Synthesis and non-linear optical properties of (alkyne)dicobalt octacarbonyl complexes and their substitution derivatives

Article abstract of DOI:10.1016/S0020-1693(02)01185-4

A series of new donor-acceptor compounds of the form [(HC≡C-CH=CH-C₆H₄-X-p)Co₂(CO) ₄(L¹)(L²)])] (2, X=Br, L¹=L²=CO; 3, X=NO₂, L¹=L²=CO; 6, X=NO₂, L¹=CO, L²=PPh₃; 7, X=NO₂, L¹=L²=PPh₃; 8, X=NO₂, L¹=AsPh₃, L²=PPh₃), where X is a π-acceptor group and the (alkyne)Co₂(CO)₄(L¹)(L²) moiety is a donor, has been synthesized. The different σ-donor/π-acceptor abilities of the ligands L¹ and L² allow tuning of the electronic and optical properties of complexes 2, 3 and 6-8: the hyperpolarizability values increase in the order 2<3<6<7<8. Density functional calculations reveal that the absolute values of β do not agree with experimental results, but the general trends are consistent with experiments. The X-ray crystal structures of 2, 6, and 7 are reported.

Full text of DOI:10.1016/S0020-1693(02)01185-4

Inorganica Chimica Acta 343 (2003) 41Á50
/
www.elsevier.com/locate/ica
Synthesis and non-linear optical properties of (alkyne)dicobalt
octacarbonyl complexes and their substitution derivatives
In Su Lee, Dong Mok Shin, Yeohoon Yoon, Seok Min Shin, Young Keun Chung *
School of Chemistry and Center for Molecular Catalysis, Seoul National University, Seoul 151-747, Republic of Korea
Received 15 February 2002; accepted 8 July 2002
Abstract
A series of new donorÁ
L2ꢀ NO2, L1ꢀ
CO; 3, Xꢀ
L2ꢀPPh3), where X is a p-acceptor group and the (alkyne)Co2(CO)4(L1)(L2) moiety is a donor, has been synthesized. The different
s-donor/p-acceptor abilities of the ligands L1 and L2 allow tuning of the electronic and optical properties of complexes 2, 3 and 6Á
8:
the hyperpolarizability values increase in the order 2B3B6B7B8. Density functional calculations reveal that the absolute values
/
acceptor compounds of the form [(HCÅ
/
CÃ
/
CHÄ
/
CHÃ
/
C6H4Ã
/
X-p)Co2(CO)4(L1)(L2)])] (2, Xꢀ
/
Br, L1ꢀ
AsPh3,
/
/
/
/
L2ꢀ NO2, L1ꢀCO, L2ꢀ
/
CO; 6, Xꢀ
/
/
/
PPh3; 7, Xꢀ
/
NO2, L1ꢀ
/
L2ꢀ NO2, L1ꢀ
/
PPh3; 8, Xꢀ
/
/
/
/
/
/
/
/
of b do not agree with experimental results, but the general trends are consistent with experiments. The X-ray crystal structures of 2,
6, and 7 are reported.
# 2002 Elsevier Science B.V. All rights reserved.
Keywords: Crystal structures; Nonlinear optics; Cobalt complexes; Carbonyl complexes; Alkyne complexes
1. Introduction
and s-enynyl metal complexes (Mꢀ/Ru, Ni, Au) have
attracted much attention as promising candidates for
NLO materials [3]. However, to our knowledge, little
study has been conducted on p-alkyne transition metal
complexes. It is a general feature of p-alkyne complexes
that electrons are back-donated from a metal d-orbital
into the ligand LUMO [4]. Thus, it is expected that an
electron-rich p-alkyne complex having (an) electron-
withdrawing group(s) on the alkyne can behave like a
Molecular materials that exhibit non-linear optical
properties are of great interest for potential applications
in optical data processing technology. A wide variety of
organic compounds have been shown to exhibit such
properties and, more recently, organometallic com-
pounds have been found to exhibit significant effects [1].
Metals can have a large diversity of coordination
mode with various organic ligands and changing a
ligand in the coordination sphere can affect the function
of the metal fragment. For organometallic compounds,
it is particularly easy to finely tune either the electronic
and/or steric effect by substitution of labile ligands
pushÁpull NLO molecule. Furthermore, increasing the
/
electron-withdrawing ability enhances the stability of
alkyne complexes.
