Mononuclear copper(I) complexes containing redox-active 1,2-bis(arylimino)acenaphthene acceptor ligands: Synthesis, crystal structures and tuneable electronic properties

Article abstract of DOI:10.10.1002/ejic.201000061

A series of pseudo-tetrahedral copper(I) complexes carrying bis(imino)acenaphthene (BIAN) ligands as acceptor subunits and various phosphane derivatives was prepared and characterized by elemental analysis, X-ray crystallography and spectroscopic techniques. The electronic spectra of the compounds are dominated by low-lying metal-to-ligand charge transfer (MLCT) transitions which could be systematically modified by different substituent patterns at the diimine acceptor subunit and by variations of the electron donating properties and bite angles of the phosphane moiety. A qualitative model based on frontier-orbital overlap arguments is introduced to describe the observed variations in optical spectra, excited state energies, solvatochromic behaviour, charge transfer character, and extent of electronic coupling following moderate changes in orbital mixing. Due to their readily tuneable properties and the potential of the BIAN ligands to reversibly store up to four redox equivalents, these systems are of considerable interest for the development of novel multi-electron transfer photosensitizers which are based on the abundant and environmentally benign transition metal copper.

Full text of DOI:10.10.1002/ejic.201000061

FULL PAPER
DOI: 10.1002/ejic.201000061
Mononuclear Copper(I) Complexes Containing Redox-Active 1,2-Bis(aryl-
imino)acenaphthene Acceptor Ligands: Synthesis, Crystal Structures and
Tuneable Electronic Properties
Thomas Kern,[a] Uwe Monkowius,*[a] Manfred Zabel,[b] and Günther Knör*[a]
Keywords: Copper / Electronic spectra / Solvatochromism / Charge transfer
A series of pseudo-tetrahedral copper(I) complexes carrying
bis(imino)acenaphthene (BIAN) ligands as acceptor subunits
and various phosphane derivatives was prepared and char-
acterized by elemental analysis, X-ray crystallography and
spectroscopic techniques. The electronic spectra of the com-
pounds are dominated by low-lying metal-to-ligand charge
transfer (MLCT) transitions which could be systematically
modified by different substituent patterns at the diimine ac-
ceptor subunit and by variations of the electron donating
properties and bite angles of the phosphane moiety. A quali-
tative model based on frontier-orbital overlap arguments is
introduced to describe the observed variations in optical
spectra, excited state energies, solvatochromic behaviour,
charge transfer character, and extent of electronic coupling
following moderate changes in orbital mixing. Due to their
readily tuneable properties and the potential of the BIAN li-
gands to reversibly store up to four redox equivalents, these
systems are of considerable interest for the development of
novel multi-electron transfer photosensitizers which are
based on the abundant and environmentally benign transi-
tion metal copper.
ligands, which are acting as electron transfer cofactors. Fol-
lowing this latter strategy, we have combined a mononu-
clear copper centre with 1,2-bis(arylimino)acenaphthene
(Ar-BIAN) derivatives as redox-active bidentate N-donor
chelates.[10,11] The strong π-acceptor properties of Ar-BIAN
ligands have already been successfully employed to intro-
duce exceptionally low-lying metal-to-ligand charge trans-
fer (MLCT) transitions in several d6 chlorotricarbonyl ReI
complexes,[12] and the beneficial properties of these com-
pounds have soon led to interesting applications such as
low-band-gap sensitizers in bulk-heterojunction photovol-
taic devices.[13,14] Similar bathochromic shifts of charge
transfer transitions expanding far into the visible spectral
region of the solar spectrum could also be expected for the
corresponding d10 CuI derivatives of 1,2-bis(arylimino)-
acenaphthene, which should be able to significantly improve
the efficiency of new types of solar cells based on conven-
tional copper 2,2Ј-bipyridine sensitizers.[15,16] Moreover, the
properties of Ar-BIAN derivatives are particularly attract-
ive for the development of novel types of photocatalysts,
since the delocalized π-electron system of these ligands has
recently been demonstrated to reversibly store up to four
electrons upon consecutive two-electron reductions,[17] thus
acting as a potential electron reservoir for catalytic multi-
electron reactions.
Introduction
There is currently an increasing interest in the develop-
ment of novel catalyst systems based on cheap, abundant
and environmentally benign metal ions. Especially, the re-
placement of quite expensive second- and third-row transi-
tion elements, such as the commonly employed rhenium,
ruthenium, iridium, palladium or platinum coordination
compounds by first-row transition metals or main group
elements as catalytically active centres is gaining more and
more attention.[1–5] In this context, copper-based reagents
offer an attractive alternative to complexes of the noble
metals, according to their prominent role in enzymatic re-
dox catalysis[6,7] and to the significance of Cu-containing
heterogeneous catalysts[8,9] already used in many important
technical processes.
In order to promote multi-electron transfer reactivity,
which is crucially required for many permanent substrate
transformation processes, individual copper centres are fre-
quently attached to other redox-active subunits. This may
be achieved by the formation of multinuclear metal com-
plexes or by establishing an efficient coupling to organic
[a] Institut für Anorganische Chemie, Johannes Kepler Universität
Linz,
4040 Linz, Austria
E-mail: uwe.monkowius@jku.at
Here, we report the synthesis, structural characterization
and spectroscopic properties of a series of air-stable mono-
nuclear CuI Ar-BIAN systems with Ar = phenyl, p-tolyl,
p-methoxyphenyl or o-bis(isopropyl)phenyl and additional
phosphane-based mono- or bidentate P, _PP and _PO ligands
guenther.knoer@jku.at
[b] Zentrale Analytik der Universität Regensburg,
Röntgenstrukturanalyse,
Universitätsstr. 31, 93053 Regensburg, Germany
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201000061.
View this journal online at
wileyonlinelibrary.com
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Mononuclear Cu(I) Complexes with Redox-Active Ligands
in the coordination sphere of the copper centre. The suit- Information). Therefore, no further chemical analyses were
ability of these systems to accumulate reduction equivalents performed. Interestingly, with some other substituents R in
and to act as a redox relay for catalytic applications will the Ar-BIAN ligand series, the homoleptic bis-1,2-diimine
also be discussed in this paper.
complexes were isolated as unexpected main products under
the standard reaction conditions applied. These almost
black compounds showed very interesting spectroscopic
and redox properties, which will be presented in a separate
publication.
