Mg1−xCoxLi2(3,5-pdcH)2(DMF)2 (x = 0, 0.285, 0.575, 1): a series of heterometallic coordination polymers doped with magnetic Co2+ ions

Abstract

The introduction of heterometal ions into coordination polymers (CPs) could yield novel structural types and thus unprecedented properties. This work reports on the syntheses, characterizations and magnetic properties of a series of heterometallic CPs (HCPs), namely Mg_1−xCo_xLi₂(3,5-pdcH)₂(DMF)₂ (x = 0 (1), 0.285 (2), 0.575 (3) and 1 (4); 3,5-pdcH₃ = pyrazole-3,5-dicarboxylic). The CPs are isostructural to each other with a three dimensional neutral framework of apo type topology, which is constructed by 3,5-pdcH²⁻ ligands interconnecting infinite chain-like SBUs of [MLi₂(COO)₄(DMF)₂]_n (M = Mg (1), Mg_0.715Co_0.285 (2), Mg_0.425Co_0.575 (3) and Co (4)). Compound 1 represents a rare example of an s–s block HCP based on lightweight Mg²⁺ and Li⁺ ions. Compound 1 is magnetically inactive, while the successful doping of Co²⁺ ions into Mg²⁺ sites endows the resulting heterometallic compounds with antiferromagnetic behaviour. The magnetic behaviour of compounds 2–4 was analyzed and was shown to come from the zero field split or the spin–orbit coupling of the high-spin mononuclear Co²⁺ ions. Compounds 2 and 3 represent a rare type of HCP which simultaneously contains independent metal ions (Li⁺) and co-occupied ones (Mg²⁺ and Co²⁺) in different crystallographic sites.