Since there are many possible cluster structures adopted by Zr and Hf in solution, we first identified all the relevant clusters that could be present in our system via a systematic search of the Cambridge Structural Database (CSD). This search yielded over 1300 structures containing 3 to 21 Zr or Hf atoms † (including "infinite" structures with repeating subunits) [Figure References: n=3; 36 n=4; n=6; n=7; 73 n=8; 10 n=9; n=11; 71 n=12; n=13; 77 n=17; 50 n=18; 'infinite' structures Initial examination of an in situ XPDF dataset of a linker-free reaction in DFW 65:25:10 solvent [Error! Reference source not found. (c)] revealed that low-r peaks were only experimentally observed in six regions (as illustrated in Figure ). We therefore used this constraint to narrow down the 25 chemically feasible core clusters to five [Figure ], removing those core clusters with peaks outside these regions. We edited all five core cluster models to obtain the Hf (rather than Zr) analogues, in keeping with the composition of our reaction mixtures.