Spin Canting and Metamagnetism in the First Hybrid Cobalt-Hypoxanthine Open Framework with umr Topology

Hydrothermal reactions generated a cobalt-hypoxanthine framework [Co-3(OH)(4)(Hpxt)(2)]center dot 2H(2)O (H(2)pxt= 6-hydroxypurine, 1 center dot 2H(2)O), which became a microporous framework [Co-3(OH)(4)(Hpxt)(2)] (1) through a single-crystal-to-single-crystal transformation. Compound 1 center dot 2H(2)O shows a three-dimensional umr topological structure with two types of spiral channels constructed by rod-shaped {Co-3(mu-OH)(4)(N-C-N)(2)(N-C-C-O)(2)} second building units (SBUs). The larger channel is filled by fourfold spiral water chains. An unprecedented mu(5)-O6,N3,N7,N9 coordination mode of the Hpxt anion was observed. Both complexes 1 center dot 2H(2)O and 1 qualitatively show similar metamagnetism from anti-parallel to parallel ferromagnetic cobalt-hydroxide chains. Compared with 1 center dot 2H(2)O, a smaller Curie constant and more negative Weiss constant in 1 indicate that the helical water chains tend to suppress antiferromagnetic coupling between Co-3(OH)(4) ferromagnetic chains. Detailed magnetic studies of 1 center dot 2H(2)O revealed that the competitive interactions between interchain antiferromagnetic exchange coupling and single-ion anisotropy of Co-II resulted in a partly canted antiferromagnetic sate in low fields. Anti-parallel arrangement of adjacent ferromagnetic chains in middle fields gives 3D antiferromagnetic ordering, and magnetic ground states in high fields are a parallel arrangement of ferromagnetic chains.