A series of three isostructural 1D lanthanide coordination network based on 4,4′,4″-((benzene-1,3,5-triyltris(methylene))tris(oxy))tribenzoate ligand: Synthesis, crystal structure and photophysical properties

Article abstract of DOI:10.1016/j.ica.2019.05.005

Three 1D-coordination networks namely {[Ln(L)(DMF)(H₂O)]·DMF}_n. represented as EuL, GdL and TbL were obtained using the synthetized 4,4′,4″-((benzene-1,3,5-triyltris(methylene))tris(oxy))tribenzoic acid (H₃L) as a ligand a

Full text of DOI:10.1016/j.ica.2019.05.005

Accepted Manuscript
Research paper
A series of three isostructural 1D lanthanide coordination network based on 4,4',
4''-((benzene-1,3,5-triyltris(methylene))tris(oxy))tribenzoate ligand: Synthesis,
crystal structure and photophysical properties
Lanousse Petiote, Filipe M. Cabral, André L.B. Formiga, Italo O. Mazali,
Fernando A. Sigoli
PII:
S0020-1693(19)30102-1
https://doi.org/10.1016/j.ica.2019.05.005
ICA 18906
DOI:
Reference:
Inorganica Chimica Acta
To appear in:
Received Date:
Revised Date:
Accepted Date:
19 January 2019
17 March 2019
2 May 2019
Please cite this article as: L. Petiote, F.M. Cabral, A.L.B. Formiga, I.O. Mazali, F.A. Sigoli, A series of three
isostructural
1D
lanthanide
coordination
network
based
on
4,4',4''-((benzene-1,3,5-
triyltris(methylene))tris(oxy))tribenzoate ligand: Synthesis, crystal structure and photophysical properties,
Inorganica Chimica Acta (2019), doi: https://doi.org/10.1016/j.ica.2019.05.005
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A series of three isostructural 1D lanthanide coordination network based
on 4,4',4''-((benzene-1,3,5-triyltris(methylene))tris(oxy))tribenzoate ligand:
Synthesis, crystal structure and photophysical properties
Lanousse Petiote, Filipe M. Cabral, André L. B. Formiga, Italo O. Mazali, Fernando A.
Sigoli*
Laboratory of Functional Materials, Department of Inorganic Chemistry, Institute of
Chemistry, UNICAMP, Campinas, 13083-970, Brazil
*fsigoli@unicamp.br
Abstract
Three 1D-coordination networks namely {[Ln(L)(DMF)(H2O)]·DMF}n.
represented as EuL, GdL and TbL were obtained using the synthetized 4,4',4''-
((benzene-1,3,5-triyltris(methylene))tris(oxy))tribenzoic acid (H3L) as a ligand
and lanthanide nitrate salts (Ln(NO3)3) (Ln = EuIII, GdIII or TbIII). The reactions
were carried out under solvothermal conditions using a mixture of DMF and
H2O. Single crystal X-ray analyses revealed that all three compounds are
isostructural crystalizing in the triclinic space group P . They show an
1
interesting binodal connected one-dimensional structure, with a static crystal
disorder due to the different spatial orientations of DMF molecules. The triplet
state energy of the H3L ligand obtained from {[Gd(L)(DMF)(H2O)]·DMF}n lies
energetically above the main emitting states of both EuIII and TbIII. The
photophysical properties were investigated in terms of excitation, emission
spectra and emission lifetime at three different temperatures. EuL and TbL
exhibit characteristic emission bands of the EuIII and TbIII with emission lifetimes
of 0.51 ms and 0.90 ms, respectively. The emission lifetime values of EuL and
TbL remain practically constant in the temperature range from 77 to 300 K.
Furthermore, it is mentioned a possible effect of a crystal disorder on the
luminescence profile of EuIII in EuL.
Keywords
Lanthanide coordination network, single crystal, photoluminescence
4,4',4''-((Benzene-1,3,5-triyltris(methylene))tris(oxy))tribenzoic acid.

Introduction
The luminescent properties of lanthanide-based coordination networks
(Ln-CPs) have attracted considerable interest in the supramolecular chemistry
and crystal engineering not only due to their diverse topologies and intriguing
structures but also owing to their unique photophysical properties resulting from
the 4fn electronic configurations of the trivalent ions [1–3]. This class of
compounds combine the intrinsic characteristics of the metal organic framework
[4] with the peculiar photophysical properties of the trivalent lanthanide (LnIII)
ions including reasonable luminescence quantum yield, narrow emission band
and long emission lifetimes [5]. These characteristics make them potential
candidates for applications in many fields such as: lighting devices [6], optical
communications, chemical sensing [7], photonics and biomedical devices [8].
Furthermore, lanthanide coordination networks have been investigated in gas
storage and separation [9], proton conductivity [10], catalysis [11] and molecular
magnetism [12] exploring magneto-luminescent bimodal systems [13]. As some
examples of the latter application, Huang et al. reported weak TbIII–TbIII
ferromagnetic interactions in [Tb2(tdc)3(H2O)4] (tdc
=
thiophene-2,5-
dicarboxylate di-anions) and TbIII typical luminescence[14]. Ferromagnetic
coupling between trivalent lanthanides centers in [Er(pza)(OH)(H2O)] and
[Dy(cit)(H2O)n] (cit = citrate tri-anions) was reported by Weng and Li,
respectively [14,15]. More recently, Kumar and co-authors reported interesting
magnetic properties owing from DyIII-DyIII and ErIII-ErIII interactions in two 3D
coordination polymers constructed from the ligands 3,5-pyridinedicarboxylic and
adipic acids [16]. Using the thiophene-2,5-dicarboxylate as main building ligand.
Mohd Yawer and co-authors also reported antiferromagnetic interactions
between lanthanide ions in 3D metal organic frameworks [17]. Trivalent
lanthanide ions form complexes with variable coordination numbers and
geometries that may influence their photophysical properties [18]. Among
trivalent lanthanides, EuIII and TbIII ions are the most used as optical centers in
the visible range due their pure-color emissions owing from the 5D0→7FJ (J = 0-
5
4) and D4→7FJ (J = 6-3) electronic transitions [19], respectively. Additionally,
lanthanide based networks containing TbIII and EuIII are suitable for

