Microwave-assisted synthesis of ternary lanthanide(2-thenoyltrifluoroacetone)3(triphenylphosphine oxide)2 complexes

Article abstract of DOI:10.1016/j.ica.2017.04.021

We report here the fast synthesis by microwave assisted technique of four ternary Ln(TTA)₃(TPPO)₂ complexes, where Ln?=?La(III), Eu(III), Tb(III) and Tm(III), TTA?=?2-thenoyltrifluoroacetone, and TPPO?=?triphenylphosphine oxide, which are of interest in luminescence applications. Using this method, the reaction time was decreased to one minute with minimal purification step and the yields are comparable to literature values. The target complexes were characterized using ¹H, ¹³C, ¹⁹F, ³¹P NMR and FTIR spectroscopy, MALDI-TOF mass spectrometry and single-crystal X-ray diffraction. Further, we discuss here a hitherto unreported extensive network of hydrogen bonding interactions present in these complexes.

Full text of DOI:10.1016/j.ica.2017.04.021

Accepted Manuscript
Research paper
Microwave-Assisted Synthesis of Ternary Lanthanide(2-Thenoyltrifluoroace-
tone)3(Triphenylphosphine oxide)2 Complexes
Marites A. Guino-o, Brian Bustrom, Rodney A. Tigaa, Ana de Bettencourt-Dias
PII:
S0020-1693(17)30178-0
http://dx.doi.org/10.1016/j.ica.2017.04.021
ICA 17526
DOI:
Reference:
Inorganica Chimica Acta
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Received Date:
Accepted Date:
7 February 2017
11 April 2017
Please cite this article as: M.A. Guino-o, B. Bustrom, R.A. Tigaa, A. de Bettencourt-Dias, Microwave-Assisted
Synthesis of Ternary Lanthanide(2-Thenoyltrifluoroacetone)3(Triphenylphosphine oxide)2 Complexes, Inorganica
Chimica Acta (2017), doi: http://dx.doi.org/10.1016/j.ica.2017.04.021
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Microwave-Assisted Synthesis of Ternary Lanthanide(2-
Thenoyltrifluoroacetone)3(Triphenylphosphine oxide)2 Complexes
Marites A. Guino-oa*, Brian Bustroma, Rodney A. Tigaab, and Ana de Bettencourt-Diasb
aDepartment of Chemistry, University of St. Thomas
Mail OSS 402, 2115 Summit Avenue, St. Paul MN 55105-1079 USA
Tel: 1 651 962 5526, E-mail: maguinoo@stthomas.edu
bDepartment of Chemistry, University of Nevada-Reno, Reno, Nevada,
USA. E-mail: abd@unr.edu; Fax: +1 775 784 6804; Tel: +1 775 682 8421
Abstract
We report here the fast synthesis by microwave assisted technique of four ternary
Ln(TTA)3(TPPO)2 complexes, where Ln = La(III), Eu(III), Tb(III) and Tm(III), TTA =
2-thenoyltrifluoroacetone, and TPPO = triphenylphosphine oxide, which are of interest in
luminescence applications. Using this method, the reaction time was decreased to one
minute with minimal purification step and the yields are comparable to literature values.
1
The target complexes were characterized using H, 13C, 19F, 31P NMR and FTIR
spectroscopy, MALDI-TOF mass spectrometry and single-crystal X-ray diffraction.
Further we discuss here a hitherto unreported extensive network of hydrogen bonding
interactions present in these complexes.
Keywords:
Lanthanide(2-thenoyltrifluoroacetone)3(triphenylphosphineoxide)2
Ln(III) β-diketonate complexes, microwave synthesis, 2-
Complexes,
thenoyltrifluoroacetone, triphenyl phosphine oxide, hydrogen bonding
1. Introduction
Each lanthanide ion has a characteristic emission color with sharp line-like bands that is
suitable for applications in solar energy conversion, anti-counterfeiting dyes, OLEDs, and
biomolecular imaging systems.1,2,3,4 The emission is due to transitions within the 4f
orbitals and the sharp bands arise the atomic core nature of these f orbitals, which are
shielded from the coordination environment by the filled 5s and 5p orbitals of the
lanthanide core.1-3 However, f-f transitions are parity forbidden, thus direct excitation of
the f electrons to the emissive state is inefficient, and instead sensitization is used.
Sensitization or the “antenna effect” refers to population of the emissive state through
ligand-to-metal energy transfer.1-3 In particular, β-diketonato ligands are excellent
sensitizers to trivalent lanthanide ions [Ln(III)],1, 5
and these complexes are
predominantly used in Ln(III)-based organic-inorganic hybrid materials for luminescence
applications.1,5 However, the neutral ternary Ln(III) β-diketonate complexes, Ln(β-
diketone)3L2, where L is a neutral base adduct, are synthetically challenging to make. It
often takes several hours to days to synthesize them because of, as one group pointed out,
an extensive intermediate purification step.5,6,7,8 Thus, our group is interested in finding a
faster synthesis for these complexes. We used the β-diketone, 2-thenoyltrifluoroacetone
1

