The dicopper(II) complex of the novel asymmetric dinucleating ligand Hpy3asym as a structural model of catechol oxidase

Article abstract of DOI:10.1002/ejic.200200650

The new asymmetric dinucleating ligand 2-{[bis(2- pyridinylmethyl)amino]methyl}-4-methyl-6-{[(2-pyridinyl- methyl)amino]methyl}phenol (Hpy3asym) has been designed in order to model the type-3 active site of the copper proteins. This phenol-based "end-off" compartmental ligand has one tridentate and one didentate arm attached to the 2- and 6- positions of the phenolic ring, respectively. A dinuclear copper(II) nitrate complex with this ligand [Cu₂(py3asym)- (H₂O)_1.5(NO₃)₂]NO₃ has been obtained and structurally characterized. In this complex both copper ions have a distorted octahedral geometry and are endogenously bridged by the phenolic oxygen atom of the deprotonated ligand. The complex shows a donor-atom asymmetry that consists of an N₃O₃ donor set for the Cu1 ion and an N₂O₄ donor set for the Cu2 ion. The electrochemical, magnetic behavior and spectral properties of the complex are discussed. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003.

Full text of DOI:10.1002/ejic.200200650

SHORT COMMUNICATION
The Dicopper(II) Complex of the Novel Asymmetric Dinucleating Ligand
Hpy3asym as a Structural Model of Catechol Oxidase
Iryna A. Koval,[a] Daniel Pursche,[b] Arno F. Stassen,[a] Patrick Gamez,[a] Bernt Krebs,[b] and
Jan Reedijk*[a]
Keywords: Copper / Cyclic voltammetry / Enzyme models / Ligand design / Magnetic properties
The new asymmetric dinucleating ligand 2-{[bis(2-
pyridinylmethyl)amino]methyl}-4-methyl-6-{[(2-pyridinyl-
methyl)amino]methyl}phenol (Hpy3asym) has been designed
in order to model the type-3 active site of the copper proteins.
This phenol-based ‘‘end-off’’ compartmental ligand has one
tridentate and one didentate arm attached to the 2- and 6-
positions of the phenolic ring, respectively. A dinuclear cop-
acterized. In this complex both copper ions have a distorted
octahedral geometry and are endogenously bridged by the
phenolic oxygen atom of the deprotonated ligand. The com-
plex shows a donor-atom asymmetry that consists of an N3O3
donor set for the Cu1 ion and an N2O4 donor set for the Cu2
ion. The electrochemical, magnetic behavior and spectral
properties of the complex are discussed.
per(II
)
nitrate complex with this ligand [Cu2(py3asym)-
( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2003)
(H2O)1.5(NO3)2]NO3 has been obtained and structurally char-
per ions. Taking our inspiration from the natural molecule,
our attention has turned to the deliberate design of novel
model systems of the type-3 active site, where the two cop-
Introduction
The copper proteins with the type-3 active site, such as per ions would have distinctively different coordination sur-
hemocyanins, tyrosinases and catechol oxidases, have at- roundings. The site specificity of the copper ions may help
tracted the attention of scientists due to their ability to pro- to answer an important question concerning the binding of
cess primary dioxygen under ambient conditions.[1Ϫ3] The
latter two enzymes use it to perform selective oxidations of
organic substrates, such as tyrosine and catechol, to pro-
duce various melanins, whereas hemocyanin is the dioxygen
transport and storage protein in some arthropods and mol-
luscs.
The type-3 active site is characterized by a dicopper core
where each of the metal ions is surrounded by three histi-
dine residues. In the met-CuII-CuII form two copper ions
are antiferromagnetically coupled via the µ-OH bridge, re-
sulting in an EPR-silent active site.
the substrate in the natural enzyme, i.e. is the catechol sub-
strate forming a bridge between the two copper() centers
rather than binding to only one of them?
