Luminescent coordination polymers for the VIS and NIR range constituting LnCl3 and 1,2-bis(4-pyridyl)ethane

Article abstract of DOI:10.1039/c6dt00152a

A series of 14 lanthanide containing coordination polymers LnCl₃ with 1,2-bis(4-pyridyl)ethane (bpe) was synthesized from either thiazole or pyridine. Depending on the ligand content, a structural diversity from 3D-frameworks 3∞[LnCl₃(bpe)₂]·thz, Ln = Ce-Lu, to 1D-strands 1∞[La₂Cl₆(bpe)₂(thz)₆] and 1∞[LnCl₃(bpe)(py)₂]·(bpe/py), Ln = Gd, Er, was obtained and characterized by X-ray single crystal diffraction, powder diffraction, differential thermal analysis and thermogravimetry (DTA/TG), IR-spectroscopy and photoluminescence spectroscopy. The compounds exhibit a variety of luminescence properties and different phenomena. This includes ligand centred fluorescence, metal-centred 5d-4f/4f-4f emission in the visible and the NIR range, antenna effects via Dexter and F?rster energy transfer mechanisms, excitation dependent emission with a correlating shift of the chromaticity coordinates and inner filter effects by combined re-absorption/emission.

Full text of DOI:10.1039/c6dt00152a

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ARTICLE
Luminescent Coordination Polymers for the VIS
and NIR Range Constituting from LnCl3 and 1,2-
bis(4-pyridyl)-ethane
Cite this: DOI: 10.1039/x0xx00000x
N. Dannenbauer,a P. R. Matthesa and K. MüllerꢀBuschbauma
Received 00th January 2012,
Accepted 00th January 2012
A series of 14 lanthanide containing coordination polymers LnCl3 of with 1,2ꢀbis(4ꢀpyridyl)ꢀ
ethane (bpe) was synthesized from either thiazole or pyridine. Depending on the ligand
content, a structural diversity from 3Dꢀframeworks 3∞[LnCl3(bpe)2]·thz, Ln = CeꢀLu, to 1Dꢀ
strands 1∞[La2Cl6(bpe)2(thz)6] and 1∞[LnCl3(bpe)(py)2]·(bpe/py), Ln = Gd, Er, were obtained and
characterized by Xꢀray single crystal diffraction, powder diffraction, differential thermal analysis
and thermogravimetry (DTA/TG), IRꢀspectroscopy and photoluminescence spectroscopy. The
compounds exhibit a variety of luminescence properties and different phenomena. This
DOI: 10.1039/x0xx00000x
www.rsc.org/
includes ligand centred fluorescence, metalꢀcentred 5dꢀ4f/4fꢀ4f emission in the visible and the
NIR range, antenna effects via Dexter and Förster energy transfer mechanisms, excitation
dependent emission with a correlating shift of the chromaticity coordinates and inner filter
effects by combined reꢀabsorption/emission.
3∞[Ce(Tz)3], Tzꢀ = 1,2,3ꢀtriazolate (UV to blue), or CeꢀYAG
(yellow) as laser and for pcꢀLEDs to generate white light.[8,7]
Introduction
In the last decade, coordination polymers (CPs) and metal
organic frameworks (MOFs) have been of growing scientific
interest due to their wide variety of possible applications.[1] One
feature, which makes them particularly attractive, is the
extraordinary broad variety of photoluminescence (PL)
properties, e.g. in lanthanide containing coordination
polymers.[2] In addition to ligandꢀ and metalꢀcentred
luminescence, energy transfer processes are remarkable, for
example to circumvent the low light absorption of Ln3+ ions[3].
The latter can be circumvented by the so called antenna effect
[4] by means of inserting suitable organic linker molecules with
high absorption coefficients and suitable energetic states for a
following energy transfer from the linker to the lanthanide ions.
In this report the linker ligand 1,2ꢀbis(4ꢀpyridyl)ethane (bpe)
proves to function as a suitable sensitizer due to the pyridyl πꢀ
systems. The option of effective antenna effects for Ln3+ ions in
For the ligand bpe various coordination compounds are known,
in which bpe functions as linker between metal centres: For
example, in the dinuclear complexes [Sn2Cl2(bpe)Ph6][9], in
oneꢀdimensional coordination polymers with tetrahedrally
coordinated metal ions 1∞[MCl2(bpe)] with M = Co[10], Ni[11]
Zn[12] or in 1∞[FeCl2(bpe)(dmp)2][13] (dmp
3,5ꢀ
,
=
dimethylpyridine) with octahedral coordination of the metal
centre. Further structural condensation can be observed in the
2
luminescent 2Dꢀnetwork [Ag3Cl3(bpe)2][14] or in combination
∞
with the carboxyl ligands in [Zn2Cl(dcb)(bpe)][15] (dcb = 1,4ꢀ
3
∞
dicarboxybenzene). Lanthanide containing compounds with bpe
coordination are rather rare. Exemplary compounds are the
complex [Nd(tta)3(bpe)][16] (tta = thenoyltrifluoroacetone) or the
coordination polymer [bpeH]1∞[La(bpe)(H2O)(NO3)4][17] based
on bpe connected hydrated lanthanum nitrate units.
In the following, we present a series of fourteen threeꢀ
dimensional networks and single strands based on LnCl3, the
linker bpe and the coꢀligands thiazole and pyridine that exhibit
a large variety of luminescence properties.
[5]
the visible and the NIR range is well known and results in
typical 4fꢀemission spectra with respective chromaticity based
on 4
of trivalent lanthanide ions, the photoluminescence of Ce3+ can
utilize 5 ꢀ4
transitions resulting in broad emission bands.[7]
The participation of 5 orbitals the luminescence results in a
fꢀ4f
transitions and sharp line emissions.[6] As an exception
d
f
Results and Discussion
d
dependence of the chemical surrounding of the Ce3+ ion on the
luminescence and the emission maximum can be shifted from
the UV to the visible area, as shown for coordination polymers
such as 2∞[Ce2Cl6(bipy)4]·py, bipy = 4,4'ꢀbipyridine, and
Synthesis
All compounds were synthesized using a solvothermal reaction
pathway either in thiazole or pyridine. Hereby, the
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corresponding anhydrous LnCl3 is reacted within pyridine or
thiazole in addition to the linker ligand 1,2ꢀbis(4ꢀpyridyl)ethane
(bpe). As bpe itself did not prove to be sufficiently reactive, we
use the ability of pyridine and thiazole to act as chemical
scissors, breaking up the anhydrous LnCl3 structure by the
formation of lewisꢀacid base adducts. Solvent complexes such
as [LnCl3(thz)4]·0.5thz, with Ln = Sm, Eu, Gd, Tb, Dy,[18]
[LnCl3(py)4]·0.5py,[19] with Ln = Y, La, Er, Yb, or [La2(
ꢀ2ꢀ
Cl)2Cl4(py)8][20] can be formed a room temperature. The
addition of the liker ligand bpe, increasing reaction temperature
and a shift of the molar ratio of the organic compounds to the
bpe ligand leads to the formation of coordination polymers with
bpe. Solvothermal reaction parameters cause a connection of
lanthanideꢀchloride building units with bpe molecules, due to
the thermodynamically favourite displacement of solvent
molecules by linker molecules. We have already applied this
reaction route for the synthesis of the series of complexes
[Ln2Cl6(bipy)(py)6] for Ln = Pr, Nd, SmꢀYb, bipy = 4,4’ꢀ
bipyridine.[21] Different from bpe, bipy was shown to be
sufficiently reactive without the formation of precursor
complexes with py or thz, e.g. in solventꢀfree reactions yielding
Figure 1. Top: Coordination sphere of 1∞[La2Cl6(bpe)2(thz)6](1), thermal ellipsoids
MOFs and coordination polymers in the presence of anhydrous in this and all following figures depict 50 % of the probability level of the atoms,
metalꢀchlorides.[22]
symmetry operations: I 1ꢀx,2ꢀy,ꢀz; II xꢀ1, 1+y, zꢀ1; III 2ꢀx, 1ꢀy, 1ꢀz. Bottom:
Depiction of the parallel stacking of the oneꢀdimensional zigꢀzag strands of
1∞[La2Cl6(bpe)2(thz)6](1).
