Crystallisation solvent influence on the crystal structures of MnII and NiII complexes with 2,6-bis(1-salicyloylhydrazonoethyl)pyridine, H4daps

Article abstract of DOI:10.1002/(sici)1521-3749(200002)626:2<506::aid-zaac506>3.0.co;2-e

Neutral manganese and nickel complexes of the empirical formulae Mn(H₂daps)(H₂O)_0.5 and Ni(H₂daps) · (H₂O)_1.5(CH₃CN) have been prepared by electrochemical syntheses. The structur

Full text of DOI:10.1002/(sici)1521-3749(200002)626:2<506::aid-zaac506>3.0.co;2-e

Crystallisation Solvent Influence on the Crystal Structures of MnII and NiII
Complexes with 2,6-bis(1-salicyloylhydrazonoethyl)pyridine, H4daps
Manuel R. Bermejo*, Antonio Sousa*, Matilde Fondo, Ana M. GonzaÂlez, Olga L. Hoyosa, Rosa Pedrido, Miguel
A. Maestrob, Jose MahõÂab
Santiago de Compostela/Spain, Departamento de QuõÂmica InorgaÂnica, Facultad de QuÂõmica, Universidad de Santiago de Com-
postela, E-15706
a PopayaÂn/Colombia, Departamento de QuõÂmica, Universidad del Cauca
b La CorunÄa/Spain, Servicios Generales de Apoyo a la InvestigacioÂn, Universidad de La CorunÄa
Received June 24th, 1999.
Abstract. Neutral manganese and nickel complexes of the
empirical formulae Mn(H2daps)(H2O)0.5 and Ni(H2daps) ´
(H2O)1.5(CH3CN) have been prepared by electrochemical
syntheses. The structures of the complexes formed from sol-
vents with different donor ability were investigated. Recrys-
tallisation of Mn(H2daps)(H2O)0.5 from pyridine and ethanol
yields [Mn(H2daps)(py)2] 1 and [Mn(H2daps)(C2H5OH) ´
(H2O)] 2. Slow evaporation of dichloromethane and metha-
nol solutions of Ni(H2daps)(H2O)1.5(CH3CN) allows the iso-
lation of single crystals of [Ni2(H2daps)2] ´ CH2Cl2 4 and
[Ni2(H2daps)2(CH3OH)2] ´ 3 CH3OH ´ H2O 5, suitable for X-
ray diffraction studies. Recrystallisation of 4 from pyridine
yields [Ni2(H2daps)2(py)2] ´ CH2Cl2 6, previously charac-
terised by us. This study shows the versatility of the H4daps
ligand and the influence that the crystallisation solvent can
have on the crystal structure of these complexes.
Keywords: Manganese complexes; Nickel complexes; Helical
structures; Schiff bases; Solvent effects
Einfluss des Losungsmittels auf die Kristallstrukturen der MnII-
È
und NiII-Komplexe von 2,6-Bis(1-salicyloylhydrazonoethyl)pyridin, H4daps
InhaltsuÈbersicht. Mittels Elektrosynthese wurden die neu-
tralen Mangan- und Nickel-Komplexe Mn(H2daps) ´
0,5 (H2O) und Ni(H2daps) ´ (H2O) ´ 1,5 (CH3CN) syntheti-
siert. An Komplexen, die aus LoÈsungsmitteln unterschied-
licher DonorstaÈrke auskristallisiert waren, wurden Struk-
turuntersuchungen durchgefuÈhrt. Mn(H2daps) ´ 0,5 (H2O)
kristallisiert aus Pyridin bzw. Ethanol als [Mn(H2daps)(py)2]
1 bzw. [Mn(H2daps) ´ (C2H5OH)(H2O)] 2, die kristallogra-
phisch charakterisiert wurden. Durch langsames Eindunsten
der LoÈsungen von [Ni(H2daps)2] ´ 1,5 (H2O) ´ (CH3CN) in
Dichlormethan bzw. Methanol konnten fuÈr die RoÈntgenbeu-
gung geeignete Einkristalle von [Ni2(H2daps)2] ´ (CH2Cl2) 4
und [Ni2(H2daps)2(CH3OH)] ´ 3 (CH3OH) ´ (H2O) 5 erhal-
ten werden. Umkristallisieren von 4 aus Pyridin ergab
[Ni2(H2daps)2(py)2] 6, welches wir schon fruÈher charakteri-
siert hatten. Die Untersuchungen belegen den Einfluss des
H4daps-Liganden und des eingebauten LoÈsungsmittels auf
die Kristallstrukturen der Komplexe.
Introduction
some emerging patterns [6, 7]. However, many ques-
tions still remain and the predicted systems are not al-
ways obtained.
The desire for an in depth understanding of the
rules that lead to helicates and other systems of differ-
ent nuclearity, together with their pharmacological ac-
tivity [10±12], as well as their interesting electric and
magnetic properties [13±15], makes further investiga-
tion into the chemistry of hydrazone ligands even
more attractive.
We have recently characterised one manganese and
two dinickel complexes containing H4daps in its dian-
ionic form [16]. We have found that the manganese
complex is a mononuclear compound when it is re-
crystallised in a donor solvent, such as pyridine. In
contrast, the nickel complexes occur as a double heli-
cal structure when recrystallised from both dichloro-
methane and pyridine.
