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, beta-P-4 crystallizes in the space group P (1) over bar and gamma-P4 in the space group C2/m. alpha-P-4 forms soft plastic crystals with a proposed structure in the cubic space group I (4) over bar 3m with the lattice constant a = 18.51 (3) angstrom, consisting of 58 rotationally disordered tetrahedra and thus is similar to the structure of alpha-Mn. Here we present a new polymorph, delta-P-4. It crystallizes as a sixfold twin with the cell dimensions a = 18.302 (2), b = 18.302 (2), c = 36.441 (3) angstrom 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 alpha-Mn, but delta-P-4 differs from alpha-P-4. DFT calculations show delta-P-4 to be metastable at a similar energy level to that of gamma-P-4.