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 2 O) 2 ] n , {H 3 L=(HO) 2 P(O)CH 2 CO 2 H; Ln=Dy 3+ (CP 1 ), Er 3+ (CP 2 )} and [{Gd 2 (L) 2 (H 2 O) 3 } . H 2 O] 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, τ 0 =3.05×10 −7  s) and 38.42 K (relaxation time, τ 0 =4.60×10 −8  s) respectively. Ab‐initio calculations suggest that the g tensor of Kramers doublet of the lanthanide ion (Dy 3+ and Er 3+ ) is strongly axial in nature which reflects in the slow magnetic relaxation behavior of both CPs. CP 3 exhibits a significant magnetocaloric effect with −Δ 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 1.13×10 −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).