Synthesis and characterization of trinuclear square-planar Ni II3 and CuII3 complexes of an extended phloroglucinol ligand: Experimental evidence for the relative contributions of benzene-like and radialene-like

Article abstract of DOI:10.1016/j.poly.2011.02.029

The synthesis and characterization of the extended phloroglucinol ligand H₃felddien, its trinuclear Ni^II complex [(felddien)Ni ₃](BF₄)₃ and its trinuclear Cu^II complex [(felddien)Cu₃

Full text of DOI:10.1016/j.poly.2011.02.029

Polyhedron 30 (2011) 3038–3047
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Polyhedron
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Synthesis and characterization of trinuclear square-planar NiII3 and CuII3 complexes
of an extended phloroglucinol ligand: Experimental evidence for the relative
contributions of benzene-like and radialene-like resonance structures
⇑
Bastian Feldscher, Anja Stammler, Hartmut Bögge, Thorsten Glaser
Lehrstuhl für Anorganische Chemie I, Fakultät für Chemie, Universität Bielefeld, Universitätsstr. 25, D-33615 Bielefeld, Germany
a r t i c l e i n f o
a b s t r a c t
The synthesis and characterization of the extended phloroglucinol ligand H3felddien, its trinuclear NiII
complex [(felddien)Ni3](BF4)3 and its trinuclear CuII complex [(felddien)Cu3](ClO4)3 is presented. Detailed
NMR studies provide strong evidence that the ligand H3felddien has to be described as the N-protonated
tautomer and not as the O-protonated tautomer, with strong contribution of a radialene-like keto-enam-
ine resonance structure resulting in a Cs and a C3h isomer. The trinucleating tris(tetradentate) ligand pro-
vides three donor sets comprised of a phenolate, an imine, and two tertiary amine donors. This donor set
enables the synthesis of the diamagnetic square-planar coordinated NiII complex [(felddien)Ni3](BF4)3
which provides the opportunity to perform detailed NMR spectroscopic characterizations for the evalu-
ation of the electronic structure of the central phloroglucinol unit. In conjunction with a single-crystal X-
ray diffraction and a UV–vis absorption spectroscopic analysis, these data indicate that in the coordinated
form, the benzene-like phenolate-imine and the radialene-like keto-enamine resonance structures have
Article history:
Available online 21 February 2011
Keywords:
Magnetic properties
Cu complexes
Ni complexes
N ligands
O ligands
Electronic absorption spectroscopy
contributions to the overall resonance hybrid. The weakening of the central
p system as a consequence of
the contribution of the keto-enamine resonance structure explains the relative small ferromagnetic inter-
actions in the trinuclear CuII complex [(felddien)Cu3](ClO4)3. This detailed analysis identifies the strong
resonance with unsaturated groups in 2,4,6 position of phloroglucinol as the main source for the low fer-
romagnetic couplings by the spin-polarization mechanism in all our extended phloroglucinol ligands. A
replacement of the unsaturated imine functions by saturated amine functions may be a synthetic oppor-
tunity to enhance the ferromagnetic interactions by the spin-polarization mechanism in this ligand
system.
Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction
complexes antiferromagnetic interactions prevail. Moreover, se-
vere ligand foldings have been observed in the complexes of the li-
2
The synthesis of molecule-based magnets has attracted consid-
erable interest over the past two decades [1,2]. For a rational devel-
opment of new types of molecule-based magnets, the design of
molecular building blocks with ferromagnetic interactions be-
tween the paramagnetic centers was supposed to be essential
[3]. In this respect, we have recently established a family of trinu-
cleating ligands sharing a common bridging phloroglucinol (1,3,5-
trihydroxybenzene) unit consisting of tris(tridentate) ligands like
gand H6talent-Bu resulting in overall bowl-shaped molecular
structures [6,23,25]. We have taken advantage of this ligand fold-
ing by using the trinuclear complexes [(talent-Bu ){M (solv)n}3]
t
m+
2
to act as molecular building blocks [23] with hexacyanometallates
[Mc(CN)6]3ꢀ for the formation of heptanuclear complexes
[Mt6Mc]n+ ([{(talent-Bu )M 3}2{M (CN)6}]3+): [MnIII6CrIII
]
,
[29]
t
c
3+
2
[MnIII6FeIII
]
3+, [30] and [MnIII6CoIII
]
[31] with [MnIII6CrIII
]
3+
3+
being a single-molecule magnet (SMM) [23].
H3L [4] and the tris(tetradentate) triplesalen ligands H6talenX
The syntheses of the ligands H3L and H6talenX are based on the
triketone 1 (Scheme 1a). Recently, we have been able to synthesize
the ligand H3felden [32] (Scheme 1b) following a protocol for the
trialdehyde 2 established by MacLachlan et. al. [33]. A detailed
analysis of the ligand H3felden and its trinuclear CuII complex [(fel-
den){Cu(bpy)}3](ClO4)3 revealed, that the central phloroglucinol
backbone is not in the anticipated conventional phenol form, that
is mainly described by the benzene-like enol-imine resonance
structure I (Scheme 1c), but in the N-protonated tautomer with se-
2
2
[5,6] (Scheme 1a), as well as further modifications [7–10]. The
phloroglucinol bridging unit was chosen to behave as a ferromag-
netic coupler by the spin-polarization mechanism [11–23]. Indeed,
trinuclear CuII [4,7,24,25] and VIV [26] complexes exhibit weak but
ferromagnetic interactions, while in MnIII [10,27,28] and FeIII [8]
⇑
Corresponding author.
E-mail address: thorsten.glaser@uni-bielefeld.de (T. Glaser).
0277-5387/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2011.02.029

B. Feldscher et al. / Polyhedron 30 (2011) 3038–3047
3039
Scheme 1.
vere contributions from the keto-enamine resonance structure IV,
which may be described as radialene-like [32].
d), 2.23 (s, CH3 8a–d). 13C NMR (125.75 MHz, CDCl3): d = 187.89,
185.23, 182.78, 181.14 (all CarO); 158.13, 157.58, 157.25, 156.53
(all C1a–d); 104.92, 104.88, 104.73, 104.67 (all CarCN); 58.13,
58.08, 57.96, 57.92 (all CH2 4a–d); 57.32, 57.24 (all CH2 7a–d);
55.97, 55.95, 55.88, 55.85 (all CH2 6a–d); 48.01, 48.00, 47.97,
47.92 (all CH2 3a–d); 45.84, 45.81(all CH3 8a–d), 42.63, 42.62 (all
Herein, we present the synthesis of the ligand H3felddien
(Scheme 1b). This ligand was chosen to provide tetradentate ligand
compartments to allow the synthesis of four-coordinate diamag-
netic NiII complexes, which have not been accessible with the li-
gand H3felden. The diamagnetic trinuclear NiII complex should
CH3 5a-d). ESI-MS (positive ion mode): m/z = 296.7 [M+2H]2+
,
3
allow a NMR spectroscopic study, enabling to estimate relative
contributions of the benzene-like and the radialene-like resonance
structures in the complexes. In this respect, the synthesis and char-
acterization of the two complexes [(felddien)Ni3](BF4)3 and [(feld-
dien)Cu3](ClO4)3 is presented.
