INTRAMOLECULAR ENERGY-TRANSFER AND MN4+ LUMINESCENCE IN POLYOXOMETALLOMANGANATE LATTICES

Photoexcitation of the oxygen (O)-to-metal (RS=VV: Mo, and Nb), Ligand -to-metal charge transfer (O-->M l.m.c.t.) bands of the polyoxometallo manganates such as K6Na2[MnW6O24]. 12H(2)O (1), K-6[MnMo9O32]. 6H(2)O (2), and Na-12[Mn(Nb6O19)(2)]. 50H(2)O (3) leads to an intramolecular energy transfer from O-->M l.m.c.t. triplet states into Mn4+,followed by the luminescence of the (2)E-->(4)A(2) transition. Quantum yield of the Mn4+ luminescence is discussed in terms of both hydrogen bonding at the MnO5 octahedron and the disparity of the electronic configurati ons between the excited and ground states for the ligands of condensed MO(6) octahedra. The thermal quenching temperatures of the Mn4+ lumin escence for complexes 1, 2, and 3 were around 50, 350, and 200 K, resp ectively, which are associated with the potential expansion due to the hydrogen bonding beyond the first coordination sphere of the central MnO6 octahedron in the anion.