Short Strong Hydrogen Bonds can Hinder Complex Formation: A Stability and Structure Study of Copper(II) Alkyl-N-iminodiacetic Acid Complexes in Aqueous Systems and Solid State

Abstract In the present study solution and coordination chemistry of copper(II)–alkyl- N -iminodiacetate systems are studied in aqueous by potentiometry, using ion selective copper pH electrodes, EXAFS (extended X-ray absorption fine structure) dye probe molecular spectrophotometry. Alkyl- -iminodiacetates with varying alkyl chain length, methyl (CH 3 –), n -hexyl (C 6 H 13 -dodecyl 12 25 –) -octadecyl 18 37 were used to tune amphiphilic properties ligands. The polar head groups have both oxygen (hard Lewis base) nitrogen donor (border-line atoms. This means that metal ions different bonding characteristics may bind these ligands differently. Furthermore, chelating group be regulated as acid–base imine carboxylic acid different. Copper(II) forms two stable complexes alkyl- short chains, monomers solution, log 10 β 1 = 11.10(2), 2 19.5(2) for methyl- -iminodiacetate, 12.22(4), 21.9(2) -hexyl- -iminodiacetate. -Octadecyl- -iminodiacetic acid, large aggregates acidic has strong hydrogen bonds between carboxylate surface aggregates, which hinder complex formation at values below 4, obstructs it region 4–7, while behaves short-chained > 7. structure around solid state formed copper(II):alkyl- ratios been determined EXAFS. copper(II) shows four equatorial plane, Cu–O/N bond distances, ca. 0.2 Å apart, axial positions a non-centrosymmetric tetragonally elongated octahedron.