Sr18Ru1.9Bi4.1O33: crystallization of a Ru(V)/Bi(V) oxide from molten hydroxide

Abstract

Single crystals of a new complex oxide, Sr18Ru1.9Bi4.1O33, were precipitated from a mixture of molten alkali and alkaline earth metal hydroxides at 750°C. The structure was determined from a ruby-red crystal using single-crystal X-ray diffraction. Sr18Ru1.88Bi4.12O33 crystallizes in the space group C2/c (monoclinic) and has unit-cell dimensions: a=10.2102(11) Å, b=17.882(2) Å, c=19.579(2) Å, and β=102.043(2)°. The structure (refined to R1=4.5%, wR2=9.2%) is an unusual ABO3 defect perovskite, with 1/12 th of the oxygen positions vacant. All the A sites and half of the B sites are occupied by Sr2+, while the remaining B sites are occupied by Bi5+ or Ru5+. The oxygen atom vacancies are located within the Bi coordination sphere exclusively. The bonding in the BO3 sublattice is less covalent than that in the perovskite archetype from which it is derived due to the presence of 50% Sr2+ on the B sites. Thus, the structure of Sr18Ru1.9Bi4.1O33 can also be viewed as being made up of isolated bismuthate anions (BiO55−, BiO5.56− and BiO67−) and ruthenate anions (RuO67−) separated by strontium cations.