Correlation between the donor strength of N-heterocyclic carbenes (NHC) and the M–Ccarbene bond distances in complexes of the type trans-[MX2(iPr2-bimy)(NHC)] (MX2 = PtCl2, PdBr2; iPr2-bimy = 1,3-diisopropylbenzimidazolin-2-ylidene) and [Au(iPr2-bimy)(NHC)]? was investigated for a selection of 20 carbenes.The structures of the complexes were first optimized in gas phase. The bond lengths betweenmetal (Pt, Pd and Au) and the carbene carbon of iPr2-bimy probe andNHCcarbene under studiedwere thenmeasured. Their correlation to the donor strength, evaluated using Huynh’s electronic parameter (HEP) was then examined. The results show good linear fitting betweenHEP value and Pd–Cprobe carbene distances or Hirchfeld atomic charge of the iPr2-bimy probe(Cprobe), suggesting the possibility of using theoretical approach for evaluation of donor strength forN-heterocyclic carbenes. In addition to the determination ofNHC donicity, the optimized geometries can also be utilized as inputsfor calculation of the steric properties, namely percent volume buried of the NHC ligands