MAGNETIC-PROPERTIES OF (M-MPYNN-) - ENHANCEMENT OF MAGNETIC-RELAXATION IN THE MN-12 CLUSTER CAUSED BY THE ORGANIC RADICAL()[MN12O12(O2CPH)(16)(H2O)(4)]()

We report magnetic properties of the organic/inorganic hybrid salt, (m -MPYNN+)[Mn12O12(O2CPh)(16)(H2O)(4)](-) (2) where m-MPYNN+ (=m-N-methy lpyridinium nitronylnitroxide) is a stable organic radical cation with S=1/2 and [Mn12O12(O2CPh)(16)(H2O)(4)](-) a 12-nuclei Mn cluster anio n with S=19/2 together with the simple salt, [PPh4+(=tetraphenylphosph onium)] [Mn12O12(O2CPh)(16)(H2O)(4)](-). 2H(2)O ( 1). The EPR spectra of 2 are composed of the separate absorption signals of the Mn-12, clu ster and m-MPYNN+ indicating a negligible exchange interaction between them. Below 65 K, however an overlap between the absorption tails is clearly observed. suggesting all energy 1 transfer between the resonan ces. While the temperature dependences of the paramagnetic susceptibil ities of 1 and 2 are similar above similar to 4 K, the two salts show quite different spin dynamics below it. The magnetization curve and sc susceptibility measurements reveal that the organic radical enhances the relaxation of the magnetization of the Mn-12 cluster and prevents the magnetization freezing.