Microscopic Mechanism for Precise Control of the Sizes\nof Molybdenum Blue Nanorings

Molybdenum\nblue (MB) nanorings with monodispersed, well-defined\nstructures can be feasibly prepared via treatment of molybdate solutions\nwith reducing agents at acidic conditions. However, the hidden constraints\nthat control their ring sizes have been unknown for decades. Herein,\nthe formation of 3.4 and 4.1 nm nanorings, {Mo<sub>154</sub>} and\n{Mo<sub>176</sub>}, is monitored using small-angle X-ray scattering\n(SAXS) with systematically varied synthetic conditions. Results suggest\nthat {Mo<sub>154</sub>} forms quickly in solution and then undergoes\nslow transformation into {Mo<sub>176</sub>} when reducing agents are\nused, while {Mo<sub>176</sub>} can form directly with MoCl<sub>5</sub> supplied as reduced Mo<sup>V</sup>. These are attributed to {Mo<sub>154</sub>} being the kinetic product catalyzed by the template-effect\nwhile {Mo<sub>176</sub>} is the thermodynamic product due to its low\nring tension. Our findings unravel one of the long-standing mysteries\nin MB and point out effective routes for the precise synthesis of\nnanorings.