Synthesis, structure, and second-order nonlinear optical properties of copper(II) and palladium(II) acentric complexes with N-salicylidene-N′-aroylhydrazine tridentate ligands

Article abstract of DOI:10.1021/ic020127k

Two new N-salicylidene-N′-aroylhydrazines ligands have been prepared: N-4-diethylaminosalicylidene-N′-4-nitrobenzoyl-hydrazine (L₁) and N-4-diethylaminosalicylidene-N′-4-(4-nitrophenylethylidene) -benzoyl-hydrazine (L₂). The ligands are properly functionalized with strong electron donor-acceptor groups and are of potential interest in second-order nonlinear optics (NLO). Dimeric copper(II) and palladium(II) complexes with L₁ and L₂ have been prepared, and, starting from these, mononuclear acentric adducts with pyridine as a further ligand have been prepared and characterized. The X-ray structures of three adducts are also reported. The NLO activity of the adducts has been determined by EFISH measurements giving μβ values up to 1500 x 10^-48 esu for an incident wavelength of 1.907 μm.

Full text of DOI:10.1021/ic020127k

Inorg. Chem. 2002, 41, 6597−6603
Synthesis, Structure, and Second-Order Nonlinear Optical Properties of
Copper(II) and Palladium(II) Acentric Complexes with
N-Salicylidene-N ′-aroylhydrazine Tridentate Ligands
,‡
,‡
F. Cariati,† U. Caruso,‡ R. Centore,* W. Marcolli,†,§ A. De Maria,‡ B. Panunzi,| A. Roviello,* and
A. Tuzi‡
Dipartimento di Chimica, UniVersita` degli Studi di Napoli “Federico II”, Via Cinthia,
80126 Napoli, Italy, Dipartimento di Chimica Inorganica, Metallorganica ed Analitica,
UniVersita` degli Studi di Milano, Via Venezian 21, 20133 Milano, Italy,
Consorzio InteruniVersitario Nazionale per la Scienza e Tecnologia dei Materiali,
Via B. Varchi 59, 50132 Firenze, Italy, and Dipartimento di Scienza degli Alimenti,
UniVersita` degli Studi di Napoli “Federico II”, Via UniVersita` 100, 80055 Napoli, Italy
Received February 14, 2002
Two new N-salicylidene-N ′-aroylhydrazines ligands have been prepared: N-4-diethylaminosalicylidene-N ′-4-
nitrobenzoyl-hydrazine (L ) and N-4-diethylaminosalicylidene-N ′-4-(4-nitrophenylethylidene)-benzoyl-hydrazine (L ).
1
2
The ligands are properly functionalized with strong electron donor−acceptor groups and are of potential interest in
second-order nonlinear optics (NLO). Dimeric copper(II) and palladium(II) complexes with L and L have been
1
2
prepared, and, starting from these, mononuclear acentric adducts with pyridine as a further ligand have been
prepared and characterized. The X-ray structures of three adducts are also reported. The NLO activity of the
adducts has been determined by EFISH measurements giving µâ values up to 1500 × 10-48 esu for an incident
wavelength of 1.907 µm.
Introduction
along a push-pull organic system. In that case, the choice
of metals that give planar coordination geometry may force
a coplanar arrangement of the organic skeleton, so improving
conjugation and, possibly, NLO properties.5,6
Metal coordination has been used in several ways to
improve the behavior of all organic push-pull chromophores
for applications in second-order nonlinear optics (NLO). The
most common approach is the use of organometallic or metal
coordinated fragments attached at the end of organic π
conjugated systems: proper choice of the metal and its
oxidation state and of the ligands allows the fragment to
behave as an electron donor or acceptor group.1 In some cases
metals have been used as cations involved in ionic bonds
with negatively charged conjugated π systems giving non-
centrosymmetric crystals (phenate or carboxylate salts).2-4
Another possibility is using metals as conjugation bridges
The step toward a NLO material is based on the inclusion
of the NLO active molecules (chromophores) within a
polymer matrix; this may be performed without covalent
bonding (guest-host systems) or with. In the latter case NLO
active fragments of the polymer chain are oriented under a
strong electric field by heating the polymer above the glass
transition temperature (poling) and the orientation is frozen
by cooling the poled polymer below the glass transition.7
(2) Minemoto, H.; Sonoda, N.; Miki, K. Acta Crystallogr. 1992, C48,
737-738.
† Universita` degli Studi di Milano.
‡ Dipartimento di Chimica, Universita` degli Studi di Napoli “Federico
II”.
(3) Brahadeeswaran, S.; Venkataramanan, V.; Sherwood, J. N.; Bhat, H.
