Organophosphonate-Functionalized Lanthanopolyoxomolybdate: Synthesis, Characterization, Magnetism, Luminescence, and Catalysis of H2O2-Based Thioether Oxidation

Article abstract of DOI:10.1021/acs.inorgchem.7b02672

A novel class of organophosphonate-based polyoxomolybdate derivatives, K₄H₅[Ln₃(H₂O)₁₄{(Mo₈O₂₄)(O₃PCH₂COO)₃}₂]·23H₂O (Ln = Gd (1Gd), Tb (2Tb), Dy (3Dy)), have been fully investigated by a few characterization methods such as single-crystal X-ray crystallography, XRPD, elemental analysis, TGA, and IR spectra. The magnetic properties of 1Gd, 2Tb, and 3Dy were investigated, as well as the solid-state luminescence properties of 2Tb and 3Dy. The catalysis properties of 1Gd, 2Tb, and 3Dy for thioether oxidization have been investigated using hydrogen peroxide (H₂O₂) as an oxidant. The catalysis study demonstrated the efficient and selective conversion of various thioethers to their corresponding sulfones in excellent yields.

Full text of DOI:10.1021/acs.inorgchem.7b02672

Article
Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
pubs.acs.org/IC
Organophosphonate-Functionalized Lanthanopolyoxomolybdate:
Synthesis, Characterization, Magnetism, Luminescence, and Catalysis
of H O ‑Based Thioether Oxidation
2
2
Jiawei Wang, Yanjun Niu, Meng Zhang, Pengtao Ma, Chao Zhang, Jingyang Niu,* and Jingping Wang*
Henan Key Laboratory of Polyoxometalate, Institute of Molecular and Crystal Engineering, College of Chemistry and Chemical
Engineering, Henan University, Kaifeng 475004, Henan, People’s Republic of China
*
S Supporting Information
ABSTRACT: A novel class of organophosphonate-based polyoxomolyb-
date derivatives, K H [Ln (H O) {(Mo O )(O PCH COO) } ]·23H O
4
5
3
2
14
8
24
3
2
3
2
2
(
Ln = Gd (1Gd), Tb (2Tb), Dy (3Dy)), have been fully investigated by a
few characterization methods such as single-crystal X-ray crystallography,
XRPD, elemental analysis, TGA, and IR spectra. The magnetic properties of
1
Gd, 2Tb, and 3Dy were investigated, as well as the solid-state
luminescence properties of 2Tb and 3Dy. The catalysis properties of
Gd, 2Tb, and 3Dy for thioether oxidization have been investigated using
hydrogen peroxide (H O ) as an oxidant. The catalysis study demonstrated
1
2
2
the efficient and selective conversion of various thioethers to their
corresponding sulfones in excellent yields.
1
8
INTRODUCTION
example, {(O CCH PO ) Mo O }, {(HOOCC H PO ) -
2 2 3 2 5 15 2 4
3 2
20
■
1
9
Mo O },
{(HOOCC H NCH PO ) Mo O },
5
1 5
5 9 2 3 2 5 1 5
Polyoxometalates (POMs) have become a family of early-
transition-metal clusters (W, Mo, or V) that possess abundant
surface oxygen atoms and controllable structures, which
generally show significant structural diversity and intriguing
{
{
(HO CC H PO )Mo O }, {(O CC H PO )MoO F},
2 6 4 3 2 6 2 6 4 3 2
(O CC H PO ) Mo O }, and {(HO CC H PO ) -
Mo F O (H O) }. From the details of the examples
above, it is easy to figure out that a majority of structures
2
6
4
3
2
5
15
2
6
4
3 2
2
1
1
2
4
34
2
4
1
,2
properties such as magnetism, catalysis, electrochemistry, etc.
just anchor some common transition metals (Co, Ni, Cu) or
In particular, organo-functionalized POMs, for instance,
carboxylic acid-/alkoxy-/organophosphonate-modified POMs,
have become an important and hot research topic in the POM
22
even do not anchor any metal ions. In contrast, lanthanide
2−
(
Ln) ions incorporated in the system of Mo/O/RPO3 have
been rarely explored. Only a series of Ln species based on 1,1-
diphosphonic acid (HEDP) functionalized polyoxomolybdates
have been reported. These compounds form three-dimen-
sional cage structures and have strong dye degradation activity
3
family. A large number of organophosphonate-based poly-
2
−
oxomolybdates (Mo/O/RPO3 ) have been successfully
prepared, and their potential applications have been fully
23
4
5
6
7
8
explored by Pope, Kortz, Zubieta, Dolbecq, et al. A
thorough literature survey indicates that monophosphonate-
functionalized polyoxomolybdates, such as the Strandberg type
(
rhodamine B (RhB)).
As a continuation of previous work, we have focused research
4
−
on Ln-containing organophosphonate-based polyoxomolyb-
dates as they possess 4f electrons, which may lead to novel
structures and attractive properties, such as magnetism and
photoluminescence properties. Therefore, we chose sodium
molybdate and organophosphonate ligands with Ln ions to
prepare multidimensional structures by one-pot reactions.
