We present the synthesis of a new adamantane derivative containing Os(II) centers and investigate its function as a dissolved redox mediator in thin-layer ion-selective membranes for voltammetric ion sensing. The pronounced lipophilicity of the designed compound, herein termed as adamantane Os(II), ensures exceptional compatibility with the thin-layer membrane and its constituents (cation exchanger, ionophore, plasticizer, polymer), presenting complete dissolution at elevated concentrations (160 mmol/kg), absence of leaching into the sample during membrane electrode polarization, and reversible electrochemical behavior. The electrochemistry of the adamantane Os(II) is thoroughly characterized in organic medium, with variations in the counter ions of the background electrolyte and 19 distinct membrane compositions, which include control compositions, various plasticizers (DOS, o-NPOE) and polymeric matrix (PVC, PU) as well as sodium ion ionophore. The membrane composition is refined considering three interrogation strategies (namely thin-layer, diffusion, and accumulation regimes) to quantify sodium ion concentrations across several ranges (from micromolar to millimolar) in environmental samples. The accuracy of the methodology was experimentally validated using ion chromatography as the gold standard, revealing a discrepancy of < 3 % between them. Furthermore, a comprehensive theory for ionophore-based thin-layer membranes is established and supplemented by relevant numerical simulations for the three operational modes; successfully, the empirical data align closely with the proposed theoretical hypothesis. The advancement of novel lipophilic and reversible metallic-based redox mediators may create new prospects for the detection of ions and biomolecules.

Crystallisation of anthraquinone substituted p-tert-butylthiacalix[4]arene in the partial cone conformation from a range of solvents led to the isolation of two solvates, containing a mixture of chloroform and acetonitrile (PC1a) or toluene (PC1d) molecules, the structures of which were uncovered by SCXRD studies. Upon heating, the former solvate undergoes a single-crystal-to-single-crystal transformation, leading to removal of the acetonitrile molecules from the host and repositioning of the chloroform molecules (PC1b). This is connected with rearrangements of the non-covalent interactions, nicely reflected by a change in the hydrogen bond acceptor of the weak C-H⋯O hydrogen bonds. The transformation process is reversible, as confirmed by exposure of the crystal to acetonitrile vapour. Furthermore, the guest free phase of PC1 was obtained by melt crystallisation (PC1c).