Intramolecular electron transfer in Cu(ii) complexes with aryl-imidazo-1,10-phenanthroline derivatives: experimental and quantum chemical calculation studies

Article abstract of DOI:10.1039/C8NJ05697H

1H-Imidazo[4,5-f][1,10]phenanthrolines containing phenyl (1), 4-(N,N-dimethylamino)phenyl (2), 4-(azadithiacrown-ether)phenyl (3), 3,4-dimethoxyphenyl (4) and 2,2′-bithiophen-5-yl (5) were synthesized and their Cu(ii) complexes were studied to determine the effect of substituents, geometry of complexes and solvent nature on the spectral and redox properties of the copper complexes. It was found that in the case of 4-(N,N-dimethylamino)phenyl- and 4-(azadithiacrown-ether)phenyl substituents, the formation of a L₂·Cu²⁺ complex of pseudo-tetrahedral geometry causes the appearance of an intense metal-to-ligand charge transfer (MLCT) band in the visible region and induces a positive shift in the reduction potential causing the occurrence of autoreduction of Cu(ii). Density functional theory (DFT) and its extension to time dependent density functional theory (TD-DFT) were employed to study the molecular structure and electronic and spectroscopic properties of copper with the 4-(N,N-dimethylamino)phenyl-1H-imidazo[4,5-f][1,10]phenanthroline ligand (2). The calculation results are in agreement with those obtained from optical measurements. Electrochemical studies showed that the autoreduction is observed when Cu²⁺/Cu⁺ transfer and oxidation of the ligand occur under the closed electrochemical condition.

Full text of DOI:10.1039/C8NJ05697H

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Tokarev, N. Shepel, E. V. Lukovskaya, Y. A. Sotnikova, A. A. Moiseeva, A. D'Aleo, F. Fages, F. Maurel and Y.
V. Fedorov, New J. Chem., 2019, DOI: 10.1039/C8NJ05697H.
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ISSN 1144-0546
PAPER
Jason B. Benedict et al.
The role of atropisomers on the photo-reactivity and fatigue of
diarylethene-based metal–organic frameworks
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DOI: 10.1039/C8NJ05697H
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Intramolecular electron transfer in Cu(II) complexes with
aryl-imidazo-1,10-phenanthroline derivatives: experimental
and quantum chemical calculation studies
Olga A. Fedorova,a,b* Nikolai E. Shepel,a Sergey D. Tokarev,a,b Elena V.
Lukovskaya,b Yulia A. Sotnikova,b Anna A. Moiseeva,b Anthony D’Aléo,c Frédéric
Fages,c François Maureld and Yury V. Fedorov a
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
www.rsc.org/
1H-imidazo[4,5-f][1,10]phenanthrolines containing phenyl- (1), 4-(N,N-dimethylamino)phenyl- (2), 4-(azadithiacrown-
ether)phenyl- (3) 3,4-dimethoxyphenyl- (4) and 2,2’-bithiophen-5-yl- (5) were synthesized and their Cu(II) complexes were
studied to determine the effect of substituent, geometry of complex and solvent nature on the spectral and redox
properties of the copper complexes. It was found that in case of 4-(N,N-dimethylamino)phenyl- and 4-(azadithiacrown-
ether)phenyl substituents the formation of L2Cu2+ complex of pseudo-tetrahedral geometry causes the appearance of an
intense metal-to-ligand charge transfer (MLCT) band at the visible region and induces a positive shift in the reduction
potential providing the occurrence of autoreduction of Cu(II). Density functional theory (DFT) and its extension to time
dependent density functional theory (TD-DFT) were performed to study the molecular structure, electronic and
spectroscopic properties of copper with the 4-(N,N-dimethylamino)phenyl-1H-imidazo[4,5-f][1,10]phenanthroline ligand
(2). The calculation results are in agreement with those obtained from optical measurements. Electrochemical study
showed that the autoreduction is observed when Cu2+/Cu+ transfer and oxidation of ligand occur at the closed
electrochemical condition.
and IPh ligands.12,13 Benisvy’s group was obtained a square-
like neutral tetra-Cu(II) complex using a similar dianionic IPh
Introduction
ligand
through
N,O-phenolate-imidazolate/N,N-
1H-imidazo[4,5-f][1,10]phenanthroline (abbreviated as
IPh) as N-donor ligand possesses several interesting
structural characteristics appropriate for coordination with
phenanthroline coordinating sites.14 In addition, IPh-Cu(II)
complexes have been prepared to analyze the binding with
DNA and their ability to cause DNA cleavage.15
different types of metal ions (Zn2+, Mn2+ 1, Cd2+ 2, Co2+ 3, Pt2+ 4
,
Our research aimed the studying of autoreduction of
Cu(II) in complex with IPh derivatives which has not been
observed early. Copper(I) complexes with 2,9-
dialkylphenanthroline or 6,6’- dialkyl-2,2’-bipyridine have
been prepared via chemical16 or photochemical reduction17,18
of the corresponding copper(II) compounds. Autoreduction
of bis-chelated copper(II) complexes of 6,6’-dialkyl- 2,2’-
bipyridines19 and 8-dimethylarsinoquinoline20 has also been
reported. In those papers, the reduction of copper(II) is not
attributed to the donor atoms of ligands (that is, the
electronic properties) but to the geometry of a complex,
which is exclusively defined by the sterically hindered group
of a ligand. Thus, upon the control of the geometry of a
complex, which prefers Cu(I) to Cu(II), the reduction of
copper(II) complexes to copper(I) complexes occurs.
lanthanides (III) (Ln = Eu, Dy, Er, Tb, Sm, Yb)5, Ru2+ 6)). Also
1H-imidazo[4,5-f][1,10]phenanthrolines (IPh) are versatile
chelating ligands employed in the design of DNA
metallointercallators and photocleaving agents. 7–9
The copper complexes constitute an important class of
compounds from several point of view viz. bioinorganic,
catalysis and magnetism.10,11 Some groups synthesized a
series of ionic and neutral Cu(I) complexes with diphosphine
a. A. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of
Sciences, 28 Vavilova str., 119991, Moscow, Russia.
b. Department of Chemistry, M. V. Lomonosov Moscow State University, Leninskie
Gory, 119992 Moscow, Russia.
c. Aix Marseille Univ, CNRS, CINaM UMR 7325, Campus de Luminy, Case 913,
Marseille, 13288 France.
d. Université Paris Diderot, Sorbonne Paris Cité, ITODYS, UMR CNRS 7086, 15 rue
Jean-Antoine de Baïf, 75205 Paris Cedex 13, France.
The formation of copper(I) complexes upon interaction of
copper(II) salts with organic sulfides, containing, as a rule,
† Footnotes relating to the title and/or authors should appear here.
Electronic Supplementary Information (ESI) available: [details of any additional nitrogen donor atoms and representing
supplementary information available should be included here]. See
tetradentate ligands has been also described. In most cases,
DOI: 10.1039/x0xx00000x
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the oxidation product was not isolated but it might be arising Cu(I) ions and because in this solventVitehweArtsictleuOdnileinde
assumed that during the reaction the one- electron oxidation ligands as well as Cu(ClO4)2 have got sufficient solubility.
DOI: 10.1039/C8NJ05697H
of the thioether group by the Cu(II) ion occurs with the Keeping of Cu(II) complexes in DMSO or ethanol showed that
formation of the sulfur-centered radical-cation, which is autoreduction process did not occur.
further oxidized by the air oxygen or hydrolyzed to
sulfoxide.21, 22 The phenomenon is qualitatively attributed to Complex formation study
the ability of the thioether donors to accept electron density
into vacant 3d orbitals and stabilize the Cu(I) state.23,24 - 5 in MeCN with concentration 2·10-5 mol·L-1 at room
Bis(benzimidazolyl)bis(thioether)copper chelates temperature are shown in Fig.1. All the ligands display
UV–Vis electronic absorption spectra of IPh derivatives 1
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demonstrated reduction of the Cu(II) upon the irradiation several strong absorption peaks with wavelengths shorter
with light.25 The reaction proceeds via excitation of chelate than 400 nm. The position of an intense long wavelength
complex, or eventually directly through LMCT reaction. absorption band depends on the electronic nature of
Combination of azaheterocyclic residue and organic substituent R (Fig. 1). The presence of donor dimethoxy- (4)
thioether or thiolate is similar to active centers of the most or especially dimethylamino-groups (2, 3) at position 4 of the
26, 27
of mononuclear
and binuclear28 copper containing aryl moiety results in the substantial red shift of long
enzymes in which the metal atom is coordinated just by the wavelength absorption band relative to that of ligand 1. In
donor sulfur atoms and nitrogen atoms (usually imidazole). case of ligand 5 functionalized with donor bithiophene
Such
copper
containing
enzymes
(hemocyanins, substituent the largest shift of the long wavelength
thyrosinases, etc.) are capable to react with oxygen29 and in
the course of the reaction the exchange of electrons
between the copper ion and the ligand occurs.
absorption band is observed because of more extended -
conjugation.
