Second order optical nonlinearities of copper(II) and palladium(II) complexes with N-salicylidene-N′-aroylhydrazine tridentate ligands

Article abstract of DOI:10.1002/ejic.200300735

Three new N-salicylidene-N′-aroylhydrazines tridentate ligands have been prepared: N-4-diethylaminosalicylidene-N′-(4-nitrocinnamoylhydrazine (L¹), N-4-diethylaminosalicy-lidene-N′-4-(2,4- dinitrophenylethylidene)benzoylhydrazine (L2), N-4-diethylaminosalicylidene- N′-4-(6-nitro-2-benzoxazolyl)benzoylhydrazine (L3). From these ligands, mononuclear acentric complexes of Copper(II) and Palladium(II), with pyridine as further ligand, have been prepared and characterized, also by single-crystal X-ray analysis. These complexes show high second order nonlinear optical activity (EF-ISH, |αβ| up to 3000·10^-48 esu, incident wavelength 1.907 pm). The properties of metallorganic polymers obtained by grafting commercial poly(4-vinylpyridine) with ML¹ fragment (M = Cu^II or Pd^II) are also reported. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.

Full text of DOI:10.1002/ejic.200300735

FULL PAPER
Second Order Optical Nonlinearities of Copper(II) and Palladium(II
)
Complexes with N-Salicylidene-NЈ-aroylhydrazine Tridentate Ligands
Fabio Borbone,[a] Ugo Caruso,[a] Roberto Centore,*[a] Antonella De Maria,[a] Alain Fort,[b]
Michela Fusco,[a] Barbara Panunzi,[c] Antonio Roviello,*[a] and Angela Tuzi[a]
Dedicated to Prof. A. Sirigu on the occasion of his 65th birthday
Keywords: Tridentate ligands / Nonlinear optics / Polymers / Copper / Palladium
Three new N-salicylidene-NЈ-aroylhydrazines tridentate li-
terized, also by single-crystal X-ray analysis. These com-
gands have been prepared: N-4-diethylaminosalicylidene- plexes show high second order nonlinear optical activity (EF-
NЈ-(4-nitrocinnamoylhydrazine (L1), N-4-diethylaminosalicy-
lidene-NЈ-4-(2,4-dinitrophenylethylidene)benzoylhydrazine
ISH, |µβ| up to 3000·10−48 esu, incident wavelength 1.907 µm).
The properties of metallorganic polymers obtained by graft-
(L2), N-4-diethylaminosalicylidene-NЈ-4-(6-nitro-2-benzox- ing commercial poly(4-vinylpyridine) with ML1 fragment
azolyl)benzoylhydrazine (L3). From these ligands, mononu- (M = CuII or PdII) are also reported.
clear acentric complexes of Copper(II) and Palladium(II), with
pyridine as further ligand, have been prepared and charac-
( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2004)
Introduction
stability of the noncentrosymmetric polar order and in the
low solubility of the chromophore in the polymer matrix
(the latter effect is probably enhanced in the case of metal-
lorganic NLO-phores); in the second approach, on the
other hand, the chemical synthesis of the organometallic
chromophore must include steps for its functionalization as
monomer for polymerization reactions (e.g. as diol or meth-
acrylate ester).
We have recently proposed a new approach to metal-co-
ordinated second order NLO active polymer materials,
based on the use of tridentate ligands of the N-salicylidene-
NЈ-aroylhydrazine type.[4] The use of such ligands, properly
functionalized with strong electron donor-acceptor groups,
is based on two factors (see Scheme 1). First, upon coordi-
nation, the ligand changes from the cheto (amide) to the
enolic form with extension of π conjugation along the
whole structure; second, the formed complex is electrically
neutral but the metal (CuII, PdII) is coordinatively unsatu-
rated.
In the absence of other ligands the coordination sphere
of the metal is completed by centrosymmetric coupling and
dimers are formed (see Scheme 2); however, if other ligands
are present, acentric monomeric complexes may be formed,
as witnessed by the strong tendency of dimers to form
monomeric adducts by reaction with neutral molecules con-
taining N donor atoms (e.g. pyridine, imidazole, etc.).[4,5]
This feature is of relevant interest inasmuch as it allows
the anchorage of NLO active metallorganic fragments to a
suitable preformed polymer chain [e.g. poly(4-vinylpyri-
The design of dipolar metallorganic chromophores with
second order optical nonlinearities has been carried out till
now according to two chemical architectures: organometal-
lic fragments as electron donor-acceptor groups at the end
of a π conjugated system[1] or metals as constituents of the
conjugation bridge between the donor and acceptor
groups.[1c,2]
A nonlinear optically (NLO) active polymer material is
obtained from the chromophore following two approaches
widely used in the case of purely organic compounds:[3]
noncovalent incorporation of active molecules (guest) in an
organic polymeric matrix (host) or covalent incorporation
of chromophores into a polymer chain or in a three dimen-
sional network. In both cases a noncentrosymmetric polar
alignment of the NLO active fragments (‘‘poling’’) must be
achieved (generally by applying a strong electric field while
the polymer is kept above its glass transition temperature)
which is a necessary condition for bulk second order NLO
activity. Drawbacks of the first approach are in the low time
[a]
`
Dipartimento di Chimica, Universita di Napoli ‘‘Federico II’’,
Via Cinthia, 80126 Napoli, Italy
E-mail: centore@chemistry.unina.it
roviello@chemistry.unina.it
[b]
[c]
´
IPCMS-CNRS,
Groupe
d’Optique
Nonlineaire
et
´
d’Optoelelectronique,
23 Rue du Loess, 67037 Strasbourg Cedex, France
`
Dipartimento di Scienza degli Alimenti, Universita degli Studi
di Napoli ‘‘Federico II’’,
`
Via Universita 100, 80055 Napoli, Italy
Eur. J. Inorg. Chem. 2004, 2467Ϫ2476
DOI: 10.1002/ejic.200300735
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R. Centore, A. Roviello et al.
