Metallo-helicates with an N4-Schiff base containing a flexible alkyl spacer

Article abstract of DOI:10.1016/S0020-1693(02)01441-X

Neutral Mn(II), Fe(II) and Co(II) complexes with an N-tosyl substituted N₄-Schiff base containing a tetra-methylene spacer have been prepared. The X-ray crystal structures of ligand H₂BTs [N,N′-bis(2-tosylaminobenzylidene)-1,4-diaminobutane] and helical Co(BTs)·0.5H₂BTs have been solved. The Co(II) ion assumes a distorted tetrahedral coordination geometry, involving the four donor N-atoms of the dianionic ligand. Additionally, secondary interactions between the metal centre and one of the O-atoms of each tosyl group were detected. These groups are differently conformed, so that the ligand behaves as a non-symmetric helicand.

Full text of DOI:10.1016/S0020-1693(02)01441-X

Inorganica Chimica Acta 347 (2003) 53Á60
/
www.elsevier.com/locate/ica
Metallo-helicates with an N4-Schiff base containing a flexible alkyl
spacer
M.R. Bermejo *, J. Sanmart´ın, A.M. Garc´ıa-Deibe, M. Fondo, F. Novio, D. Navarro
Departamento de Qu´ımica Inorga´nica, Facultade de Qu´ımica, Universidade de Santiago de Compostela, Campus Sur, Santiago de Compostela 15782,
Spain
Received 11 March 2002; accepted 27 May 2002
Dedicated to Professor Rafael Uso´n on the occasion of his 75th birthday
Abstract
Neutral Mn(II), Fe(II) and Co(II) complexes with an N-tosyl substituted N4-Schiff base containing a tetra-methylene spacer have
been prepared. The X-ray crystal structures of ligand H2BTs [N,N?-bis(2-tosylaminobenzylidene)-1,4-diaminobutane] and helical
Co(BTs)×/0.5H2BTs have been solved. The Co(II) ion assumes a distorted tetrahedral coordination geometry, involving the four
donor N-atoms of the dianionic ligand. Additionally, secondary interactions between the metal centre and one of the O-atoms of
each tosyl group were detected. These groups are differently conformed, so that the ligand behaves as a non-symmetric helicand.
# 2002 Elsevier Science B.V. All rights reserved.
Keywords: Supramolecular chemistry; Helicates; Metal complexes; Schiff bases; X-ray crystal structures
1. Introduction
adequate to prepare tetra-coordinated single helicates,
better than double helicates or cages [5]. However, a
flexible three-membered spacer derived from 1,3-diami-
nopropane provides a notable versatility. This spacer
allows obtaining both single and double helical metal
complexes, even when metal ionic radii and coordina-
tion geometries are quite similar. In fact, we have
The synthesis and characterisation of self-assembled
supramolecular structures is a topical area in inorganic
chemistry, as an approach to materials with novel
physicochemical properties [1]. The general construction
principles of helical complexes, and particularly double
helicates, have been thoroughly investigated and are
well-established at present [2]. It is also well-known that
some aspects related to the ligand spacer (length,
flexibility, aromaticity, etc.) play an important role,
which can be crucial, in the obtaining of helicates and
even on the microarchitecture of the helix [3,4].
reported two [4ꢀ4] nickel(II) and zinc(II) bishelicates
/
[6,7], as well as cobalt(II) and copper(II) monohelicates
[7] prepared with N,N?-bis(2-tosylaminobenzylidene)-
1,3-diaminopropane. Likewise, we have recently com-
municated the synthesis and X-ray characterisation of a
trinuclear double helicate with a bis(2,3-dihydroxyben-
zylidene)diimine linked by a (CH2)4 spacer [8]. Mono-
and dinuclear copper complexes with a symmetrical N4-
diimine containing this alkyl spacer have also been
reported [9].
A bis(2-tosylaminobenzylidene)diimine linked by a
rigid two-membered spacer, as trans-1,2-diaminocyclo-
hexane or 1,2-diaminobenzene residues, seems clearly
Here, we would like to explore how the flexibility of
the 1,4-diaminobutane residue spacer can influence the
obtaining of metal(II) helicates with this type of N-tosyl
substituted N4-Schiff base ligands (Scheme 1).
