Comparative Magnetic Studies in the Solid State and Solution of Two Isostructural 1D Coordination Polymers Containing Co-II/Ni-II-Curcuminoid Moieties

Abstract

Two novel 1D coordination chains containing the curcuminoid (CCMoid) ligand 9Accm have been characterized: [Co-II(9Accm) 2(4,4'-bpy)](n) (1) and [Ni-II(9Accm) 2(4,4'-bpy)](n) (2). The two compounds were synthesized by solvothermal and microwave (MW) assisted techniques, respectively, and crystals of both systems were directly obtained from the mother solutions. Crystal structures of 1 and 2 prove that both systems are isostructural, with the ligands in a trans configuration. The two chains have been magnetically characterized in solution by paramagnetic H-1 NMR, where 1 displayed typical features from Co-II systems, with spread out signals; meanwhile, 2 showed diamagnetic behaviour. The dissociation of the latest in solution and the stability of the "[Ni(9Accm)(2)]" unit were proved by further experiments in C5D5N. Additional UV-Vis absorption and fluorescence studies in solution were performed using exclusively 1. In the solid state chi(MT) vs. T and M/N mu(B) vs. H/T data were collected and fitted for 1 and 2; both systems display Ising plane anisotropy, with significant D values. System 1 presented slow relaxation of the magnetization, displaying frequency dependence in the in-phase/out-phase ac magnetic susceptibility data, when an external dc field of 0.2 T was applied. Finally, 1 was deposited on a HOPG (highly oriented pyrolytic graphite) substrate by spin-coating and analysed by AFM.