Among the vast organophosphonate family, phosphonoacetic
acid has been generally used as an organic ligand to obtain
polyanions [(O PR) Mo O ] (R = CH , C H , C H ,
3
2
5
15
3+
3
2
5
6
5
3
+
3+
C H NH , CH C H NH , CH CHNH , CH CH(CH )-
2
4
2
6
4
3
3
3
3
+
9
CHNH , etc.), have been consistently explored for a long
time. In particular, bis-phosphonate-functionalized polyoxomo-
lybdates have achieved a dominant position in the field of Mo/
O/RPO32 : for example, {(O PCR(OH)PO ) MoO } (R =
−
3
3 2
2
1
0
V
11
C H NH ),
{(Mo O ) (O PCH PO ) },
O PCH CH PO )}, {(O PCROPO ) O(Mo O ) } (R =
3 2 2 3 3 3 2 3 8 2
{Mo O -
3
6
2
2
4
4
3
2
3
4
2
5
12
(
1
9−22
inorganic−organic hybrid compounds.
Notably, the
CH S(CH ) , C H N ), {Mo O O P(CH ) PO } (n = 2−
2
3 2
4
5
2
5
15
3
2 n
1 4
3
1
3
polyfunctional bridging ligand phosphonoacetic acid displays
the following features: (1) phosphonoacetic acid allows
multifunctional coordination modes to coordinate various
4
),
{Mo O (O P(CH ) PO )},
{Mo O
-
2 2
6
1 8
3
2
5
3
6
1
5
16
(
O PCH PO )}, and {Mo O (O PCH PO ) }. Organo-
3
2
3
7
16
3
2
3 3
2−
triphosphonates grafted into the Mo/O/RPO3 framework,
17
such as {[N(CH PO ) ]Mo O (OH)(H O) }, have been
2
3 3
6
16
2
4
previously reported. Furthermore, great developments in
phosphonocarboxylate derivatives have also been made: for
Received: October 17, 2017
©
XXXX American Chemical Society
A
DOI: 10.1021/acs.inorgchem.7b02672
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Table 1. Crystallographic Data for 1Gd, 2Tb, and 3Dy
1
Gd
2Tb
3Dy
formula
C H K O P Mo Gd
C H K O P Mo Tb
C H K O P Mo Dy
12 78 4 111 6 16 3
1
2
78
4
111
6
16
3
12 78
4
111
6
16
3
M (g mol−1)
4347.71
4352.73
4363.45
r
space group
cryst syst
a (Å)
C2/c
C2/c
C2/c
monoclinic
monoclinic
monoclinic
29.8359(13)
11.1754(5)
39.2899(17)
94.2560(10)
13064.2(10)
4
29.7923(12)
11.1666(4)
39.2587(15)
94.2470(10)
13024.7(9)
4
29.7519(16)
11.1479(6)
39.204(2)
94.2030(10)
12967.9(12)
4
b (Å)
c (Å)
β (deg)
V (Å3)
Z
3
cryst size (mm )
ρcalcd (g cm−3)
μ (mm−1)
0.23 × 0.21 × 0.18
2.210
0.21 × 0.19 × 0.15
2.220
0.28 × 0.16 × 0.15
2.235
3.287
3.398
3.506
Rint
0.0224
0.0239
0.0213
limiting indices
−35 ≤ h ≤ 35
−35 ≤ h ≤ 34
−13 ≤ k ≤ 13
−46 ≤ l ≤ 36
32361
−34 ≤ h ≤ 35
−13 ≤ k ≤ 13
−40 ≤ l ≤ 46
32503
−
−
13 ≤ k ≤ 8
46 ≤ l ≤ 46
no. of rflns collected
no. of indep rflns
F(000)
32630
11548
11507
11491
8272.0
8284.0
8296.0
GOF on F2
1.068
1.066
1.086
R1, wR2 (I > 2σ(I))
R1, wR2 (all data)
0.0586, 0.1595
0.0627, 0.1628
0.0573, 0.1546
0.0629, 0.1589
0.0598, 0.1642
0.0642, 0.1677
−
1
metal centers to construct multidimensional structures with
fascinating properties and (2) phosphonoacetic acid, possessing
phosphonate and carboxylate groups, has multiple oxygen
atoms which can act in various acidity-dependent coordination
modes, allowing the construction of different coordination
structures.
C, 3.20, H, 1.859. Selected IR (KBr, cm ): 3413 (s), 1711 (m), 1622
(
(
s), 1531 (s), 1434 (m), 1382 (m), 1219 (w), 1142 (s), 1107 (s), 1061
s), 908 (s), 754 (s), 730 (s), 651 (s), 608 (s).
Synthesis of Compound 2Tb. The preparation procedure of 2Tb is
similar to that for 1Gd but with TbCl ·6H O instead of GdCl ·6H O.
Yield: 0.120 g (17.6%) for 2Tb based on TbCl ·6H O. Anal. Calcd:
Mo, 34.64; Tb, 10.76; P, 4.19; K, 3.53; C, 3.25; H, 2.07. Found: Mo,
4.79; Tb, 10.92; P, 4.30; K, 3.62; C, 3.15, H, 1.984. Selected IR (KBr,
cm ): 3411 (s), 1713 (m), 1625 (s), 1532 (s), 1436 (s), 1381 (m),
1216 (w), 1145 (s), 1108 (s), 1063 (s), 905 (s), 750 (s), 733 (s), 652
(s), 610 (s).
3
2
3
2
3
2
On the basis of this strategy, our group has successfully
synthesized a series of isostructural Ln-containing phosphono-
a c e t i c a c i d b a s e d p o l y o x o m o l y b d a t e s
K H [Ln (H O) {(Mo O )(O PCH COO) } ]·23H O (Ln
3
−1
4
5
3
2
14
8
24
3
2
3
2
2
=
Gd (1Gd), Tb (2Tb), Dy (3Dy)), constituted by two
Synthesis of Compound 3Dy. The preparation procedure of 3Dy is
also similar to that for 1Gd but with DyCl ·6H O instead of GdCl ·
open {Mo } groups as building blocks, six organic components,
3
2
3
8
6
H O. Yield: 0.118 g (17.4%) for 3Dy based on DyCl ·6H O. Anal.
and three Ln ions as bridging fragments.
2
3
2
Calcd: Mo, 34.56; Dy, 10.96; P, 4.18; K, 3.52; C, 3.25; H, 2.07. Found:
Mo, 34.82; Dy, 11.13; P, 4.34; K, 3.72; C, 3.18, H, 1.896. Selected IR
EXPERIMENTAL SECTION
−1
(
(
KBr, cm ): 3408 (s), 1715 (m), 1625 (s), 1532 (s), 1436 (s), 1381
m), 1219 (w), 1142 (s), 1110 (s), 1063 (s), 906 (s), 756 (s), 728 (s),
■
Materials and Physical Measurements. All chemicals were used
as obtained without further purification. Elemental analyses for carbon
and hydrogen were performed with a PerkinElmer 2400-II CHNS/O
analyzer. XRPD measurements were carried out with a Bruker SMART
Apex II CCD-based diffractometer at 293 K. Elemental analyses of Mo,
P, K, and Ln were performed with a PerkinElmer Optima 2000 ICP-
OES spectrometer. Infrared spectra were recorded with a Bruker
VERTEX 70 IR spectrometer as KBr pellets. TG analyses were carried
6
53 (s), 607 (s).
Catalytic Oxidation of Thioethers. Catalyst (3.6 μmol), substrate
(
1 mmol), solvent (3 mL), and 30% H O (2 mmol) were loaded into
2 2
a 50 mL round-bottom tube at a certain temperature with constant
stirring. During the reaction, a trace of the reaction solution was taken
out from the mixture by using a microsyringe and followed with gas
chromatogaphy (GC) analyses. Products were identified from GC-MS
spectra with toluene as an internal standard.
out under a N atmosphere on a PerkinElmer TGA7 instrument at a
2
−
1
range of 25−1000 °C (heating rate: 10 °C min ).
Synthesis of Compound 1Gd. A quantity of phosphonoacetic acid
0.14 g, 1.022 mmol) was dissolved in 25 mL of distilled water
followed by the addition of solid Na MoO ·2H O (0.606 g, 2.505
mmol) and KCl (0.228 g, 3.058 mmol) with stirring. The pH of the
reaction mixture was adjusted to 3.0 by 6 M HCl. To this reaction
mixture was added 0.172 g (0.461 mmol) of GdCl ·6H O, and the pH
X-ray Crystallography. Structural measurements for 1Gd, 2Tb, and
3Dy were performed at 296(2) K on a Bruker Apex-II CCD
diffractometer using graphite-monochromated Mo Kα radiation (λ =
0.71073 Å). This data reduction, including a correction for routine
Lorentz and polarization, was solved by an applied multiscan
(
2
4
2
2
4
absorption correction SADABS program.
Direct methods
(SHELXS97) were used to solve their structures, and the heavy
3
2
25
value was carefully maintained at 3.0 with 6 M NaOH. After it was
stirred at 60 °C for 2 h, the mixed solution was gradually cooled to
room temperature, filtered, and allowed to evaporate slowly at room
temperature. The colorless block-shaped crystals of 1Gd were
obtained after about one month. Yield: 0.123 g (18.0%) for 1Gd
based on GdCl .6H O. Anal. Calcd: Mo, 34.69; Gd, 10.66; P, 4.20; K,
atoms were located using the SHELXTL-97 program package. In the
final refinement cycles, the Mo, P, and Ln atoms were refined
anisotropically; the O and C atoms were refined isotropically. The
lattice water molecules were determined by the TGA results. Four
+
disordered K cations were located by a Fourier map. The hydrogen
atoms of organic groups were fixed in calculated positions and then
refined using a riding model. All H atoms on water molecules were
3
2
3
.53; C, 3.25; H, 2.01. Found: Mo, 34.76; Gd, 10.83; P, 4.29; K, 3.73;
B
DOI: 10.1021/acs.inorgchem.7b02672
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Figure 1. (a) Ball and stick/polyhedral representation of the polyanion 1Gd. (b) Structure of [Gd(H O) {(Mo O )(O PCH COO) } ]15−. (c)
2
4
8
24
3
2
3 2
9
−
Structure of [(Mo O )(O PCH COO) ] . (d) Structure of {Mo O }. Color code: MoO , aqua octahedra; P, yellow; O, red; C, black; Gd, blue. H
8
24
3
2
3
8
24
6
atoms are omitted for clarity.