We have prepared dicobalt carbonyl complexes of
alkyne with an electron-withdrawing group and examine
their non-linear optical properties. These complexes
offer the possibility of a new class of NLO chromophore
with tuning of their optical properties by carbonyl
substitution. Herein we report the synthesis and non-
linear optical study of new alkyne dicobalt complexes.
Recently, the semiempirical calculations of the NLO
1b[2]. For example, Muller’s and Tamm’s groups
¨
reported the facile tuning of the electronic and optical
properties of transition metal p-arene tricarbonyl com-
plexes by carbonyl substitution [2a,2b].
Alkynes can be complexed with transition metal
metals through the s- or p-bond. Recently, s-acetylide
properties of [Co2{mÁ
/
h2-(C6H5)CC(C6H4NO2)}(CO)6]
* Corresponding author. Fax: ꢁ
/
82-2-889 1568
have been published [5].
E-mail address: ykchung@plaza.snu.ac.kr (Y.K. Chung).
0020-1693/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved.
PII: S 0 0 2 0 - 1 6 9 3 ( 0 2 ) 0 1 1 8 5 - 4

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I.S. Lee et al. / Inorganica Chimica Acta 343 (2003) 41Á50
/
2. Experimental
Jꢀ
ppm; IR (KBr): nCO 2094 (s), 2054 (s), 2025 (s), 1999 (s)
cmꢂ1
/
11.4 Hz, 1H), 6.69 (d, Jꢀ
/
11.4 Hz, 1H), 5.97 (s, 1H)
2.1. General considerations
.
All reactions with air- or moisture-sensitive materials
were carried out under nitrogen using standard Schlenk
techniques. Freshly distilled, dry, and oxygen-free
solvents were used throughout. 1H and 31P NMR
spectra were obtained with a Bruker 300 or 500 spectro-
meter. Elemental analyses were carried out at the
National Center for Inter-University Research Facil-
ities, Seoul National University. Infrared spectra were
2.1.3. Synthesis of 4
Compound 1 (0.20 g, 0.59 mmol), PPh3 (0.16 g, 0.59
mmol), and 30 ml of THF were added to a Schlenk
flask. The reaction mixture was heated at reflux under
N2 for 3 h. After the solution was cooled to r.t., any
solids were filtered off and the filtrate was evaporated to
dryness. The crude product was purified by chromato-
graphy on a silica gel column eluting with C6H14 and
Et2O (v/v, 3:1). Removal of the solvent by a rotary
evaporator and keeping in vacuo for a day gave brown
solids in 68% yield (0.23 g, 0.40 mmol). 1H NMR
(CDCl3): d 9.58 (s, 1H), 7.43 (br s, 15H), 5.50 (br s, 1H)
ppm; 31P NMR (CDCl3): d 51.12 ppm; IR (KBr): nCO
2071 (s), 2014 (s), 1976 (s), 1652 (s) cmꢂ1. Anal. Found:
C, 54.08; H, 2.95. Calc. for C26H17Co2O6P: C, 54.38; H,
2.98%.
recorded on a Shimadzu IR-470 spectrometer. UVÁVis
/
electronic absorption spectra were recorded on a Uni-
kon 930 spectrophotometer. Compounds 1, 9a, and 9b
were previously reported [6].
2.1.1. Synthesis of 2
To 30 ml of THF solution of (4-bromobenzyl)triphe-
nylphosphonium bromide (0.37 g, 0.71 mmol) and 18-
crown-6 (a catalytic amount), KotBu (0.09 g, 0.77
mmol) was added. After the solution was stirred for 1
h, 1 (0.20 g, 0.59 mmol) was added to the solution. The
resulting solution was stirred for 3 h at room tempera-
ture (r.t.). Excess water (50 ml) and Et2O (50 ml) was
added to quench the solution. The etheral layer was
collected and evaporated to dryness. Compounds 2 and
2-1 were separated by chromatography on a silica gel
2.1.4. Synthesis of 4*
To the solution of 9* (2.80 g, 3.4 mmol) in 20 ml of
Et2O was added HBF4×OMe2 (0.86 ml) at 0 8C. The
/
solution was allowed to warm to r.t. and stirred for 1 h.
