A solution and solid state study of niobium complexes University of ...

3.7.2.4 Synthesis of [NbCl4(acac)]:
Chapter 3
[NbCl5]2 (0.313 g, 0.58 mmol) was dissolved in tetrahydrofuran (5 ml) and formed a
yellow solution. One molar equivalent of acacH (0.119 ml, 1.16 mmol) was added
and the yellow solution changed colour to orange. The solution was stirred for 1
hour. Small, orange, needle-like crystals were obtained after 24 hours. Yield: 0.266
g (69 %). IR (cm -1 ): ν(C–O) 1138; ν(C–H) 1334. UV/Vis (λmax): 269 nm. ε = 482 cm -
1 .M -1 . 1 H NMR (methanol-d4): δ = 1.59 (s, 1H), 2.21 (s, 6H). 13 C NMR (methanol-
d4): δ = 19.2, 141.4, 179.5. 93 Nb NMR (methanol-d4): δ = -896.
3.7.2.5 Synthesis of [NbCl4(hfacac)]:
[NbCl5]2 (0.313 g, 0.58 mmol) was dissolved in tetrahydrofuran (5 ml) and formed a
yellow solution. One molar equivalent of hfacacH (0.164 ml, 1.16 mmol) was added
and the dark yellow solution was stirred for 2 hours. An orange powder was obtained
after 24h. Yield: 0.185 g (39 %). IR (cm -1 ): ν(C–O) 1033; ν(C=C) 1603. UV/Vis
(λmax): 205 nm. ε = 386 cm -1 .M -1 . 1 H NMR (methanol-d4): δ = 1.67 (s, 1H). 13 C NMR
(methanol-d4): δ = 123.4, 141.2, 180.2. 93 Nb NMR (methanol-d4): δ = -911.
3.7.2.6 Synthesis of [NbCl(trop)(OMe)3]:
[NbCl5]2 (0.313 g, 0.58 mmol) was dissolved in tetrahydrofuran (8 ml). Tropolone
(0.1417 g, 1.16 mmol) was added and the reaction mixture was stirred for 2 hours. A
yellow precipitate formed and the tetrahydrofuran was removed in vacuo. The
precipitate was partially dissolved in methanol (5 ml) and the remaining precipitate
turned white. The yellow methanol solution was collected and the remaining
precipitate was dissolved in toluene (6 ml) forming a colourless solution. After 48
hours the methanol solution formed a yellow powder and the toluene solution formed
a white powder. The white powder obtained from the toluene solution was
determined as the uncoordinated tropolone ligand. Further characterization was
done on the yellow powder. Yield: 0.111 g (28 %). IR (cm -1 ): ν(C–O) 1172; ν(C–H)
1323, 1401; ν(C=C) 1519, 1522. UV/Vis (λmax): 388 nm. ε = 443 cm -1 .M -1 . 1 H NMR
(methanol-d4): δ = 5.18 (s, 9H), 6.84 (s, 1H), 7.47 (s, 5H). 13 C NMR (methanol-d4):
δ = 17.8, 53.9, 106.4, 126.6, 127.5, 130.9, 131.1, 183.2. 93 Nb NMR (methanol-d4):
δ = -964.
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