[Mn(terpy)Sb₂S₄]ₙ, a 1D Network of MnSb₄S₅ Rings Exhibiting a Pronounced Magnetocaloric Effect and Luminescence

The solvothermal reaction of an aqueous solution of Na₃SbS₃ or Schlippe's Salt (Na₃SbS₄·9H₂O) in the presence of Mn(ClO₄)₂·6H₂O and terpy (terpy = 2,2':6',2''-terpyridine) or the [Mn(terpy)]²⁺ complex led to crystallization of the new compound [Mn(terpy)Sb₂S₄]_n (I). The unique crystal structure of I features chains formed by fused MnSb₄S₅ rings. The Mn²⁺ cation is coordinated by one terpy ligand and two S^2– anions resulting in a distorted MnN₃S₂ trigonal bipyramid. The terpy ligands point to the exterior of the chains, distances between neighbored ligands indicate π···π stacking. Magnetic investigations show paramagnetic behavior (µ_eff = 5.92 µ_B/Mn²⁺ at room temperature). Field-dependent magnetic susceptibility measurements at different temperatures evidence a significant magnetocaloric effect of –ΔS = 20.54 J kg^–1K^–1 at T = 2 K for a magnetic field change of ΔB = 9 T. The compound exhibits blue luminescence, and a detailed analysis allowed assignment of the emission and excitation bands to the different constituents of the compound.