Role of the ancillary ligand N,N-dimethylaminoethanol in the sensitization of EuIII and TbIII luminescence in dimeric β-diketonates

Article abstract of DOI:10.1021/jp711305u

Two types of dimeric complexes [Ln₂(hfa) ₆(μ₂-O(CH₂)₂NHMe ₂)₂] and [Ln(thd)₂(μ₂, η²O(CH₂)₂NMe₂)]₂ (Ln = Y_III Eu_III, Gd_III, Tb_III, Tm _III, Lu_III; hfa^- = hexafluoroacetylacetonato, thd^- = dipivaloylmethanato) are obtained by reacting [Ln(hfa) ₃(H₂O)₂] and [Ln(thd)₃], respectively, with N,N-dimethylaminoethanol in toluene and are fully characterized. X-ray single crystal analysis performed for the Tb^III compounds confirms their dimeric structure. The coordination mode of N,N-dimethylaminoethanol depends on the nature of the β-diketonate. In [Tb₂(hfa)₆(μ₂-O(CH₂) ₂NHMe₂)₂], eight-coordinate Tb^III ions adopt distorted square antiprismatic coordination environments and are O-bridged by two zwitterionic N,N-dimethylaminoethanol ligands with a Tb1...Tb2 separation of 3.684(1) A. In [Tb(thd) ₂(μ₂,η²-O(CH₂) ₂NMe₂)]₂, the N,N-dimethyIaminoethanol acts as chelating-bridging O,N-donor anion and the Tb^III ions are seven-coordinate; the Tb1...Tb1A separation amounts to 3.735(2) A within centrosymmetric dimers. The dimeric complexes are thermally stable up to 180°C, as shown by thermogravimetric analysis, and their volatility is sufficient for quantitative sublimation under reduced pressure. The Eu ^III and Tb^III dimers display metal-centered luminescence, particularly [Eu₂(hfa)₆(O(CH₂) ₂NHMe₂)₂] (quantum yield Q_Ln ^L = 58%) and [Tb(thd)₂(O(CH₂) ₂NMe₂)]₂ (32%). Consideration of energy migration paths within the dimers, based on the study of both pure and Eu ^III- or Tb^III-doped (0.01-0.1 mol %) Lu^III analogues, leads to the conclusion that both the β-diketone and N,N-dimethylaminoethanol ligands contribute significantly to the sensitization process of the Eu^III luminescence. The ancillary ligand increases considerably the luminescence of [Eu₂(hfa)₆(O(CH ₂)₂NHMe₂)₂], compared to [Ln(hfa)₃(H₂O)₂], through the formation of intra-ligand states while it is detrimental to Tb^III luminescence in both β-diketonates. Thin films of the most luminescent compound [Eu ₂(hfa)₆(O(CH₂)₂NHMe ₂)₂] obtained by vacuum sublimation display photophysical properties analogous to those of the solid-state sample, thus opening perspectives for applications in electroluminescent devices.

Full text of DOI:10.1021/jp711305u

3614
J. Phys. Chem. A 2008, 112, 3614-3626
Role of the Ancillary Ligand N,N-Dimethylaminoethanol in the Sensitization of EuIII and
TbIII Luminescence in Dimeric â-Diketonates
Svetlana V. Eliseeva,*,† Oxana V. Kotova,† Fre´de´ric Gumy,‡ Sergey N. Semenov,†,
Vadim G. Kessler,§ Leonid S. Lepnev,| Jean-Claude G. Bu1nzli,‡ and Natalia P. Kuzmina†
Department of Chemistry, Department of Materials Sciences, LomonosoV Moscow State UniVersity,
Leninskie Gory 1-3, 119991 Moscow, Russia, Laboratory of Lanthanide Supramolecular Chemistry, EÄ cole
Polytechnique Fe´de´rale de Lausanne (EPFL), BCH 1405, 1015 Lausanne, Switzerland, Department of
Chemistry, Swedish UniVersity of Agricultural Sciences, P.O. Box 7015, 75007 Uppsala, Sweden, and
VaViloV Luminescence Laboratory, LebedeV Physical Institute of Russian Academy of Sciences,
Leninsky Prospect 53, 119991 Moscow, Russia
ReceiVed: NoVember 29, 2007; In Final Form: January 29, 2008
Two types of dimeric complexes [Ln2(hfa)6(µ2-O(CH2)2NHMe2)2] and [Ln(thd)2(µ2,η2-O(CH2)2NMe2)]2 (Ln
) YIII, EuIII, GdIII, TbIII, TmIII, LuIII; hfa- ) hexafluoroacetylacetonato, thd- ) dipivaloylmethanato) are
obtained by reacting [Ln(hfa)3(H2O)2] and [Ln(thd)3], respectively, with N,N-dimethylaminoethanol in toluene
and are fully characterized. X-ray single crystal analysis performed for the TbIII compounds confirms their
dimeric structure. The coordination mode of N,N-dimethylaminoethanol depends on the nature of the
â-diketonate. In [Tb2(hfa)6(µ2-O(CH2)2NHMe2)2], eight-coordinate TbIII ions adopt distorted square antiprismatic
coordination environments and are O-bridged by two zwitterionic N,N-dimethylaminoethanol ligands with a
Tb1‚‚‚Tb2 separation of 3.684(1) Å. In [Tb(thd)2(µ2,η2-O(CH2)2NMe2)]2, the N,N-dimethylaminoethanol acts
as chelating-bridging O,N-donor anion and the TbIII ions are seven-coordinate; the Tb1‚‚‚Tb1A separation
amounts to 3.735(2) Å within centrosymmetric dimers. The dimeric complexes are thermally stable up to
180 °C, as shown by thermogravimetric analysis, and their volatility is sufficient for quantitative sublima-
tion under reduced pressure. The EuIII and TbIII dimers display metal-centered luminescence, particularly
[Eu2(hfa)6(O(CH2)2NHMe2)2] (quantum yield QL ) 58%) and [Tb(thd)2(O(CH2)2NMe2)]2 (32%). Consider-
Ln
ation of energy migration paths within the dimers, based on the study of both pure and EuIII- or TbIII-doped
(0.01-0.1 mol %) LuIII analogues, leads to the conclusion that both the â-diketone and N,N-dimethylami-
noethanol ligands contribute significantly to the sensitization process of the EuIII luminescence. The ancillary
ligand increases considerably the luminescence of [Eu2(hfa)6(O(CH2)2NHMe2)2], compared to [Ln(hfa)3(H2O)2],
through the formation of intra-ligand states while it is detrimental to TbIII luminescence in both â-diketonates.
Thin films of the most luminescent compound [Eu2(hfa)6(O(CH2)2NHMe2)2] obtained by vacuum sublimation
display photophysical properties analogous to those of the solid-state sample, thus opening perspectives for
applications in electroluminescent devices.
Introduction
tuning of the coordination properties of the lanthanide ions and
an adequate choice of both primary and ancillary ligands to
control the competitive coordination of substrates, solvents, and
other molecules. Aminoalcohols behave either as anionic or
neutral (respectively zwitterionic) ligands and adopt a variety
of binding modes due to the presence of two donor atoms,
nitrogen and oxygen, which are easily accessible for coordina-
tion. For instance, they can act as monodentate ligands binding
metal ions through either oxygen, similarly to alcohols and
alkoxides,5 or nitrogen, such as amines, as shown in [Cu(hfa)-
(L)] where L is deprotonated triethanolamine or N,N-dimeth-
ylethanolamine.6 Alternatively, they can bind in a bidentate
fashion through both oxygen and nitrogen atoms, adopting
terminal/bridging, chelating, or bridging/chelating modes.7-10
Taking into account the pronounced hard Lewis acid character
of trivalent lanthanide ions,11 it is anticipated that coordination
to these ions will essentially be achieved through oxygen
binding.
Lanthanide(III) â-diketonates are among the most thoroughly
investigated classes of coordination compounds. The consider-
able attention they have been attracting until now stems from
both their easy synthesis and the variety of practical applications
in which they can be involved.1 In neutral lanthanide tris(â-
diketonates), the central ions are bound to six oxygen atoms
and thus coordinatively unsaturated. This results in the pos-
sibility of binding one or more ancillary ligands to achieve the
usual coordination numbers observed in most lanthanide com-
plexes (8-10) and to implement a desired functionality. The
latter property is widely used in NMR shift reagents,2 catalysis,3
and sensing/probing devices.4 Such applications require a precise
* To whom correspondence should be addressed. E-mail: eliseeva@
inorg.chem.msu.ru. Phone: +7-495-939-3836. Fax: +7-495-939-0998.
† Lomonosov Moscow State University.
‡ EÄ cole Polytechnique Fe´de´rale de Lausanne (EPFL).
§ Swedish University of Agricultural Sciences.
Recently, Tsukube et al.12 have reported the use of lanthanide
tris(â-diketonates) as chirality sensing agents for aminoalcohols.
For instance, fluorinated lanthanide â-diketonates form 1:1
| Lebedev Physical Institute of Russian Academy of Sciences.
Present address: University of Zu¨rich, Institute of Inorganic Chemistry,
Winterthurerstrasse 190, CH 8057, Switzerland.
10.1021/jp711305u CCC: $40.75 © 2008 American Chemical Society
Published on Web 03/22/2008

