Synthesis, structure, and spectroscopic and electrochemical properties of copper(II/I) Complexes with symmetrical and unsymmetrical 2, 9-Diaryl-1,10-phenanthroline ligands

Article abstract of DOI:10.1002/ejic.200900024

A series of copper(II) and copper(I) complexes, [CuX₂L] (16) and [CuL₂](CuX₂) (7-12) (X = Cl, Br; L = 2-R-9-R′-l, 10phenanthroline, dpp: R = R′ = Ph; npp: R = naphthyl, R′ = Ph; dnp: R = R′ = naphthyl) were synthesized and characterized by elemental analysis, UV/Vis and IR spectroscopy, and Xray crystal diffraction (for 1, 3, 6, and 12), The copper(II) complexes are four-coordinate with one phenanthroline ligand and two halogen atoms, whereas the copper(I) complexes are tetrahedrally coordinated by two bidentate phenanthroline ligands. Cyclic voltammetry studies of the Cu^I complexes in CH₂Cl₂ reveal that bulky groups in the 2,9-positions have significant effects on the redox potential of the Cu^II/I couple, which is more positive for the complexes with the dnp ligand than those with the dpp and npp ligands,

Full text of DOI:10.1002/ejic.200900024

FULL PAPER
DOI: 10.1002/ejic.200900024
Synthesis, Structure, and Spectroscopic and Electrochemical Properties of
Copper(II/I) Complexes with Symmetrical and Unsymmetrical
2,9-Diaryl-1,10-phenanthroline Ligands
Peiju Yang,[a] Xiao-Juan Yang,*[a,b] and Biao Wu*[a,b]
Keywords: Copper / Structure elucidation / Electrochemistry / N ligands
A series of copper(II) and copper(I) complexes, [CuX2L] (1–
6) and [CuL2](CuX2) (7–12) (X = Cl, Br; L = 2-R-9-RЈ-1,10-
tetrahedrally coordinated by two bidentate phenanthroline
ligands. Cyclic voltammetry studies of the CuI complexes in
phenanthroline, dpp: R = RЈ = Ph; npp: R = naphthyl, RЈ = Ph; CH2Cl2 reveal that bulky groups in the 2,9-positions have
dnp: R = RЈ = naphthyl) were synthesized and characterized
by elemental analysis, UV/Vis and IR spectroscopy, and X-
ray crystal diffraction (for 1, 3, 6, and 12). The copper(II) com-
plexes are four-coordinate with one phenanthroline ligand
and two halogen atoms, whereas the copper(I) complexes are
significant effects on the redox potential of the CuII/I couple,
which is more positive for the complexes with the dnp ligand
than those with the dpp and npp ligands.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2009)
We recently synthesized a series of symmetrical and un-
symmetrical 2,9-diaryl-1,10-phenanthroline ligands and
their transition-metal complexes.[15,16] In the preparation of
the copper complexes, a novel four-coordinate CuII species
[CuBr2(dpp)] was obtained, which could be converted into
the CuI complex [Cu(dpp)2](CuBr2) under certain condi-
tions.[16] It is known that the CuII complexes usually have a
five- or six-coordinate, Jahn–Teller-distorted geometry with
1,10-phenanthrolines, whereas non-square-planar, four-co-
ordinate CuII complexes are very rare.[17–19] To gain more
insight into the structural features of such CuII complexes
and the steric effects of the substituents on their properties,
we prepared a series of CuII and CuI complexes of three 2,9-
diaryl-1,10-phenanthroline ligands, dpp (2,9-diphenyl-1,10-
phenanthroline), npp (2-naphthyl-9-phenyl-1,10-phenan-
Introduction
The chelating N-donor system 1,10-phenanthroline and
its derivatives represent a widely studied family of ligands
in transition-metal coordination chemistry as a result of the
rigidity of the phenanthroline backbone and the ease of
modifying their properties by appending various substitu-
ents at different positions of the phenanthroline moiety.[1,2]
A large number of metal complexes with phenanthroline
ligands have been synthesized, and they display promising
properties in a variety of fields such as photochemistry,
electron-transfer processes, biological systems, and self-as-
sembly of supramolecular architectures.[3–6] In particular,
copper complexes of phenanthroline ligands are of great
interest because of their photoluminescent behavior and
DNA and RNA binding properties.[7–14] Furthermore, it
has been shown that the substituents on the phenanthroline
ring can have significant effects on the structure and prop-
erties of the copper complexes. Among the 1,10-phenan-
throline derivatives, the 2,9-disubstituted agents are proba-
bly the most studied, as these sterically demanding ligands
can provide a highly protected coordination environment
for metal ions.
[a] State Key Laboratory for Oxo Synthesis & Selective Oxidation,
Lanzhou Institute of Chemical Physics, Chinese Academy of
Sciences,
Lanzhou 730000, China
E-mail: yangxj@lzb.ac.cn
wubiao@lzb.ac.cn
[b] State Key Laboratory of Applied Organic Chemistry, Lanzhou
University,
Lanzhou 730000, China
Scheme 1. Synthesis of complexes 1–12.
