Improved Topotactic Reactions for Maximizing Organic Coverage of Methyl Germanane

The topotactic transformation of Zintl phases such as CaGe 2 into organic-terminated germanium graphane analogues using haloalkanes is a powerful route for generating new 2D optoelectronic and spintronic building blocks. However, uniform ligand coverage is necessary for optimizing the properties and stability of these single-atom-thick frameworks. Here, we compare the effectiveness of different topochemical methods to maximize methyl-termination in GeCH 3 . We show that a previously developed CH 3 I/H 2 O phase transfer route produces a small percentage of partially oxidized germanane. The partially oxidized termination is readily removed upon HCl treatment, which leads to Ge–Cl termination, but rapidly reoxidizes after exposure to the ambient atmosphere. We then show that a one-pot route with CH 3 I in distilled CH 3 CN solvent and at least six equivalents of H 2 O results in no oxidation. The GeCH 3 prepared from this one-pot route also has an increased −CH 3 /–H ratio of termination from ∼90:10 to ∼95:5, is air-stable, has greater thermal stability, has a sharper absorption onset, and has more narrow band edge photoluminescence, all of which are signatures of a less defective semiconductor.