Heteroleptic Cu(II) dipyrromethene complexes linked via hydrogen bonds, coordinative bonds, and covalent bonds: Probing the coordination environment by electron paramagnetic resonance spectroscopy

Article abstract of DOI:10.1021/ic0515047

meso-Phenyldipyrromethene acetylacetonato copper(II) complexes [Cu(dpm-C₆H₄R)(acac)] (dpm-C₆H₄R = phenyl-substituted dipyrromethene, acac = acetylacetonato) with different substituents R at the phenyl moiety were synthesized. These substituents determine the mode of assembly into polymeric chains, namely, via hydrogen bonds, coordinative bonds, or covalent bonds (by immobilization on a polymer). Although the primary coordination sphere around the copper center is essentially identical for all complexes reported in this study (square-planar geometry with N₂O₂ coordination), subtle differences due to the different microenvironments have been observed in their structures, properties, and reactivity as probed by IR spectroscopy, electron paramagnetic resonance spectroscopy, magnetic measurements, thermal analyses, density functional theory calculations, and reaction with pyridine.

Full text of DOI:10.1021/ic0515047

Inorg. Chem. 2006, 45, 2695−2703
Heteroleptic Cu(II) Dipyrromethene Complexes Linked via Hydrogen
Bonds, Coordinative Bonds, and Covalent Bonds: Probing the
Coordination Environment by Electron Paramagnetic Resonance
Spectroscopy
Katja Heinze* and Anja Reinhart
Department of Inorganic Chemistry, UniVersity of Heidelberg, Im Neuenheimer Feld 270,
69120 Heidelberg, Germany
Received September 2, 2005
meso-Phenyldipyrromethene acetylacetonato copper(II) complexes [Cu(dpm-C6H4R)(acac)] (dpm-C6H4R
) phenyl-
substituted dipyrromethene, acac
) acetylacetonato) with different substituents R at the phenyl moiety were
synthesized. These substituents determine the mode of assembly into polymeric chains, namely, via hydrogen
bonds, coordinative bonds, or covalent bonds (by immobilization on a polymer). Although the primary coordination
sphere around the copper center is essentially identical for all complexes reported in this study (square-planar
geometry with N2O2 coordination), subtle differences due to the different microenvironments have been observed
in their structures, properties, and reactivity as probed by IR spectroscopy, electron paramagnetic resonance
spectroscopy, magnetic measurements, thermal analyses, density functional theory calculations, and reaction with
pyridine.
Introduction
Self-complementary copper(II) complexes of meso-
substituted pyridyl- and thioether-dipyrromethene (dpm)
ligands have been employed by Cohen and co-workers to
form coordination polymers and discrete oligomeric struc-
tures by linking the complexes through coordination
bonds.20-23 The use of different glues to assemble molecular
complexes is expected to modify the properties of the
There is currently an intense research effort to develop
coordination polymers based on molecular precursors held
together by forces of varying strength such as hydrogen
bonds, coordinative bonds, and covalent bonds for magnetic
and electronic materials as well as new classes of adsorbents,
sensors, and storage materials.1,2 The covalent immobilization
of complexes on polymers has been used in heterogeneous
catalysis,3,4 chromatography,5 and sensing applications6,7 as
well as in metal-complex-assisted solid-phase organic
synthesis8-14 and solid-phase synthesis of metal complexes.15-19
(8) Comely, A. C.; Gibson, S. E.; Hales, N. J. Chem. Commun. 1999,
2075.
(9) Gibson, S. E.; Hales, N. J.; Peplow, M. A. Tetrahedron Lett. 1999,
40, 1417.
(10) Bandoli, C.; Maiorana, S.; Licandro, E.; Casiraghi, L.; Zinzalla, G.;
Senesi, P.; De Magistris, E.; Paio, A.; Marchioro, C. J. Comb. Chem.
2003, 5, 809.
(11) Mensi, N.; Isied, S. S. J. Am. Chem. Soc. 1987, 109, 7882.
(12) Arbo, B. E.; Isied, S. S. Int. J. Pept. Protein Res. 1993, 42, 138.
(13) Maiorana, S.; Seneci, P.; Rossi, T.; Baldoli, C.; Circao, M.; de
Magistris, E.; Licandro, E.; Papagni, A.; Provera, S. Tetrahedron Lett.
1999, 40, 3635.
* To whom correspondence should be addressed. E-mail:
katja.heinze@urz.uni-heidelberg.de. Tel.: (+49)6221-548471. Fax: (+49)-
6221-545707.
(1) Kitagawa, S.; Kitaura, R.; Noro, S.-I. Angew. Chem. 2004, 116, 2388;
Angew. Chem., Int. Ed. 2004, 43, 2334.
(2) Moulton, B.; Zaworotko, M. J. Chem. ReV. 2001, 101, 1629.
(3) Chiral Catalyst Immobilization and Recycling; De Vos, D. E.,
Vankelecom, I. F. J., Jacobs, P. A., Eds.; Wiley-VCH: Weinheim,
Germany, 2000.
(14) Klapdohr, S.; Do¨tz, K. H.; Assenmacher, W.; Hoffbauer, W.; Hu¨sing,
N.; Nieger, M.; Pfeiffer, J.; Popall, M.; Schubert, U.; Trimmel, G.
Chem.sEur. J. 2000, 6, 3006.
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Chem. 2003, 115, 164; Angew. Chem., Int. Ed. 2003, 42, 156.
(5) Shepherd, R. E. Coord. Chem. ReV. 2003, 247, 147.
(6) Albrecht, M.; Gossage, R. A.; Lutz, M.; Spek, A. L.; van Koten, G.
Chem.sEur. J. 2000, 6, 1431.
(7) Wu, D. G.; Ashkenasy, G.; Shvarts, D.; Ussyshkin, R. V.; Naaman,
R.; Shanzer, A.; Cahen, D. Angew. Chem. 2000, 112, 4670; Angew.
Chem., Int. Ed. 2000, 39, 4496.
(15) Heinze, K.; Toro, J. B. Eur. J. Inorg. Chem. 2004, 3498.
(16) Heinze, K.; Jacob, V.; Feige, C. Eur. J. Inorg. Chem. 2004, 2053.
(17) Heinze, K.; Toro, J. B. Angew. Chem. 2003, 115, 4671; Angew. Chem.,
Int. Ed. 2003, 42, 4533.
