Compounds combining Cu(I) and early transition-metal cations have attracted much attention as small-bandgap semiconductors. However, synthetic progress and new discoveries in these systems have been inhibited by their limited stability. Two new Cu(I)-molybdovanadates and one new Cu(I)-tungstovanadate have been synthesized in the Cu(I)-V(V)-M(VI)-O (M = Mo, W) systems, CuVMoO6 (1), Cu1.51(1)V3.57(1)Mo0.43(1)O11 (2) and Cu1.59(1)V3.52(1)W0.48(1)O11 (3). Their structures were characterized by single crystal X-ray diffraction to contain layers of distorted VO6/MO6 octahedra with their mixed occupancy driven by the similar atomic radii of the early transition-metal cations. Interlayer sites are occupied by uncommon octahedrally-coordinated Cu, and in 2 and 3 by ~25-30% occupancy of distorted tetrahedral sites. Electronic structure Calculations show that while 1 is stable versus binary oxides, the CuVWO6 analogue is not stable and could not be synthesized. The isostructural compounds, 2 and 3, also exhibited greater stability when the CuO4 occupied sites are directly bridged to the VO6 octahedra rather than the MoO6/WO6 octahedra. A small optical bandgap of ~0.8 eV was measured for 1, with 2 and 3 being undetectable and calculated to be semi-metals. Thus, these results provide deeper insights into the energetic driving forces underlying the successful synthesis of Cu(I)-containing oxides.
Mongkhonratanachai et al. (Fri,) studied this question.