A Structural Study of the Iminodiacetate Moiety Conformation in N-(1-adamantyl)-iminodiacetate(2-) Copper(II) Complexes

N,N-bis(carboxymethyl)-1-adamantylamine acid (H2BCAA) or N-(1-adamantyl)-iminodiacetic acid forms zwitterions that are intra-stabilized by a bifurcated N+-H···O(carboxyl)2 interaction. In the crystal, both half-protonated carboxyl groups of H2BCAA± are involved in linear O-H···O inter-molecular bridges of 2.46Å. In the studied BCAA-CuII derivatives, the iminodiacetate-moiety of the BCAA chelating ligand exhibits a mer-NO2 conformation in [Cu(BCAA)(H2O)2] (1) and [Cu(BCAA)(Him)]2 (2), but a fac-O2+N(apical) conformation in [Cu(BCAA)(bpy)(H2O)]·3.5H2O (3) [Him = imidazole, bpy =2,2-bipyridine]. In clear contrast, dipyridylamine (dpya), as auxiliary ligand, seems to be unable to promote the fac-O2+N(apical) conformation in BCAA, as reveal the structures of two new salts with the trinuclear cation [(dpya)2Cu-2-Cu(BCAA)2-Cu(dpya)2]2+ and the anions [Cu(BCAA)2]2- (4) or NO3- (5), respectively.