Synthesis, molecular characterization by infrared spectroscopy, and crystal structure determination by X-ray powder diffractometry of [ZnCl 2(TdTz)] [TdTz = 2-(3,4-dichlorophenyl)imino-N-(2-thiazin-2-yl) thiazolidine]

Article abstract of DOI:10.1016/j.poly.2005.06.003

The title zinc(II) complex, dichloro[2-(3,4-dichlorophenyl)imino-κN- N-(2-thiazin-κN-2-yl)thiazolidine]zinc(II), was synthesized in the form of small crystals unsuitable for structure determination by X-ray single-crystal diffractometry. It was therefore characterized firstly in the solid state by elemental analysis and infrared spectroscopy, and then its crystal structure was determined by X-ray powder diffractometry. The procedure followed to resolve the crystal structure used direct-space methods with a 'Monte Carlo/parallel tempering' search algorithm, where the starting configuration was obtained by means of infrared spectroscopy and molecular mechanics. A final refinement of the crystal structure was performed using the Rietveld method. It was found that the environment around the zinc(II) ion may be described as a distorted tetrahedral geometry, with the metallic atom coordinated to two chlorine atoms [Zn-Cl(1) = 2.158(5) A?; Zn-Cl(2) = 2.145(4) A?], one imino nitrogen [Zn-N(3) = 2.237(4) A?] and one thiazine nitrogen [Zn-N(1) = 2.273(5) A?]. In addition, we also report in this study the crystal structure of the 2-(3,4-dichlorophenyl)imino-N-(2-thiazin-2-yl)thiazolidine (TdTz) ligand determined by X-ray single-crystal diffractometry.

Full text of DOI:10.1016/j.poly.2005.06.003

Polyhedron 24 (2005) 1975–1982
www.elsevier.com/locate/poly
Synthesis, molecular characterization by infrared spectroscopy,
and crystal structure determination by X-ray powder
diffractometry of [ZnCl2(TdTz)]
[TdTz = 2-(3,4-dichlorophenyl)imino-N-(2-thiazin-2-yl)thiazolidine]
a
Fernando J. Barros-Garcıa , Alvaro Bernalte-Garcıa , Francisco L. Cumbrera ,
a
b
´
´
Ana M. Lozano-Vila , Francisco Luna-Giles , Juan J. Melendez-Martınez ,
´
a
a,
b
*
´
´
c
´
Angel L. Ortiz
a
Department of Inorganic Chemistry, University of Extremadura, 06071 Badajoz, Spain
b
Department of Physics, University of Extremadura, 06071 Badajoz, Spain
c
Department of Electronic and Electromechanical Engineering, University of Extremadura, 06071 Badajoz, Spain
Received 12 April 2005; accepted 2 June 2005
Available online 19 July 2005
Abstract
The title zinc(II) complex, dichloro[2-(3,4-dichlorophenyl)imino-jN-N-(2-thiazin-jN-2-yl)thiazolidine]zinc(II), was synthesized
in the form of small crystals unsuitable for structure determination by X-ray single-crystal diffractometry. It was therefore charac-
terized firstly in the solid state by elemental analysis and infrared spectroscopy, and then its crystal structure was determined by
X-ray powder diffractometry. The procedure followed to resolve the crystal structure used direct-space methods with a ÔMonte–
Carlo/parallel temperingÕ search algorithm, where the starting configuration was obtained by means of infrared spectroscopy and
molecular mechanics. A final refinement of the crystal structure was performed using the Rietveld method. It was found that the
environment around the zinc(II) ion may be described as a distorted tetrahedral geometry, with the metallic atom coordinated
˚
˚
˚
to two chlorine atoms [Zn–Cl(1) = 2.158(5) A; Zn–Cl(2) = 2.145(4) A], one imino nitrogen [Zn–N(3) = 2.237(4) A] and one thiazine
˚
nitrogen [Zn–N(1) = 2.273(5) A]. In addition, we also report in this study the crystal structure of the 2-(3,4-dichlorophenyl)imino-N-
(2-thiazin-2-yl)thiazolidine (TdTz) ligand determined by X-ray single-crystal diffractometry.