L. J. Mater. Chem. 1998, 8, 613-618.
§ Consorzio Interuniversitario Nazionale per la Scienza e Tecnologia dei
Materiali.
(4) Centore, R.; Tuzi, A. Acta Crystallogr. 2001, C57, 698-701.
(5) Buey, J.; Coco, S.; Diez, L.; Espinet, P.; Martin-Alvarez, J. M.; Miguel,
J. A.; Garcia-Granda, S.; Tesoro, A.; Ledoux, I.; Zyss, J. Organome-
tallics 1998, 17, 1750-1755.
(6) Centore, R.; Panunzi, B.; Roviello, A.; Tuzi, A. Acta Crystallogr. 2002,
C58, m26-m28.
(7) Dalton, L.; Harper, A.; Ren, A.; Wang, F.; Todorova, G.; Chen, J.;
Zhang, C.; Lee, M. Ind. Eng. Chem. Res. 1999, 38, 8-33.
| Dipartimento di Scienza degli Alimenti, Universita` degli Studi di Napoli
“Federico II”.
* Authors for correspondence. E-mail: centore@chemistry.unina.it
(R.C.); roviello@chemistry.unina.it (A.R.).
(1) Whittall, I. R.; McDonagh, A. M.; Humphrey, M. G.; Samoc, M. AdV.
Organomet. Chem. 1998, 42, 291-361 and references therein.
10.1021/ic020127k CCC: $22.00 © 2002 American Chemical Society
Published on Web 11/14/2002
Inorganic Chemistry, Vol. 41, No. 25, 2002 6597

Cariati et al.
Scheme 1
Scheme 2
In the present paper we report the synthesis and charac-
further coordination with donor atoms is possible (N atom
of the coordinated pyridine in the reported compounds); this
feature, which is well-known in this class of complexes,8 is
particularly attractive in our case, since the donor atom might
belong to a polymer matrix, this allowing automatically the
covalent anchorage of the NLO active organometallic frag-
ments to a preformed polymer chain. We have explored
successfully this possibility using commercial poly(4-vi-
nylpyridine).11
terization, including NLO measurements, of some [(N-
salicylidene-N′-aroylhydrazine) ONO (pyridine)] Cu(II) and
Pd(II) complexes of potential interest in second-order NLO,
as depicted in Scheme 1.
N-Aroyl-N-salicylidene-hydrazine copper (II) complexes
and their adducts with monodentate neutral Lewis bases have
been studied up to now for biological and magnetic
properties.8-10
In the present compounds the organic tridentate ligand has
been properly functionalized with strong electron donor
acceptor groups, this making them of potential interest in
second-order NLO. Furthermore, these compounds have
some peculiarities with respect to the above-described
approaches for generating NLO active metal coordinated
materials that are worth being briefly summarized.
First of all the ligand alone is not expected to show a high
NLO activity because its electronic structure should be in
the keto (amide) form (I, Scheme 2) with rather low
conjugation from the dialkylamino donor to the nitro acceptor
group. Upon coordination to the metal, the electronic
structure of the ligand changes in the enolic form (II) with
increase in the conjugation and, hence, in NLO activity.
Therefore, in this case, the primary role played by the
metal is that of generating the actual push-pull chromophore.
Furthermore, the use of square planar coordinating metals
(Cu(II) or Pd(II)) should force the organic ligand in a planar
conformation so as to maximize conjugation.
Experimental Section
Synthesis. Compounds Cu1, Cu2, Cu2*, Pd1, and Pd2 were
synthesized according to the general procedure depicted in Scheme
3 starting with the synthesis of the organic ligands (L1 and L2),
followed by the synthesis of the dinuclear complexes (CuL1)2,
(PdL1)2, (CuL2)2, and (PdL2)2 and, from these, of the final
compounds.
Synthesis of L1. N-4-Diethylaminosalicylidene-N ′-4-nitroben-
zoyl-hydrazine. 4-Nitrobenzoyl hydrazide (9.06 g, 0.050 mol) and
9.26 g (0.050 mol) of 4-N,N-diethylamino-2-hydroxybenzaldehyde
are dissolved in 70 mL of DMF. The solution is heated to boiling
for 5 min and then is cooled to room temperature and poured into
400 mL of water containing crushed ice and 8 mL of concentrated
sulfuric acid. The formed red solid is recovered by filtration, washed
repeatedly with water, and recrystallized from DMF/water. Yield:
12.47 g (70%). Mp: 230 °C.
1H NMR (DMSO-d6) δ (ppm): 1.07 (m, 6H); 3.31 (m, 4H);
6.09 (s, 1H); 6.30 (d, 1H, J ) 8.79 Hz); 7.20 (dd, 1H, J1 ) 8.79
Hz, J2 ) 3.42 Hz); 8.18 (m, 2H); 8.37 (m, 3H); 11.25 (s, 1H);
12.04 (s, 1H).