Crystal structures of 1∞[La2Cl6(bpe)2(thz)6](1)
Further crystallographic information and interatomic distances
1∞[La2Cl6(bpe)2(thz)6](
1) crystallizes in the centrosymmetric
are given in table 1 and table S1. The trivalent lanthanide ions,
which again occupy only one crystallographic site, are 7ꢀfold
coordinated by four nitrogen and three chlorine atoms, forming
a pentagonalꢀbipyramidal coordination polyhedron (see Fig. 2
and S2). The nitrogen atoms belong to four different bpe
molecules spanning a plane with one chlorine atom, the other
two chlorides are in axial positions. The interatomic distances
for CeꢀCl with 2.7373(7)ꢀ2.744(7) pm and YbꢀCl with
2.5609(11)ꢀ2.6002(13) pm are in good accordance to the
space group P¯1 as a oneꢀdimensional coordination polymer.
The corresponding crystallographic data and interatomic
distances are given in table 1 and table S1.
The trivalent lanthanum is positioned on one crystallographic
site and is coordinated in a distorted doubleꢀcapped prism by
four chlorine atoms and four nitrogen atoms, which belong to
three thiazole molecules and one bpe molecule, giving a C.N of
eight. Two of the chlorine atoms are linked to an adjacent
lanthanide centre which results in a dinuclear unit (see Fig. 1
and S1). The LaꢀCl and LaꢀN distances are in the range of
2.8212(11) to 2.9263(11) Å and 2.710(2) to 2.816(2) Å,
respectively. These distances are in good accordance to
respective interatomic distances, e.g. in the MOF
3∞[La2Cl6(bipy)5]·4bipy[22b] with LaꢀCl = 2.760ꢀ2.964 Å and Laꢀ
corresponding distances in [CeCl2(ꢁꢀCl){pyꢀ(
R
,
R
)ꢀchxn}]2 (pyꢀ
(
R
,
R
)ꢀchxn
=
N, N'ꢀbis(2ꢀpyridylꢀmethylidene)ꢀ1,2ꢀ(R, R)ꢀ
cyclohexanediamine)[23], [CeCl3 (CH3OH)4][24], YbCl3(py)4,[25]
and [Yb2Cl6(ꢁꢀbipy)(py)6][21]. The LnꢀN distances are also in
the reported range.[23,
25, 26]
They match with the lanthanide
contraction, beginning with the shortest distance for YbꢀN
(2.473(3)ꢀ2.509(3) pm, followed by DyꢀN (2.522(3)ꢀ
2.571(4) pm), and CeꢀN (2.653(2)ꢀ2.693(2) pm). The crystal
structure analysis reveals a layered 2D structure with a
honeycombꢀlike topology interconnected by bpe molecules to a
3D structure with dia topology (Fig. 2). The honeycombꢀlike
sheets are interconnected by bpe molecules and are shifted in
the acꢀplane to one another by the length of half a comb.
Additionally, one thiazole molecule is intercalated in pores of
the framework structure.
N
2.750ꢀ2.818 Å as well as in the complex [La2(ꢁꢀ
Cl)2Cl4(py)8][20] with LaꢀCl = 2.778ꢀ2.929 Å and LaꢀN 2.722ꢀ
2.789 Å. The dimeric unit La2Cl6 is interconnected to two other
dimers by one bridging bpe molecule forming a single strand.
Due to the alternating coordination of the bpe ligand within the
dimeric unit, zigzag chains result. These chains are shifted
against each other by the length of one bpe molecule within the
acꢀplane.
Crystal structures of 3∞[LnCl3(bpe)2]·thz with Ln = Ce(2), Pr(3),
Dy(8), Yb(11)
Crystal structures of 1∞[LnCl3(bpe)(py)2]·(bpe/py) with Ln =
Gd(13) and Er (14)
The threeꢀdimensional (3D) framework structure of
3∞[LnCl3(bpe)2]·thz is found for compounds
2
–
12 and was in
particular supported by single crystal structure analysis for Ln =
Ce( ), Pr( ), Dy( ), Yb(11), which are istopypic and crystallize
1
The oneꢀdimensional coordination polymers ∞[LnCl3(bpe)
(py)2]·(bpe/py) with Ln = Gd(13) and Er(14) crystallize in the
2
3
8
in the monoclinic space group C2/c.
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triclinic space group P¯1. Crystallographic data and selected 2.548(2)ꢀ2.584(2) Å for the nitrogen atoms of the bpe ligand.
interatomic distances are listed in table 1 and table S1.
All atomic distances are in good accordance with their
equivalents in the dinuclear complexes [Ln2Cl6(bipy)(py)6],[21]
Ln = Gd, Er with GdꢀCl 2.6301ꢀ2.6785 Å, ErꢀCl 2.5834ꢀ
2.6471 Å, GdꢀN 2.558ꢀ2.616 Å and ErꢀN 2.4807ꢀ2.576 Å. The
chloride ions are positioned in a tꢀshape form around the Ln3+
ions with an ClꢀLnꢀCl angle for the axial chlorine atoms of
171.74(3)° for Gd(13) and 172.98(2)° for Er(14), indicating ta
certain distortion from the ideal coordination polyhedron with
180°. The lanthanide ions are again connected via bridging bpe
molecules to oneꢀdimensional strands. The strands of the oneꢀ
dimensional coordination polymer are arranged parallel to one
another (see Fig. S4) and shifted by half of the elemental cell
along cꢀaxis. In addition, one nonꢀcoordinating bpe and one py
molecule are intercalated in the structure. The py molecule
exhibits a rotational disorder along the perpendicular line
through the barycenter of the pyridyl ring.
Figure 3. Top: Coordination sphere of 1∞[GdCl3(bpe)(py)2]·(bpe/py)(13). The
intercalated pyridine molecule is described with a benzene molecule, due to
rotational disorder effects, Symmetry operations: Ix,y,zꢀ1; II1ꢀx,1ꢀy,2ꢀz; III1ꢀx,ꢀ
y,1ꢀz. Bottom: The crystal structure of 13 with a view along [100].
Figure 2. Top: Coordination sphere of 3∞[PrCl3(bpe)2]·thz(
3
), symmetry
operations: ½ꢀx, yꢀ½,3/2ꢀz; ½ꢀx,½+y,3/2ꢀz; IIIꢀx,y,½ꢀz; IVꢀx,1ꢀy,ꢀz (top). Center:
View along the aꢀaxis of the crystal structure of 3∞[PrCl3(bpe)2]·thz(
). Bottom:
Depiction of the dia topology of the crystal structure 3∞[PrCl3(bpe)2]·thz(
).
I
II
3
3
Powder Xꢀray diffraction (PXRD)
In the structure, the trivalent lanthanide ions are positioned on
one crystallographic independent site and coordinated by three
terminal chloride anions and four nitrogen atoms of bpe and
pyridine (Fig. 3 and S3). The coordination polyhedron is
constituted by a distorted pentagonalꢀbipyramid with two
chloride ions in axial position and one chloride ion and four
nitrogen atoms in equatorial position, giving a C.N. of seven.