* Corresponding author. Tel.: ꢀ
525.
E-mail address: qimb45@uscmail.usc.es (M.R. Bermejo).
/
34-981-591-076; fax: ꢀ34-981-597-
/
0020-1693/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved.
doi:10.1016/S0020-1693(02)01441-X

54
M.R. Bermejo et al. / Inorganica Chimica Acta 347 (2003) 53Á60
/
2.3. Ligand synthesis
N,N?-Bis(2-tosylaminobenzylidene)-1,4-diaminobu-
tane (H2BTs) was prepared by condensation of 2-
tosylaminobenzaldehyde (5.0 g, 18.16 mmol) [12] with
1,4-diaminobutane (0.80 g, 9.1 mmol) in a chloroform
solution (150 cm3). This was heated at reflux (about
70 8C) in a DeanÁStark trap reducing the volume to ca.
/
50 cm3 over a 6-h period. The resultant solution was
filtered and then concentrated. The obtained powdery
yellow solid was collected by filtration, washed with
methanol and diethyl ether (30 ml), and finally, dried in
vacuum. Yield 5.1 g (93%); Anal. Found: C, 63.3; H,
10.0; N, 9.0; O, 10.1; S, 10.5. Calc. for C32H34N4O4S2:
C, 63.8; H, 10.6; N, 9.3; O, 10.6; S, 10.6%; IR spectro-
Scheme 1. Schematic representation of H2BTs ligand and labelling
scheme for 1H NMR studies.
2. Experimental
2.1. Materials and methods
scopy (KBr, cmꢁ1): n(NÁ
n(CÁN) 1330(s), nas(SO2) 1294(s), ns(SO2) 1159(s); FAB
/
H) 3400(w), n(Cꢀ
/
N) 1636(s),
/
Chemicals of the highest commercial grade available
(Aldrich) were used as received. Metals (Aldrich) were
used as plates and washed with a dilute solution of
hydrochloric acid prior to the electrochemical proce-
dure.
(m/z): 603.2 (100%, Mꢀ). 1H NMR (250 MHz, DMSO-
d6, ppm) d 12.43 (b, 2H, Ha), 8.57 (s, 2H, Hb), 7.57 (d,
4H, Hg), 7.50 (m, 4H, Hf, Hc), 7.36 (t, 2H, He), 7.06 (t,
2H, Hd), 7.00 (d, 4H, Hh), 3.74 (m, 4H, Hj), 2.04 (s, 6H,
Hi), 1,83 (m, 4H, Hk). DR (nm): 440(vs), 335(vs) and
275(vs).
Elemental analyses were performed on a CarloÁErba
/
EA 1108 analyser. The NMR spectra were recorded on a
Bruker DPX-250 spectrometer, using DMSO-d6 as
solvent. Infrared spectra were recorded in the range
4000Á
spectrophotometer. Electrospray mass spectra were
performed on a HewlettÁPackard LC/MS spectrometer,
/
600 cmꢁ1 as KBr pellets on a Bio-Rad FTS 135
2.4. Complexes syntheses
/
Complexes have been obtained by an electrochemical
method [13], in which a metal anode was oxidised in an
acetonitrile solution of H2BTs. A typical preparation is
outlined below.
employing acetonitrile as solvent. Diffuse reflectance
spectra were recorded on a Shimadzu UV-3103 PC
spectrophotometer. UVÁ
were registered in the range 250Á
/
Vis spectra of DMF solutions
800 nm on a HP 8452
/
The cell can be summarised as: Co(ꢀ) j H2BTsꢀ
/
spectrophotometer. Magnetic susceptibility measure-
ments were performed on pulverised samples at room
temperature with a Quantum Design MPMS-5 SQUID
magnetometer.
