Dinuclear Cu(II) complexes of compartmental Schiff base ligands formed from unsymmetrical tripodal amines of varying arm lengths: Crystal structure of [Cu2L1](ClO4)2 and theoretical studies

Article abstract of DOI:10.1016/j.molstruc.2016.02.004

Three new dinuclear copper complexes were synthesized via condensation reaction of three new unsymmetrical N-capped tripodal amines and 2,6-diformyl-4-methylphenol, in the presence of copper(II) perchlorate. The solid-state structure of the dinuclear complex, [Cu₂L¹](ClO₄)₂, has been determined by X-ray crystallography, showing that the Cu^II centers have distorted square-pyramidal geometry with N₃O₂ coordination. The copper (II) ions are bridged by phenolic and hydroxyalkyl groups when in both cases, deprotonation of the hydrogen atoms of the OH groups occurs. The distance between the copper atoms is 3.062 ?. This compound consists of the dication [Cu₂L¹]²⁺ and two ClO₄^- anions in which one of ClO₄^- groups has a week interaction with one of the Cu atoms. All complexes were characterized by a variety of physico-chemical techniques such as elemental analyses, IR, mass spectra, conductivity measurements and electronic spectral studies. Computational investigation of mentioned binuclear Cu(II) complexes was done by using M062X method with LANL2DZ basis set in vacuo.

Full text of DOI:10.1016/j.molstruc.2016.02.004

Accepted Manuscript
Dinuclear Cu(II) complexes of compartmental Schiff base ligands formed from
1
unsymmetrical tripodal amines of varying arm lengths: Crystal structure of [Cu L ]
2
(ClO ) and theoretical studies
4 2
Hassan Keypour, Maryam Shayesteh, Majid Rezaeivala, Koray Sayin
PII:
S0022-2860(16)30098-9
10.1016/j.molstruc.2016.02.004
MOLSTR 22213
DOI:
Reference:
To appear in: Journal of Molecular Structure
Received Date: 18 October 2015
Revised Date: 29 January 2016
Accepted Date: 2 February 2016
Please cite this article as: H. Keypour, M. Shayesteh, M. Rezaeivala, K. Sayin, Dinuclear Cu(II)
complexes of compartmental Schiff base ligands formed from unsymmetrical tripodal amines of varying
1
arm lengths: Crystal structure of [Cu L ](ClO ) and theoretical studies, Journal of Molecular Structure
2
4 2
(2016), doi: 10.1016/j.molstruc.2016.02.004.
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Graphical Abstract pictogram

ACCEPTED MANUSCRIPT
Dinuclear Cu(II) complexes of compartmental Schiff base ligands formed
from unsymmetrical tripodal amines of varying arm lengths: Crystal
structure of [Cu2L1](ClO4)2 and theoretical studies
Hassan Keypoura,*, Maryam Shayesteha, Majid Rezaeivalab, Koray Sayin C
a Faculty of Chemistry, Bu-Ali Sina University, Hamedan 65174, Iran
b Department of Chemical Engineering, Hamedan University of Technology, Hamedan 65155, Iran
C Department of Chemistry, Institute of Science, Cumhuriyet University, Sivas 58140, Turkey
ABSTRACT
Three new dinuclear copper complexes were synthesized via condensation reaction of three
new unsymmetrical N-capped tripodal amines and 2,6-diformyl-4-methylphenol, in the presence
of copper(II) perchlorate. The solid-state structure of the dinuclear complex, [Cu2L1](ClO4)2, has
been determined by X-ray crystallography, showing that the CuII centers have distorted square-
pyramidal geometry with N3O2 coordination. The copper (II) ions are bridged by phenolic and
hydroxyalkyl groups when in both cases, deprotonation of the hydrogen atoms of the OH groups
occurs. The distance between the copper atoms is 3.062 A˚. This compound consists of the
-
dication [Cu2L1]2+ and two ClO4 anions in which one of ClO4- groups has a week interaction
with one of the Cu atoms. All complexes were characterized by a variety of physico-chemical
techniques such as elemental analyses, IR, mass spectra, conductivity measurements and
electronic spectral studies. Computational investigation of mentioned binuclear Cu(II) complexes
was done by using M062X method with LANL2DZ basis set in vacuo.
Keywords: Binuclear Cu complexes; Compartmental Schiff base ligands; Unsymmetrical
tripodal amines; X-ray crystal structure; Theoretical studies.

