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Title: Identification of the Dinuclear and Tetranuclear Air-Oxidized Products Derived from Labile Phenolate-Bridged Dimanganese(II) Pyridyl-Chelate Compounds

Abstract

Dioxygen-sensitive dinuclear manganese complexes of the phenoxo-hinged dinucleating ligand 2,6-bis{l_brace}[N,N{prime}-bis(2-picolyl)amino]methyl{r_brace}-4-tert-butylphenolato (bpbp{sup -}) containing exogenous labile THF, water and perchlorato ligands are described. The manganese(II) complexes [Mn{sub 2}(bpbp)(ClO{sub 4}){sub 2}(THF)]{sup +} (1) and [Mn{sub 2}(bpbp)(ClO{sub 4})(H{sub 2}O){sub 2}]{sup 2+} (2) have been isolated as the salts 1{center_dot}ClO{sub 4}{center_dot}THF{center_dot}3H{sub 2}O, 1{center_dot}B(C{sub 6}H{sub 5}){sub 4}{center_dot}4THF and 2{center_dot}(ClO{sub 4})2{center_dot}H{sub 2}O. Complexes 1 and 2 are spontaneously oxidised in air in solution and the solid state. The reaction products of the air oxidation in THF, water and methanol solutions are labile dinuclear Mn{sup II}-Mn{sup III}, Mn{sup III}{sub 2} and Mn{sup III}-Mn{sup IV} complexes containing water- and methanol-derived exogenous ligands. In addition, a Mn{sub 4} complex has been isolated. Magnetic susceptibility data confirm the Mn{sup II}-Mn{sup III} oxidation state assignment with an S = 2/S = 5/2 model with weak antiferromagnetic coupling (J = -3.7 cm{sup -1}) in [Mn{sub 2}(bpbp)(CH{sub 3}O){sub 2}(H{sub 2}O){sub 2}](ClO{sub 4}){sub 2} [3{center_dot}(ClO{sub 4}){sub 2}]. A tetranuclear complex, [Mn{sub 4}(O){sub 4-n}(OH){sub n}(bpbp){sub 2}](ClO{sub 4}){sub 4} [n = 1 or 2; 7{center_dot}(ClO{sub 4}){sub 4}], recovered from THF shows a Mn{sub 4}O{sub 6} adamantane-type core with the O bridges furnished by the two phenolato groups and four hydroxide/oxide bridges. We have arrived at twomore » feasible formulations for the core metal oxidation states and oxo-bridge protonation states, namely [Mn{sup III}{sub 4}(O){sub 2}(OH){sub 2}(bpbp){sub 2}]{sup 4+} and [Mn{sup III}{sub 3}Mn{sup IV}(O){sub 3}(OH)(bpbp){sub 2}]{sup 4+}, for 7, on the basis of a bond valence sum analysis of the crystal structure, elemental analysis and XANES. Thus, complex 7 is at least two oxidation state levels lower than known complexes with the Mn{sub 4}O{sub 6} adamantane core structure. The magnetism of 7 was fitted well to an MnIII4 three-J model. Complex cations related to 3 by homology, and to 7 by hydration/solvation, have been identified by ESI mass spectrometry. The [Mn{sub 2}(bpbp)(OH){sub 2}(H{sub 2}O){sub 2}]{sup 2+} ion (4) present in aqueous solutions on dissolution of 1{center_dot}ClO4{center_dot}THF{center_dot}3H2O in air or by simple dissolution of 3 in water-containing solvent is isoelectronic to 3. In the presence of significant amounts of water the Mn{sup II}-Mn{sup III} complexes 3 and 4 are susceptible to further metal oxidation and concomitant aquo ligand deprotonation to give ions assignable to [Mn{sup III/IV}{sub 2}(bpbp)O(OCH{sub 3}){sub 2}(H{sub 2}O)]{sup 2+} (5) and [Mn{sup III}{sub 2}(bpbp)(OH){sub 3}(H{sub 2}O)]{sup 2+} (6). ESI mass spectra of water or methanol solutions of 1, 2, 3 and 7 show predominantly an ion assignable to the oxide [Mn{sub 2}(bpbp)(O)]{sup 2+} (8). Cation 8 is most likely not present in solution. Using mild source conditions and MS-MS techniques, the gas-phase fragmentation pathways to generate 8 have been mapped.« less

Authors:
; ; ; ; ; ; ;
Publication Date:
Research Org.:
Brookhaven National Laboratory (BNL) National Synchrotron Light Source
Sponsoring Org.:
Doe - Office Of Science
OSTI Identifier:
914195
Report Number(s):
BNL-78763-2007-JA
Journal ID: ISSN 1434-1948; EJICFO; TRN: US200804%%590
DOE Contract Number:
DE-AC02-98CH10886
Resource Type:
Journal Article
Resource Relation:
Journal Name: Eur. J. Inorg. Chem.; Journal Volume: 2006
Country of Publication:
United States
Language:
English
Subject:
10 SYNTHETIC FUELS; 36 MATERIALS SCIENCE; AIR; AQUEOUS SOLUTIONS; CRYSTAL STRUCTURE; MAGNETIC SUSCEPTIBILITY; MANGANESE COMPLEXES; MASS SPECTRA; MASS SPECTROSCOPY; METHANOL; OXIDATION; WATER; national synchrotron light source

Citation Formats

Larsen,F., Boisen, A., Berry, K., Moubaraki, B., Murray, K., McKee, V., Scarrow, R., and McKenzie, C. Identification of the Dinuclear and Tetranuclear Air-Oxidized Products Derived from Labile Phenolate-Bridged Dimanganese(II) Pyridyl-Chelate Compounds. United States: N. p., 2006. Web. doi:10.1002/ejic.200600488.