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10.1021/ic0515047 CCC: $33.50
Published on Web 02/25/2006
© 2006 American Chemical Society
Inorganic Chemistry, Vol. 45, No. 6, 2006 2695

Heinze and Reinhart
Scheme 1. Schematic Formation of Dipyrromethene Copper(II) Containing Polymers via (i) Hydrogen Bonds (X ) C6H4CONHiPr), (ii) Coordinative
Bonds (X ) 3-Pyridyl, 4-Pyridyl, Quinolyl, C6H4SCH3,20-23 and C6H4NO2), and (iii) Covalent Bonds (X ) C6H4COO); L ) Spectator Ligand; N∩N )
Dipyrromethene Ligand
theory) series of programs.26 The B3LYP formulation of density
resulting materials, for example, magnetic behavior, stability,
functional theory was used employing the LANL2DZ or SDD basis
sets for geometry optimizations (unrestricted, no symmetry con-
straints).26 The structures of 2a-2c and model compounds were
characterized as minima by frequency analysis (Nimag ) 0).
Hyperfine coupling constants were obtained using the EPR-II basis
set of Barone for H, C, N, and O, which is specifically optimized
for the evaluation of hyperfine coupling constants.27 For Cu, an
all-electron basis set was used, namely, the 6-311G(d) basis set,
because no optimized basis sets are available for transition metals.28
and reactivity.
Herein, we report on the assembly of dipyrromethene
copper(II) complexes into polymers by comparatively weak
hydrogen bonds and coordinative bonds via self-assembly
processes as well as strong covalent bonds via immobilization
on an insoluble polymer (Scheme 1). The influence of the
different microenvironments on the coordination geometry,
magnetic properties, stability, and reactivity of the dipyr-
romethene copper(II) complexes is probed by a variety of
techniques.
Complex Synthesis. The substituted dipyrromethane 1a, 1b, or
1c (0.5 mmol) was dissolved in CH2Cl2 (20 mL). 2,3-Dichloro-
5,6-dicyano-1,4-benzoquinone (DDQ; 114 mg, 0.5 mmol) was
added, and the solution was stirred for 10 min. [Cu(acac)2] (acac
) acetylacetonato;198 mg, 0.75 mmol) was added as a solid, and
the mixture was stirred for 12 h. The solution was evaporated to
dryness, and the product was purified by column chromatography
(SiO2; 8:1 CH2Cl2/ethyl acetate) to afford dichroic red/green
crystals.
Experimental Section
General Methods. Unless otherwise noted, the starting materials
were obtained from commercial suppliers and used without further
purification. The dipyrromethane precursors 1a-1d were synthe-
sized according to literature procedures.24,25 IR spectra were
recorded on a BioRad Excalibur FTS 3000 spectrometer using CsI
disks. UV/vis spectra were recorded on a Perkin-Elmer Lambda
19, with 0.2 cm cells (Hellma, suprasil). Electron paramagnetic
resonance (EPR) spectra were recorded with a Bruker ELEXSYS
E500 spectrometer (X-band). Xsophe, version 1.0.2â was used for
simulation of the spectra. Mass spectra were recorded on a Finnigan
MAT 8400 spectrometer. Susceptibility measurements were per-
formed on polycrystalline powders or dry polymers on a Quantum
Design MPMS-XL-5 SQUID magnetometer in the temperature
range 2-300 K with an applied field of 0.1 T in gelatin capsules.
The diamagnetic contribution of the polymer was determined in a
separate run. Differential scanning calorimetry (DSC) measurements
were carried out on a Mettler DSC 30 under argon from 30 to 600
°C, at a heating rate of 10 K min-1. Thermogravimetric measure-
ments were carried out on a Mettler TC 15 under argon from 30 to
800 °C, at a heating rate of 10 K min-1. Elemental analyses were
performed by the microanalytical laboratory of the Organic
Chemistry Department at the University of Heidelberg.
2a. Yield: 20%. Anal. Calcd. for C22H20N2O4Cu: C, 60.06; H,
4.58; N, 6.37. Found: C, 60.75; H, 4.54; N, 6.74. EI-MS m/z: 439,
[M+]; 397, [M - C2H2O]+; 340, [M - acac]+. HR-EI m/z: 441.0727
[M+, 65Cu], 439.0744 [M+, 63Cu] (Calcd. m/z: 441.0715, 439.0819).
UV/vis (CH2Cl2) λmax (ꢀ/L mol-1 cm-1): 305 (19 600), 494 nm
(32 900). IR (CsI) ν: 1724 (s, CdOester), 1582 (s, acac), 1555 (s,
dpm), 1404 (s, dpm), 1381 (s, dpm), 1339 (s, dpm), 1281 (s, C-O),
1246 (s, dpm) cm-1
.
(26) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb,
M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.; Kudin,
K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone,
V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G.
A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.;
Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai,
H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.;
Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R.
E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J.
W.; Ayala, P. Y.; Morokuma, K.; Voth, G. A.; Salvador, P.;
Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich, S.; Daniels, A. D.;
Strain, M. C.; Farkas, O.; Malick, D. K.; Rabuck, A. D.; Raghavachari,
K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.;
Cioslowski, J.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.;
Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.;
Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.;
Johnson, B.; Chen, W.; Wong, M. W.; Gonzalez, C.; Pople, J. A.
Gaussian 03, revision B.03; Gaussian, Inc.: Wallingford, CT, 2004.
(27) Barone, V. In Recent AdVances in Density Functional Methods; Chong,
D. P., Ed.; World Scientific Singapore: Singapore, 1995; Part 1.
(28) Munzarova´, M.; Kaupp, M. J. Phys. Chem. A. 1999, 103, 9966.
Computational Method. Density functional calculations were
carried out with the Gaussian03/DFT (DFT ) density functional
(21) Halper, S. R.; Cohen, S. M. Angew. Chem. 2004, 116, 2439; Angew.
Chem., Int. Ed. 2004, 43, 2385.
(22) Halper, S. R.; Cohen, S. M. Inorg. Chem. 2005, 44, 4139.
(23) Do, L.; Halper, S. R.; Cohen, S. M. Chem. Commun. 2004, 2662.
(24) Heinze, K.; Reinhart, A. Z. Naturforsch., B: Chem. Sci. 2005, 60,
758.