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1. Introduction
In recent years, the chemistry of multinuclear metal compounds has received much attention
due to their relevance to the multimetal active sites of various metallo-proteins and metallo-
enzymes [1, 2]. Among them, the synthesis and characterization of polynuclear Cu(II)
compounds have attracted amazing interest over the past decades due to their numerous
biological activities. These complexes have potential application as models for the active sites of
important biological systems [3, 4]. Moreover, considerable interest has been placed to the
interaction of copper(II) complexes with DNA [5-9] due to their significance in the development
of new therapeutic agents in medicine. Much effort has been devoted to the synthesis of new
multinuclear copper complexes for a better understanding of the various properties of these
complexes in bioinorganic chemistry [10], medicine [11] and catalysis [12]. Also, binuclear
copper (II) complexes are of interest as models to investigate intramolecular magnetic-exchange
interactions between two metal centers in different structural motifs, viz. the ‘‘paddle-wheel’’ di-
copper(II) tetracarboxylates, symmetrically dibridged hydroxo or alkoxo species, and
asymmetrically di-bridged complexes with a (l-hydroxo/alkoxo)(l-carb-oxylato)dicopper(II) core
[13-22]. Dicopper (II) complexes are also of importance as precursors in the chemistry of
supramolecular and discrete molecular high-nuclearity copper (II) complexes [23-32]. There has
been growing interest in using bridging ligands in the synthesis of di- and multinuclear metal
complexes. Ligands which contain potentially bridging phenoxo or hydroxo oxygen and nitrogen
donor atoms have been widely used in the synthesis of multinuclear copper complexes [33–35].
Among the binuclear copper (II) complexes, bis-l-alkoxo, -hydroxo or -phenoxo bridged
binuclear copper(II) complexes have great deal of importance in terms of correlating structure
and magnetic properties [36–42]. However, bridged binuclear Cu(II) complexes have
considerable interest as they provide examples of the simplest case of magnetic interaction

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including only two unpaired electrons [43,44]. The present study demonstrates the synthesis and
characterization of new double asymmetric-bridged copper (II) complexes which were obtained
by using H2L1, H2L2 and H2L3 compartmental Schiff-base ligands. These complexes were
characterised by elemental analysis, IR, conductance measurements, UV-Vis, Mass spectra and
in the case of [Cu2L1](ClO4)2 with single crystal X-ray diffraction analysis. The molecular
structure of the title molecule is illustrated in Fig. 1. It is a new binuclear Schiff base copper (II)
complex, with the Cu(II) ion having a N3O2 square pyramidal geometry. Computational studies
of relevant Cu(II) complexes were performed by using restricted M062X method. Optimized
structures, IR spectrum, frontier molecular orbitals (FMOs) of Cu(II) complexes are investigated
in detail. Additionally, nonlinear optical (NLO) properties of Cu(II) complexes are examined by
using total static dipole moment (µ), the average linear polarizability (α), the anisotropy of
polarizability (∆α) and first hyperpolarizability (β), energy of the highest occupied molecular
orbital (EHOMO) and energy gap between the LUMO and HOMO (ELUMO-HOMO).
2. Experimental
2.1. General remarks
Pyridine-2-carbaldehyde,
2-aminoethanol,
3-aminopropan-1-ol,
N-(3-
bromopropyl)phthalimide, N-(4-bromobutyl)phthalimide and metal salt were obtained from
Aldrich and used without further purification. 2,6-diformyl-4-methylphenol was synthesised
according to the literature procedure [45]. All other chemicals and solvents were of reagent grade
and used as received.