Dinucleating phenol-based ‘‘end-off’’ compartmental[5]
ligands have previously been successfully used for modeling
dimetallic biosites.[6Ϫ8] In this paper, the synthesis of the
novel phenol-based ligand 2-{[bis(2-pyridinylmethyl)-
amino]methyl}-4-methyl-6-{[(2-pyridinylmethyl)amino]-
methyl}phenol, Hpy3asym, is reported. This dinucleating
ligand was designed to hold two copper ions in close prox-
imity and to provide them with different coordination sur-
roundings, thus making one of the two copper ions more
readily accessible for the binding of the substrate. This was
achieved by substituting the 2- and the 6-positions of the
phenol ring by tridentate and didentate arms, respectively,
containing nitrogen donor atoms. The reaction of
Hpy3asym with copper() nitrate yields the new dinuclear
asymmetric complex, which is regarded as a structural
model of the type-3 active site. The dinuclear copper core
exhibits a donor-atom asymmetry in the solid state, com-
prised of an N3O3 donor set for the Cu1 ion and an N2O4
donor set for the Cu2 ion. The crystal structure, spec-
troscopy, electrochemical and magnetic behavior of the
complex are reported below.
The determination of the crystal structure of catechol
oxidase from sweet potatoes (Ipomoea batatas) by some of
us[4] offered new insight into the catalytic mechanism of the
enzyme with the possibly different functions of the two cop-
[a]
Leiden University, Leiden Institute of Chemistry,
P. Box 9502, 2300 RA Leiden, Netherlands
Fax: (internat.) ϩ31-71/527-4451
E-mail: reedijk@chem.leidenuniv.nl
Institut für Anorganische und Analytische Chemie der
[b]
Westfälischen Wilhelms-Universität Münster,
Wilhelm-Klemm-Straße 8, 48149 Münster, Germany
Fax: (internat.) ϩ49-251/833-8366
E-mail: krebs@uni-muenster.de
Eur. J. Inorg. Chem. 2003, 1669Ϫ1674
DOI: 10.1002/ejic.200200650
 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1669

I. A. Koval, D. Pursche, A. F. Stassen, P. Gamez, B. Krebs, J. Reedijk
SHORT COMMUNICATION
Figure 1. The reaction scheme of the synthesis of the phenol-based compartmental ‘‘end-off’’ ligand Hpy3asym
The oxygen atom O20 (occupancy 0.4886) from the water
molecule is at a distance of 2.535(3) A. The loosely bound
Results and Discussion
˚
oxygen atom O10 (occupancy 0.5114) from the disordered
nitrate counteranion [the Cu1ϪO10a distance is 3.007(6) A]
Ligand Design
˚
Hpy3asym was synthesized in three steps (Figure 1) from
commercially available 5-methylsalicylaldehyde. The first
step includes the introduction of the dichloromethane
group in the 3-position of the phenol ring. The chloride
atom was subsequently substituted by di(2-picolyl)amine.
Finally, the reductive amination of the aldehyde group by
2-aminomethylpyridine and sodium borohydride led to the
desired ligand.
is at a much larger distance, which, however, still matches
the range of bond lengths observed for copper-oxygen
bonds along the JahnϪTeller axis.[10Ϫ13] The in-plane cis
angles around the Cu1 ion vary over quite a broad range,
viz. 83.92(8)° for the N1ϪCu1ϪN3 angle and 96.92(7)° for
the O2ϪCu1ϪN2 angle. Their sum amounts to 357.76°.
The OϪCu1ϪO angle along the JahnϪTeller axis is equal
to 173.85(8)° for the O1ϪCu1ϪO20 angle and 165.46(10)°
for the O1ϪCu1ϪO10 angle, thus indicating a significant
distortion from a regular octahedral geometry.
Crystal Structure Description
The coordination sphere around the second copper ion
Cu2 can also be described as a distorted octahedron, but
with an N2O4 donor set. The equatorial plane around the
Cu2 ion is formed by two cis located nitrogen atoms N4 from
Very small green rectangular crystals of [Cu2(py3asym)-
(H2O)1.5(NO3)2](NO3) were obtained by slow evaporation
of the solvent from an acetonitrile solution of the complex.
The Platon[9] projection of the complex is depicted in Fig-
ure 2. The compound crystallizes in the space group P21/n.
