Complexes of Cu(II) with α-[(ethylamino)methyl]-3-hydroxy, benzenemethanol (Effortil). Crystal structure of the mononuclear Cu(II) complex with Effortil

Article abstract of DOI:10.1016/S0277-5387(00)00468-X

The complexation processes between Cu(II) and the antihypotension drug Effortil (HEff) at different reaction conditions lead to the formation of two types of complex - a mononuclear violet one, CuEff₂·2CH₃OH, and the binuclear green Cu₂Eff₂Cl₂. Monocrystals of the mononuclear CuEff₂·2CH₃OH complex were isolated and their structure determined by X-ray diffraction. Copper is coordinated through O^- and N of OH and NH groups from the ligands in a perfectly flat tetragon. The crystal structure also includes two solvent CH₃OH molecules per CuEff₂ unit. The CuEff₂ fragments are linked by hydrogen bonds. The binuclear Cu₂Eff₂Cl₂ complex was characterized using electronic and IR spectra, EPR, magnetochemical, calorimetric, thermogravimetric methods and elemental analysis. The complex contains bidentately bound monoanionic ligands and chloride ions. Each Cu atom is coordinated with NH, and bridged by the deprotonated OH group of Effortil with the second Cu center. The chloride ions are coordinated with copper as terminal ligands. (C) 2000 Elsevier Science Ltd.

Full text of DOI:10.1016/S0277-5387(00)00468-X

www.elsevier.nl/locate/poly
Polyhedron 19 (2000) 1843–1848
Complexes of Cu(II) with a-[(ethylamino)methyl]-3-hydroxy,
benzenemethanol (Effortil). Crystal structure of the mononuclear
Cu(II) complex with Effortil
P.R. Bontchev a,*, B.B. Ivanova a, R.P. Bontchev b, D.R. Mehandjiev c, D.S. Ivanov d
a Faculty of Chemistry, Sofia Uni6ersity, 1, J. Bourchier Boule6ard, Sofia 1164, Bulgaria
b Department of Chemistry, Uni6ersity of Houston, Houston, TX 77204-5641, USA
c Institute of Inorganic Chemistry, Bulgarian Academy of Sciences, Sofia, Bulgaria
d Faculty of Pharmacy, Medical Uni6ersity-Sofia, Sofia, Bulgaria
Received 22 February 2000; accepted 15 June 2000
Abstract
The complexation processes between Cu(II) and the antihypotension drug Effortil (HEff) at different reaction conditions lead
to the formation of two types of complex — a mononuclear violet one, CuEff2·2CH3OH, and the binuclear green Cu2Eff2Cl2.
Monocrystals of the mononuclear CuEff2·2CH3OH complex were isolated and their structure determined by X-ray diffraction.
Copper is coordinated through O− and N of OH and NH groups from the ligands in a perfectly flat tetragon. The crystal
structure also includes two solvent CH3OH molecules per CuEff2 unit. The CuEff2 fragments are linked by hydrogen bonds. The
binuclear Cu2Eff2Cl2 complex was characterized using electronic and IR spectra, EPR, magnetochemical, calorimetric, ther-
mogravimetric methods and elemental analysis. The complex contains bidentately bound monoanionic ligands and chloride ions.
Each Cu atom is coordinated with NH, and bridged by the deprotonated OH group of Effortil with the second Cu center. The
chloride ions are coordinated with copper as terminal ligands. © 2000 Elsevier Science Ltd. All rights reserved.
Keywords: Effortil; Cu(II) complexes; Structures; Stability constants; EPR; Magnetochemical data
drugs most widely used for this purpose, which repre-
sent aminoalcohols of type I, and differ by the sub-
stituent R in the phenyl ring.
1. Introduction
Recently it was assumed and found that arterial
blood pressure is a process regulated by the biometals
copper and zinc [1–4]. On the other hand, the drugs for
treatment of arterial hypertension are effective ligands
and it could be presumed that their action is at least
partially related to complexation with the two metals,
causing a shift in their homeostasis. From this point of
view, we have already studied the complex formation
between Cu(II) and different anti-hypertensives such as
ACE-inhibitors [5], vasodilators [6] and diuretics [7,8].
Special attention was paid to the b-blockers [8–13], the
It seems worth noting however, that one of the most
efficient drugs used against arterial hypotension, Effor-
til, II also represents an aminoalcohol of the same type.
It was interesting therefore, to study whether its behav-
ior towards copper is analogous and why its effect on
the blood pressure is just the opposite.
Hence, the aim of the present study was investigation
of the complexation processes between copper(II) and
Effortil.
* Corresponding author. Tel.: +35-92-628-323; fax: +35-92-962-
5438.
E-mail address: prbontchev@chem.uni-sofia.bg (P.R. Bontchev).
0277-5387/00/$ - see front matter © 2000 Elsevier Science Ltd. All rights reserved.
PII: S0277-5387(00)00468-X

