www.elsevier.nl/locate/poly
Polyhedron 19 (2000) 841–847
Structural and spectral studies of a heterocyclic N(4)-substituted
bis(thiosemicarbazone), H22,6AcheximPH2O, its heptacoordinated
tin(IV) complex [Bu2Sn(2,6Achexim)], and its binuclear zinc(II)
complex [Zn(2,6Achexim)]2
´ F. de Sousa a, Douglas X. West b,*, Christine A. Brown b, John K. Swearingen b,
Gerimario
c
c
d
´
´
´ A. Toscano c, Simon Hernandez-Ortega
´
¨
´ Valdes-Martınez
, Ruben
, Manfredo Horner
,
Jesus
d
´
Adaılton
J. Bortoluzzi
a
´
´ 70919.900 Brasılia,
´ D.F, Brazil
Instituto de Quımica,
Universidade de Brasılia,
Department of Chemistry, Illinois State University, Normal, IL 61790-4160, USA
c
´
´
´
´ 04510, D.F. Mexico
´
Instituto de Quımica,
Universidad Autonoma
de Mexico,
Circuito Exterior, Ciudad Universitaria, Coyoacan
d
´
Departamento de Quımica,
Universidade Federal de Santa Maria, Santa Maria, 97119.900, Rio Grande do Sul, R.S, Brazil
b
Received 16 August 1999; accepted 26 January 2000
Abstract
The multidentate ligand, 2,6-diacetylpyridine bis(3-hexamethyleneiminylthiosemicarbazone) monohydrate, H22,6AcheximPH2O, crystallizes with one thiosemicarbazone moiety in an intramolecular hydrogen bonded, bifurcated E9 form. The other thiosemicarbazone moiety is
E and is not involved in intramolecular hydrogen bonding, but is involved in hydrogen bonding with the hydrate water molecule. The dianion
(loss of N3a and N3b hydrogens) of H22,6Achexim acts as a pentadentate ligand, 2,6Achexim, in a planar conformation to a central tin(IV)
ion, and as a bridging tetradentate ligand with the two thiosemicarbazone moieties of 2,6Achexim coordinating to different zinc atoms. The
tin(IV) is heptacoordinate in a distorted pentagonal dipyramidal configuration, with the five SNNNS donor atoms of 2,6Achexim in the
pentagonal plane and the two n-butyl groups in the axial positions. The binuclear zinc complex has two equivalent tetrahedral zinc centers,
with the pyridyl nitrogens of the two ligands not coordinated.
q2000 Elsevier Science Ltd All rights reserved.
Keywords: Heterocyclic bis(thiosemicarbazone); Heptacoordinate complexes; Organotin(IV) complexes; Binuclear zinc complexes
1. Introduction
Considerable interest has been shown in 2,6-diacetylpyridine bis(thiosemicarbazone), and its metal complexes [1].
Crystal structures have been reported for three different zinc
complexes, and two are binuclear [2]. Of the two binuclear
complexes, one features distorted octahedral zinc atoms that
are nearly equivalent, and the second binuclear complex contains a distorted octahedral and a tetrahedral zinc center. More
recently, the former of these binuclear complexes has been
prepared under different conditions and a new crystal structure reported [3]. De Sousa et al. reported the crystal structures of heptacoordinate tin(IV) complexes, namely
[MeSnCl(H2,6Ac4DH)]ClPMeOH [4] and [Ph2Sn(H2,6* Corresponding author. Tel.: q1-309-438-7019; fax: q1-309-438-5538;
e-mail: dxwest@ilstu.edu
Ac4DH)]Cl [5], where H22,6Ac4DHs2,6-diacetylpyridine bis(thiosemicarbazone). Other reports on
H22,6Ac4DH complexes include the following: a third
tin(IV) heptacoordinate complex [Ph2Sn(2,6Ac4DH)]P
2DMF [6], the structure of a manganese(II) complex [7],
and the structures of several indium(III) complexes [8].
