Synthesis, structure, and magnetic properties of new layered phosphate halides Sr2Cu5(PO4)4X2·8H2O (X = Cl, Br) with a crown-like building unit

Abstract

Two new compounds Sr₂Cu₅(PO₄)₄X₂·8H₂O (X = Cl and Br) are synthesized by a conventional hydrothermal method. Sr₂Cu₅(PO₄)₄Cl₂·8H₂O crystallizes in the tetragonal system with a space group of P42₁2, while Sr₂Cu₅(PO₄)₄Br₂·8H₂O crystallizes in the space group P4/nmm, which are found to have a similar framework of layered structure, in which the crown-like {Cu₅(PO₄)₄X₂} building units connect to each other forming a 2D corrugated sheet with vacancies, while the Sr²⁺ cations are located along the vacancies. The spin lattice of two compounds built by Cu²⁺ ions shows a new type of corrugated square. Magnetic measurements confirmed that both Sr₂Cu₅(PO₄)₄X₂·8H₂O (X = Cl and Br) exhibit antiferromagnetic ordering at low temperatures. A fit of theoretical model shows exchange interaction J = −25.62 K for the Cl-analogue and J/k_B = −26.47 K for the Br-analogue.