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 P₄ tetrahedra, have been described. Among these, β-P₄ crystallizes in the space group P1 and γ-P₄ in the space group C2/m. α-P₄ forms soft plastic crystals with a proposed structure in the cubic space group I43m 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-P₄. 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 P2₁2₁2₁ with 29 P₄ tetrahedra in the asymmetric unit. The arrangement resembles the structure of α-Mn, but δ-P₄ differs from α-P₄. DFT calculations show δ-P₄ to be metastable at a similar energy level to that of γ-P₄.