Metal chelates of N-(2-pyridylmethyl)iminodiacetate(2-) ion (pmda). Part I. Two mixed-ligand copper(II) complexes of pmda with N,N-chelating bases. Synthesis, crystal structure and properties of H(2)pmda center dot 0.5H(2)O, [Cu(pmda)(pca)]center dot

摘要

N-(2-Pyridylmethyl)iminodiacetic acid hemi-hydrate (H(2)pmda.0.5H(2)O) was prepared and characterized by X-ray crystallography (final R1=0.042). The zwitterion H(2)pmda(+/-) is intra-stabilized by a trifurcated hydrogen bond. Intermolecular carboxylic-carboxylate hydrogen bonds and the parallel inter-ligand pi,pi-stacking (3.57(2) Angstrom) 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)].3H(2)O (1) and [Cu(pmda)(Hpb)].5H(2)O (2) were obtained by stoichiometric reaction of Cu-2(CO3)(OH)(2), H(2)pmda.0.5H2O and alpha-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 pi,pi-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 anti-parallel pi,pi-stacking of adjacent Hpb ligands (5.3degrees, 3.41(2) Angstrom) forming pairs of complex units. (C) 2002 Elsevier Science Ltd. All rights reserved. [References: 76]