Nanoscale self-hosting of molecular spin-states in the intermediate phase of a spin-crossover material.

A new spin-crossover (SC) complex [Fe(II)H(2)L(2-Me)][AsF(6)](2) has been synthesized, in which H(2)L(2-Me) denotes the chirogenic hexadentate N(6) Schiff-base ligand bis{[(2-methylimidazol-4-yl)methylidene]-3-aminopropyl}ethylenediamine. This complex has revealed a rich variety of phases during its two-step thermal crossover, as well as photoinduced spin-state switching. A high-symmetry high-spin (HS, S=2) phase, a low-symmetry low-spin (LS, S=0) phase, an intermediate phase characterized by an unprecedented lozenge pattern of 12 predominantly HS molecular crystallographic sites confining 18 predominantly LS molecular crystallographic sites, and a photoinduced low-symmetry HS phase have been accurately evidenced by temperature-dependent magnetic susceptibility, Mössbauer spectroscopy, and crystallographic studies. This variety of phases illustrates the multi-stability of this system, which results from coupling between the electronic states and structural instabilities.

Face-sharing heterotrinuclear M(II)-Ln(III)-M(II) (M = Mn, Fe, Co, Zn; Ln = La, Gd, Tb, Dy) complexes: synthesis, structures, and magnetic properties.

Trinuclear linear 3d-4f-3d complexes (3d = Mn(II), Fe(II), Co(II), Zn(II) and 4f = La(III), Gd(III), Tb(III), Dy(III)) were prepared by using a tripodal nonadentate Schiff base ligand, N,N',N''-tris(2-hydroxy-3-methoxybenzilidene)-2-(aminomethyl)-2-methyl-1,3-propanediamine. The structural determinations showed that in these complexes two distorted trigonal prismatic transition metal complexes of identical chirality are assembled through 4f cations. The Mn and Fe entities crystallize in the chiral space group P2(1)2(1)2(1) as pure enantiomers; the cobalt complexes exhibit a less straightforward behavior. All Mn, Fe, and Co complexes experience M(II)-Ln(III) ferromagnetic interactions. The Mn-Gd interaction is weak (0.08 cm(-1)) in comparison to the Fe-Gd (0.69 cm(-1)) and Co-Gd (0.52 cm(-1)) ones while the single ion zero field splitting (ZFS) term D is larger for the Fe complexes (5.7 cm(-1)) than for the cobalt ones. The cobalt complexes behave as single-molecules magnets (SMMs) with large magnetization hysteresis loops, as a consequence of the particularly slow magnetic relaxation characterizing these trinuclear molecules. Such large hysteresis loops, which are observed for the first time in Co-Ln complexes, confirm that quantum tunnelling of the magnetization does not operate in the Co-Gd-Co complex.

Synthesis, structure, and catalase-like activity of dimanganese(III) complexes of 1,5-bis[(2-hydroxy-5-X-benzyl)(2-pyridylmethyl)amino]pentan-3-ol (X = H, Br, OCH3).

New diMn(III) complexes of general formula [Mn(2)L(mu-OR)(mu-OAc)]BPh(4) (H(3)L = 1,5-bis[(2-hydroxy-5-X-benzyl)(2-pyridylmethyl)amino]pentan-3-ol, 1: X = H, R = Me, 2: X = OMe, R = Me, 3: X = Br, R = Me, 4: X = Br, R = Et) have been prepared and structurally characterized. The synthesized complexes possess a triply bridged (mu-alkoxo)(2)(mu-acetato)Mn(2)(3+) core, a short intermetallic distance of 2.95/6 A modulated by the aliphatic spacers between the central alcoholato and N-amino donor sites, and the remaining coordination sites of the two Mn(III) centers occupied by the six donor atoms of the polydentate ligand. In dimethylformamide, complexes 1-3 are able to disproportionate more than 1500 equiv of H(2)O(2) without significant decomposition, with first-order dependence on catalyst and saturation kinetic on [H(2)O(2)]. Spectroscopic monitoring of the reaction mixtures revealed that the catalyst converts into [Mn(2)(III)(mu-O)(mu-OAc)L], which is the major active form during cycling. Overall, kinetics and spectroscopic studies of H(2)O(2) dismutation by these complexes converge at a catalytic cycle between Mn(III)(2) and Mn(II)(2) oxidation levels. Comparison to other alkoxo-bridged complexes suggests that the binding mode of peroxide to the metal center of the Mn(III)(2) form of the catalyst is a key factor for tuning the Mn oxidation states involved in the H(2)O(2) dismutation mechanism.

