Visible and Near-Infrared Emission from Lanthanoid β-Triketonate Assemblies Incorporating Cesium Cations

Article abstract of DOI:10.1021/acs.inorgchem.7b00928

The reaction of the β-triketonate ligands tris(4-methylbenzoyl)methanide and tribenzoylmethanide with the trivalent lanthanoids Eu³⁺, Er³⁺, and Yb³⁺ in the presence of Cs⁺ afforded polymeric structures where the

Full text of DOI:10.1021/acs.inorgchem.7b00928

Article
pubs.acs.org/IC
Visible and Near-Infrared Emission from Lanthanoid β‑Triketonate
Assemblies Incorporating Cesium Cations
Laura Abad Galan,† Brodie L. Reid,† Stefano Stagni,‡ Alexandre N. Sobolev,§ Brian W. Skelton,§
́
Massimo Cocchi,∥ Joanna M. Malicka,∥,¶ Eli Zysman-Colman,*,⊥ Evan G. Moore,*,# Mark I. Ogden,*,†
and Massimiliano Massi*,†
†Department of Chemistry and Curtin Institute of Functional Molecules and Interfaces, Curtin University, Kent Street, Bentley 6102,
Western Australia, Australia
‡Department of Industrial Chemistry “Toso Montanari”, University of Bologna, viale del Risorgimento 4, Bologna 40136, Italy
§School of Molecular Sciences, University of Western Australia, 35 Stirling Highway, Crawley, Perth, Western Australia 6009,
Australia
∥Institute for Organic Synthesis and Photoreactivity (ISOF), Consiglio Nazionale delle Ricerche (CNR), Via P. Gobetti 101, 40129
Bologna, Italy
⊥Organic Semiconductor Centre, EaStCHEM School of Chemistry, University of St. Andrews, St. Andrews, Fife KY16 9ST, United
Kingdom
#School of Chemistry and Molecular Biosciences, University of Queensland, St Lucia, Queensland 4072, Australia
S
* Supporting Information
ABSTRACT: The reaction of the β-triketonate ligands tris(4-
methylbenzoyl)methanide and tribenzoylmethanide with the
trivalent lanthanoids Eu3+, Er3+, and Yb3+ in the presence of Cs+
afforded polymeric structures where the repeating units are
represented by bimetallic tetranuclear assemblies of formulation
{[Ln(Cs)(β-triketonate)4]2}n. The only exception is the
structure formed by the reaction of tris(4-methylbenzoyl)-
methanide, Yb3+, and Cs+, which yielded a polymeric assembly
where the repeating units are mononuclear Yb3+ complexes
bridged by Cs+ cations. Photophysical measurements on the
obtained materials confirmed efficient sensitization from the
ligand excited states to the 4f* excited states of the three
lanthanoids. According to transient absorption data, Er3+ and
Yb3+ are sensitized via energy transfer from the triplet state of the β-triketonate ligands. On the other hand, energy transfer to
Eu3+ seems to occur via an alternative pathway, possibly directly via the singlet state or through ligand to metal charge transfer
states. The emission measurements confirm efficient sensitization for all three lanthanoids and bright near-infrared emission for
Er3+ and Yb3+, a characteristic that seems to be linked to the specific chemical structure of the β-triketonate ligands.
the triplet excited state of the antenna - populated via
intersystem crossing (ISC) from the singlet state and facilitated
by the strong spin−orbit coupling of lanthanoid cations  and
the accepting 4f* state.11−13 However, it has been established
that alternative pathways are also possible, such as direct
sensitization from the ligand singlet excited state or energy
transfer mediated by population of charge transfer states.14−16
Another important consideration for the design of emissive
lanthanoid complexes is the minimization of quenching via
multiphonon relaxation, where the 4f* excited state transfers
the energy to vibrational overtones of OH, NH, and CH bonds
in close proximity to the lanthanoid cation.11 This aspect is
INTRODUCTION
■
The photophysical properties of trivalent lanthanoid cations are
currently the focus of extensive investigation, stemming from
their potential application in a variety of fields including optical
displays, night vision devices, telecommunication signaling, life
science, and counterfeiting technologies.1−6 Lanthanoid cations
cannot be directly excited in an efficient manner, a limitation
that arises from f−f transitions being parity and often spin
forbidden.7−10 Therefore, efficiently luminescent lanthanoid
complexes are obtained by exploiting sensitization through π-
conjugated ligands. These ligands act as antennas by absorbing
energy more efficiently and subsequently transferring this
energy to populate the 4f* lanthanoid excited states. The
general rules that govern efficient sensitization are well
established and usually rely on the energy difference between
Received: April 17, 2017
© XXXX American Chemical Society
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Figure 1. Summary of the isolated assemblies according to reaction conditions.
particularly important for those lanthanoid elements emitting
near-infrared (NIR) radiation (e.g., Nd3+, Er3+, and Yb3+),
which are more susceptible than visible emitters (e.g., Eu3+ and
Tb3+) to these quenching phenomena.17,18
While the luminescent properties in the case of Eu3+ were
similar to those of analogous complexes bound to diketonate
ligands, exceptional NIR emission was recorded for assemblies
of Er3+ and Yb3+.29 In particular, these assemblies exhibited
remarkably elongated excited state lifetime decays, with values
usually obtained from complexes bound to deuterated or
fluorinated organic ligands designed to minimize quenching via
multiphonon relaxation.30 Furthermore, we demonstrated how
these assemblies can be exploited as material precursors for the
fabrication of near-infrared organic light emitting devices (NIR-
OLEDs).31
In this work, we focus on completing the series, synthesizing
lanthanoid assemblies incorporating Cs+ as the alkali-element
cation. Furthermore, we extend our investigation by using the
new ligand tris(4-methylbenzoyl)methane (mtbmH) alongside
the previously employed tribenzoylmethane (tbmH). Studying
mtbmH is an initial step toward establishing how chemical
modifications of the ligand might influence the specific
structure of the species obtained. As in our previous studies,
the resulting assemblies have been investigated by means of
absorption and emission spectroscopy to characterize their
photophysical properties. Additional transient absorption
experiments have been conducted using simpler model
complexes in an effort to further elucidate the detailed
sensitization pathways that characterize lanthanoid species
bound to β-triketonate ligands.
β-Diketonate ligands have been extensively investigated in
lanthanoid coordination chemistry.3,19 In fact, these types of
ligands easily chelate the strongly oxophilic lanthanoid cations.