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throline), and dnp (2,9-dinaphthyl-1,10-phenanthroline) complexes bearing the unsymmetrical ligand npp, as many
(Scheme 1). The conversion of the [CuX2L] complexes into attempts to crystallize the complexes failed. The molecular
the CuI species, [CuL2](CuX2), was also studied. Herein we structures of 1, 3, 6, and 12 are depicted in Figures 1, 2, 3,
report the syntheses, structures, and spectroscopic and elec- and 4, respectively, and selected bond lengths and angles
trochemical properties of the complexes [CuIIX2L] and are given in Table 1.
[CuIL2](CuX2) (1–12, X = Cl, Br; L = dpp, npp, or dnp).
Table 1. Selected bond lengths [Å] and bond angles [°] for com-
plexes 1, 3, 6, and 12.
Results and Discussion
Complex 1
Cu–N1
Cu–N2
N1–Cu–N2
N1–Cu–Cl1
N1–Cu–Cl2
2.023(2)
2.012(2)
83.33(8)
135.55(6)
100.67(6)
Cu–Cl1
Cu–Cl2
N2–Cu–Cl1
N2–Cu–Cl2
Cl1–Cu–Cl2
2.200(1)
2.217(1)
104.90(6)
127.90(6)
107.00(4)
Synthesis
The dpp, npp, and dnp ligands were synthesized as pre-
viously reported.[15] Copper(II) complexes 1–6 were pre-
pared by the reaction of an equimolar amount of CuX2 (X
= Cl, Br) and the ligand in THF as brick-red solids (for 1–
3), or in dichloromethane as brown powders (for 4–6).
Dark-red copper(I) complexes 7–12 were prepared by the
reaction of anhydrous CuX with the corresponding ligand
in a 1:1 ratio. Because conversion of (dibromido)copper(II)
complex 4 into the corresponding CuI complex 10 was ob-
served previously,[16] we examined CuII species 1–6 under
different conditions and found that the ligand steric bulk,
the halide ligand (Cl or Br), and the solvent could affect
this process significantly. The complexes with the smallest
ligand (dpp), 1 and 4, can readily undergo this conversion
to form the corresponding CuI species, 7 and 10, in acetone
or CH2Cl2 at room temperature (or by heating to speed up
the process), and the conversion of dibromido analogue 4
is much faster than that of dichlorido 1. The dibromido
complexes with the other two bulkier ligands (npp and
dnp), 5 and 6, can also be partially converted into the corre-
sponding monovalent CuI complexes (11, 12) by heating
their CH2Cl2 or acetone solution, whereas their dichlorido
analogues (2, 3) do not show detectable change under the
same conditions. Moreover, the conversion in acetone is
easier than in CH2Cl2. These results reveal that bulky
groups in the 2,9-positions of phenanthroline can provide
efficient protection for the metal center to prevent ligand
redistribution, and the more labile bromido ligand can pro-
mote the process. Such processes were also supported by
MS (ESI) studies. In the MS (ESI) spectrum of complex
1, both [CuCl(dpp)]+ [m/z (%) = 430.6 (20.2)] and
[Cu(dpp)2]+ [m/z (%) = 727.8 (100)] can be found, whereas
complex 4 shows almost complete conversion to the
[CuL2]+ species [m/z (%) = 727.8 (100)] for [Cu(dpp)2]+ with
only a trace amount of [CuBr(dpp)]+ (Ͻ5%).
Complex 3
Cu1–N1
Cu2–N2
2.014(4)
2.019(4)
Cu1–Cl1
2.210(1)
2.201(1)
131.2(1)
Cu2–Cl2
N1–Cu1–N1A[a] 82.9(2)
N1–Cu1–Cl1A[a]
N1–Cu1–Cl1
102.3(1)
Cl1–Cu1–Cl1A[a] 108.8(1)
N2–Cu2–N2A[b] 83.2(2)
N2–Cu2–Cl2A[b]
Cl2–Cu2–Cl2A[b] 109.4(1)
130.8(1)
N2–Cu2–Cl2
Complex 6
Cu–N1
102.2(1)
1.99(1)
Cu–Br1
2.343(3)
102.7(3)
110.5(1)
N1–Cu–N1A[c] 82.5(6)
N1–Cu–Br1A[c] 129.6(3)
N1–Cu–Br1
Br1–Cu–Br1A[c]
Complex 12
Cu1–N1
Cu1–N3
Cu2–Br1
N1–Cu1–N3
N3–Cu1–N4
N3–Cu1–N2
Br1–Cu2–Br2
2.017(4)
2.022(4)
2.205(2)
139.1(2)
81.6(2)
127.4(2)
177.22(6)
Cu1–N2
Cu1–N4
Cu2–Br2
N1–Cu1–N4
N1–Cu1–N2
N4–Cu1–N2
2.120(5)
2.109(4)
2.205(2)
124.6(2)
82.4(2)
99.9(2)
[a] Symmetry code: 1 – x, y, z. [b] –x, –y, z. [c] 1 – x, 1 – y, z.
