Synthesis, structural and solvent influence studies on solvatochromic of acetylacetonatocopper(II) with N,N′-dibenzylic or thiophene derivatives of ethylenediamine complexes

Article abstract of DOI:10.1016/j.molstruc.2005.07.018

Five mixed-chelate copper(II) complexes with the general formula [Cu(acac)(diam)]ClO₄, where acac is acetylacetonate ion and diam is N,N′-dibenzylic or thiophene derivatives of ethylenediamine were prepared and characterized by elemental analysis, spectroscopic and conductance measurements. The X-ray crystal analysis of these complexes demonstrated that ClO4- ions are bound weakly above and below of the chelate plane. In solution, the perchlorate ions are driven out by solvent molecules leading to their solvatochromism.

Full text of DOI:10.1016/j.molstruc.2005.07.018

Journal of Molecular Structure 779 (2005) 30–37
www.elsevier.com/locate/molstruc
Synthesis, structural and solvent influence studies on solvatochromic
of acetylacetonatocopper(II) with N,N0-dibenzylic or thiophene
derivatives of ethylenediamine complexes
a
Hamid Asadi , Hamid Golchoubia , Richard Welter
a,
b
*
aDepartment of Chemistry, University of Mazandaran, P.O. Box 453, Babol-sar 47415, Iran
´
Laboratoire DECMET, ILB, Universite Louis Pasteur, 4, rue Blaise Pascal 67000, Strasbourg
b
Received 14 June 2005; revised 12 July 2005; accepted 14 July 2005
Available online 25 August 2005
Abstract
Five mixed-chelate copper(II) complexes with the general formula [Cu(acac)(diam)]ClO4, where acac is acetylacetonate ion and diam is
N,N0-dibenzylic or thiophene derivatives of ethylenediamine were prepared and characterized by elemental analysis, spectroscopic and
conductance measurements. The X-ray crystal analysis of these complexes demonstrated that ClOK4 ions are bound weakly above and below
of the chelate plane. In solution, the perchlorate ions are driven out by solvent molecules leading to their solvatochromism.
q 2005 Elsevier B.V. All rights reserved.
Keywords: Mixed-chelate: Copper(II) complexes; Solvatochromism; N-ligand; X-ray crystal structure; Acetylacetonate
1. Introduction
attached to the acac moiety in order to study the electronic
properties, that imposed by these ligands on the copper ion
[14–18]. Another focus of attention was to study the
influence of the steric hindrance to the axial salvation
caused by N-alkyl ethylenediamine derivatives [19–23].
Copper (II) ions in these complexes show a strong Jahn–
Teller effect and can be anticipated to show simple and
regular changes in their electronic spectra according to the
strength of interaction with solvent molecules at the axial
sites.
Solvatochromic phenomenon in the mixed-chelates
metal complexes has received great attention because they
may be used as a Lewis acid–base color indicator [1] and
also utilizes to develop optical sensor materials to monitor
pollutant levels in the environment [2,3]. In this regard,
extensive studies have been concentrated on the mixed-
chelate complexes of copper(II) with acac and diamine
derivatives (acac, stands for acetylacetonate ion) [4–8].
Aside from the beautiful and exciting aspects of the color
chemistry of these compounds which may target such
systems, three principal goals have guided many of the
investigations of solvatochromism of the mixed-chelates
copper(II) complexes. Some of these complexes were
synthesized in order to better understand the role of the
counter ion in [Cu(acac)(diamine)]X (X is an univalent
anion such as ClOK4 , NOK3 and etc.) [9–13]. At other times,
these complexes were made with various substituents
In this work, the syntheses and the solvatochromic
behaviour of some of the perchlorate mixed-chelate
copper(II) complexes, that shown in Scheme 1, where x is
different aromatic derivative were studied. Based on our
knowledge, such investigations have not been employed on
any aromatic derivatives of diamine ligand.
