Metal complexes of a novel achiral symmetric pentadentate ligand - Crystal structures of monohelical zinc(II) and cadmium(II) complexes

Article abstract of DOI:10.1002/ejic.200300089

By both electrochemical synthesis and a traditional chemical procedure the interaction of the pentadentate ligand 2,6-bis{1-[2-(tosylamino)phenylimino]ethyl}pyridine (H₂DAPATs), with Mn^II, Fe^II, Co^II, Ni^II<

Full text of DOI:10.1002/ejic.200300089

FULL PAPER
Metal Complexes of a Novel Achiral Symmetric Pentadentate Ligand ؊
Crystal Structures of Monohelical Zinc(II) and Cadmium(II) Complexes
[a]
[a]
[a]
[a]
´
´
Rosa Pedrido, Manuel R. Bermejo,* Ana M. Garcıa-Deibe, Ana M. Gonzalez-Noya,
[a]
[a]
´
Marcelino Maneiro, and Miguel Vazquez
Keywords: Supramolecular chemistry / Helical structures / Schiff bases / Electrochemistry
By both electrochemical synthesis and a traditional chemical
procedure the interaction of the pentadentate ligand 2,6-
[Cd(DAPATs)(H2O)] (2). Both 1 and 2 are monohelical single-
stranded compounds with different coordination geometries.
In the zinc complex, the metal ion assumes a distorted tri-
gonal-bipyramidal geometry involving the N5 atoms of the
dianionic ligand. For cadmium complexes the metal ion is in
a distorted pentagonal-pyramidal environment, as the result
of coordination to the N5 ligand donor set and an additional
water molecule.
bis{1-[2-(tosylamino)phenylimino]ethyl}pyridine
(H2DA-
PATs), with MnII, FeII, CoII, NiII, CuII, ZnII and CdII gives rise
to neutral mononuclear complexes that have been charac-
terised by elemental analyses, FAB mass spectrometry, IR, 1H
and COSY NMR spectroscopy and magnetic measurements,
where appropriate. Recrystallisation of the zinc complex ob-
tained electrochemically yielded single crystals of [Zn(DA-
PATs)] (1), while recrystallisation of cadmium complexes ob- ( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
tained by both techniques afforded the same structure,
Germany, 2003)
Introduction
complexes for Mn,[10,11] Co[10] and Cd[12] by electrochemi-
cal synthesis.
We have also shown that introducing bulky tosyl groups
in Schiff-base ligands with different spacers is very useful
in obtaining mono- and dihelical species.[16]
Helical complexes are an active research area in supra-
molecular chemistry.[1Ϫ5] Nevertheless, predicting the out-
come of a self-assembly process is still difficult and depen-
dent upon numerous factors, such as the nature of the metal
(coordination numbers and stereochemical preferences), the
structure of the ligand, the existence of weak non-covalent
interactions, etc.
Most ligands employed in the synthesis of helicates are
predominantly benzimidazole,[6] catechole[7] or polypyridine
types,[8] and they usually imply long and complicated syn-
thetic routes. More recently, readily prepared Schiff-base li-
gands have been used to obtain helical species.[9,10]
We then wanted to check the effect of the simultaneous
presence of a bulky group, such as tosyl, and a rigid
spacer, like pyridine, in a pentadentate Schiff-base ligand.
Therefore, we have designed the novel pentadentate N5
ligand 2,6-bis{1-[2-(tosylamino)phenylimino]ethyl}pyridine
(H2DAPATs).
The interaction of H2DAPATs with MnII, FeII, CoII, NiII,
CuII, ZnII and CdII using electrochemical and chemical pro-
cedures was investigated and the results obtained are de-
scribed herein.
In recent years part of our research program has focused
on using pentadentate hydrazone ligands derived from 2,6-
diacetylpyridine to produce helical compounds.[10Ϫ12] Pre-
vious works have demonstrated that such ligands react with
metal chlorides to yield complexes containing the non-de-
protonated ligand, while complexes with the bis(deproton-
ated) ligand could be obtained with metal acetates.[13,14] We
have recently found that pentadentate ligands incorporating
a rigid spacer such as pyridine yield dinuclear helical com-
plexes for Ni[10,11] and Cu[15] and non-helical mononuclear
Results and Discussion
Synthesis of the Ligand
The Schiff base H2DAPATs has been prepared according
to a two-step synthetic route (Scheme 1) with an overall
yield of 50%. The first step involves the N-tosylation of 1,2-
diaminobenzene[17] (I), to obtain 2-(tosylamino)aniline (II).
