Probing Electronic and Geometric Effects on δ( 71 Ga) by Means of Ab Initio Chemical Shift Computations

71 Ga chemical shifts computed with the GIAO (gauge‐including atomic orbitals)‐SCF method and medium‐sized basis sets for optimized geometries are reported for GaMe 3 , GaMe 3 –NMe 3 , GaCl 4 − , Ga 2 Cl 6 , Ga(OH 4 ) − , GaH 4 − , Ga(OH 2 ) 6 3+ , Ga(NCMe) 6 3+ , Ga(C 5 Me 5 ), Ga[GaCl 4 ] and Ga(C 5 H 5 ). Experimental trends are well reproduced, but the slope of the δ calc vs . δ exp correlation is only 0.93 instead of unity. For selected compounds, the electron‐correlated GIAO‐MP2 method affords an improved description of the chemical shift range covered ( ca . 1400 ppm). Geometry effects on δ( 71 Ga) are small in most cases, but can be notable for certain Ga I species, e.g. for Ga I [GaCl 4 ], the calculated Ga I chemical shift of which also depends strongly on aggregation and solvation. δ( 71 Ga) values no larger than 153 ppm are computed for LiGaH 4 and aggregates thereof, in sharp contrast to the published experimental value of 682 ppm. Based on accurate GIAO‐CCSD(T) calculations (at a highly correlated coupled‐cluster level), a δ( 71 Ga) value of ca . 615 ppm is predicted for GaH 3 . At the GIAO‐MP2 level, δ( 71 Ga) = 312 ppm is predicted for GaMe 4 − , which should be accessible experimentally. The computed σ(Ga) values in the most strongly shielded Ga I species approach that of isolated Ga + . Since σ(Ga) of isolated Ga 3+ is similar, the deshielding in molecules containing Ga III is attributed to large paramagnetic contributions of the bonding MOs in the valence shell. For a number of molecules, trends in experimental δ( 71 Ga) linewidths can be rationalized in terms of the relative magnitudes of the electric field gradient at the Ga atom.