Synthesis, spectral, structural, second-order nonlinear optical properties and theoretical studies on new organometallic donor-acceptor substituted nickel(ii) and copper(ii) unsymmetrical schiff-base complexes

Article abstract of DOI:10.1021/ic902126a

The synthesis, spectroscopic and structural characterization, linear and nonlinear optical properties, as well as the electrochemical behavior of a series of robust neutral binuclear M[Fc-C(O)CH=C(CH₃)N-X-N=CH-(2-O,5- R-C₆H₃)] (M = Ni (4), Cu (5), X = o-C₆H ₄, R = H; M = Ni (9), X = CH₂CH₂, R = OH), and their corresponding ionic trinuclear [M{Fc-C(O)CH=C(CH₃)N-X-N=CH- (η⁶-2-O,5-R-C₆H₃)RuCp*}][PF ₆] (6, 7, 10), M[ONNO]-type unsymmetrical Salophen and salen complexes featuring ferrocenyl (Fc) donor and the mixed sandwich acceptor [Cp*Ru(η⁶-salicylidene)]⁺ as a push-pull moiety are reported in this paper (Fc = CpFe(η⁵-C₅H ₄); Cp = η⁵-C₅H₅; Cp* = η⁵-C₅Me₅). The single-crystal X-ray structure of the bimetallic iron-nickel derivative 4 indicates a bowed structure of the unsymmetrical Schiff base skeleton. The Ni(II) ion is tetracoordinated in a square planar environment, with two nitrogen atoms and two oxygen atoms as donors. The new metalloligand [Fc-C(O)CH=C(CH₃)N-(H)CH ₂CH₂N=CH-(2,5-(OH)₂C₆H₃)] (8) obtained from the Schiff base condensation of 2,5-dihydroxobenzaldehyde with the half-unit precursor, Fc-C(O)CH=C(CH₃)N(H)CH ₂CH₂NH₂ (2), is reported with its crystal structure showing partial derealization of the heteroconjugated [O-C-C-C-N] frameworks with a dihedral angle between the respective planes of 60.76°. Second order nonlinear optical (NLO) measurements were achieved using the Harmonic Light Scattering technique to probe the role of the M[ONNO] chromophores and of the π-complexation of the salicylidene ring in the nonlinearity. All the complexes exhibit a second-order nonlinear response increasing with the nuclearity, the hyperpolarizability (β) value of the trinuclear complex 10 being 1.5 time larger than that of the metalloligand 8 (β = 155 x 10^-30 esu). A rationalization of the structural, electronic, and redox properties of the title compounds is provided, based on a theoretical investigation at the density functional theory (DFT) level. Their UV-visible spectra has been assigned with the help of time-dependent (TD) DFT calculations. They are dominated by LMCT, MLCT, and π - π* transitions.

Full text of DOI:10.1021/ic902126a

2750 Inorg. Chem. 2010, 49, 2750–2764
DOI: 10.1021/ic902126a
Synthesis, Spectral, Structural, Second-Order Nonlinear Optical Properties and
Theoretical Studies On New Organometallic Donor-Acceptor Substituted
Nickel(II) and Copper(II) Unsymmetrical Schiff-Base Complexes
Alexander Trujillo,† Mauricio Fuentealba,‡,§ David Carrillo,*,† Carolina Manzur,*,† Isabelle Ledoux-Rak,
Jean-Rene Hamon,*,^,X and Jean-Yves Saillard*,^,X
ꢀ
†
´
ꢀ
´
ꢀ
´
Laboratorio de Quımica Inorganica, Instituto de Quımica, Pontificia Universidad Catolica de Valparaıso,
‡
´
´
Campus Curauma, Avenida Parque Sur 330, Valparaıso, Chile, Laboratorio de Crystalografıa, Departamento
´
´
ꢀ
de Fısica, Facultad de Ciencias Fısicas y Matematicas, Universidad de Chile, Av. Blanco Encalada 2008,
§
´
ꢀ
ꢀ
Santiago, Chile, Facultad de Ecologıa y Recursos Naturales, Universidad Andres Bello, Avenida Republica 275,
ꢀ
Santiago, Chile, Laboratoire de Photonique Quantique et Moleculaire, UMR 8537 CNRS-ENS Cachan,
^
ꢀ
Institut d’Alembert, 61 Avenue du President Wilson, 94235 Cachan Cedex, France, UMR 6226 Sciences
ꢀ
Chimiques de Rennes, CNRS-Universite de Rennes 1, Campus de Beaulieu, 35042 Rennes-Cedex, France, and
X
ꢀ
ꢀ
€
Universite Europeenne de Bretagne, 5 Bd Laennec, 35000 Rennes, France
Received October 27, 2009
The synthesis, spectroscopic and structural characterization, linear and nonlinear optical properties, as well as the
electrochemical behavior of a series of robust neutral binuclear M[Fc-C(O)CHdC(CH3)N-X-NdCH-(2-O,5-R-C6H3)]
(M = Ni (4), Cu (5), X = o-C6H4, R = H; M = Ni (9), X = CH2CH2, R = OH), and their corresponding ionic trinuclear
[M{Fc-C(O)CHdC(CH3)N-X-NdCH-(η6-2-O,5-R-C6H3)RuCp*}][PF6] (6, 7, 10), M[ONNO]-type unsymmetrical
Salophen and salen complexes featuring ferrocenyl (Fc) donor and the mixed sandwich acceptor [Cp*Ru(η6-
salicylidene)]þ as a push-pull moiety are reported in this paper (Fc = CpFe(η5-C5H4); Cp = η5-C5H5; Cp* = η5-
C5Me5). The single-crystal X-ray structure of the bimetallic iron-nickel derivative 4 indicates a bowed structure
of the unsymmetrical Schiff base skeleton. The Ni(II) ion is tetracoordinated in a square planar environment,
with two nitrogen atoms and two oxygen atoms as donors. The new metalloligand [Fc-C(O)CHdC(CH3)N-
(H)CH2CH2NdCH-(2,5-(OH)2C6H3)] (8) obtained from the Schiff base condensation of 2,5-dihydroxobenzaldehyde
with the half-unit precursor, Fc-C(O)CHdC(CH3)N(H)CH2CH2NH2 (2), is reported with its crystal structure showing
partial delocalization of the heteroconjugated [O-C-C-C-N] frameworks with a dihedral angle between the
respective planes of 60.76ꢀ. Second order nonlinear optical (NLO) measurements were achieved using the Harmonic
Light Scattering technique to probe the role of the M[ONNO] chromophores and of the π-complexation of
the salicylidene ring in the nonlinearity. All the complexes exhibit a second-order nonlinear response increasing with
the nuclearity, the hyperpolarizability (β) value of the trinuclear complex 10 being 1.5 time larger than that of the
metalloligand 8 (β = 155 ꢀ 10-30 esu). A rationalization of the structural, electronic, and redox properties of the title
compounds is provided, based on a theoretical investigation at the density functional theory (DFT) level. Their
UV-visible spectra has been assigned with the help of time-dependent (TD) DFT calculations. They are dominated by
LMCT, MLCT, and π-π* transitions.
Introduction
variations of the dipole moment during the electronic excita-
tion.3 These properties can be accomplished by compounds
with a push-pull D-π-A type structure, containing both an
electron donor group (D) and an electron acceptor group (A)
In the past decade there has been a growing interest in the
design and construction of new molecular materials dis-
playing second-order nonlinear optical (NLO) properties
because of their potential applications in emerging opto-
electronic and photonic technologies.1,2 Molecules with
high NLO responses (molecular hyperpolarizability, β) must
possess strong electronic transitions of low energy and strong
(1) (a) Goovaerts, E.; Wenseleers, W. E.; Garcia, M. H.; Cross, G. H.
Nonlinear Optical Materials. In Handbook of Advanced Electronic and
Photonic Materials and Devices; Nalwa, H. S., Ed.; Academic Press: New
York, 2001; Vol. 9, p 127. (b) Handbook of Optics IV, Fiber Optics & Nonlinear
Optics 2nd ed.; Bass, M., Enoch, J. M., Stryland, E. W. V., Wolfe, W. L., Eds.;
McGraw-Hill: New York, 2001. (c) Nonlinear optical properties of matter:
From molecules to condensed phases; Papadopoulos, M. G., Sadlej, A. J.,
Leszczynski, J., Eds.; Springer: India, 2006.
*To whom correspondence should be addressed. E-mail: david.carrillo@
ucv.cl (D.C.), cmanzur@ucv.cl (C.M.), jean-rene.hamon@univ-rennes1.fr
(J.-R.H.), saillard@univ-rennes1.fr (J.-Y.S.).
r
pubs.acs.org/IC
Published on Web 02/10/2010
2010 American Chemical Society