(TTA) and the Lewis adduct, triphenyl phosphine oxide (TPPO) as ligands to coordinate
with the La(III), Eu(III), Tb(III) and Tm(III) ions.
Herein we report our investigation on how microwave (MW) irradiation affected the
synthesis of these complexes. MW assisted chemical reactions has become very popular
in organic syntheses due to the technique’s short reaction times and ease of use. The
technique works due to dipolar polarization and ionic conduction.9,10 Dipolar polarization
operates through the dipoles of polar molecules. When irradiated, these dipoles attempt to
line up with the applied field. Ionic conduction is a process through which ions in
solution absorb microwaves causing them to oscillate and collide with neighboring
molecules. Both of these processes cause kinetic friction that not only heats up the
system, but also increases the collision rate, leading therefore to faster reactions.9,10
2. Experimental
2.1. Materials, Spectroscopic Experiments and Single Crystal X-ray Diffraction
Materials
2-Thenoyltrifluoroacetone (99%, Aldrich), triphenylphosphine oxide (98%, Aldrich),
lanthanum chloride hexahydrate (99.99%, Fisher Scientific), europium nitrate
hexahydrate (99.99%, Aldrich), terbium chloride hexahydrate (99.9%, Aldrich), thulium
nitrate pentahydrate (99.9%, Aldrich) and potassium hydroxide (pellet, VWR) were used
without further purification. Isopropanol (99% ACS, Pharmo-Aaper) was dried with 3Å
molecular sieves overnight prior to use.
NMR Spectroscopy
1
31
All H, 19Fand P NMR spectra were recorded on JEOL 400 MHz spectrometer, using
deuterated chloroform as the solvent. Spectra are reported in ppm and are calibrated
against tetramethylsilane.
FTIR Spectroscopy
Infrared spectra of the complexes were recorded on a Bruker Alpha FT-IR spectrometer
with a platinum-diamond sampling module in the range 4000-400 cm-1 at 4 cm-1
resolution with 32 scans in ATR mode. Before each acquisition, a background spectrum
was acquired to correct for CO2 and H2O interference.
MALDI-TOF Mass Spectrometry
The MALDI-TOF mass spectra were analysis was acquired on a Bruker Microflex
instrument under positive ion mode. Each sample was prepared by applying drops of α-
cyano-4-hydroxycinnamic acid matrix (5 mg/mL) in acetone to a target plate and
allowing it to dry. Next, drops of the sample (5 mg/mL) dissolved in acetone were
applied to the dried matrix area and allowed to dry before the analysis was carried out.
Single-crystal X-ray Diffraction
A suitable crystal was mounted on a glass fiber and placed in the low-temperature
nitrogen stream of a Bruker SMART CCD area detector diffractometer. A full sphere of
data was collected using graphite-monochromated Mo Kα radiation (λ = 0.71073 Å)
source. Multi-scan absorption corrections were applied using SADABS.11 The structures
2

