Effects of Solvation on the Spin State of Iron(III) in 2,8,12,18- Tetrabutyl-3,7,13,17-tetramethyl-5,10-diazaporphyrinatoiron(III) Chloride

摘要

The chloroiron(III) complex of 2,8,12,18-tetrabutyl-3,7,13,17-tetramethyl- 5,10-diazaporphyrin, [(Cl)FeMBDAP], was prepared and studied by X-ray crystallography and by solution ~1H NMR and UV-vis measurements. In the crystal structure of hemisolvate [(Cl)FeMBDAP] × 0.5CHCl_3, two nonequivalent [(Cl)FeMBDAP] units containing Fe1 and Fe2 are arranged in φ-dimers with considerable overlap on their concave sides. Axial chloride bonded to Fe2 is solvated by hydrogen bonding with CHCl_3. Parameters of the coordination pyramid have typical values for the spin-mixed (S = 3/2/5/2) Fe~(III) complexes in the case of Fe1 and are characteristic for the pure intermediate-spin state for Fe2 (displacement from the (N _(Pyr))_4 planes-0.385 and 0.290 ? and the average N _(Pyr)-Fe bond lengths-1.992 and 1.954 ? for Fe1 and Fe2, respectively). Effective magnetic moments in CHCl_3 and CH _2Cl_2 capable of specific solvation of chloride by hydrogen bonding (4.5-4.6 μ_B at 298 K) are indicative about mixed intermediate/high-spin state S = 3/2/5/2, with the S = 3/2 contribution increasing upon lowering of the temperature (4.02 μ_B in CD _2Cl_2 at 193 K). In nonsolvating CCl_4, C _6D_6, and THF-d_8, the μ_(eff) values are consistent with the predominantly high-spin state at ambient temperature (5.5-5.75 μ_B at 298 K) and almost pure S = 5/2 state at low temperature (ca. 5.9 μ_B in THF-d_8 below 270 K). Downfield isotropic shifts from 35 to 50 ppm are observed for α-alkyl protons and upfield shifts from-5 to-15 ppm for meso-CH protons, which is characteristic for the presence of the intermediate-spin state. The splitting of signals of the diastereotopic α-CH_2 protons is increased with growth of the S = 3/2 state contribution from 1.5 to 4 ppm in nonsolvating to 11 ppm in specifically solvating solvents at 298 K and further to 31 ppm at 193 K (in CD_2Cl_2). In the presence of DMSO addition and in methanol solution, the single CH_2 signal is observed at 25-28 ppm, and the meso-CH resonance is also shifted downfield to ca. 30 ppm, indicating the formation of six-coordinated complexes [(DMSO)_2FeMBDAP] ~+ and [(MeOH)_2FeMBDAP]~+, the latter having the μ_(eff) value of 4.92 μ_B at 291 K is a spin-mixed species. The electron spin resonance spectra recorded at 77 K indicates that in frozen glasses in CD_2Cl_2 and THF molecules in the high-spin state (g_⊥ ～ 6) and the predominantly intermediate-spin state (g_⊥ ～ 4.2-4.3) coexist together.