Comprehensive study of the structure and bonding of disodium, dipotassium and diam-monium di-o-phthalatocuprates(II) dihydrates has been undertaken. The crystal structure of am-monium o-phthalatocuprate has been determined. The identity of structures of phthalatocuprate chains in potassium and ammonium salts has been revealed. Vibrational spectra of all three compounds have been recorded, and the assignment of vibrational bands has been made. Force field calculations have shown a minor effect of outer-sphere cations (Na⁺, K⁺, NH4⁺) on both intraligand (C-O) and metal–ligand bond strengths. Synthesized compounds have been tested as electrochemical sensors on D-glucose, dopamine and paracetamol. Their sensitivity to analytes varied in the order of Na⁺ > K⁺ > NH4⁺. This effect has been explained by the more pronounced steric hindrance of copper ions in potassium and ammonium salts.