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Chapter 3 37<br />
Table 3.1. Comparison of the integrals of the 1 H NMR signals in the samples 1-4 (before solvent<br />
exchange) in comparison with 1-4_ex (after solvent exchange) to determine the linker to guest<br />
molecular ratios (BTC = 1, 3, 5-benzentricarboxylate, AcO = acetate, PivO= pivalate).<br />
Ru-MOFs H(BTC) : H(AcO) H(BTC) : H(PivO)<br />
1 1 : 2.4 -----<br />
1_ex 1 : 0.8 -----<br />
2 1 : 1.5 1 : 1.5<br />
2_ex 1 : 1.2 1 : 0.8<br />
3 1 : 1.6 -----<br />
3_ex 1 : 0.9 -----<br />
4 1 : 0.7 -----<br />
4_ex 1 : 0.7 -----<br />
3.1.4 Pre-activation by solvent exchange<br />
The presence of high amounts of acetic acid and pivalic acid arising from both, the Ru<br />
precursor and the reaction solvent mixture (which contains excess of acetic acid)<br />
apparently leads to partly pore-filling with the residual solvent (acid), which<br />
consequently may considerably affect or restrict the Ru-MOF properties. As revealed,<br />
these components cannot be removed completely regardless of the applied activation<br />
procedure (i.e. 150 °C for 24 h under dynamic vacuum (ca. 10 -3 )). Our attempts to slightly<br />
modify the reaction conditions, namely by reducing the quantity of acetic acid and/or<br />
using acetic acid free conditions yielded either amorphous products and/or prevented the<br />
substitution of RCCOOH in Ru-SBUs, affording just non-reacted starting materials (Figure<br />
7.12). Noteworthy, the reactants concentration in synthesis of the Ru-MOF 1 is quite<br />
crucial and attempting to vary the amounts of solvent with the same molar ratio of Ruprecursor<br />
and H3BTC was not so successful to get crystalline materials. Therefore, we<br />
conducted additional experimental studies directed to improve the activation procedure<br />
(i.e., minimize the amount of the strongly retained guest molecules) and, thus, improve<br />
the sample quality and access to the pores and open metal sites. For this reason we<br />
introduced an additional step to the activation procedure earlier mentioned. [138] Namely,
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