Assemblies of substituted salicylidene-2-ethanolamine copper(II) complexes: From square planar monomeric to octahedral polymeric halogen analogues

Article abstract of DOI:10.1016/j.poly.2012.09.029

A series of copper(II) complexes with tridentate salicylidene-2- ethanolamine type ligands is described. The complexes were isolated and characterized by single crystal X-ray diffraction, elemental analysis, IR and UV-Vis spectroscopy as well as cyclic voltammetry and magnetic susceptibility measurements. Single-crystal X-ray structure measurements for complexes with unsubstituted as well as 5-chloro and 5-bromo substituted salicylidene-2- ethanolamines demonstrate interesting differences in copper coordination geometry as well as topology of the crystal lattices. It was found, that the nature of the substituent in meta position affects supramolecular assembly in solid state and physicochemical properties such as magnetic susceptibility and redox potentials. Structural differences of studied systems impact the magnetic features by lowering the expected magnetic moments for d⁹ electronic configuration of copper(II). Cyclic voltammetry measurements show several irreversible reduction and oxidation processes attributed to coordinated ligands and metal centre. The resemblance of the solid state UV-Vis reflectance spectra of octahedral and square planar copper complexes makes them indistinguishable.

Full text of DOI:10.1016/j.poly.2012.09.029

Polyhedron 49 (2013) 74–83
Contents lists available at SciVerse ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Assemblies of substituted salicylidene-2-ethanolamine copper(II) complexes: From
square planar monomeric to octahedral polymeric halogen analogues
⇑
´
Piotr Zabierowski , Janusz Szklarzewicz, Katarzyna Kurpiewska, Krzysztof Lewinski, Wojciech Nitek
Faculty of Chemistry, Jagiellonian University, R. Ingardena 3, 30-060 Kraków, Poland
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 28 June 2012
Accepted 13 September 2012
Available online 26 September 2012
A series of copper(II) complexes with tridentate salicylidene-2-ethanolamine type ligands is described.
The complexes were isolated and characterized by single crystal X-ray diffraction, elemental analysis,
IR and UV–Vis spectroscopy as well as cyclic voltammetry and magnetic susceptibility measurements.
Single-crystal X-ray structure measurements for complexes with unsubstituted as well as 5-chloro and
5-bromo substituted salicylidene-2-ethanolamines demonstrate interesting differences in copper coordi-
nation geometry as well as topology of the crystal lattices. It was found, that the nature of the substituent
in meta position affects supramolecular assembly in solid state and physicochemical properties such as
magnetic susceptibility and redox potentials. Structural differences of studied systems impact the mag-
netic features by lowering the expected magnetic moments for d9 electronic configuration of copper(II).
Cyclic voltammetry measurements show several irreversible reduction and oxidation processes attrib-
uted to coordinated ligands and metal centre. The resemblance of the solid state UV–Vis reflectance spec-
tra of octahedral and square planar copper complexes makes them indistinguishable.
Keywords:
Schiff base
Copper complex
X-ray crystal structure
Cyclic voltammetry
Salicylidene-2-ethanolamine
Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction
cesses of electro polymerization and as a result the modified elec-
trodes can be applied as sensors [7]. In addition, mononuclear
Coordination chemistry of Schiff bases is an object of interest
for many inorganic chemists mainly due to a possibility to project
and synthesize ligands possessing a desirable chemical nature.
Knowledge about the crystal structure of solid material helps to
understand and somehow predict its potential applications as a
functional material. Hereby, we present the synthesis and charac-
terization of copper(II) complexes with salicylidene-2-ethanol-
amine and its substituted derivatives.
The first infrared spectrum analysis of salicylidene-2-ethanol-
amine was reported by Hanninen et al. in 1950 [1]. Since then, li-
gands of this type were investigated in context of inhibition of
corrosion of steel [2] and as antimicrobial agents [3]. Transition
metal complexes of Cu(II), Ni(II) and Mn(IV) with potentially tri-
dentate salicylidene-2-ethanolamine type ligands have intriguing
magnetic properties, being a consequence of magnetic interactions
in polynuclear cubane like clusters [4], or mixed metal complexes
[5]. The hydroxylic group in ligands of this type can coordinate in
bridging mode affording formation of multinuclear clusters pos-
sessing spectacular magnetic features, for instance, Mn4 core tetra-
nuclear complexes display slow relaxation of magnetization in
susceptibility measurements [6]. The features of hanging hydrox-
ylic groups, in case of square planar salicylaldimine complexes of
copper and nickel, favor formation of conducting polymers in pro-
Ni(II) and Cu(II) square planar complexes have been investigated
in context of non-linear optical properties [8] and liquid crystalline
phases [9]. On the other hand, in catalysis, copper(II), oxovana-
dium(IV) and dioxomolybdenum(IV) complexes with salicylid-
ene-2-ethanolamines were found effective in applications in
reactions of epoxidation of olefins [10] and degradation of lignin
[11]. Finally, studies of polynuclear complexes of iron with this
type of ligand provided information helpful in understanding of
biological systems [12].
