Synthesis and crystal structure of a mixed-ligand compound di-n-butyl(4-chlorobenzoxy)(4-chlorobenzohydroxamato)tin(IV)

Article abstract of DOI:10.1016/j.jorganchem.2005.05.043

Reaction of dibutyltin dichloride with 4-chlorobenzohydroxamic acid and 4-chlorobenzoic acid in 1:1:1 stoichiometry yields the new title compound di-n-butyl(4-chlorobenzoxy)(4-chlorobenzohydroxamato)tin(IV) 1, which had been characterized by IR and ¹H, ¹³C, ¹¹⁹Sn NMR. Single X-ray crystal structure analysis has been determined for 1, which crystallizes as the five-coordinate mixed-ligand dibutyltin(IV) complex containing both monodentate and bidentate ligands. The crystal structure of the compound reveals that the tin atom adopts distorted trigonal bipyramidal geometry with the Bu groups trans to each other. The C-Sn-C angle is 145.9(3)°, and the Sn-O bonds are 2.083(4) and 2.158(4) A? in one ligand and 2.242(4) A? in the other. An unusual feature of the structure is the presence of a kind of intermolecular hydrogen bonding which serves to stabilize the crystal structure.

Full text of DOI:10.1016/j.jorganchem.2005.05.043

Journal of Organometallic Chemistry 690 (2005) 3997–4000
www.elsevier.com/locate/jorganchem
Synthesis and crystal structure of a mixed-ligand compound
di-n-butyl(4-chlorobenzoxy)(4-chlorobenzohydroxamato)tin(IV)
a
Xianmei Shang , Qingshan Li
a,b,
a,
*
*, Jizhou Wu
a
School of Pharmaceutical Science, Tongji Medical University, HUST, 13 Hangkong Road, Wuhan 430030, PR China
b
School of Pharmaceutical Science, Shanxi Medical University, Taiyuan 030001, PR China
Received 12 April 2005; received in revised form 27 May 2005; accepted 28 May 2005
Available online 18 July 2005
Abstract
Reaction of dibutyltin dichloride with 4-chlorobenzohydroxamic acid and 4-chlorobenzoic acid in 1:1:1 stoichiometry yields the
new title compound di-n-butyl(4-chlorobenzoxy)(4-chlorobenzohydroxamato)tin(IV) 1, which had been characterized by IR and 1H,
13C, 119Sn NMR. Single X-ray crystal structure analysis has been determined for 1, which crystallizes as the five-coordinate mixed-
ligand dibutyltin(IV) complex containing both monodentate and bidentate ligands. The crystal structure of the compound reveals
that the tin atom adopts distorted trigonal bipyramidal geometry with the Bu groups trans to each other. The C–Sn–C angle is
˚
˚
145.9(3)ꢀ, and the Sn–O bonds are 2.083(4) and 2.158(4) A in one ligand and 2.242(4) A in the other. An unusual feature of the
structure is the presence of a kind of intermolecular hydrogen bonding which serves to stabilize the crystal structure.
ꢁ 2005 Elsevier B.V. All rights reserved.
Keywords: Dibutyltin(IV); Mixed-ligand; Crystal structure; 4-Chlorobenzohydroxamic acid; 4-Chlorobenzoic acid; Distorted trigonal bipyramid
1. Introduction
ties such as antifungicidal and the promising antitumor
activity in some cases as reported by our group [9,10],
several of whose crystal structure data are available [10].
Less attention has been devoted to the mixed-ligand
complexes [11]. To the best of our knowledge, no diorg-
anotin(IV) complexes containing both monodentate
carboxylate ligand and bidentate O-donors hydroxamic
acid ligand as supporting ligands have ever been reported.
In general, the antitumor activity of organotin com-
pounds is greatly influenced by the structure of the mole-
cule and the coordination number of the tin atoms [12]. In
order to explore the relationship between the biological
activity and structure, in this paper, we introduce two
different types of ligands into SnBu2 group to obtain a five-
coordinate compound di-n-butyl(4-chlorobenzoxy)(4-
chlorobenzohydroxamato)tin(IV) (1, Scheme 1). The
elemental analysis, IR, and 1H, 13C, 119Sn NMR spectra
and crystal structure of the new compound have been car-
ried out, and the results of this study are reported herein.
The chemistry of organotin(IV) complexes has devel-
oped considerably during last 30 years, highlighting the
syntheses of a number of complexes with interesting
properties [1–3]. The diorganotin(IV) complex contain-
ing carboxylate ligand has been investigated for its anti-
tumor activities [4,5]. Crystallographic studies have
revealed that organotin carboxylates adopt structures
which are dependent on both the nature of the substitu-
ent bound to the tin atom and on the type of carboxylate
ligand [6,7]. In recent years, considerable interest has
also been shown in diorganotin(IV) derivatives of
hydroxamic acids [8] because of their biological proper-
*
Corresponding authors. Tel.: +86 351 469 0322; fax: +86 351 469
0114 (Q. Li); tel./fax: +86 27 8369 2739 (J. Wu).
E-mail addresses: qingshanl@yahoo.com (Q. Li), ywjz@mails.
tjmu.edu.cn (J. Wu).
0022-328X/$ - see front matter ꢁ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2005.05.043