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2.2. Caution
Whilst no problems were encountered in the course of this work, perchlorate mixtures are
potentially explosive and should therefore be handled with appropriate care.
2.3. Physical measurements
Infrared spectra were obtained between 4000-400 cm-1 on a Bruker Alpha FT-ATR IR
spectrometer with a diamond anvil Alpha-P module and also KBr pellets on a BIO-RAD FTS-
40A spectrophotometer. UV-vis spectra were recorded on a Jasco V550 spectrophotometer.
Conductance measurements were performed using a Hanna HI 8820 conductivity meter. ESI
mass spectra were recorded at the University of Otago on a Bruker MicrOTOFQ spectrometer.
Standard microanalysis for all complexes was carried out by a Perkin–Elmer, CHNS/O elemental
1
analyzer model 2400. H and 13C NMR spectra were taken in CDCl3 on a Jeol 90 MHz
spectrometer using Si(CH3)4 as an internal standard. Crystals suitable for X-ray diffraction were
obtained by slow diffusion of diethyl ether vapor into a mixture of methanol and acetonitrile.
Crystal data and structure refinement are given in Table 1. Single crystal X-ray crystallographic
data were collected at 293 K for [Cu2L1](ClO4)2 (λ = 0.71073) on a Bruker SMART CCD area
diffractometer. All data were corrected for Lorentz and polarization effects. Empirical absorption
corrections were also applied for the crystal structure obtained [46]. Complex scattering factors
were taken from the program package SHELXTL [47]. The structure was solved by direct
methods which revealed the position of all non-hydrogen atoms. The structure was refined on F2
by a full-matrix least-squares procedure using anisotropic displacement parameters for all non
hydrogen atoms. The hydrogen atoms were located in their calculated positions and refined using
a riding model.

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2.4. Computational method
Numerical calculations and computational processes were done by using GaussView 5.0.8
[48], Gaussian 09 RevD.01 package program [49] and ChemBioDraw Ultra Version
(13.0.0.3015) [50]. M062X is one of the hybrid density functional theory methods [51]. In
calculations, LANL2DZ basis set was used for its effective core potential [52-54]. All
calculations were made in vacuo. Imaginary frequency was not obtained in whole calculations.
Fig.1 here
2.5 Synthesis
2.5.1. General synthesis of unsymmetrical tripodal amines (1, 2 and 3).
2-Aminoethanol (1.22 g, 20 mmol) or 3-aminopropan-1-ol (1.50 g, 20 mmol) dissolved in
dry EtOH (100 mL) was added dropwise to a solution of pyridine-2-carbaldehyde (2.14 g, 20
mmol) dissolved in dry EtOH (100 mL) over a period of 2h, separately. The mixture was
refluxed under stirring for 12 h. Solid sodium borohydride (3.02 g, 80 mmol) was then added
slowly and the reaction mixture was stirred for a further 12 h before it was filtered. The filtrate
volume was reduced to 20 mL by rotary evaporation. Water (50 mL) was added and the products
were extracted with chloroform (3×50 mL). The combined extracts were dried over magnesium
sulfate, filtered, and then taken to dryness by rotary evaporation. The resulting brown oil (1.52 g,
10 mmole, l' (starting with 2-aminoethanol) or 1.66 g, 10 mmole, 2' (starting with 3-
aminopropanol) was dissolved in acetonitrile (70 mL), solid K2CO3 (2.07 g, 15 mmol) was
added, and the mixture was brought to reflux before a solution of N-(4-bromobutyl)phthalimide
(2.81 g, 10 mmole) was added dropwise to l', or N-(3-bromopropyl)phthalimide (2.67 g, 10
mmole) or N-(4-bromobutyl)phthalimide (2.81 g, 10 mmole) in acetonitrile (70 mL) to 2'. The
mixture was refluxed for 48 h and then filtered hot. The filtrate was reduced to dryness by rotary

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evaporation. The brown oil residue was boiled under reflux for 12 h in aqueous HCl (25%, 100
mL) and then evaporated to a small volume (ca. 25 mL) under vacuum and cooled in a
refrigerator for several hours. The resulting solid was filtered off and discarded, and the filtrate
was evaporated to dryness under vacuum. Water (50 mL) was added to the resulting brown
residue and the pH adjusted to 12 with sodium hydroxide before extracting with chloroform
(3×50 mL). The combined extract was dried over magnesium sulfate, filtered and the chloroform
was removed from the filtrate by rotary evaporation to leave the products, 1, 2 and 3, as brown
oils.
2.5.1.1. Synthesis of 2-((4-aminobutyl)(pyridin-2-ylmethyl)amino)ethanol (1)
Yield: 1.34 g (60%). Anal. Calc. for C12H21N3O (MW: 223.17): C, 64.54; H, 9.48; N, 18.82.
Found: 64.35; H, 9.25; N, 19.10%. IR (Nujol mull, cm-1) 3354, 3272 ν (NH2), 1591 ν (C=N)py.
1H NMR (CDCl3, ppm) δ = 1.36-1.55 (m, 4H); 2.15-2.48 (b, 3H), 2.54-2.63 (m, 4H) 2.71 (t, 2H);
3.58 (t, 2H); 3.78 (s, 2H); 7.14–7.17 (m, 1H); 7.28-7.31 (m, 1H); 7.64 (td, 1H); 8.52 (d, 1H). 13C
NMR (CDCl3, ppm) δ = 24.0; 29.2; 40.4; 54.1; 56.1; 58.7; 59.69; 121.3, 122.5; 135.9; 148.3;
159.2.
2.5.1.2. Synthesis of 3-((3-aminopropyl)(pyridin-2-ylmethyl)amino)propan-1-ol (2)
Yield: 1.92 g (86%). Anal. Calc. for C12H21N3O (MW: 223.31): C, 64.54; H, 9.48; N, 18.82.
Found: 64.20; H, 9.65; N, 18.90%. IR (Nujol mull, cm-1) 3352, 3271 ν (NH2), 1591 ν (C=N)py.
1H NMR (CDCl3, ppm) δ = 1.5 (m, 4H); 2.3-2.5 (m, 6H); 3.5 (s, 4H); 4.4 (s, 3H); 6.9–7.5 (m,
3H); 8.3 (d, 1H). 13C NMR (CDCl3, ppm) δ = 25.9; 28.6; 39.2; 50.7; 51.8; 59.0; 59.7; 121.5,
122.5; 136.1; 148.2; 158.4.

