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Rac.-p-(tris(2-aminoethyl)amine-2-(nitromethyl)ornithine)cobalt(III) trichloride (2d) was obtained by a simple three-step procedure from ornithine using cobalt template chemistry. p-(Tris(2-aminoethyl)amine-ornithine)cobalt(III) trichloride (2a) was obtained from tris(2-aminoethyl)amine (tren) and (S)-ornithine in the presence of cobalt(II), which was oxidised to cobalt(III) during the reaction. Complex 2a was selectively oxidised with thionyl chloride–dimethyl formamide to p-(tris(2-aminoethyl)amine-dehydro-ornithine)cobalt(III) trichloride 2b. Complex 2c, in which reaction of thionyl chloride–dimethyl formamide has also occurred at the δ-amine of ornithine, was obtained at longer reaction times. Complex 2b reacted with nitromethane anion to give rac.-p-(tris(2-aminoethyl)amino-2-(nitromethyl)ornithine)cobalt(III) trichloride (2d). The amino acid rac.-2-(nitromethyl)ornithine (1b) was released by reducing complex 2d with aqueous ammonium sulfide. Complex 2d was expected to release 2-(nitromethyl)ornithine (1b) in hypoxic cells, where the amino acid could act as an inhibitor of ornithine decarboxylase. Preliminary data indicated that complex 2d was weakly cytotoxic in one cell type studied.

The syntheses of a cobalt(III) complex, 2, containing N-(2-pyridylmethyl)urea and of six complexes, 3, containing phenyl-substituted N-2-pyridylmethyl-N'-(X)phenylureas (where X = 4-H, 4-CH(3), 4-Br, 3-Cl, 4-CF(3), and 4-NO(2)), have been accomplished by reaction of [(en)(2)Co(OSO(2)CF(3))(2)](CF(3)SO(3)) with the urea ligands in tetramethylene sulfone. The complexes have been characterized by UV-vis, FTIR, (1)H NMR, and (13)C NMR spectra along with elemental analysis. Also, X-ray crystallographic analysis of 2 confirms that the urea ligand chelates as a bidentate through the pyridyl nitrogen atom and the endo deprotonated, urea nitrogen atom to form a stable five-membered ring. Crystals of the perchlorate salt of 2 were monoclinic, space group P2(1)/c with a = 9.743(1) Å, b = 13.924(3) Å, c = 15.006(4) Å, beta = 97.07(1) degrees, and Z = 4. Reflection data (3454) with I = 3sigma(I) were refined to conventional R factors of 0.037 and 0.051. In acidic solution (0.05-1.00 M HCl at 55 degrees C), the phenyl-substituted complexes undergo hydrolysis to form the bis(ethylenediamine)(2-picolylamine-N,N')cobalt(III) ion, 4, aniline, and CO(2). The hydrolysis kinetics of the phenyl-substituted complexes were studied by UV-vis spectroscopy (I = 1.00 M HCl/LiCl). At 55 degrees C the observed rate constants fit the rate law k(obsd) = kK[H(+)]/(1 + K[H(+)]). It is proposed that the protonated urea eliminates aniline to give a coordinated isocyanate intermediate that hydrolyzes rapidly to the pyridyl methylamine complex and CO(2) via the carbamate complex. Since all of the studies of this kind to date appear to involve the NCO intermediate, it raises the prospect that urease also functions by a similar path and that urease should be tested with NCO(-) as a substrate.

Two new, trigonally symmetrical, triamide tripodal ligands and their complexes with the cobalt(III) ion, [1,1,1-tris(4-amino-1-oxo-2-azabutyl)ethanato]cobalt(III)trihydrate 1 and [1,1,1-tris(4-amino-4-methyl-3-oxo-2-azapentyl)ethanato]cobalt(III)–water–ethanol (1/8/0.5) 2 have been prepared. The hexadentate structures of the neutral, trigonal, triamido complexes have been established by an X-ray study of 1 and 13C NMR spectrometry of both molecules. The chemical, spectroscopic and electrochemical properties of the complexes have been investigated as well as those of the monoamido tripodal complex [1,9-diamino-5-(4-amino-2-azabutyl)-5-ethoxycarbonyl-4-oxo-3,7-diazanonanato]cobalt(III) chloride.

