Pt29Zn49, a complex defective AlB2-type derivative structure

The crystal structure of the title compound has been determined by X-ray diffraction means. Pt29Zn49 forms a complex superstructure of a defective AlB2-type derivative of the order 58: a = 279.0(1) pm, b = 11895.2(4) pm, c = 698.0(1) pm, space group Amm2, Z = 2. Ordering of vacancies is accompanied by a particular distortion of defective graphite-like 63 nets consisting exclusively of Zn atoms. The ordering induces a modulation of the structure along ah of an AlB2-type structure with a periodicity of nearly 12 nm. A mechanistic model is proposed elucidating how Pt29Zn49 evolves from the eutectoid decomposition of the inter-mediate high temperature precursor Pt7Zn12.