SYNTHESES AND X-RAY-DIFFRACTION STUDIES OF [N(CH3)4]2BKCL6 AND [N(CH3)4]2ZRCL6 - ABSORPTION-SPECTRUM OF BK4+ IN [N(CH3)4]2BKCL6

[N(CH3)4]2BkCl6 was synthesized from cold, concentrated HCl(aq) using 249Bk (t1/2 = 320 days) separated from 249Cf on the milligram scale. For comparison [N(CH3)4]2ZrCl6 was also synthesized and single crystals were grown. Both compounds were studied by X-ray powder diffraction, and [N(CH3)4]2ZrCl6 was also studied by single-crystal X-ray diffraction. Powder patterns of [N(CH3)4]2BkCl6 have f.c.c. symmetry, a = 13.08(2) angstrom, isostructural with K2PtCl6 and other [N(CH3)4]2MCl6 salts. [N(CH3)4]2ZrCl6 has f.c.c. symmetry, space group Fm3m (disregarding hydrogen positions) with a = 12.882(1) angstrom and d(Zr-Cl) = 2.428(8) angstrom. A transition to lower symmetry was found in [N(CH3)4]2ZrCl6 at -110-degrees-C by Guinier powder diffraction. Optical spectra of Bk4+ in [N(CH3)4]2BkCl6 in KBr and KCl pellets were recorded and interpreted.