Synthesis of copper (II) complexes incorporating N,N-dimethyl-N′- benzylethylenediamine and NCX (X = O, S and Se) ligands: A combined crystallographic, spectroscopic and DFT study

Article abstract of DOI:10.1016/j.poly.2012.12.009

Three copper (II) complexes of type [Cu(L)₂(NCX)]ClO ₄, 1-3, (L = N,N-dimethyl,N^′-benzyl-1,2- diaminoethane and X = O, S and Se) were synthesized and characterized on the basis of microanalytical, spectroscopic and molar conductance. An X-ray diffraction study of [Cu(L)₂(NCO)]ClO₄ (1) reveals that the copper (II) center located in a distorted square pyramidal environment through coordination of four amine N atoms and a N atom of the terminal NCO ^-. Density functional theory (DFT) calculations were performed to understand the linkage isomerism of NCX^- ligand from a theoretical point of view, to study the electronic structure of the complexes and the relative stabilities of the Cu-NCX/Cu-XCN isomers. DFT computational results buttressed the experimental observations indicating that the Cu-NCX isomer is more stable than Cu-XCN linkage isomer. Complexes 1 and 2 exhibit solvatochromism as evidenced from visible study in different solvents.

Full text of DOI:10.1016/j.poly.2012.12.009

Polyhedron 51 (2013) 1–9
Contents lists available at SciVerse ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Synthesis of copper (II) complexes incorporating N,N-dimethyl-N0-benzylethylen-
ediamine and NCX (X = O, S and Se) ligands: A combined crystallographic,
spectroscopic and DFT study
⇑
Hamid Golchoubian , Sara Koohzad, Maedeh Ramzani, Davood Farmanzadeh
Department of Chemistry, University of Mazandaran, Babolsar 47416-95447, Iran
a r t i c l e i n f o
a b s t r a c t
Three copper (II) complexes of type [Cu(L)2(NCX)]ClO4, 1–3, (L = N,N-dimethyl,N0 -benzyl-1,2-diaminoe-
thane and X = O, S and Se) were synthesized and characterized on the basis of microanalytical, spectro-
scopic and molar conductance. An X-ray diffraction study of [Cu(L)2(NCO)]ClO4 (1) reveals that the copper
(II) center located in a distorted square pyramidal environment through coordination of four amine N
atoms and a N atom of the terminal NCOꢀ. Density functional theory (DFT) calculations were performed
to understand the linkage isomerism of NCXꢀ ligand from a theoretical point of view, to study the
electronic structure of the complexes and the relative stabilities of the Cu–NCX/Cu–XCN isomers. DFT
computational results buttressed the experimental observations indicating that the Cu–NCX isomer is
more stable than Cu–XCN linkage isomer. Complexes 1 and 2 exhibit solvatochromism as evidenced from
visible study in different solvents.
Article history:
Received 24 October 2012
Accepted 4 December 2012
Available online 27 December 2012
Keywords:
Copper (II), DFT study
Linkage isomer
X-ray structure
Pseudohalide ligand
Solvatochromism
Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction
tendency to coordinate to the nitrogen [11–14]. Prettiness of cop-
per ions in these compounds is mainly due to the magnetic prop-
Linkage isomerism is a type of phenomenon that is characteris-
tic of transition metal complexes, where the ambidentate ligands
are capable binding through different binding sites. A large verity
of linkage isomers involving ligands such as NCOꢀ, NCSꢀ, NCSeꢀ,
CNꢀ, NOꢀ, NO2ꢀ, SO3ꢀ, and so forth were reported in recent years.
The coordination compounds of these ligands involve mostly in
mononuclear form. Among the ambidentate ligands the NCXꢀ
(X = O, S, Se) ion has been the most well known and is able to coor-
dinate through either N or X end. Indeed, the NCXꢀ ion has the
capabilities of N- and X-coordinations as a unidentate ligand, and
of bridging bonding. So far, several studies on the linkage isomer-
ism of thiocyanate and isothiocyanate have been conducted for the
third (Pt(II) [1,2], Re(V) [3–5] Ru(III) [6]), second (Pd(II) [7], Ru(III)
[8]) and first raw (cobalt (III) [9], Cu(II) [10]) transition metal ions
but less attention has been focused on NCOꢀ and NCSeꢀ linkage
isomers. Normally, the softness or hardness of metal ions deter-
mines the coordination mode of the NCXꢀ ion. The S or Se-bonding
has been generally associated to the softness of the metal ion, but
this not provide a sufficient condition, since this depends on the
nature of the ancillary coordinated ligands as well as steric factor.
Copper (II) ion is a borderline Lewis acid and it is expected to bind
through the two sides of the X and N of the NCXꢀ, but higher
erties of copper (II) ion, photoluminescence, mixed-valance
oxidation state, structural features, color, conductivity and biolog-
ical relevance concerning the dinuclear site in cytochrome oxi-
dases and associated model compounds [15]. Another attractive
aspect of copper (II) complexes is the coordination geometry about
the metal ion. Copper (II) can exist in coordination numbers four,
five and six. In five-coordinate, copper (II) ion usually demonstrate
intermediate stereochemical environment ranging between square
pyramidal and trigonal bipyramidal, depending on the nature of
the co-ligands [16,17].
Recently, theoretical calculations using the DFT formalism are
becoming very popular in order to understand detailed electronic
structures of complicated coordination compounds from
a
microscopic viewpoint. In particular, we are interested in applying
the DFT calculations for understanding and predicting linkage
isomerism of various systems. Several DFT calculations on linkage
isomerism of ruthenium complexes have previously been per-
formed [18–23]. For example, Stener and Calligaris calculated the
relative energy of O-bonded and S-bonded isomers of [RuII(NH3)5
(dmso)]2+ [24], where the S-bonded isomer was found to be
slightly more stable than the O-bonded isomer by 13 kJ molꢀ1
using the gas-phase model. Ghosh et al. performed the DFT calcu-
lations of linkage isomers of [RuII(H3tctpy)(SCN)3]ꢀ (H3tctpy
= 4,40,400-tricarboxy-2,20:6,200-terpyridine) in order to assign the
experimentally-observed electronic absorption spectra [20].
