Two isotypic diphosphates LiM2H3(P2O7)(2) (M = Ni, Co) containing ferromagnetic zigzag MO6 chains

Two new isotypic phosphates LiNi2H3(P2O7)2 (1) and LiCo2H3(P2O7)(2) (2) have been hydrothermally synthesized and structurally characterized by the single-crystal X-ray diffraction technique. They crystallize in the monoclinic space group C2/c with the lattice: a = 10.925(2) angstrom, b = 12.774(3) angstrom, c = 8.8833(18) angstrom, beta = 123.20(3)degrees for 1 and a = 10.999(2) angstrom, b = 12.863(3) angstrom, c = 8.9419(18) angstrom, beta = 123.00(3)degrees for 2. The transition metal atoms are octahedrally coordinated, whereas the lithium and phosphorus atoms are all tetrahedrally coordinated. As the lithium-induced derivatives of MH2P2O7 (M = Ni, Co), 1 and 2 possess the same structure with MH2P2O7 in terms of topology, comprising the MO6 zigzag chains and P2O7 as the interchain groups. The magnetisms of 1 and 2 could be interpreted by adopting a quasi-one-dimensional (1D) zigzag chain model as that in their parent compounds: both 1 and 2 have ferromagnetic (FM) NiO6/CoO6 chains; 1 shows a FM cluster glass behavior at low temperatures, which is originated from the possible antiferromagnetic (AFM) next-nearest-neighbour intrachain interactions; 2 shows a AFM ordering at T-N = 2.6 K and a metamagnetic transition at H-C = 4.2 kOe at 1.8 K. (c) 2008 Elsevier Inc. All rights reserved.