A2VNb6Cl18 (A = Rb, In, Tl):: synthesis, crystal structure and magnetic properties of a new series of quaternary niobium chloride cluster compounds

A new series of quaternary mobium chloride cluster compounds corresponding to the general formula, A(2)VNb(6)Cl(18) (A= Rb, Tl or In), has been prepared in sealed quartz tubes from a mixture containing NbCl5, Nb, VCl3 and RbCl, or In or Tl metal by solid state reactions at 750degreesC. The structure of Tl2VNb6Cl18 was determined using single-crystal X-ray diffraction: Crystal data: rhombohedral, R (3) over bar (No. 148), a = 9.1122(17), c = 25.178(7),Angstrom, V = 1810.5(7) Angstrom(3) and Z = 3. The full-matrix least-squares refinement against F-2 converged to R-1 = 0.0515, wR(2) = 0. 1104 (all data). The structure consists of discrete octahedral cluster units, Cl-6(a)] (4-) V2+ [(Nb6Cl12Cl6a)-Cl-i]linked by V2+ and A(+) cations, located in a 6-coordinated octahedral and 12-coordinated anticubeoctahedral chloride environment, respectively. The intra-cluster bond lengths indicate 16 valence electrons per cluster. Magnetic susceptibility studies show paramagnetic behavior with a magnetic moment of 3.37mu(B) per formula unit. Electrical resistivity measurements indicate a semiconducting behavior. (C) 2002 Published by Elsevier Science (USA).