Abstract

A new layered manganese(II) phosphate, [Mn₂(HPO₄)₃]·(NH₃(CH₂)₂NH₃)_3/2·H₂PO₄, has been synthesised under solvothermal conditions at 433 K in the presence of ethylenediamine and the structure determined at 150 K using single-crystal X-ray diffraction data (M_r = 587.95, triclinic, space group, P, a = 6.651(1), b = 9.343(1), c = 14.512(2) Å, α = 87.687(3), β = 84.096(4), γ = 89.066(4)°, V = 896.20 Å³, Z = 2, R = 0.0409 and R_w = 0.0462 for 2939 observed data (I > 3(σ(I))). The structure consists of anionic manganese-phosphate layers of formula [Mn₂(HPO₄)₃]²⁻ containing trans edge sharing chains of MnO₆ octahedra linked via MnO₅ and HPO₄ polyhedra. H₂PO₄⁻ and (NH₃(CH₂)₂NH₃)²⁺ ions lie between the manganese-phosphate layers. Magnetic measurements indicate Curie–Weiss paramagnetism above 25 K with μ_eff = 5.77(1) μ_B and θ = −30(1) K, consistent with the presence of high-spin Mn²⁺ ions and antiferromagnetic interactions. The latter result in magnetic ordering at T_N = 2.5(1) K. The temperature dependence of the susceptibility can be successfully fitted assuming a triangular antiferromagnetic lattice of S = 5/2 spins, yielding an exchange parameter J/k of −0.72(1) K and a g-value of 1.930(3). On treatment with water, a phase of composition [Mn₂(HPO₄)₃]·(NH₃(CH₂)₂NH₃)·(H₂O)_x (x ∼ 0.2) is formed with retention of the MnPO layers but removal of the interlayer H₂PO₄⁻ groups.