The anions [B24H23](3-) and [B36H34](4-) from the thermal protolysis of [B12H12](2-)

The thermolysis of the hydrated free acids [H(H2O)m]2 [BnHn] (n = 12, 11, 10) is described. The anion [B12H12](2-) is transformed into [B24H23](3-) at 80 degrees C and into [B36H34]4- at 90 degrees C, with [B12H11(OH)(2-) as a side-product. The novel anion [B36H34](4-), isolated after neutralization as a salt with the cation NMe4, is considered by NMR arguments to consist of two icosahedral B12H11 units connected to a central B12H10 unit by BHB bridges. According to an ab initio computation, the two or three icosahedral cages of [B24H23](3-) and [B36H34](4-), respectively, are connected by bent BHB-bridges in the ground-state. Upon acidification, the anion B11H112- is transformed into nido[B H-11(13)(OH)](-),which is completely degraded, when water is removed from the solution of the free acid. The anion [B10H10](2-) is degraded into the arachno-[B9H14](-) anion, when the free acid is heated (100 degrees C) in the presence of oxalic acid.