Synthesis and second-order nonlinear optical properties of new palladium(II) and platinum(II) schiff-base complexes

Article abstract of DOI:10.1021/om9708900

The second harmonic generations of the dimeric complexes [M₂(μ-X)(μ-SC_nH_2n+1)(RC₆H ₃-CH=NC₆H₄R′)] (M = Pd, Pt; X = Cl, CH₃COO, (R)-CH₃CHClCOO; R, R′ = NO₂ and OC₈H₁₇ or N(C₄H₉)₂; n = 4 or 8) and the monomeric complexes [Pd(RC₆H₃CH=NC₆H₄R′)L] (L = C₅H₅ (Cp), CH₃COCHCOCH₃ (acac)) and [Pd(RC₆H₃CH=NC₆H₄R′)(CNC ₆H₄R″)Cl] (R″ = NO₂, OC_nH_2n+1, N(C_mH_2m+1)2; n = 4 or 8; m = 1 or 4) have been measured, and the influence of the position of donor and acceptor groups is discussed and compared with that of the free imine ligands. The value of the hyperpolarizability (β) is raised only when a strong donor group is located in the cyclometalated ring. Moreover, the β value has been enhanced, too, in the cyclopentadienyl monomer complex by as much as 80% with respect to the β value of the corresponding free imine. The molecular structure of [Pd₂(μ-Cl)(μ-SC₄H₉)(N(C₄H ₉)₂C₆H₃-CH=NC₆H ₄NO₂] has been determined by an X-ray diffraction analysis.

Full text of DOI:10.1021/om9708900

1750
Organometallics 1998, 17, 1750-1755
Syn th esis a n d Secon d -Or d er Non lin ea r Op tica l
P r op er ties of New P a lla d iu m (II) a n d P la tin u m (II)
Sch iff-Ba se Com p lexes
J ulio Buey, Silverio Coco, Laura D´ıez, Pablo Espinet,*,†
J ose´ M. Mart´ın-Alvarez, and J esu´s A. Miguel
Departamento de Quı´mica Inorga´nica, Facultad de Ciencias, Universidad de Valladolid,
E-47005 Valladolid, Spain
Santiago Garc´ıa-Granda and Ana Tesouro
Departamento de Quı´mica Fı´sica y Analı´tica, Facultad de Qu´ımica, Universidad de Oviedo,
E-33006 Oviedo, Spain
Isabelle Ledoux and J oseph Zyss
France Te´le´com-CNET-Laboratoire de Bagneux, 196 Avenue Henri Ravera,
92220 Bagneux, France
Received October 14, 1997
The second harmonic generations of the dimeric complexes [M2(µ-X)(µ-SCnH2n+1)(RC6H3-
CHdNC6H4R′)] (M ) Pd, Pt; X ) Cl, CH3COO, (R)-CH3CHClCOO; R, R′ ) NO2 and OC8H17
or N(C4H9)2; n ) 4 or 8) and the monomeric complexes [Pd(RC6H3CHdNC6H4R′)L] (L )
C5H5 (Cp), CH3COCHCOCH3 (acac)) and [Pd(RC6H3CHdNC6H4R′)(CNC6H4R′′)Cl] (R′′ ) NO2,
OCnH2n+1, N(CmH2m+1)2; n ) 4 or 8; m ) 1 or 4) have been measured, and the influence of
the position of donor and acceptor groups is discussed and compared with that of the free
imine ligands. The value of the hyperpolarizability (â) is raised only when a strong donor
group is located in the cyclometalated ring. Moreover, the â value has been enhanced, too,
in the cyclopentadienyl monomer complex by as much as 80% with respect to the â value of
the corresponding free imine. The molecular structure of [Pd2(µ-Cl)(µ-SC4H9)(N(C4H9)2C6H3-
CHdNC6H4NO2] has been determined by an X-ray diffraction analysis.
In tr od u ction
and acceptor groups at the ends of the molecule, thus
making them suitable for second harmonic generation.
However, their nonlinear optical activity is reduced by
a loss of conjugation derived from the noncoplanarity
of the arylic rings and the iminic double bond.
Imine orthometalation is a well-known reaction fre-
quently used in our research group. The cyclometala-
tion forces the metalated ring and the iminic bond to
be coplanar, resulting in a more planar molecule, with
a higher degree of conjugation and, thus, more polariz-
able. This effect has been already used in our previous
There is currently considerable interest in the devel-
opment of new molecular materials with nonlinear
optical properties.1,2 The first-order hyperpolarizability
(â) of a molecule is associated with the donor-acceptor
characteristics of the substituents and with the nature
of the conjugation path linking these substituents. The
introduction of a metal center as a donor or acceptor
subunit may lead to large nonlinear responses.3 How-
ever, there are very few studies concerning the influence
of a metal located in the conjugation path.
Benzilideneanilines are very polarizable systems that
can be easily derivatized by the introduction of donor
(3) (a) Cheng, L.-T.; Tam, W.; Meredith, G. R.; Marder, S. R. Mol.
Cryst. Liq. Cryst. 1990, 189, 137. (b) Green, M. L. H.; Marder, S. R.;
Thompson, M. E.; Bandy, J . A.; Bloor, D.; Kolinsky, P. V.; J ones, R. J .