Research in this domain has yielded a wide variety of structural
motifs, ranging from mononuclear complexes to architecturally
more sophisticated discrete oxo/hydroxo clusters.20,21 Indeed,
not only have β-diketonate ligands been useful in stabilizing a
wide variety of structures but also their chemical composition
can include aromatic moieties that favor the efficient
sensitization of lanthanoid cations.22−25
In comparison to β-diketonates, β-triketonate ligands have
been scarcely considered in lanthanoid coordination chemistry,
with only a handful of examples being reported during the
1960s.26−28 This lack of investigation is rather surprising,
especially when one considers that these systems can be easily
obtained by starting from ubiquitously available β-diketonates
and well-established synthetic procedures based on Claisen-
type condensation reactions. We have therefore endeavored to
fill this gap and investigate the potential of β-triketonates for
the synthesis of luminescent lanthanoid complexes. Our initial
results highlighted the serendipitous discovery of discrete
bimetallic tetranuclear assemblies of formulation [Ln(Ae·
HOEt)(tbm)4]2, where Ae+ is an alkali-metal cation and
tbm− is the tribenzoylmethanide ligand.29 Our studies have
RESULTS AND DISCUSSION
■
shown that this assembly is consistently obtained upon
variation of the lanthanoid cation (Eu3+, Er+, and Yb3+),
alkali-metal cation (Na+, K+, or Rb+), and alcoholic solvent
(ethanol or n-butanol). Despite the structural novelty of these
species, the most remarkable discovery occurred on investigat-
ing the photophysical properties of these lanthanoid assemblies.
Synthesis of the Lanthanoid Assemblies. The mtbmH
ligand was synthesized following the same procedure previously
reported for tbmH.31 Following the same methodology used
for the preparation of discrete tetranuclear [Ln(Ae·HOEt)-
(tbm)4]2 (Ae+ = Na+, K+, Rb+) assemblies,29 1 equiv of
hydrated LnCl3 (Ln3+ = Eu3+, Er3+, Yb3+) was made to react
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Figure 2. Representation of the X-ray crystal structure of {[Ln(Cs)(tbm)4]2}n (Ln3+= Eu3+, Er3+, Yb3+). Hydrogen atoms are omitted for clarity.
Figure 3. Representation of the X-ray crystal structure of {[Ln(Cs)(mtbm)4]2}n (Ln3+ = Eu3+, Er3+). Hydrogen atoms are omitted for clarity.
with 4 equiv of either tbmH or mtbmH in the presence of 4
equiv of CsOH in ethanol (Figure 1). In general, slow
evaporation of the solvent over several days resulted in the
deposition of crystals suitable for X-ray diffraction. The
formulation of all the isolated species was further confirmed
by means of elemental analysis and IR spectroscopy. In
particular, the former revealed the presence of various degrees
of solvation, which is typical for these bimetallic Ln3+/Ae+
assemblies.
Structural characterization revealed the formation of unique
coordination polymers with formulation {[Ln(Cs)(tbm)4]2}n
(Ln3+ = Eu3+, Er3+, Yb3+) or {[Ln(Cs)(mtbm)4]2}n (Ln = Eu3+,
Er3+), upon reaction of LnCl3 with CsOH and either tbmH or
mtbmH (Figure 1). In each case, the repeating unit of these
polymeric species was found to be a tetranuclear assembly
analogous to the previously reported species obtained when the
alkali metal was Na+, K+, or Rb+.29,31 On the other hand,
reaction of YbCl3 with mtbmH and CsOH yielded a different
coordination polymer that was identified as [Yb(Cs·HOEt)-
(mtbm)4]n (Figure 1). In this case, the repeating unit can be
more appropriately described as mononuclear Yb3+ complexes
linearly bridged by Cs+ cations.
Notably, when crystals obtained from the reaction of
hydrated EuCl3 and mtbmH were analyzed, a second product
was also identified by the presence of crystals having a different
morphology with respect to those belonging to {[Eu(Cs)-
(mtbm)4]2}n. This byproduct was identified as a linear polymer
where mononuclear Eu3+ complexes bearing bis(4-
methylbenzoyl)methanide ligands (mdbm−) were linked by
Cs+ cations, [Eu(Cs·2HOEt)(mdbm)4]n. This arrangement is
analogous to a previously published structure formed by
lanthanoid cations and dibenzoylmethanide.32 The presence of
this species seems to indicate possible retro-Claisen reactivity of
the triketonate ligands under the alkaline reaction conditions,
with formation of the analogous diketonate species. This
hypothesis is supported by the fact that the 1H NMR spectrum
of mtbmH does not show the presence of mdbmH (see the
Supporting Information).
Analogous reactions were attempted by substituting CsOH
with Cs2CO3; however, no lanthanoid-containing species could
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Figure 4. Representation of the X-ray crystal structure of [Yb(Cs)(mtbm)4]n. Hydrogen atoms are omitted for clarity. The hydrogen-bonding
interaction is highlighted with a light blue line.
be identified upon deposition of the crystals. In fact, only the
formation of the cesium-containing coordination polymer
[Cs(tbm)]n was identified (see the Supporting Information
for a description of this structure). The use of Cs2CO3 was
therefore not further explored.
by four anionic mtbm− ligands. Each Yb3+ is octacoordinated
and bound to four ligands in a bidentate mode. The third keto-
O atoms on three of the ligands are not coordinated, while the
fourth, O(13), is bridging to the Cs+ cation. The bridging
interaction also involves a close approach with the second ring
of the first ligand, with a Cs+···centroid distance of 3.473 Å. The
remainder of the coordination sphere of the Cs+ cation includes
three μ-O atoms bridging to Yb3+ (one from ligand 2, two from
ligand 4) and a molecule of ethanol, which presents a
hydrogen-bond interaction with the keto-O(43) atom
(O(1)···O(43), 2.838 Å).
X-ray Diffraction Studies. The repeating units of the three
{[Ln(Cs)(tbm)4]2}n (Ln3+ = Eu3+, Er3+, Yb3+) polymers were
analogous to those of previously reported Ln3+/Ae+ assem-
blies.29,31 A Ln3+/Cs+ dimer is formed by two Ln3+ and two Cs+
metal centers surrounded by eight anionic triketonates (Figure
2). Each Ln3+ ion is eight-coordinate, with the four tbm−
ligands binding in a bidentate mode. The third O-keto atoms of
two of the ligands, O(23,43), are not involved in any contact,
one O-keto atom, O(33), bridges to a Cs+ ion to form the
dimer, and the fourth, O(13), bridges to a neighboring Cs+ to
form the polymeric structure. In the previously reported
dimeric structures,29 this last position in the coordination
sphere of the Ae+ cation was occupied by the O atom of an
ethanol molecule. Here, an EtOH molecule is found in the
lattice, with a hydrogen bond formed with the keto O(43)
atom. The remainder of the coordination sphere of the Cs+
comprises three μ-O atoms (one each from ligands 1−3)
bridging to the Ln3+ cation.
The [Eu(Cs)(HOEt)2(mdbm)4]n species (Figure 5), pre-
sumably formed due to a retro-Claisen reaction of mtbm− in
The structures of the two {[Ln(Cs)(mtbm)4]2}n (Ln3+
=
Eu3+, Er3+) polymers are unsolvated and are structurally similar
to the tbm− coordination polymers (Figure 3). The
tetranuclear Ln3+/Ae+ dimeric assembly is again observed,
with the polymeric structure formed by coordination to the Cs+
cations. The specifics of these bridging interactions between the
tetranuclear assemblies do differ. On comparison of the two
Eu3+ polymeric structures, in the mtbm− system, the closest
approaches between aromatic rings and the Cs+ cations occur
within the tetranuclear assembly (Cs···C(216,316), 3.324,
3.521; Cs···centroid(2,3), 3.926, 4.257 Å), consistent with an
attractive interaction.33,34 In contrast, the closest such
approaches occur between the tetranuclear assemblies in the
tbm− polymers (Cs···C(115), 3.580 Å; Cs···centroid, 3.542 Å).
