metal-organic compounds
Acta Crystallographica Section C
Crystal Structure
Communications
imines may be easily functionalized with electron donor or
acceptor groups, resulting in quite highly NLO active
compounds (Morley, 1995).
ISSN 0108-2701
We have recently started a systematic investigation of the
syntheses and structures of orthopalladated aromatic imines
as precursors of fragments to be incorporated in polymers, and
in the two complexes reported here, (I) and (II), a Pd atom is
coordinated to two aromatic Schiff bases.
Two orthopalladated chromophores
Roberto Centore,a* Antonio Roviello,a Angela Tuzia and
Barbara Panunzib
a
Á
Dipartimento di Chimica, Universita di Napoli `Federico II', Complesso di Monte
S. Angelo, Via Cinthia, 80126 Napoli, Italy, and bDipartimento di Scienza degli
Á
Á
Alimenti, Universita di Napoli `Federico II', Via Universita 100, 80055 Napoli, Italy
Correspondence e-mail: centore@chemistry.unina.it
Received 25 June 2001
Accepted 28 August 2001
Online 14 December 2001
In both title compounds (Figs. 1 and 2), the imines are
functionalized with strong electron donor±acceptor groups. In
particular, one imine is of the push±pull type and contains
methoxy donor and nitro acceptor groups, while the second
coordinated imine is of the electron-rich type as it contains
only electron-donor groups (i.e. methoxy and dialkylamino).
The two complexes substantially differ in the nature of the
cyclometallated imine which is the push±pull group in the case
of (I) and the electron-rich group in the case of (II).
Furthermore, in both (I) and (II), the strongest electron-donor
group (i.e. dialkylamino) and the nitro acceptor group are
placed in opposite directions with respect to the Pd atom, so as
to favour a charge transfer possibly involving the metal.
Both compounds show a strong absorption band in the UV-
vis region which should correspond to the HOMO±LUMO
transition (the HOMO is the highest occupied molecular
orbital and the LUMO is the lowest unoccupied molecular
orbital). A positive solvatochromic effect is observed for this
band (see Experimental), as generally found in second-order
NLO active compounds. The effect, though rather small, is
comparable with values reported in the literature for other
organometallic compounds (Di Bella et al., 1994). The NLO
activity of the compounds has been tested by EFISH (electric
®eld induced second harmonic) measurements in chloroform
The title compounds, {5-(dimethylamino)-2-[N-(4-methoxy-
phenyl)iminomethyl]phenyl}[N-(4-methoxyphenyl)-4-nitro-
salicylaldiminato]palladium(II),
[Pd(C14H11N2O4)(C16H17-
N2O)], (I), and [4-(diethylamino)-N-(4-methoxyphenyl)sali-
cylaldiminato]{2-[N-(4-methoxyphenyl)iminomethyl]-5-nitro-
phenyl}palladium(II) dichloromethane hemisolvate, [Pd-
(C14H11N2O3)(C18H21N2O2)]Á0.5CH2Cl2, (II), both contain
push±pull chromophores coordinated to Pd in a square-
planar arrangement. In both compounds, the ®ve-membered
orthopalladated ring is essentially planar, while the coordi-
nated six-membered ring is not. Deviations from a coplanar
arrangement of the phenylene rings of the coordinated Schiff
bases are observed in both (I) and (II) as a result of
intramolecular steric interactions.
Comment
Organometallic complexes containing metallic centres bonded
to organic ꢀ-electron conjugated systems are materials under
investigation for applications in second-order non-linear
optics (NLO). In comparison with organic compounds, they
show additional chemical variables (the nature of the metal, its
oxidation state, coordination geometry etc.) that may lead, in
principle, to enhanced NLO properties. Some interesting
results have been reported for organometallic fragments
attached at the end of organic conjugated systems and acting
as electron donor or acceptor groups (Whittall et al., 1998).
A less investigated possibility is the use of metallic centres
acting as conjugation bridges along push±pull systems (Buey et
al., 1998). In this case, conjugation should involve ꢀ interac-
tions between the metal and the organic ligands. This
obviously poses some limitations on the nature of the metal,
since its coordination geometry should allow, in the optimal
case, a coplanar arrangement of the metal coordination sphere
and the organic conjugated ligands. Cyclometallated
compounds (e.g. cyclometallated Schiff bases) seem a suitable
choice since, in these compounds, a coplanar arrangement of
metallated and ortho-aromatic rings must occur (Dehand &
Pfeffer, 1976; Churchill et al., 1980); furthermore, aromatic
solution at ꢁ = 1907 nm (Levine & Bethea, 1975). The values
48
obtained, i.e. ꢂꢃ = 120 Â 10
e.s.u. for (I) and ꢂꢃ = 75 Â
10 48 e.s.u. for (II), indicate a moderate activity (Dalton et al.,
1999) (e.s.u. = electric standard unit).
The coordination around the Pd atom is substantially
square planar in both complexes, showing standard values for
the distances from the metal to the coordinated atoms
(O'Keefe & Steel, 2000). Of the two rings to which the metal
atom belongs, the cyclopalladated (®ve-membered) ring is
substantially planar, while the salicylaldiminate (six-
membered) ring is not, mainly as a result of the metal atom
being out of the mean plane de®ned by the remaining ®ve
atoms. A trigonal planar geometry is observed around the N
atom of the amino group [N1 in (I) and N3 in (II)]. The sp2
hybridization of this atom should favour electron donation to
the adjacent phenyl ring. This is consistent with the observed
m26 # 2002 International Union of Crystallography
DOI: 10.1107/S0108270101014147
Acta Cryst. (2002). C58, m26±m28
Centore, Roberto