0.8
This manuscript concerns the reduction of Cu(II) to Cu(I)
in complexes with IPh ligands containing phenyl- (1), 4-
dimethylaminophenyl- (2), 4-(azadithiacrown-ether)phenyl-
(3) 3,4-dimethoxyphenyl- (4) and 2,2’-bithiophen-5-yl- (5)
(Figure 1). The change of the substituents in the phenyl ring
of IPh was realized to analyze the effect of substituent in
ligand on the reduction. Thus, dimethylamino- (2) and
dimethoxy- (4) substituents possess good donor
1
3
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
2
4
5
characteristics. Ligand
3 is ditopic receptor able to
coordinate Cu(II) cations through both the phenantroline and
azadithticrown ether centers. The thiophene residue in 5 is
suitable for stabilization of radicals arising upon the
reduction process. The occurrence of reduction reaction was
examined by optical, ESI-MS, electrochemical and quantum-
chemical methods. Furthermore, we elucidated the factors
governing this reduction reaction.
200
250
300
350
400
450
500
Wavelength / nm
H
N
H
N
Figure 1. Electronic absorption spectra of IPh derivatives
1(1), 2(2), 3(3), 4(4), 5(5) in MeCN, CLig = 2·10-5 mol·L-1, T =
20°C.
H
N
S
S
N
N
N
N
N
N
O
O
N
N
N
N
N
3
2
1
OMe
OMe
H
H
N
The addition of Cu(II) perchlorate to a solution of 1 in
MeCN resulted in a substantial changes in absorption
spectrum, which are evidently due to formation of
complexes of 1 with Cu2+ (Fig. 2). The strong distortion of an
isosbestic points upon spectrophotometric titration of 1 with
Cu2+ was observed, indicating more than one kind of complex
formation.
N
N
N
N
N
N
S
N
S
5
4
Scheme 1. Structures of ligands 1-5 applied for preparing of
complexes with Cu(II).
To estimate the stoichiometry of prevailing ligand-metal
complex the mole-ratio method and the method of
continuous variations have been used (Figs. S15, S16 in SI).
The analysis of spectrophotometric data (the mole-ratio
method) showed the formation of complex 13Cu2+ as a
major component at law metal to ligand ratio. The method
Results and discussion
Ligands 1-5 complexes with Cu(ClO4)2 have been
prepared and analyzed by optical, ESI-MS, elemental
analysis, IR and electrochemical methods in MeCN. This
solvent was chosen as more appropriate for stabilization of
2 | J. Name., 2012, 00, 1-3
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of continuous variations indicates the formation of This fact is in good agreement with that theViCewu(AIrIt)ic-le COunli(nIe)
complexes 13Cu2+ or 12Cu2+.
DOI: 10.1039/C8NJ05697H
autoreduction occurs in complexes with 2 and 3 ligands.
The ESI-MS analysis of Cu2+ complexes with 5 did not
show the molecular peak due to intensive polymerization of
ligand in curse of analysis. To avoid the polymerization of
thiophene-containing ligands the mass-spectral analysis is
usually carried out by using of soft ionization methods
(MALDI, FAB)39,40. Unfortunately, these methods are not
The ESI-MS spectra were recorded for free ligands 1-5
and their copper complexes in the presence of 3-fold excess
of ligand and 3-fold excess of Cu(ClO4)2 salt. The obtained
spectra of complexes contain a set of peaks in which we
found and analysed the peaks belonging copper complexes.
To confirm the assignment of obtained peaks, the
comparison of experimental and theoretical mass-spectra
has been done (the examples of the comparison of
theoretical and experimental mass-spectra are presented in
Figs 3a and S1, S2 in SI).
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suitable for analysis of positively charged complexes.
a)
+
[2( ) - (H ) + (Cu2+)]+
1
[3( + (Cu2+)]2+
1)
1.0
0.9
0.8
0.7
0.6
0.5
+
+
1
[ + (H )]
0.4
1
0.3
0.2
0.1
0.0
b)
[2(1)+(Cu2+)]2+
328
329
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350
400
450
500
96
88
80
72
64
56
48
40
32
24
16
8
Wavelength / nm
Figure 2. Electronic absorption spectra of 1 alone (1) and in
the presence of increasing concentration of Cu2+. Initial
concentration of 1 was C1=1.8×10-5 mol·L-1, concentration of
copper(II) perchlorate was varied from 0 to 0.00023 mol·L-1.
Solvent – acetonitrile, Т = 294K.
[2(
1)+(Cu2+)+ (ClO4-)]+
754
[2(1)+(Cu2+)+ (OH-)]+
400
[3(1)+(Cu2+)]2+
690
402
476
555
According to ESI-MS analysis the formation of two types
of complexes, namely, 13Cu2+(m/z: [476.5]2+) and 12Cu2+(
m/z: [328]2+) has been observed depending on Cu2+ amount
in solution (Scheme 2 and Figs. 3a, b and S2, S3 in SI). In the
presence of 3-fold excess of ligand 1, ESI-MS spectrum
contains the peaks belonging to free ligand, complexes
13Cu2 and 12Cu2+ (Fig. 3a). At 3-fold excess of Cu2+ cations,
the content of 13Cu2+ decreases, the spectrum contains
peaks of 12Cu2+ with one perchlorate or one hydroxyl anion
group (Fig. 3b). According to ESI-MS data the consequence
formation of complexes L3Cu2+ and L2Cu2+ upon increase of
Cu2+ amount is typical for all studied ligands 1-4 (see Figs. S4-
S14 in SI).
777
800
613
600
288
250
300
350
400
450
500
550
650
700
750
m/z
Figure 3. ESI-MS of a) mixture of ligand 1 with Cu2+, ratio 3:1;
b) ligand 1 in the presence of 3-fold excess of Cu(ClO4)2.
A series of copper(II) complexes with 1-5 in solid state
were formed and precipitated out from acetonitrile solution
when dry diethyl ether was added. At 3-fold excess of ligand
L2Cu2+ complexes were isolated and characterized by
different physico-chemical methods (see Experimental part).
According observation by elemental analysis, complexes with
composition L3Cu2+ can be isolated only in mixture with
L2Cu2+.
In accordance with the known literature data cited in the
introduction of the paper, phenanthroline is the preferable
place for Cu2+ ion coordination with imidazophenanthrolines.
Nevertheless due to the complexity of the system we could
Another important observation is that ESI-MS spectra of
copper complexes of ligand 1 and 4 contain the complexes of
Cu2+ ions only, whereas, in ESI-MS spectra of complexes of
ligands 2 and 3 one can see remarkable amount of Cu+
complexes also especially at 3-fold excess of Cu(ClO4)2 salt.
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not determine the stability constants for the complexes of 1 than the imidazole site whatever the charge of the complex.
View Article Online
2+
with Cu2+ by direct spectrophotometric titration method.
Density functional theory (DFT) and its extension to time
dependent density functional theory (TD-DFT) were
performed to study the molecular structure, electronic and
spectroscopic properties of copper with the4-
dimethylaminophenyl ligand 2. The ligand 2 possesses two
site of complexation though the phenantroline (Phen) or
imidazole (Im) units and can coordinate the copper as a
bidentate or mono-dentate manner via the pyridine nitrogen
or imidazole nitrogen atoms. To determine the most
favorable site of coordination for 2 with copper we
optimized the geometries and calculated the binding
energies for Cu2+ and Cu+ complexes involving several
numbers of ligands. Indeed since the ligand can coordinate
as bidentate or mono-dentate and to ensure a tetrahedral or
square-planar environment about copper we studied
complexes involving two, three and four ligands. The Figs 4
and S28, S29 in SI show the calculated geometries of
complexes 22Cu2 (Phen2), 23Cu2+(PhenIm2), 24Cu2+(Im4),
22Cu+(Phen2), Cu+(PhenIm2) and 24Cu2+(Im4). In title of
complexes type (Phen – phenantroline and Im – imidazole)
and quantity of binding sites are presented in parentheses.
