Two novel macrocyclic organotin(iv) carboxylates based on amide carboxylic acids

Article abstract of DOI:10.1039/c3ra46198j

Two novel macrocyclic organotin(iv) carboxylates [(n-Bu₂Sn) L¹]₂?C₇H₈ (1) (L¹ = 2-(4-carboxyphenylcarbamoyl)benzoic acid) and [(n-Bu₂Sn)L ²]₃?H₂O (2) (L² = 5-(1,3-dioxo-1,3-dihydro-isoindol-2-yl)-isophthalic acid) were generated by the reactions of dibutyltin oxide with amide dicarboxylic acids and characterized by elemental analysis, IR, ¹H and ¹³C NMR spectroscopy. X-ray crystallography diffraction analyses reveal that 1 is a di-nuclear dicarboxylate ring and 2 is a trinuclear tricarboxylate macrocycle. With the help of intermolecular interactions, 1 and 2 construct supramolecular 3D architectures filled with cavities. Free toluene and water molecules are located in the cavities of 1 and 2 respectively as guests. Thermal analyses suggest that complex 2 is thermally more stable than 1. The antitumour activity of 1 and 2 has also been studied.

Full text of DOI:10.1039/c3ra46198j

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Two novel macrocyclic organotin(IV) carboxylates
based on amide carboxylic acids†
Cite this: RSC Adv., 2014, 4, 3096
a
b
c
a
Xiao Xiao, Lisong Yan, Zemin Mei, Dongsheng Zhu and Lin Xua
*
Two novel macrocyclic organotin(IV) carboxylates [(n-Bu2Sn)L1]2 C7H8 (1) (L1 ¼ 2-(4-carboxypheny-
c
lcarbamoyl)benzoic acid) and [(n-Bu2Sn)L2]3 H2O (2) (L2
¼
5-(1,3-dioxo-1,3-dihydro-isoindol-2-yl)-
c
isophthalic acid) were generated by the reactions of dibutyltin oxide with amide dicarboxylic acids and
characterized by elemental analysis, IR, 1H and 13C NMR spectroscopy. X-ray crystallography diffraction
analyses reveal that 1 is a di-nuclear dicarboxylate ring and 2 is a trinuclear tricarboxylate macrocycle.
With the help of intermolecular interactions, 1 and 2 construct supramolecular 3D architectures filled
with cavities. Free toluene and water molecules are located in the cavities of 1 and 2 respectively as
guests. Thermal analyses suggest that complex 2 is thermally more stable than 1. The antitumour activity
of 1 and 2 has also been studied.
Received 29th October 2013
Accepted 2nd December 2013
DOI: 10.1039/c3ra46198j
www.rsc.org/advances
(L1 and L2) as ligands for following reasons: (a) dicarboxylic acid
providing various bridging abilities and strong coordination
Introduction
tendency with metals inducing rich coordination modes,
interesting molecular macrocyclic composition and supramo-
lecular structure; (b) different constructions of them which will
help us study the relation of them and the structure of produced
complex; (c) exible L1 and rigid L2 inclined to cause different
rigidity of 2- and 3D networks. Based on the above, di-nuclear
centrosymmetric dicarboxylate 1 and trinuclear tricarboxylate
macrocycle 2 are obtained through the reactions of L1 and L2
with Bu2SnO respectively. By the search of CSD, we found that
macrocyclic organotin complexes are less studied, much of
which are tri-, tetra-, and hexanuclear.5 The reports about di-
nuclear dicarboxylate macrocycle are fewer, while 1 has the
dimeric structure of macrocycle with two tin centers. Via inter-
molecular interactions, 1 and 2 form 3D supramolecular
architectures with intermolecular cavities occupied by free
toluene and water molecules respectively.
The molecular constructions with cavities or possessing
intrinsic physical properties have the potential to create new
materials.1a The supramolecular class possessing cavities can be
used for molecular recognition, storage, absorption, separation,
host–guest system and polymeric structures with voids or
channels are available for the inclusion of guest molecules.1
However, compared to the transition metals and lanthanides,
few supramolecular polymers containing main group elements
have been studied.1a,2
Macrocyclic organotin carboxylates are attractive for these
reasons. Although receiving attention, the relevant reports are
numbered.3 To further the eld of organotin carboxylate mac-
rocycle with esthetic architecture and to explore the rules of
molecular ring formation, we suppose to synthesize novel
organotin carboxylate macrocycle with fascinating supramo-
lecular structure.
As we know, metal–ligand binding, hydrogen bonds and
p/p interactions play key roles for the generation of innite
number of supramolecular entities with intra- and inter-
molecular cavities.4 We chose two amide dicarboxylic acids
Results and discussion
Synthesis
Through the reaction of (n-Bu)2SnO and ligand (L1 and L2), 1
and 2 are obtained (Scheme 1). From the structure analyses of
complexes 1 and 2, it can be concluded that (n-Bu)2SnO reacting
with dicarboxylic acid (L1 and L2) is apt to produce expected
aNortheast Normal University, Department of Chemistry, Changchun, China. E-mail:
zhuds206@nenu.edu.cn; Fax: +86 0431 85684009; Tel: +86 0431 85098620
bChangchun Institute of Optics Fine Mechanics and Physics Chinese Academy of
Sciences, Key Laboratory of Optical System Advanced Manufacturing Technology, organotin carboxylate with macrocycle structure. And different
Changchun, China
cBaicheng Normal University, Department of Chemistry, Baicheng, China
structure of the ligand will lead different construction of the
macrocycle. The reaction of (n-Bu)2SnO with L1 tends to produce
ring with two metal centers. When with L2, it inclines to form
ring with three nucleus. Meanwhile, the number of ligands
participating in ring formation changes with that of the tin
centers.
† Electronic supplementary information (ESI) available: Antitumor activity
ꢀ
˚
experiment; selected bond lengths (A) and angles ( ) for complexes 1 and 2;
crystal data for 1 and 2; TGA-DTG curves of 1 and 2; Inhibition effects of 1, 2, L1
and L2 against S180. CCDC 827597 and 827595. For ESI and crystallographic
data in CIF or other electronic format see DOI: 10.1039/c3ra46198j
3096 | RSC Adv., 2014, 4, 3096–3101
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rectangle with the benzene rings [IA and IIA, IB and IIB in
Fig. 1(a)] paralleled. Distance between two tin centers is calcu-
˚
lated as 9.950 A. The cross section of the cavity is probable
˚
˚
11.958 A ꢁ 5.561 A which is larger than those reported in
[(n-Bu)2SnFc(CO2)2]2 and [Bn2SnFc(CO2)2]2.5d
The dinuclear macrocyclic rings in the crystal lattice are
linked into 1D polymeric chains through an extensive set of
weak intermolecular Sn(1)/O(1) interactions [Fig. 2(a)]. These
˚
Sn/O interactions (3.066 A) give rise to the formation of a
˚
Sn2O2 distannoxane unit [Sn(1)/O(1)/Sn(1)/O(1) 2.503 A ꢁ
˚
3.066 A]. The unit demonstrates as a parallelogram evidenced
by the O–Sn–O bond angle 64.83ꢀ and Sn–O–Sn bond angle
115.17ꢀ. Considering these Sn/O interactions, the coordina-
tion geometry of tin atom is best described as a skew-pentag-
onal bipyramid [Fig. 2(b)]. The 1D chain links with other four
Scheme 1 Syntheses of complexes 1 and 2.
