  Molecular nanomagnets, besides promising to open new frontiers in technology,
have attracted huge interest in the scientific community because they can
exhibit the phenomenon known as quantum tunnelling of the magnetization, i.e.
coherent fluctuations of the direction of the total spin vector. In this paper
we study a different quantum phenomenon involving fluctuations of the magnitude
of the total spin vector. These fluctuations are related to the mixing between
states with different spin quantum number, and imply new macroscopic effects,
which we theoretically investigated in the Mn-[3x3] grid.