3998
X. Shang et al. / Journal of Organometallic Chemistry 690 (2005) 3997–4000
HO
O
Dibutyltin compounds exhibit resonances in the 0.83–
O
+
Bu2SnCl2
+
Cl
Cl
1.74 ppm. For 1 the signals from the other groups, such
as phenyl H, appear in similar positions to the free
ligand, but exhibit two groups of peaks because the
protons on the two p-chlorobenzoyl groups of the com-
pound are chemically different. This finding is consistent
with the formulation of 1 as a mixed-ligand complex.
119Sn NMR spectra of 1 display only one resonance
at ꢀ157.8 ppm indicating one type of tin site. The chem-
ical shift is in agreement with the penta-coordinated tin
atom [20], which shows that the structure of the type of
tin atom in the solid state is still retained in solution.
HN OH
Bu
Sn
Bu
O
O
KOH
MeOH
Cl
Cl
O
HN
O
Scheme 1.
2. Results and discussion
2.1. Spectroscopy
2.2. X-ray crystallography
The assignments of the IR bands of the complex have
been made by comparison with the IR spectra of the free
ligands. The free ligands show a broad O–H absorption
in the regions of 2600–2900 cmꢀ1 and 3210–3010 cmꢀ1
which are absent in the spectrum of the complex, be-
cause of their deprotonation and coordination [13].
The N–O absorptions in the free ligand occur in the
range of 847–971 cmꢀ1 [14], and at 913–1043 cmꢀ1in
the complex. The shift towards higher frequencies of
m(N–O) rules out coordination through the N atom
[15,16]. Therefore, the IR spectra indicate coordination
via both O atoms of the CONHO group. In the 553–
400 cmꢀ1 region, the two (or more) strong absorptions
of the diorganotin(IV) complexes are assigned to the
stretching mode of the Sn–O linkage [17–19]. The pres-
ence of more than one Sn–O band, is more obvious
for the mixed-ligand complexes, and reflects the different
Sn–O bond lengths as proved by the X-ray analysis.
The 1H NMR spectrum shows the expected reso-
nances with appropriate multiplicities and intensities.
The molecular structure of 1 is shown in Fig. 1. It can
be seen that the tin atom has a coordination number of
five. There are two types of chlorophenyl substituted li-
gands. The chlorobenzohydroxamo is found to be che-
lating to the Sn atom through the carbonyl O atom
and the hydroxyl O atom, and Sn–O bond distances
˚
are 2.242(4) and 2.083(4) A. The carboxylate is monod-
entate, coordinating to Sn atom through atom O(2),
˚
Sn(1)–O(2) 2.158(4) A. The O(1) and Sn(1) distance of
˚
3.031(4) A are too long to be a strong covalent bond.
However, this Sn–O distance is shorter than the sum
˚
of the van der Waals radii for these atoms (3.68 A)
[21], and thus may be considered as a weak bond. We
think there are two important reasons for this. Firstly,
the strong electron-withdrawing nature of Cl decreases
the electron density on the O atom of the C@O and re-
duces its ability for coordinating to the tin atom. Sec-
ondly, steric interactions of two bulky butyl groups
and the chelating five membered ring may prevent the
formation of the Sn1–O1 bond. In addition, the strain
Fig. 1. Molecular structure of 1 with atom labeling.

