Four heterometallic formate frameworks templated by various alkylamine cations with the general, formula [cat] [(GaMnII)-Mn-III(HCOO)(6)] {cat is MA (CH3NH3+) for 1, DMA [(CH3)(2)NH2+] for 2, EtA. (CH3CH2NH3+) for 3, and DEtA [(CH3CH2)(2)NH2+] for 4} have been prepared and characterized by X-ray diffraction, differential scanning calorimetry, and dielectric studies. All of the complexes have niccolite-like structures, which possess the same [GaMn(HCOO)6](-) anionic framework with binodal (4(12).6(3))(4(9).6(6)) topology; only the counterions. in the cavity are different. Complex 4 undergoes a reversible ferroelastic phase transition around 220 K accompanied by a thermally switchable dielectric constant transition triggered by the freezing of the order-disorder DEtA cations.