A new small molecule gelator and 3D framework ligator of lead(ii)

Abstract

Reacting equimolar quantities of 5-allenyl-1,3-benzenedicarboxylic acid (H₂abd) with lead(II) acetate trihydrate in N,N-dimethylformamide (DMF) under solvothermal conditions results in formation of a metallogel with a critical gelation percentage of 1% w/v. Elemental analysis performed on the gel provided a molecular composition ratio of [Pb(abd)(H₂O)]_n (1). Viewing the gel by scanning electron microscopy (SEM) identified an entangled network of cross-linked nano-fibres. ¹H-NMR aliquots of hydrated lead(II) acetate added to a solution of H₂abd in deuterated DMF allows inferences to be made about solution-state behaviour that occurs during the initial gel aggregation stage. Under non-solvothermal conditions, combining H₂abd and hydrated lead(II) acetate resulted in formation of single crystals suitable for X-ray diffraction, which were identified as a 3D coordination polymer with composition [Pb(abd)(DMF)] (2). Structural features observed within this 3D coordination polymer provide the basis for assigning the molecular structure to the fibrils present within gel 1. This assertion is supported by comparable vibrational profiles taken from a sample of dried gel 1 to that of crystalline 2, and the matching of early solution-state ¹H-NMR spectroscopic trends to later solid-state observations.