Article
Inorganic Chemistry, Vol. 49, No. 6, 2010 2751
Chart 1
linked through a delocalized π system, which provides the
polarizable electrons. In this regard, organic molecules with
extensive π-delocalization have been the focus of the most
intense activity because of their ultrafast NLO responses,
good processability as thin-film devices, and enhanced non-
resonant NLO responses.4 More recently, the introduction of
a metal center as a donor or acceptor subunit has led to the
development of new second-order NLO materials based on
organotransition metal complexes owing to the unique
structural, electronic and optical properties associated with
organometallic5-7 and coordination compounds.7-9 In this
latter family, N2O2 Schiff base complexes (Chart 1, type A) in
which ligands are derived from salicylaldehyde and diamines
(generically coined as salen or salophen)10 have appeared to
be a promising class of efficient chromophores exhibiting
potentially large NLO responses,7a,11 and are currently
attracting considerable interest.12-15 They are particularly
interesting because (i) of their preparative accessibility and
the ease with which the salen-type structure can be deriva-
tized, (ii) of their thermal stability, (iii) of the active role,
strategic position, and nature (closed-shell vs open-shell)16 of
the metal ion which is a constituent of the polarizable bridge
in the D-π-A structure, and (iv) of the presence of charge
transfer (CT) transitions at low energies.7a,11 In such com-
pounds, metal complexation leads to formation of geome-
trically constrained acentric, generally planar structures that
always involves an enhancement of optical nonlinearity of
the Schiff base complex compared to that of its related free
ligands. Note that in all the aforementioned NLO studies on
salen- and bis(salicylaldiminato)-based complexes, including
that recently reported with unsymmetrical Schiff bases
(Chart 1, type B) of S-methylisothiosemicarbazide,12b organic
groups have always been used to structurally and electro-
nically modify the properties of the donor-acceptor Schiff
base frameworks.
(2) (a) Zyss, J. Molecular Nonlinear Optics: Materials, Physics and
Devices; Academic Press: Boston, 1994. (b) Prasad, P. N.; Williams, D. J.
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95, 10643.
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Nonlinear Optics of Organic Molecules and Polymers; Nalwa, H. S., Miyata, S.,
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and Photonics; Messier, J., Kajzar, F., Prasad, P., Eds.; Kluwer Academic
Publishers: Dordrecht, The Netherlands, 1991. (d) Organic Materials for Non-
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Optics of Organic Materials III; Proceedings of SPIE; SPIE: San Diego, CA,
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17, 502.
Furthermore, the electron-donating and -accepting cap-
abilities of organoligand-metal fragments have been suc-
cessfully applied to design and develop new highly efficient
dipolar chromophores to achieve high second-order NLO
responses.1a,5-7 For instance, the attractive NLO properties
of ferrocene-based complexes are coupled with good thermal
and photochemical stability,17 excellent donor capability,18
(10) (a) The Chemistry of the Carbon-Nitrogen Double Bond; Patai, S., Ed.;
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Acc. Chem. Res. 2005, 38, 691. (c) Andraud, C.; Maury, O. Eur. J. Inorg. Chem.
2009, 4357. (d) Calvete, M.; Yang, G. Y.; Hanack, M. Synth. Met. 2004, 141,
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K. Inorg. Chem. 2004, 43, 4743. (e) Costes, J.-P.; Lamere, J.-F.; Lepetit, C.;
Lacroix, P. G.; Dahan, F.; Nakatani, K. Inorg. Chem. 2005, 44, 1973.
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7, 3738. (b) Di Bella, S.; Fragala, I. New J. Chem. 2002, 26, 285. (c) Di Bella, S.;
Fragala, I.; Guerri, A.; Dapporto, P.; Nakatani, K. Inorg. Chim. Acta 2004, 357,
1161. (d) Di Bella, S.; Consiglio, G.; Leonardi, N.; Failla, S.; Finocchiaro, P.;
Fragala, I. Eur. J. Inorg. Chem. 2004, 2701.
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Zecchin, S.; Quici, S.; Garbalau, N. Inorg. Chem. 2007, 46, 884.
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2752 Inorganic Chemistry, Vol. 49, No. 6, 2010
Trujillo et al.
and redox switching abilities.19 On the other hand, its
cationic electron-withdrawing isolobal counterparts, namelþy,
the robust mixed sandwich derivatives [Cp0M(η6-arene)] ,
(M = Fe, Ru; Cp0 = Cp = η5-C5H5, Cp0 = Cp* = η5-
C5Me5),20 have also proven their efficiency as an organome-
tallic chromophore to achieve second order NLO re-
sponses.21 On the basis of the considerations above, we
developed an approach which utilizes the advantages of both
ferrocenyl and [Cp*Ru(η6-arene)]þ units (ferrocenyl =
CpFe(η5-C5H4)), such as chemical and thermal stability,
three-dimensional structure, and aromatic chemistry, for
obtaining heterotrinuclear π-conjugated donor-acceptor
unsymmetrical Schiff base complexes (Chart 1, type B with
R = ferrocenyl and R0 = Cp*Ruþ).22 In such organome-
tallic-inorganic hybrids, the ferrocenyl fragment was intro-
duced as a preformed tridentate enaminone metalloligand,23,24
while the cationic entity [Cp*Ru(η6-salicylidene)]þ was
generated through a ligand exchange reaction with the
arenophile source [Cp*Ru(NCCH3)3]PF6,25 and both orga-
nometallic building blocks were linked together by a MII
classical Werner type coordination core {M(ONNO)} (M =
Ni, Cu). The crucial role of this Cp*Ruþ moiety has very
recently been highlighted by Sessler and co-workers in the
chemistry of ruthenocene-porphyrin and ruthenocene-
porphycene hybrid complexes, where they showed that the
intrinsic electronic properties of the metalloporphyrins and
metalloporphycenes are altered in a dramatic way upon
fusion of the cationic arenophile to one or more pyrrolic
subunits of these macrocycles.26
In branching such donor and acceptor organometallic end
groups at the contour of the unsymmetrical Schiff base
platform, one would expect some synergistic effects to occur,
leading for instance to theenhancement of NLO properties of
these new salen-type derivatives. Thus, to continue this work,
two series of new D-π-A type compounds were designed and
prepared, which consist of thermally stable organometallic
substituted donor-acceptor nickel(II) and copper(II) un-
symmetrical Schiff base complexes exhibiting second-order
NLO responses, tunable by the metal center and the areno-
phile appendix, and a theoretical investigation allowing
rationalization and substantiation of the experimental find-
ings. The paper reports on the syntheses, spectroscopic char-
acterization, electrochemical and linear optical properties of a
family of binuclear M[Fc-C(O)CHdC(CH3)N-X-NdCH-(2-
O,5-R-C6H3)] (M= Ni(4), Cu(5), X= o-C6H4, R=H;M=
Ni (9), X= CH2CH2, R = OH), and their corresponding ionic
trinuclear inorganic NLO chromophores [M{Fc-C(O)CHdC-
(CH3)N-X-NdCH-(η6-2-O,5-R-C6H3)RuCp*}][PF6] (6, 7,
10), as well as of the new metalloligand precursor [Fc-C-
(O)CHdC(CH3)N(H)CH2CH2NdCH-(2,5-(OH)2C6H3)] (8),
and the X-ray structural determinations of 4 and 8. We
report also the values of the first hyperpolarizability (β)
of selected compounds obtained from Harmonic Light
Scattering (HLS) experiments. In addition, the optimized
geometries of all compounds were obtained by density
functional theory (DFT) computational studies. Moreover,
DFT and its time-dependent DFT extension (TDDFT)
provide a rationalization of the electrochemical and spec-
troscopic properties, and analyzes the electronic communi-
cation between the metal centers.
(17) (a) Rosenblum, M. Chemistry of the Iron Group Metallocenes; Wiley:
New York, 1965. (b) Neuse, E. W.; Woodhouse, J. R.; Montaudo, G.; Puglis, C.
Appl. Organomet. Chem. 1988, 2, 53. (c) Ferrocenes: Homogenous Catalysis,
Organic Synthesis, Materials Science; Togni, A., Hayashi, Eds.; Wiley-VCH:
Weinheim, 1995. (d) Ferrocenes: Ligands, Materials and Biomolecules; Step-
nicka, P., Ed.; Wiley-VCH: Weinheim, 2008.
Experimental Section
Materials. All manipulations were carried out under a
dinitrogen atmosphere using standard Schlenk techniques.
The solvents were dried and distilled according to standard
procedures. Ethylenediamine, o-phenylenediamine, 2-hydroxo-
benzaldehyde (salicylaldehyde), 2,5-dihydroxobenzaldehyde
(5-hydroxosalicylaldehyde), nickel(II) acetate tetrahydrate,
and copper(II) acetate monohydrate were purchased from
Aldrich and used without further purification. The organo-
metallic tridentate “half units” CpFe(η5-C5H4)-C(O)CHdC-
(CH3)N(H)-o-C6H4NH2) (1),23 and CpFe(η5-C5H4)-C(O)CHd
C(CH3)N(H)C2H4NH2 (2),22b pentamethylcyclopentadienyl-
tris(acetonitrile) ruthenium(II) hexafluorophosphate,25,27 and
pentamethylcyclopentadienyl(η6-salicylaldehyde)ruthenium hexa-
fluorophosphate28 were synthesized using the established
literature procedures. The synthesis and spectroscopic charac-
terization of the heterobinuclear iron-ruthenium metalloligand
3 is provided in the Supporting Information.
(18) (a) Kinnibrugh, T. L.; Salman, S.; Getmanenko, Y. A.; Coropceanu,
ꢀ
V.; Porter, W. W.; Timofeeva, T. V.; Matzger, A. J.; Bredas, J.-L.; Marder, S.
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Kondo, M.; Uchikawa, M.; Namiki, K.; Zhang, W.-W.; Kume, S.; Nishibori, E.;
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J. A.; Ward, M. D.; Asselberghs, I.; Clays, K.; Persoons, A. Chem. Commun.
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Rak, I.; Hamon, J.-R. J. Organomet. Chem. 2007, 692, 1099. (b) Millan, L.;
Fuentealba, M.; Manzur, C.; Carrillo, D.; Faux, N.; Caro, B.; Robin-Le Guen, F.;
Sinbandhit, S.; Ledoux-Rak, I.; Hamon, J.-R. Eur. J. Inorg. Chem. 2006, 1131.
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Characterization and Instrumentation. Solid IR spectra were
recorded on a Perkin-Elmer, Model Spectrum One, FT-IR
spectrophotometer with KBr disks in the 4000 to 400 cm-1
range. Electronic spectra were obtained with a Spectronic,
1
Genesys 2, spectrophotometer. The H and 13C NMR spectra
were recorded on either Bruker Avance 400 Digital or Avance
500 Instruments. All NMR spectra are reported in parts per
million (ppm, δ) relative to tetramethylsilane (Me4Si), with the
residual solvent proton resonance and carbon resonances used
as internal standards. Coupling constants (J) are reported in
(26) (a) Cuesta, L.; Karnas, E.; Lynch, V. M.; Sessler, J. L.; Kajonkijya,
W.; Zhu, W.; Zhang, M.; Ou, Z.; Kadish, K. M.; Ohkubo, K.; Fukuzumi, S.
Chem.;Eur. J. 2008, 14, 10206. (b) Cuesta, L.; Karnas, E.; Lynch, V. M.; Chen,
P.; Shen, J.; Kadish, K. M.; Ohkubo, K.; Fukuzumi, S.; Sessler, J. L. J. Am. Chem.
Soc. 2009, 131, 13538.
(27) Mbaye, M. D.; Demerseman, B.; Renaud, J.-L.; Toupet, L.;
Bruneau, C. Adv. Synth. Catal. 2004, 346, 835.
(28) The procedure used to prepare the corresponding triflate salt was
followed: Wheeler, D. E.; Baetz, N. W.; Holder, G. N.; Hill, S. T.; Milos, S.;
Luczak, K. A. Inorg. Chim. Acta 2002, 328, 210.