were solved by Patterson methods and refined by least square methods on F2 using the
SHELXTL program package.12 The hydrogen atoms were geometrically added and all the
non-hydrogen atoms refined anisotropically. The crystal structure for 2 was already
published but was either not reported in the Cambridge Crystallographic Database7 or
was collected at room temperature (CCD identifier: SABHIM).13 The structures were
deposited with the Cambridge Crystallographic Database and their reference numbers are
CCDC 1531346 for 1, 1531347 for 2, and 1531348 for 3. These data can be obtained
from
The
Cambridge
Crystallographic
Data
Centre
via
www.ccdc.cam.ac.uk/data_request/cif. The cif files are also available as supplementary
information.
The data collection and refinement details for 1-3 are given in Table 1. Comments on the
remaining checkcif errors are located in the cif file for the complex under the
refine_special_details loop. Lanthanide(III) 1-3 complexes yielded X-ray quality single
crystals after recrystallization in acetone at room temperature for 2-3 days. Disorder in
one of the thiophene rings, as observed in the reported structures for complex 1 and 2,
was handled by modeling the occupancies of the individual orientations using free
variables to refine the respective occupancy of the affected fragments.12 The thiophene
disordered positions were refined using split positions. The respective occupancies for
complex 1 is 77/22 and complex 2 is 80/20. The disordered thiophene ring in complexes
1 and 2 correspond to a rotation of about 180o about the single C–C bond similar to
literature reports.14,15 While the disorder in these complexes, led to non-integer number
for the hydrogen count, the formulas in Table 1 were corrected to show the appropriate
number of hydrogen atoms.
Table 1. Crystallographic data for complexes 1-3.
1
2
3
Formula
M (g mol–1)
a (Å)
C60H42LaF9O8P2S3
1357.45
11.0590(1)
12.0055(1)
23.1940(3)
80.0144(5)
77.0074(5)
71.2160(4)
2823.71(5)
2
C60H42EuF9O8P2S3
1370.50
11.0288(1)
11.9459(1)
23.3460(3)
90.955(1)
103.661(1)
109.410(1)
2803.69(5)
2
C60H42TbF9O8P2S3
1378.97
11.0246(1)
11.9540(1)
23.3591(2)
90.8066(5)
103.4382(5)
109.5868(5)
2806.66(4)
2
b (Å)
c (Å)
α (o)
β (o)
γ (o)
V (Å3)
Z
Crystal system
Space group
Dcalc (mg/m3)
µ/Mo Kα (mm–1)
T (K)
Triclinic
P-1
1.597
1.01
100
Triclinic
P-1
1.623
1.37
100
Triclinic
P-1
1.632
1.52
100
Independent
reflections,
Rint [Fo≥σ(Fo)]
11105, 0.0184
10962, 0.0500
16893, 0.0341
3

