Synthesis, crystal structure and properties of novel isostructural two-dimensional lanthanide-based coordination polymers with 2,3,5,6-tetrafluoro- 1,4-benzenedicarboxylic acid

Article abstract of DOI:10.1016/j.ica.2010.09.013

Five new isostructural two-dimensional lanthanide-based coordination polymers with the formula Ln₂(F₄BDC)₃(DEF) ₂(EtOH)₂-2(DEF) (Ln = Tb, 1; Gd, 2; Eu, 3; La, 4; Nd, 5; F₄BDC^2- =

Full text of DOI:10.1016/j.ica.2010.09.013

Inorganica Chimica Acta 365 (2011) 196–203
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Synthesis, crystal structure and properties of novel isostructural
two-dimensional lanthanide-based coordination polymers with
2,3,5,6-tetrafluoro-1,4-benzenedicarboxylic acid
⇑
Christopher M. MacNeill, Cynthia S. Day, Amy Marts, Abdessadek Lachgar, Ronald E. Noftle
Department of Chemistry, Wake Forest University, P.O. Box 7486, Winston-Salem, NC 27106-7485, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 19 July 2010
Accepted 9 September 2010
Available online 14 October 2010
Five new isostructural two-dimensional lanthanide-based coordination polymers with the formula
Ln2(F4BDC)3(DEF)2(EtOH)2-2(DEF) (Ln = Tb, 1; Gd, 2; Eu, 3; La, 4; Nd, 5; F4BDC2ꢀ = 2,3,5,6-tetrafluoro-
1,4-benzenedicarboxylate ligands; DEF = N,N0-diethylformamide), have been synthesized by reaction of
Ln(NO3)3 and F4BDC in a DEF/EtOH solvent mixture. The compounds were characterized by single-crystal
and powder X-ray diffraction. In all cases, the metal ion is coordinated by nine oxygen atoms from two
bidentate
molecule and one EtOH molecule forming a tri-capped trigonal prism. The Ln(1) metal ion is linked to
an adjacent Ln(1) metal ion through the oxygen atoms of two bridging
2-F4BDC2ꢀ ligands and two
3-F4BDC2ꢀ bridging ligands to form a Ln2O18 dimer. The Ln2O18 polyhedra building units are linked
l l l
2-F4BDC2ꢀ ligands, two bridging 2-F4BDC2ꢀ ligands, one 3-F4BDC2ꢀ ligand, one DEF
Keywords:
Coordination polymers
Biginelli reaction
Lanthanide materials
Tetrafluoroterephthalic acid
Metal organic frameworks
l
l
to each other through four F4BDC2ꢀ ligands to form 2D sheets that are held together by hydrogen bonding
to form a 3D framework. Compounds 1–5 were further characterized using thermogravimetric analysis
and infrared spectroscopy. Studies of the photoluminescence properties of compounds 1 and 3, as well
as the catalytic activity of compounds 3–5 in the Biginelli reaction, are presented.
Ó 2010 Elsevier B.V. All rights reserved.
1. Introduction
its environment which prevents quenching of the excited state
[9]. Lanthanide ions are hard acids, and, thus, organic ligands,
In recent years, the design and construction of hybrid inorganic
organic materials (HIOMs) derived from metal ions or metal clus-
ters with organic linkers has attracted much interest due to their
chemical and physical properties that make them potentially useful
for applications in catalysis, magnetism, luminescence, gas storage,
and drug release [1–5]. Among more than 15,000 HIOMs reported,
most are based on transition metal ions. Only a relatively small
number of lanthanide-based frameworks has been reported even
though they are potentially important owing to their larger coordi-
nation number and numerous coordination environments giving
rise to less predictable geometries.
Materials containing lanthanide ions are mainly used in electro-
luminescent devices because of their photophysical properties [6].
Unlike most organic light emitting devices, lanthanides have sharp
emission bands that range over the entire visible spectrum (Eu, Tb
and Tm) to the near IR region (Nd, Er, Yb) [7,8]. In some cases,
lanthanide emissions can be very weak due to the parity forbidden
f–f transitions. However, aromatic ligands can sensitize the emis-
sion. In addition, suitable ligands act to shield the metal ion from
which are hard bases, are required. Oxygen-donating ligands, such
as carboxylates, are used for this purpose, and the versatility of
their coordination modes makes them attractive linkers for
bridging lanthanide centers. Lanthanide frameworks, bound to
carboxylate linkers such as 1,4-benzenedicarboxylic acid and 2,2-
bipyridine-4,40-dicarboxylic acid, have been studied in terms of
their photophysical properties [7,10].
Linkers with electron withdrawing groups, such as 2,3,5,6-
tetrafluoro-1,4-benzenedicarboxylylate (F4BDC), have been used
to build coordination polymers with transition metals [11]. How-
ever, it has been reported that transition metal hybrids do not crys-
tallize well in acidic environments, and the acidity of the parent
acid requires a basic co-ligand such as a nitrogen base in order
for the HIOM to crystallize [11a]. The acidity of the metal site is
of paramount importance in catalysis, and our object was to utilize
the more weakly basic F4BDC ligand as a secondary building unit
without the assistance of a basic co-ligand, which might be accom-
plished by removing protons from the parent acid using triethyl-
amine in a vapor diffusion process. It was hoped that acidity of
the metal ion in the framework would be enhanced considerably
by this. To our knowledge, only one lanthanide HIOM in which
erbium metal ions are linked by F4BDC ligands has been reported;
it was studied for its photophysical properties [12]. This material
⇑
Corresponding author. Tel.: +1 336 758 5520.
E-mail address: noftle@wfu.edu (R.E. Noftle).
