One-, two-, and three-dimensional arrays of Eu3+-4,4,5,5,5- pentafluoro-1-(naphthalen-2-yl)pentane-1,3-dione complexes: Synthesis, crystal structure and photophysical properties

Article abstract of DOI:10.1021/ic8004757

A novel β-diketone, 4,4,5,5,5-pentafluoro-1-(naphthalen-2-yl)pentane- 1,3-dione (HPFNP), which contains polyfluorinated alkyl group, as well as the long conjugated naphthyl group, has been used for the synthesis of a series of new tris(β-diketonate)europium(III) complexes of the general formula Eu(PFNP)₃·L [where L = H₂O, 2,2′-bipyridine (bpy), 1,10-phenanthroline (phen), 4,7-diphenyl-1,10-phenanthroline (bath)] and characterized by various spectroscopic techniques. The single-crystal X-ray diffraction analysis of Eu(PFNP)₃.bpy revealed that the complex is mononuclear, the central Eu³⁺ ion is coordinated by six oxygen atoms furnished by three β-diketonate ligands, and two nitrogen atoms from a bidentate bipyridyl ligand, in an overall distorted square prismatic geometry. Further, analysis of the X-ray crystal data of the above complex also revealed interesting 1D, 2D, and 3D networks based on intra- and intermolecular hydrogen bonds. The room-temperature PL spectra of the complexes are composed of typical Eu³⁺ red emissions, assigned to transitions between the first excited state (⁵D₀) and the multiplet (⁷F _0-4). The results demonstrate that the substitution of solvent molecules by bidentate nitrogen ligands in Eu(PFNP)₃·H ₂O·EtOH greatly enhances the quantum yields and lifetime values.

Full text of DOI:10.1021/ic8004757

Inorg. Chem. 2008, 47, 8091-8100
One-, Two-, and Three-Dimensional Arrays of
Eu3+-4,4,5,5,5-pentafluoro-1-(naphthalen-2-yl)pentane-1,3-dione
complexes: Synthesis, Crystal Structure and Photophysical Properties
D. B. Ambili Raj, S. Biju, and M. L. P. Reddy*
Chemical Sciences and Technology DiVision, National Institute for Interdisciplinary
Science & Technology (NIIST), CSIR, ThiruVananthapuram-695 019, India
Received March 15, 2008
A novel ꢀ-diketone, 4,4,5,5,5-pentafluoro-1-(naphthalen-2-yl)pentane-1,3-dione (HPFNP), which contains polyflu-
orinated alkyl group, as well as the long conjugated naphthyl group, has been used for the synthesis of a series
of new tris(ꢀ-diketonate)europium(III) complexes of the general formula Eu(PFNP)3 · L [where L ) H2O, 2,2′-
bipyridine (bpy), 1,10-phenanthroline (phen), 4,7-diphenyl-1,10-phenanthroline (bath)] and characterized by various
spectroscopic techniques. The single-crystal X-ray diffraction analysis of Eu(PFNP)3.bpy revealed that the complex
is mononuclear, the central Eu3+ ion is coordinated by six oxygen atoms furnished by three ꢀ-diketonate ligands,
and two nitrogen atoms from a bidentate bipyridyl ligand, in an overall distorted square prismatic geometry. Further,
analysis of the X-ray crystal data of the above complex also revealed interesting 1D, 2D, and 3D networks based
on intra- and intermolecular hydrogen bonds. The room-temperature PL spectra of the complexes are composed
of typical Eu3+ red emissions, assigned to transitions between the first excited state (5D0) and the multiplet (7F0-4).
The results demonstrate that the substitution of solvent molecules by bidentate nitrogen ligands in
Eu(PFNP)3 ·H2O · EtOH greatly enhances the quantum yields and lifetime values.
Introduction
always require sensitization by suitable organic chro-
mophores. Furthermore, for practical applications, Ln3+ ion
must be incorporated into highly stable coordinated com-
plexes. The efficiency of ligand-to-metal energy transfer,
which requires compatibility between the energy levels of
the ligand excited states and accepting levels of Ln3+ ions,
is crucial in the design of high performance luminescent
molecular devices. Moreover, ligands containing high-energy
oscillators, such as C-H and O-H bonds, are able to quench
the metal excited states nonradiatively, thereby leading to
lower luminescence intensities and shorter excited-state
lifetimes. Thus the replacement of C-H bonds with C-F
bonds is important in the design of new lanthanide lumi-
nescent complexes with efficient emission properties.
The ꢀ-diketone ligand is one of the important “antennas”,8
from which the energy can be effectively transferred to Ln3+
ions for high harvest emissions and has the following
advantages. The ꢀ-diketone ligand has strong absorption
The versatile photophysical properties of lanthanide ions
have inspired vigorous research activities because of the wide
range of photonic applications, such as tunable lasers,
amplifiers for optical communications, luminescent probes
for analytes, components of the emitting materials in
multilayer organic light emitting diodes, and efficient light
conversion molecular devices.1-6 The Eu3+ and Tb3+ ions
are of particular interest because of their long luminescence
lifetime and narrow emission bands in the visible region.7
Because the Laporte-forbidden 4f-4f transition prevents
direct excitation of lanthanide luminescence, Ln3+ ions
* To whom correspondence should be addressed. E-mail: mlpreddy@
yahoo.co.uk.
(1) Bu¨nzli, J-C. G.; Piguet, C. Chem. Soc. ReV 2005, 34, 1048–1077.
(2) de Bettencourt-Dias, A. Dalton Trans. 2007, 2229–2241.
(3) Kuriki, K.; Koike, Y.; Okamoto, Y. Chem. ReV. 2002, 102, 2347–
2356.
(4) Kido, J.; Okamoto, Y. Chem. ReV. 2002, 102, 2357–2368.
(5) Sun, P. P.; Duan, J. P.; Lih, J. J.; Cheng, C. H. AdV. Funct. Mater.
2003, 13, 683–691.
(6) Hao, R.; Li, M.; Wang, Y.; Zhang, J.; Ma, Y.; Fu, L.; Wen, X.; Wu,
Y.; Ai, X.; Zhang, S.; Wei, Y. AdV. Funct. Mater. 2007, 17, 3663–
3669.
