Ligand, axial ammonia

This Vanquickenborne and Ceulemans model has also been used to explain the substitution behavior of fluoro complexes such as CrF(NH3)5 CrF(NH3)(en)2 and CrF2(en)2, although initially there was some doubt as to whether such a ligand field model was applicable. As an example, photolysis of trans-CrF(NH3)(en)2 into the band leads to dissociation of ammonia and the formation of d.y-CrF(H20)(en)2. Application of this model concludes that the excitation energy in the axial Cr-N ligand is double that in the equatorial Cr-N ligand, and therefore the axial ammonia is preferentially labilized over the equatorial ethyle-nediamine ligands. 

The rate of substitution of the axial water ligand by ammonia in the complexes [RCo(dmgH)2(OH2)] (18) with R = Me, Et, and CH2CI has been... 

In the solid state, the metal atoms in bis(salicylaIdoximato)copper(II) show two additional contacts with the oxime oxygens of adjacent molecules, resulting in a distorted octahedral structure. However, the axial Cu—O distance (2.66 A) is much longer than the metal—ligand distances in the square-planar array (Cu—O, 1.92 A and Cu—N, 1.94 A).154 Studies by ESR of copper(II) extracts of the commercial reagent SME 529 (14 R = Me, R = C9H)9) have shown that the copper complex exists as a square-planar species in hydrocarbon solutions, but that five-coordinate adducts are formed in the presence of ammonia or pyridine.155... 

The existence of a tetracyanocobaltate(II) ion in aqueous solution has been inferred from studies at high dilution and a brown polymeric complex of composition K2[Co(CN)4] has been isolated from solutions of [Co(SCN)2] and KCN in ammonia.20 Recently, the monomeric air-sensitive complex [(PPh3)2N]2[Co(CN)4] DMF has been crystallized from DMF solution.29 The complex is essentially square planar but does feature a very weak axial interaction to a neighbouring DMF molecule (Co—O separation 264 pm). The [Co(CN)4]2 anion appears to be the sole example of a square-planar low-spin (ji = 2.15 BM) cobalt(II) complex containing solely unidentate ligands. 

Cations [Cr(NH3)4X2]+ have as and trans geometrical isomers (see Coordination Organometallic Chemistry Principles). The higher syrmnetry of the trans form makes its d d spectrum easier to analyze. We assume NH3 to be a pure a donor (see Ammonia N-donor Ligands). Hence e (NH3) is zero. The axial hgands are n donors (e r > 0). The AOM orbital energies E are given in equations (27-30). 

The stoicheiometry and kinetics of reaction of aqueous ammonia solutions of copper(ii) ions with thiosulphate ion in the presence of oxygen have been examined. The amount of oxygen consumed and the relative amounts of the final sulphur products, namely trithionate and sulphate ions, are dependent on the initial 8203 concentration and pH. The most active species for SjOe" formation is a tetra-amminecopper(ii) complex having one axial 8303 and one axial O2 ligand. A complex having both axial and equatorial 8203 ligands as well as an axial O2 was suggested as the reactive intermediate for sulphate formation. 

Details of the photoaquation mechanism of [Rh(NH3)5Br] have been probed by the use of N labeling, at the ammonia ligand trans to the bromide. Photoaquation results mainly in the loss of this axial ammine ligand, though about 10% involves replacement of cis ammines. Photoisomerization of [Rh(NH3)4(OH2)Br] has also been studied. " The quantum yield for the cis trans isomerization of this type of complex increases twofold when the H2O... 

These authors also developed the synthesis of three-fold axially chiral tri-podal ligands, since virtually no studies have been reported on the combination of Cs-symmetry and axial chirality (Scheme 5.51). The first step was the reaction between a chiral bromide with liquid ammonia giving the corresponding primary amine, which was further alkylated in situ with two additional equivalents of the chiral bromide. A final deprotection with BCI3 furnished the required tripodal ligand, the biarylic portions of which formed a cavity capable of incorporating oxophilic Lewis acidic elements. 

---