Enantiomeric bis(μ-N,N′-hexamethylenedisalicylaldiminato)dicopper(II) complexes

Article abstract of DOI:10.1107/S0108270102006297

Dimeric complex, bis(μ-N,N′-hexa-methylenedisalicylaldiminato)-dicopper(II) was investigated using single crystal X-ray diffraction, thermogravimetric analysis, differential scanning calorimetry and Fourier transform infrared spectroscopy. The complex was

Full text of DOI:10.1107/S0108270102006297

metal-organic compounds
Acta Crystallographica Section C
Crystal Structure
Communications
environment. We concluded that it would be interesting to
examine the folding of the rather long polymethylene chain in
such a compound, so the title complex was prepared and
crystallized using a diffusion reaction technique, to give (I), or
by evaporation of a dioxane solution of the complex, to give
(II). The results obtained by the present structure determi-
nations are not in agreement with the structure proposed
previously by Duggal & Agarwala (1988). The title complex
was found to be dimeric in the solid state, with anions of N,N0-
hexamethylenebis(salicylaldimine) functioning as bridging
bis-bidentate ligands.
ISSN 0108-2701
Enantiomeric bis(l-N,N0-hexa-
methylenedisalicylaldiminato)-
dicopper(II) complexes
a
b
c
ÏÏ
Â
Tomislav Friscic, Alan J. Lough, George Ferguson and
Branko Kaitnera*
aDepartment of Chemistry, Laboratory of General and Inorganic Chemistry, Faculty of
Science, University of Zagreb, HR-10002 Zagreb, Croatia, bLash Miller Chemical
Laboratories, University of Toronto, Toronto, Ontario, Canada M5S 3H6, and
cDepartment of Chemistry and Biochemistry, University of Guelph, Guelph, Ontario,
Canada N1G 2W1
Correspondence e-mail: kaitner@chem.pmf.hr
Received 2 April 2002
Accepted 8 April 2002
Online 30 April 2002
One set of crystals of the title copper complex was grown by
evaporation from a dioxane solution, and the compound
obtained, (II), was found to crystallize in space group P43.
However, crystals obtained by slow interdiffusion of a basic
methanolic N,N0-hexamethylenebis(salicylaldimine) solution
and a copper(II) nitrate solution, (I), exhibited space group
P41. Structure determination from room-temperature data
The title dimeric complex, bis{ꢀ-2,20-[hexane-1,6-diylbis-
(nitrilomethylidyne)]diphenolato-1:2ꢁ4O,N:N0,O0}dicopper(II),
[Cu2(C20H22N2O2)2], has been investigated by single-crystal
X-ray diffraction, by thermogravimetric analysis and differ-
ential scanning calorimetry, and also by FT±IR spectroscopy.
Different synthetic and crystallization procedures gave
crystals which were quite different in appearance, and it was
initially thought that these were different polymorphic forms.
Subsequent structure determination showed, in fact, serendi-
pitous preparation of crystals in the P41 space group by one
method and in space group P43 by the other. In these
enantiomorphic structures, the Cu atoms have a distorted
¯attened tetrahedral coordination, with CuÐN and CuÐO
distances in the ranges 1.954 (4)±1.983 (4) and 1.887 (4)±
Ê
1.903 (4) A, respectively.
Figure 1
A view of (I) with the atom-numbering scheme. Displacement ellipsoids
are drawn at the 10% probability level and H atoms have been omitted.
Comment
Although copper(II) and nickel(II) complexes with Schiff
base ligands containing bridging aliphatic chains containing
two, three or four methylene groups have been the subject of
several crystallographic investigations (Freiburg et al., 1980;
Akhtar, 1981; Akhtar & Drew, 1982; Drew et al., 1985; Yao et
al., 1997), less work has been performed on homologous
compounds containing longer bridging chains (Martin et al.,
1978; Kitajima et al., 1986). The aliphatic chain length can have
a pronounced in¯uence on the coordination polyhedron of the
metal ion, and also on intermolecular oligomerization and
polymerization in the solid state and in solution.
Previous work (Duggal & Agarwala, 1988) carried out on
the complex of copper(II) with N,N0-hexamethylenebis-
(salicylaldimine) concluded, on the basis of IR and diffuse-
re¯ectance spectroscopy measurements, that the complex
should be monomeric, with the CuII ion in a cis-square-planar
Figure 2
A view of (II) with the atom-numbering scheme. Displacement ellipsoids
are drawn at the 10% probability level and H atoms have been omitted.
