New condensed cluster structure with triple metal layers: La{sub 2}INi{sub 2} and La{sub 2}ICu{sub 2}. Synthesis, structure, and bonding
- Iowa State Univ., Ames, IA (United States). Dept. of Chemistry
Syntheses of the title compounds result from appropriate reactions of the elements and LaI{sub 3} in sealed Nb or Ta containers at 800 C. These exhibit a new structural type with an unusual metal-rich layered structure, detailed for La{sub 2}INi{sub 2} by single-crystal X-ray diffraction. This is related to the Gd{sub 2}IFe{sub 2}-type structure known for La{sub 2}IZ{sub 2} for Z = Fe, Co, and others. Both structures contain AlB{sub 2}-like slabs, namely, graphite-like Z{sub 2} (Z = Ni, Fe) layers between eclipsed pairs of La layers, but these are instead separated by single iodine layers. The La{sub 2}INi{sub 2} structure differs in that the iodine positions along {rvec c} project onto only one Z position instead of both and the cell is half as large. An additional set of very weak reflections and streaks revealed in widely varying amounts by precession photographs suggests a superstructure in c or intergrowths by small amounts of disordered components, but a reasonable model could not be derived beyond some possible short-range disordering in the iodine layers. Comparisons of La{sub 2}INi{sub 2} with La{sub 2}IFe{sub 2} in terms of electronic band structures show that filling of antibonding states occurs in the Ni layers. Integrated overlap populations in the Fe vs Ni compounds show corresponding decreases for Z-Z and La-Z bonding and a smaller strengthening of La-La bonding in the layers, while the a lattice parameter increases and the trigonal prismatic La{sub 6}Z units decrease in height. These conflicts are reflected in the Z-layer puckering and the doubled c dimension found in La{sub 2}IFe{sub 2} and other phases with the Gd{sub 2}IFe{sub 2}-type structure.
- Sponsoring Organization:
- National Science Foundation, Washington, DC (United States); USDOE, Washington, DC (United States)
- OSTI ID:
- 642405
- Journal Information:
- Inorganic Chemistry, Vol. 37, Issue 13; Other Information: PBD: 29 Jun 1998
- Country of Publication:
- United States
- Language:
- English
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