Sensitization of EuIII and TbIII in Dimeric â-Diketonates
J. Phys. Chem. A, Vol. 112, No. 16, 2008 3615
highly coordinated complexes with aminoalcohols in MeOH/
CH2Cl2 solution in which the aminoalcohol acts as ancillary
bidentate neutral ligand. The resulting complexes exhibit largely
enhanced luminescence and intense induced circular dichroism
signals. The latter depend on the structure and chirality of the
bound aminoalcohol. However, only one crystal structure of
such a mixed complex, namely [Pr2(hfa)4(bdmap)2(H2O)2(thf)2]
(bdmap ) 1,3-bis(dimethylamino)-2-propoxide, thf ) tetrahy-
drofuran), is described.9
In this work, we investigate the reaction of N,N-dimethyl-
aminoethanol with fluorinated (hexafluoroacetyl-acetonato, hfa-)
and bulky (dipivaloylmethanato, thd-) lanthanide â-di-ketonates,
which turned to yield dimeric species. The two series of
complexes, namely [Ln2(hfa)6(O(CH2)2NHMe2)2] and [Ln(thd)2-
(O(CH2)2NMe2)]2 (Ln ) YIII, EuIII, GdIII, TbIII, TmIII, LuIII),
are structurally characterized, and their thermal and photophysi-
cal properties are investigated. To access more information about
energy-transfer processes in the reported EuIII and TbIII com-
pounds, the photophysical properties of both pure and EuIII- or
TbIII-doped LuIII complexes are also studied. Finally, to evaluate
the potential of the new dimeric complex [Eu2(hfa)6(O(CH2)2-
NHMe2)2] as an emitting layer in electroluminescent devices,
thin films of this derivative are produced by vacuum sublima-
tion, and their emissive properties are compared with those of
the corresponding solid-state sample.
s; 1210 br s; 1146 br s; 1098 s; 1078 s; 1006 w; 986 w; 952 w;
920 w; 886 w; 798 s; 768 w; 742 m; 722 w; 662 s; 588 m; 528
w; 466 w cm-1
.
C38H28F36N2O14Eu2 (1724.52): calcd C 26.47, H 1.64, N 1.62;
found C 26.35, H 1.81, N 1.82%. IR data: ν˜ ) 3396 br w;
3306 w; 3098 m; 2902 w; 1662 br s; 1654 br s; 1606 m; 1560
s; 1532 s; 1510 s; 1476 s; 1460 s; 1438 m; 1424 m; 1390 m;
1348 m; 1322 m; 1256 br s; 1206 br s; 1142 br s; 1100 s; 1078
s; 1068 m; 1008 w; 984 w; 950 w; 922 w; 884 w; 838 w; 798
s; 766 w; 758 w; 742 m; 722 w; 662 s; 586 s; 528 w; 462 w
cm-1. LDI-TOF MS (EI+): 519, [Eu(CF3COCHCO)2(O(CH2)2-
NHMe2) + 2H+]+ (7%); 608, [Eu(CF3COCHCO)2(O(CH2)2-
NHMe2)2 + 2H+]+ (7%); 959, [Eu2(hfa)(CF3COCHCO)2-
(O(CH2)2NHMe2)2 - 3CH3 + 2F + H+]+ (90%); 1053,
[Eu2(hfa)2(CF3COCHCO)(O(CH2)2NHMe2)2 + F)]+ (100%);
1148, [Eu2(hfa)2(CF3COCHCO)2(O(CH2)2NHMe2)2 - 3CH3 +
F]+ (80%); 1243, [Eu2(hfa)3(CF3COCHCO)(O(CH2)2NHMe2)2
+ 2H+]+ (45%); 1429, [Eu2(hfa)4(CF3COCHCO)(O(CH2)2-
NHMe2)2 - F]+ (7%); 1524, [Eu3(hfa)4(CF3COCHCO)(O(CH2)2-
NHMe2)2 - 3CH3 - F + 3H+]+ (15%).
C38H28F36N2O14Gd2 (1735.09): calcd C 26.31, H 1.63, N
1.61; found C 26.30, H 1.75, N 1.74%. IR data: ν˜ ) 3396 br
w; 3306 w; 3098 m; 2903 w; 1662 br s; 1654 br s; 1604 m;
1560 s; 1534 s; 1510 s; 1475 s; 1460 s; 1438 m; 1424 m; 1402
w; 1390 m; 1348 m; 1322 w; 1256 br s; 1206 br s; 1142 br s;
1100 s; 1078 s; 1068 m; 1008 m; 984 m; 950 w; 922 w; 886 w;
838 w; 798 s; 766 w; 758 w; 742 m; 722 w; 662 s; 586 s; 528
Experimental Section
w; 462 w cm-1
.
Reagents and Physical Methods. Commercially available
starting reagents Hhfa (Merck), Hthd (Aldrich), and N,N-
dimethylaminoethanol (Aldrich) were of analytical grade and
used as received. Lanthanide nitrate hydrates Ln(NO3)3‚xH2O
were obtained by treating the respective lanthanide oxides Ln2O3
(99.998%) or Tb4O7 (99.998%) with concentrated nitric acid,
followed by evaporation of excess acid. [Ln(hfa)3(H2O)2] and
[Ln(thd)3(H2O)2] were synthesized according to procedures
described in ref 13 and 14, respectively. [Ln(thd)3] were obtained
by sublimation of the corresponding hydrated complexes at
180-200 °C under a pressure of 10-2 Torr.
Elemental analyses (C, H, N) were performed by the
Microanalytical Service of the Center for Drug Chemistry
(Moscow, Russia). IR spectra were recorded in Nujol mull or
hexachlorobutadiene between KBr plates in the 4000-400 cm-1
range using a Perkin-Elmer 1600 FT-IR spectrometer. LDI-TOF
mass spectra were run on an Autoflex II (Bruker Daltonics,
Germany) using the electron-impact positive mode (accelerating
voltage 19 kV) and a nitrogen laser (337 nm, impulse duration
1 ns). Thermogravimetric analysis was performed on a Q-1500
thermal analyzer in nitrogen atmosphere at a heating rate of 5
°C‚min-1. Isothermal dynamic sublimation experiments were
run with samples (∼100 mg) placed into glass test tubes for
periods of about 30 min at 220-240 °C and a pressure of 10-2
Torr. Weight loss was equal to ∼95-100%.
C38H28F36N2O14Tb2 (1738.44): calcd C 26.25, H 1.62, N 1.61;
found C 26.36, H 1.50, N 1.73%. IR data: ν˜ ) 3396 br w;
3304 w; 3094 m; 2904 w; 1664 br s; 1654 br s; 1604 m; 1560
s; 1535 s; 1512 s; 1474 s; 1460 s; 1438 w; 1424 w; 1400 w;
1392 w; 1348 m; 1322 w; 1256 br s; 1206 br s; 1142 br s;
1100 s; 1080 s; 1068 s; 1008 m; 986 m; 950 w; 922 w; 886 w;
838 w; 798 s; 766 w; 758 w; 742 m; 722 w; 662 s; 586 s; 528
w; 462 w cm-1
.
C38H28F36N2O14Tm2 (1758.46): calcd C 25.96, H 1.60, N
1.59; found C 25.96, H 1.58, N 1.62%. IR data: ν˜ ) 3392 br
w; 3306 w; 3108 m; 2906 w; 1666 br s; 1656 br s; 1612 m;
1600 m; 1560 s; 1536 s; 1518 s; 1472 s; 1464 s; 1438 m; 1422
m; 1400 m; 1388 m; 1350 m; 1324 m; 1260 br s; 1210 br s;
1146 br s; 1100 m; 1080 m; 1068 m; 1008 w; 988 w; 952 w;
922 w; 886 w; 840 w; 798 m; 768 w; 742 w; 722 w; 662 s; 588
m; 528 w; 464 w cm-1
.
C38H28F36N2O14Lu2 (1770.51): calcd C 25.78, H 1.59, N 1.58;
found C 25.61, H 1.58, N 1.58%. IR data: ν˜ ) 3410 br w;
3306 w; 3114 m; 3118 m; 2916 w; 1660 br s; 1604 m; 1560 s;
1536 s; 1508 s; 1474 s; 1464 s; 1438 m; 1422 m; 1400 m; 1388
m; 1350 m; 1324 m; 1260 br s; 1210 br s; 1144 br s; 1100 s;
1082 s; 1068 m; 996 w; 988 w; 952 w; 922 w; 888 w; 848 w;
800 s; 768 m; 742 m; 724 m; 662 s; 588 m; 528 w; 466 w
cm-1
.
Syntheses. [Ln2(hfa)6(µ2-O(CH2)2NHMe2)2]. To a suspension
of [Ln(hfa)3(H2O)2] (0.40 mmol) in 5 mL of toluene, N,N-
dimethylaminoethanol (0.04 mL, 0.40 mmol) was added drop-
wise under stirring. The resulting transparent solution was
allowed to stay for 2-3 days at 258 K. The crystalline frac-
tion was isolated by decantation and dried in vacuum. Yield:
85-90%.
C38H28F36N2O14Y2 (1598.39): calcd C 28.55, H 1.77, N 1.75;
found C 28.76, H 1.59, N 1.75%. IR data: ν˜ ) 3392 br w;
3306 w; 3114 br m; 2974 w; 2906 w; 1666 br s; 1656 br s;
1600 m; 1562 s; 1536 s; 1518 s; 1502 m; 1478 m; 1470 m;
1464 m; 1440 m; 1402 m; 1390 m; 1350 m; 1322 m; 1260 br
[Ln(thd)2(µ2,η2-O(CH2)2NMe2)]2. N,N-Dimethylaminoethanol
(0.04 mL, 0.40 mmol) was added dropwise and under stirring
to a suspension of [Ln(thd)3] (0.40 mmol) in 5 mL of toluene.
The mixture first became transparent, and then a polycrystalline
precipitate appeared. The solid was isolated by filtration or
decantation. An additional portion was obtained by storing the
mother liquor at 258 K. The obtained products were dried in
vacuum. Overall yield: 85-90%.
C52H96N2O10Y2 (1087.14): calcd C 57.45, H 8.90, N 2.58;
found C 57.60, H 8.98, N 2.64%. IR data: ν˜ ) 2978 s; 2956 s;
2924 s; 2898 s; 2862 s; 2834 s; 2790 m; 1594 s; 1574 s; 1548