FULL PAPER
Scheme 1
Scheme 2
dine)] through a coordination bond.[4b] The advantages of
this approach are evident. Among others, we stress that the
chemical synthesis of the chromophore and of the polymer
can be worked out in a substantially independent way, no
functionalization of the organic ligand is required and com-
mercially available polymers can be used.
In this paper we report the synthesis and characterization
of new monomeric complexes of this type exhibiting high
NLO activity, whose formulae are shown in Scheme 3.
In addition we will also demonstrate the anchorage of
one NLO active metallorganic fragment to commercial
poly(4-vinylpyridine), according to Scheme 4, so that our
complexes can be considered as rare examples of highly
NLO active metallorganic chromophores from which poly-
mers are successfully obtained. A full account of the
properties of various commercial polymers grafted with all
the above reported organometallic fragments will be given
in a forthcoming publication from our laboratory.
Results and Discussion
Drawings of the crystallographic independent units of
Cu1, Cu2, Pd2, and Cu3 are reported in Figures 1, 2, 3,
and 4; selected bond lengths, bond angles, and torsion
angles are reported in Table 1.
Scheme 3
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Second Order Optical Nonlinearities of Copper(II) and Palladium(II) Complexes
FULL PAPER
˚
1.298(7) to 1.320(5) A] are respectively longer and shorter
as compared with the values expected for an amide group.[6]
On the other hand, IR spectra of free ligands in the solid
state clearly show bands typical of the amide group. The
structural change of the ligands upon coordination is also
confirmed by the UV/Vis absorption patterns. In fact, as it
is shown for L1 in Figure 5, a significant red-shift of λmax
is observed upon coordination, with the λmax of the coordi-
nated ligand being substantially unchanged in the dimer,
monomer, and grafted polymer.
The conformation of the ligands is close to be planar in
all cases. In the complexes containing the ligand L2 the
nitro group in para position to the vinylene group is sub-
stantially coplanar with the phenyl, while the ortho nitro
group is significantly twisted by torsion around the bond
C26ϪN5 (Table 1). This is probably due to the close intra-
Scheme 4
In all the reported structures the tridentate ligand is in molecular contact between O6 and H atom bonded to C20
˚
˚
the enolic form. In fact, bond lengths C12ϪO2 [ranging (the distance O6···C20 is 2.83 A in Cu2 and 2.86 A in Pd2).
˚
from 1.286(5) to 1.306(5) A] and C12ϪN3 [ranging from This contact could be relaxed also by torsion around the
Figure 1. ORTEP view of Cu1; thermal ellipsoids are at 30% probability level; only one position of the non-coordinated pyridine molecule
is shown
Figure 2. ORTEP view of Cu2; thermal ellipsoids are at 30% probability level
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R. Centore, A. Roviello et al.
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Figure 3. ORTEP view of Pd2; thermal ellipsoids are at 30% probability level
Figure 4. ORTEP view of Cu3; thermal ellipsoids are at 30% probability level
bond C20ϪC21, i.e. at cost of planarity of the ligand. The
In the complexes reported here and in the similar com-
fact that this possibility is not adopted (it occurs instead in plexes already reported by us[4a] the tendency of CuII to the
trans-stilbene which is twisted in the gas phase essentially pentacoordination appears to be favored by longer ligands.
for a similar reason[7]) seems to indicate a higher torsional Since pentacoordination implies deviations from a flat mo-
potential around the bond C20ϪC21, probably resulting lecular shape, may be that packing forces have a role in
from charge transfer (CT) contributions to the ground state. driving this behavior.
A coordination variability has been observed in the com-
Both in tetracoordinate and in pentacoordinate com-
plexes of CuII. In fact, Cu1 is tetracoordinate (square plexes the ligand pyridine molecule in the basal plane is not
planar) while Cu2 and Cu3 are pentacoordinate (square coplanar with this plane but torsions around the MϪN6
pyramidal with the metal atom lying substantially in the bond are observed (up to ca. 20°).
basal plane) and an additional pyridine molecule is bonded
In the pentacoordinate complexes Cu2 and Cu3 the two
to the metal. For PdII, on the other hand, we have observed ligand pyridine molecules are bonded to the metal with dif-
square-planar coordination with the same ligand giving a ferent strength, as it may be inferred by the corresponding
pentacoordinate copper complex; furthermore, the ad- bond lengths (Table 1). The more weakly bonded pyridine
ditional pyridine molecule present in the independent unit (i.e. the one-coordinated in apical position) is more easily
of crystals of Pd2 is not coordinated to the metal (Figure 3). lost as it is shown for example in the thermogravimetric
This difference between CuII and PdII complexes is consist- analysis of Figure 6, while the second pyridine is lost at a
ent with our previous results[4a] and is an evidence of the much higher temperature.
general tendency of PdII to give preferentially 16-electron
complexes.
