Fig. displays the three lowest energy 2 × 2 × 2 TiOF 2 structures, each of which are comprised entirely of cis-Ti-[O 2 F 4 ] sub-units. This local coordination achieves local electroneutrality, in accordance with Pauling's second rule , while also avoiding collinear O-Ti-O subunits. The energy difference between these three low-energy structures is only 12 meV, and all 2×2×2 structures containing only cis-Ti-[O 2 F 4 ] units are within 80 meV of the lowest energy structure. Consequently, our calculations predict that ReO 3 -type TiOF 2 exhibits a preference for polar cis-Ti-[O 2 F 4 ] coordination, but these cis-Ti-[O 2 F 4 ] units expected to adopt a variety of different relative arrangements within the crystal structure, resulting in correlated anion disorder . To further quantify the relationship between the Ti-(O/F) bond lengths and bonding strength, we calculated integrated crystal-orbital Hamilton populations (iCOHPs) for each Ti-(O/F) bond in our DFT dataset, which are plotted against corresponding bond length in Fig. . iCOHP values serve as indicators of bonding strength, with more negative values attributed to stronger and more covalent bonding . Both Ti-O and Ti-F bonds are predicted to become stronger with as the Ti-(O/F) distance decreases. Moreover, both plots of bond strength versus bond length are concave, which indicates that Ti centres with a mix of shorter-than-average and longer-than-average bonds Ti-X bonds have greater net bond strength than Ti centres where all six Ti-X bonds are of equal length. The DFT and cluster-expansion analysis detailed above (Section III C) predicts that ReO 3 -type TiOF 2 exhibits short-range anion order characterised by preferential cis-Ti[O 2 F 4 ] coordination. Our calculations also provide an explanation for this preference: anion configurations that avoid collinear O-Ti-O units allow local distortions from TiX 6 coordination with six equallength Ti-X bonds, resulting in shorter Ti-O (and consequently longer Ti-F) bonds, thereby increasing the net Ti-X bonding.