Intense Photosensitized Emission from Stoichiometric Compounds Featuring Mn²⁺ in Seven- and Eightfold Coordination Environments

Abstract

Synthetic, structural and luminescence studies of stoichiometric crown ether compounds of Mn(2+) in well-defined coordination environments were undertaken in an effort to understand the origin of emitting crystal defects found in cubic F23 [(K18C6)(4)MnBr(4)][TlBr(4)](2) crystals (Fender, N. S.; et al. Inorg. Chem. 1997, 36, 5539). The new compound [Mn(12C4)(2)][MnBr(4)](2)[N(CH(3))(4)](2) (3) features Mn(2+) ions in eight- and fourfold coordination environments of [Mn(12C4)(2)](2+) and MnBr(4)(2)(-) respectively, while Mn(2+) in [Mn(15C5)(H(2)O)(2)][TlBr(5)] (4) is in the sevenfold coordination polyhedron of [Mn(15C5)(H(2)O)(2)](2+). Crystal data for 3: monoclinic, P2(1)/c (No. 14); a = 14.131(3) Å, b = 12.158(1) Å, c = 14.239(2) Å, beta = 110.37(1) degrees, Z = 2, R1 = 0.039 and wR2 = 0.083. For 3, long-lived emission (77 K decay rate approximately 3 x 10 s(-)(1)) from [Mn(12C4)(2)](2+) (the first for eight-coordinate Mn(2+) in stoichiometric compounds) is observed (lambda(max) approximately 546 nm) along with that of the sensitizing MnBr(4)(2)(-) (lambda(max) approximately 513 nm), which is partially quenched. Emission from the seven-coordinate [Mn(15C5)(H(2)O)(2)](2+) species of 4 and [Mn(15C5)(H(2)O)(2)][MnBr(4)] (the first for seven-coordinate Mn(2+) in stoichiometric compounds) peaks at lambda(max) approximately 592 nm. Unusually intense absorptions attributable to the seven-coordinate species are observed at 317 ((2)T(2)((2)I) <-- (6)A(1)), 342 ((4)T(1)((4)P) <-- (6)A(1)), 406 ((4)E((4)G) <-- (6)A(1)), and 531 ((4)T(1)((4)G) <-- (6)A(1)) nm.

A linear supramolecular array of {[Mn(H2O)2(15-crown-5)]Br2}n

“…Compounds of Mn 2+ and 15-crown-5 were prepared in search of crystals with emissive Mn II ions in environments other than tetrahedral or octahedral geometries (Reid et al, 1998(Reid et al, , 1999. In one of these, [Mn(H 2 O) 2 (15-crown-5)]Br 2 , (I), the cation was found to have crystallographically imposed twofold rotation symmetry, with the axis passing through O1, Mn and the midpoint of the C5-C5A bond.…”

Synthesis, structural characterization and alcohol oxidation activity of a new mononuclear manganese(II) complex

“…In fact, many catalytic studies in recent years have found that manganese complexes can exhibit a diversity of catalytic oxidation reactions on organic substrates in organic solvents [20,21]. Numerous complexes of terpyridine and oligopyridines with manganese have been investigated because of their interesting structural, redox, photochemical, catalytic, and water oxidation properties [22][23][24][25][26][27][28][29][30][31][32][33].…”

Seven-coordinate Mn2+ ions in [Mn(15-crown-5)(H2O)2]2+ as luminescent probes for dynamic supramolecular events†

“…The good response of the manganese(ii) 4 T 1 ( 4 G) state to changing ligand field strength and symmetry as well as the high sensitivity of luminescence techniques, such as time resolved luminescence spectroscopy, make the Mn 2+ [ 4 T 1 ( 4 G)? 6 A 1 ] emission attractive as a potential diagnostic tool for coordination characteristics of divalent metal ions.…”

“…1,2 Besides classical four-and six-coordinate oxide and halide species, 3 Mn 2+ [ 4 T 1 ( 4 G)? 6 A 1 ] emission was recently shown to occur in well defined seven-and eight-coordinate environments 4 thereby expanding the range of Mn 2+ coordination environments accessible by luminescence techniques. Herein we demonstrate the diagnostic efficacy of the Mn 2+ [ 4 T 1 ( 4 G)?…”

“…Herein we demonstrate the diagnostic efficacy of the Mn 2+ [ 4 T 1 ( 4 G)? 6 A 1 ] emission by probing the behaviour of coordinated H 2 O in response to thermal tuning of the structural rigidity of [Mn(15-crown-5)(OH 2 ) 2 ] 2+ cations anchored in two-and one-dimensional supramolecular arrays of {[Mn(15-crown-5)(H 2 O) 2 ][TlBr 5 ]} n 1 4 and {[Mn(15-crown-5)(H 2 O) 2 ]Br 2 } n 2. 5 Compounds 1 4 and 2 5 were prepared as described previously, whilst compound 3 was obtained by a procedure similar to that used for 2 but with D 2 O and CH 3 OD replacing H 2 O and CH 3 OH respectively.…”