Exchange coupling in an isostructural series of face-sharing bioctahedral complexes [LMII(mu-X)(3)M(II)L]BPh4 (M=Mn, Fe, Co, Ni, Zn; X=Cl, Br; L=1,4,7-trimethyl-1,4,7-triazacyclononane)

Bossek U, Nuhlen D, Bill E, et al. Exchange coupling in an isostructural series of face-sharing bioctahedral complexes [LMII(mu-X)(3)M(II)L]BPh4 (M=Mn, Fe, Co, Ni, Zn; X=Cl, Br; L=1,4,7-trimethyl-1,4,7-triazacyclononane). Inorganic Chemistry. 1997;36(13):2834-2843.The reaction of the divalent metal halides ZnCl2, ZnBr2, MnCl2 . 4CH(3)CN, MnBr2, FeCl2 . 4CH(3)CN, CoCl2 . 4CH(3)-CN, CoBr2, NiCl2 . 6H(2)O, and NiBr2, respectively, with the macrocycle 1,4,7-trimethyl-1,4,7-triazacyclononane (L) (1:1) in anhydrous acetonitrile, acetone, chloroform, or ethanol affords upon addition of NaBPh4 the isomorphous series of complexes [LMII(u-X)(3)(ML)-L-II]BPh4: 1, M = Zn, X = Cl; 2, Zn, Br; 3, Mn, Cl; 4, Mn, Br; 5, Fe, Cl; 6, Co, Cl; 7, Co, Br; 5, Ni, Cl; 9, Ni, Br, Six of these complexes have been structurally characterized by single-crystal X-ray crystallography; they crystallize in the triclinic space group (No. 2) with Z = 4. Crystal data areas follows 1, a = 16.654(1), b = 17.042(1), c = 17.684(1) Angstrom, alpha = 97.30(1), beta = 93.58(1), gamma = 117.46(1)degrees; 3, a = 16.632(8), b = 17.012(8), c = 17.855(5) Angstrom, alpha = 97.16(3), beta = 93.37(3), gamma = 117.24(3)degrees; 5, a 16.658(3), b = 17.064(3), c = 17.741(4) Angstrom, alpha = 97.32(3), beta = 93.47(3), gamma = 117.36(3)degrees; 6, a = 16.640(3), b = 17.040(3), c = 17.686(4) Angstrom, alpha = 97.39(3), beta = 93.58(3), gamma = 117.39(3)degrees; 8, a = 16.608(3), b = 16.995(3), c = 17.555(3) Angstrom, alpha = 97.36(1), beta = 93.52(1), gamma = 117.52(1)degrees; 9, a 16.680(3), b = 17.016(2), c = 17.715(3)Angstrom, alpha = 96.99(1), beta = 93.70(1), gamma = 117.42(1)degrees. All complexes consist of a dinuclear, face-sharing bioctahedral monocation with three mu(2)-Cl or mu(2)-Br bridging Ligands and two LM fragments and well-separated tetraphenylborate actions (1:1). The cations cocrystallize in two different forms: an enantiomeric form with (lambda lambda lambda) (or (delta delta delta)) conformation at both LM fragments and a meso form with an (lambda lambda lambda) conformation at one LM fragment and (delta delta delta) at the other (ratio 1:1). From temperature-dependent magnetic susceptibility measurements (2-293 K) it was established that the spins of the unpaired electrons in 3 (d(5)d(5) high spin), 4 (d(5)d(5)), 6 (d(7)d(7) high spin), 7 (d(7)d(7)), 8 (d(8)d(8)), and 9 (d(8)d(8)) are intramolecularly, weakly antiferromagnetically coupled in each case. Surprisingly, the spins order ferromagnetically in 5 (d(6)d(6) high spin). This is in contrast to the previously reported complex [(thf)(3)-Fe-II(mu-Cl)(3)Fe-II(thf)(3)][SnCl5(thf)] (thf = tetrahydrofuran)(5) for which a new analysis of the temperature-dependence of the magnetic susceptibility and of field-dependent Mossbauer spectra establish a weak intramolecular antiferromagnetic coupling. The origin of this difference is analyzed

Unsymmetrical Bimetallic Complexes with M II

Heterobimetallic cores are important unit within the active sites of metalloproteins, but are often difficult to duplicate in synthetic systems. We have developed a synthetic approach for the preparation of a complex with a Mn(II)–(μ-OH)–Fe(III) core, in which the metal centers have different coordination environments. Structural and physical data support the assignment of this complex as a heterobimetallic system. Comparison with the analogous homobimetallic complexes, those containing Mn(II)–(μ-OH)–Mn(III) and Fe(II)–(μ-OH)–Fe(III) cores, further supports this assignment

