International Science Community Association Research Journal of Recent Sciences 14 4 2025 10 2 Anion effect on selectivity in 18-crown-6 ether interaction with alkali metal cations 1 4 EN Patil Kalpesh H. 1 Department of Chemistry, Ranilaxmibai Mahavidyalay, Parola Dist- Jalgaon, India Borse Gokul P. 2 Department of Chemistry, Ranilaxmibai Mahavidyalay, Parola Dist- Jalgaon, India Sonawane Narendra 3 Department of Chemistry, BSSMP’S, Arts, Commerce and Science College, Songir, India Garud Rahul 4 Department of Chemistry, Ranilaxmibai Mahavidyalay, Parola Dist- Jalgaon, India > Research Paper 2025 8 2 2025 10 2 The Selectivity complexation of alkali metal cations by 18-crown-6 ether was investigated with particular focus on the effect of various cations at 298.15K using viscosity and density study elucidates how different anions influences the interaction ability and selectivity of alkali metal ions. The presence and nature of anions were found to modulate the host-guest interaction energies, impacting the structural confirmation of common ether complex as well as salvation and electrostatic effects. The excess parameters such as excess molar volume (VE), viscosity deviation (∆η), apparent molar volume (ϕv) were calculated from the experimental data of viscosity and density at 298.15K. These excess calculated data reveals that anions identify significantly changes the thermodynamic parameters and binding selectivity these finding contributes to a deeper understanding of ion recognition mechanism in 18-crown-6 ether system and suggest strategic manipulation of anions for enhanced the selectivity in applications such as ion extraction sensing and catalyst at 298.15K. Copyright@ International Science Community Association