The DQF-COSY NMR Experiment, a Way to Detect Small J Couplings in the Case of Fast Relaxing Nuclei: Application to <sup>59</sup>Co in the Tetrahedral Mixed-Metal Cluster HRuCo<sub>3</sub>(CO)<sub>11</sub>(PPh<sub>3</sub>)

Abstract

The first investigation and analysis of 59Co 2D NMR homonuclear chemical shift correlation spectra for a ruthenium-based tetrahedral mixed-metal cluster HRuCo3(CO)11(PPh3) are reported. For this cluster in solution and by contrast to the conventional COSY NMR experiment, the double-quantum filtered (DQF) COSY NMR spectrum proves the existence of a scalar coupling constant between 59Co nuclei. In order to obtain a value of this coupling, the 2D COSY spectrum for a three-spin 7/2 AX2 system has been simulated by numerical density matrix calculations. The comparison between experimental and theoretical 2D NMR COSY spectra gives a spin-coupling constant |1J(59Co-59Co)| ＜ 300 Hz for this cluster.