X-ray structures of mononuclear complexes with halogen
substituted salicylidene-2-ethanolamine Schiff bases were re-
ported previously for several transition metals including Ni(II),
[13] Mn(III), [14] Cd(II) [15] and Co(III) [16]. Salicylidene-2-etha-
nolamine copper(II) complex was synthesized earlier and structur-
ally analyzed by Paulus et al. [17] and was tested for catalytic
applications in reactions of mild oxidation of alcohols by Midões
and co-workers [18]. The mixed ligand copper(II) complexes with
dibromo- and hydroxo- substituted salicylidene-2-ethanolamines
were synthesized earlier by Chumakov et al. [19]. It is worth to
note, that mononuclear complexes of copper(II) with halogen
meta-substituted salicylidene-2-ethanolamines have not been nei-
ther synthesized nor characterized structurally. In this work we
present synthesis of four mononuclear complexes of copper(II),
their characterization including IR and electronic spectroscopy
and cyclic voltammetry. For three complexes single-crystal X-ray
structural studies are also included.
⇑
Corresponding author. Tel.: +48 12 6632223; fax: +48 12 6340515.
E-mail address: zabierow@chemia.uj.edu.pl (P. Zabierowski).
0277-5387/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.poly.2012.09.029

P. Zabierowski et al. / Polyhedron 49 (2013) 74–83
75
EtOH,
N
OH
O
reflux,
30 min
OH
R2
OH
R2
H2N
OH
-H2O
R1
R1
EtOH,
reflux,
30 min
N
OH
(1) [Cu(heimp)2]; [R1=H; R2=H]
2
( ) [Cu(cheimp)2]; [R1=Cl; R2=H]
2
OH
R2
Cu(CH3COO)2
3
( ) [Cu(bheimp)2]; [R1=Br; R2=H]
in situ
(4) [Cu(mbheimp)2]; [R1=Br; R2=OCH3]
R1
Scheme 1. Synthesis of copper complexes 1, 2, 3 and 4.
Table 1
Summary of crystallographic data for [Cu(heimp)2] (1), [Cu(cheimp)2] (2) and [Cu(bheimp)2] (3). Standard deviations are
included in parentheses.
Compound
1
2
3
Chemical formula
Mr
Crystal system
Space group
Temperature (K)
a (Å)
C
18H20CuN2O4
C18H18Cl2CuN2O4
460.78
monoclinic
P21/n
C18H18Br2CuN2O4
549.70
monoclinic
P21/n
391.90
monoclinic
P21/c
293
293
110
18.317(5)
4.822(5)
19.765(5)
90
4.9393(1)
16.7975(4)
10.7076(2)
90
13.1588(3)
4.4005(1)
16.4511(3)
90
b (Å)
c (Å)
a
(°)
b (°)
98.792(5)
90
1725.22(2)
4
94.593(2)
90
885.53(3)
2
90.174(2)
90
952.60(4)
2
c
(°)
V (Å3)
Z
Radiation type
l
Mo K
1.29
a
Mo K
1.56
a
Mo K
5.37
a
(mmꢁ1
)
Measured reflections
Independent reflections
Observed [I > 2r(I)] reflections
6402
3813
2481
3983
1960
1681
4375
2059
1806
Rint
0.020
0.038
0.103
1.04
0.025
0.031
0.070
1.04
0.025
0.030
0.068
1.04
R1[F2 > 2
wR2(F2)a
S
r
(F2)]a
Number of parameters
237
0.26
ꢁ0.35
125
0.40
ꢁ0.37
125
0.62
ꢁ0.53
D
D
qmax (e Åꢁ3
qmin (e Åꢁ3
)
)
a
w = 1/[r
2(Fo2) + (0.0297P)2 + 0.0712P] where P = (Fo2 + 2Fc2)/3, R1
=
R
(|F0| ꢁ |Fc|)/
R
(|F0|) and wR2 = {
R
[w(F0 ꢁ Fc2)2}1/2
.
2.2. Synthesis
2. Experimental
2.1. Materials and methods
General synthetic approach is depicted in Scheme 1. Complex 1
was synthesized previously [17] and characterized structurally
(see Section 1) while complexes 2, 3 and 4 were not. The
synthesis method of 1 was different from that previously reported
– it is less time consuming and gives comparable yield, as well.
All reagents were purchased from Sigma–Aldrich and used as
supplied. Microanalyses on carbon, hydrogen and nitrogen were
performed using the Vario Micro Cube elemental analyzer. Solid
samples for IR spectroscopy were compressed as KBr pellets and
the IR spectra were recorded on a Bruker EQUINOX 55 FT-IR
spectrophotometer. Electronic absorption spectra were measured
2.2.1. Synthesis of bis{2-[(2-hydroxyethyl)iminomethyl]phenolato}
copper(II), [Cu(heimp)2], (1)
with
a
Shimadzu UV–Vis–NIR UV-3600 spectrophotometer.