Nature 1987, 330, 360. (c) Marder, S. R.; Perry, J . W.; Schaefer, W. P.;
Tiemann, B. G. Organometallics 1991, 10, 1896. (d) Calabrese, J . C.;
Cheng, L.-T.; Green, J . C.; Marder, S. R.; Tam, W. J . Am. Chem. Soc.
1991, 113, 7227. (e) Kanis, D. R.; Ratner, M. A.; Marks, T. J . J . Am.
Chem. Soc. 1990, 112, 8203. (f) Coe, B. J .; J ones, C. J .; McCleverty, J .
A.; Bloor, D.; Kolinsky, P. V.; J ones, R. J . J . Chem. Soc., Chem.
Commun. 1989, 1485. (g) Richardson, T.; Roberts, G. G.; Polywka, M.
E. C.; Davies, S. G. Thin Solid Films 1989, 179, 405. (h) Calabrese, J .
C.; Tam, W. Chem. Phys. Lett. 1987, 133, 244. (i) Bourgault, M.;
Mountassir, C.; Le Bozec, H.; Ledoux, I.; Pucetti, G.; Zyss, J . J . Chem.
Soc., Chem. Commun. 1993, 1623. (j) Thami, T.; Bassoul, P.; Petit, M.
A.; Simon, J .; Fort, A.; Barzoukas, M.; Villaeys, A. J . Am. Chem. Soc.
1992, 114, 915. (k) Laidlaw, W. M.; Denning, R. G.; Verbiest, T.;
Chauchard, E.; Persoons, A. Nature 1993, 363, 58. (l) Dhenaut, C.;
Ledoux, I.; Samuel, I. D. W.; Zyss, J .; Bourgault, M.; Le Bozec, H.
Nature 1995, 374, 339. (m) Di Bella, S.; Fragala, I.; Ledoux, I.; Marks,
T. J . J . Am. Chem. Soc. 1995, 117, 9481.
† E-mail: espinet@cpd.uva.es.
(1) (a) Nonlinear Optics of Organic Molecules and Polymers; Nalwa,
H. S., Miyata, S.; CRC Press: New York, 1997. (b) Molecular Nonlinear
Optics: Materials, Physics and Devices; Zyss, J ., Ed.; Academic Press:
Boston, MA, 1993. (c) Introduction to Nonlinear Optical Effects in
Molecules and Polymers; Prasad, P. N., Williams, D. J ., Eds.; Wiley:
New York, 1991. (d) Materials for Nonlinear Optics: Chemical Perspec-
tives; Marder, S. R., Sohn, J . E., Stucky, G. D., Eds.; ACS Symposium
Series 455; American Chemical Society: Washington, DC, 1991. (e)
Organic Materials for Nonlinear Optics II; Hahn, R. A., Bloor, D., Eds.;
Royal Society of Chemistry: London, 1991. (f) Nonlinear Optical
Properties of Organic Molecules and Crystals; Chemla, D. S., Zyss, J .,
Eds.; Academic Press: Orlando, FL, 1987; Vols. 1 and 2.
(2) For recent reviews, see: (a) Denning, R. G. J . Mater. Chem. 1995,
5, 365. (b) Optical Nonlinearities in Chemistry; Burland, D. M., Ed.
Chem. Rev. 1994, 94, 1.
S0276-7333(97)00890-X CCC: $15.00 © 1998 American Chemical Society
Publication on Web 03/31/1998

Pd(II) and Pt(II) Schiff-Base Complexes
Organometallics, Vol. 17, No. 9, 1998 1751
Sch em e 1
work for the synthesis of liquid crystals,4 and we can
reasonably expect that such “planarization” can be
advantageous to obtain molecules with increased first-
order hyperpolarizability.
isomeric purity and a cis arrangement of the two imine
moieties in these complexes.
The mixed-bridge thiolato-carboxylato complexes
with an alkoxy or amino group attached to the cyclom-
etalated ring show a broad signal (or even two signals
separated by ca. 0.3 ppm in the case of the complexes
with the dibutylamino group) for the first methylene of
the chains, as expected for these protons being dias-
terotopic as a consequence of the folded structure of this
kind of complexes, as discussed below (see Figure 1).
An upfield shift (0.3-0.5 ppm) of the signals for the
aromatic protons next to the dibutylamino group is
observed in each case because of the strong electron-
releasing properties of this group.
We have therefore synthesized a new series of dimeric
palladium and platinum complexes with mixed bridges
(chloro-thiolato or thiolato-carboxylato). In these
derivatives the two imine moieties in the dimer have a
cisoid disposition, which leads to positive addition of the
nonlinear effects from each moiety. Moreoever, we have
studied the influence of the introduction of a new ligand
in the orthopalladated imine system on the nonlinear
optical behavior. To this end, we have obtained mon-
omeric complexes with cyclopentadienyl, acetylaceto-
nato, and isonitrile ligands.