The LnꢀCl distances are in the range of 2.6330(12)ꢀ
2.6864(13) Å for Gd(13) and 2.5822(7)ꢀ2.6460(7) Å for Er(14),
the LnꢀN distances are in the range of 2.570(3)ꢀ2.582(3) Å for
Gd(13) and 2.520(2)ꢀ2533(2) Å for Er(14) for the nitrogen
atoms of the pyridine ligands and 2.542(3)ꢀ2.594(3) Å and
PXRD investigations were performed on all compounds 1ꢀ14 to
prove the phase purity, the isotypic/isostructural character
among the isoconstitutional compounds and to check the single
crystal structure determinations. The simulated diffraction
patterns of 1(La), 13(Gd) and 14(Er) are in good accordance
with the observed ones, indicating correct structure
determination and phase purity (Fig. S5 and S6). For the series
of the frameworks
2(Ce)ꢀ12(Lu) all PXRD investigations
revealed similar diffraction patterns (Fig. 4), indicating their
isotypic structure and phase purity.
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Table 1. Crystallographic data for La(1), Ce(2), Pr(3), Dy(8), Yb(11), Gd(13) and Er(14).
La (1)
Ce (2)
Pr (3)
Dy (8)
Yb (11)
C27H27Cl3YbN5S
733.01
Gd (13)
Er (14)
C15H15Cl3LaN4
593.18
C27H27Cl3CeN5S
700.09
C27H27Cl3PrN5S
700.88
C27H27Cl3DyN5S
722.90
C61H61Cl6Gd2N11 C61H61Cl6Er2N11
Formula
fw / g molꢀ1
Crystal system
Space group
a/Å
1475.44
triclinic
P¯1
1495.46
triclinic
P¯1
triclinic
P¯1
monoclinic
C2/c
monoclinic
C2/c
monoclinic
C2/c
monoclinic
C2/c
9.198(2)
9.727(2)
12.425(3)
77.92(3)
79.77(3)
79.08(3)
1056.3(4)
2
36.032(7)
9.260(2)
18.688(4)
90
35.828(2)
9.2397(4)
18.6155(9)
90
35.642(2)
9.2416(6)
18.5076(11)
90
35.641(8)
9.257(2)
18.512(4)
90
9.339(2)
12.925(3)
14.064(3)
103.44(3)
102.03(3)
101.85(3)
1556.4(6)
1
9.3175(10)
12.8780(14)
13.971(2)
103.280(2)
102.030(3)
101.880(2)
1538.0(3)
1
b/Å
c/Å
α/°
108.34(3)
90
108.312(1)
90
109.0580(10)
90
109.781(7)
90
β/°
γ/°
V/Å3
5919(2)
8
5850.5(5)
8
5762.1(6)
8
5747(2)
8
Z
ρcalc/g/cm3
ꢀ/cmꢀ1
1.865
1.5711
1.5913
1.657
1.6908
1.573
1.614
2.708
1.905
2.036
2.969
3.631
2.417
3.018
100(3)
100(3)
100(3)
100(3)
167(3)
168(5)
168(5)
T/K
3.38 to 56.76
2.38 to 56.70
4.48 to 56.64
4.50 to 56.68
2.42 to 56.58
3.86 to 54.18
3.38 to 54.14
data range/°
Xꢀray radiation
MoꢀKα, λ = 0.71073 Å
Collected
reflections
15684
43306
38871
42289
41295
19153
18949
No. of unique
reflections
5201
238
7360
333
7282
333
7149
449
7146
357
6810
361
6716
361
No of parameters
R1 for reflections
F0>2σ (F0)]a
0.0230
0.0219
0.0274
0.0332
0.0338
0.0369
0.0251
R1 (all)a
wR2 (all)b
S
0.0252
0.0573
1.028
0.0320
0.0518
1.029
0.0456
0.0664
1.051
0.0584
0.0750
1.030
0.0583
0.0813
1.046
0.0417
0.0744
1.208
0.0296
0.0554
0.980
Res.
electron
1.04/ꢀ0.52
0.79/ꢀ0.54
0.83/ꢀ1.15
[27]
1.13/ꢀ2.30
1.96/ꢀ2.15
1.31/ꢀ1.11
0.86/ꢀ0.38
density (e/Å3)
a R1 = ∑[|Fo|ꢀ|Fc|]/∑| Fo|.b R2 = [ ∑ w (|Fo|2ꢀ|Fc|2)2 /∑ w (|Fo|2)2]1/2
.
However, the presence of a phase transition at low temperatures pattern at 293 K. In order to prove this assumption, a cell
can be assumed, as the simulated diffraction pattern based on indexing was carried out for the observed powder pattern of
the singleꢀcrystal structure investigation at 100 K shows 10(Er) as an exemplary of the room temperature data. It
differences in reflection positions compared to the observed revealed an elemental cell related to the singleꢀcrystal indexing
powder diffraction patterns recorded at 293 K. The reflections with the monoclinic space group
in the range of 15 to 17° and the first three reflections of the a = 36.626(8) Å, b = 9.344(9)
C
2 and cell parameters of
Å, c = 9.443(5) Å,
simulated pattern are not superimposing the observed powder β = 111.42(5)°. Compared to the cell indexed by singleꢀcrystal
patterns, indicating minor structural change between the xꢀray data, the axis c is halved. We therefore verified our
observed single crystal structure at 100 K and the observed bulk singleꢀcrystal diffraction data, which does not allow reduction
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of a cell axis by one half, but confirmed the determination by side maximum at
singeꢀcrystal diffraction based investigations at 100 K for max. = 292 nm and 306 nm), that can be assigned to excited
Ce( ), Pr( ), Dy( ), Yb(11). Accordingly, we assume the singlet states. The emission spectra of thiazole shows one broad
existence of a phase transition between 100 K and 293 K for fluorescence band in the range of = 330ꢀ460 nm ( max. =
Ce( )ꢀLu(12). 376 nm, obs = 2.1(1) ns) and the excitation spectra reveals an
absorption process with a maximum at λmax 260 nm and a
λmax. = 322 nm in the solid state (iꢀPrOH:
λ
2
3
8
λ
λ
2
τ
.
<
side maximum at λmax. = 320 nm. The energetic position of the
triplet level T1 was reported at 26045 cmꢀ1 around 380 nm.[28]
Figure 4. Comparison of the observed powder Xꢀray diffraction patterns (Cuꢀ
radiation) of isotypic 3∞[LnCl3(bpe)2]·thz, Ln = Ce(2)ꢀLu(12), at RT with the
simulated diffraction pattern of the singleꢀcrystal Xꢀray structure determination of
Pr(3) at 100 K.
Photoluminescence spectroscopy
The series of threeꢀdimensional networks
2ꢀ11 and single
strands 13 14 reveals six different photoluminescence effects
ꢀ
subsequent to excitation with UVꢀlight. Figure 5, 6 and S7/S8
show the recorded emission and excitation spectra of the
compounds at room temperature in solid state including the
Figure 5. Emission spectra of the compounds 2, 4ꢀ7, 10, 11, 13, 14 and the ligands
bpe in solid state and in iꢀPrOH as well as thiazole at RT (λexc = 300 nm).
ligands thiazole and bpe (the latter also dissolved in
In the solid state, the ligand bpe reveals two emission bands in
the range of = 300ꢀ400 nm ( max. = 347 nm, obs < 1 ns) and
= 400ꢀ650 nm ( max. = 469 nm, obs = 9.9(8) ns), which can be
assigned to fluorescence. Participation of triplet states is
excluded due to the short decay times of the processes. The
second band could possibly result from an exciplex formation,
iꢀPrOH).
