Crystal structures of NaNiIO6, NaMnIO6, and KMnIO6

NaNiIO6 (a = 4.962, c = 5.148 A, space group P312) is shown from X-ray powder patterns to be isostructural with trigonal KNiIO6. Approximate coordinates for the oxygen atoms are given. NaMnIO6 (a = 4.972, c = 5.136 A) and KMnIO6 (a = 5.009, c = 6.000 A) are probably also isostructural but the broadening of the X-ray powder lines in these compounds makes a complete analysis impossible. Powder patterns for all three compounds are given.