Number
of 749
1.045
749
748
parameters
GoF on F2
1.495
1.050
R1, wR2 [I˃2r(I)]
0.0201 (10990),
0.0485 (11105)
0.0298 (9475),
0.0464 (10962)
0.55, –0.62
0.0318 (15274),
0.0731 (16893)
1.32, –1.33
Largest diff. peak 0.56, –0.43
and hole/e. (e Å–3)
2.2 Microwave Syntheses
We employed the Biotage Initiator Microwave Reactor in all of the syntheses described
below.
General Procedure:
A 20 mL Biotage microwave vessel with a stir bar was charged with 3:2:3 molar
equivalents of thenoyltrifluoroacetone (TTA), triphenylphosphine oxide (TPPO), and
KOH solution in 10 mL isopropanol. To this mixture, a 4 mL water-isopropanol (1:4)
solution with one equivalent lanthanide(III) salt was added drop-wise while stirring at
room temperature. The microwave reactor was set to 100 oC at normal absorbance for 1-
20 mins, then cooled to room temperature. Once completed, a precipitate usually forms.
o
The vial was placed inside a 5 C fridge overnight to allow for more precipitate to form,
then product was filtered and dried via vacuum filtration the next day.
1: La(TTA)3(TPPO)2, Lanthanum(III) bis(triphenylphosphine oxide)
tri(thenoyltrifluoroacetonato)
TTA (0.900 mmol, 0.200 g), TPPO (0.633 mmol, 0.175 g), KOH (0.900 mmol, 1.8 mL of
0.5 M) and LaCl3ꢀ6H2O (0.330 mmol, 0.117 g).
1
White powder (0.308 g, 79%). H NMR (400 MHz, CDCl3): δ 8.91-8.86 (m, 12H,
TPPO), 8.71-8.61 (m, 12H total, 6H TPPO, 6H TTA), 8.53-8.52 (s, 3H, methine TTA),
8.51-8.46 (m, 12H, TPPO), 8.22-8.19 (t, 3H, TTA), 7.26 (CDCl3).
19F NMR (376 MHz, CDCl3): δ -76.4.
31P NMR (400 MHz, CDCl3): δ -32.6.
FTIR (cm-1): ν 1159, 1120 (P=O), 1605 (C=O).
MALDI-TOFMS m/z calc. for F9O8P2S3C60H43La+ (1358.05): Found m/z 1358.34.
Recrystallized using 5 mL acetone and placed in a hood at room temperature for 2-3
days. The resulting crystals are colorless blocks.
2: Eu(TTA)3(TPPO)2, Europium(III) bis(triphenylphosphine oxide)
tri(thenoyltrifluoroacetonato)
TTA (0.900 mmol, 0.200 g), TPPO (0.633 mmol, 0.175 g), KOH (0.900 mmol, 1.8 mL of
0.5 M) and Eu(NO3)3ꢀH2O (0.330 mmol, 0.114 g).
Off-white powder (0.298 g, 73%).
4

1H NMR (400 MHz, CDCl3): δ 13.52 (b, 6H, TPPO), 11.04-10.93 (m, 15H should be
24H, TPPO), 10.50 (s, 3H, methine TTA), 10.05-10.04 (b, 3H, TTA), 9.66-9.64 (b, 3H,
TTA), 9.23-9.22 (b, 3H, TTA), 7.26 (CDCl3).
19F NMR (376 MHz, CDCl3): δ -80.2.
31P NMR (400 MHz, CDCl3): δ 0.6.
FTIR (cm-1): 1168, 1119 (P=O), 1607 (C=O).
MALDI-TOFMS m/z calc. for F9O8P2S3C60H43EU+ (1372.07): Found m/z 1372.14.
Recrystallized using 5 mL acetone and placed in a hood at room temperature for 2-3
days. The resulting crystals are colorless blocks.
3: Tb(TTA)3(TPPO)2, Terbium(III) bis(triphenylphosphine oxide)
tri(thenoyltrifluoroacetonato)
TTA (0.900 mmol, 0.200 g), TPPO (0.633 mmol, 0.175 g), KOH (0.900 mmol, 1.8 mL of
0.5 M) and TbCl3ꢀ6H2O (0.330 mmol, 0.123 g).
White powder (0.305 g, 74%).
1H NMR (400 MHz, CDCl3): δ 9.21, 8.52, 8.05, 5.81 all are very broad peaks, please
refer to the supplementary material.
19F NMR (376 MHz, CDCl3): δ -47.8.
31P NMR (400 MHz, CDCl3): δ -0.0.
FTIR (cm-1): 1169, 1120 (P=O), 1608 (C=O).
MALDI-TOFMS m/z calc. for F9O8P2S3C60H43Tb+ (1379.07): Found m/z 1380.92.
Recrystallized using 5 mL acetone and placed in a hood at room temperature for 2-3
days. The resulting crystals are pale yellow blocks.
4: Tm(TTA)3(TPPO)2, Thulium(III) bis(triphenylphosphine oxide)
tri(thenoyltrifluoroacetonato)
TTA (0.900 mmol, 0.200 g), TPPO (0.633 mmol, 0.175 g), KOH (0.900 mmol, 1.8 mL of
0.5 M) and Tm(NO3)3ꢀ5H2O (0.330 mmol, 0.147 g).
White powder (0.061 g, 44%).
1H NMR (400 MHz, CDCl3): δ 10.43, 9.61, 8.29 all are very broad peaks, please refer to
the supplementary material.
19F NMR (376 MHz, CDCl3): δ -102.9.
31P NMR (400 MHz, CDCl3): δ 21.1.
FTIR (cm-1): 1166, 1122 (P=O), 1608 (C=O).
MALDI-TOFMS m/z calc. for F9O8P2S3C60H43Tm+ (1389.08): Found m/z 1389.82.
Recrystallized using 5 mL acetone and placed in a hood at room temperature for 2-3
days. The resulting crystals were colorless plates but, during our single-crystal X-ray
diffraction experiment, the crystals were twinned. We were unable to resolve the crystal
structure but assume that it would have a similar coordination environment as complexes
1-3.
3. Results and discussion
5

