Copper Phosphonates based on 2-Phosphonic-isonicotinate: Structures and Magnetic Properties

Hydrothermal reactions of 2-phosphonic isonicotinic acid (pinH3, HOOC-C5H3N-PO3H2) with cupric chloride afford two copper phosphonates: Cu3(pin)2(H2O)2 (1) and Cu(pinH2)2 (2). Compound 1 crystallizes in the monoclinic space group C2/c with a = 15.913(5) Å, b = 6.016(2) Å, c = 18.043(5) Å, β = 90.518(9)°, and V = 1727.2(8) Å3. In this structure, dimers of {Cu2O2} are linked by {CuO6} octahedra through O(1W) forming an inorganic chain. The adjacent chains are further connected by {CPO3} tetrahedra to form an undulating inorganic layer. The inorganic layers are pillared by the pyridyl groups of the ligand, resulting in a three-dimensional framework structure. Compound 2 crystallizes in the monoclinic space group C2/c with a = 19.039(3) Å, b = 7.185(1) Å, c = 12.355(2) Å, β = 116.666(3)°, and V = 1510.4(4) Å3. It shows a chain structure in which the adjacent {CuN2O4} octahedra are doubly bridged by two phosphonate ligands. Ferromagnetic interactions are found to be mediated between the Cu(II) centers in 1. Ac magnetic susceptibility measurements suggest a long-range ferromagnetic ordering at ca. 1.8 K. For 2, the magnetic behavior is in principle paramagnetic.