˚
via N–H(1A)/O(5) (2.151 A) hydrogen bonds along four
different directions. Two locate below and two upon the chain
[Fig. 2(a)]. Both the hydrogen and oxygen atoms involved in the
N–H/O interactions belong to the imide group. Through this
kind of connections, intermolecular channel is formed by four
chains [Fig. 3(a)]. Each two on the opposite sides of the chains
are almost paralleled. Toluene guest resides inside the channel
and is stabled by C–H/p interactions (Fig. S1†). In Fig. 3(b) the
macrocyclic molecule is simplied into a dark green sphere for
clarity. The red bonds stand for Sn/O interactions and green
ones are representative of N–H/O bonds. These connections
help the molecules construct 3D cages locking guest toluene
molecules in.
Complex 2. The molecular structure of complex 2 is shown in
Fig. 4. Sn(2), N(2) and C(25) atoms lie on the twofold axis in this
structure. Selected bond distances and angles are listed in Table
S1.† The trinuclear tin complex is symmetric with a two-fold axis
and characterized by a 24-membered C15O6Sn3 macrocyclic ring
system with all six oxygen atoms directed into the interior of the
cavity. Six n-butyl groups attached to the tin centers are three
below and three upon the ring. Sn(1) adopts distorted trigonal
bipyramidal coordination geometry. It is ve coordinated by
three O atoms from carboxylate groups of L2 and two n-Bu
groups. The C–Sn–C angle of Sn(1) is 160.82(4)ꢀ. It can be seen
from Fig. 4 that one L2 coordinates with Sn(1) by monodentate
Molecular structure
Complex 1. The molecular structure of complex 1 is shown in
Fig. 1(a). Selected bond lengths and angles are listed in Table
S1.† The unit cell includes a dinuclear tin ring and a free
toluene molecule. The complex lies about an inversion centre
and the free toluene lies disordered about another inversion
centre. 1 is a symmetric 26-membered dinuclear macrocycle
with an inversion center. The macrocycle is linked by n-Bu2Sn
groups and ligands L1 alternately. Two tin atoms are hexa-
coordinated by two carbon atoms of n-butyl moieties in the axial
site and four carboxylate oxygen atoms of L1 occupying the
equatorial plane. The axial angle of C–Sn–C is 144.86(13)ꢀ and
the O–Sn–O angles around tin are 55.57(7)ꢀ [O(3)–Sn(1)–O(1)]
and 56.15(8)ꢀ [O(4)–Sn(1)–O(2)], which are commonly observed
for diorganotin carboxylate.6 For the tension of ring formation,
each ligand L1 binds to two tin atoms by two types of Sn–O bond
˚
distances: short Sn–O distance [Sn(1)–O(3): 2.152(2) A; Sn(1)–
˚
˚
O(4): 2.118(2) A] and long Sn–O distance [Sn(1)–O(1): 2.503(2) A;
˚
Sn(1)–O(2): 2.507(2) A], which prove the anisobidentate
chelating coordination mode of the carboxylate groups. The
long Sn–O distance is much shorter than the sum of the van der
Waals radii of tin and oxygen (3.7 A)7a which indicates a strong
˚
coordinating bond. These Sn–O and relative Sn–C [2.114(3) and
˚
2.118(3) A] bond lengths may be compared with those found in
the analogous complex [(n-Bu)2SnFc(CO2)2]2.5d Thus the coor-
dination environment of Sn can be described as a distorted
octahedron [Fig. 1(b)]. The ring demonstrates as a twisty
Fig. 2 (a) Supramolecular 1D chain structure of 1. Butyl groups are
Fig. 1 (a) Molecular structure of 1 (30% probability displacement omitted for clarity. (b) Coordination polyhedron concerning inter-
ellipsoids). (b) Coordination polyhedron of Sn.
molecular Sn/O interaction of Sn.
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Sn(1) and Sn(2) are among 52.67–57.49ꢀ. The cross section of
the cavity can be evaluated by alternant Sn/Sn and O/O
[O(2)/O(3), O(2A)/O(3A), O(5)/O(5A)] distances, which are
˚
among 9.02–9.14 and 4.86–4.94 A, respectively.