This behavior is fairly reproducible so that loss of the
apical pyridine is accomplished in all complexes in a tem-
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Second Order Optical Nonlinearities of Copper(II) and Palladium(II) Complexes
FULL PAPER
˚
Table 1. Selected bond lengths (A), bond angles (°), and torsion
angles (°) for Cu1, Cu2, Pd2, Cu3
Cu1
Cu2
Pd2
Cu3
MϪO1
MϪO2
MϪN2
MϪN6
MϪN7
O2ϪC12
N1ϪC5
N2ϪC11
N2ϪN3
N3ϪC12
O1ϪMϪN2
N2ϪMϪO2
O1ϪMϪN6
O2ϪMϪN6
N2ϪMϪN6
N2ϪMϪN7
N6ϪMϪN7
C11ϪN2ϪN3ϪC12
C7ϪC8ϪC11ϪN2
N3ϪC12ϪC13ϪC18
O6ϪN5ϪC26ϪC21
C17ϪC16ϪC19ϪN4
C15ϪC16ϪC19ϪC20
C19ϪC20ϪC21ϪC26
O1ϪMϪN6ϪC25
O1ϪMϪN6ϪC26
O1ϪMϪN6ϪC27
1.906(7)
1.946(8)
1.910(4)
1.992(4)
1.908(2)
1.953(2)
1.931(2)
2.035(2)
2.299(2)
1.289(3)
1.379(3)
1.281(3)
1.396(2)
1.306(3)
93.63(8)
80.28(8)
91.72(8)
92.40(8)
161.84(8)
100.64(8)
96.39(9)
179.6(2)
Ϫ178.2(2)
Ϫ179.2(3)
Ϫ37.7(4)
1.966(3)
1.994(3)
1.927(4)
2.051(4)
1.912(4)
1.954(4)
1.910(5)
2.014(5)
2.409(6)
1.295(6)
1.379(8)
1.280(7)
1.402(6)
1.298(7)
93.0(2)
80.7(2)
92.2(2)
93.2(2)
168.0(2)
96.7(2)
1.286(5)
1.370(7)
1.286(5)
1.395(7)
1.320(5)
93.8(2)
81.3(2)
92.4(2)
92.6(2)
173.8(1)
1.306(5)
1.376(5)
1.290(5)
1.406(5)
1.299(5)
95.3(1)
80.4(1)
89.5(1)
94.9(1)
175.2(1)
Figure 6. TGA/DTA curves of Cu2
Table 2. Relevant analytical data of grafted polymers MW
93.6(2)
175.9(3)
179.7(4)
Ϫ180.0(4)
Ϫ179.6(4)
172.7(4)
48.0(7)
Ϫ177.4(5)
Ϫ175.9(6)
167.1(5)
W ϭ % (ML1)2
grafted (by weight) Tg
Cu
Pd
ηinh
x[b]
Tg
ηinh
x[b]
(°C) (dL/g)[a]
(°C) (dL/g)[a]
Ϫ178.5(6)
0
35
60
147 0.28
192 0.12
217 0.09
0
147 0.28
0
Ϫ169.7(3)
167.3(3)
Ϫ179.5(5)
Ϫ175.1(5)
0.130 191 0.27
0.360 227 0.18
0.118
0.328
168.9(3)
Ϫ164.4(5)
[a]
Inherent viscosity measured in DMF at 25 °C in 0.05 g/dL solu-
161.1(3)
159.7(3)
[b]
tions (for Cu60 the measurement was performed at 60 °C). Mo-
lar ratio of coordinated and uncoordinated pyridine units in the
polymer.
Figure 5. UV/Vis absorption spectra for: L1 (curve a), (PdL1)2
(curve b), Pd1 (curve c), Pd35 (curve d)
Figure 7. DSC thermograms, poly(2-vinylpyridine) (curve a); Pd35
(curve b); Cu35 (curve c); Pd60 (curve d); Cu60 (curve e)
perature interval ranging from 115 °C to 130 °C, while the
basal pyridine is lost between 180 °C and 200 °C. The only polymers are reported in Table 2. In Figure 7 are reported
relevant exception is given by Pd3 in which the pyridine the DSC thermograms.
ligand is lost around 276 °C (we have not succeeded in
The inflection corresponding to the glass transition is the
growing suitable single crystals of Pd3). In all cases, losing only signal present in the curves. A regular increase of the
of all pyridine ligands restores (MLN)2 dimers as it is sug- glass transition temperature is observed upon grafting, with
gested by the decomposition temperatures which are ident- Tg’s almost independent from the nature of the metal (PdII
ical.
or CuII). The lack of any other inflection at temperatures
Starting from commercial poly(4-vinylpyridine) we have lower than the Tg of the ungrafted polymer is an evidence
prepared grafted polymers with a (ML1)2 content (by of the absence of uncoordinated complex acting as a plas-
weight) of 35% and 60% both for CuII and PdII. The re- ticizing agent; a further evidence, at least in the case of Pd
1
sulting polymers have good solubility in NMP, tetrachloro- containing polymers, is given by H NMR analysis. In fact,
ethane and DMF. Some thermal and analytical data of the in the spectra of Pd polymers, recorded in [D2]dichlorome-
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R. Centore, A. Roviello et al.
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thane, only broad peaks of resonance are present, which are sults; in fact, we have found that the ortho nitro group is
typical of polymer samples, and no sharp signal pertaining significantly twisted with respect to the phenyl ring which
to free low molecular weight compounds is observed.[4b]
is attached to (cf. Table 1) and so it gives a little contri-
All polymers are amorphous, as confirmed by DSC and bution, if any, to the charge transfer.
X-ray diffraction experiments. From concentrated solutions
The datum measured for Pd3 is consistent with the ex-
of polymers in NMP (ca. 0.10 g/mL) we have obtained pected increase of nonlinear activity following the replace-
clear, transparent films of optical quality by spin coating. ment of phenyl rings by low aromaticity heterocycles.[10]
The decomposition temperatures of the grafted polymers, The high activity of this complex, which is among the high-
which are around 300 °C, are well above the glass transition est reported to date for metallorganic chromophores,[1] cou-
temperature, which, in any case, can be modulated by vary- pled with the known features of high thermochemical and
ing the extent of grafting, and this allows poling procedures photochemical stability of the benzoxazole group,[11] make
to be safely done on the films. We think that these grafted
polymers can show advantages as compared to all organic
polymers tailored for second order NLO applications, par-
ticularly for what concerns the poling procedure. In fact,
the peculiar nature of the bond between the NLO active
fragment and the polymer chain (a coordinative bond) and
the large molar excess of pyridine ligand groups, should al-
low some mobility of MLN fragment (through com-
plexation-decomplexation equilibria) and, therefore, a high
degree of orientation in the poling at high temperature (Ͼ
Tg), with the mobility reduced (and the polar order frozen)
at low temperature.