The two Gd3+ꢀcompounds,
6 and 13 are good examples to
observe effects of ligandꢀcentered luminescence in compounds
isostructural to other lanthanides without participation of Gd3+
in the luminescence, as the respective 4fꢀtransiton at 307nm is
not populated. Accordingly, the emission is ligand centred
λ
λ
τ
λ
λ
τ
fluorescence (e.g. in 6: λmax. = 355 nm, τobs < 1 ns) and derives
from the linking bpe molecules with a shoulder of the thz
emission. The maxima of the fluorescence band of bpe are
shifted slightly to higher wavelengths and energy as result of
the coordination as donor ligand. This can be also observed in
as it is not present in any of the products
1ꢀ14. However, by
dissolving and freezing bpe in ꢀPrOH, the intensity ratio of the
i
second fluorescent band is significantly reduced but not
quenched. The corresponding excitation spectra of bpe exhibit
the compounds Pr(3) (Fig. S7) Nd(4), Ho(9), Yb(11) and
an absorption process with a maximum at λmax. = 307 nm and a
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Lu(12) (Fig. S7), as the excitation spectra of these compounds not allow a simplified deduction from related bonding partners
resemble the excitation spectrum of bpe (Fig. S8).
such as pyridyl ligands.
In the compounds with Sm(5), Tb(7) and Dy(8) the typical
visible 4fꢀ4f
transitions are observed in the emission spectra.[6]
The nonꢀcentrosymmetric pentagonalꢀbipyramidal coordination
sphere of N and Cl atoms around Ln influences the
finestructure and intensities of the 4fꢀstates slightly according
to ligand and crystal field.[6c] Ligand centred emission is also
observed, the intensity ratio strongly depending on the intensity
of the Ln3+ꢀemission (the latter being strongest for Tb3+ and less
pronounced for Dy3+ and Sm3+. Only weak 4fꢁexcitation is
present for the three Ln3+. We therefore assume a sensitization
of these lanthanide ions by the linker ligand bpe via an antenna
effect.[4] The organic ligand transfers excitation energy to the
metal centres, as excited ligand states of the organic linker bpe
and the Ln3+ꢀ4
fꢀstates have a suitable energetic match for the
energy transfer.[4,21] However, this energy transfer is limited by
the short decay times of the excited states of bpe in the nsꢀ
region. Besides the antenna effect of the linker bpe via the
Dexter energy transfer mechanism, we consider the intercalated
thiazole molecules another source for energy transfer to the
lanthanide ions via the Förster energy transfer mechanism.
Within this mechanism, the ligand (donor) can transmit energy
to the lanthanide ion (acceptor) over long distances (up to
1000 pm) [29]. Thiazole itself can potentially function as another
antenna with broad band singlet and triplet excitation and
excited states in the correct energetic range to transfer energy
on to excited 4fꢀstates of lanthanide ions (see Fig. 6).
According to the short lifetimes of excited states of bpe,
thiazole, even if intercalated only, can add to sensitizer effects
according to the longer decay times of its triplet states.
However, as thz is no direct coordination partner for
2ꢀ12,
energy transfer for this ligand on to lanthanides is likely to
happen via space. In order to elaborate the interplay of Dexter
and Förster transfer, threeꢀdimensional photoluminescence
(14)
spectra were recorded for compounds
(Tb3+) and (Dy3+). They show excitation possibilities of bpe
and thz next to the typical intra 4
5 7
(Sm3+, see Fig. 7),
8
Figure 6. Excitation spectra of the compounds 2, 4ꢀ7, 10, 11, 13, 14 and the ligand
bpe in solid state and in iꢀPrOH as well as thiazole at RT.
fꢀline emission of the Lnꢀ
ions[6]. The spectra also illustrate that the emission of the
compounds is excitation dependent. Figure 7 shows a 3Dꢀ
spectrum of the Sm3+ꢀcompound (
5), which is translated into a
In contrast, the emission of
results in a broad metalꢀcentred band (
8.3(1) ns) based on 5 ꢀ4
transitions of Ce3+.[7,8] No ligandꢀ
2
containing the Ln3+ꢀion Ce3+
max. = 550 nm, τobs
λ
=
2Dꢀheight profile of the intensity and the corresponding
chromaticity coordinates for selected excitation wavelengths. In
d
f
centred emission is observed, however, as the Ceꢀcentred
emission is parity allowed and therefore strong, it cannot
substantially be resolved, if the bpe ligand functions as a
sensitizer for Ce3+ or if the respective ligandꢀcentred emission
is too weak compared to Ce3+ to be observed. The resulting
emission colour (chromaticity) appears as a strong lemon
yellow (see TOC). The energetic positions of the emissive
the emission spectrum of
be found excitation dependent in addition to emission of Sm3+.
For excitation in the region = 260ꢀ280 nm, the emission is
5, both, emission of bpe and thz can
λ
dominated by Sm3+, and the chromaticity coordinates remain all
in the red part of the chromaticity diagram together with weak
thz related triplet emission. This indicates that the antenna
effect for bpe is effective in this excitation area, as most of the
excitation energy of the ligand is transferred to the Sm3+ꢀion,
wherefrom it is emitted in the visible red region, whereas the
energy transfer from thz is less effective for its excited singlet
states. This is in accordance with attributing bpe to Dexter and
thz to Förster energy transfer mechanisms for the two ligands.
With higher excitation wavelengths, the emission colors move
excited 5d
ꢀstates of Ce3+ are therefore closer to the oxide Ceꢀ
YAG (yellow)[8c] than to 2∞[Ce2Cl6(bipy)4]·py, containing the
related ligand 4,4’ꢀbipyridine.[8b] This shows the complex
behaviour and influence of ligand and crystal field splitting
influencing the energetic positions of Lnꢀ5dꢀstates, which do
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ARTICLE
DOI: 10.1039/C6DT00152A
to the bluishꢀwhite region due to a higher proportion of ligand aromatic ν(CꢀC, CꢀN) ring vibration at 1594 cmꢀ1. For the
emission addressed to bpe. The intensity of the metalꢀcentered compounds La( )ꢀLu(12), an energetic shift of the vibration
1
emission is also increasing for excitation >290nm but not as bands to higher energies (829ꢀ831cmꢀ1, 1608ꢀ1613 cmꢀ1) can be
strong as the emission of bpe. The efficacy of the energy observed, which confirms the presence of interconnecting bpe.
transfer from bpe is partly moved to thz. A possible reason for For the compounds Gd(13) and Er(14), an energetic shift of the
this observation is the fact that the emission of bpe in this vibration bands in combination with signal splitting to higher
region comes from an aggregation induced effect with decay energies indicates the presence of coordinated and intercalated
times in the nanosecond and does not originate from triplet bpe. Therefore the energies of the bpe vibration bands in the
states, whereas thz can populate triplet states in this energetic compounds Gd(13) and Er(14) can be observed at a split signal
region. It also illustrates that such an aggregation induced effect at 831 cmꢀ1 and at two well dividable bands in the range of
is less suitable as sensitizer.
1600ꢀ1601 cmꢀ1 and 1611ꢀ1612 cmꢀ1.