1844
P.R. Bontche6 et al. / Polyhedron 19 (2000) 1843–1848
these solutions with Cu–HEff molar ratio 1:2 were
2. Experimental
2.1. Apparatus and analysis
titrated with 9.95×10−3 mol dm−3 HClO4 to obtain
the stability constants. The ionic strength was adjusted
to 0.1 mol dm−3 with NaClO4·H2O. Argon was bub-
bled through the samples to remove O2 and CO2 and
for stirring the solution. Measurements were performed
on a Radiometer PHM84 pH-meter with accuracy of
90.001 pH units, equipped with a GK240C combined
electrode and an ABU80 automatic burette for poten-
tiometric titration. The stability constants were calcu-
lated by means of a general computation program
The IR spectra in the 4000–100 cm−1 range were
recorded on a Perkin–Elmer 893 spectrometer both in
Nujol and CsI, the X-band EPR spectra on a Bruker
ER 420 spectrometer and the electronic spectra were
obtained on a Specord UV–Vis (Carl–Zeiss, Jena). The
calorimetric and gravimetric studies were performed on
DSC-2C and TGS-2 Perkin–Elmer equipment in argon.
The magnetic measurements were carried out in argon
atmosphere by the Faraday balance. The elemental
analysis was performed according to the standard
methods: C and H were determined as CO2 and H2O, N
through the Duma’s method, chlorine by titration with
Hg(NO3)2 after wet digestion of the sample. Copper(II)
was determined after ignition of a sample, dissolution
of the residue in diluted HNO3 and titration with
standard solution of EDTA using indicator Murexide
at pH 8 (ammonia buffer). The potentiometric mea-
surements were provided with aqueous solutions of
(Cu(ClO4)2·6H2O) containing 5×10−4 Cu(II) and 1×
10−3 mol dm−3 of Effortil base (HEff). Aliquots of
(
PSEQUAD) [14]. X-ray diffraction was studied on a
monocrystal using an Enraf–Nonius CAD-4 diffrac-
tometer. transparent violet crystal of CuEff2·
A
2CH3OH was selected and mounted on an Enraf–Non-
ius CAD-4 diffractometer. A hemisphere of 1743 inde-
pendent reflections, of which 1620 with I\2|(I), was
collected at r.t. using graphite monochromated Mo Ka
,
radiation (u=1.71073 A). The structure was solved by
direct methods (SHELXTL) [15] and refined by least
squares on F2 (SHELX-96) [16]. First the Cu, N and O
atoms were located according to the difference Fourier
map and their positions refined isotropically. Next the
C atoms were found and all the atoms refined an-
isotropically. Finally the H atoms were refined using a
riding model. The main crystal and refinement data are
listed in Table 1.
Table 1
2.2. Synthesis
Crystal data and structure refinement for the mononuclear complex
CuEff2·2CH3OH
The ligand was obtained from Sopharma, Bulgaria,
CuCl2·2H2O and CH3OH (both of analytical grade)
were supplied by Riedel E. de Hae¨n AG.
Empirical formula
Formula weight
Temperature (K)
Cu(C10NO2H14)2·2CH3OH
488.08
293(2)
,
Wavelength (A)
0.71073
monoclinic
P21/n (no. 14)
2.2.1. The mononuclear complex
Crystal system
Space group
HEff·HCl (0.0541 g) was dissolved in 10 ml
methanol. The addition of 1 ml methanolic Cu(II)
solution containing 0.0043 g CuCl2·2H2O and NaOH
(0.0200 g in 20 ml methanol) at molar ratio Cu–
HEff·HCl–NaOH=1:10:20 leads to the formation of a
violet solution from which a crystalline violet mononu-
clear complex was obtained after four months. It was
filtered, washed with methanol and dried over P2O5.
Anal. Found: C, 54.21; H, 6.97; N, 5.63; Cu, 12.01.
Calc. for CuEff2·2CH3OH: C, 54.36; H, 7.05; N, 5.76;
Cu, 12.07%. The mononuclear complex was also ob-
tained in aqueous solution, at excess of the ligand,
Cu–HEff·HCl=1:2–1:10 and pH 10.5.
The synthesis of the binuclear complex was realized
using 0.0541 g HEff·HCl in 10 ml methanol, Cu(II) salt
(0.0213 g CuCl2·2H2O in 5 ml methanol) and NaOH
(0.0100 g in 10 ml methanol). The molar ratio was
Cu–HEff·HCl–NaOH=1:2:2. After three days a green
precipitate was formed and it was filtered, washed with
methanol and dried over P2O5. Anal. Found: C, 42.94;
H, 5.00; N, 5.04; Cu, 22.61. Calc. for Cu2Eff2Cl2: C,
43.02; H, 5.05; N, 5.02; Cu, 22.76%.
Unit cell dimensions
,
a (A)
7.7373(6)
13.5607(10)
11.7331(9)
90
99.1470(10)
90
1215.4(2)
2
,
b (A)
,
c (A)
h (°)
i (°)
k (°)
3
,
Volume (A )
Z
Dcalc (g cm−3
)
1.295
0.935
518
Absorption coefficient (mm−1
F(000)
)
Crystal size (mm)
q Range for data collection (°)
Index ranges
Reflections collected
Independent reflections
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I\2|(I)]
R indices (all data)
0.20×0.15×0.10
2.31–23.26
−85h58, 05k515, 05l513
1743
1743 [Rint=0.052]
full-matrix least-squares on F2
1743/0/143
1.139
R1=0.0442, wR2=0.1267
R1=0.0470, wR2=0.1290
Largest difference peak and hole 0.634 and −0.269
−3
,
(e A
)