Microwave syntheses and spectroscopic studies
One of the most luminescent ternary lanthanide(III) β-diketonate complexes is the
Eu(TTA)3(TPPO)2.1,16 While reported syntheses have good to excellent yields they take
hours to complete (Eqn. 1).5,6 To investigate the microwave-assisted synthesis, we first
1
used La(III) ion to monitor the reaction progress through H, 19F and 31P NMR
spectroscopy. We also utilized FTIR spectroscopy to follow the C=O and P=O stretches
from the TTA and TPPO ligands.
In our first microwave assisted trial, three equivalents of TTA and two equivalents of
TPPO were dissolve in 10 mL of isopropanol and placed in a microwave vial at room
temperature, followed by the addition of three equivalents of potassium hydroxide. In a
separate container, one equivalent of LaCl3ꢀ6H2O was dissolved in 4 mL solution of one-
part water and four-parts isopropanol, and then added to the ligand mixture. The solvent
mixture was chosen based on Teotonio’s literature method.7 The microwave reactor was
then set to run at 120 oC for 5 min on high absorbance with 15 sec of pre-stirring. A white
precipitate and yellow solution formed after the reaction. The reaction vial was placed
o
inside a 5 C fridge overnight to allow for more precipitate to form. The next day, the
precipitate was filtered and dried using vacuum filtration.
1
Figure 1 shows a comparison of the H NMR spectra between the starting TTA and
TPPO ligands and the ternary La(TTA)3(TPPO)2 complex. The methine proton of the β-
diketonate ligand after complexation shifted downfield to 8.53 ppm from 8.07 ppm in the
31
free ligand. Figure 2 shows the P NMR spectra comparing the starting TPPO ligand
and the ternary La(TTA)3(TPPO)2 complex, indicating that there is a 3 ppm downfield
shift of the signal of the phosphorus nuclei. Proton integration of the ternary
La(TTA)3(TPPO)2 complex indicates that there are three TTA and two TPPO ligands in
the complex as shown in Figure 1 and in Figure S1a in the supplementary information.
6

Figure 1. 1H NMR spectra comparing between the starting TTA (green) and TPPO (blue)
ligands and the ternary La(TTA)3(TPPO)2 complex (red). The methine –CH peak of the
β-diketonate ligand in complex 1 shifts downfield shift (8.53 ppm) from the free ligand
(8.07 ppm).
7

