Supporting Information

Characterization of Three Members of the Electron Transfer Series n [Fe(pda)2] (n = 2–, 1– 0) by Spectroscopy and Density Functional Theoretical Calculations (pda = Redox Non-innocent Derivatives of N,N’-Bis(pentafluorophenyl)-o-phenylenediamide(2–, 1•–, 0))

Marat M. Khusniyarov,*[a,b] Eckhard Bill,[a] Thomas Weyhermüller,[a] Eberhard Bothe,[a] Klaus Harms,[b] Jörg Sundermeyer,*[b] Karl Wieghardt*[a]

[a] Max Planck Institut für Bioanorganische Chemie Stiftstrasse 34-36, 45470 Mülheim an der Ruhr (Germany)

[b] Fachbereich Chemie, Phillips-Universität Marburg Hans-Meerwein-Straße, 35032 Marburg (Germany)

Vzz

Axx

Azz

V A Vyy xx yy

Figure S1. Orientation of the electric field gradient tensor (Vi) vs. hyperfine coupling tensor (Ai) in 1 as obtained from applied-field 57Fe Mössbauer spectroscopy.

15 –1

cm 10 –1 / M –3 5 ·10 ε

0 600 900 1200 1500 1800 λ / nm

Figure S2. Electronic spectra of 1 measured in DME (red), toluene (blue), and MeCN (green).

S2 DFT calculations. Geometry optimization of 1 utilizing different functionals. A straightforward geometry optimization with the B3LYP[1] functional, successfully applied to similar systems,[2] proved inadequate to reproduce the geometry for 1. Whilst the quinoid-type distortion within the pda ligands is satisfactorily replicated, the dihedral angle between the two

C6H4N2Fe planes optimized to 76.8° with B3LYP is considerably larger than the crystallographically determined dihedral angle of 54.0° (Table S1). The use of larger basis sets for nitrogen, fluorine, and iron atoms, or the inclusion of a conductor like screening model[3] (COSMO) failed to improve the correspondence between the calculated and the experimental structure. If the intramolecular π−π interactions between the two pairs of C6F5 rings are the key to stabilizing the twisted geometry of 1, then this poor correspondence could result from the generally poor ability of the B3LYP functional to reproduce weak interactions.[4] Pure density functionals BP86[5, 6] and PW91[7] were tested. Both functionals provided very similar results; the π−π interactions were well reproduced providing dihedral angles much closer to the experiment. However, the quinoid-type distortion became insubstantial (Table S1). The use of the hybrid functional B3P86[5] replicated both the π−π interactions and the quinoid-type distortion. The twist angle of 55.1° in the optimized structure is very close to the crystallographically determined, although the Fe–N bonds are overestimated by 0.065 Å, which can not be accepted in this case. Ultimately, geometry optimization with the B3LYP functional including empirical Van der Waals corrections[8] (B3LYP+vdw) reproduced well the π−π pattern, the quinoid-type distortion and the Fe–N bond lengths. Table S1. Geometry optimization of 1 with different functionals. B3LYP BP86 PW91 B3P86 B3LYP Exp.b +vdwa C2–C3 1.422 1.414 1.411 1.416 1.412 1.405(4) C3–C4 1.381 1.399 1.396 1.382 1.388 1.373(4) C4–C5 1.421 1.414 1.412 1.415 1.415 1.406(5) C2–C7 1.458 1.437 1.436 1.445 1.441 1.424(4) C2–N1 1.358 1.388 1.385 1.362 1.374 1.382(4) Fe1–N1 2.000 1.896 1.890 1.962 1.921 1.897(3) α,c ° 76.8 46.9 47.8 55.1 48.0 54.0 π−π – + + + + + interactions a The B3LYP functional with empirical Van der Waals corrections b The average values are given c The dihedral angle between the two C6H4N2Fe planes

