Bis-silyl substituted ferrocenylenes, including dicyanovinyl electron-withdrawing groups, as potential non-linear optical materials

Article abstract of DOI:10.1016/j.jorganchem.2003.07.006

1,1′-Bis-silylferrocenylenes (p-XC₆H₄ SiMe₂-C₅H₄)₂Fe, X=Br (1), CHO (2), CH=C(CN)₂ (3) have been synthesized and characterized by NMR and M?ssbauer spectroscopy, single crystal X-ray diffraction and electrochemistry. Complex 1 crystallizes in the centrosymmetric space group P2₁/n whereas 3 forms in the non-centrosymmetric group Cc. The latter complex exhibits a chain-like structure in the solid state via C-H?N intermolecular hydrogen bonding. The hyperpolarizability of 3 is significantly greater than the related mono-silylferrocene complex (C₅H₅) Fe(C₅H₄SiMe₂C₆H₄ CH=C(CN)₂) while M?ssbauer spectroscopy exhibits negligible charge transfer between the cyano groups and the ferrocenylene iron center.

Full text of DOI:10.1016/j.jorganchem.2003.07.006

Journal of Organometallic Chemistry 686 (2003) 235ꢁ241
/
www.elsevier.com/locate/jorganchem
Bis-silyl substituted ferrocenylenes, including dicyanovinyl electron-
withdrawing groups, as potential non-linear optical materials
Xiaoming Zhao a, Hemant K. Sharma a, Francisco Cervantes-Lee a,
Keith H. Pannell a,*, Gary J. Long b, Ahmed M. Shahin b
a Department of Chemistry, University of Texas at El Paso, 500 W. University Avenue, El Paso, TX 79968-0513, USA
b Department of Chemistry, University of Missouri- Rolla, Rolla, MO 65409-0010, USA
Received 8 April 2003; received in revised form 24 July 2003; accepted 24 July 2003
Abstract
1,1?-Bis-silylferrocenylenes (p-XC6H4SiMe2-C5H4)2Fe, Xꢀ
¨
the centrosymmetric space group P21/n whereas 3 forms in the non-centrosymmetric group Cc. The latter complex exhibits a chain-
/
Br (1), CHO (2), CHꢀ
/
C(CN)2 (3) have been synthesized and
characterized by NMR and Mossbauer spectroscopy, single crystal X-ray diffraction and electrochemistry. Complex 1 crystallizes in
like structure in the solid state via Cꢁ
/
HÁ Á ÁN intermolecular hydrogen bonding. The hyperpolarizability of 3 is significantly greater
than the related mono-silylferrocene complex (C5H5)Fe(C5H4SiMe2C6H4CHꢀ
/
C(CN) ) while Mossbauer spectroscopy exhibits
¨
2
negligible charge transfer between the cyano groups and the ferrocenylene iron center.
# 2003 Published by Elsevier B.V.
Keywords: Ferrocenylenesilyl; NLO; Mossbauer
¨
1. Introduction
materials with better non-linear optical properties and
now report the synthesis, characterization, electrochem-
istry, Mossbauer spectra and non-linear optical proper-
¨
Organometallic compounds consisting of conjugated
ties of new 1,1?-bis(silyl)ferrocenylenes.
donorꢁacceptor systems have been shown to possess
/
large second order non-linearities [1]. There has been
considerable interest in the use of ferrocene as a donor
group [2] in the synthesis of potentially non-linear
optical materials since Green in 1987 demonstrated
that ferrocene connected via an ethylene linkage to an
acceptor moiety had an excellent second harmonic
generation (SHG) efficiency [3]. Zyss et al. reported
the second-order optical non-linear properties with a
2. Results and discussion
Treatment of 1,1?-dilithioferrocene with (p-bromo-
phenyl)chlorodimethylsilane at ꢂ25 8C in THF resulted
in the formation of bis-bromoferrocenylene derivative 1
in 17% yield. The subsequent reaction of 1 with t-BuLi
/
at ꢂ78 8C followed by the addition of DMF provided
/
wide range of transparency of the donorꢁacceptor
/
orange crystals of 2 in 45% yield. Knoevenagel con-
densation of 2 with malanonitrile resulted in the
formation of 3 in 60% yield an air-stable red crystalline
solid. The synthetic sequence is shown in Scheme 1 [5,6].
