Synthesis and characterization of triphenyltin esters of heteroaromatic carboxylic acids and the crystal structure of [Ph3SnO 2CC5H4N·0.5H2O] ∞

Article abstract of DOI:10.1016/j.poly.2004.04.012

The reaction of triphenyltin hydroxide with 2-furanyl, 2-furanvingl, 2-(5-terbutyl) furanyl, 2-(5-benzoyl) furanyl, 2-pyridinyl, 4-pyridinyl, 3-indolyl, 3-indolmethyl, 3-indolethyl and 3-indolpropyl carboxylates in 1:1 stoichiometry yields triphenyltin esters of heteroaromatic carboxylic acids Ph₃SnO₂CR. All compounds are characterized by elemental analysis, IR and ¹H NMR. The crystal structure of the triphenyltin ester of 4-pyridinyl carboxylic acid (6) is determined by single crystal X-ray diffraction. In compound (6), the tin atom is rendered five-coordinate in a trigonal bipyramidal structure by coordinating with the 4-pyridinyl carboxlate group. The resulting structure is a linear polymer containing Sn-O bond lengths of 0.2160(5)-0.2166(5) nm and Sn-N bond lengths of 0.2512(6)-0.2612(6) nm.

Full text of DOI:10.1016/j.poly.2004.04.012

Polyhedron 23 (2004) 1805–1810
www.elsevier.com/locate/poly
Synthesis and characterization of triphenyltin esters of
heteroaromatic carboxylic acids and the crystal structure
of [Ph3SnO2CC5H4N ꢀ 0.5H2O]
Han-Dong Yin , Chuan-Hua Wang, Qiu-Ju Xing
1
*
Department of Chemistry, Liaocheng University, Liaocheng 252059, China
Received 3 February 2004; accepted 13 April 2004
Available online 4 May 2004
Abstract
The reaction of triphenyltin hydroxide with 2-furanyl, 2-furanvingl, 2-(5-terbutyl) furanyl, 2-(5-benzoyl) furanyl, 2-pyridinyl, 4-
pyridinyl, 3-indolyl, 3-indolmethyl, 3-indolethyl and 3-indolpropyl carboxylates in 1:1 stoichiometry yields triphenyltin esters of
heteroaromatic carboxylic acids Ph3SnO2CR. All compounds are characterized by elemental analysis, IR and 1H NMR. The crystal
structure of the triphenyltin ester of 4-pyridinyl carboxylic acid (6) is determined by single crystal X-ray diffraction. In compound
(6), the tin atom is rendered five-coordinate in a trigonal bipyramidal structure by coordinating with the 4-pyridinyl carboxlate
group. The resulting structure is a linear polymer containing Sn–O bond lengths of 0.2160(5)–0.2166(5) nm and Sn–N bond lengths
of 0.2512(6)–0.2612(6) nm.
Ó 2004 Elsevier Ltd. All rights reserved.
Keywords: Heteroaromatic carboxylic acid; Triphenyltin; Synthesis; Crystal structure
1. Introduction
from 2-furanyl, 2-furanvingl, 2-(5-terbutyl)furanyl, 2-(5-
benzoyl)furanyl, 2-pyridinyl, 4-pyridinyl, 3-indolyl, 3-
indolmethyl, 3-indolethyl and 3-indolpropyl carboxylic
acids and determined the crystal structure of [Ph3SnO2-
CC5H4N ꢀ 0.5H2O]1. The results of these studies are
reported herein.