3616 J. Phys. Chem. A, Vol. 112, No. 16, 2008
Eliseeva et al.
TABLE 1: Crystallographic Data and Some Details of Data Collection and Structures Refinement for the TbIII Complexes with
N,N-dimethylaminoethanol
compound
[Tb2(hfa)6(O(CH2)2NHMe2)2]‚C7H8
[Tb(thd)2(O(CH2)2NMe2)]2
formula unit
molecular weight
crystal system
space group
a, Å
b, Å
c, Å
C45H36F36N2O14Tb2
1830.60
C52H96N2O10Tb2
1227.15
monoclinic
P21/c (No. 14)
12.817(6)
16.192(1)
14.550(1)
90
monoclinic
P21/n (No. 14)
20.334(5)
13.796(3)
23.228(4)
90
95.03(4)
90
6491(2)
R, °
â, °
91.77(5)
90
3018(4)
γ, °
volume, Å3
Z
8
2
F
calc., g‚cm-3
1.873
295(2)
1.350
295(2)
T, K
crystal size, mm
0.35 × 0.25 × 0.20
0.45 × 0.40 × 0.35
linear absorption coefficient µ, cm-1
θ range for data, °
23.2
23.7
1.3 - 23.0
9008/5218
907/174
1.9 - 28.4
6878/4102
298/0
total/observed [I > 2σ(I)] reflections
parameters refined/ restraints
R1, ωR2
0.059, 0.104
0.040, 0.072
s; 1538 s; 1504 s; 1490 s; 1480 s; 1450 s; 1426 s; 1408 s; 1398
s; 1356 s; 1276 m; 1260 m; 1244 m; 1226 s; 1198 m; 1178 s;
1138 s; 1116 m; 1094 s; 1040 m; 1026 m; 952 m; 930 m; 898
m; 866 s; 820 w; 792 m; 784 m; 758 m; 732 m; 606 m; 580 m;
1140 m; 1096 m; 1072 m; 1024 w; 954 w; 930 w; 900 w; 868
m; 820 w; 792 m; 784 w; 758 w; 732 w; 606 w; 584 w; 478 m
cm-1
.
Preparation of the doped by EuIII (or TbIII) LuIII complexes.
A toluene solution of LuIII and EuIII (or TbIII) complexes in
calculated amounts (0.01, 0.05, 0.1%) were mixed under stirring.
The resulting mixtures were left for crystallization until full
evaporation of the solvent and then the solid products were
thoroughly grinded in a mortar and dried in vacuum.
474 s cm-1
.
C52H96N2O10Eu2 (1213.25): calcd C 51.48, H 7.98, N 2.31;
found C 51.58, H 8.05, N 2.40%. IR data: ν˜ ) 2962 s; 2902 s;
2864 s; 2836 m; 2792 m; 1588 s; 1574 s; 1546 s; 1538 s; 1506
s; 1492 s; 1480 s; 1462 s; 1454 s; 1418 s; 1398 s; 1388 s; 1358
s; 1284 m; 1244 s; 1226 s; 1198 m; 1178 s; 1140 s; 1102 m;
1072 s; 1034 m; 1024 m; 962 m; 938 m; 868 s; 820 w; 792 m;
780 w; 756 m; 734 m; 722 w; 668 w; 602 m; 572 w; 476 s
cm-1. LDI-TOF MS (EI+): 1029, [Eu2(thd)3((H3C)3CCOCH)-
(O(CH2)2NMe2)]+ (10%); 1124, [Eu2(thd)4(O(CH2)2NMe2)]+
(30%); 1219, [Eu2(thd)5]+ (100%).
Data Collection and Structural Refinement. Diffraction
data were collected on a Bruker SMART charge-coupled device
(CCD) diffractometer at room-temperature routinely to 2θ )
56°. The data was then limited intentionally by introducing a
high-angle cutoff for the ranges, where only a minor fraction
of all reflections was really observed. The SAINT PLUS and
the SHELXTL-NT program packages were used for data
reduction and computations.15 Empirical absorption correction
was applied using the Bruker SADABS program package. The
positions of all non-hydrogen atoms were refined anisotropically
by full-matrix least-squares techniques. In the crystal structure
of [Tb2(hfa)6(O(CH2)2NHMe2)2]‚C7H8, a noticeable rotational
disorder through elongated thermal ellipsoids for the F atoms
of the CF3 groups in the hfa- ligand was observed. The latter
in combination with low reflectivity at higher angles did not
permit to resolve the geometric disorder in the crystal structure
of hfa--containing complex. The hydrogen atoms, except for
H1N and H2N in [Tb2(hfa)6(O(CH2)2NHMe2)2]‚C7H8, which
were found in differential Fourier syntheses and refined iso-
tropically, were included in calculated positions and refined in
a riding mode. Crystallographic data and some details of data
collection and structures refinement are listed in Table 1.
Electrochemical Measurements. Cyclic voltammograms
were recorded with a BAS CV-100W voltammetric analyzer
and a three-electrode system consisting of a stationary Pt disk
as working electrode, Pt wire auxiliary electrode, and nonaque-
ous silver reference electrode (Ag wire in 0.1 M NBu4PF6 +
0.01 AgNO3 solution in CH3CN or THF) in an argon glove
box. NBu4PF6 (0.1 M in CH3CN or THF) served as inert
electrolyte and the concentration of the complex in solution was
10-2 M. The scan rate was 0.1 V‚s-1. The voltammograms were
analyzed according to the established procedures.16
C52H96N2O10Gd2 (1223.83): calcd C 51.03, H 7.91, N 2.29;
found C 50.96, H 7.98, N 2.35%. IR data: ν˜ ) 2960 s; 2900 s;
2864 m; 2836 m; 2792 w; 1590 s; 1574 s; 1546 s; 1538 s; 1506
s; 1492 s; 1480 s; 1458 s; 1418 s; 1398 s; 1388 s; 1358 s; 1284
m; 1244 s; 1226 s; 1198 m; 1178 s; 1140 s; 1102 m; 1094 w;
1072 s; 1034 m; 1024 m; 962 m; 938 m; 868 s; 820 w; 792 m;
780 w; 756 m; 734 m; 722 w; 602 m; 574 w; 476 s cm-1
.
C52H96N2O10Tb2 (1227.18): calcd C 50.89, H 7.88, N 2.28;
found C 50.50, H 7.85, N 2.15%. IR data: ν˜ ) 2958 s; 2952 s;
2900 m; 2862 m; 2836 w; 2792 w; 1590 s; 1576 s; 1546 s;
1538 s; 1506 s; 1490 s; 1480 s; 1452 s; 1418 s; 1396 s; 1388
s; 1356 s; 1284 m; 1244 m; 1226 m; 1198 m; 1178 m; 1140 m;
1102 w; 1092 w; 1072 m; 1034 w; 1024 w; 962 w; 938 w; 868
m; 820 w; 792 m; 780 w; 756 w; 734 w; 604 w; 576 w; 476 m
cm-1
.
C52H96N2O10Tm2 (1247.19): calcd C 50.08, H 7.76, N 2.25;
found C 49.71, H 7.80, N 2.08%. IR data: ν˜ ) 2978 s; 2962 s;
2924 s; 2900 m; 2860 m; 2834 w; 2790 w; 1594 s; 1574 s;
1548 m; 1538 m; 1504 s; 1490 s; 1480 s; 1454 s; 1426 s; 1408
s; 1398 s; 1356 s; 1276 m; 1244 m; 1226 m; 1198 w; 1180 m;
1140 m; 1094 m; 1072 m; 1026 w; 954 w; 930 w; 868 m; 820
w; 792 m; 784 w; 758 w; 730 w; 606 w; 582 w; 476 m cm-1
.
C52H96N2O10Lu2 (1259.26): calcd C 49.60, H 7.68, N 2.22;
found C 49.35, H 7.68, N 2.28%. IR data: ν˜ ) 2980 s; 2956 s;
2922 s; 2902 m; 2862 m; 2834 m; 2790 w; 1596 s; 1576 s;
1548 m; 1538 m; 1504 s; 1490 s; 1482 s; 1452 s; 1426 s; 1410
s; 1398 s; 1356 s; 1276 m; 1244 m; 1226 m; 1198 w; 1180 m;
Luminescence Measurements. At 295 K, the luminescence
data (spectra, lifetimes) were recorded with a Fluorolog FL3-