The properties of hydrazone ligands have been largely
investigated in the past few years [1±9]. The interest
in the co-ordination chemistry of this type of ligand
has increased, in part, due to the interesting donor
systems which could result. Intense activity has been
focussed on this new field in order to design ligands
which can control the selective preparation of compli-
cated, organised chemical architectures. The structural
characterisation of the resultant complexes has led to
* Manuel R. Bermejo,
Departamento de QuõÂmica InorgaÂnica,
Facultad de QuõÂmica,
Universidad de Santiago de Compostela,
15706 Santiago de Compostela, Spain,
Telephone number: 00-31-(9)81-59 10 76,
Fax number: 00-31-(9)81-59 75 25
E-mail address: qimb45@uscmail.usc.es
506
Ó WILEY-VCH Verlag GmbH, D-69451 Weinheim, 2000
0044±2313/00/626506±513 $ 17.50+.50/0
Z. Anorg. Allg. Chem. 2000, 626, 506±513

About Solvent Influence on the Crystal Structure of MnII and NiII Complexes
Previous results in the literature seemed to indicate
that if a metal ion with a strong ligand field-imposed
preference for an octahedral geometry was selected,
together with a ligand with a central pyridine unit and
two other bidentate domains in each thread was used,
a double helicate would result [7]. The only difficulty
to get helicates would be to prevent the metal centres
from adopting a pentagonal bipyramidal geometry.
This could be avoided by introducing bulky substitu-
ents on the hydrazone. Thus, it seemed that H4daps
could be an appropriate ligand to obtain helical com-
pounds. An additional complication in these systems,
however, is that the solvent of crystallisation appears
to play an important role in the preparation of heli-
cates. It has previously been reported that the pres-
ence of a good donor solvent could break the pyridine
bridges in a double helical complex to give rise to
monomeric compounds with a co-ordination number
of seven [7].
With these considerations in mind we were inter-
ested in checking the effect of the solvent of recrystal-
lisation on the nuclearity of complexes mentioned
above. For this reason, we have prepared again the re-
ported manganese and nickel complexes and they
were recrystallised in solvents of different donor prop-
erties in order to study their behaviour. In this paper
we describe the results achieved.
bipyramid, with the apical positions filled with two
pyridine molecules. As the pyridine solvent is a good
donor, we were interested in knowing if Mn(H2daps) ´
(H2O)0.5 could be a helical compound where the pyri-
dine bridges were broken by the presence of pyridine
as solvent. For this reason, we tried to recrystallise
Mn(H2daps)(H2O)0.5 from a poorer donor solvent.
Unfortunately, this complex is insoluble in non polar
or chlorinated solvents such as carbon tetrachloride,
chloroform and dichloromethane, but it is sparingly
soluble in alcohols. Recrystallisation from ethanol
allowed us to isolate crystals of [Mn(H2daps) ´
(C2H5OH)(H2O)] 2, suitable for X-ray diffraction stu-
dies.
FAB mass and IR spectra and magnetic measurements
The FAB mass spectrum of 2 shows a peak (Table 1)
due to the fragment [Mn(H2daps)]+ at 485 amu, that
indicates co-ordination of the ligand to the metal. No
fragments containing ethanol or water could be ob-
served.
The IR spectrum shows a negative shift of 63 cm±1
and 62 cm±1 of the amide I [m(CO)] and amide II
[d(NH) + m(CN)] modes, respectively. This behaviour
suggests the participation of the oxygen atoms of both
carbonyl CO groups in co-ordination to the metal, in
agreement with previous results [18]. The spectrum
also shows the absence of the m(N±H) band, which in
the free ligand appears at 3208 cm±1. This is in accord-
ance with the dianionic nature of the ligand. This is
further supported by the room temperature magnetic
moment of 5.6 B.M., which is consistent with the pres-
ence of a magnetically dilute high spin MnII ion [19].
Results and Discussion
Mn(H2daps)(H2O)0.5 and Ni(H2daps)(H2O)1.5(CH3CN)
have been prepared by means of an electrochemical
synthesis, as previously reported [16, 17]. The electro-
chemical efficiency of the cell is close to 0.5 molF±1 in
both cases, which is in accordance with the following
mechanism for the reaction:
Crystal structure of [Mn(H2daps)(C2H5OH)(H2O)] 2
Cathode: H4daps + 2e± ® H2(g) + H2daps2±
Anode: H2daps2± + M ® M(H2daps) + 2e±
An ORTEP view of the compound is shown in Fig. 1.
Experimental details are given in Table 2 and selected
bond lengths and angles in Table 3.
Manganese complexes. Recrystallisation of Mn(H2daps) ´
(H2O)0.5 from pyridine allows the mononuclear com-
plex [Mn(H2daps)(py)2] 1 to be isolated, as previously
described [16]. It shows a pentagonal bipyramidal geo-
metry, with the ligand H4daps, acting as a pentaden-
tate donor, occupying the equatorial positions of the
The crystal structure of 2 shows the compound to
consist of a distorted pentagonal bipyramidal geome-
try about the manganese ion, with the pentadentate li-
gand H2daps2± occupying the equatorial belt of the bi-
pyramid. The pentadentate ligand gives rise to four
five-membered chelate rings. Four of the five angles
Table 1 Analytical and some selected data for the complexes
b)
Complex
Analysis (%)a)
C
leff
FABc)
Colour
N
H
Mn(H2daps)(H2O)0.5
Ni(H2daps)(H2O)1.5(CH3CN)
56.0(55.9)
53.6(53.9)
14.4(14.2)
15.4(15.1)
3.6(4.0)
4.6(4.5)
5.7
2.9
485
488
Dark orange
Yellow brown
976*
485
488
[Mn(H2daps)(C2H5OH)(H2O)] 2
[Ni2(H2daps)2(CH3OH)2] ´ 3 CH3OH ´ H2O 5
55.1(54.8)
53.5(53.1)
12.9(12.8)
11.1(11.1)
4.6(4.7)
4.9(5.2)
5.6
2.9
Dark orange
Yellow green
976*
a)
Found(calculated); b) In B.M.; c) Peaks corresponding to [ML]+ except * that correspond to [M2L2]+
Z. Anorg. Allg. Chem. 2000, 626, 506±513
507

M. R. Bermejo, A. Sousa, M. Fondo, A. M. GonzaÂlez, O. L. Hoyos, R. Pedrido, M. A. Maestro, J. MahÂõa
subtended at manganese by adjacent equatorial atoms
range from 67.3(2) to 69.71(18)° while the fifth angle
O1±Mn±O3 has a value of 84.89(17)°. This clearly
shows the distortion of the polyhedron from ideal geo-
metry (ideal value of a = 72°). The apical positions
are filled by a water and an ethanol molecules, from
the crystallisation solvents. The interaxial angle O1S±
Mn±O2S is 178.75(18)°, very close to the ideal value
of 180°. The structure of this compound is very similar
to those previously reported for manganese com-
pounds containing neutral hydrazone ligands [20] and
to [Mn(H2daps)(py)2] 1. All bond distances and angles
in the two structures are also very similar and in the
range of those expected for this type of compound.
Fig. 1 Molecular structure of [Mn(H2daps)(C2H5OH) ´
(H2O)] 2 showing the atomic numbering scheme.
The planarity of the pentagon formed by the N3O2 do-
nor set of the hydrazone is also comparable in both
cases but it shows a more planar ligand in 2, maybe as
a consequence of the reduced steric bulk of the apical
ligands. The maximum deviation from the N3O2 calcu-
Table 2 Crystal data and details of refinement
Ê
lated least square plane is 0.084 A in 1, with the man-
Ê
2
5
ganese atom sitting on the plane, and 0.040 A for 2,
Ê
with the manganese atom 0.027 A above this plane.
Formula
M. W.
C25H26MnN5O6
547.45
10.4242(4)
14.8371(6)
16.1221(6)
90
90.697(2)
90
4
C51H60N10Ni2O14
1154.51
14.360(2)
18.208(4)
20.870(3)
90
90
90
4
However, if we compare 1 and 2 some differences are
note worthy (see Table 4):
1. Compound 1 has a crystallographic 2-fold axis
which bisects the molecule through the Mn and pyri-
dine nitrogen atom of the [H2daps]2± ligand. This does
not occur in compound 2.
Ê
a (A)
Ê
b (A)
Ê
c (A)
a (°)
b (°)
c (°)
Z
3
Ê
V (A )
2493.34(17)
1.458
5456.7(15)
1.405
2. The Mn-Npyridine distance is significantly shor-
Ê
and
Dc (g/cm3)
ter in
2
[M±Npyridine = 2.380(6) A for
1
Space group
P21/n
P212121
Ê
Crystal system
Crystal size (mm)
h range (°)
Monoclinic
0.20 ´ 0.10 ´ 0.05
1.87±25.03
x scan
Orthorhombic
0.45 ´ 0.20 ´ 0.15
1.48±25.05
x scan
2.292(5) A for 2]. Opposite, the distances Mn±Nimine
are slightly longer in 2 [M±Nimine = 2.267(5) A for 1
and 2.280(6), 2.292(5) A for 2]. The different strength
Ê
Ê
Scan type
Reflections collected
No. unique reflections
No. variables
10041
4390 (Rint. = 0.1363)
343
13848
9230 (Rint. = 0.0709)
689
of these bonds in both complexes is also reflected in
the C±Npyridine and C±Nimine bond lengths. As ex-