An important feature of the H-NMR spectra of the
bis-substituted ferrocenylenes, 1ꢁ3, is the small systema-
compounds linked via oligosilanes [4]. Previous studies
from our laboratories on mono-substituted ferrocenylo-
ligosilanes show weak ferroceneꢁaryl interactions
/
through the silicon chain [5], and this observation has
been verified by other groups [6]. Despite these rather
unimpressive results we continue our quest for new
1
/
tic low field chemical shifts of the Cp resonances in the
1H-NMR spectra which is indicative of the inductive
effects of the Br, ꢁ
/
CHO and ꢁ
/
CHꢀ
/
C(CN)2 substitu-
ents. For example, the 1H-NMR spectra of 1 and 2 show
a pair of triplets (d 3.84 and 4.06 for 1 and at d 3.95 and
* Corresponding author. Tel.: ꢃ
5748.
E-mail address: kpannell@utep.edu (K.H. Pannell).
/
1-915-747-5796; fax: ꢃ1-915-747-
/
0022-328X/03/$ - see front matter # 2003 Published by Elsevier B.V.
doi:10.1016/j.jorganchem.2003.07.006

236
X. Zhao et al. / Journal of Organometallic Chemistry 686 (2003) 235ꢁ241
/
observed (Fig. 3): (a) The methyl H of the silyl group
and the N4 of the cyano group of the adjacent molecules
are involved in intermolecular hydrogen bonding with
˚
interatomic distance of 2.57 A for C11ꢁ
/
H11hÁ Á ÁN4. (b)
The other type of Cꢁ
/
HÁ Á ÁN hydrogen bond involves one
of the hydrogen of aromatic ring carbon C18 and N1 of
the cyano group with a slightly longer interatomic
˚
distance of 2.68 A for C18ꢁ
/
H18cÁ Á ÁN1 bond. These two
types of unconventional Cꢁ
rise to a chain structure, a relatively rare type of H-
bonding. The CꢁH...N interatomic distances are shorter
than that observed in CꢁHÁ Á ÁN hydrogen-bonded
pyridine derivatives (3.37ꢁ3.44 A) [8,9] and longer
than that in 3-methyl-4-propargylthioquinoline (2.28
/
HÁ Á ÁN hydrogen bonds give
/
Scheme 1.
/
˚
/
4.15 for 2) assigned to Cp protons. Thus, the difference
in chemical shifts between the C5H4 protons for (1 and
2), and (2 and 3), Dd, is 0.1 ppm clearly demonstrating
the deshielding effects of the substituents on the
cyclopentadienyl ring. The 29Si-NMR chemical shifts
˚
A) [10]. We retrieved the atomic coordinates from the
Cambridge Crystallographic Data Base [11] for 3-
methyl-4-propargylthioquinoline and reviewed the hy-
˚
drogen bonding distance and found the value of 2.406 A
for CꢁHÁ Á ÁN bonds probably due to hydrogen normal-
ization in the deposited data. The hydrogen bonds are
not linear and the C18ꢁH18cÁ Á ÁN1 and C11ꢁH11hÁ Á ÁN4
angles of 1578 and 1648 respectively are wider than those
observed in the tetrakis(2-vinylpyridyl)benzeneꢁdichlor-
for 1ꢁ
indicate the weak electronic effects of the substituents.
The UVꢁvis absorption maximum in 3 is present at
/
3 (ꢂ
/
6.8, ꢂ
/
6.6 and ꢂ
/
6.0 ppm respectively) also
/
/
/
/
436 nm, a substantial blue shift from lmax observed in 1
(453 nm in CH2Cl2) indicating a charge communication
between ferrocene and dicyanovinyl groups.