Solvent was removed by cannular transfer. THF (20 ml)
and saturated aq. Na2CO3 solution (20 ml) were added
to the residue. The THF layer was treated with CH2Cl2
(20 ml) and NH4Cl solution (20 ml). The CH2Cl2 layer
was collected and chromatographed on a silica gel
eluting with C6H14 and Et2O (v/v, 10:1). Removal of
the solvent gave 10* in 63% yield. To the activated
DMSO (0.45 ml of DMSO and 1.26 ml of oxalyl
column eluting with C6H14. Compound 2: Yield: 34%
1
(0.10 g, 0.20 mmol); H NMR (CDCl3): d 7.47 (d, Jꢀ
/
8.1 Hz, 2H), 7.33 (d, Jꢀ
/
8.1 Hz, 2H), 7.20 (d, Jꢀ15.3
/
Hz, 1H), 6.87 (d, Jꢀ15.3 Hz, 1H), 6.28 (s, 1H) ppm; IR
/
(KBr): nCO 2093 (s), 2026 (s), 2000 (s) cmꢂ1. Anal.
Found: C, 38.68; H, 1.26. Calc. for C16H7BrCo2O6: C,
chloride) in 20 ml of CH2Cl2 was added 10* at ꢂ
78 8C. After the solution was stirred for 15 min at ꢂ
/
1
38.98; H, 1.43%. Compound 2-1: Yield: 34%; H NMR
/
(CDCl3): d 7.50 (d, Jꢀ
/
8.3 Hz, 2H), 7.23 (d, Jꢀ
/
8.3 Hz,
78 8C, Et3N (5 ml) was added. The resulting solution
was allowed to warm to r.t. for 40 min. To the solution
were added CH2Cl2 (20 ml) and NH4Cl solution (20 ml).
The CH2Cl2 layer was chromatographed on a silica gel
column eluting with C6H14 and Et2O (5:1). Removal of
2H), 6.64 (d, Jꢀ11.3 Hz, 1H), 6.59 (d, Jꢀ
/
/11.3 Hz, 1H),
5.98 (s, 1H) ppm; IR (KBr): nCO 2093 (s), 2053 (s), 2022
(s) cmꢂ1. Anal. Found: C, 38.77; H, 1.69. Calc. for
C16H7BrCo2O6: C, 38.98; H, 1.43%.
the solvent gave 4* in 28% yield (0.40 g). Compound
1
2.1.2. Synthesis of 3
10*: H NMR (CDCl3): d 7.49Á
/
7.26 (m, 15H), 5.21 (d,
4.7, 14.2 Hz, 1H), 3.89
7.4, 14.3 Hz, 1H) ppm; 31P NMR (CDCl3): d
The same procedure as for the syntheses of 2 and 2-1
was applied except for the use of (4-nitrobenzyl)triphe-
nylphosphonium bromide instead of (4-bromoben-
zyl)triphenylphosphium bromide. trans- and cis-
Isomers were separated by chromatography on a silica
gel column eluting with C6H14 and Et2O (v/v, 5:1).
Compound 3: Yield: 37%; 1H NMR (CDCl3): d 8.20 (d,
Jꢀ
/
3.6 Hz, 1H), 4.18 (dd, Jꢀ
/
(dd, Jꢀ
/
53.83 ppm; IR (KBr): nCO 2059 (s), 2005 (s) cmꢂ1. Anal.
Found: C, 53.82; H, 3.50. Calc. for C26H17Co2O6P: C,
54.19; H, 3.32%.
2.1.5. Synthesis of 5
Jꢀ
/
8.4 Hz, 2H), 7.59 (d, Jꢀ
/
8.4 Hz, 2H), 7.40 (d, Jꢀ
/
Compound 1 (0.20 g, 0.59 mmol), PPh3 (0.48 g, 1.77
mmol), and 30 ml of THF were added to a Schlenk
flask. The solution was heated at reflux under N2 for 3
h. After the solution was cooled to r.t., any solids were
filtered off and the filtrate was evaporated to dryness.
The crude product was purified by chromatography on
a silica gel column eluting with C6H14 and Et2O (v/v,
15.3 Hz, 1H), 6.95 (d, Jꢀ
/15.3 Hz, 1H), 6.32 (s, 1H)
ppm; IR (KBr): nCO 2093 (s), 2055 (s), 2022 (s), 2000 (s),
1961 (s) cmꢂ1. Anal. Found: C, 41.71; H, 1.68; N, 3.05.
Calc. for C16H7Co2NO8: C, 41.86; H, 1.54; N, 3.05%.
