Characterization of two linear chain compounds: Ferromagnet NiCl2(CH3OH)2(1,4-dioxane)0.5 (1) and paramagnet [NiCl2(H2O)2(1,4-dioxane)](1,4-dioxane) (2)

The solvent-mediated crystal-to-crystal transformation was observed from yellow crystal of NiCl2(CH3OH)2(1,4-dioxane)0.5 (1) to green crystal of [NiCl2(H2O)2(1,4-dioxane)](1,4-dioxane) (2) under high humidity or adding of H2O in CH3OH/1,4-dioxane solution. The μ-Cl2 bridge in 1 replaced by 1,4-dioxane bridge in 2. In 1, the chlorine-bridged linear chains of NiCl2(CH3OH)2 and 1,4-dioxane molecules stack along the b- and c-axis alternatively with hydrogen bonds intrachain, interchain, between chain and solvent. These hydrogen bonds and dipolar interaction between ferromagnetic coupling chlorine-bridged chains result in long-range ferromagnetic ordering at 3.1 K and a strong frequency dependence of the ac-susceptibilities associated to domain structures with very large shape anisotropy was observed below 3.1 K. In 2, layers of 1,4-dioxane-bridged linear chains of NiCl2(H2O)2(1,4-dioxane) are intercalated by layer of 1,4-dioxane molecules with hydrogen bonds between chain and solvent. Compound 2 is paramagnet to 2 K.

Graphical abstractFerromagnetically coupled Ni(II) in the chlorine-bridged linear chain compound, NiCl2(CH3OH)2(1,4-dioxane)0.5 exhibits long-range ferromagnetism below 3.1 K due to hydrogen bonds and dipolar interaction which is confirmed by ac-susceptibilities and specific heat measurement. In contrast, negligible magnetic interaction is transmitted through 1,4-dioxane in linear chain compound [NiCl2(H2O)2(1,4-dioxane)](1,4-dioxane).Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Due to weak transverse magnetic interactions, LRO was observed in chain compounds. ► The yellow block crystal 1 can be transformed to the green plate crystal 2 by solvent-mediation. ► Ferromagnetic interaction and LRO have been evidenced in the dc, ac, specific heat measurement in 1. ► 2 shows no magnetic ordering above 2 K. ► The Cl-bridge plays an important role to molecular magnet than 1,4-dioxane-bridge.