Synthesis, characterization, and second-harmonic generation studies of surfactant rhenium(I) diimine complexes in Langmuir-Blodgett films. X-ray crystal structure of fac-ClRe(CO)3L (L = 9-heptylamino-4,5-diazafluorene)

Article abstract of DOI:10.1021/om970998f

A series of surfactant complexes of general formula, fac-CIRe(CO)₃L (L = 9-octadecylamino4,5-diazafluorene, 9-(4′-hexadecylanilino)-4,5-diazafluorene, N-(4′-hexadecylphenyl)pyridine2-carbaldimine, and 9-heptylamino-4,5-diazafluorene), were synthesized and characterized by elemental analyses and ¹H NMR, UV-vis, IR, and luminescence spectroscopy. The complex fac-CIRe(CO)₃L (L = 9-heptylamino-4,5-diazafluorene) was structurally characterized. The formation and optical properties of their Langmuir-Blodgett (LB) films were studied by surface pressure-area (π-A) isotherms and UV-vis and luminescence spectroscopy, and the second-harmonic generation (SHG) behavior was also investigated.

Full text of DOI:10.1021/om970998f

2440
Organometallics 1998, 17, 2440-2446
Syn th esis, Ch a r a cter iza tion , a n d Secon d -Ha r m on ic
Gen er a tion Stu d ies of Su r fa cta n t Rh en iu m (I) Diim in e
Com p lexes in La n gm u ir -Blod gett F ilm s. X-r a y Cr ysta l
Str u ctu r e of fa c-ClRe(CO)3L (L )
9-Hep tyla m in o-4,5-d ia za flu or en e)
Vivian Wing-Wah Yam,* Ke-Zhi Wang, Chun-Ru Wang, Yu Yang, and
Kung-Kai Cheung
Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong
Received November 13, 1997
A series of surfactant complexes of general formula, fac-ClRe(CO)3L (L ) 9-octadecylamino-
4,5-diazafluorene, 9-(4′-hexadecylanilino)-4,5-diazafluorene, N-(4′-hexadecylphenyl)pyridine-
2-carbaldimine, and 9-heptylamino-4,5-diazafluorene), were synthesized and characterized
by elemental analyses and 1H NMR, UV-vis, IR, and luminescence spectroscopy. The
complex fac-ClRe(CO)3L (L ) 9-heptylamino-4,5-diazafluorene) was structurally character-
ized. The formation and optical properties of their Langmuir-Blodgett (LB) films were
studied by surface pressure-area (π-A) isotherms and UV-vis and luminescence spectros-
copy, and the second-harmonic generation (SHG) behavior was also investigated.
In tr od u ction
been found to show interesting optical, electrical, and
magnetic properties but so far have not been as well-
explored as those of their organic counterparts.7,8 As a
d6 luminescent transition-metal system, Ru(II) surfac-
tant complexes for LB films have been well investi-
gated,8 aimed at modification of properties such as those
of film formation, luminescence and UV-vis spectros-
copy, modified electrodes, photochemical cleavage of
water into H2 and O2, and second-order nonlinear optical
behavior.8,9 However, surfactant Re(I) complexes for LB
films have not been reported so far. To extend the types
of compounds available for LB film studies and to
increase their potential applications, a research program
studying LB films of Re(I) complexes has been launched
by our group.10
Rhenium(I) complexes of general formula fac-ClRe-
(CO)3L (L ) R,R′-diimine) have been receiving growing
interest in recent years, largely due to their potential
uses as sensitizers and catalysts for solar energy
conversion, electron-transfer reactions, and reduction
of carbon dioxide in homogeneous solution and at
electrode surfaces.1-4 These complexes have been found
to show attractive excited-state redox properties and
intense luminescence in the visible region of the spec-
trum, are stable to photodecomposition,5 and are well-
suited for the applications addressed above.
The Langmuir-Blodgett technique is one of the
powerful tools of making highly homogeneous, ordered
ultrathin films for the development of future molecular
devices.6 The LB films based on metal complexes have
On the other hand, second-order nonlinear optical LB
films have become one of the active fields of research
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S0276-7333(97)00998-9 CCC: $15.00 © 1998 American Chemical Society
Publication on Web 05/13/1998

Crystal Structure of fac-ClRe(CO)3L
Organometallics, Vol. 17, No. 12, 1998 2441
due to their promising applications in photonic devices.11
Most of the second-order nonlinear optical materials
reported are of conventional donor-π-acceptor struc-
tures. Recently, strong second-harmonic generation
from the LB films of surfactant Ru(II) complexes
without the conventional donor-π-acceptor structures
has been observed and attributed to metal-to-ligand
charge-transfer (MLCT) excitation.9 It was also found
that several powder samples of Re(I) pyridine and
bipyridine complexes had SHG efficiencies roughly
comparable to urea (SHG at 532 nm). For example,
[ReCl(CO)3(2,2′-bipyridine)] had a powder efficiency of
1.7-2 times that of urea.12
La n gm u ir -Blod gett F ilm s. Ultrapure water (resistance
> 18 MΩ cm) was obtained from an Elga UHQ PS apparatus
and immediately used for LB film preparation. The complexes
in chloroform (0.89 mg cm-3 for fac-ClRe(CO)3L1, 1.38 mg cm-3
for fac-ClRe(CO)3L2, and 1.0 mg cm-3 for fac-ClRe(CO)3L3)
were spread onto a pure water phase (pH 5.4, 18 °C) in a Nima
model-622 computer-controlled trough. After a 15-min vapor-
ization of the solvent, surface pressure-area (π-A) isotherms
were recorded at a barrier compression speed of 150 cm2 min-1
.
