Derek J. Hodgson

Synthesis, characterization and catalytic properties of manganese(III) schiff base complexes

Abstract The syntheses and spectral and electrochemical characterization of five manganese(III) complexes with Schiff base ligands are described. The crystal structure of the complex [Mn(SALENCY)(H 2 O)(CH 3 CH 2 OH)]ClO 4 where SALENCY, C 20 H 20 N 2 O 2 2-− , is the dianion of the product formed from the condensation of two moles of salicylaldehyde with one mole of 1,2-diaminocyclohexane, has been established by X-ray diffraction techniques. The complex crystallizes in the space group P 2 1 / n of the monoclinic system with four molecules in a cell of dimensions a =11.678(3), b =15.654(3), c = 13.356(2) A, and β=93.00(2)°. The structure was solved by direct methods and refined by least-squares techniques to a final value of the weighted R factor of 0.0437 based on 1484 independent observed reflections. The complex is roughly octahedral, the Schiff base ligand occupying four basal sites while the axial sites are occupied by one water molecule and one ethanol molecule. The complex [Mn(TETRAMESALEN)Cl], where TETRAMESALEN, C 20 H 22 N 2 O 2 2− , is the dianion of the product formed from the condensation of two moles of 2′-hydroxy- 5′-methylacetophenone with one mole of 1,2- diaminoethane, crystallizes in the monoclinic space group P 2 1 / c with four molecules in a cell of dimensions a =11.009(4), b =12.459(3), c =13.967(4) A, β=97.25(3)°. The structure was solved by direct methods and refined to a final R factor of 0.0535 based on 2342 observed independent intensities. The complex is tetragonal pyramidal, the Schiff base ligand occupying the basal sites while the chloride is axial. The complex [Mn(MEPHSALEN)(C 2 H 5 OH) 2 ]- ClO 4 , where MEPHSALEN, C 30 H 26 N 2 O 2 2-− , is the dianion of the product formed from the condensation of two moles of 2′-hydroxy- 5′-methylbenzophenone with one mole of 1,2-diaminoethane, crystallizes in the triclinic space group P 1 with four molecules in a cell of dimensions a =9.492(3), b =17.404(6), c = 21.265(9) A, α=86.60(3), β=88.57(3), γ= 86.34(3)°. The data for this complex are of lower quality than those obtained for the other two complexes, but the structure has been refined to a final value of 0.090 based on 1263 independent intensities. There are two crystallographically independent molecules in the cell, but the geometry of each is substantially similar. In each case, the manganese atom is six-coordinate, the base of the pseudo-octahedron being occupied by the Schiff base ligand while the axial sites are occupied by ethanol ligands. The two six-coordinate complexes (SALENCY and MEPHSALEN) are very effective at catalyzing the epoxidation of cyclohexene by iodosobenzene, while the five-coordinate complex yields both epoxide and cyclohexenol.

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.

Synthesis and magnetic and structural characterization of the binuclear complex di-μ-hydroxobis{[tris(2-pyridylmethyl)amine]chromium(III)} perchlorate tetrahydrate, [(tpa)CrOH]2(ClO4)4·4H2O

Abstract The binuclear complex di-μ-hydroxobis{[tris(2-pyridylmethyl)amine]chromium(III)} perchlorate tetrahydrate, [Cr(C18H18N4)OH]2(ClO4)4·4H2O or [Cr(tpa)OH]2(ClO4)4·4H2O, has been synthesized and characterized. The complex crystallizes in space group P21/n of the monoclinic system with two binuclear units in a cell of dimensions a = 11.381(5), b = 17.856(4), c = 13.050(7) A, β = 111.83(4)°. The structure has been refined to a final value of the conventional R factor of 0.056 on the basis of 3546 independent intensities. The geometry at the chromium is roughly octahedral, and the bridging unit has a CrOCr angle (φ) of 100.53(8)°. The CrCr separation is 3.003(1) A, and the hydrogen atom on the bridging OH group sits 0.30 A from the Cr2O2 plane, leading to a dihedral angle θ of 26.6°. The magnetic susceptibility of the complex indicates antiferromagnetic coupling, with the ground state singlet lying 30.58(6) cm−1 below the lowest lying triplet state.

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.

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.

Synthesis and characterization of copper(II) iodo complexes of diethylenetriamine: isolation of an iodo-bridged copper(II) chain

