By reaction of Na-2[B9H9] with the appropriate N-halogenosuccinimide, the monohalogenated anion [1-XB9H8](2-)(X = Cl, Br, or I) is formed. The X-ray diffraction analyses performed on single crystals of (Ph4P)(2)[1-XB9H8]. CH3CN (X = Cl, Br, I) reveal that the tricapped trigonal prismatic geometry of the cluster is retained after substitution in the 1-position. Crystallographic data are as follows for (Ph4P)(2)[1-XB9H8]. CH3CN. X = Cl, Br: monoclinic, space group P2(1), a = 10.7 Angstrom, b = 32.9 Angstrom, c = 13.8 Angstrom, beta = 96 degrees, Z = 4, R1 = 0.038 and R1 = 0.036, respectively. X = I: monoclinic, space group P2(1)/n, a = 10.5 Angstrom, b = 13.6 Angstrom, c = 33.4 Angstrom, beta = 94 degrees, Z = 4, R1 = 0.094. The compounds have been characterized by vibrational and B-11 NMR spectroscopy as well.