The binary systems with the immiscibility in the liquid state are considered as a tool for synthesis and crystallization of borides. New preparation method using two solvents (immiscibility gap method) is compared with the conventional solution-melt method using one solvent (flux method). The appropriate systems are analyzed with respect to the temperature and concentration limits of the immiscibility gap, density ratio of solvents and reagents, interaction of reagents, formation and crystallization of compounds, and allocation of products in the metallic matrix.