A study on the nickel(II)-famotidine complexes

Potentiometric studies have shown that Ni(II) forms three pH-dependent complexes with famotidine (L), namely: [NiHL](3+), [NiL](2+) and [NiH_L-2]. Two of them have been isolated from solution with a Ni/famotidine ratio of 1:1. At pH 6.0, a paramagnetic complex [NiL](2+) with octahedral geometry is formed in which, most likely thiazole N(9) and guanidine N(3) nitrogens are involved in the metal binding. Additionally, two water molecules and two perchlorate anions, CIO4, fulfil the coordination sphere. The second complex, [NiH_L-2], that precipitates at pH 8 is diamagnetic and takes square-planar geometry in which four nitrogen donors: N(3), N(9), N(16) and N(20) coordinate to Ni(II). Potentiometric studies, mass spectrometry, FF-IR and Raman spectroscopy are employed to determine and discuss the structure of both complexes. Additionally, H-1, C-13 and N-15 NMR spectroscopy is used to confirm the binding site in a square-planar complex. The assignment of vibrational bands are made using ab initio HF/CEP-31G method. (C) 2002 Elsevier Science Inc. All rights reserved.