(α-Diimine)chromium Complexes: Molecular and Electronic Structures; A Combined Experimental and Density Functional Theoretical Study

Abstract

Dark brown crystals of [Cr( (1)L) 2] ( 1) were obtained from the reaction of [Cr (III)(acac) 3] (acac (-) = 2,4-pentanedionate) with 2 equiv of 2-methyl-1,4-bis(2,6-dimethylphenyl)-1,4-diaza-1,3-butadiene ( (1)L) and 3 equiv of sodium in tetrahydrofuran (thf) under an Ar atmosphere. Complex 1 possesses an S = 1 ground state, which is attained via intramolecular antiferromagnetic coupling between a high-spin Cr (II) ion ( S Cr = 2) and two anionic alpha-diiminato(1-) ligand pi radicals ( (1)L (*)) (1-). The molecular structure of 1 exhibits a distorted tetrahedral, nearly square-planar geometry. The average C-N imine bond length at 1.346 A is characteristic for the pi radical anion ( (1)L (*)) (1-), and therefore, the electronic structure of 1 is best described as [Cr (II)( (1)L (*)) 2]. This has been confirmed by broken symmetry density functional theoretical calculations BS(4,2) (DFT) at the B3LYP level. The reaction of [Cr (III)(acac) 3] with 1 equiv of 2,3-dimethyl-1,4-bis(2,6-diisopropylphenyl)-1,4-diaza-1,3-butadiene ( (2)L) and 1 equiv of Na in thf under Ar yields red-brown crystals of [Cr (III)( (2)L (*))(acac) 2] ( 2) ( S = 1). The oxidation of 2 with 1 equiv of Fc(PF 6) (Fc (+) = ferrocenium) in CH 2Cl 2 affords crystals of [Cr (III)( (2)L (ox))(acac) 2](PF 6) ( 3) ( S = (3)/ 2). The crystal structure determinations of 2 and 3 revealed that 2 contains a neutral, octahedral Cr (III) species [Cr (III)( (2)L (*))(acac) 2], whereas in 3 the ligand is oxidized, yielding an octahedral monocation [Cr (III)( (2)L (ox))(acac) 2] (+). These electronic structures have been confirmed by DFT calculations.

Reactions of a quintuply bonded chromium dimer with alkynes

“…10 We note that the backbone bond lengths of the diimine ligands in 1 and 2a do not appreciably differ; thus the two electrons used to reduce the alkyne to an alkenediyl ligand must have come from the chromium atoms rather than from the redox non-innocent ligands; the latter maintain radical anion character throughout the reaction. 13,14 If the formal oxidation state of chromium in 2a is Cr(II), as seems reasonable, it must have been Cr(I) in 1, consistent with our original assignment of a quintuple bond between two d 5 -ions.…”

Use of Ethylenediaminetetraacetic Acid as a Scavenger for Chromium from “Wet Blue” Leather Waste: Thermodynamic and Kinetics Parameters

“…To investigate the thermodynamic properties of the complexation between chromium (Cr +3 and Cr +6 ) and the ligands EDTA, NTA, and collagen, electronic structure calculations were performed on another level. For this, all structures were exported to the GAUSSIAN 09 [26] program, where the vibrational frequency calculations were performed using the method of Density Functional Theory (DFT) [12,27] combined with functional exchange-correlation (XC) BP86 [28]-expression Becke for exchange and Perdew for correlation-and the basis set 6-31G [29] for the atoms C, H, O, and N and LANL2DZ [30,31] for the chromium atom. The latter, by including pseudopotential, is indicated for atoms that are from the fourth period of the periodic table.…”

Synthesis of Amphiphilic Azo‐Anion‐Radical Complexes of Chromium(III) and the Development of Ultrathin Redox‐Active Surfaces by the Langmuir–Schaefer Technique

“…[5,44] Therefore, the calculations of the ground-state singlet states were performed using either spin-restricted-or spin-unrestricted approaches (in G03, combined with GUESS = MIX). The stability of this unrestricted Kohn-Sham solution has been checked by stability analysis as implemented in G03.…”