Molecular iodine adsorption within Hofmann-type structures M(L)[M'(CN)₄] (M=Ni, Co;M' = Ni, Pd, Pt): impact of their composition

A series of thermally stable Hofmann-type clathrate structures with the general formula M(pz)[M'(CN)₄], where M and M' are bivalent metal ions M(II) = Ni(II), Co(II), M(II)' = Ni(II), Pd(II), Pt(II), and pz is the pyrazine bidentate ligand, was synthesized and investigated for the efficient entrapment of iodine (I₂) in solution and in the gas phase. Iodine-containing clathrates thus prepared were analysed to determine the saturation capacity, thermal stability, guest-induced structural changes of the clathrate's lattice and the nature of the confined iodine according to the chemical composition of the host structure. An efficient confinement of about 1 I₂ per unit cell is observed for the series of clathrates with the Ni(II) and Pd(II) ions in the square planar position whatever the bivalent metal ion in the octahedral position. Specific responses in the lattice adjustment are detected for CoII in the octahedral and PdII in the square planar positions. (authors)