A New Manganese Dinuclear Complex with Phenolate Ligands and a Single Unsupported Oxo Bridge. Storage of Two Positive Charges within Less than 500 mV. Relevance to Photosynthesis (original) (raw)
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Inorganica Chimica Acta, 2006
Chemical oxidation in acetonitrile of the previously reported phenolato-bridged binuclear Mn(II) complex [(mL)MnMn(mL)] 2+ (1), where mLH is pentadentate N,N 0 -bis-(2-pyridylmethyl)-N-(2-hydroxybenzyl)-N 0 -methyl-ethane-1,2-diamine ligand [C. Hureau, et al., Chem. Eur. J. 2004, 10, 1998-2010 using iodosylbenzene PhIO (dissolved in methanol) is described. The addition of one to four equivalents of PhIO per Mn ion leads to the transient formation of the mono-l-oxo binuclear Mn 2 (III,III) complex [(mL)Mn(l-O)Mn(mL)] 2+ (2), previously studied. After addition of five equivalents of PhIO per Mn ion, the mononuclear Mn(III) species [(mL)Mn(OMe)] + (3) is quantitatively generated. The UV-Vis spectrum of 3 displays a broad band at 456 nm (e = 1000 L mol À1 cm À1 ) attributed to phenolato to Mn(III) charge transfer transition. Complex 3 exhibits a reversible oxidation wave at E 1/2 = 0.68 V versus SCE, and the mononuclear Mn(IV) complex [(mL)Mn(OMe)] 2+ (3 ox ) can thus be generated by exhaustive electrolysis at 1.0 V versus SCE. The 9.4 GHz EPR spectrum of complex 3 ox shows a strong transition near g = 4 consistent with a rhombically distorted S = 3/2 system with a zero-field splitting dominating the Zeeman effect. UV-Vis spectrum displays a large phenolato to Mn(IV) charge transfer transition at 670 nm (e = 2450 L mol À1 cm À1 ).
Journal of the American Chemical Society, 1996
The compound [Mn 2 III,IV O 2 (bisimMe 2 en) 2 ](ClO 4 ) 3 ‚H 2 O (bisimMe 2 en ) N, N′-dimethyl-N,N′-bis(imidazol-4-ylmethyl)ethane-1,2-diamine) was synthesized. It crystallizes in the monoclinic space group C2/c with a ) 18.139-(8) Å, b ) 12.694(5) Å, c ) 17.694(8) Å, ) 107.5(6)°, V ) 3885(6) Å 3 , and Z ) 4. The cation [Mn 2 III,IV O 2 (bisimMe 2 en) 2 ] 3+ contains a di-manganese di-µ-oxo unit. The Mn-Mn axis is a C 2 axis. The Mnimidazole distances for Mn III or Mn IV are distinct: respectively, 2.208(9) and 2.004(8) Å. The ground state is a |S A d2,S B d 3 / 2 ,Sd 1 / 2 〉 state separated by 420 cm -1 from the S ) 3 / 2 state. The EPR spectrum has been simulated with |A 1x,y | ) 160.10 -4 cm -1 , |A 1z | ) 136.10 -4 cm -1 , |A 2x,y | ) 72.10 -4 cm -1 , |A 2z | ) 71.10 -4 cm -1 , g xy ) 1.997, g z ) 1.993. The ESEEM spectrum is reported. The 2 H nuclei corresponding to the exchangeable hydrogen atoms of imidazole groups in D 2 O have been detected at 2.4 MHz at 3480 G. In cyclic voltammetry, [Mn 2 III,IV O 2 (bisimMe 2en) 2 ] 3+ presents in oxidation two reversible waves at 1.04 and 1.40 V (all potentials versus NHE) in strong contrast with what has been always observed on other Mn 2 III,IV O 2 units, for which only one wave in oxidation ([III,IV] f [IV,IV]) is observed. EPR spectroelectrochemistry reveals the disappearance of the 16 line spectrum of the [III,IV] species on oxidation at 1.24 V. UV-vis spectroelectrochemistry at this potential confirms the formation of the [IV,-IV] dimer. The existence of two waves was related to the presence of slow equilibrium between two different [III,IV] forms. UV-irradiation of the starting [Mn 2 III,IV O 2 (bisimMe 2 en) 2 ] 3+ complex in an aqueous borate buffer at pH ) 10 at 77 K resulted in the formation of an EPR signal that is attributed to an imidazole radical coupled to the Mn III -Mn IV pair. This signal is unsplit and is understandable in a simple model of two spins S ) 1 / 2 in magnetic interaction. It has some analogy with that observed by Boussac et al. (Nature 1990, 347, 303-306) on the S 3 state of the Ca 2+ and Cl --depleted oxygen-evolving center, although in that case the signal was split. We relate this difference to small differences in the magnetic interaction of the two spins S ) 1 / 2 . ESEEM spectra of the irradiated [Mn 2 III,IV O 2 (bisimMe 2 en) 2 ] 3+ complex are reported for magnetic fields corresponding to the resonance of the radical or the metal cluster. These results suggest that the formed imidazole radical stays linked to the metal core despite the weak magnetic interaction detected. This rises the possibility that the S 3 radical in the natural system, is a direct ligand to Mn cluster.