Both copper ions have distinctively different coordination
surroundings, showing a donor-atom asymmetry. An en-
dogenous phenolato bridge is present in the dinuclear core,
but there is no exogenous bridge. The N3O3 coordination
sphere around the Cu1 ion can be regarded as a very dis-
torted octahedron. The equatorial plane is formed by the
tertiary amine nitrogen atom N1 at a distance of 2.0182(18)
˚
the secondary amine [the Cu2ϪN4 distance is 1.9838(17) A],
N5 from the pyridine ring [the Cu2ϪN5 distance is
˚
2.0181(17) A], and two cis oxygen atoms, O1 from the bridg-
˚
ing phenolate [the Cu2ϪO1 distance is 1.9353(14) A] and O3
from the chelating nitrate anion [the Cu2ϪO3 distance is
˚
1.9910(14) A]. The second oxygen atom O5 from the chelat-
ing nitrate anion and the oxygen atom O6 from the mono-
coordinated nitrate anion occupy the axial positions, thus
adjusting the coordination sphere around the copper ion to
a very distorted octahedron [the distances Cu2ϪO5 and
˚
A, two trans located nitrogen atoms N2 and N3 from two
˚
pyridine rings at a distance of 1.9860(17) A and 1.9760(18)
˚
˚
˚
Cu2ϪO6 are equal to 2.5431(16) A and 2.5982(16) A,
respectively]. The in-plane cis angles vary in the range
87.36°Ϫ94.64°. The angle O5ϪCu2ϪO6, which should be
equal to 180° in the regular octahedron, is only 157.37(5)°,
A, respectively, and the oxygen atom from a water molecule
˚
at a distance of 1.9701(16) A. One of the axial positions is
occupied by the bridging phenolate oxygen atom O1 at a
˚
relatively long distance of 2.3070(13) A. The second apical
position has a weak O-donor ligand, which was refined for indicating an even greater distortion from a regular octa-
50% to be water and for 50% a disordered nitrate anion. hedral geometry than observed in the case of the Cu1 ion.
1670
 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Eur. J. Inorg. Chem. 2003, 1669Ϫ1674

A Structural Model of Catechol Oxidase
SHORT COMMUNICATION
Table 1. Hydrogen bonds (D-H···A) with the distance H···A Ͻ r(A)
˚
ϩ 2.000 A and the angle DHA Ͼ 110°
˚
˚
˚
DϪH
d(DϪH), A d(H···A), A ϽDHAϾ, ° d(D···A), A
A
O2ϪH2a
O2ϪH2a
O2ϪH2a
0.736
0.736
0.736
1.971
2.518
2.611
174.09
127.91
155.96
2.704
3.026
3.296
O11
O10
N8
O2ϪH2b
O2ϪH2b
O2ϪH2b
0.915
0.915
0.915
1.802
2.443
2.448
154.44
174.95
145.50
2.657
3.356
3.245
O7
N7
O6
N4ϪH4
N4ϪH4
N4ϪH4
0.930
0.930
0.930
2.119
2.574
2.624
143.16
156.83
156.58
2.917
3.448
3.497
O7[a]
O8[a]
N7[a]
O20ϪH20a 0.759
2.087
163.07
2.821
O9[b]
O20ϪH20b 0.999
O20ϪH20b 0.999
O20ϪH20b 0.999
2.010
2.476
2.486
164.96
145.58
127.27
2.985
3.348
3.191
O9
N8A
O11
Figure 2. Platon[9] projection of [Cu2(py3asym)(H2O)1.5
-
(NO3)2]NO3; hydrogen atoms are omitted for clarity; the second
axial position at Cu1 ion has a O-donor ligand, which was refined
to be 50% water and 50% a disordered nitrate anion
The absence of the exogenous bridge between the two
copper ions promotes the large copper-copper separation
˚
of 3.9003 A, which is significantly longer than the distances
observed for similar complexes with two types of bridges
between the copper ions.[7,8,14] It is interesting to note that
potentially bridging nitrate anions are present in the com-
plex; however, they fail to bridge the two copper ions, in-
stead being coordinated as monodentate and didentate
chelating ligands. The distribution of charged and neutral
ligands in the complex is also remarkable: 1.5 neutral water
molecules are coordinated to the Cu1 ion, whereas two
charged nitrate anions are coordinated to the Cu2 ion.
