Magnetic dimensionality and the crystal structure of two copper(ii) coordination polymers containing Cu6 and Cu2 building units

Abstract

The electrostatic self-assembly reaction of the [Cu(HL)]²⁺ cation, where HL = 2-(2-aminoethylamino) ethanol, and the N₃⁻ or [Fe(CN)₆]⁴⁻ anion leads to the formation of two coordination polymers with the general formula of [Cu₆(μ_1,1-N₃)₆(μ_1,3-N₃)₂(μ_1,1,3-N₃)₂(μ_1,1,1,3-N₃)₂(HL)₂]_n (1) and {[Cu(HL)]₂[Fe(CN)₆]·H₂O}_n (2), respectively. The resulting compounds have been structurally characterized by a single-crystal X-ray diffraction technique. Compound 1 possesses a rare 3D structure. It contains centrosymmetric hexanuclear repeating units, which act as six-connected nodes in the final network and copper(II) ions are joined together by azide anions with four different types of bridging modes, μ_1,1, μ_1,1,3, μ_1,1,1,3, and μ_1,3. The structure of compound 2 is a 2D heterometallic Cu^II/Fe^II layer in which the [Cu(HL)]₂ nodes and the octahedral [Fe(CN)₆]⁴⁻ linkers are joined by μ₂- and unusual μ₃-CN bridging modes. Detailed static and dynamic magnetic analyses of 1 reveal a dominant ferromagnetic intracluster interaction and a ferromagnetic 3D ordering transition below T_c = 5 K. The variable temperature magnetic susceptibility measurements of compound 2 show a very weak ferromagnetic coupling between the nearest Cu(II) ions. Also, EPR spectroscopy of these compounds has been investigated in the solid state. Nanocrystals of compound 2 have also been synthesized by a sonochemical process under different reaction conditions. The results show that the crystallinity degree and uniform distribution of nanosheets are inversely dependent on the irradiation time.