Dinuclear Mn Research Articles

Bio-relevant manganese(II) compartmental ligand complexes: Syntheses, crystal structures and studies of catalytic activities

Three new mono-manganese(II) complexes of a compartmental ligand, namely [Mn(HL)(H 2O) 3](NO 3) 2·H 2O ( 1), [Mn(HL)(SCN) 2(H 2O)]·H 2O ( 2), and [Mn(HL){N(CN) 2}(H 2O) 2](NO 3)·H 2O ( 3), where L = 2,6-bis{2-(N-ethyl)pyridineiminomethyl}-4-methylphenolato, have been synthesized and characterised by routine physicochemical techniques and complexes 1, 2 also by X-ray single crystal structure analysis. All the mono nuclear complexes contain Mn II high spin species at octahedral core as evidenced by magnetic moment (measured at 300 K) and EPR study at 77 K. As revealed by crystal structure analyses, the protonation of one imine nitrogen atom of the potential dinucleating ligand L hampers to form the expected dinuclear Mn II complex. However, complexes 1– 3 show excellent catecholase-like activity with both 3,5-di- tert-butylcatechol and tetrachlorocatechol as substrates. In addition complexes 1 and 2 also exhibit phosphatase activity, while 3 forms an adduct with p-nitrophenyl phosphate as substrate. To the best of our knowledge this is the first report of Mn II complexes being able to catalyze the oxidation of TCC to TCQ. Catecholase and phosphatase activities have been monitored by UV–vis spectrophotometer and Michaelis–Menten equation has been applied to rationalize all the kinetic parameters where complex 1 shows maximum k cat value followed by 2 and 3 (where for phosphatase activity 3 only forms an adduct).

Magneto-structural correlations in dinuclear Mn(iii) compounds with formula [{Mn(L)(NN)}(μ-O)(μ-2-RC6H4COO)2{Mn(L′)(NN)}]n+

Three dinuclear Mn(III) compounds with oxo and carboxylato bridges have been synthesized and characterized by X-ray diffraction: [{Mn(L)(NN)}(μ-2-ClC(6)H(4)COO)(2)(μ-O){Mn(L')(NN)}](n+) with NN = 2,2'-bipyridine (1 and 2) or 1,10-phenanthroline (3). The counteranion is either NO(3)(-) (1 and 3) or ClO(4)(-) (2) and the monodentate positions (L, L') could be occupied by molecules of water or the counteranion. For compound 1, L = H(2)O and L' = NO(3)(-); compound 2 shows two different dinuclear units and L and L' could be H(2)O or ClO(4)(-), and for compound 3 both monodentate positions are occupied by nitrate anions. The magnetic properties of the three compounds have been analyzed using the Hamiltonian H = -JS(1)·S(2). Compound 1 exhibits a dominant ferromagnetic behavior, with J = 3.0 cm(-1), |D(Mn)| = 1.79 cm(-1), |E(Mn)| = 0.60 cm(-1) with intermolecular interactions zJ' = -0.18 cm(-1). Due to the anisotropy of the Mn(III) ions, the ground state S = 4 shows ZFS with |D(4)| = 0.58 cm(-1). Compounds 2 and 3 show antiferromagnetic couplings, with J = -10.9 and -0.3 cm(-1), respectively. The magnetic interaction in this kind of compound depends on several structural factors. In the present work, the distortion around manganese ions, the torsion angle between the phenyl ring and the carboxylate group and the relative disposition of the coordination octahedra have been analyzed.

2L1424 水の酸化を触媒する2核Mn錯体の理論的研究(光生物_光合成,第49回日本生物物理学会年会)

2L1424 水の酸化を触媒する2核Mn錯体の理論的研究(光生物_光合成,第49回日本生物物理学会年会)