Thirty millilitre of ethanolic solution of 2 mmol (0.122 ml) of
aminoethanol and 2 mmol (0.213 ml) of salicylaldehyde was re-
fluxed for 30 min, then 1 mmol (182 mg) of copper(II) diacetate
was added. The solution colour changed from slightly yellow to
dark brown during 30 min of heating under reflux. The solvent
was removed (ꢀ15 ml) under reduced pressure on a rotary evapo-
rator and the bright green crystalline precipitate was filtered off,
washed with cold ethanol and dried in air. The single crystals suit-
able for X-ray analysis were grown in the filtrate solution,
employing a slow evaporation of solvent at 298 K. Yield: 225 mg
(57%); Anal. Calc. for C18H20CuN2O4: C, 55.16; H, 5.14; N, 7.15.
Found: C, 55.26; H, 5.14; N, 7.06%. IR (KBr, cmꢁ1): 458w, 579w,
Cyclic voltammetry measurements were carried out in dimethyl
sulfoxide (DMSO) with [Bu4N]PF6 (tetrabuthyloammonium hexa-
fluorophospate) (0.10 M) as the supporting electrolyte using Pt
working and counter and Ag+/AgCl reference electrodes on an
AUTOLAB/PGSTAT 128 N Potentiostat/Galvanostat. E1/2 values
were calculated from the average anodic and cathodic peak
potentials, E1/2 = 0.5(Ea + Ec). The redox potentials were calibrated
versus ferrocene, which was used as an internal potential standard
for measurements in organic solvents to avoid the influence of
liquid junction potential; the final values are reported versus
standard hydrogen electrode (SHE).

76
P. Zabierowski et al. / Polyhedron 49 (2013) 74–83
Table 2a
The selected bond lengths (Å) and angles (°) for complexes 1, 2 and 3. Standard deviations are included in parentheses.
1
2
3
Selected bond lengths
Cu2–N21
Cu2–O13
N21–C22
C20–N21
O13–C14
C11–O12
N09–C10
O01–C02
Cu1–O01
Cu1–N09
C23–O24
C08–N09
1.994(2)
1.881(2)
1.465(3)
1.291(4)
1.304(4)
1.429(4)
1.477(3)
1.312(3)
1.871(2)
1.999(2)
1.419(4)
1.289(3)
Cu–N1
Cu–O1
1.991(2)
1.956(1)
1.477(3)
1.283(3)
1.314(3)
1.421(3)
1.754(2)
2.503(2)
Cu–N1
Cu–O1
N1–C8
C7–N1
O1–C1
C9–O2
Br1–C4
2.005(2)
1.894(2)
1.475(3)
1.285(3)
1.309(3)
1.430(3)
1.906(3)
N1–C08
C07–N1
O1–C01
O2–C09
Cl1–C04
Cu–O20
Selected angles
O01–Cu1–N09
O01–Cu1–N09
O01–Cu1–O01
N09–Cu1–N09
Cu1–O01–C02
Cu1–N09–C08
Cu1–N09–C10
C07–C08–N09
C08–N09–C10
C20–N21–C22
N21–C22–C23
O01–C02–C03
O01–C02–C07
N09–C10–C11
O13–Cu2–O13
C19–C20–N21
Cu2–N21–C20
Cu2–N21–C22
Cu2–O13–C14
N21–Cu2–N21
N21–Cu2–O13
O13–Cu2–N21
92.06(8)
87.94(8)
180.00(8)
180.00(8)
130.6(2)
123.6(2)
120.4(2)
127.7(2)
115.9(2)
116.2(2)
111.2(2)
118.5(2)
123.3(2)
112.2(2)
180.00(9)
127.4(3)
124.0(2)
119.8(2)
130.3(2)
180.00(9)
88.55(9)
91.45(9)
O1–Cu–N1
O1–Cu–N1
O1–Cu–O1
N1–Cu–N1
91.14(7)
88.86(7)
180.00(6)
180.00(7)
120.8(1)
122.2(1)
121.1(1)
125.5(2)
116.6(2)
119.9(2)
119.3(2)
120.7(2)
122.1(2)
113.1(2)
89.24(6)
84.70(6)
95.30(6)
180.00(5)
118.6(1)
O1–Cu–N1
O1–Cu–N1
O1–Cu–O1
N1–Cu–N1
Cu–O1–C1
Cu–N1–C7
Cu–N1–C8
C6–C7vN1
C7–N1–C8
Br1–C4–C3
Br1–C4–C5
O1–C1–C2
O1–C1–C6
N1–C8–C9
C8–C9–O2
91.70(8)
88.30(8)
180.00(8)
180.00(8)
129.8(2)
124.5(2)
119.8(2)
126.7(2)
115.7(2)
118.9(2)
120.4(2)
118.9(2)
123.6(2)
111.1(2)
111.8(2)
Cu–O1–C01
Cu–N1–C07
Cu–N1–C08
C06–C07–N1
C07–N1–C08
Cl1–C04–C03
Cl1–C04–C05
O1–C01–C02
O1–C01–C06
N1–C08–C09
N1–Cu–O20
O1–Cu–O200
O1–Cu–O20
O20–Cu–O200
C09–O2–Cu
Selected torsion angles
Cu1–O01–C02–C03
Cu1–O01–C01–C07
Cu1–N09–C08–C07
172.71
7.04
1.27
Cu–O1–C01–C02
Cu–O1–C01–C06
Cu–N1–C07–C06
145.19
36.20
7.58
Cu–O1–C1–C2
Cu–O1–C1–C6
Cu–N1–C7–C6
171.40
8.79
0.44
741w (
1128w, 1149m (
1434m ( C@C), 1452s (
C@N), 2911w ( C–H), 2972w (
3226w ( O–H).
