Synthesis and characterization of a homologous series of mononuclear palladium complexes containing different cyclometalated ligands

Article abstract of DOI:10.1016/S0020-1693(00)00216-4

New mononuclear palladium(II) complexes formed by with 2-hydroxy-4-(n-hexyloxybenzylidene)-4'-n-hexyaniline (HL) and 2-phenylpyridine (I), benzo[h]quinoline (II), azobenzene (III), 2-benzoylpyridine (IV) or phenyl-2-pyridylketone-2,4-dinitrophenylhydrazone (V) have been synthesized and characterized by analytical and spectroscopic methods and the single-crystal structures of [(IVa)Pd(L)] and [(Va)Pd(L)] have been established. The spectroscopic and diffractrometric data account for molecular structures wherein the palladium(II) center is part of two chelate rings involving HL and one of the I-V ligands which form a five-member N,C{[(Ia)PdL], [(IIa)Pd(L)] and [(IIIa)Pd(L)]}, a six-member N,C{[IVa)Pd(L)]}, or a six-member N,N{[(Va)Pd(L)]} metallacycle. The electronic spectra of [(IIIa)Pd(L)] and [(Va)Pd(L)] show an absorption maxima, at 495 (ε ~ 3 x 10³ M^-1 cm^-1) and 531 nm (ε ~ 2 x 10⁴ M^-1 cm^-1), respectively, which results are significantly affected by the polarity of the solvent. These chromophores should therefore be of interest for the preparation of nonlinear optical materials. (C) 2000 Elsevier Science S.A.

Full text of DOI:10.1016/S0020-1693(00)00216-4

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Inorganica Chimica Acta 308 (2000) 121–128
Synthesis and characterization of a homologous series of
mononuclear palladium complexes containing different
cyclometalated ligands
Iolinda Aiello a, Alessandra Crispini a, Mauro Ghedini a,*, Massimo La Deda a,
Francesco Barigelletti b
a Dipartimento di Chimica, Uni6ersita` della Calabria, I-87030 Arca6acata (CS), Italy
b Istituto FRAE-CNR, Via Gobetti 101, I-40129 Bologna, Italy
Received 17 March 2000; accepted 5 June 2000
Abstract
New mononuclear palladium(II) complexes formed by with 2-hydroxy-4-(n-hexyloxybenzylidene)-4%-n-hexyaniline (HL) and
2-phenylpyridine (I), benzo[h]quinoline (II), azobenzene (III), 2-benzoylpyridine (IV) or phenyl-2-pyridylketone-2,4-dinitrophenyl-
hydrazone (V) have been synthesized and characterized by analytical and spectroscopic methods and the single-crystal structures
of [(IVa)Pd(L)] and [(Va)Pd(L)] have been established. The spectroscopic and diffractrometric data account for molecular
structures wherein the palladium(II) center is part of two chelate rings involving HL and one of the I–V ligands which form a
five-member N,C{[(Ia)PdL], [(IIa)Pd(L)] and [(IIIa)Pd(L)]}, a six-member N,C{[(IVa)Pd(L)]}, or a six-member N,N%{[(Va)Pd(L)]}
metallacycle. The electronic spectra of [(IIIa)Pd(L)] and [(Va)Pd(L)] show an absorption maxima, at 495 (mꢀ3×103 M−1 cm−1
)
and 531 nm (mꢀ2×104 M−1 cm−1), respectively, which results are significantly affected by the polarity of the solvent. These
chromophores should therefore be of interest for the preparation of nonlinear optical materials. © 2000 Elsevier Science S.A. All
rights reserved.
Keywords: Cyclopalladate complexes; Schiff base complexes; Crystal structures; Palladium complexes
thometalation of imines has been considered. Thus,
comparing the uncomplexed ligands with their dinu-
clear or mononuclear complexes, it has been observed
that the nonlinearity of these systems increases when a
strong donor group is located in the cyclometalated
ring [1c]. Moreover, it has been shown that the five-
membered metalacycle of orthopalladated species ex-
hibits a certain degree of aromaticity [5]. Hence, the
electro-optical properties, which arise from the metal
containing molecular fragment should ultimately de-
pend on both the nature and electronic environment
experienced by the different atoms which are part of the
palladacycle. In this context we planned to synthesize
new mononuclear cyclopalladated complexes in order
that they be subsequently tested for nonlinear optical
properties and/or photorefractivity.
1. Introduction
The great interest in materials which feature physical
properties of potential use in new technologies presently
drives many new investigations into organometallic and
coordination compounds. In particular, with reference
to applications for optoelectronic devices, research has
been focused on the synthesis of materials with nonlin-
ear optical [1], photorefractive [2,3] or electrolumines-
cent [4] properties and the promising results reported to
date confirm that the incorporation of a metal center
into a molecular structure plays an important role.
In a recent study the influence of palladium(II) or
platinum(II) ions involved in rings formed by or-
The ligands we selected are the salicylideneaniline HL
and the species I–V shown in Scheme 1. We report here
on the synthesis, characterization and spectroscopic
* Corresponding author. Tel. and fax: +39-0984-492 062.
E-mail address: m.ghedini@unical.it (M. Ghedini).
