Central Cobalt Ion Research Articles

Structural and mechanistic studies of co-ordination compounds. Part VIII. Preparation, aquation, and base hydrolysis of some trans-monosubstituted tetra-aminecobalt(III) cations

The preparation and characterization of trans-[Co(NH3)4CNBr]+, trans-[Co(cyclam)CNBr]+, and trans-[Co(NH3)4N3Cl]+ cations and an improved preparation of trans-[Co(cyclam)N3Cl]+ cation are described. The aqation and base hydrolysis of these complex cations have been studied over a range of temperature. The thermodynamic and kinetic data are discussed, as before, in terms of the nephelauxetic effect of the amine ligands on the central cobalt(III) ion. Kinetic evidence is produced to support a dissociative mechanism for the base hydrolysis of octahedral cobalt(III)–amine complexes.

Structural and mechanistic studies of co-ordination compounds. Part XI. Preparation and acid hydrolysis of some octahedral cobalt(III) complexes of meso-1,4,8,11-tetra-aza-5,5,7,12,12,14-hexamethylcyclotetradecane and -tetradeca-1,7-diene

The preparation and characterization of trans-[CoL′(A)Br]+(I; L′=meso-1,4,8,11-tetra-aza-5,5,7,12,12,14-hexamethylcyclotetradecane; A = N3 and NCS) and trans-[CoL″(A)X]n+(II; L″=meso-1,4,8,11-tetra-aza-5,5,7,12,12,14-hexamethylcyclotetradeca-1,7-diene; A = OH2, N3, and NCS; X = Cl and Br) cations are described. The acid hydrolysis of the azido- and isothiocyanato-cations has been studied over a range of temperature. The ratio of the rate constant with bromide to that with chloride as leaving group, kBr : kCl, at 25 °C is ca. 10 : 1 for complexes (I) but decreases to ca. 2 : 1 for (II), independent of the nature of the orienting ligands A. This observation is consistent with the proposition that the relative ‘softness’ of the central cobalt(III) ion increases in going from complexes (I) to (II).

Structural and mechanistic studies of co-ordination compounds. Part VI. Preparation, aquation, and base hydrolysis of some octahedral trans-chlorocyanocobalt(III) amine complexes

The preparation of the complex trans-[Co(NH3)4(CN)Cl]+ is described. The kinetics of aquation and base hydrolysis of this complex and the base hydrolysis of the complex trans-[Co (cyclam)(CN)Cl]+(cyclam = 1,4,8,11-tetra-azacyclotetradecane) have been studied over a range of temperature, and the following parameters have been obtained: trans-[Co(NH3)4(CN)Cl]+, kOH2(at 25 °C)= 9·8 × 10–4 s–1, ΔHOH2‡= 20·7 kcal mol–1, ΔSOH2‡=–3 cal K–1 mol–1, and kOH(at 0 °C)= 3·5 × 10–2 l mol–1 s–1, ΔHOH‡= 23·8 kcal mol–1, ΔSOH‡= 22 cal K–1mol–1; trans-[Co(cyclam)(CN)Cl]+,KOH(at 0 °C)= 8·1 × 10–1 l mol–1 s–1, ΔHOH‡= 22·6 kcal mol–1, ΔSOH‡= 24 cal K–1 mol–1. Thermodynamically, it was found that the extent of aquation of complexes of the type trans-[Co(amine)4(CN)Cl]+ increases in the order cyclam < (en)2 < (NH3)4(en = ethylenediamine). Kinetically, the aquation rate constants of these complexes increase, but the base-hydrolysis rate constants decrease in the above order. The results support the proposed nephelauxetic effects which these amine ligands exert on the central cobalt(III) ion. Spectroscopic evidence is produced to support the above conclusion.

