Single crystal X-ray diffraction (SCXRD) at 100 and 300 K was used to determine the structure of all perovskite materials. All compounds in the [A]Ni(C2N3)3 series crystallise with the targeted AMX3 perovskite structure (Fig. ). and Fig. ). To quantify the extent of network distortions across the series, we have applied an established group theoretical analysis to SCXRD data of 300 K for all compounds. In this approach, the structures are first simplified to the underlying octahedral network and subsequently compared to an idealised cubic parent network. By using ISODISTORT, the active distortions are then identified and described via their irreducible representation and amplitude. The latter enables the calculation of the overall parent-cell normalised distortion amplitude of the network (Ap), providing a rigorous measure for network distortions across our series, see Table for Ap values of the different compounds at 300 K and SI for further tilt analysis details (S-69 and Table -S24).