Trivalent-intermediate valent cerium ordering in CeRuSn - A static intermediate valent cerium compound with a superstructure of the CeCoAl type

摘要

New equiatomic starmide CeRuSn was synthesized from the elements by arc-melting. CeRuSn was investigated by X-ray powder and single crystal diffraction: C2/m, a = 1156.1(4), b = 475.9(2) and c = 1023.3(4) pm, beta = 102.89(3)degrees, wR2 = 0.0466, 1229 F 2 values and 38 variables. CeRuSn adopts a superstructure of the monoclinic CeCoAl type through a doubling of the subcell c axis. In the superstructure two crystallographically independent cerium sites occur. Based on the interatomic distances the two sites can be assigned to trivalent Ce2 and intermediate valent Ce1. This trivalent-intermediate valent cerium ordering is underlined by magnetic susceptibility measurements chi(m)(T): below 150 chi(m), measured with decreasing temperature, follows a Curie-Weiss law chi(m) = C-m/(T-theta(p)) giving C. = 0.38 emuK/mol as Curie constant per CeRuSn mol; a value showing that only half of the cerium atoms are trivalent in CeRuSn (C. = 0.807 emuK/mol for one free Ce3+ ion). A remarkable feature of the CeRuSn structure are the short Cel-Ru1 (233 pm) and Cel-Ru2 (246 pm) distances. The crystal chemistry of CeRuSn is discussed on the basis of a group-subgroup scheme.