Enhanced near-infrared luminescence in Ln2Cd2 (Ln = Nd, Yb) heterotetranuclear complexes

Article abstract of DOI:10.1039/d0ce00341g

The syntheses of highly efficient NIR-emitting lanthanide complexes are challenging due to the lack of an effective strategy that can both simultaneously suppress the nonradiative transition caused by high energy oscillators and enhance the sensitization

Full text of DOI:10.1039/d0ce00341g

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DOI: 10.1039/D0CE00341G
Enhanced near-infrared luminescence in Ln2Cd2 (Ln = Nd, Yb)
heterotetranuclear complexes
Yue Qi, Ou Sun, Yanyan Zhou, Yuan Yao, Zhenyu Cheng, Ting Gao* and Hongfeng Li*
In combination of the rigid structure and synergistic interactions of two ligands on energy transfer,
the heterotetranuclear Cd‒Ln complexes show excellent NIR luminescence properties with the
QYs reaching 0.34% for Nd3+ and 2.13% for Yb3+ in CH3CN.

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DOI: 10.1039/D0CE00341G
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Enhanced near-infrared luminescence in Ln2Cd2 (Ln = Nd,
Yb) heterotetranuclear complexes
Yue Qi, Ou Sun, Yanyan Zhou, Yuan Yao, Zhenyu Cheng, Ting Gao* and Hongfeng Li*
Received 00th January 20xx,
Accepted 00th January 20xx
The syntheses of highly efficient NIR-emitting lanthanide complexes are challenging due to the lack of the effective
strategy that can both simultaneously suppress the nonradiative transition caused by high energy oscillators and enhance
DOI: 10.1039/x0xx00000x
the sensitization efficiency. Herein,
a ditopic rigid Schiff base, N,N'-bis(2-oxy-3-methoxybenzylidene)-1,4-
www.rsc.org/
phenylenediamine (H2L) with p-phenylenediamine as spacer was designed, which self-assembled with the Cd2+ and
Ln3+ ions and TTA (2-thenoyltrifluoroacetone) forming the tetranuclear Cd‒Ln complexes,
Ln2Cd2L2(TTA)4(OAc)2(CH3OH)2 (Ln = Nd (1), Yb(2) and La (3)). X-ray crystallographic analysis revealed that
complex 1 adopted a double-stranded tetranuclear structure, in which the two heteronuclear Cd‒Nd units were linked
together by phenylene, and each Nd(III) ion was nine-coordinated by four oxygen atoms from two L, four oxygen atoms
from TTA and one oxygen atom from an acetate anion. The photophysical studies demonstrated that the helicates
showed the excellent NIR luminescence with the luminescence quantum yields reaching 0.34% for Nd3+ and 2.13% for
Yb3+ in CH3CN. The high NIR luminescence quantum yields should profit from the rigid structure of the complexes and
the synergistic interactions between two ligands. Additionally, the large π-conjugating system of H2L makes the
absorption edge of the complexes extend to 450 nm blue light region, which make the complexes be suitable for
biomedical applications.
use deuterium (D) or F atoms to replace hydrogen (H) atoms in
the first coordination spheres.6 For instance, a highest overall
quantum yield of 63% for ytterbium complex was achieved
based on a perfluorinated porphyrin and a partially deuterated
Kläui's ligand.7 Although it is an effective strategy, the
difficulties on deuterated and perfluorinated of ligands limit
their practical applications. For non-heavy atom substituted and
non-deuterated systems, the NIR luminescence quantum yields
were modest, typically in the range of 10‒3‒10‒2.8
Introduction
Near-infrared (NIR) emitting lanthanide complexes have been
attracting extensive research interest due to their sharp emission
bandwidths and longer excited-state lifetimes (τ on
microsecond time scale), which enable them a broad range of
practical applications such as bioanalysis,1 medical imaging
and therapy,2 OLED devices,3 and telecommunications.4 The
abundant ground/excited state energy levels of Ln3+ ions make
their emissions cover a broad spectral region of 800‒1700 nm.
In this field, the development of highly efficient NIR-emitting
materials is one of the main challenge.
