Metal-Formate Framework Stiffening and Its Relevance to Phase Transition Mechanism

In the last decade, one of the most widely examined compounds of motel-organic frameworks was undoubtedly ((CH3)2NH2)(Zn(HCOO)3), but the problem of the importance of framework dynamics in the order–disorder phase change of the mechanism has not been fully clarified. In this study, a combination of temperature-dependent dielectric, calorimetric, IR, and Raman measurements was used to study the impact of ((CH3)2NH2)(Zn(DCOO)3) formate deuteration on the phase transition mechanism in this compound. This deuteration led to the stiffening of the metal-formate framework, which in turn caused an increase in the phase transition temperature by about 5 K. Interestingly, the energetic ordering of DMA+ cations remained unchanged compared to the non-deuterated compound.

Ordered B-Site Vacancies in an ABX3 Formate Perovskite

<p>We report the synthesis and structural characterisation of a series of aliovalently doped metal–formate ABX₃ perovskite frameworks [C(NH₂)₃]Mn²⁺_1–<i>x</i>(Fe³⁺_2<i>x</i>/3,V_<i>x</i>/3)(HCOO)₃ (V = B-site vacancy). For sufficiently large <i>x</i>, the vacancies order, lowering the crystal symmetry from orthorhombic <i>Pnna</i> to monoclinic <i>P</i>2/<i>n</i>. This system establishes B-site vacancies as a new type of defect in formate perovskites, and one with important chemical, structural, and functional implications. Monte Carlo simulations driven by a nearest-neighbour vacancy repulsion model show checkerboard vacancy order to emerge for <i>x</i> > 0.6, in accord with experiment.</p>

Ordered B-Site Vacancies in an ABX3 Formate Perovskite

<p>We report the synthesis and structural characterisation of a series of aliovalently doped metal–formate ABX₃ perovskite frameworks [C(NH₂)₃]Mn²⁺_1–<i>x</i>(Fe³⁺_2<i>x</i>/3,V_<i>x</i>/3)(HCOO)₃ (V = B-site vacancy). For sufficiently large <i>x</i>, the vacancies order, lowering the crystal symmetry from orthorhombic <i>Pnna</i> to monoclinic <i>P</i>2/<i>n</i>. This system establishes B-site vacancies as a new type of defect in formate perovskites, and one with important chemical, structural, and functional implications. Monte Carlo simulations driven by a nearest-neighbour vacancy repulsion model show checkerboard vacancy order to emerge for <i>x</i> > 0.6, in accord with experiment.</p>