Structural and mechanistic studies of co-ordination compounds. Part IV. The preparation, aquation, and base hydrolysis of trans-chloronitro- and trans-bromonitro-(1,4,8,11-tetra-azacyclotetradecane)cobalt-(III) cations

The preparation and characterization of trans-[Co(cyclam)NO2Br]+ cation is described. The kinetics of the aquation and base hydrolysis of this complex cation and those of the base hydrolysis of trans-[Co(cyclam)NO2Cl]+ have been studied over a range of temperature. The first-order aquation rate constants are slower than those of the corresponding bis(ethylenediamine) and tetra-ammine analogues, whereas the second-order base hydrolysis rate constants are faster. These results support the earlier prediction made on the basis of the kinetic nephelauxetic effect of these amine ligands on the central cobalt(III) ion. Unimolecular mechanisms are assigned to these reactions.

Structural and mechanistic studies of co-ordination compounds. Part V. The preparation, aquation, and base hydrolysis of octahedral cobalt(III)–amine complexes containing isothiocyanate as an orienting ligand

The prepration and characterization of trans-[Co(NH3)4(NCS)Cl]+ cation is described. The kinetics of the aquation and base hydrolysis of this complex cation and those of trans-[Co(cyclam)(NCS)Cl]+ have been studied over a range of temperature. These results are discussed in terms of the influence of nephelaxetic effects of these amine ligands on the central cobalt(III) ion.

Some New Oxygenated Cobalt Complexes

Abstract Cobalt(II) complexes with ornithine, 2,4-diaminobutyric acid and 2,3-diaminopropionic acid were studied as new oxygen complexes. The former complex was reversibly, while the latter two complexes were irreversibly oxygenated at room temperature. These oxygenated complexes were diamagnetic and showed electronic absorption spectra similar to that of oxygenated cobalt histidine complex, and they were assumed to be O2-bridged binuclear complexes, L2Co–O2–CoL2 (L: ligand). Cobalt and O2 of the binuclear complexes existed in the state of Co(III) and O22−, respectively. Thermodynamic measurements showed that oxygenation was an exothermal process, and deoxygenation an endothermal one. The reversibility correlated with the reduction potential of the central cobalt(III) ion and the enthalpy change of the oxygenation. Easier deoxygenation corresponded to more positive reduction potential and to smaller enthalpy change.

Structural and mechanistic studies of co-ordination compounds. Part II. Preparation, aquation, and base hydrolysis of trans-chloronitro- and trans-bromonitro-tetra-amminecobalt(III) cations

The preparation and characterization of trans-[Co(NH3)4NO2Cl]+ and trans-[Co(NH3)4NO2Br]+ cations are described. The assignment of geometric configuration is based on 1H n.m.r. spectroscopy. The kinetics of the aquation and base hydrolysis of these two complex cations have been studied over a range of temperature. The first-order aquation rate constants are greater than those of the corresponding bis(ethylenediamine) and 1,4,8,11-tetra-azacyclotetradecane complexes, whereas the second-order base hydrolysis rate constants are less. These results are consistent with the kinetic nephelauxetic effect of these amine ligands on the central cobalt(III) ion. Unimolecular reaction mechanisms are assigned to these reactions.

Kinetics and mechanism of substitution reactions of complexes…-XXI: New derivatives of the dithiocyanato-bis-dimethylglyoximato-cobalt(III)-acid and the aquation of the [Co(DH) 2(NCS) 2] − ion

The kinetics of the aquation of the [Co(DH) 2(NCS) 2] − ion was followed. Contrary to the analogous dihalogeno-derivatives, a single NCS − is replaced by water and even this Reaction (1) leads to an equilibrium. This can be explained by presuming the formation of π bonds between the central cobalt ion and the thiocyanate groups. First order rate constants have been determined at various temperatures. The activation energy for the process: E α 32·2 ± 0·4 kcal/mol and the pre-exponential factor log PZ = 15·7 ± 1·2. Equilibrium constants for Reaction (1) at different temperatures have been determined, giving ΔH = 8·65 ± 0·15 kcal/mol. Results are compared with those obtained for the analogous dihalogeno-derivatives. Meanwhile 26 new salts of the anion [Co(DH) 2-(NCS) 2] − have been synthesized and characterized.

