Coordination chemistry of sulfamethizole: Crystal structures of [Cu(sulfamethizolate)2(py)2(OH2)]·H2O, [M(sulfamethizolate)2(py)2(OH2)2] [M = Co and Ni] and {Cu(sulfamethizolate)2(dmf)2}(∞)

Article abstract of DOI:10.1016/S0277-5387(00)00474-5

The synthesis and characterisation of copper, cobalt, nickel and zinc compounds with sulfamethizole (4-amino-N-(5-methyl-1,3,4-thiadiazole-2-yl)sulfanilamide) (Hsmtz) are described. The first crystal structures of ternary sulfamethizole complexes are reported. The crystal structures of Cu(smtz)₂(py)₂(OH₂)·H₂O (1), M(smtz)₂(py)₂(OH₂)₂ [M=Co (2), Ni (3)] and {Cu(smtz)₂(dmf)₂}(∞) (5) were determined by X-ray diffraction. The Cu(II) ion exhibits a square pyramidal geometry in complex 1, while in the other compounds the metal ion presents a distorted octahedral environment. In compounds 1, 2 and 3 the deprotonated sulfamethizole acts as monodentate ligand coordinating through the thiadiazole N atom and in compound 5 it behaves as a bridge linking two metal cations via the thiadiazole and the amino nitrogen atoms. The IR, electronic, EPR and thermal data are consistent with the crystal structures. (C) 2000 Elsevier Science Ltd.

Full text of DOI:10.1016/S0277-5387(00)00474-5

www.elsevier.nl/locate/poly
Polyhedron 19 (2000) 1859–1866
Coordination chemistry of sulfamethizole: crystal structures of
[Cu(sulfamethizolate)2(py)2(OH2)]·H2O,
[M(sulfamethizolate)2(py)2(OH2)2] [M=Co and Ni] and
{Cu(sulfamethizolate)2(dmf)2}ꢀ
b
Elisa Borra´s a, Gloria Alzuet b, Joaqu´ın Borra´s b,*, Juan Server-Carrio´ ,
Alfonso Castin˜eiras c, Malva Liu-Gonza´lez d, Francisco Sanz-Ruiz d
a Departamento de Bioqu´ımica y Biologia Molecular, Facultad de Medicina y Odontolog´ıa, Uni6ersidad de Valencia, A6da. Vicente Blasco Iba´n˜ez,
17, E-46010 Valencia, Spain
b Departamento de Qu´ımica Inorga´nica, Facultad de Farmacia, Uni6ersidad de Valencia, A6da. Vicent Andre´s Estelle´s s/n,
E-46100 Burjassot, Spain
c Departamento de Qu´ımica Inorga´nica, Facultad de Farmacia, Uni6ersidad de Santiago de Compostela, E-15703 Santiago de Compostela, Spain
d Departamento de Termolog´ıa, Facultad de Fisicas, Uni6ersidad de Valencia, Dr Moliner, 50, 46100 Burjassot, Spain
Received 2 March 2000; accepted 16 June 2000
Abstract
The synthesis and characterisation of copper, cobalt, nickel and zinc compounds with sulfamethizole (4-amino-N-(5-methyl-
1,3,4-thiadiazole-2-yl)sulfanilamide) (Hsmtz) are described. The first crystal structures of ternary sulfamethizole complexes are
reported. The crystal structures of Cu(smtz)2(py)2(OH2)·H2O (1), M(smtz)2(py)2(OH2)2 [M=Co (2), Ni (3)] and
{Cu(smtz)2(dmf)2}ꢀ (5) were determined by X-ray diffraction. The Cu(II) ion exhibits a square pyramidal geometry in complex
1, while in the other compounds the metal ion presents a distorted octahedral environment. In compounds 1, 2 and 3 the
deprotonated sulfamethizole acts as monodentate ligand coordinating through the thiadiazole N atom and in compound 5 it
behaves as a bridge linking two metal cations via the thiadiazole and the amino nitrogen atoms. The IR, electronic, EPR and
thermal data are consistent with the crystal structures. © 2000 Elsevier Science Ltd. All rights reserved.
Keywords: Sulfamethizole; Metal complexes; Crystal structures; Spectroscopic properties
taining contrast medium for assessment of gastric emp-
tying in functional dyspepsia patients [2].
