Redox Potential Tuning of Dimolybdenum Systems through Systematic Substitution by Guanidinate Ligands
Redox Potential Tuning of Dimolybdenum Systems through Systematic Substitution by Guanidinate Ligands
复制标题
通过胍酸酯配体的系统取代来调节二钼系统的氧化还原电位
DOI：
10.1021/acs.inorgchem.9b03394
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发表时间：
2020
影响因子：
4.6
通讯作者：
Villagrán, Dino
中科院分区：
文献类型：
--
作者：
Rodríguez-López, Nancy;Metta, Nathalie;Metta-Magana, Alejandro J.;Villagrán, Dino
本文报道了一系列Mo_2（DAniF）_4-n（hpp）_n（n= 1-3）型双钼叶轮配合物的合成与表征。DAniF为N，N′-二对茴香基甲脒的阴离子，hpp为1，3，4，6，7，8-六氢-2H-嘧啶并[1，2-a]嘧啶的阴离子。研究了胍基取代甲脒基配体对四氢轮状二钼化合物电子结构的影响。当胍基取代时，叶轮结构中的Mo-Mo距离减小，Mo_2（DAniF）_3（hpp）（1）和trans-Mo_2（DAniF）_2（hpp）_2（2）的Mo-Mo距离分别为2.0844（6）和2.0784（6）。电化学研究表明，Mo 25 +/Mo 24+电对的半波电位在辅助配体取代后发生阴极偏移，范围从tetraformamidinate络合物的−0.286 V到tetraguanidinate类似物的−1.795 V，1、2和3（Mo 2（DAniF）（hpp）3）的氧化还原电位分别为−0.75、−1.07和−1.14 V。直到引入两个胍基配体才观察到分配给Mo 26 +/Mo 25+对的第二氧化还原事件的存在。拉曼光谱表明，v（M-M）伸缩得到系统地加强后，甲脒配体取代胍配体hpp。通过追踪前线轨道的能量，使用DFT计算测量由碱性hpp配体引起的δ键不稳定。HOMO-LUMO能隙的减小由化合物的紫外-可见光谱中的红移支持：对于1、2和3，分别为412、442和450 nm。
We report the synthesis and characterization of a series of dimolybdenum paddlewheel complexes of the type Mo2(DAniF)4–n(hpp)n(n= 1–3), where DAniF is the anion ofN,N′-di-p-anisyl-formamidine and hpp is the anion of 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine. The effect on the electronic structure of these tetragonal paddlewheel dimolybdenum compounds was studied upon systematic substitution of formamidinate ligands by the more basic guanidinates. Mo–Mo distances in the paddlewheel structures decreased upon guanidinate ligand substitution, and were found to be 2.0844(6) and 2.0784(6), for Mo2(DAniF)3(hpp) (1) andtrans-Mo2(DAniF)2(hpp)2(2), respectively. Electrochemical studies show that the half-wave potential of the Mo25+/Mo24+couple shifts cathodically upon ancillary ligand substitution ranging from −0.286 V for the tetraformamidinate complex to −1.795 V for the tetraguanidinate analogue and with redox potentials of −0.75, −1.07, and −1.14 V for1,2, and3(Mo2(DAniF)(hpp)3), respectively. The presence of a second redox event assigned to the Mo26+/Mo25+couple was not observed until two guanidinate ligands were introduced. Raman spectroscopy shows that thev(M–M) stretch gets systematically strengthened upon formamidinate ligand substitution by the guanidinate ligand hpp. The induced delta bond destabilization by the basic hpp ligand was measured using DFT calculations by tracking the energy of the frontier orbitals. The decrease in the HOMO–LUMO energy gap was supported by the red shift in the UV–vis spectra of the compounds: 412, 442, and 450 nm for1,2, and3, respectively.