Water-soluble, luminescent iridium(iii)-ytterbium(iii) complexes using dipyrido[3,2-a:2',3'-c]phenazine derivatives as bridging units

Amino-substituted dipyrido[3,2-a:2',3'-c]phenazine (L(1)) and dimethyl-dipyrido[3,2-a:2',3'-c]phenazine (L(2)) have been investigated as: (i) chromophores in cyclen-based ligands for lanthanide(iii) ions; (ii) ancillary co-ligands in cyclometalated iridium(iii) complexes; (iii) bridging, linker units in covalently linked, water-soluble bimetallic lanthanide(iii) iridium(iii) hybrid complexes. The dipyrido[3,2-a:2',3'-c]phenazine (dppz) derivatives can act as sensitising chromophores (λ(ex) 400 nm) for Yb(iii), resulting in characteristic near-IR emission at 950-1050 nm. The incorporation of dppz-type ligands into cyclometalated Ir(III) complexes of the general type [Ir(epqc)(2)(L(n))](PF(6)) (where epqc = ethylphenylquinoline carboxylate) gave luminescent species with solvent-sensitive emission properties. Steady state and time-resolved luminescence measurements on the water-soluble d-f hybrid species showed that Yb(III) can be sensitised using visible light.     

An oximate-based hexanuclear mixed-valence Mn(III)4Mn(II)2 edge-sharing bitetrahedral core with an St = 5 spin ground state

The synthesis, structures and magnetic properties of two hexanuclear Mn(6) clusters are reported: Mn(6)(mu(4)-O)(2)(dapdo)(2)(dapdoH)(4)(mu(2)-OH)(2)](ClO(4))(2).6MeCN (.6MeCN) and [Mn(6)(mu(4)-O)(2)(dapdo)(2)(dapdoH)(4)(mu(2)-OCH(3))(2)](ClO(4))(2).2Et(2)O (.2Et(2)O) [dapdo(2-) is the dianion of 2,6-diacetylpyridine dioxime and dapdoH(-) is the monoanion of the aforesaid dioxime ligand]. Both complexes are mixed-valent with two Mn(II) and four Mn(III) atoms disposed in an edge-sharing bitetrahedral core. Both complexes and display the same [Mn(III)(4)Mn(II)(2)(mu(4)-O)(2)(mu(2)-OR)(2)](10+) core in which R = H for and R = Me for . The [Mn(III)(4)Mn(II)(2)] core is rather uncommon compared to the reported [Mn(III)(2)Mn(II)(4)] core in the literature. DC magnetic susceptibility measurements on and reveal the presence of competing exchange interactions resulting in an S(t) = 5 ground spin state. The magnetic behavior of the compounds indicates antiferromagnetic coupling between the manganese(iii) centers, whereas the coupling between the manganese(iii) and manganese(ii) is weakly antiferromagnetic or ferromagnetic depending on the bridging environments. Finally the interaction between the manganese(ii) centers from the two fused tetrahedra is weakly ferromagnetic in nature stabilizing S(t) = 5 ground spin state in compounds and .     

Tetranuclear polybipyridyl complexes of Ru(II) and Mn(II), their electro- and photo-induced transformation into di-mu-oxo Mn(III)Mn(IV) hexanuclear complexes