pected from the above observations, the C±Npyridine
l (mm±1
)
0.580
0.763
F(000)
1136
2416
Ê
bond distances in 1 [1.313(6) A] are shorter than in 2
Largest Peak and
hole/e A
0.350 and ±0.438
1.325 and ±0.848
Ê
±3
Ê
[1.333(8) and 1.357(8) A] and the C±Nimine distances
Ê
R
0.0773 [1837, I > 2r]
0.2052
0.1865
0.0819 [5534, I > 2r]
0.1318
0.2188
are longer in 1 [1.376(7) A for 1 and 1.270(7),
R (all data)
wR2
Ê
1.287(8) A for 2]. These latter distances are closer to
Ê
the ideal value of 1.28 A for a C±Nimine bond in 2
and seem to indicate a lack of electronic delocalisa-
Ê
Table 3 Selected bond lengths (A) and angles (°) for
[Mn(H2daps)(C2H5OH)(H2O)] 2
Ê
Table 4 Comparison of bond lengths (A) in 1, 2
Ê
Distance (A)
[Mn(H2daps)(py)2]a)
[Mn(H2daps) ´
Mn±N1
Mn±N2
Mn±N4
Mn±O1
Mn±O3
Mn±O2S
Mn±O1S
2.292(5)
2.280(6)
2.292(5)
2.227(4)
2.247(5)
2.236(6)
2.268(5)
N2±Mn±N1
O2S±Mn±N4
O1S±Mn±N4
O1±Mn±O3
O1±Mn±O1S
O3±Mn±O1S
O2S±Mn±N2
O1S±Mn±N2
O2S±Mn±N1
O1S±Mn±N1
O1±Mn±N4
O3±Mn±N4
N2±Mn±N4
N1±Mn±N4
68.7(2)
(C2H5OH)(OH2)]b)
89.75(17)
90.25(18)
84.89(17)
93.29(17)
92.78(18)
92.29(19)
86.84(19)
92.50(17)
86.35(18)
154.23(19)
69.43(17)
136.0(2)
Mn±Npyridine
Mn±Nimine
Mn±Ocarbonyl
C±Npyridine
Cpyridine±Cimine
C±Nimine
Nimine±Nhydrazide
Nhydrazide±Ccarbonyl
C±Ocarbonyl
2.380(6)
2.292(5)
2.267(5); 2.267(5)
2.243(4); 2.243(4)
1.313(6); 1.313(6)
1.436(7); 1.436(7)
1.376(7); 1.376(7)
1.347(6); 1.347(6)
1.340(7); 1.340(7)
1.263(6); 1.263(6)
1.323(8)
2.280(6); 2.292(5)
2.227(4); 2.247(5)
1.333(8); 1.357(8)
1.470(9); 1.488(9)
1.270(7); 1.287(8)
1.379(7); 1.389(7)
1.341(8); 1.348(8)
1.279(8); 1.284(8)
1.316(8); 1.337(8)
2.497(7); 2.545(8)
O1±Mn±O2S
O2S±Mn±O3
O2S±Mn±O1S
O1±Mn±N2
O3±Mn±N2
O1±Mn±N1
O3±Mn±N1
87.25(16)
88.39(17)
178.75(18)
69.71(18)
154.52(19)
138.35(19)
136.75(18)
C±Ophenol
Nhydrazide ´ ´ ´ Ophenol
2.499(6); 2.499(6)
67.3(2)
a) Ref. 16; b) This work
508
Z. Anorg. Allg. Chem. 2000, 626, 506±513

About Solvent Influence on the Crystal Structure of MnII and NiII Complexes
tion in this compound. Longer Nhydrazide-Nimine
(Fig. 2). The molecules are also interacting by p-p
stacking between two parallel phenol rings.
Ê
Ê
distances (ca. 1.35 A for 1 and 1.38 A for 2) also point
to the lower degree of electronic delocalisation in 2.
These facts reflect the different donor nature of etha-
nol and water compared with pyridine.
The solution of the crystal structure of 2 shows that
the different donor ability of ethanol and pyridine
does not introduce a change in the nuclearity of the
complex but affects the electronic distribution on the
hydrazone ligand. From these results, it seems that
manganese has a low tendency to form helicate com-
plexes with this class of ligand. In fact, to the best of
our knowledge, no helical compounds have been de-
scribed for manganese complexes containing hydra-
zone ligands. It, thus, appears that the central atom
plays an essential role in the isolation of helicates and
that the role of the solvent is secondary.
Nickel complexes. Slow evaporation of a dichloro-
methane solution of Ni(H2daps)(H2O)1.5(CH3CN)
yields [Ni2(H2daps)2] ´ CH2Cl2 4, the structure of
which has previously been reported by us [16]. It is a
binuclear complex with a distorted octahedral envi-
ronment around the Ni atoms. Each ligand [H2daps]2±
uses one imine nitrogen atom and one carbonyl oxy-
gen atom of one of its molecular threads to join a
nickel centre and then use the same atoms of the sec-
ond molecular thread to link the second metal centre.
The co-ordination number 6 is attained by means of
two bridges between the metal centres via the two ni-
trogen atoms of the central pyridine rings of both hy-
drazone ligands. Thus, the complex has a double heli-
cal structure, in contrast to the mononuclear structure
found for the manganese compounds.
