Crystal structure and magnetic properties of Na2NiII(HPO3)2

Na2Ni(HPO3)2, obtained as light yellow-green crystals under mild hydrothermal conditions, crystallizes in the orthorhombic Pnma space-group with lattice parameters: a=11.9886(3), b=5.3671(2), c=9.0764(3) Å, V=584.01 Å3, Z=4. The structure consists of zig-zag chains of NiO6 octahedra bridged by two HPO32− and the chains are further connected through HPO32− to four nearest chains to form a three dimensional framework, delimiting intersecting tunnels in which the sodium ions are located. The Na cations reside in the irregular Na(1)O5, Na–O of 2.276–2.745 Å, and Na(2)O9, Na–O of 2.342–2.376 Å, environments. The presence of the phosphite monoanion has been further confirmed by IR spectroscopy. Due to the 3D framework of Ni connected by O–P–O bridges, the magnetic susceptibility behaves as a paramagnet above 100 K (C=1.49(2) emu K mol−1, μeff=3.45 μB, Θ=−39(2) K) and below 6 K, it orders antiferromagnetically as confirmed the sharp drop and the non-Brillouin behavior of the isothermal magnetization at 2 K.