P.R. Bontche6 et al. / Polyhedron 19 (2000) 1843–1848
1845
3. Results and discussion
3.1. Mononuclear CuEff2·2CH3OH complex
3.1.1. X-ray data and crystal structure
The structure is shown in Fig. 1, and selected bond
lengths and angles in Table 2.
In the structure the Cu atoms occupy one crystallo-
graphically independent special position. Each Cu atom
is coordinated by two OH groups and two N atoms
from two ligand molecules in a perfectly flat tetragon.
,
The CuꢀO and CuꢀN distances (1.905 and 2.042 A) and
Fig. 1. The asymmetric unit and coordination of the copper atoms in
CuEff2·2CH3OH, 50% thermal ellipsoids.
OꢀCuꢀN angles (85.60 and 94.40°) are typical for a
four-fold square coordination and compare well with
the distances reported for similar copper complexes
[17]. The CuEff2 and the solvent methanol molecules
are arranged in layers parallel to the b-axis. A complex
network of hydrogen bonds links these layers in a 3D
structure (Fig. 2). The closest CuꢀCu separation corre-
Table 2
a
,
Selected bond lengths (A) and angles (°) for CuEff2·2CH3OH
Cu coordination
Effortil
,
sponds to the a-axis (7.737 A) which clearly indicates
Cu(1)ꢀO(2)
Cu(1)ꢀO(2)
Cu(1)ꢀN(1)
Cu(1)ꢀN(1)
1.905(2)
1.905(2)
2.042(3)
2.042(3)
C(8)ꢀN(1)
C(5)ꢀN(1)
C(2)ꢀO(1)
C(6)ꢀO(2)
1.489(5)
1.484(4)
1.370(4)
1.412(4)
that there is no direct magnetic interaction between the
Cu centers in the structure. The CꢀC, CꢀN and CꢀO
distances in the Effortil and methanol molecules range
,
from 1.375 to 1.528 A and the CꢀH distances are of the
,
CꢀC range within 1.375(5)–1.528(5) A
,
order 0.8–1.1 A.
O(2)ꢀCu(1)ꢀO(2)
O(2)ꢀCu(1)ꢀN(1)
O(2)ꢀCu(1)ꢀN(1)
O(2)ꢀCu(1)ꢀN(1)
O(2)ꢀCu(1)ꢀN(1)
N(1)ꢀCu(1)ꢀN(1)
180.0
85.65(10)
94.35(10)
94.35(10)
85.65(10)
180.0
3.1.2. Electronic spectra
In methanolic solution the mononuclear complex
shows an absorbence at 519 nm (m=92 l mol−1 cm−1
)
and 626 nm (m=75 l mol−1 cm−1). These data are in
accordance with the assumption for the formation of
CuꢀN and CuꢀO bonds. As a rule the first ones are
a Symmetry transformation used to generate equivalent atoms:
1−x, −y+1, −z.
Fig. 2. The 3D structure of CuEff2·2CH3OH, view along the b-axis. Copper, nitrogen, carbon and oxygen atoms are depicted as black, hatched,
filled and open circles, respectively, hydrogen atoms are omitted for clarity. The hydrogen bonds are shown as dotted lines.