Abstract The synthesis and characterization of two complexes of the formulation Cu(dien)I2, Cu(C4H13N3)I2, are described. The polymeric complex {[Cu(C4H13N3)I]I}n crystallizes in the orthorhombic space group Pnm21 with two molecules in a cell of dimensions a=8.873(2), b=8.890(3), c=6.658(1) A. The structure has been refined to a final R factor of 0.046 based on 596 independent observed intensities. The structure consists of chains of iodide-bridged copper(II) ions along the crystallographic c direction. The coordination geometry about copper is tetragonally-elongated (4+2) octahedral, the equatorial plane consisting of three nitrogen atoms from the dien ligand and one iodide while the axial sites are occupied by the other (chain-propagating) iodide ligands. The equatorial CuI bond length is 2.585(1) A while the axial distances are 3.325(1) and 3.371(1) A. The intrachain CuCu separation is 6.658(1) A, the c axis length, and the bridging CuI(2)Cu angle is 167.7(1)°. The magnetic susceptibility data for the polymeric complex reveal antiferromagnetic coupling. The monomeric complex [Cu(dien)I2] crystallizes in the monoclinic space group P21/a with four molecules in a cell of dimensions a=15.140(4), b=9.690(4), c=7.526(2) A, β=105.95(2)°. The structure has been refined to a final R factor of 0.0723 based on 2460 independent observed intensities. The complex is five coordinate, the structure being best described as a distorted trigonal bipyramid in which N(1) and N(3) are axial while N(2), I(1) and I(2) are in the trigonal plane. As is expected for a trigonal bipyramid, copper lies in the trigonal plane. The CuI distances are very different, one being 2.619(2) A while the other is 3.049(2) A.

Nickel(II) and manganese(II) complexes of substituted phenanthroline ligands

The synthesis and characterization of nickel(II) and manganese(II) complexes of substituted 1, 10-phenanthroline ligands are described.; The ligands include 2, 9-di(o-tolyl)-1, 10-phen (dtphen), 2, 9-di(2-methoxyphenyl)-1, 10-phen (dmophen), 2, 9-di(2-ethoxyphenyl)-1,10-phen (deophen), 2-(o-tolyl)-1, 10-phen (tphen), 2-(2-ethoxyphenyl)-1, 10-phen (eophen) and 2, 9-bis(N-pyrazolylmethyl)1, 10-phen (bpmp). 1:1 Metal-to-ligand complexes have been isolated with dmophen and bpmp, and 1:2 metal-to-ligand complexes have been isolated with all ligands except bpmp. The structure of 1:1 nickel(II) complex with dmophen has been determined by three-dimensional X-ray diffraction methods. The complex [Ni(dmophen)Cl2], [NiC26H20N2O2Cl2], crystallizes in the space group Pccn of the orthorhombic system with eight molecules in a cell of dimensions a=14.572(3), b=16.741(3) and c=19.209(4) A. The structure has been refined to a final value of the crystallographic R factor of 0.0427 based on 2618 observed independent reflections. There are two crystallographically independent, but geometrically very similar, molecules in the cell, each lying on a twofold axis. The complex is roughly tetrahedral, the coordination being provided by two ligand phen nitrogen atoms and by two chloride ions. Electrochemical data for the 1:2 complexes suggest that the M(II)↔M(I) electron transfer process is essentially metal localized, but that the M(I)↔M(0) electron transfer process is ligand localized. Moreover, the electrochemical results demonstrate that the 2, 9-di(o-substituted phenyl)-1,10-phen ligands are able to stabilize lower oxidation states, and that ligand binding to the reduced metal ion prevents its dissociation into free ligand and metal.

Monomeric complexes of manganese(II) with tetradentate ligands: isolation of cis-diaquamanganese(II) and cis-dichloromanganese(II) species

The synthesis and characterization of the monomeric complexes cis -diaqua( N , N ′-bis(2-methylpyrazyl)ethane-1,2-diamine)manganese(II) perchlorate monohydrate ( 1 ), or cis -[Mn(bispyzen)- (H 2 O) 2 ](ClO 4 ) 2 ·H 2 O, and cis -dichloro( N , N -bis((6-methylpyrid-2-yl)methyl)- N -2-pyridylmethylamine) manganese(II) ( 2 ) are reported. The diaqua complex crystallizes in the monoclinic space group P 2 1 / c with four molecules in a cell of dimensions a =13.394(4), b =9.778(3), c =17.434(7) A, β=103.15(3)°. The structure has been refined to an R factor of 0.0485 based on 3857 independent intensities. The OMnO bond angle in the complex is 93.9(1)°, and the MnO bond lengths are 2.137(3) and 2.158(3) A. There is extensive hydrogen bonding in the crystals. The dichloro complex crystallizes in the monoclinic space group P 2 1 / n with four molecules in a cell of dimensions a =8.993(2), b =28.717(7), c =9.053(2) A. β=118.84(1)°. The structure has been refined to an R factor of 0.0370 based on 3276 independent intensities. The ClMnCl bond angle in the complex is 99.4(1)°, and the MnCl bond lengths are 2.402(1) and 2.467(1) A. The axial MnN bond lengths of 2.423(2) and 2.456(3) A are much longer than the equatorial MnN distances of 2.285(3) and 2.329(3) A; this observed elongation of the axial bonds is presumably due to the steric crowding caused by the presence of the 6-methyl groups on the axial pyridine rings. The dichloro complex shows a quasi-reversible redox wave at 0.80 V versus Ag/AgCl corresponding to the Mn(II)↔Mn(III) couple.