592.3 [M+H]+. IR (KBr): max/cmꢀ1 2951br, 2857w, 2822br, 1611s,
m
1547m, 1462m, 1356w, 1325w. Elemental analysis: Found: C,
57.91; H, 9.44; N, 20.77. Calc. for H3felddienꢁ1.5H2O
(C30H60N9O4.5): C, 58.22; H, 9.77; N, 20.37.
2.1.2. [(felddien)Ni3](BF4)3
2. Experimental section
A solution of H3felddien (191 mg, 0.32 mmol) in methanol
(17 mL) was added dropwise to a solution of Ni(BF4)2ꢁ6H2O
(335 mg, 0.98 mmol) in methanol (30 mL). The resulting suspen-
sion was heated to reflux for 2 min during which the precipitate
dissolves. While the solution was still warm, triethylamine
(98 mg, 0.97 mmol) dissolved in methanol (2 mL) was added. After
cooling to room temperature the complex can be isolated as a red
solid. Yield: 194 mg (59%). ESI-MS (positive ion mode) m/z = 254.6
2.1. Preparation of compounds
Solvents and starting materials were of the highest commer-
cially available purity and used as received. The synthesis of
2,4,6-triformylphloroglucinol (2) [33] and of the triamine
3
[34,35] has already been published.
[(felddien)Ni3]3+. IR (KBr): max/cmꢀ1 3013w, 2932m, 1605s, 1514s,
m
2.1.1. H3felddien
1470m, 1439w, 1420m, 1400w, 1375w, 1362w, 1343w, 1329w,
1298w, 1285w, 1254m, 1244m, 1055br, 950w, 889w, 797m,
766w, 638w, 584w, 523w. Elemental analysis: Found: C, 35.04;
H, 5.21; N, 12.13. Calc. for [(felddien)Ni3](BF4)3 (C30H54N9O3-
Ni3B3F12): C, 35.14; H, 5.31; N, 12.30. To enhance the solubility in
noncoordinating solvents (see text for details), [(felddi-
en)Ni3](BF4)3 has been converted into the B(ArF)4-salt
2,4,6-Triformylphloroglucinol (2) (36 mg, 0.15 mmol) and tri-
amine 3 (135 mg, 0.93 mmol) were stirred in dichloromethane
(12 mL) for 16 h. The resulting yellow solution was dried over so-
dium sulfate and the volatiles were removed under vacuum, yield-
ing the product as a viscous yellow oil. Yield 79 mg (78%). 1H NMR
(500.25 MHz; CDCl3): d = 11.32 (m, NH2a + NH2b), 10.95 (m,
NH2c + NH2d), 8.22 (d, 3J(H,H) = 14 Hz, HCN 1b), 8.20 (d,
3J(H,H) = 14 Hz, HCN 1c), 8.12 (d, 3J(H,H) = 14 Hz, HCN 1a), 8.08
(d, 3J(H,H) = 14 Hz, HCN 1d), 3.45 (m, CH2 3a–d), 2.62 (m, CH2
4a–d), 2.53 (m, CH2 6a–d), 2.41 (m, CH2 7a–d), 2.29 (m, CH3 5a–
(B(ArF)4ꢀ = tetrakis[3,5-bis(trifluoromethyl)phenyl]borate)
via
salt-metathesis. All NMR-spectra have been collected from this
salt. 1H NMR (500.25 MHz; CD2Cl2): d = 7.77 (s, B(ArF)4ꢀ), 7.59 (s,
B(ArF)4ꢀ), 7.33 (s, CArCHCN), 3.79–2.10 (m, CH2, CH3). 13C NMR

3040
B. Feldscher et al. / Polyhedron 30 (2011) 3038–3047
1
(125.75 MHz, CD2Cl2): d = 169.3 (s, CArO), 162.3 (q, JBC = 50 Hz,
bilities, vm, the measured susceptibilities were corrected for the
B(ArF)4ꢀ), 153.4 (s, B(ArF)4ꢀ), 125.2 (q, JCF = 270 Hz, B(ArF)4ꢀ),
underlying diamagnetism of the sample holder and the sample
by using tabulated Pascal’s constants. The JULX program package
was used for spin-Hamiltonian simulations and fitting of the data
by a full-matrix diagonalization approach [39].
1
129.5 (q, JCF = 32 Hz, B(ArF)4ꢀ), 118.1 (s, B(ArF)4ꢀ), 106.1 (s,
2
CArCCN), 62.1, 61.5, 59.4, 59.2, 50.1, 48.2, 42.8.
2.1.3. [(felddien)Cu3](ClO4)3
A solution of H3felddien (228 mg, 0.39 mmol) in methanol
(27 mL) was added dropwise to a solution of Cu(ClO4)2ꢁ6H2O
(431 mg, 1.16 mmol) in methanol (30 mL). The resulting suspen-
sion was heated to reflux for 2 min and triethylamine (117 mg,
1.16 mmol) dissolved in methanol (2 mL) was added. After cooling
to room temperature the reaction mixture was filtered. Vapor dif-
fusion of diethyl ether into the filtrate results in the deposition of
small needles. Yield: 147 mg (35%). ESI-MS (positive ion mode) m/
3. Results and discussion
3.1. Synthesis and characterization
The ligand H3felddien has been synthesized analogous to the
previously reported ligands H3L [4] and H3felden [32] by a Schiff-
base condensation of the triamine 3 and 2,4,6-triformylphloroglu-
cinol (2) (Scheme 2). NMR spectroscopy, FTIR spectroscopy, mass
spectrometry, and elemental analysis confirmed the successful
synthesis of the ligand H3felddien. The reaction of H3felddien with
nickel tetrafluoroborate hexahydrate in methanol in presence of
triethylamine affords red solid [(felddien)Ni3](BF4)3. The trinuclear
copper complex [(felddien)Cu3]3+ can be obtained in analogy to the
nickel complex with copper perchlorate hexahydrate as starting
material. Vapor diffusion of diethyl ether into the reaction mixture
yielded the complex as green needles. The identity and purity of
the complexes has been confirmed by FTIR spectroscopy, mass
spectrometry, and elemental analysis.
z = 259.7 [(felddien)Cu3]3+. IR (KBr):
m
max/cmꢀ1 2980m, 2926m,
2878m, 1609s, 1499s, 1466s, 1412m, 1360m, 1343m, 1329m,
1296w, 1248m, 1227m, 1090s, 963w, 941m, 926m, 883w, 791m,
760m, 923s, 579w, 503m. Elemental analysis: Found: C, 31.99; H,
5.12; N, 11.01. Calc. for [(felddien)Cu3](ClO4)3ꢁ3H2O (C30H60N9O6-
Cu3Cl3O12): C, 31.84; H, 5.34; N, 11.14.
