Tungsten Hexabromide.

Schaffer, Herbert A.; Smith, Edgar F.

doi:10.1021/ja02098a015

Cited by 6 publications

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“…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. The experimental studies and electron density calculations showed that the pho tophysical properties (the position of the spectral maximum, quantum yield, and emission lifetime) depended, to a considerable extent, on the type of internal (Q, X) and apical (L) ligands.Tungsten(II) bromide has been known since the end of the 19th century [19,20], but the cluster nature of W 6 Br 12 and derivatives was established much later, in 1967 [21]. 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].…”

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

et al. 2012

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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. The experimental studies and electron density calculations showed that the pho tophysical properties (the position of the spectral maximum, quantum yield, and emission lifetime) depended, to a considerable extent, on the type of internal (Q, X) and apical (L) ligands.Tungsten(II) bromide has been known since the end of the 19th century [19,20], but the cluster nature of W 6 Br 12 and derivatives was established much later, in 1967 [21]. 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].In the present work, we describe the synthesis, structure, and luminescence properties of the finely crystalline sample (H 3 O) 2 [{W 6 Br 8 }Br 6 ] ⋅ 4H 2 O (I). EXPERIMENTALTungsten powder, dibromine, ethanol, and con centrated HBr (not lower than analytical grade) were used as received. Powder diffraction patterns were recorded at room temperature on a Philips APD 1700 diffractometer (CuK α radiation, graphite monochro mator). For compound I, the ratio of heavy elements was determined by energy dispersive X ray analysis (EDXA) using a JSM 6700F scanning electron microscope. The IR spectrum was recorded on a Scimitar FTS 2000 spectrometer (pellets with KBr). Thermal gravimetric analysis (TGA) was carried out on a Netzch TG 209 F1 Iris instrument: the sample was heated in a helium flow from 25 to 400°С with a rate of 10°C/min. To study the luminescence proper ties, the pure crystalline substance was divided in an agate mortar, and the obtained powder was placed between two non fluorescing glass plates. The cor rected emission spectrum and the emission decay were recorded at room temperature using a Hamamatsu Photonics PMA 11 multichannel photodetector and a Hamamatsu Photonics C4334 streak camera, respec tively. When recording the luminescence spectrum and analyzing the emission decay, the sample was excited by a LOTIS TII LS 2137/3 ND:YAG pulse laser (pulse duration 6 ns) with the wavelength 355 nm. The luminescence quantum yield was detected using a Hamamatsu Photonics C9920 03 complex setup for the determination of the absolute photoluminescence quantum yield. The setup consists of a xenon lamp as an excitation source (excitatio...

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“…Tungsten(II) bromide has been known since the end of the 19th century [19,20], but the cluster nature of W 6 Br 12 and derivatives was established much later, in 1967 [21]. 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].…”

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confidence: 99%

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

et al. 2012

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“…The only method reported for preparing tungsten(II) bro mide is the hydrogen reduction of the pentabromide at 400°C. (19,21,27). The dibromide is a green solid with properties very similar to those of tungsten(II) chloride.…”

Section: Tungsten(ii) Halidesmentioning

confidence: 99%

“…Tungsten(VI) bromide was first prepared by Schaffer and Smith (19) by passing a stream of nitrogen saturated with bromine vapor over warmed tungsten. The hexabromide sublimes readily and is deposited as blue-black needles.…”

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“…X-ray diffraction powder patterns of this volatile fraction showed that the major con stituent was tungsten(V) bromide= The presence of the pentabromide as one of the decomposition products may be explained as a reaction between tungsten(II) bromide and bromine or a disproportionation of the trihalide at the elevated temperature as shown in Equations 19 and 20. 2WBr2(s) + 3Br 2 (g) = 2WBr 5 (g)(19) 3WBr 3 (s) = 2WBr 2 (s) + WBr 5 (g)…”

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