31
Figure 2. P NMR spectra comparing the starting TPPO (green) ligands and the ternary
La(TTA)3(TPPO)2 complex (red). There is a downfield shift of about 3 ppm for the
TPPO in complex 1 and the free ligand.
Figure 3. FTIR spectra comparing the starting TTA (orange) ligand and the complex 1
(black). The inset illustrates the C=O stretch difference between TTA and complex 1.
8

Figure 4. FTIR spectra comparison between the starting TPPO (orange) ligand and the
complex 1 (black). The inset illustrates the P=O stretch difference between TPPO and
complex 1.
The C=O stretches at 1638 cm-1 and 1577 cm-1 from the TTA ligand combined into one
C=O stretch at 1605 cm-1 for the ternary La(III) complex indicating that TTA chelates to
the metal through the C=O functional groups as shown in Figure 3, similar to literature
values.7 In addition, a shift in the phosphine oxide peak from sharp peaks at 1182 and
1119 cm-1 to a slightly broader ones at 1159 and 1120 cm-1 indicates that TPPO
coordinates through the P=O functional group to the metal (Figure 4).
Based on NMR and FTIR spectra, we have successfully synthesized the
La(TTA)3(TPPO)2 complex. To further verify our result, we also grew crystals using
acetone as our recrystallization solvent. The crystallography is discussed below.
Our succeeding trials using La(III) ion involved the optimization of the microwave
reaction conditions by tracking the percent yield of the target complex. Based on Table
2, the optimized reaction condition is 1 min at 100 oC with 79 percent yield.
Table 2. Microwave reaction trials for La(TTA)3(TPPO)2 complex.
Microwave-Reactor Settings
21 min at 1200C
11 min at 1200C
5 min at 1200C
Yield (%)
56
48
74
67
71
79
72
72
3 min at 1200C
1 min at 1200C
1 min at 1000C
1 min at 1400C
1 min at 800C
In our succeeding reactions we replaced the La(III) ion with Eu(III), Tb(III) and Tm(III)
o
ions, but we kept the microwave reactor settings at 100 C for one minute. Table 3
summarizes the relevant chemical shifts and stretches of the ligands in the complexes
obtained from these trials and the percent yield for each complex. Actual spectral results
are provided in the supplementary information. Based on spectroscopic evidence, we
were able to synthesize the target ternary Ln(III) β-diketonate complexes using the
microwave technique in a much shorter reaction time with high yields comparable to
literature values (see Tables 2 and 3).6,7,8 This method also circumvents the intermediate
purification steps,6,7,8 the main advantage when using this technique.
9

Table 3. Relevant chemical shifts and stretches for the ligands TTA, TPPO and the
ternary Ln(III) β-diketonate complexes.
1H NMR 19F
δ (ppm) NMR
31P
NMR
FTIR
FTIR
MALDI- Yield
TOFMS (%)
m/z
ν (cm–1) ν (cm–1)
–CH,
δ (ppm) δ (ppm)
C=O
stretch
1638
1577
---
P=O
stretch
---
methine –CF3
–P=O
---
Free TTA
8.07
---
-75.6
---
---
---
---
---
79
Free TPPO
29.9
32.6
1182
1119
1159
1120
1,
8.53
-75.4
1605
1607
1608
1608
calc:
La(TTA)3(TPPO)2
1358.05
found:
1358.34
calc:
1372.07
found:
1372.14
calc:
1379.07
found:
1380.92
calc:
2,
10.50
broad
-80.2
-47.8
-102.9
0.6
1168
1119
73
74
44
Eu(TTA)3(TPPO)2
3,
0.0
1169
1120
Tb(TTA)3(TPPO)2 peaks
4,
broad
21.1
1166
1122
Tm(TTA)3(TPPO)2 peaks
1389.08
found:
1389.82
Crystallography
The crystal structures for complexes 1-3 were determined. All three complexes are
isostructural to the Eu(TTA)3(TTPO)2 structures reported in the literature.7,13
Furthermore, complexes 2 and 3 are isomorphous with each other. The central Ln(III)
metal ions are coordinated to eight oxygen atoms from the three bidentate TTA ions and
two monodentate TPPO ligands, as shown in Figure 5a. The resulting crystals for
complex 4 are colorless plates but all the crystals we were able to isolate were twinned.
We were unable to resolve the crystal structure but assume that Tm(III) has a
coordination environment similar to the ions in complexes 1-3.
The Ln – O bond length for complexes 1-3 are in the range of 2.329(2) – 2.540(1) Å with
the longer bonds belonging to the relatively bigger La(III) ion as summarized in Table 4.
These values are comparable to the ones reported in the literature.13 The TPPO ligands
are located across each other due to steric effects but are not directly opposite as
demonstrated by the 145o bond angle separation (refer to Table 2). This is due to the bite
angles of the TTA ion that range from 68.23(4) to 72.71(6)o. The three TTA ions around
the lanthanide ions do not form a plane, but are instead titled against each other (torsion
angles are listed in Table 2).
10