The ability of available molecular mechanics programs to calculate structures and relative energies of metal complexes is examined via a comparative study of five different force fields: Molmec, Momec91(H), Momec91(C), Xnviron, and Spartan. The method used for assessing the validity of the force fields showed that four of the force fields were able to reproduce successfully the structures of various Co(III) hexaamine cations determined by X-ray analysis, even when these structures were considerably distorted. In certain cases, the calculated relative steric energies were not reliable. Small variations in force fields parameters sometimes led to large changes in the calculated steric energies, and in some instances, in the order of steric strain for different isomers. The most notable changes occurred when metal-dependent parameters were altered.

The template syntheses of various CoIII-hexaazaicosane-type cage complexes with aromatic substituents are described. The parent template, [Co(sen)]3+ ion {sen = 4,4′,4″-ethylidynetris(3-azabutan-1-amine)}, paraformaldehyde, a methyl aryl ketone and a base were reacted in acetonitrile to give aroyl substituents attached to the fully saturated sarcophagine cage (1-aroyl-8-methyl-3,6,10,13,16,19-hexaazabicyclo[6.6.6]-icosane cobalt(III) ion) and aryl substituents attached to an analogous imine-type cage (2-aryl-8-methyl-3,6,10,13,16,19-hexaazabicyclo[6.6.6]icosa-2-ene cobalt(III) ion). Phenyl, napthyl, phenanthryl, anthracenyl and anthraquinonyl substituents have been bound to the cage simply by this route to give molecules that can act as intercalators in DNA or as photosensitizers attached to reversible redox-active metal centres and can couple an organic two-electron reagent with an inorganic one-electron reagent. An X-ray crystallographic analysis of a phenanthroyl cage complex has also been carried out. These substances and their progeny should be useful as biological probes and fluorescent indicators and for energy capture and conversion.

A study of high- and low-spin cobalt(II) derivatives having hexadentate encapsulated ligands known as ‘sar’ is reported (sar = 3,6,10,13,16,19-hexaazabicyclo(6.6.6)icosane). The chemically prepared derivatives have well defined EPR spectra at 4 K especially in the g = 9 region, and were clearly high-spin Co(II). However, when the Co II centres were prepared by radiation-induced electron addition to the Co(III) complex at 77 K, a low-spin species was initially formed with g values in the free-spin region. These were converted into the normal high-spin form on annealing to ∼ 115 K.

A new template synthetic route to hexa-aza macropentacyclic cobalt(III) complexes is described together with the X-ray crystal structure of a new conformationally rigid cobalt cage complex.

The three monodentate pentaamminecobalt(III) linkage isomers of glycinamide have been synthetized and characterized by visible and 1 H and 13 C NMR spectroscopy and microanalysis. A nitrile-bonded ammonioacatonitrile complex was synthesized, it reacts in liquid ammonia to produce the amidine-bonded aminoacatamidine complex while in aqueous base it hydrolyzes to the amido-N-bonded glyanamida ion. Both [(NH 3 ) 5 CoNHCOCH 2 NH 2 ] 2+ and [(NH 3 ) 5 CoNHC(OH)CH 2 NH 3 ] 2+ have been isolatad

Electron transfer kinetics for the reduction of spinach plastocyanin and horse cytochrome c by several cobalt-cage complexes have been determined. The reduction of plastocyanin by [Co((N(CH 3 ) 3 ) 2 -sar)] 4+ shows saturation kinetics with K Co(II) = (1.5±0.2)×10 3 M -1 , and κ' et =4.0±0.2 s -1 . This reaction is stereoselective (κ Δ /κ Δ = 1.7) and the stereoselectivity is independent of ionic strength.

