Synthesis, solid-state characterization and antimicrobial activities of three different polymorphs of a copper(II) complex with 4-isopropyltropolone (hinokitiol)

Abstract

There exist at least three different polymorphs in the copper(II) complex [Cu(hino)2] with a hinokitiol ligand (Hhino; 4-isopropyltropolone1The systematic names for tropolone and 4-isopropyltropolone are 2-hydroxycyclohepta-2,4,6-trienone and 2-hydroxy-4-isopropylcyclohepta-2,4,6-trienone, respectively.1). In addition to deep-green plate crystals 1a and deep-green rod crystals 1b, whose crystal structures have been recently reported, novel green needle crystals 1c of [Cu(hino)2] were found, the crystal structure of which was here determined by single-crystal X-ray analysis. Since only one crystal structure has been reported for the copper(II) complex [Cu(trop)2] with a tropolone ligand (Htrop), the polymorphism found in the crystals of [Cu(hino)2] would be due to the presence of the isopropyl group on the tropolone ring. The synthetic conditions giving the three polymorphs in good yields were found and the crystals were characterized with elemental analysis, FT-IR, TG/DTA and X-ray powder diffraction (XPD) measurements, as well as solution molecular weight measurements for 1a. The solid-state magnetic behaviors or the temperature-dependent magnetic susceptibilities were measured with Superconductivity Quantum Interference Devices (SQUID): 1a showed a weak ferromagnetic interaction, 1b showed a paramagnetic nature with S=1/2, while 1c showed a weak antiferromagnetic interaction. The antimicrobial activities for selected bacteria, yeasts and molds were also measured in the water-suspension system: 1a and 1b showed no activity, while 1c showed modest activities, and these activities were compared with those of the neutral Hino and the anionic hino− ligands.