Crystallographic studies of some transuranic trihalides: 239PuCl 3, 244CmBr 3, 249BkBr 3 and 249CfBr 3

Abstract

Single-crystal X-ray diffraction methods were used to refine the structures of PuCl 3, CmBr 3, and CfBr 3. In PuCl 3 (UCl 3-type) the Pu ion has nine Cl-ion neighbors, three at 2·919(1) Å and six at 2·886(1) Å. A radius of 0·995 Å was derived for the six-coordinated Pu 3+ ion. In CmBr 3 (PuBr 3-type) the eight-coordinated Cm ion has two Br ions at 2·865(6) Å, four at 2·983(4) Å, and two at 3·137(4) Å. Californium tribromide was shown to crystallize in both the AlCl 3- and FeCl 3-type structures. In the former type, the Cf ion is six coordinated and the three independent CfBr bond lenghts are 2·795(9) Å, 2·827(11) Å and 2·828(8) Å. Berkelium tribromide was prepared and shown by powder X-ray diffraction to exhibit the AlCl 3-, PuBr 3-, and possibly FeCl 3-type structures. The new findings on CfBr 3 and BkBr 3 were used to produce a more complete description of the structural relationships among the lanthanide and actinide tribromides.