The reaction of niobium pentachloride with three equivalents of 2-t-butylphenol in carbon tetrachloride afforded [NbCl 2 (OC 6 H 4 C(CH 3 ) 3 -2) 3 ]. The identity of the complex has been established by elemental analyses, molar conductance, molecular weight determination, IR, 1 H, and 13 C-NMR and UV-Vis spectral studies. Based upon these studies, a square-pyramidal geometry around niobium has been proposed. Thermal behavior of the complex has been studied by TGA and DTA. Acceptor behavior of [NbCl 2 (OC 6 H 4 C(CH 3 ) 3 -2) 3 ] toward Ph 3 P, Ph 3 As, Ph 3 PO, Ph 3 AsO, and an uncommon ligand arsenictrithiophenoxide As(SPh) 3 allows the isolation of 1 : 1 addition compounds as shown by physicochemical, IR, and 1 H-NMR spectral studies. The formation of [NbCl 2 (OC 6 H 4 C(CH 3 ) 3 -2) 3 ] Á As(SPh) 3 appears to be the first adduct of its class and suggests the suitability of As(SPh) 3 as a ligand.