Literature on the relevant properties of the π phases is currently sparse, and the largest n-type carrier concentrations of 4×10 17 reported to date are orders of magnitude lower than we predict are required to achieve high thermoelectric performance. p-type orthorhombic SnS and SnSe have been prepared with n up to 4 × 10 19 cm -1 , but experiments on n-doped SnSe have only achieved 10 19 cm -3 . Our prediction of superior performance in the n-type Pnma Sn and Ge chalcogenides suggests the exploration of strategies for n-type doping the IV-VI chalcogenides would be worthwhile. The structural preferences of the IV-VI chalcogenides can be understood in terms of the activity of the tetrel lone pair driven by the interaction between the tetrel and chalcogen atoms. Generally, the lighter chalcogenides prefer lower-symmetry phases (e.g. SnS/SnSe and GeS/GeSe adopt the orthorhombic Pnma phase), while heavier chalcogenides prefer higher-symmetry phases (e.g. SnTe, GeTe and the Pb chalcogenides adopt the rhombohedral and rocksalt phases). Previous studies have found that π SnS is closer to the convex hull than π SnSe (∆G = 2.3 and 3 kJ mol -1 per F.U. at 300 K). The existence of a direct conversion pathway to the orthorhombic phase has not, to our knowledge, been established, but we have previously considered conversion to the structurally-similar rocksalt phases and obtained energy barriers of 8.5 and 2.2 kJ mol -1 per F.U. for π SnS and SnSe. Based on this, admittedly incomplete, information, we suggest that the π phases might be stabilised by elements that favour the Pnma/R3m-like local geometry over the six-coordinate geometry in the rocksalt phases. This suggests that a SnS/SnSe solid solution could be used to stabilise π-SnSe, or that alloying with GeS/GeSe could be used to stabilise the π phases of both Sn chalcogenides.