IR (KBr, cm-1): 3366 (m), 3187 (w, N-H str), 2976 (m), 2934
(w), 1631 (vs, CdO str), 1594 (vs, N-H bend), 1519 (vs), 1360
(s), 1342 (s), 1245 (m), 1134 (m), 706 (m).
UV-vis λmax (nm), ꢀmax (dm3 mol-1 cm-1): 358, 2.3 × 104.
Second, the metal coordinated to the ligand is electrically
neutral but coordinatively unsaturated. This means that
(8) Kato, M.; Muto, Y. Coord. Chem. ReV. 1988, 92, 45.
(9) Warda, S. A.; Dahlke, P.; Wocadlo, S.; Massa, W.; Friebel, C. Inorg.
Chim. Acta 1998, 268, 117-124.
(10) Iskander, M. F.; Khalil, T. E.; Werner, R.; Haase, W.; Svoboda, I.;
Fuess, H. Polyhedron 2000, 19, 1181-1191.
(11) Caruso, U.; De Maria, A.; Panunzi, B.; Roviello, A. J. Polym. Sci.,
Part A: Polym. Chem. 2002, 40, 2987-2993.
6598 Inorganic Chemistry, Vol. 41, No. 25, 2002

NoWel N-Salicylidene-N ′-aroylhydrazine Ligands
Scheme 3
Synthesis of (CuL1)2. L1 (0.40 g, 1.12 mmol), 0.22 g (1.12
mmol) of copper(II) acetate, and 0.50 g (6.10 mmol) of sodium
acetate are suspended, under stirring, in hot absolute ethanol. After
being stirred for 10 min, the formed dark red solid is recovered by
filtration and recrystallized from DMF/water. Yield: 0.30 g (65%).
Mp: 340 °C dec.
1H NMR (DMSO-d6) δ (ppm): 1.23 (m, 12H); 3.45 (m, 8H);
6.24 (s, 2H); 6.35 (d, 2H, J ) 8.79 Hz); 7.43 (d, 2H, J ) 8.79 Hz);
8.20 (m, 10H).
UV-vis λmax (nm), ꢀmax (dm3 mol-1 cm-1): 460, 3.6 × 104.
Synthesis of Cu1 and Pd1. In both cases 300 mg of the
corresponding dinuclear precursor is dissolved in 5 mL of boiling
pyridine. After 5 min the mononuclear complex is obtained by
addition of water. The solid is recovered by filtration and recrystal-
lized several times from pyridine/water. Final yields are about 75%
in both cases.
Anal. Calcd for C36H36N8O8Cu2: C 51.74, H 4.55, N 13.41, Cu
15.21. Found: C 51.72, H 4.44, N 13.43, Cu 15.06.
UV-vis λmax (nm), ꢀmax (dm3 mol-1 cm-1): 460, 4.7 × 104.
Synthesis of (PdL1)2. L1 (0.73 g, 2.05 mmol) is dissolved in 10
mL of THF at 50 °C. To this is added a solution obtained by
dissolving 0.77 g (2.01 mmol) of bis(benzonitrile) Pd(II) dichloride
in 15 mL of THF. A yellow suspension is formed to which sodium
acetate (1.0 g dissolved in 20 mL of water) is added. A red solution
is obtained, whose pH is raised to 9 by proper addition of KOH
(pellets). After stirring for some minutes, 60 mL of water is added
to the solution, affording the precipitation of a red-orange solid,
which is filtered off, washed repeatedly with water, dried, and
finally washed with boiling heptane. Yield: 0.63 g (67%). Mp:
280 °C dec.
Cu1. Anal. Calcd for C23H23N5O4Cu: C 55.58, H 4.66, N 14.09,
Cu 12.79. Found: C 55.55, H 4.70, N 14.22, Cu 12.65.
UV-vis λmax (nm), ꢀmax (dm3 mol-1 cm-1): 460, 2.4 × 104.
Pd1. Anal. Calcd for C23H23N5O4Pd: C 51.17, H 4.29, N 12.97,
Pd 19.71. Found: C 50.94, H 4.33, N 12.90, Pd 19.16.
1H NMR (CDCl3) δ (ppm): 1.19 (m, 6H), 3.37 (q, 4H, J )
7.10 Hz), 6.23 (d, 1H, J ) 8.79 Hz), 6.39 (s, 1H), 7.25 (m,
overlapped to solvent), 7.78 (m, 2H), 7.82 (s, 1H), 7.98 (t, 1H, J
) 7.33 Hz), 8.21 (m, 4H), 9.30 (d, 2H, J ) 5.37 Hz).
