Substituted phenanthrolines as antennae in luminescent EuIII complexes

Article abstract of DOI:10.1002/ejic.201301000

Eight novel europium(III)-based coordination compounds with 1,10-phenanthroline (phen) ligands with a chloro, methoxy, ethoxy, cyano, carboxylic acid, methyl carboxylate, ethyl carboxylate, and amino substituent on the 2-position have been prepared in yields ranging from 43 to 89 %. Additionally, one lanthanum(III) coordination compound of 2-amino-1,10- phenanthroline has been isolated. All compounds have the general formula [Ln(L)₂(NO₃)₃], except for the compound with the carboxylate ligand, which has the formula [Eu(O₂Cphen) ₃]. Three of the Eu^III complexes as well as the La ^III compound crystal structures have been determined, all of which show similar N₄O₆ coordination spheres for the Ln ^III ion. Seven compounds exhibit bright luminescence that is characteristic of Eu^III upon irradiation with near-UV radiation, thus indicating efficient ligand-to-metal energy transfer. The complex with 2-amino-1,10-phenanthroline is nonluminescent. The solid-state photoluminescent quantum yields range from 10 to 79 %, and the luminescence lifetimes vary from 0.43 to 1.57 ms. Analysis of the spectral intensities with the Judd-Ofelt theory shows a significant contribution of nonradiative processes that quench the luminescence of the ⁵D₀ level on Eu^III. Eight new Eu^III complexes with 1,10-phenanthroline ligands substituted on the 2-position have been prepared, analyzed, and the photoluminescence properties studied. The complex with the 2-chloro substituent exhibits bright photoluminescence with a high quantum yield of 78 %. The complex with the 2-amino substituent is nonluminescent. Copyright

Full text of DOI:10.1002/ejic.201301000

FULL PAPER
DOI:10.1002/ejic.201301000
Substituted Phenanthrolines as Antennae in Luminescent
EuIII Complexes
Sebastiaan Akerboom,[a] Jos J. M. H. van den Elshout,[a]
Ilpo Mutikainen,[b] Maxime A. Siegler,[c] Wen Tian Fu,[a] and
Elisabeth Bouwman*[a]
Keywords: X-ray diffraction / Lanthanides / Substituent effects / Luminescence / N ligands
Eight novel europium(III)-based coordination compounds
with 1,10-phenanthroline (phen) ligands with a chloro, meth-
oxy, ethoxy, cyano, carboxylic acid, methyl carboxylate, ethyl
carboxylate, and amino substituent on the 2-position have
been prepared in yields ranging from 43 to 89%. Addition-
ally, one lanthanum(III) coordination compound of 2-amino-
1,10-phenanthroline has been isolated. All compounds have
the general formula [Ln(L)2(NO3)3], except for the compound
with the carboxylate ligand, which has the formula [Eu-
(O2Cphen)3]. Three of the EuIII complexes as well as the LaIII
compound crystal structures have been determined, all of
which show similar N4O6 coordination spheres for the LnIII
ion. Seven compounds exhibit bright luminescence that is
characteristic of EuIII upon irradiation with near-UV radia-
tion, thus indicating efficient ligand-to-metal energy transfer.
The complex with 2-amino-1,10-phenanthroline is nonlumi-
nescent. The solid-state photoluminescent quantum yields
range from 10 to 79%, and the luminescence lifetimes vary
from 0.43 to 1.57 ms. Analysis of the spectral intensities with
the Judd–Ofelt theory shows a significant contribution of
nonradiative processes that quench the luminescence of the
5D0 level on EuIII.
rently, three solutions to generate white light using LED
technology exist.[3] Firstly, a blue, green, and red LED can
be combined to yield white-light emission. A major draw-
back of this construction is the relatively low efficiency of
the green LED relative to the red and blue ones. In ad-
dition, long-term color stability can be an issue as the LED
chips degrade at different rates. Secondly, an LED chip that
emits at 470 nm can be combined with a phosphor coating
of Y3Al5O12:Ce, which exhibits a broadband emission in
the yellow spectral region upon excitation by the blue LED.
This solution generates white light with a high color tem-
perature (Ͼ6500 K), and is widely used in applications that
require a simple, long-life source of white light, such as car
lamps, flashlights, and traffic lights.[2b,4] The major problem
of this solution is that the generated white light lacks emis-
sion in the red spectral region, thereby giving it a relatively
cold hue. Thirdly, an LED that emits in the near-UV (nUV)
spectral region (380 to 420 nm) can be combined with a
coating of different phosphor materials that completely
converts the LED emission into visible light. These phos-
phor-converted white LEDs (pcWLEDs) can produce white
light with high lumen efficiency and a high color-rendering
index (CRI) combined with long-term color stability. Un-
fortunately, red-emitting phosphors that can be efficiently
excited in this wavelength range of interest are scarce, and
therefore the development of new phosphor materials is
highly desired.[3,5] Phosphors based on EuIII ions are of par-
ticular interest for this application, because of their intense
line emission at 615 nm.
Introduction
The progress made in the early 1990s in the field of wide-
bandgap III–V InGaN semiconductor technology has re-
sulted in the establishment of light-emitting diode (LED)
chips that emit in the near-UV to blue spectral region.[1]
Consequently, these LEDs have opened a pathway towards
the production of semiconductor-based white-light sources,
which in turn can provide significant energy savings on ac-
count of their high efficiency.[2] Current artificial lighting
sources such as incandescent lamps and luminescent tubes
are relatively inefficient as they rely either on thermal radia-
tion at very high temperatures or on gas discharge com-
bined with phosphor materials that show large Stokes shifts.
In an LED, on the other hand, current injection leads to
radiative electron–hole recombination at the PN junction
so that electrical energy is converted directly into light.
However, an LED emits monochromatic light, whereas for
general illumination white light is generally needed. Cur-
[a] Leiden Institute of Chemistry, Gorlaeus Laboratories, Leiden
University,
P. O. Box 9502, 2300 RA Leiden, The Netherlands
E-mail: bouwman@chem.leidenuniv.nl
mcbim.lic.leidenuniv.nl
[b] Laboratory of Inorganic Chemistry, Department of Chemistry,
P. O. Box 55 (A. I. Virtasenaukio 1), 00014 University of
Helsinki, Finland
[c] Small Molecule X-ray Facility, Department of Chemistry, Johns
Hopkins University,
Baltimore, MD 21218, USA
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201301000.