The binding energy decreases in the oDrdOeI:r102.120C39u/C8(PNhJ0e5n629)7H>
23Cu2+(PhenIm2) > 24Cu2+(Im4) demonstrating that the
complexation through the imidazole leads to a less strong
bond than with phenantroline moiety. Similar trend is found
with Cu+ complexes.
Table S1 in SI lists some main geometrical characteristic
of the calculated complexes. The dihedral angle between the
planes defined by the copper centre and each set of nitrogen
atoms is found to be 80.8° and 81.2° in the 22Cu2+(Phen2)
22Cu+(Phen2) complexes. These angles are slightly smaller
than the 90° value expected for regular tetrahedral
geometry.
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Table 1. Binding energies (in kcal/mol) in the copper (Cu2+ or
Cu+) complexes with ligand 2 through imidazole (Im) or
phenantroline (Phen) units.
E
-207.4
-77.0
-185.9
-173.8
-129.1
-82.2
23Cu2+(Phen3)
23Cu+(2-Phen3)
22Cu2+(Phen2)
23Cu2+(PhenIm2)
24Cu2+(Im4)
22Cu+(Phen2)
23Cu+(PhenIm2)
24Cu+(Im4)
-65.7
-47.5
This change from tetrahedral to planar square when the
number of imidazole interacting with copper increases
seems to be correlated with the increase of the Cu…N
distances. In the mixed complex involving both
phenantroline and imidazole, the geometry of the nitrogen
atoms around the copper is found strongly distorted and in
between tetrahedral and square-planar.
Therefore it is clear from calculations that the
phenanthroline moieties impose a tetrahedral mode of
complexation while the coordination through imidazole unit
leads to a more square planar arrangement.
Figure 4. The optimized structure of (a) 22Cu2+(Phen2)
(coordination of metal ion with two phenantroline moieties);
(b) 23Cu2+(PhenIm2) (coordination of metal ion with one
phenantroline and two imidazole moieties); (c) 24Cu2+(Im4)
(coordination of metal ion with four imidazole moieties);
and (d) 23Cu2+(Phen3) (coordination of metal ion with three
phenantroline moieties).
Autoreduction of Cu(II) to Cu(I) in complexes with IPh
ligands
It should be pointed out that the solution of Cu2+
complexes with ligand 1 remains stable over time at any
excess of copper cations, so that the changes in absorption
spectrum were not observed even after a few days. Another
behavior was observed for ligands 2, 3. The addition of Cu(II)
perchlorate to a solution of 2 in MeCN in molar ratio 1:3
resulted in a small red shift of long wavelength absorption
band due to complex formation (Fig. 5).
However at molar ratio 10:1 the new intensive
absorption band at 766 nm appears immediately after Cu2+
addition. The spectrum recorded at molar ratio 10:1
demonstrates significant changes in time, consisting in the
fact that the intensity of the 766 nm band decreases and
From energetic point of view we calculated the binding
energy defined as follows:
∑
― 풊푬풍풊품풂풏풅풔
∆푬 = 푬풄풐풎풑풍풆풙 ― 푬푪풐풑풑풆풓
(i=2,
3
or
4
depending the complex).
The energies binding gathered in Table 1 clearly show
that complexation of the phenantroline site is most favorable
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of copper(II) cations to complex 23Cu2+ should lead to the
simultaneously a new band at 463 nm is appeared (Fig. S17
in SI). The observed band at 766 nm could be assigned as
LMCT band. The LMCT excited state arises as a result of
promotion of an electron from ligand-localized fully occupied
orbitals to a not completely filled 3d-orbital of a copper ion.
The LMCT excited states of Cu(II) complexes have been
thoroughly reviewed in the literature.30 Therefore, ligand 2
→ Cu(II) LMCT is expected to result in reduction of Cu(II) with
the formation of copper(I) complex. In our case, the
autoreduction of Cu(II) to Cu(I) complexes occurs
spontaneously in the dark and without additional reducing
agents in about 80 min. As a result, after 80 minutes the
intensity of the band at 766 nm disappears, and the intensity
of the 463 nm band reaches its maximum value (Fig. S18 in
SI). The absorption band at 463 nm could be assigned to
MLCT transition in Cu(I) complex.19 The absorption bands
centered at 292 and 336 nm which could be assigned to
intraligand π→ π* transitions31 also changed their positions
and intensity.
View Article Online
DOI: 10.1039/C8NJ05697H
formation of 22Cu2+ complex similar to what was observed
for ligand 1. The results of ESI-MS observation supported
interpretation and are presented in Figs. S6 in SI. The
formation of 22Cu2+ complex is believed to force a
tetrahedral geometry about the copper atom and induces a
positive shift in the reduction potential providing the
occurrence of autoreduction of Cu(II).19 The effect that Cu2+
to Cu+ transformation occurs more effectively in the
presence of excess of Cu(ClO4)2 salt was firstly observed and
described in detail for dioximate complexes of Cu2+.31 Finally,
the stabilization of Cu(I) in MeCN solution was described
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earlier in literature.31,33
R
N
NH
N
Cu(ClO4)2
N
N
N
N
N
N
N
N
Cu2+
N
R
R
N
H
N
H
0.9
N
,
,
NMe2
R =
HN
0.8
2
S
S
O
O
N
,
S
S
1
R
0.7
CuClO4)2
0.6
N
N
N
Cu2+
3
N
N
0.5
R
R
N
H
N
H
N
0.4
0.3
0.2
0.1
0.0
S
N
O
N
2+
Cu(II)-Cu(I)
autoreduction
Cu2+
,
NMe2
N
:
Cu
S
R =
N
H
O
N
S
S
O
N
O
N
N
N
N
N
Cu+
R
Rox
N
H
N
H
N
300
400
500
600
700
800
900
1000
Scheme 2. Complex formation of ligands 1-5 with Cu2+
cations and Cu(II)-Cu(I) autoreduction.
Wavelength / nm
Figure 5. Electronic absorption spectra of 2×10-5 mol·L-1 of 2
alone (1) and in the presence of 6.67×10-6 mol·L-1 (2) and
1×10-4 mol·L-1 (3) Cu(ClO4)2. Spectra (2) and (3) were
recorded in 10 sec after Cu(ClO4)2 addition. Solvent –
acetonitrile, Т = 294K.
Ligand 3 contains macrocyclic azadithiacrown ether
moiety. Cu2+ can form complexes with
3 through
coordination via both macrocyclic and heterocyclic parts of
the molecule (Scheme 2).34 The formation of complex 33Cu2+
causes the shift of absorption bands presented in Fig. 6. The
presence of excess of Cu2+ cations leads to the appearance of
additional intensive band centered at 836 nm which could be
assigned as LMCT band in Cu(II)-ligand 3 complex in view of
its high molar extinction coefficient ( = 12000 L mol-1 cm-1)
(Fig. 6). The conformation of the macrocyclic-Cu(II) complex
may affect the position of the LMCT band at 836nm in Cu(II)-
ligand 3 complex which is bathochromically shifted relative
to these for ligand 2 (766 nm). Also some complexes of Cu(II)
with azadithiacrown ether demonstrated the long
wavelength band in region near 800 nm.35,36
The observed autoreduction of Cu(II) to Cu(I) is provided
by at least three reasons. These are the presence of donor
substituent in the phenyl ring of ligand 2, the geometry
around the copper ion and the solvent effect. While the
strong donor N,N-dimethylaniline in ligand 2 provides the
occurrence of LMCT, ligand 1, lacking N,N-dimethylamino
group, did not show the LMCT transition and autoreduction
of Cu(II). At large excess of ligand 2 the complex 23Cu2+ was
formed. For trisbidentate chelates of Cu(II), like the complex
23Cu2+, the stable tetragonally distorted octahedral
configuration about Cu(II) could be expected.32 The addition
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2
3
4
The changes in UV-Vis spectra of ligand 3 in the presence S22). The low-intensive absorption in the range of 420-480
of 10-fold excess of Cu(ClO4)2 during 40 minutes at ambient nm in copper(II) complexes of ligand 4 could be assigned as
View Article Online
DOI: 10.1039/C8NJ05697H
temperature are shown in Fig.S18 in SI. Copper(II) seems to LMCT based on the earlier obtained results on copper(II)
be reduced partly by a concomitant oxidation of coordinated complexes with bipyridine ligand.37 The absorption in this
ligands. According ESI-MS spectra (Fig. S10 in SI) the region slightly increases for 40 minutes, which was not
formation of mixed-valence Cu(I)/Cu(II) complex of 3 was observed in the case of ligand 1 (Fig. S17 in SI).