Copper(II) Complexes 1, 3, and 6
The structures of three non-square-planar, four-coordi-
nate copper(II) complexes [CuX2L] (1, 3, 6) were deter-
mined, and they all display a metal-to-ligand ratio of 1:1
similar to 4. Complex 1 contains a [CuCl2(dpp)] molecule
in an asymmetrical unit, whereas complex 3 contains two
independent halves of the [CuCl2(dnp)] molecule (ZЈЈ =
2),[21] and 6 consists of a half [CuBr2(dnp)] molecule per
asymmetrical unit, because there is a crystallographic C2
axis bisecting the N–Cu–N and X–Cu–X angles in the latter
two complexes (3 and 6). The CuII centers of the complexes
are coordinated by one bidentate ligand and two halide ions
(Figures 1, 2, and 3). According to a new four-coordinate
geometry index (τ4) established by Houser et al.,[22] the co-
ordination geometry about the CuI center in complexes 1,
X-ray Crystal Structures
The crystal structures of complexes 4 and 10 were re- 3, and 6 is best described as seesaw with τ4 values of 0.68,
ported previously by this group.[16] The CuI complex 0.69, and 0.71, respectively (the value of τ4 ranges from 1.00
[Cu(dpp)2](CuCl2)·2/3CH3CN was also structurally charac- for a perfect tetrahedral geometry to zero for a perfect
terized.[20] Here we present the structures of three CuII com- square-planar geometry, whereas intermediate structures,
plexes (1, 3, and 6)and one CuI complex (12). Single crystals including trigonal-pyramidal and seesaw, fall within the
suitable for X-ray diffraction were obtained from CH2Cl2/ range of 0 to 1.00). The dihedral angle between the N–Cu–
CH3CN (50:50 for 1, 3, and 6) or acetone (for 12). Notably, N and X–Cu–X planes is 65.7 (for 1), 65.5/65.8 (for 3), 67.4
it is very difficult to obtain crystals of either CuII or CuI (for 6), and 59.2° (for 4), which is smaller than that for the
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Copper(II/I) Complexes with 2,9-Diaryl-1,10-phenanthroline Ligands
analogous compound [CuCl2(phen)] (80.3°).[18] There are tio. In complex [Cu(phen)2](PF6)2, however, the CuII coor-
no significant intermolecular or intramolecular π-stacking dination sphere is enhanced by a secondary Cu–F interac-
–
interactions in these complexes.
tion (2.75 Å) with the PF6 ion. The 1:1 complexes,
[CuBr2L] [L = 2,9-bis(2,6-dimethoxyphenyl)-1,10-phenan-
throline] and [CuCl2(phen)], which are similar to CuII com-
plexes 1–6 presented in this work, have also been re-
ported.[24]
The Cu–N bond lengths (1.978–2.023 Å) in complexes 1,
3, and 6 are comparable to those in 4 (2.03 Å)[16] and in
other phenanthroline or bipyridine copper(II) complexes,
for example, [CuBr2L] [2.05 Å, L = 2,9-bis(2,6-dimeth-
oxyphenyl)-1,10-phenanthroline], [Cu(dpp)2](ClO4)2 (1.98–
2.00 Å),[17] and [CuII(dpq)2](ClO4)2 (1.987–2.026 Å).[19] The
Cu–Cl distances in 1 and 3 (mean value ca. 2.21 Å) are
similar to that in [CuCl2(phen)] (≈2.21 Å)[18] and slightly
shorter than that in [CuIICl(tet)]+ {2.30 Å, tet = 2,2Ј-bis[6-
(2,2Ј-bipyridyl)biphenyl]}.[25] The Cu–Br distance in 6
[2.346(3) Å] is close to that (2.35 Å) in [CuBr2(dpp)] (4),[16]
but it is longer than that in the [CuBr2L] compound [L =
2,9-bis(2,6-dimethoxyphenyl)-1,10-phenanthroline]
Figure 1. The molecular structure of complex 1 with 50% prob-
ability ellipsoids.
(2.01 Å). There are only minor differences in the N–Cu–N
bite angle (82.9–83.7°) and the Cl–Cu–Cl angle (107.0–
109.4° for 1 and 3) in the complexes. However, the Br–Cu–
Br angle of complex 6 (110.5°) is wider than that in complex
4 (104.6°), indicating larger steric hindrance in the complex
with the dinaphthyl ligand dnp (6) than with the diphenyl
derivative dpp (4). The dihedral angle between the phenan-
throline moiety and the attached phenyl or naphthyl sub-
stituent [34.7 and 47.4° for 1, 64.0/53.4° (two independent
molecules) for 3, and 58.2° for 6] also reflects the steric
effects of the ligands.
