A novel macrocyclic dimeric dicarboxylato distannoxane assembled from a flexible dicarboxylic acid

Article abstract of DOI:10.3184/030823407X255524

The novel macrocyclic complex [(Bu₂Sn)₂OL] ₂?CH₃CN (2) has been prepared from the flexible dicarboxylic acid, LH₂, (1). Single crystal X-ray diffraction shows that complex 2 has a centrosymmetric stru

Full text of DOI:10.3184/030823407X255524

JOURNAL OF CHEMICAL RESEARCH 2007
OCTObER, 577–579
RESEARCH PAPER 577
A novel macrocyclic dimeric dicarboxylato distannoxane assembled from
a flexible dicarboxylic acid
Dongsheng Zhua,b, Wanli Kangc, Dewen Dongb, Qun Liub and Lin Xua*
aInstitute of Polyoxometalate Chemistry, Northeast Normal University, Changchun 130024, P.R. China
bDepartment of Chemistry, Northeast Normal University, Changchun, 130024, P.R. China
cEor Research Centre, China University of Petroleum, Dongying, 257061, P.R. China
The novel macrocyclic complex [(Bu2Sn)2OL]2•CH3CN (2) has been prepared from the flexible dicarboxylic acid, LH2,
(1). Single crystal X-ray diffraction shows that complex 2 has a centrosymmetric structure, with a central rhomboid
cyclic Bu4Sn2O2 unit, linked at the oxygen atoms to two exocyclic tin atoms. The dicarboxylate ligands bridge
exocylic and endocyclic tin atoms, completing two rings each of 22 atoms, and two of the four carbonyl oxygen
atoms coordinate to the exocyclic tin atoms, to raise their coordination state to five and complete two more six-
membered, rings.
Keywords: tin complex, organotin(IV) compounds, crystal structures, dicarboxylic acid ligands
In the past several decades, organotin carboxylates have
emerged as an important class of compounds and attracted
much research attention owing to their significant anti-tumour
activity and catalytic activity and also their considerable
structural diversity.1-5 Depending on the carboxylic acid
used and the stoichiometry of the reactants, various
organotin carboxylates such as monomers, dimers, tetramers,
oligomeric ladders and hexameric drums can be produced.
Among these organotin carboxylates, the dicarboxylato
tetraorganodistannoxanes with the general formula
{[R'2Sn(O2CR)]2O}2 adopt five types of crystal structures
in the crystalline state.6,7 All these structural forms involve
a centrosymmetric structure built up around a planar, four-
membered cyclic Sn2O2 unit with two exocyclic Sn atoms
which are five-coordinate. Each of the two exocyclic five-
coordinate Sn atoms is bound to one bridging O atom of the
four-membered ring, making these O atoms tri-coordinate.
However, the small differences or the combination of very
subtle factors based on the ligating mode between carboxylate
groups and Sn atoms lead to the preference for a particular
carboxylate to adopt a particular type of structure. For the
structure type A as shown in Fig. 1, by far the predominant
structure form, the two independent carboxylate groups
are characterised by two distinct ligating modes.8-10 One
is unidentate and coordinated exclusively to the exocyclic
Sn atoms. The other is bidentate with one O atom of the
carboxylate group being coordinated to the exocyclic Sn atom
and the other O atom to the endocyclic Sn atom. For type B,
it retains the same Sn2O2 unit as existing in Type A structures,
but the two bidentate bridging carboxylates each utilise only
one O atom in bridging the two Sn centres.11-13 As a result, the
type B has a central core consisting of a ladder structure of
three condensed four-membered rings.
R
O
R'
O
C
O
R'
O
C
R
R'
R'
Sn
Sn
O
R'
R'
Sn
Sn
O
O
O
R
C
R'
O
C
O
R'
Type A
R
Fig.
1
Type A dimeric organotin carboxylate, {[R'2Sn
(O2CR)]2O}2.
stretching motion and the ν(OH…O) mode due to the intra-
and inter- molecular H-bonding. Moreover, the νas(COO) and
νsym(COO) bands at ν1735 and 1674 cm-1 for 1 disappeared,
while two types of COO absorption bands were observed at
1692, 1514cm-1[νas(COO)]andat1454, 1334cm-1[νsym(COO)]
for the complex 2, respectively. The disappearance or shifts
of these absorptions in the spectrum of complex 2 indicate
that there is interaction between a carboxylate group and
the metal ions in two distinct ligating modes. The difference
Δ [νas(COO)–νsym(COO)] between these frequencies for 2
is close to that found for a unidentate chelate mode (ca 238
cm-1) and a bridging bidentate carboxylato group (ca 180
cm-1), respectively.9 Two bands at 435 and 423 cm-1 for 2 are
assigned to symmetric and asymmetric (SnO)2 vibrations,
indicating nonlinear O–Sn–O moieties. The absorption bands
at 543 cm-1 are attributed to ν(Sn-C) stretching modes.14,15
A view of the distannoxane unit in complex 2 is shown in
Fig. 2. The ORTEP drawing of complex 2 is shown in Fig. 3.