Compound 3-1: Yield: 37%; H NMR (CDCl3): d 8.24
(d, Jꢀ
1
/
8.7 Hz, 2H), 7.53 (d, Jꢀ8.7 Hz, 2H), 6.81 (d,
/

I.S. Lee et al. / Inorganica Chimica Acta 343 (2003) 41Á
/
50
43
3:1). Removal of the solvent gave brown solids in 85%
1
yield (0.41 g, 0.50 mmol). H NMR (CDCl3): d 9.08 (s,
and crystals of 7 by slow evaporation of 7 in C6H14,
respectively. Single-crystal X-ray diffraction experi-
1H), 7.38 (m, 30H), 4.61 (t, Jꢀ
/
3.0 Hz, 1H) ppm; 31P
ments were performed on an EnrafÁ
/
Nonius CAD4 for
NMR (CDCl3): d 49.46 ppm; IR (KBr): nCO 2026 (br s),
1971 (s), 1644 (s) cmꢂ1. Anal. Found: C, 63.58; H, 4.20.
Calc. for C43H32Co2O5P2: C, 63.88; H, 3.99%.
2 and 6 and an EnrafÁNonius CCD diffractometer for
/
7. Unit cells were determined by centering 25 reflections
in the appropriate 2u range. Other relevant experimen-
tal details are listed in Table 3. Structures were solved by
direct methods using SHELXS-86 and refined by full-
matrix least-squares with SHELXL-93. All non-hydrogen
atoms were refined anisotropically; hydrogen atoms
were refined isotropically using the riding model with
1.2 times the equivalent isotropic temperature factors of
the atoms to which they are attached.
2.1.6. Synthesis of 6
The same procedure as for the synthesis of 2 was
applied except using 4 instead of 1. Yield: 76%. 1H
NMR (CDCl3): d 8.11 (d, Jꢀ
15H), 7.23 (d, Jꢀ8.9 Hz, 2H), 6.68 (d, Jꢀ
6.36 (d, Jꢀ15.4 Hz, 1H), 5.47 (d, Jꢀ3.3 Hz, 1H) ppm;
/8.8 Hz, 2H), 7.37 (m,
/
/15.3 Hz, 1H),
/
/
31P NMR (CDCl3): d 53.15 ppm; IR (KBr): nCO 2061
(br s), 2010 (s), 1961 (s) cmꢂ1. Anal. Found: C, 57.05;
H, 3.18; N, 1.92. Calc. for C34H32Co2NO8P: C, 57.16;
H, 3.20; N, 2.02%.
2.3. Hyperpolarizability measurement
The experiments were performed at a wavelength of
1064 nm with a mode-locked Q-switched Nd:YAG laser
(Spectron SL803G). Solutions of p-nitroaniline in
2.1.7. Synthesis of 6*
Ylide (0.50 g, 1.0 mmol) and t-BuOK (0.13 g, 1.4
mmol) in 10 ml of THF were stirred with a catalytic
amount of 18-crown-6 for 1 h. Compound 4* (0.40 g,
0.70 mmol) was added to the solution. After the
resulting solution was stirred for 5 h, excess CH2Cl2
(50 ml) and saturated aq. NaCl solution (50 ml) were
added. The CH2Cl2 layer was chromatographed on a
silica gel column eluting with C6H14 and Et2O (5:1).
Removal of the solvent gave 6* in 82% yield (0.40 g).
MeCN were used as internal reference (b (CH3CN)ꢀ
/
29.2ꢃ
/
10ꢂ30 esu) [7]. The general experimental setup is
described in Ref. [2c].
2.4. Calculation of hyperpolarizability
The computational study of the quadratic hyperpo-
larizability of compounds 2Á8 has been carried out with
/
the ab initio method. The starting geometries are chosen
from the experimentally determined X-ray structures 2
and 6 without further optimizations. For 7 and 8, the
2.1.8. Synthesis of 7
The same procedure as for the synthesis of 6 was
applied using excess PPh3. Yield: 91%. 1H NMR
geometry is first optimized in the HartreeÁFock (HF)
/
level from the starting structures based on the X-ray
structures of the related structure of the series. Geome-
try optimization and energy calculation were carried out
by the density functional (B3-LYP) method using the 3-
21G* basis set. The dipole moment and hyperpolariz-
ability were calculated by the five-point finite difference
method [7,8], which employs the results from 13 SCF
calculations with the STO3G basis set on the optimized
structure. Numerical calculations have been performed
with the program JAGUAR 4.0 [8].
(CDCl3): d 7.99 (d, Jꢀ
6.81 (d, Jꢀ8.9 Hz, 2H), 6.61 (d, Jꢀ
(d, Jꢀ
15.2 Hz, 1H), 4.60 (br s, 1H) ppm; 31P NMR
/8.9 Hz, 2H), 7.36 (m, 30H),
/
/
15.2 Hz, 1H), 5.24
/
(CDCl3): d 52.07 ppm; IR (KBr): nCO 2014 (s), 1966 (s),
1953 (s), 1925 (s) cmꢂ1. Anal. Found: C, 64.34; H, 4.08;
N, 1.36. Calc. for C50H37Co2NO6P2: C, 57.16; H, 3.20;
N, 2.02%.
2.1.9. Synthesis of 8
The same procedure as for the synthesis of 7 was
applied except for the use of AsPh3 instead of PPh3.
1
Yield: 45%. H NMR (CDCl3): d 7.89 (d, Jꢀ
/
9.0 Hz,
8.7 Hz, 2H), 6.39 (d,
15.5 Hz, 1H), 4.53 (br s,
3. Results and discussion
2H), 7.30 (m, 30H), 6.71 (d, Jꢀ
Jꢀ15.5 Hz, 1H), 5.19 (d, Jꢀ
/
/
/
3.1. Synthesis
1H) ppm; 31P NMR (CDCl3): d 52.36 ppm; IR (KBr):
nCO 2061 (s), 2015 (s), 1953 (s), 1926 (s) cmꢂ1. Anal.
Found: C, 61.73; H, 3.92; N, 1.43. Calc. for C50H37As-
Co2NO6P: C, 61.81; H, 3.84; N, 1.44%.
Enyne dicobalt carbonyl complexes 2 and 3, in which
electron-rich (alkyne)Co2(CO)6 fragment is conjugated
with an electron withdrawing organic part, have been
prepared by applying the Wittig reaction to an aldehyde
2.2. Crystal structure determinations of 2, 6, and 7
complex 1, (HCÅ
/
CÃ
/
CHO)Co2(CO)6, using an appro-
priate ylide. Compound 1 has been prepared by a
published procedure [6]. Treatment of 1 with ylides p-
Crystals of 2 were grown by slow evaporation of a
mixture solution of 2 in C6H14 and CH2Cl2, crystals of 6
by slow diffusion of C5H12 to a CH2Cl2 solution of 6,
XÃ
/
C6H4CHÄ
/
PPh3 (XꢀBr, NO2), generated in situ by
/
the reaction of the corresponding phosphonium bro-

44
I.S. Lee et al. / Inorganica Chimica Acta 343 (2003) 41Á
/
50
Scheme 1.
mide and KtOBu in THF, afforded (HCÅ
C6H4ÃX-p)Co2(CO)6 (2, XꢀBr; 3, Xꢀ
mixture of E and Z isomers in the ratio 1:1 (Eq. (1)).
/
CÃ
/
CHÄ
/
CHÃ
/
In general, an asymmetric electron distribution, which
is closely related to quadratic hyperpolarizability, is
improved by increasing the strength of the electron
/
/
/
NO2) as a
ð1Þ
Chromatography of the mixture on a silica gel led to
isolation of 2 and 3 with an E configuration in 34 and
37% yield, respectively. We expected that these com-
pounds would fulfil the basic requirements for NLO
chromophores: they contain (alkyne)Co2(CO)6 as an
electron donor group and nitro- or bromobenzene as an
electron acceptor group, and a conjugated bridge linking
the two fragments.
donor or acceptor [9]. To increase the electron donor
ability of alkyne dicobalt carbonyl fragment, the p-
accepting CO ligand of 1 was replaced by a s-donating
phosphine ligand. Refluxing 1 with an equivalent of
PPh3 gave (HCÅ
major product. Treatment of 1 with excess PPh3
afforded the doubly substituted CÃ
(HCÅ
CHO)Co2(CO)4(PPh3)2 in 85% yield (Eq. (2)).
/
CÃ/CHO)Co2(CO)5(PPh3) (4), as a
5
/
/
ð2Þ

I.S. Lee et al. / Inorganica Chimica Acta 343 (2003) 41Á
/
50
45
Table 1
Measured quadratic hyperpolarizabilities
wavelength using p-nitroaniline in chloroform as an
external standard (Table 1) [7]. The hyperpolarizability
a
values increase in the order 2B
/
3B
/
6B
/
7B8. Since all
/
2
3
6
7
8
studied compounds have absorption around 532 nm, the
contribution of resonance enhancement to b should be
considered. To estimate the dispersion-corrected b
(static hyperpolarizability, b0), the two-state model has
been used [10]. The order of the static hyperpolariz-
ability b0 is the same as that of b. Hyperpolarizability
calculation has been carried out with the ab initio
method. The results of the theoretical calculations are
summarized in Table 2. The order of hyperpolarizability
lmax (nm)
b (10ꢂ30 esu)
328
52
352
84
372
144
394
227
395
244
a
All the measurements were carried out in chloroform.
Treatment of 4 with p-NO2Ã
/
C6H4CHÄ
/
PPh3 yielded
[(E)-(HCÅCÃCHÄCHÃC6H4ÃNO2-p)Co2(CO)5(PPh3)
/
/
/
/
/
(6) in 76% yield as a sole product. Formation of a Z-
isomer was not observed. When 5 was treated with p-
NO2Ã
/
C6H4CHÄ
/
PPh3, no reaction occurred presumably
values (2B
/
3B
/
6B
/
7B8) is correctly reproduced in the
/
due to the increased electron density on the metal.
To increase the electron density on the metal center, a
carbonyl ligand in 6 was replaced by phosphine or
theoretical predictions. Considering the limitations of
theoretical calculations and the uncertainties in the
estimation of b0 from the experimental results, quanti-
tative comparisons between them are somewhat diffi-
cult.
arsine. Refluxing 6 with PPh3 gave [(E)-(HCÅ
CHÃC6H4ÃNO2-p)Co2(CO)4(PPh3)2] (7) in 91% yield
and treatment of 6 with AsPh3 gave [(E)-(HCÅCÃCHÄ
NO2-p)Co2(CO)4(PPh3)(AsPh3)] (8) in 45%
/
CÃ
/
CHÄ
/
/
/
/
/
/
Molecular hyperpolarizabilities increase in the order
CHÃ
/
C6H4Ã
/
2B/3, reflecting the high electron acceptability of the
yield (Eq. (3)).
nitro group. This observation implies that (alky-
ð3Þ
3.2. Hyperpolarizability measurement
ne)Co2(CO)6 fragment serves as an electron-donating
group. It is not unusual for metal carbonyls to act as an
electron-donating group in the second order NLO
Chart 1 shows compounds for which hyperpolariz-
ability measurements were made, and Table 1 shows the
results. The hyperpolarizability values of all complexes
were determined in chloroform at 1064 nm fundamental
pushÁpull system [2].
/
Substitution of carbonyl ligand by weaker p-accepting
and better s-donating ligands such as PPh3 and AsPh3
Table 2
Hyperpolarizabilities for a series of compounds given in Chart 1
2
3
6
7
8
a
DE (au)
0.12648
1.92
5.81
0.12628
3.24
0.11458
3.29
0.10203
2.36
0.00664
1.57
b
m
(au)
b0 (10ꢂ30esu)
c
20.2
30.4
64.7
87.7
a
DEꢀELUMOꢂEHOMO
m, the dipole moment.
b0, the static obtained from the ab initio calculations.
.
b
c

46
I.S. Lee et al. / Inorganica Chimica Acta 343 (2003) 41Á50
/
Fig. 1. Molecular structure of 2, with the atom-labelling scheme.
leads to more electron-rich metal fragments. The order
of hyperpolarizabilities of 3B6B7B8 is exactly coin-
between C1Ã
/
C2Ã
/
C3 is 142.158. The fragment Ã
/
CHÄ
/
/
/
/
CHÃC6H4Ã
/
/
of a conjugated pathway between the
electron donor and acceptor is almost planar with a
cident with that of the electron richness of metal
fragment. The increased electron density of the metal
center should rise with the increase of the electron-
donating ability of the metal fragment and thereby
enhance the molecular non-linearity. Especially, the
hyperpolarizabilities of 7 and 8, in which two carbonyl
ligands are substituted, are about three times larger than
that of 3. Thus, the ligand substitution can be used to
optimize non-linear properties.
dihedral angle of 9.188. The centrosymmetric nature of
¯
crystal structure of 2 (space group, P1) suggests that
there may be no NLO behavior in the bulk phase.
Single crystals of 6 were obtained by slow diffusion of
pentane to a dichloromethane solution. The bond length
˚
(2.4737(8) A) between Co1 and Co2 is similar to that of
˚
2. The bond length between C1 and C2 is 1.340(5) A,
˚
which is about 0.03 A greater than that of 2. The greater
C1Ã/C2 bond length of 6 may reflect the increased
electron density on the metal center and suggests a
larger molecular hyperpolarizability. The conjugated
3.3. X-ray crystal structures of 2, 6, and 7
electron pathway Ã
with a dihedral angle of 13.118. In the unit cell two
enantiomers of 6 are located with an inverse relation
/
CHÄ
/
CHÃ
/
C6H4Ã
/
is roughly planar
The thermal ellipsoid plots shown in Figs. 1Á3 depict
/
the structures determined in this work. Crystal data and
structure refinements for 2, 6, and 7 are given in Table 3
and selected bond lengths and angles in Table 4. The
¯
(space group, P1):
/
Single crystals of 7 were obtained by slow evaporation
of a hexane solution of 7. The bond length between
˚
Co(1) and Co(2) is lengthened to 2.4986(7) A presum-
perpendicular geometry between the CÃ
/
C triple bond
and the CoÃCo bond is consistent with the alkyne-
/
dicobalt geometry described in previous literature [11].
Single crystals of 2 were grown in a mixture solvent of
hexane and dichloromethane. The coordination geome-
try of the metal center does not exhibit any noticeable
ably due to the steric effects of two phosphine ligands.
The presence of two trans phosphine ligands pushes
C(1) and C(2) close to each other and the resulting bond
˚
length between C1 and C2 is 1.314(5) A, which is about
deviation from that of regular alkyne dicobalt com-
˚
0.02 A shorter than that of 6. The conjugated electron
˚
˚
plexes [12]. The CoÃ
shorter than the CoÃ
[Co2(CO)8] [13], but is similar to CoÃ
in related m-alkyne complexes [14]. The bond length
/
Co bond length (2.468(2) A) is
pathway Ã
/
CHÄ
/
CHÃ
/
C6H4Ã
/
is quite twisted with a
/
Co bond length of 2.52 A in
Co lengths found
dihedral angle of 21.048 presumably due to the ancillary
ligand. It has been well known that steric interactions
with the ancillary ligands bound to cobalt play a major
/
˚
between C1 and C2 is 1.301 A and the dihedral angle

I.S. Lee et al. / Inorganica Chimica Acta 343 (2003) 41Á
/
50
47
Fig. 2. Molecular structure of 6, with the atom-labelling scheme.
role in determining the confirmation of m-alkyne ligand
coordinated to dicobalt [15].
The centrosymmetric nature of crystal structures of 2,
¯
6, and 7 (space group, P1) suggests that there may be no
NLO behavior in the bulk phase.
3.4. Synthesis of optically pure 6*
As mentioned in the previous sections, compounds 2Á
8 exhibit a molecular response. However, due to their
/
centrosymmetric nature in the crystal structures they do
ð4Þ

48
I.S. Lee et al. / Inorganica Chimica Acta 343 (2003) 41Á50
/
Fig. 3. Molecular structure of 7, with the atom-labelling scheme.
not show NLO behavior in the bulk phase. Non-zero
bulk NLO activity requires non-centrosymmetric crystal
packing. One way to ensure non-centrosymmetric crys-
tal packing is to introduce chiral element(s) into the
molecule. Thus, we synthesized optically pure 6*.
4. Conclusion
In this paper we have synthesized a series of new
donorÁ
CHÃC6H4Ã
L2ꢀ
CO; 3, Xꢀ
L1ꢀCO, L2ꢀ
PPh3; 7, Xꢀ
Xꢀ PPh3). The concept of using
NO2, L1ꢀAsPh3, L2ꢀ
/
acceptor compounds of the form [(HCÅ
X-p)Co2(CO)4(L1)(L2)] (2, XꢀBr, L1ꢀ
NO2, L1ꢀL2ꢀ
CO; 6, XꢀNO2,
NO2, L1ꢀL2ꢀ
PPh3; 8,
/
CÃ
/
CHÄ
/
/
/
/
/
/
/
/
/
/
Diastereomer
9*
of
[(ꢂ)-mentyl-propargyl
/
/
/
/
/
/
ether]Co2(CO)5(PPh3) was prepared and separated ac-
cording to a published procedure [16]. The molecular
crystal structure of 9* was determined by X-ray diffrac-
tion study. Nicholas reaction [17] of 9* followed by
/
/
/
the (alkyne)Co2(CO)4(L1)(L2) moiety as an electron
donor was rewarded by high b values of complexes
with good s-donor and poor p-acceptor ligands L1 and
L2. Transformation of 2 into 8 led to five times increase
of b values. An optically pure 6* has been synthesized
but racemized slowly at room temperature.
