Axial Mn–CCN Bonds of Cyano Manganese(II) Porphyrin Complexes: Flexible and Weak?

Three
five-coordinate high-spin (cyano)­manganese­(II) complexes,
utilized tetraphenylporphyrin (TPP), tetratolylporphyrin (TTP), and
tetramesitylporphyrin (TMP) as ligands, are prepared and studied by
single-crystal X-ray, FT-IR, UV–vis, and EPR spectroscopies.
The crystal structure studies revealed noteworthy structural features
including unexpectedly wide tilting angles of the axial Mn–CCN bonds, which is contrasted to the isoelectronic Fe­(III)–CCN bonds. Solid-state EPR measurements (90 K) and simulations
are applied to obtain the ZFS parameters (D, E, and E/D (λ)),
which are compared to Mn­(II) porphyrin analogues of hemes to understand
the ligand field of the cyanide. The solution EPR studies gave new
insights into the chemical equilibrium of four- and five-coordinate
species, which has been monitored by UV–vis spectroscopy.

本研究制备并研究了以四苯基卟啉（TPP）、四托尔基卟啉（TTP）和四甲氧基苯基卟啉（TMP）为配体的三价高自旋（氰基）锰（II）配合物。通过单晶X射线、傅里叶变换红外光谱（FT-IR）、紫外-可见光谱（UV–vis）和电子顺磁共振光谱（EPR）对配合物进行了表征。晶体结构研究表明，轴向Mn–CCN键的倾斜角度出人意料地宽，与等电子的Fe（III）–CCN键形成鲜明对比。在固态EPR测量（90 K）和模拟中，应用以获得零场分裂参数（D、E以及E/D（λ）），并与血红素中锰（II）卟啉类似物进行比较，以理解氰基配体的配位场。溶液EPR研究为四配位和五配位物种的化学平衡提供了新的见解，这些平衡已通过紫外-可见光谱进行监测。