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70 Chapter 4<br />
Table 4.1. The molar fractions (%) of the DLs used for the synthesis and observed in the final Ru-<br />
DEMOFs in respect to the total amount of linkers (H 3 BTC + 5-X-ipH 2 = 100%). The values were<br />
obtained from the integrals of proton peaks in 1 H-NMR spectra of the acid-digest sample. For the<br />
samples 1a-1d DL is 5-OH-ip; for 2a-2c – ip; for 4a-4c – 5-Br-ip, respectively.<br />
Sample<br />
Feeding<br />
(used for synthesis)<br />
Obtained<br />
1a 10% 8%<br />
1b 20% 20%<br />
1c 30% 32%<br />
1d 50% 37%<br />
2a 10% 15%<br />
2b 20% 28%<br />
2c 30% 47%<br />
4a 10% 17%<br />
4b 20% 25%<br />
4c 30% 42%<br />
A similar scenario was observed also for the samples with ip DL (series 2a-c). Resonances<br />
corresponding to the protons of ip are seen at 8.4 ppm, 8.1 ppm and 7.6 ppm (Figure 4.10).<br />
The framework incorporation amount of ip in 2a-c increases upon increasing the<br />
concentration of the DL in the reactant solutions. However, the incorporated amount of ip<br />
was found to be higher than expected from the H3BTC:H2ip feeding ratio, which is in<br />
contrast with that in the case of Ru-DEMOF series 1 where the incorporation of 5-OH-ip<br />
stay the same (or a little less) than the feeding concentration in the starting reactants. This<br />
result might be attributed to the slightly different coordination equilibria that correlate<br />
with the Brønsted acid dissociation constants of the used linkers: pKa (H3BTC) = 3.12,<br />
3.89, 4.70 and pKa (H2ip) = 3.46, 4.46. [224] However, the pKa differences are small and a<br />
conclusive explanation based on pKa is not straightforward. Dincă et al. argued that<br />
deprotonated BTC could serve as a counter-ion to provide the charge balance of [Ru2] 5+<br />
units in Ru-analogue of Cu-HKUST-1. [83] From our earlier investigation we concluded that<br />
H3BTC is present in the pores of [Ru3(BTC)2Yy]n in the form of fully protonated species,<br />
rather than as deprotonated counter-ions. [208] Both studies indicate that the linker used<br />
for the synthesis could still be present in the obtained materials. Hence, it is conceivable<br />
that the defect generating H2ip linker can also reside either as a counter-ion or as a guest
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