NA3AS REVISITED - HIGH-PRESSURE SYNTHESIS OF SINGLE-CRYSTALS AND STRUCTURE REFINEMENT

Single crystals of Na3As have been obtained from the elements by high- pressure-high-temperature reaction in a modified Belt-type apparatus. The compound crystallizes hexagonally, space group P6(3)cm, with a=8.7 838(8) Angstrom, c=8.9990(12) Angstrom, c/a=1.0245 and Z=6. The struct ure refinement (R=0.027, R(w)=0.017 for 303 absorption-corrected uniqu e reflections) shows unequivocally that Na3As is isostructural with Cu 3P and that the structure models proposed by Brauer and Zintl (referre d to as ''Na3As type'' in the literature, space group P6(3)/mmc) and M ansmann (anti-LaF3, type, space group P (3) over bar cl) are wrong.