Assembly and polymerisation of some aromatic amines in α-VOPO4·2H2O
Abstract
Under soft conditions (dry EtOH, 25 °C), pyrazole, pyrazine and phenazine intercalate into α-VOPO4.2H2O as protonated, non-coordinated amines. Intermediates during pyrazine uptake include a metastable phase with d001= 13.3 Å, ascribed to bilayer formation. Benzidine (bz) instead gives two bz+ charge transfer (CT) bronzes: VOPO4(bz)0.5·2H2O (dry EtOH) and VOPO4(bz)0.7·3.5H2O (95% EtOH) with interlayer distances lower (7.05 Å and 6.65 Å, respectively) than in α-VOPO42H2O itself. Interlayer ‘pocket’ orientation with layer shifting and turbostraticity to accommodate bz+ cations is suggested, which differs from the assembly of bz+ in smectites and V2O5. VOPO4(bz)0.5·2H2O shows ‘moving solid’ behaviour, probably due to changes in specific H-bonding between intercalate and sheet with water content. It is concluded that surface ruffling and specific H-bonding influence composite formation and assembly.
Pyrrole (pyrr) almost completely polymerises on intercalation into α-VOPO4.2H2O, giving ‘nestled’ polymer composites with differing polypyrrole (Ppyrr) oxidation levels, whereas aniline uptake is governed by base protonation and proton induced reassembly. Both give differently loaded nanocomposites (with interlayer distances in the range 6.4–17.9 Å) depending on amine delivery (vapour, liquid, solution) and intercalant state (powder dispersion, film). Pyrrole loadings are higher with dispersions and lower with films, but the opposite is the case for aniline (An). For example, neat An gives VOPO4(An)1.3·13.5H2O (interlayer distance 17.9 Å), An-EtOH gives VOPO4(An)0.4(14.8 Å), and gaseous An gives VOPO4(An)0.66·2.2H2O (6.65 Å). As prepared, the Ppyrr shows mixed-polaron states, and both series give EPR spectra characteristic of highly anisotropic VIV-containing clusters and do not conduct. All become amorphous on calcination (160 °C), the An-containing composites polymerising to completion. Calcined VOPO4(Ppyrr)066·1.4H2O (from neat pyrrole) is a semiconductor, the EPR spectra (cationic amine and separated VIV ions) further supporting strong polymer-sheet electronic interactions with the formation of VIV island clusters. Assemblies of the two amines in VOPO4 are suggested.