Syntheses of mixed chelate copper(II) complexes containing β-ketoaminato and diamine ligands: Solvatochromism study

Article abstract of DOI:10.1016/j.ica.2012.08.008

Three new mixed-chelate Cu(II) complexes incorporating N,N,N′, N′-tetramethylenediamine (tmen) or N,N-dimethyl,N′-benzyl- ethylenediamine (dmben) as diamine chelate and a β-ketoaminato such as 4-amino-3-penten-2-onato (APO) or 3-amino-3-phenyl-2-buten-1-onato (APBO) with the general formula [Cu(β-ketoamine)(diamine)]ClO₄ were prepared and characterized. Their solvatochromic properties were studied by visible spectroscopy. X-ray crystal analysis confirmed that copper (II) ion in [Cu(APO)(tmen)]ClO₄ and[Cu(APBO)(tmen)]ClO₄ is almost in a square planar environment. Structure of [Cu(APO)(dmben)]ClO₄ was investigated by DFT calculation. The solvent-dependent visible spectroscopic absorption maxima, ν_max, were analyzed using stepwise multiple linear regression (SMLR) method to find the best model explaining the observed positive solvatochromism. The analysis demonstrated that among different solvent parameters, donor number (DN) is a dominant factor responsible for the shift in the d-d absorption band of the complexes to the lower wavenumber with increasing its values. The importance of steric effect in the diamine ligand and more delocalization of pi-bands in the β-ketoamine on the spectral and SMLR measurements are discussed.

Full text of DOI:10.1016/j.ica.2012.08.008

Inorganica Chimica Acta 394 (2013) 1–9
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Inorganica Chimica Acta
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Syntheses of mixed chelate copper(II) complexes containing b-ketoaminato
and diamine ligands: Solvatochromism study
a
b
b
Hamid Golchoubian a, , Ehsan Rezaee , Giuseppeh Bruno , Hadi Amiri Rudbari
⇑
a Department of Chemistry, University of Mazandaran, Babol-sar 47416-95447, Iran
b Dipartimento di Chimica Inorganica, Vill. S. Agata, Salita Sperone 31, Università di Messina, 98166 Messina, Italy
a r t i c l e i n f o
a b s t r a c t
Three new mixed-chelate Cu(II) complexes incorporating N,N,N0,N0-tetramethylenediamine (tmen) or
N,N-dimethyl,N0-benzyl-ethylenediamine (dmben) as diamine chelate and a b-ketoaminato such as
4-amino-3-penten-2-onato (APO) or 3-amino-3-phenyl-2-buten-1-onato (APBO) with the general
formula [Cu(b-ketoamine)(diamine)]ClO4 were prepared and characterized. Their solvatochromic proper-
ties were studied by visible spectroscopy. X-ray crystal analysis confirmed that copper (II) ion in
[Cu(APO)(tmen)]ClO4 and[Cu(APBO)(tmen)]ClO4 is almost in a square planar environment. Structure of
[Cu(APO)(dmben)]ClO4 was investigated by DFT calculation. The solvent-dependent visible spectroscopic
Article history:
Received 29 June 2012
Received in revised form 24 July 2012
Accepted 2 August 2012
Available online 24 August 2012
Keywords:
Mixed-chelate
b-Ketoamine
Solvatochromism
SMLR method
Copper(II) complexes
Diamine
absorption maxima, mmax, were analyzed using stepwise multiple linear regression (SMLR) method to find
the best model explaining the observed positive solvatochromism. The analysis demonstrated that
among different solvent parameters, donor number (DN) is a dominant factor responsible for the shift
in the d–d absorption band of the complexes to the lower wavenumber with increasing its values. The
importance of steric effect in the diamine ligand and more delocalization of pi-bands in the b-ketoamine
on the spectral and SMLR measurements are discussed.
Ó 2012 Elsevier B.V. All rights reserved.
1. Introduction
vast collection of solvatochromic complexes and compounds, a
certain class of complexes such as mixed-chelate complexes of
Through the past decade, chromotropism behaviors of inorganic
complexes have been interested and investigated by many
researchers [1–3]. Chromotropism means the reversible color
transformation of the materials due to the surrounding physical
and chemical conditions such as temperature (thermochromism),
solvent (solvatochromism), pressure (piezochromism), light
(photochromism) and electro-redox reaction (electrochromism)
[4]. This phenomenon has many applications in thermo-sensitive,
imaging, photo-switching and sensor materials [5,6]. One of the
most attractive applications in inorganic chemistry is the use of
solvatochromism behavior of complexes in Lewis acid–base indica-
tors [7]. The origin of solvatochromism phenomena in metal com-
plexes are classified into two general types [8,9]; in the first type,
metal complexes in solution are interacted by solvent molecules in
a direct fashion due to the direct attachment of the solvent mole-
cules onto metal center and by indirect interactions between sol-
vent molecules and ligands in the second type. In copper(II) and
nickel(II) complexes with square planar structures the first type
solvatochromism often observed while coordinatively saturated
complexes are examples of the second type. Although there are a
copper(II) exhibit considerable color change over a wide range of
solvent used [1,10,11]. This is due to presence of strong John–Teller
effect in these complexes, the d–d transition of copper(II) can be
shifted because of the interactions of the solvent molecules with
the axial sites of the copper center. Although there are many
reports for syntheses and solvatochromic properties of mixed-
chelate copper(II) complexes derived by b-diketones and diamines
[12–15], based on our knowledge, such investigations have not
been employed on synthesis and solvatochromism of mixed-che-
late complex containing b-ketoaminato. By now, only some reports
are available in literature concerning preparation of bis(b-ketoam-
inato) complexes and their properties and applications [16–20].
