Photoluminescent metal-organic frameworks - Rapid preparation, catalytic activity, and framework relationships

Article abstract of DOI:10.1002/ejic.201300637

An optimized microwave-assisted synthesis has been used to prepare an isotypical series of 3D Ln³⁺ metal-organic frameworks (MOFs) based on residues of 2,5-pyridinedicarboxylic (pydc), namely, [Ln₂(pydc) ₃(H₂O)<

Full text of DOI:10.1002/ejic.201300637

FULL PAPER
DOI:10.1002/ejic.201300637
Photoluminescent Metal–Organic Frameworks – Rapid
Preparation, Catalytic Activity, and Framework
Relationships
Patrícia Silva,[a] Duarte Ananias,*[a,b] Sofia M. Bruno,[a]
Anabela A. Valente,[a] Luís D. Carlos,[b] João Rocha,[a] and
Filipe A. Almeida Paz*[a]
Keywords: Microwave chemistry / Luminescence / Heterogeneous catalysis / Metal–organic frameworks / Lanthanides
An optimized microwave-assisted synthesis has been used to
[Ln2(pydc)3(H2O)2] compounds are very similar to the pre-
prepare an isotypical series of 3D Ln3+ metal–organic frame- viously reported microporous 3D [Ce2(pydc)2(Hpydc)(H2O)2]-
works (MOFs) based on residues of 2,5-pyridinedicarboxylic
Cl·(9 + y)H2O; layered [{Ce2(pydc)2(Hpydc)2(H2O)4}·2H2O]n
can be isolated at lower temperatures and transforms to [Ce2-
(pydc)3(H2O)2] under certain experimental conditions. Com-
pound 1 is an effective solid catalyst for the ring opening of
styrene with methanol under mild reaction conditions (55 °C)
to give 2-methoxy-2-phenylethanol in 100% selectivity and
ca. 80% conversion. The mixed-lanthanide materials are ef-
fective UV-to-visible light converters (red 1-LaEu, green 1-
LaTb, and orange 1-LaEuTb). The compounds have very
high absolute emission quantum yields (43% for 1-LaEu and
75% for 1-LaTb) under indirect excitation of the UV ligand
bands with lifetimes of 0.50 and 1.06 ms for 1-LaEu and 1-
LaTb, respectively, and these properties result from effective
intersystem crossing and ligand-to-metal transfer processes.
(pydc), namely, [Ln2(pydc)3(H2O)2] with Ln3+ = Ce3+ (1),
3+
3+
(La0.95Eu0.05
)
(1-LaEu), (La0.95Tb0.05
)
)
(1-LaTb), and
3+
(La0.90Eu0.05Tb0.05
(1-LaEuTb). The materials can be read-
ily isolated as microcrystals after 1 min of reaction time at
120 °C. The compounds have been extensively studied in the
solid state by vibrational spectroscopy (FTIR and FT-Raman),
thermogravimetry, powder X-ray diffraction, elemental
analysis, and electron microscopy (SEM, SEM mapping, and
TEM). The structural relationships between the isolated ma-
terials and other solids reported in the literature have been
investigated in detail from a structural and topological per-
spective with attention focused on the different connectivi-
ties of the employed organic ligand. The 3D densely packed
Later in the 1990s, coordination chemists transposed the
hydro(solvo)thermal method from zeolite chemistry to the
MOF field.[4] This mimicking of zeolite chemistry allowed
immediately a considerable reduction of reaction times
(nowadays, a couple of days are typically employed) by in-
creasing the temperature and (autogenously) the pressure,
and also the isolation of other less stable thermodynamic
phases. This method drove chemists worldwide to a rapid
screen of possible structural architectures[4a,5] and the pro-
duction of enough material to allow the study of their vari-
ous potential applications[6] in the gas storage and (selec-
tive) adsorption fields,[7] enantioselective separation of mo-
lecules,[8] biomedicine,[9] heterogeneous catalysis,[10] magnet-
ism,[11] fabrication of membranes[7g,12] or thin films,[13] and
photoluminescence.[11j,11k,14]
At present, an outstanding question in the MOF field is
how to produce functional materials by economically viable
synthetic approaches. It is clear that even only the two or
three days usually employed in the hydro(solvo)thermal
method may not be viable. The most striking example con-
cerns one of the few commercial MOFs: Basolite is pro-
duced by BASF by an electrochemical approach that com-
pletely replaces the traditional hydrothermal method re-
Introduction
Synthetic approaches towards the isolation of metal–or-
ganic frameworks (MOFs), also commonly designated as
coordination polymers, have changed considerably since the
seminal paper by Hoskins and Robson.[1] Initially, the isola-
tion of large single crystals was a strict requirement owing
to the limitations of the single-crystal instruments. Ap-
proaches such as slow evaporation, diffusion in various me-
dia, and reflux reactions were preferred; however, these
methods provided limited yields and were particularly time
consuming.[2] These approaches led to the discovery of
amazing structural architectures and to the self-assembly of
highly interpenetrated frameworks, which allowed struc-
tural chemists to find countless structures with topological
features that mimic those typically found in minerals.[3]
[a] Department of Chemistry, CICECO, University of Aveiro,
3810-193 Aveiro, Portugal
E-mail: filipe.paz@ua.pt
dananias@ua.pt
http://www.ciceco.ua.pt/filipepaz
[b] Department of Physics, CICECO, University of Aveiro,
3810-193 Aveiro, Portugal
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201300637.
Eur. J. Inorg. Chem. 2013, 5576–5591
5576
© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
ported by Williams.[15] This alternative method is faster, results concerning the use of a new, faster, and cleaner syn-
more efficient, and also cleaner (with a minimum of waste thetic methodology to obtain these functional materials and
disposal). If MOFs are to be employed in the near future a detailed investigation of their catalytic and photolumines-
in the fabrication of functional devices, more rapid, effec- cent properties.
tive, and highly controllable synthetic approaches must be
devised.
Results and Discussion
Microwave heating is a highly efficient method because it
can heat simultaneously the whole reactants and ultimately
remove convection and conduction effects inside the reac-
tor. This approach has been successfully used in various
branches of organic synthetic chemistry,[16] as the smooth
reaction conditions can improve and make some difficult
chemical processes possible and, in addition, cleaner
(“green”) solvents can be used. Owing to the faster heating
and higher homogeneous temperature distribution, micro-
wave-assisted synthesis (MWAS) usually implies a consider-
able reduction in reaction times and increased overall yields.
MWAS may allow morphology control and phase selectiv-
ity, which, in many cases, is accompanied by uniform par-
ticle-size distribution and a quicker and more efficient
evaluation of the reaction parameters.[17] The use of MWAS
in MOF preparation is still in its infancy and remains far
from industrial application. However, a number of interest-
ing reports are now available.[18]
Microwave-Assisted Hydrothermal Synthesis
Shao and Hong have reported the structures of
[Pr2(pydc)3(H2O)2] and [La2(pydc)3(H2O)2] based on single-
crystal data sets: the crystals were grown from hydrother-
mal synthesis over a period of three days.[22a,22b] Based on
our recent studies, this synthetic method is not only time
consuming but also highly inefficient from the energetic
standpoint.[19] The change of the experimental conditions
to MWAS[18e] resulted in the isolation of microcrystalline
powders, which were identified from powder X-ray diffrac-
tion (PXRD) as mixtures of phases. Therefore, the optimi-
zation of the MWAS conditions (hereafter, samples are de-
noted TmPntp, the subscripts indicate the specific experi-
mental conditions employed for temperature T, power P,
and reaction time t) for the [Ln2(pydc)3(H2O)2] materials
was pertinent to avoid the formation of secondary materials
and take advantage of the short reaction times typical of
this synthetic method.[18e]
In the last decade or so, we have been interested in all
aspects of the synthesis and characterization of MOFs, and
this has included specific studies towards the investigation
of the best conditions to obtain a certain material.[19] In
particular, we have focused our attention on the use of lan-
thanides owing to their intrinsic photoluminescent proper-
ties.[14b,14c,14g,20] While investigating MWAS for the lantha-
nide/2,5-pyridinedicarboxylic acid system (H2pydc),[14g,21]
for which only a handful of structures is available in the
literature,[14g,22] we discovered a new MOF structure with
largeone-dimensionalchannels,[Ce2(pydc)2(Hpydc)(H2O)2]-
Cl·(9 + y)H2O.[18g] Although large single crystals of this
compound were directly isolated from the reaction vial by
filtration, a second phase was also systematically present.
This latter material was identified as isotypical with the
structures of [Pr2(pydc)3(H2O)2][22b] and [La2(pydc)3-
(H2O)2][22a] reported by Shao and Hong. During our con-
tinuing studies on these systems, we have discovered that
the substitution of small amounts of La3+ cations in the
latter network by optically active lanthanide centers pro-
duces materials with remarkable photoluminescent proper-
ties, a feature that is highly unusual among related materi-
als.[14e] Indeed, even with one water molecule attached to
the Ln3+ ions, the materials have very high absolute emis-
sion quantum yields (up to 43 and 75%), with lifetimes of
Rationale
In general, the test compounds have been prepared by
using a different composition of the reactive gels used by
Shao and Hong.[22a,22b] We discovered that our experimen-
tal conditions produce better results for microwave irradia-
tion:
(a) NaOH has been added to the reactive gel (in excess
for the complete deprotonation of 2,5-H2pydc). As MWAS
is expected to induce a fast rate of nucleation, the addition
of a strong base before the reaction ensures the immediate
availability of carboxylate groups for coordination.
(b) We have selected Ce3+ as the metallic node because
(i) [Ce2(pydc)3(H2O)2][22b] is a secondary phase that appears
in the preparation of microporous [Ce2(pydc)2(Hpydc)-
(H2O)2]Cl·(9 + y)H2O[18g] and, more importantly, (ii) Ce3+
compounds find countless technological applications in
photoluminescent materials, fuel cells, glass, the ceramic
and metallurgic industries, catalytic materials, and several
others.[24]
For the engineering of photoluminescent materials, the
presence of dilute amounts of Eu3+ and Tb3+ ions dispersed
in a matrix of nonemitting ions, such as La3+ ions, is usually
desirable. As [Pr2(pydc)3(H2O)2] and [La2(pydc)3(H2O)2] are
isotypical,[22a,22b] we have employed La3+ as the main met-
allic node for the functional materials.
ca. 0.50 and 1.06 ms for the isotypical La3+/Eu3+ and La3+
/
Tb3+ materials, respectively. We have further explored the
use of this framework as a heterogeneous catalyst in the
conversion of styrene oxide into 2-methoxy-2-phenyleth-
anol by epoxide ring opening with methanol under mild
conditions. This reaction represents an important step in
the preparation of β-alkoxy alcohols, which are often used
Optimization of MWAS for the Isolation of [Ce2(pydc)3-
(H2O)2] (1)
To identify the best experimental MWAS conditions
as solvents or intermediates in several branches of organic (temperature, microwave irradiation power, and time of re-
and inorganic synthesis.[23] In this paper, we summarize our action) that lead to the desired material as a highly crystal-
Eur. J. Inorg. Chem. 2013, 5576–5591
5577
© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
line phase-pure compound with uniform crystal mor-
phology, a series of test compounds from distinct experi-
mental conditions have been prepared (Scheme 1). The
compounds were analyzed by using a combination of pow-
der X-ray diffraction, SEM imaging, and CHN elemental
analyses.
