Syntheses and Crystal Structures of the Cyclotriphosphate Hydrates Nd(P 3 O 9 )·3H 2 O, Nd(P 3 O 9 )·4.5H 2 O, RE (P 3 O 9 )·5H 2 O ( RE = Pr, Nd), and Na 3 RE (P 3 O 9 ) 2 ·6H 2 O ( RE = Pr, Nd)

Several rare‐earth cyclotriphosphate hydrates were obtained from mixtures of sodium cyclotriphosphates and the respective rare‐earth chlorides. Nd(P 3 O 9 ) · 3H 2 O [ P $\bar{6}$ , Z = 3, a = 677.90(9), c = 608.67(9) pm, R 1 = 0.016, wR 2 = 0.038, 312 data, 36 parameters] was obtained by a solid state reaction and is isotypic with respective rare‐earth phosphate hydrates, while all the others adopt new structure types. Nd(P 3 O 9 ) · 4.5H 2 O [ C 2/ c , Z = 8, a = 1644.6(3), b = 756.11(15), c = 1856.1(4) pm, β = 97.25(3)°, R 1 = 0.032, wR 2 = 0.081, 1763 data, 194 parameters], Nd(P 3 O 9 ) · 5H 2 O [ P 2 1 / c , Z = 4, a = 773.75(15), b = 1149.1(2), c = 1394.9(3) pm, β = 106.07(3)°, R 1 = 0.042, wR 2 = 0.082, 1338 data, 194 parameters], Pr(P 3 O 9 ) · 5H 2 O [ P $\bar{1}$ , Z = 2, a = 745.64(15), b = 889.07(18), c = 934.55(19) pm, α = 79.00(3), β = 80.25(3), γ = 66.48(3), R 1 = 0.059, wR 2 = 0.089, 1468 data, 193 parameters], Na 3 Nd(P 3 O 9 ) 2 · 6H 2 O [ P 2 1 / n , Z = 4, a = 1059.78(18), b = 1207.25(15), c = 1645.7(4) pm, β = 99.742(17), R 1 = 0.047, wR 2 = 0.119, 1109 data, 351 parameters] and Na 3 Pr(P 3 O 9 ) 2 · 6H 2 O [ P 2 1 / n , Z = 4, a = 1061.42(16), b = 1209.0(2), c = 1635.5(3) pm, β = 99.841(13), R 1 = 0.035, wR 2 = 0.062, 1323 data, 350 parameters] were obtained by careful crystallization at room temperature. A thorough structure discussion is given. The infrared spectrum of Nd(P 3 O 9 ) · 4.5H 2 O is also reported.