Organotin esters of carboxylic acid are widely used as
biocides, fungicides and as homogeneous catalysts in
industry [1–4]. Recently, pharmaceutical properties of
organotin esters of carboxylic acid have been investigated
for their antitumor activity [5,6]. In general, the biocidal
activity of organotin compounds is influenced greatly by
the structure of the molecule and the coordination
number of the tin atom(s) [7,8]. Studies on organotin
compounds containing carboxylate ligands with an ad-
ditional donor atom (e.g., N, O or S) that are available
for coordinating to the tin atom, have revealed that new
structural types may lead to different activity [9,10]. As an
extension of our studies of organotin esters of carboxylic
acid with additional donor atoms residing on the car-
boxylate ligand [11], we have synthesized and structurally
characterized a series of triorganotin compounds derived
2. Experimental
2.1. General procedures
All reactants were reagent grade. Infrared spectra
were recorded on a Nicolet-460 spectrophotometer us-
ing KBr discs. 1H NMR spectra were obtained on
Mercury Plus-400 NMR spectrometer, chemical shifts
are given in parts per million relative to Me4Si in CDCl3
solvent. Elemental analyses were performed with a PE-
2400 II elemental apparatus. Tin was estimated as SnO2.
X-ray measurements were made on a Bruker Smart-
1000 CCD diffractometer with graphite monochromated
Mo Ka (0.071073 nm) radiation.
* Corresponding author. Tel./fax: +866358238121/+86-635-8239121.
E-mail address: handongyin@lctu.edu.cn (H.-D. Yin).
0277-5387/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2004.04.012

1806
H.-D. Yin et al. / Polyhedron 23 (2004) 1805–1810
2.2. Synthesis of triphenyltin esters of heteroaromatic
carboxylic acids
trix least-squares on F 2. All non-hydrogen atoms were
refined anisotropically. The positions of hydrogen atoms
were calculated and refined isotropically. The weighting
2
Heteroaromatic carboxylic acids (1.2 mmol) were
added to a benzene solution of Ph3SnOH (1.0 mmol).
Then the mixture was refluxed for 5 h, with water
formed during the reaction being removed azeotropi-
cally with a Dean and Stark apparatus. The clear solu-
tion obtained after filtration was evaporated in vacuum
to give a white solid. The products were recrystallized
from acetone–hexane to give colorless crystals (see
Scheme 1 for compounds R).
scheme was w ¼ 1=½s2ðFo2Þ þ ð0:0720PÞ þ 0:0000Pꢄ,
p ¼ ðFo2 þ 2Fc2Þ=3. The refinement was converged to the
final R ¼ 0:0540, wR ¼ 0:1237, ðD=rÞmax ¼ 0:001 and
S ¼ 0:999. In the final difference map, the residuals are
3
ꢀ
1.074 and )1.238 e/A .
3. Results and discussion
3.1. Physical properties
Ph3SnOH þ RCOOH ! Ph3SnOOCR
Physical data for compounds 1–10 are listed in Table
1. All compounds are colorless crystals. They are soluble
in many organic solvents such as CCl4, CHCl3, C6H6,
(CH3)2CO, but are insoluble in hexane, petroleum ether
and water.
2.3. Crystallographic measurements of Ph3SnO2CC5H4-
N-4 ꢀ 0.5H2O
A colorless crystal having approximate dimensions of
0.50 mm ꢁ 0.50 mm ꢁ 0.20 mm was mounted on a glass
capillary. All measurements were made on a Bruker
Smart 1000 CCD diffractometer with graphite mono-
chromated Mo Ka (0.071073 nm) radiation. The data
were collected at room temperature (298 ꢂ 2 K) using
the x ꢃ 2h scan technique to a maximum 2h value of
52.9°. The crystal structure belongs to orthorhombic
crystal system, with space group P21212, a ¼ 1:4882ð3Þ,
b ¼ 2:3802ð5Þ, c ¼ 1:2366ð2Þ nm, a ¼ b ¼ c ¼ 90°,
Z ¼ 4, V ¼ 4:3805ð15Þ nm3, Dc ¼ 1:459 g/cm3,
l ¼ 1:187 mmꢃ1, F ð000Þ ¼ 1928. The structure was
solved by direct method and differential Fourier map
using the SHELXL-97 program, and refined by full-ma-
3.2. Analyses of spectroscopies
3.2.1. IR spectra
The characteristic IR spectral data of compounds 1–
10 are shown in Table 2. The assignment of IR bands of
these compounds has been determined by a comparison
with the IR spectra of related organotin compounds,
carboxylates and Ph3SnOH. It is worth noting that the
difference Dm between mas(COO) and ms(COO) is impor-
tant because these frequencies can be used to determine
the type of bonding between the metal and carboxylate
ligand [1,12]. Generally triorganotin esters of carboxylic
4,
1,
2,
3,
R=
5,
N
6,
O
CH=CH-
O
PhCO
O
O
N
t-Bu
CH2-
(CH2)3-
CH2CH2-
7,
8,
9,
10
N
N
H
N
N
H
H
H
Scheme 1.
