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

The reaction between CuSO4 center dot 5H(2)O and [NMe2H2]Cl in N,N'-dimethylformamide (DMF) at 95 degrees C yielded green crystals of (NMe2H2)(4)[Cu6O2(SO4)(6)(DMF)(4)] 1. The discrete [Cu-6(mu(4)-O)(2)(mu(3)-SO4)(4)(mu(2)-SO4)(2)(DMF)(4)](4-) anions present in 1 contain two edge-sharing Cu-4(mu(4)-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(H) 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 center dot 5H(2)O and [NMe2H2]Cl in DMF at room temperature gave (NMe2H2)[Cu-2(OH)-(SO4)(2)(H2O)(2)] 3, the structure of which contains triangular Cu-3(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.