Each cell in the crystal has one molecule of the complex 2 and
one molecule of acetonitrile. The selected bond lengths and
angles are listed in Table 1.
The structure of complex 2 is centro-symmetric and features
a central rhomboid cyclic Bu4Sn2O2 unit with two exocyclic
five-coordinate Sn atoms linked at the O atoms of the four-
membered ring. The central rhomboid cyclic Bu4Sn2O2
unit is present in the dimeric tetraorganodistannoxanes of
planar ladder arrangement with distorted square-bipyramidal
geometry around the four five-coordinated tin centres, Sn(1),
Sn(1A), Sn(2) and Sn(2A). In the molecule, the two O atoms
of the Bu4Sn2O2 unit are tridentate, of which the O(9) atom
links three Sn(1), Sn(1A) and Sn(2) atoms and O(9A) links
three Sn(1), Sn(1A) and Sn(2A) atoms. The bond distances
Keeping in view the structural and biological diversity of
organotin carboxylates and in connection with our interest
in the coordination chemistry of organotin compounds with
different carboxylic acids, we now present the preparation and
characterisation of a novel complex [(Bu2Sn)2OL]2•CH3CN
(2), where LH2 is a symmetric and flexible dicarboxylic
acid (1). Single crystal X-ray diffraction studies reveal that
complex 2 adopts a Type A structure in the crystalline state,
with the Sn2O2 unit of the centro-symmetric dimer connected
to two quite different macroheterocycles.
The ligand 1 and the complex 2 were characterised by
means of FTIR and NMR spectra. In the IR spectrum of 1, the
strong bands at 3440 and 2860 cm-1 were assigned to the O–H
* Correspondent. E-mail: xulin@nenu.edu.cn
PAPER: 07/4771

578 JOURNAL OF CHEMICAL RESEARCH 2007
Fig. 3 ORTEP drawing of complex [(Bu2Sn)2OL]2•CH3CN (2).
exo- and endo-cyclic Sn atoms. As a result, complex 2 exhibits
a novel macrocyclic structure with a central rhomboid cyclic
Bu4Sn2O2 unit joining two macroheterocycles.
Fig. 2 View of the distannoxane unit in complex 2.
of Sn(1)–O(9), Sn(1)–O(9A) and Sn(2)–O(9) are 2.146(4)
Å, 2.055(3) Å and 2.028(3) Å, respectively, which are
close to Sn–O distances found in the type A compounds.7-10
The Sn(1), O(9), Sn(1A), O(9A) atoms form one exocyclic
six-membered chelating ring and the Sn(1), O(7), C(26A),
O(8A), Sn(2A), O(9A) and Sn(1A), O(7A), C(26), O(8),
Sn(2), O(9) form two endocyclic six-membered chelating
rings, respectively. Additional links between the endo- and
exo-cyclic Sn atoms are provided by bidentate carboxylate
ligands that form essentially symmetrical bridges (Sn(1)–O(7)
2.282(5) Å and Sn(2)–O(8) 2.228(5) Å). Each exocyclic Sn
atom is coordinated by a monodentate carboxylate ligand
(Sn(2)–O(1) 2.190(4) Å). This configuration leads to five
coordination Sn centres, each existing in a distorted trigonal
bipyramidal geometry. The trigonal plane about Sn(1) is
defined by C(31), C(41) and O(9A) atoms with the axial
positions being occupied by the O(7) and O(9) atoms [O(7)–
Sn(1)–O(9) 165.90(14)°], and the Sn(1) atom lies 0.1936 Å
out of this plane in the direction of the O(9) atom. For the
Sn(2) atom, the trigonal plane is defined by C(51), C(61) and
O(9) atoms and the axial positions occupied by the O(1) and
O(8) atoms [O(1)–n(2)–O(8) 169.50(15)°], and the Sn(2)
atom lies 0.0029 Å out of this plane in the direction of the
O(1) atom.
