Bipyramidal Au microcrystallites have been synthesized by thermalizing a Au-organic complex in the presence of Ag(Ⅰ) ions,the latter acting as a shapedirecting agent.With a highly corrugated morphology leading to strain-induced non-face-centered cubic (non-FCC) Au phases,the non-FCC portion can be tuned by varying the Ag/Au ratio,as verified by diffraction measurements.For a Ag/Au ratio of 0.34,the non-FCC Au portion was as high as 85%.X-ray microdiffraction and electron diffraction measurements reveal that the non-FCC contribution comes primarily from bipyramids,while other microcrystallites,namely,tetrahexahedrons and hexagrams,host non-FCC phases only at the edges and,to an even lesser extent,at the corners.When used as a catalyst for p-nitrophenol reduction,the non-FCC microcrystallites exhibit a significantly enhanced activity compared to FCC Au,which shows only negligible activity.These results are in accordance with trends in the values of two descriptors of reactivity calculated from first principles:The effective coordination number is found to decrease and the d-band center is found to increase in energy going from the FCC to the non-FCC phases of Au.Our findings contradict the general notion that Au is catalytically active only in nanodimensions and is otherwise inert;in this system,its activity arises from the non-FCC phases.