development of ratiometric thermal optical probes for luminescence based
thermometry [20] and chemical sensing [21]. Using the Eu-CP
[Eu(pdc)1.5(DMF)]·(DMF)0.5(H2O)0.5 (pdc = pyridine-3,5-dicarboxylate), Chen and
co-authors reported the detection of CuII in a DMF solution. The weak binding of
the pyridyl nitrogen to the d-metal ion reduces the energy transfer efficiency
from the pdc ligand to EuIII leading to its luminescence quenching [3]. The same
group pioneered the use of lanthanide coordination networks for sensing in
biological systems [22] using the Ln-CP Eu2(FMA)2(OX)(H2O)4 where FMA =
fumarate and OX = oxalate [23]. Subsequently, many works were reported
about optical sensing. Luo and co-authors. exploited the EuIII-doped
coordination polymer [NH4]0.7[Eu][ZnL][Cl]1.7(H2O)8 (L = 1,2,4,5-benzenetetra-
carboxylate) for CuII sensing in aqueous solution [24]. Song and co-authors
reported
the
EuIII-CP
based
on
the
tetrakis[4-
(carboxyphenyl)oxamethyl]methane acid tetrakis[4-(carboxy phenyl) oxa
methyl]methane acid) with potential for FeIII sensing [25].
Due to the Laporte forbidden nature of the f-f electronic transitions, the
trivalent lanthanides have very small molar absorptivity, less than 10 L-1 mol-1
cm-1 [26], resulting in weak photoluminescence upon direct excitation [19]. To
overcome this limitation, the organic ligand takes a decisive role. The Ln-CP
building normally incorporate strong absorbing groups which will sensitize, via
the antennae effect [27], the trivalent lanthanide luminescence [21]. As it is well
known, organic ligand with suitable singlet and triplet energies may significantly
enhance lanthanide trivalent luminescence [28]. In specific cases of EuIII and
TbIII ions, the organic ligand must have an appropriate energy of the triplet state
in the range of 22000 to 27000 cm-1 to match the main accepting energy levels
of TbIII (5D4: 20500 cm-1) and EuIII (5D1:19030 cm-1) [5,29]. Considering the
oxophilicity of the trivalent lanthanide ions [30], one strategy for CP building
consist in using polydentate aromatic carboxylic acids which can strongly bound
to the metal ion in a versatile coordination modes [31,32], offering several types
of coordination [29] polyhedral geometries, and at the same time act as
chromophoric moieties for luminescence sensitization [33]. In this work the
ligand,
4,4',4''-((Benzene-1,3,5-triyltris(methylene))tris-(oxy))tribenzoic
acid
(H3L) (ESI Scheme S1) was synthetized and subsequently used to prepare
three Ln-CPs (Ln = Eu, Gd, Tb). The H3L ligand contains three carboxylate and

four phenyl groups being promising for versatile coordination mode and
sensitizing the luminescence of both EuIII and TbIII ions. The three compounds
namely EuL, GdL and TbL were obtained via solvothermal approach using an
DMF / water mixing solvents and they were structurally characterized by single
crystal and powder X-ray diffractions, TG, FT-IR, UV-Vis spectroscopy and their
photophysical properties were investigated in terms of photoluminescence
spectra and emission lifetimes.
2. Experimental section
2.1 Materials and methods.
The ligand 4,4',4''-((benzene-1,3,5-triyltris(methylene))tris(oxy))tribenzoic acid
was prepared by a one pot synthesis as further described. Aqueous solutions
of lanthanide nitrate salts (pH ~6) were prepared dissolving lanthanide oxide in
concentrated nitric acid. All other reagents and solvents were purchased and
used as received without further purification. The solvothermal reactions were
performed in a 40 mL Teflon-lined stainless-steel autoclave under autogenous
pressure. 1H nuclear magnetic resonance (1H-NMR) spectrum was collected on
a Brucker AVANCE 400 spectrometer. Single-crystal X-ray diffraction data were
collected on a Bruker Apex Duo diffractometer equipped with a graphite-
monochromatized Mo K radiation ( = 0.71073 Å) at 150 K. All structures
were solved and refined by direct methods with full-matrix least-squares
refinements based on F2 using SHELXS-97and SHELXL-97program packages
[34]. All non-hydrogen atoms were refined anisotropically and hydrogen atoms
were placed in geometrically calculated positions. The R1 and wR2 values are
2
2
2
2
2
2
∑
∑
∑ ∑
푤(퐹 ‒ 퐹 ) / 푤(퐹 )
0 푐 0
|
|
|
|
|
|
and
|
|
defined as
,
푅1 = ( 퐹0 ‒ 퐹푐 / 퐹0 )
푤푅2 =
[
]
[
]
{
}
respectively. CCDC 1875767 (TbL), CCDC 1875768 (EuL) and CCDC 1875769
(GdL) contain the crystallographic data in CIF format. Calculated P-XRD were
obtained by using the Mercury program [35]. To determine the crystalline phase
of the samples obtained as a microcrystalline powder together with mono-
crystals of the Ln-CPs, P-XRD measurements were performed on a Bruker D8
ADVANCE X-ray powder diffractometer using a Cu-α radiation (1.5418 Å) at
room temperature with 2 ranging from 5° to 50°. Thermogravimetric analyses
were conducted under synthetic air on a Universal V2.6 DTA system by heating

