X-ray-absorption studies of thed-orbital occupancies of selected 4d/5dtransition metals compounded with group-III/IV ligands

X-ray-absorption spectroscopy (XAS) is used to explore the systematic variations in the 4d/5d transition-metal {T=Au, Pt, Ir, Re, Pd, Ag} d-orbital occupancy in binary T-X compounds {X=Al, Ga, In, Si, Ge, Sn}. Specifically, the strength of the white line (WL) feature at the T-${\mathit{L}}_{2,3}$ edges is used to quantify the changes in the d-orbital occupancy induced by T-X bond formation. Systematic chemical trends in bonding-induced d-orbital-occupancy changes, evidenced by the data, are discussed. A charge-transfer scale (C scale) is developed to approximately summarize the number of T-d holes created in all of the ${\mathit{T}}_{1\mathrm{-}\mathit{x}}$ ${\mathit{X}}_{\mathit{x}}$ compounds studied. Comparison with the electronegativity scale emphasizes that, although the C scale deals with a more restricted type of charge transfer, it provides insight into the T-X bonding that is not contained in the traditional scale.