Di- and triheteronuclear Cu-Gd and Cu-Gd-Cu complexes with dissymmetric double bridge.

The study of the Cu-Gd interaction is simplified by the use of heteronuclear Cu-Gd complexes of low nuclearity, such as dinuclear Cu-Gd or trinuclear Cu-Gd-Cu complexes. In the large majority of cases published until now, this interaction presents the advantage of being ferromagnetic. Among the known examples, the complexes with the largest J values have been prepared with use of symmetric Schiff base compartmental ligands, so that the active cores of the molecules involve two phenoxo bridges between the copper and gadolinium ions. Keeping this remark in mind, we decided to synthesize simple complexes in which two different bridges link the copper and gadolinium ions. The structural determinations of a heterodinuclear Cu-Gd and a trinuclear Cu-Gd-Cu complex confirm the asymmetry of the central cores, involving phenoxo and hydroxo bridges. The magnetic studies evidence again the presence of ferromagnetic interactions. These results corroborate preponderance of the planarity of the Cu-O2-Gd core over the dissymmetry of the bridges.

Reversible core-interconversion of an iron(III) dihydroxo bridged complex.

Complexes [Fe(Hhbi)(2)(NO(3))].2EtOH (1.2EtOH) and [Fe(2)(mu-OH)(2)(Hhbi)(4)].2H(2)O.8EtOH (2.2H(2)O.8EtOH) crystallize in the orthorhombic Fdd2 and P4(2)2(1)2 space groups, respectively (Hhbi(-) = the monoanion of 2-(2'-hydroxyphenyl benzimidazole). Complex 1 exhibits paramagnetic relaxation as evidenced by Mossbauer spectroscopy, and significant axial zero-field splitting (1.5 cm(1)

An unprecedented co-crystal including a cis-high-spin and a trans-low-spin FeII complex molecule.

Two structurally and magnetically nonequivalent isomeric molecules, a cis-high-spin and a trans-low-spin isomer constitute the unit cell of a new iron(II) complex {cis-[FeL(B5)(NCS)(2)].trans-[FeL(B5)(NCS)(2)]}.CH(3)OH, , (L(B5) = N,N'-bis((2-N-methylimidazol-1-yl)methylene))-2,2-dimethylpropane-1,3-diamine); the synthesis, X-ray structure, and magnetic and Mössbauer study of this unique example of co-crystallised geometric, conformational and electronic isomers are reported.

New dimanganese(III) complexes of pentadentate (N2O3) Schiff base ligands with the [Mn2(mu-OAc)(mu-OR)2]3+ core: synthesis, characterization and mechanistic studies of H2O2 disproportionation.

