Reversal Topotactic Removal of Acetone from (HMTH)₂BiI₅·(CH₃)₂C═O Accompanied by Rearrangement of Weak Bonds, from 1D to 3D Patterns

Hexamethylenetetramine (HMT) was used as a strong base for the preparation of new hybride iodobismuthates, (HMTH)2BiI5·(CH3)2C═O (1) and (HMTH)2BiI5 (2). They crystallize in the orthorhombic system, space group Cmcm, a = 14.4345(3), b = 20.2851(6), c = 10.1637(2) Å for 1 and space group Pnma, a = 12.7739(18), b = 10.2589(18), c = 19.264(4) Å for 2. In both crystal structures, [BiI6] octahedra share cis-vertices to form (BiI5)2– zigzag chains that run along the c-axis in 1 and b-axis in 2 leaving the space filled with organic moieties. 1 loses acetone upon heating transforming into 2; in turn, soaking 2 in acetone yields 1. These transformations do not affect the conformation of the (BiI5)2– chains but impact greatly hydrogen bonds that glue together the inorganic anionic chains and organic cations. Rearrangement of hydrogen bonds leads to the change in dimensionality of weak interaction patterns from 1D in 1 to 3D in 2. Electronic structures and spectral and optical properties of these two compounds are also discussed.