PbP7 – a polyphosphide with a three-dimensional [P7]2− network of condensed and P-bridged P6 hexagons
The first lead polyphosphide PbP7 was synthesized from the elements in a lead flux through a low-temperature route. The PbP7 structure was determined from single crystal X-ray diffractometer data: new type, P21/c, a = 970.70(11), b = 673.34(10), c = 1243.89(18) pm, β = 122.55(1)°, wR = 0.0488, 2022 F2 values and 74 variables. PbP7 exhibits a pronounced three-dimensional phosphorus substructure that derives from the modification of black phosphorus: rows of trans-edge-sharing P6 hexagons in chair conformation are condensed via P bridges. Two of the seven crystallographically independent phosphorus atoms have two and five of them have three P neighbours, leading to an electron-precise Zintl-like description Pb2+P−P−P0P0P0P0P0. The P–P distances lie in a small range of 219 to 225 pm, indicating P–P single bond character. The lead atoms fill large cages left by the phosphide substructure. Each lead atom is coordinated to six P atoms (283–333 pm Pb–P) in the form of a half-shell (capped pentagon). The opposite side claims the space for the lead lone pair (L) leading to very long Pb–Pb distances of 473 pm between adjacent P6PbL pairs. Consistent with the crystal structure, 31P magic-angle spinning (MAS) NMR spectra show seven distinct signal components with equal peak areas.