3. The C±Ophenol bond distances are very similar
Ê
in both cases (ca. 1.32 A) and smaller than the ideal
Ê
value (C±OH = 1.36 A), indicating some double bond
character. This is in agreement with a hydrogen bond
between the phenol oxygen and the hydrazide nitro-
gen atom. This intramolecular hydrogen bond is also
Ê
suggested by the N ´ ´ ´ O distances of ca. 2.5 A for 1
and 2 and it is indicative of the dianionic nature of
[H2daps]2±. In addition, two hydrogen bonds between
the water molecule of one unit and the carbonyl
oxygen atoms of one neighbouring molecule are ob-
Ê
served in 2 [distances O1 ´ ´ ´ O2S' = 2.731(6) A and
Ê
O3 ´ ´ ´ O2S' = 2.771(6) A]. These interactions lead to a
weakly joined dimer that is repeated in the space
It has been previously reported that
a bi-
nuclear cobalt complex containing qpy (qpy =
2,2' : 6',2@ : 6@,2@ : 6'@,2@@-quinquepyridine) could be con-
verted to a monomeric species simply by adding a
strong donor solvent such as pyridine. We therefore
anticipated that addition of pyridine to the binuclear
nickel helicate might also result in conversion to
a monomeric species [7]. Thus, we tried to react 4
with pyridine in order to obtain the mononuclear
[Ni(H2daps)(py)2] complex. However, this attempt
was unsuccessful and we obtained a different binu-
clear helical Ni complex, [Ni2(H2daps)2(py)2] ´ CH2Cl2
6, that we have previously reported [16]. The structure
of this compound could be rationalised by breaking
the pyridine bridges in complex 4 (Scheme 1). The li-
gands still use one imine nitrogen atom and one car-
bonyl oxygen atom of one of its molecular threads to
join a nickel centre and the same atoms of the second
molecular thread to link the second metal atom. The
two pyridine nitrogen atoms of the central rings are
now linked to the same metal centre, Ni1, acting as
terminal, rather than bridging donors. In the absence
of donor solvent molecules this would lead to a co-or-
dination number of six for one metal centre and to a
co-ordination number of four for the other one. Two
pyridine molecules from the solvent of crystallisation
increase the co-ordination number of the second me-
Fig. 2 Molecular packing for [Mn(H2daps)(C2H5OH) ´
(H2O)] 2 showing the hydrogen bonds between neighbouring
units.
Z. Anorg. Allg. Chem. 2000, 626, 506±513
509

M. R. Bermejo, A. Sousa, M. Fondo, A. M. GonzaÂlez, O. L. Hoyos, R. Pedrido, M. A. Maestro, J. MahÂõa
Scheme 1 Reaction of [Ni2(H2daps)2] ´ CH2Cl2 4 with pyridine to yield [Ni2(H2daps)2(py)2] ´ CH2Cl2 6.
tal centre, Ni2, to six. This experiment seems to indi-
cate that the solvent of crystallisation can lead to dif-
ferent crystal structures. However we could not con-
vert the dinuclear helicate into a monomer.
The dianionic nature of the ligands is also supported
by the magnetic moment of the compound at room
temperature (2.9 B.M.), which is in the expected range
for Ni(II) in an octahedral environment [16, 22].
In view of this unsuccessful attempt we tried to re-
crystallise the initial bulk material Ni(H2daps) ´
(H2O)1.5(CH3CN) again, as it was perhaps too diffi-
cult to break the helical structure once formed. We
knew that when the manganese compound prepared
electrochemically was recrystallised from ethanol a
mononuclear complex forms. Furthermore, the crystal
structure of [Ni(H4daps)(H2O)2](NO3)2, obtained
from an ethanol solution, has been reported [21] and
the compound is mononuclear. Therefore, an alcohol
seemed to be an appropriate solvent to obtain the de-
sired neutral mononuclear complex [Ni(H2daps)L2]
(L = solvent). Recrystallisation of Ni(H2daps) ´
(H2O)1.5(CH3CN) from methanol resulted in isolation
of single crystals of [Ni2(H2daps)2(CH3OH)2] ´
3 CH3OH ´ H2O 5, suitable for X-ray diffraction stu-
dies.
Crystal structure
of [Ni2(H2daps)2(CH3OH)2] ´ 3 CH3OH ´ H2O 5
An ORTEP view of the structure is shown in Fig. 3.
Experimental details are presented in Table 2 and se-
lected bond distances and angles in Table 5.
The compound is a binuclear nickel complex, with
the [H2daps]2± ligands spanning both metal centres.
Each ligand uses one imine nitrogen atom (N2, N7),
the pyridine nitrogen (N1, N6) atom and one carbonyl
oxygen atom (O1, O5) to coordinate to one nickel
centre, leading to a co-ordination number of six
around Ni1. The remaining imine nitrogen (N4, N9)
and carbonyl oxygen (O3, O7) atoms of both
[H2daps]2± moieties are used to bind the second nickel
atom. Two methanol molecules from the solvent of
crystallisation complete the co-ordination sphere of
this second metal centre (Ni2). Thus, the structure
could be related to that found for 6. The environment
of both metals could be described as distorted octahe-
dral, as found for [Ni2(H2daps)2(py)2] ´ CH2Cl2, with
FAB mass and IR spectra and magnetic measurements
The FAB mass spectrum of 5 shows a peak assigned to
the fragment [Ni(H2daps)]+ at 488 amu and a second
+
Ê
peak, due to the fragment [Ni(H2daps)]2 , at 976 amu.
comparable Ni1 ´ ´ ´ Ni2 distances (ca. 4.5 A). However,
This latter peak was previously observed for the bulk
material Ni(H2daps)(H2O)1,5(CH3CN). This is in direct
contrast to the behaviour of the mononuclear non heli-
cal Mn(H2daps)(H2O)0.5, which shows no fragments re-
lating to [Mn(H2daps)]2 . Therefore it seems that this
technique is useful in distinguishing between the pre-
sence of mononuclear and dinuclear species.