ꢀ 2005 Elsevier Ltd. All rights reserved.
Keywords: Crystal structures; X-ray powder diffractometry; Zinc(II) complexes; Thiazolidine; Thiazine
1. Introduction
the 1,3-thiazine derivatives, have been reported in the lit-
erature to be cholecystokinin antagonists [2], and anti-
malarial [3], anti-inflammatory [4,5], antiviral [6,7], or
antimycobacterial agents [8]. It has also been demon-
strated that this biological activity can be modified or
even improved with the coordination of metal ions or
atoms [9].
The heterocycles containing nitrogen or sulfur (or
both) are common features within the structures of
numerous natural products and pharmaceutical com-
pounds [1]. Owing to their chemical and biological inter-
est, syntheses of various of these heterocycles, such as
The 1,3-thiazine nucleus is the active core of cephalo-
sporins which are among the widely used b-lactam anti-
biotics, with physico-chemical properties very similar to
*
Corresponding author. Tel.: +34 924289397; fax: +34 924289395.
E-mail address: pacoluna@unex.es (F. Luna-Giles).
0277-5387/$ - see front matter ꢀ 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2005.06.003

´
F.J. Barros-Garcıa et al. / Polyhedron 24 (2005) 1975–1982
1976
those of the penicillin group. Cephalosporins interfere
with the synthesis of the bacterial cell wall and conse-
quently, act as bactericides [10]. With epidemic strains
of bacteria often being resistant to several antibiotics,
and the growing problem worldwide of Gram-negative
antimicrobial resistance, cephalosporins, rather than
penicillin, constitute the essential tool with which to face
this problem [11,12].
2. Experimental
2.1. Preparation of 2-(3,4-dichlorophenyl)imino-N-
(2-thiazin-2-yl)thiazolidine (TdTz)
The synthesis of the TdTz ligand was performed
according to the procedure reported elsewhere [19],
and was recrystallized from ethanol 96% (1.5 g; 53%).
Considerable attention has been paid recently to the
synthesis and characterization of siderophore analogues.
Siderophores are low-molecular-weight organic ligands
(0.5–1.5 kDa) with high affinity and specificity for iron.
Under iron-limiting conditions, siderophores are ex-
creted by cyanobacteria and heterotrophic bacteria
[13–15]. Due to their attributes, this type of compound
has been investigated for clinical use in the detoxifica-
tion of certain metals [16]. Among them, there have been
characterized siderophores containing thiazine rings,
such as the desferrithiocin analogue DL-2-(3-hydroxy-
pyridin-2-yl)-4H-5,6-dihydro-1,3-thiazine-4-carboxylic
acid [17]. Unfortunately, many of these substances can-
not be crystallized as single crystals of appropriate size
and quality for conventional single-crystal diffractome-
try. For such cases, therefore, the structure has to be
determined by powder diffractometry, which is very far
from being routine.
The method followed in this study to resolve the
crystal structure of the title compound can be catego-
rized as one of the so-called Ôdirect-space methodsÕ
[18]. Here, a structural model of the compound is first
elaborated and then optimized by molecular modelling
without reference to the experimental XRD pattern.
Subsequently, these molecules are placed arbitrarily
within the unit cell previously determined from the dif-
fraction data. The position of the molecules is then
modified by global optimization techniques (typically
Monte Carlo methods, genetic algorithms, or grid
search methods) with the objective of finding the best
agreement between the theoretical and experimental
XRD patterns (the comparison between both patterns
is quantified in terms of the R-factors). Finally, the
best model of the crystal structure is refined using the
Rietveld method.
