A Crystal Field Model for the Spectral Relationships inMonoacidopentaammine and Diacdotetraammine Complexes of Cobalt(III)

. Can. J. Chem. 63, 3558 (1985). The chemical and spectroscopic properties of the hexanitrocobaltate(lII) anion are not in accord with the classification of the N-bonded nitrite ion as a strong field ligand. The nitro groups are rapidly displaced by other ligands, including water, and in dilute aqueous solution spontaneous reduction to Co(l1) occurs. Comparison of solid state and solution vibrational and '"Co nmr spectra demonstrates that the principal species in solution is the same as in the solid. All ligands are N-bonded. However, within 2 or 3 min of dissolution new species appear. An electron transfer mechanism for ligand exchange is suggested. It is shown that the band at 480 nm arises from the first d-d transition of the pentanitroaquacobaltate(l1l) ion and not from a hexanitrocobaltate(l1I) transition. The composition of the aged solutions has been studied by '"Co, '"N, and I7O nmr. At least 10 different species are apparent in the '"Co spectra. They have been assigned to mixed nitro/nitrito/aqua ions. Electron transfer can also lead to the formation of Co" and NO; ions, both ions being detccted by "N and 170 nmr spcctroscopy. The Co complexed nitro ligand has been detected for the first time in the "N nmr spectrum. Analysis of "Co chemical shifts shows that the crystal field strength of the nitro ligand falls steadily with the number of nitro groups in the molecule. The cis groups are four times more effective than the trclrls groups in causing this change. The cyano ligand shows the opposite behaviour -the crystal field strength increases with substitution and trc1n.s groups have a larger effect than cis groups. The reactions of the hexanitrocobaltate(Il1) ion with ethylenediamine and with cyanide ions havc bcen studied by '"Co nmr. Mixed nitro complexes are formed with ethylencdiamine but mixed nitrito complexes predominate with cyanide. RICHARD J. BUIST, STEVE C. F. Au-YEUNG et DONALD R. EATON. Can. J. Chem. 63, 3558 (1985). Les proprittes chirniques et spectroscopiques de I'anion hexanitrocobaltate(lII) ne correspondent pas a la classification de I'ion nitrite lik par I'azote cornrne une ligand de champ fort. Les groupcments nitro sont rapidement remplacks par d'autres ligands, y cornpris I'cau, et, en solutions aqueuscs dilutes, il se produit une rtduction spontanke en Co(1l). Une comparaison des spectres vibrationnels ainsi que rnm du '"Co, tant a 1'Ctat solide qu'en solution, dtmontre que les principales espkces en solution sont les m&mes qu'i I'ttat solide. Tous les ligands sont lies par I'azote. Toutefois, il apparait de nouvelles espkces en moins de trois minutes aprks leur dissolution. On suggkre que I'tchange de ligand se produit par un mtcanisme impliquant un transfert d'tlectron. On dtrnontre que la bande a 480 nm provient de la premikre transition d-d de I'ion pentanitroaquacobaltate(111) et non pas d'une transition de 1'hexanitrocobaltatc(lII). Faisant appel a la rmn du '"Co, du "N et du 17 0 , on a ttudik la composition de solutions qui avaient vieilli. On peut dtceler la prtsence d'au...

Section: The Assignment Of the Nmr Spectra Of Cobaltinitrite Solutionsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 98%

The crystal field strength of the nitro ligand and the chemistry of the hexanitrocobaltate(III) anion

Buist¹,

Au-Yeung²,

Eaton³

1985

“…The e, levels are o * and it would appear that changes from N to 0 donor ligands predominately change o bonding levels. A appears to be determined by A, not A, effects in the language of Wentworth and Piper (2).…”

Section: The Charge Transfer Bandsmentioning

confidence: 86%

“…To our knowledge, the average field model (ref. 2, and earlier references cited therein), which treats the spectra of mixed nearly octahedral complexes in terms of the average of spectral parameters of the unmixed species, has not yet been subjected to test against such complete spectral data. Triplet bands have been recorded only comparatively rarely.…”

mentioning

confidence: 99%

Electronic spectra of carbonato and oxalato ammine complexes of cobalt(III); average field model for singlet, triplet, and charge transfer bands

Sastri¹,

Langford²

1969

The electronic spectra in ligand field (singlet and triplet) and charge transfer regions have been determined for a series of mixed carbonato and oxalato ammine complexes of Co(II1). An average field model is shown to be quite adequate to complete interpretation of the spectra. The values of A appear to be dominated by (T bonding interactions. Full analysis of triplet bands reveals an abnormal C / B ratio which emphasizes the limitations to be placed on the interpretation of the values of parameters derived from first order perturbation theory parameterization of experimental spectra.

“…It can, therefore, be easily identified in the spectrum. The separation between v, and v, is, to first order, 35/4Dt and Dt is related to the inplane and out-of-plane field strengths via (17) Since the first order energy of v, is lODq -(35/4)Dt, and the sign of Dt is generally identifiable through expression 1, assignment of v, to the band on the low or high energy side of v, (according to whether the in-plane field is greater than or less than the out-of-plane field strength, respectively) is generally unambiguous. The inclusion of off-diagonal terms into the energy through configurational interaction between the various E, levels will very rarely invert this sequence (2).…”

Section: Calculationmentioning

confidence: 99%

The Electronic Spectra of Tetragonal Chromium(III) Complexes

Keeton¹,

Chou²,

Lever³

1971

Methods for processing the electronic spectra of tetragonal chromium(II1) complexes are briefly reviewed. New criteria for assigning the spectra of these complexes are introduced and the data processed to yield a series of crystal field and molecular orbital parameters. The validity of these are discussed with particular reference to the apparent x bond contribution in the chromium ligand bonds.It is concluded that the bonding is better described in ionic rather than covalent terms.