Two new diMn(III) complexes [Mn(2)(III)L(1)(mu-AcO)(mu-MeO)(methanol)(2)]Br (1) and [Mn(2)(III)L(2)(mu-AcO)(mu-MeO)(methanol)(ClO(4))] (2) (L(1)H(3)=1,5-bis(2-hydroxybenzophenylideneamino)pentan-3-ol; L(2)H(3)=1,5-bis(2-hydroxynaphtylideneamino)pentan-3-ol) were synthesized and structurally characterized. Structural studies evidence that these complexes have a bis(mu-alkoxo)(mu-carboxylato) triply bridged diMn(III) core in the solid state and in solution, with two substitution-labile sites--one on each Mn ion--in cis-position. The two complexes show catalytic activity toward disproportionation of H(2)O(2), with saturation kinetics on [H(2)O(2)], in methanol and dimethyl formamide at 25 degrees C. Spectroscopic monitoring of the H(2)O(2) disproportionation reaction suggests that (i) complexes 1 and 2 dismutate H(2)O(2) by a mechanism involving redox cycling between Mn(2)(III) and Mn(2)(IV), (ii) the complexes retain the dinuclearity during catalysis, (iii) the active form of the catalyst contains bound acetate, and (iv) protons favors the formation of inactive Mn(II) species. Comparison to other dimanganese complexes of the same family shows that the rate of catalase reaction is not critically dependent on the redox potential of the catalyst, that substitution of phenolate by naphtolate in the Schiff base ligand favors formation of the catalyst-substrate adduct, and that, in the non-protic solvent, the bulkier substituent at the imine proton position hampers the binding to the substrate.

[Fe(II)(TRIM)(2)]F(2), the First Example of Spin Conversion Monitored by Molecular Vibrations.

The new [Fe(II)(TRIM)(2)]F(2) spin-crossover complex (TRIM = 4-(4-imidazolylmethyl)-2-(2-imidazolylmethyl)imidazole) has been synthesized, crystallizing in the monoclinic system, space group P2/n, with Z = 2, a = 9.798(2) Å, b = 8.433(2) Å, c = 14.597(3) Å, and beta = 90.46(1) degrees. The structure was solved by direct methods and refined to conventional agreement indices R = 0.032 and R(w) = 0.034 with 1378 unique reflections for which I > 3sigma(I). The molecular structure consists of [Fe(TRIM)(2)](2+) complex cations hydrogen-bonded to six fluoride anions. The crystal packing results from this highly symmetrical and dense 3D network of hydrogen bonds. The coordination geometry of the iron(II) center can be described as a weakly distorted octahedron, including six nitrogen atoms originating from the two TRIM ligands coordinated to Fe(II) through their imine nitrogen atoms. Investigation of [Fe(II)(TRIM)(2)]F(2) by magnetic susceptibility measurements and Mössbauer spectroscopy as a function of temperature indicates a 5% thermal variation of the spin fraction between 50 and 150 K, at variance with all previous litterature data. The spin conversion is gradual with 6% LS fraction below 50 K and less than 1% above 150 K. A theoretical approach based on the Ising-like model, completed with harmonic oscillators associated with the 15 vibration modes of the FeN(6) coordination octahedron, successfully fits the data with an energy gap of approximately 40 K between the lowest LS and HS electrovibrational states, an average vibration frequency omega(LS) of 232 K in the LS state, and an average omega(LS)/omega(HS) ratio of 1.3. Taking these results into account, the computed molar entropy change DeltaS associated with a complete conversion between the HS and LS states of Fe(II)(TRIM)(2)F(2) ( approximately 40 J.K(-)(1).mol(-)(1)) is in fair agreement with the expected value.

pH-Dependent Monomer <--> Oligomer Interconversion of Copper(II) Complexes with N-(2-R-imidazol-4-ylmethylidene)-2-aminoethylpyridine (R = Methyl, Phenyl).