The monolayers formed under a constant surface pressure (10
mN m-1 for both fac-ClRe(CO)3L1 and fac-ClRe(CO)3L2 and
20 mN m-1 for fac-ClRe(CO)3L3) were transferred onto hy-
drophilically treated substrates of quartz after maintaining a
constant pressure at the transfer pressure for 30 min for
stabilization, at a dipping speed of 15 mm min-1. The transfer
ratios were close to unity. The substrates were made hydro-
philic by consecutive sonication in detergent for 30 min and
chloroform-ethanol for 15 min and soaking in both chromic
acid and piranha solution14 (30% H2O2-H2SO4, 3:7 v/v) for 8
h each before they were finally washed repeatedly with copious
amounts of distilled and ultrapure water.
Herein, we report the synthesis, characterization, and
LB film studies of a series of new, robust, and easily
accessible surfactant Re(I) complexes and the second-
order nonlinear optical properties of these LB films.
Exp er im en ta l Section
Secon d -Ha r m on ic Gen er a tion (SHG). The setup for
SHG was similar to that reported previously.7a,b The source
was the fundamental 1064 nm light of a Quanta-Ray Q-
switched GCR-150-10 pulsed Nd:YAG laser. The 532-nm light
signals generated were recorded on a Tektronix TDS-620A
digital oscilloscope. Prior to the SHG measurements, the
monolayer films at the backsides of the substrates were wiped
off carefully with lens tissues soaked in chloroform in order
to prevent interference between signals arising from the
monolayers at the front and backside of the substrate.
Syn th esis. Synthetic schemes for the ligands and the
rhenium(I) complexes are summarized in Scheme 1.
Liga n d Syn th esis. 9-Octa d ecyla m in o-4,5-d ia za flu o-
r en e (L1). L1 was synthesized by modification of a literature
method.15 A mixture of octadecylamine (1.9 mmol), 4,5-
diazafluoren-9-one (1.8 mmol), and 4-toluenesulfonic acid
(0.013 g, 0.068 mmol) was dissolved in 20 mL of toluene. The
mixture was refluxed in an oil bath for 24 h, during which a
Dean-Stark apparatus was used to drive the reaction. Most
of the solvent was then driven off under reduced pressure in
a water bath. Petroleum ether (40-60 °C) was added with
vigorous stirring until the solution became cloudy. On cooling
in a refrigerator overnight, the precipitate formed was filtered
off and characterized as mainly unreacted 4,5-diazafluoren-
9-one. The filtrate was then evaporated to dryness, and the
residue was recrystallized twice from petroleum ether (60-
80 °C) to afford the desired product (0.28 g). Yield: 63%. Mp:
79.5 °C. 1H NMR (300 MHz, CDCl3, relative to Me4Si): δ 8.75
(m, 2H), 8.18 (m, 2H), 7.34 (m, 2H), 4.18 (t, 2H, J ) 7.1 Hz),
1.94 (m, 2H), 1.54 (m, 2H), 1.26 (m, 28H), 0.88 (t, 3H, J ) 6.7
Hz). UV-vis (CHCl3, λ/nm (ꢀ × 10-3/dm3 mol-1 cm-1)): 306
(8.90), 316 (9.75). EI-MS m/z: 443 (M+). Anal. Calcd for
Ma ter ia ls. Pyridine-2-carboxaldehyde (Aldrich) was dis-
tilled before use. Heptylamine (Aldrich) was distilled over
KOH. Octadecylamine (98%, Aldrich), 4-hexadecylaniline
(97%, Aldrich), and Re(CO)5Cl (98%, Strem) were used as
received. 4,5-Diazafluoren-9-one was prepared as reported
previously.13
In str u m en ta tion a n d Equ ip m en t. The UV-vis spectra
were obtained on
a Hewlett-Packard 8452A diode array
spectrophotometer, IR spectra as Nujol mulls on a Bio-Rad
FTS-7 spectrophotometer, and steady-state excitation and
emission spectra on a Spex Fluorolog-2 111 spectrofluorometer
with or without Corning filters. Low-temperature (77 K)
spectra were recorded using an optical Dewar sample holder.
Proton NMR spectra were recorded on a Bruker DPX-300
NMR spectrometer with chemical shifts reported relative to
tetramethylsilane. Positive-ion fast-atom bombardment (FAB)
and electron-impact (EI) mass spectra were recorded on a
Finnigan MAT95 mass spectrometer. Elemental analyses
were performed on a Carlo Erba 1106 elemental analyzer at
the Institute of Chemistry, Chinese Academy of Sciences.
Emission lifetime measurements were made using a con-
ventional laser system. The excitation source was the 355 nm
output (third harmonic) of a Quanta-Ray Q-switched GCR-
150-10 pulsed Nd:YAG laser. Luminescence decay signals
were recorded on a Tektronix TDS 620A digital oscilloscope
and analyzed using a program for exponential fits according
to the equation I(t) ) I0 exp(-t/τ), where I(t) is the emission
intensity at time t after laser pulse and I0 is the initial
intensity at t ) 0. All solutions for photophysical studies were
prepared under vacuum in
a
10-cm3 round-bottom flask
equipped with a sidearm 1-cm fluorescence cuvette sealed from
the atmosphere by a Kontes quick-release Teflon stopper.
Solutions were rigorously degassed with no fewer than 4
freeze-pump-thaw cycles.
C
29H43N3: C, 80.37; H, 9.93; N, 9.70. Found: C, 80.52; H, 10.1;
N, 9.80.
