Synthesis and stability studies of derivatives of the 2-sulfanyl-closo-decaborate anion [2-B10H9SH]2−

By acylation of [2-B10H9SH]2− (1) with trifluoroacetic anhydride was synthesized the anion [B10H9SCOCF3]2− (2). The alkaline and acid hydrolysis of the [B10H9S(CH2COOEt)2]− anion leading to the formation of [B10H9S(CH2COOH)2]− (3) gave evidence of high stability of sulfonium derivatives. While in phosphate buffer at pH = 5 the semi-hydrolysis time of thioesters [B10H9SCOCH3]2−, [B10H9SCOCF3]2− (2), and [B10H9SCOC6H5]2− were 600, 17 and 168 h. The substituted closo-decaborates were characterized by IR and NMR (1H, 11B, 13C) spectroscopy. The crystal structures of (Bu4N)3[B10H9(CH2COO)2H]2 (3) and Cs5(Bu4N)[B10H9SC(O)CF3]3 (2a) were determined by X-ray diffraction. In structure 3, anions were associated via strong O H⋯O hydrogen bonds into centrosymmetric hexacharged tetramers. In structure 2a, anions formed the environment of all cesium cations and chelated one of them due to Cs O and Cs HB bonds.