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2.5.1.3. Synthesis of 3-((4-aminobutyl)(pyridin-2-ylmethyl)amino)propan-1-ol (3)
Yield: 1.73 g (73%). Anal. Calc. for C13H23N3O (MW: 237.18): C, 65.79; H, 9.77; N, 17.70.
Found: 65.10; H, 9.45; N, 17.20%. IR (Nujol mull, cm-1) 3360, 3288 ν (NH2) 1591 ν (C=N)py. 1H
NMR (CDCl3, ppm) δ = 1.3-1.5 (m, 6H); 2.3-2.5 (m, 6H); 3.5 (s, 4H); 4.5 (s, 3H); 6.9–7.5 (m,
3H); 8.3 (s, 1H). 13C NMR (CDCl3, ppm) δ = 23.5; 28.6; 29.6; 40.3; 51.6; 53.2; 59.4; 60.7,
121.2; 122.4; 135.8; 148.0, 158.7.
2.5.2. General synthesis of the complexes
A solution of 0.5 mmol of dialdehyde (0.082 g, 0.5 mmol) in methanol (50 ml) and 7 drops
of triethyl amine were added dropwise to a refluxing solution of Cu(ClO4)2.6H2O (0.368 g, 1
mmol) and the appropriate amine, 1 (0.224 g, 1 mmol) or 2 (0.224 g, 1 mmol) or 3 (0.238 g, 1
mmol) in the same solvent (50 mL). After being refluxed for 12 h, the solution was concentrated
in a rotary evaporator at room temperature to ca. 5–10 mL. A small volume of diethyl ether was
added slowly, producing powdery precipitate. The powdery Cu(II) products were filtered off,
washed with cold diethyl ether and dried under vacuum. Crystalline or powdery compounds were
obtained by slow diffusion of diethyl ether vapor into a solution of these compounds in methanol
or mixture of methanol and acetonitrile, as detailed below.
2.5.2.1. Synthesis of the [Cu2L1](ClO4)2
Recrystallisation of the initial solid from mixture of CH3OH and MeCN in a 1:1 ratio via
slow vapour diffusion of Et2O yields green crystals (0.348g, 75%). Anal. Calc. for
C34H48Cl2Cu2N6O12: C, 43.87; H, 5.20; N, 9.03. Found: C, 43.79; H, 5.05; N, 8.97%. IR (KBr,
cm-1) 1638 and 1628 ν(C=N)imi; 1609 ν(C=N)py; 1096, 623 ν(ClO4). ESI-MS (MeOH, m/z+):