m
O–H), 761s (
C–O), 1208m, 1327s
C–N), 1471s ( C–N), 1540s (
C–H), 3024w ( C–H), 3050w (m
m
O–H)., 869w, 891w, 1043m, 1060m (
C–O), 1350m, 1396m,
C–N), 1624vs
C–H),
m
C–O),
5-bromosalicylaldehyde was used (30 ml of ethanol; 0.122 ml,
2 mmol of aminoethanol; 402 mg, 2 mmol of 5-bromosalicylalde-
hyde; 182 mg, 1 mmol of Cu(CH3COO)2). The green single crystals
of 3 were grown in ethanol using a slow evaporation method in
temperature of 298 K. Yield: 480 mg (87%); Anal. Calc. for C18H18
Br2CuN2O4: C, 39.33; H, 3.30; N, 5.10. Found: C, 39.37; H, 3.25;
m
(m
m
m
m
m
(m
m
m
m
m
N, 5.08%. IR (KBr, cmꢁ1): 461w, 479w, 555w, 650w, 684s (
mO–H),
2.2.2. Synthesis of bis{4-chloro-2-[(2-hydroxyethyl)iminomethyl]phe-
nolato}-copper(II), [Cu(cheimp)2], (2)
711w, 824s (
m
O–H), 874w, 903w, 973w, 1040m (
C–O), 1132w, 1176m, 1197m, 1216w, 1243w
C–O), 1340w, 1361w, 1385s ( C–N), 1432m (
C@N), 2872w C–H), 2914w
C–H), 3258m ( O–H), 3338m ( O–H).
m
C–O), 1055s
(
(
m
m
(mC–O), 1322s
C@C), 1466vs (
The preparation method of complex 2 was similar to that of
complex 1 with one exception; instead of salicylaldehyde 5-chloro-
salicylaldehyde was used (30 ml of ethanol; 0.122 ml, 2 mmol of
aminoethanol; 313 mg, 2 mmol of 5-chlorosalicylaldehyde; 182 mg,
1 mmol of Cu(CH3COO)2). Green single crystals of complex 2,
suitable for X-ray analysis, were grown in the filtrate by slow solvent
evaporation at 298 K. Yield 400 mg (87%); Anal. Calc. for C18H18Cl2
CuN2O4: C, 46.92; H, 3.94; N, 6.08. Found: C, 47.09; H, 3.98; N,
6.10%; IR (KBr, cmꢁ1): 429w, 462w, 486w, 587w, 660w, 707s
m
m
m
m
C–N),
C–H),
1528m, 1589m, 1625vs
(
m
(
m
(
2975w ( C–H), 3041w (
m
m
m
m
2.2.4. Synthesis of bis{4-bromo-6-methoxy-2-[(2-hydroxyethyl)-
iminomethyl]phenolato}copper(II), [Cu(mbheimp)2], (4)
Forty millilitre of ethanolic solution of 2 mmol (0.122 ml) of
aminoethanol and 2 mmol of 5-bromo-3-methoxy-salicylaldehyde
(464 mg) was refluxed for 30 min, then 1 mmol of copper(II) diac-
etate (182 mg) was added. The solution colour changed from or-
ange to yellowish green. In the first five minutes of heating
under reflux the product precipitated and the small yellowish
green needle like crystals were filtered off, washed with cold eth-
anol and dried in air. Yield: 517 mg (85%); Anal. Calc. for C19H20-
BrCuN2O5: C, 39.40; H, 3.64; N, 4.59. Found: C, 39.41; H, 3.64; N,
(
m
O–H), 808m (
1056s ( C–O), 1079w, 1129w, 1178m, 1199m, 1215w, 1243w
C–O), 1323s ( C–O), 1339w, 1359w, 1388s ( C–N), 1434m ( C@C),
1467vs ( C–N), 1531s ( C–N), 1626vs ( C@N), 2852m ( C–H), 2918m
C–H), 2973m ( C–H), 3048w ( C–H), 3252m ( O–H), 3335m ( O–H).
mO–H), 825s (mO–H), 873w, 940w, 973w, 1041s (mC–O),
m
(m
m
m
m
m
m
m
m
(m
m
m
m
m
2.2.3. Synthesis of bis{4-bromo-2-[(2-hydroxyethyl)iminomethyl]-
phenolato}copper(II), [Cu(bheimp)2], (3)
4.81%. IR (KBr, cmꢁ1): 475vw, 521vw, 684vw (
798w ( O–H), 875vw, 913vw, 982vw, 1066w (
1123vw, 1187vw, 1243s ( C–O), 1326m ( C–O), 1357w, 1397vw,
mO–H), 765vw,
The preparation method of complex 3 was similar to that of
m
mC–O), 1087vw,
complex
1
with one exception; instead of salicylaldehyde
m
m

P. Zabierowski et al. / Polyhedron 49 (2013) 74–83
77
Table 2b
The hydrogen bonds parameters.