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Nearly all of the phosphor materials used in modern allow for efficient excitation in the nUV range. To investi-
technology, such as luminescent lighting, plasma displays, gate the influence of substituents on 1,10-phenanthroline
and photodetectors, are based on inorganic oxides. While (phen) on the luminescence properties of complexes with
those materials have many advantages, such as high stability EuIII, a series of phenanthroline ligands with both electron-
and a high efficiency, there are some major drawbacks. Ox- donating and electron-withdrawing substituents at the 2-po-
ide materials are usually synthesized at high temperatures, sition has been prepared. Coordination compounds with
typically Ն1500 °C, and require high-purity starting com- EuIII have been synthesized and their photophysical proper-
pounds (Ͼ4 n) to avoid luminescence quenching, thereby ties are reported. An overview of the compounds studied is
making these phosphors rather expensive. For example, the given in Figure 1.
quantum efficiency of Y2O3:Eu is reduced by as much as
7% in the presence of only 5 ppm of Fe impurity.[6] In ad-
dition, a cost-effective method to recover rare-earth metals
from these oxides is still to be found.[7]
Lanthanide coordination compounds are the class of ma-
terials that can overcome these drawbacks. Direct excitation
of the trivalent lanthanide ions is, however, not efficient, as
the 4f–4f transitions involved are parity- and in many cases
also spin-forbidden.[8] Current lanthanide(III) oxide based
phosphors circumvent this problem by relying on charge-
transfer bands or a sensitizer for light absorption, followed
by energy transfer to the luminescent center.[6,9] As early as
1942, it was found by Weisman that suitable organic ligands
are capable of enhancing the photoluminescence intensity
of lanthanide compounds.[10] This phenomenon, widely
known as the antenna effect, relies on the ligand to absorb
incoming radiation by means of allowed transitions. Subse-
quent energy transfer to an excited state of the lanthanide
ion yields luminescence characteristic of the central ion.[11]
Figure 1. An overview of the compounds described in this work.
The complexes have the general formula [Ln(L)2(NO3)3], Ln = Eu,
La, except for Eu2 (see text).
Results
Synthesis and Characterization
All ligands were readily synthesized following procedures
The synthesis of lanthanide complexes is typically per- reported in literature and were analyzed using IR and
formed at low temperatures (Ͻ200 °C). As lanthanide com- NMR spectroscopy. Formation of the corresponding EuIII
plexes are of a molecular nature there is no need for highly complexes was performed by addition of a hot solution of
pure reactants, which can greatly reduce the production Eu(NO3)3·5H2O in ethanol to a hot stirred solution of the
costs. Moreover, recycling the rare-earth metals can be ac- ligand. The solutions were heated to boiling to ensure com-
complished by simply burning off the ligands, or by dissolv- plete dissolution of the ligand and inorganic salt and to
ing the complexes in inorganic acids. Besides these advan- slow down precipitation of the product. In general, the lan-
tages, the absorption properties can, in principle, be tuned thanide complexes Eu1–La8 are poorly soluble in ethanol
to the excitation source by making small modifications to and addition of the lanthanide nitrate solution to the ligand
the ligands (e.g., by introducing substituents). At the mo- solution at room temperature leads to the immediate forma-
ment, the major shortcomings to overcome before applica- tion of a fine precipitate. Unfortunately, the poor solubility
tion of lanthanide(III) complexes as phosphor materials of the compounds severely hampers purification and proper
can be considered are the typically low quantum efficiency analysis. Attempts were undertaken to analyze the lantha-
and poor long-term stability of the complexes.[12] Neverthe- nide coordination compounds with ESI-MS, but due to the
less, EuIII complexes with a photoluminescence quantum poor solubility and inherent high kinetic lability of the lan-
yield in the range of 75 to 85% are known.[11b,13] Further- thanide compounds, only signals of the ligands were found
more, the use of EuIII complexes as a red phosphor for nUV in the mass spectra. Elemental analysis was performed to
LEDs has been demonstrated recently.[12a,14]
determine the composition of the complexes. All complexes
Examples of ligands that are known to efficiently sensit- were found by analysis to be [Ln(L)2(NO3)3], with the ex-
ize the luminescence of the lanthanides include β-diketon- ception of Eu2, which was found to be [Eu(L)3]. The devia-
ates, aromatic carboxylates, and salicylates.[12b,15] Another tions between the calculated and found values for the ele-
promising class of ligands comprises 1,10-phenanthrolines. mental analyses for compounds Eu2, Eu3, Eu4, and La8 are
Used either as a solitary sensitizer or as a neutral co-ligand readily explained by the inclusion of minor quantities of
used to saturate the lanthanide coordination sphere of com- Eu(NO3)3 in the samples, which cannot be removed by
plexes with anionic ligands, 1,10-phenanthrolines are cap- recrystallization. The molecular nature of these compounds
able of efficient sensitization of EuIII-centered lumines- ensures, however, that these minor impurities do not nega-
cence.[16] The complex [Eu(1,10-phenanthroline)2(NO3)3] is tively affect their photoluminescent properties, in contrast
known to be highly luminescent, but efficient excitation at to phosphor materials that are based on solid-state com-
wavelengths above 355 nm is not possible.[16a,17] A redshift pounds. Compounds Eu6 and Eu7 were dried prior to ele-
of the excitation maximum by at least 20 nm is required to mental analysis and luminescence studies. As a result, the
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disordered solvent molecule that are observed in the crystal around the EuIII ion is best described as a distorted spheno-
structure (see above) is not apparent from the elemental corona. Compounds Eu8 and La8 are isostructural, with a
analysis. When exposed to air, the initially shiny crystals C2 axis passing through a nitrato N–O bond and the lan-
turn lusterless, thus indicating that solvent molecules are thanide ion, whereas in Eu6 and Eu7 a pseudo-C2 axis is
easily lost. TGA analysis showed that, with the exception present. The coordination geometry of Eu6 with an indica-
of Eu3 and Eu4, the compounds are thermally stable to at tion of the pseudo-C2 axis is shown in Figure S10 of the
least 200 °C, as shown in Figures S1–S9 of the Supporting Supporting Information. In both Eu6 and Eu7, for each
Information. The infrared spectra recorded for the ligands complex a disordered molecule of ethanol is present in the
are complicated and show many bands, which complicates crystal lattice. In Eu6 and Eu7, the Eu–O bond lengths
full assignment of the signals. Signals due to characteristic range from 2.502(3) to 2.555(3) Å, whereas Eu–N bond
functional groups can be seen; for example, the signal at lengths vary from 2.572(3) to 2.590(3) Å, which is rather
2230 cm–1 can be attributed to the CN group of 1, whereas long but in line with closely related compounds.[16a,19] The
strong bands around 1700 cm–1 recorded for ligands 2–4 coordination angle of the nitrato ligands is around 50°,
are typical of the C=O stretching vibration. NMR spectra whereas the phenanthroline N–Eu–N angles are around
recorded for the ligands agree with the literature values or 63°.
can be readily assigned to the ligand structures. Comparing
The structures of Eu8 and La8 are mostly ordered, but
the IR spectra obtained for the coordination compounds the substituted carbon atom with the attached amine group
Eu1–La8 to those of the ligands reveals strong similarities of the phenanthroline ligands is located partially on C12
with minor peak shifts. Additional peaks are observed in and partially on C19; the major component of the disor-
the IR spectra of compounds Eu1 and Eu3–La8: all show dered C–NH2 group is positioned on C12 (66.3% for Eu8
strong bands around 1030, 1290, and 1490 cm–1 that can be and 60.1% for La8). In both positions the amine hydrogen
ascribed to vibrations of the nitrate ions.[18] Bands around atoms form strong intramolecular hydrogen-bonding inter-
1650 cm–1 are observed for Eu2–Eu4 due to the C=O actions with a coordinated nitrate oxygen atom, with an
stretching, which is slightly lower in energy than observed H···O distance of 1.96 Å in Eu8 and 2.06 Å in La8; inter-
for the separate ligands, thus indicating that the carbonyl molecular hydrogen-bonding interactions of the amine hy-
group is participating in a binding interaction in the com- drogen atoms with nitrate ions influence the packing of the
plexes.
molecules. The coordination bond lengths vary from
2.484(2) to 2.577(2) Å for Eu–O and from 2.534(2) to
2.600(2) Å for Eu–N. These values are in line with those
found for Eu6 and Eu7. In La8, the La–O bond lengths
range from 2.622(2) to 2.701(2) Å and from 2.585(2) to
2.653(2) Å for La–N. These values are slightly higher than
those found for Eu8, which is readily explained by lantha-
nide contraction and can be considered normal.[19]
X-ray Crystal Structure Determination
Experimental data on the crystal structure determination
for compounds Eu6–La8 are given in Table S1 of the Sup-
porting Information. Projections of the structures of Eu6–
Eu8 are shown in Figure 2; relevant bond lengths and
angles are given in Table S2 of the Supporting Information.