The monomer <--> oligomer interconversion of the reported metal complexes is generated by proton abstraction/supply as a common external information input. The mononuclear copper(II) complexes 1 and 2 with [CuCl(2)(HL(n)())] chemical formula have been prepared (HL(1) = N-(2-methylimidazol-4-ylmethylidene)-2-aminoethylpyridine; HL(2) = N-(2-phenylimidazol-4-ylmethylidene)-2-aminoethylpyridine). The crystal structures were determined. 1.H(2)O, C(12)H(16)N(4)OCl(2)Cu: a = 13.773(2) Å, b = 8.245(2) Å, c = 13.861(2) Å, beta = 110.10(1) degrees, monoclinic, P2(1)/n, and Z = 4. 2, C(17)H(16)N(4)Cl(2)Cu: a = 7.6659(7) Å, b = 16.287(1) Å, c = 14.103(1) Å, beta = 95.058(7) degrees, monoclinic, P2(1)/c, and Z = 4. Complexes 1.H(2)O and 2 assume a pentacoordinated square pyramidal geometry with a N(3)Cl(2) donor set consisting of the nitrogen atoms of the protonated tridentate ligand and two chloride ions in the solid state, while in aqueous solution the Cu(II) ion is tetracoordinated (N(3)Ow donor set). When 1 and 2 are treated with an equimolar amount of sodium hydroxide or triethylamine, the deprotonation of the imidazole moiety promotes a self-assembly process, arising from coordination of the imidazolate nitrogen atom to a Cu(II) ion of an adjacent unit, to yield compounds 1'.4H(2)O as the perchlorate salt, and 2'a.6H(2)O as the perchlorate salt and( )()2'b as the hexafluorophosphate salt, respectively. 1'.4H(2)O, C(12)H(15)N(4)O(5)ClCu: a = b = 13.966(2) Å, c = 33.689(3) Å, tetragonal, I4(1)/a, and Z = 16. 2'a.6H(2)O, C(51)H(51)N(12)O(15)Cl(3)Cu(3): a = 15.177(3) Å, b = 15.747(3) Å, c = 14.128(3) Å, alpha = 100.06(2) degrees, beta = 110.37(2) degrees, gamma = 63.54(1) degrees, triclinic, P&onemacr;, and Z = 2. 2'b, C(17)H(15)N(9)F(6)PCu: a = b = 29.812(5) Å, c = 11.484(3) Å, trigonal, R&thremacr;, and Z = 18. The nuclearity of the self-assembled molecules and their detailed structure were confirmed to be cyclic imidazolate-bridged tetranuclear for 1'.4H(2)O and hexanuclear for 2'a.6H(2)O and 2'b, respectively, through single-crystal X-ray analyses and FAB-MS spectra. Variable-temperature experimental magnetic susceptibility data were well reproduced by using the Heisenberg model based on a cyclic tetranuclear structure for 1' and a cyclic hexanuclear structure for 2'a and 2'b. The reversible interconversion between the protonated monomeric and deprotonated oligomeric species were confirmed by pH-dependent potentiometric and electronic spectral titrations in aqueous solution, whereas the Pd(II) complex did not show a perfect disassembly process.

Deprotonation-Induced Enantioselective Aggregation and Deprotonation-Induced Ligand Rearrangement of Copper(II) Complexes Yield 1D Homochiral and Heterochiral Chains and a Cyclic Tetramer, Respectively.

