PbP7 – a polyphosphide with a three-dimensional [P7]2− network of condensed and P-bridged P6 hexagons

Abstract

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.