1. Introduction
The Hsmtz has several groups with donor atoms that
are able to interact with metal ions. Metal complexes of
Among the N-substituted sulfanilamides, sulfamethi-
zole
(4-amino-N-(5-methyl-1,3,4-thiadiazole-2-yl)sul-
Hsmtz have been reported [3], but until now no crystal
structure of binary or ternary sulfamethizole metal
complexes had been determined. Previously, we have
undertaken an investigation on the coordination prop-
erties of the sulfathiazole [4-amino-N-2-thiazolylben-
zenosulfonamide, Hstz], a sulfonamide closely related
fanilamide) (Hsmtz) (Scheme 1) is one of the most used
antibacterial drugs. It is expended as ‘thiosulfil’. Sulfa-
methizole is extensively used in the treatment of the
urinary tract infections [1]. The mechanism of action is
based on the competitive antagonism of PABA (p-
aminobenzoic acid) and the sulfanilamide derivative.
Recently, sulfamethizole has been used as capsules con-
* Corresponding author. Tel.: +34-6-386-4530; fax: +34-6-386-
4960.
Scheme 1. 4-amino-N-(5-methyl-1,3,4-thiadiazole-2-yl)sulfanilamide
E-mail address: joaquin.borras@uv.es (J. Borra´s).
(sulfamethizole).
0277-5387/00/$ - see front matter © 2000 Elsevier Science Ltd. All rights reserved.
PII: S0277-5387(00)00474-5

1860
E. Borra´s et al. / Polyhedron 19 (2000) 1859–1866
2.2.2. M(smtz)2(py)2(OH2)2 [M=Co (2), Ni (3), Zn
(4)]
to sulfamethizole. We have found that it presents differ-
ent coordination behaviour as a ligand, acting as: (i)
monodentate through the amino group [4,5]; (ii)
monodentate via the thiazole N atom [6]; (iii) bidentate
bridging two metal ions through the Namino and the
Nthiazole [7]; (iv) bidentate through the Nthiazole and the
Nsulfonamido [8]; (v) bidentate to one Cu(II) through the
Nthiazole and the Nsulfonamido and bridging to an adjacent
Cu(II) through the Namino [9].
The different coordination abilities of the sulfathia-
zole have led us to study the chelating properties of the
sulfamethizole in order to compare the behaviour of
both sulfanilamides. In this work we synthesise and
characterise Cu, Co, Ni and Zn complexes of sulfame-
thizole and report the first crystal structures of sulfame-
thizolate complexes.
The compounds were obtained by a procedure simi-
lar to that described for the copper complex but using
CoCl2·6H2O, NiCl2·6H2O and ZnCl2·2H2O instead of
CuSO4·5H2O. The resulting solutions were orange, blue
and white, respectively. They were left to stand at r.t.
and after few days single crystals suitable for X-ray
diffraction were obtained for the Co and Ni complexes,
while a white solid was obtained for the Zn complex.
Anal. Calc. for C28H32CoN10O6S4: C, 42.5; H, 4.0;
N, 17.7. Found: C, 42.8; H, 4.0; N, 17.6%. Anal.
Calc. for C28H32N10O6S4: C, 43.2; H, 3.8; N, 18.0.
Found: C, 42.4; H, 4.0; N, 17.7%. Anal. Calc. for
C28H32ZnN10O6S4 C, 42.1; H, 4.0; N, 17.5. Found: C
42.6; H 3.9; N 17.8%.
2.2.3. {Cu(smtz)2(dmf)2}ꢀ (5)
Sulfamethizole (3 mmol) was added to 1 mmol of
copper acetate in 30 ml of dimethylformamide. The
resulting solution was left to stand at r.t. and after few
days prismatic green crystals were obtained. Anal. Calc.
for C24H32CuN10O6S4: C, 38.5; H, 4.3; N, 18.7. Found:
C, 38.9; H, 4.1; N, 18.9%.