Results and Discussion
Syntheses
The remarkable variety of coordination patterns of the
isolated species formed by a supposedly straightforward
synthetic procedure is a typical feature, which reflects the
well-known lability of copper(I) phosphane complexes in
solution.[18,19] Therefore, it is important to keep in mind
that the preparation of defined species requires a delicate
balance and control of the reaction conditions, and that a
thorough structural characterization of the products be-
comes necessary. On the other hand, however, this feature
may be quite advantageous for potential catalytic applica-
tions of such systems, since rapid ligand exchange at a labile
substrate binding site similar to the reduced forms of mono-
nuclear “type 2” copper centres in oxidoreductases[7] is a
highly desirable feature for functional enzyme mimics and
bio-inspired catalysis.[3]
The series of Ar-BIAN compounds (1a–1d) and phos-
phane derivatives (2a–2d) studied as ligands for copper(I)
in this work is summarized in Scheme 1.
Scheme 1.
Structural Studies
Reaction of the 1,2-bis(arylimino)acenaphthene deriva-
tives 1a–1d with [Cu(NCCH3)4]PF6 as a low-valent copper
precursor and different phosphane ligands in CH2Cl2 leads
to deeply coloured compounds, which are obtained as crys-
talline materials upon precipitation with n-pentane. All
metal complexes isolated were stable in the solid state with
respect to air and moisture. They were characterized by ele-
Single crystals suitable for X-ray diffraction of com-
pounds 1, 2, and 4 were obtained from acetonitrile/pentane.
Crystals of 1 and 2 are monoclinic with P21/n (Z = 4). 4
crystallizes in the monoclinic space group P21/c (Z = 4)
with one molecule of ethyl ether in the asymmetric unit.
Characteristic bond lengths and angles are summarized in
Table 1. In compounds 1 and 2, the copper atom is coordi-
nated by the BIAN and phosphane ligands in a distorted
tetrahedral environment (see Figures 1 and 2). In analogy
to other CuI complexes of 2b there are no sub-van der
Waals contacts between the oxygen atom of the phosphane
ligand and the copper atom in 2.[20] In contrast, the copper
centre in complex 4 is coordinated by the BIAN and one
phosphane ligand and shows a distorted trigonal-planar co-
ordination geometry (Figure 3). Due to the weak contacts
between the copper centre and the oxygen atom of the alde-
1
mental analysis and H NMR, FTIR and ESI-MS spectro-
scopic methods. In the case of the heteroleptic compounds
1–3 carrying mono or bidentate phosphane ligands, red or
violet crystals were formed according to the stoichiometric
reaction shown in Scheme 2.
Table 1. Bond lengths and angles of 1, 2, and 4.
Bond length [Å]
1
2
4
Cu1–N1
Cu1–N2
Cu1–P1
Cu1–P2
Cu1–O1
2.132(3)
2.088(3)
2.246(1)
2.280(1)
–
2.068(2)
2.087(2)
2.252(1)
2.224(1)
–
2.045(2)
2.080(2)
2.172(1)
–
Scheme 2.
In another case, the initially expected formation of the
heteroleptic Ar-BIAN phosphane derivative was incom-
plete, and a defined copper(I) complex 4 carrying only one
phosphorus donor 2d was obtained following the general
conditions of Scheme 2. This compound could also be pro-
duced in comparable yield, when the correct 1:1 stoichiome-
try was applied. Surprisingly, the combinations 1c/2a and
1a/2d result in the formation of a product mixture in only
low yields. Recrystallisation gave only a few crystals of the
unintended compounds shown in Figure S1–S3 (Supporting
2.495(2)
Bond angles [°]
N1–Cu1–N2
P1–Cu1–P2
P1–Cu1–O1
N1–Cu1–P1
N2–Cu1–P2
N2–Cu1–P1
N2–Cu1–O1
79.2(1)
119.4(1)
–
121.1(1)
108.4(1)
118.9(1)
–
80.1(1)
112.3(1)
–
105.9(1)
112.6(1)
111.7(1)
–
81.8(1)
–
75.9(1)
141.1(1)
–
133.6(1)
108.7(1)
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hyde function [Cu1–O1 2.495(2) Å] the copper atom lies out whereas in 4 this bond is significantly shorter [Cu1–P1
of the plane defined by the atoms N1, N2, and P1. With 2.172(1) Å]. The bite angle of the BIAN ligand lies in a
the exception of the Cu1–N1 distance in 1 [2.132(3) Å] all narrow range [79.2(1)–81.8(1)°] comparable to other Cu–
Cu–N distances are very similar (2.045–2.088 Å). Likewise, BIAN complexes.[11] The lower steric flexibility of the che-
1 and 2 exhibit similar Cu–P distances (2.224 and 2.280 Å), lating DPEPhos ligand 2b leads to a smaller P–Cu–P angle
in 2 compared to 1 [1: 119.4(1)° vs. 2: 112.3(1)°].
Electronic Spectra
The absorption spectra of all copper(I) Ar-BIAN com-
plexes investigated in this study display various electronic
transitions below 400 nm and an additional broad chromo-
phoric feature in the visible spectral region (Figure 4,
Table 2).
Figure 1. Complex cation in crystals of 1 (ORTEP, displacement
ellipsoids at the 50% probability level).
Figure 4. Electronic absorption spectra of compounds 1–4 in DCM
solutions.
Table 2. UV/Vis spectroscopic data of the complexes 1–4 in DCM
solution at 298 K.
λmax [nm] (ε [L/(molcm)])
1
2
3
4
461 (7400), 332 sh (16400), 319 (18100), 255 sh (45000)
481 (12100), 333 sh (28500), 315 sh (40900)
518 (6800), 310 sh (29800), 289 sh (33100)
405 sh (7500), 340 sh (7400), 323 (33300), 312 sh (31700),
257 sh (62200)
Figure 2. Complex cation in crystals of 2.