Although spectral and biological studies have been carried
out on metal complexes of 2,6-diacetylpyridine bis(N(4)substituted thiosemicarbazones) [9,10], no structural information has been provided even though the N(4)-substituent
in other types of thiosemicarbazones, including bis(thiosemicarbazones), has been shown to affect their biological
activity [11].
X-ray studies [12–14] have previously shown that 2-formyl-, 2-acetyl- and 2-benzoylpyridine N(4)-substituted thiosemicarbazones exist in the solid state in at least four different
0277-5387/00/$ - see front matter q2000 Elsevier Science Ltd All rights reserved.
PII S 0 2 7 7 - 5 3 8 7 ( 0 0 ) 0 0 3 2 6 - 0
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structural modifications: E isomers without hydrogen bonding by N3H to the pyridine nitrogen, two forms of hydrogen
bonding Z isomers, and as a bifurcated hydrogen bonded E9
isomer. The four modifications are shown in Fig. 1 and can
be described as follows: (a) E with respect to the imine
function of the thiosemicarbazone [12] without hydrogen
bonding to the pyridyl nitrogen; (b) hydrogen bonding to the
pyridyl nitrogen by N3H, Z with respect to the imine function
of the thiosemicarbazone and Z with respect to the N3–C8
bond [12–14]; (c) hydrogen bonding to the pyridyl nitrogen
by the N3H, Z with respect to the imine function of the
thiosemicarbazone, but E with respect to the N3–C8 bond
[13]; (d) the bifurcated E9 tautomer in which the N3 hydrogen has shifted to the imine nitrogen, N2, and is hydrogen
bonding to both the pyridyl nitrogen and sulfur of the thiosemicarbazone moiety [12,15]. A representation of
H22,6Achexim showing that one thiosemicarbazone moiety
is E and the other is E9 is included in Fig. 1.
Since tin(IV) [16] and zinc(II) complexes [1,17] have
significant pharmacological activity and little research has
been done on N-heterocyclic bis(thiosemicarbazones), we
report in this work the X-ray crystal structures of
H22,6AcheximPH2O, [Bu2Sn(2,6Achexim)], and [Zn(2,6Achexim)]2.
2. Experimental
2.1. Materials
Solvents were purified and dried according to standard
procedures. 2,6-Diacetylpyridine (Aldrich), di-n-butyltin(IV)dichloride (Aldrich) and zinc acetate were used without further purification. IR spectra were recorded on a Nicolet
5ZDX-FT spectrophotometer in the 4000–400 cmy1 range
using KBr pellets. NMR spectra were obtained with a Varian
300 MHz Gemini spectrometer using [2H6]DMSO or CDCl3
as the solvents with chemical shifts reported in parts per
million downfield from Me4Si.
2.2. Preparation of H22,6AcheximPH2O,
[Bu2Sn(2,6Achexim)] and [Zn(2,6Achexim)]2
The bright yellow bis(thiosemicarbazone), H22,6AcheximPH2O, was prepared by refluxing a 2:1 molar mixture of hexamethyleneiminylthiosemicarbazide (1.73 g, 10
mmol) [18] with 2,6-diacetylpyridine (0.82 g, 5 mmol) in
absolute EtOH (50 ml). The tin(IV) complex was obtained
by mixing H22,6AcheximPH2O (0.10 g, 0.20 mmol) and the
acid n-Bu2SnCl2 (0.15 g, 0.21 mmol) in 15 ml of EtOH, and
slow evaporation of the solvent led to the appearance of a
crystalline product suitable for X-ray structure analysis. The
zinc complex was prepared by refluxing zinc acetate dihydrate (0.22 g, 1 mmol) and H22,6AcheximPH2O (0.5 g, 1
mmol) in 40 ml of EtOH for 2 h. The resulting orange solid
was filtered, washed with anhydrous Et2O and dried on a
Thursday Apr 13 09:56 AM
Fig. 1. (a) A representation of an E isomer of 2-acetylpyridine N(4)ethylthiosemicarbazone, HAc4E; (b) a representation of a ZZ isomer of
2-benzoylpyridine 3-piperidylthiosemicarbazone, HBzpip; (c) a representation of a ZE isomer of 2-benzoylpyridine 3-hexamethyleneiminylthiosemicarbazone, HBzhexim; (d) a representation of an E9 isomer of
2-acetylpyridine 3-hexamethylene-iminylthiosemicarbazone, HAchexim;
(e) 2,6-diacetylpyridine bis(3-hexamethyleneimylthiosemicarbazone),
H22,6Achexim.