Dissociation kinetics of Mn2+ complexes of NOTA and DOTA

The kinetics of transmetallation of [Mn(nota)](-) and [Mn(dota)](2-) was investigated in the presence of Zn(2+) (5-50-fold excess) at variable pH (3.5-5.6) by (1)H relaxometry. The dissociation is much faster for [Mn(nota)](-) than for [Mn(dota)](2-) under both experimental and physiologically relevant conditions (t(½) = 74 h and 1037 h for [Mn(nota)](-) and [Mn(dota)](2-), respectively, at pH 7.4, c(Zn(2+)) = 10(-5) M, 25 °C). The dissociation of the complexes proceeds mainly via spontaneous ([Mn(nota)](-)k(0) = (2.6 ± 0.5) × 10(-6) s(-1); [Mn(dota)](2-)k(0) = (1.8 ± 0.6) × 10(-7) s(-1)) and proton-assisted pathways ([Mn(nota)](-)k(1) = (7.8 ± 0.1) × 10(-1) M(-1) s(-1); [Mn(dota)](2-)k(1) = (4.0 ± 0.6) × 10(-2) M(-1) s(-1), k(2) = (1.6 ± 0.1) × 10(3) M(-2) s(-1)). The observed suppression of the reaction rates with increasing Zn(2+) concentration is explained by the formation of a dinuclear Mn(2+)-L-Zn(2+) complex which is about 20-times more stable for [Mn(dota)](2-) than for [Mn(nota)](-) (K(MnLZn) = 68 and 3.6, respectively), and which dissociates very slowly (k(3)∼10(-5) M(-1) s(-1)). These data provide the first experimental proof that not all Mn(2+) complexes are kinetically labile. The absence of coordinated water makes both [Mn(nota)](-) and [Mn(dota)](2-) complexes inefficient for MRI applications. Nevertheless, the higher kinetic inertness of [Mn(dota)](2-) indicates a promising direction in designing ligands for Mn(2+) complexation.

Asymmetric epoxidation of olefins using novel chiral dinuclear Mn(III)-Salen complexes with inherent phase-transfer capability in ionic liquids

Two new chiral dinuclear Mn(III)-Salen complexes with inherent phase-transfer capability have been synthesized, which serve as catalysts in the asymmetric epoxidation of nonfunctionalized alkenes. Experimental results show these complexes are effective catalysts for the asymmetric epoxidation of some cyclic alkenes and the catalysts have certain inherent phase-transfer capability during the epoxidation because of their weak water solubility. In general, good enantioselectivity and acceptable yields were achieved when NaClO was used as oxidant under three different reaction systems. Among these alkenes, the catalyst 6a gave the highest ee (94%) for 6-chloro-2,2-dimethylchromene in the presence of ionic liquid 2. Additionally, the recovery and recycling of one dimeric Mn(III)-Salen complex were tested to investigate atom efficiency of the catalyst in different reaction systems on the alkenes epoxidations. The catalyst 6a could be recovered and recycled for six times without losing activity and selectivity.

Synthesis and structure of novel Mn(II) complex with in situ synthesized ligand

Based on in situ synthesized Schiff base ligand Dppd (Dppd = N-(di(2-pyridyl)methylene)-p-phenylenediamine), a novel dinuclear Mn(II) complex, [Mn2(Dppd)4(OAc)2](ClO4)2(CH2Cl2)2 · 2(H2O) (I), was synthesized and characterized by IR and single-crystal X-ray diffraction. The crystals belong to monoclinic system, space group C2/c with a = 26.3868(2), b = 20.0379(4), c = 19.16260(10)A, β = 126.6900(10)°, V = 8124.61(18) A3, Z = 4. The complex exhibits a dinuclear structure in which two symmetric Mn(II) atoms adopt somewhat distorted octahedral geometry. The 2D structure is further constructed through intermolecular benzene-benzene offset π···π interactions.

Isolation of a novel intermediate during unsymmetrical to symmetrical rearrangement of a tetradentate Schiff base ligand in a manganese(III) complex: Catalytic activity of the rearranged product towards alkene epoxidation

An attempt for the synthesis of a Mn III complex with unsymmetrical tetradentate Schiff base ligand uspen (1:1:1 condensate of salicylaldehyde, 2,4-pentanedione and 1,2-ethanediamine) resulted in the isolation of a novel complex, {[{Mn(salen)}{Mn(uspen)}(HCOO)]·ClO 4} n ( 1) as an intermediate species that contains both the unsymmetrical and symmetrical tetradentate ligand uspen and salen (2:1 condensate of salicylaldehyde and 1,2-ethanediamine) respectively. The structure of the complex shows that half of the unsymmetrical Schiff base, uspen rearranged to its symmetrical analogue, salen. A phenoxo bridged dinuclear Mn III complex [Mn(salen)(sal)] 2·2H 2O ( 2) with only the symmetrical Schiff base was also obtained. Compound 1 that contains both unsymmetrical and symmetrical Schiff base ligands in one molecule is unprecedented and provides an insight into the unsymmetrical to symmetrical rearrangement of tetradentate Schiff base ligand. Complex 2 acts as an efficient catalyst in the alkene (( E)-stilbene, styrene) epoxidation reaction in presence of two terminal oxidants PhIO and NaOCl in solvents CH 3CN and CH 2Cl 2 independently and it retains its reactivity with high efficiency for a long time.