The redox potentials, E 1/2 , for the reversible cobalt (III/II) redox couples of complexes of substituted macrobicyclic ligands derived from 3,6,10,13,16,19-hexaazabicyclo[6.6.6]icosane show a substantial variation with the type of substituent. The variation was subjected to a Hammett type treatment yielding a series of inductive or polar substituent constants σ E that correlate with the organic substituent constants obtained by a variety of other methods

Various (α-amino acidato) cobalt (III) complexes have been treated with SOCl 2 in DMF. Provided the amino acid side chain does not contain functionalities that react with SOCl 2 , the complex undergoes a facile oxidation to give the related α-imino acidato complex. A mechanism is proposed for these reactions

Low-spin hexadentate cobalt(II) and cobalt(III) complexes of the hexathioether cage (1,8-dimethyl-3,6,10,13,16,19-hexathiabicyclo[6.6.6]icosarie) have been synthesised, their redox and spectral properties have been investigated, and the encapsulation of the cobalt(II) ion has been established by an X-ray crystal structure determination, which shows the metal ion to be coordinated to six thioether sulphur atoms at distances ranging from 2.265(3) to 2.354(2)A.

The cobalt(III) complex of the large hexathioether cage (1,9-dimethyl-3,7,11,15,18,22-hexathiabicyclo[7.7.7]tricosane) shows substantially different redox and spectral properties relative to the smaller homologous [6.6.6]icosane.

The oxidation of bis(1,2-ethanediamine)(sarcosinato)cobalt(III) ion with SOCl2 in dimethylformamide gave the N-methylthiooxamato complex as the final product. The results, along with others, implicate the acid chloride chelate, a sulfine, and the methyl thiooxamato chelate as intermediates en route. The thiooxamato sulfur atom retains a nucleophilic capability and adds readily to cyclohexene in the thionyl chloride-dmf reaction medium to give an unusual imido hydroxycyclohexane thioester complex. Various results, including those in this paper, indicate that the chelated acid chloride readily loses an alpha-carbon proton and the resulting carbanion captures SOCl+. Elimination of HCl yields the sulfine and further addition of SOCl+, eliminations, and rearrangement yield chelated thiooxamate, which reacts even further under the pseudo-Vilsmeier conditions to the N-methyloxamato chelate complex.

The redox potentials, E 1/2 , for the reversible cobalt (III/II) redox couples of complexes of substituted macrobicyclic ligands derived from 3,6,10,13,16,19-hexaazabicyclo[6.6.6]icosane show a substantial variation with the type of substituent. The variation was subjected to a Hammett type treatment yielding a series of inductive or polar substituent constants σ E that correlate with the organic substituent constants obtained by a variety of other methods

Stereospecific sequential condensation of paraformaldehyde and propionaldehyde with a tripodal bis(triamine)cobalt(III) template rapidly encapsulates the metal, and a subsequent facile reduction of imine functions gives an expanded cavity hexaazabicyclic cage system with unusual structural and chromophore electron properties, complemented by an exceptional stability and relatively fast CoII/III electron exchange rates.

A versatile and efficient template synthesis has been developed to synthesise novel polyamines [e.g. rac-N3-(3-aminopropyl)butane-1,3-diamine, isospermidine 1] via amino acids [e.g. (2R,4S/2S,4R)-N4-(3-aminopropyl)-2,4-diaminopentanoic acid] using cobalt(III) to assemble the three precursor components in a biomimetic manner.

The reaction of [Co(ten)]3+ {ten = 4,4′,4″-ethylidynetris(3-thiabutan-1-amine)} with methanal and base in acetonitrile or water led to the synthesis of an unusual pendant-arm macrocyclic complex, 8-(4′-ammonio-2′-thiabutyl)-8-methyl-1-oxa-6,10-dithia-3,13-diazacyclo-tetradecane(chloro)cobalt(III) triperchlorate trihydrate. The structure of the complex has been established by X-ray crystallographic analysis and such molecules can readily be tied to polymers and proteins. The synthesis, chemical reactions, spectroscopy and electrochemical properties of the macrocyclic complex are described.