Interestingly, intermolecular Sn/O coordinations [Sn(1)/
˚
O(6A) and Sn(1A)/O(6)] with relative short distance 2.61 A are
observed in the crystal lattice. The rigid macrocyclic ring in the
complex is squeezed as a twisty dimensional triangle for these
strong intermolecular coordinations (Fig. S2 and S3†). This
torsion and intermolecular Sn/O coordination is rare for the
rigid tri-nuclear macrocyclic organotin.1a,b,5c,6f,7c The intermo-
lecular Sn/O coordinations connect the rings and form inter-
molecular distannoxane units [Sn(1)/O(6)/Sn(1A)/O(6A)]
[Fig. 5(a)]. The units are parallelogram proved by the O–Sn–O
and Sn–O–Sn bond angles 68.11ꢀ and 111.89ꢀ respectively. The
˚
˚
width of this type of units (2.61 A ꢁ 2.68 A) is close to that in 1.
Considering this type of interaction, the coordination environ-
ment of Sn(1) can also be regarded as distorted bipyramidal-
pentagon [Fig. 5(b)]. And the molecular cyclic rings are linked
into a one-dimensional zig-zag chain along c axis via these
interactions [Fig. 5(d)].
Intermolecular hydrogen bonds help the chains connect
with each other and form the supramolecular 3D architecture.
As shown in Fig. 6(a), two kinds of hydrogen bonds C(16)–
Fig. 3 Supramolecular 3D structure of 1.
˚
˚
H(16A)/O(5) (2.57 A) and C(15)–H(15A)/O(2) (2.58 A) extend
every chain into four different spatial orientations (two up and
two below the chain) and construct the supramolecular 3D
architecture of 2. Intermolecular channels are formed by four
chains linked with the hydrogen bonds as complex 1. In
Fig. 6(b), the supramolecular 3D structure with intermolecular
channels serve as host and the guest water molecules are
located in the channels disorderly.
1
IR, H, and 13C NMR spectra
In the IR spectra of 1 and 2, a broad band in the region 3400–
2800 cmꢂ1 owing to the COOH group of ligands L1 and L2 is
absent, which indicates the deprotonation of the carboxylic acid
and metal–ligand bond formation through these sites.7d The Dn
(nasymCOO ꢂ nsymCOO) value for complex 1 is 144 cmꢂ1 smaller
Fig. 4 Molecular structure of 2 (30% probability displacement ellip-
soids). Part of butyl groups are omitted for clarity. “A” indicates atoms
at equivalent position (1 ꢂ x, y, ꢂ1/2 ꢂ z).
2
˚
mode with Sn–O bond length 2.170(5) A. Another L adopts
bidentate chelating mode as complex 1 with two kinds of Sn–O
˚
˚
bond lengths [Sn(1)–O(1): 2.390(5) A; Sn(1)–O(2): 2.173(5) A].
Sn(2) is different from Sn(1) for that both of the coordinated
ligands use monodentate coordination mode with Sn–O
˚
distance 2.107(6) A. Thus Sn(2) has a distorted tetrahedron
conguration coordinated by two carboxylate O atoms and two
C atoms from butyl groups. For the tremble of n-Bu groups, the
C–Sn–C angle of Sn(2) is 141.2(8)ꢀ, which also makes Sn(2)
difficult to chelate with other atoms. Besides the coordination
˚
bonds mentioned above, the distances of Sn(1)/O(6) (2.680 A)
˚
and Sn(2)/O(4) (2.568 A) lie in the range of intramolecular Sn–
O bond distances.7b Therefore the oxygen atoms [O(4) and O(6)]
are involved in a weak coordinative interaction with tin and all
tin centers can be considered as hexa-coordinated with a
Fig. 5 (a) 1D chain structure of 2. Butyl groups are omitted for clarity.
