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Issue 8, 2019
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Temperature- and pressure-dependent studies of a highly flexible and compressible perovskite-like cadmium dicyanamide framework templated with protonated tetrapropylamine

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Abstract

We report temperature-dependent X-ray diffraction, thermal, dielectric, electron paramagnetic resonance (EPR), Raman and IR studies of [(C3H7)4N][Cd(N(CN)2)3] ([TPrA][Cd(dca)3]) exhibiting a rich sequence of temperature-induced phase transitions occurring at T3 = 386 K, T2 = 362 K, T1 = 241 K and T0 = 228 K. The X-ray diffraction study confirms the I4/mcm, P[4 with combining macron]21c and P21/n symmetry of the high-temperature phase, the phase stable between T2 and T1 and the low-temperature phase stable below T0, respectively. Our data show that the driving forces for the phase transitions at T3 and T2 are the partial ordering of the tetrapropylammonium cations (TPrA+) and dicyanamide (dca) linkers as well as the off-center shifts of TPrA+ cations and the tilting of the CdN6 octahedra. X-ray diffraction data reveal that two low-temperature (LT) structural phase transitions at T1 and T0 are associated with strong monoclinic distortion of the [Cd(dca)3] framework and further ordering of the TPrA+ cations and dca linkers. Raman and EPR data confirm the strong distortion of the framework, while dielectric data are consistent with the partial ordering of the TPrA+ cations at T1. Dielectric and Raman data also prove that the phase transition at T0 is associated with further freezing of the propyl groups’ motions of the TPrA+ cations, whereas EPR data indicate that this phase transition is also associated with some distortion of the cadmium-dicyanamide framework. In the family of [TPrA][M(dca)3] compounds (M = Cd2+, Mn2+, Fe2+, Co2+, Ni2+), phase transitions into monoclinic phases are unique only for the Cd analogue, and our data indicate that this behaviour can be attributed to the higher flexibility of the [TPrA][Cd(dca)3] framework compared to the other analogues. We also report high-pressure X-ray powder diffraction and Raman studies of [TPrA][Cd(dca)3]. Fitting of the pressure dependence of the unit cell volume to the third order Birch–Murnaghan equation of state gives a bulk modulus of 6.2(6) GPa and its pressure derivative B′ = 12(2). The small value of the bulk modulus demonstrates the highly compressible nature of [TPrA][Cd(dca)3]. X-ray diffraction and Raman data show that this compound undergoes a pressure-induced phase transition between 0.3 and 0.4 GPa into a monoclinic structure, probably the same as that observed at ambient pressure below T0.

Graphical abstract: Temperature- and pressure-dependent studies of a highly flexible and compressible perovskite-like cadmium dicyanamide framework templated with protonated tetrapropylamine

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Publication details

The article was received on 19 Dec 2018, accepted on 24 Jan 2019 and first published on 08 Feb 2019


Article type: Paper
DOI: 10.1039/C8TC06401F
Citation: J. Mater. Chem. C, 2019,7, 2408-2420

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    Temperature- and pressure-dependent studies of a highly flexible and compressible perovskite-like cadmium dicyanamide framework templated with protonated tetrapropylamine

    M. Mączka, M. Ptak, A. Gągor, A. Sieradzki, P. Peksa, G. Usevicius, M. Simenas, F. F. Leite and W. Paraguassu, J. Mater. Chem. C, 2019, 7, 2408
    DOI: 10.1039/C8TC06401F

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