Therefore, the solvatochromism of this class of mixed-chelate com-
plexes is still unexplored. In this report we synthesized and char-
acterized three new mixed-chelate copper(II) complexes with a
general formula [Cu(b-ketoamine)(diamine)]ClO4 shown in Fig. 1,
where b-ketoamine is 4-amino-3-penten-2-onato (APO) or 3-
amino-3-phenyl-2-buten-1-onato (APBO) and diamine stands for
N,N-dimethyl,N0-benzylethylenediamine (dmben) or N,N,N0,N0-tet-
ramethylethylenediamine (tmen). Furthermore, solvatochromism
behaviors of the mixed-chelate complexes in a number of organic
solvents have been investigated. The effects of substitutions
attached to the diamine and b-ketoaminato ligands on the
solvatochromism of these complexes have been examined. There
⇑
Corresponding author. Tel./fax: +98 (112) 5342350.
E-mail addresses: h.golchobian@umz.ac.ir (H. Golchoubian), gbruno@unime.it
(G. Bruno), hamirirudbari@unime.it (H.A. Rudbari).
0020-1693/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.ica.2012.08.008

2
H. Golchoubian et al. / Inorganica Chimica Acta 394 (2013) 1–9
ber of the complexes and solvent parameters (DN, AN, ET(30), a, b,
p⁄) was studied using multiple linear regression (MLR) method.
2. Experimental
2.1. Materials and methods
N,N-dimethyl,N0-benzyl-ethylenediamine [28], APO [29] and
the complexes of [Cu2(OH)2(tmen)2](ClO4)2, [Cu2(OH)2(dmben)2](-
ClO4)2 [30] and [Cu(APO)2] [31], were prepared according to pub-
lished procedures. All solvents were spectral-grade and all other
reagents were used as received. All the samples were dried to con-
stant weight under a high vacuum prior to analysis. Caution: per-
chlorate salts are potentially explosive and should be handled with
appropriate care. Conductance measurements were made at 25 °C
with a Jenway 400 conductance meter on 1.00 ꢀ 10ꢁ3 M samples
in selected solvents. Infrared spectra (potassium bromide disk)
were recorded using a Bruker FT-IR instrument. The electronic
absorption spectra were measured using a Braic2100 model UV–
Vis spectrophotometer. 1H NMR and 13C NMR spectra were re-
corded on a Bruker 400DRX Spectrometer. 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 following solvents
were used for solvatochromic study: dichloromethane (DCM),
nitromethane (NM), nitrobenzene (NB), benzonitrile (BN), acetoni-
trile (AN), propionitrile (PN), acetone (Ac), tetrahydrofuran (THF),
ethanol (EtOH), methanol (MeOH), dimethylformamide (DMF),
dimethylsulfoxide (DMSO), pyridine (Py) and hexamethylphospho-
rictriamide (HMPA).
Fig. 1. The three complexes used in this study.
are some empirical scales due to nature of solute–solvent interac-
tion such as Dimroth and Reichardt’s ET(30), Kosower’s Z, Kamlet
and Taft’s
a e and Gutman’s donor, DN
, b, p⁄, dielectric constant,
and acceptor numbers, AN [21–26]. While ET(30) is used widely
in organic compounds [27], DN and AN have spread use for transi-
tion metal complexes [3]. Utilization of some statistical software
like SPSS has been interested recently by researches to find an opti-
mized model to describe the relation between mmax in absorption
spectra of complexes in solution and the solvent’s polarity scales
[1,10,11]. In this study, correlation between maximum wavenum-
Table 1
Crystal data and structure refinement for the complex of 1 and 3.
