falling to zero around 36 Å. The longest distance maximum is much more prominent in this molecule than for [2(1B)6], [2(1C)6] and [2(1D)6]. An attempt was made to use the molecular geometries adopted in the crystal structure as a starting point to calculate theoretical SAXS data for comparison. However, the experimental SAXS data for each of the [7]rotaxanes are not consistent with the conformers adopted in the crystal (Figure ). Conformational changes therefore likely to contribute to the differences in the theoretical and experimental results. For these static conformations the SAXS spectrum and its corresponding electron pair-pair distribution function P(r), were then calculated for each of the four [7]rotaxanes (Figures ). Each of the conformations may be found in solution, but due to steric hinderance, have relatively little freedom to interconvert between conformers without dissociating so to do. Based on the agreement between these theoretical SAXS data and the experiment, a single conformer was chosen for each [7]rotaxane as the basis for a molecular dynamics simulation (MDS). Figure shows a comparison of the experimental and theoretical SAXS data for each of the [7]rotaxanes after the MDS step, and in each case the experimental SAXS and the SAXS calculated for MD averaged structure match well. Calculations on the low energy static conformers are less consistent with the experimental observations as the electron distribution is significantly higher at certain distances. These extra peaks are averaged in the MD and experimental SAXS data. As there is little freedom to interconvert between each of the low energy conformations without dissociation, each conformer from which MD simulations were performed has been compared to the crystal structures (Figure ). Significant curvature of threads within the crystal is less likely than in solution due to favourable intermolecular packing interactions between [7]rotaxanes. For this reason, each calculated conformer contains shorter {Cr7Ni} -{Cr7Ni} distances ( Conformational flexibility of the thread leads to large differences in the angles between mean planes of 1X and 2 when comparing the MDS with those observed in the crystal (Tables and). The angle of pyridyl coordination to the {Ni12} plane is consistent in the MDS and differs very little from those measured in the crystal structure (Table ).