Synthesis and solid state structures of copper(II) complexes of Schiff bases derived from cyclopropyl and cyclobutylamine

Article abstract of DOI:10.1016/S0022-2860(03)00296-5

The Schiff base copper(II) complexes (1)-(6) were prepared and characterised by mass, IR, and electronic spectra. Their solid states structures, determined by X-ray crystallography, indicate that the geometry around copper is determined by a combination of steric and electronic effects, as well as crystal packing forces. Thus, complex (1) is the only one in the series to have a square planar geometry. In contrast, complexes (2) and (3) display deformed square planar geometries, despite the small steric effect of the N-cyclopropyl and cyclobutyl groups. Furthermore, a purely electronic argument, based on which complexes (5) and (6) must have deformed tetrahedral structures, fails to account for the observed stepped square planar structures. Finally, complex (4) also has a stepped square planar geometry.

Full text of DOI:10.1016/S0022-2860(03)00296-5

Journal of Molecular Structure 657 (2003) 25–35
www.elsevier.com/locate/molstruc
Synthesis and solid state structures of copper(II) complexes
of Schiff bases derived from cyclopropyl and cyclobutylamine
*
Ivan Castillo, Juan M. Fernandez-Gonzalez , Jose Luis Garate-Morales
´
´
´
´
´ ´ ´ ´ ´
Departamento de Quımica Inorganica, Instituto de Quımica, UNAM, Circuito Exterior, CU, Coyoacan C.P. 04510, D.F., Mexico
Received 28 January 2003; revised 28 April 2003; accepted 2 May 2003
Abstract
The Schiff base copper(II) complexes (1)–(6) were prepared and characterised by mass, IR, and electronic spectra. Their
solid states structures, determined by X-ray crystallography, indicate that the geometry around copper is determined by a
combination of steric and electronic effects, as well as crystal packing forces. Thus, complex (1) is the only one in the series to
have a square planar geometry. In contrast, complexes (2) and (3) display deformed square planar geometries, despite the small
steric effect of the N-cyclopropyl and cyclobutyl groups. Furthermore, a purely electronic argument, based on which complexes
(5) and (6) must have deformed tetrahedral structures, fails to account for the observed stepped square planar structures. Finally,
complex (4) also has a stepped square planar geometry.
q 2003 Elsevier B.V. All rights reserved.
Keywords: Copper chelates; Schiff base ligands; Solid state structures
1. Introduction
to the nitrogen atom such as a cyclopropyl or
cyclobutyl group should have a small steric effect
on the geometric arrangement of the ligands around
the copper centre. Therefore, Schiff base complexes
derived from cyclopropylamine and cyclobutylamine
would allow us to focus on the relevance of electronic
effects and crystal packing forces in these systems.
We had previously reported the synthesis and solid
state structures of copper(II) Schiff base complexes
prepared from the condensation products of salicy-
laldehyde, 2-hydroxy-1-naphthalenecarboxaldehyde,
and 3-hydroxy-2-naphthalenecarboxaldehyde, and the
series of amines substituted with cycloalkyl groups
from cyclopentyl to cyclooctyl [9–11]. Despite the
instrinsic electronic differences among the aromatic
groups of the Schiff base ligands, which correspond to
a larger negative charge on the oxygen atom of the
3-oxo-2-naphthalenecarboxaldiminate ligand, an
There has been continuous interest in bis-bidentate
Schiff base Cu(II) complexes derived from salicyl and
naphthalenecarboxaldehydes because in the solid
state the ligands display a wide range of geometric
arrangements around copper, going from the ideal
trans-square planar structure to deformed tetrahedral
geometry [1–6]. It has been proposed that the extent
of distortion from the square planar geometry in such
molecules and the nickel(II) analogues depends on the
volume of the substituent at the coordinating nitrogen
atom [2]. In some cases, however, both electronic
effects [3,6,7] and crystal packing [6,8,9] have been
invoked as the driving forces responsible for the
distortion. The presence of a small substituent bound
*
Corresponding author. Tel.: þ52-55-5622-4506.
0022-2860/03/$ - see front matter q 2003 Elsevier B.V. All rights reserved.
doi:10.1016/S0022-2860(03)00296-5

26
I. Castillo et al. / Journal of Molecular Structure 657 (2003) 25–35
intermediate one on that of salicylaldiminate, and a
smaller one on that of the 2-oxo-1-naphthalenecar-
boxaldiminate ligand [7], the expected electronic
effects are not reflected in the structural features of the
coordination geometry of copper. Therefore, it is
reasonable to assume that crystal packing forces play
a significant role in the coordination geometry around
copper in the solid state structures.
spectra (KBr disks) were recorded on a Perkin–Elmer
203-B spectrometer, and UV-visible spectra on a
Shimadzu UV-160U spectrophotometer. Positive ion
fast atom bombardment (FAB) mass spectra were
obtained on a JEOL JMS-SX-102A mass spec-
trometer operated at an accelerating voltage of
10 kV. Samples were desorbed from a nitrobenzyl
alcohol matrix by using xenon atoms at 6 keV.
