A structural evidence for the preferential coordination of the primary amide group versus the unionised carboxyl group:: synthesis, molecular and crystal structure, and properties of [Cu(HADA)2], a new copper(II) bis-chelate (H2ADA = N-(2-carbamoylmethyl)iminodiacetic acid)

Bis(N-carboxymethyl-N-(2-carbamoylmethyl)glycinato)copper(II) has been synthesised by reaction of Cu-2(CO3)(OH)(2) and N(2-carbamoylmethyl)-iminodiacetic acid (H(2)ADA) in water. The new compound [Cu(HADA)(2)] (1) has been characterised by thermal, spectral, magnetic and X-ray diffraction methods. Its crystal structure was solved to a final value of R1 = 0.036. The crystal consists in a 3D hydrogen bonded network builds up by centro-symmetric molecules where the Cu(II) atom exhibits an elongated octahedral coordination. The ligand HADA(-) adopts a fac-NO + 0(apical amido). tridentate chelating conformation [Cu1-N1(amino) = 2.063(2), Cu1-O31(carboxylato) = 1.917(2), Cu1-O11(amido) = 2.380(2) Angstrom] and has a free N-carboxymethyl arm. A structural comparison between 1 and bis(N,N-bis(carboxymethyl)glycinato)copper(II) dihydrate (compound 2) reveals that the amide primary group is preferred to the unionised carboxyl group to form a Cu(II)-N, O-glycinamide-like chelate ring instead of a Cu(II) N, O-glycine-like one. (C) 2002 Elsevier Science B.V. All rights reserved.