New iron(II) and manganese(II) complexes of two ultra-rigid, cross-bridged tetraazamacrocycles for catalysis and biomimicry

The high-spin dichloro Mn2+ and Fe2+ complexes of 4,11 dimethyl-1,4,8,11-tetraazabicyclo[6.6.2]-hexadecane (1) and 4.10-dimethyl-1,4,7,10-tetraazabicyclo[5.5.2]tetradecane (2) provide durable new compounds of these elements for important fundamental studies and applications. The compounds are especially noteable for their exceptional kinetic stabilities and redox activity. The X-ray crystal structures of all four complexes demonstrate that the ligands enforce a distorted octahedral geometry on the metals with two cis sites occupied by labile chloride ligands. Magnetic measurements reveal that all are high spin with typical magnetic moments. Cyclic voltammetry of the complexes shows reversible redox processes at +0.110 and +0.038 V (versus SHE) for the Fe3+/Fe2+ couples of Fe(1)Cl2 and Fe(2)Cl2, respectively, while the Mn3+/Mn2+ and Mn4+/Mn2+ couples were observed at +0.585 and +1.343 V, and +0.466 and +1.232 V for the complexes Mn(1)Cl2 and Mn(2)Cl2, respectively. Mn2+(1) was found to react with H2O2 and other oxidizing agents to produce the Mn4+(1) complex. The catalytic efficacy of Mn4+(1) in aqueous solution has been assessed in the epoxidation reaction of carbamazepine and hydrogen abstraction reaction with 1,4-cyclohexadiene The complex has been found to be a selective catalyst, exhibiting moderate catalytic activity in oxygen transfer, but significantly more effective catalytic activity in hydrogen abstraction reactions

Spin-dependent delocalization in three isostructural complexes [LFeNiFeL](2+/3+/4+) (L = 1,4,7-(4-tert-butyl-2-mercaptobenzyl)-1,4,7-triazacyclononane)

Glaser T, Kesting F, Beissel T, et al. Spin-dependent delocalization in three isostructural complexes [LFeNiFeL](2+/3+/4+) (L = 1,4,7-(4-tert-butyl-2-mercaptobenzyl)-1,4,7-triazacyclononane). Inorganic Chemistry. 1999;38(4):722-732.The reaction of mononuclear [LFe(III)] where L represents the trianionic ligand 1,4,7-tris(4-tert-butyl-2-mercaptobenzyl)-1,4,7-triazacyclononane with NiCl(2). 6H(2)O and subsequent oxidations with [Ni(III)(tacn)(2)](ClO(4))(3) (tacn = 1,4,7-triazacyclononane) and PbO(2)/methanesulfonic acid produced an isostructural series of complexes [LFeNiFeL](n+) (n = 2 (1), n = 3 (2), n = 4 (3)), which were isolated as PF(6)(-) (1, 3) or ClO(4)(-) salts (2). The molecular structures were established by X-ray crystallography for [LFeNiFeL](ClO(4))(2). 5CH(3)CN (1*), C(88)H(123)Cl(2)Fe(2)N(11)NiO(8)S(6), and [LFeNiFeL](ClO(4))(3). 8acetone (2*), C(102)H(156)Cl(3)Fe(2)N(6)NiO(20)S(6). Both compounds crystallize in the triclinic space group P (1) over bar with a = 13.065(2) Angstrom (13.155(2) Angstrom), b = 13.626(3) Angstrom (13.747(3) Angstrom), c = 14.043(3) Angstrom (16.237(3) Angstrom), alpha = 114.47(3)degrees (114.20(2)degrees), beta = 97.67(3)degrees (96.57(2)degrees), gamma = 90.34(3)degrees (98.86(2)degrees), Z = 1(1) (values in parentheses refer to 2*). The cations in 1, 2, and 3 have been determined to be isostructural by Fe and Ni K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy. All compounds contain linear trinuclear cations (face-sharing octahedral) with an N(3)Fe(mu-SR)(3)Ni(mu-SR)(3)FeN(3) core structure. The electronic structures of 1, 2, and 3 have been studied by Fe and Ni K-edge X-ray absorption near edge (XANES), UV-vis, EPR, and Mossbauer spectroscopy as well as by temperature-dependent magnetic susceptibility measurements. Complexes 1 and 3 possess an S(t) = 0 whereas 2 has an S(t) = 1/2 ground state. It is shown that the electronic structures cannot be described by using localized valences (oxidation states). Delocalized models invoking the double-exchange mechanism are appropriate; i.e., spin-dependent delocalization via a double-exchange mechanism yields the correct ground state in each case, 1, 2, and 3 represent the first examples where double exchange stabilizes a ground state of minimum spin multiplicity