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 ethylamineElectronic supplementary information (ESI) available: Fig. S1-S15: powder X-ray diffraction, DSC curves, detailed Raman and IR spectra at room temperature, temperature-dependent IR and Raman spectra, temperature dependencies of wavenumbers and FWHMs of selected Raman and IR bands, geometrical parameters of MIO6 an

• Main Authors: Ptak, Maciej, G gor, Anna, Sieradzki, Adam, Bondzior, Bartosz, Dere, Przemys aw, Ciupa, Aneta, Trzebiatowska, M, M czka, Miros aw
• Format: Article
• Language: English
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/c7cp01336a

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: [(CH 3 ) 2 NH 2 ][K 0.5 Cr 0.5 (HCOO) 3 ] (DMAKCr) and [C 2 H 5 NH 3 ][K 0.5 Cr 0.5 (HCOO) 3 ] (EtAKCr). DMAKCr crystallizes in a trigonal structure ( R 3&cmb.macr; space group) and undergoes an order-disorder phase transition to the monoclinic system ( P 1&cmb.macr; 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 ( P 2 1 / 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]M I M III (cat = DMA + , EtA + , M I = Na + , K + and M III = Cr 3+ and Fe 3+ ) 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 Cr 3+ -based emission characteristics for intermediate ligand field strength. We report the synthesis, crystal structure, and dielectric, vibrational and emission spectra of novel heterometallic DMAKCr and EtAKCr MOFs.