2. Experimental
2.1. Materials and methods
*
Corresponding author. Fax: C98 1125242002.
E-mail addresses: h.golchobian@umz.ac.ir (H. Golchoubia), welter@
Diamine compounds of 1,6-bis(2-chlorobenzyl)-2,5-
diazahexane [24] and 1,6-bis(2-thiophene)-2,5-diazahexane
[25] were prepared according to published procedure. All
solvents were spectral-grade and all other reagents were
chimie.u-strasbg.fr (R. Welter).
0022-2860/$ - see front matter q 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2005.07.018

H. Asadi et al. / Journal of Molecular Structure 779 (2005) 30–37
31
display a strong band around 1640 cmK1 attributed to CaN
stretching mode.
Graphical abstract
X
The characterization data for 1,2-ethanediamine,N,N0-
bis(2-bromophenylmethylene): mp, 95–97 8C. IR, a strong
band at 1636 cmK1. 1H NMR (500 MHz in CDCl3) d: 4.03
(s, 4H, N–CH2), 7.19–7.34 (m, 6H, Ph–H), 7.95–8.06 (m,
2H, Ph–H), 8.66 (s, 2H, N]CH). Anal. calcd for
C16H14N2Br2: C, 48.76; H, 3.58; N, 7.11%. Found: C,
48.95; H, 3.27; N 7.34%.
+
O
O
N
N
Cu
The characterization data for 1,2-ethanediamine,N,N0-
bis(2-methylphenylmethylene): mp, 44–45 8C. IR, a strong
band at 1643 cmK1. 1H NMR (500 MHz in CDCl3) d: 2.41
(s, 6H, Ph–CH3), 4.02 (s, 4H, N–CH2), 7.13–7.29 (m, 6H,
Ph–H), 7.80–7.90 (m, 2H, Ph–H), 8.58 (s, 2H, NaCH).
Anal. calcd for C18H20N2: C, 81.78; H, 7.63; N, 10.60%.
Found: C, 81.54; H, 7.44; N 10.94%.
The characterization data for 1,2-ethanediamine,N,N0-
bis(phenylmethylene): mp: 48 49 8C. IR: a strong band at
1636 cmK1. 1H NMR (500 MHz in CDCl3) d, 3.98 (s, 4H, N–
CH2), 7.34–7.42 (m, 6H, Ph–H), 7.65–7.77 (m, 4H, Ph–H),
8.29 (s, 2H, NaCH). Anal. calcd for C16H16N2: C, 81.32; H,
7.82; N, 11.85%. Found: C, 81.73; H, 6.47; N 12.11%.
X
X=Ph, o-CH3-Ph, o-Cl-Ph, o-Br-Ph, o-thiophen
Scheme 1.
used as received. All the samples were dried to constant
weight under a high vacuum prior to analysis. Caution:
perchlorate salts are potentially explosive and should be
handled with appropriate care.
Conductance measurements were made at 25 8C with a
Jenway 400 conductance meter on 1.00!10K3 M samples
in CH3CN and ClCH2CH2Cl. Infrared spectra (potassium
bromide disk) were recorded using a Bruker FT–IR
instrument; only strong peaks are given. The electronic
absorption spectra were measured using a Braic2100 model
UV–Vis spectrophotometer. Elemental analyses were
performed on a LECO 600 CHN elemental analyzer.
Absolute metal percentages were determined by a Varian-
spectra A-30/40 atomic absorption-flame spectrometer. The
1H NMR spectra were recorded on a Bruker 500 Fourier
transform spectrometer.
2.2.2. General procedure for preparation of diamine
To the stirred solution of diimine (50 mmol) in 400 mL
methanol at room temperature was added gradually
NaBH4 (230 mmol) over 1 h. The resulting mixture was
allowed to stand overnight and was then warmed to the
boiling point for 1 h. To the obtained yellow solution was
added 5 mL acetic acid, so that a small amount of gas
evolution was observed. The resulting solution was
filtered and was taken basic by NaOH (4 M). The cloudy
mixture was then extracted from dichloromethane (6!