Treatment of II with 2,6-diacetylpyridine in a 1:2 stoichio-
metric ratio in ethanol under reflux yields the N5 Schiff-
base ligand H2DAPATs.
[a]
´
´
´
Departamento de Quımica Inorganica, Facultade de Quımica,
Universidade de Santiago de Compostela,
15782 Santiago de Compostela, Spain
Fax: (internat.) ϩ 34-981/597525
The deep yellow powdery solid formed was satisfactorily
characterised by elemental analysis, FAB mass spec-
E-mail: qimb45@usc.es
Eur. J. Inorg. Chem. 2003, 3193Ϫ3200
DOI: 10.1002/ejic.200300089
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3193

M. R. Bermejo et al.
FULL PAPER
Scheme 1. Synthesis of H2DAPATs
Table 1. Elemental analysis and selected data for the ligand and its complexes obtained by electrochemical synthesis
Compound
Yield (%)
Colour
C[a]
H[a]
N[a]
S[a]
FAB[b]
µ[c]
H2DAPATs
50
85
55
95
85
55
95
95
yellow
brown
brown
black
brown
black
55.3 (55.4)
55.1 (55.3)
57.6 (57.8)
56.3 (56.5)
54.7 (54.8)
54.7 (54.8)
56.1 (55.9)
53.8 (53.9)
5.0 (4.9)
4.7 (4.9)
4.6 (4.8)
4.9 (4.7)
4.8 (4.6)
4.8 (4.6)
4.9 (4.7)
4.2 (4.3)
9.0 (9.2)
9.1 (9.2)
9.7 (9.6)
9.4 (9.4)
8.0 (8.1)
8.0 (8.1)
9.2 (9.3)
8.8 (9.0)
8.2 (8.4)
8.5 (8.4)
8.8 (8.8)
8.6 (8.6)
8.4 (8.1)
8.4 (8.1)
8.4 (8.5)
8.1 (8.2)
652
705
706
709
709
713
716
765
Ϫ
Mn(DAPATs)(H2O)3
Fe(DAPATs)(H2O)3
Co(DAPATs)(H2O)
Ni(DAPATs)(H2O)2
Cu(DAPATs)(H2O)3
Zn(DAPATs)(H2O)2
Cd(DAPATs)(H2O)
5.6
5.0
3.9
2.9
2.0
Ϫ
orange
orange
Ϫ
[a]
[b]
[c]
Found (calcd.). amu; peaks corresponding to [ML]ϩ. In B.M.
Table 2. Selected IR data [cmϪ1] for the ligand and its complexes
obtained by electrochemical synthesis
These metal compounds were also obtained by a tra-
ditional chemical procedure, in which a solution of the li-
gand was refluxed in the presence of a metal() acetate. As
the characterisation patterns of these complexes are similar
to those obtained by electrochemical synthesis we shall dis-
cuss only the latter ones.
Compound
H2DAPATs
ν(NϪH) ν(CϭN) ν(CϪN)py νas(SO2) νs(SO2)
3273 m 1627 s 1596 s
1335 s 1167 s
1335 s 1162 s
1361 s 1159 s
1374 s 1154 s
1372 s 1163 s
1381 s 1138 s
1370 s 1138 s
1370 s 1130 s
Mn(DAPATs)(H2O)3 Ϫ
1656 s 1597 s
1636 s 1596 s
1621 m 1590 s
1656 m 1588 s
1621 m 1590 s
1634 m 1587 s
1636 s 1586 s
Elemental analyses (Table 1) show that metal ions react
with the ligand in a molar ratio of 1:1 to afford solvated
Fe(DAPATs)(H2O)3
Co(DAPATs)(H2O)
Ni(DAPATs)(H2O)2
Cu(DAPATs)(H2O)3
Zn(DAPATs)(H2O)2
Cd(DAPATs)(H2O)
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
complexes of the bis(deprotonated) ligand DAPATs2Ϫ
.