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799.16 [Cu2L1+2H](ClO4)+. Λm (CH3CN): 290 ꢀ-1 cm2 mol-1 (220–300 ꢀ-1 cm2 mol-1 for a 2:1
conductor in MeCN) [55]. UV-Vis. {λmax, nm (ɛmax, M-1 cm-1)} in CH3CN: 262 (21480), 372
(4730), 648 (146).
2.5.2.2. Synthesis of the [Cu2L2](ClO4)2
Recrystallisation of the initial solid from CH3OH via slow vapour diffusion of Et2O yields
green powder (0.305 g, 68 %). Anal. Calc. for C33.5H46Cl2Cu2N6O11.5: C, 43.99; H, 5.07; N, 9.19.
Found: C, 43.64; H, 5.24; N, 9.03%. IR (KBr, cm-1) 1638 and 1629 ν(C=N)imi; 1611 ν(C=N)py;
1094, 623 ν(ClO4). ESI-MS (MeOH, m/z+): 799.16 [Cu2L2+2H](ClO4)+. Λm (CH3CN) = 303 ꢀ-1
cm2 mol-1 (220–300 ꢀ-1 cm2 mol-1 for a 2:1 conductor in MeCN) [55]. UV–Vis. {λmax, nm (ɛmax
,
M-1 cm-1)} in CH3CN: 265 (22210), 377 (4130), 622 (187).
2.5.2.3. Synthesis of the [Cu2L3](ClO4)2
Recrystallisation of the initial solid from mixture of CH3OH and MeCN in a 1:1 ratio via
slow vapour diffusion of Et2O yields green powder (0.328 g, 71 %). Anal. Calc. for
C35H48Cl2Cu2N6O11: C,45.36; H, 5.22; N, 9.07. Found: C, 45.27; H, 5.28; N, 8.92%. IR (KBr,
cm-1) 1638 and 1629 ν(C=N)imi; 1612 ν(C=N)py; 1092, 624 ν(ClO4). ESI-MS (MeOH, m/z+):
827.18 [Cu2L3+2H](ClO4)+, 725.23[Cu2L3+H] +. Λm (CH3CN) = 296 ꢀ-1 cm2 mol-1 (220–300 ꢀ-1
cm2 mol-1 for a 2:1 conductor in MeCN) [55]. UV–Vis. {λmax, nm (ɛmax, M-1 cm-1)} in CH3CN:
263 (17930), 401(4020), 643 (125).
3. Results and discussion
Three
new
unsymmetrical
tripodal
amines,
2-((4-aminobutyl)(pyridin-2-
ylmethyl)amino)ethanol (1), 3-((3-aminopropyl)(pyridin-2-ylmethyl)amino)propan-1-ol (2) and

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3-((4-aminobutyl)(pyridin-2-ylmethyl)amino)propan-1-ol (3), were prepared in good yields (to
see the spectra refer to Fig. S1–S9, ESI†).
Subsequently, one- pot reactions of amines 1-3 with 2,6-diformyl-4-methylphenol in the
presence of cooper perchlorate were employed to generate new dinuclear Cu(II) complexes of
Schiff-base ligands H2L1-3 (Figure 1). Recrystallisation of the powders obtained from the
reaction mixtures as detailed in the experimental section, by vapour diffusion of diethyl ether,
yields powders, or in one case single crystal [Cu2L1](ClO4)2, which are dinuclear complexes (see
next sections).
3.1. Infrared spectroscopy
The infrared spectra of all these complexes show two bands, at ca. 1628-1629 and 1638 cm-
1, attributable to the asymmetric imine groups, and no bands due to ν(C=O) vibrations. Medium
to strong bands at ca. 1609–1612 and 1446–1449 cm-1 are present in all cases, and correspond to
the two highest energy ring vibrations of the coordinated pyridine [56, 57]. Absorptions
attributable to the perchlorate ions are seen at approximately 1092–1096 and 623–624 cm-1. Lack
of splitting suggests that they are not coordinated (to see the spectra refer to Fig. S10–S12,
ESI†).
3.2. Mass spectrometry
The positive ion electrospray mass spectra of all complexes (to see the spectra refer to Fig.
S13–S15, ESI†) show a common peak, the fragment [Cu2L1-3+2H](ClO4)+ which is associated
with the loss of the ClO4 anion. The mass spectra of these complexes indicate that these
complexes are dinuclear.

