Synthesis, Structures, And Magnetic Behavior of New Anionic Copper(II) Sulfate Aggregates and Chains

The reaction between CuSO4·5H2O and [NMe2H2]Cl in N,N′-dimethylformamide (DMF) at 95 °C yielded green crystals of (NMe2H2)4[Cu6O2(SO4)6(DMF)4] 1. The discrete [Cu6(μ4-O)2(μ3-SO4)4(μ2-SO4)2(DMF)4]4– anions present in 1 contain two edge-sharing Cu4(μ4-O) tetrahedra, with the copper­(II) centers bridged by sulfato ligands. These anions are linked into a two-dimensional network through hydrogen bonds involving the dimethylammonium cations. When the reaction was carried out in the absence of [NMe2H2]­Cl, yellow-green crystals of (NMe2H2)4[Cu6O2(SO4)6(DMF)2] 2 were obtained. The anions in 2 contain similar Cu6O2(SO4)6 aggregates to those in 1, though these differ in terms of the copper­(II) coordination geometries. In addition, the anions in 2 are linked into chains through bridging sulfato ligands. The Cu6O2(SO4)6 aggregates observed in 1 and 2 are related to those present in the rare copper sulfate mineral fedotovite, K2Cu3O­(SO4)3, and in common with this mineral both 1 and 2 decompose in the presence of moisture. The reaction between CuSO4·5H2O and [NMe2H2]­Cl in DMF at room temperature gave (NMe2H2)­[Cu2(OH)­(SO4)2(H2O)2] 3, the structure of which contains triangular Cu3(OH)­(SO4) units that share vertices to form tapes. Magnetic measurements revealed that 1 and 3 are both spin-canting metamagnetic systems. Field-induced responses were observed below 5 K, with the critical field indicating metamagnetic behavior from antiferromagnetic to ferromagnetic equal to 110 Oe for both compounds.