⇑
Corresponding author. Tel./fax: +98 1125342350.
E-mail address: h.golchobian@umz.ac.ir (H. Golchoubian).
0277-5387/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.poly.2012.12.009

2
H. Golchoubian et al. / Polyhedron 51 (2013) 1–9
2.2.2. Preparation of [Cu(L)2(NCS)]ClO4 (2)
X
C
This complex was prepared by a similar method used for
[Cu(L)2(NCO)]ClO4 except that NaNCS was used in place of NaNCO.
The compound was obtained as a green solid with typical yield of
Ph
CH 3
H3C
53%. Selected IR data (
m
/cmꢀ1 using KBr): 3254 (s, NꢀH str.), 2077
N
N
NH
N
(s, SCNꢀ str.), 1455 (m, CH2ꢀPh str.), 1088 (s, ClO4 str.), 811, (w,
C–N str.), 622 (m, ClO4 bend). Anal. Calc. for C23H36CuN5ClO4S
(MW = 577.63 g molꢀ1): C, 47.83; H, 6.28; N, 12.12; Cu, 11.00.
Found: C, 47.85; H, 6.39; N, 12.07; Cu, 11.08%.
Cu
ClO 4
NH
H3C
CH 3
2.2.3. Preparation of [CuL2(NCSe)]ClO4 (3)
Ph
This compound was synthesized with the similar procedure
used for [Cu(L)2(NCO)]ClO4 except that NaNCSe was used instead
of NaNCO. The compound was obtained as an olive green solid with
X=O, S, Se
typical yield of 46%. Selected IR data (m
/cmꢀ1 using KBr): 3248 (s,
Fig. 1. The complexes used in this study.
NꢀH str.), 2126 (s, SeCNꢀ str.), 1455 (m, CH2ꢀPh str.), 1087 (s,
ClO4 str.), 813, (w, C–N str.), 626 (m, ClO4 bend). Anal. Calc. for C23-
H36CuN5ClO4Se (MW = 624.52 g molꢀ1): C, 44.23; H, 5.81; N, 11.21;
Cu, 10.18. Found: C, 44.54; H, 5.30; N, 10.98; Cu, 11.29%.
In order to get further insight into the different stability of NCXꢀ
linkage isomers and into the nature of metal to X bond in case of
‘‘borderline’’ metal like copper (II), we have undertaken a DFT
study on the three new copper (II) complexes [Cu(L)2(NCX)]ClO4,
where L = N,N-dimethyl,N0-benzyl-1,2-diaminoethane and X = O, S
and Se as shown in Fig. 1. The aim of this study is to investigate
the bonding mode of the NCXꢀ in the most stable isomer.
2.3. X-ray structure determination
A suitable single crystal of 1 was glued on the tip of a glass fiber.
The X-ray data were collected at room temperature by
x-scans on
STOE IPDS-II diffractometer with graphite-monochromated Mo K
a
radiation (k = 0.71073 Å). Data reduction, including the absorption
correction, was performed with the X-Area Software software
package [26]. Solution, refinement and analysis of the structure
were performed by using SHELXTL programs [27,28]. The structure
was solved by direct method (SIR92) [29] and refined by the full-
matrix least-squares method based on F2 against all reflections
[30]. Geometrical calculations were carried out with PLATON [31]
and the figures were made by the use of the Diamond [32] and
MERCURY [33] programs. The complete conditions of data collec-
tion and structure refinements are given in Table 1. The hydrogen
atoms of NH groups were found in difference Fourier synthesis. The
H(C) atom positions were calculated. All hydrogen atoms were re-
fined in isotropic approximation in riding model with the Uiso(H)
parameters equal to 1.2 Ueq(Ci), for methyl groups equal to 1.5
Ueq(Cii), where U(Ci) and U(Cii) are respectively the equivalent
thermal parameters of the carbon atoms to which corresponding
H atoms are bonded. The weighted R-factor wR and goodness of
fit S are based on F2, conventional R-factors R are based on F, with
2. Experimental
2.1. Materials and measurements
N,N-dimethyl,N0-benzyl-ethylenediamine was prepared accord-
ing to our published procedure [25]. All solvents were spectral-
grade and all other reagents were used as received. All the samples
were dried to constant weight under a high vacuum prior to anal-
ysis. Caution! Perchlorate 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 ꢁ 10ꢀ3 M samples in selective sol-
vents. 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 spectrophotome-
ter. 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 spectrome-
ter. The following solvents were used for solvatochromic study:
dichloromethane (DCM), benzonitrile (BN), acetone (Ac), dimethyl-
formamide (DMF), dimethylsulfoxide (DMSO) and hexamethyl-
phosphorictriamide (HMPA).
F set to zero for negative F2. The threshold expression of F2 > 2 (F2)
r
is used only for calculating R-factors(gt) etc., and is not relevant to
the choice of reflections for refinement. The atomic coordinates
correspond to the absolute structure of the molecule in the crystal.
2.4. Computational method
2.2. Synthesis
Calculations were carried out using GUASSIAN09 package program
[34]. The X-ray crystallographic structure for [Cu(L)2(NCO)]ClO4
was used as a starting coordinate to generate [CuL2(NCX)]ClO4
(X = NCS, NCSe) geometries. In the computational model, the
perchlorate anion was ignored and the monocationic complex
was taken into account. The optimized geometries were verified
by performing a frequency calculation. The vibrations in the calcu-
lated vibrational spectrum were real, thus the optimized geome-
tries correspond to true energy minimum. Density functional
theory (DFT) was carried out on the gas phase of complexes using
the Beck three parameters hybrid exchange [35] and the Lee–
Yang–Parr correlation hybrid functional [36] (B3LYP) and mixed
basis set, LANL2DZ basis set including effective core potential
(ECP) of Hay and Wadt [37–39] used for Cu and 6-31+G(d,p) for
the others(GEN).
