Photophysics and electrochemistry of hexanuclear tungsten halide clusters

Abstract

1351backgrounds was equal to half of the time required for the peak scan. The intensities of three standard reflections were measured every 1.5 h of X-ray exposure time for both compounds, and no decay with time was noted. The data were corrected for Lorentz, polarization, and background effects. The effects of absorption were not significant as judged by empirical $-scan data" (less than 3% in intensity), and therefore absorption corrections were not applied.Solution and Refinement. The structures were solved by conventional heavy-atom techniques. The Ru atoms were located by Patterson syntheses. Full-matrix least-squares refinement and difference Fourier calculations were used to locate all remaining non-hydrogen atoms. The atomic scattering factors were taken from the usual tabulation,12 and the effects of anomalous dispersion were included in F, by using Cromer and Ibers'l, values of Af' and Af". For compound 6 the positions of the phenyl and anion hydrogen atoms were calculated with use of the program HYDRO' (C-H distance set at 0.95 A) and included in the structure factor calculations but were not refined. The Ru hydride in 6 was lwated by difference Fourier analysis. The positional parameters of the hydride were refined, but its thermal parameter was fixed. In compound 3, the Ru hydrides were not located. The bridging S02CF3 group was found to be disordered such that the S1, C3, and F3 atoms had two positions each with a 50% occupancy. The two positions, labeled primed and unprimed, were refined to give reasonable distances and angles. The two positions found for the bridging S02CF3 correspond to isomers that result from tilting of the SCF, group in different directions. Only one of the

Preparation and Luminescence of Cluster Compounds [W6Br8L6]2– with L = CF3COO and C7H7SO3

“…[10] Interestingly, this trend behaves oppositional to the (calculated) [27] [10] which is in line with our [W 6 X 8 L 6 ] 2-compounds.…”

“…The electronic structure of [M 6 X 14 ] 2-clusters appears sufficiently well understood, [3][4][5] and photophysical studies have been carried out since the late 1980s. [6][7][8][9][10][11] Detailed accounts on the binary tungsten bromides W 6 Br 12 , W 6 Br 14 , W 6 Br 16 , and W 6 Br 18 have been published by Siepmann [1] and von Schnering [2] in 1968, followed by extensive work on tungsten halide clusters by Hogue and McCarley in 1970. [12] Single-crystal structures of A 2 [W 6 Br 14 ] (A = K, Rb, and Cs) have been reported in 1998.…”

“…[22] Among them, (TBA) 2 6 ]. [21] Although it has been reported that the iodide cluster [W 6 I 8 I 6 ] 2-is showing the highest luminescence quantum yields (in solution, 39 %) among halides (Cl, Br, I) [10] …”

Synthesis, crystal structure, and photophysical properties of acid (H3O)2[{W6Br8}Br6] · 4H2O

“…

It is well known that upon UV irradiation many chalcogenide and halide hexanuclear clusters of tran sition metals, for example, [{Re 6 Q 8 }L 6 ] (Q = S, Se) and [{M 6 X 8 }L 6 ] (M = Mo, W; X = Cl, Br), where L are various inorganic and organic ligands, luminesce in the red spectral range with microsecond emission life times [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. Phosphorescence in the red spectral range and, as a consequence, the ability to generate singlet oxygen, as well as specific features of the struc tures of similar octahedral clusters of heavy metals, suggest that these compounds are potentially promis ing for the use as photosensitizers in photodynamic therapy and as X ray contrast preparations in diagnos tics of oncological diseases.

…”

“…It should be mentioned that the lumines cence properties of the compounds based on the {W 6 Br 8 } 2+ cluster were studied very rarely in spite of their many year history [12,13,18,22].…”