Electron transfer from the electron donor of p-phenylenediamine (PPD) to the electron acceptor of (H+)3[PMo12O 40]3- forms a one-electron-reduced Keggin cluster of [PMO12O40]4-, bearing a S = 1/2 spin, while proton transfer from the proton donor of (H+)3[PMO 12O40]3- to the proton acceptor of PPD yielded mono- and diprotonated cations of 4-aminoanilinium (HPPD+) and p-phenylenediammonium (H2PPD2+). By introduction of crown ether receptors during the crystallization process, supramolecular cations of (HPPD+)(crown ethers) and/or (H2PPD2+)(crown ethers) were successfully introduced into three new α-[PMo 12O40]4- salts of (H2PPD 2+)2(crown-4)4[PMo12O 40]4- (1), (HPPD+)4-(crown-5) 4[PMo12O40]4- (2), and (HPPD +)2(H2PPD2+)(crown-6) 4[PMo12O40]4- (3) as the countercation. The protonated states of PPD and moleoular-assembly structures of the supramolecular cations depended on the size of the crown ethers. In salt 3, a novel mixed-protonated state of HPPD+ and H2PPD 2+ was confirmed to be complexed in the cation structure. According to the changes in the cation structures, the anion arrangements were modulated from those of the two-dimensional layer for salt 1 to the isolated cluster for salts 2 and 3. The temperature-dependent magnetic susceptibilities of salts 1-3 were consistent with the isolated spin arrangements of [PMo12O 40]4-. The electronic spectra of salts 1-3 indicated the intervalence optical transition from pentavalent MoV to hexavalent MoVI ions within the [PMo12O40]4- cluster. Temperature-dependent electron spin resonance spectra of salt 2 revealed the delocalization-localization transition of the S = 1/2 spin at 60 K. The spin on the [PMo12O40]4- cluster was localized on a specific MoV site below 60 K, which was thermally activated with an activation energy of 0.015 eV.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Inorganic Chemistry