This results in a Cs+···Cs+ distance between linked tetranuclear
assemblies of 7.332 Å in the tbm− system, in comparison to
8.168 Å in the mtbm− system.
Figure 5. Representation of the X-ray crystal structure of [Eu(Cs)-
(HOEt)2(mdbm)4]n. Hydrogen atoms are omitted for clarity.
the presence of CsOH and hydrated EuCl3, is a coordination
polymer analogous to previous reports. Each subunit comprises
one octacoordinate Eu3+ and one Cs+ counterbalanced by four
deprotonated ligands. The Cs+ is coordinated to two molecules
of solvent and six μ-O atoms bridging to the Eu3+.
The [Yb(Cs)(mtbm)4]n polymer crystallized with a sig-
nificantly different structure (Figure 4). This species is
comprised of one Yb3+ and one Cs+ that are counterbalanced
Photophysical Properties. The photophysical data, which
include excited state lifetime decay (τobs), calculated radiative
Ln
Ln
decay (τR), intrinsic photoluminescence quantum yield (Φ ),
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overall photoluminescence quantum yield (ΦLLn), and calculated
sensitization efficiency (ηsens), are reported in Table 1.
that the emission originates in each case from a unique Eu3+
and is in agreement with the fact that the two Eu3+ cations in
each assembly unit are related by an inversion center.7,29,37
7
5
The magnetic dipole allowed transition, F1 ← D0, appears
to be split into two bands in the case of {[Eu(Cs)(tbm)4]2}n
and into three bands (with two being quasi-degenerate) for
{[Eu(Cs)(mtbm)4]2}n. This trend suggests slightly different
degrees of distortion between the two coordination spheres,37
which is supported by the results found in the shape analysis
study, where {[Eu(Cs)(mtbm)4]2}n is more distorted than
{[Eu(Cs)(tbm)4]2}n with respect to an ideal triangular
dodecahedron (see the Supporting Information).38 Slight
differences can also be observed in the splitting of the
Table 1. Photophysical Data for the Complexes in the Solid
State
c
Ln
Ln
complex
τobs (μs) τR (ms)
Φ
ΦLLn
ηsens
{[Eu(Cs)(tbm)4]2}n
{[Eu(Cs)(mtbm)4]2}n
{[Er(Cs)(tbm)4]2}n
{[Er(Cs)(mtbm)4]2}n
{[Yb(Cs)(tbm)4]2}n
[Yb(Cs)(mtbm)4]n
355
424
7
0.660
0.798
0.660
0.660
1.200
1.200
0.54
0.53
0.01
0.01
0.04
0.31
0.37
0.57
0.64
a
a
b
b
7
46
19
0.01
7
5
a
b
c
Literature τR for Er3+. Literature τR for Yb3+.7 Measured with the
hypersensitive F2 ← D0 peaks.
Excited state lifetime decay values (τobs) were measured to be
355 and 424 μs for {[Eu(Cs)(tbm)4]2}n and {[Eu(Cs)-
(mtbm)4]2}n, respectively. In both cases, the decays were
satisfactorily fitted with monoexponential functions. From the
emission spectra, the values of the radiative lifetimes could be
estimated at 0.660 and 0.798 ms for {[Eu(Cs)(tbm)4]2}n and
{[Eu(Cs)(mtbm)4]2}n, respectively. The overall quantum
yields of the compounds were measured with values of 0.51
and 0.57 for {[Eu(Cs)(tbm)4]2}n and {[Eu(Cs)(mtbm)4]2}n,
respectively. From these data, the intrinsic quantum yields, as a
ratio of τobs/τR, could be calculated at 0.54 and 0.53, providing
information on the sensitization efficiency for the tbm− (0.57)
and mtbm− ligand (0.64).
use of an integrating sphere.
The emission properties were recorded in the solid state, as
we have previously demonstrated that these assemblies do not
persist in polar coordinating solvents and are generally
insoluble in nonpolar solvents.29 This was also the case for
species bound to the mtbm− ligand, as the substitution with a
simple methyl group does not appear to be sufficient to impart
solubility in common noncoordinating solvents. In each case,
the emission of the various species originates as a consequence
of the antenna effect, an argument that is supported by the
broad excitation spectra that are analogous to the correspond-
ing absorption profiles of the tbm− and mtbm− ligands (see the
Supporting Information). The triplet states of tbm− and
mtbm− were found to be approximately the same and in the
range 21500−20500 cm−1 (0−phonon transition at 465−488
nm), on the basis of measurements of the phosphorescent
emission at 77 K of their corresponding Gd3+ complexes in
ethanol (see the Supporting Information).35 The energy of the
triplet state is therefore high enough to sensitize emission from
the excited states of Eu3+, Er3+, and Yb3+ (the last possibly via
charge transfer excited states).16,36
Taken together, the photophysical data for the two Eu3+
species indicate that in these complexes energy transfer from
the tbm− and mtbm− ligands is quite efficient and is in line
with the previously reported Eu3+ assemblies obtained with
Na+, K+, and Rb+.29
The emission spectra of both {[Er(Cs)(tbm)4]2}n and
{[Er(Cs)(mtbm)4]2}n show the characteristic Er3+-based NIR
emission in the 1450−1650 nm spectral region. This peak is
4
4
attributed to the spin-allowed I15/2 ← I13/2 transition (Figure
7). The peak appears structured as a consequence of the crystal
The emission spectra of {[Eu(Cs)(tbm)4]2}n and {[Eu(Cs)-
(mtbm)4]2}n are very similar and show the characteristic Eu3+-
centered linelike bands in the region 580−750 nm (Figure 6),
corresponding to the 7FJ ← 5D0 (J = 0−4) transitions. The 7F0
←
5D0 peak appears narrow (full width at half-maximum
smaller than ∼30 cm−1), albeit of very weak intensity, indicating
Figure 7. Normalized emission plots for {[Er(Cs)(tbm)4]2}n (red
trace) and {[Er(Cs)(mtbm)4]2}n (black trace), with excitation
wavelength at 350 nm.
field effect exerted by the ligands.39 The fine structure of the
splitting is slightly different, which is ascribed to a different
degree of distortion in the coordination sphere around the Er3+
centers in the two species (see the Supporting Information).38
The values of τobs were measured to be 7 μs for both
{[Er(Cs)(tbm)4]2}n and {[Er(Cs)(mtbm)4]2}n. Both decay
Figure 6. Normalized emission plots for {[Eu(Cs)(tbm)4]2}n (red
trace) and {[Eu(Cs)(mtbm)4]2}n (black trace), with excitation
wavelength at 350 nm. Inset: highlight of the peaks corresponding
7
5
to the F1 ← D0 transition.