2.2.1. Preparation of [Cu(L)2(NCO)]ClO4 (1)
A typical procedure is as follow: to the solution of the diamine
ligand (0.356 g, 2 mmol) and NaNCO (0.065 g, 1 mmol) in ethanol
(30 mL) were slowly added Cu(ClO4)2ꢂ6H2O (0.37 g, 1 mmol) in
ethanol (10 mL). The resultant mixture was stirred for 1 h at room
temperature. The desired compound precipitated from the reaction
mixture as a blue solid. The crude compound was recrystallized
from diffusion of diethyl ether into acetonitrile solution. The typi-
cal yield was 41%. Selected IR data (
m
/cmꢀ1 KBr disk): 3257 (s, NꢀH
str.), 2210 (s, OCNꢀ str.), 1455 (m, CH2ꢀPh str.), 1097 (s, ClO4 str.),
808, (w, C–N str.), 622 (m, ClO4 bend). Anal. Calc. For C23H36CuN5-
ClO5 (MW = 561.56 g molꢀ1): C, 49.21; H, 6.52; N, 12.53; Cu, 11.32.
Found: C, 49.31; H, 6.66; N, 12.51; Cu, 11.22%.

H. Golchoubian et al. / Polyhedron 51 (2013) 1–9
3
observed at around 3350 cmꢀ1 and broader in the free diamine
ligands. As the lone pair of electrons of the donor nitrogen atoms
become involved in the metal–ligand bond, the transfer of the
electron density to the metal and the subsequent polarization of
the ligands involves electron depopulation of the N–H bond that
culminates in a shift to lower frequencies. The vibrational bands
around 1040 cmꢀ1 are corresponded to the stretching vibration
of C–N bond and the bands around 1450 cmꢀ1 are associated to
the scissoring vibration of –CH2– phenyl groups [42]. The strong
bands around 1365 cmꢀ1 are associated to the bending vibrations
of CH3 groups. The existence of an intense and sharp band occur-
ring at 2210 cmꢀ1 together with a band of weak intensity at
808 cmꢀ1 attributed to the stretching frequency of mCO that con-
firms the coordination of NCO ligand through N-atom to the Cu(II)
ion in complex 1 [43–45]. This coordination mode was confirmed
by the X-ray analysis. The presence of NCSꢀ group in complex 2
and coordination through the nitrogen atom to the copper (II)
ion is declared by an intense band at 2077 cmꢀ1 which is attributed
Table 1
Crystal data and structure refinement of complex 1.
Empirical formula
Formula weight
Color
T (K)
k (Å)
Crystal system
Space group
Crystal size (mm)
Unit cell dimensions
a (Å)
C23H36CuN5OꢂClO4
561.57
needle, blue
295(2)
0.71073
monoclinic
P21
0.20 ꢁ 0.11 ꢁ 0.09
9.961(2)
9.2187 (18)
14.583 (3)
94.92 (3)
1334.2 (5)
b (Å)
c (Å)
b (°)
V (Å3)
Z
2
Calculated density
Absorption coefficient
F(000)
h (°)
Index ranges
1.398 Mg/m3
0.96 mmꢀ1
590
2.09–25.00
ꢀ11 6 h 6 11
ꢀ10 6 k 6 10
ꢀ17 6 I 6 17
0.96
10493/2659 [R(int) = 0.089]
99.5%
to the symmetric mNCS stretching vibration mode [46,47]. This band
is consistent with N-bonded thiocyanato ligand, a fact that can be
further substantiated from an absorption band at 811 (medium)
cmꢀ1, which is attributed to the stretching frequency of mCS for
N-bonded thiocyanato ligand. The infrared spectrum of the isose-
lenocyanato, complex 3 shows a sharp band at 2126 cmꢀ1 that is
l
(mmꢀ1
)
Reflections collected/unique
Completeness to h = 30.10
Absorption correction
multi-scan
Refinement method
full-matrix least-square on F2a
4324/1/30
assigned to the stretching frequency of mNCSe. This assignment is
Data/restraints/parameters
Final R indicesa [I > 2
r
(I)]b
R1 = 0.0860, wR2 = 0.0861
1.006
R1 = 0.1483, wR2 = 0.0753
0.802 and ꢀ0.478
0.01(5)
combined with a weak band at 813 cmꢀ1 that account for the
stretching frequency of mCSe and indicated the monodentate
N-coordination of the NCSe ligand to the Cu(II) ion [48].
Goodness-of-fit (GOF) on F2c
R indices (all data)
Largest difference in peak and hole (e Åꢀ3
Flack parameter
)
The calculated (non-scaled) vibrational spectra of compounds
1–3 stay in good agreement with the experimental data, as
a
b
c
R =
wR = {[(
S =
R
(||Fo| ꢀ |Fc||)/|
R|Fo.
2
R
[Fo ꢀ Fc2)2]/
R .
w[(Fo2)2]}1/2
[w(Fo ꢀ Fc2)2/(Nobs ꢀ Nparam).
2
R
3. Results and discussion
All complexes were synthesized by mixing of diamine,
Cu(ClO4)2ꢂ6H2O and NaNCX with the molar ratios of 2:1:1, respec-
tively in ethanol as shown in Eq. (1).