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3.3. UV-Vis spectra
Although the UV-Vis spectra of complexes with polydentate Schiff base ligands are not
generally good indicators of geometry, they may help to support it.
The UV-Vis spectra of the dinuclear Cu(II) complexes, in CH3CN solution , exhibit a broad low-
intensity absorption band occurring in the range 622 nm < λmax < 648 nm with 125 M-1 cm-1 < ɛ
< 187 M-1 cm-1. This is assigned to a d–d transition and is typical for five-coordinate copper(II)
complexes with square pyramidal or distorted square pyramidal geometries, which generally
exhibit a band in the 550-660 nm range (dxz, dyz→dx2-y2) [58-66]. In addition, a few absorption
bands are found in the range 262–401 nm for all Cu(II) complexes, due to either charge transfer
or π– π* transitions [61, 63, 67-69].
3.4. Molar conductivity measurements
The electrolytic nature of the dinuclear metal complexes can be predicted from the molar
conductance values. The molar conductivity values in MeCN for all dinuclear Cu(II) complexes
are in the literature range for a 2:1 electrolyte in CH3CN (220-300 ꢀ−1 cm2 mol−1) [55].
3.5. Crystal structure of [Cu2L1](ClO4)2
Green single crystals of [Cu2L1](ClO4)2 suitable to be studied by X-ray diffraction were
obtained by slow diffusion of diethyl ether into a solution of the complex in mixture of CH3OH
and MeCN. It is crystallised in the monoclinic crystal system and P21/n space group. The
molecular structure , the selected bond lengths and bond angles relating to the coordination

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environment of the metal and also bond lengths related to similar compounds are given in Figure
2 and Table 2, respectively [56, 61, 70-81]. The X-ray crystal structure of this complex consists
of [Cu2L1]2+ cation and two perchlorate anion. The charge distribution was assigned based on the
-
presence of only two ClO4 anions which make the complex a dication with a dideprotonated
ligand [L1]2-. The structure is a dinuclear, comprising two Cu(II) centers. Each Cu atom is
coordinated by two different bridged oxygen atoms related to phenoxy and hydroxyalkyl groups
and three imino, amine and pyridine nitrogen atoms. Each of phenoxy and hydroxyalkyl oxygen
atoms bridges the two copper atoms. Cu(1) and Cu(2) atoms lie in an N3O2 coordination
environment which takes the form of a distorted square pyramidal. The coordination geometry
around the copper centers is best described by the use of the τ-criterion [78], which indicates that
the coordination geometry in [Cu2L1]2+ is only slightly distorted (τ = 0.018 Cu(1) and τ = 0.121
Cu(2)) from square-pyramidal. For Cu(l), the pyridine nitrogen N(3), imino nitrogen N(1),
phenoxy oxygen O(1) and deprotonated hydroxyalkyl oxygen atom O(3) occupy equatorial
positions, and the tertiary nitrogen N(2) occupies axial position. For Cu(2), the amino nitrogen
N(5), imino nitrogen N(4), phenoxy O(1) and hydroxyalkyl O(3) oxygen atoms occupy
equatorial positions and one pyridine nitrogen atom N(6) occupies axial position. The phenoxy
oxygen atom O(1) and deprotonated hydroxyalkyl oxygen atom O(3) bridge the two Cu(II)
centers. The bond distances of Cu(1)-N and Cu(2)-N are in the range of 1.954-2.467 A°, being
normal coordination bonds. The bridging oxygen atoms form asymmetric linkages to the Cu
atoms with a range of Cu–Ophenoxy and Cu–Oalkoxy distances 1.988-2.003 and 1.902-1.925 A˚
respectively and Cu(1)–Ophenolate–Cu(2) and Cu(1)–Oalkoxy–Cu(2) bridging angles of 100.20 and
106.29, respectively. In this compound, one of the hydroxyalkyl arms (O2) of the ligand remains
uncoordinated (Figure 2). The distance between Cu(l) and Cu(2) is 3.062 A°..This long distance

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between two Cu(II) centers suggests that there is no interaction between these two metal centers.
In addition, in this complex one of the oxygen atoms related to one of the perchlorate groups
(O2p) has a very week interaction with Cu(1) atom. The tripodal ligand is capable of forming
five, six and seven membered chelate rings incorporating the copper ion in [Cu2L1](ClO4)2
complex. In this complex, both the Namine-Cu-Npy angles and also Namine-Cu2-Ohydroxyalkyl angle
are smaller than 90° [75.68-82.82°] for five membered chelate rings. The larger six- and seven-
membered chelate rings lead to Ophenolic-Cu-Nimine and Oamine-Cu-Nimine angles, respectively, that
are larger than 90° [91.55-105.32°] (Table 2).

