Reactions between arachno-4-SB8H12 (1) and Lewis bases L in benzene or without solvent generate a series of the corresponding exo-6-L-arachno-4-SB8H10 (2) compounds [L SMe(2) (2a), PPh(3) (2b), MeCN (2c), NMe(3) (2d), pyridine (py) (2e), urotropine (uro) (2f)], and a bidentate-ligand adduct exo,exo’-6,6’-(uro)-(arachno-4-SB8H10)2 (2g) has also been isolated. Compound 2d has also been prepared by a ligand displacement reaction between 2a and trimethylamine, and similar adducts with L = MeNC and quinoline (quin) (2h,2i) were isolated as side products from the reactions between nido-B-SB9H11 (3) and corresponding Lewis bases. All these compounds are characterized by mass spectrometry and B-11 and H-1 NMR spectroscopy. Single-crystal X-ray diffraction studies have been carried out on three representatives of the series, viz. those with L uro (2f), 1/2 uro (2g), and MeNC (2h). Crystal data for 2f (at 200 K) : mol wt 268.9; monoclinic; space group C2/c; Z = 8; a = 2064.16(9), b = 680.85(5), c = 2061.61(12) pm; beta 104.467(5)degrees; R = 0.0647; R(w) = 0.0743. Crystal data for 2g (at 200 K) : mol wt 397.6; monoclinic; space group P2(1)/c; Z = 4; a 1228.24(8), b = 1296.79(8), c 1452.62(10) pm; beta = 110.394(4)degrees; R = 0.046; R(w) = 0.0543. Crystal data for 2h (at 200 K) : mol wt 169.8; monoclinic; space group P2(1)/m; Z = 2; a = 557.93(8), b = 909.36(9), c = 987.16(11) pm; R = 0.0377; R, 0.0436.