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.