Copper(I) Complex [Cu(dnp)2](CuBr2) (12)
Figure 2. The molecular structure of complex 3, showing the two
independent molecules. Hydrogen atoms are omitted for clarity.
Similar to the analogous compound [Cu(dpp)2](CuBr2)
(10) reported by this laboratory, CuI complex 12 consists of
–
a [Cu(dnp)2]+ cation and a CuBr2 anion. In the complex
cation the Cu atom is coordinated by two dnp ligands in a
seesaw geometry (τ4 = 0.66, Figure 4)[22] with a dihedral
angle of 77.4° between the two chelating N–Cu–N planes,
which is smaller than that in 10 (84.3°). As in other bi-
s(phenanthroline)copper(I) complexes,[17,26,27] there are two
long Cu–N bonds (to N2 and N4) and two short Cu–N
bonds (to N1 and N3) in complex 12 (Table 2). The in-
–
clusion of CuBr2 as the counteranion in 12 is similar to
that in the cases of [Cu(dpp)2](CuBr2) (10),[16] [Cu(phen)2]-
(CuBr2),[28] and the chloride analog [Cu(dpp)2](CuCl2).[20]
–
The CuBr2 ion is slightly bent with a Br–Cu–Br angle of
177.2° in 12, which is comparable to the Cl–Cu–Cl angle of
–
177.3° in [Cu(dpp)2](CuCl2). In contrast, the same CuBr2
anion is linear in 10 and in [Cu(phen)2](CuBr2), and the
Cu–Br distance of 2.205(2) Å is close to that in these com-
pounds.
Figure 3. The molecular structure of complex 6. Hydrogen atoms
are omitted for clarity.
Bis(phenanthroline)copper(I) complexes generally dis-
It is noteworthy that four-coordinate copper(II) com- play distorted tetrahedral geometries, and the distortion
plexes with 1,10-phenanthroline ligands are not typical. In from D2d symmetry can be described by a set of angles θx,
the few known examples, [Cu(dpp)2](ClO4)2, [Cu(phen)2]- θy, and θz, which represent the interligand angles based on
(PF6)2,[23] and [CuII(dpq)2](ClO4)2 (dpq = dipyrido[3,2-f: the CuN4 core of the complexes.[29] The θz value is a mea-
2Ј,3Ј-h]quinoxaline)[19] have a 1:2 metal-to-ligand molar ra- sure of the dihedral angle relating two opposing phenan-
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one between naphthyl (F) and the phenanthroline (A) (dihe-
dral angle 1.9°, centroid–centroid distance 3.56 Å, and the
vertical displacements between ring centroids 0.70 and
0.81 Å) being stronger than that between the naphthyl D
and the phenanthroline B (dihedral angle 3.0°, centroid–
centroid distance 3.84 Å, the vertical displacements between
ring centroids 1.23 and 1.41 Å). Moreover, the π-stacking
interactions are stronger than those between the phenyl and
the phenanthroline planes in analogous complex 10 (the
centroid–centroid distances are 3.94 and 4.09 Å).[16] These
two interactions between the phenanthroline planes and the
aryl substituents have also been reported in similar
[Cu(NN)2]+ complexes.[17,20]
Most interestingly, a third intramolecular π-stacking in-
teraction occurs in 12 between two naphthyl planes (C and
E) of the dnp ligands (Figure 4). Although the orientations
of the two naphthyl groups are not the same, there is suf-
Figure 4. The molecular structure of complex 12. Hydrogen atoms
are omitted for clarity.
Table 2. Room-temperature spectroscopic and electrochemical data ficient stacking between them (dihedral angle 6.9°,
of 1–12.
centroid–centroid distance 3.56 Å, the vertical displace-
ments between ring centroids 0.17 and 0.59 Å). In contrast,
there is no such interaction between two phenyl planes in
the complexes with the diphenyl-substituted phenanthroline
ligand. In fact, an edge-to-face interaction of two phenyl
groups was observed in the compound [Cu(dpp)2](PF6).[17]
This difference could be ascribed to the stronger π-conjuga-
tion effect of the naphthyl group than the phenyl group.
The dihedral angles between the phenanthroline systems
and the naphthyl groups are 69.8 (A/D), 56.0 (A/C), 47.1
(B/E), and 65.3° (B/F; Figure 4). There are several factors
that affect the conformation of the ligands, for example,
steric hindrance, intramolecular π-stacking interactions,
and π-conjugation properties. It is noteworthy that the dihe-
dral angles involving the naphthyl–naphthyl interaction
(B/E and A/C) is smaller than those involving the phen–
naphthyl interactions, implying the importance of both π-
conjugation and stacking effects of the ligands.
