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Effect of K+ cations on phase transitions, structural, dielectric and luminescent properties of [cat][K0.5Cr0.5(HCOO)3], where cat is protonated dimethylamine or ethylamine

Abstract

We report synthesis, crystal structure, 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 trigonal structure ( space group) and undergoes an order-disorder phase transition to the monoclinic system ( 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 two-fold one. This partial ordering is accompanied by a small distortion of the metal-formate framework. EtAKCr crystallizes in monoclinic structure (P21/n space group) with ordered EtA+ cations and doeas not experience any phase transition. The differences in the thermal behavior caused by the substitution of Na+ ions by larger K+ ions in [cat]MIMIII (cat=DMA+, EtA+, MI=Na+, K+ and MIII=Cr3+ and Fe3+) heterometallic MOFs family are discussed taking into account the impact of hydrogen bonds (HBs) pattern and other factors affecting the stability of metal-formate frameworks. The optical studies show that DMANaCr and EtAKCr exhibit Cr3+-based emission characteristic for intermediate ligand field strength.

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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, Accepted Manuscript
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    Effect of K+ cations on phase transitions, structural, dielectric and luminescent properties of [cat][K0.5Cr0.5(HCOO)3], where cat is protonated dimethylamine or ethylamine

    M. Ptak, A. Gągor, A. Sieradzki, B. Bondzior, P. J. Dereń, A. Ciupa, M. Trzebiatowska and M. Maczka, Phys. Chem. Chem. Phys., 2017, Accepted Manuscript , DOI: 10.1039/C7CP01336A

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