warm plate. H22,6AcheximPH2O, yield 60%; m.p.s167–
1698C. Anal. Found: C, 55.4; H, 7.5; N, 19.4. Calc.: C, 55.6;
H, 7.4; N, 19.6%. [Bu2Sn(2,6Achexim)], yield 74%;
m.p.s261–2648C. Anal. Found: C, 52.7; H, 7.3; N, 13.9.
Calc.: C, 52.6; H, 7.1; N, 13.7%. [Zn(2,6Achexim)]2, yield,
67%, m.p.s266–2688C (dec.).
2.3. X-ray crystallography
Crystals of H22,6AcheximPH2O, [Bu2Sn(2,6Achexim)]
and [Zn(2,6Achexim)]2 were grown by evaporation of
EtOH solutions and mounted on glass fibers. The structures
were solved with direct methods and missing atoms were
found by difference-Fourier synthesis. All non-hydrogen
atoms were refined with anisotropic temperature factors, and
all hydrogens were found on the difference Fourier map. The
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Table 1
Crystallographic data for H22,6AcheximPH2O, [Bu2Sn(2,6Achexim)] and [Zn(2,6Achexim)]2
Formula
Formula weight
Crystal system
Crystal color, habit
Z
Space group
Crystal dimensions (mm)
T (K)
˚
a (A)
˚
b (A)
˚
c (A)
b (8)
˚ 3)
V (A
Dcalc (g cmy3)
Index ranges
F(000)
Diffractometer
Absorption coefficient (mmy1)
Radiation
˚
Wavelength (A)
Reflections collected
Observed reflections
Goodness-of-fit
R (%)
Rw (%)
˚ y3)
Largest difference peak/hole (e A
H22,6AcheximPH2O
[Bu2Sn(2,6Achexim)]
[Zn(2,6Achexim)]2
C23H37N7OS2
491.7
orthorhombic
yellow, laminar
8
Pbcn
0.38=0.30=0.18
293
33.071(2)
8.915(2)
17.608(2)
90
5191.3(4)
1.258
0FhF35
0FkF9
0FlF18
2112
Siemens P4/PC
2.088
Cu Ka
1.54178
6274
3361 (F)4.0s(F))
1.26
6.80
10.05
0.45/y0.48
C31H51N7S2Sn
704.6
orthorhombic
red, prism
4
Pnma
0.40=0.25=0.20
193
10.183(2)
15.197(3)
22.509(5)
90
3483.3(12)
1.340
0FhF12
y1FkF18
y1FlFy26
1472
Nonius CAD-4
0.884
Mo Ka
0.71073
3633
2024 (I)2.0s(I))
1.031
5.40
11.24
0.831/y0.734
C23H33N7S2Zn
537.1
monoclinic
orange, prism
4
P2/c
0.40=0.24=0.12
293
10.617(2)
13.443(2)
18.635(2)
106.42(2)
2551.1(5)
1.398
0FhF12
0FkF15
y22FlF21
1128
Siemens P4/PC
1.152
Mo Ka
0.71073
4758
2316 (F)3.0s(F))
1.02
5.27
5.22
0.40/y0.37
H atoms attached to carbons were allowed to ride on the C
atoms and assigned a fixed isotropic temperature factor,
˚ 2 (Us0.08 A
˚ 2 for [Bu2Sn(2,6Achexim)]). Only
Us0.06 A
the coordinates of the H atoms attached to nitrogens and
oxygen were refined. Both seven-membered rings of
H22,6AcheximPH2O display conformational disorder such
that atoms C13A and C11B split into two alternative positions
with complementary occupancy factors (0.65 and 0.35).