Three heterotetranuclear complexes, [{Ru(II)(bpy)(2)(L(n))}(3)Mn(II)](8+) (bpy = 2,2'-bipyridine, n = 2, 4, 6), in which a Mn(II)-tris-bipyridine-like centre is covalently linked to three Ru(II)-tris-bipyridine-like moieties using bridging bis-bipyridine L(n) ligands, have been synthesised and characterised. The electrochemical, photophysical and photochemical properties of these complexes have been investigated in CH(3)CN. The cyclic voltammograms of the three complexes exhibit two successive very close one-electron metal-centred oxidation processes in the positive potential region. The first, which is irreversible, corresponds to the Mn(II)/Mn(III) redox system (E(pa) approximately 0.82 V vs Ag/Ag(+) 0.01 M in CH(3)CN-0.1 M Bu(4)NClO(4)), whereas the second which is, reversible, is associated with the Ru(II)/Ru(III) redox couple (E(1/2) approximately 0.91 V). In the negative potential region, three successive reversible four electron systems are observed, corresponding to ligand-based reduction processes. The three stable dimeric oxidized forms of the complexes, [Mn(2)(III,IV)O(2){Ru(II)(bpy)(2)(L(n))}(4)](11+), [Mn(2)(IV,IV)O(2){Ru(II)(bpy)(2)(L(n))}(4)](12+) and [Mn(2)(IV,IV)O(2){Ru(III)(bpy)(2)(L(n))}(4)](16+) are obtained in fairly good yields by sequential electrolyses after consumption of respectively 1.5, 0.5 and 3 electrons per molecule of initial tetranuclear complexes. The formation of the di-micro-oxo binuclear complexes are the result of the instability of the {[Ru(II)(bpy)(2)(L(n))](3)Mn(III)}(9+) species, which react with residual water, via a disproportionation reaction and the release of one ligand, [Ru(II)(bpy)(2)(L(n))](2+). A quantitative yield can be obtained for these reactions if the electrochemical oxidations are performed in the presence of an added external base like 2,6-dimethylpyridine. Photophysical properties of these compounds have been investigated showing that the luminescence of the Ru(II)-tris-bipyridine-like moieties is little affected by the presence of manganese within the tetranuclear complexes. A slight quenching of the excited states of the ruthenium moieties, which occurs by an intramolecular process, has been observed. Measurements made at low concentration (<1 x 10(-5) M) indicate that some decoordination of Mn(2+) arises in 1a-c. These measurements allow the calculation of the association constants for these complexes. Finally, photoinduced oxidation of the tetranuclear complexes has been performed by continuous photolysis experiments in the presence of a large excess of a diazonium salt, acting as a sacrificial oxidant. The three successive oxidation processes, Mn(II)--> Mn(III)Mn(IV), Mn(III)Mn(IV)--> Mn(IV)Mn(IV) and Ru(II)--> Ru(III) are thus obtained, the addition of 2,6-dimethylpyridine in the medium giving an essentially quantitative yield for the two first photo-induced oxidation steps as found for electrochemical oxidation.     

High-spin chloro mononuclear MnIII complexes: a multifrequency high-field EPR study.

The isolation, structural characterization, and electronic properties of two six-coordinated chloromanganese (III) complexes, [Mn(terpy)(Cl)3] (1) and [Mn(Phterpy)(Cl)3] (2), are reported (terpy = 2,2':6'2"-terpyridine, Phterpy = 4'-phenyl-2,2':6',2"-terpyridine). These complexes complement a series of mononuclear azide and fluoride Mn(lll) complexes synthesized with neutral N-tridentate ligands, [Mn(L)(X)3] (X = F- or N3 and L = terpy or bpea [N,N-bis(2-pyridylmethyl)-ethylamine)], previously described. Similar to these previous complexes, 1 and 2 exhibit a Jahn-Teller distortion of the octahedron, characteristic of a high-spin Mn(III) complex (S = 2). The analysis of the crystallographic data shows that, in both cases, the manganese ion lies in the center of a distorted octahedron characterized by an elongation along the tetragonal axis. Their electronic properties were investigated by multifrequency EPR (190-475 GHz) performed in the solid state at different temperatures (5-15 K). This study confirms our previous results and further shows that: i) the sign of D is correlated with the nature of the tetragonal distortion; ii) the magnitude of D is not sensitive to the nature of the anions in our series of rhombic complexes, contrary to the porphyrinic systems; iii) the [E/D] values (0.124 for 1 and 0.085 for 2) are smaller compared to those found for the [Mn(L)(X)3] complexes (in the range of 0.146 to 0.234); and iv) the E term increases when the ligand-field strength of the equatorial ligands decreases.     

Synthesis and Structural Investigations of [Mn(3)O(4)(phen)(4)(H(2)O)(2)](NO(3))(4).2.5H(2)O: A Water-Bound Complex Obtained by Cerium(IV) Oxidation

The trinuclear manganese complex [Mn(3)O(4)(phen)(4)(H(2)O)(2)](NO(3))(4).2.5H(2)O, 1 (where, phen = 1,10-phenanthroline), has been synthesized by the Ce(IV) oxidation of a concentrated solution of manganese(II) acetate and phen in 1.6 N nitric acid. The complex crystallizes in the triclinic space group P&onemacr; with a = 10.700(2) ?, b = 12.643(3) ?, c = 20.509(4) ?, alpha = 78.37(3) degrees, beta = 83.12(3) degrees, gamma = 82.50(3) degrees, and Z = 2. The structure was solved by direct methods and refined by least-squares techniques to the conventional R (R(w)) factors of 0.055 (0.076) based on 4609 unique reflections with F(o) >/= 6.0sigma(F(o)). The structure of the cation consists of an oxo-bridged Mn(3)O(4)(4+) core, with the geometry of the manganese atoms being octahedral. The coordination polyhedron of one of the manganese atoms (Mn(1)) consists of two &mgr; oxo ligands and two pairs of nitrogen atoms of two phen moieties, whereas that of each of the remaining two manganese atoms consists of three &mgr;-oxo ligands, two nitrogen atoms of a phen moiety, and the oxygen atom of a water molecule. The complex represents the second example for water coordination to manganese(IV) centers in complexes with a Mn(3)O(4)(4+) core. Optical spectra in ligand buffer (pH 4.5) reveal complete conversion of the complex into a Mn(III)Mn(IV) species. The observed room-temperature (298 K) magnetic moment of 3.75 &mgr;(B) indicates the presence of strong antiferromagnetic coupling in the complex.     

