P2(2-) and P(3-) units in the [Rh8P9]δ- polyanion of La4Rh8P9.

Pfannenschmidt U, Johrendt D, Behrends F, Eckert H, Eul M, Pöttgen R

Abstract

The phosphide La(4)Rh(8)P(9) 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 F(2) values, 65 variables. The rhodium and phosphorus atoms build up a three-dimensional [Rh(8)P(9)] 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 (P(3-) units), while the P4 atoms form dimers with double bond character (208 pm P-P). The P(2)(2-) diphosphenide units bond side-on to a Rh3 and end-on to four Rh5 atoms. (31)P 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 = σ(33) - σ(iso) = 257 ppm. Electronic band structure calculations prove the metallic character and reveal the significant difference between the isolated P(3-) and the phosphorus atoms of the P(2)(2-) units. Magnetic susceptibility measurement reveals Pauli paramagnetism.