UV-vis λmax (nm), ꢀmax (dm3 mol-1 cm-1): 459, 2.5 × 104.
Synthesis of L2. N-4-Diethylaminosalicylidene-N ′-4-(4-nitro-
phenylethylidene)-benzoyl-hydrazine. 4-Nitrostilbene hydrazide
Anal. Calcd for C36H36N8O8Pd2: C 46.92, H 3.90, N 12.16, Pd
23.09. Found: C 46.73, H 4.12, N 12.19, Pd 23.65.
Inorganic Chemistry, Vol. 41, No. 25, 2002 6599

Cariati et al.
(6.86 g, 0.024 mol) and 4.80 g (0.025 mol) of 4-diethylamino-2-
hydroxybenzaldehyde are dissolved in 50 mL of boiling DMF
containing 0.5 mL of concentrated sulfuric acid. After 5 min of
stirring, 5 mL of water is added. The orange solid formed is filtered,
washed with water, and dried. Final recrystallization from DMF
gives 8.25 g of the compound (75% yield). Mp: 286 °C.
1H NMR (DMSO-d6) δ (ppm): 1.07 (t, 6H, J ) 6.83 Hz); 3.35
(m, 4H); 6.10 (s, 1H); 6.23 (d, 1H, J ) 8.79 Hz); 7.16 (d, 1H, J )
8.79 Hz); 7.56 (s, 2H); 7.89 (m, 6H); 8.25 (d, 2H, J ) 8.79 Hz);
8.41 (s, 1H); 11.45 (s, 1H); 11.80 (s, 1H).
a Mettler FP5 microfurnace, scanning rate 10 K/min, glass slides),
and combined TGA-DTA analysis (TA Instruments SDT 2960, air
atmosphere, scanning rate 10 K/min). Proton NMR spectra were
recorded on a Varian XL 200 and Bruker MW 400 spectrometers.
UV-vis spectra were recorded with a Perkin-Elmer Lambda 7 UV-
vis spectrophotometer. IR spectra were recorded from KBr pellets
on a FT-IR JASCO spectrometer.
X-ray Analysis. Single crystals suitable for X-ray analysis were
obtained by slow evaporation, at ambient temperature, of a pyridine
solution for Cu1; for Pd1 they were grown from a hot pyridine/
ethanol/water solution (70/30/10 vv) by slow cooling at 4 °C; for
Cu2*, single crystals were obtained from a saturated pyridine
solution at 100 °C by slow cooling.
IR (KBr, cm-1): 3419 (m), 3225 (w, N-H str), 2975 (mw),
2931 (w), 1632 (vs, CdO str), 1591 (vs, N-H bend), 1519 (vs),
1341 (vs), 1248 (s), 1134 (s), 855 (m), 696 (m).
UV-vis λmax (nm), ꢀmax (dm3 mol-1 cm-1): 380, 4.9 × 104.
Accurate cell parameters were obtained through a least-squares
fit to the setting angles of 25 accurately centered strong reflections
in the ranges 12.10° e θ e 13.42° for Cu1, 12.19° e θ e 13.96°
for Pd1, and 11.92° e θ e 15.72° for Cu2* on an Enraf-Nonius
MACH 3 automated single-crystal diffractometer, using graphite-
monochromated Mo KR radiation (λ ) 0.71069 Å). Data collection
was performed on the same apparatus in the ω/θ scan mode. In all
cases crystal specimens remained stable during data collection as
confirmed by the intensity of control reflections periodically
measured, which showed only random fluctuations. Semiempirical
absorption correction (ψ scans) was applied in all cases. The
structures were solved by direct methods (SHELXS program of
SHELX 97 package12), completed by difference Fourier methods
and refined by the full matrix least-squares method (SHELXL
program of the same package). Refinement was on F2 against all
independent measured reflections; σ weights were introduced in
the last refinement cycles. The largest peaks and holes in the last
Fourier difference were (e Å-3) 0.426 and -0.454 for Cu1, 0.673
and -0.690 for Pd1, and 0.858 and -0.766 for Cu2*. In all
structures C, O, N, 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 case of Cu1 one of the ethyl groups is
disordered on two sites corresponding to the two common
geometries found for the diethylamino group, i.e., binary symmetry
around the N to phenyl bond and mirror symmetry through the
plane perpendicular to the phenyl and containing the N to phenyl
bond. The two sites were handled with 0.5 occupation factor without
introducing constraints. A search in the April 2001 release of the
CSD file13 has given three cases of identical disorder.14-16 H atoms
of the water molecule in Pd1 have not been considered. Some
crystal, collection, and refinement data are reported in Table 1.