Laser flash photolysis generation and kinetic studies of corrole-manganese(V)-oxo intermediates

Corrole-manganese(V)-oxo intermediates were produced by laser flash photolysis of the corresponding corrole-manganese(IV) chlorate complexes, and the kinetics of their decay reactions in CH2Cl2 and their reactions with organic reductants were studied. The corrole ligands studied were 5,10,15-tris(pentafluorophenyl)corrole (H3TPFC), 5,10,15-triphenylcorrole (H3TPC), and 5,15-bis(pentafluorophenyl)-10-(p-methoxyphenyl)corrole (H3BPFMC). In self-decay reactions and in reactions with substrates, the order of reactivity of (Cor)Mn(V)(O) was TPC > BPFMC > TPFC, which is inverted from that expected based on the electron-demand of the ligands. The rates of reactions of (Cor)Mn(V)(O) were dependent on the concentration of the oxidant and other manganese species, with increasing concentrations of various manganese species resulting in decreasing rates of reactions, and the apparent rate constant for reaction of (TPFC)Mn(V)(O) with triphenylamine was found to display fractional order with respect to the manganese-oxo species. The kinetic results are consistent in part with a reaction model involving disproportionation of (Cor)Mn(V)(O) to give (Cor)Mn(IV) and (Cor)Mn(VI)(O) species, the latter of which is the active oxidant. Alternatively, the results are consistent with oxidation by (Cor)Mn(V)(O) which is reversibly sequestered in non-reactive complexes by various manganese species.     

Syntheses and reactivity of 'sulfur rich' Re(iii) and Tc(iii) complexes containing trithioperoxybenzoate, dithiobenzoate and dithiocarbamate ligands

Reduction-substitution reactions of [M(O)Cl(4)](-)(M=Re, (99)Tc) precursors with an excess of substituted dithiobenzoate ligands (R-PhCS(2))(-) in dichloromethane/methanol mixtures afford a series of six-coordinated neutral mixed-ligand complexes of the type M(III)(R-PhCS(3))(2)(R-PhCS(2))(M=Re; Rel--9; M=99)Tc; Tel--9). The coordination sphere is entirely filled by sulfur donor atoms, and the complexes adopt a distorted trigonal prismatic arrangement, as assessed by the X-ray crystal structure analysis of Re(4-Me-PhCS(3))(2)(4-Me-PhCS(2)), Re 2. These compounds show sharp proton and carbon NMR profiles, in agreement with the diamagnetism typical of low spin d(4) trigonal prismatic configurations. The red-ox processes involve reduction of the metal from Re(v) to Re(iii) and oxidation of dithiobenzoate to trithioperoxybenzoate. M2--9 complexes contain a substitution-inert [M(R-PhCS(3))(2)](+) moiety including the metal and two trithioperoxybenzoate fragments, while the third dithiobenzoate ligand is labile. The latter is efficiently replaced by reaction with better nucleophiles such as diethyldithiocarbamate giving a further class of mixed ligand complexes of the type M(III)(R-PhCS(3))(2)(Et(2)NCS(2))(M=Re; Re 10--18; M=(99)Tc; Tc--18), which retain the trigonal prismatic arrangement, as determined by the X-ray analyses of the representative compounds Re(PhCS(3))(2)(Et(2)NCS(2)), Re 10 and (99)Tc(PhCS(3))(2)(Et(2)NCS(2)), Tc 10.     

Mononuclear and dinuclear manganese compounds stabilized by supramolecular interactions

New manganese compounds [Mn(HphpzMe)(2)(H(2)phpzMe)(HCO(2))] (1), [Mn(2)(phpzMe)(2)(HphpzMe)(2)(OCH(3))]·2CH(3)OH (2), Na{[Mn(HphpzPh)(phpzPh)(MeOH)(2)](2)}(HCO(2)) (3), [Mn(HphpzPh)(2)(EtOH)(2)]ClO(4)·2EtOH (4) and [Mn(HphpzPh)(2)N(3)] (5) were synthesized and characterized with various techniques. 1, 4 and 5 are mononuclear manganese(iii) compounds, 2 is a mixed-valence dinuclear manganese(iii/iv) compound, and 3 is a trinuclear compound containing two manganese(iii) ions and a sodium(i) ion. A remarkable feature is the spontaneous formation of the formate ion as a result of the methanol or methoxide oxidation in compounds 1 and 3. Using ethanol precludes the formation of the formate and compound 4 is obtained. The molecular structure of all compounds is stabilized by supramolecular interactions, including strong hydrogen bonding and π-π interactions.     