In order to determine the importance of crystal
packing forces in these systems, and to complete a
systematic study of the geometric arrangement of
bidentate Schiff base ligands around copper in the
solid state structures, we have undertaken the
synthesis and solid state structure determination of
copper(II) Schiff base complexes which include the
two smaller members of the cycloalkyl-substituted
series of primary amines, cyclopropyl and cyclobuty-
lamine. Thus, we herein report the preparation and
single crystal X-ray diffraction studies of the com-
pounds bis-{(cyclopropyl)[(2-oxo-1H-benzo-1-ylide-
ne)methyl]aminato}copper(II) (1), bis-{(cyclobutyl)
[(2-oxo-1H-benzo-1-ylidene)methyl]aminato}cop-
per(II) (2), bis-{(cyclopropyl)[(2-oxo-1H-naphth-1-
ylidene)methyl]aminato}copper(II) (3), bis-{(cyclo-
butyl)[(2-oxo-1H-naphth-1-ylidene)methyl]aminato}
copper(II) (4), bis-{(cyclopropyl)[(3-oxo-2H-naphth-
2-ylidene)methyl]aminato}copper(II) (5), and bis-
{(cyclobutyl)[(3-oxo-2H-naphth-2-ylidene)methyl]
aminato}copper(II) (6), which are obtained from the
corresponding Cu(II) bis-aldehydate precursors and
the appropriate cycloalkylamine.
2.2. Synthetic procedures
The copper bis-aldehydate precursors were pre-
pared by a method analogous to that of Tyson and
Adams [13]. Complexes (1)–(6) were synthesized by
treating CH2Cl2 suspensions (solution in the case of
copper bis-salicylaldehydate) of the corresponding
Cu(II) bis-aldehydate precursors with a small excess
of the appropriate cycloalkylamine. The following
preparation represents a typical example.
To
a solution of salicylaldehyde (0.25 g,
2.05 mmol) in 50 ml of EtOH was added an equimolar
amount of KOH (0.11 g, 2.05 mmol), and the reaction
mixture was stirred for an hour. A solution containing
Cu(OAc)2. H2O (0.20 g, 1.03 mmol) in 7 ml of H2O
was then added, and the resulting brownish-green
suspension was heated to reflux for 2 hours. The green
copper(II) bis-aldehydate obtained was concentrated
to dryness with a rotary evaporator, and dissolved in
100 ml of CH2Cl2. A small excess of cyclopropyla-
mine (0.16 ml, 2.26 mmol) was then added, and the
mixture was heated to a gentle reflux to avoid loss of
the amine by evaporation overnight. During the
course of the reaction the solution changed colour
from green to brown, indicative of the formation of
the copper Schiff base complex. The volatile materials
were removed with a rotary evaporator, and the brown
solid obtained was washed with 3 £ 20 ml portions of
H2O/MeOH (9:1), until the washings appeared
colourless. The products were dissolved in 20 ml of
CH2Cl2, and slow diffusion of 80 ml of MeOH
afforded deep brown crystalline (1) in 83 % yield
(0.33 g, 0.85 mmol).
2. Experimental
2.1. Reagents and techniques
Cyclopropylamine, cyclobutylamine, copper(II)
acetate monohydrate, salicylaldehyde, and 2-
hydroxy-1-naphthalenecarboxaldehyde were pur-
chased from Aldrich Chemical Co. Inc., and were
used without further purification. 3-hydroxy-2-
naphthalenecarboxaldehyde was prepared as
described in the literature [12]. Methanol (MeOH)
and ethanol (EtOH) were distilled prior to use from
magnesium, while CH2Cl2 was distilled from CaH2.
Melting points were determined on a Fisher–Johns
melting point apparatus and are uncorrected. Infrared
Bis-{(cyclopropyl)[(2-oxo-1H-benzo-1-ylidene)
methyl]aminato}copper(II) (1). Deep brown crystals
were obtained by recrystallization from CH2Cl2/
MeOH (1:4) in 83 % yield (0.33 g, 0.85 mmol). Mp
145–147 8C. FAB-MS m/z: Mþ 384 (base peak 154).

I. Castillo et al. / Journal of Molecular Structure 657 (2003) 25–35
27
IR (KBr): n(CyN) 1614 cm21. UV/vis (CHCl3) l/nm
(1/M21 cm21): 254 (30089), 372 (10626).
A Bruker SMART Apex CCD area detector diffract-
ometer was employed for collecting the diffraction
data of complexes (3)–(6). In both cases the
diffractometers operated with graphite-monochro-
mated Mo Ka radiation. In the case of complexes (1)
and (2), orientation matrices and unit-cell constants
were obtained from the least-squares refinements of
the setting angles of 40 reflections, collected by using
the XSCANS program [14]. Lorentz and polarization
corrections were applied [15]. For complexes (3)–(6),
unit-cell constants were obtained from the least-
squares refinements of the observed reflections in the
range ð2:28 , 2u , 32:08Þ; using the Bruker SMART
program [16]. Data were corrected for crystal decay
with the Bruker SAINT Plus program [17]. All data sets
were collected using the v scan mode. Additional
crystallographic data are collected in Table 1.
Bis-{(cyclobutyl)[(2-oxo-1H-benzo-1-ylidene)-
methyl]aminato}copper(II) (2). Dark brown crystals
were obtained by recrystallization from CH2Cl2/-
MeOH (1:4) in 97 % yield (0.42 g, 1.02 mmol). Mp
167–169 8C. FAB-MS m/z: Mþ 412 (base peak 154).
IR (KBr): n(CyN) 1621 cm21. UV/vis (CHCl3) l/nm
(1/M21 cm21): 251 (28153), 308 (8686), 368 (10197).