2. Experimental
2.1. Physical measurements
All reagents were of the highest grade commercially
available and used without further purification. Ele-
mental analyses (C, H, N) were done at the microana-
lytical laboratory of the University of Salamanca. IR
spectra were recorded on a Mattson Satellite FTIR
spectrometer. Samples were prepared using the KBr
technique. Electronic spectra were registered on a Shid-
mazu UV 2101PC spectrophotometer using the diffuse
reflectance technique. EPR spectra were carried out
with a Brucker ER 200 D spectrometer. Magnetic
susceptibility measurements at r.t. were taken with a
fully automatized AZTEC DSM8 pendulum-type sus-
ceptometer. Mercury tetrakis(thyocianato)cobaltate(II)
was used as a susceptibility standard. Data were cor-
rected for diamagnetic contribution, which were esti-
mated from Pascal’s constants. Thermogravimetric
analyses were made in air atmosphere using a Shi-
madzu TGA-50H.
2.3. Crystallographic data and structure determination
2.3.1. Cu(smtz)2(py)2(OH2)·H2O (1) and
Ni(smtz)2(py)2(OH2)2 (3)
Diffraction measurements of the selected blue (Cu)
and pale green (Ni) prismatic crystals, with approxi-
mate sizes 0.10×0.20×0.25 mm (Cu) and 0.15×
0.25×0.25 mm (Ni), were carried out at 290 K using
an Enraf–Nonius CAD-4 single-crystal diffractometer
with graphite monochromated Mo Ka radiation (u=
,
0.7107 A). The unit cell dimensions were determined
from the angular settings of 25 reflections with 9BqB
13° (Cu) and 8BqB14° (Ni). The intensity data of
6965 (Cu) and 3281 (Ni) reflections were measured in
the limits 1BqB25° using ꢀ–2q scan technique, vari-
able speed, width (0.80+0.35tan q)° in ꢀ and maxi-
mum scan time of 60 s per reflection in the hkl ranges
0–18, 0–13, −23–23 (Cu) and 0–9, −12–12, −12–
12 (Ni). Three reflections were measured every hour as
intensity controls without significant decay. Some dou-
ble measured reflections were averaged, Rint=0.025
(Cu) and 0.007 (Ni), resulting in 6079 (Cu) and 2957
(Ni) independent reflections of which 3673 (Cu) and
2441 (Ni) were considered, observed with the [I\2|(I)]
criterion. Absorption correction was not applied. The
structure was solved by direct methods using the pro-
gram SIR92 [10]. All non-hydrogen atoms were an-
isotropically refined by least-squares on Fobs using the
X-RAY76 System [11]. The hydrogen atoms, kept fixed
in the refinement with a common isotropic thermal
parameter, were located by difference synthesis. In the
2.2. Synthesis of the complexes
2.2.1. Cu(smtz)2(py)2(OH2)·H2O (1)
A 50 ml sample of a 1:1 aqueous pyridine solution
containing 5 mmol of Hsmtz was added to an equal
volume of an aqueous solution of CuSO4·5H2O (10
mmol) containing 25% per volume of pyridine, slowly
and with continuous stirring. Immediately, the mixture
took on an intense blue colour. After 3 days prismatic
blue crystals were obtained. They were filtered, washed
and dried at vacuum. Anal. Calc. for C28H30N10O5S4:
C, 43.2; H, 3.8; N, 18.0; Cu, 8.2. Found: C, 42.4; H,
4.0; N, 17.7; Cu, 8.1%.

E. Borra´s et al. / Polyhedron 19 (2000) 1859–1866
1861
Table 1
graphics from PLATON-98 [21]. A summary of the crys-
tal data, experimental details and refinement results are
listed in Table 1.
Crystal data and structure refinement for Cu(smtz)2(py)2(OH2)·
H2O (1), M(smtz)2(py)2(OH2)2 (M=Co (2), Ni(3)) and
{Cu(smtz)2(dmf)2}ꢀ (5)
1
2
3
5
2.3.3. {Cu(smtz)2(dmf)2}ꢀ (5)
A green crystal, size 0.2×0.2×0.2 mm was mounted
on an Enraf–Nonius CAD-4 single-crystal diffractome-
ter with graphite monochromated Mo Ka radiation
Formula
C28H32Cu- C28H32Co- C28H32N10
-
C24H32N10
O6S4Cu
monoclinic
P21/c
-
N10O6S4
monoclinic triclinic
N10O6S4
NiO6S4
triclinic
Symmetry
Space
group
,
(u=0.7173 A). The unit cell dimensions were deter-
(
(
P21/a
P1
P1
mined from the angular settings of 25 reflections with
3.57BqB25.98°. The space group was determined to
be P21/c from systematic absences. The intensity data
of 3025 reflections, in the hkl range (0, 0, −14) to (11,
18, 13) and limits (0BqB25°) were measured using the
ꢀ–2q scan technique and variable scan rate with a
maximum scan time of 60 s per reflection. The intensity
of the primary beam was checked throughout the data
collection by monitoring three standard reflections ev-
ery 60 min. On all reflections profile analysis was
performed [22]. Lorentz-polarization corrections were
applied and then the data were reduced to Fo2 values.