0020-1693/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S0020-1693(00)00216-4

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I. Aiello et al. / Inorganica Chimica Acta 308 (2000) 121–128
On treating the I–V ligands with palladium(II) ac-
etato, the dimeric species [(Ia–Va)Pd (m-OAc)] (1–5) in
Scheme 2, were obtained (Section 3). The I–V sub-
strates were selected because of their ability to undergo
the orthometalation process. In complexes 1 [9], 2 [10],
3 [11] and 4 [12], the occurrence of the expected N,C
metalacycle was confirmed by comparison with the
literature data. In complex 5, unlike 1–4, both C,N,
and N,N% six-membered metalacycle formation (Scheme
3) can take place [13]. However, the N,N% coordination
mode was inferred from both the IR spectrum, which
lacks the absorption attributable to NꢀH stretching,
and the molecular structure of complex 10 (Scheme 2
and Fig. 2).
Compounds [(Ia–Va)Pd(L)] (6–10), have been ob-
tained from complexes 1–5 by a subsequent bridge
splitting reaction performed with HL. The L coordina-
tion (Scheme 2) was proved by inspection of the IR and
1H NMR spectra. In particular, the shifts of the CꢁN
stretching [14] and of the imine proton (Hb) resonance
[15] with respect to the homologous HL signals, are
both accounted for by the occurrence of the metal
complexation (Section 3).
In complexes 6–10 the palladium coordination
sphere consists of two chelate systems with an C,N and
O,N (6–9) or an N,N% and O,N (10) set of bonding
atoms. In principle, products 6–10 can be isomeric
mixtures of N,N-trans or cis isomers. However, for
Scheme 1. Aromatic protons numbering scheme and molecular struc-
ture of the reacted ligands, HL and I–V.
properties of the homologous series of mononuclear
complexes [(Ia–Va)Pd(L)] which contain the palladacy-
cles [(Ia–Va)Pd], Ia–Va and L standing for the depro-
tonated form of I–V and HL, respectively. The crystal
structures of complexes [(IVa)Pd(L)] and [(Va)Pd(L)]
are also described.
2. Results and discussion
Scheme 2. Synthesis of complexes 1–10.
2.1. Synthesis and structures
The commercially unavailable ligands HL and V
were prepared through the reaction of 2-hydroxy-4-(n-
hexyloxy)benzaldehyde [6] with 4-n-hexylaniline and IV
with 2,4-dinitrophenylhydrazine [7], respectively (Sec-
tion 3). Both products are solids, which give the ex-
pected analytical and spectroscopic data. Moreover,
HL displays thermotropic mesomorphism (Section 3)
which consists in an enantiotropic smectic C (SmC) and
a nematic (N) mesophases [8].
Scheme 3. Possible cyclopalladation modes of ligand V.

I. Aiello et al. / Inorganica Chimica Acta 308 (2000) 121–128
123
similar cyclopalladated salicylideneaminato species, it
has been shown previously that such isomers, if any,
differ in the position of the imine hydrogen signal in the
The ring obtained from chelation of the salicylide-
neaminato ligand HL, of type P¸d¹ꢀN¹C¹3ºO, is essentially
planar, with a maximum deviation from the mean plane
1
1H NMR spectrum [16]. In the present case, the H
,
o¸f ¹0¹.0¹4º6(4) A at N(1). The torsion angles for the
NMR spectra of all the 6–10 synthesized species show
a single imine proton resonance. Therefore 6–10 are
pure complexes and their molecular geometries, which
are N,N-trans and N,N-cis in 9 and 10, respectively
(Figs. 1 and 2), are N,N-trans in 6–8 [16].
The molecular structure of complexes 9 and 10,
[(IVa)Pd(L)] and [(Va)Pd(L)], respectively, was deter-
mined by single crystal X-ray analysis. A perspective
view of complex 9 is shown in Fig. 1. Selected bond
distances and angles are given in Table 1. The palla-
dium atom is coordinated in a slightly distorted square
planar geometry with a trans arrangement of the N
donor atoms. The two chelating organic ligands give
rise, upon coordination to the palladium atom, to two
six-membered rings at a dihedral angle of 29.7(2)°.
PdꢀNC3O cycle are reported in Table 1. The bond
lengths and angles agree well with those found for
palladium bis-salicylideneaminato complexes [17].
,
However, the PdꢀO(1) bond distance of 2.069(4) A is
found to be slightly longer than trans to oxygen atoms,
because of the trans effect of the s-bonded C atom.
This feature is found to be similar in complex
[N-(phenyl)-2-salicylideneaminato]-[4%-(methoxyphenyl-
NNO-azoxy-N2)-4-methoxyphenyl-2-ato] palladium(II)
[14] The N-bonded phenyl ring is tilted by 60.6(2)° with
respect to the salicylideneaminato plane. Both the alkyl
and alkoxy chains of the salicylideneaminato ligand
include one gauche bond [C(14)ꢀC(15) and
C(22)ꢀC(23)] with torsion angles of −70(1) and 45(5)°,
Fig. 1. Molecular structure and atomic labeling scheme (50% probability thermal ellipsoids) of complex 9, [(IVa)Pd(L)]. Hydrogen atoms omitted
for clarity.