Treatment of the cobalt(III) complex of the hexadentate tripodal N(3)S(3) ligand ten (4,4',4' '-ethylidynetris(3-thiabutan-1-amine) with propanal and paraformaldehyde under basic conditions, followed by borohydride reduction and reoxidation of the metal center, leads largely to the encapsulated (red) metal complex cation [Co(Me(2)-N(3)S(3)sar)](3+) (Me(2)-N(3)S(3)sar = 1,8-dimethyl-3,13,16-trithia-6,10,19-triazabicyclo[6.6.6]icosane). Unexpectedly, significant amounts of the homologous (yellow) complex cation [Co(Me(2)-N(3)S(3)absar)](3+) (Me(2)-N(3)S(3)absar = 1,8-dimethyl-3,13,16-trithia-6,10,19-triazabicyclo[6.6.5]nonadecane) were also obtained. This macrobicyclic complex has a contracted cavity resulting from a cap containing one fewer methylene units than Me(2)-N(3)S(3)sar. The structures of both cobalt(III) complexes have been determined by X-ray crystallography. [Co(Me(2)-N(3)S(3)sar)]Cl.ZnCl(4).H(2)O crystallizes in the cubic space group P2(1)3 with Z = 4, a = 13.9683(11) Å. [Co(Me(2)-N(3)S(3)absar)](ClO(4))(3).0.5CH(3)CN.0.5H(2)O crystallizes in the triclinic space group Ponemacr; with Z = 4, a = 12.036(4) Å, b = 15.932(9) Å, c = 17.212(14) Å, alpha = 64.93(7) degrees, beta = 72.77(5) degrees, gamma = 88.91(7) degrees. The surprising structural rearrangement is examined, along with the spectral and redox properties of both cobalt complexes. The influence of the reduced cavity size in the absar type cage is reflected in a shift of the bands in the electronic spectrum of both the cobalt(II) and cobalt(III) complexes to higher energy, and a more negative value for the Co(III/II) redox potential. The demetalation of the complexes is also described.

A novel hexa aza cage, N(1)-(4-isothiocyanatobenzyl)-3,6,10,13,16,19-hexaazabicyclo[6.6.6]icosane-1,8-diamine (SarAr-NCS) was synthesized in good yield and characterized by (1)H NMR and electrospray mass spectrometry. A new method for the synthesis of the related N(1)-(4-carboxybenzyl)-3,6,10,13,16,19-hexaazabicyclo[6.6.6]icosane-1,8-diamine (AmBaSar) using the p-carboxybenzaldehyde is reported. The complexation of Cu(2+), Co(2+) and Zn(2+) by the two ligands over a range of pHs was found to be similar to the parent derivative SarAr. SarAr-NCS was conjugated to both silica particles (≈90 nm diam.) and the model B72.3 murine antibody. The SarAr-NCSN-silica particles were radiolabeled with Cu(2+) doped (64)Cu and the number of ligands conjugated was calculated to be an average of 7020 ligands per particle. Conjugation of SarAr-NCS to the B72.3 antibody was optimized over a range of conditions. The SarAr-NCSN-B72.3 conjugate was stored in buffer and as a lyophilized powder at 4 °C over 38 days. Its radiolabeling efficiency, stability and immunoreactivity were maintained. The development of a high yielding synthesis of SarAr-NCS should provide an entry point for a wide range of Cu and Zn radiometal PET imaging agents and potentially radiotherapeutic agents with (67)Cu.

Our work on the preparation of zeolite ship-in-a-bottle complexes, which involves the encapsulation of metal complexes during zeolite synthesis, encouraged us to explore the relatively unknown structure directing properties of metal complexes. In particular, we have shown that bis(pentamethylcyclopentadienyl) cobalt(III) hydroxide, Cp*2CoOH was a template for the novel high silica zeolite UTD-1 which is the first zeolite having greater than a 12 membered ring pore structure. We have extended this strategy to other oxide compositions and metal complexes. In this paper we describe the preparation and characterization (XRD, SEM) of the gallophosphates Cloverite and UTD-10 using the metal complex [Co(NMe3)2sar]5+ (where (NMe3)2sar = 1,8-bis(trimethylammonio)-3,6,10,13,16,19-hexaazabicyclo[6.6.6]-icosane) as the template.