There are several reasons for the typically lower quantum
yield in NIR-emitting lanthanide complexes, in which the large
nonradiative transition is one of the most critical factors.
According to the energy gap law,5 the nonradiative decay rate
constant (knr) is inversely related to the energy gap between the
donor energy state and acceptor energy state. Thus, the lower
NIR-emissive energy is prone to quenching by multiphoton de-
excitation caused by the coupling of high energy oscillators like
O‒H, N‒H and C‒H that present in the organic ligands or
solvents. The general strategy to address this issue involves the
Scheme 1 Synthetic routes of H2L and complexes.
a.Key Laboratory of Functional Inorganic Material Chemistry, Ministry of
Education, P. R. China; School of Chemistry and Materials Science, Heilongjiang
University, Harbin 150080, P. R. China. E-mail: lihongfeng@hlju.edu.cn;
gaotingmail@sina.cn
b.†Electronic Supplementary Information (ESI) available: [details of any
supplementary information available should be included here]. CCDC 1977217.
For ESI and crystallographic data in CIF or other electronic format see
DOI:10.1039/x0xx00000x
The development of multinuclear assemblies with rigid
structures are the other strategy to depress the nonradiative
transition. As previously reported by us, most of the oscillator
strengths (f) in dinuclear helicate are lower than that in
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1
mononuclear analogue, which was suggested to play an
important role for enhancing Yb3+ ions luminescence.9 In
previous works,10 many hetero-dinuclear/multinuclear
assemblies have been extensively reported besides a few
homonuclear complexes.11 Schiff bases were the most widely
used chelating agents for constructing multinuclear
architectures. However, the drawback was that the Ln3+ centers
were generally saturated by the counterion anions from
lanthanide salts and solvent molecules,12 which significantly
quenched the luminescence from the Ln3+ ions.
solution. Because of the poor resolution of the ViHew ANrtMicleROnflioner
3+
complexes 1 and 2, the corresponding LaDOcI:o1m0.1p0l3e9x/Dw0aCsEc0h0o34se1Gn
as substitute for 1H NMR experiment. As shown in Figure 1b,
the complex 2 shows a single set of broadened but
distinguishing signals. However, in comparison with the free
ligands L, most of the resonance peaks undergo high-field shifts.
Although there are four ligand in one complex, the single set of
signals indicate the complex matching the C2 symmetry of the
structure.
Energy transfer efficiency is another factor to affect the
luminescence quantum yields of lanthanide complexes, which
is generally determined by the energy level match between the
triplet state of chromophores and Ln3+ ions’ exciting state.
Moreover, the synergistic interactions between different
ligands in multi-chromophores sensitized system were said to
play an important role in shaping the emission processes of the
center ion.13 On the basis of above points, herein a ditopic rigid
Schiff base (L) was designed by condensation of o-Vanillin
with p-phenylenediamine, which self-assembled with the Cd2+
and Ln3+ ions and TTA (2-thenoyltrifluoroacetone) forming the
rigid
tetranuclear
Cd‒Ln
complexes,
Ln2Cd2L2(TTA)4(OAc)2(CH3OH)2 (Ln = Nd (1) and Yb (2)).
The extended π-conjugation in L makes the absorption edge of
the complexes extend to visible light region, which
significantly decrease the excited state energy level of ligand,
and enhance the energy transfer efficiency. Additionally, the
visible light excitation is especially important for the NIR
emitting materials that are employed in biochemistry and cell
biology, since living tissues are generally damaged under UV
light irritation.14 In combination the inter-ligand synergistic
interactions with the rigid tetranuclear structure, the complexes
show the excellent NIR luminescence performance with the
quantum yields reaching 0.34% for 1 and 2.13% for 2.
Fig. 1 (a) ESI-TOF-MS of Yb2Cd2L2(TTA)4(OAc)2(CH3OH)2 with inset showing the
observed (Obs.) and simulated (Sim.) isotopic patterns. (b) 1H NMR (400 MHz)
spectra of free ligand L and La2Cd2L2(TTA)4(OAc)2(CH3OH)2.