These neutral complexes are either insoluble or sparingly
soluble in water and common organic solvents, but soluble
in polar coordinating organic solvents such us DMSO,
DMF and pyridine. The powdery complexes appear to be
stable both in the solid state and in solution, and all of
them melt above 300 °C without decomposition.
trometry, IR and 1H and COSY NMR spectroscopy
(Tables 1, 2 and 6).
X-ray Studies
Synthesis of the Complexes
The crystal structures of complexes [Zn(DAPATs)] (1)
and [Cd(DAPATs)(H2O)] (2) are shown in Figures 1, 2 and
3. Selected bond lengths and angles are given in Tables 4
and 5. The complexes are considered together here in order
to comment on their structural similarities and differences.
They consist of discrete neutral molecules of [Zn(DA-
PATs)] (1) and [Cd(DAPATs)(H2O)] (2), the ligand being
bis(deprotonated), DAPATs2Ϫ. In complex 1 all five nitro-
gen donor atoms of the ligand (two imine, two amide and
one pyridine nitrogen atoms) bind to the same zinc ion. No
A series of neutral complexes were obtained by electro-
chemical oxidation of the corresponding metal anode in the
presence of the ligand.[18] The electrochemical efficiency of
the cell was close to 0.5 mol·FϪ1, which is compatible with
the following reaction scheme:
Cathode: H2DAPATs ϩ 2 eϪ Ǟ H2 (g) ϩ DAPATs2Ϫ
Anode: DAPATs2Ϫ ϩ M Ǟ M(DAPATs) ϩ 2 eϪ
This synthetic procedure allowed us to obtain neutral additional ligands are coordinated to the zinc ion, resulting
complexes of the type M(DAPATs)(H2O)n with high purity in a coordination number of five and a distorted bipyrami-
and in very good yield.
dal-trigonal geometry. In this complex the Schiff-base li-
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Eur. J. Inorg. Chem. 2003, 3193Ϫ3200

Metal Complexes of a Novel Achiral Symmetric Pentadentate Ligand
FULL PAPER
Table 3. Crystal data and structure refinement for 1 and 2
[Zn(DAPATs)] (1)
[Cd(DAPATs)(H2O)] (2)
Empirical formula
Formula mass
Temperature [K]
Crystal system
Space group
C35H31N5O4S2Zn
715.14
293.0(2)
C35H33CdN5O5S2
780.18
298.0(2)
monoclinic
P21/c
11.2037(10)
10.6130(2)
28.4432(3)
90
triclinic
¯
P1
˚
a [A]
9.3474(14)
10.8789(14)
17.853(3)
73.691(3)
84.882(3)
65.678(3)
2
1587.1(4)
0.954
0.15ϫ0.10ϫ0.02
10909
3900 [R(int) ϭ 0.0925]
SADABS
3900/0/424
R1 ϭ 0.0432
wR2 ϭ 0.0821
R1 ϭ 0.1343
wR2 ϭ 0.1368
˚
b [A]
˚
c [A]
α [°]
β [°]
γ [°]
Z
97.46(7)
90
4
3
˚
Volume [A ]
3353.41(8)
0.826
0.24ϫ0.20ϫ0.14
17862
8197 [R(int) ϭ 0.0824]
SADABS
8197/0/437
R1 ϭ 0.0697
wR2 ϭ 0.1099
R1 ϭ 0.1533
wR2 ϭ 0.1457
Absorption coefficient [mmϪ1
Crystal size [mm]
]
Reflections collected
Independent reflections
Absorption correction
Data/restraints/parameters
Final R indices [I Ͼ 2σ(I)]
R indices (all data)
Figure 1. ORTEP view of the crystal structure of [Zn(DAPATs)]
(1); ellipsoids are drawn at 50% of probability; hydrogen atoms
have been omitted for clarity
Figure 2. ORTEP view of the crystal structure of [Cd(DAPATs)-
gand fulfills all the stereochemical requirements of the me-
(H2O)] (2); ellipsoids are drawn at 50% of probability; hydrogen
tal, and subsequently it can be considered a saturated com- atoms have been omitted for clarity
pound.[4]
However, 2 is an unsaturated compound because the cad-
mium ion is coordinated to the same five nitrogen donor addition, helicity in cadmium compounds is uncommon Ϫ
atoms of the bis(deprotonated) ligand but also needs one only two monohelical cadmium complexes with Schiff-base
additional water molecule, leading to a coordination num- ligands have been reported.[12,19]
ber of six and to a distorted pentagonal-pyramidal ge-
ometry.