The crystal packing is stabilized by an extensive net of
intra- and intermolecular hydrogen bonds (see Table 1). In Figure 3. The Platon[9] projection of the ‘‘herring bone’’ packing
arrangement along the crystallographic a axis; all hydrogen atoms,
except for those participating in hydrogen bonding, are omitted
particular, a bifurcated intramolecular hydrogen bonding is
realized between the proton H2b of the water molecule co-
ordinated to the Cu1 ion and the two oxygen atoms O6 and
O7 of the monodentate nitrate anion coordinated to the
found one. Thus, the 1.5 water molecules coordinated to
Cu2 ion, giving an impression of an exogenous pseudo-
the Cu1 ion, observed in the solid state, are lost during the
bridge between the two copper ions. Furthermore, each for-
measurement. The UV/Vis spectrum of the solid exhibits
mula unit is connected via intermolecular hydrogen bonds
two peaks at 456 and 640 nm. The first peak is assigned to
to three neighboring units. The Platon[9] projection of the
an LMCT transition between the bridging phenoxo group
and copper ions,[14] whereas the second one is characteristic
for CuII d-d transitions.[15] The positions of these bands do
not significantly change when the spectrum of the complex
is taken in acetonitrile solution, suggesting no important
modifications in the copper-ligand chromophores.
crystal packing along the crystallographic a axis is shown
in Figure 3. As can be seen, the molecules are assembled by
means of hydrogen bonds to form a ‘‘herring bone’’ pattern.
Physical Characterization
Besides the crystal structure determination, the complex
A cyclic voltammogram of the complex recorded in
was characterized spectroscopically and magnetically. The acetonitrile, when scanning towards the negative region of
electrospray mass spectrum (ESI-MS) of the complex per- potentials, shows two successive one-electron electrochemi-
formed in acetonitrile reveals one major peak at m/z ϭ 688, cal signals. The first one, at Ϫ0.13 V vs. Ag/AgCl, is as-
corresponding to [Cu2(py3asym)(NO3)2]ϩ. The theoretical signed to the CuI2I,II/Cu2II,I redox couple. The second one, at
isotope pattern calculated for the empirical formula Ϫ0.33 V, is attributed to the formation of Cu2I,I species.
C27H28Cu2N7O7 is in agreement with the experimentally They both appear to be irreversible. In addition, a very
Eur. J. Inorg. Chem. 2003, 1669Ϫ1674
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1671

I. A. Koval, D. Pursche, A. F. Stassen, P. Gamez, B. Krebs, J. Reedijk
SHORT COMMUNICATION
broad peak at ca. Ϫ0.7 V suggests the reduction of both
copper ions to Cu0 and the deposition of the free metal on
the electrode surface. On the reverse scan, an additional
sharp anodic peak is observed at Ϫ0.27 V. This is the so-
called stripping peak, caused by the redissolution of the
metallic copper. This peak is absent if the potential sweep
is reversed at ca. Ϫ0.5 V, before the reduction to Cu0 can
take place. The anodic part of the cyclic voltammogram is
characterized by three successive fully irreversible oxidation
waves at 1.16, 1.48 and 1.68 V, apparently corresponding to
the oxidation of the ligand and/or water molecules.
Conclusion
The asymmetric phenol-based ‘‘end-off’’ compartmental
ligand 2-{[bis(2-pyridinylmethyl)amino]methyl}-4-methyl-
6-{[(2-pyridinylmethyl)amino]methyl}phenol forms a di-
nuclear asymmetric copper() nitrate complex which can be
regarded as a new structural model of the type-3 active site
of the copper proteins. The ligand holds a tridentate and a
didentate arms attached to the 2- and 6-positions of the
phenol ring. In the solid state the complex possesses donor-
atom asymmetry, constituted by an N3O3 donor set for the
Cu1 ion bound to a tridentate arm, and an N2O4 donor set
for the Cu2 ion bound to a didentate arm. The magnetic
behavior of the complex was interpreted in terms of weak
ferromagnetic coupling between the two copper ions, with
the exchange integral J ϭ Ϫ4.6 cmϪ1, and a CurieϪWeiss
temperature θ of 0.87 K.