MeCNꢀ
/
NMe4ClO4 j Pt(ꢁ). An acetonitrile solution
(80 cm3) of H2BTs (100 mg, 0.166 mmol), containing
about 30 mg of tetramethylammonium perchlorate, was
electrolysed for 1 h and 47 min using a current intensity
of 5 mA and a voltage of 14 V. A platinum wire was
used as cathode and a cobalt sheet as anode. (Caution:
although no problem has been encountered in this work,
all perchlorate compounds are potentially explosive, and
should be handled in small quantities and with great
care!) Filtration and concentration of the resulting
solution to a third of its initial volume yielded a reddish
solid. This was washed with diethyl ether and vacuum
dried. Likewise, we have prepared in nitrogen atmo-
sphere Mn(II) and Fe(II) complexes of the type
2.2. X-ray diffraction studies
Two crystal structures were determined: Co(BTs)×
0.5H2BTs and H2BTs×H2O. Their data were collected
at room temperature on a Siemens CCD diffractometer,
/
/
using graphite-monochromated Mo Ka radiation (lꢂ
/
˚
0.71073 A) from a fine focus sealed tube source. The
structures were solved by direct methods (SHELXS-97)
[10] and refined by full-matrix least-squares techniques
M(BTs)×
/
xH2O (Mꢂ
/
Mn, Fe, Co; xꢂ
/
1Á
/
5). Mn(BTs)×
/
(
SHELXL-97) [10]. All non-hydrogen atoms were aniso-
H2O could also be prepared by two chemical methods
with equivalent yield: (a) refluxing an ethanol solution
containing H2BTs, NaOH and Mn(acac)2 (1:2:1) for 6 h
or (b) using Mn(ClO4)2 instead of Mn(acac)2 and simply
stirring at room temperature (r.t.) for 96 h. The end of
these reactions was determined by TLC chromatogra-
phy.
tropically treated. All hydrogen atoms were included in
the model at geometrically calculated positions and
refined using a riding model, except those bonded to
water molecules, which were located from the difference
map, their thermal parameter and coordinates were
fixed. Molecular graphics were represented by ORTEP-3
for Windows [11].

M.R. Bermejo et al. / Inorganica Chimica Acta 347 (2003) 53Á
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55
2.4.1. Mn(BTs)×/5H2O
3.2. Single crystal X-ray diffraction studies
Gray solid. Yield 80%. M.p.: 270 8C. Anal. Found:
C, 51.1; H, 5.4; N, 7.7; S, 8.6; Calc. for C32H42Mn-
N4O9S2: C, 51.5; H, 5.7; N, 7.5; S, 8.6%; IR (KBr,
Slow evaporation of saturated solutions of H2BTs
(HCCl3) and Co(BTs)×H2O (MeCN) yielded prismatic
crystals of H2BTs×H2O (yellow) and Co(BTs)×0.5H2BTs
/
cmꢁ1): n(OÁ
/
H) 3443(b), n(Cꢀ
1303(s), nas(SO2) 1262(s), ns(SO2) 1122(s); FAB (m/z):
656.3 (25%, Mꢀꢁ
5H2O). Magnetic moment: 5.8 BM.
DR (nm): 515(sh) (4T1g(G)16A1g), 455(sh), 350(vs),
275(vs).
/
N) 1623(s), n(CÁ
/
N)
/
/
(red), respectively, resulting to be suitable for single
crystal X-ray diffraction studies. The ligand molecular
structure appears in both crystal units with two different
spatial arrangements. We think that a joint discussion of
their general features is the most adequate, and subse-
quently the complex molecular structure will be sepa-
rately discussed. Table 1 summarises crystal data, data
collection and refinement parameters of both crystal
structures.
/
/
2.4.2. Fe(BTs)×/5H2O
Orangish solid. Yield 70%. M.p.: 285 8C. Anal.
Found: C, 53.9; H, 5.2; N, 7.5; S, 8.8; Calc. for
C32H42FeN4O9S2: C, 54.1; H, 5.4; N, 7.9; S, 9.0%; IR
(KBr, cmꢁ1): n(OÁ
/
H) 3440(b), n(Cꢀ
N) 1298(s), nas(SO2) 1262(s), ns(SO2) 1130(s); FAB (m/
z): 656.2 (45%, Mꢀꢁ
5H2O). Magnetic moment: 5.2
BM. DR (nm): 875 (5Eg15T2g), 475(vs) (Fe(II)0
p*
MLCT), 340(vs), 275(vs). UVÁVis (DMF, 0.001 M,
nm): 465 (Fe(II)0p* MLCT),
/
N) 1612(s), n(CÁ
/
3.2.1. H2BTs molecular structures
The crystal structure of H2BTs×
/
H2O was solved,
/
despite its very weak diffraction, prior to preparing its
metal complexes. This ligand molecular structure (1a) is
shown in Fig. 1. Its asymmetric unit additionally
contains a water molecule in two disordered occupation
sites (50% probability), which was omitted for clarity.