Table 1
Physical and analytical data of compounds 1–10
Compound
Yield (%)
M.p. (°C)
Found (Calc.)%
C
H
N
Sn
1
2
90
88
76
67
87
81
92
87
93
80
102–104
120–122
93–95
59.68(59.91)
61.75(61.64)
62.91(62.70)
63.97(63.75)
61.28(61.06)
59.58(59.92)
63.41(63.57)
64.00(64.16)
62.91(62.62)
65.09(65.25)
3.87(3.93)
25.79(25.74)
24.55(24.37)
22.80(22.95)
21.24(21.00)
25.33(25.14)
24.33(24.67)
23.34(23.27)
22.85(22.64)
21.21(21.34)
21.65(21.49)
4.21(4.14)
5.16(5.07)
4.05(3.92)
4.12(4.06)
4.22(4.19)
4.17(4.15)
4.39(4.42)
4.92(4.89)
5.17(4.93)
3
4
74–76
5
151–152
210–212
134–135
123–125
110–112
84–85
2.90(2.97)
2.87(2.91)
2.70(2.75)
2.73(2.67)
2.47(2.52)
2.62(2.54)
6
7
8
9
10

H.-D. Yin et al. / Polyhedron 23 (2004) 1805–1810
1807
Table 2
IR data (cmꢃ1) of compounds 1–10
Compound
m(C–H) (aryl)
mas(COO)
ms (COO)
m(Sn–C)
m(Sn–N) or (N–H)
m(Sn–O)
1
2
3057w
3050w
3051w
3058m
3065w
3060w
3052m
3057w
3061m
3054m
1541s(1650)
1591s(1648)
1594s(1650)
1654(1657)
1631s(1639)
1658s(1656)
1593s(1652)
1588s(1649)
1590s(1646)
1586s(1640)
1371s(1357)
1401s(1340)
1395s(1346)
1343(1347)
1354s(1347)
1355s(1352)
1396s(1355)
1401s(1340)
1405s(1354)
1400s(1341)
562w
545w
559w
547w
557w
552w
556w
554w
558w
545w
453w
447w
450m
442w
453w
460w
443w
438w
435w
443m
3
4
5
484w(489)
483w
3423s
6
7
8
3425s
3423s
3426s
9
10
The parentheses give the vibration of compounds in CCl4.
R'
organotin compound is inter-molecular or intra-molec-
ular may be deduced. It is shown that the N hetero atom
on the pyridine group in the carboxylate group coordi-
nates to the tin atom [15]. In CCl4 solution, this band is
not observed in compound 6. This indicates that the
Sn N bond breaks up for the compound in CCl4 so-
lution, Thus it is proved that compound 6 contains an
inter-molecular Sn N bond and exists as a polymer
[15]. However, this difference is not observed for com-
pound 5. Since the intra-molecular coordination bond is
not influenced by solvent [14], the Sn N bond existing
in the compound with structure E can also be observed
in solution. So it is possible for compound 6 to be
structure D and compound 5 to be structure E [15] (see
Scheme 3).
O
O
C
R
R
R
R
R
R
R
C
Sn
Sn
C
R'
R'
O
Sn
O
n
O
O
R
R
(B)
(A)
(C)
Scheme 2.
acid adopt three types of structures in the solid state (as
shown in Scheme 2).
