Valence Tautomeric Transitions of Three One-Dimensional Cobalt Complexes
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Three novel complexes, namely, [CoIII(3,5-DBCat)(3,5-DBSq)(bpe)]·2CH3CN·2H2O (1·S), [CoIII(3,5-DBCat)(3,5-DBSq)(azpy)]·2CH3CN·2H2O (2·S), and [CoII(3,5-DBSq)2(bpb)][CoIII(3,5-DBCat)(3,5-DBSq)(bpb)]0.5·2CH3CN·2H2O (3·S), were synthesized and characterized by valence tautomeric (VT) X-ray diffraction and magnetic measurements [where 3,5-DBCatH2 = 3,5-di-tert-butyl-catechol, 3,5-DBSqH = 3,5-di-tert-butyl-semiquinone, bpe = trans-bis(4-pyridyl)ethylene, azpy = trans-4,4′-azopyridine, and bpb = 1,4-bis(4-pyridyl)benzene]. The three complexes have similar one-dimensional chain structure building from bidentate-bridging pyridine ligands and planar 3,5-DBCat/3,5-DBSq-fixed CoII/III entities. Complexes 1·S and 2·S could retain the crystallinity during desolvation, and the crystal structures of 1 and 2 were therefore able to be determined. Only when 1·S and 2·S desolvated above 310 K did the magnetic susceptibilities × temperatures values of the two complexes rise sharply, and then thermally induced complete, one-step VT transitions for 1 and 2 were available and repeatable. Complex 3·S showed an incomplete, one-step VT transition independent of solvent molecules. Among these complexes, only 1 was sensitive to photoexcitation at low temperature, its photoinduced metastable state relaxed with temperature-independent behavior at low temperature range (5–10 K) and with thermally assisted behavior at high temperature range (above 20 K), respectively.
本研究合成了三种新型配合物，分别为[CoIII(3,5-DBCat)(3,5-DBSq)(bpe)]·2CH3CN·2H2O（记为1·S）、[CoIII(3,5-DBCat)(3,5-DBSq)(azpy)]·2CH3CN·2H2O（记为2·S）以及[CoII(3,5-DBSq)2(bpb)][CoIII(3,5-DBCat)(3,5-DBSq)(bpb)]0.5·2CH3CN·2H2O（记为3·S），并通过价态互变异构（valence tautomeric, VT）X射线衍射与磁学测量手段对其进行了表征；其中3,5-DBCatH2=3,5-二叔丁基邻苯二酚，3,5-DBSqH=3,5-二叔丁基半醌，bpe=反式双(4-吡啶基)乙烯，azpy=反式4,4'-偶氮吡啶，bpb=1,4-双(4-吡啶基)苯。 三种配合物均具有相似的一维链状结构，由双齿桥联吡啶配体与被3,5-DBCat/3,5-DBSq配位固定的CoII/CoIII单元构筑而成。 配合物1·S与2·S在脱溶剂过程中可保持晶体完整性，因此可测定脱溶剂后产物1与2的晶体结构。 仅当1·S与2·S在310 K以上温度下完成脱溶剂时，二者的磁化率-温度乘积值会急剧升高，此时可实现热诱导的一步完全价态互变异构转变，且该转变具有良好的可重复性。 配合物3·S则表现出不完全的一步价态互变异构转变，且该转变不受溶剂分子的影响。 在上述三种配合物中，仅配合物1在低温下对光激发敏感：其光诱导亚稳态在低温区间（5~10 K）以与温度无关的方式弛豫，而在高温区间（20 K以上）则表现为热辅助弛豫行为。