up from 30 to 900 °C with a heating rate of 10 °C min-1. FT-IR spectra were
recorded using an Agilent FT-IR spectrometer (CARY 630) in ATR mode using
a diamond crystal in the range of 4000–400 cm−1. Elemental analyses (C, H, N)
were determined using an elemental analyzer Perkin Elmer (CHN 2400). The
photoluminescence data were obtained on a Fluorolog-3 spectrofluorometer
(Horiba FL3-22-iHR320), with double-gratings (1200 g mm−1, 330 nm blaze) in
the excitation monochromator and double-gratings (1200 g mm−1, 500 nm
blaze) in the emission monochromator. An ozone-free xenon lamp of 450 W
(Ushio) was used as the radiation source. The excitation spectra were corrected
in real time according to the lamp intensity and the optical system of the
excitation monochromator using a silicon diode as reference. The emission
spectra were recorded using the front face mode at 22.51°. All of them were
corrected according to the optical system of the emission monochromator and
the
photomultiplier
response
(Hamamatsu
R928P).
Time-resolved
phosphorescence emission spectra of the analogous GdIII compound (GdL)
were obtained at ∼77 K using a time-correlated single photon counting
(TCSPC) system, in order to get only emission bands from triplet levels of the
ligand. The emission decay curves were obtained with a flash 150 W xenon
lamp using the same TCSPC accessory.
2.2 Synthesis of H3L
A mixture of 1,3,5-tris(bromomethyl)benzene (1.5 g; 4.2 mmol), ethyl 4-
hydroxybenzoate (2.1 g, 12.6 mmol), sodium carbonate (2.0 g, 18.9 mmol) in
dimethylformamide (DMF) (20 mL) was carried out in a single neck round
bottom flask and magnetically stirred at 80 °C for 72 h. After cooling to room
temperature, the solvent was removed at 60 °C by vacuum assisted rotary
evaporation to obtain a white powder that was subsequently suspended in
acetone (20 mL) and combined with NaOH (1.0 g) dissolved in water (20 mL).
This mixture was stirred at 80 °C for 24 h. After cooling to room temperature,
the acetone fraction was eliminated by vacuum assisted evaporation at 50 °C
and the resulting aqueous solution was acidified (pH~1) by addition
concentrated hydrochloric acid dropwise resulting in a yellow gelatinous
precipitate which was collected by vacuum filtration and washed with water until
pH=4-5. The crystallized powder was obtained by dissolving the product in

acetone and using water as poor solvent. After drying, 1.85 g (yield = 83%) of
1
the protonated ligand was isolated as a yellow powder. H-NMR (400 MHz,
DMSO):   ppm = 5.23 (s, 6 H, CH2), 7.13 (d, JHH = 8.9 Hz, 6 H, Ar-H), 7.55 (s,
3 H, Ar-H), 7.90 (d, JHH = 8.9 Hz, 6 H, Ar-H), 12.66 (s, 3 H, COOH). Elemental
analysis (%) - found (calculated) for C30H24O9 C = 68.10 (68.18); H = 4.60
(4.58).
2.3 Synthesis of the coordination networks
Three syntheses were carried out following a solvothermal method [36]
as follow: 60.0 mg (0.14 mmol) of 4,4',4''-((benzene-1,3,5-triyltris(methylene))-
tris(oxy))tribenzoic acid (H3L) was dissolved in 10 mL of DMF in the 40 mL
Teflon-lined stainless-steel vessel. Then 100 µL of concentrated HCl and 0.14
mol of Ln(NO3)3 in 2 mL of water were added sequentially. After sealed, the
reaction mixture was heated at 120°C for 72 hours. After cooling down to room
temperature, the resulting yellow crystals were washed using DMF and water
and dried in reduced pressure at 50°C yielding ca. 50 % based on the
lanthanide ions. {[Eu2(L)2(DMF)2(H2O)2].DMF}n. (EuL). Yield 54 %. Elemental
analysis (%) - found (calcd) for Eu2C69H67N3O23 (MW = 1610.22 g.mol-1), C =
51.10 (51.47); H = 4.23 (4.19); N = 2.65 (2.61). {[Gd2(L)2(DMF)2(H2O)2].DMF}n.
(GdL). Yield 55 %. Elemental analysis (%)- found (calcd) for Gd2C69H67N3O23
(MW = 1620.79 g mol-1), C = 51.10 (51.13); H = 4.27 (4.17); N = 2.61 (2.59).
{[Tb2(L)2(DMF)2(H2O)2].DMF}n (TbL) Yield 49 %. Elemental analysis (%)-found
(calcd) for Tb2C69H67N3O23 (MW = 1624.14 g.mol-1), C = 50.89 (51.03); H = 4.20
(4.16); N = 2.62 (2.59).
3. Results and discussion
3.1 Synthesis and characterization of the ligand 4,4',4''-((benzene-1,3,5-
triyltris(methylene))-tris(oxy))tribenzoic acid (H3L)
The ligand 4,4',4''-((benzene-1,3,5-triyltris(methylene))tris(oxy))tribenzoic
acid (H3L) was prepared using a one pot synthesis based on a modified
reported procedure [37]. The scheme of the synthesis is shown on electronic
supporting information (ESI Scheme S2). Firstly, the tri-ester (ESI Scheme S2 -
III) was obtained by reaction of 1,3,5- tris(bromomethyl)benzene (ESI Scheme
S2 - II) with ethyl 4-hydroxybenzoate (ESI Scheme S2 - I) in the presence of

