Observation of Haldane magnetism in organically templated vanadium phosphate ( en H 2 ) 0.5 VPO 4 OH

We prepared an organically templated magnet, ( H ) VPO OH ( H = diprotonated ethylenediamine), hydrothermally and characterized its crystal structure by powder X-ray diffraction and Fourier-transform infrared spectroscopy, and its physical properties by magnetization, specific heat and nuclear magnetic resonance measurements and density functional theory calculations. ( H ) VPO OH consists of uniform chains of V (d , = 1) ions and exhibits Haldane magnetism with spin gap = 59.3 K from the magnetic susceptibility ( ) at = 0.1 T, which is reduced to 48.4 K at = 9 T according to the P shift. The NMR data evidence the formation of a spin-glass state of unpaired = 1/2 spins at ≈ 3 K and indicate that the Haldane = 1 spin chain segments are much longer in the organically templated magnet ( H ) VPO OH than in the ammonium counterpart NH VPO OH. The single-ion anisotropy and the interchain exchange ' in ( H ) VPO OH and NH VPO OH were estimated in density functional calculations to find them very weak compared to the intrachain exchange .