Lanthanide-Based Layer-Type Two-Dimensional Coordination Polymers Featuring Slow Magnetic Relaxation, Magnetocaloric Effect and Proton Conductivity.

Three lanthanide-based two-dimensional (2D) coordination polymers (CPs), [Ln(L)(H O) ] , {H L=(HO) P(O)CH CO H; Ln=Dy (CP 1), Er (CP 2)} and [{Gd (L) (H O) } H O] , (CP 3) were hydrothermally synthesized using phosphonoacetic acid as a linker. Structural features revealed that the dinuclear Ln nodes were present in the 2D sheet of CP 1 and CP 2 while in the case of CP 3, nodes were further connected to each other forming a chain-type arrangement throughout the network. The magnetic studies show field-induced slow magnetic relaxation property in CP 1 and CP 2 with U values of 72 K (relaxation time, τ =3.05×10  s) and 38.42 K (relaxation time, τ =4.60×10  s) respectively. Ab-initio calculations suggest that the g tensor of Kramers doublet of the lanthanide ion (Dy and Er ) is strongly axial in nature which reflects in the slow magnetic relaxation behavior of both CPs. CP 3 exhibits a significant magnetocaloric effect with -ΔS =49.29 J kg  K , one of the highest value among the reported 2D CPs. Moreover, impedance analysis of all the CPs show high proton conductivity with values of 1.13×10  S cm , 2.73×10  S cm and 2, 6.27×10  S cm for CPs 1-3, respectively, at high temperature (>75 °C) and maximum 95 % relative humidity (RH).