For 5 the Co-N bonds were found to average out at ~1.96 Å whereas they adopted mean lengths of ~1.98 Å for 6 (Table ). The distances Co1-N3 and Co1-N4 defined between the central ion and the pyridine nitrogen atoms were 2.1215(26) Å and 2.0989 (27) Å and are comparable to the Co(II) -pyridine nitrogen distance in 6 (Co1-N4; 2.1248(21) Å). The distance between the ion and the imine nitrogen amounts to 2.1425 (21) thus being only slightly longer. In comparison to 3 however, the bond is notably longer. The distorted tetrahedral coordination environment in 5 and 6 is reflected by τ4 and τ4' values of 0.802 and 0.801 for the BPIY adduct and 0.783 as well as 0.762 for the IMPY adduct, respectively. The latter is thus slightly more distorted which may be attributed to the influence of the spatially demanding tert-butyl group. When one plane is defined between the Co(II) ion and the TMSA nitrogen atoms on the one hand and another plane created between the central atom and the Lewis base nitrogen atoms, an angle between both planes can be measured that reflects the twist of the Lewis base towards the Co(TMSA)2 fragment. For 3 -6, this angle was found to be the least for 4 (42.95 °) and the largest for 6 (77.01 °), thus directly correlating to the spatial demand of the respective Lewis base (Table ).