Compound
[Cu(APO)(tmen)]ClO4, 1
44H96Cl4Cu4N12O20
[Cu(APBO)(tmen)]ClO4, 3
Formula
Formula weight
C
C16H26ClCuN3O5
439.39
1509.29
Color
T (K)
dark blue
296(2)
dark blue
296(2)
k (Å)
0.71073
0.71073
Crystal system
Space group
monoclinic
P21/c
orthorhombic
Pbca
Crystal size (mm)
Unit cell dimensions
0.45 ꢀ 0.26 ꢀ 0.16
0.49 ꢀ 0.21 ꢀ 0.14
a (Å)
b (Å)
c (Å)
15.8361(7)
30.3950(12)
15.2061(7)
106.291(2)
7015.4(5)
15.0967(5)
15.7021(5)
16.8468(6)
90
b (°)
V (Å3)
3993.5(2)
Z
4
8
Calculated density (Mg/m3)
1.427
1.462
F(000)
3152
1832
h (°)
Index ranges
1.34–27.00
ꢁ20 6 h 6 20,
ꢁ38 6 k 6 38,
ꢁ18 6 19
2.23–27.00
ꢁ19 6 h 6 19,
ꢁ20 6 k 6 20,
ꢁ21 6 21
Reflections collected
197186
190140
Independent reflections Rint
Completeness to 2 h = 27.00 (%)
Absorption correction
15342 (0.0558)
100.0
multi-scan
15342/6/811
R1 = 0.0533, wR2 = 0.1441
1.036
4361 (0.0272)
100.0
multi-scan
4361/0/276
R1 = 0.0331, wR2 = 0.0892
1.072
Data/restraints/parameters
Final R indicesa[I > 2 (I)]b
r
Goodness-of-fit on F2c
R indices (all data)
R1 = 0.1010, wR2 = 0.1815
0.830 and ꢁ0.556
R1 = 0.0404, wR2 = 0.1061
0.381 and ꢁ0.496
Largest difference in peak and hole (e Åꢁ3
)
P
P
a
b
c
R = ||Fo| ꢁ |Fc||/ |Fo|.
P
P
2
wR = [( [Fo ꢁ Fc2)2]/ [w(Fo2)2]½.
P
S = [w(Fo ꢁ Fc2)2/(Nobs ꢁ Nparam)]½.
2

H. Golchoubian et al. / Inorganica Chimica Acta 394 (2013) 1–9
3
2.1.1. Preparation of APBO
A
B
Ph
Ph
Benzoylacetone (1.6 g, 10 mmol) was dissolved in methanol
(4 mL), and the bright yellow solution was cannulated into a 3-
neck flask equipped with a reflux condenser and an addition funnel
containing aqueous ammonia 25% (50 mL). The stirred solution
heated to 90 °C followed by slow dropwise addition of ammonia
solution. Stirring was continued at 90 °C for 2.5 h. The resulting
solution was then allowed to cool slowly to room temperature.
The milky crystals were collected, washed with carbon tetrachlo-
ride. The typical yields were 65–75%. Anal. calc. for C10H11NO
(MW: 161.20 g molꢁ1): C, 74.51; H, 6.88; N, 8.69%. Found: C,
NH
Cu
O
NH
N
NH
N
Cu
NH
O
74.62; H, 6.68; N, 8.74%. Selected IR data (
m
/cmꢁ1 using KBr):
(C@O) (ketone). 1H NMR (400 MHz,
Fig. 2. The two possible structures for complex 2.
3330 (NH2) (amine), 1610
m
m
CDCl3, d, ppm): 2.09 (s, 3H, CH3); 5.53 (s, 1H, NHꢂ ꢂ ꢂO); 5.76 (s,
1H, CH); 7.28–7.91 (m, 5H, Ar–H); 10.24 (s, 1H, NH). 13C NMR
(400 MHz, CDCl3, d, ppm): 22.93 (–CO–CH3), 92.28 (–CO–CH–
CNH2–), 127.12–130.85 (C-aromatic), 140.14 (C–NH2), 189.49
(C@O).
2.1.2. Preparation of [Cu(APBO)2]
Cu(APBO)2 was synthesized according to similar published pro-
cedure [31] as follow: to the solution of APBO (2 mmol, 0.32 g) and
aqueous ammonia 25% (1 mL) in ethanol (10 mL), were added
Cu(SO4)2ꢂ5H2O (2 mmol, 0.5 g). The resultant solution was allowed
to stir for one hour and the green precipitate was filtered and col-
lected. The yield was 45%. Anal. calc. for C20H20ClCuN2O6 (MW:
483.38 g molꢁ1): C, 49.69; H, 4.17; N, 8.80; Cu, 13.15%. Found: C,
49.40; H, 4.38; N, 8.66; Cu, 13.09%. Selected IR data (
m
/cmꢁ1 KBr
(C@N).
disk): 3320 (NH2) (amine), 1587 (C@O) (ketone), 1531 m
m
m
2.1.3. Preparation of [Cu(APO)(tmen)]ClO4, complex 1
To the solution of N,N,N0,N0-tetramethylethylenediamine
(tmen) (6 mmol, 0.9 mL), APO (6 mmol, 0.6 g), Na2CO3 (3 mmol,
0.32 g) in ethanol (20 mL) were slowly added Cu(ClO4)2ꢂ6H2O
(6 mmol, 2.2 g) in water (20 mL). The mixture was stirred for 1 h
in room temperature. The resultant clear brown solution was al-
lowed to stand overnight. After concentration at room tempera-
ture, dark blue crystals were collected by filtration. Appropriate
single crystals for X-ray crystallography were obtained directly
from the reaction mixture. The typical yield was 60%. M.P. = 123–
124 °C. Anal. calc. for C11H24N3O5CuCl (MW = 377.32 g moleꢁ1): C,
35.01; H, 6.41; N, 11.14; Cu, 16.84%. Found: C, 35.10; H, 6.50; N,
Fig. 3. ORTEP view of complex 1. For clarity. Only one complex cation of the
asymmetric unit is shown. Non H-atoms represented as displacement ellipsoids are
plotted at the 50% probability level, while H atoms are shown as small spheres of
arbitrary radius.