NLO Measurements. Measurements of second-order nonlinear
optical properties were performed by the EFISH (electric field
induced second harmonic generation) technique.17
Synthesis of (CuL2)2. L2 (5.0 g, 0.011 mol), 2.2 g (0.011 mol)
of copper(II) acetate, and 3.5 g (0.045 mol) of sodium acetate are
dissolved in 120 mL of boiling DMF. After 10 min of stirring, the
dark red solid formed is recovered by filtration and recrystallized
from DMF/water. Yield: 3.43 g (60%). Mp: 335 °C dec.
UV-vis λmax (nm), ꢀmax (dm3 mol-1 cm-1): 460, 7.8 × 104.
Anal. Calcd for C52H48N8O8Cu2: C 60.06, H 4.61, N 10.78, Cu
12.22. Found: C 59.87, H 4.71, N 10.77, Cu 12.37.
Synthesis of (PdL2)2. L2 (0.85 g, 1.86 mmol) is dissolved in 10
mL of THF at 50 °C. To this is added a solution obtained by
dissolving 0.70 g (1.83 mmol) of bis(benzonitrile) Pd(II) dichloride
in 15 mL of THF. A yellow suspension is formed to which sodium
acetate (1.0 g dissolved in 20 mL of water) is added. A red solution
is obtained, whose pH is raised to 9 by proper addition of KOH
(pellets). After stirring for some minutes, 60 mL of water is added
to the solution, affording the precipitation of a red-orange solid,
which is filtered, washed repeatedly with water, dried, and finally
washed with boiling heptane. Yield: 0.72 g (70%). Mp: 320 °C
dec.
Anal. Calcd for C52H48N8O8Pd2: C 55.47, H 4.30, N 10.00, Pd
18.90. Found: C 54.66, H 4.67, N 10.80, Pd 18.97.
1H NMR (DMSO-d6) δ (ppm): 1.07 (m, 12H); 3.29 (m, 8H);
6.14 (s, 2H); 6.22 (d, 2H, J ) 8.79 Hz); 7.30 (d, 2H, J ) 8.79 Hz);
7.55 (m, 8H); 7.87 (m, 10H); 8.19 (d, 4H, J ) 7.82 Hz).
UV-vis λmax (nm), ꢀmax (dm3 mol-1 cm-1): 450, 7.5 × 104.
Synthesis of Cu2* and Pd2. In both cases 300 mg of the
corresponding dinuclear precursor are dissolved in 5 mL of boiling
pyridine and stirred for 5 min. By cooling at room temperature
crystals of complexes are formed and recovered by filtration. Yields
are 77% in both cases.
Cu2*. Anal. Calcd for C36H34N6O4Cu: Cu 9.37. Found: 9.43.
Pd2. Anal. Calcd for C31H29N5O4Pd: C 58.00, H 4.55, N 10.91,
Pd 16.58. Found: C 57.84, H 4.53, N 10.99, Pd 17.03.
Measurements were carried out in DMSO or in chloroform
solutions at a fundamental wavelength of 1.907 µm, using a
Q-switched, mode locked Nd3+:YAG laser with pulse durations of
15 ns at a 10 Hz repetition rate, whose 1.064 µm initial wavelength
was shifted by stimulated Raman scattering in a high-pressure
hydrogen cell.
1H NMR (CD2Cl2) δ (ppm): 1.23 (m, 6H); 3.40 (q, 4H, J )
7.10 Hz); 6.25 (d, 1H, J ) 8.79 Hz); 6.39 (s, 1H); 7.25 (d, 1H, J
) 8.79 Hz); 7.31 (d, 2H, J ) 6.81 Hz), 7.65 (m, 7H); 8.14 (t, 1H,
J ) 7.33 Hz); 8.18 (m, 4H), 9.03 (d, 2H, J ) 5.37 Hz).
UV-vis λmax (nm), ꢀmax (dm3 mol-1 cm-1): 450, 4.1 × 104.
Synthesis of Cu2. Cu2 was obtained by thermal treatment of
Cu2* in an oven at 120 °C for 2 h.
(12) Sheldrick, G. M. SHELX-97; University of Go¨ttingen: Go¨ttingen,
Germany, 1997.
Cu2. Anal. Calcd for C31H29N5O4Cu: C 62.15, H 4.88, N 11.69,
(13) CSD April 2001 release; Cambridge Crystallographic Data Centre:
Cambridge, England, 2001.
(14) Maurin, J. K. Pol. J. Chem. 1988, 62, 857. CSD refcode FUGTIK01.
(15) Suchod, B.; Baldeck, P. Acta Crystallogr. 1995, C51, 432-434. CSD
refcode WINLUA.