2diamine þ NaNCX þ CuðClO4Þ2
ꢂ 6H2O E!tOH½CuðdiamineÞ NCXꢃCLO4 þ NaClO4
ð1Þ
2
The complex, 3 was only partially soluble in dimethyl sulfoxide
and was nearly insoluble in all other solvents investigated. Thus,
thorough characterization and establishment of the purity of this
compound were hindered by its poor solubility. Analytical data,
molar conductivity, IR spectra and X-ray crystallography indicated
formation of the desired copper (II) complexes.
3.1. IR spectra
In the IR spectra of compounds 1–3 several bands appear in the
region 600–3500 cmꢀ1 that are also observed, although with minor
shifts, in the spectra of the free ligands. In addition, certain absorp-
tion bands that are characteristic of the NCXꢀ ions exist in the IR
spectra of the complexes. Appearance of the perchlorate bands at
around 1100 and 630 cmꢀ1 in complexes are indicative of the ionic
nature of the complexes. The intense absorption band in the region
around 2100 cmꢀ1 in the complexes is assigned to the NCXꢀ vibra-
tional mode in which shifted to the lower wave numbers in com-
pared to the free NCXꢀ because of coordination to the copper
center [40,41]. Dependence on coordination of the diamine chelate
is also exhibited by an intense and narrow band occurring at
3290 10 cmꢀ1 which is associated with N–H vibration and is
Fig. 2. Comparison of the experimental IR spectra (–NCX and N–H vibrations) of
solid [Cu(L)2(NCO)]ClO4, [Cu(L)2(NCS)]ClO4 and [Cu(L)2(NCSe)]ClO4 on KBr pellets
(top) with theoretical results (bottom) in the 1700–4000 cmꢀ1 frequency range.

4
H. Golchoubian et al. / Polyhedron 51 (2013) 1–9
Table 2
N(3) and N(4) have R and S configurations, respectively in the
Fig. 3; the benzyl substituent on the amine chelates are situated
cis to each other. The packing of the structure in the unit cell is
shown in Figs. 4 and 5. This arrangement shows that perchlorate,
as the counter ion, has no any interaction with copper (II) center
probably due to steric hindrance around the copper and is located
far-off from this center. In the compound, through N(4)Hꢂ ꢂ ꢂO(3)
(2.493 Å) and N(2)Hꢂ ꢂ ꢂO(4) (2.554 Å) hydrogen bonds, an 1D zigzag
chain structure is found (Fig. 4), which is further linked to the
neighboring one via weak contacts C(1)ꢂ ꢂ ꢂH(21)C (2.883 Å),
extending to a hydrogen-bonded 2D supramolecular layer (Fig. 5).
Molar conductivity data (Km) of the complexes 1 and 2 (Oꢀ1 cm2 molꢀ1, at 25 °C) in
different solvents.
Complex
NM
NB
ACN
AC
EtOH MeOH DMF
1
2
74.2
70.7
17.5
16.3
134.8
149.0
107.6
114.6
36.0
21.0
76.2
57.5
60.0
59.5
1:1 Electrolyte 95–75 30–20 160–120 140–100 45–35 115–80 90–65
presented in Fig 2. The calculated mCN strong absorptions occur at
2214, 2060 and 2010 cmꢀ1 for complex 1, 2 and 3, respectively.
These values are in agreement with the corresponding experimen-
tal ones by ꢄ1% error. Similarly, the calculated absorptions due to
3.4. Theoretical considerations
mN–H, mC@ modes of the diamine ligand appearing at 3450 and
3459 cmꢀC1, fall in the experimental ranges.
There are two linkage isomers for all three complexes as Cu–
NCX and Cu–XCN. The DFT calculations were therefore performed,
in order to interpret the experimental results. The X-ray structure
available for the family of the complexes in this work is [Cu(L)2(-
NCO)]ClO4. We started by optimizing the geometry of this com-
plex, without any symmetry constraints in order to calibrate the
method. The optimized structure with labeling of the atoms is
shown in Fig. 3. Consistent with the crystallographic results gath-
ered in Table 3 geometrical parameters for complex 1 are in agree-
ment with the experimental results (with deviations ranging from
+0.030 to ꢀ0.086 Å for basal Cu–N bonds). The error for the axial
Cu–N bond length is larger (+0.203 Å). The deviation may come
from the basis sets which are approximated to a certain extent
or may indicate the influence of the crystal packing on the values
of the experimental bond lengths because the theoretical calcula-
tions do not consider the effects of chemical environment. Unfortu-
nately there is no way to predict the energy difference in the solid
state. The relative stability of Xꢀ and Nꢀ isomers in the complexes
has been evaluated from the difference between their total ener-
3.2. Conductometric data
Table 2 shows the molar conductivity values of complexes 1 and
2 and the standard values for 1:1 electrolytes in different solvents
[49]. The results exhibited that the complexes are 1:1 electrolyte in
all solvents investigated.
3.3. X-ray structure
An ORTEP view of the cationic part of complex 1 is depicted in
Fig.
3 together with the numbering scheme. Selected bond
distances and angles are presented in Table 3. The compound crys-
tallizes in the monoclinic space group P21. The geometry about the
copper can be regarded as a distorted square-pyramid with the N5
donor atoms. The geometric discrimination parameter
tween square-pyramid ( = 0) and trigonal-bipyramid (
s
[50] be-
s = 1) is
s
0.28. The two five-membered rings of the diamine chelate are al-
most perpendicular to each other in around of the copper center
(79.69°). The cyanate ligand is located in the base and the nitrogen
atom of the diamine chelate, N(5) is at apex. The OCNꢀ group is al-
most linear, with N–C–O angles of 175.0(2). The NCO- group in the
equatorial plane forms Cu–N–C angle of 164.4(1). The copper (II)
ion is displaced by 0.245(4) Å from the basal least square plane
toward the N(5) atom. The mean bite angle of N–Cu–N of the dia-
mine ligand is 82.4 (5)° and close to the related values of the anal-
ogous copper (II) complexes [51–53]. The mean basal Cu–N
distance of the diamine chelate is 2.084 (9) Å but axial Cu–N(5)
(diamine) bond is elongated [2.326 (7) Å] owing to Jahn–Teller ef-
fect for d9 electronic configuration. The asymmetric nitrogen atoms
gies,
D
E
N–X = /EN ꢀ /EX. The greater the
D
ENꢀX value, the greater
the stability of the N-isomers. According to the present DFT
calculations, the N-bonded isomers appear more stable than the
X-isomers in all complexes (Table 4). Calculations show that
D
ENꢀX
increases with the increasing of the donor power of X (Se > S > O).