11.04; Cu, 17.02%. Selected IR data (
(NH2) (amine), 1580 (C@O) (ketone), 1520
(Cl–O str.) (perchlorate), 610
m
/cmꢁ1 KBr disk): 3322
(C@N), 1405 (–
(Cl–O be d.)
Table 2
m
m
m
m
m
Selected bond lengths (Å) and angles (°) for complex 1.
CH2– bend.), 1105
m
m
Bond distances(Å)
Bond angles(°)
(perchlorate).
N(1)–Cu(1)
N(2)–Cu(1)
N(3)–Cu(1)
O(1)–Cu(1)
C(2)–N(1)
1.907(5)
2.037(6)
2.041(6)
1.901(5)
1.316(8)
1.277(8)
1.906(5)
2.052(5)
2.040(5)
1.895(5)
1.303(8)
1.284(8)
1.911(5)
2.059(5)
2.046(5)
1.895(5)
1.285(8)
1.93(9)
O(1)–Cu(1)–N(1)
O(1)–Cu(1)–N(2)
N(1)–Cu(1)–N(2)
O(1)–Cu(1)–N(3)
N(1)–Cu(1)–N(3)
N(2)–Cu(1)–N(3)
O(2)–Cu(2)–N(4)
O(2)–Cu(2)–N(5)
N(4)–Cu(2)–N(5)
O(2)–Cu(2)–N(6)
N(4)–Cu(2)–N(6)
N(5)–Cu(2)–N(6)
O(3)–Cu(3)–N(7)
O(3)–Cu(3)–N(8)
N(7)–Cu(3)–N(8)
O(3)–Cu(3)–N(9)
N(7)–Cu(3)–N(9)
N(8)–Cu(3)–N(9)
O(4)–Cu(4)–N(10)
O(4)–Cu(4)–N(11)
N(10)–Cu(4)–N(11)
O(4)–Cu(4)–N(12)
N(10)–Cu(4)–N(12)
N(11)–Cu(4)–N(12)
92.72(2)
172.22(2)
95.01(2)
87.62(14)
178.74(3)
85.52(2)
92.79(2)
171.13(2)
95.65 (2)
86.23(2)
178.85(2)
85.35(2)
92.56(2)
170.54(2)
95.83 (2)
87.38(2)
169.01(2)
85.21(2)
92.21(2)
171.30(2)
95.76(2)
87.52(19)
174.58(2)
84.87(2)
2.1.4. Preparation of [Cu(APO)(dmben)]ClO4, complex 2
This compound was prepared according with the same
procedure used for compound 1, except that N,N-dimethyl-
N0-dibenzyl-1,2-diaminoethane (dmben) was used instead of N
N,N0,N0-tetramethylethylenediamine (tmen). The complex was
obtained as dark green–brown solid with typical yield of 50%.
C(4)–O(1)
N(4)–Cu(2)
N(5)–Cu(2)
N(6)–Cu(2)
O(2)–Cu(2)
C(15)–N(4)
C(13)–O(2)
N(7)–Cu(3)
N(8)–Cu(3)
N(9)–Cu(3)
O(3)–Cu(3)
C(26)–N(7)
C(24)–O(3)
N(10)–Cu(4)
N(11)–Cu(4)
N(12)–Cu(4)
O(4)–Cu(4)
C(35)–N(10)
C(37)–O(4)
M.P. = 76 °C (°). Anal. calc. for
(MW = 466.42 g moleꢁ1): C, 41.20; H, 6.07; N, 9.01; Cu, 13.62%.
Found: C, 41.15; H, 5.71; N, 8.97; Cu, 13.80%. Selected IR data (
cmꢁ1 KBr disk): 3318 (m, N–H str.), 3280
(NH2) (amine), 1583
(C@O) (ketone), 1520 (C@N), 1410 (–CH2– bend.), 1100
str.) (perchlorate), 612 (Cl–O bend.) (perchlorate).
C16H26N3O5CuClꢂ1.5 H2O
m
/
m
m
m
m
m
(Cl–O
m
2.1.5. Preparation of [Cu(APBO)(tmen)]ClO4, complex 3
1.904(5)
2.042(5)
2.043(5)
1.912(4)
1.313(8)
1.277(7)
This compound was prepared according with the similar proce-
dure used for compound 1, but APBO was used in place of APO. The
complex was obtained as dark blue solid with typical yield of 65%.