Second order optical nonlinearities of the complexes
CuN and PdN are reported in Table 3. The discussion of
their NLO properties can be usefully done at a comparative
level with the similar complexes we have already studied.[4a]
Table 3. EFISH Results for the studied complexes
[a]
Complex
|µg·βvec|
Cu1
Pd1
Cu2
Pd2
Pd3
1100
1500
1300
1100
3000
[a]
Estimated errors are: Ϯ10% for Cu1, Pd1, Cu2, Pd2 and Ϯ20%
for Pd3.
The NLO activity of Cu1 and Pd1 is considerably higher
as compared with Cu1 and Pd1 complexes of ref.[4a] whose
ligand only differs by lack of the vinylene group.[8] Actually,
introduction of the vinylene group produces a fairly long
polyene-like chain between the donor and acceptor groups
(see Scheme 5) and it is well-known that push-pull polyenes
are highly NLO active chromophores.[9]
Scheme 5
The NLO activity of Cu2 and Pd2 is not significantly
different as compared with Cu2 and Pd2 complexes of
ref.[4a] whose ligand lacks the ortho nitro group. This finding
may be explained on the basis of the crystallographic re- Scheme 6
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Second Order Optical Nonlinearities of Copper(II) and Palladium(II) Complexes
FULL PAPER
[D6]DMSO, 25 °C): δ ϭ 1.09 ppm (m, 12 H), 3.45 (m,8 H), 6.16
(s, 2 H), 6.26 (d, 2 H), 7.08 (d, 2 H), 7.33 (d, 2 H), 7.46 (d, 2 H),
it a promising candidate for further developments of our re-
search.
7.90 (d,
4 H), 8.19 (d, 6 H). UV/Vis: λmax (nm), εmax
(dm3molϪ1cmϪ1): 459, 6.6·104.
4-(2,4-Dinitrophenylethylidene)benzoic Acid: 4-Formylbenzoic acid
(10.0 g, 66.6 mmol) is dissolved in pyridine (50 mL) and piperidine
(2 mL) and refluxed. 2,4-Dinitrophenylacetic acid (15.0 g,
66.6 mmol) is added in fractions of 3 g every 15 minutes. After 3 h
the solution is concentrated to 30 mL and cooled. A yellow crystal-
line solid precipitates, then it is filtered off and washed with etha-
Experimental Section
Synthesis: Complexes CuN and PdN (N ϭ 1, 2, 3) were synthesized
according to the general procedure outlined in the scheme below
(Scheme 6) which starts with the synthesis of the organic ligands
LN (N ϭ 1, 2, 3), followed by the synthesis of dinuclear complexes
(MLN)2 and, from these, of the final mononuclear complexes MN,
according to Scheme 2.
1
nol. Yield 72%. M.p. 263 °C. H NMR (200 MHz, [D6]DMSO, 25
°C): δ ϭ 7.61 ppm (s, 2 H), 7.75 (d, J ϭ 8.2 Hz, 2 H), 7.96 (d, J ϭ
8.2 Hz, 2 H), 8.23 (d, J ϭ 8.8 Hz, 1 H), 8.50 (d, J ϭ 8.8 Hz, 1 H),
8.72 (d, J ϭ 2.2 Hz, 1 H).
4-Nitrocinnamohydrazide: 4-Nitrocinnamoyl chloride (obtained
from the acid refluxed in SOCl2) is dissolved in boiling ethanol
to obtain the ethyl ester. 4-Nitrocinnamic acid ethyl ester (5.00 g,
22.6 mmol) is dissolved in THF (50 mL). The solution is poured
into a mixture of water (25 mL), ethanol (50 mL), hydrazine
(18 mL) and it is stirred for 1.5 h at room temperature. Finally the
mixture is poured into water (100 mL) and cooled in a freezer for
12 h. An orange solid is recovered by vacuum filtration. Yield 30%.
M.p. 214 °C. 1H NMR (200 MHz, [D6]DMSO, 25 °C): δ ϭ 4.52
ppm (s, 2 H), 6.80 (d, J ϭ 16.2 Hz, 1 H), 7.53 (d, J ϭ 16.2 Hz, 1
H), 7.77 (d, J ϭ 8.7 Hz, 2 H), 8.22 (d, J ϭ 8.3 Hz, 2 H), 9.50 (s,
1 H).
4-(2,4-Dinitrophenylethylidene)benzohydrazide: 4-(2,4-Dinitrophen-
ylethylidene)benzoyl chloride (0.941 g, 2.83 mmol, obtained from
the corresponding acid by reaction with thionyl chloride according
to standard methods) is dissolved in hot anhydrous dioxane
(20 mL). The solution is cooled and poured into a mixture of hy-
drazine (2.8 mL), dioxane (10 mL) and water (5 mL) whilst stirring.
The reaction is rapid and after some minutes the mixture is poured
in water (50 mL), affording the precipitation of a yellow solid, reco-
vered by filtration, and washed repeatedly with water. Yield 86%.
M.p. 234 °C. 1H NMR (200 MHz, [D6]DMSO, 25 °C): δ ϭ 4.53
ppm (s, 2 H), 7.59 (s, 2 H), 7.72 (d, J ϭ 7.8 Hz, 2 H), 7.87 (d, J ϭ
7.8 Hz, 2 H), 8.23 (d, J ϭ 8.8 Hz, 1 H), 8.51 (d, J ϭ 8.6 Hz, 1 H),
8.74 (s, 1 H).9.83 (s, 1 H).