1416vw, 1436w (
m
C@C), 1477s (
m
C–N), 1543w, 1588vw, 1622vs
(m
C@N), 2927vw (
m
C–H), 3005vw (mC–H), 3054vw (mC–H), 3427vw
(mO–H).
Complex
D–A
d(D. . .A) [Å]
DHA [°]
1
O24–O12
O12–O24
C05–O12
C04–O24
C22–O12
C09–Cl1
C09–Cl1
C07–Cl1
C08–Cl1
O2–O1
2.726
2.748
3.712
3.512
3.607
3.876
3.761
3.804
3.431
2.656
2.705
3.979
3.670
170.64
171.04
167.48
135.06
125.25
147.00
121.22
165.17
118.69
171.30
162.92
162.52
147.16
2.3. Crystallographic data collection and structure refinement
The crystals of 1, 2 and 3 suitable for X-ray analysis were se-
lected from the materials prepared as described in Section 2. Inten-
sity data were collected on a SuperNova diffractometer (Agilent
Technologies) at 293 and 110 K equipped with Atlas detector and
2
3
microfocus Mo–Ka (k = 0.71073 Å) radiation source operating at
O2–O2
C7–Br1
C3–C2
50 kV and 1 mA for 1, 2 and 3, respectively. Data were processed
using CRYSALISPro.[20] The crystal data and details of data collection
and structure refinement parameters are summarized in Table 1.
The positions of most atoms were determined by direct methods
(SIR92) [21], other non-hydrogen atoms were located on difference
Fourier maps. All hydrogen atoms bonded to carbon were included
Fig. 1. The molecular structure (a) and crystal packing (b) of 1; ellipsoids represent 50% displacement probability; hydrogen atoms in (b) were omitted for clarity.
Fig. 2. The molecular structure (a) and crystal packing (b) of 2 with hydrogen bonds presented as dotted lines; ellipsoids represent 50% displacement probability; hydrogen
atoms in (b) were omitted for clarity.

78
P. Zabierowski et al. / Polyhedron 49 (2013) 74–83
Fig. 3. The molecular structure (a) and crystal packing (b) of 3 with hydrogen bonds presented as dotted lines; ellipsoids represent 50% displacement probability; hydrogen
atoms in (b) were omitted for clarity.
Fig. 6. Chains parallel to ac plane in crystal lattice of 2. Ellipsoids represent 50% of
displacement probability.
in the structure factor calculations at idealized positions. The struc-
tures were refined by SHELXL program [22]. Structural description
graphics were performed with program ORTEP III for Windows [23]
and MERCURY 2.3.
3. Results and discussion
3.1. Crystal structures
Crystal structure of 1 has been reported previously [17], but the
current experimental and unit cell parameters are more accurate,
thus we decided to include them in this work. The selected bond
lengths and angles for complexes 1, 2 and 3 are presented in Tables
2a and 2b. All of the complexes crystallize in monoclinic crystal
system in P21/c and P21/n space groups.
Fig. 4. The distances from square planes (gray colour) defined by positions of the
N2O2 donor aoms; molecular structures of complexes 1(a), 2(b) and 3(c). Ellipsoids
represent 50% of displacement probability. Given numbers are distances in Å.
3.1.1. Cu(heimp)2, (1)
The molecular structure of neutral centrosymmetric square pla-
nar copper(II) complex 1 is presented in Fig. 1. The unit cell of 1
contains 4 molecules and two symmetrically inequivalent copper
centers. The both central copper(II) atoms are in N2O2 coordination
environment of two chelating ligands with slightly different angles
and bond lengths. The bite angles for different copper centers are
O01–Cu1–N09 92.06(8)°, O13–Cu2–N21 91.45(9)° and are faintly
distorted from ideal 90.0°. The Cu–N and Cu–O bond lengths are
1.999(2) and 1.871(2) Å for Cu1, respectively. The equatorial NO
distances are 2.688(3), 2.787(3) Å for Cu1 and 2.706(3) Å and
2.776(3) Å for Cu2. In both cases, coordinating atoms lay on the
same plane as centre atom with N–Cu–N and O–Cu–O angles equal
to 180°, within standard deviation.
Fig. 5. The layers along plane ab in crystal lattice of 1. Ellipsoids represent 50% of
displacement probability.

P. Zabierowski et al. / Polyhedron 49 (2013) 74–83
79
Fig. 7. Layers along bc plane in crystal lattice of 3. Ellipsoids represent 50% of displacement probability.