Fig. 2. Molecular structure and atomic labeling scheme (50% probability thermal ellipsoids) of complex 10, [(Va)Pd(L)]. Hydrogen atoms omitted
for clarity.

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I. Aiello et al. / Inorganica Chimica Acta 308 (2000) 121–128
Table 1
The crystal structure of complex 10 [(Va)Pd(L)], with
the pertinent atom-labeling scheme, is shown in Fig. 2.
Selected bond lengths and angles are listed in Table 2.
The palladium atom is in a distorted square planar
geometry, coordinated from one side to the nitrogen
and oxygen atoms of the salicylideneaminato ligand
HL. The ligand V completes the coordination to the
palladium atom behaving as an N,N bidentate
monoanionic ligand. As in complex 9, the palladium
atom is part of two six-membered rin¸gs¹, ¹ti¹ltºed with
respect to each other by 32.4(5)°. The PdꢀNC3O cycle
from the salicylideneaminato ligand HL is planar to
,
Selected bond distances (A), angles (°) and torsion angles (°) for
complex 9, [(IVa)Pd(L)]
PdꢀO(1)
PdꢀN(2)
O(1)ꢀC(1)
C(2)ꢀC(7)
C(26)ꢀC(31)
C(32)ꢀC(33)
O(3)ꢀC(32)
2.069(4)
2.029(5)
1.301(7)
1.389(9)
1.415(10)
1.491(12)
1.230(10)
PdꢀN(1)
2.051(5)
1.986(7)
1.439(9)
1.318(8)
1.469(12)
1.350(9)
PdꢀC(26)
C(1)ꢀC(2)
N(1)ꢀC(7)
C(31)ꢀC(32)
N(2)ꢀC(33)
C(26)ꢀPdꢀN(2)
N(2)ꢀPdꢀN(1)
N(2)ꢀPdꢀO(1)
87.4(3)
174.1(2)
84.95(19) N(1)ꢀPdꢀO(1)
C(26)ꢀPdꢀN(1)
C(26)ꢀPdꢀO(1)
97.0(3)
172.3(2)
90.73(18)
,
within 0.06 A (torsion angles in Table 2). Unlike com-
,
plex 9, the PdꢀO(1) bond distance of 1.966(8) A is in
PdꢀO(1)ꢀC(1)ꢀC(2)
−5.2(9)
O(1)ꢀC(1)ꢀC(2)
ꢀC(7)
0.7(11) C(2)ꢀC(7)ꢀN(1)ꢀPd −6.8(10)
5.4(5) N(1)ꢀPdꢀO(1)ꢀC(1) 0.1(5)
5.9(10)
the range of values found for palladium bis-salicylid-
eneaminato complexes [17]. The other bond lengths and
the bond angles agree with those found for complex 9.
The rotationally free phenyl ring of HL is tilted by
55.3(2)° with respect to its best mean plane. While the
conformation of the hexyl chain is almost completely
trans-planar, the hexyloxy chain shows one gauche
bond [C(20)ꢀC(21)] with torsion angle of −70(3)°.
Ligand V upon cyclopalladation forms a six-mem-
bered ring, P¸dꢀ¹N¹C¹3¹NºN, using the Npy atom and the
deprotonated nitrogen atom N(3). The ring conforma-
tion is a half-twist, with the N(3), N(4), C(30) and
C(31) atoms lying approximately on the same plane
C(1)ꢀC(2)ꢀC(7)ꢀN(1)
C(7)ꢀN(1)ꢀPdꢀO(1)
PdꢀC(26)ꢀC(31)ꢀC(32) −11.7(10) C(26)ꢀC(31)ꢀC(32) −35.7(10)
ꢀC(33)
C(31)ꢀC(32)ꢀC(33)
31.1(10) C(32)ꢀC(33)ꢀN(2)
ꢀPd
19.2(9)
ꢀN(2)
C(33)ꢀN(2)ꢀPdꢀC(26) −49.1(6)
N(2)ꢀPdꢀC(26)ꢀ
C(31)
43.5(6)
Table 2
,
Selected bond distances (A), angles (°) and torsion angles (°) for
complex 10, [(Va)Pd(L)]
,
(within 0.02 A). Some differences in terms of bond
distances and angles within the PdꢀNC3NN cycle are
¸¹¹¹¹¹º
PdꢀO(1)
PdꢀN(2)
O(1)ꢀC(1)
C(2)ꢀC(7)
N(2)ꢀC(30)
N(4)ꢀC(31)
1.966(8) PdꢀN(1)
1.975(10) PdꢀN(3)
1.326(14) C(1)ꢀC(2)
1.412(17) N(1)ꢀC(7)
1.349(15) C(30)ꢀC(31)
1.265(13) N(3)ꢀN(4)
2.067(10)
2.058(9)
1.416(16)
1.287(15)
1.495(16)
1.358
found with respect to the only example of a palladiu-
m(II) complex containing a similar type of six-mem-
bered chelate ring reported up to now [13]. On the
other hand, the bond lengths and angles of ligand V
compare favorably with those found in a structurally
characterized hydrazone ligand [19].
