Unusual crystal structures and magnetic properties of nitronylnitroxide radical ions

We report unusual crystal structures and magnetic properties of nitronylnitroxide radical ions, (i) A nitronylnitroxide anion, p-(nitronylnitroxide)benzoate (p-NNBA), is found to crystallize with Mn2+ and water molecules in the form of Mn(p−, NNBA)2(H2O2. In this crystal, the manganese(II) ion is in an octahedral environment, surrounded by two NO groups, two CO2 groups and two H2O. The magnetic properties are well interpreted in terms of the trimer model of [p-NNBA (S=l/2)]-[Mn2+ (S=5/2)]-[p-NNBA (S=1/2)]. (ii) A nitronylnitroxide cation, m-N-methylpyridinium nitronylnitroxide (m-MPYNN), crystallizes with I−, BF4−, or ClO4− into a trigonal space group, where the spin system is regarded as a spin-1 Kagome antiferromagnet with spin frustration. Low-temperature magnetic measurements reveal a spin-gap state below 0.24 K.