sodium carbonate DMF for 72 hours. After the reaction time, the solvent was
removed, and the white crude precipitate was dissolved in the mixture of
acetone and aqueous solution of NaOH to obtain the ligand as his sodium salt
(ESI Scheme S2 - IV) after 24 hours. It is noteworthy that the use of the mixture
of solvents was important to guarantee that the reaction was carried out in the
liquid state, once the ester is not water-soluble. After elimination of the acetone,
concentrated chloride acid was added to precipitate the acid (ESI Scheme S2 -
V), which was isolated, washed and dried to yield 83 % of the expected mass.
As can be seen in Fig. 1, single crystals were obtained on slow water
diffusion into a diluted solution of the ligand in DMF. As reported by Sebastian
et. al. [37], the as-synthesized ligand crystalizes in the triclinic space
with a
P1
asymmetric unit consisting in one molecule (Fig. 1). Its molecular geometry
differs completely from the trigonal one . Two of the molecular branches are
arranged in a pincer-like fashion stabilized by an intra-molecular π-π interaction
between two aromatic rings that are 4.013 Å apart. The third molecular arm is
oriented in the opposite direction conferring an elongated conformation of the
molecule in the crystal. Crystallographic data, experimental parameters and
selected details of the refinements are summarized in Table 1.
Fig. 1: Matt illustration of the molecular structure of the ligand 4,4',4''-((Benzene-1,3,5-
triyltris(methylene))tris(oxy))tribenzoic Acid (H3L). The dark dots and the dotted-line between
aromatic rings represent the centroids and distance between them, respectively.
The 1H-NMR spectrum (Figure S1) suggests that the ligand was obtained
in high purity corroborating the elemental analysis result. Its UV-Vis electronic
spectrum in acetonitrile solution (Figure S4) shows two absorption bands
centered at 253 nm and at ca. 200 nm which may be assigned to (π* ← n)
involving non-bonding electron pairs of the oxygen atoms and (π* ← π)

electronic transitions in the aromatic rings, respectively. Using the single crystal
molecular structure, a TD-DFT calculation was performed to estimate the first
excited state of the free ligand. Firstly, the hydrogen atoms were optimized by
DFT calculations using PBE0 [38,39] functional and the basis def2-TZVP
[40,41] in the Orca 4.0.1 [42] software. Using the optimized structure, the TD-
DFT calculations were performed to estimate the energy of excited states. As
can be seen in Figure S4, the calculated absorption spectrum of the free ligand
agrees with the experimental spectrum obtained experimentally in a dilute
acetonitrile solution.
3.2 Syntheses and characterization of the coordination networks.
Solvothermal conditions have been proven to be a useful methodology to
obtain crystalline coordination networks. As the ligand is soluble in DMF, the
chloridric acid was used to reduce the coordination speed and consequently
potentialize growth of high-quality single crystals [43]. As the acid slows down
the deprotonation of the carboxylate group and consequently, the binding of the
linkers to the metal centers, it promotes growth of larger crystals and prevents
formation of amorphous and polycrystalline phases, which may be formed if the
reaction is allowed to proceed with no acid added [26]. X-ray single crystal
structure analyses reveal that the three synthesized compounds EuL, GdL, TbL
are isostructural (see Table1) and simulated powder X-ray diffraction pattern
(Figure S8) crystallizing in the triclinic space group crystal system P and
1
feature an extended isolated 1D structure. Thus, the representative structure
description and discussion will be restricted to the EuIII compound EuL. As can
be seen in Fig. 2, the asymmetric unit of EuL contains one EuIII ion, one totally
deprotonated ligand L, one DMF and one water molecule coordinated to the
metal center and one lattice DMF molecule. Each europium ion is eight-
coordinated and binds two oxygen atoms from one DMF and one H2O molecule
(average bond length of 2.415 and 3.093 Ǻ, respectively) and carboxylate
oxygen atoms belonging to three different L3- tri-anions that coordinate to the
metal ion in the bridging and the chelating bis-dentate modes (average Eu-O
bond length of 2.292 and 2.461 Ǻ, respectively). The coordination geometry of
the EuIII ion (Fig. 3) can be viewed as a distorted square antiprism, where the
basal planes is formed by O4, O5, O6, O10, and O7, O8, O9 O11 atoms,