The shorter-wavelength bands are dominated by the typi-
cal structured intraligand (IL) transitions localized at the
Ar-BIAN π-electron system,[12] which are only slightly
shifted with respect to the corresponding UV absorptions
of the free diimine ligands. The broad chromophoric visible
bands are ascribed to metal-to-ligand charge transfer
(MLCT) transitions from predominately copper(I) localized
d-electrons to the lowest unoccupied π*-orbitals of the Ar-
BIAN ligand.[21] While metal centered ds- and dp-excited
states may be present at higher energies, no other low-lying
transitions involving the copper valance electrons are ex-
pected due to the d10 electronic configuration of the central
metal. The phosphane moiety of the complexes also does
not directly contribute to significant spectral features, since
the IL bands of these subunits are covered by the more
intense diimine-based ππ*-transitions of the compounds.
Figure 3. Complex cation in crystals of 4.
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Mononuclear Cu(I) Complexes with Redox-Active Ligands
The charge transfer assignment of the visible spectral
bands of the complexes, which is in agreement with the reg-
ular spectroscopic properties of many other copper(I) di-
imine systems such as the extensively studied phenan-
throline derivatives,[22–24] is strongly supported by the oc-
currence of a conspicuous negative solvatochromism, shift-
ing the visible absorption maxima of all compounds to
higher energy with increasing solvent polarity. This charac-
teristic effect, resulting in drastic colour changes in com-
pounds such as 1, can be quantified by applying different
solvent polarity scales such as the empirical E*MLCT pa-
rameters[25] (Figure 5).
Figure 6. Contour plots of the highest occupied (left) and the low-
est unoccupied molecular orbitals of complex 1 [DFT calculation
at the B3LYP/6-31G(d,p) level].
It turns out that the HOMO of the heteroleptic com-
plexes is not purely localized at the copper d-orbitals, but
also carries a substantial portion of admixed phosphane
ligand character, as illustrated in Figure 6. Therefore, the
phosphane moiety, although spectroscopically attracting
minor attention, can not only be regarded as a spectator
subunit with regard to the photophysical properties, but sig-
nificantly modifies the electronic structure and orbital cou-
pling of the systems as will be described later in more detail.
The LUMO predominately consists of the π-electron system
of the coordinating diazabutadiene moiety (N=C–C=N),
which is forced to stay rigid because of the aromatic acen-
aphthene backbone.[10] The LUMO-energy of the ligands
can be moderately influenced by variations of substituents
R, which are situated in p-position of the non-coplanar aryl
groups directly attached to the nitrogen atoms of the diaza-
butadiene moiety. This allows to lower the MLCT transi-
Figure 5. Correlation of the charge transfer transition energies of
compounds 1 (᭡) and 2 (᭿) with the E*MLCT values of different
solvents.
A reasonably linear correlation is observed for the solva- tion energies by increasing the π-acceptor strength of the
tochromic behaviour of all compounds investigated in this Ar-BIAN system. In a certain solvent, the bathochromic
study, although for 1 a significant deviation from a simple shift of the charge-transfer band maximum slightly in-
polarity character of solvent interactions seems to be opera- creases in the series R = OMe Ͻ Me Ͻ H Ͻ COOMe,
tive in systems containing a carbonyl group, such as DMF which linearly correlates to the trend predictable by the
and acetone (Figure 5). In this context it is interesting to Hammet σp parameters, as already observed before in a
recall that the preparation of copper Ar-BIAN complex similar system.[12]
with the carbonyl containing phosphane ligand (compound
A much more drastic effect on the electronic structure,
4) also leads to larger deviations from the regular synthetic however, is induced by small modifications at the phos-
pathways. Therefore, it is tempting to speculate about domi- phane moiety of the heteroleptic Ar-BIAN copper com-
nant exchange equilibria between phosphane and carbonyl plexes. For example, the exchange of R = H (1a) vs. Me
ligands in solution as a general property of these copper(I) (1b) at the Ar-BIAN acceptor side should induce a moder-
compounds. This feature should be very useful for the de- ate blue-shift of approximately 500 cm–1 for the MLCT
velopment of catalytic cycles involving carbonyl group con- transition of complex 2 relative to 1.[12] In contrast to this
taining substrates, but still has to be further confirmed by prediction, the MLCT band of 2 is actually 900 cm–1 red-
a more systematic study exceeding the scope of this work.
shifted, because the additional structural variation at the
Another support for the proposed MLCT assignment of phosphane moiety overcompensates the expected effect of
the lowest-lying electronic transitions of the copper Ar- the methyl groups. It therefore turns out that the partially
BIAN complexes is provided by the results of TD-DFT cal- mixed copper-phosphane character of the metal-dominated
culations, which clearly indicate the charge transfer charac- donor subunit of the complexes deserves more attention for
ter of the frontier orbital (HOMO–LUMO) transition re- a detailed discussion of origin and properties of the lowest-
sulting in a shift of electron density from the electron-rich lying charge transfer transitions. In Figure 7, a simplified
copper phosphane donor moiety to the 1,2-diimine ac- MO picture is provided to illustrate some of the relevant
ceptor side of the molecule. The excited state with the high- interactions involving the dπ and π* frontier orbitals of the
est calculated oscillator strength results predominately from compounds, assuming a pseudo-tetrahedral ligand sphere
such a transition (Figure 6, S6, and Table S2).
around the copper(I) center.
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Figure 7. Metal–ligand frontier orbital overlap interactions in pseu-
dotetrahedral copper(I) diazabutadiene complexes carrying ad-
ditional P-donor ligands.
As shown in this qualitative picture, the P-localized lone-
pairs of the phosphane σ-donor moiety may directly inter-
act with one of the occupied dπ-orbitals of the copper cen-
ter in a tetrahedral environment. This orbital interaction
induces a destabilization of the copper(I) oxidation state
and thus should lead to a decreasing excitation energy (ba-
thochromic shift) of the corresponding MLCT transitions
in heteroleptic complexes carrying 1,2-diimine acceptor li-
gands. According to angular orbital model considerations,
the destabilization of the copper d-orbital shown in Fig-
ure 7 can be minimized by increasing the angle θ between
Figure 8. Walsh-diagram illustrating the effects of variable phos-
phane bite angles θ on the three highest occupied orbital energies
of the copper complex cation [(Ph-BIAN)Cu(PPh3)2]+ obtained by
single point calculations at the B3LYP/6-31G(d,p) level.
