Photochemical studies of alkylammonium molybdates.: Part 12.: O → Mo charge-transfer triplet-states-initiated self-assembly to {Mo154} ring- and tube-molybdenum-blues

The chemically induced dynamic electron-spin-polarization technique is employed in order to investigate the primary steps of the photoredox reaction between polyoxomolybdates and alkylammonium cations as both proton and electron-donors in solutions. An observation of emissive electron-spin-polarization signals of alkylamino radical cations for the photoredox reaction between polyoxomolybdates and alkylammonium cations in solutions reveals that the 0 --> Mo ligand-to-metal charge-transfer triplet states are involved in the transfers of both proton and electron from alkylammonium cation to polyoxomolybdate anions. Prolonged photolysis of aqueous solutions containing [Mo36O112(H2O)(16)](8-) [(PrNH3)-Pr-i](+), and LaCl3 at pH 1.0 leads to formation of two kinds Of {Mo-154} molybdenum-blues, [(Mo28Mo126O462H28)-Mo-V-O-VI(H2O)(70)].156.5H(2)O (1) and [(PrNH3)-Pr-i](8) [(Mo28Mo126O458H12)-Mo-V-O-VI(H2O)(66)].127H(2)O (2), which were X-ray crystallographically characterized. The former exhibits the intact car-tire-shaped {MO154} ring structure (with thickness of about 1.1 run and with outer- and inner-rings of approximately 3.5- and 2.3-nm diameters, respectively) derived formally from the dehydrated cyclic heptamerization of four-electron reduced building blocks of {Mo-22} (drop[(Mo4Mo18O70H12)-Mo-V-O-VI(H2O)(10)]) with overall symmetry of D-7d. The anion for the latter, [(Mo28Mo126O458H12)-Mo-V-O-VI(H2O)(66)](8-) (2a), exhibits a nanotube structure of {Mo-154} rings, each inner ring of which contains a bis(mu-oxo)-linkaged [MoO2(mu-O)(mu-H2O)MoO2](2+) Unit replacing one of seven [Mo(H2O)O-2(mu-O)Mo(H2O)O-2](2+) linker units. The neighboring {Mo-154} rings are connected by six Mo-O-Mo bridge between inner-rings consisting of 7 head- and 14 linkers-MoO6 octahedra for each. (C) 2003 Elsevier B.V. All rights reserved.