10 mL). The combined CH2Cl2 fractions were dried over
anhydrous Na2SO4. Filtration and concentration under
reduced pressure gave a pale-yellow oil as a quantitative
yield and sufficiently pure for the next reaction. However,
this compound can be purified more as follows: the
resulting diamine was dissolved in dichloromethane (5 mL
per a gram of the crude compound) and the solution was
cooled on an ice bath, and then hydrochloride salt of
amine compound was precipitated by the addition of conc.
hydrochloric acid. The white precipitate of the amine salt
was separated by suction filtration. The pure diamine was
liberated by dissolving the diamine salt in a minimum
amount of water and adding sodium hydroxide (4 M) until
the solution became basic. The resulting cloudy solution
was extracted by dichloromethane (6!10 mL). The
combined CH2Cl2 fractions were dried over anhydrous
Na2SO4. Filtration and concentration under reduced
pressure gave colorless oil. Typically 20% of the yield
was lost in the purification step. The significant difference
in the spectrum of the diamine from that of the diimine
was the disappearance CaN stretching band at around
1640 cmK1 and the emergence of a band at around
3300 cmK1 with medium intensity corresponding to
2.2. Synthesis
2.2.1. General procedure for preparation of diimine
A mixture of ethylenediamine (50 mmol) and the desired
benzaldehyde derivative (100 mmol) in 30 mL absolute
ethanol was stirred for 4 h at room temperature, during
which time, the desired diimine compound formed as a
precipitate. The precipitate was separated by filtration and
was then washed with cold ethanol and diethylether. The
desired diimine was obtained as colorless solid (26.5 mmol,
53%). The resultant diimine was sufficiently pure for the
further treatment. However, it can be purified more as
follows: the residue was dissolved in a minimal volume of
hot ethanol. After filtration, water was added dropwise to
the resulting clear solution, until the solution turned cloudy,
then an additional aliquot of water was added over time
(one-fourth of the volume that was added before). The
resulting mixture was allowed to stand overnight, during
which time, the crystalline compound was obtained. After
filtration it was then washed with cold ethanol (2!3 mL),
diethylether (2!3 mL) and hexane (2!3 mL), and dried
under a vacuum. Typically, 15% of the yield is lost in the
purification step. IR spectra of the diimine compounds

32
H. Asadi et al. / Journal of Molecular Structure 779 (2005) 30–37
the N–H stretching of secondary amine. For CHN analysis
purposes, these oily products were converted to the
corresponding solid ammonium chloride salts.
slowly added Cu(ClO4)2$6H2O (5 mmol) in water
(40 mL). The resulting mixture was allowed to stand
over night at room temperature. The obtained
crystals were collected by filtration and washed with
hexane.
The characterization data for 1,6-bis(2-boromophenyl)-
2,5-diazahexane (enBrPh): 1H NMR (500 MHz in CDCl3) d,
1.69 (s, 2H, N–H), 2.75 (s, 4H, –CH2–Ph), 3.64 (s, 4H, –
CH2–CH2–), 7.07 (m, 8H, Ph–H). Anal. calcd for
ammonium chloride salt C16H20N2Cl2Br2: C, 40.80; H,
4.28; N, 5.95%. Found: C, 40.58; H, 4.65; N, 6.12%.
The characterization data for 1,6-bis(2-methylphenyl)-2,
2.3. X-ray structure determination
Single crystals of I and IV were mounted on a Nonius
Kappa-CCD area detector diffractometer (Mo Ka lZ
˚
0.71073 A). The complete conditions of data collection
1
5-diazahexane (enmPh): H NMR (500 MHz in CDCl3) d,
1.70 (s, 2H, N–H), 2.42 (s, 6H, Ph–CH3), 2.90 (s, 4H, –CH2–
Ph), 3.64 (s, 4H, –CH2–CH2–), 7.25 (m, 8H, Ph–H). Anal.
calcd for ammonium chloride salt C18H26N2Cl2: C, 63.34;
H, 7.68; N, 8.21% Found: C, 63.13; H, 7.92; N, 7.83%.