Experimental
Elemental analyses were carried out on a Perkin-Elmer PE 2400
CHN instrument and by gravimetric analysis for Sn. 1H NMR spectra
were recorded in CDCl3 on a Varian Mercury 300 MHz spectrometer.
IR spectra (KBr pellets) were recorded on an Alpha Centauri FI/IR
spectrometer (400-4000 cm-1 range).
2-(2-Formylphenoxy)acetic acid was obtained from commercial
sources and used without further purification. 3-(1,3-dithiolan-2-
ylidene)pentane-2,4-dione was prepared by a modified literature
18
method. Solvents were used without purification.
Synthesis of ligand 1: To a solution of 2-(2-formylphenoxy)acetic
acid (3.60 g, 20 mmol) and 3-(1,3-dithiolan-2-ylidene)pentane-
2,4-dione (2.02 g, 10 mmol) in 150 ml ethanol, sodium ethoxide
(44 mmol, 1.0 g sodium dissolved in 20 ml ethanol) was added
dropwiseat0°Cwithin30minutes.Thereactionmixturewasstirredfor
10 h at room temperature, then poured into cold water (ca 100 ml).
After neutralisation with aqueous HCl (20%), a yellow solid was
precipitated, which was collected by filtration and washed with water.
The pure product was obtained by recrystallisation from ethanol as
a yellow powder, yield 65%, m.p. 170–172°C. Anal. Found (Calc)
for C26H22O8S2: C, 59.33(59.30), H, 4.25(4.21)%. IR: 3440 cm-1,
1735 cm-1, 1674 cm-1, 1626 cm-1, 1480 cm-1, 1377 cm-1, 1220 cm-1.
1H NMR (DMSO-d6, δ): 3.65(s, 4H), 4.66 (s, 4H), 7.03 (d, 2H,
J = 16.0 Hz), 7.49(d, 2H, J = 16.0 Hz), 6.80–6.78,7.14–7.23 (m, 8H),
11.25(s, 2H). 13C NMR (DMSO-d6, δ): 37.88, 66.02, 112.10, 113.81,
123.27, 125.39, 128.30, 128.75, 143.51, 149.84, 150.46, 170.74,
175.45, 187.98.
The endocyclic tin atom Sn(1) forms five primary bonds:
one to the carboxylate oxygen atom O(7), two to the O(9) and
O(9A), and two to the tin-bound n-butyl groups. In addition,
the Sn(1) makes a close contact of 2.634 Å with the O(1)
atom. The contact is significantly less than 3.68 Å, the sum of
the van der Waals radii for Sn and O atoms).17 It is observed
that the bond angle C(31)–Sn(1)–Sn(41) is 143.2(2)°, which is
8.8° wider than that of C(51)–Sn(2)–C(61). This phenomenon
is attributed to the weak coordination of O(1) and Sn(1).
It is of interest that the two carboxylate groups of
dicarboxylic acid 1 both participate in the coordination to
the Sn atoms but in distinct ligating modes, namely one is
monodentate and coordinated exclusively to the exocyclic
Sn atoms, whereas the other is bidentate linked with a pair of
Synthesis of complex 2: The mixture of di-n-butyltin oxide (1.24 g,
5.0 mmol) and LH2(1) (2.63 g, 5.0 mmol) in 80 ml benzene was
refluxed for 10 h and the binary azeotrope water/benzene was
distilled off with a Dean–Stark condenser. The resulting clear
solution was reduced to a small volume under reduced pressure.
Drops of acetonitrile were added and after slow evaporation, yellow
crystals were grown. The product was collected by filtration, washed
with acetonitrile and dried in vacuo, yield 61%, m.p. 176–178°C.
Anal. Found (Calc) for C84H112O18S4Sn4·0.5CH3CN: C, 50.1 (50.03),
H, 5.55 (5.61), Sn, 23.3 (23.27), N, 0.71 (0.67)%. IR: 1692,
1
1624, 1514, 1454, 1334, 1223, 561, 543, 435, 423 cm-1. H NMR
(DMSO-d6, δ): 0.83 (t, 24H), 1.25–1.57 (m, 48H), 3.38 (s, 8H), 4.67
(s, 8H), 6.72 (d, 4H, J = 15.6 Hz), 6.90 (d, 4H, J = 15.6 Hz,), 7.22–
7.99 (m, 16H). 13C NMR (DMSO-d6, δ): 13.53, 26.13, 26.45, 26.74
(4 × C), 37.14, 65.00, 111.52, 121.48, 124.46, 127.93, 128.31, 130.06,
131.074, 138.40, 156.78, 177.33, 188.77.
