Crystal structure of the low-temperature form and evolution during the phase transition of the electronic properties of a mixed-valence vanadium oxide inserting quinuclidinium cations

The layered solid (VV3O10)-V-IV-O-V, NC7H14 is obtained either by thermal decomposition of the decavanadate H2V10O28, (NC7H14)(4) or by hydrothermal synthesis in the quaternary system V2O5:HF:quinuclidine:H2O. It undergoes a reversible phase transition between 200 and 230 K evidenced by single-crystal X-ray diffraction, DSC, conductivity, and ESR measurements. The low-temperature two-dimensional form is orthorhombic ( space group P2(1)cn (no. 33)) with lattice parameters a = 11.770(2) Angstrom, b = 18.289(4) Angstrom, c = 19.740(4) Angstrom, V= 4249(3) Angstrom(3). The structure was solved from 4533 reflections (I greater than or equal to 2 sigma(I)) with reliability factors R1(F-0) = 0.0573 and wR2(F-0(2)) = 0.1572. The ordering of the amines in the interlayer space is responsible for the transition and implies some changes in the geometry of the layers. The onset of a partial V-IV/V-V Segregation is evidenced, which could explain the different regimes observed in the ESR and conductivity characteristics above and below the transition.