For complex 1 the ZnϪNimine distances [Zn(1)ϪN(2)
2.160(6) A, Zn(1)ϪN(4) 2.172(7) A] are of the order of
˚
˚
This geometry is unusual for cadmium complexes derived those found for the unique monohelical zinc complex re-
from pentadentate Schiff-base ligands because, to the best ported with similar geometry,[20] [Zn(SpyNpy2)]2ϩ. The dis-
˚
of our knowledge, only one such cadmium complex with tance ZnϪNpyridine [Zn(1)ϪN(3) 2.102(7) A] is shorter than
this type of geometry has been previously reported.[12] In those found for penta-[21] or heptacoordinated[13,22] com-
Eur. J. Inorg. Chem. 2003, 3193Ϫ3200
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M. R. Bermejo et al.
FULL PAPER
containing tosyl groups[16,27,28] and do not merit further
analysis.
The four bond angles NϪZnϪN formed by the four che-
late rings are close to 75°. The fifth one, N(5)ϪZn(1)ϪN(1),
is 108.9(3)°. These values explain the distorted trigonal-bi-
pyramidal geometry adopted in 1. In complex 2 the distor-
tion from the ideal geometry is clearly shown by the angles
between water, cadmium and the donor set of the ligand
(Table 5). Four of the five angles subtended at Cd by adjac-
ent equatorial atoms are slightly smaller than those of an
ideal pentagonal-pyramidal arrangement, being close to
70°, while the fifth, N(1)ϪCd(1)ϪN(5) is 105.33(16)°.
Moreover three bond angles O(1s)ϪCd(1)ϪN are in the
range 81Ϫ84° while the other two are in the range
101Ϫ125°, reinforcing the highly distorted pyramidal-pen-
tagonal geometry adopted by 2.
Figure 3. Stick view of [Zn(DAPATs)] (1) and [Cd(DAPATs)(H2O)]
(2), showing the screwing of the ligand
˚
Table 4. Selected bond lengths [A] for 1 and 2
[Zn(DAPATs)] (1)
[Cd(DAPATs)(H2O)] (2)
The
bond
angles
C(5)ϪS(1)ϪN(1)
and
Zn(1)ϪN(5)
2.006(7)
2.017(6)
2.102(7)
2.160(6)
2.172(7)
3.052
4.147
3.092
4.273
Cd(1)ϪN(1)
2.237(4)
2.345(4)
2.350(5)
2.360(4)
2.377(4)
2.464(5)
3.126
4.475
4.749
3.540
C(29)ϪS(3)ϪN(5) are quite similar for the zinc complex
[108.2(4) and 108.7(4)°, respectively]; both tosyl groups ad-
opt a similar conformation (Figure 3). Nevertheless, in the
cadmium complex these angles, C(5)ϪS(1)ϪN(1) and
C(29)ϪS(2)ϪN(5), are slightly different [107.0(3) and
111.1(2)°, respectively], causing an anti orientation of the
tosyl groups to reduce the steric hindrance.
Why do zinc and cadmium complexes show different co-
ordination numbers and geometries? We suggest that two
factors could be responsible:
Zn(1)ϪN(1)
Zn(1)ϪN(3)
Zn(1)ϪN(2)
Zn(1)ϪN(4)
Zn(1)···O(1)
Zn(1)···O(2)
Zn(1)···O(3)
Zn(1)···O(4)
Cd(1)ϪN(5)
Cd(1)ϪN(3)
Cd(1)ϪN(4)
Cd(1)ϪO(1s)
Cd(1)ϪN(2)
Cd(1)···O(1)
Cd(1)···O(2)
Cd(1)···O(3)
Cd(1)···O(4)
i. Steric hindrance of the bulky tosyl groups.
