Spin crossover in chromium(II) complexes

Halepoto, Dost Muhammad; Holt, David G.L.; Larkworthy, L. F.; Povey, David C.; Smith, G. W.; Leigh, G.J.

doi:10.1016/s0277-5387(00)80658-0

Cited by 12 publications

(4 citation statements)

References 3 publications

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“…Typically these examples involve coordination environments possessing relatively weak ligand field effects, such as FeN 4 O 2 and FeS 6 . , The HS state would need to be significantly stabilized for Fe II for spin equilibrium in Fe III to exist, in direct contrast to the findings here where the LS state is slightly favored in Fe II . Spin state accessibility for Cr II is less well documented, , being a fringe case for spin equilibrium (d 4 ), and bona fide low-spin examples typically involve relatively strong field ligands like CN − . Recently, experimental and theoretical , work on homoleptic cyano Cr II species in nonaqueous solution documented that the low-spin hexacyano species is kinetically well-defined, though thermodynamically unstable.…”

Section: Resultsmentioning

confidence: 99%

Spin Crossover-Coupled Electron Transfer of [M(tacn)₂]^3+/2+Complexes (tacn = 1,4,7-Triazacyclononane; M = Cr, Mn, Fe, Co, Ni)

2009

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The role of spin state equilibria on the thermodynamics of electron transfer in [M(tacn)(2)](3+/2+) complexes (tacn = 1,4,7-triazacyclononane; M = Cr, Mn, Fe, Co, Ni) was examined using density functional theory at the B3LYP*/cc-pVTZ(-f) level coupled to a continuum solvation model to afford excellent agreement between computed and experimental redox properties. An intuitive explanation of the previously observed nonperiodic trend in reduction potentials, which display a sawtooth pattern along the first-row transition metal series, is offered utilizing a novel diagrammatic illustration of the relationship between spin state energetics and reduction potentials. This representation leads to a generalized proposal for analyzing and designing nearly isoenergetic spin states of transition metals in a given ligand environment. A new ligand specific parameter alpha that allows for quantifying the differential reduction potential as a function of the metal identity is introduced, and a novel protocol is presented that divides the ligand-metal interactions into primary and secondary characteristics, which we anticipate will be useful for rationally designing the electronics of transition metal complexes in general.

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Section: Resultsmentioning

confidence: 99%

Spin Crossover-Coupled Electron Transfer of [M(tacn)₂]^3+/2+Complexes (tacn = 1,4,7-Triazacyclononane; M = Cr, Mn, Fe, Co, Ni)

2009

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“…Additionally, the ligand sets that have formerly demonstrated spin switching in Cr(II) and Mn(II) complexes do not include diimines or iminopyridines. 60 Spin switching has been observed for the d 4 [Cr(depe) 2 I 2 ], 61,62 where depe is 1,2-bis-(diethylphosphino)ethane, and for methyl and ethyl monoalkylated Mn(II) manganocenes and the parent unfunctionalized compound, which all have d 5 configuration. Therefore, it is unsurprising that 1 remains S = 1 and 2 remains S = 5/2 down to the lowest temperatures probed (5 K).…”

Section: ■ Discussionmentioning

confidence: 99%

Structural and Electronic Comparison of 1st Row Transition Metal Complexes of a Tripodal Iminopyridine Ligand

2012

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We report the preparation and characterization of a series of divalent 3d transition metal complexes (Cr to Zn, 1-7), featuring the multidentate, tripodal iminopyridine Schiff-base ligand trimethyl 6,6',6″-((1E,1'E,1″E)-((nitrilotris(ethane-2,1-diyl))tris(azanylylidene))tris-(methanylylidene))trinicotinate (L(5-OOMe)). X-ray structural studies carried out on 1-5 and 7 reveal complex geometries ranging from local octahedral coordination to significant distortion toward trigonal prismatic geometry to heptacoordinate environments. Regardless of coordination mode, magnetic and spectroscopic studies show the ligand to provide moderately strong ligand fields: the Fe complex is low-spin, while the Co and Mn complexes are high-spin at all temperatures probed. Cyclic voltammograms exhibit multiple reversible ligand-based reductions, which are relatively consistent throughout the series; however, the electrochemical behavior of the Cr complex 1 is fundamentally different from those of the other complexes. Time-dependent (TD) density functional theory (DFT) and natural transition orbital (NTO) computational analyses are presented for the ligand, its anion, and complexes 1-7: the computed spectra reproduce the major differential features of the observed visible absorption spectra, and NTOs provide viable interpretations for the observed features. The combined studies indicate that all complexes contain neutral ligands bound to M(II) ions, except for the Cr complex 1, which is best described as a Cr(III) species bound to a radical anionic ligand.

