Fig. outlines 5-step topochemical conversion of the parent Sr2MnO2Cu1.5S2 phase leading to collapse of its copper sulfide layers (See Methods). First reductive Li-Cu exchange was performed following Rutt et al; reaction with n-butylithium extruded metallic copper from, and inserted Li + into, the parent oxysulfide, giving the mixture Sr2MnO2LixS2 (x ~ 1.9) + 1.5 Cu (See Fig. ). The Li-containing material functions as a reactive intermediate to enable metal deintercalation from the sulfide layer. The extruded elemental Cu was then removed using disulfiram (Step 2). The S-S bond of this dithiocarbamate dimer oxidises Cu 0 and the reduced anion chelates Cu 2+ cations (Fig ). After Step 2, Cu 0 metal was no longer evident in the powder diffraction pattern while the Sr2MnO2LixS2 phase exhibited cell contraction, implying partial oxidative Li deintercalation by disulfiram (Fig. ). A second treatment with nbutylithium (Step 3) extruded ca. 0.1 equiv. of Cu 0 metal, suggesting that in Step 2 partial Cu reinsertion to compensate Li deintercalation competes with Cu dissolution giving Sr2MnO2Lix'Cuy'S2 (x' >> y'). Reaction with disulfiram contrasts with the reaction of the Step 1 product with I2 in acetonitrile, a conventional oxidant for chemical deintercalation, which led to Li deintercalation and almost complete Cu reinsertion to restore the parent phase, but no Cu dissolution (Fig. ).