In MnPS 3 @PEI, PEI has primary, secondary, and tertiary amino groups, probably protonated at pH = 5 in the MnPS 3 @H 2 O suspension where PEI is added. These groups can interact with some of the P 2 S 6 bipyramids through sulfur electron pairs, distorting their vibration, affecting the ν(PS 3 ) signal and the characteristic amine bands (ESI Fig. ). In the MnPS 3 @PVP this capping agent is not expected to present an effective interaction with the nonbonding S electrons. However, it may be able to interact with metallic atoms through the carbonyl groups present. Such interaction is confirmed by the red-shift observed for the carbonyl band of the PVP 23 from 1644 cm -1 to 1632 cm -1 (Fig. ). This interaction could indirectly affect Mn-S bonds and as a result, the P-S stretching.