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“…In an attempt to access the Cr II iodo and bromo complexes, Cr(dmpe) 2 Cl 2 was reduced to Cr(dmpe) 2 (N 2 ) 2 using 2 equiv of n -butyllithium . Oxidation of Cr(dmpe) 2 (N 2 ) 2 with 2 equiv of iodobenzene then afforded Cr(dmpe) 2 I 2 ( 5 ), while analogous reactions employing bromobenzene or t -butylbromide were found to yield [Cr(dmpe) 2 Br 2 ]Br ( 3 ) . Further oxidation of Cr(dmpe) 2 (N 2 ) 2 to [Cr(dmpe) 2 I 2 ]I ( 7 ) can be accomplished using 1.5 equiv of I 2 .…”

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Enhancing the Magnetic Anisotropy of Cyano-Ligated Chromium(II) and Chromium(III) Complexes via Heavy Halide Ligand Effects

et al. 2010

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A method of increasing the axial zero-field splitting parameter for transition metal complexes of utility in the assembly of magnetic clusters is demonstrated through the use of heavy atoms as auxiliary ligands. The octahedral complexes [Cr(dmpe)(2)(CN)X](+) (dmpe = 1,2-bis(dimethylphosphino)ethane, X = Cl, Br, I) and Cr(dmpe)(2)(CN)X (X = Cl, I) are synthesized and structurally characterized. Variable-field magnetization measurements show the magnitude of D for these complexes to increase significantly as the halide ligand varies from chloride to iodide, ranging from 0.11 cm(-1) for [Cr(dmpe)(2)(CN)Cl](+) to 6.26 cm(-1) for Cr(dmpe)(2)(CN)I.

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Spin crossover in chromium(II) complexes

Cited by 12 publications

References 3 publications

Spin Crossover-Coupled Electron Transfer of [M(tacn)₂]^3+/2+Complexes (tacn = 1,4,7-Triazacyclononane; M = Cr, Mn, Fe, Co, Ni)

Spin Crossover-Coupled Electron Transfer of [M(tacn)₂]^3+/2+Complexes (tacn = 1,4,7-Triazacyclononane; M = Cr, Mn, Fe, Co, Ni)

Structural and Electronic Comparison of 1st Row Transition Metal Complexes of a Tripodal Iminopyridine Ligand

Enhancing the Magnetic Anisotropy of Cyano-Ligated Chromium(II) and Chromium(III) Complexes via Heavy Halide Ligand Effects

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Spin crossover in chromium(II) complexes

Cited by 12 publications

References 3 publications

Spin Crossover-Coupled Electron Transfer of [M(tacn)2]3+/2+Complexes (tacn = 1,4,7-Triazacyclononane; M = Cr, Mn, Fe, Co, Ni)

Spin Crossover-Coupled Electron Transfer of [M(tacn)2]3+/2+Complexes (tacn = 1,4,7-Triazacyclononane; M = Cr, Mn, Fe, Co, Ni)

Structural and Electronic Comparison of 1st Row Transition Metal Complexes of a Tripodal Iminopyridine Ligand

Enhancing the Magnetic Anisotropy of Cyano-Ligated Chromium(II) and Chromium(III) Complexes via Heavy Halide Ligand Effects

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Spin Crossover-Coupled Electron Transfer of [M(tacn)₂]^3+/2+Complexes (tacn = 1,4,7-Triazacyclononane; M = Cr, Mn, Fe, Co, Ni)

Spin Crossover-Coupled Electron Transfer of [M(tacn)₂]^3+/2+Complexes (tacn = 1,4,7-Triazacyclononane; M = Cr, Mn, Fe, Co, Ni)