The characterization data for 1,6-bis(benzyl)-2,5-diaza-
(Denzo software [26]) and structure refinements are given
in Table 1. The cell parameters were determined from
reflections taken from one set of 10 frames (1.08 steps in
phi angle), each at 20 s exposure. The structures were
solved using direct methods (SHELXS97) and refined on F2
using the SHELXL97 software [27]. The absorption
corrections were not applied. All non-hydrogen atoms
were refined anisotropically. Hydrogen atoms were
generated according to stereochemistry and refined using
a riding model in SHELXL97.
1
hexane (enPh): H NMR (500 MHz in CDCl3) d, 1.70 (s,
2H, N–H), 2.74 (s, 4H, –CH2–Ph), 3.76 (s, 4H, –CH2–
CH2–), 7.20 (m, 10H, Ph–H). Anal. calcd for ammonium
chloride salt C16H22N2Cl2: C, 61.34; H, 7.08; N, 8.94%.
Found: C, 61.57; H, 6.70; N, 9.11%.
The suitable crystals of [Cu(acac)(enTph)]ClO4, I and
[Cu(acac)(enCl)]ClO4, IV for the X-ray crystal structure
determination were grown by recrystallization from water:
methanol (4:1).
2.2.3. General procedure for preparation
of copper complexes
To the desired diamine (5 mmol), acetylacetone
(5 mmol), Na2CO3 (2.5 mmol) in ethanol (40 mL) were
Table 1
Crystallographic data
Compound
I
IV
Formula
C
17H23ClCuN2O6S2
C21H23Cl3CuN2O6
569.30
Formula weight
Temperature (K)
Crystal system
Space group
514.51
173(2)
173(2)
Tetragonal
43212
Tetragonal
P41212
˚
a (A)
˚
b (A)
˚
c (A)
13.4750(4)
13.4750(4)
13.0080(3)
90.00
13.682(4)
13.682(4)
13.612(4)
90.00
a (8)
b (8)
g (8)
90.00
90.00
90.00
90.00
3
˚
V (A )
2361.94(11)
4
2548.1(13)
4
Z
Dx (g cmK3
)
1.441
1.484
m(Mo Ka) (mmK1
F(000)
)
1.247
1.209
1060
1164
Crystal size (mm)
0.20!0.08!0.08
Blue polyhedron
0.71070
0.10!0.08!0.06
Blue polyhedron
0.71070
Crystal color and shape
Radiation (A); Mo Ka
qminKmax
2.14–30.01
0/18, 0/13, K18/18
3459, 1814, 0.047
O2s(I)
2.11–30.03
K19/13, K12/19, K18/19
3724, 2411, 0.0350
O2s(I)
Dataset [h,k,l]
Tot., uniq. data, R(int)
Observed data
No. of rfls, no. of parameters
R2, R1, wR2, wR1, Goof
Weighting function, where PZðF02 C2Fc2Þ=3
Max. and Av. shift/error
Flack x
3459, 128
3724, 151
0.1241, 0.0649, 0.1779, 0.1587, 0.956
2
0.1077, 0.0681, 0.1955, 0.1715, 1.035
2
wZ1=½s2ðF02ÞCð0:0800PÞ C0:0000Pꢀ
wZ1=½s2ðF02ÞCð0:1090PÞ C0:6880Pꢀ
0.000, 0.000
K0.01(3)
K0.561, 1.034
0.001, 0.000
K0.03(3)
K0.636, 1.095
K3
˚
Min, Max. Residual Den. (e A
)

H. Asadi et al. / Journal of Molecular Structure 779 (2005) 30–37
33
Table 2
Color, yields and analytical data of the complexes obtained
No.