All complexes have a tenfold coordination geometry around
the central lanthanide ion as a result of two phenanthroline
ligands binding in a bidentate mode and three bidentate
Luminescence
The solid-state photoluminescence spectra of complexes
nitrato ligands. The resulting coordination geometry Eu1–Eu7 are shown in Figure 3. Excitation spectra were ob-
Figure 2. Thermal ellipsoid plots (50% probability contours) of the structures of (a) Eu6 [Eu(MeOphen)2(NO3)3]·EtOH, (b) Eu7
[Eu(EtOphen)2(NO3)3]·EtOH, and (c) Eu8, [Eu(NH2phen)2(NO3)3] showing the relevant atomic-numbering scheme Only the major disor-
der component in Eu8 and the amine hydrogen atoms and the intramolecular hydrogen-bonding interactions are shown; hydrogen atoms
and lattice ethanol molecules have been omitted for clarity.
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5
tained by constantly monitoring the D0Ǟ7F2 transition at mation). Complex Eu8, with 2-aminophenanthroline as a
615 nm while scanning the excitation wavelength from 220 ligand, shows no photoluminescence upon excitation in the
to 400 nm. All complexes feature a broad excitation band (near-)UV region, whereas the analogous LaIII complex
in the nUV region that originates from phenanthroline-cen- La8 shows broadband luminescence from 400 to 600 nm,
tered excitation. The excitation maxima are all fairly close as shown in Figure S13 of the Supporting Informaiton.
and range from 351 to 372 nm. The emission spectra of
Eu1–Eu7 obtained by exciting the compounds in the ligand-
centered excitation band are characteristic of EuIII with
Discussion
lines at 580, 595, 615, 649, and 685 nm that originate from
5
the D0Ǟ7FJ (J = 0, 1, 2, 3, 4) transitions. In all cases, the
most dominant line corresponds to the 5D0Ǟ7F2 transition.
Photoluminescence quantum yields and lifetimes are listed
in Table 1. The quantum yields range from 10% for Eu1 to
79% for Eu5, and luminescence lifetimes vary from 0.43 for
Eu1 to 1.57 ms for Eu2 (Table S3 in the Supporting Infor-
X-ray Crystal Structure Determination
The structures as determined for Eu6, Eu7, Eu8, and La8
are rather similar in that the coordination sphere comprises
two substituted phenanthrolines that bind in a bidentate
mode, and three nitrato ligands that bind in a bidentate
mode. In all cases, the geometry around the LnIII center
closely resembles a distorted sphenocorona. In Eu6 and
Eu7, a weak additional interaction between the EuIII center
and the ether oxygen atoms of the ligand appears to be
present, with each forming an apex on top of the square
faces of the sphenocorona. These are the largest faces of
the coordination polyhedron that offer a possibility for
bonding to atoms in a second coordination sphere. Fig-
ure S10 in the Supporting Information illustrates how these
two additional Eu–O bonds are oriented with respect to the
polyhedron formed by the first coordination sphere. The
bond lengths are 3.351(3) Å for Eu–O7 and 3.372(3) Å for
Eu–O8 in Eu6. For Eu7, the bond lengths of Eu–O7 and
Eu–O8 are 3.375(6) Å for Eu–O7 and 3.411(5) Å, respec-
tively. These values are much larger than expected for a nor-
mal Eu–O bond but within the reasonable range for an oxy-
gen atom in the second coordination sphere of EuIII [20]
Al-
.
though complexes Eu6 and Eu7 have very similar structures
that closely resemble the structure of the EuIII complex with
unsubstituted phenanthroline, the crystal packing is very
different for both compounds.[16a,17] In the structure of Eu6
and Eu7, π stacking between the phenanthrolines of neigh-
boring complexes with a interplanar distance of 3.400(1)
and 3.408(6) Å, respectively, is observed, whereas the dis-
tance between two nearest-neighbor EuIII ions is 9.632(1)
and 9.440(2) Å, respectively. Compounds Eu8 and La8 are
isostructural and adopt a structure that closely resembles
that of [Eu(phen)2(NO3)3].[16a,17] The most notable differ-
ence compared to the complexes Eu6, Eu7, and the parent
phenanthroline complex is the non-coplanarity of the LnIII
ion with the aromatic system of the phenanthroline ligands.
As shown in Figure S11 of the Supporting Information, in
complexes Eu8 and La8, the planes defined by the ligands
do not contain the LnIII ion. In case of Eu6 and Eu7, the
LnIII ion is in the plane defined by one of the ligands and
only slightly out of the least-squares plane defined by the
second ligand.
Figure 3. Photoluminescence spectra of Eu1–Eu7. The excitation
spectra are shown on the left-hand side with the wavelength of
maximum excitation intensity indicated. The right-hand side shows
the luminescence spectra of the compounds, which are characteris-
tic of EuIII with lines at 595, 616, 649, and 685 nm corresponding
5
to D0Ǟ7FJ, J = 1, 2, 3, 4 transitions.
Table 1. The photophysical properties of complexes Eu1–Eu7.
Φtot
Ω2
Ω4
τexp
τrad
[ms]
ΦLn
[%]
ηsens
[%]
[%] [10–20 cm2] [10–20 cm2] [ms]
Eu1 10
Eu2 n.d.
Eu3 27
Eu4 n.d.
Eu5 79
Eu6 20
Eu7 24
8.82
n.d.
9.75
n.d.
11.93
10.29
9.65
5.25
n.d.
4.53
n.d.
5.98
4.92
4.24
0.43
1.57
0.66
0.57
1.00
1.04
1.13
2.56
n.d.
2.37
n.d.
1.94
2.20
2.40
17
n.d.
28
n.d.
52
47
47
61
n.d.
98
n.d.
ca. 100
43
52
Luminescence
[a] Value of Φtot [%]: overall photoluminescence quantum yield at
355 nm excitation; τexp: total lifetime of D0 state, ΩJ: intensity pa-
Compared to the excitation spectrum of [Eu(phen)2-
(NO3)3], which has a maximum at 355 nm, the excitation
maxima of Eu1–Eu7 are slightly redshifted, as shown in
5
rameters, τrad: radiative lifetime, ΦLn: intrinsic quantum yield, ηsens
:
sensitizer efficiency; n.d.: not determined.