2.2. Preparation of [ZnCl2(TdTz)]
The [ZnCl2(TdTz)] complex was isolated from an eth-
anol–water solution of ZnCl2 (39.4 mg, 0.3 mmol) that
was added to an ethanol–water solution of TdTz
(100 mg, 0.3 mmol). The resulting solution was allowed
to evaporate slowly at room temperature. After a few
days, colourless crystals were isolated from the solution
(83 mg, 60%). The crystals were first separated by filtra-
tion, then washed with cold ether and finally air-dried.
Anal. Calc. for C13H13Cl4ZnN3S2: C, 32.36; H, 2.71;
N, 8.71; S, 13.29. Found: C, 32.74; H, 2.85; N, 8.83;
S, 13.19%.
2.3. Instrumental procedures
Chemical analyses of carbon, hydrogen, nitrogen,
and sulfur were performed by microanalytical methods
using a Leco CHNS-932 microanalyser. IR spectra were
recorded on a Perkin–Elmer FT-IR 1720 spectropho-
tometer from KBr pellets for the 4000–370 cmꢀ1 range,
and on a Perkin–Elmer FT-IR 1700X spectrophotome-
ter from polyethylene pellets for the 500–150 cmꢀ1
range.
2.4. Crystal structure determinations
Crystals of the TdTz ligand with the appropriate size
and quality for X-ray single-crystal diffractometry were
isolated and used for the structural analysis. Unfortu-
nately, this was not possible for the [ZnCl2(TdTz)] com-
plex, and therefore its crystal structure was determined
by X-ray powder diffractometry. The crystals resulting
from the synthesis of the [ZnCl2(TdTz)] complex were
highly elongated needles (aspect ratio of about 20) with
lengths ranging from 100 to 800 lm (see Fig. 1). To
avoid texture effects in the XRD pattern, these crystals
were ground to a fine powder consisting of equiaxed
particles (aspect ratio of about 1.1) with sizes ranging
from 0.5 to 5 lm (see Fig. 2).
The experimental details of the crystal structure
determination, including crystal data, data collection,
structure determination, and refinement are listed in
Table 1 for the ligand. X-ray single-crystal diffraction
measurements were performed using a Bruker SMART
CCD diffractometer. The first fifty frames were col-
lected at the completion of data recording to monitor
This is the methodological framework of the present
study, which determines the crystal structure of the title
zinc(II) coordination compound from powder diffrac-
tion data. Because of the challenge represented by the
alternative to the conventional single-crystal diffrac-
tometry and the biological reasons mentioned above,
we report the characterization by elemental analysis,
infrared (IR) spectroscopy, and X-ray powder diffrac-
tometry of the zinc(II) complex [ZnCl2(TdTz)] [TdTz =
2-(3,4-dichlorophenyl)imino-N-(2-thiazin-2-yl)thiazoli-
dine]. In addition, we report the crystal structure of
the TdTz ligand determined by X-ray single-crystal
diffractometry.

´
F.J. Barros-Garcıa et al. / Polyhedron 24 (2005) 1975–1982
1977
Table 1
Details of the crystal data, data collection, and refinement for the
[TdTz] ligand
Crystal shape
Colour
Size (mm)
prism
colourless
0.47 · 0.39 · 0.35
C13H13Cl2N3S2
Chemical formula
Formula weight
Crystal system
Space group
346.30
monoclinic
C121
Unit cell dimensions
˚
a (A)
˚
25.997(4)
7.895(1)
b (A)
˚
c (A)
7.357(1)
99.26(1)
1490.4(4)
b (ꢁ)
Cell volume (A )
3
˚
Z
4
298(2)
T (K)
Dcalc (g cmꢀ3
l (mmꢀ1
F(0 0 0)
Diffractometer
)
1.543
0.708
Fig. 1. Scanning electron microscopy image of the [ZnCl2(TdTz)]
complex crystals in the as-synthesized condition.
