Kirsten Michelsen

Binuclear oxo-bridged iron(III) complexes of N,N′-bis(2-pyridylmethyl)ethane-1,2-diamine (bispicen) and related ligands

Abstract The syntheses and characterization of a series of binuclear iron(III) complexes of the ligands N,N′-bis(2- pyridylmethyl)ethane-1,2-diamine (bispicen), C14H18N4, N,N′-bis(2-pyridylmethyl)propane-1,3-diamine (bispictn), C15H20N4, and N,N′-bis(2-pyridylmethyl)-N,N′-bis(methyl)-1,2-ethanediamine, C16H22N4, are described. The μ- oxo,μ-carbonatodiiron(III) complex {[(bispictn)Fe]2(μ-O)(μ-CO3)}(ClO4)2·3H2O C31H46Cl2Fe2N8O15 (1) crystatlizes in space group P 1 of the triclinic system with two binuclear species in a cell of dimensions a=12.552(3), b=12.980(3), c=15.016(3) A, α=88.49(3), β=68.57(3), γ=64.56(3)°. The tetradentate ligand binds the iron center in cis-β fashion. The structure has been refined to a final R factor of 0.0531 based on 2624 observed independent reflections. The complex contains a bent FeOFe unit with a bridging FeOFe angle of 129.7(3)° and associated average FeO and Fe···Fe separations of 1.803(7) and 3.264(2) A, respectively. The FeO (carbonato) distances are 1.960(5) and 1.968(5) A. The complex {[(bispicMe2en)Fe]2(μ-O)(μ-CO3)}(ClO4)2·2H2O, C33H48Cl2Fe2N8O14 (2) crystallizes in space group C2/c of the monoclinic system with eight binuclear species in a cell of dimensions a=19.580(4), b=13.442(3), c=32.727(7) A, β=94.07(3)°. The structure has been refined to a final R factor of 0.0634 based on 3279 observed independent reflections. The ligand binds the iron centers in cis-α fashion. The structure of the complex cation contains a bent FeOFe unit with a bridging FeOFe angle of 125.5(3)° and associated average FeO and Fe···Fe separations of 1.810(18) and 3.220(2) A, respectively. The FeO (carbonato) distances are 1.930(6) and 1.925(7) A. The novel μ-oxo,μ-sulfatodiiron(III) complex {[(bispicMe2en)Fe]2(μ-O)(μ-SO4)}(ClO4)2·2H2O, C32H48Cl2Fe2N8O15S (4) crystallizes in space group Pbca of the orthorhombic system with eight binuclear species in a cell of dimensions a=16.049(3), b=16.875(3), c=31.325(6) A. The structure has been refined to a final R factor of 0.0682 based on 1776 observed independent reflections. The ligand binds the iron centers in cis-α fashion. The structure of the complex cation contains a bent FeOFe unit with a bridging FeOFe angle of 132.4(5)° and associated average FeO and Fe···Fe separations of 1.806(4) and 3.306(2) A, respectively. The FeO (sulfato) distances are 1.980(11) and 1.981(11) A. Cyclic voltammograms of the complexes reveal an irreversible reduction at c. −0.70 V versus Ag/AgCl reference electrode for 1, 3 and 4 and a quasi-reversible reduction for 2 at −0.585 V corresponding to the Fe2(III/III) ↔ Fe2(II/III) redox process.

Syntheses and characterization of binuclear manganese(III,IV) and (IV,IV) complexes with 1,4,7,10-tetraazacyclododecane (cyclen)