The magnitude of Dm [mas(COO)–ms(COO)] of 170–199
cmꢃ1 for compounds 1–3 and 7–10 is approximately
equal to that for the corresponding sodium salt of the
carboxylic acids. This information indicates the presence
of bidentate carboxylate groups [1–4]. So it is impossible
for these compounds to be structure A. The IR spectra
of these compounds in CCl4 are also studied in order to
find out whether the ligand linkage of the C@O bond to
the tin atom is intra-molecular or inter-molecular [1,13].
Because in solution the inter-molecular bond of a five-
coordinated organotin polymer which belongs to struc-
ture C is destroyed, the polymeric structure is decom-
posed into mono-molecules and as a result, the Dm value
increases greatly [14,15]. However, the Dm value for
compounds with structure B and structure A do not
change obviously when they are determined in solvent
[14]. The results showed that the magnitude of Dm 292–
308 cmꢃ1 in CCl4 is much greater than that in KBr for
compounds 1–3 and 7–10 (shown in Table 2). This fact
reveals that the structure of these compounds might be
structure C, not be structure B. The magnitude of 277–
311 cmꢃ1 for compounds 4–6 strongly indicates the
unidentate bonding of the carboxylate groups, and the
result in KBr is similar to that in CCl4. But the struc-
tures of compounds 5 and 6 are different from structure
A. One obvious feature of the IR spectra in the com-
pounds at 484 and 483 cmꢃ1 is the similarity of the
stretching band arising from Sn–N [15]. Because the
inter-molecular bond of Sn N will break in solvent,
while the intra-molecular bond of Sn N is not influ-
enced basically by solvent [14], whether Sn N of an
1
3.2.2. H NMR spectra
1
The H NMR spectra of compounds 1–10 are given
in Table 3. It is shown that the chemical shifts of the
protons on the phenyl groups of compounds 1–10 ex-
hibit signals at about 7.21–7.68 ppm as multiplets.
The chemical shifts of the protons of heteroaromatic
rings of compounds 1–10 exhibit signals in the range
6.10–8.82 ppm as multiplets (see Table 3). In com-
pounds 1–4 and 7–10, they are similar to that of the
corresponding free heteroaromatic acid but in com-
pounds 5 and 6 they obviously increase to be higher
values than that of the corresponding free heteroaro-
matic acid. This finding may be consistent with previous
studies that suggest that only pyridine type N atoms,
present in the carboxylate R0 group, coordinate to Sn,
and there is no evidence of intra- or inter-molecular
coordination to Sn by the O atoms of furanyl groups
O
O
Ph
Sn
Ph
O
C
Sn
C
N
Ph
Ph
n
O
N
Ph
Ph
(D)
(E)
Scheme 3.