/
omethane [9] but the value of 1578 is the same as that
observed in 3-methyl-4-propargylthioquinoline [10].
2.1. Crystal structures for 1 and 3
2.2. Electrochemistry
The molecular structures of 1 and 3 are shown in Figs.
1 and 2. A summary of cell constants and data collection
parameters is included in Table 1. Selected bond lengths
and bond angles are given in Table 2.
Compounds 1ꢁ3 were studied by cyclic voltammetry
/
which was performed on samples containing 10ꢂ3 M of
the compound in 0.1 M solution of [Bu4N][BF4] in
CH2Cl2 at room temperature. Each compound under-
goes a reversible one-electron oxidation (Table 3).
Compounds 1 and 2 are oxidized at higher potential
(0.1 V) in comparison with ferrocene due to the
The most interesting and, in view of the NLO
properties, the most important feature is that whereas
1 crystallized in the centrosymmetric space group P21/n,
3 is in the non-centrosymmetric space group Cc. As
expected in both compounds the two silyl substituents
on the two cyclopentadienyl rings are oriented trans to
each other presumably minimizing the steric strain.
Interestingly, 3 is an example of a molecule exhibiting
the recently discussed self-assembly [7] of organometal-
lics. In this example, two types of hydrogen bonds are
inductive effects of the ꢁ
/
Br and ꢁ
/
CHO groups. How-
ever, 3 is oxidized at a potential close to that of
ferrocene and small uncharacterized species also appear
at a higher oxidation potential (1.05 V). The irreversible
wave in 3 at higher reduction potential (ꢂ0.6 V) is
/
attributed to the dicyanovinyl groups and appears at a
lower reduction potential than in a similar complex 4
[6b].
2.3. NLO properties
The preliminary results on the hyperpolarizability of 3
10ꢂ30 esu indicates moderate
interactions between ferrocene and dicyanovinyl portion
with a b0 value of 57.0ꢄ
/
Fig. 1. Thermal ellipsoid (50%) drawing of 1.

X. Zhao et al. / Journal of Organometallic Chemistry 686 (2003) 235ꢁ
/241
237
Fig. 2. Thermal ellipsoid (50%) drawing of 3.
Table 1
Crystal data for 1 and 3
Table 2
˚
Selected bond lengths (A) and angles (8) for 1 and 3
Compound
1
3
1
Bond lengths
Empirical formula
Color; habit
C
26H28Br2Si2Fe
C34H30N4Si2Fe
Orange fragment
Fe(1)ꢁ
Fe(1)ꢁ
Fe(1)ꢁ
Fe(1)ꢁ
Br(1)ꢁ
Br(2)ꢁ
Si(1)ꢁ
/
C(3)
C(1)
C(6)
C(9)
2.027(9) Si(1)ꢁ
2.060(6) Si(1)ꢁ
2.064(6) Si(1)ꢁ
2.058(8) Si(2)ꢁ
1.910(7) Si(2)ꢁ
1.909(7) Si(2)ꢁ
1.840(7) Si(2)ꢁ
/
C(12)
C(11)
C(13)
C(19)
C(6)
1.853(9)
Orange fragment
0.48ꢄ0.28
Monoclinic
/
/
1.850(8)
1.884(7)
