Undecahalo-closo-undecaborates [B(11)Hal(11)](2-)

The closo-undecaborate A(2)[B11H11] (A = NBzlEt(3)) can be halogenated with excess N-chlorosuccine imide, bromine or iodine, respectively, to give the perhalo-closo-undecaborates A(2)[B(11)Hal(11)] (Hal = Cl, Br. I). The chlo rination in the 11:1 ratio of the reagents yields A(2)[B11HCl10] whose subs equent iodination makes A(2)[B11Cl10I] available. The three type [B(11)Hal( 11)](2-) anions show only one and the two type [B11Cl(10)X](2-) anions (X = H, I) only two B-11 NMR peaks in the ratio 10:1, thus exhibiting the same degenerate rearrangement of the octadecahedral B-11 skeleton as is well-kno wn for [B11H11](2-) The crystal structure analysis of A(2)[B11Br11] and A(2 )[B11I11] reveals a rigid octadecahedral skeleton in the solid state, up to 330 K, whose B-B bond lengths deviate more or less from the idealized C-2v gas phase structure, but are in good accordance with the distances of A(2) [B11H11] Electrochemical experiments elucidate the mechanism of the known o xidation of [B11H11](2-) to give [B22H22](2-): A first one-electron transfe r is followed by the dimerization of the [B11H11](-) monoanion. whereas neu tral B11H11, a presumably most reactive species, does not play a role as an intermediate. The electrochemical oxidation of [B(11)Hal(11)](2-) anions a lso starts with a one-electron transfer, which is perfectly reversible only in the case of Hal = Br. There is no electrochemical indication for the fo rmation of [B(22)Hal(22)](2-). The neutral species B(11)Hal(11) should be a short-lived, very reactive species.