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Figure 3. Of the entire series of complexes, Eu3 and Eu4 the compounds are the same except for the central ion, this
have the highest maximum excitation wavelength at around difference can only be explained by the difference in the
370 nm. A slight shift of the maximum to shorter wave- chemical nature of the lanthanide ions. Finally, an explana-
lengths is observed only for Eu2. The broad bands are due tion can be found from the crystal structure: as the EuIII
to the absorption by phenanthroline and clearly indicate ion does not lie in the plane defined by the planar ligand
that the ligands are acting as antennae. It seems that there molecule, ligand-to-metal energy transfer can be hampered.
is no simple correlation between the electronic properties of It has been suggested that a rigid planar structure of the
the substituent and the optimal excitation wavelength. All ligand within the complex is beneficial for energy trans-
compounds except for Eu8 exhibit luminescence character- fer.[26]
istic of EuIII, with most of the emission intensity arising
5
from the D0Ǟ7F2 transition, which is of a forced electric
dipole (ED) nature. The fact that this transition is much
stronger than the D0Ǟ7F1 magnetic dipole (MD) transi-
tion is in agreement with the structures determined for Eu6
and Eu7, which show that the Eu ion is situated in a non-
centrosymmetric coordination environment.[21] Photolumi-
nescence quantum yields and radiative lifetimes of com-
plexes Eu1 to Eu7 are given in Table 1. Luminescence life-
times are on the order of one millisecond, which is as ex-
pected for EuIII complexes. The most intense luminescence
is observed for Eu5, which has a high quantum yield of
79%. Complexes Eu1, Eu3, and Eu5–Eu7 show moderately
bright photoluminescence at quantum yields ranging from
10 to 27%, values that are comparable to those found for
solutions of similar complexes in CH3CN.[16a] Complex Eu8
does not exhibit detectable photoluminescence, which can
be due to several reasons. Firstly, a spectral mismatch be-
tween the donor level of the ligand and the EuIII 5DJ ac-
ceptor levels can result in poor energy transfer between the
ligand and the metal.[8b,11a,22] Since LaIII, being a 4f0 ion,
has no excited states below the excited states of the ligand,
LaIII complexes can be used to study the ligand-centered
energy levels in the presence of a lanthanide ion.[23] Since
no ligand-to-metal energy transfer can take place in these
complexes, the ligand-centered triplet states can be deter-
mined from the phosphorescence spectrum. The room-tem-
perature emission spectrum recorded for La8 (see the Sup-
porting Information) shows an emission band with a maxi-
mum at 488 nm (20500 cm–1), thereby revealing an excited
5
Analysis of Emission Spectra
The Judd–Ofelt theory (JO theory) provides a powerful
framework for analysis of the intensities of the forced ED
transitions in the lanthanide ions.[27] According to JO
theory, the intensity of a forced ED transition depends on
only three parameters that contain information on the local
structure around the lanthanide ion, such as the symmetry
and the degree of covalency of the bonds.[28] The emission
intensity I of a transition from an initial state of multiplicity
J to a final state of multiplicity JЈ is proportional to the
Einstein coefficient A of spontaneous emission, which is
given by Equation (1).[28c,29]
(1)
In this equation, J is the multiplicity of the initial state
(0 for EuIII), h is Planck’s constant, n is the refractive index
of the medium, and DED and DMD are the electric- and
magnetic-dipole strengths, respectively. In EuIII, the transi-
5
tion D0Ǟ7F1 has no electric-dipole contribution, and can
therefore be considered practically insensitive to the sur-
roundings of the EuIII ion. The strength of this transition
can be derived theoretically (DMD = 9.6ϫ10–42 esu2 cm2)
and used as an internal reference.[28c] With J = 0, the ex-
pression of the Einstein coefficient for this transition be-
comes [Equation (2)].
5
state with an energy that is well above the D0 resonance
level of EuIII at 17300 cm–1, which suggests that energy
transfer should be possible.[24] Secondly, the absence of
photoluminescence in Eu8 can be explained by the presence
of a quenching mechanism, for example, by means of a low-
lying ligand-to-metal charge-transfer (LMCT) state. The
(2)
The transitions D0Ǟ7F2,4,6 are of a purely forced elec-
5
presence of a low-lying LMCT state near the energy of the tric-dipole character. According to Judd–Ofelt theory, the
excited 5DJ multiplet of EuIII is known to compete with the electric-dipole strengths for such transitions can be ex-
ligand-to-metal energy transfer and can result in quenching pressed in terms of three phenomenological intensity pa-
of the luminescence.[22b,25] A low-energy LMCT state can rameters: Ω2, Ω4, and Ω6 as given in Equation (3).
be expected for lanthanide complexes in which the ligands
have a low oxidation potential and the lanthanide ion a
high electron affinity, as is the case for EuIII [22c]
Unlike
.
(3)
complex La8, which has a pale color, Eu8 is deep yellow,
which suggests that an LMCT transition might be present.
In Equation (3), ||U(λ)||2 represents the squared reduced
The absorption spectra for compounds Eu8 and La8 are matrix elements that are independent of the host matrix of
indeed different: both show a ligand-centered absorption the lanthanide ion. The values for these elements have been
band that extends to approximately 420 nm, but Eu8 has an calculated and are listed in Table S5 of the Supporting In-
additional absorption that extends to almost 500 nm. As formation.[28c,29a] Thus, on substituting Equation (3) into
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5
Equation (1), the Einstein coefficients of the forced ED Equation (5). The total emissive relaxation rate of the D0
transitions are given by Equation (4).
state, AT, can be found from Equation (6).
(6)
(4)
The radiative lifetime τrad of the emissive state is simply
5
The remaining transitions D0Ǟ7F0,3,5 are forbidden in
the reciprocal of AT and is given in Table 1. From the exper-
5
imentally obtained lifetime, τexp of the D0 state and τrad
,
both MD and forced ED schemes, and as a result DMD
=
the intrinsic quantum yield ΦLn of the lanthanide ion can
be calculated from τexp/τrad. The experimentally determined
lifetime contains contributions of radiative and nonradia-
tive decay processes of the emissive state, and ΦLn indicates
the relative contribution of radiative transitions. The intrin-
sic quantum yields have been calculated and are given in
Table 1. The values range from 17 to 52%, thus indicating
that nonradiative decay processes contribute substantially
DED = 0 for these transitions. In practice, these transitions
are indeed very weak. In the case of EuIII, calculation of
the intensity parameters from an emission spectrum is par-
ticularly straightforward. Relative intensities of the transi-
tions are readily found by integrating the corresponding
5
lines in the spectrum, using the intensity of the D0Ǟ7F1
MD transition as an internal reference. It is important that
the recorded spectra are corrected for the spectral sensitiv-
ity of the detection system, and that the spectrum repre-
sents the relative photon flow.[30] Hence, the intensity of the
ED transitions relative to the MD transition can be found
on combining Equation (2) and Equation (4), thereby re-
sulting in Equation (5).