The IR spectrum also indicates the co-ordination of
the ligand to the metal. The bands due to the amide I
[m(CO)] and amide II [d(NH) + m(CN)] modes undergo
negative shifts of 56 cm±1 and 67 cm±1, respectively, in
agreement with the co-ordination of the oxygen atoms
of both carbonyl CO groups to the nickel atom. Addi-
tionally, the absence of the band at 3208 cm±1, as-
signed in the free ligand to m(N±H), is in accordance
with the dianionic character of both H4daps ligands.
in complex 6 both metal centres are surrounded by an
N4O2 donor set while in 5 one of the nickel atoms is
in a N4O2 and the other one in a N2O4 environment,
due to the replacement of two nitrogen donors (pyri-
dine) by oxygen donor ligands (methanol). The
presence of methanol leads to a higher degree of
hydrogen bonding in 5. The co-ordinated solvent mo-
lecules interact with methanol solvates [distances
+
Ê
Ê
O1S ´ ´ ´ O4S = 2.744(12) A, O2S ´ ´ ´ O5S = 2.718(11) A].
A further intramolecular hydrogen bonding interac-
tion is observed between one phenol oxygen atom
(O4) and a solvent methanol molecule [distance
Ê
O4 ´ ´ ´ O3S = 2.742(12) A]. Moreover, intermolecular
hydrogen bonds are established between the carbonyl
oxygen atoms linked to Ni1 and two different metha-
nol molecules from two neighbouring asymmetric
510
Z. Anorg. Allg. Chem. 2000, 626, 506±513

About Solvent Influence on the Crystal Structure of MnII and NiII Complexes
In spite of the marked similarities between 5 and 6,
some differences can be seen (see Table 6):
1. The Ni2±Nimine distances are clearly shorter for
Ê
5 [2.096(7) and 2.104(7)] than for 6 [2.148(12) A].
2. The Ni1±Ocarbonyl distances are significantly
Ê
Ê
different in 5 [2.106(6) A and 2.145(7) A] while they
Ê
are equal in 6 [2.120(10) A]. This leads to a more
distorted environment around Ni1 in 5. However,
no significant differences are observed for the dis-
tances Ni2±Ocarbonyl for 5 or for 6, the standard de-
viations in bond lengths are taking in account. The Ni-
mine±Nhydrazine bonds are also equal for 6 while in 5
one of the Nimine±Nhydrazine bond length is
shorter than the other one for one [H2daps]2± ligand
Ê
Ê
[N2±N3 = 1.370(11) A and N4±N5 = 1.427(10) A], the
longer distance corresponding to the thread around
Ni2. In addition, the Nhydrazine±Ccarbonyl bonds
are also more asymmetrical in 5. One of the bonds in
Ê
each ligand is significantly longer [1.315(12) A and
Ê
Ê
Ê
1.366(12) A; 1.322(12) A and 1.409(12) A] and again
this corresponds to the thread around Ni2. All these
seem to be, newly, an effect of the higher electronega-
tivity of the oxygen atom in methanol compared with
the nitrogen atom in pyridine.
Fig. 3 An ORTEP view of the crystal structure of
[Ni2(H2daps)2(CH3OH)2] ´ 3 CH3OH ´ H2O 5. Thermal ellip-
soids are drawn at the 30% probability level. Lattice
CH3OH and H2O are not depicted.
The comparison of the crystal structure of 4, 5 and 6,
as well as the experimental conditions in which they
were obtained, allow us to draw some conclusions. It
seems that Ni has a high preference for an octahedral
environment and a great tendency to form helicates
with appropriate hydrazone ligands. Thus, the solvent
of crystallisation does not seem to be able to reverse
this tendency although it can change the structure of
the helicate. The presence of a very poor donor solvent,
such as dichloromethane, force the central pyridine ring
Ê
Table 5 Selected bond lengths (A) and angles (°) for
[Ni2(H2daps)2(CH3OH)2] ´ 3 CH3OH ´ H2O 5
Ni1±O1
Ni1±O5
Ni1±N1
Ni1±N2
Ni1±N6
Ni1±N7
2.106(6)
2.145(7)
2.155(7)
1.995(7)
2.147(7)
1.999(7)
4.372(10)
77.0(3)
Ni2±O3
Ni2±O7
Ni2±O1S
Ni2±O2S
Ni2±N4
Ni2±N9
2.026(6)
2.016(7)
2.127(7)
2.111(7)
2.096(7)
2.104(7)
Ni1 ´ ´ ´ Ni2
N2±Ni1±N1