Owing to the site symmetry of [Bu2Sn(2,6Achexim)] the
atoms N1, C4, Sn and the carbon atoms of the n-butyl groups
are located in special crystallographic positions, with y/b
s0.25 and site multiplicity 0.50. One of the n-butyl groups
is apparently disordered (C31–C34) while the other group
(C41–C44) does not show any sign of disorder. The C32
atom is split between two positions related by the mirror
plane, and the C31, C33 and C34 atoms show largely elongated displacement ellipsoids perpendicular to the mirror
plane also indicating disorder. Attempts to refine C32 with
the two positions did not cause any decrease in R values,
however. The alternative structure solution involving the
space group Pn21a, one maximal non-isomorphic subgroup
of Pmna, was also possible and all non-hydrogen atoms were
found by subsequent Fourier difference synthesis and refined
isotropically. However, the molecule with site symmetry 1
shows one n-butyl group (C31–C34) that is chemically
incorrect. The crystallographic experimental details are given
Thursday Apr 13 09:56 AM
in Table 1 and selected bond lengths and angles for
H22,6AcheximPH2O and the complexes are reported in
Tables 2 and 3, respectively.
Table 2
˚ for H22,6AcheximPH2O, [Bu2Sn(2,6Selected bond distances (A)
Achexim)] and [Zn(2,6Achexim)]2
[Bu2Sn(2,6Achexim)]
H22,6Achexim
Sn–N1
Sn–N2a
Sn–N2b
Sn–S1
Sn–S2
Sn–C31
Sn–C41
S1–C8a
S2–C8b
N3a–C8a
N3b–C8b
N4a–C8a
N4b–C8b
N2a–N3a
N2b–N3b
N2a–C7a
N2b–C7b
C7a–C2
C7b–C6
1.716(6)
1.689(7)
1.364(7)
1.359((7)
1.346(7)
1.337(9)
1.347(6)
1.372(7)
1.291(6)
1.313(7)
1.471(7)
1.474(7)
2.415(6)
2.437(5)
2.437(5)
2.6924(16)
2.6924(16)
2.148(10)
2.170(8)
1.744(6)
1.744(6)
1.350(8)
1.350(8)
1.369(7)
1.369(7)
1.375(6)
1.375(6)
1.330(7)
1.330(7)
1.491(8)
1.491(8)
[Zn(2,6Achexim)]2
Zn1–N2a
Zn1–N2b
Zn1–S1
Zn1–S2
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2.053(5)
2.050(6)
2.352(2)
2.363(2)
1.732(7)
1.728(7)
1.348(9)
1.349(12)
1.345(9)
1.348(11)
1.378(8)
1.358(9)
1.299(8)
1.306(10)
1.454(10)
1.456(10)
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G.F. de Sousa et al. / Polyhedron 19 (2000) 841–847
Table 3
Selected bond angles (8) for H22,6AcheximPH2O, [Bu2Sn(2,6Achexim)] and [Zn(2,6Achexim)]2
[Bu2Sn(2,6Achexim)] a
H22,6Achexim
C2–C7a–N2a
C6–C7b–N2b
N3a–N2a–C7a
N3b–N2b–C7b
N2a–N3a–C8a
N2b–N3b–C8b
N3a–C8A–N4a
N3b–C8b–N4b
N3a–C8a–S1
N3b–C8b–S2
N4a–C8a–S1
N4b–C8b–S2
a
[Zn(2,6Achexim)]2
N2a–Sn–S1
N2a–Sn–S2
N2a–Sn–N2b
N2a–Sn–N1
N2a–Sn–C31
N2a–Sn–C41
N2b–Sn–S1
N2b–Sn–S2
N2b–Sn–N1
N2b–Sn–C31
N2b–Sn–C41
N1–Sn–S1
N1–Sn–S2
N1–Sn–C31
N1–Sn–C41
S1–Sn–S2
S1–Sn–C31
S1–Sn–C41
C31–Sn–C41
Sn–S1–C8a
71.62(11)
154.5(7)
133.3(2)
66.88(10)
87.36(18)
89.31(15)
154.5(7)
71.62(11)
66.88(10)
87.36(18)
89.31(15)
138.19(4)
138.19(4)
90.7(4)
80.9(3)
83.34(7)
92.4(3)
93.91(16)
171.6(4)
98.6(2)
Sn–N2a–N3a
