Synthesis and structures of new niobium cluster compounds with pyridinium cations: (PyrH)2[Nb6Cl18]·EtOH (Pyr: pyridine, Et: ethyl) and the cubic modification of (PyrH)2[Nb6Cl18]

Slow crystallization of (PyrH)2[Nb6Cl18] from hot ethanol solution affords triclinic (PyrH)2[Nb6Cl18]·EtOH. Treatment of [Nb6Cl14(H2O)4]·4H2O with pyridine in a methanol solution gives the second title compound, the cubic modification of (PyrH)2[Nb6Cl18]. Both structures were determined by single crystal X-ray diffraction, (PyrH)2[Nb6Cl18]·EtOH: P1¯, a=9.3475(3), b=9.3957(3), c=10.8600(3) Å, α=82.582(1)°, β=78.608(1)°, and γ=78.085(1)°, Z=1, R1(F)/wR2(F2)=0.0254/0.0573, cub.-(PyrH)2[Nb6Cl18]: Fd3¯m, a=19.935(2) Å, Z=8, R1(F)/wR2(F2)=0.0557/0.1796. The cluster compounds contain isolated, molecular [Nb6Cli12Cla6]2− cluster anions with an octahedron of metal atoms edge bridged by chlorido ligands with additional ones on all the six exo positions. These cluster anions are separated by the pyridinium cations and ethanol solvent molecules, respectively. For the cubic modification of (PyrH)2[Nb6Cl18], a structural comparison is given to the known rhombohedral modification using the group–subgroup relations as expressed by a Bärnighausen tree.