Open p-shell anionic mixed-valence compounds have been recently proposed as intriguing model systems for disentangling the complex interplay of charge, lattice, orbital, and spin degrees of freedom in Verwey-type charge ordering processes. Our preliminary electron paramagnetic resonance experiments on Rb4O6 have shown a zero-field spin gap of about 450 GHz, which can be closed with a magnetic field of 14.5 T. The results are consistent with formation of O2- (S = 1/2) dimers with a singlet ground state and indicate the presence of additional inter-dimer isotropic and intra-dimer Dzyaloshinskii-Moriya interactions, thus questioning the true ground state that could either be a valence bond solid or a long-range magnetic order with reduced ordered moments. Here we propose to carry out a muSR investigation down to the lowest experimentally accessible temperatures to answer this question.