Colossal Negative Linear Compressibility in Porous Organic Salts

Negative linear compressibility
(NLC) is a common sense violation
(that is, crystal phases expand in one or more directions under hydrostatic
compression). The excellent NLC performance of crystal materials is
intrinsically related to the geometric structure of its skeleton.
Here, we discovered a crystalline porous organic salt (CPOS-1); high-pressure
X-ray diffraction experiments reveal that the CPOS-1 shows colossal
NLC (Kc = −90.7 T Pa–1) behavior along the c axis. This incredible performance
arises from the flexible “supramolecular spring” formed
by the charge-enhanced N–H+···–O–S hydrogen bond interaction between the anionic
sulfonate and the cationic ammonium ion. Furthermore, we reveal the
relationship between this rare NLC behavior and single crystal proton
conductivity using high-pressure electrochemical impedance spectroscopy
(EIS) method. We believe that NLC behavior research on such inexpensive
and readily available porous organic materials is of great significance
for accelerating the research and application of NLC materials, especially
in organic system.