directly included in the molecular formula. Crystallographic data for
the three compounds reported in this paper have been deposited with
the Cambridge Crystallographic Data Center with CCDC numbers
organic ligands incorporated into Ln-containing polyoxomo-
lybdates need to overcome the steric hindrance. It is
noteworthy that the polyfunctional bridging ligand phosphono-
acetic acid possesses three O−H bonds, three protons of which
could be ionizable and coordinate with polyoxomolybdates and
Ln ions to form novel structures. We utilized a one-pot
synthetic strategy to prepare a series of Ln-containing
organophosphonate-substituted polyoxomolybdates by reacting
Na MoO ·2H O, phosphonoacetic acid, LnCl ·6H O (Gd, Tb,
1
569825, 1569826, and 1569827 for 1Gd, 2Tb, and 3Dy, respectively.
Collected crystal data and structure refinement parameters for 1Gd,
2
Tb, and 3Dy are given in Table 1.
Analyses of BVS, IR, and XRPD. Bond Valence Sum
Calculations. Complete single-crystal X-ray data for the three
compounds 1Gd, 2Tb, and 3Dy are available, and selected interatomic
distances are presented in Table S1. The bond valence sum (BVS)
2
6
2
4
2
3
2
calculations (Tables S2−S4) show that the oxidation states of the Mo
and Ln atoms in 1Gd, 2Tb, and 3Dy are +6 and +3, respectively. The
BVS values for P atoms are in the range of 2.56−3.145 (average value
Dy), and KCl with a molar ratio of 5.43:2.22:1:6.63 in 60 °C
aqueous solution with stirring for 2 h. Notably, the pH value of
the reaction system plays a key role in the formation of the
crystals. Our experimental investigations indicate that the
optimal pH range of 2.9−3.1 is helpful for the formation of
1Gd, 2Tb, and 3Dy, whereas their yields will be the highest
when the pH value is 3.0 with other conditions kept
unchanged. In addition, the amount of phosphonoacetic acid
used should be controlled at around 1.022 mmol. Crystals of
compounds 1Gd, 2Tb, and 3Dy cannot be obtained if the
amount of phosphonoacetic acid used is increased to 1.50
mmol or decreased to 0.50 mmol. During our exploration, we
2
.70), indicating the +3 oxidation state. Furthermore, five protons
were added by the charge balance of compounds 1Gd, 2Tb, and 3Dy.
IR Spectra. The IR spectra of compounds 1Gd, 2Tb, and 3Dy show
−1
very similar characteristic vibrations in the range of 450−4000 cm
Figure S1), suggesting that the polyanions in 1Gd, 2Tb, and 3Dy are
isostructural, which is consistent with the results of single-crystal X-ray
(
−1
structural analysis. The peaks at 992, 929, and 904 cm for 1Gd, 993,
−1
−1
9
28, and 904 cm for 2Tb, and 992, 928, and 903 cm for 3Dy can
be regarded as the characteristic Mo−O vibrations. The absorption
t
−
1
bands at 754−650 cm are attributed to the Mo−O−Mo stretching
vibrations. In addition, the characteristic peaks at 1061, 1107, and 1142
−
1
−1
3+
3+
3+
cm for 1Gd, 1063, 1108, and 1142 cm for 2Tb, and 1063, 1110,
first used LnCl
3 2
·6H O (0.172 g, Ln = Gd , Tb , Dy ) to
−1
and 1143 cm for 3Dy can be respectively assigned to P−O
react with other simple materials, giving rise to 1Gd, 2Tb, and
−1
3+
vibrations. The apparent peaks in the range 1370−1530 cm are
3
Dy. Because of the influence of the nature of Ln cations on
characteristic of the carboxyl vibrations from phosphonoacetic acid.
3+
3+
the structures of the compounds, we replaced Gd , Tb , and
−1
The signals appearing around 1630 cm and the peaks around 3400
cm are assigned to the bending and stretching modes of lattice and
3+
3+
Dy cations by using other Ln cations under the same
conditions; however, the desired product were not obtained. In
−1
27
coordinated water molecules.