The structure was solved by Patterson methods using
DIRDIF [23]. Isotropic least squares refinement on F2
was made using SHELX-93[24]. During the final stages
of the refinement on F2 the positional parameters and
the anisotropic thermal parameters of the non-H atoms
were refined. All non-hydrogen atoms were anisotropi-
cally refined. All hydrogen atoms were geometrically
placed and isotropically refined. The final conventional
agreement factors were R=0.044 and wR2=0.147 for
3016 observed reflections and 236 variables. The func-
,
a (A)
15.668(3)
11.279(1)
19.559(2)
90.0
90.75(1)
90.0
3456.2(8)
4
1.53
8.4013(14)
10.5612(17) 10.520(1)
10.7828(12) 10.831(1)
75.099(13)
76.034(12)
68.555(12)
848.9(2)
1
8.3700(4)
9.408
14.737
11.882
90.0
111.27
90.0
1535.2
2
1.619
,
b (A)
,
c (A)
h (°)
i (°)
k (°)
75.16(1)
76.01(1)
68.48(1)
846.0(1)
1
3
,
V (A )
Z
Dcalc
1.549
1.55
(g cm−3
)
M
796.4
1644
9.31
791.81
409
8.09
791.6
410
8.78
1.24
748.36
774
10.29
1.0152
F(000)
v (cm−1
)
Goodness- 0.85
of-fit
1.044
R
Rw
0.053
0.058
0.0330
0.0779
0.046
0.051
0.0440
0.1470
final stages an empirical weighting scheme was chosen
as to give no trends in ŽwZ2F versus ŽFo and versus
Žsen q/u using the program PESOS [12]. Geometrical
calculations were made with PARST [13]. Atomic scat-
tering factors and anomalous dispersion corrections
were taken from reference [14]. All calculations were
performed on a VAX6410. Graphical manipulations
were produced by the ORTEP-3 for Windows program
[15]. Other relevant parameters of the crystal structure
determination are listed in Table 1.
tion minimised was Sw(Fo2−Fc2)/SwFo2]1/2
, w=1/
[|2(Fo2+0.0828P)2] with |Fo2 from counting statistic
and P=(max(Fo2)+2Fc2)/3. The final difference
3
,
Fourier map showed a peak of 0.54 A very close to the
3
,
C11%, the others peak no deeper than −0.39 A .
Atomic scattering factors were taken from Interna-
tional Tables for X-ray Crystallography [14]. Geometri-
cal calculations were made with PARST [13]. Graphical
manipulations were performed with EUCLID [25]. All
calculations were made at the University of Valencia on
the S.C.S.I.E. X-ray section VAX-computers. Other
relevant parameters are collected in Table 1.
2.3.2. Co(smtz)2(py)2(OH2)2 (2)
A rose-coloured prismatic crystal of Co(smtz)2(py)2-
(H2O)2 was mounted on a glass fibre and used for data
collection. Cell constants and an orientation matrix for
data collection were obtained by least-squares refine-
ment of the diffraction data from 25 reflections in the
range of 11.00BqB18.12° in an Enraf–Nonius
MACH3 automatic diffractometer [16]. Data were col-
,
lected at 293 K using Mo Ka radiation (u=0.71073 A)
3. Results and discussion
and the ꢀ-scan technique, and corrected for Lorentz
and polarisation effects [17]. A semi-empirical absorp-
tion correction („-scans) was made [18]. The structure
was solved by direct methods [19] and subsequent dif-
ference Fourier maps, and refined on F2 by a full-
matrix least-squares procedure using anisotropic dis-
placement parameters [20]. All hydrogen atoms were
located from difference Fourier maps and were refined
isotropically. Atomic scattering factors from Interna-
tional Tables for X-ray Crystallography [14]. Molecular
3.1. Crystal structures of Cu(smtz)2(py)2(OH2)·H2O
(1), Co(smtz)2(py)2(OH2)2·(2) and Ni(smtz)2(py)2(OH2)2
(3)
Selected bond distances and angles of the three crys-
tal structures are shown in Table 2. Figs. 1–3 show
ORTEP drawings of compounds 1, 2 and 3, respectively.