the Cu-center and the two σ-donor ligands situated at the strongly influence the chromophore delocalization and
corners of the tetrahedron. In fact, when two individual therefore the actual charge transfer character of the corre-
phosphane ligands are coordinated, as is the case in com- sponding excited states, which again will control the ex-
pound 1, a quite large distortion from the idealized tetrahe- pected photoreactivity of the compounds. As can be seen
dral geometry occurs, and the P–Cu–P angle θ reaches a in Figure 7, the copper dπ-orbital directly influenced by the
value of 119.4°, which is exceeding the hypothetical rectan- phosphane donor moiety has the proper symmetry to inter-
gular arrangement corresponding to a maximum d-orbital act with the π-electron system of the 1,2-diimine acceptor
overlap by almost 30°. In the case of compound 2, where a site. Since the N–Cu–N bite angle of the Ar-BIAN ligands
P–Cu–P angle of 112.3° is imposed by the chelating bis- (79° in 1 and 80° in 2) is quite small and nearly approaches
phosphane ligand, the corresponding overlap integral the 72° value of an aromatic five-membered ring such as
should be larger due to the reduced bite angle.[26] Therefore, a cyclopentadienyl anion, this π-interaction should not be
the d-orbital destabilization (wavelength of the MLCT neglected. In principle, for symmetry reasons, the π-orbital
maximum) and the effects of admixed phosphane electron overlap with the copper center may only influence the
density are expected to be higher in 2 (λmax = 481 nm) com- HOMO–1 (ψ1) and the LUMO (ψ3*) of the diazabutadiene
pared to 1 (λmax = 461 nm). Within a series of phosphanes fragment (see Figures 7 and 9), while the HOMO (ψ2) and
of very similar basicity, as is the case with the coordinating LUMO+1 (ψ4*) linear combinations remain non-bonding.
P atoms in the σ-donor ligands 2a and 2b, in fact the bite The lowest unoccupied MO (ψ3*) of the Ar-BIAN ligand
angle θ seems to be a dominant parameter for tuning the depicted in Figure 9 has the largest orbital coefficients at
excited state energies of such types of complexes. A calcu- the nitrogen atoms directly connected to the copper(I) cen-
lated Walsh diagram supporting such arguments is given ter.[28] Therefore, the LUMO is predominately affected by
in Figure 8: whereas the HOMO energy is pushed up with this orbital interaction.
decreasing P–Cu–P angle θ the energies of the LUMOs are
hardly effected upon changing of θ (Figure S8).
Whenever the electron density of the copper phosphane
donor fragment is rising and the energy of the dπ-orbital is
Besides variations in the P–Cu–P angle, larger changes high, also the mixing with the 1,2-diimine-based LUMO
of the σ-donor strength of different phosphane ligands will becomes more pronounced. As a consequence, the MLCT
also lead to modifications of orbital mixing and MLCT en- states are not only red-shifted, but at the same time become
ergies, with electron rich phosphanes such as 2c resulting in more delocalized between the copper center and the Ar-
even stronger effects than decreasing bite-angles, and thus BIAN acceptor side. The corresponding excited states will
shifting the lowest-lying electronic transitions significantly no longer display pure charge transfer properties and less
to the red (λmax = 518 nm in 3).[27] Removal of one of the pronounced dipole moment changes will occur between
phosphorus ligands and thus lowering the average ligand ground- and MLCT-excited states. Experimentally, this fea-
field around the copper center has the opposite effect, re- ture is drastically illustrated by the different solvatochromic
sulting in higher MLCT transition energies in compounds behaviour of complexes 1 and 2 (Figure 5), where the less
such as 4.
delocalized derivative 1 carrying monophosphane ligands
While all these electronic effects discussed here certainly contains the more typical charge transfer chromophore
determine the optical properties of the compounds, another with obviously much larger electron density rearrangements
crucial frontier orbital interaction has the potential to occurring in the lowest excited state.
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Mononuclear Cu(I) Complexes with Redox-Active Ligands
tronically decoupled acceptor ligand. Such a process is ex-
tremely useful for the development of photocatalytic sys-
tems suitable for multi-electron transfer reactions similar to
the ones involving biologically relevant organic redox cofac-
tors such as hydroquinones, NADH or reduced flavines,
which have evolved in natural systems as efficient redox re-
lays for the prevention of free radical product formation
and undesired catalyst degradation processes.
Of course, this ideal situation for photoredox reactivity
gradually changes in the more delocalized MLCT cases oc-
curring in compounds such as 3, where the formal copper
oxidation states are less settled and coupling between the
copper center and the Ar-BIAN ligand might be dominant
also in the excited states due to the larger orbital interac-
tions. As a consequence, besides the differences in solva-
tochromic features also the structural changes following the
MLCT excitation should be less pronounced in this case.
Such drastic differences in excited state distortion are well-
known to strongly influence the luminescence properties
Figure 9. Approximate composition of the π-molecular orbitals of
1,4-diazabutadiene.
When such typical MLCT states with a pronounced and photochemical reactivity of other copper 1,2-diimine
charge transfer characteristics are populated, the transition complexes.[22] A systematic study, which is certainly neces-
metal center in terms of a classical radical pair model for- sary to further support all the basic concepts developed in
mally reaches the copper(II) oxidation state with a d9 elec- the present work is currently underway.
tron configuration. At the same time, the Ar-BIAN ligand
is formally reduced by one electron to form a radical anion.
Conclusions
According to the Jahn–Teller effect, a distortion of the
pseudo-tetrahedral coordination sphere around copper(II)
occurs when the molecule is relaxing from the initial
Franck–Condon state to reach a significantly flattened ther-
mally equilibrated excited state geometry.[22] In the course
of this relaxation process, the copper(II) oxidation state is
stabilized and nucleophilic substrate or solvent molecules
may approach the coordinatively unsaturated “axial” sites
at the Cu center. In terms of the orbital interactions dis-
cussed above, it is important to note that this well-estab-
lished flattening distortion occurring in the charge transfer
excited state will also lead to an orbital decoupling of the
donor and acceptor subunits in the compounds, since the
dπ-overlap of copper with the diazabutadiene moiety shown
in Figure 7 is gradually lost with an increasing distortion of
the tetrahedron and should even vanish completely in a
square planar system.
