Phosphide Oxides RE2AuP2O (RE = La, Ce, Pr, Nd): Synthesis, Structure, Chemical Bonding, Magnetism, and 31P and 139La Solid State NMR

Polycrystalline samples of the phosphide oxides RE2AuP2O (RE = La, Ce, Pr, Nd) were obtained from mixtures of the rare earth elements, binary rare earth oxides, gold powder, and red phosphorus in sealed silica tubes. Small single crystals were grown in NaCl/KCl fluxes. The samples were studied by powder X-ray diffraction, and the structures were refined from single crystal diffractometer data: La2AuP2O type, space group C2/m, a = 1515.2(4), b = 424.63(8), c = 999.2(2) pm, β = 130.90(2)°, wR2 = 0.0410, 1050 F2 values for Ce2AuP2O, and a = 1503.6(4), b = 422.77(8), c = 993.0(2) pm, β = 130.88(2)°, wR2 = 0.0401, 1037 F2 values for Pr2AuP2O, and a = 1501.87(5), b = 420.85(5), c = 990.3(3) pm, β = 131.12(1)°, wR2 = 0.0944, 1143 F2 values for Nd2AuP2O with 38 variables per refinement. The structures are composed of [RE2O]4+ polycationic chains of cis-edge-sharing ORE4/2 tetrahedra and polyanionic strands [AuP2]4–, which contain gold in almost trigonal–planar phosphorus coordination by P3– and P24– entities. The isolated phosphorus atoms and the P2 pairs in La2AuP2O could clearly be distinguished by 31P solid state NMR spectroscopy and assigned on the basis of a double quantum NMR technique. Also, the two crystallographically inequivalent La sites could be distinguished by static 139La NMR in conjunction with theoretical electric field gradient calculations. Temperature-dependent magnetic susceptibility measurements show diamagnetic behavior for La2AuP2O. Ce2AuP2O and Pr2AuP2O are Curie–Weiss paramagnets with experimental magnetic moments of 2.35 and 3.48 μB per rare earth atom, respectively. Their solid state 31P MAS NMR spectra are strongly influenced by paramagnetic interactions. Ce2AuP2O orders antiferromagnetically at 13.1(5) K and shows a metamagnetic transition at 11.5 kOe. Pr2AuP2O orders ferromagnetically at 7.0 K.