5
to the depopulation of the D0 state. From ΦLn and the
overall photoluminescence quantum yield, Φtot, the effi-
ciency of the sensitization process ηsens can be estimated
[34]
from the relation Φtot = ηsens ϫΦLn
.
It indicates how ef-
fective the ligand is at transferring energy to the lumines-
cent center. The ligands in Eu3 and Eu5 seem to be particu-
larly effective at sensitizing EuIII luminescence, with the
main quenching mechanism being nonradiative deactiva-
tion of the luminescent center. In the case of Eu5, because
Φtot Ͼ ΦLn, the calculated sensitizer efficiency is over 100%,
(5)
which is not plausible. This unusual result was also found
using a completely different setup (Table S4 in the Support-
ing Information) and is likely the result of one or more
assumptions used to derive Equation (5) being incorrect.
For instance, the refractive index was taken to be a constant
of 1.5, whereas it is known that the luminescent properties
of the EuIII ion are sensitive to the refractive index.[35]
Here, IJ,exp represents the experimentally observed inten-
5
sity of a D0Ǟ7FJ transition, νJ and ν1 the wavenumber of
5
5
the D0Ǟ7FJ and D0Ǟ7F1 transitions, respectively, and nJ
and n1 the refractive index of the medium at the wave-
number of the transitions. As Table S4 in the Supporting
Information has only nonzero values along its diagonal, the
value for Ωλ can be found directly from the ratio (IJ,exp)/
(I0,exp), J = λ by using Equation (5). As it is known that the
influence of the Ω6 parameter can be neglected, and since
the 5D0Ǟ7F6 transition was not detected, Ω6 was not deter-
Conclusion
Eight new europium(III) complexes with different 1,10-
mined.[31] The Judd–Ofelt intensity parameters have been phenanthroline ligands substituted on the 2-position have
calculated for compounds Eu1–Eu7 and are given in been synthesized in yields ranging from 43 to 89%. In ad-
Table 1. An average refractive index of 1.5 was used in the dition, one isostructural lanthanum(III) compound has
calculations.[29b,32] It is known that the intensity ratio been synthesized for the estimation of the triplet excited
I(5D0Ǟ7F2)/I(5D0Ǟ7F1) of the ED versus MD transitions state of the ligand. Solid-state photoluminescence studies
is a measure of the site symmetry of EuIII. The higher this on the complexes reveal ligand-centered excitation for all
ratio, the further the site symmetry departs from inversion complexes except Eu8, which suggests that 2-amino-1,10-
symmetry.[21a] From Equation (5) it is clear that the magni- phenanthroline is unsuitable for sensitizing EuIII lumines-
tude of Ω2 directly depends on this ratio. In general, a large cence. A low-lying charge-transfer band provides a means
Ω2 is indicative of a low site symmetry and a covalent char- of nonradiative relaxation of the 5D0 level on the EuIII ion.
acter of the chemical bonds to the LnIII ion.[28b,33] From The luminescent complexes are efficiently excited in the
the emission spectra shown in Figure 3, it is clear that the near-UV region and exhibit medium to high photolumines-
5D0Ǟ7F2 transition is much more intense than the cence quantum yields. Compared to [Eu(phen)2(NO3)3], the
5D0Ǟ7F1 transition, thereby resulting in high Ω2 param- excitation maximum of Eu1, Eu3, Eu4, Eu6, and Eu7 has
eters. There seems to be no well-defined interpretation of shifted to longer wavelengths. Unfortunately, there seems to
the Ω4 parameter.[28b]
be no clear correlation between the electronic properties of
From Equation (5), it is possible to estimate the radiative the ligand substituent on the excitation maximum of the
lifetime of the complexes. From Equation (2), A0–1 can be complex. Although the crystal structure determinations
calculated (ca. 49 s–1), whereas the Einstein coefficients for show similar coordination geometries for the lanthanide
the other transitions can be found from the first relation in ions, the crystal packings of Eu6, Eu7, and Eu8 are dif-
Eur. J. Inorg. Chem. 2013, 6137–6146
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FULL PAPER
ferent. Notably, the EuIII ion in Eu8 does not reside in the
plane of the sensitizing ligand, which might be another
cause of the ligand-to-metal energy transfer being severely
hampered. This suggests that not only the electronic prop-
erties of the substituents should be considered when analyz-
ing the antenna properties, but also the steric demands. The
emission spectra are characteristic for EuIII centers in a
non-centrosymmetric coordination site, which for Eu6 and
Eu7 is confirmed by single-crystal X-ray diffraction data.
Analysis of the spectral intensities shows a significant con-
tribution of nonradiative processes that quench the lumi-
gram CrysAlisPro was used to refine the cell dimensions and for
data reduction. The structure was solved with the program
SHELXS-97 and was refined on F2 with SHELXL-97.[38a] Analyti-
cal numeric absorption corrections based on a multifaceted crystal
model were applied using CrysAlisPro. The temperature of the data
collection was controlled using a Cryojet system (manufactured by
Oxford Instruments). The hydrogen atoms were placed at calcu-
lated positions using the instruction AFIX 43 or AFIX 93 with
isotropic displacement parameters that had values 1.2Ueq of the
attached C or N atoms.
Synthesis: Detailed descriptions of the synthetic procedures are
given in the Supporting Information.
5
nescence of the D0 level on EuIII, thereby resulting in low
1,10-Phenanthroline-2-carbonitrile (CNphen; 1): The compound was
intrinsic quantum yields. The high thermal stability and the
excitation maxima of Eu4 and Eu6 make these compounds
suitable for application in nUV LED chips, but the rela-
tively low quantum yields limit their application as phos-
phor materials in pcWLEDs.
prepared following the procedures reported by Engbersen et al. and
Corey et al.[39] IR: ν = 3068 (br. m), 2230 (m), 1584 (m), 1506 (s),
˜
1486 (s), 1417 (m), 1403 (m), 1390 (s), 1296 (m), 1313 (m), 1135
(m), 1098 (s), 986 (m), 961 (w), 950 (w), 899 (m), 850 (vs), 827 (s),
816 (m), 777 (s), 737 (vs), 717 (s), 652 (vs), 628 (s), 578 (m), 523
(m), 461 (m), 417 (m) cm–1.
1,10-Phenanthroline-2-carboxylic Acid (HO2Cphen; 2): Following
the procedures described by Ten Brink et al., 1 was hydrolyzed to
Experimental Section
the carboxylic acid.[40] IR: ν = 3468 (br. m), 3140 (br. m), 1700 (vs),
˜
General: Phenanthroline was supplied by Merck, triethylamine was
supplied by Acros, and all other chemicals were purchased from
Sigma–Aldrich and used as received. NMR spectra were recorded
with a Bruker DPX-300 spectrometer. Infrared spectra were re-
corded with a Perkin–Elmer Paragon 1000 FTIR spectrometer
equipped with a Golden Gate ATR. Elemental analysis for C, H,
and N was performed with a Perkin–Elmer 2400 series II analyzer.