Sensitization of EuIII and TbIII in Dimeric â-Diketonates
J. Phys. Chem. A, Vol. 112, No. 16, 2008 3617
22 spectrofluorimeter from Horiba-Jobin-Yvon-Spex. At 77 K,
the luminescence spectra were measured using a multichan-
nel spectrometer S2000 (Ocean Optics) with nitrogen laser
LGI-21 (λex ) 337 nm) as an excitation source, and lifetimes
were determined using boxcar averager system (model 162)
including gated integrators (model 164) and wide-band pream-
plifier (model 115) from EG&G Princeton applied research.
Lifetimes of the compounds were recorded upon excitation of
either the EuIII (5D2) or TbIII (5D4) or the organic ligands and
monitoring the 5D0 f 7F2 or 5D4 f 7F5 transitions, respectively.
Lifetimes are averages of at least three independent measure-
ments. All luminescence decays proved to be perfect single-
exponential functions. Excitation spectra were measured at 295
K with a Fluorolog FL3-22 spectrofluorimeter from Horiba-
SCHEME 1: Possible Ways of Interaction between
[M(dik)x(H2O)n] and N,N-dimethylaminoethanol in
Toluene
5
7
5
Jobin-Yvon-Spex upon monitoring the D0 f F2 and D4 f
7F5 transitions for EuIII and TbIII compounds, respectively. All
excitation and luminescence spectra were corrected for the
instrumental functions. All measurements were performed on
well grinded thick solid samples in special cells.
Quantum yields were determined on solid samples with a
Fluorolog FL3-22 spectrofluorimeter from Horiba-Jobin-Yvon-
Spex at 295 K, under ligand excitation, according to the absolute
method of Wrighton.17 Each sample was measured several times
under slightly different experimental conditions. The estimated
error for quantum yields is (10%.
Diffuse Reflectivity Spectra. UV-vis reflectance spectra for
solid samples of GdIII complexes (Figure S1, Supporting
Information) were recorded with a Lambda 35 spectrophotom-
eter (Perkin-Elmer).
Refractive Index and Thickness of Thin Films. Thin films
of [Eu2(hfa)6(O(CH2)2NHMe2)2] were deposited on quartz
substrates by vacuum evaporation (P ∼ 10-6 Torr, Leybold
Heraeus). The refractive index (n) and the thickness of the
layer (d) were determined with a Filmetric F20 Thin Film
Analyzer. The results are averages of at least three measure-
ments. [Eu2(hfa)6(O(CH2)2NHMe2)2] (thin film): n ) (1.5127
( 0.0008), d ) (292 ( 16) nm.
reaction mixture. In our case, interaction between [Ln(hfa)3-
(H2O)2] and N,N-dimethylaminoethanol in toluene results in the
formation of [Ln2(hfa)6(µ2-O(CH2)2NHMe2)2] (type 1, Scheme
1) only and a prolonged reflux (>12 h) of the reaction mixture
does not lead to the isolation of mixed hexafluoroacetylaceto-
nato-alkoxide complexes (type 2). Because LnIII ions are harder
Lewis acids than CuII, the formation of mixed â-diketonato-
alkoxide complexes is more difficult and requires special
conditions to shift the equilibrium (Scheme 1) toward the
formation of type 2 products, for instance, a â-diketone having
comparable acidity as N,N-dimethylaminoethanol. This is indeed
the case for the reaction of [Ln(thd)3] (pKa,Hthd(H2O) ) 11.6 -
14.4)22 with N,N-dimethylaminoethanol which results in the
displacement of one of the thd- ligands; the proton of the
aminoalcohol is transferred onto one of the â-diketonato moiety
which is then eliminated under the form of Hthd; the overall
process yields exclusively the mixed â-diketonato-alkoxide
complexes, [Ln(thd)2(µ2,η2-O(CH2)2NMe2)]2.
Results and Discussion
Infrared spectra of [Ln2(hfa)6(O(CH2)2NHMe2)2] and
[Ln(thd)2(O(CH2)2NMe2)]2 are similar for all the studied lan-
thanide ions. They display the typical ν(CdO) and ν(CdC)
modes in the range 1700-1500 cm-1, as observed for other
lanthanide â-diketonates.23 For [Ln2(hfa)6(O(CH2)2NHMe2)2],
typical C-F vibrations are observed in the range 1300-1100
cm-1 and bands of C-H vibrations of N,N-dimethylamino-
ethanol ligand can be seen at 3000-2900 cm-1, and for
[Ln(thd)2(O(CH2)2NMe2)]2 the latter are overlapped with strong
Synthesis and Characterization. The reaction of N,N-
dimethylaminoethanol with lanthanide(III) hexafluoroacetyl-
acetonates and dipivaloylmethanates in a molar ratio 1:1 in
toluene afforded two different types of mixed-ligand complexes
depending on the nature of the â-diketone, Hdik. According to
previously reported studies6,18 of similar reactions between
[Cu(hfa)2] and different aminoalcohols, the following scheme
can be proposed to discuss the interaction between N,N-
dimethylaminoethanol and [M(dik)x(H2O)n] in toluene (Scheme
1, with x ) 3 in the case of LnIII ions and 2 for CuII).
Obviously, the formation of the mixed â-diketonato-alkoxide
complexes (type 2, Scheme 1) is governed by the acidity of
Hdik. In principle, the acidity of aliphatic alcohols is much
smaller (pKa(H2O) ∼ 15)19 than the acidity of most â-diketones,
for example, pKa(H2O) ) 4.420 or 5.321 for Hhfa. In the case of
[Cu(hfa)2] in toluene, aminoalcohols such as triethanolamine
or N,N-dimethylethanolamine coordinate in a bidentate fashion
and the binding of the N atom causes a weakening of the Cu-O
bonds resulting in an increase in the Brønsted basicity of hfa-
oxygen atoms; as a consequence, the ancillary ligand replaces
a hfa- anion and mixed, monomeric or dimeric complexes
form.6 The same authors have also mentioned that the formation
of mixed â-diketonato-alkoxide complexes in toluene can be
initiated by rising the temperature over the boiling point of Hhfa
(63 °C),20 which is then displaced by evaporation from the
C-H vibrations characteristic for thd- at 3000-2800 cm-1
.
Evidence for the formulation of the compounds with respect to
the coordination mode of the aminoalcohol is seen in the range
3500-3200 cm-1 in which O-H and N-H vibrations occur
for [Ln2(hfa)6(O(CH2)2NHMe2)2] although they are absent from
the spectra of [Ln(thd)2(O(CH2)2NMe2)]2.
In view of the “soft” desorption/ionization of the sample
provided by LDI-TOF mass spectrometry, which avoids de-
structive fragmentation of the compounds,24 we have resorted
to this technique to ascertain the presence of dimeric species in
our samples and have chosen the EuIII samples for their typical
isotopic distribution. Interpretation of these spectra was made
using the general rules of fragmentation of lanthanide â-dike-
tonates described for other mass-spectrometry techniques.25 The
two dimeric complexes present different patterns of fragmenta-
tion. The spectrum of [Eu2(hfa)6(O(CH2)2NHMe2)2] is relatively
complicated by the strong ability of metal hexafluoroacetyl-

3618 J. Phys. Chem. A, Vol. 112, No. 16, 2008
Eliseeva et al.
Figure 2. Molecular structure of [Tb2(hfa)6(O(CH2)2NHMe2)2]‚C7H8.
Fluorine atoms and solvate toluene molecule are omitted for clarity.
Figure 1. (top) Isotopic distribution of [Eu2(thd)4(O(CH2)2NMe2)]+
peak in LDI-TOF mass spectrum of [Eu(thd)2(O(CH2)2NMe2)]2. (bot-
tom) Calculated isotopic distribution in this species using IsoPro 3.0
MS/MS software.
acetonates to form intermolecular F‚‚‚F contacts resulting in
oligomeric fragments, as well as by the easy splitting of CF3
fragments and possibility of migration of the F atoms. The three
main peaks at m/e ) 959, 1053, and 1148 are assigned to
dimeric fragments with two bridging N,N-dimethylaminoethanol
ligands; additional peaks correspond to monomeric and trimeric
fragments. The spectrum of [Eu(thd)2(O(CH2)2NMe2)]2 is
simpler and displays only three peaks assigned to dimeric
fragments, [Eu2(thd)5]+ (m/e ) 1219, 100%), [Eu2(thd)4-
(O(CH2)2NMe2)]+ (1124, 30%), and another entity with a
partially fragmented â-diketonato moiety. The isotopic patterns
for all the species in mass spectra closely resemble calculated
ones as is exemplified in Figure 1 for [Eu2(thd)4(O(CH2)2-
NMe2)]+.
Crystal and Molecular Structures. Single crystals of the
TbIII derivatives were isolated from toluene solutions and
analyzed by X-ray diffraction. Both compounds crystallize in
monoclinic space groups (Table 1) and their crystal structures
consist in dimeric units [Tb2(hfa)6(O(CH2)2NHMe2)2] (Figure
2) and [Tb(thd)2(O(CH2)2NMe2)]2 (Figure 3). Selected bond
lengths and angles are summarized in Tables 2 and 3.
Figure 3. Molecular structure of [Tb(thd)2(O(CH2)2NMe2)]2. Hydrogen
atoms are omitted for clarity.
TABLE 2: Selected Bond Lengths (Å) and Angles (°) in the
Crystal Structure of [Tb2(hfa)6(O(CH2)2NHMe2)2]‚C7H8
bond lengths
angles
Tb1‚‚‚Tb2
Tb1 - O1
Tb1 - O2
Tb1 - O3
Tb1 - O4
Tb1 - O5
Tb1 - O6
Tb2 - O7
Tb2 - O8
Tb2 - O9
Tb2 - O10
Tb2 - O11
Tb2 - O12
Tb1 - O13
Tb2 - O13
Tb1 - O14
Tb2 - O14
3.684(1)
2.492(7)
2.360(8)
2.344(7)
2.435(8)
2.362(7)
2.372(7)
2.374(6)
2.395(7)
2.421(7)
2.363(7)
2.372(7)
2.430(7)
2.281(6)
2.307(6)
2.314(6)
2.309(6)
O2 - Tb1 - O1
O3 - Tb1 - O4
O5 - Tb1 - O6
O7 - Tb2 - O8
O10 - Tb2 - O9 70.6(2)
O11 - Tb2 - O12 68.9(2)
O13 - Tb1 - O14 71.1(2)
O14 - Tb2 - O13 70.8(2)
Tb1 - O13 - Tb2 106.8(2)
Tb2 - O14 - Tb1 105.8(2)
N1 - H1N‚‚‚‚O13 103.6(6)
N2 - H2N‚‚‚O14 114.6(6)
68.2(2)
70.1(2)
72.7(2)
70.2(2)
In [Tb2(hfa)6(O(CH2)2NHMe2)2], the two TbIII centers are
bridged by two oxygen atoms from the two zwitterionic
N,N-dimethylaminoethanol (+HN(Me)2(CH2)2O-) ligands. The
Tb1‚‚‚Tb2 separation is 3.684(1) Å while the mean deviation
from the plane of the bridging Tb1OOTb2 core is 0.173 Å.
Within a noncentrosymmetric dimer, each TbIII ion is also bound
to six oxygen atoms from three bidentate chelating hexafluo-
roacetylacetonato groups resulting in an eight-coordinate envi-
ronment. The Tb-Ohfa distances range from 2.344(7) to 2.492(7)
Å for Tb1 and from 2.363(7) to 2.430(7) Å for Tb2 with an
overall mean value of 2.39 Å in conformity with the suggestion
that coordination of aminoalcohol induces a noticeable length-
ening and weakening of some M-O bonds.6 As a comparison,
the mean Tb-Ohfa distance is 2.35 Å for [Tb(hfa)3(H2O)2] in
N1 - H1N‚‚‚O13/N1‚‚‚O13 2.47(6)/2.83(1)
N2 - H2N‚‚‚O14/N2‚‚‚O14 2.32(7)/2.86(1)
{[Tb2(hfa)4(µ2-O2CCF3)2(H2O)4][Tb(hfa)3(H2O)2]2‚H2O}26 and
[Tb(hfa)3(TPPO)2],27 2.36 Å for [Tb(hfa)3(4-cpyNO)]2,28 and
2.38 Å for [Tb(hfa)3(diglyme)].29 The average Tb-O bond
length in the Tb2(µ-O)2 core (2.30 Å) is shorter than the average
distance with the anionic hexafluoroacetylacetonato ligands,
which is not typical for dimeric structures with neutral bridging
ligands27,28,30 for which an inverse situation has usually been
observed. On the other hand, similar variations in the Ln-O
bond lengths have been found in the mixed â-diketonato-