2.2. X-Ray crystallography
Single-crystals of [(felddien)Ni3](BF4)3ꢁ0.5C3H6O suitable for sin-
gle-crystal X-ray diffraction were obtained by slow evaporation of a
solution of the complex in an acetone/cyclohexane mixture, re-
moved from the mother liquor and immediately cooled to
100(2) K on a Bruker KAPPA APEX II CCD diffractometer at a detector
distance of 3.51 cm. Crystal data for [(felddien)Ni3](BF4)3ꢁ0.5C3H6O:
3.2. NMR spectroscopy
3.2.1. H3felddien
The 1H NMR spectrum of the ligand H3felddien exhibits multi-
ple signals between 8.3–8.0 and 11.4–10.8 ppm for the imine and
for the ‘‘phenolic OH’’ protons, respectively (Fig. 1a). This is not
in agreement with the ligand as it is pictured in Scheme 2, since
the imine and the phenolic OH protons should only give rise to
singlets. However, this splitting pattern of the NMR spectra and
various NMR experiments (see below) provide evidence that the li-
gand has to be described as the N-protonated tautomer, where the
radialene-like resonance structure IV has strong contributions
(Scheme 1c). Additionally, due to the radialene-like description,
two different geometrical isomers (with C3h and Cs symmetry,
Scheme 3) are present [32,33,40–43].
M = 1054.42 g molꢀ1, C31.5H57F12B3Ni3N9O3.5, triclinic, space group
ꢀ
P1, a = 11.6183(11), b = 14.3983(13), c = 14.7360(15) Å,
a =
69.698(4)°, b = 74.652(5)°,
c
= 71.889(4)°, V = 2163.1(4) Å3, Z = 2,
= 1.390 mmꢀ1
(0 0 0) = 1088, Crystal si-
total of 105492 reflections
q
= 1.619 g cmꢀ3
,
l
, F
ze = 0.10 ꢂ 0.04 ꢂ 0.02 mm3.
A
(2.18 <
H < 25.00°) were collected of which 7606 reflections were
unique (R(int) = 0.0501). An empirical absorption correction using
equivalent reflections was performed with the program SADABS
2008/1 [36]. The structure was solved with the program SHELXS-97
[37,38] and refined using SHELXL-97 [38] to R = 0.0397 for 6003 reflec-
tions with I > 2r(I), R = 0.0589 for all reflections; Max/min residual
electron density 0.538 and ꢀ0.318 e Åꢀ3. Two of the ligand arms
It is possible to simplify the observed 1H NMR spectra notably in
order to facilitate the assignment of the resonances. The exchange
were found to be disordered over two positions (see text). The three
ꢀ
BF4 anions are so severely disordered, that not all found fluorine
positions can be assigned to well resolved BF4 tetrahedra.
2.3. Other physical measurements
Infrared spectra (400–4000 cmꢀ1) of solid samples were re-
corded on a Shimadzu FTIR-8400S spectrometer as KBr disks.
UV–vis–NIR absorption spectra of solutions were measured on a
Shimadzu UV-3101PC spectrophotometer in the range of 200–
1200 nm at ambient temperatures. ESI mass spectra were recorded
on a Bruker Esquire 3000 ion trap mass spectrometer equipped
with a standard ESI source. 1H and 13C NMR spectra were measured
on a Bruker DRX500 or a Bruker AV300 spectrometer using the sol-
vent as an internal standard. The electrochemical experiments
were performed on Ar-flushed CH3CN solutions containing 0.1 M
[NBu4]PF6 in a classical three electrode cell. The working electrode
was a platinum electrode, the counter electrode a platinum wire
and the reference electrode was Ag/0.01 M AgNO3/CH3CN. All
potentials are referenced to the ferrocenium/ferrocene (Fc+/Fc)
couple used as an internal standard. The electrochemical cell was
connected to an EG&G potentiostat/galvanostat (VersaStat). Tem-
perature-dependent magnetic susceptibilities were measured by
using a SQUID magnetometer (MPMS XL-7 EC, Quantum Design)
at 1 T (2–290 K). For calculations of the molar magnetic suscepti-
Scheme 2.

B. Feldscher et al. / Polyhedron 30 (2011) 3038–3047
3041
tra exhibit no temperature dependence up to 140 °C, demonstrat-
ing a very strong energy barrier for rotation, which is a clear
indication of the double bond character for the CAr–Cimine bond.
NMR spectra recorded in CDCl3 and CD2Cl2 solutions result in
only poorly resolved multiplets between 11.4 and 10.8 ppm, prob-
ably due to fast exchange of the acidic NH protons 2a–d with resid-
ual water in the solvents. However, the use of dmso-d6 (upper
spectrum in Fig. 1c) or conducting the NMR experiment at low
temperatures enhanced the resolution of the multiplets notably.
Coupling of the NH protons 2a–d with the vinylic protons 1a–d
and with the methylene unit next to it (3a–d) leads to the observed
coupling pattern. Irradiation into the resonance for the methylene
protons 3a–d leads to a collapse of the multiplets into a set of four
doublets due to the remaining coupling with the vinylic protons
1a–d (Fig. 1c).
The 13C NMR spectra exhibit four sets of signals for each carbon
atom, which is consistent with the presence of the C3h and Cs iso-
mers. The carbonyl resonances of the two isomers can be assigned
to the signals between 188.0 and 181.0 ppm, confirmed by HMQC
and HMBC experiments. These chemical shifts are more character-
istic for a C@O double bond rather than for a phenolic C–OH single
bond. Already Claramunt et al. remarked that the CArO resonance
varies from 151 ppm for an enol-imine, like in resonance structure
I, to 180 ppm for a pure keto-enamine tautomer, like in resonance
structure IV, and is therefore the parameter which is most sensitive
towards the relative tautomeric population [44].