Modeling the photosynthetic water oxidation center. Preparation and properties of tetranuclear manganese complexes containing [Mn4O2]6+,7+,8+ cores, and the crystal structures of Mn4O2(O2CMe)6(bipy)2 and Mn4O2(O2CMe)7(bipy)2
Journal of the American Chemical Society, 1989
An inorganic model approach to the photosynthetic water oxidation enzyme has been initiated, and synthetic entry into tetranuclear Mn complexes containing \Mn402]6+~7+~8+ cores has been achieved. They have been obtained by bipyridine (bipybmediated conversion of trinuclear [Mn30]-containing species, with the product oxidation level governed by the exact identity of the [Mn30] reagent employed. Treatment of Mn3O(O,CMe),(py), with -3 equiv of bipy in MeCN yields Mn402(02cMe),(bipy), (1) in 91% yield. Complex 1.2CHCl3 crystallizes in triclinic space group Pi with (at -160 "C) a = 13.883 (3) A, b = 10.592 (2) A, c = 8.848 (1) A, a = 91.18 (l)", / 3 = 72.14 (I)", y = 71.44 (l)", V = 1163.84 A3, and Z = 1. A total of 3064 unique data with F > 3u(F) were refined to values of R and R,of 3.23 and 3.75%, respectively. The molecule lies on an inversion center and contains a planar Mn4 rhombus with two p 3 -0 atoms, one above and one below the Mn4 plane. The resulting [ M I I , O~]~+ core is mixed valence (2Mn", 2Mn"') and can be considered as fusion of two M n 3 0 units by edge-sharing. Peripheral ligation is by six p2-02CMe and two terminal bipy groups to yield a complex with imposed C, symmetry. Treatment of Mn3O(o,CR),(py),(H2o) (R = Ph, 3-Me-Ph) with -3 equiv of bipy in MeCN yields Mn4O2(O2CR),(bipy), (R = Ph (2) or 3-Me-Ph (3)) containing Mn", 3Mn"'. Similarly, treatment of [Mn30(02CR),(py)3](C104) (R = Me, Et, Ph) with -3 equiv of bipy in MeCN yields [Mn4O2(0,CR),(bipy),](C1O4) (R = Me (4), Et (8), Ph (9)) containing 4Mn"'. Use of 4,4'-Mez-bipy instead of bipy results in the corresponding complex [Mn402(02CMe)7(4,4'-Mez-bipy),l(C104)
Journal of The American Chemical Society, 1996
The compound [Mn 2 III,IV O 2 (bisimMe 2 en) 2 ](ClO 4 ) 3 ‚H 2 O (bisimMe 2 en ) N, N′-dimethyl-N,N′-bis(imidazol-4-ylmethyl)ethane-1,2-diamine) was synthesized. It crystallizes in the monoclinic space group C2/c with a ) 18.139-(8) Å, b ) 12.694(5) Å, c ) 17.694(8) Å, ) 107.5(6)°, V ) 3885(6) Å 3 , and Z ) 4. The cation [Mn 2 III,IV O 2 (bisimMe 2 en) 2 ] 3+ contains a di-manganese di-µ-oxo unit. The Mn-Mn axis is a C 2 axis. The Mnimidazole distances for Mn III or Mn IV are distinct: respectively, 2.208(9) and 2.004(8) Å. The ground state is a |S A d2,S B d 3 / 2 ,Sd 1 / 2 〉 state separated by 420 cm -1 from the S ) 3 / 2 state. The EPR spectrum has been simulated with |A 1x,y | ) 160.10 -4 cm -1 , |A 1z | ) 136.10 -4 cm -1 , |A 2x,y | ) 72.10 -4 cm -1 , |A 2z | ) 71.10 -4 cm -1 , g xy ) 1.997, g z ) 1.993. The ESEEM spectrum is reported. The 2 H nuclei corresponding to the exchangeable hydrogen atoms of imidazole groups in D 2 O have been detected at 2.4 MHz at 3480 G. In cyclic voltammetry, [Mn 2 III,IV O 2 (bisimMe 2en) 2 ] 3+ presents in oxidation two reversible waves at 1.04 and 1.40 V (all potentials versus NHE) in strong contrast with what has been always observed on other Mn 2 III,IV O 2 units, for which only one wave in oxidation ([III,IV] f [IV,IV]) is observed. EPR spectroelectrochemistry reveals the disappearance of the 16 line spectrum of the [III,IV] species on oxidation at 1.24 V. UV-vis spectroelectrochemistry at this potential confirms the formation of the [IV,-IV] dimer. The existence of two waves was related to the presence of slow equilibrium between two different [III,IV] forms. UV-irradiation of the starting [Mn 2 III,IV O 2 (bisimMe 2 en) 2 ] 3+ complex in an aqueous borate