9-(4′-h exa d ecyla n ilin o)-4,5-d ia za flu or en e (L2). L2 was
synthesized as described for L1 except that 4-hexadecylaniline
was used instead of octadecylamine. The product was purified
by recrystallization from dichloromethane-petroleum ether
twice (40-60 °C). Yield: 79%. Mp: 107 °C. 1H NMR (300
MHz, CDCl3, relative to Me4Si): δ 8.80 (m, 1H), 8.64 (m, 1H),
8.25 (m, 1H), 7.40 (m, 1H), 7.24 (d, 2H, J ) 8.4 Hz), 6.96 (m,
4H), 2.67 (t, 2H, J ) 7.7 Hz), 1.26 (m, 28H), 0.88 (t, 3H, J )
6.4 Hz). UV-vis (CHCl3, λ/nm (ꢀ × 10-3/dm3 mol-1 cm-1)): 306
(8.02), 316 (8.01), 424 (1.50). EI-MS m/z: 481 (M+). Anal.
Calcd for C33H43N3: C, 82.33; H, 8.94; N, 8.73. Found: C, 82.19;
H, 9.03; N, 8.52.
(10) (a) Yam, V. W. W.; Lau, V. C. Y.; Wang, K. Z.; Cheung, K. K.;
Huang, C. H. J . Mater. Chem. 1998, 8, 89. (b) Lau, V. C. Y. Ph.D.
Thesis, The University of Hong Kong, 1997.
(11) (a) Materials for Nonlinear Optics, Chemical Perspectives;
Marder, S. R.; Sohn, J . E.; Stucky, G. D., Eds.; ACS Symp. Series;
American Chemical Society: Washington, DC, 1991; p 455. (b) Prasad,
P. N.; Williams, D. J . Introduction to Nonlinear Optical Effects in
Molecules and Polymers; Wiley: New York, 1991. (c) Marks, T. J .;
Ratner, M. A. Angew. Chem., Int. Ed. Engl. 1995, 34, 155. (d) Green,
M. L. H.; Marder, S. R.; Thompson, M. E. Nature 1987, 330, 108. (e)
Richardson, T.; Roberts, G. G.; Polywka, M. E. C.; Davies, S. G. Thin
Solid Films 1989, 179, 405.
(12) (a) Calabrese, J . C.; Tam, W. Chem. Phys. Lett. 1987, 133, 244.
(b) Anderson, A. G.; Calabrese, J . C.; Tam, W.; Williams, I. D. Chem.
Phys. Lett. 1987, 134, 392.
(13) Henderson, L. J . J r.; Fronczek, F. R.; Cherry, W. R. J . Am.
Chem. Soc. 1984, 106, 5876.
(14) Ulman, A. Ultrathin Organic Films; Academic Press: Boston,
1991; p 108.
(15) Tai, Z. H.; Zhang, G. C.; Qian, X. P.; Xiao, S. J .; Lu, Z. H.; Wei,
Y. Langmuir 1993, 9, 1601.

2442 Organometallics, Vol. 17, No. 12, 1998
Yam et al.
Sch em e 1. Syn th etic Rou tes of Liga n d s a n d Cor r esp on d in g Su r fa cta n t Re(I) Com p lexes
N-(4′-Hexa d ecylp h en yl)p yr id in e-2-ca r ba ld im in e (L3).
L3 was synthesized by modification of a literature procedure16
by the condensation of pyridine-2-carboxaldehyde with hexa-
decylaniline overnight in ethanol in the presence of a catalytic
amount of glacial acetic acid. The precipitate formed on
cooling was recrystallized from ethanol. Removal of any
colored impurities could be accomplished by column chroma-
tography on silica gel using diethyl ether as the eluent. Yield:
87%. Mp: 43 °C. 1H NMR (300 MHz, CDCl3, relative to Me4-
Si): δ 8.70 (d, 1H, J ) 4.9 Hz), 8.64 (s, 1H), 8.20 (d, 1H, J )
7.9 Hz), 7.83 (m, 1H), 7.38 (m, 1H), 7.26 (m, 4H), 2.63 (t, 2H,
J ) 7.7 Hz), 1.63 (m, 2H), 1.26 (m, 26H), 0.88 (t, 3H, J ) 6.7
Hz). UV-vis (CHCl3, λ/nm (ꢀ × 10-3/dm3 mol-1 cm-1)): 286
(9.17), 332 (8.47). EI-MS m/z: 408 ({M + 2}+). Anal. Calcd
for C28H42N2: C, 82.72; H, 10.35; N, 6.90. Found: C, 82.85;
H, 10.74; N, 6.68.
9-Hep tyla m in o-4,5-d ia za flu or en e (L4). L4 was synthe-
sized as described for L1 except heptylamine was used instead
of octadecylamine. Yield: 65%. Mp: 84 °C. 1H NMR (300
MHz, CDCl3, relative to Me4Si): δ 8.74 (m, 2H), 8.17 (m, 2H),
7.33 (m, 2H), 4.17 (t, 2H, J ) 7.1 Hz), 1.94 (m, 2H), 1.59 (m,
2H), 1.35 (m, 6H), 0.90 (t, 3H, J ) 6.5 Hz). 1H NMR (300 MHz,
CD3CN, relative to Me4Si): δ 8.70 (s, 2H), 8.31 (d, 1H, J ) 7.3
Hz), 8.06 (d, 1H, J ) 7.5 Hz), 7.40 (m, 2H), 4.16 (t, 2H, J )
6.5 Hz), 1.88 (m, 2H), 1.53 (m, 2H), 1.34 (m, 6H), 0.90 (t, 3H,
J ) 6.8 Hz). EI-MS m/z: 280 ({M + 1}+).