Magnetic Properties
In Figure 4, the magnetic susceptibility of the complex
[Cu2(py3asym)(H2O)1.5(NO3)2]NO3 is shown, plotted as
both χϪ1 and χ versus the temperature. The compound dis-
plays a weak ferromagnetic coupling with a Curie tempera-
ture θ of 0.87 K and a CurieϪWeiss constant C of 0.39
cm3·K·molϪ1. The value for µ is 1.10 B.M.
Experimental Section
General Remarks: Most of the synthetic work was carried out using
standard Schlenk techniques. All chemicals were commercially
available and used without further purification. 5-Methylsalicylal-
dehyde was purchased from Fluka, 2-(aminomethyl)pyridine from
Acros, and di(2-picolyl)amine from Aldrich. 3-Chloro-5-methylsal-
icylaldehyde (1) was prepared according to the procedure described
by Lock.[18] Tetrahydrofuran and methanol were dried by refluxing
over sodium. Water was demineralized prior to use. C,H,N deter-
minations were performed on a PerkinϪElmer 2400 Series II ana-
lyzer. NMR spectra were recorded on a JEOL FX-200 (200 MHz)
FT NMR spectrometer. Solid-state ligand field spectra
(300Ϫ2000 nm, diffuse reflectance) and in solution were taken on
a PerkinϪElmer 330 spectrophotometer equipped with a data
station. IR spectra were recorded of pure solids on a PerkinϪElmer
FT-IR Paragon 1000 spectrophotometer with a Specac single-re-
flection diamond ATR P/N 10500, using the diffuse reflectance
technique (4000Ϫ300 cmϪ1, res. 4 cmϪ1). Electrospray mass spectra
(ESI-MS) were recorded on the Thermo Finnigan AQA apparatus.
Cyclic voltammetry measurements were performed with an Auto-
lab PGSTAT 10 cyclic voltammeter, using a Pt working electrode
and a Ag/AgCl reference electrode in acetonitrile (10Ϫ3 ), with
tetrabutylammonium perchlorate as supporting electrolyte, at a
scan rate of 0.1 mV/s. DC magnetic susceptibility measurements
(5Ϫ150 K) were carried out at 0.1 Tesla using a Quantum Design
MPMS-5 5T SQUID magnetometer. Data were corrected for mag-
netization of the sample holder and for diamagnetic contributions,
which were estimated from the Pascal constants.[19]
Figure 4. Magnetic susceptibility plotted as χϪ1 versus T (O) and
as χ versus T (ᮀ); the dashed line is the CurieϪWeiss plot from
near field theory and the solid line is the theoretical curve accord-
ing to the Bleany-Bowers equation
The magnetic properties of this dinuclear copper() com-
plex have been interpreted in terms of the BleaneyϪBowers
equation [Equation (1)], where g is the magnetic field split-
ting factor, J is the exchange integral of magnetic theory
and Nα is the temperature-independent paramagnetism of
one mol of copper() ions.[16,17]
3-{[Bis(2-pyridinylmethyl)amino]methyl}-2-hydroxybenzaldehyde (2):
A solution of di(2-picolyl)amine (1.08 g, 5.4 mmol) and triethyl-
amine (1.09 g, 10.8 mmol) in 50 mL of dry THF was added drop-
wise with stirring to a solution of 1 (1 g, 5.4 mmol) in 250 mL of
dry THF under an Ar atmosphere. After completion of the ad-
dition, the resulting white suspension was refluxed for two hours
and cooled to room temperature. After the removal of the triethyl-
amine hydrochloride salt by filtration, the resulting solution was
evaporated under reduced pressure, yielding a yellow oil, from
which compound 2 crystallized within a few minutes. Recrystalliza-
tion from a methanol/diethyl ester mixture gave slightly yellowish
crystals of the pure compound 2. Yield: 1.55 g, 4.5 mmol (82%).