(7) (a) Yang, C.; Fu, L. -M.; Wang, Y.; Zhang, J.-P.; Wong, W.-T.; Ai,
X.-C.; Qiao, Y.-F.; Zou, B.-S.; Gui, L.-L. Angew Chem., Int. Ed. 2004,
43, 5010–5013. (b) Xin, H.; Li, F. Y.; Shi, M.; Bian, Z. Q.; Huang,
C. H. J. Am. Chem. Soc. 2003, 125, 7166–7167.
10.1021/ic8004757 CCC: $40.75  2008 American Chemical Society
Inorganic Chemistry, Vol. 47, No. 18, 2008 8091
Published on Web 08/21/2008

Ambili Raj et al.
within a large wavelength range for its π-π* transition and,
consequently, has been targeted for its ability to sensitize
the luminescence of the Ln3+ ions. Further it has ability to
form stable and strong adducts with Ln3+ ions, which can
have practical usage.9,10
Experimental Section
Materials and Instrumentation. Commercially available chemi-
cals [europium(III) nitrate hexahydrate, 99.9% (Arcos Organics);
gadolinium(III) nitrate hexahydrate, 99.9% (Aldrich), 2-acetonaph-
thone 98% (Aldrich), methyl pentafluoropropionate 99% (Aldrich),
sodium hydride 60% dispersion in mineral oil, (Aldrich), 2,2′-
dipyridyl, 99%, (Aldrich), 4,7-diphenyl-1,10-phenanthroline, 97%,
(Aldrich), 1,10-phenanthroline monohydrate (Merck)] are used
without further purification. All the other chemicals used were of
analytical reagent grade.
Recently, a large number of highly coordinated complexes
of lanthanide tris(ꢀ-diketonates) containing several nitrogen
ligands such as 1,10-phenanthroline,11,12 2,2′-bipyridine,13,14
4,4′-disubstituted-2,2′-bipyridines,15,16 and 2,2′:6′,6′′-terpy-
ridine17,18 have been reported. Earlier reports demonstrate
that the replacement of C-H bonds in a ꢀ-diketone with
low-energy oscillators (C-F) is able to lower the vibrational
energy of the ligand, which minimizes the energy loss caused
by ligand vibration and enhances the luminescent intensity
of the Ln3+ ion. Further because of the heavy-atom effect,
which facilitates intersystem crossing, the lanthanide-centered
luminescent properties are enhanced.9,19,20 These factors have
prompted us to synthesize a new ꢀ-diketone ligand, 4,4,5,5,5-
pentafluoro-1-(naphthalen-2-yl)pentane-1,3-dione, which has
the polyfluorinated alkyl group, as well as the long conju-
gated naphthyl group. The synthesized ligand has been
utilized for the synthesis of various Eu3+ complexes with
bidentate nitrogen donors and investigated their photophysi-
cal properties for possible use in OLEDs as emitting
materials.
Elemental analyses were performed with a Perkin-Elmer Series
2 Elemental Analyzer 2400. A Perkin-Elmer Spectrum One FT-IR
Spectrometer, using KBr (neat), was used to obtain IR spectral data,
1
and a Bruker 300 MHz NMR spectrometer was used to obtain H
NMR spectra of the compounds in CDCl3 media. Mass spectra were
recorded using JEOL JMS 600 fast atom bombardment (FAB) mass
spectrometer. Thermogravimetric analysis (TGA) was performed
using a TGA-50 Shimadzu thermogravimetric analyzer. DSC
measurements were performed on a DSC-Perkin-Elmer Pyris 6 DSC
instrument at a heating rate of 10 °C/min under nitrogen atmosphere.
X-ray powder diffraction (XRD) analyses were performed with a
Philips X’Pert Pro diffractometer. The XRD patterns were recorded
in the 5-70° 2θ range using Ni-filtered Cu KR radiation. Optical
reflectance of the powder samples and absorbance of the samples
in CH3CN solution were measured with UV-vis spectrophotometer
(Shimadzu, UV-2450) with an integrated sphere attachment. Pho-
toluminescence (PL) spectra were recorded using a Spex-Fluorolog
FL3-22 spectrofluorometer with double-grating 0.22 m Spex
FL3-22 monochromators and a 450W Xe lamp as the excitation
source using the front face mode. The lifetime measurements were
carried out at room temperature using Spex FL-1040 phosphorim-
eter. X-ray single-crystal data were recorded at room-temperature
on a Bruker AXS (Kappa Apex II) diffractometer equipped with a
CCD detector and a copper tube source. Data were processed using
SAINTPLUS (SAINTPLUS, program suite for data processing,
Bruker AXS, Inc., Madison, WI). Structures were solved and refined
using SHELXTL.
(8) (a) Lehn, J.-M. Angew. Chem., Int. Ed. Engl. 1990, 29, 1304–1319.
(b) de Sa, G. F.; Malta, O. L.; de Mello Donega, C.; Simas, A. M.;
Longo, R. L.; Santa-Cruz, P. A.; da Silva, E. F., Jr. Coord. Chem.
ReV. 2000, 196, 165–195.
(9) (a) Sun, L.-N.; Yu, J.-B.; Zheng, G.-L.; Zhang, H.-J.; Meng, Q.-G.;
Peng, C.-Y.; Fu, L.-S.; Liu, F.-Y. Eur. J. Inorg. Chem. 2006, 396,
2–3973. (b) Yu, J.; Zhou, L.; Zhang, H.; Zheng, Y.; Li, H.; Deng, R.;
Peng, Z.; Li, Z. Inorg. Chem. 2005, 44, 1611–1618. (c) Fratini, A.;
Richards, G.; Larder, E.; Swavey, S. Inorg. Chem. 2008, 47, 1030–
1036. (d) Hasegawa, Y.; Yamamuro, M.; Wada, Y.; Kanehisa, N.;
Kai, Y.; Yanagida, S. J. Phys. Chem. A. 2003, 107, 1697–1702. (e)
Eliseeva, S. V.; Ryazanov, M.; Gumy, F.; Troyanov, S. I.; Lepnev,
L. S.; Bu¨nzli, J.-C. G.; Kuzmina, N. P. Eur. J. Inorg. Chem. 2006,
480, 9–4820.
(10) (a) Biju, S.; Ambili Raj, D. B.; Reddy, M. L. P.; Kariuki, B. M. Inorg.
Chem. 2006, 45, 10651–10660. (b) Yang, L.; Gong, Z.; Nie, D.; Lou,
B.; Bian, Z.; Guan, M.; Huang, C.; Lee, H. J.; Baik, W. P. New
J. Chem. 2006, 30, 791–796. (c) Pavithran, R.; Saleesh Kumar, N. S.;
Biju, S.; Reddy, M. L. P.; Alves, S., Jr.; Freire, R. O. Inorg. Chem.
2006, 45, 2184–2192. (d) Binnemans, K. Handbook on the Physics
and Chemistry of Rare Earths, Elsevier: Amsterdam, 2005; Vol. 35,
Chapter 225, pp 107-272.
(11) (a) Christidis, P. C.; Tossidis, I. O.; Paschalidis, D. G.; Tzavellas,
L. C. Acta Crystallogr. 1998, C54, 1233–1236. (b) Watson, W. H.;
Williams, R. J.; Stemple, N. R. J. Inorg. Chem. 1972, 34, 501–508.