By comparison of the redox properties of known rheni-
um(I) Ar-BIAN complexes[12] with the corresponding data
available for phenanthroline-copper(I) and -rhenium(I)
complexes,[18,29] it can be predicted that the MLCT-excited
copper(I) Ar-BIAN systems such as 1 should be very versa-
tile redox reagents for photoinduced electron transfer pro-
cesses in solution.[30] Besides the possibility of back-electron
transfer re-forming the copper(I) ground state species, the
decoupled 1,2-diimine radical anion subunit of the MLCT
excited species might for example further react in a second-
ary electron transfer process by reductive quenching involv-
ing a donor substrate. This type of reaction, which is ex-
pected to be favoured due to a low reorganization energy,
should then result in the formation of the diamagnetic Ar-
BIAN2– dianion[17,29] in the coordination sphere of copper
Pseudo-tetrahedral copper(I) complexes carrying bis-
(imino)acenaphthene ligands are versatile new photosensi-
tizers with rather low-lying metal-to-ligand charge transfer
(MLCT) states which are expected to be suitable for pho-
toredox processes. Their electronic properties can be sys-
tematically modified by different substituents at the diimine
acceptor subunit and by variations of the electron donating
properties and bite angles of the phosphane moiety. Espe-
cially, the delocalization between central metal and the li-
gands is quite sensitive to minor structural distortions at the
phosphane ligand site and thus can be exploited to dictate
excitation energies, solvatochromism, charge transfer reac-
tivity and the stability of the copper(I) oxidation state in
these complexes. The suitability of such systems for the ac-
cumulation of reduction equivalents and to act as a multi-
electron redox reagent for catalytic applications seems very
promising. Therefore, such copper-based systems may be-
come an attractive alternative to classical photosensitizers
such as ruthenium polypyridine complexes in the context
of typical applications such as dye-sensitized solar cells or
photocatalytic redox reactions.
Experimental Section
General Methods: All chemicals were purchased in reagent-grade
quality and directly used as received. Unless otherwise stated, com-
mercially available organic solvents of standard quality were puri-
fied and dried according to the accepted general procedures. Ele-
mental analyses were performed at the Centre for Chemical Analy-
sis of the Faculty of Natural Sciences of the University of Regens-
burg. Electronic absorption spectra were recorded with a Cary 300
and thus could store two reduction equivalents on an elec- Bio UV/Vis spectrophotometer using 1-cm quartz cells. NMR spec-
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tra were recorded with a Bruker Digital Avance NMR spectrometer
DPX200 (1H: NMR 200.1 MHz; 13C: 50.3 MHz; T = 303 K). The
chemical shifts are reported in ppm relative to external standards
(solvent residual peak), and coupling constants are given in Hertz.
The spectra were analysed as being first order. Error of reported
formed. The product was washed with n-pentane, filtered and dried
in vacuo.
[(Ph-BIAN)(Ph3P)2Cu]PF6 (1): Reaction of [Cu(NCCH3)4]PF6
(100 mg, 0.27 mmol) with Ph-BIAN (1a, 89.29 mg, 0.27 mmol) and
PPh3 (2a, 140.74 mg, 0.54 mmol) yielded 208.68 mg (73%) as a red
1
values: 0.01 ppm for H NMR, 0.1 ppm for 13C NMR and 0.1 Hz
3
powder. 1H NMR (200 MHz, CDCl3): δ = 8.19 (d, J = 8.54 Hz, 2
for coupling constants. The solvent used is reported for each spec-
trum. Mass spectra were recorded with a LCQ DECA XP Plus
(ESI). Infrared spectra were recorded with a FT-IR-Spectrometer
Paragon PC.
3
H, o-H-An), 8.13 (d, J = 7.02 Hz, 2 H, p-H-An), 7.86 (dd, 3J =
7.88 Hz, 2 H, p-H-An), 7.62–7.34 (m, 40 H, Ph-H) ppm. 13C NMR
(50 MHz, CDCl3): δ = 162.45 (+, N=C, 2 C), 146.43 (+, N-C, 2
C), 129.36–133.38 (-, aromatic, 4 C), 130.84 (+, 6 C), 125.23 (+, 4
C) ppm. MS (ESI, MeOH/CHCl3): m/z (%) = 658.28 (100) [M –
PPh3]+, 436.00 (24.33) [(Ph – BIAN)Cu + MeCN]+, 395.20 (1.91)
[(Ph – BIAN)Cu]+. C60H46CuF6N2P3 (1065.5): calcd. C 67.64, H
4.35, N 2.63; found C 68.76, H 4.48, N 2.30. UV/Vis (CH2Cl2): λ
(logε) = 255 sh (4.65), 319 (4.26), 332 sh (4.22), 461 nm (3.87). IR
Computational Details: The Gaussian03 program was used in the
calculations.[31] Initial coordinates were taken from the correspond-
ing X-ray crystal structure if available. All quantum-chemical cal-
culations were carried out using a density functional theory (DFT)
based method with the hybrid B3LYP[32] functional. The 6-
31G(d,p) basis set[33] was used through the calculations, whereas
for the complexed metal a LanL2DZ basis set[34] was applied. The
obtained geometries were verified to correspond to a real minimum
by establishing an absence of imaginary IR frequencies. The elec-
tronic transition energies and oscillator strengths were calculated
using the time-dependent density functional response theory (TD-
DFT)[35] at the B3LYP/6-31G(dЈ,pЈ) level.[36] Single point energies
were calculated applying the B3LYP/6-31G(d,p) method. The pa-
rameters from the optimized geometry were held fixed while the
bond P–Cu–P angle θ were changed from 95–135° in intervals of
5°.
(KBr): ν = 3054 (m, =C–H), 1736 (s, C=O), 1652 (s, C=N–), 1440
˜
(s, P–C), 1280 (s, C–N), 840 (ss, P–F) cm–1.
[(Tol-BIAN)(DPEPhos)Cu]PF6 (2): Reaction of [Cu(NCCH3)4]PF6
(100 mg, 0.27 mmol) with Tol-BIAN (1b, 97.25 mg, 0.27 mmol)
and DPEPhos (2b, 144.50 mg, 0.27 mmol) yielded 234.75 mg (79%)
1
3
as a violet powder. H NMR (200 MHz, CDCl3): δ = 8.29 (d, J =
3
8.54 Hz, 2 H, o-H-An), 8.13 (d, J = 7.70 Hz, 2 H, p-H-An), 7.58
3
(dd, J = 7.68 Hz, 2 H, m-H-An), 6.74–7.65 (m, 34 H, Ph-H), 6.30
(d, 3J = 8.55 Hz, 2 H, Ph-H), 2.40 (s, 6 H, Me) ppm. MS (ESI,
MeOH/CHCl3): m/z (%) = 962.28 (100) [M]+, 601.33 (53.98) [M –
(Tol-BIAN)]+, 642.53 (14.19) [Cu
+ DPEPhos +
MeCN]+.
