Studies of the quasi-two-dimensional organic conductors λ-(D) 2 MCl 4 [D = donor molecules, M = Ga, Fe] have shown that λ-(BETS) 2 GaCl 4 [BETS = bis(ethylenedithio)tetraselenafulvalene] undergoes an unconventional superconducting transition and λ-(BETS) 2 FeCl 4 undergoes a field-induced superconducting transition. In λ-type salts, the interactions between donor molecules and FeCl − 4 (π -d interactions) are important.To investigate π -d interaction, a pair of magnetic M = Fe and nonmagnetic M = Ga salts which have the same ground state in the donor layer is desired. However, no such pair has been found, and few experimental studies have considered π -d interaction paths. λ-(BEST) 2 MCl 4 [BEST = bis(ethylenediseleno)tetrathiafulvalene] are obtained for both anions, and M = Ga salt shows an antiferromagnetic transition, but the ground state has not been analyzed in M = Fe salt. We perform x-ray diffraction, magnetic susceptibility measurement, and Mössbauer spectroscopy in λ-(BEST) 2 FeCl 4 . We find that a magnetic transition is observed at around 26 K. The λ-(BEST) 2 MCl 4 system is a system in which both FeCl − 4 and GaCl − 4 salts show antiferromagnetic transitions. In addition, the ethylene motions observed at room temperature are ordered around 108 K, resulting in the establishment of the π -d interaction path between chalcogens and the anion, and low-field magnetization suggests that the π -d interaction in λ-(BEST) 2 FeCl 4 is smaller than that in λ-(BETS) 2 FeCl 4 . Our results show that the inner chalcogen of donor molecules is important as the path of the interaction.