Likewise, half molecule of the free ligand was also found
/
/
/
/
2.4.3. Co(BTs)×
/
H2O
Red solid. Yield 67%. M.p.: 230 8C. Anal. Found: C,
56.3; H, 5.3; N, 8.5; S, 9.1; Calc. for C32H34CoN4O5S2:
in the Co(BTs)×
molecule (1b) shown in Fig. 2 is symmetry generated
(ꢁxꢀ1, ꢁyꢀ1, ꢁzꢀ1) since it is located on an
/0.5H2BTs asymmetric unit. The whole
C, 56.7; H, 5.1; N, 8.3; S, 9.5%; IR (KBr, cmꢁ1): n(OÁ
/
/
/
/
/
/
/
H) 3452(b), n(Cꢀ
1262(s), ns(SO2) 1138(s); FAB (m/z): 660.1 (62%, Mꢀ
H2O). Magnetic moment: 4.0 BM. DR (nm): 1380
(4T1(F)14A2), 525 (4T1(P)14A2), 430(sh), 355(vs),
270(vs). UVÁVis (DMF, 0.001 M, nm): 530
(4T1(P)14A2).
/
N) 1623(s), n(CÁN) 1295(s), nas(SO2)
/
inversion centre. Some selected bond distances and
angles are listed in Table 2 for both molecules.
Bond lengths and angles are within the usual range
found in other very related and previously characterised
ꢁ
/
/
/
/
/
Table 1
Crystal and structure refinement data
H2BTs×/H2O
Co(BTs)×0.5H2BTs
/
3. Results and discussion
Empirical formula
M
C32H36N4O5S2
620.77
C48H49CoN6O6S3
961.04
3.1. Analytical and spectroscopic data
Crystal system
Space group
Crystal dimensions
(mm3)
monoclinic
P21/c
monoclinic
P21/c
The found empirical formula of the type M(BTs)×
/
0.51ꢃ
/
0.44ꢃ
/0.43
0.47ꢃ
/
0.39ꢃ0.26
/
xH2O (MꢂMn, Fe, Co; xꢂ1Á5) suggests that the
/
/
/
ligand used acts as bisdeprotonated in these neutral
complexes.
˚
a (A)
10.782(3)
15.326(4)
20.113(5)
91.432(5)
3322.7(14)
293(2)
8.593(2)
20.425(5)
26.615(7)
93.164(5)
4664(2)
293(2)
˚
b (A)
˚
c (A)
Electrospray mass spectra show medium intensity
peaks related with M(BTs) fragments for all the com-
plexes, as expected for monomeric species. This points
out rather to a solvated nature, than to a coordinating
behaviour of water molecules in these complexes.
IR spectra of these complexes show a shifting in the
b (8)
3
U (A )
˚
T (K)
Z
m(Mo Ka) (mmꢁ1
Max. and min. trans-
4
0.204
4
0.5584
)
1.000000 and
0.623595
4785
1.000000 and
0.857354
27686
24 cmꢁ1 to lower wavenumber values of n(Cꢀ
/
mission
Reflections collected
range 13Á
N) respect to the observed for the free ligand. Other
bands attributable to n(CÁN), nas(SO2) and ns(SO2)
/
Independent reflections 4785
Rint
9585
0.0465
9585/0/577
/
0.0000
4785/0/400
modes undergo substantial shifts to lower values as a
result of the coordination. These facts and the absence
Data/restraints/para-
meters
R1, wR2 [I ꢀ
/
2s(I)]
0.0798, 0.2177
0.1392, 0.2725
0.0394, 0.0814
0.0976, 0.1014
of the n(NÁ
participation of the amide and imine N-atoms in the
coordination to the metal centre [5Á7].