Article
Inorganic Chemistry, Vol. 49, No. 6, 2010 2753
Chart 2. Labeling Scheme Used for NMR Assignments
hertz (Hz), and integrations are reported as number of protons.
The following abbreviations are used to describe peak patterns:
s = singlet, d = doublet, t = triplet, m = multiplet, br = broad.
1H and 13C NMR chemical shift assignments are supported
1H, H-12), 8.15 (s, 1H, NdCH). 13C{1H} NMR (125 MHz,
CDCl3): δ 24.68 (CH3), 68.73 (CR C5H4), 70.07 (Cp), 70.62 (Cβ
C5H4), 79.79 (Cipso C5H4), 102.81 (CHdC), 114.37 (C-12), 115.46
(C-5), 120.21 (C-1), 121.64 (C-9), 121.97 (C-3), 122.78 (C-11),
126.20 (C-10), 132.99 (C-6), 134.47 (C-4), 142.42 (C-7), 145.32
(C-8), 162.23 (CH=C), 165.56 (C-2), 180.18 (CdO).
1
1
by data obtained from H-1H COSY, H-13C HMQC, and
1H-13C HMBC NMR experiments, and are given according to
the numbering scheme of Chart 2. High resolution electrospray
ionization mass spectra (ESI-MS) were obtained at the Centre
Synthesis of Cu[CpFe(η5-C5H4)-C(O)CHdC(CH3)N-o-C6H4-
NdCH-(2-O-C6H4)] (5). The synthesis of this orange complex
was carried out following a procedure similar to that described
above for complex 4, using in this case 400 mg (1.10 mmol) of 1,
117 μL (1.10 mmol) of salicylaldehyde and 215 mg (1.10 mmol) of
copper acetate monohydrate. Yield 256 mg, 44%. Mp 213 ꢀC
ꢀ
Regional de Mesures Physiques de l’Ouest (CRMPO, Rennes)
on a MS/MS ZabSpec TOF Micromass spectrometer (4 kV).
Poly(ethylene glycol) (PEG) was used as internal reference and
dichloromethane was used as solvent. Elemental analyses were
conducted on a Thermo-FINNIGAN Flash EA 1112 CHNS/O
analyzer by the Microanalytical Service of the CRMPO at the
University of Rennes 1, France. Cyclic voltammetry (CV)
measurements were performed using a Radiometer Analytical
model PGZ 100 all-in one potentiostat, using a standard
three-electrode setup with a vitreous carbon or a platinum disk
working electrode, platinum wire auxiliary electrode, and Ag/
AgCl as the reference electrode. Dichloromethane solutions
were 1.0 mM in the compound under study and 0.1 M in the
(dec). Anal. Calcd for C27H22CuFeN2O2 0.5CH2Cl2 (crystalli-
3
zation solvent): C, 58.12; H, 4.08; N, 4.93. Found: C, 58.47; H,
4.22; N, 4.87. ESI MS (m/z), calcd for C27H22N2O256Fe63Cu:
525.03267, found: 525.0326 [M]. IR (KBr, cm-1): 3089(w)
ν(C-H arom); 2991(w), 2922(w), 2859(w) ν(C-H aliph);
1615-1520(m) ν(C3 3 3 O), ν(C3 3 3 C) and/or ν(C3 3 3 N); 1278(vw)
ν(C-O).
Synthesis of [Ni{CpFe(η5-C5H4)-C(O)CHdC(CH3)N-o-C6H4-
NdCH-(η6-2-O-C6H4)RuCp*}][PF6] (6). A Schlenk tube was
charged with complex 3 (150 mg, 0.20 mmol), nickel acetate
tetrahydrate (45 mg, 0.2 mmol), methanol (10 mL), and a
magnetic stir bar. The reaction mixture was stirred for 2 h at RT
while a dark precipitate formed. The solid material was filtered,
washed with diethyl ether (2 ꢀ 5 mL), and recrystallized from
CH2Cl2/Et2O mixture as a brown-violet crystalline solid. Yield
121 mg, 66%. Mp 203 ꢀC. Anal. Calcd for C37H37F6FeN2O2Ni-
PRu: C, 49.25; H, 4.13; N, 3.11. Found: C, 48.87; H, 3.93; N, 3.05.
ESI MS (m/z), calcd for C37H37N2O256Fe58Ni102Ru: 757.06014,
found: 757.0606 [M-(PF6)]. IR (KBr, cm-1): 3047(w) ν(C-H
arom); 2963(w), 2920(w), 2852(w) ν(C-H aliph); 1606-1519(m)
ν(C3 3 3 O), ν(C3 3 3 C) and/or ν(C3 3 3 N); 1286(w) ν(C-O); 840(s)
ν(PF6); 557(s) δ(P-F). 1H NMR (500 MHz, acetone-d6): δ 2.10
(s, 15H, C5(CH3)5), 2.50 (s, 3H, CH3), 4.24 (s, 5H, Cp), 4.47 (m,
supporting electrolyte n-Bu4NþPF6 with the voltage scan
-
rate = 100 mV s-1. Under these experimental conditions the
ferrocene/ferrocenium couple, used as an internal reference
for the potential measurements, was located at E1/2 = 0.560 V
(ΔEp = 82 mV). E1/2 is defined as equal to (Epa þ Epc)/2, where
Epa and Epc are the anodic and cathodic peak potentials,
respectively. Melting points were determined in evacuated
capillaries and were not corrected.
Synthesis of Ni[CpFe(η5-C5H4)-C(O)CHdC(CH3)N-o-C6H4-
NdCH-(2-O-C6H4)] (4). To a Schlenk tube containing a stirred
solution of CpFe(η5-C5H4)-C(O)CHdC(CH3)N(H)-o-C6H4NH2
(1) (400 mg, 1.11 mmol) in ethanol (30 mL) was added dropwise
120 μL of salicylaldehyde (1.11 mmol). The resulting solution was
stirred for 15 min at room temperature (RT). A solution of nickel
acetate tetrahydrate (553 mg, 2.22 mmol) in ethanol (10 mL) was
then added, and the resulting solution was refluxed for 4 h. The
mixture was allowed to cool to RT overnight. Evaporation of the
solution to half of its volume under vacuum gave a purple
microcrystalline precipitate. The solid material was filtered off,
washed with methanol (2 ꢀ 3 mL), and dried in vacuo. Yield 151
mg, 26%. Slow evaporation of a concentrated dichloromethane
solution deposited X-ray quality crystals. Mp 218 ꢀC (dec). Anal.
Calcd for C27H22FeN2NiO2: C, 62.24; H, 4.26; N, 5.38. Found: C,
62.14; H, 4.34; N, 5.24. IR (KBr, cm-1): 3047(w) ν(C-H arom);
2963(w), 2920(w), 2852(w) ν(C-H aliph); 1606-1519(m)
ν(C3 3 3 O), ν(C3 3 3 C) and/or ν(C3 3 3 N); 1279(vw) ν(C-O). 1H
NMR (500 MHz, CDCl3): δ 2.42 (s, 3H, CH3), 4.20 (s, 5H, Cp),
4.36 (br t, 3JHH =1.7Hz, 2H, Hβ C5H4), 4.77 (brt, 3JHH =1.7Hz,
2H, HR C5H4), 5.64 (s, 1H, CHdC), 6.61 (t, 3JHH = 7.4 Hz, 1H, H-
5), 6.96 (t, 3JHH = 7.8 Hz, 1H, H-11), 7.06 (m, 2H, H-3 and H-10),
7.25 (t, 3JHH = 7.4 Hz, 1H, H-4), 7.26 (d, 3JHH = 7.8 Hz, 1H, H-
9), 7.32 (br d, 3JHH = 7.4 Hz, 1H, H-6), 7.60 (d, 3JHH = 7.8 Hz,
0
1H, Hβ C5H4), 4.48 (m, 1H, Hβ3 C5H4), 4.78 (m, 1H, HR C5H4),
4.80 (m, 1H, HR C5H4), 5.76 (d, JHH = 6.4 Hz, 1H, H-3), 5.87 (s,
0
1H, CHdC), 5.86 (t, 3JHH = 5.8 Hz, 1H, H-5), 5.94 (t, 3JHH = 5.8
=
Hz, 1H, H-4), 6.35 (d, 3JHH = 5.3 Hz, 1H, H-6), 7.07 (t, 3JHH
3
7.5 Hz, 1H, H-11), 7.31 (t, JHH = 7.5 Hz, 1H, H-10), 7.50 (d,
3JHH = 7.5 Hz, 1H, H-9), 7.98 (d, 3JHH = 7.5 Hz, 1H, H-12), 8.83
(s, 1H, NdCH). 13C{1H} NMR (125 MHz, acetone-d6): δ 10.56
0
(C5(CH3)5), 24.59 (CH3), 69.27 (CR C5H4), 69.64 (CR C5H4),
0
70.87 (Cp), 71.87 (Cβ C5H4), 71.91 (Cβ C5H4), 79.64 (C-3), 79.65
(Cipso C5H4), 82.06 (C-1), 84.93 (C-5), 89.13 (C-6), 89.63 (C-4),
95.56 (C5(CH3)5), 104.00 (CHdC), 116.75 (C-12), 123.06 (C-9),
124.39 (C-11), 130.25 (C-10), 139.69 (C-2), 142.14 (C-7), 146.96
(C-8), 160.44 (NdCH), 164.38 (CH=C), 181.40 (CdO).
Synthesis of [Cu{CpFe(η5-C5H4)-C(O)CHdC(CH3)N-o-C6H4-
NdCH-(η6-2-O-C6H4)RuCp*}][PF6] (7). The synthesis of this
dark orange complex was carried out following a procedure similar
to that described above for complex 6, using in this case, 200 mg
(0.24 mmol) of 3 and 53.4 mg (0.24 mmol) of copper acetate