Fig. 8.
p–p Stacking interactions in crystal lattice of 1: (a) a parallel assembly of molecules; (b) a perpendicular view to aromatic rings plane. Ellipsoids represent 50% of
displacement probability.
Fig. 9.
p–p Stacking interactions in crystal lattice of 2: (a) a parallel assembly of molecules; (b) a view perpendicular to aromatic rings. Ellipsoids represent 50% of
displacement probability.
3.1.2. Cu(cheimp)2, (2)
the measure of angular distortion from ideal value of 90.0°, which
should be maintained between square plane and the axial oxygen
atom. The non-bonding NO distances of equatorially coordinating
donor atoms are 2.819(2) and 2.763(2) Å. The N090–Cu–N09 and
O20–Cu–O200 angles are equal to 180° within standard deviation.
The crystal structure of 2 consists of chains along axis a, built up
from bis chelated copper centers tied axially by hanging hydroxyl
groups of other monomers. The molecular structure as well as
crystal packing of 2 is depicted in Fig. 2. Compared to 1, complex 2
contains only one symmetrically inequivalent metal centre in the
asymmetric unit and two molecules per unit cell. The bite angle is
equal to 88.86(7)° and is smaller than for 1. The Cu–N09, Cu–O1
(equatorial) and Cu–O20 (axial) bond lengths are 1.991(2), 1.956(1)
and 2.503(2) Å respectively, indicating very weak bonding of the
hydroxylic group. The O1–Cu–O20 angle is 95.30(6)°, which gives
3.1.3. Cu(bheimp)2, (3)
Compound 3 is neutral centrosymmetric square planar chelate
of copper(II) and strongly resembles complex 1. The molecular
structure and crystal packing of 3 are presented in Fig. 3. Central
atom is in N2O2 coordination environment, the bite angle of the

80
P. Zabierowski et al. / Polyhedron 49 (2013) 74–83
Fig. 10.
p–p
Stacking interactions in crystal lattice of 3: (a) a parallel assembly of molecules; (b) a view perpendicular to aromatic rings. Ellipsoids represent 50% of
displacement probability.
Fig. 11. The cyclic voltammograms of 1(a), 2(b), 3(c) and 4(d) registered in three electrode system with platinum working, auxiliary and Ag+/AgCl reference electrodes in
DMSO with 0.1 M Bu4NPF6 as a supporting electrolyte and Fc/Fc+ as an internal standard; room temperature; 100 mV/s sweep rate.
ligand is 91.70(8)°, which is similar value to that for 1. The Cu–N
and Cu–O bond lengths are also close to that of 1, with values
2.005(2) and 1.894(2) Å, respectively. The equatorial contacts be-
tween coordinating imine nitrogen and phenolic oxygen are also
demonstrating values similar to these for complex 1, 2.779(3)
and 2.717(3) Å, respectively.
the strongest deviation from planarity in case of complex 2 and
similarities between complexes 1 and 3.
Taking into consideration flexibility of the described molecules,
particularly in fragments consisting of the oxygen and nitrogen do-
nor atoms, the deviation from co-planarity with square plane in
each case is mediated by the strength of hydrogen bonds involving
the substituents. Bromine atom is larger than chlorine, therefore it
is soft Lewis base and this explains the less pronounced affinity to
forming hydrogen bonds in case of 3. The shortest halogen–halo-
gen distance is equal to that of Cuꢂ ꢂ ꢂCu in 2, whereas in crystal lat-
tice of 3 this value is smaller. Another deviations which can be
considered, are distances of hydroxylic oxygen and halogen atoms
to the square planes (Fig. 4). The former value is the biggest for
complex 1 and 3. The latter value is connected with the angular
distortion between square and aromatic ring planes due to the fact
that the meta substituent lies on the aromatic ring plane to which
it is bonded.
3.1.4. Supramolecular assemblies
There are significant differences among described complexes.
The shortest Cuꢂ ꢂ ꢂCu non-bonding distance in crystal lattice of 1
is 4.822(5) Å while in 2 this distance is 4.939(1) Å. The shortest
Cuꢂ ꢂ ꢂCu non-bonding distance among characterized complexes oc-
curs in crystal lattice of 3 with the value of 4.401(1) Å. The two
symmetrically different molecules in the unit cell of complex 1
are located spatially in planes defined by positions of square plane
atoms under angle of 71.94°. The deviations of the complex mole-
cules from planarity are presented in Fig. 4. The angular deviations
of the aromatic ring planes to the square planes are different for
each Cu1 and Cu2 copper centers with values of 5.33° (Cu1) and
10.59° (Cu2). The same angles in crystal lattices of complexes 2
and 3 are 39.09° and 10.01°, respectively. These values indicate
Several types of hydrogen bonds are responsible for observed
crystal packing of synthesized complexes. The hydrogen bond
parameters are presented in Table 2. In case of 1, the O12 oxygen
is not only a donor of hydrogen bond with O24 but also is an accep-
tor of hydrogen bond from O24 atom of the nearest molecule. Thus,

P. Zabierowski et al. / Polyhedron 49 (2013) 74–83
81
Further, the bromine atom forms very weak hydrogen bonds with
aliphatic C07 carbon atom. Assuming the weak hydrogen bonds
involving bromine atoms, the topology of hydrogen bonding net
is also three dimensional in crystal structure of 3, as it is in case
of complex 1 and 2.