Water exchange on seven-coordinate Mn(II) complexes with macrocyclic pentadentate ligands: insight in the mechanism of Mn(II) SOD mimetics

Seven-coordinate manganese(II) complexes [Mn(L)(H2O)2]2+, where L represents an equatorial pentadentate macrocyclic ligand with five nitrogen donor atoms, were studied with regard to their acid-base properties, water-exchange rate constants, and corresponding activation parameters (DeltaH, DeltaS, and DeltaV). Three of the studied complexes without imine bonds in the macrocyclic ligand are proven superoxide dismutase (SOD) mimetics. Their water-exchange parameters were compared with those of the imino groups containing complex [Mn(L1)(Cl)2] (dichloro-2,13-dimethyl-3,6,9,12,18-pentaazabicyclo[12.3.1]-octadeca-1(18),2,12,14,16-pentaenemanganese(II)), which does not show SOD activity. In addition the X-ray crystal structure of a new complex, dichloro-2,6-bis[1-(2-(N-methylamino)ethylimino)ethyl]pyridine-manganese(II) [Mn(L2)(Cl)2], which is the acyclic analog of [Mn(L1)(Cl)2], is reported. Stability constants of the complexes and the pKa values of the ligands were measured by potentiometric titration. The titrations of [Mn(L1)(H2O)2]2+ and [Mn(L2)(H2O)2]2+ led to complicated species distribution curves because of their ligands containing imine bonds. Water exchange was measured by temperature- and pressure-dependent 17O NMR techniques. In addition to the measurements on [Mn(EDTA)(H2O)]2- and its derivatives, this is the only study of water exchange on seven-coordinate manganese complexes. The water exchange rate constants vary between 1.6 x 107 s-1 and 5.8 x 107 s-1 at 25 degrees C and are mainly controlled by the pi-acceptor abilities of the ligands. The exchange rate constant of the diaqua-1,4,7,10,13-pentaazacyclopentadecanemanganese(II) [Mn([15]aneN5)(H2O)2]2+ complex seems to be even higher but could not be exactly determined. On the basis of the obtained activation parameters, the exchange mechanism of the studied seven-coordinate manganese(II) complexes follows a dissociative pathway (Id mechanism). DFT calculations (UB3LYP/LANL2DZp) were performed to obtain the energy required for the dissociation of the coordinated water molecule, that is, the energy difference between the starting seven-coordinate complex and a six-coordinate intermediate. The results have been discussed in terms of the catalytic mechanism of the proven SOD mimetics.     

The infrared spectra and theoretical calculations of frequencies of fac-tricarbonyl octahedral complexes of manganese(I)

The carbonyl stretching frequencies in the infrared spectra of 38 fac-tricarbonyl octahedral complexes of manganese(I) prepared in this laboratory were determined. These complexes may be grouped into three types: (a) neutral complexes of the structure (CO)(3)Mn(P-P)Z where P-P represents depe, dppe, or dppp, and Z represents various anionic functional groups bonded to the manganese; (b) ionic complexes of the structure [(CO)(3)Mn(P-P)Z](+)BF(4)(-) where Z represents various neutral molecules possessing one phosphorous, nitrogen, or oxygen atom coordinated to the manganese; (c) complexes of the structure (CO)(3)Mn(pn)Z where the chelating pn represents 1,1-diphenylphosphino-2,2-dimethylaminoethane, Ph(2)PCH(2)CH(2)NMe(2). All of these complexes show three carbonyl stretching modes (2A' + A"). The effects on the frequencies of these modes induced by both the various Z groups and the various ligands are discussed. Theoretical calculations (B3LYP/6-31G) with optimization of the full molecule make it possible to distinguish between the three stretching modes and to make unambiguous assignments of appropriate symmetry species to each.     