In conclusion, the aldimine-based ligand H3felddien has to be
described, like the recently reported H3felden, [32] as the N-pro-
tonated tautomer with strong contributions of the radialene-like
resonance structure IV. Moreover, this appears to apply not only
for our aldimine-based compounds, but to all our ketimine-based
triplesalen ligands which exhibit either broad (H6talentꢀBu
:
2
185.6 ppm, H6talenNO : 185.9 ppm) [6] or even multiple signals
2
Fig. 1. (a) 1H NMR spectrum of H3felddien in CDCl3 measured at 500 MHz
(H6talen [5]: 185.0–186.2 ppm) for the chemical shift of the CAr
O
(
⁄ = CHCl3) (b) simplification of the 1H NMR spectrum via substitution of NH with
resonance in the 13C NMR spectra. This indicates on the one hand
a strong contribution of a N-protonated radialen-like resonance
structure and on the other hand that also the triplesalen ligands
exist as two isomers in solution.
deuterium oxide in CDCl3 measured at 300 MHz. (c) Simplification of the 1H NMR
spectrum in dmso-d6 via irradiation in the resonances at 3.5 ppm.
3.2.2. [(felddien)Ni3]3+
Since the CArO resonance appears to be a good measure for the
relative contribution of a radialene-like resonance structure, we
synthesized the diamagnetic four-coordinate square-planar com-
plex [(felddien)Ni3](BF4)3 to investigate the electronic structure
of the central unit after metal coordination by NMR spectroscopy.
NMR experiments have been conducted in acetone-d6, dmf-d7,
CD3CN and dmso-d6. However, all spectra exhibit significant line
broadening of the signals which we refer to some paramagnetism
due to coordination of solvent molecules to the NiII ions. Since the
BF4-salt of the complex is insoluble in non-coordinating solvents
ꢀ
Scheme 3.
we performed a salt metathesis. The exchange of BF4 with
ꢀ
B(ArF)4
(=tetrakis(3,5-bis(trifluoromethyl)phenyl)borate) en-
hanced the solubility in CD2Cl2 significantly allowing a detailed
NMR spectroscopic analysis of the complex. The proton NMR spec-
tra are complicated since all protons of the ethylene bridges are
diastereotopic leading to multiplets between 3.8 and 2.1 ppm.
Additionally, this demonstrates that the interconversion of the k
and the d conformations of the chelate rings (vide infra) is slow
on the NMR time scale. This is different to the behavior of
of the acidic NH-protons (proton 2a–d in Scheme 3) with deute-
rium by addition of D2O to a NMR sample leads to the collapse of
the doublets between 8.3 and 8.0 ppm of the vinylic protons (1a–
d) to four singlets (Fig. 1b). The singlet at 8.12 ppm can be assigned
to the three equivalent vinylic protons of the C3h isomer (1a in
Scheme 3) and the three singlets at 8.22, 8.20, and 8.08 ppm to
the three protons (1b, 1c, and 1d) of the particular arms of the Cs
isomer. This experiment also simplified the determination of the
ratio of the two isomers to be ca. 1:1.6 (C3h/Cs) in CDCl3. This diver-
gence from a statistically ratio of the isomers, generated by a ran-
domly orientation of the three enamines, of 1:3 (C3h/Cs) in favor of
the more symmetric compound can be attributed to the NH-ketone
hydrogen bonds in the C3h isomer without competition. The spec-
[(talenX )Ni3] [6]. A characteristic signal of the complex is the
2
imine proton which shows one single resonance at 7.33 ppm. This
is comparable to resonances reported for several NiII salen com-
plexes [45–47]. Of special interest are the 13C NMR resonances of
the central ring. The CArO resonances can be assigned to a signal
at 169.3 ppm, which has been confirmed by HMQC and HMBC
experiments. The triplesalen complexes [(talenX )Ni3] exhibit this
2

3042
B. Feldscher et al. / Polyhedron 30 (2011) 3038–3047
resonance between 170.8 and 172.3 ppm [6], while the mononu-
clear analog [(salen)Ni] shows this signal at 161.0 ppm. Appar-
ently, the NMR shifts observed for the trinuclear complex
[(felddien)Ni3]3+ as well as the trinuclear nickel triplesalen com-
plexes are ꢃ10 ppm higher compared to those reported for mono-
nuclear NiII salen complexes.
In this respect, it is interesting to analyze the relative contribu-
tions of the phenolate-imine and keto-enamine resonance struc-
tures in the mononuclear NiII salen complex. Mg-phenolate
complexes exhibit CArO resonances between 161 and 165 ppm,
[48,49] while Zn-phenolate complexes exhibit these resonances
between 166 and 167 ppm [50]. Quite astonishing, the chemical
shift of ZnII salen complexes has been described between 168
and 174 ppm, [51,52] which is significantly higher compared to
those of 161 ppm in NiII salen complexes. These data exemplify
that there is no simple relation between the extent of a keto-enam-
ine contribution and the 13C NMR chemical shifts for metallated
phenolates, as it is seen in the free ligands. However, the direct
comparison of the mononuclear NiII salen complex to the trinuclear
phloroglucinol-bridged complexes demonstrates that in the latter
there is a significant contribution from the radialene-like reso-
nance structure, but it appears that this contribution is less strong
than in the free ligand.
3.3. Structural characterization
The crystal structure of [(felddien)Ni3](BF4)3ꢁ0.5acetone incor-
porates one cation [(felddien)Ni3]3+ in the asymmetric unit, which
exhibits no crystallographically imposed symmetry (Fig. 2). Se-
lected interatomic distances and angels are summarized in Table 1.
The deprotonated ligand felddien3ꢀ acts as a triple(tetradentate) li-
gand for three NiII ions. The NiII ions are in a square-planar coordi-
nation environment coordinated by one phenolate, one imine, and
two amine donors of the ligand. In contrary to the nickel triplesa-
len complexes the molecule [(felddien)Ni3]3+ shows no significant
ligand folding (Fig. 2b). This is manifested by small distances of the
NiII ions to the best plane through the central ring (dNi = 0.43 Å,
1
dNi = 0.13 Å, dNi = 0.07 Å). The mean values of the Ni–O, Ni–Nimine
,
2
3
Ni–Namine, and Ni–Nterm-amine bond lenghts are 1.84, 1.84, 1.90, and
1.95 Å, respectively. The C–O and the C–C bond distances of the
central ring have mean values of 1.30 and 1.43 Å, respectively.