Figure 1. Electron microscopy images of 1 (a) isolated from hydro-
thermal synthesis (170 °C for 72 h) and (b) synthesized by using
optimal MWAS conditions.
Crystal Structure
Description
All isotypical materials prepared and studied in the pres-
ent manuscript have been systematically isolated as micro-
crystalline powders directly from the MWAS reaction vial:
[Ce2(pydc)3(H2O)2] (1), [(La0.95Eu0.05)2(pydc)3(H2O)2] (1-
LaEu), [(La0.95Tb0.05)2(pydc)3(H2O)2] (1-LaTb), [La2-
(pydc)3(H2O)2] (1-La), and [(La0.90Eu0.05Tb0.05)2(pydc)3-
(H2O)2] (1-LaEuTb). Powder X-ray diffraction unequivo-
cally identified the materials as having identical frameworks
to those reported for [Pr2(pydc)3(H2O)2] and [La2(pydc)3-
(H2O)2] by Shao and Hong.[22a,22b] Rietveld and Le Bail
whole-powder-profile fittings have been performed for all
prepared materials, and the data for 1 is provided in the
present manuscript (Figure 2 and Table 1; the data for the
remaining four samples not shown).
Scheme 1. TmPntp diagram for the MWAS optimization of the syn-
thesis of [Ce2(pydc)3(H2O)2] (1). Red, absence of the desired mate-
rial or amorphous phase; mixture, a mixture of the desired material
with other phases; green, [Ce2(pydc)3(H2O)2] (1) as a phase-pure
material.
The study of the influence of the reaction parameters
revealed the following:
(i) [Ce2(pydc)3(H2O)2] (1) can be obtained over a wide
range of experimental conditions as a pure material with
high crystallinity.
(ii) Small modifications to the experimental conditions
have considerable effects on the crystal size and overall crys-
tallinity of the products; the crystallinity is significantly im-
proved with increasing irradiation power.
Table 1. X-ray data collection, crystal data, and structure refine-
ment details for 1.
(iii) At 90 °C, the recovered products were composed of
1 (for 1 min reaction periods) and another compound,
which was, a posteriori, identified from PXRD as isotypical
with the layered material [{Ce2(pydc)2(Hpydc)2(H2O)4}·
2H2O]n, which is isotypical with the Nd3+-based compound
reported by Zhang et al.[22i] For 5 min of reaction, the phys-
ical mixture was essentially composed of 1. Longer reaction
periods ensured the presence of phase-pure, highly crystal-
line compounds (Scheme 1 and Figure S1).
(iii) At 120 °C, highly crystalline 1 is isolated for most
tested conditions. We further note that for this temperature,
after the initial formation of the crystals, increased irradia-
tion times lead to crystal degradation (Figure S2). This be-
havior is not unprecedented under MWAS and it was re-
ported by Choi for the iconic MOF-5 structure.[18d]
(iv) For most experimental conditions, crystals of 1 were
obtained as large aggregates of microsized platelike crystals
(Figure 1): we found that for this system under MWAS,
there is a tendency for crystallites to aggregate, which leads
to spherical clusters with dimensions ranging from a few
micrometers to dozens of micrometers.
Formula
C21H13Ce2N3O14
811.58
monoclinic
P21/c
6.5503(4)
17.9777(10)
9.4217(5)
95.419(4)
1104.54(11)
2
Formula weight
Crystal system
Space group
a [Å]
b [Å]
c [Å]
β [°]
Volume [Å3]
Z
Dc [gcm–3]
Profile function
η
2.440
pseudo-Voigt
0.489(9)
U = –0.10(1)
V = 0.101(6)
W = 0.0168(7)
0.069(3) and 0.0451(7)
–0.010(2)
989
1
11
64
3.99
Caglioti law parameters
Asymmetry parameters (up to 25° 2θ)
Zero shift [2θ°]
Independent reflections
Global refined parameters
Profile refined parameters
Intensity-dependent refined parameters
[a]
Rp
[a]
Rwp
5.39
1.08
25.0
13.0
[a]
Rexp
In summary, the optimal experimental conditions to ob-
tain 1 as a pure phase are 120 °C, 50–80 W, and 1–10 min.
Lower irradiation power and shorter reaction times ensure
a significantly more efficient synthetic procedure than those
reported for the analogous materials.[22a,22b]
χ2[a]
RBragg
RF
19.0
[a] Reliability factors for all nonexcluded data points with Bragg
contribution conventional – not corrected for background).
Eur. J. Inorg. Chem. 2013, 5576–5591
5578
© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
Figure 2. Final Rietveld plot for 1. Observed data points are indicated as red circles, and the best-fit profile (upper trace) and the
difference pattern (lower trace) are drawn as solid black and blue lines, respectively. Green vertical bars indicate the angular positions of
the allowed Bragg reflections. The refinement details are given in Table 1. Inset: Crystal packing of 1 viewed in perspective along the
[001] direction of the unit cell.
Compound 1 is formed by a single crystallographically in- pydc2– ligand (Figure 3, a and Table 2). Notably, although the
dependent Ce3+ metallic center, which is coordinated to one O1/O6/O3/O5 base of the antiprism is almost planar, the O1/
water molecule plus six organic ligands (Figure 3). However, O2/O4/O7 base is significantly more distorted with distances
the asymmetric unit of the material is only composed of a from the atoms to the average plane of ca. 0.075–0.093 Å. In
whole N,O-chelated pydc2– organic ligand plus another half addition, the two average planes are not parallel and subtend
of such a moiety with its center of gravity located at a crystal- a small angle of ca. 4.4° towards the coordinated water mole-
lographic inversion center. This latter crystallographic feature cule (owing to the presence of hydrogen bonds with nearby
has a strong influence on the crystal features, as described carboxylate groups). As also depicted in Figure 3 (a), the cen-
below in more detail. Thus, the Ce3+ center is nine-coordinate tral Ce3+ cation is also closer to the former basal plane (ca.
with an overall {CeNO8} coordination sphere, which strongly 0.93 Å) than to the latter (ca. 1.82 Å), most likely because of
resembles a distorted square antiprism with one of the basal the attractive effect of the coordinated nitrogen atom of the
planes capped by the nitrogen atom of the N,O-chelated N,O-chelated pydc2– organic ligand.
Figure 3. (a) Schematic representation of the capped nine-coordination {CeNO8} coordination environment of the Ce3+ cation, which
resembles a distorted square antiprism. The N,O-chelated pydc2– organic ligand is depicted to emphasize the capped polyhedral base. (b)
Portion of the crystal structure of 1 showing the one-dimensional tape of {CeNO8} polyhedra interconnected through the syn,syn bridges
of the aforementioned N,O-chelated pydc2– ligand. For selected bond lengths and angles see Table 2. Symmetry transformations used to
generate equivalent atoms: (i) –1 + x, y, z; (ii) 1 – x, –1/2 + y, 1.5 – z; (iii) 1 – x, 2 – y, 1 – z; (iv) x, 1.5 – y, –1/2 + z.
Eur. J. Inorg. Chem. 2013, 5576–5591
5579
© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
Table 2. Selected bond lengths [Å] and angles [°] for the crystallo- (hence, the presence of small channels with solvent mole-
graphically independent Ce3+ coordination environment in 1.[a]
cules). For 1 (and its isotypical members of the series), the
Ce–pydc layers coalesce instead along the [100] direction of
the unit cell, which leads to a densely packed material. This
occurs mainly because the release of the extra organic li-
gand (see empirical formulae of the compounds) permits
the remaining ones to accommodate and establish new con-
nections. Under MWAS, this process seems to be clearly
driven by increased reaction temperature (Scheme 1).
Ce1–O1
2.555(4)
2.682(7)
2.723(12)
2.401(5)
2.432(10)
Ce1–O5
Ce1–O6i
Ce1–O7
Ce1–N1
2.644(14)
2.650(14)
2.618(15)
2.745(6)
Ce1–O1iv
Ce1–O2iv
Ce1–O3iii
Ce1–O4ii
O1–Ce1–O1iv
O1–Ce1–O2iv
O1iv–Ce1–O2iv
O1–Ce1–O3iii
O1iv–Ce1–O3iii
O1iv–Ce1–O4ii
O1–Ce1–O5
142.4(4)
94.5(3)
48.3(2)
135.2(3)
77.9(3)
93.4(3)
84.0(5)
79.1(5)
71.2(3)
72.7(4)
138.7(4)
130.8(4)
62.9(4)
58.7(3)
142.4(4)
124.6(4)
65.8(4)
87.0(4)
O2iv–Ce1–O6i
O2iv–Ce1–O5
O2iv–Ce1–N1
O3iii–Ce1–O4ii
O3iii–Ce1–O5
O3iii–Ce1–O6i
O3iii–Ce1–O7
O3iii–Ce1–N1
O4ii–Ce1–O5
O4ii–Ce1–O6i
O4ii–Ce1–O7
O4ii–Ce1–N1
O5–Ce1–O6i
O5–Ce1–O7
O5–Ce1–N1
O6i–Ce1–O7
O6i–Ce1–N1
O7–Ce1–N1
143.2(4)
71.6(4)
137.3(4)
140.6(7)
88.6(7)
84.3(6)
77.3(6)
76.9(2)
127.8(5)
77.4(5)
64.8(5)
123.6(3)
137.8(5)
141.3(5)
73.0(5)
77.1(5)
64.9(5)
135.6(5)
Topological Studies
The chemical possibility of the simultaneous formation
of 1 and the porous [Ce2(pydc)2(Hpydc)(H2O)2]Cl·(9 + y)-
H2O material[18g] previously reported by us can structurally
be better understood by mathematically reducing both net-
works to nodes and connecting rods and, in this way, the
materials can be topologically classified and mutual rela-
tionships can be found. By following the recommendations
of Alexandrov et al.,[25] who have suggested that any moiety
(ligand or atoms) that connects more than two metallic cen-
ters (μn) should be considered as a network node, in 1 all
crystallographically independent moieties (the Ce3+ cation
and the two organic ligands) must then be considered as
O1iv–Ce1–O5
O1–Ce1–O4ii
O1–Ce1–O6i
O1iv–Ce1–O6i
O1–Ce1–O7
O1iv–Ce1–O7
O1–Ce1–N1
O1iv–Ce1–N1
O2iv–Ce1–O3iii
O2iv–Ce1–O4ii
O2iv–Ce1–O7
[a] Symmetry transformations used to generate equivalent atoms:
(i) –1 + x, y, z; (ii) 1 – x, –1/2 + y, 1.5 – z; (iii) 1 – x, 2 – y, 1 – z; network nodes. Interestingly, [Ce2(pydc)2(Hpydc)(H2O)2]Cl·
(iv) x, 1.5 – y, –1/2 + z.
