Mercury(II) Complexes of the Carba-closo-dodecaboranyl Ligands [closo-1-CB11X11]2– (X = H, F, Cl, Br, I)

Salts of the mercury­(II) complexes [Hg­(closo-1-CB11X11)2]2– (X = H (1), Cl (3), Br (4)) and [PhHg­(closo-1-CB11X11)]− (X = H (6), Cl (8), Br (9), I (10)) were synthesized and characterized by multi-NMR spectroscopy, mass spectrometry, elemental analysis, and differential scanning calorimetry. Single crystals of Cs21·2Et2O, Cs23·MeCN, Cs24·4Me2CO, Cs9, and [Et4N]6·0.5Me2CO were studied by X-ray diffraction, and the interpretation of the bond properties is supported by theoretical data. In contrast to the mercury atom of the previously published [Hg­(closo-1-CB11F11)2]2– (2), which coordinates either acetonitrile or water, the metal atom of the related dianionic complexes 1, 3, and 4 does not reveal any further coordination. According to results derived from DFT and ab initio calculations, this different behavior is reasoned in the case of 1 by a reduced Lewis acidity at mercury and in the case of 3 and 4 by the increased shielding of the central mercury atom as a result of the bulky halogenated carba-closo-dodecaboranyl ligands [closo-1-CB11X11]2– (X = Cl, Br). The dianionic complex [Hg­(closo-1-CB11I11)2]2– (5) with the bulkiest carba-closo-dodecaboranyl ligand was generated via collision-induced dissociation and characterized by (−)-ESI mass spectrometry. The fragmentation pathways of the anionic complexes [Hg­(closo-1-CB11X11)2]2– (X = H, F, Cl, Br, I (1–5)) and [PhHg­(closo-1-CB11X11)]− (X = H, F, Cl, Br, I (6–10)) were studied by (−)-ESI mass spectrometry.