(16) Kliegel, W.; Metge, J.; Rettig, S. J.; Trotter, J. Can. J. Chem. 1998,
76, 1082-1092. CSD refcode BIBQEI.
(17) Ledoux, I.; Zyss, J., J. Chem. Phys. 1982, 73, 203.
Cu 10.61. Found: C 61.88, H 4.86, N 11.74, Cu 10.67.
UV-vis λmax (nm), ꢀmax (dm3 mol-1 cm-1): 455, 4.0 × 104.
Physical Measurements. The thermal behavior of compounds
was examined by differential scanning calorimetry (Perkin-Elmer
DSC-7, nitrogen atmosphere, scanning rate 10 K/min), temperature
controlled polarizing microscopy (Zeiss microscope combined with
6600 Inorganic Chemistry, Vol. 41, No. 25, 2002

NoWel N-Salicylidene-N ′-aroylhydrazine Ligands
Table 1. Crystal, Collection and Refinement Data for Cu1, Pd1, and
Cu2*
Cu1
Pd1
Cu2*
chem formula C23H23N5O4Cu C23H23N5O4Pd‚0.25H2O C36H34N6O4Cu
fw
T (K)
497.01
293
544.39
293
678.23
293
cryst syst
space group
a (Å)
b (Å)
c (Å)
triclinic
P1h
orthorhombic
Pbcn
24.507(3)
10.092(5)
37.047(9)
90
90
90
9163(5)
16, 1.577
0.851
triclinic
P1h
8.576(4)
11.143(6)
12.990(5)
104.44(4)
104.94(5)
103.58(4)
1100.6(9)
2, 1.500
1.033
12.219(2)
13.831(1)
20.948(6)
83.77(2)
77.98(2)
70.66(1)
3264(1)
4, 1.380
0.718
R (deg)
â (deg)
γ (deg)
V (Å3)
Z, Dx (g/cm3)
µ (mm-1
)
Figure 3. Pd1. Crystallographically independent molecule B.
θ range (deg)
data/params
R1, wR2 on
F (I >2σ(I))a
R1, wR2 (all
data) on F2
1.72-29.96
6392/316
0.0513, 0.1389 0.0681, 0.1224
0.1354, 0.1649 0.2960, 0.197
1.10-27.98
11040/600
1.56-27.98
15702/847
0.0682, 0.1406
A common feature is given by the structure of the
tridentate ligand which is in the enolic form. This is clearly
shown by the increase in the length of C12-O2 bond which
ranges between 1.286(5) and 1.31(1) Å as compared to the
value expected for an amide carbonyl group (1.23 Å18) and
shortening of C12-N3 which ranges between 1.29(1) and
1.320(6) Å. The structure of free ligands L1 and L2, on the
other hand, is in the keto form as clearly evidenced by the
IR data showing, among other indicative bands, the CdO
stretching and N-H bending bands (amide I and amide II
bands). The change in the electronic structure of ligands is
also consistent with the UV-vis data showing a significant
red shift of the λmax upon coordination. Furthermore, among
dimeric complexes and monoadducts λmax is substantially
unchanged while the molar extinction coefficient is almost
doubled, as expected.
0.2394, 0.1879
2 2
a R1 ) [∑||Fo| - |Fc||]/∑|Fo|; wR2 ) {[∑[w(Fo2 - Fc2)2]]/∑[w(Fo ) ]}1/2
.
To our knowledge organic ligands L1 and L2 are the first
reported examples of hydrazine-based, donor-acceptor
derivatives.
Figure 1. Cu1. Crystallographically independent molecule.
The geometry around the N1 amino atom is planar in all
the compounds. Shortening of the N to phenyl distance,
which ranges between 1.361(6) and 1.38(1) Å in the five
molecular structures, as compared to the value of 1.43 Å
reported for pyramidal N,18 is indicative of π conjugation
from the lone pair of N1 to the adjacent phenyl ring.
The conformation of the organic fragment is substantially
planar. For the tridentate part of the ligand, planarity is
imposed by the coordination geometry. However, in the two
independent molecules of Cu2* a substantially planar ar-
rangement is observed also for the stilbene moiety which is
not involved in coordination.
Figure 2. Pd1. Crystallographically independent molecule A.
The coordination geometry is substantially square planar,
as expected, in Cu1 and Pd1 with trans arrangement of N
and O atoms around the metal and the plane of the pyridine
molecule being substantially coplanar with the metal coor-
dination plane. In Cu2* a different geometry is observed, as
metal atoms are bonded to five coordinating atoms and, in
particular, two pyridine molecules are coordinated to the
metal. Although evidence of the possibility of further
coordination of a nitrogen ligand to Cu (II) monoadducts
Results and Discussion
Drawings of the crystallographically independent units of
Cu1, Pd1, and Cu2* are reported in Figures 1-5. Selected
bond lengths, bond angles, and torsion angles are reported
in Table 2. A fair agreement among corresponding structural
data of the five molecular structures within the three crystal
structures is observed. In particular, in Pd1 the two crystal-
lographically independent molecules almost only differ
because molecule B is involved in hydrogen bonding with
the water molecule (N3‚‚‚OW ) 2.89(1) Å).
