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

Salts of the mercury­(II) complexes [Hg­(<i>closo</i>-1-CB₁₁X₁₁)₂]^2– (X = H (<b>1</b>), Cl (<b>3</b>), Br (<b>4</b>)) and [PhHg­(<i>closo</i>-1-CB₁₁X₁₁)]⁻ (X = H (<b>6</b>), Cl (<b>8</b>), Br (<b>9</b>), I (<b>10</b>)) were synthesized and characterized by multi-NMR spectroscopy, mass spectrometry, elemental analysis, and differential scanning calorimetry. Single crystals of Cs₂<b>1</b>·2Et₂O, Cs₂<b>3</b>·MeCN, Cs₂<b>4</b>·4Me₂CO, Cs<b>9</b>, and [Et₄N]<b>6</b>·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(<i>closo</i>-1-CB₁₁F₁₁)₂]^2– (<b>2</b>), which coordinates either acetonitrile or water, the metal atom of the related dianionic complexes <b>1</b>, <b>3</b>, and <b>4</b> 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 <b>1</b> by a reduced Lewis acidity at mercury and in the case of <b>3</b> and <b>4</b> by the increased shielding of the central mercury atom as a result of the bulky halogenated carba-<i>closo</i>-dodecaboranyl ligands [<i>closo</i>-1-CB₁₁X₁₁]^2– (X = Cl, Br). The dianionic complex [Hg­(<i>closo</i>-1-CB₁₁I₁₁)₂]^2– (<b>5</b>) with the bulkiest carba-<i>closo</i>-dodecaboranyl ligand was generated via collision-induced dissociation and characterized by (−)-ESI mass spectrometry. The fragmentation pathways of the anionic complexes [Hg­(<i>closo</i>-1-CB₁₁X₁₁)₂]^2– (X = H, F, Cl, Br, I (<b>1</b>–<b>5</b>)) and [PhHg­(<i>closo</i>-1-CB₁₁X₁₁)]⁻ (X = H, F, Cl, Br, I (<b>6</b>–<b>10</b>)) were studied by (−)-ESI mass spectrometry