Formula (color/yield)
X
Analysisa
H%
C%
N%
Cu%
I
[Cu(acac)(enTph)]ClO4 (Bluish violet/76%)
[Cu(acac)(enPh)]ClO4 (Bluish violet/74%)
[Cu(acac)(enmPh)]ClO4 (Bluish violet/77%)
[Cu(acac)(enClPh)]ClO4 (Bluish violet/93%)
[Cu(acac)(enBrPh)]ClO4 (Bluish violet/75%)
o-Thiophene
Ph
4.73 (4.47)
5.64 (5.37)
5.47 (5.84)
3.64 (4.37)
3.70 (3.78)
39.94 (39.65)
49.93 (50.15)
51.89 (52.04)
44.34 (44.11)
38.50 (38.17)
5.63 (5.44)
5.70 (5.57)
5.39 (5.27)
4.66 (4.90)
5.32 (5.44)
12.23 (12.34)
12.56 (12.63)
12.08 (11.97)
11.01 (11.12)
9.48 (9.61)
II
III
IV
V
o–CH3–Ph
o–Cl–Ph
o–Br–Ph
a
Calculated values are in parentheses.
3. Results and discussion
complexes cations are nearly planar and have a 2-fold
symmetry; the two Cu–N bonds in both complexes are
˚
practically of the same length (2.032(4) A for compound I
˚
and 2.040(4) A for compound IV), as well as the two Cu–O
The diamine ligands were readily prepared by a two-step
reaction. In the first step, an equivalent of ethylenediamine
was reacted with two equivalents of suitable aromatic
aldehyde to prepare the desired diSchiff bases. These
compounds were reduced by NaBH4 to give the correspond-
ing diamine, in the second step. The prepared diamine
compounds were sufficiently pure to prepare the mixed-
chelate complexes. The total yields of diamine formations
were typically greater than 90%. Finally, the mixed-ligand
copper(II) chelates were obtained with mixing of Cu(ClO4)
$6H2O, acacH, the diamine and Na2CO3 with molar ratios
of 1:1:1:0.5, respectively in ethanol–water mixture. The
typical yields were more than 74%. The color, yields and the
analytical data of the obtained complexes are shown in
Table 2 and indicated the formation of the mixed-chelate
copper(II) complexes.
˚
bonds (1.894(3) A for compound I and 1.891(3) A for
˚
compound IV). The bite distance for acac is 2.806 (6) and
˚
2.737(7) A for I and IV and for diamine chelate these values
˚
are 2.743(7) and 2.770(7) A, respectively. These distances
are similar to those observed in some [Cu(diamin)(acac)]2C
complexes [20]. The dihedral angle between CuO2 and
CuN2 coordination planes of complexes I and IV are 3.0(2)
and 7.6(1)8, respectively. The phenyl groups are directed
away from the N2CuO2 plane so that the angle between the
N2CuO2 plane and phenyl ring is 55(1)8 to minimize the
steric hindrance in equatorial coordinations. The same
behavior is observed in complex I, so that the angle between
the N2CuO2 plane and thiophene ring is 56(1)8. The five-
membered chelate ring in both complexes is puckered; the
torsion angle of N–C1–C1b–Nb of K52(1)8 for I and 56(1)8
for IV are quite normal, but the mean values of C–C–N–Cu
of 39(1)8 for I and 41(1)8 for IV in the chelates show a slight
deformation.
3.1. X-ray structure
The ORTEP plots of compounds I and IV are depicted,
respectively, in Figs. 1 and 2 with atom numbering scheme
(the hydrogen atoms are omitted for clarity). The selected
bond lengths and angles are given in Table 3. In both
Two ClOK4 ions lie above and below the plane of chelate
˚
rings; both length of Cu–OClO3 is 2.60(1) A in I and
˚
2.71(1) A in IV, which is within the range of 2.2–2.9 A,
˚
known as the axial Cu–O bond length [28], and hence the
Fig. 1. ORTEP drawing of [Cu(acac)(enTph)]ClO4 (I).