Bis-{(cyclopropyl)[(2-oxo-1H-naphth-1-ylidene)-
methyl]aminato}copper(II) (3). Deep brown crystals
were obtained by recrystallization from CH2Cl2/EtOH
(1:2) in 84 % yield (0.25 g, 0.52 mmol). Mp 193–
196 8C. FAB-MS m/z: Mþ 484 (base peak 274). IR
(KBr): n(CyN) 1611 cm21. UV/vis (CHCl3) l/nm
(1/M21 cm21): 252 (51304), 318 (34170), 385
(15101).
Bis-{(cyclobutyl)[(2-oxo-1H-naphth-1-ylidene)-
methyl]aminato}copper(II) (4). Dark brown crystals
were obtained by recrystallization from CH2Cl2/EtOH
(1:1) in 64 % yield (0.20 g, 0.39 mmol). Mp 232–
234 8C. FAB-MS m/z: Mþ 512 (base peak 154). IR
(KBr): n(CyN) 1613 cm21. UV/vis (CHCl3) l/nm
(1/M21 cm21): 254 (50921), 316 (35095), 396
(15081).
2.4. Structure solution and refinement
Structures of complexes (1) and (2) were solved by
direct methods by using the SHELXS-97 program [18],
and refined with the SHELXL-97 program [19]. In the
case of complexes (3)–(6), the Bruker SAINT Plus
program was used [17]. In all cases, the refinements
were carried out by full matrix least-squares on F2:
Weighted R-factors, Rw; and all goodness of fit
indicators, S; were based on F2: The observed criterion
of (F2 . 2sF2) were used only for calculating the R-
factors. The number of observed reflections is pre-
sentedinTable 1. Allnon-hydrogenatomswere refined
with anisotropic thermal parameters in the final cycles
ofrefinement.Hydrogenatomswereplacedinidealised
Bis-{(cyclopropyl)[(3-oxo-2H-naphth-2-ylidene)-
methyl]aminato}copper(II) (5). Deep brown crystals
were obtained by slow evaporation of a concentrated
CH2Cl2 solution in 65 % yield (0.24 g, 0.49 mmol).
Mp 208 8C. FAB-MS m/z: Mþ 484 (base peak 154).
IR (KBr): n(CyN) 1603 cm21. UV/vis (CHCl3) l/nm
(1/M21 cm21): 267 (73272), 307 (45207), 439
(51130).
˚
˚
Bis-{(cyclobutyl)[(3-oxo-2H-naphth-2-ylidene)-
methyl]aminato}copper(II) (6). Brown crystals were
obtained by slow evaporation of a concentrated
CH2Cl2 solution in 71 % yield (0.45 g, 0.88 mmol).
Mp . 300 8C (dec). FAB-MS m/z: Mþ 512 (base
peak 154). IR (KBr): n(CyN) 1617 cm21. UV/vis
(CHCl3) l/nm (1/M21 cm21): 264 (71690), 442
(5460).
positions, with C–H distances of 0.93 A and 0.98 A for
sp2 and sp3 hybridised carbon atoms, respectively. The
isotropic thermal parameters of the hydrogen atoms
were assigned the values of Uiso ¼ 1:2 times the
thermal parameters of the parent non-hydrogen atom.
Neutral atomic scattering factors were taken from the
International Tables for X-ray Crystallography [20].
2.3. X-ray crystallography data collection
and processing
3. Results and discussion
3.1. Spectroscopic studies
The crystals were each mounted on a glass fiber.
Measurements were performed on a Siemens P4/PC
four-circle diffractometer for complexes (1) and (2).
Initial
bis-aldehydate complexes Cu(salicylaldehydate)2,
preparation
of
the
copper(II)

28
I. Castillo et al. / Journal of Molecular Structure 657 (2003) 25–35
Table 1
Crystal data and structure refinement for compounds (1)–(6)
1
2
3
4
5
6
Formula
C
20H20
C22H24
CuN2O2
411.97
C28H24
CuN2O2
484.03
C30H28
CuN2O2
512.08
C28H24
CuN2O2
484.03
C30H28CuN2O2
512.08
CuN2O2
383.92
Molecular
weight
Crystal
system
Space
Ortho
Mono
clinic
C2=c
Tri
Mono
clinic
P21=c
Mono
clinic
P21=n
Monoclinic
P21=n
rhombic
Pbca
clinic
P1bar
group
˚
Wavelength (A)
Crystal color
T (K)
0.71073
Brown
0.71073
Brown
0.71073
0.71073
Brown
0.71073
Red
0.71073
Brown
Brown
291(2)
291(2)
291(2)
291(2)
291(2)
291(2)
Crystal dimensions
(mm)
˚
a (A)
0.36 £ 0.22
£ 0.06
0.36 £ 0.20
£ 0.14
0.33 £ 0.27
£ 0.06
0.36 £ 0.16
£ 0.14
0.33 £ 0.17
£ 0.04
0.30 £ 0.10
£ 0.08
8.5976(7)
13.8379(14)
14.6574(9)
90
21.434(2)
8.7412(5)
21.177(3)
90
9.3225(12)
10.4481(14)
12.1392(16)
72.273(3)
77.675(3)
84.361(3)
1099.6(3)
9.6234(6)
12.7504(8)
10.1370(6)
90
9.0436(7)
5.6897(5)
21.7238(18)
90
9.7792(8)
5.6979(4)
21.2508(16)
90
˚
b (A)
˚
c (A)
a (o)
b (o)
g (8)
90
90.513(1)
90
107.849(1)
90
91.306(2)
90
