Emeritus Professor Geoffrey Lawrance

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. © 1994 ASEG.

The outer-sphere interaction between the Co(CN)|¿anion with the two protonated forms of DABCO (l,4-diazabicydo[2.2.2]octane) was investigated by a spectrophotometric titration method. The resulting outer-sphere stability constant for the diprotonated DABCOH|+ cation was determined as log Kos = 2.53 ± 0.01, compared to the value of 2.77 ± 0.12 obtained using conventional potentiometric titration results. Absorption changes were very small; however, good reproducible results were obtained for the higher charged diprotonated cation interaction and the method may have general application.© 1994 Gordon and Breach Science Publishers SA

Reactions of transition metal complexes of ligands with predominantly amine donors with formaldehyde alone, or with formaldehyde and additional reagents (ammonia, primary amines, and mono- or Afunctional methylene compounds) are of ten facile, and lead to new acyclic and macrocyclic molecules. Formaldehyde reacts with coordinated amines to form an imine (or aminol) which is susceptible to further nucleophilic attack by a suitably disposed group of the precursor complex or by an additional external reagent. Condensation involving two formaldehyde molecules, two cis-disposed coordinated primary amines and ammonia, an additional primary amine or a carbon acid with at least two acidic protons can generate a new six-membered chelate ring, of ten cariying additional pendant groups. These reactions are central to formation of the wide range of coordinated and largely saturated cyclic, macromonocyclic and macropolycyclic polyamine molecules reported herein. © 1993, Walter de Gruyter. All rights reserved.

The redox potentials, E1/2, 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 sE that correlate with the organic substituent constants (s1)obtained by a variety of other methods. Changes in E1/2 with substituent are not reflected in changes in the ligand field spectra of either oxidation states. We deduce, therefore, that the effects are not transmitted via through-space overlap of orbitals or through-bond induction. The effects can be attributed to either a through-space Coulombic mechanism or interactions through the s framework. In the case of the NHR2+ and NR3+ substituents, there is a steric substituent effect that forces the Co(III) cage complexes from a lel3 to ob3 conformation and results in quite different spectroscopic and electrochemical properties. The correlations of sE values with the 1H, 13C, and 59Co NMR chemical shifts are also examined. The sE constants are readily obtained, and this may prove to be a more versatile method of obtaining polar substituent constants than those currently used in physical organic chemistry. © 1990, American Chemical Society. All rights reserved.

Volumes of activation (¿V*exptl) and reaction volumes (¿VBH) for the base hydrolysis of 16 different cobalt(III) amine complexes of the type CoL5X3+, CoL5X2+, CoL4X2+, and CoL4XY+were determined from high-pressure kinetic and dilatometric measurements, respectively. The values of ¿V*Mptlrange from 43 to 19 cm3mol-1, and those for ¿VBHrange from 24 to 9 cm3mol-1, depending on the charge on the complex as determined by that on the leaving group X. The data are very consistent with earlier reported data for closely related systems and demonstrate clearly both the minor role played by the nonparticipating ligands L, and the influence of complex charge. The reported results are all in line with a SN1CB mechanism. However, evidence for apparent cases involving rate-limiting deprotonation rather than the usual rate-determining ligand dissociation process was not forthcoming, since no differentiation on the basis of ¿V#exptwas observed. © 1989, American Chemical Society. All rights reserved.

The enzyme p-cresolmethylhydroxylase, from Pseudomonas putida, is involved in the degradative pathway of p-cresol. The direct, un-mediated reversible electron transfer between the heme of the flavocytochrome enzyme and an edge-plane graphite electrode in the presence of redox-inactive cationic species as promoters of the enzyme electrochemistry is reported. Diffusion controlled heterogeneous electron transfer is modulated by the levels and type of promoter used, which range from simple and complex cations to polyamines and aminoglycosides. The promoter-enzyme assembly affords a degree of macromolecular recognition at the electrode as both the cationic charge and the flexible nature of the promoter are important to achieve direct electron transfer. A quasi-reversible cyclic voltammetric response was observed in the absence of substrate from which the heterogeneous rate of electron transfer between the enzyme and the electrode was determined as ks ~ ~ 1.8 × 10-4 cm2 s-1. An enzyme titration with optimal concentrations of promoter and substrate p-cresol yielded a linear relationship between catalytic current and enzyme concentration up to 1.2 µM. Similarly, relationships were obtained to p-cresol and p-hydroxybenzylalcohol concentrations with fixed amounts of enzyme and promoter, both yielding a linear current vs. substrate response up to 0.5 m M. Furthermore, the magnitude of the catalytic current of p-cresol is greater than that obtained for mediation with the enzyme's natural redox partner, azurin, but comparable to those obtained with a ferrocene mediator. Catalytic response was also obtained at a peptide-modified gold electrode in the presence of a promoter, spermine. © 1989.

Modification of a gold working electrode with apparently equivalent amounts of -S-(CH2)2-COO- and -S-(CH2)-NH+3 produces an electrode which permits direct unmediated electrochemistry of both positively-charged horse heart cytochrome c and negatively-charged (at pH 7) membrane-cleaved cytochrome b5, proteins. By varying the ratio of carboxylate : amine modifiers, the relationship between " active " groups on the surface and current could be probed: for cytochrome c, 1 : 9 carboxylate: amine is sufficient to obtain a maximum current; for cytochrome b5, approximately 3:1 carboxylate : amine is necessary for a maximum current, after which the current is unaffected by the ratio of carboxylate : amine. The overall behaviour is consistent with the demand by the particular protein for a certain density of appropriate groups on the surface to accommodate hydrogen-bonding interactions which facilitate the formation of an electrode/protein complex prior to electron transfer. With surfaces modified with a very dilute amount of the required group, initially sigmoidal voltammograms are observed, most consistent with a radial diffusion model based on an array of isolated sites on the surface. However, this changes slowly with time to display " normal " cyclic voltammetry, consistent with rearrangement of modifier groups on the surface to configurations more appropriate for regular electron transfer. This protein-directed surface rearrangement is also observed using cytochrome c and a dilute coverage of the modifier 1-thio-ß-D-glucose tetraacetate. Normally, modification with this molecule produces an efficient and, presumably, dense monolayer coverage of the surface which shows stable voltammetry with cytochrome c, but no response with cytochrome b5. Hydrogen bonding between acetate groups on the modifier and lysine residues on the protein are considered important, since hydrolysis of the acetates removes electrochemical response. © 1989.

Formatopentaamminecobalt(III) perchlorate is oxidized relatively rapidly by AgO in acid conditions (1 m H2SO4, HNO3 or HO3SCF3), with approximately 97% of the total cobalt retained in the cobalt(III) state as [Co(NH3)5(OH2)]3+ and [Co(NH3)5X]n+ (X = S042- or NO3-). A combination of product distribution, silver(I) and silver(II) concentration dependence and 18O-labelling experiments indicate that the major pathway (97%) is oxidation of [Co(NH3)5(OCHO)]2+ directly to [(NH3)5Co(OCO)]3+ and [(NH3)5Co(O2COH)]2+ by AgIII (through the disproportionation 2AgII ¿AgIII + AgI) in a relatively rapid hydride extraction. A minor path (3%) appears to involve a one-electron oxidation by AgII to the complexed radical anion [(NH3)5Co(OC¿O)]2+ which then decays intramolecularly to yield CoII and CO2. In 1 M H2SO4 the cobalt(III) intermediate, [(NH3)5Co(OCO)]3+, has been shown by 18O-labelling and competition experiments to decay by dissociation into [Co(NH3)5]3+ and CO2. The pentacoordinate intermediate [Co(NH3)5]3+ immediately captures OH2 and HSO4-. © 1988 ASEG.