124.03(3)
Sn–N2a–C7a
123.0(2)
117.0(5)
113.6(5)
123.0(4)
117.1(5)
112.4(4)
126.6(5)
113.1(5)
121.5(6)
124.1(4)
115.1(5)
122.7(4)
123.4(5)
115.3(5)
115.1(5)
114.8(5)
114.4(5)
128.4(5)
117.3(5)
N2a–Zn1–S1
N2a–Zn1–S2
N2a–Zn1–N2b
83.6(2)
105.5(2)
159.2(2)
N2b–Zn1–S1
N2b–Zn1–S2
110.6(2)
82.9(2)
S1–Zn1–S2
114.6(1)
Zn1–S1–C8a
Zn1–S2–C8b
Zn1–N2a–N3a
Zn1–N2b–N3b
Zn1–N2a–C7a
Zn1–N2b–C7b
94.7(2)
94.8(3)
120.8(4)
121.7(5)
122.9(5)
122.9(5)
115.5(6)
116.0(6)
115.6(3)
115.3(6)
114.4(5)
114.7(6)
115.2(6)
114.9(6)
126.2(5)
125.7(6)
118.6(5)
119.4(6)
The two thiosemicarbazone moieties of [Bu2Sn(2,6Achexim)] are equivalent.
3. Results and discussion
3.1. Molecular structure of H22,6AcheximPH2O
The molecular structure of H22,6AcheximPH2O is shown
in Fig. 2. Much of H22,6AcheximPH2O is planar, except for
the hexamethyleneimine rings, which are tilted in opposite
directions from the plane of the molecule and make dihedral
angles of 8.2(1) and 8.0(1)8 with the pyridine ring (Fig. 3
is a stereoview of H22,6AcheximPH2O). H22,6AcheximP
H2O, like its tin(IV) complex [Bu2Sn(2,6Achexim)],
crystallizes in the orthorhombic system, in contrast to 2acetylpyridine 3-hexamethyleneiminylthiosemicarbazone,
HAchexim [12], which is monoclinic. However, both
ligands possess the bifurcated E9 structure with the N1 atom
of the pyridyl ring and the S1 atom of the moiety hydrogen
bonded intramolecularly to the N2a hydrogen (Fig. 1(d,e)).
Intermolecular hydrogen bonds between the H2O molecule
Thursday Apr 13 09:56 AM
and the N3b hydrogen and S2 atoms helps to cause differences in bond distances and angles between the two thiosemicarbazone moieties of H22,6AcheximPH2O (Tables 2
and 3).
Fig. 2. Perspective view of H22,6AcheximPH2O showing the atom numbering scheme.
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845
3.2. Molecular structure of [Bu2Sn(2,6Achexim)]
Fig. 3. Stereoview of the unit cell packing of H22,6AcheximPH2O.
˚ and is
The E arm has a S2–C8b distance of 1.689(7) A
intermediate between typical C–S single- and double-bond
lengths [5]. This agrees well with the N3b–C8b (1.359(7)
˚ and N4b–C8b (1.337(9) A)
˚ bond distances, which indiA)
cate partial double-bond character for both bonds. The N2b–
˚ is significantly shorter than a N–C
C7b bond, 1.313(7) A,
single bond, as expected for a thiosemicarbazone. The E9 arm
˚ is longer than S2–C8b of the
S1–C8a distance, 1.716(6) A,
˚
E arm, 1.689(7) A, which is consistent with its involvement
in the bifurcated hydrogen bonding resulting in a formal
single C–S bond, and similar to that found for HAchexim,
˚ [12]. Other bonds in the E9 thiosemicarbazone
1.70(1) A
moiety of H22,6AcheximPH2O and HAchexim are as fol˚ N2a–N3a,
lows: N2a–C7a, 1.291(6) and 1.29(1) A;
˚
1.347(6) and 1.37(1) A; N3a–C8a, 1.364(7) and 1.36(2)
˚ N4a–C8a, 1.346(7) and 1.36(1) A.
