FTIR investigations of solid precursor materials for sol-gel deposition of WO3 based electrochromic films

Peroxypolytungstic acid derivative (APTA) and peroxypolytungstic acid derivative coupled with a dicarboxylic acid additive i.e., oxalic acid dihydrate (APTA + OAD) in xerogel form, synthesized by a wet chemistry route were the solid sol-gel precursors for casting WO3 films. These bulk materials have a complex structure owing to the presence of several groups such as acetate, peroxy anions and water molecules in their basic matrix. Additionally, oxalate ions constitute an integral part of the structure in the APTA + OAD xerogel. Detailed FTIR analysis of these coordination compounds has thrown light on the modes of association of the various anions or groups with tungsten metal ion. The mode of coordination of the acetate ion as a bidentate as well as a monodentate ligand enabling chelate formation and the several other chemical linkages prevalent in APTA have been established. Upon the incorporation of OAD in APTA, the net ramifications are drastic changes in the structure inclusive of changes in the nature and strength of metal - ligand bonding, which is exemplified by FTIR studies of (APTA + OAD) xerogel.