2+
2+
2+
3+
2+
3+
addition, we tried to use Cu , Co , Ni , Fe , Zn , and Cr
X-ray Powder Diffraction. The experimental XRPD patterns for
Gd, 2Tb, and 3Dy are consistent with the simulated patterns
cations rather than Ln3+ under the same conditions, while
unexpectedly, nothing except for some precipitates were
obtained in the end. Now, we will continue to research the
influence of Ln-containing organophosphonate-based polyox-
omolybdates on the structural variation and relevant properties
of the resulting compounds.
1
obtained from single-crystal X-ray diffraction, which indicates that the
samples are pure (Figure S2). The differences in intensity between the
experimental and simulated patterns might be due to the variation in
crystal orientation for the powder samples.
RESULTS AND DISCUSSION
■
Description of the Structures. X-ray analyses reveal that
compounds 1Gd, 2Tb, and 3Dy are isomorphous and
crystallize in the same monoclinic space group C2/c. Therefore,
only 1Gd is chosen to describe in detail here as an example.
Syntheses. There are rare examples of the organo-
phosphonate ligands and Ln synchronously grafted into the
framework of polyoxomolybdates, which have been an
28
+
enormous challenge to create. Ln-containing polyoxomolyb-
dates have generally high surface negative charges, which make
the introduction of organic ligands difficult. Simultaneously,
The structure of 1Gd contains 4 K ions, 23 water molecules, 1
9
−
[Gd (H O) {(Mo O )(O PCH COO) } ] (1a), and 5
3
2
14
8
24
3
2
3 2
protons for the charge balance. As shown in Figure 1, the
C
DOI: 10.1021/acs.inorgchem.7b02672
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
polyoxoanion 1a consists of a [Gd(H O) ] cation and a
Article
3
+
displays a nine-coordinated distorted monocapped quadran-
2
5
sandwich polyanion of [Gd(H O) {(Mo O )-
gular antiprism and is made up of four μ -O atoms from the
2
4
8
2 4
2
1
5−
(
(
O PCH COO) } ]
(1b). The polyanion [Gd-
{COO} group (O1, O2, O9, and O10, Gd1−O1 = 2.492(8) Å,
3
2
3 2
1
5−
H O) {(Mo O )(O PCH COO) } ]
can be viewed as
Gd1−O2 = 2.475(9) Å, Gd1−O9 = 2.473(8) Å, Gd1−O10 =
2
4
8
24
3
2
3
2
9
−
two [(Mo O )(O PCH COO) ] fragments sandwiching a
disordered [Gd(H O) ] ion. The fragment [(Mo O )-
2.468(7) Å), and five O atoms from H O (O1W−O4W and
8
24
3
2
3
2
3
+
2
4
8
24
O8W, Gd1−O = 2.411(8)−2.431(9) Å) (Figure 2a). The Gd2
9
−
(O PCH COO) ] (1c) features V-shaped {Mo O } building
ion adopts an eight-coordinated highly distorted quadrangular
3
2
3
8
24
blocks (1d) combining with three organic groups, which could
antiprism and is achieved by four μ -O atoms (O12 and O24
2
be considered as two corner-sharing {Mo } units decorated by
from the {Mo O } fragment, O26 from the {PO } group,
4
8
24
3
the H O PCH COOH, one {O PCH COO} ligand residing in
2
3
2
3
2
Gd2−O12 = 2.467(8) Å, Gd2−O24 = 2.540(7) Å, Gd2−O26
2
the center of V-shaped {Mo } structure unit, and two other
8
= 2.286(7) Å, Gd2−O 26 = 2.305(6) Å) and four O atoms
{
{
O PCH COO} ligands sticking out like two arms. Each
3 2
from water ligands (O5W and O11W−O13W, Gd2−O(H O)
2
Mo } subunit is composed of four edge-sharing {MoO }
4
6
= 2.182(19)−2.500(18) Å) (Figure 2b). Two Gd ions (Gd2
and Gd2′) in the center of the compound are equivalent with
two Gd−O(12W) bonds joining the clusters (average length
octahedra, and all of the Mo cations in the {Mo } unit are
4
basically located in the same plane. The two {Mo } subunits are
4
placed against each other, forming a “V” type structure, and
their dihedral angle is 77.335° (Figure S3). In addition, there
are two crystallographically unique types of P atoms in the
symmetric unit. One P atom is connected to two corner-sharing
2
.192(18) Å), while the remaining three coordination sites are
occupied by H O (average length 2.463 Å). As we can observe,
2
two neighboring sandwich [Gd(H O) {(Mo O )-
2
4
8
24
15−
(
O PCH COO) } ]
(1b) clusters are connected by [Gd-
3
2
3 2
{
Mo } units by two μ -O atoms and a Gd atom by one μ -O
3+
2
3
3
(H O) ] anions, and the structure further extends to a 1D
2
5
atom; simultaneously, a {COO} group from phosphonoacetic
chain in the ac plane (Figure 3a). A more interesting feature of
acid links to the remaining two corner-sharing {Mo } units.