(12) Fernandes, J. A.; Sa’ Ferreira, R. A.; Pillinger, M.; Carlos, L. D.;
Jepsen, J.; Hazell, A.; Ribeiro-Claro, P.; Goncalves, I. S. J. Lumin.
2005, 113, 50–63.
The overall quantum yields (Φoverall) of the europium complexes
were measured at room temperature using the technique for powdered
samples described by Bril et al.,21 through the following expression:
1 - rst AX
Φoverall
)
Φst
(1)
(
)( )
1 - rX Ast
where, rst and rX are the diffuse reflectance (with respect to affixed
wavelength) of the complexes and of the standard phosphor,
respectively, and Φst is the quantum yield of the standard phosphor.
The terms AX and Ast represents the area under the complex and
the standard emission spectra, respectively. To have absolute
intensity values, BaSO4 was used as a reflecting standard. The
standard phosphor used was Pyrene (Aldrich), whose emission
spectrum is formed as a large broadband peaking around 471 nm,
with a constant Φ value (Φst ) 61%, λex ) 313 nm).22Three
measurements were carried out for each sample, so that the
presented Φ value corresponds to the arithmetic mean value.
(13) Bekiari, V.; Lianos, P. AdV. Mater. 1998, 10, 1455–1458.
(14) Pucci, D.; Barberio, G.; Crispini, A.; Francescangeli, O.; Ghedini, M.;
La Deda, M. Eur. J. Inorg. Chem. 2003, 364, 9–3661.
(15) Bellusci, A.; Barberio, G.; Crispini, A.; Ghedini, M.; La Deda, M.;
Pucci, D. Inorg. Chem. 2005, 44, 1818–1825.
(16) Batista, H. J.; de Andrade, A.V. M.; Longo, R. L.; Simas, A. M.; de
Sa, G. F.; Ito, N. K.; Thompson, L. C. Inorg. Chem. 1998, 37, 3542–
3547.
(17) Fukuda, Y.; Nakao, A.; Hayashi, K. J. Chem. Soc., Dalton Trans.
2002, 527–533.
(18) Cotton, S. A.; Noy, O. E.; Liesener, F.; Raithby, P. R. Inorg. Chim.
Acta 2003, 344, 37–42.
(19) Omary, M. A.; Rawashdeh-Omary, M. A.; Diyabalanage, H. V. K.;
Dias, H. V. R. Inorg. Chem. 2003, 42, 8612–8614.
(20) Grushin, V. V.; Herron, N.; LeCloux, D. D.; Marshall, W. J.; Petrov,
V. A.; Wang, Y. Chem. Commun. 2001, 16, 1494–1495.
(21) Bril, A.; De Jager-Veenis, A. W. J. Electrochem. Soc. 1976, 123, 396–
398.
(22) Melhuish, W. H. J. Opt. Soc. Am. 1964, 54, 183–186.
8092 Inorganic Chemistry, Vol. 47, No. 18, 2008

Eu3+-4,4,5,5,5-pentafluoro-1-(naphthalen-2-yl)pentane-1,3-dione
Scheme 1. Synthesis of the Ligand HPFNP
Scheme 2. Synthesis of Ln(PFNP)3 ·H2O·C2H5OH
crystals of complex 2 were formed after ∼2 weeks. However, our
efforts to grow single crystals of complexes 3 and 4 were
unsuccessful.
Eu(PFNP)3 ·bpy (2). Elemental analysis (%) Calcd for C55H32F15
N2O6Eu (1253.80): C, 52.69; H, 2.57; N, 2.23. Found: C, 52.77;
H, 2.53; N, 2.37. IR (KBr)νmax: 3058, 1637, 1610, 1594, 1507,
1473, 1328, 1281, 1197, 1162, 1013, 790 cm-1. m/z) 1255.10 (M+)
+ 1. mp: 200 °C.
Eu(PFNP)3 · phen (3). Elemental analysis (%) Calcd for
C57H32F15N2O6Eu (1277.82): C, 53.58; H, 2.52; N, 2.19. Found:
C, 53.62; H, 2.49; N, 2.36. IR (KBr) νmax: 3056, 1609, 1592, 1568,
1506, 1327, 1279, 1197, 1153, 1009, 791 cm-1. m/z) 1278.21
(M+). mp: 185 °C.
Eu(PFNP)3 · bath (4). Elemental analysis (%) Calcd for
C69H40F15N2O6Eu (1430.03): C, 57.95; H, 2.82; N, 1.96. Found:
C, 57.92; H, 2.87; N, 1.96. IR (KBr): νmax: 1610, 1570, 1524, 1384,
1329, 1285, 1214, 1195, 791 cm-1. m/z ) 1431.12 (M+). mp: 200
°C.
Synthesis of Gd(bath)2(NO3)3. To a 50 mL ethanol solution
containing 2.0 mmol of 4,7-diphenyl-1,10-phenanthroline, 1.0 mmol
of Gd(NO3)3(H2O)6 was added dropwise under constant stirring,
and then the solution was refluxed for 6 h at 80 °C. The resulting
solution was filtered to obtain a white powder. Elemental analysis
(%) Calcd for C48H32N7O9Gd (1008.08): C, 57.19; H, 3.20; N, 9.72.
Found: C, 57.50; H, 3.45; N, 9.72. IR (KBr) νmax: 1492, 1384, 1307,
1029, 835, 766, 740, 702 cm-1. m/z ) 946.11 (M+ - NO3).
The errors in the quantum yield values associated with this
technique were estimated within 10%.23
Synthesis of 4,4,5,5,5-Pentafluoro-1-(naphthalen-2-yl)pen-
tane-1,3-dione (HPFNP). A modified method of typical Claisen
condensation procedure is used as shown in Scheme 1. 2-Acet-
onaphthone (0.34 g, 0.002 mmol) and methyl pentafluoropropionate
(0.356 g, 0.002 mmol) were added into 20 mL dry THF, and the
mixture was stirred for 10 min. To this sodium hydride was added
in inert atmosphere and stirred at room temperature for 12 h. The
resulting solution was quenched with water; 2 M HCl (50 mL) was
added, and the solution was extracted twice with chloroform (70
mL). The organic layer was dried over Na2SO4, and the solvent
was evaporated to obtain a maroon oily liquid, which was purified
by chromatography on a silica gel column with chloroform and
hexane as the eluent to get the maroon liquid as the product (0.51
g, 80% yield). 1H NMR (300 MHz, CDCl3): δ 7.57-7.46 (m, 2H),
δ 7.89-7.78 (m, 4H), δ 8.42 (s, 1H), δ 6.68 (s, 1H), δ 15.38 (broad,
1H). IR (KBr) νmax: 3063, 1602, 1328, 1202, 1010, 795 cm-1. m/z
) 317 (M + 1)+.