Synthesis: The preparation of all compounds described in this work
was carried out according to the following general procedure: stoi-
chiometrical amounts of [Cu(NCCH3)4]PF6 and the phosphane li-
gand in 20 mL of dichloromethane were stirred at room tempera-
ture for 2 h and then combined with a solution of the Ar-BIAN
ligand in 5 mL of dichloromethane. This reaction mixture was
stirred for an additional hour. After this period, approximately
10 mL of n-pentane were added to fully precipitate the complex
C62H48CuF6N2OP3 (1107.5): calcd. C 67.24, H 4.37, N 2.53; found
C 66.93, H 4.56, N 2.22. UV/Vis (CH2Cl2): λ (logε) = 315 sh (4.61),
333 sh (4.46), 481 nm (4.08). IR (KBr): ν = 3054 (m, =C–H), 1654
˜
(s, C=N–), 1436 (s, P–C), 1280 (w, C–N), 842 (ss, P–F) cm–1.
[(MeO-Ph-BIAN)(dppe)Cu]PF6 (3): Reaction of [Cu(NCCH3)4]PF6
(100 mg, 0.27 mmol) with MeO-Ph-BIAN (1c, 105.3 mg,
0.27 mmol) and dppe (2c, 106.9 mg, 0.27 mmol) yielded 211.83 mg
Table 3. Crystal data, data collection and structure refinement for compounds 1, 2, and 4.
1
2
4
Formula
MW [g/mol]
Crystal size [mm]
Crystal system
Space group
a [Å]
b [Å]
c [Å]
α [°]
C60H46CuN2P2·PF6
1065.50
0.28ϫ0.24ϫ0.20
monoclinic
P21/n
15.262(12)
17.002(16)
20.145(18)
90
C62H48CuN2OP2·PF6
1107.48
0.22ϫ0.18ϫ0.12
monoclinic
P21/n
14.395(10)
17.457(10)
21.240(2)
90
C55H55CuN2OP·C4H10O·PF6
1073.62
0.32ϫ0.29ϫ0.11
monoclinic
P21/c
15.4477(1)
18.3784(1)
19.3020(1)
90
β [°]
8.65(10)
90
5168.1(8)
1.369
4
0.579
296(1)
94.68(9)
90
5319.64(7)
1.383
4
1.982
123
98.518(1)
90
5419.47(6)
1.316
γ [°]
V [Å3]
ρber [mg cm–3]
Z
4
µ [mm–1]
T [K]
1.662
123
Θ range [°]
λ [Å]
Reflections collected
Unique reflections
2.57–26.94
0.71073
70487
3.28–62.24
1.54184
25805
8146 [R(int) = 0.0273]
6201
2.89–62.21
1.54184
71918
8517 [R(int) = 0.0398]
6579
11172 [R(int) = 0.1468]
Observed reflections [I Ͼ 2σ(I)] 4427
Data/restraints/parameters
Absorption correction
Tmin., Tmax.
11172/0/649
8146/0/679
semi-empirical
1.00000, 0.77370
0.707/–0.475
0.0369
8517/0/659
semi-empirical
1.00000, 0.59687
0.896/–0.394
0.0394
analytical
0.9212, 0.7981
0.425/–0.252
0.0477
σfin. (max/min) [eÅ–3]
R1 [IՆ2σ(I)]
wR2
0.1060
0.1015
0.1165
4154
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Eur. J. Inorg. Chem. 2010, 4148–4156

Mononuclear Cu(I) Complexes with Redox-Active Ligands
1
[9]
C. L. Bracey, P. R. Ellis, G. J. Hutchings, Chem. Soc. Rev. 2009,
38, 2231.
N. J. Hill, I. Vargas-Baca, A. H. Cowley, Dalton Trans. 2009,
240, and references cited therein.
Some related copper(II) and dimeric copper(I) complexes car-
rying Ar-BIAN ligands have recently been investigated, see: a)
U. El-Ayaan, A. Paulovicova, Y. Fukuda, J. Mol. Struct. 2003,
645, 205; b) U. El-Ayaan, A. Paulovicova, S. Yamada, Y. Fu-
kuda, J. Coord. Chem. 2003, 56, 373; c) U. El-Ayaan, F. Mur-
ata, S. El-Derby, Y. Fukuda, J. Mol. Struct. 2004, 692, 209; d)
K. V. Vasudevan, M. Findlater, A. H. Cowley, Chem. Commun.
2008, 1918.
(79%) as a red powder. H NMR (200 MHz, CDCl3): δ = 8.62 (d,
3J = 8.02 Hz, 2 H, o-H-An), 6.84–7.49 (m, 32 H, Ph-H), 3.93 (s, 6
H, Me), 2.39 (t, 3J = 5.32 Hz, 4 H) ppm. 13C NMR (50 MHz,
[10]
[11]
2
CDCl3): δ = 24.94 (+, dd, JCP = 18.95 Hz; 2 C), 55.30 (-, 2 C),
114.53 (-, 4 C), 131.87 (-, dd, J = 7.95 Hz, Ph), 131.41 (+, Ph),
130.75 (+, Ph), 130.46 (-, Ph), 128.69 (-, m, Ph), 127.82 (-, Ph),
124.08 (-, Ph), 158.42 (-, 2 C) ppm. C52H44CuF6N2O2P3 (999.39):
calcd. 62.50, H 4.44, N 2.80; found C 61.97, H 4.09, N 2.68. UV/
Vis (CH2Cl2): λ (logε) = 289 sh (4.52), 310 sh (4.47), 518 nm (3.83).
IR (KBr): ν = 3052 (m, =C–H), 1638 (s, C=N–), 1446 (s, P–C),
˜
1295 (s, C–N), 1246 (s, C–O), 839 (ss, P–F) cm–1.