O(1)ꢀPdꢀN(2)
N(2)ꢀPdꢀN(3)
N(2)ꢀPdꢀN(1)
170.3(3) O(1)ꢀPdꢀN(3)
82.4(4) O(1)ꢀPdꢀN(1)
97.0(4) N(3)ꢀPdꢀN(1)
88.6(3)
92.3(4)
171.8(4)
2.2. UV–Vis spectroscopy of complexes 6–10
PdꢀO(1)ꢀC(1)ꢀC(2)
C(1)ꢀC(2)ꢀC(7)ꢀN(1)
C(7)ꢀN(1)ꢀPdꢀO(1)
8.5(17) O(1)ꢀC(1)ꢀC(2)ꢀC(7)
1.0(2) C(2)ꢀC(7)ꢀN(1)ꢀPd
−11.5(10) N(1)ꢀPdꢀO(1)ꢀC(1) −12.1(8)
0.0(2)
−8.7(19)
The electronic absorption spectra of the cyclometa-
lated species 6–10, recorded in dichloromethane solu-
tions, exhibit two bands peaking at about 300 and 400
nm (Table 3). The higher energy band is attributable to
intense p–p* transitions (m\104 M−1 cm−1) centered
on both the HL and I–V ligands. The lower energy
band is less intense (mB104 M−1 cm−1) and can be
assigned to a CT transition involving, most likely, the
palladium-bonded oxygen atom, as suggested by the
presence of this center in all complexes [20]. Compari-
son of the spectroscopic properties with the molecular
structures (Scheme 2) allows some tentative assignment
to be made. Complexes 6 and 7 show a band, at 360
(mꢀ10 900 M−1 cm−1) and 378 nm (mꢀ10 800 M−1
cm−1) respectively, which can likely due to transitions
involving the cyclometalated 2-phenylpyridine I in 6 or
benzo[h]quinoline II in 7 [20]. For 8, a band at 344 nm
is present, which could be of p–p* origin, arising from
the orthopalladated azobenzene fragment [21].
PdꢀN(2)ꢀC(30)ꢀC(31) −6.0(19) N(2)ꢀC(30)ꢀC(31)
ꢀN(4)
−33.9(18)
50.1(11)
43.1(8)
C(30)ꢀC(31)ꢀN(4)ꢀ
N(3)
6.8(16) C(31)ꢀN(4)ꢀN(3)ꢀPd
N(4)ꢀN(3)ꢀPdꢀN(2)
−64.9(7) N(3)ꢀPdꢀN(2)ꢀC(30)
respectively, and show some evidence of disorder as
indicated by their thermal factors.
¸¹¹¹º
The second six-membered ring, PdꢀNC3C, obtained
from cyclometallation of ligand IV is in a boat confor-
mation (Table 1) with the Pd and C(32) atoms lying
,
(0.903(4) and 0.355(6) A) above the mean plane
through N(2), C(26), C(31) and C(33) atoms, respec-
tively. The conformation as well as the bond distances
and angles within the cycle are found to be in agree-
ment with those observed in other palladium(II) com-
plexes containing similar six-membered rings [18].

I. Aiello et al. / Inorganica Chimica Acta 308 (2000) 121–128
125
Table 3
Spectroscopic data a of complexes 6–10, [(Ia–Va)Pd(L)]
Complexes
Absorption u (m M−1 cm−1
)
Toluene b
Dichloromethane b
Acetone b
6
7
8
314 (25000) 405 (6430)
314 (19850) 360 (10940) 402 (8340)
294:312 (23300:23040) 378 (10820)
310 (25160) 344 (20970) 495 (3310)
301 (20100) 394 (11200)
324 (9040) 362 (5430) 402 (4350)
330 (12540) 379 (10290)
344 (17350) 494 (2900)
393 (9680)
293:313 (20950:20590) 382 (10650)
310 (27260) 344 (25790) 500 (3030)
292 (23460) 390 (8810)
9
10
308 (26250) 396 (14980) 537 (18340)
305 (29670) 391 (14710) 531 (20130)
388 (12070) 523 (17460)
a Room temperature.
b Static dielectric constant m: toluene, 2.4; dichloromethane, 9.1; acetone, 20.7.
Finally, 8 and 10 display absorption maxima at 495
(mꢀ3×103 M−1 cm−1) and 531 nm (mꢀ2×104 M−1
cm−1), respectively. The nature of these bands is not
easily identified, but in 10 the presence of the stronger
electron acceptor dinitro substituted hydrazone ligand,
V, suggest p−p* transitions which might be affected by
CT interactions.
It is known that molecules exhibiting solvatochromism
usually display second-order nonlinear optical properties
[22]. For this reason, the spectra of the synthesized
complexes were recorded in solvents with different polar-
ity (Table 3). Noteworthy, the lowest energy band of
complexes 8 and 10 is moderately affected by the polarity
of the solvent (Table 3 and Fig. 3). Thus, interesting
nonlinear optical properties should also be expected for
compounds 8 and 10.
3.2.1. 2-Hydroxy-4-(n-hexyloxybenzylidene)-4%-n-
hexylaniline (HL)
A solution of 4-n-hexylaniline (1.34 ml, 6.97 mmol) in
ethanol (5 ml) was added slowly to a stirred solution of
2-hydroxy-4-(n-hexyloxy)benzaldehyde (1.550 g, 6.97
mmol) in ethanol (25 ml). Immediately, the solution
turned yellow. After stirring for 4 h under reflux, the
yellow precipitate, which formed at room temperature,
was collected by filtration, washed with a small amount
of ethanol and vacuum dried. The analytically pure
product was obtained as a yellow solid upon recrystal-
lization from chloroform–methanol. Yield 0.645 g, 75%.
