Crystal Growth & Design
Article
Strem Chemicals); Eu(NO3)3·6H2O (99% Acros Organics). The IR
spectra were recorded from KBr pellets in the range 4000−250 cm−1
on a Bruker IFS 66 V/S. The thermogravimetric and differential
thermal analyses (TGA-DTA) were performed using Seiko TG/DTA
320U equipment in a temperature range between 25 and 1000 °C in
air (100 mL/min flow) with a heating rate of 10 °C/min. A Perkin-
Elmer CNHS Analyzer 2400 was employed for the elemental analysis.
Synthesis. Three RPF-21-Ln with formula [Ln(3,5-DSB)(H2O)5]
(Ln = La, Pr, Nd) were synthesized under the same reaction
conditions. For the Pr compound, 0.075 g (0.23 mmol) of 3,5-
DSBNa2 was added to a solution of Pr(NO3)3·6H2O (0.1 g, 0.23
mmol) in water (6 mL); subsequently, an aqueous solution of sodium
hydroxide (1 mol/L) was dropwise added, adjusting the pH value of
the initial reaction mixture to ∼6−7. The mixture was then
magnetically stirred at room temperature for 5 min and afterward
was transferred to a Teflon-lined stainless steel autoclave and heated at
170 °C for 24 h. After the mixture was cooled to room temperature,
the crystalline product was filtered and washed with water and acetone.
As mentioned above, using the same procedure, La and Nd
compounds were obtained. Elemental analysis: calculated for La
(C7H13O13S2La): C, 16.54; H, 2.58; S, 12.61. Found: C, 16.68; H,
2.54; S, 11.81. Calculated for Pr (C7H13O13S2Pr): C, 16.48; H, 2.57; S,
12.56. Found: C, 16.49; H, 2.43; S, 12.06. Calculated for Nd
(C7H13O13S2Nd): C, 16.37; H, 2.55; S, 12.49. Found: C, 16.24; H,
2.44; S, 11.34.
RPF-22-Ln. [Ln(3,5-DSB)(H2O)3] (Ln = La, Pr, Nd, Sm, and Eu).
For the Pr compound, 3,5-DSBNa2 (0.075 g, 0.23 mmol) was added to
a solution of Pr(NO3)3·6H2O (0.1 g, 0.23 mmol) in water (6 mL); an
aqueous solution of sodium hydroxide (1 mol/L) was dropwise added,
adjusting the pH value to ∼7, and magnetically stirred at room
temperature for 5 min. The resultant reaction mixture was transferred
to a Teflon-lined stainless steel autoclave and heated at 200 °C for 24
h. After the mixture was cooled to room temperature, the crystalline
product was filtered and washed with water and acetone. The same
procedure was used for the synthesis of the La, Nd, and Sm
compounds. Elemental analysis: calculated for La (C7H9O11S2La): C,
17.81; H, 1.92; S, 13.58. Found: C, 17.29; H, 1.63; S, 12.50. Calculated
for Pr (C7H9O11S2Pr): C, 17.73; H, 1.91; S, 13.52. Found: C, 17.74;
H, 1.77; S, 13.31. Calculated for Nd (C7H9O11S2Nd): C, 17.61; H,
1.90; S, 13.43. Found: C, 17.60; H, 2.07; S, 12.58. Calculated for Sm
(C7H9O11S2Sm): C, 17.38; H, 1.88; S, 13.26. Found: C, 15.56; H,
1.54; S, 12.23. Calculated for Eu (C7H9O11S2Eu): C, 17.33; H, 1.87; S,
13.22. Found: C, 16.81; H, 1.73; S, 12.87.
Using the same reaction conditions as for RPF-22-Ln but
augmenting the time of the hydrothermal reaction up to 3 days,
RPF-23-Ln [Ln3(3,5-DSB)2(OH)3(H2O)3] (Ln = Pr, Nd, and Eu)
were obtained. Elemental analysis: calculated for Pr (C14H15O22S4Pr3):
C, 15.48; H, 1.39; S, 11.80. Found: C, 15.61; H, 1.52; S, 11.09.
Calculated for Nd (C14H15O22S4Nd3): C, 15.34; H, 1.38; S, 11.70.
Found: C, 15.3; H, 1.51; S, 12.36. Calculated for Eu
(C14H15O22S4Eu3): C, 15.02; H, 1.35; S, 11.46. Found: C, 16.87; H,
1.63; S, 11.11.
