This review highlights fundamental concepts and synthetic strategies of SMMs and selected examples of 3d, 4f, 5f and mixed 3d–4f, 4d–5d and 3d–5f based SMMs are discussed.

A new 2D Gd(III)-based coordination polymer has close to the highest cryogenic magnetocaloric effect of any MOF reported so far. The experimental results reveal its structural features and magnetic properties.

The reaction of 2,6-bis(1-salicyloylhydrazonoethyl)pyridine [H₄daps] with Dy(NO₃)₃·5H₂O led to the formation of two new Dy(III) based complexes with formulae [Dy(H₄daps)(H₂O)₃(NO₃)] (NO₃)₂ (H₂O) (1) and [Dy(H₃daps)(H₂O)₂(NO₃)] (NO₃) (MeOH) (2). Complexes 1 and 2 were characterized by crystal structure determination, magnetic measurements and photoluminescence studies. In comparison with complex 1, complex 2 shows a slight difference of local symmetry around the Dy(III) center which is attributed to deprotonation of the ligand and also to different binding modes of the peripheral NO₃ ⁻ anion. AC magnetic susceptibility measurements reveal that both complexes exhibit single-molecule magnet (SMM) behavior, with the thermal energy barrier of 1 being higher than that of 2 (U_eff = 32.7 K for 1 and 23.8 K for 2). Our investigation discloses that small differences in the coordination environment around the metal centre played an important role in the difference in relaxation dynamics of the complexes. Solid state photoluminescence studies showed their photoluminescence behaviour with quantum yields of 0.98 and 1.44%.

Three lanthanide one-dimensional coordination polymers, obtained using Ln³⁺ salts and croconate dianion, were structurally characterized. Magnetic studies reveal that the gadolinium analogue exhibits a large magnetocaloric effect while single-molecule magnet behaviour is observed in the dysprosium analogue.