Results and Discussion
Synthesis of Ln(PFNP)3 ·C2H5OH ·H2O [Ln ) Eu3+ (1),
Gd3+(5)]. To an ethanolic solution of HPFNP (0.6 mmol), NaOH
(0.6 mmol) is added, and the mixture was stirred for 5 min. To
this a saturated ethanolic solution of Ln(NO3)3 ·6H2O (0.2 mmol)
is added dropwise and stirred for 10 h. Water is then added to this
mixture, and the precipitate thus formed is filtered, washed with
water, dried, and purified by recrystallization from diethyl
ether-hexane mixture (Scheme 2). Unfortunately, all efforts to grow
single crystals of complexes 1 and 5 were unsuccessful. Elemental
analysis (%) Calcd for C47H32F15O8Eu (1) (1161.70): C, 48.59; H,
2.78. Found: C, 48.92; H, 2.51. IR (KBr) νmax: 3435, 1610, 1527,
1457, 1326, 1197, 1013, 792 cm-1. m/z ) 1120.12 (M+ - H2O,
C2H5OH) + Na. Elemental analysis (%) Calcd for C47H32F15O8Gd
(5) (1166.98): C, 48.37; H, 2.76. Found: C, 48.52; H, 2.80. IR (KBr)
Structural Characterization of Europium(III) Com-
plexes. The synthesis procedures for the europium complexes
1-5 are shown in Schemes 2 and 3. The microanalyses and
HRMS studies of the complexes 1-5 shows that Ln3+ ion
has reacted with HPFNP in a metal-to-ligand mole ratio of
1:3 and in 2-4, one molecule of bidentate nitrogen ligand
is involved. The IR spectrum of the complexes 1 and 5 shows
a broad absorption in the region 3000-3500 cm-1, indicating
the presence of solvent molecules in the complex. On the
other hand, the absence of the broadband in the region
3000-3500 cm-1 for complexes 2-4, suggests that solvent
molecules have been displaced by the bidentate neutral donors.
The carbonyl stretching frequency of HPFNP (1602 cm-1) has
been shifted to longer wave numbers in complexes 1-5 (1610
cm-1 in 1; 1613 cm-1 in 2; 1610 cm-1 in 3-5) indicating the
involvement of carbonyl oxygen in the complex formation with
Ln3+ ion. Further, the red shifts observed in the CdN stretching
frequencies of nitrogen donors (1615 cm-1) in complexes 2-4
(1594 cm-1 in 2; 1592 cm-1 in 3; 1598 cm-1 in 4) show the
involvement of nitrogen atoms in the complex formation with
Eu3+ ion. The X-ray powder diffraction patterns of complexes
1 and 5 are similar, indicating they are isostructural and
amorphous (Figure S1a). Similarly, from the XRD patterns of
ν
max: 3421, 1613, 1574, 1470, 1327, 1196, 1013, 790 cm-1. m/z )
1125.05 (M+ - H2O, C2H5OH) + Na. Ln ) Eu (1), Gd (5).
Syntheses of Complexes 2-4. Synthesis routes of the complexes
2-4 are shown in Scheme 3. All these complexes were prepared
by stirring equimolar solutions of Eu(PFNP)3 ·C2H5OH·H2O and
the nitrogen donor in CHCl3 for 24 h at room-temperature. The
products were obtained after solvent evaporation and are purified
by recrystallization from a chloroform-hexane mixture. A crop of
(23) (a) Mello Donega, C. D.; Junior, S. A.; de Sa, G. F. Chem. Commun.
1996, 11, 1199–1200. (b) Carlos, L. D.; Mello Donega, C. D.;
Albuquerque, R. Q.; Junior, S. A.; Menezes, J. F. S.; Malta, O. L.
Mol. Phys. 2003, 101, 1037–1045.
Inorganic Chemistry, Vol. 47, No. 18, 2008 8093

Ambili Raj et al.
Scheme 3. Synthetic Procedures for Complexes 2-4
complexes 2-4 (Figure S1b), one can conclude that they are
isostructural and crystalline.
X-Ray Structural Characterization. The structure of
complex 2 was characterized by single-crystal X-ray crystal-
lography. The asymmetric unit is shown in Figure 1a, and
the structures with the intramolecular H-bonding interactions
are shown in Figures 1b and S4. The details of crystal data
and data collection parameters for complex 2 are given in
Table 1. The selected bond lengths and bond angles for 2
are listed in Table 2. As predicted from the mass spectral
analysis and the elemental analysis observations, the central
Eu3+ ion is coordinated with six oxygen atoms from the three
ꢀ-diketonate ligands and two nitrogen atoms from a bidentate
bipyridyl ligand. The coordination geometry of the metal
center is best described as a distorted square antiprism. The
central Eu3+ ion is thus completely surrounded by the bulky
aromatic anionic ligand PFNP and the synergistic bpy ligand,
and this encapsulated structure therefore meets the structural
requirements of an efficient lanthanide luminescent material
by protecting the Eu3+ ion from vibrational coupling and
increasing the light absorption cross-section by the so-called
“antenna effect”. The average Eu-N bond distance (2.56
Å) is longer than the Eu-O bonds of HPFNP ligands
(2.34-2.37 Å), as observed in the X-ray single crystal data
of the complexes, tris(4,4,4,-trifluoro-1-(2-naphthyl)-1,3-
butanedionato)europium(III)-dipyridyl (Eu-O bonds 2.34-
2.39 Å NTA; Eu-N, 2.58 Å in bpy)24 and tris(4,4,4,-
trifluoro-1-phenyl 2,4-butanedionato) europium(III)-dipyridyl
(Eu-O bonds 2.32-2.40 Å in btfa; Eu-N, 2.58 Å in bpy).16
It is clear from the thermogravimetric analysis data that
complex 1 (Figure S2 in the Supporting Information)
undergoes a mass loss of about 6% (calcd 5.5%) in the first
step (120-230 °C), which corresponds to the elimination
of the coordinated solvent molecules. Complex 1 is stable
up to 230 °C, and then it under goes a single step
decomposition. On the other hand, complexes 2-4 are more
stable than the precursor sample 1, and they undergo single-
step decomposition at 275 °C. The total weight loss occurred
in the TGA of all these complexes are much higher than
that calculated for the thermal decomposition of these
complexes into nonvolatile europium(III) oxide, indicating
the partial sublimation of these complexes under atmospheric
pressure, which is common in poly fluorinated ꢀ-diketonate
complexes.9e
The DSC curve of the precursor sample (1) shows a
shallow broad endothermic peak in the temperature range
from 90-150 °C relative to the release of solvent molecules,
as observed in the first event of the TG curve. Further, the
absence of sharp endothermic peak in 1, indicates the
amorphous nature of the complex or at least it is difficult
for it to crystallize. On the other hand, DSC curve of
complexes 2-4 shows sharp endothermic peaks at 200, 185,
and 200 °C, respectively, corresponding to their melting
points (Figure S3).