Fig. 2. ORTEP drawing of [Cu(acac)(enClPh)]ClO4 (IV).

34
H. Asadi et al. / Journal of Molecular Structure 779 (2005) 30–37
Table 3
˚
Selected bond lengths (A) and angles (deg.) for [Cu(acac)(enTph)]ClO4 (I)
and [Cu(acac)(enClPh)]ClO4 (IV)
(I)
1.894(3)
IV
1.891(3)
Cu–O1
Cu–N
2.032(4)
95.6(3)
2.040(4)
92.7(2)
O1–Cu–O1
O1–Cu–N
O1–Cu–Nc
N–Cu–N
89.79(19)
174.22(19)
84.9(2)
91.17(14)
173.55(16)
85.5(2)
perchlorate anions may weakly coordinate in the both
complexes. The distance shows that the forces holding ClOK4
ions in these complexes are relatively weak. Such ions will
be easily driven out from the coordination sphere by solvent
molecules in solution, which will be more sensible bonded
with the increase in their donor power, leading to the
observed solvatochromism.
Fig. 4. Crystal packing of complex [Cu(acac)(enClPh)]ClO4 (IV).
the free ligands. The absorption band around 1040 cmK1
is probably due to the stretching vibration of carbon–
nitrogen bond [14]. The strong bands at 1440–1464 cmK1
are very likely associated with the scissoring vibration of
–CH2– groups [14]. The band at around 750 cmK1 that
in the spectra of free diamine ligands appears broader
and is split in two in region of 730–790 cmK1 may be
due to the rocking vibration of CH2 groups [14]. The
stretching vibrations of N–CH2 groups in the free
ligands, and the well-known bands in the region
2850G100 cmK1 that are associated with it, are more
important since they serve as an indication of coordi-
nation of diamine ligand. Upon covalent bond formation,
these absorption bands apparently lose intensity, become
shifted to the higher frequencies and mix with other C–H
absorption bands. Dependence on coordination is also
exhibited by the intense and narrow band occurring at
3230G30 cmK1 which is associated with N–H vibration
and is observed at around 3300 cmK1 and broader in
the free diamine ligands. As the lone pair of electrons of
the donor nitrogen atoms becomes involved in the metal–
ligand bond, the transfer of electron density to the metal
and the subsequent polarization of the ligands involves
electron depopulation of the N–H bond which culminates
in a shift to lower frequencies.
Figs. 3 and 4 show the packing arrangement in the
crystals of complexes I and IV. The structures comprises
layers of cations aligned in the ab plane and intercalated
anions. From these figures, it is clearly seen that the
complex molecules form intermolecular stacking through
weak contacts of Cu–O–(ClO2)O–Cu along the c-axis
(Table 1). The elongation of c value in IV is due to the
longer bond distances of Cu–OClO3 than that of I. To
accommodate large Ph–Cl groups instead of thiophene
groups, the cell volume of IV is larger than I. The density of
crystal IV (1.484 g cmK3) is slightly higher than that of I
(1.441 g cmK3).
3.2. IR spectra
In the IR spectra of compounds I–V several bands
appear in the region 700–1600 cmK1 that are also
observed, although with minor shifts, in the spectra of
Formation of a six-membered chelate ring comprising
the copper(II) and the oxygen atoms of the acac ligand is
disclosed by two intense absorption bands in the region
1520–1590 cmK1 that can be assigned to the CaC and CaO
vibrational modes [29–32].