Larsen,F., Boisen, A., Berry, K., Moubaraki, B., Murray, K., McKee, V., Scarrow, R., & McKenzie, C. Identification of the Dinuclear and Tetranuclear Air-Oxidized Products Derived from Labile Phenolate-Bridged Dimanganese(II) Pyridyl-Chelate Compounds. United States. doi:10.1002/ejic.200600488.
Larsen,F., Boisen, A., Berry, K., Moubaraki, B., Murray, K., McKee, V., Scarrow, R., and McKenzie, C. Sun . "Identification of the Dinuclear and Tetranuclear Air-Oxidized Products Derived from Labile Phenolate-Bridged Dimanganese(II) Pyridyl-Chelate Compounds". United States. doi:10.1002/ejic.200600488.
@article{osti_914195,
title = {Identification of the Dinuclear and Tetranuclear Air-Oxidized Products Derived from Labile Phenolate-Bridged Dimanganese(II) Pyridyl-Chelate Compounds},
author = {Larsen,F. and Boisen, A. and Berry, K. and Moubaraki, B. and Murray, K. and McKee, V. and Scarrow, R. and McKenzie, C.},
abstractNote = {Dioxygen-sensitive dinuclear manganese complexes of the phenoxo-hinged dinucleating ligand 2,6-bis{l_brace}[N,N{prime}-bis(2-picolyl)amino]methyl{r_brace}-4-tert-butylphenolato (bpbp{sup -}) containing exogenous labile THF, water and perchlorato ligands are described. The manganese(II) complexes [Mn{sub 2}(bpbp)(ClO{sub 4}){sub 2}(THF)]{sup +} (1) and [Mn{sub 2}(bpbp)(ClO{sub 4})(H{sub 2}O){sub 2}]{sup 2+} (2) have been isolated as the salts 1{center_dot}ClO{sub 4}{center_dot}THF{center_dot}3H{sub 2}O, 1{center_dot}B(C{sub 6}H{sub 5}){sub 4}{center_dot}4THF and 2{center_dot}(ClO{sub 4})2{center_dot}H{sub 2}O. Complexes 1 and 2 are spontaneously oxidised in air in solution and the solid state. The reaction products of the air oxidation in THF, water and methanol solutions are labile dinuclear Mn{sup II}-Mn{sup III}, Mn{sup III}{sub 2} and Mn{sup III}-Mn{sup IV} complexes containing water- and methanol-derived exogenous ligands. In addition, a Mn{sub 4} complex has been isolated. Magnetic susceptibility data confirm the Mn{sup II}-Mn{sup III} oxidation state assignment with an S = 2/S = 5/2 model with weak antiferromagnetic coupling (J = -3.7 cm{sup -1}) in [Mn{sub 2}(bpbp)(CH{sub 3}O){sub 2}(H{sub 2}O){sub 2}](ClO{sub 4}){sub 2} [3{center_dot}(ClO{sub 4}){sub 2}]. A tetranuclear complex, [Mn{sub 4}(O){sub 4-n}(OH){sub n}(bpbp){sub 2}](ClO{sub 4}){sub 4} [n = 1 or 2; 7{center_dot}(ClO{sub 4}){sub 4}], recovered from THF shows a Mn{sub 4}O{sub 6} adamantane-type core with the O bridges furnished by the two phenolato groups and four hydroxide/oxide bridges. We have arrived at two feasible formulations for the core metal oxidation states and oxo-bridge protonation states, namely [Mn{sup III}{sub 4}(O){sub 2}(OH){sub 2}(bpbp){sub 2}]{sup 4+} and [Mn{sup III}{sub 3}Mn{sup IV}(O){sub 3}(OH)(bpbp){sub 2}]{sup 4+}, for 7, on the basis of a bond valence sum analysis of the crystal structure, elemental analysis and XANES. Thus, complex 7 is at least two oxidation state levels lower than known complexes with the Mn{sub 4}O{sub 6} adamantane core structure. The magnetism of 7 was fitted well to an MnIII4 three-J model. Complex cations related to 3 by homology, and to 7 by hydration/solvation, have been identified by ESI mass spectrometry. The [Mn{sub 2}(bpbp)(OH){sub 2}(H{sub 2}O){sub 2}]{sup 2+} ion (4) present in aqueous solutions on dissolution of 1{center_dot}ClO4{center_dot}THF{center_dot}3H2O in air or by simple