Alkylamine-Templated Niccolite Frameworks of [Ga^IIIM^II(HCOO)₆]⁻ (M = Fe, Ni): Structure, Magnetism, and Dielectricity

The five heterometallic formate frameworks [EtA]­[Ga^IIIFe^II(HCOO)₆] (1; EtA = CH₃CH₂NH₃⁺), [DMA]­[Ga^IIIFe^II(HCOO)₆] (2; DMA = (CH₃)₂NH₂⁺), [DEtA]­[Ga^IIIFe^II(HCOO)₆] (3; DEtA = (CH₃CH₂)₂NH₂⁺), [MA]­[Ga^IIINi^II(HCOO)₆] (4; MA = CH₃NH₃⁺), and [DMA]­[Ga^IIINi^II(HCOO)₆] (5) were synthesized through solvothermal methods. Complexes 1–5 are isotructural, and all crystallize in the trigonal P3̅₁c 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.