The free ligand pyridine exhibits an intense
ω(CꢀH)ꢀwag
vibration at 1439 cmꢀ1, and the nonꢀcoordinating ligand thiazole
the vibration band δ
(CꢀH) at 1041 cmꢀ1. Coordination to Ln3+
ion leads to a shift of the vibrations to higher energy, exhibiting
an intense band at 1444 cmꢀ1 for pyridine and 1049 cmꢀ1 for
thiazole. The intercalated py molecule can be observed in a
band shoulder at 1432 cmꢀ1.
bpe
Thermal investigations
In order to obtain information about the thermal properties of
the synthesized coordination polymers and networks,
exemplarily DTA/TG investigations were performed on the
thz
compounds Pr(3), Nd(4), Gd(6), Yb(11) and Gd(13). For the
interpretation of results, the thermal properties of the free
ligands are: bpe (mp: 110ꢀ111 °C[31], decomposition: 272ꢀ
273 °C[32]), thiazole (bp = 117ꢀ118 °C)[33] and pyridine
(bp = 114°C).[34] The corresponding thermal properties are
shown in Figures 8 for Pr(3) and Gd(13) (and for Nd(4), Gd(6),
Yb(11) in Fig. S9ꢀ11)).
Figure 7. 3Dꢀphotoluminescense spectra of 3∞[SmCl3(bpe)2]·thz (5) and the
corresponding CIEꢀcoordinates for different excitation wavelengths indicating.
For a brief discussion, only one 3Dꢀframework (
3) and one 1Dꢀ
The coordination polymers Nd(
reveal a combination of ligandꢀcentred emission in the visible
range as well as the 4 ꢀ4 emission of the corresponding
lanthanide ions in the NIR range.[6,7] As the excitation spectra
show no direct Ln3+ꢀexcitations, the 4
ꢀ4 ꢀtransitions for
4), Yb(11) Er(10), and Er(14)
strand polymer 13 are discussed, here (for further
(
)
determinations, see Fig. S9ꢀS11). The threeꢀdimensional
frameworks all show the release of one equivalent of nonꢀ
coordinating thiazole in the first mass loss step, which is
combined with an endothermic signal around 205 °C. In the
f
f
f
f
emission are also triggered by antenna effects of the ligands, as
described before. The respective NIRꢀemission is strong for Nd
compound Pr(3), the endothermic signal 2 at 270°C coincides
with a second mass loss step (Pr: 25.5 %) that can be identified
with the loss of one equivalent of bpe (theo.: Pr: 26.3 %). The
remaining equivalent of bpe is lost thereafter at 400°C (mass
loss: Pr: 23.5 %; theo.: Pr: 26.3 %). Based on the difference in
measured and theoretical value, it can be assumed that the
ligand bpe is not released completely, but rather appears to
decompose slightly at temperatures >400°C. This correlates
in
4 and Yb in 11, in contrast it is weak for Er in 10 and 14.
Instead of high intensity, for Er3+ꢀions (10 and 14), the so called
inner filter effect can be observed.[8a] The profile of the ligandꢀ
centred emission band exhibits indentations that can be
attributed to the reꢀabsorption of the emitted fluorescence by
direct excitation based on the 4fꢀ4f
transitions of the Er3+ꢀions
within the same compound. Such effects were observed
especially for several Erꢀcontaining coordination polymers with
Nꢀdonor ligands before.[8a]
with a further mass loss after the endothermic signal
The theoretical value of the remaining mass of the inorganic
salt is 35.3 % for Pr( ), which suits with the actual mass at
800 °C (Pr( ): 33.0 %). Furthermore, black remnants could be
3 for 3.
3
3
Vibrational Spectroscopy
observed after measurement, corroborating the partly
carbonization of the bpe ligand. A melting point of reformed
LnCl3 could only be observed in the investigated temperature
For all compounds La(1)ꢀEr(14), the presence of the free or
coordinated ligands bpe, thz and py can be confirmed by IRꢀ
spectroscopy investigations, performed for all compounds. The
vibration profile of coordinated bpe is related to 1,2ꢀdi(4ꢀ
pyridyl)ethylene coordinated to metal ions in known
compounds[30]. The interconnecting ligand bpe can be identified
at the interplanar CꢀHꢀbending vibration at 827 cmꢀ1 and the
range for Nd(4
) at 755 °C (theoretical: mp = 770°C).[35] DTA
signal 1 of the ladder like coordination polymer 1∞[GdCl3
(bpe)(py)2]·(bpe/py) (13) is split into three sub signals (1a:
105°C; 1b: 170°C, 200°C) indicating a complex endothermic
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DOI: 10.1039/C6DT00152A
release process of 2.5 equivalents of intercalated and units were used for experiments in sealed glass ampoules.
coordinated pyridine (Figure 8).
Anhydrous rare earth chlorides were synthesised according to
[36]
the ammonium halide route
using the oxides Er2O3, Yb2O3,
Lu2O3 (99.9 %, RCꢀNukor), La2O3, Nd2O3, Sm2O3, Tb4O7
(99.9 %, AuerꢀRemy), Pr6O11, Dy2O3 (99.9 %, Serva), Gd2O3
(99.9 %, Koch Chemicals), Ho2O3 (99.9 %, Strem), HCl
solution (10 mol lꢀ1, reagent grade) and NH4Cl (99.9 %, Fluka).
The anhydrous CeCl3 was prepared by a modified ammonium
halide route, in which high temperature calcined CeO2 (99.9 %,
AuerꢀRemy) was solubilized by hoursꢀlong boiling in various
mixtures of concentrated acids HCl (37 %, fuming)/HNO3
(69 %, fuming) and HCl (37 %, fuming)/H2O2 (30 %).
Colourless, pure Ce(OH)3 was obtained by alkaline
precipitation with concentrated aqueous NaOH solution (37 %).
As al alternative, Ceriumꢀhydroxide was also obtained by
alkaline treatment of an aqueous Ce(NO3)3·6(H2O) (99 %,
Riedelꢀde Haën) solution. The corresponding precipitates were
then dissolved in HCl acid (10 mol lꢀ1, reagent grade) and
NH4Cl (99.9 %, Fluka) was added. For all Ln, the initially
formed
trivalent
lanthanideꢀammoniumꢀchlorides
were
thermally decomposed to LnCl3 and purified by sublimation
under vacuum. 1,2ꢀBi(4ꢀpyridyl)ethane (bpe, 97 %, Sigmaꢀ
Aldrich) was dried under vacuum, anhydrous thiazole (thz, ≥ 99
%, SigmaꢀAldrich) was dried over molecular sieves and
anhydrous pyridine (py, 99 %, Acros) was used as purchased.
Synthesis
The respective lanthanide chlorides, 1,2ꢀbis(4ꢀpyridyl)ethane and
thiazole or pyridine were sealed into evacuated (1ꢂ10ꢀ3 mbar) glass
3) and ampoules by using Quickfit techniques and degassed by freezing
Figure 8. Simultaneous DTA/TG investigation of 3∞[PrCl3(bpe)2]·thz (
1∞[GdCl3(bpe)(py)2]·(bpe/py) (13) performed with a heating rate of 10°C/min with liquid nitrogen. Subsequently, deliberate heating programs wer
and a flow rate of 20 ml minꢀ1 Ar and 20 ml N2 minꢀ1.