1H NMR (CDCl3, 200 MHz): δ ϭ 10.42 (s, 1 H, aldehyde proton),
(1)
The fit was accomplished by minimization of the re-
liability factor, defined as R ϭ Σ(χmTcalc Ϫ χmTobs)2/
(χmTobs)2, by a least-squares procedure. The best fit was ob-
tained for the exchange integral J ϭ Ϫ4.6 cmϪ1, the mag-
netic field splitting factor g ϭ 2.02 and R ϭ 2.9 ϫ 10Ϫ3
.
1672
 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Eur. J. Inorg. Chem. 2003, 1669Ϫ1674

A Structural Model of Catechol Oxidase
SHORT COMMUNICATION
8.56 (d, 2 H, 6Јpy-H), 7.63 (td, 2 H, 4Јpy-H), 7.40 (t, 2 H, 5Јpy- green needles, 0.17 ϫ 0.08 ϫ 0.07 mm, a ϭ 10.3731(2), b ϭ
˚
H), 7.20 (d, 2 H, 3Јpy-H), 7.15 (s, 1 H, 2Јphenol-H), 7.13 (s, 1 H, 22.1430(4), c ϭ 14.2325(2) A, β ϭ 105.709(10)°, Z ϭ 4, V ϭ
3
3146.98(9) A , ρcalcd. ϭ 1.644 g cmϪ3, µ ϭ 2.322 cmϪ1, absorption
˚
5Јphenol-H), 3.89 [s, 4 H, N-(CH2py)2], 3.80 (s, 2 H, phenol-CH2-
N), 2.23 (s, 3 H, CH3) ppm.
correction: SADABS,[21] monoclinic, space group P21/n (no. 14),
reflections collected: 18421, independent reflections: 5871 (Rint
ϭ
2-{[Bis(2-pyridinylmethyl)amino]methyl}-4-methyl-6-{[(2-pyridinyl-
methyl)imino]methyl}phenol (3): A solution of 2-pyridylmethylam-
ine (0.39 g, 3.6 mmol) in 50 mL of dry methanol was added drop-
wise with stirring to a solution of 2 (1.26 g, 3.6 mmol) in 250 mL
of dry methanol under argon. After the addition was complete, the
resulting bright yellow solution was heated for two hours at 50 °C.
The successful formation of the imine derivative was verified by
NMR spectroscopy. The imine was reduced in situ to the respective
amine with sodium borohydride. 1H NMR (CDCl3, 200 MHz): δ ϭ
8.51 (d, 3 H, 6Јpy-H), 8.34 (s, 1 H, CHϭN), 7.62 (td, 3 H, 4Јpy-
H), 7.33 (t, 3 H, 5Јpy-H), 7.26(d, 2 H, 3Јpy-H), 7.09 (s, 1 H, 3Јphe-
nol-H), 7.03 (2, 1 H, 5Јphenol-H), 4.92 (s, 2 H, CHϭN-CH2), 3.88
[s, 4 H, N-(CH2py)], 3.80 (s, 2 H, phenol-CH2-N), 2.29 (s, 3 H,
CH3) ppm.
0.0314). The structure was solved by direct methods and refined
using the SHELX program package.[22,23] All hydrogen atoms were
placed at idealized positions riding on the carrier atom, with iso-
tropic thermal parameters, except for two hydrogen atoms located
close to O20. They were assigned to rest electron density on the
electron density map. The final cycle refinement, including 475 par-
ameters, converted to R1 ϭ 0.0312 (R1 ϭ 0.0388 all data) and
wR2 ϭ 0.0800 (wR2 ϭ 0.0826 all data) with a maximum (mini-
Ϫ3
˚
mum) residual electron density of 0.463 (Ϫ0.293) e·A
.
CCDC-197305 contains the supplementary crystallographic data
for this paper. These data can be obtained free of charge at
www.ccdc.cam.ac.uk/conts/retrieving.html [or from the Cambridge
Crystallographic Data Centre, 12, Union Road, Cambridge
CB2 1EZ, UK; fax: (internat.) ϩ44-1223/336-033; E-mail:
deposit@ccdc.cam.ac.uk].