[12]
[13]
G. Knör, M. Leirer, T. E. Keyes, J. G. Vos, A. Vogler, Eur. J.
Inorg. Chem. 2000, 749.
H. L. Wong, L. S. M. Lam, K. W. Cheng, K. Y. K. Man, W. K.
Chan, C. Y. Kwong, A. B. Djurisˇic´, Appl. Phys. Lett. 2004, 84,
2557.
C. S. K. Mak, H. L. Wong, Q. Y. Leung, W. Y. Tam, W. K.
Chan, A. B. Djurisˇic´, J. Organomet. Chem. 2009, 694, 2770.
T. Bessho, E. C. Constable, M. Grätzel, A. Hernandez-Re-
dondo, C. E. Housecroft, W. Kylberg, Md. K. Nazeeruddin, M.
Neuburger, S. Schaffner, Chem. Commun. 2008, 3717.
E. C. Constable, A. Hernandez-Redondo, C. E. Housecroft, M.
Neuburger, S. Schaffner, Dalton Trans. 2009, 6634.
I. Fedushkin, A. A. Sakatova, V. K. Cherkasov, V. A. Chu-
dakova, S. Dechert, M. Hummert, H. Schuhmann, Chem. Eur.
J. 2003, 9, 5778.
For monodentate copper(I) phosphane complexes see: S. J. Lip-
pard, J. J. Mayerle, Inorg. Chem. 1972, 11, 753, and references
cited therein.
For bidentate phosphane-copper(I) complexes, see: S. Berners-
Price, R. K. Johnson, C. K. Mirabelli, L. F. Faucette, F. L.
McCabe, P. J. Sadler, Inorg. Chem. 1987, 26, 3383, and refer-
ences cited therein.
[(iPr2-Ph-BIAN)(PCHO)Cu]PF6 (4): Reaction of [Cu(NCCH3)4]-
PF6 (100 mg, 0.27 mmol) with Pr2-Ph-BIAN (1d, 134.3 mg,
0.27 mmol) and PCHO (2d, 140.7 mg, 0.54 mmol) yielded
168.95 mg (63%) of a brown powder. 1H NMR (200 MHz, CDCl3):
δ = 9.67 (s, 1 H, CHO), 8.21 (d, 3J = 8.14 Hz, 2 H, o-H-An), 7.93–
7.99 (m, 1 H), 7.77 (dd, 3J = 7.64 Hz, 1 H), 7.16–7.62 (m), 6.97 (m,
4 H), 6.86 (d, J = 7.17 Hz, 2 H), 3.07 (sept, J = 6.68 Hz, Me2C-
H), 1.26 (br., 1 H, Me), 0.93 (br., 23 H, Me) ppm. C55H55CuF6-
N2OP2 (999.54): calcd. C 66.09, H 5.55, N 2.80; found C 64.36, H
4.62, N 2.68. UV/Vis (CH2Cl2): λ (logε) = 257 sh (4.79), 312 sh
[14]
[15]
3
3
[16]
[17]
(4.60), 323 (4.52), 340 sh (3.87), 405 sh nm (3.88). IR (KBr): ν =
˜
2959 (m, –C–H), 1670 (s, C=O), 1641 (s, C=N–), 1435 (s, P–C),
1297 (s, C–N), 837 (ss, P–F) cm–1.
Crystal Structures: Diffraction data for crystals of the compounds
1 and 8 were collected with a STOE-IPDS diffractometer[37] with
[18]
[19]
graphite-monochromated Mo-Kα radiation (λ
= 0.71073 Å),
whereas crystal data of 2, 4, 6 and 7 were collected with an Oxford
Diffraction Gemini Ultra CCD diffractometer with multilayer op-
tics and Cu-Kα radiation (λ = 1.5418 Å). Further crystallographic
and refinement data can be found in Table 3 and Table S1. The
structures were solved by direct methods (SIR-97)[38] and refined
by full-matrix least-squares an F2 (SHELXL-97).[39] The H atoms
were calculated geometrically and a riding model was applied dur-
ing the refinement process.
[20]
[21]
U. Monkowius, S. Ritter, B. König, M. Zabel, H. Yersin, Eur.
J. Inorg. Chem. 2007, 4597; U. Monkowius, Y. N. Svartsov, M.
Zabel, H. Yersin, Inorg. Chem. Com. 2007, 10, 1473.
I
It is well known that heteroleptic diimine-phosphane Cu com-
plexes of the type [(_NN)CuP2]+ undergo ligand scrambling re-
actions in solution forming the species [(_NN)2Cu]+ and
[CuPn]+. Under our experimental conditions we rule out the
presence of such complexes. The homoleptic cations
[(_NN)2Cu]+ feature an absorption band at longer wavelength.
This and further results will be presented separately.
a) O. Horváth, K. L. Stevenson, Charge Transfer Photochemis-
try of Coordination Compounds, VCH, New York, 1993, p. 45;
b) S. Sakaki, H. Mizutani, Y.-i. Kase, Inorg. Chem. 1992, 31,
4575.
CCDC-756603 (for 1), -756606 (for 2) and -756601 (for 4), contain
the supplementary crystallographic data for this paper. These data
can be obtained free of charge from The Cambridge Crystallo-
graphic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
[22]
Supporting Information (see also the footnote on the first page of
this article): Further experimental details on synthesis, structures,
and quantum chemical calculations.
[23]
[24]
D. R. McMillin, K. M. McNett, Chem. Rev. 1998, 98, 1201.
a) N. Armaroli, G. Accorsi, F. Cardinali, A. Listorti, Top. Curr.
Chem. 2007, 280, 69; b) N. Armaroli, G. Accorsi, G. Bergamini,
P. Ceroni, M. Holler, O. Moudam, C. Duhayon, B. Delavaux-
Nicot, F. Nierengarten, Inorg. Chim. Acta 2007, 360, 1032.
D. M. Manuta, A. J. Lees, Inorg. Chem. 1983, 22, 3825.
T. A. Albright, J. K. Burdett, M.-H. Whangbo, Orbital Interac-
tions in Chemistry, Wiley, New York, 1985, p. 9.