)
712
bruker SMART CCD
˚
Radiation
Collection method
Mo Ka (k = 0.71073 A)
/–x
3.2–56.5
2h range
Index ranges
ꢀ34 6 h 6 23, ꢀ10 6 k 6 9, ꢀ9 6 l 6 9
Independent reflections
Observed reflections
Absorption correction
Max/min transmission
No. of refined parameters
R [I > 2r(I)]a
3018
2472 [F > 4.0r(F)]
empirical
0.732/0.790
182
0.0474
0.1353
wR [I > 2r(I)]b
GOFc
1.062
0.435, ꢀ0.327
ꢀ3
˚
q
max, qmin (e A
)
P
P
a
R ¼ jjF oj ꢀ jF cjj= jF oj.
R ¼
n
h
i.
h
io
1=2
ꢀ
ꢁ
ꢀ
ꢁ
P
P
2
2
b
c
w F 2o ꢀ F 2c
w F 2o
.
n
h
i.
ꢀ
ꢁ
ꢀ
P
2
The goodness-of-fit (GOF) equals
w F 2o ꢀ F 2c
Nrf ln s
ꢀ
o
1=2
ꢁ
Nparams
.
Fig. 2. Scanning electron microscopy image of the powder particles
obtained after milling the [ZnCl2(TdTz)] complex crystals.
Table 2
Details of the data collection, structure solution, and refinement for
the [ZnCl2(TdTz)] complex
for decay. Absorption corrections were applied using
the program SADABS. The crystal structure was solved
by means of direct methods and subsequent Fourier
differences using the WINGX package [20], followed by
a full-matrix least-squares refinement. The H atoms
attached to the C atoms were positioned geometrically
with the Uiso values derived from the Ueq values of the
corresponding C atom. In the structure of ligand, C(3)
and C(4) are disordered at two sites and refined with
occupancy of two alternate orientations constrained
to unity. The EADP restraints were applied to the
disordered atoms to achieve convergence during least-
squares refinement. The refined occupancy factor was
0.62 for orientation named A and 0.38 for orientation
named B.
2h range (ꢁ)
5–90
0.02, 20
Step scan increment (ꢁ), counting time (s)
Program used for structure solution
Structure refinement
FOX [47]
FULLPROF [44,45]
Number of reflections
2045
23
Number of atoms (H excluded)
Number of global parameters refined
Number of profile parameters refined
Number of structural parameters refined
47
10
74
0.093, 0.071, 6.23
R
wp; Rp; v2r
Diffractometer: D5000 Siemens; Radiation: Cu Ka, graphite mono-
chromator.
conditions used. Sample preparation included spreading
the fine powder onto the holder (about 3 mm thick) and
pressing slightly with a glass slide to ensure a flat
surface.
The XRD pattern for the structural determination of
the complex was obtained via conventional powder dif-
fractometry. Table 2 gives the experimental and set-up

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F.J. Barros-Garcıa et al. / Polyhedron 24 (2005) 1975–1982
1978
˚
3. Results and discussion
[C(5)–N(3) = 1.261(3) A], which are indicative of an
imino-thiazolidine form [23]. It is known that the imino
tautomers can exist as two geometrical isomers, syn (Z)
and anti (E), although in this crystal only Z isomers were
observed.
3.1. Description of the crystal structure of the organic
ligand (TdTz)
The X-ray single-crystal study of the TdTz ligand
showed that the crystals are made up of monoclinic unit
cells, each one containing four TdTz molecules. Fig. 3 is
a diagram of the molecular structure with the atomic
labelling. Selected bond lengths and angles are given in
Table 3.
The thiazolidine ring is essentially planar, with max-
˚
imum mean-plane deviation for C(6) (0.037 A). Due to
the disorder found in C(3) and C(4), discussion of the
thiazine ring conformation is pointless.
The crystal structure presents a static disorder affect-
ing the Cl atom linked to the aromatic ring in position 3,
due to an alternation of the Cl(1A)–H10 and Cl(1B)–
H12 pairs with occupancy degrees of 48% and 52%,
respectively.