The molecular structure of 6d was studied by X-ray
diffraction (Figure 1, Table 1). The cyclometalated
carbon coordinates trans to the oxygen atoms of the
bridging carboxylate (in agreement with the usual
antisymbiotic behavior of the soft metal atom).5 The
angle between the palladium coordination planes in this
structure is 74°, somewhat more opened than that
reported for [Pd2(CH2C9H6N)2(µ-O2CCF3)(µ-SBut)]
(CH2C9H6N ) 8-quinolylmethyl) of 55°.6 The distance
between the two palladium atoms is 3.3 Å, so that there
is no interaction between the metal centers. The palla-
dium-carbon distances are very similar to those found
in other imine orthopalladated complexes.7,8 Selected
bond distances and angles are given in Table 2.
Syn th esis a n d Str u ctu r es
The compounds studied in this work were synthesized
starting from the corresponding chloro-bridged com-
plexes as shown in Scheme 1.
Reaction of 2 and 3 with silver alkanethiolate leads
to the dinuclear complexes containing mixed chloro-
thiolato bridges. The palladium chloro-thiolato-bridged
complexes 4 react with silver acetate (1:1) or potassium
(R)-2-chloropropionate (1:1.1) yielding the mixed-bridge
thiolato-carboxylato complexes 6 and 7. The platinum
thiolato-chloropropionato-bridged complexes 8 have
been prepared in a similar way, but the thiolato-acetato
complexes were unstable.
(5) Hartley, F. R. Chem. Soc. Rev. 1973, 2, 163.
(6) Ruiz, J .; Cutillas, N.; Torregrosa, J .; Garc´ıa, G.; Lo´pez, G.;
Chaloner, P. A.; Hitchcock, P. B.; Harrison, R. M. J . Chem. Soc., Dalton
Trans. 1994, 2353.
1
The H NMR resonances of the orthometalated imine
ligand in the dimeric complexes 4-8 indicate their
(7) Ghedini, M.; Armentano, S.; de Munno, G.; Crispini, A.; Neve,
F. Liq. Cryst. 1990, 8, 739.
(8) Buey, J .; D´ıez, G. A.; Espinet, P.; Garc´ıa-Granda, S.; Pe´rez-
Carren˜o, E. To be published.
(4) Baena, M. J .; Barbera´, J .; Espinet, P.; Ezcurra, A.; Ros, M. B.;
Serrano, J . L. J . Am. Chem. Soc. 1994, 116, 1899 and references
therein.

1752 Organometallics, Vol. 17, No. 9, 1998
Buey et al.
Ta ble 3. Lin ea r a n d Non lin ea r Op tica l P r op er ties
of th e Im in e Liga n d s RC6H4CHdNC6H4R′ (1)
ꢀ (L mol-1
cm-1
â (10-30
â(0) (10-30
compd λmax (nm)
)
µ (D) cm5 esu-1
)
cm5 esu-1
)
1a
1b
1c
1d
383
474
345
416
21 400
32 400
37 000
34 200
4.4
6.6
5.7
7.9
36 ( 5
187 ( 11
35 ( 4
22 ( 3
82 ( 5
24 ( 3
38 ( 3
69 ( 6
ments on a similar complex without a nitro group ([Pt2-
(µ-SC6H13)(µ-Cl)(L6)2], L6 ) H13C6OC6H3CHdNC6H4-
OC6H13)9 show the signal of the first methylene as a
virtual triplet, confirming the above statement.
The mononuclear species 9-15 are obtained by reac-
tion of the dinuclear chloro complexes with [TlCp], [Tl-
(acac)], and the corresponding isonitrile.
Their 1H NMR spectra are very similar to those of
the dimeric complexes. They display the characteristic
signals of the aromatic protons of the cyclometalated
ring, the arylic ring attached to the iminic nitrogen and
the alkyl chains, and the corresponding signals of the
introduced ligand. Thus, for the acetylacetonato com-
plexes a singlet at ca. 5.4 ppm corresponding to the R
proton and two singlets at ca. 2.1 and 1.9 ppm (that
integrate as 3 H) for the inequivalent methyl groups
are observed. For the cyclopentadienyl derivatives a
singlet at ca. 5.8 ppm that integrates as 5 H is observed
as expected. In the isonitrile derivatives two pseudo-
doublets appear, corresponding to the AA′XX′ system
of the isonitrile. When the isonitrile has an alkoxy
group, the corresponding signals of the aliphatic chains
are observed. To elucidate the position of the isonitrile
moiety in the complexes, a NOE experiment was
performed on compound 14a . With irradiation of the
H3 signal of the cyclometalated ring, a NOE effect on
one pseudodoublet of the aromatic ring of the isonitrile
can be observed. This allows us to assign a trans
disposition of the isonitrile with respect to the iminic
nitrogen, as can be expected from the antisymbiotic
behavior usually found in palladium complexes.
F igu r e 1. Molecular structure of 6d , showing the labeling
scheme.
Ta ble 1. Deta ils of th e Cr ysta l Str u ctu r e
Deter m in a tion of 6d
chem formula: C48H64N6O6Pd2S
cryst syst: triclinic
a ) 11.401(5) Å
b ) 13.678(9) Å
c ) 17.988(10) Å
R ) 74.37(8)°
fw ) 1065.91
space group: P1h
T ) 293(2) K
λ ) 0.710 73 Å
Dx ) 1.432 Mg m-3
µ ) 0.822 mm-1
F(000) ) 1100.0
R1 ) 0.0384
â ) 81.42(3)°
γ ) 66.34(5)°
V ) 2471(2) Å3
Z ) 2
wR2 ) 0.0793
Ta ble 2. Selected Bon d Len gth s (Å) a n d
An gles (d eg) for 6d
Non lin ea r Op tica l P r op er ties
The linear and nonlinear optical properties of the free
imines and the imine palladium and platinum com-
plexes are collected in Tables 3-6.