Results and discussion
Synthesis and characterization of the ligand and complexes
X-ray crystal structure of Nd2Cd2L2(TTA)4(OAc)2(CH3OH)2
The synthetic routes and procedures for the ligand and its
corresponding complexes are outlined in Scheme 1. The ligand
was synthesized by simple one-step condensation reaction
To obtain
a
better structural insight into this
heterotetranuclear structure, X-ray-quality crystals of
Nd2Cd2L2(TTA)4(OAc)2(CH3OH)2 were obtained by slow
diffusion of methanol into the CH2Cl2 solution of the complex.
The result reveals that complex crystallize in triclinic space
group P-1 with four free CH2Cl2 solvents in the unit cell. As
shown in Fig. 2, the complex adopts a double-stranded
tetranuclear structure, in which the two heteronuclear Cd‒Nd
units are linked together by two phenylenes, and each Nd3+ ion
is nine-coordinated by four oxygen atoms from two L, four
oxygen atoms from TTA and one oxygen atom from an acetate
anion and forming a capped square antiprism geometry (Figure
2b). Notably, the strong intermolecular π‒π interaction can be
observed between the two phenylenes with the distance of
about 3.356 Å, which is proposed to have positive effect on
stabilizing this structure. In one Nd‒Cd unit, the distance
between two metal centers is measured to be 3.616 Å, wherein
three oxygen atoms from two hydroxyl of L and one from
1
between p-phenylenediamine and O-vanillin in methanol. H
NMR spectrum of the resulting orange needles displayed the
formation of H2L and the high purity (Figure S1). The
heterotetranuclear Ln2Cd2L2(TTA)4(OAc)2(CH3OH)2 (Ln =
Nd(1) and Yb(2)) were obtained by reaction of the ligand H2L
with Cd2+ and Ln3+ ions and TTA (2-thenoyltrifluoroacetone)
in a 2:2:2:4 ratio in MeOH at room temperature for 24 h.
High-resolution electrospray ionization mass spectrometry
(ESI-TOF-MS) analysis confirmed the formation of
heterotetranuclear
structure
with
a
formula
of
Ln2Cd2L2(TTA)4(OAc)2(CH3OH)2 (Figures 1a and S2). Fig. 1a
displays the molecular ion peak of complex 2, and the isotopic
patterns agree well with the simulated isotopic distributions
(inset). 1H NMR characterization also supported the formations
of the heterotetranuclear structures and their integrities in
2 | J. Name., 2012, 00, 1−3
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Fig. 3 UV‒Vis absorption spectra of H2L, TTA, complexes 1 and 2 in CH3CN (c =
acetate are employed as bridging atoms. The Cd2+ ion is six-
coordinated by two imine nitrogen atoms, two phenol oxygen
atoms from two different L ligands, one oxygen atom from an
acetate anion and one methanol oxygen atom, forming an
octahedron geometry (Figure 2c). The Nd‒O distances are in
the range of 2.422‒2.681 Å, the Cd–O and Cd–N bond
distances involving the L are 2.276 and 2.279 Å, respectively.
Additionally, the intramolecular C‒H···F interactions between
the F atoms of TTA and H atoms of L are observed at terminal
of the complex (Figure S3). We suggest that these weak
interactions could further stabilize the structure and reduce the
vibration of skeleton. Additionally, the complex 2 show the
similar powder X-ray diffraction (PXRD) pattern of complex 1
that simulating from the single-crystal X-ray data (Fig. S4†).
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2.0 × 10−5 M for TTA; c =1.0 × 10−5 M for H2L, 1 and 2).