1846
P.R. Bontche6 et al. / Polyhedron 19 (2000) 1843–1848
connected with absorbencies at wavelengths below 600
nm and the second type in the range 600–750 nm, but
quite often these regions are not so strictly localized and
separated. The position and the intensity of the bands
observed are characteristic for Cu(II) complexes with a
tetragonal geometry [18,19].
3.1.3. Magnetic measurements
The temperature dependence of the magnetic suscep-
tibility is typical for a normal mononuclear paramag-
netic complex (Fig. 3(a)), without any measurable
exchange interaction between the Cu(II) centers. The
Curie–Weiss law is not obeyed in the temperature
range studied and in such conditions the magnetic
moment was calculated using the equation veff
=
2.828(sMT−q)1/2; q= −80. At low temperatures, the
magnetic moment v is temperature dependent and
corresponds to a tetrahedral coordination of copper(II)
(Fig. 4) but at higher temperatures (\253 K), the
v-value differs from the theoretical one. Most probably
the deviation observed is due to a deformation of the
tetrahedral structure to a nearly square-planar one, a
fact supported by the obtained EPR data, is also ob-
served in other similar complexes [10,11] and is directly
confirmed in the present work by X-ray diffraction data.
Fig. 4. Graphs veff vs. T for the monouclear complex (a) theoretical
dependence for a tetrahedral Cu(II) complex; (b) experimental data
(q= −80).
2.23, gÞ= 2.07, A//=204, AÞ=24, AN=14 G) are
typical for Cu(II) complexes with a nearly square-planar
symmetry. The EPR data for the solid state complex at
ambient temperature are analogous to those for frozen
solutions at 77 K as in other similar cases [10,11,13].
3.1.4. EPR spectra
The methanolic solution of the complex at room
temperature shows an isotropic spectrum with a re-
solved hyperfine structure from 63,65Cu and parameters
3.1.5. IR spectra
The Effortil base shows absorption bands at 3450 and
3200 cm−1 corresponding to w(OH) and w(NH), a broad
band in the 2600–2800 cm−1 range, that can be at-
tributed to w(NH+2 ) and a band at 1600 cm−1 assigned
to l(NH). In the complex the band at 3450 cm−1 is
observed with a low intensity, as a result of OH group
deprotonation in the aminoalcohol fragment and the
presence of CH3OH. The coordination of NH follows
from the shift of the bands of the complex to 3180 and
1650 cm−1. The absorbence in the 2600–2800 cm−1
range practically disappears in the complex, which is
also an indication for coordination of NH. In the far IR
spectrum of the complex, new bands at 475 and 370
cm−1 are observed, corresponding to w(CuꢀN) and
w(CuꢀO) respectively [20].
giso=2.103, Aiso=86 at Hiso=3300 G. The spectrum of
the same solution at 77 K exhibits an anisotropic signal
with an additional resolved SHFS from 14N in the
perpendicular region of the magnetic field due to the
formation of CuꢀN bonds. The EPR parameters (g//=
3.1.6. Calorimetric and thermogra6imetric data
The thermogravimetric study of the complex shows a
reduction of the sample weight with about 13.20% in the
temperature range 350–430 K. This fact correlates well
with the expected value of 13.17% that corresponds to
the elimination of two methanol molecules. It is also
supported by the DSC data obtained (Fig. 5) showing
an endothermic effect at about 400 K, with an enthalpy
change of 13.3 cal g−1. The value is higher than the
expected one, probably due to another endothermic
process at the same temperature interval, indications for
which are observed in the DSC curve in Fig. 5.
Fig. 3. Magnetic susceptibility vs. T for (a) mononuclear complex
CuEff2·2CH3OH and (b) binuclear Cu2Eff2Cl2 complex.