Abstract The synthesis and characterization of di-μ-oxodimanganese(III,IV) and (IV, IV) complexes employing the tetradentate ligand 1,4,7,10-tetraazacyclododecane (cyclen) are reported. The crystal structure of the Mn(III,IV) complex, di-μ-oxo-bis(1,4,7,10-tetraazacyclododecane)dimanganese(III,IV) chloride lithium chloride pentahydrate, [(cyclen)Mn(III)O 2 Mn(IV)(cyclen)]Cl 3 ·LiCl·5H 2 O( 1a ), has been established by three dimensional X-ray diffraction techniques. The complex, of formula Mn 2 C 16 H 50 N 8 O 7 Cl 4 Li, crystallizes in the monoclinic space group C2/c with four molecules in a cell of dimensions a =20.284(4), b =10.576(2), c =15.345(2) A and β=105.70(1)°. The structure was solved by direct methods and refined by least-squares techniques to a final agreement factor of 0.0344 based on 3445 observed independent intensities. The dimer has a crystallographic inversion center in the middle, which is due to a static disorder in the crystals. The Mn-Mn distance in the complex is 2.694(1) A and the bridging Mn-O-Mn angle is 95.7(1)°. The magnetic properties of the III/IV complex are consistent with a doublet ground state, the observed J value of -138(2) cm −1 for la and -156.5(5) cm −1 for the corresponding perchlorate salt being similar to those observed in other III/IV complexes. The Mn(IV,IV) complex has a singlet ground state, with J =-144.5(10) cm −1 The EPR spectrum of the III/IV complex exhibits the commonly-occurring sixteen line pattern, with a significant degree of anisotropy. The EPR spectrum has been simulated by diagonalization of the energy matrix for the doublet state. The complex exhibits two quasi-reversible waves in the cyclic voltammogram, with redox potentials of 0.069 and 0.846 V (versus Ag/AgCI) for the III/III↔III/IV and III/ IV↔IV/IV couples, respectively. The electronic spectra of both the (III,IV) and (IV,IV) forms of the complex are similar to those of analogous complexes.

Synthesis and characterization of the mixed-valent complex ion di-μ-oxobis( 1,4,8,11-tetraazacyclotetradecane)dimanganese(III, IV), [(cyclam)MnO]23+

Abstract The synthesis and characterization of several salts of the mixed-valence binuclear cation [(cyclam)MnO]23+, where cyclam is 1,4,8,11-tetraazacyclotetradecane, are reported. The bromide salt, [(cyclam)MnO]2Br3·4H2O, crystallizes in the monoclinic space group P21/n with two molecules in a cell of dimensions a = 9.903(3), b = 11.565(3), c = 14.927(4) A, β = 107.87(2)° at −100 °C. Consequently, the two manganese centers are crystallographically equivalent. An analysis of the anisotropic displacement parameters (Uij), coupled with evidence from other experiments, demonstrates a static disorder in the crystals between chemically inequivalent Mn(III) and Mn(IV) sites. The structure has been refined to a weighted R factor of 0.0378 based on 2368 independent intensities. The manganese-manganese separation in the dimer is 2.731(2) A. The dithionate salt crystallizes in the monoclinic space group P21/a with four molecules in a cell of dimensions a = 15.216(3), b = 11.716(4), c = 18.745(6) A, β = 92.49(2)° at −100 °C. The complex crystallizes with two independent centrosymmetric dimers in the cell, but again this is due to a static disorder in the crystals. Disorder about one of the dithionate ions fits a model in which some of the dithionate ion has been converted to thiosulfate. The Mn-Mn separations are 2.729(5) and 2.738(5) A. The EPR spectrum of the complex at 4 K shows the sixteen line pattern commonly observed in di-μ-oxodimanganese(III,IV) complexes. The magnetic susceptibility of the complex demonstrates that the complex has a doublet ground state, exhibiting antiferromagnetic coupling with 2J = −237 cm−1.

Synthesis and characterization of the binuclear complex di-µ-oxo-bis[N,N′-bis(2-methylpyridyl)ethane-1,2-diamine]dimanganese(III,IV)perchlorate trihydrate,[(bispicen)MnO]2(ClO4)3·3H2O

The title complex, a new binuclear di-µ-oxo complex of manganese-(III) and -(IV) with a single tetradentate ligand in place of the previously reported bidentate bpy or phen ligands, has been synthesised and characterised by X-ray crystallography and cyclic voltammetry.