(25) Littler, B. J.; Miller, M. A.; Hung, C.-H.; Wagner, R. W.; O’Shea, D.
F.; Boyle, P. D.; Lindsey, J. S. J. Org. Chem. 1999, 64, 1391.
2696 Inorganic Chemistry, Vol. 45, No. 6, 2006

Heteroleptic Cu(II) Dipyrromethene Complexes
Table 1. X-ray Data for 2a, 2b, and 2c
2b. Yield: 23%. Anal. Calcd. for C24H25N3O3Cu: C, 61.72; H,
5.40; N, 9.00. Found: C, 60.90; H, 5.40; N, 8.60. EI-MS m/z: 466,
[M+]; 424, [M - C2H2O]+; 367, [M - acac]+. HR-EI m/z:
468.1199 [M+, 65Cu], 466.1255 [M+, 63Cu] (Calcd. m/z: 468.1190,
466.1292). UV/vis (CH2Cl2) λmax (ꢀ/L mol-1 cm-1): 303 (19 400),
494 nm (30 400). IR (CsI) ν: 3264 (m, NH), 1628 (s, CdOamide),
1585 (s, acac), 1562 (s, CN), 1547 (s, dpm), 1408 (s, dpm), 1377
2a
2ba
2c
empirical formula
fw
C22H20N2O4Cu C24H24N3O3Cu C20H17N3O4Cu
439.94
466.00
426.91
P21/c (No.14)
space group
P21/c (No.14) Cc (No. 9)
a ) 10.144(2) a ) 9.4560(19) a ) 13.917(3)
b ) 23.902(5) b ) 36.660(7) b ) 8.9550(18)
c ) 8.3310(17) c ) 6.8970(14) c ) 14.856(3)
unit cell dimensions
(Å, deg)
(s, dpm), 1335 (s, dpm), 1261 (m), 1242 (s, dpm) cm-1
.
R ) 90
R ) 90
R ) 90
â ) 105.81(3) â ) 114.51(3) â ) 93.21(3)
2c. Yield: 20%. Anal. Calcd. for C20H17N3O4Cu: C, 56.27; H,
4.01; N, 9.84. Found: C, 55.73; H, 3.98; N, 9.82. EI-MS m/z: 426,
[M+]; 327, [M - acac]+. HR-EI m/z: 428.0514 [M+, 65Cu],
426.0518 [M+, 63Cu] (Calcd. m/z: 428.0510, 426.0615). UV/vis
(CH2Cl2) λmax (ꢀ/L mol-1 cm-1): 304 (20 100), 496 nm (29 600).
IR (CsI) ν: 1593 (s, acac), 1554 (s, dpm), 1520 (s, NOasym), 1404
(s, dpm), 1377 (s, dpm), 1350 (s, NOsym), 1339 (s, dpm), 1246 (s,
γ ) 90
1943.5(7), 4
200
0.710 73
1.504
γ ) 90
2175.5(8), 4
200
0.710 73
1.423
γ ) 90
1848.5(6), 4
200
0.710 73
1.534
V (Å3), Z
temp (K)
λ (Å)
D
calcd (mg m-3
)
µ (mm-1
)
1.156
1.035
1.214
final R indices [I > 2σ(I)]b R1 ) 0.0413
R1 ) 0.0792
R1 ) 0.0665
wR2 ) 0.0931 wR2 ) 0.1942 wR2 ) 0.1531
final R indices (all data)b R1 ) 0.0722
R1 ) 0.1343
R1 ) 0.1221
dpm) cm-1
.
wR2 ) 0.1054 wR2 ) 0.2390 wR2 ) 0.1821
1e. Wang resin (loading ca. 0.6-1.0 mmol g-1; 500 mg; ca. 0.3-
0.5 mmol) was suspended in CH2Cl2 (10 mL). 1d (266 mg, 1.0
mmol) was dissolved in a minimum amount of N,N-dimethylfor-
mamide (DMF), and the solution was added to the resin. 4-(Di-
methylamino)pyridine (DMAP; 6 mg, 0.05 mmol) and N,N′-
diisopropylcarbodiimide (DIC; 128 mg, 1.0 mmol) were added, and
the suspension was stirred for 16 h. Unreacted OH groups of the
resin were protected by the addition of acetic anhydride (100 mg,
0.5 mmol) and pyridine (80 mg, 0.5 mmol) and stirring for 30 min.
The resin was collected by filtration; washed with DMF (3×), CH2-
Cl2 (2×), ethanol (1×), and CH2Cl2 (3×); and dried in vacuo. IR
a The crystal examined was a racemic twin with Flack x ) 0.48(3). b R1
) ∑|Fo - Fc|/|Fo|. R2 ) {∑[w(Fo - Fc )2]/∑[wFo ]}1/2
.
2
2
4
Scheme 2. Synthesis of [Cu(dpm-C6H4R)(acac)] Complexes 2a-2c;
R ) COOMe, CONHiPr, and NO2
(CsI) ν: 3417 (NH), 1720 (CdOester) cm-1
.
2d. 1e (500 mg, 0.3 mmol) was suspended in CH2Cl2 (30 mL).
DDQ (228 mg, 1.0 mmol) was added, and the suspension was
stirred for 10 min. [Cu(acac)2] (396 mg, 1.5 mmol) was added,
and the mixture was stirred for 12 h. The resin was collected by
filtration, washed with DMF until the filtrate was colorless, and
washed alternately with CH2Cl2 and ethanol (5×). After drying in
vacuo, a green-reddish shining dark resin was obtained. IR (CsI)
dures.24,25 Oxidation of the dipyrromethanes to the corre-
sponding dipyrromethenes was accomplished by DDQ.
Subsequent reaction with a slight excess of [Cu(acac)2] gave
red solutions from which the heteroleptic complexes 2a-2c
(Scheme 2) were obtained by column chromatography.