The template synthesis, structure and properties of an unusual tricyclic amidine-functionalized triaza-trithia cobalt(III) cage complex are described.

Steric forces within a hexaaza bicyclic cobalt cage system cause chromophore expansions which bring about extraordinary transformations in the CoN6 chemistry, leading to CoIII/IIN6 redox potentials close to +0.8 V (vs. SHE) and CoII hexaamine complexes that are air and substitution stable.

Amphiphilic cobalt(III) cage complexes with bridgehead octyl, dodecyl and hexadecyl hydrocarbon chain substituents have been synthesized simply by co-condensation of formaldehyde and long chain aliphatic aldehydes with the tripodal cobalt(III) hexaamine complex, [Co(sen)]3+ {sen = 4,4′,4″-ethylidynetris(3-azabutan-1-amine)}. The synthetic methodology was also used to prepare a novel chiral surfactant by capping the Λ-(−)D-[Co(sen)]3+ stereoisomer. The cobalt(III) cage complexes with octyl to hexadecyl substituents are all surface active and reduce the surface tension of water to levels approaching those of organic solvents. The dodecyl substituted cage complex forms aggregates in aqueous solution with a critical micelle concentration of (1.3 ± 0.1) × 10−3 mol dm−3 at 25.00 °C. The surfactant cage complexes are biologically active and are lethal at millimolar levels to the tapeworm Hymenolepis diminuta, and the parasitic eukaryote, Tritrichomonas foetus, in vitro. The biological activity of these surfactants appears to involve insertion of the paraffin tail into the organism's exterior membrane and consequent incorporation of the highly charged head-group, which perturbs the normal membrane potential and leads to disintegration of the membrane and death of the organism. The cobalt(III) cage head-group of these surfactants also undergoes a chemically reversible one-electron reduction to the corresponding cobalt(II) cage complex and the construction of oriented films of such redox reagents should be feasible. The reduction potential of the cobalt(III)/(II) couple is shifted from −0.72 to −0.61 V (vs. saturated calomel electrode) by replacing a bridgehead hydrocarbon chain substituent with an alkoxy substituent. The shift in potential correlates with the electrochemical polar substituent constants of alkyl versus alkoxy chains.

Facile new methods of synthesizing derivatised bicyclic amine complexes using a cobalt(III) amine template, with formaldehyde and aromatic ketones or diketones as condensing agents, are described.

The synthesis, properties and crystal structure of the cage complex (1-hydroxy-8-methyl-3,6,10,13,15,18-hexaazabicyclo[6.6.5] nonadecane )cobalt(III) chloride hydrate ([Co( Me,OH-absar )]Cl3.H2O) are reported. The mechanism of the formation of this contracted cavity cage from a nitro-capped hexaazabicycloicosane type cage has been investigated. Treatment of (1- methyl-8-nitro-3,6,10,13,16,19-hexaazabicyclo[6.6.6] icosane )cobalt(III) chloride ([Co(Me,NO2- sar )]3+) with excess base in aqueous solution leads initially to rapid (t½. < 1 ms) and reversible deprotonation of one coordinated secondary amine. This species undergoes a retro-Mannich type reaction and imine hydrolysis (t½ ≈ 90 s). Quenching the reaction with acid gives rise to a pair of isomeric intermediate species which have been isolated and characterized. They have a pendant arm macrocyclic structure, resulting from the loss of a methylene unit from one of the arms of the cap. Heating either isomer in aqueous solution gives the new cage compound with the contracted cap. It is postulated that this occurs through a Nef reaction, resulting in the formation of a ketone which then condenses with the coordinated primary amine. A comparison with the corresponding bicycloicosane analogue indicates a reduced chromophoric cavity size for the contracted cage. The reduction potential of the cobalt(III)/cobalt(II) couple is 170 mV more negative for the smaller cage, and, in the electronic spectrum of the cobalt(III) complex, the d-d transitions are both shifted to higher energy, corresponding to a stronger ligand field.