2754 Inorganic Chemistry, Vol. 49, No. 6, 2010
Trujillo et al.
monohydrate. Yield 124 mg, 57%. Mp 281 ꢀC. Anal. Calcd for
C37H37CuF6FeN2O2PRu: C, 48.98; H, 4.11; N, 3.08. Found: C,
Table 1. Crystal Data, Data Collection, and Structure Refinement Parameters
for 4 and 8
56-
48.72; H, 3.92; N, 2.85 ESI MS (m/z), calcd for C37H37N2O2
4
8
Fe63Cu102Ru: 762.05439, found: 762.0558 [M-(PF6)]. IR (KBr,
cm-1): 3093(w) ν(C-H arom); 2964(w), 2918(w), 2854(w) ν(C-H
aliph); 1616-1519(m) ν(C3 3 3 O), ν(C3 3 3 C) and/or ν(C3 3 3 N);
1285(w) ν(C-O); 841(s) ν(PF6); 557(m) δ(P-F).
empirical formula
formula mass, g mol-1
collection T, K
crystal system
space group
a (A)
C
521.03
298(2)
monoclinic
P21/c
9.9892(13)
18.584(3)
12.0417(16)
95.004(2)
2227.0(5)
4
27H22FeN2NiO2
C23H24FeN2O3
432.29
150(2)
monoclinic
P21/n
12.1725(7)
11.4739(6)
14.6825(8)
97.7380(10)
2031.97(19)
4
Synthesis of CpFe(η5-C5H4)-C(O)CHdC(CH3)N(H)CH2-
CH2NdCH-(2,5-(OH)2-C6H3) (8). A round-bottom 50 mL flask
equipped with a reflux condenser was loaded with CpFe(η5-
C5H4)-C(O)CHdC(CH3)N(H)CH2CH2NH2 (2) (300 mg, 0.98
mmol), 2,5-dihydroxobenzaldehyde (133.6 mg, 0.98 mmol), a
magnetic stir bar, and dichloromethane (10 mL). The reaction
mixture was stirred and refluxed for 2 h while a red precipitate
formed. At RT, it was filtered off and washed with CH2Cl2 (3 ꢀ
5 mL) and dried under vacuum. X-ray quality crystals were
obtained by recrystallization from hot dichloromethane. Yield
310 mg, 72%. Mp 204-206 ꢀC. Anal. Calcd for C23H24FeN2O3:
C, 63.90; H, 5.59; N, 6.48. Found: C, 63.77; H, 5.57; N, 6.54. ESI
MS (m/z), calcd for C23H24N2O3Na56Fe: 455.10340, found:
455.1055 [MþNa]. IR (KBr, cm-1): 3109(w) ν(O-H); 3088(w),
3053(vw) ν(C-H arom); 2996(vw), 2954(vw), 2907(vw) ν(C-H
aliph); 1639(w), 1595(m), 1535(m) ν(C3 3 3 O), ν(C3 3 3 C) and/or
ν(C3 3 3 N), 1305(w) δ(OH). 1HNMR (400 MHz, DMSO-d6):
b (A)
c (A)
β (deg)
V (A3)
Z
Dcalcd (g cm-3
crystal size (mm)
)
1.554
0.32 ꢀ 0.24 ꢀ 0.06
1.413
0.49 ꢀ 0.22 ꢀ 0.04
F(000)
1072
1.525
904
0.769
abs coeff (mm-1
θ range (deg)
range h, k, l
)
2.02 to 28.12
-13/12, -24/23,
-15/15
18572
5032
5032/0/299
2.04 to 27.82
-15/15, -14/13,
-18/19
15787
4480
4480/0/275
no. total refl.
no. unique refl.
data/restraints/
parameters
3
final R
[I > 2σ(I)]
R indices (all data)
R1 = 0.0544
wR2 = 0.1074
R1 = 0.1018
wR2 = 0.1234
0.993
R1 = 0.0433
wR2 = 0.0918
R1 = 0.0607
wR2 = 0.1006
1.038
δ 1.95 (s, 3H, CH3), 3.02 (q, JHH = 5.4 Hz, 2H, H-8), 3.75
(t, 3JHH = 5.8 Hz, 2H, H-7), 4.08 (s, 5H, Cp), 4.29 (t, 3JHH = 1.9
Hz, 2H, Hβ C5H4), 4.65 (t, 3JHH = 1.9 Hz, 2H, HR C5H4), 5.32 (s,
1H, CHdC), 6.51 (d, 3JHH = 8.8 Hz, 1H, H-3), 6.76 (d, 3JHH
=
goodness of fit/F2
largest diff. peak
2.9 Hz, 1H, H-6), 6.72 (dd, 3JHH = 8.8 Hz, 4JHH = 2.4Hz, 1H, H-
4), 8.48 (t, 3JHH = 5.8 Hz, 1H, NdCH), 8.98 (s, 1H, OH), 10.86
(t, 3JHH = 5.8 Hz, 1H, NH), 12.34 (s, 1H, OH). 13C{1H} NMR
(100 MHz, DMSO-d6): δ 18.93 (CH3), 43.14 (C-8), 59.01 (C-7),
67.94 (CR C5H4), 69.30 (Cp) 70.06 (Cβ C5H4), 82.95 (Cipso C5H4),
92.60 (CHdC), 116.48 (C-6), 116.84 (C-1), 118.55 (C-3), 119.93
(C-4), 149.31 (C-5), 152.88 (C-2), 162.14 (NdCH), 166.94
(CH=C), 190.09 (CdO).
0.578 and -0.324
0.435 and -0.249
and hole (e A-3
)
compound 9 (170 mg, 0.35 mmol), a magnetic stir bar and CH2Cl2
(5 mL). The reaction mixture was stirred at RT overnight. The
solvent was then evaporated under reduced pressure and the
residue washed with diethyl ether (2 ꢀ 5 mL). The resulting solid
was redissolved in CH2Cl2 (5 mL). The solution was filtered off and
reduced to half of its volume. Addition of diethyl ether (10 mL)
caused the formation of a red microcrystalline precipitate which
was collected by filtration and dried under vacuum. Yield 133 mg,
44%. Mp 312 ꢀC. Anal. Calcd for C33H37F6FeN2NiO3PRu: C,
45.55; H, 4.28; N, 3.21. Found: C, 45.28; H, 4.06; N, 2.95. ESI MS
(m/z), calcd for C33H37N2O356Fe58Ni102Ru: 725.05505, found:
725.0545 [M-(PF6)]. IR (KBr, cm-1): 3241(w) ν(O-H); 3088(w)
ν(C-H arom); 2960(w), 2861(w) ν(C-H aliph); 1636(m),
1573(m), 1510(s) ν(C3 3 3 O), ν(C3 3 3 C) and/or ν(C3 3 3 N); 1258(w)
ν(C-O); 843(s) ν(PF6); 558(s) δ(P-F). 1H NMR (500 MHz,
acetone-d6): δ 2.05 (s, 3H, CH3), 2.09 (s, 15H, C5(CH3)5), 3.19
(m, 1H, H-8), 3.24 (m, 1H, H-80), 3.57 (m, 1H, H-7), 3.61 (m, 1H,
Synthesis of Ni[CpFe(η5-C5H4)-C(O)CHdC(CH3)NCH2-
CH2NdCH-(2-O,5-OH-C6H3)] (9). A solution of 2,5-dihydroxo-
benzaldehyde (220.7 mg, 1.59 mmol) in CH2Cl2 (3 mL) and
methanol (5 mL) was added dropwise to a stirred solution of
compound 2 (500 mg, 1.60 mmol) in CH2Cl2 (3 mL). The
resulting solution was stirred for 10 min at RT. A solution of
nickel acetate tetrahydrate (455.7 mg, 1.60 mmol) in methanol
(3 mL) was then added by cannula, and the resulting solution was
heated at reflux for 2 h. Upon cooling to RT, a brown orange
precipitate formed. The solid was collected by filtration, washed
with CH2Cl2 (2 ꢀ 5 mL), and dried under vacuum. Yield 553 mg,
71%. Mp 279 ꢀC (dec). Anal. Calcd for C23H22FeN2-
H-70), 4.16 (s, 5H, Cp), 4.30 (br s, 1H, Hβ C5H4), 4.32 (br s, 1H, Hβ
NiO3 CH2Cl2 (crystallization solvent): C, 50.35; H, 4.20; N,
0
3
4.90. Found: C, 50.16; H, 4.38; N, 4.88. ESI MS (m/z), calcd
for C23H22N2O356Fe58Ni: 488.03333, found: 488.0328 [M]. IR
(KBr, cm-1): 3128(w) ν(O-H); 3085(w), 3069(w) ν(C-H arom);
2941(w), 2923(w), 2844(w) ν(C-H aliph); 1619(m), 1575(m),
1544(m) ν(C3 3 3 O), ν(C3 3 3 C) and/or ν(C3 3 3 N); 1297(m) δ(OH).
1H NMR (500 MHz, DMSO-d6): δ 1.97 (s, 3H, CH3), 3.02 (t,
3JHH = 6.8 Hz, 2H, H-8), 3.37 (t, 3JHH = 6.8 Hz, 2H, H-7), 4.14
0
C5H4), 4.63 (br s, 1H, HR C5H4), 4.67 (br s, 1H, HR C5H4), 5.25
3
(s, 1H, CHdC), 5.48 (d, JHH = 6.3 Hz, 1H, H-3), 5.66 (br d,
3JHH = 6.3 Hz, 1H, H-4), 5.77 (br s, 1H, H-6), 7.96 (s, 1H,
NdCH), 9.14 (br s, 1H, OH). 13C{1H} NMR (125 MHz, aceto-
ne-d6): δ 10.22 (C5(CH3)5), 21.59 (CH3), 52.30 (C-8), 62.26
0
(C-7), 68.02 (CR C5H4), 69.19 (CR C5H4), 70.52 (Cp), 70.56 (Cβ
0
C5H4), 70.60 (Cβ C5H4), 76.19 (C-6), 77.42 (C-3), 79.06 (C-1),
(s, 5H, Cp), 4.29 (t, 3JHH = 1.9 Hz, 2H, Hβ C5H4), 4.56 (t, 3JHH
=
79.31 (C-4), 81.48 Cipso C5H4), 94.85 (C5(CH3)5), 97.75 (CHdC),
126.64 (C-5), 138.14 (C-2), 165.97 (CH=C), 166.58 (NdCH),
175.77 (CdO).
1.9 Hz, 2H, HR C5H4), 5.42 (s, 1H, CHdC), 5.80 (s, 2H, CH2Cl2),
6.51 (d, 3JHH = 9.0 Hz, 1H, H-3), 6.57 (d, 3JHH = 3.2 Hz, 1H, H-
6), 6.72 (dd, 3JHH = 9.0 Hz, 4JHH = 3.2 Hz, 1H, H-4), 7.68 (s, 1H,
NdCH), 8.49 (s, 1H, OH). 13C{1H} NMR (125 MHz, DMSO-
d6): δ 21.32 (CH3), 51.06(C-8), 54.82 (CH2Cl2), 59.47 (C-7), 67.48
(CR C5H4), 69.26 (Cβ C5H4), 69.46 (Cp), 81.21 (Cipso C5H4), 96.59
(CHdC), 114.49 (C-6), 119.21 (C-1), 120.19 (C-3), 123.67 (C-4),
145.43 (C-5), 158.24 (C-2), 161.27 (NdCH), 164.27 (CH=C),
173.91 (CdO).
X-ray Crystal Structure Determinations. Suitable X-ray single
crystals of compounds 4 and 8 were obtained as described above
and were mounted on top of glass fibers in a random orienta-
tion. Crystal data, data collection, and refinement parameters
are given in Table 1. Compound 4 was studied at 298(2) K
whereas complex 8 was studied at 150(2) K on a Bruker Smart
Apex diffractometer equipped with bidimensional CCD detec-
tor employing graphite-monochromated Mo KR radiation (λ=
0.71073 A). Semiempirical corrections, via Τ-scans, were ap-
plied for absorption. The diffraction frames were integrated
Synthesis of [Ni{CpFe(η5-C5H4)-C(O)CHdC(CH3)NCH2-
CH2NdCH-(η6-2-O,5-OH-C6H3)RuCp*}][PF6] (10). A Schlenk
tube was loaded with [Cp*Ru(NCCH3)3]PF6 (175 mg, 0.35 mmol),