The copper(II) complexes of protonated pentadentate Schiff-base ligands with [Cu(H(2)L(n))](ClO(4))(2) formula (n = 3-6, 3-6) have been synthesized and characterized (H(2)L(3) = N-((2-methylimidazol-4-yl)methylene)-3-aminpropyl-N'-((2-methylimidazol-4-yl)methylene)-4'-aminobutylamine, H(2)L(4) = N-((2-phenylimidazol-4-yl)methylene)-3-aminpropyl-N'-((2-phenyl-imidazol-4-yl)methylene)-4'-aminobutylamine, H(2)L(5) = N,N'-bis((2-phenylimidazol-4-yl)methylene)-3,3'-diaminodipropylmethylamine, H(2)L(6) = N-((2-methylimidazol-4-yl)methylene)-2-aminoethyl-N'-((2-methylimidazol-4-yl)methylene)-3'-aminopropylamine. The mono-deprotonated complexes 3', 4', and 5' contain one imidazole and one imidazolate groups per unit and are Delta (clockwise) or Lambda (anticlockwise) enantiomorphs due to the spiral arrangement of the ligand around copper(II) ion. They function as chiral building components for a self-assembly process resulting from the formation of hydrogen bonds between the imidazole and imidazolate groups of adjacent units to yield 1D zigzag-chain structures. The distance between hydrogen-bonded nitrogen atoms is 2.81(2), 2.832(9), and 2.875(9) Å for 3', 4', and 5', respectively. The crystal lattice of 3' yielded either.DeltaDeltaDelta. or.LambdaLambdaLambda. isotactic 1D zigzag-chains, while the crystal lattices of 4' and 5' yielded.DeltaLambdaDeltaLambda. syndiotactic 1D zigzag-chains. In 3', two adjacent methyl groups at the 2-position connected by hydrogen bond array in the same direction, thus allowing homochiral aggregation of the complex molecules in a 1D chain. On the other hand, in 4' and 5', two adjacent bulky phenyl groups require opposite orientations, thus allowing heterochiral aggregation. Enantioselective aggregation with homochirality or heterochirality can thus be controlled with suitable substituents. While its mononuclear precursor 6 is pentacoordinated with the N(5) donor set of the pentadentate ligand H(2)L(6), the deprotonated complex 6' has an imidazolate-bridged tetranuclear cyclic structure with a Cu-Cu distance of 6.086(2) Å. The ligand in 6' is tetradentate and includes an hexahydropyrimidine ring resulting from a deprotonation induced rearrangement reaction.

Two-Step Spin Conversion for the Three-Dimensional Compound Tris(4,4'-bis-1,2,4-triazole)iron(II) Diperchlorate.

The title compound, [Fe(btr)(3)](ClO(4))(2), has been synthesized. The investigation of its magnetic properties has revealed a low-spin <--> high-spin conversion occurring in two steps, each step involving 50% of the Fe(2+) ions. The low-temperature step is very abrupt and occurs with a thermal hysteresis whose width is about 3 K around T(1) = 184 K. The high-temperature step, centered around T(2) = 222 K, is rather gradual. Differential scanning calorimetric measurements have confirmed the occurrence of a two-step spin conversion. The enthalpy and entropy variations associated with the two steps have been found as DeltaH(1) = 5.7 kJ mol(-)(1) and DeltaS(1) = 30.1 J mol(-)(1) K(-)(1), and DeltaH(2) = 6.5 kJ mol(-)(1) and DeltaS(2) = 28.6 J mol(-)(1) K(-)(1), respectively. The crystal structure of [Fe(btr)(3)](ClO(4))(2) has been solved at three temperatures, namely, above the high-temperature step (260 K), between the two steps (190 K), and below the low-temperature step (150 K). The compound crystallizes in the trigonal system, space group R&thremacr;, at the three temperatures. The structure is three-dimensional. There are two Fe(2+) sites, denoted Fe1 and Fe2. Each of them is located on a 3-fold symmetry axis and an inversion center and is surrounded by six btr ligands through the nitrogen atoms occupying the 1- or 1'-positions. Each btr ligand bridges an Fe1 and an Fe2 site, with an Fe1-Fe2 separation of 8.67 Å at 260 K. The perchlorate anions are located in the voids of the three-dimensional architecture and are hydrogen bonded to the triazole rings of the btr ligands. These anions do not interact with the Fe1 and Fe2 sites exactly in the same way. At 260 K, both the Fe1 and Fe2 sites are high-spin (HS) with Fe-N bond lengths of 2.161(3) and 2.164(3) Å, respectively. At 190 K, the Fe1 site remains HS while the Fe2 site is low-spin (LS) with Fe-N bond lengths of 2.007(3) Å. Finally, at 150 K, both the Fe1 and Fe2 sites are LS with Fe-N bond lengths of 1.987(5) and 1.994(5) Å, respectively. It turns out that the two-step spin conversion is associated with the presence of two slightly different Fe(2+) sites. The spin conversion regime has also been followed by Mössbauer spectroscopy. These findings have been discussed and compared to the previously reported cases of two-step spin conversions.

