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Redox Non‐Innocence of Thioether Crowns: Spectroelectrochemistry and Electronic Structure of Formal Nickel(III) Complexes of Aza–Thioether Macrocycles
Author(s) -
Stephen Emma,
Huang Deguang,
Shaw Jennifer L.,
Blake Alexander J.,
Collison David,
Davies E. Stephen,
Edge Ruth,
Howard Judith A. K.,
McInnes Eric J. L.,
Wilson Claire,
Wolowska Joanna,
McMaster Jonathan,
Schröder Martin
Publication year - 2011
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201100812
Subject(s) - thioether , homoleptic , crystal structure , electron paramagnetic resonance , chemistry , crystallography , nickel , octahedron , redox , stereochemistry , metal , inorganic chemistry , physics , organic chemistry , nuclear magnetic resonance
The Ni II complexes [Ni([9]aneNS 2 ‐CH 3 ) 2 ] 2+ ([9]aneNS 2 ‐CH 3 =N‐methyl‐1‐aza‐4,7‐dithiacyclononane), [Ni(bis[9]aneNS 2 ‐C 2 H 4 )] 2+ (bis[9]aneNS 2 ‐C 2 H 4 =1,2‐bis‐(1‐aza‐4,7‐dithiacyclononylethane) and [Ni([9]aneS 3 ) 2 ] 2+ ([9]aneS 3 =1,4,7‐trithiacyclononane) have been prepared and can be electrochemically and chemically oxidized to give the formal Ni III products, which have been characterized by X‐ray crystallography, UV/Vis and multi‐frequency EPR spectroscopy. The single‐crystal X‐ray structure of [Ni III ([9]aneNS 2 ‐CH 3 ) 2 ](ClO 4 ) 6 ⋅(H 5 O 2 ) 3 reveals an octahedral co‐ordination at the Ni centre, while the crystal structure of [Ni III (bis[9]aneNS 2 ‐C 2 H 4 )](ClO 4 ) 6 ⋅(H 3 O) 3 ⋅ 3H 2 O exhibits a more distorted co‐ordination. In the homoleptic analogue, [Ni III ([9]aneS 3 ) 2 ](ClO 4 ) 3 , structurally characterized at 30 K, the NiS distances [2.249(6), 2.251(5) and 2.437(2) Å] are consistent with a Jahn–Teller distorted octahedral stereochemistry. [Ni([9]aneNS 2 ‐CH 3 ) 2 ](PF 6 ) 2 shows a one‐electron oxidation process in MeCN (0.2 M NBu 4 PF 6 , 293 K) at E 1/2 =+1.10 V versus Fc + /Fc assigned to a formal Ni III /Ni II couple. [Ni(bis[9]aneNS 2 ‐C 2 H 4 )](PF 6 ) 2 exhibits a one‐electron oxidation process at E 1/2 =+0.98 V and a reduction process at E 1/2 =−1.25 V assigned to Ni II /Ni III and Ni II /Ni I couples, respectively. The multi‐frequency X‐, L‐, S‐, K‐band EPR spectra of the 3+ cations and their 86.2 % 61 Ni‐enriched analogues were simulated. Treatment of the spin Hamiltonian parameters by perturbation theory reveals that the SOMO has 50.6 %, 42.8 % and 37.2 % Ni character in [Ni([9]aneNS 2 ‐CH 3 ) 2 ] 3+ , [Ni(bis[9]aneNS 2 ‐C 2 H 4 )] 3+ and [Ni([9]aneS 3 ) 2 ] 3+ , respectively, consistent with DFT calculations, and reflecting delocalisation of charge onto the S‐thioether centres. EPR spectra for [ 61 Ni([9]aneS 3 ) 2 ] 3+ are consistent with a dynamic Jahn–Teller distortion in this compound.