In compound 1 the copper atom is five co-ordinated
with a geometry near to a regular square pyramidal.

1862
E. Borra´s et al. / Polyhedron 19 (2000) 1859–1866
Table 2
,
Selected bond distances (A) and angles (°) for compounds Cu(smtz)2(py)2(OH2)·H2O (1) and M(smtz)2(py)2(OH2)2 (M=Co (2), Ni (3))
1
2
3
CuꢀO(3)
2.183(4)
2.002(4)
2.001(5)
2.045(5)
2.046(5)
CoꢀO(3)
CoꢀN(1)
CoꢀN(11)
2.0457(18)
2.2110(18)
2.157(2)
NiꢀO(3)
NiꢀN(1)
NiꢀN(11)
2.040(2)
2.163(2)
2.100(3)
CuꢀN(11)
CuꢀN(12)
CuꢀN(111)
CuꢀN(112)
O(3)ꢀCuꢀN(11)
O(3)ꢀCuꢀN(111)
O(3)ꢀCuꢀN(12)
O(3)ꢀCuꢀN(112)
N(11)ꢀCuꢀN(111)
N(11)ꢀCuꢀN(12)
N(11)ꢀCuꢀN(112)
N(111)ꢀCuꢀN(12)
N(111)ꢀCuꢀN(112)
N(12)ꢀCuꢀN(112)
95.7(2)
97.9(2)
97.8(2)
91.4(2)
88.4(2)
166.5(2)
90.6(2)
88.4(2)
170.7(2)
90.4(2)
O(3)1ꢀCoꢀN(1)
O(3)ꢀCoꢀN(11)
N(1)ꢀCoꢀN(11)
90.61(7)
90.44(8)
90.25(7)
O(3)ꢀNiꢀN(1)
O(3)ꢀNiꢀN(11)
N(1)ꢀNiꢀN(11)
90.7(1)
90.7(1)
89.6(1)
The equatorial plane is defined by two thiadiazole N
atoms from two sulfamethizolate ligands in trans posi-
tion and by two pyridine N atoms. The axial site is
occupied by a water O atom at longer distance, 2.183(4)
with those of the compound 1. The equatorial CuꢀN
lengths are significantly shorter than the CoꢀN and the
NiꢀN ones. In particular, the MꢀNthiadiazole is the short-
,
,
A. The CuꢀNthiadiazole bond length 2.002(4) A, is signifi-
cantly shorter than the CuꢀNthiadiazole of the related
[Cu(Hacm)2(tn)2] compound (H2acm=acetazolamide,
,
tn=propylenediamine) [26]. The CuꢀNpy, 2.045(5) A
ones are comparable to those found in other pyridine
compounds [6]. The cis angles in the equatorial plane
ranging from 90.6(2) to 88.4(2)° do not deviate signifi-
cantly from 90°. The ~ value of 0.07 [~=(h−i/60)]
indicates a small distortion from a regular square pyra-
midal geometry [27].
The Co(II) ion in compound 2 and the Ni(II) ion in
compound 3 are six co-ordinated by two pyridine N
atoms and two thiadiazole N pertaining to two sulfa-
methizolate ligands in the equatorial sites and two
water O atoms are in the apical positions. In both
complexes the MꢀNthiadiazole and the MꢀNpy are
markedly longer than the MꢀOw distance. So, the ge-
ometry of the complexes can be described as com-
pressed distorted octahedral. As expected from the
ionic radii of the divalent metal ions the CoꢀNthiadiazole
,
,
,
2.2110(18) A and the CoꢀNpy, 2.157(2) A are longer
,
than the NiꢀNthiadiazole, 2.163(2) A and the NiꢀNpy,
,
2.100(3) A. However, the corresponding MꢀOw are
,
practically the same [CoꢀOw, 2.0457(18) A and NiꢀOw,
,
2.040(2) A]. The NiꢀNthiadiazole bond is slightly longer
than the same distance in the [Ni(Hacm)2(NH3)4] com-
plex [28]. The MꢀNpy are similar to those of the
M(macm)2(py)2(OH2)2 (M=Co, Ni; macm=methazo-
lamidate) [29]. Angles around the metal do not differ
significantly from those of a regular octahedron.