The least-squares plane of the imino-thiazolidine
moiety is practically coplanar to the best plane of the
thiazine (8.2ꢁ) and is rotated 89.3ꢁ with respect to the
least-squares plane of the 3,4-dichlorophenyl ring.
In the S(1)–C(1)–N(1)–C(2)–C(3)–C(4) ring, the short
˚
endocyclic C@N bond [C(1)–N(1) = 1.259(3) A] is
accompanied by a high S–C–N angle [S(1)–C(1)–
N(1) = 127.3(2)ꢁ] and a relatively large SII-C(sp2) bond
[S(1)–C(1) = 1.762(2) A]. This is characteristic of a
˚
thiazine ring, as was deduced from comparison with
24 compounds containing a thiazine ring in their struc-
ture, obtained by the CONQUEST software [21] from the
Cambridge Structural Database (CSD) [22] [mean
3.2. Spectroscopic study
˚
values: C(1)–N(1) = 1.276 A; S(1)–C(1)–N(1) = 128.5ꢁ;
S(1)–C(1) = 1.751 A]. In contrast, the S(2)–C(5)–N(2)–
C(6)–C(7) ring shows a smaller S–C–N angle [S(2)–
C(5)–N(2) = 111.2(2)ꢁ] and a short exocyclic C@N bond
˚
The IR spectrum of the TdTz organic-ligand has been
described elsewhere [19]. The IR spectrum of the
complex [ZnCl2(TdTz)] shows bands assignable to: the
thiazine ring vibrations at 1545 (W1), 1006 (W2), 943
(W3), 838 (W4), 757 and 748 (W5), 721 (W6), 628 (W7),
589 (W8), and 538 cmꢀ1 (/1) [25–27]; the thiazolidine ring
vibrations at 1030 (mn1), 914 (mn2), 893 (mn3), 696 (mn4),
671 (mn5), and 475 cmꢀ1 (dn2) [28,29]; and the 3,4-
dichlorophenyl ring vibrations at 1588 (8b), 1463 (19b),
1373 (19a), 1251 (14), and 1119 (1) cmꢀ1 [25]. Other rel-
evant bands are observed at 1613 [m(C@N)imine], 1357
[m(C–N)], and 1064 cmꢀ1 [m(C–Cl)ortho] [30,31].
Comparison of the strong m(C@N)imine absorption of
the complex (1613 cmꢀ1) to that of the uncoordinated
imine function of the ligand (1631 cmꢀ1) shows the for-
mer to be significantly shifted to a lower wavenumber.
The same is the case with the in-plane stretching vibra-
tion corresponding to m(C@N) skeletal vibration of the
heterocyclic ring (W1 of the complex: 1545 cmꢀ1), which
is also shifted towards lower wavenumbers compared to
the free ligand (1604 cmꢀ1). One may hence deduce coor-
dination via the imino nitrogens of the ligand [32–35].
The far IR spectrum of this complex shows the pres-
ence of three bands due to the metal–ligand stretching
vibrations at 330, 304, and 218 cmꢀ1. Of these, the band
at 330 cmꢀ1 may include the m(Zn–Nimino) vibration
[32–34,36] and one m(Zn–Cl) vibration [37,38], whereas
the band at 304 cmꢀ1 is assigned to the other m(Zn–Cl)
vibration [37,38]. Finally, the band at 218 cmꢀ1 is
assignable to m(Zn–Nthiazine), in good agreement with
the literature data for several complexes containing
thiazoline or thiazine derivative ligands [19,38–40].
The results of this study together with the elemental
analysis allow one to deduce a tetra-coordinated geom-
etry for the complex.
Fig. 3. Molecular structure of the [TdTz] ligand, showing the atom
numbering scheme. The thermal ellipsoids are drawn at the 40% level.
