Rare Earth Nitrate Hybrid Double Perovskites [Me₄N]₂[MLn(NO₃)₆] (M = Na–Cs; Ln = La–Gd, ex. Pm)

Abstract

An exploration of the synthetic and structural phase space of rare earth hybrid double perovskites A 2 B′BX 6 (A = organocation, B′ = M +, B = M 3+, X = molecular bridging anion) that include X = NO 3 – and B′ = alkali metal is reported, complementing earlier studies of the [Me 4 N] 2 [KB(NO 3 ) 6 ] (B = Am, Cm, La–Nd, Sm–Lu, Y) (Me 4 N = (CH 3 ) 4 N + ) compounds. In the present efforts, the synthetic phase space of these systems is explored by varying the identity of the alkali metal ion at the B′-site. Herein, we report three new series of the form [Me 4 N] 2 [B′B(NO 3 ) 6 ] (B = La–Nd, Sm–Gd; B′ = Na, Rb, Cs). The early members of the Na-series crystallize in the trigonal space group R 3̅ from La to Nd where a phase transition occurs in the phase between 273 and 300 K, going from R 3̅ to the high-symmetry, cubic space group Fm 3̅ m . The preceding trigonal members of the Na-series also undergo phase transitions to cubic symmetry at temperatures above 300 K, establishing a decreasing trend in the phase-transition temperature. The remainder of the Na-series, as well as the Rb- and Cs-series, all crystallize in Fm 3̅ m at 300 K. The temperature-dependent phase behavior of the synthesized phases is studied via variable-temperature spectroscopic methods and high-resolution powder X-ray diffractometry. All phases were characterized via single-crystal and powder X-ray diffraction and Fourier transform infrared (FT-IR) and Raman spectroscopic methods. These results demonstrate the versatility of the perovskite structure type to include rare earth ions, nitrate ions, and a suite of alkali metal ions and serve as a foundation for the design of functional rare earth hybrid double perovskite materials such as those possessing useful multiferroic, optical, and magnetic properties.

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