/H) band, are in agreement with the
R1, wR2 (all data)
ꢁ3
˚
Residuals (e A
)
0.657, ꢁ
/
0.241
0.496, ꢁ0.283
/
/

56
M.R. Bermejo et al. / Inorganica Chimica Acta 347 (2003) 53Á60
/
related ligands similarly conformed [5a,15] have yielded
monohelicates [5]. Likewise, anti-open conformed bind-
ing domains of 1b seem more adequate to coordinate
two different metal centres, as occurred for another
related ligand conformed alike [14a], which have yielded
[4ꢀ
[6,7].
With respect to the interactions that lead to these two
/4] bishelical complexes, as well as monohelicates
conformations we can say that a face-to-face p-stacking
interaction seems to exist between both terminal tosyl
rings for each ligand [5a,14b,15] conformed as 1a.
˚
(interplane mean distance of ca. 4.3 A and aꢂ
/
20.48).
This molecule also presents intramolecular edge-to-face
interactions between benzylidene and tosyl rings (CÁ
/
˚
Hꢀ ꢀ ꢀcentroid distances about 2.8 A). On the contrary,
Fig. 1. ORTEP view of H2BTs (1a) from H2BTs×H2O crystal structure.
Ellipsoids are drawn at 30% probability and parentheses and water
molecules are omitted for clarity.
/
no intramolecular p-stacking interactions are possible in
1b, as Fig. 2 clearly shows, but a significant intermole-
cular face-to-face p-interaction appears to exist between
a terminal tosyl group of 1b and one of the benzylidene
compounds [5a,14,15] and do not merit further discus-
sion. Typical hydrogen bonds are present between the
amide N-atoms and their contiguous imine ones (aver-
˚
rings of the Co(II) complex (centroids at 3.9 A, aꢂ
/
21.68). This and other weaker p-stacking interactions
are responsible for the crystal packing of 1a and 1b
˚
age Namide
Á
/
Hꢀ ꢀ ꢀNimine distances of 2.67 A). The most
˚
(face-to-face with centroids at 4.9Á
face with CÁ
Hꢀ ꢀ ꢀcentroids at 2.8Á
water molecule in 1a is also weakly interacting with an
/5.9 A, and edge-to-
remarkable feature of these two molecular structures is
their different spatial arrangement allowed by the
flexible (CH2)4 spacer.
˚
/
/
3.3 A). The solvated
˚
3.013(17) A].
O-atom of a tosyl group [O(2w)ꢀ ꢀ ꢀO(3)ꢂ
/
Fig. 1 shows that 1a displays a folded conformation
that resembles those displayed by other very related
ligands containing two-membered spacers as 1,2-cyclo-
hexanediamine [5a], ethylendiamine [14b] or ortho-
phenylenediamine [15] residues, whereas the anti-open
conformation [16] of 1b is similar to that observed in the
related Schiff base with a (CH2)3 spacer [14a]. These two
different conformations for 1a and 1b could be indica-
tive of a potential versatility of H2BTs to yield
compounds of different nuclearity. Thus, 1a seems
predisposed to provide a single N4 compartment by
simple rapprochement of both bidentate donor domains
and the subsequent tosyl groups repulsion. In fact,
3.2.2. Co(BTs) molecular structure
The molecular structure of the neutral complex
Co(BTs) coexists in the Co(BTs)×0.5H2BTs asymmetric
unit with half molecule of H2BTs (whose molecular
structure has been discussed above). The ORTEP view
[11] of this Co(II) complex with the atom labelling
scheme is shown in Fig. 3, whilst Table 2 lists the most
relevant bond distances and angles. Fig. 3 shows that
coordination of the four potential donor N-atoms wrap
the bisdeprotonated Schiff base ligand around the Co(ii)
/
centre, as a non-symmetric helicand. These CoÁ
/N
distances show very similar values, being in the usual
Fig. 2. ORTEP view of the H2BTs (1b) molecule contained in the unit cell of Co(BTs)×
/0.5H2BTs. Ellipsoids are drawn at 50% probability and
parentheses are omitted for clarity.

