In this study, bis(tetra-iodo-phthalocyanine)s containing different lanthanide (III) metals, namely, samarium (III) (SmPc 2 ), europium (III) (EuPc 2 ), gadolinium (III) (GdPc 2 ), dysprosium (III) (DyPc 2 ), and terbium (III) (TbPc 2 ) were synthesized for the first time, and their structural characterizations were determined by elemental analyses and different spectroscopic methods such as Ultraviolet-Visible (UV-Vis), Fourier transform infrared (FT-IR), and matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF). Moreover, voltammetric, in situ spectroelectrochemical, chemical redox, and quartz crystal microbalance (QCM) gas adsorption properties of the synthesized compounds were evaluated. The distinct spectral and color changes during the redox reactions for the complexes indicated a potential use in electrochromic materials. In addition, ammonia gas adsorption properties of the complexes were found to be relevant to central metal atom size, and the value for the ammonia gas adsorption at 15 μg/L was the highest for SmPc 2 (20 ng), and the lowest was DyPc 2 (1.4 ng).