Catalase-like catalytic reaction of the dinuclear manganese–salen complex

Catalase-like activity of a dinuclear manganese-salen (Mn–salen) complex, [Mn(salen)(H2O)]2(ClO4)2 (salen = N,N ′-bis(salicylidene)-1,2-diaminoethane), was investigated. The dinuclear Mn–salen complex exhibits higher catalase-like activity than that of the mononuclear Mn–salen compound, and its activity can be enhanced by an external base. Different reaction intermediates in the presence and absence of an external base were observed, and the catalytically active species was dimeric as evidenced by UV-Vis spectroscopic studies and mass spectrometry data.

EPR spectroscopy and catalase activity of manganese-bound DNA-binding protein from nutrient starved cells

DNA-binding proteins from nutrient-starved cells (DPS) protect cells from oxidative stress by removing H(2)O(2) and iron. A new class of DPS-like proteins has recently been identified, with DPS-like protein from Sulfolobus solfataricus (SsDPS) being the best characterized to date. SsDPS protects cells from oxidative stress and is upregulated in response to H(2)O(2) but also in response to iron depletion. The ferroxidase active site of SsDPS is structurally similar to the active sites of manganese catalase and rat liver arginase. The present work shows that the ferroxidase center in SsDPS binds two Mn(2+) ions with K (D) = (1/K (1) K (2))(1/2) = 48(3) microM. The binding constant of the second Mn(2+) is significantly higher than that of the first, inducing dinuclear Mn(II) cluster formation for all but the lowest concentrations of added Mn(2+). In competition experiments, equimolar amounts of Fe(2+) were unable to displace the bound manganese. EPR spectroscopy of the Mn(2) (2+) cluster showed signals comparable to those of other characterized dimanganese clusters. The exchange coupling for the cluster was determined, J = -1.4(3) cm(-1) (H = -2JS (1) S (2)), and is within the range expected for a mu(1,1)-carboxylato bridge between the manganese ions. Manganese-bound SsDPS showed catalase activity at a rate 10-100 times slower than for manganese catalases. EPR spectra of SsDPS after addition of H(2)O(2) showed the appearance of an intermediate in the reaction with H(2)O(2).

Bis{μ-4,4′-dibromo-2,2′-[o-phenylenebis(nitrilomethylidyne)]diphenolato}bis[chloridomanganese(III)]N,N-dimethylformamide disolvate

The asymmetric unit of the title compound, [Mn2(C20H12Br2N2O2)2Cl2]·2C3H7NO, contains one half of a centrosymmetric dinuclear MnIII complex and an N,N-dimethyl­formamide solvent mol­ecule. In the complex, the two MnIII ions are bridged by two O atoms from two symmetry-related N,N′-bis­(5-bromo­salicyl­idene)-1,2-diimino­benzene dianionic ligands with the longer Mn—O distance of 2.703 (3) Å, thus each Mn ion is six-coordinated by two N and three O atoms from the two dianionic ligands and one capping Cl atom in a distorted octa­hedral environment. The crystal structure displays inter­molecular π–π inter­actions between adjacent benzene rings, with a shortest centroid–centroid distance of 3.673 (2) Å, and inter­molecular C—H⋯O, C—H⋯ Cl and C—H⋯ Br hydrogen bonds.

A μ1,1- or μ1,3-carboxylate bridge makes the difference in the magnetic properties of dinuclear MnII compounds

Six new dinuclear Mn(II) compounds with carboxylate bridges have been synthesized and characterized by X-ray diffraction: [{Mn(phen)(2)}(2)(μ-RC(6)H(4)COO)(2)](ClO(4))(2) with R = 2-Cl (1), 2-CH(3) (2), 3-Cl (3), 3-CH(3) (4), 4-Cl (5) and 4-CH(3) (6). Compounds 1 and 2 show two μ(1,3)-carboxylate bridges in a syn-anti mode while compounds 3-6 present a very uncommon coordination mode of the carboxylate ligand: the μ(1,1)-bridge. The magnetic properties of these compounds are very sensitive to the bridging mode of the carboxylate ligands. While compounds 1 and 2 (μ(1,3)-bridge) display antiferromagnetic interactions, with J values of -1.41 and -1.66 cm(-1), respectively, compounds 3-6 (μ(1,1)-bridge) show ferromagnetic interactions, with J values of 1.01, 0.98, 1.04 and 1.06 cm(-1), respectively. It is worth noting that compounds 3-6 are the first of their class to be magnetically characterized. The EPR spectra at 4 K for compounds with antiferromagnetic coupling (1 and 2) are more complex than those for compounds with a ferromagnetic interaction (3-6). Quite good simulations can be obtained with the ZFS parameters of the Mn(II) ion D(Mn) ~ 0.095 cm(-1) and E(Mn) ~ 0.025 cm(-1) for compounds 1 and 2 and D(Mn) ~ 0.060 cm(-1) and E(Mn) ~ 0.004 cm(-1) for compounds 3-6.