1.833(8)
1.850(7)
1.879(7)
1.859(8)
Crystal size (mm) 0.80ꢄ
/
/
0.60ꢄ
/
0.32ꢄ0.28
/
/
/
Crystal system
Space group
Unit cell dimen-
sions
Monoclinic
Cc
/
/
P21/n
/C(16)
/
/C(24)
/
C(21)
C(20)
/
C(1)
/
˚
a (A)
9.0166(2)
16.601(3)
17.894(4)
90
28.10(9)
9.190(5)
15.527(6)
90
Bond angles
C(1)ꢁSi(1)ꢁ
C(1)ꢁSi(1)ꢁ
C(12)ꢁ
C(1)ꢁSi(1)ꢁ
C(12)ꢁSi(1)ꢁ
C(11)ꢁSi(1)ꢁ
˚
b (A)
/
/
C(12)
C(11)
110.3(4) C(19)ꢁ
109.7(4) C(19)ꢁ
111.5(5) C(6)ꢁSi(2)ꢁ
108.1(3) C(19)ꢁSi(2)ꢁ
108.5(4) C(6)ꢁSi(2)ꢁC(20)
108.9(4) C(21)ꢁSi(2)ꢁ
/
Si(2)ꢁ
/
C(6)
110.9(4)
108.8(3)
106.6(3)
111.2(4)
111.2(4)
108.0(4)
˚
c (A)
/
/
/
Si(2)ꢁ
/
C(21)
a (8)
b (8)
g (8)
/
Si(1)ꢁ
/C(11)
/
/
C(21)
98.17(2)
90
103.31(3)
90
/
/
C(13)
/
/
C(20)
/
/C(13)
/
/
3
˚
V (A )
2651.1(10)
1.53
3167(2)
1.27
0.58
/
/C(13)
/
/
C(20)
Density (g mlꢂ1
Absorption coeffi- 3.69
)
3
Bond lengths
cient (mmꢂ1
Z
)
Fe(1)ꢁ
Fe(1)ꢁ
Fe(1)ꢁ
Fe(1)ꢁ
Fe(1)ꢁ
/
C(8)
C(7)
C(9)
C(5)
C(10)
2.033(7) Si(2)ꢁ
2.040(7) Si(2)ꢁ
2.049(7) Si(2)ꢁ
2.042(6) Si(2)ꢁ
2.051(7) N(1)ꢁ
1.856(7) N(2)ꢁ
1.887(6) N(3)ꢁ
1.855(7) N(4)ꢁ
1.868(8)
/
C(6)
1.862(7)
1.879(6)
1.844(7)
1.860(9)
1.120(13)
1.117(10)
1.138(12)
1.136(10)
4
4
/
/
C(25)
C(23)
C(24)
C(21)
C(22)
C(33)
C(34)
20 Range (8)
Scan type
3.5ꢁ
v
/
50
3.5ꢁ/50
/
/
v
/
/
Scan speed (8
minꢂ1
Scan range (v) (8) 1.20
4ꢁ
/
20
4ꢁ/20
/
/
)
Si(1)ꢁ
Si(1)ꢁ
Si(1)ꢁ
Si(1)ꢁ
/
C(1)
/
1.40
3 measured every 197 3 measured every 197
reflections reflections
105h 5 275h 5
19, ꢂ215l 5 k 510, ꢂ185
/
C(13)
C(12)
C(11)
/
Standard reflec-
tions
/
/
/
Index ranges
ꢂ
/
/
/0, 05
/
k 5
/
ꢂ/
/
/
27, ꢂ
/
105
/
/
/
/
21
/
/
/l 5
/18
Bond angles
C(1)ꢁSi(1)ꢁ
C(1)ꢁSi(1)ꢁ
C(13)ꢁ
C(1)ꢁSi(1)ꢁ
C(13)ꢁSi(1)ꢁ
C(12)ꢁSi(1)ꢁ
C(6)ꢁSi(2)ꢁ
C(6)ꢁSi(2)ꢁ
C(25)ꢁ
C(6)ꢁSi(2)ꢁ
Reflection col-
lected
4923
6488
/
/
C(13)
C(12)
106.4(3) C(25)ꢁ
109.5(3) C(23)ꢁ
108.9(3) N(1)ꢁC(21)ꢁ
111.0(4) N(2)ꢁC(22)ꢁ
107.8(3) C(32)ꢁC(31)ꢁ
113.0(4) C(31)ꢁC(32)ꢁ
107.6(3) C(31)ꢁC(32)ꢁ
109.9(3) C(34)ꢁC(32)ꢁ
109.5(3) N(3)ꢁC(33)ꢁ
110.6(4) N(4)ꢁC(34)ꢁ
/
Si(2)ꢁ
/
C(24)
C(24)
C(20)
C(20)
108.0(3)
111.1(5)
178.5(14)
178.2(10)
131.0(7)
121.0(8)
124.4(7)
114.0(7)
177.3(9)
176.7(8)
/
/
/
Si(2)ꢁ
/
Independent re-
flections
4614
4116
/
Si(1)ꢁ
/C(12)
/
/
/
/
C(11)
/
/
Observed reflec-
tions
2580(F ꢀ
280
Semi-empirical
/2.0s(F))
4717 (F ꢀ/2.0s(F))
/
/C(11)
/
/
C(28)
C(34)
C(33)
C(33)
/
/C(11)
/
/
Refined para-
meters
373
/
/
C(25)
C(23)
/
/
/
/
/
/
Absorption cor-
rection
Semi-empirical
0.100/0.113
/
Si(2)ꢁ
/C(23)
/
/
C(32)
C(32)
/
/
C(24)
/
/
Min./max. trans- 0.009/0.027
mission
Flack’s parameter
Final R indices
