“…Since the proposal of penta-graphene, 1 a pentagon-based two-dimensional (2D) carbon allotrope, a family of over 100 pentagon-based 2D materials has been reported with novel physical properties and vast potential applications. 2,3 For instance, a negative Poisson's ratio (NPR) has been found in penta-BN 2 , 4,5 penta-ZnO 2 , 6 and penta-PdSe 2 , 7,8 topological electronic states have been reported in penta-RuS 4 , 9 MoS 2 , 10 and p-PbS 2 , 11 ferromagnetism and antiferromagnetism have been found in penta-MnN 2 , 12 and CoS 2 , 13 ferroelasticity was reported in penta-PdS 2 , 14 piezoelectric responses have been found in penta-BCN, 15,16 penta-CNP 17 and some transition metal-based ternary pentagonal sheets, 18 and second harmonic generation was predicted in penta-ZnS 2 . 19 Meanwhile, considerable effort has been made to synthesize such pentagon-based materials.…”