N2±Ni1±N6
N2±Ni1±O1
N2±Ni1±O5
N7±Ni1±O5
N7±Ni1±O1
N7±Ni1±N1
N7±Ni1±N6
N7±Ni1±N2
O1±Ni1±O5
O1±Ni1±N1
O1±Ni1±N6
O5±Ni1±N1
O5±Ni1±N6
N1±Ni1±N6
N4±Ni2±O1S
N4±Ni2±O2S
N4±Ni2±N9
N9±Ni2±O2S
N9±Ni2±O1S
N9±Ni2±O3
O1S±Ni2±O2S
O3±Ni2±N4
O3±Ni2±O1S
O3±Ni2±O2S
O7±Ni2±N4
O7±Ni2±N9
O7±Ni2±O3
O7±Ni2±O2S
O7±Ni2±O1S
164.3(3)
107.0(3)
77.2(3)
98.1(3)
76.4(3)
91.9(3)
113.6(3)
77.5(3)
167.5(3)
94.0(3)
154.1(3)
84.9(3)
87.7(3)
84.2(3)
106.7(3)
164.2(3)
84.6(3)
106.3(3)
87.2(3)
77.9(3)
88.5(3)
86.8(3)
103.9(3)
77.3(3)
175.4(3)
89.1(3)
89.1(3)
Ê
Table 6 Comparison of bond lengths (A) in 5 and 6
Ê
Distance (A)
[Ni2(H2daps)2(py)2]a) [Ni2(H2daps)2 ´
(CH3OH)2]b)
Ni1±Npyridine
Ni1±Nimine
Ni2±Nimine
Ni1±Ocarbonyl
Ni2±Ocarbonyl
Ni1 ´ ´ ´ Ni2
2.175(11); 2.175(11)
1.990(12); 1.990(12)
2.148(12); 2.148(12)
2.120(10); 2.120(10)
2.036(10); 2.036(10)
4.51(2)
2.147(7); 2.155(7)
1.995(7); 1.999(7)
2.096(7); 2.104(7)
2.106(6); 2.145(7)
2.016(6); 2.026(6)
4.372(10)
153.9(3)
104.5(3)
C±Npyridine
1.36(2); 1.34(2)
1.36(2); 1.34(2)
1.50(2); 1.44(2)
1.50(2); 1.44(2)
1.30(2); 1.30(2)
1.30(2); 1.30(2)
1.39(2); 1.39(2)
1.39(2); 1.39(2)
1.35(2); 1.34(2)
1.35(2); 1.34(2)
1.28(2); 1.25(2)
1.28(2); 1.25(2)
1.34(2); 1.27(2)
1.34(2); 1.27(2)
2.56(2); 2.56(2)
1.357(11); 1.368(11)
1.343(11); 1.351(11)
1.501(13); 1.520(13)
1.488(13); 1.495(12)
1.269(12); 1.275(12)
1.269(11); 1.290(11)
1.370(11); 1.427(10)
1.368(11); 1.390(10)
1.315(12); 1.409(12)
1.322(12); 1.366(12)
1.241(10); 1.285(11)
1.248(10); 1.286(11)
1.351(14); 1.370(14)
1.358(12); 1.359(13)
2.505(10); 2.540(10)
2.569(12); 2.569(12)
Cpyridine±Cimine
C±Nimine
Ê
units [distances O1 ´ ´ ´ O4S' = 2.889(11) A, O5 ´ ´ ´ O5S@ =
Ê
2.810(11) A].
An important difference between 5 and 6 is that
[Ni2(H2daps)2(py)2] ´ CH2Cl2 is symmetrically related
(space group C2/c), with the nickel atoms located in a
crystallographic two fold axis. This does not occur in
complex 5, leading to a less symmetrical compound.
However all the bond distances and angles are com-
parable between the complexes and are in the range
of those expected for Ni complexes with hydrazone li-
gands [16, 21, 23].
Nimine±Nhydrazine
Nhydrazine±Ccarbonyl
C±Ocarbonyl
C±Ophenol
Nhydrazine ´ ´ ´ Ophenol
a) Ref. 16; b) This work
Z. Anorg. Allg. Chem. 2000, 626, 506±513
511

M. R. Bermejo, A. Sousa, M. Fondo, A. M. GonzaÂlez, O. L. Hoyos, R. Pedrido, M. A. Maestro, J. MahÂõa
2 ´ 2 cm2 plates. Elemental analyses were performed on a
of the hydrazone ligand to act as a bridge, in order to
Carlo Erba EA 1108 analyser. NMR spectra were recorded
on a Bruker WM-250 spectrometer using DMSO-d6 as sol-
vent. Infrared spectra were recorded as KBr pellets on a
Bio-Rad FTS 135 spectrophotometer in the range 4000±
600 cm±1. Fast atom bombardment mass spectra (FAB) were
obtained on a Kratos MS-50 mass spectrometer, employing
Xe atoms at 70 KeV in m-nitrobenzylalcohol as a matrix.
Room-temperature magnetic susceptibilities were measured
using a Digital Measurement system MSB-MKI, calibrated
using tetrakis(isothiocyanato)cobaltate(II).
satisfy the desire for a co-ordination number of six
around the nickel atoms. The addition of a stronger do-
nor solvent, such as methanol, can satisfy the co-ordi-
nation number six of both metals, without the need for
formation of pyridine bridges, by co-ordination to the
metal centre itself. However, the solvent is not able to
force the nickel atom to attain a co-ordination number
of seven and, thus, to lead to the isolation of the mono-
mer. Similarly, a strong donor solvent such as pyridine,
leads to the same situation: a co-ordination number of
six around each metal centre is attained without neces-
sity of central pyridine bridges, but this does not con-
vert the helicate into a mononuclear complex.