Detection of phosphorylated T and B cell antigen receptor species by Phos-tag SDS- and Blue Native-PAGE

Detection of phospho-proteins and differently phosphorylated forms of the same protein are important in understanding cell behaviour. One novel method is Phos-tag SDS-PAGE. A dinuclear Mn 2+ complex that binds to phosphate groups (the Phos-tag) is covalently attached to the polyacrylamide gel matrix. Thus, phosphorylated proteins are retarded in their migration and can be distinguished from their non-phosphorylated counterparts. We applied Phos-tag SDS-PAGE to the analysis of the ζ, CD3ɛ and CD3δ subunits of the T cell antigen receptor (TCR-CD3). Pervanadate stimulation generated six different phospho-ζ and each two different CD3ɛ and CD3δ forms. This corresponds to the phosphorylatable tyrosines on their cytoplasmic tails. The phosphorylation pattern was compatible with random phosphorylation events. Further, we showed that the Phos-tag technology can be applied to Blue Native (BN)-PAGE. This extends the applicability to the analysis of native protein complexes. Upon pervanadate stimulation the TCR-CD3 complex was predominantly detected as two distinct phospho-complexes. In contrast, the B cell antigen receptor (BCR) appeared as one phospho-form. Thus, Phos-tag BN-PAGE is useful for the analysis of different phosphorylation states of multiprotein complexes.

Peroxidase activity of dimanganese(III) complexes with the [Mn 2(μ-OAc)(μ-OR) 2] 3+ core

Catalytic activity of three dinuclear Mn III complexes of general formula [Mn 2(μ-OAc)(μ-OMe)(L)]BPh 4 (H 3L = 1,5-bis[(2-hydroxy-5-X-benzyl)(2-pyridylmethyl)amino] pentan-3-ol, 1: X = H, 2: X = OMe, 3: X = Br) in the oxidation of phenol, 2,6-dimethoxyphenol and wood pulp by H 2O 2 has been investigated. The role of pH, electronic properties of the ligand and metal coordination environment on the ability of these complexes to activate H 2O 2 has been examined. The three catalysts showed similar activity independently of the aromatic substituent in the ligand and were found to be 2–3 times more active at pH 9.00 than at neutral pH. Bleaching of Kraft pulp by H 2O 2 activated by 1 in alkaline media decreased the kappa number of the pulp by 16%, at room temperature and low catalyst concentration, without damage of cellulose fibers. It was found that the exchange of the methoxo- and acetato-bridges by an oxo-bridge reduces the catalytic activity of these compounds, probably by direct binding of phenolate to a vacant site on the metal center.

Synthesis, Characterization and Crystal Structure of a Novel Mn(II) Coordination Polymer Material with Rigid Tetracarboxylate and Chelating N-Donor Co-Ligand

A new metal-organic framework, [Mn(DDA)0.5(phen)(H2O)2· 2H2O]n (1) (H4DDA = 4,4′ -diazenediyldiphthalic acid and phen = 1,10-phenanthroline) have been syntheiszed through hydrogen methods and characterized by IR and single-crystal X-ray diffraction. It crystallizes in triclinic, space group p-1 with a = 9.432(11) Å, b = 10.697(12) Å, c = 10.751(12) Å, α = 87.95(2)°, β = 67.76(1)°, γ = 76.08(2)°, Z = 2. The complex exhibits interesting 1D chain structure containing dinuclear Mn subunits, which is further extended into 2D supramolecuar double chain framework via π–π interactions.