Pd(1)-C(21)
Pd(1)-N(1)
Pd(1)-O(1)
Pd(1)-S(1)
S(1)-C(45)
1.960(8)
2.098(6)
2.130(6)
2.277(3)
1.818(8)
Pd(2)-C(15)
Pd(2)-N(2)
Pd(2)-O(2)
Pd(2)-S(1)
1.973(7)
2.094(6)
2.112(13)
2.295(2)
The imine ligands (Table 3) display higher values of
the hyperpolarizability (â) when the donor-acceptor
substituents of π-conjugated rings are strong (deriva-
tives 1b,d ). Moreover their â values are greater when
the strong donor group is located in the ring joined to
the iminic nitrogen (1b), as expected according to
Dewar’s rules.10 The same tendency is observed when
the imine ligands are orthometalated to give dimeric
(Table 4) and monomeric (Tables 5 and 6) palladium and
platinum complexes.
If the â values of metal complexes are compared with
those corresponding to the free imines, it is observed
that complexation produces a slight decrease of â per
imine unit for the dimeric compounds except in some
complexes containing the strong donor-acceptor groups
NBu2 and NO2 situated respectively in the aldehydic
C(21)-Pd(1)-N(1)
C(21)-Pd(1)-O(1) 173.6(3)
C(21)-Pd(1)-S(1)
N(1)-Pd(1)-O(1)
N(1)-Pd(1)-S(1)
O(1)-Pd(1)-S(1)
Pd(1)-S(1)-Pd(2)
81.5(3)
C(15)-Pd(2)-N(2)
C(15)-Pd(2)-O(2) 166.2(6)
C(15)-Pd(2)-S(1)
N(2)-Pd(2)-O(2)
N(2)-Pd(2)-S(1)
O(2)-Pd(2)-S(1)
82.5(3)
92.3(3)
92.6(2)
167.6(2)
94.0(2)
93.3(2)
91.8(4)
174.4(2)
93.2(4)
92.45(10)
The chloro-thiolato-bridged complexes must be pla-
nar in the solid state, assuming that their structure is
similar to that determined by X-ray diffraction for the
analogous complex without the nitro group.8 However,
some chloro-thiolato complexes (4d with palladium and
5c with platinum, both with the corresponding donor
group located in the cyclometalated ring) also show the
first methylene protons of the chains as diasterotopic,
because at room temperature the dynamic process that
averages the molecule to planar is slow on the NMR
time scale. High-temperature (320 K) NMR experi-
(9) Buey, J .; D´ıez, L.; Espinet, P.; Kitzerow, H.-S.; Miguel, J . A.
Chem. Mater. 1996, 8, 2375.
(10) Dewar, M. J . S. J . Chem. Soc. 1950, 2329.

Pd(II) and Pt(II) Schiff-Base Complexes
Organometallics, Vol. 17, No. 9, 1998 1753
Ta ble 4. Lin ea r a n d Non lin ea r Op tica l P r op er ties
of th e [M2(µ-SCn H2n +1)(µ-X)(RC6H3CHdNC6H4R′)2]
Com p lexes (4-8)
is the difference between excited- and ground-state
dipole moments, λ0 is the wavelength corresponding to
the charge-transfer transition, and λ is the fundamental
wavelength of the laser beam.
λmax ꢀ (L mol-1
µ
â (10-30
%
â(0) (10-30 % var
compd (nm)
m-1
)
(D) cm5 esu-1
)
vara m5 esu-1
)
â(0)a
This model predicts that â increases with the wave-
length of the charge-transfer absorption. Although the
two-level model is an oversimplification for molecule-
based second nonlinear optical chromophores, it does
provide some qualitative insight into the second-order
nonlinear optical properties of organic and organome-
tallic compounds.
4a
4b
4c
4d
5a
5c
6a
6b
6c
6d
7a
7c
8a
8c
378
501
400
464
377
349
375
498
404
466
375
400
373
349
21 300
39 100 13.1 260 ( 17 -30
24 900 7.7 52 ( 3 -26
153 100 17.1 217 ( 45 +57
22 800 10.8 42 ( 4 -42
54 ( 12 -23
54 ( 3 -25
27 200 15.7 212 ( 20 -43
26 300 8.6 52 ( 6 -26
104 200 13.1 192 ( 23 +39
6.3 56 ( 1
-22
35 ( 1
99 ( 6
30 ( 2
99 ( 10
26 ( 2
37 ( 8
34 ( 2
82 ( 8
30 ( 3
87 ( 10
26 ( 1
27 ( 1
16 ( 4
40 ( 7
-20
-40
-37
+30
-41
-23
-22
-50
-37
+10
-41
-44
-63
-17
26 400
20 700
9.5
7.7
The orthometalation of these ligands in the dinuclear
metal complexes produces in general a red shift for λmax
,
21 100
27 500
20 700 12.5
32 200 10.0
8.6
9.4
41 ( 2
47 ( 2
26 ( 7
-43
-33
-64
except for the derivatives with the donor group OC8H17
located in the anilinic ring (4a , 5a , 6a , 7a , and 8a ).
Although some care has to be exercised when these
kinds of results are discussed, because nonlinear be-
havior is influenced by several electron factors, a red
shift upon complexation implies lower energy difference
between the LUMO and HOMO orbitals of the com-
plexed imine group, and consequently, an enhancement
of the â value is to be expected. Such a behavior can
be easily predicted by considering that the orthometa-
lation forces coplanarity of the aldehydic ring with the
imine double bond, then increasing the conjugation on
the molecule. This effect can be reinforced by participa-
tion of the metal orbitals: It has been shown recently
that there is a certain level of aromaticity within the
five-membered palladacycle of orthopalladated imines.12
Thus, an increase of the intraligand charge transfer
should produce an enhancement of λmax, in agreement
with the general trend observed.
59 ( 11 -16
a
% var â refers to the change of â values as compared to 2âimine
.
Ta ble 5. Lin ea r a n d Non lin ea r Op tica l P r op er ties
of th e [ML(RC6H3CH)NC6H4R′)] (L ) Cp or a ca c)
Com p lexes (9, 10)
λmax ꢀ (L mol-1
µ
â (10-30
% var â(0) (10-30 % var
compd (nm)
cm-1
)
(D) cm5 esu-1
)
âa
cm5 esu-1
)
â(0)a
9a
9b
9c
9d
10a
10b
10c
10d
405
494
413
483
396
502
418
486
22 800
54 700
45 100
68 100
13 500
20 000
14 400
60 700
6.6
32 ( 11
-11
-18
+23
+142
-25
-28
-40
18 ( 6
61 ( 5
24 ( 13
70 ( 3
16 ( 2
51 ( 5
12 ( 1
58 ( 4
-18
-25
0
+84
-27
-38
-50
+53
9.8 154 ( 13
5.6 43 ( 23
7.7 167 ( 7
6.3 27 ( 3
9.1 135 ( 14
3.6 21 ( 2
7.7 141 ( 10 +104
a
% var â refers to the change of â values as compared to âimine
.
Another factor that influences the magnitude of the
molecular hyperpolarizability is the extinction coef-
ficient ꢀmax, related to oscillator strength f and mainly
governed by the extent of overlap between the HOMO
and LUMO orbitals.13 Thus, the metal complexes that
display greater ꢀmax values respect to the free imine
ligands (4d and 6d ) should show the more important
increasing of hyperpolarizability, as observed.
On the other hand, the Pd atom acts as an electron
acceptor, mainly through its bond with the iminic
nitrogen, as it has been proved in orthopalladated
ferrocenylimines by means of Mo¨ssbauer spectroscopy.14
This withdrawal of electron density by the palladium
atom should make the charge-transfer more difficult
and therefore diminish the â value.
Ta ble 6. Lin ea r a n d Non lin ea r Op tica l P r op er ties
of th e [M(RC6H3CH)NC6H4R′)Cl(CNC6H4R′′)]
Com p lexes (11-15)
λmax ꢀ (L mol-1
µ
â (10-30 % var â(0) (10-30 % var
compd (nm)
cm-1
)
(D) cm5 esu-1
)
âa
cm5 esu-1
)
â(0)a
11a
11c
11e
12a
12c
13b
13d
14a
14c
15b
15d
414
390
384
415
392
530
464
382
385
528
464
16 100
15 900
11 900
12 800
21 900
31 400
59 000
13 500
20 000
25 400
45 100
4.7
9.2
8.1
3.1
11.3
2.4 263 ( 39
13.2
2.3
12.3
48 ( 17
17 ( 1
24 ( 15
10 ( 2
29 ( 2
33
-51
27 ( 9
10 ( 1
15 ( 9
6 ( 1
17 ( 1
83 ( 12
40 ( 2
17 ( 4
23 ( 4
35 ( 6
38 ( 3
+23
-58
-72
-17
40
27
-25
6
-74
-29
+1
+5
-23
-4
88 ( 4
27 ( 7
37 ( 6
3.7 111 ( 19
15.4 83 ( 7
-40
20
-57
0
a
% var â refers to the change of â values as compared to âimine
.
This compensation of the induced coplanarity of the
aldehydic ring and the iminic double bond by the
withdrawal of electron density by the palladium atom,
as well as other effects that may be produced, is
responsible for the relative decrease of â values per
imine units upon complexation in the case of dimers.
Only the presence of the strong donor group NBu2
attached to the aldehydic ring leads to a significant
increase of â as compared to the free imine.
The nonlinearity of the system may be improved by
increasing the electronic density on the Pd atom, thus
reducing its undesired acceptor behavior, or by the
introduction of a new chelate ring in order to extend
and the anilinic rings (4d , 6d , 9d , and 10d ). These last
complexes show a clear enhancement of the â values.
The understanding of how molecular design is related
to â has been provided by the two-level model:11
3e2
16pmπ3c3
1
â )
f∆µλ3
)
0
(1 - (2λ0/λ)2)(1 - (λ0/λ)2)
1
â(0)
(1 - (2λ0/λ)2)(1 - (λ0/λ)2)
where e and m are the charge and the mass of the
electron, respectively, c is the velocity of light, f is the
oscillator strength of the charge-transfer transition, ∆µ
(12) Crispini, A.; Ghedini, M. J . Chem. Soc., Dalton Trans. 1997,
75.
(13) Yoshimura, T. Mol. Cryst. Liq. Cryst. 1990, 182A, 43.
(14) Lo´pez, C.; Bosque, R.; Solans, X.; Font-Bard´ıa, M.; Tramuns,
D.; Fern, G.; Silver, J . J . Chem. Soc., Dalton Trans. 1994, 3039.
(11) Oudar, J . L. J . Chem. Phys. 1977, 67, 446.

1754 Organometallics, Vol. 17, No. 9, 1998
Buey et al.
The replacement of Pd in the dimeric complexes with
Pt does not change significantly the magnitude of the
molecular hyperpolarizability. This behavior has also
been observed for the series M(CO)4(1,10-phenantroline)
(M ) Cr, Mo, W) despite the MLCT nature of the
relevant CT excited state.16 However EFISH measure-
ments of complexes bearing a ferrocene donor group and
a metal halide acceptor group reported by Balavoine
indicate that â slightly increases along the series Ni-
(II) < Pd(II) < Pt(II).17 Eisenberg also reported a series
of M(diimine)(dithiolate) complexes in which Pt(II)
complexes display enhanced â values over Pd(II) ana-
logues.18 These different trends indicate that an un-
derstanding of how metal d orbitals affect molecular
hyperpolarizabilities requires further studies on orga-
nometallic chromophores.
F igu r e 2. Sketches of the relative orientations of the first-
order hyperpolarizability â vectors for isocyanide-substi-
tuted compounds (11).
Exp er im en ta l Section
Literature methods were used to prepare bis(µ-chloro)bis-
(η3-(2-methylallyl)platinum),19 potassium (R)-2-chloropropi-
the electronic delocalization. With this ideas in mind
we have synthesized a new series of derivatives with
the good π-donor cyclopentadienyl group (9a -d ) or
acetylacetonato ligand (acac) (10a -d ) and measured
their optical properties (Table 5).
The relationship between the â value of the mono-
meric complexes and the free imines follows the same
trend observed in the dimeric complexes: â enhance-
ment is observed only when the donor group is dibuty-
lamino and is located in the cyclometalated ring,
reaching a value 80% higher than âimine in the cyclo-
pentadienyl complex 9d and 50% higher than âimine in
the acetylacetonato complex 10d .
However, in the Cp and acac derivatives it must be
taken into account that the EFISH experiment mea-
sures the vector projection of the â tensor along the
molecular dipole axis, µ. In these monomeric complexes,
the charge transfer and dipole axes are not parallel to
each other, resulting in experimentally determined âµ
values that are smaller than the contribution of â along
the CT axis.15
The last series of compounds synthesized (11-15)
contains an isonitrile substituted with appropriate
donor and acceptor groups that introduces a new charge
transfer in the system. In a first approach one can
consider the total effect as a vectorial addition of the
imine and isonitrile contributions.
21
onate,20 AgSCnH2n+1
,
thallium cyclopentadienyle,22 and thal-
lium acetylacetonate.23
The imines used to prepare the complexes were synthesized
by p-toluenesulfonic acid-catalyzed condensation of the corre-
sponding aldehyde and amine in toluene.24 They were reacted
with palladium acetate to prepare the acetato-bridged com-
plexes from which the chloro-bridged derivatives (2) can be
obtained by reaction with HCl by following literature meth-
ods.25
The dinuclear platinum chloro-bridged complexes 3 are
prepared directly by reaction of the corresponding imine with
[Pt2(µ-Cl)2(η3-C4H7)2] by following a method already reported
by us.9
Column chromatography was performed with silica gel
(230-400 mesh ASTM). Infrared spectra were run on a
Perkin-Elmer 883 or 1720 X spectrophotometer. 1H NMR
spectra were recorded on a Bruker AC 300 and on an ARX
300 spectrometer at room temperature. Chemical shifts are
expressed in parts per million upfield from Si(CH3)4. UV-vis
spectra were run on a Shimadzu UV-160A spectrophotometer.
Combustion analyses were made with a Perkin-Elmer 2400
CHN elemental analyzer.
EF ISH Mea su r em en ts. Second-order molecular hyper-
polarizability analyses were performed using a Q-switched
mode-locked Nd:YAG laser operating at 1.34 µm by the electric
field induced second harmonic generation method.26 The laser
delivers 60 ns pulses focused onto a liquid cell and synchro-
nized with a dc field applied to a solution containing the
chromophore. By translation of the cell perpendicularly to the
incident beam, the variation of the propagation length in the
The experimental values of the linear and nonlinear
optical properties (Table 6) show that in some cases the
â value of the complex is higher than the corresponding
value of the free imine. The fact that the other
compounds show a smaller â value may be explained
by the nonparallelism of dipole moment and â vectors
as discussed previously for Cp and acac derivatives.
The behavior observed in this series of compounds
may be summarized as follows: When the angle be-
tween the charge transfer in the imine and in the iso-
nitrile is less than 90°, the two contributions add pos-
(16) Cheng, L.-T.; Tam, W.; Eaton, D. F. Organometallics 1990, 9,
2856.
(17) Doisneau, G.; Balavoine, G.; Fillebeen-Khan, T.; Clinet, J .-C.;
Delaire, J .; Ledoux, I.; Loucif, R.; Puccetti, G. J . Organomet. Chem.
1991, 421, 299.
(18) Cummings, S. D.; Cheng, L.-T.; Eisenberg, R. Chem. Mater.
1997, 9, 440.
(19) Mabbot, D. J .; Mann, B. E.; Maitlis, P. M. J . Chem. Soc., Dalton
Trans. 1977, 294.
(20) Sierra, T.; Serrano, J . L.; Ros, M. B.; Ezcurra, A.; Zub´ıa, J . J .
Am. Chem. Soc. 1992, 114, 7645.
(21) Baena, M. J .; Espinet, P.; Lequerica, M. C.; Levelut, A. M. J .
Am. Chem. Soc. 1992, 114, 4182.
(22) Nielson, A. J .; Rickard, C. E. F.; Smith, J . M. Inorg. Synth. 1990,
28, 315.
(23) Taylor, E. C.; Hawks, G. H.; Mckillop, A. J . Am. Chem. Soc.
1968, 90, 2421.
itively and âmeasured is higher than âimine
.
On the
contrary, when the angle between the two charge trans-
fers is higher than 90°, the hyperpolarizabilities are sub-
tracted and âmeasured is smaller than âimine (Figure 2).
(24) Keller, P.; Liebert, L. Solid State Phys., Suppl. 1978, 14, 19.
(25) Ros, M. B.; Ruiz, N.; Serrano, J . L.; Espinet, P. Liq. Cryst. 1991,
9, 77.
(15) Kanis, D. R.; Ratner, M. A.; Marks, T. J . J . Am. Chem. Soc.
1992, 114, 10338.
(26) (a) Oudar, J . L. J . Chem. Phys. 1977, 67, 446. (b) Reference 1c,
p 106.

Pd(II) and Pt(II) Schiff-Base Complexes
Organometallics, Vol. 17, No. 9, 1998 1755
solution creates Maker fringes, whose amplitude and periodic-
ity are related to the nonlinearity of the solution. The
experiment was performed for each compound, by using
solutions of increasing concentrations (x ) 10-4-5 × 10-3 mol/
L) in chloroform.
The ground-state dipole moment was determined by the
standard method of Guggenheim.27 Further details of the
experimental methodology and data analyses are reported
elsewhere.28
Representative preparation procedures are given below as
the syntheses were similar for the rest of the complexes.
Spectral and analytical data for all compounds have been
included as Supporting Information.
tions, in hkl range (-12, -14, 0) to (12, 15, 19) and θ limits 0
< θ < 23° were measured, using the ω-2θ scan technique and
a variable scan rate with a maximum scan time of 60 s per
reflection. The intensity of the primary beam was checked
throughout the data collection by monitoring three standard
reflections every 60 min. The final drift correction factors were
between 0.983 and 1.048. On all reflections a profile analysis
was performed.29,30 Some double measured reflections were
averaged Rint ) ∑I - I /∑I ) 0.0394 resulting in 6863 “unique”
reflections of which only 3289 were observed with I > 2σ(I).
Lorentz and polarization corrections were applied, and the
data were reduced to ΩFoΩ values. The structure was solved
by Patterson methods and phase expansion using DIRDIF.31
Isotropic least-squares refinement on F2 was made using
SHELXL93.32 At this stage an empirical absorption correction
was applied using XABS.33 The relative maximum and
minimum transmision factors were respectively 0.595 and
1.000.
[M2(µ-SR)(µ-Cl)(Ln )2] (4, 5). To a suspension of 2 or 3
(0.296 mmol) in 30 mL of dichloromethane was added the
corresponding AgSR (0.300 mmol). The mixture was stirred
in the dark for 12 h at room temperature. After the AgCl
precipitate was filtered off, ethanol (10 mL) was added, and
the resulting solution was concentrated to a small volume on
a rotary evaporator. A solid appeared which was filtered off,
washed with ethanol (2 × 3 mL), and air-dried.
During the final stages of the refinement the positional
parameters and the anisotropic thermal parameters of the
non-H atoms were refined. All non-hydrogen atoms were
anisotropically refined. All hydrogen atoms were geometrically
placed. The final conventional agreement factors were R )
[P d 2(µ-SC8H17)(µ-OAc)(Ln )2] (6). To a solution of 2 (0.192
mmol) in 20 mL of dichloromethane was added silver acetate
(0.320 g, 0.192 mmol). The workup was as described above
affording compounds 6a -d .
0.0384 and wR2 ) 0.080 for the 3289 “observed” reflections
2
and 580 variables. The function minimized was [∑w(Fo
-
[M2(µ-SC8H17)(µ-(R)-ClP r )(Ln )2] (7, 8). A mixture of 2
(0.115 mmol) and potassium (R)-2-chloropropionate (0.126
mmol) in dichloromethane/acetone (2:1, 30 mL) was stirred for
24 h at room temperature. After removal of the precipitate
by filtration, the resulting solution was concentrated to dry-
ness. The residue was triturated in a mixture of dichlo-
romethane/methanol (1:3) to obtain a solid, which was filtered
out, washed with 2 × 3 mL of methanol, and air-dried.
