Origin of the hydridic H-1 NMR chemical shift in low-valent transition-metal hydrides

We present a theoretical study of the H-1 NMR chemical. shifts in low-valent transition metal hydrides based on density functional theory and gauge-including atomic orbitals (DFT-GIAO). Calculations have been carried out on the representative hydrides HM(CO)(5) (M = Mn, Tc, Re), H2Fe(CO)(4), HCo(CO)(4), [HCr(CO)(5)](-), and [HCr2(CO)(10)](-). In general, the calculated chemical shifts are in good agreement with the available experimental data. The paramagnetic and diamagnetic contributions to the H-1 chemical shielding have been analyzed in detail. Our calculations show that the paramagnetic current localized in the adjacent metal fragment, ML(n), is responsible for the negative ''hydridic'' shia observed in transition metal hydrides H-ML(n).