8094 Inorganic Chemistry, Vol. 47, No. 18, 2008

Eu3+-4,4,5,5,5-pentafluoro-1-(naphthalen-2-yl)pentane-1,3-dione
Figure 1. (a) Asymmetric unit of complex 2. (b) Coordination environment of the Eu3+ ion in complex 2. The intramolecular H-bonding interactions are
shown in broken lines.
Table 1. Crystal Data, Collection, and Structure Refinement Parameters
for Complex 2
be caused by the inductive effect of the fluorine atoms present
in the HPFNP. In the ꢀ-diketone rings of the Eu3+ complex,
the average distances for the C-C and C-O bonds are
shorter than a single bond but longer than a double bond.
This can be explained by the fact that there exists a strong
conjugation between the naphthyl ring and the coordinated
ꢀ-diketone, which leads to the delocalization of electron
density of the coordinated ꢀ-diketonate chelate ring.9a,25
Two types of intramolecular interactions are observed
between C1-H1 · · · F3 and C53-H53 · · · F8 with the dis-
tances of 2.63 and 2.83 Å, and the angles are 161.49 and
155.84°, respectively (Figure 1b). Apart from the strong
intramolecular hydrogen bonding interactions, three different
intermolecular hydrogen bonding interactions are also ob-
served in 2. Two of them form the self-assembled dimer
(dimer a and b), while the third one adopts 1D structure
(c) in the solid state. All the three interactions are shown
in Figures 2 and S4. The bipyridyl ring in A and the
napthyl ring in D interact with the -CF3 groups of another
molecule to form the self-assembled dimer and the
observed interactions in C3-H3 · · · F14 (dimer a) and
C50-H50 · · · F7 (dimer b) with the distances of 2.68 and
2.60 Å and the angles of 145.9° and 168° On the other
hand, the bridging CH group and the bipyridyl group in
ring B interact with the -CF3 group of another molecule
to form the rodlike 1D network. The distances and angles
in 1D network are: 2.70 Å and 168° (C15-H15 · · · F15)
and 2.84 Å and 176° (C12-H12 · · · F15). The distance
between the two Eu centers is from 10.34 to 14.83 Å
params
2
empirical formula
fw
C57H36Cl3EuF15N2O6.50
1396.19
cryst syst
space group
cryst size (mm3)
temp (K)
a (Å)
triclinic
P1
j
0.20 × 0.15 × 0.15 mm
293(2) K
10.338(4)
14.784(6)
19.431(7)
96.238(19)
93.336(18)
90 96.523(19)
2925.7(18)
2
b (Å)
c (Å)
R (deg)
ꢀ (deg)
γ (deg)
V (Å3)
Z
Fcalcd (g cm-3
)
1.585
1.308
1386
µ (mm-1
F(000)
)
R1 [I > 2σ(I)]
wR2 [I > 2σ(I)]
R1 (all data)
wR2 (all data)
GOF
0.0436
0.1252
0.0520
0.1400
1.111
Table 2. Selected Bond Lengths (Å) and Angles (deg) for Complex 2
Eu1-N1
Eu1-N2
Eu1-O1
Eu1-O2
Eu1-O3
Eu1-O4
Eu1-O5
Eu1-O6
2.554(4)
2.570(4)
2.367(4)
2.352(3)
2.374(3)
2.336(3)
2.359(4)
2.343(3)
N1-Eu1-N2
O1-Eu1-O2
O3-Eu1-O4
O5-Eu1-O6
63.03(10)
71.32(18)
71.92(19)
71.24(18)
(24) Thompson, L. C.; Atchison, F. W.; Young, V. G. J. Alloys Compds.
1998, 275-278, 765–768.
(25) Yu, J.; Zhang, H.; Fu, L.; Deng, R.; Zhou, L.; Li, H.; Liu, F.; Fu, H.
Inorg. Chem. Commun. 2003, 6, 852–854.
Further, in this complex, the Eu-O bonds adjacent to the
naphthyl ring are slightly shorter than the others, which may
Inorganic Chemistry, Vol. 47, No. 18, 2008 8095

Ambili Raj et al.
Figure 2. Self-assembled dimer and 1D network of 2. In a, b, and c, except for the intermolecular H-bonding interactions, all the other H groups are omitted
for clarity.
which is considerably longer than the Eu-Eu single bond
distance.
Apart from the self-assembled dimer and 1D network, a
series of 2D networks are seen in 2. Three different 2D
networks are observed: (i) the two self-assembled dimers
interact with each other to form the first one. Further, each
of the self-assembled dimer interacts with 1D network to
form the (ii and iii) 2D networks. All the 2D networks (both
the top and side views) are shown in the Supporting
Information (Figure S5). Finally, all the dimers, 1D and 2D
networks combine each other to form the hitherto unknown
three-dimensional networks in the solid state. The observed
supramolecular assembly is shown in Figure S6. To the best
of our knowledge, this is the first example of Eu-ꢀ-diketonate
complex which shows all the 1D, 2D, and 3D networks.
UV-vis Spectra. The UV-vis absorption spectra of the
free ligand HPFNP and the corresponding Eu3+ complexes
were measured in CH3CN solution (c ) 1 × 10-5 M), and
Figure 3. UV-visible absorption spectra of HPFNP and complexes 1-4
in acetonitrile (c ) 1 × 10-5 M).
are displayed in Figure 3. UV-vis absorption spectra of the
neutral donors (bpy, phen, bath) are shown in Figure S8.
free nitrogen donors (297, 293, and 300 nm). The spectral
The maximum absorption band at 345 nm for HPFNP, and
shapes of the complexes in CH3CN are similar to that of the
the hump observed at around 333 nm in complexes 1-4 are
attributed to singlet-singlet π-π* enol absorption of
ꢀ-diketonate ligand.26 Compared with the ligand HPFNP
(λmax) 345), the absorption maxima are blue-shifted to 333
nm in all the complexes. The absorption maxima at 290,
289, and 287 nm in complexes 2-4, respectively, are the
free ligands, suggesting that the coordination of Eu3+ ion
1
does not have a significant influence on the π-π* state
energy. However, a small blue shift observed in the absorp-
tion maximum of all the complexes is caused by the
perturbation induced by the metal coordination. The deter-
mined molar absorption coefficient values of the complexes
1-4 at 333 nm, 5.67 × 104, 5.7 × 104, 5.2 × 104, and 5.3
× 104 L mol-1 cm-1, respectively, are about three times
higher than that of the HPFNP (1.8 × 104 at 345 nm),
indicating the presence of three ꢀ-diketonate ligands in the
corresponding complexes. Further the higher molar absorp-
1
result of the π-π* absorption of the aromatic rings of
bidentate nitrogen donors. These values also shows a blue
shift of 7, 4, and 13 nm, respectively in complexes than in
(26) Sun, Y.; Gao, J.; Zheng, Z.; Su, W.; Zhang, Q. Spectrochim. Acta
Part A 2006, 64, 977–980.
