Structural and magnetic diversity based on different imidazolate linkers in Cu(II)-azido coordination compounds

Abstract

This Article reports the syntheses, structural characterization, and magnetic studies of four different Cu(II)-azido compounds based on imidazole or substituted imidazole ligand. The compounds, [Cu₂(μ_1,1-N₃)₂(EtimiH)₄(ClO₄)₂] (1) (EtimiH = 2-ethylimidazole), [Cu₂(µ-Meimi–)(MeimiH)₂(µ_1,1-N₃)₂(µ_1,3-N₃)]_n (2) (MeimiH = 2-methylimidazole; µ-Meimi– is the bridging mononegative anion of 2-methylimidazole), [Cu₂(µ-imi–)(imiH)₂(µ_1,1-N₃)₂(µ_1,3-N₃)]_n (3), and [{Cu₂(µ_1,1-N₃)₂(µ_1,3-N₃)(µ-imi–)(imiH)₃}·H₂O]_n (4) (imiH = imidazole; µ-imi– = bridging mononegative anion of imidazole), have been synthesized by the self-assembly of Cu(II) salts, azide ion, and the corresponding imidazole bridging ligands. By changing the substitution on the second linker (imidazole or substituted imidazole) and varying synthetic conditions, diverse structural and magnetic features have been achieved in compounds 1–4. Compound 1 has a double end-on azido bridged dinuclear core, while the other compounds (2–4) have 2D networks. Compound 2 and 3 contain 1D chains with alternate µ_1,1-N₃ and µ-Meimi– bridging, and such chains are further connected through a µ_1,3-N₃ bridge to result in the formation of the 2D network. Compound 4 is a novel 2D coordination polymer consisting of a zigzag 1D coordination chain having (µ_1,3-N₃)₂, µ-imi–, and (µ_1,3-N₃)₂ bridging groups and the chains undergo bridging through a µ_1,3-N₃ group resulting in the 2D network. Temperature dependent magnetic measurements show diverse magnetic properties of 1–4. Such versatile magnetic behaviors have been correlated to the respective bridging mode of azide and the corresponding imidazole bridging ligands.