2 h. After removal of the solvent, the residue was triply
recrystallized from CH2Cl2-hexane. Yield: 80%. Slow diffu-
sion of diethyl ether vapor into an acetonitrile solution of fac-
ClRe(CO)3L4 afforded pale yellow platelike crystals suitable
for X-ray crystallographic studies.
fa c-ClRe(CO)3L1. Mp: 129 °C. 1H NMR (300 MHz, CDCl3,
relative to Me4Si): δ 8.80 (t, 2H, J ) 5.5 Hz), 8.31 (t, 2H, J )
8.4 Hz), 7.60 (m, 2H), 4.24 (t, 2H, J ) 7.0 Hz), 1.95 (m, 2H),
1.26 (m, 30H), 0.88 (t, 3H, J ) 6.4 Hz). UV-vis (CH2Cl2, λ/nm
(ꢀ × 10-4/dm3 mol-1 cm-1)): 322 (2.86), 382 (0.69). UV-vis
(LB film, λ/nm): 324. IR (Nujol, ν/cm-1): 2033 (s) ν(CO), 1928
(s) ν(CO), 1888 (vs) ν(CO). Positive FAB-MS m/z: 739 (M+);
704 ({M - Cl}+). Anal. Calcd for C32H43N3O3ClRe‚0.5H2O:
C, 51.34; H, 5.88; N, 5.61. Found: C, 51.29; H, 5.64; N, 5.57.
fa c-ClRe(CO)3L2. Mp: 138 °C. 1H NMR (300 MHz, CDCl3,
relative to Me4Si): δ 8.84 (d, 1H, J ) 7.3 Hz), 8.71 (d, 1H, J )
5.2 Hz), 8.41 (d, 1H, J ) 7.7 Hz), 7.66 (t, 1H, J ) 7.3 Hz), 7.30
(d, 2H, J ) 8.1 Hz), 7.27 (m, 1H), 7.20 (d, 1H, J ) 7.8 Hz),
6.98 (d, 2H, J ) 8.0 Hz), 2.70 (t, 2H, J ) 7.6 Hz), 1.69 (m,
2H), 1.27 (m, 26H), 0.88 (t, 3H, J ) 6.5 Hz). UV-vis (CH2Cl2,
λ/nm (ꢀ × 10-4/dm3 mol-1 cm-1)): 322 (1.49), 414 (0.56). UV-
vis (LB film, λ/nm): 328. IR (Nujol, ν/cm-1): 2038 (s) ν(CO)
1926 (vs) ν(CO), 1867 (s) ν(CO). Positive FAB-MS m/z: 787
(M+); 752 ({M - Cl}+). Anal. Calcd for C36H43ClN3O3-
Re‚0.5H2O: C, 54.27; H, 5.53; N, 5.28. Found: C, 54.42; H,
5.35; N, 5.26.
fa c-ClRe(CO)3L3. Mp: 111 °C. 1H NMR (300 MHz, CDCl3,
relative to Me4Si): δ 9.10 (d, 1H, J ) 5.4 Hz), 8.77 (s, 1H),
8.10 (m, 1H), 8.00 (d, 1H, J ) 7.5 Hz), 7.63 (m, 1H), 7.44 (d,
2H, J ) 8.4 Hz), 7.30 (d, 2H, J ) 8.3 Hz), 2.68 (t, 2H, J ) 7.8
Hz), 1.64 (m, 2H), 1.26 (m, 26H), 0.88 (t, 3H, J ) 6.6 Hz).
UV-vis (CH2Cl2, λ/nm (ꢀ × 10-4/dm3 mol-1 cm-1): 348 (1.63),
426 (0.69). UV-vis (LB film, λ/nm): 352, 434. IR (Nujol,
ν/cm-1): 2023 (s) ν(CO), 1928 (vs) ν(CO), 1895 (vs) ν(CO). Posi-
tive FAB-MS m/z: 712 (M+), 677 ({M - Cl}+). Anal. Calcd for
Syn th esis of Rh en iu m (I) Diim in e Com p lexes. fa c-
ClRe(CO)3L (L ) L1, L2, L3, a n d L4). These complexes
were synthesized by modification of a literature procedure.17
A mixture of Re(CO)5Cl (54.3 mg, 0.15 mmol) and L (0.15
mmol) in 8 mL of benzene was heated to reflux under N2 for
(16) J ohnson, D. W.; Mayer, H. K.; Minard, J . P.; Banatida, J .;
Miller, C. Inorg. Chim. Acta 1988, 144, 167.
(17) (a) Wrighton, M. S.; Morse, D. L. J . Am. Chem. Soc. 1974, 96,
998. (b) Dominey, R. N.; Hauser, B.; Hubbard, J .; Dunham, J . Inorg.
Chem. 1991, 30, 4754. (c) Caspar, J . V.; Meyer, T. J . J . Phys. Chem.
1983, 87, 952.