M.P. = 190 °C (dec). Anal. calc. for
C16H26N3O5CuCl (MW =
439.39 g moleꢁ1): C, 43.74; H, 5.96; N, 9.56; Cu, 14.46%. Found:

4
H. Golchoubian et al. / Inorganica Chimica Acta 394 (2013) 1–9
Fig. 4. Crystal packing of complex 1. Dotted lines indicate weak interactions.
Fig. 5. ORTEP view of complex 3. Non H-atoms represented as displacement ellipsoids are plotted at the 30% probability level, while H atoms are shown as small spheres of
arbitrary radius. The perchlorate is omitted for clarity.
C, 43.47; H, 6.00; N, 9.53; Cu, 14.54%. Selected IR data (
disk): 3320 (NH2) (amine), 1594 (C@O) (ketone), 1521
1415 (–CH2– bend.), 1076 (Cl–O str.) (perchlorate), 624
bend.) (perchlorate).
m
/cmꢁ1 KBr
(C@N),
(Cl–O
Table 3
Selected bond lengths (Å) and angles (h) for complex 3.
m
m
m
m
m
m
Bond distances(Å)
Bond angles(°)
N(1)–Cu(1)
N(2)–Cu(1)
N(3)–Cu(1)
O(1)–Cu(1)
C(2)–N(1)
C(4)–O(1)
1.9220(18)
2.0481(18)
2.0497(18)
1.9049(15)
1.297(3)
O(1)–Cu(1)–N(1)
O(1)–Cu(1)–N(2)
N(1)–Cu(1)–N(2)
O(1)–Cu(1)–N(3)
N(1)–Cu(1)–N(3)
N(2)–Cu(1)–N(3)
92.14(7)
170.46(7)
96.94(8)
86.75(7)
167.79(8)
84.98(8)
2.2. X-ray structure determination
The X-ray data for compound 1 and 3 were collected on a Bru-
ker–Nonius X8 ApexII diffractometer equipped with a CCD area
detector by using graphite-monochromated Mo Ka radiation
(k = 0.71073 Å) generated from a sealed tube source. Data were
collected and reduced by SMART and SAINT software [32] in the
Bruker package. The structure was solved by direct methods [33]
1.288(2)
and then developed by least squares refinement on F2 [34,35].
The non-H atoms found in the electron density map were refined
anisotropically. All non-H atoms were placed in calculated

H. Golchoubian et al. / Inorganica Chimica Acta 394 (2013) 1–9
5
Fig. 6. Infrared spectra of [Cu(APO)2], [Cu2(dmben)2(OH)2](ClO4)2 and [Cu(APO)(dmben)](ClO4) complexes.
positions with the ‘‘riding-model technique’’. Details concerning
collection and analysis are reported in Table 1.
number of the complexes with the solvent parameters using the
SPSS/PC software package [36]. The best model is obtained in step-
wise method after passing three main steps, identifying an initial
model, changing the model of previous step by adding or removing
a parameter and obtaining the best model at the final step. This
procedure is continued until stepping is no longer possible and
the best model obtained. The attained model is evaluated by some
2.3. MLR analysis
A stepwise multiple linear regression procedure was used to
present the best models for description of the maximum wave-

6
H. Golchoubian et al. / Inorganica Chimica Acta 394 (2013) 1–9
Table 4
The molar conductivities data (Km) of the complexes (
X
ꢁ1 cm2 molꢁ1, at 25 °C) in some solvents.
DCM
NM
NB
MeOH
EtOH
ACN
ACO
DMF
1
2
3
9.47
2.53
3.46
0.0–24
87.15
81.89
80.95
30.31
21.05
28.73
20–30
90.52
80.00
100.00
80–115
33.26
33.68
47.47
35–45
119.37
151.87
153.16
120–160
123.16
139.00
144.21
100–140
67.37
68.73
75.78
65–90
1:1 electrolyte
75–95
’’p⁄’’ Gutmann’s donor number ‘‘DN’’, Mayer and Gutmann’s accep-
tor number ‘‘AN’’ as well as Dimorth and Richardt’s ‘‘ET(30)’’. In
selection of parameter, variables with small variance t (not signif-
icant at the 5% level) were then removed. ‘‘t’’ value is the solvent-
independent coefficients divided by SE.
2.4. Computational methods
The density functional theory (DFT) calculations were carried
out on the gas phased structure of complex 2 using the GAUSSIAN
09w program package [38]. The hybrid functional by Becke, (B3)
[39] with non-local correlation functional of Lee–Yang–Parr (LYP)
[40,41] was used, which includes a mixture of Hartree–Fock ex-
change with DFT exchange–correlation. For C, H, N, and O, the 6-
31+G (d,p) basis sets and for Cu, the LanL2DZ basis set was used
[42]. Frequency analysis is also performed to ensure that the re-
sulted geometries are in equilibrium structure.