Synthesis and characterization of the dimeric chromium(III) complex di-μ- hydroxobis[{N,N′-bis(2-pyridylmethyl)-1,3-propanediamine}-chromium(III)] perchlorate, [(bispictn)Cr(OH)]2(ClO4)4·3H2O

Abstract The synthesis and spetroscopic properties of two isomers of the complex [(bispictn)Cr(OH)] 2 4+ where bispictn = N,N′-bis(2-pyridylmethyl)-1,3-propanediamine, C 15 H 20 N 4 , are described. The crystal structure of the perchlorate salt trihydrate of the violet isomer has been determined from 3-dimensional counter X-ray data. The complex crystallizes in the monoclinic space group C2/c with eight dinuclear formula units in a cell of dimensions α = 38.323(11), b = 14.458(7), c = 17.027(7) A, β = 106.24(3)°. The structure has been refined to a final R-factor of 0.065 based on 3710 independent intensities. The crystals contain a racemic mixture, but in any given molecule the configurations at both chromium centers are the same (ΔΔ or ΛΛ). Both ligands bind in the cis -β form, the configurations at all four secondary nitrogen atoms being the same, so the complex is best described as a racemic mixture of the {Λ(β)(RR′)Λ(β)(RR′)} and {Δ(β)(SS′)} isomers. The six-membered chelate rings from a chair conformation at one metal and a skew-boat at the other. The magnetic susceptibility of the complex indicates antiferromagnetic coupling between the chromium centers, the triplet state lying approximately 32.5 cm −1 higher in energy than the ground state singlet.

Synthesis and magnetic characterization of the dioxo- and oxohydroxo-bridged dimeric chromium(III) cations di-μ-oxobis[bis{1-(2-pyridyl)ethylamine}-chromium(III)] and μ-oxo-μ-hydroxobis[bis{1-(2-pyridyl)ethylamine}-chromium(III)], and structure of the bromide salt of the oxohydroxo complex

The syntheses of the title complex cations, di-μ-oxobis[bis{1-(2-pyridyl)ethylamine}chromium(III)], [(2-picetam) 2 Cr(O)] 2+ 2 or [(C 7 H 10 N 2 ) 2 Cr(O)] 2+ 2 , and μ-oxo-μ-hydroxobis[bis{1-(2-pyridyl)ethylamine}chromium(III)], [Cr 2 (2-picetam) 4 (OH)(O)] 3+ or [(C 7 H 10 N 2 ) 4 Cr 2 (O)(OH)] 3+ , are reported, and their electronic and circular dichroism spectra in a variety of media are compared. The crystal and molecular structure of the μ-oxo-μ-hydroxo complex as the bromide salt, [(2-picetam) 4 Cr 2 (O)(OH)]Br 3 ·5H 2 O, has been determined from three-dimensional X-ray counter data. The complex crystallizes in the tri-clinic space group P with two binuclear complexes in a cell of dimensions a = 13.491(5), b = 13.762(3), c = 11.389(4) A, α = 104.41(2), β = 106.39(3), and γ = 84.44(2)°. Least-squares refinement of the structure using 2969 independent intensities has yielded a weighted R-factor (on F) of 0.052. The cation consists of two roughly octahedral chromium(III) centers, with terminal CrN distances in the range 2.057(5)–2.130(6) A. The CrCr separation is 2.883(2) A. and the bridging CrOCr angles at the oxo and hydroxo oxygen atoms are 100.6(2)° and 95.0(2)°, respectively. The CrO distances to the oxo oxygen atom are 1.869(4) and 1.878(4) A, while those to the hydroxo bridge are 1.960(4) and 1.950(4) A. The magnetic susceptibility of this μ-oxo-hydroxo complex shows a maximum near 100 K. A Fit of the data to a model assuming independent triplet, quintet, and septet energies is almost consistent with the Heisenberg model corrected for biquadratic exchange, and leads to a triplet energy of 46.45(2) cm −1 . In the di-μ-oxo complex, examined as the chloride salt, the triplet energy is approximately 83 cm −1 .