Synthesis and crystal structures of pH-dependent Mn(II) coordination polymers with 3-pyrid-3-ylbenzoic acid

Two pyridinecarboxylato-bridged coordination polymers [Mn(pbc)2] n (1) and [Mn(pbc)2(H2O)2] n (2) (Hpbc = 3-pyrid-3-ylbenzoic acid) have been synthesized by the hydrothermal method and characterized by elemental analysis, IR spectra and single crystal X-ray diffraction. X-ray diffraction analysis reveals that pbc− adopts two coordination modes: μ 2-N, O, O and μ 3-N, O, O in 1 and as diconnectors linking two Mn(II) centers through μ 2-N, O in 2. Compound 1 is a dinuclear Mn2(pbc)2 metallocycle. Compound 2 is a double-stranded chain running along a.

Bis[4-(4-pyridyl)pyridinium] μ-4,4′-bipyridine-bis[tetraaqua(4,4′-bipyridine)manganese(II)] bis(5-sulfonatobenzene-1,3-dicarboxylate) 4,4′-bipyridine solvate pentadecahydrate

The crystal structure of the title compound, (C10H9N2)2[Mn2(C10H8N2)3(H2O)8](C8H3O7S)2·C10H8N2·15H2O, consists of dinuclear MnII complex cations, sulfonato­benzene­dicarboxyl­ate trianions, 4-(4-pyridyl)pyridinium cations, uncoordin­ated 4,4′-bipyridine and uncoordinated water mol­ecules. One 4,4′-bipyridine mol­ecule bridges two Mn atoms, forming a centrosymmetric dinuclear complex; the mid-point of the C—C bond linking the pyridine rings of the bridging ligand is located on an inversion center. Each MnII atom is coordinated by four water and two 4,4′-bipyridine mol­ecules in a distorted octa­hedral geometry. The MnII atom deviates by 0.591 (5) and 0.209 (2) Å from the mean planes of the coordinated pyridine rings. In the 4-(4-pyridyl)pyridinium cation, the two pyridine rings are twisted with respect to each other, making dihedral angle of 34.78 (17)°. The uncoordinated bipyridine mol­ecule is also centrosymmetric. One of uncoordinated water mol­ecules has site symmetry 2, and the other uncoordinated water mol­ecule is located close to an inversion center and its one H atom is disordered equally over two sites. Extensive π–π stacking between pyridine rings is observed and an extensive hydrogen-bonding network of the types N—H⋯N, O—H⋯N and O—H⋯O is present.

Metal-Ion Mutagenesis: Conversion of a Purple Acid Phosphatase from Sweet Potato to a Neutral Phosphatase with the Formation of an Unprecedented Catalytically Competent MnIIMnII Active Site

The currently accepted paradigm is that the purple acid phosphatases (PAPs) require a heterovalent, dinuclear metal-ion center for catalysis. It is believed that this is an essential feature for these enzymes in order for them to operate under acidic conditions. A PAP from sweet potato is unusual in that it appears to have a specific requirement for manganese, forming a unique Fe(III)-mu-(O)-Mn(II) center under catalytically optimal conditions (Schenk et al. Proc. Natl. Acad. Sci. U.S.A. 2005, 102, 273). Herein, we demonstrate, with detailed electron paramagnetic resonance (EPR) spectroscopic and kinetic studies, that in this enzyme the chromophoric Fe(III) can be replaced by Mn(II), forming a catalytically active, unprecedented antiferromagnetically coupled homodivalent Mn(II)-mu-(H)OH-mu-carboxylato-Mn(II) center in a PAP. However, although the enzyme is still active, it no longer functions as an acid phosphatase, having optimal activity at neutral pH. Thus, PAPs may have evolved from distantly related divalent dinuclear metallohydrolases that operate under pH neutral conditions by stabilization of a trivalent-divalent metal-ion core. The present Mn(II)-Mn(II) system models these distant relatives, and the results herein make a significant contribution to our understanding of the role of the chromophoric metal ion as an activator of the nucleophile. In addition, the detailed analysis of strain broadened EPR spectra from exchange-coupled dinuclear Mn(II)-Mn(II) centers described herein provides the basis for the full interpretation of the EPR spectra from other dinuclear Mn metalloenzymes.

