# ZIF-75 under Pressure: Negative Linear Compressibility and Pressure-Induced Instability
###### Abstract  
The behavior of the crystal structure of the zeolitic imidazolate framework ZIF-75 under pressure was studied by means of periodic density functional theory methods. Experimentally, it was shown that this material is tetragonal, space group A1/_a_ at room temperature. However, according to the calculations, at zero temperature this material is monoclinic, space group C2/_c_. Irrespective of the symmetry of the material, the results show that ZIF-75 exhibits a negative linear compressibility effect and is unstable under relatively small applied pressures of the order of 0.1 GPa.  
zeolitic imidazolate frameworks; ZIF-75; pressure-induced instability; negative linear compressibility; periodic density functional theory +
Footnote †: _Scienced Journal of Applied Sciences_
practical importance. The pressure-induced amorphization in ZIF-8 has long been investigated [11; 29; 30; 32; 38; 44], and the detection of pressure-induced phase transitions and amorphizations in other ZIF materials could be extremely interesting. Additional potential applications for microporous materials are possible because these materials frequently appear to exhibit the negative linear compressibility [67; 68; 69; 70; 71; 72; 73; 74; 75; 76; 77; 78; 79; 80; 81; 82; 83] and negative Poisson's ratio [84; 81; 85; 86; 87] phenomena. These phenomena [88; 89; 90; 91] have multiple potential applications in the development of ultrasensitive pressure-sensing devices [88; 92], pressure-driven actuators [92; 93], optical telecommunication cables [88], artificial muscles [94], and body armor [92; 95], as well as sound attenuation [96], superconductivity modulation [97], ferroelectric enhancement [88], and transmission stabilization [98]. However, for the evaluation of the suitability of these compounds for practical, specific applications, the behavior of their structures under the effect of pressure must be investigated. The study of the mechanical properties of microporous compounds has been the subject of a large amount of research in recent decades [29; 30; 31; 32; 33; 34; 35; 36; 37; 38; 39; 40; 41; 42; 43; 44; 45; 46; 47; 48; 49; 50; 51; 52; 53; 54; 55; 56; 57; 58; 59; 60; 61; 62; 63; 64; 65; 67; 68; 69; 70; 71; 72; 73; 74; 75; 76; 77; 78; 79; 80; 81; 82; 83; 86; 87]. The first principles solid-state methodology have been satisfactorily applied for this purpose and have enhanced our knowledge of the mechanical properties of these materials since they give access to the full tensorial elasticity of these materials [34; 35; 36; 37; 38; 39; 40; 41; 42; 43; 44; 45; 46; 47; 48; 49; 50; 51; 52; 53; 54; 55; 56; 57; 58; 59; 60; 61; 62; 63; 64; 65; 66; 67; 68; 69; 70; 71; 72; 73; 74; 75; 76; 77; 78; 79; 80; 81; 82; 83; 86; 87]. The results obtained using the _state-of-the-art_ theoretical methodology are consistently in agreement with the experiment, even for the theoretical study of complex anomalous negative mechanical phenomena [81; 82; 83; 83; 84; 85; 86; 87] and for crystal structure determination [109; 110; 111; 112; 113]. For example, the negative area compressibility of silver oxalate, predicted using first-principles methods [107], was recently experimentally verified [108]. The ZIF material, ZIF-75, was synthetized for the first time by [PERSON] et al. [2]. Its structure shows the presence of large structural channels; therefore, it should be extremely useful in various applications due to the large pore space and accessible surface. However, as far as we know, it has not been used in practical applications and its behavior under pressure has not been investigated.