“…Layered crystal structure of (a) (C n H 2 n +1 NH 3 ) 2 PbI 4 ( n = 18) with bulk alkylammonium cation. Reproduced with permission, Copyright 2010, American Chemical Society, (b) (C 6 H 11 NH 3 ) 2 PbBr 4 with cycloalkylammonium cation, Reproduced with permission, Copyright 2009, the Royal Society of Chemistry, (c) (NH 4 ) 3 Sb 2 I 9 single crystal with trivalent antimony cation, Reproduced with permission, Copyright 2017, Wiley‐VCH, (d) MA 2 CuCl 2 Br 2 with divalent copper cation, Reproduced with permission, Copyright 2015, American Chemical Society, (e) (C 6 H 5 C 2 H 4 NH 3 ) 2 GeI 4 with divalent germanium cation, Reproduced with permission, Copyright 2017, American Chemical Society, (f) MA 2 Pb(SCN) 2 I 2 with thiocyanate anion, Reproduced with permission, Copyright 2016, American Chemical Society.…”