UV/vis and IR spectroscopy as well as mass spectrometry
confirmed the formation of the desired heteroleptic com-
plexes. In the UV/vis spectra, the characteristic charge-
transfer bands20 of heteroleptic [Cu(dpm)(acac)] complexes
are observed at 494 nm, while the IR spectra show signals
due to the dpm and acac ligands.20 In addition, for 2a, signals
at 1724 and 1281 cm-1 characteristic for unperturbed ester
groups are observed in the IR spectrum, while 2b displays
signals at 3264 cm-1 (amide A), 1628 cm-1 (amide I), and
1562 cm-1 (amide II) characteristic for hydrogen-bonded
amide groups. Thus, the IR data of 2b provide evidence for
self-assembly of the complexes via hydrogen bonds (see
below). The bands for the asymmetric and symmetric NO
stretching vibrations of the nitro group present in 2c are
observed at 1520 and 1350 cm-1. The EI mass spectra show
signals for molecular ions with expected isotopic distribution,
further confirming the successful synthesis of 2a-2c.
The heteroleptic copper complexes are immobilized on a
polymer by a two-step procedure (Scheme 3). The dipyr-
romethane ligand precursor 1d24 is attached to insoluble
Wang resin (polystyrene-bound 4-benzyloxybenzyl alcohol;
0.6-1.0 mmol g-1; 1% divinyl benzene) via esterification
ν: 1721 (s, CdOester), 1407 (w, dpm), 1343 (w, dpm) cm-1
.
X-ray Crystallographic Analysis. The measurements were
carried out on an Enraf-Nonius Kappa CCD diffractometer using
graphite-monochromated Mo KR radiation. The data were processed
using the standard Nonius software.29 All calculations were
performed using the SHELXT PLUS software package. Structures
were solved using direct or Patterson methods with the SHELXS-
97 program and refined with the SHELXL-97 program.30 Graphical
handling of the structural data during refinement was performed
using XMPA31 and WinRay.32 Atomic coordinates and anisotropic
thermal parameters of the non-hydrogen atoms were refined by full-
matrix least-squares calculations. Data relating to the structure
determinations are collected in Table 1.
Results and Discussion
Synthesis of Heteroleptic Complexes. The dipyrromethanes
1a-1c were synthesized according to literature proce-
(29) Hooft, R. Collect; Nonius: The Netherlands, 1998. http://www.non-
ius.com (accessed Feb 2006).
(30) (a) Sheldrick, G. M. SHELXS-97; University of Go¨ttingen: Go¨ttingen,
Germany, 1997. Sheldrick, G. M. SHELXL-97; University of Go¨ttin-
gen: Go¨ttingen, Germany, 1997. http://shelx.uni-ac.gwdg.de/SHELX/
index.html (accessed Feb 2006). (b) International Tables for X-ray
Crystallography; Kynoch Press: Birmingham, U.K., 1974; Vol. 4.
(31) Zsolnai, L.; Huttner, G. XPMA: University of Heidelberg: Heidelberg,
Germany, 1998. http://www.rzuser.uni-heidelberg.de/∼il1/laszlo/
xpm.html (accessed Feb 2006).
(32) Soltek, R.; Huttner, G. WinRay; University of Heidelberg: Heidelberg,
Germany, 1999. http://www.uni-heidelberg.de/institute/fak12/AC/hutt-
ner/frame/frame_soft.html (accessed Feb 2006).
Inorganic Chemistry, Vol. 45, No. 6, 2006 2697

Heinze and Reinhart
Scheme 3. Immobilization of [Cu(dpm-C6H4R)(acac)] on Wang
Resin
Table 2. Selected Bond Lengths (Å) and Angles (deg) for 2a-2c
2a
2b
2c
Cu1-N1
1.951(2)
1.956(2)
1.9282(19)
1.9380(18)
91.57(9)
177.41(9)
89.08(8)
88.82(8)
171.10(9)
90.93(8)
-73.1(3)
4.5
1.976(7)
1.952(8)
1.929(6)
1.924(7)
90.6(3)
176.1(3)
91.3(3)
87.7(3)
1.963(4)
1.966(4)
1.938(3)
1.937(3)
90.47(16)
178.66(15)
89.30(15)
88.66(15)
179.05(14)
91.55(13)
-64.9(6)
5.2
Cu1-N2
Cu1-O2
Cu1-O3
N1-Cu1-N2
N1-Cu1-O2
N1-Cu1-O3
N2-Cu1-O2
N2-Cu1-O3
O2-Cu1-O3
C3-C4-C8-C9
Cu‚‚‚Cu (shortest)
ωa
176.5(3)
90.6(3)
-61(1)
6.3
9.2
4.6
1.4
a Angle between CuO2 and CuN2 planes.
using DMAP and DIC as activators. This reaction is easily
monitored by IR spectroscopy19,33 because characteristic
bands of the immobilized dipyrromethane appear at 3417
cm-1 (NH stretching vibration) and 1720 cm-1 (CO stretch-
ing vibration) in the IR spectrum of the washed and dried
yellow polymer.
Notably, the signal of the NH stretching vibration of 1e
appears at a higher energy as compared to that of 1a-1d
(∼3350 cm-1).24 For 1a-1d, intermolecular hydrogen bonds
between the pyrrole NH groups and the substituent R have
been observed in the solid state.24,34 Obviously, this inter-
molecular interaction is suppressed by the polymer; that is,
site isolation35,36 of the dipyrromethanes seems to be opera-
tive under the conditions used (loading, cross-linking).
The immobilized dipyrromethane is oxidized by DDQ to
the corresponding dipyrromethene and coordinated to the Cu-
(acac) fragment to give dark reddish-green 2d analogously
to the synthesis of the soluble complexes 2a-2c.
Figure 1. Structural diagram of 2a with atom numbering scheme (hydrogen
atoms omitted).
The absence of bands for NH stretching vibrations in the
IR spectrum of 2d confirms the successful oxidation and
complexation. The band for the CO stretching vibration of
the ester remains unchanged as expected, while in the
fingerprint region, new weak signals appear at 1407 and 1343
cm-1, which can be assigned to dpm vibrations. All of the
other characteristic bands of [Cu(dpm)(acac)] complexes are
obscured by the signals of the polystyrene polymer.
Solid-State Structures of 2a-2c. Lustrous dichroic red/
green crystals typical for complexes of dpm ligands were
obtained from solutions of 2a-2c. All of the complexes
exhibit essentially square-planar geometry with Cu-N and
Cu-O bond lengths of 1.96 and 1.93 Å, respectively, similar
to other [Cu(dpm)(acac)] complexes (Table 2).20-23 The aryl
substituents are twisted out of plane with the dpm π system
by 66°.