E
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profiles were satisfactorily fitted by monoexponential functions
are ascribed to a variable degree of distortion for the two Yb3+
centers (see the Supporting Information).38
(after deconvolution from instrumental response). This value
Ln
Ln
provides an estimation of the intrinsic quantum yield Φ of
The observed lifetime decays τobs were fitted to a
monoexponential function and gave values of 46 and 19 μs
for {[Yb(Cs)(tbm)4]2}n and [Yb(Cs·HOEt)(mtbm)4]n, re-
spectively. If the radiative lifetime is assumed to be 1200 μs
(which is the standard assumption for Yb3+ diketonate
complexes, but experimental data are known to range between
500 and 1200 μs),7,41,42 the complexes would have intrinsic
quantum yield values of 0.04 and 0.01, respectively. The value
of τobs for {[Yb(Cs)(tbm)4]2}n is still relatively high in
comparison to those of Yb3+ diketonate compounds (4−5
μs,)43 and it is analogous to the previously reported series of
Yb3+/Ae+ (Ae+ = Na+, K+, Rb+) assemblies.29 This new result
suggests that the presence of the molecule of ethanol
coordinated to Ae+ in the tetranuclar assemblies is not a
0.01. As in the case of the previously published assemblies
bearing Er3+ and Na+, K+, or Rb+,29 τobs is longer than the
average excited state lifetime values for Er3+ diketonate species
(1−2 μs) and is within the range of Er3+ species that have
complexes with perfluorinated and deuterated ligands (6−11 μs
at 58−98% α-deuteration).39,40
Characteristic NIR emission from both {[Yb(Cs)(tbm)4]2}n
and [Yb(Cs·HOEt)(mtbm)4]n was observed in the 900−1100
2
2
nm region, corresponding to the spin-allowed F7/2 ← F5/2
transition (Figure 8). This transition is split into four main
2
dominant factor for nonradiative deactivation of the F5/2
excited state of Yb3+. Interestingly, the [Yb(Cs·HOEt)-
(mtbm)4]n species has a composition similar to that of the
tetranuclear assemblies, but its excited state lifetime is halved.
On the basis of the previous consideration, it might be excluded
that the shorter value of τobs for [Yb(Cs·HOEt)(mtbm)4]n will
be due to multiphonon relaxation caused by the molecule of
ethanol coordinated to the Cs+ cation. Given that energy
migration is unlikely due to the distance between Yb3+
centers,41 the difference in excited state lifetime decays could
be caused by a shorter value of τR for [Yb(Cs·HOEt)-
(mtbm)4]n, and this aspect is currently under investigation.
To gain a more detailed insight into the kinetics involved in
the sensitization process for the triketonate ligands, we have
also performed transient absorption (TA) measurements on
the femtosecond time scale, which have proven useful in
understanding the excited state properties for diketonate
species.44−47 However, as noted earlier, we have shown that
the tetranuclear assemblies do not persist in polar coordinating
solvents,29 which necessitated these measurements to be
Figure 8. Normalized emission plots for {[Yb(Cs)(tbm)4]2}n (red
trace) and [Yb(Cs·HOEt)(mtbm)4]n (black trace), with excitation
wavelength at 350 nm.
bands due to crystal field effects and shows emission from hot
bands as a shoulder in the 930−960 nm region.7 As in the
previous cases, slight differences in the fine splitting of the band
Figure 9. TA spectra (left) of Gd3+ complexes of mtbm− (top) and tbm− (bottom), along with corresponding decay kinetic plots (middle) and
decay associated difference spectra (right).
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Table 2. Summary of Excited State Properties Determined by fs-TA Spectroscopy
complex
τ1(S1→Sn) (ps)
kobs‑S1 (s−1
)
τ2(T1→Tn) (ps)
kobs‑T1 (s−1
)
kEET‑T1 (s−1
)
ΦEET‑T1 (%)
[Gd(tbm)]2+
[Gd(mtbm)]2+
[Yb(tbm)]2+
[Yb(mtbm)]2+
[Er(tbm)]2+
[Er(mtbm)]2+
[Eu(tbm)]2+
[Eu(mtbm)]2+
15.3
20.1
2.4
6.54 × 1010
4.98 × 1010
4.17 × 1011
2.27 × 1011
1.39 × 1011
1.85 × 1011
1.96 × 1011
2.33 × 1011
961
2076
28.4
72.0
37.4
36.5
1.04 × 109
4.82 × 108
3.52 × 1010
1.39 × 1010
2.67 × 1010
2.74 × 1010
3.42 × 1010
1.34 × 1010
2.57 × 1010
2.69 × 1010
97.0
96.5
96.1
98.2
4.4
7.2
5.4
5.1
4.3
performed using simpler model complexes. To that end,
solutions of the tbm− and mtbm− ligands were prepared using
a K2CO3-saturated EtOH solution as the solvent, in order to
ensure deprotonation of the ligand in solution. To these
solutions was added a large molar excess (>10 equiv) of the
Ln3+ = Gd3+, Eu3+, Yb3+, Er3+ cation as their trifluorometha-
nesulfonate salts. Formation of 1:1 [Ln(tbm)(H2O)x]2+ and
[Ln(mtbm)(H2O)x]2+ complexes was confirmed using UV−vis
spectroscopy, which showed a shift in the absorption peak
maxima to ca. 340 nm upon metal ion complexation.
calculate the rate of electronic energy transfer from the excited
T1 state (kEET‑T1) and hence the efficiencies for this triplet-
mediated sensitization pathway (ΦEET‑T1), which are summar-
ized in Table 2. The calculated rate constants are on the order
of ∼1010 s−1 and reveal that both the tbm− and mtbm− ligands
are efficient sensitizers, with ΦEET‑T1 values of ≥96%.
For the corresponding Eu3+ complexes, a close analysis of the
TA spectra revealed a very interesting result. For both the tbm−
and mtbm− ligands, while the initial ΔOD spectra obtained at
early time delays were similar to those for the other complexes,
the broader spectral feature appearing at ca. 650 nm due to T1
→ Tn excited state absorption was clearly absent, and in both
cases the observed TA kinetics were more accurately
represented by a monoexponential decay function of the form
The resulting TA spectra for the Gd3+ complexes of tbm−
and mtbm− are shown in Figure 9. The excited state difference
spectra (ΔOD) at early time delays reveal a negative ground
state bleach (GSB) signal at wavelengths less than 380 nm and
a positive excited state absorption (ESA) peak centered at ca.
400 nm, with the latter decaying rapidly to form a more broad
feature centered at ca. 650 nm, which subsequently decays. The
corresponding kinetic plots for the observed ΔOD dynamics
integrated over 10 nm data intervals from 350 to 650 nm are
shown in Figure 9, and these data were globally fit to a
biexponential decay function of the form
It = A1 exp−1/τ t
1
The lack of an observed T1 → Tn signal suggests that ISC to
form the excited T1 state may be less efficient for these
complexes and furthermore that either a singlet mediated
energy transfer pathway and/or a competing ligand to metal
charge transfer (LMCT) pathway, involving the formation of
reduced Eu2+, may play an important role in the sensitization of
Eu3+ observed using these ligands. This result is in line with
recent reports that have highlighted the importance of the
LMCT state in sensitized Eu3+ luminescence.7,14,37 However, it
should also be recognized that the situation may differ in the
isolated solid {[Ln(Cs)(tbm)4]2}n and {[Ln(Cs)(mtbm)4]2}n
coordination polymers, since differences in the redox potential
(and hence LMCT excited state energies) would be expected
when comparing the tetranuclear assemblies in the solid state
and the analogous simple model complexes in solution.