(18) Allen, F. H.; Kennard, O.; Watson, D. G.; Brammer, L.; Guy Orpen,
A.; Taylor, R. J. Chem. Soc., Perkin Trans. 2 1987 S1-S19.
Inorganic Chemistry, Vol. 41, No. 25, 2002 6601

Cariati et al.
Figure 4. Cu2*. Crystallographically independent molecule A.
Figure 5. Cu2*. Crystallographically independent molecule B.
Table 2. Selected Bond Lengths (Å), Bond Angles (deg), and Torsion
Angles (deg)
In molecule A a square pyramidal geometry is observed,
with the metal atom almost lying in the basal plane. Bond
distances between the metal and two coordinated pyridine
molecules are significantly different. The bond length with
basal pyridine is clearly shorter than the length with that
out of the basal plane, this meaning that the second pyridine
is more weakly bonded and may become lost easily.
In molecule B the geometry is substantially trigonal
bipyramidal, with the three coordinated N atoms belonging
to the equatorial plane, the two O atoms being apical, and
the planes of the two pyridine molecules being almost parallel
to the O1-O2 direction (axis of the bipyramid). Also in this
case bond lengths between Cu and N atoms of the two
coordinated pyridine molecules are significantly different.
The results of combined TGA-DTA analysis are consis-
tent with the crystal structure analysis. As an example, in
Figure 6, which reports TGA-DTA curves for Cu2*, it is
clearly shown that the first pyridine molecule is lost near
100 °C while the second is lost near 180 °C. In the case of
Cu1 loss of the only pyridine molecule occurs near 170 °C,
giving a product whose TGA-DTA curves are identical to
those of the corresponding dinuclear complex, (CuL1)2. This
behavior is consistent with literature data suggesting that
thermal loss of the pyridine should correspond to restoring
of dinuclear complexes.19 For Pd complexes, on the other
hand, the temperature ranges for loss of pyridine are broader,
not so well defined, and in some cases partially superimposed
with thermal degradation of the compound.
Pd1
Cu2*
Cu1
A
B
A
B
M-O1
1.881(3)
1.926(3)
1.914(3)
2.006(3)
1.969(6) 1.977(6) 1.920(3) 1.907(3)
1.990(6) 2.009(6) 1.962(3) 1.948(3)
1.927(7) 1.931(7) 1.921(4) 1.918(4)
2.037(7) 2.063(8) 2.005(4) 2.088(4)
2.354(4) 2.243(5)
M-O2
M-N2
M-N5
M-N6
O2-C12
N1-C5
N2-C11
N2-N3
1.293(4)
1.362(5)
1.294(4)
1.395(4)
1.317(4)
1.418(5)
1.481(5)
93.8(1)
1.30(1) 1.31(1) 1.286(5) 1.294(5)
1.38(1) 1.37(1) 1.361(6) 1.372(6)
1.30(1) 1.32(1) 1.287(5) 1.283(5)
1.406(9) 1.39(1) 1.393(5) 1.403(5)
1.29(1) 1.31(1) 1.320(6) 1.301(6)
1.40(1) 1.43(1) 1.420(6) 1.427(6)
1.47(1) 1.46(1) 1.479(6) 1.481(6)
N3-C12
C8-C11
C12-C13
O1-M-N2
N2-M-O2
O1-M-N5
O2-M-N5
N2-M-N5
N2-M-N6
N5-M-N6
C2-N1-C4
94.2(3) 95.1(3) 93.3(2)
80.8(3) 80.2(3) 80.0(1)
90.4(3) 88.7(3) 92.9(2)
94.7(3) 96.0(3) 92.6(1)
93.4(2)
80.7(2)
91.4(2)
92.3(2)
81.4(1)
92.3(1)
93.6(1)
166.0(2) 119.6(2)
97.0(2)
95.4(2)
144.3(2)
95.6(2)
115.4(5)- 115.6(9) 115.8(8) 116.3(5) 116.9(4)
112.4(5)
C2-N1-C5
C4-N1-C5
118.2(5)- 121.9(9) 121.4(9) 121.2(5) 121.5(5)
121.9(5)
123.1(3)
122.4(9) 122.7(9) 122.4(5) 121.5(4)
179.2(9) 177.0(9) 172.1(4) 177.4(4)
C11-N2-N3-C12 178.0(3)
C7-C8-C11-N2
N3-C12-C13-C18 -178.8(3) -176(1) 178(1) -173.3(4) -174.9(4)
-179.8(3) 178.4(9) -179(1) 178.1(5) 178.5(4)
C15-C16-C19-C20
C16-C19-C20-C21
C19-C20-C21-C26
-176.3(6) -166.1(5)
-177.4(5) 177.4(5)
171.7(6) 176.4(5)
has already been given in the literature,19,20 to our knowledge
this is the first direct crystallographic evidence of that
behavior. Furthermore, different coordination geometries are
observed in the two crystallographically independent mol-
ecules of Cu2*.