0020-1693/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2010.09.013

C.M. MacNeill et al. / Inorganica Chimica Acta 365 (2011) 196–203
197
was prepared by a different method, had a different composition,
and a different structure in which two different types of Eu atoms
were present in a distorted square antiprism geometry [12].
HIOMs have been studied for their heterogeneous catalytic
activity in a variety of reactions. One such reaction, the Biginelli
reaction, is significant in organic chemistry and involves the cyclo-
condensation of an aldehyde, a dicarbonyl compound and urea
in the presence of a catalytic amount of a Lewis acid to give a
substituted dihydropyrimidinone. Dihydropyrimidinones and their
derivatives have long been known to have important pharmacolog-
ical properties as anti-virals [13] as well as other related medicinal
applications [14]. The Biginelli reaction has been used to assess the
catalytic properties of rare earth frameworks in a few studies [15];
however, in some of these, an acidic ligand was present [15a,16]
which makes it unclear whether the metal ion (Lewis acid) or the
proton in the acidic group was responsible for the catalysis. This
manuscript contains the first reported catalytic study of a lantha-
nide HIOM containing a fluorinated aromatic compound without
acidic species in the lattice structure.
Fisher Chemical Co. All solvents were used as received without fur-
ther purification.
2.2. Physical measurements
Crystals suitable for single crystal X-ray diffraction were micro-
scopically examined and selected from solution held on a slide
cooled with dry ice to minimize loss of solvent. Intensity data for
all compounds were measured on a Bruker SMART APEX CCD area
detector system at 193 K using Mo K
a radiation (k = 0.7107 Å).
Absorption effects were corrected using the SADABS program [17].
All structures were determined and refined using the Bruker SHELXTL
software package (Version 6.1) [18]. Crystal and structure refine-
ment data for compounds 1–5 as well as selected bond lengths
and angles are reported in Tables 1 and 2. X-ray powder diffraction
data were collected at room temperature using a BRUKER P4 gen-
eral-purpose four-circle X-ray diffractometer modified with a
GADDS/Hi-Star detector with Cu K
a radiation (k = 1.5406 Å). The
goniometer was controlled using GADDS software suite [19]. The
samples were mounted on tape and two frames were measured
at 2h = 5 and 26° with exposure time of 180 s/frame. Infrared spec-
tra were recorded either on a Mattson Genesis II FT-IR spectrometer
or on a Perkin–Elmer Spectrum 100 spectrophotometer with an
ATR sampling accessory equipped with a diamond anvil. Thermo-
gravimetric analysis of compounds 1–5 was performed by heating
10–30 mg samples at a rate of 5 °C/min from 40 to 900 °C under
air (40 mL/min) using a Perkin–Elmer Pyris 1 TGA system. Elemen-
tal analyses were carried out by Atlantic Microlabs, Inc. Solid state
photoluminescence spectra were recorded at room temperature on
a Perkin–Elmer LS50B luminescence spectrophotometer using a
solid state attachment. GC–MS data were recorded on an Agilent
6850 Series GC system coupled to an Agilent 5973 Mass Selective
Detector run in electron impact mode. A 50-split method was
The synthesis, crystal structure determination, infrared spectros-
copy and thermal stability of five isostructural 2D lanthanide-based
metal–organic frameworks with 2,3,5,6-tetrafluoro-1.4-benzenedi-
carboxylic acid are reported in this work. Studies of the photolumi-
nescence properties of compounds 1 and 3, as well as the catalytic
activity of compounds 3–5 in the Biginelli reaction, are also
presented.
2. Experimental
2.1. Materials and methods
Eu(NO3)3ꢁ6H2O was purchased from Johnson Matthey.
La(NO3)3ꢁ6H2O was purchased from J.T. Baker Chemical Co.
Nd(NO3)3ꢁ5H2O, Tb(NO3)3ꢁ5H2O, Gd(NO3)3ꢁ6H2O, triethylamine,
benzaldehyde and ethyl acetoacetate were obtained from Aldrich
Chemical Co. 2,3,5,6-Tetrafluoro-1,4-benzenedicarboxylic acid
was obtained from Matrix Scientific Co. All chemicals were used
as received. Urea and N,N-diethylformamide was obtained from
Acros Chemical Co., while ethanol was purchased from Aaper Alco-
hol and Chemical Co. Toluene and methanol were purchased from
chosen to run on an Agilent column (13 ꢂ 0.25 mm ꢂ 0.25
lm) at
a ramp rate of 13 °C/min from 50 °C to 280 °C.
2.3. Synthesis of Tb2(F4BDC)3(DEF)2(EtOH)2-2(DEF) (1)
Tb(NO3)3ꢁ5H2O (54.2 mg, 0.125 mmol) and H2F4BDC acid
(41.8 mg, 0.176 mmol) were added to a 10 mL vial containing
Table 1
Table of crystallographic data for Tb2(F4BDC)3(DEF)2(EtOH)2ꢁ2DEF (1), Gd2(F4BDC)3(DEF)2(EtOH)2ꢁ2DEF (2), Eu2(F4BDC)3(DEF)2(EtOH)2ꢁ2DEF (3), La2(F4BDC)3(DEF)2(EtOH)2ꢁ2DEF
(4) and Nd2(F4BDC)3(DEF)2(EtOH)2ꢁ2DEF (5).
Compound 1
48H56F12Tb2N4O18
1522.81
193
Compound 2
Compound 3
Compound 4
Compound 5
Formula
Formula weight
T (K)
C
C48H56F12N4O18Gd2
1519.47
193
C48H56F12N4O18Eu2
1508.89
193
C48H56F12N4La2O18
1482.79
193
C48H56F12N4Nd2O18
1493.45
193
Crystal structure
Space group
Unit cell dimensions
monoclinic
C2/c
monoclinic
C2/c
monoclinic
C2/c
monoclinic
C2/c
monoclinic
C2/c
a = 23.282(3) Å
b = 11.185(2) Å
c = 23.230(3) Å
b = 108.650(2)°
5731.6(13)
4
a = 23.312(3) (Å)
b = 11.301(1) (Å)
c = 23.249(3) (Å)
b = 108.630(2)°
5762.2(14)
4
a = 23.300(3) Å
b = 11.229(1) Å
c = 23.285(3) Å
b = 108.658(1)°
5771.9(12)
4
a = 23.542(2) Å
b = 11.3837(8) Å
c = 23.623(2) Å
b = 108.650(2)°
5998.9(7)
4
a = 23.398(2) Å
b = 11.301(1) Å
c = 23.425(2) Å
b = 108.634(1)°
5869.4(9)
4
Volume (Å3)
Z
Dcalc (g cmꢀ3
)
1.765
1.752
1.736
1.642
1.690
Data/parameters
8299/390
1.048
2.559
7269/390
1.145
2.393
8404/90
1.180
2.264
8664/390
1.064
1.512
6694/390
1.126
1.858
Goodness-of-fit (GOF) on F2
l
(mmꢀ1
)
F(0 0 0)
3016
3008
3000
2952
2976
h Range (°)
3.96–30.05
0.0594
0.0412
3.96–28.50
0.0577
0.0472
3.95–30.05
0.0434
0.0426
3.90–30.05
0.0432
0.0396
3.93–27.50
0.0608
0.0486
Rint
R1 [I > 2
r
(I)]a
(I)]b
wR2 [I > 2
r
0.0829
0.0930
0.0899
0.0892
0.1001
R1 (all data)
0.0576
0.0591
0.0527
0.0498
0.0605
wR2 (all data)
0.0888
0.0971
0.0933
0.0938
0.1047
a
R
||Fo| ꢀ |Fc||/
R|Fo|.
b
2
{[
R
w(Fo ꢀ Fo2)2]/
R .
[w(Fo2)2]}1/2

198
C.M. MacNeill et al. / Inorganica Chimica Acta 365 (2011) 196–203
Table 2
beaker was then covered with parafilm and the mixture of ethanol
Bond lengths (Å) and angles (°) for compounds 1–5.
and triethylamine vapor was allowed to diffuse into the solution
for a period of 48 h. A white crystalline product formed which
was washed with DEF and acetone and allowed to dry in air. The
purity of the product was checked by PXRD, which can be seen
in the supporting information Fig. S1. (Yield: 44.7 mg, 52%, based
on F4BDC). Anal. Calc. for Tb2(F4BDC)3(DEF)2(EtOH)2-1.5(DEF): C,
37.12; H, 3.46. Found: C, 37.06; H, 3.52%. FT-IR (KBr): 3450 (br),
2989 (w), 2950 (w), 1652 (s), 1614(s), 1481 (s), 1411 (br), 1268
(m), 1216 (m), 1128 (m), 995 (s), 827 (w), 738 (s), 661 (m), 480 (m).
Compound 1
Tb(1)–O(1)
Tb(1)–O(2)#1
Tb(1)–O(3)
Tb(1)–O(4)
Tb(1)–O(5)#3
O(2)#1–Tb(1)–O(6)#2
O(2)#1–Tb(1)–O(1)
O(6)#2–Tb(1)–O(1)
O(2)#1–Tb(1)–O(7)
O(6)#2–Tb(1)–O(7)
O(1)–Tb(1)–O(7)
O(2)#1–Tb(1)–O(8)
2.366(2)
2.319(2)
2.469(2)
2.457(3)
2.478(3)
74.77(9)
131.17(9)
72.72(8)
139.38(9)
145.00(8)
75.65(9)
73.10(10)
Tb(1)–O(6)#3
Tb(1)–O(6)#2
Tb(1)–O(7)
2.747(3)
2.349(3)
2.381(2)
2.409(3)
Tb(1)–O(8)
O(7)–Tb(1)–O(3)
O(8)–Tb(1)–O(3)
O(4)–Tb(1)–O(3)
O(2)#1–Tb(1)–O(5)#3
O(6)#2–Tb(1)–O(5)#3
O(1)–Tb(1)–O(5)#3
O(7)–Tb(1)–O(5)#3
114.06(9)
72.89(9)
52.89(9)
78.25(9)
120.29(9)
87.83(9)
72.51(9)
2.4. Synthesis of Gd2(F4BDC)3(DEF)2(EtOH)2-2(DEF) (2)
A
similar procedure using Gd(NO3)3ꢁ6H2O (88.7 mg,
Compound 2
Gd(1)–O(2)#1
Gd(1)–O(6)#2
Gd(1)–O(1)
Gd(1)–O(7)
Gd(1)–O(8)
O(2)#1–Gd(1)–O(6)#2
O(2)#1–Gd(1)–O(1)
O(6)#2–Gd(1)–O(1)
O(2)#1–Gd(1)–O(7)
O(6)#2–Gd(1)–O(7)
O(1)–Gd(1)–O(7)
O(2)#1–Gd(1)–O(8)
2.333(3)
2.370(3)
2.380(3)
2.401(3)
Gd(1)–O(4)
Gd(1)–O(3)
Gd(1)–O(5)#3
Gd(1)–O(6)#3
2.470(3)
2.489(3)
2.490(3)
2.726(3)
0.196 mmol) and F4BDC (35.4 mg, 0.149 mmol) gave a white crys-
talline product. Yield: 47.2 mg, 61%, based on F4BDC. Anal. Calc. (%)
for Gd2(F4BDC)3(DEF)2(EtOH)2: C, 34.61; H, 2.60. Found: C, 34.95;
H, 2.61%. FT-IR (KBr): 3448 (br), 2989 (w), 2952 (w), 1648 (s),
1614 (s), 1481 (s), 1411 (br), 1268 (m), 1214 (m), 1128 (m), 983
(s), 827 (w), 738 (s), 659 (m), 478 (m).
