Heterogeneously Catalyzed Oxidation Reactions Using ... - CHEC

6.3 Results
out in 1 mm quartz tubes at a temperature of 100 °C with the same substrate concentrations as in
the batch experiments over several hours. The DMF solutions of (E)‐stilbene were kept saturated
with dioxygen by passing a continuous stream of the gas from a Teflon capillary over the DMF. 40
spectra were accumulated from each sample to obtain enough sensitivity. In addition, 60 mg of dry
catalyst was measured in 5 mm quartz tubes (also with accumulation). The formation of products
under these conditions was checked by GC. EPR measurements were done in collaboration with
Reinhard Kissner (ETH Zürich).
6.3 Results
6.3.1 Synthesis of the MOF and characterization
Powders obtained from the reaction of cobalt(II) acetate with H4L were characterised by powder
X‐ray diffraction and were found, as previously reported [43], to have a similar characteristic
diffraction pattern as observed for STA‐12(Ni) (Figure 6‐1) [36]. Optimization of the reaction
conditions indicated that a cobalt acetate to H4L ratio of 2:1 at a starting pH of 8 yields phase pure
samples of STA‐12(Co). Powder diffraction data were analysed by Le Bail fitting, using the routines
within the GSAS suite of programs [44] and with the unit cell of as‐prepared STA‐12(Ni) [36] as the
starting point. Refinement of the unit cell parameters indicated as‐prepared STA‐12(Co) crystallized
in the same rhombohedral space group as STA‐12(Ni), but with a slightly larger cell (space group: R‐3,
hexagonal setting: a = 28.0942(19) Å; c = 6.2846(3) Å). Thermo‐gravimetric analysis (TGA) in air, with
a ramp rate of 1.5 °C min ‐1 up to 900 °C, showed two weight loss events (not shown). The first weight
loss of 18.3 wt.‐% (20‐85 °C) was assigned to the removal of physisorbed water from the pores. This
was immediately followed by an increase in gradient of the TGA plot, marking a second weight loss of
6.8 wt.‐% (85‐108 °C), assigned to the loss of chemisorbed water from the Co 2+ cations. There were
no further weight losses up to 270 °C, above which the structure began to collapse underlining the
stability of the MOF for high‐temperature reactions. Energy dispersive X‐ray spectroscopy (EDX)
indicated a Co:P ratio of 1.0 and in combination with the TGA data, a composition for STA‐12(Co) of
Co2(H2O)2L.5H2O, where L = C6H12N2P2O6, was postulated. This hypothetical composition shows
reasonable agreement with obtained elemental analysis data (expected: C = 14.0 %, N = 5.5 %;
found: C = 14.53 %, N = 4.95 %).
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