X. Shang et al. / Journal of Organometallic Chemistry 690 (2005) 3997–4000
3999
of the four-member ring that would be formed also
needs to be considered.
3.2. Synthesis of di-n-butyl(4-chlorobenzoxy)
(4-chlorobenzohydroxamato)tin(IV)
The C(15)–Sn–C(19) linkage is not linear, having an
angle of 145.9(3)ꢀ, which is much smaller than the value
expected for a regular octahedron. This coordination
geometry is best described as distorted trigonal bipyra-
mid. Another important distortion is caused by the
asymmetric Sn–O bond lengths, since all three of them
are significantly different. Therefore, the bite angle
O(4)–Sn(1)–O(3) of 1, 74.31(15)ꢀ, is not consistent with
a true trigonal geometry of 120ꢀ, but instead with a dis-
torted trigonal bipyramidal geometry. As a result, the
Sn atom in 1 exists in a distorted trigonal planar geom-
etry in which the basal plane is defined by the three O
atoms, and the axial positions are occupied by the two
butyl substituents which are found to be disordered ow-
ing to high thermal motion. In addition, the dihedral an-
gles between the O(1)–C(7)–O(2)/C(2)–C(3)–C(4)–C(5)
and O(3)–C(14)–N(1)/C(9)–C(10)–C(11)–C(12) planes
are 12.1ꢀ and 17.3ꢀ, respectively, indicating little conju-
gation between the –COO or –CONH and benzene ring
[22].
Dibutyltin dichloride (0.303 g, 1.0 mmol) was added
to an anhydrous methanolic solution (30 ml) of 4-chlo-
robenzohydroxamic acid (HL1, 0.172 g 1.0 mmol),
4-chlorobenzoic acid (HL2, 0.157 g 1.0 mmol) and
KOH (0.112 g 2.0 mmol). The solution was stirred under
N2 at room temperature overnight. Water (30 ml) was
added to form a white precipitate, which was separated
by filtration, washed with water and cold methanol. The
white solid was then recrystallized from ethanol. Color-
n
less needle-shaped crystals of BuSn(L1)(L2) were col-
lected, washed with ethanol and dried under reduced
pressure. Yield: 0.20 g, 36%. M.p. 148–149 ꢀC. Anal.
Calc. for C22H26Cl2NO4Sn: C, 47.35; H, 4.70; N, 2.51.
Found: C, 47.17; H, 4.77; N, 2.47%. IR(KBr):
m = 3205 s (N–H); 1559 m and 1594 vs (CO)/(NC);
1363 m (COO) 913 s (N–O); 421 m and 527 s (Sn–O);
553 s and 572 w (Sn–C) cmꢀ1 1H NMR (CDCl3)
;
for (H3C4H2C3H2C2H2C1)2Sn–[OC(O)C6H4–Cl-4]–[O–
NH–C(O)C6H4–Cl-4]: d (t, 6H, 2C4H3) 0.85; d (m, 4H,
2C3H2) 1.38; d (m, 8H, 2C2H2C1H2) 1.68; d (m, 8H,
2C6H4) 7.40–7.98 ppm. 13C NMR (CDCl3) d 176.1,
168.2 (CO); 139.2, 132.0, 129.8, 128.9 and 128.2 (Carom);
27.32–14.12 ppm (m, Sn–R); 119Sn NMR (CDCl3): d
ꢀ157.8 ppm.
There are some weak intermolecular interactions in
the crystal lattice. Firstly, the oxygen atom(O1) of car-
bonyl in 4-chlorobenzoic acid participates in intermolec-
ular hydrogen bond formation with the hydrogen atom
H(12) of benzene ring; the O(1)ꢁ ꢁ ꢁH(12) separation is
˚
2.57 A (symmetry operation: x, 1/2 ꢀ y, 1/2 + z). This
has the result that the lattice consists of loosely associ-
ated dimers linked by hydrogen bonding. Secondly,
the dihedral angles between the C9–C11–C13/C90–
C110–C130 and C1–C3–C5/C10–C30–C50 planes are 0ꢀ
and 0.02ꢀ, respectively, indicating the one aromatic ring
is parallel to another. The centroid–centroid distances of
3.3. Crystal structure determination
A colorless crystal of approximately 0.40 · 0.10 ·
0.08 mm3 was mounted in a glass capillary. Data collec-
tion was carried out on a Bruker SMART CCD diffrac-
tometer with Mo Ka radiation at room temperature. A
preliminary orientation matrix and unit cell parameters
were determined from three runs of 15 frames each, each
frame corresponding to a 0.3ꢀ scan in 15 s, followed by
spot integration and least-squares refinement. Data were
measured using an x scan of 0.3ꢀ per frame for 5 s until
a complete hemisphere had been collected. Cell parame-
ters were retrieved using SMART [25] software and refined
with SAINT on all observed reflections. Data reduction
was performed with the SAINT software and corrected
for Lorentz and polarization effects. Absorption correc-
tions were applied with the program SADABS. The struc-
tures were solved by direct methods with the SHELX-97
program and refined by full-matrix least-squares meth-
ods on F2 with SHEXLTL-PC V. Details of the crystal data,
data collection, structure solution and refinement are re-
ported in Supplementary materials.
˚
aromatic ring planes are 4.0318 and 3.8271 A, suggest-
ing a weak p–p stacking interaction [23].
3. Experimental
3.1. General
Dibutyltin(IV) dichloride and 4-chlorobenzoic acid
were purchased from Aldrich Chemical Co. They are
used as received. The other reagents were of analytical
grade. 4-Chlorobenzohydroxamic acid was prepared
according to the literature method [24].
Elemental analyses were performed on PE-2400-II
elemental analyzer. IR spectra in the range 4000–
400 cmꢀ1 were recorded on Perkin–Elmer one FT-IR
spectrophotometer with samples investigated as KBr
1
discs. H, 13C, 119Sn NMR spectra were recorded on a
1
Varian INOVA 600 spectrometer (600.0 MHz for H,
4. Supplementary materials
150.8 MHz for 13C, 223.6 MHz for 119Sn) at ambient
temperature [d values in ppm relative to Me4Si (1H,
13C) or Me4Sn (119Sn)].
CCDC No. 268394 contains the supplementary
crystallographic data for this paper. These data can be

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X. Shang et al. / Journal of Organometallic Chemistry 690 (2005) 3997–4000
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