Deuterium quadrupolar coupling constants of deuteride bridging ligands : A study on rhenium hydrido carbonyl clusters

Deuterium variable-temperature T, measurements have been performed for a series of rhenium carbonyl clusters containing doubly and triply bridging deuterides, namely Re-2(mu-D)(2)(CO)(8) (1), Re-3(mu-D)(3)(CO)(12) (2), Re-4(mu(3)-D)(4)(CO)(12) (3), [NEt4] [Re-3(mu-D)(4)(CO)(10)] (4), [NEt4] [Re3-(mu-D)(3)(mu-Cl)(CO)(10)] (5), and [NEt4] [Re-3(mu-D)(4)(CO)(9)] (6). The deuterium quadrupolar coupling constants (DQCC) of the deuteride ligands have been evaluated for compounds 1-5, while the fluxionality of 6 hampered such a determination. The experimental DQCC of compound 3 (21.8 kHz) was, until now, the smallest found for organometallic compounds. Overall the DQCC values span a 4-fold range, and their fine-tuning depends on the bridging mode of the deuteride ligands (mu 3 vs mu), the local unsaturation degree of the Re atoms bridged by the deuteride, and the presence of other bridging ligands. The experimental DQCC's of rhenium derivatives and those of bridging deuterides in Cr, W, and Os clusters linearly correlate with the respective metal-hydrogen stretching frequencies.