Novel organic polyradicals, BIP-BNO and BIP-TENO, are synthesized and cryst
allized to form ladder systems, where BIP-BNO and BIP-TENO denote 3,5'-bis(
N-tert-butylaminoxyl)-3',5'-dibromobiphenyl and 3,3',5,5'-tetrakis(N-tert-b
utylaminoxyl)biphenyl respectively. The BIP-BNO crystals form a two-leg lad
der of S double bond1/2 with antiferromagnetic legs and rungs. The BIP-TENO
crystals can be regarded as a two-leg ladder of S double bond1 species. Th
e magnetic measurements revealed that both compound have singlet ground sta
tes.