91.766(2)
90
90
3
˚
V (A )
1743.8(3)
3967.6(7)
1183.96(13)
1117.52(16)
1183.55(16)
hkl ranges
0 # h # 10
0 # k # 16
0 # l # 17
1.462
0 # h # 30
0 # k # 12
229 # l # 29
1.379
211 # h # 11
212 # k # 12
214 # l # 14
1.462
211 # h # 11
215 # k # 15
212 # l # 12
1.436
210 # h # 10
26 # k # 6
225 # l # 25
1.438
211 # h # 11
26 # k # 6
225 # l # 25
1.437
rcalc (g cm23
)
Z
4
8
2
2
4
4
F(000)
m (mm21
796
1720
502
534
502
534
)
1.268
1.120
1.022
0.954
1.006
0.954
u range (8)
Absorption
correction
2.78–25.00
Analytical
1.92–30.00
Analytical
1.80–25.00
None
2.22–25.00
None
1.88–25.00
None
1.92–24.99
None
T
max; Tmin
0.9239, 0.7276
Full-matrix
least-squares
on F2
0.8516, 0.7819
Full-matrix
least-squares
on F2
N/A
N/A
N/A
N/A
Refinement
method
Full-matrix
least-squares
on F2
Full-matrix
Full-matrix
Full-matrix
least-squares
on F2
least-squares on F2 least-squares
on F2
Independent
reflections
1541
5796
3873
2088
1967
2091
Data/restraints
/parameters
Goodness
-of-fit on F2
R
1541/0/116
0.843
5796/0/246
0.752
3873/0/298
0.992
2088/0/160
0.956
1967/0/151
1.000
2091/0/160
0.950
0.0370
0.0747
0.0388
0.0644
0.0400
0.0829
0.0348
0.0883
0.0497
0.0938
0.0365
0.0828
Rw
Largest diff. peak
23
0.212 and 20.219 0.239 and 20.318 0.555 and 20.189 0.699 and 20.154 0.737 and 20.271 0.523 and 20.186
˚
and hole (e A
)
Cu(2-oxo-1-naphthalenecarboxaldehydate)2, and
Cu(3-oxo-2-naphthalenecarboxaldehydate)2 was
required in order to synthesize the desired Schiff
base complexes (1)–(6). The former complexes were
obtained upon treatment of copper(II) acetate
monohydrate with ethanolic solutions of potassium
salicylaldehydate, 2-oxo-1-naphthalenecarboxaldehy-
date, and 3-oxo-2-naphthalenecarboxaldehydate,
respectively. Suspensions of the Cu(II) bis-aldehy-
dates in CH2Cl2 were treated with a small excess of

I. Castillo et al. / Journal of Molecular Structure 657 (2003) 25–35
29
cyclopropyl or cyclobutylamine, and heated to a
gentle reflux to avoid loss of the amine by evapora-
tion. Complexes (1)–(6) were obtained in good to
moderate yields after recrystallization from the
appropriate solvent systems, as shown in Scheme 1.
The dichloromethane and chloroform soluble
copper Schiff base complexes were characterised by
spectroscopic methods. FAB mass spectra of (1)–(6)
confirm the presence of the expected molecular ions
with a 2:1 ligand-to-metal stoichiometric ratio.
Molecular ions with the characteristic copper isotopic
distribution were detected as well as the [Mþ þ H]
ions which are commonly observed in FAB mass
spectra [21]. The main feature of the infrared spectra
consists of the n(CyN) vibration at 1614, 1621, 1611,
1613, 1603, and 1617 cm21 for (1)–(6), respectively.
Thus, the stretching frequencies for all complexes are
close to the mean value of 1612 cm21, which is
characteristic of these systems [22]. In the electronic
spectra of all complexes (1)–(6), bands associated
with d ! d transitions were not detected, perhaps due
to the intensity of the charge transfer and intraligand
transitions [23].
position. A list of selected bond distances and angles
is presented in Table 2, and the molecular structures of
compounds (1)–(6), which were generated with the
XP feature of SHELX, are presented with atom
numbering schemes in Figs. 1–6, respectively.
Thermal ellipsoids in all figures are shown at the
40% probability level.
Complex (1) has square planar geometry, while
complexes (4)–(6) have stepped square planar
geometries with relatively small step values of 0.49,
˚
0.36, and 0.60 A, respectively. Based on steric
considerations, such planar coordination environ-
ments are expected for Schiff base Cu(II) complexes
with small substituents at the coordinating nitrogen
atoms. Nonetheless, complexes (2) and (3) display
deformed square planar geometries with dihedral
angles between the two coordination planes of 21.99
(average) and 30.268, respectively.