5
6
7
8
observed. Earlier it was found that in binuclear dicopper(II)
The calculated absorption spectrum of 2 (Figure 7 and
9
ligand based on benzoimidazole the autoreduction occurs Figure S30 for a more detailed description) is found in good
and the mixed-valence Cu(I)/Cu(II) complex is more stable in agreement with the experimental and indicate a large
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comparison with Cu(II)/Cu(II) one.21
absorption around 350 nm arising from two single excitation
at 369 nm (f=0.359) and 331 (f=0.915). These absorptions
can explain the strong absorption peak around 350 nm. It
could be noted that a weak electronic transition is calculated
at 404 nm and is assigned to a charge transfer excitation
from the amino-phenyl to the phenantroline part of the
ligand.
TD-DFT calculations in acetonitrile were performed with
the B3LYP, M062X and MPW1PW91 functionals on the most
stable complexes 22Cu2+ and 22Cu+. The spin-allowed
predicted transitions (singlet–singlet for ligand 2 and 22Cu+
complex and doublet–doublet for 22Cu2+ complexes) are
listed in Table 2 and Table S2 in SI as well as with their
assignment. Comparison of TDDFT results with experimental
data reveals that B3LYP functional produce optical spectrum
which is more close to experiment and only these results will
discuss in the following.
0.8
2
0.7
1
0.6
0.5
0.4
0.3
0.2
0.1
0.0
3
300
400
500
600
700
800
900
1000
Wavelength / nm
Figure 6. Electronic absorption spectra of 2×10-5 mol·L-1 of 3
alone (1) and in the presence of 6.67×10-6 mol·L-1 (2) and
1×10-4 mol·L-1 (3) Cu(ClO4)2. Spectra (2) and (3) were
recorded in 10 sec after Cu(ClO4)2 addition. Solvent –
2
acetonitrile, Т = 294K.
Cu2+(2)2
Cu+(2)2
From ESI-MS spectra (Figs. S7 and S11 in SI) recorded
after keeping of complexes 22Cu2+ and 32Cu2+ for 48 hours
we proposed the structure of oxidized ligands (Scheme 3).
The obtained peak with m/z 442 belongs to
phenylimidazophenetroline ligand with hydroxymethylamino
substituent at 4-th position in phenyl ring. Thus, NMe2 group
is involved in oxidation process. In ligand 3 the oxidation
occurs with participation of sulphur atom of macrocyclic
residue as showed in Scheme 3 below.
200
300
400
500
600
700
800
900 1000 1100 1200
O
H
H
Wavelength / nm
S
O
N+
N+
N
N
N
N
NHCH2OH
N
H+
-
H+
-
Figure 7. B3LYP calculated absorption spectra of ligand 2
(blue) and the complexes Cu2+(2)2 (black) and Cu+(2)2 (red).
O
N
H
N
H
S
ClO4
ClO4
m/z 442
m/z 662
Scheme 3. The proposed structure of oxadized ligands 2 and
3.
For the 22Cu2+ complex the calculations predicted a
strong allowed transition at 751 nm, at the B3LYP level of
calculation. The orbitals implied in the transition are
displayed in Figure S33 in SI and show that H-8()
corresponds to  orbital delocalized on the ligand 2 while the
LUMO is  orbital mainly on the phenantroline moiety
on the same ligand. Therefore this transition can be
characterized as ligand charge transfer transition (LCT). The
The ligands 4 and 5 display strong absorption bands at
short wavelength (200-400nm) that can be assigned as
intraligand   transitions. Addition of Cu(ClO4)2 to ligands
4 and 5, even in a large excess, has a much smaller effect on
the absorption spectra as compared with ligands 2 and 3, so
that the appearance of an intensive long-wave absorption
band in the 650-950 nm region was not observed (Figs.S19-
6 | J. Name., 2012, 00, 1-3
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After reduction of the copper in the 22Cu+ complex, the
analysis of the electron population in the complex shows a
significant charge transfer from ligand to copper in the
ground state of complex. Indeed the calculated Mulliken
charge on copper is found to be +0.28. Therefore, the remain
charge (+1.72) of the complex is distributed on the ligand
suggesting that their optical properties could be different
from the neutral state. To test this hypothesis, we calculated
the optical properties of cationic state of the ligand 2 and
compared the obtained results with that of neutral state (see
supporting information Figs. S30, S31 in SI). The result clearly
View Article Online
calculated spectra show three allowedDeOleI:c1t0r.o10n3i9c/Ctr8aNnJs0i5t6io97nHs
at 475, 436 and 406 nm. The first lowest transition originate
from H-1L+1, HOMOLUMO single excitations. HOMO
and H-1 are similar and localized on the amino-phenyl part of
the ligand while both LUMO and LUMO+1 are mainly
distributed on the part of the ligand in close interaction with
the copper. This electronic transition is then a * charge
transfer on the ligand. The second transition is built on single
excitations involving H-2 or H-3 localized on copper to LUMO
or LUMO+1 localized on phenantroline part of the ligand.
This transition can thus be characterized as a metal to ligand
charge transfer (MLCT) transition. The electronic transition
calculated at 406 nm is a charge transfer electronic transition
localized on the ligand as previously showed.
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shows
a large bathochromic shift of the maximum
absorption upon oxidation of the ligand. This simple
calculation suggests that the absorption at 751 nm of the
22Cu+ is the result of the ligand charge transfer in the
complex. The appearance of strong absorption around 750
nm is strongly related to the nature of the ligand. We
calculated the optical properties of the copper complex with
the ligand 1 and the obtained absorption spectrum showed
no significant absorption in infrared region in agreement
with experiment observation (see supporting information
Figure S32).
Voltammetry studies
To determine the redox potentials of complexes, cyclic
voltammograms of all the ligands and their Cu(II) complexes
were recorded in MeCN solvent using tetra-butylammonium
perchlorate (TBAP) as
a supporting electrolyte. Cyclic
voltammograms of Cu(ClO4)2, ligands 1-5 and their
complexes with copper(II) are shown in Figs. S23-S24 in SI.
The obtained values of ЕрRed and EpOx are collected in Table 3.
The cyclic voltammetry curve of Cu(ClO4)2 (Fig. S23 in SI,
Table 4) show two couples at the following peak potentials:
1.04/1.13 and -0.67/-0.44. The first reversible step
corresponded to Cu(II) Cu(I) transformation, the second
pair describes Cu(I)Cu(0) reduction. Also after the second
step of the reduction process the desorption of metallic
copper on electrode was observed.
Table 2. Selected computed UV-vis energies transitions in
acetonitrile for 22Cu2+ and 22Cu+ complexes calculated at
the B3LYP level.
States
Oscillator
strength
(f)
Assignmenta
Characterb
calc
(nm)
22Cu2+
(Phen2)
S8
751
479
0.599
0.221
LCT
H-8()L()
S21
S22
S26
MLCT +
*
H-1()L(),
H()L+2(),
H-2(L+2()
H2()L+2(),
H()L+4(),
H()L+2()
H-1()L(),
H(L+2(),
H-1()L+1()
Table 3. Electrochemical data in MeCN with 0.1 M TBAP as
supporting electrolyte; potentials were measured relative to
Ag|AgCl|KCl aq. sat. reference electrode. The potentials of
the peaks on the reverse scans of the cyclic voltammetry
curves are given after the slash.