N-4-Diethylaminosalicylidene-NЈ-(4-nitrocinnamoyl)hydrazine (L1):
4-Nitrocinnamohydrazide (4.50 g, 21.7 mmol) and 4-N,N-diethyl-
amino-2-hydroxybenzaldehyde (4.60 g, 23.8 mmol) are dissolved in
boiling DMF (80 mL). After 15 minutes the solution is cooled and
then poured into water (400 mL) containing concentrated sulfuric
acid (5 mL). The red solid obtained is recovered by filtration,
washed several times with water, dried, and recrystallized from
DMF. Yield 6.06 g (73%). M.p. 223 °C. 1H NMR (200 MHz,
[D6]DMSO, 25 °C): δ ϭ 1.08 ppm (t, J ϭ 6.8 Hz, 6 H), 3.33 (m, 4
H), 6.10 (s, 1 H), 6.25 (d, J ϭ 8.6 Hz, 1 H), 6.83 (d, J ϭ 15.6 Hz,
1 H), 7.22 (d, J ϭ 8.8 Hz, 1 H), 7.70 (d, J ϭ 8.8 Hz, 1 H), 7.87 (d,
J ϭ 8.8 Hz, 2 H), 8.24 (s, 1 H), 8.26 (d, J ϭ 8.8 Hz, 2 H), 11.23 (s,
1 H), 11.71 (s, 1 H). IR (KBr): ν˜ ϭ 3409 cmϪ1 (m), 3206 (m, NϪH
str.), 2978 (m), 2933 (w), 1632 (vs, CϭO str.), 1592 (vs, NϪH bend),
1520 (vs), 1355 (s), 1339 (s), 1247 (m), 1134 (m). UV/Vis: λmax
(nm), εmax (dm3molϪ1cmϪ1): 406, 2.2·104.
N-4-Diethylaminosalicylidene-NЈ-4-(2,4-dinitrophenylethylidene)-
benzoylhydrazine (L2): 4-(2,4-dinitrophenylethylidene)benzohydraz-
ide (3.55 g, 10.8 mmol) and 4-N,N-diethylamino-2-hydroxyibenzal-
dehyde (2.20 g, 11.4 mmol) are dissolved in boiling DMF (50 mL).
After 15 minutes the solution is cooled and then poured into water
(100 mL) containing concentrated sulfuric acid (2 mL). The brown
solid obtained is recovered by filtration, washed several times with
water, dried and recrystallized from DMF/water. Yield 5.06 g
1
(93%). M.p. 276 °C. H NMR (200 MHz, [D6]DMSO, 25 °C): δ ϭ
1.09 ppm (t, J ϭ 6.8 Hz, 6 H), 3.33 (m, 4 H), 6.10 (s, 1 H), 6.23
(d, J ϭ 8.8 Hz, 1 H), 7.17 (d, J ϭ 8.8 Hz, 1 H), 7.62 (s, 2 H), 7.79
(d, J ϭ 7.6 Hz, 2 H), 7.95 (d, J ϭ 7.6 Hz, 2 H), 8.23 (d, J ϭ 8.8 Hz,
1 H), 8.41 (s, 1 H), 8.50 (d, J ϭ 8.6 Hz, 1 H), 8.73 (s, 1 H), 11.43
(s, 1 H), 11.82 (s, 1 H). IR (KBr): ν˜ ϭ 3334 cmϪ1 (m), 3208 (w,
NϪH str.), 2977 (m), 2933 (w), 1630 (vs, CϭO str.), 1595 (vs, NϪH
bend), 1520 (vs), 1355 (s), 1334 (s), 1246 (m), 1133 (m). UV/Vis:
λmax (nm), εmax (dm3molϪ1cmϪ1): 370, 5.6·104.
Synthesis of (CuL1)2: L1 (1.00 g, 2.61 mmol) and copper() acetate
(0.521 g, 2.61 mmol) are dissolved in DMF (35 mL). The solution
is heated to boiling and stirred for 15 minutes, then it is cooled and
poured into water (100 mL) containing sodium acetate (0.700 g,
8.53 mmol). A red-brown solid is recovered by filtration, washed
repeatedly with water, and recrystallized from DMF. Yield 91%.
M.p. 312 °C dec. C40H40N8O8Cu2: calcd. C 54.11, H 4.51, N 12.63,
Cu 14.31; found C 54.22, H 4.64, N 12.57, Cu 13.91%. UV/Vis:
λmax (nm), εmax (dm3molϪ1cmϪ1): 469, 4.5·104.
Synthesis of (CuL2)2: L2 (1.00 g, 1.99 mmol) and copper() acetate
(0.397 g, 1.99 mmol) are dissolved in DMF (35 mL). The solution
is heated to boiling and stirred for 15 minutes, then it is cooled and
poured into water (100 mL) containing sodium acetate (0.700 g,
8.53 mmol). A dark brown solid is recovered by filtration, washed
repeatedly with water, and recrystallized from DMF. Yield 90%.
M.p. 308 °C dec. C52H46N10O12Cu2: Cu 11.25, C 55.27, H 4.10, N
12.39; found Cu 10.92, C 54.98, H 4.02, N 12.11%. UV/Vis: λmax
(nm), εmax (dm3molϪ1cmϪ1): 400, 5.8·104.
