New representatives of the A2M3(SO4)4 (A = Rb and Cs, M = Co, Ni) family were found, inspired by the discovery and characterization of itelmenite, a mineral of composition Na2CuMg2(SO4)4. Four new compounds were obtained by high-temperature solid-state reactions in air. All new compounds were structurally characterized by single-crystal and powder X-ray diffraction. Rb2Ni3(SO4)4 and Rb2Co3(SO4)4 crystallize in the monoclinic space group P21/c, Cs2Ni3(SO4)4 in P21/n whereas Rb2Co3(SO4)4 crystallizes in the orthorhombic space group P212121. In order to determine the temperature of crystallization of the new phases DTA and TG were performed for the mixtures of the precursors. Several synthesis strategies were tested and discussed. The investigation of the reactivity upon heating highlights the stability of the precursors before they collapse, explaining the difficulties to get pure powder samples.