3 ) and two equivalent out-of-phase tilts along the a and b directions Γ + 4 near-rigid octahedral tilts, so belongs to the a -a -c + (conventionally a + b -b -) octahedral tilt system in the Glazer notation [Fig. ]. Perhaps surprisingly, these very distorted structures thus adopt the most common tilt system for double perovskites, and that the non-standard cooperative perovskite distortions, although common in other molecular perovskite-type frameworks, do not play a significant role. The origin of tilting in both inorganic and molecular perovskite structures is ordinarily driven by the size mismatch between the A-site cation and the pore size of the anionic frameworks. In contrast, Prussian blue structured materials, like these M III [Bi(SCN) 6 ] frameworks, have no A-site cation and the framework is neutral and thus the electrostatic driving force for tilting is weaker. Therefore, although the tendency towards higher density structures is still present, the size of the tilts is driven largely by the geometry of ligand bonding: the M-N-C bonds are approximately linear (ω ≈ 180 • ) and the M'-S-C bonds are bent (θ ≈ 100 • ) [Fig. ]. The linear M-N-C angle, stabilised by the ligand field of the transition metal, means that the M(NCS) 6 unit behaves as a larger rigid octahedron, and so the structure can be described using conventional tilts. This is also borne out by symmetry analysis of the only other examples of perovskite-derived thiocyanate-frameworks: (NH 4 ) 2 Ni[Cd(SCN) 6 ], with Ni(NCS) 6 octahedra, also belongs to the conventional a + b -b -tilt system whereas CsCd(SCN) 3 , with more flexible Cd(NCS) 6 octahedra, permits Cd-N-C bond angles (as small as 116.5 • ) and so contains significantly more complex cooperative distortions, including unconventional tilts. The origin of the tilts in the molecular orbitals of the thiocyanate ligand also explains their magnitudes. The size of a tilt can be most straight-forwardly quantified by the angle between the axes of the octahedron and the pseudo-cubic unit cell axes [Fig. is nearly linear, the sum of the tilts of the BiS 6 and MN 6 octahedra will be determined principally by the size of the Bi-S-C bond angle (i.e. Θ + Ω ≈ 180θ ). The scale of the octahedral tilts in NCS perovskites is therefore set by the bent Bi-SCN bonding which is due to the shapes of the frontier molecular orbitals of the SCN -ligand. The tilt-angles are therefore likely to be only weakly dependent on temperature, and so octahedral-tilt driven phase transitions are not likely to be common in this series of compounds.