(9 + y)H2O has almost identical composition for the asym-
metric unit: the inclusion of a chloride anion in the material
The aforementioned N,O-chelated pydc2– organic ligand
is also the moiety responsible for the interconnection of in-
dividual {CeNO8} polyhedra along the [001] direction of
the unit cell by establishing a syn,syn bridge with an adja-
cent Ce3+ cation (Figure 3, b). This leads to the formation
of a tape in which the shortest intermetallic Ce···Ce dis-
tance is 4.8875(4) Å. These moieties constitute the “core”
of the densely packed Ce–pydc layers described in the fol-
lowing subsection. The centrosymmetric pydc2– anionic li-
gand attaches itself to the remaining polyhedra coordina-
tion sites (depicted as orange circles in Figure 3, b), which
leads to the densely packed crystal structure of 1 shown in
the inset in Figure 2. As the nitrogen atom of this moiety
is not attached to the metallic center and is located on a
crystallographic center of inversion, the moiety appears
highly disordered in the crystal structure.
promotes the protonation of the uncoordinated nitrogen
atom and, hence, leads to a completely distinct network. By
considering (1) the centers of gravity of each crystallograph-
ically independent pydc2– anionic ligand and the Ce3+ met-
allic center as nodes and (2) the internodal connections
through the organic ligands (only connections through the
carboxylate ligands were considered) as bridges, the
TOPOS[26] software package reveals that although 1 is a
4,4,6-trinodal network with an overall Schäfli symbol of
{42·84}{44·62}2{49·66}2 (Figures 5 and S6), as described by
Hong et al.,[22a] [Ce2(pydc)2(Hpydc)(H2O)2]Cl·(9 + y)H2O
must only be considered as a 4,6-binodal network described
by the {44·62}3{49·66}2 Schäfli symbol.
In both compounds, the crystallographically independent
Ce3+ cation appears as a six-connected node with identical
point symbol ({49·66}). Nevertheless, the coordination se-
quences are distinct, and N10 is 252 for 1 and 227 for [Ce2-
(pydc)2(Hpydc)(H2O)2]Cl·(9 + y)H2O, which clearly dem-
Framework Relationships
For low reaction temperatures, compound 1 could be iso- onstrates that the latter material is more open (i.e., it corre-
lated alongside the layered compound [{Ce2(pydc)2(Hpydc)2- sponds to a less dense network). Identical features are
(H2O)4}·2H2O]n, which is isotypical with that reported by found for the N,O-chelated pydc2– organic ligand: in both
Zhang et al.[22i] By inspecting both crystal structures, one structures, these moieties are 4-connected nodes with
can find striking structural relationships that help explain {44·62} point symbol. Remarkably, the topological distinc-
the reason for this.
tion between the two networks arises mainly from the disor-
Both structures are formed by a core well-defined Ln– dered organic ligand: although the two ligands in [Ce2-
pydc layer in which the organic ligand is strongly N,O-che- (pydc)2(Hpydc)(H2O)2]Cl·(9 + y)H2O have identical coordi-
lated to the metallic center (Figure 4). For the Ce3+ frame- nation sequences up to the 10th shell, which makes the two
work that is isotypical with the Nd3+-based material, there ligands topologically equivalent (hence, the aforementioned
is an extra ligand per formula unit and this same moiety is binodal description), small differences occur in the fourth
also N,O-chelated. As a consequence, the core Ce–pydc lay- and eighth shells in 1 (even though N10 is the same for both
ers are very distant from each other and the external ligands). Notably, the topological density (TD10) of the
Hpydc– ligand imposes steric hindrance in the structure structures clearly shows that 1 is significantly more dense
Eur. J. Inorg. Chem. 2013, 5576–5591
5580
© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
Figure 4. Framework deconstruction and comparison between the 3D [Ce2(pydc)3(H2O)2] (1) material herein reported and the 2D network
[{Nd2(pydc)2(Hpydc)2(H2O)4}·2H2O]n described by Zhang et al.[22i] The latter material has one extra organic ligand per metallic center,
which occupies the interlayer spaces. This creates considerable steric hindrance and removes coordination sites at the Nd3+ center and
ultimately prevents the connections along the [010] direction of the unit cell. In 1, this extra Hpydc ligand does not exist and this permits
the formation of skew–skew bridging connections to form the 3D network.
have already been enumerated and found for MOF struc-
tures. Compound 1 belongs to the 4,4,6T19 topological
type, whereas [Ce2(pydc)2(Hpydc)(H2O)2]Cl·(9 + y)H2O,
as described previously, shares the topology with the
stp framework. However, a literature search reveals that
the 4,4,6T19 topology is also not very common and
only appears for lanthanide-containing frameworks to
date.[22a,22b,29]
Thermal Stability – Influence of Crystal Size
Microcrystals of 1, obtained under MWAS, have a con-
siderably higher external surface area, which can have a sig-
nificant impact on the properties of the materials, for exam-
ple, their thermal stability. In this context, the thermal sta-
bility of bulk (phase-pure) 1 was investigated between ambi-
ent temperature and ca. 800 °C for the materials prepared
both under conventional hydrothermal conditions (see Ex-
perimental Section for details of the synthesis) and MWAS
Figure 5. Topological representation of the trinodal framework of
1 with overall Schäfli symbol of {42·84}{44·62}2{49·66}2.
than [Ce2(pydc)2(Hpydc)(H2O)2]Cl·(9 + y)H2O (TD10
=
1226 and 1100, respectively).
Searches in the Reticular Chemistry Structure Resource (Figure 6). We note that the thermal behavior described be-
(RCSR)[27] and in EPINET[28] reveal that both networks low only for the Ce3+-based compounds was also observed
Eur. J. Inorg. Chem. 2013, 5576–5591
5581
© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
Figure 6. Thermograms of 1 prepared by different synthetic procedures. Black line: phase-pure 1 obtained by MWAS; red line: phase-
pure 1 obtained by conventional hydrothermal heating. Inset: SEM images of 1 isolated from (a) typical hydrothermal synthesis (170 °C,
72 h) and (b) optimal MWAS conditions (120 °C, 50–80 W, 1–10 min).
for the mixed-lanthanide materials in an independent ex- mal synthesis) does not seem to be so uniform and most
periment (data not shown).
likely leads to the isolation of mixed-valence Ce3+/Ce4+ ox-
[Ce2(pydc)3(H2O)2] prepared under static hydrothermal ides and/or to the presence of charcoal in the residue.
conditions is thermally stable to ca. 140 °C. Above this tem-
perature, a gradual weight loss of ca. 4.8% is attributed to
the release of two coordinated water molecules per formula
unit (calculated 4.4%). Above ca. 340 °C, there is a second
Catalytic Studies
abrupt weight loss globally corresponding to ca. 50.9%,
Our recent investigations of new phosphonic-based
which is attributed to the decomposition of the organic MOFs introduced compounds with remarkable catalytic
component and the concomitant collapse of the framework. performances among other properties. Catalytic screening
The materials prepared under MWAS do not show such tests based on cis-cyclooctene epoxidation, acid-catalyzed
remarkable distinct regions of thermal stability. As shown isomerization of α-pinene oxide, ring opening of styrene ox-
in Figure 6, decomposition starts immediately at low tem- ide, and cyclodehydrogenation of xylose to furfural under
peratures, and there are no well-defined stages of frame- different experimental conditions have been evaluated and
work stability as described above for the large crystals. For reported.[14b,20,30] As the ring-opening reaction of styrene
example, the first and the second decomposition stages al- oxide with methanol gave the best results, for comparative
most overlap. Clearly, these profile differences are a direct purposes, this reaction was chosen for the present set of
consequence of the expected larger surface area of the mate- catalytic tests for 1. Cerium-containing salts such as Ce-
rials prepared by MWAS, which facilitates both the release (OTf)4 and (NH4)8[CeW10O36]·20H2O are effective catalysts
of water molecules and the decomposition of the frame- in the latter reaction.[31] However, high regioselectivity and
work.
conversions have been also reported for the lanthanide pre-
Another striking difference of the decomposition of the cursor CeCl3·7H2O used herein.[32] Nevertheless, the major
two materials prepared by the distinct synthetic approaches limitation of these homogeneous catalysts is the difficult
concerns the residue at ca. 500 °C. For 1 obtained by stan- catalyst recyclability, which ultimately makes their potential
dard hydrothermal synthesis, the residue is ca. 44.2% of the application unattractive. Cu- and Fe-based MOFs have
initial mass, whereas for the small crystallites obtained by been tested in the same reaction. Despite their good cata-
MWAS, the residue is only ca. 41.0%. For the formation of lytic performance, the 2-methoxy-2-phenylethanol yield was
a stoichiometric amount of Ce2O3 with respect to the em- not quantitative because product selectivity was less than
pirical formula of 1, a residue of ca. 40.4% would be ex- 100%.[10m,33] We have reported lanthanide polyphosphon-
pected. This value agrees much better with that observed ate MOFs as effective catalysts for this reaction, and, al-
for the calcination of the smaller crystallites of 1. The de- though they may have lower catalytic activities than other
composition of the large crystals (obtained from hydrother- compounds (only up to 80% yield), they are truly hetero-
Eur. J. Inorg. Chem. 2013, 5576–5591
5582
© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
Figure 7. Kinetic curves of the ring-opening reaction of styrene oxide with methanol at 55 °C in the presence of a mixture of [Ce2(pydc)2-
(Hpydc)(H2O)2Cl]·(9 + y)H2O and 1 (black square, ratio ca. 4:1) and phase-pure 1 (red circle, green triangle, blue upside down triangle).
Black squares and red circles: similar catalyst amounts were used. Green triangles: half of the initial catalyst quantity was used. Blue
upside down triangle: one fifth of the initial catalyst quantity was used. The dashed lines are guidelines and do not represent the tendency
of the catalytic reaction. SEM images of 1 (top) and [Ce2(pydc)2(Hpydc)(H2O)2Cl]·(9 + y)H2O (needles) with ca. 20% of 1 (bottom) are
shown on the right. The insets represent the structural drawings of 1 (top) and [Ce2(pydc)2(Hpydc)(H2O)2Cl]·(9 + y)H2O (bottom).
geneous in nature, highly selective, and typically present (H2O)2Cl]·(9 + y)H2O was used, and gave superior catalytic
multifunctional behavior.[20,30]
results in the former case. Hence, compound 1 possesses
The microporous [Ce2(pydc)2(Hpydc)(H2O)2]Cl·(9 + y)- higher catalytic activity than [Ce2(pydc)2(Hpydc)-
H2O material can be obtained from the present reaction (H2O)2]Cl·(9 + y)H2O. Possibly, the concentration of ac-
system under specific experimental conditions.[18g] Its isola- cessible active sites is higher for 1 than for [Ce2(pydc)2-
tion as a pure phase could never be achieved; it always ap- (Hpydc)(H2O)2]Cl·(9 + y)H2O or the porosity of latter ma-
peared as a mixture of phases with 1. The reported opti- terial may lead to strong internal diffusion limitations. On
mized synthetic conditions to obtain this material gave a the other hand, we cannot rule out the possibility that de-
maximum yield of 80 wt.-% with 1 as the other phase. This fect sites possess intrinsic catalytic activity and these are
mixture was tested for the catalytic reaction of PhEtO with different for the two materials.
methanol under similar reaction conditions as those used
for pure 1. MeOPhEtOH was the only product and formed
in 18 and 32% yield after 24 and 48 h reaction (black
squares in Figure 7). However, when the reaction of PhEtO
was performed in the presence of phase-pure 1, a higher
yield of MeOPhEtOH was obtained (73 and 77% after 24
Engineering Optically Active Materials
and 48 h reaction; Figure 7, red circles). The use of half of
the initial amount of 1 did not significantly affect the reac-
To design photoluminescent materials, we have included
tion rate (77% conversion after 24 h), whereas 1/5 of the stoichiometric amounts of optically active lanthanide cat-
initial amount of 1 led to slower reaction of PhEtO (50% ions such as Eu3+ and Tb3+ into a La3+-based isotypical
conversion after 24 h, Figure 7). The catalytic experiment matrix. We have prepared [La2(pydc)3(H2O)2] (1-La),
with 1/5 of the initial amount of 1 simulated the catalytic [(La0.95Eu0.05)2(pydc)3(H2O)2] (1-LaEu), [(La0.95Tb0.05)2-
contribution of this phase (a similar mass of 1 was loaded), (pydc)3(H2O)2] (1-LaTb), and [(La0.90Eu0.05Tb0.05)2(pydc)3-
when the mixture of
1
and [Ce2(pydc)2(Hpydc)- (H2O)2] (1-LaEuTb; see Experimental Section for ad-
Eur. J. Inorg. Chem. 2013, 5576–5591
5583
© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
ditional details). Powder X-ray diffraction (Figure 8) and share the same structural features and that the optically
electron microscopy studies (Figures S7–S9) of the prepared active lanthanide cations are uniformly distributed in the
bulk mixed-lanthanide materials showed that all materials optically inert La3+ matrix.
