A Family of Luminescent Halido Cadmates with Bifunctional Diammonium Cations

This study presents the synthesis, single crystal structures, and optical properties of a series of six halido cadmates featuring the diammonium cations 4‐(ammoniomethyl)pyridinium (H 2 AMP 2+ ) and 4‐(ammonioethyl)pyridinium (H 2 AEP 2+ ). The chlorido cadmates (H 2 AMP) 2 Cd 3 Cl 10 ·4H 2 O ( 1 ) and (H 2 AEP) 4 Cd 5 Cl 18 ( 2 ) feature complex polymeric anion motifs, while the bromido and iodio cadmates (H 2 AMP)CdBr 4 ·H 2 O ( 3 ), (H 2 AEP)CdBr 4 ( 4 ), (H 2 AMP)CdI 4 ( 5 ), and (H 2 AEP)CdI 4 · H 2 O ( 6 ) are composed of mononuclear {CdX 4 } units (X = halogen) packed in different arrangements. (H 2 AEP) 4 Cd 5 Cl 18 ( 2 ) displays a phase transition between 100 K and room temperature, which is studied in detail. All compounds show decomposition temperatures above 180 °C. Optical bandgaps of the compounds are estimated in the range from 3.4 to 4.4 eV, with all compounds showing significant sub‐bandgap absorption. Compounds 1 – 6 also show broad low‐temperature emission centred between 1.95 and 2.5 eV.