Synthesis, Structure, and Magnetic Property of a New Open-Framework Manganese Borophosphate, [NH₄]₄[Mn₉B₂(OH)₂(HPO₄)₄(PO₄)₆]

A new three-dimensional (3-D) manganese(II) borophosphate, [NH 4 ] 4 [Mn 9 B 2 (OH) 2 (HPO 4 ) 4 (PO 4 ) 6 ] (denoted MnBPO-CJ26), has been synthesized by a hydrothermal method. The structure has been determined by single-crystal X-ray diffraction. It crystallizes in the monoclinic space group C 2 /c (No. 15) with a = 32.603(7) Å, b = 10.617(2) Å, c = 10.718(2) Å, and β = 108.26(3)°. Its structure features anionic manganese-phosphate layers [Mn 9 (OH) 2 (HPO 4 ) 4 (PO 4 ) 6 ] 10 -, which are made up from MnO 5, MnO 6, PO 4, and HPO 4 polyhedral units. These anionic layers, parallel to the bc plane, are further connected by BO 4 tetrahedra through vertex oxygen atoms forming a novel open framework with 2-D eight-membered ring (8-MR) channels along the [010] and [001] directions. Charge neutrality is achieved by protonated NH 3 molecules. The structure has unique B/P and Mn/P ratios (B/P = 1/5, Mn/P = 9/10). Magnetic measurements indicate that Curie−Weiss behavior above 100 K with C = 4.404(3) cm 3 mol -1 K and θ = −51.2(5) K. The value of C is consistent with an S = 5 / 2 ion with g ∼ 2.0 (4.38 cm 3 mol -1 K). However, the magnetic data reveal a spontaneous magnetization at 8.0 K, indicating a canting of Mn 2+ moments in the antiferromagnetic ground state.