Article
Inorganic Chemistry, Vol. 49, No. 6, 2010 2755
using the SAINT package,29 and corrected for absorption with
SADABS.30 The structures were solved using XS in SHELXTL-
PC,31 by direct methods and completed (non-H atoms) by
difference Fourier techniques. The complete structure was then
refined by the full-matrix least-squares procedures on reflection
intensities (F2).32 The non-hydrogen atoms were refined with
anisotropic displacement coefficients, and all hydrogen atoms
were placed in idealized locations. CCDC reference numbers of
compounds 4 and 8 are 646871 and 713025, respectively. These
data can be obtained free of charge from the Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk.
with gradient corrections added for exchange (Becke88)38 and
correlation (Perdew),39 respectively. The numerical integra-
tion procedure applied for the calculation was developed by te
Velde.35d The standard ADF TZP basis set was used for all the
atoms. The frozen core approximation was used to treat core
electrons at the following levels: Ru, 4p; Cu, 3p; Ni, 3p; Fe, 3p;
C, 1s; N, 1s and O, 1s.35d Full geometry optimizations were
carried out on each complex using the analytical gradient
method implemented by Versluis and Ziegler.40 The geometry
for all the model compounds discussed in the text were fully
optimized, with a good agreement between the computed
geometric parameters and the available structural data. Spin-
unrestricted calculations were carried out on all the odd-
electrons and open-shell systems. The UV-visible electronic
absorption transitions were computed on the DFT-optimized
geometries using the TDDFT41 method implemented within the
ADF program, using the LB94 functional.
HLS Measurements. Because of the presence of ionic species
in the series of compounds investigated here, we chose the HLS
at 1.91 μm to measure the first order hyperpolarizabilities β of
the molecules. The 1.91 μm fundamental beam was emitted by a
high-pressure (30 bar), 50 cm long Raman cell pumped by a
Nd3þ:YAG laser operating at 1.06 μm and providing pulses
of 15 ns duration at a 10 Hz repetition rate. The backscattered
1.91 μm Raman emission was collected at a 45ꢀ incidence angle
by use of a dichroic mirror, to eliminate most of the residual
1.06 μm pump photons. Choosing the 1.91 μm wavelength,
whose harmonics at 955 nm is far from any resonance of the
molecules to be investigated, prevents the contribution of
possible two-photon fluorescence emission to the HLS signal.
We have evidenced the absence of any wide-band two-photon
fluorescence by checking that no HLS signal can be detected for
wavelengths different from 955 nm. Our reference sample was a
concentrated (10-2 M) solution of ethyl violet, its octupolar
β value being 170 ꢀ 10-30 esu at 1.91 μm.33 Chloroform (for
neutral species) and dimethylformamide (DMF) (for the ionic
compounds) solvents were used for the HLS measurements.
Both solvents appear to be transparent at 1.91 μm. The HLS
photons at 955 nm were focused onto a Hamamatsu R632-01
photomultiplier tube using two collecting lenses. The signal
detected was then sampled and averaged using a boxcar, and
processed by a computer. The reference beam was collected at a
45ꢀ incidence angle by a glass plate, and focused onto a highly
nonlinear N-4-nitrophenyl-prolinol (NPP) powder, which was
used as the frequency doubler. The variation of the scattered
second harmonic intensity from the solution was recorded on
the computer as a function of the reference second harmonic
signal provided by the NPP powder, both signals scaling as the
square of the incoming fundamental intensity. Values for β were
then inferred from the slopes of the resulting lines.34
Results and Discussion
Synthesis and Common Spectral Characteristics. The
investigated Schiff-base complexes were synthesized either
by complexation of the organometallic ligands with the
appropriate metal(II) ion or by one-pot template synthesis.
In both cases, the reaction involves a condensation of the
appropriate salicylaldehyde with the free amino group of
the corresponding tridentate metalloligand. Thus, the neu-
tral unsymmetrical Schiff base complexes 4 and 5 were
readily synthesized by a well-known template procedure
starting from the half-unit 1 bearing the o-phenylene amine
arm,23 anequimolar amount of salicylaldehyde, and nickel-
(II) acetate tetrahydrate and copper(II) acetate mono-
hydrate, respectively, as outlined in Scheme 1. Heating this
reaction mixture for 4 h in refluxing ethanol afforded
compounds 4 and 5 that were isolated as violet and orange
microcrystalline solids in 26 and 44% yield, respectively.
The corresponding ionic trinuclear counterparts usual-
ly result from the π-complexation of the salicylidene ring
by the Cp*Ruþ arenophile (see below and Scheme 3).
However, in the present cases, competitive complexation
of both the central and terminal o-phenylenes forming the
Schiff base skeleton of 4 and 5 might occur and give rise
to untractable mixtures of compounds.22b Therefore,
an alternative regioselective route to the unsymmetrical
trinuclear Schiff base complex 6 and 7, avoiding this
competitive π-coordination, was designed. The first
step consists in the preparation of the binuclear iron-
ruthenium intermediate 3, which is then treated with the
appropriate metal acetate salt (Scheme 2). Thus, the
organometallic salicylaldehyde brick [Cp*Ru(η6-2-OH-
C6H4CHO)][PF6] was reacted with the metalloligand 1 in
dichloromethane to provide, after stirring for 4 h at RT,
an orange solid material that was isolated in 36% yield
and identified as the expected heterobimetallic ligand 3
(see Supporting Information). The target organometallic-
inorganic hybrids 6 and 7 were obtained by treatment of a
Computational Details. DFT35 calculations were carried out
using the Amsterdam Density Functional (ADF) program.36
The Vosko-Wilk-Nusair parametrization37 was used to treat
electron correlation within the local density approximation,
(29) SAINT-PLUS, Version 6.02; Bruker Analytical X-Ray Systems Inc.:
Madison, WI, 1999.
(30) Sheldrick, G. M. SADABS, Version 2.05; Bruker Analytical X-Ray
Systems Inc.: Madison, WI, 1999.
(31) SHELXTL Reference Manual, Version 6.14; Bruker Analytical X-Ray
Systems Inc.: Madison, WI, 1998.
(32) Sheldrick, G. M. SHELX97, Program for the Refinement of Crystal
€
€
Structures; University of Gottingen: Gottingen, Germany, 1997.
(33) Le Bozec, H.; Le Bouder, T.; Maury, O.; Bondon, A.; Ledoux, I.;
Deveau, S.; Zyss, J. Adv. Mater. 2001, 13, 1677.
(34) Zyss, J.; ChauVan, T.; Dhenaut, C.; Ledoux, I. Chem. Phys. 1993,
177, 281.
(35) (a) Baerends, E. J.; Ellis, D. E.; Ros, P. Chem. Phys. 1973, 2, 41. (b)
Baerends, E. J.; Ross, P. Int. J. Quantum Chem. 1978, S12, 169. (c) Boerrigter, P.
M.; te Velde, G.; Baerends, E. J. Int. J. Quantum Chem. 1988, 33, 87. (d) te
Velde, G.; Baerends, E. J. J. Comput. Phys. 1992, 99, 84.
(36) Amsterdam Density Functional (ADF) program; Vrije Universiteit:
Amsterdam, The Netherlands, 2005.
(37) Vosko, S. D.; Wilk, L.; Nusair, M. Can. J. Chem. 1990, 58, 1200.
(38) (a) Becke, A. D. J. Chem. Phys. 1986, 84, 4524. (b) Becke, A. D. Phys.
Rev. A 1988, 38, 2098.
(40) Versluis, L.; Ziegler, T. J. Chem. Phys. 1988, 88, 322.
(41) (a) Casida, M. Time Dependent Functional Response Theory for
Molecules. In Recent Advances in Density Functional Methods; Chong, D. P.,
Ed.; World Scientific: Singapore, 1995; Vol. 1, p 155. (b) Gross, E. U. K.; Dobson,
J. F.; Petersilka, M. In Density Functional Theory; Nalewajski, R. F., Ed.;
Springer Series, Topics in Current Chemistry; Springer: Heidelberg, 1996. (c) van
Gisbergen, S. J. A.; Snijders, J. G.; Baerends, E. J. Comput. Phys. 1999, 118, 119.
(42) Averseng, F.; Lacroix, P. G.; Malfant, I.; Lenoble, G.; Cassoux, P.;
Nakatani, K.; Maltey-Fanton, I.; Delaire, J. A.; Aukauloo, A. Chem. Mater.
1999, 11, 995.
(39) (a) Perdew, J. P. Phys. Rev. B 1986, 33, 8882. (b) Perdew, J. P. Phys.
Rev. A 1986, 34, 7406.

2756 Inorganic Chemistry, Vol. 49, No. 6, 2010
Trujillo et al.
Scheme 1. Synthesis of the Neutral Binuclear Unsymmetrical Binuclear Schiff Base Complexes 4 and 5
Scheme 2. Synthesis of the Ionic Unsymmetrical Trinuclear Schiff Base Complexes 6 and 7
Scheme 3. Synthesis of the 5-Functionalized Metalloligand 8 and of Its Bi- and Trinuclear Unsymmetrical Schiff Base Complexes 9 and 10
suspension of 3 in methanol with nickel(II) and copper(II)
acetate salt, respectively (Scheme 2). The two products
precipitated directly from the reaction mixture and were
collected by filtration as brown-violet and dark orange
solid materials in 66 and 57% yield, respectively.
construction of donor-acceptor materials because of their
simple structures with a potential single point of attach-
ment, taking advantage of an efficient, straightforward,
and inexpensive method for the synthesis of Schiff base
ligands and their subsequent transition metal complexes.
Thus, the synthesis of the mononuclear functionalized
Schiff base complex 8 was successfully accomplished by
The mono- (8), bi- (9) and trinuclear (10) salen-type
complexes (Scheme 3) were targeted as scaffolds for the

Article
Inorganic Chemistry, Vol. 49, No. 6, 2010 2757
direct condensation of the metalloligand 2 bearing the ethy-
lene amine arm with 2,5-dihydroxobenzaldehyde for 2 h in
refluxing dichloromethane (Scheme 3). The product precipi-
tated directly from the reaction mixture and was isolated as a
red powder in 72% yield. The corresponding neutral bi-
nuclear Schiff base complex 9 was prepared according to the
template one-pot two-step procedure depicted above for 4
and 5. The metalloligand 2 was reacted with 2,5-dihydrox-
obenzaldehyde and then with hydrated nickel(II) acetate in
refluxing CH2Cl2/MeOH (1:1) mixture for 2 h. Compound 9
was isolated as a brown-orange powder in 71% yield. Treat-
ing this binuclear Schiff base precursor 9 with 1 equiv of the
arenophile source [Cp*Ru(NCCH3)3][PF6] overnight in di-
chloromethane at RT gave a clean conversion to the corre-
sponding ionic trinuclear counterpart 10, isolated as a red
microcrystalline solid in 44% yield (Scheme 3). Note that 10
as well as the two other trinuclear complexes 6 and 7 contain
the neutral electron-releasing ferrocenyl subunit and the
cationic electron-withdrawing mixed sandwich, [Cp*Ru(η6-
salicylidene)]þ, linked by a MII classical Werner type coordi-
nation sets [M(ONNO)] (M = Ni, Cu).
In each case, compounds 4-10 were isolated as solid
samples in moderate to good yields. They exhibit a good
solubility in common polar organic solvents. The ionic
derivatives 6, 7, and 10 are, however, insoluble in diethy-
lether, hydrocarbons, and water. They are thermally very
stable with temperatures of decomposition rising from
203 ꢀC (6) to 312 ꢀC (10). This feature may deserve some
interest, as a good thermal stability is required for in-
corporation of chromophores into polymers matrix with
high glass transition temperature (Tg), an important
prerequisite for various practical uses.4b,42
Composition and identity of the new complexes were
deduced from elemental analysis, multidimensional
NMR spectroscopic methods, mass spectrometry, and
absorption spectroscopy (see Experimental Section). Ad-
ditionally, the crystal and molecular structures of 4 and 8
were determined by single crystal X-ray diffraction ana-
lysis (see below). We were unable to obtain single crystals
of trinuclear species, but their molecular structures are
readily assigned from spectroscopic data. Mass spectra of
measured compounds show the presence of peaks of
molecular ion [M]þ with 100% intensity, corresponding
to the neutral species or to the cationic fragment, in the
case of the trinuclear salts 6, 7, and 10. For all these peaks,
the envelope of the isotopic pattern was in good agree-
ment with the simulated ones.
at frequencies higher than 3100 cm-1 of the 5-OH sub-
stituent is also observed in the IR spectra of 8-10.
1
The H and 13C{1H} NMR data for the diamagnetic
derivatives (4, 6, 8, 9, and 10) are reported in the Experi-
mental Section with the atom labeling scheme in Chart 2.
The presence of the imine proton NdCH between 7.68
and 9.12 ppm confirms the assembly of quadridentate
Schiff base ligands. In each compound, the ferrocenyl
enamidoketone fragment is clearly identified by the three
sharp singlets in the chemical shift ranges 1.95-2.50,
4.08-4.24, and 5.32-5.87 ppm (integral ratio 3:5:1),
attributed to the methyl, the unsubstituted cyclopenta-
dienyl ring, and the pseudoaromatic methine protons,
respectively. The o-phenylene and ethylene bridge pro-
tons show up as four and two (or four in the case of 10)
distincts resonances, respectively, confirming the unsym-
metrical nature of the complexes. Moreover, the salicyli-
dene ring protons of 4 and 6 give again rise to four distinct
resonances, while for 8-10 a typical doublet, double
doublet, doublet multiplicity pattern assigned to H-3,
H-4, and H-6 protons (integral ratio 1:1:1), respectively,
stands for the signature of the 5-hydroxosalicylidene ring.
Interestingly, the substituted cyclopentadienyl ring HR
and Hβ protons which appear as two triplets for the
dinuclear complexes 4 and 9, give rise to four resonances
(integral signal ratio 1:1:1:1) on passing to their respective
trinuclear counterparts 6 and 10 (see Supporting Infor-
mation, Figure S1). This feature, we have previously
reported for trinuclear relatives, arises from sterically
hindered rotation of the ferrocenyl moiety about the
Cipso-C(O)- bond, further to complexation of the salicy-
lidene ring by the bulky arenophile Cp*Ruþ.22,43 Note
that this splitting does not occur in the more flexible
dinuclear compound 3 (see Supporting Information). As
expected, spectra of both 6 and 10 show sharp singlets
integrating for 15 H at 2.10 ppm for the pentamethylcy-
clopentadienyl protons and the characteristic upfield shift
(0.75 < Δδ < 1.31 ppm) of the salicylidene ring proton
signals, thus firmly establishing the η6-coordination of
the Cp*Ruþ arenophile.44 All these assignments are con-
firmed by 13C NMR data which fully support the un-
symmetrical nature of the compounds (see Experimental
Section and Supporting Information).
In the case of the two paramagnetic copper(II) com-
pounds 5 and 7, the solution effective magnetic moments
were determined by Evans’ NMR method,45 at 297 K in
CD3COCD3, to be 1.98 μB and 2.05 μB, respectively.
These values, in close agreement with, albeit slightly
greater than, the spin-only magnetic moment value for
a d9 CuII ion (S = 1/2, 1.73 μB), are in the observed range
1.80-2.00 μB and consistent with the expected mono-
meric structure of the two complexes.14b,22a,46
The IR spectral data of the six Schiff base complexes
4-7, 9, and 10 support the coordination of the tetraden-
tate acyclic ligand (ONNO) to the central 3d metal ions by
means of nitrogen atoms of the 1,2-diamino bridge and
two oxygen atoms of the ferrocenylacetonic and salicyli-
dene fragments.22 For instance, the ν(CdN) stretch-
ing vibration of the organometallic Schiff base ligand 8
(1639 cm-1) is shifted by 20 cm-1 toward lower frequen-
cies upon complex formation, revealing coordination of
the imine nitrogen atom to the nickel ion in 9. Moreover,
the spectra of the ionic derivatives 6, 7, and 10 exhibit a
very strong absorption band at about 840 cm-1 and a
medium intensity band at 557 cm-1, assigned to the
(43) Such a splitting has also been observed in sterically constrained
Diferrocenylbispyran systems: Ba, F.; Cabon, N.; Robin-Le Guen, F.; Le
Poul, P.; Le Poul, N.; Le Mest, Y.; Golhen, S.; Caro, B. Organometallics
2008, 27, 6396.
(44) Hubig, S. M.; Lindeman, S. V.; Kochi, J. K. Coord. Chem. Rev. 2000,
200-202, 831.
(45) (a) Evans, D. F. J. Chem. Soc. 1959, 2003. (b) Crawford, T. H.;
Swanson, J. J. Chem. Educ. 1971, 48, 382. (c) Schubert, E. M. J. Chem. Educ.
1992, 69, 62.
-
ν(PF6) and δ(P-F) modes of the PF6 anion, respec-
(46) Cotton, F. A.; Wilkinson, G.; Murillo, C. A.; Bochmann, M.
Advanced Inorganic Chemistry, 6th ed.; Wiley-Interscience: New York, 1999;
p 867.
tively, testifying to the complexation of the Cp*Ruþ
arenophile. The characteristic ν(O-H) stretching bands

