*2.2. Syntheses of Multicomponent Solids*

*Solution syntheses*. In general, mixtures of 9ETADE and oxalic acid dihydrate in 1:1 or 2:1 molar ratio were suspended in Milli-Q water (for **1** and **3**) or in acetonitrile (for **2** and **4**) at room temperature for two days. After that, the solids were filtered and air-dried. Additional detailed data are included in Supplementary Information (SI).

*Grinding Screening***.** As a general method, mechanochemical syntheses of the new compounds were performed using a Retsch MM400 mixer mill (Retsch, Haan, Germany) in 10 mL

agate grinding jars with two 5 mm agate balls. Mixtures containing 1:1 or 2:1 stoichiometric molar ratio of 9ETADE and oxalic acid dihydrate and the selected solvent were ground for 30 min at 30 Hz. Additional details are included in Supplementary Information (SI).
