109Ag and 29Si NMR Investigations of Scalar Couplings and Relaxation on Cyclo-tetrakis[tri-tert-butoxysilanethiolatosiIver(I)],[(t-C4H9O)3SiSAg]4

Abstract

Abstract From the 29Si NMR spectrum of [(t-BuO)3SiSAg]4 with a partly resolved fine structure recorded at 9.4 T, the coupling constants |J(29Si,109Ag)| = (4.49 ±0.04) Hz and | J(29Si, 107Ag)| = (3.90 + 0.03) Hz were derived. The 109Ag spectra at 9.4 T and at 2.1 T are single lines without fine structure shifted to higher frequency by δ = (725.8 ± 1.5) ppm relative to the resonance of the Ag + ion in aqueous solution at infinite dilution. No hint of any {Ag, Ag}-coupling can be derived from these spectra and from a comparison of the FID- and steady-state-signal intensities, i.e. | J (Ag, Ag) | < 1 Hz. This result is in contrast to the assumption of an Ag-Ag bond to explain the spatial shift of the Ag atoms towards the centre of the alternating Ag4S4-eight-membered central ring of the molecule. For the first time silver relaxation was investigated in a molecule. T1(109Ag) was determined at 9.4 T and at 2.1 T and at different temperatures to separate the contributions of different mechanisms: chemical shift anisotropy is the dominating one. T1=20.2 s at 2.1 T and at 301 K in this molecule is shorter by nearly two orders of magnitude than T1 of the Ag+ ion in aqueous solution