Template syntheses based on tris (ethane-1,2-diamine)cobalt(III) lead to cobalt(III) complexes of cage hexamines of the ' sarcophagine ' type ( sarcophagine = sar = 3,6,10,13,16,19- hexaazabicyclo [6.6.6] icosane ) rapidly and in high yield. Reduction of these species to their cobalt(II) forms enables the ligands to be removed in concentrated acids at elevated temperatures, and in hot aqueous solutions containing excess cyanide ion. The free sarcophagine and 1,8-diaminosarcophagine [(NH2)2sar or diamsar] ligands are strong bases, accepting up to four and five protons, respectively, in aqueous solution. In chloride medium, I = 1.0, at 298 K, pK1 = 11.95, pK2 = 10.33, pK3 = 7.17, pK4 ≈ 0 for sarcophagine , and pK1 = 11.44, pK2 = 9.64, pK3 = 6.49, pK4 = 5.48, pK5 ≈ 0 for diaminosarcophagine , with very similar values being found for triflate medium. Crystal structure determinations for both free bases, the chloride, sulfate, perchlorate and nitrate salts of diamsar , the complex of zinc chloride with sar, and the magnesium nitrate complex with diamsar show remarkably small variations in the cavity defined by the bicyclic ligands, though relatively subtle bond length and bond angle changes can be rationalized in terms of the effects of proton and metal ion binding. Exhaustive methylation of sarcophagine produces the highly lipophilic, hexatertiary base hexamethylsarcophagine , which, in the solid state, adopts quite different conformations and nitrogen-atom configurations to those of sar itself. All the ligands rapidly form metal ion complexes of generally exceptional kinetic and thermodynamic stability.

For the first time a helical dinuclear metal complex has been separated into enantiomers by transformation of a labile cobalt(II) triple-helical complex into the kinetically stable cobalt(III) complex [Co2(2a)3]6+ which has been characterized structurally and resolved by chromatography.

The sulfonium salt [(en)2CoO2CCH(NH2)(CH2)2S(CH3)2]3+ (en = ethane-1,2-diamine), prepared by methylation of the thioether group of N,O-coordinated methionine , undergoes a set of complex, intramolecular condensations, oxidations, and rearrangements in aqueous base to give a novel pentadentate cobalt(III) complex (c. 20%) of the 1,9-diamino-4-hydroxy-3,7-diazanonane-4-carboxylate ion ( dhnc ). Its structure has been determined by X-ray crystallographic analysis as trans(O,O)-[Co( dhnc )(OH2)](ClO4)2.2H2O. The crystals were monoclinic, space group P 21/c with a 9.053(2), b 29.437(7), c 7.661(1) Ǻ, β 106.63(1)°, and Z 4; 2383 data with I ≥ 3σ(I) were refined to conventional R factors of 0.046 and 0.060. Investigations concerning the mechanism for the formation of this complex are described.

Treatment of the N3S3 donor cage complex [Co(NO2-capten)]3+ (1-methyl-8-nitro-3,13,16-trithia-6,10,19-triazabicyclo[6.6.6]icosanecobalt(III)) with excess base leads to deprotonation of a secondary coordinated amine group, followed by loss of a methylene unit from the cap by a retro-Mannich type reaction. Subsequent intermolecular hydride transfer gives a novel oxidized and partly delocalized macrocyclic complexed carbanion (13-(4-amino-2-thiabutyl)-13-methyl-6-nitro-1,11-dithia-4,8-diazacyclotetradec-4-enato(6)cobalt(III)) that is stabilized by deprotonation, and which remains deprotonated even in strong acid.

