A new polymorph of white phospho­rus at ambient conditions

Phospho­rus exists in several different allotropes: white, red, violet and black. For industrial and academic applications, white phospho­rus is the most important. So far, three polymorphs of white phospho­rus, all consisting of P(4) tetrahedra, have been described. Among these, β-P(4) crystallizes in the space group P 1 and γ-P(4) in the space group C2/m. α-P(4) forms soft plastic crystals with a proposed structure in the cubic space group I 43m with the lattice constant a = 18.51 (3) Å, consisting of 58 rotationally disordered tetrahedra and thus is similar to the structure of α-Mn. Here we present a new polymorph, δ-P(4). It crystallizes as a sixfold twin with the cell dimensions a = 18.302 (2), b = 18.302 (2), c = 36.441 (3) Å in the space group P2(1)2(1)2(1) with 29 P(4) tetrahedra in the asymmetric unit. The arrangement resembles the structure of α-Mn, but δ-P(4) differs from α-P(4). DFT calculations show δ-P(4) to be metastable at a similar energy level to that of γ-P(4).