METAL-COMPLEXES OF CIMETIDINE - SYNTHESIS, X-RAY STRUCTURE DETERMINATION AND SEMIEMPIRICAL CALCULATIONS ON THE [CIMETIDINATECOPPER(II)]+ CATION

The addition of a methanolic solution of cimetidine (1) to a methanolic solution of M2+ cations (M = Co, Ni, Cu, Zn) affords the cationic complexes [M(1)2]2+. In the case of M = Cu the addition of KOH in the reaction medium at 60-degrees-C gives the [Cu(2')]+ cation, where 2' is an anionic ligand resulting from deprotonation of a cimetidine molecule modified by methanolic solvolysis of the nitrilic function. The X-ray structure characterization of [Cu(2')]X.0.5H2O has been performed for X = ClO4- (5) and I- (6). Compound 5 is monoclinic, space group C2/c with a = 20.732(8), b = 7.471(3), c = 23.734(5) angstrom, beta = 100.76(3)-degrees, Z = 8, R = 0.034, R(w) = 0.045 for 1767 reflections with I > 3-sigma(I). Compound 6 is monoclinic, space group C2/c with a = 20.736(3), b = 7.426(3), c = 22.786(2) angstrom, beta = 99.65(1)-degrees, Z = 8, R = 0.029, R(w) = 0.045 for 2498 reflections with I > 3-sigma(I). In both compounds the 2' anion acts as a tetradentate ligand coiled around the almost square planar metal center. Quantomechanical semiempirical calculations (CNDO/2) have been carried out on simple models of 2', 5 and 6.