Sensitization of EuIII and TbIII in Dimeric â-Diketonates
J. Phys. Chem. A, Vol. 112, No. 16, 2008 3619
TABLE 3: Selected Bond Lengths (Å) and Angles (°) in the
TABLE 4: Comparison of the “Shape Measure” Criteria S33
(°) for the Crystal Structures of the Novel Mixed-Ligand
Complexes and Known â-diketonates
Crystal Structure of [Tb(thd)2(O(CH2)2NMe2)]2
bond lengths
Tb1‚‚‚Tb1Aa
angles
[Gd2(thd)6] a
3.735(2)
2.277(4)
2.288(3)
2.344(4)
2.274(4)
2.268(3)
2.256(3)
2.655(4)
O1 - Tb1 - O2
73.5(1)
72.3(1)
68.2(2)
68.6(2)
around around
Tb1 - O1
Tb1 - O2
Tb1 - O3
Tb1 - O4
Tb1 - O5
Tb1 - O5A
Tb1 - N1
O4 - Tb1 - O3
O5 - Tb1 - N1
O5A - Tb1 - O5
[Tb(thd)2(O(CH2)2NMe2)]2
8.88
Gd1
Gd2
S(C2V)
10.50
10.33
monocapped
trigonal prism
S(C3V)
8.54
6.23
6.00
monocapped
octahedron
a Symmetry code 1-x, -y, -z.
[Tb2(hfa)6(O(CH2)2NHMe2)2]
alkoxide complexes [Er(hfa)2(µ-OCH3)(Q)]2 (Q ) 2,2′-bipyri-
dine or 1,10-phenanthroline)31 and [Pr2(hfa)4(bdmap)2(H2O)2-
(THF)2] (bdmap ) 1,3-bis(dimethylamino)-2-propoxide).9 The
zwitterionic character of the bridging (+HN(Me)2(CH2)2O-)
ligands is further highlighted by the fact that the proton
linked to the nitrogen atom of the alkoxide ligand interacts
with the bridging oxygen of the same ligand. This intramolec-
ular hydrogen bond is characterized by distances of 2.84(1)
(N1‚‚‚O13) and 2.86(1) Å (N2‚‚‚O14), and by angles of
111.5(5) (N1-H1N‚‚‚O13) and 112.9(5)° (N2-H2N‚‚‚O14).
The crystal structure of [Tb(thd)2(O(CH2)2NMe2)]2 (Figure
3) consists in centrosymmetric dimers in which the TbIII centers
are bridged by two oxygen atoms from the alkoxide ligand with
a Tb1‚‚‚Tb1A separation of 3.735(2) Å. In addition, each TbIII
ion coordinates to four oxygen atoms from two bidentate
chelating thd- ligands and one nitrogen atom from one N,N-
dimethylaminoethoxide thus adopting a seven-coordinate en-
vironment. Therefore, N,N-dimethylaminoethanol acts as anionic
ligand with both chelating and bridging modes. Due to the
presence of the inversion center, the Tb1OOTb1A core is
completely planar. The mean Tb-Othd bond length (2.30 Å) is
similar to the one reported for terbium tris(dipivaloylmethanato)
complexes with different neutral ancillary ligands.32 The Tb-O
distances within the bridging Tb2(µ-O)2 moiety range from
2.256(3) to 2.268(3) Å, and the average value (2.26 Å) is shorter
than the mean Tb-Othd bond length, which is in line with the
reported data for mixed â-diketonato-alkoxide complexes.9,31
The Tb-N distance (2.655(4) Å) is significantly longer than
the Tb-O one. This agrees with poorer affinity of the nitrogen
atoms to the lanthanide center in comparison with oxygen.11
To describe and compare the geometry of the parent lan-
thanide tris(â-diketonates) with the new mixed-ligand complexes
and to evaluate the degree of distortion from ideal geometry,
the “shape measure” criterion S, suggested by Raymond et al.,
was estimated as33
around Tb1
12.58
around Tb2
8.44
[Tb(hfa)3(H2O)2]b
4.62
S(D4d) square
antiprism
b
a From ref 38. From ref 26.
(0.105 Å), the dihedral angles between the corresponding planes
being 2.5° and 7.4°, respectively. In comparing the shape
measure for [Tb2(hfa)6(O(CH2)2NHMe2)2] and the parent
[Tb(hfa)3(H2O)2] â-diketonate,26 one notes the lower value for
the latter thus indicating that the presence of the ancillary ligand
is distorting the idealized SAP geometry to a greater extent than
water. A similar analysis for [Tb(thd)2(O(CH2)2NMe2)]2 shows
that the coordination polyhedron is closer to a monocapped
trigonal prism or monocapped octahedron than to a pentagonal
bipyramid, but a precise attribution is not possible in view of
the very similar values of S(C2V) and S(C3V). The lighter
lanthanides (La-Gd) form monoclinic dimers with Hthd with
space group P21/c upon crystallization from n-hexane or vapor
phase, and the heavier lanthanide tris(dipivaloylmethanates)
crystallize as orthorhombic monomers in space group Pmn21;
furthermore, the existence of both types of complexes has been
evidenced for TbIII and DyIII.34-36 Atom coordinates are only
available for PrIII,37 GdIII,38 ErIII,34 and LuIII 39 tris(dipivaloyl-
methanates) so that we have used [Gd2(thd)6] data for a
comparison of the shape measure values with [Tb(thd)2-
(O(CH2)2NMe2)]2. The coordination polyhedron around the two
GdIII ions can be described as monocapped octahedron with a
S(C3V) value being approximately 1.4-fold smaller than the one
for the TbIII ions in [Tb(thd)2(O(CH2)2NMe2)]2. Consequently,
a higher degree of distortion is induced by the presence of the
N,N-dimethylaminoethanol ligand, as in the case of hfa--
containing complexes.
Thermal Analysis and Vacuum Sublimation. The thermal
behavior of the new mixed-ligand complexes was examined by
means of thermogravimetric analysis under nitrogen atmosphere.
The general profile of the weight loss is similar for all the
studied lanthanides. As an example, TGA curves are presented
for the TbIII derivatives in Figure 4. Weight loss occurs in a
single step in the temperature ranges of 180-270 °C and 180-
300 °C for [Tb2(hfa)6(O(CH2)2NHMe2)2] and [Tb(thd)2(O(CH2)2-
NMe2)]2, respectively. The total weight loss for [Tb2(hfa)6-
(O(CH2)2NHMe2)2](∼79%)correspondstothethermaldecomposition
of the complex into nonvolatile Tb4O7 (∼79%) and/or oxyfluo-
ride (∼78%). However, under reduced pressure (∼10-2 Torr),
[Tb2(hfa)6(O(CH2)2NHMe2)2] can be quantitatively sublimed at
240 °C. The total weight loss for [Tb(thd)2(O(CH2)2NMe2)]2
(∼86%) is higher than that calculated for the transformation
into Tb4O7 (∼69%). This can be attributed to partial sublimation
of the mixed â-diketonato-alkoxide complex even under atmo-
spheric pressure. Indeed, when [Tb(thd)2(O(CH2)2NMe2)]2 is
m
S ) min ((1/m) (δ - θ )2)
(1)
∑
i
i
x
i)1
where m is the number of all possible edges, δi is the observed
dihedral angle (angle between the normal of adjacent faces)
along the ith edge of the experimental polyhedron δ, and θi is
the same angle for the corresponding ideal polytopal shape θ.
Detailed analysis of the data (Tables 4, S1-S3, Figures S2,
S3, Supporting Information) shows that in the crystal structure
of [Tb2(hfa)6(O(CH2)2NHMe2)2] both TbIII ions adopt a highly
distorted square antiprismatic (SAP) coordination geometry. The
square faces of the SAP around Tb1 are formed by the atoms
O3, O4, O6, O14 (mean deviation ) 0.257 Å) and O1, O2,
O5, O13 (0.242 Å), and the ones around Tb2 are delineated by
atoms O7, O8, O11, O12 (0.162 Å) and O9, O10, O13, O14