Of particular value for the experimental evaluation of the rela-
tive contributions of a radialen-like and a benzene-like resonance
structure in the complex are the bond lengths of the central ring
compared with related structures from the literature. A good com-
parison for [(felddien)Ni3]3+ are its mononuclear analog, the phenol
complex A [53–55] (Scheme 4), and [(salen)Ni] [56]. Both com-
plexes exhibit the same mean value for the C–C bond distances
of the central ring of 1.39 Å which is particularly smaller than
the value observed for [(felddien)Ni3]3+ (1.43 Å). This might indi-
cate a prevalence of the benzene-like enolate-imine resonance
structure for the mononuclear compounds [(salen)Ni] and A, and
of the radialene-like keto-enamine resonance structure (IV in
Scheme 1c) for [(felddien)Ni3]3+. However, a close inspection of
Table 1
Selected interatomic distances [Å] and angles [°] for [(felddien)Ni3](BF4)3ꢁ0.5acetone.
Ni1–O11
Ni1–N11
Ni1–N12
Ni1–N13
Ni2–O21
Ni2–N21
Ni2–N22
Ni2–N23
Ni3–O31
Ni3–N31
Ni3–N32
Ni3–N33
O11–C1
O21–C3
O31–C5
N11–C11
N21–C21
N31–C31
C1–C2
1.824(2)
1.841(3)
1.903(3)
1.950(3)
1.839(2)
1.832(3)
1.901(3)
1.941(3)
1.849(2)
1.841(3)
1.910(3)
1.956(3)
1.302(4)
1.305(4)
1.303(4)
1.292(4)
1.294(4)
1.288(4)
1.421(4)
1.434(4)
1.411(5)
1.448(4)
1.410(4)
1.413(5)
1.419(5)
1.414(4)
1.426(4)
O11–Ni1–N11
O11–Ni1–N12
O11–Ni1–N13
N11–Ni1–N12
N11–Ni1–N13
N12–Ni1–N13
O21–Ni2–N21
O21–Ni2–N22
O21–Ni2–N23
N21–Ni2–N22
N21–Ni2–N23
N22–Ni2–N23
O31–Ni3–N31
O31–Ni3–N32
O31–Ni3–N33
N31–Ni3–N32
N31–Ni3–N33
N32–Ni3–N33
Ni1–O11–C1
94.32(11)
176.71(12)
90.36(12)
87.13(12)
170.58(13)
88.63(13)
94.65(11)
177.99(12)
90.47(11)
87.03(13)
173.51(13)
87.93(14)
95.15(11)
174.62(13)
91.22(11)
86.33(12)
168.67(13)
88.19(13)
128.5(2)
C2–C3
C3–C4
C4–C5
C5–C6
Ni2–O21–C3
Ni3–O31–C5
128.7(2)
127.7(2)
Fig. 2. Molecular structure of [(felddien)Ni3]3+ in crystals of [(felddi-
en)Ni3](BF3)4ꢁ0.5 acetone (a) drawn perpendicular to the central benzene ring of
the phloroglucinol backbone, and (b) drawn parallel to the central benzene ring of
the phloroglucinol backbone. (c) Disorder of the ethylene bridge enclosing Ni2 in
the conformation kd 75% (solid line) and dk 25% (dashed line). See text for details.
Hydrogen atoms are omitted for clarity.
C1–C6
C2–C11
C4–C21
C6–C31

B. Feldscher et al. / Polyhedron 30 (2011) 3038–3047
3043
shown in Fig. 2 is a 3:1 mixture of (kd, kd, kd) and (dk, dk, kd), since
the chelating arm of Ni3 exhibits no disorder in the solid state. The
enantiomeric position generated by the crystallographic center of
inversion therefore consists of a mixture of (dk, dk, dk) and (kd, kd,
dk), with the same ratio 3:1, which leads overall to an excess of
the more symmetric isomers compared to a statistical mixture.
The fact that the two isomers can be packed in the same position
in the crystal structure without loss of the 3D regularity shows, that
the alteration in the molecule structure for the isomers is small.
This might be an explanation for the problems we experienced by
obtaining a single-crystal of [(felddien)Cu3]3+ suitable for single-
crystal X-ray diffraction. Moreover, the knowledge of the presence
of these two diasteromeric pairs in solution is important for the use
of these trinuclear complexes for the construction of heptanuclear
complexes by reaction with hexacyanometallates. Only the sym-
metric (kd, kd, kd) and (dk, dk, dk) isomers appear to be ideally pre-
organized for the reaction with a hexacyanometallate.
Scheme 4. Mean value of the bond distances [Å] of three reported structures of the
mononuclear analog of [(felddien)Ni3]3+ the complex A, [53–55] phloroglucinol
bridged B, [57] [(salen)Ni] [56] and the mean value of two tetrahydro salen
[(salan)Ni] complexes.[83,84] (Tp⁄ = tris(3,5-dimethylpyrazolyl)hydroborate).
the central ring of [(salen)Ni] and A reveals a strong spread of the
C–C bond distances which is not observed in the reduced analog
[(salan)Ni] (Scheme 4), although this compound exhibits the same
mean value of 1.39 Å for the central ring. This distribution of the
bond distances indicates a significant contribution of the keto-en-
amine resonance structure even in the mononuclear [(salen)Ni]
and phenol complex A. Another interesting comparison is the
phloroglucinol-bridged trinuclear molybdenum complex B [57],
which has a mean value for the central C–C bond lengths of
1.38 Å. This implies that [(felddien)Ni3]3+ but also [(salen)Ni] and
complex A cannot be regarded as pure phenolate-imine resonance
structures. This remarkable result has also been observed by other
authors for salphen complexes [58–60] and recently discussed by
us for [(salen)Cu] and [(felden){Cu(bpy)}3](ClO4)3 [32].
3.4. Electronic absorption spectroscopy
The electronic absorption spectra of the ligands H3felddien,
H3felden, H6talent-Bu , and H2salen (Fig. 3a) as well as of their Ni
II
2
(Fig. 3b) and CuII complexes (Fig. 3c) are compared to obtain more
insight into the variation of the electronic structures.
H2salen (Fig. 3a) exhibits a transition involving the imine group
around 32000 cmꢀ1 and a transition above 36000 cmꢀ1 which has
been assigned to the phenolic chromophores [61–63]. Contrary,
the spectrum of the ketimine-based ligand H6talent-Bu [6] as well
2
as the aldimine-based ligands H3felddien and H3felden [32] exhibit
two stronger absorption features in the region 26000–35000 cmꢀ1
.