˚ The similarity in bond
A;
distances of the two E9 forms of the two compounds is also
true for their bond angles. In summary, the bonding in
H22,6AheximPH2O has considerable delocalization of the
electron density along both moieties, and although conventional bonding theory makes the two thiosemicarbazone moieties appear different, the bond distances between the two do
not differ greatly. Far greater differences occur in the bond
angles with the greatest differences being N2a–N3a–C8a,
112.4(4) and N2b–N3b–C8b, 126.6(5)8; N3a–C8a–S1,
124.1(4) and N3b–C8b–S2, 115.1(5)8; N3a–N2a–C7a,
123.0(4) and N3b–N2b and C7b, 117.1(5)8. This difference
in bond angles may be due to the requirements of the thiolato/
thione sulfur’s difference in hydrogen bonding interactions;
˚ and
the intramolecular H2a∆S1 has a distance of 2.38(6) A
the hydrogen bond involving the water molecule, H1a∆S2,
˚ (Fig. 2).
has a distance of 2.29(6) A
Thursday Apr 13 09:57 AM
The heptacoordinate neutral complex, [Bu2Sn(2,6Achexim)], has approximately pentagonal dipyramid stereochemistry, with the bis(thiosemicarbazone) ligand lying in
the equatorial plane as shown in Fig. 4. As a result of chelation
to the metal center, both five-membered rings and therefore
also their symmetry related counterparts, are almost planar
˚ and Sn–
Sn–S1–C8–N3–N2 (RMS plane deviation 0.093 A)
˚ respecN2–C7–C2–N1 (RMS plane deviation 0.0548 A),
tively. As a consequence, the sums of the respective internal
angles, 537.4 and 538.48, are in good agreement with the
ideal value of 5408. The observed angle of 8.0(6)8 between
these rings and the angle between the ring Sn–N2–C7–C2–
N1 and its symmetry related ring Sn–N29–C79–C29–N19 of
6.14(16) underline the planarity of the pentagonal ring S–
˚ from which the
N2–N1–N29–S9 (RMS deviation 0.0751 A)
tin(IV) ion is moved away by 0.008(3)8.
Owing to the geometric requirements of the thiosemicarbazonato moieties, the pentagon is not regular; the angle
subtended at tin(IV) by the two sulfur atoms is significantly
enlarged to 83.31(7)8 from that in an idealized pentagonal
bipyramid (728), while the other equatorial angles range
from 66.86(11) to 71.65(11)8. The axial butyl groups also
contribute to the observed distortion since they have a C–Sn–
C angle of 171.6(4)8. The bond distances Sn–S1 2.6921(17),
Sn–N2a 2.436(5), Sn–N1 2.417(6), Sn–C31 2.145(11),
˚ are in good agreement with the bond
and Sn–C41 2.171(8) A
distances Sn–S 2.593(1) and 2.603(1), Sn–N(imine)
2.427(4) and 2.421(4), Sn–N(py) 2.368(3), and Sn–C
˚ found in [Ph2Sn(2,62.178(4) and 2.179(4) A,
Ac4DH)]P2DMF (2,6Ac4DH is the dianion of 2,6-diacetylpyridine bis(thiosemicarbazone)), another heptacoordinated pentagonal dipyramidal diorganotin(IV) deriva-
Fig. 4. ORTEP plot with atom-labeling scheme of [Bu2Sn(2,6Achexim)],
displacement ellipsoids at the 30% probability level. Atoms labeled with a
and b are related by the symmetry operation x, yyq1/2, z.