3. Results and discussion
All complexes were synthesized by mixing of diamine, b-keto-
amine, Cu(ClO4)2ꢂ6H2O and Na2CO3 with the molar ratios of
1:1:1:0.5, respectively in ethanol–water mixture as shown in Eq
(1).
b ꢁ ketoamine þ diamine þ 0:5Na2CO3 þ CuðClO4Þ2
2O=EtOH
ꢂ 6H2O H
½Cuðb ꢁ ketoamineÞðdiamineÞꢃClO þ CO
ꢀꢀꢀ!
4
2
þ NaClO4
ð1Þ
Compound 2 can exist in two different structures due to the rel-
ative position of NH groups in two chelated ligands as shown in
Fig. 2. All attempts to obtain single crystals of the desired quality
for X-ray crystallography have been failed. As a result, DFT (Density
Functional Theory) calculation has been carried out to find the
most stable structure of this compound. In this regard, two geo-
metrical isomers A and B shown in Fig. 2 have been optimized.
Although according to results obtained the isomer B is more stable
than A the electronic energy difference of two structures is not en-
ough to have a definite judgment (see supplementary material).
3.1. X-ray structure
3.1.1. [Cu(APO)(tmen)]ClO4
This compound crystallizes in space group P21/c with four sym-
metry independent complex cations in the asymmetric unit. The
ORTEP plot of one [Cu(APO)(tmen)]+ is depicted in Fig. 3 with atom
numbering scheme. The selected bond lengths and angles are given
in Table 2.The crystallographic result clearly demonstrates that all
Cu(II) ions have a square planar environment made by b-ketoami-
nato ion and tmen chelate ligands. The dihedral angle between
CuON and CuN2 coordination plane is ꢄ1.88°. There is a small dif-
ference between Cu–O and Cu–N bond distances in b-ketoaminato
Fig. 7. Absorption spectra of three complexes in selected solvents. Absorption
spectra in other solvents are omitted for clarity.
statistical criteria; multiple correlation coefficients (R), standard
error (SE), F-statistic and the number of parameters used. The best
model is the one with higher R and F-values, lower standard error,
the least number of parameters and high ability for prediction [37].
The solvent parameters considered in this study for interpreting
chelate ring perhaps due to a similar degree of
p bonding delocal-
ization at the six-membered ring. The bite angles of ꢄ92.5° in
six-membered chelate ring are close to the corresponding average
values of the analogous copper complexes with acac chelate
solute–solvent interactions are hydrogen bonding ability ‘‘
a’’, elec-
tron pair donating ability ‘‘b’’, polarity/polarizability parameter

H. Golchoubian et al. / Inorganica Chimica Acta 394 (2013) 1–9
7
Table 5
The solvent parameter values and electronic absorption maxima of the complexes in various solvents:
m
max/103 cmꢁ1 /Mꢁ1 cmꢁ1).
(e
Solvent
DN
AN
ET(30)
b
a
p⁄
Complex 1
Complex 2
Complex 3
DCM
0.0
2.7
4.4
20.4
20.5
14.8
15.5
18.9
16.0
12.5
41.3
8.0
37.1
16.0
19.3
14.2
10.6
40.7
46.3
41.2
41.5
45.6
43.6
42.2
55.4
37.4
51.9
43.2
45.1
40.5
40.9
0.0
0.13
0.22
0.0
0.0
0.19
0.0
0.08
0.9
0.0
0.86
0.0
0.0
0.1
18.83 (122.5)
18.48 (113.5)
18.83 (125.5)
18.28 (114.9)
18.12 (115.7)
17.92 (109.5)
17.80 (105.3)
17.80 (118.6)
18.32 (102.4)
17.61 (104.7)
17.39 (115.7)
17.06 (120.2)
16.26 (116.4)
16.61 (103.5)
2.57 ꢀ 103
18.34 (139.4)
18.40 (121.9)
18.66 (108.9)
18.08 (109.2)
18.04 (118.1)
18.01 (117.2)
17.98 (116.9)
17.79 (108.9)
17.97 (126.1)
17.92 (110.5)
17.43 (117.7)
17.14 (110.0)
16.26 (104.5)
16.71 (99.7)
2.14 ꢀ 103
18.59 (138.4)
18.67 (122.1)
18.62 (147.0)
18.05 (136.8)
17.97 (152.3)
17.92 (127.6)
18.01 (129.4)
17.38 (112.4)
17.93 (78.7)
17.60 (144.6)
17.18 (128.9)
17.00 (128.7)
16.14 (113.9)
15.76 (96.9)
2.91 ꢀ 103
Nitromethane
Nitrobenzene
Benzonitryl
Acetonitrile
Propionitryl
Acetone
MeOH
THF
EtOH
DMF
DMSO
0.06
0.39
0.41
0.31
0.39
0.48
0.62
0.55
0.77
0.69
0.76
0.64
1.05
0.85
1.01
0.9
0.75
0.71
0.71
0.6
0.58
0.75
0.88
1.0
0.87
0.87
11.9
14.1
16.1
17.0
19.0
20.0
20.0
26.6
29.8
33.1
38.8
Py
0.0
0.0
HMPA
D
mmax (cmꢁ1
)
bands in IR spectra in the free form and with a little shift in the
complex, but there is not any distinctive band for tmen ligand. The
bands observed at around 3250 and 3300 cmꢁ1 in the free ligand
are associated to N–H stretching vibration which becomes narrow
in complex. In the case of complex 2 there are two N–H bonds asso-
ciated to APO and dmben, which are apparent in the IR spectrum.
