Synthesis, Structure, and Magnetic Properties of the New Layered Compound HNiPO_4·H_2O. Study of Alkylamine Intercalated Compounds

摘要

The new layered HNiPO_4·H_2O compound has been prepared and characterized, and its crystal structure resolved. It crystallizes in the monoclinic P2_1 space group with cell parameters a = 8.069(3), b = 4.726(1), c = 5.597(1) A, β = 109.62(2)°, V = 201.04 A~3, Z = 2. The structure consists of (100) sheets of NiO_6 corner-sharing octahedra cross-linked by (HPO_4) groups. These sheets are linked by a zig-zag system of hydrogen bonds along the [010] direction, involving the (OH) group of the (HPO_4) tetrahedra arranged toward the interlayer space. Five different alkyl amines, C_nH_(2n+1)NH_2 (n = 3-7), have been intercalated in this compound to form the (C_nH_(2n+1)NH_2)_xHNiPO_4·H_2O phases. The intercalated derivatives present the inserted alkylamines arranged in bilayers and tilted at an angle of approximately 53.2° with respect to the inorganic sheets. The extent of intercalation is approximately constant (0.75) with the only exception being butylamine. No changes in particle size and morphology have been observed during the intercalation reactions. Thermal studies suggest that the alkyl amine desorption in these compounds takes place in only one step. Magnetic measurements of (C_7H_(15)NH_2)_(0.76)HNiPO·H_2O show the existence of essential 2D antiferro-magnetic intralayer interactions. In the case of HNiPO_4·H_2O, an increase 3D interlayer ordering appears when temperature decreases due to the presence of hydrogen bonds between layers in the structure of this compound.