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.
