Dinuclear and layered copper 2-pyridylphosphonates with weak ferromagnetism observed in layer compound Cu(C5H4NPO3)

This paper reports the syntheses and structures of three new copper phosphonates based on 2-pyridylphosphonate, namely, Cu(C5H4NPO3H)2 (1), Cu3(OH)2(C5H4NPO3)2·2H2O (2) and Cu(C5H4NPO3) (3). Compound 1 has a discrete dimeric structure in which the {CuO4N} square pyramids are linked by the {CPO3} tetrahedra through corner-sharing. The dimers are further connected into a chain through hydrogen bonds. In compound 2, edge-sharing {Cu(1)O4N} square pyramids and {Cu(2)O4} planes are found to form an infinite chain with composition {Cu3(µ-OH)2(µ-O)4}. Neighboring chains are linked by the phosphonate groups of the 2-pyridylphosphonate ligands, resulting in inorganic layers containing 4-, 8- and 12-membered rings. The pyridyl groups and the lattice water molecules occupy the inter-layer space. In compound 3, the {Cu(1)O4} and {Cu(2)O2N2} planes are each corner-shared with the {CPO3} tetrahedra, forming an inorganic layer containing 8- and 16-membered rings. The pyridyl groups reside between the layers. Crystal data for 1: space group P, a = 8.4045(19), b = 8.751(2), c = 10.632(2) A, α = 66.673(4), β = 72.566(4), γ = 70.690(4)°, V = 664.7(2) A3, Z = 2. Crystal data for 2: space group P21/c, a = 7.9544(17), b = 21.579(4), c = 5.0243(10) A, β = 105.332(3)°, V = 831.7(3) A3, Z = 2. Crystal data for 3: space group P21/c, a = 4.7793(11), b = 15.319(3), c = 8.6022(19) A, β = 97.156(4)°, V = 624.9(2) A3, Z = 4. Magnetic measurements reveal that dominant antiferromagnetic interactions are propagated between the copper centers in compounds 1–3. For 3, spin canting is observed with a ferromagnetic transition occurring at 9 K.