λmax [nm]
Epa (Epc)
Epa
Epc
–
(ε, –1cm–1)
CuII/I ([CuL2]+) CuII/I (CuX2 )
1
2
3
445 (750)
444 (730)
452 (760)
540 (410)
445 (1400)
592 (690)
466 (1500)
591 (910)
468 (1400)
582 (720)
441 (2200)
569 (970)
457 (2400)
0.89 (0.85)
0.70
0.70
0.70
0.25
0.19
0.14
4
0.90
(0.83)
0.95
(0.87)
1.04
(0.94)
0.90
(0.85)
0.75
(0.64)
0.75
(0.64)
0.76
0.32
0.28
0.25
0.28
0.28
0.20
5
6
7
8
1.00 (0.90),
0.91 (0.81)
1.05 (0.98),
0.96 (0.87)
0.92
≈0.74
≈0.74
9
461 (2400)
10
441 (2700)
563 (1300)
453 (3300)
460 (2800)
(0.85)
11
12
0.99 (0.91)
1.06 (0.98)
≈0.81
≈0.81 (0.6)
UV/Vis Spectra
The electronic spectra of the ligands and complexes were
throline ligands, and θx and θy indicate the degree of a recorded in CH2Cl2. The ligands show absorptions at 260
“rocking” distortion. In D2d symmetry, θx = θy = θz = 90°, and 308 nm for dpp and at 230 and 290 nm for npp and
and deviation of θz from 90° indicates a flattening of the dnp. The complexes display very intense bands in the UV
molecule. In complex 12, these angles are θx = 105.7°, θy = region and much weaker bands in the visible region (400–
105.8°, and θz = 77.4°. Similar to a related copper(I) com- 650 nm). The intense UV absorptions can be assigned to
pound [Cu(dpp)2](CuCl2)·CH3CN (θz = 71.8°),[20] the large the corresponding ligand-centered πǞπ* transitions,
deviation of the θz value from 90° is due to intramolecular whereas the visible bands are characteristic metal-to-ligand
π-stacking interactions, which cause considerable distortion or ligand-to-metal charge transfer (MLCT or LMCT) pro-
of the coordination geometry. The θz value of [Cu(dpp)2]- cesses.[4,13,31] The absorption spectra of the copper(II) com-
(PF6) (100.2°)[17]and [Cu(dpp)2](CuBr2) (95.7°) is larger plexes are similar, and those of dibromido complexes 4–6
than that in complex 12.
are shown in Figure 5a. The band at 430–460 nm is as-
There are three important intramolecular π-stacking in- signed to MLCT, and the lower-energy band at 550–600 nm
teractions in complex 12 involving all the six conjugation is due to the LMCT transition. Such LMCT transitions of
systems (four naphthyl and two phenanthroline groups).[30] four-coordinate CuII complexes are also observed in the
Two of the interactions are between the naphthyl and the complex [Cu(dpp)2](ClO4)2.[17] Furthermore, the complexes
phenanthroline moieties and the third one is between the with the more sterically demanding ligands (npp and dnp)
two remaining naphthyl planes (Figure 4). The two sets of exhibit a significant redshift relative to those with dpp, es-
naphthyl–phen stacking interactions are different, with the pecially for the dibromido complexes (Table 2).
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Copper(II/I) Complexes with 2,9-Diaryl-1,10-phenanthroline Ligands
particular, the redox potential becomes more positive when
the steric constraint in the 2- and 9-positions increases, as
this can prevent the rearrangement of the coordination
sphere to the favored square-planar for the oxidized CuII
species and thus stabilize the CuI state.[14,33,34] A compari-
son of the complexes studied here revealed a complete
agreement with this trend: increasing the 2,9-substituents
on 1,10-phenanthroline from diphenyl (complexes 7, 10) to
phenyl/naphthyl (8, 11), and then to dinaphthyl (9, 12)
shifted the [CuL2]2+/+ couple to more positive potentials
(Figure 6a,b; Table 2).
Notably, CuI complexes 8, 9, 11, and 12 show another
(quasi)reversible or irreversible redox process, occurring as a
shoulder for 8 (≈0.74 V) and 11 (≈0.81 V) and well-resolved
for 9 (≈0.74 V) and 12 (≈0.81 V), in a less-positive potential
(Ͻ[CuL2]2+/+), which could be attributed to the CuII/CuI cou-
–
ple of the CuX2 anion in the complex [CuL2](CuX2). Com-
plexes 7 and 10 display only one reversible process, probably
due to the overlapping of the two CuII/CuI couples of
–
[CuL2]+ and CuX2 (Table 2). For the complexes with the
CuCl2– anion, 7–9, there is also an irreversible reduction peak
at 0.2–0.3 V, which might be caused by the dissociation or
ligand exchange during the redox process.[14,38]
For the CuII complexes [CuX2L] there are significant dif-
ferences between the dichlorido (1–3) and dibromido (4–6)
analogues. An irreversible reduction occurs at the 0.14–
0.32 V range for all complexes, which can be assigned to
the reduction of the CuII center to the CuI state. These pro-
cesses are often related to the dissociation of halide species
that are adsorbed on the electrode surface and rebound in
the return course,[18,25,38,39] leading to a corresponding
irreversible oxidation at around 0.7 V. There is a reversible
shoulder at 0.8–0.9 V for complex 1 as a result of the reoxi-
dation and reduction of the [CuL2]2+/+ couple as in the CuI
complexes, but no redox signal in this region is found for
complexes 2 and 3 (Figure 6c). This agrees well with the
aforementioned observations that the (dichlorido)cop-
per(II) complex [CuCl2(dpp)] (1) can undergo partial ligand
redistribution and reduction of CuII to give the CuI species
[Cu(dpp)2](CuCl2) (7), whereas the more sterically crowded
2 and 3 cannot be converted into the corresponding CuI
compounds.