8096 Inorganic Chemistry, Vol. 47, No. 18, 2008

Eu3+-4,4,5,5,5-pentafluoro-1-(naphthalen-2-yl)pentane-1,3-dione
Figure 4. Room temperature (303 K) emission spectra of complexes 1-4.
Figure 5. Experimental luminescence decay profiles of complexes 1 and
4 monitored around 612 nm and excited at their maximum emission
wavelengths.
5
Table 3. Radiative (ARAD) and Nonradiative (ANR) Decay Rates, D0
Lifetime (τobs), Intrinsic Quantum Yield (ΦLn,%), Energy Transfer
Efficiency (Φtransfer, %), and Overall Quantum Yield (Φoverall, %) for
Complexes 1-4 at 303 K
induced electric dipole transition and its corresponding
intense emission at λ ) 613 nm is very sensitive to the
coordination environment.27 This very intense D0 f F2
peak, pointing to a highly polarizable chemical environment
around the Eu3+ ion and is responsible for the brilliant red
emission of these complexes. A relevant feature may be noted
5
7
ARAD
(s-1
ANR
τobs
(µs)
ΦLn
(%)
Φtransfer
(%)
Φoverall
(%)
complex
)
(s-1
)
1
2
3
4
899
560
591
661
557
248
255
160
687 ( 4
1238 ( 8
1183 ( 8
1218 ( 8
62
69
70
81
10
23
53
59
6
16
37
48
5
for the complexes 1-4 is the very high intensity of D0 f
7F2 transition, relative to the5D0 f 7F1 lines, indicating that
the Eu3+ ion coordinated in a local site without an inversion
center. Further, the emission spectra of the complexes show
tion coefficient of HPFNP reveals that the ꢀ-diketonate ligand
has a strong ability of absorbing light.
PL Properties of Complexes 1-4. The normalized
5
7
excitation spectra of the Eu3+ complexes 1-4 recorded at
only one peak for D0 f F0 transition and three stark
components for 5D0 f 7F1 transition indicating the presence
of a single chemical environment around the Eu3+ ion.
5
7
303 K, monitored around the intense D0 f F2 transition
of the Eu3+ ion, are shown in Figure S9. The excitation
spectra of all the complexes exhibit a broadband between
250 and 450 nm and it is completely overlapped by the
absorption spectra of the ligand employed in the correspond-
ing complexes. Thus it is clear that, the central europium(III)
is effectively sensitized by the coordinated ligands. A series
5
The D0 lifetime values (τobs) were determined from the
luminescent decay profiles for the complexes 1-4 at room-
temperature by fitting with a monoexponential curve, indicat-
ing the presence of single chemical environment around the
emitting Eu3+ ion and the values are depicted in Table 3.
Typical decay profiles of complexes 1 and 4 are shown in
Figure 5. The relatively shorter lifetime observed for complex
1 may be caused by dominant nonradiative decay channels
associated with vibronic coupling because of the presence
of solvent molecules, as well documented in many of the
hydrated europium ꢀ-diketonate complexes.9,10 On the other
hand, longer lifetime values have been observed for com-
plexes 2-4 because of the absence of nonradiative decay
pathways (Figure S10 in Supporting Information).
7
of sharp lines assigned to transitions between the F0,1 and
5
5
the L6, D3,2,1 levels are also observed in the excitation
spectra of all these complexes. These transitions are weaker
than the absorption of the organic ligands and are overlapped
by broad excitation band, which proves that luminescence
sensitization via excitation of the ligand is much more
efficient than the direct excitation of the europium(III) ion
absorption level.
Upon excitation under the wavelengths that maximizes the
europium(III) emission intensity, complexes 1-4 showed
characteristic narrow band emissions of Eu3+ corresponding
The overall quantum yield (Φoverall) for a lanthanide
complex treats the system as a “black box”, in which the
internal process is not explicitly considered. Given that the
complex absorbs a photon (i.e., the antenna is excited), the
overall quantum yield can be defined as28
5
7
to the D0 f FJ (J ) 0-4) transitions (Figure 4). The five
5
7
expected peaks for the D0 f F0-4 transitions are well
resolved, and the emission bands at 580 and 650 nm are
very weak since their corresponding transitions 5D0 f 7F0,3
are forbidden both in magnetic and electric dipole schemes.27
The intensity of the emission band at 593 nm is relatively
strong and independent of the coordination environment
because the corresponding transition 5D0 f 7F1 is a magnetic
Φoverall ) ΦtransferΦLn
(2)
Here Φtransfer is the efficiency of energy transfer from the
ligand to Eu3+, and ΦLnrepresents the intrinsic quantum yield
of the lanthanide ion, which can be calculated as
5
7
transition; on the contrary, the D0 f F2 transition is an
Inorganic Chemistry, Vol. 47, No. 18, 2008 8097

Ambili Raj et al.
