Layered lanthanide phosphonates Ln(2-qpH)(SO4)(H2O)2 (Ln = La, Ce, Pr, Nd, Sm): polymorphism and magnetic properties

Abstract

Polymorphic layered lanthanide coordination polymers provide opportunities to study the effect of intralayer and interlayer interactions on their magnetic dynamics. Herein we report a series of layered lanthanide phosphonates, namely, α-Ln(2-qpH)(SO₄)(H₂O)₂ (Ln = Sm) (α-Ln), β-Ln(2-qpH)(SO₄)(H₂O)₂ (Ln = Pr, Nd, Sm) (β-Ln) and γ-Ln(2-qpH)(SO₄)(H₂O)₂ (Ln = La, Ce, Pr, Nd, Sm) (γ-Ln) (2-qpH₂ = 2-quinolinephosphonic acid), which crystallize in monoclinic P2₁/c (α-Ln), triclinic P (β-Ln) and orthorhombic Pbca (γ-Ln) space groups, respectively. The structural differences between the β- and γ-phases lie not only in the intralayer but also in the interlayer. Within the layers, the Ln₂O₂ dimers are aligned parallel in the β-phase, but are non-parallel in the γ-phase. In the interlayer, there are π–π interactions between the quinoline groups in the α- and β-phases but not in the γ-phase. Magnetic studies reveal a field-induced slow relaxation of the magnetisation at low temperatures for compounds γ-Ce, β-Nd, and γ-Nd, and the impact of polymorphism on the magnetic dynamics of Nd(III) compounds is discussed.