The p–p stacking intermolecular interactions are present in the
crystal structures of all described complexes. In complex 1 (Fig. 8)
the distance between parallel aromatic rings planes is equal to
3.250 Å. In complex 2 (Fig. 9) this distance is 3.228 Å while in com-
plex 3 (Fig. 10) 3.382 Å, – the longest among all three complexes.
The IR data is consistent with the presented structures (spectra
are included in supplementary information). The characteristic
strong band at ca. 1620 cmꢁ1, associated with imine C@N stretch-
ing vibration is present in IR spectra of each compound. Moreover,
the strong and medium bands at ca. 1320 cmꢁ1 indicate deproto-
nation as well as coordination of the phenolic group (stretching
C–O vibrations). Strong and medium bands in the range 680–
830 cmꢁ1 can be assigned to out of plane bending vibrations of
the alcoholic –OH group.
3.2. Magnetic susceptibility measurements
Magnetic susceptibility measurements show typical values for
d9 system in case of 1 and 2 with values 1.67 and 1.71 BM, respec-
tively (without diamagnetic corrections). Complexes 3 and 4 are
showing lower than expected values of magnetic moment 1.36
and 1.50 BM, respectively (without diamagnetic corrections). Sig-
nificant difference between these magnetic moments can be attrib-
uted to short copper–copper distance [in 3 4.401 Å) compared to 1
(4.822 Å) and 2 (4.939 Å)] enabling antiferromagnetic coupling.
3.3. Cyclic voltammetry
Fig. 12. The cyclic voltammograms of 1(a), 2(b) and 3(c) registered in a three
electrode system with platinum working, auxiliary and Ag+/AgCl reference
electrodes in DMSO with 0.1 M Bu4NPF6 as a supporting electrolyte and Fc/Fc+ as
an internal standard; room temperature; 100 mV/s sweep rate.
The cyclic volatammetry measurements were carried out in di-
methyl sulfoxide and acetonitryle. The initial scans registered in
DMSO and MeCN are depicted in Fig. 11 and in Fig. 12, respectively.
The peak positions are presented in Table 3. Measurements in
DMSO reveal the presence of several reduction and oxidation peaks
of irreversible nature. In acetonitrile, a quasi reversible system is
observed (Fig. 12a) for 1, whereas in cases of the rest of the com-
plexes the potential-current response contains only irreversible re-
dox waves. Complex 4 is poorly soluble in acetonitrile, thus the
cyclic voltammetry measurements were not possible to perform.
The first reduction peak in DMSO, Ired, located at the most nega-
tive potential, occurs in voltammograms of all four compounds and
can be assigned to the reduction of imine. This process requires
source of protons and probably occurs with intramolecular proton
transfer [25]. The redox potentials of this peak are similar in case
of complexes 1, 2 and 4 while the complex 3 shows significant dif-
ference in this potential. In case of 3 the potential is shifted to high-
er values by 145 mV in comparison to the most negative value for
complex 2. The reason for such difference can be explained by the
individual influence of the substituent in the ꢁ5 and ꢁ3 positions
on the electronic structure of the molecule. In comparison to the
molecules are forming layers parallel to ab plane (Fig. 5). Addition-
ally, the same hydroxylic oxygen (O12) forms very weak hydrogen
bonds with aliphatic C22 and aromatic C05 carbon atoms (Fig. 1,
Table 2). Therefore, we observe three-dimensional topology of
hydrogen bonds in this case. In contrast, in the described family
of complexes only in 2 the hydroxylic group forms intramolecular
hydrogen bonds, what contributes to formation on chains parallel
to ac plane (Fig. 6). The chlorine atom takes part in three intermo-
lecular hydrogen bonds as an acceptor from two C09 and C07 car-
bon atoms from another three molecules. These weak interactions
can be classified as hydrogen bonds, according to Kovacs et al. and
contribute to formation of three dimensional net of hydrogen
bonds [24].
The hydroxylic group in complex 3 is also involved in hydrogen
bonding (Fig. 7), being a donor as well as an acceptor of intermo-
lecular hydrogen bonds from the nearest two hydroxyl groups.
Table 3
Cyclic voltammetry peak positions vs. SHE [V] in DMSO and acetonitrile at 100 mV/s scan rate, 298 K.
