (A) and angles (°) of C–H-p, p ! p interactions and intramolecular hydrogen bonds for 2 and 3
C–H-p, p–p interactions and intramolecular hydrogen bonds for 2
C–H(I) ! Cg(J)
H–Cg
2.9607
3.0084
C–Cg
3.741(19)
3.85(2)
\C–H–Cg
141.13
153.86
C(15)–H(5) ! Cg(4)i
C(30)–H(23) ! Cg(4)ii
Cg(I) ! Cg(J)a
Cg(3) ! Cg(5)iii
Cg(5) ! Cg(3)ii
Cg–Cgb
3.941(7)
3.941(7)
bc
16.18
25.10
CgI-Perpd
3.568
3.785
CgJ-Perpe
3.784
3.568
D
H
A
Dꢂ ꢂ ꢂA
Hꢂ ꢂ ꢂA
1.91
1.92
2.43
2.61
2.36
\D–Hꢂ ꢂ ꢂA
130
130
N(1)
N(2)
C(15)
C(14)
C(30)
H(63)
H(64)
H(4)
H(15)
H(24)
O(1)
O(5)
N(2)
N(2)
N(1)
2.654(13)
2.662(14)
2.846(17)
2.949(18)
2.859(19)
106
101
111
C–H-p, p–p interactions and intramolecular hydrogen bonds for 3
C–H(I) ! Cg(J)
H–Cg
3.152
C–Cg
\C–H–Cg
140.52
134.09
C(12B)–H(8) ! Cg(3)iv
3.935(13)
3.95(2)
3.69(3)
3.69(3)
C(19B)–H(27) ! Cg(4)iv
3.2304
3.2978
3.2379
C(19A)–H(31) ! Cg(2)vi
107.92
110.39
C(19A)–H(32) ! Cg(2)vi
Cg–Cgb
3.745(6)
bc
17.03
CgI-Perpd
3.581
CgJ-Perpe
Cg(3) ! Cg(3)vii
D
H
A
Dꢂ ꢂ ꢂA
Hꢂ ꢂ ꢂA
2.04
1.99
2.40
2.43
2.38
2.41
2.38
\D–Hꢂ ꢂ ꢂA
124
124
N(1A)
N(1B)
C(7B)
C(14A)
C(15A)
C(15B)
C(14B)
H(45)
H(46)
H(12)
H(1)
O(1A)
O(1B)
O(2B)
N(1A)
N(1A)
N(1B)
N(1B)
2.701(11)
2.665(10)
2.734(12)
2.842(14)
2.842(15)
2.874(16)
2.868(13)
100
106
H(20)
H(21)
H(24)
109
110
111
a Where Cg(1), Cg(4), Cg(3) and Cg(5), are referred to the centroids Sn(2)–O(3)–Sn(2a)–O(3a), C(9)–C(12), C(2)–C(7) and C(17)–C(22) for 2,
Cg(2), Cg(3) and Cg(4), are referred to the centroids C(2b)–C(7b), C(8a)–C(13a), C(8b)–C(13b) for 3.
b Cg–Cg is the distance between ring centroids; symmetry transformations, (i) ꢀx, ꢀy, 1 ꢀ z; (ii) ꢀ1 þ x, y, z; (iii) ꢀ1 þ x, y, z; (iv) 1 þ x, y, ꢀ1 þ z;
(v) 2 ꢀ x, 1 ꢀ y, 1 ꢀ z; (vi) 2 ꢀ x, ꢀy, 1 ꢀ z; (vii) 1 ꢀ x, 1 ꢀ y, 2 ꢀ z.
c Where b 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.
Fig. 3. Perspective view of [Bu2Sn(DMPA)2] (3) showing the atomic numbering scheme.

