Metal chelates of N-(2-pyridylmethyl)iminodiacetate(2-) ion (pmda). Part I. Two mixed-ligand copper(II) complexes of pmda

N -(2-Pyridylmethyl)iminodiacetic acid hemi-hydrate (H2pmda /0.5H2O) was prepared and characterized by X-ray crystallography (final R1 /0.042). The zwitterion H2pmda 9 is intra -stabilized by a trifurcated hydrogen bond. Intermolecular carboxyliccarboxylate hydrogen bonds and the parallel inter-ligand p,p-stacking (3.57(2) Å) between pyridyl rings from pairs of adjacent zwitterions generate 2D frameworks (bi-layers with the carboxyl groups towards the external surfaces and py /pmda rings towards the inside). In the crystal, the bi-layered structures are connected by equivalent hydrogen bonds, which link each water molecule to two symmetry related O-carboxylate atoms from the adjacent external faces of two 2D frameworks. The compounds [Cu(pmda)(pca)] /3H2O (1) and [Cu(pmda)(Hpb)] /5H2O (2) were obtained by stoichiometric reaction of Cu2(CO3)(OH)2, H2pmda /0.5H2O and a-picolylamine (pca) or 2-(2?-pyridyl)benzimidazole (Hpb), respectively, and characterized by single crystal X-ray diffractometry. Compound 2 was also studied by TG analysis (with FTIR study of the evolved gasses in the pyrolysis), magnetic susceptibility at 80 /300 K range, and FTIR, electronic, ESR spectra. In 1 and 2 the copper(II) atom exhibits a distorted octahedral coordination (type 4 /1 /1) and pmda acts as tripodal tetra-dentate ligand. However, pmda displays different coordination roles. The pmda supplies two N ,O -meridional and two trans -apical N (py),O -donors in 1, whereas links the metal by three N ,N (py),O -meridional and one O -apical atoms in 2. No p,p-stacking of pyridyl /(pmda) rings is observed in these complexes. The pyridyl /(pca) ring of 1 is not involved in ring /ring stacking interactions, but compound 2 recognizes itself by a roughly antiparallel p,p-stacking of adjacent Hpb ligands (5.38, 3.41(2) Å) forming pairs of complex units. # 2002 Elsevier Science Ltd. All rights reserved.