P22− and P3− Units in the [Rh8P9]δ− Polyanion of La4Rh8P9

The phosphide La4Rh8P9 was synthesized from the elements in a bismuth flux. The structure was refined from single crystal diffractometer data: space group Cmcm, a = 1303.1(2), b = 1893.2(2), c = 576.70(6) pm, wR2 = 0.0277, 1380 F2 values, 65 variables. The rhodium and phosphorus atoms build up a three-dimensional [Rh8P9] polyanion which leaves larger cages for the three crystallographically independent lanthanum sites. The rhodium atoms have between four and six phosphorus neighbors at Rh−P distance ranging from 229 to 254 pm. Three of the four crystallographically independent phosphorus atoms are isolated (P3− units), while the P4 atoms form dimers with double bond character (208 pm P−P). The P22− diphosphenide units bond side-on to a Rh3 and end-on to four Rh5 atoms. 31P magic angle spinning (MAS) NMR spectroscopy is able to resolve three of the four crystallographically distinct phosphorus sites. The doubly bonded phosphorus site P4 is characterized by an axially symmetric shielding tensor of moderate anisotropy Δσ = σ33 − σiso = 257 ppm. Electronic band structure calculations prove the metallic character and reveal the significant difference between the isolated P3− and the phosphorus atoms of the P22− units. Magnetic susceptibility measurement reveals Pauli paramagnetism.