Replacement of H-bonded bridged water by transition metal ions in poly(1-vinylimidazole-co-methylmethacrylate) copolymers: a vibrational spectroscopy study using mid-FTIR, far-FTIR and ab initio calculations

A detailed structural analysis of the vibrational spectra of hydrophobic PVM (poly(1-vinylimidazole-co-methylmethacrylate)) copolymers PVM-4 (4 wt% 1-VIm) and PVM-44 (44 wt% 1-VIm) is provided with respect to bridging water and subsequent replacement by bridging transition metal ions. PVM-44 (44 wt% 1-VIm) with a high fraction of 1-VIm forms water bridges as evident by the water bending vibration, which is shifted up to 1665 cm ^-1. This band vanishes as transition metal ions are introduced and a new band at 952 cm ^-1 appears which is ascribed as a δ(ring) band involving the entire [M(Im) _n] ²⁺ unit. This fact is affirmed using ab initio calculations. The transition metal ions coordinate exclusively the imidazole groups. Although the imidazole associated water is replaced by transition metal ions, the amount of sorbed water for the very hydrophobic PVM-4 is increased as indicated by the ν(OH) region.