Synthesis, characterisation and catalase-like activity of dimanganese(III) complexes of 1,5-bis(5-X-salicylidenamino)pentan-3-ol (X=nitro and chloro).

The dimanganese(III,III) complexes [Mn(2)(III)(5-NO(2)-salpentO)(mu-AcO)(mu-MeO)(methanol)(2)]Y (1: Y=Br, 2a: Y=I, 2b: Y=I(3)), [Mn(2)(III)(5-NO(2)-salpentO)(mu-AcO)(mu-MeO)(methanol)(ClO(4))] (3) and [Mn(2)(III)(5-Cl-salpentO)(mu-AcO)(mu-MeO)(methanol)(2)]Br (4), where salpentOH is the symmetrical Schiff base ligand 1,5-bis(salicylidenamino)pentan-3-ol, were synthesised and structurally characterized. Complex 2b crystallises in the monoclinic system, space group P2(1)/c, and exhibits Mn. . .Mn separation of 2.911 A. This Mn. . .Mn separation is very close to the other characterized (mu-alkoxo)(2)(mu-acetato)Mn(2)(III) complexes of X-salpentOH (X=MeO, Br and H) and reveals that the aromatic substituent has little influence on the geometric parameters of the bimetallic core. A correlation between the electronic character of the different ring substituents, the redox potentials of the dinuclear complexes and their catalase activity was evidenced. Complexes 1-4 show saturation kinetics with [H(2)O(2)] and the H(2)O(2) disproportionation involves redox cycling between the Mn(2)(III)/Mn(2)(IV) levels. The catalytic activity studies show that bound acetate is required for catalase activity and that the acetato and alkoxo bridges serve as internal bases facilitating the proton transfer coupled to oxidation of the metal centre.

Calixarene-Based Copper(I) Complexes as Models for Monocopper Sites in Enzymes.

A cavity that acts as a molecular funnel is formed from calix[6]arene 1 and [CuI (NCCH3 )4 ]PF6 [Eq. (a)]. An exchange of the well-protected acetonitrile ligand for other nitriles RCN is only possible with small R groups. The protection of the copper ions precludes oxidative dimerization; thus, the complexes mimic the mononuclear site of copper enzymes.

Synthesis, characterization, and reactivity studies of a water-soluble bis(alkoxo)(carboxylato)-bridged diMn(III) complex modeling the active site in catalase.

A new diMn(III) complex, Na[Mn2(5-SO3-salpentO)(µ-OAc)(µ-OMe)(H2O)]·4H2O, where 5-SO3-salpentOH = 1,5-bis(5-sulphonatosalicylidenamino)pentan-3-ol, has been prepared and characterized. ESI-mass spectrometry, paramagnetic (1)H NMR, EPR and UV-visible spectroscopic studies on freshly prepared solutions of the complex in methanol and 9 : 1 methanol-water mixtures showed that the compound retains the triply bridged bis(µ-alkoxo)(µ-acetato)Mn2(3+) core in solution. In the 9 : 1 methanol-water mixture, slow substitution of acetate by water molecules took place, and after one month, the doubly bridged diMn(III) complex, [Mn2(5-SO3-salpentO)(µ-OMe)(H2O)3]·5H2O, formed and could be characterized by X-ray diffraction analysis. In methanolic or aqueous basic media, acetate shifts from a bridging to a terminal coordination mode, affording the highly stable [Mn2(5-SO3-salpentO)(µ-OMe)(OAc)](-) anion. The efficiency of the complex in disproportionating H2O2 depends on the solvent and correlates with the stability of the complex (towards metal dissociation) in each medium: basic buffer > aqueous base > water. The buffer preserves the integrity of the catalyst and the rate of O2 evolution remains essentially constant after successive additions of excess of H2O2. Turnovers as high as 3000 mol H2O2 per mol of catalyst, without significant decomposition and with an efficiency of k(cat)/K(M) = 1028 M(-1) s(-1), were measured for the complex in aqueous buffers of pH 11. Kinetic and spectroscopic results suggest a catalytic cycle that runs between Mn(III)2 and Mn(IV)2 oxidation states, which is consistent with the low redox potential observed for the Mn(III)2/Mn(III)Mn(IV) couple of the catalyst in basic medium.

