Effects of Solvation on the Spin State of lron(lll) in 2,8,12,l8letrabutyl-3,7,13,17-tetramethyl-5,10-diazaporphyrinatoiron(lll) Chloride.

The chloroiron(lll) 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. tn the crystal structure of hemisolvate [(Cl)FeMBDAP] × 0.5CHCI3, two nonequivalent [(Cl)FeMBDAP] units containing Fe1 and Fe2 are arranged in π-dimers whh considerable overlap on their concave sides. Axial chloride bonded to Fe2 is solvated by hydrogen bonding with CHCI3. Parameters ot the coordination pyramid have typical values for the spin-mixed (S = 3/2 ÷ 5/2) FeIII complexes in the case ot Fe1 and are characteristic tor the pure intermediate-spin state tor Fe2 (displacement from the (NPyr)4 planes - 0.385 and 0.290 Å and the average NPyr-Fe bond lengths-1.992 and 1.954 Å tor Fe1 and Fe2, respectively). Effective magnetic moments in CHCI3 and CH2CI2 capable of specific solvation ot chloride by hydrogen bonding (4.S-4.6μB at 298 K) are indicative about mixed intermediate/high-spin state S = 3/2 ÷ 5/2, wth the S = 3/2 contribution increasing upon lowering of the temperature (4.02 μB in CD2CI2 at 193 K). In nonsolvating CCI4, C6D6, and THF-d8, the μeff values are consistent with the predominantiy high-spin state at ambient temperatare (5.5-5.75μB at 298 K) and almost pure S 5/2 state at low temperatare (ca. 5.9μB in THF-d8 below 270K). 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 splithng of signals of the diastereotopic α-CH2 protons is increased with growth of the S = 3/2 state contribution from 1.5 to 4 ppm in nonsolvating to 11 ppm in specificaty solvating solvents at 298 K and furtherto 31 ppm at 193K (in CD2CI2). In the presence of DMSO addition and in methanol solution, the single CH2 signal is observed at 25-28 ppm, and the meso-CH resonance is also shifted downfield to ca. 30 ppm, indicating the formation of aix-coordinated complexes [(DMSO)2FeMBDAP]+ and [(MeOH)2FeMBDAP]+, the latter having the the μeff value of 4.92 μB at 291 K is a spin-mixed species. The electron spin resonance spectra recorded at 77K indicates that in frozen glasses in CD2CI2 and ThF molecules in the high-spin state (g˔ ∼ 6) and the predominantly intarmediata-spin state (g˔ ∼ 4.2-4.3) coexist together. [ABSTRACT FROM AUTHOR]