(b) Coordination polyhedron concerning intermolecular Sn/O
coordination of Sn(1). (c) Coordination polyhedron of Sn(2). (d) 1D
skewed trapezoidal bipyramid conguration. O–Sn–O angles of chain structure of 2 along c axis.
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four n-Bu groups, 28.83% residual mass is observed. 2 exhibits a
ꢀ
weight loss of 1.99% in the range of 50–365 C, which agrees
with the calculated value of free water molecule. Successive two-
step decomposition is observed in the temperature range 365–
490 ꢀC. 60.90% weight loss in 365–800 ꢀC is consistent with
three ligands and six n-Bu groups. Thus, the nal percentage of
residual mass observed is 37.11%. From the above, it can be
concluded that complex 2 is thermally more stable than 1. There
ꢀ
is virtually no weight loss until 365 C.
Antitumor activity
The cell cytotoxicity of 1, 2, L1 and L2 against mouse sarcoma
cells S180 was studied by MTT assays. The inhibition effects of
them are shown in Fig. S6.† It can be seen that the growth rates
of S180 are 39.46%, 37.15%, 81.49% and 85.75% aer being
added with test samples 1, 2, L1 and L2 respectively. And the
relative inhibition ratios of them are 60.54%, 62.85%, 18.51%
and 14.25%. L1 gives higher cell cytotoxicity than L2, while
complex 1 exhibits a little lower antitumor activity than 2. Due
to very low cytotoxicity of the ligands, the complexation of these
ligands with Sn(IV) has great contribution to the antitumor
activity of the compounds. Generally the high antitumor activity
shows the potential of complexes 1 and 2 in being used as an
anticancer drug for chemotherapy.
Fig. 6 Supramolecular 3D structure of 2.
than 200 cmꢂ1, indicative of the bidentate chelating mode for
the carboxyl ligand L1. For 2, the values are 195 and 210 cmꢂ1
,
which are representative of that both monodentate and biden-
tate coordinating modes exist in 2.2a,3b,d These are totally
consistent with the X-ray structures. The bands at 564 and
556 cmꢂ1 for 1 and 2 respectively are assigned to the stretching
frequency associated with the Sn–C bond. Strong bands of
459 and 467 cmꢂ1 are assigned to n(Sn–O), indicating the Sn–O
coordinated structure.4c,7e
Conclusion
In summary, we have synthesized and characterized two unique
macrocyclic organotin carboxylates based on amide carboxylic
acids. 1 has the rare structure of macrocycle with two tin
centers. 2 is a trinuclear tricarboxylate ring. With the help of
intermolecular interactions, 1 and 2 form attractive 3D supra-
molecular architectures with cavities. Free toluene and water
The 1H NMR spectra show that the signals of the –COOH
proton in ligands are absent in 1 and 2, standing for the removal
of –COOH proton and the formation of Sn–O bond.3b,5b Expected
integration and peak multiplicities for the hydrogen protons on
aromatic rings of ligands are observed in 7.65–9.10 ppm range. molecules are situated in the intermolecular cavities of 1 and 2
The chemical shi for “–NH–” group of L1 in 1 is at 7.92 as
as guest. Their structures which can serve as host–guest system
single peak.7e Signals for the hydrogen protons on butyl groups
of tin can also be appropriately attributed.
help us further understand the group of organotin carboxylates.
Moreover, it is interesting that Bu2SnO reacts with dicarboxylic
amide acids with different structures resulting different
constructions of the macrocycle: with L1, the reaction produces
ring with two tin centers; with L2 it forms ring with three
nucleus. This provides an exploration and an effective exem-
In the 13C NMR spectra, Single resonances at 172.31 and
174.66 ppm of 1 and 2 are assigned to COO groups, and the ones
at 167.25 and 166.79 ppm are owing to C]O groups.2a,3b,7e The
peaks of aromatic rings and butyl groups can be appropriately
attributed. The tin–carbon coupling constants 1J
C are 778 plication for projecting the structure of ligand to change the
119Sn–13
macrocyclic composition of organotin carboxylate and conse-
quently adjust the width of molecular cavity.
and 801 Hz for 1 and 2; on the basis of Holecek and Lycka
equation,8a,b the C–Sn–C angles are estimated to 145ꢀ and 147ꢀ
respectively, which agrees well with the coordination geometry
around tin atoms in X-ray crystallography diffraction analyses.