M.R. Bermejo et al. / Inorganica Chimica Acta 347 (2003) 53Á
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57
Table 2
Selected bond distances and angles for ligand H2BTs×
/
H2O and complex Co(BTs)×
0.5H2BTs
H2BTs (1b)
/0.5H2BTs
H2BTs×
/
H2O (1a)
Co(BTs)×
/
Co(BTs)
Bond lengths
N(2)Á
N(2)Á
N(3)Á
N(3)Á
S(1)Á
S(1)Á
S(1)Á
S(2)Á
S(2)Á
S(2)Á
/
C(14)
C(15)
C(18)
C(21)
1.275(8)
1.468(8)
1.450(8)
1.259(8)
1.624(5)
1.424(5)
1.430(5)
1.603(5)
1.455(5)
1.409(5)
N(6)Á
/
C(53)
C(54)
1.268(4)
1.462(4)
Co(1)Á
Co(1)Á
Co(1)Á
Co(1)Á
N(2)Á
N(2)Á
N(3)Á
N(3)Á
N(1)Á
N(4)Á
/
N(1)
N(2)
N(3)
N(4)
1.978(2)
1.993(2)
1.999(2)
1.989(2)
1.279(4)
1.476(3)
1.477(3)
1.271(3)
1.609(2)
1.603(2)
/
N(6)Á
/
/
/
/
/
/
/
N(1)
O(1)
O(2)
N(4)
O(3)
O(4)
S(3)Á
S(3)Á
S(3)Á
/
N(5)
O(5)
O(6)
1.630(2)
1.425(2)
1.434(2)
/
C(14)
C(15)
C(18)
C(19)
S(1)
/
/
/
/
/
/
/
/
/
/
/
/
S(2)
Bond angles
C(14)ÁN(2)Á
C(18)ÁN(3)Á
S(1)ÁN(1)Á
S(2)ÁN(4)Á
O(1)ÁS(1)Á
O(3)ÁS(2)Á
/
/
C(15)
119.7(6)
120.3(6)
128.7(5)
128.5(4)
119.9(3)
118.7(3)
C(53)Á
S(3)ÁN(5)Á
O(5)ÁS(3)Á
/
N(6)Á
/
C(54)
118.6(3)
120.8(2)
119.35(15)
N(1)Á
N(1)Á
N(1)Á
N(2)Á
N(2)Á
N(3)Á
/
Co(1)Á
Co(1)Á
Co(1)Á
Co(1)Á
Co(1)Á
Co(1)Á
/
N(2)
N(3)
N(4)
N(3)
N(4)
N(4)
92.65(9)
/
/C(19)
/
/
122.58(9)
127.61(9)
98.21(9)
121.78(9)
92.55(9)
/
/
C(8)
/
/
C(47)
/
/
/
/
C(25)
/
/
/
/
O(2)
O(4)
/
/O(6)
/
/
/
/
/
/
Intramolecular distances
N(2)ꢀ ꢀ ꢀN(3)
4.667
6.123
N(6)ꢀ ꢀ ꢀN(6)#1
N(5)ꢀ ꢀ ꢀN(5)#1
5.128
9.362
N(2)ꢀ ꢀ ꢀN(3)
N(1)ꢀ ꢀ ꢀN(4)
3.018
3.560
N(1)ꢀ ꢀ ꢀN(4)
Torsion angles
N(2)Á
C(16)Á
C(15)Á
/
C(15)Á
C(17)Á
C(16)Á
/
C(16)Á
C(18)Á
C(17)Á
/
C(17)
ꢁ
/
64.1(8)
60.8(8)
178.3(6)
N(6)Á
/
C(54)Á/C(55)Á
/
C(55)#1
61.9(5)
180.0
N(2)Á
C(16)Á
C(15)Á
/
C(15)Á
C(17)Á
C(16)Á
/
C(16)Á
C(18)Á
C(17)Á
/
C(17)
ꢁ
/
82.0(4)
75.5(4)
63.6(5)
/
/
/N(3)
ꢁ
/
/
/
/N(3)
ꢁ
/
/
/
/C(18)
ꢁ
/
C(54)Á/C(55)Á
/
C(55)#1 Á
/
C(54)#1
xꢀ1; ꢁ
/
/
/C(18)
Symmetry transformations used to generate equivalent atoms: #1: ꢁ
/
/
/
yꢀ
/
1; ꢁ
/
zꢀ1.
