ABSTRACT
We present the influence of positional isomerism on the crystal structure of fluorobenzylammonium copper(II) chloride perovskites A2CuCl4 by incorporating ortho-, meta-, and para-fluorine substitution in the benzylamine structure. Two-dimensional (2D) polar ferromagnet (3-FbaH)2CuCl4 (3-FbaH+ = 3-fluorobenzylammonium) is successfully obtained, which crystallizes in a polar orthorhombic space group Pca21 at room temperature. In contrast, both (2-FbaH)2CuCl4 (2-FbaH+ = 2-fluorobenzylammonium) and (4-FbaH)2CuCl4 (4-FbaH+ = 4-fluorobenzylammonium) crystallize in centrosymmetric space groups P21/c and Pnma at room temperature, respectively, displaying significant differences in crystal structures. These differences indicate that the position of the fluorine atom is a driver for the polar behavior in (3-FbaH)2CuCl4. Preliminary magnetic measurements confirm that these three perovskites possess dominant ferromagnetic interactions within the inorganic [CuCl4]∞ layers. Therefore, (3-FbaH)2CuCl4 is a polar ferromagnet, with potential as a type I multiferroic. This work is expected to promote further development of high-performance 2D copper(II) halide perovskite multiferroic materials.
ABSTRACT
We present three new hybrid copper(II) chloride layered perovskites of generic composition ACuCl4 or A2CuCl4, which exhibit three distinct structure types. (m-PdH2)CuCl4 (m-PdH22+ = protonated m-phenylenediamine) adopts a Dion-Jacobson (DJ)-like layered perovskite structure type and exhibits a very large axial thermal contraction effect upon heating, as revealed via variable-temperature synchrotron X-ray powder diffraction (SXRD). This can be attributed to the contraction of an interlayer block, via a slight repositioning of the m-PdH22+ moiety. (3-AbaH)2CuCl4 (3-AbaH+ = protonated 3-aminobenzoic acid) and (4-AbaH)2CuCl4 (4-AbaH+ = protonated 4-aminobenzoic acid) possess the same generic formula as Ruddlesden-Popper (RP) layered perovskites, A2BX4, but adopt different structures. (4-AbaH)2CuCl4 adopts a near-staggered structure type, whereas (3-AbaH)2CuCl4 adopts a near-eclipsed structure type, which resembles the DJ rather than the RP family. (3-AbaH)2CuCl4 also displays static disorder of the [CuCl4]∞ layers. The crystal structures of each are discussed in terms of the differing nature of the templating molecular species, and these are compared to related layered perovskites. Preliminary magnetic measurements are reported, suggesting dominant ferromagnetic interactions.
ABSTRACT
Two-dimensional (2D) organic-inorganic hybrid copper halide perovskites have drawn tremendous attention as promising multifunctional materials. Herein, by incorporating ortho-, meta-, and para-chlorine substitutions in the benzylamine structure, we first report the influence of positional isomerism on the crystal structures of chlorobenzylammonium copper(II) chloride perovskites A2CuCl4. 2D polar ferromagnets (3-ClbaH)2CuCl4 and (4-ClbaH)2CuCl4 (ClbaH+ = chlorobenzylammonium) are successfully obtained. They both adopt a polar monoclinic space group Cc at room temperature, displaying significant differences in crystal structures. In contrast, (2-ClbaH)2CuCl4 adopts a centrosymmetric space group P 21/ c at room temperature. This associated structural evolution successfully enhances the physical properties of the two polar compounds with high thermal stability, discernible second harmonic generation (SHG) signals, ferromagnetism, and narrow optical band gaps. These findings demonstrate that the introduction of chlorine atoms into the interlayer organic species is a powerful tool to tune crystal symmetries and physical properties, and this inspires further exploration of designing high-performance multifunctional copper-based materials.
ABSTRACT
A family of hybrid Perovskite-oxalates ("Perovzalates") of general composition AILi3MII(C2O4)3 (A = K+, Rb+, Cs+; M = Fe2+, Co2+, Ni2+) are presented. All eight new compounds are isostructural with the previously reported examples NH4Li3Fe(C2O4)3 and KLi3Fe(C2O4)3, crystallising in the rhombohedral space group R3[combining macron]c, with aâ¼11.3-11.6 Å, câ¼14.8-15.2 Å. In contrast to other families of "hybrid perovskites" such as the formates, these compounds can be regarded as closer structural relatives to inorganic (oxide) perovskites, in the sense that they contain direct linkages of the octahedral sites via bridging oxygen atoms (of the oxalate groups). It is of note, therefore, that monoatomic cations as large as Cs+ can be incorporated into the perovskite-like A sites of this structure type, which is not feasible in traditional ABO3 perovskites; indeed CsLi3Ni(C2O4)3 appears to exhibit the 'mostly tightly bound' 12-coordinate Cs+ ion in an oxide environment, according to a bond valence analysis.
ABSTRACT
The title compound is the first example of a layered fluoroperovskite containing an interlayer organic cation. Preliminary magnetic characterisation is reported, and structural relationships to related layered perovskites are discussed.