Band Structure Engineering by Substitutional Doping in Solid-State Solutions of [5-Me-PLY(O,O)]2B(1鈥?i>x)Bex Radical Crystals

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• 作者：Pradip Bag ; Mikhail E. Itkis ; Dejan Stekovic ; Sushanta K. Pal ; Fook S. Tham ; Robert C. Haddon
• 刊名：Journal of the American Chemical Society
• 出版年：2015
• 出版时间：August 12, 2015
• 年：2015
• 卷：137
• 期：31
• 页码：10000-10008
• 全文大小：660K
• ISSN：1520-5126

文摘

We report the substitutional doping of solid-state spiro-bis(5-methyl-1,9-oxido-phenalenyl)boron radical ([2]₂B) by co-crystallization of this radical with the corresponding spiro-bis(5-methyl-1,9-oxido-phenalenyl)beryllium compound ([2]₂Be). The pure compounds crystallize in different space groups ([2]₂B, P1虆, Z = 2; [2]₂Be, P2₁/c, Z = 4) with distinct packing arrangements, yet we are able to isolate crystals of composition [2]₂B_(1鈥?i>x)Be_x, where x = 0鈥?.59. The phase transition from the P1虆 to the P2₁/c space group occurs at x = 0.1, but the conductivities of the solid solutions are enhanced and the activation energies reduced for values of x = 0鈥?.25. The molecular packing is driven by the relative concentration of the spin-bearing ([2]₂B) and spin-free ([2]₂Be) molecules in the crystals, and the extended H眉ckel theory band structures show that the progressive incorporation of spin-free [2]₂Be in the lattice of the [2]₂B radical (overall bandwidth, W = 1.4 eV, in the pure compound) leads to very strong narrowing of the bandwidth, which reaches a minimum at [2]₂Be (W = 0.3 eV). The results provide a graphic picture of the structural transformations undergone by the lattice, and at certain compositions we are able to identify distinct structures for the [2]₂B and [2]₂Be molecules in a single crystalline phase.