Table 5. Selected bond angles [°] for 1 and 2
The pentadentate dianionic ligand, DAPATs2Ϫ
, is
wrapped around the metal ions to afford a helical arrange-
ment in both complexes. This screwed disposition of the
[Zn(DAPATs)] (1)
[Cd(DAPATs)(H2O)] (2)
N(5)ϪZn(1)ϪN(1) 108.9(3) N(1)ϪCd(1)ϪN(5)
105.3(16) ligand seems to be clearly favoured by the two terminal
N(1)ϪZn(1)ϪN(2)
N(3)ϪZn(1)ϪN(2)
N(3)ϪZn(1)ϪN(4)
N(5)ϪZn(1)ϪN(4)
C(5)ϪS(1)ϪN(1)
C(29)ϪN(5)ϪS(3)
75.9(3) N(1)ϪCd(1)ϪN(2)
73.3(3) N(2)ϪCd(1)ϪN(3)
73.7(3) N(3)ϪCd(1)ϪN(4)
75.4(3) N(5)ϪCd(1)ϪN(4)
108.2(4) N(1)ϪCd(1)ϪO(1S) 125.2(15)
108.4(4) N(5)ϪCd(1)ϪO(1S)
N(3)ϪCd(1)ϪO(1S)
67.7(16)
bulky tosyl groups. The steric hindrance these groups in-
66.8(17)
duce appears to provoke a twisting of the Schiff base to
73.7(17)
minimise the sterically unfavourable interactions.
69.4(15)
Therefore, a rigid spacer such as pyridine, containing a
83.9(14)
81.5(14)
81.7(14)
donor atom, and the torsion around the CϭN bonds will
˚
allow the imine nitrogen atoms to be quite close (ca. 4.2 A
N(2)ϪCd(1)ϪO(1S)
N(4)ϪCd(1)ϪO(1S) 101.8(14)
C(5)ϪS(1)ϪN(1)
C(29)ϪS(2)ϪN(5)
˚
for 1 and 4.4 A for 2) and coordinate to the same metal
centre. This permits the five nitrogen atoms to bind to the
same metal centre, leading to the isolation of mononuclear
single-stranded helical complexes.
107.0(3)
111.1(2)
ii. Closeness of the tosyl oxygen atoms to the metal
plexes with pentadentate ligands containing ZnϪNpyridine centre.
bonds. For 1, one oxygen atom of each tosyl group, O(1) and
For complex 2 all CdϪN distances are significantly O(3), seems to weakly interact with the metal ion [distances
˚
˚
longer than the corresponding ZnϪN distances, and in O(1)···Zn(1) 3.052 A and O(3)···Zn(1) 3.092 A]. These
both complexes MϪNimine are longer than MϪNamide. In Zn···O distances are too long to be true coordinated bonds,
˚
addition, the CdϪNpyridine bond [Cd(1)ϪN(3) 2.350(5) A] but could be considered as secondary intramolecular inter-
is shorter than that of the distorted pyramidal-pentagonal actions that could be responsible for the distorted trigonal-
cadmium complex with the pentadentate Schiff base bipyramidal disposition around the metal centre, instead of
H4daps[12] [2.403(6) A], but longer than those found in octa- the usual bipyramidal-pentagonal or pyramidal-pentagonal
˚
hedral complexes with quite similar Schiff-base ligands geometries, because these oxygen atoms avoid coordinating
[23Ϫ26]
˚
(ranging from 2.310 to 2.346 A).
additional donor ligands in the apical positions.
In complex 2 the bigger cadmium ion leads to longer
metalϪdonor distances, in general, and in CdϪOtosyl es-
˚
The distance CdϪO(1s) [2.377(4) A] is of the order of
those found for similar cadmium complexes.[12]
The remaining distances for both compounds are in the pecially. Thus, only one oxygen atom of one tosyl group,
usual range for complexes derived from Schiff-base ligands O(1) could weakly interact with the cadmium ion [distance
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Eur. J. Inorg. Chem. 2003, 3193Ϫ3200

Metal Complexes of a Novel Achiral Symmetric Pentadentate Ligand
FULL PAPER
˚
Cd(1)···O(1) 3.126 A], while in the other tosyl group both FAB Mass and IR Spectra
oxygen atoms are too far to interact with the cadmium ion
All the FAB mass spectra show peaks due to the frag-
ments [M(DAPATs)]ϩ, indicating ligand coordination to
the metal centres (Table 1). No additional peaks appear,
suggesting that the complexes are mononuclear.
˚
˚
[Cd(1)···O(4) 3.540 A, Cd(1)···O(3) 4.749 A]. Such a situ-
ation affords an easy entrance and binding for a new ad-
ditional ligand such as water, increasing the coordination
number to six.