It = A1 exp−1/τ t + A2 exp−1/τ t
1
2
where It is the intensity of the transient absorption data at time
t, τ1 and τ2 are the observed lifetimes, and A1 and A2 are pre-
exponential scaling factors. The best fit to the experimental data
are shown in Figure 9, and resulting lifetimes are summarized in
Table 2, together with the decay associated difference spectra
(DADS) shown in Figure 9.
Notably, the data for the Gd3+ complexes of tbm− and
mtbm− are very similar, which is not surprising given their
chemical structures. For both complexes, a fast decay
component (τ1 = 15−20 ps) at ca 400 nm (positive DADS
signal) is matched by a fast rise at ca 650 nm (negative DADS
signal). Hence, these spectral features may be assigned to decay
of the initially populated S1 excited state to form the T1 excited
state via ISC, with subsequent decay of the T1 state on the
nanosecond time scale leading to ground state recovery.
Corresponding data for the remaining Ln3+ = Eu3+, Er3+, and
Yb3+ complexes of the tbm− and mtbm− ligands were also
collected and are shown in the Supporting Information. For the
Yb3+ and Er3+ complexes, the spectra obtained are again very
similar and yielded excellent fits to a biexponential decay
model. As summarized in Table 2, the evaluated decay lifetimes
for both the S1 and T1 excited states of these complexes are
shorter than those for the corresponding Gd3+ complexes,
indicating efficient ISC and energy transfer to the correspond-
ing 4f* accepting states.
CONCLUSION
■
This work has focused on synthesizing bimetallic assemblies
composed of Ln3+ cations (Eu3+, Er3+, and Yb3+), Cs+ cations,
and triarylmethanide ligands. The ligands of choice were
tribenzoylmethanide and tris(4-methylbenzoyl)methanide. In
the case of Eu3+ and Er3+, structural assemblies were obtained
that are analogous to those in the previously reported study
when Na+, K+, and Rb+ were used as alkali-element cations.
However, in the present work these assemblies are the
repeating units of one-dimensional polymers. These units are
linked through the Cs+ cations binding to the O atoms of the
triketonate ligands. The only exception to this series was the
structure obtained by combining Yb3+, Cs+, and tris(4-
methylbenzoyl)methanide. In this case, the repeating unit of
the linear polymer was represented by mononuclear Yb3+
complexes bridged together via coordination of Cs+ cations.
The photophysical properties were investigated by means of
absorption, emission, and transient absorption spectroscopy. In
particular for Er3+ and Yb3+, the transient absorption data reveal
Using the Gd3+ complexes as model compounds, and
assuming the other radiative and nonradiative decay pathways
will be equivalent for the Ln3+ complexes, we are able to
G
DOI: 10.1021/acs.inorgchem.7b00928
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
BenFlect.48 Experimental uncertainties are estimated to be 15% for
quantum yields.
efficient and fast energy transfer from the triplet excited state of
the ligand after ISC. On the other hand, the transient
absorption data for Eu3+ seems to suggest an alternative energy
transfer pathway, occurring either directly via the ligand singlet
state or through the population of an intermediate LMCT state.
The emission profiles, excited state lifetimes, and quantum yield
data for the Eu3+ species confirm efficient sensitization and
relatively high quantum yields, with values in line those for
previously reported Eu3+ diketonate complexes. On the other
hand, the NIR emission of Er3+ and Yb3+ highlights rather
elongated excited state lifetimes with respect to analogous
diketonate species, similar to those previously observed for
assemblies of these elements, tribenzoylmethanide, and Na+,
K+, or Rb+. This work concludes the series of Ln3+/Ae+
assemblies and reinforces our previous results confirming that
these species constitute viable building blocks for the
preparation of efficient NIR emitters.
Excited-state decays (τ) were recorded on the same Edinburgh
FLSP980-stm spectrometer using a microsecond flashlamp. The
goodness of fit was assessed by minimizing the reduced χ2 function
and by visual inspection of the weighted residuals. Experimental
uncertainties are estimated to be 8% for lifetime determinations.
To record the luminescence spectra at 77 K, the samples were
placed in quartz tubes (2 mm diameter) and inserted in a special
quartz Dewar filled with liquid nitrogen. All of the solvents used in the
preparation of the solutions for the photophysical investigations were
of spectrometric grade.
Transient Absorption Measurements. The excitation source
utilized for femtosecond transient absorption measurements was an
amplified laser system (Spitfire ACE, Spectra Physics) delivering 800
nm laser pulses of 110 fs duration and a 1 kHz repetition rate.
Approximately 0.1 mJ of this output was attenuated and focused onto
a 15 mm CaF2 window mounted on an automated z-stage translation
mount to generate a white light continuum probe pulse from 350 to
650 nm. The remainder of the laser fundamental was coupled to an
OPA system (Topas Prime, Light Conversion) which was tuned to
deliver excitation pulses at 340 nm. The pump pulse polarization was
set to magic angle with respect to the probe, and ground and excited
state difference spectra (ΔOD) at various delay times were measured
using a femtosecond TA spectrometer (Helios, Ultrafast Systems)
incorporating two 512 pixel CCD sensors as the sample and reference
channel. Sample absorbances were ca. 0.4 over the 2 mm path length
cell used, and these were continuously stirred mechanically. No
detectable changes were observed in the UV−vis absorption spectrum
of the complex at the completion of transient absorption studies,
indicating no decomposition. The instrument response function (IRF)
had a full width at half-maximum (fwhm) of ca. 200 fs, measured
experimentally by a Gaussian fit to the scattered laser excitation profile,
and spectra were corrected for the chirp of the probe pulses. The
resulting time traces were analyzed globally using commercially
available software (Igor, Version 6.1.2.1, Wavemetrics). Experimental
uncertainties are estimated to be 10% for lifetime determinations.
Synthesis of Bis(4-methylbenzoyl)methane (mdbmH). The
mdbmH precursor was synthesized following a slightly modified
procedure.49 Ethyl 4-methylbenzoate (500 mg, 3 mmol) and 4-
acetyltoluene (400 mg, 3 mmol) were combined in 40 mL of THF. To
this solution, a suspension of NaH (60% in mineral oil, 360 mg, 9.0
mmol) in 40 mL THF was added dropwise at 0 °C. After 1 h, the
combined mixture was heated to 40 °C for 16 h under a nitrogen
atmosphere. The solvent was then removed under reduced pressure,
and water (20 mL) was added to the residual solid paste. The pH was
adjusted approximately to neutral by addition of HCl solution (1 M).
The aqueous phase was then extracted with ethyl acetate (3 × 15 mL),
and the combined organic phase was dried over MgSO4. After
filtration, the crude product was obtained by removal of the solvent
under reduced pressure and the target compound was isolated
following purification via recrystallization in ethanol as a yellow solid.