Note that the presence of a methoxy group in complex 3 makes
the Ar-BIAN ligand a less favourable electron acceptor than
the one in complex 2. This effect alone should induce a blue-
shift of approximately 500 cm–1 for the MLCT maximum in-
stead of the observed 1500 cm–1 red-shift.
This can be readily derived by qualitative Hückel MO consider-
ations for the parent system butadiene: I. Fleming, Frontier
Orbitals and Organic Chemical Reactions, Wiley, New York,
1976, p. 17.
a) K. Kalyanasundaram, Photochemistry of Polypyridine and
Porphyrin Complexes, Academic Press, London, 1992; b) S.
Sakaki, H. Mizutani, Y.-i. Kase, K.-j. Inokuchi, T. Arai, T.
Hamada, J. Chem. Soc., Dalton Trans. 1996, 1909.
Acknowledgments
Partial support of this work by the Austrian Science Fund (FWF
project P21045: “Bio-inspired Multielectron Transfer Photosensi-
tizers”) and the European Commission (ERA Chemistry Project
I316: “Selective Photocatalytic Hydroxylation of Inert Hydro-
carbons”) is gratefully acknowledged.
[25]
[26]
[27]
[1] J. Messinger, ChemSusChem 2009, 2, 47.
[2] P. Du, J. Schneider, G. Luo, W. W. Brennessel, R. Eisenberg,
Inorg. Chem. 2009, 48, 4952.
[28]
[29]
[3] G. Knör, Chem. Eur. J. 2009, 15, 568.
[4] M. W. Kanan, D. G. Nocera, Science 2008, 321, 1072.
[5] H. Tributsch, Electrochim. Acta 2007, 52, 2302.
[6] Y. Lee, K. D. Karlin, in: Concepts and Models in Bioinorganic
Chemistry (Eds.: H.-B. Kraatz, N. Metzler-Nolte), Wiley-VCH,
2006.
[7] M. Rolff, F. Tuczek, Angew. Chem. Int. Ed. 2008, 47, 2344.
[8] C. Ratnasamy, J. P. Wagner, Catal. Rev. 2009, 51, 325.
Eur. J. Inorg. Chem. 2010, 4148–4156
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
4155

T. Kern, U. Monkowius, M. Zabel, G. Knör
FULL PAPER
[30] Cyclovoltammograms of 1 (DCM, Pt, 0.2 V/s) display two re-
versible waves at –0.67 V and –0.91 V vs. SCE ascribed to re-
duction processes of the Ar-BIAN ligand, and an irreversible
oxidation with Epa = +1.10 V vs. SCE tentatively assigned to
the copper (I/II) redox couple. Rough estimates for the MLCT
excited state redox potentials (electronic origin around 600 nm
or 2.07 eV) are therefore +1.40 V and –0.97 V vs. SCE (+1.64 V
and –0.73 V vs. NHE) for reductive and oxidative quenching
processes, respectively.
[31] M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria,
M. A. Robb, J. R. Cheeseman, J. A. Montgomery Jr., T.
Vreven, K. N. Kudin, J. C. Burant, J. M. Millam, S. S. Iyengar,
J. Tomasi, V. Barone, B. Mennucci, M. Cossi, G. Scalmani, N.
Rega, G. A. Petersson, H. Nakatsuji, M. Hada, M. Ehara, K.
Chen, M. W. Wong, C. Gonzalez, J. A. Pople, Gaussian 03, Re-
vision C.02, Gaussian, Inc., Wallingford CT, 2004.
[32] A. D. Becke, Phys. Rev. A 1988, 38, 3098; C. T. Lee, W. T. Yang,
R. G. Parr, Phys. Rev. B 1988, 37, 785; A. D. Becke, J. Chem.
Phys. 1993, 98, 5648.
[33] R. Ditchfield, W. J. Hehre, J. A. Pople, J. Chem. Phys. 1971, 54,
724; W. J. Hehre, R. Ditchfield, J. A. Pople, J. Chem. Phys.
1972, 56, 2257; V. A. Rassolov, M. A. Ratner, J. A. Pople, P. C.
Redfern, L. A. Curtiss, J. Comput. Chem. 2001, 22, 976.
[34] P. J. Hay, W. R. Wadt, J. Chem. Phys. 1985, 82, 270; W. R.
Wadt, P. J. Hay, J. Chem. Phys. 1985, 82, 284; P. J. Hay, W. R.
Wadt, J. Chem. Phys. 1985, 82, 299.
[35] R. E. Stratmann, G. E. Scuseria, M. J. Frisch, J. Chem. Phys.
1998, 109, 8218.
Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. [36] a) G. A. Petersson, A. Bennett, T. G. Tensfeldt, M. A. Al-La-
Honda, O. Kitao, H. Nakai, M. Klene, X. Li, J. E. Knox, H. P.
Hratchian, J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R.
Gomperts, R. E. Stratmann, O. Yazyev, A. J. Austin, R.
ham, W. A. Shirley, J. Mantzaris, J. Chem. Phys. 1988, 89, 2193;
b) G. A. Petersson, M. A. Al-Laham, J. Chem. Phys. 1991, 94,
6081.
Cammi, C. Pomelli, J. W. Ochterski, P. Y. Ayala, K. Morok- [37] Stoe IPDS software, version 2.89, Stoe & Cie GmbH, Darm-
uma, G. A. Voth, P. Salvador, J. J. Dannenberg, V. G. Zakrzew-
ski, S. Dapprich, A. D. Daniels, M. C. Strain, O. Farkas, D. K.
Malick, A. D. Rabuck, K. Raghavachari, J. B. Foresman, J. V.
Ortiz, Q. Cui, A. G. Baboul, S. Clifford, J. Cioslowski, B. B.
Stefanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaromi, R. L.
Martin, D. J. Fox, T. Keith, M. A. Al-Laham, C. Y. Peng, A.
Nanayakkara, M. Challacombe, P. M. W. Gill, B. Johnson, W.
stadt, Germany, 1998.
[38] A. Altomare, G. Cascarano, C. Giacovazzo, A. Guagliardi, J.
Appl. Crystallogr. 1993, 26, 343.
[39] G. M. Sheldrick, SHELXL-97, Program for crystal structure
refinement, University of Göttingen, Germany, 1997.
Received: January 21, 2010
Published Online: July 27, 2010
4156
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Eur. J. Inorg. Chem. 2010, 4148–4156