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Title: Charge Disproportionation in Tetragonal La 2MoO 5 , a Small Band Gap Semiconductor Influenced by Direct Mo–Mo Bonding

The structure of the novel compound La 2MoO 5 has been solved from powder X-ray and neutron diffraction data and belongs to the tetragonal space group P4/m (no. 83) with a = 12.6847(3) Å and c = 6.0568(2) Å and with Z = 8. It consists of equal proportions of bioctahedral (Mo 2O 10) and square prismatic (Mo 2O 8) dimers, both of which contain direct Mo-Mo bonds and are arranged in 1D chains. The Mo-Mo bond length in the Mo 2O 10dimers is 2.684(8) Å, while there are two types of Mo 2O 8 dimers with Mo-Mo bonds lengths of 2.22(2) and 2.28(2) Å. Although the average Mo oxidation state in La 2MoO 5 is 4+, the very different Mo-Mo distances reflect the fact that the Mo 2O 10 dimers contain only Mo5+ (d(1)), while the prismatic Mo2O8 dimers only contain Mo 3+ (d 3), a result directly confirmed by density function theory calculations. This is due to the complete disproportionation of Mo 4+, a phenomenon which has not previously been observed in solid-state compounds. La 2MoO 5 is diamagnetic, behavior which is not expected for a nonmetallic transition-metal oxide whose cation sites have an odd number of d-electrons.more » The resistivity displays the Arrhenius-type activated behavior expected for a semiconductor with a band gap of 0.5 eV, exhibiting an unusually small transport gap relative to other diamagnetic oxides. Diffuse reflectance studies indicate that La 2MoO 5 is a rare example of a stable oxide semiconductor with strong infrared absorbance. Lastly, we show that the d-orbital splitting associated with the Mo 2O 8 and Mo 2O 10 dimeric units can be rationalized using simple molecular orbital bonding concepts.« less
Authors:
 [1] ;  [2] ;  [3] ;  [2] ;  [4]
  1. Stony Brook Univ., NY (United States). Dept. of Chemistry
  2. Brookhaven National Lab. (BNL), Upton, NY (United States). Center for Functional Nanomaterials (CFN)
  3. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Spallation Neutron Source (SNS)
  4. Stony Brook Univ., NY (United States). Dept. of Chemistry; Brookhaven National Lab. (BNL), Upton, NY (United States). Dept. of Chemistry
Publication Date:
OSTI Identifier:
1261409
Grant/Contract Number:
AC05-00OR22725; DMR-095564; AC02-06CH11357; AC02-98CH10886.
Type:
Accepted Manuscript
Journal Name:
Journal of the American Chemical Society
Additional Journal Information:
Journal Volume: 137; Journal Issue: 3; Journal ID: ISSN 0002-7863
Publisher:
American Chemical Society (ACS)
Research Org:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Spallation Neutron Source (SNS)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Metal-metal bonding; small band gap oxide semiconductor; charge disproportionation; infrared absorption; structure solution from powder diffraction data; 1D chains; edge-sharing bioctahedra; square prisms