used for the syntheses. The heating program for the syntheses of
La(1)ꢀLu(12) consisted of five steps starting with heating to 120°C
The corresponding mass loss of 25.5% corresponds well with with a rate of 5°C hꢀ1, then to 160°C at 2°C hꢀ1. The temperature was
the theoretical mass loss of 26.8 %. The combined signals 2a maintained for 96 h then cooled to 120°C with 2°C hꢀ1 and to room
and 2b (290°C) indicate evaporation and partly decomposition temperature with 1°C hꢀ1. For compounds Gd(13) and Er(14) the
of the half equivalent of intercalated bpe. Furthermore, the heating program included four steps starting with heating to 50°C
mass loss of 12.0 % corresponds well to the theoretical mass with a rate of 5 °C hꢀ1, then to 190°C with 1°C hꢀ1. The temperature
loss of 12.5 %. With the release of free bpe a possible was maintained for 168 h then cooled down to room temperature
condensation product “GdCl3(bpe)” could be formed from 13
.
with 1°C hꢀ1. All reactions yielded crystalline compounds. For
Due to the metal coordination of bpe in 13, the thermal release purification, the compounds containing pyridine were washed with
temperature for the linking bpe molecules is increased to 2x 1 ml anhydrous pyridine, removing remaining nonꢀreacted bpe
455°C. A decomposition of the released bpe ligand is assumed and were dried under vacuum. The thiazole containing compounds
due to differences in mass loss 20.0 %, compared to the were washed with 2x 1 ml anhydrous dichloromethane. All products
theoretical value of a full equivalent of bpe (24.9 %), and black are air and moisture sensitive.
remnants were observed after the investigation.
Synthesis of 1∞[La2Cl6(bpe)(thz)6] (1)
Experimental
LaCl3 (0.3 mmol; 74 mg), bpe (0.6 mmol; 109 mg) and thz (4.5 mmol;
383 mg) were reacted according to the synthesis procedure described above.
The reaction yielded a colourless crystalline product within excess thz. Yield:
General considerations
All experiments were carried out under inert conditions (Argon
62 mg, 35%. Elemental analysis: Anal. calcd. for C30H30Cl6La2N8S6
(Mr = 1185.55 gmolꢀ1): C 30.39, H 2.55, N 9.45, S 16.23; Found: C, 30.93;
H, 2.68; N, 9.07; S 15.60. IR (ATR): (3088 w, 3050 w, 1608 vssh, 1560 m,
1491 m, 1455 w, 1421 ssh, 1379 s, 1311 s, 1237 m, 1123 vw, 1049 vs,
1006 m, 940 w, 900 s, 872 m, 826 vs, 744 s) cmꢀ1.
atmosphere) using glove box (MBraun, LabMaster SP and
Innovative technology, Pure Lab), vacuum line, Schlenk and
and DURAN™ ampoule techniques. Heating furnaces based on
Al2O3 tubes with Kanthal wire resistance heating and NiCr/Ni
temperature elements controlled by Eurotherm 2416 control
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DOI: 10.1039/C6DT00152A
Synthesis of 3∞[CeCl3(bpe)2]·thz (2)
3.79, N 9.74, S 4.46; Found: C, 45.90; H, 3.84; N, 9.86; S 4.33. IR (KBr):
(3083 w, 3036 w, 2929 vw, 2859 vw, 1612 vssh, 1558 m, 1504 m, 1480 m,
1424 vs, 1380 m, 1318 m, 1227 vs, 1120 m, 1071 vs, 1041 m, 1013 vs,
878 vw, 861 m, 831 s, 811 s, 731 s, 625 m, 600 m, 537 s, 521 m, 491 w) cmꢀ
CeCl3 (0.3 mmol; 74 mg), bpe (0.6 mmol; 109 mg) and thz (4.5 mmol;
383 mg) were reacted according to the synthesis procedure described above.
The reaction yielded a colourless crystalline product. Yield: 87 mg, 41%.
Elemental analysis: Anal. calcd. for C27H27Cl3CeN5S (Mr = 700.08 gmolꢀ1): C
1
.
46.32, H 3.89, N 10.00, S 4.58; Found: C, 47.75; H, 4.10; N, 9.66; S 4.52. IR Synthesis of 3∞[DyCl3(bpe)2]·thz (8)
(KBr): (3084 w, 3049 w, 2962 vw, 1609 vssh, 1558 m, 1501 m,
1424 vs, 1379 ssh, 1314 w, 1261 m, 1226 vs, 1104 w, 1070 m, 1043 m,
DyCl3 (0.3 mmol; 81 mg), bpe (0.6 mmol; 109 mg) and thz (4.5 mmol;
383 mg) were reacted according to the synthesis procedure described above.
The reaction yielded a colourless crystalline product. Yield: 154 mg, 71%.
Elemental analysis: Anal. calcd. for C27H27Cl3DyN5S (Mr = 722.47 gmolꢀ1): C
44.89, H 3.77, N 9.69, S 4.43; Found: C, 44.65; H, 3.76; N, 9.33; S 3.65. IR
(KBr): (3086 w, 3038 w, 2919 vw, 2862 vw, 1613 vssh, 1558 m, 1504 m,
1480 m, 1427 vs, 1381 m, 1319 m, 1228 vs, 1115 m, 1072 s, 1035 m,
1013 vs, 878 vw, 860 m, 827 s, 811 s, 726 s, 623 m, 603 m, 533 s, 517 m)
cmꢀ1.
1010 vs, 862 w, 829 m, 810 s, 736 m, 625 w, 604 m, 536 s, 489 w) cmꢀ1.
Synthesis of 3∞[PrCl3(bpe)2]·thz (3)
PrCl3 (0.3 mmol; 74 mg), bpe (0.6 mmol; 109 mg) and thz (4.5 mmol;
383 mg) were reacted according to the synthesis procedure described above.
The reaction yielded a light greenish crystalline product. Yield: 142 mg,
68%.
Elemental
analysis:
Anal.
calcd.
for
C27H27Cl3PrN5S
(Mr = 700.88 gmolꢀ1): C 46.27, H 3.88, N 9.99, S 4.58; Found: C, 46.69; H,
3.85; N, 9.86; S 3.75. IR (KBr): (3080 w, 3034 w, 2930 vw, 2858 vw, Synthesis of 3∞[HoCl3(bpe)2]·thz (9)
1610 vssh, 1558 m, 1503 m, 1479 m, 1423 vs, 1379 ssh, 1318 w, 1226 vs,
1120 w, 1071 m, 1040 m, 1011 vs, 878 vw, 861 w, 830 s, 814 s, 728 m,
HoCl3 (0.3 mmol; 81 mg), bpe (0.6 mmol; 109 mg) and thz (4.5 mmol;
383 mg) were reacted according to the synthesis procedure described above.
The reaction yielded a light pink crystalline product in excess thz. Yield: 147
mg, 67 %. Elemental analysis: Anal. calcd. for C27H27Cl3HoN5S
(Mr = 724.90 gmolꢀ1): C 44.74, H 3.75, N 9.66, S 4.42; Found: C, 45.56; H,
3.91; N, 9.53; S 4.10. IR (KBr): (3065 w, 3036 w, 2929 vw, 2859 vw,
1613 vssh, 1558 m, 1504 m, 1480 m, 1425 vs, 1380 m, 1318 m, 1228 vs,
1120 m, 1072 s, 1041 w, 1013 s, 878 vw, 861 m, 831 s, 814 s, 733 m, 625 m,
601 m, 537 s, 522 m, 493 w) cmꢀ1.
625 w, 600 m, 537 s, 521 vw, 489 w) cmꢀ1.