Excitation and emission spectra were recorded with a Shimadzu
RF-5301PC spectrofluoriphotometer equipped with a solid-state
sample holder and a UV-blocking filter. Photoluminescence quan-
tum yields were determined with an Edinburgh Instruments
FLS920 spectrophotometer equipped with an integrating sphere
and by following a modified version of the procedure reported by
de Mello et al.[36] All spectra were corrected for the response of
the detection system and reflectivity of the integrating sphere. For
lifetime measurements, a pulsed laser source was used as an exci-
tation source with the same machine. The nitrate salt of EuIII was
obtained by dissolving Eu2O3 in hot concentrated nitric acid to
give a clear solution. Subsequent evaporation of the solvent under
reduced pressure gave the nitrate salt as a white crystalline com-
pound, for which the composition Eu(NO3)3·5H2O was assumed.
1694 (vs), 1652 (s), 1616 (m), 1564 (m), 1456 (s), 1424 (s), 1358 (br.
vs), 1294 (s), 1204 (br. s), 1155 (s), 861 (vs), 834 (s), 792 (s), 770
(s), 720 (vs), 602 (s), 536 (br. s), 419 (s), 354 (m), 338 (m), 324 (m)
cm–1.
Methyl-1,10-Phenanthroline-2-carboxylate (MeO2Cphen; 3): Ac-
cording to a procedure reported by Weijnen et al., 1 was converted
into the methyl carboxylate.[41] IR: ν = 3528 (br. m), 3410 (br. m),
˜
1714 (vs), 1668 (s), 1651 (s), 1616 (s), 1558 (s), 1506 (s), 1496 (s),
1398 (s), 1364 (m), 1304 (s), 1282 (br. vs), 1172 (s), 1141 (s), 1087
(s), 1019 (s), 971 (m), 861 (vs), 832 (s), 812 (m), 772 (m), 725 (vs),
714 (s), 668 (s), 628 (s), 419 (s), 384 (s), 374 (s), 358 (s) cm–1.
Ethyl-1,10-Phenanthroline-2-carboxylate (EtO2Cphen; 4): A pro-
cedure similar to that described for 3 was adopted, except that
25 mL of ethanol was used instead of methanol. IR: ν = 3488 (br.
˜
m), 3182 (br. m), 1723 (vs), 1684 (m), 1616 (s), 1507 (m), 1456 (m),
1442 (s), 1404 (s), 1302 (s), 1278 (br. vs), 1196 (m), 1157 (s), 1141
(vs), 1088 (m), 970 (s), 892 (w), 861 (s), 836 (m), 828 (m), 814 (s),
762 (s), 724 (vs), 718 (vs), 630 (s), 492 (vbr. m), 448 (vs), 344 (s)
cm–1.
2-Chloro-1,10-phenanthroline (Clphen; 5): 2-Chloro-1,10-phen-
anthroline was prepared starting from 1,10-phenanthroline N-oxide
prepared from 1,10-phenanthroline as described following litera-
ture procedures.[39] The N-oxide was converted to 1-methyl-1,10-
phenanthrolin-2(1H)-one following the procedure given by Kol-
ling.[42] Subsequently, this compound was chlorinated following the
X-ray Crystal Structure Determination: For the determination of
the structures of Eu6 and Eu7, a crystal was selected for the X-ray
measurements and mounted to the glass fiber using the oil-drop
method; data were collected at 173 K with a Nonius Kappa CCD
diffractometer (Mo-Kα radiation, graphite monochromator, λ =
0.71073).[37] The intensity data were corrected for Lorentz and po-
larization effects and for absorption. The Collect, SHELXS-97,
and SHELXL-97 programs were used for data reduction, structure
solution, and structure refinement, respectively.[38] The non-hydro-
gen atoms were refined anisotropically. The hydrogen atoms were
introduced in calculated positions and refined with fixed geometry
with respect to their carrier atoms. In compound Eu6 the solvent
ethanol is disordered in two positions with population parameters
0.5.
procedure given by Halcrow et al.[43] IR: ν = 3054 (br. w), 1621
˜
(w), 1582 (s), 1553 (s), 1494 (s), 1440 (s), 1414 (s), 1387 (s), 1312
(m), 1212 (m), 1152 (m), 1140 (s), 1123 (vs), 1071 (s), 870 (s), 839
(vs), 824 (s), 767 (s), 730 (vs), 711 (s), 624 (s), 611 (s), 574 (m), 514
(m), 492 (m), 420 (s), 352 (s), 321 (m), 314 (m) cm–1.
2-Methoxy-1,10-phenanthroline (MeOphen; 6): This compound was
synthesized from 5 following a procedure reported by Claus et
al.[44] IR: ν = 3372 (vbr. m), 3010 (w), 2949 (w), 1662 (w), 1652
˜
(w), 1646 (w), 1609 (s), 1593 (s), 1564 (s), 1558 (m), 1540 (w), 1506
(vs), 1464 (vs), 1430 (m), 1410 (s), 1394 (m), 1354 (vs), 1303 (m),
1266 (vs), 1225 (s), 1132 (s), 1075 (m), 1020 (vs), 914 (m), 876 (m),
845 (vs), 831 (vs), 792 (m), 770 (s), 748 (m), 732 (s), 718 (s), 683
(vs), 655 (s), 627 (s), 569 (m), 458 (m), 437 (s), 396 (m), 375 (m),
334 (m), 316 (m) cm–1.
For Eu8 and La8, all reflection intensities were measured at
110(2) K with a KM4/Xcalibur (detector: Sapphire3) with en-
hanced graphite-monochromated Mo-Kα radiation (λ = 0.71073 Å)
using the program CrysAlisPro (version 1.171.35.11 for Eu8, ver-
sion 1.171.36.20 for La8, Oxford Diffraction Ltd., 2011). The pro-
Eur. J. Inorg. Chem. 2013, 6137–6146
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FULL PAPER
2-Ethoxy-1,10-phenanthroline (EtOPhen; 7): A procedure similar to
that described for 6 was adopted but using ethanol instead of meth-
(0.059 g, 0.14 mmol) in ethanol (5 mL) were heated to boiling. The
former solution was added slowly to the latter. Upon cooling, a
very small amount of a yellowish precipitate formed, which was
removed by filtration. Addition of diethyl ether to the filtrate
anol. IR: ν = 3290 (vbr. m), 2978 (m), 1684 (m), 1652 (m), 1622
˜
(s), 1612 (s), 1594 (s), 1560 (s), 1506 (s), 1499 (s), 1457 (vs), 1422
(s), 1398 (m), 1386 (m), 1366 (s), 1345 (s), 1299 (m), 1280 (vs), 1226 caused a white powder to precipitate from the solution. This pre-
(m), 1139 (s), 1098 (m), 1076 (m), 1043 (s), 948 (m), 882 (m), 848 cipitate was collected on a Buchner funnel and air-dried to give
(vs), 832 (m), 804 (m), 783 (s), 740 (vs), 718 (s), 698 (vs), 668 (s),
0.107 g of powder, yield 89% based on Eu. IR: ν = 3300 (br. w),
˜
660 (s), 626 (vs), 583 (s), 564 (s), 487 (s), 429 (m), 326 (m), 322 (m), 1684 (m), 1616 (m), 1569 (m), 1558 (w), 1516 (m), 1496 (s), 1464
314 (m) cm–1.