The syntheses and characterization of the macrobicyclic hexaamine chromium(III) complexes of diamsar (1,8-diamino-3,6,10,13,16,19-hexaazabicyclo[6.6.6]eicosane) and sar (3,6,10,13,16,19-hexaazabicyclo[6.6.6]eicosane) ligands (1¿3) are reported. The complexes were isolated as stable, paramagnetic, and monomeric salts. crystallized in the space group P21/c, (Z = 4, a = 9.474 (2) A, b = 13.331 (3) A, c = 18.221 (5) A, ß = 92.756 (0)°) with the octahedral cation in the C3-lel conformation and an average Cr-N distance of 2.070 (3) A. The complexes are high-spin d3 with room-temperature magnetic moments near the spin-only value of 3.87 µB¿ The aqueous electrochemistry exhibits a quasi-reversible Cr(III/II) couple below -1 V for each complex and a further irreversible Cr(II/0) reduction near -1.6 V; the chromium(II) complexes are not stable in the coulometric time scales (minutes). The Cr(III) electronic spectra show the expected spin-allowed absorption bands of 4T2g4A2gand 4T1g4A2g origin as well as weak spin-forbidden bands of 2Eg, 2Tlg4Agorigin in the visible region. The first of these (4T2gtransition) is split by -400 cm-1and is relatively high in intensity, and the splitting is probably due to the lowered symmetry (D3). Cr(sar)3+ and Cr(diamsar)3+ emit rather strongly at 77 K 0.02), but give no detectable emission above 273 K. Photodecomposition of Cr(diamsar)3+ is ~ 104-fold smaller than that of the Cr(en)33+ ion, and possible reasons for this are discussed. © 1986, American Chemical Society. All rights reserved.

The synthesis, structure, and preliminary aspects of electrochemical, magnetic, e.s.r., and electronic spectroscopic properties of a stable, near-trigonal-prismatic hexa-aminevanadium(IV) complex are reported.

The pale yellow ruthenium(iii) complex cis-[Ru(H2NCH2CH2NH2)2(OH2)Cl] (CF3SO3)2.H2O crystallized in the space group P1, a 11·661(2), b 9·961(2), c 9·130(2) Å, a 78·83(3), ß 70·42(2), ¿ 85·29(2)°, Z 2. The Ru-N, Ru-Cl and Ru-O bond distances in the essentially octahedral ion are 2·10 (average), 2·323(1) and 2·093(2) Å respectively. The complex hydrolyses with retention of configuration in aqueous acid (0·01 m HOSO2CF3, kaq 2·70 × s-1 at 25°C, ¿H¿ 90·6(±1·5) kJ mol-1, ¿S ¿ -28 (± 5) 5K-1 mol-1) and base (0·01 m NaOH, kOH 0·44 mol-1 1. s-1 at 25°C, ¿H ¿ 73·5(± 2·0) kJ mol-1, ¿S ¿ -43(± 7) J K-1 mol-1). © 1987, CSIRO. All rights reserved.

The synthesis and characterization of the sulfido-bridged oxomolybdenum(V) dimer of dithiocarbamate (NH2CS2-), [Mo2O2S2(dtc)2].2CH3CN, is reported. The complex crystallized in the orthorhombic space group Pnma, a = 9.407 (2) Å,b = 20.877 (4) Å, c = 9.010 (2) Å, Z = 4, with the neutral complex molecules hydrogen bonded to the nitrogen of the acetonitrile via the amine group of the dithiocarbamate ligand. Each molybdenum atom is centered above the base of a square-based pyramid, with the oxygen atoms coordinated on the same side of the bent MoS2Mo bridge and a Mo-Mo distance of 2.820 (1) Å. Electrochemistry of the compound in dimethyl sulfoxide and acetonitrile was investigated by dc and ac polarography, cyclic voltammetry at Hg, Pt, and Au working electrodes, and controlled-potential electrolysis. The complex is reduced irreversibly in a two-electron process on both voltammetric and coulometric time scales, apparently with dissociation of the dithiocarbamate ligands occurring. The complex dissolves in aqueous base to produce an ESR-inactive solution that is stable at pH 12 in the absence of oxygen and whose absorption spectrum is consistent with retention of the Mo2O2S22+ core; in air, this solution bleaches by a base-catalyzed path to a colorless solution in which the molybdenum is predominantly present as MoO42-. © 1984, American Chemical Society. All rights reserved.

Facile synthetic routes to complexes of the labile unidentate coordinated trifluoromethanesulfonate (-OSO2CF3) ion are reported for M(NH3)5(OSO2CF3)n+(M = Rh(III), Ir(III), Cr(III), Ru(III) where n = 2; M = Pt(IV) where n = 3), M(NH2CH3)5(OSO2CF3)2+(M = Co(III), Rh(III), Cr(III)), cis-M(en)2(OSO2CF3)2+(M = Rh(III), Ir(III), Cr(III)), and trans-M(en)2Cl(OSO2CF3)+ (M = Rh(III), Ir(III)). The utility of these synthetically versatile intermediates in the preparation of a variety of complexes containing neutral ligands is illustrated. Rate constants for the aquation of the triflato complexes in 0.1 M CF3SO3H at 25 °C span 3 orders of magnitude and for the pentaammine complexes show a reactivity order of Ru(III) > Co(III) ~ Cr(III) ~ Rh(III) » Ir(III) » Pt(IV). For the pentakis(methylamine) complexes, the aquation rate is greater for Co(III), slightly greater for Rh(III), and smaller for Cr(III) in comparison to the corresponding pentaammine complexes. The aquations of M(en)2X(OSO2CF3)+proceed largely without isomerization (<5%), and the triflato complexes are prepared stereospecifically by this route. For the m-M(en)2(0S02CF3)2+ ions, consecutive first-order aquation processes are observed with rate constants k1~ 2k2. © 1984, American Chemical Society. All rights reserved.