respectively, leading to a C1 point group, therefore a low-symmetry coordination
sphere without inversion center around the metal center. Each ligand L3- binds
to three metal ions through two chelating and one bidentate carboxylate groups
(Figure S2). Two non-centrosymmetric Eu atoms bridged trough the same
carboxylate group generate a binuclear Eu2(µ2-COO)2) unit where the distance
between the metal ions is 4.816 Ǻ (Fig. 4). The binuclear units are linked along
the b axis in the infinite 1D chains (Fig. 5), which are further packed in a 3D
network (Fig. 6). Each dinuclear unit is surrounded by four L3- ligands (Figure
S3) and each ligand connects to two binuclear units, the 1D chain of EuL is
defined as a 2,4-connected network.
Fig. 3: The coordination geometries of EuIII
ions in EuL resulting in a C1 site for the
central ion.
Fig. 2: Matt drawing of the asymmetric unit of
EuL.
Fig. 4: The connection mode of EuIII ions in a binuclear unit.
Fig. 5: View of the 1D chain as the infinite secondary building units (SBUs) along the
crystallographic b-axis obtained from binuclear units linked through carboxylate group. H atoms
and free solvent molecules were omitted for clarity.

Fig. 6: View of the 3D supramolecular structure of the coordination network EuL along the
crystallographic b-axis.
Table 1: Crystal data of the free ligand (H3L) and the lanthanides-based coordination networks
Compounds
Emp. Form.
MW
H3L
C30H24O9
528.49
150
TbL
Tb2C69H67N3O23
1624.09
150
GdL
Gd2C69H67N3O23
1620,79
150
EuL
Eu2C69H67N3O23
1610.17
150
T/K
Ǻ
Cu K
Triclinic
P1
Mo K
Triclinic
P1
Mo K
Triclinic
P1
Mo K
Triclinic
P1
Crystal syst.
Space group
a/ Å
6.3171(5)
10.6482(7)
18.1883 (1)
86.360 (3)
88.548 (3)
79.326 (3)
1199.74 (15)
2
8.5108 (5)
14.2208 (9)
14.3990 (9)
98.265 (2)
106.718 (1)
96.164 (1)
1631.26 (17)
1
8.5212 (12)
14.186 (2)
14.434 (2)
98.010 (3)
106.609 (3)
96.382 (4)
1634.6 (4)
1
8.5361 (6)
14.2116(10)
14.4375(10)
98.093 (1)
106.628 (1)
96.329 (1)
1640.4 (2)
1
b/ Å
c/ Å



V/ Å3
Z
Z’
1
0.5
0.5
0.5
D/Mgm-3
µ/mm−1
F(000)
 range/°
a R1/%
b wR2/%
Rint/%
GooF
1.463
0.91
552
4.2-68.8
3.19
8.60
1.51
1.050
1.653
2.23
816
2.7–28.2
3.08
7.08
2.95
1.054
1.646
2.10
814
2.5–28.2
2.98
6.70
5.17
1.035
1.630
1.98
812
2.7–30.4
1.70
4.61
1.51
1.084
2
}
2
2
2
2
2
a 푅1 = ( 퐹0 ‒ 퐹푐 / 퐹0 ) b 푤푅2 =
∑
∑
∑
{
∑
푤(퐹 ‒ 퐹 ) / 푤(퐹 )
0 푐 0
|
|
|
|
|
|
|
|
[
]
[
]
The Infrared spectra of the three compounds (Figure S6) exhibit a similar
profile with a broad vibrational band in the range of 3000–3500 cm-1 assigned
to the vibrations of the coordinated water molecules and the C-H stretching
modes of the aromatic ring [44,45]. The weak bands at around 2930 and 2890

cm-1 correspond to the symmetric and asymmetric stretching modes of the -
CH2- groups. The red shift from 1674 to 1650 cm-1 of the carbonyl absorption
band, comparing to the protonated H3L, indicates a total deprotonation of the
ligand in the CPs, thus in agreement with the single crystal data. The vibration
bands of the carboxylate group occur at around 1603 cm-1 and at 1407 cm-1
attributed to the asymmetric stretching and symmetric stretching, respectively.
In order to check the crystalline phase of the microcrystalline compounds
obtained together with mono-crystals, the X-ray powder diffraction (P-XRD)
patterns were recorded at room temperature and compared to the simulated
ones [46]. As shown in Figure S8 and Figure S9, the peaks positions simulated
for EuL and the experimental patterns are in agreement with each other
indicating they are isostructural. The difference in reflection intensities between
the simulated and experimental patterns is probably due to the variation in
preferred orientation of the powder samples during the collection of the
experimental P-XRD data.
The thermal stabilities of the compounds were evaluated in the
temperature range of 30 to 800°C in a synthetic air atmosphere at a heating
rate of 10 °C/min. The thermograms shown in Figure S7 (b-d) exhibit a very
similar profile with three weight loss steps beginning at ca. 85, 205 and 325 °C
that can be assigned to the loss of lattice solvent molecules, the coordinated
ones and the decomposition of the organic part, respectively.
3.3 Electronic properties and photoluminescence study
The absorption spectra recorded in solid state (Figure S4) of the free
ligand exhibits an intense band centralized at 248 nm which is bathochromically
shifted after coordination to the metal center indicating an extended conjugation
probably caused by the metal-perturbed π*–π transition of the ligand-centered
[47].
In lanthanide complexes, the indirect excitation (called sensitization or
antennae effect) of the active ion occurs from an energy migration in terms of
the ligand centered absorption followed, mainly, by a singlet to triplet
3
intersystem crossing (1S* → T*) and finally the triplet to lanthanide energy
transfer (3T* → LnIII). The efficiency of this complex process involves numerous