In order to understand the source of the observed difference in
relative energies more quantitatively, we have performed atomic
charge analyses. Table 5 summarizes the results of NPA calcula-
tions for the Cu–NCX and Cu–XCN structures. This result shows
the effective charge on the Cu atom significantly affects the
strength of the Cu–X or Cu–N bond in coordination complexes.
Taking two fragments, [Cu(L)2]2+ and XCNꢀ, as references, we can
also calculate the value of the transferred charge. From Table 5,
Fig. 3. ORTEP view (right) and the optimized geometry (left) of the complex 1 together with its labeling.

H. Golchoubian et al. / Polyhedron 51 (2013) 1–9
5
Table 3
The selected experimental and optimized bond lengths (Å) and angles (°) for complex 1.
Bond distances(Å)
Bond angles(°)
Experimental
Theoretical
Experimental
Theoretical
N(1)–Cu(1)
N(2)–Cu(1)
N(3)–Cu(1)
N(4)–Cu(1)
N(5)–Cu(1)
C(1)–N(1)
C(1)–O(1)
Bond angles(°)
N(1)–Cu(1)–N(4)
N(1)–Cu(1)–N(3)
1.934 (10)
2.105 (9)
2.077 (9)
2.072 (8)
2.326 (7)
1.119 (15)
1.207 (15)
1.964
2.149
2.163
2.123
2.528
1.213
1.215
N(4)–Cu(1)–N(3)
N(4)–Cu(1)–N(2)
N(3)–Cu(1)–N(2)
N(1)–Cu(1)–N(5)
N(4)–Cu(1)–N(5)
N(5)–Cu(1)–N(3)
N(2)–Cu(1)–N(5)
N(1)–Cu(1)–N(2)
C(1)–N(1)–Cu(1)
N(1)–C(1)–O(1)
173.9 (4)
94.1 (3)
82.8 (4)
97.1 (4)
82.3 (3)
103.6 (4)
105.7 (3
157.1 (4)
165.4 (11)
175.0 (15)
169.09572
95.77873
83.11360
98.17514
80.39524
110.48869
93.90039
167.8
90.7 (4)
90.2 (4)
87.3
91.6
144.95409
178.32873
Fig. 4. 1D zigzag chain structure of compound 1 along the b-axis with hydrogen bonds indicated by dotted lines.
Table 4
Differences between total molecular energies (
DE
NꢀX, kJ molꢀ1) for N and X bonded
isomers of the complexesa.
Complexes
E (kJ/mol)
E (kJ/mol)
E (kJ/mol)
Cu–NCO–
Cu–OCN
0.0
40
Cu–NCSꢀ
Cu–SCN
ꢀ847960
ꢀ847910
Cu–NCSeꢀ
Cu–SeCN
ꢀ6100880
ꢀ6100840
a
The molecular energy of [Cu(L)2(NCO)]+ was taken as a reference.
Table 5
Results of natural population analysis for Cu–NCX and Cu–XCN isomers.
Cu
N
C
X
NCX
Cu–NCX
X = O
X = S
X = Se
Cu–XCN
X = O
0.99
0.989
0.969
ꢀ0.859
ꢀ0.69
ꢀ0.66
0.70
0.11
0.03
ꢀ0.54
ꢀ0.12
ꢀ0.03
ꢀ0.70
ꢀ0.70
ꢀ0.66
1.04
0.85
0.80
ꢀ0.49
ꢀ0.33
ꢀ0.32
0.52
0.03
ꢀ0.04
ꢀ0.75
ꢀ0.23
ꢀ0.09
ꢀ0.70
ꢀ0.53
0.55
X = S
X = Se
Fig. 5. 2D supramolecular architecture of compound 1 viewing down the a-axis
with hydrogen bonds indicated by dotted lines.
the charges transferred from the XCNꢀ moiety to the metallic moi-
ety are in the ranges of 0.66–0.70 |eꢀ| and 0.53–0.70 |eꢀ| for Cu–N
and Cu–X, respectively. From charge transfer interactions we can
see that the contribution of nitrogen atoms coordinating to the
copper ion is much greater than that of sulfur atom.
[Cu(L)2(NCSe)]+ are gathered in Tables 6 and 7, respectively. Their
optimized structures are shown in Fig. 6. The optimized geometries
for the complexes display distorted square pyramidal environ-
ments and general trends observed in the experimental data are
satisfactorily reproduced in the calculations.
The Cu–N bond distances in all three complexes of Cu–NCX are
shorter than in their counterparts Cu–S bond lengths of Cu–SCN
complexes. The differences are between 0.496–0.456 Å.
The geometries of complexes 2 and 3 were optimized in doublet
state using the DFT method with the B3LYP functional in gas phase.
The calculated geometric parameters of [Cu(L)2(NCS)]+ and
A schematic illustration of the energy and character of the fron-
tier orbitals of the cations [Cu(L)2(NCO)]+, [Cu(L)2(NCS)]+ and
[Cu(L)2(NCSe)]+ are shown in Figs. 7–9, respectively. For all com-
plexes the highest the MO presents significant ligand character. It
is predominately of –NCX ligand (>70%) with some contributions
from the d orbitals of the copper (II) ion (ꢄ1–8%). The LUMO

6
H. Golchoubian et al. / Polyhedron 51 (2013) 1–9
Table 6
Selected theoretical bond distances and angles for Cu–NCS and Cu–SCN isomers of [Cu(L)2(NCS)]ClO4 calculated at B3LYP/6-311G level of theory.