1,12-Diazaperylene and 2,11-dialkylated-1,12-diazaperylene iridium(iii) complexes [Ir(C^N)(2)(N^N)]PF(6): new supramolecular assemblies

A series of new monocationic iridium(iii) complexes [Ir(C^N)(2)(N^N)]PF(6) with "large-surface"α,α'-diimin ligands N^N (dap = 1,12-diazaperylene, dmedap = 2,11-dimethyl-1,12-diazaperylene, dipdap = 2,11-diisopropyl-1,12-diazaperylene) and different cyclometalating ligands C^N (piq = 1-phenylisoquinoline, bzq = benzo[h]quinoline, ppz = 1-phenylpyrazole, thpy = 2-(2-thienyl)pyridine, ppy = 2-phenylpyridine, meppy = 2-(4-methylphenyl)pyridine, dfppy = 2-(2,4-difluorophenyl)pyridine) were synthesized. The solid structures of the complexes [Ir(piq)(2)(dap)]PF(6), [Ir(bzq)(2)(dap)]PF(6), [Ir(ppy)(2)(dipdap)]PF(6), [Ir(piq)(2)(dmedap)]PF(6), [Ir(ppy)(2)(dap)]PF(6) and [Ir(ppz)(2)(dap)]PF(6) are reported. In [Ir(piq)(2)(dap)]PF(6), the dap ligand and one of the piq ligands of each cationic complex are involved in π-π stacking interactions forming supramolecular channels running along the crystallographic c axis. In the crystalline [Ir(bzq)(2)(dap)]PF(6)π-π stacking interactions between the metal complexes lead to the formation of a 2D layer structure. In addition, CH-π interactions were found in all compounds, which are what stabilizes the solid structure. In particular, a significant number of them were found in [Ir(piq)(2)(dap)]PF(6) and [Ir(bzq)(2)(dap)]PF(6). The crystal structures of [Ir(ppy)(2)(dipdap)]PF(6) and [Ir(ppy)(2)(dmedap)]PF(6) are also presented, being the first examples of bis-cyclometalated iridium(iii) complexes with phenanthroline-type α,α'-diimin ligands bearing bulky alkyl groups in the neighbourhood of the N-donor atoms. These ligands implicate a distorted octahedral coordination geometry that in turn destabilized the Ir-N(N^N) bonds. The new iridium(iii) complexes are not luminescent. All compounds show an electrochemically irreversible anodic peak between 1.15 and 1.58 V, which is influenced by the different cyclometalated ligands. All of the new complexes show two reversible successive one-electron "large-surface" ligand-centred reductions around -0.70 V and -1.30 V. Electrospray ionisation mass spectrometry (ESI-MS) and collision induced decomposition (CID) measurements were used to investigate the stability of the new complexes. Thereby, the stability agreed well with the order of the Ir-N(N^N) bond lengths.     

Two new terpyridine dimanganese complexes: a manganese(III,III) complex with a single unsupported oxo bridge and a manganese(III,IV) complex with a dioxo bridge. Synthesis, structure, and redox properties

Two new terpyridine dimanganese oxo complexes [Mn(2)(III,IV)(mu-O)(2)(terpy)(2)(CF(3)CO(2))(2)](+) (3) and [Mn(2)(III,III)(mu-O)(terpy)(2)(CF(3)CO(2))(4)] (4) (terpy = 2,2':6,2' '-terpyridine) have been synthesized and their X-ray structures determined. In contrast to the corresponding mixed-valent aqua complex [Mn(2)(III,IV)(mu-O)(2)(terpy)(2)(H(2)O)(2)](3+) (1), the two Mn atoms in 3 are not crystallographically equivalent. The neutral binuclear monooxo manganese(III,III) complex 4 exhibits two crystallographic forms having cis and trans configurations. In the cis complex, the two CF(3)CO(2)(-) ligands on each manganese adopt a cis geometry to each other; one CF(3)CO(2)(-) is trans to the oxygen of the oxo bridge while the second is cis. In the trans complex, the two coordinated CF(3)CO(2)(-) have a trans geometry to each other and are cis to the oxo bridge. The electrochemical behavior of 3 in organic medium (CH(3)CN) shows that this complex could be oxidized into its corresponding stable manganese(IV,IV) species while its reduced form manganese(III,III) is very unstable and leads by a disproportionation process to Mn(II) and Mn(IV) complexes. Complex 4 is only stable in the solid state, and it disproportionates spontaneously in CH(3)CN solution into the mixed-valent complex 3 and the mononuclear complex [Mn(II)(terpy)(2)](2+) (2), thereby preventing the observation of its electrochemical behavior.     

Synthesis and structural characterization of manganese(III,IV) and ruthenium(III) complexes derived from 2-hydroxy-1-naphthaldehydebenzoylhydrazone