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Fig 2. here
Table 2 here
3.6. Theoretical studies
3.6.1. Fully optimization of copper(II) complexes
Mentioned copper (II) complexes are optimized at M062X/LANL2DZ level in vacuo.
Optimized structures of [Cu2L1]2+ (1), [Cu2L2]2+ (2) and [Cu2L3]2+ (3) are represented in Figs. 3,
4 and 5, respectively. Structural parameters of these complexes are given in Table 3.
Figs 3-5 here
Table 3 here
Experimental and calculated structural parameters of [Cu2L1]2+ complex ions are subjected to
correlation analyses. Distribution graphs are plotted and regression coefficients are calculated
from this graph. Distribution graph and its regression coefficient are represented in Fig. 6.
Fig. 6. Here
According to Fig. 6, there are some differences between experimental and calculated
structural parameters but they are mainly similar to each other. Therefore, regression coefficient
is calculated as 0.908 from distribution graph. It shows that there is an agreement between
experimental and calculated structures of [Cu2L1]2+. As a result, complex structures of [Cu2L2]2+
and [Cu2L3]2+ are as shown in Figs. 4 and 5.
Vibrational spectra of mentioned copper complexes are calculated at the same level of
theory. Some selected harmonic frequencies of mentioned complexes are given in Table 4.

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Table 4. here
In Table 4, frequencies of mentioned complexes are harmonic while experimental
frequencies are anharmonic frequencies. Therefore, there are some differences which are in
acceptance limits.
3.6.2. Frontier molecular orbitals and NLO properties of Cu(II) complexes
Frontier molecular orbitals of copper(II) complexes and some quantum chemical descriptors
which are energy gap (ELUMO-HOMO), total static dipole moment (µ), the average linear
polarizability (α), the anisotropy of polarizability (∆α) and first hyperpolarizability (β) are
calculated by using Eqs. (1)-(5) [82, 83]:
ELUMO−HOMO = ELUMO − EHOMO
(1)
(2)
1
2
2
2
2
µ
=
µ
+
µy
+
µz
(
)
)
x
1
a = a + a + a
(3)
(4)
(
xx
yy
zz
3
1
a − a 2 + a − a 2 + a − a 2 + 6axz2 + 6axy2 + 6ayz
2
1
2
2


∆a =
(
)
(
)
(
)
xx
yy
yy
zz
zz
xx




2

2 1
2
2
(5)
β
=
β
+
βxyy
+
βxzz
+
β
+
βyzz
+
βyxx
+
β
+ βzxx + βzyy
zzz
(
)
(
)
(
)
xxx
yyy




Frontier molecular orbitals which are the highest occupied molecular orbital (HOMO) and
the lowest unoccupied molecular orbital (LUMO) and their energies are represented in Fig. 7.
Fig. 7. here
Mentioned quantum chemical descriptors are used to evaluate the non-linear optical (NLO)
properties of mentioned complexes. These parameters are calculated and given in Table 5.

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Non linear optical properties increase with the increase of total static dipole moment, the average
linear polarizability, the anisotropy of polarizability, first hyperpolarizability, energy of HOMO
and energy gap between LUMO and HOMO. Urea is selected as reference substance and
mentioned parameters of urea are calculated with 6-31G(d,p) basis set. For urea, total static
dipole moment, the average linear polarizability, the anisotropy of polarizability and first
hyperpolarizability are taken from Ref. [82] as 1.671 Debye, 2.182 Å3, 9.3119 Å3 and 3.18x10-28
cm5/esu, respectively [82]. According to Table 5, all values of each mentioned complexes are
greater than their urea values. Therefore, NLO properties of mentioned complexes are better than
those of urea. The general ranking of NLO properties should be as follows:
Complex (3) > Complex (2) > Complex (1) (according to µ,
Complex (1) > Complex (3) > Complex (2) (according to ꢁα
Complex (2) > Complex (3) > Complex (1) (according to
α and EHOMO)
)
β)
As can be seen from above rankings, complex (3) is mainly the best candidate for NLO
aplication.
Table 5 here
4. Conclusion
We report the successful synthesis of a series of new unsymmetrical tripodal amines, and
then three new unsymmetrical Schiff-base ligands from them, isolated as three new dinuclear Cu
complexes by condensation of amines (1-3) with 2,6-diformyl-4-methylphenol in the presence of
Cu(II) metal ion. X-ray crystal structure determinations of [Cu2L1](ClO4)2 revealed them to be
dinuclear. In this complex, there is a distorted square pyramidal environment around the central
ions. Each Cu atom is coordinated by two different bridged oxygen atoms related to phenoxy and
deprotonated hydroxyalkyl groups and three imino, amine and pyridine nitrogen atoms. Each of
phenoxy and hydroxyalkyl oxygen atoms bridges the two copper atoms. Cu(1) and Cu(2) atoms