Cu–NCS
Cu–SCN
Cu–NCS
Cu–SCN
Bond distances (Å)
Bond angles (°)
N(1)–Cu(1)
S(1)–Cu(1)
N(2)–Cu(1)
N(3)–Cu(1)
N(4)–Cu(1)
N(5)–Cu(1)
C(1)–N(1)
C(1)–S(1)
Bond angles (°)
N(1)–Cu(1)–N(4)
N(1)–Cu(1)–N(3)
N(1)–Cu(1)–N(2)
1.984
–
–
N(4)–Cu(1)–N(3)
N(4)–Cu(1)–N(2)
N(3)–Cu(1)–N(2)
N(1)–Cu(1)–N(5)
N(4)–Cu(1)–N(5)
N(5)–Cu(1)–N(3)
N(2)–Cu(1)–N(5)
C(1)–N(1)–Cu(1)
N(1)–C(1)–S(1)
C(1)–S(1)–Cu(1)
168.3
96.4
83.3
97.9
80.8
110.9
95.5
145.0
179.3
–
166.4
92.9
82.7
–
81.8
111.5
70.0
–
2.494
2.235
2.160
2.124
2.414
1.182
1.729
2.150
2.160
2.128
2.489
1.201
1.661
179.4
109.2
87.6
90.1
166.4
–
–
–
Table 7
Selected theoretical bond distances and angles for Cu–NCSe and Cu–SeCN isomers of [Cu(L)2(NCSe)]ClO4 calculated at B3LYP/6-311G level of theory.
Cu–NCSe
Cu–SeCN
Cu–NCSe
Cu–SeCN
Bond distances (Å)
Bond angles (°)
N(1)–Cu(1)
Se(1)–Cu(1)
N(2)–Cu(1)
N(3)–Cu(1)
N(4)–Cu(1)
N(5)–Cu(1)
C(1)–N(1)
C(1)–Se(1)
Bond angles (°)
N(1)–Cu(1)–N(4)
N(1)–Cu(1)–N(3)
N(1)–Cu(1)–N(2)
1.994
–
–
N(4)–Cu(1)–N(3)
N(4)–Cu(1)–N(2)
N(3)–Cu(1)–N(2)
N(1)–Cu(1)–N(5)
N(4)–Cu(1)–N(5)
N(5)–Cu(1)–N(3)
N(2)–Cu(1)–N(5)
N(1)–Cu(1)–N(2)
C(1)–N(1)–Cu(1)
N(1)–C(1)–Se(1)
C(1)–Se(1)–Cu(1)
168.2
96.6
83.3
96.2
80.9
110.9
96.3
165.4
147.6
180.0
–
167.8
92.7
82.8
–
81.6
110.1
96.3
–
2.616
2.256
2.150
2.119
2.436
1.181
1.851
2.155
2.169
2.136
2.479
1.120
1.789
–
87.4
90.0
165.4
–
–
–
179.7
106.9
Fig. 6. Calculated molecular structures of [Cu(L)2(NCS)]+, and [Cu(L)2(NCSe)]+.
orbitals of the complexes are composed of the copper d-orbitals
(ꢄ50%), –NCX and chelated ligands, L.
change in solvent polarity. The origin of the color changes in these
compounds are attributed to the shift in the d–d transition of
the copper (II) ions as results of solvent–solute interactions. The
spectra in all solvent have nearly the same pattern of octahedral
complexes with almost equal intensities. The visible spectral
changes of these complexes in the selected solvents are illustrated
in Fig. 10. The positions of the mmax values of the complexes along
with the molar absorptivities are collected in Table 8.
3.5. Solvatochromism
The complexes 1 and 2 are fairly soluble in various organic
solvents and demonstrate distinctive solvatochromism. Solvato-
chromism is the ability of a compound to change color due to a

H. Golchoubian et al. / Polyhedron 51 (2013) 1–9
7
Fig. 9. The energy (eV), character and some contours of the molecular orbitals of
[Cu(L)2(NCSe)]+. Positive values of the orbital contour are represented in yellow and
negative values in blue.
Fig. 7. The energy (eV), character and some contours of the molecular orbitals of
[Cu(L)2(NCO)]+. Positive values of the orbital contour are represented in yellow and
negative values in blue.
Fig. 10. Absorption spectra of complexes 1 and 2 in selected solvents.
The broad structureless visible band is related to the transition
2
2
of the electron from the lower energy orbitals to the hole in dx
ꢀy
orbital of the copper (II) ion (d9). The electronic absorption spectra
of the complexes were measured in solution state in some organic
solvents with different donor number (DN). The donor number ex-
presses a measure of coordinating ability of solvent on the
Fig. 8. The energy (eV), character and some contours of the molecular orbitals of
[Cu(L)2(NCS)]+. Positive values of the orbital contour are represented in yellow and
negative values in blue.

8
H. Golchoubian et al. / Polyhedron 51 (2013) 1–9
Table 8
Electronic absorption maxima of the complexes in various solvents:
m
max/103 cmꢀ1
AC
(e
/Mꢀ1 cmꢀ1).