Yield: 80%. The spectroscopic data match those previously reported.49
Synthesis of Tris(4-methylbenzoyl)methane (mtbmH). 4-
Methylbenzoic acid (625 mg, 4.8 mmol) was added to thionyl chloride
(5 mL) and heated at reflux for 2 h. After this time, the solvent was
removed under reduced pressure and the remaining solid 4-
methylbenzoyl chloride was immediately added to diethyl ether (20
mL). NaH (60% in mineral oil, 144 mg, 3.6 mmol) and mdbmH (300
mg, 1.2 mmol) were combined in 20 mL of diethyl ether, and the
suspension was maintained at 0 °C. To this suspension was added a
solution of 4-methylbenzoyl chloride in diethyl ether dropwise. After
the addition, the mixture was stirred under a nitrogen atmosphere at
40 °C for 16 h. The formed precipitate was filtered and washed with a
HCl solution (1 M). The solid was then dried under reduced pressure
for several hours and afforded the target compound as a white solid.
Yield: 60%. Mp: 233−234 °C. Anal. Calcd for C25H22O3: C, 80.67; H,
6.01. Found: C, 80.61; H, 5.93. IR (ATR): ν 2920 w, 1685 s, 1669 s,
1605 s, 1574 w, 1509 w, 1446 w, 1406 w, 1376 w, 1316 m, 1284 s,
1260 m, 1218 m, 1192 m, 1181 s, 1123 w, 1020 m, 1011 m, 957 w, 906
EXPERIMENTAL SECTION
■
General Procedures. All reagents and solvents were purchased
from chemical suppliers and used as received without further
purification. The ligand tribenzoylmethane (tbmH) was prepared as
previously reported.31 Hydrated LnCl3 (Ln = Eu3+, Er3+, Yb3+) was
prepared by the reaction of Ln2O3 with hydrochloric acid (5 M),
followed by evaporation of the solvent under reduced pressure.
Infrared spectra (IR) were recorded on solid-state samples using an
attenuated total reflectance PerkinElmer Spectrum 100 FT-IR
instrument. IR spectra were recorded from 4000 to 650 cm−1; the
intensities of the IR bands are reported as strong (s), medium (m), or
weak (w), with broad (br) bands also specified. Melting points were
determined using a BI Barnsted Electrothermal 9100 apparatus.
Elemental analyses were obtained at Curtin University, Bentley,
Australia. Nuclear magnetic resonance (NMR) spectra were recorded
1
using a Bruker Avance 400 spectrometer (400.1 MHz for H; 100
MHz for 13C) at 300 K. The data were acquired and processed by the
Bruker TopSpin 3.1 software. All of the NMR spectra were calibrated
to residual solvent signals.
Selected Equations. The values of the radiative lifetime (τR) and
intrinsic quantum yield (ΦLnLn), can be calculated with the equations37
Itot
IMD
1
τR
= 14.65 s−1 × n3 ×
(1)
(2)
τ
τR
Ln
Ln
obs
Φ
=
In eq 1, the refractive index (n) of the solvent is used (assumed value
of 1.5 in the solid state), The value 14.65 s−1 is the spontaneous
7
5
emission probability of the F1 ← D0 transition reported previously.
Itot is the total integration of the Eu3+ emission spectrum, and IMD is
the integration of the 7F1 ← 5D0 transition. The sensitization efficiency
(ηsens) can be determined using eq 3:
ΦLLn
Φ
η
=
sens
Ln
Ln
(3)
Photophysical Measurements. Absorption spectra were re-
corded at room temperature using a PerkinElmer Lambda 35 UV/vis
spectrometer. Uncorrected steady-state emission and excitation spectra
were recorded using an Edinburgh FLSP980-stm spectrometer
equipped with a 450 W xenon arc lamp, double excitation and
emission monochromators, a Peltier cooled Hamamatsu R928P
photomultiplier (185−850 nm), and a Hamamatsu R5509-42
photomultiplier for detection of NIR radiation (800−1400 nm).
Emission and excitation spectra were corrected for source intensity
(lamp and grating) and emission spectral response (detector and
grating) by a calibration curve supplied with the instrument. Quantum
yields were measured with the use of an integrating sphere coated with
H
DOI: 10.1021/acs.inorgchem.7b00928
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
1
w, 859 s, 841 w, 815 s, 783 w, 711 m cm−1. H NMR (400 MHz,
DMSO-d6): δ 7.95 (s, 1H, αCH), 7.89 (d, J = 8.0 Hz, 6H, Hortho), 7.35
(d, J = 8.0 Hz, 6H, Hmeta), 2.38 (s, 9H, CH3) ppm. 13C NMR(101
MHz, DMSO-d6) δ 193.3 (CO), 144.9 (αCH), 133.3 (C1), 129.7
(Cortho), 128.9 (Cmeta), 65.1 (Cpara), 21.4 (CH3) ppm.
indices based on 20172 reflections with I > 2σ(I) (refinement on F2),
|Δρ|max = 1.3(1) e Å−3, 944 parameters, 6 restraints.
{[Er(Cs)(tbm)4]2}n: empirical formula C88H60O12CsEr, C2H6O; MW
= 1655.59, colorless plate, 0.30 × 0.26 × 0.10 mm3, triclinic, space
group P1, a = 14.6999(2) Å, b = 16.6792(3) Å, c = 17.5946(3) Å, α =
̅
75.643(2)°, β = 76.758(2)°, γ = 83.394(1)°, V = 4060.28(11) Å3, Z =
2, Dc = 1.354 g/cm3, μ = 1.536 mm−1, F000 = 1666, Mo Kα radiation, λ
= 0.71073 Å, T = 100(2) K, 2θmax = 69.2°, 108898 reflections
collected, 32735 unique reflections (Rint = 0.0359), final GOF = 1.004,
R1 = 0.0415, wR2 = 0.1026, R indices based on 26538 reflections with
I > 2σ(I) (refinement on F2), |Δρ|max = 1.9(1) e Å−3, 946 parameters,
24 restraints.
General Procedure for the Synthesis of Lanthanoid
Assemblies. CsOH (4 equiv) was added to a mixture containing
mtbmH or tbmH (4 equiv) and hydrated LnCl3 (ca. 20 mg) in
ethanol (10 mL). The mixture was heated at reflux for 30 min and
filtrered over a glass frit while still hot. The filtered solution was then
left undisturbed at ambient temperature, and slow evaporation of the
solvent over several days afforded crystals suitable for X-ray diffraction.
{[Eu(Cs)(tbm)4]2}n. Mp 271−272 °C. Anal. Calcd for
C88H60CsO12Eu: C, 66.30; H, 3.79. Found: C, 65.93; H, 3.31. IR
(ATR): ν 3057 w, 1646 w, 1584 m, 1545 s, 1446 m, 1368 s, 1273 m,
1153 m, 1073 w, 1027 w, 1013 w, 924 w, 896 s, 823 m, 780 m, 744 m,
693 s, 666 m cm−1.
{[Er(Cs)(tbm)4]2}n. Mp 260−261 °C. Anal. Calcd for
C88H60CsO12Er·1.6H2O: C, 64.51; H, 3.89. Found: C, 64.00; H,
3.31. IR (ATR): ν 3056 w, 1646 w, 1585 m, 1548 s, 1446 m, 1371 s,
1275 m, 1153 m, 1073 w, 1027 w, 1013 w, 924 w, 896 s, 823 m, 780 m,
743 m, 693 s, 667 m cm−1.