2758 Inorganic Chemistry, Vol. 49, No. 6, 2010
Trujillo et al.
to a potential tetradentate acyclic ligand. The two C5-
ligands in the same ferrocenyl group are essentially
parallel, with the ring centroid-iron-ring centroid angles
of 178.36ꢀ for 4 and 177.72ꢀ for 8. For the two molecules,
the ring centroid-iron distances of 1.637, 1.645 A and
1.644, 1.651 A for the ring with and without the side
chain, respectively, indicate that there is a FeII oxidation
state in the metallocenes.47
Organometallic-inorganic hybrid 4 can be described as
a classical Werner-type coordination compound where a
dianionic unsymmetrical quadridentate Schiff base li-
gand formally binds nickel(II) ion through two nitrogen
atoms (amido and imine) and two oxygen atoms (ketone
and phenolato). This tetradentate binding leads to the
formation of a six-, five-, six-membered chelate ring
arrangement around the central metal ion which is essen-
tially square planar with the nitrogen and oxygen atoms
occupying mutually trans positions. This is reflected in
the two diagonal O-Ni-N angles of 178.95(12) and
178.34(12)ꢀ, barely deviating from linearity. As a result,
the deviation of the nickel atom away from the plane
defined by the chelating hetero atoms [O(1)-N(1)-
N(2)-O(2)] is only 0.006 A. As the NMR spectrum was
free from line broadening it can be assumed that the
deviation from square planar is not significant. As usually
observed for this family of complexes,22,48 the bond
lengths associated with the nickel atom are virtually equal
within the error of the measurement (see caption of
Figure 1 and Supporting Information, Table S1).
Figure 1. ORTEP diagram for compound 4 showing the atom number-
ing scheme. Displacement ellipsoids are at the 40% probability level.
Selected bond distances (A) and angles (deg): Ni(1)-O(1) 1.842(2),
Ni(1)-O(2) 1.849(2), Ni(1)-N(1) 1.868(3), Ni(1)-N(2) 1.848(3), O-
(1)-C(11) 1.283(4), O(2)-C(27) 1.304(4), N(1)-C(13) 1.325(4), N-
(2)-C(21) 1.307(4); O(1)-Ni(1)-N(1) 94.85(12), O(1)-Ni(1)-O(2)
83.82(11), O(2)-Ni(1)-N(2) 95.16(12), N(1)-Ni(1)-N(2) 86.17(13).
The two external chelate rings [O(1) to N(1)] and [O(2)
to N(2)] are planar. The former is almost coplanar with
the substituted cyclopentadienyl ring of the ferro-
cenyl unit (dihedral angles = 8.73ꢀ), whereas the dihedral
angles between the plane of the latter and that of the
salicylidene C6-ring is 1.79ꢀ. These two subunits are held
together by the five-membered ring defined by the nickel
atom, the two nitrogens, and their two linked ortho carbons
of the o-phenylene ring; the N-C-C-N torsion angle is of
4.66ꢀ. Most notably, the chelating Schiff base unit is
actually quite strongly bowed with an angle between the
two central carbon atoms, C(12) and C(22), of the
6-membered chelate rings and the Ni atom of 159.5ꢀ. This
may be a consequence of the rigidity brought about by the
o-phenylene bridge as the corresponding angle of the more
flexible ethylene-bridged counterpart is almost linear
(177.9ꢀ).22a Finally, the bond lengths of the chelate rings
(see Supporting Information, Table S1) are very similar to
those measured previously in NiII(N2O2) derivatives, inde-
pendent of the ligand.12a,c,22,48 Overall, the structural data
reported here are indicative of substantial π delocalization
Figure 2. ORTEP diagram for compound 8 showing the atom number-
ing scheme. Displacement ellipsoids are at the 40% probability level.
Selected bond distances (A) and angles (deg): O(1)-C(11) 1.271(3),
O(2)-C(23) 1.363(3), N(1)-C(13) 1.323(3), N(2)-C(17) 1.282(3), N-
(1)-C(15) 1.457(3), N(2)-C(16) 1.459(3); O(1)-C(11)-C(12) 122.4(2),
O(2)-C(23)-C(18) 122.3(2), C(13)-N(1)-C(15) 127.2(2), C(16)-
N(1)-C(17) 119.5(2).
X-ray Crystallographic Studies. Figures 1 and 2 show
the structures of the binuclear derivative 4 and of the
metalloligand 8, respectively, with selected bond dis-
tances and angles given in the captions (see Supporting
Information, Tables S1 and S2, respectively, for more
complete data). Compounds 4 and 8 crystallize in the
monoclinic space groups P21/c and P21/n, respectively,
with in each case four molecules present in the asymmetric
unit. Complex 4 consists of a ferrocenyl fragment linked
to an unsymmetrical Schiff base complex of nickel(II),
whereas in compound 8 the ferrocenyl moiety is attached
(47) For a reference gathering a large number of interatomic and metal-
ligand distances obtained from the Cambridge Crystallographic Data Base
Centre, see: Orpen, A. G.; Brammer, L.; Allen, F. H.; Kennard, D.; Watson,
D. G.; Taylor, R. J. Chem. Soc., Dalton Trans. 1989, S1.
(48) For recent structural characterizations of Ni(N2O2) Schiff base
compounds, see, for example: (a) Trujillo, A.; Fuentealba, M.; Carrillo,
D.; Manzur, C.; Hamon, J.-R. J. Organomet. Chem. 2009, 694, 1435. (b)
ꢀ
Rotthaus, O.; Jarjayes, O.; Philouze, C.; Perez Del Valle, C.; Thomas, F. Dalton
Trans. 2009, 1792. (c) Maity, D.; Chattopadhyay, S.; Ghosh, A.; Drew, M. G. B.;
Mukhopadhyay, G. Polyhedron 2009, 28, 812. (d) Wu, J.-C.; Liu, S.-X.; Keene,
T. D.; Neels, A.; Mereacre, V.; Powell, A. K.; Decurtins, S. Inorg. Chem.
2008, 47, 3452. (e) Maity, D.; Mukherjee, P.; Ghosh, A.; Drew, M. G. B.;
Mukhopadhyay, G. Inorg. Chim. Acta 2008, 361, 1515.

Article
Inorganic Chemistry, Vol. 49, No. 6, 2010 2759
Table 2. Formal Electrode Potentials and Peak-to-Peak Separations for the
FeII/FeIII Redox Processes Exhibited by the Schiff Base Complexes 4-10a
Table 3. UV-vis Data for the Schiff Base Complexes 4-10
λ/nm (Log ε)
(CH2Cl2)
λ/nm (Log ε)
(DMSO)
solv. shift
(cm-1
)
compound
E1/2/V (ΔEp/mV)
compound
E1/2/V (ΔEp/mV)
compd
4b
5b
8c
9c
0.130 (170)
0.110 (95)
0.090 (95)
0.050 (60)
6b
7b
0.140 (120)
0.120 (150)
4
252 (4.82)
304 (4.35)
376 (4.56)
407 (3.51)
440 (3.60)
587 (3.16)
290 (3.2)
389 (3.3)
440 (2.3)
445 (2.8)
229 (4.47)
319 (4.12)
395 (4.10)
454 (3.34)
490 (3.48)
612 (3.25)
274 (3.84)
368 (3.57)
474 (3.08)
237 (3.3)
342 (4.6)
459 (3.3)
245 (3.9)
310 (3.4)
390 (2.8)
434 (3.4)
471 (3.1)
287 (4.2)
369 (3.9)
387 (3.5)
455 (3.1)
276 (4.41)
376 (3.39)
404 (3.52)
425 (3.89)
577 (3.11)
290 (3.2)
390 (3.3)
445 (2.5)
449 (2.7)
-3340
0
-182
-802
-292
0
-66
þ255
þ200
10c
0.070 (66)
-
a Recorded in dichloromethane at 293 K, 0.1 M n-Bu4NþPF6 as
supportingelectrolyte; all potentialsare quoted vs Cp2Fe0/þ, scan rate =
5
6
0.1 V s-1
electrode.
.
b Vitreous carbon working electrode. c Platinum disk working
of the electron density through these rings, thus allowing
electronic communication between both metal centers.
The single-crystal X-ray diffraction study of the poten-
tially tetradentate metalloligand 8 confirms both the
monomeric nature of the compound and the Z-s-Z con-
formational form49 adopted by the ferrocenyl enaminone
part of the molecule (Figure 2), as it was previously found
for its precursor 2.22b The structure reveals that the plane
made by the enaminone side chain is virtually coplanar with
the substituted cyclopentadienyl ring (dihedral angle=
9.06ꢀ), and partial delocalization of the heteroconjugated
[O-C-C-C-N] frameworks (see Supporting Informa-
tion, Table S2) with a dihedral angle between the respective
planes of 60.76ꢀ. Moreover, the structure of 8 is stabilized
by a network of intra- and intermolecular hydrogen
bonds through N-H, two O-H and CdO groups
(see Supporting Information, Figure S2 and Table S3).
Electrochemistry. Electrochemical potentials also offer
information regarding donor-acceptor interactions.
Compounds 4-10 were studied using CV in CH2Cl2/
0.1 M n-Bu4NPF6; potentials are summarized in Table 2
and representative voltammograms are shown in the
Supporting Information (Figure S3). Each complex dis-
plays one chemically reversible oxidation process with
current ratio ipa/ipc equal to unity, assignable as a mono-
electronic transition at the ferrocenyl moiety. These redox
events arise from the oxidation of the monosubstituted
ferrocene unit and correspond to the generation at the
electrode of the respective mono- and dicationic FeIII
species. Interestingly, the potential of each compound
under investigation is shifted to more oxidizing potential
than that of free ferrocene; the E1/2 values of the trinuclear
derivatives 6, 7, and 10 are slightly more shifted to the
anodic regime than those of their binuclear counterparts
4, 5, and 9, respectively (Table 2). These differences
between the E1/2 values for the three pairs 4/6, 5/7, and
9/10 are indeed small (10-20 mV), falling almost within
the experimental errors of CV measurements. One must,
therefore, be cautious in interpreting those data but the
observed anodic shift tendency is real and expected on
passing from the neutral species to its cationic counter-
part. Moreover, the present data are in accordance with
our previous observations within this family of bi- and
trinuclear macroacyclic unsymmetrical Schiff base com-
plexes.22 However, this increased difficulty of oxidation
309 (4.06)
398 (3.97)
451 (3.20)
484 (3.50)
590 (3.10)
-1014
þ191
-147
-253
-609
7
8
9
384 (3.69)
452 (3.29)
244 (4.3)
343 (3.5)
455 (3.2)
þ1130
-1030
þ1210
þ85
-192
319 (4.1)
396 (3.4)
426 (3.4)
460 (3.6)
288 (4.1)
364 (3.7)
388 (3.4)
416 (3.4)
þ910
þ388
-433
-508
þ121
-372
þ67
10
-2060
Figure 3. Deconvoluted UV-vis spectra of 4 (dashed line) and 6 (solid
line) showing the bathochromic shift of the absorption peaks upon
complexation of the arenophile.
of the FeII center features the electron withdrawing ability
of both the neutral and the cationic Schiff base side chain.
The experimental results for the 8-10 series are also
supported by DFT calculations (vide infra).
Electronic Absorption Spectra. The electronic absorp-
tion spectra in the UV-visible region were measured in
CH2Cl2 and DMSO for the Schiff base complexes 4-10
and are reported in Table 3. The spectra are rather similar
and consist of two intense broad absorption bands
(Supporting Information, Figure S4), which strongly sug-
gest thattheelectronic propertiesof these systems are domi-
nated by the donor-acceptor substituted organometallic
(49) (a) Greenhill, J. V. Chem. Soc. Rev. 1977, 6, 277. (b) Tietze, L. F.;
Bergmann, A.; Brill, G.; Br€uggemann, K.; Hartel, U.; Voss, E. Chem. Ber. 1989,
122, 83. (c) Shi, Y. C.; Yang, H. M.; Shen, W. B.; Yan, C. G.; Hu, X. Y.
Polyhedron 2004, 23, 15. (d) Shi, Y. C.; Yang, H. M.; Shen, W. B.; Yan, C. G.; Hu,
X. Y. Polyhedron 2004, 23, 1541.
€

2760 Inorganic Chemistry, Vol. 49, No. 6, 2010
Trujillo et al.
Chart 3
Table 4. Experimental Values of the Dipolar First Hyperpolarizability β for
Schiff Base Derivatives 4-7, 10, and Related Complexesa
wavelength using the HLS technique (see Experimental
Section). The experimental values of the multipolar first
hyperpolarizability β values are presented in Table 4. For
solubility reason, the HLS measurements were carried
out in chloroform for the neutral binuclear species and in
DMF for the trinuclear salts. Comparison of NLO re-
sponses must be done with great care owing to the relative
error (about 10%) in the determination of the hyper-
polarizabilities and the different techniques and experimen-
tal conditions used. Although data collected in Table 4
indicate a NLO response for this family of chromophores
comparable to that previously calculated and observed
for salicylaldiminato NiII and CuII derivatives,7a,11 they
do not allow the establishment of any clear structure-
activity relationships as they are close to the experimental
errors. Nevertheless, a slight enhancement of β values can
be noted on passing from the neutral binuclear complexes
to the trinuclear salts and upon substitution of nickel(II)
for copper(II). However, the measurements of the sec-
ond-order nonlinearity for both the metalloligand 8 and
its trinuclear counterpart 10 have been carried out under
the same conditions in DMF and showed an enhance-
ment of the NLO response, with the hyperpolarizabilities
of the complex equal to 1.5 times that of the free ligand
(β = 155 ꢀ 10-30 esu). Complexation of 8 by NiII ion is
accompanied by the formation of a geometrically con-
strained acentric planar structure which is expected to
enhance the bridge conjugation and, hence, the non-
linearity. Therefore, this 1.5-fold enhancement arises pre-
sumably from a combination of geometric and electronic
effects.
Theoretical Investigations. To get a better understand-
ing of the structure and properties of compounds 4-10,
we have investigated the electronic structure of their
simplified models in which the methyl group on the
N2O2 Schiff base core has been replaced by a hydrogen
atom. These models, labeled 40-100, are depicted in
Chart 4. Their optimized geometries are shown in
Figure S5 (see Supporting Information) and some of their
relevant computed data is given in Table 5. When avail-
able, metrical data obtained from X-ray structure deter-
mination of related complexes are provided in parentheses.
A good agreement between the computed and experimen-
tal values can be noted. In the case of the trinuclear
complexes, two conformations, namely, anti and syn, are
compd
(10-30 esu)b
compd
(10-30 esu)c
4
5
250
212
230
226
206
6
7
10
13d
14d
235
237
247
241
215
15d
11d
12d
a Obtained by means of HLS measurements. b As 10-2 M CHCl3
solutions. c As 10-2 M DMF solutions. d Structures depicted in Chart 3.
chromophore. Upon deconvolutions of the spectra with
Gaussian curves, these two absorption bands give rise to a
set of three to six transitions. The origin of the high-energy
absorption bands in the range 230-395 nm, is assumed
to be intraligand π-π* transitions, and the low-energy
absorption bands in the 400-600 nm region presum-
ably involve metal-to-ligand and ligand-to-metal CT.50,51
In addition, the CT band is influenced by the presence of the
Cp*Ruþ arenophile, which produces a bathochromic shift
(Figure 3). This behavior suggests a ligand-to-metal CT
(LMCT) nature of this transition. All those major features
of the experimental spectra are well reproduced by the
calculated transitions (see the Theoretical Section below).
On the other hand, upon moving from CH2Cl2 (ε = 8.90)
to the more polar solvent DMSO (ε = 47.6), the low
energy structures exhibit a moderate hypsochromic shift
(Supporting Information, Figure S4, Table 3), character-
isticof adipolemomentchangebetween thegroundandthe
excited state, and indicative of CT character. This behavior
(blue shift in solvents of higher polarity), which seems to be
a trend observed in donor-acceptor salicylaldiminato
Schiff base complexes,11 is usually associated with reduc-
tion in the dipole moment upon electronic excitation, and
therefore potential NLO capabilities (see below).
Quadratic NLO Studies. The quadratic nonlinearities
of the new Schiff base complexes 4-7 and 10, two pairs of
bi- and trinuclear relatives (11/1322b and 12/14)52 and the
functionalized allyloxo derivative 1548a (see formulas in
Chart 3) have been determined at the 1.91 μm incident
(50) (a) Fuentealba, M.; Garland, M. T.; Carrillo, D.; Manzur, C.;
Hamon, J.-R.; Saillard, J.-Y. Dalton Trans. 2008, 77. (b) Houjou, H.;
Motoyama, T.; Araki, K. Eur. J. Inorg. Chem. 2009, 533. (c) Bosnich, B.
J. Am. Chem. Soc. 1968, 90, 627.
(51) Lever, A. B. P. Inorganic Electronic Spectroscopy; 2nd edn., Elsevier:
New York, 1984.
(52) Trujillo, A.; Carrillo, D.; Manzur, C.; Hamon, J.-R. work in
progress.
(53) Albright, T. A.; Burdett, J. K.; Whangbo, M. H. Orbitals Interactions
in Chemistry; Wiley: New York, 1985.

Article
Inorganic Chemistry, Vol. 49, No. 6, 2010 2761
Chart 4
a
Table 5. Major Metrical Data (in A) for the Optimized Geometries of 40-100
b
c
40
50
60
70
80
90
100
M-N(1)
M-O(1)
1.887 (1.868)
1.904 (1.842)
1.889 (1.848)
1.886 (1.849)
1.335 (1.325)
1.291 (1.283)
1.318 (1.307)
1.304 (1.304)
1.697 (1.645)
1.690 (1.637)
1.973
1.976
1.987
1.950
1.334
1.287
1.313
1.301
1.695
1.685
1.875
1.882
1.892
1.901
1.342
1.294
1.311
1.290
1.700
1.688
1.878
1.852
1.962
1.969
2.025
1.977
1.339
1.289
1.302
1.288
1.701
1.698
1.879
1.848
1.869 (1.856)
1.901 (1.846)
1.862 (1.851)
1.894 (1.844)
1.323 (1.315)
1.295 (1.298)
1.310 (1.302)
1.308 (1.322)
1.694 (1.648)
1.685 (1.642)
1.866 (1.834)
1.873 (1.825)
1.871 (1.881)
1.921 (1.852)
1.327 (1.328)
1.302 (1.244)
1.301 (1.249)
1.290 (1.309)
1.697 (1.630)
1.686 (1.639)
1.883 (1.793)
1.847 (1.732)
M-N(2)
M-O(2)
C-N(1)
1.346 (1.323)
1.267 (1.271)
1.294 (1.282)
1.348 (1.363)
1.693 (1.651)
1.686 (1.644)
C-O(1)
C-N(2)
C-O(2)
Fe-CpCNT
Fe-Cp0CNT
Ru-Cp*CNT
Ru-SalCNT
aAbbreviations: Cp = η5-C5H5, Cp0 = η5-C5H4, Cp* = η5-C5Me5, Sal = salicylidene ring, CNT = centroid. Experimental values are in parentheses.
For atom numbering scheme see Figure 1. b Experimental values taken from ref 48a. c Experimental values taken from ref 22a.
possible, depending if the organometallic moieties lie on
opposite sides or on the same side of the planar Schiff base
skeleton, respectively. Itshouldbenotedthatall theknown
experimental structures of complexes discussed in this
paper exhibit the syn configuration.22,50a Even so, geo-
metry optimization for models 60 and 100 was performed
for both conformations. Their difference in energy was
found to be less than 1 kcal/mol indicating that both
isomers are isoenergetic at the considered level of theory.
Consistently, their electronic structures were found to be
very similar. These results prompted us to carry out the
geometry optimization of the odd-electron model 70 in
the syn conformation only. All the results discussed here
correspond to those obtained in the syn conformation.
The molecular orbital diagrams of the computed
models are shown in Figure 4 in which all the highest
occupied molecular orbital (HOMO) energies have been
set to zero for sake of comparison. For graphical simpli-
city, the diagrams of the odd-electron species 50 and 70
correspond to spin-restricted calculations, whereas all
their other computed data given in this paper correspond
to spin-unrestricted calculations (see Computational
Details). Related computed pertinent numerical data
are gathered in Table 6. We start the MO analysis with
the 8-10 series which offers the possibility to analyze the
changes when the metal nuclearity varies from one to
three. In the case of the mononuclear model 80 the FeII
center lies in a pseudo-octahedral environment and there-
fore its five d-type orbitals split into three occupied non-
bonding orbitals so-called “t2g” lying far below two
antibonding ones so-called “eg*”.53 Two π* orbitals of
the Schiff base ligand constitute the lowest vacant levels.
Thus, the frontier orbitals of 80 follow the order “t2g”-Fe
(occupied) < π*CN (LUMO) < π*CO < “eg*”-Fe. When
replacing two ligand protons in 80 by a Ni(II) atom to
generate the dinuclear model 90, two levels of large nickel
character appear in the HOMO-LUMO area. The
HOMO is now a nickel dπ-type orbital (33%) mixed in
an antibonding way with some occupied π ligand levels
(48%) and with some iron admixture (12%) (Table 6).
The lowest unoccupied molecular orbital (LUMO) is a
dx2-y2 orbital mixed in a strongly antibonding way with
the ligand σ-type lone pairs. Adding a Cp*Ruþ moiety to
90 to make 100, results in significant changes in the frontier
MO diagram, not only because supplementary orbitals
are added but also because of the effect of the positive
charge on the ruthenium center. This charge effect is to
stabilize the orbitals to an extent related to their degree of
localization close to the ruthenium center. Thus, the
orbitals having significant ligand participation are parti-