Crystal Structure of fac-ClRe(CO)3L
Organometallics, Vol. 17, No. 12, 1998 2443
Ta ble 1. Selected Bon d Dista n ces (Å) a n d Bon d
An gles (d eg) for Com p lex fa c-ClRe(CO)3L4
Distances
Re-Cl(1)
Re-N(2)
Re-C(2)
2.471(2)
2.233(5)
1.900(7)
Re-N(1)
Re-C(1)
Re-C(3)
2.230(5)
1.911(7)
1.921(7)
Angles
82.5(1)
89.7(2)
176.0(2)
171.2(2)
96.6(2)
172.1(2)
90.8(3)
89.1(3)
Cl(1)-Re-N(1)
Cl(1)-Re-C(1)
Cl(1)-Re-C(3)
N(1)-Re-C(1)
N(1)-Re-C(3)
N(2)-Re-C(2)
C(1)-Re-C(2)
C(2)-Re-C(3)
Cl(1)-Re-N(2)
Cl(1)-Re-C(2)
N(1)-Re-N(2)
N(1)-Re-C(2)
N(2)-Re-C(1)
N(2)-Re-C(3)
C(1)-Re-C(3)
83.4(1)
94.9(2)
78.3(2)
93.9(2)
96.8(2)
92.6(2)
90.8(3)
F igu r e 1. Perspective drawing of the complex fac-ClRe-
(CO)3L4 with atomic numbering scheme. Hydrogen atoms
have been omitted for clarity. The thermal ellipsoids are
shown at the 40% probability levels.
Resu lts a n d Discu ssion
C31H42N2ClO3Re: C, 52.27; H, 5.90; N, 3.93. Found: C, 52.25;
H, 5.76; N, 3.58.
Syn th eses. Ligand L1 was first synthesized by Tai
et al.15 in which BF3 was used as the catalyst. We
modified the procedure with the use of the more easily
handled solid 4-toluenesulfonic acid as the catalyst
instead of BF3 to give L1 and L2 in good and reproduc-
ible yields. The Re(I) complexes were subsequently
synthesized by a slight modification of a literature
method,17 by the reaction of stoichiometric amounts of
Re(CO)5Cl and L in refluxing benzene under an inert
atmosphere of nitrogen to afford fac-ClRe(CO)3L. All
of the newly synthesized complexes gave satisfactory
elemental analysis and were characterized by IR, UV-
fa c-ClRe(CO)3L4. Mp: 171 °C. 1H NMR (300 MHz, CDCl3,
relative to Me4Si): δ 8.80 (t, 2H, J ) 5.5 Hz), 8.31 (t, 2H, J )
8.8 Hz), 7.60 (m, 2H), 4.24 (t, 2H, J ) 7.0 Hz), 1.95 (m, 2H),
1.26 (m, 8H), 0.91 (t, 3H, J ) 6.5 Hz). UV-vis (CH2Cl2, λ/nm
(ꢀ × 10-4/dm3 mol-1 cm-1)): 322 (1.24), 382 (0.28). IR (Nujol,
ν/cm-1): 2025 (vs) ν(CO), 1921 (vs) ν(CO), 1890 (vs) ν(CO).
Positive FAB-MS m/z: 585 (M+), 550 ({M - Cl}+). Anal. Calcd
for C21H21ClN3O3Re: C, 43.08; H, 3.59; N, 7.18. Found: C,
43.30; H, 3.49; N, 7.16.
Cr ysta llogr a p h ic Wor k . Crystal data: [ReClO3N3C21H21],
Mr ) 585.08, triclinic, space group P1h(No. 2), a ) 9.767(1) Å,
b ) 10.934(3) Å, c ) 12.153(4) Å, R ) 108.87(2)°, â ) 95.26-
(2)°, γ ) 115.11(1)°, V ) 1071.6(6) Å3, Z ) 2, DC ) 1.813 g
cm-3, (Mo KR) ) 58.23 cm-1, F(000) ) 568, T ) 298 K. A pale
yellow crystal of dimensions 0.45 × 0.20 × 0.08 mm was used
for data collection at 25 °C on an Enraf-Nonius CAD4 diffrac-
tometer with graphite-monochromated Mo KR radiation (λ )
0.710 73 Å) using ω-2θ scans with a ω-scan angle (0.65 + 0.35
tan θ)° at a scan speed of 1.37-5.49 deg min-1. Intensity data
(in the range of 2θmax ) 48°; h, 0 to 11; k, -12 to12; l, -13 to
13; and three standard reflections measured after every 300
reflections showed decay of 3.98%) were corrected for decay,
Lorentz and polarization effects, and empirical absorption
corrections based on the Ψ-scan of four strong reflections
(minimum and maximum transmission factors 0.354 and
1.000). Upon averaging the 3586 reflections, 3361 of which
were uniquely measured (Rint ) 0.029), 3169 reflections with
I > 3σ(I) were considered observed and used in the structural
analysis. The centric space group was based on a statistical
analysis of intensity distribution, and the successful solution
and refinement of the structure was solved by direct methods
(SIR9218a), expanded by Fourier methods and refined by full-
matrix least-squares using the software package TeXsan18b on
a Silicon Graphics Indy computer. A crystallographic asym-
metric unit comprised of one molecule and all 29 non-H atoms
of the molecule were refined anisotropically. Twenty-one H
atoms of the complex at calculated positions with thermal
parameters equal to 1.3 times that of the attached C atoms
were not refined. Convergence for 262 variable parameters
by least-squares refinement on F with w ) 4Fo2/σ2(Fo2), where
σ2(Fo2) ) [σ2(I) + (0.035Fo2)2] for 3169 reflections with I > 3σ-
(I), was reached at R ) 0.037 and Rw ) 0.046 with a goodness-
of-fit of 2.25. (∆/σ)max ) 0.02. The final difference Fourier map
was featureless, with maximum positive and negative peaks
of 3.42 and -1.00 e Å-3, respectively. The positive peak was
in the vicinity of the Re atom. The atomic coordinates, thermal
parameters, and bond lengths are given in the Supporting
Information. Selected bond distances and angles for complex
fac-ClRe(CO)3L4 are given in Table 1.