The excitation spectra of 1-LaEu, 1-LaTb, and 1-
LaEuTb were recorded and the strongest Eu3+ 5D0Ǟ7F2
and Tb3+ 5D4Ǟ7F5 emission transitions were monitored
(Figure 9). The spectra are dominated by two broad UV
bands in the range 240–350 nm (peaking at ca. 276 and
310 nm for 1-LaEu at ambient temperature), which are at-
tributable to the excited states of the organic ligands. The
presence of two broad UV bands could arise from (1) the
two crystallographically independent coordination modes
of the organic ligand to the Ln3+ ions (see crystal structure
description and Figure S3), (2) the distinct excited singlet
states of the ligand, or (3) a combination of both. This attri-
bution was further confirmed from the excitation spectrum
of 1-La at 12 K (Figure 9) with the phosphorescence emis-
sion at 450 nm monitored (see discussion below).
The spectra of 1-LaEu, 1-LaTb, and 1-LaEuTb show a
series of sharp lines assigned to the typical intra-4f6 and
-4f8 transitions of Eu3+ and Tb3+, respectively. The fact that
Figure 8. Comparison between the experimental powder X-ray dif-
the Tb3+ intra-4f8 transitions are only recognized after
fraction patterns for the isotypical 1, 1-LaEu, and 1-LaTb materi-
proper magnification indicates a more efficient sensitization
through the ligand excited states for the Tb3+ emission than
that of Eu3+. For 1-LaEuTb, there is no strong evidence for
the occurrence of additional energy transfer from the Tb3+
to the Eu3+ cations as the intra-4f8 Tb3+ excited lines are
absent in the excitation spectrum of the Eu3+ emission mon-
als. Vertical bars indicate the angular positions of the allowed
Bragg reflections for each material as refined from a Le Bail[46]
whole-powder-pattern fitting of the powder patterns. Refined unit-
cell parameters for 1-LaEu: a = 6.5656(4) Å, b = 18.0098(9) Å, c
= 9.4416(5) Å, β = 95.419(3)°, monoclinic P21/c. Refined unit-cell
parameters for 1-LaTb: a = 6.5676(3) Å, b = 18.0273(8) Å, c =
9.4432(5) Å, β = 95.405(4)°, monoclinic P21/c.
Figure 9. Excitation spectra of 1-LaEu (λEm. = 616 nm, red), 1-LaTb (λEm. = 543 nm, green), 1-LaEuTb (λEm. = 616 nm, orange; λEm.
=
543 nm, cyan), and 1-La (λEm. = 450 nm, black) with monitoring of the emission of the Eu3+ and Tb3+ ions and the ligand. The spectra
were recorded at ambient temperature (solid lines) and 12 K (dotted lines).
Eur. J. Inorg. Chem. 2013, 5576–5591
5584
© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
Figure 10. Room-temperature emission spectra of 1-LaEu (red), 1-LaTb (green), and 1-LaEuTb (orange) with excitation at 310 nm. For
1-LaEu, the emission spectrum at 12 K (black line) and a magnification of the 5D0Ǟ7F0 spectral region are also provided. The inset
images show the corresponding bright emissions of small pellet samples under a laboratory UV lamp (λ = 254 nm) and their corresponding
CIE color coordinates.
itored at 616 nm. However, the presence of Eu3+ cations has
a strong influence on the decrease of the Tb3+ sensitization
by the ligand antenna effect. This is clearly demonstrated
by the increase of the intra-4f8 Tb3+ transitions with respect
to the excited broad bands of the ligand.
The emission spectra of 1-LaEu, 1-LaTb, and 1-LaEuTb
recorded at ambient conditions (293 K) and excited at
310 nm are provided in Figure 10. The sharp Eu3+ and Tb3+
5
emission lines are mostly assigned to the D0Ǟ7F0–4 and
5D4Ǟ7F6–0 transitions, respectively, which originate bright
red, green, and orange emitted light (demonstrated by the
inset pictures associated with each emission spectra of Fig-
ure 10). Although they have a negligible contribution to the
total emission, for Eu3+ it is also possible to detect the
5D1Ǟ7F0–3 emission transitions, particularly at 12 K. The
corresponding CIE (Commission International d’Eclairage)
chromaticity (x,y) color coordinates are represented in Fig-
Figure 11. CIE chromaticity diagram showing the location of the
ure 11. For the Eu3+ and Tb3+ materials, the emission spec-
red, green, and orange room-temperature emission from 1-LaEu,
tra are independent of the excited wavelength selected,
namely, the ligand UV bands or intra-4f levels. For the
mixed-lanthanide 1-LaEuTb material, the pure Eu3+ emis-
1-LaTb, and 1-LaEuTb under 310 nm excitation.
sion spectrum can be obtained by exciting at 393 nm (5L6 spectrum, both at ambient temperature and 12 K, shows a
excited Eu3+ level).
single 5D0Ǟ7F0 transition, a local-field splitting of the 7F1,2
The Eu3+ emission is highly sensitive to small modifica- levels into three and five Stark components, respectively,
5
tions to the first coordination sphere of the metal. In this and the predominance of the D0Ǟ7F2 transition relative
way, this optical feature is widely used as a local probe for to the 5D0Ǟ7F1 transition, which agrees well with the pres-
detailed structural features.[34] For 1-LaEu, the emission ence of a single low-symmetry Eu3+ environment in the
Eur. J. Inorg. Chem. 2013, 5576–5591
5585
© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
5
structure. The small redshift of the D0Ǟ7F0 transition ob- ligands. Higher absolute emission quantum yields were ob-
served at 12 K relative to that at ambient temperature is tained for the Tb3+-containing samples, and a maximum of
presumably caused by a slight contraction of the unit cell. 75% was reached for 1-LaTb excited at 310 nm. These high
Additionally, the Eu3+ 5D0 and Tb3+ 5D4 decay curves re- values, even with a water molecule coordinated to the Eu3+
corded at ambient temperature can be well-fitted by single and Tb3+ acceptor ions in the studied compounds, demon-
exponential functions to yield lifetimes of 0.50Ϯ0.01 and strate a favorable balance between absorption and energy
1.06Ϯ0.01 ms for 1-LaEu and 1-LaTb, respectively (Fig- transfer emission process through the rates involved in the
ure S10). These data agree well with the presence of a single processes such as ligand-to-Ln3+ energy transfer (including
Ln3+ crystallographic site for the mixed-lanthanide materi- intersystem-crossing relaxation), multiphonon relaxation,
als, in agreement with the crystallographic studies. For 1- and back-transfer processes.[37]
LaEuTb, similar decay curves with exactly the same lifetime
To get additional insight into the measured high absolute
values were obtained by selecting the excitation and emis- emission quantum yields under UV ligand excitation, we
sion wavelengths for Eu3+ (λEm. = 616 nm, λExc. = 393 nm) have recorded the photoluminescence of 1-La, which does
and Tb3+ (λEm. = 543 nm, λExc. = 376 nm).
not present detectable emission at ambient temperature.
5
Based on the emission spectra, the D0 lifetimes, empiri- The stationary-state emission spectrum at 12 K is domi-
cal radiative and nonradiative transition rates, and as- nated by a structured broad band centered on the blue re-
suming that only nonradiative and radiative processes are gion (Figure 12; 390–550 nm) with a maximum intensity at
involved in the depopulation of the 5D0 state, the 5D0 quan- ca. 450 nm. A similar spectrum was obtained in the time-
tum efficiency φ[27,35] was determined for 1-LaEu. The theo- resolved mode with an initial delay of 20 ms (Figure 12);
retical basis of these calculations is provided in the Sup- this allows the emission to be unequivocally attributed to a
porting Information. These data, including the absolute phosphorescence emission, presumably from the ligand
emission quantum yield, defined as the ratio between the triplet states, and the corresponding zero-phonon energy
number of emitted photons and the number of absorbed level is estimated at ca. 390 nm (25640 cm–1), which is much
photons (measured experimentally), are collected in Table 3 larger than those reported for a series of Eu3+ com-
for the three studied compounds.
plexes.[37,38] Furthermore, the emission decay curve moni-
tored at ca. 450 nm with excitation at 300 nm (inset in Fig-
ure 12) reveals a biexponential behavior, which results in
two distinct lifetime values of 82Ϯ1 and 562Ϯ5 ms. The
nonexponential behavior can be attributed to the presence
of the two distinct ligand modes, which can induce more
complex ligand-to-ligand and ligand-to-metal energy trans-
fer mechanisms.[39] The higher absolute emission quantum
yield of Tb3+ relative to Eu3+ can most probably be justified
by a smaller energy difference between the ligand triplet
zero-phonon energy level and the corresponding excited ac-
Table 3. Experimental 5D0 lifetime (τ), radiative (kr) and nonradia-
tive (knr) transition rates, and absolute emission quantum yield (φ)
for 1-LaEu. The absolute emission quantum yield is also given for
1-LaTb and 1-LaEuTb. The data were collected at 293 K.
τ
kr
knr
φ [%] (λExc., nm)
[ms] [s–1]
[s–1]
1-LaEu 0.50 469
1531
–
–
32 (254), 43 (310), 4 (393)
63 (254), 75 (310), 3 (376)
37 (254), 49 (310), 3 (376), 4
(393)
1-LaTb 1.06
–
–
1-
–
ceptor levels (5D4, 486 nm/20576 cm–1 for Tb3+
;
5D1,
LaEuTb
526 nm/19011 cm–1 for Eu3+) as illustrated in Figure S11.