M.p. (°C) 43 (SmC) 82 (N) 94 (I). Found: C, 78.69; H,
9.19; N. C25H35NO2 requires: C, 78.70; H, 9.25; N,
3.71%. wmax (KBr, cm−1) 2362–2342 (OH), 1615 (CꢁN).
l (CDCl3, ppm) 13.93 (1H, s, OH), 8.52 (1H, s, Hb), 7.20
(5H, m, Hc,d,e,f,g), 6.47 (2H, m, Ha,b), 3.99 (2H, t, OꢀCH2),
2.61 (2H, t, PhꢀCH2).
Investigations using the electric-field-induced second
harmonic generation (EFISH) method are now under
way.
3.2.2. Phenyl-2-pyridylketone-2,4-dinitrophenylhydra-
zone (V)
A 1.0 g (5.05 mmol) sample of 2,4-dinitrophenylhy-
drazine was suspended in ethanol (15 ml) and the
red–orange mixture heated to 50°C. Concentrated hy-
drochloric acid (0.2 ml) was then added with stirring. The
mixture turned dark red in a few seconds. A solution of
2-benzoylpyridine (IV) (0.924 g, 5.05 mmol)
3. Experimental
3.1. Materials and procedures
All the commercially available chemicals were pur-
chased from Aldrich Chemical Co. and were used with-
out further purification.
1H NMR spectra were recorded on a Bruker WM-300
(CDCl3 solutions, Me4Si internal standard) and IR
spectra with a Perkin–Elmer 2000 FT-IR (KBr pellets).
Elemental analyses were performed with a Perkin–Elmer
2400 analyzer. Solutions room-temperature absorption
spectra were recorded with a Perkin–Elmer Lambda 9
spectrometer.
3.2. Syntheses of the ligands
The 2-hydroxy-4-(n-hexyloxy)benzaldehyde, interme-
diate for the synthesis of HL, was prepared as reported
in the literature [6]. The ligand V [7] was prepared
according to the reported procedure modified as follows.
Fig. 3. Electronic spectrum of 10 in toluene (···), dichloromethane
(---) and acetone (—).

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I. Aiello et al. / Inorganica Chimica Acta 308 (2000) 121–128
in ethanol (10 ml) was then added. A red–orange
suspension was obtained after approximately 5 min.
After being stirred for 30 min at 50°C, the mixture was
dilute with water (5 ml) and the so formed orange–yel-
low solid filtered off at room temperature and recrystal-
lized from concentrated acetic acid. Yield 0.740 g, 40%.
M.p. 208–210°C. Found: C, 59.33; H, 4.00; N, 19.28.
C18H13N5O4 requires: C, 59.50; H, 3.61; N, 19.28%.
wmax (KBr, cm−1) 3096 (NꢀH), 1582 (CꢁN). l (CDCl3,
ppm) 11.94 (1H, s, NꢀH), 9.16 (1H, d, H3%), 9.01 (1H,
m, H2), 8.32 (1H, dd, H5%), 8.24 (1H, d, H6%), 7.85 (1H,
td, H4), 7.65 (2H, m, H6,10), 7.51 (3H, m, H7,8,9), 7.49
(1H, m, H3), 7.45 (1H, m, H5).
(dec.) 275–276°C. Found: C, 52.79; H, 3.24; N, 4.32.
C30H22N2O4Pd2 requires: C, 52.42; H, 3.23; N, 4.08%.
wmax (KBr, cm−1) 1565 (asym. CꢁO), 1411 (sym. CꢁO).
l (CDCl3, ppm) 7.87 (1H, dd, H2), 7.50 (1H, dd, H4),
7.30 (3H, m, Ha,6,7), 7.14 (1H, dd, H8), 7.04 (1H, d, H5),
6.28 (1H, dd, H3), 2.45 (3H, s, OCH3).
3.3.3. [(IIIa)Pd(v-OAc)]2 (3)
A sample of azobenzene (III) (0.405 g, 2.23 mmol)
was added to a solution of palladium(II) acetate (0.50
g, 2.23 mmol) in acetic acid (80 ml) and the dark
mixture, resulting after stirring for 6 h at 50°C, was
filtered at room temperature through a short Celite
column. The filtrate was concentrated under reduced
pressure and the addition of methanol afforded a red
dark solid after cooling at −10°C. Yield 0.705 g, 91%;
M.p. (dec.) 200–205°C. Found: C, 48.52; H, 3.39; N,
8.03. C28H24N4O4Pd2 requires: C, 48.50; H, 3.49; N,
8.08%. wmax (KBr, cm−1) 1560 (asym CꢁO), 1415 (sym.
CꢁO). l (CDCl3, ppm) 7.71 (1H, dd, H7), 7.35 (2H, m,
H2,6), 7.25 (3H, m, H3,4,5), 7.14 (1H, td, H8), 6.81 (1H,
td, H9), 6.49 (1H, dd, Ha), 2.06 (3H, s, CH3).