/
range for this type of complexes, although those
corresponding to the Nimine-atoms are slightly longer
corresponding aromatic rings, forming angles of 4.47
and 1.568.
than the CoÁ/Namide [7,18]. Additionally, one of the O-
atoms of each tosyl group [O(1) and O(4), respectively]
˚
is close to the Co(II) centre (2.806 and 2.635 A,
respectively). These Coꢀ ꢀ ꢀO distances cannot be con-
sidered as true coordinated bonds but, as they are
shorter than the sum of their van der Waals radii [17],
they can be regarded as secondary interactions. Thus,
the Co(II) coordination environment can be described as
pseudo-tetrahedral. This is confirmed by the dihedral
angle between the two NCoN terminal planes (uꢂ
/
78.658). This value indicates a lower distortion of the
tetrahedral geometry than that found for Co(PTs)
(69.388), which differs from Co(BTs) in that contains a
trimethylene spacer [7].
The found values for the NÁ
/
CoÁ
/
N angles (92.5Á
/
127.68) also support a distorted tetrahedral coordina-
tion. The bite angles related to the two terminal chelate
planes (ca. 92.58) are typical of this type of ligands [5Á7].
/
These two six-membered chelate rings are rather planar,
with maximum half-stepped distances to the least-
Fig. 3. ORTEP view of Co(BTs) contained in the asymmetric unit of
squares calculated plane of only ꢁ
/
0.067 and ꢀ0.049
/
Co(BTs)×
/
0.5H2BTs. Dotted lines indicate the secondary Coꢀ ꢀ ꢀO
˚
A, for their respective imine C-atoms, C(14) and C(19).
These planes keep a high planarity respect to their
interactions. Ellipsoids are drawn at 50% probability and parentheses
are omitted for clarity.

58
M.R. Bermejo et al. / Inorganica Chimica Acta 347 (2003) 53Á60
/
The highest bite angle value corresponds to the
(CH2)4 spacer, being logically higher than that corre-
sponding to a Co(II) complex containing the (CH2)3
spacer [7]. This seven-membered chelate ring shows a
scarce planar arrangement (half-stepped distances be-
˚
˚
tween ꢁ
/
0.438 and ꢀ
/
0.403 A, Co(1) at ꢀ0.179 A) as
/
corresponds to an aliphatic chain. Its Newman projec-
tions show an all-gauche conformation, which is typical
of mononuclear compounds, although with a wide range
of torsion angles (35Á
H2BTs in both conformations studied above, where
exhibits a rather regularly staggered gauche Áanti Á
gauche series (torsion angles 54Á648), which also allows
/
828). This clearly differs from free
/
/
/
to observe only two methylene signals in the free ligand
1H NMR spectrum [3.74 (m, 4H, Hj), 1,83 (m, 4H, Hk),
see Scheme 1]. The all-gauche conformation shown by
the complex is possible by simple rotation around the
central CÁC bond of the free ligand. This leads to
/
approach the four donor N-atoms with respect to the
free ligand (1a), as the remarkable shortening of the
Nimineꢀ ꢀ ꢀNimine and Namideꢀ ꢀ ꢀNamide distances shows
(Table 2). This allows to wind the ligand around the
cobalt ion forming the helical complex.
Fig. 4. Sticks representations of Co(BTs) showing the wrapping angle
and pitch of its left-handed helix (M).
The Co(II) single-stranded helical complex can be
considered as saturated [2a], as the Schiff base fulfils the
stereochemical requirements of the Co(II) ion. Since the
P21/c space group is centrosymmetric, two enantiomeric
pairs of (M)- and (P)-helixes are present in the unit cell,
as well as two free ligand molecules. In view of the
significant changes that both wrapping angle or pitch
values can show depending on different considerations
(actual helix top-ends, helical axis declination, . . .) only
some qualitative aspects will be considered. Thus, if we
only consider the donor atoms, Co(BTs) does not
complete a whole twist around the Co(II) centre, so
that the wrapping angle would be less than 3608 (ca.
