ИСТИНА

Metal selenites attract attention at the last time due to the variety of crystal structures and possible appearance of structure derived physical properties. The main feature of selenite group is the presence of strongly stereochemically active lone electron pair that needed to be located somewhere in the crystal structure. These pairs tend to form cavities or even layers in the crystal structure. Combination of 3d metals ions and selenite groups may lead to form low dimensional magnetic properties. Such phenomena are in stat of the art in modern magnetic materials chemistry and physics. Usually the Cu2+ (3d9 S = 1/2) or Ni2+ (3d8 S = 1) systems are studied in this aspect. Recently it was shown that Fe3+ (3d5 S = 5/2) selenites may possess quasi one-dimensional magnetic properties 1, 2. In order to extend Fe3+ containing compounds with low dimensional magnetic subsystem we have try to search for new iron selenites and found that Fe2O(SeO3)2 selenite was known for about 20 years3 but no magnetic properties were reported so far. This selenite crystallize in orthorhombic space group P ccn and has three different types of Fe3+ ions in the structure. The crystal structure of the Fe2O(SeO3)2 may be described as sequence of iron-oxygen octahedrons tetrahedrons openwork layers in ab plan of the structure bridged together by selenite groups along [0 0 1] direction. From this consideration it may be assumed, that Fe2O(SeO3)2 may exhibit two dimensional magnetic behavior. In the present study we report new method of single phase Fe2O(SeO3)2 samples preparation as crystals or powder, magnetic susceptibility and heat capacity measurements in combination with Mössbauer spectroscopy. Single crystals of Fe2O(SeO3)2 were obtained by chemical vapor transport method from the mixture of anhydrous FeCl3, Fe2O3 and SeO2 in sealed quartz tube in the temperature gradient 450/400C. Small amount of FeCl3·6H2O was added into the tube before the sealing to improve phase transfer into cold zone. As the result stick like crystals with 1.2 cm biggest length were obtained. The powder sample was prepared in mild hydrothermal conditions from FeCl3·6H2O, H2SeO3 and NaOH in water solution. The measurements of magnetic susceptibility of Fe2O(SeO3)2 reveal short range antiferromagnetic correlations producing broad maximum in (T) curve at about 120 K and the formation of antiferromagnetically ordered state below TN = 110K. The magnetic phase transition is confirmed by  - type anomaly in specific heat at TN and appearance of magnetic sextets in Moessbauer spectra at the same temperature. We want to thank RFBR project 16-03-00463a for the financial support 1. Sh. Hu, M. Johnsson, J. M. Law, J. L. Bettis, Jr., M.-H. Whangbo and R. K. Kremer, Inorg. Chem. 2014, 53, 4250. 2. P. S. Berdonosov, E. S. Kuznetsova, V. A. Dolgikh, A. V. Sobolev, I. A. Presniakov, A. V. Olenev, B.Rahaman, T. Saha-Dasgupta, K. V. Zakharov, E.A. Zvereva, O. S. Volkova, and A. N. Vasiliev, Inorg. Chem. 2014, 53, 5830 3. G. Giester Z. Kristallogr 1996 211 603