Photophysical and Magnetic Properties in Zero-Dimensional (H2DABCO)MX4·nH2O (M = Mn and Cu; X = Cl and Br; n = 0, 1, and 4)

We report five new manganese and copper organic–inorganic hybrid (OIH) halides based on 1,4-diazabicyclo[2.2.2]­octane (DABCO: C6H12N2). The materials obtained have general formula (H2DABCO)­MX4·nH2O where M = Mn and Cu, X = Cl and Br, and n = 0, 1, and 4. The compounds (H2DABCO)­MnX4·4H2O (X = Cl and Br) crystallize in a chiral P212121 structure with unique zero-dimensional (0D) manganese octahedra, whereas anhydrous (H2DABCO)­MnBr4 exhibits a monoclinic crystal structure (space group P21/c) with isolated MnBr4 tetrahedra. While (H2DABCO)­MnCl4·4H2O is nonluminescent, the bromine analogue displays red emission with a photoluminescence quantum yield (PLQY) of 10.8%. Interestingly, anhydrous (H2DABCO)­MnBr4 demonstrates intense green emission due to the tetrahedral coordination of Mn2+ ion. The PLQY for (H2DABCO)­MnBr4 is 52.16%, and it shows a longer lifetime of the photoexcited electrons than the hydrated compound. In contrast, the copper OIH halides (X = Cl and Br) reveal an identical 0D tetrahedral structure crystallizing with one water molecule in the P21/c space group. Both manganese and copper OIH halides exhibit a magnetocaloric effect at low temperatures.