Coordination polymers of Cd^II and Pb^II with croconate show remarkable differences in coordination patterns: a structural and spectroscopic study

Abstract

The croconate dianion is a highly versatile ligand with two tautomeric forms making it useful for building large superstructures in the solid state. The single‐crystal X‐ray structures of PbII– and CdII–croconate coordination polymers, namely catena‐poly[[[diaqualead(II)]‐μ‐croconato‐κ4O1,O2:O3,O4] monohydrate], {[Pb(C5O5)(H2O)2]·H2O}n, 1, and catena‐poly[[triaquacadmium(II)]‐μ‐croconato‐κ4O1,O2:O3,O4], [Cd(C5O5)(H2O)3]n, 2, have been determined. Both polymers form one‐dimensional (1D) structures; 1 is a nonplanar 1D zigzag coordination polymer extended along the crystallographic b axis, whereas 2 is a planar 1D ribbon parallel to the [101] direction. In 2, three H2O molecules are coordinated directly to the metal atom, while in 1, only two H2O molecules are directly coordinated to the metal atom. A third interstitial H2O molecule is involved in hydrogen bonding with O atoms of the croconate ligands of an adjacent layer and other H2O molecules, resulting in stacked double layers parallel to the [105] plane. Solid‐state FT–IR and solution UV–Vis spectra also substantiate the croconate coordination.