2-{[Bis(2-pyridinylmethyl)amino]methyl}-4-methyl-6-{[(2-pyridinyl-
methyl)amino]methyl}phenol
(Hpy3asym):
NaBH4
(0.41 g,
10.9 mmol, 3 equiv./CHϭN) was added in situ to a solution of 3
in methanol. After the hydrogen evolution stopped, the resulting
colorless solution was refluxed for two hours and the solvent was
evaporated under reduced pressure. The residue was dissolved in
acidified water and washed three times with dichloromethane. The
water layer was made alkaline (pH ഠ 9) by addition of concen-
trated ammonia. The resulting white suspension was extracted
three times with dichloromethane. The organic layers were collected
and dried over Na2SO4. After evaporation under reduced pressure,
the pure compound was obtained as a clear yellow oil. Yield:
1.54 g, 3.5 mmol (96%). 1H NMR (CDCl3, 200 MHz): δ ϭ 8.55 (d,
3 H, 6Јpy-H), 7.59 (td, 3 H, 4Јpy-H), 7.36 (d, 3 H, 3Јpy-H), 7.14
(t, 3 H, 5Јpy-H), 6.93 (s, 1 H, 3Јphenol-H), 6.84 (s, 1 H, 5Јphenol-
H), 3.95 (s, 2 H, NH-CH2-py), 3.91 (s, 2 H, phenol-CH2-NH), 3.85
[s, 4 H, N(CH2-py)2], 3.75 (s, 2 H, phenol-N-CH2), 2.22 (s, 3 H,
CH3) ppm. 13C NMR (CDCl3, 200 MHz): δ ϭ 159.35, 154.80,
147.32, 136.17, 128.35, 126.35, 124.00, 123.11, 122.85, 121.67,
59.06, 56.12, 54.65, 50.95, 26.22 ppm.
Acknowledgments
Financial support from the NRSC Catalysis (a Research School
Combination of HRSMC and NIOK) is kindly acknowledged. Tra-
vel and exchange of information and students between Leiden Uni-
versity and Westfälische Wilhelms-Universität Münster through a
NWO and DFG grant in the framework of the Joint Graduierten
Kolleg is gratefully acknowledged, as is support and sponsorship
under COST Action D21/003/2001.
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[Cu2(py3asym)(H2O)1.5(NO3)2](NO3): The bulk sample was pre-
pared by dissolving Hpy3asym (0.076 g, 0.17 mmol) and
Cu(NO3)2·3H2O (0.09 g, 0.37 mmol) in 10 mL of an acetonitrile/
water mixture (1:1). The resulting solution was stirred for one hour
at room temperature and the solvents evaporated to dryness under
reduced pressure. After washing with a small amount of acetone,
0.08 g (0.1 mmol, 59% yield) of the pure compound was obtained
as a dark green powder. C27H31Cu2N8O11.5 (778.68): calcd. C 41.7,
H 3.9, N 14.7; found C 41.3, H 4.0, N 14.4. MS(ESI): m/z ϭ 688
([Cu2(py3asym)(NO3)2]ϩ). IR: ν˜ ϭ 3600Ϫ3200, broad band (H2O,
asymmetric and symmetric OH stretching), 3184 (NϪH stretch-
ing), 1613 (HOH bending), 1484 (chelating didentate NO3Ϫ, NϭO
stretching), 1396 (monodentate NO3Ϫ, NO2 asymmetric stretch-
ing), 1290 (monodentate NO3-, symmetric NO2 stretching, and
chelating didentate NO3Ϫ, asymmetric NO2 stretching).[20]
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Single crystals of the complex, suitable for X-ray crystal structure
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Cu(NO3)2·3H2O and the ligand.
[13]
[14]
X-ray Crystallographic Study: A single crystal of [Cu2(py3asym)(-
H2O)1.5(NO3)2](NO3) was mounted at 100 K on a Bruker AXS
SMART 6000 diffractometer equipped with Cu-Kα radiation (λ ϭ
[15]
1.54184 A). C27H31Cu2N8O11.5, M ϭ 778.68 g molϪ1, rectangular
ier, Amsterdam 1984.
˚
Eur. J. Inorg. Chem. 2003, 1669Ϫ1674
www.eurjic.org
 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Received November 27, 2002
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1674
 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
Eur. J. Inorg. Chem. 2003, 1669Ϫ1674