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Issue 19, 2017
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The effect of K+ cations on the phase transitions, and structural, dielectric and luminescence properties of [cat][K0.5Cr0.5(HCOO)3], where cat is protonated dimethylamine or ethylamine

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Abstract

We report the synthesis, crystal structure, and dielectric, vibrational and emission spectra of two novel heterometallic perovskite-type metal–organic frameworks (MOFs) of the following formula: [(CH3)2NH2][K0.5Cr0.5(HCOO)3] (DMAKCr) and [C2H5NH3][K0.5Cr0.5(HCOO)3] (EtAKCr). DMAKCr crystallizes in a trigonal structure (R[3 with combining macron] space group) and undergoes an order–disorder phase transition to the monoclinic system (P[1 with combining macron] space group) at about 190 K. The dielectric studies confirm the presence of first-order relaxor-like structural transformation. In the high-temperature phase, the dimethylammonium cations are dynamically disordered over three equal positions and upon cooling the dynamical disorder evolves into a two-fold one. This partial ordering is accompanied by a small distortion of the metal–formate framework. EtAKCr crystallizes in a monoclinic structure (P21/n space group) with ordered EtA+ cations and does not experience any phase transition. The differences in the thermal behavior caused by the substitution of Na+ ions by larger K+ ions in the [cat]MIMIII (cat = DMA+, EtA+, MI = Na+, K+ and MIII = Cr3+ and Fe3+) heterometallic MOF family are discussed taking into account the impact of the hydrogen bond (HB) pattern and other factors affecting the stability of metal–formate frameworks. The optical studies show that DMANaCr and EtAKCr exhibit Cr3+-based emission characteristics for intermediate ligand field strength.

Graphical abstract: The effect of K+ cations on the phase transitions, and structural, dielectric and luminescence properties of [cat][K0.5Cr0.5(HCOO)3], where cat is protonated dimethylamine or ethylamine

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Publication details

The article was received on 01 Mar 2017, accepted on 07 Apr 2017 and first published on 19 Apr 2017


Article type: Paper
DOI: 10.1039/C7CP01336A
Citation: Phys. Chem. Chem. Phys., 2017,19, 12156-12166
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    The effect of K+ cations on the phase transitions, and structural, dielectric and luminescence properties of [cat][K0.5Cr0.5(HCOO)3], where cat is protonated dimethylamine or ethylamine

    M. Ptak, A. Gągor, A. Sieradzki, B. Bondzior, P. Dereń, A. Ciupa, M. Trzebiatowska and M. Mączka, Phys. Chem. Chem. Phys., 2017, 19, 12156
    DOI: 10.1039/C7CP01336A

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