The structure of [(felddien)Ni3]3+ exhibits an interesting disor-
der phenomenon concerning the ethylene diamine units of the
chelating arms of Ni1 and Ni2 (Fig. 2c). Coordinated ethylene dia-
mine units are not planar but exhibit a gauche conformation. The
five-membered chelate rings can adopt two enantiomeric confor-
mations, labeled by k and d (Fig. 2c). The two chelate rings of Ni3
are in the kd conformations, where the first designation (k) refers
to the conformation of the chelate ring involving N31 and N32,
while the second designation (d) refers to the chelate ring involving
N32 and N33. The chelate ring of the pendent arms around Ni2 and
Ni3 exhibit a disorder of kd and dk orientations of 3:1 ratio.
For each of the three ligand compartments of felddien3ꢀ exist
four different stereoisomers: kk, kd, dk, dd. Statistically, the trinu-
clear unit may exhibit 64 conformations (23 ꢂ 23), where several
of these conformations are equivalent by symmetry. However, con-
sidering the situation in Fig. 2c, the position of the methyl group
C25 defines the conformation of both chelate rings: position C25
(i.e. pointing downwards) forces the configuration k in the chelat-
ing Ni2–N22–C24–C23–N21 and the configuration d in the chelate
ring Ni2–N22–C26–C27–N23. The orientation C25B of the methyl
group results in the opposite dk configuration. Thus, the covalent
connection of the two chelate rings reduces the accessible number
of stereoisomers per ligand compartment to two: kd and dk; kk and
dd conformations are not accessible due to the sp3-type hybridiza-
tion of the amine nitrogen donor. This restriction reduces the over-
all number of stereoisomers to four: the enantiomeric pairs (kd, kd,
kd) and (dk, dk, dk) on the one hand and (kd, kd, dk) and (dk, dk, kd)
on the other hand (note that e.g. (kd, kd, dk), (kd, dk, kd) and (dk, kd,
kd) are equivalent by symmetry). These two pairs are diasteromeric
and therefore different in energy.
Therefore, these features cannot be assigned as a three-fold super-
position of the electronic structure of a salen ligand. This has al-
ready been realized in the study on the triplesalen ligands [6,25]
and supports the interpretation of the NMR spectra that the ligand
systems cannot be described in the anticipated benzene-like, but
rather in the radialene-like resonance structure. The absorption
features above 36000 cmꢀ1 are absent in the spectra of H3felddien
and H3felden consistent with the assignment of these transitions to
the terminal enol-imine chromophores of H2salen and H6talent-Bu
.
2
The spectrum of [(salen)Ni] (Fig. 3b) consists of one weak band
at 18400 cmꢀ1
(e
ꢄ 10 Mꢀ1 cmꢀ1) assigned to the d–d transition
(1A1g ? 1A2g; C2v symmetry: dxy ! dx2 ) [62,64–66], three re-
ꢀy2
solved absorption features in the 21000–27000 cmꢀ1 region as-
signed to CT transitions, and absorption features between 27000
and 35000 cmꢀ1 originating from imine
p–
p⁄ transitions.[61] The
complex [(felddien)Ni3]3+ exhibits absorptions in the 20000–
35000 cmꢀ1 region that are distinct from [(salen)Ni] as well as
from [(talent-Bu )Ni3], [6] which allows a self-consistent assignment
2
of these transitions. The absorptions of [(felddien)Ni3]3+ between
27000 and 35000 cmꢀ1 are much more intense than those of [(sale-
n)Ni] while the CT bands in the 21000–27000 cmꢀ1 region are
missing. On the other hand, [(talent-Bu )Ni3] not only exhibits these
2
CT bands but also shows stronger intensities in the 27000–
35000 cmꢀ1 region. This is consistent with the transitions between
27000 and 35000 cmꢀ1 being characteristic for the central bridging
unit being a resonance hybrid of a benzene-like and a radialene-
like resonance structure. In addition to this feature,
[(talent-Bu )Ni3] has additional intensity of imine
p–
p⁄ transitions
2
of the terminal phenolate-imine donors in this 27000–
35000 cmꢀ1 region. The intensity in the 21000–27000 cmꢀ1 region
of [(talent-Bu )Ni3] can thus be assigned to CT transitions of the ter-
2
ꢀ
The crystal structure (space group P1 would require two inde-
pendent positions for one enantiomer of the two enantiomeric
pairs. The other enantiomer would then be generated by the crys-
tallographic center of inversion. However, the asymmetric unit con-
sists only of one position for the trinuclear complex. The position
minal NiII-phenolate-imine units. The d–d transition (inset in
Fig. 3b) is shifted from 18000 cmꢀ1 in [(talent-Bu )Ni3] to
2
22200 cm-1 in [(felddien)Ni3]3+, which is a remarkable experimen-
tal signature of the stronger ligand field of felddien3ꢀ in compari-

3044
B. Feldscher et al. / Polyhedron 30 (2011) 3038–3047
son to (talent-Bu
)
6ꢀ due to strong
r
-donating amine donors and the
p-donor phenolate.
en)Cu3]3+ has a strong absorption feature between 27000 and
35000 cmꢀ1 attributed to the central bridging chromophore. De-
2
absence of the terminal strong
spite this feature, [(talent-Bu )Cu3] has additional intensity between
2
The overall assignment of the nickel complexes can be also ap-
plied to the copper complexes (Fig. 3c). The complex [(felddi-
24000 and 27000 cmꢀ1 and a strong feature at 36000 cmꢀ1, [25]
which are also observed for [(salen)Cu] and are therefore mainly
assigned to the terminal CuII-phenolate-imine chromophore. The
additional strong intensity in [(felden){Cu(bpy)}3]3+ [32] around
32000 is due to CuII ? p⁄ MLCT transitions involving the bpy
ligands.