{[Yb(Cs)(tbm)4]2}n: empirical formula C88H60CsO12Yb, C2H6O;
MW = 1661.37, colorless plate, 0.29 × 0.17 × 0.06 mm3, triclinic,
space group P1, a = 14.7042(3) Å, b = 16.6321(3) Å, c = 17.6009(4)
̅
Å, α = 75.677(2)°, β = 76.631(2)°, γ = 83.400(2)°, V = 4050.07(14)
Å3, Z = 2, Dc = 1.362 g/cm3, μ = 1.658 mm−1, F000 = 1670, Mo Kα
radiation, λ = 0.71073 Å, T = 100(2) K, 2θmax = 64.6°, 84523
reflections collected, 26691 unique reflections (Rint = 0.0437), final
GOF = 1.010, R1 = 0.0426, wR2 = 0.1041, R indices based on 21048
reflections with I > 2σ(I) (refinement on F2), |Δρ|max = 1.8(1) e Å−3,
948 parameters, 12 restraints.
{[Eu(Cs)(mtbm)4]2}n: empirical formula C100H84CsEuO12; MW =
{[Yb(Cs)(tbm)4]2}n. Mp 252−253 °C. Anal. Calcd for
C88H60CsO12Er·0.3H2O: C, 65.18; H, 3.37. Found: C, 64.70; H,
3.36. IR (ATR): ν 3056 w, 3026 w, 1646 w, 1585 m, 1550 s, 1446 m,
1372 s, 1313 m, 1274 m, 1177 w, 1154 m, 1103 w, 1073 w, 1027 w,
1013 w, 1000 w, 973 w, 924 w, 896 s, 823 m, 811 w, 780 m, 743 m,
693 s, 667 m cm−1.
1762.54, colorless needle, 0.13 × 0.05 × 0.03 mm3, triclinic, space
group P1, a = 14.8674(5) Å, b = 16.1731(5) Å, c = 18.0171(6) Å, α =
̅
84.406(2)°, β = 74.987(3)°, γ = 87.816(2)°, V = 4164.1(2) Å3, Z = 2,
Dc = 1.406 g/cm3, μ = 9.255 mm−1. F000 = 1796, Cu Kα radiation, λ =
1.54178 Å, T = 100(2)K, 2θmax = 134.9°, 40590 reflections collected,
14792 unique reflections (Rint = 0.0490), final GOF = 1.001, R1 =
0.0370, wR2 = 0.0833, R indices based on 12187 reflections with I >
2σ(I) (refinement on F2), |Δρ|max = 1.05(9) e Å−3, 1027 parameters, 0
restraints.
{[Eu(Cs)(mtbm)4]2}n. Mp 291−290 °C. Anal. Calcd for
C100H84O12EuCs·2H2O: C, 66.78; H, 4.93. Found: C, 66.36; H,
4.49. IR (ATR): ν 3058 w, 3024 w, 1642 m, 1583 s, 1537 s, 1448 m,
1428 m, 1366 s, 1310 m, 1292 m, 1275 m, 1176 w, 1154 m, 1101 w,
1072 w, 1027 w, 1013 w, 1000 w, 968 w, 920 w, 895 m, 863 w, 844 w,
823 w, 810 w, 780 w, 743 m, 729 w, 721 w, 692 m, 667 w cm−1.
{[Er(Cs)(mtbm)4]2}n. Mp 298−299 °C. Anal. Calcd for
C100H84CsO12Er: C, 66.54; H, 4.86. Found: C, 66.43; H, 4.46. IR
(ATR): ν 3057 w, 3027 w, 1646 w,1595 m, 1585 m, 1549 s, 1447 m,
1373 s, 1312 m, 1276 m, 1219 w, 1178 w, 1154 m, 1073 w, 1000 w,
972 w, 924 w, 896 m, 847 w, 823 w, 781 w, 743 m, 692 s, 668 m cm−1.
[Yb(Cs)(mtbm)4]n. Mp 278−279 °C. Anal. Calcd for C100H84O12Yb·
4.5H2O: C, 64.41; H, 5.03. Found: C, 64.09; H, 4.53. IR (ATR): ν
3023 w, 2920 w, 1635 m, 1603 m, 1577 m, 1538 s, 1452 w, 1407 m,
1360 s, 1316 m, 1308 m, 1281 m, 1183 m, 1154 m, 1113 w, 1033 w,
1013 w, 961 w, 900 s, 850 m, 824 m, 781 s, 762 m, 734 w, 723 m, 690
w cm−1.
{[Er(Cs)(mtbm)4]2}n: empirical formula C100H84CsErO12; MW =
1777.84, colorless needle, 0.28 × 0.12 × 0.05 mm3, triclinic, space
group P1, a = 14.8243(3) Å, b = 16.1860(4) Å, c = 17.9760(4) Å, α =
̅
83.768(2)°, β = 75.176(2)°, γ = 87.485(2)°, V = 4144.49(17) Å3, Z =
2, Dc = 1.425 g/cm3, μ = 1.509 mm−1, F000 = 1806, Mo Kα radiation, λ
= 0.71073 Å, T = 100(2) K, 2θmax = 64.4°, 92120 reflections collected,
27193 unique reflections (Rint = 0.0591), final GOF = 1.003, R1 =
0.0455, wR2 = 0.0998, R indices based on 20682 reflections with I >
2σ(I) (refinement on F2), |Δρ|max = 2.6(1) e Å−3, 1027 parameters, 6
restraints.
[Yb(Cs)(mtbm)4]n: empirical formula C102H90CsO13Yb; MW =
1829.68, colorless prism, 0.23 × 0.15 × 0.13 mm3, triclinic, space
group P1, a = 11.5606(2) Å, b = 16.2195(3) Å, c = 26.5428(5) Å, α =
̅
81.060(2)°, β = 83.329(2)°, γ = 81.209(2)°, V = 4836.93(15) Å3, Z =
2, Dc = 1.256 g/cm3, μ = 1.395 mm−1, F000 = 1862, Mo Kα radiation, λ
= 0.71073 Å, T = 100(2) K, 2θmax = 52.7°, 81814 reflections collected,
19778 unique reflections (Rint = 0.0415), final GOF = 1.005, R1 =
0.0336, wR2 = 0.0810, R indices based on 17759 reflections with I >
2σ(I) (refinement on F2), |Δρ|max = 1.26(8) e Å−3, 1066 parameters, 6
restraints.
X-ray Crystallography. Crystallographic data for the structures
were collected at 100(2) K on an Oxford Diffraction Gemini or
Xcalibur diffractometer fitted with Mo Kα or Cu Kα radiation.
Following absorption corrections and solution by direct methods, the
structures were refined against F2 with full-matrix least squares using
the program SHELX-2014.50
Unless stated below, anisotropic displacement parameters were
employed for the non-hydrogen atoms. All hydrogen atoms were
added at calculated positions and refined by use of a riding model with
isotropic displacement parameters based on those of the parent atom.