As Ce3+ usually has the first possible emitting levels (5D1,
Compound 1-LaEu has moderate quantum efficiency below 360 nm/27778 cm–1) at higher energy than that of the
(23%) mostly because of the high nonradiative transition zero-phonon triplet state, ligand-to-metal energy transfer
rate. This is most likely promoted by the presence of O–H does not occur for this lanthanide cation in the present ma-
oscillators associated with the coordinated water molecules, terial.
which lead to the concomitant decrease of the radiative
An inspection of the literature for photoluminescent co-
transition rate. The measured absolute emission quantum ordination polymers based on lanthanide centers, in par-
yield under 4f direct excitation at 393 nm (4%) is far from ticular, the recent work by Daiguebonne and collaborators
the calculated quantum efficiency. Notably, the calculated on benzene-polycarboxylate ligands,[40] further supports
5D0 quantum efficiency, determined under 4f6 excitation at that the properties of the compounds herein described are
393 nm, by definition gives a limit for the corresponding unusual among related materials. Studies on lanthanide co-
absolute emission quantum yield if only nonradiative and ordination polymers based on terephthalate (bdc2–) or 4,4Ј-
radiative processes are involved in the depopulation of the oxybis(benzoic acid) (oba) ligands show interesting lumi-
5D0 state.[36] In the present case, under excitation of the UV nescent quantum yields and lifetimes of 72% and 0.85 ms
ligand bands, the maximum absolute emission quantum for [Tb2(oba)3(H2O)6·3H2O][40d] and 20% and 0.41 ms for
yield (43% at 310 nm excitation) almost doubles the calcu- [Eu6O(OH)8(NO3)2(bdc)(Hbdc)2·2NO3·H2bdc].[40c]
The
lated 5D0 quantum efficiency, which invalidates the assump- main breakthrough from the Daiguebonne group arises
tion that only nonradiative and radiative processes are in- from heteronuclear lanthanide-based coordination poly-
volved in the depopulation of the 5D0 state. Additional pro- mers, in particular [{Y6xTb6–6x}6O(OH)8(NO3)2(bdc)-
cesses must then be present on population/depopulation of (Hbdc)2·2NO3·H2bdc].[40c] The dilution of Tb3+ ions by Y3+
5
the D0 state under UV excitation within the states of the ions resulted in quantum yields close to 100% and lifetimes
Eur. J. Inorg. Chem. 2013, 5576–5591
5586
© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
Figure 12. Time-resolved (dotted line; initial delay 20 ms and integration time of 20 ms) and stationary-state emission spectra (solid line)
of 1-La recorded at 12 K under 300 nm excitation. The time-resolved emission spectrum was not corrected for the detection and optical
spectral response of the spectrofluorimeter. The inset shows the decay curve and the best fit to a biexponential decay function of the
phosphorescence emission detected at 450 nm.
of ca. 1.41 ms (ca. 59% and 1.40 ms for the solely Tb-based ported by Zhang et al.[22i] Investigations into the fine struc-
isotypical material). Mixtures of {Tb6xEu6–6x} also showed tural details of these materials revealed that the latter lay-
relevant values (53% and 1.12 ms).[40c]
ered materials are strongly related to the compounds herein
reported and share almost identical structural building
blocks. A transformation associated with the release of ex-
tra organic ligands can lead to the densely packed 3D
Conclusions
In this manuscript, we have described a rapid and ef- [Ln2(pydc)3(H2O)2] compounds, and this is achieved by pre-
ficient microwave-assisted synthesis of an isotypical series paring the materials at a higher temperature. On the other
of 3D Ln3+-based MOFs based on residues of 2,5-pyridine- hand, the ability to either isolate dense, nonporous
dicarboxylic acid, namely, [Ce2(pydc)3(H2O)2] (1), [Ln2(pydc)3(H2O)2] MOFs or the cationic microporous
[(La0.95Eu0.05)2(pydc)3(H2O)2] (1-LaEu), [(La0.95Tb0.05)2- [Ce2(pydc)2(Hpydc)(H2O)2]Cl·(9 + y)H2O material was also
(pydc)3(H2O)2] (1-LaTb), and [(La0.90Eu0.05Tb0.05)2(pydc)3- studied from a topological perspective. As observed for the
(H2O)2] (1-LaEuTb). The reaction time was reduced from relationship between the 2D and 3D compounds, differ-
the typical 3 d (hydrothermal synthesis) to just 1 min under ences between the dense and microporous materials also
MWAS, and the reaction temperature was reduced from arise with the variation of one type of connecting pydc2–
170 to 120 °C (or 90 °C if the reaction time is increased to ligand. Whereas the two crystallographically independent
10 min). So far, the method herein described represents the ligands in the latter material have identical coordination se-
optimal experimental settings for a quick and economically quences up to the 10th shell, in the former dense isotypical
viable isolation of these functional materials. In addition, series, small differences occur in the fourth and eighth shells
this approach allows the simple preparation of optically of the “gluing” ligands between the Ce–pydc layers. These
active materials with intense photoluminescence in the vis- subtle coordination differences are the main reason why, on
ible region.
the one hand, such distinct materials can ultimately be iso-
By systematically varying the experimental conditions lated from the same reaction batch and, on the other hand,
under MWAS (i.e., temperature, power of irradiation, and why the microporous structure could not be isolated as a
reaction time), at least three distinct phases could be iso- phase-pure material to date.
lated: 3D [Ln2(pydc)3(H2O)2], which is isotypical with the
Compound 1 is an effective catalyst for the ring-opening
La3+- and Pr3+-based materials reported by the groups of reaction of styrene oxide with methanol to give 2-methoxy-
Shao and Hong,[22a,22b] the 3D microporous [Ce2(pydc)2- 2-phenylethanol as the sole product at 80% conversion.
(Hpydc)(H2O)2]Cl·(9 + y)H2O previously reported by This result was superior to that for the microporous mate-
us,[18g] and layered [{Ce2(pydc)2(Hpydc)2(H2O)4}·2H2O]n, rial [Ce2(pydc)2(Hpydc)(H2O)2]Cl·(9 + y)H2O, obtained as
which is isotypical with the Nd3+-based compound re- an 80 wt.-% mixture with 1, for which the maximum 2-
Eur. J. Inorg. Chem. 2013, 5576–5591
5587
© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
TEM images were acquired with a Hitachi H9000na HR-TEM
microscope. A suspension was sonicated for 180 s and one drop was
placed on a carbon-coated copper grid and left to dry in air. TEM
analysis revealed that the investigated materials are extremely sensi-
tive to the electron beam, and under normal conditions the crystal-
lites are destroyed after a few seconds of intense irradiation. To
minimize damage, a minimum electron voltage was employed for
TEM measurements (200 kV), and the magnification was kept as
low as possible.
methoxy-2-phenylethanol yield was 32% after 48 h reac-
tion.
Optically active lanthanide cations have been stoichio-
metrically included and uniformly distributed among an
isotypical La3+ matrix of 1 (as shown by electron micro-
scopy studies) to promote the isolation of the effective UV-
to-visible light converters 1-LaEu (red), 1-LaTb (green),
and 1-LaEuTb (orange). Detailed photoluminescent studies
of 1-LaEu and 1-LaTb showed the presence of a single crys-
tallographic lanthanide centre with lifetimes of ca. 0.50 and
1.06 ms, respectively. The materials have very high absolute
emission quantum yields (43% for 1-LaEu and 75% for 1-
LaTb) when the UV ligand bands are excited. Such values
are much higher than the intrinsic calculated quantum effi-
ciency and show that intersystem crossing and ligand-to-
metal transfer processes are both favorable for the presented
compounds. These results, allied to the fact that the materi-
als can be prepared as pure phases in high yields and in just
under 1 min of microwave irradiation open up the possibil-
ity for future studies of their possible application in the fab-
rication of photoluminescent devices. In particular, we are
exploring the preparation of thin photoluminescent films
based on the deposition of nanocrystals directly isolated
from the microwave-assisted synthesis procedure. Addition-
ally, we are also designing and preparing new organic li-
gands with energy levels that can simultaneously sensitize
effectively a wide range of optically active lanthanide cat-
ions, and the main objective is to produce efficient materials
with a wide range of color pallets.
Conventional powder X-ray diffraction data suitable for structural
refinements were collected at ambient temperature with a Philips
X’Pert MPD diffractometer (Cu-Kα1,2 radiation, λ1 = 1.540598 Å
and λ2 = 1.544426 Å) equipped with an X’Celerator detector and a
flat-plate sample holder in a Bragg–Brentano para-focusing optics
configuration (40 kV, 50 mA). The intensity data were collected by
the step-counting method (step 0.01°; 700 s per step) in continuous
mode in the ca. 5.0Յ 2θՅ 90° range.
Reagents: All chemicals were readily available from commercial
sources and were used as received without further purification: 2,5-
pyridinedicarboxylic acid (2,5-H2pydc, C7H5NO4, purumՆ 98%,
Fluka), lanthanide (III) chloride hydrates (LnCl3·xH2O, Ln3+
=
Ce3+, Eu3+, Tb3+, La3+, and Pr3+; Sigma–Aldrich), sodium hydrox-
ide (NaOH pellets, Panreac), styrene oxide (Fluka,Ն 97%), and
methanol (Sigma–Aldrich, 99%).
Hydrothermal Synthesis by Standard Convection Heating: A pro-
cedure based on that described by Shao and co-workers has been
employed.[22a,22b]
A
suspension
containing
2,5-H2pydc,
LnCl3·xH2O, and NaOH in distilled water (molar ratio of ca.
1:1:2.5:800) was stirred thoroughly in air (ambient temperature) for
1 h. The resulting homogeneous suspension was transferred to a
Teflon-lined Parr reaction vessel and placed inside a preheated
MMM Venticell oven. The reaction occurred at 165 °C over 72 h,
after which time the oven was turned off, and the samples were
cooled slowly to ambient temperature (inside the oven). After that,
the obtained compound was collected by vacuum filtration, washed
with copious amounts of distilled water, and dried at room tem-
perature. [Ce2(pydc)3(H2O)2] (817.62): calcd. C 30.85, H 2.34, N
5.14 (C/N = 6.00); found C 29.76, H 1.83, N 4.85 (C/N = 6.14).
Experimental Section
General Instrumentation: Fourier-transform infrared (FTIR) spec-
tra (in the spectral range 4000–400 cm–1) were recorded in the at-
tenuated total reflectance (ATR) mode with a Mattson 7000 galaxy
series spectrometer equipped with a DTGS CsI detector and a
Golden Gate ATR accessory by averaging 128 scans at a maximum
resolution of 2 cm–1.
FT-Raman spectra (spectral range 4000–50 cm–1) were recorded
with a Bruker RFS 100 spectrometer with a Nd:YAG coherent la-
ser (λ = 1064 nm) by averaging 256 scans at resolution of 2 cm–1
and using a power of 300 mW.
Microwave-Assisted Hydrothermal Synthesis
Optimization with Ce3+: A suspension similar to that described in
the previous section was used (molar ratio 1:1:2.5:800). Typically,
the reaction mixture was stirred thoroughly in air (ambient tem-
perature) for five minutes, and the resulting homogeneous suspen-
sion was transferred to a 10 mL IntelliVent reactor, which was
placed inside a CEM Focused Microwave™ Synthesis System Dis-
cover S-Class equipment. The reactions occurred with constant
magnetic stirring (controlled by the microwave equipment), and the
temperature and pressure inside the vessels were monitored. A con-
stant flow of air (ca. 10 bar of pressure) ensured close control of
the temperature inside the vessel. After completion of the reaction,
a pale yellow suspension was obtained. The final product was reco-
vered by vacuum filtration, washed with copious amounts of dis-
tilled water, and then air-dried overnight.
C, H, N elemental analyses were performed with an Exeter Analyti-
cal CE-440 Elemental Analyzer at the Department of Chemistry of
the University of Cambridge. Samples were combusted under an
oxygen atmosphere at 975 °C for 1 min with helium as the purge
gas.