2.426(3)
74.83(11)
131.78(10)
72.57(10)
139.13(11)
145.17(10)
75.70(11)
73.15(12)
O(7)–Gd(1)–O(3)
O(8)–Gd(1)–O(3)
O(4)–Gd(1)–O(3)
O(2)#1–Gd(1)–O(5)#3
O(6)#2–Gd(1)–O(5)#3
O(1)–Gd(1)–O(5)#3
O(7)–Gd(1)–O(5)#3
114.16(11)
72.91(12)
52.47(11)
78.25(11)
120.24(11)
88.57(11)
72.36(11)
2.5. Synthesis of Eu2(F4BDC)3(DEF)2(EtOH)2-2(DEF) (3)
Eu(NO3)3ꢁ5H2O (55.4 mg, 0.124 mmol) and F4BDC (40.4 mg,
0.170 mmol) gave a white crystalline product. Yield: 48.5 mg,
64%, based on F4BDC. Anal. Calc. for Eu2(F4BDC)3(DEF)2(EtOH)2-
0.4(DEF): C, 35.67; H, 2.87. Found: C, 35.63; H, 2.61%. FT-IR
(KBr): 3459 (br), 2996 (w), 2958 (w), 1648 (s), 1614 (s), 1473 (s),
1413 (br), 1270 (m), 1216 (m), 1128 (m), 995 (s), 827 (w), 788
(m), 750 (m), 659 (m), 480 (m). Eu2(F4BDC)3(DEF)n (3a) was formed
by heating at 5 °C/min to 150 °C and holding for 1 h. The evacuated
framework was brought back to RT at 5 °C/min and stored over
argon until use.
Compound 3
Eu(1)–O(2)#1
Eu(1)–O(6)#2
Eu(1)–O(1)
Eu(1)–O(7)
Eu(1)–O(8)
O(2)#1–Eu(1)–O(6)#2
O(2)#1–Eu(1)–O(1)
O(6)#2–Eu(1)–O(1)
O(2)#1–Eu(1)–O(7)
O(6)#2–Eu(1)–O(7)
O(1)–Eu(1)–O(7)
O(2)#1–Eu(1)–O(8)
2.340(2)
2.386(3)
2.391(2)
2.407(3)
2.434(3)
74.61(9)
131.61(9)
72.37(9)
139.27(10)
145.14(9)
75.66(9)
72.95(10)
Eu(1)–O(6)#3
Eu(1)–O(4)
Eu(1)–O(3)
2.725(3)
2.479(3)
2.487(3)
2.511(3)
Eu(1)–O(5)#3
O(7)–Eu(1)–O(3)
O(8)–Eu(1)–O(3)
O(4)–Eu(1)–O(3)
O(2)#1–Eu(1)–O(5)#3
O(6)#2–Eu(1)–O(5)#3
O(1)–Eu(1)–O(5)#3
O(7)–Eu(1)–O(5)#3
114.29(9)
72.95(10)
52.34(9)
78.31(10)
120.02(9)
88.69(10)
72.17(9)
2.6. Synthesis of La2(F4BDC)3(DEF)2(EtOH)2-2(DEF) (4)
Compound 4
La(1)–O(2)#1
La(1)–O(1)
La(1)–O(6)#2
La(1)–O(7)
2.439(2)
2.482(2)
2.494(2)
2.508(2)
2.527(2)
130.63(7)
73.07(7)
71.49(7)
140.06(8)
75.84(7)
145.30(7)
72.76(8)
La(1)–O(3)
La(1)–O(4)
La(1)–O(5)#3
La(1)–O(6)#3
2.570(2)
2.581(2)
2.625(2)
2.761(2)
La(NO3)3ꢁ6H2O (64.0 mg, 0.148 mmol) and F4BDC (50.0 mg,
0.212 mmol) gave a white crystalline product. Yield: 46.0 mg,
49%, based on F4BDC. Anal. Calc. for La2(F4BDC)3(DEF)2(EtOH)2-
0.5(DEF): C, 36.54; H, 2.99. Found: C, 36.56; H, 2.82%. FT-IR
(KBr): 3436 (br), 2989 (w), 2950 (w), 1648 (s), 1614 (s), 1475 (s),
1405 (br), 1268 (m), 1214 (m), 1128 (m), 995 (s), 827 (w), 748
(s), 655 (m), 474 (m).
La(1)–O(8)
O(2)#1–La(1)–O(1)
O(2)#1–La(1)–O(6)#2
O(1)–La(1)–O(6)#2
O(2)#1–La(1)–O(7)
O(1)–La(1)–O(7)
O(6)#2–La(1)–O(7)
O(2)#1–La(1)–O(8)
O(1)–La(1)–O(8)
O(6)#2–La(1)–O(8)
O(7)–La(1)–O(4)
O(8)–La(1)–O(4)
O(3)–La(1)–O(4)
O(2)#1–La(1)–O(5)#3
O(1)–La(1)–O(5)#3
151.06(8)
137.34(8)
76.16(8)
92.98(9)
50.52(7)
78.92(8)
89.06(8)
2.7. Synthesis of Nd2(F4BDC)3(DEF)2(EtOH)2-2(DEF) (5)
Nd(NO3)3ꢁ6H2O (78.4 mg, 0.179 mmol) and F4BDC (52.8 mg,
0.222 mmol) gave a white crystalline product. Yield: 47.7 mg,
45%, based on F4BDC. Anal. Calc. for Nd2(F4BDC)3(DEF)2(EtOH)2-
1.5(DEF): C, 37.87; H, 3.53. Found: C, 37.86; H, 3.52%. FT-IR
(KBr): 3446 (br), 2985 (w), 2950 (w), 1654 (s), 1616 (s), 1475 (s),
1409 (br), 1268 (m), 1214 (m), 1128 (m), 995 (s), 827 (w), 748
(s), 657 (m), 476 (m).
