The scarcity of NCS-perovskites has thus far prevented investigation of the relationship between cation size and tilts. We find, contrary to simple geometric arguments, that the average size of the NiN 6 octahedral tilt (measured by the N-Ni-Bi angle) and the BiS 6 tilt ( S-Bi-Ni) change very little for these four compounds from the parent M[Bi(SCN) 6 ] frameworks. This conforms to the general finding that the metal-thiocyanate bond-angles do not vary in NCS-perovskites and that guest-framework interactions exert only second-order effects. Compound 4 crystallises with both A-and M-site vacancies, suggesting that there is a maximum average size of A-site cation that can be incorporated within the {Ni[Bi(SCN) 6 ]} -framework and providing further evidence of the ease of formation of [Bi(SCN) 6 ] 3 -vacancies in these materials. The tolerance factor therefore may provide a useful upper bound on cation size for NCS-perovskites (the lower bound not being meaningful due to the variety of ReO 3 structure NCS-frameworks), but we have not found it to be predictive of the tilts or A-site ordering-just as for other molecular perovskites.