Perovskite-Like Polar Lanthanide Formate Frameworks of [NH₂NH₃][Ln(HCOO)₄] (Ln = Tb–Lu and Y): Synthesis, Structures, Magnetism, and Anisotropic Thermal Expansion

Abstract

A series of isostructural hydrazinium lanthanide (Ln) formate framework compounds of [NHNH][Ln(HCOO)] for Ln ions from Tb to Lu and Y have been successfully prepared by utilizing NHNH. The compounds crystallize in orthorhombic polar space group Pca2, with cell parameters at 180 K of a = 18.2526(7)-18.1048(5) Å, b = 6.5815(2)-6.5261(2) Å, c = 7.6362(3)-7.5044(2) Å, and V = 917.33(6)-886.67(4) Å, showing the effect of lanthanide contraction. The compounds possess polar perovskite-like structures incorporating the hydrazinium cations in the cavities of the NaCl-like framework, in which the Ln ions in a bicapped trigonal prism are connected by anti-anti and syn-anti formate groups. The N-H···O hydrogen-bonding interactions are between the hydrazinium cations and the anionic framework. One anti-anti formate group is frustrated by the competitive N-H···O hydrogen-bonding interactions. It thus twists or flips upon warming, resulting in large anisotropic thermal expansion and negative thermal expansion below 180 K. A comparison with the transition metal and magnesium analogues revealed that the structural compactness, tighter binding of the hydrazinium cation by the framework, and symmetrically better match between the framework and ammonium cation for Ln compounds could inhibit the occurrence of phase transition in the series. The IR spectroscopic, thermal, and magnetic properties are investigated.

Three New Niccolites: High‐Temperature Phase Transitions, Prominent Anisotropic Thermal Expansions, Dielectric Anomalies, and Magnetism

“…The dmpnH 2 2+ cation locates in the cavity. The mismatch in the symmetry between the intrinsically trigonal cavity and the accommodated non‐trigonal diammonium provides the opportunity for the phase transition . The three materials display similar phase transition behaviors.…”

A Series of Bimetallic Ammonium AlNa Formates

“…However, in the M II analogs, amM II (the chiral phase), maM II , and hyzM II (of both phases), phase transitions were observed. By contrast, for the present AlNa bimetallic perovskites, the small size of Al 3+ and the stronger N−H⋅⋅⋅O Na hydrogen bonds can bind the ammonium cations in the framework cavities more tightly, and the bimetallic frameworks of lowered symmetries probably match or adapt the low symmetric ammonium cations better, as those observed for Ln AMFFs of low symmetric frameworks, thus reducing the chance for phase transitions. Compound 5 eta showed no phase transition below 360 K in our investigation.…”

Di-functional luminescent sensors based on Y3+ doped Eu3+ and Tb3+ coordination polymers: fast response and visible detection of Cr3+, Fe3+ ions in aqueous solutions and acetone

“…Y1 is coordinated by seven carboxylate oxygen atoms and one from DMA molecule. 41 The whole framework could be simplied into a (4,4)-connected sql-type net with the point symbol (4 4 ,6 2 ).…”