The redox chemistry of the mixed nitrogen-sulfur donor cobalt(III) complexes with the macrobicyclic ligands 8-methyl-6, 10, 19-trithia-l, 3, 14, 16-tetraazabicyclo[6.6.6]icosane (azacapten), l-methyl-8-nitro-3, 13, 16-trithia-6, 10, 19-triazabicyclo[6.6.6]icosane ((NO2)capten), and 8-ammonio-1-methyl-3, 13, 16-trithia-6, 10, 19-triazabicyclo[6.6.6]icosane ((NH3+)capten) qnd of the hexadentate precursor ligand 5-(4-amino-2-thiabutyl)-5-methyl-3,7-dithia-l,9-nonanediamine (ten) has been investigated in aqueous and aprotic solutions. The macrobicyclic complexes exhibit a chemically and electrochemically reversible Co(III)/Co(II) couple near 0 V in aqueous (NHE) and aprotic solutions (Ag/AgCl) and a chemically irreversible but elctrochemically reversible 1-e couple near-1 V, nominally Co(II)/Co(I). In addition, a further multielectron couple is observed for the azacapten complex at more negative potentials. No evidence for oxidation processes was forthcoming. The low-spin d7 cobalt(II) complex of (NH3+)capten has been characterized by ESR spectroscopy at 4.2 K, and the nominally d8 cobalt(I) complex, at 100 K. The former compound exhibits g values at 1.94, 2.21, and 4.22, while the latter compound shows an eight-line pattern at g = 2.17 (A = 67 G) consistent with its formulation as d8 Co(I) and not as a d7 Co(II)-S radical state. © 1984, American Chemical Society. All rights reserved.

The reduction potentials of a large range of [M(NH3)5L]n+ complexes (M = CoIII, RhIII, IrIII) have been determined in aqueous solution (µ 0.1 m, NaClO4). Irreversible reductions span the range from +0.22 to -0.47 V for cobalt(iii) complexes and from -0.86 to -1.45 V for rhodium(iii), and occur near -1.7 V for iridium(iii), determined against the standard (KCl) calomel electrode. Despite several reports to the contrary in the literature, no correlations exist of E1/2 with absorption spectra (Co and Rh), nuclear magnetic resonance spectra [d(1HN), Co, Rh, Ir, and d(59Co)], vibrational spectra [v(Co-N)], or rates of aquation and base hydrolysis (Co, Rh, Ir). Complexes which undergo outer-sphere [e.g., with Ru(NH3)62+] and predominantly inner-sphere (e.g., with V2+aq) homogeneous electron transfer can be distinguished by the presence or absence of a correlation of ln kex with E1/2 respectively, consistent with the expectations of the Marcus-Hush theory of outersphere electron transfer. © 1983 ASEG.

Syntheses based on the reaction of Pt(en)34+ with formaldehyde, and ammonia or nitromethane, yielded the macrobicyclic complexes (1,3,6,8,10,13,16,19-octaazabicyclo[6.6.6]icosane)platinum(IV), Pt(sep)4+, and (1,8-dinitro-3,6,10,13,16,19-hexaazabicyclo[6.6.6]icosane)platinum(IV), Pt(dinosar)4+, respectively. Reduction of the latter complex with SnCl2 in acid yielded (1,8-diamino-3,6,10,13,16,19-hexaazabicyclo[6.6.6]icosane)platinum(IV), Pt(diamsar)4+. These complexes are substitution-inert, diamagnetic octahedral ions and were characterized by X-ray crystallographic analysis of the Pt(sep)4+ by absorption and NMR spectroscopy. Addition of an electron to the Pt(IV) complexes, radiolytically or electrochemically, yielded transient monomeric macrobicyclic Pt(III) ions. ¿-Radiolysis of crystalline samples yielded a Pt(III) complex stabilized in the crystalline lattice, detected by ESR spectroscopy. Polarography of Pt(diamsar)4+ in aprotic solvents showed essentially irreversible one-electron reductions at +0.17 and -1.00 V and a two-electron irreversible reduction at -2.20 V (in acetone, vs. Ag/AgCl). The Pt(III) transient of the first reduction decayed (t1/2 < 10-3 s) to yield the monodeprotonated Pt(IV) complex and 0.5 mol of hydrogen/mol of complex. The lifetime of the related Pt(sep)3+ transient was longer, though still in the millisecond range. This intramolecular redox process in aprotic solvents was not observed in water, however. In aqueous solution, the Pt(diamsar)3+ transient decayed with a first-order rate constant of 6 × 10-3 s-1 (pH 6.8 or 10.0) in pulse radiolysis experiments. A rate-determining C-N ring opening of the platinum(III) chelate, followed by rapid disproportionation, appears to be the major route for decay of Pt(lll) in aqueous solution. This is supported by voltammetric studies and the detection of both Pt(II) and Pt(IV) macromonocyclic products. © 1983, American Chemical Society. All rights reserved.

The complexes Cr(NH3)5L3+ [L = OCHNH2, OC(NH2)2 and OC(NHMe)2] have been synthesized as the O-bound isomers. At 25°C in aqueous base (pH c. 10-14) they isomerize to the deprotonated N-bound isomers without competitive hydrolysis. Reacidification regenerates the O-bound isomer rapidly and completely. The second-order rate constants and pKa values of the amide complexes (I 1.0 m, 25°C) are respectively: 37.01 ± 1.5 dm3 mol-1 s-1 and 11.72 ± 0,06 for formamide; 0.324 ± 0.004 dm3 mol-1 s-1 and 13.50 ± 0.05 for urea; 0.0375 ± 0.0020 dm3 mol-1 s-1 and 14.0 ± 0.2 for N, N¿-dimethylurea. The observations for chromium(III) parallel isimilar behaviour in cobalt(III) and rhodium(III) analogues, but are unusual for chromium(III) chemstry. © 1983 ASEG.

The electrochemistry of a wide range of macrobicyclic hexaamine (¿cage¿) and polyamine complexes of coball(III) is reported. All of the substituted [Co(sar)]3+ and [Co(absar)]3+ cage complexes exhibit chemically reversible Co(III)/Co(II) couples (sar = sarcophagene = 3,6,10,13,16,19-hexaazabicyclo[6.6.6]icosane, absar = 3,6,10,13,15,18-hexaazabicyclo[6.6.5]nonadecane). The Co(II) oxidation state for these complexes is substitutionally inert and undergoes irreversible reduction at very negative potentials in nonaqueous solvents (<-2 V). Quasi-reversible behavior is apparent with all the complexes under study m both aqueous (ClO4- and CF3SO3- media) and nonaqueous (acetone and acetonitnle, CF3SO3- media) solvents. However, in aqueous perchlorate media, at a mercury interface, these reductions are complicated by adsorption processes. The potential of the Co(III)/Co(II) couple is markedly dependent on the nature of substituents on the cage ligand and varies by ~0.6 V for the apically substituted [Co(sar)3+/2+ series. Other factors that influence the potential are preferred cavity size of the cage ligand and outer-sphere medium effects. For each series of structurally similar ligands with constant medium and electrode, the heterogeneous rate constants are the same within experimental erro. In addition to the metal-centered electrochemistry, many of the complexes exhibit redox processes of electroactive organic substituents. These processes are utilized in selected electroorganic syntheses of new cage complexes. The pH dependence of the Co(III)/Co(II) couple is a useful probe to the acidity of various functional groups, and some applications in determining pKa values are described. © 1983, American Chemical Society. All rights reserved.