Synthesis of (PdL1)2: L1 (1.00 g, 2.61 mmol) is dissolved in boiling
THF (20 mL). The solution is added with THF (20 mL) containing
bis(benzonitrile) PdII dichloride (1.00 g, 2.61 mmol). After 15 mi-
nutes of stirring, a solution of sodium acetate (1.00 g, 12.2 mmol)
Synthesis of (PdL2)2: L2 (1.00 g, 1.99 mmol) is dissolved in boiling
in water (20 mL) is added. The pH is raised to about 8Ϫ9 by adding THF (15 mL). The solution is added with THF (10 mL) containing
a 10 wt.% solution of KOH. After some minutes, the addition of
100 mL of water affords the precipitation of a dark red solid, which
is filtered off, washed repeatedly with water, dried and finally
washed with boiling heptane. Yield 91%. M.p. 311 °C dec.
bis(benzonitrile)PdII dichloride (0.763 g, 1.99 mmol). A solution of
sodium acetate (1.00 g, 12.2 mmol) in water (20 mL) is added. The
pH is raised to 8Ϫ9 by adding a solution of 0.300 g of KOH in
100 mL of water. On heating, a dark red-brown solid coagulates,
C40H40N8O8Pd2: calcd. C 49.34, H 4.11, N 11.51, Pd 21.90; found then filtered off, washed repeatedly with water, dried, and washed
C 49.66, H 4.27, N 11.51, Pd 22.30%. 1H NMR (200 MHz, with boiling heptane. Yield 85%. M.p. 291 °C dec.
Eur. J. Inorg. Chem. 2004, 2467Ϫ2476
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2473

R. Centore, A. Roviello et al.
FULL PAPER
C52H46N10O12Pd2: Pd 17.50, C 51.37, H 3.81, N 11.52%; found Pd
Synthesis of (PdL3)2: L3 (1.00 g, 2.11 mmol) is suspended in 20 mL
17.21,
C 51.08, H 3.65, N
11.24%. 1H NMR (200 MHz, of boiling THF. The solution is added with THF (10 mL) contain-
[D6]DMSO, 25 °C): δ ϭ 1.09 ppm (t, 12 H), 3.33 (m, 8 H), 6.15 (s, ing bis(benzonitrile)PdII dichloride (0.809 g, 2.11 mmol), obtaining
2 H), 6.25 (d, 2 H), 7.32 (d, 2 H), 7.59 (s, 4 H), 7.66 (d, 4 H), 7.97
(d, 4 H), 8.25 (d, 2 H), 8.41 (s, 2 H), 8.48 (d, 2 H), 8.72 (s, 2 H).
UV/Vis: λmax (nm), εmax (dm3molϪ1cmϪ1): 369, 5.2·104.
a yellow heterogeneous mixture which becomes a dark red solution
by adding 20 mL of water containing sodium acetate (1.00 g,
12.2 mmol). The pH is raised to 8Ϫ9 with a solution of 0.300 g of
KOH in 100 mL of water and a brown solid coagulates, which is
filtered off, washed repeatedly with water, dried, and washed with
boiling heptane. Yield 85%. M.p. 298 °C dec. C50H42N10O10Pd2:
Pd 18.41, C 51.96, H 3.66, N 12.12%; found Pd 18.35, C 51.85, H
3.55, N 12.01%. UV/Vis: λmax (nm), εmax (dm3molϪ1cmϪ1): 446,
6.0·104.
N-(4-Carboxybenzylidene)-2-hydroxy-4-nitroaniline: 4-Formylben-
zoic acid (5.00 g, 33.3 mmol) is suspended in boiling absolute etha-
nol (60 mL). Successively a solution of 2-hydroxy-4-nitroaniline
(5.00 g, 32.4 mmol) in ethanol (60 mL) is added. After boiling
30 min the solution is cooled, obtaining a pure yellow solid, then
filtered off. Yield 54%. M.p. 246 °C. 1H NMR (200 MHz,
[D6]DMSO, 25 °C): δ ϭ 7.35 ppm (d, J ϭ 6.3 Hz, 1 H), 7.76 (d,
J ϭ 1.8 Hz, 1 H), 7.78 (dd, J1 ϭ 1.8, J2 ϭ 6.3 Hz, 1 H), 8.05 (d,
J ϭ 6.3 Hz, 2 H), 8.17 (d, J ϭ 6.3 Hz, 2 H), 8.80 (s, 1 H), 13.32 (s,
1 H).
Synthesis of CuN and PdN: The corresponding dinuclear precursor
is dissolved in pyridine at room temperature, then the solvent is
allowed to evaporate from the solution leaving crystals of the
mononuclear complex.
4-(6-Nitro-2-benzoxazolyl)benzoic Acid: N-(4-Carboxybenzylidene)-
2-hydroxy-4-nitroaniline (5.20 g, 18.2 mmol) is suspended in glacial
acetic acid (100 mL). Lead() acetate (9.68 g, 21.8 mmol) is added
slowly under strong stirring. The reaction takes 2 h. The product
is filtered off, washed with acetic acid, and recrystallized from
Cu1: C25H25N5O4Cu·1/2C5H5N: calcd. C 58.71, H 4.93, N 13.69;
found C 58.41, H 4.96, N 13.42. UV/Vis: λmax (nm), εmax
(dm3molϪ1cmϪ1): 471, 2.8·104.
Pd1: C30H30N6O4Pd: calcd. C 55.86, H 4.69, N 13.03; found C
55.33, H 4.68, N 12.86. UV/Vis: λmax (nm), εmax (dm3molϪ1cmϪ1):
463, 3.3·104.
1
DMF. Yield 31%. M.p. 319 °C. H NMR (200 MHz, [D6]DMSO,
25 °C): δ ϭ 7.90 ppm (d, J ϭ 5.8 Hz, 1 H), 8.25 (d, J ϭ 5.2 Hz, 2
H), 8.37 (d, J ϭ 5.8 Hz, 1 H), 8.39 (d, J ϭ 5.2 Hz, 2 H), 8.54 (s,
1 H).
Cu2: C36H33N7O6Cu: calcd. C 59.79, H 4.60, N 13.56; found 59.51,
H 4.70, N 13.36. UV/Vis: λmax (nm), εmax (dm3molϪ1cmϪ1): 400,
2.9·104.
