DFT methods applied to answer the question: how accurate is the ligand acidity constant method for estimating the pKa of transition metal hydride complexes MHXL4 when X is varied?

Additive ligand acidity constants AL of anionic ligands are calculated for neutral hydrides of iron(ii), ruthenium(ii) and osmium(ii) with phosphine and carbonyl co-ligands; constant AL in green, more variable AL in red.