{alpha}-K{sub 4}R{sub 6}I{sub 14}Os (R = La, Pr): A novel iodine-rich structure with a layered network of electron-poor clusters. An incipient delocalized system with metal-like conductivity
The title compounds are obtained from reactions of KI, RI{sub 3}, R, and Os at 750--850 C in sealed Nb or Ta containers. The structure was established by single-crystal X-ray diffraction studies for three samples, La and Pr at 23 C and La at {minus} 100 C. This particular combination of large R, interstitial Z, and halogen results in the highest X:R ratio known among rare-earth-metal cluster halides and an unprecedented structure type. The cluster units are interconnected according to the pattern [(R{sub 6}Os)I{sub 8}{sup i}I{sub 4/2}{sup i-a}I{sub 4/2}{sup a-i}I{sub 2}{sup a}]{sup 4{minus}} in which four R in the waist of each cluster, the Os, and four bridging I{sup i-a,a-i} pairs generate a planar 2D network of geometrically nearly ideal, 16-electron R{sub 6}Os octahedra. This contrasts with the tetragonal compression found for many other 16-e{sup {minus}} examples with the parallel disappearance of Curie-Weiss paramagnetism. Powdered {alpha}-K{sub 4}La{sub 6}I{sub 14}Os exhibits an exceptionally low resistivity for a cluster halide ({approximately} 120 {micro}{Omega}{center{underscore}dot}cm) over 110--280 K and a small paramagnetism over about 35 to {approximately} 250 K associated with a probable Mott-Hubbard state that changes to a temperature-independent (presumably Pauli) paramagnetism above about 300 K. EHTB band calculations show that a significant broadening of the HOMO ({approximately}t{sub 1u}) states takes place in the plane of the intercluster bridging. The unique structure, properties, and band picture for the compound indicate a transition to a delocalized (band) state.
- Research Organization:
- Iowa State Univ., Ames, IA (US)
- Sponsoring Organization:
- National Science Foundation (NSF); USDOE
- OSTI ID:
- 20003341
- Journal Information:
- Inorganic Chemistry, Vol. 38, Issue 17; Other Information: PBD: 23 Aug 1999
- Country of Publication:
- United States
- Language:
- English
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