Spiro-biphenalenyl (SBP) boron radicals constitute an important family of molecules for the preparation of functional organic materials. The building blocks of several SBP-based crystals are π-dimers of these radicals, in which two phenalenyl (PLY) rings face each other and the other two PLYs point away from the superimposed PLYs. The dimers of ethyl-substituted-SBP and butyl-substituted-SBP undergo a spin transition that results in changes in the magnetic, optical and conducting properties of the material. The spin transition of ethyl-SBP occurs at around 140 K, while the spin transition of butyl-SBP occurs with a hysteretic loop 25 K wide centered at 335 K. In this talk, the results of a computational study aimed at identifying the driving forces of these spin transitions will be presented. The origin of the hysteresis in the phase transition of butyl-SBP will be also disclosed. In particular, it will be shown that electrostatic interactions between radicals play a key role in enabling the spin transitions and that the bistability of butyl-SBP originates in the coupling between the spin transition of its π-dimers and the conformational switch of its butyl chains.