Magnetic properties of some neptunyl(+1) complexes

A summary report on the magnetic properties of some neptunyl(+1) complexes (two formates; (NH4)[NpO2(O2CH)2](1), [NpO2(O2CH)(H2O)](2), and a phthalate, [(NpO2)2(O2C)2C6H4(H2O)3] (3)) is presented based on the magnetic and 237Np Mossbauer data obtained in our group for powder samples and the available single-crystal structural data. It is demonstrated that the remarkable correlations exist between the magnetic properties, the 237Np Mossbauer parameters and the structural features (dimensionality, neptunyl (O=Np=O) bonding network structure, etc.) among these uniquely low-dimensional neptunyl complexes. The magnetic data show that 1 with neptunyl (O=Np=O) 1D chain structure is paramagnetic (or only marginally ferromagnetic) down to 2 K, while 2 and 3 with similar 2D neptunyl sheet structure order ferromagnetically at Tc = 12 and 4.5 K, respectively. In addition, 3 having two kinds of Np sites exhibited a two-step magnetization behavior below Tc. Consistent with these magnetic data, 237Np Mussbauer spectra o...