Figure 5. The UV/Vis spectra of complexes (a) 4–6 and (b) 10–12
(5ϫ10–4  in CH2Cl2).
For copper(I) complexes 7–12 the MLCT band occurs as
a broad peak with a maximum absorption at 430–460 nm
(Table 2 and Figure 5b). This is similar to most of the
known bis(phenanthroline)copper(I) complexes with aryl
substituents in the 2,9-positions of the phenanthroline
backbone (maximum absorption in the range 440–
470 nm).[32–35] For 7 and 10, there is a shoulder in the 550–
600 nm range, which can be attributed to the distortion of
the complex molecule from D2d symmetry caused by intra-
molecular π-stacking interactions, as in some known CuI
complexes, for example, [Cu(phen)2]ClO4 (580 nm)[28] and
[Cu(tmp)2]PF6 (595 nm).[36] This lower-energy shoulder de-
creases with increasing steric bulk of the ligands (well re-
solved for 10, much weaker for 11, and disappeared for 12;
see Figure 5b), as more sterically demanding ligands may
enforce the D2d symmetry.
The cyclic voltammograms of (dibromido)copper(II)
complexes 4–6 also confirm the conversion of the CuII com-
plexes into the CuI species. As shown in Figure 6d, two
(quasi)reversible redox processes appear in the 0.8–1.0 V
range, which are similar to those of CuI complexes 10–12
(Figure 6b). The peak at the more-positive potential can be
Electrochemical Properties
The redox behavior of CuI and CuII complexes 1–12 was assigned to the reoxidation/reduction of the [CuL2]2+/+ cou-
studied by cyclic voltammetry in dichloromethane. CuI ple, whereas the other less-positive process should be the
–
complexes 7–12 undergo a reversible (for 7 and 10) or qua- redox of the CuBr2 anion. The potential of the [CuL2]2+/+
sireversible (for 8, 9, 11, and 12) one-electron oxidation pro- couple increases in the order 4 Ͻ 5 Ͻ 6 (dpp Ͻ npp Ͻ dnp)
cess at 0.90–1.06 V as a result of the CuII/CuI couple (Fig- as observed for 10–12. Moreover, the potential of the
ure 6a,b), which is similar to many (phenanthroline)copper [CuL2]2+/+ couple for the complexes with the same ligand
complexes.[4,31,34,37] The peaks for complexes 8 and 9 show is very close, for example, 0.89 V (for 1), 0.90 V (for 4),
a slight split with a shoulder. It has been reported that the 0.90 V (for 7), and 0.92 V (for 10) for the complexes with
–
CuII/CuI couple of [Cu(NN)2]n+ complexes depends largely the dpp ligand. The (CuIIX2)/(CuIX2 ) couple is also com-
on the nature of the substituents on the phenanthroline. In parable for the complexes (Table 2).
Eur. J. Inorg. Chem. 2009, 2951–2958
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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2955

P. Yang, X.-J. Yang, B. Wu
FULL PAPER
Br) can affect the ligand redistribution reaction. The
smaller dpp and dibromido ligands can promote the pro-
cess, as proved by MS (ESI) and electrochemical studies.
Cyclic voltammetry of the complexes also revealed that
bulkier groups in the 2,9-positions lead to a more-positive
CuII/CuI couple than that for the less-bulky complexes.
Experimental Section
General Considerations: All manipulations were carried out under
an atmosphere of nitrogen by using standard Schlenk vacuum line
techniques. Solvents were heated at reflux over an appropriate dry-
ing agent and distilled under an atmosphere of nitrogen prior to
use. 1,10-Phenanthroline, 1-bromonaphthalene, bromobenzene, the
copper(II) and copper(I) salts, and other chemicals were commer-
cially available and used without further purification. 1H NMR
spectra were obtained with a Mercury plus-400 spectrometer with
TMS as the internal standard. IR spectra were recorded as KBr
pellets with an HP5890 II GC/NEXUS-870 spectrometer. Element
analyses were performed with an Elementar VarioEL instrument.
Electronic spectra were recorded with an HP 8453 spectrometer.
MS (ESI) spectra were measured with a Waters ZQ 4000 instru-
ment.
