Jørgen Glerup

Mononuclear and binuclear oxo-bridged iron(III) complexes of N,N'-bis(2-pyridylmethyl)ethane-1,2-diamine (bispicen)

Abstract The syntheses and characterization of a series of iron(III) complexes of the ligand N , N′ -bis(2-pyridylmethyl)ethane- 1,2-diamine (bispicen), C 14 H 18 N 4 are described. The monomeric complexes [(bispicen)FeCl 2 ]ClO 4 ( 1 ) and the corresponding chloride salt [(bispicen)FeCl 2 ]Cl ( 1a ) have been isolated and the structure of the perchiorate salt ( 1 ) has been determined from three-dimensional crystallographic data. The complex crystallizes in space group P 2 1 / c of the monoclinic system with four mononuclear species in a cell of dimensions a =7.323(2), b =14.370(3), c =18.103(4) A, β=90.71(2)°. The structure has been refined to a final R factor of 0.0496 based on 2948 observed independent reflections. The central iron(III) atom is pseudo-octahedrally bonded to the four nitrogen atoms of the ligand and to two cis chloride ligands. The μ-oxodiiron(III) complex {[(bispicen)(Cl)Fe] 2 (μ-O)}(I 3 ) 2 ( 2 ), C 28 H 36 Cl 2 Fe 2 I 6 N 8 O, crystallizes in space group P 2 1 / n of the monoclinic system with two binuclear species in a cell of dimensions a = 8.570(2), b = 14.756(3), c = 17.083(3) A, β = 99.68(2)°. The structure has been refined to a final R factor of 0.0417 based on 2272 observed independent reflections. The complex contains a linear FeOFe unit with FeO and Fe···Fe separations of 1.798(1) and 3.596(2) A, respectively. The μ-oxo, μ-acetatodiiron(III) complex {[(bispicen)Fe] 2 (μ-O)μ-OAc)}I 3 ·2H 2 O (3), C 30 H 43 Fe 2 I 3 N 8 O 5 , crystallizes in space group P 1 of the triclinic system with two binuclear species in a cell of dimensions a = 10.785(2), b = 12.378(2), c = 15.834(2) A, α = 87.060(10), β = 87.180(10), γ = 70.630(10)°. The structure has been refined to a final R factor of 0.0386 based on 4739 observed independent reflections. The complex contains a bent FeOFe unit with a bridging FeOFe angle of 129.8(2)° and associated average FeO and Fe···Fe separations of 1.794(1) and 3.248(2) A, respectively. The FeO (acetato) distances are 2.009(3) and 2.040(4) A. The μ-oxo, μ-carbonatodiiron(III) complex {[(bispicen)Fe] 2 (μ- O)(μ-CO 3 )}I 2 ·6H 2 O ( 4 ), C 29 H 48 Fe 2 I 2 N 8 O 10 , also crystallizes in space group P 1 of the triclinic system with two binuclear species in a cell of dimensions a = 10.158(2), b = 13.459(2), c = 15.712(3) A, α = 73.020(10), β = 85.290(10), γ = 79.230(10)°. The structure has been refined to a final R factor of 0.0348 based on 4294 observed independent reflections. The structure of the complex cation is very similar to that in 3, and contains a bent FeOFe unit with a bridging Fe OFe angle of 129.0(2)° and associated average FeO and Fe···Fe separations of 1.796(11) and 3.241(2) A, respectively. The FeO (carbonato) distances are 1.962(4) and 1.963(4) A. The binuclear complexes exhibit antiferromagnetic interactions with J values of −102.1, −118.2, and −113.6 cm −1 for 2, 3 and 4, respectively. The electronic spectra are similar to those observed in related species.

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.