DMF
Solvent
DCM
BN
DMSO
HMPA
DN
0.0
4.4
17.0
26.6
29.8
38.8
Complex 1
Complex 2
16.12 (122)
15.87 (170)
15.5 (120)
15.5 (150)
14.97 (123)
15.22 (139)
14.88 (100)
14.97 (136)
14.72 (124)
14.88 (153)
14.24 (129)
14.18 (135)
isostructural as elucidated by spectroscopic and X-ray diffraction
analysis. DFT calculations show that Cu–NCX is more stable than
Cu–XCN by 43.71 kJ molꢀ1 for complex 1, 49.8 kJ molꢀ1 for com-
plex 2 and 39.9 kJ molꢀ1 for complex 3. Complexes 1 and 2 showed
solvatochromism. The complexes confirmed a good correlation be-
tween their d–d absorption maxima in solution and the donor
number of the solvent used (positive solvatochromism) due to
coordination of solvent molecules with different donor power to
the axial site of the copper (II) ion that results in changing
the geometry of the complexes from square pyramid to the
octahedron.
Acknowledgment
We are grateful for the financial support of university of Maz-
andaran of the Islamic Republic of Iran.
Fig. 11. Dependence of the mmax values of compounds 1 and 2 on the solvent donor
number values.
Appendix A. Supplementary material
CCDC 901582 contains 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: (+44) 1223 336033; or e-mail: deposit@ccdc.cam.ac.uk.
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.poly.2012.12.009.
standard of that of dichloromethane (DCM) or dichloroethane
(DCE) [54]. The values of DN of the solvents used are as follows:
DCM and DCE = 0.0; MeNO2 = 2.7; acetone = 17.0; MeOH = 19.0;
THF = 20.0 DMF = 26.6; DMSO = 29.8; HMPA = 38.8.
In solution the d–d band of all complexes moves to the red with
the increase of the DN of the solvent (Table 7 and Fig. 10). As the
results illustrate, the energy change on the absorption spectra of
the compounds is as large as 1690–1880 cmꢀ1 over the solvents
studied. The greatest solvatochromic effect is displayed by com-
plex 1 (1880 cmꢀ1). Assuming that the approach of the solvent oc-
curs along the empty z axis, the solvent molecule is repelled by the
two electrons in the dz2 orbital of the copper (II) and only the more
basic species can force their way into 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 less effect in the band max-
ima, others that are considerably more basic induce large red
shifts.
References
[1] C. Buda, A.B. Kazi, A. Dinescu, T.R. Cundari, J. Chem. Inf. Model. 45 (2005) 965.
[2] A.R. Khan, S.M. Socol, D.W. Meek, R. Yasmeen, Inorg. Chim. Acta 234 (1995)
109.
[3] S. Chowdhury, N. Koshino, A. Canlier, K. Mizuoka, Y. Ikeda, Inorg. Chim. Acta
359 (2006) 2472.
[4] J.S. Gancheff, Á. Acosta, D. Armentano, G. De Munno, R. Chiozzone, R. González,
Inorg. Chim. Acta 387 (2012) 314.
[5] R. González, N. Barboza, R. Chiozzone, C. Kremer, D. Armentano, G. De Munno,
J. Faus, Inorg. Chim. Acta 361 (2008) 2715.
[6] T.P. Brewster, W. Ding, N.D. Schley, N. Hazari, V.S. Batista, R.H. Crabtree, Inorg.
Chem. 50 (2011) (1946) 11938.
[7] M. Cusumano, G. Guglielmo, P. Marricchi, V. Ricevuto, Inorg. Chim. Acta 30
(1978) 29.
[8] H. Ohtsu, N. Oka, T. Yamaguchi, Inorg. Chim. Acta 383 (2012) 1.
[9] L.J. Cavichiolo, T. Hasegawa, F.S. Nunes, Spectrochim. Acta, Part A 64 (2006)
161.
[10] L.K. Das, A. Biswas, A. Frontera, A. Ghosh, Polyhedron http://dx.doi.org/
10.1016/j.poly.2012.04.029, 2012.
Regression analysis of the band maxima of the complexes
against donor number of solvents is shown in Fig. 11 and indicates
good correlations and also confirms the solvatochromic behavior of
the complexes. A linear correlation of the mmax values with the
solvent donor number (DN) yields the following expression. Thus
the solvatochromic behavior the complex can be studied
quantitatively.
[11] B. Machura, A. Switlicka, M. Penkala, Polyhedron 45 (2012) 221.
[12] J. Lu, H.-T. Liu, D.-Q. Wang, X.-X. Zhang, J. Mol. Struct. 938 (2009) 299.
[13] M. Kabešova, R. Bocꢀa, M. Melnik, D. Valigura, M. Dunaj-Jurcꢀo, Coord. Chem.
Rev. 140 (1995) 115.
[14] M. Du, Ch.-Peng Li, X.-J. Zhao, Cryst. Eng. Commun. 8 (2006) 552.
[15] J.Y. Lu, Coord. Chem. Rev. 246 (2003) 327.
Complex 1:
Complex 2:
m
m
max/103 = ꢀ0.0417DNsolv + 15.822, R = 0.963
max/103 = ꢀ0.037DNsolv + 15.822, R = 0.969
[16] F.H. Allen, Acta Crystallogr., Sect. B 58 (2002) 380.
[17] B.J. Hathaway, in: G. Wilkinson, R.D. Gillard, J.A. McCleverty (Eds.),
Comprehensive Coordination Chemistry, vol. 5, Pergamon Press, Oxford,
England, 1987, p. 533.
4. Conclusion
[18] P. Coppens, I. Novozhilova, A. Kovalevsky, Chem. Rev. 102 (2002) 861.
[19] A.Y. Kovalevsky, K.A. Bagley, P. Coppens, J. Am. Chem. Soc. 124 (2002) 9241.
[20] G.K. Chaitanya, K. Bhanuprakash, M.K. Nazeeruddin, M. Grätzel, P.Y. Reddy,
Inorg. Chem. 45 (2006) 7600.
