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PENTADECACOPPER(II) BISDIBORATE HEXAORTHOBORATE DIOXIDEis the only structure in which the isolated anions B2 O4-, BO]-and 0 2-are found together. ment with the diamagnetism observed for ReP a. The structure can be described as a stacking of identical layers of puckered pentagons and hexagons. In this way it is closely related to the structures of many compounds with compositions TX 2 and TX 4 (X = P, As, Sb, S, Se).

Chicago, Chicago, Illinois 60637. \Ve consider the incontrovertible global success of the structural sorting maps for solid state AB compounds produced by St. John and Bloch (Phys. Rev. Letts. (1974) 33 1095), Chelikowsky and Phillips (Phys. Rev. B (1978) 17 2453), and Zunger (Phys. Rev. B (1980) 5839).These authors construct t\\i'O dimensional di5Plays, using combinations of atomic parameters from pseudopotential theory, which produce a remarkable topological clustering of AB compounds with the same structure.We find a justification for this phenomenology in terms of a very simple molecular orbital model for the interactions betHeen atoms A and B. By using a slightly more rigorous molecular orbital treatment, l

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