Reaction of 2-hydroxy-1-naphthaldehydebenzoylhydrazone(napbhH₂) with manganese(II) acetate tetrahydrate and manganese(III) acetate dihydrate in methanol followed by addition of methanolic KOH in molar ratio (2 : 1 : 10) results in [Mn(IV)(napbh)₂] and [Mn(III)(napbh)(OH)(H₂O)], respectively. Activated ruthenium(III) chloride reacts with napbhH₂ in methanolic medium yielding [Ru(III)(napbhH)Cl(H₂O)]Cl. Replacement of aquo ligand by heterocyclic nitrogen donor in this complex has been observed when the reaction is carried out in presence of pyridine(py), 3-picoline(3-pic) or 4-picoline(4-pic). The molar conductance values in DMF (N,N-dimethyl formamide) of these complexes suggest non-electrolytic and 1 : 1 electrolytic nature for manganese and ruthenium complexes, respectively. Magnetic moment values of manganese complexes suggest Mn(III) and Mn(IV), however, ruthenium complexes are paramagnetic with one unpaired electron suggesting Ru(III). Electronic spectral studies suggest six coordinate metal ions in these complexes. IR spectra reveal that napbhH₂ coordinates in enol-form and keto-form to manganese and ruthenium metal ions in its complexes, respectively. ESR studies of the complexes are also reported.     

Nucleophilic reactivity of a series of peroxomanganese(III) complexes supported by tetradentate aminopyridyl ligands

Peroxomanganese(iii) adducts have been postulated as important intermediates in manganese-containing enzymes and small molecule oxidation catalysts. Synthetic peroxomanganese(iii) complexes are known to be nucleophilic and facilitate aldehyde deformylation, offering a convenient way to compare relative reactivities of complexes supported by different ligands. In this work, tetradentate dipyridyldiazacycloalkane ligands with systematically perturbed steric and electronic properties were used to generate a series of manganese(ii) and peroxomanganese(iii) complexes. X-Ray crystal structures of five manganese(ii) complexes all show the ligands bound to give trans complexes. Treatment of these Mn(II) precursors with H(2)O(2) and Et(3)N in MeCN at -40 °C results in the formation of peroxomanganese(iii) complexes that differ only in the identity of the pyridine ring substituent and/or the number of carbons in the diazacycloalkane backbone. To determine the effects of small ligand perturbations on the reactivity of the peroxo group, the more thermally stable peroxomanganese(iii) complexes were reacted with cyclohexanecarboxaldehyde. For these complexes, the rate of deformylation does not correlate with the expected nucleophilicity of the peroxomanganese(iii) unit, as the inclusion of methyl substituents on the pyridines affords slower deformylation rates. It is proposed that adding methyl-substituents to the pyridines, or increasing the number of carbons on the diazacycloalkane, sterically hinders nucleophilic attack of the peroxo ligand on the carbonyl carbon of the aldehyde.     

Topologically constrained manganese(III) and iron(III) complexes of two cross-bridged tetraazamacrocycles

A family of Mn3+ and Fe3+ 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) has been prepared by the chemical oxidation of the divalent manganese and iron analogues. The ligands are ethylene cross-bridged tetraazamacrocycles derived from cylam and cyclen, respectively. The synthesis and characterization of these complexes, including X-ray crystal structure determinations, are described. The structural evidence demonstrates that the tetradentate ligands enforce distorted octahedral geometries on the metal ions, with two cis sites occupied by labile ligands. Magnetic measurements reveal that the complexes are high spin with typical magnetic moments. Cyclic voltammetry shows reversible redox processes for the Fe3+/Fe2+ couples of the iron(III) complexes, while Mn3+/Mn2+ and Mn4+/Mn3+ couples were observed for the complexes with manganese(III). The manganese chemistry of 1 was studied in depth. The dichloro manganese(III) cation of 1 undergoes facile ligand substitution reactions at the labile, monodentate sites, for example substituting azide for chloride ligands. Air oxidation of the dichloro complex of Mn (1)2+ in basic solution does not give the expected mu-oxo dimeric product common to manganese. Instead, an unusual manganese(III)-OH complex has been isolated from this reaction and structurally characterized. A similar reaction under slightly different conditions gives a putative MnIII(OH)2 complex that metathesizes to MnIII(OMe)2 upon recrystallization from methanol.     

Binuclear manganese compounds of potential biological significance. 1. Syntheses and structural,magnetic, and electrochemical properties of dimanganese(II) and -(II,III) complexes of a bridging unsymmetrical phenolate ligand