dissolution of 3 in water-containing solvent is isoelectronic to 3. In the presence of significant amounts of water the Mn{sup II}-Mn{sup III} complexes 3 and 4 are susceptible to further metal oxidation and concomitant aquo ligand deprotonation to give ions assignable to [Mn{sup III/IV}{sub 2}(bpbp)O(OCH{sub 3}){sub 2}(H{sub 2}O)]{sup 2+} (5) and [Mn{sup III}{sub 2}(bpbp)(OH){sub 3}(H{sub 2}O)]{sup 2+} (6). ESI mass spectra of water or methanol solutions of 1, 2, 3 and 7 show predominantly an ion assignable to the oxide [Mn{sub 2}(bpbp)(O)]{sup 2+} (8). Cation 8 is most likely not present in solution. Using mild source conditions and MS-MS techniques, the gas-phase fragmentation pathways to generate 8 have been mapped.},
doi = {10.1002/ejic.200600488},
journal = {Eur. J. Inorg. Chem.},
number = ,
volume = 2006,
place = {United States},
year = {Sun Jan 01 00:00:00 EST 2006},
month = {Sun Jan 01 00:00:00 EST 2006}
}
  • Charge-transfer (CT) excited states of RuL{sub 2}(L{prime}-L{prime}){sup 2+} and RuL{sub 2}(L{prime}-L{prime}){sup 4+} have been studied by means of emission and transient absorption (TA) spectroscopy at 77-300 K. The bridging ligand (L{prime}-L{prime}) is either 2,2{prime}-bis(2-pyridyl)benzimidazole (bpbimH{sub 2}) or 1,2-bis(2-(2-pyridyl)benzimidazolyl)ethane (dpbime) and L is 2,2{prime}-bipyridine (bpy), 4,4{prime}-dimethyl-2,2{prime}-bipyridine (dmbpy), or 1,10-phenanthroline (phen). Transient absorption (TA) spectra of the ruthenium(II) compounds subjected to laser excitation, whose molar extinction coefficients were determined, are deconvoluted to {pi}-{pi}* bands of L and L{prime}-L{prime} coordinating to Ru(III), L (or L{prime}-L{prime})-to-Ru(III) CT bands, and a {pi}-{pi}* band of (L{prime}-L{prime}){sup {center dot}-} (or L{sup {center dot}-}) by comparison with themore » absorption spectra of the oxidized compounds (RuL{sub 2}(L{prime}-L{prime}){sup 3+}). The degree of electron population on the ligand decreases in the order bpbimH{sub 2} > bpy {approximately} phen > dpbime > dmbpy in the excited CT states, while there is no discernible difference in the reduction potential between bpbimH{sub 2} (or dpbime) and bpy coordinating to Ru(II). The excitation efficiency of the metal sites in (Ru(bpy){sub 2}){sub 2}(dpbime){sup 4+} is lower than 50% when the laser power was large enough to excite more than 80% of the mononuclear compounds. The low excitation efficiency of the former is ascribed to rapid intramolecular annihilation of the excited states.« less
  • New dinuclear complexes [M(L)[sub 2](bpbimH[sub 2])M(L)[sub 2]][sup 4+] (M = Ru, Os; L = bpy, phen; bpbimH[sub 2] = 2,2[prime]-bis(2-pyridyl)bibenzimidazole) act as dibasic acids. Both the absorption spectra and oxidation potentials are strongly dependent on the solution pH, which is responsible for the deprotonation of the N-H group on the coordinated bridging ligand. The pK[sub a] values reflect the metal oxidation states, M(II) and M(III). The pK[sub a] values of the mixed-valence dinuclear complexes are quite close to those of each M(II) and M(III) component, which suggests that mixed-valence complexes bridged by the protonated ligand bpbimH[sub 2] exhibit the intervalencemore » (IT) band at 7300 cm[sup [minus]1] for M = Ru and at 9100 cm[sup [minus]1] for M = Os, respectively. When the bridging ligand is deprotonated, this IT band is shifted to lower energy at 5880 cm[sup [minus]1] for M = Ru and 7700 cm[sup [minus]1] for M = Os and intensified. The degree of metal-metal interaction of the deprotonated dinuclear complexes becomes 4-6 times larger than that of the protonated complexes. This proton-induced change of metal-metal interaction can be rationalized by change of HOMO energy levels on deprotonation or protonation in the bridging ligands. Thus, proton transfer in the bpbimH[sub 2] bridging dinuclear complexes can be utilized to serve as a trigger signal for switching the metal-metal interaction.« less
  • Hydrocarbon solutions of Mo{sub 2}(NMe{sub 2}){sub 6} and 2,2{prime}-methylenebis(6-tert-butyl-4-methylphenol)({ge}2 equiv), HO(2,2{prime}-methylenebis(6-tert-butyl-4-methylphenol)) CH{sub 2}(2,2{prime}-methylenebis(6-tert-butyl-4-methylphenol)) OH, yield Mo{sub 2}(NMe{sub 2}){sub 2}(O(2,2{prime}-methylenebis(6-tert-butyl-4-methylphenol))CH{sub 2}(2,2{prime}-methylenebis(6-tert-butyl-4-methylphenol))O){sub 2}, I, which exists in bridged Ib and chelated Ic isomers. These are formed under kinetic control, and recrystallization allows the separation of Ib (orange cubes) from Ic (yellow cubes) both of which have been crystallographically characterized. In each there is an ethane-like O{sub 2}NMo{triple_bond}MoO{sub 2}N core with Mo-Mo = 2.2 {Angstrom} (average). In Ib the two O(2,2{prime}-methylenebis(6-tert-butyl-4-methylphenol))CH{sub 2}(2,2{prime}-methylenebis(6-tert-butyl-4-methylphenol))O ligands span the Mo{triple_bond}Mo bond yielding a molecule of C{sub 2} symmetry. In Ic the molecule has near-C{sub 2} symmetry inmore » the solid state, but in solution there is either rapid rotation about the M{triple_bond}M bond or the anti-rotamer is preferred. In benzene-d{sub 6}, Ib and Ic do not interconvert at 110 {degrees}C over a period of days. However, the addition of pyridine or acetonitrile causes the isomerization of Ib to Ic, thereby establishing that Ic is the thermodynamic isomer. The rate of conversion of Ib to Ic has been shown to be dependent on the square of the concentration of added pyridine: k{sub obs} = k[py]{sup 2}. From the temperature dependence of k{sub obs}, we determine {Delta}H{sup {double_dagger}} = 19 ({+-}1) kcal/mol and {Delta}S{sup {double_dagger}} =-25 ({+-}3) eu for the pyridine-promoted isomerization of Ib to Ic. 25 refs., 10 figs., 9 tabs.« less
  • In this paper, extended X-ray absorption fine structure studies on the manganese contained in spinach chloroplasts and on certain di-p-oxo-bridged manganese dimers of the form (X 2Mn)O 2(MnX 2) (X = 2,2'-bipyridine and 1 ,10-phenanthroline) are reported. From these studies, the manganese associated with photosynthetic oxygen evolution is suggested to occur as a bridged transition-metal dimer with most likely another manganese. Finally, extensive details on the analysis are included.
  • Extended x-ray absorption fine structure studies on the manganese contained in spinach chloroplasts and on certain di-..mu..-oxo-bridged manganese dimers of the form (X/sub 2/Mn)O/sub 2/(MnX/sub 2/) (X = 2,2'-bipyridine and 1,10-phenanthroline) are reported. From these studies, the manganese associated with photosynthetic oxygen evolution is suggested to occur as a bridged transition-metal dimer with most likely another manganese. Extensive details on the analysis are included.