A
GAUSSIAN analysis of the d–d transitions of [(felddien)Cu3]3+ is
provided in Fig. 3d. The fitting process was performed with a min-
imum number of GAUSSIANS and the line widths of the ligand field
transitions have been correlated to the same value. In order to ob-
tain a good reproduction of the experimental data, the incorpora-
tion of four GAUSSIAN peaks at 13400, 16900, 19500 and
23400 cmꢀ1 and
a less intense but clearly distinct band at
9700 cmꢀ1 was necessary. These d–d transitions are all shifted by
ꢃ1500 cmꢀ1 to higher energy in comparison to [(fel-
den){Cu(bpy)}3]3+ reflecting the stronger
r
-donation of the sp3-
hybridized terminal amines in [(felddien)Cu3]3+ compared to the
sp2-hybridized
N-donor
bipyridine
ligands
in
[(fel-
den){Cu(bpy)}3]3+. Contrarily, the comparison of the d–d transitions
of the square-planar coordinated CuII complex of the tris(tetraden-
tate) triplesalacen ligand H6talacen [(talacen)Cu3] [7] to those of
[(felddien)Cu3]3+ reveals larger shifts in the lower energy d–d tran-
sitions and smaller shifts in the higher energy d–d-transitions
indicative of significant
pared to [(felddien)Cu3]3+
This reduced -contribution (mainly
p-contributions in [(talacen)Cu3] as com-
.
p
p-acceptor) in complexes
of felddien3- shifts the ligand field from a typical ligand field of
four-coordinate NiII complexes to a ligand field which may also sta-
bilize six-coordinate NiII complexes. This is consistent with the
experimental observation of paramagnetic affected NMR spectra
of [(felddien)Ni3]3+ measured in coordinating solvents as CD3CN
indicating an equilibrium between NiII in a diamagnetic square-
planar form and a paramagnetic octahedral form.
This is in conjunction with measurements of the effective mag-
netic moment in CD3CN solution by the Evans method [67,68]. A
rough estimate of 7% NiII in the paramagnetic octahedral form
has been calculated from the solution magnetic moment [69].
The weak band around 11000 cmꢀ1
(e
ꢄ 6 Mꢀ1 cmꢀ1) of [(feld-
dien)Ni3]3+ in acetonitrile (Fig. 4) may be assigned to the
3A2 ? 3T1 transition in octahedral NiII complexes. Recording the
UV–vis spectra in the stronger donor solvent pyridine, a clear
new absorption with small extinction arises at 10950 cmꢀ1
(e
= 26 Mꢀ1 cmꢀ1). Concomitantly, the intensity of the bands as-
Fig. 3. (a) Electronic spectra of the ligands H3felddien, H3felden, H2salen, and
H6talent-Bu all measured in CH3CN. (b) Electronic spectra of the complexes
2
[(felddien)Ni3](BF4)3 (CH3CN), [(talent-Bu )Ni3] (CH2Cl2), and [(salen)Ni] (CH3CN).
2
(c) Electronic spectra of the complexes [(felddien)Cu3](ClO4)3 (CH3CN), [(fel-
den){Cu(bpy)}3](ClO4)3 (CH3CN), [(talent-Bu )Cu3] (CH2Cl2), and [(salen)Cu] (CH3CN).
2
(d) GAUSSIAN fit to the d–d region of [(felddien)Cu3](ClO4)3. Thin lines represent the
GAUSSIAN peaks, the thick solid line their sum, and the open circles the experimental
data.
Fig. 4. d–d Region of the electronic spectra of [(felddien)Ni3](BF4)3 in pyridine and
CH3CN.

B. Feldscher et al. / Polyhedron 30 (2011) 3038–3047
3045
signed to the d–d transitions of the square-planar NiII ions de-
creases roughly by 30% in intensity. This indicates that even in pyr-
idine solution the major species is still four-coordinate. However,
this borderline situation of the ligand field between favoring a
four- and a sixfold-coordination for NiII might make the complex
suitable for the preparation of a [NiII6Mc]n+ heptanuclear com-
pound by reaction with hexacyanometallates. The electrostatic
interactions between the [(felddien)Ni3]3+ cation and the
[Mc(CN)6]3ꢀ anion should be an additional driving force for the for-
mation. Such a heptanuclear complex should have interesting
magnetic properties, as the interaction of a central metal ion like
CrIII, FeIII l.s., OsIII l.s., MnIII l.s. with unpaired electrons in the t2g
orbitals and NiII with unpaired electrons in the eg. orbitals might
lead to ferromagnetic exchange couplings by the orthogonality of
the magnetic orbitals [70–73].
The CV of [(felddien)Cu3]3+ shows one irreversible reduction
wave at Ep,red = ꢀ1.50 V, which can be assigned to the CuII/CuI re-
dox couple [76]. At positive potentials [(felddien)Cu3]3+ shows a
reversible oxidation at E1/2 = 0.80 V followed by two irreversible
oxidation waves at Ep,ox = 1.24 and 1.45 V. The triplesalen complex
[(talent-Bu )Cu3] exhibits at ꢀ30 °C three reversible waves at 0.26,
2
0.59, and 0.81 V oxidation waves [25].
The overall anodic shift of the potentials of the complexes with
felddien3ꢀ versus (talent-Bu
)
might reflect the strong electron
6ꢀ
2
density provided by p-donor effects of the terminal phenolato do-
nor ligand in triplesalen complexes.
3.6. Spectroelectrochemistry
We have followed the formation of the oxidized species [(feld-
dien)Cu3]4+ by UV–vis spectroscopy during a CV in an OTTLE cell at
ambient temperature, which took roughly 2 min (inset of Fig. 5b).
The oxidized species exhibits an increased absorption at
26800 cmꢀ1, which is characteristic for the formation of phenoxyl
radicals [77–80]. A similar intensity increase has been observed in
3.5. Electrochemistry
Cyclic and square-wave voltammograms of [(felddi-
en)Ni3](BF4)3 and [(felddien)Cu3](ClO4)3 have been recorded in
acetonitrile solutions containing 0.1 M [NBu4]PF6 as supporting
electrolyte and representative examples of the CVs are provided
in Fig. 5. The CV of [(felddien)Ni3]3+ shows three reversible reduc-
tion waves with E1/2 of ꢀ1.69, ꢀ1.88, and ꢀ2.10 V (all potentials
are referenced vs Fc+/Fc couple) which might be attributed to
NiII/NiI couples [74,75] and one irreversible oxidation wave with
[(talent-Bu )Cu3] , but was obscured by the strong absorbance of the
central unit (vide supra), which we have assigned to the oxidation
of the central phloroglucinol unit [25]. Due to the absence of termi-
nal phenolate units in [(felddien)Cu3]3+, the band observed here is
a strong support for this assignment. Further attempts to isolate
the oxidized species are currently in progress in our laboratory.
+
2
Ep,ox = 1.27 V. By contrast, the triplesalen complex [(talent-Bu )Ni3]
2
exhibits no reduction waves and three reversible oxidation waves
with E1/2 of 0.22, 0.55 and 1.00 V [6].