buffer at pH ) 10 at 77 K resulted in the formation of an EPR signal that is attributed to an imidazole radical coupled to the Mn III -Mn IV pair. This signal is unsplit and is understandable in a simple model of two spins S ) 1 / 2 in magnetic interaction. It has some analogy with that observed by Boussac et al. (Nature 1990, 347, 303-306) on the S 3 state of the Ca 2+ and Cl --depleted oxygen-evolving center, although in that case the signal was split. We relate this difference to small differences in the magnetic interaction of the two spins S ) 1 / 2 . ESEEM spectra of the irradiated [Mn 2 III,IV O 2 (bisimMe 2 en) 2 ] 3+ complex are reported for magnetic fields corresponding to the resonance of the radical or the metal cluster. These results suggest that the formed imidazole radical stays linked to the metal core despite the weak magnetic interaction detected. This rises the possibility that the S 3 radical in the natural system, is a direct ligand to Mn cluster.
Journal of the American Chemical Society, 1996
The compound [Mn 2 III,IV O 2 (bisimMe 2 en) 2 ](ClO 4) 3 ‚H 2 O (bisimMe 2 en) N,N′-dimethyl-N,N′-bis(imidazol-4-ylmethyl)ethane-1,2-diamine) was synthesized. It crystallizes in the monoclinic space group C2/c with a) 18.139-(8) Å, b) 12.694(5) Å, c) 17.694(8) Å,) 107.5(6)°, V) 3885(6) Å 3 , and Z) 4. The cation [Mn 2 III,IV O 2 (bisimMe 2 en) 2 ] 3+ contains a di-manganese di-µ-oxo unit. The Mn-Mn axis is a C 2 axis. The Mnimidazole distances for Mn III or Mn IV are distinct: respectively, 2.208(9) and 2.004(8) Å. The ground state is a |S A d2,S B d 3 / 2 ,Sd 1 / 2 〉 state separated by 420 cm-1 from the S) 3 / 2 state. The EPR spectrum has been simulated with |A 1x,y |) 160.10-4 cm-1 , |A 1z |) 136.10-4 cm-1 , |A 2x,y |) 72.10-4 cm-1 , |A 2z |) 71.10-4 cm-1 , g xy) 1.997, g z) 1.993. The ESEEM spectrum is reported. The 2 H nuclei corresponding to the exchangeable hydrogen atoms of imidazole groups in D 2 O have been detected at 2.4 MHz at 3480 G. In cyclic voltammetry, [Mn 2 III,IV O 2 (bisimMe 2en) 2 ] 3+ presents in oxidation two reversible waves at 1.04 and 1.40 V (all potentials versus NHE) in strong contrast with what has been always observed on other Mn 2 III,IV O 2 units, for which only one wave in oxidation ([III,IV] f [IV,IV]) is observed. EPR spectroelectrochemistry reveals the disappearance of the 16 line spectrum of the [III,IV] species on oxidation at 1.24 V. UV-vis spectroelectrochemistry at this potential confirms the formation of the [IV,-IV] dimer. The existence of two waves was related to the presence of slow equilibrium between two different [III,IV] forms. UV-irradiation of the starting [Mn 2 III,IV O 2 (bisimMe 2 en) 2 ] 3+ complex in an aqueous borate buffer at pH) 10 at 77 K resulted in the formation of an EPR signal that is attributed to an imidazole radical coupled to the Mn III-Mn IV pair. This signal is unsplit and is understandable in a simple model of two spins S) 1 / 2 in magnetic interaction. It has some analogy with that observed by Boussac et al. (Nature 1990, 347, 303-306) on the S 3 state of the Ca 2+ and Cl-depleted oxygen-evolving center, although in that case the signal was split. We relate this difference to small differences in the magnetic interaction of the two spins S) 1 / 2. ESEEM spectra of the irradiated [Mn 2 III,IV O 2 (bisimMe 2 en) 2 ] 3+ complex are reported for magnetic fields corresponding to the resonance of the radical or the metal cluster. These results suggest that the formed imidazole radical stays linked to the metal core despite the weak magnetic interaction detected. This rises the possibility that the S 3 radical in the natural system, is a direct ligand to Mn cluster.