2
1a is that a two-dimensional layer (Figure 3b) is constructed by
The other P atom is bonded to two isolated {MoO } octahedra
15−
6
sandwich [Gd(H O) {(Mo O )(O PCH COO) } ]
clus-
2
4
8
24
3
2
3 2
by two μ -O atoms and two edge-sharing {MoO } octahedra by
3+
2
6
ters and [Gd(H O) ] bridges. In this framework, five
2
5
a μ -O atom, with one {COO} group from phosphonoacetic
3+
3
polyanions 1a are joined together by two [Gd(H O) ]
2
5
acid combining with a Gd atom.
3+
cations and every 1a links to two [Gd(H O) ] cations via
3
+
2
5
As shown in Figure 2, the Gd cation in 1a shows two types
(
1
C)−O−Gd1−O−(C) bridges. The polyanions of compound
of coordination geometries (Gd1 and Gd2). The Gd1 ion
+
Gd are further extended into a 3D framework by K cations
(
Figure 3c).
Magnetic Properties. Variable-temperature magnetic
susceptibilities of 1Gd, 2Tb, and 3Dy have been investigated
in the temperature range of 300−2K. The plots of χ T versus T
M
3
are presented in Figure 4. For 1Gd, the χ T value is 22.56 cm
M
K mol− at 300 K, slightly lower than the theoretical value of
1
3
−1
III
2
3.63 cm K mol of three isolated Gd ions (S = 7/2, g = 2)
in the S7 ground state. The χ T product slowly drops
8
29
/2
M
3
−1
down and reaches a minimum of 21.88 cm K mol at 2 K.
The compound 1Gd shows Curie−Weiss behavior in the
temperature range of 300−2 K, with a Curie constant of C =
3
−1
2
2.56 cm K mol and Weiss constant of Θ = −0.018 K
3 −1
Figure 2. Coordination environmenta of the Gd1 (a) and Gd2 (b)
atoms.
(Figure S7a). For 2Tb, the value of χ T is 34.69 cm K mol
M
at 300 K, which is quite close to the theoretical value of 35.43
3
−1
III
7
cm K mol for three noninteracting Tb ions ( F , g = 3/
6
30
3
−1
2
). At 2 K, the χ T value decreases to 24.02 cm K mol and
M
Figure 3. (a) 1D framework of 1Gd stretching along the ac plane constructed by Gd1 ions. (b) 2D framework of 1Gd stretching along the ab plane
constructed by Gd1 ions. (c) Packing arrangement of 1Gd along the b axis. Color code: MoO , aqua octahedra; P, yellow; O, red; C, black; Gd, blue;
6
K, orange.
D
DOI: 10.1021/acs.inorgchem.7b02672
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Inorganic Chemistry
Article
spectrum of 2Tb was recorded and included three characteristic
bands at 341, 359, and 378 nm, which are assigned to the
5
5
5
transitions of L , L , and G levels, respectively (Figure
6
9
6
33
S6a). Similarly, the solid-state sample of 3Dy was excited
under 387 nm ultraviolet light (Figure 5b), and the emission
spectrum demonstrates three apparent emission peaks at 479,
5
74, and 662 nm, which can be separately ascribed to the
4
6
34
transitions of F9 to H (J = 15/2, 13/2, 11/2). The yellow-
green emission at 574 nm (Figure S8) from the F9 → H
/2
J
4
6
/2
13/2
transition was the most prominent. In addition, the excitation
spectrum of 3Dy was obtained, in which four characteristic
bands centered at 351, 365, 387, and 427 nm are attributed to
6
the transitions from the H
ground state to the different
15/2
6
6
4
4
excited states P , P , I , and G11/2, in sequence (Figure
7/2
5/2
13/2
35
S6b).
Figure 4. χ T versus T plots of 1Gd, 2Tb, and 3Dy in the 2−300 K
M
Decay Analyses. The lifetime measurements of 2Tb and
Dy were studied under forceful excitation and emission bands.
range.
3
For 2Tb, the decay times under the most intense emission at
544 nm conform to a single-exponential decay behavior by the
equation I = A exp(−t/τ), affording a lifetime of 616.31 μs
(100%) (Figure 5c), which is evidently longer than most of the
reported values for the corresponding Tb complexes. For
3Dy, the lifetime curve (Figure 5d) under emission at 574 nm
is fitted successfully by a second-order exponential function by
the 1/χ versus T plots obey the Curie−Weiss law (C = 34.06
M
3
−1
cm K mol and Θ = −1.97 K) (Figure S7b). For 3Dy, the
3
−1
experimental χ T value is 37.77 cm mol K at room
M
III
36
temperature, which is evidently lower than three noninteracting
III
3
−1
31
Dy ions (42.50 cm mol K, S = 5/2, g = 4/3). The χMT
value undergoes a gradual reduction and reaches a minimum of
3
−1
2
7.14 cm K mol at 2 K. The 1/χ versus T plot obeys the
the formula I = A exp(t/τ ) + A exp(t/τ ), giving τ and τ
1 1 2 2 1 2
M
Curie−Weiss law indicating antiferromagnetic coupling with C
values of 5.05 μs (22.58%) and 9.37 μs (77.42%), respectively.