Binuclear oxo-bridged iron(III) complexes of chiral tetradentate ligands

Abstract The syntheses and characterization of a series of binuclear iron(III) complexes of the chiral ligands N,N′-bis(2-pyridylmethyl)-(−) d 1,2-propanediamine, bispic(−)pn, C15H20N4. N,N′-bis(2-pyridylmethyl)-(−) d -1,2-cyclohexanediamine, bispic(−)chxn, C18H24N4, and N,N′-bis(2-pyridylmethyl)-N,N′-dimethyl-(−) dd -1,2-cyclohexanediamine, bispicMe2(−)chxn, C20H28N4, are described. The μ-oxoμ-carbonatodiiron(III,III) complex, [{Fe(bispicMe2(−)chxn)}2(μ-O)(μ-CO3)](ClO4)2-4H2O, [Fe2C41H56N8O4](CIO4)2 · 4H2O (1), crystallizes in the space group P212121 of the orthorhombic system with four binuclear species in a cell of dimensions a = 14.066(3), b = 18.405 (4), c = 19.164(4) A. The structure was refi ned to a final R-factor of 0.0941 based on 2045 observed independent reflections. The μ-oxo-μ-bicarbonatodiiron (III,III) complex, [{Fe(bispicMe2(−)chxn)}2(μ-O)(μ-HCO3)][ClO4)3 · H2O. [Fe2C41H57N8O4](ClO4)3 · H2O (2), crystallizes in the space group I4122 of the tetragonal system with eight binuclear species in a cell of dimensions a = 20.527(3), c = 24.499(5) A. The structure was refined to a final R-factor of 0.0527 based on 2604 observed independent reflections. The μ-oxu-μ acetatodiiron(III,III) complex, [{Fe(bispicMe2(−)chxn)}2(μ-O)(μ-OAc)](CIO4)3 · H2O, [Fe2C42H59N8O3] (ClO4)3 · H2O (3), is isomorphous with 2 with eight binuclear species in a cell of dimensions a = 20.527(3), c = 24.377(5) A. The structure was refined to a final R-factor of 0.0673 based on 1954 observed independent reflections. The complexes contain bent Fe-O Fe units with bridging Fe-O-Fe angles of 124.2(8), 130.7(4), and 130.6(6)° and associated Fe … Fe separations of 3.212(5), 3.283(2), and 3.287(5) A for 1, 2, and 3, respectively. The ligand binds the iron centers in cis-α fashion in all three complexes. The complexes exhibit electronic absorption bands similar to methemerythrin enzymes in the 400 to 550 nm region, but they do not exhibit negative circular dichroism spectral features like the enzymes. Cyclic voltammograms of the complexes reveal a reversible one-electron reduction, corresponding to the FeIIIFeIII→FeIIFeIII redox process, at −0.43, +0.08, and +0.12 V versus an Ag/AgCl reference electrode for 1, 2, and 3, respectively. Complexes 2 and 3 also exhibit an irreversible reduction peak at −0.86 and −0.83 V. respectively.

Novel tetranuclear mixed-metal complexes containing the heteronuclear ions [MII{(OH)2CrA4}3]5+ and [MII{(OH)2CoA4}3]5+(A = amine ligand)

The synthesis and structural characterization of new tetranuclear complex ions with a central bivalent metal ion [MgII, ZnII, CoII, MnII, or NiII] octahedrally co-ordinated to six hydroxo groups which act as bridging ligands to three trivalent metal ions [CrIII or CoIII], is reported.

Synthesis and structure of novel mixed-metal complexes containing the heteronuclear ions [MIII{(OH)2Cr(NH3)4}4]7+ and [MIII{(OH)2Co(NH3)4}4]7+

The synthesis and structural and magnetic properties of new pentanuclear complex ions containing a central tervalent metal ion [CeIII, YIII, LaIII, PrIII, or GdIII] co-ordinated to eight hydroxo groups which act as bridging ligands to four tervalent metal ions [CrIII or CoIII], are described.