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tive containing a quinquedentate thiosemicarbazone ligand
in the pentagonal girdle [6]. Coordination to the tin(IV)
center by the imine nitrogen and the thiolato sulfur lengthens
˚ as well as S1–C8a
N2a–C7a and N2b–C7b to 1.331(7) A,
˚ from an average of 1.302(7) and
and S2–C8b to 1.746(7) A,
˚ respectively, in H22,6AcheximPH2O. Therefore,
1.703(7) A,
as a result of their coordination, both bonds lose substantial
p-character. The bond angles of the entire thiosemicarbazone
moiety, which lose the amide hydrogen on coordination,
show substantial changes compared to the angles in
H22,6AcheximPH2O, and the changes are greater for
[Bu2Sn(2,6Achexim)] than for [Zn(2,6Achexim)]2, Table
3. The butyl group bonded to Sn by C31 shows considerable
disorder and contributes to the relatively high R value for
[Bu2Sn(2,6Achexim)].
3.3. Molecular structure of [Zn(2,6Achexim)]2
The bonding in [Zn(2,6Achexim)]2, Fig. 5, is best
described as distorted tetrahedral stereochemistry about the
two zinc centers, which are equivalent. As expected, the Zn–
˚ are longer than the Zn–
S bonds, 2.352(2) and 2.363(2) A,
˚ In the
N2a (and Zn–N2b) bonds, 2.053(5) and 2.050(6) A.
octahedral-tetrahedral binuclear zinc complex of 2,6-diacetylpyridine bis(thiosemicarbazone), H22,6Ac4DH, the
tetrahedral Zn center has Zn–S bond distances of 2.317(3)
˚ shorter than in [Zn(2,6Achexim)]2, and
and 2.327(4) A,
˚ [2]. The longer Zn–
both Zn–N bond distances of 2.07(1) A
S bond distances, which likely contribute to the shorter Zn–
N distances for [Zn(2,6Achexim)]2, probably result from
the bulkiness of the hexamethyleneiminyl rings.
The distortion from tetrahedral symmetry is substantial;
the largest bond angle is N(imine)–Zn–N(imine),
159.2(2)8, the S–Zn–S angle with the two largest donor
atoms is 114.6(1)8, and the smallest is a chelating S–Zn–
N(imine), 82.9(2)8. The smallness of the latter angle is due
to the requirements of the chelating thiosemicarbazonato
moiety. For the octahedral-tetrahedral binuclear complex
[Zn(2,6Ac4DH)]2, the angles around the tetrahedral zinc
center are as follows: N(imine)–Zn–N(imine), 140.8(4)8,
the S–Zn–S angle is 118.3(2)8 and the smallest is a chelating
S–Zn–N(imine), 83.8(4)8. The chelating S–Zn–N(imine)
angles are essentially the same, but the other two angles show
significant differences. Differences are not surprising since
in [Zn(2,6Ac4DH)]2 the two arms are from different
2,6Ac4DH ligands, as is the case for 2,6Achexim, but both
ligands in [Zn(2,6Ac4DH)]2 coordinate their pyridyl nitrogens to the octahedral zinc center while the pyridyl nitrogens
are uncoordinated in [Zn(2,6Achexim)]2.
3.4. IR spectra
The most significant difference which emerges from a
comparison of the vibrational spectra of H22,6AcheximPH2O
and its complexes is the disappearance of the band n(N–H)
at 3221 cmy1 as a consequence of the dianionic nature it
Thursday Apr 13 09:57 AM
Fig. 5. Perspective view of [Zn(2,6Achexim)]2 showing the atom numbering scheme.
assumes upon coordination. Assignment of n(C_N) is complicated by the differences in the thiosemicarbazone moieties
(i.e. the bifurcated E9 and the E arm, which is involved in
hydrogen bonding to the hydrate water molecule), as well as
the partial double bond character possessed by all of the C–
N bonds of the molecule. In the bifurcated E9 arm N3a–C8a
is formally a double bond and the bond distances C8a–N4a
and C8b–N4b suggest considerable double bond character.