2762 Inorganic Chemistry, Vol. 49, No. 6, 2010
Trujillo et al.
Figure 4. Computed MO diagrams of 40-100 models. The HOMO energies have been arbitrarily set to zero for clarity.
cularly stabilized. This is the case for most of the lowest
unoccupied orbitals. The result is a significant reduction
of the HOMO-LUMO gap when going from 90 (1.3 eV)
to 100 (0.6 eV). The LUMO is now a π* ligand orbital with
some Ru participation (Table 6). The Ni-centered
LUMOþ1 corresponds to the LUMO of 90. The “eg*”-
Ru orbitals are the next highest levels, the “eg*”-Fe
orbitals lying now far above. The three highest occupied
MOs of 100 are the “t2g”-Fe orbitals, whereas its
HOMOþ4 corresponds to the HOMO of 90. The “t2g”-
Ru levels lie farther below. The level ordering of 40 is
similar to that of 90, except that the dπ-Ni/ π-ligand
combination is now the HOMOþ3. Similarly, the MO
diagram of 60 resembles that of its trinuclear relative 100.
With one electron more than 40 and 60, their copper
analogues 50 and 70 exhibit qualitatively similar MO
diagrams (see Figure 4), except that the extra electron
lies in a Cu(dx2-y2)-ligand antibonding orbital which
corresponds to the LUMO of 40 and 60, respectively.
To obtain a rationalization of the experimental redox
properties of the compound series 8-10 we explored the
changes in the electronic structure of the mono-oxidized

Article
Inorganic Chemistry, Vol. 49, No. 6, 2010 2763
Table 6. Relevant Energetic and Electronic Data Computed for Complexes 40-100
40
1.4
50
60
0.6
Mulliken Charges (Spin Density)
70
80
1.6
90
1.3
100
0.6
HOMO-LUMO gap (eV)
Fe
M
Ru
Ligand
0.05
0.57
0.05(0.00)
0.69(0.47)
0.02
0.57
0.77
-0.36
0.02(0.07)
0.68(0.45)
0.79(0.00)
-0.49(0.48)
0.05
0.06
0.57
0.03
0.59
0.79
-0.41
-0.62
-0.74(0.53)
-0.05
-0.63
Orbital Contributions HOMO/LUMO
%Fe
%M
%Ru
%Ligand
75/0
2/56
-/-
13/35
82/0
0/3
0/13
12/76
81/0
-/-
-/-
13/96
12/0
82/0
0/5
0/16
12/71
33/55
-/-
48/37
Figure 5. Experimental (top) and calculated (bottom) electronic spectra for complexes 80-100.
þ
þ
þ
complexes þ80 , 90 , and 100 . In the mono oxidized
complex 80 , the computed spin densities exhibit values
close to 1 (0.92) on the iron atom. Moreover, the
computed Mulliken charges shows the localization of
the positive charge over the ferrocenyl group. As ex-
pected, the one-electron oxidation of 80 corresponds to
the oxidation of the iron center in the ferrocenyl frag-
ment. On the other hand, the oxidation of 90 corresponds
to the removal of one electron from his HOMO, resulting
in a spin density distributed on the iron atom (0.50), the
ligand (0.34), and the nickel atom (0þ.16). The ionization
potentials (IP) of the processes 80 f 80 (6.12 eV) and 90 f
wavelengths and oscillator strengths. A good agreement
between them is observed. The major features of the
experimental spectra are satisfactorily well reproduced
by the simulated spectra. This allowed us to propose a
band indexation shown in Figure 5. The analysis of the
major components of the various transitions associa-
ted with the computed bands led to the identification of
the corresponding CTs. For compound 80, most of the
electronic transitions are π-π* intraligand CT (ILCT),
with some metal-to-ligand Fe(t2g) f π* and ligand-to-
metal π f Fe(eg*) CTs (MLCT and LMCT, respectively).
For the dinuclear complex 90 the band of lower energy (e)
is dominated by Fe(t2g) f π* and Ni f π* transfer
(MLCT). The adjacent band (d) is mainly π f Ni LMCT
with some nickel d f d character. The middle band (c) is
associated with Ni f Fe(eg*) d-d CT. No significant
participation of iron d f d CT was found in the investi-
gated energy range for models 80 and 90. Finally, in the
cationic compound 100 we observed in the high-energy
bands (a-b) ruthenium d-d transitions and Ni f Ru(eg*)
d-d transitions. The low-energy band (c) exhibits iron d-d
transitions and Ru(t2g) f π* MLCT transitions. The rest
of the electronic transitions are similar to those described
for compounds 80 and 90. The lowest energy band (d) is for
the most part due to Fe(t2g) f π* MLCT transition. The
general tendency of the computed long wavelength bands
to be red-shifted relative to experiment (see Figure 5) is
þ
90 (5.81 eV) are consistent with the experimental oxida-
tion potentials observed in Table 2. Finally, the oxidation
of 100 involves an energy level that is mainly based on the
iron atom of the ferrocenyl fragment (88%) and the rest on
the ligand (12%). The ionization potential value (8.23 eV)
is much larger than the IP value computed for 80 and 90.
This is because in the case of the cation 100, the calculations
do not account for the existence of interacting counterions
which are likely to modify significantly its orbital energies.
We complemented our theoretical investigation by
analyzing the electronic spectra of complexes 8-10
through TDDFT calculations. Figure 5 shows the experi-
mental (top) and theoretical (bottom) spectra of 8-10
and 80-100, respectively. The theoretical spectra have
been simulated from the computed TDDFT transition

2764 Inorganic Chemistry, Vol. 49, No. 6, 2010
Trujillo et al.
related to the well-known underestimation by TDDFT of
low-lying excitation energies associated with significant
charge-transfer.54 On the other hand, the corresponding
blue-shift observed for some of the short wavelength
bands (in particular band b) is related to the antibonding
nature of most of the involved excited states whose energy
is systematically overestimated by TDDFT which does
not account for electronic relaxation effects.54d
served for most of complexes, and the ILCT and the
MLCT contributions in the overall band have been deter-
mined. Finally, HLS measurements showed that all the
compounds exhibited a second-order nonlinear response,
the hyperpolarizability (β) value increasing with the nucle-
arity of the complexes, and that the donor-acceptor
substituents dominate the nonlinearity. Immobilization
of such unsymmetrical redox and NLO active Schiff base
systems onto resin and solid materials is currently the
subject of further investigations.
Conclusion
Two series of robust neutral binuclear and their corres-
ponding cationic trinuclear organometallic donor-acceptor
substituted unsymmetrical Salophen- and salen-type com-
plexes have been synthesized and fully characterized, and
their electrochemical, linear, and second order NLO proper-
ties have been thoroughly investigated. All the organo-
metallic-inorganic D-π-A conjugated molecules investigated in
this work contain ferrocene and M[ONNO] units (M = NiII,
CuII); the salicylidene ring of the acyclic tetradentate Schiff
base core being π-coordinated to the 12-electron cationic
arenophile Cp*Ruþ in the trinuclear series. The studies of
single crystal X-ray diffraction analysis shows for the bime-
tallic Fe-Ni derivative 4 the coplanarity of Ni[ONNO] core
inserted into a bowed unsymmetrical Schiff base framework
(C(12)-Ni(1)-C(22) ca. 160ꢀ), whereas for the mononuclear
metalloligand 8 the two heteroconjugated [O-C-C-C-N]
frameworks make a dihedral angle of 60.76ꢀ. Theoretical
calculations have also been performed using DFT and
TDDFT, allowing a detailed understanding of the electronic
structure and absorption spectra of the complexes. The
DFT calculated energy levels of frontier orbitals and large
spin density of iron centers for the 80-100 series are in
accordance with the experimental electrochemical results.
As well, a fairly good correlation of the measured and
calculated (TDDFT) absorption maxima has been ob-
Acknowledgment. We thank P. Hamon (Rennes) for
measuring the magnetic susceptibility moments of 5 and
7. Thanks are also addressed to Drs. S. Sinbandhit and P.
Jehan (CRMPO, Rennes) for assistance with the 2D
NMR and HRMS experiments, respectively. Computing
facilities were provided by the IDRIS-CNRS Center at
Orsay (France). This research has been performed as part
of the Chilean-French Joint Laboratory for Inorganic
Functional Materials (LIA MIF Nꢀ 836). Finan-
cial support from the Fondo Nacional de Desarrollo
ꢀ
Cientıfico y Tecnologico (FONDECYT, Chile), Grant
´
1040851 (C.M. and D.C.), the ECOS-SUD (France) -
CONICYT (Chile) agreement no. C05E03, the Vicerrec-
ꢀ
´
a de Investigacion y Estudios Avanzados, Pontificia
torı
Universidad Catolica de Valparaı
ꢀ
´
so, Chile (C.M. and
D.C.), the University of Rennes 1, the CNRS and the
Institut Universitaire de France (J.-Y.S.) is gratefully
acknowledged. A.T. thanks the CONICYT (Chile) for
support of a graduate fellowship.
Supporting Information Available: Synthesis and spectro-
scopic characterization of 3, discussion of the 13C NMR spectra,
details on the X-ray crystallographic study of 4 and 8, tables of
bond distances and angles for 4 and 8, hydrogen bonding
pattern of 8, 1H NMR spectra of 4 and 6, CVs of 4-7, electronic
absorption spectra of 6, 7, and 10, optimized geometries of
40-100, and tables of Computed Cartesian Coordinates for
40-100. Crystallographic files in CIF format for the two reported
X-ray crystal structures. This material is available free of charge
via the Internet at http://pubs.acs.org.
(54) (a) Neugebauer, J.; Gritsenko, O.; Baerends, E. J. J. Chem. Phys.
2004, 124, 21402. (b) Peach, M. J. G.; Benfield, P.; Helgaker, T.; Tozer, D. J.
J. Chem. Phys. 2008, 128, 4418. (c) Ziegler, T.; Seth, M.; Krykunov, M.;
Autschbach, J.; Wang, F. J. Mol. Struc: THEOCHEM 2009, 914, 106.
(d) Neese, F. Coord. Chem. Rev. 2009, 253, 526.