ΦLn ) ARAD ⁄ (ARAD + ANR) ) τobs ⁄ τrad
(3)
Energy Transfer Processes between Ligands and
Eu3+. In general, the sensitization pathway in luminescent
Eu3+ complexes consists of excitation of the ligands into their
excited singlet states, subsequent intersystem crossing of the
ligands to their triplet states, and the energy transfer from
the triplet state to the 5DJ manifold of the Eu3+ ions, followed
by internal conversion to the emitting 5D0 state. Finally, the
Eu3+ ion emits when transition to the ground-state occurs.32
Moreover, the electron transition from the higher excited
The radiative lifetime (τrad) can be calculated using eq 4,29
5
7
assuming that the energy of the D0 f F1 transition (MD)
and its oscillator strength are constant
ARAD ) 1 ⁄ τrad ) AMD,0n3(Itot ⁄ IMD
where, AMD,0(14.65 s-1) is the spontaneous emission prob-
)
(4)
5
7
ability of the D0 f F1 transition in vacuo, Itot/IMD is the
5
states, such as D3 (24 800 cm-1), 5D2 (21 200 cm-1), and
ratio of the total area of the corrected Eu3+ emission spectrum
5
5D1 (19 000 cm-1) to D0 (17 500 cm-1) becomes feasible
5
7
to the area of the D0 f F1 band, and n is the refractive
index of the medium. An average index of refraction equal
to 1.5 was considered.10a
by internal conversion, and most of the photophysical
processes take place in this orbital. Consequently, most Eu3+
complexes give rise to typical emission bands at ∼581, 593,
614, 654, and 702 nm corresponding to the deactivation of
Table 3 gives the radiative (ARAD) and nonradiative (ANR
)
decay rates, 5D0 lifetime (τobs), intrinsic quantum yield (ΦLn),
energy transfer efficiency (Φtransfer), and overall quantum yield
(Φoverall) for complexes 1-4 at 303 K. According to energy
gap theory, radiation less transitions is prompted by ligands
and solvents with high frequency vibrational modes. Creation
of Eu3+ complexes with higher quantum yields is directly
linked to suppression of radiation less transitions caused by
vibrational excitations in surrounding media.30,31 It is clear
from the Table 3 that complex 1, having solvent molecules
in the coordination sphere exhibits lower overall quantum
yield and lifetime values. This is caused by the presence of
O-H oscillators in this system, which effectively quenches
the luminescence of the Eu3+ ion. On the other hand,
complexes 2-4 exhibit high overall quantum yield and
lifetime values because of the displacement of solvent
molecules from the coordination sphere by the bidentate
nitrogen donors. Among complexes 2-4, 3 and 4 exhibits
better quantum yields than 2 because of the presence of
additional aromatic chromophore moieties in the bidentate
nitrogen donors. Considerable enhancement in the lumines-
cent intensity noticed, especially in complex 4 can be
explained on the basis of extended conjugation induced by
the introduction of two phenyl groups in the 4, 7- positions
of the phenanthroline ligand. It is notable from the present
investigations that the intrinsic quantum yield and 5D0
lifetime values obtained for Eu3+ complexes 2-4 are
significantly higher than that of Eu3+-naphthoyltrifluoroac-
etone-phenanthroline (ΦLn ) 40%; τobs ) 662 µs).12 or Eu3+-
naphthoyltrifluoroacetone-bipyridyl complexes (ΦLn ) 51%;
τobs ) 620 µs).31
5
7
the excited state D0 to the ground states FJ (J ) 0-4).
Thus, matching the energy levels of the triplet state of the
5
ligands to D0 of Eu3+ is one of the key factors that affect
the luminescent properties of the europium complexes.
It is well-known that in organolanthanide complexes
neutral ligands often play a role in absorbing and transporting
energy to other ligands or to the central metal ion.33 For
energy transfer to occur efficiently, the overlap between the
emission spectrum of the donor and the absorption spectrum
of the acceptor is essential.34 Considering complex 2 as a
typical example, the possible energy transfer channels are
explained from the absorption and emission spectra of the
ligands. According to absorption and photoluminescence
spectra of HPFNP and bidentate nitrogen donors (Figures
S11-S13 for bpy, phen and bath), it is clear that there is an
overlap between the room-temperature emission spectrum
of bidentate nitrogen donors and the absorption spectrum of
the HPFNP (from 315-395 nm for bpy; 340-395 nm for
phen; 350-395 nm for bath). It means that the radiations
from the singlet state of bidentate nitrogen donor can be
absorbed by the ꢀ-diketonate ligand. The singlet state of
nitrogen donor can also transfer energy to the triplet level
of HPFNP or to its own triplet level (overlap between the
room-temperature emission of bpy with the low-temperature
emission spectra of HPFNP). The singlet level of HPFNP
can transfer energy to the emitting level of metal ion through
its own triplet energy level (overlap between the room-
temperature and low-temperature emission of HPFNP). The
triplet level of neutral ligand, bpy can also transfer energy
to the central Eu3+ ion directly or through the triplet state of
HPFNP (low-temperature emission spectra of bpy and
HPFNP are overlapped). Thus the energy transfer process
can be summarized in four steps (Figures 6 and S14).
Absorbed energy is transferred from the singlet state of bpy
to that of the singlet state of HPFNP, then from singlet
excited-state to triplet state of the HPFNP or from singlet
(27) Werts, M. H. V.; Jukes, R. T. F.; Verhoeven, J. W. Phys. Chem. Chem.
Phys. 2002, 4, 1542–1548.
(28) (a) Xiao, M.; Selvin, P. R. J. Am. Chem. Soc. 2001, 123, 7067–7073.
(b) Quici, S.; Cavazzini, M.; Marzanni, G.; Accorsi, G.; Armaroli,
N.; Ventura, B.; Barigelletti, F. Inorg. Chem. 2005, 44, 529–537. (c)
Comby, S.; Imbert, D.; Anne-Sophie, C.; Bu¨nzli, J.-C. G.; Charbon-
niere, L. J.; Ziessel, R. F. Inorg. Chem. 2004, 43, 7369–7379.
(29) (a) Viswanathan, S.; de Bettenacourt-Dias, A. Inorg. Chem. 2006, 45,
10138–10146. (b) Kim, Y. H.; Baek, N. S.; Kim, H. K. Chem. Phys.
Chem. 2006, 7, 213–221.
(30) (a) Peng, C.; Zhang, H.; Yu, J.; Meng, Q.; Fu, L.; Li, H.; Sun, L.;
Guo, X. J. Phys. Chem. B. 2005, 109, 15278–15287. (b) Wada, Y.;
Okubo, T.; Ryo, M.; Nakazawa, T.; Hasegawa, Y.; Yanagida, S. J. Am.
Chem. Soc. 2000, 122, 8583–8584.
(32) (a) Bu¨nzli, J.-C. G. In Lanthanide Probes in Life, Chemical and Earth
Sciences; Bu¨nzli, J.-C. G., Choppin, G. R., Eds.; Elsevier: Amsterdam,
1989. (b) Huang, C. H.; Ed. Coordination Chemistry of Rare Earth
Complexes; Science Press: Beijing, 1997.
(33) Xu, H.; Wang, L.-H.; Zhu, X.-H.; Yin, K.; Zhong, G.-Y.; Hou, X.-
Y.; Huang, W. J. Phys. Chem. B. 2006, 110, 3023–3029.
(34) (a) Forster, T. Z. Naturforsch. 1949, A4, 321. (b) Berlman, I. B. Energy
Transfer Parameters of Aromatic Compunds; Academic Press: New
York, 1973.
(31) Fu, L.; Sa’ Ferreira, R. A.; Silva, N. J. O.; Fernandes, J. A.; Ribeiro-
Claro, P.; Goncu¨alves, I. S.; de Zea Bermudez, V.; Carlos, L. D. J.
Mater. Chem. 2005, 15, 3117–3125.
8098 Inorganic Chemistry, Vol. 47, No. 18, 2008

Eu3+-4,4,5,5,5-pentafluoro-1-(naphthalen-2-yl)pentane-1,3-dione
of Gd(PFNP)3 · C2H5OH · H2O and Gd(bath)2(NO3), which
correspond to their lower emission edge wavelengths, are
20 000 (500 nm) and 21 000 cm-1 (476 nm), respectively.