Swern oxidation gave an enantiomerically pure [(HCÅ
CÃCHO)Co2(CO)5(PPh3)] (4*), in 28% yield. Wittig
reaction of 4* with p-NO2ÃC6H4ÃCÄPPh3 gave an
optically pure [((E)-HCÅCÃCHÄCHÃC6H4ÃNO2-
p)Co2(CO)5(PPh3)] (6*), in 82% yield (Eq. (4)).
/
/
/
/
/
/
/
/
/
/
The optical purity of 6* could be confirmed by chiral
HPLC. Unfortunately, 6* is an oily compound. Thus,
we could not measure the SHG of 6*. It was slowly
racemized at room temperature to give a solid com-
pound.
5. Supplementary material
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic

I.S. Lee et al. / Inorganica Chimica Acta 343 (2003) 41Á
/
50
49
Table 3
Crystal data and refinement for 2, 6 and 7
(fax:
ac.uk or www: http://www.ccdc.cam.ac.uk).
ꢁ44-1223-336-033; e-mail: deposit@ccdc.cam.
/
2
6
7
Empirical for-
mula
C
16H7BrCo2O6 C33H22Co2NO7P C50H37Co2NO6P2
Acknowledgements
Formula
weight
Crystal system triclinic
492.99
693.35
927.61
Y.K.C. is grateful for the financial support from
KOSEF (1999-1-122-001-5) and KOSEF through the
Center for Molecular Catalysis at Seoul National
University, and I.S.L. and D.M.S. acknowledge the
award of fellowship by the Brain Korea 21.
triclinic
¯
triclinic
¯
¯
Space group
˚
/
P1/
/
P1/
/
P1/
a (A)
˚
6.8109(10)
7.7813(10)
17.6658(10)
80.051(10)
86.534(10)
76.257(10)
895.6(2)
2
9.6315(12)
10.026(2)
18.899(5)
97.92(2)
96.59(2)
118.059(13)
1561.0(6)
2
9.9966(5)
12.8973(6)
18.3542(8)
79.433(3)
89.428(3)
69.590(2)
2176.47(18)
2
b (A)
˚
c (A)
a (8)
b (8)
g (8)
V (A )
Z
Dcalc (Mg
mꢂ3
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Selected bond distances (A) and angles (8) for 2, 6 and 7
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6
7
Bond distances
Co(1)ÃC(1)
Co(1)ÃCo(2)
BrÃC(8)
Co(1)ÃC(2)
Co(2)ÃC(1)
Co(1)ÃC(05)
C(1)ÃC(2)
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Co(1)ÃC(1)
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Co(2)ÃC(2)
C(8)ÃN(1)
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2.4737(8)
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1.956(4)
1.976(4)
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2.2055(11)
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1.459(6)
Co(1)ÃC(1)
Co(1)ÃCo(2)
Co(2)ÃP(2)
N(1)ÃC(8)
Co(1)ÃC(2)
Co(2)ÃC(1)
Co(1)ÃC(11)
N(1)ÃO(5)
Co(1)ÃP(1)
Co(2)ÃC(2)
C(1)ÃC(2)
1.951(4)
2.4986(7)
2.2252(11)
1.469(5)
1.977(4)
1.945(4)
1.776(4)
1.205(5)
2.2254(10)
1.982(3)
1.314(5)
Co(2)ÃC(2)
Bond angles
C(1)ÃC(2)ÃC(3)
Co(2)ÃC(1)ÃCo(1)
Co(1)ÃC(2)ÃCo(2)
139.5(12)
79.34(4)
77.6(3)
Co(1)ÃC(2)ÃCo(2)
C(1)ÃC(2)ÃC(3)
Co(1)ÃC(1)ÃCo(2)
77.93(13)
142.3(4)
78.44(14)
C(1)ÃC(2)ÃC(3)
Co(2)ÃC(1)ÃCo(1)
Co(1)ÃC(2)ÃCo(2)
147.8(4)
79.78(14)
78.26(12)

50
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