Photo-catalytic oxidation of a di-nuclear manganese centre in an engineered bacterioferritin ‘reaction centre’

Photosynthesis involves the conversion of light into chemical energy through a series of electron transfer reactions within membrane-bound pigment/protein complexes. The Photosystem II (PSII) complex in plants, algae and cyanobacteria catalyse the oxidation of water to molecular O 2. The complexity of PSII has thus far limited attempts to chemically replicate its function. Here we introduce a reverse engineering approach to build a simple, light-driven photo-catalyst based on the organization and function of the donor side of the PSII reaction centre. We have used bacterioferritin (BFR) (cytochrome b1) from Escherichia coli as the protein scaffold since it has several, inherently useful design features for engineering light-driven electron transport. Among these are: ( i.) a di-iron binding site; ( ii.) a potentially redox-active tyrosine residue; and ( iii.) the ability to dimerise and form an inter-protein heme binding pocket within electron tunnelling distance of the di-iron binding site. Upon replacing the heme with the photoactive zinc–chlorin e 6 (ZnCe 6) molecule and the di-iron binding site with two manganese ions, we show that the two Mn ions bind as a weakly coupled di-nuclear Mn 2 II,II centre, and that ZnCe 6 binds in stoichiometric amounts of 1:2 with respect to the dimeric form of BFR. Upon illumination the bound ZnCe 6 initiates electron transfer, followed by oxidation of the di-nuclear Mn centre possibly via one of the inherent tyrosine residues in the vicinity of the Mn cluster. The light dependent loss of the Mn II EPR signals and the formation of low field parallel mode Mn EPR signals are attributed to the formation of Mn III species. The formation of the Mn III is concomitant with consumption of oxygen. Our model is the first artificial reaction centre developed for the photo-catalytic oxidation of a di-metal site within a protein matrix which potentially mimics water oxidation centre (WOC) photo-assembly.

Electro‐ and Photoinduced Formation and Transformation of Oxido‐Bridged Multinuclear Mn Complexes

AbstractThe extensive chemistry of oxido‐bridged multinuclear manganese complexes arises to a large extent from their relevance to redox‐active metalloenzymes such as manganese catalases and the oxygen‐evolving complex of photosystem II containing, as active centres, oxido‐ and carboxylato‐bridged dinuclear and tetranuclear Mn complexes, respectively. During the enzymatic catalytic cycles the oxidation state changes of the Mn ions induce some structural changes of these active centres such as the formation of oxido bridges. In this area, this review is focused on examples from the literature of the formation and transformation of oxido‐bridged multinuclear manganese complexes that are induced by electrochemical or photochemical means. Representative examples of such transformations are provided by polypyridyl Mn complexes, with interconversion between mononuclear, dinuclear and tetranuclear cores accompanied by the concomitant formation or breaking of μ‐oxido bridges. Other important examples are furnished by dinuclear Mn complexes having multipodal amino‐pyridyl ligands, some of which contain phenolic units, for which a clean interconversion between μ‐oxido and μ‐acetato bridges are observed.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Visible Light-Induced Electron Transfer from Di-μ-oxo-Bridged Dinuclear Mn Complexes to Cr Centers in Silica Nanopores

The compound (bpy) 2Mn (III)(mu-O) 2Mn (IV)(bpy) 2, a structural model relevant for the photosynthetic water oxidation complex, was coupled to single Cr (VI) charge-transfer chromophores in the channels of the nanoporous oxide AlMCM-41. Mn K-edge EXAFS spectroscopy confirmed that the di-mu-oxo dinuclear Mn core of the complex is unaffected when loaded into the nanoscale pores. Observation of the 16-line EPR signal characteristic of Mn (III)(mu-O) 2Mn (IV) demonstrates that the majority of the loaded complexes retained their nascent oxidation state in the presence or absence of Cr (VI) centers. The FT-Raman spectrum upon visible light excitation of the Cr (VI)-O (II) --> Cr (V)-O (I) ligand-to-metal charge transfer reveals electron transfer from Mn (III)(mu-O) 2Mn (IV) (Mn-O stretch at 700 cm (-1)) to Cr (VI), resulting in the formation of Cr (V) and Mn (IV)(mu-O) 2Mn (IV) (Mn-O stretch at 645 cm (-1)). All initial and final states are directly observed by FT-Raman or EPR spectroscopy, and the assignments are corroborated by X-ray absorption spectroscopy measurements. The endoergic charge separation products (Delta E o = -0.6 V) remain after several minutes, which points to spatial separation of Cr (V) and Mn (IV)(mu-O) 2Mn (IV) as a consequence of hole (O (I)) hopping as a major contributing mechanism. This is the first observation of visible light-induced oxidation of a potential water oxidation complex by a metal charge-transfer pump in a nanoporous environment. These findings will allow for the assembly and photochemical characterization of well-defined transition metal molecular units, with the ultimate goal of performing endothermic, multielectron transformations that are coupled to visible light electron pumps in nanostructured scaffolds.