(obs. data)
ꢁ
Rꢀ
/
0.085 (0.0261)
2.4. Mossbauer spectra
¨
/
5.80%, wRꢀ
/
Rꢀ
/
5.75%, wRꢀ
/
15.45%
16.48%
The use of Mossbauer spectroscopy to aid in the
¨
analysis of organoiron complexes is well established.
Indeed, there have been several such studies [6] of
silylferrocenes with potentially useful NLO properties.
of the molecule. The hyperpolarizability of 3 is eight
times greater than that of 5 (b0ꢀ7.0ꢄ
10ꢂ30 esu) [5].
/
/
In general the observed room temperature Mossbauer
¨

238
X. Zhao et al. / Journal of Organometallic Chemistry 686 (2003) 235ꢁ241
/
Fig. 3. H-bonding scheme for self-assembly of 3.
Table 3
Cyclic voltammetry data (V) at scan rate 50 mV sꢂ1
a
Compound
Epa
Epc
DE
Ferrocene
0.59
0.69
0.70
0.60
0.38
0.55
0.56
0.50
0.21
0.14
0.14
0.10
1
2
3
a
Anodicꢁ
/
cathodic peak separation.
spectra are in accord with the expected low-spin iron (II)
character of the ferrocenyl groups as is the case at 296 K
for complex 3. However, there are some reports that
such compounds exhibit Mossbauer spectra which
¨
indicate the presence of iron(III) at lower temperatures
and, as a consequence, some authors have indicated that
some degree of charge transfer has been observed.[6]
The Mossbauer spectra of 3 have been measured at
¨
Fig. 4. Mossbauer spectra of 3.
¨
296 and 78 K (Fig. 4), and the resulting hyperfine
parameters, based on symmetric Lorentzian quadrupole
doublet fits, are given in Table 4. Although the 296 K
spectrum shows the presence of an iron(III) component,
this component is not apparent at 78 K. As a con-
sequence of this absence, we attribute the weak doublet
observed at 296 K to a trace of an iron(III) impurity.
Although this impurity component must be present in
both spectra, it is only apparent at 296 K, a temperature
at which the recoil-free fraction of the iron(II) in 3 is, as
expected, very small relative to that of the iron(III) trace
impurity. It is well known that the recoil-free fraction of
ferrocene-like iron(II) increases dramatically upon cool-
ing from 296 to 78 K. This is apparent in Fig. 4 as the
large increase in the percent absorption between 296 and
78 K; the corresponding increase in the iron(II) spectral
absorption area from 0.25 to 2.15 (%o)/(mm sꢂ1) is
indeed large. If one makes the reasonable assumption
that the iron recoil-free fractions of the iron(II) in 3 and
the iron(III) impurity are similar at 78 K, a fit of the
spectrum indicates that the sample contains at most 0.3
weight percent of the iron as an iron(III) impurity.
