COREO4, A NEW RUTILE-TYPE DERIVATIVE WITH ORDERING OF 2 CATIONS

CoReO4 crystallizes in space group Cmmm with a = 6.5156(7)Å, b = 6.7418(8)Å, c = 2.8923(3)Å. It is most likely to be formulated as Co+3Re+5O4. The bonding topology of the connections of the coordination octahedra around the Co and the Re atoms is identical to the arrangement of the coordination octahedra in the rutile type. Octahedral edge-sharing rutile-type chains of compositions CoO4 and ReO4 are present which are connected via corners, resulting in an overall chemical formula of CoReO4. The space group type of CoReO4, Cmmm, is a maximal nonisomorphic subgroup of order two of the space group type of rutile, P42/mnm; it is translationengleich with its supergroup. The space group type of MgUO4, Imam, is in turn a maximal nonisomorphic subgroup of order two of space group Cmmm; it is klassengleich with its supergroup. Thus the structure type of CoReO4 can be seen as an intermediate step in the reduction of the symmetry of the rutile type proper to the distorted rutile-type variant represented by MgUO4. The crystal structure of CoReO4 represents a new type derived from the rutile type by ordering of two cations. It is the fourth structure type of this kind. © 1992 Academic Press, Inc. All rights reserved.