Synthesis of 3∞[NdCl3(bpe)2]·thz (4)
NdCl3 (0.3 mmol; 75 mg), bpe (0.6 mmol; 109 mg) and thz (4.5 mmol;
383 mg) were reacted according to the synthesis procedure described above
yielding a light bluish crystalline product. Yield: 138 mg, 65%. Elemental
analysis: Anal. calcd. for C27H27Cl3NdN5S (Mr = 704.21 gmolꢀ1): C 46.05, H
3.86, N 9.94, S 4.55; Found: C, 46.48; H, 3.94; N, 9.71; S 4.42. IR (KBr):
(3081 w, 3034 w, 2930 vw, 2858 vw, 1611 vssh, 1558 m, 1503 m, 1479 m, Synthesis of 3∞[ErCl3(bpe)2]·thz (10)
1424 ssh, 1380 m; 1318 w, 122 6vs, 1125 w, 1072 vs, 1042 m, 1012 vs,
878 vw, 861 m, 830 s, 810 s, 729 m, 625 w, 600 m, 537 s, 521 w, 4901 w,
ErCl3 (0.3 mmol; 82 mg), bpe (0.6 mmol; 109 mg) and thz (4.5 mmol;
383 mg) were reacted according to the synthesis procedure described above.
yielding a slightly pink crystalline product within the solvent. Yield: 153 mg,
425 m) cmꢀ1.
Synthesis of 3∞[SmCl3(bpe)2]·thz (5)
70 %.
Elemental
analysis:
Anal.
calcd.
for
C27H27Cl3ErN5S
(Mr = 727.23 gmolꢀ1): C 44.59, H 3.74, N 9.63, S 4.41; Found: C, 44.42; H,
3.79; N, 9.90; S 4.52. IR (KBr): (3065 w, 3036 w, 2929 vw, 2859 vw,
1613 vssh, 1558 m, 1503 m, 1480 m, 1425 vs, 1380 m, 1318 m, 1228 vs,
1120 m, 1071 s, 1042 m, 1013 vs, 878 vw, 861 m, 831 s, 811 s, 732 m,
625 m, 601 m, 537 s, 522 m, 493 w) cmꢀ1.
SmCl3 (0.3 mmol; 77 mg), bpe (0.6 mmol; 109 mg) and thz (4.5 mmol;
383 mg) were reacted according to the synthesis procedure described above.
The reaction yielded a colourless crystalline product. Yield: 113 mg, 53%.
Elemental analysis: Anal. calcd. for C27H27Cl3SmN5S (Mr = 710.33 gmolꢀ1):
C 45.65, H 3.83, N 9.86, S 4.51; Found: C, 46.27; H, 3.87; N, 9.83; S 4.52.
IR (KBr): (3064 w, 3035 w, 2929 vw, 2859 vw, 1611 vssh, 1558 m, 1503 m, Synthesis of 3∞[YbCl3(bpe)2]·thz (11)
1480 m, 1424 vs, 1380 m, 1318 m, 1227 vs, 1120 w, 1071 s, 1040 m,
1012 vs, 878 w, 861 m, 831 s, 814 s, 730 m, 701 vs, 625 m, 600 m, 537 vs,
YbCl3 (0.3 mmol; 84 mg), bpe (0.6 mmol; 109 mg) and thz (4.5 mmol;
383 mg) were reacted according to the synthesis procedure described above.
The reaction yielded a colourless crystalline. Yield: 139 mg, 63 %. Elemental
analysis: Anal. calcd. for C27H27Cl3YbN5S (Mr = 733.01 gmolꢀ1): C 44.24, H
3.71, N 9.55, S 4.37; Found: C, 44.30; H, 3.73; N, 9.57; S 4.61. IR (KBr):
(3066 w, 3032 w, 2926 vw, 2859 vw, 1612 vssh, 1558 m, 1504 m, 1480 m,
1425 vs, 1380 m, 1318 m, 1227 vs, 1120 m, 1071 vs, 1042 m, 1014 s,
878 vw, 861 m, 830 s, 811 s, 731 s, 625 m, 601 m, 546 s, 522 m, 492 w) cmꢀ
521 w, 491 w) cmꢀ1.
Synthesis of 3∞[GdCl3(bpe)2]·thz (6)
GdCl3 (0.3 mmol; 79 mg), bpe (0.6 mmol; 109 mg) and thz (4.5 mmol;
383 mg) were reacted according to the synthesis procedure described above.
The reaction yielded a colourless crystalline product within excess thz. Yield:
132 mg, 62 %. Elemental analysis: Anal. calcd. for C27H27Cl3GdN5S
(Mr = 717.22 gmolꢀ1): C 45.22, H 3.79, N 9.76, S 4.47; Found: C, 46.10; H,
1
.
3.92; N, 9.62; S 4.43. IR (KBr): (3083 w, 3035 w, 2929 vw, 2858 vw, Synthesis of 3∞[LuCl3(bpe)2]·thz (12)
1612 vssh, 1558 m, 1503 m, 1480 m, 1424 s 1380 w, 1318 m, 1227 vs,
1120 m, 1072 m, 1040 w, 1013 vs, 978 m, 861 vw, 830 vs, 811 s, 728 s,
LuCl3 (0.3 mmol; 84 mg), bpe (0.6 mmol; 109 mg) and thz (4.5 mmol;
383 mg) were reacted according to the synthesis procedure described above
yielding a colourless crystalline product. The obtained product was washed
with 2 x 1 ml dichloromethane. Yield: 98 mg, 44%. Elemental analysis: Anal.
calcd. for C27H27Cl3LuN5S (Mr = 734.94 gmolꢀ1): C 44.13, H 3.70, N 9.53, S
4.36; Found: C, 44.08; H, 3.75; N, 9.27; S 4.15. IR (KBr): (3083 w, 3036 w,
2929 vw, 2859 vw, 1613 vssh, 1557 m, 1503 m, 1480 m, 1424 vs, 1380 m,
1318 m, 1230 vs, 1120 m, 1070 vs, 1041 m, 1015 vs, 878 vw, 861 m, 828 s,
809 s, 731 s, 619 m, 600 m, 537 s, 521 m, 493 w) cmꢀ1.
625 s, 600 w, 537 s, 521 w, 492 m) cmꢀ1.
Synthesis of 3∞[TbCl3(bpe)2]·thz (7)
TbCl3 (0.3 mmol; 80 mg), bpe (0.6 mmol; 109 mg) and thz (4.5 mmol;
383 mg) were reacted according to the synthesis procedure described above
yielding a colourless crystalline product. Yield: 144 mg, 67%. Elemental
analysis: Anal. calcd. for C27H27Cl3TbN5S (Mr = 718.89 gmolꢀ1): C 45.11, H
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DOI: 10.1039/C6DT00152A
Synthesis of 1∞[GdCl3(bpe)(py)2]·(bpe/py) (13)
geometry. XꢀRay radiation (CuꢀKα1; λ = 154.06 pm) was applied,
focused with a Goebel mirror, and CuꢀKα2 radiation was eliminated
by the application of a Ni absorber. Diffraction patterns were
recorded and analysed with the BRUKER AXS DiffracꢀSuite. For
comparison, diffraction data was also collected on a STOE Stadi P
powder diffractometer in DebyeꢀScherrer geometry with Ge(111)ꢀ
monochromatized CuꢀKα radiation (λ = 154.06 pm) using the Winꢀ
XꢀPow software.[41]
GdCl3 (0.5 mmol; 132 mg), bpe (1.5 mmol; 276 mg) and py (1.6 mmol;
126 mg) were reacted according to the synthesis procedure described above
yielding a colourless crystalline product within excess py. Yield: 150 mg,
41%.