4-(6-Nitro-2-benzoxazolyl)benzohydrazide: 4-(6-Nitro-2-benzoxazo-
lyl)benzoyl chloride (3.00 g, 9.91 mmol, obtained from the corre-
sponding acid by reaction with thionyl chloride according to stand-
ard methods) is dissolved in hot anhydrous dioxane (60 mL). The
solution is cooled and poured into a mixture of ethanol (50 mL)
and hydrazine monohydrate (5 mL) whilst stirring. The product is
a yellow solid which is recrystallized from DMF. Yield 57%. M.p.
280 °C. 1H NMR (200 MHz, [D6]DMSO, 25 °C): δ ϭ 4.67 ppm (s,
2 H), 8.06 (d, J ϭ 8.4 Hz, 1 H), 8.18 (d, J ϭ 8.4 Hz, 1 H), 8.30 (d,
J ϭ 8.6 Hz, 2 H), 8.39 (d, J ϭ 8.4 Hz, 2 H), 8.76 (s, 1 H), 10.02 (s,
1 H).
Pd2: C36H33N7O6Pd: calcd. C 56.44, H 4.34, N 12.80; found C
56.05, H 4.45, N 12.69. UV/Vis: λmax (nm), εmax (dm3molϪ1cmϪ1):
361, 2.4·104.
Cu3: C35H31N7O5Cu: calcd. C 60.64, H 4.51, N 14.14; found C
59.21, H 4.40, N 13.80. UV/Vis: λmax (nm), εmax (dm3molϪ1cmϪ1):
460, 2.8·104.
Pd3: C30H26N6O5Pd: calcd. C 54.85, H 3.99, N 12.18; found C
54.71, H 4.12, N 12.53. UV/Vis: λmax (nm), εmax (dm3molϪ1cmϪ1):
450, 2.9·104.
N-4-Diethylaminosalicylidene-NЈ-4-(6-nitro-2-benzoxazolyl)benzoyl-
hydrazine (L3): 4-(6-Nitro-2-benzoxazolyl)benzohydrazide (1.67 g,
Synthesis of Grafted Polymers: Commercial poly(4-vinylpyridine)
(Aldrich, Mav ഠ 60000 D, Tgϭ 147 °C) was used as the starting
material after drying at 120 °C in oven for 16 h. Grafted polymers
were prepared according to a standard procedure. The polymer and
the dinuclear complex (ML1)2 (total amount 1.0 g) in the proper
weight ratio are solved in DMF (10 mL) at 90 °C. After stirring
for 15Ј at 90 °C, the mixture is poured in water (100 mL) containing
2% sodium acetate (by weight). The precipitated polymer is reco-
vered by filtration (90% yield), washed repeatedly with water and
dried in oven at 130 °C. Grafted polymers are indicated as MW,
where M stands for Cu or Pd and W is the weight percent ratio of
(ML1)2 to polymer. Grafted polymers Cu35, Pd35, Cu60, and Pd60
were prepared. Analytical data: Cu35: %Cu calcd. 5.01; found 5.08.
Cu60: %Cu calcd. 8.59; found 8.47. Pd35: %Pd calcd. 7.67; found
7.67. Pd60: %Pd calcd. 13.13; found 13.21.
5.60 mmol)
and
4-N,N-diethylamino-2-hydroxyibenzaldehyde
(1.14 g, 5.90 mmol) are dissolved in boiling DMF (30 mL). After
15 minutes the solution is cooled and then poured into water
(100 mL) containing concentrated sulfuric acid (1 mL). The prod-
uct is recovered by filtration, washed several times with water,
dried, and recrystallized from DMF. Yield 2.39 g (90%). M.p. 257
°C. 1H NMR (200 MHz, [D6]DMSO, 25 °C): δ ϭ 1.13 ppm (t, J ϭ
6.6 Hz, 6 H), 3.37 (m, 4 H), 6.13 (s, 1 H), 6.27 (d, J ϭ 6.9 Hz, 1
H), 7.21 (d, J ϭ 8.7 Hz, 2 H), 8.05 (d, J ϭ 8.4 Hz, 2 H), 8.16 (d,
J ϭ 8.4 Hz, 2 H), 8.23 (m, 2 H), 8.45 (s, 1 H), 8.73 (s, 1 H), 11.40
(s, 1 H), 11.99 (s, 1 H). IR (KBr): ν˜ ϭ 3474 cmϪ1 (w), 3201 (m,
NϪH str.), 2979 (m), 1654 (vs), 1628 (vs, CϭO str.), 1593 (vs, NϪH
bend), 1520 (vs), 1360 (s), 1342 (s), 1248 (m), 1135 (m). UV/Vis:
λmax (nm), εmax (dm3molϪ1cmϪ1): 343, 2.8·104.
Synthesis of (CuL3)2: L3 (1.00 g, 2.11 mmol) and copper() acetate
(0.422 g, 2.11 mmol) are solved in DMF (35 mL). The solution is
heated to boiling and stirred for 15 minutes, then it is cooled and
Physical Measurements: The thermal behavior of compounds was
studied by differential scanning calorimetry (PerkinϪElmer Pyris,
N2 atmosphere, scanning rate 10 K/min), temperature controlled
poured into water (100 mL) containing sodium acetate (0.700 g, polarizing microscopy (Zeiss microscope, Mettler hot stage) and
8.53 mmol). A dark orange solid is recovered by filtration, washed TGA-DTA analysis (TA Instruments SDT 2960, air atmosphere,
repeatedly with water, and recrystallized from DMF. Yield 89%. scanning rate 10 K/min). Proton NMR spectra were recorded on a
M.p. 327 °C dec. C50H42N10O10Cu2: Cu 11.88, C 56.12, H 3.96, N
13.09 ; found Cu 12.30, C 55.96, H 3.77, N 12.86%. UV/Vis: λmax
(nm), εmax (dm3molϪ1cmϪ1): 435, 5.2·104.