Several interesting aspects can be deduced from a
comparison of bond distances of the 2 and 3 complexes
Fig. 1. ORTEP drawing of Cu(smtz)2(py)2(OH2)·H2O (1).

E. Borra´s et al. / Polyhedron 19 (2000) 1859–1866
1863
atom closest to the deprotonated sulfonamido group
although it presents several donor atoms and therefore
it offers different coordination possibilities. The same
coordination behaviour has been exhibited by the re-
lated acetazolamide in the octahedral [Cu(Hacm)2(tn)2]
and [Ni(Hacm)2(NH3)4] complexes [26,28] and by the
sulfathiazole in the [Cu(stz)(py)3Cl] and [Cu(stz)2-
(mim)2]·H2O compounds [6,9].
3.2. Crystal structure of {Cu(smtz)2(dmf)2}ꢀ (5)
A drawing of the complex is presented in Fig. 4.
Selected bond and angles of the coordination polyhe-
dron are listed in Table 3.
The structure is a coordination polymer in which
each Cu(II) ion presents an octahedral geometry. The
equatorial plane is defined by two Nthiadiazole atoms
trans one another and two Namino atoms from four
sulfamethizolate ligands. Two O atoms of two disor-
dered dimethylformamide molecules are placed in the
Fig. 2. ORTEP drawing of Co(smtz)2(py)2(OH2)2 (2).
,
apical positions at the distance of 2.391(4) A. Each
cupric ion is connected with the other Cu ions by four
sulfamethizolate anions acting as bridges via the
Nthiadiazole and Namino atoms.
The four in-plane CuꢀN bond distances
,
[CuꢀNthiadiazole, 2.083(4); CuꢀNamino, 2.056(4) A] are
similar. The CuꢀNthiadiazole is longer than this distance
in compound 1. Regarding to the CuꢀNamino length it is
in the range found for the corresponding distances in
Cu complexes of the sulfathiazole ligand [from 2.020 to
,
2.071 A] [4]. The CuꢀOdmf bond lengths can be re-
garded as normal [30].
The largest deviation from a regular octahedral ge-
ometry is found in the axial angles involving the amino
N atoms [94.8(2) and 85.2(2)°].
The sulfamethizolate anion behaves as a bridging
ligand through the Nthiadiazole and Namino atoms. This
coordination behaviour is different to that exhibit by
the ligand in the complexes described above, although
is similar to that observed for the sulfathiazole in the
[Zn(stz)2]·H2O complex [7].
A comparison of the four crystal structures described
in this paper shows that no remarks can be noted as far
as the sulfamethizole bond distances are concerned.
From a different coordination behaviour of the sulfa-
methizole in compound 5 with respect to complexes 1,
2 and 3, only a slight difference can be observed in the
N(4)ꢀC(7) bond lengths [1.424(6) compound 5, 1.382(9)
,
compound 1, 1.398(3) complex 2 and 1.402(5) A com-
plex 3]. Moreover, the different strength binding of the
Nthiadiazole does not modify significantly the NꢀN dis-
tance [1.390(5) compound 5, 1.376(9) compound 1,
Fig. 3. ORTEP drawing of Ni(smtz)2(py)2(OH2)2 (3).
,
est bond distance in the copper complex, whereas it is
the longest one in the nickel and cobalt compounds.
It must be noted that the sulfamethizole ligand acts
as monodentate coordinating through the thiadiazole N
1.387(3) complex 2 and 1.386(3) A complex 3]. This fact
could be related to the charge delocalization through
the thiadiazole ring as a consequence of the deprotona-
tion of the sulfonamide group.

1864
E. Borra´s et al. / Polyhedron 19 (2000) 1859–1866
Fig. 4. ORTEP drawing of {Cu(smtz)2(dmf)2}ꢀ (5).
The SO2 group modes of the ligand appear as strong
3.3. IR spectra
bands at 1325 (was) and 1128 cm−1 (ws). In the com-
plexes, the asymmetric mode is shifted to 1290–1260
cm−1 and the symmetric vibration gives rise a band
practically unchanged with respect to that of the ligand.
