Assembly of alternating spin-chains with magnetically anisotropic cobalt(ii) dimers

A dimeric carboxylato complex of cobalt(ii), [Co₂ ^II(1,2-chedc)₂(Im)₂] (1) (1,2-chedc = cyclohex-1-ene-1,2-dicarboxylate and Im = imidazole), has been isolated. This complex can be further linked by chloro- or carboxylato-ligands, affording respectively one-dimensional chain structures of 1∞[Co₂ ^II(μ-Cl)₂(1,2-chedc)(Im)₂] (2) and 1∞[Co^II(1,2-chedc)(Im)] (3). Compound 1 shows weak antiferromagnetic interactions passing through the body of the dicarboxylate as well as substantial single-ion magnetic anisotropy (zero-field splitting energy Δ = 8.5 cm^-1). Both 2 and 3 exhibit typical alternating spin-chain behaviour in the higher-temperature region, but they display disparate behaviours at lower temperatures. For 2, alternating F-AF interactions compete (J₁ = 6.7 K and J₂ = -8.2 K), resulting in paramagnet-like behaviour with no clear evidence of three-dimensional contact. Compound 3 exhibits stronger intrachain AF-AF exchange-coupling interactions (J₁ = -9.3 K and J₂ = -4.3 K), leading to non-diamagnetic ground state due to the tiling of adjacent spins. Long-range magnetic ordering was observed below 10 K. Its narrow hysteresis loop suggests the use of 3 as a soft magnet.