Three mononuclear copper (II) pseudohalide complexes were
synthesized and characterized. X-ray structure determination of
[Cu(L)2(NCO)]ClO4 showed a square pyramidal structure around
the metal center. The scope of these studies was extended to in-
clude a series of XCNꢀ-terminal mononuclear complexes. A similar
coupling scheme was used to synthesize the copper(II) analogue,
yielding the cationic complexes. All the copper complexes are
[21] M. Calligaris, Coord. Chem. Rev. 248 (2004) 351.
[22] I. Ciofini, C.A. Daul, C. Adamo, J. Phys. Chem. A 107 (2003) 11182.
[23] N.S. Panina, M. Calligaris, Inorg. Chim. Acta 334 (2002) 165.
[24] M. Stener, M. Calligaris, J. Mol. Struct. (THEOCHEM) 497 (2000) 91.
[25] H. Golchoubian, E. Rezaee, J. Mol. Struct. 929 (2009) 154.

H. Golchoubian et al. / Polyhedron 51 (2013) 1–9
9
[26] Stoe & Cie, X-AREA (version 1.26), Stoe & Cie GmbH, Darmstadt, Germany,
[36] C. Lee, W. Yang, R.G. Parr, Phys. Rev. B37 (1988) 785.
2007.
[37] P.J. Hay, W.R. Wadt, J. Chem. Phys. 82 (1985) 270 (and also 299).
[38] W.R. Wadt, P.J. Hay, J. Chem. Phys. 82 (1985) 284.
[39] P.J. Hay, W.R. Wadt, J. Chem. Phys. 82 (1985) 299.
[40] M.G.B. Drew, D. Das, S. De, D. Datta, Inorg. Chim. Acta 362 (2009) 1501.
[41] F.A. Mautner, R. Vicenta, S.S. Massoud, Polyhedron 25 (2006) 1673.
[42] C. Tsiamis, M. Themeli, Inorg. Chim. Acta 206 (1993) 105.
[43] H. Chowdhury, S.H. Rahaman, R. Ghosh, S.K. Sarkar, H.K. Fun, B.K. Ghosh, J. Mol.
Struct. 826 (2007) 170.
[44] S. Banerjee, M.G.B. Drew, C.Z. Lue, J. Tercero, C. Diaz, A. Ghosh, Eur. J. Inorg.
Chem. (2005) 2376.
[45] C. Diaz, J. Ribas, M.S. El Fallah, X. Solans, M. Font-Bardia, Inorg. Chim. Acta 312
(2001) 1.
[46] S. Banerjee, M.G.B. Drew, C.Z. Lue, J. Tercero, C. Diaz, A. Ghosh, Eur. J. Inorg.
Chem. (2005) 237.
[47] S. Massoud, F. Mautner, Inorg. Chim. Acta 358 (2005) 3334.
[48] Z.D. Georgousis, P.C. Christidis, D. Hadjipavlou-Litinac, C.A. Bolos, J. Mol. Struct.
837 (2007) 30.
[49] W.J. Geary, Coord. Chem. Rev. 7 (1971) 81.
[50] A.W. Addison, T.N. Rao, J. Chem. Soc., Dalton Trans. 1 (1984) 1349.
[51] H. Asadi, H. Golchoubian, R.J. Welter, Mol. Struct. 779 (2005) 30.
[52] H. Golchoubian, G. Moayyedi, G. Bruno, H.A. Rudbari, Polyhedron 30 (2011)
1027.
[53] H. Golchoubian, R.Z. Zarabi, Polyhedron 28 (2009) 3685.
[54] V. Gutmann, Coordination Chemistry in Non-aqueous Solutions, Springer,
Vienna, 1968.
[27] G.M. Sheldrick, SADABS, University of Göttingen, Germany.
[28] G.M. Sheldrick, Acta Crystallogr., Sect. A 64 (2008) 112.
[29] Stoe & Cie, X-RED (version 1.28b), Stoe & Cie GmbH, Darmstadt, Germany,
2005.
[30] G.M. Sheldrick, Acta Crystallogr., Sect. A 64 (2008) 112.
[31] A.L. Spek, Acta Crystallogr., Sect. D 65 (2009) 148.
[32] K. Brandenburg, DIAMOND, Crystal Impact GbR, Bonn, Germany, 2001.
[33] C.F. Macrae, I.J. Bruno, J.A. Chisholm, P.R. Edgington, P. McCabe, E. Pidcock, L.
Rodriguez-Monge, R. Taylor, J. van de Streek, P.A. Wood, J. Appl. Crystallogr. 41
(2008) 466.
[34] GAUSSIAN 09, Revision A.02, M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria,
M.A. Robb, J.R. Cheeseman, G. Scalmani, V. Barone, B. Mennucci, G.A. Petersson,
H. Nakatsuji, M. Caricato, X. Li, H.P. Hratchian, A.F. Izmaylov, J. Bloino, G.
Zheng, J.L. Sonnenberg, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa,
M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, T. Vreven, J.A.
Montgomery, Jr., J.E. Peralta, F. Ogliaro, M. Bearpark, J.J. Heyd, E. Brothers,
K.N. Kudin, V.N. Staroverov, R. Kobayashi, J. Normand, K. Raghavachari, A.
Rendell, J.C. Burant, S.S. Iyengar, J. Tomasi, M. Cossi, N. Rega, J. M. Millam, M.
Klene, J.E. Knox, J.B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R.E.
Stratmann, O. Yazyev, A.J. Austin, R. Cammi, C. Pomelli, J.W. Ochterski, R.L.
Martin, K. Morokuma, V.G. Zakrzewski, G.A. Voth, P. Salvador, J.J. Dannenberg,
S. Dapprich, A.D. Daniels, O. Farkas, J.B. Foresman, J.V. Ortiz, J. Cioslowski, D.J.
Fox, Gaussian, Inc., Wallingford, CT, 2009.
[35] A.D. Becke, J. Chem. Phys. 98 (1993) 5648.