Table 3
˚
Selected bond lengths (A) and bond angles (ꢁ) for the [TdTz] ligand
S(2)–C(5)
S(1)–C(1)
S(1)–C(4B)
N(2)–C(1)
C(8)–N(3)
1.755(2)
1.762(2)
1.890(16)
1.403(3)
1.421(3)
S(2)–C(7)
S(1)–C(4A)
N(2)–C(5)
C(5)–N(3)
C(1)–N(1)
1.786(3)
1.859(10)
1.386(3)
1.261(3)
1.259(3)
C(5)–S(2)–C(7)
C(5)–N(2)–C(1)
C(9)–C(8)–C(13)
S(2)–C(5)–N(3)
C(8)–N(3)–C(5)
C(1)–N(1)–C(2)
N(2)–C(1)–N(1)
C(1)–S(1)–C(4B)
93.1(1)
127.0(2)
119.1(2)
124.6(2)
119.2(2)
124.1(2)
115.9(2)
97.7(5)
C(5)–N(2)–C(6)
C(1)–N(2)–C(6)
N(3)–C(8)–C(9)
S(2)–C(5)–N(2)
N(2)–C(5)–N(3)
S(1)–C(1)–N(1)
C(1)–S(1)–C(4A)
115.1(2)
117.7(2)
117.0(8)
111.2(2)
123.9(2)
127.3(2)
97.9(3)

´
F.J. Barros-Garcıa et al. / Polyhedron 24 (2005) 1975–1982
1979
3.3. Structural determination of the complex
mented in the FOX software package [47]. The structure
was described in the Z-matrix formalism, which is espe-
cially useful for organic molecules of relative complexity
[48,49]. In this formalism the geometry of the molecules
is described by the bond distances, the bond angles, and
the dihedral angles between the different atoms [50].
From the optimized molecular structure, the corre-
sponding Fenske–Hall Z-matrix was built using the BA-
BEL program [51], with the heavy Zn atom as pivot. In
a first step we treated the molecule as a rigid body,
and only refined the six translational and rotational
degrees of freedom. After 800 000 movements, the
weighted residual was Rwp = 0.169. To check for
‘‘uniqueness’’, this step was repeated several times using
different random starting positions for the Zn pivot and
molecule orientations. In the next step we relaxed the
constraints on the Z-matrix parameters, and, after
450 000 additional movements, the weighted residual de-
creased to Rwp = 0.148. The Z-matrix coordinates were
next converted to crystallographic coordinates for the
Rietveld refinement.
The sequence used in the determination of the struc-
ture from the XRD pattern was: data reduction and
indexing, molecular modelling, use of direct-space meth-
ods with a ÔMonte–Carlo/parallel temperingÕ search
algorithm, and finally Rietveld refinement [18].
3.3.1. Data reduction and indexing
The peak positions were identified using a deriva-
tive-based algorithm that is implemented in CELREF
[41]. The XRD pattern was then indexed in the mono-
clinic system using the CRYSFIRE software package [42];
the best solution was obtained with the TREOR90 in-
dexer, and had a de Wolff figure-of-merit of M(20) =
39.5. By analyzing the XRD data with CHECKCELL
˚
˚
3
[43] we obtained a = 10.640(1) A, b = 9.019(1) A,
˚
˚
c = 20.435(2) A, b = 108.35(1)ꢁ, and V = 1861(4) A ,
whereas the space group was unambiguously found
to be P121/c1. From this space group, we deduced
the existence within the monoclinic unit cell of four
molecules of C13H13Zn1N3S2Cl4. This result is in clear
agreement with the experimental density of 1.72(1)
Mg mꢀ3 determined by the Archimedes method.
In this first stage, we also performed the Le Bail fit
implemented as an option in the FULLPROF program
[44,45], which will be used later for the final Rietveld
refinement. The Le Bail fit, which makes no reference
to any structure model, had a threefold objective: (1)
to assess the goodness of the space group and the choice
of cell; (2) to estimate the shape and width of the Bragg
reflections, and the instrumental shifts; and (3) to evalu-
ate the error not associated with the structure model.
The R-factors obtained were Rwp = 0.058 and Rp =
0.045.