Figure 2. Structural diagram of 2b with partial atom numbering scheme
(hydrogen atoms omitted, except H1).
between the copper ion and the nitro group of a neighboring
molecule (O1‚‚‚Cu1 ) 2.96 Å37) furnish a square-pyramidal
[4 + 1] coordination geometry of the copper center (Figure
3) similar to pyridyl and C6H4SCH3 meso-substituted [Cu-
(dpm)(acac)] complexes.20-23 The long O1‚‚‚Cu1 distance
is probably the result of “packing effects” in the crystal lattice
rather than the formation of a strong copper-oxygen bond
(no aggregation is observed in solution), but the intermo-
lecular contact influences the properties of the solid material
(see below). Thus, the nature of the remote substituent
determines the mode of interaction in the solid state (no
interaction, hydrogen bonds, or coordinative contacts).
DFT Modeling of 2a-2c. The geometries of 2a-2c and
the parent complex [Cu(dpm)(acac)] were modeled by DFT
The ester-substituted complex 2a crystallized as discrete
complex molecules showing no short intermolecular contacts
(Figure 1). As inferred from the IR data, the amide-
substituted complex 2b displays hydrogen bonding between
the amide groups with N3‚‚‚O1 ) 2.85(1) Å (Figure 2),
resulting in chains of molecules. In the crystal of 2c, contacts
(33) Yan, B. Acc. Chem. Res. 1998, 31, 621.
(34) Patra, G. K.; Diskin-Posner, Y.; Goldberg, I. Acta Crystallogr., Sect.
E 2002, 58, o530.
(35) Hodge, P. Chem. Soc. ReV. 1997, 26, 417.
(36) Scott, L. T.; Rebek, J.; Ovsyanko, L.; Sims, C. L. J. Am. Chem. Soc.
1977, 99, 625.
(37) For an example of Ar-NO2 coordination to Cu(II), see: Kazak, C.;
Yilmaz, V. T.; Yazicilar, T. K. Acta Crystallogr., Sect. E 2004, 60,
m593.
2698 Inorganic Chemistry, Vol. 45, No. 6, 2006

Heteroleptic Cu(II) Dipyrromethene Complexes
Table 3. Selected Bond Lengths (Å) and Angles (deg) for 2a, 2b, and 2c and the Model Complexes [Cu(dpm)(acac)] and [Cu(dpm)(acac)(py)]
(B3LYP and LANL2DZ/SDD Basis Sets)
2a
2b
2c
[Cu(dpm)(acac)]a
[Cu(dpm)(acac)(py)]a
Cu1-N1
1.970/1.960
1.970/1.960
1.981/1.970
1.980/1.970
91.5/92.0
178.2/177.8
90.1/89.8
90.1/89.8
178.2/177.8
88.4/88.3
-61.8/-62.1
1.3/1.6
1.970/1.959
1.970/1.959
1.982/1.970
1.982/1.970
91.4/92.0
178.0/177.6
90.1/89.9
90.1/89.9
178.1/177.6
88.3/88.3
-61.5/-61.7
1.6/2.2
1.972/1.962
1.972/1.962
1.979/1.967
1.979/1.967
91.4/92.0
178.4/178.1
90.3/89.8
90.0/89.8
178.4/178.1
88.5/88.5
-62.6/-62.8
1.2/0.9
1.967
1.967
1.969
1.969
93.1
177.7
89.2
89.2
1.992
1.990
2.004
2.006
92.5
167.7
88.9
88.6
Cu1-N2
Cu1-O2
Cu1-O3
N1-Cu1-N2
N1-Cu1-O2
N1-Cu1-O3
N2-Cu1-O2
N2-Cu1-O3
O2-Cu1-O3
C3-C4-C8-C9
ωb
177.7
88.5
171.2
88.2
0.0
a SDD basis set. b Angle between CuO2 and CuN2 planes.
Table 4. Magnetic and EPR42 Data of 2a-2d
2a
2b
2c
2da
µ
eff (300 K)/µB
1.76
0.385
-0.93
2.119
77
10
2.230
185
1.79
0.421
+2.37
2.118
77
10
2.230
185
1.75
0.409
+3.08
2.116
79
1.70
C/emu K mol-1 b
0.385
-0.04
2.116
76
θ/Kb
giso
A
A
iso(Cu)/G
iso(N)/G
11
n.o.c
2.226c
177d
n.o.c
2.05d
14d
g|
2.230
185
A|(Cu)/G
A|(N)/G
g
11.6
2.05
15
11.6
2.05
15
n.o.c
2.05
15
A (N)/G
a Calculated for M ) 5000 g mol-1 corresponding to a loading of 0.2
mmol g-1 b Fitted using the Curie-Weiss law øM ) C/(T - θ) in the
.
temperature range 2-300 K (see the Supporting Information). c n.o., not
observed. d These measurements were performed at 300 K without adding
solvent to the resin.
Figure 3. Structural diagram of 2c with partial atom numbering scheme
(hydrogen atoms omitted).
) 0.383-0.403 emu K mol-1) at 300 K as expected for
1
noninteracting S ) /2 systems.
For 2a, the product øMT remains constant down to ca. 50
K and drops to 0.291 emu K mol-1 at 2 K (Figure 4),
indicative of weak antiferromagnetic interactions (Weiss
constant θ ) -0.93 K), while for 2b and 2c, øMT increases
to 0.47 emu K mol-1 at 4.6 K, indicative of weak ferro-
magnetic coupling (θ ) +2.37 K and +3.08 K, respectively).
It is reasonable to ascribe the different magnetic behaviors
to the different environments in the crystal structures.
In the crystal structure of 2a, the complexes are stacked
along the c axis with Cu‚‚‚Cu distances of 4.5 Å (Table 2,
Supporting Information), which could be the reason for the
observed antiferromagnetic coupling (Scheme 4). For 2b and
2c, the Cu‚‚‚Cu contacts are larger (Table 2) while these
complexes are connected through hydrogen bonds and
coordinative bonds, respectively, so that spin polarization
along the dpm-C6H4R backbone could lead to the ferromag-
netic coupling (Scheme 4).
