Formation of p-phenylenediamine-crown ether-[PMo12O40]4- salts

Electron transfer from the electron donor of p-phenylenediamine (PPD) to the electron acceptor of (H+)(3)[PMo12O40](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)[PMo12O40](3-) to the proton acceptor of PPD yielded mono- and diprotonated cations of 4- aminoanilinium (HPPD+) and p- phenylenediammonium (H2PPD(2+)). By introduction of crown ether receptors during the crystallization process, supramolecular cations of (HPPD+)(crown ethers) and/or (H2PPD(2+))(crown ethers) were successfully introduced into three new alpha-[PMo12O40](4-) salts of (H2PPD2+)(2)([12] crown-4)(4)[PMo12O40](4-) (1), (HPPD+)(4)-[ 15] crown-5)(4)[PMo12O40](4-) (2), and (HPPD+)(2)(H2PPD2+)([18]crown-6)(4)[PMo12O40](4-) (3) as the countercation. The protonated states of PPD and molecular-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 H2PPD2+ 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 [PMo12O40](4-). The electronic spectra of salts 1-3 indicated the intervalence optical transition from pentavalent MoV to hexavalent Mo-VI 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.