At this point, we must note that [Ni(H4daps) ´
(H2O)2](NO3)2 was previously reported [21] as a
mononuclear complex with a pentagonal bipyramidal
geometry. Thus, if this has been obtained from an
ethanol solution, it seems that there are more factors
involved in obtaining helical arrays than the metal,
the ligand and the solvent itself. The charge on the li-
gand seems to be essential in same cases. But, why the
neutral ligand H4daps can easier afford a co-ordina-
tion number seven for the nickel centre than the bis-
deprotonated ligand? This question still remains un-
clear but it is the only reasonable difference which
can explain the different structures observed in 5 and
the related monomer [Ni(H4daps)(H2O)2](NO3)2.
Preparation: 2,6-bis(1-salicyloylhydrazonoethyl)pyridine,
H4daps, was prepared as previously described [2]. The purity
1
of the ligand was checked by H NMR and IR spectroscopy.
The yield was almost quantitative.
1H NMR(250 MHz, DMSO-d6): d = 2.50 (s, 6 H), 6.97±8.17
(m, 11 H), 11.51 (s, b, 2 H), 11.80 (b, 2 H) ppm.
IR (KBr): m(NH) 3208 cm±1.
Mn(H2daps)(H2O)0.5 and Ni(H2daps)(H2O)1.5(CH3CN): The
complexes Mn(H2daps)(H2O)0.5 and Ni(H2daps)(H2O)1.5
´
(CH3CN) were obtained using an electrochemical procedure
[16, 17].
An acetonitrile solution of the ligand containing about
10 mg of tetramethylammonium perchlorate, as supporting
electrolyte, was electrolysed using a platinum wire as the
cathode and a metal plate as the anode. The cell can be sum-
marised as:
Pt(±)|H4daps + MeCN|M(+), where M stands for the metal.
The synthesis of Mn(H2daps)(H2O)0.5 and Ni(H2daps) ´
(H2O)1,5(CH3CN) is typified by the preparation of
Mn(H2daps)(H2O)0.5: A suspension of the ligand (0.2 g,
0.464 mmol) in acetonitrile (80 mL), containing tetramethyl-
ammonium perchlorate (ca. 10 mg), was electrolysed for
2.5 h. using a current of 10 mA. Concentration of the result-
ing solution to a third of its initial volume yielded a solid
that was washed with diethyl ether and dried under vacuum.
Analytical and some selected data are given in Table 1.
Diffusion of dichloromethane into a pyridine solution con-
taining Mn(H2daps)(H2O)0.5, yields crystals of [Mn(H2daps) ´
(py)2] 1, previously reported [16]. Slow evaporation of an
ethanol solution of Mn(H2daps)(H2O)0.5 allows the isolation
of crystals of [Mn(H2daps)(C2H5OH)(H2O)] 2, suitable for
X-ray diffraction studies.
Ni(H2daps)(H2O)1.5(CH3CN) was obtained by the same
electrochemical procedure. Its crystallisation from dichloro-
methane/hexane and from methanol produced crystals of
[Ni2(H2daps)2] ´ CH2Cl2 4, as previously described [16] and
[Ni2(H2daps)(CH3OH)2] ´ 3 CH3OH ´ H2O 5, respectively,
also suitable for X-ray diffraction.
Yellow crystals of [Ni2(H2daps)2(py)2] ´ CH2Cl2 6, suitable
for single-crystal X-ray studies, were obtained by diffusion of
dichloromethane into a pyridine solution of [Ni2(H2daps)2] ´
CH2Cl2 [16].
Conclusions
From the experimental results previously reported by
us [16] and others [20, 21, 23] and reported herein by
us, we can conclude:
1. Nickel(II) has a higher preference for an octahe-
dral environment than manganese(II), favouring the
formation of helicates with appropriate pentadentate
hydrazone ligands. Thus, selection of the right ligand
and the metal seems to be the first step in the isola-
tion of helical structures.
2. The charge of a pentadentate hydrazone ligand
seems to play an active role in the isolation of heli-
cates containing metals with a high preference for an
octahedral environment.
3. The solvent of crystallisation can change the
structure of one helicate complex. However the rules
that govern this change are still unclear. Although it
has been reported that a mononuclear cobalt complex
could be obtained from a double helical compound in
the presence of a donor solvent, the helicates derived
from Ni and H4daps do not become mononuclear
compounds by influence of the crystallisation solvent.
Crystallographic measurements. Crystal data and details of
refinement are given in Table 2.
[Mn(H2daps)(C2H5OH)(H2O)]
2
and [Ni2(H2daps)2 ´
Experimental Section
(CH3OH)2] ´ 3 CH3OH ´ H2O 5. Block like orange crystals of
2 and block yellow-green crystals of 5 were obtained as de-
scribed above. Data were collected at 298 K using a Sie-
mens CCD diffractometer employing graphite-monochro-
General: All solvents, 2,6-diacetylpyridine and salicylhydra-
zide are commercially available and they were used without
further purification. Metals (Ega Chemie) were used as ca.
512
Z. Anorg. Allg. Chem. 2000, 626, 506±513

About Solvent Influence on the Crystal Structure of MnII and NiII Complexes
Ê
mated Mo±Ka (k = 0.71073 A) radiation, using the x scan
mode. The structures were solved by direct methods and re-
fined by full matrix least squares [24±26]. An absorption cor-
rection (Sadabs) was applied. All non-hydrogen atoms were
refined anisotropically. Hydrogen atoms were included in
calculated positions except those attached to the water oxy-
gen atom in 2. These were located in an electronic density
map and isotropically refined.
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513