The spontaneous rate of nitrito to nitro isomerization of [(NH3)5CO(ONO)]2+ spans two orders of magnitude for 16 solvents studied. The volume of activation is small and negative (from -3·5 to - 7 cm3 mol-1) for water, dimethyl sulfoxide, N-methylformamide and sulfolane. Combined with the observation of negligible competitive solvolysis, and of an isokinetic plot of ¿H¿ against AS¿, this indicates that isomerization is intramolecular in all solvents. The solvent dependence is interpreted in terms of a dual-parameter equation involving terms for the Lewis basicities (DN) and Lewis acidities and polarity (ET). By use of this approach both DN and ET of the solvents are shown to be major contributing factors to reactivity. Further studies on base-catalysed nitrito to nitro isomerizations reveal mild catalysis by F-, AcO- and Et3N in Me2SO. The metal ions Hg2+ Ag+ and Cd2+ also catalyse the isomerization in water [km 1 · 16 × 10-2 dm3 mol-1 s-1, kAg 2·85 × 10-4 dm3 mol-1 s-1, kcd 4·4 × 10-5 dm3 mol-1 s-1; µ 1¿0 M (CIO4-), 25°C]. The lack of competition by AcO-, NO3- and H2O in the Hg2+ -catalysed isomerization reaction also implicates an intramolecular process for this path. In acetone, the ions Hg2+, Ag+, Cd2+ and Zn2+ catalyse the isomerization reaction with a rate law of the form, except for Ag+, where the rate law takes the form, with kAg = kK = 2·11 × 10-3 dm3 mol-1 s-1, k = 1.74 × 10-4 s-1 and K = 12± 1 dm3 mol-1. The limiting rate is ascribed to a high stability constant for the silver adduct intermediate. The analogous RhIII and IrIII complexes also exhibit catalysis by Ag+ and Hg2+ in aqueous solution. © 1982, CSIRO. All rights reserved.

Synthetic routes to the resolved unsymmetrical (u) isomers of [Co(dats)Cl] (C104)2 [dats = 4,7-bis- (2-aminoethyl)-l-thia-4,7-diazacyclononane] and [Co(datn)Cl] (C104)2 [datn = l,4-bis(2-aminoethyl)- 1,4,7-triazacyclononane] are reported. The new macrocyclic ligand l-thia-4,7-diazacyclononane (tasn) was synthesized during the former preparation, and the cis-[Co(tasn)2] (C104)3 complex prepared. Base hydrolysis of each chlorocobalt(III) complex proceeds with two consecutive steps. The first reaction in each case is chloride hydrolysis, with kOH(dats) 3¿6 × 104dm3 mol-1 s-1 and k/1(datn) 2¿85 × 103 dm3 mol-1 s-1 at 25°C and 10¿1 M. The second reaction for the dats complex is a base-catalysed dissociation of the thioether to the cis-[Co(dats)(OH)2]+ complex, characterized by 13C n.m.r. experiments, and occurring approximately 20 times slower than chloride hydrolysis. However, the datn complex undergoes a base-catalysed terminal ring opening to the cis-[Co(datn)- (OH)2]+ complex at a rate approximately 30 times slower than chloride hydrolysis. © 1982 ASEG.

The pressure dependence of the spontaneous aquation of a series of Co(NH3)5L3+ complexes with L = methanol, ethanol, 2-propanol, formamide, N-methylformamide, N,N-dimethylformamide, urea, N-methylurea, N,N'-dimethylurea, and dimethyl sulfoxide has been determined. The activation volume (¿V*) lies in the limited range +0.3-+3.8 cm3 mol-1 across the series and is essentially independent of the size of the leaving group. The average ¿V* of ~2 cm3 mol-1 is an estimate of the solvent-independent intrinsic component of ¿V* and is interpreted as being indicative of a dissociative interchange (Id) mechanism. Apparent molar volumes of the series of complexes are reported. The ¿volume profile¿ approach for a dissociative mechanism has been applied to these and earlier data for both neutral and anionic leaving groups; variation in the estimated molar volume of the putative pentacoordinate intermediate with the type of leaving group is discussed in terms of the limited validity of the volume profile approach when an mechanism operates. © 1982, American Chemical Society. All rights reserved.

Facile synthetic routes to cobalt(III) amine complexes of the labile unidentate trifluoromethanesulfonate anion (CF3SO3-), namely, Co(NH3)5(OSO2CF3)2+, cis-Co(en)2(OSO2CF3)2+, and fac-Co(dien)(OSO2CF3)3, are reported. The use of these complexes as synthetic precursors for a range of complexes involving direct solvolysis or reactions in poorly coordinating solvents such as sulfolane or acetone is described. For example, in the pentaamminecobalt(III) system, syntheses of Co(NH3)5Ln+ (L = OH2, NH3, OHCH3, OHCH2CH3, OHCH(CH3)2, NCCH3, OP(OCH3)3, OCH.N(CH3)2, OS(CH3)2, OC(NH2)2, NCNH2, -OOCCH3, -OOCCHCl2) in high yield are reported. The kinetics and the stereochemical course of aquation of the labile trifluoromethanesulfonato complexes and derivatives are reported. © 1981, American Chemical Society. All rights reserved.

The macrocyclic compexes trans-[Co(dtcd)(N3)X] ClO4 (dtcd = meso-5, 12-dimethyl-1, 4, 8, 11-tetra- azacyclotetradeca-4, 11 -diene; X = Cl- or Br-) have been prepared and characterized. Halide aquation in O·1 mHNO3 at 25°C proceeds at rates of 4·6 × 10-4 s-1, ¿H¿ 77(±2) kJ mol-1, ¿S¿ - 51 (±6) J K-1 mol-1 (X = Cl-) and 10·2 × 10-4 s-1, ¿H¿ 80(±3)kJ mol-1, ¿S¿ -34(± 10) J K-1 mol-1 (X = Br-). The pressure dependence of the aquation rate at eevated pressures yields ¿V¿ +8·3(±0·5) cm3 mol-1 (X = Cl-) and ¿V¿ +5·3(±10·7) cm3 mol-1 (X = Br-). While the observed positive ¿V¿ values are consistent with a dissociative mechanism they differ markedly from reported negative ¿V¿ values for acid hydrolysis of [Co(NH3)5X]2+ions. © 1980 Australian Journal of Chemistry.

The pressure and temperature dependence of the trans ¿ cis isomerization reaction of trans- Co(en)2(X)(OH2)n+ (X = OH2, 0Se02H- or AcO-; en = ethane-1, 2-diamine) has been determined in D20, and compared with results previously determined in H2O under analogous conditions of acidity and ionic strength. Generally positive activation volumes (¿V¿) and activation entropies (¿S¿) in both solvents are consistent with a dissociative mechanism with aqua ligand release in the activated state. Isomerization in D20 is characterized by slightly higher ¿H¿ and ¿S¿ values and a less positive ¿V¿ value in each case. The clear change in ¿V¿ from H2O to D2O supports the existence of an appreciable contribution from solvent rearrangement in forming the activated state to the activation volume. Variations in solvent structure and ionic solvation apparently account for the deuterium solvent isotope effect. © 1980, CSIRO. All rights reserved.