Thermogravimetric analyses (TGA) were performed with a Shim-
adzu TGA 50 instrument from ambient temperature to ca. 800 °C
with a heating rate of 5 °Cmin–1 under a continuous air stream
with a flow rate of 20 cm3 min–1.
The following experimental conditions were systematically varied:
(i) temperature (T), from 90 to 170 °C; (ii) power (P), from 50 and
150 W; (iii) reaction time (t), between 1 and 10 min of microwave
irradiation. For simplicity, each sample is identified as TmPntp; the
subscripts indicate the specific experimental conditions employed.
[Ce2(pydc)3(H2O)2] (817.62): calcd. C 30.85, H 2.34, N 5.14 (C/N
= 6.00); found C 28.28, H 1.67, N 4.68 (C/N = 6.05).
SEM images were collected with either a Hitachi S4100 field emis-
sion gun tungsten filament instrument at 25 kV or a high-resolu-
tion Hitachi SU-70 instrument at 4 kV. The samples were prepared
by deposition on aluminum sample holders followed by carbon
coating by using an Emitech K950X carbon evaporator. EDS (en-
ergy-dispersive X-ray spectroscopy) data and SEM mapping images
were recorded by using the latter microscope at 15 kV and with a
Bruker Quantax 400 or a Sprit 1.9 EDS microanalysis system.
Optically Active Materials with Other Lanthanides: Mixed-lanth-
anide materials were prepared by using a similar experimental pro-
Eur. J. Inorg. Chem. 2013, 5576–5591
5588
© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
cedure to that described above. For simplicity, mixed-lanthanide
samples will be mentioned on the basis of the lanthanides and the
CCDC-930516 contains the supplementary crystallographic data
for this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
3+
different percentages used in [La2(pydc)3(H2O)2]: La0.95Eu0.05 (1-
3+
3+
LaEu), La0.95Tb0.05
(1-LaTb), and La0.90Eu0.05Tb0.05
(1-
LaEuTb). The mixed-lanthanide materials were obtained by using
microwave settings chosen to ensure the preparation of phase-pure
compounds (see Scheme 1 for additional details).
The spatial distribution of the Eu3+ and Tb3+ ions in the La3+
matrices was further confirmed by electron microscopy EDX map-
ping studies on portions of 1-LaEu, 1-LaTb, and 1-LaEuTb. The
EDX profiles (Figures S7–S9) indicate a homogeneous dispersion
of the chemical elements in the [Ln2(pydc)3(H2O)2] surface, and no
compositional zoning was observed in any of the tested com-
pounds.
Catalytic Studies: The batchwise reaction of the ring opening of
styrene oxide in methanol was performed at 55 °C under air (auto-
genous pressure) and stirred magnetically in a closed borosilicate
10 mL reaction vessel immersed in a thermostatted oil bath. The
reactor was loaded with [Ce2(pydc)2(Hpydc)(H2O)2Cl]·(9+y)-
H2O (35.9 mg) and [Ce2(pydc)2(H2O)2] (1, 32.5 mg), styrene oxide
(0.82 mmol), and methanol (2.0 mL). The progress of the reactions
was monitored by using a Varian 3800 GC equipped with a BR-5
(Bruker) capillary column (30 mϫ0.25 mm; 0.25 μm) and a flame
ionization detector with H2 as the carrier gas. The reaction prod-
ucts were identified by GC–MS with a GC 2000 Series (Thermo
Quest CE Instruments) instrument and DSQ II (Thermo Scientific)
spectrometer equipped with a fused silica capillary DB-5 column
(30 mϫ0.25 mm; 0.25 μm film thickness) and He as carrier gas.
Metal ion ratios estimated from EDX data. For 1-LaEu, La3+/Eu3+
ca. 9.7. For 1-LaTb, La3+/Tb3+ ca. 12.5. For 1-LaEuTb, La3+/Eu3+
ca. 8.5 and La3+/Tb3+ ca. 10.2.
Powder X-ray Diffraction Studies: The collected powder X-ray dif-
fraction pattern for [Ce2(pydc)3(H2O)2] (1, pydc2– is the diproton-
ated residue of 2,5-pyridinedicarboxylic acid) was indexed by
means of the routines provided with DICVOL04[41] and by em-
ploying the first 20 well-resolved reflections (located by using the
derivative-based peak search algorithm provided with Full-
prof.2k)[42] and a fixed absolute error on each line of 0.03° 2θ. The
initial unit-cell metrics were obtained with reasonable figures-of-
merit: M(20) = 33.3,[43] F(20) = 65.0.[44] An analysis of the system-
atic absences was performed by using CHECKCELL,[45] which
identified the monoclinic P21/c space group as the most suitable,
in good agreement with the crystal structure published by Shao
and collaborators.[22b] A Le Bail[46] whole-powder-diffraction-
pattern profile decomposition with fixed (and manually selected)
background points produced a reasonable fit.
A Rietveld structural refinement[47] of 1 was performed with
FullProf.2k[42] by using the reported atomic coordinates[22b] for the
isotypical Pr3+ compound as the starting premise. Fixed back-
ground points throughout the entire angular range and determined
by the linear interpolation between consecutive (and manually se-
lected) breakpoints in the powder pattern were employed. Typical
pseudo-Voigt profile functions along with two asymmetry correc-
tion parameters were selected to generate the line shapes of the
simulated diffraction peaks. The angular dependence of the individ-
ual reflections was also taken into account by employing a Caglioti
function correction.[48]
Photoluminescence: The emission and excitation spectra were re-
corded at 12 and 300 K by using a Fluorolog-3® Horiba Scientific
(Model FL3–2T) spectroscope with a modular double grating exci-
tation spectrometer (fitted with a 1200 grooves/mm grating blazed
at 330 nm) and a TRIAX 320 single emission monochromator (fit-
ted with a 1200 grooves/mm grating blazed at 500 nm, reciprocal
linear density of 2.6 nm/mm) coupled to a R928 Hamamatsu pho-
tomultiplier in the front-face acquisition mode. The excitation
source was a 450 W Xe arc lamp. The emission spectra were cor-
rected for the detection and optical spectral response of the spectro-
fluorimeter, and the excitation spectra were corrected for the spec-
tral distribution of the lamp intensity by using a photodiode refer-
ence detector. Time-resolved measurements were performed with a
1934D3 phosphorimeter coupled to the Fluorolog-3® spectroscope,
and a Xe–Hg flash lamp (6 μs/pulse half-width and 20–30 μs tail)
was used as the excitation source. The variable-temperature mea-
surements were performed by using a helium closed-cycle cryostat
with a vacuum system measuring ca. 5ϫ 10–6 mbar and a Lake-
shore 330 auto-tuning temperature controller with a resistance
heater. The temperature can be adjusted from ca. 12 to 450 K.
The absolute emission quantum yields were measured at ambient
temperature by using a Hamamatsu C9920-02 quantum yield
measurement system with a 150 W Xenon lamp coupled to a
monochromator for wavelength discrimination, an integrating
sphere as sample chamber, and a multichannel analyzer for signal
detection. Three measurements were made for each sample, and
the average value is reported. The method is accurate to within
10%.
The overall structural refinement was performed in consecutive
stages to avoid instability and divergence. Zero-shift, scale-factor
parameters related to peak shape and unit-cell parameters were
consecutively added as fully refineable variables upon previous full
convergence of the remaining parameters to their optimal values.
The fractional atomic coordinates for all non-hydrogen atoms were
ultimately allowed to refine in conjunction with weighted soft dis-
tance constraints solely applied to the organic ligand (N–C,
C–C, C–O, and O···O bond lengths and internuclear distances).
This approach has the advantage of ensuring a final chemically
feasible geometry for the organic moiety and allows the crystallo-
graphically independent Ce3+ center to refine freely. Each type of
atom has been refined by using a common refineable isotropic pa-
rameter. No correction was made for absorption effects.
Supporting Information (see footnote on the first page of this arti-
cle): Additional experimental data on the microwave-assisted syn-
thesis optimization, electron microscopy and vibrational spec-
troscopy, photoluminescence studies for the optically active materi-
als.
Acknowledgments
The authors are grateful to the Portuguese FCT, the European
Union (EU), QREN, FEDER, COMPETE, CICECO (PEst-C/
CTM/LA0011/2011) for their general funding. The authors further
wish to thank Fundação para a Ciência e a Tecnologia (FCT) for
funding the R&D project PTDC/QUI-QUI/098098/2008 (FCOMP-
01-0124-FEDER-010785), for the Ph. D. scholarship No. SFRH/
BD/46601/2008 (to PS), and for the postdoctoral research grant
number SFRH/BPD/46473/2008 (to S. M. B.).
Table 1 collects the laboratory X-ray data collection, crystal data,
and final Rietveld refinement details (profile and reliability factors)
for 1. The final Rietveld plot is supplied in Figure 2. Structural
drawings have been created by using the Crystal Impact Diamond
software package.[49]
Eur. J. Inorg. Chem. 2013, 5576–5591
5589
© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
[10]
a) C. Chizallet, S. Lazare, D. Bazer-Bachi, F. Bonnier, V. Lec-
ocq, E. Soyer, A.-A. Quoineaud, N. Bats, J. Am. Chem. Soc.
2010, 132, 12365–12377; b) A. Corma, H. Garcia, F. X.
Llabres i Xamena, Chem. Rev. 2010, 110, 4606–4655; c) D.
Dang, P. Wu, C. He, Z. Xie, C. Duan, J. Am. Chem. Soc. 2010,
132, 14321–14323; d) H. Fei, D. L. Rogow, S. R. J. Oliver, J.
Am. Chem. Soc. 2010, 132, 7202–7209; e) J. Lee, O. K. Farha,
J. Roberts, K. A. Scheidt, S. T. Nguyen, J. T. Hupp, Chem. Soc.
Rev. 2009, 38, 1450–1459; f) Y. Liu, W. Xuan, Y. Cui, Adv.
Mater. 2010, 22, 4112–4135; g) L. Ma, C. Abney, W. Lin,
Chem. Soc. Rev. 2009, 38, 1248–1256; h) L. Ma, C.-D. Wu,
M. M. Wanderley, W. Lin, Angew. Chem. 2010, 122, 8420; An-
gew. Chem. Int. Ed. 2010, 49, 8244–8248; i) P. K. Thallapally,
C. A. Fernandez, R. K. Motkuri, S. K. Nune, J. Liu, C. H. F.
Peden, Dalton Trans. 2010, 39, 1692–1694; j) M. Yoon, R. Srir-
ambalaji, K. Kim, Chem. Rev. 2012, 112, 1196–1231; k) A.
Dhakshinamoorthy, H. Garcia, Chem. Soc. Rev. 2012, 41,
5262–5284; l) A. Dhakshinamoorthy, M. Alvaro, H. Garcia,
Catal. Sci. Technol. 2011, 1, 856–867; m) A. Dhakshinamoor-
thy, M. Alvaro, H. Garcia, Chem. Eur. J. 2010, 16, 8530–8536.
[1]
[2]
B. F. Hoskins, R. Robson, J. Am. Chem. Soc. 1990, 112, 1546–
1554.
a) H. Li, M. Eddaoudi, T. L. Groy, O. M. Yaghi, J. Am. Chem.
Soc. 1998, 120, 8571–8572; b) H. Li, M. Eddaoudi, M.
O’Keeffe, O. M. Yaghi, Nature 1999, 402, 276–279.