1808
H.-D. Yin et al. / Polyhedron 23 (2004) 1805–1810
Table 3
1H NMR data (ppm) for compounds 1–10
Compound
1H NMR
1
2
3
4
5
6
7
8
9
7.25–7.68 (16H, m, Ph-H, 5-furan-H), 7.11 (1H, d, 3-furan-H), 6.53 (1H, d, 4-furan-H)
7.19–7.65 (17H, m, Ph-H, 5-furan-H, C@CHCO2), 6.91 (1H, d, 3-furan-H), 6.64 (1H, d, 4-furan-H), 6.38 (1H, d, C@CHAr)
7.21–7.67 (15H, m, Ph-H,), 6.10 (1H, d, 3-furan-H), 7.87 (1H, d, 4-furan-H), 1.33 (9H, s, CH3)
7.94 (2H, br, 2,3-furan-H), 7.20–7.64 (20H, m, Ph-H)
8.21 (1H, br, 3-pyridine-H), 7.90 (1H, d, 6-pyridine-H), 7.51 (1H, d, 4-pyridine-H), 7.24–7.69 (16H, m, Ph-H, 5-pyridine-H)
8.82 (2H, d, 2,6-pyridine-H), 7.84 (2H, d, 3,5-pyridine-H), 7.35–7.75 (15H, m, Ph-H)
8.02 (1H, s, N–H), 7.21–7.67 (16H, m, Ph-H, 2-indole-H), 6.84–7.18 (4H, m, indole-H)
8.00 (1H, s, N–H), 7.22–7.62 (16H,m, Ph-H, 2-indole-H), 6.78–7.17 (4H, m, indole-H), 3.62 (2H, s, ArCH2CO2)
7.95 (1H, s, N–H), 7.23–7.66 (16H, m, Ph-H, 2-indole-H), 6.72–7.20 (4H, m, indole-H), 2.91 (2H, br, CH2CO2), 2.23 (2H, br,
ArCH2)
10
7.97 (1H, s, N–H), 7.21–7.69 (16H, m, Ph-H, 2-indole-H), 6.75–7.18 (4H, m, indole-H), 2.72 (2H, t, CH2CO2), 2.05 (2H, t,
ArCH2), 1.52 (2H, m, CH2)
[10]. In addition, the presence of the N–H proton signal
in the spectra of compounds 7–10 supports that the in-
dolyl group N atom is not coordinated to the Sn atom.
coordination of the nitrogen atom from a 4-pyridinyl
carboxylate group from an adjacent molecule. The
central tin atoms are surrounded axially by one oxygen
atom and one nitrogen atom, and equatorially by three
carbon atoms of the phenyl groups. The intra-molecular
Sn(1)–O(1) and Sn(2)–O(3) bond distances are 0.2166(5)
and 0.2160(5) nm, which are longer than that in
{[nBu2Sn(2-pic)]2O}2 [7] (0.20544 and 0.2110 nm), but
are shorter than those in Me3SnO2CC5H4N ꢀ H2O
(0.218 and 0.221 nm) [16]. The Sn(1)–O(2) and Sn(2)–
O(4) distances are 0.3237 and 0.3311 nm, which are
much greater than the sum of the van der Waals radii
for Sn and O of 0.280 nm. It is shown that the O(2) and
O(4) atoms do not make any significant contacts with
the Sn atom. The Sn(1)–N(2) and Sn(2)–N(1)#1 dis-
tances, 0.2512(6) and 0.26612(6) nm, are greater than
the sum of the covalent radii of Sn and N (0.215 nm),
but are considerably less than the sum of the van der
3.2.3. X-ray crystal structure of Ph3SnO2CC5H4N-
4 ꢀ 0.5H2O (6)
Selected bond distances and angles are listed in Table
4. The molecular structure is shown in Fig. 1. Fig. 2
shows the packing of the molecules in the unit cell as
seen in a projection onto its face.
