Role of Spin State and Ligand Charge in Coordination Patterns in Complexes of 2,6-Diacetylpyridinebis(semioxamazide) with 3d-Block Metal Ions: A Density Functional Theory Study

We report here a systematic computational study on the effect of the spin state and ligand charge on coordination preferences for a number of 3d-block metal complexes with the 2,6-diacetylpyridinebis(semioxamazide) ligand and its mono- and dianionic analogues. Our calculations show excellent agreement for the geometries compared with the available X-ray structures and clarify some intriguing experimental observations. The absence of a nickel complex in seven-coordination is confirmed here, which is easily explained by inspection of the molecular orbitals that involve the central metal ion. Moreover, we find here that changes in the spin state lead to completely different coordination modes, in contrast to the usual situation that different spin states mainly result in changes in the metal ligand bond lengths. Both effects result from different occupations of a combination of pi- and sigma-antibonding and nonbonding orbitals.