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)(H2O)(2)](n), {H3L=(HO)(2)P(O)CH2CO2H; Ln=Dy3+ (CP 1), Er3+ (CP 2)} and [{Gd-2(L)(2)(H2O)(3)}(H2O)-H-.](n), (CP 3) were hydrothermally synthesized using phosphonoacetic acid as a linker. Structural features revealed that the dinuclear Ln(3+) 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-eff values of 72 K (relaxation time, tau(0)=3.05x10(-7) s) and 38.42 K (relaxation time, tau(0)=4.60x10(-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 -Delta S-m=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 1.13x10(-6) S cm(-1), 2.73x10(-3) S cm(-1) and 2, 6.27x10(-6) S cm(-1) for CPs 1-3, respectively, at high temperature (>75 degrees C) and maximum 95 % relative humidity (RH).