Further it should be noted that the hyperfine para-
meters of 3 are typical of ferrocene-like complexes.
Specifically, 3 exhibits a 78 K isomer shift of 0.537 mm

X. Zhao et al. / Journal of Organometallic Chemistry 686 (2003) 235ꢁ
/241
239
Table 4
Mossbauer spectral hyperfine parameters
¨
a
Compound
T (K) d (mm sꢂ1
)
DEQ (mm sꢂ1
)
G (mm sꢂ1
)
Area (%)
Area (%o) (mm sꢂ1
)
Assignment
3
296
0.458
0.199
0.537
0.447
0.533
2.33
0.50
2.34
2.40
2.40
0.26
0.29
0.25
0.23
0.26
86
14
0.25
0.04
2.15
Iron(II)
Iron(III) trace impurity
Iron(II)
78
295
85
100
100
100
Cp2Fe
ꢁ/
ꢁ/
Iron(II)
Iron(II)
a
The isomer shifts are given relative to room temperature a-iron foil.
sꢂ1 and a quadrupole splitting of 2.34 mm sꢂ1. The
comparable values for ferrocene [12] are 0.533 mm sꢂ1
and 2.40 mm sꢂ1 (see Table 4). We conclude that there
is no evidence for any charge transfer which would lead
to a ferrocenium-like species in 3. The EPR spectra of 3
recorded at room temperature 300 K and at 77 K exhibit
no signal due to Fe(III) component in the compound.
The origin of the iron(III) trace impurity in 3 is
unknown at this time and two independently synthesized
samples of 3 provided exactly identical results.
135.6, 138.5 (Ph); 29Si-NMR (C6D6): ꢂ
(CH2Cl2): lmax 453 nm.
/
6.8; UVꢁvis
/
3.2. Synthesis of 2
A 100 ml Schlenk flask was charged with 1.10 g (1.8
mmol) of 1 in 20 ml THF. To this solution, maintained
at ꢂ78 8C, was added slowly via a syringe 4.72 ml t-
/
butyl lithium (1.7 M in hexanes). The orange reaction
mixture was stirred for 5 min at low temperature and
then 4 ml of DMF was added. The temperature of the
reaction was allowed to rise to r.t. and the reaction
mixture was stirred at r.t. for 16 h. The reaction was
quenched with 30 ml of satd aq NH4Cl solution, the
resulting mixture was extracted with 100 ml benzene.
The organic layer was dried over MgSO4, and the
solvent was removed. Column chromatography on silica
3. Experimental
All syntheses were performed under a dry nitrogen
atmosphere using standard Schlenk techniques. Tetra-
hydrofuran and hexanes were distilled over sodium and
benzophenone ketal. N,N?-Tetramethylethylenediamine
(TMEDA) was distilled over calcium oxide. Me2SiCl2
gel (hexaneꢁ
powder, recrystallized from hexaneꢁ
mmol, 45% yield). m.p. 96ꢁ97 8C. Anal. Calc. for
/benzene 50/50 v/v) yielded 2 as an orange
/benzene (0.41g, 0.8
˚
was distilled before use and stored over 4 A molecular
/
sieves. Dilithioferrocene was synthesized according to a
literature procedure [13]. NMR spectra were recorded
on Bruker 300 MHz spectrometer.
C28H30FeO2Si2: C, 65.87; H, 5.92. Found: C, 65.84; H,
1
5.92%. H-NMR (C6D6): 0.40 (s, 6H, SiMe2); 3.95 (t,
Jꢀ
7.48 (dd, 2H, Ph), 7.59ꢁ
CHO); 13C-NMR (C6D6): ꢂ
72.1, 73.7 (Cp); 128.7,134.4, 137.1, 147.7 (Ph), 191.8
(CHO); 29Si-NMR (C6D6): ꢂ
6.6; UVꢁvis (CH2Cl2):
/
1.5 Hz, 2H, Cp), 4.15 (t, Jꢀ
7.61 (dd, 2H, Ph), 9.70 (s, 1H, ꢁ
1.84 (SiMe2); 69.2 (ipso),
/
1.5 Hz, 2H, Cp); 7.46ꢁ
/
/
/
/
3.1. Synthesis of 1
/
/
To a stirred slurry of 1,1?-dilithioferrocene (3.76 g,
lmax 434 nm.