(s), 1456 (s), 1436 (s), 1404 (s), 1286 (br. vs), 1096 (m), 1029 (m),
871 (m), 826 (s), 739 (s), 721 (vs), 668 (s), 643 (s), 610 (s), 423 (m),
398 (m), 350 (s), 328 (m) cm–1. C30H24EuN7O13 (842.5) +
0.15Eu(NO3)3 (50.7) [Eu(EtO2Cphen)2(NO3)3 + 0.15Eu(NO3)3]: C
40.34, H 2.71, N 11.68; found C 40.05, H 2.44, N 11.81.
2-Amino-1,10-phenanthroline (NH2Phen; 8): Following the pro-
cedure reported by Engel, starting from 5.[45] IR: ν = 3320 (vbr.
˜
m), 1704 (w), 1662 (m), 1652 (s), 1646 (m), 1634 (m), 1568 (s), 1558
(s), 1520 (m), 1436 (s), 1414 (s), 1332 (s), 1249 (s), 1206 (m), 1134
(m), 1068 (s), 840 (s), 813 (s), 709 (vs), 680 (s), 576 (s), 552 (vs),
403 (s), 367 (s), 364 (s) cm–1.
[Eu(Clphen)2(NO3)3] (Eu5): A solution of 5 (0.13 g, 0.6 mmol) in
ethanol (3 mL) and
a solution of Eu(NO3)3·5H2O (0.12 g,
0.3 mmol) in ethanol (3 mL) were heated to boiling. The Eu solu-
tion was slowly added to the phenanthroline solution. Heating and
stirring was continued for 5 min. Upon cooling to room tempera-
ture, a precipitate formed. The precipitate was collected on a Buch-
ner filter and washed with ethanol. The precipitate was allowed to
[Eu(CNphen)2(NO3)3]·4H2O (Eu1):
A solution of 1 (0.500 g,
2.4 mmol) in ethanol (30 mL), and a solution of Eu(NO3)3·5H2O
(0.348 g, 0.8 mmol) in ethanol (20 mL) were heated to boiling for
15 min to ensure complete dissolution. The Eu(NO3)3 solution was
added to the former slowly. Precipitate formed on cooling to room
temperature. The solids was collected on a sintered glass funnel
and dried in air to give 0.55 g of powder, yield 84% based on Eu.
dry in air, yield 225 mg, 97% based on Eu. IR: ν = 1616 (w), 1580
˜
(w), 1481 (vs), 1424 (s), 1374 (w), 1294 (vs), 1212 (m), 1198 (m),
1180 (w), 1143 (m), 1114 (w), 1031 (m), 995 (w), 953 (s), 886 (s),
809 (s), 780 (w), 733 (vs), 723 (s), 638 (s), 619 (m), 576 (w), 556
(w), 522 (w) cm–1. C24H14Cl2EuN7O9 (767.3) [Eu(Clphen)2(NO3)3]:
C 37.37, H 1.84, N 12.78; found C 37.56, H 1.76, N 12.66.
IR: ν = 3351 (vbr. m), 3066 (br. m), 2240 (m), 1635 (m), 1616 (s),
˜
1594 (s), 1538 (m), 1506 (m), 1472 (m), 1432 (s), 1393 (vs), 1299
(br. vs), 1264 (vs), 1232 (s), 1214 (s), 1152 (m), 1040 (m), 871 (vs),
840 (m), 818 (m), 788 (m), 760 (m), 742 (m), 730 (s), 624 (vs), 642
(vs), 586 (m), 462 (vs), 418 (s), 385 (s), 328 (s) cm–1.
[Eu(MeOphen)2(NO3)3] (Eu6): A solution of 6 (600 mg, 2.8 mmol)
in ethanol (15 mL) and a solution of Eu(NO3)3·5H2O (375 mg,
0.88 mmol) in ethanol (10 mL) were heated to boiling for 5 min.
The salt solution was slowly added to the ligand solution. Precipi-
tate appeared upon cooling to room temperature and was collected
on a sintered funnel. The precipitate was washed with four portions
of ethanol (30 mL) and dried in air, yield 0.567 g, 85% based on
C26H22EuN9O13 (820.5) [Eu(CNphen)2(NO3)3·4H2O]: calcd.
38.06, H 2.70, N 15.36; found C 38.07, H 2.37, N 15.13.
C
[Eu(O2Cphen)3]·H2O (Eu2): NEt3 (20 mg) and triethyl orthoform-
ate (TEOF; 2 mL) were added to a solution of 2 (37 mg,
0.18 mmol) in ethanol (10 mL). TEOF (4 mL) was added to a solu-
tion of Eu(NO3)3·5H2O (24 mg, 0.06 mmol) in ethanol (10 mL).
Both solutions were heated to 70 °C, after which the europium
solution was added to the phenanthroline solution. A white precipi-
tate appeared and heating was continued for 30 min. The solids
were filtered through a paper filter, washed with diethyl ether
(30 mL), and dried in air, yield 34 mg of microcrystalline powder,
Eu. IR: ν = 1610 (m), 1594 (m), 1575 (m), 1516 (s), 1496 (s), 1471
˜
(vs), 1456 (vs), 1436 (s), 1418 (vs), 1399 (m), 1346 (s), 1323 (vs),
1287 (vs), 1240 (m), 1181 (m), 1156 (m), 1122 (m), 1092 (m), 1052
(m), 1035 (vs), 903 (m), 848 (vs), 814 (m), 781 (m), 740 (vs), 728
(s), 692 (m), 659 (m), 642 (m), 586 (m), 572 (m), 490 (m), 427
(m), 398 (m), 374 (m), 344 (m), 334 (m), 327 (m), 314 (m) cm–1.
C26H20EuN7O11 (758.4) [Eu(MeOphen)2(NO3)3]: C 41.17, H 2.66,
N 12.93; found C 40.64, H 2.70, N 12.66.
61% based on Eu. IR: ν = 3420 (vbr. m), 1658 (m), 1652 (s), 1622
˜
(vs), 1616 (vs), 1568 (vs), 1558 (s), 1540 (m), 1515 (m), 1495 (s),
1456 (m), 1394 (m), 1362 (br. vs), 1327 (s), 1301 (s), 1197 (m), 1178
(m), 1135 (m), 1092 (m), 1048 (m), 910 (m), 876 (m), 839 (m), 818
(vs), 743 (m), 721 (vs), 641 (s), 609 (s), 421 (s), 422 (vs), 344 (s)
cm–1. C39H23EuN6O7 (839.6) + 0.1Eu(NO3)3 (33.8) [Eu(O2Cphen)3-
(H2O) + 0.1Eu(NO3)3]: C 53.61, H 2.69, N 10.10; found C 53.76,
H 2.81, N 10.05.
Single crystals were obtained by means of a diffusion setup experi-
ment using a Y tube. One leg of the tube was charged with 6
(300 mg, 1.4 mmol), whereas the other was charged with Eu(NO3)3·
5H2O (187 mg, 0.44 mmol). The tube was filled with ethanol such
that the solvent level was 4 mm above the intersection of both legs.
After three weeks at room temperature, orange platelike crystals
had formed in the tube.
