The five heterometallic formate frameworks [EtA][(GaFeII)-Fe-III(HCOO)(6)] (1; EtA = CH3CH2NH3+), [DMA][(GaFeII)-Fe-III(HCOO)(6)] (2; DMA = (CH3)(2)NH2+), [DEtA][(GaFeII)-Fe-III(HCOO)(6)] (3; DEtA = (CH3CH2)(2)NH2+), [MA][(GaNiII)-Ni-III(HCOO)(6)] (4; MA = CH3NH3+), and [DMA][(GaNiII)-Ni-III(HCOO)(6)] (5) were synthesized through solvothermal methods. Complexes 1-5 are isotructural, and all crystallize in the trigonal P (3) over bar (1)c space group. Each metal center is 6-connected, with each HCOO(-)bridging ligand in an anti-anti mode to build a three-dimensional niccolite-like architecture. All of the complexes exhibit weak ferromagnetism at low temperature. A variable-temperature (VT) dielectric study indicates that the dielectric anomaly is induced by the freezing of motions from the protonated amines during the freezing process.