[Nb 2 S 4 (aq)] 4 + , prepared by acidolysis of [Nb 2 S 4 (NCS) 8 ] 4 - , reacts with β-diketones in the presence of NH 3 to form Nb 2 S 4 (β-dike) 4 . In this way, the following complexes were prepared: Nb 2 S 4 (acac) 4 (1), Hacac = CH 3 COCH 2 COCH 3 ; Nb 2 S 4 (tfa) 4 (2), Htfa = CH 3 COCH 2 COCF 3 ; Nb 2 S 4 (ptfa) 4 (3), Hptfa = t-BuCOCH 2 COCF 3 ; Nb 2 S 4 (btfa) 4 (4), Hbtfa = PhCOCH 2 COCF 3 ; Nb 2 S 4 (tta) 4 (5), Htta = C 4 H 3 SCOCH 2 COCF 3 ; Nb 2 S 4 (dfhd) 4 (6), Hdfhd = C 3 F 7 COCH 2 COCF 3 ; Nb 2 S 4 (chf) 4 (7), Hchf = (C 5 F 1 0 )CFCOCH 2 COCF 3 (1,1,1-trifluoro-4-perfluorecyclohexyl-2,4-butanedione). They were characterized by IR, Raman and electronic spectroscopy. For 2, the crystal structure was solved. The crystals of 2 are monoclinic, a = 25.265(5), b = 8.195(1), c = 18.096(4) 9, β = 121.02(2)°, Z = 4, space group C2/C, R(R w ) = 0.0388(0.0733), Nb-Nb 2.879(1), S-S 2.008(4) 9.