Elemental
analysis:
Anal.
calcd
for
C61H55Cl6GdN11
(Mr = 1475.44 gmolꢀ1): C 49.66, H 4.17, N 10.44; Found: C, 48.73; H, 4.19;
N, 10.18. IR (KBr): (3066 w, 3029 w, 2955 vw, 2927 vw, 2860 vw,
1611 vssh, 1600 vssh, 1558 m, 1504 m, 1488 m, 1444 vs, 1432 vssh,
1417 ssh, 1220 vs, 1154 vw, 1068 vs, 1037 m, 1009 vs, 989 m, 871 vw,
831 vs, 752 s, 701 vs, 623 s, 600 vw, 645 s, 623 m, 600 vw, 545 vs, 532 vs,
487 vw, 425 m) cmꢀ1.
Photoluminescence and vibrational spectroscopy
Synthesis of 1∞[ErCl3(bpe)(py)2]·(bpe/py) (14)
Excitation and emission spectra were recorded with a HORIBA
Jobin Yvon Spex Fluorolog 3 spectrometer equipped with a 450 W
Xeꢀlamp, double grated excitation and emission monochromators
and a photo multiplier tube (R928P) at RT, using the FluorEssence
software. Excitation spectra were corrected for the spectral
distribution of the lamp intensity using a photodiode reference
detector. Additionally, both excitation and emission spectra were
corrected for the spectral response of the monochromators and the
detector using correction spectra provided by the manufacturer. All
samples were investigated as solids in spectroscopically pure quartz
cuvettes in front face mode at room temperature and 77 K. NIR
photoluminescence investigations were performed on a Photon
Technology International Quanta Master TM Model QMꢀ2000ꢀ4
spectrometer with an InGaAsꢀNIR detector and a 75 W xenon short
arc lamp (UXLꢀ75XE, Ushio). Additional filters for excitation
(300 nm banbpess, ꢃ20 nm, OD 5, Edmund Optics), as well as an
edge filter for emission (GG 650, Reichmann Optics) were used
together with quartz cuvettes (Suprasil). For the luminescence decay
investigations, an Edinburgh Instruments FLSP920 spectrometer was
used equipped with pulsed picosecond laser (375 nm, 5 mW), with
double grated excitation and emission monochromators and a PMT
ErCl3 (0.5 mmol; 137 mg), bpe (1.5 mmol; 276 mg) and py (1.6 mmol;
126 mg) were reacted according to the synthesis procedure described above.
The reaction yielded a violet crystalline product. Yield: 183 mg, 41%.
Elemental analysis: Anal. calcd for C61H55Cl6Er2N11 (Mr = 1495.46 gmolꢀ1): C
48.99, H 4.11, N 10.30; Found: C, 48.66; H, 4.02; N, 10.05. IR (KBr):
(3066 w, 3030 w, 2955 vw, 2928 vw, 2861 vw, 1612 vssh, 1601 vssh,
1558 m, 1505 m, 1488 m, 1444 vs, 1432 vssh, 1417 ssh, 1221 vs, 1155 w,
1069 s, 1038 s, 1012 vs, 990 m, 872 vw, 831 vs, 753 s, 701 vs, 624 m,
601 vw, 545 s, 533 ssh, 489 vw, 428 vw, 408) cmꢀ1
Single crystal Xꢀray diffraction
Suitable
single
crystals
of
1∞[La2Cl6(bpe)2(thz)6]
(1),
3∞[LnCl3(bpe)2]·thz with Ln = Ce(2), Pr(3), Dy(8), Yb(11) and
1∞[LnCl3(bpe)(py)2]·(bpe/py) with Gd(13) and Er(14) were selected
for Xꢀray diffraction from the crystalline product from motherꢀliquor
mixed with high viscosity perfluorinated ether (99.9%, ABCR). Data
collection for the compounds were carried out on a BRUKER AXS
Smart Apex 1 diffractometer at 168 K equipped with a graphite
monochromator (MoꢀKα radiation; λ = 0.7107 Å) and on
a
BRUKER AXS Apex II diffractometer with Heliosꢀmirror at 100 K
using either the BRUKER AXS Smart Software package or the
BRUKER AXS Apex Suite.[37] All structure solutions were carried
out with direct methods using SHELXS[27] and the crystal structures
(Peltier cooled: ꢀ20 °C), and F900 software.
τꢀDecay time
investigations were carried out in right angle mode and corrected for
the instrument response function. IRꢀspectra were recorded with a
THERMO Nicolet 380 FTꢀIR spectrometer in transmission mode
using OMNIC 32 software. Either, 5 mg of the compounds were
mixed with 300 mg of anhydrous KBr and pressed to transparent
pellets at 5 kbar, or an ATR unit was used.
were refined using SHELXL[27] on the graphical platform XSEED[38]
39]
and OLEX2.[
Integrity of symmetry was checked with the
PLATON program.[40] For all compounds, the nonꢀhydrogen atoms
were refined anisotropically by least square techniques, all hydrogen
atoms with geometrical constraints regarding their positions. For 1,
two thz rings show positional disorder for one CꢀS bond of the rings
and were constrained to mixed C/Sꢀpositions in the refinement.
Further information was deposited at the Cambridge
Crystallographic Data Centre, CCDC, 12 Union Road, Cambridge
CB2 1EZ, UK (eꢀmail: deposit@ccdc.cam.ac.uk) and may be
requested by citing the deposition numbers CCDCꢀ1414453 (1),
1414454 (2), 1414455 (3), 1414456 (8), 1414457 (11), 1023837
(13), and 1023838 (14) or the names of the authors and the literature
citation.
Thermal and elemental analysis
Thermal investigations were carried out by simultaneous
DTA/TG on a Netzsch STA 409 thermal analyzer using the
Proteus Software package on 15ꢀ30 mg of the samples. The
compounds were investigated in an inert gas atmosphere
(50% Ar and 50% N2) and heated from 20 °C to 900 °C with a
heating rate of 10 °C hꢀ1 in a constant gas flow of 20 ml minꢀ1
Ar and 20 ml minꢀ1 N2. Carbon, nitrogen and hydrogen
elemental analysis was performed with a vario micro cube
(Elementar Analysensysteme GmbH).
Powder XꢀRay diffraction
Conclusions
For powder diffraction, all samples were mortared and sealed in
Lindemann glass capillaries (Ø 0.3 mm). Diffraction data was
collected on a BRUKER AXS D8 Discover powder Xꢀray
diffractometer, equipped with LynxꢀEye detector in transmission
A
series of fourteen lanthanide coordination polymers
1∞[La2Cl6(bpe)2(thz)6] (1) 3∞[LnCl3(bpe)2]·thz with Ln = Ce(2)
,
,
10 | J. Name., 2012, 00, 1-3
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ARTICLE
DOI: 10.1039/C6DT00152A
Pr(3), Nd(4), Sm(5), Gd(6), Tb(7), Dy(8), Ho(9), Er(10),
5
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Yb(11) and Lu(12), 1∞[LnCl3(bpe)(py)2]·(bpe/py) with Gd(13) and
Er(14) was obtained from anhydrous halides with the linker 1,2ꢀ
bis(4ꢀpyridyl)ethane and the solvents thiazole or pyridine. The
majority of the compounds exhibit a remarkable amount of
photoluminescence properties ranging from the VIS to the NIR
region that prove the linker bpe as suitable sensitizer for
lanthanide emission. Interesting phenomena apply, such as
excitation dependent emission with a correlating shift of the
chromaticity coordinates, antenna effects by the Dexter and
Förster energy transfer mechanisms, ligand centred as well as
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Acknowledgements
The authors gratefully acknowledge the support of the Deutsche
Forschungsgemeinschaft for the SPPꢀ1362 funding Muꢀ1562/5ꢀ
2 and the Evangelisches Studienwerk Villigst foundation for a
PhD scholarship for P. R. Matthes.
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