rate constants and is highly dependent of the energy gap between the lowest
ligand triplet state and the LnIII emitting level [48]. In the cases of EuIII and TbIII,
respectively, the triplet ligand state should be localized sufficiently above the
5
5D0 (17290 cm-1) and D4 (20500 cm-1) levels, respectively, allowing efficient
energy transfer and prevent quenching via the back-energy transfer [29].
Therefore, it becomes an important issue to determine the triplet state energy of
the ligand, which can be calculated by referring to the lower wavelength
emission edge of the corresponding phosphorescence spectrum obtained at low
temperature of the GdIII complex [49]. When coordinated to the GdIII, the ligand
phosphorescence is intensified due to the heavy paramagnetic ion that
enhances the intersystem crossing (ISC) from the singlet (1S) to the triplet (1T)
state because of mixing of the triplet and singlet states assigned to the
paramagnetic effect [50,51] and the absence of energy transfer from the ligand
to GdIII ion which has the first excited level (6P7/2) at 32 200 cm-1 [52].
Therefore, photoluminescence of GdIII complexes involving ligands with
aromatic rings is due to electronic transitions between perturbated ligand
localized states in the conformation acquired in the crystal structure of this
family of compounds [53,54]. Fig. 7 shows the photoluminescence spectra of
GdL and of the free ligand for comparison, both upon excitation at 283 nm. The
emission spectrum of the free ligand shows the phosphorescence represented
by three vibronic bands at 405, 440 and 470 nm but is dominated by the
1
fluorescence band with the maximum at 338 nm (29585 cm-1) owing to the S
→1S0 electronic transitions. The assignments of these bands were based on the
emission spectrum of the equivalent LaIII complex shown in Fig. 8. With a delay
of 0.05 ms, the two bands at 300 and 354 nm disappear completely indicating
that they are owing to allowed singlet to singlet electronic transitions. The more
intense phosphorescence band in comparison to fluorescence one can be
attributed to the heavy atom effect [55]. After complexation to the GdIII, the
fluorescence band is completed attenuated and the vibronic bands are not well
defined probably due to the paramagnetic effect that improve the internal
conversion and the intersystem crossing [56].

3
T1
T = 77 K
H3L: ex = 283 nm
GdL: ex = 283 nm
non-crystalline LaL
T = 77 K
fd = 0 ms
fd = 0.05 ms
403 nm
338 nm
416 nm
300 nm
1
s2
354 nm
1
s1
3T
300
320
340
360
380
400
420
440
460
480
500
520
300
350
400
450
500
550
600
650
700
Wavelength (nm)
Wavelength (nm)
Fig. 8: Stead-state (fd=0ms) (black) and
time-resolved (fd=0.05ms) (red) emission of
LaL upon excitation at 283 nm at 77 K.
Fig. 7: Emission spectra of the free ligand
(Dark) and the gadolinium compound (GdL)
(red) at 77 K upon excitation at 283 nm.
By assuming the shortest phosphorescence band wavelength to be the
0-0 phonon transition (Fig. 7) [57], the triplet state energy was estimated to
26316 cm-1, therefore 9052 and 5816 cm-1 above the emitting states of EuIII
(5D0) and TbIII (5D4), respectively. These results suggest that the ligand may
sensitize luminescence of both active ions but is more suitable for TbIII.
According to the general antennae effect principle, the ligand to metal energy
transfer efficiency depends directly on the energy difference between the
lowest triplet state level energy of ligands and the emitting level of optically
active ion [58].
The solid-state photophysical properties of the compounds EuL and TbL
were investigated at three different temperatures. In all cases, the excitation
spectra (Fig. 9 and Fig. 15) obtained by monitoring the strongest intensity
emission bands, exhibit a broad excitation band with the maximum around 290
nm, which may be attributed to the π*←π transitions of the benzene rings in the
L3- ligand [45] demonstrating that energy transfer occurs from the ligand to the
EuIII and TbIII ions. The excitation spectrum of the EuL coordination network
(Fig. 9) shows a series of narrow lines in the longer wavelength region (350 nm
7
to 600 nm) owing to intra-configurational electronic transitions between F0 and
7
5
5L6 electronic states at 393 nm and transitions between F0,1 and D2,1 levels.
The detection of these intra-configurational bands indicates the poor efficiency
of the
energy transfer from ligand to EuIII. Unexpectedly, the intra-
configurational transition becomes more intense at room temperature regarding
to the ligand excitation band. This result may suggest an increase of possible

deactivation mechanisms of the singlet state at the expense of the intersystem
crossing process.
7F0
5L6
7F2


