Reid, Howard O.,; Kahwa, Ishenkumba A.; White, Andrew J.P.; Williams, David J.
Author Affiliation, Ana.
Chemistry; Faculty of Pure and Applied Sciences
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 either 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]2b 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 sevenforl 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)° , 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)2]2+ species of 4 and [Mn(15C5)(H2O)2]-[MnBr4] (the first for seven-coordinate Mn2+ in stoichiometric compounds) peaks at lmax @592 nm. Unusally intense absorptions attributable tot he seven-coordinate species are observed at 317 (2T2(2I) ¬ 6A1), 406 (4E(4G) ¬ 6A1), and 531 (4T1(4G) ¬ 6A1] nm....