2788). Anyway, its longer spacer allows an angle
significantly higher than that found for Co(PTs)
(2648), where the spacer is (CH2)3 [7]. However, if we
consider the whole ligand, the tosyl groups clearly
exceed a whole turn as Fig. 4 shows (top). Similar
problems do not allow an easy calculation of the pitch.
However, if we consider the quasi-superimposition of
N(4) and S(1) shown in Fig. 4 (bottom), an approxima-
tion could be regarded as their intramolecular distance is
3.3. UVÁVis and magnetism
/
The diffuse reflectance spectrum of H2BTs displays
three absorption bands at about 275, 335 and 440 nm
that can also be observed slightly shifted for the
corresponding complexes. UVÁ
/
Vis spectra for
Co(BTs)×H2O show the two bands expected for a
/
tetrahedral geometry, both in solid state and solution.
This could indicate that the tetrahedral geometry
observed in solid state, remains in solution, even in a
coordinating solvent as DMF. Room temperature
magnetic moment values measured for Co(BTs)×
and Co(BTs)×0.5H2BTs (4.0 and 3.9 BM, respectively)
are considerably lower than those expected for a Co(II)
ion in a tetrahedral field (4.4Á4.8 BM). However, it
/H2O
/
/
must be noted that values around 4.3 BM have been also
found for X-ray characterised tetrahedral cobalt(II)
complexes containing related Schiff base ligands [7,19].
Fe(BTs)×
/
5H2O presents a magnetic moment value
(5.2 BM) coherent with an octahedral geometry. The
diffuse reflectance spectrum of this complex displays,
apart from the typical intraligand absorptions, a very
strong metal to ligand charge transfer band reported for
Fe(II) pseudooctahedrally coordinated [20]. A weak and
˚
about 4.26 A.
Finally, there is a clear steric hindrance between both
tosyl groups that also favours the helical arrangement,
but they are differently conformed. Many subtle factors
can lead to this difference. In this case, they could be
related to the rather high values of wrapping and pitch,
allowing that the tosyl groups do not need to adopt an
opposite pseudo-apical disposition. Likewise, it could be
broad dÁd transition, which is characteristic of a high
/
spin d6 octahedral configuration, can be detected at
about 875 nm. This band shows a secondary lower
energy component at about 1175 nm, arising from a
JahnÁ
excited state [21].
Mn(BTs)×5H2O presents a typical magnetic moment
(5.8 BM) of a high spin d5 configuration. The diffuse
/
Teller distortion in the (t2g)3 (eg)3 electronically
associated to the profuse pÁ
/
p interactions above men-
/
tioned.

M.R. Bermejo et al. / Inorganica Chimica Acta 347 (2003) 53Á
/60
59
reflectance spectrum displays
shoulder at about 515 nm. Although this could be
a
scarcely defined
Copies of this information may be obtained free of
charge from The Director, CCDC, 12 Union Road,
4
attributable to the T1g(G)1
/
6A1g transition, expected
Cambridge, CB2 1EZ, UK (fax: ꢀ44-1223-336-033;
/
for a high spin Mn(II) complex in an octahedral field, its
low absorption intensity leads to take this attribution
with caution.
e-mail: deposit@ccdc.cam.ac.uk or www: http://
www.ccdc.cam.ac.uk).
The octahedral geometry postulated for the Fe(II)
and Mn(II) complexes requires involving two additional
bond interactions, apart from those established with the
N4 donor set of the Schiff base. Both terminal tosyl
groups of BTs2ꢁ seem to exert a very significant steric
hindrance that could prevent to achieve further coordi-
nation to exogenous ligands, even those so small as
water molecules. This hypothesis is supported by mass
spectrometry data and the X-ray crystal structure
described for the Co(II) complex as well. Thus, we
attribute these pseudooctahedral environments to stron-
Acknowledgements
The authors are grateful to Xunta de Galicia
(PGIDT99XI20903B) for financial support.
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