The IR spectra of the complexes (Table 2) show a strong
band between 1621 and 1656 cmϪ1 attributable to ν(CϭN).
This band appears 6 cmϪ1 shifted to lower energy from that
in cobalt and copper complexes. With manganese, iron,
nickel, zinc and cadmium complexes the ν(CϭN) band is
shifted to higher wavenumbers (7Ϫ29 cmϪ1), indicating a
slight shift of charge towards the CN group on coordi-
nation. However, the ν(CϪN)py stretching frequency is not
shifted for manganese and iron complexes and is slightly
shifted to lower energy (6Ϫ10 cmϪ1) for the other com-
pounds. This behaviour is compatible with the participation
of both imine and amide nitrogen atoms in the coordination
to the metal centres. Additionally, two bands in the ranges
1335Ϫ1381 and 1130Ϫ1167 cmϪ1 are assigned to the asym-
metric and symmetric vibration modes of SO2 groups,
respectively.[29,30]
Thus, the different monohelical dispositions of these two
complexes can be attributed to the tosyl groups, which show
different spatial orientations (Figure 3). In the zinc complex
the angle between the benzene rings of the tosyl groups is
11.75°. This nearly parallel orientation for the terminal to-
syl aromatic rings is unusual for complexes with Schiff-base
ligands containing these bulky groups. It can be explained
by the lack of superposition of the tosyl groups, which
avoid the unfavourable steric interactions.
In the cadmium complex the angle between the benzene
rings is 47.60°, yielding a spatial conformation quite similar
to that of other monohelical complexes derived from tetra-
dentate Schiff bases containing tosyl groups.[16]
The DAPATs2Ϫ thread forms four five-membered chelate
rings around the metal centres. The angles between adjacent
calculated chelate planes (36.65 and 37.76° for 1; 29.48 and
26.10° for 2) confirm the different twisting degree of the
ligand for both complexes. The smaller degree of twisting
for the cadmium complex is also confirmed by the angles
formed between the benzylidene rings (63.45° for 1 and
37.21° for 2).
Furthermore, no bands around 3270 cmϪ1 are seen, indi-
cating the deprotonation of the NH groups, and therefore
the dianionic character of the ligand.
Finally, the ν(OϪH) bands around 3400 cmϪ1 agree with
the hydrate nature of these complexes.
If the tosyl groups are not considered, we can clearly ob-
serve that the wrapping angle is less than 360°, and slightly
higher for the zinc complex than for the cadmium (287° for
1 and 274° for 2). All these considerations agree with the
ionic radius of the metals, as expected. The size of the cad-
mium ion forces the N5 donor set of the ligand to deviate
from planarity when it surrounds this metal, resulting a
smaller twisting degree.
Magnetic Characterisation
Magnetic measurements were performed at room tem-
perature for all paramagnetic complexes. Their magnetic
moments are close to those expected for magnetically dilute
MII ions, confirming the oxidation state  for the central
atom and, therefore, that the ligands are dianionic.
1H NMR Spectroscopy
¯
[Zn(DAPATs)] crystallises in the achiral space group P1
The 1H NMR spectra of the zinc and cadmium com-
plexes were recorded in [D6]DMSO at room temperature
and CD3CN at low temperatures (273 and 233 K). Selected
1H NMR data are shown in Table 6. The room-temperature
spectra were totally assigned by COSY experiments. The
spectra do not show significant changes with temperature,
being quite similar to those recorded at room temperature.
All spectra show a single set of signals that could be com-
pletely assigned. This seems to indicate a single species in
and [Cd(DAPATs)(H2O)] in P(2)1/c, so that both right- (P)
and left-handed (M) helixes[4] can be simultaneously ob-
served (in 50% yields) in their unit cells. Helicates obtained
from ligands not containing chiral groups usually crystallise
as racemic mixtures and self-recognition is not a very com-
mon process.
Finally, no face-to-face π-stacking interactions between
the terminal tosyl aromatic rings can be identified in
either complex.