Compound 5
Nd(1)–O(2)#1
Nd(1)–O(1)
Nd(1)–O(6)#2
Nd(1)–O(3)
Nd(1)–O(4)
O(2)#1–Nd(1)–O(1)
O(2)#1–Nd(1)–O(6)#2
O(1)–Nd(1)–O(6)#2
O(2)#1–Nd(1)–O(7)
O(1)–Nd(1)–O(7)
O(6)#2–Nd(1)–O(7)
O(2)#1–Nd(1)–O(8)
2.381(3)
2.431(3)
2.436(3)
2.523(3)
Nd(1)–O(5)#3
Nd(1)–O(6)#3
Nd(1)–O(8)
2.559(3)
2.729(3)
2.475(4)
2.447(3)
Nd(1)–O(7)
2.527(3)
131.51(11)
74.03(11)
71.98(11)
139.54(12)
75.81(11)
145.29(11)
72.80(12)
O(7)–Nd(1)–O(4)
O(8)–Nd(1)–O(4)
O(3)–Nd(1)–O(4)
O(2)#1–Nd(1)–O(5)#3
O(1)–Nd(1)–O(5)#3
O(6)#2–Nd(1)–O(5)#3
O(7)–Nd(1)–O(5)#3
75.53(12)
93.25(13)
51.57(11)
78.67(12)
89.02(12)
119.40(11)
71.97(12)
2.8. Catalysis
2.8.1. Synthesis of 5-(ethoxycarbonyl)-6-methyl-4-phenyl-3,4-
dihydropyrimidin-2(1H)-one (6a)
2.8.1.1. Heterogeneous catalysis. Benzaldehyde (30
aThe numbers in parentheses are the estimated standard deviations in the last
significant digit.
lL, 0.29 mmol),
bAtoms are labeled in agreement with Figs. 1 and 2.
ethyl acetoacetate (35 L, 0.28 mmol), urea (30.0 mg, 0.49 mmol),
l
cSymmetry transformations used to generate equivalent atoms: #1 x, y ꢀ 1, z; #2
ꢀx, ꢀy, ꢀz + 1; #3 x, ꢀy, z ꢀ 1/2; #4 x, y + 1, z; #5 x, ꢀy, z + 1/2; #6 ꢀx, y, ꢀz + 1/2.
3 (21.8 mg, 0.014 mmol) and toluene (0.2 mL) were added to a
10 mL round-bottom flask equipped with a reflux condenser. The
mixture was held at 80 °C for 1.5 h, then cooled to RT and diluted
with ethyl acetate. The catalyst was filtered off and the ethyl ace-
tate solution was washed with water (2 ꢂ 15 mL). The organic
phase was dried over MgSO4, filtered, and evaporated to give the
DEF (6 mL) and ethanol (1 mL). The vial was covered with parafilm
which was pierced several times with a needle and set inside a
beaker containing ethanol (5 mL) and triethylamine (0.2 mL). The

C.M. MacNeill et al. / Inorganica Chimica Acta 365 (2011) 196–203
199
crude product. The product was purified by filtration of an ethyl
acetate/petroleum ether solution to give 6a. Yield: 40.5 mg, 50%.
FT-IR (KBr): 3230, 3101, 2974, 2918, 1713, 1697, 1642, 1465,
1418, 1341, 1313, 1291, 1218, 1085, 950, 771. 1H NMR (DMSO-
d6): d = 9.17 (s, 1H, NH); 7.71 (s, 1H, NH); 7.28 (m, 5H, Ar-H);
5.14 (d, 1H, CH); 3.98 (q, 2H, OCH2); 2.25 (s, 3H, CH3); 1.10 (t,
3H, OCH2). GC–MS (m/e, %): 260 [parent M+] (19); 231 (75); 214
(13); 183 (100); 155 (40); 137 (25); 110 (8); 77 (11); 40 (16).
Room temperature reactions followed the same procedure but,
instead of heating, the solution was stirred for three days at ambi-
ent temperature in toluene or MeOH (0.5 mL) (see Table 3).
17.5 mg, 12%. FT-IR (KBr): 3232, 3099, 2975, 2920, 1696, 1644,
1512, 1430, 1376, 1318, 1279, 1267, 1219, 1086, 1025, 949, 766.
1H NMR (DMSO-d6): d = 9.24 (s, 1H, NH); 8.30 (d, 1H, Ar-H); 7.95
(d, 1H, Ar-H); 7.85 (d, 1H, Ar-H); 7.73 (s, 1H, NH); 7.55 (m, 4H,
Ar-H); 6.05 (s, 1H, CH); 3.80 (q, 2H, OCH2); 2.36 (s, 3H, CH3);
0.81 (t, 3H, OCH2).
3. Results and discussion
3.1. Synthesis
The synthesis of compounds 1–5 was carried out by a vapor dif-
fusion method which resulted in precipitation of high purity sam-
ples as confirmed by elemental analyses and powder X-ray
diffraction. Initially, a solvothermal method was employed at vary-
ing temperatures (100, 120 and 145 °C) from 18–48 h in an array of
2.8.1.2. Homogeneous catalysis. Benzaldehyde (50
lL, 0.49 mmol),
ethyl acetoacetate (62 L, 0.49 mmol), urea (49.1 mg, 0.81 mmol),
l
3 (33.3 mg, 0.022 mmol) and water (0.5 mL) were added to a
10 mL round-bottom flask. The solution was stirred at ambient
temperature for 3 days after which the reaction mixture was
diluted with ethyl acetate (10 mL) and washed with water
(2 ꢂ 15 mL). The organic phase was dried over MgSO4, filtered,
and evaporated to give the crude product. The product was purified
by filtration of an ethyl acetate/petroleum ether solution to give
pure 6a.