An understanding of how variations in the cage ligands modify the redox behaviour of cobalt(II)/(III) couples has led to rational syntheses of a series N3S3 donor cobalt cage complexes that have redox potentials and electron self-exchange rates appropriate for their use as electron carriers in systems devised for the photoreduction of water. Diazotization of [Co(NH3-capten)]Cl4 (NH3-capten = 8-ammonio-1-methyl-3,13,16-trithia-6,10,19-triazabicyclo[6.6.6] icosane ) in nitric acid resulted in a mixture of five complexes: [Co(NO2-capten)]3+, [Co( Cl-capten )]3+ and [Co(HO- capten )]3+ (8-nitro-, 8-chloro- and 8-hydroxy-1-methyl-3,13,16-trithia-6,10,19-triazabicyclo[6.6.6] icosanecobalt (III) respectively), in which the cage framework remained intact, together with two complexes with a contracted cap, [Co(ClCH2-abcapten)]3+ and [Co(HOCH2-abcapten)]3+, (8-chloromethyl- and 8-hydroxymethyl-1-methyl-3,13,16-trithia-6,10,19-triazabicyclo[6.6.5] nonadecanecobalt (III), respectively). Reductive elimination occurred with [Co( Cl-capten )]3+ in the presence of Zn or Ni/Al alloy to give the parent cage complex, [Co( capten )]3+ (1-methyl-3,13,16-trithia-6,10,19-triazabicyclo[6.6.6] icosanecobalt (III)). When [Co(ten)]3+(4,4′,4″-ethylidynetris(3-thiabutan-1-amine)cobalt(III)) and an aqeuous solution of diethyl malonate and formaldehyde were reacted under basic conditions, the amide cage complex, [Co( EtOOC-oxocapten-H )]2+, (8-ethoxycarbonyl-1-methyl-3,13,16-trithia-6,10,19-triazabicyclo [6.6.6]icosan-7-onato(1-)cobalt(III)) was obtained. Hydrolysis of the ester group in base yielded the carboxylate derivative [Co(OOC- oxocapten - H)]+(8-carboxylate-1-methyl-3,13,16-trithia-6,10,19-triazabicyclo[6.6.6]icosan-7-onato(1-)cobalt(III)). The complexes were characterized by microanalyses, 1H and 13C n.m.r. spectroscopy, and electrochemistry. The values of the cobalt(III)/(II) redox potentials change with the nature of the apical substituents in a similar manner to that observed for the analogous hexaamine cage complexes, but they are all more positive, and the cobalt(II) complexes are low spin. The N3S3 donor set stabilizes the lower oxidation state and the low-spin electronic configuration. All of these cage complexes are effective at quenching the lowest lying triplet excited state of the [ Ru ( bpy )3]2+ complex, with rate constants typically c. 109 dm3 mol-1s-1. [Co( EtOOC-oxocapten-H )]2+ quenches [ Ru*( bpy )3]2+ very efficiently and has a suitable redox potential for hydrogen production, but it is only moderately efficient as an electron-transfer agent in the photoreduction of water. It is apparent that the high molar absorption coefficients of these cage complexes in the visible region, the too positive redox potentials and competing energy transfer and/or back electron-transfer inhibit their ability to be used as effective electron-transfer agents in these reactions at pH c. 5. However, the molecules are inherently interesting and stable redox reagents which undergo rapid one-electron reactions.

The cobalt(III) complex of the large hexathioether cage (1,9-dimethyl-3,7,11,15,18,22-hexathiabicyclo[7.7.7]tricosane) shows substantially different redox and spectral properties relative to the smaller homologous [6.6.6]icosane.

Low-spin hexadentate cobalt(II) and cobalt(III) complexes of the hexathioether cage (1,8-dimethyl-3,6,10,13,16,19-hexathiabicyclo[6.6.6]icosarie) have been synthesised, their redox and spectral properties have been investigated, and the encapsulation of the cobalt(II) ion has been established by an X-ray crystal structure determination, which shows the metal ion to be coordinated to six thioether sulphur atoms at distances ranging from 2.265(3) to 2.354(2)A.

L'oxydation par le chlore du centre S dans les complexes [Co(en) 2 (NH 2 CH(R)CH 2 S)] 2+ . Formation d'un sulfonate chelate [Co(en) 2 (NH 2 CH(CO 2 H)CH 2 SO 2 O] 2+ . Stereochimie des transpositions

Synthese au coordinat hexadente tris(amino-2 ethyl)-1,4,7 triaza-1,4,7 cyclononane et de [CoL] 3+ . Synthese des complexes ou L est egalement: amino-9 hexaazatricyclodocosane, heptaazatricyclodocosane. Etude de configuration et electrochimique