Tunable Synchronicity of Molecular Valence Tautomerism with Macroscopic Solid‐Liquid Transition by Molecular Lattice Engineering.

The combination of a cobalt‐dioxolene core that exhibits valence tautomerism (VT) with pyridine‐3,5‐dicarboxylic acid functionalized with chains bearing two, four, or six oxyethylene units led to new complexes ConEGEspy (n = 2, 4, and 6). These complexes commonly form violet crystals of the low‐spin (ls)‐[CoIII(nEGEspy)2(3,6‐DTBSQ)(3,6‐DTBCat)] (ls‐[CoIII], 3,6‐DTBSQ = 3,6‐di‐tert‐butyl semiquinonato, 3,6‐DTBCat = 3,6‐di‐tert‐butyl catecholato). Interestingly, violet crystals of Co2EGEspy in the ls‐[CoIII] transitioned into a green liquid, accompanied by an almost complete VT shift (94 %) to the high‐spin (hs)‐[CoII(nEGEspy)2(3,6‐DTBSQ)2] (hs‐[CoII]) upon melting. In contrast, violet crystals of Co4EGEspy and Co6EGEspy in the ls‐[CoIII] exhibited partial VT (33 %) and only a 9.3 % VT shift after melting, respectively. These data demonstrate the tunability of the synchronicity of the molecular VT and macroscopic solid‐liquid transitions by optimizing the tethered chains, thus establishing a new strategy for coupling bistable molecules with the macroscopic world. [ABSTRACT FROM AUTHOR]