2.9. Synthesis of 5-(ethoxycarbonyl)-6-methyl-4-(3-thienyl)-3,4-
dihydropyrimidin-2(1H)-one (6b)
The procedure was similar to that for 6a using 3-thiophenecarb-
oxaldehyde (60 lL, 0.29 mmol) in toluene (1 mL) as the aldehyde.
The product was recrystallized from ethanol to give 6b. Yield:
29.6 mg, 13%. FT-IR (KBr): 3220, 3096, 2968, 1720, 1697, 1645,
1457, 1419, 1369, 1319, 1291, 1228, 1086, 950, 763. 1H NMR
(DMSO-d6): d = 9.18 (s, 1H, NH); 7.74 (s, 1H, NH); 7.45 (m, 1H,
Ar-H); 7.15 (s, 1H, Ar-H); 6.98 (d, 1H, Ar-H); 5.21 (d, 1H, CH);
4.05 (q, 2H, OCH2); 2.22 (s, 3H, CH3); 1.15 (t, 3H, OCH2). GC–MS
(m/e, %): 266 [parent M+] (86); 237 (80); 219 (20); 193 (100);
183 (49); 155 (32); 137 (31); 110 (25); 40 (36).
2.10. Synthesis of 5-(ethoxycarbonyl)-6-methyl-4-(1-napthyl)-3,4-
dihydropyrimidin-2(1H)-one (6c)
Using 1-napthylenecarboxaldehyde (76 lL, 0.29 mmol) in tolu-
ene (1 mL) gave 6c after recrystallization from ethanol. Yield:
Table 3
Catalytic syntheses of dihydropyrimidinones under different reaction conditions.a
R1
Solvent
Catalystb
Product
Yield (%)
Temperature (°C)
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
toluene
toluene
none
toluene
MeOH
toluene
MeOH
toluene
MeOH
H2O
none
Yb(OTf)3
Yb(OTf)3
3
6a
6a
6a
6a
6a
6a
6a
6a
6a
6a
6a
6a
6a
6b
6c
6b
6c
6a
6a
0
110
110
110
70
70
70
70
RT
RT
RT
RT
RT
RT
70
70
70
70
70
70
49
55
28
33
38
39
10
21
41
12
19
37
13
12
16
9
3
3a
3a
*
3
*
*
3
3
*
toluene
MeOH
H2O
3a
*
*
3a
C6H5
3a
3-thienyl
1-napthyl
3-thienyl
1-napthyl
C6H5
toluenec
toluenec
toluenec
toluenec
toluene
toluene
3
3
3a
3a
4
28
27
C6H5
5
a
Fig. 1. (a) View of Tb polyhedron. (b) A view of the contents of the asymmetric unit
for Tb2(F4BDC)3(DEF)2(EtOH)2 – 2(DEF) 1. Hydrogen atoms have been omitted for
clarity. (c) A view of the formula unit of 1 containing two identical terbium atoms
represented as polyhedra.
For Yb(OTf)3; 1 mL, reflux, 5 h. For 3–5; 0.2 mL, 70 °C, 1.5 h.
5 mol% MOF 3–5; a = framework activated at 150 °C. *Room temperature,
b
3 days.
c
1.0 mL, 70 °C, 1.5 h.

200
C.M. MacNeill et al. / Inorganica Chimica Acta 365 (2011) 196–203
different solvent systems without adjustment of pH, but no crys-
tals suitable for single-crystal X-ray diffraction were obtained.
Stoichiometric ratios of 1:1 lanthanide metal to H2F4BDC were
utilized for all syntheses, and, in all cases, the same framework
resulted, as indicated by single crystal and powder X-ray diffrac-
tion. DEF was the preferred solvent since use of DMF resulted in
microcrystalline products. Ethanol was chosen as a co-solvent be-
cause enhanced crystal growth resulted compared to use of DEF/
H2O, DEF/MeOH, and DEF/n-propanol mixtures. Powder diffraction
patterns of the synthesized compounds compared to the simulated
powder pattern are reported in the supporting information
(Fig. S1). Since all of the compounds studied are isostructural, only
the structure of 1 is described in detail (Ln2(F4BDC)3(DEF)2(EtOH)2-
2(DEF); Ln = Tb, 1; Gd, 2; Eu, 3; La, 4; and Nd, 5). The bound solvent
cannot be removed at RT, but the compounds tend to lose lattice
DEF upon exposure to air and under vacuum. This is reflected in
the analytical results which show varying amounts of remaining
DEF in the lattice. One sample (Eu) was heated to 150 °C to remove
any lattice and bound DEF, cooled to room temperature and then
pumped at high vacuum overnight. IR analysis (supporting infor-
mation Fig. S4) showed essentially no remaining DEF in the com-
pound. Studies of other MOFs have shown complete removal of
DEF under vacuum at temperatures above 140 °C [20].