The singlet energy levels (1ππ*) of HPFNP and 4,7-diphenyl-
1,10-phenanthroline are estimated by referencing their higher
absorption edges, which are 25 900 (386 nm) and 29 000
cm-1 (344 nm), respectively. The singlet and triplet energy
levels of bpy (29 900 and 22 900 cm-1) and phen (31 000
and 22 100 cm-1) were taken from the literature.36
According to Reinhoudt’s empirical rule,37 the intersystem
crossing process becomes effective when ∆E(1ππ* - 3ππ*)
is at least 5000 cm-1. The energy gap ∆E(1ππ* - 3ππ*) for
HPFNP, bpy, phen, bath are 5900, 7000, 8900, and 8000
cm-1, respectively. Thus, the intersystem crossing is effective
in all the ligands. According to the empirical rule proposed
by Latva, for an optimal ligand-to-metal energy transfer
Figure 6. Schematic energy level diagram and energy transfer processes
for complex 2. S1 represents the first excited singlet state, and T1 represents
the first excited triplet state.
38
5
process 2500 < ∆E(3ππ* - D0) > 3500 cm-1 for Eu3+.
It is also noted that the energy gaps, ∆E(3ππ* - 5D0) of the
HPFNP, bpy, phen, and bath are 2500, 5400, 4600, and 3500
cm-1, respectively. The triplet energy levels of HPFNP
(20 000 cm-1), bpy (22 900 cm-1), phen (22 100 cm-1), and
5
bath (21 000 cm-1) are higher than the D0 level of Eu3+
(17 500 cm-1), and also their energy gaps are too high to
allow an effective back energy transfer. The schematic energy
level diagrams for the complexes 1-4 are shown in Figures
6 and S14. Luminescence studies demonstrated that the
4,4,5,5,5-pentafluoro-1-(naphthalen-2-yl)pentane-1,3-dione
ligand exhibits a good antennae effect with respect to the
Eu3+ ion because of efficient intersystem crossing and ligand-
to-metal energy transfer. Moreover, the triplet state of the
4,4,5,5,5-pentafluoro-1-(naphthalen-2-yl)pentane-1,3-dione
ligand is located at 20 000 cm-1, which results in a sizable
sensitization of the Eu3+-centered luminescence.
Figure 7. Phosphorescence spectra of Gd(PFNP)3 ·H2O·C2H5OH at 77 K.
Conclusions
Based on the novel ꢀ-diketone, HPFNP, four new Eu3+
complexes 1-4 have been synthesized, one of which
has been structurally characterized by single crystal
X-ray crystallography. The X-ray crystal structure of
Eu(PFNP)3.bpy reveals a distorted square antiprismatic
around the Eu3+ atom. Further, analysis of the X-ray crystal
data reveals interesting one-, two-, and three-dimensional
arrays of Eu3+-4,4,5,5,5-pentafluoro-1-(naphthalen-2-yl)pen-
tane-1,3-dione-2,2′-bipyridine complex through intra- and
intermolecular hydrogen bonds. The luminescent studies
demonstrates that the displacement of solvent molecules by
bidentate nitrogen donors in Eu(PFNP)3 · C2H5OH · H2O
greatly enhances the metal-centered luminescence quantum
yields and lifetime values. The introduction of polyfluorinated
alkyl group, as well as long conjugated naphthyl group in
ꢀ-diketonate ligand, significantly improves the intrinsic
luminescent quantum yields of Eu3+ ion in complexes 1-4
excited-state of HPFNP to the triplet state of bpy. The triplet
state of bpy can transfer energy to the emitting level of Eu3+
ion directly or through the triplet level of HPFNP. Finally,
energy transfers from triplet excited-state of HPFNP to the
emitting level of Eu3+.
To elucidate the energy transfer process of the Eu3+
complexes, the energy levels of the relevant electronic states
of the ligands have been determined. The singlet and triplet
energy levels of HPFNP and bidentate nitrogen donors were
estimated by referring to their wavelengths of UV-vis
absorbance edges and the lower wavelength emission
edges of the corresponding phosphorescence spectra. The
triplet energy level of the ligand was not affected signifi-
cantly by the Ln3+ ion, and the lowest-lying excited
level (6P7/2 f 8S7/2) of Gd3+ is located at 32 150 cm-1.35 On
this basis, the phosphorescence spectra of Gd(PFNP)3 ·
C2H5OH · H2O (Figure 7) and Gd(bath)2(NO3)3 (Figure S15)
allow one to evaluate the triplet energy levels (3ππ*)
corresponding ligand anions for all the lanthanide chelates.
From the phosphorescence spectra, the triplet energy levels
(36) Yu, X.; Su, Q. J. Photochem. Photobiolog. A: Chem. 2003, 155, 73–
78.
(37) Steemers, F. J.; Verboom, W.; Reinhoudt, D. N.; van der Tol, E. B.;
Verhoeven, J. W. J. Am. Chem. Soc. 1995, 117, 9408–9414.
(38) Latva, M.; Takalo, H.; Mukkala, V. -M.; Matachescu, C.; Rodriguez-
Ubis, J. C.; Kankare, J. J. Lumin. 1997, 75, 149–169.
(35) Dieke, G. H. Spectra and Energy LeVels of Rare Earth Ions in Crystals;
Wiley-Interscience: New York, 1968.
Inorganic Chemistry, Vol. 47, No. 18, 2008 8099

Ambili Raj et al.
(62-81%) as compared to existing Eu3+-naphthoyltrifluo-
roacetone-nitrogen donor complexes (40-50%). Thus our
results clearly highlights that Eu3+-4,4,5,5,5-pentafluoro-1-
(naphthalen-2-yl)pentane-1,3-dione complexes involving bi-
dentate nitrogen donors may find potential applications as
light conversion molecular devices in many photonic ap-
plications.
Technology Division, and Dr. A. Srinivasan, National Institute
for Interdisciplinary Science & Technology (NIIST), Trivan-
drum, India, for their constant encouragement and valuable
discussions. Dr. Babu Varghese, Senior Scientific Officer
Grade I, SAIF, IIT-Madras, is also acknowledged for X-Ray
crystallographic analysis.
Supporting Information Available: Crystallographic data, TG
data, luminescence decay profiles, phosphorescence spectrum,
absorption and emission spectra of HPFNP, bpy, and phen at 303
and 77 K in CH3CN solution, and schematic energy level diagram.
This material is available free of charge via the Internet at
http://pubs.acs.org.
Acknowledgment. The authors acknowledge financial
support from the Council of Scientific and Industrial
Research (NWP0023), Defence Research and Development
Organization, and University Grants Commission, New
Delhi. The authors also thank Prof. T. K. Chandrashekar,
Director, and Dr. Suresh Das, Head, Chemical Sciences &
IC8004757
8100 Inorganic Chemistry, Vol. 47, No. 18, 2008