Reid, Howard O.; Kahwa, Ishenkumba A.; White, Andrew J.; Williams, David J.
Author Affiliation, Ana.
Department of Chemistry
Intense photosensitized emission from stoichiometric compounds featuring Mn2+ in seven- and eightfold coordination environments
Date of Publication
Synthetic, structural and luminescence studies of stoichiometric crown ether compounds of Mn2+ in well-defined coordination environments were undertaken in an effort to understand the origin of emitting crystal defects found in cubic F23 [(K18C6)4MnBr4][T1Br4]2 crystals (Fender, N. S.; et al. Inorg. Chem. 1997, 36, 5539). The new compound [Mn(12C4)2][MnBr4]2[N(CH3)4]2 (3) features Mn2+ ions in eight-and fourfold coordination environments of [Mn(12C4)2]2+ and MnBr42- respectively, while Mn2+ in [Mn(15C5)(H2O)2][T1Br5] (4) is in the sevenfold coordination polyhedron of [Mn(15C5)(H2O)2]2+. Crystal data for 3: monoclinic, P21/c (No. 14); a = 14.131 (3) Å, b=12.158(1) Å, c =14.239(2) Å, b = 110.37(1)º, Z = 2, R1 = 0.039 and wR2 = 0.083. For 3, long-lived emission (77 K decay rate » 3 x 10s-1) from [Mn(12C4)2]2+ (the first for eight-coordinate Mn2+ in stoichiometric compounds) is observed (lmax »546 nm) along with that of the sensitizing MnBr42- (lmax »513 nm), which is partially quenched. Emission from the seven-coordinate [Mn(15C5)(H2O)22+ species of 4 and [Mn(15C5)(H2O)2]- [MnBr4] (the first for seven-coordinate Mn2+ in stoichiometric compounds) peaks at lmax »592 nm . Unusually intense absorptions attributable to the seven-coordinate species are observed at 317 (2T2(²I) ¬ 6A1), 342 (4T1(4P) ¬ 6A1), 406 (4E(4G) ¬ 6A1), and 531 (4T1(4G) ¬ 6A1) nm.....