[3]
a) J. Kim, B. L. Chen, T. M. Reineke, H. L. Li, M. Eddaoudi,
D. B. Moler, M. O’Keeffe, O. M. Yaghi, J. Am. Chem. Soc.
2001, 123, 8239–8247; b) G. Férey, C. Serre, C. Mellot-Draz-
nieks, F. Millange, S. Surble, J. Dutour, I. Margiolaki, Angew.
Chem. 2004, 116, 6456; Angew. Chem. Int. Ed. 2004, 43, 6296–
6301; c) M. Eddaoudi, H. L. Li, O. M. Yaghi, J. Am. Chem.
Soc. 2000, 122, 1391–1397.
[4]
[5]
a) N. Stock, S. Biswas, Chem. Rev. 2012, 112, 933–969; b) D. M.
Ciurtin, M. D. Smith, H. C. zur Loye, Chem. Commun. 2002,
74–75; c) C. Serre, F. Millange, S. Surble, G. Férey, Angew.
Chem. Int. Ed. 2004, 43, 6286–6289; d) O. I. Lebedev, F. Mil-
lange, C. Serre, G. Van Tendeloo, G. Férey, Chem. Mater. 2005,
17, 6525–6527.
a) N. R. Champness, in: Making Crystals by Design - Methods,
Techniques and Applications, 1st ed. (Eds.: D. Braga, F. Gre-
pioni), Wiley-VCH, Weinheim, Germany, 2007, p. 193–208; b)
S. Kitagawa, R. Kitaura, S. Noro, Angew. Chem. 2004, 116,
2388; Angew. Chem. Int. Ed. 2004, 43, 2334–2375; c) S. Kita-
gawa, K. Uemura, Chem. Soc. Rev. 2005, 34, 109–119; d) S.
Natarajan, P. Mahata, Chem. Soc. Rev. 2009, 38, 2304–2318;
e) D. J. Tranchemontagne, J. L. Mendoza-Cortes, M. O’Keeffe,
O. M. Yaghi, Chem. Soc. Rev. 2009, 38, 1257–1283; f) M. Edda-
oudi, D. B. Moler, H. L. Li, B. L. Chen, T. M. Reineke, M.
O’Keeffe, O. M. Yaghi, Acc. Chem. Res. 2001, 34, 319–330.
[11]
a) D. Maspoch, N. Domingo, D. R. Molina, K. Wurst, J. M.
Hernandez, G. Vaughan, C. Rovira, F. Lloret, J. Tejada, J. Veci-
ana, Chem. Commun. 2005, 5035–5037; b) D. Maspoch, D.
Ruiz-Molina, J. Veciana, J. Mater. Chem. 2004, 14, 2713–2723;
c) D. Maspoch, D. Ruiz-Molina, J. Veciana, Chem. Soc. Rev.
2007, 36, 770–818; d) D. Maspoch, D. Ruiz-Molina, K. Wurst,
N. Domingo, M. Cavallini, F. Biscarini, J. Tejada, C. Rovira, J.
Veciana, Nat. Mater. 2003, 2, 190–195; e) N. Roques, V. Mug-
naini, J. Veciana, in: Topics in Current Chemistry, vol. 293
(Functional Metal–Organic Frameworks: Gas Storage, Separa-
tion and Catalysis) (Ed.: M. Schroder), Springer, Heidelberg,
Germany, 2010, p. 207–258; f) D. W. Ryu, W. R. Lee, J. W. Lee,
J. H. Yoon, H. C. Kim, E. K. Koh, C. S. Hong, Chem. Com-
mun. 2010, 46, 8779–8781; g) H. Tian, Q.-X. Jia, E.-Q. Gao,
Q.-L. Wang, Chem. Commun. 2010, 46, 5349–5351; h) X.-L.
Tong, T.-L. Hu, J.-P. Zhao, Y.-K. Wang, H. Zhang, X.-H. Bu,
Chem. Commun. 2010, 46, 8543–8545; i) D. Dusan, H. Youcef,
C. L. Lin, Y. Tan, L. Kunhao, L. Jing, J. Appl. Phys. 2012, 111,
07E335; j) J. Rocha, F. A. A. Paz, F. N. Shi, D. Ananias,
N. J. O. Silva, L. D. Carlos, T. Trindade, Eur. J. Inorg. Chem.
2011, 2035–2044; k) B. V. Harbuzaru, A. Corma, F. Rey, P.
Atienzar, J. L. Jorda, H. Garcia, D. Ananias, L. D. Carlos, J.
Rocha, Angew. Chem. 2008, 120, 1096; Angew. Chem. Int. Ed.
2008, 47, 1080–1083; l) E. Chelebaeva, J. Larionova, Y. Guari,
R. A. S. Ferreira, L. D. Carlos, F. A. A. Paz, A. Trifonov, C.
Guerin, Inorg. Chem. 2008, 47, 775–777.
a) T.-H. Bae, J. S. Lee, W. Qiu, W. J. Koros, C. W. Jones, S. Nair,
Angew. Chem. 2010, 122, 10059; Angew. Chem. Int. Ed. 2010,
49, 9863–9866; b) J. Gascon, F. Kapteijn, Angew. Chem. 2010,
122, 1572; Angew. Chem. Int. Ed. 2010, 49, 1530–1532; c) Y.
Hu, X. Dong, J. Nan, W. Jin, X. Ren, N. Xu, Y. M. Lee, Chem.
Commun. 2011, 47, 737–739; d) A. Huang, W. Dou, J. Caro, J.
Am. Chem. Soc. 2010, 132, 15562–15564; e) R. Ranjan, M.
Tsapatsis, Chem. Mater. 2009, 21, 4920–4924; f) S. R. Venna,
M. A. Carreon, J. Am. Chem. Soc. 2010, 132, 76–78.
a) R. Ameloot, L. Pandey, M. Van der Auweraer, L. Alaerts,
B. F. Sels, D. E. De Vos, Chem. Commun. 2010, 46, 3735–3737;
b) P. Horcajada, C. Serre, D. Grosso, C. Boissiere, S. Perruchas,
C. Sanchez, G. Férey, Adv. Mater. 2009, 21, 1931–1935; c) G.
Lu, J. T. Hupp, J. Am. Chem. Soc. 2010, 132, 7832–7833; d) D.
Zacher, O. Shekhah, C. Woell, R. A. Fischer, Chem. Soc. Rev.
2009, 38, 1418–1429; e) A. Betard, R. A. Fischer, Chem. Rev.
2012, 112, 1055–1083; f) D. Bradshaw, A. Garai, J. Huo, Chem.
Soc. Rev. 2012, 41, 2344–2381; g) O. Shekhah, J. Liu, R. A.
Fischer, C. Woll, Chem. Soc. Rev. 2011, 40, 1081–1106.
[6]
[7]
a) A. U. Czaja, N. Trukhan, U. Muller, Chem. Soc. Rev. 2009,
38, 1284–1293; b) U. Mueller, M. Schubert, F. Teich, H.
Puetter, K. Schierle-Arndt, J. Pastre, J. Mater. Chem. 2005, 16,
626–636.
a) H. J. Choi, M. Dinca, J. R. Long, J. Am. Chem. Soc. 2008,
130, 7848–7850; b) N. Lamia, M. Jorge, M. A. Granato, F. A.
Almeida Paz, H. Chevreau, A. E. Rodrigues, Chem. Eng. Sci.
2009, 64, 3246–3259; c) J. R. Li, J. Sculley, H. C. Zhou, Chem.
Rev. 2012, 112, 869–932; d) M. A. Moreira, J. C. Santos,
A. F. P. Ferreira, J. M. Loureiro, F. Ragon, P. Horcajada, K.-
E. Shim, Y.-K. Hwang, U. H. Lee, J.-S. Chang, C. Serre, A. E.
Rodrigues, Langmuir 2012, 28, 5715–5723; e) M. G. Plaza,
A. M. Ribeiro, A. Ferreira, J. C. Santos, Y. K. Hwang, Y. K.
Seo, U. H. Lee, J. S. Chang, J. M. Loureiro, A. E. Rodrigues,
Microporous Mesoporous Mater. 2012, 153, 178–190; f) I. Sen-
kovska, E. Barea, J. A. R. Navarro, S. Kaskel, Microporous
Mesoporous Mater. 2012, 156, 115–120; g) M. Shah, M. C. Mc-
Carthy, S. Sachdeva, A. K. Lee, H.-K. Jeong, Ind. Eng. Chem.
Res. 2012, 51, 2179–2199; h) S. Shimomura, M. Higuchi, R.
Matsuda, K. Yoneda, Y. Hijikata, Y. Kubota, Y. Mita, J. Kim,
M. Takata, S. Kitagawa, Nat. Chem. 2010, 2, 633–637; i) M. P.
Suh, H. J. Park, T. K. Prasad, D. W. Lim, Chem. Rev. 2012,
112, 782–835; j) B. Z. Yuan, D. Y. Ma, X. Wang, Z. Li, Y. W.
Li, H. M. Liu, D. H. He, Chem. Commun. 2012, 48, 1135–1137.
[12]
[13]
[8]
[9]
J. S. Seo, D. Whang, H. Lee, S. I. Jun, J. Oh, Y. J. Jeon, K. Kim,
Nature 2000, 404, 982–986.
a) G. A. Pereira, J. A. Peters, F. A. A. Paz, J. Rocha, C. F. G. C.
Geraldes, Inorg. Chem. 2010, 49, 2969–2974; b) P. Horcajada,
R. Gref, T. Baati, P. K. Allan, G. Maurin, P. Couvreur, G.
Férey, R. E. Morris, C. Serre, Chem. Rev. 2012, 112, 1232–
1268; c) H. X. Deng, S. Grunder, K. E. Cordova, C. Valente,
H. Furukawa, M. Hmadeh, F. Gándara, A. C. Whalley, Z. Liu,
S. Asahina, H. Kazumori, M. O’Keeffe, O. Terasaki, J. F. Stod-
dart, O. M. Yaghi, Science 2012, 336, 1018–1023; d) C. Y. Sun,
C. Qin, C. G. Wang, Z. M. Su, S. Wang, X. L. Wang, G. S.
Yang, K. Z. Shao, Y. Q. Lan, E. B. Wang, Adv. Mater. 2011,
23, 5629–5632; e) D. M. Liu, R. C. Huxford, W. B. Lin, Angew.
Chem. 2011, 123, 3780; Angew. Chem. Int. Ed. 2011, 50, 3696–
3700.
[14]
a) M. D. Allendorf, C. A. Bauer, R. K. Bhakta, R. J. T. Houk,
Chem. Soc. Rev. 2009, 38, 1330–1352; b) L. Cunha-Silva, S.
Lima, D. Ananias, P. Silva, L. Mafra, L. D. Carlos, M. Pill-
inger, A. A. Valente, F. A. A. Paz, J. Rocha, J. Mater. Chem.
2009, 19, 2618–2632; c) L. Cunha-Silva, L. Mafra, D. Ananias,
Eur. J. Inorg. Chem. 2013, 5576–5591
5590
© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
L. D. Carlos, J. Rocha, F. A. A. Paz, Chem. Mater. 2007, 19,
3527–3538; d) C. B. Liu, R. A. S. Ferreira, F. A. A. Paz, A. Ca-
diau, L. D. Carlos, L. S. Fu, J. Rocha, F. N. Shi, Chem. Com-
mun. 2012, 48, 7964–7966; e) J. Rocha, L. D. Carlos, F. A. A.