DOI: 10.1039/D0CE00341G
The NIR-luminescent properties of the complexes 1 and 2 are
investigated in CH3CN at room temperature. Upon excited with
the maxima excitation band at 380 nm, the complex 1 show
three emitting bands at 873, 1057, and 1330 nm, which are
4
4
attributed to F3/2→4I9/2
,
4F3/2→4I11/2
,
and F3/2→4I13/2
transitions, respectively. In complex 2, only an emission band
at 975 nm is observed, which is the characteristic transition of
2F5/2 → 2F7/2. The excitation spectra of the complexes were
recorded by monitoring the maximum emitting bands at 975 nm
for 2 and 1057 nm for 1 complexes, which covers the spectral
region of 250–450 nm with the maxima at 380 nm (Fig. 3). This
spectral range well match the corresponding absorption region,
confirming that the energy transfer takes place from the ligands
to the Ln3+ ions. In addition to the steady-state emission, the
NIR emission lifetimes of two complexes were determined by
2
monitoring the emission decay curves within the F5/2–2F7/2
4
4
transition at 975 nm for 2 and F3/2 → I11/2 transition at 1057
nm for 1. Typical decay profiles of 1 and 2 are shown in Figures
S4 and S5. The decay curve of complex 1 can be fitted by
double exponential functions with the observed lifetimes of 2.6
and 13.5 μs. While the decay curve of complex 2 was
reproduced well by single exponential function with the
lifetime found to be 16.0 μs. To quantify the capacity of the two
ligands to sensitize the NIR-emitting lanthanides, the absolute
quantum yields were determined upon ligand excitation with
respect to Yb(TTA)3(H2O)2 as a reference(Φ = 0.35% in
toluene).15 The absolute quantum yields were calculated to be
0.34% for 1 and 2.13% for 2, respectively. These values are
obviously higher than most of the Nd3+ and Yb3+ complexes
with H-containing ligand and the complexes assembled with
Schiff bases and/or diketonate ligands.16 The absolute
luminescence quantum yields are listed in Table S1.
Fig.
2 (a) The crystal structure of Nd2Cd2L2(TTA)4(OAc)2(CH3OH)2; (b)
perspective view of the coordination polyhedron for the Nd(III) ions in 1; (c)
perspective view of the coordination polyhedron for the Cd(II)
Photophysical properties of the complexes
The UV‒Vis absorption spectra of ligands, H2L and TTA and
the complexes 1 and 2 are presented in Fig. 3. In CH3CN, H2L
shows two main absorption bands at 278 and 349 nm, which are
assigned to the singlet–singlet π–π* electronic transition of
ligand. In TTA, two π–π* transitions present at the relatively
high energy absorption bands at 265 and 340 nm. In two
complexes, the obvious spectral red-shifts are observed, where
three broad absorbance bands locate at 233, 276 and 345 nm,
respectively. Notably, the lowest energy absorbance extend to
the visible light region with the edge at 450 nm. The red-shift
should arise from the formation of rigid structure, which
enhance the conjugation of the system to some extent.
Fig. 3 Excitation (left) and emission (right) spectra of complexes 1 (Nd) and 2
(Yb) in CH3CN (λex = 380 nm, 1.0 × 10‒5 M).
In luminescent lanthanide complexes, the ligands act as
“antenna” to absorb excited light and then transfer the energy
to the excited state of Ln3+ ion, and turn on the emission of
metal center. In this process, the intrinsic quantum yield (ΦLn)
of Ln3+ ion and the efficiency of the energy transfer (ηET) are
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the two essential factors to determine the total luminescence
quantum yield of the complexes. It can be described by eqn (1)
extremely decrease the molecular thermal vibratVioienw,AratilctlheoOunlginhe
DOI: 10.1039/D0CE00341G
the quantitative data cannot be offered.
훷푡표푡 = 휂퐸푇훷퐿푛 (1)
To get large total luminescence quantum yield, Φtot, the
intrinsic quantum yield and efficiency of the energy transfer
should be improved.
The intrinsic luminescence quantum yields of complex 2
could be estimated using the equation 2, where kr and knr
represent radiative and non-radiative rate constants, while τobs
and τrad are the observed lifetimes and the radiative lifetime,
respectively. The radiative lifetime (τrad) can be calculated from
the absorption spectrum of Yb3+ ion in complexes (Figure S6)
with a modified Einstein equation (eqn. 3):17
Fig. 5 Schematic energy level diagram and energy transfer processes. S1: first
excited singlet state and T1: first excited triplet state.
푘푟
휏표푏푠
훷퐿푛
=
=
(2)
푘푟 + 푘푛푟 휏푟푎푑
On the other hand, the energy transfer efficiency is another
important parameter to affect total emission efficiency, which
is estimated to be 41% based on eqn. 1. We suggest that the
high energy transfer efficiency should originates from the
synergistic interaction between TTA and L. In view of heavy
atom effect of lanthanide ions, the sensitization process of Ln3+
complexes generally involve the intersystem crossing from the
singlet state S1 to the triplet state T1, T1→ Ln3+ transfer, and
metal-centered emission.
8휋푐푛2푣2푚(2퐽 + 1)
푁퐴(2퐽’ + 1)
1
= 푘푟 = 2303 ×
휀(푣)푑푣 (3)
∫
휏푟푎푑
∫푣 ∙ 휀(푣)푑푣
푣푚
=
∫휀(푣)푑푣
Where, NA is Avogadro’s number, c is the speed of light in
centimeters per second, J and J' are the quantum numbers for
the ground and excited states, respectively.
∫(푣)푑푣
is the
To investigate the energy transfer processes between TTA,
L and excited state of Yb3+ ion, the singlet/triplet state energies
were firstly determined. The singlet and triplet energy levels
were estimated from the by referring to the lowest energy
absorbance edges and the high energy emission band of the
corresponding phosphorescence spectrum of the Gdcomplexes.
Because the lowest excited energy level of Gd3+ ion (6P7/2) is
too high to accept energy from ligands, the triplet state energy
level of ligand is not significantly affected by the Gd(III) ion.
As shown in Figure S7, the Gd3+ complex displayed a broad
emission bands in the range of 440–800 nm at 77 K. To avoid
possible emission from residual fluorescence of ligands, the
time-resolution experiments were performed (100 μs delay).
푣
integrated spectrum of the f‒f transition, 푚 is the barycenter of
the transition, and n = 1.3456 for CH3CN solution. On the basis
of these equations, the radiative lifetime (τrad) of complex 2 was
calculated to be 305 μs. In terms of the observed lifetimes (τobs
)
and the calculated radiative lifetimes (τrad), the intrinsic
quantum yields are calculated to be 5.52%. From the eqn (2), it
can be observed that the intrinsic quantum yield is the result of
radiative transition that competes with the nonradiative
transition processes. From the radiative lifetimes, and observed
lifetime, the radiative rate constant (kr) and non-radiative rate
constant are calculated to be 3277 s‒1and 5.9 × 104 s‒1,
respectively. Generally, the low geometrical symmetry of
coordinated atoms around the metal center could lead to large
radiative rate constants.18
3
The triplet state energy levels ππ* of L was calculated to be
17637 cm–1 by referring to the maxima emission wavelengths.
While the singlet state energy levels are calculated to be 22727
cm–1 for L. On the basis of the above experimental results, the
schematic energy level diagram and the energy transfer
processes were drawn as Fig. 5. In view of the existence of
gradient exited state energy gaps, there exist the energy
transfers between the singlet states and triplet states of L and
TTA besides the singly intra-ligand energy transfer. We suggest
that the inter-ligand energy transfer is favored to improve the
energy transfer efficiency from ligands to Ln3+ ions. For
The nonradiative transition is one of the most critical factors
to determine absolute quantum yield of NIR emission systems.
Because the lower radiation energy are prone to quenching by
multiphoton de-excitation caused by the coupling of high
energy oscillators like O‒H, N‒H and C‒H that present in the
organic ligands or solvents. Herein, the TTA is employed as the
second ligand, which effectively prevent the coordination of
solvent molecules. However, the excited state energy loss
arising from the skeleton vibration was rarely taken into
consideration in luminescent lanthanide complexes. As
previously reported by us,9 the rigid structures of the complexes
indeed played an important role to depress non-radiative
transition from skeleton vibration. From the crystal structure, it
could be observed that the rigid tetranuclear double-stranded
structure in combination with intramolecular interactions
between TTA and L well stabilize this structure, which could
3
2
instance, the lower energy gap between the ππ* and F5/2
,
10250 cm‒1 of Yb3+ ion is favored to increase the energy
transfer efficiency. In this case, the TTA has the lager energy
gap that that of L, which implies the energy transfer efficiency
would be less effective for TTA than that of in L. However, the
inter-ligand energy transfer would make TTA more effectively
transfer energy to Ln3+ ions due to the involving of L in this
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process. Thus, the synergistic interactions between TTA and L
The luminescence quantum yields of the Nd(III) and Yb(III)
View Article Online
should be responsible for this high energy transfer efficiency.
