The preparation of three new single-molecule magnets (SMM), [Mn 12O12(O2CCX3)16(H 2O)4], where X = F, Cl or Br, was attempted. Reaction of [Mn12O12(O2C′Bu)16(H 2O)4] (1) with the carboxylic acid CF3COOH yielded small black needle-like crystals of complex [Mn12O 12(O2CCF3)16(H2O) 4] · 2.5H2O (2). Frequency-dependent out-of-phase ac signals in the range 4-7 K were observed, which indicates that complex 2 functions as an SMM. On the contrary, the use of the bulkier trihaloacetic acids CCl3COOH and CBr3COOH is shown to disrupt the formation of the [Mn12O12(O2CR)16(H 2O)4] single-molecule magnets, giving rise to the formation of low nuclearity clusters. On the basis of these results and by comparison with the stability of previously described Mn12 complexes, an interplay of steric and inductive effects is proposed as the critical factor in determining the thermal stability of these complexes. © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2005.
|Journal||New Journal of Chemistry|
|Publication status||Published - 1 Jan 2005|