PHYSICO-CHEMICAL CHARACTERISTICS OF MATERIALS BASED ON CERIUM AND CHROMIUM LANTHANOIDES

Abstract

Some physical and chemical characteristics of hexa(thiocyanate-N)chromate complexes of cerium lanthanides with 3-pyridine-3-carboxylic acid are studied. It was shown by IR spectroscopy for displacement of the main absorption bands that the compounds are N-thiocyanate, the organic ligand is bidentate due to the proton transfer of the carboxyl group to atom nitrogen with the formation of a conjugate system: imino-amine tautomerism of organic ligand leads to the occurrence of pyridinium-3-carboxylic ion. It was established by X-ray diffraction analysis of monocrystals that substances have an isle structure, crystallize according the same structural type, and their crystallographic parameters change regularly in accordance with the change in the radii of Ln3+ ions. The obtained substances of the isle type are isostructural. Iintermolecular hydrogen bonds between crystallization water molecules and N–H groups of coordinated molecules of organic ligands are found. The compositions of the substances differ only in the content of crystallization water in the molecules. Studies of the magnetic properties of the samples were carried out taking into account their stability in the range of 80-360 K. The decomposition sequence is established and composition of thermolysis products. The experimental and calculated values effective magnetic moments is in agreement. Values effective magnetic moments characterize the antiferromagnetic nature of the interaction between paramagnetic centers. At temperatures below 100 K, discrepancies between the experimental and calculated values are observed, which may be due to the transition of compounds from the paramagnetic to antiferromagnetic state. The thermal behavior of substances in an inert atmosphere and oxidizing atmospheres to interval of tempetures 293-1273 K are presented. Compounds obtained determine the promising magnetic and thermal properties of substances as precursors for the low-temperature production of heterometallic oxide ceramic materials, as well as molecular magnets and thermoindicators for visual control of temperatures and temperature fields.