New binuclear Mn(II) and Fe(II) complexes supported by 1,4,8-triazacycloundecane.

Two new binuclear metal complexes supported by 1,4,8-triazacycloundecane (tacud) are reported. [Fe(2)(tacud)(2)(µ-Cl)(2)Cl(2)] (1) and [Mn(2)(tacud)(2)(µ-Cl)(2)Cl(2)] (2) are isomorphs consisting of bis(µ-chloro) bridged metal centers along with terminal chloro groups and tacud ligands. Both compounds 1 and 2 crystallize in the P1 space group. For 1, a = 7.7321(12) Å, b = 7.8896(12) Å, c = 11.4945(17) Å, α = 107.832(2)°, ß = 107.827(2)°, γ = 92.642(2)°, V = 627.85(17) Å(3) and Z = 1. For 2, a = 7.7607(12) Å, b = 7.9068(12) Å, c = 11.6111(18) Å, α = 108.201(2)°, ß = 108.041(2)°, γ = 92.118(3)°, V = 636.47(17) Å(3) and Z = 1. Variable-temperature and variable-field magnetic susceptibility studies on 1 indicate the presence of weak ferromagnetic interactions between the high-spin iron(ii) centers in the dimer (J = + 1.6 cm(-1)) and the crystalline field anisotropy of the ferrous ion (D = - 2.8, E = - 0.1 cm(-1)). Variable temperature magnetic susceptometry studies on 2 indicate that weak antiferromagnetic coupling exists between the manganese(ii) centers (J = - 1.8 cm(-1)). Compounds 1 and 2 retain their dinuclearity in weakly coordinating or low polarity solvents, while both become mononuclear in solvents such as methanol.

Synthesis, characterization and antioxidant activity of water soluble MnIII complexes of sulphonato-substituted Schiff base ligands.

Two new Mn(III) complexes Na[Mn(5-SO(3)-salpnOH)(H(2)O)]5H(2)O (1) and Na[Mn(5-SO(3)-salpn)(MeOH)]4H(2)O (2) (5-SO(3)-salpnOH=1,3-bis(5-sulphonatosalicylidenamino)propan-2-ol, 5-SO(3)-salpn=1,3-bis(5-sulphonatosalicylidenamino)propane) have been prepared and characterized. Electrospray ionization-mass spectrometry, UV-visible and (1)H NMR spectroscopic studies showed that the two complexes exist in solution as monoanions [Mn(5-SO(3)-salpn(OH))(solvent)(2)](-), with the ligand bound to Mn(III) through the two phenolato-O and two imino-N atoms located in the equatorial plane. The E(1/2) of the Mn(III)/Mn(II) couple (-47.11 (1) and -77.80mV (2) vs. Ag/AgCl) allows these complexes to efficiently catalyze the dismutation of O(2)(-), with catalytic rate constants 2.4x10(6) (1) and 3.6x10(6) (2) M(-1)s(-1), and IC(50) values of 1.14 (1) and 0.77 (2) muM, obtained through the nitro blue tetrazolium photoreduction inhibition superoxide dismutase assay, in aqueous solution of pH 7.8. The two complexes are also able to disproportionate up to 250 equivalents of H(2)O(2) in aqueous solution of pH 8.0, with initial turnover rates of 178 (1) and 25.2 (2) mM H(2)O(2) min(-1)mM(-1)catalyst(-1). Their dual superoxide dismutase/catalase activity renders these compounds particularly attractive as catalytic antioxidants.