CRYSTAL-STRUCTURES OF DIPYRIDINIOMETHANE MONOHALOGENOHYDRO-CLOSO-DECABORATES(2-), [(C5H5N)(2)CH2][2-XB(10)H(9)] X=CL, BR, I

[B10H10](2-) reacts with chlorine, bromine and iodine or with N-halogenosuccinimide, yielding the monohalogenodecaborates [2-XB(10)H(9)](2-) (X = Cl, Br, I), which are separated by ion exchange chromatography on diethylaminoethyl(DEAE) cellulose from the starting compound and higher halogenated products. The X-ray structure determinations of the isotypic chloro and bromo compounds [(C5H5N)(2)CH2][2-XB(10)H(9)] (monoclinic, space group C2/c, Z = 8; for X = Cl: a = 33.174(5), b = 7.2809(4), c = 16.2232(7) Angstrom, beta = 113.307(7)degrees; for X = Br: a = 33.525(11), b = 7.281(2), c = 16.297(4) Angstrom, beta = 113.62(2)degrees) and of the iodo compound [(C5H5N)(2)CH2][2-IB10H9] (monoclinic, space group P2(1), Z = 2, a = 7.143(3), b = 13.568(4), c = 9.479(7) Angstrom, beta = 97.57(5)degrees) show columns of substituted boron clusters [2-XB(10)H(9)](2-), X = Cl, Br, I and bent dications [(C5H5N)(2)CH2](2+) along the shortest axis wich are assembled to alternating layers in the crystal lattice.