2D Coordination Polymer Built from Lithium Dimethylmalonate and CoII Ions: The Influence of Dehydration on Spectral and Magnetic Properties

• Published in: European journal of inorganic chemistry 2017-03, Vol.2017 (10), p.1396-1405
• Main Authors: Zorina‐Tikhonova, Ekaterina N., Gogoleva, Natalya V., Sidorov, Aleksei A., Kiskin, Mikhail A., Kolotilov, Sergey V., Ivanova, Tatiana M., Maslakov, Konstantin I., Dobrokhotova, Zhanna V., Efimov, Nikolay N., Novotortsev, Vladimir M., Eremenko, Igor L.
• Format: Article
• Language: eng ; jpn
• Subjects: Bridging ligands; Cobalt; Coordination modes; Coordination polymers; Dimethylmalonic acid; Magnetic properties
• ISSN: 1434-1948; 1099-0682
• DOI: 10.1002/ejic.201601376

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‐κ‐O,O′)} anions linked by CoII cations through bridging water molecules and Me2Mal2– dianions. Upon heating to 130–190 °C, compound 1 loses water molecules and transforms into [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 a drastic color change from pink to violet. The temperature dependency of magnetic susceptibility χM for 1 in the range 2–300 K was analyzed by 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 the temperature range 2–300 K; this small change of magnetic susceptibility is consistent with conclusions that most of the CoII ions in 2 are in pseudo‐octahedral donor sets. Analysis of the χMT versus T curve for 2 was performed by using three models, which consider magnetism of uniform CoII ions or the co‐existence of CoII species in different donor sets. A new layer coordination polymer of CoII with anions of dimethylmalonic acid was obtained. The polymer can be dehydrated, and this hydration/dehydration process is reversible. Dehydration was associated with color change from pink to violet. The transformation of the compounds led to a change of their spectral and magnetic properties.