Inframolecular Energy Transfer and Mn4 +  Luminescence in Polyoxometallomanganate Lattices

Photoexcitation of the oxygen (O)‐to‐metal (M = W, Mo, and Nb), ligand‐to‐metal charge transfer (O→M l.m.c.t.) bands of the polyoxometallomanganates such as K 6 Na 2 [ MnW 6 O 24 ] · 12 H 2 O (1), K 6 [ MnMo 9 O 32 ] · 6 H 2 O (2), and Na 12 [ Mn ( Nb 6 O 19 ) 2 ] · 50 H 2 O (3) leads to an intramolecular energy transfer from O→M l.m.c.t. triplet states into Mn 4 + , followed by the luminescence of the 2 E → 4 A 2 transition. Quantum yield of the Mn 4 + luminescence is discussed in terms of both hydrogen bonding at the MnO 6 octahedron and the disparity of the electronic configurations between the excited and ground states for the ligands of condensed MO 6 octahedra. The thermal quenching temperatures of the Mn 4 + luminescence for complexes 1, 2, and 3 were around 50, 350, and 200 K, respectively, which are associated with the potential expansion due to the hydrogen bonding beyond the first coordination sphere of the central MnO 6 octahedron in the anion.