In [Ph3SnO2CC5H4N ꢀ 0.5H2O]1 6, two kinds of tin
atoms with different chemical environments can be
found. Each molecule of compound 6 in the unit cell
possesses an unequivocally polymeric structure, but this
structure differs from the tributyltin 2-(5-tertbutyl)
furanylcarboxylate [8] and tribenzyltin 2-(5-tertbu-
tyl)furanylcarboxylate [8]. Each tin atom is rendered
five-coordinate in a trigonal bipyramidal structure by
Table 4
Selected bond distances (nm) and angles (°) for compound 6
Bond distances
Sn(1)–O(1)
Sn(2)–N(1)#1
Sn(1)–C(13)
Sn(2)–C(43)
O(1)–C(1)
0.2166(5)
0.26612(6)
0.2125(8)
0.2115(8)
0.1276(10)
0.1206(9)
Sn(1)–N(2)
Sn(1)–C(7)
Sn(2)–C(31)
O(2)–C(1)
N(1)–C(4)
N(2)–C(28)
0.2512(6)
0.2142(9)
0.2125(8)
0.1208(10)
0.1338(11)
0.1336(10)
Sn(1)–C(19)
Sn(2)–C(37)
Sn(2)–O(3)
O(3)–C(25)
N(1)–C(5)
0.2129(8)
0.2130(7)
0.2160(5)
0.1245(9)
0.1300(10)
0.1289(9)
O(4)–C(25)
N(2)–C(29)
Bond angles
C(13)–Sn(1)–C(7)
C(13)–Sn(1)–O(1)
C(13)–Sn(1)–N(2)
O(1)–Sn(1)–N(2)
C(31)–Sn(2)–N(1)#1
O(3)–Sn(2)–N(1)#1
C(1)–O(1)–Sn(1)
C(8)–C(7)–Sn(1)
C(24)–C(19)–Sn(1)
C(32)–C(31)–Sn(2)
C(44)–C(43)–Sn(2)
C(48)–C(43)–Sn(2)
N(1)–C(4)–C(3)
120.2(4)
96.2(3)
88.0(2)
C(13)–Sn(1)–C(19)
C(7)–Sn(1)–O(1)
C(19)–Sn(1)–N(2)
C(37)–Sn(2)–O(3)
C(37)–Sn(2)–N(1)#1
C(31)–Sn(2)–O(3)
C(29)–N(2)–Sn(1)
C(14)–C(13)–Sn(1)
C(20)–C(19)–Sn(1)
C(25)–O(3)–Sn(2)
C(38)–C(37)–Sn(2)
O(2)–C(1)–O(1)
115.0(4)
93.2(3)
88.2(3)
C(7)–Sn(1)–C(19)
C(19)–Sn(1)–O(1)
C(7)–Sn(1)–N(2)
C(43)–Sn(2)–O(3)
C(43)–Sn(2)–N(1)#1
C(28)–N(2)–Sn(1)
C(12)–C(7)–Sn(1)
C(18)–C(13)–Sn(1)
C(36)–C(31)–Sn(2)
C(42)–C(37)–Sn(2)
C(4)–N(1)–C(5)
124.0(3)
89.9(3)
84.9(3)
175.8(2)
84.5(2)
88.4(2)
84.8(2)
97.8(3)
99.5(3)
84.4(3)
173.1(2)
120.9(5)
120.1(7)
126.8(8)
124.0(6)
123.0(6)
120.4(6)
123.6(8)
119.8(5)
123.4(7)
124.0(9)
116.9(6)
120.9(7)
116.7(7)
113.9(7)
118.9(8)
124.7(5)
119.2(8)
116.8(6)
115.1(5)
120.9(6)
127.1(8)
124.0(8)
O(1)–C(1)–C(2)
O(2)–C(1)–C(2)
N(1)–C(5)–C(6)

H.-D. Yin et al. / Polyhedron 23 (2004) 1805–1810
1809
Fig. 1. The molecular structure of compound 6.
88.2(3)°, all are not 90°, and only one approximates to
90°. The angle of O(1)–Sn(1)–N(2), 175.8(2)°, shows
that the atoms O(1), Sn(1) and N(2) are nearly linear.
The Sn(2) atom is similar to the Sn(1) atom and it has a
distorted trigonal bipyramidal structure too.
4. Supplementary material
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Center, CCDC No. 200373 for compound 6.
Copies of this information may be obtained from The
Director, CCDC, 12 Union Road, Cambridge CB2 1EZ,
UK (fax: +44-1233-336-033; E-mail: deposit@ccdc.cam.
ac.uk, or www: http://www.ccdc.cam.ac.uk).
Fig. 2. Projection of compound 6.