479
465
0.134
0.028
MLCT
ЕрRed, V
1.04/1.13; -0.67/-
ЕрOx, V (ЕрOx, mV)
Compound
Cu(ClO4)2
*
-
0.44;-0.19
1
-
1.13; 1.45; 1.65
1.55 (420); 1.69
0.75; 1.01; 1.62;1.81
1:Cu2+ (1:3)
0.47; 0.20; -0.61;
-
22Cu+
2
(Phen2)
H-1L+1,
S2
S7
S8
475
0.252
0.325
0.309
HOMOLUMO
H-3LUMO, H-
2L+1
H-1L+2,
HOMOL+3
*
MLCT
436
*
406
2:Cu2+ (1:3)
0.83/1.00; 0.47; 0.20; -
1.31 (560); 1.56; 1.75
[a] H=HOMO, L=LUMO. [b] MLCT = ligand to metal charge
transfer, LCT = ligand charge transfer
0.69
3
-
0.97; 1.36; 1.52
1.32; 1.55
3:Cu2+ (1:1)
0.51; 0.30; -0.78
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3:Cu2+ (1:3)
0.42; 0.20; -0.76
1.28 (310); 1.60
View Article Online
DOI: 10.1039/C8NJ05697H
4
-
0.54; 0.22; -0.64;
-
1.08; 1.42; 1.66
1.43 (350)
1.42
4:Cu2+ (1:3)
5
5:Cu2+ (1:3)
0.64; -0.39
1.66 (240)

8
9
oxidative desorption of copper(0) on electrode
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In the presence of Cu2+ cations the first oxidation peak of
ligands 1-5 was found to be anode shifted up to ЕрOx = 240-
560 mV suggesting the occurring of complex formation with
all studied ligands (Table 2). Furthermore, in complexes
Cu(II)Cu(I) and Cu(I)Cu(0) reduction exhibits peaks differ
than those for free Cu(II) perchlorate. The complexation is
corroborated by an appearance of the additional peaks
corresponding to the Cu(II)Cu(I) and Cu(I)Cu(0)
reduction processes at the potentials differing from that one
of free Cu(II) perchlorate.
From one point of view, the tendency of the oxidation
and reduction potential changes upon complex formation
with Cu(II) of all studied ligands are similar what can be
explained by the formation of one type of complexes when
copper cation is coordinated with phenantroline part of each
ligands. Also the found changes are similar to what was early
1-4
Cu(II) - Cu(I)
Cu(II) - Cu(I) free
in complex
Cu(I) - Cu(0) in complex
Figure 8. Changes in cyclic voltammogram of 1.6710-4M
solution of ligand 2 in the presence of 3-fold excess of
copper(II) perchlorate (1-4) recorded each one hour during 4
hours in 0.1 M TBAP in MeCN at 200 mV/s.
observed
for
described
in
literature
aryl-1H-
imidazole[4,5f][1,10]phenanthroline Cu(II) complexes.15
Otherwise, the electrochemical behavior of each ligands in
the presence of copper cations has got some peculiarities.
Thus, the oxidation of 2 proceeds via several one electron
steps; with the initial two steps presumably involving the
amino group (Fig. 8, Table 3). The addition of 3-fold excess of
copper(II) perchlorate causes a color change of the solution
that turns to purple and then to colorless. The reduction
cyclic voltammetry curves of the complexes were recorded
at potential between 1.3 V and –1.0 V (i. e. in the reduction
of Cu(II) region) each hour for 4 hours until the cyclic
voltammograms became unchanged (Fig. 8). The obtained
cyclic voltammograms demonstrated the series of EpRed peaks
belonging to reduction of the copper(II). The reduction peak
of Cu(II)Cu(I) from Cu(II) perchlorate taken in the excess
From the obtained data we can propose that the
reduction of Cu(II) in complex with ligand 2 proceeds through
the electron transfer from dimethylamino group of 2.
Indeed, there are no oxidation peaks associated with the
dimethylamino group in the cyclic voltammogram of the
complex (Fig. 9). This fact is in agreement with ESI-MS data
pointed on the occurring of oxidation of NMe2 group after
keeping of 22Cu2+ complexes for some hours.
The
important condition for successful ligand-copper(II) electron
transfer process is overlapping of the oxidation potential of
ligand 2 (E1/2 0.75 V) with the reduction potential of the
Cu2+/Cu+ (E1/2 1.085 V).
The electrochemical behavior of ligand 3 depends on the
amount of copper(II) presented in the acetonitrile solution
along with the two reduction peaks of Cu(II)Cu(I) at 0.47 V (Fig. 9).
and 0.20 V from the complexed Cu(II) are present at positive
potentials. The remarkable increase of Cu(I)Cu(0)
reduction peak at Еpc = -0.69 V was also observed. This
phenomenon could be connected with occurring of
autoreduction process producing increasing amount of Cu(I).
0 . 0
0 . 0
0 . 0
6
4
2
0
2
peak of potential
of NMe2 oxidation
3
2
1
- 0 . 0
- 2 0 0 0
- 1 0 0
0
0
1 0 0
0
2 0 0 0
E
,
m
V
8 | J. Name., 2012, 00, 1-3
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Figure 9. Cyclic voltammogram of 1.6710-4M solution of Figure 10. Cyclic voltammogram of 1.6710-4M solution of
Cu(ClO4)2 (1), ligand 2 (2) and complex of 2 formed in the Cu(ClO4)2 (1), ligand 3 (2) and in the presence of copper(II) (3-
presence of 3-fold excess of copper(II) (3) recorded after 5) (ratio 1:1) recorded each one hour during 4 hours in 0.1 M
View Article Online
DOI: 10.1039/C8NJ05697H
TBAP in MeCN at 100 mV/s.
keeping for 4 hours in 0.1 M TBAP in MeCN at 100 mV/s.
8
9
As with ligand 2, the oxidative potential of ligand 3 (0.97
V) overlaps the reduction potential of Cu(II), although to the
less extend. Thus, when ratio 3:Cu2+ is 1:1, the remarkable
increase of Cu(I)Cu(0) reduction peak at Еpc = -0.75 V was
observed similar to that we have observed for ligand 2 (Table
3, Fig. 10). This phenomenon is explained by occurring of
autoreduction process producing increasing amount of Cu(I).
Because the phenantroline moiety is the preferable site for
binding of copper(II), all cations are bound with this part of
ligand. Thus, the uncomplexed crown ether moiety acts as a
donor group in the Cu(II) reduction process. In the presence
of 3-fold or more excess of copper(II) the Cu(I)Cu(0)
reduction in complex with 3 is not observed. This is because
the copper(II) at this condition is coordinated both with IPh
and with azathiacrown ether part switching the donor
macrocycle from the conjugation with IPh chromophore (Fig.
S24 in SI). The ESI-MS analysis supports the formation of
complexes through the macrocycle part at the excess of
copper(II) (Fig. S10 in SI). The interpretation of
electrochemical data obtained in this study has been done by
taking into account the results of electrochemical
observation of Cu(II) complex with thia-containing ligands52
Experimental
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Materials
Phenantoline-5,6-dion,
benzaldehyde,
4-
(dimethylamino)benzaldehyde, 3,4-dimethoxybenzaldehyde,
2,2'-bithiophene-5-carbaldehyde, ferrocene, Cu(ClO4)2·6H2O,
tetrabutylammonium perchlorate (TBAP) (Fluka) were
commercially available and were used without further
purification.
4-(1,4-Dioxa-7,13-dithia-10-
azacyclopentadecan-10-yl)benzaldehyde was prepared as
described elsewhere.31 Anhydrous acetonitrile (MeCN) and
dimethylformamide
(DMF)
for
electrochemical
measurements were electronic grade purity and were used
as received. Spectroscopic grade MeCN was used for
recording of the absorption spectra.
Instruments
1H NMR and 13C (APT-method) spectra were recorded on
a Bruker Avance 400 (operating frequency 400.13 MHz,
100.61 MHz) and Avance 600 (operating frequency 600.22
MHz, 150.93 MHz) spectrometers using DMSO-d6 as a
solvent and the internal standard. The chemical shifts and
spin-spin coupling constants were determined with accuracy
of 0.01 ppm and 0.1 Hz, respectively.
and Cu(II)Cu(I) autoreduction in complex with some
ligands cited in the Introduction.16-20
The Cu(II)  Cu(I) autoreduction process for the
complexes of ligands 1, 4 has not been observed (Fig. S25,
S26 in SI). This is obviously due to the oxidation potentials of
ligands 1, 4 do not overlap with the reduction potential of
Cu(II)  Cu(I). Our attempts to study the complex formation
of ligand 5 failed due to its poor solubility in acetonitrile and
polymerization on the electrode (Fig. S27 in SI).
0 . 0 3
ESI mass spectra (ESI-MS) were acquired on a Finnigan
LCQ Advantage tandem dynamic mass spectrometer (USA)
equipped with a mass analyzer with an octapole ionic trap, a
MS Surveyor pump, a Surveyor autosampler, a Schmidlin-Lab
nitrogen generator (Germany), and a system of data
collection and processing using the X Calibur program,
version 1.3 (Finnigan). The mass spectra were measured in
the positive ion mode. Samples in MeCN were injected
directly into the source at flow rate 50 µL min-1 through a
Reodyne injector with a loop of 20 µL. The temperature of
the transfer capillary was 150°C, and the electrospray needle
was held at potential 4.0 kV.
