The Anions [B 24 H 23 ] 3− and [B 36 H 34 ] 4− from the Thermal Protolysis of [B 12 H 12 ] 2−

The thermolysis of the hydrated free acids [H(H 2 O) m ] 2 [B n H n ] (n = 12, 11, 10) is described. The anion [B 12 H 12 ] 2− is transformed into [B 24 H 23 ] 3− at 80 °C and into [B 36 H 34 ] 4− at 90 °C, with [B 12 H 11 (OH)] 2− as a side‐product. The novel anion [B 36 H 34 ] 4− , isolated after neutralization as a salt with the cation NMe 4 , is considered by NMR arguments to consist of two icosahedral B 12 H 11 units connected to a central B 12 H 10 unit by BHB bridges. According to an ab initio computation, the two or three icosahedral cages of [B 24 H 23 ] 3− and [B 36 H 34 ] 4− , respectively, are connected by bent BHB‐bridges in the ground‐state. Upon acidification, the anion B 11 H 11 2− is transformed into nido ‐[B 11 H 13 (OH)] − , which is completely degraded, when water is removed from the solution of the free acid. The anion [B 10 H 10 ] 2− is degraded into the arachno ‐[B 9 H 14 ] − anion, when the free acid is heated (100 °C) in the presence of oxalic acid.