DIMORPHIC THNI2P2 WITH BACU2S2 AND CABE2GE2 TYPE-STRUCTURE

Two modifications of ThNi2P2 were prepared in a tin flux at 850 degree s C (alpha-ThNi2P2) and 1000 degrees C (beta-ThNi2P2). The crystal str uctures of both modifications were refined from single-crystal X-ray d ata, alpha-ThNi2P2 (BaCu2S2 type structure): Pnma, n = 819.69(5). b = 394.28(3), c = 981.54(7) pm, R = 0.028 for 32 variables and 654 struct ure factors; beta-ThNi2P2 (CaBe2Ge2 type structure): P4/nmm, a = 408.5 (1), c = 908.0(3) pm, R = 0.033 for 15 variable parameters and 261 F v alues. Although the two structures are closely related, they can be tr ansformed into each other only by a reconstructive phase transformatio n. The differences and similarities of the two structures are discusse d. The high temperature form has higher symmetry, a smaller number of variable positional parameters, and a tendency for higher coordination numbers.