A comparative study of the IR spectra of the com-
plexes with that of the free ligand and those of the
complexes of related ligands gives some positive infor-
mation regarding the binding sites of the sulfamethi-
zole. All the complexes show very similar spectral
pattern. The strong bands at 3440, 3360 and 3250 cm−1
in the IR of the ligand attributed to was(NH2), ws(NH2)
and w(NH) of the amino group appear at the same
range in the IR spectra of complexes 1, 2, 3 and 4.
However, these bands are modified in the IR spectrum
of the compound 5 as a consequence of the interaction
of the amino group with the copper(II) ion.
With respect to the 1,3,4-thiadiazole ring modes,
because of the rigidity of the penta-atomic ring, the
vibrational spectra can not be interpreted in terms of
localised vibrations, being many atoms involved in
several vibration modes. The strong band at 1550 cm−1
in the ligand is shifted to 1450–1440 cm−1 in the
complexes. On the one hand this is due to deprotona-
tion of the sulfonamido group that gives rise to a
delocalization of the negative charge between the
Nsulfonamidate and the thiadiazole ring and on the other
hand, to the interaction of the Nthiadiazole with the metal
ions.
Table 3
,
Selected bond distances (A) and angles (°) for {Cu(smtz)2(dmf)2}ꢀ
(5) a
CuꢀO(3)c1
Cu(1)ꢀO(3)c2
CuꢀN(1)
Cu(1)ꢀN(1)c3
CuꢀN(4)c1
Cu(1)ꢀN(4)c2
2.391(4)
2.391(4)
2.083(4)
2.083(4)
2.056(4)
2.056(4)
O(3)c1ꢀCuꢀO(3)c2
180.0
N(4)c1ꢀCuꢀN(1)
88.4(2)
91.6(2)
180.0
94.8(2)
85.2(2)
89.2(2)
90.8(2)
180.0
N(4)c2ꢀCuꢀN(1)
N(4)c1ꢀCuꢀN(4)c2
N(4)c1ꢀCuꢀO(3)c1
N(4)c2ꢀCuꢀO(3)c1
N(1)ꢀCuꢀO(3)c1
N(1)c1ꢀCuꢀO(3)c1
N(1)ꢀCuꢀN(1)c3
a Symmetry transformations used to generate equivalent atoms
c1: −x+2, y−1/2, −z+5/2; c2: x, −y+1/2, z−1/2; c3 −x+2,
−y, −z+2; c4: −x+2, y+1/2, −z+5/2.

E. Borra´s et al. / Polyhedron 19 (2000) 1859–1866
1865
In spite of the coordination of one of the Nthiadiazole
to metal ions, the complexes present the same NꢀN
bond distances so, the band located at 990 cm−1 as-
signed to a w(NꢀN) mode does not change in the IR
spectra of the complexes.
ters extracted from the experimental spectrum by simu-
lation [33], gꢀꢀ= 2.26, gÞ=2.07 and Aꢀꢀ=140×104
cm−1 are in good agreement with a square pyramidal
geometry. The compound 5 shows a rhombic polycrys-
talline powder EPR spectrum with g3=2.20; g2=2.13
and g1=2.08 values, according to the copper coordina-
tion polyhedron.
A shift of the w(SꢀN) band is observed in the IR
spectra of the complexes (940–930 cm−1) with respect
to that of the ligand (920 cm−1). This could be at-
tributed to deprotonation of the sulfonamido group
and consequently the shortening of the SꢀN bond
distance.
3.5. Thermal analyses of compounds 1–4
The thermal study of the compound 1 has a first step
at 120°C corresponding to the loss of two water
molecules (% experimental weight 4.78; calculated
weight 4.52). The second step, that take place at 180°C,
corresponds to a loss of the two pyridine molecules (%
experimental weight 17.94; calculated weight 19.86).
There is a third step at 350°C where the two aniline
groups of the sulfonamidate are lost (% experimental
weight 25.62, calculated 23.38) and a fourth step where
the pyrolytic decomposition takes place leaving a per-
centage residual weight of 12.85% that can be at-
tributed to a mixture of CuO and CuSO4.
A band at 3470 cm−1 in the IR spectra of the
compounds 1 and 4 is attributed to w(OꢀH) vibration.
