High pressure behaviour and elastic properties of a dense inorganic-organic framework.

The high pressure behaviour of a cubic dense inorganic-organic framework [DABCOH2(2+)][K(ClO4)3] (DABCOH2(2+) = diazabicyclo[2.2.2]octane-1,4-diium) has been systematically studied via synchrotron X-ray powder diffraction, over the range of 0-3.12 GPa. The framework [DABCOH2(2+)][K(ClO4)3] shows a more rigid response, with a bulk modulus of 30(1) GPa and an axial compressibility of 7.6(4) × 10(-3) GPa(-1), compared with ZIF-8 and the dense hybrid solar cell perovskite CH3NH3PbI3. Density functional theory calculations reveal that the structural change in [DABCOH2(2+)][K(ClO4)3] is attributed to the contraction of the KO12 polyhedra, which consequently results in the rotation of the perchlorate linkers and synergistic movement of the DABCOH2(2+) guest. Further extensive theoretical calculations of full elastic tensors give full mapping of the Young's moduli, shear moduli and Poisson's ratios of [DABCOH2(2+)][K(ClO4)3], which are in the range of 31.6-36.6, 12.3-14.6 GPa and 0.2-0.32, respectively. The Young's and shear moduli of [DABCOH2(2+)][K(ClO4)3] are larger than those of cubic MOF-5, ZIF-8 and CH3NH3PbI3. In addition, the narrow range of Poisson's ratios in [DABCOH2(2+)][K(ClO4)3] indicates its very isotropic nature in response to biaxial stress.