Synthesis and characterization of homo- and heterodinuclear complexes containing the N3M(mu(2)-SR)(3)MN3 core (M = Fe, Co, Ni)

A novel amine-thiolate ligand, H(3)3 . 6HCl (N,N',N"-tris-[2-thio-3-aminome thyl-5-tert-butylbenzyl]1,1,1-tris-(aminomethyl)ethane), has been synthesiz ed and used in the preparation of dinuclear complexes of Fe, Co, and Ni. Th e nonadentate N6S3 ligand H(3)3 is formally derived from the symmetric trid entate N2S Ligand H(1)1 (2,6-bis(aminomethyl)-4-tert-butylthiophenol). It p rovides two dissimilar octahedral N3S3 and N'S-3(3) coordination sites to g ive complexes with a central N3M(mu(2)-SR)(3)MN'(3) core structure (N and N ' denote primary and secondary amine nitrogen atoms, respectively). The com plexes of H(3)3 exist as dinuclear [M-2(II)(3)](+), [(MMII)-M-III(3)](2+), or [M-2-(III)(3)](3+) species which are all accessible by chemical or elect rochemical reduction/oxidation. The following complexes were isolated as mi crocrystalline solids: [Co-2(III)(3)][ClO4](3) (4b), [(NiNiII)-Ni-III(3)][B Ph4](2) (5b), and [(FeFeII)-Fe-III(3)1[BPh4](2) (6b). The chemical and phys icochemical properties of the respective species are very similar to those of Fe, Co, and Ni complexes of H(1)1, [M-2(1)(3)](n+) (M = Co, n = 3, (4a); M = Ni, n = 2 (5a); M = Fe, n = 2 (6a)), and support the formulation of 4b -6b as discrete dinuclear species with a central N3M(mu(2)-SR)(3)MN'(3) cor e. NMR spectra of diamagnetic cobalt complexes 4a and 4b reveal the complex es to be C-3h and C-3 symmetric, respectively, in the solution state. The c rystal structure determination of [Co-2(III)(1)(3)][Fe(CN)(6)]. 7MeOH . 3H( 2)O (4c) (monoclinic, space group C2/c, a = 28.037(2) Angstrom, b = 17.861( 1) Angstrom, c = 25.727(2) Angstrom, beta = 90.24(1)degrees 1, and Z = 8) r eveals 4c to consist of dinuclear [Co-2(III)(1)(3)](3+) trications featurin g two fac-octahedral N3CoIII(SR)(3) units bridged at the thiolate sulfur at oms. Compound Je represents the first structurally characterized M-2(III) c omplex of H(1)1. The ability of H(3)3 to form heterodinuclear complexes is demonstrated with the synthesis of [(CoNiII)-Ni-III(3)][BPh4](2) (7) and it s linkage isomer [(NiCoIII)-Co-II(3)][BPh4](2) (8). All complexes undergo t wo electrochemically and chemically reversible one-electron-transfer reacti ons which convert the respective [M-2(3)](n+) species. For M-2(III)/(MMII)- M-III (E-1/2(1)) and (MMII)-M-III/ M-2(II) (E-1/2(2)): -0.40 V, -0.84 V (M Co), +0.49 V, +0.05 V (M = Ni), +0.21 V, -0.33 V (M = Fe) vs SCE. Heterodin uclear complexes 7 and 8 also give rise to two consecutive one-electron-tra nsfer processes at E-1/2(1) (Ni-III/II) and E-1/2(2) (Co-III/II): +0.55 V, -0.71 V (for 7) and +0.60 V, -0.86 V (for 8), respectively. Comparison of t he electrochemical properties of [(CoNiII)-Ni-III(3)](2+) and [(NiNiII)-Ni- III(3)](2+) reveals the Ni-III/II redox potential in the dinuclear complexe s to be influenced by the oxidation state of the adjacent metal ion. At 77 K the mixed-valent (NiNiII)-Ni-III (S = 3/2 spin ground states) and ( FeFeII)-Fe-III complexes (S = 1/2 spin ground states) exhibit localized and delocalized valencies, respectively, as indicated by UV-vis, EPR, and Fe-5 7 Mossbauer spectroscopy.