(a)
(b)
Figure 5. Crystal structure of complex 1. (a) Illustration of the octacoordinate
environment of the central La(III) and (b) Unit cell containing two La(TTA)3(TPPO)2
complexes with ellipsoids at 50% occupancy. H atoms are omitted for clarity. Ellipsoids
in (b) are shown with 50% occupancy. Color legend: blue green = Ln(III), red = O, pink
= P, green = F, yellow = S, gray = C.
Table 4. Selected bond length (Å) and angles (o) for complexes 1 – 3.
Ln = La, Eu, Tb
Bond length (Å)
Ln – O (TPPO)
1
2
3
2.476(1)
2.457(1)
2.522(1)
2.471(1)
2.540(1)
2.452(2)
2.538(1)
2.463(1)
2.376(2)
2.355(2)
2.442(2)
2.362(1)
2.446(2)
2.361(1)
2.457(2)
2.351(2)
2.356(2)
2.329(2)
2.340(1)
2.421(2)
2.338(1)
2.429(2)
2.332(2)
2.440(2)
Ln – O (TTA)
Bond angle (o)
O – Ln – O (TPPO) 145.64(4)
144.79(6)
70.46(6)
71.16(6)
72.11(6)
144.59(6)
70.98(6)
71.62(6)
72.71(6)
O – Ln – O
68.60(4)
69.72(4)
68.23(4)
(each TTA ion)
Torsion angle (o)
between each TTA 76.27(4)
74.07(6)
151.24(7)
156.71(7)
66.21(6)
115.10(6)
178.11(6)
planes
154.12(5)
158.55(5)
Each unit cell for complexes 1-3 contain two molecules as shown in Figure 5b. There are
extensive C – H···F hydrogen bond interactions in all of the solid state structures, which
have not been previously reported. For all complexes, there are intramolecular C –
H···F hydrogen bonds between the –CH (methine) and –CF3 in all three TTA ligands
11