Acknowledgements
Waals radii (0.375 nm) [17] and should be considered as
bonding interactions. In this connection it is relevant to
note the Sn–N bond distances found in three other
crystal structures of organotin compounds containing
the pyridine carboxylate ligand. In polymeric
[Me2SnCl(2-pic)]n [18] the two unique Sn–N bond dis-
tances are 0.250(3) and 0.247(2) nm, in polymeric
[Me2Sn(2-pic)2]n [9] the two Sn–N bond distances are
0.2507(4) and 0.2477(4) nm and in dicarboxylato te-
traorganostannoxane {[nBu2Sn(2-pic)]2O}2 [7] the two
Sn–N bond distances are 0.2550(5) and 0.3150(5) nm. In
compound 6, the distortions from true trigonal bipyra-
midal symmetry are reflected in the interatomic angles.
For instance around the Sn(1) atom of compound 6 the
angles of C(7)–Sn(1)–O(1) 93.2(3)°, C(13)–Sn(1)–O(1)
96.2(3)°, C(19)–Sn(1)–O(1) 89.9(3)°, C(7)–Sn(1)–N(2)
84.9(3)°, C(13)–Sn(1)–N(2) 88.0(2)°, C(19)–Sn(1)–N(2)
We acknowledge the financial support of the Shan-
dong Province Science Foundation, and the State Key
Laboratory of Crystal Materials, Shandong University,
PR China.
References
[1] Q.L. Xie, S.H. Li, D.K. Zhang, Z.G. Zhang, J.M. Hu, Acta Chim.
Sinica 49 (1991) 723.
[2] H.D. Yin, D.Z. Zhu, Y. Wang, C.L. Liu, F.G. Ma, Chin. J. Org.
Chem. 22 (2002) 575.
[3] H.D. Yin, C.H. Wang, Y. Wang, C.L. Ma, J.X. Shao, J.H. Zhang,
Acta Chim. Sinica 60 (2002) 143.
[4] H.D. Yin, C.L. Ma, Y. Wang, H.X. Fang, J.X. Sao, Acta Chim.
Sinica 60 (2002) 897.
[5] H.D. Yin, C.H. Wang, Y. Wang, C.L. Ma, G.F. Liou, Chin. J.
Org. Chem. 22 (2002) 590.

1810
H.-D. Yin et al. / Polyhedron 23 (2004) 1805–1810
[6] M. Grelen, A.M. Khloufi, M. Biesmans, R. Kayser, Appl.
Organomet. Chem. 7 (1993) 201.
[12] S.G. Teoh, S.H. Ang, J.P.D. Declercq, Polyhedron 16 (1997) 3729.
[13] H.D. Yin, C.H. Wang, Y. Wang, C.L. Ma, D.Q. Wang, Indian J.
Chem. 42B (2003) 881.
[7] C.S. Parulekar, X.K. Jain, T.K. Das, A.R. Gupta, B.F. Hoskins,
E.R.T. Tiekink, J. Organoment. Chem. 372 (1989) 193.
[8] Q.L. Xie, X.H. Xu, H.G. Wang, X.K. Yao, R.J.Z.G. Zhang, J.M.
Hu, Acta Chim. Sinica 49 (1991) 1085.
[14] Z.Q. Yang, Q.L. Xie, X.Z. Zhou, Chem. J. Chin. Univ. 16 (1995)
59.
[15] H.D. Yin, C.H. Wang, C.L. Ma, D.Q. Wang, J. Organomet.
Chem. 689 (2004) 246.
[9] T.P. Lockhart, F. Davidson, Organometallics 6 (1987) 2471.
[10] C. Vatsa, V.K. Jain, T. Kesavadas, E.R.T. Tiekink, J. Organomet.
Chem. 410 (1991) 135.
[16] P.G. Harrison, R.C. Philips, J. Organomet. Chem. 182 (1979) 37.
[17] A. Bondi, J. Phys. Chem. 68 (1964) 441.
[18] I.W. Nowell, J.S. Brooks, G. Beech, R. Hill, J. Organomet. Chem.
244 (1983) 119.
[11] H.D. Yin, R.F. Zhang, C.L. Ma, Chin. J .Inorg. Chem. 14 (1998)
101.