On the giant deformation and ferroelectricity of guanidinium nitrate

The extraordinary properties of materials accompanying their phase transitions are exciting from the perspectives of scientific research and new applications. Most recently, Karothu et al.1 described guanidinium nitrate, [C(NH2)3]+[NO3]-, hereafter GN, as a ferroelectric semiconducting organic crystal with exceptional actuating properties. However, the ferroelectric and semiconducting properties of this hybrid organic-inorganic material were not confirmed by the experimental results, and the reproducibility of the large stroke associated with the first-order transition is questionable, because the GN crystals are inherently susceptible to the formation of defects. Besides, previous extensive studies on GN were not acknowledged

Supramolecular structure of the 1:2 complex of 1,4-dimethylpiperazine mono-betaine with squaric acid

The 1: 2 complex of 1,4-dimethylpiperazine mono-betaine (MBPZ) with squaric acid (H(2)SQ) has been characterised by single-crystal X-ray analysis, FTIR and NMR spectroscopies, and by DFT calculations. The crystals are monoclinic, space group P2(1)/c. Two MBPZ cations and four hydrogen squarate anions (HSQ(-)) are linked by strong O(1)=H center dot center dot center dot O(13) (2.525(4) angstrom), O(14)-H center dot center dot center dot O(21) (2.511(4) angstrom) and N(4)-H center dot center dot center dot O(23) (2.607(3)angstrom) hydrogen bonds into a cyclamer R-6(6)(38). In turn, the cyclamers are linked into a helix C-4(4)(20) through two O(24)-H center dot center dot center dot O(11) hydrogen bonds of 2.516(4)angstrom. The piperazinium ring has a chair conformation with N(4)-CH3 and N(1)-CH2COOH substituents in the equatorial positions, and N(1)-CH3 in the axial position. The FTIR spectrum is consistent with the crystal data. Two models of the 1: 2 complex of MBPZ with H(2)SQ have been optimised at the B3LYP/6-311++G(d,p) level of theory and have been used to calculate harmonic IR frequencies. One of the models (2) is dominated by electrostatic attraction between NH(4)(+) and HSQ(-), whereas in the other (3) squaric acid interacts with a zwitterionic MBPZ through the O-H center dot center dot center dot O and O-H center dot center dot center dot N hydrogen bonds

How to quench ferromagnetic ordering in a CN-bridged Ni(II)-Nb(IV) molecular magnet? : a combined high-pressure single-crystal X-ray diffraction and magnetic study

High-pressure (HP) structural and magnetic properties of a magnetic coordination polymer {[NiII(pyrazole)4]2[NbIV(CN)8]·4H2O}n (Ni2Nb) are presented, discussed and compared with its two previously reported analogs {[MnII(pyrazole)4]2[NbIV(CN)8]·4H2O}n (Mn2Nb) and {[FeII(pyrazole)4]2[NbIV(CN)8]·4H2O}n (Fe2Nb). Ni2Nb shows a significant decrease of the long-range ferromagnetic ordering under high pressure when compared to Mn2Nb, where the pressure enhances the Tc (magnetic ordering temperature), or to Fe2Nb exhibiting a pressure-induced spin crossover. The different HP magnetic responses of the three compounds were rationalized and correlated with the structural models as determined by single-crystal X-ray diffraction

Thermostructural and Elastic Properties of PbTe and Pb 0.884 Cd 0.116 Te: A Combined Low-Temperature and High-Pressure X-ray Diffraction Study of Cd-Substitution Effects