S3 Single point calculations on 1, optimized with different functionals. Single point calculations at the B3LYP level have been performed on the structures optimized with BP86, PW91, B3P86, and B3LYP+vdw functionals as well as on the non-optimized structure. Attempts to find broken symmetry[9],[10] (BS) states BS(3,1) and BS(4,2), and a conventional triplet state MS = 1 have been undertaken for all given geometries. For all given geometries, except the B3P86 optimized structure, all calculations converged to the BS(3,1) solution, which is lower than the –1 corresponding high-spin (HS) solutions (MS = 2) by 5.7 – 8.4 kcal mol . The MO scheme shown in Figure 13 generally remains the same for the structures optimized with the B3LYP+vdw, BP86 and PW91 functionals, as well as for the not optimized geometry. However, a single point calculation on the structure optimized with the B3P86 functional gives the BS(4,2) state as the lowest energy solution, which corresponds to the electronic description of 1 as II •– II [Fe (pda )2] – a HS Fe antiferromagnetically (AF) coupled to the two ligand radicals. To judge the correct description of the electronic structure of 1 we can calculate the Mössbauer parameters for these two solutions. Calculation of Mössbauer parameters for 1, optimized with different functionals. The large quadrupole splitting of the zero-field Mössbauer doublet for 1 is well reproduced for all calculated geometries (Table S2). The isomer shift calculated on the B3P86 optimized structure is overestimated by 0.16 mm s–1, while the perfect agreement between the experimental (0.23 mm s–1) and the calculated (0.23 mm s–1) isomer shift is achieved for the B3LYP+vdw optimized structure. Thus, the correct description of the electronic structure of 1 is [FeIII(pda•–)(pda2–)], i.e. an intermediate- spin FeIII ion coupled AF to one ligand radical. Since the best results for 1 are obtained for the B3LYP+vdw optimized structure, the anions in 2 and 3, which also have π−π interacting fragments, were also optimized with the B3LYP+vdw.

Table S2. Calculation of properties performed on different geometries of 1. BP86 PW91 B3P86 B3LYP+vdwa X-rayb Exp. δ, mm s–1 0.14 0.13 0.39 0.23 0.17 0.23 –1 ΔEQ, mm s 3.99 4.02 4.74 4.32 4.14 4.45 η 0.31 0.33 0.55 0.26 0.40 0.64 c ρFe 2.62 2.61 3.28 2.92 2.82 d 2.57 2.57 3.32 2.89 2.79 a B3LYP function with empirical Van der Waals corrections b Not-optimized structure c Total spin density at iron including s and p orbitals d Expectation value of the total spin squared operator Ŝ2 S4 References. [1] a) A. D. Becke, J. Chem. Phys. 1993, 98, 5648; b) C. T. Lee, W. T. Yang, R. G. Parr, Phys. Rev. B 1988, 37, 785; c) P. J. Stephens, F. J. Devlin, C. F. Chabalowski, M. J. Frisch, J. Phys. Chem. 1994, 98, 11623. [2] a) K. Chlopek, E. Bothe, F. Neese, T. Weyhermüller, K. Wieghardt, Inorg. Chem. 2006, 45, 6298; b) C. C. Lu, E. Bill, T. Weyhermüller, E. Bothe, K. Wieghardt, Inorg. Chem. 2007, 46, 7880; c) N. Muresan, K. Chlopek, T. Weyhermüller, F. Neese, K. Wieghardt, Inorg. Chem. 2007, 46, 5327. [3] A. Klamt, G. Schuurmann, J. Chem. Soc., Perkin Trans. 2 1993, 799. [4] W. Koch, M. C. Holthausen, A Chemist's Guide to Density Functional Theory, second ed., Wiley-VCH Verlag GmbH, Weinheim, 2001. [5] a) A. D. Becke, Phys. Rev. A 1988, 38, 3098; b) J. P. Perdew, Phys. Rev. B 1986, 33, 8822. [6] J. P. Perdew, Phys. Rev. B 1986, 34, 7406. [7] J. P. Perdew, Y. Wang, in Electronic Structure of Solids (Eds.: P. Ziesche, H. Eschrig), Akademie Verlag, Berlin, 1991. [8] a) S. Grimme, J. Comput. Chem. 2004, 25, 1463; b) S. Grimme, J. Comput. Chem. 2006, 27, 1787. [9] a) C. Adamo, V. Barone, A. Bencini, F. Totti, I. Ciofini, Inorg. Chem. 1999, 38, 1996; b) A. P. Ginsberg, J. Am. Chem. Soc. 1980, 102, 111; c) L. Noodleman, J. Chem. Phys. 1981, 74, 5737; d) L. Noodleman, J. G. Norman, J. H. Osborne, A. Aizman, D. A. Case, J. Am. Chem. Soc. 1985, 107, 3418; e) L. Noodleman, E. R. Davidson, Chem. Phys. 1986, 109, 131; f) L. Noodleman, D. A. Case, A. Aizman, J. Am. Chem. Soc. 1988, 110, 1001; g) L. Noodleman, C. Y. Peng, D. A. Case, J. M. Mouesca, Coord. Chem. Rev. 1995, 144, 199; h) A. A. Ovchinnikov, J. K. Labanowski, Phys. Rev. A 1996, 53, 3946. [10] a) D. Herebian, K. E. Wieghardt, F. Neese, J. Am. Chem. Soc. 2003, 125, 10997; b) V. Bachler, G. Olbrich, F. Neese, K. Wieghardt, Inorg. Chem. 2002, 41, 4179.