Catalysis. In recent years, there has been growing interest in
the catalytic oxidation of thioethers owing to their wide
3
−1
=
38.15 cm K mol and Θ = −1.49 K (Figure S7c).
Photoluminescence Properties. Luminescence. When
the solid-state sample of 2Tb was excited under visible light at
37
potential utilities. According to previous reports, POMs as
catalysts display excellent catalytic performance in the catalytic
3
6
78 nm, an emission spectrum was observed between 450 and
50 nm (Figure 5a), in which four obvious characteristic
38
oxidation of thioethers. Compound 2Tb was selected as a
representative example to research the oxidation reactions of
thioethers. Then the influences of various reaction parameters
on the catalytic activities were investigated by using diphenyl
sulfide as a model substrate. Products were identified by GC-
emission bands at 489, 544, 584, and 621 nm are respectively
attributed to the transitions of D to F (J = 6, 5, 4, 3). The
5
7
32
4
J
most intense peak at 544 nm presents a strong green
luminescence (Figure S8). Furthermore, the excitation
Figure 5. (a) Solid-state emission spectrum of 2Tb under excitation at 378 nm. (b) Solid-state emission spectrum of 3Dy under excitation at 387
nm. (c) Lifetime decay curve of 2Tb monitored under excitation at 378 nm. (d) Lifetime decay curve of 3Dy monitored under excitation at 387 nm.
E
DOI: 10.1021/acs.inorgchem.7b02672
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Inorganic Chemistry
Article
MS spectra. The selectivity to sulfoxide and sulfone products
and the conversion of initial sulfides were taken for the
qualitative analysis with GC. The influences of reaction time,
reaction temperature, and amounts of catalyst and H O are
Table 3. Selective Oxidation of Various Thioethers to
Sulfones Using 2Tb by H O
2
2
2
2
shown in Table 2. Blank reactions were performed for diphenyl
a
Table 2. Oxidation of Diphenyl Sulfide with H O
2
2
b
c
d
catalyst
entry (μmol)
H O
temp
(°C)
time conversn
sel
sel
2
2
(mmol)
(min)
(%)
(%)
(%)
1
2
3
4
5
6
3.6
2
2.0
2.0
1.0
1.5
2.0
2.0
30
50
50
50
50
50
120
120
120
120
60
82.3
99
51.4
77
48.6
23
76
55
30
1
3.6
3.6
3.6
3.6
85
24
97
45
98
70
120
100
99
a
Reaction conditions: diphenyl sulfide (1 mmol), 30% H O (1.5
2
2
mmol, 2 mmol), and catalyst (2 μmol, 3.6 μmol) in CH CN (3 mL).
3
b
Conversion was determined by GC-FID using an internal standard
technique based on diphenyl sulfide. Selectivity to diphenyl sulfone.
c
d
Selectivity to diphenyl sulfoxide.
sulfide, giving a 37% conversion and 52% selectivity for sulfone
in the absence of the catalyst 2Tb after 2 h; the conversion of
diphenyl sulfide and selectivity to diphenyl sulfone of the
reaction are low (Figure S9). The conversion was significantly
increased to 99% (Table 2, entry 2) by the addition of 2 μmol
of 2Tb. If addition of 2Tb was incrementally increased from 2
to 3.6 μmol, the conversion increased from 99 to 100% (Table
2
7
, entries 2 and 6) and the selectivity to sulfone increased from
7% to 99%. With these conditions, conversions were observed
to increase gradually and selectivity to sulfone increased
dramatically with a rise in the dosage of oxidant and catalysts
a
(
Table 2, entries 2−4 and 6). Furthermore, the results of
Reaction conditions for entries 1−8: substrate (1 mmol), 30% H O
2
2
2
parallel experiments indicated that the conversion and
selectivity increased as the reaction time was prolonged
(2 mmol), and catalyst (3.6 μmol) in CH
3
CN (3 mL) at 50 °C.
b
Reaction conditions for entries 9−11: sulfide (1 mmol), 30% H O
2
c
(
3 mmol), and catalyst (3.6 μmol) in CH CN (3 mL) at 60 °C. 2
3
d e
(
Table 2, entries 5 and 6) and remarkably declined with a
MPaO2. Conversion value determined by GC-FID. Selectivity to
decrease in reaction temperature (Table 2, entries 1 and 6),
which demonstrated that both reaction time and temperature
were crucial factors for the transformation from diphenyl sulfide
to diphenyl sulfone. A series of experimental results showed
that 1 mmol of diphenyl sulfide was completely converted to
oxidation products and excellent selectivity (99%) was obtained
under the optimal conditions, 3 mL of MeCN with 2 mmol of
sulfones.
