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+·C10H14N2O82−·2H2O, (I), tripotassium 2,2′-({2-[bis(carboxylatomethyl)amino]ethyl}ammonio)diacetate dihydrate, 3K+·C10H13N2O83−·2H2O, (II), and tetra­potassium 2,2′,2′′,2′′′-(ethane-1,2-diyldinitrilo)­tetra­ace­tate 3.92-hydrate, 4K+·C10H12N2O84−·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 HY3− 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 HY3− anions is very similar to that of the Y4− anions in (III), although a slightly different spatial arrangement of the –CH2COO− groups in relation to (III) is observed, whereas the H2Y2− 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.