Synthesis and crystal structures of ATi[Nb6Cl18] compounds (A = K, Rb, Cs, In, Tl)

New quaternary niobium cluster chlorides corresponding to the general formula ATi[Nb6Cl18] (A = K, Rb, Cs, In, Tl) have been synthesized in sealed quartz tubes at 720 degrees C, starting from stoichiometric amounts of NbCl5, niobium metal, TiCl3, and ACI (A = K, Rb, Cs), or In or Tl metals. The structures of RbTi[Nb6Cl18] and CsTi[Nb6Cl18] were determined using single crystal X-ray diffraction. RbTi[Nb6Cl18] crystallizes in the rhombohedral crystal system, space group R (3) over bar (no. 148), Z = 3, with lattice parameters: a = 9.163(4), c = 25.014(14) Angstrom (hexagonal setting). The structure refinement converged to R-1 = 0.044 and wR(2) = 0.058 for all data. In this structure, discrete [Nb6Cl18](4-) cluster units are linked by Rb+ and Ti3+ cations, located in a 12-coordinated anticubeoctahedral and octahedral chloride coordination environment, respectively. In contrast, CsTi[Nb6Cl18] crystallizes in the trigonal crystal system, space group P (3) over bar 1c (no. 163), Z = 2. The lattice parameters were determined to be a = 9.1075(6), c = 17.0017(8) Angstrom. The structure refinement gives the reliability factors R-1 = 0.029 and wR(2) = 0.063 for all data. The structure is built up of discrete octahedral [Nb6Cl18](4-) cluster units, linked by Cs+ and Ti3+ cations which are located in a distorted hexagonal antiprismatic and octahedral chloride coordination environment, respectively The structures of the compounds ATi[Nb6Cl18] (A = K, In, Tl) were found to be isotypic with RbTi[NbsCl(18)], and their unit cell parameters were refined using X-ray powder diffraction analysis.