Hybrid organic-inorganic bismuth(III)-based material [4-NH2C5H4NH]7[BiCl6]2Cl. Crystal structure, dielectric properties and molecular motions of 4-aminopyridinium cations

Abstract

4-aminopyridinium analogue, [4-NH2PyH]7[BiCl6]2Cl, has been synthesized and characterized by single-crystal X-ray diffraction at 100 K, calorimetric, dilatometric and dielectric studies. The crystal structure is centrosymmetric with the monoclinic space group, P21/n. It consists of two discrete [BiCl6]3- octahedra, one loose Cl− anion and seven, partially disordered, 4-aminopyridinium cations. The compound reveals a reversible first-order phase transition (I→II) at 305/304 K of the ‘order-disorder’ type. The dielectric studies disclosed a relaxation process in the kilohertz frequency region, assigned to the dynamics of organic cations, described well by the Cole-Cole relation. The 1H NMR spin–lattice relaxation time measurements indicate a complex cations motion over the Phase II. The possible mechanism of the I → II phase transition in [4-NH2PyH]7[BiCl6]2Cl is discussed.