A comparative study of the structural, optical, and electrochemical properties of squarate-based coordination frameworks

Abstract

Systematic studies of the thermal expansion, optical, and redox properties of a series of six squarate-based frameworks, [MII(C4O4)(H2O)2] (MII = MnII, FeII, CoII, NiII, ZnII, CdII) have revealed that five members of the series exhibit cubic structures in which the squarate ligands are configured in an ‘eclipsed’ phase, while the CdII analogue exhibits a trigonal structure with a ‘staggered’ orientation of the ligands. The ‘eclipsed’ structures are characterised by a positive coefficient of thermal expansion, while the CdII analogue exhibits zero thermal expansion. Ultraviolet-visible-near infrared (UV-Vis-NIR) spectra and electrochemical measurements indicate that electron delocalisation across the dianionic squarate bridge is absent.