P.R. Bontche6 et al. / Polyhedron 19 (2000) 1843–1848
1847
result of disturbance of the exchange interaction. At
high temperatures the complex exhibits a normal para-
magnetic character.
These results are in accordance with the other spec-
tral and EPR data indicating the formation of binu-
clear species in this case, namely the EPR signals at
lower and higher fields (1350 and 5470 G, respectively)
and the absorbence at 385 nm in the electronic spectra
as well.
3.2.3. EPR spectra
In methanolic solution at room temperature, the
complex is EPR silent. The spectrum of the same
solution at 77 K shows a weak signal at 3300 G and
two signals at 1350 and 5470 G. The last two signals
are connected with an antiferomagnetic coupling be-
tween Cu(II) centers in bi- and polynuclear structures
[22]. The spectrum of the solid phase complex shows
the same signals as the frozen solution. Similar EPR
spectra for Cu(II) complexes with a nearly square-pla-
nar geometry were already reported [10,13].
Fig. 5. DSC data for the mononuclear complex CuEff2·2CH3OH.
3.1.7. Dissociation and stability constant
3.2.4. IR spectra
The dissociation (acidity) constant of Effortil using
a free base was determined as pKa=8.8390.09. For
a molar ratio Cu–HEff=1:2, two stability con-
stants were calculated: lgi1[Cu(Eff)]+=5.5290.05;
lgi2[Cu(Eff)2]=10.5590.04.
Two Effortil molecules are coordinated to Cu(II),
consequently forming the complexes [Cu(Eff)]+ and
[Cu(Eff)2].
The absorption bands at 3450 and 3200 cm−1
(w(OH) and w(NH)) of the Effortil base are trans-
formed into one broad band at 3400–3250 cm−1 in
the spectrum of the complex. The band at 1600 cm−1
(l(NH)) shifts to 1620 cm−1 in the complex and the
absorbance in the 2600–2800 cm−1 range (w(NH2+))
practically disappears. The far IR spectrum of the
complex shows three new bands at 538, 420 and 251
cm−1 assigned to w(CuꢀN), w(CuꢀO) and w(CuꢀCl),
respectively [20].
3.2. Binuclear complex — Cu2Eff2Cl2
3.2.1. Electronic spectra
3.2.5. Calorimetric and thermogra6imetric data
The calorimetric and thermogravimetric studies were
provided in the 300–500 K range. The results ob-
tained have shown that no solvent molecules are
present in the structure of the solid binuclear green
complex.
All data obtained for the Cu2Eff2Cl2 complex indi-
cate that they are similar to those for the analogous
binuclear Cu(II) complexes of pindolol and ox-
prenolol, studied by X-ray diffraction [12,13,23]. On
the grounds of all these considerations, structure III
was suggested for the Cu2Eff2Cl2 binuclear complex
III.
The methanolic solution of the green complex shows
absorbance at 700 nm (m=96 l mol−1 cm−1) and 385
nm (m=106 l mol−1 cm−1). The first band is associ-
ated with d–d transitions in Cu(II), engaged in CuꢀO
bonds. The second band at 385 nm is attributed to a
ligand-to-metal charge-transfer when a polynuclear
copper(II) complex with oxygen-bridge ligand is
formed [10,11,13]. It is interesting to notice that in
such binuclear complexes, with both CuꢀN and CuꢀO
bonds there is usually no separate bond at uB600
nm, typical for CuꢀN bond, but only one broad com-
plex band at 600–700 nm [9–13,22].
3.2.2. Magnetic data
The temperature dependence of the magnetic suscep-
tibility (Fig. 3(b)) is typical for cases of antiferromag-
netic exchange interaction between copper(II) centers
(see for example [21]). In complexes of that type, the
intramolecular antiferromagnetism leads first to an in-
crease of the magnetic susceptibility to a maximum (at
the Neel’s temperature) and then it decreases as a

1848
P.R. Bontche6 et al. / Polyhedron 19 (2000) 1843–1848
4. Discussion
Acknowledgements
Effortil forms two types of complex, depending on
the solvent and the metal-to-ligand molar ratio. At
excess of the ligand, the mononuclear soluble violet
complex Cu(Eff)2·2CH3OH was formed in alkaline
methanolic solution, from which the neutral complex
very slowly spontaneously precipitated.
The authors greatly acknowledge the financial sup-
port given by the National Research Fund of Bulgaria.
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the charged complex thus formed remains in solution.
The negative charge of this complex was confirmed by
its sorption on anionite (Amberlite IRA-400, Merck).
That was the reason for isolating the mononuclear
complex in a solid phase only from methanol.
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5. Supplementary data
Crystallographic data have been deposited with the
Cambridge Crystallographic Centre, CCDC No.
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free of charge from The Director, CCDC 12 Union
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.
033; e-mail: deposit@ccdc.cam.ac.uk or www: http://
www.ccdc.cam.ac.uk).