Metal--metal bonding in reduced scandium halides. Synthesis and characterization of heptascandium decachloride (Sc/sub 7/Cl/sub 10/). A novel metal-chain structure
The reaction of scandium metal with scandium trihalide in a sealed tantalum container under a temperature gradient 880 to 900/sup 0/C results in transport of monocrystals of heptascandium decachloride (ScCl/sub 1/./sub 43/) to the hot zone. The compound crystallizes in the monoclinic space group C2/m with a = 18.620 (7) A, b = 3.5366 (7) A, c = 12.250 (5) A, ..beta.. equals 91.98 (4)/sup 0/, and Z = 2. Full-matrix least-squares refinement of all atoms with anisotropic thermal parameters gave final residuals R = 0.059 and R/sub w/ = 0.072 for 705 independent reflections with 2 theta less than or equal to 50/sup 0/ and I greater than 3 sigma (I). The unique feature of the structure is the presence of infinite chains composed of two parallel chains of scandium octahedra which share a common edge. Chlorine atoms cap all outward facing metal triangles and also bridge (a) to and (b) between isolated Sc(III) metal ions, giving the connectivity description (ScCl/sub /sup 4///sub 2//sup b/Cl/sub /sup 2///sub 3///sup a/)/sub infinity/(Sc/sub 6/Cl/sub 6/Cl/sub /sup 4///sub 3///sup a/)/sub infinity/ where the fractional atoms Cl/sup a/ and Cl/sup b/ provide the bridging functions. The structure is thus intermediate between the single chains of octahedra found in GdCl/sub 1/./sub 5/ and the infinite two-dimensional sheets of edge-shared octahedra in ScCl. Magnetic susceptibility measurements between 79 and 297/sup 0/K (Faraday method) indicate a Curie--Weiss behavior above approximately 120/sup 0/K (..mu.. = 1.04 ..mu../sub B/, THETA = -498/sup 0/K) with evidence of magnetic ordering at T less than 79/sup 0/K. This and a sharp EPR signal at room temperature (g = 1.97) are interpreted in terms of localized, weakly interacting (at 297/sup 0/K) d/sup 1/ configurations for two (of six) particular scandium atoms in the chain. The occurrence of strongly bonded and well-separated metal chains and the physical properties resulting therefrom suggest the phase can be described as a crystalline analogue of a metal fiber composite.
- Research Organization:
- Iowa State Univ., Ames
- OSTI ID:
- 7143553
- Journal Information:
- Inorg. Chem.; (United States), Vol. 16:5
- Country of Publication:
- United States
- Language:
- English
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