The nitrito ions [M(NH3)5(ONO)]2+ (M = Co(III), Rh(III), or Ir(III)) rearrange to their nitro forms [M(NH3)5(N02)]2+ in aqueous base according to the rate law kobsi = ks + £0h[OH¿] where at u = 1.0 M, 25.0 °C: ks = 6.9 (±0.2) X 10¿5 s-1, ¿H¿ = 95 ± 4 kJ mol-1, ASs¿ = -4 ± 12 J K-1 mol-1, k0H = 5.9 (±0.2) X 10-6 dm3 mol-1 s-7, ¿H0H¿ = 110 ± 1 kJ moL1, ASoh¿ = +82 ± 4 J K-1 mol-1, M = Co; ks = 9.6 (±0.2) X 10-8 s¿1, ¿H¿ = 85 ± 2.5 kJ moL1, ¿S¿ = -18 ± 9 J K-1 moL1, k0H = 7.6 (±0.2) X 10-3 dm3 mol-1 s-1, ¿Hoh¿ = 96 ± 2 kJ mol-1, ASOH¿ = +38 ± 6 J K-1 mol-1, M = Rh; ks = 3.0 (±0.1) X 10-5 s-1, AHs¿ = 94 ± 2 kJ mol-1, ¿S¿ = 16 ± 5 J K-1 mol-1, k0H = 2.7 (±0.1) X 10-5 dm3 mol-1 s-1, AHoh¿ = 109 ± 2 kJ mol-1, ASoh¿ = 34 ± 6 J K-1 mol-1, M = Ir. For the cobalt complex the pressure dependence of k0h (¿V¿ = +27 (±1.4) cm3 mol-1, ¿d¿ = 5 (±2) cm3- kbar-1 mol-1) points to a conjugate base preequilibrium for the base-catalyzed path. The metal ion dependence of koli/ks (95:9:1 for Co:Rh:Ir) is also consistent with a conjugate base process. [Co(NFl3)5(ONO)]2+ rearranges to [Co(NH3)5(NO2)]2+ without exchange of oxygen with H2180, 18OH]-, or free N18O2- (1 M); both the ks and k0H paths are intramolecular. Up to 1 M OH there is <1% competitive hydrolysis to [M(NH3)5(OH)]2+. Both rate constants ks and k0H for M = Co decrease with increasing ionic strength (25 °C, 105fcs = 6.9, 7.4, 103oh = 5-9, 14.5; u = 1.0, 0.1, respectively), cis- and tram-[Co(en)2(ONO)2]+ and [Co(en)2(ONO)(N02)] + rearrange by both pathways to the dinitro complexes without change in configuration, and (+)cw-[Co(en)2(ONO)(N02)] + rearranges without loss of chirality. For the /c0h reaction these results also differ from the normal substitution chemistry where there is some steric change. In addition to the O to N rearrangement, a much faster O to O scrambling process has been identified for the cobalt complex using lsO tracers. © 1980, American Chemical Society. All rights reserved.

The pressure-dependent racemization of Co(pyrdtc)3 (pyrdtc = pyrrolidinecarbodithioate) determined over the pressure range 1-1380 bar yielded activation volumes (¿v*) of +9.8 (±0.5) cm3 mol-1 (in ethanol), +5.2 (±0.7) cm3 mol-1 (dimethylformamide), +5.4 (±0.5) cm3 mol-1 (acetonitrile), and +7.8 (±0.6) cm3 mol-1 (toluene). The activation volume in each solvent is pressure dependent; hence nonzero compressibility coefficients of activation (¿ß*) are observed in each solvent. The compressibility of activation (¿k*) is independent of solvent at 0.43 (±0.03) kbar-1. A twist mechanism involving a low-spin ¿ high-spin preequilibrium is proposed on the basis of the experimental data. The Co(Ph2-dtc)3 complex (Ph2-dtc = diphenyldithiocarbamate), by contrast, exhibits negative ¿V* values of between -2 and -9.3 cm3 mol-1 in five different nonaqueous solvents. The alternative one-ended dissociative mechanism is favored for this complex. © 1980, American Chemical Society. All rights reserved.

The nitrate ion competition and rates of nitrosation of Co(NH3)5N32+ have been measured in NaC104/NaN03 solution over the range of nitrate ion concentration 0-1.0 M (25.0 °C, u = 1.0 M), yielding a rate law -d[CoN32+]/d; = (fc, + fc2[N03¿])[H+][HN02][CoN32+], One mechanistic model which assumes anion-dependent competition by both the ktand k2 pathways leads to the same competition ratio R for each path (R = [CoN32+]/[CoOH23+][N03~] = 0.405 M-1)-However it is shown that other models lead to an equally good fit of the data. A similar two-term rate law has been reported for the Hg2-induced aquation of Co(NH3)5C12+ in N03- media, 3 and it is demonstrated that an earlier analysis of this rate and competition data is also not unique. One solution requires a five-coordinate intermediate for the path independent of N03- and direct insertion of N03- by Hg2+ ion for the path dependent on N03-. Acceptance of this solution gives the same competition ratio as the nitrosation reaction. Some data are also given which support the direct insertion of anions by the Hg2+-catalyzed path and the problems of interpreting the competition results, and some methods for resolving the ambiguities are discussed. © 1980, American Chemical Society. All rights reserved.

The effect of high pressure on the rates of substitution of Fe(phen)32+ and Fe(bpy)32+ (phen = 1,10-phenanthroline; bpy = 2,2'-bipyridyl) with hydroxide and cyanide ion has been evaluated. All reaction rates are significantly retarded upon the application of pressure. The hydroxide-dependent component of the rate expression exhibits volumes of activation (A¿V¿) of + 19.7 ± 0.3 and +21.5 ± 0.4 cm3 mol-1 for substitution of Fe(phen)32+ and Fe(bpy)32+, respectively. The cyanide-dependent term exhibits ¿V¿ of + 19.8 ± 1.0 and +20.9 ± 1.6 cm3 mol-1 for substitution of Fe(phen)32+ and Fe(bpy)32+, respectively. A rate-determining dissociative interchange mechanism is most consistent with the observation that ¿V¿ for substitution of each complex is positive, pressure-independent, and independent of nucleophile. © 1979, American Chemical Society. All rights reserved.

Syntheses of ten binuclear µ-peroxo cobalt(III) complexes with coordinated cyclic tetraamines 5,7-dimethyl-1,4,8,11-tetraazacyclotetradeca-4,11-diene and 5,7,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradeca-4,11-diene or chelated diamines and triamines are reported. Absorption maxima of the µ-peroxo and of three µ-superoxo binuclear complexes generated in solution are tabulated. ESR solution spectra of the µ-superoxo binuclear complexes and of a new mononuclear superoxo complex of the cyclic tetraamine rac-5,7,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane are presented. © 1979.

From activation volume evidence a twist mechanism incorporating a low-spin ¿ high-spin pre-equilibrium in the transition state is indicated for racemization of Co(pyrdtc)3 (pyrdtc = pyrrolidyldithio-carbamato) in non-aqueous solvents.