3
0 . 0 2
0 . 0 1
0
2
UV-Vis spectra were measured using two channel
spectrophotometer Varian-Cary 300, and Avantes AvaSpec-
2048 spectrophotometer.
1
Electrochemical measurements were carried out at 22°C
3-5
with an IPC-Pro
M potentiostat. Cyclic voltammetry
- 0 . 0 1
- 0 . 0 2
experiments were performed in a 1.0 mL cell equipped with
a glassy carbon (GC) electrode (disk d=2 mm), Ag/AgCl/KCl
(aq. saturated; reference electrode), and platinum electrode
(counter electrode). The complexes were dissolved in
degassed dry CH3CN or DMF containing TBAP as the
supporting electrolyte (0.10 M). Dry argon gas was bubbled
- 2 0 0 0
- 1 0 0 0
0
1 0 0 0
2 0 0 0
E ,
m
V
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through the solutions for 30 min before cyclic voltammetry found 357.18 [3+H]+. Calculated for С29H31N5O2S2 (%): С,
View Article Online
experiments. The scan rate was 200 mVs-1. A 1 mM solution 63.83; Н, 5.73; N, 12.83, found (%): С, 63.51; Н, 5.78; N,
DOI: 10.1039/C8NJ05697H
of ferrocene along with 0.1 M TBAP in the respective 12.72.
solvents were employed during calibration. The number of 2-(3,4-Dimethoxyphenyl)-1H-imidazo[4,5-
electrons transferred was determined by comparing with the f][1,10]phenanthroline (4). By using of a similar technique a
height of Fc2+/Fc3+ wave for the same concentration and by mixture of 3,4-dimethoxybenzaldehyde (0.476 mmol, 80
rotating disk electrode method (RDE) as well. The same cell mg), 1,10-phenanthroline-5,6-dione (0.476 mmol, 100 mg)
and electrodes were used for measurements carried out by and ammonium acetate (9.5 mmol, 730 mg) was refluxed in
RDE method. The rate of rotating was 2800 min-1. The 7 ml of glacial acetic acid for 7 hours. The precipitate formed
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50
51
52
53
54
55
56
57
58
59
60
solutions of Cu(ClO4)26H2O with concentration 510-4 M, and
ligands with Cligand = 1.6710-4 M were used.
was filtered on a glass porous filter, washed with water and
diethyl ether and dried on a rotary evaporator at 75°С. The
pure product was obtained as a beige powder (93 mg, 0.261
1
mmol). Yield 55%. Н NMR (DMSO-d6, δ; ppm, J/Hz): 3.83 (s,
Synthesis of ligands
3Н), 3.91 (s, 3Н) [OCH3], 7.16 (d, 1Н, 3J=8.8, Ph), 7.80 (m, 2Н,
Synthesis
of
2-phenyl-1H-imidazo[4,5-
3
IPh), 7.85 (d, 1Н, J=8.8, Ph), 7.86 (s, 1H, Ph), 8.91 (m, 2Н,
f][1,10]phenantrolines 1-5 were carried out as described in
38. The synthetic procedure includes the reaction of
phenatroline-5,6-dione with corresponding aldehyde at
reflux in the presence of ammonium acetate in a solution of
glacial acetic acid for 4-8 hours (Scheme 4). The
physicochemical characteristics of the compounds 1, 2, 5 are
described in39-41. The structures of novel compounds 3, 4
IPh), 8.99 (m, 2Н, IPh). 13C NMR (DMSO-d6, δ; ppm, J/Hz):
55.62, 55.68, 109.73 (C), 111.87(C), 119.22(C), 121.59 (СН),
122.91 (2СH), 123.15 (2C), 123.18 (C), 129.63 (2C), 143.40
(2CH), 147.53(2C), 148.95(CH), 150.08 (CH), 151.02 (CH),
172.82 (CH). ESI-MS 4 in MeCN, m/z: calcd. 546.13; found
546.14 [4+H]+.Calculated for С21H16N4O2 (%):С, 70.77; Н, 4.53;
N, 15.72, found (%): С, 70.66; Н, 4.61; N, 17.58.
were confirmed by Н, 13С NMR spectroscopy, elemental
1
analysis and mass-spectrometry methods (Figs. S8, S12 in SI).
Synthesis of complexes
The solutions of complexes of ligands 1-5 with Cu(II) were
NH4OAc,
CH3COOH ice-cold
O
+
N
N
N
N
N
prepared by the addition of required amount of 110-1
M
R
R
boil, 4-8h.
N
H
O
O
Cu(ClO4)26H2O to 1.6710-5 M (for UV-Vis spectroscopy) or
1.6710-4 M (for electrochemical measurements) solutions of
ligand in MeCN in order to obtain a ligand-copper ratio from
3:1 to 1:10. The analysis of complexes was made by UV-Vis
spectrophotometry and ESI-MS spectrometry. The UV-Vis
spectra were recorded for 100 minutes at intervals of 10
seconds.
OMe
OMe
S
N
O
R =
NMe2 ( ),
2
1
( ),
4
( , 55%),
3
(
, 64%),
O
S
5
( )
S
S
Scheme 4. Synthetic scheme of compounds 1-5 preparing.
2-[4-(1,4-Dioxa-7,13-dithia-10-azacyclopentadecan-10-
yl)phenyl]-1H-imidazo[4,5-f][1,10]phenanthroline (3). 4-
(1,4-dioxa-7,13-dithia-10-azacyclopentadecan-10-
The copper(II) complexes in solid state were synthesized
following a common procedure as described below, using
copper(II) perchlorate hexahydrate and the respective
organic ligands.
yl)benzaldehyde
(0.338
mmol,
120
mg),
1,10-
phenanthroline-5,6-dione (0.338 mmol, 71 mg) and
ammonium acetate (6.6 mmol, 520 mg) were dissolved in 5
ml of glacial acetic acid. The mixture was stirred for 7 hours
at reflux. An aqueous solution of NH4OH (13%) was added to
pH ~ 8. The precipitate formed was filtered on a glass porous
filter, washed with water and diethyl ether. After washing
the sediment was boiled in 10 ml of ethyl alcohol for 10
minutes, filtered and dried on a rotary evaporator at 75° C.
The pure product was obtained as a beige precipitate (118
Cu(1)2(H2O)](ClO4)2. To a suspension of 1 (26.5 mg, 0.09
mmol) in 25 mL acetonitrile, Cu(ClO4)26H2O (11.1 mg, 0.03
mmol) was added and the mixture was allowed to stir for 24
h
under ambient condition. Acetonitrile was partially
evaporated under reduced pressure and 40 ml of dry diethyl
ether was added to precipitate a light-green solid. The solid
was isolated by filtration. Yield: 17.9 mg (52%). Anal. Calcd
for C38H26Cl2CuN8O9: C, 52.27; H, 3.00; N, 12.83; Cu, 7.28.
Found: C, 52.89; H, 3.09; N, 13.07; Cu, 7.2. IR (cm-1): N
,
1
mg, 0.216 mmol). Yield 64%. Н NMR (DMSO-d6, δ; ppm,
3203 and 3075; CN, 1562; Hetaryl, 1458; ClO4, 1103 and
1078. ESI-MS (positive ion mode, MeCN): m/z = 643.05 (89%,
[2(1) - (H+) + (Cu2+)]+). UV-vis in MeCN: λ, nm (ε, M -1cm -1):
395, 308, 281 (120,000).
J/Hz): 2.74 (t, 4Н, 3J=5.5), 2.84 (t, 4Н, 3J=7.2) [CH2S], 3.56 (m,
3
4H, CH2N), 3.68 (m, 8H, CH2O), 6.80 (d, 2Н, J=8.8, Ph), 7.79
3
(m, 2Н, IPh), 8.06 (d, 2Н, J=8.8, Ph), 8.87 (m, 2Н, IPh), 8.98
(m, 2Н, IPh), 13.37 (s, 1Н, NH). 13C NMR (DMSO-d6, δ; ppm,
J/Hz): 29.06, 30.69 (2CH2S), 51.19 (2CH2N), 70.00, 72.89
(2CH2O), 111.49 (2CH), 117.39 (2C), 119.25 (C), 122.99,
123.22 (CH), 123.65, 125.78 (C), 127.77 (2CH), 129.32,
129.53 (CH), 135.72, 143.06, 143.45 (C), 147.27, 147.50 (CH),
147.83, 151.58 (2C). ESI-MS 3 in MeCN, m/z: calcd. 357.17;
[Cu(2)2(H2O)](ClO4)2. Yield: 71%. Anal. Calcd for
C38H28Cl2CuN10O9: C, 50.54; H, 3.12; N, 15.51; Cu, 7.04.