complexes were measured in CH3CN atDrOoIo:m10.1te0m39p/De0raCtEu0r0e3a4n1Gd
cited relative to a reference solution of [Yb(TTA)3(H2O)2] (Φ =
0.35%), and were calculated according to the well-known
equation:
Conclusions
In summary, we have successfully synthesized two
heterotetranuclear Cd‒Ln complexes, Ln2Cd2L2(TTA)4 (Ln =
Nd(1) and Yb(2)). X-ray crystallographic analysis confirms the
double-stranded tetranuclear structure. The designed rigid ditopic
ligand, L ligated four metal ion at the two terminal of the
structure, where the mechanical coupling of two Ln‒Cd units
through the rigid ligands in combine with inter-ligand interaction
well stabilized the complex structure and effectively suppress the
non-radiative transition originating from the skeleton vibration.
The photophysical studies demonstrate that the helicates show
excellent NIR luminescence of Nd3+ and Yb3+ with the
luminescence quantum yields reach to 0.34% and 2.13%. On the
other hand, the synergistic interactions between two ligands play
an important role to improve the energy transfer efficiency from
ligands to metal centers. Additionally, large π-conjugating
system of L make the absorption edge of the complexes extend
to 450 nm blue light range which make their suitable for
biomedical applications.
n2퐴푟푒푓
퐼
∅
∅
풓풆풇
=
풐풗풆풓풂풍풍
푛푟푒푓2퐴퐼푟푒푓
Where n, A, and I denote the refractive index of solvent, and
the absorbance at the excitation wavelength, and the area of the
emission spectrum respectively. Φref represents the quantum
yield of the standard [Yb(TTA)3(H2O)2] solution. The subscript
ref denotes the reference, and the absence of a subscript implies
an unknown sample.
Synthetic procedures
Synthesis of N,N'-bis(2-oxy-3-methoxybenzylidene)-1,4
phenylenediamine (H2L). To
a
solution of p-
phenylenediamine (1.0 g, 10.0 mmol) in methanol (40 ml) was
added 2-Hydroxy-3-methoxy-benzaldehyde (3.0 g, 20.0
mmol). The reaction system was stirred and refluxed under
reflux for 3 h to ensure the completion of the reaction. After
cooling to temperature, the red needle-like crystals were
obtained, which was then filtered and washed three times with
methanol, and dried to afford the product (1.10 g, 75%). Anal.
Calc. for C22H20N2O4 (376.14): C, 70.20; H, 5.36; N, 7.44.
Found: C, 70.12; H, 5.45; N, 7.32. 1H NMR (CDCl3 400 MHz)
δ 13.62 (s, 2H), 8.69 (s, 2H), 7.38 (s, 2H), 7.05 (dd, J = 7.6 Hz,
8.0 Hz, 2H), 6.92 (t, J = 7.6 Hz, 2H), 3.96(s, 6H). ESI-MS m/z
= 399.13 [M + Na]+.
Experimental
Materials and instruments
All operations were performed in an open atmosphere. The
H2L, TTA and all other reagents and chemicals involved in this
experiment were purchased commercially and used without
further purification if not otherwise stated.The details of
reagents and chemicals involved were shown in Table S3.