3620 J. Phys. Chem. A, Vol. 112, No. 16, 2008
Eliseeva et al.
Figure 4. Curves of weight loss of [Tb2(hfa)6(O(CH2)2NHMe2)2] and
[Tb(thd)2(O(CH2)2NMe2)]2 at nitrogen atmosphere.
Figure 5. Luminescence spectra of LuIII complexes under excitation
at 337 nm; T ) 77 K.
heated under reduced pressure (∼10-2 Torr), quantitative
sublimation is observed at 220 °C.
Cyclic Voltammetry. Ligand-to-metal charge transfer (LMCT)
states are known to play an important role in quenching the
EuIII luminescence,40 but the presence of intense absorption in
UV range for lanthanide(III) complexes with organic ligands
often prevent the determination of the weaker LMCT absorption
expected in the range 300-350 nm. To overcome this limitation,
one can resort to cyclic voltammetry, and if the reorganization
and solvation energies are assumed to be similar for the EuII
and EuIII complexes the difference ∆E between half peak
potentials for ligand oxidation and EuIII reduction will reflect
the relative energies of the LMCT states.16 Taking into account
the nature of the organic ligands around the EuIII ion in the
reported complexes, the presence of a low-lying LMCT state
seems to be most probable in the hfa--containing â-diketonate.
The parent [Eu(hfa)3(H2O)2] hexafluoroacetylacetonate (Figure
S4, Supporting Information) displays an irreversible wave for
the reduction of EuIII in acetonitrile, which is not the case of
[Eu2(hfa)6(O(CH2)2NHMe2)2] because it has a quasi-reversible
character. The oxidation waves of the organic ligands are
irreversible for both complexes. A rough estimate (in case of
irreversible character of reduction/oxidation waves one should
operate only with peak potentials) shows that the energy of the
LMCT state does not change significantly upon complexation
with N,N-dimethylaminoethanol, and the energy difference
between the highest occupied molecular orbital (HOMO) and
the lowest unoccupied molecular orbital (LUMO) is around
24 800-25 400 cm-1 for the two compounds. Thus, deactivation
through the LMCT state is predicted to play a similar and minor
role in quenching the luminescence in both the tris(hexafluo-
roacetylacetonato) complex and in the studied dimer.
On the other hand, the voltammogram of [Eu2(hfa)6(O(CH2)2-
NHMe2)2] in THF (Figure S5, Supporting Information) features
quasi-reversible waves both for the reduction of EuIII and
oxidation of the organic ligands. The energy difference between
HOMO and LUMO levels is then estimated to be much smaller
(16 990 cm-1) than in the case of the solution in acetonitrile.
Accordingly, mixing of the LMCT state with 4f functions is
expected, as well as a quenching of the EuIII luminescence. The
difference with acetonitrile solutions may arise from the basic
assumption about solvation and reorganization energies is not
valid in our case.
Photophysical Properties. Ligand-Centered Luminescence
in LuIII Complexes. The luminescence spectra of the LuIII
complexes (Figure 5) were measured to determine the energy
of the ligand triplet states that may be implied in ligand-to-
metal energy transfer processes, because the energy gap between
these states and the accepting LnIII states has a significant effect
on energy transfer efficiency and thus on the overall lumines-
cence quantum yield.41 Because of the filled 4f-shell of LuIII
and heavy-atom effect,42 LuIII complexes provide a mean to
probe the ligand excited-state properties in systems structurally
very similar to those containing luminescent LnIII ions. The
energies of the 0-phonon transitions of the â-diketonato ligands
were determined from the luminescence spectra of [Lu(hfa)3-
(H2O)2] and [Lu(thd)3], and were at around 21 930 and 24 750
cm-1, respectively, in line with literature data.28,43 Several
attempts were made to synthesize adducts of N,N-dimethylami-
noethanol with GdIII and LuIII nitrates to determine the energy
of the triplet state. It was difficult to obtain perfectly reproduc-
ible results, but all of the solid products obtained displayed broad
emission in the range 350-650 nm with bands centered at 385-
405, 450-470, and 595-605 nm (Figure S6, Supporting
Information). Thus, the energy of the zero-phonon transition
of the triplet state of N,N-dimethylaminoethanol can be estimated
to be g26 000 cm-1 (λe385 nm).
The LuIII dimer [Lu2(hfa)6(O(CH2)2NHMe2)2] emits in the
range 440-800 nm with two maxima at ∼456 (21 930 cm-1
)
and 482 nm (20 750 cm-1), a shoulder at ∼518 nm (19 305
cm-1) and a less intense broad band with maximum at ∼625
nm (16 000 cm-1). Comparing with the emission spectrum of
the parent tris(hexafluoroacetylacetonate) (cf. Figure 5), one
notes that the latter is characteristic of the dimer with the other
features of the spectrum remaining very similar except for small
blue shifts (7-8 nm) and a more pronounced shoulder at ∼518
nm. Since the LuIII ion is difficult to reduce or oxidize because
of its f14 electronic configuration, the band centered at ∼625
nm cannot be assigned to metal-to-ligand charge transfer
(MLCT) or LMCT transitions; thus, it likely results from
intraligand transitions.44,45 Considering the proposed optimal
energy gaps for efficient ligand-to-metal energy transfer46 the
appearance of this long-wavelength band is predicted to have a
drastic effect on the sensitization of the LnIII luminescence,
increasing the probability of energy back-transfer in the TbIII
dimer, although for the EuIII compound it may result in either
an increase or a decrease of the metal-centered luminescence.
The luminescence spectra of thd--containing LuIII complexes
present broad bands with maxima at ∼408 nm (24 510 cm-1
)
and vibrational components at ∼427 nm (23 420 cm-1), 445
nm (22 470 cm-1) and 470 nm (21 280 cm-1). The envelope
of the spectra does not change significantly upon substitution
of one of the thd- by N,N-dimethylaminoethoxide (Figure 5).
In this case and with reference again to the optimal energy gap,46
it appears that the organic ligands in [Ln(thd)2(O(CH2)2NMe2)]2

Sensitization of EuIII and TbIII in Dimeric â-Diketonates
J. Phys. Chem. A, Vol. 112, No. 16, 2008 3621
Figure 7. Luminescence spectra of (a) [Lu(thd)3] and (b) [Lu(thd)2-
(O(CH2)2NMe2)]2 doped by (top) EuIII and (bottom) TbIII (doping
rates: s 0.01 mol %, - - 0.05 mol %, - ‚ - ‚ 0.1 mol %) under
excitation at 337 nm; T ) 77 K (normalized on ligand-centered
emission).
Figure 6. Luminescence spectra of (a) [Lu(hfa)3(H2O)2] and (b)
[Lu2(hfa)6(O(CH2)2NHMe2)2] doped by (top) EuIII and (bottom) TbIII
(doping rates: s 0.01 mol %, - - 0.05 mol %, - ‚ - ‚ 0.1 mol %)
under excitation at 337 nm; T ) 77 K (normalized on ligand-centered
emission).
are best suited for the sensitization of TbIII luminescence while
the energy gaps are too large for EuIII.
increases more with the doping rate in the dimers compared to
the parent tris(â-diketonates). Because of the negligible overlap
between ligand- and metal-centered emission, this phenomenon
could be characterized by the corresponding integral intensity
ratios (∫Ln/∫L) and ∫Ln/∫total (Tables S4, S5, Supporting Informa-
tion). For a doping rate of 0.1 mol %, the increase is about
∼2.4-fold in ∫Eu/∫total but it is only ∼1.2-fold for ∫Tb/∫total. In
addition to this, it is noteworthy that the absolute values of these
ratios, 0.29 (parent compound) and 0.69 (dimer) for EuIII and
0.40 and 0.49 for TbIII, are intrinsically large, reflecting the
probable existence of extra energy transfer to EuIII or TbIII from
the organic ligands coordinated to LuIII. Finally, when the doping
rate is increased to 1-2% (data not shown), the ligand-centered
luminescence is completely quenched in all the studied mon-
omeric and dimeric compounds, exemplifying a rather efficient
L f LnIII energy transfer.
Metal-Centered Luminescence. The excitation spectra of the
hfa--containing EuIII and TbIII complexes present broad bands
corresponding to the ligand electronic transitions as well as weak
and sharp features assigned to f-f transitions (see assignment
in Figure 8a). It is noteworthy that the spectrum of the EuIII
tris(hexafluoroacetylacetonate) differs markedly from the other
excitation spectra in that the feature at around 350-365 nm
has a much lower intensity than in the other spectra. In the case
of the thd--containing samples, there is a notable difference
between the EuIII and TbIII compounds: the metal-centered f-f
transitions largely dominate the spectra of the former, while
the TbIII intraconfigurational transitions remain weak compared
to the ligand-centered bands (Figure 9a). This is in line with
Luminescence of EuIII- and TbIII-Doped LuIII Complexes. To
get more information about the role of the ancillary ligand in
the energy transfer processes, both EuIII- and TbIII-doped LuIII
parent complexes and dimers (doping rates 0.01, 0.05 and 0.1
mol %) were synthesized by cocrystallization and their photo-
luminescent properties were determined at 77 K. All of these
compounds have luminescence spectra containing both the
7
7
linelike EuIII (5D0 f FJ) or TbIII (5D4 f FJ) transitions and
the broad-band ligand-centered emission (Figures 6, 7). As
expected, the intensity of the metal-centered emission increases
with increasing doping rate. The behavior of the ∼625 nm
feature in the hfa--containing doped LuIII dimers is very
different dependent on the doping ion. For EuIII, the intensity
of this feature is maximum for the smaller doping rate and then
decreases sharply, and the feature is absent from the spectra of
the TbIII-doped samples. A comparison of the intensity ratio of
metal-centered to ligand-centered transitions (ILn/IL) between
equally doped LuIII parent tris(â-diketonates) and mixed-ligand
complexes sheds light on the influence of N,N-dimethylamino-
ethanol on the efficiency of the energy transfer process (Tables
S4, S5, Supporting Information). For 0.1 mol % EuIII-doped
hfa--containing samples, the ratio ILn/IL is practically unchanged
and for TbIII samples it decreases ∼6.6-fold, pointing to a
significant negative effect of the ancillary ligand on the metal-
centered luminescence (via an increase in back-transfer, vide
infra). For thd--containing complexes, for which the 625 nm
feature is absent, the intensity of the metal-centered emission