Rocksalt-type (Pb,Cd)Te belongs to IV–VI semiconductors exhibiting thermoelectric properties. With the aim of understanding of the influence of Cd substitution in PbTe on thermostructural and elastic properties, we studied PbTe and Pb0.884Cd0.116Te (i) at low temperatures (15 to 300 K) and (ii) at high pressures within the stability range of NaCl-type PbTe (up to 4.5 GPa). For crystal structure studies, powder and single crystal X-ray diffraction methods were used. Modeling of the data included the second-order Grüneisen approximation of the unit-cell-volume variation, V(T), the Debye expression describing the mean square atomic displacements (MSDs), u2>(T), and Birch–Murnaghan equation of state (BMEOS). The fitting of the temperature-dependent diffraction data provided model variations of lattice parameter, the thermal expansion coefficient, and MSDs with temperature. A comparison of the MSD runs simulated for the PbTe and mixed (Pb,Cd)Te crystal leads to the confirmation of recent findings that the cation displacements are little affected by Cd substitution at the Pb site; whereas the Te displacements are markedly higher for the mixed crystal. Moreover, information about static disorder caused by Cd substitution is obtained. The calculations provided two independent ways to determine the values of the overall Debye temperature, θD. The resulting values differ only marginally, by no more than 1 K for PbTe and 7 K for Pb0.884Cd0.116Te crystals. The θD values for the cationic and anionic sublattices were determined. The Grüneisen parameter is found to be nearly independent of temperature. The variations of unit-cell size with rising pressure (the NaCl structure of Pb0.884Cd0.116Te sample was conserved), modeled with the BMEOS, provided the dependencies of the bulk modulus, K, on pressure for both crystals. The K0 value is 45.6(2.5) GPa for PbTe, whereas that for Pb0.884Cd0.116Te is significantly reduced, 33.5(2.8) GPa, showing that the lattice with fractional Cd substitution is less stiff than that of pure PbTe. The obtained experimental values of θD and K0 for Pb0.884Cd0.116Te are in line with the trends described in recently reported theoretical study for (Pb,Cd)Te mixed crystals

Enforcing Multifunctionality: A Pressure-Induced Spin-Crossover Photomagnet

Photomagnetic compounds are usually achieved by assembling preorganized individual molecules into rationally designed molecular architectures via the bottom-up approach. Here we show that a magnetic response to light can also be enforced in a nonphotomagnetic compound by applying mechanical stress. The nonphotomagnetic cyano-bridged Fe^II–Nb^IV coordination polymer {[Fe^II(pyrazole)₄]₂[Nb^IV(CN)₈]·4H₂O}_<i>n</i> (<b>FeNb</b>) has been subjected to high-pressure structural, magnetic and photomagnetic studies at low temperature, which revealed a wide spectrum of pressure-related functionalities including the light-induced magnetization. The multifunctionality of <b>FeNb</b> is compared with a simple structural and magnetic pressure response of its analog {[Mn^II(pyrazole)₄]₂[Nb^IV(CN)₈]·4H₂O}_<i>n</i> (<b>MnNb</b>). The <b>FeNb</b> coordination polymer is the first pressure-induced spin-crossover photomagnet

High-Pressure Preference for the Low <i>Z</i>′ Polymorph of a Molecular Crystal

High pressure destabilizes the high <i>Z</i>′ polymorph of 3-hydroxy-4,5-dimethyl-1-phenylpyridazin-6-one (<b>1</b>α); however, recrystallization is needed for obtaining a low <i>Z</i>′, more dense polymorph. Three polymorphs α, β, and γ can be monotonically compressed to 2.0 GPa at least. At ambient pressure <b>1</b> crystallizes in space group <i>C</i>2/<i>c</i>, <i>Z</i>′ = 4 as polymorph <b>1</b>α, or as lower-density polymorph <b>1</b>β, of space group <i>P</i>2₁/<i>c</i> and <i>Z</i>′ = 1. Polymorph β is metastable, and after about one year, it transforms to phase α. The isochoric recrystallization above 0.40 GPa yields a new polymorph γ of space group <i>P</i>2₁/<i>a</i> and <i>Z</i>′ reduced to 1. The γ polymorph retrieved to ambient conditions for months has showed no signs of transformations. The main motif of OH···O bonded chains is retained in all three phases, but high pressure enforced identical conformation of closely packed molecules and their identical crystal environment in phase γ