3.3. Syntheses of the acetato-bridged complexes (1–5)
The complexes [(Ia)Pd(m-OAc)]2 (1) [9], [(IIa)Pd(m-
OAc)]2 (2) [10], [(IIIa)Pd(m-OAc)]2 (3) [23] and
[(IVa)Pd(m-OAc)]2 (4) [12], were prepared according to
the reported procedures modified as follows.
3.3.1. [(Ia)Pd(v-OAc)]2 (1)
To a stirred hot solution of palladium(II) acetate
(0.50 g, 2.23 mmol) in 80 ml of acetic acid, the stoichio-
metric amount of 2-phenylpyridine (I) (0.32 ml, 2.23
mmol) was added and the resulting dark orange solu-
tion stirred at 50°C for 3.5 h. The brown cloudy
suspension formed after that time, was filtered at room
temperature through a short Celite column to separate
a small amount of black insoluble solid. The solvent
was removed from the filtrate under reduced pressure.
The crude product was dissolved in acetone and the
addition of ethanol gave green–yellow microcrystals.
The solid was collected by filtration and dried under
vacuum. Yield 0.680 g, 95%. M.p. (dec.) 294–296°C.
Found: C, 48.85; H, 3.41; N, 4.69. C26H22N2O4Pd2
3.3.4. [(IVa)Pd(v-OAc)]2 (4)
A slight excess of 2-benzoylpyridine (IV) (0.489 g,
2.67 mmol) was added to a stirred solution of palladiu-
m(II) acetate (0.50 g, 2.23 mmol) in acetic acid (75 ml)
and the resulting orange solution stirred at 50°C. The
solution immediately turned yellow and cloudy. A
creme solid by-product was removed by filtration and
washed with dichloromethane while the yellow filtrate,
after evaporation of the solvent, gave a yellow viscous
oil which was extracted by dichloromethane. Extracts
were combined and dried over anhydrous Na2SO4. A
slow addition of hexane induced the precipitation of a
pale yellow powder. This product was filtered, washed
with hexane and dried under vacuum. Yield 0.630 g,
81%. M.p. (dec.) 271–275°C. Found: C, 48.06; H, 3.13;
N, 3.86. C28H22N2O6Pd2 requires: C, 48.37; H, 3.19; N,
4.03%. wmax (KBr, cm−1) 1665 (CꢁO ketone), 1578
(asym. CꢁO acetate) 1423 (sym. CꢁO acetate). l
(CDCl3, ppm) 8.28 (1H, d, H2), 7.85 (1H, d, H5), 7.81
(1H, d, H4), 7.44 (1H, d, H6), 7.15 (1H, td, H3), 6.99
(1H, td, H7), 6.87 (1H, td, H8), 6.84 (1H, dd, Ha), 2.07
(3H, s, CH3).
requires: C, 48.45; H, 3.47; N, 4.38%. wmax (KBr, cm−1
)
1571 (asym. CꢁO), 1416 (sym. CꢁO). l (CDCl3, ppm)
7.87 (1H, dd, H2), 7.37 (1H, td, H4), 7.08 (1H, d, H5),
6.92 (1H, dd, Ha), 6.84 (3H, m, H6,7,8), 6.44 (1H, m,
H3), 2.27 (3H, s, CH3).
3.3.2. [(IIa)Pd(v-OAc)]2 (2)
The complex palladium(II) acetate (2.23 mmol, 0.50
g) was dissolved in hot acetic acid (70 ml) and an excess
of solid benzo[h]quinoline (II) (2.54 mmol, 0.455 g) was
added in one portion with stirring. The suspension,
which turned dark red in few minutes, was stirred
overnight under N2 at reflux and a yellow solution
formed. The yellow suspension obtained by addition of
water (120 ml) was extracted with dichloromethane.
Extracts were combined, dried over anhydrous Na2SO4
and filtered. Partial evaporation of the solvent under
reduced pressure and addition of ethyl acetate afforded
a gold yellow solid precipitate which was filtered off
and dried under vacuum. Yield 0.555 g, 72%. M.p.
3.3.5. [(Va)Pd(v-OAc)]2 (5)
To a solution of palladium(II) acetate (0.50 g, 2.23
mmol) in 50 ml of hot acetic acid was added a stoichio-
metric amount of the phenyl-2-pyridylketone-2,4-dini-
trophenylhydrazone (V) (0.809 g, 2.23 mmol). The
mixture was stirred for 1 h at 50°C and after cooling to
room temperature the bordeaux solid which formed
was filtered off and suspended in dichloromethane. The
dark red solid was removed by filtration and diethyl

I. Aiello et al. / Inorganica Chimica Acta 308 (2000) 121–128
127
ether was added to the dark red filtrate. Cooling
overnight at −10°C led to a red bordeaux microcrys-
talline solid which was filtered and dried under vacuum.
Yield 0.480 g, 40%. M.p. (dec.) 273–275°C. Found: C,
45.36; H, 2.66; N, 13.21. C40H30N12O12Pd2 requires: C,
45.51; H, 2.86; N, 13.27%. wmax (KBr, cm−1) 1596
(CꢁN), 1559 (asym. CꢁO), 1440 (sym. CꢁO).