Elemental C, H and N analyses were performed using an
Elementar Vario EL cube analyzer. The UV‒Vis spectra in
CH3CN were recorded on a Perkin-Elmer Lambda 25
spectrometer. The 1H NMR spectra are recorded on a Bruker
Avance III 400 MHz spectrometer. IR spectra were obtained on
a Perkin-Elmer 60000 spectrophotometer by using KBr disks in
the range of 4000–450 cm−1. The fluorescence spectra of the
complexes were recorded using an Edinburgh FLS 1000
fluorescence spectrophotometer equipped with a red-sensitive
Synthesis of Ln2Cd2L2(TTA)4(OAc)2(CH3OH)2
H2L (3.76 g, 10 mmol), TTA (4.44 g, 20 mmol) and NEt3 (4.04
g, 40 mmol) were dissolved in 120 mL CH3OH and the mixture
was allowed to stir for 3 min. To this solution, LnCl3·6H2O (Ln
= La, Nd and Yb; 10 mmol) and Cd(OAc)2(H2O)2 (2.66 g, 10
mmol) in methanol (40 mL) was added dropwise and stirred for
24 h at room temperature. The yellow precipitate was filtered
and washed with 10 mL CH3OH and 10 mL H2O, then dried
under vacuum to give the desired products.
La2Cd2L2(TTA)4(OAc)2(CH3OH)2. Yield: 82%. Anal. Calc.
for C82H66Cd2F12N4La2O22S4 (2318.29) :C, 42.28; H,2.87; N,
2.42; found: C, 42.30; H, 2.85; N, 2.44; IR(KBr, cm−1 ):3430 s,
2957 w, 1615 s, 1544 s, 1469 s, 1413 m, 1302 s, 1226 m, 1186
s, 1141 m, 974 w, 845 w, 793 w, 730 w. ESI-MS: m/z = 2341.28
[M + Na]+.
Nd2Cd2L2(TTA)4(OAc)2(CH3OH)2. Yield: 80%. Anal. Calc.
for C82H66Cd2F12N4Nd2O22S4(2328.96) :C, 42.29; H, 2.86; N,
2.41; found: C, 42.32; H, 2.77; N, 2.44; IR(KBr, cm−1 ):3433 s,
2958 w, 1618 s, 1542 s, 1467 s, 1410 m, 1304 s, 1228 m, 1189
s, 1143 m, 971 w, 847 w, 792 w, 733 w. ESI-MS: m/z =
2178.9630 [M - 2(OAc) - CH3OH]+.
Yb2Cd2L2(TTA)4(OAc)2(CH3OH)2. Yield: 83%. Anal. Calc.
for C82H66Cd2F12N4Yb2O22S4 (2386.59) :C, 41.27; H, 2.79; N,
2.35; found: C, 41.62; H, 2.82; N, 2.38; IR(KBr, cm−1 ):3436 s,
2960 w, 1622 s, 1538 s, 1458 s, 1408 m, 1312 s, 1232 m, 1184
photomultiplier
detector
(Hamamatsu
R928).
The
luminescence lifetimes were recorded on a single-photon-
counting spectrometer from Edinburgh Instrument (FLS 1000)
with a microsecond pulse lamp as the excitation sources. The
data were analyzed by software supplied by Edinburgh
Instruments. The fluorescence quantum yield was determined
using an Edinburgh Instruments’ FLS1000 fluorescence
spectrophotometer attached with an integrating sphere through
an absolute method. Powder X-ray diffraction (PXRD) data
were recorded on a Rigaku D/Max-3B X-ray diffractometer
with CuKα as the radiation source in the angular range of θ =
5–50° at room temperature. The data was collected under 293
K. The structure was solved by direct methods and refined on
F2 by full-matrix least-squares using the SHELXTL-2014
program.19
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1−3 | 5
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CrystEngComm
Page 7 of 7
ARTICLE
Journal Name
2019, 6, 550; (c) S. Biju, Y. K. Eom, J.-C. G. Bünzli and H.
s, 1142 m, 968 w, 852 w, 784 w, 742 w. ESI-MS: m/z =
2409.5932 [M + Na]+.
View Article Online
K. Kim, J. Mater. Chem. C, 2013, 1, 6935.
DOI: 10.1039/D0CE00341G
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P. Gillin and P. B. Wyatt, Chem. Commun., 2013, 49, 1933–
1935.
Conflicts of interest
There are no conflicts to declare.
Acknowledgements
This work is financially supported by the National Natural Science
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