Synthesis of Complexes 1–12
Complexes [CuBr2(dpp)] (4) and [Cu(dpp)2](CuBr2) (10): Synthesized
as previously reported.[16]
General Procedure for the Synthesis of Dichlorido- or Dibromido-
(2,9-diaryl-1,10-phenanthroline)copper(II) Complexes [CuX2(L), 1–
6]: The ligand (0.30 mmol) and CuX2·2H2O (0.30 mmol) were
stirred in THF (10 mL) for 8 h, followed by filtration of the reac-
tion mixture.
General Procedure for the Synthesis of [Bis(2,9-diaryl-1,10-phenan-
throline)copper(I)]dichlorocuprate or -dibromocuprate {[CuL2]-
(CuX2), 7–12}: Ligand (0.30 mmol) and anhydrous CuX
(0.30 mmol) were stirred in CH2Cl2 (10 mL) for 8 h. The reaction
mixture was filtered and the product was obtained as a red powder.
[CuCl2(dpp)] (1): Yield: 104 mg (74.9%). M.p. 232–234 °C. MS
(ESI): m/z (%) = 430.6 (20.2) [CuCl(dpp)]+, 727.8 (100) [Cu-
(dpp) ]+. IR (KBr): ν = 3432, 3050, 1622, 1587, 1549, 1509, 1487,
˜
2
1446, 1423, 1360, 1278, 1155, 1122, 1078, 907, 867, 776, 762, 742,
656 cm–1. C24H16Cl2CuN2 (466.85): calcd. C 61.94, H 3.44, N 6.02;
found C 61.78, H 3.52, N 5.75.
[CuCl2(npp)] (2): Yield: 110 mg (79.4%). M.p. 243–245 °C. MS
(ESI): m/z (%) = 480.6 (100) [CuCl(npp)]+. IR (KBr): ν = 3446,
˜
3056, 1623, 1586, 1553, 1512, 1486, 1427, 1363, 1296, 1243, 1188,
1149, 1024, 985, 908, 878, 802, 780, 744, 704 cm–1. C28H18Cl2CuN2
(516.91): calcd. C 65.24, H 3.50, N 5.44; found C 64.89, H 3.64, N
5.12.
Figure 6. Cyclic voltammograms of the CuI and CuII complexes in
dichloromethane (conc. 5ϫ10–4 ): (a) 7–9; (b) 10–12; (c) 1–3; and
(d) 4–6.
[CuCl2(dnp)] (3): Yield: 128 mg (75.6%). M.p. 264–266 °C. MS
(ESI): m/z (%) = 530.6 (100) [CuCl(dnp)]+ IR (KBr): ν = 3432,
˜
3052, 1623, 1586, 1554, 1514, 1492, 1429, 1393, 1364, 1245, 1188,
Conclusions
1152, 972, 908, 878, 799, 778, 612 cm–1. C32H20Cl2CuN2 (566.97):
The synthesis, structure, and spectroscopic and electro- calcd. C 67.96, H 3.54, N 4.96; found C 67.52, H 3.69, N 4.62.
chemical properties of a series of copper(II) and copper(I)
[CuBr2(npp)] (5): Yield: 113 mg (64.3%). M.p. 236–238 °C. MS
complexes with 2,9-diaryl-1,10-phenanthroline ligands are
reported. The conversion of the CuII complexes into the
corresponding CuI species was studied, and it was found
(ESI): m/z (%) = 526.6 (100) [CuBr(npp)]+. IR (KBr): ν = 3443,
˜
3053, 1621, 1584, 1550, 1509, 1489, 1423, 1360, 1149, 865, 780,
778, 745, 700 cm–1. C28H18Br2CuN2 (605.81): calcd. C 55.72, H
that the ligand steric bulk and the auxiliary ligand (Cl or 2.99, N 4.64; found C 55.75, H 3.21, N 4.30.
2956 Eur. J. Inorg. Chem. 2009, 2951–2958
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© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Copper(II/I) Complexes with 2,9-Diaryl-1,10-phenanthroline Ligands
Table 3.Crystallographic data for compounds 1, 3, 6, 12.