3.2. Structure of Tb2(F4BDC)3(DEF)2EtOH2-2(DEF) (1)
Compound 1 crystallizes in the monoclinic space group C2/c
with Z = 4. The framework has an overall two-dimensional struc-
ture. The asymmetric unit contains one terbium TbIII ion, one and
a half F4BDC2ꢀ ligands, one DEF molecule, one EtOH molecule,
and one lattice DEF molecule (Fig. 1a). Each terbium ion is 9-coor-
dinated by the oxygen atoms of two bridging F4BDC2ꢀ ligands (O(1)
and O(2)), two bidentate F4BDC2ꢀ ligands (O(3), O(4)), one
l
3-F4BDC2ꢀ ligand (O(5), O(6)), one oxygen (O(7)) from a DEF
molecule and one oxygen (O(8)) from an EtOH molecule to form
a TbO9 polyhedron. The lattice DEF oxygen (O(9)) is hydrogen-
bonded to the hydrogen on the sp2 carbon of the EtOH molecule
(O(8)–H(O8)ꢁ ꢁ ꢁO(9) 2.699(4) Å). The TbO9 polyhedron can be de-
scribed as a tri-capped trigonal prism. The TbO9 polyhedron is
linked to its adjacent terbium atom (Tb1–Tb1 distance is
4.1450(4) Å) through oxygen atoms from two bridging F4BDC2ꢀ
ligands (O(1), O(2)), and two
l
3-F4BDC2ꢀ ligands (O(5), O(6)) to
form Tb2O16 dimers, due to sharing of the O(6) atom between TbIII
ions (Fig. 1b and c). The Tb–O (from F4BDC2ꢀ) bond lengths of the
dimer range from 2.319(2) Å to 2.478(2) Å, which corresponds well
to known terbium–oxygen bond distances [21]. The two TbIII ions
are related by a two-fold rotation along the b-axis. The dimers re-
sult from slightly offset face to face pi interactions between the
benzene rings within the 1D chain, which have a distance of
3.981 Å.
The dimers are connected to each other by the oxygen atoms of
four F4BDC2ꢀ linking units O(3), O(4), O(5) and O(6) to form a 1D
chain along the c-axis (Fig. 2a). The 1D chains are connected
Fig. 2. (a) A view of the dimer of 1 connected to other dimers through four F4BDC2ꢀ
linkers. (b) A view of (a) forming the overall 2D sheet with solvent molecules and
hydrogen atoms omitted for clarity.
Fig. 3. (a) A view of the 2D sheet of compound 1 along the b-axis. (b) The formation of a 3D layered topology by stacking of the infinite 2D sheets from (a). Lattice DEFs were
omitted for clarity.

C.M. MacNeill et al. / Inorganica Chimica Acta 365 (2011) 196–203
201
through the oxygen atoms of two F4BDC2ꢀ ligands (O(1) and O(2)).
This connection forms an infinite 2D sheet along the bc-plane
with cavities where the hydrogen bonded lattice DEF molecules
lie (Fig. 2b). The distances between dimers along the b- and
c-directions are 11.212 and 10.212 Å, respectively [22]. The layers
stack along the crystallographic a-axis and are held together by
EtOH and DEF solvent molecules located between the sheets
(Fig. 3a and b). The separation between planes along the a-axis is
11.045 Å.
The powder X-ray diffraction data comparing the simulated
pattern to the as-synthesized pattern for this compound can be
seen in Fig. 4b.
3.3. Thermal stability study
The thermal stability of compounds 1–5 was investigated using
thermogravimetric analysis by heating the samples in air to 900 °C
at a rate of 5 °C/min. In the case of compound 1 (Fig. 4a), there was
a loss of two coordinated EtOH molecules between 40 and 115 °C,
followed by loss of two lattice DEF molecules from 115 to 200 °C
(calc. 19.3% exp. 19.2%). A final weight loss of two coordinated
DEF molecules occurred between 250 and 325 °C (calc. 13.2%
exp. 13.0%). The compound is stable to 250 °C and begins to
decompose at 325 °C to give terbium oxyfluoride (TbOF) at
900 °C as determined by PXRD [23]. Similar solvent losses were
Fig. 4. (a) The TGA of compound 1 from 40 to 900 °C at 5 °C/min. (b) Powder
diffraction patterns of compound 1 (simulated), compound 1 (as-synthesized),
compound 1 after heating (TGA) to 250 °C and compound (1) after heating (TGA) to
900 °C.
Fig. 5. (a) A picture of Tb 1, Eu 3 and La 4 under visible light. (b) A picture of Tb 1, Tb
1 and La 4 under UV light. (c) The solid state photoluminescence spectrum of Tb 1
excited at 392 nm. (d) The solid state photoluminescence spectrum of Eu 3 excited
at 300 nm.

202
C.M. MacNeill et al. / Inorganica Chimica Acta 365 (2011) 196–203
Scheme 1. The Biginelli reaction.
observed for compounds 2–5 and can be seen in the supporting
information Fig. S2 and Table S1.
The catalytic activity of 3 and its activated catalyst 3a, from
which solvent had been removed, were compared and the results
are presented in Table 3. Compound 3 is interesting in that it is
insoluble in everything except water, so its homogeneous catalytic
activity in water as well as its heterogeneous activity in toluene and
methanol was investigated. The europium catalyst gave greater
than 50% of the yield observed for Yb(OTf)3 but at a lower
temperature (70°) in about 30% of the time. In the case of heteroge-
neous reactions, the catalyst was easily recovered and re-used
without loss of activity (supporting information, Figs. S5 and S6).