1
vis, positive FAB-MS, and H NMR spectroscopy. The
IR spectra of the complexes show three intense absorp-
tion bands in the region 1860-2040 cm-1, typical of the
facial arrangement of the three carbonyl groups.19 The
structure of fac-ClRe(CO)3L4 was also determined by
X-ray crystallography.
Cr ysta l Str u ctu r e. A perspective drawing of the
structure of the complex fac-ClRe(CO)3L4 with atomic
numbering is shown in Figure 1. The coordination
geometry at the Re atom is distorted octahedral with
the three carbonyl ligands arranged in a facial fashion.
The N(1)-Re-N(2) bond angle of 78.3° (less than 90°)
is a result of the steric requirement of the bidentate
diimine ligand. All other bond distances and bond
angles are not remarkable and are comparable to those
found for the related rhenium(I) polypyridyl com-
plexes.20,21
Su r fa ce P r essu r e-Ar ea (π-A) Isoth er m s. π-A
isotherms for the Re(I) complexes are shown in Figure
2. The complexes showed stable monolayer film-forming
properties and had two well-defined phase transitions.
Compression-expanding cycles showed that the first
phase transition at the lower surface pressure is as-
sociated with monolayer film formation from gaseous
phase and the other one at high surface pressure is
(19) Giordano, P. J .; Wrighton, M. S. J . Am. Chem. Soc. 1979, 101,
2888.
(20) (a) Lees, A. J . Comm. Inorg. Chem. 1995, 17, 319. (b) Moya, S.
A.; Guerrero, J .; Pastene, R.; Schmidt, R.; Sariego, R.; Sartori, R.; Sanz-
Aparicio, J .; Fonseca, I.; Maertiez-Ripoll, M. Inorg. Chem. 1994, 33,
2341. (c) Abel, E. W.; Dimitrov, V. S.; Long, N. J .; Orrel, K. G.; Osborne,
A. G.; Pain, H. M.; Hursthouse, M. B.; Mazid, M. A. J . Chem. Soc.,
Dalton Trans. 1993, 597. (d) Civitello, E. R.; Dragovich, P. S.;
Karpishin, T. B.; Novick, S. G.; Bierach, G.; O’Connell, J . F.; West-
moreland, T. D. Inorg. Chem. 1993, 32, 237. (e) Porter, L. H.; Reid, A.
H.; Fackler, J . P., J r. Acta Crystallogr. 1992, 48, 908.
(21) (a) Yam, V. W.-W.; Lau, V. C.-Y.; Cheung, K. K. Organometallics
1995, 14, 2749. (b) Yam, V. W.-W.; Lau, V. C.-Y.; Cheung, K. K. J .
Chem. Soc., Chem. Commun. 1995, 259. (c) Yam, V. W.-W.; Lo, K. K.
W.; Cheung, K. K.; Kong, R. Y. C. J . Chem. Soc., Chem. Commun. 1995,
1191. (d) Yam, V. W.-W.; Lo, K. K. W.; Cheung, K. K.; Kong, R. Y. C.
J . Chem. Soc., Dalton Trans. 1997, 2067.
(18) (a)SIR92: Altomare, A.; Cascarano, M.; Giacovazzo, C.; Gua-
gliardi, A.; Burla, M. C.; Polidori, G.; Camalli, M. J . Appl. Crystallogr.
1994, 27, 435. (b) TeXsan: Crystal Structure Analysis Package; Mo-
lecular Structure Corp., 1985 and 1992.

2444 Organometallics, Vol. 17, No. 12, 1998
Yam et al.
(a )
(b)
F igu r e 2. Surface pressure-area (π-A) isotherms: (a)
ReCl(CO)3L3; (b) ReCl(CO)3L1; (c) ReCl(CO)3L2.
F igu r e 4. UV-vis spectra of ReCl(CO)3L1 (s), ReCl-
(CO)3L2 (- - -), and ReCl(CO)3L3(‚‚‚): (a) in CH2Cl2, (b) in
LB film.
that observed for fac-ClRe(CO)3L3, indicative of their
poorer film-formation property compared to fac-ClRe-
(CO)3L3.
F igu r e 3. Compression-expanding isotherms for ReCl-
(CO)3L3.
UV-Vis Absor p tion Sp ectr a . The UV-vis absorp-
tion spectra of the rhenium(I) complexes showed intense
absorption bands at ca. 300-350 nm, attributable to
ligand-centered transitions, and a broad band at ca.
380-430 nm, which is attributed to a metal-to-ligand
charge transfer (MLCT, dπ (Re) f π*(L)) transi-
tion.1-3,5,17,20,21 The only exception is ClRe(CO)3L2,
where the low-energy absorption at ca. 414 nm is
attributed to an admixture of intraligand (IL, π f π*-
(L2)) and metal-to-ligand charge transfer (MLCT, dπ
(Re) f π*(L2)) transitions, in view of the presence of
the low-energy IL band at ca. 420 nm in the free ligand
L2. Both ClRe(CO)3L2 and ClRe(CO)3L3 absorbed at
lower energies than ClRe(CO)3L1, in line with the
lower-lying π* orbital energy of the more conjugated L2
and L3 ligands. Figure 4 shows the UV-vis spectra of
the complexes in LB film and in chloroform solution.