representative example of POMs, possess a strong redox
nature, which is responsible for the splendid catalytic activity of
the thioether−POM system. As shown in Figure S9, the
catalytic activity of 2Tb is superior to that of its raw material,
which causes us to speculate that the catalytic reaction may be
concentrated on the isopolymolybdate units. On addition of
30% H O to a suspension of 2Tb in CH CN at 50 °C, the
solid is completely dissolved and finally changes to a yellow
solution, which indicate the formation of an active species. The
IR spectra of the catalyst 2Tb (a), the sample after the reaction
with excess H O (b), and the recycled catalyst 2Tb (c) are
3
0% H O and 3.6 μmol of 2Tb at 50 °C for 2 h (Table 2,
2 2
entry 6), which were superior to the results for the catalyst
[
3
Bmim] Mo O (Bmim = 1-butyl-3-methylimidazolium) with
4
8
26
2
2
3
39
mmol of 30% H O . Encouraged by the catalysis of 2Tb for
2
2
the oxidation of diphenyl sulfide, catalytic oxidations of various
thioethers were carried out under the optimal conditions
(
Table 3). The results of experiments demonstrate that alkyl
thioethers (Table 3, entries 1−3) and aryl alkyl thioethers
Table 3, entries 4−7) give excellent conversion (100%) and
2
2
provided in Figure 6. It is observed that the IR spectrum of 2Tb
has Mo−O−Mo bridge vibrations in the range between 650
and 754 cm . However, as can be seen from the spectrum after
(
−1
selectivity to sulfone (≥99%). Diphenyl sulfide shows a
relatively slow reaction, which might be due to the low
electron density on the sulfur atom of the substrate (Table 3,
entry 8). It is noted that refractory sulfur-containing
compounds benzothiophene (BT), dibenzothiophene (DBT),
and 4,6-dimethyldibenzothiophene (4,6-DMDBT) are also
oxidized to sulfones with excellent conversion and selectivity
despite their expressed super conjugation and large steric
hindrance for the oxidative process at mild temperatures (up to
the reaction with excess H O , the characteristic Mo−O−Mo
2
2
peaks disappear after the reaction with excess H O . However, a
2
2
strong peak at 861 cm− can be observed, which is assigned to
1
40
the peroxo bond ν(O−O) stretching vibration (Figure 6b).
Therefore, the species MoO(O ) is the possible active species
in catalysis. On the basis of previous reports and the
experimental results in the current work, a possible mechanism
of the reaction has been provided. Peroxomolybdic active
species can be formed by the nucleophilic attack of H O on
2
2
40
41
6
0 °C; Table 3, entries 9−11). Compound 2Tb, as a
2
2
F
DOI: 10.1021/acs.inorgchem.7b02672
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
for the synthesis and design of a novel benign catalytic system
for sulfoxidation reactions. In subsequent work, more intriguing
structures and properties of organophosphonate-functionalized
Ln-containing POMs will be introduced.
ASSOCIATED CONTENT
Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.7b02672.
■
*
S
Details on equipment used for complexes 1Gd, 2Tb, and
3Dy and Figures S1−S11 as described in the text (PDF)
Accession Codes
Figure 6. Infrared spectra of compound 2Tb before the catalytic
CCDC 1569825−1569827 contain the supplementary crystal-
lographic data for this paper. These data can be obtained free of
charge via www.ccdc.cam.ac.uk/data_request/cif, or by email-
ing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
reaction (a), after the reaction with H O2 (b), and for recycled
compound 2Tb (c).
2
the Mo atom of the polyoxometalates. Electrons are withdrawn
from the peroxyl moiety, thereby increasing the electrophilic
character of the peroxidic oxygens, oxidizing the sulfur
42
compounds into sulfones.
AUTHOR INFORMATION
Corresponding Authors
E-mail for J.N.: jyniu@henu.edu.cn.
E-mail for J.W.: jpwang@henu.edu.cn.
To confirm that the 2Tb is a truly heterogeneous catalyst, a
hot filtration experiment was performed under the optimal
conditions. The catalyst was separated after a reaction time of
■
*
*
45 min, and the reaction was allowed to proceed with the
filtrate. There was no further conversion observed in the filtrate,
which suggested that this reaction process is a heterogeneous
oxidation process (Figure S12). The catalyst was subsequently
removed by filtration after completion of the oxidation reaction,
and the leaching of Mo species was determined by ICP-AES
analysis. These species are essentially undetectable in the
filtrates (below the detection limit). These results show that
ORCID
Chao Zhang: 0000-0002-7400-5803
Jingyang Niu: 0000-0001-6526-7767
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
We gratefully acknowledge support from the NSFC (2117205)
and the Natural Science Foundation of Henan Province
■
2
Tb is truly heterogeneous and catalyst leaching is negligible
under these conditions.
The recycling of 2Tb in the oxidation of diphenyl sulfide was
also investigated. After each run, the catalyst was separated by
(
162300410015).
simple filtration, followed by washing with CH CN, and then
3
REFERENCES
■
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potentially heterogeneous and stable catalyst. Moreover, IR
spectra confirmed that 2Tb could maintain its structural
integrity after catalytic reactions (Figure S11). Finally, oxidation
reactions of thioethers with 1Gd and 3Dy as catalysts were
performed, which shows that they also have superior catalytic
performance (Figure S9).
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