The octahedral hexazirconium cluster compound [PPh4](3)[Zr6Cl18H5] has been structurally characterized by both neutron and X-ray single-crystal diffraction studies. The compound [PPh4](3)[Zr6Cl18H5]. 3CH(2)Cl(2) crystallizes in the triclinic space group PT with unit cell parameters of a = 15.993(3), b = 22.237(3), and c = 14.670(4) Angstrom, alpha = 95.31(1), beta = 112.07(2), and gamma = 82.06(2)degrees, V = 4784(2) Angstrom(3), and Z = 2 at ambient temperature and a = 15.780(6), b = 21.96(3), and c 14.521(7) Angstrom, alpha = 94.96(8), beta = 111.59(4), and gamma = 81.72(5)degrees, V = 4627(11) Angstrom(3), and Z = 2 at T = 15 K. The hydrogen atoms in the cluster anion, [Zr6Cl18H5](3-), were found to be distributed at the centers of the eight triangular faces of the Zr-6 octahedron from neutron diffraction data. The occupancy parameters of the sites range from 0.32 to 0.92 with a total of 5.3(1) hydrogen atoms per cluster, close to the value from H-1 NMR measurement (5.0). The average Zr-H distance is 1.96(4) Angstrom. A variable temperature H-1 NMR study indicated that the cluster hydrogen atoms undergo rapid movement at room temperature. One of the five hydrogen atoms in the cluster [Zr6Cl18H5](3-) was readily removed as a proton with primary linear amines with formation of the corresponding ammonium cations, while the cluster anion, [Zr6Cl18H5](3-), was thus converted into a new cluster anion, [Zr6Cl18H4](4-). The feasibility of such a deprotonation reactions is controlled by the size of both the Lewis base and the cavity available on the Zr-3 triangular faces of the Zr-6 clusters, and also by the basicity of the deprotonating reagents. Two products, [PPh4](4)[Zr6Cl18H4]. 4CH(2)Cl(2) and [H3NEt](4)[Zr6Cl18H4]. 4MeCN from the deprotonation reactions were characterized by X-ray crystallography.