The absorption patterns are similar with those in LB
film having less features than those in chloroform
solution, indicative of the presence of aggregates in the
LB films.22 The UV-vis spectra of fac-ClRe(CO)3L3 in
LB films are found to show a linear dependence of
related to the formation of aggregates or multilayer
films from the monolayer film. This can be seen from
the compression-expanding cycle of fac-ClRe(CO)3L3
as shown in Figure 3. A large hysteresis appeared when
the reverse pressure is larger than the critical phase
transition point. However, the π-A isotherms could be
reversibly compressed and expanded when the reverse
pressure was lower than the critical phase transition
point. The molecular area for fac-ClRe(CO)3L3 obtained
by extrapolation from the linear region of the first phase
transition at the lower surface pressure is 0.48 nm2,
which agrees well with the calculated value of 0.5 nm2,
considering that both the N-containing ligand plane and
the long alkyl chain are oriented vertically with respect
to the water surface, with the molecules closely packed
in the films. On the contrary, the molecular area of the
other two complexes fac-ClRe(CO)3L1 and fac-ClRe-
(CO)3L2 are much larger than the calculated value,
indicating that the alkyl chains were highly tilted in
their films. In addition, the region associated with
monolayer film formation in the π-A curves for fac-
ClRe(CO)3L1 and fac-ClRe(CO)3L2 is not as steep as
(22) Chen, H.; Law, K.-Y.; Whitten, D. G. J . Phys. Chem. 1996, 100,
5949.

Crystal Structure of fac-ClRe(CO)3L
Organometallics, Vol. 17, No. 12, 1998 2445
Ta ble 2. Em ission Da ta for th e Rh en iu m (I)
Com p lexes fa c-ClRe(CO)3L
CH2Cl2 (298 K),
CHCl3 glass (77 K),
LB film,
L
λem/nm (τ0/µs)
λem/nm
λ
em/nm
L1
L2
L3
595 (0.10)
590 (0.30)
720 (<0.02)
555
535
645
575
a
660
a
Not measured.
F igu r e 6. Polarization dependence of the SHG (arbitrary
units) from monolayer films of ReCl(CO)3L3; the peak and
troughs correspond to the signal from the p-polarized and
s-polarized fundamental beams, respectively. The abscissa
corresponds to the angle of rotation of the half-wave plate.
strong second-harmonic (SH) signals. A similar mech-
anism of second-harmonic generation to that of the Ru-
(II) complexes may operate in the amphiphilic Re
complexes studied, and assuming that the MLCT tran-
sition moments have a common tilt angle, φ, to the
surface normal, with a random azimuthal distribution,
and that second-order molecular hyperpolarizability (â)
is dominated by the component along the MLCT axis,
the following eqs 1-3 can be derived.25
F igu r e 5. Normalized emission spectra (s, LB film; - - -,
complex at glassy state (77 K); ‚‚‚, complex in CH2Cl2) of
ReCl(CO)3L1.
absorbance on the number of layers deposited, indicative
of its good deposition behavior. On the contrary, the
complexes fac-ClRe(CO)3L1 and fac-ClRe(CO)3L2 were
found to show poor deposition behavior which became
irreproducible after the deposition of five layers.
Lu m in escen ce Sp ectr a . Emission data for the
complexes in various media are summarized in Table
2, and the emission spectra of ClRe(CO)3L1 are shown
in Figure 5. The emission spectra exhibited a broad
unstructured emission band, attributed to a triplet
MLCT-based emission, typical of Re(I) diimine com-
plexes.1-3,5,17,20,21,23 The emission energies of the com-
plexes in 77 K glass and in LB films were found to be
blue-shifted with respect to that in fluid solutions,
attributed to the phenomenon of luminescence rigido-
chromism.5a,19,24
I
2ω(p f p)/ I2ω(s f p) ) (ø(2)(zzz)sin3 θ +
3ø(2)(zxx)sin θ cos2 θ)2/ (ø(2)(zxx)sin θ)2 (1)
ø(2)(zzz) ) ø(2)cos3 φ ) Nf2ω(fω)2â cos3 φ
(2)
ø(2)(zxx) ) 0.5ø(2) cos φ sin2 φ )
0.5Nf2ω(fω)2â cos φ sin2 φ (3)
Substitution of eqs 2 and 3 into eq 1 gives eq 4 for
the calculation of φ:
Secon d -Ha r m on ic Gen er a tion (SHG). For con-
ventional nonlinear optical (NLO) organic compounds,
the NLO property originated from intramolecular charge
transfer and the second-order molecular hyperpolariz-
ability (â) is dominated by the component along the
intramolecular donor-π-acceptor axis. In 1989, SHG
from LB films of Ru(II) complexes was first observed9
and subsequently verified to result from a dπ(Ru) f
π*(bpy) metal-to-ligand charge transfer excited state
with the transition dipole moment mainly oriented
along the 2,2′-bipyridine moiety attached to the long
alkyl chain. In the SHG measurements, the monolayer
film of fac-ClRe(CO)3L3 has been shown to exhibit very
tan φ ) [(I2ω(p f p)/ I2ω(s f p))1/2 - 3/2]-1/2 (4)
where I2ω(p f p) is the p-polarized double-frequency
signal intensity with p-polarized incidental fundamental
light; I2ω(s f p) is s-polarized double-frequency signal
intensity with p-polarized incidental fundamental light;
s and p stand for perpendicular and parallel to the plane
of incidence.