3.3.4. Rietveld refinement
According to the Le Bail criterion [52], the final refine-
ment of the structures determined from powder diffrac-
tometry must be performed using the Rietveld method
[53]. We used the FULLPROF program implemented in the
WINPLOTR software package [44,45], and refined the
following items: background (cubic spline interpolation),
scale factor, instrumental shifts, cell parameters, atomic
positions (excluding the H atoms, which were rigidly
linked to their bonding atoms), and Debye–Waller atomic
thermal parameters, as well as the shape, width, and
asymmetry of the Bragg reflections assumed to have pseu-
do-Voigtian form. The Rietveld refinement was initialized
using the profile and instrumental parameters obtained
previously with the Le Bail fit. In a first step the molecule
was treated as rigid body, and then the atomic coordinates
were refined applying restrains on bond lengths and an-
gles. The final residuals were v2r ¼ 6.23, Rwp = 0.093,
Rp = 0.071, and RF = 0.106, and the refined cell parame-
3.3.2. Molecular modelling
A first approximation to the molecular structure in-
side the crystal was obtained by molecular optimization
using semi-empirical methods, since the compounds
bonded by the weak van der Waals–London interaction
(and perhaps hydrogen bonds) remain almost unmodi-
fied when switching from the isolated molecules to the
crystalline states. We used the AM1, PM3, MNDO,
and MNDO/d force fields included in the HYPERCHEM
software package [46], with the starting model built
from IR-spectroscopy data and the ligand structure
determined by single-crystal diffractometry. The best
optimization was obtained with MNDO/d (binding
energy Eb = ꢀ3530 kcal molꢀ1), with a conclusive differ-
ence in Eb of 12 kcal molꢀ1 with respect to the second-
best optimized model.
˚
˚
ters were a = 10.612(6) A, b = 9.006(5) A, c = 20.385(9)
˚
A, and b = 108.364(3)ꢁ. Comparison of this Rwp value
with that obtained from the Le Bail fit showed that the er-
ror associated with the structural model was small – 3.5%
– thereby confirming the validity of the crystal structure.
The plotted output from the Rietveld analysis is shown
in Fig. 4. Table 4 gives the most representative crystallo-
graphic parameters. Fig. 5 shows a representation of the
refined crystal structure.
3.4. Description of the structure of [ZnCl2(TdTz)]
3.3.3. Monte Carlo methods
The crystal structure was determined by Monte Carlo
methods, using the Ôparallel temperingÕ algorithm imple-
We discuss next the crystal structure of the zinc(II)
complex, although our interpretation should be treated
with caution since the crystallographic data were

´
F.J. Barros-Garcıa et al. / Polyhedron 24 (2005) 1975–1982
1980
Fig. 4. Plot output from the Rietveld analysis of the X-ray diffraction
pattern corresponding to the [ZnCl2(TdTz)] complex. Points are the
experimental X-ray diffraction data; the solid line is the calculated
pattern; the residuals are plotted at the bottom.
Fig. 5. Representation of the crystal structure of the [ZnCl2(TdTz)]
complex after refinement using the Rietveld method.