Experimental section
Materials and measurements
Di-n-butyltin oxide and L1 are commercial available and was
Thermal analysis
Thermal analyses of 1 and 2 were studied by TGA and DTG used without further purication. L2 was prepared by a modi-
(Fig. S4 and S5†). According to the DTG, it is observed that ed literature method.9a The solvents were puried according to
complexes 1 and 2 decompose in two steps.8c,d Complex 1 shows standard procedures before used.9b The melting point was
a gradual weight loss until 293 ꢀC (weight loss of 8.60% is obtained with Koer micro-melting point apparatus and was
identical with a free toluene molecule). Continued two-step uncorrected. Elemental analysis (C, H, N) was carried out on a
decomposition is revealed between 293 ꢀC and 507 ꢀC. With the Perkin-Elmer PE 2400 CHN instrument. IR spectrum (KBr
weight loss of 62.57% which are accorded with two ligands and pellets) was recorded on an Alpha Centauri FI/IR spectrometer
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(400–4000 cmꢂ1 range). 1H, 13C NMR spectra were recorded on Ar-C: C5, C25), 124.03 (6C, Ar-C: C7, C9, C23), 26.61 (6C, Bu-C:
Varian Mercury operating at 300 and 75 MHz, respectively. The –CH2–), 26.02 (6C, Bu-C: –CH2–), 13.54 (6C, Bu-C: –CH3), 7.35
1
thermostability of 1 and 2 was measured on a Q500 TGA ther- (6C, J
mogravimetric analyzer (V6.5 Build 196).
¼ 801 Hz, Bu-C: Sn–CH2–).
119Sn–13
C
Acknowledgements
X-ray crystallography
We acknowledged the Science and technology department of
Jilin province (no. 20120440).
Diffraction intensities for complex 1 and 2 were collected on a
Bruker CCD Area Detector image plate diffractometer by using
˚
the u/4 scan technique with Mo-Ka radiation (l¼ 0.71073 A).
Absorption corrections were applied by using multiscan tech- Notes and references
niques. The structure was solved by direct methods with
¨
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SHELXS-97 (ref. 9c) and rened using SHELXL-97.9d All non-
hydrogen atoms were rened with anisotropic temperature
parameters; hydrogen atoms were rened as rigid groups.
Crystal data for 1 and 2 are listed in Table S2.†.
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Synthesis of [(n-Bu2Sn)L1]2$C7H8 (1)
A solution of L1 (0.285 g, 1.0 mmol) and di-n-butyltin(IV) oxide
(0.249 g, 1.0 mmol) in toluene (50 ml) was reuxed for 8 h using
a Dean–Stark trap to facilitate the dynamic removal of the water
formed in the reaction by azeotropic distillation. Aer cooling
to room temperature, the solvent mixture was ltrated. The
ltrate was allowed to slow evaporation of toluene at room
temperature to afford white powder. Recrystallization of the
powder with toluene produces colourless crystals of complex 1.