1
Table 6. Selected H NMR spectroscopic data for the ligand H2DAPATs and its diamagnetic complexes (in ppm)
Compound
H2DAPATs
H1
H2
H3
H4
H5
H6
H7
H8
H9
H10
7.21
H11
2.31
8.09
8.31
2.06
6.75
7.10
(t, 2 H)
7.19
7.09
7.32
9.34
7.56
(t, 1 H) (d, 2 H) (s, 6 H) (d, 2 H)
Zn(DAPATs)(H2O)2 8.57 8.47 2.60 7.31
(t, 1 H) (d, 2 H) (s, 6 H) (m, 2 H)
Cd(DAPATs)(H2O) 8.50 8.37 2.48
(t, 1 H) (d, 2 H) (s, 6 H) (m, 2 H)
(t, 2 H) (d, 2 H)
7.28 7.48
(m, 2 H) (d, 2 H)
(s, 2 H) (d, 4 H) (d, 4 H) (s, 6 H)
Ϫ
7.36
(d, 4 H) (d, 4 H) (s, 6 H)
7.64 7.03 2.24
(d, 4 H) (d, 4 H) (s, 6 H)
7.09
2.20
(t, 2 H)
7.23Ϫ7.12 7.23Ϫ7.12 6.88
7.23Ϫ7.12
Ϫ
(m, 2 H)
(t, 2 H) (m, 2 H)
Eur. J. Inorg. Chem. 2003, 3193Ϫ3200
www.eurjic.org
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3197

M. R. Bermejo et al.
FULL PAPER
1
Figure 4. H NMR spectra in [D6]DMSO at room temperature for: (1) H2DAPATs, (2) Zn(DAPATs)(H2O)2 and (3) Cd(DAPATs)(H2O)
solution. Comparison of the 1H NMR spectrum of the free
ligand with those of the complexes (Figure 4) shows some corresponding to tosyl and acetyl groups are shifted
Ϫ Finally, in both complexes the methyl proton signals
interesting aspects:
slightly downfield.
Ϫ The NH (H8) protons present in the free ligand dis-
appear for both complexes, in agreement with the bis(dep-
rotonation) of the ligand.
1
Comparison of the H NMR spectra of zinc and cad-
mium complexes suggests that the tosyl groups adopt differ-
Ϫ The aromatic proton signals of the pyridine ring are ent spatial orientations in each complex, as the X-ray struc-
shifted downfield, and the displacements are higher for the tures confirm, because of the size of the metal ions and
zinc complex. The spectra show that complexation through their different geometrical preferences.
the Npyridine atom affects the environments of the H1 and
H2 atoms, and these signals appear with their positions ex- work, some general points can be made. All complexes seem
changed with respect to the free ligand. to be mononuclear, as FAB mass spectrometry suggests.
From the characterisation techniques employed in this
Ϫ The aromatic proton signals of the tosyl groups also The magnetic studies, the similar IR patterns and X-ray re-
shift on complexation, but the displacements differ for the sults agree with the coordination of the N5 donor set of the
1
zinc and cadmium complexes. For the zinc complex the H9 ligand to the metal centres. In addition H NMR studies,
and H10 signals are shifted upfield, whilst in the cadmium and other data, indicate that the solid-state structures of 1
compound the H10 signal is shifted upfield and the H9 sig- and 2 are retained in solution.
nal is shifted downfield. This could be attributed to an in-
teraction between the tosyl groups and the metal centres, as
the solid-state X-ray structures of 1 and 2 seem to confirm.
Conclusion
Ϫ The aromatic proton signals of the benzylidene rings
The novel potentially dianionic and pentadentate Schiff-
also appear to show different behaviour on complexation. base ligand H2DAPATs readily stabilises neutral mononu-
In the zinc complex the H5 signal moves its position slightly clear complexes of MnII, FeII, CoII, NiII, CuII, ZnII and
while the H4, H6 and H7 signals are shifted downfield, with CdII formed by either an electrochemical method or a tra-
the H4 and H6 signals overlapped. With the cadmium com- ditional chemical procedure. The electrosynthesis is both
plex the H4, H5 and H7 signals are completely overlapped. simpler and shorter.
The H5 signal does not show significant changes in its posi-
tion, while the H6 and H7 signals are shifted upfield and bulky terminal groups, such as tosyl, favour the formation
the H4 signal is strongly shifted downfield. of monohelical single-stranded compounds.