Chemical modeling of the oxygen-evolving center in plants. Synthesis, structure, and electronic and redox properties of a new mixed valence Mn-oxo cluster: (Mn2O2)-O-III,IV(bisimMe(2)en)(2) (bisimMe(2)en=N,N'-dimethyl-N,N'-bis(imidazol-4-ylmethyl)et
The compound [(Mn2O2)-O-III.IV(bisimMe(2)en)(2)](ClO4)(3) . H(2)0 (bisimMe(2)en = N,N'-dimethyl-N,N'-bis(imidazol-4-ylmethyl)ethane-1,2-diamine) was synthesized. It crystallizes in the monoclinic space group C2/C with a = 18.139(8) Angstrom, b = 12.694(5) Angstrom, c = 17.694(8) Angstrom, beta = 107.5(6)degrees, V = 3885(6) Angstrom(3), and Z = 4. The cation [(Mn2O2)-O-III.IV(bisimMe(2)en)(2)](3+) contains a di-manganese di-mu-oxo unit. The Mn-Mn axis is a C-2 axis. The Mn-Mn axis is a C-2 imidazole distances for Mn-III or Mn-IV are distinct: respectively, 2.208(9) and 2.004(8) Angstrom. The ground state is a \S-A=2,S-B=3/2,S=1/2] state separated by 420 cm(-1) from the S = 3/2 state. The EPR spectrum has been simulated with \A(lxy)\ = 160 10(-4) cm(-1), \A(1z)\ = 1.36.10(-4) cm(-1), \A(2xy)\ = 72.10(-4) cm(-1), \A(2z)\ = 71.10(-4) cm(-1), g(xy) = 1.997, g(z) = 1.993. The ESEEM spectrum is reported. The H-2 nuclei corresponding to the exchangeable hydrogen atoms of imidazole ...
European Journal of Inorganic Chemistry, 2006
The X-ray structure of a new dinuclear phenolato-bridged Mn 2 II complex abbreviated as [(L)MnMn(L)] 2+ (1), where LH is the [N 4 O] phenol containing ligand N,N-bis(2-pyridylmethyl)-NЈ-salicylidene-ethane-1,2-diamine ligand, is reported. A J value of -3.3 cm -1 (H = -JŜ 1 ·Ŝ 2 ) was determined from the magnetic measurements and the 9.4 GHz EPR spectra of both powder and frozen acetonitrile solution samples were analyzed with temperature. The cyclic voltammetry of 1 displays a reversible anodic wave at E 1/2 = 0.46 V vs. SCE associated with the two-electron oxidation of 1 yielding the dinuclear Mn 2 III complex [(L)MnMn(L)] 4+ (2). The easy air oxidation of 1 gives the mono-µ-oxido Mn 2 III complex [(L)-Mn(µ-O)Mn(L)] 2+ (3). A rational route to the formation of the mixed-valence Mn 2 III,IV complex [(L)Mn(µ-O)Mn(L)] 3+ (4) starting from 1 by bulk electrolysis at E P = 0.75 V vs. SCE in the presence of one equiv. of base per manganese ion is also briefly reported. Addition of chloride ions to 1 led to the [a]
Journal of Photochemistry and Photobiology B: Biology, 2011
The Mn cluster in photosystem II (PS II) is believed to play an important role in the UV photoinhibition of green plants, but the mechanism is still not clear at a molecular level. In this work, the photochemical stability of [Mn III (O) 2 Mn IV (H 2 O) 2 (Terpy) 2 ](NO 3 ) 3 (Terpy = 2,2 0 :6 0 ,2 00 -terpyridine), designated as Mn-oxo mixed-valence dimer, a well characterized functional model of the oxygen-evolving complex in PS II, was examined in aqueous solution by exposing the complex to excess light irradiation at six different wavelengths in the range of 250 to 700 nm. The photodamage of the Mn-oxo mixed-valence dimer was confirmed by the decrease of its oxygen-evolution activity measured in the presence of the chemical oxidant oxone. Ultraviolet light irradiation induced a new absorption peak at around 400-440 nm of the Mn-oxo mixed-valence dimer. Visible light did not have the same effect on the Mn-oxo mixed-valence dimer. We speculate that the spectral change may be caused by conversion of the Mn(III)O 2 Mn(IV) dimer into a new structure -Mn(IV)O 2 Mn(IV). In the processes, the appearance of a 514 nm fluorescence peak was observed in the solution and may be linked to the hydration or protonation of Terpy ligand in the Mn-oxo dimer. In comparing the response of the PS II functional model compound and the PS II complex to excess light radiation, our results support the idea that UV photoinhibition is triggered at the Mn 4 Ca center of the oxygen-evolution complex in PS II by forming a modified structure, possibly a Mn(IV) species, and that the reaction of Mn ions is likely the initial step.