The spectrum of H22,6AcheximPH2O has bands at 1574 and
1561 cmy1 that are likely due to n(C_N). When two bands
are present in the spectra of coordinated anionic thiosemicarbazones that are assignable to n(C_N), one is usually at
lower energy, e.g. C7_N2, and one at higher energy, e.g.
N3_C8, compared to n(C_N) of the uncoordinated neutral
thiosemicarbazone [12–15]. The spectrum of [Zn(2,6Achexim)]2 has bands at 1591 and 1564 cmy1 that we
suggest are due to n(C_N) for N3_C8 and C7_N2, respectively. Although the bands at ca. 1272, 1100 and 836 cmy1
in the spectrum of H22,6AcheximPH2O have a significant
contribution from n(C_S), only the first absorption is shifted
to lower frequency (1213 cmy1) in the spectrum of
[Bu2Sn(2,6Achexim)] and the third absorption to lower frequency (739 cmy1) in the spectrum of [Zn(2,6Achexim)]2.
3.5. NMR spectra
The 1H NMR spectrum (CDCl3) of H22,6AcheximPH2O
shows the two different thiosemicarbazone arms with the E9
arm having NH3a at 15.18 ppm and NH3b for the E arm at
8.52 ppm. Its 13C NMR spectrum shows two peaks for thione
carbons, C8a and C8b, at 184.3 and 180.9 ppm, and for imine
carbons, C7a and C7b, 147.6 and 147.4 ppm, but we are not
able to assign these to a specific carbon atom with certainty.
The 1H NMR spectrum (CDCl3) of [Bu2Sn(2,6Achexim)]
shows no peaks assignable to N3aH (or N3bH), but shows
a triplet at 8.17 and a doublet at 7.85 ppm for pyridyl protons,
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G.F. de Sousa et al. / Polyhedron 19 (2000) 841–847
two singlets for N_C–CH3 protons at 2.83 and 2.57 ppm,
two doublets at 3.86, 1.54 ppm and a singlet at 1.79 ppm for
the magnetically non-equivalent hexamethyleneiminyl protons. The Sn–CH2–CH2–CH2– protons appear as a complicated multiplet centered at about 0.99 ppm, while the n-bu–
CH3 protons appear as a triplet at 0.60 ppm. In CDCl3
[Zn(2,6Achexim)]2 shows a triplet centered at 7.93 ppm
and a doublet at 7.30 ppm for the pyridyl protons, a singlet
at 2.53 ppm for N_C–CH3, and a multiplet centered at 3.69
ppm and broads singlets at 1.85 and 1.59 ppm for the hexametheneiminyl protons.
3.6. Biological activity
Although other bis(thiosemicarbazones) derived from 2acetylpyridine have shown antitumor activity when tested by
the National Cancer Institute, H22,6AcheximPH2O showed
insufficient activity against 60 tumor lines and showed no
activity in the HIV test. In antifungal tests H22,6AcheximPH2O shows no activity against Aspergillus niger
and modest activity at a concentration of 103 mg mly1 against
Paecilomyces variotii.
Supplementary data
Crystallographic data (excluding structure factors), a
complete listing of the atomic positions, bond distances, bond
angles and anisotropic thermal parameters, for the structures
reported in this paper have been deposited with the Cambridge Crystallographic Data Center as supplementary publication CCDC 118877. Copies of available material can be
obtained, free of charge, on application to the Director,
CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (fax:
q44-1223-336033; e-mail: deposit@ccdc.cam.ac.uk).
Thursday Apr 13 09:57 AM
847
Acknowledgements
The authors thank the CNPq, CAPES/PROBRAL for
financial support, and Professor Ademir Neves and Professor
´
Ivo Vencato (UFSC, Florianopolis,
Brazil) and Professor
¨
¨
Joachim Strahle
(University of Tubingen,
Germany) for the
diffractometer facilities.
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