ja511745q_si_002.cif (9.45 kB)
Nb2O2F3: A Reduced Niobium (III/IV) Oxyfluoride with a Complex Structural, Magnetic, and Electronic Phase Transition
dataset
posted on 2015-01-21, 00:00 authored by T. Thao Tran, Melissa Gooch, Bernd Lorenz, Alexander P. Litvinchuk, Maurice
G. Sorolla, Jakoah Brgoch, Paul C. W. Chu, Arnold M. GuloyA new
niobium oxyfluoride, Nb2O2F3, synthesized
through the reaction of Nb, SnO, and SnF2 in Sn flux, within
welded Nb containers, crystallizes in a monoclinic
structure (space group: I2/a; a = 5.7048(1)Å, b = 5.1610(1)Å, c = 12.2285(2)Å, β = 95.751(1)°). It features
[Nb2X10] units (X = O, F), with short (2.5739(1)
Å) Nb–Nb bonds, that are linked through shared O/F vertices
to form a 3D structure configurationally isotypic to ζ-Nb2O5. Nb2O2F3 undergoes
a structural transition at ∼90 K to a triclinic structure (space
group: P1̅; a = 5.1791(5)Å, b = 5.7043(6)Å, c = 6.8911(7)Å,
α = 108.669(3)°, β = 109.922(2)°, γ =
90.332(3)°). The transition is described as a disproportionation
or charge ordering of [Nb2]7+ dimers: (2[Nb2]7+ → [Nb2]6+ + [Nb2]8+), resulting in doubly (2.5000(9) Å) and
singly bonded (2.6560(9) Å) Nb2 dimers. The structural
transition is accompanied by an unusual field-independent “spin-gap-like”
magnetic transition.