Mössbauer, electron paramagnetic resonance, and density functional theory studies of synthetic S = 1/2 Fe(III)-O-Fe(IV)═O complexes. Superexchange-mediated spin transition at the Fe(IV)═O site.
Previously we have characterized two high-valent complexes [LFe(IV)(μ-O)(2)Fe(III)L], 1, and [LFe(IV)(O)(μ-O)(OH) Fe(IV)L], 4. Addition of hydroxide or fluoride to 1 produces two new complexes, 1-OH and 1-F. Electron paramagnetic resonance (EPR) and Mössbauer studies show that both complexes have an S = 1/2 ground state which results from antiferromagnetic coupling of the spins of a high-spin (S(a) = 5/2) Fe(III) and a high-spin (S(b) = 2) Fe(IV) site. 1-OH can also be obtained by a 1-electron reduction of 4, which has been shown to have an Fe(IV)═O site. Radiolytic reduction of 4 at 77 K yields a Mössbauer spectrum identical to that observed for 1-OH, showing that the latter contains an Fe(IV)═O. Interestingly, the Fe(IV)═O moiety has S(b) = 1 in 4 and S(b) = 2 in 1-OH and 1-F. From the temperature dependence of the S = 1/2 signal we have determined the exchange coupling constant J (ℋ = JS(a)·S(b) convention) to be 90 ± 20 cm(-1) for both 1-OH and 1-F. Broken-symmetry density functional theory (DFT) calculations yield J = 135 cm(-1) for 1-OH and J = 104 cm(-1) for 1-F, in good agreement with the experiments. DFT analysis shows that the S(b) = 1 → S(b) = 2 transition of the Fe(IV)═O site upon reduction of the Fe(IV)-OH site to high-spin Fe(III) is driven primarily by the strong antiferromagnetic exchange in the (S(a) = 5/2, S(b) = 2) couple.
De Hont
Raymond F
RF
Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA.
Xue
Genqiang
G
Hendrich
Michael P
MP
Que
Lawrence
L
Bominaar
Emile L
EL
Münck
Eckard
E
D004578:Electron Spin Resonance Spectroscopy / Q000379:methods*; D007501:Iron / Q000737:chemistry*; D008958:Models, Molecular; D008968:Molecular Conformation; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry*; D011789:Quantum Theory; D015204:Spectroscopy, Mossbauer / Q000379:methods*
D009942:Organometallic Compounds; D007501:Iron; D010100:Oxygen
J Am Chem Soc. 2007 Jul 25;129(29):9049-65
17602477
Chem Rev. 2003 Jun;103(6):2385-419
12797835
J Am Chem Soc. 2009 Apr 29;131(16):5823-30
19338307
Proc Natl Acad Sci U S A. 2007 Dec 26;104(52):20713-8
18093922
Proc Natl Acad Sci U S A. 2007 Dec 4;104(49):19181-6
18048327
Chem Rev. 2000 Jan 12;100(1):235-350
11749238
Inorg Chem. 2003 Sep 22;42(19):5974-88
12971768
J Am Chem Soc. 2002 Apr 17;124(15):3993-4007
11942838
Biochemistry. 1998 Oct 20;37(42):14664-71
9778341
Proc Natl Acad Sci U S A. 2009 Sep 1;106(35):14814-9
19706422
Angew Chem Int Ed Engl. 2005 Oct 28;44(42):6871-4
16206322
Acc Chem Res. 2007 Jul;40(7):484-92
17542550
Nat Chem. 2010 May;2(5):400-5
20414242
Biochemistry. 2007 Dec 25;46(51):14795-809
18044971
J Am Chem Soc. 2007 Nov 21;129(46):14500-10
17967027
J Inorg Biochem. 2006 Apr;100(4):697-706
16510189
Inorg Chem. 2006 Aug 21;45(17):6922-7
16903750
Chem Rev. 1996 Nov 7;96(7):2625-2658
11848839
Acc Chem Res. 2007 Jul;40(7):466-74
17518435
J Am Chem Soc. 2003 Dec 17;125(50):15554-70
14664603
J Biol Chem. 1993 Oct 15;268(29):21569-77
8408008
Biochim Biophys Acta. 1966 Sep 5;126(1):176-8
4291218
Science. 1997 Jan 24;275(5299):515-8
8999792
Biochemistry. 2003 Feb 11;42(5):1354-64
12564939
J Am Chem Soc. 2005 Nov 16;127(45):15778-90
16277521
Biochemistry. 2003 Jun 24;42(24):7497-508
12809506
J Biol Chem. 1991 Jan 5;266(1):540-50
1845980
J Am Chem Soc. 2006 Jul 5;128(26):8590-606
16802826
J Am Chem Soc. 2001 Oct 24;123(42):10421-2
11604007
J Biol Inorg Chem. 1999 Jun;4(3):292-301
10439074
J Am Chem Soc. 2009 Mar 11;131(9):3370-6
19220056
Annu Rev Biochem. 2006;75:681-706
16756507
J Inorg Biochem. 2006 Apr;100(4):434-47
16516297
Acc Chem Res. 2004 Jul;37(7):421-9
15260504
Biochemistry. 1972 Feb 29;11(5):855-63
4333945