Identification of the Dinuclear and Tetranuclear Air-Oxidized Products Derived from Labile Phenolate-Bridged Dimanganese(II) Pyridyl-Chelate Compounds
✍ Scribed by Frank Bartnik Larsen; Astrid Boisen; Kevin J. Berry; Boujemaa Moubaraki; Keith S. Murray; Vickie McKee; Robert C. Scarrow; Christine J. McKenzie
- Publisher
- John Wiley and Sons
- Year
- 2006
- Tongue
- English
- Weight
- 326 KB
- Volume
- 2006
- Category
- Article
- ISSN
- 1434-1948
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✦ Synopsis
Abstract
Dioxygen‐sensitive dinuclear manganese complexes of the phenoxo‐hinged dinucleating ligand 2,6‐bis{[N,N′‐bis(2‐picolyl)amino]methyl}‐4‐tert‐butylphenolato (bpbp^–^) containing exogenous labile THF, water and perchlorato ligands are described. The manganese(II) complexes [Mn~2~(bpbp)(ClO~4~)~2~(THF)]^+^ (1) and [Mn~2~(bpbp)(ClO~4~)(H~2~O)~2~]^2+^ (2) have been isolated as the salts 1·ClO~4~·THF·3H~2~O, 1·B(C~6~H~5~)~4~·4THF and 2·(ClO~4~)~2~·H~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^II^–Mn^III^, Mn^III^~2~ and Mn^III^–Mn^IV^ complexes containing water‐ and methanol‐derived exogenous ligands. In addition, a Mn~4~ complex has been isolated. Magnetic susceptibility data confirm the Mn^II^–Mn^III^ oxidation state assignment with an S = 2/S = 5/2 model with weak antiferromagnetic coupling (J = –3.7 cm^–1^) in Mn~2~(bpbp)(CH~3~O)~2~(H~2~O)~2~~2~ [3·(ClO~4~)~2~]. A tetranuclear complex, Mn~4~(O)~4–n~(OH)~n~(bpbp)~2~~4~ [n = 1 or 2; 7·(ClO~4~)~4~], recovered from THF shows a Mn~4~O~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^III^~4~(O)~2~(OH)~2~(bpbp)~2~]^4+^ and [Mn^III^~3~Mn^IV^(O)~3~(OH)(bpbp)~2~]^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~4~O~6~ adamantane core structure. The magnetism of 7 was fitted well to an Mn^III^~4~ 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~2~(bpbp)(OH)~2~(H~2~O)~2~]^2+^ ion (4) present in aqueous solutions on dissolution of 1·ClO~4~·THF·3H~2~O 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^II^–Mn^III^ complexes 3 and 4 are susceptible to further metal oxidation and concomitant aquo ligand deprotonation to give ions assignable to [Mn^III/IV^~2~(bpbp)O(OCH~3~)~2~(H~2~O)]^2+^ (5) and [Mn^III^~2~(bpbp)(OH)~3~(H~2~O)]^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~2~(bpbp)(O)]^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. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)