Complex
Ired
IIred
Iox
IIox
IIIox
DMSO
MeCN
DMSO
MeCN
DMSO
MeCN
DMSO
MeCN
DMSO
MeCN
1
2
3
4
ꢁ1.536
ꢁ1.569
ꢁ1.424
ꢁ1.556
–
–
–
–
ꢁ0.672
ꢁ0.721
ꢁ0.649
ꢁ0.719
ꢁ0.602
ꢁ0.598
ꢁ0.608
–
ꢁ0.628
ꢁ1.043
ꢁ0.757
–
ꢁ0.388
0.241
ꢁ0.065
0.295
ꢁ0.131
0.072
ꢁ0.028
ꢁ0.107
–
0.708
0.612
–
0.949
0.978
0.940
–
ꢁ0.301
–
–
0.628

82
P. Zabierowski et al. / Polyhedron 49 (2013) 74–83
Fig. 13. The UV–Vis spectra of 1, 2, 3 and 4 in MeCN (black solid line) and DMSO (black dashed line) at the room temperature.
Table 5
Solid state diffuse reflectance UV–Vis spectroscopic data (k [nm]).
Complex
1
2
3
4
212 230 247 272
–
305
–
–
374 396 447 614 694
213 245 265 290 301 318 353 380 405 429 615 691
–
223 233 250 274
214 228 246 278
–
–
303
–
–
375 404 444 615 686
303 318 335 387 414 472 630 706
The second reduction peak IIred can be attributed to the one
electronic reduction to copper(I) [26]. In acetonitrile complex 1 ex-
hibit quasi reversible behaviour with peak to peak separation
0.214 V and peak current ratio ca. 1.0, indicating a very slow elec-
tron transfer kinetics. The process is diffusion controlled and the
dependence of peak current from the square root of the potential
sweep rate is characteristic for a quasi-reversible system. The val-
ues of peak potentials of the IIred peak are shifted towards positive
potentials in MeCN in comparison to DMSO. It is worth to note that
the IIred potentials in MeCN are very similar while in DMSO these
potentials are shifted to lower values. This difference is probably
caused by significant change in polarity of the solvents. The differ-
ences between voltammetric curves of the corresponding com-
pounds in the shape of the IIox oxidation peak are significant in
DMSO and acetonitrile. Taking into consideration its characteristic
stripping shape, it can be attributed to reoxidation of the metallic
copper electrodeposited as a result of previous reduction reactions
occuring in acetonitrile. The positions of this peak differ among
characterized complexes. On the basis of current data the differ-
ence could not be explained. Factors which can influence the po-
tential and shape of the stripping-like copper reoxidation peak
were previously investigated by Grujicic et al. [27]. It is worth to
note that measurements in the multiscan mode in DMSO revealed
peak current increase of some peaks during subsequent scans,
which can indicate electro polymerisation process on the surface
of the working electrode (see supporting information). The oxida-
tion peaks IIIox can be attributed to oxidation processes occurring
at the phenolic groups coordinated to metal center.[28] The peak
positions of IIIox in acetonitrile are shifted towards positive
Fig. 14. The reflectance spectra of 1, 2, 3 and 4 after Kubelka–Munk transformation,
in the right upper corner of the picture are presented the d–d bands.
Table 4
UV–vis spectral data in DMSO and MeCN at room temperature after deconvolution to
Gaussian functions. Spectroscopic data; k [nm] (
e
ꢃ 103[Mꢁ1 cmꢁ1]).
Complex
1
2
3
4
DMSO
MeCN DMSO
MeCN DMSO
MeCN DMSO
MeCN
–
–
–
–
–
–
–
–
–
–
–
–
–
–
204
233
248
277
307
222
243
267
306
367
223
243
267
228
247
266
299
372
245(34)
282(21)
293(17)
375(8.1) 377
646(0.2)
269(32)
304(16)
363(17)
264(18)
264(50)
304(26)
369(23)
301(9.6) 303
365(9.5) 373
630(0.1) 610
622(0.2) 609
626(0.3) 610
–
rest of the peaks there is no simple correlation between peak poten-
tial and substituent withdrawing effect.

P. Zabierowski et al. / Polyhedron 49 (2013) 74–83
83
potentials, in comparison to DMSO, indicating strong influence of
the electron donating solvent properties.
CCDC 888232, CCDC 888233 and CCDC 888234 contains the
supplementary crystallographic data for 1, 2 and 3, respectively.
These data can be obtained free of charge via http://www.ccdc.ca-
m.ac.uk/conts/retrieving.html, or from the Cambridge Crystallo-
graphic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK;
fax: (+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk. The
additional data concerning cyclic voltammetry of studied systems
as well as IR spectra are also available free of charge as supporting
information on the journal website.
Copper(II) complexes with Schiff bases synthesized from sali-
cylaldehyde and different amine half units were previously studied
by means of cyclic voltammetry and various spectroelectrochemi-
cal methods [26c,29]. Similar redox processes have been reported
for these systems likewise in case of the title compounds.
3.4. UV–VIS spectra
The UV–VIS spectra were recorded in MeCN and DMSO (Fig. 13)
in the room temperature as well as in solid state (Fig. 14). The peak
positions and absorption coefficients are presented in Tables 4 and
5. The strongest bands in solution occurring in the UV range can be
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Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.poly.2012.09.029.