The IR spectrum of the complex 5 shows a strong band
at 1650 cm−1 assigned to a w(CꢁO) vibration of the
dmf molecules. The pyridine ring breathing band in
compounds 1, 2, 3 and 4 is found at 1040 cm−1
,
according to the fact that the pyridine molecules are
coordinated [31].
3.4. Magnetic properties, electronic and EPR spectra
At room temperature the Cu(II) complexes have
magnetic moment (2.01 BM for 1 and 1.94 BM for 5)
somewhat higher than the spin-only value. Such diver-
gence is not uncommon in mononuclear Cu(II) com-
plexes due to mixing-in of some angular momentum
from the closely lying excited states via spin–orbit
coupling [32]. The cobalt complex presents a magnetic
moment (4.11 BM) slightly lower than the common
values of octahedral complexes. This fact could be
attributed to the distortion of the coordination polyhe-
dra that leads to a minor orbital contribution to the
magnetic moment. The magnetic moment value for the
Ni(II) compound (2.90 BM), indicative of a slight or-
bital contribution, is in the range found for octahedral
complexes.
The diffuse reflectance (DR) spectra of the
Cu(smtz)2(py)2(OH2)·H2O (1) and the {Cu(smtz)2-
(dmf)2}ꢀ (5) with a well-defined d–d maximum at 595
(compound 1) and 660 nm (compound 5) agree well
with the square pyramidal geometry and the octahedral
geometry deduced from their crystal structures. The
DR spectra of compounds 2 and 3 (with maxima at 490
and 600 nm, respectively) fit for an octahedral environ-
ment according to their crystal structures.
Intense absorption in the ultraviolet region (ca. 300
nm) is a feature common to all the complexes and it is
attributed to an intra-ligand transition.
The polycrystalline powder EPR spectrum at room
temperature of the compound 1 is axial in nature with
a poorly resolved parallel component. The EPR spec-
trum of the zinc copper-doped compound is also axial
anisotropy with a four-line hyperfine structure due to
the interaction of the unpaired electron with the nuclear
spin of the copper nucleus. The ground state parame-
The compound 2 is stable to 110–120°C. At this
temperature range the first step of the thermal decom-
position starts. This step corresponds to the loss of the
two pyridine ligands (% experimental weight 19.06,
calculated weight for two pyridines 19.98). Between
200–250°C a second step occurs where the weight loss
corresponds to a water molecules and aniline groups of
the sulfonamidate ligand (% experimental weight 34.25,
calculated weight 31.62). In a third step the pyrolytic
decomposition of the rest takes place, yielding a residue
that it is a mixture of cobalt sulphate and cobalt oxide.
The TG curve of the compound 3 presents a first step
(150°C) where the loss of the pyridine and water
molecules takes place at the same time (% experimental
weight 23.07. calculated weight 24.54). The second
(250–500°C) and third (500–600°C) steps agree with
the pyrolytic decomposition of the compound. As in the
other processes the residue is a mixture of nickel sul-
phate and nickel oxide.
The TG curve of the compound 4 shows two sepa-
rate thermal events. Until 150°C the compound does
not present any loss of weight. Between 150–400°C a
first step takes place with a weight loss of 52.68% that
can be attributed to a loss of two pyridine, two water
molecules and two aniline groups. The second step
corresponds to the pyrolytic decomposition of the com-
pound. The residue is composed of a mixture of zinc
sulphate and zinc oxide.
From a comparison of the first step of the thermal
process we can observe a different stability of the water
molecules between the compound 1 and the rest of the
complexes. The lower temperature of water loss in the
compound 1 can be related with the larger CuꢀOH2
bond length observed in this compound with respect to

1866
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4. Supplementary data
Supplementary crystallographic data have been de-
posited with the Cambridge Crystallographic Data
Centre, CCDC Nos. 140608, 140609, 140610 and
140611. Copies of this information may be obtained
free of charge from The Director, CCDC, 12 Union
Road, Cambridge, CB2 1EZ, UK (fax: +44-1223-336-
033; e-mail: deposit@ccdc.cam.ac.uk or www: http://
www.ccdc.cam.ac.uk).
Acknowledgements
G.A. and J.B. would like to thank the Spanish
CICYT (PM97-0105-C02-01) for financial support.
A.C. thanks the Xunta de Galicia (Project
XUGA20309B97) for financial support. The authors
thank Professor J. Niclo´s-Gutierrez (University of
Granada) for the thermal studies.
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