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

Abstract

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 π- and σ-antibonding and nonbonding orbitals.

Density functional approximations for consistent spin and oxidation states of oxoiron complexes

“…The best performance for the correct description of spin ground state is obtained with OPBE, S12g and SSB‐D. These three DFAs are especially designed to deal with this delicate and demanding task, and they showed success in many similar works from the past . Spin ground states determined with OPBE, S12g and SSB‐D are in accordance with the experiment for all examined iron‐oxo complexes, except for the [Fe II (OH)(Hdidpa)(CH 3 CN)] 2+ (1) complex.…”

Density Functional Approximations for Consistent Spin and Oxidation States of Oxoiron Complexes

“…These three DFAs are especially designed to deal with this delicate and demanding task, and they showed success in many similar works from the past. 45,73,[105][106][107][108] Spin ground states determined with OPBE, S12g and SSB-D are in accordance with the experiment for all examined iron-oxo complexes, except for the [Fe II (OH)(Hdidpa)(CH3CN)] 2+ (1) complex. However, this result is obtained by looking only at the electronic energy; if we actually focus on the Gibbs free energy, the ∆∆G correction is 4.06 kcal•mol -1 in favor of the high-spin.…”

Combined Experimental and Theoretical Investigation of the Origin of Magnetic Anisotropy in Pentagonal Bipyramidal Isothiocyanato Co(II), Ni(II), and Fe(III) Complexes with Quaternary-Ammonium-Functionalized 2,6-Diacetylpyridine Bisacylhydrazone

“…The chelating diversity of these types of ligands is influenced by their flexibility in assuming different conformations, the possibility of coordination in neutral, mono-and doubly deprotonated forms and high coordination capacity. 49 In the complexes, hydrazone pentadentate ligand is coordinated in an equatorial plane through the pyridine nitrogen atom, two azomethine nitrogen atoms and two carbonyl…”