Acta Cryst. (2002). C58, m313±m315
DOI: 10.1107/S0108270102006297
# 2002 International Union of Crystallography m313

metal-organic compounds
1
obtained was identi®ed by FT±IR, and H and 13C NMR spectro-
scopy. The copper(II) complex was obtained as a brown powder by
slow simultaneous dropwise addition of ethanol solutions of the
Schiff base (containing an equimolar amount of triethylamine) and
copper(II) nitrate trihydrate into a small volume of ethanol. The
concentrations of the reactants varied from 0.05 to 0.10 mol dm 3. It
was observed that the rate of addition, as well as the concentration of
the reacting solutions, strongly in¯uenced the nature of the product.
Higher addition rates and reagent concentrations favoured the
formation of green precipitates of unknown composition. The title
compound was separated from the insoluble products by extraction
with chloroform and subsequent precipitation with n-hexane or
diethyl ether. The compound was crystallized by evaporation of a
dioxane solution, giving red crystals of (II) in the shape of bicapped
tetragonal prisms. As the compound dissolved in dioxane tends to
decompose, yielding an insoluble green precipitate (of currently
unknown composition), another method of preparation of the
compound, by slow diffusion of solutions of the Schiff base and
copper(II) nitrate, was used. As a result, long red needle-like crystals
of (I) were obtained. As mentioned above, we initially considered
that the crystals of (I) and (II) might be polymorphs, but the present
X-ray structure determinations establish that the different prepara-
tion and crystallization conditions have instead yielded crystals of the
same compound in enantiomorphic space groups, i.e. (I) in P41 and
(II) in P43. The differential scanning calorimetry measurements,
performed in an inert gas ¯ow atmosphere (Ar, 200 cm3 min 1) over
the temperature range 298±873 K using aluminium crucibles, revealed
a weak exothermic change at 499 K, followed by melting combined
with decomposition at 587 K, for both crystal forms. The thermo-
gravimetric analyses, made in an oxygen gas ¯ow atmosphere
(200 cm3 min 1) over the temperature range 298±873 K, gave the
expected copper content of 15.73% (calculated copper content
16.38%) in both crystal forms and con®rmed the chemical composi-
tion.
Figure 3
A view of the two disordered hexamethylene chains in (I). Displacement
ellipsoids are drawn at the 30% probability level. The corresponding view
for (II) is very similar.
indicated that the molecular geometries were the same in both
crystals, the only difference being the direction of the polar
axis.
Space-group determinations and data collection were
performed on several crystals from each set at room
temperature, and the Flack data (Flack, 1983) were always
consistent with space group P41 for the diffusion-grown and
P43 for the dioxane-grown crystals. However, the data
collected at room temperature indicated the existence of
disorder in one of the bridging aliphatic chains of the dimeric
complex molecule. The ®nal structure determinations
reported here were undertaken using low-temperature data,
which enabled the resolution of the disorder (see Experi-
mental).
The molecular geometries in both (I) (Fig. 1) and (II)
(Fig. 2) are identical. The CuII ions in the dimers are coordi-
nated in the form of very ¯attened tetrahedra, with the N- and
O-donor atoms in a trans arrangement around each CuII
centre. There is similar signi®cant disorder in one of the two
hexamethylene chains in each compound; a view of the pair of
disordered chains in (I) is shown in Fig. 3.
Enantiomorph (I)
Crystal data
The distance between the two CuII centres in the dimer is
[Cu2(C20H22N2O2)2]
Mr = 771.81
Tetragonal, P41
Mo Kꢂ radiation
Cell parameters from 4153
re¯ections
Ê
Ê
7.7019 (8) A in (I) and 7.7186 (8) A in (II). The degree of the
distortion of the metal coordination tetrahedron can be
expressed by the dihedral angle between the corresponding
OÐCuÐN planes; in (I), this is 35.0 (2)ꢁ for atom Cu1 and
23.3 (2)ꢁ for Cu2, and in (II), the angle is 34.5 (2)ꢁ for Cu1 and
23.6 (2)ꢁ for Cu2. These values fall in the range of previously
reported angles in similar complexes (Bear et al., 1970; Elder
& Hill, 1979). Details of the bond lengths at the Cu atoms are
given in Tables 1 and 2. The molecular dimensions in both
complexes are all in accordance with values previously
reported for copper(II) salicylaldiminates (Bhadbhade &
Srinivas, 1993; Kani et al., 1998).
Ê
a = 13.2963 (2) A
ꢃ = 2.9±27.5ꢁ
1
Ê
c = 20.6366 (5) A
Ê
V = 3648.38 (12) A
ꢀ = 1.21 mm
T = 150 (1) K
3
Z = 4
Dx = 1.405 Mg m
Needle, red
0.22 Â 0.21 Â 0.20 mm
3
Data collection
Nonius KappaCCD area-detector
diffractometer
' scans, and ! scans with ꢁ offsets
Absorption correction: multi-scan
(DENZO-SMN; Otwinowski &
Minor, 1997)
7755 independent re¯ections
5429 re¯ections with I > 2ꢄ(I)
Rint = 0.072
ꢃmax = 27.5ꢁ
h = 17 ! 17
k = 12 ! 12
Tmin = 0.776, Tmax = 0.794
20 156 measured re¯ections
l = 23 ! 26
The reasons for the observed dependence of the orientation
of the polar axis on crystallization conditions are, as yet,
unclear.
Table 1
Selected interatomic distances (A) for (I).
Ê
Experimental
Cu1ÐO2
Cu1ÐO1
Cu1ÐN2
Cu1ÐN1
1.890 (3)
1.895 (3)
1.959 (4)
1.972 (3)
Cu2ÐO4
Cu2ÐO3
Cu2ÐN4
Cu2ÐN3
1.895 (3)
1.903 (3)
1.965 (4)
1.980 (4)
The Schiff base ligand N,N0-hexamethylenebis(salicylaldimine) was
prepared by the condensation of salicylaldehyde with 1,6-diamino-
hexane in the molar ratio 2:1 in methanol. The yellow product so
ꢀ
ÏÏ Â
m314 Tomislav Friscic et al.
Two enantiomorphs of [Cu2(C20H22N2O2)2]
Acta Cryst. (2002). C58, m313±m315

metal-organic compounds
Table 2
Selected interatomic distances (A) for (II).
P43 for (II) from the Flack parameters (Flack, 1983). H atoms were
Ê
treated as riding, with aromatic CÐH = 0.95 A and aliphatic CÐH =
Ê
Ê
0.99 A. Both structures were solved independently and it soon
Cu1ÐO2
Cu1ÐO1
Cu1ÐN2
Cu1ÐN1
1.887 (4)
1.898 (4)
1.961 (4)
1.979 (4)
Cu2ÐO4
Cu2ÐO3
Cu2ÐN4
Cu2ÐN3
1.896 (3)
1.903 (3)
1.954 (4)
1.983 (4)
became apparent that, in each case, there was essentially identical
disorder of one of the (CH2)6 chains. The occupancies of the major
and minor chains were 0.714 (6) and 0.286 (6), respectively, for (I),
and 0.747 (6) and 0.253 (6), respectively, for (II). Minor occupancy
2
Ê
atoms were assigned an overall Uiso value of 0.06 A and their
Re®nement
geometries were restrained to reasonable values via SHELXL97
(Sheldrick, 1997) DFIX restraints.
Re®nement on F2
R[F2 > 2ꢄ(F2)] = 0.046
wR(F2) = 0.108
S = 1.00
7755 re¯ections
470 parameters
H-atom parameters constrained
w = 1/[ꢄ2(Fo2) + (0.0485P)2]
where P = (Fo2 + 2Fc2)/3
(Á/ꢄ)max = 0.003
For both compounds, data collection: COLLECT (Nonius, 1997±
2000); cell re®nement: DENZO±SMN (Otwinowski & Minor, 1997);
data reduction: DENZO±SMN; program(s) used to solve structure:
SHELXS97 (Sheldrick, 1997); program(s) used to re®ne structure:
SHELXL97; molecular graphics: ORTEPII (Johnson, 1976) and
PLATON (Spek, 2002); software used to prepare material for
publication: SHELXL97 and PRPKAPPA (Ferguson, 1999).
3
Ê
Áꢅmax = 0.32 e A
3
Ê
0.36 e A
Áꢅmin
=
Absolute structure: Flack (1983),
3489 Friedel pairs
Flack parameter = 0.007 (14)
Enantiomorph (II)
X-ray data were collected at the University of Toronto using
a Nonius KappaCCD diffractometer purchased with funds
from NSERC, Canada.
Crystal data
[Cu2(C20H22N2O2)2]
Mr = 771.81
Tetragonal, P43
Mo Kꢂ radiation
Cell parameters from 4153
re¯ections
ꢃ = 2.9±27.5ꢁ
Ê
a = 13.3288 (2) A
Supplementary data for this paper are available from the IUCr electronic
archives (Reference: SK1547). Services for accessing these data are
described at the back of the journal.
1
Ê
c = 20.5834 (7) A
ꢀ = 1.21 mm
T = 150 (1) K
3
Ê
V = 3656.78 (15) A
Z = 4
Dx = 1.402 Mg m
Prism, red
0.20 Â 0.18 Â 0.10 mm
3
References
Data collection
Nonius KappaCCD area-detector
diffractometer
' scans, and ! scans with ꢁ offsets
Absorption correction: multi-scan
(DENZO-SMN; Otwinowski &
Minor, 1997)
7763 independent re¯ections
4824 re¯ections with I > 2ꢄ(I)
Rint = 0.103
Akhtar, F. (1981). Acta Cryst. B37, 84±88.
Akhtar, F. & Drew, M. G. B. (1982). Acta Cryst. B38, 1149±1154.
Bear, C. A., Waters, J. M. & Waters, T. N. (1970). J. Chem. Soc. A, pp. 2494±
2498.
Bhadbhade, M. M. & Srinivas, D. (1993). Inorg. Chem. 32, 6122±6130.
Drew, M. G. B., Prasad, R. N. & Sharma, R. P. (1985). Acta Cryst. C41, 1755±
1758.
Duggal, H. K. & Agarwala, B. V. (1988). Spectrosc. Lett. 21, 1±10.
Elder, R. C. & Hill, M. C. (1979). Inorg. Chem. 18, 729±732.
Ferguson, G. (1999). PRPKAPPA. University of Guelph, Canada.
Flack, H. D. (1983). Acta Cryst. A39, 876±881.
Freiburg, C., Reichert, W., Melchers, M. & Engelen, B. (1980). Acta Cryst. B36,
1209±1211.
Johnson, C. K. (1976). ORTEPII. Report ORNL-5138. Oak Ridge National
Laboratory, Tennessee, USA.
Kani, Y., Ohba, S., Ishikawa, T., Sakamoto, M. & Nishida, Y. (1998). Acta
Cryst. C54, 191±193.
Kitajima, N., Whang, K., Moro-oka, Y., Uchida, A. & Sasada, Y. (1986). J.
Chem. Soc. Chem. Commun. pp. 1504±1505.
ꢃ
max = 27.5ꢁ
h = 17 ! 17
k = 12 ! 12
l = 26 ! 23
Tmin = 0.794, Tmax = 0.889
20 308 measured re¯ections
Re®nement
Re®nement on F2
R[F2 > 2ꢄ(F2)] = 0.049
wR(F2) = 0.098
S = 0.96
7763 re¯ections
w = 1/[ꢄ2(Fo2) + (0.0212P)2]
where P = (Fo2 + 2Fc2)/3
(Á/ꢄ)max < 0.001
3
Ê
Áꢅmax = 0.35 e A
3
Ê
0.47 e A
Áꢅmin
=
470 parameters
H-atom parameters constrained
Absolute structure: Flack (1983),
3505 Friedel pairs
Flack parameter = 0.000 (14)
Martin, J. W. L., Payne, N. C. & Willis, C. J. (1978). Inorg. Chem. 17, 3478±3484.
Nonius (1997±2000). COLLECT. Nonius BV, Delft, The Netherlands.
Otwinowski, Z. & Minor, W. (1997). Methods in Enzymology, Vol. 276,
Macromolecular Crystallography, Part A, edited by C. W. Carter Jr & R. M.
Sweet, pp. 307±326. New York: Academic Press.
Sheldrick, G. M. (1997). SHELXS97 and SHELXL97. University of
GoÈttingen, Germany.
Spek, A. L. (2002). PLATON. Version of March 2002. University of Utrecht,
The Netherlands.
Yao, H., Lo, J., Chen, B. & Lu, T. (1997). Acta Cryst. C53, 1012±1013.
The crystal structure determination of both crystal forms using
room-temperature data indicated a hardly resolvable disorder in one
of the bridging hexamethylene chains. Therefore, low-temperature
diffraction experiments were performed. Crystals of (I) and (II) were
signi®cantly different in appearance and both crystallized in the
tetragonal system, with space groups of either P41 or P43 determined
from the systematic absences. P41 was shown to be correct for (I) and
ꢀ
ÏÏ Â
Acta Cryst. (2002). C58, m313±m315
Tomislav Friscic et al.
Two enantiomorphs of [Cu2(C20H22N2O2)2] m315