The experimental and refinement details are given in Figure . The crystal structure of D-U anhyd has been deposited in CCDC as no. 2247776. Periodic DFT simulations. Periodic plane-wave DFT calculations were performed with Quantum Espresso 46,47 using GBRV pseudopotentials and vdW-DF-cx exchangecorrelation functional that is well suited for this type of systems. The plane-wave basis set cutoff is 600 eV, and the first Brillouin zone is sampled by the Monkhorst-Pack k-point mesh with a density of 5 Å. Coordinates from experimental XRD were relaxed according to BFGS algorithm, first by keeping cell parameters equal to experimental, and then further relaxed allowing for combined unit cell and positions relaxations. From these two DFT calculations (0 K) minimization, we respectively obtained rigid-cell formation energy: