Intense photosensitized emission from stoichiometric compounds featuring Mn2+ in seven- and eightfold coordination environments

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)(4)MnBr4][TlBr4](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)] [TlBr5] (4) is in the sevenfold coordination polyhedron of [Mn(15C5)(H2O)(2)](2+). Crystal data for 3: monoclinic, P2(1)/c (No. 14); a = 14.131(3) Angstrom, b = 12.158(1) Angstrom, c = 14.239(2) Angstrom, beta = 110.37(1)degrees, Z = 2, R1 = 0.039 and wR2 = 0.083. For 3, long-lived emission (77 K decay rate similar or equal to 3 x 10 s(-1)) from [Mn(12C4)(2)](2+) (the first for eight-coordinate Mn2+ in stoichiometric compounds) is observed (lambda(max) similar or equal to 546 nm) along with that of the sensitizing MnBr42- (lambda(max) similar or equal to 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 lambda(max) similar or equal to 592 nm. Unusually intense absorptions attributable to the seven-coordinate species are observed at 317 (T-2(2)(I-2) <-- (6)A(1)), 342 (T-4(1)(P-4) <-- (6)A(1)), 406 (E-4((4)G) <-- (6)A(1)), and 531 (T-4(1)((4)G) <-- (6)A(1)) nm.