[P d Cp Ln ] (9). TlCp (0.030 g, 0.111 mmol) was added to a
suspension of 2 (0.101 mmol) in 20 mL of dichloromethane.
The mixture was stirred in the dark for 10 h at room
temperature. The solution was filtered through Kieselguhr
and evaporated to ca. 3 mL under reduced pressure. Addition
of ethanol afforded 9 as an orange-red solid, which was filtered
out and washed with 2 × 3 mL of ethanol.
Fc2)2/∑w(Fo2)2]1/2, with w ) 1/[σ2(Fo2) + (0.0315P)2 + 2.59P],
σ(Fo2) from counting statistics, and P ) (Max(Fo2,0) + 2Fc2)/3.
The final difference Fourier map showed no peaks higher than
0.458 e Å-3 nor deeper than -0.578 e Å-3
. Figure 1 shows
the atomic numbering scheme.34
Atomic scattering factors were taken from ref 35. Geo-
metrical calculations were made with PARST.36 All calcula-
tions were made at the University of Oviedo on the Scientific
Computer Center and X-ray group VAX computers.
Ack n ow led gm en t. The authors in Valladolid are
indebted to the Comisio´n Interministerial de Ciencia y
Tecnolog´ıa (Project MAT96-0708) and to the J unta de
Castilla y Leo´n (Project VA23/97) for financial support,
S.G.-G. and A.T. thank the DGICYT for support (Project
PB96-0556) .
[P d (a ca c)Ln ] (10). To a suspension of 2 (0.192 mmol) in
20 mL of dichloromethane was added the stoichiometric
amount of [Tl(acac)] (0.384 mmol). After the mixture was
stirred for 2 h, the white precipitate of TlCl was filtered off,
the solution was evaporated to dryness, and the residue was
stirred with 10 mL of ethanol to give the complexes.
[P d Ln (CNR)Cl] (11-15). To a suspension of 2 (0.101
mmol) in 20 mL of dichloromethane was added the corre-
sponding isonitrile CNR (0.212 mmol). The precipitate im-
mediately disappeared, and the resulting solution was stirred
for 15 min. The solvent was taken off under reduced pressure,
and the residue was stirred with ethyl ether to obtain a solid,
which was filtered off, washed with 2 × 3 mL of ethyl ether
and air-dried.
X-r a y Cr ysta llogr a p h ic An a lysis of 6d . Details of the
structure analysis are listed in Table 1. X-ray diffraction
measurements were performed on a single crystal of size 0.17
× 0.26 × 0.10 mm. Throughout the experiment Mo KR
radiation was used with a graphite crystal monochromator on
an Enraf-Nonius CAD4 single-crystal diffractometer (λ )
0.710 73 Å). The unit cell dimensions were determined from
the angular settings of 25 reflections with θ between 7 and
10°. The space group was determined to be P1h, from the
structure determination. The intensity data of 7208 reflec-
Su p p or tin g In for m a tion Ava ila ble: Tables of yields,
elemental analyses, and IR and NMR data and, for the crystal
structure of 6d , complete tables of atomic coordinates, thermal
parameters, bond distances and angles, and least-squares
planes and atomic deviations therefrom (20 pages). Ordering
information is given on any current masthead page.
OM9708900
(29) Lehman, M. S.; Larsen, F. K. Acta Crystallogr. 1974, A30, 580-
584.
(30) Grant, D. F.; Gabe, E. J . J . Appl. Crystallogr. 1978, 11, 114-
120.
(31) Beurskens, P. T.; Admiraall, G.; Beurskens, G.; Bosman, W.
P.; Garc´ıa-Granda, S.; Gould, R. O.; Smits, J . M. M.; Smykalla, C.
DIRDIF user’s guide; Technical report; Crystallography Laboratory,
University of Nijmegen: Nijmegen, The Netherlands, 1992.
(32) Sheldrick, G. M. SHELXL93. In Crystallographic Computing
6. Ed. Flack, H. D., Parkanyi, P., Simon, K., Eds.; IUCr/Oxford U.
Press: Oxford, U.K., 1993.
(33) Parking, S.; Moezzi, B.; Hope, H. J . Appl. Crystallogr. 1995,
28, 53-56.
(34) Spek, A. L. The EUCLID package. In Computational Crystal-
lography; Sayre, D., Ed.; Clarendon Press: Oxford, U.K., 1982; p 528.
(35) International Tables for X-ray Crystallography; Kynoch Press:
Birmingham, U.K., 1974; Vol. IV (present distributor Kluwer Academic
Publishers, Dordrecht, The Netherlands).
(27) Guggenheim, E. A. Trans. Faraday Soc. 1949, 45, 203.
(28) (a) Ledoux, I.; Zyss, J . Chem. Phys. 1982, 73, 203. (b) Barzoukas,
M.; J osse, D.; Fremaux, P.; Zyss, J .; Nicoud, J . F.; Morley, J . O. J .
Opt. Soc. Am. B 1987, 4, 977.
(36) Nardelli, M. Comput. Chem. 1983, 7, 95-98.