Found: C, 50.92; H, 3.27; N, 15.23; Cu, 7.39. IR (cm-1): N
,
3076 and 2921; CN, 1609; Hetaryl, 1485; ClO4, 1093 and
1077; p-Aryl 821 and 803. ESI-MS (positive ion mode, MeCN):
10 | J. Name., 2012, 00, 1-3
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ARTICLE
1
2
3
4
5
6
7
8
9
-
m/z = 784.11 (98%, [2(2) +(Cu2+)+ (ClO4 )]+). UV-vis in MeCN:
The studied 1H-imidazo[4,5-f][1,10]phenanthrolines
containing phenyl- (1), 4-(N,N-dimethylamino)phenyl- (2), 4-
View Article Online
DOI: 10.1039/C8NJ05697H
λ, nm (ε, M -1cm -1): 356 (111,000), 310, 290.
[Cu(3)2(H2O)](ClO4)2. Yield: 80%. Anal. Calcd for (azadithiacrown-ether)phenyl- (3) 3,4-dimethoxyphenyl- (4)
C58H64Cl2CuN10O13S4: C, 50.78; H, 4.70; N, 10.21; Cu, 4.63. and 2,2’-bithiophen-5-yl- (5) substituents demonstrate the
Found: C, 50,87; H, 4,10; N, 10,89; Cu, 4,21. IR (cm-1): N
complex formation with Cu(II) cations through the
coordination of metal ions with phenantroline part of
ligands. In case of 4-(azadithiacrown-ether)phenyl-1H-
,
3366, 2917 and 2861; CN, 1609; Hetaryl, 1484; ClO4, 1093
and 1077; p-Aryl 816 and 803; CS, 742. ESI-MS (positive ion
mode, MeCN): m/z = 1255.05 (58%, [2(3) +(Cu2+)+ (ClO4 )]+).
-
imidazo[4,5-f][1,10]phenanthroline
the
additional
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11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
UV-vis in MeCN: λ, nm (ε, M -1cm -1): 352 (109950), 282.
[Cu(4)2(H2O)](ClO4)2. Yield: 93%. Anal. Calcd for
C42H34Cl2CuN8O13: C, 50.79; H, 3.45; N, 11.28; Cu, 6.40.
coordination of Cu(II) with crown ether fragments at the
metal ion excess also occurs. The stable Cu(II) complex forms
mixture of L3Cu2+ and L2Cu2+ complexes. When IPh ligand
contains donor 4-(N,N-dimethylamino)phenyl-(2) or 4-
Found: C, 51.05; H, 3.87; N, 11.16; Cu, 6.5. IR (cm-1): N
,
(azadithiacrown-ether)phenyl-
(3)
substituents
the
3366, 2917 and 2861; CN, 1563; Hetaryl, 1491; OMe, 1262
and 1228; ClO4, 1093 and 1077. ESI-MS (positive ion mode,
MeCN): m/z = 810 (58%, [2(4) + (Cu2+) + (HO-) + (H2O)]+. UV-
vis in MeCN: λ, nm (ε, M -1cm -1): 450, 312, 279 (87,000)
[Cu(5)2(H2O)](ClO4)2. Yield: 37%. Anal. Calcd for
C54H34Cl2CuN8O9S4: C, 53.98; H, 2.85; N, 9.33; Cu, 5.29.
autoreduction of Cu(II) to Cu(I) proceeds. The formation of
L2Cu2+ complex force a tetrahedral geometry about the
copper atom and induces a positive shift in the reduction
potential providing the occurrence of autoreduction of
copper(II). The formed Cu(I) cations are stable in MeCN
solution. Electrochemical study showed that the
autoreduction is observed when Cu2+/Cu+ transfer and
oxidation of ligand occur at the closed electrochemical
condition. The potentials of oxidation of donor ligands 3,4-
dimethoxyphenyl- and 2,2’-bithiophen-5-yl-1-H-imidazo[4,5-
f][1,10]phenanthrolines (4, 5) are substantial differ from the
reduction potential of Cu2+/Cu+ transfer, in this case the
Cu2+/Cu+ autoreduction has not been found.
The present studies have revealed the requirements for
the occurrence of the process of Cu2+/Cu+ autoreduction
demonstrating that how small changes in the molecular
structure has a pronounced effect on the properties of metal
complexes. This observation of a system, stabilizing both
Cu(I) and Cu(II), is of interest in view of current studies of
model compounds mimicking biological structure and redox
properties.
Found: C, 53.27; H, 2.70; N, 9.68; Cu, 5.36. IR (cm-1): N
,
3366 and 2922; CN, 1571; Hetaryl, 1488;
ClO4, 1093 and
1077; thiophene, 678. UV-vis in MeCN: λ, nm (ε, M -1cm -1): 370
(56,250), 312, 281, 265
Computational details
All computations were performed using the Gaussian 09
software package42 by using the PBE1PBE functional.43 In the
calculation 6-31G(d) basis set was assigned to all elements
with the exception of copper for which the Los Alamos
effective core potentials plus the Double Zeta (LanL2DZ)44
basis set were employed. Open-shell Cu(II) complexes were
treated with a spin-unrestricted formalism. The geometric
structures of the complexes in the ground state (doublet)
were fully optimized without any symmetry restriction and
vibration frequency calculations were performed to ensure
that the optimized geometries represent local minima
associated with positive eigenvalues only. This level of
computation shows a very good agreement with experiment
(see supplementary materials). Solvent effects were
accounted for according to the experimental conditions. The
solvation effects of acetonitrile were considered by using the
polarizable continuum model by the integral equation
formalism (IEFPCM)45 with default convergence criteria.
From ground stated optimized geometries, vertical electronic
excitations were obtained with the time dependent density
functional theory (TD-DFT) formalism46,47 and the B3LYP,
MPW1PW91 and M062X functionals. GaussSum48-51 was
used to display the absorption spectra and to calculate the
fractional contributions of various groups to each molecular
orbital.
Conflicts of interest
There are no conflicts to declare.
Acknowledgements
Financial support from the Russian Science Foundation (RSCF
№ 17-73-30036) and equipment facilities from Center of
collective facilities of A. N. Nesmeyanov Institute of
Organoelement compounds are gratefully acknowledged.
Notes and references
1. Z.-B. Zhenga, Z.-M. Duan, J.-X. Zhang, K.-Z. Wang, Sensor
and Actuator B 2012, 169, 312-319.
2. X.-L. Chen, Z.-X. Han, H.-M. Hu, J.-J. Wang, S.-H. Chen, N.
Li, F. Fu, M.-L. Yang, G.-L. Xue, Inorg. Chim. Acta 2009, 362,
3963-3968.
Conclusions
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Page 12 of 15
ARTICLE
Journal Name
1
2
3
4
3. Y.Wang, Y. Zhang, D. Zhu, K. Ni. Ma, G. Tang, Spectrochim. 29. T. N. Sorrell, E. H. Cheesman,. Synth. Commun, 1981, 11,
View Article Online
DOI: 10.1039/C8NJ05697H
Acta A 2015, 147, 31-42.
909-912.
4. X.-J.Luo, Q.-P.Qin, Y.-L. Li, Liu, Z.-F.Chen, H. Liang, Inorg. 30. D. R. McMillin, K. M. McNett, Chem. Rev. 1998, 98, 1201-
Chem. Comm. 2014, 46, 176-179. 1220.
5. Q.-Q. Liu, J. Geng, X.-X. Wang, K.-H. Gu, W. Huang, Y.-X. 31. O. Das, S. Paria, E. Zangrando, T. K. Paine, Inorg. Chem.
Zheng, Polyhedron 2013, 59, 52-57. 2011, 50, 11375–11383.
6. L.-F. Tan, H. Chao, Y.-F. Zhou, L.-N. Ji, Polyhedron 2007, 26, 32. O. P. Anderson, J. Chem. Soc., Dalton Trans, 1973, 1237-
3029-3036. 1241.
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
7. T. K. Goswami, S. Gadadhar, B. Balaji, B. Gole, A. A. 33. E. K. Beloglazkina, A. V. Shimorsky, A .G. Majouga, A.
Karande, A. R. Chakravarty, Dalton Trans. 2014, 43, 11988- A.Moiseeva, N. V. Zyk, Rus. Chem. Bull. 2007, 56, 2189-2199.
11999.