7.10 (1H, d, Hc), 7.04 (1H, t, H8), 6.69 (1H, m, H9),
6.20 (1H, dd, Hb), 6.16 (1H, d, Ha), 5.60 (1H, d, Ha),
3.93 (2H, t, OCH2), 2.66 (2H, t, PhꢀCH2).
3.4.4. [(IVa)Pd(L)] (9)
Yellow solid. Yield 0.203 g, 77%. M.p. 185–187°C.
Found: C, 66.42; H, 6.24; N, 4.52. C37H42N2O3Pd
requires: C, 66.41; H, 6.33; N, 4.19%. wmax (KBr, cm−1
)
3.4. Synthesis of the mononuclear complexes 6–10
1663 (CꢁO ketone), 1612 (CꢁN).l (CDCl3, ppm) 9.26
(1H, d, H2), 8.16 (1H, dd, H5), 8.02 (1H, td, H4), 7.98
(1H, s, Hb), 7.61 (1H, td, H3), 7.54 (1H, dd, Ha or 6),
7.16 (1H, d, Hc), 6.88 (2H, d, Hd,e), 6.81 (1H, d, H7 or 8),
6.78 (2H, d, Hf,g), 6.73 (1H, d, H7 or 8), 6.48 (1H, td,
Ha or 6), 6.37 (1H, d, Ha), 6.24 (1H, dd, Hb), 4.00 (2H,
t, OꢀCH2), 2.44 (2H, t, PhꢀCH2).
A typical preparation is reported for 6; all analogous
complexes, 7–10, were prepared using the same syn-
thetic procedure. Color, yield, melting point, elemental
1
analyses, IR and H NMR data are as follows.
3.4.1. [(Ia)Pd(L)] (6)
The ligand HL (0.150 g, 0.393 mmol) was suspended
in ethanol and added to 0.125 g (0.196 mmol) of
[(Ia)Pd(m-OAc)]2 (1), in one portion with stirring. A
pale orange precipitate formed in approximately 15 m.
After stirring for 24 h at room temperature, the cream
yellow solid which was obtained was filtered off, sus-
pended in chloroform and the suspension filtered
through a short Celite column. The solvent was par-
tially evaporated under reduced pressure and ethanol
added dropwise. The resulting yellow solid was filtered
off and dried under vacuum. Yield 0.211 g, 84%. M.p.
177–182°C. Found: C, 67.19; H, 6.68; N, 3.97.
C36H42N2O2Pd requires: C, 67.44; H, 6.60; N, 4.37%.
wmax (KBr, cm−1) 1612 (CꢁN). l (CDCl3, ppm 9.31
(1H, d, H2), 7.99 (1H, s, Hb), 7.81 (1H, td, H4), 7.62
(1H, d, H5), 7.44 (2H, d, Hd,e), 7.35 (1H, d, Ha), 7.25
(1H, m, H3), 7.14 (2H, d, Hf,g), 7.12 (1H, d, Hc), 6.88
(1H, t, H8), 6.56 (1H, t, H7), 6.44 (1H, d, Ha), 6.20 (1H,
dd, Hb), 5.78 (1H, d, H6), 4.00 (2H, t, OꢀCH2), 2.63
(2H, t, PhꢀCH2).
3.4.5. [(Va)Pd(L)] (10)
Bordeaux solid. Yield 0.152 g, 45%. M.p. (dec.)
220–223°C. Found: C, 60.40; H, 5.31; N, 10.02.
C43H47N6O6Pd requires: C, 60.74; H, 5.57; N, 9.88%.
wmax (KBr, cm−1) 1611 (CꢁN), 1594 (CꢁN hydrazone).
l (CDCl3, ppm) 8.84 (1H, d, H3%), 8.50 (1H, d, H6%),
8.13 (1H, dd, H5%), 7.90 (1H, d, H2), 7.74 (1H, dd,
H7 or 8), 7.53 (6H, m, Hb,4,6,7 or 8,9,10), 7.29 (1H, d, H3),
7.06 (2H, d, Hd,e), 7.01 (1H, d, Hc), 6.93 (2H, d, Hf,g),
Table 4
Crystallographic data for complexes 9 and 10
[(IVa)Pd(L)] (9)
[(Va)Pd(L)] (10)
Empirical formula
Formula weight
Crystal system
Space group
C37.H42N2O3Pd
669.13
monoclinic
P21/c
22.503(9)
10.125(2)
14.709(5)
90
91.45(3)
90
3350(2)
4
C43H46N6O6Pd
849.26
triclinic
(
P1
,
a (A)
12.331(4)
13.780(5)
14.178(6)
103.33(3)
104.78(3)
109.82(3)
2054(1)
2
,
b (A)
,
c (A)
h (°)
i (°)
k (°)
3.4.2. [(IIa)Pd(L)] (7)
Greenish–yellow solid. Yield 0.202 g, 77%. M.p.
161–168°C. Found: C, 68.44; H, 6.48; N, 3.89.
C38H42N2O2Pd requires: C, 68.62; H, 6.36; N, 4.21%.
wmax (KBr, cm−1) 1610 (CꢁN). l (CDCl3, ppm) 9.50
(1H, dd, H2), 8.28 (1H, dd, H4), 8.00 (1H, s, Hb), 7.68
(1H, d, H6), 7.59 (1H, dd, H3), 7.54 (1H, d, H5), 7.47
(2H, d, Hd,e), 7.39 (1H, d, Ha), 7.19 (2H, d, Hf,g), 7.15
(1H, d, Hc), 6.94 (1H, t, H8), 6.52 (1H, d, Ha), 6.23 (1H,
dd, Hb), 5.75 (1H, d, H7), 4.04 (2H, t, OꢀCH2), 2.68
(2H, t, PhꢀCH2).
3
,
V (A )
Z
F(000)
1392
1.327
0.591
880
1.373
0.506
Dcalc (g cm−3
)
Absorption coefficient
(mm−1
)
Transmission factors
Temperature (K)
Total number of
reflections
Number of unique
reflections
0.989/0.719
298
5539
1.00/0.873
298
4692
5293
[Rint=0.0343]
4492
[Rint=0.0460]
2892
[I\2|(I)]/10/465
0.082
0.211
Data/restraints/parameters 3808
3.4.3. [(IIIa)Pd(L)] (8)
[I\2|(I)]/2/363
0.065
0.177
1.041
Bordeaux solid. Yield 0.155 g, 58%. M.p. 100–
104°C. Found: C, 66.77; H, 6.37; N, 5.93.
C37H43N3O2Pd requires: C, 66.51; H, 6.49; N, 6.29%.
wmax (KBr, cm−1) 1611 (CꢁN). l (CDCl3, ppm) 7.98
(1H, s, Hb), 7.92 (2H, m, H2,6), 7.86 (1H, m, H7), 7.54
(3H, d, H3,4,5), 7.35 (2H, d, Hd,e), 7.17 (2H, d, Hf,g),
R1 a[I\2|(I)]
b
wR2
Goodness-of-fit (F2)
1.078
a R=ꢀꢁꢁFoꢁ−ꢁFcꢁꢁ/ꢀꢁFoꢁ.
b wR2=[ꢀ w(Fo2−Fc2)2/ꢀ w(Fo2)2]1/2
.

128
I. Aiello et al. / Inorganica Chimica Acta 308 (2000) 121–128
6.80 (1H, m, H5), 6.21 (1H, dd, Hb), 5.87 (1H, d, Ha),
3.87 (2H, t, OꢀCH2), 2.48 (2H, t, PhꢀCH2).
Chem. Soc. 119 (1997) 9550. (b) M. Bourgault, K. Baum, H.L.
Bozec, G. Pucetti, I. Ledoux, J. Zyss, New J. Chem. (1998) 517.
(c) J. Buey, S. Coco, L. D`ıez, P. Espinet, J.M. Mart`ın-Alvarez,
J.A. Miguel, S. Garc`ıa-Granda, A.Tesouro, I. Ledoux, J. Zyss,
Organomet. 17 (1998) 1750.
3.5. Structure determinations of 9, [(IVa)Pd(L)], and 10,
[(Va)Pd(L)]
[2] (a) W.G. Ng, W.K. Chan Adv. Mater. 9 (1997) 716. (b) Z. Peng,
A.R. Gharavi, L. Yu, J. Am. Chem. Soc. 119 (1997) 4622.
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Eur. J. Inorg. Chem. (1999) 1367.
Details of the data collection, structure analysis and
refinement are listed in Table 4. Diffraction measure-
ments were carried out on a Siemens R3m/V automated
four-circle diffractometer equipped with a graphite-
,
monochromated Mo Ka radiation (u=0.71073 A). Cell
dimensions for each analysis were determined from the
setting-angle values of centered reflections. The data
were corrected for Lorentz, polarization and X-ray
absorption effects. A semi-empirical absorption correc-
tion was applied using a method based upon azimuthal
(c) scan data [24] (transmission coefficients min/max of
0.719/0.989 for 9 and 0.873/0.998 for 10). The struc-
tures were solved by heavy-atom (Patterson and
Fourier difference) by using the SHELXTL [25] computer
program and refined by full-matrix least-squares
against F2. All the non-hydrogen atoms were refined
anisotropically with exception of some C atoms of the
aliphatic and alkoxy chains assigned with isotropic
displacement parameters [C(17), C(18), C(19), C(23),
C(24) and C(25) for complex 9; from C(14) to C(19),
C(24) and C(25) for complex 10]. As a result of a
disorder, simililarity constraints were applied to the
CꢀC bond distances between these carbon atoms and
even so in some cases the geometry was not readily
modeled. The hydrogen atoms were included as ideal-
ized atoms riding on the respective carbon atoms with
CꢀH bond lengths appropriate to the carbon atom
hybridization. Calculations were made with programs
of the SHELXL-97 package [26].
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Acknowledgements
The present work was supported by the Italian Min-
istero dell’Universita` e della Ricerca Scientifica e Tec-
nologica (MURST) and Regione Calabria (POP
1994–1999).
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References
[1] Recent papers on this subject are, for example: (a) S. Di Bella, I.
Fragala`, I. Ledoux, M.A. Diaz-Garcia, T.J. Marks, J. Am.
[26] G.M. Sheldrick, SHELXL-97, Program for the Refinement of
Crystal Structures, University of Go¨ttingen, Germany, 1997.
.