3622 J. Phys. Chem. A, Vol. 112, No. 16, 2008
Eliseeva et al.
Figure 8. (a) Excitation and (b) emission spectra under ligand excitation of hfa--containing EuIII and TbIII complexes at 295 K.
the above discussion on the suitability of thd- for sensitizing
the EuIII luminescence. Despite the latter observation, all of the
studied EuIII and TbIII complexes display exclusively the narrow
metal-centered emission bands upon excitation in the ligand
levels (330-380 nm, Figures 8b, 9b). However significant
variations in the emission probabilities to the various sublevels,
luminescence lifetimes, and quantum yields are observed. The
relative integral intensities of the 5D0 f 7FJ (J ) 0-4) and 5D4
variations in integral intensities for tris(dipivaloylmethanates)
can be attributed to a difference in the crystal structures for
light (from La to Gd) and heavy (from Tb to Lu) lanthanides
(vide supra), which leads to changing the local environment
5
around central ions. The intensity of the highly forbidden D0
f 7F0 transition for EuIII-containing samples is also indicative
of the symmetry of the metal ion site. It has a relatively large
intensity in Cn and CnV symmetries, a geometry easily achieved
in [Ln(dik)3(H2O)2] and [Ln(dik)3] (or [Ln2(dik)6]) complexes
by distortion from the idealized D4d, respectively D3h (or C3V),
geometry. Therefore, the results reported in Table 5 showing
7
f FJ (J ) 6-0) transitions are listed in Table 5. It is well
documented47,48 that the luminescent properties of lanthanide
ions are very sensitive to variations in the symmetry of the
coordination sphere and the polarizability of the coordinated
groups. This effect is more sizable for EuIII than for TbIII and
results in significant changes in the relative emission intensities,
mainly of the hypersensitive transition 5D0 f 7F2 and, to a lesser
5
7
that the intensity of the D0 f F0 transition is smaller in the
mixed-ligand complexes than in the parent tris(â-diketonates)
are consistent with the lowering in symmetry induced by the
ancillary ligand, as discussed above (cf. Table 4).
extend, of the 5D0
f
7F4 transition. In both mixed-ligand
The parameters characterizing the photophysical properties
of solid-state samples of the EuIII and TbIII complexes are
summarized in Table 6. At room temperature, substitution of
the water molecules in EuIII tris(hexafluoroacetylacetonate) by
N,N-dimethylaminoethanol leads to a 4.5-fold increase in the
observed luminescence lifetime (τobs) and to an approximately
22-fold enhancement in absolute overall quantum yield % QELu
as determined upon ligand excitation. Because the intensity of
the purely magnetic dipole transition 5D0 f 7F1 is independent
of the chemical environment around the metal ion, the sensitiza-
tion efficiency of the organic ligands (ηsens) can be estimated
5
7
complexes, the integral intensity of the D0 f F2 transition
decreases by a factor of ∼1.3 when compared to the corre-
sponding parent EuIII tris(â-diketonates). The influence of the
local environment around the metal ions is further demonstrated
for the doped LuIII samples of thd--containing complexes
(Figures S7, S8, Tables S6, S7, Supporting Information). For
EuIII-containing samples with 0.1 mol % doping rate, the relative
integral intensity of the 5D0 f 7F2 transition is ∼1.7-fold smaller
(∼1.2-fold for 5D0 f 7F4) than in the bulk tris(dipivaloylmetha-
nate); in the case of the mixed complex with N,N-dimethylami-
noethoxide, it is however ∼1.3-fold smaller (∼1.5-fold for 5D0
f 7F4) compared to the bulk sample. For the TbIII samples, the
using the following equation after calculating the radiative
Eu
lifetime (τrad) and the intrinsic quantum yield (Q ):49
Eu
5
7
5
7
integral intensities of the D4 f F4 and D4 f F3 transitions
are 2.0- and 2.4-fold larger in 0.1% doped [Lu(thd)3] than in
the bulk sample, although these values remains practically
unchanged for the mixed-ligand complexes. Such significant
QLEu
τ
Itot
1
τrad
Eu
Eu
ηsens
)
,
with Q
)
obs and
τrad
) AMD,0n3
(2)
Eu
(
)
IMD
Q
Eu

Sensitization of EuIII and TbIII in Dimeric â-Diketonates
J. Phys. Chem. A, Vol. 112, No. 16, 2008 3623
Figure 9. (a) Excitation and (b) emission spectra under ligand excitation of thd--containing EuIII and TbIII complexes at 295 K.
5
7
TABLE 5: Integral Corrected Intensities of the D0 f FJ
increase is observed. The much larger increase in ηsens compared
with % QEEuu is reflecting the contribution of the ancillary ligand
to the energy transfer process. In contrast, substitution of water
molecules in [Tb(hfa)3(H2O)2] by N,N-dimethylaminoethanol
is detrimental to luminescent properties at room temperature:
both the lifetime (too short to be determined) and quantum yield
drop dramatically. This can be traced back to the low energy
of the ligand-centered states in the dimeric complex allowing
efficient back-energy transfer. The latter is confirmed by the
Tb(5D4) lifetime increasing to 1.27 ms at 77 K. Because the
lifetime for [Tb2(hfa)6(O(CH2)2NHMe2)2] at liquid nitrogen
temperature is ∼1.8-fold larger compared to [Tb(hfa)3(H2O)2],
an obvious conclusion is that the ancillary ligand reduces
vibrational (O-H) quenching but increases back transfer; its
influence on the energy transfer step cannot be assessed in
absence of data for the intrinsic quantum yield.
5
7
5
7
5
7
and D4 f FJ Relative to the D0 f F1 and D4 f F5
Transitions of EuIII and TbIII Complexes, Respectively, upon
Ligand Excitation at 295 K
compound
[Eu(hfa)3(H2O)2]a
[Eu2(hfa)6(O(CH2)2NHMe2)2]
∫
∫
∫
∫
∫
0-0
0-1
0-2
0-3
0-4
0.17 1.00 14.30 0.38 1.72
0.01 1.00 10.83 0.41 1.98
[Eu2(hfa)6(O(CH2)2NHMe2)2] thin film 0.04 1.00 11.17 0.37 2.14
[Eu(thd)3]
[Eu(thd)2(O(CH2)2NMe2)]2
1.11 1.00 23.27 1.07 2.41
0.22 1.00 17.52 0.31 2.10
∫
4-6
∫
∫
∫
∫
4-5
4-4
4-3
4-2,1,0
[Tb(hfa)3(H2O)2] a
0.22 1.00 0.11 0.08
0.04
0.06
0.04
0.04
[Tb2(hfa)6(O(CH2)2NHMe2)2] 0.24 1.00 0.13 0.10
[Tb(thd)3]
[Tb(thd)2(O(CH2)2NMe2)]2
0.20 1.00 0.11 0.07
0.22 1.00 0.14 0.08
a From ref 28.
The situation is different for thd--containing complexes. In
going from the unsolvated [Ln(thd)3] complexes to the
[Ln(thd)2(O(CH2)2NMe2)]2 dimers, a significant increase in τobs
(295 K) is observed for EuIII: from a value too short to be
measured up to 0.47 ms, while an 1.5-fold lengthening results
for TbIII. At 77 K, lifetimes of the parent tris(dipivaloylmetha-
nates) and dimers are the same within experimental errors for
both EuIII (∼0.5 ms) and TbIII (∼0.6 ms), which is in contrast
to what is measured at room temperature. In addition, a small
(EuIII) or no significant (TbIII) increases are denoted between
295 and 77 K for the mixed-ligand compounds, which is by
large not the case for the parent complexes. Interpretation of
these data is straightforward in that they again point to less
phonon-assisted deactivation processes in the dimeric com-
plexes; in addition, back-energy transfer is minimized for TbIII.
A large enhancement (∼8-fold) in the absolute quantum yield
where AMD, 0 t 14.65 s-1 is the spontaneous emission prob-
5
7
ability of the magnetic dipole D0 f F1 transition, n is the
5
refractive index, Itot is the total integrated emission of the D0
f 7FJ transitions, and IMD is the integrated emission of the 5D0
7
f F1 transition. Thus, the substantial contribution of N,N-
dimethylaminoethanol ligand to the overall sensitization process
of EuIII-centered luminescence in [Eu2(hfa)6(O(CH2)2NHMe2)2]
is confirmed by (i) the increase in the intrinsic quantum yield
by a factor of 3.7 resulting from removing the quenching effect
of the O-H vibrations, and (ii) the substantial enhancement of
η
sens from 13 to 81% (i.e., 6.2-fold). Other vibrations contribute
only faintly to the nonradiative deactivation processes in the
mixed-ligand compound, as demonstrated by the constancy
(within experimental error) of τobs between room and liquid
nitrogen temperatures; for [Eu(hfa)3(H2O)2], an ∼1.5-fold

