Control of spins by ring deformation in a diiron(iii)bisporphyrin: reversal of ClO4− and CF3SO3− ligand field strength in the magnetochemical series

Abstract

The complete reversal of the ligand field strength of ClO(4)(-) and CF(3)SO(3)(-) in the magnetochemical series is observed in a diiron(III)bisporphyrin. While ClO(4)(-), as the axial ligand, gives a typical high-spin complex, just twisting the conformation of the porphyrin macrocycle gives properties of a pure intermediate-spin state with CF(3)SO(3)(-), although the axial ligand strengths suggest the reverse order of spin stabilization.

Protonation of an Oxo‐Bridged Diiron Unit Gives Two Different Iron Centers: Synthesis and Structure of a New Class of Diiron(III)‐μ‐hydroxo Bisporphyrins and the Control of Spin States by Using Counterions

“…Resonance assignments have been made based on the relative intensities and line widths of the peaks and on the basis of COSY experiment (for a representative case, see Figure S5 in the Supporting Information). The 1 H NMR spectra of 3 is compared with previously reported complexes 1⋅ ClO 4 and 1⋅ OSO 2 CF 3 in Figure 7 10. 12a For high‐spin complex 1⋅ ClO 4 , eight C H 2 proton signals are observed at approximately δ =40 ppm (average position), whereas two meso signals in an intensity ratio of 1:2 occur in the far upfield regions at δ =−35.2 and −52.4 ppm, respectively (Figure 7, trace A).…”

“…The free ligand 1,2‐bis( meso ‐octaethylporphyrinyl)ethane was synthesized as reported previously 14. Iron was inserted into the bisporphyrin core to produce complex 1⋅ X with various axial ligands X (X: Cl, Br, I, ClO 4 , OSO 2 CF 3 ) as reported previously 10. 12a,c…”

“…As the iron moves toward the porphyrin mean plane in the spin‐admixed complexes, the d–a 2u interaction becomes less favorable and as a result the meso proton signals move downfield toward the diamagnetic region and the C H 2 protons move upfield. In complex 1⋅ OSO 2 CF 3 , eight sharp methylene resonances are observed in a relatively narrow region (from δ =21.6 to 16.0 ppm; average δ =18.2 ppm), whereas two sharp meso resonances arise at δ =−3.7 and −15.6 ppm in a 2:1 intensity ratio (Figure 7, trace B) and the complex has been demonstrated to contain iron in a pure intermediate spin state 10…”

Effect of Heme–Heme Interactions and Modulation of Metal Spins by Counter Anions in a Series of Diiron(III)‐μ‐hydroxo Bisporphyrins: Unusual Stabilization of Two Different Spins in a Single Molecular Framework

“…10 Resonances could be assigned on the basis of the relative intensities and line widths of the peaks, with the assistance of a COSY experiment (for a representative case, see Figure S4 in the Supporting Information). Ethane‐ and ethene‐bridged bisiron(III) porphyrins axially ligated with chloride have previously been reported to be high‐spin in nature, with their spectra featuring methylene proton signals shifted downfield to δ ≈+40 ppm (average) and the meso proton signals appearing far upfield at δ ≈−60 ppm (average) 9b–d. As the iron moves towards the porphyrin mean plane in spin‐admixed complexes, the meso proton signals are shifted downfield and the methylene proton signals are shifted upfield toward the diamagnetic region compared to the high‐spin complexes 9…”

Effect of Inter‐Porphyrin Distance on Spin‐State in Diiron(III) μ‐Hydroxo Bisporphyrins

“…The two iron centers in the complex are in a five‐coordinate square‐pyramidal geometry and arranged in a cofacial manner. The average Fe−N p bond lengths, 2.085(3) (core I) and 2.085(3) Å (core II), and the Fe−O bond lengths, 1.771(2) (core I) and 1.789(2) Å (core II), are similar to those observed for μ‐oxo iron(III)porphyrin dimers –. The out‐of‐plane displacements of iron from the mean plane of the C 20 N 4 porphyrinato core (Δ Fe 24 ) are 0.58 (core I) and 0.64 Å (core II), which are in the range of five‐coordinate high‐spin iron(III) porphyrins .…”