Fragmentation of an infinite Zn[O.sub.2] square plane into discrete [[Zn[O.sub.2]].sup.2-] linear units in the oxyselenide [Ba.sub.2]An[O.sub.2][Ag.sub.2][Se.sub.2]

The crystal structure of the analogous compound [Ba.sub.2]Zn[O.sub.2][Ag.sub.2][Se.sub.2] is described. The studies have shown that when the Zn[O.sub.2] plane is placed under tension in order to accommodate the large [Ba.sup.2+], [Ag.sup.+] and [Se.sup.2-] ions, the square planar coordination of zinc by oxide is unsustainable.