At room temperature over three days, reactions in water give higher
yields of dihydropyrimidinone, comparable to those of Yb(OTf)3, as
would be expected for homogeneous catalysis. To determine
whether catalysis was occurring in the layers or on the surface of
the framework, we compared the catalytic activity of the activated
catalyst 3a to 3. The activated catalyst gave somewhat higher yields
at 70° than did the unactivated catalyst, but the difference may be
due to better access at the surface rather than access to voids in the
framework. There was no significant difference at room tempera-
ture. Aldehyde reactants of different sizes (3-thio-phenecarboxal-
dehyde, 5.7 Å; benzaldehyde 6.1 Å; 1-napthylcarboxaldehyde,
7.9 Å) [27] were chosen to see if catalytic activity decreased as
the size of the reactant increased. The distance between the layers
in 3 is 7.4 Å (based on the Eu(1)–Eu(1) distance). The yields of the
corresponding dihydropyrimidinones at 70° were similar for the
different aldehydes (6b, 13%; 6c, 12%) indicating a constant activity,
regardless of size. These results suggest that catalysis occurs at the
surface and not between the layers. Finally, the catalyst was finely
ground to increase surface area. If catalysis were taking place on the
surface, as the surface area increased, the yield of the Biginelli prod-
uct should also have increased. A modest increase in Biginelli prod-
uct was observed (7–10%) consistent with the conclusion that
catalysis occurs on the surface. Compounds 4 and 5 gave yields
comparable to those obtained for 3 at 70 °C for 1.5 h.
3.4. Infrared spectroscopy
Infrared spectra of compounds 1–5 were measured between
400 and 4000 cmꢀ1 (Fig. S3). The IR spectrum of 1 shows a broad
band at 3450 cmꢀ1 which corresponds to the O–H stretch of the
ethanol. The weak vibrations at 2989 cmꢀ1 and 2950 cmꢀ1 corre-
spond to the DEF C–H methyl and DEF C–H aldehyde stretching
modes. The stretching frequency for the carbonyl group on the
benzene ring, normally in the range of 1680–1720 cmꢀ1, was low-
ered after coordination to the lanthanide metal ion. The asymmet-
ric and symmetric stretching modes for the bound carboxylate
groups occur at 1623 cmꢀ1 and 1411 cmꢀ1. The DEF C@O stretch
can be seen at 1660 cmꢀ1
.
3.5. Solid state photoluminescence
The room temperature solid state photoluminescence spectra for
1 and 3 were taken and can be seen in Fig. 5. Upon excitation, 1 emits
a green luminescence (Fig. 5a). The transitions appear at 489, 544,
585 and 620 nm and are attributed to the 5D4–7Fj (J = 6, 5, 4, 3) bands
[7,24]. The 5D4–7F5 transition (hypersensitive) is the most intense
peak and the 5D4–7F6 transition is second in intensity consistent
with other Tb-based systems [3a]. Compound 3 emits a red lumines-
cence. The emission peaks which appear at 590, 615, 650 and
695 nm are attributed to the 5D0–7Fj, (J = 1, 2, 3, 4) transitions
respectively, with the strongest emission attributed to the 5D0–7F2
transition at 615 nm (Fig. 5d). The appearance of the broad, low
intensity, forbidden 5D0–7F0 transition indicates that the metal is
in a non-centrosymmetric ligand field. The 5D0–7F2 electric-dipole
transition is sensitive to the coordination environment around the
europium ion and is almost twice the intensity of the 5D0–7F1 tran-
sition (a magnetic dipole transition relatively insensitive to the
coordination environment) which again indicates that the euro-
pium ion does not sit on an inversion center. This information was
very helpful in the crystal structure analysis [25].
4. Conclusions
Five new 2D lanthanide-based coordination polymers incorpo-
rating 2,3,5,6-tetrafluoro-1,4-benzenedicarboxylate have been
synthesized using a vapor diffusion method and characterized by
single crystal X-ray diffraction, powder diffraction, infrared spec-
troscopy and thermogravimetric analysis. The frameworks consist
of lanthanide metal ions linked by [F4BDC]2ꢀ ligands to form 2D
sheets, which stack to form a layered topology with solvent mole-
cules between the sheets. DEF and EtOH can be removed from the
layers with full retention of the framework upon heating to 150 °C.
Compounds 1 and 3 showed photoluminescent properties upon
excitation at 392 nm and 350 nm, respectively. Compounds 3–5
showed catalytic activity in the Biginelli reaction, which provided
a more rapid synthesis compared to previous methods [28].
Evidence suggests that the catalysis is taking place at the surface
of the framework and not within the layers of the framework.
3.6. Catalytic properties
Lanthanide triflate salts are the most widely used homogeneous
Lewis acid catalyst giving moderate yields in a number of solvents,
under a range of conditions, and using a variety of different starting
reagents [26]. Lanthanide triflates, however, are difficult to recover
because excess solvent must be removed and the triflates must be
dried under vacuum for several hours in order to reuse them. The
Biginelli reaction has been used to assess the Lewis acid catalytic
properties of HIOMs by other groups [15,16]. However; their syn-
theses were carried out at room temperature, some contained
potentially catalytic acid groups, and most required 2–3 days for
moderate yields. In light of this fact, we explored the catalytic
activity of the compounds reported here under a shorter time per-
iod (1.5 h) and a longer period (3 days) under different conditions
of temperature. Compounds 3–5 all gave similar yields so we chose
to focus on compound 3 for this study (Scheme 1).
Acknowledgements
The authors thank the Wake Forest University Scientific
Research Fund for support and the National Science Foundation
(NSF-02344889) for support of X-ray equipment.

C.M. MacNeill et al. / Inorganica Chimica Acta 365 (2011) 196–203
[14] (a) C.O. Kappe, Eur. J. Med. Chem. 35 (2000) 1043;
203
Appendix A. Supplementary material
(b) C.O. Kappe, Tetrahedron 49 (1993) 6937;
(c) C.O. Kappe, Acc. Chem. Res. 33 (2000) 879.
CCDC 768795, 768796, 768797, 768798 and 768799 contain the
supplementary crystallographic data for compounds 1–5. These
data can be obtained free of charge from The Cambridge Crystallo-
graphic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.ica.2010.09.013.
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