Structural and magnetic characterization of an adamantane-like complex ion of chromium(III) and 1,3,5-triaminocyclohexane, [Cr4(tach)4(OH)6]6+

Abstract The synthesis and characterization of a tetranuclear chromium(III) complex of the ligand 1,3,5-triaminocyclohexane, (tach), C6H15N3, are described. The complex [Cr4(tach)4(OH)6] (ClO4)n(CF3SO3)6−n, where n refines to approximately 3.57, has been isolated and its structure has been determined from three-dimensional crystallographic data. The complex crystallizes in space group P21/c of the monoclinic system with four tetranuclear species in a cell of dimensions a=22.365(4), b=12.581(3), c=22.508(5) A, β=101.75(3)°. The structure has been refined to a final R factor of 0.0737 based on 6023 observed independent reflections. Each chromium(III) center is pseudo-octahedrally bonded to the three nitrogen atoms of the ligand and to three hydroxo groups; each hydroxo group acts as a bridge between two chromium atoms. The complex adopts the adamantane structure in which all four chromium atoms are chemically equivalent, as are all six hydroxide groups. The six independent Cr···Cr separations in the tetramer are in the narrow range 3.660–3.685 A. The temperature dependence of the magnetic susceptibility of the complex is consistent with the observed structure, the tetranuclear complex exhibiting an antiferromagnetic interaction with a J value of 8.91(2) cm−1. A model is presented which makes it possible to compare the antiferromagnetic interaction in complexes containing different numbers of metal atoms.

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.

Single crystal electron paramagnetic resonance spectra of Cs2MnF6 and K2MnF6 diluted in the isomorphous germanium salts.

In this work single crystal electron paramagnetic resonance (EPR) spectra of Cs(2)MnF(6) and K(2)MnF(6) diluted in the similar germanium salts have been interpreted and fitted. The spectra of the cubic cesium salt were recorded with the magnetic field parallel with the 4-fold axis and with the 3-fold axis. The spectrum along the 4-fold axis looks as expected with six groups from the manganese nuclear spin each split into seven lines caused by the nuclear spin from the six fluorine ligands. The spectrum along the 3-fold axis contains considerably more lines. This can be explained by the fact that only the transitions with the M(S) values -1/2<-->1/2 are observed together with the fact that the nuclear Zeeman effect from the six fluorine ligands mixes states and makes forbidden transitions allowed. The spectra of the trigonal potassium salt are recorded along the 3-fold axis and perpendicular to this axis. The sign of the zfs parameter was determined by high frequency EPR spectroscopy at low temperature. The knowledge of this meant that we could determine the sign of the two fluorine hyperfine coupling parameters both in this case and in the cubic case.

Dinuclear 1,4,7-triazacyclononane (tacn) complexes of cobalt(III) with amido and tacn bridges. Synthesis, characterization and reversible acid-accelerated bridge cleavage.

Amido-bridged dinuclear cobalt(III) complexes with 1,4,7-triazacyclononane (tacn) were synthesized from [Co(tacn)(O3SCF3)3] by treatment with potassium amide in liquid ammonia at 100 degrees C. Two isomeric triply bridged complexes, [(tacn)Co(mu-NH2)3Co(tacn)]3+ and [(tacn)Co(mu-NH2)2[mu-tacn(-H)]Co(NH3)]3+, were isolated as perchlorates, and the crystal structure of the perrhenate of the latter complex was determined by X-ray diffraction. In this compound a nitrogen atom (deprotonated) from one of the tacn ligands forms a third bridge together with two amido bridges. In 1.0 M (Na,H)ClO4 ([H+] 0.1-1.0 M) the two isomers undergo acid-accelerated amido bridge cleavage, as earlier found for chromium(III) analogues, in spite of the fact that such bridges are co-ordinatively saturated. The triamido-bridged isomer is in this acid medium in equilibrium with [(H2O)(tacn)Co(mu-NH2)2Co(tacn)(NH3)]4+. An isolated perchlorate of this complex appeared to be the salt of the trans-ammineaqua isomer as determined by X-ray diffraction. Equilibration from both sides fits the first-order rate constant dependence k(obs)=6.2(3) x 10(-5)[H+] + 2.1(2) x 10(-5)(s(-1)) at 40 degrees C. Prolonged treatment of the two triply bridged isomers in 1.0 M HClO4 at elevated temperature produces primarily triply bridged dinuclear species where one or two amido bridges have been replaced by hydroxo bridges.