Yield: 68.2%, 0.38 g. Mp: >300 ꢀC. Anal. calcd for
¨
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C
45H51N2O10Sn2$C7H8: C, 56.29; H, 5.36; N, 2.52. Found: C,
56.78; H, 5.39; N, 2.55%. IR (cmꢂ1): 1662 [s, n (O]C)]; 1594 [s,
nasym(COO)]; 1450 [s, nsym(COO)]; 564 [m, n(Sn–C)]; 459 [s, n(Sn–
O)]. 1H NMR (CDCl3): d 8.02–8.08 (m, 8H, Ar-H), 7.92 (s, 2H,
–NH–), 7.79 (d, 4H, J ¼ 7.6 Hz, Ar-H), 7.65 (d, 4H, J ¼ 7.6 Hz, Ar-
H), 1.63 (t, 8H, J ¼ 6.7 Hz, Bu-H), 1.25–1.36 (m, 16H, Bu-H), 0.81
(t, 12H, J ¼ 6.9 Hz, Bu-H). 13C NMR (CDCl3): d 172.31 (4C, COO),
167.25 (2C, C]O), 142.72 (2C, Ar-C: C10), 135.12 (2C, Ar-C: C4),
134.23 (2C, Ar-C: C6), 131.76 (2C, Ar-C: C7), 130.27 (4C, Ar-C:
C12, C14), 130.14 (2C, Ar-C: C8), 129.04 (2C, Ar-C: C3), 128.23
(2C, Ar-C: C5), 126.46 (2C, Ar-C: C13), 123.56 (4C, Ar-C: C11,
C15), 26.57 (4C, Bu-C: –CH2–), 25.26 (4C, Bu-C: –CH2–), 13.48
(4C, Bu-C: –CH3), 8.76 (4C, 1J
¼ 778 Hz, Bu-C: Sn–CH2–).
119Sn–13
C
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I. Goldberg, CrystEngComm, 2009, 11, 1217; (e) C. Ma,
G. Tian and R. Zhang, J. Organomet. Chem., 2006, 691, 2014.
Synthesis of [(n-Bu)2Sn(L2)]3$H2O (2)
The synthesis of 2 is similar to that of 1 except that L2 (0.311 g,
1.0 mmol) was used to take place of L1. And the crystals of 2
suitable for X-ray analysis are obtained directly by slow evapo-
ration of toluene at room temperature without recrystal.
Yield: 61.4%, 0.34 g. Mp:
72H75N3O18Sn3H2O: C, 52.58; H, 4.72; N, 2.56. Found: C, 52.18;
300 ꢀC. Anal. calcd for 5 (a) H. I. Beltran, L. S. Z. Rivera, T. Mancilla, R. Santillan and
´
>
´
C
N. Farfan, Chem.–Eur. J., 2003, 9, 2291; (b) C. Ma, Q. Wang and
H, 4.68; N, 2.61%. IR (cmꢂ1): 1732 [s, n(O]C)]; 1618, 1575
[s, nasym(COO)]; 1423, 1365 [s, nsym(COO)]; 556 [m, v(Sn–C)]; 467
[s, v(Sn–O)]. 1H NMR (CDCl3): d 9.10 (s, 3H, Ar-H), 8.45 (s, 6H, Ar-
H), 8.01 (d, 6H, J ¼ 7.1 Hz, Ar-H), 7.85 (dd, 6H, J ¼ 7.1 Hz, Ar-H),
1.71 (t, 12H, J ¼ 6.9 Hz, Bu-H), 1.37–1.45 (m, 24H, Bu-H), 0.91 (t,
18H, J ¼ 6.5 Hz, Bu-H). 13C NMR (CDCl3): d 174.66 (6C, COO),
166.79 (6C, C]O), 134.74 (3C, Ar-C: C8, C22), 133.31 (6C, Ar-C:
R. Zhang, Inorg. Chem., 2008, 47, 7060; (c) R. G. Zarracino,
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J. R. Quinones and H. Hop, Inorg. Chem., 2003, 42, 3835;
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2007, 26, 5415; (e) J. C. Huerta, M. C. Morales, E. S. Juarez,
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I. F. H. Ahuactzi, J. E. Garcıa, C. G. Alcantar, J. A. G. Alvarez,
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H. Hop, H. M. Rojas and M. Sanchez, Inorg. Chem., 2008,
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Ar-C: C4, C6, C24), 131.68 (6C, Ar-C: C14, C17, C19), 131.56 (3C,
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