Calcium perchlorate tetrahydrate

Calcium perchlorate tetrahydrate (99 %, Sigma Aldrich) was dried (8 h) under reduced pressure to obtain a white powder of anhydrous Ca(ClO₄)₂. Tetrabutylammonium perchlorate (≥99 %, Sigma Aldrich), silver nitrate (99 %, CHEMPUR), and Dimethyl sulfoxide (99.7 %, extra dry, over molecular sieve) were used as received. DMSO, CaClO₄ and TBAClO₄ were stored inside an MBraun glovebox under argon atmosphere. For purging and electrolyte saturation argon (99.999 %, Air liquide), nitrogen (99.999 %, Air liquide), oxygen (99.9995 %, Air liquide) and argon oxygen mixture (80 %/20 %, Air liquide) were used.

For metal cation complexation, lithium perchlorate (99.9%, Sigma Aldrich, Milwaukee, WI, USA), sodium perchlorate monohydrate (>99%, Fluka, Buchs, Switzerland), potassium perchlorate (>99%, Sigma Aldrich, Milwaukee, WI, USA), magnesium perchlorate (≤100%, Sigma Aldrich, Steinhaim, Germany), calcium perchlorate tetrahydrate (99%, Sigma Aldrich, Milwaukee, WI, USA), strontium perchlorate trihydrate (≤100%, Sigma Aldrich, Steinhaim, Germany), barium perchlorate (97%, Sigma Aldrich, Steinhaim, Germany. For acid-base properties studies p-toluenesulfonic acid monohydrate (pure, POCH, Gliwice, Poland), tetra-n-butylammonium hydroxide 30-hydrate (98%, Sigma-Aldrich, Steinhaim, Germany) were used. Complexation studies were performed by spectrophotometric titration of the crown solution in acetonitrile with the respective metal perchlorate (for metal cations). The stock solutions of azobenzocrowns (~10⁻⁴ M) and metal perchlorates were prepared by weighing their respective quantities and dissolving in acetonitrile in volumetric flasks. For titrations, azobenzocrown solutions of 2.3 mL starting volume in the cuvette were used. The stability constant values from UV-Vis experiments were calculated with the use of the OPIUM [39 ] program.

Calcium perchlorate tetrahydrate (99 %, Sigma Aldrich) was dried under reduced pressure at 356 K in a Büchi‐oven for 48 h. Extra‐dry DMSO (99.7 %, over molecular sieve, Acros Organics) and potassium superoxide (Acros Organics) were used as received. As supporting salt for the reference electrolyte AgNO₃ (>99.5 %, ChemPure) was used. All electrolyte preparations were made in an Ar‐filled (Air Liquid, 99.999 %) glovebox by GS.