The isomerization of trans-Co(en)2(acet)(OH2)2+ (en = 1,2-diaminoethane; acet- = acetate anion) in aqueous acid is retarded upon the application of pressure. In 0.05 M HClO4, a pressure-independent volume of activation (¿V¿) of +7.9 ± 0.3 cm3 mol-1 is obtained, together with ¿H¿=117.1 ± 3.0 kJ mol-1 and ¿S¿= +61 ± 9 J K-1 mol-1. In 0.05 M HCIO4 with added NaClO4 (I = 1.0 M), ¿V¿= +6.5 ± 0.4 cm3mol-1, ¿H¿ = 112.6 ± 2.4 kJ mol-1 and ¿S¿=+46 ± 7 J K-1 mol-1. In 1.0 M HC1O4, ¿V¿ = +5.6 ±0.6 cm3 mol-1, ¿H¿= 112.9 ± 2.8 kJ mol-1 and ¿S¿= +47 ± 8 J K-1 mol-1. This data is most consistent with isomerization proceeding via dissociative aquo ligand release in a dissociative interchange (Id) mechanism. Analogous Idor D dissociative) mechanisms have been assigned previously to isomerizations of several trans-Co(en)2 (X)(OH2)n+ complexes (X = OH2, SeO3 H- or SeO32-) on the basis of ¿V¿data, and the results for the X = acet¿ complex presented here support a general dissociative mechanism for complexes of this type. © 1979, Taylor & Francis Group, LLC. All rights reserved.

The circular dichroism spectra are reported for tetraamminecobalt(III) complexes with the chiral amino alcohols 2-aminopropan-1-ol, 2-aminobutan-1-ol, l-aminopropan-2-ol, 2-amino-1-phenyl- ethanol, ¿-ephedrine and ephedrine with the alcohol groups protonated (OH) and deprotonated (O-). The solvent dependence of the chemical shifts of the NH protons was investigated to determine the effects of stereoselective solvation on the circular dichroism, but, in contrast to some other related systems, the chemical shift difference between the two NH2protons was relatively insensitive to solvent. Consistent with this, the circular dichroism spectra of the tetraphenylborate salts of the deprotonated complexes were found not to be markedly dependent on solvent. Tetraammine- ((-)-¿-ephedrine)cobalt(III) and tetraammine((-)-ephedrine)cobalt(iii) were found to have the same signs of Cotton effects for the various d-d transitions, whereas bis((-)-¿-ephedrine)copper(ii) and bis((-)-ephedrine)copper(ii) had opposite signs. This has been explained in terms of different conformer populations in the cobalt(iii) and copper(ii) systems. © 1978, CSIRO. All rights reserved.

The effect of high pressure on The rate of racemization and aquation of Ni(phen)32+ and Fe(phen)32+ (en = 1, 10-enanthroline) in solution has been evaluated. Reactions of Fe(phen)32+ exhibit a significant retardation upon the application of pressure, with volumes of activation (¿V¿) of +14.2 and +15.6 cm3 mol-1 for racemization in 0.01 and 1.0 M aqueous HC1, respectively, while aquation in 1.0 M aqueous HC1 exhibits a ¿V¿4 cm3 mo1-1. Possible mechanisms are considered, and a positive contribution to ¿¿xcitation to a high-spin transition state, associated with a general Fe-N bond expansion, is proposed as a component of the mechanism for aquation and racemization. Reactions of Ni(en)32+ show only a minor acceleration of rates upon the application of pressure with ¿V¿ = -0.4 cm3 mol-1 and ¿V¿ = -1.5 cm3 mol-1 for racemization in 0.01 and 1.0 M aqueous HC1, respectively, while aquation in 1.0 M aqueous HC1 exhibits a ¿V¿ of-1.2 cm3 mol-1. A common mechanistic pathway is favored since determined rates and enthalpies and entropies of activation as well as volumes of activation for aquation and racemization are very similar. A dissociative mechanism for release of a en ligand with possible formation in the transition state of a high-spin four-coordinate species of reduced volume compared with the low-spin octahedral precursor is favored from analysis with ¿V¿ data. © 1978, American Chemical Society. All rights reserved. © 1978, American Chemical Society. All rights reserved.

The Raman spectra of a range of binuclear µ-peroxo and µ-superoxo cobalt (III) complexes with principally amine donor ligands in other coordination sites have been measured in the characteristic O-O stretching regions. Monobridged µ-peroxo complexes exhibit a strong resonance Raman band in solution or as solid-state pressed disks at 800±10 cm-1 and monobridged µ-superoxo complexes a band at 1120µ10 cm-1 in solution. These vO2 are generally far stronger than other vibrations of the complexes. Binuclear dicobalt complexes with a second µ-hydroxo or µ-amido bridge in addition to the µ-peroxo or µ-superoxo bridge exhibit relatively weak and generally broad vO2 bands. Dibridged µ-peroxo complexes exhibit the O22- stretch at 812±5 cm-1 in solution and 820 ± 10 cm-1 in the solid state, while dibridged µ-superoxo complexes exhibit the O2- stretch at 1075 ± 10 cm-1. The observation of strong Raman bands near 795 cm-1 for complexes of the macrocyclic tetraamines 5,7,7,12,14,14-hexamethyl-l,4,8,11-tetraazacyclotetradeca-4,ll-diene (Me6[14]diene) and 5,12-dimethyl-1,4,8,1 l-tetraazacyclotetradeca-4,11-diene (Me2[14]diene) supports their characterization as monobridged µ-peroxo-dicobalt (III) complexes and indicates that Raman spectroscopy is useful in the characterization of new binuclear dioxygen complexes. © 1978, American Chemical Society. All rights reserved.

The effect of high pressure on the rates of isomerization in aqueous perchlorate solutions of trans-[Cr(ox)2(OH2)2]- and trans-[Cr(mal)2(OH2)2]- (ox2- = oxalate; mal2- = malonate) has been evaluated. The isomerization of trans-[Cr(ox)2(OH2)2]-at pH 3.15 exhibits a volume of activation (¿V¿) of -16.6 cm3mol-1 with a compressibility coefficient of activation (¿ß¿) of -1.8 cm3 mol-2 kbar-1 which is shown to be consistent with isomerization through one-ended dissociation of an oxalato ligand. For the isomerization of trans-[Cr(mal)2(OH2)2]- at pH 3.0, ¿V¿ is +8.9 cm3mol-1 with no measurable ¿ß¿, consistent with a mechanism via dissociative interchange of an aquo ligand. Enthalpies and entropies of activation evaluated for these systems are consistent with these separate mechanisms. The effect of high pressure on the acid-catalyzed aquation of cis-[Cr(ox)2(OH2)2]- and cis-[Cr(mal)2(OH2)2]- in perchloric acid solutions has also been determined. Volumes of activation are ¿V¿ = +1.7 cm3mol-1 for cis-[Cr(ox)2(OH2)2]- and ¿V¿ = +2.4 cm3mol-1 for cis-[Cr(mal)2(OH2)2]- and are consistent with one mechanism operating for both aquation reactions. A mechanism involving direct proton attack at a coordinated carboxylate and subsequent dissociative release of the protonated acid is most consistent with the determined volumes of activation. Enthalpies and entropies of activation were evaluated for each system; the negative ¿S¿ observed for both reactions is also consistent with a common mechanistic pathway. © 1978, American Chemical Society. All rights reserved.

The effect of pressure on the rates of racemization of Ni (phen)2(bpy)2+ and Ni (phen) (bpy)22+ in solution has been evaluated. Reactions of Ni (phen)2(bpy)2+ exhibit only a minor pressure dependence of the rate, with a volume of activation (¿V¿) of+0.6 cm3 mol-1 and-0.1 cm3 mol-1 for racemization in 0.01 and 1.0 M aqueous HC1, respectively. Aquation of Ni (phen)2(bpy)2+ in 1.0 M aqueous HC1 exhibits no measurable pressure dependence, with ¿V¿ = 0.0 cm3 mol-1. Racemization of Ni (phen)(bpy)22+ proceeds with a minor acceleration upon the application of pressure, with ¿V¿=-1.9 cm3 mol-1 and ¿V¿=-5.2 cm3 mol-1 in 0.01 and 1.0 M aqueous HC1, respectively. Variation of ¿V¿ with acidity observed suggests an acid-dependent pathway is the dominant mechanism at high acidity but is not important at low acidity. A common mechanistic pathway for racemization and aquation of these complexes is favored since reported rates, enthalpies, entropies and volumes of activation are very similar. A one-ended dissociative mechanism via a half-bonded bpy ligand is consistent with experimental ¿V¿ data. © 1978, American Chemical Society. All rights reserved.

The circular dichroism spectra of trans-disubstituted bis(R-propane-1,2-diamine)cobalt(III) complexes are reported for an extended series of solvents. The observed variations in the spectra of the dichloro and dibromo complexes are analysed in terms of stereoselective solvation at the diamine N-H protons, and also the ion association between the complexes and their counter-ions. The solvation of these dihalo complexes, which was studied by p.m.r., showed a preference for hydrogen-bond formation with the equatorial N-H protons, rendering the donor nitrogens asymmetric and thus introducing a new source of dissymmetry close to the metal ion chromophore. This affected a decrease in the positive rotational strength of the 1A1g {equivalent to} 1Eg (D4h) transition, and a positive contribution to the rotational strength of the 1A1g {equivalent to} 1A2g (D4h) component. Ion association of the dihalo complexes was evaluated by a comparison of the circular dichroism of the tetraphenylborate and halide salts. The tendency for ion association was much greater for the tripositive diammine complex. However, stereospecific solvation was of little importance and the circular dichroism spectra did not show any marked solvent dependence for the tetraphenylborate salt. © 1977, CSIRO. All rights reserved.

The effect of high pressure on the rates of racemization of metal complexes in solution has been evaluated for the first time. The racemization of Cr(phen)33+ exhibits a volume of activation, ¿V¿ = +3.3 ± 0.2 cm3 mol-1, which is shown to be consistent with an intramolecular twist mechanism. The racemization of Cr(C2O4)33- exhibits ¿V¿ = -16.3 ± 0.4 cm3mol-1, consistent with racemization through one-ended dissociation of an oxalato ligand. Cr(phen)(C2O4)2- arid Cr(bpy)(C2O4)2- exhibit ¿V¿ = -12.3 ± 0.3 and ¿V¿ = -12.0 ± 0.3 cm3 mol-1, respectively, and these racemizations are assigned a one-ended dissociation mechanism. Cr(phen)2(C2O4)+, Cr(bpy)2(C2O4)+, and Cr(bpy)33+ exhibit ¿V¿ = -1.5 ± 0.2, -1.0 0.1, and +3.4 ± 0.3 cm3 mol-1, respectively, and these are all assigned intramolecular twist mechanism. Enthalpies and entropies of activation were evaluated for all of these systems; ¿H¿ values are least for Cr(C2O4)33- and greatest for Cr(phen)33+ and Cr(bpy)33+ while ¿S¿ values, all large and negative, show the reverse trend. © 1977, American Chemical Society. All rights reserved.

The kinetics of the successive base hydrolysis of both halogen ligands in trans-[Co(hctd)Cl2]+ and trans-[Co(hctd)Br2]+ (hctd = meso-5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradeca-4,11-diene) have been investigated at 25°C in formic acid-NaOH buffers (pH range 3.0-3.7) and 2,6-lutidine-perchloric acid buffers (pH range 6.4-7.4). Hydrolysis reactions in each buffer system, consistent with release of first and second coordinated halogen respectively, follow rate expressions of the type kobs = kaq+ kOH]OH-], with base hydrolysis rates kOH' = 7.8(±0.8) x 108 dm3 mol-1 s-1 and 1.9(±0.3)x109 dm3 mol-1 s-1 respectively for first chloride and bromide hydrolysis, and kOH' = 7.3(±0.4)x104 dm3 mol-1 s-1 and 2.4(±0.2)x105 dm3 mol-1 s-1 for second chloride and bromide hydrolysis respectively. Comparison with the analogous complex trans-[Co(dtcd)Cl2]+ (dtcd = meso-5,12-dimethyl-1,4,8,11-tetraazacyclotetradeca-4,11-diene) shows a ninefold acceleration for base hydrolysis of the first chloride in the hctd complex over the dtcd complex, but an 80-fold rate retardation for base hydrolysis of the second chloride in the hctd complex compared with the dtcd complex, interpreted in terms of steric effects arising from gem-dimethyl substitution in the hctd ligand. © 1977, CSIRO. All rights reserved.

The macrocyclic complex trans-[Co(dtcd)(NO2)Br] [ClO4] (dtcd = 5, 12-dimethyl-l, 4, 8, 1l-tetraaza-cyclotetradeca-4, 11-diene) has been prepared and its hydrolysis kinetics investigated. At 25oC and 0.1 M HN03 the aquation occurs with kaq = 6.2 × 10-3 s-1 to give the trans-Co(dtcd)(NO2)- (OH2)]2+ cation. The activation parameters at 298 K are ¿H = 75.0 kJ mol-1 and ¿S = -35.6 J K-1 mol-1. Hydrolysis of the bromide in the pH range 7.5-8.8 follows the rate expression kobs = kaq + kOH[OH-]. At 25oC (I = 0.1 M, NaClO4) kOH = 1.21 x 103 1. mol-1 s-1 with the activation parameters for base hydrolysis being ¿H = 74.2 kJ mol-1 and ¿S = +63.2 J K-1 mol-1 at 298 K. Aquation and base hydrolysis of the bromo complex at 25oC occur at rates 14 and 5 times faster respectively than those previously reported for the analogous trans-[Co(dtcd)(NO2)Cl]+ complex, the acceleration being due to a more favourable entropy of activation in each case. © 1976 CSIRO.

The quadridentate N<inf>2</inf>S<inf>2</inf> donor ligands 1,9-bis(tritylthio)-3,7-diazanonane (L¹) and 1,9-bis(benzylthio)-3,7-diazanonane (L²) have been prepared as their dihydrobromide salts and allowed to react with metal(II) acetates (M = Ni^II, Co^II, and Hg^II) in methanol solution. Both ligands react with Hg^II with concomitant dealkylation at the sulphur donor atoms to give a trinuclear complex [Hg(HgL)<inf>2</inf>]Br<inf>2</inf>·3H<inf>2</inf>O (L = 3,7-diazanonane-1,9-dithiolato). Treatment of this complex (dissolved in aqueous HCl) with H<inf>2</inf>S gives the dihydrochloride of 3,7-diazanonane-1,9-dithiol. Dealkylation does not occur in the presence of Co^II, the isolated complexes in this case being blue tatrahedral [CoL¹]Br<inf>2</inf> and purple octahedral [CoBr<inf>2</inf>(L²)]. Nickel(II) gives the blue octahedral [NiBr<inf>2</inf>(L²)], but catalyses rapid detritvlation of L¹ to give the black. <inf>1</inf>diamagnetic, trinuclear complex [Ni(NiL)<inf>2</inf>]Br<inf>2</inf>. Reaction of [Ni(NiL)<inf>2</inf>]Br<inf>2</inf>, with a,a'-dibromo-o-xylene in methanol solution gives blue dibromo{3,13-dithia-6,10-diazabicyclo[ 13.4.0]nonadeca-1(15),16,18-triene}nickel(II).

The kinetics of hydrolysis of the title cations trans-[CoX2(N-meso-L4)]+ (X = Cl or Br; L4 = 5,12-dimethyl-1,4,8,11-tetra-azacyclotetradeca-4,11-diene) have been studied at I = 0.1 mol dm-3 over the range pH 3.0-4.5. Hydrolysis of the first halogen ligand obeys a rate expression of the form kobs. = kOH2 + k1OH[OH-], where kobs. is the observed first-order rate constant at constant pH. The values of k1OH are 8.5 × 107 (X = Cl)and ca. 1 × 109 dm3 mol-1 s-1 (X = Br) at 25 °C. The base-hydrolysis rates are the highest yet reported for halogenocobalt(III) complexes of the [CoX2(N4)]2+ type. Ths pH-independent process is represented by kOH2 = 5.4 × 10-3 s-1 for the chloro-complex. Hydrolysis of the second halogen ligand proceeds more slowly and in this case kobs. = k2OH[OH-] with k2OH = 5.9 × 106 (X = Cl) and 1.2 × 107 dm3 mol-1 s-1 (X = Br) at 25 °C. The thermodynamic activation parameters for the hydrolysis of the second halogen ligand are ¿H¿ = 57 kJ mol-1 and ¿S298¿ = 75 J K-1 mol-1 (X = Cl) and ¿H¿ = 56 kJ mol-1 and ¿S298¿ = 80 J K-1 mol-1 (X = Br). These values may indicate rate-determining deprotonation of the substrate in the base-hydrolysis reactions.

The macrocyclic complex trans-[Co(dtcd)(NO<inf>2</inf>) Cl][ClO<inf>4</inf>] (dtcd = 5,12-dimethyl- 1,4,8,11 -tetra-azacyclotetradeca-4,11 -diene) has been prepared and its hydrolysis kinetics investigated. At 25 °C and 0.1 M-HNO<inf>3</inf> the aquation occurs with k<inf>aq</inf> = 4.4 × 10^-4 s^-1 to give the trans-[Co(dtcd)(NO<inf>2</inf>)(OH<inf>2</inf>)]²⁺ cation. The activation parameters are ¿H^¿ = 77.4 kJ mol^-1 and ¿S^¿ = -49.8 J K^-1 mol^-1 at 298 K. Hydrolysis of the chloride in the pH range 7.7-8.9 follows the rate expression k<inf>obs.</inf> = k<inf>aq</inf> + k<inf>2</inf>[OH^-]. At 25 °C (I = 0.1 M Na[ClO<inf>4</inf>]) k<inf>2</inf> = 2.5 × 10² l mol^-1 s^-1 and the activation parameters for base hydrolysis are ¿H^¿ = 69 kJ mol^-1 and ¿S^¿ = +24.5 J K^-1 mol^-1. Base hydrolysis of the nitro-group has been studied at 25 °C and 0.1 M-NaOH and k = 2.1 l mol^-1 s^-1. Slow decomposition of the complex occurs, possibly as a result of hydrolysis of the imine linkages; however, this decomposition (k<inf>oba.</inf> = 2.2 × 10^-3 s^-1) is much slower than nitro-hydrolysis. The analogous complex trans-[Co(htcd)(NO<inf>2</inf>)Cl] [ClO<inf>4</inf>] (htcd = 5,7,7,12,14,14-hexamethyl-1,4,8,11-tetra-azacyclotetradeca-4,11-diene) exhibits similar kinetic behaviour for base hydrolysis of the chloride. At 25 °C (I = 0.1M), k<inf>2</inf> = 2.2 × 10² l mol^-1 s^-1 and k<inf>aq</inf> = 5.5 × 10^-4 s^-1. The additional methyl substituents in the macrocyclic ligand have little or no effect on the hydrolysis rates.

A convenient synthetic route to the ligand 3,7-dithianonane-1,9-diamine (dtnd) has been developed. A series of cobalt(III) complexes, [Co(dtnd)Cl2]+, [Co(dtnd)O3C]+, [Co(dtnd) (NO2)2]+, [Co(dtnd)(NO2)Cl]+, [Co(dtnd)-(NO2)Br]+, [Co(dtnd)(ox)]+ (ox = oxalate), with a variety of anions have been prepared and characterised. The cis-complexes have the cis-ß-configuration in contrast to the complexes of 3,6-dithiaoctane-1,8-diamine (dtod) which give only the cis-a-isomers. In the case of [Co(dtnd)Cl2]+, both the cis-ß- and the trans-isomers can be prepared. In the complex [Co(dtnd) (NO2)2]+, one nitro-group is readily replaced by Cl- or Br- on treatment with the appropriate mineral acid. A recent crystal-structure determination on the complex [Co(dtnd)(NO2)Cl]Cl has shown that the nitro-group trans to the sulphur atom is displaced. The complex has the cis-ß-configuration with the six-membered chelate ring in the chair conformation. The sulphur centres have the same chirality. N.m.r., i.r., and electronic spectra of the complexes are discussed.

The circular dichroism spectra in the region 190-300 nm have been measured at pH 1 and pH 13 in aqueous solution for a series of N, N-dimethyl-L-amino acids. A dominant positive Cotton effect is generally observed between 205 and 225 nm as has been found previously for the parent L-amino acids. These results are consistent with the same conformer being dominant for both series of compounds. © 1973, CSIRO. All rights reserved.

The preparations of pentaamminecobalt(III) complexes of a series of asymmetric unidentate amines are reported. The circular dichroism spectra for the (S)-amines show negative Cotton effects under the 1A1g ¿ 1T1g absorption band, which are somewhat solvent dependent but independent of temperature down to -190°C. The vicinal effect from 1-cyclohexylethylamine was comparable to that from analogous aromatic compounds, but the simpler alkyl derivatives were found to impose smaller rotational strengths on the d-d transitions. The lack of measurable c.d. in the visible region for tetraammine((S)-butane-1, 3-diamine)cobalt(III) is reported and discussed in the light of the other studies. © 1973, CSIRO. All rights reserved.

The preparations of a series of optically active complexes with the general formula Co(NH2)5(OCOCH(X)CH3)2+ are reported for X = NH3+, OH, F, Cl, Br, C2H5, and C6H5. The circular dichroism spectra of the complexes have been measured in aqueous solution, in the presence of salts of polarizable anions, and in KBr disks. The spectra have been analysed in terms of three Cotton effects under the 1A1g ¿ 1T1g cubic absorption band and found to be consistent with a +, -, - sign pattern for the L-isomer, corresponding to the two components of the 1A1g ¿ 1Eg (D4h) and to the 1A1g ¿ A2g(D4h) transition, respectively. © 1971 CSIRO. All rights reserved.