New coordination modes in potassium edta salts: K2[H2edta]·2H2O,K3[Hedta]·2H2O and K4[edta]·3.92H2O

Three potassium edta (edta is ethylenediaminetetraacetic acid, H₄Y) salts which have different degrees of ionization of the edta anion, namely dipotassium 2‐({2‐bis(carboxylatomethyl)azaniumyl]ethyl}(carboxylatomethyl)azaniumyl)acetate dihydrate, 2K⁺·C₁₀H₁₄N₂O₈^2?·2H₂O, (I), tripotassium 2,2′‐({2‐bis(carboxylatomethyl)amino]ethyl}ammonio)diacetate dihydrate, 3K⁺·C₁₀H₁₃N₂O₈^3?·2H₂O, (II), and tetrapotassium 2,2′,2′′,2′′′‐(ethane‐1,2‐diyldinitrilo)tetraacetate 3.92‐hydrate, 4K⁺·C₁₀H₁₂N₂O₈^4?·3.92H₂O, (III), were obtained in crystalline form from water solutions after mixing edta with potassium hydroxide in different molar ratios. In (II), a new mode of coordination of the edta anion to the metal is observed. The HY^3? anion contains one deprotonated N atom coordinated to K⁺ and the second N atom is involved in intramolecular bifurcated N—H...O and N—H...N hydrogen bonds. The overall conformation of the HY^3? anions is very similar to that of the Y^4? anions in (III), although a slightly different spatial arrangement of the –CH₂COO^? groups in relation to (III) is observed, whereas the H₂Y^2? anions in (I) adopt a distinctly different geometry. The preferred synclinal conformation of the –NCH₂CH₂N– moiety was found for all edta anions. In all three crystals, the anions and water molecules are arranged in three‐dimensional networks linked via O—H...O and C—H...O and N—H...O in (I) and (II)] hydrogen bonds. K...O interactions also contribute to the three‐dimensional polymeric architecture of the salts.