ex = 290 nm
ex = 393 nm

em = 616 nm
77 K
EuL
EuL
T = 77 K
110 K
300 K
5D0
5D2
7F0
7F4
5D1
7F0
7F1
7F0
7F3
560
580
600
620
640
660
680
700
720
250
300
350
400
450
500
550
600
Wavelength (nm)
wavelength (nm)
Fig. 10: Normalized emission spectra of EuL
obtained at 77 K upon excitation at 290 nm
(dark) and at 393 nm (red).
Fig. 9: Normalized excitation spectra
obtained at 77 K (red), 110 K (green) and
300 K (blue) of EuL monitoring at 616 nm.
7F2
7F2

ex = 290 nm
ex = 393 nm

ex = 290 nm
ex = 393 nm
T = 110 K


T = 300 K
5D0
5D0
7F1
7F1
7F4
7F4
7F0
580
7F0
7F3
7F3
560
580
600
620
640
660
680
700
720
560
600
620
640
660
680
700
720
Wavelength (nm)
Wavelength (nm)
Fig. 11: Normalized emission spectra of EuL Fig. 12: Normalized emission spectra of EuL
obtained at 110 K upon excitation at 290 nm obtained at 300 K upon excitation at 290 nm
(dark) and at 393 nm (red).
(dark) and at 393 nm (red).
ex = 290 nm
ex = 393 nm
EuL
T = 77 K
EuL
l
ex = 290 nm
lex = 393 nm
T = 77 K
5D0
7F2
5D0
7F1
5D0
7F2
586
588
590
592
594
596
605
610
615
620
625
5D0
7F4
5D0
7F1
-1
FWHM = 16.8 cm
FWHM = 23.9 cm
5D0
7F0
5D0
7F3
-1
577
578
579
580
581
560
580
600
620
640
660
680
700
720
Wavelength (nm)
Wavelength (nm)
5
7
Fig. 14: High resolution D0 → F0
Fig. 13: Emission spectra of EuL at 77 upon
excitation at 290 nm and 393 nm. The Insets
show the 5D0→F1 and 5D0→F2 regions
magnified.
emission band of the EuL coordination
network obtained at 77 K upon excitation at
290 and 393 nm.

TbL
TbL
7F5
77 K
T = 77K
300 K
110 K
T = 300 K
em = 543 nm


ex = 280 nm
5D4
7F6
7F4
7F3
260 280 300 320 340 360 380 400 420 440 460 480 500
Wavelength (nm)
480
500
520
540
560
580
600
620
640
Wavelength (nm)
Fig. 15: Excitation spectra obtained at 77 K Fig. 16: Emission spectra obtained at 77 K
(dark) and at 300 K (red) of TbL monitoring at (dark), 110 K (green) and 300 K (red) of TbL
543 nm, normalized with respect to the upon excitation at 280 nm.
higher intensity band.
The emission spectra were recorded for all the compounds under ligand
excitation and under intra-configurational excitation at 393 nm for EuL (Fig. 10 -
Fig. 12 and Fig. 16). EuL and TbL emission spectra show typical EuIII red and
TbIII green emissions as narrow and well separated emission bands. For EuL,
the well-resolved emission bands are centered at ∼579, 592, 616, 651, and 700
5
nm, corresponding to electronic transitions from the EuIII centered D0 excited
state to the 7FJ (J = 0−4) multiplet ground state with the hypersensitive 5D0→7F2
transition band dominating the spectra, thus in agreement with the fact that the
EuIII is located in low-symmetry site without inversion center. The intensity ratio
of 8.32 between the 5D0→7F2 forced electric dipole and symmetry sensitive and
5
the D0→7F1 magnetic dipole allowed transitions is in good agreement with the
low symmetry around the EuIII [21,59]. When excited in the intra-configurational
5
5
band at 393 nm, the emission bands attributed to D0→7F1 and D0→7F2
transition are splited in four and seven Stark components, respectively (Fig.
13). The resolved emission band attributed to 5D0→7F0 transition remains as an
asymmetric and relatively broad one-component band (Fig. 14). A different
profile of the emission band attributed to 5D0→7F4 transition is observed when it
is compared to the emission spectrum obtained upon excitation at 290 nm.
These results suggest an inhomogeneous coordination environment of EuIII
ions, which may be assigned to the crystal disorder owing from the two different
spatial orientations of the coordinated DMF molecules. Such special orientation
probably leads to slight differences around the EuIII sites probably due to small
distortions and variations in the Eu-O bond lengths.

Considering the TbL emission spectra, the bands are centered at 489,
5
7
542, 586 and 622 nm assigned to the transitions between D4 and FJ (J= 6, 5,
4, 3) states. The emission lifetimes values were determined, at three different
temperatures (77 K, 110 K and 300 K), from the luminescent decay profiles of
7
EuL and TbL by monitoring the most intense emission lines within the 5D0→ F2
5
7
and D4→ F5 transitions bands, respectively (Fig. 17). The values, depicted in
Table 2, were obtained by fitting with mono-exponential functions, indicating
that even with the slight differences in symmetry around the ions due to the
crystal disorder, in average the emitting states contribute with just one emission
5
7
lifetime value. This result is corroborated with the D0→ F0 band shape
obtained at 77K (Fig.14). [27] and it was also observed by Monteiro and co-
authors. [60].
EuL
EuL
77 K
110 K
300K
77K

ex   nm
110 K
300 K
em = 616 nm
ex   nm
em = 616 nm
0
1
2
3
4
5
6
0
1
2
3
4
5
6
time / ms
time / ms
time / ms
0
1
2
3
4
5
6
0
1
2
3
4
5
6
time / ms
77 K
TbL
110 K
293 K

ex = 280 nm
em = 543 nm

0
1
2
3
4
5
6
7
8
9
10
11
time (ms)
0
1
2
3
4
5
6
7
8
9
10
11
time (ms)
Fig. 17: Experimental luminescence decay curves obtained at 77, 110 and 300 K of the EuL and
TbL monitored at 616 nm and 543 nm, respectively, upon excitation at 290 nm and at 393 nm
for EuL and 280 nm for TbL.
The observed emission lifetime of EuL and TbL (Fig. 17 and Table 2) obtained
in three different temperatures upon excitation in the broad band or at 393 nm