In the SHG experiment, the monolayer film of fac-
ClRe(CO)3L3 showed strong SH signals and evident
polarization dependence (Figure 6). By a comparison
of the signal to that obtained from a Y-cut quartz crystal
reference (d11 ) 1.2 × 10-9 esu),26 ø(2) and â can be
(23) (a) Tapolsky, G.; Duesing, R.; Meyer, T. J . Inorg. Chem. 1990,
29, 2285. (b) Shaw, J . P.; Schmehl, R. H. J . Am. Chem. Soc. 1991, 113,
389. (c) Lin, R.; Fu, Y.; Brock, C. P.; Guarr, T. F. Inorg. Chem. 1992,
31, 4346. (d) Yoon, K. I.; Berg-Brennan, C. A.; Lu, H.; Hupp, J . T. Inorg.
Chem. 1992, 31, 3192.
(24) (a) Kotch, T. G.; Lees, A. J . Inorg. Chem. 1993, 32, 2570. (b)
Moya, S. A.; Schmidt, R.; Pastene, R.; Sartori, R.; Muller, U.; Frenzen,
G. Organometallics 1996, 15, 3465.
(25) Ashwell, G. J .; Hargreaves, R. C.; Baldwin, C. E.; Bahra, C. S.;
Brown, C. R. Nature 1992, 357, 393.
(26) (a) J erphagnon, J .; Kurtz, S. K. J . Appl. Phys. 1970, 41, 1667.
(b) Levine, B. F.; Bethea, C. G.; Thurmond, C. D.; Lynch, R. T.;
Bernstein, J . L. J . Appl. Phys. 1979, 50, 2533. (c) Bloembergen, N.;
Pershan, P. S. Phys. Rev. 1962, 128, 602.

2446 Organometallics, Vol. 17, No. 12, 1998
Yam et al.
Ta ble 3.
ø
(2), â, a n d Tilt An gle O for Mon ola yer
complexes could not be measured with certainty due to
their very weak I2ω(s f p) signal. Assuming that the
SHG behavior originates from the metal-to-ligand charge
transfer (MLCT), one would expect that for fac-ClRe-
(CO)3L3 the charge-transfer axis should be tilted away
from the film surface normal the most among the
complexes fac-ClRe(CO)3L1, fac-ClRe(CO)3L2, and fac-
ClRe(CO)3L3, leading to fac-ClRe(CO)3L3 having the
worst SHG property. However, the observation of a
reverse trend in which a strong SHG signal is found
for fac-ClRe(CO)3L3 while weak SHG properties are
observed for fac-ClRe(CO)3L1 and fac-ClRe(CO)3L2 is
most probably associated with the poor film-forming
behavior of these latter two complexes, which does not
result in an ordered acentrosymmetric structure.
F ilm s
ø(2) × 107/ â × 1029
/
compound
φ/deg
esu
esu
refs
fac-ClRe(CO)3L3a
BI
BI
25.2
25.0
50.0
1.8
3.9
5.1
5.4
13
15
this work
this work
27
a
Molecular area of 0.48 nm2 and film thickness of 0.23 nm
calculated based on molecular modeling. BI ) E-N-methyl-4-(2-
(4-octadecyloxyphenyl)ethenyl)pyridinium iodide.
obtained using eqs 2 and 3,25,27 in which θ ) 45° is the
angle of the laser beam to the film; ø(2) is the second-
order susceptibility; ø(2)(zzz) and ø(2)(zxx) are the two
independent components characterized by the substrate
normal (z-axis) and xy plane on the film surface with
the y-axis perpendicular to the plane of incidence; fω,2ω
) [(nω,2ω)2 + 2]/3 is a local field correction factor, where
nω and n2ω are the refractive indices of the film at the
fundamental and the second-harmonic frequencies,
respectively, with n2ω usually slightly higher than nω.
Con clu sion
Several newly synthesized surfactant Re(I) complexes
have been shown to exhibit stable air-water interface
behaviors, one of which is capable of forming a stable
multilayer LB film on quartz substrate with the mono-
layer film showing relatively strong second-harmonic
signals, which could be ascribed to the good film-forming
properties and the metal-to-ligand charge transfer
characteristic of the complex.
In the actual treatment, n is taken to be nω = n2ω
)
1.5; N ) (lA)-1 is the number of molecules per unit
volume, where l is the film thickness and A the molec-
ular area of film-forming materials under study.
The SHG results were summarized in Table 3 and
compared with those reported for the monolayer film
of E-N-methyl-4-(2-(4-octadecyloxyphenyl)ethenyl)py-
ridinium iodide (BI). The â value obtained for a film of
BI in this work agrees quite well with the value reported
in the literature.27 The â value of 5.4 × 10-29 esu
obtained for fac-ClRe(CO)3L3 is higher than that ob-
served for the NLO material 2-methyl-4-nitroaniline (4.5
× 10-29 esu).28 On the contrary, the monolayer film of
both fac-ClRe(CO)3L1 and fac-ClRe(CO)3L2 gave very
weak SH signals. The SHG parameters for the two
Ack n ow led gm en t. V.W.-W.Y. acknowledges finan-
cial support from the Research Grants Council and The
University of Hong Kong. C.-R.W. acknowledges the
receipt of a Postdoctoral Fellowship and Y.Y. the receipt
of a part-time Demonstratorship, both administered by
The University of Hong Kong.
Su p p or tin g In for m a tion Ava ila ble: Tables of atomic
coordinates, thermal parameters, and all bond distances and
angles for complex fac-ClRe(CO)3L4 (9 pages). Ordering
information is given on any current masthead page.
(27) Lupo, D.; Prass, W.; Scheunemann, U.; Laschewsky, A.; Rings-
dorf, H.; Ledoux, I. J Opt. Soc. Am. B. 1988, 5, 300.
(28) Teng, C. C.; Garito, A. F. Phys. Rev. B. 1983, 28, 6766.
OM970998F