Paz, D. Ananias, Chem. Soc. Rev. 2011, 40, 926–940; f) B. V.
Harbuzaru, A. Corma, F. Rey, J. L. Jordá, D. Ananias, L. D.
Carlos, J. Rocha, Angew. Chem. 2009, 121, 6598; Angew. Chem.
Int. Ed. 2009, 48, 6476–6479; g) P. C. R. Soares-Santos, L.
Cunha-Silva, F. A. A. Paz, R. A. S. Ferreira, J. Rocha, T. Trin-
dade, L. D. Carlos, H. I. S. Nogueira, Cryst. Growth Des. 2008,
8, 2505–2516.
8886; d) D. T. de Lill, C. L. Cahill, Cryst. Growth Des. 2007, 7,
2390–2393; e) J. J. Luo, L. Xu, Inorg. Chem. 2006, 45, 11030–
11034; f) L. Q. Yu, R. D. Huang, Y. Q. Xu, T. F. Liu, W. Chu,
C. W. Hu, Inorg. Chim. Acta 2008, 361, 2115–2122.
[30] S. M. F. Vilela, D. Ananias, A. C. Gomes, A. A. Valente, L. D.
Carlos, J. A. S. Cavaleiro, J. Rocha, J. P. C. Tome, F. A. A. Paz,
J. Mater. Chem. 2012, 22, 18354–18371.
[31] a) N. Iranpoor, M. Shekarriz, F. Shiriny, Synth. Commun. 1998,
28, 347–366; b) V. Mirkhani, S. Tangestaninejad, B. Yadollahi,
L. Alipanah, Tetrahedron 2003, 59, 8213–8218.
[32] G. Sabitha, R. S. Babu, M. Rajkumar, C. S. Reddy, J. S. Yadav,
Tetrahedron Lett. 2001, 42, 3955–3958.
[33] D. Jiang, T. Mallat, F. Krumeich, A. Baiker, J. Catal. 2008,
257, 390–395.
[34] J. C. G. Bünzli, in: Lanthanide Probes in Life, Chemical, and
Earth Sciences: Theory and Practice (Eds.: J. C. G. Bünzli,
G. R. Choppin), Elsevier, Amsterdam, 1989.
[35] a) M. F. Hazenkamp, G. Blasse, Chem. Mater. 1990, 2, 105–
110; b) O. L. Malta, H. F. Brito, J. F. S. Menezes, F. Silva, S.
Alves, F. S. Farias, A. V. M. deAndrade, J. Lumin. 1997, 75,
255–268; c) O. L. Malta, M. A. C. dos Santos, L. C. Thomp-
son, N. K. Ito, J. Lumin. 1996, 69, 77–84; d) M. H. V. Werts,
R. T. F. Jukes, J. W. Verhoeven, Phys. Chem. Chem. Phys. 2002,
4, 1542–1548.
[36] L. D. Carlos, R. A. S. Ferreira, V. D. Bermudez, S. J. L. Rib-
eiro, Adv. Mater. 2009, 21, 509–534.
[37] G. F. de Sa, O. L. Malta, C. D. Donega, A. M. Simas, R. L.
Longo, P. A. Santa-Cruz, E. F. da Silva, Coord. Chem. Rev.
2000, 196, 165–195.
[15] S. S. Y. Chui, S. M. F. Lo, J. P. H. Charmant, A. G. Orpen,
I. D. Williams, Science 1999, 283, 1148–1150.
[16] a) A. de la Hoz, A. Diaz-Ortiz, A. Moreno, Chem. Soc. Rev.
2005, 34, 164–178; b) N. Kuhnert, Angew. Chem. 2002, 114,
1943; Angew. Chem. Int. Ed. 2002, 41, 1863–1866; c) F. A. Bas-
syouni, S. M. Abu-Bakr, M. A. Rehim, Res. Chem. Intermed.
2012, 38, 283–322.
[17] S. H. Jhung, J. H. Lee, J. W. Yoon, C. Serre, G. Férey, J. S.
Chang, Adv. Mater. 2007, 19, 121–124.
[18] a) Z. J. Lin, D. S. Wragg, R. E. Morris, Chem. Commun. 2006,
2021–2023; b) Z. Ni, R. I. Masel, J. Am. Chem. Soc. 2006, 128,
12394–12395; c) P. Amo-Ochoa, G. Givaja, P. J. S. Miguel, O.
Castillo, F. Zamora, Inorg. Chem. Commun. 2007, 10, 921–924;
d) J.-S. Choi, W.-J. Son, J. Kim, W.-S. Ahn, Microporous Meso-
porous Mater. 2008, 116, 727–731; e) J. Klinowski, F. A. A. Paz,
P. Silva, J. Rocha, Dalton Trans. 2011, 40, 321–330; f) C. Ebner,
T. Bodner, F. Stelzer, F. Wiesbrock, Macromol. Rapid Commun.
2011, 32, 254–288; g) P. Silva, A. A. Valente, J. Rocha, F. A. A.
Paz, Cryst. Growth Des. 2010, 10, 2025–2028.
[19] S. M. F. Vilela, R. F. Mendes, P. Silva, J. A. Fernandes, J. P. C.
Tomé, F. A. A. Paz, Cryst. Growth Des. 2013, 13, 543–560.
[20] P. Silva, F. Vieira, A. C. Gomes, D. Ananias, J. A. Fernandes,
S. M. Bruno, R. Soares, A. A. Valente, J. Rocha, F. A. A. Paz,
J. Am. Chem. Soc. 2011, 133, 15120–15138.
[38] W. M. Faustino, L. A. Nunes, I. A. A. Terra, M. Felinto, H. F.
Brito, O. L. Malta, J. Lumin. 2013, 137, 269–273.
[39] P. C. R. Soares-Santos, L. Cunha-Silva, F. A. A. Paz, R. A. S.
Ferreira, J. Rocha, L. D. Carlos, H. I. S. Nogueira, Inorg.
Chem. 2010, 49, 3428–3440.
[40] a) C. Daiguebonne, N. Kerbellec, O. Guillou, J.-C. Buenzli, F.
Gumy, L. Catala, T. Mallah, N. Audebrand, Y. Gerault, K.
Bernot, G. Calvez, Inorg. Chem. 2008, 47, 3700–3708; b) N.
Kerbellec, D. Kustaryono, V. Haquin, M. Etienne, C. Daigue-
bonne, O. Guillou, Inorg. Chem. 2009, 48, 2837–2843; c) F.
Le Natur, G. Calvez, C. Daiguebonne, O. Guillou, K. Bernot,
J. Ledoux, L. Le Polles, C. Roiland, Inorg. Chem. 2013, 52,
6720–6730; d) Y. Luo, Y. Zheng, G. Calvez, S. Freslon, K.
Bernot, C. Daiguebonne, T. Roisnel, O. Guillou, Crys-
tEngComm 2013, 15, 706–720.
[21] F. N. Shi, L. Cunha-Silva, T. Trindade, F. A. A. Paz, J. Rocha,
Cryst. Growth Des. 2009, 9, 2098–2109.
[22] a) Y. G. Huang, F. L. Jiang, D. Q. Yuan, M. Y. Wu, Q. Gao,
W. Wei, M. C. Hong, J. Solid State Chem. 2009, 182, 215–222;
b) Y. Huang, Y. S. Song, B. Yan, M. Shao, J. Solid State Chem.
2008, 181, 1731–1737; c) Y. G. Huang, F. L. Jiang, D. Q. Yuan,
M. Y. Wu, Q. Gao, W. Wei, M. C. Hong, Cryst. Growth Des.
2008, 8, 166–168; d) Y. G. Huang, B. L. Wu, D. Q. Yuan, Y. Q.
Xu, F. L. Jiang, M. C. Hong, Inorg. Chem. 2007, 46, 1171–
1176; e) C. M. Liu, D. Q. Zhang, D. B. Zhu, Inorg. Chem. Com-
[41] A. Boultif, D. Louer, J. Appl. Crystallogr. 2004, 37, 724–731.
mun. 2008, 11, 903–906; f) F. Luo, Y. X. Che, J. M. Zheng, [42] J. Rodriguez-Carvajal, FULLPROF - A Program for Rietveld
Cryst. Growth Des. 2008, 8, 2006–2010; g) C. Qin, X. L. Wang,
E. B. Wang, Z. M. Su, Inorg. Chem. 2005, 44, 7122–7129; h)
Y. S. Song, B. Yan, Z. X. Chen, J. Mol. Struct. 2005, 750, 101–
108; i) X. F. Zhang, D. G. Huang, C. N. Chen, Q. T. Liu, D. Z.
Liao, L. C. Li, Inorg. Chem. Commun. 2005, 8, 22–26.
[23] J. G. Smith, Synthesis 1984, 629–656.
Refinement and Pattern Matching Analysis, Abstract of the Sat-
ellite Meeting on Powder Diffraction of the XV Congress of
the IUCR, Toulouse, France, 1990.
[43] A. Boultif, D. Louer, J. Appl. Crystallogr. 1991, 24, 987–993.
[44] D. Louer, in: Automatic Indexing: Procedures and Applications,
Accuracy in Powder Diffraction II, NIST, Gaithersburg, 1992,
p. 92–104.
[45] J. Laugier, B. Bochu, CHECKCELL – A Software Performing
Automatic Cell/Space Group Determination, Collaborative
Computational Project Number 14 (CCP14), Laboratoire des
Matériaux et du Génie Physique de l’Ecole Supérieure de Phys-
ique de Grenoble (INPG), 2000.
[46] A. LeBail, H. Duroy, J. L. Fourquet, Mater. Res. Bull. 1988,
23, 447–452.
[47] H. M. Rietveld, J. Appl. Crystallogr. 1969, 2, 65–71.
[48] G. Caglioti, A. Paoletti, F. P. Ricci, Nucl. Instrum. 1958, 3, 223–
228.
[24] T. S. Martins, T. L. R. Hewer, R. S. Freire, Quim. Nova 2007,
30, 2001–2006.
[25] E. V. Alexandrov, V. A. Blatov, A. V. Kochetkov, D. M. Pros-
erpio, CrystEngComm 2011, 13, 3947–3958.
[26] V. A. Blatov, A. P. Shevchenko, TOPOS, version 4.0, Profes-
sional (beta evaluation), Samara State University, Samara,
Russia, 2006.
[27] L. D. Carlos, Y. Messaddeq, H. F. Brito, R. A. S. Ferreira,
V. D. Bermudez, S. J. L. Ribeiro, Adv. Mater. 2000, 12, 594–
598.
[28] EPINET, see: http://epinet.anu.edu.au.
[29] a) J. Albertss, A. Oskarsso, Acta Chem. Scand. 1968, 22, 1700;
b) J. Albertss, A. Oskarsso, Acta Chem. Scand. 1974, 28, 347–
355; c) B. L. Chen, Y. Yang, F. Zapata, G. D. Qian, Y. S. Luo,
J. H. Zhang, E. B. Lobkovsky, Inorg. Chem. 2006, 45, 8882–
[49] K. Brandenburg, DIAMOND, version 3.2f, Crystal Impact
GbR, Bonn, Germany, 1997–2010.
Received: May 17, 2013
Published Online: September 19, 2013
Eur. J. Inorg. Chem. 2013, 5576–5591
5591
© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim