In:
Zeitschrift für Naturforschung B, Walter de Gruyter GmbH, Vol. 48, No. 11 ( 1993-11-1), p. 1581-1588
Abstract:
Cocondensation of 2,3,5,6-tetramethyl-pyrazine with vanadium atoms affords [2,3,5,6-(CH 3 ) 4 -η 6 -1,4-C4N 2 ] 2 V (6) which has been studied by X-ray crystallography, EPR-spectro-scopy and cyclic voltammetry. As shown by unequal metal ring-atom distances (V—C = 219.6, V—N = 210.9 pm) the ligand in 6 is folded along the N—N axis (dihedral angle 13.6°). The conformation adopted by the cyclic ligands in the crystal has a torsional angle of 44.2° which comes close to the angle of 45° expected for maximum back-bonding, the filled vanadium orbitals 3 d x 2 -γ 2 and 3 d xy interacting separately with unoccupied b 3u (π*) orbitals of the individual pyrazine rings. The hyperfine coupling constant a( 51 V) = 4.45 mT attests to comparatively small spin density at the metal nucleus. It is proposed, that substantial transfer of spin density is effected by V 3d z 2 →a g (σ n+ ) overlap, the latter function representing the in-phase combination of the nitrogen “lone pair” orbitals. Contrary to bis(η 6 -phosphinine)vanadium 8, for the pyrazine complex 6 only the anion 6⁻ is formed reversibly in cyclovoltammetry, oxidation to 6 + being irreversible. However, in common with 8, the redox potentials for 6 show pronounced anodic shifts. Attempts towards η 6 -coordination of 2,4,6-trimethyl-1,3,5-triazine failed. Apparently, the 1:1 ratio of CH 3 /N is insufficient to furnish the triazine ring with the appropriate combination of π-donor and δ-acceptor properties essential for synergetic bond formation.
Type of Medium:
Online Resource
ISSN:
1865-7117
,
0932-0776
DOI:
10.1515/znb-1993-1117
Language:
English
Publisher:
Walter de Gruyter GmbH
Publication Date:
1993
detail.hit.zdb_id:
2078109-X
detail.hit.zdb_id:
124635-5
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