However, in two other complexes, the band appeared at
3300 cmꢁ1 is associated to N–H stretching of b-ketoaminato. Also
presence of b-ketoaminato in the mixed-chelate complexes can be
established by shift in C@O stretching vibration band, which ap-
peared at around 1700 cmꢁ1 in the free b-ketoaminato and
1600 cmꢁ1 in the complexes. Upon coordination of b-ketoaminato
to the copper(II) and formation of a six-membered ring due to delo-
Table 6
The equations resulted from the linear correlation of the mmax values with DN of the
solvents.
a
Complex
number
Equationb
F
SE
R
1
2
3
m
max = -0.063
( 0.007)DNsolv + 18.957 ( 0.146)
max = ꢁ0.054 ( 0.007)
DNsolv + 18.735 ( 0.143)
max = ꢁ0.074
( 0.006)DNsolv + 18.966( 0.135)
85.1
62.8
0.282 0.936
0.278 0.916
m
m
134.6 0.261 0.958
a
Based on 14 data points (solvents) indicated in Table 5.
Data in parentheses are standard error (SE).
b
calization of p-bond and reduction in bond order the C@C, C@O and
C@N stretching vibrations moved to lower wavenumber. In all com-
plexes, the presence of perchlorate ion is confirmed by appearance
of a strong band at 1100 cmꢁ1 and a relatively medium band at
610 cmꢁ1 in the spectra. The perchlorate ion is supposed to be
non-coordinated with Td symmetry because the former band is not
split [47]. Formation of mixed-chelate complex 2 is supported by
addition of the IR spectra of [Cu(APO)2] and [Cu2(dmben)2(OH)2]
(ClO4)2 complexes which give a composite spectrum of with peak
positions that match with those in the spectrum of mixed-chelate
complex [Cu(APO)(dmben)]ClO4. This can be seen by inspection of
the relevant peak positions of the individual spectra for those
complexes shown In Fig. 6.
reported previously [43–45]. Also, The mean Cu–N(amine) distance
of ꢄ2.04 Å and the bite angle N–Cu–N of ꢄ85.5° in five-membered
rings are close to the average values of the corresponding cop-
per(II) complexes with ethylenediamine chelate reported before
[46]. One of the perchlorate is very weakly bonded to copper atom
through O19 [Cu(1)–O(19) = 2.791(3) Å], while the other perchlo-
rates have no any interaction with copper ion. The weak interac-
tions between perchlorates and methyl hydrogen and imine
hydrogen atoms help to stabilize the crystal packing (Fig. 4).
3.1.2. [Cu(APBO)(tmen)]ClO4
The ORTEP plot of compound 3 is shown in Fig. 5 and the se-
lected bond lengths and angles are gathered in Table 3. The cation
is comprised of a tmen, a APBO chelated ligands and one Cu(II). The
perchlorate ion is free from coordination. The copper ion is located
in a tetrahedral distortion environment made by chelated ligands,
the deviations from the least-squares plane through the CuN3O
atoms are N(1) ꢁ0.132, N(2) 0.131, O(1) 0.145, N(3) ꢁ0.144,
Cu(1) 0.072 Å. The inter-planar angle between CuON and CuN2
plane is 12.81°. The tmen and APBO bite angles are of 84.98(8)°
and 92.14(7)°, respectively and similar to compounds 1. The
five–membered chelate ring is puckered; the torsion angle of
N(2)–C(8)–C(9)–N(3) of ꢁ53.50° is quite normal for coordinated
ethylenediamine to copper(II) ion. Because the phenyl groups are
directed away from the N2CuON plane, the angle between the
CuON3 plane and phenyl ring is 36.29(1)° to minimize the steric
hindrance.
3.3. Conductometric data
The molar conductivity values of the mixed-chelate complex in
some organic solvents have been studied. The results are shown in
Table 4. The standard values for 1:1 electrolytes in the respective
solvents are demonstrated in the same table [48,49]. The results
show that the molar conductivity values in all solvent investigated
are consistence with 1:1 electrolyte and confirm that the perchlo-
rate ion is free from coordination even in solvents with non-coor-
dinating power like dichloromethane. However, in the analogues
mixed-chelate complexes with diketonate ligand the perchlorate
ion was weakly coordinated to metal center and was ejected from
coordination sphere in solvent with medium to high coordinating
power [2,28].