Figure 4. Variable-temperature magnetic data for 2a (O), 2b (4), 2c (b),
and 2d (9).
calculations at the B3LYP level. The square-planar coordina-
tion environment (ω) and the torsion angle C3-C4-C8-
C9 are well reproduced by the calculations. However, with
the LANL2DZ basis set, the Cu-O and Cu-N bond lengths
are overestimated by 0.05 and 0.01 Å, respectively (Tables
2 and 3). A better agreement with the experimental structures
(Table 2) is obtained using the SDD pseudopotential (Table
3), so the SDD-derived geometry is used for further
calculations (see below).
The immobilized copper complex 2d, however, behaves
as an almost ideal paramagnet (θ ) -0.04 K; øMT ) 0.362
emu K mol-1 at 2 K). Thus, magnetic dilution of the spin
carriers in the polymer is sufficient to prevent intermolecular
magnetic interactions. This finding is also consistent with
the absence of hydrogen-bonding interactions in the copper-
free polymer 1e (see above).
Magnetic Properties of 2a-2d. The temperature depen-
dence of the product øMT of microcrystalline 2a-2d has been
measured at 0.1 T from 2 to 300 K (Figure 4, Table 4).
Complexes 2a-2c are paramagnetic with µeff ) 1.76 µB (øMT
The loading of polymer 2d was 0.18 mmol g-1, determined
by integrating the EPR signal of 2d (see below) using a
Inorganic Chemistry, Vol. 45, No. 6, 2006 2699

Heinze and Reinhart
Scheme 4. Possible Magnetic Interaction Pathways in 2a-2c
Figure 5. Isotropic X-band EPR spectra of 2a-2d in THF at 300 K.
calibration curve of mechanically mixed polystyrene/divinyl
benzene polymers and 2a (Supporting Information). This
value confirms the molecular mass estimated from magnetic
measurements (5000 g mol-1; 0.2 mmol g-1). Thus, statisti-
cally, every complex unit in 2d is surrounded by 45-50
styrene units of the polymer, accounting for the observed
magnetic dilution.
EPR Spectroscopy of 2a-2d. The X-band EPR spectra
of 2a-2c were measured in solution at room temperature
and in frozen solution at low temperature, while 2d was
investigated in the tetrahydrofuran (THF) gel phase at room
temperature and low temperature and in the dry state at room
Figure 6. Top: anisotropic X-band EPR spectra of 2a-2c (130 K, THF)
and 2d (300 K, solid; 130 K, THF). Bottom: expansion of the g| region
for 2b and 2d.
temperature is similar to that observed for 2a-2c in a
solution environment.40,41
The A|(Cu) values obtained from X-band EPR spectra in
a frozen solution (Figure 6)42 also reflect the difference in
the coordination environment between square-planar 2a-
2c [A|(Cu) ) 185 G] and distorted homoleptic [Cu(dpm)2]
complexes [A|(Cu) < 165 G38]. Similar observations have
been reported for planar and saddled copper porphyrin
complexes [A|(Cu,planar) ) 220 G; A|(Cu,saddled) ) 209
G].43
temperature (Table 4). From the isotropic spectra, giso
∼
2.117, Aiso(Cu) ∼ 77 G, and Aiso(N) ∼ 10 G can be derived
(Figure 5). The isotropic hyperfine coupling to the copper
nucleus in 2a-2d is significantly larger than that observed
for bis(dipyrromethene) complexes [Cu(dpm)2] [Aiso(Cu) ∼
63 G38]. This finding can be ascribed to the larger twisting
of the ligand planes in homoleptic complexes (ω ∼ 44° 39
)
(40) Vaino, A. R.; Goodin, D. B.; Janda, K. D. J. Comb. Chem. 2000, 2,
330.
as compared to that of the square-planar heteroleptic
complexes 2a-2d with less steric congestion. Thus, the
room-temperature EPR data confirm the square-planar
geometry of the complexes in solution (2a-2c) and in the
THF-swollen polymer (2d). In addition, the mobility of the
immobilized copper complexes in the gel phase at room
(41) Regen, S. L. J. Am. Chem. Soc. 1974, 96, 5275.
(42) The anisotropic EPR spectrum of 2b has been simulated with Xsophe
using the following parameters: natural isotope distribution 63/65Cu,
14/15N; g- and A-strain Gaussian line shape model; matrix diagonal-
ization; 25 θ orientations; five field segments; orthorhombic symmetry;
gx ) 2.042; gy ) 2.054; gz ) 2.230; Ax(Cu) ) Ay(Cu) ) 25 G; Az(Cu)
) 185 G; Ax(N) ) Ay(N) ) 15 G; Az(N) ) 11.6 G. In the text, gx and
gy are expressed as g|, gz is expressed as g , Ax and Ay are expressed
as A|, and Az is expressed as A for convenience.
(38) Murakami, Y.; Matsuda, Y.; Sakata, K. Inorg. Chem. 1971, 10, 1734.
(39) Halper, S. R.; Cohen, S. M. Chem.sEur. J. 2003, 9, 4661.
(43) Shao, J.; Steene, E.; Hoffman, B. M.; Ghosh, A. Eur. J. Inorg. Chem.
2005, 1609.
2700 Inorganic Chemistry, Vol. 45, No. 6, 2006

Heteroleptic Cu(II) Dipyrromethene Complexes
Table 5. Selected Isotropic and Anisotropic Hyperfine Coupling Constants, Mulliken Spin Populations, Natural Atomic Charges, and Natural Electron
Configurations of Selected Atoms Calculated for 2a-2c Model Complex [Cu(dpm)(acac)] in Square-Planar and Distorted Geometries, and Model
Complex [Cu(dpm)(acac)(py)]
[Cu(dpm)(acac)]
(square-planar)
[Cu(dpm)(acac)]
(mode a)a
[Cu(dpm)(acac)]
(mode b)b
2a
2b
2c
[Cu(dpm)(acac)(py)]c
A
A
iso(Cu)/G
iso(N)/G
-122
17.1
-122
17.1
-122
17.0
-122
16.7
-113
14.6
-118
17.4
-108
15.8
A|(Cu)/G
-299
-299
-299
-299
-289
-290
-291
spin population Cu
spin population N
spin population O
spin population C22
natural charge on Cu
Cu natural electron
configuration
0.6531
0.0934
0.0693
0.0006
1.40
0.6530
0.0937
0.0690
0.0006
1.40
0.6533
0.0915
0.0711
0.0007
1.40
0.6549
0.0918
0.0704
0.0004
1.40
0.6708
0.0870
0.0671
0.0082
1.43
0.6403
0.0943
0.0747
0.0004
1.42
0.6914
0.0839
0.0620
0.0005
1.46
3d9.254s0.35
3d9.254s0.35
3d9.254s0.35
3d9.254s0.354p0
3d9.234s0.334p0.01
3d9.264s0.324p0
3d9.224s0.314p0.01
4s contribution/%
3.7
3.7
3.7
3.7
3.5
3.3
3.3
a ω ) 40° (saddling, mode a). b C8-Cu1-C22, 130° (doming, mode b). c C8-Cu1-C22, 169°; Cu1-Npy, 2.342 Å.