34. Y.Sotnikova, E. Lukovskaya, A. Bobylyova, Y. Fedorov, V.
8. S. S. Bhat, A. A. Kumbhar, H. Heptullah, A. A. Khan, V. V. Novikov, A. Peregudov, A. Anisimov, A. D’Aléo,; F. Fages,; O.
Gobre, S. P. Gejji, V. G. Puranik, Inorg. Chem. 2011, 50, 545- Fedorova, Inorg. Chim. Acta 2016, 445, 103-109.
558.
9. S. I. Kirin, C. M. Happel, S. Hrubanova, T. Weyhermüller, C. Jonusauskas, A.V. Anisimov, J. Phys. Org. Chem. 2008, 21,
Klein, N. Metzler-Nolte, Dalton Trans. 2004, 1201-1207. 372-380.
10. A. Siegel, H. Siegel, Metal Ions in Biological Systems, 36. D. V. Berdnikova, Y. V. Fedorov, O. A. Fedorova, Dyes and
35. E. V. Tulyakova, O. A. Fedorova, Yu. V. Fedorov, G.
Marcel Dekker, New York, 2002.
11. E. I. Solomon; R. K. Szilagyi, S. D. George, L. Basumallick,
Chem. Rev. 2004, 104, 419-458.
Pigments 2013, 96, 287-295.
37. R. Liu, M.-M. Huang, X.-X. Yao, H.-H. Li, F.-L.Yang, X.-L. Li,
Inorg. Chim. Acta 2015, 434, 172-180.
12. M. M.Huang, Y. M. Guo, Y. Shi, L. Zhao, Y. W. Niu, Y. Shi, 38. A. R. Day, E. A. Steck, J. Am. Chem. Soc. 1943, 65, 452-
X. L. Li, .Inorg. Chim. Acta 2017, 457, 107-115. 456.
13. X. Liu, R. Li, L. Ma, X. Feng, Y. Ding, New J. Chem. 2016, 39. R. M. F. Batista, S. P. G.Costa, M. Belsley, C. Lodeiro, M.
40, 619-625. M. M. Raposo, Tetrahedron 2008, 64, 9230-9238.
14. J. Mathias, H. Arora, R. Lavi, H. Vezin, D. Yufit, M. Orio, N. 40. J.-Z.Wu, B.-H. Ye, L. Wang, L.-N. Ji, J.-Y. Zhou; R.-H. Li, Z.-
Aliaga-Alcaded, L.B enisvy, Dalton Trans. 2013, 42, 2358- Y. Zhouc, J. Chem. Soc., Dalton Trans. 1997, 1395-1402.
2361. 41. J. Bingwen , W. Tao , T. Chunhong, Z. Manhua, S. Tao,
15. B. S. Rajebhosale, S. N. Dongre, S. S. Deshpande, A. N. Bull. Chem. Soc. Japan. 2000, 73, 1749-1755.
Kate, A. A. Kumbhar, J. Inorg. Biochem. 2017, 175, 129-137.
16. G.Davies, D. J. Loose, Inorg. Chem. 1976, 15, 694-700.
42. G. W. T. M. J. Frisch, H. B. Schlegel, G. E. Scuseria, M. A.
Robb, J. R. Cheeseman, G. Scalmani, V. Barone, B. Mennucci,
17. S. Sundararajan, E. L. Wehry, J. Inorg. Nucl. Chem. 1972, G. A. Petersson, H. Nakatsuji, M. Caricato, X. Li, H. P.
34, 3699-3709. Hratchian, A. F.Izmaylov, J. Bloino, G. Zheng, J. L.
18. S. Sundararajan, E. L. Wehry, J. Phys. Chem. 1972, 76, Sonnenberg, M. Hada, M .Ehara, K. Toyota, R.Fukuda, J.
1528-1536. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H.
19. U. S. Kitawara, M. Munakata, A. Higashi, Inorg. Chim. Nakai, T. Vreven, J. A. Montgomery, J. E. Peralta, F. Ogliaro,
Acta 1984, 84, 79-84. M. Bearpark, J. J. Heyd, E. Brothers, K. N. Kudin, V. N.
20. F. H. Jardine, Adv. Inorg. Chem. Radiochem. 1975, 17, Staroverov, T. Keith, R. Kobayashi, J.Normand, K.
115-163. Raghavachari, A. Rendell, J. C. Burant, S. S.Iyengar, J.Tomasi,
21. L J. Matour, D. Limosin, P. Rey, J. Chem. Soc., Chem. M. Cossi, N. Rega, J. M. Millam, M. Klene, , J. E. Knox, J. B.
Commun. 1985, 1414-1416. Cross, V. Bakken, C. Adamo, J.mJaramillo, R. Gomperts, R. E.
22. Е. K. Beloglazkina, A. V. Shimorsky, A. G. Mazhuga,. О. V. Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W.
Shilova, V. А. Tafeenko, N. V. Zyk, Rus. J. Gen. Chem. 2009, Ochterski, R. L.Martin, K. Morokuma, V. G. Zakrzewski, G. A.
79, 1504-1508.
23. D. E.Nickless, M. J. Powers, F. L. Urbach, Inorg. Chem. O. Farkas, J. B. Foresman, Ortiz, J. V.; J .Cioslowski, D. J. Fox,
1983, 22, 3210-3217. Gaussian 09, Revision D.01, Gaussian, Inc., Wallingford, CT,
24. A. Benzekri, C.Cartier, J.-M.Latour, D. Limosin, P. Rey, M. 2009.
Voth, P. Salvador, J. J. Dannenberg, S. Dapprich, A. D. Daniels,
Verdaguer, Inorg. Chim. Acta 1996, 252, 413-420.
43. C. Adamo, V. Barone, J. Chem. Phys. 1999, 110, 6158-
25. P. I. Verheijdt, J. G.Hassnoot, J. Reedijk, Inorg. Chim. Acta 6169.
1983, 76, L43-L46.
44. P. J. Hay, W. R. Wadt, J. Chem. Phys. 1985, 82, 270-283.
26. C P. Molman, H. C. Freeman, J. M. Guss, M. Murata, V. A. 45. E.Cances, B.Mennucci, J. Tomasi, J. Chem. Phys. 1997,
Norris, J. A. M. Ramshaw, M. P. Venkatappa, Nature 1978, 107, 3032−3041.
272 , 319-324. 46. R. E. Stratmann, G. E.Scuseria, M. J. Frisch, J. Chem. Phys.
27. E. T. Adman, R. E. Stenkamp, L. C. Sieker, L. H. Jensen, J. 1998, 109, 8218-8224.
Mol. Biol. 1978, 123, 35-47.
28. J. M. Latour, Bull. Soc. Chim. France 1988, 508-514.
47. M. E. Casida, C.Jamorski, K. C. Casida, D. R. Salahub, J.
Chem. Phys. 1998, 108, 4439-4449.
48. C. Lee, W. Yang, R. G. Parr, Phys. Rev. 1988, 37B, 785-789.
12 | J. Name., 2012, 00, 1-3
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49. J. P. Safko, J. E. Kuperstock, S. M. McCullough, A. M.
Noviello, X. Li, J. P. Killarney, C.Murphy, H. H. Patterson, C. A.
Bayse, R. D. Pike, Dalton Trans. 2012, 41, 11663-11674.
50. Y. Zhao, D. G. Truhlar, Theor. Chem. Acc. 2008, 120, 215-
241.
ARTICLE
1
2
3
4
5
6
7
8
View Article Online
DOI: 10.1039/C8NJ05697H
51. O N. M.'Boyle, T A. Lenderholt, K. Langner, J. Comput.
Chem. 2008, 29, 839-845.
9
52. U. Sivagnanam, M. Palaniandavar, J. Chem. Soc. Dalton
Trans. 1994, 2277-2283.
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Graphical abstarct
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DOI: 10.1039/C8NJ05697H
Intramolecular electron transfer in Cu(II) complexes with aryl-imidazo-1,10-phenanthroline
derivatives: experimental and quantum chemical calculation studies
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8
9
Olga A. Fedorova, Nikolai E. Shepel, Sergey D. Tokarev, Elena V. Lukovskaya, Yulia A. Sotnikova, Anna A. Moiseeva,
Anthony D’Aléo, Frédéric Fages, François Maurel and Yury V. Fedorov
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
1.1
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
200
300
400
500
600
700
800
900
1000 1100
Wavelength / nm
First observation of Cu(II)-Cu(I) autoreduction in complex with aryl-imidazo-1,10-
phenanthroline derivatives