O
O
S
S
CHO
O
O
OH
O
O
O
O
S
S
EtOH/EtONa
O
O
1
HO
OH
Scheme 1 The preparation of dicarboxylic acid 1.
PAPER: 07/4771

JOURNAL OF CHEMICAL RESEARCH 2007 579
Table 1 Selected bond distance (Å) and angles (°) of complex 2
Sn(1)–O(9A)
2.055(3)
2.110(6)
2.119(5)
2.146(4)
2.282(5)
2.054(4)
107.48(19)
106.50(19)
143.2(2)
75.68(14)
101.4(2)
100.3(2)
90.39(15)
84.6(2)
Sn(2)–O(9)
Sn(2)–C(61)
Sn(2)–C(51)
Sn(2)–O(1)
Sn(2)–O(8)
2.028(3)
2.106(6)
2.124(6)
2.190(4)
2.228(5)
Sn(1)–C(31)
Sn(1)–C(41)
Sn(1)–O(9)
Sn(1)–O(7)
O(9)–Sn(1A)
O(9A)–Sn(1)–C(31)
O(9A)–Sn(1)–C(41)
C(31)–Sn(1)–C(41)
O(9A)–Sn(1)–O(9)
C(31)–Sn(1)–O(9)
C(41)–Sn(1)–O(9)
O(9A)–Sn(1)–O(7)
C(31)–Sn(1)–O(7)
C(41)–Sn(1)–O(7)
O(9)–Sn(1)–O(7)
C(26A)–O(7)–Sn(1)
C(26)–O(8)–Sn(2)
Sn(2)–O(9)–Sn(1A)
O(9)–Sn(2)–C(61)
O(9)–Sn(2)–C(51)
C(61)–Sn(2)–C(51)
O(9)–Sn(2)–O(1)
C(61)–Sn(2)–O(1)
C(51)–Sn(2)–O(1)
O(9)–Sn(2)–O(8)
C(61)–Sn(2)–O(8)
C(51)–Sn(2)–O(8)
O(1)–Sn(2)–O(8)
Sn(2)–O(9)–Sn(1)
Sn(1A)–O(9)–Sn(1)
113.68(19)
111.9(2)
134.4(2)
76.84(14)
96.3(2)
94.0(2)
92.81(16)
86.2(2)
81.4(2)
91.4(2)
165.90(14)
135.5(5)
135.8(5)
135.17(19)
169.50(15)
120.06(16)
104.32(14)
5
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Crystal data (2): C86H115NO18S4Sn4, Mr = 2053.79, monoclinic,
P2/n, a = 17.030(3) (2) Å, b = 11.915(2) Å, c = 23.470(5) Å,
β = 102.40(3)°, V = 4651.4(16) (4) Å3, Z = 2, F(000) = 2092,
Dx = 1.466 g cm-3, μ = 1.214 mm-1, T = 293(2) K, R1 = 0.0515,
wR2 = 0.0874. Single-crystal X-ray diffraction data for 2 were
recorded on a bruker CCD Area Detector diffractometer by using
the ω/φ scan technique with MoKα radiation (λ = 0.71073 Å).
Absorption corrections were applied by using multiscan techniques18.
The structure was solved by direct methods with SHELXS-9719
and refined by full-matrix least squares with SHELXL-9720 within
WINGX21. All nonhydrogen atoms were refined with anisotropic
temperature parameters, hydrogen atoms were refined as rigid
groups.
6
7
8
9
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CCDC 610953 contains the supplementary crystallographic
data for (2). The data can be obtained free of charge from the
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request.cif.
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We acknowledge the Postdoctoral Science Foundation
PR China (No. 2005038561).
17 For reviews on the synthesis and application of α-oxo ketene (S,S)acetals,
see (a) R.K. Dieter, Tetrahedron, 1986 42, 3029; (b) Y. Tominaga,
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18 T. Higashi, A program for absorption correction, Rigaku Corporation,
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19 G.M. Sheldrick, SHELXS-97, A program for automatic solution of crystal
structure, University of Göttingen, Germany, 1997.
20 G.M. Sheldrick, SHELXL-97, A program for crystal structure refinement,
University of Göttingen, Germany, 1997.
Received 31 July 2007; accepted 16 September 2007
Paper 07/4771
doi: 10.3184/030823407X255524
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