Reactions of the unsymmetrical phenol ligand 2-(bis(2-pyridylmethyl)aminomethyl)-6-((2-pyridylmethyl)(benzyl)aminomethyl)-4-methylphenol with Mn(OAc)(2).4H(2)O or Mn(H(2)O)(6)(ClO(4))(2) in the presence of NaOBz affords the dimanganese(II) complexes 1(CH(3)OH), [Mn(2)(L)(OAc)(2)(CH(3)OH)](ClO(4)), and 2(H(2)O), [Mn(2)(L)(OBz)(2)(H(2)O)](ClO(4)), respectively. On the other hand, reaction of the ligand with hydrated manganese(III) acetate furnishes the mixed-valent derivative 3(H(2)O), [Mn(2)(L)(OAc)(2)(H(2)O)](ClO(4))( 2). The three complexes have been characterized by X-ray crystallography. 1(CH(3)OH) crystallizes in the monoclinic system, space group P2(1)/c, with a = 10.9215(6) A, b = 20.2318(12) A, c = 19.1354(12) A, alpha = 90 degrees, beta = 97.5310(10) degrees, gamma = 90 degrees, V = 4191.7 A(3), and Z = 4. 2(H(2)O) crystallizes in the monoclinic system, space group P2(1)/n, with a = 10.9215(6) A, b = 20.2318(12) A, c = 19.1354(12) A, alpha = 90 degrees, beta = 97.5310(10) degrees, gamma = 90 degrees, V = 4191.7 A(3), and Z = 4. 3(H(2)O) crystallizes in the monoclinic system, space group P2(1)/c, with a = 11.144(6) A, b = 18.737(10) A, c = 23.949(13) A, alpha = 90 degrees, beta = 95.910(10) degrees, gamma = 90 degrees, V = 4974(5) A(3), and Z = 4. Magnetic measurements revealed that the three compounds exhibit very similar magnetic exchange interactions -J = 4.3(3) cm(-)(1). They were used to establish tentative magneto-structural correlations which show that for the dimanganese(II) complexes -J decreases when the Mn-O(phenoxo) distance increases as expected from orbital overlap considerations. For the dimanganese(II,III) complexes, crystallographic results show that the Mn(II)-O(phenoxo) and Mn(III)-O(phenoxo) bond lengths are inversely correlated. An interesting magneto-structural correlation is found between -J and the difference between these bond lengths, delta(Mn)(-)(O) = d(Mn)()II(-)(O) - d(Mn)()III(-)(O): the smaller this difference, the larger -J. Electrochemical studies show that the mixed-valence state is favored in 1-3 by ca. 100 mV with respect to analogous complexes of symmetrical ligands, owing to the asymmetry of the electron density as found in the analogous diiron complexes.     

Metal-bis[poly(pyrazolyl)borate] complexes. Electrochemical,magnetic, and spectroscopic properties and coupled electron-transfer and spin-exchange reactions

Electrochemical, magnetic, and spectroscopic properties are reported for homoleptic divalent (M = Mn, Fe, Co, Ni, Ru) and trivalent (M = Cr, Mn, Fe, Co) metal-bis[poly(pyrazolyl)borate] complexes, [M(pzb)(2)](+/0), where pzb(-) = hydrotris(pyrazolyl)borate (Tp), hydrotris(3,5-dimethylpyrazolyl)borate (Tp), or tetrakis(pyrazolyl)borate (pzTp). Ligand field strengths in metal-pzb complexes increase as Tp < Tp < pzTp, which reflects the importance of steric rather than electronic effects on spectroscopic properties. However, metal-centered redox potentials become more negative as pzTp < Tp < Tp, which follows the electron-donating ability of the ligands. Co(III)/Co(II) and Mn(III)/Mn(II) electrode reactions are accompanied by a change in metal atom spin-state; i.e., (S = 0) [Co(pzb)(2)](+) + e(-) <==> (S = 3/2) [Co(pzb)(2)] and (S = 1) [Mn(pzb)(2)](+) + e(-) <==> (S = 5/2) [Mn(pzb)(2)]. Apparent heterogeneous electron-transfer rate constants derived from sweep-rate dependent cyclic voltammetric peak potential separations in 1,2-dichloroethane are small and decrease as pzTp > Tp > Tp for the Co(III)/Co(II) couples. Slow electron transfer is characteristic of coupled electron transfer and spin exchange. [M(Tp)(2)](+/0) redox potentials relative to values for other homoleptic MN(6)(3+/2+) couples change as M varies from Cr to Ni. For early members of the series, [M(Tp)(2)](+/0) potentials nearly equal those of complexes with aliphatic N-donor ligands (e.g., triazacyclononane, sarcophagine). However, [M(Tp)(2)](+/0) potentials approach those of [M(bpy)(3)](3+/2+) for later members of the series. The variation suggests a change in the nature of the metal-pzb interaction upon crossing the first transition row.     

