Single Crystal Electron Paramagnetic Resonance of Dimethylammonium and Ammonium Hybrid Formate Frameworks: Influence of External Electric Field

Abstract

We present a continuous wave electron paramagnetic resonance (EPR) study of a Mn2+ doped [(CH3)2NH2][Zn(HCOO)3] hybrid dense metal–organic framework (MOF) that exhibits an order–disorder structural phase transition at Tc = 163 K. The W-band EPR measurements of a powder sample are performed to verify the previously reported spin Hamiltonian parameters of the Mn2+ centers in the low-temperature phase. The temperature dependent single crystal X-band EPR experiments reveal that Mn2+ probe ions are susceptible to the phase transition, as the spectrum changes drastically at Tc. The angular dependent EPR spectra of Mn2+ centers are obtained by rotating the single crystal sample about three distinct directions. The simulation of the determined angular dependences reveals six MnO6 octahedra in the ordered phase that originate from a severe crystal twinning of the [(CH3)2NH2][Zn(HCOO)3] MOF. The possible ferroelectric origin of the crystalline twins is investigated by single crystal EPR measurements with an applied...