Abstract
A purely-organic magnetic charge-transfer salt, δ¤-(BEDT-TTF) 2 (PO-CONHCH(cyclopropyl)SO 3)¢1.7H 2 O, has been prepared. Conducting layers consist of BEDT-TTF tetramers, in which two holes are localized, which obeys a Singlet-Triplet model. The similarity between the semiconductor-to-semiconductor transition temperature and the temperature where triplet excitation becomes negligible, suggesting that the conductions of spin singlet and triplet states become dominant in the lower and higher temperatures, respectively.