ACCEPTED MANUSCRIPT
lie in an N3O2 coordination environment. In this compound, one of the hydroxyalkyl arms (O2)
of the ligand remains uncoordinated. Also, copper (II) complexes were investigated by
computational chemistry methods. Relevant complexes were optimized at M062X/LANL2DZ
level in vacuo. IR spectrum, FMO and NLO properties of relevant complexes were examined at
the same level of theory.
Supplementary material
Crystallographic data for the crystal structure analyses has been deposited with the
Cambridge Crystallographic Data Centre, CCDC no. (1412483), for [Cu2L1](ClO4)2. Copies of
this information may be obtained free of charge from the Director, CCDC, 12 Union road,
Cambridge, CB2 1EZ, UK (fax: +44 1223 336033; mail:deposit@ccdc.cam.ac.uk).
Acknowledgements
We are grateful to the Faculty of Chemistry of Bu-Ali Sina University, Ministry of Science,
Research and Technology of Iran, the University of Otago and the MacDiarmid Institute for
Advanced Materials and Nanotechnology for financial support (PhD scholarship for SD), and
Professor Sally Brooker for hosting MS for a 6-month research visit. Also, we are grateful of the
office of scientific research projects of Cumhuriyet University (Project No.: F-429) for financial
supports. The numerical calculations reported in this paper are performed at TUBITAK
ULAKBIM, High Performance and Grid Computing Center (TRUBA Resources).
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Figures

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( )
m
OH
N
( )
n
N
O
N
N
O
N
( )
H2N
( )
n
n
Cu(ClO4)2 6H2O, N(Et)3
Cu
Cu
CH3OH
N
N
( )
m
( )
m
O
HO
N
OH
O
[H2L1], m=1, n=3
[H2L2], m=2, n=2
[H2L3], m=2, n=3
Figure 1.structural motifs for new complexes of the ligands highlighted in the box, H2L1, H2L2
and H2L3resulting from the condensation of 2,6-diformyl-4-methylphenol with the
unsymmetrical triamines
lengths.
1 (n = 3, m=1) 2 (n = 2, m=2) and 3 (n = 3, m = 2) with different arm

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Figure 2. Perspective view of [Cu2L1](ClO4)2. Hydrogen atoms and anions are omitted for
clarity. Cu, C, N and O are represented in brown, gray, blue and red, respectively.
Fig. 3. Optimized structure of [Cu2L1]2+ at M062X/LANL2DZ level in vacuo with atomic
labelling.

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Fig. 4. Optimized structure of [Cu2L2]2+ at M062X/LANL2DZ level in vacuo with atomic
labelling.
Fig. 5. Optimized structure of [Cu2L3]2+ at M062X/LANL2DZ level in vacuo with atomic
labelling.

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Fig. 6. Distribution graph and its regression coefficients for [Cu2L1]2+ complex ion.
Fig. 7. Frontier molecular orbitals of mentioned Cu(II) complexes at M062X/LANL2DZ level in
vacuo.

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Table 1.Crystal data and structure refinement parameters for [Cu2L1](ClO4)2.
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
Unit cell dimensions
a (Å)
C34H48Cl2Cu2N6O12
930.76
293(2)
0.71073
Monoclinic
P21/n
9.5930 (13)
31.382 (4)
13.1055 (18)
96.295 (3)
b (Å)
c (Å)
β (°)
Volume (Å3)
3921.5 (9)
Z
4
Calculated density(Mg/m3)
1.576
Absorption coefficient (mm-1)
Crystal size ( mm3)
0.740
0.34 × 0.29 × 0.20
Theta range for data collection (°)
Limiting indices
1.3 to 25.1
-11≤h≤11, -37≤k≤37, -15≤l≤15
5194 / 2822 [R(int) = 0.041]
99.4 %
Reflections collected / unique
Completeness to theta=25.00
Absorption correction
Empirical
Max. and min. transmission
0.773 and 0.651
Refinement method
Full-matrix least-squares on F2
Data / restraints / parameters
Goodness-of-fit on F2
6956 / 0 / 508
1.046
Final R indices [I>2σ(I)]
R1 = 0.041, wR2 = 0.1162
R1 = 0.0666, wR2 = 0.996
R indices (all data)
Largest diff. peak and hole(e.A-3)
0.71 and -0.75