V. Dokorou et al. / Journal of Organometallic Chemistry 689 (2004) 317–325
323
Table 4
Selected IR (cmꢀ1) of organotin(IV) complexes
No
m(NH)
mas(COO)
msym(COO)
D
m(SnO)2
m(SnC)
m(SnO)
d(SnO)
NaDMPA
3348s
3289s
2980br
1610s
1448s
162
2
3
3319s
3258s
1615s
1576s
1388s
1452s
227
124
481s
426s
529ms
506ms
295s
245m
172m
147m
3314s
1618s
1368
250
519ms
503m
291ms
251m
180m
149m
which appears in the IR spectra of the ligand, is assigned
to the NH stretching motion and the broad band at 2980
cmꢀ1 is taken to represent the m(NHꢂ ꢂ ꢂO) mode, due to
intramolecular hydrogen bonding [4,5,12]. The absence
of large systematic shifts of the m(NH) and d(NH) bands
in the spectra of the complexes compared with those of
the ligand indicates that there is no interaction between
the NH group and the metal ions, which is also con-
firmed by X-ray analysis. The mas(COO) and msym(COO)
group and the carbonyl oxygen of the carboxylato
group. Deshielding of protons H(3) and H(4) is ob-
served in complex 3, which should be related to the
electrophilicity of the tin. A r-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 C(5), para to the tin
center, could be due to the flow of charge from the tin
into the aromatic ring [5,13]. Involvement of the car-
boxyl group in bonding to Sn is confirmed by the res-
onances ascribed to carboxyl carbon and C(3), which
exhibit the greatest shifts upon coordination. The re-
maining resonances due to the aromatic carbon atoms
do not shift significantly on binding to Sn. In the 13C
NMR spectra, the greatest downfield shift is exhibited
by the C(2) (7.4 ppm) and the carbonyl C (7.0 ppm) for
3. The C(5) resonance, by contrast, shifts upfield.
Shielding of protons H(3), H(4) and H(6) is observed in
complex 2, which could be due to the flow of charge
from the tin into the aromatic ring [5,13].
bands appear at ꢃ1610–1500 and ꢃ1450–1260 cmꢀ1
,
respectively [12]. The difference, D[mas(COO)-msym(COO)]
between these frequencies for 2 is close to that found for
anisobidentate (227 cmꢀ1) and bridging bidentate
carboxylato groups (124 cmꢀ1), for 3 (250 cmꢀ1) is close
to that observed for asymmetric bidentate chelate mode
[4,5,12]. This is totally consistent with the X-ray struc-
tures. Two bands at 490–470 for 2, are assigned to
m
as;sym(SnO)2, indicating non-linear O–Sn–O moieties,
while the bands at 250–200 cmꢀ1 are assigned to the tin–
oxygen (COO) stretching modes [4,5,12].
3.2.2. NMR spectra
Table 5 gives the 1H and 13C-NMR chemical shifts of
ligand and its complexes in CDCl3 solution. The
downfield chemical shift for HN in the spectra of ligand
indicates that this proton is involved in hydrogen bon-
ding. The existence of the HN resonance in the 1H-
NMR spectra of complexes indicates that the nitrogen
atom remain protonated and the downfield chemical
shift for this group indicates that this proton is involved
in an intramolecular hydrogen bond between the HN
3.2.3. Electronic spectroscopy
The electronic spectrum of HDMPA in DMF solu-
tion exhibits two broad bands at ꢄ338 and 275 nm. The
band at 338 nm is assigned to a p ! p* and the band at
275 nm is assigned to a p ! p* transition. The electronic
spectra of the complexes are shown in Fig. 4. The
€
complexes 2 and 3 were studied by the extended-Huckel
Table 5
1H and 13C-NMR dataa
COOH
NH
H(3)
H(4)
H(5)
H(6)
H(30)-H(50)
20-CH3, 60-CH3
b
HDMPA
8.90s
9.20s
8.92S
C(1)
8.04d
7.91d
8.12d
C(2)
6.66t
6.47d
6.69d
C(3)
7.27t
7.36t
7.23t
C(4)
6.22d
6.19d
6.21d
C(5)
7.15
7.13
7.14
C(6)
2.22s
2.198s
2
3
Bu2Sn: Hd:0.82, Hc:1.25, Hb:1.76, Ha;:1.40m
Bu2Sn: Hd:0903, Hc:1.269, Hb:1.830, Ha:1.431m
COOH
20-CH3
30-CH3
HDMPA
3a
170.68
COOH 177.6
Bu2Sn: Cc:26.8 Cd :13.5 Ca:25.6 Cb:26.3
150.64 116.2
156.8 126.1
132.5
133.3
115.7
115.6
135.6
134.8
112.7
110.4
18.2
18.3
a Spectra recorded in CDCl3.
b Carboxyl proton exchanged in CDCl3.

324
V. Dokorou et al. / Journal of Organometallic Chemistry 689 (2004) 317–325
CCDC-1003/m. Copies of available material can be
obtained, free of charge, on application to CCDC, 12
Union Road, Cambridge CB2 1EZ, UK, (fax: +44-1223-
336033 or e-mail: deposit@ccdc.cam.ac.uk.
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