Extended hydrogen network in the structures of Na6M(SO4)4·2H2O (M = Fe, Co, Ni): Synthesis, crystal structures, spectroscopic and magnetic properties

Three hexasodium transition metal sulfates, Na 6 M (SO 4 ) 4 ·2H 2 O ( M  = Fe, Co, Ni) were obtained by a dissolution and precipitation route and by hydrothermal reactions . The compounds were characterized by single crystal X-ray diffractions, UV/vis and IR spectroscopy , thermal analyses, and magnetization measurements. The title compounds all crystallize in the triclinic space group P 1 ‾ (No. 2) with Z  = 1 and lattice parameters : a  = 6.0679(8), b  = 6.8658(8), c  = 10.1508(12) Å, β  = 92.557(4)° for Na 6 Fe(SO 4 ) 4 ·2H 2 O; a  = 6.0595(5), b  = 6.8446(6), c  = 10.1149(8), β  = 92.548(2)° for Na 6 Co(SO 4 ) 4 ·2H 2 O; a  = 6.0490(4), b  = 6.8265(5), c  = 10.0793(7), β  = 92.5470(10)° for Na 6 Ni(SO 4 ) 4 ·2H 2 O, respectively. [M(SO 4 ) 4 ] 6- anions are interconnected by hydrogen bonds to form two-dimensional layers in these structures. The solid-state UV/vis/NIR diffuse reflectance spectroscopy indicates that Na 6 M (SO 4 ) 4 ·2H 2 O ( M  = Co, Ni) are insulators. Magnetization experiments show a nearly linear temperature dependence of the inverse susceptibility down to 2 K, which indicates a paramagnetic behavior for all three compounds.