La3Cu4P4O2 and La5Cu4P4O4Cl2: synthesis, structure and 31P solid state NMR spectroscopy

The phosphide oxides La3Cu4P4O2 and La5Cu4P4O4Cl2 were synthesized from lanthanum, copper(I) oxide, red phosphorus, and lanthanum(III) chloride through a ceramic technique. Single crystals can be grown in a NaCl/KCl flux. Both structures were refined from single crystal X-ray diffractometer data: I4/mmm, a = 403.89(4), c = 2681.7(3) pm, wR2 = 0.0660, 269 F-2 values, 19 variables for La3Cu4P4O2 and a = 407.52(5), c = 4056.8(7) pm, wR2 = 0.0905, 426 F-2 values, 27 variables for La5Cu4P4O4Cl2. Refinement of the occupancy parameters revealed full occupancy for the oxygen sites in both compounds. The structures are composed of cationic (La2O2)(2+) layers and covalently bonded (Cu4P4)(5-) polyanionic layers with metallic characteristics, and an additional La3+ between two adjacent (Cu4P4)(5-) layers. The structure of La5Cu4P4O4Cl2 comprises two additional LaOCl slabs per unit cell. Temperature-dependent magnetic susceptibility studies revealed Pauli paramagnetism. The phosphide substructure of La3Cu4P4O2 was studied by P-31 solid state NMR spectroscopy. By using a suitable dipolar re-coupling approach the two distinct resonances belonging to the P-2(4-) and the P3- units could be identified.