CCDC-1539972 ([Eu(Cs)(tbm)4]n), CCDC-1539973 ([Er(Cs)-
(tbm)4]n). CCDC-1539974 ([Yb(Cs)(tbm)4]n), CCDC-1539975
([Eu(Cs)(mtbm)4]n), CCDC-1539976 ([Er(Cs)(mtbm)4]n),
CCDC-1539977 ([Yb(Cs)(mtbm)4]n), CCDC-1539978 ([Eu(Cs)-
(EtOH)2(mdbm)4]n), and CCDC-1539979 ([Cs(tbm)]n) contain
supplementary crystallographic data.
[Eu(Cs)(EtOH)2(mdbm)4]n: empirical formula C72H72CsEuO10; MW
= 1382.16, colorless plate, 0.18 × 0.15 × 0.06 mm3, monoclinic, space
group C2/c, a = 29.9314(14) Å, b = 8.4707(3) Å, c = 26.1484(11) Å, β
= 105.325(5)°, V = 6393.9(5) Å3, Z = 4, Dc = 1.436 g/cm3, μ = 11.859
mm−1, F000 = 2808, Cu Kα radiation, λ = 1.54178 Å, T = 100(2) K,
2θmax = 134.3°, 15957 reflections collected, 5670 unique reflections
(Rint = 0.0398), final GOF = 1.022, R1 = 0.0650, wR2 = 0.1834, R
indices based on 4887 reflections with I > 2σ(I) (refinement on F2),
|Δρ|max = 2.8(2) e Å−3, 397 parameters, 4 restraints.
[Cs(tbm)]n: Empirical formula C22H15CsO3; MW = 460.25,
colorless prism, 0.63 × 0.48 × 0.20 mm3, monoclinic, space group
P21/n, a = 7.0968(1) Å, b = 15.2205(1) Å, c = 16.7822(1) Å, β =
99.828(1)°, V = 1786.16(3) Å3, Z = 4, Dc = 1.712 g/cm3, μ = 2.092
mm−1, F000 = 904, Mo Kα radiation, λ = 0.71073 Å, T = 100(2) K,
2θmax = 77.9°, 68792 reflections collected, 10066 unique reflections
(Rint = 0.0234), final GOF = 1.103, R1 = 0.0180, wR2 = 0.0449, R
indices based on 9419 reflections with I > 2σ(I) (refinement on F2),
|Δρ|max = 0.84(8) e Å−3, 235 parameters, 0 restraints.
X-ray Data Refinement. {[Eu(Cs)(tbm)4]2}n: empirical formula
C88H60CsEuO12, C2H6O; MW = 1640.29, colorless plate, 0.32 × 0.28
× 0.02 mm3, triclinic, space group P1, a = 14.6063(4) Å, b =
̅
16.8300(4) Å, c = 17.6843(4) Å, α = 74.721(2)°, β = 77.698(2)°, γ =
83.202(2)°, V = 4088.34(17) Å3, Z = 2, Dc = 1.332 g/cm3, μ = 1.266
mm−1, F000 = 1656, Mo Kα radiation, λ = 0.71073 Å, T = 100(2) K,
2θmax = 64.5°, 90077 reflections collected, 26973 unique reflections
(Rint = 0.0599), final GOF = 1.005, R1 = 0.0485, wR2 = 0.1002, R
I
DOI: 10.1021/acs.inorgchem.7b00928
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Inorganic Chemistry
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ASSOCIATED CONTENT
* Supporting Information
■
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.7b00928.
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ing decay kinetic plots and decay associated difference
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Sensitised Lanthanide Luminescence: Investigation of the Nature of
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Accession Codes
CCDC 1539972−1539979 contain the supplementary crystal-
lographic data for this paper. These data can be obtained free of
charge via www.ccdc.cam.ac.uk/data_request/cif, or by email-
ing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
(13) Latva, M.; Takalo, H.; Mukkala, V. M.; Matachescu, C.;
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AUTHOR INFORMATION
Corresponding Authors
■
(14) Eliseeva, S.; Bunzli, J.-C. G. Lanthanide Luminescence for
̈
Functional Materials and Bio-Sciences. Chem. Soc. Rev. 2010, 39 (1),
189−227.
*E-mail for E.Z.-C.: eli.zysman-colman@st-andrews.ac.uk.
*E-mail for E.G.M.: egmoore@uq.edu.au.
*E-mail for M.I.O.: m.ogden@curtin.edu.au.
*E-mail for M.M.: m.massi@curtin.edu.au.
(15) Biju, S.; Gopakumar, N.; Bunzli, J.-C. G.; Scopelliti, R.; Kim, H.
̈
K.; Reddy, M. L. P. Brilliant Photoluminescence and Tribolumines-
cence From Ternary Complexes of DyIII and TbIII with 3-Phenyl-4-
Propanoyl-5-Isoxazolonate and a Bidentate Phosphine Oxide
Coligand. Inorg. Chem. 2013, 52 (15), 8750−8758.
ORCID
Massimiliano Massi: 0000-0001-6949-4019
(16) Horrocks, W. D.; Bolender, J. P.; Smith, W. D.; Supkowski, R.
M. Photosensitized Near Infrared Luminescence of Ytterbium (III) in
Proteins and Complexes Occurs via an Internal Redox Process. J. Am.
Chem. Soc. 1997, 119 (25), 5972−5973.
(17) De Bettencourt-Dias, A.; Barber, P. S.; Bauer, S. A Water-
Soluble Pybox Derivative and Its Highly Luminescent Lanthanide Ion
Complexes. J. Am. Chem. Soc. 2012, 134 (16), 6987−6994.
(18) Glover, P. B.; Bassett, A. P.; Nockemann, P.; Kariuki, B. M.; Van
Deun, R.; Pikramenou, Z. Fully Fluorinated Imidodiphosphinate Shells
for Visible- and NIR-Emitting Lanthanides: Hitherto Unexpected
Effects of Sensitizer Fluorination on Lanthanide Emission Properties.
Chem. - Eur. J. 2007, 13 (22), 6308−6320.
(19) Andreiadis, E. S.; Gauthier, N.; Imbert, D.; Demadrille, R.;
́
Pecaut, J.; Mazzanti, M. Lanthanide Complexes Based on β-
Diketonates and a Tetradentate Chromophore Highly Luminescent
as Powders and in Polymers. Inorg. Chem. 2013, 52 (24), 14382−
14390.
Present Address
¶Laboratory of Micro and Submicro Enabling Technologies of
the Emilia-Romagna Region S.c.r.l. (MIST E-R S.c.r.l.) via
GobeD 101, Bologna 40129, Italy
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was supported by the Australian Research Council
and a Royal Society International Exchanges Grant. E.Z.-C.
thanks the EPSRC (EP/M02105X/1) for support. L.A.G. and
B.L.R. thank Curtin University for a postgraduate scholarship.
The authors acknowledge access to the facilities at the Centre
for Microscopy, Characterisation and Analysis, University of
Western Australia.
(20) Andrews, P. C.; Gee, W. J.; Junk, P. C.; Massi, M. Variation of
Structural Motifs in Lanthanoid Hydroxo Clusters by Ligand
Modification. New J. Chem. 2013, 37 (1), 35−48.
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