Crystal Structures and Magnetic Properties of Rare-Earth Ultraphosphates, RP5O14 (R=La, Nd, Sm, Eu, Gd)

The single-crystal X-ray structures of lanthanum, europium, and gadolinium ultraphosphate, RP₅O₁₄ (R=rare-earth) are reported herein monoclinic, P2₁/c, a=8.8206(1), 8.7491(1), 8.7493(1) Å, b=9.1196(2), 8.9327(1), 8.9189(1) Å, c= 13.1714(2), 12.9768(2), 12.9717(1) Å, β=90.661(1), 90.534(1), 90.6682(3)°, respectively; Z=4; R1=0.0250, 0.0346, 0.0270, respectively]. The structures are all type (I) compounds as classified by Bagieu-Beucher and Tranqui Bull. Soc. Fr. Miner. Cryst. 93, 505 (1970)]. The minimum R…R separations are compared with all other structural reports of lanthanide ultraphosphates. Type (I) compounds have the lowest minimum R…R separation, which decreases with atomic number and appears not to perturb the optical properties of any rare-earth ultraphosphate. In each case, R is surrounded exclusively by eight oxygen atoms that form a distorted square antiprism. A P–O network holds together the three-dimensional structure. The magnetic susceptibilities of neodymium, samarium, and gadolinium ultraphosphate as a function of temperature are also reported along with corresponding magnetization measurements. All compounds exhibit a paramagnetic response, following Curie's law except in the regions where crystal field splittings are significant.