Dioxo-bridged dinuclear manganese(III) and -(IV) complexes of pyridyl donor tripod ligands: combined effects of steric substitution and chelate ring size variations on structural,spectroscopic, and electrochemical properties

The syntheses and structural, spectral, and electrochemical characterization of the dioxo-bridged dinuclear Mn(III) complexes [LMn(mo-O)(2)MnL](ClO(4))(2), of the tripodal ligands tris(6-methyl-2-pyridylmethyl)amine (L(1)) and bis(6-methyl-2-pyridylmethyl)(2-(2-pyridyl)ethyl)amine (L(2)), and the Mn(II) complex of bis(2-(2-pyridyl)ethyl)(6-methyl-2-pyridylmethyl)amine (L(3)) are described. Addition of aqueous H(2)O(2) to methanol solutions of the Mn(II) complexes of L(1) and L(2) produced green solutions in a fast reaction from which subsequently precipitated brown solids of the dioxo-bridged dinuclear complexes 1 and 2, respectively, which have the general formula [LMn(III)(mu-O)(2)Mn(III)L](ClO(4))(2). Addition of 30% aqueous H(2)O(2) to the methanol solution of the Mn(II) complex of L(3) ([Mn(II)L(3)(CH(3)CN)(H(2)O)](ClO(4))(2) (3)) showed a very sluggish change gradually precipitating an insoluble black gummy solid, but no dioxo-bridged manganese complex is produced. By contrast, the Mn(II) complex of the ligand bis(2-(2-pyridyl)ethyl)(2-pyridylmethyl)amine (L(3a)) has been reported to react with aqueous H(2)O(2) to form the dioxo-bridged Mn(III)Mn(IV) complex. In cyclic voltammetric experiments in acetonitrile solution, complex 1 shows two reversible peaks at E(1/2) = 0.87 and 1.70 V (vs Ag/AgCl) assigned to the Mn(III)(2) <--> Mn(III)Mn(IV) and the Mn(III)Mn(IV) <--> Mn(IV)(2) processes, respectively. Complex 2 also shows two reversible peaks, one at E(1/2) = 0.78 V and a second peak at E(1/2) = 1.58 V (vs Ag/AgCl) assigned to the Mn(III)(2) <--> Mn(III)Mn(IV) and Mn(III)Mn(IV) <--> Mn(IV)(2) redox processes, respectively. These potentials are the highest so far observed for the dioxo-bridged dinuclear manganese complexes of the type of tripodal ligands used here. The bulk electrolytic oxidation of complexes 1 and 2, at a controlled anodic potential of 1.98 V (vs Ag/AgCl), produced the green Mn(IV)(2) complexes that have been spectrally characterized. The Mn(II) complex of L(3) shows a quasi reversible peak at an anodic potential of E(p,a) of 1.96 V (vs Ag/AgCl) assigned to the oxidation Mn(II) to Mn(III) complex. It is about 0.17 V higher than the E(p,a) of the Mn(II) complex of L(3a). The higher oxidation potential is attributable to the steric effect of the methyl substituent at the 6-position of the pyridyl donor of L(3).     

Isolation of the first ferromagnetically coupled Mn(III/IV) complex

Binuclear manganese complexes Mn2(III/IV)(dtsalpn)2DCBI, 1, Mn2(III/III)(dtsalpn)2HDCBI, 2, containing the ligand dicarboxyimidazole (DCBI) have been prepared in order to address the issue of imidazole bridged and ferromagnetically coupled Mn sites in high oxidation states of the OEC in Photosystem II (PS II). Temperature dependent magnetic susceptibility studies of 1 indicates that the interaction between the two Mn(III)/Mn(IV) ions is ferromagnetic (J = +1.4 cm(-1)). Variable temperature EPR spectra of 1 shows that a g = 2 multiline is as an excited state signal corresponding to S = 1/2.     

Mononuclear manganese(III) complexes as building blocks for the design of trinuclear manganese clusters: study of the ligand influence on the magnetic properties of the [Mn3(mu3-O)](7+) core

The synthesis, crystal structure, and magnetic properties of three new manganese(III) clusters are reported, [Mn 3(mu 3-O)(phpzH) 3(MeOH) 3(OAc)] (1), [Mn 3(mu 3-O)(phpzMe) 3(MeOH) 3(OAc)].1.5MeOH (2), and [Mn 3(mu 3-O)(phpzH) 3(MeOH) 4(N 3)].MeOH (3) (H 2phpzH = 3(5)-(2-hydroxyphenyl)-pyrazole and H 2phpzMe = 3(5)-(2-hydroxyphenyl)-5(3)-methylpyrazole). Complexes 1- 3 consist of a triangle of manganese(III) ions with an oxido-center bridge and three ligands, phpzR (2-) (R = H, Me) that form a plane with the metal ions. All the complexes contain the same core with the general formula [Mn 3(mu 3-O)(phpzR) 3] (+). Methanol molecules and additional bridging ligands, that is, acetate (complexes 1 and 2) and azide (complex 3), are at the terminal positions. Temperature dependent magnetic susceptibility studies indicate the presence of predominant antiferromagnetic intramolecular interactions between manganese(III) ions in 1 and 3, while both antiferromagnetic and ferromagnetic intramolecular interactions are operative in 2.