Bimetallic Cu/Ru/Os Complexes: Observation of Conformational Differences Between the Solution Phase and Solid State by Atomic Pair Distribution Function Analysis.

High-energy X-ray scattering and pair distribution function analysis (HEXS/PDF) is a powerful method to reveal the structure of materials lacking long-range order, but is underutilized for molecular complexes in solution. Here we demonstrate the application of HEXS/PDF with 0.26 A resolution to uncover the solution structure of five bimetallic Os(II)/Ru(II)/Cu(I) complexes. HEXS/PDF of each complex in acetonitrile solution confirms the pairwise interactions in the local coordination sphere of each metal center as well as the metal···metal interactions separated by over 12 A. The metal···metal distance detected in solution is compared with that from the crystal structure and molecular models to confirm that distortions to the metal bridging ligand are unique to the solid state. This work presents the first example of observing sub-A conformational difference by direct comparison of solution phase and solid-state structures and shows the potential for HEXS/PDF in the determination of solution structure of single molecules.