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Hybrid metal halides have attracted considerable attention as functional materials owing to their structural diversity and tunable optical and electronic properties. In particular, hybrid perovskites are promising candidates for applications in optoelectronics, photodetection, and light-emitting devices. However, the widespread use of lead-based perovskites raises concerns regarding the toxicity of lead and its potential environmental impact. The development of lead-free alternatives is therefore an important direction in the search for more environmentally compatible functional materials. Cadmium-based hybrid halides represent an alternative compositional family with potentially useful optical properties[1,2].
The properties of hybrid metal halides depend on both the inorganic framework and the organic cation[3]. While methylammonium-based cadmium halides, such as CH3NH3CdBr3, have previously been investigated in terms of their crystal structures and optical band gaps, the effects of introducing alternative organic cations remain less explored. In particular, aziridinium, a cyclic organic cation, offers an opportunity to investigate how changes in cation identity influence the structural and optical characteristics of cadmium halides. Extending this family may help establish broader structure–property relationships in hybrid metal-halide materials.
Herein, we report the synthesis and characterization of two aziridinium cadmium halides, (AzrH)CdCl3 and (AzrH)CdBr3 (AzrH = aziridinium), expanding the range of organic cations investigated in cadmium-based hybrid halides. The compounds were prepared by reacting the corresponding starting materials in the respective acids, followed by isolation of the crystalline products by filtration and drying. Their crystal structures were determined by single-crystal X-ray diffraction. The phase consistency of the bulk crystalline samples was examined by powder X-ray diffraction, with the experimental patterns showing agreement with those simulated from the single-crystal structural data.
Optical measurements revealed band gaps of 5.36 eV for (AzrH)CdCl3 and 3.62 eV for (AzrH)CdBr3. The substantial decrease in band gap upon replacing chloride with bromide demonstrates the pronounced influence of halide composition on the optical properties of these materials. These findings establish aziridinium cadmium halides as an additional family of hybrid metal-halide compounds and provide a starting point for further investigations of their structural diversity and composition-dependent optical behaviour.
[1] Kalthoum, R.; Ben Bechir, M.; Ben Rhaiem, A. CH3NH3CdCl3: A Promising New Lead-Free Hybrid Organic–Inorganic Perovskite for Photovoltaic Applications. Physica E: Low-dimensional Systems and Nanostructures 2020, 124, 114235.
[2] Alonso, J. A.; Kayser, P.; Hong, B. K.; Álvarez-Galván, M. C.; Fauth, F.; López, C. A. Mechano-Chemical Synthesis, Structural Features and Optical Gap of Hybrid CH3NH3CdBr3 Perovskite. Materials 2021, 14 (20), 6039.
[3] Hautzinger, M. P.; Mihalyi-Koch, W.; Jin, S. A-Site Cation Chemistry in Halide Perovskites. Chem. Mater. 2024, 36 (21), 10408–10420.
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