NEW TERNARY AND QUATERNARY TRANSITION-METAL SELENIDES: SYNTHESES AND CHARACTERIZATION.

New ternary and quaternary transition-metal selenides have resulted from substitutional chemistry of the phase Nb//2Pd//3Se//8 and examination of the system Nb/Pd/Se. The structures of the phases Ta//2Pd//3Se//8, Co//2Ta//4PdSe//1//2, and Nb//2Pd//0//. //7//1Se//5 have been established through single-crystal X-ray methods. The compound Ta//2Pd//3Se//8 forms in space group Pbam with two formula units in a cell of dimensions a equals 15. 152(2), b equals 10. 631(2), and c equals 3. 540(1) A. This material is isostructural with Nb//2Pd//3Se//8. The compound Co//2Ta//4PdSe//1//2 forms in space group C2/m with two formula units in a cell of dimensions a equals 12. 951(3), b equals 3. 413(1), c equals 19. 277(5)A, and beta equals 110. 37(2) degree .