posted on 2021-05-05, 07:14authored byJianping Zhao, Fei Qian, Wenping Guo, Jianfeng Li, Zeyuan Lin
Three
different manganese(II) porphyrins have been exploited to
react with 4-methylimidazolate (4-MeIm–), and the
five-coordinate products are characterized by ultraviolet–visible,
single-crystal X-ray, and electronic paramagnetic resonance spectroscopies.
Interestingly, 4-MeIm– is found to bond to the metal
center through either of the two N atoms (N1 or N3), which yielded
two linkage isomers with either an unhindered or a hindered ligand
conformation, respectively. Investigations revealed it is the large
metal out-of-plane displacements (Δ24 and Δ4 ≥ 0.59 Å) that have rendered the equivalence
of two isomers with a small energy difference (5.2–8.3 kJ/mol).
The nonbonded intra- and intermolecular interactions thus become crucial
factors in the balance of linkage isomerization. All of the products
in both solution and solid states show the same characteristic resonances
of high-spin Mn(II) (S = 5/2) with g⊥ ≈ 5.9 and g∥ ≈ 2.0 at 4 K, consistent with
the weak effects of the axial ligand on core conformation and metal
electronic configurations. Zero-field splitting parameters obtained
through simulations are also reported.