Metal complexes of cimetidine. Synthesis, X-ray structure determination and semiempirical calculations on the [cimetidinatecopper(II)] + cation

Abstract

The addition of a methanolic solution of cimetidine ( 1) to a methanolic solution of M 2+ cations (M = Co, NJ, 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 °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·0.5H 2O has been performed for X = ClO 4 − ( 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) Å, β 100.76(3)°, Z=8, R=0.034, R w=0.045 for 1767 reflections with I>3σ( I). Compound 6 is monoclinic, space group C2/ c with a=20.736(3), b=7.426(3), c=22.786(2) Å, β=99.65(1)°, Z=8, R=0.029, R w=0.045 for 2498 reflections with I>3σ( 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.