3624 J. Phys. Chem. A, Vol. 112, No. 16, 2008
Eliseeva et al.
TABLE 6: Observed and Radiative Lifetimes, Intrinsic and Absolute ((10%) Quantum Yields, and Sensitization Efficiencies of
EuIII and TbIII Complexesa
τobs, ms
Eu
Eu
compound
[Eu(hfa)3(H2O)2] b
[Eu2(hfa)6(O(CH2)2NHMe2)2]
[Eu2(hfa)6(O(CH2)2NHMe2)2] thin film
[Eu(thd)3]
λ
em, nm
295 K
77 K
τ
rad, ms
% Q ,%
% QLLn, %
ηsens, %
610.7
611.0
611.0
609.5
610.1
545.0
542.0
542.6
547.1
0.22 ( 0.01
0.99 ( 0.02
0.85 ( 0.05
d
0.48 ( 0.01
0.54 ( 0.03
d
0.32 ( 0.01
1.04 ( 0.02
c
0.50 ( 0.01
0.53 ( 0.01
0.72 ( 0.01
1.27 ( 0.01
0.64 ( 0.01
0.62 ( 0.01
1.13
1.39
1.39
c
0.94
c
c
c
c
19
71
61
c
51
c
2.6
58
c
0.05
0.41
27
0.04
40
13 ( 2
81 ( 12
c
c
[Eu(thd)2(O(CH2)2NMe2)]2
0.8 ( 0.1
[Tb(hfa)3(H2O)2] b
c
c
c
c
[Tb2(hfa)6(O(CH2)2NHMe2)2]
[Tb(thd)3]
[Tb(thd)2(O(CH2)2NMe2)]2
c
c
c
0.46 ( 0.04
0.68 ( 0.02
32
a Unless otherwise stated, all photophysical data are listed for 295 K; τrad, % QEu, ηsens were calculated under the assumption that n ) 1.5127 for
Eu
b
c
d
[Eu2(hfa)6(O(CH2)2NHMe2)2] and n ) 1.51 for the other EuIII complexes. From ref 28. Not determined. Not measurable (<5 × 10-4 ms).
Figure 10. Simplified energy level diagram for (left) [Lu2(hfa)6(O(CH2)2NHMe2)2] and (right) [Lu(thd)2(O(CH2)2NMe2)]2 and TbIII and EuIII ions.
of the EuIII mixed-ligand complex is observed over the parent
tris(dipivaloylmethanate), but its value remains largely under
1%; for this compound, although the value of intrinsic quantum
yield is equal to ∼51%, the sensitization efficiency is quite low
(0.8%).50 For TbIII, the absolute quantum yield decreases by
about 20% in going from the parent tris(dipivaloylmethanates)
to the dimeric compounds, while the lifetime increases 1.5-fold.
This reflects a combination of minimizing phonon-assisted
quenching and diminishing the ligand-to-metal energy transfer
efficiency.
Conclusions
This study has demonstrated that the coordination mode of
N,N-dimethylaminoethanol in mixed-ligand lanthanide â-di-
ketonates depends on the nature of the reacting complex,
[Ln(hfa)3(H2O)2], or [Ln(thd)3]. Accordingly, two types of
dimeric complexes can be obtained: [Ln2(hfa)6(O(CH2)2-
NHMe2)2] in which N,N-dimethylaminoethanol acts as bridging
ancillary zwitterionic ligand and [Ln(thd)2(O(CH2)2NMe2)]2 in
which it operates as a bridging-chelating anionic ligand. The
insertion of N,N-dimethylaminoethanol in the â-diketonate
structures has several consequences on the photophysical
properties of the resulting edifices. First, phonon-assisted
nonradiative deactivation processes are minimized, especially
when the ancillary ligand is replacing water molecules in [Ln-
(hfa)3(H2O)2]; for Ln ) EuIII, this leads to a huge enhancement
in observed lifetime (from ∼0.2 to ∼1.0 ms). Assuming that
the increase in τobs arises solely from the removal of the water
molecules from the inner coordination sphere, one calculates
from the data reported in Table 6 a contribution to the
nonradiative rate constant of 505 s-1 per water molecule, about
half the value found for the aquo-ion.51 Substitution of one of
the thd- ligands in [Ln(thd)3] has much less influence, as
expected, and similar effects are anticipated for TbIII and EuIII
complexes. Second, the ancillary ligand introduces new elec-
tronic states, the energy of which depends on its form (zwit-
terionic or anionic). Thus, a combination of +HN(Me)2(CH2)2O-
and hfa- in studied dimeric complexes leads to formation of
low-lying energy states that influences both the ligand-to-metal
and metal-to-ligand energy transfer processes (Figure 10). With
respect to these electronic effects, the consequences differ largely
for EuIII compared to TbIII. For samples containing the former
ion, luminescence properties are considerably enhanced: in the
Luminescence Properties of [Eu2(hfa)6(O(CH2)2NHMe2)2]
Thin Films. Thin films of the most luminescent compound
studied, [Eu2(hfa)6(O(CH2)2NHMe2)2], have been obtained by
vacuum sublimation at 10-6 Torr. Their average thickness was
close to 300 nm, and their excitation and emission spectra are
reported in Figures 8a and 8b, respectively. The long wavelength
feature extending from 358 to ∼460 nm in the excitation
spectrum of the bulk compound disappears for the thin film
sample. The excitation spectrum of the latter displays a clean
cutoff at around 350 nm and is in excellent correspondence with
the reflectance spectrum of the corresponding GdIII mixed-ligand
complex (Figure S1, Supporting Information). This may be
related to intermolecular interactions taking place in the bulk
sample, which are minimized (or absent) in the thin film. On
the other hand, the photoluminescence spectra of the thin film
and the bulk sample are very similar (cf. Figure 8b, Tables 5
and 6). The integrated intensities of the 5D0 f 7F2,4 transitions
are slightly larger for the thin film, and the observed lumines-
cence lifetimes at room temperature and intrinsic quantum yield
are smaller by about 15%. As a consequence, it is anticipated
that the overall quantum yield (not measured) will also be
somewhat smaller than for the bulk sample.

Sensitization of EuIII and TbIII in Dimeric â-Diketonates
J. Phys. Chem. A, Vol. 112, No. 16, 2008 3625
hfa--containing dimer, not only are the nonradiative processes
minimized, but in addition the efficiency of the ligand-to-metal
energy transfer is improved. This results in a highly luminescent
compound with a quantum yield of 58% in the solid state, and
an overall sensitization efficiency of ∼80%. On the other hand,
thd- has no adequate electronic level for an efficient energy
transfer onto EuIII, so that despite the large improvement in
quantum yield brought by the insertion of the ancillary ligand
(8.2-fold increase in QLEu over the parent tris(â-diketo-
nate)), the resulting complex is poorly emissive. For TbIII,
coordination of the ancillary ligand has a negative influence in
both studied systems: in the hfa--containing dimer, back
transfer is increased substantially, which more than offsets the
advantage of decreasing vibronic-based deactivation and the
quantum yield drops by a factor of about 670; the situation is
better for the thd--containing dimeric complex, although the
latter is less luminescent than the un-solvated tris(â-diketonate).
As a conclusion, N,N-dimethylaminoethanol is found to be a
simple and an interesting ligand that allows one to tune the
metal-centered luminescent properties in lanthanide tris(â-
diketonates), generating drastic effects. In addition, the dimeric
lanthanide(III) complexes reported are thermally stable, which
opens the way to production of highly luminescent thin films,
as demonstrated with [Eu2(hfa)6(O(CH2)2NHMe2)2], which is
certainly an outstanding candidate for the design of red-emitting
electroluminescent materials.
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Acknowledgment. We thank Dr. Vladislav V. Lobodin
(Organic Chemistry Division, Lomonosov Moscow State Uni-
versity, Moscow) for measuring the LDI-TOF mass spectra, Mr.
Andrei A. Vaschenko (Lebedev Physical Institute of Russian
Academy of Sciences, Moscow) for his assistance in obtaining
the thin films, and the Russian Foundation for Basic Research
(Grants 05-03-33090-a, 07-02-00495-a) for financial support.
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Supporting Information Available: Crystallographic data
in CIF format, figures with comparison of coordination poly-
hedra around central ions for parent and novel dimeric com-
plexes, cyclic voltammograms, luminescence spectra of EuIII
and TbIII complexes and doped by those ions LuIII complexes
at 77 K, reflectance spectra; tables with angles and shape
measure values and analysis of integral intensities and photo-
physical data of doped LuIII complexes. This material is available
free of charge via the Internet at http://pubs.acs.org.
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520-521.
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J.-C. G.; Kuzmina, N. P. Eur. J. Inorg. Chem. 2006, 4809-4820.
(29) Evans, W. J.; Giarikos, D. G.; Johnston, M. A.; Greci, M. A.; Ziller,
J. W. J. Chem. Soc., Dalton Trans. 2002, 520-526.
(30) Ma, S.-L.; Zhu, W.-X.; Huang, G.-H.; Yuan, D.-Q.; Yan, X. J.
Mol. Struct. 2003, 646, 89-94.
(31) van Staveren, D. R.; Haasnoot, J. G.; Maire Manotti Lanfredi, A.;
Menzer, S.; Nieuwenhuizen, P. J.; Spek, A. L.; Ugozzoli, F.; Reesijk, J.
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