(EuL) remain practically invariable in the temperature range of 77-300 K,
indicating a rigid stacking of the crystal lattice.
Table 2: Observed luminescence lifetimes at 77, 110, and 300 K of the coordination networks
upon excitation in the ligand for both EuL and TbL and also at 393 for EuL monitoring the
emissions at 616 and 543 nm for EuL and TbL, respectively.
77 K
110 K
300 K
exnm em/nm
/ms
ms
ms
EuL
EuL
TbL
290
393
280
616
616
543
0.507 ± 0.001
0.560 ± 0.004
0.888 ± 0.004
0.505 ± 0.002
0.526 ± 0.001
0.907 ± 0.001
0.514 ± 0.001
0.530 ± 0.001
0.928 ± 0.008
These slight variations of the emission lifetime values as a function of
temperature is probably related to the fact that the efficiency of the ligand to
metal energy transfer process is improved as a temperature increases as
shown in Figure S11 which shows the emission spectra of GdL at 77 K and 300
K excited in the ligand band. When collected at 77 K, the spectrum shows only
the broad band assigned to the ligand owing from the radiative decay of the
triplet state, while, at 300 K, the ligand emission is completely attenuated, and
narrow emission bands attributed to both TbIII and EuIII were observed due to
the presence of EuIII and TbIII as impurities in the compound. As can be seen in
Table 2, for the coordination network EuL, the lifetime values obtained exciting
at 393 nm are slightly higher than obtained upon excitation in the ligand broad
band at 290 nm. The same effect which may be an indication of an increase in
5
7
the radiative decay rate upon L6 ← F0 intra-configurational excitation was
observed for a Europium coordination framework based on the terephthalic acid
[61].
During the last years, many 1D lanthanide coordination networks were
reported in the literature. Sheng and co-authors published a series of 1D
coordination polymers containing the ions SmIII, EuIII, TbIII, and DyIII based on
the 2,4,6-pyridinetricarboxylic acid ligand [62]. Excited at 305nm, all compounds
exhibited interesting metal centered luminescence. Using the Schiff-base ligand
of N-salicylidenesalicylhydrazide, Feng and co-authors reported a series of Ln-
CPs based on the ions TbIII, DyIII, HoIII and ErIII with interesting magnetic
properties [63]. Recently, Ana and co-authors published a set of eight isolated
1D chains lanthanide networks base on the ligand 3-((anthraquinone-1-

yl)amino)propanoate (aapc) [54]. However, characteristic emission of the EuIII
and TbIII, upon excitation in the ligand band, were observed only at low
temperature (10 K) even though the lower triplet state level of the ligand aapc
(25000 cm-1) comparing to the ligand (H3L) used in this work (26316 cm-1). In
all cases, the compounds showed single molecule magnet behavior making the
isolated 1D chain lanthanide coordination network promising for potential
applications in quantum-computing devices and molecular spintronics [64]. It
worth mention that, despite the large number of Ln-CPs reported until now, to
the best of our knowledge, the present work is the first example about the effect
of a crystal disorder on the photophysical properties of the trivalent europium
ion.
4. Conclusions
In
summary,
the
three
dentate
4,4',4''-((Benzene-1,3,5-
triyltris(methylene))tris(oxy))tribenzoic acid ligand has been successfully
synthesized and used to prepare three new coordination networks containing
the EuIII, TbIII and GdIII ions, under solvothermal conditions. Single crystal X-ray
and the P-XRD data confirm that the three compounds are isomorphic 1D chain
structure. The photoluminescence investigations reveal that both EuIII and TbIII
compounds display strong emission bands with lifetimes that slight variates as a
temperature function despite presence of solvent molecules in the first
coordination sphere of the central ions. Interestingly for the first time, to our
knowledge, it is reported a possible effect of crystal disorder of coordination
network on the emission profile of the trivalent europium ion.
Acknowledgements
LP is indebted to CNPq (Process: 141691/2015-8) for the Ph.D.
fellowship. IOM, ALBF and FAS are indebted to INOMAT (FAPESP:
2014/50906-9), CNPq, CAPES and FAPESP (grant: 2013/22127-2) for financial
support. All authors would like to thank the Multiuser Laboratory of Advanced
Optical Spectroscopy - Institute of Chemistry-UNICAMP
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Highlights
Photophysics of EuIII and TbIII 1D-coordination networks
Static crystal disorder due to the different spatial orientations of DMF molecules
Influence of DMF oriemtations on EuIII chemical environments and emission
Stark sublevels
EuIII emission lifetime invariability as function of temperature