Figure 8. Singly occupied Kohn-Sham orbital of [Cu(dpm)(acac)] in
square-planar (i) and distorted geometries; (ii) mode a (ω ) 40°); (iii) mode
b (C8-Cu1-C22 ) 130°) [isosurfaces at 0.05 au].
To substantiate the above assumptions, hyperfine coupling
parameters were calculated by DFT methods for 2a-2c and
the model complex [Cu(dpm)(acac)] in square-planar and
distorted geometries along modes a and b (Scheme 5,
Supporting Information). For this purpose, the EPR-II basis
set of Barone27 for C, H, O, and N and an all-electron basis
set 6-311G(d) for copper was employed in single-point
calculations on the SDD-optimized geometry.
Figure 7. Photograph of THF-swollen and dry 2d.
Scheme 5. Schematic Drawing of Nonplanar Distortions of
[Cu(dpm)(acac)] Complexes: Saddling (mode a) and Doming (mode b)
The calculated coupling constants are independent of the
remote substituent R as observed experimentally (Tables 4
and 5). Coupling to dpm nitrogen nuclei is overestimated
by about 170% and coupling to copper by about 160%
(Tables 4 and 5).45 The latter deviation is probably due to
the 6-311G(d) basis set being used for copper because this
basis set is not optimized for magnetic properties calculations
and the employed B3LYP functional.46
However, hyperfine coupling to the copper nucleus in dry
2d A|(Cu) ) 177 G is significantly (96%) smaller than that
observed for 2a-2c (Figure 6, Table 4). This reduction of
A|(Cu) could be due to a distortion of the complexes in the
dry polymer. Drying of the THF-swollen polymer results in
shrinking of the polymer to approximately 60-65% of the
original volume (Figure 7).15,18,44 Thus, the internal pressure
of the dry polymer is larger than in a frozen glass, and steric
interactions with adjacent polymer chains might induce some
deformation of the complexes. At 130 K (frozen glass),
signals of the THF-swollen polymer 2d in the g| region are
broader than those of the dry polymer 2d (Figure 6, bottom),
indicating the presence of both square-planar [A|(Cu) ) ∼
185 G] and distorted complexes [A|(Cu) ∼ 177 G].
Upon distortion from square-planar geometry along mode
a or b, the isotropic and anisotropic coupling constants
Aiso(Cu) and A|(Cu) decrease as both distortions reduce the
s character of the odd electron (Table 5, Supporting Informa-
tion). In addition, spin density is delocalized onto the central
carbon atom C22 of the acac ligand (mode a) or onto the
nitrogen and oxygen donor atoms of the ligands (mode b;
Table 5), which is reflected in the shape of the corresponding
singly occupied molecular orbitals (Figure 8). To achieve a
96% reduction in A|(Cu), the ligands have to twist by 40°
Possible low-energy deformations (deduced from DFT
frequency analyses of 2a-2c; around 20 cm-1) are the
twisting of the ligand planes (Scheme 5, left; mode a;
saddling) and the out-of-plane displacement of the copper
center (Scheme 5, right; mode b; doming), which both could
account for the reduction of A|(Cu) in dry 2d.
(45) For the bis(benzene)chromium radical cation [(C6H6)2Cr]•+, hyperfine
coupling to chromium has been calculated as too small (66% of
experimental value) with a similar DFT setup: Perrier, A.; Gourier,
D.; Joubert, L.; Adamo, C. Phys. Chem. Chem. Phys. 2003, 5, 1337.
(46) Szilagyi, R. K.; Metz, M.; Solomon, E. I. J. Phys. Chem. A 2002,
106, 2994.
(44) Santini, R.; Griffith, M. C.; Qi, M. Tetrahedron Lett. 1998, 39, 8951.
Inorganic Chemistry, Vol. 45, No. 6, 2006 2701

Heinze and Reinhart
the pyridine adducts 2a‚py-2d‚py.47 In a THF solution, the
adduct formation is fast, while it is very slow and incomplete
when the dry solids are exposed to pyridine vapor.
The adducts are characterized by their EPR spectra in fluid
and frozen solution. In all cases, 2a‚py-2d‚py, the hyperfine
coupling to copper is reduced as compared to the parent four-
coordinate complexes 2a-2d [2a‚py-2d‚py: Aiso(Cu) ) 70
G47 and A|(Cu) ) 170 G; Table 4]. The reduction of copper
hyperfine coupling is due to the smaller s character of the
odd electron in the pyridine adducts, which is well repro-
duced by a DFT calculation on the model complex [Cu-
(dpm)(acac)(py)] (Tables 3 and 5). The optimized geometry
of the model complex matches the X-ray structures of [Cu-
(dpm-3-py)(acac)] and [Cu(dpm-4-py)(acac)],20 with pyridine
occupying the axial position of a square pyramid (observed:
Figure 9. DSC plots and TGA curves of 2a-2c (2a, full line; 2, dashed
line; 2c, dotted line).