(19) Iskander, M. F.; El-Aggan, A. M.; Refaat, L. S.; El Sayed, L. Inorg.
Chim. Acta 1975, 14, 167-172.
(20) Jezierska, J.; Jezierski, A.; Jezowska-Trzebiatowska, B.; Ozarowsky,
A. Inorg. Chim. Acta 1983, 68, 7-13.
6602 Inorganic Chemistry, Vol. 41, No. 25, 2002

NoWel N-Salicylidene-N ′-aroylhydrazine Ligands
chromophore,7 which is the up to date reference for possible
NLO applications of organic polymers.22
Actually the reported values should be considered as lower
limits because a partial restoring of dinuclear complexes
through solution equilibria, which are dependent on the
nature of the metal but also of the ligand and the solvent,
would give a reduced contribution to µâvec as they are
centrosymmetric and, hence, not NLO active; furthermore
evidence of the possibility of centrosymmetric coupling also
of monoadducts has been reported.9,10 The strongly reduced
µâvec value measured for a sample of Cu2* after loss of the
more weakly bounded pyridine molecule (i.e., for a sample
of Cu2) could point to this possibility.
Figure 6. TGA-DTA curves for Cu2*.
Some of the features discussed above are of potential
interest within the approach depicted in the Introduction for
obtaining NLO active polymer materials based on these
complexes. In particular the possibility of coordination of a
second pyridine molecule to metal atoms is noteworthy as
it could act as a partial networking of the polymer structure
with further constraint of the NLO active fragments. In
conclusion, the system should couple, at least partially, the
advantages of guest-host systems (higher mobility of NLO
active fragments and, hence, higher degree of orientation
during the poling) with those of truly covalent systems (better
time stability of the polar orientation).
Table 3. EFISH Results for the Studied Complexes
compd
µâvec (10-48 esu)
solvent
DMSO
chloroform
DMSO
chloroform
DMSO
Cu1
Pd1
+460
+380
Cu2a
Cu2*
Pd2
+650
+1390
+1500
a In this case the measurement was performed on a sample of Cu2*
crystals after loss of the more weakly bounded pyridine molecule (treatment
in oven at 120 °C).
The results of EFISH measurements are shown in Table
3. We note that the measured values are consistent with the
expected increase of the NLO activity in going from L1 to
L2 ligand, on account of the increase of the conjugation
length. In fact, it is known that pseudolinear π-delocalized
organic systems substituted by donor and acceptor groups
at the two ends show significant second-order NLO responses
due to a reduced energy gap between ground and intramo-
lecular charge-transfer excited states, together with large
oscillator strengths and a significant difference between
ground and excited-state dipole moments.21 Furthermore the
values are comparable to or even higher than those reported,
under similar experimental conditions, for DR (Disperse Red)
Acknowledgment. Financial support of PRIN 2000
(Italy) is gratefully acknowledged. Thanks are due to the
Centro Interdipartimentale di Metodologie Chimico-Fisiche
of the Universita` di Napoli “Federico II” for NMR, X-ray
(MACH3 Nonius diffractometer) and CSD facilities. Thanks
are also due to CIRA (Centro Italiano di Ricerche Aerospa-
ziali) for TGA-DTA measurements.
Supporting Information Available: Crystallographic data in
CIF format. This material is available free of charge via the Internet
at http://pubs.acs.org.
IC020127K
(21) Ledoux, I.; Zyss, J. Molecular Nonlinear Optics: Fundamentals and
Applications. In NoVel Optical Materials and Applications; Khoo, I.
C., Simoni, F., Umeton, C., Eds.; John Wiley & Sons: New York,
1977.
(22) Plisˇka, T.; Cho, W.-R.; Meier, J.; Le Duff, A.-C.; Ricci, V.; Otomo,
A.; Canva, M.; Stegeman, G. I.; Raimond, P.; Kajzar, F. J. Opt. Soc.
Am. B 2000, 17 (9), 1554-1564.
Inorganic Chemistry, Vol. 41, No. 25, 2002 6603