19.0 mmol) in 40 ml of THF at ꢂ25 8C was added
/
slowly via a dropping funnel, a solution of (4-bromo-
phenyl)chlorodimethylsilane (9.47 g, 37.94 mmol) in 40
ml of THF. The mixture was stirred at low temperature
for 30 min and then warmed to room temperature (r.t.)
and further stirred for 14 h. The solvent was removed
under vacuum, and the orange residue was extracted
into 60 ml of hexanes and filtered on Celite. The filtrate
was concentrated to 10 ml and chromatographed on
3.3. Synthesis of 3
A 100 ml Schlenk was charged with 0.2 g (0.4 mmol)
of 2 in a mixture of THF (3 ml) and EtOH (15 ml). To
this solution was added 0.06 g (0.82 mmol) of solid
malanonitrile and four drops of piperidine. An immedi-
ate color change from light orange to dark red was
observed. The mixture was stirred at r.t. for 1 h, and the
solvents were removed in vacuum. The red sticky residue
was dissolved in 5 ml of methylene chloride and passed
silica gel (80ꢁ
/
200 mesh) column (2ꢄ15 cm). Elution
/
with hexane produced an orange band that eluted to
yield 2.0 g (3.26 mmol, 17%) of 1 as an orange powder,
m.p. 122ꢁ
51.00; H, 4.61. Found: C, 50.52; H, 4.66%. H-NMR
(C6D6): 0.29 (s, 6H, SiMe2); 3.84 (t, Jꢀ1.5 Hz, 2H, Cp),
4.06 (t, Jꢀ1.5 Hz, 2H, Cp); 7.08ꢁ7.11 (dd, 2H, Ph),
7.25ꢁ 1.65
7.28 (dd, 2H, Ph); 13C-NMR (C6D6): ꢂ
(SiMe2); 69.6 (ipso), 71.9, 73.6 (Cp); 124.1,131.2,
/
124 8C. Anal. Calc. for C26H28Br2FeSi2: C,
through a silica gel column (25ꢄ
band was eluted with 90:10 methylene chlorideꢁ
mixture. Evaporation of the solvent yielded the red solid
of 3 (0.145 g, 0.24 mmol 60% yield). m.p. 170ꢁ172 8C.
Anal. Calc. for C34H30FeN4Si2: C, 67.32; H, 4.98; N,
9.24. Found: C, 66.72; H, 5.13; N, 9.21%. 1H-NMR
/
2 cm), and the red
1
/hexane
/
/
/
/
/
/

240
X. Zhao et al. / Journal of Organometallic Chemistry 686 (2003) 235ꢁ241
/
(CDCl3): 0.51 (s, 6H, SiMe2); 4.06 (t, Jꢀ
Cp), 4.29 (t, Jꢀ1.5 Hz, 2H, Cp); 7.58ꢁ7.61 (dd, 2H,
Ph), 7.75ꢁ7.78 (dd, 2H, Ph), 7.69 (s, 1H, CHꢀ
C); 13C-
NMR (CDCl3): ꢂ1.72 (SiMe2); 69.0 (ipso), 72.4, 73.8
(Cp); 83.2 (CHꢀC); 113.0, 114.2 (ꢀC(CN)2); 128.9,
131.4, 135.1, 149.7 (Ph), 160.4 (CHꢀ
C); 29Si-NMR
(CDCl3): ꢂ6.0; UVꢁvis (CH2Cl2): lmax 436 nm.
/
1.5 Hz, 2H,
technique was used for intensity measurements in all
cases. A range of 1.28 in v was used for 1 and 3. A
variable speed of 4.00 to 20.00 8 minꢂ1 was used for
compound 1 whereas for 3 this range was 1.4 due to the
higher background present in this case. Background
counts were taken with stationary crystal and total
background time to scan time ratio of 0.5. Three
standard reflections were monitored in all cases every
197 reflections and showed no significant decay. The
data were corrected for Lorentz and polarization effects
and a semi-empirical absorption correction was also
applied to each data set giving a Min./Max. transmis-
sion ratio of 0.009/0.027 for 1 and 0.100/0.113 for 3.
Compound 1 is centrosymmetric, space group No. 14,
P21/n but compound 3 is non-centric, space group No.
9, Cc, therefore Friedel paired reflections were collected
to determine the correct absolute structure of the
asymmetric unit. All structures were solved by direct
methods and refined using the PC-version of the
SHELEXTL PLUS crystallographic software by Siemens.
Full-matrix least-squares refinement of F2 against all
reflections was carried out with anisotropic thermal
/
/
/
/
/
/
/
/
/
/
3.4. Electrochemistry
Electrochemical studies were performed with a 263A
Princeton Applied Research potentiostat in 10ꢂ3
M
CH2Cl2 solution with tetrabutylammonium tetrafluor-
oborate (0.1 M) as supporting electrolyte in a cell
equipped with platinum working electrode, and an
Ag ½ AgCl (saturated NaCl) reference electrode and
counter electrode.
3.5. NLO measurements
The quadratic hyperpolarizability (b) of 3 was
measured in solution by the electric field induced
second-harmonic generation (EFISH) technique as
described previously [4].
parameters for non-hydrogen atoms. Hydrogen atoms
˚
Hꢀ0.96 A;
were placed at calculated positions (Cꢁ
/
/
UHꢀ
has the form wꢂ1ꢀ
[2F2cꢃMax(F2o,0)]/3. and the final R factors the form
R1ꢀ
F2c)2/
/
0.08) during refinements. The weighing scheme
3.6. Mossbauer spectra
¨
/
s2(F2o)ꢃ(aP)2ꢃ
/
/bP, where P is
/
The Mossbauer spectra were obtained at 78 and 295
¨
/
a½Foꢂ
/
Fc½/aFo
and
Rw2
ꢀ
/
{a[w(F2oꢂ
/
K on a constant-acceleration spectrometer which used a
r.t. rhodium matrix cobalt-57 source and was calibrated
at r.t. with alpha-iron foil. The spectra have been fit with
one or two quadrupole doublets and the resulting
isomer shifts and quadrupole splittings are accurate to
a[w(F2o)2]}1/2, these and some other relevant crystal-
lographic parameters are given in Table 1.
0.005 and 9
0.01 mm sꢂ1, respectively.
/
Acknowledgements
9
/
This research has been supported by the NIH-MARC
program and the R.A. Welch Foundation, Houston,
TX. (Grant # AH-0546). We thank Drs. Isabelle
Ledoux and Joseph Zyss from the Laboratoire de
Chimie des Polymeres, Universite Pierre et Marie Curie,
UMR 7610-CNRS, Paris, France for the preliminary
NLO measurement. We thank Dr. Martin Kirk and Mr.
Antonio Williams of University of New Mexico, Albu-
querque, NM for evaluating the EPR properties of 3.
3.7. EPR measurements
Solution and frozen glass EPR spectra were measured
at X-band (ꢁ9.3 GHz) using a Bruker EMX spectro-
/
meter. The r.t. (300 K) solution spectra were measured
in CH2Cl2. For the low temperature measurements, a
1:1 tolueneꢁCH2Cl2 mixture was used as a glassing
/
solvent, and the temperature was held at 77 K in a
nitrogen Dewar.
3.8. X-ray crystal structures for 1 and 3
References
Two orange crystals of approximate dimensions
0.80ꢄ
/
0.48ꢄ
/
0.28 mm (1), 0.60ꢄ
/
0.32ꢄ0.28 mm (3)
/
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