Chemical significance of ligand-field parameters in chromium(III) complexes of quadrate symmetry

Barton, T. J.; Slade, R. C.

doi:10.1039/dt9750000650

Cited by 19 publications

(12 citation statements)

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“…The relative position of the latter two levels depends on the relative Dq values of the X and Y ligands. In the present case Dq (O 2 CR − ) is expected to be larger than Dq (F − ) 50. This means that 4 E should be higher in energy than 4 B 2 51.…”

Section: Resultsmentioning

confidence: 62%

“…From a combination of the UV/Vis spectra and literature data, reasonable values can be obtained for the mentioned parameters. In a first‐order approximation the energy of the spin‐forbidden 4 A 2g → 2 E g transition (in O h notation) is given by 9 B + 3 C. 49 A typical value for the Racah B parameter in Cr III complexes is 600 cm −1 49, 50. Since the spin‐forbidden quartet–doublet transition is observed for 1 at 14 728 cm −1 in hexane, this yields a value of ≈3000 cm −1 for C. The symmetry of the coordination around the chromium atoms in 1 is actually C 2 v and not O h .…”

Section: Resultsmentioning

confidence: 99%

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Magnetic Anisotropy of the Antiferromagnetic Ring [Cr8F8Piv16]

et al. 2002

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A new tetragonal (P42(1)2) crystalline form of [Cr8F8Piv16] (HPiv = pivalic acid, trimethyl acetic acid) is reported. The ring-shaped molecules, which are aligned in a parallel fashion in the unit cell, form almost perfectly planar, regular octagons. The interaction between the CrIII ions is antiferromagnetic (J = 12 cm(-1)) which results in a S = 0 spin ground state. The low-lying spin excited states were investigated by cantilever torque magnetometry (CTM) and high-frequency EPR (HFEPR). The compound shows hard-axis anisotropy. The axial zero-field splitting (ZFS) parameters of the first two spin excited states (S = 1 and S = 2, respectively) are D1 = 1.59(3) cm(-1) or 1.63 cm(-1) (from CTM and HFEPR, respectively) and D2 = 0.37 cm(-1) (from HFEPR). The dipolar contributions to the ZFS of the S = 1 and S = 2 spin states were calculated with the point dipolar approximation. These contributions proved to be less than the combined single-ion contributions. Angular overlap model calculations that used parameters obtained from the electronic absorption spectrum, showed that the unique axis of the single-ion ZFS is at an angle of 19.3(1) degrees with respect to the ring axis. The excellent agreement between the experimental and the theoretical results show the validity of the used methods for the analysis of the magnetic anisotropy in antiferromagnetic CrIII rings.

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Section: Resultsmentioning

confidence: 62%

Section: Resultsmentioning

confidence: 99%

Magnetic Anisotropy of the Antiferromagnetic Ring [Cr8F8Piv16]

et al. 2002

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“…Indeed, through the observation of splitting in at least one of the two t 2g AEe g spin-allowed bands of [CrA 5 X] 2+ or cis-or trans-[CrA 4 X 2 ] + complexes (A=NH 3 or one arm of ethylenediamine), AOM parameters for a fair number of ligands have been determined [22][23][24][25]. A similar effort has not been made for Co(III) complexes, because two interelectronic repulsion parameters are required to fit the two spin-allowed bands, rather than the one required for Cr(III) complexes.…”

Section: Anchor Parameters By Setting E P P For Saturated Amines To Zeromentioning

confidence: 99%

“…The value of e sN for NH 3 , for example, varied only from 6950 to 7220 cm -1 among several different compounds, different investigators, and different techniques [23][24][25]. On the other hand, e sN for ethylenediamine was assigned values between 6640 and 7830 cm -1 , varying substantially with the other ligand present [23,24].Within a series of trans-[CrA 4 F 2 ] + complexes with different amines, e sF was assigned values between 7450 and 8480 cm -1 , and e pF values between 1620 and 2050 cm -1 [24]. The precision with which the component peaks within a broad band can be located is not high even at low temperature and even for single crystals.…”

Section: Anchor Parameters By Setting E P P For Saturated Amines To Zeromentioning

confidence: 99%

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Angular Overlap Model Parameters

Hoggard

2004

Structure and Bonding

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Since the introduction of the Angular overlap model (AOM) in the mid-1960s, expressing d orbital energies in terms of the s-and p-antibonding parameters e s and e p , the AOM has failed to supplant crystal field theory as the standard model to explain structure and electronic spectra in transition metal complexes. This is so despite the much more obvious connection in the AOM between structure and d orbital energies, the pictorial simplicity of the AOM approach, and the more consistent transferability of AOM parameters from one complex to another. The main reason is probably that AOM parameters cannot be determined uniquely when all the ligands are on the Cartesian axes. The scales for e s and e p must then be fixed arbitrarily, as is done automatically in the crystal field model. A number of experimental approaches have evolved to solve, or at least evade, the nonuniqueness problem, including: (a) the assignment of e p for saturated amines to zero, reflecting their inability to p-bond; (b) the simultaneous use of magnetic and spectroscopic data; (c) the inclusion of data from sharp, spinforbidden lines in Cr(III) spectra, along with application of the exact geometry and full d n configuration interaction in computations, or any combination of these; (d) the use of charge transfer bands involving dp orbitals to determine e p values. As of yet, the level of consistency among different techniques leaves something to be desired, and even with a common technique, reported AOM parameter values for particular metal-ligand combinations show a much higher variability than one would like, given even minimum expectations for transferability. Some of the variability can be ascribed to differences in the other ligands present. Even with these variations, AOM parameter sets can be usefully correlated with kinetic and thermodynamic data from both photochemical and thermal reactions.

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The Functional Group in Ligand‐Field Studies: the Empirical and Theoretical Status of the Angular Overlap Model

Gerloch¹,

Woolley

1984

Progress in Inorganic Chemistry

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Chemical significance of ligand-field parameters in chromium(III) complexes of quadrate symmetry

Cited by 19 publications

References 0 publications

Magnetic Anisotropy of the Antiferromagnetic Ring [Cr8F8Piv16]

Magnetic Anisotropy of the Antiferromagnetic Ring [Cr8F8Piv16]

Angular Overlap Model Parameters

The Functional Group in Ligand‐Field Studies: the Empirical and Theoretical Status of the Angular Overlap Model

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