Discovery of γ-MnP4 and the Polymorphism of Manganese Tetraphosphide

A new polymorph of MnP4 was prepared by reaction of the elements via chemical vapor transport with iodine as transporting agent. The crystal structure was refined using single-crystal diffraction data (space group Cc, no. 9, a = 5.1049(8) A, b = 10.540(2) A, c = 10.875(2) A, β = 93.80(2)°). The phase is called γ-MnP4 as it is isostructural with γ-FeP4. It is the fourth reported binary polymorph in the MnP4 system, all of which are stacking variants of nets built with manganese and phosphorus atoms. In γ-MnP4, there are two Mn–Mn distances (2.93 and 3.72 A) arising from a Peierls-like distortion effectively forming Mn2 dumbbells in the structure. Magnetic and electrical conductivity measurements show diamagnetism and a small anisotropic band gap (100–200 meV) with significantly enhanced conductivity along the crystallographic a axis. Calculations of the electronic and vibrational (phonon) structures show the P–P and Mn–P bonds within the nets are mainly responsible for the stability of the phase. The simil...