Abstract

New MNb₆Cl₁₂O₂ (M = Rb, Cs) oxychlorides have been synthesized from MCl, Nb₂O₅, NbCl₅ and Nb, heated at 650 °C. The structure of CsNb₆Cl₁₂O₂ has been determined by single-crystal X-ray diffraction. It crystallizes in the monoclinic system (a = 6.807(3) Å, b = 11.714(2) Å, c = 12.665(5) Å, β = 101.60(2)°, V = 989.2(6) Å³ and Z = 2) with the P2₁/c space group. The structure is built from [(Nb₆Clⁱ₁₀Oⁱ₂)O^a₂Cl^a₄] units interconnected by O^i–a, O^a–i ligands in one dimension, giving chains of units with short Nb–Nb intercluster distances (3.345(2) Å). These chains are linked together along the two other dimensions by Cl^a–a ligands, which build voids in which the caesium atoms are randomly distributed. Thus, the developed formula of the compounds can be written: M[Nb₆Clⁱ₁₀O^i–a_2/2)O^a–i_2/2Cl^a–a_4/2]. These new oxychlorides exhibit 15 valence electrons per Nb₆ cluster.