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)(H2 O)2 ]n , {H3 L=(HO)2 P(O)CH2 CO2 H; Ln=Dy3+ (CP 1), Er3+ (CP 2)} and [{Gd2 (L)2 (H2 O)3 }. H2 O]n , (CP 3) were hydrothermally synthesized using phosphonoacetic acid as a linker. Structural features revealed that the dinuclear Ln3+ 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 Ueff values of 72 K (relaxation time, τ0 =3.05×10-7  s) and 38.42 K (relaxation time, τ0 =4.60×10-8  s) respectively. Ab-initio calculations suggest that the g tensor of Kramers doublet of the lanthanide ion (Dy3+ and Er3+ ) is strongly axial in nature which reflects in the slow magnetic relaxation behavior of both CPs. CP 3 exhibits a significant magnetocaloric effect with -ΔSm =49.29 J kg-1  K-1 , one of the highest value among the reported 2D CPs. Moreover, impedance analysis of all the CPs show high proton conductivity with values of 1.13×10-6  S cm-1 , 2.73×10-3  S cm-1 and 2, 6.27×10-6  S cm-1 for CPs 1-3, respectively, at high temperature (>75 °C) and maximum 95 % relative humidity (RH).