Complex
1
3
6
12
Formula
Fw
Crystal system
Space group
C24H16Cl2N2Cu
466.83
monoclinic
P21/n
C32H20Cl2N2Cu
566.94
orthorhombic
Pba2
C32H20Br2N2Cu
655.86
orthorhombic
P21212
C64H40Br2Cu2N4
1151.90
monoclinic
P21/c
a [Å]
b [Å]
c [Å]
α [°]
8.832(2)
13.269(3)
18.097(4)
90
15.411(1)
17.183(2)
9.670(1)
90
15.837(3)
8.493(2)
9.733(2)
90
8.5372(4)
24.504(1)
23.581(1)
90
β [°]
100.76(3)
90
2083.4(7)
4
1.488
948
90
90
2560.7(4)
4
1.471
1156
1.09
90
90
1309.2(4)
2
1.664
650
3.91
95.472(2)
90
4910.5(4)
4
1.558
2320
γ [°]
V [Å3]
Z
Dcalcd. [gcm–3]
F(000)
µ [mm–1]
1.32
2.54
θ range [°]
Reflections collected (Rint
Independent reflections
1.92–28.30
13043 (0.036)
5022
1.77–25.34
12722 (0.050)
4499
2.09–26.86
7274 (0.135)
2803
1.74–26.83
28932 (0.088)
10418
)
Observed reflns [IϾ2σ(I)]
R1; wR2 [IϾ2σ(I)]
R1; wR2 (all data)
GOF (F2)
3414
2856
1356
3755
0.0395; 0.0926
0.0661; 0.1012
1.057
0.0427; 0.0810
0.0821; 0.0945
1.041
0.0777; 0.2073
0.1662; 0.2444
1.050
0.0607; 0.1346
0.2002; 0.1827
0.940
[CuBr2(dnp)] (6): Yield: 134 mg (65.3%). M.p. 263–264 °C. MS
The structures were solved by direct methods by using the
SHELXS program. All non-hydrogen atoms were refined aniso-
tropically by full-matrix least-squares on F2 by the use of the pro-
(ESI): m/z (%) = 576.5 (100) [CuBr(dnp)]+. IR (KBr): ν = 3440,
˜
3053, 1623, 1586, 1554, 1514, 1493, 1430, 1364, 1245, 1188, 1152,
973, 908, 797, 777, 663, 611 cm–1. C32H20Br2CuN2 (655.87): calcd. gram SHELXL.[41] The hydrogen atoms were included in idealized
C 58.81, H 3.06, N 4.29; found C 58.93, H 3.38, N 3.97.
geometric positions with thermal parameters equivalent to 1.2
times those of the atom to which they were attached. Crystallo-
graphic data for 1, 3, 6, and 12 are listed in Table 3.
[Cu(dpp)2](CuCl2) (7): Yield: 93 mg (73.5%). M.p. 128–130 °C. MS
(ESI): m/z (%) = 727.8 (100) [Cu(dpp) ]+. IR (KBr): ν = 3444, 3051,
˜
2
1620, 1579, 1547, 1507, 1445, 1418, 1356, 1149, 1111, 1021, 861,
775, 742, 698 cm–1. C48H32Cl2Cu2N4 (862.79): calcd. C 66.98, H
3.72, N 6.51; found C 67.21, H 3.89, N 6.23.
CCDC-715827 (for 1), -715828 (for 3), 715829 (for 6), and 715830
(for 12) contain the supplementary crystallographic data for this
paper. These data can be obtained free of charge from The Cam-
bridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
[Cu(npp)2](CuCl2) (8): Yield: 94 mg (73.4%). M.p. 134–135 °C. MS
(ESI): m/z (%) = 827.8 (100) [Cu(npp) ]+. IR (KBr): ν = 3407, 3045,
˜
2
1729, 1620, 1578, 1548, 1509, 1496, 1486, 1420, 1392, 1357, 1239,
1185, 1146, 1022, 863, 801, 777, 740, 699 cm–1. C56H36Cl2Cu2N4
(962.91): calcd. C 70.00, H 3.75, N 5.83; found C 70.23, H 4.10, N
5.66.
Electrochemical Measurements: Cyclic voltammetry was performed
with a CHI660B electrochemistry workstation by using a one-com-
partment cell with a Pt button working electrode, a Pt thread
counter electrode, and a Ag/AgCl reference electrode. The working
electrode was polished to mirror finish with 0.05 µmol alumina and
sonicated in pure water for 2 min. Typical solutions of 0.5 m of
the copper compounds with 0.1  TBAH in CH2Cl2 were scanned
at room temperature at 50 mVs–1.
[Cu(dnp)2](CuCl2) (9): Yield: 110 mg (69.3%). M.p. 159–160 °C.
MS (ESI): m/z (%) = 927.8 (100) [Cu(dnp) ]+. IR (KBr): ν = 3440,
˜
2
3050, 1621, 1581, 1548, 1511, 1495, 1392, 1358, 1185, 1148, 1130,
972, 865, 788, 774, 664, 611 cm–1. C64H40Cl2Cu2N4 (1063.03):
calcd. C 72.45, H 3.77, N 5.28; found C 72.06, H 4.09, N 5.09.
[Cu(npp)2](CuBr2) (11): Yield: 96 mg (68.3%). M.p. 219–220 °C.
Acknowledgments
MS (ESI): m/z (%) = 827.8 (100) [Cu(npp) ]+. IR (KBr): ν = 3393,
˜
2
3043, 1729, 1620, 1578, 1548, 1509, 1496, 1486, 1420, 1392, 1357,
1239, 1185, 1146, 1076, 1022, 864, 801, 792, 777, 740, 700 cm–1.
C56H36Br2Cu2N4 (1051.81): calcd. C 64.12, H 3.44, N 5.34; found
C 64.33, H 3.72, N 5.50.
This work was supported by the “Bairen Jihua” project of the Chi-
nese Academy of Sciences.
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FULL PAPER
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Received: January 10, 2009
Published Online: June 5, 2009
2958
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© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2009, 2951–2958