Laboratoire de Chimie Moléculaire, CNRS, Ecole Polytechnique , Palaiseau, France.
J Am Chem Soc. 2014 Jun 18;136(24):8626-41. doi: 10.1021/ja502271q. Epub 2014 Jun 9.
The electronic structure and associated magnetic properties of the 1,10-phenanthroline adducts of Cp2Yb are dramatically different from those of the 2,2'-bipyridine adducts. The monomeric phenanthroline adducts are ground state triplets that are based upon trivalent Yb(III), f(13), and (phen(•-) ) that are only weakly exchange coupled, which is in contrast to the bipyridine adducts whose ground states are multiconfigurational, open-shell singlets in which ytterbium is intermediate valent ( J. Am. Chem. Soc 2009 , 131 , 6480 ; J. Am. Chem. Soc 2010 , 132 , 17537 ). The origin of these different physical properties is traced to the number and symmetry of the LUMO and LUMO+1 of the heterocyclic diimine ligands. The bipy(•-) has only one π1 orbital of b1 symmetry of accessible energy, but phen(•-) has two π* orbitals of b1 and a2 symmetry that are energetically accessible. The carbon pπ-orbitals have different nodal properties and coefficients and their energies, and therefore their populations change depending on the position and number of methyl substitutions on the ring. A chemical ramification of the change in electronic structure is that Cp2Yb(phen) is a dimer when crystallized from toluene solution, but a monomer when sublimed at 180-190 °C. When 3,8-Me2phenanthroline is used, the adduct Cp2Yb(3,8-Me2phen) exists in the solution in a dimer-monomer equilibrium in which ΔG is near zero. The adducts with 3-Me, 4-Me, 5-Me, 3,8-Me2, and 5,6-Me2-phenanthroline are isolated and characterized by solid state X-ray crystallography, magnetic susceptibility and LIII-edge XANES spectroscopy as a function of temperature and variable-temperature (1)H NMR spectroscopy.
1,10-菲咯啉与 Cp2Yb 的加合物的电子结构和相关磁性与 2,2'-联吡啶加合物有很大的不同。单体菲咯啉加合物是基于三价 Yb(III)、f(13)和(phen(•-))的基态三重态，它们只是弱的交换耦合，这与联吡啶加合物形成对比，联吡啶加合物的基态是多组态的、开壳层的单重态，其中镱是中间价态（J. Am. Chem. Soc 2009, 131, 6480; J. Am. Chem. Soc 2010, 132, 17537）。这些不同物理性质的起源可以追溯到杂环二亚胺配体的最低未占据分子轨道（LUMO）和最低占据分子轨道+1（LUMO+1）的数目和对称性。Bipy(•-)只有一个可及能量的 b1 对称的π1轨道，但 phen(•-)有两个π轨道，b1 和 a2 对称，能量可及。碳 pπ-轨道具有不同的节点性质和系数，以及它们的能量，因此它们的分布取决于环上甲基取代的位置和数量。电子结构变化的一个化学后果是，Cp2Yb(phen)从甲苯溶液中结晶时是二聚体，但在 180-190°C 升华时是单体。当使用 3,8-Me2phenanthroline 时，Cp*2Yb(3,8-Me2phen)在溶液中以二聚体-单体平衡存在，其中ΔG 接近零。具有 3-Me、4-Me、5-Me、3,8-Me2 和 5,6-Me2-phenanthroline 的加合物通过固态 X 射线晶体学、磁化率和 LIII 边 XANES 光谱以及温度和变温（1）H NMR 光谱进行了分离和表征。