The rigid spacer in this ligand, such as pyridine, and the
3198
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Eur. J. Inorg. Chem. 2003, 3193Ϫ3200

Metal Complexes of a Novel Achiral Symmetric Pentadentate Ligand
FULL PAPER
Cd(DAPATs)(H2O): A mixture of H2DAPATs (0.2 g, 0.31 mmol)
and Cd(C2H3O2)2·2H2O (0.08 g, 0.31 mmol) in ethanol (60 mL)
was refluxed for 3 h to afford a black suspension. Filtration fol-
lowed by washing with diethyl ether and drying in vacuo yielded
an orange powdery solid. Recrystallisation of Cd(DAPATs)(H2O)
complex in DMSO yielded [Cd(DAPATs)(H2O)] (2).
It thus seems that careful design of the ligand is useful in
controlling the selective formation of monohelical com-
plexes.
Experimental Section
X-ray Crystallographic Studies: Crystals of 1 and 2, suitable for X-
ray diffraction studies, were grown as described above. Data were
collected with a Smart CCD-1000 Bruker diffractometer, using
General: Elemental analyses were performed with a Carlo Erba EA
1108 analyser. NMR spectra were recorded with Bruker DPX-250
and AMX-500 spectrometers with [D6]DMSO (296 K) and
CD3CN (273 and 233 K) as solvents. Infrared spectra were regis-
tered as KBr pellets with a Bio-Rad FTS 135 spectrophotometer
in the range 4000Ϫ600 cmϪ1. Fast atom bombardment (FAB) mass
spectra were obtained with a Kratos MS-50 mass spectrometer, em-
ploying Xe atoms at 70 keV in m-nitrobenzyl alcohol as matrix.
Room-temperature magnetic susceptibilities were measured using a
Digital Measurement system MSB-MKI, calibrated by using tetra-
kis(isothiocyanato)cobaltate().
˚
graphite-monochromated Mo-Kα radiation (λ ϭ 0.71073 A) from
a fine focus sealed tube source. The structures were solved by direct
methods[31] and DIRDIF-99.2 for Windows and finally refined by
full-matrix least squares based on F2. An empirical absorption cor-
rection was applied using SADABS.[32] All non-hydrogen atoms
were anisotropically refined, and all hydrogen atoms were included
in the model at geometrically calculated positions. CCDC-203518
(1) and -203519 (2) contain the supplementary crystallographic
data for this paper. These data can be obtained free of charge at
www.ccdc.cam.ac.uk/conts/retrieving.html [or from the Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge
Syntheses: All solvents, 2,6-diacetylpyridine, 1,2-diaminobenzene,
tosyl chloride and MII acetates are commercially available and were
used without further purification. Metals (Ega Chemie) were used
as ca. 2 ϫ 2 cm2 plates and were cleaned of oxides in dilute hydro-
chloric acid prior to electrolysis. 2-(Tosylamino)aniline was pre-
pared and characterised according to a method previously re-
ported[17] (Scheme 1).
CB2 1EZ, UK; Fax: (internat.)
deposit@ccdc.cam.ac.uk].
ϩ 44-1223/336-033; E-mail:
Acknowledgments
The authors would like to thank Xunta de Galicia (Spain)
(PGIDIT03PXIB20901PR) for financial support. R. P. would like
to thank Xunta de Galicia for a grant.
Ligand Synthesis: H2DAPATs has been prepared by condensation
of 2,6-diacetylpyridine (2 g, 12.3 mmol) with 2-(tosylamino)aniline
(6.4 g, 24.6 mmol) in ethanol (250 cm3). The solution was heated
under reflux over a 5-h period, concentrated with a DeanϪStark
trap to ca. 30 mL and cooled during 12 h (4 °C). The yellow pre-
cipitate that then formed was collected by filtration and purified
by Soxhlet extraction (with EtOH as solvent) over a period of 12 h.
The resulting solid was finally washed with diethyl ether (3 ϫ
10 mL) and dried in vacuo.
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as supporting electrolyte, was electrolysed using a platinum wire as
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as: Pt(Ϫ) | H2DAPATs ϩ MeCOMe | M(ϩ), where M ϭ Mn, Fe,
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suitable for X-ray diffraction studies. The other complexes were
obtained by the same method, using the appropriate metal anode.
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single X-ray diffraction studies, were obtained by slow concen-
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Eur. J. Inorg. Chem. 2003, 3193Ϫ3200