Spectroscopic Studies of Poly nuclear Complexes. I. Preparations and Circular Dichroisms of Tetrakis(l-propylenediamine)-dicobalt(III) Complexes Containing μ-Amido Group

Abstract New binuclear cobalt(III) complexes, (−)D-[(l-pn)2Co(μ-NH2,O2)Co(l-pn)2](NO3)4·3H2O, (+)D-[(l-pn)2Co(μ-NH2,O2)Co(l-pn)2]I3·6H2O, (+)D-[(l-pn)2Co(μ-NH2,NO2)Co(l-pn)2]Br4·6H2O, (+)D-[(l-pn)2Co(μ-NH2,OH)Co(l.pn)2](NO3)4·2H2O and (−)D-[(l-pn)2Co(μ-NH2,SO4)Co-(l-pn)2](NO3)3 were prepared and their absolute configurations determined to be ΛΛ on the consideration of the stereospecific coordination of l-propylenediamine (l-pn) to the metal ion. On the basis of these identifications, absolute configurations of the corresponding ethylenediamine-(en) complex ions were assigned. The nature of the d–d bands of these polynuclear complexes seems to be very similar to those of uninuclear cobalt(III) complexes. One of the two central cobalt(III) ions is regarded as a member of an asymmetric chelate ligand to the other cobalt ion, and the CD corresponding to the d–d bands appears to depend mainly on the strength of vicinal effect due to such a chelate ring.

A survey of the reaction of the coordinated nitrite ions of the nitro-ammine-Co (III) complexes.

Both the reduction and the oxidation of the nitrite of the nitro-ammine-cobalt(III) complexes are much slower than that of the free nitrite. In general there is a parallelism between the rate of aquation of the complex and the rate of the redox reaction of the coordinated nitrite. In oxidation reactions there is no detectable intermediate. Oxidizing the mononitro complex the original valence state of the central cobalt(III) ion is preserved, with other complexes a gradual reduction of the central ion occurs. In reduction reactions more or less stable intermediates can be detected. With azide ion the intermediate is not identical with that of the reaction of the azidopentaamminecobalt (III) complex with nitrate. The coordinated ligands act on the reactivity of a particular ligand either through their effect on the electron distribution of the whole complex or by means of a direct chemical interaction between adjacent ligands.

Absorption Spectra and Chemical Behavior of the Hexahydroxylamine Cobalt (III) Complex

Abstract The absorption spectrum of hexahydroxylamine cobalt(III) complex was measured and compared with the hitherto obtained data of the other hexammine cobalt (III) complexes. The frequencies of the first and second absorption bands of this complex were 68.5×1013 and ca. 94×1013 sec.−1 respectively. These values are much greater than those found in other hexammine cobalt (III) complexes, and this fact may indicate the strong interaction between the central cobalt (III) ion and nitrogen atoms of the co-ordinating hydroxylamine. In addition to the study of absorption spectra, the rate of decomposition of this complex was measured. The rate of decomposition was proportional to the concentration of the hydroxyl ion, and the activation energy was 32.5 kcal. mole−1. In order to explain the above results, the following equilibrium, assuming the proton dissociation, was proposed; [Co(NH_2OH)_6]^3++H_2O\ightleftarrows[Co(NH_2OH)_5NHOH]^2++H^3O^+

The Relation between the Geometrical Configurations of Inorganic Complexes and their Absorption Bands. II. The Configurations of Two Isomers of Sodium Disulfono-tetrammine-cobaltiate

Abstract The visible and ultra-violet absorption spectra of Na[Co(NH3)4(SO3)2]·2H2O (brown salt) and Na[Co(NH3)4(SO3)2]·4H2O (yellow salt) have been measured. The results have proved that the SO3=-radical coördinates around the central cobalt (III) ion by the lone pair electrons of its sulfur atom, and that the brown salt has trans-configuration concerning the positions of the SO3=-radicals and the yellow salt cis-configuration. The absorption spectrum of NH4[Co(NH3)4(SO3)2]·3H2O (dark brown form) has also been studied and it has been assumed that the salt is trans-isomer contrary to several investigators’ assignmints of cis-strusture.