The presence of the ClOK4 group is declared by two
intense bands at around 1110 and 620 cmK1 which are
attributed to the anti-symmetric stretching and anti-
symmetric bending vibration modes, respectively. The
former band at 1110 cmK1 of compound I–V, not with-
standing other groups that also absorb in the same region, is
split with a poorly defined maximum showing the
deformation from Td symmetry.
Fig. 3. Crystal packing of complex [Cu(acac)(enTph)]ClO4 (I).

H. Asadi et al. / Journal of Molecular Structure 779 (2005) 30–37
35
Table 4
Molar conductivities data (Lm) of the complexes (UK1 cm2 molK1, at 25 8C)a in 1,2-dichloroethane and acetonitrile
Complexes
I
II
III
IV
4.9
155.4
V
b
–
ClCH2CH2Cl
CH3CN
4.6
160.3
4.2
155.0
4.8
140.9
157.5
Standard values for a 1:1 electrolyte type in ClCH2CH2Cl and CH3CN are in the range of 10–20 and 120–160 (UK1 cm2 molK1, at 25 8C), respectively. From
Ref. [33].
a
Concentration: ca.1!10K3 M.
This complex is sparingly soluble in ClCH2CH2Cl.
b
Table 5
Electronic spectra of the complexes in solid state and various solvents: lmax (nm) (3 (MK1 cmK1
)
Complex-
esa
lmax/nm (3max)
Py
DMSO
DMF
THF
MeOH
Acetone
CH3CN
MeNO2
CH2Cl2
Solid state
I
638(97)
646(117)
645(115)
654(93)
653(92)
612(102)
616(113)
614(121)
622(99)
624(98)
605(97)
610(107)
606(116)
615(93)
618(92)
586(96)
591(93)
581(94)
583(97)
584(110)
583(118)
590(99)
590(97)
552(95)
571(86)
572(96)
–
570
572
568
575
576
II
III
IV
V
594(103)
b
–
594(111)
b
–
585(102)
b
–
554(111)
b
–
598(91)
598(90)
608(94)
602(93)
591(91)
594(90)
560(96)
560(98)
576(99)
574(100)
a
Cf. Table 1.
b
Complex of III is sparingly soluble in these solvents.
3.3. Conductometric data
In solution however, the d–d band of all complexes
moves to the red with the increase of the DN of the solvent
(Table 5 and Fig. 5). In general, all spectra in solvents with
low donor numbers are very similar to the solid state spectra
and show nearly the same lmax (Fig. 6). The lmax values of
the complexes in any solvent shift gradually to the red in
order of I!II–III!IV–V and the complexes become
somewhat more solvatochromic in the same order. This
solvation, which tends to shift the d–d band to the red, is
increased by the donor power of the solvents. It is known
that the increase of steric hindrance of the axial coordination
of incoming solvents tends to make the complex more
solvatochromic, bringing about a large structural change
with progressive solvation of the complex caused by the
increase of DN. It is suggested that these spectral changes
are due to in general, to the changes in the degree of axial
salvation of the complexes. A comparison in the spectra of
complexes I to III in Fig. 5 shows no notable differences in
lmax of these complexes in each selected solvent, although
complex III imposes a larger steric hindrance to the axial
Table 4 illustrates the molar conductivity values of
complexes I–V in solvents of ClCH2CH2Cl and acetonitrile.
The results show that in acetonitrile all of the five
complexes are 1:1 electrolyte [33]. However, in solvent of
1,2-dichloroethane the values are much lower than that for
1:1 electrolyte. Thus, it seems that an ion-pair formation (or
anion coordination) might exist in some extent in ClCH2-
CH2Cl. These results are in general agreement with the
expectation from the spectral data and the X-ray results.
