Coordination polymers and metal-organic frameworks can be modified by high pressure, according to its effects on the radii of central and ligand atoms. The pressure reduces the ligands' radii, and the coordination number is usually increased. Such transformations of the coordination quite generally conform to the inverse rule of pressure and temperature effects, although the temperature-induced transformations are much less frequently observed. The two-dimensional coordination polymer Cd(APP)NO·NO [APP = 1,4-bis(3-aminopropyl)piperazine] undergoes a pressure-induced isostructural phase transition triggered by a topochemical reaction, yielding Cd(APP)(NO). The transition retains the symmetry of both phases, and their structures have been determined by X-ray diffraction for the single crystals compressed in a diamond-anvil cell. The reaction increases the Cd coordination, from 6-fold in phase I to 7-fold in phase II, where the new Cd-O bond involves an additional nitrate anion in the Cd coordination sphere.

Porous 1,2-bis[2-methyl-5-(pyridyl)-3thienyl] cyclopentene cocrystal with 1,4-diiodotetrafluorobenzene exhibits large negative linear compression correlated with the shape of pores.

Strong strain shuttering ferroelastic crystals that self-heal after releasing the strain has been revealed for a new metal-organic framework Cd(BDC)(AZPY) (BDC=terephthalic acid; AZPY=4,4’-azobispyridine), with the Cd(II) cation hepta-coordinated. It has...

Ta rgeted synthesis of piezoresponsive small molecules and in-depth understanding of their mechanism is of utmost importance for the development of smart devices.T his work reports the synthesis, structure and piezosensitivity of ab ola-amphiphile 1,4-bis(pentyloxy)-2,5-bis(2-pyridineethynyl)-benzene (C5-PPB). Dependingo nt he rate of compression, two different phases in C5-PPB can be generated.T he ambient-pressure aphase is stable up to 0.8 GPa, beyond which it undergoes an isostructural transformation to b-phase, accompanied by ac learly visible elongationo ft he crystal.T his a-to-b phase transitionr equirest he sample to be compressed slowly.W hen quicklyc ompressed, phase a persistst o about 1.5 GPa, beyond which its amorphization starts, accompanied by the appearance of irregular grooves on the largest faces. Mechanical pressure also affectst he optical property of C5-PPB,w hich shows reversible mechanochromism with ag reen to cyan transformation in the emission, associated with a1 5nms hift in the maxima. The conductivity of C5-PPB as ad irect outcome of its crystal packing has also been studied.Development of purely organic p-conjugated oligomers that are light, flexible and external-stimuli responsive is highlydesirable for multifarious applicationsi ns mart devices. [1] Molecules that are capable of responding to external mechanicalf orces [2] are sought after for human-machine or robotic interfaces, sensors, security inks, memory storage, and healthcared evices. [3] In condensed forms like crystals, liquid crystals, or micelles, the