Table 5
˚
Selected bond lengths (A) and bond angles (ꢁ) for the [ZnCl2(TdTz)]
complex
Table 4
Main crystallographic data for the [ZnCl2(TdTz)] complex obtained by
X-ray powder diffractometry
Zn–Cl(1)
Zn–N(1)
2.158(5)
2.273(5)
1.414(6)
1.632(5)
1.493(5)
Zn–Cl(2)
Zn–N(3)
2.145(4)
2.237(4)
1.558(4)
1.199(4)
Chemical formula
Space group
C13H13Cl4ZnN3S2
P121/c1
C(1)–N(1)
N(2)–C(1)
C(5)–N(3)
N(2)–C(5)
C(8)–N(3)
Cell parameters
˚
a (A)
˚
10.612(6)
9.006(5)
Cl(1)–Zn–Cl(2)
Cl(2)–Zn–N(3)
Cl(2)–Zn–N(1)
C(5)–N(2)–C(1)
Zn–N(3)–C(8)
Zn–N(1)–C(1)
N(2)–C(1)–N(1)
112.7(3)
Cl(1)–Zn–N(3)
Cl(1)–Zn–N(1)
N(3)–Zn–N(1)
Zn–N(3)–C(5)
C(5)–N(3)–C(8)
C(1)–N(1)–C(2)
N(3)–C(5)–N(2)
113.0(3)
109.6(3)
97.4(2)
b (A)
115.3(3)
107.5(3)
129.2(3)
118.4(4)
121.5(4)
122.4(5)
˚
c (A)
20.385(9)
108.364(3)
b (ꢁ)
116.1(3)
122.6(5)
119.0(5)
128.1(4)
Coordinates
Atoms
x
y
z
Zn
0.6065(3)
0.7536(3)
0.6383(3)
0.4548(3)
0.7571(3)
0.8748(3)
0.9780(3)
0.9268(3)
0.5027(3)
0.6685(4)
0.5347(4)
0.3397(3)
0.2432(3)
0.1074(3)
0.0681(3)
0.1653(3)
0.3004(2)
0.8462(4)
0.4039(4)
0.6982(3)
0.5440(3)
0.1874(4)
0.3477(5)
0.5777(4)
0.3555(4)
0.4993(5)
0.2788(6)
0.3775(6)
0.5120(6)
0.5118(4)
0.6949(4)
0.7733(4)
0.3248(4)
0.4000(6)
0.3663(6)
0.2596(6)
0.1863(6)
0.2185(5)
0.6279(5)
0.6439(4)
0.0772(4)
0.0355(4)
0.4577(8)
0.2166(7)
0.6625(1)
N1
N2
N3
C1
0.7328(2)
0.6539(2)
0.6075(1)
0.7154(2)
0.7834(2)
0.8302(2)
0.8445(2)
0.6091(1)
0.6189(2)
0.5911(2)
0.5949(1)
0.6172(3)
0.5855(2)
0.5317(2)
0.5094(3)
0.5410(2)
0.7687(2)
0.5681(1)
0.5952(2)
0.7272(1)
0.6138(3)
0.4923(2)
C2
C3
C4
C5
C6
C7
C8
C9
C10
C11
C12
C13
S1
Fig. 6. Molecular structure of the [ZnCl2(TdTz)] complex, showing the
atom numbering scheme. The thermal ellipsoids are drawn at the 50%
level.
S2
Cl1
Cl2
Cl3
Cl4
ꢀ0.0092(3)
ꢀ0.0973(3)
The crystalÕs structure is a monoclinic lattice with four
complex molecules per unit cell. The zinc(II) is bound to
˚
two chlorine atoms [Zn–Cl(1) = 2.158(5) A; Zn–Cl(2) =
˚
2.145(4) A], one thiazine nitrogen [Zn–N(1) = 2.273(5) A],
˚
and one imino nitrogen [Zn–N(3) = 2.237(4) A] in a dis-
torted tetrahedral geometry.
˚
determined from powder diffractometry. Selected bond
lengths and angles of the complex are listed in Table 5,
and the molecular structure is shown in Fig. 6.

´
F.J. Barros-Garcıa et al. / Polyhedron 24 (2005) 1975–1982
1981
The [ZnCl2(TdTz)] complex is the first compound
with a 1,3-thiazine linked to zinc(II) that has been char-
acterized structurally. The Zn–Cl bond lengths are
ER [Project 2PR02A098] and [Project 2PR04A011] for
financial support.
˚
slightly shorter than the average value [2.225(30) A]
calculated for 161 tetrahedral zinc(II) complexes with
a chromophore group ZnCl2N2 found in a survey using
the CSD. The Zn–Nimino bond distance is comparable to
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conts/retrieving.html (or from the CCDC, 12 Union
Road, Cambridge CB2 1EZ, UK; fax: +44 1223
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