Varian XL 200 spectrometer. UV/Vis (DMF solution) and FT-IR
(KBr) spectra were recorded with JASCO spectrometers. Films of
the grafted polymers were obtained by the spin coating technique
2474
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
Eur. J. Inorg. Chem. 2004, 2467Ϫ2476

Second Order Optical Nonlinearities of Copper(II) and Palladium(II) Complexes
Table 4. Crystal, collection and refinement data for Cu1, Cu2, Pd2, Cu3
FULL PAPER
Cu1
Cu2
Pd2
Cu3
Chemical formula
Molecular mass
T [K]
2(C25H25N5O4Cu)·C5H5N
1125.20
293
monoclinic
P21/c
15.85(5)
19.10(1)
16.12(4)
90
146.9(1)
C36H33N7O6Cu
723.23
293
C31H28N6O6Pd·C5H5N
766.09
293
monoclinic
C2/c
36.84(1)
8.605(2)
27.73(1)
90
129.9(1)
90
6744(3)
8, 1.509
0.608
C35H31N7O5Cu
693.21
293
monoclinic
P21/c
16.029(7)
12.924(9)
16.59(1)
90
109.03(6)
90
3249(3)
4, 1.417
0.727
Crystal system
Space group
triclinic
¯
P1
˚
a [A]
9.224(4)
˚
b [A]
10.793(2)
18.132(7)
101.71(3)
100.74(5)
98.69(2)
1703(1)
2, 1.411
˚
c [A]
α [°]
β [°]
γ [°]
90
2660(10)
2, 1.402
3
˚
V [A ]
Z, Dx [g/cm3]
µ [mmϪ1
]
0.863
0.698
Theta range
1.71°Ϫ27.97°
6284/343
0.0515, 0.1281
0.1416, 0.1562
1.18°Ϫ27.97°
8198/451
0.0419, 0.1090
0.0792, 0.1231
1.44°Ϫ27.97°
8084/451
0.0507, 0.1095
0.1285, 0.1319
1.35°Ϫ27.97°
7759/433
0.0662, 0.1307
0.3336, 0.1924
Data/parameters
R1, wR2 [I Ͼ 2σ(I)]
R1, wR2 (all data)
(NMP solutions, SCS P6700 spincoater operating at 800Ϫ1000
rounds/min). Residual solvent was removed by keeping the films in
oven at 120 C for 12 h.
Union Road, Cambridge CB2 1EZ, UK; Fax: (internat.) ϩ44-
1223-336-033; E-mail: deposit@ccdc.cam.ac.uk].
NLO Measurements: Second order optical nonlinearities of chrom-
ophores, in the form of µgβ products (µg is the ground state perma-
nent dipole moment and β the quadratic hyperpolarizability of the
molecules), were measured by the EFISH (Electric Field Induced
Second Harmonic generation) technique.[15] Measurements were
carried out in DMSO solutions at a fundamental wavelength of
1.907 µm, using a Q-switched, mode locked Nd3:YAG laser, whose
1.064 µm initial wavelength was shifted by stimulated
Raman scattering in a high-pressure hydrogen cell.
X-ray Analysis: Single crystals of Cu1, Cu2, Pd2, and Cu3 suitable
for X-ray analysis were obtained by slow evaporation of pyridine
solutions at ambient temperature. Cell parameters were obtained
through a least-squares fit[12] to the θ angles of 25 accurately cen-
tered strong reflections in the ranges 12.173°Յ θ Յ 13.480° for
Cu1, 15.907°Յ θ Յ 17.512° for Cu2, 12.009°Յ θ Յ 13.551° for Pd2
and 9.140°Յ θ Յ 12.147° for Cu3 on an EnrafϪNonius MACH 3
automated single crystal diffractometer, using graphite monochro-
˚
mated Mo-Kα radiation (λϭ 0.71069 A). Data collection was per-
formed on the same apparatus. Semiempirical absorption correc-
tion (ψ scans) was applied in all cases. The structures were solved
by direct methods (SIR92 program[13]), completed by difference
Fourier methods and refined by the full-matrix least-squares
method (SHELXL program of SHELX 97 package[14]). Refinement
was on F2 against all independent measured reflections; sigma
weights were introduced in the last refinement cycles. The largest
Acknowledgments
`
We thank the CIMCF of the Universita di Napoli ‘‘Federico II’’ for
permission to use the Nonius MACH3 diffractometer and NMR
spectrometers. Financial support of MIUR of Italy (PRIN 2002)
is also acknowledged.
peaks and holes in the last Fourier difference were (e·AϪ3): 0.689
˚
and Ϫ0.514 for Cu1, 0.379 and Ϫ0.235 for Cu2, 0.691 and Ϫ0.498
for Pd2, and 0.448 and Ϫ0.498 for Cu3. In all structures C, N, O
and metal atoms were given anisotropic displacement parameters.
H atoms were placed in calculated positions and refined by the
riding model with Uiso equal to Ueq of the carrier atoms. In the
crystals of Cu1 the pyridine molecule not coordinated to the metal
is located on a crystallographic inversion center and therefore is
statistically disordered (two centrosymmetrically related sites with
0.5 occupation factor). Some crystal, collection and refinement
data are reported in Table 4. CCDC-221599 (for Cu1), -221600 (for
Cu2), -221601 (for Pd2), and -221602 (for Cu3) contain the sup-
plementary crystallographic data for this paper. These data can be
obtained free of charge at www.ccdc.cam.ac.uk/conts/retriev-
ing.html [or from the Cambridge Crystallographic Data Centre, 12
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`
R. Centore, CELLFIT; Universita di Napoli ‘‘Federico II’’:
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2476
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