3.4. Solvatochromism
The electronic absorption spectra of complexes I–V were
measured in solid state and in the solution state in some
organic solvents with different donor number (DN). The
donor number expresses a measure of coordinating ability of
solvent on the standard of that of dichloromethane (DCM)
or dichloroethane (DCE) [34]. Values of DN of the solvents
used are as follows: DCM and DCEZ0.0; MeNO2Z2.7;
MeCNZ14.1; acetoneZ17.0; THFZ20.0; MeOHZ23.0;
DMFZ26.6; DMSOZ29.8; pyZ33.1. The solid-state
spectra of compounds I–V were nearly identical to each
other, showing a broad structureless band (envelop) in
visible region 572G4 nm. This band shows slightly bath-
ochromic shifts as the substituent attached to the amine
moiety is varied. This suggested that the steric and/or
electronic effects might affect the shift in d–d band of the
copper(II) mixed-chelate complexes. The similarities in the
spectroscopic behavior of these complexes with those of
known structures [21] and also the X-ray structures
0.6
0.5
DMSO
py
0.4
0.3
0.2
0.1
0
MeOH
acetone
MeNO2
400
450
500
550
600
650
700
750
800
λ (nm)
indicated
chromophore.
a
square-planar geometry of CuN2O2
Fig. 5. Absorption spectra of [Cu(acac)(enBrPh)]ClO4 in selected solvents.

36
H. Asadi et al. / Journal of Molecular Structure 779 (2005) 30–37
λ /nm
660
670 655 640 625 610 595 580 565 550
640
620
600
580
560
540
c
i
II
a
b
g
d e
h
f
[Cu(acac)(enTph)]ClO4, I
III
IV
V
[Cu(acac)(enPh)]ClO4, II
[Cu(acac)(enmPh)]ClO4, III
[Cu(acac)(enClPh)]ClO4, IV
[Cu(acac)(enBrPh)]ClO4, V
I
0
10
20
30
40
Fig. 6. lmax values of complexes I–V in various solvents. The lmax in solid
state is indicated by short arrows. The symbols a to i represent: aZpy, bZ
DMSO, cZDMF, dZMeOH, eZTHF, fZacetone, gZCH3CN, hZ
MeNO2 and iZCH2Cl2.
DN
Fig. 7. Dependence of the lmax values of compounds I–V on the solvent
donor number value.
Thus reducing the axial interactions of the ClOK4 and
eliminating the tetragonal distortion [11].
coordination of incoming solvents than complex I or II.
These evidences might reveal that steric hindrance is not
operative in the solvatochromic behavior of these
complexes. On the other hand, if electronic effect has a
contribution in the solvatochromic behavior of these
complexes it is expected that substitution of electron-
attracting or electron releasing substituents on the diamine
moiety changes the Lewis acidity of CuN2O2 chromophore.
Hence, if we assume II as a base compound it is anticipated
that compounds IV and V might enhance the Lewis acidity
of CuN2O2 chromophore and promote covalent interactions
of the solvent molecules to the copper center and the d–d
band moves to the longer wavelength (red shift). In contrast,
compound III decrease the Lewis acidity of the central atom
and the d–d band moves to the shorter wavelength (blue
shift). Although this shift is observed in number of the
solvents, a lack of solubility of compound III in other
solvents impedes us to make a definite conclusion.
4. Supplementary material
CCDC 267195 and 267196 contain the supplementary
crystallographic data for this paper. These data can be
obtained free of charge via www.ccdc.cam.ac.uk/conts/
retrieving.html (or from the Cambridge Crystallographic
Data Centre, 12, Union Road, Cambridge CB2 1EZ, UK;
fax: C44 1223 336033).
Acknowledgements
We are grateful for the financial support of Mazandaran
University of the Islamic Republic of Iran.
Assuming that the approach of the solvent occurs along
the z-axis, the solvent molecules are repelled by the two
electrons in the d2z orbital of copper(II) and only the more
basic species can force their way in to form relatively strong
bonds. Upon coordination, they exert a z component field
proportional to their position in the spectrochemical series.
Thus while solvents of low basicity (low donor number)
have no effect in the band maxima, other that are
considerably more basic induce large red shifts.
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