2D coordination polymer built from lithium dimethylmalonate and CoII ions: the influence of dehydration on spectral and magnetic properties

2D coordination polymer [Li2Co(H2O)4(Me2Mal)2]n (1) was synthesized by interaction of lithium dimethylmalonate (Li2Me2mal) and cobalt(II) acetate. The structure of 1 can be described as {Li(H2O)2(Me2Mal-κO,O')} anions linked by CoII cations through bridging water molecules and Me2Mal2- dianions. Upon heating to 130 - 190 °C compound 1 looses water molecules and transforms to [Li2Co(Me2Mal)2]n (2). Compound 2 is non-porous and amorphous, its rehydration by water leads to formation of 1, as shown by powder XRD. Dehydration of 1 is associated with drastic color change from pink to violet. The temperature dependency of magnetic susceptibility χM for 1 in 2-300 K range was analyzed using a model, which takes into account spin-orbit coupling in CoII and exchange interactions as a molecular field. Transformation 1 → 2 leads to less than 6 % change of χMT in temperature range 2 - 300 K, small change of magnetic susceptibility is consistent with conclusions that most of CoII ions in 2 are in pseudo-Oh donor sets. Analysis of χMT vs. T curve for 2 was performed using three models, which consider magnetism of uniform CoII ions or co-existence of CoII species in different donor sets.