3.7. Magnetochemistry
Temperature-dependent measurements of the magnetic sus-
ceptibility (SQUID, 2–290 K) at different magnetic fields of samples
of [(felddien)Cu3]3+ were performed. The effective magnetic mo-
ment,
leff, is 3.07 lB at 290 K and varies barely by lowering the
temperature and increases only slightly at T ꢄ 60 K and then rap-
idly drops below this maximum to a value of 3.02 lB at 2 K. This
temperature behavior indicates that there are two weak couplings
effective in the system: a weak ferromagnetic coupling and a weak
antiferromagnetic coupling. Both couplings seem to be of the same
order of magnitude and it is therefore difficult to assign either one
to an intra- or an intermolecular interaction. We tried to simulate
the temperature-dependence of leff with the appropriate spin-
Hamiltonian (1) for an equilateral CuII (Si = 1/2) triangle by a
3
full-matrix diagonalization approach including Heisenberg-Dirac-
van Vleck (HDvV) exchange and Zeeman interactions using the pro-
gram package JULX [39]. In this procedure, saturation effects are ta-
ken into account. Intermolecular interactions are modeled by a
Weiss temperature
H. Fitted values of vTIP are subtracted from
the simulated and experimental data.
3
X
H ¼ ꢀ2JðS1S2 þ S2S3 þ S1S3Þ þ
½gi
l
BSiBꢅ
ð1Þ
i¼1
The overall temperature-dependence of leff can be modeled in
two different scenarios: 1. using a weak ferromagnetic intramolec-
ular coupling modeled by the HDvV term including a weak antifer-
romagnetic intermolecular interaction modeled by a negative
Weiss temperature
H; 2. a weak antiferromagnetic intramolecular
interaction modeled by a negative J value including a ferromag-
netic intermolecular interaction modeled by a positive Weiss tem-
perature
H. While the observed temperature-dependence of the
data excludes a definite assignment to one of the two scenarios,
the second scenario seems to be rather unlikely, as it would exhibit
a ferromagnetic intermolecular pathway through space and via
non-magnetic orbitals. Therefore, the scenario of an intramolecular
Fig. 5. (a) CV of [(felddien)Ni3](BF4)3 and (b) CV of [(felddien)Cu3](ClO4)3. Both
spectra recorded at a platinum working electrode at 20 °C {0.1 M [NBu4]PF6} in
CH3CN solution. Scan rate 200 mV sꢀ1. The inset shows the UV–vis spectra of
[(felddien)Cu3](ClO4)3 before (solid line) and after oxidation at 1.1 V (dashed line) in
a CV in an OTTLE cell.
interaction as observed for all other CuII complexes seems to be
3
more realistic. The solid line provided in Fig. 6 is obtained for

3046
B. Feldscher et al. / Polyhedron 30 (2011) 3038–3047
analysis of the structural and spectroscopic data of the trinuclear
nickel complex [(felddien)Ni3]3+ indicates that after coordination
both resonance structures, a radialene-like keto-enamine and a
benzene-like phenolate-imine, have strong contributions. This re-
duced central
p system leads to a relative weak ferromagnetic cou-
pling not only in the trinuclear copper complex of H3felddien but
also in all our other trinuclear copper complexes of modified phlor-
oglucinol ligands.
The substitution of the terminal phenolate-imine donor set in
H2salen and H6talent-Bu by a bis terminal amine donor set changes
2
the preference of the ligand field from a four-coordinate square-
planar coordination environment to a borderline situation for NiII
between a four-coordinate square-planar versus a six-coordinate
octrahedral coordination environment. This tendency of the NiII
ions in felddien3ꢀ complexes to accept suitable donors in the axial
positions makes this complex suitable for the preparation of hepta-
nuclear complexes of the kind [NiII6Mc]n+. These complexes prom-
ise interesting magnetic properties, as the interaction of a central
metal ion like CrIII, FeIII l.s., OsIII l.s., MnIII l.s. with unpaired elec-
trons in the t2g orbitals and NiII with unpaired electrons in the eg.
orbitals may lead to ferromagnetic exchange couplings by the
orthogonality of the magnetic orbitals [70–73].
Fig. 6. Temperature-dependence of the effective magnetic moment, leff, of
[(felddien)Cu3](ClO4)3ꢁ3H2O. The solid line corresponds to the best fits:
J = 0.57 cmꢀ1, g = 2.05,
v
TIP = 430 ꢂ 10ꢀ6 cm3 molꢀ1 and
H
= ꢀ0.70 K.
J = 0.57 cmꢀ1
,
g = 2.05,
v
TIP = 430 ꢂ 10ꢀ6 cm3 molꢀ1
,
and
H
= ꢀ0.70 K. The decrease of leff at lower temperatures is thus
due to the combined effect of Zeeman interactions (taken into ac-
count in our analysis), intermolecular antiferromagnetic interac-
tions, and anisotropy of the St = 3/2 ground state. The latter has
Acknowledgment
been observed in several ferromagnetically coupled CuII com-
3
This work was supported by the DFG (FOR945 ‘Nanomagnets:
from Synthesis via Interactions with Surfaces to Function’), the
Fonds der Chemischen Industrie, and Bielefeld University.
plexes [24,81,82].
All trinuclear copper complexes based on extended phloroglu-
cinol ligands exhibit ferromagnetic interactions with coupling con-
stants in the range of J = 1.02–3.31 cmꢀ1 [4,7,24,25,32]. This
means, that [(felddien)Cu3]3+ has the lowest coupling constant
yet observed in extended phloroglucinol ligands. The pronounced
low coupling in [(felddien)Cu3]3+ can probably be attributed to
the interplay of ferromagnetic and antiferromagnetic interactions.
As we already discussed for CuII triplesalen complexes [22,25] the
ligand folding of the complexes is crucial for a ferromagnetic inter-
Appendix A. Supplementary data
CCDC-802298 contains the supplementary crystallographic
data for this paper. These data can be obtained free of charge
http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the
Cambridge Crystallographic Data Centre, 12 Union Road, Cam-
bridge CB2 1EZ, UK; fax: (+44)1223-336-033; or e-mail:
deposit@ccdc.cam.ac.uk.
action via the central ring. In almost planar complexes the mag-
netic CuIIdx2
orbital and the phenolate
O
p
orbital are
p
ꢀy2
orthogonal to each other and therefore the overlap integral is zero,
resulting in no spin-delocalization onto the phenolate oxygen atom
[22]. A slight bending of the basal plane relative to the central
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We have synthesized the new ligand H3felddien, which is an
extension of our previously reported ligand H3felden, and its trinu-
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