Single-Crystal Structure Determination. Single-crystal X-ray
data for all compounds were obtained in a Bruker-Siemens Smart
CCD diffractometer equipped with a normal focus and with a 2.4 kW
sealed tube X-ray source (Mo Kα radiation = 0.71073 Å) operating at
50 kV and 30 mA. Data were collected over a hemisphere of the
reciprocal space by a combination of three sets of exposure. Each
exposure of 20 s covered 0.3° in ω. The unit cell dimensions were
determined for least-squares fit of reflections with I > 20σ. The
structures were solved by direct methods. The final cycles of
refinement were carried out by full-matrix least-squares analyses with
anisotropic thermal parameters of all non-hydrogen atoms. The
hydrogen atoms were fixed at their calculated positions using distances
and angle constraints. All calculations were performed using SMART
software for data collection,9 SAINT for data reduction,10 and
SHELXTL to resolve and refine the structure.11
measurements were used to check the purity of the obtained
microcrystalline products by comparison of the experimental results
with the simulated patterns obtained from single crystal X-ray
diffraction data. The residues of the compounds after TG analyses
were analyzed by X-ray powder diffraction and compared with the
ICSD patterns reported.
Computational Details. Ab-initio calculations were performed by
plane-wave density functional (PW-DF) calculations using the VASP
package.12 The energy is calculated by employing the generalized
gradient approximation, in particular, the exchange and correlation
functional of Perdew and Wang (PW91).13 The effect of the core
electrons on the valence electron density was described by the
projector augmented wave (PAW) method.14 The cutoff for the
kinetic energy of the plane waves has been set to 415 eV throughout,
which after extensive test proved to ensure a total energy convergence
better than 10−6 eV. Geometry optimization on selected starting
geometries obtained from single-crystal X-ray diffraction (see
corresponding experimental details) was carried out using a
gradient-conjugate method. The apparent formation energy was
calculated as an energy difference between the corresponding reagents
and MOFs structures.
Catalytic Study. The detailed reaction conditions are shown in the
captions of Tables 2 and 3 and Scheme 2. The cyanosilylation reaction
of aldehydes was carried out at 40 °C. Into a Pyrex-glass screw cap vial
(volume: ca. 10 mL) were successively placed catalyst (5 mg, 1 mol %)
and aldehyde (1 mmol), in the absence of solvent. A Teflon-coated
magnetic stir bar was added, and the reaction was initiated by addition
of trimethylsilyl cyanide, TMSCN (1.5 mmol). The reaction mixture
was vigorously stirred (800 rpm) at 40 °C under N2 atmosphere. The
progress of the reaction was monitored by GC analysis. After the
reaction was completed, the solid was removed by centrifugation of the
reaction mixture. All products (cyanohydrin trimethylsilyl ethers) were
identified by comparison of their GC retention times, GC-MS spectra,
1
and/or H and 13C NMR spectra with those of authentic data. GC
analysis was performed using Konik HRGC 4000B GCMS with a
cross-linked (95%)-dimethyl-(5%)-diphenylpolysiloxane (Teknokro-
ma TRB-5MS) column of 30 m.
Recycling Experiment. The reuse experiment was carried out for
the cyanosilylation of benzaldehyde. The reaction was carried out
under the standard conditions. After the reaction was completed
(more than 90% conversion, 240 min), the catalyst was recovered by
filtration (4.3 mg, 86% recovery), washed with acetone, and air-dried
prior to being used for the reuse experiment. The PXRD pattern of the
retrieved catalyst was identical to that of the fresh (Supporting
Information Figure S5). In addition, the recovered catalyst can be
reused for cyanosilylation of benzaldehyde without an appreciable loss
of its high catalytic performance. When the cyanosilylation of
benzaldehyde was carried out with the recovered catalyst under the
standard conditions, cyanohydrin trimethylsilyl ether was obtained in
91% yield (in 240 min).
RESULTS AND DISCUSSION
■
Effect of Synthesis Conditions. In order to obtain pure
phases in the system Ln3+−3,5-DSB, several synthetic experi-
ments were carried out. Different compounds were obtained by
hydrothermal reaction of a stoichiometric (1:1) mixture of
reactants. The reaction variables were the temperature and
time. First, it was found that at temperatures lower than 170 °C
no product was formed. When performing the synthesis at 170
°C during 24 h, RPF-21-Ln structural type (ST) with formula
[Ln(3,5-DSB)(H2O)5] (Ln = La, Pr and Nd) is obtained as a
pure phase. By increasing the reaction temperature up to 200
°C, [Ln(3,5-DSB)(H2O)3](Ln = La, Pr, Nd, Sm, and Eu) with
RPF-22-Ln ST comes up as a unique phase in 24 h. However,
when performing the synthesis at these last conditions during 3
days, a new more condensed phase is obtained as the only
reaction product: [Ln3(3,5-DSB)2(OH)3(H2O)3] (Ln = Pr,
X-ray Powder Diffraction. Powder X-ray diffraction (PXRD)
patterns were measured with a Bruker D8 diffractometer, with step size
= 0.02° and exposure time = 0.5 s/step. X-ray powder diffraction
3
Nd, Eu), RPF-23-Ln, with Ln/DSB ratio = /2. To understand
5536
dx.doi.org/10.1021/cg301096d | Cryst. Growth Des. 2012, 12, 5535−5545