The asymmetric unit of complex (2) is defined by 2
independent molecules which possess Cu–O bond
˚
lengths of 1.885(2) and 1.881(2) A, and Cu–N bond
˚
lengths of 1.996(2) and 1.998(2) A. The dihedral
angles of the planes defined by O(1)–Cu(1)–N(1) and
O(1a)–Cu(1)–N(1a) in one molecule, and O(2)–
Cu(2)–N(2) and O(2a)–Cu(2)–N(2a) in the other
molecule of compound (2), are very similar, with
values of 22.02(5) and 21.96(5)8. Complex (3) has
only one molecule in the asymmetric unit, but the two
ligands are inequivalent with slightly different Cu–O
and Cu–N bond distances of 1.892(2), 1.902(2),
3.2. Crystallographic studies
The X-ray crystal structures of (1)–(6) reveal four
coordinate copper centres bound to both nitrogen and
oxygen atom donors. The usual N,O-trans arrange-
ment of ligands is observed in all cases, as well as N-
cycloalkyl substituents and aryl groups in a cisoid
˚
and 1.956(2), 1.946(2) A, respectively. In contrast,
Scheme 1. Synthesis of N-cycloalkyl copper(II) Schiff base complexes.

30
I. Castillo et al. / Journal of Molecular Structure 657 (2003) 25–35
Table 2 (continued)
Table 2
˚
Selected bond lengths (A) and angles (8) for complexes (1)–(6)
Complex (4)
Cu(1)–O(1)
Complex (1)
1.895(2)
O(1)–Cu(1)–O(1a)
O(1)–Cu(1)–N(1)
O(1)–Cu(1)–N(1a)
O(1a)–Cu(1)–N(1)
O(1a)–Cu(1)–N(1a)
N(1)–Cu(1)–N(1a)
C(2)–O(1)–Cu(1)
C(11)–N(1)–Cu(1)
C(12)–N(1)–Cu(1)
O(1)–C(2)–C(1)
180.0(1)
90.2(1)
Cu(1)–O(1)
Cu(1)–O(1a) 1.892(3)
Cu(1)–N(1) 2.004(3)
Cu(1)–N(1a) 2.004(3)
1.892(3)
O(1)–Cu(1)–O(1a)
O(1)–Cu(1)–N(1)
O(1)–Cu(1)–N(1a)
O(1a)–Cu(1)–N(1)
O(1a)–Cu(1)–N(1a)
N(1)–Cu(1)–N(1a)
C(2)–O(1)–Cu(1)
C(7)–N(1)–Cu(1)
C(8)–N(1)–Cu(1)
O(1)–C(2)–C(1)
N(1)–C(7)–C(1)
180.000(1)
91.02(13)
88.98(13)
88.98(13)
91.02(13)
180.000(1)
128.9(3)
Cu(1)–O(1a) 1.895(2)
Cu(1)–N(1) 1.993(2)
Cu(1)–N(1a) 1.993(2)
89.8(1)
89.8(1)
O(1)–C(2)
N(1)–C(11)
N(1)–C(12)
C(1)–C(11)
C(1)–C(2)
C(2)–C(3)
C(3)–C(4)
1.301(3)
1.294(3)
1.470(3)
1.428(3)
1.404(3)
1.427(3)
1.349(3)
90.2(1)
O(1)–C(2)
N(1)–C(7)
N(1)–C(8)
C(1)–C(7)
C(1)–C(2)
C(2)–C(3)
C(3)–C(4)
1.299(5)
1.286(5)
1.460(5)
1.439(5)
1.402(6)
1.413(6)
1.372(6)
180.0(1)
129.7(1)
123.4(2)
119.7(1)
124.4(2)
128.4(2)
124.2(3)
117.9(3)
124.1(4)
N(1)–C(11)–C(1)
126.5(4)
Complex (5)
Cu(1)–O(1)
Complex (2)
Cu(1)–O(1)
1.866(2)
O(1)–Cu(1)–O(1a)
O(1)–Cu(1)–N(1)
O(1)–Cu(1)–N(1a)
O(1a)–Cu(1)–N(1)
O(1a)–Cu(1)–N(1a)
N(1)–Cu(1)–N(1a)
C(3)–O(1)–Cu(1)
C(11)–N(1)–Cu(1)
C(12)–N(1)–Cu(1)
O(1)–C(3)–C(2)
180.00(11)
91.55(11)
88.45(11)
88.45(11)
91.55(11)
180.00(13)
129.9(2)
1.885(2)
O(1)–Cu(1)–O(1a)
O(1)–Cu(1)–N(1)
O(1)–Cu(1)–N(1a)
O(1a)–Cu(1)–N(1)
O(1a)–Cu(1)–N(1a)
N(1)–Cu(1)–N(1a)
C(2)–O(1)–Cu(1)
C(7)–N(1)–Cu(1)
C(8)–N(1)–Cu(1)
O(1)–C(2)–C(1)
162.9(1)
93.1(1)
Cu(1)–O(1a) 1.866(2)
Cu(1)–N(1) 2.026(3)
Cu(1)–N(1a) 2.026(3)
Cu(1)–O(1a) 1.885(2)
Cu(1)–N(1) 1.996(2)
Cu(1)–N(1a) 1.996(2)
89.0(1)
89.0(1)
O(1)–C(3)
N(1)–C(11)
N(1)–C(12)
C(2)–C(11)
C(1)–C(2)
C(2)–C(3)
C(3)–C(4)
C(1)–C(9)
1.313(4)
1.291(4)
1.464(4)
1.435(4)
1.387(4)
1.421(4)
1.383(5)
1.399(4)
O(1)–C(2)
N(1)–C(7)
N(1)–C(8)
C(1)–C(7)
C(1)–C(2)
C(2)–C(3)
C(3)–C(4)
Cu(2)–O(2)
1.302(3)
1.279(3)
1.467(3)
1.438(3)
1.422(3)
1.407(3)
1.371(4)
1.881(2)
93.1(1)
165.3(1)
128.4(2)
122.8(2)
119.9(2)
124.2(2)
127.8(2)
162.7(1)
93.1(1)
122.3(2)
119.7(2)
121.6(3)
N(1)–C(11)–C(2)
126.8(3)
N(1)–C(7)–C(1)
O(2)–Cu(2)–O(2a)
O(2)–Cu(2)–N(2)
O(2)–Cu(2)–N(2a)
O(2a)–Cu(2)–N(2)
O(2a)–Cu(2)–N(2a)
N(2)–Cu(2)–N(2a)
C(22)–O(2)–Cu(2)
C(27)–N(2)–Cu(2)
C(28)–N(2)–Cu(2)
O(2)–C(22)–C(21)
N(2)–C(27)–C(21)
Cu(2)–O(2a) 1.881(2)
Cu(2)–N(2) 1.998(2)
Cu(2)–N(2a) 1.998(2)
Complex (6)
Cu(1)–O(1)
89.1(1)
1.876(2)
O(1)–Cu(1)–O(1a)
O(1)–Cu(1)–N(1)
O(1)–Cu(1)–N(1a)
O(1a)–Cu(1)–N(1)
O(1a)–Cu(1)–N(1a)
N(1)–Cu(1)–N(1a)
C(3)–O(1)–Cu(1)
C(11)–N(1)–Cu(1)
C(12)–N(1)–Cu(1)
O(1)–C(3)–C(2)
180.00(9)
91.76(8)
89.1(1)
Cu(1)–O(1a) 1.876(2)
Cu(1)–N(1) 2.018(2)
Cu(1)–N(1a) 2.018(2)
O(2)–C(22)
N(2)–C(27)
N(2)–C(28)
1.304(3)
1.280(3)
1.473(3)
93.1(1)
88.24(8)
165.6(1)
128.2(2)
122.5(2)
119.6(2)
124.3(3)
127.6(2)
88.24(8)
O(1)–C(3)
N(1)–C(11)
N(1)–C(12)
C(2)–C(11)
C(1)–C(2)
C(2)–C(3)
C(3)–C(4)
C(1)–C(9)
1.314(3)
1.289(3)
1.468(3)
1.441(3)
1.383(3)
1.434(3)
1.382(4)
1.399(3)
91.76(8)
C(21)–C(27) 1.434(4)
C(21)–C(22) 1.411(4)
C(22)–C(23) 1.410(4)
C(23)–C(24) 1.369(4)
180.00(11)
129.26(17)
122.35(17)
120.21(16)
122.0(2)
Complex (3)
Cu(1)–O(1)
Cu(1)–O(2)
Cu(1)–N(1)
Cu(1)–N(2)
O(1)–C(2)
O(2)–C(22)
N(1)–C(11)
N(1)–C(12)
N(2)–C(31)
N(2)–C(32)
C(1)–C(11)
C(1)–C(2)
C(2)–C(3)
C(3)–C(4)
1.8917(18) O(1)–Cu(1)–O(2)
1.9020(18) O(1)–Cu(1)–N(1)
158.86(9)
91.62(8)
N(1)–C(11)–C(2)
127.4(2)
1.956(2)
1.946(2)
1.304(3)
1.308(3)
1.290(3)
1.453(3)
1.290(3)
1.463(4)
1.424(3)
1.409(4)
1.422(4)
1.349(4)
O(1)–Cu(1)–N(2)
O(2)–Cu(1)–N(1)
O(2)–Cu(1)–N(2)
N(1)–Cu(1)–N(2)
C(2)–O(1)–Cu(1)
C(11)–N(1)–Cu(1)
C(12)–N(1)–Cu(1)
O(1)–C(2)–C(1)
91.39(9)
93.01(8)
92.03(8)
compounds (1) and (4)–(6) have crystallographically
equivalent bidentate ligands with Cu–O bond lengths
˚
of 1.892(3), 1.895(2), 1.866(2), and 1.876(2) A. The
corresponding Cu–N bond lengths are 2.004(3),
˚
1.993(2), 2.026(3), and 2.018(2) A.
The average Cu–O bond lengths of 1.892(3),
˚
1.883(2), 1.897(2), 1.895(2), 1.866(2), and 1.876(2) A
157.90(9)
128.71(18)
124.59(19)
117.73(16)
124.0(3)
N(1)–C(11)–C(1)
C(22)–O(2)–Cu(1)
C(31)–N(2)–Cu(1)
C(32)–N(2)–Cu(1)
O(2)–C(22)–C(21)
N(2)–C(31)–C(21)
127.8(3)
127.05(17)
124.71(19)
116.53(19)
124.5(3)
for compounds (1)–(6), respectively, are all similar to
those observed in related copper(II) complexes,
˚
1.868(4)–1.901(4) A [9–11,24]. The Cu(1)–O(2)
C(21)–C(31) 1.427(4)
C(21)–C(22) 1.405(4)
C(22)–C(23) 1.425(4)
C(23)–C(24) 1.346(4)
127.4(3)
˚
distance of 1.902(2) A in complex (3), and

I. Castillo et al. / Journal of Molecular Structure 657 (2003) 25–35
31
Fig. 1. Molecular structure of (1) with atom numbering Scheme.
the Cu(1)–O(1) distance of 1.866(2) in complex (5),
however, represent the longest and shortest Cu–O
bond lengths reported to date for the series of known
N-cycloalkyl substituted copper(II) Schiff base com-
plexes. The average Cu–N bond distances of
2.004(3), 1.997(2), 1.951(2), 1.993(2), 2.026(3), and
2.018(2), are also similar to those of related copper(II)
˚
complexes, 1.962(4)–2.034(2) A. It is important to
notice, however, that both Cu–N bond lengths in (3)
˚
[Cu(1)–N(1) 1.956(2) A, and Cu(1)–N(2)
˚
1.946(2) A] are shorter than those reported to date
for the series of complexes with N-cycloalkyl
Fig. 2. Molecular structure of (2) with atom numbering Scheme.

32
I. Castillo et al. / Journal of Molecular Structure 657 (2003) 25–35
Fig. 3. Molecular structure of (3) with atom numbering Scheme.
substituents [9–11,24]. Moreover, the shortest
Cu(1)–N(2) bond distance in (3) is associated with
˚
the longest Cu(1)–O(2) bond distance of 1.902(2) A
bond angles of 165.3(1) and 165.6(1)8, respectively.
The geometric parameters of (3) are characterised by
the O(1)–Cu(1)–O(2) and N(1)–Cu(1)–N(2) bond
angles of 158.9(1) and 157.9(1)8, respectively. Other
bond lengths and angles within the ligand framework
of all complexes show expected values.
mentioned above. Likewise, the long Cu(1)–N(1)
bond distance in compound (5) is associated with the
˚
short Cu(1)–O(1) bond distance of 1.866(2) A.
The deformed square planar geometry of (2) is
characterised by O(1)–Cu(1)–O(1a) and O(2)–
Cu(2)–O(2a) bond angles of 162.9(1) and 162.7(1)8,
and N(1)–Cu(1)–N(1a) and N(2)–Cu(2)–N(2a)
In order to search for intra- and intermolecular
interactions in the solid state structures of compounds
(1)–(6), a geometric analysis was carried out with the
PLATON program [25]. The type of interactions that
Fig. 4. Molecular structure of (4) with atom numbering Scheme.

I. Castillo et al. / Journal of Molecular Structure 657 (2003) 25–35
33
Fig. 5. Molecular structure of (5) with atom numbering Scheme.
have been described as being relevant in determining
the packing of molecules in a lattice include weak
C–H· · ·O and C–H· · ·N hydrogen bonds [26], C–
H· · ·p [26], and p· · ·p interactions [27], among
others. In the crystal structure of square planar (1),
an intermolecular interaction between the copper
atoms and H(5) from adjacent molecules appears to
exist. This interaction must be relatively weak since
the H(5) atoms, which are directed towards the axial
˚
positions of the Cu, are at a distance of 3.07 A. No
Fig. 6. Molecular structure of (6) with atom numbering Scheme.

34
I. Castillo et al. / Journal of Molecular Structure 657 (2003) 25–35
significant p· · ·p interactions are present in the solid
state structure of (1), perhaps due to the small size of
the aromatic ring.
(6), which incorporate the relatively electron rich
3-oxo-2-naphthalenecarboxaldiminate ligand, it was
instead observed in compounds (2) and (3). Thus, the
electronic influence of the aromatic portion of the
ligands does not seem to be so strong as to determine
the geometry of the complexes. The apparent lack of
correlation between a steric or electronic parameter
and the observed molecular structures of the series of
N-cycloalkyl substituted copper (II) Schiff base
complexes, indicates that crystal packing forces are
at least as important as steric and electronic effects in
determining the solid state structures of such
complexes.
In the distorted square planar structures of (2) and
(3), there is no axial position in the copper
coordination sphere. Despite the fact that no
Cu· · ·H interaction can take place, there are other
intra- and intermolecular interactions that need
comment. Thus, the pair of intramolecular C–
˚
H· · ·O hydrogen bonds [C(8)–H(8)· · ·O(1), 2.61 A,
˚
and C(19)–H(19)· · ·O(2), 2.59 A] could be respon-
sible for the distortion in compound (2). A similar
hydrogen bond exists in the structure of complex (3),
characterised by a C(32)–H(32)· · ·O(1) distance of
˚
2.46 A. This interaction, together with the p· · ·p
˚
interaction (3.43 A) between the aromatic rings
5. Supplementary material
defined by C(1)–C(4), C(9), C(10), and C(5)–C(10)
from an adjacent molecule, could be responsible for
the distortion in the latter compound.
Crystallographic data for compounds (1)–(6) have
been deposited at the Cambridge Crystallographic
Data Centre, 12 Union Road, Cambridge, CB2 1EZ,
UK, and are available free of charge from the Director
upon request quoting the CCDC deposition numbers
202414–202419.
In the structures of complexes (4)–(6), the
presence of the large naphthalenic rings seems to
˚
˚
favour p· · ·p interactions [3.04 A, and 3.44 A for
complexes (4) and (5), respectively], with the
exception of compound (6). There are also intramo-
lecular hydrogen bonds involving C(12)–
H(12)· · ·O(1) in all 3 complexes (4)–(6) [with
Acknowledgements
˚
H· · ·O distances of 2.44, 2.23, and 2.43 A], although
the factor that appears to determine the observed
geometries is the intermolecular Cu· · ·H(axial) inter-
We wish to thank Consejo Nacional de Ciencia y
´ ´
Tecnologıa (CONACyT) for financial support, Simon
´
Hernandez-Ortega for crystallographic work, and
´ ´
Fred A. Lopez-Duran for synthesizing complexes
(1) and (2).
˚
action [at 3.10, 3.05, and 2.93 A for (4)–(6),
respectively], which is absent in the deformed
tetrahedral structures of (2) and (3).
4. Conclusions
References
In the solid state structures of complexes (1)–(6),
the steric influence of the small cyclopropyl and
cyclobutyl substituent at the coordinating nitrogen
atom must play a minor role in determining the
geometric arrangement of the ligands around the
copper centres, for which a square planar coordination
environment is expected. Based on an electronic
argument, it seems plausible that the more electron
rich ligands, which by donation create a copper centre
resembling Cu(I), can favour the deformed tetrahedral
structure [3,7,28,29]. Although this kind of distortion
was therefore expected for compounds (5) and
[1] R.H. Holm, G.W. Everett Jr., A. Chakraborty, Prog. Inorg.
Chem. 7 (1966) 83.
[2] R.H. Holm, M.J. O’Connor, Prog. Inorg. Chem. 14 (1971) 241.
[3] H.S. Maslen, T.N. Waters, Coord. Chem. Rev. 17 (1975) 137.
[4] A.D. Garnovskii, A.L. Nivorozhin, V.I. Minkin, Coord. Chem.
Rev. 126 (1993) 1.
[5] A.D. Garnovskii, A.P. Sadimenko, M.I. Sadimenko, D.A.
Garnovskii, Coord. Chem. Rev. 173 (1998) 31.
[6] G.V. Panova, N.K. Vikulova, V.M. Potapov, Russ. Chem.
Rev. 49 (1980) 655.
´
[7] J.M. Fernandez-G, M. J. Rosales-Hoz, M. F. Rubio-Arroyo, R.
Salcedo, R. A. Toscano, A. Vela, Inorg. Chem. 26 (1987) 349.
[8] H. Yokoi, Bull. Chem. Soc. Jpn. 47 (1974) 3037.

I. Castillo et al. / Journal of Molecular Structure 657 (2003) 25–35
35
´ ´
[9] M. Aguilar-Martınez, R. Saloma-Aguilar, N. Macıas-Ruval-
´ ´
caba, R. Cetina-Rosado, A. Navarrete-Vazquez, V. Gomez-
[18] G. M. Sheldrick, SHELXS-97, Crystal Structure Solution,
Version 97-1, Institut Anorg. Chemie, University of Gottin-
gen, Germany, 1997.
´
Vidales, A. Zentella-Dehesa, R.A. Toscano, S. Hernandez-
´
Ortega, J.M. Fernandez-G, J. Chem. Soc., Dalton Trans. (2001)
[19] G. M. Sheldrick, SHELXL-97, Crystal Structure Refinement,
Version 97-1, Institut Anorg. Chemie, University of Gottin-
gen, Germany, 1997.
2346.
´
[10] J.M. Fernandez-G, M.R. Patin˜o-Maya, R.A. Toscano, L.
´ ´
Velasco, M. Otero-Lopez, M. Aguilar-Martınez, Polyhedron
[20] A.J.C. Wilson (Eds.), International Tables for X-ray Crystal-
lography, Kluwer, Dordrecht, 1992.
16 (1997) 4371.
´ ´
[11] J.M. Fernandez-G, S. Hernandez-Ortega, R. Cetina-Rosado,
[21] M. Takayama, Y. Tanaka, T. Nomura, Org. Mass Spectrom.
28 (1993) 1529.
´ ´
N. Macıas-Ruvalcaba, M. Aguilar-Martınez, Polyhedron 17
(1998) 2425.
[22] J.E. Kovacic, Spectrochim. Acta, Part A. 23 (1967) 183.
[23] L. Sacconi, M. Ciampolini, J. Chem. Soc. A (1964) 276.
[24] H. Tamura, K. Ogawa, A. Takeuchi, S. Yamada, Chem. Lett.
(1977) 889.
[12] M.L. Khorana, S.Y. Pandit, J. Indian, Chem. Soc. 40 (1963)
789.
[13] G.N. Tyson Jr., S.C. Adams, J. Am. Chem. Soc. 62 (1940)
1228.
[25] A.L. Spek, PLATON for MS-Windows, Multipurpose Crystal-
lographic Tool, Version 1.06, Utrecht University, Utrecht, The
Netherlands, 2003.
[14] Siemens, XSCANS. X-ray Single Crystal Analysis System,
Version 2.1b, Siemens Analytical X-ray Instrumental Inc,
Madison, Wisconsin, USA, 1994.
[26] George A. Jeffrey, An Introduction to Hydrogen Bonding,
Oxford University Press, New York, 1997.
[15] L.V. Azaroff, Acta Cryst. 8 (1955) 701.
[16] Bruker AXS SMART. Bruker Molecular Structure Analysis
Research Tool, Version 5.62, Bruker, Inc., Madison, USA,
2001.
[27] J. W. Steed, J.L. Atwood, Supramolecular Chemistry, Wiley,
New York, 2000.
[28] B. Pullman, P. Pullman, Progr. Org. Chem. 4 (1958) 31.
[29] H.H. Greenwood, R. McWeeny, Advan. Phys. Org. Chem. 4
(1966) 73.
[17] Bruker AXS SAINT. SAX Area-Detector Integration Pro-
gram, Version 6.04, Bruker, Inc., Madison, USA, 2001.