with bond distances in the range of 2.3313(16) – 2.3996(13) Å (see Table 5 and Figures 6
– 8). These might explain the absence of the rotational disorder in the –CF3 functional
group of the TTA ligand. Interestingly, the –CF3 functional group of the TTA ligand also
forms both intra- and intermolecular –CH interactions with a thiophene ring of the TTA
ligand and a phenyl ring of the TPPO ligand within the molecules in the unit cell or a
neighboring molecule in an adjacent cell. These interactions are more predominant in
complex 1 than complexes 2 and 3. The bond distances are in the range of 2.3687(23) –
2.5559(13) Å (see Table 5 and Figures 6 – 8). In addition, there is a weak C–F···F–C
intermolecular interaction in complexes 1 and 2, with bond distance range of 2.8048(16)
– 2.9327(32) Å. C–F···F–C contacts are reported in the literature to be weak but still
relevant for crystal packing.17
Table 5. Hydrogen-bond (C–H···F) and weak C–F···F–C interactions and bond distances
(Å) for complexes 1-3.
1
2
3
intramolecular (C – H···F)
between –CH (methine) TTA and –CF3 TTA in the unit cell
C42–H42···F2 2.3516(13)
C50–H50···F6 2.3996(13)
C58–H58···F9 2.3360(13)
intramolecular (C – H···F)
C42–H42···F1 2.3313(16)
C50–H50···F5 2.3540(13)
C58–H58···F9 2.3778(19)
C39–H39···F3 2.3389(22)
C47–H47···F5 2.3492(18)
C55–H55···F9 2.3686(25)
between –CH (phenyl) TPPO and –CF3 TTA in the unit cell
C11–H11···F7 2.5559(13)
---
---
intermolecular (C – H···F)
between –CH (phenyl) TPPO and –CF3 TTA in the unit cell
C10–H10···F5 2.5436(14)
---
C18–H18···F2 2.5369(27)
intermolecular (C – H···F)
between –CH (thiopene) TTA and another –CF3 TTA molecule in a neighboring unit cell
C3–H3···F8
C45–H45···F2 2.5257(11)
C55A–H55A···F1 2.5439(12) ---
2.4534(15)
---
---
---
---
---
intermolecular (C – H···F)
between –CH (phenyl) TTA and another –CF3 TTA molecule in a neighboring unit cell
---
C3–H3···F3
2.3687(23)
C11–H11···F1
2.3188(24)
---
---
C35–H35···F5
2.5462(15)
intermolecular (C – F···F – C)
between –CF3 TTA and another –CF3 TTA molecule in a neighboring unit cell
C52–F5···F8–C60 2.8048(16) C60–F7···F3–C44 2.9327(32) ---
C52–F5···F9–C60 2.9119(18) ---
---
12

Figure 6. Hydrogen-bond (C–H···F) and C–F···F–C interactions for complex 1. H
atoms not participating in the contact pairs are not shown.
Figure 7. Hydrogen-bond (C–H···F) and C–F···F–C interactions for complex 2.
H
atoms not participating in the contact pairs are not shown.
13

Figure 8. Hydrogen-bond (C–H···F) interactions for complex 3.
H atoms not
participating in the contact pairs are not shown.
Conclusion
We describe here a simple and extremely fast synthesis of the target ternary Ln(III) β-
diketonate complexes using the microwave technique with high yields comparable to
literature values but no intermediate purification steps.
We also successfully
characterized the target complexes using spectroscopic techniques and single-crystal X-
ray diffraction. The latter technique enabled us to describe, for the first time, an
extensive network of hydrogen bonds, both intra- and intermolecular.
Acknowledgements
For financial support, we are indebted to the University of St. Thomas Chemistry
department research funds for MAG; work-study study funds for BB; the University of
St. Thomas Dean’s Office for the purchase of the Bruker Alpha FT-IR Spectrometer with
Platinum-Diamond sampling module; the NSF–MRI grant No. 095322 ‘MRI–R2:
Acquisition of a 400 MHz Nuclear Magnetic Resonance (NMR) Spectrometer’; AdBD
acknowledges NSF (CHE-1363325) for financial support of this work.
Appendix A. Supplementary data
Additional experimental details (1H, 13C, 19F and 31P NMR, FTIR and MALDI-TOF mass
spectra for complexes 1-4 and cif files for complexes 1-3) are provided in the
supplementary materials.
14

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16

Highlights
• Ln(TTA)3(TPPO)2 complexes, where Ln = La(III), Eu(III), Tb(III) and Tm(III), TTA
= 2-thenoyltrifluoroacetone, and TPPO = triphenylphosphine oxide, were synthesized
via microwave assisted technique.
• The reaction time was decreased to one minute with minimal purification step and the
yields are comparable to literature values.
• Through single-crystal X-ray diffraction, we discussed an unreported extensive
network of hydrogen bonding interactions in these complexes.
17