The Praseodymium Zinc Arsenide Pr3Zn2As6: Crystallizing with a Vacancy Variant of the HfCuSi2Type Structure

The new compound Pr3Zn2As6has been prepared by reaction of the elemental components in a NaCl–KCl flux. It crystallizes with a very pronounced subcell of the HfCuSi2type structure with two formula units PrZn2/3As2in the tetragonal subcell witha= 400.6(1) pm andc=1019.7(4) pm. The ordered distribution of occupied and unoccupied zinc positions leads to a three times larger cell. This structure was determined from four-circle X-ray diffractometer data of a twinned crystal:Pmmn,a=399.89(9) pm,b=1204.2(3) pm,c=1019.7(4) pm,Z=2,R=0.039 for 2663 structure factors and 39 variable parameters. Chemical bonding in this compound is briefly discussed.