3.4. Solvatochromism
3.2. IR spectra
The complexes are soluble in organic solvents and demonstrate
a drastic color change from brown to green. The electronic absorp-
tion spectra of the complexes in various solvents are shown in
Formation of mixed-chelate complexes can be confirmed by IR
spectroscopy. b-ketoaminato and dmben ligands have characteristic

8
H. Golchoubian et al. / Inorganica Chimica Acta 394 (2013) 1–9
literature [21–23,25] and shown in Table 5 were offered in Eq.
(2) one by one to the statistical computer program until certain
statistical criteria are met. The solvent parameters used include
Gutmann’s donor DN and acceptor numbers AN, Dimroth and
Reichardt’s ET(30), Kamlet and Taft’s electron pair donating ability
b, hydrogen bonding ability
a
and polarity/polarisability p⁄
parameters.
mmax
¼
mꢅmax þ aDN þ bAN þ cETð30Þ þ db þ e
a
þ fpꢆ
ð2Þ
It is assumed that all the explanatory variables are independent
of each other and truly additive as well as relevant to the problem
under study [50,51]. In this equation, mmax is the value of the
absorption energies in the solvent under study and mꢅmax is the va-
lue of the absorption energies in an inert solvent. DN, AN, ET(30), b,
a
and p⁄ represent independent but complementary solvent
parameters, which account for the different solute/solvent interac-
tion mechanisms and defined in the experimental section.a, b, c, d,
e and f values are the regression coefficients describing the sensi-
tivity of the property mmax to the different solute/solvent interac-
tion mechanisms. A final set of selected equations was examined
for stability and validity by stepwise method through a variety of
statistical methods. The results of the correlation of the absorption
frequencies with solvent parameters are illustrated in Table 6. As
the data show, the DN parameter has a dominate contribution on
the shift of the absorption maxima of the complexes. The contribu-
tion of the other solvent parameters was rejected based on the sta-
tistical criteria explained in the experimental section. Although
Fig. 8 show linear correlation between DN of solvent and mmax val-
ues in the corresponding solvents, a deviation from this general
trend is found in low and high donor power solvents, which was
discussed previously in the analogous compounds [1,2,28]. Accord-
ingly, linear correlation of the mmax values with the solvent donor
number (DN) yields the expressions that are depicted in Table 6.
Thus the solvatochromic behaviors of the complexes can be stud-
ied quantitatively.
These complexes can be classified as two categories, type a,
including complexes 1 and 2, the b-ketoaminato chelate ligand is
the same, but the diamine ligands are different. On the other hand,
in type b, with two complexes 1 and 3, the diamine ligand is anal-
ogous but, b-ketoaminato ligands are dissimilar. In class a complex
1 displayed more solvatochromic than complex 2, this might be
due to more steric hindrance around the copper(II) in complex 1
than complex 2 [2,28]. The steric hindrance is as a result of scissor-
ing motion of four methyl groups in the diamine chelate tmen. It is
known that the increase in the steric crowding of the axial coordi-
nation sites of arriving solvent molecules tends to make the com-
plex more solvatochromic, bringing about
a large structural
change with progressive solvation of the complex. In type b, com-
plexes 1 and 3, steric hindrance around the copper (II) ion is rela-
tively similar, but the electronic effect arisen from the presence of
Fig. 8. Dependence of the mmax values of three complexes on the solvent donor
number (DN) values.
phenyl ring in APBO leads to formation of a greater degree of
p
delocalization system in this chelate. The electronic effect makes
the copper(II) ion more electron deficient and increase the Lewis
acidity of CuN3O chromophore and consequently, its equatorial
ligand field strength. In other words, presence of phenyl moiety
makes it easier for solvent molecules to approach the axial center
and accordingly, leading to a greater solvatochromic effect. As evi-
Fig. 7. All the complexes show a broad structureless absorption
band of copper(II) ion with d9 electron configuration, is related to
the transition of the electron from the lower energy orbitals to
the hole in dx2ꢁy2 orbital. The red shift on the absorption spectra
of the complexes is as large as 2910–2140 cmꢁ1 over the solvents
studied. The SMLR technique was performed to explore the main
solvent parameters that are responsible in the solvatochromic
properties of the complexes.
dent from Table 5
D
mmax = (mmax)DCM – (mmax)HMPA values decreases
in the following order of the complexes: complex 3 > complex
1 > complex 2.
Therefore, solvatochromic Eq. (2) was used to determine rela-
tionship between the frequencies of the d–d absorption transition
band (
parameters. In this fashion, the frequencies of the d–d absorption
transition band ( max) of each complex in various solvents with
their own solvent parameters that were obtained directly from
m
max) of each complex in various solvents with solvent
4. Conclusion
m
Three new mixed chelate complexes with the ligand N,N,N0,N0-
tetramethylenediamine and N,N-dimethyl,N0-benzyl-ethylenedia-

H. Golchoubian et al. / Inorganica Chimica Acta 394 (2013) 1–9
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