Electronic fine tuning of the structures of reduced rare-earth metal halides

Electronic band-structure calculations on Pr3I3Ru and Y3I3Ru have been perf ormed in order to analyze the large structural differences found in these i soelectronic compounds. These constitute two structural extremes within the family of monoclinic RE3I3Ru phases (RE = rare-earth metal) that exhibit d istortions ranging from one-dimensional double chains of trans-edge-sharing octahedra (bioctahedral chains, BOH) to one-dimensional chains of trans-ed ge-sharing square pyramidal units bonded base to base (bisquare pyramidal c hains, BSP). The structure of La3I3Ru was established by single-crystal X-r ay diffraction (monoclinic, P2(1)/m, Z = 4, a = 9.343(1) Angstrom, b = 4.34 69(8) Angstrom ,c = 12.196(3) Angstrom, beta = 93.42(2)degrees) and found t o be isomorphous with the BOH Pr3I3Ru. It is determined thar the structural variation in this RE(3)I(3)Z family of materials depends largely on the di fferences in orbital energies between the corresponding rare-earth metal an d the interstitial. These bonding considerations can be generalized to acco unt for structural variations in a variety of other rare-earth halides as w ell as several group 4 or 5 reduced metal halide cluster phases.