Table 6. Thermal Analyses Data of 2a-2c
2a
2b
2c
TGA
5.9 (170)
6.4 [CO]
20.9 (350)
22.5 [acac]
15.2
∆m/mexp/% (T/°C)
∆m/mcalcd/% [X]
∆m/mexp/% (T/°C)
∆m/mcalcd/% [X]
exptl. final weight/%
6.4 (202)
6.0 [CO]
21.2 (350)
21.2 [acac]
13.6
7.0 (202)
7.0 [NO]
20.5 (350)
23.2 [acac]
15.8
Cu1-Npy ) 2.28 Å and 2.32 Å; calculated: Cu1-Npy
)
2.34 Å; observed: C8-Cu1-C22 ) 158° and 179°;
calculated: C8-Cu1-C22 ) 169°; for the numbering
scheme, see Figure 1). For the model complex [Cu(dpm)-
(acac)(py)], Aiso(Cu) is reduced to 88% and A|(Cu) to 97%
as compared to that of [Cu(dpm)(acac)], which also repro-
duces the experimentally observed reductions to 91% and
92%, respectively. Pyridine coordination is reversible, and
2d is especially easily recovered from 2d‚py by simply
washing and filtering the insoluble polymer.
calcd. final weight/% [X] 14.4 [Cu]
13.6 [Cu]
14.9 [Cu]
DSC
T/°C (∆H/kJ mol-1
T/°C (∆H/kJ mol-1
T/°C (∆H/kJ mol-1
)
)
)
188 (-25.1) 228 (-51.1) 223 (-5.6)
234 (-33.4)
258 (40.4)
258 (49.3)
263 (44.2)
(saddling, mode a, halfway to a tetrahedron) or the ligands
have to bend from 180° to 130° (doming, mode b, square-
pyramid). Thus, both distortions may play a role for the
complexes in the dry polymer 2d.
In summary, we have synthesized and characterized
heteroleptic copper complexes with meso-substituted dipyr-
romethene ligands dpm-C6H4R. The substituent R determines
whether the complexes remain monomeric in the solid state
(2a, R ) COOMe) or assemble to polymeric chains via
hydrogen bonds (2b, R ) CONHiPr) or coordinative contacts
(2c, R ) NO2). Immobilization has been achieved by
attaching [Cu(dpm)(acac)] complexes to Wang resin (2d).
Although the primary coordination sphere around the copper
center is essentially identical for all of the complexes reported
in this study (square-planar geometry with N2O2 coordina-
tion) subtle differences have been observed in their structures,
properties, and reactivity.
Thermal Stability of 2a-2d. Thermal gravimetric analy-
sis (TGA) was employed to evaluate the thermal stability of
the copper(II) complexes 2a-2d and their decomposition
behavior with increasing temperature. The TGA plots of 2a-
2c show a three-step decomposition process (Figure 9, Table
6) with a sequential loss of a small molecule such as CO or
NO (∆m/m ∼7%), the acac ligand (∆m/m ∼ 22%), and the
dpm-C6H4R ligand (∆m/m ∼ 57%). Decomposition is
complete at 550 °C, and the final weight percentage of ∆m/m
∼ 14% is in good agreement with that calculated for
elemental copper (Table 6).
Weak antiferromagnetic coupling is found for monomeric
2a, while polymeric 2b and 2c are ferromagnetically coupled
in the solid state. The polymer-bound complex 2d behaves
as an ideal paramagnet because of site isolation of the
magnetic centers in the polymer. EPR spectroscopy in
The DSC profiles of 2a-2c show exothermic features at
188, 228, and 223/234 °C, respectively, which are associated
with the liberation of a small molecule (Table 6). Thus, the
thermal stability increases in the order 2a < 2b ∼ 2c. An
endothermic process tentatively assigned to melting and
further decomposition (loss of the acac ligand; cf. mass
spectrometric analyses; Experimental Section) is observed
around 260 °C, which is in accordance with the observations
made on [Cu(dpm)(acac)] complexes with pyridyl-substituted
dpm ligands.20
48
combination with DFT calculations have been employed
to study the coordination sphere of the copper center in
different microenvironments because the hyperfine coupling
to copper is very sensitive toward geometric changes
(distortion and adduct formation). In the dry polymer 2d,
the complexes are distorted because of steric congestion and
no pyridine adducts are formed. However, in the gel phase
(47) The amide-substituted complex 2b does not form the pyridine adduct
at room temperature in THF (1 equiv pyridine). Probably, the pyridine
is hydrogen-bonded to the amide group in solution. In the frozen THF
glass, however, pyridine coordinates to the copper center.
(48) For one example of combining DFT calculations and spectroscopy
for “enzyme-immobilized” copper centers, see: DeBeer George, S.;
Basumallick, L.; Szilagyi, R. K.; Randall, D. W.; Hill, M. G.;
Nersissian, A. M.; Valentine, J. S.; Hedman, B.; Hodgson, K. O.;
Solomon, E. I. J. Am. Chem. Soc. 2003, 125, 11314.
For the immobilized complex 2d, only the characteristic
two-step decomposition of the polymer above 400 °C could
be observed, very similar to that of the copper-free polymer
1d.
Pyridine Uptake of 2a-2d. The square-planar complexes
2a-2d were reacted with pyridine in a THF solution to form
2702 Inorganic Chemistry, Vol. 45, No. 6, 2006

Heteroleptic Cu(II) Dipyrromethene Complexes
Supporting Information Available: Plots of øM-1 versus T for
2a-2d, view of the stacking of 2a along the c axis; EPR calibration
using mechanically mixed polystyrene/divinyl benzene and 2a; EPR
simulation of 2b; plot of DFT-calculated A|(Cu) versus angle
between ligand planes ω for [Cu(dpm)(acac)]; plot of DFT-
calculated A|(Cu) versus angle C8-Cu1-C22 for [Cu(dpm)(acac)];
Cartesian coordinates of the DFT-calculated geometry (B3LYP/
SDD) of 2a, 2b, 2c, [Cu(dpm)(acac)], and [Cu(dpm)(acac)(py)];
and crystallographic data in CIF format. This material is available
free of charge via the Internet at http://pubs.acs.org. X-ray crystal-
lographic files in CIF format are available free of charge via the
Internet at http://www.ccdc.cam.ac.uk. Refer to CCDC reference
numbers 282430, 282431, and 282432.
of 2d, the immobilized complexes exhibit the stable square-
planar geometry and are mobile enough to exhibit isotropic
EPR spectra. In addition, the swollen polymer 2d reacts
easily and reversibly with pyridine to form immobilized
square-pyramidal complexes.
Acknowledgment. This work was supported by the
Deutsche Forschungsgemeinschaft, the Fonds der Chemis-
chen Industrie, and the Dr. Otto Ro¨hm Geda¨chtnisstiftung.
The permanent generous support from Prof. Dr. G. Huttner
is gratefully acknowledged. We thank Simone Leingang and
Jens Na¨gele for preparative assistance.
IC0515047
Inorganic Chemistry, Vol. 45, No. 6, 2006 2703