Distorted phosphorus and copper square-planar layers in LaCu1+xP2 and LaCu4P3: synthesis, crystal structure, and...

Two new lanthanum copper phosphides, LaCu(1+x)P(2) and LaCu(4)P(3), were synthesized from elements. Their crystal structures were determined by means of single-crystal X-ray diffraction. LaCu(1+x)P(2) crystallizes in a complex crystal structure, a derivative of the HfCuSi(2) structure type, in the space group Cmmm (No. 65) with unit cell parameters of a = 5.564(3) Å, b = 19.96(1) Å, c = 5.563(3) Å, and Z = 8. Its crystal structure features disordered Cu(2x)P(2) layers alternated with fully ordered PbO-like Cu(2)P(2) layers. The Cu-P layers are separated by La counter-cations. The Cu(2x)P(2) layers are composed of rectangular P(4) polyphosphide rings connected by partially occupied Cu atoms. Investigations of the electrical resistivity and Seebeck thermopower for LaCu(1+x)P(2) reveal metallic-type behavior with holes as the main charge carriers. LaCu(1+x)P(2) exhibits unexpectedly low thermal conductivity presumably because of disorder in the Cu(2x)P(2) layers. LaCu(4)P(3) crystallizes in a new structure type, in the tetragonal space group P4/nmm (No. 129) with unit cell parameters of a = 5.788(2) Å, c = 7.353(2) Å, and Z = 2. Its crystal structure features distorted square nets of Cu atoms within the Cu(4)P(3) slabs. Electron localization function analysis indicates that both P atoms in LaCu(4)P(3) have 1 + 4 coordination involving multicenter Cu-P bonding. According to the density of states and band structure, LaCu(4)P(3) is predicted to be a metallic conductor.