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A Fractional Bond Order of 1/2 in Pd 2 5+ −Formamidinate Species; The Value of Very High-Field EPR Spectra

2007; American Chemical Society; Volume: 129; Issue: 5 Linguagem: Inglês

10.1021/ja067328y

1943-2984

John F. Berry, Eckhard Bill, E. Bothe, F. Albert Cotton, Naresh S. Dalal, S.A. Ibragimov, Narpinder Kaur, Chun Y. Liu, C.A. Murillo, Saritha Nellutla, J. M. North, D. Villagrán,

Magnetism in coordination complexes

Reaction of Pd2(DAniF)4, 1, (DAniF = di-p-anisylformamidinate) with 1 equiv of AgPF6 in CH2Cl2 at or below −10 °C produces the paramagnetic species [Pd2(DAniF)4]PF6, 1-PF6, that has been studied by X-ray crystallography, UV−vis spectroscopy, electrochemistry, and multifrequency (9.5, 34.5, 110, and 220 GHz) EPR spectroscopy. Upon oxidation of the precursor, the Pd−Pd distance decreases by 0.052 Å from 2.6486(8) to 2.597(1) Å. The EPR spectra show broad signals with line widths of about 1000 G. The spectra collected at high field show a large spread of g tensor components (∼0.03), but these are masked at lower frequencies (9.5 and 34.5 GHz). A reinvestigation using high-field EPR of the p-tolyl analogue, which is the only other structurally characterized Pd25+ species (Cotton, F. A.; Matusz, M.; Poli, R.; Feng, X. J. Am. Chem. Soc. 1988, 110, 1144), shows that this species, which had been reported to give an isotropic 9.5 GHz EPR spectrum, also gives anisotropic 110 and 220 GHz EPR spectra with a similarly large spread of g tensor components consistent with the unpaired electron residing in a metal-based MO. The results of these studies and calculations using density functional theory are consistent with the oxidation being metal-based, resulting in an uncommon Pd25+ species with a Pd−Pd bond order of 1/2.