[Eu(MeO2Cphen)2(NO3)3] (Eu3): A solution of 3 (0.25 g, 1 mmol)
in methanol (20 mL) and a solution of Eu(NO3)3·5H2O (0.15 g,
0.33 mmol) in methanol (20 mL) were heated to boiling. The
Eu(NO3)3 solution was added to the ligand solution. After the mix-
ture had cooled to room temperature, diethyl ether (20 mL) was
added to aid in precipitation of the complex. The white precipitate
was collected by filtration and dried, yield 0.17 g, 64% based on
[Eu(EtOphen)2(NO3)3] (Eu7): A solution of 7 (640 mg, 2.85 mmol)
in ethanol (15 mL) and a solution of Eu(NO3)3·5H2O (407 mg,
0.95 mmol) in ethanol (10 mL) were heated to boiling for five min-
utes. The salt solution was slowly added to the ligand solution.
The precipitate that formed on cooling to room temperature was
collected on a sintered glass funnel. The precipitate was washed
with four portions of ethanol (30 mL) and dried in air and in a
Eu. IR: ν = 3400 (br. m) 1674 (m), 1622 (m), 1575 (m), 1464 (br.
˜
vs), 1410 (s), 1378 (m), 1281 (br. vs), 1187 (m), 1143 (m), 1096 (m),
1028 (m), 868 (m), 840 (s), 816 (m), 738 (m), 721 (vs), 668 (m), 642
(s), 611 (m), 472 (m), 423 (m), 398 (m), 376 (m), 352 (m) cm–1.
C28H20EuN7O13 (814.5) + 0.14Eu(NO3)3 (47.3) [Eu(MeO2Cphen)2-
(NO3)3 + 0.14Eu(NO3)3]: C 39.02, H 2.34, N 12.06; found C 39.03
H 2.50 N 11.60.
desiccator, yield 0.62 g, 64% based on Eu. IR: ν = 1612 (m), 1593
˜
(m), 1575 (m), 1512 (s), 1472 (s), 1456 (vs), 1424 (m), 1339 (s), 1308
(vs), 1286 (br. vs), 1236 (m), 1157 (m), 1121 (m), 1090 (m), 1051
(m), 1034 (vs), 959 (m), 878 (m), 845 (s), 813 (m), 780 (m), 739 (vs),
[Eu(EtO2Cphen)2(NO3)3] (Eu4):
0.28 mmol) in ethanol (5 mL) and a solution of Eu(NO3)3·5H2O
A
solution of
4
(0.070 g, 727 (s), 708 (m), 668 (m), 655 (m), 642 (s), 572 (m), 510 (m), 425
(m), 375 (m), 358 (m), 324 (m) cm–1. C28H24EuN7O11 (786.5)
6144 © 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2013, 6137–6146

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FULL PAPER
[4]
H. A. Höppe, Angew. Chem. 2009, 121, 3626; Angew. Chem.
Int. Ed. 2009, 48, 3572–3582.
C. C. Lin, R.-S. Liu, J. Phys. Chem. Lett. 2011, 2, 1268–1277.
G. Blasse, B. C. Grabmaier, Luminescent Materials, Springer
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a) T. Saito, H. Sato, T. Motegi, J. Alloys Compd. 2006, 425,
145–147; b) M. A. Rabah, Waste Management 2008, 28, 318–
325.
a) P. A. Tanner, C.-K. Duan, Coord. Chem. Rev. 2010, 254,
3026–3029; b) J.-C. G. Bünzli, S. Comby, A.-S. Chauvin,
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Funct. Mater. 2003, 13, 511–516; b) G. Blasse, Mater. Chem.
Phys. 1987, 16, 201–236.
[Eu(EtOphen)2(NO3)3]: C 42.76, H 3.08, N 12.47; found C 42.51,
H 2.95, N 12.49.
[5]
[6]
Crystals were obtained as for Eu6, except that 25 mg (0.11 mmol)
of 7 and 16 mg (0.04 mmol) of Eu(NO3)3·5H2O were used. After
three weeks at room temperature, yellow platelike crystals had
formed in the tube.
[7]
[8]
[9]
[Eu(NH2phen)2(NO3)3] (Eu8): A solution of 8 (0.32 g, 1.6 mmol) in
ethanol (20 mL) and
a solution of Eu(NO3)3·5H2O (0.23 g,
0.54 mmol) in ethanol (10 mL) were heated and stirred at 60 °C for
10 min. The salt solution was added dropwise to the ligand solu-
tion. A yellow precipitate formed immediately. After cooling to
room temperature, the precipitate was collected on a sintered fun-
nel and washed with three portions of ethanol (20 mL). The pre-
cipitate was allowed to dry in air to yield 0.33 g (84% based on
[10]
[11]
S. I. Weissman, J. Chem. Phys. 1942, 10, 214–217.
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Eu). IR: ν = 3484 (m), 3440 (m), 3379 (m), 3252 (m), 1657 (m),
˜
1646 (s), 1616 (m), 1594 (m), 1564 (m), 1540 (w), 1520 (m), 1496
(vs), 1472 (vs), 1456 (vs), 1436 (s), 1423 (s), 1385 (vs), 1318 (br. s),
1275 (s), 1216 (m), 1156 (m), 1093 (m), 1031 (s), 841 (vs), 811 (s),
778 (m), 732 (s), 721 (s), 702 (s), 659 (s), 643 (s), 583 (m), 518 (m),
448 (s), 433 (s), 413 (vs), 398 (vs), 374 (s), 349 (m), 342 (m), 328
(s) cm–1. C24H18EuN9O9 (728.4) [Eu(NH2phen)2(NO3)3]: C 39.57,
H 2.49, N 17.31; found C 39.45, H 2.80, N 16.72. Single crystals
of Eu8 were obtained using the procedure described for Eu6, but
with 0.15 g (0.75 mmol) of 8 and 0.11 g (0.38 mmol) of Eu(NO3)3·
5H2O and slow cooling of the reaction mixture to room tempera-
ture.
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[La(NH2phen)2(NO3)3] (La8): The procedure for the synthesis of
Eu8 was followed, except that 0.21 g (0.5 mmol) La(NO3)3·5H2O
was used instead of Eu(NO3)3·5H2O and 0.29 g (1.5 mmol) of 8,
[15]
yield 0.23 g (65% based on La). IR: ν = 3482 (m), 3431 (m), 3379
˜
(m), 3246 (m), 1645 (s), 1588 (m), 1562 (m), 1465 (vs), 1438 (vs),
1423 (s), 1385 (vs), 1317 (br. s), 1269 (s), 1215 (m), 1031 (s), 842
(vs), 812 (s), 775 (m), 731 (s), 719 (s), 701 (s), 659 (m), 642 (s), 582
(w), 537 (w), 514 (w) cm–1. C24H18LaN9O9 (715.4) + 0.1La(NO3)3
(32.5) [La(NH2phen)2(NO3)3 + 0.1La(NO3)3]: C 38.55, H 2.43, N
17.42; found C 38.03, H 2.32, N 17.41. Single crystals were ob-
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Received: August 2, 2013
Published Online: November 15, 2013
Eur. J. Inorg. Chem. 2013, 6137–6146
6146
© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim